We observed the optical bistability and the self-oscillation in a nonlinear Fairy-Perot etalon filled with Norland optical adhesive (NOA81). The kind of instability was belong to the relaxation type regenerative oscillation suggested by McCall in 1978. The two phase change mechanisms relating to the self-oscillation was found to be due to the competition effect between the negative thermal refractive index change and linear thermal expansion of the NOA81 spacer. Experiments were performed with various types of etalons. In the etalons with 1 mm substrate thickness normal and inverting bistable loop was observed but the self-oscillation was not. While in the etalon with 200μm substrates the oscillation was occurred. The oscillation periods became longer along with an increasing the spacer thickness and was in the range of 0.2 to 3 seconds. The changes of the oscillation parameters according to the spacer and substrate thicknesses were investigated by fitting the experimental results of the I/O characteristics for three triangular input pulse durations (80msec, 1.2sec, 15sec) with theory.
The addition of 10% absorption layer at the outside of the etalon back mirror resulted in the reduction of the input intensity level for obtaining the self-oscillation without the changes of oscillation parameters. The input intensity level was lowered about 10 times compared with the etalons which had same finesse, spacer and substrate thicknesses except the absorption layer.
