Abstract: An optical detector including an avalanche photodiode (APD) and protection circuitry for protecting the APD from excessive power dissipation therewithin, wherein the protection circuitry includes a switching element connected in parallel with the APD, which switching element is switched from a high resistance state to a low resistance state if the level of current through the APD exceeds a predetermined level, and wherein switching back of the switching element to the high resistance state is dependent on a reset signal from a controller. An optical detector including an avalanche photodiode (APD), and protection circuitry for protecting the APD from excessive power dissipation therewithin by switching the APD to a relatively low voltage power supply if the level of current through the APD exceeds a predetermined level, and wherein switching back of the APD to a higher voltage power supply is dependent on a reset signal from a controller.

Abstract: A method and assembly for frequency stabilization of an optical signal especially from a laser, the assembly (11) comprising beam splitter (15), a passive frequency discriminator (16), and a pair of photodiodes (17 & 18). The beam splitter (15) in use receives a collimated optical beam (B) and diverts a sample beam (B1) which is directed towards the discriminator (16) which transmits a portion (B2) of said sample beam to one of the photodiodes (17) and reflects a second portion (B3) of said sample beam to the other photodiode (18). A control signal (S3) is derived from the respective intensities of the transmitted and reflected portions of the sample beam, and utilized to operate the electronic control to adjust the frequency of the laser output signal, if required, to maintain a specified frequency.

Abstract: A control (20) and a method of controlling a tunable laser having a gain section (4), a phase change section (5) and a segmented Bragg grating reflector section (6) comprising a series of grating units (9-17) each of a different pitch, and an electrode (9a-17a) associated with each grating so that an electrical current is applicable to each individual grating. The control (20) includes a plurality of digitally controlled sources (31, 32) of electrical current which are each connected to switch means (33 or 35, 36) operable to independently connect each of said sources (31, 32) to a respective electrode (e.g. 11a or 12a) associated with a grating (e.g. 11 or 12) which is one of a subset of consecutive gratings (e.g. 11 & 12) selected from said series of grating units (9-17).

Abstract: A method and assembly for frequency stabilisation of an optical signal especially from a laser, the assembly (11) comprising beam splitter (15), a passive frequency discriminator (16), and a pair of photodiodes (17 & 18). The beam splitter (15) in use receives a collimated optical beam (B) and diverts a sample beam (B1) which is directed towards the discriminator (16) which transmits a portion (B2) of said sample beam to one of the photodiodes (17) and reflects a second portion (B3) of said sample beam to the other photodiode (18). A control signal (S3) is derived from the respective intensities of the transmitted and reflected portions of the sample beam, and utilised to operate the electronic control to adjust the frequency of the laser output signal, if required, to maintain a specified frequency.