A spectral sensor comprising a Fabry-Perot interferometer having a pair of reflectors, a photodetector located beneath the Fabry-Perot interferometer, a capacitance measurement circuit configured to measure a capacitance of the Fabry-Perot interferometer, and a controller configured to control a voltage applied across the reflectors of the Fabry-Perot interferometer.

A spectral sensor comprising a Fabry-Perot interferometer having a pair of reflectors, a photodetector located beneath the Fabry-Perot interferometer, a capacitance measurement circuit configured to measure a capacitance of the Fabry-Perot interferometer, and a controller configured to control a voltage applied across the reflectors of the Fabry-Perot interferometer.

A system includes a first optical unit that emits light to a measurement target object and receives first interference light incident from the measurement target object, a second optical unit that emits the light to a reference object configured to have a constant optical path length with respect to a temperature fluctuation and receives second interference light incident from the reference object, a spectroscope connected to the first optical unit and the second optical unit and receives the first interference light and the second interference light to be incident, and a control unit connected to the spectroscope, and the control unit calculates a fluctuation rate of a measurement optical path length with respect to a reference optical path length under a predetermined temperature environment on the basis of the optical path length of the reference object calculated on the basis of the second interference light incident on the spectroscope under the predetermined temperature environment, and the reference optical path length of the reference object acquired in advance, and corrects, on the basis of the fluctuation rate, the optical path length of the measurement target object calculated on the basis of the first interference light incident on the spectroscope under the predetermined temperature environment.

An optical filter device includes a wavelength variable interference filter that includes a pair of reflective films which face each other, and a fixed substrate in which one of the pair of reflective films is provided; a base to which the fixed substrate is fixed; and a fixing member which fixes one place on the fixed substrate to the base, a surface which is on other place of the one place of the substrate and the base are disposed with a gap therebetween.

An optical filter device includes a wavelength variable interference filter that includes a pair of reflective films which face each other, and a fixed substrate in which one of the pair of reflective films is provided; a base to which the fixed substrate is fixed; and a fixing member which fixes one place on the fixed substrate to the base, a surface which is on other place of the one place of the substrate and the base are disposed with a gap therebetween.

In an illustrative configuration, a method for monitoring air quality is disclosed. The method includes accepting analyte gas into a cell and reflecting light rays into the analyte gas repeatedly across the cell into at least one sensor. The light scattered by particulate matter in the analyte gas and amount of spectra-absorption due to presence of a gaseous chemical is then measured. Based on the determined amount of spectra-absorption and the measured scattered light the gaseous chemical is then measured.

In an illustrative configuration, a method for monitoring air quality is disclosed. The method includes accepting analyte gas into a cell and reflecting light rays into the analyte gas repeatedly across the cell into at least one sensor. The light scattered by particulate matter in the analyte gas and amount of spectra-absorption due to presence of a gaseous chemical is then measured. Based on the determined amount of spectra-absorption and the measured scattered light the gaseous chemical is then measured.

Disclosed are embodiments of an improved apparatus and system, and associated methods for optically diagnosing a semiconductor manufacturing process. A hyperspectral imaging system is used to acquire spectrally-resolved images of emissions from the plasma, in a plasma processing system. Acquired hyperspectral images may be used to determine the chemical composition of the plasma and the plasma process endpoint. Alternatively, a hyperspectral imaging system is used to acquire spectrally-resolved images of a substrate before, during, or after processing, to determine properties of the substrate or layers and features formed on the substrate, including whether a process endpoint has been reached; or before or after processing, for inspecting the substrate condition.

Optical spectrometers may be used to determine the spectral components of electromagnetic waves. Spectrometers may be large, bulky devices and may require waves to enter at a nearly direct angle of incidence in order to record a measurement. What is disclosed is an ultra-compact spectrometer with nanophotonic components as light dispersion technology. Nanophotonic components may contain metasurfaces and Bragg filters. Each metasurface may contain light scattering nanostructures that may be randomized to create a large input angle, and the Bragg filter may result in the light dispersion independent of the input angle. The spectrometer may be capable of handling about 200 nm bandwidth. The ultra-compact spectrometer may be able to read image data in the visible (400-600 nm) and to read spectral data in the near-infrared (700-900 nm) wavelength range. The surface area of the spectrometer may be about 1 mm.sup.2, allowing it to fit on mobile devices.

A light-receiving element, comprising a plurality of photodiodes formed by stacking in this sequence, a lower reflection mirror, a resonator including a photoelectric conversion layer, and an upper reflection mirror on a semiconductor substrate, wherein the plurality of photodiodes share the semiconductor substrate and the lower reflection mirror, the plurality of photodiodes includes a first photodiode having a resonance wavelength λ1 and a second photodiode having a resonance wavelength λ2 that is larger than the resonance wavelength λ1, and a reflectance of the lower reflection mirror has a first peak corresponding to the resonance wavelength λ1 and a second peak corresponding to the resonance wavelength λ2.