TEMPERATURE COMPENSATION OF LIQUID-CRYSTAL ETALON FILTERS

摘要

A compensator for thermal or other uncontrollable effects in a liquid-crystal etalon filter (10). The narrow pass band of the filter is controlled by adjusting the amplitude (48) of an AC drive signal (44, 46) applied to the electrodes (22, 24) on either side of the liquid crystal (26) in the filter. An optical detector (36) detects the intensity of light (30) from a narrow-bandwidth input beam (34) passed by the detector. Electrical circuitry (40) determines the bipolar amplitude of the component of the light intensity that is at twice the frequency of the AC drive signal (the doubled-frequency amplitude) and adjusts the amplitude (48) of the AC drive signal in response to the doubled-frequency amplitude so as to reduce the doubled-frequency amplitude toward zero.