Tunable fabry-perot filters and lasers utilizing feedback to reduce frequency noise

摘要

A tunable optical cavity constructed from a fixed mirrorÄ214Ü and a movable mirror. The fixed mirrorÄ214Ü is attached to a substrateÄ203Ü having a first electrically conducting surface. A support memberÄ216Ü having the moveable mirrorÄ213Ü supported thereon and having a second electrically conducting surface, is suspended above the substrateÄ203Ü. A circuit applies an electrical potential between the first and second electrically conducting surfaces thereby adjusting the distance between the fixed and movable mirrors. The fixed mirrorÄ214Ü and the moveable mirrorÄ213Ü are positioned such that the mirrors form the opposite ends of the optical cavity. The distance between the fixed mirrorÄ214Ü and the moveable mirrorÄ213Ü is a function of the applied electrical potential. The thermally induced vibrations are reduced by utilizing an electrical feedback circuit that measures the distance between the mirrors. The feedback circuit dynamically changes the potential between the substrateÄ203Ü and the support memberÄ216Ü so as to reduce fluctuations in the cavity resonance frequency. The instantaneous cavity resonance frequency can be measured by comparing the cavity resonance frequency with a standard optical signal, or by using a circuit for measuring capacitative coupling between the support memberÄ216Ü and the substrateÄ203Ü. The feedback circuit varies the potential between the substrateÄ203Ü and the support memberÄ216Ü so as to reduce the fluctuations in said measured cavity resonance frequency or the capacitance. The optical cavity of the present invention can be utilized in constructing a tunable laser by including an active layerÄ355Ü for amplifying light trapped in the cavity. In the case of a tunable laser, the thermally induced fluctuations can be reduced by including an interferometerÄ360Ü or other frequency-selective device to determine the instantaneous wavelength of the light from the laser. An electrical feedback circuitÄ375Ü varies the potential between the substrateÄ203Ü and the support memberÄ216Ü so as to maintain the measured instantaneous wavelength at a specified value. <IMAGE>