Optical Resonance

As discussed in Section 5.3, multiple reflections take place between the two reflective surfaces of a Fabry–Pérot interferometer, resulting in multiple transmitted fields. A transmittance peak occurs when the round-trip phase shift φRT between the two reflective surfaces is an integral multiple of 2π so that all of the transmitted fields are in phase. From the viewpoint of the field inside the interferometer, this condition results in optical resonance between the two reflective surfaces. Thus a Fabry–Pérot interferometer behaves as an optical resonator, also called a resonant optical cavity. At resonance, the field amplitude inside an optical resonator reaches a peak value due to constructive interference of multiple reflections. The optical energy stored in an optical cavity peaks at its resonance frequencies.