Abstract

Silicon Nitride (Si₃N₄) waveguides with ultralow propagation loss [1] provides an ideal platform to develop high performance lasers exhibiting high output power and low phase noise. Such lasers are key components in a wide-range of applications such as coherent communication systems [2], ultraprecise timing [3], LiDAR [4], etc. Lasers require minimal optical loss since it directly correlates to performance, including lasing threshold, output power, and wall-plug efficiency. An extended laser cavity increases the photon lifetime in the laser cavity, which increases the coherence of a narrow linewidth laser. An extended Bragg grating with a narrow bandwidth and high side-lobe suppression is an excellent option among external cavity designs. The narrow mode spacing of the extended cavity can be effectively counteracted by the narrower bandwidth of the extended Bragg grating resulting in an extended-distributed Bragg reflector (E-DBR) laser [5]. The narrow-band feedback of the E-DBR laser helps in reducing the white frequency noise as compared to that of solitary gain section lasers such as monolithic III-V DFB lasers. Integration of microheaters enables tuning of Bragg wavelength via thermo-optic effect and hence leading to mode-hop free tuning of the E-DBR laser. The E-DBR laser requires no specific tuning of its laser cavity, effectively making it a turn-key laser system for on-field applications.

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