Switching dynamics of DS-DBR laser under optical injection locking to achieve fast optical switching with enhanced coherence

Wavelength switching is a promising candidate for future optically switching flat data center network due to its high scalability. The wavelength switching latency of a tunable laser must be maintained within few nanoseconds to ensure high network throughput, because data center IT traffic is dominated by small-sized packets (e.g., hundreds of ns). In addition to this, the increasing data capacity demand has triggered the need for coherent transmission in next-generation data center interconnection. As a result, tunable laser must simultaneously feature low linewidth and fast switching time. However, these two requirements are inherently contradictory, as narrow linewidth requires laser designs to achieve a long photon lifetime, while fast switching requires a short photon lifetime. We demonstrate using the optical injection locking (OIL) technique to improve the phase noise of a ns-scale switching digital supermode (DS) distributed Bragg reflector (DBR) laser. With -24 dBm injection power, we show that DS-DBR laser coherence is significantly improved, with linewidth performance following seed laser ($≤$15 kHz). With optical injection locking, the switching latency is also slightly improved, with $≤$5 ns for both rising and falling edges.