Patent ID: 7151789

Claim:
A polarized external-cavity laser comprising: a cavity formed by a first optical reflector means and a second optical reflector means aligned with said first optical reflector, at least one of the first and second reflector means being only partially reflective to permit light emission therethrough and at least the first optical reflector means being wavelength-selective; and an optical gain medium disposed in the cavity and having an active waveguide formed therein defining part of an optical path between the first and second reflector means; wherein the wavelength-selective first reflector means comprises a grating comprising a plurality of concatenated grating sections, physical characteristics of each section differing from physical characteristics of each adjacent section thereby defining a transition therebetween, at least some of the sections each comprising a waveguide structure formed by a thin strip of material having a relatively high free charge carrier density surrounded by material having a relatively low free charge carrier density, the strip having finite width (w) and thickness (t) with dimensions such that optical radiation having a wavelength in a predetermined range couples to the strip and propagates along the length of the strip as a plasmon-polariton wave, said wave being partially reflected at the transition between said waveguide structure and the following said adjacent section, the arrangement being such that reflections at the different said transitions along said grating add constructively, and wherein the width (w) of the strip is considerably larger than the thickness (t) of the strip to such an extent that the strip only propagates light having one predetermined substantially linear state of polarization and the grating thus reflects light having said one predetermined substantially linear state of polarization, and wherein interface means between the active waveguide and the wavelength-selective reflector means provides mode-matching and reduction of parasitic reflections from facets of the active waveguide and the wavelength-selective reflector means such that the laser emits substantially linearly polarized light at the wavelength selected by the grating.