Filter array including optical filters having different light transmittances from each other, photodetector, and photodetection system
A filter array, which is to be used in a photodetection system that generates image data of each of N wavelength bands (where N is an integer greater than or equal to 4), includes optical filters whose light transmittances in each of the N wavelength bands differ from each other. (σ 1 /μ 1 )≥0.1, . . . , and (σ N /μ N )≥0.1, where μ i is a mean value of transmittances, corresponding one-to-one to the optical filters, with respect to light of an i-th wavelength band (where i is an integer greater than or equal to 1 and less than or equal to N) among the N wavelength bands, and where σ i is a standard deviation of the transmittances, corresponding one-to-one to the optical filters, with respect to the light of the i-th wavelength band.
1. A filter array utilized in a photodetection system that generates image data of each of N wavelength bands, where N is an integer greater than or equal to 4, the filter array comprising:
optical filters whose light transmittances in each of the N wavelength bands differ from each other,
wherein (σ 1 /μ 1 )≥0.1, . . . , and (σ N /μ N )≥0.1,
where μ i is a mean value of transmittances of the optical filters with respect to light of an i-th wavelength band, where i is an integer greater than or equal to 1 and less than or equal to N, among the N wavelength bands, the transmittances of the optical filters with respect to light of the i-th wavelength band corresponding one-to-one to the optical filters,
wherein the mean value μi of the transmittances is represented by
μ
i
=
1
M
∑
j
=
1
M
T
ij
,
and
wherein T ij denotes a transmittance of a j-th filter among M optical filters with respect to light of the i-th wavelength band among the N wavelength bands, and
where σ i is a standard deviation of the transmittances.
2. The filter array according to claim 1 ,
wherein at least one of the optical filters is a Fabry-Pérot filter.
3. The filter array according to claim 1 ,
wherein at least one of the optical filters includes a first reflection layer, a second reflection layer, and an intermediate layer between the first reflection layer and the second reflection layer, and includes a resonance structure having resonance modes whose orders differ from each other.
4. A photodetector utilized in a photodetection system that generates image data of each of N wavelength bands, where N is an integer greater than or equal to 4, the photodetector comprising:
optical filters whose light transmittances in each of the N wavelength bands differ from each other; and
an image sensor that detects light that has passed through the optical filters,
wherein the image sensor detects only light corresponding to an i-th wavelength band, where i is an integer greater than or equal to 1 and less than or equal to N, among the N wavelength bands, and thereby outputs data that represents a pixel value distribution corresponding to the i-th wavelength band, and
wherein (σ 1 /μ 1 )≥0.1, . . . , and (σ N /μ N )≥0.1,
where μ i is a mean value of pixel values of the pixel value distribution corresponding the i-th wavelength band, and
where σ i is a standard deviation of the pixel values of the pixel value distribution corresponding the i-th wavelength band.
5. The photodetector according to claim 4 ,
wherein at least one of the optical filters is a Fabry-Pérot filter.
6. The photodetector according to claim 4 ,
wherein at least one of the optical filters includes a first reflection layer, a second reflection layer, and an intermediate layer between the first reflection layer and the second reflection layer, and includes a resonance structure having resonance modes whose orders differ from each other.
7. The photodetector according to claim 4 ,
wherein a transmission spectrum of each of the optical filters has a maximal value of transmittance at each of wavelengths included in a target wavelength range,
wherein the image sensor includes photodetection elements, and
wherein each of the photodetection elements is disposed at a position that receives transmitted light that has passed through at least one of the optical filters, and detects light having the wavelengths included in the transmitted light.
8. A photodetection system comprising:
the photodetector according to claim 4 ; and
a signal processing circuit that generates the image data about each of the N wavelength bands based on a signal that is output from the image sensor.
9. The photodetection system according to claim 8 ,
wherein the signal processing circuit generates the image data by performing an operation that uses compressed sensing.
10. The photodetector according to claim 4 , wherein
the data includes the pixel values corresponding to pixels included in the image sensor.
11. A photodetector utilized in a photodetection system that generates image data of each of N wavelength bands, where N is an integer greater than or equal to 4, the photodetector comprising:
a coding element whose light transmittance in each of the N wavelength bands differs between positions; and
an image sensor that detects light that has passed through the coding element,
wherein the image sensor detects only light corresponding to an i-th wavelength band, where i is an integer greater than or equal to 1 and less than or equal to N, among the N wavelength bands, and thereby outputs data that represents a pixel value distribution corresponding to the i-th wavelength band, and
wherein (σ 1 /μ 1 )≥0.1, . . . , and (σ N /μ N )≥0.1,
where μ i is a mean value of pixel values of the pixel value distribution corresponding the i-th wavelength band, and
where σ i is a standard deviation of the pixel values of the pixel value distribution corresponding the i-th wavelength band.
12. The photodetector according to claim 11 , wherein
the data includes the pixel values corresponding to pixels included in the image sensor.