In a Peltier device, a pair of n-type and p-type semiconductors are sandwiched by two types of metal. The Peltier effect transfers heat and cools down an object. The Peltier device is effective for thermal control with high accuracy and local cooling. The Peltier device is employed to control the temperature of LD with an accuracy of 0.01 degree or more with detecting temperature around the LD by thermistor. In LD, the oscillation wavelength depends on the temperature (~0.1 nm/degree).
In LD module for pumping in optical amplifiers, such as Er-doped fiber amplifier (EDFA) and Raman amplifier, fiber Bragg grating (FBG) is attached to pigtail fiber. The oscillation wavelength is fixed into the blaze wavelength of FBG, even when driving current and environmental temperature of LD change. Consequently, the oscillation spectrum is sharpen (0.1~several nanometers at 95 % output power) and stabilized (~0.01 nm/degree at FBG temperature).
Requirements for the pumping light source
Low electricity consumption (= high efficiency) and high output power (400 mW or higher) are required for the specification of pumping light source for fiber laser. For polarization maintained (PM) laser, then, PM fiber (PANDA) is necessary.
The requirement depends on the application. For instance, the Raman amplifier requires, in particular, wavelength stability (fluctuation of the osciilation wavelength causes fluctuation of gain wavelength range), spectral sharpness of oscillation line (broad oscillation line yields a large wave mixing loss in the wavelength-mixing coupler, and increases the number of longitudinal mode in the oscillation line, resulting in a noise and gain fluctuation caused by the oscillation of a number of longitudinal modes), low relative intensity noise (RIN, intensity fluctuation of the excitaiton light results in fluctuation of the Raman gain because an amplification process in the Raman amplifier is fast), and longitudinally multi-modes (when high power light is focused in the narrow wavelength range, the pumping efficiency decreases due to stimulated Brillouin scattering), of the pumping light source.