1 May 2014 Wavelength stabilisation of a DFB laser diode using measurement of junction voltage
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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.
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A. Asmari, A. Asmari, J. Hodgkinson, J. Hodgkinson, E. Chehura, E. Chehura, S. E. Staines, S. E. Staines, R. P. Tatam, R. P. Tatam, "Wavelength stabilisation of a DFB laser diode using measurement of junction voltage ", Proc. SPIE 9135, Laser Sources and Applications II, 91351A (1 May 2014); doi: 10.1117/12.2052449; https://doi.org/10.1117/12.2052449

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