Inversionless distributed feedback semiconductor lasers: Ultranarrow linewidth and immunity against spatial hole burning

TL;DR: In this paper, an inversionless intrinsically single-mode distributed feedback laser structure is proposed and parametrically studied, where the laser is optically excited by a control laser field that is responsible for transferring a fully transparent waveguide structure into a coherent state, wherein a periodic variation of gain without inversion in the absence of any refractive index perturbation is generated.

Abstract: We propose and parametrically study an inversionless intrinsically single-mode distributed feedback laser structure. This laser is optically excited by a control laser field that is responsible for transferring a fully transparent waveguide structure into a coherent state, wherein a periodic variation of gain without inversion in the absence of any refractive index perturbation is generated. We show that such a laser can perform under the conditions where its gain is equal or even less than its loss, i.e., zero and negative net gain regimes. The results suggest that, via coherent control of the longitudinal mode intensity profile and standing wave effects, in the negative net gain regime such a laser can be operated at the Bragg wavelength with ultranarrow linewidth and virtual elimination of any sidemode. The inherent resistance of such a laser against spatial hole burning, despite of having strong nonuniform longitudinal mode intensity, and the effects of facet reflectivities are discussed.