Abstract

Distributed-feedback (DFB) resonators [1, 2] are of interest for inherently producing narrow-linewidth laser emission, without the need of external cavities or filters. The single-frequency emission is obtained by designing an additional phase shift δϕ_design of π/2, thereby producing a resonance that is spectrally located at the centre of the reflection band. Conventionally, δϕ_design is introduced abruptly in the Bragg grating, but this method has the important disadvantage of causing spatial-hole burning in the laser resonator due to a high photon density where the phase shift is located. An attractive solution is to distribute the phase shift, e.g. by widening the waveguide region, thus increasing the effective refractive index [3].

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