Wavelength-locking of a semiconductor laser using an electronic technique

This work describes a novel system to control the stability of a 1583 nm telecommunications laser diode via measurement of junction voltage. This electronic technique dispenses with the optical components used in conventional

wavelength locking schemes and shifts wavelength control to system level electronic instrumentation. The approach employs real-time measurement of diode series resistance (Rs), which is used to compensate the measured forward voltage (Vf) and recover the junction voltage (Vj) of the laser. Control of Vj provides wavelength control without introducing a significant error when the package temperature varies. This was implemented by measuring Rs as the dynamic resistance, δV/δI, by modulating the injection current. Recent work has reduced the modulation amplitude and noise in the electronics. Using a frequency deviation of 1 GHz, we achieved a centre wavelength variation of ± 2 pm over a package temperature variation of 20-55 °C. This gives a wavelength/ temperature coefficient of 0.03 pm/ °C, which is an improvement on 0.34 pm/ °C, as typically achieved for optical locking systems. The system has been further developed using board-level components within a compact demonstrator unit. Work is on-going to further enhance this performance over a package temperature variation of 0-70 °C.