NeoPhotonics : Model and Design for High Performance Silicon Photonics Modulators

By Jianying Zhou, Ph.D. on January 24, 2019 | Leave a Comment

I will represent NeoPhotonics and give a presentation entitled 'Model and Design of Silicon Photonic Carrier-depletion Mach-Zehnder Modulators for 400Gb/s and beyond PAM and QAM Applications', at 2:10 pm on Wednesday February 6, as part of the SPIE Photonics West - XIV Silicon Photonics Conference, in San Francisco.

Silicon Photonics (SiPho) has generated considerable research interest and achieved rapid progress for advanced modulation formats in recent years as it enables cost-efficient small form factor optical transceivers and exhibits many unique advantages such as high-yield photonic-electronic integration by leveraging fabless CMOS processes, high reliability, and cost effective mass production.

SiPho based optoelectronic devices have been shown to provide energy efficient, low cost, and high bandwidth solutions for short-reach optical interconnects and coherent links. Optical transceivers with high baud rate and high order pulse amplitude modulation (PAM) or quadrature amplitude modulation (QAM) are attractive for intra-datacenter connectivity, Data Center Interconnect (DCI) and communication applications. In intra-datacenter connectivity with reach requirements ranging from 0.5 to 10 km, it is widely accepted that the 400 Gb/s systems will be realized using single carrier 100 Gb/s with PAM4 modulation at 50Gbaud via wavelength division multiplexing, as defined in IEEE P802.3BS 400GBE Force. Dual polarization 16QAM at 60Gbaud is an efficient single carrier 400Gb/s solution with 80-120km fiber links, as 400ZR defined by Optical Internetworking Forum (OIF), for DCI applications. 400Gb/s and higher bit rate optical transceivers are of high interest for researchers.

Carrier depletion traveling waveguide Mach-Zehnder modulators (TW-MZM) may be the most cost-efficient with all-silicon material for commercial use. The design for a high speed, high performance SiPho modulator is challenging as it involves a number of key elements, such as PN junction, phase shifter, RF traveling waveguide and termination, which have varying impacts on performance. Compared to conventional modulators based on InP and LiNbO3, SiPho modulators have high insertion losses due to the strong free-carrier absorption and relatively low electro-optic effect. Furthermore, the wide bandwidth and high modulation efficiency require a phase match between optical and RF propagation waves and an impedance match between RF travelling waveguide and terminal, which are strong dependence on PN doping and applied voltage. To overcome these challenges, some analytical circuit equivalent model were used. However, these models may not be accurate for design optimization of carrier depletion modulator.

In this presentation, we will report a hybrid model by an innovative segmental method, which allows us to combine electromagnetic and circuit models to accurately represent distributed characterizations for a SiPho traveling waveguide modulator. This model provides not only the accuracy, but also the efficiency to simulate the wave propagation including PN effects. To maximize EO bandwidth and modulation efficiency, the phase match and the impedance match can be achieved by the optimization of doping, optical and RF design assisted by the model.

We fabricated high speed, high performance SiPho carrier depletion Mach-Zehnder modulators with commercial processes in open foundries, and experimentally achieved 6dB electro-optic BW over 50GHz through design optimization using the new developed model. These modulators have great potentials for bit rates at 400Gb/s and beyond applications using PAM or QAM modulation.