Publisher’s Note: This paper, originally published on 4/1/2016, was replaced with a corrected/revised version on 4/14/2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
We describe the performance of versatile high-performance multi-rate WDM laser transmitters using next-generation compact high-extinction-ratio power-efficient (CHERPe) transmitter designs. These leverage periodic time-frequency windowing of directly modulated laser signals to efficiently generate nearly ideal WDM waveforms with only mW-class drive power. facilitating WDM-channelization and providing straightforward access to many THz of available optical spectrum with low-bandwidth electronics. Furthermore, this approach can support scalable multi-rate operation with good power- and photon-efficiency and enable new architectural options. This approach is attractive for numerous applications and systems ranging from small airborne or CubeSAT-sized communication payloads to larger interplanetary lasercom platforms.
The Lunar Lasercom Ground Terminal (LLGT) is the primary ground terminal for NASA’s Lunar Laser
Communication Demonstration (LLCD), which demonstrated for the first time high-rate duplex laser
communication between Earth and satellite in orbit around the Moon. The LLGT employed a novel
architecture featuring an array of telescopes and employed several novel technologies including a custom PM
multimode fiber and high-performance cryogenic photon-counting detector arrays. An overview of the LLGT
is presented along with selected results from the recently concluded LLCD.
Improvements to a ground-based 40W 1.55 micron uplink transmitter for the Lunar Laser Communications
Demonstration (LLCD) are described. The transmitter utilizes four 10 W spatial-diversity channels to broadcast 19.4 -
38.9 Mbit/s rates using a variable-duty cycle 4-ary pulse position modulation. At the lowest rate, with a 32-to-1 duty
cycle, this leads to 320 W peak power per transmitter channel. This paper discusses a simplification of the transmitter
that uses super-large-area single mode fiber and polarization control to mitigate high peak power nonlinear impairments.
Three-dimensional (3D) imaging systems are being researched extensively for purposes of sensing and visualization in
fields as diverse as defense, medical imaging, art, and entertainment. An overview on a multi-view imaging system in an
axially distributed sensing architecture for three dimensional is presented. In this configuration, the sensor moves along
its optical axis and collects 2D imagery which can be computationally reconstructed at arbitrary depths in the object
space. When compared to traditional 2D imaging techniques, 3D imaging offers advantages in ranging, robustness to
scene occlusion, and target recognition performance. The proposed imaging system is different than conventional multiview
imaging systems, such as integral imaging, in the sense that collection of 3D information is not uniform across the
field of view and in many cases the inherent linear motion of the platform can be exploited for 3D image acquisition.
The system parameters are analyzed and experimental results are presented.
In this keynote address paper, an overview of multi-view three-dimensional (3D) imaging with passive sensing for
underwater applications is presented. The 3D Synthetic Aperture Integral Imaging (SAII) technique is adapted for
underwater sensing. The change in apparent object distance caused by the refractive index of water must be accounted
for in computational 3D image reconstructions. An experimental environment with objects in water and SAII system in
air or water is presented. Experimental results are presented to demonstrate the ability of the underwater 3D SAII system.
The 3D Synthetic Aperture Integral Imaging (SAII) technique is adapted for in-water applications. The traditional SAII
system is adapted for in-water use by compensating for the known changes in beam propagation due to the differing
indices of refraction of air and water. An imaging situation is discusses where the SAII system is placed in water along
with objects. Laboratory based experimental results are presented and demonstrate the ability of the in-water SAII
system to image through heavy occlusion. This paper serves as an overview of work completed on in-water integral
Sampling rates of high-performance electronic analog-to-digital converters (ADC) are fundamentally limited by the timing jitter of the electronic clock. This limit is overcome in photonic ADC's by taking advantage of the ultra-low timing jitter of femtosecond lasers. We have developed designs and strategies for a photonic ADC that is capable of 40 GSa/s at a resolution of 8 bits. This system requires a femtosecond laser with a repetition rate of 2 GHz and timing jitter less than 20 fs. In addition to a femtosecond laser this system calls for the integration of a number of photonic components including: a broadband modulator, optical filter banks, and photodetectors. Using silicon-on-insulator (SOI) as the platform we have fabricated these individual components. The silicon optical modulator is based on a Mach-Zehnder interferometer architecture and achieves a VπL of 2 Vcm. The filter banks comprise 40 second-order microring-resonator filters with a channel spacing of 80 GHz. For the photodetectors we are exploring ion-bombarded silicon waveguide detectors and germanium films epitaxially grown on silicon utilizing a process that minimizes the defect density.
Three dimensional imaging is a powerful tool for object detection, identification, and classification. 3D imaging allows
removal of partial obscurations in front of the imaged object. Traditional 3D image sensing has been Laser Radar
(LADAR) based. Active imaging has benefits; however, its disadvantages are costs, detector array complexity, power,
weight, and size. In this keynote address paper, we present an overview of 3D sensing approaches based on passive
sensing using commercially available detector technology. 3D passive sensing will provide many benefits, including
advantages at shorter ranges. For small, inexpensive UAVs, it is likely that 3D passive imaging will be preferable to
active 3D imaging.
Photonic Analog-to-Digital Conversion (ADC) has a long history. The premise is that the superior noise performance of
femtosecond lasers working at optical frequencies enables us to overcome the bottleneck set by jitter and bandwidth of
electronic systems and components. We discuss and demonstrate strategies and devices that enable the implementation
of photonic ADC systems with emerging electronic-photonic integrated circuits based on silicon photonics. Devices
include 2-GHz repetition rate low noise femtosecond fiber lasers, Si-Modulators with up to 20 GHz modulation speed,
20 channel SiN-filter banks, and Ge-photodetectors. Results towards a 40GSa/sec sampling system with 8bits resolution
Advances in femtosecond lasers and laser stabilization have led to the development of sources of ultrafast optical pulse
trains that show jitter on the level of a few femtoseconds over tens of milliseconds and over seconds if referenced to
atomic frequency standards. These low jitter sources can be used to perform opto-electronic analog to digital conversion
that overcomes the bottleneck set by electronic jitter when using purely electronic sampling circuits and techniques.
Electronic Photonic Integrated Circuits (EPICs) may enable in the near future to integrate such an opto-electronic
analog-to-digital converters (ADCs) completely. This presentation will give an overview of integrated optical devices
such as low jitter lasers, electro-optical modulators, Si-based filter banks, and high-speed Si-photodetectors that are
compatible with standard CMOS processing and which are necessary for the implementation of EPIC-chips for advanced