KR102643832B1 - lnterferometer, wide-angle spectral imaging device with the same, and depth imaging device with the same - Google Patents

Abstract

The present invention relates to an interference filter, a wide-angle spectral imaging device equipped therewith, and a depth imaging device equipped therewith. The present invention includes a first reflective layer having a first surface on which light is incident, a second surface on the opposite side, a third surface facing the second surface at a distance, and a third surface on the opposite side from which light exits. a second reflective layer having four surfaces, 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; An interference filter is provided so that the sum of the multiplied values increases as the distance from the optical axis increases. The interference filter according to the present invention can transmit light in the target wavelength band and block light in other bands even in the outer portion where the angle of incidence 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 area.

Description

Interference filter, wide-angle spectral imaging device having the same, and depth imaging device having the same {lnterferometer, wide-angle spectral imaging device with the same, and depth imaging device with the same}

The present invention relates to an interference filter, a wide-angle spectral imaging device equipped therewith, and a depth imaging device equipped therewith.

[Spectral imaging technology]

Spectral imaging technology refers to a technology that provides two-dimensional image information according to the spectral band. Spectral imaging technology is used in a variety of fields, including PCB inspection, counterfeit money inspection, skin characteristic measurement, and food inspection.

A spectral imaging device includes an optical system such as a light receiving lens or a light projection lens, a light receiver including a light receiving sensor, and a spectroscopic device.

The optical receiver is divided into a plurality of areas and receives light from the subject to generate an electrical signal.

The spectroscopic device is placed in front of the light receiving sensor of the optical receiver. Spectroscopic devices are largely divided into monochromator type and optical tunable filter type. Optical variable filters can be broadly divided into fixed and variable types. The optical variable filter serves to pass only light in a specific wavelength range. Representative fixed variable filters include the filter wheel type and Fabry-Perot interference filter.

1 is a diagram for explaining a Fabry-Perot Interferometer (FPI), which is an example of an optical tunable filter. As shown in Figure 1, the Fabry-Perot interference filter has a pair of reflective surfaces (R ₁ , R ₂ ) facing each other. The incident light is reflected between the reflecting surfaces (R ₁ , R ₂ ). Since the reflectivity of the reflective surfaces (R ₁ , R ₂ ) is not 100%, a certain percentage of light (L _t ) interferes in the process of repeatedly reflecting light of the transmission wavelength between the reflective surfaces (R ₁ , R ₂ ). It passes through the filter, and the rest is reflected again. In this process, light of a specific wavelength (transmission wavelength) causes constructive interference, and the remaining light disappears due to destructive interference.

In the Fabry-Perot interference filter, the transmission wavelength is determined depending on the distance (t _op ) and the angle of incidence (θ) between a pair of reflecting surfaces (R ₁ , R ₂ ). The reflective surface can be implemented as a single layer of metal, or can be composed 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 on the reflective surface. On the other hand, the latter allows for a filter configuration with high reflectance and narrow half width.

Equation 1 below is the formula for determining the transmission wavelength of the Fabry-Perot interference filter. Here, n is the refractive index of the material filled between the reflective surfaces, t _op is the distance between the reflective surfaces, θ is the angle of incidence, m is an integer, and λ is the transmission wavelength.

According to Equation 1, the transmission wavelength of the Fabry-Perot interference filter changes depending on the angle of incidence. That is, when m is 1, the distance (t _op ) between a pair of reflective surfaces is λ ₀ /2 (t _op =λ ₀ /2), and air is filled between the reflective surfaces (n = 1), the fabric -The transmission wavelength of light perpendicularly incident on the Ferot interference filter is λ ₀ . And as the incident angle of incident light increases, the cosθ value decreases, so the transmission wavelength becomes shorter than λ ₀ . For example, if the angle of incidence is 30 degrees, the transmitted wavelength is 0.866λ ₀ shortened to In other words, for light incident perpendicularly to the Fabry-Perot interference filter, only the component with a wavelength of λ ₀ passes through the Fabry-Perot interference filter, and for light incident at 30 degrees, only the component with a wavelength of 0.866λ ₀ passes through the filter.

Additionally, as explained above with reference to Equation 1, since incident light does not always enter the Fabry-Perot interference filter at an ideal angle of incidence, that is, perpendicularly, deviations depending on the angle of incidence may occur. When the incident light does not enter the Fabry-Perot interference filter perpendicularly, light with a short wavelength of about 10 to 20 nm shorter than the target center wavelength passes through the Fabry-Perot interference filter, and rather, light with the target center wavelength passes through the Fabry-Perot interference filter. It can be blocked by a Fabry-Perot interference filter.

The angle of incidence may vary depending on the location of the interference filter. In general, the angle of incidence of light incident on the center of the Fabry-Perot interference filter is close to vertical, and the light incident on the outer part of the Fabry-Perot interference filter is incident at an angle, so light of shorter wavelength passes through the outer part than the central part. . Therefore, at the outside of the Fabry-Perot interference filter, light of the target center wavelength may be blocked by the interference filter.

For example, a Fabry-Perot interference filter with a central wavelength of 940 nm and a full width at half maximum of 30 nm was used as an optical filter. However, the angle of incidence of light incident on the outer part of the Fabry-Perot interference filter increased, so the transmission wavelength shifted toward the short wavelength of 20 nm. When moving, 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 with a wavelength range of 935 to 955 nm is transmitted in the outer part of the Fabry-Perot interference filter. Outside the upper limit of 935 nm, it is blocked by the outer part of the Fabry-Perot interference filter. Therefore, the outer portion of the image acquired with a spectral imaging device may be distorted.

Additionally, if the incident light does not enter the Fabry-Perot interference filter perpendicularly, there is a problem that a haze phenomenon may occur due to crosstalk.

FIG. 2 is a diagram illustrating the progression of light between reflective surfaces R ₁ and R ₂ when incident light with a large incident angle enters a conventional Fabry-Perot interference filter.

As shown in FIG. 2, when the angle of incidence is large, the distance that light travels in the direction perpendicular to the reflective surfaces (R ₁ , R ₂ ) while repeatedly reflecting between the reflective surfaces (R ₁ , R ₂ ) is increases (the distance increases from Zone 1 to Zone 3). This distance becomes longer as the reflectivity of the reflective surfaces (R ₁ , R ₂ ) is high and the angle of incidence is large.

More specifically, incident light with an incident angle of 5 degrees does not move much in the lateral direction until its intensity is weakened by repeated reflection, but light with an incident angle of 25 degrees travels a fairly long distance and is transmitted to the array sensor in the optical receiver (LR). It is incident not only on the pixel corresponding to the subject segmentation area, but also on the adjacent pixel.

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

Referring to Table 1, when the incident angle is 0 degrees (vertically incident), the moving distance is 0㎛ regardless of the reflectance, and when the incident angle is 30 degrees, it is about 9.3㎛ when the reflectance is 0.9, and about 24.4㎛ when the reflectance is 0.95. As reflectivity increases, the number of reflections increases, so the travel distance increases. As the angle of incidence increases, the distance it travels until it is reflected increases.

Therefore, as the reflectance and angle of incidence increase, the moving distance becomes longer, which greatly affects adjacent areas and ultimately reduces the resolution of the spectral imaging device. Figure 3 is a graph showing light leakage to adjacent angles (pixels) according to haze (cloudiness) component. The horizontal axis of Figure 3 represents the scattering angle, and the vertical axis represents the output (intensity). According to Figure 3, it can be seen that as the haze component increases, angular crosstalk increases at adjacent angles (pixels).

In summary, the conventional spectroscopic imaging device using the conventional Fabry-Perot interference filter had the following problems.

First, because the angle of incidence of light incident on 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 the light in the target wavelength band is transmitted through the Fabry-Perot interference filter. It can pass through the Ferot interference filter.

Second, when the angle of incidence of the incident light incident on the Fabry-Perot interference filter is large, the distance that the reflected light travels in the direction perpendicular 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 pixel corresponding to the subject division area of the corresponding array sensor but also to adjacent pixels, and the haze component increases and resolution decreases toward the outer edge of the Fabry-Perot interference filter.

[Depth imaging technology]

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

The method of using structured light is to irradiate an infrared pattern consisting of tens of thousands of dots to a subject and then read the distortion of the infrared pattern caused by the subject. This method has the disadvantage that the recognition rate drops significantly as the distance between the camera and the subject increases.

The TOF method includes a direct method that continuously radiates 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. There is an indirect method of measuring changes in the phase of light.

A TOF camera divides the subject into multiple areas and measures the distance to each area to obtain a 3D image. Depending on how the area is divided, it is divided into a mechanical scanning method, a solid state TOF method using MEMS mirrors, and a flash TOF method that irradiates the subject all at once.

A TOF camera includes an optical system such as a light receiving lens or a flood lens, a light receiver including a light receiving sensor, a light transmitter including a light source and a driving device, and an optical filter.

The optical receiver is divided into a plurality of areas, and each area receives light irradiated from the optical transmitter towards the subject and then reflected, external light towards the optical receiver, or external light reflected from the subject, and generates an electrical signal. External light may be light from the sun or artificial lighting.

The optical transmitter serves to irradiate light toward the subject. For example, the optical transmitter may irradiate light with a narrow bandwidth belonging to the ultraviolet rays, visible rays, and infrared rays in the form of a pulse.

The optical filter is disposed in front of the light receiving sensor of the optical receiver and serves to block external light other than light emitted from the optical transmitter from flowing into the optical receiver. The optical filter may be an interference filter, an absorptive filter, a dichroic filter, etc. The optical filter may be a band-pass filter that passes only a specific wavelength range.

When an interference filter is used as an optical filter, the depth imaging device also has the same problems as the conventional spectral imaging device described above.

That is, first, because 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.

Second, when the angle of incidence of the incident light incident on the band pass filter is large, the distance that the reflected light travels in the direction perpendicular 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 pixel corresponding to the subject division area of the corresponding array sensor but also to adjacent pixels, and the haze component increases and resolution decreases toward the outer part of the depth imaging device.

As a method for solving the first problem among these problems, the US2019/0162885A1 US published patent discloses an optical transmitter configured to transmit source light, an optical receiver configured to receive reflected light of the source light, and a band before the received source light is transmitted to the photodetector. A device comprising an infrared or near-infrared band pass filter disposed in front of a photo detector of an optical receiver to be received at a pass filter, wherein the band pass filter has a first region capable of transmitting light within a first wavelength range and a second wavelength range. A device including a plurality of regions including a second region capable of transmitting light is disclosed.

More specifically, a filter with a bandwidth of about 5 nm is used in the first area, which is the center where incident light is mainly incident close to vertical, and a filter with a bandwidth of about 5 nm is used in the second area, which is the outer area where incident light is relatively often incident obliquely. By using a filter with a bandwidth of around 30 nm, external light is blocked, at least in the center where reflected light is incident close to vertical, thereby increasing sensitivity.

However, this method cannot respond to deviations caused by manufacturing deviations of the light source itself, temperature around the light source, output of the light source, etc., so there is a problem in that the bandwidth of the band-pass filter cannot be sufficiently reduced even in the center.

Additionally, there is a problem that the signal-to-noise ratio cannot be improved in the outer area.

Additionally, there is a problem that the crosstalk phenomenon cannot be improved.

US published patent US2019/0162885A1 Korean public patent KR10-2012-0089312 A Japanese public patent JP2016-050803A Japanese public patent JP2016-011932A

The present invention is intended to improve the above-mentioned problems, and aims to provide a wide-angle spectral imaging device with improved sensitivity in the outer area and improved crosstalk phenomenon, a depth imaging device, and an interference filter therefor.

In order to achieve the above-described object, the present invention includes a first reflective layer having a first surface on which light is incident and a second surface on the opposite side, a third surface facing the second surface at a distance, and a second reflective layer having a fourth surface on the opposite side from which light exits, and all media in 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. An interference filter is provided so that the sum of the product of the thickness and refractive index on each path increases as the distance from the optical axis increases.

In addition, at least one of the first reflective layer and the second reflective layer is such 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 from the optical axis increases. Provides an interference filter, one of which is curved.

In addition, the curvature of the curved reflective layer of the first reflective layer and the second reflective layer becomes smaller as the distance from the optical axis increases.

In addition, the thickness between the first reflective layer and the second reflective layer of the interference filter increases as the distance from the optical axis increases, and an optical material with a higher refractive index than other media is filled between the first reflective layer and the second reflective layer. provides an interference filter.

In addition, at least one of the first reflective layer and the second reflective layer includes a plurality of dielectric layers, and at least one of the plurality of dielectric layers provides an interference filter whose thickness becomes thicker as the distance from the optical axis increases.

In addition, the sum of the values obtained by multiplying the thickness and refractive index of all media on a path parallel to the optical axis between the first surface of the first reflective layer and the fourth surface of the second reflective layer is [Equation 2] below. Accordingly, an interference filter is provided that grows in inverse proportion to the COSθ(x) value as the distance from the optical axis increases.

[Equation 2]

(t _k (x) and n _k (x) represent the thickness (length of the path passing through each medium) and refractive index on each path of the media parallel to the optical axis at a distance x from the optical axis, θ ( x) is the angle of incidence according to the distance (x) from the optical axis, m is an integer, and λ means the transmission wavelength of the interference filter.)

Additionally, the present invention includes an optical receiver configured to receive light from a subject, and an optical distance adjustment mechanism configured to adjust an optical distance parallel to the optical axis direction between the first reflective layer and the second reflective layer, wherein the optical receiver A wide-angle spectral imaging device including an interference filter disposed at the front end, wherein the interference filter is the interference filter described above.

In addition, the optical distance adjustment mechanism provides a wide-angle spectral imaging device that is an intelligent optical material that is filled between the first and second reflective layers of the interference filter and whose thickness or refractive index changes depending on external stimuli.

In addition, the optical distance adjustment mechanism provides a wide-angle spectral imaging device in which the optical distance adjustment mechanism is a gap adjustment mechanism configured to move the first reflective layer relative to the second reflective layer along the optical axis direction.

In addition, the present invention is a depth imaging device including 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 A depth imaging device that is the above-described interference filter is provided.

In addition, a central wavelength monitoring device that measures a change in the central wavelength of the source light, an optical distance adjustment mechanism configured to adjust an optical distance parallel to the optical axis direction between the first reflective layer and the second reflective layer, and the central wavelength monitoring device It provides a depth imaging device further comprising a controller that controls the optical distance adjustment mechanism in response to a change in the center wavelength of the source light measured from.

In addition, the optical distance adjustment mechanism provides a depth imaging device that is an intelligent optical material that is filled between the first and second reflective layers of the interference filter and whose thickness or refractive index changes depending on external stimuli.

In addition, the optical distance adjustment mechanism provides a depth imaging device in which the optical distance adjustment mechanism is a gap adjustment mechanism configured to move the first reflective layer relative to the second reflective layer along the optical axis direction.

In addition, the central wavelength monitoring device includes a first optical sensor configured to improve sensitivity as the wavelength of the source light increases, and a second optical sensor configured to decrease sensitivity as the wavelength of the source light increases, A depth imaging device is provided that measures a change in the center wavelength of source light based on the difference in sensitivity between a first optical sensor and a second optical sensor.

The interference filter according to the present invention can transmit light in the target wavelength band and block light in other bands not only in the center but also in the outer portion where the angle of incidence 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 area and do not distort the image.

In addition, in the interference filter according to some embodiments of the present invention, the distance between the reflective layers on the outer part of the interference filter is long, and thus the crosstalk shape caused by light with a large incident angle can be reduced.

1 is a diagram for explaining a Fabry-Perot Interferometer (FPI), which is an example of an optical tunable filter.
Figure 2 is a diagram for explaining the progression of light between reflective surfaces when incident light with a large incident angle enters a conventional Fabry-Perot interference filter.
Figure 3 is a graph showing light leakage to adjacent angles (pixels) according to haze (cloudiness) component.
Figure 4 is a schematic diagram of a wide-angle spectral imaging device according to an embodiment of the present invention.
Figure 5 is a schematic diagram of the interference filter and optical receiver shown in Figure 4;
FIG. 6 is a diagram showing a portion of the interference filter shown in FIG. 5.
Figure 7 (a) shows the spectrum of light passing through a conventional interference filter with constant spacing between reflection layers, and (b) shows the spectrum of light passing through the interference filter shown in Figures 5 and 6. .
FIG. 8 is a diagram for explaining the operation of the interference filter shown in FIG. 5.
Figure 9 is a diagram showing another example of an interference filter and a part of an optical receiver.
10-12 are schematic diagrams of further examples of interference filters.
Figure 13 is a schematic diagram of a depth imaging device according to an embodiment of the present invention.
Figure 14 is a diagram to explain the principle of a center wavelength measuring instrument using a dual sensor.

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 and will be implemented in various different forms. These embodiments only serve to ensure that the disclosure of the present invention is complete and to those skilled in the art to fully convey the scope of the invention. This is provided to inform you. Like symbols in the drawings refer to like elements.

[Wide-angle spectral imaging device]

Figure 4 is a schematic diagram of a wide-angle spectral imaging device according to an embodiment of the present invention. As shown in FIG. 4, the wide-angle spectral 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 projection lens, an optical receiver 20, an interference filter 40, and , including a controller 50.

The wide-angle spectral imaging device 100 according to an embodiment of the present invention can obtain an image using light in a specific target wavelength band by adjusting the pass band of the interference filter 40. For example, it is possible to obtain an image of only red light or an image of only green light among the light 6 reflected from the subject 8.

The optical receiver 20 serves to receive the light 6 that is irradiated from a light source such as the sun or an indoor light, is reflected from the subject 8, and then passes through the interference filter 40. The optical receiver 20 is divided into a plurality of areas, and each area receives light 6 from the subject 8 that has passed through the interference filter 40 and generates an electrical signal.

The interference filter 40 serves to pass only light in a specific wavelength band among the light heading to the optical receiver 20. The interference filter 40 is disposed between the optical system 10 and the light receiving sensor array of the optical receiver 20.

FIG. 5 is a schematic diagram of an example of an interference filter and an optical receiver shown in FIG. 4, and FIG. 6 is a diagram showing a part of the interference filter shown in FIG. 5.

The interference filter 40 of the present invention has a structure to reduce position-specific deviations that occur because incident light does not enter all positions of the interference filter 40 at an ideal angle of incidence, that is, perpendicularly.

As shown in FIG. 5, the angle of incidence (θ(x)) of the 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 about 0 to 30°. That is, the incident angle (θ(x)) of the 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 the light incident on the outermost part farthest from the optical axis OA )) can be close to 30°.

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

As shown 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 disk-shaped or elliptical-plate shaped.

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

As shown in FIG. 6, the first reflective layer 44 has a first surface 441 on which light is incident, and a second surface 442 on the opposite side. And the second reflective layer 46 has a third surface 461 facing the second surface 442 at a distance, and a fourth surface 462 on the opposite side from which light is emitted. The first reflective layer 44 may include 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. Sub-layers may be dielectric layers.

In the present invention, the interference filter 40 is a virtual path 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. The sum of the values multiplied by the thickness (t _k (x)) and the refractive index (n _k (x)) on each virtual path (P (x)) of all media on P (x)) is the distance from the optical axis (OA). It is configured to increase as the distance (x) increases. The optical axis (OA) refers to the optical axis of the optical system 10 disposed in front of the interference filter 40.

Here, the media includes all of the medium constituting the first reflective layer 44, the medium filling the gap G between the first reflective layer 44 and the second reflective layer 46, and the medium constituting the second reflective layer 46. Includes. When the first reflective layer 44 includes a plurality of sub-layers, it includes media constituting each sub-layer. When the second reflective layer 46 includes a plurality of sub-layers, it includes media constituting each sub-layer. Additionally, 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.

In more detail, the interference filter 40 is a path (P) 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. The sum of the values obtained by multiplying the thickness and refractive index of each path of all media on (x)) is configured to increase in inverse proportion to the COSθ(x) value as the distance from the optical axis OA increases according to Equation 2 below.

(t _k (x) and n _k (x) are on the respective paths (P(x)) of the medium on the path (P(x)) parallel to the optical axis (OA) with a distance x from the optical axis (OA). It represents the thickness (length of the path (P(x)) passing through each medium) and refractive index, and θ(x) is the angle of incidence of incident light depending on the distance (x) from the optical axis (OA), m is an integer, λ means the transmission wavelength of the interference filter, and θ(x) increases as the distance (x) from the optical axis increases.)

Of course, the left side of Equation 2 is a term related to the first reflective layer 44 (the first term on the right side) as shown in Equation 3 below, and the gap between the first reflective layer 44 and the second reflective layer 46 ( It can also be divided into a term regarding G) (the second term on the right side) and a term regarding the second reflective layer 46 (the third term on the right side).

(t _RAa (x) and n _RAa (x) represent the thickness and refractive index on the path (P(x)) of each sub-layer constituting the first reflection layer 44. t _Gb (x) and n _Gb (x ) represents the thickness and refractive index on the path (P(x)) of each of the media filling the gap between the first reflective layer 44 and the second reflective layer 46. And t _RBc (x) and n _RBc (x) represents the thickness and refractive index of the path (P(x)) of each sub-layer constituting the second reflective layer 46.

As can be seen from Equation 2, if the value of the left side is constant regardless of the distance (x) from the optical axis (OA), as the incident angle (θ(x)) increases, the transmission wavelength (λ) of the interference filter 40 It moves to short wavelengths.

As shown in FIG. 5, the angle of incidence (θ(x)) increases as the distance (x) from the optical axis (OA) increases, so if the value on the left side remains constant, the angle of incidence (θ(x)) increases as the distance (x) from the optical axis (OA) increases. Short-wavelength light passes through the interference filter 40. Accordingly, the outer and central parts of the image obtained from the wide-angle spectral imaging device 100 are displayed in different colors. The center of the image will be displayed in the selected color, but the outer edges of the image will be displayed in a different color.

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

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 distance between the first reflective layer 44 and the second reflective layer 46 The refractive index of the medium filling the gap (G) is maintained constant regardless of the distance (x) from the optical axis (OA), and the gap (t _G (x)) between the first reflective layer 44 and the second reflective layer 46 By adjusting only ), the change in incident angle (θ(x)) according to the distance (x) from the optical axis (OA) is compensated.

The interference filter 40 illustrated in FIGS. 5 and 6 is configured such that the gap (t _G (x)) between the first reflective layer 44 and the second reflective layer 46 becomes wider as the distance from the optical axis OA increases. The reflective layer 44 is curved. At this time, the curvature of the first reflective layer 44 decreases as the distance from the optical axis OA increases.

t _RAa (x) and n _RAa (x) of the interference filter 40 in FIGS. 5 and 6 are constant regardless of the distance (x) from the optical axis OA, and t _RBc (x) and n _RBc (x) Since the degree is constant, only the gap (t _G (x)) between the first reflective layer 44 and the second reflective layer 46 is adjusted, and the incident angle (θ(x) according to the distance (x) from the optical axis (OA) )) compensates for the change.

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

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

As can be seen in (b) of FIG. 7, according to Equation 2, the gap (t _G (x)) between the first reflective layer 44 and the second reflective layer 46 becomes wider as the distance from the optical axis OA increases. When adjusted, only light of the target central wavelength (850 nm) passes through, regardless of the angle of incidence (θ(x)) (regardless of the distance (x) from the optical axis (OA)).

Additionally, as shown in FIG. 8, the interference filter 40 of this embodiment serves to reduce the crosstalk phenomenon.

As can be seen from Equation 2, the wavelength of light passing through the interference filter 40 is determined according to the gap (t _G1 (x)) between the first reflective layer 44 and the second reflective layer 46. However, as shown in FIG. 8, the gap (t _G1 (x)) becomes wider as it progresses to the outer part, so light incident at a specific angle exhibits reflection behavior between the first reflective layer 44 and the second reflective layer 46. As the light moves in a direction perpendicular to the second reflective layer 46, the light travel path between the first reflective layer 44 and the second reflective layer 46 of the reflected light gradually becomes longer. Ultimately, the distance between the first reflective layer 44 and the second reflective layer 46 no longer satisfies Equation 2 for the reflected light, and the reflected light no longer passes through the interference filter 40 and enters the optical receiver 20. It does not enter pixels in adjacent areas of the light receiving sensor array.

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

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

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 the product of the refractive index of the medium and the distance. The optical distance adjustment mechanism can adjust the optical distance by changing the distance between the first reflective layer 44 and the second reflective layer 46 or the refractive index of the medium filling between the first reflective layer 44 and the second reflective layer 46. . Since the optical distance adjustment mechanism is to adjust the transmission wavelength of the interference filter 40, the distance between the first reflective layer 44 and the second reflective layer 46 is adjusted at the same time regardless of the distance (x) to the optical axis (OA). Adjust.

As shown in FIG. 5, in this embodiment, the optical distance adjustment mechanism moves the first reflective layer 44 relative to the second reflective layer 46 along the optical axis (OA) direction to create a relationship between the first reflective layer 44 and the second reflective layer 46. There may be a spacing adjustment mechanism 49 configured to adjust the geometric distance between the two reflective layers 46.

The spacing adjustment mechanism 49 may be, for example, an actuator and spring member. The actuator pushes or pulls 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 approach each other or in a direction that moves away from each other. Can be installed. 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 the actuator to maintain the gap between the first reflective layer 44 and the second reflective layer 46. .

Additionally, the gap adjustment mechanism 49 may be a device that uses electromagnetic force. For example, electrode layers are formed on the first optical member 41 and the second optical member 42, and they are made to have different polarities so that they become closer to each other, and they are made to have different polarities so that they move away from each other. You can do it.

The controller 50 generates a control signal that adjusts the gap between the pair of reflection layers 44 and 46 of the interference filter 40 in response to a specific target wavelength band and transmits it to the gap adjustment mechanism 49. do.

Figure 9 is a diagram showing another example of an interference filter and a part of an optical receiver.

As shown in FIG. 9, the optical distance adjustment mechanism includes a smart optical material (SOM, Smart Optical Material) 247 that fills the space between the first reflective layer 244 and the second reflective layer 246, and a smart optical material 247. A means of applying an external stimulus (not shown) may be used. A transparent electrode formed on an optical member can be used as a means of applying external stimulation. The intelligent optical material 247 is a material whose thickness or refractive index changes depending on external stimuli. The controller 50 can change the geometric gap or refractive index between the first reflective layer 244 and the second reflective layer 246 by adjusting the external stimulus applied to the intelligent optical material 247. Additionally, the geometric spacing and refractive index can be changed simultaneously. As 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.

10 to 12 are schematic diagrams of further examples of the interference filter shown in FIG. 4.

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

Here, the optical material layer 347 is formed to become thicker as it progresses to the outer part. Accordingly, the gap (t _g(x) ) between the first reflective layer 344 and the second reflective layer 346 formed on the optical material layer 347 widens toward the outer portion. 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.

Therefore, 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 The sum of the values obtained by multiplying the thickness and the refractive index on each virtual path (P(x)) increases as the distance (x) from the optical axis (OA) increases.

The interference filter 440 shown in FIG. 11 has an optical material 447 having a higher refractive index than air at a portion between the first reflective layer 444 and the second reflective layer 446 based on the thickness direction of the interference filter 440. filled. The remaining space between the first reflective layer 444 and the second reflective layer 446 is filled with air. The first reflective layer 444 side is filled with an optical material 447, and the second reflective layer 446 side is filled with air (or another optical material). Conversely, as shown in FIG. 11, the second reflective layer 446 may be filled with the optical material 447. And this optical material 447 becomes thicker as it moves away from the optical axis (OA).

Since the refractive index (n _G1 ) value of the optical material 447, which becomes thicker as it moves away from the optical axis OA, is greater than the refractive index of air, the product of the thickness of the optical material 447 and the refractive index increases as the distance from the optical axis OA increases. and the sum of the product of the thickness of the air layer and the refractive index (t _G1 (x) × n _G1 + t _G2 (x)×1) becomes larger. 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.

Ultimately, 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 The sum of the values obtained by multiplying the thickness and the refractive index on each virtual path (P(x)) increases as the distance (x) from the optical axis (OA) increases.

The interference filter 540 shown in FIG. 12 has a thickness t _RB3 as at least one 546c of the plurality of dielectric layers 546a to 546d constituting the second reflection layer 546 moves away from the optical axis OA. (x)) is configured to be thick.

The thickness (t _RB1 , _tRB2 , t _RB4 ) and the refractive index and the thickness and refractive index of the remaining dielectric layers 544a, 544b, 544c, and 544d constituting the first reflection layer 544 do not change depending on the distance (x) from the optical axis OA. 1 Each of all media on the virtual path (P(x)) parallel to the optical axis (OA) between the first surface (5441) of the reflective layer (544) and the fourth surface (5462) of the second reflective layer (546) The sum of the values obtained by multiplying the thickness and the refractive index on the virtual path (P(x)) increases as the distance (x) from the optical axis (OA) increases.

[Depth imaging device]

Figure 13 is a schematic diagram of a depth imaging device according to an embodiment of the present invention. As shown in FIG. 13 , the 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.

The light transmitter 110 serves to irradiate the source light 1 toward the subject 8. For example, the optical transmitter 110 may irradiate light with a narrow bandwidth belonging to the ultraviolet ray, visible ray, or infrared range in the form of a pulse. With the optical transmitter 110. For example, a vertical cavity surface emitting laser (VCSEL) can be used.

As the source light emitted from the optical transmitter 110 for a TOF camera, light with a central wavelength of 850, 940, or 1064 nm can be used. As the source light emitted from the optical transmitter 110 for vehicle LIDAR, light with a central wavelength of 905 or 1550 nm can be used. The pulse width of the pulse-shaped source light may be about 1 to 5 nS.

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 areas, and each area is irradiated from the optical transmitter 110 toward the subject and then reflects light 2, external light 4 directed toward the optical transmitter 110, or the subject. The external light 6 reflected from is received and an electrical signal is generated.

The interference filter 40 serves to improve the signal-to-noise ratio (SNR) of the optical receiver 120 by blocking external light 4 and 6 as much as possible among the light heading to the optical receiver 120. The interference filter 140 is disposed in front of the light receiving sensor array of the optical receiver 120. All of the previously described interference filters can be used as the interference filter 40.

As already explained in the [Wide Angle Spectral 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 angle of incidence, that is, perpendicularly.

In addition, the depth imaging device 200 according to this embodiment may further include a center wavelength monitoring device 130 and a controller 150, as shown in FIG. 13.

By further including this configuration, the signal-to-noise ratio of the optical receiver 120 can be improved by adjusting the passband of the interference filter 40 in response to a change in the wavelength of the source light transmitted from the optical transmitter 110.

The central wavelength monitoring device 130 serves to measure changes in the central wavelength of the source light 1. As the center wavelength monitoring device 130, a center wavelength measuring device using a dual sensor can be used.

A central wavelength measuring device using a dual sensor includes a first optical sensor configured to improve sensitivity as the wavelength of the source light 1 increases, and a second optical sensor configured to decrease sensitivity as the wavelength of the source light increases.

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

As shown in FIG. 14, the first optical sensor is configured to increase sensitivity as the wavelength of the source light increases. The first optical sensor includes a first light receiving element and a first optical filter. The first optical filter is configured to increase transmittance as the wavelength of incident light increases. The slope (k) and intercept (l) of the sensitivity graph of the first optical sensor can be changed by appropriately selecting the first light receiving element and the first optical filter.

As shown in FIG. 14, the second optical sensor is configured to have reduced sensitivity as the wavelength of the source light increases. The second optical sensor includes a second light receiving element and a second optical filter. The second optical filter is configured so that the transmittance decreases as the wavelength of incident light increases. The slope (m) and intercept (n) of the sensitivity graph of the second optical sensor can be changed by appropriately selecting the second light receiving element and the second optical filter.

In general, the transmittance of a light receiving element decreases or increases as the wavelength of incident light increases, so one of the first and second optical sensors may be composed of only a light receiving element without an optical filter. Whether the transmittance of the light receiving element increases or decreases as the wavelength of the incident light increases is determined depending on the wavelength range of the incident light.

A central wavelength measuring device using a dual sensor can measure the central wavelength of source light by measuring the difference in sensitivity between the first and second optical sensors. For example, if a first and second photosensor having a sensitivity graph as shown in FIG. 14 is used, when the difference between the sensitivity values of the first and second photosensors is 0, the center of the source light The wavelength is approximately 535 nm, and at 0.8 it is 500 nm.

Additionally, a conventional optical spectrometer may be used as the center wavelength monitoring device 130. An optical spectrometer is a device that shows the intensity of light as a function of wavelength or frequency. A center wavelength meter using a dual sensor has the advantage of being very small in size compared to an optical spectrometer.

In this embodiment, the center wavelength of the source light 1 can be known using the center wavelength monitoring device 130, so that the manufacturing deviation of the optical transmitter 110 itself, the deviation due to ambient temperature, and the optical transmitter 110 There is no need to design the pass band of the interference filter 40 to be wide in consideration of variations in the center wavelength due to factors such as power consumption or current flowing through the optical transmitter 110.

Conventionally, the interference filter 40 was designed so that the pass band of the interference filter 40 was about 30 nm, but in the present invention, the width of the pass band can be reduced to 5 nm or less. When the width of the passband of the interference filter 40 is reduced, external light incident on the optical receiver 120 is reduced, thereby improving the signal-to-noise ratio. For example, when using pulsed source light with a central 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, the area of the source light irradiation surface is 1 m2. And when the illuminance of sunlight is 100kLux, the signal-to-noise ratio improves by about 585%. The same improvement occurs even when the illuminance of sunlight is 20kLux.

The controller 150 generates a control signal to adjust the optical distance between the pair of reflection layers 44 and 46 of the interference filter 40 in response to the change in the center wavelength of the source light measured by the center wavelength monitoring device 130. It plays a role.

In more detail, when the center wavelength of the source light measured by the center wavelength monitoring device 130 becomes longer, the controller 150 adjusts the optical distance of the interference filter 40, as described in the [Wide Angle Spectral Imaging Device] section. By transmitting a control signal to the mechanism, the optical distance between the first reflective layer 44 and the second reflective layer 46 is adjusted to become larger. Conversely, if the center wavelength of the source light becomes shorter, the optical distance is adjusted to become shorter.

Although the above has been described with reference to the drawings and examples, those skilled in the art can make various modifications and changes to the present invention without departing from the technical spirit of the present invention as set forth in the claims below. You will understand.

100: Wide-angle spectral imaging device
200: depth imaging device
20: optical receiver
40: Interference filter
50: controller

Claims (14)

A first reflective layer having a first surface on which light enters, a second surface on the opposite side, a third surface facing the second surface at a distance, and a fourth surface on the opposite side from which light exits. It is provided with a second reflective layer,
The angle of incidence of light incident on the interference filter increases as it progresses to the outside of the interference filter, so that the first surface of the first reflective layer and the fourth surface of the second reflective layer are adjusted to prevent the transmission wavelength from changing depending on the position of the interference filter. An interference filter configured such that the sum of the product of the thickness and refractive index of all media on a virtual path parallel to the optical axis increases as the distance from the optical axis increases. According to paragraph 1,
At least one of the first reflective layer and the second reflective layer is configured such 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 from the optical axis increases. Curved interference filter. According to paragraph 2,
An interference filter in which the curvature of a curved reflective layer of the first reflective layer and the second reflective layer decreases as the distance from the optical axis increases. According to paragraph 1,
The thickness between the first reflective layer and the second reflective layer of the interference filter increases as the distance from the optical axis increases, and the space between the first reflective layer and the second reflective layer is filled with an optical material having a higher refractive index than other media. filter. According to paragraph 1,
At least one of the first reflective layer and the second reflective layer includes a plurality of dielectric layers,
An interference filter in which at least one of the plurality of dielectric layers becomes thicker as the distance from the optical axis increases. According to paragraph 1,
The sum of the values obtained by multiplying the thickness and refractive index of all media on a path parallel to the optical axis between the first surface of the first reflective layer and the fourth surface of the second reflective layer is the optical axis according to Equation 2 below. An interference filter that grows in inverse proportion to the COSθ(x) value as you move away from .
[Equation 2]

(t _k (x) and n _k (x) represent the thickness (length of the path passing through each medium) and refractive index on each path of the media parallel to the optical axis at a distance x from the optical axis, θ ( x) is the angle of incidence according to the distance (x) from the optical axis, m is an integer, and λ means the transmission wavelength of the interference filter.) an optical receiver configured to receive light from a subject;
An optical distance adjustment mechanism configured to adjust the optical distance parallel to the optical axis direction between the first reflective layer and the second reflective layer,
A wide-angle spectral imaging device comprising an interference filter disposed at a front end of the optical receiver,
The interference filter is a wide-angle spectral imaging device that is the interference filter of any one of claims 1 to 6. In clause 7,
The optical distance control mechanism is,
A wide-angle spectral imaging device that is filled between the first and second reflective layers of the interference filter and is an intelligent optical material whose thickness or refractive index changes depending on external stimuli. In clause 7,
The optical distance adjustment mechanism is a gap adjustment mechanism configured to move the first reflective layer relative to the second reflective layer along the optical axis direction. an optical transmitter configured to transmit source light;
an optical receiver configured to receive reflected light of the source light;
A depth imaging device comprising an interference filter disposed in front of the optical receiver,
The depth imaging device wherein the interference filter is the interference filter of any one of claims 1 to 6. According to clause 10,
a central wavelength monitoring device that measures changes in the central wavelength of the source light;
an optical distance adjustment mechanism configured to adjust an optical distance parallel to the optical axis direction between the first reflective layer and the second reflective layer;
Depth imaging device further comprising a controller that controls the optical distance adjustment mechanism in response to a change in the center wavelength of the source light measured from the center wavelength monitoring device. According to clause 11,
The optical distance control mechanism is,
A depth imaging device that is filled between the first and second reflective layers of the interference filter and is an intelligent optical material whose thickness or refractive index changes depending on external stimuli. According to clause 11,
The optical distance adjustment mechanism is a gap adjustment mechanism configured to move the first reflective layer relative to the second reflective layer along an optical axis direction. According to clause 11,
The center wavelength monitoring device,
a first optical sensor configured to improve sensitivity as the wavelength of the source light increases;
A second optical sensor configured to decrease in sensitivity as the wavelength of the source light increases,
A depth imaging device that measures a change in the center wavelength of source light based on the difference in sensitivity between the first and second optical sensors.

Images