External cavity laser using angle-tuned filter and method of making same

Abstract

An external cavity laser comprises a light source unit, preferably comprising a semiconductor light source having internal optical gain and a collimating lens, for supplying substantially collimated light to a retroreflector via an angle-tuned filter extending across an optical axis of the light source. The retroreflector is positioned so as to receive light from the light source via the angle-tuned filter and reflect the light via the angle-tuned filter back to the light source. The retroreflector may comprise a quarter pitch graded-index (GRIN) lens having a proximal end surface oriented towards the light source and a distal end surface opposite thereto, with a mirror provided on the distal end surface, preferably as a high-reflectance coating. The angle-tuned filter may be attached to the proximal end surface of the GRIN lens, preferably as a coating. The GRIN lens may be tilted in order to vary the angle of the filter relative to the optical axis and hence the wavelength. Where the external cavity laser is to be wavelength-adjustable in use, the external cavity laser may further comprise a tuning mechanism for tilting the angle-tuned filter. Alternatively, the tilt angle of the angle-tuned filter may be adjusted and then fixed during manufacture using a separate tilting mechanism which is not a part of the external cavity laser itself.

Dependencies are inferred from the claim text.