Abstract: A method of, and apparatus for, setting an operating (control) voltage of a voltage controllable optical component, such as a Mach-Zehnder optical modulator, having a periodic voltage/optical parameter (optical power) characteristic include an up/down counter and a digital to analog converter operable to set the voltage applied to the component to a predetermined initial value, a device for measuring the optical parameter, and another device for sequentially progressively increasing and decreasing the voltage (incrementing/decrementing the counter) with respect to the predetermined value, and for determining respective voltage values which produce maximum and minimum values of the optical parameter. The voltage is set to a value intermediate the maximum and minimum voltage values. Further, the apparatus determines the sense of the slope of that portion of the periodic characteristic lying between the maximum and minimum values for use by a control loop during subsequent operation of the optical component.

Abstract: A method of, and apparatus for, setting an operating (control) voltage of a voltage controllable optical component, such as a Mach-Zehnder optical modulator, having a periodic voltage/optical parameter (optical power) characteristic is described. The apparatus comprises: means (6, 7), up/down counter and D to A converter, operable to set the voltage (V) applied to the component to a predetermined initial value; means for measuring the optical parameter (P); means (5, 6) for sequentially progressively increasing and decreasing the voltage (incrementing/decrementing the counter) with respect to the predetermined value and means (5, 9, 10) for determining respective voltage values (V∞ and V0 respectively) which produce maximum and minimum values of the optical parameter; and wherein the means (6, 7) operable to set the voltage sets the voltage (V) to a value intermediate the maximum and minimum voltage values (V0+V∞)/2).

Abstract: A method of, and apparatus for, slicing a modulated input signal is disclosed. The method comprises: generating at least one slice threshold level (20); comparing (3) the magnitude of the input signal (1) with the at least one threshold level to produce a corresponding sliced signal having a first magnitude if the input signal is greater than the threshold level and having a second magnitude if the input signal is less than the threshold level. The method further comprises detecting errors (5) in the sliced signal and producing a corresponding error signal; and setting the threshold level in response to the error signal.

Abstract: A stabilised radiation source (300) comprises: (a) a distributed feedback (DFB) laser (310); (b) a back lens (340) for coupling a portion of the output radiation into first and second optical paths; (c) optical detectors (370, 380) for detecting radiation transmitted through the first and second paths, and for generating first and second signals (J1, J2) indicative of radiation power; and (d) a control circuit (390) for controlling the laser (310) in response to the signals for stabilising. The invention is characterised in that the first and second radiation paths are operable to provide substantially unfiltered and wavelength dependent filtered radiation transmission therethrough respectively to the detecting means (370, 380). Unfiltered radiation transmitted through the first path which is converted into the first signal (J1) is especially suitable for implementing laser output radiation power stabilisation which is output radiation wavelength independent.