WAVELENGTH STABILIZATION IN A TRANSMITTER OF WDM SYSTEM

摘要

The wavelength generated by lasers used in WDM systems exhibits a dependence on ambient temperature. This is because the thermal connection between the laser and the thermistor that monitors the laser temperature is not ideal. In prior-art solutions, the laser stability problem is resolved by incorporating components that stabilise wavelength in the laser module. In the present invention, non-idealness is compensated by using an external compensation circuit to change the thermistor temperature setting a. Compensation can be provided in the form of full compensation or over-compensation. Compensation can be effected by means of a control loop feedback that causes the control signal from the control circuit to the cooling element to have such an effect on the control circuit input that when the ambient temperature changes, the control signal from the control circuit is restricted, so that the laser temperature and, thus, wavelength, remain at the rated values. Compensation can also be provided by making the reference input of the comparison means included in the control loop responsive to the ambient temperature.