Method and apparatus for multiplexed Fabry-Perot spectroscopy
Inventors
Yetzbacher, Michael K. • Miller, Christopher W. • Deprenger, Michael J. • Boudreau, Andrew J.
Assignees
Publication Number
US-9915563-B2
Publication Date
2018-03-13
Expiration Date
2034-05-20
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Abstract
A method of optical spectroscopy and a device for use in optical spectroscopy. The device includes a substrate, and a plurality of etalon cavities affixed to or coupled to the substrate. A signal is received from a Fabry-Perot interferometer. The signal is sampled using the device according to a generalized Nyquist-Shannon sampling criterion. The signal is sampled using the device according to a phase differential criterion for wave number resolution. An input spectrum for the signal is reconstructed based on the signal sampled according to the generalized Nyquist-Shannon sampling criterion and the signal sampled according to the phase differential criterion for wave number resolution.
Core Innovation
The invention relates to a method of optical spectroscopy and a device for use in such optical spectroscopy. It specifically enables robust recovery of an optical spectrum or spectra associated with a scene by using Fabry-Perot transmission data and an associated low-computational burden transform. The device includes a substrate and a plurality of Fabry-Perot etalon cavities affixed or coupled to the substrate, having multiple cavity thicknesses arranged to satisfy a generalized Nyquist-Shannon sampling criterion and a phase differential criterion for wave number resolution.
The problem addressed is the limitation of existing spectral measurement methods, including dispersive elements, Michelson interferometers, and optical filters, which tend to be either bulky, heavy, or suffer from tradeoffs between spatial and spectral resolution. Prior micro-optical devices had limitations such as low fringe contrast, limited usable bandwidth, and manufacturing difficulties due to required precision in etalon step heights. Furthermore, existing scanning Fabry-Perot interferometers are only valid within one free spectral range and do not allow demultiplexing of mixed signals.
The invention overcomes these issues by providing a compact, broadband, imaging spectrometer that permits spectral measurements over the entire bandwidth of a detector whilst minimizing noise effects. The method allows adjusting the number of resolved spectral elements by changing the number of measurement points, decouples spectral resolution from step height precision, and achieves spectral resolution gains equivalent to the cavity finesse over traditional Fourier Transform techniques. This enables disambiguation of spectra from etalon signals with spectral separations greater than the free spectral range of the maximum cavity length, thereby expanding usable bandwidth and improving instrument resolving power independent of physically resolvable step size.
Claims Coverage
The claims include two independent claims covering both a method and a device for multiplexed Fabry-Perot spectroscopy with specific sampling and reconstruction criteria.
Sampling the Fabry-Perot signal according to generalized Nyquist-Shannon and phase differential criteria
A method that involves receiving a signal from a Fabry-Perot interferometer, sampling it according to a generalized Nyquist-Shannon sampling criterion and a phase differential criterion for wave number resolution, and reconstructing the input spectrum based on these sampled signals.
Fabry-Perot interferometer comprising a substrate with multiple etalon cavities satisfying sampling criteria
A Fabry-Perot interferometer device comprising a substrate and a plurality of etalon cavities affixed or coupled to the substrate, wherein the plurality of etalon cavities have respective height values arranged so that differences between adjacent etalon cavity heights satisfy the generalized Nyquist-Shannon sampling criterion, and the overall height range covers the phase differential criterion for wavenumber resolution.
Inclusion of a detector or image sensor with defined sampling parameters
Provision of a detector or image sensor coupled to the Fabry-Perot interferometer, with the generalized Nyquist-Shannon sampling criterion mathematically defined using step size, cavity finesse, refractive index, and maximum vacuum wavenumber to which the detector is sensitive.
The independent claims outline a method and device of multiplexed Fabry-Perot spectroscopy that combine specific physical arrangement of etalon cavities and defined sampling criteria to enable robust spectrum reconstruction over a broad spectral range.
Stated Advantages
Improvement in spectral resolution relative to Fourier Transform techniques, with resolution gain equal to the cavity finesse.
Increased fringe contrast leading to improved signal-to-noise ratio compared to micro-optic devices based on two-beam interference.
Disambiguation of Fabry-Perot transmission signals with spectral components separated by more than one free spectral range, expanding usable instrument bandwidth.
Ability to measure optical signals over the entire detector bandwidth.
Instrument resolving power depends on number of steps rather than physically resolvable step size, allowing more flexibility.
Capability to tune cavity finesse to optimize spectral resolution and maximum frequency for particular signal-to-noise conditions.
Documented Applications
Broadband, compact, and imaging spectrometers for optical spectroscopy.
Line scanning and imaging spectrometers for recovering optical spectra associated with a scene.
Electromagnetic wave spectroscopy beyond optical frequencies, including X-ray, ultraviolet, infrared, microwave, and radio-wave spectral analysis using reflective cavities.
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