Silicon Fabry-perot Interferometer

The resonance condition selects wavelengths whose round-trip optical path matches an integer number of wavelengths. In 2nL cosθ = mλ, changing the refractive index, cavity length, or internal angle changes the permitted values of λ. The resulting transmission spectrum therefore contains wavelength-specific features that can be tracked to identify optical or physical changes in the cavity.

Each reflection sends light through the silicon cavity again, allowing the emerging waves to combine with one another. At wavelengths satisfying the resonance condition, constructive interference increases transmission, while other wavelengths do not reinforce in the same way. Measuring transmission across wavelength reveals the resonant pattern and provides a basis for detecting shifts caused by changes within the optical system.

Cavity length, refractive index, and incident angle directly affect the round-trip optical path, so changes in any of them can move the resonance wavelengths. The integer resonance order also identifies which spectral feature is being considered. Monitoring the position of these features allows optical measurements to be related to dimensional, material, or alignment changes.

A measurement can begin by recording the device’s transmission spectrum and identifying a resonance feature. The feature is then monitored as the relevant condition changes, such as cavity length, refractive index, or incident angle. Its wavelength shift supplies the observable response, allowing the interferometer to function as a compact sensor for temperature, pressure, displacement, or chemical analysis.

Silicon-compatible fabrication supports integration of the interferometer into compact optical and photonic systems. This compatibility is especially relevant where researchers need small components for integrated photonics or telecommunications rather than a separate, large optical assembly. It also supports the development of compact sensing devices that use spectral changes to obtain information about the surrounding or operating conditions.

Transmission measurements reveal how the device responds across wavelength, including the locations of resonant features and their shifts. In spectroscopy, those wavelength-dependent responses can support optical measurements and chemical analysis. In telecommunications and integrated photonics, the same spectral selectivity is relevant to compact components that distinguish or manipulate optical signals according to wavelength.