An etalon has an effective cavity length that can be tuned to compensate for temperature-dependent frequency shift and/or for random variations in the manufacturing process. The effective cavity length of an etalon is adjusted by changing the orientation of a tuning plate positioned in the etalon cavity. A screw adjustment and bending beam spring are used to change tuning plate orientation and precisely tune the etalon resonance frequency after the manufacturing process has been completed. Orientation of the tuning plate is adjusted during operation of the etalon using a passive thermal compensation mechanism, such as a bimetal support arm, which is fixed to the tuning plate and configured to reposition the tuning plate with changing temperature.