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

摘要

A tunable optical cavity constructed from a fixed mirror[214] and a movable mirror. The fixed mirror[214] is attached to a substrate[203] having a first electrically conducting surface. A support member[216] having the moveable mirror[213] supported thereon and having a second electrically conducting surface, is suspended above the substrate[203]. 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 mirror[214] and the moveable mirror[213] are positioned such that the mirrors form the opposite ends of the optical cavity. The distance between the fixed mirror[214] and the moveable mirror[213] 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 substrate[203] and the support member[216] 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 member[216] and the substrate[203]. The feedback circuit varies the potential between the substrate[203] and the support member[216] 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 layer[355] for amplifying light trapped in the cavity. In the case of a tunable laser, the thermally induced fluctuations can be reduced by including an interferometer[360] or other frequency-selective device to determine the instantaneous wavelength of the light from the laser. An electrical feedback circuit[375] varies the potential between the substrate[203] and the support member[216] so as to maintain the measured instantaneous wavelength at a specified value.