This PDF file contains the front matter associated with SPIE Proceedings Volume 12877, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

This presentation offers an overview of the design, mass manufacturing, and operational challenges confronted in the development of SpaceX’s global satellite laser mesh operating in Low Earth Orbit (LEO). The Starlink network consists of over 5,000 free-space optical communication terminals, each achieving data transmission rates of 100Gbps and link uptime over 99%, enabling high-speed global internet coverage.

We present our results for a universal satellite free space optical antenna that is agnostic to communication, and PAT protocols across the C-band. This antenna addresses the challenges around the lack of standardisation for satellite optical communication antenna for space networks.

This paper details the progress in laser communication activities of Tesat-Spacecom. Besides the EDRS program (European Data Relay System) update of in-orbit Laser Communication Terminal (LCT) performance, with more than 81.859 data relay links executed (status Nov 2023), we report on the recent terminal projects, kicked off in 2022/2023. We present recent results of the first intradyne 1064nm coherent laser communication link from space to ground tested between GEO satellite Alphasat and the DLR/TESAT ground station (T-AOGS) at the observatory of Teide in Tenerife, Spain. Furthermore, we share results of intradyne lab measurements. Besides technology demonstrations, we present the new TESAT products in development (SCOT20 and SCOT135), that aim for the Cubesat market on the one hand and the high-performance systems for MEO / GEO satellites with data rates up to 100 Gbps, using commercial COTS technology, on the other hand. Finally, we report on the progress of the SCOT80 terminals delivered for the SDA Tranche 0 program.

The National Aeronautics and Space Administration’s (NASA) Laser Communications Relay Demonstration (LCRD) completed the first 18 months of its Experiment Program in December 2023. Geosynchronous-ground experiments to date have included demonstrations of optimetrics and of Delay/Disruption Tolerant Networking (DTN), and measurements of the effects of the atmosphere on lasercom performance and availability. Future operational scenarios have been emulated. This paper provides an overview and highlights of the first 18 months of LCRD experiments, and a preview of the upcoming experiments, including relaying data to and from the International Space Station.

The National Aeronautics and Space Administration’s (NASA) Deep Space Optical Communications (DSOC) payload, launched with the Psyche spacecraft on October 13, 2023, is facilitating an ongoing Technology Demonstration (TD) of Free-Space Optical Communications (FSOC), from beyond the earth-moon system. The DSOC Flight Laser Transceiver (FLT), can acquire a 1064 nm uplink laser from earth, and return a 1550 nm, Serially Concatenated Pulse Position Modulated (SCPPM) signal, to earth. The FLT uses a 22 cm diameter unobscured optical transceiver assembly, coupled to a 4 W average power laser transmitter, supplemented with actuators, sensors, electronics and software. A 5-7 kW average power, multi-beam 1064 nm uplink laser assembly integrated to the Optical Communications Telescope Laboratory (OCTL) near Wrightwood, CA serves as the Ground Laser Transmitter (GLT). The DSOC Ground Laser Receiver (GLR) at the Palomar Observatory, Hale telescope (operated by Caltech Optical Observatories), consists of a Superconducting Nanowire Single Photon Detector (SNSPD) array, connected to a ground signal processing assembly. Signal photon arrivals are detected and processed to extract information codewords at the GLR. A Mission Operations System (MOS) co-located with the Psyche Project Mission Operations Center, at the Jet Propulsion Laboratory (JPL), coordinates DSOC technology demonstration activities. This paper presents a system overview, mission description and operations architecture for the TD. Early results that include downlink at maximum downlink data-rate of 267 Mb/s from 0.37 Astronomical Units (AU) or 55 million kilometers are presented.

The Deep Space Optical Communications (DSOC) project launched in October 2023 hosted by the Psyche spacecraft. The DSOC flight laser terminal will be periodically closing links starting a few weeks after launch and extending out to Mars ranges. The DSOC Engineering Model (EM) flight laser transceiver terminal was built to serve as a replica of the flight terminal in space to be integrated into an EM testbed at JPL. The EM testbed characterized the EM flight laser transceiver terminal under test conditions emulating deep space. These tests helped to understand acquisition, tracking, pointing and the bi-directional communications performance. The EM testbed includes a gravity offload structure and the Laser Test Evaluation Station (LTES) testbed that emulates the ground transmitter and receiver. The LTES testbed was developed at NASA/JPL to serve as a pseudo transmitter and receiver ground station for deep-space flight terminals. This paper will describe the EM testbed capabilities that provide calibrated uplink irradiances overfilling the 22 cm aperture, provides a zero-gravity environment, and characterizes the downlink beam. Atmospheric fading and additive background noise can be injected, while performing uplink/downlink communications characterization. The gravity offload is capable of injecting a disturbance spectrum with a hexapod system allowing for a range of spacecraft environments to be emulated. The LTES architecture can be expanded to allow for multiple flight terminals to be tested in parallel for future projects. Key DSOC validation and performance tests with the EM testbed are reported in this paper.

Optical frequency comb technology has been revolutionizing optical fields of ultra-precision metrology over two decades, connecting the SI unit standards of various optical clocks with utmost accuracy and stability. With an increasing demand for free-space communication and time/frequency transfer applications, the frequency comb is stretching its versatility even the outside of laboratory. Still, the environmental disturbances of free space degrade the excellent phase noise of the optical frequencies, hindering the reliable utilization of frequency comb at any desirable location. This research performs comb-to-comb synchronization over a 1.3-km Free-Space Optical link (FSO) with frequency stability of 3.80×10^-15 at 0.1 s averaging time throughout the entire comb spectrum. Phase-locked loop compensates the Doppler shift of optical frequencies propagating atmospheric free-space channel, providing optical references for synchronizing distant frequency comb.

The Compact Hybrid Optical Rf User Segment (CHORUS) project is a collaborative research partnership between SmartSat CRC, DST Group, EOS Space Systems, EM Solutions, Shoal Group, the Australian National University, University of South Australia, and Lyrebird Antenna Research. The project has developed a prototype terminal capable of simultaneous operation in both radiofrequency and optical frequency bands through communications systems integrated into the same tactical platform. A full-size engineering model was developed and tested at the DST Group laser range at Edinburgh South Australia. The terminal is a modified existing platform from EM Solutions currently employed widely in the international defence sector focusing on maritime applications. The modifications made within this project include the integration of a custom aluminium mirror in the centre of the RF antenna. The optical communication signal is received at prime focus and a novel method for separating the RF and optical signals was designed, tested, and integrated. We report on the terminal design specifications and verification through field testing including performance of the optical and RF systems, pointing accuracy, and future technology directions.

A novel technique that for the first time enables practical free-space optical communications without line-of-sight over multi-kilometer distances is proposed. The method is based upon detection of light from a transmitted laser beam that is scattered from the atmosphere. This is received using single photon detectors, using spatial, spectral, and temporal approaches for filtering out the strong daytime light background signal. Laboratory tests are reported that indicate the feasibility of the proposed method. Communication across a lab bench using 16-PPM (pulse position modulation) encoding is reported. The modest data rate of 4 kbit/s that was obtained can be increased using optimized hardware choices. Performance outdoors at multi-km ranges is estimated using an experimentally verified model, with data rates of 100 kbit/s over a distance of 10 km estimated to be achievable.

A one-way ground-to-space optical uplink was conducted between an experimental Optical Ground Terminal (OGT) developed by The Aerospace Corporation and NASA’s Laser Communications Relay Demonstration (LCRD) terminal in geosynchronous orbit. The OGT transmitter was designed to meet the unique requirements of the LCRD receiver, which included the simultaneous emission of three wavelengths, one of which carried a burst mode DPSK waveform. A unique constraint of the experiment was to demonstrate the ability to perform a one-way uplink without using any optical return signals from the Optical Space Terminal (OST). This necessitated that the OGT point in an open loop manner with a more divergent beam than would be typically used in a closed-loop scenario. The OGT tracked LCRD using an ephemeris predict file during the link engagements. Pointing optimization prior to each link was accomplished using link status data that was downlinked via RF to the LCRD ground terminal in White Sands, New Mexico. During several engagement windows, the OGT was able to illuminate LCRD with sufficient detectable power typically within two minutes after initiating a search. Upon optimization of the OGT pointing, communication links were closed at LCRD specified data rates of 51.8, 155, and 311 Mbps using forward error correction and interleaving. End-to-end data transmission from the OGT to WSC via LCRD was demonstrated for periods ranging from seven to 30 min with transmission rates reaching 2.3 GB/min. End-to-end link performance (data sent vs. data received) was on the order of 98-99% for most of the links. Preliminary tests demonstrated end-to-end data transfer at 622 Mbps and the feasibility of link closure at 1244 Mbps.

The Space Development Agency (SDA) is developing a proliferated Low Earth Orbit (LEO) constellation of spacecraft. Spacecraft in this constellation will communicate with each other using optical intersatellite links. The US Naval Research Laboratory (NRL) has built and operated a laboratory testbed for investigating the interoperability of optical communication terminals in the SDA constellation. The challenges and design considerations of the testbed are discussed. The testbed’s different modes of operation, and some of the verification and validation that was done using NRL test terminals are described.

For free-space optical communication links where platform size, weight, and power (SWaP) tend to be at a premium, it is important to design transmitters and receivers that can operate as close as possible to the theoretical best performance. For variable duty-cycle, multi-rate optical communication systems, as demonstrated in the NASA LCRD program, finite extinction ratio can become a significant contributor to transmitter implementation loss when the duty cycle becomes low. The ability to measure waveform extinction ratio of a transmitter with high-fidelity is important for the optimization of these transmitter designs. We present a new technique to measure the extinction ratio of a variable duty-cycle transmitter using an intradyne coherent receiver to capture the full electric field of the transmitter. Average power within a burst of data and within the dead-time of the waveform are separately calculated by gating in the time domain and then by filtering in the frequency domain. Our results show that extinction ratios as high as 45 dB can be accurately measured using this technique. We discuss how to choose the optimal bandwidth for integrating power in the frequency domain. Finally, we show the effects of signal-to-noise ratio on the fidelity of the extinction ratio measurement.

Satellite-to-ground optical feeder links are envisioned in the framework of Very-High-Throughput-Satellite (VHTS) systems. Such optical feeder links need to provide aggregated useful data rates in the range of several hundred Giga-bits-per-second (Gbps). To reach this goal, one of the required fundamental technologies consists in the transmission of more spectrally and energy efficient modulation format relying on coherent intradyne detection. The latter enables complex modulation formats and the use of both polarizations of the signal to transmit polarization-multiplexed data streams. Such coherent intradyne transceivers commonly used for fiber-based applications rely on digital signal processing to recover information after having compensated a range of transmission impairments. Free-space optical communication through the atmosphere for satellite-to-ground link presents fundamentally different characteristics from which stem deleterious impairments to the signal’s quality. We present an investigation through end-to-end simulations of the performance of coherent transceivers for use in optical feeder links based VHTS systems. To base our analysis on realistic channel conditions, we use data acquired during the first demonstration of an Adaptive Optics (AO) pre-compensated uplink to a Geosynchronous (GEO) satellite as well as data generated by a representative laboratory emulator.

We present results and analysis of 5 Gb/s On-Off-Keyed (OOK) data transmission at ~ 4.6-micron wavelength using, at room temperature, a directly modulated, single-mode DFB-QCL transmitter and a Resonant-Cavity Infrared Detector (RCID) receiver. The DFB-QCL design enables relatively high 165-mW CW output power. We used a 3-mm device with ~ 4-micron aperture for stable single-spatial-mode operation, operating at 65 mW. The RCID detector suppresses background radiation while providing enhanced quantum efficiency, ~ 60%, with low polarization dependence and low dark current at room temperature. The data transmission was achieved with no transmitter pulse shaping, consistent with lower-cost transceiver implementation.

Photonic Integrated Circuits (PICs) are one of the key technologies enabling extremely high-throughput optical communications systems deployed in terrestrial fibre networks. Their inherent benefit is the co-integration and miniaturization of multiple high-speed optical devices such as lasers, photodiodes and modulators on a single chip. Compact photonic solutions have the potential to benefit satellite systems not only in terms of their demonstrated performance, but also through improvements in Size, Weight and Power (SWaP) of a satellite payload. In our approach we propose leveraging mature PIC-based solutions employed in high-speed coherent transceivers delivering 100 Gbps per wavelength using PDM-QPSK modulation format. However, the optical chip design is adapted to expand its functionality with a capability to correlate time-transfer sequences used for satellite ranging applications. The proposed solution is demonstrated with a simplified Indium Phosphide transceiver chip operating in the optical C-band. The required functionality of the current prototype is based on a combination of standard and customized integrated devices. The adaptation of the required photonic components accounts for existing reports on the space environment impact on their performances. The implemented functionalities are tested to prove the concept feasibility and gain better understanding of their performance.

An important aspect of coherent optical satellite communication technology is the power consumption of the employed laser systems. Therefore, an enhanced wall-plug efficiency of the optical amplifiers is required. We present the prototype design (technology readiness level 4, TRL) and optical characterization of a 10-channel amplifier system for the use in WDM optical communication infrastructures operating at 1 μm wavelength. Combining the experience of in-house manufactured fiber components and laser systems, an all-fiber amplifier solution was designed to realize an overall wall-plug efficiency of around 30%. All ten input channels were simultaneously amplified up to a combined power of 100W.

Free-space optical communications are becoming essential, especially in space communications. Examples include data transmission for Earth observation satellites, cislunar space networks and deep space exploration missions. One approach to enhancing the capacity of free-space optical communication is increasing transmission power. However, achieving high output power while meeting the components requirements (e.g., space-environmental resistance, long-lifetime, and performance reliability) with a single optical amplifier is challenging. To address this challenge, we propose High-Power Wavelength-Division Multiplexing (HP-WDM) that consists of a free-space multiplexer and conventional high-power amplifiers.

We consider high data rate free-space optical links between satellite and ground station, which are prone to strong variations of the received signal due to atmospheric turbulence. The high data rates towards hundreds of Gbit/s paired with channel coherence times of a few milliseconds pose a serious challenge for reliable transmission. On such non-ergodic channels, the use of appropriate diversity techniques combined with channel coding schemes is a must to ensure the required data rates. There are several ways to tackle the problem. A pragmatic approach is to rely on commercial transceivers from fiber optics, which are, however, not tailored to the free-space optical channel. Code rates are high and no suitable diversity schemes are foreseen. Such transceivers can be combined with a suitable retransmission scheme, which strongly reduces spectral efficiency. Another option is the addition of a complementary erasure coding scheme at a higher layer, which, due to its long codewords and additional redundancy, can correct longer sequences of errors. However, such a layered scheme yields a loss in achievable data rates. In this work, we rely on a theoretically optimal approach which is composed of a long physical layer interleaver as well as a long physical layer channel code. While the interleaver should provide the required time diversity, the selected strongly quantized Low-Density Parity-Check (LDPC) code should correct the errors in the data. To support the required data rates, highly optimized hardware implementation becomes mandatory for both interleaver and decoder. To achieve high error correction performance and data rates towards hundreds of Gbit/s, a cross-layer design methodology is mandatory in which interleaver design, code, and decoding algorithms are jointly considered with its hardware implementation. We show that an Application-Specific Integrated Circuit (ASIC) implementation can reach the target data rates with a moderate backoff from theoretical limits.

Optical satellite links provide increased throughput at a more competitive SWaP compared to radio frequency links. Due to the nature of the light interaction with atmosphere and the limited pointing accuracy, the propagated optical signal suffers from significant variation of the SNR. This causes error bursts in the received bit stream but can also lead to a temporary loss of synchronization causing further loss of data. Since bit rates in optical communications can reach multiple Gbps, millions of bits are affected by these error bursts and dropouts. Therefore, we propose an additional layer of protection, termed erasure coding, which is applied on top of the PHY layer of the communication system. This approach provides time diversity by long erasure code words, so that PHY interleaving can be abstained from. Therefore, optical transceiver and terminal architectures that were not specifically tailored to optical ground-to-satellite links can be reused with this layered approach. The erasure coding scheme corrects packet losses/erasures due to channel impairments, where the packet size and consequently the length of the code consisting of packets as codeword-symbols can be picked in a flexible way. Since only packet erasures need to be corrected, erasure codes show advantages compared to PHY coding schemes in terms of memory utilization and throughput. In this paper, the proposed erasure correction scheme is explained in detail and a performance analysis for typical scintillation channel models of earth-satellite laser communication links is presented. Furthermore, implementation aspects, as well as the encoding and decoding speed are discussed. In perspective, we aim at reaching a throughput in the order of 100 Gbps.

Fibertek is developing a power efficient, space qualifiable Eight WDM Channel PPM Downlink Seed Laser Module (SAM) with TDM based FWM Mitigation Capability. SAM will be compatible with the space qualifiable, high TRL, 8 WDM channel, 50W WDM Amplifier prototype that was delivered in early 2021. Together the two modules make up a complete High TRL spaceflight high power DSOC WDM Transmitter. Measurements of FWM-PEV statistics using realistic PPM patterns are presented. Measurements show that FWM mitigation is not needed for PPM orders 16 and 32. TDM based FWM mitigation algorithm using two wavelength subslots is implemented on the realistic PPM patterns for five out of the six PPM64 and PPM128 formats successfully. Mitigation in all cases results in significant improvement in PEV statistics. Achieved statistics for all PPM formats are considered manageable using FEC.

This paper reports a highly reliable piezoelectric Micro Electro Mechanical System (MEMS) Fast Steering Mirror (FSM) with large optical aperture (10 mm), which utilizes two-level-construction comprising a mirror plate and a actuator hidden beneath the mirror plate, achieving a high resonant frequency (⪆900 Hz) and a large quasi-static scanning range (4 mrad). The leverage structure is adopted not only to amplify the quasi-static deflection angle, but also to achieve a high fill factor (⪆50%). Moreover, compliant flexural structures are optimized to balance the stress to strengthen mechanical robustness. AlScN piezoelectric film is used as actuating material for high piezoelectric coefficient, high linearity and long-term stability. Through experimental verifications, the mirror has been proven to have high mechanical and thermal robustness, namely, withstands mechanical vibration (14.34 g), shock (500g@2ms) and temperature cycling (-40° to 80°) without performance degradation. Meanwhile, the on/off at equal stress experiment further demonstrates the lifetime of the mirror to be more than 12.0E9 cycles.

In this talk, we describe our experimental progress toward a laboratory link demonstration using electronically programmable beam steering metasurfaces as a proof-of-concept for implementing optical communications links with no moving parts. First, we fabricate plasmonic gate-tunable conducting oxide metasurfaces and study the beam quality of the light reflected from the metasurface. Next, we describe the design of a free-space optical communications transceiver and detail our experimental progress. The developed technologies could be instrumental for implementing inter-satellite links as well as information networks on the Moon, Mars, and beyond, needed for robotic and/or human solar system exploration.

As lasercom transitions from individual demonstrations to wide-spread deployment, diverging standards and proprietary implementations will impede interoperability between terminals from different suppliers. In this environment, there is an urgent need for a universal lasercom translator terminal capable of supporting multiple acquisition sequences and communication waveforms in order to connect disparate networks. Development of such a generalized terminal is a key goal of the DARPA Space-Based Adaptive Communication Node (Space-BACN) program. Pointing, Acquisition, and Tracking (PAT) are crucial aspects of interoperability, and multiple styles of PAT sequences have emerged. Even within a given category of beacon generation (e.g., synthesized, in-band, out-of-band), multiple parameters must be specified to define specific entry/exit criteria for each PAT stage, requiring detailed pre-coordination to ensure that terminals from different suppliers can establish a link between them. In addition, extra hardware must be incorporated into the terminal design to accommodate a superset of PAT requirements. Finally, verification testing of multiple PAT sequences in a common testbed drives the testbed implementation requirements. Here, we examine the implications of attempting to accommodate a generalized PAT sequence with a single lasercom terminal. First, we consider the performance of different styles of PAT sequence, and the trades between pointing uncertainty, maximum acquisition range, and allowable scan time. Next, we consider potential hardware requirements for terminals that support multiple PAT sequences. Finally, we consider the testing of such a terminal, and present a testbed architecture intended to accommodate multiple PAT sequences by highly flexible emulation of the remote terminal PAT behavior.

Adaptive optics and efficient light collection is critical in astronomy, optical communications, remote sensing, and optical beam manipulation to correct distortions caused by propagation through media like the Earth’s atmosphere or living tissue. Current systems are limited by their light collection efficiency and wavefront sensors, which need to be in an optical plane non-common to the science image and insensitive to certain wavefront-error modes. A relatively new waveguide technology that, by its intrinsic working mechanism, can give significant information of the light intensity and phase at its input based on its optical transmission is the photonic lantern. This technology forms a low-loss interface between a multimode waveguide and a set of few-mode and/or single-mode waveguides. We present the photonic lantern technology and a proof of concept of a focal plane low-order wavefront sensor based on a 19-core multicore photonic lantern and deep learning, while also presenting a new ¨hybrid¨ design and platform for those applications.

Free Space Optical (FSO) communications systems require robust pointing, acquisition, and tracking approaches to close and maintain links due to inherent beam directionality and susceptibility to atmospheric effects. Typically, the incoming beam must be split into two paths to align with two spatially separated detectors, one for beam position sensing and the other for data reception. We present a dual-purpose, in-line position sensor and data receiver using a 7-fiber hexagonally-packed fiber bundle. We present data collected across a 30 km terrestrial FSO link operating at 10 Gbit/sline rate with an average 95% link availability and compare these results to outputs from our link budget model.

Radio Frequency (RF) communication, while reliable, is capacity limited and faces heavy spectrum regulation. In contrast, Free Space Optical (FSO) communication providesmulti-Gbit/s rates without spectrum allocation. Yet, FSO communication experiences link degradation due to clouds, fog, beam misalignment, and line of sight blockages. This paper reviews the development of a layer two modem that combines both RF and FSO links seamlessly with error-free transmission and Quality of Service (QoS) capabilities. Test data collected on a 30 km terrestrial link demonstrates modem integration with a commercial RF link and provides insight on the QoS system performance.

Single Quantum developed a free-space coupled 6x6 squared array of Superconducting Nanowire Single-Photon Detectors (SNSPDs) for Deep Space Optical Communication (DSOC). This multipixel architecture, along with the sub-50ps timing jitter provided by NbTiN nanowires and readout electronics, is estimated to achieve data-rates beyond several hundreds of Megabits per second (Mbits) depending on the condition set by the communication protocol. The 6x6 array with 60x60 μm² active area and 10x10 μm² pixel size, demonstrated a system detection efficiency around 55% at 1550 nm and a dark count-rate around 150 counts per second per pixel owing to an effective black-body radiation cryogenic filtering. Single Quantum also developed a signal conditioning and summing board which first converts the long decaying SNSPD pulses into 300 picosecond FWHM wide pulses that are Pulse-Position Modulation (PPM) compatible. These pulses are then divided per quadrant and summed to distinguish the arrival of multiple events. The processed information is fed to a demodulator for message decoding and a tracking module to maintain contact with the satellite. The whole signal conditioning chain including the SNSPD array achieves a timing jitter ⪅50 ps FWHM. Such system will support tracking and communication with the NASA’s transmitter from the Psyche Mission at distances ⪆ 235 Million kilometers and could also be exploited for lower range missions. To assess the potential of the multipixel architecture, a DSOC link based on PPM was mimicked in the lab. We implemented the protocol and open sourced it. In this work, we used increasing modulation orders and varied the mean photon number per pulse with a fixed bin size of 1.133 ns. Finally, the Bit-Error-Rate (BER) before and after iterative decoding was evaluated. The proof-of-concept experiment was performed with a fiber-coupled 4-pixel SNSPD supporting count-rates ⪆1 Giga counts per second (-3dB point) and System Detection Efficiency (SDE) of 65%.

Optical feeder-links play crucial role in closing the global broadband coverage gaps. Point-to-point GEO satellite links provide advantage of uninterrupted availability limited only by ground conditions at the cost of higher SWaP to be able to close the link budget. By increasing field-of-view of the on-board optical terminals to approximately 1^◦ × 4^◦ , coverage over large enough area for exploitation of site diversity with more than ten optical ground stations and thus network availability above 99.9% can be achieved. We discuss design challenges and constraints together with trade-off evaluation towards the final design. We present optical and mechanical design of a payload prototype, including telescope with 250mm aperture, capable of tracking multiple optical ground stations over entire Mediterranean region. The tracking system concepts are presented to show potential compensation of the orbital effects that arise due to platform vibrations and orbital inclination. The preliminary results of the breadboard´s verification and acceptance process are presented. Insight into manufacturing, assembly, integration and testing stage of the individual prototype sub-assemblies will be given. Finally, system trade-off between various concepts as well as between the traditional use of multiple optical payloads and the presented baseline will be shown and discussed. The goal is to demonstrate the practical application potential of the multiple optical receive systems for future optical GEO feeder-links.

Free-space optical links are important for “last-mile” connectivity of future classical and quantum networks, in locations where it is impractical or too costly to run optical fibre. In this presentation, we will discuss the challenges such links present, and strategies for overcoming these. Results of a building-to-building test of such a link over approximately 150 m will be presented.

High gain optical amplifiers with low noise are desirable to pre-amplify free-space optical communications signals to usable levels prior to detection without causing significant distortion of the data stream. We report design characteristics and performance of an Optical Low Noise Amplifier (OLNA) for space applications which meet the growing needs of government and industry. Our OLNA technology features high gain ⪆ 60 dB for input powers as low as ⪅ -60 dBm, can operate without optical damage at input powers ⪆ -10 dBm, and has demonstrated noise figures ≤ 4.3 dB (3.8 dB without input isolator) in a non-PM architecture across the 1540-1560 nm band. The system architecture is specifically designed for long-term operation in space environments. Results will be presented verifying the performance of the OLNA through spectral noise figure measurements as well as testing using a variety of communications formats and data rates.

Free-space optical links theoretically allow very high-speed data rates. As the beams propagate through the atmosphere, the effects of turbulence introduce fading. To mitigate these effects, adaptive optics is commonly implemented. Recently, a spatial demultiplexer coupled to an active integrated photonic circuit has been proposed as a more compact solution to replace the adaptive optics device. This solution has been the subject of several demonstrations. In these demonstrations, the control of the photonic circuit is carried out by modulation or by criterion minimization. These techniques are demanding in terms of modulation bandwidth, particularly when the number of spatial modes to be corrected increases. We propose a control method allowing the increase of the number of corrected modes without increasing the modulation bandwidth. This control method is based on a spatial coding of the modulation, also called spatial diversity. Unlike state-of-the-art techniques in which modes are controlled sequentially, with spatial diversity, all the modes are controlled at the same time. Spatial diversity closed loop stability is demonstrated in a numerical simulation.

Since the 80s, adaptive optics is used in astronomy to remove the effects of atmospheric turbulence, and then retrieve diffraction-limited images, even in bad seeing conditions. Thanks to its strong knowledge in Shack-Hartmann wavefront sensing and deformable mirror, Imagine Optic has developed CIAO, a simple and affordable adaptive optics system for astronomers and Free Space Optics. We present the prototype architecture, the main technological choices we did and first experimental results for two applications: - High resolution imaging on natural stars and on extended sources. - Light coupling in a single mode fiber (in VIS and SWIR). We see that CIAO can be considered now as an on the shelf adaptive optics system for FSO.

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) developed and previously characterized a photon-counting optical ground receiver system. The receiver is compliant with the Consultative Committee for Space Data Systems (CCSDS) Optical Communications Coding and Synchronization High Photon Efficiency (HPE) Standard. The standard will be used on the Optical Artemis-2 Orion (O2O) communications demonstration and the Deep Space Optical Communication (DSOC) project aboard the Psyche spacecraft. The receiver system consists of a fiber interconnect, up to sixteen Superconducting Nanowire Single-Photon Detectors (SNSPDs), and a Field Programmable Gate Array (FPGA) based receive modem. Previously, the receiver system architecture was described and test results without emulated link effects were presented. SNSPD device properties, which impact detection jitter and time delay, can limit the receiver dynamic range, especially when operating with varying flux rates (⪆10 dB) between detectors. Codeword error-rate curves with and without simulated clock drifts attributed to Doppler shift and space transmitter clock differences are presented. Results with ±66 ppm clock differences show minimal performance impact (⪅0.2 dB). Test results show that the receiver dynamic range (⪆28 dB) is limited by changing SNSPD detection delays at high photon flux rates.

Free-space optical communication links with terrestrial ground stations experience fading due to atmospheric scintillation and beam pointing. Fiber-coupled receiver systems experience additional fading at the interface between the fiber and free-space optics of the telescope. The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) has characterized a real-time photon-counting optical ground receiver system with an atmospheric fade emulation system. The receiver system is comprised of a fiber interconnect, an array of Superconducting Nanowire Single Photon Detectors (SNSPDs), and a Field Programmable Gate Array (FPGA) based receive modem. Two fiber interconnect/detector architectures have been studied. One architecture uses a 70-mode photonic lantern coupled to seven single pixel SNSPDs. The other architecture uses a 10-mode Few-Mode Fiber (FMF) coupled to a 15-pixel SNSPD array. The receiver system complies with the Consultative Committee for Space Data Systems (CCSDS) optical communications high photon efficiency coding and synchronization standard, which uses Serially Concatenated convolutionally coded Pulse-Position Modulation (SCPPM). The CCSDS standard is designed for use in low photon flux missions, including the Orion Artemis-II Optical (O2O) communications demonstration. The standard utilizes a convolutional symbol interleaver which can be resized to mitigate different fades. The fade emulation system employed in this work emulates scintillation-induced, pointing-induced, and coupling-induced fading. This paper gives an overview of the real-time optical receiver system and the fade emulation system. It presents tests results which show the impact of fading on the performance on the receiver. The test results show that in the presence of channel fading, the 70-mode photonic lantern outperforms the 10-mode FMF under higher (𝐷/𝑟₀ = 9) turbulence conditions due to high fiber-coupling-induced fading and fiber coupling loss on the 10-mode FMF. When operating in lower turbulence (𝐷/𝑟₀ = 4), the 10-mode FMF outperforms the 70-mode photonic lantern. The paper also shows a larger convolutional interleaver improves the system performance as long as the receiver does not lose acquisition.

In free-space optical communications in which the signal is coupled into a single-mode fiber, atmospheric distortion leads to loss of signal and reduced receiver sensitivity. We demonstrate a coherent receiver system in which a Dual Polarization Quadrature Phase Shift-Keying (DP-QPSK) signal is coupled into a photonic lantern, which efficiently separates the light from a large multimode core into single mode fibers. Outputs from the lantern are passed to off-the-shelf integrated coherent receivers and digitized, and the resulting signals are coherently combined with optimal weight coefficients. The reconstructed signal exhibits reduced sensitivity to atmospheric distortion and demonstrates improved performance.

The Space Development Agency (SDA) is developing the Proliferated Warfare Space Architecture (PWSA) – a constellation of hundreds of satellites in low earth orbit delivering space-based capabilities to the joint warfighter. The PWSA is a mesh network of optically connected satellites providing low-latency data transport and missile warning/tracking capabilities. SDA capitalizes on a unique business model that values speed and lowers costs by harnessing commercial development. The Optical Communications Terminal (OCT) standard was created to provide optical interoperability specifications, enable a strong marketplace, and to drive advancements in optical communication capabilities to terrestrial, maritime, and airborne warfighting elements. As part of the spiral development process, the OCT standard evolves with PWSA deployment phases. SDA has incorporated feedback as well as advancements to the OCT standard, resulting in the release of version 3.1.0. In this paper we discuss key aspects of the OCT standard, such as wavelength, modulation, data rates, polarization, link distance, error correction coding, pointing, acquisition and tracking, and position, navigation, and timing.

JAXA and NICT have jointly started the research work for cislunar optical communications. Our research work aims at 2.5 Gbit/s high-speed optical communication from the Moon to the Earth. We have proposed deep space optical link configuration applying Geostationary Earth Orbit (GEO) data relay satellite and High Data Rate (HDR) method. We have conducted preliminary design of key optical components onboard Laser Communication Terminal (LCT) of the GEO data relay satellite. This paper describes design of large-aperture optical antenna and high-sensitivity optical communication system, which implements Adaptive Optics (AO) module and high-sensitivity optical receiver applying digital coherent scheme.

Hollow-Core Photonic Crystal Fibers (HC-PCFs) represent an innovative technology that alters the cross section of an optical fiber, guiding light via its photonic bandgap rather than through traditional total internal reflection. This method minimizes the overlap between the optical mode and the silica core, significantly reducing non-linear issues encountered in high peak power modulation formats. These issues currently restrict the data rate, range, and modulation options in free-space laser communication links due to the high launch peak powers from optical terminals. Traditional attempts to lessen non-linear impairment constrain optical terminal’s fiber length. Such re-designs often leave critical components, like High Power Optical Amplifiers (HPOA), vulnerable to environmental factors, thereby decreasing system reliability. Moreover, they mandate an individual HPOA for each aperture, thus limiting system flexibility. Nonlinearities also limit the utilization of multiple wavelength channels, a technique that could otherwise improve communication link throughput. In this paper, we propose and investigate a solution to these challenges by replacing the Single-Mode Fiber (SMF) post-HPOA with HC-PCFs. Guiding high peak power light through a hollow-core fiber instead of an SMF mitigates nonlinearities. This decreases the system’s Bit Error Rate (BER) for a given optical power and enhances the overall system reach by 10 dB compared to an SMF system with nonlinear constraints. Additionally, we present an analysis of various commercial HC-PCFs, describe a splicing method along with insertion loss for each type of hollow core fiber, and report on an experiment conducted to quantify the improvement in laser communication links offered by HC-PCFs.

In order to appropriately budget satellite resources for a new lasercom terminal, system architects must define an accurate size, mass and power (SWaP) estimate in advance. However, SWaP drivers are often tracked individually during initial design phases, when in reality these drivers are intertwined. Consequently, SWaP estimates attempted at the beginning of a build program can differ significantly from the results seen at the completion of the build. A more holistic initial estimate is needed to capture these complex relationships. A data-based model lends empirical insights into drivers for SWaP, providing a baseline reference for future lasercom terminals. Given the significant number of lasercom demonstrations reported over the last several years, it is now possible to explore a baseline model for SWaP founded on empirical data. These lasercom terminals span a wide range of designs with different SWaP to meet link requirements such as communication distance and data-rates. Here, we consider SWaP drivers such as orbit, maximum data rate × range², and modulation format for 80 unique lasercom terminals. Through iterative analysis of cross-correlation coefficients, p-values, root mean squared errors, and R2 metrics, we establish multivariable parametric regression models as baseline SWaP references for future system design.

Free space optical communications are impacted by atmospheric effects including clouds and aerosols. Clouds can partially or fully obscure lines of site requiring a reduction in data rate or a link handover. These impacts can be mitigated by identifying a geographically diverse set of Optical Ground Stations (OGS) that optimize Cloud Free Line of Sight (CFLOS). The Lasercom Network Optimization Tool identifies the smallest number of ground stations that achieves the required CFLOS availability. During mission operations, negative impacts are further mitigated through accurate atmospheric characterization and predictions, enabling consistent and secure communication from space to ground. The Laser communications Atmospheric Monitoring and Prediction System (LAMPS) is a critical component of operational OGSs, providing real-time situational awareness and informing prediction systems that provide advance warning of communication outages. LAMPS consists of three instruments including a laser ceilometer, an infrared whole sky cloud imager and an automated weather station. Measurements from these instruments serve as inputs to a set of neural networks which are trained to learn and predict the state of the atmospheric channel. LAMPS’ deep learning models provide cloud predictions for three time periods: days-ahead, hours-ahead, and minutes-ahead. These time scales optimize operational planning, link handovers, OGS maintenance, and inter-operability and cross support. LAMPS, which follows the best practices in the Consultative Consortium on Space Data Systems Magenta book, has been deployed to two sites. This talk will give an overview of LAMPS and provide recent observations from the Laser Communications Relay Demonstration.

To mitigate the impact of atmospheric turbulence on Free-Space Optical Communication (FSOC) systems, we present a novel turbulence profiling technique. A Ring Image Next Generation Scintillation Sensor (RINGSS), adapted for infrared wavelengths, has been deployed at the NASA/Jet Propulsion Laboratory’s Table Mountain Facility. For the first time, we use the downlink from the Laser Communication Relay Demonstration (LCRD) satellite as a reference for atmospheric turbulence profiling. The LCRD beam allows for high signal-to-noise at all times of day through the same atmospheric channel as the optical ground station conducting the link. Results demonstrate the RINGSS measurement technique is robust even in strong daytime turbulence with comparison to other instruments and the benefits of using a laser downlink are significant. We therefore demonstrate that the concept of free-space optical communication turbulence profiling could be effectively used for 24-hour operational support to GEO feeder link stations.

Free-Space Optical Communication (FSOC) links between Earth-based Optical Ground Stations (OGSs) and satellites offer immense potential to securely and efficiently exchange vast amounts of information with worldwide coverage. However, atmospheric turbulence inhibits this potential by distorting laser beams, as they propagate through the atmosphere. Adaptive Optics (AO) systems are typically employed at the OGS to correct for these adverse effects and can increase the efficiency of laser light being coupled into an optical fibre for a downlink laser beam. Concurrently, the same AO system can be used to increase the coupling of laser light into an orbiting satellite by pre-distorting the uplink laser beam. In such a scenario, the downlink laser beam is used to measure the distortions that are applied by the atmosphere, and the conjugate of these distortions can then be applied to the uplink laser beam. The atmosphere then corrects the pre-distorted beam, resulting in a flat wavefront at the top of the atmosphere, as well as stable and efficient coupling of light into the satellite. This work showcases the successful experimental ground-to-satellite links in the spring of 2023 between DLR’s recently commissioned OGS and TESAT’s laser communications terminal (LCT-135)—i.e., part of the Technology Demonstration Payload No. 1 (TDP-1) on the geostationary satellite, Alphasat. Pre-distortion was successfully applied via an AO system testbed within the OGS, which resulted in extremely power efficient bi-directional tracking links with Alphasat. The findings of this work show that the application of pre-distortion AO not only improves the coupling of laser light at the satellite, but also reduces the scintillation experienced at the satellite, thus improving the robustness of the link.

In this work, we consider the design of a self-referencing interferometer for wavefront sensing. The design is put forward as a key element for adaptive optics systems implementing laser-based (free-space optical) communication through the atmosphere. The self-referencing interferometer is pursued given its ability for operation under weak through strong atmospheric turbulence conditions. This sets it apart from traditional wavefront sensing systems, which can falter under strong turbulence conditions. The self-referencing interferometer takes the form of a traditional (Michelson) interferometer with the input beam, having wavefront/phase distortion across its transverse profile, split into signal and reference arms. The signal beam is subjected to a linear tilt, while the reference beam undergoes spatial filtering/aperturing to give it a sufficiently flat wavefront/phase profile. The signal and reference beams are then overlapped at the output of the interferometer, and the output beam is imaged on a camera. The image is processed to extract a profile of the distorted wavefront/phase across the input beam, with the conjugate of this distorted wavefront/phase profile applied to a deformable mirror for its correction. In this work, we consider the key design parameters for such a system, operating at a wavelength of 1550 nm, with particular thought given to the levels of linear tilt on the signal beam and spatial filtering/aperturing on the reference beam. We illustrate the sensitivity of the output characteristics to these levels and provide recommendations for optimal functioning of self-referencing interferometers in future laser-based (free-space optical) communication systems.

We examine the limits of receiver sensitivity at capacity for modulation formats compatible with direct detection receivers, using parameters representative of commercial Avalanche Photodiodes (APDs). Considering sources of noise to be shot noise of the signal and dark current, and thermal noise of post-detection electronics (transimpedance amplifier, or TIA), we determine Shannon capacities for On-Off Keying and M-ary Pulse Position Modulation, assuming silicon APDs for 850 nm and InGaAs APDs for 1550 nm. We also explore the Sb-based APDs presently being investigated in many laboratories. While the low k-factor in silicon produces performance approaching that of preamplified receivers, the higher k-factor in InGaAs produces performance gaps ⪆ 10 dB at 1550 nm compared to other mature detection methods. Although several reported Sb-based APDs have low k-factors, their relatively high dark currents still render performance gaps similar to those of InGaAs.

High-data rate satellites capable of communicating with ground-based terminals circumvent the cost and effort required to physically lay networks of communication fiber in rural and metropolitan areas. However, the alternative of free-space laser communication has its own challenges. First, collimated beams incur dynamic pointing and wavefront errors when propagated through atmosphere. Additionally, due to the unknown tilt of the atmosphere during open loop transmissions, an uplink system with a single uplink assembly would suffer from low irradiance at the space terminal requiring the use of multiple independent uplink assemblies. Here we describe a bi-directional ground terminal comprised of four independent uplink telescopes with communication and beacon channels and a downlink telescope with integrated Adaptive Optics (AO) tracking schemes that maximize throughput for single mode fiber coupling. A 1μrad pointing error at 3.3σ CDF was achieved for simulated disturbances under atmospheric conditions with a fried parameter of approximately 7 cm, a Greenwood frequency of nearly 270 Hz, and a measured mechanical jitter of a gimbaled assembly with an 82cm aperture telescope. Open loop calibration was conducted and verified at full system integration under outdoor conditions with stars by taking multiple data sets in a single night with a target pointing error threshold of 37μrad rms.

The Australian Nation University (ANU) Quantum Optical Ground Station (QOGS) has been constructed in Canberra, Australia. Instrumentation is under development to enable lunar communications with QOGS. A receiver system and beacon transmitter will be installed on the telescope that is compatible with the Optical to Orion (O2O) terminal that will be onboard the Artemis II mission. Communication with spacecraft beyond the Moon is also possible by moving the receiver hardware to a larger telescope. The ANU operates Siding Spring Observatory where a 3.9 m or 2.3 m telescope could be used for deep space communications.

The rapidly growing field of space-to-ground laser communication offers high throughput and secure data transfer without frequency allocation. Cailabs' TILBA-ATMO, leveraging Multi-Plane Light Conversion (MPLC) technology, provides turbulence mitigation for atmospheric communication. The 8-mode version showed promise at 100 Gbps, but for Optical Ground Stations (OGS) with large telescopes, a 45-mode system is required. Our latest research demonstrates the 45-mode TILBA-ATMO effectively achieves 10 Gbps data rates, meeting OGS requirements for Low-Earth Orbit (LEO) satellite signals at high Greenwood frequency and large D/r0.

Project Keraunos aims to experiment with a Low-Earth Orbit (LEO) to Ground optical communication link, including turbulence mitigation in the Optical Ground Station (OGS), enabling 10 Gbps or more data rates. Cailabs develops the pilot OGS, equipped with an 80 cm telescope, designed for robust operation under challenging conditions. This paper presents a comprehensive characterization of OGS subsystems, evaluating pointing, acquisition, tracking, beacons, and telecommunication performance with a 2.5 km horizontal link. Initial first light results with the Keraunos satellite are also showcased.

The current on-board communication network in spacecrafts requires a significant amount of wires, leading to relevant issues in cost and occupied volume. Optical Wireless Communication (OWC) can eliminate the need for physical cables, reducing installation and maintenance costs and improving system flexibility. We propose and demonstrate an OWC system that provides wireless data transfer among the electronic units within the satellite. The system is now successfully operated with two popular wired communication protocols on satellites, i.e., CAN-bus and MIL-STD-1553B. It has completed backward compatibility with existing protocols. Moreover, as it requires no DSP, it results in an extremely small footprint and low power consumption. It can effectively reduce the overall weight and cost of the spacecraft data network, offering the potential for a groundbreaking change in spacecraft technology.

Ranging information is routinely used for orbit determination and spacecraft positioning. Currently, RF radio links are used to periodically measure radiometric observables from which range information is derived. With the advent of high-speed free space optical links, both in the near-Earth and deep space domains, techniques for deriving range information in bidirectional optical links and mixed RF-optical links are gaining relevance. This paper presents two methods for obtaining range information between a ground station and a spacecraft, which we term Synchronous Mode (SM) and Asynchronous Mode (AM). In the synchronous mode, the spacecraft ties the arrival of a Ranging Codeword (RCW) in the uplink with the departure of a RCW in the downlink. Phases of the uplink and downlink signals (and their associated time tags) are measured at the ground station and serve as observables for deriving the range information. The AM uses a similar principle, but one phase measurement (and time tag) is performed by the ground station uplink subsystem, while the second phase measurement is performed by the spacecraft and associated with a time tag generated by the station’s downlink subsystem. This method has the advantage of not requiring synchronicity between the uplink and downlink on board the spacecraft and, at the same time, avoids stringent clock requirements on the mission.

With their high timing resolution, high detection efficiency, and large dynamic range, Superconducting Nanowire Single-Photon Detectors (SNSPDs) are the ideal detectors for deep-space optical communication ground receivers. JPL has fabricated SNSPD detectors for four ground stations and fielded full detector systems at three of them as part of the upcoming Deep Space Optical Communication, RF/Optical Hybrid, and Optical to Orion projects. In this presentation, I will discuss the current status of these different detector systems and the technological advances that made them possible. I will also discuss the future improvements in SNSPD arrays necessary for next-generation optical communication ground stations.

Free-Space Optical (FSO) communication holds the potential for data communications at high bandwidths security while minimizing size, weight, and power (SWAP). However, the effects of atmospheric turbulence on an optical beam during propagation limits and degrades communication performance and bit-error-rate. Although degradation of beam quality occurs due to many factors, typically unwanted aberrations due to fluctuations in the refractive index n along beam path causing scattering, absorption, and beam wander is the main cause. Randomly distributed cells called eddies are formed in the propagating medium giving rise to turbulence as well. In this paper, we report experimental results from a 3-meter FSO data link. An intensity modulated 10 Gbps beam in the next phase will be analyzed and correlated to real time weather. We study scintillations and deviation of the beam from its original path (beam wander and spread). A phosphor-coated silicon CCD is used to record and study the beam’s intensity profile.

A Free-Space Optics (FSO) propagation experiment is running in Milan, Italy, since September 2022, in the framework of the Joint Lab between Huawei and Politecnico di Milano in collaboration with Consiglio Nazionale delle Ricerche (CNR). The set-up includes two co-located FSO links: a prototype mid-IR link (10.6 μm) and a commercial near-IR link (1.550 μm) over an 800-m path. Meteorological data are collected by two visibility sensors, two disdrometers, and a weather station. Data from a case study of moderate fog that occurred in winter 2022 highlights that the spatial distribution of fog is highly non-homogeneous along the path, hence, simple prediction models based on single-point measurements of the visibility may incur in large errors. Moreover, the comparison of path attenuation time series shows that the mid-IR link performs better than near-IR.

Free-space optical communications (FSOC) are very sensitive to atmospheric turbulence as they induce local variations of the refractive index and alter the propagation of light. The SHAdow BAnd Ranger (SHABAR) uses solar scintillation to estimate a profile of refractive index structure constant, which can be integrated into other turbulence metrics like Fried parameter, isoplanatic angle and coherence time.

In free-space laser communications, an optical signal propagating through the atmosphere experiences power fluctuations and fading due to pointing inaccuracies and changes in the refractive index of the atmosphere. Determining how a receiver will detect the distorted signal over time is advantageous for the design of robust optical terminals, for the evaluation of mitigation techniques, and for the development of Automatic Repeat request (ARQ) and Forward Error Correction (FEC) protocols. In this work, the impact of atmospheric effects is considered to generate numerical time series of received power for a ground-to-satellite link (uplink) scenario. The generation procedure of the numerical series is described, and the generated series and their statistics are presented and compared with existing theory. As channel characteristics may vary rapidly during links with satellites at lower orbits, an uplink to a Low-Earth-Orbit (LEO) satellite is selected as scenario to illustrate the change in channel characteristics with satellite elevation and slew rate. However, this work is applicable to any uplink scenario. The results and analysis presented in this work can serve for link-budget design, for dimensioning interleavers, for delay analysis in ARQ protocols, for development of FEC schemes, for standardization, and for evaluation of power-fading mitigation techniques.

We present a Field-Programmable Gate Array (FPGA) implementation of a single photon-counting receive modem for a pulse position modulated signal. The modem is compliant with the Consultative Committee for Space Data Systems (CCSDS) High Photon Efficiency (HPE) Optical Communications Coding and Synchronization standard and is capable of a maximum data rate of 267 Mbps. The system is designed on a commercial off-the-shelf FPGA platform and utilizes superconducting nanowire single photon counting detectors, Analog to Digital Converters (ADCs) to sample the detectors, and two FPGAs. Symbol timing recovery, photon counting, convolutional deinterleaving, and codeword synchronization are performed in the first FPGA. The second FPGA performs iterative decoding on each codeword of the Serially Concatenated Pulse Position Modulated (SCPPM) signal. A digital filter is included to compensate for timing jitter of the detector, and the decoder throughput can be adjusted through reconfigurable parallelization. The decoder also implements a resource-efficient, algorithmic polynomial interleaver and deinterleaver. Both FPGAs can be reconfigured to switch between Pulse Position Modulation (PPM)-16 and PPM-32 with code rates 1/3, 1/2, and 2/3. In this paper, we describe the receiver architecture and FPGA implementation of the timing recovery loop and SCPPM decoder, FPGA utilization for the different modes, and receive modem characterization test results.

Due to their increased resilience to turbulence and scattering by aerosols or droplets, mid- and long-infrared free-space optical links are gaining recognition as an advantageous technology in challenging environmental conditions compared to those operating at shorter wavelengths, enabling groundbreaking applications like chaos-based secure optical communication. This research numerically investigates the evolution of a chaotic carrier during propagation in the presence of fog, presenting quantitative assessments of attenuation and temporal pulse elongation. The results showcase a better preservation of the properties of chaos when utilizing longer wavelengths, demonstrating enhanced performance and ensuring physical-layer security in adverse environmental conditions.

The need for higher data rates has transitioned the satellites towards laser communication, opening up new opportunities for inter-satellite distance measurements. The stringent requirements for space missions like gravimetry, formation flying, collision avoidance, and precise orbit determination require highly precise distance knowledge, which can be offered by lasers. The past and present missions depend on radio ranging and laser interferometers to achieve up to centimeter-order and picometer-order precision, respectively. However, these methods either require additional hardware or interfere with the communication data rates as the power available is shared between communication and ranging operations. Therefore, this research explores the potential of laser communication terminals in measuring the inter-satellite distance. Numerical simulations are performed to analyze the effect of the precision of inter-satellite distance measurements on atmospheric density estimation. The analysis shows that such range measurements can only improve atmospheric density estimates if the uncertainty in the drag coefficient can be reduced below the current range of 3-5%.

A system for combining laser ranging and high-speed optical communication reception into a single optical system for low-Earth orbit satellite applications at 1550 nm is proposed. This system would enable both optical data reception and ranging to be performed at one location, provided a satellite has both an SDA-compliant optical terminal and infrared retroreflectors on-board. An analysis of the expected returns is provided for both ideal and poor atmospheric conditions. The ranging system is projected to have a single-shot precision of 2.7 cm with sub-mm normal point accuracy pending further analysis. A system concept is presented, utilizing a single telescope and the same adaptive optics. Other methods of orbit determination using optical techniques are also identified. A proof-of-concept system will be considered for payload testing on the University of Alberta AlbertaSat’s Ex-Alta 4 cubesat, scheduled for launch in 2027-28.

The emerging technology of power-by-light enables power and data delivery over a single Free Space Optical (FSO) link for electrically isolated, interference-free remote operation. Telecom wavelength bands (λ ≈ 1550 nm) are well known for applications in data communication over optical fiber and overlap atmospheric transparency windows, extending the reach of FSO power and data systems through the air. This creates the opportunity to directionally deliver significant power (above 1mW) and high speed data wirelessly over long distances. FSO channels can experience turbulence and weather conditions that affect data and power transmission. Hence, they should be modeled and verified against measurements under varied atmospheric conditions. This will help improve model precision and robustness in predicting FSO channel performance. Accurate modeling of data transmission in FSO channels is urgently required to support the design of wireless optical communication systems for remote areas to which fiber deployment is difficult or uneconomic and instead long-range data communications between ground stations and High-Altitude Platform Systems (HAPS) may be employed. We have modelled an FSO channel transmitting data and power at 1550 and 1520 nm respectively under various meteorological conditions. The system model was developed in the commercially available OptiSystem software for modeling signals transmission. Different weather conditions translate directly to different FSO channel signal attenuations, impacting both data and power transmission. We also explore the impact of different modulation schemes such as Quadratic Amplitude Modulation (QAM), Pulse Amplitude Modulation (PAM), and Quadratic Phase Shift Keying (QPSK) on the bit error rate of the transmitted data thereby achieving the optimal required hardware design parameters. We found that QPSK is predicted to have the longest viable FSO range across all weather conditions and that power cannot be transmitted past 1 km in foggy weather.

Remote laser detection requires laser beam propagation through often unfavorable real-world atmospheric conditions. Turbulence is one of the main factors causing the beam to get distorted and lose its integrity and has direct implications on our ability to detect spectroscopic signatures remotely. One method to suppress turbulence effects is the use of vortex beams which have a spiral phase structure and carry the Orbital Angular Momentum (OAM). Vortex beams are generally considered to be more robust against the turbulence effects compared to conventional Gaussian beams. However, the actual vortex beam performance in remote sensing is also heavily dependent on the exact mode of vortex beam family it belongs to. In this work, we simulate the propagation of beams to a distance of 100 meters under controlled turbulence and compared the performance of a conventional Gaussian beam to two different modes of vortex beams: Hypergeometric Gaussian (HyGG) and Laguerre Gaussian (LG) beams. Through detailed evaluation of the beam circularity as a quantitative metric for beam propagation under turbulence, we demonstrate that HyGG vortex beams exhibit improved resistance against turbulence when compared to conventional Gaussian beams and LG vortex beams. This work provides insights toward a more comprehensive understanding of how vortex beams benefit long-range remote detection and identifying new strategies for long propagation-range propagation of tailored laser beams.

Free Space Optical Communications (FSOC) links with satellites are limited by atmospheric turbulence in up and downlink. Adaptive Optics (AO) systems at the Optical Ground Station (OGS) can mitigate the adverse effects on the uplink by “predistorting” the transmitted laser beam such that its wavefront is corrected by the turbulence. The Point Ahead Angle (PAA) means that the downlink light is not a perfect wavefront reference for the AO system. GEOStar is a project created to demonstrate the feasibility of using a Laser Guide Star (LGS) in the direction of the uplink path to enable better predistortion of the transmitted beam. A novel setup uses a sub-pupil of the 1m diameter ESA-OGS to transmit the communications light to the satellite and a sub-pupil on the opposite side of the telescope aperture is used to launch the LGS. An LGS WFS observes the light from the LGS whilst a similar Near Infra-Red WFS observes downlink light from the satellite such that the measurements can be directly compared. A deformable mirror is used to predistort the uplink beam. The system is currently being integrated ready for shipment to Tenerife and measurements with the optical terminal TDP-1 on AlphaSat are scheduled for Q2 2024.

Optical Camera Communication (OCC) can be employed for indoor positioning and navigation, and it is suitable for environments where GPS signals are unavailable or unreliable. We developed a novel solution based on a network of Light Emitting Diode (LED) lamps placed on the ceiling, where each lamp emits a unique identification (ID) code made of a few simple sine waves. The code is detected by the camera sensor exploiting the rolling shutter and ad-hoc signal processing which does not need synchronization. The system only requires a single image to recognize different IDs captured by the camera, reducing the power consumption of the device. The position can operate in coarse and fine modes, with meter and centimeter accuracy, respectively. In both cases, a single LED lamp is enough for localization.

Free-space optical communication systems always require a precise focusing at the receiver. Unfortunately, when the transmitted beam passes through the atmosphere the wavefront is distorted by the time variant inhomogeneity of the refractive index, causing strong fluctuations in the power coupled into single-mode fiber at the receiver. We present an optical transmission system with a Multi-Actuator Lens (MAL) capable to increase the fiber coupling efficiency from about 5% in absence of correction to the 20%. The measurements have been performed indoor with artificially generated aberrations and outdoor in a 100m horizontal link at 1550nm.

In this work we propose a simulation tool to analyze the case of conduction-driven thermal blooming and compare the results with measurements at the 2055 nm absorption line of CO₂. Using a split-step beam propagation method and incorporating the spatial refractive index change related to the absorption-driven radial temperature gradient resulting from conduction, the effect of beam distortion can be described for arbitrary wavelengths and various atmospheric conditions. The model is benchmarked by experimental investigations using a tunable 100-W thulium fiber laser.

There are some systems that have been traditionally regarded as too complex for simulation, this mindset results in expensive protypes to conduct build and break scenarios. As the need to understand increasingly complex systems evolves, so must the tools. This work seeks to demonstrate that not only is simulation possible with a complex multi-physics problem, but it is accurate, while providing incredible time and cost savings when compared to alternative methods. Simulation of complex systems early in the design and development phases can reduce the number of prototypes created, the number of test flights required and provide design insights earlier in the product life cycle. Design modification while still in the development phase facilitates potential for greater flexibility. Failure to include simulation early, can result in more costly prototyping, greater number of test flights required and the further into a product life cycle issues are discovered, the more limited the options are for modification. Simulation can provide early insights and cost savings.

Optical systems used in aerospace applications are often subject to random vibrations excited by internal and external forces; these range from engine vibrations in airborne systems to gravity and wind forces for ground-based systems. These random motions cause optical elements to shift position, thereby impacting their imaging performance and leading to lower image resolution or image registration errors. Vibration jitter analysis is a method by which such performance degradation can be quantified, and it guides the opto-mechanical design of the system. However, such jitter analysis can be very challenging, as it often incorporates data exchange among several commercial software packages or in-house codes. In this paper we proposed a multiphysics jitter analysis workflow to analyze jitter induced performance impact in optical system using the Ansys Zemax OpticStudio STAR Module and Ansys Mechanical. Ansys mechanical performs finite element analysis of the optical system under field condition. The structural and thermal information is then passed back to Zemax OpticStudio STAR module to analysis the optical performance degradation. Two main jitter impacts are considered: the slow jitter effects due to temperature gradients and the fast jitter effects due to random vibration. The insight gained from this analysis will help guide optical system packaging design to achieve better performance on the system level.

The effects of anisotropy in atmospheric turbulence is studied through imaging of intensity speckles seen on a laser beam propagated over a 16 km range over the Chesapeake Bay. A high speed InGaAs camera records images of the entrance pupil of a 150mm diameter lens for exposure times of less than 50 us, much faster than atmospheric fluctuations. Various image processing techniques are used to investigate the effects of anisotropy, including spatial correlation of intensities across the image and aperture averaging analysis. Supporting concurrent measurements of Cn2 from angle-of-arrival measurements as well as scintillation index will be presented. Wave optics simulations of spatial irradiance patterns for corresponding Cn2 levels in isotropic turbulence will be presented.

This paper provides an overview of the activities on GEO Optical Feeder Links at Viasat Inc. In the last decade, laser communication has emerged as a promising technology for advancing the performance of high-capacity satellites and enhancing the security of data transfer, making it an interesting option to explore for satcom applications. This paper compares the characteristics of satellite optical feeder links with traditional radio frequency-based systems. The potential for high data throughput, reliability, improved network resilience, and compensation for atmospheric disturbances are examined. Several approaches for terminal design are considered with their impacts on the overall data transmission efficiency compared.

In this talk we report on the development of OISL terminals at Honeywell for high-speed crosslinks in LEO mega constellations, optical downlinks for EO data transfer, and QKD applications. Since 2017 Honeywell has been actively developing a 100 mm class, high-reliability OISL laser communication terminal named the LCT100. Honeywell has also been developed terminals suitable for quantum communication and QKD applications, including a quantum-enabled version of the LCT100 crosslink terminal, and a 250 mm class terminal for Canada’s Quantum Encryption and Science Satellite (QEYSSat) which is capable of distributing provably secure encryption keys to ground stations separated by 400 km or more. Major technical challenges include accurate pointing and tracking, polarization-management throughout the optical chain, and deep suppression of background and stray light sources, given the nature of single photon exchange over large distances. Honeywell will fly both QKD and classical terminals on the upcoming QEYSSat mission and in this talk we discuss the design and the readiness of these technologies to address the current challenges in LEO crosslinks and FSO communications.

TeraNet aims to establish a three-node optical ground station network in Australia to support high-speed data downlinking from Low Earth Orbit (LEO) and beyond. The network is comprised of two 0.7m static ground stations situated at the University of Western Australia (UWA) and the Mingenew Space Precinct (300km north of UWA), and one 0.4m mobile ground station that will initially be commissioned at the European Space Agency’s Deep Space Network ground station in New Norcia (100km north of UWA). This network, strategically located with southern sky access and sharing a time zone with ⪆24% of the world’s population, will enhance global coverage and meet the evolving needs of international space missions. Additionally, the three-node architecture will offer unique opportunities to explore LEO line-of-sight handover during adverse weather conditions. Construction of this network has commenced, with two ground stations already on sky. We will present on our progress and preliminary results.

We describe the requirements and associated technology development plan for the communications data link from low mass interstellar probes. This work is motivated by several proposed deep space and interstellar missions with an emphasis on the Breakthrough Starshot project. The Starshot project is an effort to send the first low mass interstellar probes to nearby star systems and transmit back scientific data acquired during system transit within the time scale of a human lifetime. The about 104-fold increase in distance to nearby stars compared to the outer planets of our solar system requires a new form of propulsion to reach speeds of approximately 20% of the speed of light. The proposed use of a low mass sailcraft places strong constraints on the mass and power for the Starshot communications system. We compare the communications systems in current and upcoming solar system probes, New Horizons and Psyche, against the requirements for Starshot and define Figures of Merit for the communications capability in terms of data downlink rate multiplied by distance squared per unit mass. We describe current and future technology developments required for the on-board transmitter (signal generation, signal distribution, and beamforming) and for the near-Earth communications receiver (low-cost large aperture telescopes, high resolution spectrometers, and single photon counting detectors). We also describe a roadmap for technology development to meet the goals for future interstellar communications.