Commercial telecommunications and internet data centers have made integrated photonic transceivers commodity products. We discuss the evolution of optical transceiver technology from direct detection to culmination in digital and analog coherent optic products for both fiber optic and free-space optical communication. Could this be a path for the convergent evolution of optical logic? We discuss the history of optical and electronic logic devices. We review recent work on coherent all-optical logic. We discuss new approaches using all-dielectric meta-surface structures in silicon photonics.Commercial telecommunications and internet data centers have made integrated photonic transceivers commodity products. We discuss the evolution of optical transceiver technology from direct detection to culmination in digital and analog coherent optic products for both fiber optic and free-space optical communication. Could this be a path for the convergent evolution of optical logic? We discuss the history of optical and electronic logic devices. We review recent work on coherent all-optical logic. We discuss new approaches using all-dielectric meta-surface structures in silicon photonics.
Publisher’s Note: This paper, originally published on 6 September 2019, was replaced with a corrected version on 10 October 2019. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
We report on a monolithic indium phosphide photonic integrated transmitter capable of generating high-speed return-tozero differential phase shift keying (RZ-DPSK) data streams for space optical communications as high as 5 Gbps. The integrated transmitter includes a sampled grating distributed Bragg reflector laser continuously tunable over 30 nm in the C-band, a semiconductor optical amplifier for amplification, a Mach-Zehnder modulator for encoding phase-shift-keying data, and electro-absorption modulator for return-to-zero pulse carving. The transmitter is situated in a custom electronics test bed for biasing various PIC sections and driving the modulators. Furthermore, this transmitter can also be utilized for 10 Gbps DPSK or NRZ-OOK.
We present results of an indium phosphide (InP) monolithic photonic integrated circuit (PIC) transmitter suitable for space-optical communications up to 10 Gbps for NRZ-OOK and DPSK modulation and up to 5 Gbps RZ-DPSK modulation. The PIC includes an SG-DBR laser tunable across the entire telecommunications C-Band, a semi-conductor optical amplifier (SOA), a Mach-Zehnder modulator (MZM) for efficient encoding of phase information, and an electroabsorption modulator (EAM) which serves as an RZ pulse carver. The transmitter PIC is integrated in a testbed with a custom board that provides biasing and driving electronics. The commercial-off-the-shelf (COTS) differential driver generates an estimated 4.5-5 Vpp differential modulation voltage for the dual drive MZM. An identical driver was used for the EAM 50% RZ pulse carver but only a single output was used with the other output terminated with a 50Ω load. The SOA and laser gain sections were biased at 90 mA each. Clear eye openings were achieved for all modulation formats.
Deep space exploration will require laser communication systems optimized for cost, size, weight, and power. To improve these parameters, our group has been developing a photonic integrated circuit (PIC) based on indium phosphide for optical pulse position modulation (PPM). A field-programmable gate array (FPGA) was programmed to serve as a dedicated driver for the PIC. The FPGA is capable of generating 2-ary to 4096-ary PPM with a slot clock rate up to 700 MHz.
A novel 3D hybrid integration platform combines group III-V materials and silicon photonics to yield high-performance lasers is presented. This platform is based on flip-chip bonding and vertical optical coupling integration. In this work, indium phosphide (InP) devices with monolithic vertical total internal reflection turning mirrors were bonded to active silicon photonic circuits containing vertical grating couplers. Greater than 2 mW of optical power was coupled into a silicon waveguide from an InP laser. The InP devices can also be bonded directly to the silicon substrate, providing an efficient path for heat dissipation owing to the higher thermal conductance of silicon compared to InP. Lasers realized with this technique demonstrated a thermal impedance as low as 6.2°C/W, allowing for high efficiency and operation at high temperature. InP reflective semiconductor optical amplifiers were also integrated with 3D hybrid integration to form integrated external cavity lasers. These lasers demonstrated a wavelength tuning range of 30 nm, relative intensity noise lower than -135 dB/Hz and laser linewidth of 1.5 MHz. This platform is promising for integration of InP lasers and photonic integrated circuits on silicon photonics.
This work demonstrates the operation of a photonic integrated circuit transmitter for space optical communication utilizing an RZ-DPSK modulation format realized on an indium phosphide monolithic integration platform. It includes a widely tunable sampled grating distributed Bragg reflector laser, a semiconductor optical amplifier for amplification and burst mode operation, a dual drive Mach-Zehnder modulator (MZM) that efficiently encodes phase information, and an electro-absorption modulator RZ pulse carver.
The laser tuning range is approximately 35 nm across the telecommunications C-band. The MZM DC extinction ratio exceeds 15 dB for a differential drive voltage of 6 V peak-to-peak. Clear eye diagrams were demonstrated at 3 Gbps for OOK modulation and 1 Gbps for RZ-DPSK modulation.