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.
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. <p> </p>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.