Room temperature optical bistability is observed in a Fabry-Perot type interference filter with ZnS spacer of two wavelength thickness. We observe the bistability using 120 mW of $Ar^+$ laser power focused to be 37KW/㎠ intensity and the switching time of the filter is measured to be 85 us. For such a condition, the electro-optic modulator system and highly focusing objective lens are introduced into the experimental system. In order to drive the electro-optic modulator the electronic pulse generator, which can give a square or a triangle manual pulse, is made. The CW $Ar^+$ laser is modulated to be square or triangle pulse of bandwidth from 200 nsec to d.c. for observing the optical bistability.
The Fabry-Perot interference filters used in this research are made by vacuum deposition with a thermal source. The filters are designed according to the prescription $(HL)^4(HH)^4(LH)^4S$. The transmission of the filter are measured by spectrophotometer to give 60% transmission with 2.0nm band-width.
When the beam spot size is 18 μm, the switching intensity is measured to be 37 KW/㎠ . For the various initial detuning, the optical memory, the optical transphaser, or the other logic operations can be achieved. But the unexpected phenomena are observed that the bistable curve drifts as the number of laser pulse irradiations is increased.
The mechanism of the nonlinearity is also analysed in terms of the effects of the temperature increase due to absorption and the thermo-optic dispersivity.
