Laser integration on silicon

Silicon Photonics is seen as a potentially disruptive approach to design and build very high speed transceivers for datacom applications with lower cost than traditional discrete or III-V monolithic approaches. Due to the high refractive index of silicon, very low loss optical waveguides with small radius of curvature can be fabricated in silicon, allowing easy integration of wavelength multiplexers, multi-mode interference couplers, tap couplers, Bragg gratings and other optical functionalities useful in photonic integrated circuits. And thanks to carrier depletion, optical modulators with RC limited bandwidth can be efficiently designed on silicon. The ability to utilize large substrates that are manufactured in mature high volume silicon foundries opens the possibility of mass producing silicon photonics with a very high level of process control, high yield, and scale of integration unattainable in traditional III-V optoelectronic semiconductor foundries. The main challenge with Si-photonics is that there is no way to make efficient lasers in silicon. This, until now, considerably restricted the potential of Si-photonics for optical datacom and telecom markets as the main need in this area is for high speed transceivers, the compactness of which requires high performance laser sources. Pick and place of III-V lasers dies has been the most common strategy to build transceivers on silicon, but this is not an integrated approach that lends itself to wafer scale manufacturing. In addition, the coupling of III-V laser emitters to silicon optical waveguides also requires tight mechanical alignment and results in increased process time as well as non-negligible optical coupling losses, both of which can affect the overall efficiency and cost of the assembly.