There are typically three tuning technologies used in an external cavity tunable laser: 1), tuning is achieved by using a precision stepping motor to drive a grating to rotate. This technology has the following shortcomings: first, there are quite high requirements on the stepping moving precision and the repeatability of the stepping motor in achieving precision optical frequency tuning, thus the cost is relatively high; second, the miniaturization is hardly achieved due to the stepping motor used; and third, the operational stability is poor under a harsh working environment, in particular, low resistances to various mechanical vibrations. Because of these problems, the tunable laser using this technology is often used under a laboratory working environment. 2) tuning is achieved by a tunable acousto-optic filter. This technology has the advantages of high tuning speed, no mechanical moving component and small size. The major shortcoming is the low tuning precision and relatively wide filtering bandwidth, therefore, the tunable laser using this technology is only suitable for applications in which both the tuning precision and the output bandwidth are not high. 3) tuning is based upon the temperature-sensitive characteristics of the transmission optical frequency of a grating or other optical filtering devices in the laser resonant cavity, such as an optical Etalon. This tuning technology has high tuning precision and relatively narrow output spectrum bandwidth, but low tuning speed. Therefore, it is not suitable when the wide spectral range tuning is needed, for example: if the temperature coefficient of an optical filtering device is 0.02 nanometers per degree Celsius, the desired spectral range and temperature adjustment range are 20 nanometers and 100 degrees respectively, which is impracticable for some applications.