WO2020261685A1 - Optical device - Google Patents

Abstract

This optical device comprises a light detector, an optical system, and a control circuit that controls the light detector and the optical system. In the optical system, light arriving from one direction, from light arriving from the outside, is caused to impinge on the light detector. By controlling the optical system, the control circuit: changes a detection direction, which is the direction of arriving light detected by the light detector; changes the focal distance of the optical system in tandem with the change in the detection direction; causes light arriving from an object positioned in the one detection direction to be detected by the light detector in two or more states in which the focal distances of the optical system differ from each other; and generates information pertaining to the distance to the object on the basis of two or more light detection amounts that were respectively detected by the light detector in the two or more states.

Description

Optical device

This disclosure relates to an optical device.

Conventionally, various technologies have been developed to grasp the positions of objects scattered in the field of view. For example, there is a technique for measuring the distance to the surface of an object by irradiating the object with an optical pulse and measuring the time delay of the reflected light from the object for each direction. Patent Document 1 discloses an optical phased array using such a technique.

JP-A-2017-187649

The present disclosure provides a novel technique for selectively detecting reflected light from an object existing in a visual field and acquiring distance information to the object.

The optical device according to one aspect of the present disclosure includes a photodetector, an optical system that causes light coming from a part of the light coming from the outside to enter the photodetector, the photodetector, and the above. It is equipped with a control circuit that controls the optical system. By controlling the optical system, the control circuit changes the detection direction, which is the direction in which the light detected by the photodetector arrives, and the optical system is linked to the change in the detection direction. Light coming from an object located in a single detection direction is detected by the photodetector in two or more states where the focal lengths of the optical systems are different, and the two or more are detected. The distance information to the object is generated based on the amount of two or more detected lights detected by the photodetector in the state.

Comprehensive or specific embodiments of the present disclosure may be implemented in systems, devices, methods, integrated circuits, computer programs, or computer-readable recording media. Alternatively, it may be realized by any combination of systems, devices, methods, integrated circuits, computer programs, and recording media. The computer-readable recording medium may include a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). The device may consist of one or more devices. When the device is composed of two or more devices, the two or more devices may be arranged in one device, or may be separately arranged in two or more separated devices. As used herein and in the claims, "device" can mean not only one device, but also a system consisting of a plurality of devices.

According to one aspect of the present disclosure, it is possible to selectively detect the reflected light from an object existing in the field of view and acquire distance information to the object.

FIG. 1A is a perspective view schematically showing a configuration of an optical device and a path of light rays according to the first embodiment. FIG. 1B is a cross-sectional view schematically showing a part of the configuration of the optical device and the path of light rays in the first embodiment. FIG. 2 is a vector diagram showing the relationship of diffraction occurring on the side surface of the truncated cone prism. FIG. 3 is a vector diagram showing the relationship between the incident light and the waveguide light of the input grating coupler and the relationship between the waveguide light and the synchrotron radiation of the output grating coupler. FIG. 4 is a diagram schematically showing a propagation path of incident light to the input grating coupler when there is aberration correction. FIG. 5 is a diagram schematically showing the state of light refracted by the side surface of the truncated cone prism and incident on the input grating coupler. FIG. 6A is a diagram showing an example of a pattern of a transparent electrode layer for realizing aberration correction. FIG. 6B is a diagram showing an example of changes in the voltage applied to the electrodes and the effective refractive index with respect to the declination. FIG. 7A is a diagram showing an example of the relationship between the angle φ and the amount of change ΔN in the effective refractive index of the waveguide light for realizing aberration correction. FIG. 7B is a diagram showing an example of the relationship between the thickness of the waveguide layer and the effective refractive index N. FIG. 7C is a diagram schematically showing the arrangement of the buffer layer, the waveguide layer, and the liquid crystal layer. FIG. 8A is a diagram schematically showing the relationship between the electrode pattern in the transparent electrode layer and the applied voltage. FIG. 8B is a diagram schematically showing the relationship between the electrode pattern in the reflective electrode layer and the applied voltage. FIG. 8C is a diagram schematically showing the relationship between the electrode pattern in the transparent electrode layer, the configuration in which the electrode patterns in the reflective electrode layer are aligned and overlapped, and the applied voltage. FIG. 9A is a diagram schematically showing an example of an electrode pattern in the transparent electrode layer. FIG. 9B is a diagram schematically showing an example of an electrode pattern in the reflective electrode layer. FIG. 9C is a diagram schematically showing a configuration in which an electrode pattern on the transparent electrode layer and an electrode pattern on the reflective electrode layer are aligned and overlapped. FIG. 10 is a diagram schematically showing the relationship between a part of the electrode pattern shown in FIG. 9C and the propagation path of the waveguide light. FIG. 11 is a diagram showing a configuration example of a photodetector. FIG. 12A is a diagram schematically showing a state of scanning of monochromatic light in the horizontal direction and the vertical direction. FIG. 12B is a diagram schematically showing a state of horizontal and vertical scanning of light of a plurality of colors in a narrow band. FIG. 13A is a diagram showing a configuration of an optical system equivalent to the optical device according to the first embodiment. FIG. 13B is a diagram for explaining the path of the light beam passing through the truncated cone prism. FIG. 13C is a diagram showing an example of the relationship between the amount of detected light and the distance to the measurement target. FIG. 13D is a diagram showing an example of the relationship between the ratio of the two detected light amounts and the distance to the measurement target in the example of FIG. 13C. FIG. 13E is a diagram showing another example of the relationship between the amount of detected light and the distance to the measurement target. FIG. 13F is a diagram showing an example of the relationship between the ratio of the two detected light amounts and the distance to the measurement target in the example of FIG. 13E. FIG. 14 is a diagram schematically showing a configuration of an optical device and a path of light rays in the second embodiment.

Before explaining the embodiments of the present disclosure, the findings underlying the present disclosure will be explained. In this specification, the term "light" is used not only for visible light but also for invisible light such as infrared light.

There are two typical methods for grasping the positions of objects scattered in the field of view. One is a method of detecting reflected light by uniformly irradiating the entire field of view with an optical pulse. The other is a method of detecting reflected light by comprehensively scanning the entire field of view with a directional laser beam. Both methods require a light source to illuminate the entire area of the target scene with light.

However, if the distance information of the object in the target scene can be acquired by using natural light or external illumination light without using a light source, the configuration of the device can be simplified and the cost can be reduced. Therefore, the present disclosure provides a technique that makes it possible to measure the distance to an object without using a light source.

The outline of the embodiment of the present disclosure will be described below.

The optical device according to one aspect of the present disclosure includes a photodetector, an optical system that causes light coming from a part of the light coming from the outside to enter the photodetector, the photodetector, and the above. It is equipped with a control circuit that controls the optical system. By controlling the optical system, the control circuit changes the detection direction, which is the direction in which the light detected by the photodetector arrives, and the optical system is linked to the change in the detection direction. Light coming from an object located in a single detection direction is detected by the photodetector in two or more states where the focal lengths of the optical systems are different, and the two or more are detected. The distance information to the object is generated based on the amount of two or more detected lights detected by the photodetector in the state.

With such a configuration, it is possible to measure the distance to an object without using a light source. The above optical device and a light source may be used in combination. When a light source is used, the intensity of the reflected light from the object can be increased, so that the detection sensitivity can be improved.

The control circuit may periodically change the detection direction and the focal length of the optical system.

With such a configuration, it is possible to obtain information on the distance distribution of an object with simple control.

The two or more detected light amounts may include a first detected light amount and a second detected light amount. The control circuit may generate the distance information based on the ratio of the first detected light amount to the second detected light amount.

The optical device may further include a recording medium that stores data that defines the correspondence between the ratio of the first detected light amount and the second detected light amount and the distance. The control circuit may generate the distance information based on the data and the ratio of the first detected light amount to the second detected light amount.

As will be described later, the ratio of the first detected light amount to the second detected light amount depends on the distance to the object. By acquiring and recording data such as a table showing the correspondence between the ratio and the distance in advance, the distance is calculated from the ratio of the first detected light amount and the second detected light amount by referring to the data at the time of measurement. Can be sought.

The optical system can be realized by various structures. For example, the function of the optical system can be realized by a combination of a rotating body and a movable lens. Alternatively, the function of the optical system can also be realized by using an optical waveguide layer having a concentric grating structure and a liquid crystal.

The optical system includes a rotating body that rotates around a central axis, a lens that is supported by the rotating body and is configured to be movable along an optical axis, and the lens and the light detection that are supported by the rotating body. It may be provided with a slit plate located between the vessel. The slit plate member includes a slit that allows at least a part of the light focused by the lens to enter the photodetector. The control circuit can change the detection direction by rotating the rotating body, and can change the focal length by moving the lens along the optical axis.

The control circuit may rotate the rotating body at a constant speed.

The control circuit may cause the photodetector to detect the light in two or more states in which the rotation angle of the rotating body is the same and the positions of the lenses in the direction along the optical axis are different.

When two or more rotating bodies have the same rotation angle, the optical axes of the lenses overlap each other and the detection directions match. On the other hand, when the position in the direction along the optical axis of the lens changes, the focal length of the optical system changes. Therefore, according to the above configuration, it is possible for the photodetector to detect light coming from an object located in a single detection direction in two or more states in which the focal lengths of the optical systems are different.

The optical system includes an optical waveguide element that propagates light along a direction orthogonal to an axis, a bottom surface facing the surface of the optical waveguide element, a side surface that is rotationally symmetric with the axis as a central axis, and the opposite of the bottom surface. It may be provided with a transparent member having an upper surface on the side. The optical waveguide element includes a first grating that expands along the radial direction of a virtual circle centered on the axis, and a first grating that expands along the radial direction outside the first grating. May include a waveguide layer having a second grating having a different grating constant on the surface. A part of the light coming from the object enters the second grating through the transparent member, propagates in the waveguide layer and exits from the first grating, and the bottom surface of the transparent member and the said. It passes through the upper surface and enters the photodetector. The control circuit can change the detection direction and the focal length by adjusting the effective refractive index of the waveguide layer.

The optical waveguide element includes a transparent electrode layer, a liquid crystal layer having a refractive index lower than that of the waveguide layer, the waveguide layer, a dielectric layer having a refractive index lower than that of the waveguide layer, and a reflective electrode. The layers may be provided in this order. The control circuit can adjust the effective refractive index by adjusting the voltage applied between the transparent electrode layer and the reflective electrode layer.

The waveguide layer may include a third grating on the surface between the first grating and the second grating for controlling the orientation of liquid crystal molecules in the liquid crystal layer. At least one of the transparent electrode layer and the reflective electrode layer may include a first electrode, a second electrode, and a third electrode facing the first grating, the second grating, and the third grating, respectively. Good.

With such a structure, the control circuit can individually apply a voltage to each of the first electrode, the second electrode, and the third electrode. As a result, the propagation direction of the propagating light in the waveguide can be easily controlled.

The third electrode may include a plurality of divided regions arranged along the circumferential direction of the virtual circle. The plurality of divided regions may be isolated from each other.

The control circuit may individually control the voltage applied between the transparent electrode layer and the reflective electrode layer for each of the divided regions of the third electrode.

According to such a configuration, the propagation direction of the propagating light in the waveguide layer can be adjusted more finely.

The control circuit applies the voltage to each of the divided regions in such a manner that the distribution of the amplitude of the voltage applied to the plurality of divided regions of the third electrode rotates around the axis with the passage of time. By changing the distribution each time the rotation of the voltage amplitude distribution goes around, light coming from an object located in a single detection direction can be emitted from two or more states with different focal lengths of the optical system. It may be detected by the photodetector.

According to such control, light arriving from a single detection direction can be easily detected in two or more states having different focal lengths of the optical system.

Hereinafter, embodiments of the present disclosure will be specifically described with reference to the drawings. It should be noted that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, components, arrangement positions and connection forms of components, steps, step sequences, and the like shown in the following embodiments are examples, and are not intended to limit the techniques of the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components. Further, each figure is a schematic view and is not necessarily exactly shown. Further, in each figure, substantially the same components are designated by the same or similar reference numerals, and duplicate description may be omitted or simplified.

(First Embodiment)
FIG. 1A is a perspective view schematically showing a configuration of an optical device and a path of light rays according to the first embodiment. FIG. 1B is a cross-sectional view schematically showing a part of the configuration of the optical device and the path of the light beam. 1A and 1B show XYZ coordinates indicating X, Y, and Z directions perpendicular to each other. Hereinafter, the configuration and operation of the optical device will be described using the XYZ coordinates.

The optical device of this embodiment includes a photodetector 12, an optical system, and various control circuits. An optical system is a set of a plurality of optical elements. The optical system in this embodiment includes an optical waveguide element 7, a truncated cone prism 6, a wavelength spectroscope 5, and a detection condenser lens 13. The control circuit includes a detection circuit 33, a main control circuit 34, and a liquid crystal control circuit 32. The truncated cone prism 6 and the optical waveguide element 7 are arranged so that their centers are located on the axis L parallel to the Z axis. In the following description, for convenience, the direction parallel to the axis L is referred to as a vertical direction, and the direction orthogonal to this is referred to as a horizontal direction. These names are for convenience only and do not limit the posture of the optical device when it is actually used.

The liquid crystal control circuit 32 controls the orientation of the liquid crystal contained in the optical waveguide element 7. The main control circuit 34 controls the liquid crystal control circuit 32 based on the signal output from the detection circuit 33. As shown in FIG. 1A, the main control circuit 34, the liquid crystal control circuit 32, and the detection circuit 33 may be separate circuits separated from each other, or a part or the whole thereof is composed of a single circuit. It may have been done.

Note that FIG. 1A shows a state in which the truncated cone prism 6 and the optical waveguide element 7 are separated from each other for convenience of explanation. Actually, of the two opposite bottom surfaces (bottom surface and top surface) of the truncated cone prism 6, the bottom surface, which is the lower bottom surface, is in contact with the optical waveguide element 7. Further, although omitted in FIG. 1A, in reality, as shown in FIG. 1B, a hollow substrate 7h is provided on the surface of the optical waveguide element 7.

As shown in FIG. 1B, the optical waveguide element 7 is a laminated structure including a plurality of layers laminated in the Z direction. The optical waveguide element 7 includes a flat substrate 7a, a reflective electrode layer 7b, a buffer layer 7c, a waveguide layer 7d, a liquid crystal layer 7e, a transparent electrode layer 7f, a flat substrate 7g, and a hollow substrate 7h in this order. The flat substrates 7a and 7g are flat transparent substrates. The hollow substrate 7h is a transparent substrate having a truncated cone-shaped cavity or a recess in the center. The truncated cone prism 6 is arranged in the cavity or recess of the hollow substrate 7h. The truncated cone prism 6 and the hollow substrate 7h are arranged with the axis L as a common central axis, and are in close contact with the flat substrate 7g. In this embodiment, the flat substrates 7a and 7g and the hollow substrate 7h are formed of a transparent material having a refractive index of n ₁ '. However, they may be formed of materials with different refractive indexes.

A reflective electrode layer 7b, a buffer layer 7c, a waveguide layer 7d, a liquid crystal layer 7e, and a transparent electrode layer 7f are located between the flat substrate 7a and the flat substrate 7g. The refractive index of the waveguide layer 7d is higher than that of any of the buffer layers 7c and the liquid crystal layer 7e on both sides thereof. The buffer layer 7c, the waveguide layer 7d, and the liquid crystal layer 7e are sandwiched between the transparent electrode layer 7f and the reflective electrode layer 7b. The reflective electrode layer 7b can be formed of a metal material such as aluminum (Al). The buffer layer 7c is a dielectric layer formed of a transparent material having a relatively low refractive index such as silicon dioxide (SiO ₂ ). The waveguide layer 7d can be formed of a transparent material having a relatively high refractive index, for example, tantalum pentoxide (Ta ₂ O ₅ ). A reflective electrode layer 7b, a buffer layer 7c, and a waveguide layer 7d are formed on the surface of the flat substrate 7a in this order. The transparent electrode layer 7f can be formed of a translucent conductive material such as indium tin oxide (ITO).

The optical waveguide element 7 includes gratings 8a, 8b and 8c. On the surface of the waveguide layer 7d, gratings 8a, 8b and 8c having a concentric concave-convex structure centered on the axis L are provided. The grating 8a is formed in a circular region located at the center of the surface of the waveguide layer 7d. The grating 8a includes a plurality of recesses and a plurality of protrusions periodically arranged along the radial direction from the center. The grating 8a corresponds to the above-mentioned "first grating". The grating 8b is formed in a ring-shaped region located on the surface of the waveguide layer 7d outside the region where the grating 8a is formed. The grating 8b corresponds to the above-mentioned "third grating". The grating 8c is formed in a ring-shaped region located on the surface of the waveguide layer 7d outside the region where the grating 8b is formed. The grating 8c corresponds to the above-mentioned "second grating". The gratings 8b and 8c also include a plurality of recesses and a plurality of protrusions periodically arranged along the radial direction. The grating 8a and the grating 8c act as a grating coupler. The grating 8b is a grating for liquid crystal orientation. In the following description, the grating 8a may be referred to as an "output grating coupler 8a" or simply a "grating coupler 8a". Further, the grating 8c may be referred to as an "input grating coupler 8c" or simply a "grating coupler 8c". Each of the gratings 8a, 8b and 8c is not limited to a circular shape or a ring shape, and may be formed in a region having a shape in which a part is missing from those shapes, for example, a fan shape.

Grating 8a is formed in a circular region of radius r ₁ about the axis L. The pitch of the grating 8a is Λ ₀ , and the depth is d ₀ . The grating 8b is formed in a ring-shaped region having a radius r ₁ to a radius r ₂ . Pitch of the grating 8b is for example 0.8Ramuda ₁ or less, the depth is _{d 1.} The grating 8c is formed in a ring-shaped region having a radius r ₂ to a radius r ₃ . The pitch of the grating 8c is Λ ₁ , and the depth is d ₁ . The pitch Λ ₀ and depth d _{0 of} the grating 8a and the pitch Λ ₁ and depth d ₁ of the grating 8c are set to appropriate values that satisfy the coupling conditions described later. In this embodiment, Λ ₀ > Λ ₁ and d ₀ > d ₁ . Typical sizes of the radii _r 1, _{r 2} and _{r 3} are the submillimeter or the order of millimeters. Typical sizes of pitches Λ ₀ and Λ ₁ and depths d ₀ and d ₁ are on the order of submicrons. When the pitch of the grating 8b for example 0.8Ramuda ₁ below, the uneven structure of the grating 8b acts only for liquid crystal alignment, does not function as a grating coupler. Therefore, the uneven structure of the grating 8b does not radiate waveguide light. On the other hand, the uneven structure of the grating 8c inputs and couples the incident light and converts it into waveguide light.

If a concavo-convex structure appears on the surface of the waveguide layer 7d on the liquid crystal layer 7e side, a concavo-convex structure similar to that of the gratings 8a, 8b and 8c is also formed on the surface of the buffer layer 7c on the waveguide layer 7d side. May be good. Since the uneven structure appears on the surface of the waveguide layer 7d on the liquid crystal layer 7e side, the grating acts as a means for aligning the liquid crystal. The liquid crystal molecules are oriented in the direction along the circumferential direction in which each recess of the grating extends.

A transparent electrode layer 7f such as ITO is formed on the surface of the flat substrate 7g on the waveguide layer 7d side. The transparent electrode layer 7f faces the waveguide layer 7d via the liquid crystal layer 7e. The transparent electrode layer 7f and the reflective electrode layer 7b act as electrodes for controlling the orientation of the liquid crystal molecules in the liquid crystal layer 7e. The transparent electrode layer 7f in the present embodiment is divided into three regions 9A, 9B and 9C centered on the axis L. Regions 9A, 9B and 9C face gratings 8a, 8b and 8c, respectively. In a state where no voltage is applied to the liquid crystal layer 7e, the liquid crystal molecules of the liquid crystal layer 7e are oriented in the direction in which the recess of the grating on the surface of the waveguide layer 7d extends, that is, in the circumferential direction centered on the axis L. .. In other words, the orientation direction of the liquid crystal in the liquid crystal layer 7e is parallel to the surface of the waveguide layer 7d and perpendicular to the grating vectors of the gratings 8a, 8b and 8c. Regions 9A, 9B and 9C each function as independent electrodes. In the following description, the regions 9A, 9B and 9C of the transparent electrode layer 7f may be referred to as " electrodes 9A, 9B and 9C". Instead of the transparent electrode layer 7f, the reflective electrode layer 7b may be divided into three regions. Alternatively, each of the transparent electrode layer 7f and the reflective electrode layer 7b may be divided into three regions.

A concentric grating centered on the axis L, similar to the grating 8b, may be formed on the surface of the flat substrate 7g on the electrode layer 7f side. Similarly, concentric gratings centered on the axis L may be formed at positions facing the gratings 8a and 8c on the surface of the flat substrate 7g on the electrode layer 7f side. If the uneven structure is formed on the surface of the flat substrate 7g, the uneven structure is also transferred to the surface of the transparent electrode layer 7f. As a result, the liquid crystal molecules of the liquid crystal layer 7e can be oriented along the direction in which the recesses extend. Naturally, it is also possible to orient the liquid crystal molecules in the liquid crystal layer 7e by forming an alignment film such as polyimide on the surface of the waveguide layer 7d and / or the transparent electrode layer 7f and rubbing this in the circumferential direction. it can.

The light reflected by an external object and incident on the truncated cone prism 6 passes through the side surface of the truncated cone prism 6 twice, passes through the hollow substrate 7h, and becomes the light 10h incident on the flat substrate 7g at an angle θ ₁ '. This light 10h excites 10g of waveguide light that is incident on the grating 8c at an angle θ ₁ and propagates inward along the radial direction of the concentric grating.

The waveguide light 10g toward the center of the optical waveguide element 7 is radiated from the grating coupler 8a and becomes the light 10f along the axis L. The polarization direction 11f of the light 10f is orthogonal to the propagation direction of the waveguide light 10g. For example, when the waveguide light 10g propagates in the X-axis direction, the polarization direction 11f of the light 10f is parallel to the Y-axis direction. The light 10f passes through the lower surface and the upper surface of the truncated cone prism 6 to become the light 10b. The light 10b is reflected and diffracted by the wavelength spectroscope 5, condensed by the condenser lens 13 to become light 10a, and is detected by the photodetector 12. The wavelength spectroscope 5 is an optical element that separates light in the diffraction direction according to the wavelength. The wavelength spectroscope 5 can be, for example, a litho-type reflection diffraction grating.

As shown by the dotted arrow in FIG. 1B, it is assumed that light 10i is incident on the side surface of the truncated cone prism 6 from a direction inclined by an angle θ _{⊥'from the} horizontal plane. This light 10j is refracted on the side surface of the truncated cone prism 6. Here, the angle formed by the path of the light beam propagating inside the truncated cone prism 6 and the vertical direction is θ _0, and the angle formed by the side surface of the truncated cone prism 6 and the vertical direction is θ ₂ . Assuming that the truncated cone prism 6 is a transparent member having a refractive index of n ₀ , the relational expression of refraction is described by Equation 1.

The light emitted from the side surface of the truncated cone prism 6 enters the grating coupler 8c via the hollow substrate 7h and the flat substrate 7g. At this time, refraction occurs at the interface between the truncated cone prism 6 and the air and at the interface between the air and the hollow substrate 7h. Here, for simplicity, the direction of light rays inside the hollow substrate 7h having a refractive index n ₁ '(angle θ ₁ ') and the direction of light rays inside the conical prism 6 having a refractive index n ₀ (angle θ _0). ) between, and _{n 1 'sinθ 1' = n} 0 that the relationship sin [theta ₀ holds.

As shown in the circular dotted line frame in FIG. 1A, a blaze grating 6a centered on the axis L may be formed on the side surface of the truncated cone prism 6. A similar blaze grating may be formed on the truncated cone-shaped inner surface of the hollow substrate 7h. By providing a properly designed blaze grating, the direction of detectable light can be brought closer to the horizontal direction. For example, as shown in FIG. 1B, the direction of arrival of detectable light is the angle between the horizontal plane, can be reduced from the angle theta _⊥ 'the angle theta _⊥ when the blazed gratings 6a is not provided. The blaze grating 6a includes a plurality of grooves having a saw-like cross section. Let Λ ₂ be the pitch of the groove of the blaze grating 6a. Each groove has a structure extending along the circumferential direction of the side surface of the truncated cone prism 6 or the inner surface of the hollow substrate 7h, that is, the circumferential direction of a circle centered on the axis L. In other words, the lattice lines of the blaze grating 6a extend along the circumferential direction of the side surface of the truncated cone prism 6 or the inner surface of the hollow substrate 7h. Light passing through the side surface of the truncated cone prism 6 provided with the blaze grating 6a is diffracted in a plane including the axis L. As a result, as shown in FIG. 1B, the light 10i incident on the horizontal plane at an angle θ _⊥ is diffracted by the side surface of the truncated cone prism 6 to become the light 10h incident on the grating 8c at an angle θ ₁ .

FIG. 2 is a vector diagram showing the relationship of diffraction occurring on the side surface of the truncated cone prism 6. When the blaze grating 6a is formed only on the side surface of the truncated cone prism 6, the diffraction relationship is shown in FIG. In other words, _'the foot P ₂ of a perpendicular angle theta _⊥ to the longitudinal axis' angle θ _⊥ + θ ₂ vector OP 2 size 1 forming a to the longitudinal axis + theta ₂ eggplants size 1 vector OP ₃ It is expressed by the relation that the distance of the perpendicular line from the foot P ₃ is equal to 2λ / Λ ₂ , which is twice the magnitude of the lattice vector. Here, λ represents the wavelength of light in the air. That is, the relational expression of diffraction is described by Equation 2.

As can be seen from Equation 2, by providing the blazed gratings 6a pitch lambda _2, the incident angle theta _⊥ + theta ₂ of the detectable light, than the incident angle θ _⊥ '+ θ ₂ when the blazed gratings 6a is not provided Can also be made smaller.

The truncated cone prism 6 in the present embodiment is in contact with the flat substrate 7g, but may be separated from the flat substrate 7g. The light incident on the side surface of the truncated cone prism 6 is emitted from the side surface or the bottom surface of the truncated cone prism 6 and is incident on the grating 8c.

Instead of the truncated cone prism 6, a transparent member having a bottom surface facing the optical waveguide element 7 and a side surface that is a rotationally symmetric body with the axis L as the central axis may be used. If the pitch of the grating 8c is not constant along the waveguide direction, a rotationally symmetric prism having a curved generatrix on its side surface may be used instead of the truncated cone prism 6. On the other hand, when the pitch of the grating 8c is constant, a prism having a rotational symmetry whose generatrix has a linear shape, that is, a prism having a cylindrical or truncated cone shape can be used.

FIG. 3 is a vector diagram showing the relationship between the incident light and the waveguide light of the input grating coupler 8c and the relationship between the waveguide light and the synchrotron radiation of the output grating coupler 8a. Here, let N be the effective refractive index of the waveguide layer 7d. As shown in FIG. 3, assuming that the intersection of a circle having a radius N and the horizontal axis is a point P, the condition for coupling the incident light to the waveguide light is a vector having a magnitude n ₁ forming an angle θ ₁ with respect to the vertical axis. perpendicular foot to the horizontal axis of the OP 1 _'it can, is to match the end point P ₁ of the grating vector PP ₁ represented by the magnitude lambda / lambda ₁ of the dashed arrows. The coupling condition is expressed as -n ₁ sin θ ₁ = N-λ / Λ ₁ . And Snell's law _{(n 1 sinθ 1 = n 1} 'sinθ 1'), the relationship of _{n 1 'sinθ 1' = n} 0 sinθ 0 described above, the join condition is described by the number 3.

As can be seen from Equation 3, only light having a specific wavelength and phase plane is selectively coupled to the waveguide layer 7d via the grating coupler 8c. Therefore, stray light that differs in at least one of the wavelength and the phase plane is effectively removed.

On the other hand, the coupling condition to the synchrotron radiation 10f is that the magnitude of the lattice vector PO represented by the arrow having the magnitude λ / Λ ₀ is equal to the effective refractive index N of the waveguide layer 7d. That is, the binding condition is described by Equation 4.

As shown in FIG. 1B, a part of the light 10h incident on the grating coupler 8c is transmitted to become the light 10ha. The light 10ha is reflected by the reflective electrode layer 7b and is incident on the grating coupler 8c again to enhance the excitation of the waveguide light 10g. On the other hand, the light 10fa emitted from the grating coupler 8a toward the reflective electrode layer 7b is reflected by the reflective electrode layer 7b and overlaps with the synchrotron radiation 10f.

From the coupling condition −n ₁ sin θ ₁ = N−λ / Λ ₁ , the derivative of the effective refractive index N with respect to the incident angle θ ₁ is described by Equation 5.

Further, from the coupling condition −n ₁ sin θ ₁ = N−λ / Λ ₁ , the derivative of the incident angle θ ₁ with respect to the wavelength λ is described by Equation 6.

Using the relationship of n ₁ sin θ ₁ = n ₀ sin θ ₀ , the derivative of the incident angle θ _⊥ with respect to the wavelength λ of the incident beam 10i in the horizontal direction is described by _Equation 7.

From Equations 5 and 6, it can be seen that when the wavelength λ or the effective refractive index N changes, the permissible incident angle θ ₁ changes. When the refractive index of the liquid crystal layer 7e changes, the effective refractive index N also changes. Therefore, when the wavelength λ of the light from the external reflector or the refractive index of the liquid crystal layer 7e at the electrode 9C changes, the direction of the detectable incident beam 10i changes along the vertical direction (that is, the vertical direction) of FIG. 1B. To do. Therefore, by changing the voltage applied to the electrode 9C, the direction of the detectable incident beam 10i can be changed along the vertical direction according to Equation 7 and the like. This makes it possible to scan the field of view in the vertical direction.

In the present embodiment, a voltage is applied to the liquid crystal layer 7e via the transparent electrode layer 7f and the reflective electrode layer 7b by the control signal from the liquid crystal control circuit 32. The orientation of the liquid crystal changes when this voltage is applied. Along with this, the refractive index n _{1 of} the liquid crystal layer 7e with respect to 10 g of waveguide light changes, and the effective refractive index N of the waveguide layer 7d with respect to 10 g of waveguide light changes. When the effective refractive index N changes in the region of the grating 8c, the incident angle θ _{1 of the} light that can be incident on the grating 8c from the outside changes.

The liquid crystal control circuit 32 can independently send signals to the electrodes 9A, 9B and 9C. The voltage signal applied to the liquid crystal layer 7e is an alternating wave. The tilt angle of the liquid crystal molecules is determined by the magnitude of the amplitude of the AC wave. The larger the amplitude of the AC wave, the closer the orientation direction of the liquid crystal is to the normal direction of the waveguide layer 7d. In the following description, the "voltage" applied to the liquid crystal layer 7e means the magnitude of the amplitude of the alternating current wave applied to the liquid crystal layer 7e.

The light input to the grating coupler 8c is limited to a specific wavelength and a specific angle of incidence. If the angle of incidence changes, the optimum wavelength corresponding to it also changes. The wavelength of the light incident on the grating coupler 8c, coupled to the waveguide layer 7d, and guided by the waveguide has a width of about several nm. The light 10b emitted from the truncated cone prism 6 also contains the same wavelength component. The light 10b is diffracted by the wavelength spectroscope 5 and separated for each wavelength.

The dispersed light 10a is focused by the condensing lens 13, and a plurality of condensing spots 17a1, 17a2, ... Are formed on the light receiving surface of the photodetector 12. In reality, innumerable condensing spots that are continuously overlapped are formed on the light receiving surface, but in FIG. 1A, for the sake of simplicity, the condensing spots are drawn so as to be formed discretely.

The photodetector 12 includes a plurality of light receiving elements divided into strips. When each light receiving element receives light, it generates an electric signal according to the amount of light received. As a result, the photodetector 12 can separate and detect a plurality of focused spots 17a1, 17a2, ... For each wavelength range.

The photodetector 12 is connected to the detection circuit 33. The detection circuit 33 drives the photodetector 12 in accordance with a command from the main control circuit 34, and processes the detection signal output from the photodetector 12. For example, based on the signal output from the photodetector 12, the distance to the detection target can be calculated by the method described later.

The optical device of this embodiment further includes a main control circuit 34 connected to the detection circuit 33. The main control circuit 34 generates a control signal for controlling the liquid crystal control circuit 32 based on the signal output from the detection circuit 33. The liquid crystal control circuit 32 adjusts the refractive index of the liquid crystal layer 7e by adjusting the voltage between the transparent electrode layer 7f and the reflective electrode layer 7b in response to the control signal input from the main control circuit 34. .. The liquid crystal control circuit 32 and the main control circuit 34 do not have to be realized by different hardware, and may be realized by a single circuit.

In the present embodiment, the light passing through the side surface of the truncated cone prism 6 is incident on the grating coupler 8c. With such a configuration, the degree of freedom in design can be increased. The structure is not limited to this, and for example, light 10h may be incident on the grating coupler 8c from the lower surface of the prism. In the present embodiment, since the light beam passes through the side surface of the truncated cone prism 6 twice, it is affected by the diffraction by the blaze grating 6a twice. Therefore, the pitch of the blaze grating 6a can be increased, and the production becomes easy. Further, a blaze grating may be formed on the truncated cone-shaped inner surface of the hollow substrate 7h. In that case, the light beam is affected by diffraction three times. As the number of diffractions increases, the pitch of the blaze grating can be increased, the fabrication becomes easier, and the overall diffraction efficiency increases.

In the present embodiment, the hollow substrate 7h is arranged around the truncated cone prism 6. This is because the light emitted from the side surface of the truncated cone prism 6 is easily incident on the flat substrate 7g and the grating coupler 8c via the air layer. The hollow substrate 7h may be omitted as long as the light can be easily incident on the grating coupler 8c. However, as in the present embodiment, by providing the hollow substrate 7h having a truncated cone-shaped cavity, light can be incident on the grating coupler 8c regardless of the angle of incidence thereof. Therefore, the degree of freedom in design can be increased.

Next, aberration correction in this embodiment will be described.

FIG. 4 is a diagram schematically showing an example of a propagation path of incident light to the input grating coupler 8c. In FIG. 4, (a) is a plan view, (b) is a perspective view, and (c) is a cross-sectional view. In the configuration of FIG. 4, of the two refractions that occur on the side surface of the truncated cone prism 6, the influence of the refraction on the side where the light is emitted is small and can be ignored. Therefore, in the following description, only refraction on the incident side, which accounts for most of the refraction effect, will be discussed.

Light coming from various directions is incident on the truncated cone prism 6. Among them, consider light _10i that enters propagating parallel to the X axis in the truncated cone prism 6, 10i 0, 10i1, and 10i1 _0. The light 10i and 10i1 are light propagating in the X direction in the XZ plane including the central axis L of the optical waveguide element 7, and their paths are different in the Z direction. The paths of light 10i and 10i ₀ are consistent in the Z direction and different in the Y direction. Path of light 10i1 and 10i1 ₀ are consistent with respect to the Z direction are different with respect to the Y direction. Path of light 10i ₀ and light 10i1 ₀ is different for both Y and Z directions. These light _10i, 10i 0, 10i1, and 10i1 ₀ are respectively refracted at the side surface of the truncated cone prism 6, light _10h, 10h 0, 10h1, and becomes 10h1 _0. Light _10h, 10h 0, 10h1, and 10h1 ₀ passes through the axis _{L 1} away in the positive direction of the inclined and the X-axis from the central axis L. Light 10h and 10h ₀ intersect at a point _{F 1} on the axis _{L 1,} light 10h1 and 10h1 ₀ intersect at a point on the axis _{L 1} F ₁ '. Light 10h and 10h ₀ is incident on the outer portion of the grating coupler 8c, optical 10h1 and 10h1 ₀ is incident on the inner portion of the grating coupler 8c. Light 10h and 10h1 excites the guided light 10 g, light 10h ₀ and 10h1 ₀ excites the guided light 10 g _0.

The propagation direction of the waveguide light 10g and 10g ₀ is not along the radial direction at the time of excitation, but is corrected so as to be along the radial direction while passing through the region of the electrode 9B. This correction, that is, the aberration correction, can be realized by setting the voltage between the transparent electrode layer 7f and the reflective electrode layer 7b in the region of the grating 8b to a different value depending on the declination position, as will be described later.

Hereinafter, a method of estimating the amount of aberration correction for correcting a light ray in the radial direction will be described.

FIG. 5 is a diagram schematically showing the state of light refracted by the side surface of the truncated cone prism 6 and incident on the input grating coupler 8c. The refraction of the incident light occurs twice on the incident side and the exit side of the side surface of the truncated cone prism 6, but as described above, only the refraction on the incident side, which occupies most of the refraction effect, will be discussed here. The amount of aberration correction can be estimated by comparing a light ray that is incident on the side surface of the truncated cone prism 6 parallel to the X-axis with a light ray that is vertically incident on the side surface of the truncated cone prism 6 in the horizontal plane and is not refracted.

Of light path shown in FIG. 5, the path of the light beam 10i and 10i ₀ incident on the side surface parallel frustoconical prism 6 in the X-axis is as described with reference to FIG. On the other hand, the path of the light beam perpendicularly incident on the side surface of the truncated cone prism 6 in the horizontal plane is as follows. First, the light rays 10I and 10I ₀ reflected by an external object and directed toward the center F of the truncated cone prism 6 are incident on the side surfaces of the truncated cone prism 6, respectively, and become light 10H and 10H ₀ toward the center F of the truncated cone prism 6. And intersect at point F. After that, the light 10H and 10H ₀ are vertically emitted from the side surface of the truncated cone prism 6 in the horizontal plane and incident on the grating coupler 8c to excite the waveguide light 10G and 10G ₀ along the radial direction, respectively.

As shown in FIG. 5A, let Q be the intersection of the light 10h and the side surface of the truncated cone prism 6, and let Q ₁ be the intersection of the light 10h ₀ and the side surface of the truncated cone prism 6. Let the angle QFQ ₁ be ψ, the angle FF ₁ Q ₁ be φ, and the angle FQ ₁ F ₁ be ψ'. Since the light 10i ₀ is parallel to the light 10i, the _equation 8 holds.

Here, the angles φ, ψ, and ψ'satisfy the relationship of equation 9.

From equations 8 and 9, the angle ψ is given by equation 10.

On the other hand, _{f 0} the distance between the point F and the point _{F 1,} and the radius of the truncated cone prism 6 shown in FIG. 5 (a) is defined as _{r 0, f 0} is given by the number 11.

Light 10H and 10H ₀ is focused at a point F, the light 10h and 10h ₀ is focused at point _{F 1.} According to the aberration theory, the aberration that shifts the focal position of the focused light from F to F ₁ , that is, the longitudinal focal movement aberration is given by n ₀ f ₀ (1-cosφ).

FIG. 6A is a diagram schematically showing an example of a pattern of the transparent electrode layer 7f for realizing aberration correction. The electrode 9B is located at a position facing the grating 8b and is formed in a radius r ₁ to a radius r ₂ . The electrode 9B in the example of FIG. 6A forms a plurality of conductive divided regions arranged along the circumferential direction of a virtual circle centered on the point where the light 10f is emitted (that is, the intersection of the X-axis and the Y-axis). Including. Each divided region extends in a zigzag along the radial direction of the circle. The control circuit 32 can independently and sequentially apply a voltage to a region in which the waveguide light 10 g propagates among the plurality of divided regions in the electrode 9B. As a result, aberration correction can be realized, and the propagation of 10 g of waveguide light can be aligned in the radial direction.

In the example shown in FIG. 6A, the electrode 9B is equally divided in 6-degree increments in the circumferential direction, and is divided into 60 zigzag fan-shaped division regions 9B1 to 9B60. These divided regions 9B1 to 9B60 are electrically isolated from each other, and voltages can be applied independently. When different voltages are applied to the plurality of divided regions 9B1 to 9B60, the refractive index of the liquid crystal layer 7e changes depending on the declination position. As a result, the effective refractive index of 10 g of waveguide light also changes depending on the declination position.

FIG. 6B is a diagram showing an example of changes in the voltage applied to the electrode 9B and the effective refractive index with respect to the declination. In FIG. 6B, the waveform 18 shows a curve in which points corresponding to the positions of the 60 divided regions 9B1 to 9B60 are plotted on the horizontal axis and the amplitude of the AC voltage applied to each divided region is plotted. In this example, the voltage applied to the electrode 9B changes in a parabolic shape within a range of 1/5 (= 72 degrees) of the circumference with respect to the declination centered on the axis L, and becomes a constant value in other ranges. It forms a waveform 18. The voltage applied to each divided region is controlled so that the waveform 18 moves in the direction of the arrow shown in FIG. 6B (hereinafter, may be referred to as “rotational direction”). The region between the two split regions represented by the thin zigzag lines in FIG. 6A represents the split region to which a parabolic voltage is applied at a given moment. Synchronized with this applied voltage, the effective refractive index N of the waveguide layer 7d with respect to 10 g of the waveguide light also changes in a parabolic shape within a range of 1/5 of the circumference with respect to the declination, and becomes a constant value in other ranges. It forms a waveform 19. This waveform 19 also moves in the direction of the arrow shown in FIG. 6B, that is, in the direction of rotation.

In this way, the phase of the waveguide light can be changed for each declination within the range of the parabolic waveform. When the variation width of the effective refractive index and .DELTA.N, range of the phase difference that occurs between the propagation distance _(r 2 -r _{1) is} given by _(r 2 -r ₁₎ ΔN. Therefore, the condition for aligning the propagation direction of the waveguide light 10 g in the radial direction is described by Equation 12.

From Equation 12, the change width ΔN of the effective refractive index for aberration correction is given by Equation 13.

FIG. 7A is a diagram showing an example of the relationship between the angle φ and the amount of change ΔN in the effective refractive index of the waveguide light for realizing aberration correction. In FIG. 7A, the change width ΔN is plotted as a function of the angle φ based on the equation 13. In this example, the refractive index of the truncated cone prism 6 was set to n ₀ = 1.58, the radius was set to r ₀ = 1.25 mm, and the width of the electrode 9B was set to (r _2- r ₁ ) = 8 mm. It can be seen that ΔN = 0.041 should be set in order to secure the required phase difference in the range of, for example, −36 degrees to 36 degrees for the angle φ.

7B is a refractive index n ₁ of the liquid crystal layer 7e as a parameter is a diagram showing an example of a relationship between the thickness and the effective refractive index N of the waveguide layer 7d. FIG. 7C is a diagram schematically showing the arrangement of the buffer layer 7c, the waveguide layer 7d, and the liquid crystal layer 7e. In this example, the buffer layer 7c is made of SiO ₂ , and the waveguide layer 7d is made of Ta ₂ O ₅ .

The difference in refractive index of the nematic liquid crystal molecules is about 0.20 at most. Considering that 80% of them act as a difference in refractive index, the effective difference in refractive index is about 0.15. In the example shown in FIG. 7B, the wavelength of light was 0.94 μm, and the refractive index of the buffer layer 7c was 1.45. In FIG. 7B, the relationship between the thickness of the waveguide layer 7d and the effective refractive index N, which is calculated as n ₁ = 1.50 and n ₁ = 1.65, is represented by curves 23a and 23b, respectively. ing.

Assuming that the refractive index difference of the liquid crystal is 0.15 in the model of FIG. 7C, if the thickness of the waveguide layer 7d formed from Ta ₂ O _{5 is changed} from 0.10 μm to 0.15 μm from FIG. 7B, ΔN A change from = 0.04 to ΔN = 0.06 can be expected, and it can be seen that a sufficient phase difference can be secured.

Next, the principle of controlling the propagation direction of the waveguide light by applying a voltage to the liquid crystal layer 7e will be described. In the following, an example will be described in which both the transparent electrode layer 7f and the reflective electrode layer 7b have a plurality of divided zigzag electrode patterns.

FIG. 8A is a diagram schematically showing the relationship between the electrode pattern in the transparent electrode layer 7f and the applied voltage. FIG. 8B is a diagram schematically showing the relationship between the electrode pattern in the reflective electrode layer 7b and the applied voltage. FIG. 8A illustrates three zigzag electrode patterns 40a, 40b and 40c in the transparent electrode layer 7f. Similarly, FIG. 8B illustrates the three zigzag electrode patterns 40A, 40B and 40C in the reflective electrode layer 7b. These electrode patterns are isolated from each other. Voltage signals are independently applied to the electrode patterns 40a, 40b and 40c shown in FIG. 8A from the control circuits 32a, 32b and 32c, respectively. Similarly, voltage signals are independently applied to the electrode patterns 40A, 40B and 40C shown in FIG. 8B from the control circuits 32A, 32B and 32C, respectively.

FIG. 8C is a diagram schematically showing the relationship between the electrode pattern in the transparent electrode layer 7f, the configuration in which the electrode patterns in the reflective electrode layer 7b are aligned and overlapped, and the applied voltage. When the side of the transparent electrode layer 7f is on the top and the side of the reflective electrode layer 7b is on the bottom, the zigzag patterns located above and below have a relationship in which the lines formed by connecting the vertices on one side of the zigzag overlap each other on the top and bottom. It is in. The shape of the zigzag pattern on the reflective electrode layer 7b side is a shape in which the zigzag pattern on the transparent electrode layer 7f side is inverted up and down. Therefore, as shown in FIG. 8C, the pattern in which the electrode pattern on the transparent electrode layer 7f side and the electrode pattern on the reflective electrode layer 7b side are aligned and overlapped has a shape in which rhombuses are continuous.

The electrode pattern shown in FIG. 8C may be produced on only one side. However, since each rhombus is isolated, it may not be easy to route the wiring. By superimposing the electrode pattern shown in FIG. 8A and the electrode pattern shown in FIG. 8B, the pattern itself functions as wiring, so that the production can be facilitated.

AC voltage signals 41a, 41b and 41c are applied to the zigzag electrode patterns 40a, 40b and 40c in the transparent electrode layer 7f, respectively. The amplitude increases in the order of signals 41a, 41b and 41c. Assuming that the facing electrodes are grounded, this amplitude gradient causes a difference in refractive index at the positions of the liquid crystal layers corresponding to the zigzag electrode patterns 40a, 40b and 40c. The waveguide light 10 g propagating from the left to the right in the waveguide layer 7d sandwiched between the electrodes is refracted to the lower side of the figure each time it passes through the boundary between the patterns inclined with respect to the optical path. AC voltage signals 41A, 41B and 41C are applied to the zigzag electrode patterns 40A, 40B and 40C in the reflective electrode layer 7b, respectively. The amplitude increases in the order of signals 41A, 41B and 41C. Assuming that the facing electrodes are grounded, this amplitude gradient causes 10 g of the waveguide light propagating from left to right in the figure to be refracted downward in the waveguide layer 7d sandwiched between the electrodes.

The AC voltage signals 41A, 41B and 41C have the opposite polarities of the AC voltage signals 41a, 41b and 41c, respectively. Therefore, as shown in FIG. 8C, the voltage shown in FIG. 8C is applied to the electrode pattern in which the transparent electrode layer 7f and the reflective electrode layer 7b are aligned and overlapped. In the example of FIG. 8C, the AC voltage signal 41a1 and the AC voltage signal 41A1 form a pair, the AC voltage signal 41b1 and the AC voltage signal 41B1 form a pair, and the AC voltage signal 41c1 and the AC voltage signal 41C1 form a pair. To form. Since the phases of the two AC voltage signals forming each pair are inverted, the AC voltage amplitude is doubled. As a result, 10 g of waveguide light is largely refracted downward. Further, as compared with the electrode patterns shown in FIGS. 8A and 8B, the frequency with which the waveguide light 10 g straddles the boundary between the patterns increases. As a result, the bending of the waveguide light of 10 g is doubled, and the variation in the bending angle due to the difference in the optical path is also improved.

Next, an example of a method of controlling the propagation direction of the waveguide light will be described based on the principle described with reference to FIGS. 8A to 8C.

9A and 9B are diagrams schematically showing an example of the pattern of the electrode 9B in the transparent electrode layer 7f and the reflective electrode layer 7b, respectively. Both the electrode pattern shown in FIG. 9A and the electrode pattern shown in FIG. 9B are composed of 60 zigzag patterns each extending from the inner peripheral side to the outer peripheral side. Such a zigzag pattern electrode may be provided only on one of the transparent electrode layer 7f and the reflective electrode layer 7b. Of the plurality of divided regions in the electrode 9B, the boundary between two adjacent divided regions has a zigzag shape along the radial direction of the circle. Each zigzag pattern is isolated from each other, and a voltage signal is applied to each independently. In the example shown in FIGS. 9A and 9B, in the adjacent zigzag pattern, the lines formed by connecting the vertices on one side of the zigzag coincide with each other in the radial direction, and these are in a relationship of overlapping each other next to each other. In this example, the shape of the zigzag pattern on the reflective electrode layer 7b side is a shape obtained by reversing the zigzag pattern on the transparent electrode layer 7f side in the rotational direction. FIG. 9C is a diagram schematically showing a configuration in which the electrode pattern on the transparent electrode layer 7f and the electrode pattern on the reflective electrode layer 7b are aligned and overlapped.

FIG. 10 is a diagram schematically showing the relationship between a part of the electrode pattern shown in FIG. 9C and the propagation path of the waveguide light 10 g. As shown in FIG. 9C, the pattern of the electrodes 9B in which the transparent electrode layer 7f and the reflective electrode layer 7b are aligned and overlapped has a shape in which rhombuses are continuous in the radial direction. In each of the reflective electrode layer 7b and the transparent electrode layer 7f, the boundary between two adjacent divided regions in the plurality of divided regions in the region 9B has a zigzag shape along the radial direction of the circle. When viewed from a direction perpendicular to any of the buffer layer 7c, the waveguide layer 7d, and the liquid crystal layer 7e, the boundary between one of the pair of electrode layers and the boundary at the other have a shape in which rhombuses are continuous in the radial direction. Form. The magnitude of the amplitude of the AC voltage applied to the zigzag pattern is controlled to have a gradient along the circumferential direction. For example, when a voltage gradient such as the parabolic waveform 18 shown in FIG. 6B is given around the Y axis, the liquid crystal is formed in the direction of arrow 42, that is, in the direction approaching the Y axis, as shown in FIG. The refractive index increases. As a result, the propagation path of the waveguide light 10g propagating in the waveguide layer 7d from the outer peripheral side to the inner peripheral side can be bent in the direction of the arrow 42, that is, in the direction approaching the Y axis. By controlling the voltage applied to the electrode having the structure shown in FIG. 10 in this way, the parallel light incident on the side surface of the truncated cone prism 6 is taken in by the grating coupler 8c and adjusted so as to become a waveguide light toward the center. can do. As a result, it can be extracted as synchrotron radiation from the central grating coupler 8a and detected.

Next, a configuration example of the photodetector 12 in this embodiment will be described.

FIG. 11 is a diagram showing a configuration example of the photodetector 12. In this example, the photodetector 12 includes a plurality of light receiving elements arranged in a row. Each light receiving element has a strip-shaped shape. The photodetector 12 is divided into n light receiving regions 12a1, 12a2, ..., 12an having a width of d ₁ , and n pieces of light 17 dispersed according to the wavelength by the wavelength spectroscope 5 are transmitted. It can be detected separately by wavelength range or color. In the illustrated example, each light receiving region includes five strip-shaped light receiving element width d _2. That is, five light receiving elements are assigned to one wavelength region or color. Each light receiving region can be slid together by the width of the strip-shaped light receiving element or an integral multiple thereof, if necessary. The configuration of the photodetector 12 is only an example. The number of light receiving regions and the number of light receiving elements included in each light receiving region may be arbitrarily determined. Further, the photodetector 12 does not have to be divided into a plurality of light receiving regions. For example, a general one-dimensional or two-dimensional image sensor may be used as the photodetector 12.

FIG. 12A is a diagram schematically showing a state of scanning monochromatic light in the horizontal direction and the vertical direction. In the present specification, scanning or light ray scanning means, when considering a virtual optical path that reverses with respect to an optical path incident on the truncated cone prism 6 from an external reflector, the virtual optical path is transferred to an electrode. It means that it is operated by controlling the applied voltage of. Further, the movement of the virtual optical path means that the direction of the external object that can be detected by the present device is moved and controlled.

FIG. 12A shows an example of ray scanning of monochromatic light detected by a single light receiving region (for example, 12a1 only) shown in FIG. As described above, a voltage having a distribution for aberration correction as represented by the waveform 18 shown in FIG. 6B is applied to the electrode 9B, for example. This makes it possible to capture parallel light in an angle range of, for example, 2π / 5 (= 72 degrees). By moving the waveform 18 in the rotation direction, the capture direction can be scanned horizontally in the range of 360 degrees. At this time, a voltage that changes linearly is applied to the electrode 9C so that the intake direction changes in the vertical direction. There are two types of parabolic waveform 18 shapes, and by changing the coefficient value or exponential value of the function that expresses the parabolic shape, the position of the focusing point F1 is moved to a different position, and the capture angle α1 and Two types of light of α2 can be taken in. Here, the "capture angle" represents the degree of spread on the horizontal plane of the light incident on the truncated cone prism 6 from various directions and reaching the photodetector 12 at the position incident on the truncated cone prism 6. In the following description, the capture angle may be referred to as "spread angle". The capture angle depends on the voltage waveform 18 shown in FIG. 6B. The capture angle is changed by changing the coefficient value or exponential value of the function expressing the shape of the waveform 18.

In the example of FIG. 12A, the first scan is performed at the capture angle α1. The state at this time is represented by the arrow line b1 in FIG. 12A. In the second scan, the capture angle is adjusted to α2, the voltage of the electrode 9C is restored, and the same scan as the arrow line b1 is performed in the range of 360 degrees. That is, the optical device repeats scanning with different capture angles twice. In the third scan, the arrow line b2 is scanned while continuously increasing the vertical angle in the state of the capture angle α2. In the fourth scan, the intake angle is returned to α1, the voltage of the electrode 9C is returned to the initial state of the third time, and the same scan as the arrow line b2 is performed in the range of 360 degrees. The above operation is repeated while gradually changing the voltage of the electrode 9C, the angle in the vertical direction is gradually increased, and the scanning of the arrow line b15 is continued.

The period of the voltage distribution of the electrode 9B, that is, the period in which the waveform 18 goes around the range of 360 degrees depends on the responsiveness of the liquid crystal. When the period is set to 2 ms including the response time of the shape change of the waveform 18, and scanning is performed at a moving speed of 33 frames per second, that is, a period of 30 ms, the number of scanning lines in the vertical direction is 30/2 = 15. Therefore, in the example of FIG. 12A, the rotation angle in the vertical direction is divided into 15, and two horizontal scans with different capture angles are performed for each division angle range. Assuming that the change in the refractive index of the liquid crystal is 0.15, the number of scanning lines can be realized by changing the effective refractive index by about ΔN = 0.04 from FIG. 7B. From Equation 5, the width of this change in the effective refractive index corresponds to about 10 degrees as the angle difference of the incident light on the grating coupler 8c. Therefore, vertical scanning can be performed at intervals of 15 equal parts of the vertical angle range of 10 degrees. In this case, the angle at which each scanning line is separated is about 10/15 = 0.67 degrees.

FIG. 12B is a diagram schematically showing an example of horizontal and vertical scanning of light of a plurality of colors in a narrow band (hereinafter, referred to as “narrow multicolor light”). FIG. 12B shows an example of light ray scanning of narrow multicolor light detected by n light receiving regions 12a1, 12a2, ..., 12an of the photodetector 12 shown in FIG. Narrow multicolored light means the overlap of a plurality of single-mode lights forming a minute interval in the vicinity of a specific wavelength λ. The narrow multicolored light can be, for example, an overlap of single-mode light having wavelengths λ ₁ , λ ₂ , ... λ _n , which are spaced by about 0.2 nm in the vicinity of the wavelength λ. If the wavelength of these lights is within the wavelength range of several nm, the incident angle changes according to the change in wavelength, but any light can be coupled to the waveguide layer 7d via the grating coupler 8c in an optimum state. From Equation 7, the wavelength difference of 0.2 nm corresponds to about 0.1 degree as the angle difference of the incident light on the grating 8c. Therefore, if the narrow multicolored light is a set of seven monochromatic lights, the gaps between the scanning lines in FIG. 12A can be filled without gaps as shown in FIG. 12B. The detection light corresponding to each scanning line in FIG. 12B is independently detected by the light receiving region 12ak (k = 1, ..., N) of the photodetector 12. In this case, the spatial resolution in signal detection is 7 times that in the case of FIG. 12A. In other words, 15 × 7 = 105 or more vertical scanning lines can be realized.

Actually, narrow multicolored light is not a set of discontinuous monochromatic light but a set of light of continuous wavelength. However, when the photodetector 12 is composed of discrete and finite number of light receiving regions as in the present embodiment, the detection of the light is equivalent to detecting the discrete light of a plurality of wavelengths as a result. is there.

As described above, according to the configuration of the present embodiment, it is possible to detect almost parallel light with a small spread angle reflected by an external object. For example, within a field of view of 360 degrees in the horizontal direction and 10 degrees in the vertical direction, reflected light can be scanned and detected at a frame rate of 100 or more vertical scanning lines and 30 frames or more per second.

Next, the principle of distance measurement in this embodiment will be described.

FIG. 13A is a diagram showing a configuration example of an optical system equivalent to the optical device in the present embodiment. The optical system shown in FIG. 13A includes a truncated cone prism 6, a condenser lens 14a, and a slit plate 14b. The condenser lens 14a and the slit plate 14b perform an action equivalent to that of the optical waveguide element 7 in the present embodiment. As described with reference to FIG. 10, after being focused onto the axis L ₁ incident on the side surface of the truncated cone prism 6, the light entering the grating coupler 8c is controlled by the voltage applied to the electrodes, the optical waveguide The light is adjusted so as to be waveguide light toward the center of the element 7. In the present embodiment, it can be finely adjust the position of the axis L ₁ by controlling the applied voltage. This action is equivalent to the action of the condenser lens 14a that can move on the X-axis shown in FIG. 13A. Further, of the waveguide light toward the center, only the light focused on the center of the grating coupler 8a is taken out as the emitted light 10f and detected. This action is equivalent to the action of the slit plate 14b that selectively passes only the light focused at the focusing point F0 of the focusing lens 14a shown in FIG. 13A. Therefore, it can be interpreted that the optical waveguide element 7 in the present embodiment includes a lens capable of changing the focal length and a slit plate that limits the light passing through the lens.

FIG. 13A exemplifies the light 15 incident at the capture angle α (capture full-width 2α) and the light 16 incident at the capture angle α'(capture full-width 2α'). The light 15 incident at the captured full-width 2α is refracted by the side surface of the truncated cone prism 6 and focused at the point F1, and then focused at the point F0 by the condenser lens 14a. The point F0 is located at the opening of the slit 14b. Light is focused to a point F0 is detected by the photodetector 12 is transmitted through the slit opening width 2r _1, which corresponds to the diameter of the grating coupler 8c. On the other hand, the light 16 reflected from the reflector S separated from the truncated cone prism 6 by a distance d in the X-axis direction is incident on the side surface of the truncated cone prism 6 at a captured full angle of 2α'and is refracted. The refracted light is focused at a point F1'distant from the point F1 by Δs, and then focused on the slit by the condenser lens 14a with a spot diameter of 2r'. Since the spot diameter 2r'is larger than the aperture width 2r _1, only a part of the focused light can pass through the slit. Therefore, the detected light amount of the light 16 is smaller than the detected light amount of the light 15.

FIG. 13B is a diagram for explaining the path of light rays passing through the truncated cone prism 6 in the optical system shown in FIG. 13A. In the example shown in FIG. 13B, the light 15 and light 16 is incident on a point to _{Q 1} side of the truncated cone prism 6. Normal of the point Q ₁ is angled in β with respect to the X axis. With the center of the truncated cone prism 6 as the point F, the points F, F1, and F1'are all on the X-axis. If the angle formed by FQ ₁ F1 is ψ, the angle FQ ₁ F1'is ψ', the angle FF1Q ₁ is φ, and the angle FF1'Q ₁ is φ', FF1 = s, FF1'= s', the numbers 14 to 20 are It holds.

If s'-s = Δs, | Δs | tanφ'= F1F2 corresponds to the beam radius at the slit position. Using this value, the relationship between the ratio of the beam diameter and the slit diameter is transformed, and the normalized detection light amount η is defined by the following equation.

According to this definition, when the focusing point F1'matches F1 (Δs = 0), the detected light amount η becomes the maximum value 1, but when they do not match, the detected light amount η becomes smaller than 1.

The position of the light intake angle α and its focusing point F1 can be controlled by, for example, adjusting the shape of the parabolic waveform 19 shown in FIG. 6B. Further, by moving the waveform 19 in the declination direction, the light uptake direction can be rotated around the central axis L of the truncated cone prism 6. Therefore, the reflected light from the external reflector S in a single direction can be detected at high speed with two or more capture angles. Further, in the present embodiment, by adjusting the voltage of the electrode 9C, the direction of the detectable light can be changed to the vertical direction for scanning.

FIG. 13C is a diagram showing an example of the relationship between the amount of detected light and the distance to the measurement target with the capture angle (also referred to as “spread angle”) α as a parameter. FIG. 13D is a diagram showing the relationship between the ratio of the two detected light amounts and the distance to the measurement target in the example of FIG. 13C. FIG. 13E is a diagram showing another example of the relationship between the amount of detected light and the distance to the measurement target, with the capture angle α as a parameter. FIG. 13F is a diagram showing the relationship between the ratio of the two detected light amounts and the distance to the measurement target in the example of FIG. 13E.

13C and 13E show an example of the relationship between the detected light amount η and the distance d for a plurality of capture angles α. In these examples, the refractive index _n 0 = 1.58 frustoconical prism 6, the radius _r 0 = 1.5 mm, and the normal and the X-axis of the slit width _2r 1 = 0.02 mm, the point _{Q 1} The angle between the two was set to β = 30 degrees. As shown in FIG. 13C, when the intake angle α is 0 or more, all the curves monotonically increase with respect to the distance d.

Figure 13D shows the relationship between the detected light quantity eta _{alpha =} divided by _0.00 and the distance d in the quantity of detected light eta alpha = 0.00 ° in FIG. 13C, it is shown by the acceptance angle alpha to the parameters. The detected light amount ratio η / η _{α = 0.00} decreases monotonically with respect to the distance d to the reflector S at any capture angle α. In particular, since the range of change is large in the range of d <2 m, the distance to the reflector S can be accurately measured if the detected light amount ratio η / η _{α = 0.00} can be detected. The detected light amount η is standardized in the formula shown in Equation 21, but the actual light amount varies depending on the reflectance of the reflector and the sensitivity of the photodetector 12. However, since η / η _{α = 0.00} is a light intensity ratio, it is not affected by such variations and does not require calibration processing. In addition, the influence of noise and error included in the detected light amount is also removed.

In the example of FIG. 13E, the intake angle α includes a negative value (α = −0.05 degrees). The fact that α is negative means that, as in the case of light 16 shown in FIG. 13A, when a light beam is virtually reversed, the light beam is focused toward the reflector S. Represent. In the example of FIG. 13E, α = −0.05 degrees corresponds to the case where the reflector S exists at the position of d = 0.9 m, and the corresponding curve becomes the maximum at d = 0.9 m. In the other curves, the intake angle α is 0 or more, and all of them increase monotonically with respect to the distance d.

FIG. 13F, the relationship between the value obtained by dividing the distance d by in detected light intensity eta _{alpha = -0.05} to detect light intensity eta an alpha = -0.05 ° in FIG. 13E, is shown in an uptake angle alpha to the parameter .. The detected light amount ratio η / η _{α = -0.05} decreases monotonically with respect to the distance d <0.9 m and increases monotonically with respect to d> 0.9 m at any capture angle α. Compared with the example of FIG. 13D, the rate of change is particularly large in the range of d> 0.9 m. Therefore, the distance to the reflector S can be accurately measured in the range of 0.9 m <d <10 m. Similar to the example of FIG. 13D, since η / η _{α = -0.05} is a light amount ratio, there is no need for calibration processing, and the influence of noise and error included in the detected light amount is also eliminated.

In the present embodiment, data showing the relationship between one or both of FIGS. 13D and 13F is recorded in advance on the recording medium. The recording medium may be provided with a control circuit such as the detection circuit 33 shown in FIG. By referring to the data, the control circuit can obtain the distance from the ratio of two light amounts detected at different focal lengths in the same direction. When the data showing the relationship of both FIGS. 13D and 13F are used at the same time, the distance can be obtained more accurately. For example, the curve data shown in FIG. 13D may be used for a short distance (for example, d <2m), and the curve data shown in FIG. 13F may be used for a long distance (for example, d> 2m).

According to this embodiment, the distance to an external reflector can be measured without emitting light. Further, since the measurement only compares the detected light amounts of the light of at least two capture angles arriving from the same direction, the calculation load is extremely small. Further, since the direction of the captured light can be scanned at high speed in the rotation direction or the direction orthogonal to the rotation direction, the distance information in all directions can be acquired at high speed.

In the description of this embodiment, it is described that the position of the focusing point by the truncated cone prism 6 is one point, but strictly speaking, the positions of the focusing points are dispersed. The parabolic waveform 19 in FIG. 6B may be corrected or controlled in response to the dispersed focus points.

(Second Embodiment)
FIG. 14 is a plan view schematically showing the configuration of the optical device and the path of light rays in the second embodiment.

This optical device includes a rotating body 50, an optical table 51 on the rotating body 50, a condenser lens 52 on the optical table 51, a slit plate 53, a photodetector 54, and a control circuit 55. The condenser lens 52, the slit plate 53, and the photodetector 54 are arranged along the axis L0 passing through the center O of the rotating body 50. The rotating body 50 is driven to rotate around the center O by a motor (not shown). The condenser lens 52 is configured to be able to move at high speed along the axis L0 by an actuator (not shown). The condenser lens 52 can also move in a direction orthogonal to the surface of the rotating body 50 (hereinafter, referred to as a “vertical direction”). The slit of the slit plate 53 has an opening having an elongated shape in the vertical direction. The control circuit 55 synchronously controls the rotational movement of the rotating body 50 and the translational movement of the lens 52.

The rotating body 50 is controlled to rotate at a constant velocity, for example. The movement of the condenser lens 52 in the direction along the axis L0 can be, for example, a simple vibration having a period of an integral multiple or a fraction of an integral multiple of the rotation cycle of the rotating body 50. The movement of the condenser lens 52 in the vertical direction may be, for example, a simple vibration having a period of several times to several hundred times the rotation period of the rotating body 50. In the example of FIG. 14, the light 15 incident at the captured full-width 2α is focused at the point F0 by the condenser lens 52. Point F0 is located in the opening of the slit plate 53, the light is focused to a point F0 is detected through the slit opening width 2r ₁ by the light detector 54. On the other hand, the light 16 reflected by the reflector S on the axis L0, which is at a distance d from the condenser lens 52, enters the condenser lens 52 at a captured full angle of 2α'and is focused on the slit with a spot diameter of 2r'. Will be done. Since the spot diameter 2r'is larger than the aperture width 2r _1, only a part of the focused light can pass through the slit. Therefore, the detected light amount of the light 16 is smaller than the detected light amount of the light 15. When the condenser lens 52 moves in the vertical direction, the spot on the slit also moves in the vertical direction while maintaining the spot diameter. However, since the opening of the slit has a shape extending in the vertical direction, the amount of light detected through the slit does not change.

The optical device in the second embodiment has different components from the optical device in the first embodiment, but its functions and effects are the same. That is, also in the present embodiment, as in the first embodiment, the reflected light is detected through the slit plate 53 arranged at the condensing position of the reflected light from the external reflector S in a single direction. it can. Similar to the first embodiment, the detection direction can be changed at high speed in the horizontal direction and the vertical direction, and the capture angle can be changed to two or more at high speed. Therefore, the principle of distance measurement exactly the same as that of the first embodiment is established, and the same effect as that of the first embodiment can be obtained.

What is common to the first embodiment and the second embodiment is a photodetector including a condensing means, which changes the direction of detectable light, for example, periodically, and is linked to the change in the direction. The purpose is to change the focal length of the condensing means, for example, periodically. Distances can be measured based on the amount of light coming from a single direction detected using at least two different focal length optics. In particular, distance information can be obtained more accurately than before, based on the light amount ratio of the two detection lights and the data that defines the relationship between the light amount ratio and the distance recorded in advance.

As described above, according to the above-described embodiment, the distance to the external reflector can be measured more accurately. Since the measurement only compares the detected light amounts of the lights of the two capture angles facing in the same direction, the calculation load is extremely small. Further, according to the configuration in which the direction of the captured light is scanned at high speed in the rotation direction or the direction orthogonal to the rotation direction, the distance information in all directions can be acquired at high speed.

The technique of the present disclosure can be used, for example, for acquiring three-dimensional position information of an object in a target scene.

5 Wavelength spectroscope 6 Conical prism 7 Optical waveguide 7a Flat substrate 7b Reflective electrode layer 7c Buffer layer 7d waveguide layer 7e Liquid crystal layer 7f Transparent electrode layer 7g Flat substrate 7h Hollow substrate 8a, 8c Glazing coupler 8b Orientation grating 9A 9B, 9C Electrode region 12 Optical detector 13 Condensing lens 32, 34 Control circuit 33 Detection circuit 50 Rotating body 51 Optical stand 52 Condensing lens 53 Slit plate 54 Light detector 55 Control circuit

Claims (13)

1. With a photodetector
   An optical system that causes light coming from a part of the light coming from the outside to enter the photodetector, and
   A control circuit that controls the photodetector and the optical system,
   With
   The control circuit
   By controlling the optical system, the detection direction, which is the direction in which the light detected by the photodetector arrives, is changed, and the focal length of the optical system is changed in conjunction with the change in the detection direction. Let me
   Light coming from an object located in a single detection direction is detected by the photodetector in two or more states where the focal lengths of the optical systems are different.
   Distance information to the object is generated based on the amount of two or more detected lights detected by the photodetector in each of the two or more states.
   Optical device.
2. The optical device according to claim 1, wherein the control circuit periodically changes the detection direction and periodically changes the focal length of the optical system.
3. The two or more detected light amounts include a first detected light amount and a second detected light amount.
   The control circuit generates the distance information based on the ratio of the first detected light amount to the second detected light amount.
   The optical device according to claim 1 or 2.
4. A recording medium for storing data that defines the correspondence between the ratio of the first detected light amount and the second detected light amount and the distance is further provided.
   The control circuit generates the distance information based on the data and the ratio of the first detected light amount to the second detected light amount.
   The optical device according to claim 3.
5. The optical system is
   A rotating body that rotates around the central axis,
   A lens supported by the rotating body and configured to be movable along the optical axis,
   A slit plate that is supported by the rotating body and is located between the lens and the photodetector, and includes a slit that allows at least a part of the light focused by the lens to enter the photodetector. When,
   With
   The control circuit changes the detection direction by rotating the rotating body, and changes the focal length by moving the lens along the optical axis.
   The optical device according to any one of claims 1 to 4.
6. The optical device according to claim 5, wherein the control circuit rotates the rotating body at a constant speed.
7. 5. The control circuit causes the photodetector to detect the light in two or more states where the rotation angle of the rotating body is the same and the positions of the lenses in the direction along the optical axis are different. Or the optical device according to 6.
8. The optical system is
   An optical waveguide element that propagates light along a direction orthogonal to the axis,
   A transparent member having a bottom surface facing the surface of the optical waveguide element, a side surface symmetrical about the axis as a central axis, and an upper surface opposite to the bottom surface.
   With
   The optical waveguide element is
   A first grating that extends along the radial direction of a virtual circle centered on the axis, and
   A second grating that spreads along the radial direction outside the first grating and has a lattice constant different from that of the first grating.
   With a waveguide layer containing on the surface,
   A part of the light coming from the object enters the second grating through the transparent member, propagates in the waveguide layer and exits from the first grating, and the bottom surface of the transparent member and the said. Passing through the upper surface and incident on the photodetector,
   The control circuit changes the detection direction and the focal length by adjusting the effective refractive index of the waveguide layer.
   The optical device according to any one of claims 1 to 4.
9. The optical waveguide element is
   Transparent electrode layer and
   A liquid crystal layer having a refractive index lower than that of the waveguide layer,
   With the waveguide layer
   A dielectric layer having a refractive index lower than that of the waveguide layer,
   Reflective electrode layer and
   In this order,
   The optical device according to claim 8, wherein the control circuit adjusts the effective refractive index by adjusting a voltage applied between the transparent electrode layer and the reflective electrode layer.
10. The waveguide includes a third grating on the surface between the first grating and the second grating for controlling the orientation of liquid crystal molecules in the liquid crystal layer.
    At least one of the transparent electrode layer and the reflective electrode layer includes a first electrode, a second electrode, and a third electrode facing the first grating, the second grating, and the third grating, respectively.
    The optical device according to claim 9.
11. The optical device according to claim 10, wherein the third electrode includes a plurality of divided regions arranged along the circumferential direction of the virtual circle, and the plurality of divided regions are insulated from each other.
12. The optical device according to claim 11, wherein the control circuit individually controls a voltage applied between the transparent electrode layer and the reflective electrode layer for each of the divided regions of the third electrode.
13. The control circuit applies the voltage to each of the divided regions in such a manner that the distribution of the amplitude of the voltage applied to the plurality of divided regions of the third electrode rotates around the axis with the passage of time. By changing the distribution each time the rotation of the voltage amplitude distribution goes around, light coming from an object located in a single detection direction can be emitted from two or more states with different focal distances of the optical system. The optical device according to claim 12, which is detected by the photodetector.

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