New on-chip light sources for silicon photonics

The demand for high data rates and more compact and lower-cost optical devices has been the main driving force behind integrating photonics on silicon chips. Until now, many efficient optical devices such as filters, modulators, multiplexers and detectors have been developed that take advantage of state-of-the-art silicon technology.

By developing new light sources, which are other main transceiver elements, and properly integrating them on silicon chips, HYSSOP (Hybrid III-V/silicon laser for the future generation of photonic integrated circuits) sought to overcome the main obstacle hindering widespread use of silicon photonics. The focus was on semiconductor lasers fabricated from both silicon and group III-V semiconductor materials. Silicon waveguides were first fabricated on a silicon-on-insulator wafer that was then fused to a III-V epitaxial semiconductor wafer.

The project team successfully demonstrated the potential of different hybrid silicon lasers for applications ranging from short-reach optical interconnect to long-distance optical transmission.

Distributed feedback (DFB) lasers integrated with high-speed modulators are an emerging application of 100 Gb Ethernet. Scientists unveiled a standard-compliant transceiver module using a 25 mW hybrid silicon DFB laser operating at 1 550 nm integrated with a modulator. The output power exceeded the 10 mW threshold set for this standard.

Another major achievement was the development of tunable hybrid silicon lasers that can be used both at the transmitter and the receiver side in long-haul optics. Scientists performed extensive work to demonstrate lasers with wide tunability and high output power. To reach the required power value for long-distance communications, the team coupled a low-noise hybrid semiconductor optical amplifier to the laser, thereby significantly increasing the power.

Due to their low cost, directly modulated tunable lasers are highly attractive for use in access networks. The team successfully developed such lasers for 10 Gb/s single-mode fibres up to 25 km.

Silicon photonics is set to revolutionise telecommunications and data communications over the next 10 years. HYSSOP significantly contributed to this. By using quantum dots or dashes instead of quantum wells as the active material of hybrid lasers, one could get higher-power and lower-noise devices.