Method and apparatus for determining the drive currents of a laser

A novel method to characterise a multi-section semiconductor laser for use as a wavelength tunable transmitter. The invention exploits to full advantage a filter whose optical throughput or transmission varies in a know way with wavelength so that the output power is measured and this is used to compute wavelength in the described manner. Furthermore, a data input/output unit is used to increment currents, as required, to the laser and also to read back current from a photo-detector which is in turn a measure of the wavelength as modified by the filter in a known fashion. This means that a single data acquisition unit, or DAQ, which multiple input and output channels can be used to replace the host of electronic current sources and a wavelength meter or analyser, while avoiding the associated time-consuming delays. A microprocessor may be used to replace the DAQ.