Mid- to long-wave infrared computational spectroscopy using a subwavelength coaxial aperture array

Area of Science:

• Optics and Photonics
• Spectroscopy
• Nanotechnology

Background:

• Miniaturized spectrometers offer significant advantages across various applications.
• The filter-array detector-array (FADA) approach enables spectrometer miniaturization.
• Each FADA element uses an optical filter to direct light to a corresponding photodetector.

Purpose of the Study:

• To experimentally demonstrate the FADA approach for infrared spectroscopy.
• To develop a miniaturized spectrometer for the mid- to long-wave infrared spectrum (6.2–14.2 μm).
• To validate the FADA method by reconstructing known and material spectra.

Main Methods:

• Fabrication of a 101-element band-pass filter array using sub-wavelength coaxial apertures in a gold film.
• Utilizing a Fourier transform infrared (FTIR) microscope to measure optical power transmitted through each filter.
• Employing a recursive least squares (RLS) algorithm for spectral reconstruction using filter transmission data and measured optical power.

Main Results:

• Successful experimental demonstration of the FADA approach in the mid- to long-wave infrared range.
• Reconstruction of the infrared light source spectrum from the FTIR system.
• Accurate reconstruction of transmission spectra for polyethylene, cellophane, and polyvinyl chloride.
• Reconstructed spectra showed excellent agreement with direct FTIR measurements.

Conclusions:

• The FADA approach is a viable method for creating miniaturized infrared spectrometers.
• The demonstrated FADA device accurately estimates incident spectra and material transmission.
• This technology holds promise for portable and cost-effective spectroscopic analysis.