Abstract: A method of processing an optical signal, including: generating one or more electrical signals indicative of said optical signal; applying said one or more electrical signals to one or more input pins of a chip configured to generate an output indicative of a comparison of the level of said one or more electrical signals with a reference level, the chip including circuitry configurable via two control pins to function as a DC offset cancellation loop; and applying across said two control pins a potential difference dependent on a characteristic of said optical signal so as to control said reference level in dependence on said characteristic of said optical signal.

Abstract: A method of detecting jitter in a digital data signal having a waveform defined by a plurality of component frequencies, including the step of comparing an indicator of the power of a selected frequency portion of the digital data signal against a reference so as to provide an indicator of the shape of the frequency-power characteristic of the data signal.

Abstract: A system including: (i) a semiconductor device; (ii) a thermoelectric controller for controlling the temperature of the semiconductor device; (iii) an electrical power supply for powering the thermoelectric controller; (iv) a first device capable of determining both a direction and a magnitude of current through the thermoelectric controller; (v) a second device also capable of determining a magnitude of current through the thermoelectric controller; and (vi) a controller for controlling the first and second devices on the basis of an electrical indicator of the temperature of the semiconductor device so as to achieve a desired direction and magnitude of current through the thermoelectric controller at a level of power consumption lower than could be achieved using the first device alone.

Abstract: A circuit including a pair of radio frequency signal devices to each of which are connected in parallel a respective input or output and a respective dc bias input device for biasing the respective radio frequency signal device; each dc bias input device including a radio frequency transistor and at least two different types of inductors.

Abstract: A control system for operating a laser, including: a laser driver and a controller for providing the laser driver with a first electrical input indicative of a desired value for an output characteristic of the laser. The laser driver is arranged to control a second electrical input from the laser driver to the laser on the basis of the first electrical input with reference to a first electric reference. The controller is arranged to control the first electrical input on the basis of an electrical indicator of an actual value of the output characteristic of the laser with reference to a second electrical reference of greater reliability than the first electrical reference, so as to compensate for any variations of the first electrical reference.

Abstract: A bias-T circuit including a radio frequency signal input device and a dc bias input device connected in parallel with an output. The radio frequency signal input device includes a capacitive element in series with the output. The dc bias input device includes a radio frequency transistor for controlling the dc bias level at the output. The fT value of the radio frequency transistor is at least 30 GHz, more preferably at least 50 GHz and yet more preferably at least 70 GHz.

Abstract: A semiconductor diode laser of the kind in which laser radiation occurs in an active region in a layer (3) of semiconductor material wherein optical confinement of the radiation to a portion (19) of said layer so as to direct light from said region to a light waveguide is obtained by virtue of differences in the refractive index of different parts of said layer arising from mechanical stresses in said layer, produced, for example, by differential thermal contraction during fabrication of the laser of different parts (96, 11b and 13, 15 or 21 and 5 or 23 and 3) of the laser structure.