Depth imaging device having central wavelenth monitoring function, and method for acquiring depth image in correspondence with central wavelength change of source light

Abstract

The present invention relates to a depth imaging device having a central wavelength monitoring function, and a method for acquiring depth image in correspondence to a central wavelength change of a source light by using the device. The depth imaging device according to the present invention comprises: a light transmitter for transmitting a source light; a light receiver for receiving reflected light of the source light; an interferometer having a first reflective layer arranged at the front of the light receiver, and a second reflective layer arranged to be spaced a predetermined distance apart from the first reflective layer; a distance adjustment means for adjusting the distance between the first reflective layer and the second reflective layer; a central wavelength monitoring means for measuring a change in the central wavelength of the source light; and a control unit for controlling the distance adjustment means, wherein the control unit controls the distance adjustment means in correspondence to the central wavelength measured by the central wavelength monitoring means.

Description

Depth imaging device with central wavelength monitoring function and method for acquiring depth images in response to changes in the central wavelength of source light

[0001] The present invention relates to a depth imaging device having a center wavelength monitoring function and a method for acquiring a depth image corresponding to a change in the center wavelength of a source light using the device. More specifically, the present invention relates to a depth imaging device capable of capturing a depth image with an improved signal-to-noise ratio by monitoring the center wavelength emitted from an optical transmitter. In addition, the present invention relates to a method for acquiring a depth image with an improved signal-to-noise ratio by monitoring the center wavelength emitted from an optical transmitter.

[0002] Korean Patent Laid-Open Publication No. 10-2022-0160449, for which the inventors of the present invention have filed a patent application, discloses an invention relating to a depth imaging device. The present invention complements and improves upon the invention disclosed in the aforementioned patent document, and all technical details disclosed in the aforementioned patent document are incorporated herein by reference.

[0003] [Spectroscopic Imaging Technology]

[0004] Spectroscopic imaging technology provides two-dimensional image information across spectral bands. Spectroscopic imaging technology is used in a variety of fields, including PCB inspection, counterfeit money detection, skin characteristic measurement, and food inspection.

[0005] A spectroscopic imaging device includes an optical system such as a light-receiving lens or a light-projecting lens, a light receiver having a light-receiving sensor, and a spectroscopic device. The light receiver is divided into multiple regions and receives light from a subject and generates an electrical signal. The spectroscopic device is placed in front of the light-receiving sensor of the light receiver. Spectroscopic devices are broadly classified into monochromator type and optical tunable filter type. Optical tunable filters can be broadly divided into fixed type and tunable type. Optical tunable filters only allow light of a specific wavelength range to pass through. Representative fixed tunable filters include the filter wheel type and Fabry-Perot interference filter.

[0006] Fig. 1 is a drawing for explaining a Fabry-Perot Interferometer (FPI), which is an example of an optical variable filter. As shown in Fig. 1, the Fabry-Perot interference filter has a pair of reflective surfaces (R1, R2) facing each other. Incident light is reflected between the reflective surfaces (R1, R2). Since the reflectivity of the reflective surfaces (R1, R2) is not 100%, a certain percentage of light (L) is reflected repeatedly between the reflective surfaces (R1, R2) in the process of light of the transmitted wavelength being reflected repeatedly between the reflective surfaces (R1, R2). t ) passes through the interference filter, and the rest is reflected back. In this process, light of a specific wavelength (the transmission wavelength) causes constructive interference, and the rest of the light disappears due to destructive interference.

[0007] In a Fabry-Perot interference filter, the distance (t) between a pair of reflecting surfaces (R1, R2) op) and the angle of incidence (θ), the transmission wavelength is determined. The reflective surface can be implemented as a single layer of a metal series, or can be composed of a structure formed of high index and low index dielectric layers with a thickness of λ (transmission wavelength) / 4. The former has the disadvantage of low transmittance due to the absorption component in the reflective surface. On the other hand, the latter allows for the configuration of a filter with high reflectance and narrow half width.

[0008] The mathematical expression 1 below is a formula for determining the transmission wavelength of a Fabry-Perot interference filter. Here, n is the refractive index of the material filled between the reflective surfaces, and t op is the distance between the reflecting surfaces, θ is the angle of incidence, m is an integer, and λ is the transmission wavelength.

[0009]

[0010] According to mathematical equation 1, the Fabry-Perot interference filter has a transmission wavelength that varies with the angle of incidence. That is, m is 1, and the distance between a pair of reflecting surfaces (t op ) is λ0 / 2(t op =λ0 / 2), and when air is filled between the reflecting surfaces (n=1), the transmission wavelength of light incident perpendicularly on the Fabry-Perot interference filter becomes λ0. And when the incident angle of the incident light increases, the cosθ value decreases, so the transmission wavelength becomes shorter than λ0. For example, when the incident angle is 30 degrees, the transmission wavelength is 0.866λ0. That is, light incident perpendicularly to the Fabry-Perot interference filter transmits only the component with a wavelength of λ0, and light incident at a 30-degree angle transmits only the component with a wavelength of 0.866λ0.

[0011] In addition, as explained above with reference to mathematical equation 1, since the incident light does not always enter the Fabry-Perot interference filter at the ideal incident angle, i.e., perpendicularly, a deviation may occur depending on the incident angle. If the incident light is not perpendicularly incident on the Fabry-Perot interference filter, short-wavelength light with a wavelength that is about 10 to 20 nm shorter than the target center wavelength may pass through the Fabry-Perot interference filter, and light with the target center wavelength may be blocked by the Fabry-Perot interference filter. The incident angle may vary depending on the position of the interference filter. Generally, the incident angle of light entering the center of the Fabry-Perot interference filter is close to perpendicular, and light entering the outer part of the Fabry-Perot interference filter is obliquely incident, so light with a shorter wavelength passes through the outer part compared to the center. Therefore, light with the target center wavelength may be blocked by the interference filter at the outer part of the Fabry-Perot interference filter.

[0012] For example, if a Fabry-Perot interference filter with a center wavelength of 940 nm and a full width at half maximum of 30 nm is used as an optical filter, and the incident angle of light incident on the outer part of the Fabry-Perot interference filter increases, the transmission wavelength shifts toward a shorter wavelength of 20 nm, then the transmission wavelength of the Fabry-Perot interference filter at the outer part changes from 925 to 955 nm to 905 to 935 nm, so light in the wavelength range of 935 to 955 nm exceeds the upper limit of the transmission wavelength range of the outer part of the Fabry-Perot interference filter, which is 935 nm, and is blocked by the outer part of the Fabry-Perot interference filter. Therefore, the outer part of the image acquired by the spectroscopic imaging device may be distorted. In addition, if the incident light is not incident perpendicularly to the Fabry-Perot interference filter, there is also the problem that a haze phenomenon due to crosstalk may occur.

[0013] FIG. 2 is a diagram illustrating the propagation of light between reflective surfaces (R1, R2) when incident light with a large incident angle enters a conventional Fabry-Perot interference filter. As illustrated in FIG. 2, when the incident angle is large, the distance that light travels in the direction orthogonal to the reflective surfaces (R1, R2) increases as the light is repeatedly reflected between the reflective surfaces (R1, R2) (the distance increases from Zone 1 to Zone 3). This distance increases as the reflectivity of the reflective surfaces (R1, R2) increases and the incident angle increases. More specifically, incident light with an incident angle of 5 degrees does not travel much in the lateral direction until its intensity weakens due to repeated reflections, but light with an incident angle of 25 degrees travels a considerably long distance, and is incident not only on the pixels corresponding to the subject segmentation area of ​​the array sensor in the optical receiver (LR) but also on adjacent pixels.

[0014] Table 1 shows the distance traveled in the direction perpendicular to the reflective surface according to the reflectivity of the reflective surface and the angle of incidence. The array sensor of the optical receiver typically has a pixel size of several micrometers.

[0015]

[0016] Referring to Table 1, when the incident angle is 0 degrees (normally incident), the travel distance is 0 μm regardless of the reflectivity, and when the incident angle is 30 degrees, it is approximately 9.3 μm when the reflectivity is 0.9, and approximately 24.4 μm when the reflectivity is 0.95. As the reflectivity increases, the number of reflections increases, so the travel distance increases. As the incident angle increases, the travel distance until one reflection increases. Therefore, it can be seen that as the reflectivity and incident angle increase, the travel distance becomes longer, which greatly affects the adjacent area and ultimately reduces the resolution of the spectral imaging device. Fig. 3 is a graph showing the light leakage into adjacent angles (pixels) according to the haze component. The horizontal axis of Fig. 3 represents the scattering angle, and the vertical axis represents the output (intensity). According to Fig. 3, it can be seen that as the haze component increases, the light leakage (angular crosstalk) into adjacent angles (pixels) increases.

[0017] In summary, conventional spectroscopic imaging devices using conventional Fabry-Perot interference filters had the following problems.

[0018] First, since the angle of incidence of light entering the outer part of the Fabry-Perot interference filter is large, light in the target wavelength band is blocked by the Fabry-Perot interference filter, and rather, light with a shorter wavelength than light in the target wavelength band can pass through the Fabry-Perot interference filter.

[0019] Second, when the incident light entering the Fabry-Perot interference filter has a large angle of incidence, the distance the reflected light travels in the direction orthogonal to the reflective surfaces increases as it is repeatedly reflected between a pair of reflective surfaces. Therefore, a crosstalk phenomenon occurs in which the incident light is irradiated not only to the pixels corresponding to the subject segmentation area of ​​the corresponding array sensor but also to adjacent pixels, resulting in an increase in haze and a decrease in resolution as the light approaches the periphery of the Fabry-Perot interference filter.

[0020] [Depth Imaging Technology]

[0021] Depth imaging technology, which can be used in facial recognition, AR, and VR technologies, uses cameras that use structured light (SL) and TOF cameras that measure the time of flight of light.

[0022] Structured light uses an infrared pattern composed of tens of thousands of dots to illuminate a subject, then reads the distortion of that pattern caused by the subject. This method has the disadvantage that recognition rates drop significantly as the distance between the camera and the subject increases.

[0023] There are two types of TOF methods: a direct method that continuously emits infrared light at nanosecond (nS) intervals and measures the distance to the subject by measuring the time it takes for the light to hit the subject and reach the infrared sensor, and an indirect method that measures the change in the phase of the light reflected from the subject. TOF cameras divide the subject into multiple areas and measure the distance to each area to obtain a three-dimensional image. Depending on the method of dividing the areas, TOF methods are divided into a mechanical scanning method, a solid-state TOF method that uses MEMS mirrors, and a flash TOF method that irradiates the subject all at once.

[0024] A TOF camera includes an optical system such as a light-receiving lens or a light-projecting lens, a light receiver having a light-receiving sensor, a light transmitter having a light source and a driving device, and an optical filter. The light receiver is divided into multiple regions, and each region receives light that is reflected from the light transmitter toward the subject, external light directed toward the light receiver, or external light reflected from the subject, and generates an electrical signal. The external light may be light from the sun or artificial light. The light transmitter irradiates light toward the subject. The light transmitter can irradiate light with a narrow bandwidth in the ultraviolet, visible, or infrared range in the form of pulses, for example. The optical filter is placed in front of the light-receiving sensor of the light receiver and blocks external light other than the light irradiated by the light transmitter from entering the light receiver. The optical filter may be an interference filter, an absorptive filter, a dichroic filter, etc. An optical filter may be a band-pass filter that allows only a specific wavelength range to pass through.

[0025] When using an interference filter as an optical filter, the depth imaging device also has the same problems as the conventional spectral imaging device described above. First, since the incident angle of the source light incident on the outer part of the band-pass filter is large, the source light is blocked by the band-pass filter, and external light with a shorter wavelength than the source light can pass through the band-pass filter instead. Second, when the incident light incident on the band-pass filter has a large incident angle, the distance that the reflected light travels in the direction orthogonal to the reflective surfaces increases during the process of repeated reflection between a pair of reflective surfaces. Therefore, a crosstalk phenomenon occurs in which the incident light is irradiated not only to the pixels corresponding to the subject segmentation area of ​​the corresponding array sensor but also to adjacent pixels, resulting in an increase in the haze component and a decrease in the resolution as the depth imaging device approaches the outer part.

[0026] As a method for solving the first problem among these problems, US Patent Publication No. US2019 / 0162885A1 discloses a device including an optical transmitter configured to transmit source light, an optical receiver configured to receive reflected light of the source light, and an infrared or near-infrared bandpass filter disposed in front of a photodetector of the optical receiver such that the received source light is received by a bandpass filter before the photodetector, wherein the bandpass filter includes a plurality of regions including a first region capable of transmitting light within a first wavelength range and a second region capable of transmitting light within a second wavelength range. More specifically, a filter having a bandwidth of the order of 5 nm is used in the first region, which is a central region where incident light is mainly incident nearly vertically, and a filter having a bandwidth of the order of 30 nm is used in the second region, which is an outer region where incident light is relatively often incident obliquely, so that external light is blocked at least in the central region where reflected light is incident nearly vertically, thereby increasing sensitivity.

[0027] However, this method cannot account for variations caused by factors such as manufacturing variations in the light source itself, the temperature surrounding the light source, and the light source's output. Therefore, it cannot sufficiently reduce the bandwidth of the bandpass filter even in the center. Furthermore, it cannot improve the signal-to-noise ratio in the periphery. Furthermore, it cannot improve crosstalk.

[0028] [Prior Art Literature]

[0029] U.S. Patent Publication No. US2019 / 0162885A1

[0030] Korean Patent Publication No. KR10-2012-0089312 A

[0031] Korean Patent Publication No. 10-2022-0160449

[0032] Japanese Publication Patent JP2016-050803A

[0033] Japanese Publication Patent JP2016-011932A

[0034] In order to solve the above problems, the inventors of the present invention invented a new interference filter having an improved structure than the Fabry-Paro interference filter and a depth imaging device with improved sensitivity, and applied for a patent with the Korean Intellectual Property Office (Korean Patent Publication No. 10-2022-0160449).

[0035] The interference filter disclosed in the above patent document is an interference filter having a first reflective layer having a first surface on which light is incident and a second surface opposite thereto, a third surface facing the second surface at a distance therefrom, and a fourth surface opposite thereto from which light is emitted, and configured such that the sum of the values ​​obtained by multiplying the thickness and refractive index of each of all media on an imaginary path parallel to the optical axis between the first surface of the first reflective layer and the fourth surface of the second reflective layer increases as the distance from the optical axis increases.

[0036] In addition, the depth imaging device disclosed in the above patent document includes an optical transmitter configured to transmit source light, an optical receiver configured to receive reflected light of the source light, and an interference filter disposed in front of the optical receiver, wherein the interference filter has the above configuration. In addition, the spectroscopic imaging device further includes a center wavelength monitoring device configured to measure a change in a center wavelength of the source light, an optical distance adjusting mechanism configured to adjust an optical distance parallel to an optical axis direction between the first reflective layer and the second reflective layer, and a controller that controls the optical distance adjusting mechanism in response to a change in the center wavelength of the source light measured from the center wavelength monitoring device.

[0037] The present invention is an improved version of the depth imaging device described above, and aims to provide a depth imaging device that can more accurately detect changes in the central wavelength of source light and adjust the optical distance of an interference filter.

[0038] According to one aspect of the present invention, a depth imaging device having a center wavelength monitoring function is provided. The depth imaging device having a center wavelength monitoring function according to the present invention includes an optical transmitter configured to transmit source light, an optical receiver configured to receive reflected light of the source light, an interference filter having a first reflective layer disposed in front of the optical receiver and a second reflective layer disposed at a predetermined distance from the first reflective layer, a distance adjusting means for adjusting a distance between the first reflective layer and the second reflective layer, a center wavelength monitoring means for measuring a change in a center wavelength of the source light, and a control unit for controlling the distance adjusting means, wherein the control unit is configured to control the distance adjusting means in response to a change in the center wavelength measured by the center wavelength monitoring means.

[0039] In some embodiments, the central wavelength monitoring means may include a first photosensor configured to have a sensitivity that increases as the wavelength of the source light increases, and a second photosensor configured to have a sensitivity that decreases as the wavelength of the source light increases, and may be configured to compare outputs of the first photosensor and the second photosensor and measure a change in the central wavelength of the source light based on a difference in the outputs.

[0040] In some embodiments, the hyperspectral imaging device may further include a long-wavelength pass filter positioned in front of the first photosensor and a short-wavelength pass filter positioned in front of the second photosensor. In addition, it is preferable that the long-wavelength pass filter use a color glass filter whose transmission wavelength does not change depending on the angle of incidence.

[0041] In some embodiments, the interference filter may include a first reflective layer having a first surface through which light is incident and a second surface opposite thereto, a second reflective layer having a third surface facing the second surface at a distance therefrom and a fourth surface opposite thereto through which light is emitted, and a second reflective layer having a fourth surface through which light is emitted, wherein the sum of the products of thicknesses and refractive indices of each of all media on an imaginary path parallel to an optical axis between the first surface of the first reflective layer and the fourth surface of the second reflective layer may be configured such that the distance between the second surface of the first reflective layer and the third surface of the second reflective layer increases as the distance from the optical axis increases. In addition, at least one of the first reflective layer and the second reflective layer may be curved such that the distance between the second surface of the first reflective layer and the third surface of the second reflective layer of the interference filter increases as the distance from the optical axis increases.

[0042] According to another aspect of the present invention, a method for acquiring a depth image corresponding to a change in the central wavelength of source light is provided. The method for acquiring a depth image corresponding to a change in the central wavelength of source light according to the present invention includes the steps of measuring outputs of a first optical sensor and a second optical sensor for source light incident from an optical transmitter, comparing the output of the first optical sensor with the output of the second optical sensor, obtaining a difference between the outputs of the first optical sensor and the outputs of the second optical sensor, obtaining a central wavelength of the source light corresponding to the difference in output when there is a change in the difference in output, adjusting a gap between a first reflective surface and a second reflective surface of an interference filter corresponding to the obtained central wavelength, and obtaining a depth image by causing the source light passing through the interference filter with the adjusted gap to be input to an optical receiver. In addition, the first optical sensor is configured such that its sensitivity increases as the wavelength of the source light increases, and the second optical sensor is configured such that its sensitivity decreases as the wavelength of the source light increases.

[0043] A depth imaging device equipped with a central wavelength monitoring function according to the present invention is configured to adjust the spacing of interference filters in response to changes in the central wavelength of source light. Accordingly, changes in the central wavelength of the source light can be monitored, changes in the central wavelength can be measured, and the spacing of the interference filters can be immediately adjusted to capture more precise depth images.

[0044] In addition, the depth imaging device according to the present invention uses an interference filter configured such that the sum of the product of the thickness and refractive index of each medium on a virtual path parallel to the optical axis increases as the path gets farther away from the optical axis, thereby transmitting light of a target wavelength band and blocking light of other bands not only in the center but also in the outer region where the incidence angle is large. Therefore, the depth imaging device and the wide-angle spectral imaging device using the interference filter according to the present invention have improved sensitivity in the outer region and no image distortion.

[0045] In addition, the depth image acquisition method according to the present invention can acquire a depth image with an improved signal-to-noise ratio by reducing the width of a band passing through the interference filter by adjusting the spacing between the reflective surfaces of the interference filter in response to a change in the central wavelength of the source light.

[0046] Figure 1 is a drawing for explaining a Fabry-Perot Interferometer (FPI), which is an example of an optical variable filter.

[0047] Figure 2 is a drawing for explaining the propagation of light between reflective surfaces when incident light with a large incident angle enters a conventional Fabry-Perot interference filter.

[0048] Figure 3 is a graph showing the light leakage to adjacent angles (pixels) according to the haze component.

[0049] Figure 4 is a schematic diagram of a wide-angle spectral imaging device according to one embodiment of the present invention.

[0050] Figure 5 is a schematic diagram of the interference filter and optical receiver shown in Figure 4.

[0051] Fig. 6 is a drawing showing a part of the interference filter illustrated in Fig. 5.

[0052] Figure 7 (a) shows the spectrum of light passing through a conventional interference filter with a constant spacing between reflective layers, and (b) shows the spectrum of light passing through the interference filter shown in Figures 5 and 6.

[0053] Figure 8 is a drawing for explaining the operation of the interference filter illustrated in Figure 5.

[0054] FIG. 9 is a diagram illustrating another example of an interference filter and part of an optical receiver.

[0055] Figures 10 to 12 are schematic diagrams of further examples of interference filters.

[0056] FIG. 13 is a schematic diagram of a depth imaging device according to an embodiment of the present invention.

[0057] Figure 14 is a drawing for explaining the principle of a central wavelength measuring device using a dual sensor.

[0058] Figure 15 is a conceptual diagram of one embodiment of a depth imaging device having a center wavelength monitoring function according to the present invention.

[0059] FIG. 16 is a graph showing the sensitivity of an optical sensor according to an incident angle in a central wavelength monitoring means (130) according to the present invention, when the first optical filter (131a) is a shortpass filter and the second optical filter (132a) is a longpass filter.

[0060] FIG. 17 is a graph showing the sensitivity of an optical sensor according to an incident angle in a central wavelength monitoring means (130) according to the present invention, when the first optical filter (131a) is a shortpass filter and the second optical filter (132a) is a colorglass filter.

[0061] Figure 18 is a flowchart illustrating a method for acquiring a depth image corresponding to a change in the central wavelength of source light according to the present invention.

[0062] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. These embodiments are provided solely to ensure complete disclosure of the present invention and to fully inform those skilled in the art of the scope of the invention. Like reference numerals in the drawings indicate like elements.

[0063] [Wide-angle spectral imaging device]

[0064] Fig. 4 is a schematic diagram of a wide-angle spectroscopic imaging device according to an embodiment of the present invention. As illustrated in Fig. 4, a wide-angle spectroscopic imaging device (100) according to an embodiment of the present invention includes an optical system (10) such as a light-receiving lens or a light-projecting lens, an optical receiver (20), an interference filter (40), and a controller (50).

[0065] A wide-angle spectral imaging device (100) according to one embodiment of the present invention can obtain an image using light of a specific wavelength band by adjusting the passband of an interference filter (40). For example, an image of only red light or an image of only green light can be obtained among the light (6) reflected from a subject (8).

[0066] The optical receiver (20) receives light (6) that has been irradiated from a light source such as the sun or an indoor light, reflected from a subject (8), and then passed through an interference filter (40). The optical receiver (20) is divided into a plurality of regions, and each region receives light (6) from the subject (8) that has passed through the interference filter (40) and generates an electrical signal.

[0067] The interference filter (40) serves to pass only light of a specific wavelength band among the light directed to the optical receiver (20). The interference filter (40) is placed between the optical system (10) and the light receiving sensor array of the optical receiver (20).

[0068] FIG. 5 is a schematic diagram of an example of an interference filter and an optical receiver illustrated in FIG. 4, and FIG. 6 is a drawing showing a part of the interference filter illustrated in FIG. 5.

[0069] The interference filter (40) of the present invention has a structure to reduce positional deviations that occur because incident light does not strike at an ideal angle of incidence, i.e., vertically, at all positions of the interference filter (40).

[0070] As illustrated in FIG. 5, the incident angle (θ(x)) of light (L) incident on the interference filter (40) increases as the distance (x) from the optical axis (OA) increases. When a mobile imaging lens is used as the lens (10), the light incident on the interference filter (40) has an incident angle (θ(x)) of approximately 0 to 30°. That is, the incident angle (θ(x)) of light incident on the center of the interference filter (40) (near the optical axis (OA)) is close to 0°, and the incident angle (θ(x)) of light incident on the outermost part far from the optical axis (OA) can be close to 30°.

[0071] In order to reduce deviation according to the angle of incidence (θ(x)), the present invention is configured such that the optical path of incident light passing through the interference filter (40) is constant regardless of the angle of incidence (θ(x)) of the incident light. To this end, the thickness and refractive index of the media constituting the interference filter (40) are adjusted.

[0072] As illustrated in FIG. 5, the interference filter (40) includes a first optical member (41) and a second optical member (42). The first optical member (41) includes a glass substrate (43) and a first reflective layer (44) formed on the glass substrate (43). The second optical member (42) includes a glass substrate (45) and a second reflective layer (46) formed on the glass substrate (43). The first optical member (41) and the second optical member (42) may be circular or oval.

[0073] The first reflection layer (44) and the second reflection layer (46) of the interference filter (40) are spaced apart from each other by a distance (t G(x)) face each other. Light incident on the interference filter (40) is reflected by the first reflection layer (44) and the second reflection layer (46), and light of a specific wavelength passes through the interference filter (40) according to the Fabry-Perot interference principle, and the remaining light is blocked. The gap (G) between the first reflection layer (44) and the second reflection layer (46) is generally filled with air, but may be made of another medium through which light can pass.

[0074] As illustrated in FIG. 6, the first reflective layer (44) has a first surface (441) onto which light is incident, and a second surface (442) on the opposite side. The second reflective layer (46) has a third surface (461) facing the second surface (442) at a distance therefrom, and a fourth surface (462) on the opposite side from which light is emitted. The first reflective layer (44) includes a plurality of sub-layers (44-1 to 44-h), and the second reflective layer (46) may also include a plurality of sub-layers (46-1 to 46-j). The sub-layers may be dielectric layers.

[0075] In the present invention, the interference filter (40) has a thickness (t) on each of the virtual paths (P(x)) of all media on the virtual path (P(x)) parallel to the optical axis (OA) between the first surface (441) of the first reflective layer (44) and the fourth surface (462) of the second reflective layer (46). k (x)) and refractive index (n) k The sum of the values ​​multiplied by (x) is configured to increase as the distance (x) from the optical axis (OA) increases. The optical axis (OA) refers to the optical axis of the optical system (10) placed before the interference filter (40).

[0076] Here, the media include all of the media constituting the first reflective layer (44), the media filling the gap (G) between the first reflective layer (44) and the second reflective layer (46), and the media constituting the second reflective layer (46). When the first reflective layer (44) includes a plurality of sub-layers, the media constituting each of the sub-layers are included. When the second reflective layer (46) includes a plurality of sub-layers, the media constituting each of the sub-layers are included. In addition, when the gap (G) between the first reflective layer (44) and the second reflective layer (46) is filled with a plurality of media, all of these media are included.

[0077] In more detail, the interference filter (40) is configured so that the sum of the product of the thickness and the refractive index of each of all media on the path (P(x)) parallel to the optical axis (OA) between the first surface (441) of the first reflective layer (44) and the fourth surface (462) of the second reflective layer (46) increases in inverse proportion to the value of COSθ(x) as it gets farther from the optical axis (OA) according to the following mathematical expression 2.

[0078]

[0079] (t k (x) and n k (x) represents the thickness (length of the path (P(x)) passing through each medium) and refractive index on the path (P(x)) parallel to the optical axis (OA), where the distance from the optical axis (OA) is x, and θ(x) is the angle of incidence of the incident light according to the distance (x) from the optical axis (OA), m is an integer, and λ represents the transmission wavelength of the interference filter. θ(x) increases as the distance (x) from the optical axis increases.)

[0080] Of course, the left side of mathematical expression 2 can also be expressed by dividing it into a term regarding the first reflective layer (44) (the first term on the right side), a term regarding the gap (G) between the first reflective layer (44) and the second reflective layer (46) (the second term on the right side), and a term regarding the second reflective layer (46) (the third term on the right side), as in mathematical expression 3 below.

[0081]

[0082] (t RAa (x) and n RAa (x) represents the thickness and refractive index on the path (P(x)) of each of the sub-layers constituting the first reflective layer (44). t Gb (x) and n Gb (x) represents the thickness and refractive index of each of the media filling the gap between the first reflective layer (44) and the second reflective layer (46) along the path (P(x)). And t RBc (x) and n RBc (x) represents the thickness and refractive index on the path (P(x)) of each of the sub-layers constituting the second reflective layer (46).

[0083] As can be seen from mathematical expression 2, if the value of the left side is constant regardless of the distance (x) from the optical axis (OA), the transmission wavelength (λ) of the interference filter (40) moves to a shorter wavelength as the incident angle (θ(x)) increases.

[0084] As illustrated in FIG. 5, the incident angle (θ(x)) increases as the distance (x) from the optical axis (OA) increases, so if the value on the left side is kept constant, the farther away from the optical axis (OA), the more short-wavelength light passes through the interference filter (40). Therefore, the periphery and the center of the image obtained from the wide-angle spectral imaging device (100) are displayed in different colors. The center of the image is displayed in a selected color, but the periphery of the image is displayed in a different color.

[0085] In order to prevent this phenomenon, the interference filter (40) of the present invention is configured to compensate for the change in the incident angle (θ(x)) according to the distance (x) from the optical axis (OA) in order to keep the transmission wavelength (λ) constant regardless of the distance (x) from the optical axis (OA). That is, the interference filter (40) is configured to compensate for the shift in the transmission wavelength (λ) as a short wavelength according to the change in the incident angle (θ(x)) according to the distance (x) from the optical axis (OA) in the thickness (t) of each medium according to the distance (x) from the optical axis (OA). k (x)) and refractive index (n) k It is configured so that the sum of the products of (x)) increases.

[0086] For example, in the interference filter (40) illustrated in FIGS. 5 and 6, the thickness and refractive index of the first reflective layer (44) and the second reflective layer (46) and the refractive index of the medium filling the gap (G) between the first reflective layer (44) and the second reflective layer (46) are kept constant regardless of the distance (x) from the optical axis (OA), while the gap (t) between the first reflective layer (44) and the second reflective layer (46) is G By adjusting only (x)), the change in the angle of incidence (θ(x)) according to the distance (x) from the optical axis (OA) is compensated.

[0087] The interference filter (40) illustrated in FIGS. 5 and 6 has a spacing (t) between the first reflection layer (44) and the second reflection layer (46) that increases as it gets farther from the optical axis (OA). G The first reflective layer (44) is curved so that (x)) becomes wider. At this time, the curvature of the first reflective layer (44) becomes smaller as it gets farther from the optical axis (OA).

[0088] t of the interference filter (40) of Figs. 5 and 6 RAa (x) and n RAa (x) is constant regardless of the distance (x) from the optical axis (OA), and t RBc (x) and n RBc Since (x) is also constant, the gap (t) between the first reflection layer (44) and the second reflection layer (46) GBy adjusting only (x)), the change in the angle of incidence (θ(x)) according to the distance (x) from the optical axis (OA) is compensated.

[0089] Figure 7 (a) shows the spectrum of light passing through a conventional interference filter with a constant spacing between reflective layers, and (b) shows the spectrum of light passing through the interference filter shown in Figures 5 and 6.

[0090] As can be seen in (a) of Fig. 7, when the spacing between the reflective layers is fixed, the center wavelength of the passband changes depending on the incident angle, so not only light with the target center wavelength (850 nm in Fig. 7) but also light with various center wavelengths transmits through the interference filter. That is, light with a wavelength of 850 nm transmits through the center of the interference filter (40) where the incident angle is 0 degrees, but light with a wavelength shorter than 850 nm transmits through the outer part of the interference filter (40) where the incident angle is large.

[0091] As can be seen in (b) of Fig. 7, the spacing (t) between the first reflective layer (44) and the second reflective layer (46) according to mathematical expression 2 G When (x)) is adjusted to become wider as it gets farther from the optical axis (OA), only light of the target center wavelength (850 nm) passes through regardless of the incident angle (θ(x)) (regardless of the distance (x) from the optical axis (OA).

[0092] In addition, as shown in Fig. 8, the interference filter (40) of the present embodiment serves to reduce the crosstalk phenomenon.

[0093] As can be seen from mathematical expression 2, the wavelength of light passing through the interference filter (40) is the distance (t) between the first reflection layer (44) and the second reflection layer (46). G1 (x)) is determined. However, as shown in Fig. 8, as it progresses toward the outer part, the interval (t) G1As (x)) becomes wider, when light incident at a specific angle repeatedly reflects between the first reflective layer (44) and the second reflective layer (46) and moves in a direction orthogonal to the second reflective layer (46), the path of light travel between the first reflective layer (44) and the second reflective layer (46) of the reflected light becomes increasingly longer. As a result, the distance between the first reflective layer (44) and the second reflective layer (46) no longer satisfies mathematical expression 2 for the reflected light, and the reflected light no longer passes through the interference filter (40) and is not incident on the pixels of adjacent areas of the light-receiving sensor array of the optical receiver (20).

[0094] Ultimately, the crosstalk phenomenon, in which incident light is incident on and affects not only the corresponding pixel in the corresponding target area but also pixels in adjacent areas, is improved. That is, the travel distance of reflected light is shortened compared to the conventional interference filter of FIG. 2. Accordingly, haze at the periphery of the wide-angle spectral imaging device (100) is reduced, and resolution is improved.

[0095] Additionally, the wide-angle spectral imaging device (100) includes an optical distance adjustment mechanism configured to adjust an optical distance of a path parallel to the optical axis (OA) between the first reflective layer (44) and the second reflective layer (46).

[0096] The optical distance adjustment mechanism serves to adjust the transmission wavelength of the interference filter (40). The optical distance is a distance that takes into account the refractive index of the medium. In other words, it is a value obtained by multiplying the refractive index of the medium by the distance. The optical distance adjustment mechanism can adjust the optical distance by changing the distance between the first reflection layer (44) and the second reflection layer (46) or the refractive index of the medium filling the space between the first reflection layer (44) and the second reflection layer (46). Since the optical distance adjustment mechanism is for adjusting the transmission wavelength of the interference filter (40), it adjusts the distance between the first reflection layer (44) and the second reflection layer (46) simultaneously regardless of the distance (x) from the optical axis (OA).

[0097] As illustrated in FIG. 5, in the present embodiment, the optical distance adjustment mechanism may be a gap adjustment mechanism (49) configured to adjust the geometric distance between the first reflection layer (44) and the second reflection layer (46) by moving the first reflection layer (44) relative to the second reflection layer (46) along the optical axis (OA) direction.

[0098] The gap adjustment mechanism (49) may be, for example, an actuator and a spring member. The actuator may be installed to push or pull at least one of the first optical member (41) and the second optical member (42) in a direction in which the first optical member (41) and the second optical member (42) come closer to each other or move away from each other. The spring member is installed to apply an elastic force to the first optical member (41) and the second optical member (42) in a direction opposite to that of the actuator to maintain the gap between the first reflective layer (44) and the second reflective layer (46).

[0099] Additionally, the gap adjustment mechanism (49) may be a device utilizing electromagnetic force. For example, electrode layers may be formed on the first optical member (41) and the second optical member (42), respectively, and may be brought closer to each other by having different polarities, and may be brought farther away from each other by having the same different polarities.

[0100] The controller (50) generates a control signal for adjusting the gap between a pair of reflection layers (44, 46) of the interference filter (40) in response to a specific target wavelength band and transmits the control signal to the gap adjustment mechanism (49).

[0101] FIG. 9 is a diagram illustrating another example of an interference filter and part of an optical receiver.

[0102] As illustrated in FIG. 9, the optical distance control mechanism may use a Smart Optical Material (SOM, 247) filling the space between the first reflective layer (244) and the second reflective layer (246), and a means (not shown) for applying an external stimulus to the Smart Optical Material (247). A transparent electrode formed on an optical member may be used as the means for applying the external stimulus. The Smart Optical Material (247) is a material whose thickness or refractive index changes according to the external stimulus. By controlling the external stimulus applied to the Smart Optical Material (247) by the controller (50), the geometric gap or refractive index between the first reflective layer (244) and the second reflective layer (246) can be changed. In addition, the geometric gap and the refractive index can be changed simultaneously. When the gap widens or the refractive index increases, the optical distance between the first reflective layer (244) and the second reflective layer (246) increases, and the transmission wavelength of the indirect filter (240) becomes longer.

[0103] Figures 10 to 12 are schematic diagrams of further examples of the interference filter illustrated in Figure 4.

[0104] The interference filter (340) illustrated in FIG. 10 can be manufactured by forming a second reflective layer (346) on the upper surface of a glass substrate (342), forming an optical material layer (347) on the second reflective layer (346), and then forming a first reflective layer (344) on the optical material layer (347).

[0105] Here, the optical material layer (347) is formed so that the thickness becomes thicker as it goes toward the outer part. Therefore, the distance (t) between the first reflection layer (344) and the second reflection layer (346) formed on the optical material layer (347) becomes thicker as it goes toward the outer part. g(x) ) also widens. The thickness and refractive index of the remaining media constituting the first reflective layer (344) and the second reflective layer (346) do not change depending on the distance (x) from the optical axis (OA).

[0106] Therefore, the sum of the product of the thickness and refractive index of each of all media on the virtual path (P(x)) parallel to the optical axis (OA) between the first surface (3441) of the first reflective layer (344) and the fourth surface (3462) of the second reflective layer (346) increases as the distance (x) from the optical axis (OA) increases.

[0107] In the interference filter (440) illustrated in FIG. 11, an optical material (447) having a refractive index higher than that of air is filled in a portion of the thickness direction of the interference filter (440) between the first reflection layer (444) and the second reflection layer (446). The remaining space between the first reflection layer (444) and the second reflection layer (446) is filled with air. The first reflection layer (444) side is filled with the optical material (447), and the second reflection layer (446) side is filled with air (or another optical material). Contrary to what is illustrated in FIG. 11, the second reflection layer (446) side may also be filled with the optical material (447). In addition, the optical material (447) becomes thicker as it moves away from the optical axis (OA).

[0108] The refractive index (n) of the optical material (447) becomes thicker as it gets farther from the optical axis (OA) G1 ) is greater than the refractive index of air, so the further away from the optical axis (OA), the greater the sum of the product of the thickness and refractive index of the optical material (447) and the product of the thickness and refractive index of the air layer (t G1 (x)×n G1 + t G2 (x)×1) increases. The thickness and refractive index of the remaining media constituting the first reflective layer (444) and the second reflective layer (446) do not change depending on the distance from the optical axis (OA).

[0109] Ultimately, the sum of the product of the thickness and refractive index of each of all media on the virtual path (P(x)) parallel to the optical axis (OA) between the first surface (4441) of the first reflective layer (444) and the fourth surface (4462) of the second reflective layer (446) increases as the distance (x) from the optical axis (OA) increases.

[0110] The interference filter (540) illustrated in FIG. 12 has a thickness (t) of at least one (546c) of the plurality of dielectric layers (546a to 546d) constituting the second reflective layer (546) that increases as it gets farther from the optical axis (OA). RB3 (x)) is configured to be thicker.

[0111] The thickness (t) of the remaining dielectric layers (546a, 546b, 546d) constituting the second reflective layer (546) RB1 , t RB2 , t RB4 ) and the thickness and refractive index of the remaining dielectric layers (544a, 544b, 544c, 544d) constituting the first reflective layer (544) do not change according to the distance (x) from the optical axis (OA), so that ultimately, the sum of the values ​​obtained by multiplying the thickness and refractive index of each of all media on the virtual path (P(x)) parallel to the optical axis (OA) between the first surface (5441) of the first reflective layer (544) and the fourth surface (5462) of the second reflective layer (546) increases as the distance (x) from the optical axis (OA) increases.

[0112] [Depth Imaging Device]

[0113] Fig. 13 is a schematic diagram of a depth imaging device according to an embodiment of the present invention. As illustrated in Fig. 13, a depth imaging device (200) according to an embodiment of the present invention includes an optical transmitter (110), an optical receiver (120), and an interference filter (40).

[0114] The optical transmitter (110) serves to irradiate source light (1) toward the subject (8). The optical transmitter (110) can irradiate, for example, light with a narrow bandwidth belonging to the ultraviolet, visible, and infrared regions in the form of pulses. For example, a vertical cavity surface emitting laser (VCSEL) can be used as the optical transmitter (110).

[0115] As the source light irradiated from the optical transmitter (110) for the TOF camera, light having a center wavelength of 850, 940, or 1064 nm can be used. As the source light irradiated from the optical transmitter (110) for the vehicle LIDAR, light having a center wavelength of 905, or 1550 nm can be used. The pulse width of the pulse-shaped source light can be approximately 1 to 5 nS.

[0116] The optical receiver (120) serves to receive reflected light (2) of the source light (1). The optical receiver (120) is divided into a plurality of regions, and each region receives light (2) that is reflected after being irradiated toward a subject from an optical transmitter (110), external light (4) toward the optical transmitter (110), or external light (6) reflected from the subject, thereby generating an electric signal.

[0117] The interference filter (40) blocks external light (4, 6) from among the light directed to the optical receiver (120) to the greatest extent possible, thereby improving the signal-to-noise ratio (SNR) of the optical receiver (120). The interference filter (140) is placed in front of the light-receiving sensor array of the optical receiver (120). Any of the interference filters described above can be used as the interference filter (40).

[0118] As already explained in the [Wide-angle Spectroscopic Imaging Device] section, the interference filter (40) serves to reduce deviation and crosstalk that occur because incident light does not always enter the interference filter (40) at an ideal incident angle, i.e., perpendicularly.

[0119] In addition, the depth imaging device (200) according to the present embodiment may further include a center wavelength monitoring device (130) and a controller (150), as illustrated in FIG. 13.

[0120] By further including this configuration, the signal-to-noise ratio of the optical receiver (120) can be improved by adjusting the pass band of the interference filter (40) in conjunction with the wavelength change of the source light transmitted from the optical transmitter (110).

[0121] The central wavelength monitoring device (130) serves to measure changes in the central wavelength of the source light (1). A central wavelength measuring device using a dual sensor can be used as the central wavelength monitoring device (130).

[0122] A central wavelength measuring device using a dual sensor includes a first optical sensor configured to have increased sensitivity as the wavelength of the source light (1) increases, and a second optical sensor configured to have decreased sensitivity as the wavelength of the source light increases.

[0123] A central wavelength measuring device using a dual sensor measures changes in the central wavelength of source light based on the difference in sensitivity between the first and second light sensors.

[0124] The first photosensor is configured such that its sensitivity increases as the wavelength of the source light increases, as illustrated in Fig. 14. The first photosensor includes a first photodetector and a first optical filter. The first optical filter is configured such that its transmittance increases as the wavelength of the incident light increases. The slope (k) and intercept (l) of the sensitivity graph of the first photosensor can be changed by appropriately selecting the first photodetector and the first optical filter.

[0125] The second photosensor is configured such that its sensitivity decreases as the wavelength of the source light increases, as illustrated in Fig. 14. The second photosensor includes a second photodetector and a second optical filter. The second optical filter is configured such that its transmittance decreases as the wavelength of the incident light increases. The slope (m) and intercept (n) of the sensitivity graph of the second photosensor can be changed by appropriately selecting the second photodetector and the second optical filter.

[0126] Generally, the transmittance of a photodetector decreases or increases as the wavelength of the incident light increases. Therefore, either the first or second photosensor may be composed solely of a photodetector without an optical filter. Whether the transmittance of the photodetector increases or decreases as the wavelength of the incident light increases is determined by the wavelength range of the incident light.

[0127] A central wavelength measuring device using a dual sensor can measure the central wavelength of source light by measuring the difference value between the sensitivity values ​​of the first and second photosensors. For example, if a first and second photosensors having sensitivity graphs such as those illustrated in Fig. 14 are used, the central wavelength of the source light is approximately 535 nm when the difference value between the sensitivity values ​​of the first and second photosensors is 0, and 500 nm when it is 0.8.

[0128] Additionally, a conventional optical spectrometer can be used as the central wavelength monitoring device (130). An optical spectrometer is a device that displays the intensity of light as a function of wavelength or frequency. A central wavelength measuring device using a dual sensor has the advantage of being much smaller than an optical spectrometer.

[0129] In this embodiment, since the central wavelength of the source light (1) can be known by using the central wavelength monitoring device (130), there is no need to design the pass band of the interference filter (40) to be wide in consideration of the fluctuation of the central wavelength due to factors such as manufacturing deviation of the optical transmitter (110) itself, deviation according to the ambient temperature, power consumed by the optical transmitter (110), or current flowing in the optical transmitter (110).

[0130] Conventionally, the interference filter (40) was designed so that the passband of the interference filter (40) was approximately 30 nm, but in the present invention, the width of the passband can be reduced to 5 nm or less. When the width of the passband of the interference filter (40) is reduced, the external light incident on the optical receiver (120) is reduced, thereby improving the signal-to-noise ratio. For example, when using a pulsed source light having a center wavelength of 940 nm, a full width at half maximum of 0.7 nm, and a power of 75 W, if the full width at half maximum of the interference filter (40) is reduced from 30 nm to 5 nm, when the area of ​​the source light irradiation surface is 1 m2 and the illumination intensity of sunlight is 100 kLux, the signal-to-noise ratio is improved by approximately 585%. The same improvement occurs even when the illumination intensity of sunlight is 20 kLux.

[0131] The controller (150) serves to generate a control signal that adjusts the optical distance between a pair of reflective layers (44, 46) of the interference filter (40) in response to a change in the central wavelength of the source light measured from the central wavelength monitoring device (130).

[0132] To explain in more detail, when the central wavelength of the source light measured from the central wavelength monitoring device (130) becomes longer, the controller (150) transmits a control signal to the optical distance adjustment mechanism of the interference filter (40), as described in the [Wide-angle spectral imaging device] section, thereby adjusting the optical distance between the first reflection layer (44) and the second reflection layer (46) to become longer. Conversely, when the central wavelength of the source light becomes shorter, the controller adjusts the optical distance to become shorter.

[0133] Figure 15 is a conceptual diagram of one embodiment of a depth imaging device having a center wavelength monitoring function according to the present invention.

[0134] The depth imaging device (300) of the embodiment illustrated in Fig. 15 differs from the depth imaging device illustrated in Fig. 13 in that the central wavelength monitoring means (130) is more specifically illustrated in the configuration of the first optical sensor (131) and the second optical sensor (132). The first optical sensor (131) is composed of a first optical filter (131a) and a light-receiving element (131b), and the second optical sensor (132) is composed of a second optical filter (132a) and a light-receiving element (132b). In this embodiment, the central wavelength monitoring means (130) corresponds to the central wavelength monitoring device (130) illustrated in Fig. 13.

[0135] In the present invention, the central wavelength monitoring means (130) is configured such that the sensing sensitivity of the first optical sensor (131) decreases as the wavelength increases, and the sensing sensitivity of the second optical sensor (132) increases as the wavelength increases. As described above, the central wavelength monitoring means (130) measures the central wavelength based on the sensitivity ratio of the first optical sensor (131) and the second optical sensor (132) with respect to light emitted from the optical transmitter (110).

[0136] FIG. 16 is a graph showing the sensitivity of the optical sensor according to the incident angle in the center wavelength monitoring means (130) according to the present invention when the first optical filter (131a) is a shortpass filter and the second optical filter (132a) is a longpass filter. In FIG. 16, the a curve represents the sensitivity of the first optical sensor (131) when light with an incident angle of 0 degrees is incident on the shortpass filter, and the a' curve (dotted line) represents the sensitivity of the first optical sensor (131) when light with an incident angle of 30 degrees is incident on the longpass filter. The b curve represents the sensitivity of the second optical sensor (132) when light with an incident angle of 0 degrees is incident on the longpass filter, and the b' curve (dotted line) represents the sensitivity of the second optical sensor (132) when light with an incident angle of 30 degrees is incident on the longpass filter. When light emitted from the optical transmitter (110) is reflected from the lens and incident on the optical sensors (131, 132), the incident light has no directionality, and due to the characteristics of the interference filter, the transmission wavelength tends to shift to a shorter wavelength as the incident angle increases. As can be seen in the graph, as the incident angle of the light incident on the optical sensor increases, the wavelength incident on the optical sensor shortens, so the graph curve shifts to the left. In the graph, the intersection point of light incident at 0 degrees shifts from 850 nm to 840 nm when incident at 30 degrees. At this time, the sensitivity for light incident on the first optical sensor (131) decreases, so the effect on the optical sensor output is small, but the sensitivity for light incident on the second optical sensor (132) increases relatively much, so that the larger the incident angle, the larger the error in the difference in output between the first optical sensor (131) and the second optical sensor (132). That is, the difference in the output of the optical sensors changes significantly depending on the change in the incident angle of the wavelength of the source light transmitted from the optical transmitter (110). When trying to measure the change in the central wavelength by comparing the difference in the output of the first optical sensor (131) and the output of the second optical sensor (132), the influence of the change in the incident angle of the source light is large, making it difficult to accurately measure the change in the central wavelength.

[0137] FIG. 17 is a graph showing the sensitivity of the optical sensor according to the incident angle in the case where the first optical filter (131a) is a short pass filter and the second optical filter (132a) is a color glass filter in the central wavelength monitoring means (130) according to the present invention. Since the characteristic of the transmission wavelength according to the wavelength of the color glass filter is independent of the incident angle, the sensitivity of the second optical sensor (132) does not change according to the incident angle, as shown in the c curve in FIG. 17. On the other hand, the sensitivity of the first optical sensor (131) changes between the a curve and the a' curve according to the incident angle. That is, when a color glass filter is used in the second light sensor (132), the sensitivity is not affected by changes in the incident angle of the source light, so when measuring the change in the central wavelength by comparing the difference between the output of the first light sensor (131) and the output of the second light sensor (132), the difference in output according to the change in the incident angle can be limited to an appropriate range, so that the change in the central wavelength can be measured more accurately.

[0138] Figure 18 is a flowchart illustrating a method for acquiring a depth image corresponding to a change in the central wavelength of source light according to the present invention.

[0139] A method for acquiring a depth image corresponding to a change in the central wavelength of source light according to the present invention is as follows. First, the outputs of a first optical sensor and a second optical sensor for source light incident from an optical transmitter are measured (S110). Next, the outputs of the first optical sensor and the second optical sensor are compared (S120). Next, if there is a change in the difference between the outputs of the first optical sensor and the second optical sensor, the central wavelength of the source light corresponding to the difference in output is obtained (S130). Next, the gap between the first and second reflective surfaces of an interference filter is adjusted in response to the obtained central wavelength (S140). Next, a depth image of light incident on an optical receiver through the interference filter with the adjusted gap is obtained (S150). Here, the first optical sensor is configured to have increased sensitivity as the wavelength of the source light increases, and the second optical sensor is configured to have decreased sensitivity as the wavelength of the source light increases.

[0140] The above method can be performed in a depth imaging device (300) according to the present invention. The depth imaging device (300) according to the present invention includes an optical transmitter (110), an optical receiver (120), and an interference filter (40). The optical transmitter (110) serves to irradiate source light (1) toward a subject (8). The optical transmitter (110) can irradiate, for example, light with a narrow bandwidth belonging to the ultraviolet, visible, and infrared regions in the form of pulses. For example, a vertical cavity surface emitting laser (VCSEL) can be used as the optical transmitter (110). The source light irradiated by the optical transmitter (110) for a TOF camera can be light having a center wavelength of 850, 940, or 1064 nm. The source light irradiated by the optical transmitter (110) for a vehicle LIDAR can be light having a center wavelength of 905, 1550 nm, or the like. The pulse width of the source light in pulse form may be approximately 1 to 5 nS. The optical receiver (120) serves to receive the reflected light (2) of the source light (1). The optical receiver (120) is divided into a plurality of regions, and each region receives the light (2) reflected after being irradiated toward the subject from the optical transmitter (110), the external light (4) toward the optical transmitter (110), or the external light (6) reflected from the subject, thereby generating an electrical signal. The interference filter (40) may be an interference filter having the structure shown in FIG. 5. The interference filter (40) blocks the external light (4, 6) among the light directed toward the optical receiver (120) as much as possible, thereby serving to improve the signal-to-noise ratio (SNR) of the optical receiver (120). The interference filter (140) is arranged in front of the light-receiving sensor array of the optical receiver (120).

[0141] The procedure for acquiring a depth image in the depth imaging device (300) according to the present invention is as follows. The control unit (150) controls the optical transmitter (110) to emit light to the subject (8) (S100). At this time, the light emitted from the light source of the optical transmitter (110) is incident on the first optical sensor (131) and the second optical sensor (132) of the center wavelength monitoring means (130), and the center wavelength monitoring means (130) measures the output (sensitivity) of the first optical sensor (131) and the second optical sensor (132) (S110).

[0142] Next, the central wavelength monitoring means (130) compares the outputs measured by the first light sensor (131) and the second light sensor (132) to obtain the difference (difference in sensitivity) in the outputs of the first light sensor (131) and the second light sensor (132) (S120). Next, if there is a change in the difference in output (difference in sensitivity), the central wavelength monitoring means (130) determines that the central wavelength of the source light has changed and measures the central wavelength of the light source corresponding to the difference in output. The measurement of the central wavelength corresponding to the difference in output can be measured by selecting the central wavelength corresponding to the difference in output (difference in sensitivity) in the graph illustrated in FIG. 17. Therefore, the central wavelength monitoring means (130) may be equipped with a processor and a memory for performing a comparison operation, and the graph data illustrated in FIG. 17 may be stored in advance in the memory. Alternatively, the control unit (150) receives the outputs of the first light sensor (131) and the second light sensor (132) from the center wavelength monitoring means (130), compares the outputs of the first light sensor (131) and the second light sensor (132) to obtain a difference in output (difference in sensitivity), and the center wavelength monitoring means (130) determines that the center wavelength of the source light has changed when there is a change in the difference in output (difference in sensitivity) and can measure the center wavelength corresponding to the difference in output. In this case, the control unit (150) may be equipped with a processor and a memory for performing a comparison operation, and the graph data illustrated in FIG. 17 may be stored in advance in the memory.

[0143] Next, the control unit (150) controls the distance adjustment means (49) to adjust the spacing of the interference filter (40) corresponding to the measured center wavelength, thereby adjusting the distance between the first reflective surface (44) and the second reflective surface (46), thereby adjusting the optical wavelength pass band of the interference filter (40) in conjunction with the wavelength change of the source light transmitted from the optical transmitter (110) (S140). Next, the optical receiver (120) receives the light (2) reflected from the subject (8) and passed through the interference filter (40) of which the spacing is adjusted, thereby acquiring an image. The spacing between the first reflective surface (44) and the second reflective surface (46) of the interference filter (40) is adjusted corresponding to the center wavelength of the source light (1), so that the width of the band passing through the interference filter (40) is reduced, and the depth image acquired by the receiver (120) is an image with an improved signal-to-noise ratio.

[0144] Although the invention has been described above with reference to drawings and embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the invention without departing from the technical spirit of the invention as set forth in the claims below.

Claims

1. An optical transmitter configured to transmit source light, An optical receiver configured to receive reflected light of the above source light, An interference filter having a first reflective layer arranged at the front end of the optical receiver and a second reflective layer arranged at a certain distance from the first reflective layer; A distance adjusting means for adjusting the distance between the first reflective layer and the second reflective layer, A central wavelength monitoring means for measuring a change in the central wavelength of the above source light, Including a control unit for controlling the above distance control means, A depth imaging device having a center wavelength monitoring function, wherein the control unit is configured to control the distance adjustment means in response to a change in the center wavelength measured from the center wavelength monitoring means.

2. In paragraph 1, A depth imaging device having a center wavelength monitoring function, wherein the center wavelength monitoring means comprises a first light sensor configured to have increased sensitivity as the wavelength of the source light increases, and a second light sensor configured to have decreased sensitivity as the wavelength of the source light increases, and is configured to compare outputs of the first light sensor and the second light sensor, and measure a change in the center wavelength of the source light based on a difference in the outputs.

3. In paragraph 2, A depth imaging device having a center wavelength monitoring function, wherein the first optical sensor includes a long wavelength pass filter, and the second optical sensor includes a short wavelength pass filter.

4. In paragraph 3, The above long-wavelength pass filter is a depth imaging device having a center wavelength monitoring function that is a color grass filter.

5. In any one of paragraphs 1 to 3, The above interference filter is, A first reflective layer having a first surface on which light is incident and a second surface on the opposite side thereof, a second reflective layer having a third surface facing the second surface at a distance therefrom and a fourth surface on the opposite side thereof from which light is emitted, A depth imaging device having a center wavelength monitoring function configured such that the sum of the products of the thickness and refractive index of each of all media on a virtual path parallel to the optical axis between the first surface of the first reflective layer and the fourth surface of the second reflective layer increases as the distance from the optical axis increases.

6. In paragraph 5, A depth imaging device having a center wavelength monitoring function, wherein at least one of the first reflective layer and the second reflective layer is bent so that the gap between the second surface of the first reflective layer of the interference filter and the third surface of the second reflective layer becomes wider as the distance increases away from the optical axis.

7. A step of measuring the output of the first light sensor and the second light sensor for the source light incident from the optical transmitter, A step of comparing the output of the first light sensor and the output of the second light sensor, A step of calculating the difference between the output of the first light sensor and the output of the second light sensor, If there is a change in the difference in the above output, a step of obtaining the center wavelength of the source light corresponding to the difference in output, A step of adjusting the spacing between the first and second reflective surfaces of the interference filter in response to the above-determined central wavelength, A step of obtaining a depth image by inputting source light that has passed through the above-mentioned interval-controlled interference filter into an optical receiver, A method for acquiring a depth image corresponding to a change in the central wavelength of source light, wherein the first light sensor is configured to have increased sensitivity as the wavelength of the source light increases, and the second light sensor is configured to have decreased sensitivity as the wavelength of the source light increases.

8. In paragraph 7, A method for acquiring a depth image corresponding to a change in the central wavelength of source light, wherein the first optical sensor includes a long-wavelength pass filter and the second optical sensor includes a short-wavelength pass filter.

9. In paragraph 8, The above long-wavelength pass filter is a method for acquiring a depth image corresponding to a change in the center wavelength of the source light, which is a color grass filter.

10. In any one of paragraphs 7 to 9, The above interference filter is, A first reflective layer having a first surface on which light is incident and a second surface on the opposite side thereof, a second reflective layer having a third surface facing the second surface at a distance therefrom and a fourth surface on the opposite side thereof from which light is emitted, A method for acquiring a depth image corresponding to a change in the central wavelength of source light, wherein the sum of the products of the thickness and refractive index of each of all media on a virtual path parallel to the optical axis between the first surface of the first reflective layer and the fourth surface of the second reflective layer increases as the distance from the optical axis increases.

11. In paragraph 10, A method for acquiring a depth image corresponding to a change in the central wavelength of source light, wherein at least one of the first reflection layer and the second reflection layer is bent so that the gap between the second surface of the first reflection layer of the interference filter and the third surface of the second reflection layer becomes wider as the distance from the optical axis increases.

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