100Gbps Photonic Crystal VCSEL

Phase I demonstrated VCSELs capable of transmitting 76Gbps NRZ formatted data using existing Photonic Crystal VCSEL (PC-VCSELs). This was the fastest modulation of PC-VCSELs ever recorded. The data rate was limited by the bandwidth of the PC-VCSEL and in Phase II of this proposal, the plans developed in Phase I to address the laser transmitter limitations will be realized. The key technical objective is to develop a laser transmitter that in combination with the defined driver equalization and pulse shaping is capable of 100Gbps NRZ data transmission. The technical approach to the transmitter to be developed in phase II includes four fundamental and cooperative techniques. First, a VCSEL epitaxial structure supporting operation in the 940nm wavelength region will take advantage of higher differential gain and improved reliability when compared to the traditional wavelength of 850nm. An epitaxial structure with fundamental bandwidth in excess of 30GHz has been designed and multiple epi iterations will be processed in Phase II. The PC-VCSELs tested in Phase I had fundamental epitaxial bandwidth less than 20GHz. Second, to enhance the fundamental bandwidth of the VCSEL, a photonic crystal structure with two coherently locked cavities will be used. This coherence, demonstrated in Phase I exhibits a resonance that can be designed to be in the 10’s of GHz range and thereby provides an “optical feedback” that extends the fundamental bandwidth of the laser. The design of the photonic crystal will be investigated theoretically and experimentally to increase the total power output. The objective is to engineer the mode to be resonant in the 50 to 60GHz range. This additional pole in the frequency response will increase the overall small signal bandwidth to 50GHz, but more importantly enable 100Gbps NRZ operation. Third, electronic equalization and pulse shaping will be optimized to support 100Gbps by making best use of the intrinsic coupled cavity behavior while minimizing complexity to ensure a deployable transmitter is demonstrated.  In phase 1, traditional techniques of equalization and pulse shaping were shown to be effective with the PC-VCSELs. Measurements of Relative Intensity Noise, Bit Error Rates, and fiber coupling tolerances will also be made in phase II and will inform the packaging and control concepts to be developed in phase II. Work with a commercial laser driver manufacturer to develop the specifications and simulations for a commercial Driver IC will commence in Phase II. Fourth, packaging design will be optimized for minimizing parasitics while providing electrical connectivity to driver and coupling light into multi-mode fiber. The design will be iterated in Phase II and complete prototype package be demonstrated at the end of the option period for Phase II. Reliability and environmental operating tests will be performed on the first PC-VCSEL iteration in Phase II, and on the final PC-VCSEL and package in the phase II option period.