A wavelength locker is an opto-electronic device, placed in the beam path of a laser, that enables control of a precise laser wavelength for high-capacity dense WDM in telecommunications systems. The wavelength locker is used in feedback control systems to maintain the wavelength of a tunable laser at or near the center of an optical communication channel. The wavelength locker (WLL) is designed to prevent laser wavelengths from drifting into adjacent channels and causing signal degradation. Optical communication channels used in the ITU grid are spaced 50 GHz apart.
A typical wavelength locking module is deployed in the transmission beam path of a laser, where a beam splitting structure samples two beams from the main beam of the laser, where the sampled beams are a small fraction of the main beam in terms of power. The light from one beam is directly converted into electrical current by a photodiode, and the signal can be used as a power monitor. The second beam is passed through a precision etalon before being converted to electrical current, and this signal is used to set the wavelength of the laser. The power reference signal can be used to normalize the etalon signal. The wavelength locker module must be temperature stabilized to achieve full accuracy, and typically a thermistor is provided for temperature sensing and control.