Method for forming distributed bragg reflectors in optical media

A method for manufacturing a spectrally selective optical waveguide, the method comprising:

• a) providing a photosensitive, optically waveguiding glass body having at least one waveguiding axis;
• and
• b) forming in said body a first refractive index perturbation that defines a Bragg condition relative to light propagation parallel to the waveguiding axis, and that exhibits a reflectivity spectrum having a main peak relative to vacuum wavelengths of light that approximately satisfy the Bragg condition, wherein the forming step comprises the further steps of:
• c) generating an interference pattern of actinic radiation having a spatially averaged intensity profile that includes at least one rising portion of said body and at least one falling portion;
• and
• d) impinging the interference pattern on at least a portion of said body such that the interference pattern has at least a locally defined period along the waveguiding axis, and said intensity profile rises and falls along the waveguiding axis, the impinging step performed so as to lead to formation of the first refractive index perturbation;
• wherein:
• e) the impinging step leads to a spatially-averaged, refractive-index profile in the first refractive index perturbation that has at least one rising portion and at least one falling portion along the waveguiding axis, and at least one segment, to be referred to as a resonant segment, included between the rising and falling portions, whereby, absent any further exposure to actinic radiation, the reflectivity spectrum comprises at least one subsidiary peak,
• CHARACTERIZED IN THAT the method further comprises:
• f) producing a second refractive index perturbation in the body, resulting in a reduction of the amplitude of the subsidiary peak relative to the main peak.