Monolithically Integrated Narrow-Linewidth Optical-Negative-Feedback Lasers

The optical negative-feedback laser monolithically integrated on an InP substrate for obtaining narrow linewidth is investigated. Optical negative feedback (ONF) induced by reflection of light from a Fabry-Perot (FP) resonator reduces linewidth of a distributed Bragg reflector (DBR) laser by 1/14 compared to that of a free-running DBR laser. The measured reflectivity of the fabricated ONF laser is compared to reflectivity simulated with an effective reflectivity model. It is demonstrated that control of the feedback phase is necessary to reduce linewidth by exploiting optical negative feedback. Linewidth is expected to be further reduced by using an FP resonator with a higher quality factor. It is also demonstrated that ONF lasers are compatible with fabrication in the InP foundry platform.