On the basis of the gain characteristics of the Er-doped fiber in 1 550 nm
the simple structure of a tunable fiber grating laser is designed by using the fiber grating as the tuning device and its wavelength is tuned by changing the temperature of the fiber grating.What is more important is that the influences of different Er-doped fiber lengths on the laser output power are analyzed and tests are performed with fibers of different lengths of 10
20 and 30 m at 25 ℃
the results of which show that fibers of different lengths have different thresholds.