Spectral reconstruction using multi-channel color sensors

Abstract

A photodetector device comprises: a plurality of photodetector elements; and a plurality of filters, wherein each filter of the plurality of filters is arranged in front of a light detecting surface of a corresponding photodetector element to filter incoming light incident on the light detecting surface, and wherein the plurality of filters are configured to filter at least two different wavelength bands of the incoming light, respectively, and wherein the at least two wavelength bands are combined to span a predefined wavelength range, and wherein each filter of the plurality of filters has a corresponding spectral sensitivity, and wherein a sum of spectral sensitivity curves of the plurality of filters within the predefined wavelength range is a constant value.

Description

Technical Field

[0001] The present invention relates to spectral reconstruction using a multi-channel color sensor. Background Art

[0002] Color measurements of samples are performed by illuminating the sample and measuring the spectral components of the reflection. Thus, the color of the sample varies according to the illumination, and a single sample can produce different color impressions (e.g., color coordinates) under different illumination spectra. Furthermore, in some cases, spectrally different samples can also look the same under one illumination, as in metamerism. To obtain spectral properties in color measurements, the sample can be measured, and the actual spectral properties of the sample can be reconstructed based on knowledge of the illumination spectrum and the measured spectrum, and the color spectrum (e.g., color coordinates) can be determined under an arbitrary illumination spectrum. Summary of the invention

[0003] The present invention is directed to spectral reconstruction using a multi-channel color sensor, wherein the spectral responses of the different channel sensors are predefined such that narrow frequency spectral components are detected in an energetically proportional manner.

[0004] In general, in some aspects, the subject matter of the present invention can be embodied in a photodetector device comprising: at least two photodetector elements, such as at least three photodetector elements; and at least two filters, such as at least three filters, wherein each of the at least two or at least three filters is arranged in front of a photodetection surface of a corresponding photodetector element to filter incoming light incident on the photodetection surface, and wherein the at least two or at least three filters are configured to filter at least two or at least three different wavelength bands of the incoming light, respectively, and wherein the at least two or at least three different wavelength bands are combined to span a predefined wavelength range, and wherein each of the at least two or at least three filters has a corresponding spectral sensitivity, and wherein the sum of the spectral sensitivity curves of the at least two or at least three filters within the predefined wavelength range is a constant value.

[0005] Embodiments of the photodetector may have one or more of the following features. For example, in some embodiments, each of the spectral sensitivity curves used in the sum is normalized to a predefined value.

[0006] In some embodiments, the constant sum within a first wavelength range that is less than and within the predefined wavelength range is composed of the sum of the spectral sensitivity curve of the first filter and the spectral sensitivity curve of the second filter.

[0007] In some embodiments, the spectral sensitivity curve of at least one filter of the at least three filters has a shape represented by a cosine function.

[0008] In some embodiments, the spectral sensitivity curve of at least one filter has the shape of a trigonometric function.

[0009] In some embodiments, the spectral sensitivity of at least one filter has the shape of a trapezoidal function.

[0010] In some embodiments, for each of the at least three filters, the spectral sensitivity curve of the filter includes a corresponding peak value and a corresponding full-width half maximum (FWHM) value, wherein the FWHM value of the first filter is greater than the distance between the peak value of the first filter and the peak value of the second filter.

[0011] In some embodiments, the shape of the spectral sensitivity curve of each filter is the same.

[0012] In some embodiments, the shape of the spectral sensitivity curve of the first filter is different than the shape of the spectral sensitivity curve of the second filter.

[0013] In some embodiments, the shape of the spectral sensitivity curve of the first filter is a mirror image of the shape of the spectral sensitivity curve of the second filter.

[0014] In some embodiments, the predefined wavelength range spans wavelengths between about 380 nm and about 780 nm.

[0015] In some embodiments, the spectral sensitivity curve of the filter includes, for each filter, a corresponding peak value and a corresponding full width at half maximum (FWHM) value, and the FWHM of the first filter is greater than or equal to 25 nm.

[0016] In some embodiments, the at least two or the at least three filters are contained in a line array.

[0017] In some embodiments, the at least two or the at least three filters are contained in a two-dimensional array. In some embodiments, the at least three filters are arranged in a circular pattern, for example, in a symmetrical circular pattern.

[0018] In some embodiments, each filter is a bandpass filter configured to transmit light within its respective wavelength band of the incoming light.

[0019] In some embodiments, each filter is an absorptive filter configured to absorb light within its respective wavelength band of the incoming light.

[0020] In some embodiments, each filter comprises an interference filter or a plasmonic filter.

[0021] Embodiments of the present subject matter provide various advantages. For example, in some embodiments, the sensitivity function of a multi-channel spectral sensor is designed so that the target spectrum enters the sensor channels in an energetically proportional manner, and due to the narrowband spectrum, energy signal loss is limited. In some embodiments, the inhomogeneous spectrum of illumination (e.g., from a white LED) in reflectance measurements can be balanced.

[0022] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram illustrating an example of a photodetector device including a plurality of detector elements and a plurality of filters on a substrate.

[0024] Figure 2 is a plot of an exemplary spectral response of a photodetector arrangement in which the optical filters have been configured such that the sum of the spectral sensitivity curves within a predefined wavelength range is constant.

[0025] Figure 3 to Figure 4 is a plot of exemplary spectral responses of a photodetector device, wherein the optical filters have been configured such that the sum of the spectral sensitivity curves within a predefined wavelength range is constant, and wherein the shape of the spectral sensitivity curves is triangular or trapezoidal.

[0026] Figure 5 is a plot of exemplary spectral responses of a photodetector arrangement in which the optical filters have been configured such that the sum of the spectral sensitivity curves within a predefined wavelength range is constant and in which the shapes of the spectral sensitivity curves of at least two of the optical filters are different.

[0027] 6A is a plot of an exemplary spectral response of a photodetector device and a plot of the spectral sensitivity curve of silicon over a predefined wavelength range.

[0028] 6B is a plot of an exemplary spectral response of a photodetector device scaled to the spectral sensitivity curve of silicon over a predefined wavelength range.

[0029] Figure 7 is a plot illustrating the spectral sensitivity curve of a photodetector device. DETAILED DESCRIPTION

[0030] To simplify the measurement requirements of a spectrometer, spectrometer systems have been developed with a reduced number of measurement channels (e.g., photodetector elements with associated filter structures having different transmission spectral responses), allowing the implementation of smaller and cheaper spectrometers. The measurements recorded by the different channels of the spectrometer are used to reconstruct the entire spectrum of the incident light. Each channel of the spectrometer provides a so-called "support point" for the reconstructed spectrum. In general, the achievable resolution and the resulting quality of the spectral reconstruction procedure depends in part on the sensitivity function of the spectrometer and the scanning range of the spectrometer (e.g., the number and distribution of support points). If the incident spectrum includes one or more relatively steep features (e.g., high power components within a relatively narrow wavelength band), such steep features may not be reconstructed, especially when there are few support points. In contrast, the larger the number of support points (e.g., the larger the number of spectrometer channels covering different wavelength bands), the greater the probability that steep features of the incident spectrum can be reconstructed.

[0031] Figure 1 1 is a schematic diagram illustrating an example of a photodetector device 100 (e.g., a multi-spectral sensor device, such as a spectrometer device) including a plurality of detector elements 104 and a plurality of optical filters 106 on a substrate 102 according to the present disclosure. Specifically, the photodetector device 100 includes at least three photodetector elements 104 and at least three optical filters 106, wherein each of the at least three optical filters 106 is configured in front of a light detecting surface of a corresponding photodetector element 104. The photodetector element 104 may include, for example, a photodetector element, such as a photodiode (e.g., a silicon photodiode). The photodetector element 104 may be formed in or on the substrate 102. The optical filter 106 is configured to filter incident light so that only a portion of the incident wavelength is detected by the underlying photodetector element 104.

[0032] The optical filters 106 may include, for example, bandpass filters that are configured to transmit incident light within different respective wavelength bands of incoming light while blocking, absorbing, or reflecting light having wavelengths outside of the respective wavelength bands. In the case of bandpass filters, the passband of each filter 106 may cover a different wavelength band than each other filter 106 in the device 100. In some embodiments, the wavelength band may be defined as the full width at half maximum of the filter spectral response. Alternatively, the wavelength band may be defined as a wavelength range where the filter spectral response is greater than a certain minimum sensitivity value. For example, the wavelength band of one or more of the filters 106 may be defined as a wavelength range where the filter spectral response is greater than about 0.2, greater than about 0.3, greater than about 0.4, greater than about 0.5, greater than about 0.6, greater than about 0.7, or greater than about 0.8, etc.

[0033] Since the transmission wavelength bands may be different for different filters, in some embodiments, it may be advantageous to use at least three photodetector elements 104 and at least three corresponding filters 106 in the device 100. For example, at least three different filters may provide color detection across at least three different color coordinates (e.g., for red, blue, and green models). However, the multispectral sensor device may include other numbers of filter-photodetector pairs (i.e., combinations of filters and underlying photodetectors). For example, the multispectral sensor device may include 2, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, or 50 filter-photodetector pairs.

[0034] In some embodiments, the optical filters 106 include absorptive filters configured to absorb incident light within different respective wavelength bands of incoming light while allowing light outside of the wavelength bands to pass to the photodetector elements 104 located below the optical filters 106 .

[0035] The filter 106 may include, for example, an interference filter or a plasmonic filter. The interference filter may include multiple thin layers of material having alternating refractive indices, such as thin film dielectrics. For example, the filter 106 may be a stack of dielectric thin films having alternating low refractive index and high refractive index materials. The number of layers in the interference filter may vary. For example, the multiple dielectric films in the interference filter may include 2, 3, 4, 5, 6, 7, 8 or more thin film dielectric layers. Materials used as thin film dielectric layers may include, for example, SiO 2 、TiO 2 、Ta2O 5 、Nb2O 5 、Si 2 N 4 etc. The thickness and position of the layers within each stack (e.g., whether the dielectric film is the bottommost layer, the topmost layer, or an intermediate layer) can depend on the design of the filter stack and the desired transmission spectrum of the filter 106. Thus, each filter 106 of the device 100 can have a different design than the other filters 106 of the device 100. In some cases, the interference filter can be a polymer-based interference filter. In some embodiments, the interference filter can be a Fabry-Perot interference filter.

[0036] exist Figure 11 and 2 are shown as being configured in a one-dimensional linear array. However, the detectors 104 and their corresponding filters 106 may alternatively be configured in a two-dimensional array. In some embodiments, the detectors 104 and filters 106 are arranged in a circular pattern (e.g., a symmetrical circular pattern) in which the detectors 104 and filters 106 are evenly spaced from adjacent detector-filter pairs.

[0037] Each filter-detector pair in the multispectral sensor device 100 is associated with a corresponding spectral sensitivity. Spectral sensitivity is the relative efficiency of light transmission through the filter 106 and detected by the detector, which varies depending on the frequency or wavelength of the incident signal. In some embodiments, the spectral sensitivity of each optical filter 106 includes a corresponding peak value and a corresponding full width at half maximum (FWHM) value. The FWHM of one or more of the filters 106 can be greater than or equal to 25nm, greater than or equal to 30nm, greater than or equal to 35nm, greater than or equal to 40nm, greater than or equal to 45nm, greater than or equal to 50nm, greater than or equal to 60nm, greater than or equal to 75nm, greater than or equal to 100nm, greater than or equal to 125nm, or greater than or equal to 150nm, but other minimum values ​​are also possible. In some embodiments, the FWHM is less than or equal to 200 nm, less than or equal to 175 nm, less than or equal to 150 nm, less than or equal to 125 nm, less than or equal to 100 nm, less than or equal to 75 nm, less than or equal to 60 nm, less than or equal to 50 nm, less than or equal to 45 nm, less than or equal to 40 nm, less than or equal to 35 nm, or less than or equal to 30 nm, although other maximum values ​​are possible.

[0038] Figure 7 702 to 710 is a plot illustrating the spectral sensitivity of a multi-spectral sensor device including five transmission filters having different spectral sensitivity curves 702 to 710. Figure 7 As shown in , spectral sensitivity curves 702 to 710 collectively span a wavelength range between about 350 nm and slightly greater than about 750 nm. Figure 7 As shown in , each individual filter has a corresponding spectral sensitivity having a FWHM equal to about 25 nm. In view of the relatively narrow bandwidth of the spectral sensitivities 702 to 710, based on the configuration having Figure 7The spectral reconstruction process of a multi-spectral sensor device of the nature shown in may not be able to reconstruct one or more relatively sharp features (e.g., high power components within a relatively narrow wavelength band that drops between the locations corresponding to the peaks of the different spectral sensitivity curves 702 to 710). For example, dashed line 712 represents a target spectrum having peaks that drop in a region where the amplitude of curves 704 and 706 is very low or relatively insignificant. Therefore, the convolution of the spectral sensitivity curves 702 to 710 with the target spectrum will provide little or no information about these peaks. In addition, even if these features can be detected, the reconstruction of these features may not be completed in a manner that is energetically proportional to accurately reflect the incident spectrum.

[0039] However, as described herein, the spectral sensitivities of multiple filters can be reconfigured so that various target spectra can be reconstructed in an energetically proportional manner and without energy signal loss, regardless of the presence of narrowband and / or steep components within the incident spectrum. Specifically, the spectral sensitivities of various filters of a multispectral sensor device (such as device 100) can be configured so that the sum of the spectral sensitivities within a predefined wavelength range remains constant. In this way, spectral changes of extreme values ​​(flanks or peaks) within the target spectrum are not detected spectrally (such as in a device configured to exhibit Figure 7 ), but instead are detected in an overall manner. That is, the spectral sensitivities of the different channels are configured such that the summation function provides a uniform distribution over the full spectral range of the multi-spectral sensor device, where the full spectral range of the multi-spectral sensor device can be defined as the difference between the minimum wavelength associated with the peak spectral sensitivity of the filter channel and the maximum wavelength associated with the peak spectral sensitivity of the filter channel.

[0040] Figure 2 is a plot of an exemplary spectral response of a multi-spectral sensor device (eg, a spectrometer) in which the optical filters have been configured such that the sum of the spectral sensitivities within a predefined wavelength range is constant. Figure 2 As shown in FIG. 1 , the spectrometer device is composed of five separate channels, each of which has a corresponding spectral sensitivity (202, 204, 206, 208, 210). Figure 2 Each of the spectral sensitivities of the associated device can be normalized to a constant value. Figure 2 As shown in FIG. 1 , the spectral sensitivities 202 to 210 are all normalized to a value of 1. Each of the spectral sensitivities is configured to have a shape such that Figure 2 The sum 214 of the spectral sensitivities within the predefined wavelength range 212 shown in FIG. 2 is constant as a function of wavelength. Figure 2 In the example of FIG. 2 , the sum 214 within the wavelength range 212 is equal to the value 1.

[0041] Modifying the spectral sensitivity of the filter in this way allows the detection of target spectra with narrow and / or steep components in an energetically proportional manner without signal loss. For example, one can still use Figure 2 The spectral sensitivity configuration shown in detects each of the narrow frequency peaks within the target spectrum 216 in an energetically proportional manner.

[0042] In other words, the spectral sensitivity of each filter-detector pair of the multi-spectral sensor device can be expressed as follows:

[0043]

[0044] Among them, λ min is the minimum wavelength of the predefined wavelength range, λ max is the maximum wavelength of the predefined wavelength range, k is the number of filters or detector channels, S_det i is the spectral sensitivity of filter or channel i, a i is the scaling factor for filter or channel i, and const indicates a constant value.

[0045] like Figure 2 As shown in FIG. 2 , the predefined wavelength range 212 covers the wavelength starting at the wavelength corresponding to the filter channel (i.e., at λ peak ≈400 nm) and the minimum wavelength associated with the peak spectral sensitivity of the filter 202 and the filter channel (i.e., at λ peak The predefined wavelength range 212 covers a wavelength band of approximately 320 nm.

[0046] In some embodiments, the predefined wavelength range over which the sum of spectral reflectances is constant may cover, for example, wavelength bands of at least two filters within a multispectral sensor device, including, for example, wavelength bands covering at least three filters within the multispectral sensor device, wavelength bands covering at least four filters within the multispectral sensor device, wavelength bands covering at least five filters within the multispectral sensor device, wavelength bands covering at least ten filters within the multispectral sensor device, wavelength bands covering at least fifteen filters within the multispectral sensor device, wavelength bands covering at least twenty filters within the multispectral sensor device, or wavelength bands covering at least twenty-five filters within the multispectral sensor device, etc.

[0047] In some embodiments, the predefined wavelength range over which the sum of the spectral reflectance is constant may cover the visible wavelength range. For example, the predefined wavelength range over which the sum is constant may be between about 380 nm and about 780 nm. In some cases, the predefined wavelength range over which the sum of the spectral sensitivity is constant covers wavelengths in the ultraviolet, near infrared, and / or visible wavelength ranges. For example, the predefined wavelength range over which the sum is constant may be between about 10 nm and about 380 nm. In another example, the predefined wavelength range over which the sum is constant may be between about 780 nm and about 5 microns.

[0048] Figure 2 The shape of the spectral sensitivity of each channel shown in is called a "cosine" shape because the curve essentially traces the shape of the curve represented by the cosine function. However, the spectral sensitivity of the filter is not limited to this shape. For example, Figure 3 is a plot of an exemplary spectral response of a multi-spectral sensor device (e.g., a spectrometer device) in which the optical filters of the spectrometer have been configured so that the sum 300 of the spectral sensitivities (302 to 310) of the filters within a predefined wavelength range is constant, and in which the shape of the spectral sensitivities is a trapezoid. That is, the peak of the spectral sensitivity of each filter (such as peak 312 of filter 306) is constant over a wider wavelength range. The width of the broadened peak (such as peak 312) can be at least 5 nm, at least 10 nm, at least 15 nm, at least 20 nm, at least 25 nm, or at least 30 nm, but other widths are possible. The width of the peak may be limited by the filter construction design and may be less than 50 nm, less than 45 nm, less than 40 nm, or less than 35 nm.

[0049] Other spectral sensitivity shapes are possible. For example, Figure 4 is a plot of an exemplary spectral response of a multi-spectral sensor device (e.g., a spectrometer device) in which the optical filters of the spectrometer have been configured so that the sum 400 of the spectral sensitivities (402 to 410) of the filters within a predefined wavelength range is constant, and in which the shape of the spectral sensitivities is a triangle.

[0050] although Figures 2 to 4 The spectral sensitivity depicted in has the same shape for each optical filter, but the optical filters within a multispectral sensor device may exhibit different shapes. For example, Figure 5is a plot of an exemplary spectral response of a multi-spectral sensor device (e.g., a spectrometer device) in which the optical filters have been configured such that the sum of the spectral sensitivities within a predefined wavelength range is constant, and in which the shapes of the spectral sensitivities of at least two optical filters are different. Specifically, the shape of each of the spectral sensitivity curves 506, 508, and 510 is different from one another. Spectral sensitivity curve 506 is steeper on the lower wavelength side of its peak and has a shallower slope on the higher wavelength side of its peak. In contrast, sensitivity curve 508 has a shallower slope on the lower wavelength side of its peak and a steeper slope on the higher wavelength side of its peak. Furthermore, the separation of the spectral sensitivity peaks may be asymmetric. For example, as Figure 5 As shown in , the peak associated with curve 506 is further away from the peak associated with curve 508 than the peak associated with curve 504 .

[0051] Alternatively or additionally, the spectral sensitivity curves of the two filters of the multi-spectral sensor device may be mirror images of each other. For example, the shape of spectral sensitivity curve 506 is a mirror image of the shape of spectral sensitivity curve 508, as viewed around an imaginary axis extending vertically at a wavelength of 550 nm.

[0052] exist Figures 2 to 5 In each of the exemplary plots shown in FIG. 1 , the sum of the spectral sensitivity over the entire predefined wavelength range varies at each wavelength within the range according to a combination of only two spectral sensitivity curves. For example, referring again to Figure 2 , the constant sum 214 of the spectral sensitivity curves between wavelengths of about 400 nm and about 480 nm is the result of the combination of curves 202 and 204; the constant sum 214 of the spectral sensitivity curves between wavelengths of about 480 nm and about 560 nm is the result of the combination of curves 204 and 206; the constant sum 214 of the spectral sensitivity curves between wavelengths of about 560 nm and about 640 nm is the result of the combination of curves 206 and 208; the constant sum 214 of the spectral sensitivity curves between wavelengths of about 640 nm and about 720 nm is the result of the combination of curves 208 and 210. In other words, it can be said that the constant sum of the spectral sensitivity values ​​within a subset of the predefined wavelength range 212 is composed of the sum of the spectral sensitivity values ​​of the first filter and the spectral sensitivity values ​​of the second filter. The spectral sensitivity shown in the plot may have one or more advantages. For example, in some embodiments, if it is desired to analyze / reconstruct a lower spectral range of visible light in more detail, more channels with lower spectral separation in that range may be defined. If there are spectral ranges where detail is less important (eg, outside the visible range), the spectral separation in these ranges may be relaxed.

[0053] In other embodiments, the constant sum of spectral sensitivity values ​​within a subset of predefined wavelength range 212 may include the sum of spectral sensitivity values ​​of just two or more filters. For example, in some cases, the constant sum may be attributed to the sum of spectral sensitivity values ​​associated with three different filters, four different filters, five different filters, or more different filters.

[0054] In some embodiments, the FWHM value of the spectral sensitivity curve of a first filter in the spectrometer is greater than the distance between the peak of the spectral sensitivity curve of the first filter and the peak of the spectral sensitivity curve of the second filter in the spectrometer. Figure 2 , spectral sensitivity curve 202 may be modified to have a FWHM of 120 nm, and the distance between the peak of curve 202 and the peak of curve 204 may be set to 100 nm.

[0055] In some embodiments, the spectral sensitivity of the photodetector elements should be taken into account when designing a multi-spectral sensor device. In these cases, the spectral sensitivity curve of each filter is scaled to the maximum spectral sensitivity curve of the detector element. For example, FIG. 6A is a plot of exemplary spectral sensitivity curves (602, 604, 606, 608, 610) of a photodetector device scaled to the spectral sensitivity curve 600 of a silicon detector element (e.g., a silicon photodiode) within a predefined wavelength range 612. That is, the plot in FIG. 6A shows Figure 5 6A , the amplitude of curve 600 increases from a wavelength of about 350 nm to a wavelength of about 750 nm. The optical filters of the spectrometer are designed to exhibit an increased scaled spectral sensitivity curve (602a, 604a, 606a, 608a, 610a) that matches curve 600 over the same wavelength range.

[0056] FIG6B is a plot of exemplary spectral response curves of a filter of a spectrometer as calculated based on a scaling of the curves in FIG6A. Each curve in FIG6B (602b, 604b, 606b, 608b, 610b) corresponds to a spectral response curve of a spectral sensitivity curve (602a, 604a, 606a, 608a, 610a), respectively. Thus, FIG6B shows the requirements for filter design, which can be expressed as F i (λ) = S_det i (λ) / S i (λ). Due to the shape of the Si, there is some difference between the sensor sensitivity (solid line) and the filter transmission (dashed line) seen in the new graph.

[0057] As described herein, the filters of the present disclosure may be interference filters, such as interference filters formed from thin-film dielectric layers having alternating refractive indices. The configuration of the layers (e.g., thickness, number of layers, order of layers) may be determined using optimization techniques. For example, a designer provides a starting design whose properties are sufficiently close to the specifications required for the filter's spectral sensitivity curve. An optimization algorithm may then be used to adjust the thickness of the layers and (in some cases) their refractive indices until a design is achieved that best matches the desired spectral sensitivity curve characteristics. Further details on the manufacture of interference filters for a specified spectral responsivity curve may be found, for example, in S. Larouche and L. Martinu, "OpenFilters: open-source software for the design, optimization, and synthesis of optical filters," Applied Optics Vol. 47 (13), pp. C219-C230 (2008), the entire contents of which are incorporated herein by reference.

[0058] By means of the method for forming channel sensitivity according to the invention, a stable detection of any narrowband target spectrum can also be achieved. The reconstruction of the total spectrum is improved so that the energy components are proportionally imaged as sensor signals without a large increase in the number of filter-detector pairs.

[0059] A number of embodiments have been described. However, it will be appreciated that various modifications may be made without departing from the spirit and scope of the invention. Therefore, other embodiments are within the scope of the following invention claims.

Claims

1. A photodetector device, comprising: at least three photodetector elements; and at least three optical filters, wherein each of the at least three optical filters is arranged in front of a light detecting surface of a corresponding light detecting element of the at least three light detecting elements to filter incoming light incident on the light detecting surface, wherein the at least three optical filters are configured to filter at least three different wavelength bands of the incoming light, respectively, wherein the at least three different wavelength bands are combined to span a predefined wavelength range, wherein each of the at least three optical filters has a corresponding spectral sensitivity, and Wherein, a sum of the spectral sensitivities of the at least three optical filters within the predefined wavelength range is a constant value.

2. The photodetector according to claim 1, wherein Each of the spectral sensitivities of the at least three optical filters used in the sum is normalized to a predefined value.

3. The photodetector according to claim 1 or 2, wherein: The sum within a first wavelength range smaller than and within said predefined wavelength range consists of the sum of said spectral sensitivity of a first optical filter of said at least three optical filters and said spectral sensitivity of a second optical filter of said at least three optical filters.

4. The photodetector according to claim 1 or 2, wherein: The spectral sensitivity of at least one of the at least three optical filters has a shape of a curve represented by a cosine function.

5. The photodetector according to claim 1 or 2, wherein: The spectral sensitivity of at least one of the at least three optical filters has the shape of a trigonometric function.

6. The photodetector according to claim 1 or 2, wherein: The spectral sensitivity of at least one of the at least three optical filters has the shape of a trapezoidal function.

7. The photodetector according to claim 1 or 2, wherein: For each of the at least three optical filters, the spectral sensitivity of the optical filter comprises a corresponding peak value and a corresponding full width at half maximum (FWHM) value, and The full width at half maximum (FWHM) value of a first optical filter among the at least three optical filters is greater than a distance between the peak of the first optical filter and the peak of a second optical filter among the at least three optical filters.

8. The photodetector according to claim 1 or 2, wherein: The shape of the spectral sensitivity of each of the at least three optical filters is the same.

9. The photodetector according to claim 1 or 2, wherein: The shape of the spectral sensitivity of a first optical filter of the at least three filters is different from the shape of the spectral sensitivity of a second optical filter of the at least three filters.

10. The photodetector according to claim 1 or 2, wherein: The shape of the spectral sensitivity of a first optical filter of the at least three filters is a mirror image of the shape of the spectral sensitivity of a second optical filter of the at least three filters.

11. The photodetector according to claim 1 or 2, wherein: The predefined wavelength range spans wavelengths between 380 nm and 780 nm.

12. The photodetector according to claim 1 or 2, wherein: For each of the at least three optical filters, the spectral sensitivity of the optical filter comprises a corresponding peak value and a corresponding full width at half maximum (FWHM) value, and Wherein, the full width at half maximum (FWHM) value of the first optical filter among the at least three optical filters is greater than or equal to 25 nm.

13. The photodetector according to claim 1 or 2, wherein: The at least three optical filters are contained in a line array.

14. The photodetector according to claim 1 or 2, wherein: The at least three optical filters are contained in a two-dimensional array.

15. The photodetector according to claim 1 or 2, wherein: Each of the at least three optical filters is a bandpass filter configured to transmit light within its respective wavelength band of the incoming light.

16. The photodetector according to claim 1 or 2, wherein: Each optical filter of the at least three filters is an absorption filter configured to absorb light within its respective wavelength band of the incoming light.

17. The photodetector according to claim 1 or 2, wherein: Each optical filter of the at least three filters comprises an interference filter.

18. The photodetector according to claim 1 or 2, wherein: The at least three optical filters are arranged in a circular pattern.

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