In the study on the application of DFB fiber laser to underwater sound detecting

it was found that the acoustic pressure sensitivity of the DFB fiber laser was higher than that calculated under hydrostatic boundary conditions

and its frequency response curve was not smooth. However

the reason and the mechanism were to be figured out. Accordingly

dynamical characteristics of the DFB fiber laser were investigated. Firstly

a DFB fiber laser

whose both ends were fixed

and the cavity was tensioned and placed in air and water respectively

was analyzed numerically. And then

with specially designed testing assemblies

experimental study on it was also conducted. And the results indicate that the first natural frequency of the DFB fiber laser is related to the length of the optical fiber between the two fixed ends

and the length increases

the frequency decreases. When the length has been specified as 50 mm

55 mm and 60 mm respectively

the first natural frequencies have been found to be about 250 Hz

200 Hz and 125 Hz in air

and 200 Hz

160 Hz and 120 Hz in water

correspondingly. It shows that when vibration is taking place in the DFB fiber laser

fluctuation in its output will be resulted

and the first natural frequency is an important factor of it.