Fiber laser tuning using non-thermal plasma as temperature regulator

Abstract

Wavelength tuning of laser with conventional thermal based technique is a very slow process. The tuning speed is limited by the rate of heat transfer via thermal conduction of the temperature controller to the wavelength tuning element. Recent studies show that non-thermal plasma (NTP) can achieve fast gas heating due to the existence of additional heating channels. Utilizing the advantage of these heating channels, the temperature of the gas within the plasma reactor can be varied rapidly. This study presents the development of a thermal based wavelength tuning technique for fiber laser with NTP as the solution to improve the tuning speed. The NTP is generated by means of dielectric barrier discharge (DBD). Fiber Bragg grating (FBG) has been applied as temperature sensor owing to its immunity to the influence of electromagnetic interference in the plasma environment. The wavelength tuning process has been carried out by using the DBD plasma reactor as a temperature regulator that provides temperature conditioning for the laser resonator. The emission spectrum of the fiber laser has been monitored from time to time with an optical spectrum analyzer (OSA). The results show that the emission wavelength of laser shifts when there is a temperature change in the laser resonator. Besides, the tuning range and the temperature tuning resolution achieved depend on the given discharge condition to generate the plasma. Using Helium plasma generated at 5 kV, a tuning range of 3.027 nm and tuning resolution of 11.57 pm °C-1 can be achieved. During the tuning process, temperature varied from 25 °C to around 300 °C. It takes only about 10 minutes to complete the process. The laser emission is also thermally stable as it shows a very low shifting when the temperature is kept constant. In conclusion, the emission wavelength of fiber laser is successfully tuned by the NTP based temperature regulator.