The HELIOS partners demonstrated an integrated tunable transmitter on silicon. For the first time, a tunable laser source has been integrated on silicon, which represents a key milestone towards fully integrated transceivers
The transmitter incorporates a hybrid III-V/Si laser-fabricated by direct bonding, which exhibits 9 nm wavelength tunability and a silicon Mach-Zehnder modulator with high extinction ratio (up to 10 dB), leading to an excellent bit-error-rate performance at 10 Gb/s.
Based on the heterogeneous integration process developed by the CEA-Leti and III-V lab, III-V materials such as InP can be integrated onto silicon wafers. The fabrication process starts on 200mm Silicon on Insulator (SOI) wafers where the silicon waveguides and modulators are fabricated on CEA-Leti 200mm CMOS pilot line. Then, InP heterostructures are directly bonded to the SOI wafer, followed by the laser processing. Finally, metallization steps are performed for contacting the modulators, the heaters above ring resonators and the hybrid III-V/Si lasers.
The laser itself exhibits a maximum output power around 6.5 mW at 20°C, and still higher than 1 mW at 60°C. A single mode operation with SMSR larger than 35 dB is achieved. By thermally tuning the ring resonator placed inside the laser cavity, we achieved a tuning range of 7 nm.
The silicon modulator is a depletion type lateral pn junction modulator. For a reverse bias of 4 V, the 3 dB modulation bandwidth is around 13 GHz, and the 4 dB bandwidth is around 25 GHz.
Bit Error Rate (BER) measurements have been made at 10 Gb/s using a peuso-random binary sequence (PRBS) of a length of 27 – 1. At different wavelengths, we can achieve error free operation with BER < 10-9 with open eye diagrams for all those channels. The extinction ratio of all those wavelengths varies from 6 to 10 dB.
Bit error rate at 10 Gb/s
Corresponding eye diagrams for different wavelengths
The results were obtained with the contribution of Ghent University-IMEC for the design of the laser and University of Surrey for the design of the modulator.