Silicon-gap Fabry-Perot filter for far-infrared wavelengths

Area of Science:

• Optics and Photonics
• Astrophysical Instrumentation

Background:

• Fabry-Perot filters are crucial for spectral analysis in optics.
• Traditional vacuum-gap designs face limitations in resolving power and system compactness.

Purpose of the Study:

• To develop a silicon-gap Fabry-Perot filter with enhanced resolving power.
• To enable compact, high-throughput optical systems for far-infrared applications.

Main Methods:

• Fabrication of a far-infrared Fabry-Perot filter using a single silicon substrate.
• Incorporation of microlithographed metal mesh patterns (inductive crosses, capacitive squares) for wavelength-dependent reflectivity.
• Performance testing of filters, including a unit for a rocketborne astrophysics experiment.

Main Results:

• The silicon-gap filter demonstrated approximately 10 times higher resolving power than vacuum-gap filters due to silicon's high refractive index.
• A filter with capacitive square metal mesh achieved a resolving power of 160 at 158 µm.
• Peak transmittance was 37% with low absorptivity (≲1% per pass).

Conclusions:

• Silicon-gap Fabry-Perot filters offer superior performance for compact, high-throughput far-infrared optical systems.
• The developed filter is suitable for demanding applications such as rocketborne astrophysics.
• Metal mesh patterning provides effective control over filter reflectivity and performance.