Semiconductor laser

A source of laser radiation (8;108) as claimed in any preceding claim, in which said gap(s) (28;128) cause the cavity (15;115) to operate in a single longitudinal mode.

A source of laser radiation (8;108) as claimed in any preceding claim, in which there are a plurality of said gaps (28;128).

A source of laser radiation (8;108) as claimed in any preceding claim, in which the or each gap (28;128) extends between 0.2 and 2.0 μm in a longitudinal direction with respect to the cavity (15;115).

A source of laser radiation (8;108) as claimed in any preceding claim, in which the or each gap (28;128) is between 1 and 10 μm deep in a direction transverse to a longitudinal direction with respect to the cavity (15;115).

A wavelength stabilised laser unit (1;101), comprising a source of laser radiation (8;108) for generating wavelength-stabilised laser radiation (26;126), wherein the laser source is as claimed in any preceding claim.

A wavelength stabilised laser unit (1), comprising a semiconductor material laser (2), a substrate (4) to which the semiconductor laser (2) is mounted, a resonant optical cavity (15) within the semiconductor material (16,18,20), the cavity (15) having an active medium (16) for generating laser radiation (26) and one or more gaps (28) in the semiconductor material (16,18,20) within the cavity (15), a controller for stabilising the wavelength of laser radiation emitted (8) by the laser source, and an actuator (12) for applying a mechanical stress (14) to the substrate (4), wherein the actuator (12) is responsive to the controller (6) in order to deform the substrate (4) and so vary the size of said gap(s) (28) and hence to stabilise the wavelength of laser radiation generated (26) by the semiconductor laser (2).

A source of laser radiation (8) as claimed in claim 16 or claim 17, in which the piezo-electric actuator (12) is arranged to cause the substrate (4) and semiconductor laser (2) to bow and hence vary the size of said gap(s) (28).

A method of varying the wavelength of a source of laser radiation (8;108), said source comprising a semiconductor material laser (2;102), a substrate (4;104) to which the laser (2;102) is mounted, a resonant optical cavity (15;115) within the semiconductor material (16,18,20;116,118,120), the cavity (15;115) having an active medium (16;116), and one or more gaps (28;128) in the semiconductor material (16,18,20;116,118,120) within the cavity (15;115), wherein the method comprises the steps of:

• i) using the active medium (16;116) to generate laser radiation (26;126);
• ii) using said gap(s) (28;128) to selectively apply feedback within the cavity (15;115) to one or more particular wavelengths;
• iii) deforming the substrate (4;104) by the application of a mechanical stress (14;114) to vary to size of said gap(s) (28;128) and hence to vary the wavelength of laser radiation generated (26;126) by the semiconductor laser (2;102).

A method of stabilising the wavelength of a laser unit (1), the laser unit comprising a semiconductor material laser (2), a substrate (4) to which the semiconductor laser (2) is mounted, a resonant optical cavity (15) within the semiconductor material (16,18,20), the cavity (15) having an active medium (16) and one or more gaps (28) in the semiconductor material (16,18,20) within the cavity (15), a controller for stabilising the wavelength of laser radiation generated (26) by the semiconductor laser (2), and an actuator for applying a mechanical stress (14) to the substrate (4), wherein the method comprises the steps of:

• i) using the active medium (16) to generate laser radiation (26);
• ii) using said gap(s) (28) to selectively apply feedback within the cavity (15) to one or more particular wavelengths of said radiation (26);
• iii) controlling the actuator with the controller to deform the substrate (4) by the application of said mechanical stress (14) to vary to size of said gap(s) (28) and hence to stabilise the wavelength of laser radiation generated (26) by the semiconductor laser (2).