Laser diode wavelength stability is vital for applications such as spectroscopy and data communication, and the emitted
wavelength is a function of temperature. In a conventional system, the laser diode temperature is controlled using a
Peltier element with a temperature-sensing thermistor, the latter placed at a short distance from the laser diode chip.
Despite the use of good thermal design and a case, a change in ambient temperature may cause a change to internal
thermal gradients, resulting in a systematic error in the laser diode wavelength. In this paper we describe a novel system
to measure the temperature of the laser diode junction via measurement of the junction voltage. The method has been
applied to a 1651 nm DFB laser diode for use in tunable diode laser spectroscopy (TDLS) of methane. The wavelength
stability of both thermistor- and voltage- control systems are compared over a period of 30 minutes and with different
ambient temperatures. Over 30 min at constant ambient temperature, thermistor control provided a precision of ± 0.4 pm
(40 MHz) and junction voltage control gave a similar ± 0.6 pm (70 MHz). For an ambient temperature change of 20°C, conventional thermistor control suffered a wavelength change of 76 pm (8.4 GHz), whereas junction voltage control
reduced this to 0.6 pm (70 MHz), at or below the level of long-term wavelength precision.