阅读说明：本技术 光设备及光检测系统 (Optical device and optical detection system ) 是由 桥谷享 稻田安寿 江良正范 于 2020-04-14 设计创作，主要内容包括：光设备具备：第1反射镜,具有第1反射面,沿着第1方向延伸；第2反射镜,具有与所述第1反射面对置的第2反射面,沿着所述第1方向延伸；以及光波导层,位于所述第1反射镜与所述第2反射镜之间,使光沿着所述第1方向传播；所述第1反射镜的透射率比所述第2反射镜的透射率高,所述第1反射镜及所述第2反射镜中的至少一方的与从反射面的法线方向入射的光对应的反射谱为：在反射率为90％以上的波段中包含极大点、以及比所述极大点靠长波长侧的第1拐点及第2拐点。(The optical device includes: a 1 st mirror having a 1 st reflecting surface and extending in a 1 st direction; a 2 nd mirror having a 2 nd reflecting surface opposed to the 1 st reflecting surface and extending in the 1 st direction; and a light guide layer located between the 1 st mirror and the 2 nd mirror to make light propagate along the 1 st direction; the transmittance of the 1 st mirror is higher than the transmittance of the 2 nd mirror, and a reflection spectrum of at least one of the 1 st mirror and the 2 nd mirror corresponding to light incident from a normal direction of a reflection surface is: the wavelength band having a reflectance of 90% or more includes a maximum point, and a 1 st inflection point and a 2 nd inflection point which are located on a longer wavelength side than the maximum point.)

1. An optical device is provided with:

a 1 st mirror having a 1 st reflecting surface and extending in a 1 st direction;

a 2 nd mirror having a 2 nd reflecting surface opposed to the 1 st reflecting surface and extending in the 1 st direction; and

an optical waveguide layer located between the 1 st mirror and the 2 nd mirror to propagate light along the 1 st direction;

the transmittance of the 1 st mirror is higher than that of the 2 nd mirror,

a reflection spectrum of at least one of the 1 st mirror and the 2 nd mirror corresponding to light incident from a normal direction of a reflection surface is: the wavelength band having a reflectance of 90% or more includes a maximum point, and a 1 st inflection point and a 2 nd inflection point which are located on a longer wavelength side than the maximum point.

2. The optical device of claim 1, wherein the optical device,

the wavelength of the 1 st inflection point is shorter than the wavelength of the 2 nd inflection point,

the wavelength λ of the light propagating in the optical waveguide layer is a wavelength that is equal to or longer than the maximum point and equal to or shorter than the 1 st inflection point.

3. The optical device of claim 1 or 2,

the wavelength band is contained in a range of 0.8 μm or more and 1.2 μm or less.

4. The light device of any one of claims 1 to 3,

at least one of the 1 st mirror and the 2 nd mirror includes a distributed bragg reflector having a stacked structure.

5. The optical device of claim 4, wherein the optical device,

the distributed bragg reflector is a chirped DBR, i.e., a chirped distributed bragg reflector.

6. The optical device of claim 1, wherein the optical device,

the 1 st mirror has the reflection spectrum.

7. An optical scanning device is provided with:

a 1 st mirror having a 1 st reflecting surface and extending in a 1 st direction;

a 2 nd mirror having a 2 nd reflecting surface opposed to the 1 st reflecting surface and extending in the 1 st direction; and

an optical waveguide layer located between the 1 st mirror and the 2 nd mirror to propagate light along the 1 st direction;

the transmittance of the 1 st mirror is higher than that of the 2 nd mirror,

a reflection spectrum of at least one of the 1 st mirror and the 2 nd mirror corresponding to light incident from a normal direction of a reflection surface is: a maximum point P is included in a wavelength band having a reflectance of 90% or more_LMAnd a 1 st inflection point P located on a longer wavelength side than the maximum point₁And 2 nd inflection point P₂，

The light emitted via the 1 st mirror is deflected so as to scan a space.

8. The optical scanning device as claimed in claim 7,

the wavelength λ used in the scan satisfies:

(P_LM+P₁)/2＜λ＜P₁。

Technical Field

The present disclosure relates to an optical apparatus and an optical detection system.

Background

Various apparatuses capable of scanning (scan) a space with light have been proposed.

Patent document 1 discloses a configuration in which scanning can be performed by light using a driving device that rotates a mirror.

Patent document 2 discloses an optical phased array having a plurality of nanophotonic antenna elements arranged in 2 dimensions. Each antenna element is optically coupled to a variable optical delay line (i.e., a phase shifter). In the optical phased array, coherent light beams are guided to respective antenna elements by waveguides, and the light beams are phase-shifted by phase shifters. This can change the amplitude distribution of the far-field radiation pattern.

Patent document 3 discloses an optical deflection element including: a waveguide including an optical waveguide layer for guiding light therein and 1 st distributed Bragg reflector formed on upper and lower surfaces of the optical waveguide layer; a light incident port for causing light to be incident into the waveguide; and a light exit port formed on a surface of the waveguide so as to exit the light that enters from the light entrance port and is guided in the waveguide.

Prior art documents

Patent document

Patent document 1 International publication No. 2013/168266

Patent document 2 Japanese patent laid-open publication No. 2016-508235

Patent document 3 Japanese patent laid-open publication No. 2013-16591

Disclosure of Invention

Problems to be solved by the invention

One embodiment of the present disclosure provides a novel optical device capable of realizing scanning with light in a relatively simple configuration.

Means for solving the problems

An optical device according to an embodiment of the present disclosure includes: a 1 st mirror having a 1 st reflecting surface and extending in a 1 st direction; a 2 nd mirror having a 2 nd reflecting surface opposed to the 1 st reflecting surface and extending in the 1 st direction; and a light guide layer located between the 1 st mirror and the 2 nd mirror to make light propagate along the 1 st direction; the transmittance of the 1 st mirror is higher than the transmittance of the 2 nd mirror, and a reflection spectrum of at least one of the 1 st mirror and the 2 nd mirror corresponding to light incident from a normal direction of a reflection surface is: the wavelength band having a reflectance of 90% or more includes a maximum point, and a 1 st inflection point and a 2 nd inflection point which are located on a longer wavelength side than the maximum point.

The general or specific aspects of the disclosure may also be implemented by an apparatus, system, method, or any combination thereof.

Effects of the invention

According to one embodiment of the present disclosure, 1-dimensional scanning or 2-dimensional scanning can be realized by light with a relatively simple configuration.

Drawings

Fig. 1 is an oblique view schematically showing an example of an optical scanning apparatus.

Fig. 2 is a diagram schematically showing an example of the structure of the cross section of 1 waveguide element and the propagated light.

Fig. 3A is a view showing a cross section of the waveguide array that emits light in a direction perpendicular to the emission surface of the waveguide array.

Fig. 3B is a cross-sectional view of the waveguide array that emits light in a direction different from the direction perpendicular to the emission surface of the waveguide array.

Fig. 4 is an oblique view schematically showing an example of a waveguide array in a 3-dimensional space.

Fig. 5 is a schematic view of the waveguide array and the phase shifter array viewed from the normal direction (Z direction) of the light exit surface.

Fig. 6A is a diagram schematically showing a case where light is emitted from the emission surface when the propagation angle is small.

Fig. 6B is a diagram schematically showing a case where light is emitted from the emission surface when the propagation angle is large.

Fig. 7 is a diagram showing the result of calculating the relationship between the propagation length and the beam width of the outgoing light.

Fig. 8 is a diagram showing a reflection spectrum of a conventional DBR corresponding to an incident angle of 0 °.

Fig. 9 is a diagram of the reflection spectrum of the conventional DBR corresponding to the incident angles of 0 °, 10 °, and 15 °.

Fig. 10A is a graph showing an example of the relationship between the incident angle and the reflectance at a wavelength of 940 nm.

Fig. 10B is a graph showing an example of the relationship between the incident angle and the reflectance at the wavelength of 1100 nm.

Fig. 11 is a diagram showing a reflection spectrum of the chirped DBR according to the present embodiment corresponding to an incident angle of 0 °.

Fig. 12 is a graph showing an example of the relationship between the incident angle and the reflectance at a wavelength of 940 nm.

Fig. 13 is a diagram showing an example of the relationship between the emission angle and the propagation length.

Fig. 14 is a diagram showing the reflection spectrum of another chirped DBR according to the present embodiment corresponding to an incident angle of 0 °.

Fig. 15 is a diagram showing an example of the configuration of an optical scanning device in which elements such as a beam splitter, a waveguide array, a phase shifter array, and a light source are integrated on a circuit board.

Fig. 16 is a schematic diagram showing a case where a beam of laser light or the like is irradiated from the optical scanning apparatus to a far field and 2-dimensional scanning is performed.

FIG. 17 is a block diagram illustrating an example of a configuration of a LiDAR system capable of generating ranging images.

FIG. 18 is a graph showing an example of the relationship between the incidence angle φ and the reflectance at a propagation length of 100 μm.

Detailed Description

Before describing the embodiments of the present disclosure, the findings that underlie the present disclosure will be described.

The present inventors have found that the following problems exist in the conventional optical scanning apparatus: it is difficult to scan a space with light without complicating the configuration of the apparatus.

For example, in the technique disclosed in patent document 1, a driving device for rotating the mirror is required. Therefore, there is a problem that the structure of the device becomes complicated and unstable against vibration.

In the optical phase array described in patent document 2, it is necessary to branch and introduce light into a plurality of column waveguides and a plurality of row waveguides, and guide the light to a plurality of antenna elements arranged in 2 dimensions. Therefore, wiring of the waveguide for guiding the light becomes very complicated. In addition, the range of 2-dimensional scanning cannot be increased. Further, in order to change the amplitude distribution of the outgoing light in the far field in 2 dimensions, it is necessary to connect a phase shifter to each of the plurality of antenna elements arranged in 2 dimensions, and to attach a wiring for phase control to the phase shifter. This causes the phases of light incident on the plurality of antenna elements arranged in 2 dimensions to change by different amounts. Therefore, the constitution of the element becomes very complicated.

The present inventors have focused on the above problems in the prior art and studied a configuration for solving the problems. The present inventors have found that the above-mentioned problems can be solved by using a waveguide element having a pair of mirrors facing each other and an optical waveguide layer interposed between the mirrors. One of the pair of mirrors in the waveguide element has a higher light transmittance than the other, and emits a part of the light propagating through the optical waveguide layer to the outside. As described later, the direction (or emission angle) of the emitted light can be changed by adjusting the refractive index or thickness of the optical waveguide layer or the wavelength of the light input to the optical waveguide layer. More specifically, by changing the refractive index, thickness, or wavelength, the component of the wave vector (wave vector) of the outgoing light in the direction along the longitudinal direction of the optical waveguide layer can be changed. Thereby, 1-dimensional scanning is realized.

Furthermore, even when an array of a plurality of waveguide elements is used, 2-dimensional scanning can be realized. More specifically, by giving an appropriate phase difference to the light supplied to the plurality of waveguide elements and adjusting the phase difference, the direction in which the lights emitted from the plurality of waveguide elements mutually reinforce can be changed. Due to the change in the phase difference, the component of the wave vector of the outgoing light in the direction intersecting the direction along the longitudinal direction of the optical waveguide layer changes. This enables 2-dimensional scanning. In addition, even when 2-dimensional scanning is performed, it is not necessary to change the refractive index and thickness of the plurality of optical waveguide layers or the wavelength of light by different amounts. That is, 2-dimensional scanning can be performed by giving an appropriate phase difference to light supplied to the plurality of optical waveguide layers and simultaneously changing at least 1 of the refractive index, thickness, and wavelength of the plurality of optical waveguide layers by the same amount.

As described above, according to the present disclosure, 1-dimensional or 2-dimensional scanning can be realized by light with a relatively simple configuration.

In the present specification, "at least 1 of refractive index, thickness, and wavelength" means at least 1 selected from the group consisting of refractive index of the optical waveguide layer, thickness of the optical waveguide layer, and wavelength input to the optical waveguide layer. In order to change the light emission direction, any 1 of the refractive index, thickness, and wavelength may be controlled independently. Alternatively, the emission direction of light may be changed by controlling any 2 or all of the 3. The wavelength of light input to the optical waveguide layer may be controlled instead of or in addition to the control of the refractive index or the thickness.

The above basic principle can be applied not only to the use of emitted light but also to the use of received light signals. By changing at least 1 of the refractive index, the thickness, and the wavelength, the direction of light that can be received can be changed in 1 dimension. Further, if the phase difference of light is changed by a plurality of phase shifters connected to a plurality of waveguide elements arranged in one direction, the direction of light that can be received can be changed in 2 dimensions.

The Light scanning apparatus and the Light receiving apparatus of the present disclosure can be used as an antenna in a Light Detection system such as a Light Detection and Ranging (Light Detection and Ranging) system, for example. The LiDAR system uses electromagnetic waves (visible light, infrared light, or ultraviolet light) having a shorter wavelength than a radar system using radio waves such as millimeter waves, and thus can detect the distance distribution of an object with high resolution. Such a LiDAR system is mounted on a mobile body such as an automobile, an UAV (so-called Unmanned Aerial Vehicle), or an AGV (Automated Guided Vehicle), and can be used as one of collision avoidance techniques. In this specification, the optical scanning device and the optical receiving device are sometimes collectively referred to as an "optical device". In addition, a device used for an optical scanning device or an optical receiving device is also sometimes referred to as an "optical device". The term "optical device" is sometimes used for an optical component constituting an optical scanning device or an optical receiving device.

< example of construction of optical scanning apparatus >

The following describes, as an example, a configuration of an optical scanning device that performs 2-dimensional scanning. In some cases, an overly detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of substantially the same configuration may be omitted. This is to avoid over-verbose explanation below, which would be understood by one skilled in the art. In addition, the drawings and the following description are provided for the present inventors to fully understand the present disclosure, and it is not intended to limit the subject matter described in the claims by these drawings. In the following description, the same reference numerals are given to the same or similar components.

In the present disclosure, "light" means electromagnetic waves including not only visible light (having a wavelength of approximately 400nm to approximately 700nm) but also ultraviolet light (having a wavelength of approximately 10nm to approximately 400nm) and infrared light (having a wavelength of approximately 700nm to approximately 1 mm). In the present specification, ultraviolet light is sometimes referred to as "ultraviolet light", and infrared light is sometimes referred to as "infrared light".

In the present disclosure, "scanning" with light means changing the direction of light. "1-dimensional scanning" means that the direction of light is changed in a straight line along a direction intersecting with the direction. "2-dimensional scanning" means that the direction of light is changed in 2-dimensions along a plane intersecting the direction.

Fig. 1 is an oblique view schematically showing an example of an optical scanning apparatus 100. The optical scanning apparatus 100 is provided with a waveguide array including a plurality of waveguide elements 10. The plurality of waveguide elements 10 each have a shape extending in the 1 st direction (X direction in fig. 1). The plurality of waveguide elements 10 are regularly arranged in a 2 nd direction (Y direction in fig. 1) intersecting the 1 st direction. The plurality of waveguide elements 10 emit light in the 3rd direction D3 intersecting a virtual plane parallel to the 1 st and 2 nd directions while propagating the light in the 1 st direction. In the present disclosure, the 1 st direction (X direction) is orthogonal to the 2 nd direction (Y direction), but the two may not be orthogonal. In the present disclosure, the plurality of waveguide elements 10 are arranged at equal intervals in the Y direction, but need not necessarily be arranged at equal intervals.

The orientation of the structure shown in the drawings of the present application is set in consideration of the ease of description, and is not limited at all to the orientation in implementation. In addition, the shape and size of the whole or a part of the structure shown in the drawings are not limited to actual shapes and sizes.

Each of the plurality of waveguide elements 10 includes a 1 st mirror 30 and a 2 nd mirror 40 (hereinafter, each may be simply referred to as a "mirror") facing each other, and an optical waveguide layer 20 located between the mirrors 30 and 40. Each of the reflecting mirrors 30 and 40 has a reflecting surface intersecting the 3rd direction D3 at the interface with the optical waveguide layer 20. The mirrors 30 and 40 and the optical waveguide layer 20 have shapes extending in the 1 st direction (X direction).

The reflection surface of the 1 st mirror 30 and the reflection surface of the 2 nd mirror 40 are substantially parallel to each other. At least the 1 st mirror 30 among the 2 mirrors 30 and the mirror 40 has a characteristic of transmitting a part of light propagating in the optical waveguide layer 20. In other words, the 1 st mirror 30 has a higher light transmittance for the light than the 2 nd mirror 40. Therefore, a part of the light propagating through the optical waveguide layer 20 is emitted to the outside from the 1 st mirror 30. Such mirrors 30 and 40 may be multilayer mirrors formed of a multilayer film of dielectric material (also referred to as "multilayer reflective film" or "Distributed Bragg Reflector (DBR)).

By controlling the phase of light input to each waveguide element 10, the refractive index or thickness of the optical waveguide layer 20 in the waveguide elements 10, or the wavelength of light input to the optical waveguide layer 20, can be simultaneously changed in synchronization, and 2-dimensional scanning can be realized by light.

The present inventors analyzed the operation principle of the waveguide element 10 in order to realize such 2-dimensional scanning. Based on this result, by driving the plurality of waveguide elements 10 in synchronization, 2-dimensional scanning was successfully achieved by light.

As shown in fig. 1, if light is input to each waveguide element 10, light exits from the exit surface of each waveguide element 10. The emission surface is located on the opposite side of the reflection surface of the 1 st mirror 30. The direction D3 of the outgoing light depends on the refractive index and thickness of the optical waveguide layer and the wavelength of the light. In the present disclosure, at least 1 of the refractive index, thickness, and wavelength of each optical waveguide layer is synchronously controlled so that the light emitted from each waveguide element 10 is directed in substantially the same direction. This can change the component in the X direction of the wave vector of the light emitted from the plurality of waveguide elements 10. In other words, the direction D3 of the outgoing light can be changed along the direction 101 shown in fig. 1.

Further, since the light beams emitted from the plurality of waveguide elements 10 are directed in the same direction, the emitted light beams interfere with each other. By controlling the phase of the light emitted from each waveguide element 10, the direction in which the lights are mutually intensified by interference can be changed. For example, when a plurality of waveguide elements 10 having the same size are arranged at equal intervals in the Y direction, light having a certain amount of phase difference is input to the plurality of waveguide elements 10. By changing this phase difference, the component in the Y direction of the wave vector of the outgoing light can be changed. In other words, by changing the phase difference of the light introduced into each of the plurality of waveguide elements 10, the direction D3 in which the outgoing light is mutually intensified by interference can be changed along the direction 102 shown in fig. 1. Thereby, 2-dimensional scanning can be achieved by light.

The operation principle of the optical scanning apparatus 100 is explained below.

< principle of operation of waveguide element >

Fig. 2 is a diagram schematically showing an example of the structure of the cross section of 1 waveguide element 10 and the propagated light. Fig. 2 schematically shows a cross section of the waveguide element 10 parallel to the XZ plane, with the Z direction being a direction perpendicular to the X direction and the Y direction shown in fig. 1. In the waveguide element 10, a pair of the reflecting mirror 30 and the reflecting mirror 40 is disposed so as to sandwich the optical waveguide layer 20. The light 22 introduced from one end of the optical waveguide layer 20 in the X direction propagates through the optical waveguide layer 20 while being repeatedly reflected by the 1 st reflecting surface 30s of the 1 st reflecting mirror 30 provided on the upper surface (upper surface in fig. 2) of the optical waveguide layer 20 and the 2 nd reflecting surface 40s of the 2 nd reflecting mirror 40 provided on the lower surface (lower surface in fig. 2) of the 2 nd reflecting mirror 40. The light transmittance of the 1 st mirror 30 is higher than that of the 2 nd mirror 40. Therefore, a part of the light can be output mainly from the output surface 30es of the 1 st mirror 30. Hereinafter, the 1 st reflecting surface 30s may be simply referred to as "reflecting surface 30 s" and the 2 nd reflecting surface 40s may be simply referred to as "reflecting surface 40 s".

In a waveguide such as a normal optical fiber, light propagates along the waveguide while repeating total reflection. In contrast, in the waveguide element 10, light propagates while being repeatedly reflected by the mirrors 30 and 40 disposed above and below the optical waveguide layer 20. Therefore, the propagation angle of light is not restricted. Here, the propagation angle of light means an incident angle to the interface between the mirror 30 or the mirror 40 and the optical waveguide layer 20. Light incident at a more nearly normal angle with respect to mirror 30 or mirror 40 can also propagate. That is, light incident on the interface at an angle smaller than the critical angle of total reflection can also propagate. Therefore, the group velocity of light in the propagation direction of light is greatly reduced compared to the velocity of light in free space. Thus, the waveguide element 10 has a property that the propagation condition of light greatly changes with respect to the wavelength of light, the thickness of the optical waveguide layer 20, and the refractive index of the optical waveguide layer 20. The waveguide element 10 is also referred to as a "reflection waveguide" or a "slow light waveguide".

The emission angle θ of the light emitted from the waveguide 10 into the air is expressed by the following expression (1).

[ number 1]

As can be seen from the formula (1), the wavelength λ of light in the air and the refractive index n of the optical waveguide layer 20 are changed_wAnd lightThe exit direction of light can be changed by any thickness d of the waveguide layer 20.

For example, at n_wWhen d is 387nm, λ is 1550nm, and m is 1, the emission angle is 0 °. If the refractive index is changed from this state to n_wThe exit angle changes to approximately 66 ° 2.2. On the other hand, if the thickness variation d is 420nm without changing the refractive index, the emission angle variation is approximately 51 °. If the wavelength is changed to λ 1500nm without changing the refractive index and the thickness, the emission angle is changed to approximately 30 °. By changing the wavelength λ of light and the refractive index n of the optical waveguide layer 20 in this manner_wAnd the thickness d of the optical waveguide layer 20, the light emission direction can be greatly changed.

Accordingly, in the optical scanning apparatus 100 of the present disclosure, the wavelength λ of light input to the optical waveguide layer 20 and the refractive index n of the optical waveguide layer 20 are controlled_wAnd at least 1 of the thickness d of the optical waveguide layer 20, to control the light emission direction. The wavelength λ of light may be kept constant without changing during operation. In this case, the light scanning can be realized with a simpler configuration. The wavelength λ is not particularly limited. For example, the wavelength λ may be contained in a wavelength band of 400nm to 1100nm (visible light to near-infrared light) in which a photodetector that absorbs light by general silicon (Si) to detect light or an image sensor can obtain high detection sensitivity. In other examples, the wavelength λ may be included in a band of a fiber or a Si waveguide that transmits near infrared light of 1260nm to 1625nm with relatively small loss. These wavelength ranges are examples. The wavelength band of the light to be used is not limited to the wavelength band of visible light or infrared light, and may be, for example, the wavelength band of ultraviolet light.

In order to change the direction of the outgoing light, the optical scanning apparatus 100 may include a 1 st adjusting element that changes at least 1 of the refractive index, thickness, and wavelength of the optical waveguide layer 20 in each waveguide element 10.

As described above, if the waveguide element 10 is used, the refractive index n of the optical waveguide layer 20 is adjusted by_wAt least 1 of the thickness d and the wavelength λ is changed, the light emission direction can be largely changed. Thereby, the slave can be reversedThe exit angle of the light exiting from the mirror 30 varies in the direction along the waveguide element 10. Such 1-dimensional scanning can be achieved by using at least 1 waveguide element 10.

The optical waveguide layer 20 may also comprise a liquid crystal material or an electro-optic material in order to adjust the refractive index of at least a portion of the optical waveguide layer 20. The optical waveguide layer 20 may be sandwiched between a pair of electrodes. By applying a voltage to the pair of electrodes, the refractive index of the optical waveguide layer 20 can be changed.

For adjusting the thickness of the optical waveguide layer 20, for example, at least 1 actuator may be connected to at least one of the 1 st mirror 30 and the 2 nd mirror 40. The thickness of the optical waveguide layer 20 can be changed by changing the distance between the 1 st mirror 30 and the 2 nd mirror 40 by at least 1 actuator. The thickness of the optical waveguide layer 20 can be easily varied if the optical waveguide layer 20 is formed of a liquid.

Motion principle of < 2D scanning >

In a waveguide array in which a plurality of waveguide elements 10 are arranged in one direction, the emission direction of light changes due to interference of light emitted from each waveguide element 10. By adjusting the phase of the light supplied to each waveguide element 10, the light emission direction can be changed. The principle of this will be described below.

Fig. 3A is a view showing a cross section of the waveguide array that emits light in a direction perpendicular to the emission surface of the waveguide array. Fig. 3A also shows the phase shift amount of light propagating through each waveguide element 10. Here, the phase shift amount is a value based on the phase of light propagating through the left waveguide element 10. The waveguide array of the present disclosure includes a plurality of waveguide elements 10 in equally spaced rows. In fig. 3A, the circular arcs of the broken lines indicate the wave surfaces of the light emitted from the waveguide elements 10. The straight line indicates a wave surface formed by interference of light. The arrow indicates the direction of light exiting the waveguide array (i.e., the direction of the wave vector). In the example shown in fig. 3A, the phases of light propagating through the optical waveguide layers 20 of the respective waveguide elements 10 are all the same. In this case, light is emitted in a direction (Z direction) perpendicular to both the arrangement direction (Y direction) of the waveguide elements 10 and the direction (X direction) in which the optical waveguide layer 20 extends.

Fig. 3B is a cross-sectional view of the waveguide array that emits light in a direction different from the direction perpendicular to the emission surface of the waveguide array. In the example shown in fig. 3B, the phase of light propagating in the optical waveguide layers 20 of the plurality of waveguide elements 10 differs by a certain amount (Δ Φ) one by one along the arrangement direction. In this case, the light is emitted in a direction different from the Z direction. By changing the Δ Φ, the component of the wave vector of light in the Y direction can be changed. If the distance between centers of 2 adjacent waveguide elements 10 is p, the light emission angle α is set₀This is represented by the following formula (2).

[ number 2]

In the example shown in fig. 2, the exit direction of light is parallel to the XZ plane. I.e. alpha₀0 deg.. In the example shown in fig. 3A and 3B, the direction of light emitted from the optical scanning apparatus 100 is parallel to the YZ plane. That is, θ is 0 °. However, in general, the direction of light exiting from the light scanning apparatus 100 is neither parallel to the XZ plane nor parallel to the YZ plane. I.e., θ ≠ 0 ° and α₀≠0°。

Fig. 4 is an oblique view schematically showing an example of a waveguide array in a 3-dimensional space. The thick arrows shown in fig. 4 represent the direction of light exiting from the optical scanning apparatus 100. θ is an angle formed by the exit direction of light and the YZ plane. Theta satisfies the formula (1). Alpha is alpha₀Is the angle that the exit direction of the light makes with the XZ plane. Alpha is alpha₀Satisfies the formula (2).

< phase control of light introduced into waveguide array >

In order to control the phase of the light emitted from each waveguide element 10, for example, a phase shifter for changing the phase of the light may be provided at a stage before the light is introduced into the waveguide element 10. The optical scanning apparatus 100 of the present disclosure includes: a plurality of phase shifters connected to the plurality of waveguide elements 10, respectively, and a 2 nd adjusting element for adjusting the phase of light propagating through each phase shifter. Each phase shifter includes a waveguide connected to the optical waveguide layer 20 in the corresponding 1 of the plurality of waveguide elements 10 directly or via another waveguide. The 2 nd adjusting element changes the direction of light emitted from the plurality of waveguide elements 10 (i.e., the 3rd direction D3) by changing the phase difference between the light propagating from the plurality of phase shifters to the plurality of waveguide elements 10. In the following description, a plurality of phase shifters arranged in a similar manner to the waveguide array may be referred to as a "phase shifter array".

Fig. 5 is a schematic diagram of the waveguide array 10A and the phase shifter array 80A viewed from the normal direction (Z direction) of the light exit surface. In the example shown in fig. 5, all the phase shifters 80 have the same propagation characteristic, and all the waveguide elements 10 have the same propagation characteristic. The phase shifters 80 and the waveguide elements 10 may have the same length or different lengths. When the phase shifters 80 have the same length, the respective phase shift amounts can be adjusted by the driving voltage, for example. Further, by configuring each phase shifter 80 to change its length in equal steps, it is also possible to apply equal-step phase shifts using the same drive voltage. Further, the optical scanning apparatus 100 further includes: the optical splitter 90 that branches light and supplies the light to the plurality of phase shifters 80, the 1 st drive circuit 110 that drives each waveguide element 10, and the 2 nd drive circuit 210 that drives each phase shifter 80. The straight arrows shown in fig. 5 represent the input of light. By independently controlling the 1 st drive circuit 110 and the 2 nd drive circuit 210 which are separately provided, respectively, 2-dimensional scanning can be realized. In this example, the 1 st drive circuit 110 functions as 1 element of the 1 st adjustment element, and the 2 nd drive circuit 210 functions as 1 element of the 2 nd adjustment element.

The 1 st drive circuit 110 changes the angle of light emitted from the optical waveguide layer 20 by changing at least one of the refractive index and the thickness of the optical waveguide layer 20 in each waveguide element 10. The 2 nd drive circuit 210 changes the phase of light propagating inside the waveguide 20a by changing the refractive index of the waveguide 20a in each phase shifter 80. The beam splitter 90 may be constituted by a waveguide through which light propagates by total reflection, or may be constituted by a reflection waveguide similar to the waveguide element 10.

Further, after controlling the phase of each light branched by the beam splitter 90, each light may be introduced into the phase shifter 80. For this phase control, for example, a passive (passive) phase control structure can be used, which is realized by adjusting the length of the waveguide up to the phase shifter 80. Alternatively, a phase shifter which has the same function as the phase shifter 80 and can be controlled by an electric signal may be used. With this method, for example, before being introduced into the phase shifter 80, the phase may be adjusted so that light of equal phase is supplied to all the phase shifters 80. By such adjustment, the control of each phase shifter 80 by the 2 nd drive circuit 210 can be simplified.

An optical device having the same configuration as the optical scanning device 100 described above can also be used as the light receiving device. Details of the operation principle and operation method of the optical device are disclosed in U.S. patent application publication No. 2018/0224709. The disclosure of this document is incorporated in its entirety into the present specification.

< exit angle and beam width of exit light >

The beam width of the light emitted from the slow light guide 10 determines the scanning resolution. If the beam width is narrowed, the resolution of scanning is increased, and if the beam width is widened, the resolution of scanning is decreased. The following describes a relationship between a beam width and an emission angle of light emitted from the conventional slow light waveguide 10.

The far field pattern of the light emitted from the slow light waveguide 10 corresponds to the fourier transform of the electric field distribution at the emission surface 30es shown in fig. 2. That is, the longer the propagation length of the light 22 propagating through the optical waveguide layer 20, the narrower the beam width of the outgoing light in the far field. Conversely, if the propagation length of light propagating through the optical waveguide layer 20 is shorter, the beamwidth of the outgoing light in the far field is wider. Here, the propagation length means a distance at which the intensity of the light 22 propagating while being attenuated in the optical waveguide layer 20 is reduced to 1/e times. e is the base of the natural logarithm. The beam width means an angle Δ θ that spreads to both sides with the exit angle θ as the center. Specifically, the beam width is referred to as the full width at half maximum of the outgoing light in the angular spectrum.

FIG. 6A and FIG. 6B are schematic views each showing a propagation angleA diagram of a case where phi is relatively small and a case where phi is relatively large where light exits from the exit surface 30 es. For simplicity, the reflectivity of the mirror 30 is assumed to be constant regardless of the propagation angle φ. In the example shown in fig. 6A, the propagation angle Φ is small, and therefore the number of times the reflection surface 30s reflects the light 22 per unit length is large. Thus, the propagation length L_pShort. In the example shown in fig. 6B, the propagation angle Φ is large, and therefore the number of times the reflection surface 30s reflects the light 22 per unit length is small. Thus, the propagation length L_pLong. There is a positive correlation between the propagation angle φ and the exit angle θ, so the larger the exit angle θ, the longer the propagation length L_pThe larger. In addition, the propagation length L shown by a double-headed arrow in fig. 6A and 6B_pAre schematic representations and do not represent actual lengths.

FIG. 7 shows the propagation length L_pAn example of the relationship with the beam width Δ θ of the outgoing light. The graph shown in fig. 7 shows the result of calculating the propagation length by variously changing the line width of the light beam emitted from 1 slow light waveguide 10 in which the conditions such as the size and the dielectric constant of each component are appropriately set. As shown in fig. 7, the propagation length L_pThe longer the wavelength, the narrower the beam width Δ θ of the outgoing light. As described above, if the exit angle θ increases, the propagation length L_pTherefore, the beam width Δ θ of the outgoing light decreases as the outgoing angle θ increases. Since the beam width Δ θ of the outgoing light depends on the outgoing angle θ in this manner, if the outgoing angle θ changes, the resolution of scanning changes.

The present inventors have found the above problems and studied the configuration of an optical device for solving the problems. As a result, it has been found that the above problems can be solved by using a mirror having a special characteristic which has not been found in the past as at least one of the 2 mirrors in the slow light guide. The embodiments of the present disclosure described below are based on this finding. Hereinafter, exemplary embodiments of the present disclosure will be described.

For comparison, the reflection spectrum of a conventional DBR that can be used for the mirror 30 and/or the mirror 40 in the slow optical waveguide 10 will be described.

As shown in fig. 2, the light 22 propagates through the optical waveguide layer 20 while being reflected by the reflecting surface 30s of the reflecting mirror 30 and the reflecting surface 40s of the reflecting mirror 40. In this case, the reflectances of the mirror 30 and the mirror 40 are also about 99% on the light emission side. In order to achieve such high reflectance, the mirrors 30 and 40 may be formed of, for example, DBR. An example of a reflection spectrum when light enters the reflection surface of the conventional DBR is described below. The incident angle of light incident on the reflecting surface corresponds to the propagation angle phi.

Fig. 8 is a diagram showing a reflection spectrum of a conventional DBR corresponding to light at an incident angle of phi 0 °. The angle of incidence of 0 ° corresponds to the angle at which light is incident from the normal direction of the reflective surface of the DBR. For the calculation of the reflection spectrum, DiffractMod from Synopsys was used. The refractive index of the medium on the incident side of the DBR in this example is 1.68. The DBR corresponds to the mirror 30 in the slow light waveguide 10, and the medium on the incident side corresponds to the light waveguide layer 20 in the slow light waveguide 10. The DBR has a structure in which 9 high refractive index layers and 8 low refractive index layers are alternately stacked. Each high refractive index layer had a refractive index of 2.28 and a thickness of 111 nm. Each low refractive index layer had a refractive index of 1.47 and a thickness of 173 nm. As shown in fig. 8, the reflection spectrum of the conventional DBR shows a reflectance of approximately 100% in the stop band by design, and shows a low reflectance if it deviates from the stop band. Here, the stopband means a wavelength band in which incident light is strongly reflected due to bragg reflection caused by the periodic structure.

Fig. 9 is a diagram showing reflection spectra of a conventional DBR corresponding to the incidence angles of Φ equal to 0 °, 10 °, and 15 °. As shown in fig. 9, the reflection spectrum shifts to the short wavelength side with an increase in the incident angle Φ. Hereinafter, the wavelength λ will be described as an example_A940nm and wavelength lambda_BThe reflectance of light at 1100nm varies depending on the incident angle phi.

FIGS. 10A and 10B show the incident angle φ and the wavelength λ, respectively_AThe relationship between the reflectance of light at 940nm, and the angle of incidence φ and wavelength λ_BGraph of the relationship between the reflectance of light at 1100 nm. The range of the incident angle Φ to 0 ° or more and 25 ° or less corresponds to the range of the emission angle θ to 0 ° or more and substantially 60 ° or less.As shown in fig. 10A, the wavelength λ_AHas a small wavelength dependence of the reflectance of light. Therefore, for the above reason, the beam width Δ θ of the outgoing light becomes narrower as the outgoing angle θ increases. On the other hand, as shown in fig. 10B, the wavelength λ at the end portion close to the stop band_BHere, the reflectance sharply decreases too much in the vicinity of the incident angle Φ of 15 °. Therefore, the beam width Δ θ of the outgoing light becomes narrower with an increase in the outgoing angle θ in the range where the incident angle Φ is 0 ° or more and substantially 15 ° or less, and increases with an increase in the outgoing angle θ in the range where the incident angle Φ is substantially 15 ° or more and 25 ° or less. In the examples of fig. 10A and 10B, the beam width Δ θ of the outgoing light greatly changes depending on the outgoing angle θ.

As described above, the present inventors have found that by using a mirror whose reflectance is gently reduced with an increase in the incident angle Φ, it is possible to realize an optical scanning apparatus in which the beam width Δ θ of the outgoing light does not greatly vary depending on the outgoing angle θ. Specifically, by providing an inflection point on the longer wavelength side with respect to the maximum value in the reflection spectrum of the mirror, a mirror is realized in which the reflectance gradually decreases with an increase in the incident angle Φ. In this embodiment, as a mirror having an inflection point in a reflection spectrum, a chirped DBR in which thicknesses of a high refractive index layer and a low refractive index layer are appropriately adjusted is used. In the present specification, a "chirped (chirp) DBR" means a DBR in which the thicknesses of a plurality of high refractive index layers and/or the thicknesses of a plurality of low refractive index layers are different according to layers. In the chirped DBR, not only the DBR in which the thicknesses of the plurality of high refractive index layers and/or the thicknesses of the plurality of low refractive index layers gradually increase or decrease along the stacking direction but also the DBR in which the thicknesses of the plurality of high refractive index layers and/or the thicknesses of the plurality of low refractive index layers irregularly or randomly change along the stacking direction are included.

Fig. 11 is a diagram showing a reflection spectrum of the chirped DBR according to the present embodiment corresponding to an incident angle of Φ — 0 °. In the example shown in fig. 11, the reflection spectrum includes 1 local maximum point P in a wavelength band having a reflectance of 95% or more_LMAnd at the maximum point P_LMInflection point P on the long wavelength side of₁To the inflection point P₄. In the reflection spectrum, the reflectivity is at the maximum point P_LMMonotonically decreases on the long wavelength side. Here, the inflection point means a point at which the 2 nd-differentiation of the reflectance with respect to the wavelength becomes zero. At this inflection point, the reflectance varies linearly with respect to the wavelength.

In the reflection spectrum of the chirped DBR of the present embodiment, the maximum point P_LMAnd an inflection point P₁To the inflection point P₄Exists in a wavelength band showing a reflectance of 95% or more. According to the design of the chirped DBR, the maximum point P_LMAnd an inflection point P₁To the inflection point P₄The reflectance may be in a wavelength band of 90% or more.

Fig. 7 shows that the propagation length needs to be substantially 100 μm or more in order to make the beam width Δ θ substantially 0.2 ° or less. FIG. 18 is a graph showing the relationship between the incidence angle φ and the reflectance when the propagation length is set to 100 μm. As shown in fig. 18, the reflectance needs to be substantially 90% or more in order to maintain the propagation length up to an incident angle of 25 degrees.

FIG. 12 is a graph showing the calculated wavelength λ_AGraph of the results obtained for the relationship between the angle of incidence phi and the reflectivity at 940 nm. As shown in fig. 12, the reflectance is gently monotonously reduced in a very high wavelength band in which the reflectance is about 95% to 99.9%. More specifically, the reflectance decreases in stages in this wavelength band with an increase in the incident angle Φ. The wavelength band is approximately 940nm or more and approximately 1090nm or less. The reflectance is not sharply reduced as shown in fig. 10B. The reflectance is high in the case where the incident angle phi is relatively small, and is low in the case where the incident angle phi is relatively large. A design method of a chirped DBR for obtaining a desired reflection spectrum as shown in fig. 11 is described, for example, in "Thin-Film Optical Filters, 3rd ed." (p.193-p.204) IoP Publishing (Bristol and Philadelphia) of h.a. mechanical.

As above, by being at the maximum point P of the specific reflection spectrum_LMBy providing an inflection point on the longer wavelength side, the change in reflectance with respect to the change in the incident angle phi can be made gentle. Maximum point P of the reflection spectrum_LMAnd the inflection point may exist in a band showing a reflectance of 95% or more. With such a configuration, it is possible toThe reflectance is gently changed while being maintained high. Maximum point P of the reflection spectrum_LMAnd the inflection point may exist in a band showing a reflectance of 90% or more. In the present embodiment, when the number of inflection points is 1 or more, the reflectance gently changes at least in a range where the incident angle Φ is 0 ° or more and substantially 10 ° or less. In particular, when the number of inflection points is 2 or more, the reflectance changes gently at least in a range where the incident angle Φ is 0 ° or more and substantially 15 ° or less. By providing 2 or more inflection points in this manner, the change in reflectance with respect to the change in the incident angle can be made gentle over a wide angle range. In addition, it is possible to maintain a high reflectance and realize a gentle change in the reflectance.

Next, for comparison, the emission angle θ and the propagation length L in the case where the conventional DBR and the DBR of the present embodiment are used as the mirror 30 will be described_pThe relationship between them.

FIG. 13 shows the emission angle θ and the propagation length L_pA graph of an example of the relationship between them. The white circle corresponds to a case where the mirror 30 in the slow optical waveguide 10 is formed of the conventional DBR in the above example. The black dots are equivalent to the case where the mirror 30 in the slow optical waveguide 10 is formed of the chirped DBR in the above example. The reflecting mirror 40 in the slow optical waveguide 10 is formed of a conventional DBR different from the above example. The DBR has a structure in which 11 high refractive index layers and 10 low refractive index layers are alternately stacked. The high refractive index layer had a refractive index of 2.28 and a thickness of 107 nm. The low refractive index layer had a refractive index of 1.47 and a thickness of 172 nm. Optical waveguide layer 20 has a refractive index of 1.68. The refractive index of air as a medium on the light exit side was 1.0.

As shown by the white circles, in the conventional DBR, the propagation length L_pWith an increase in the exit angle theta. On the other hand, as indicated by the black dots, in the chirped DBR according to the present embodiment, even if the emission angle θ is increased, the propagation length L is found to be increased_pAnd also substantially unchanged. In this manner, the chirp DBR according to the present embodiment can suppress the propagation length L_pDependence on the exit angle theta. If the propagation length L is no matter how the exit angle theta_pAre all approximatelyThe beam width Δ θ of the outgoing light shown in fig. 7 is also substantially constant with respect to the outgoing angle θ. In the example shown in fig. 13, the propagation length L_pThe average was approximately 150 μm. As shown in fig. 7, the propagation length Lp ≈ 150 μm corresponds to the beam width Δ θ ≈ 0.1 ° of the outgoing light. Therefore, even if the emission angle θ changes, the beam width Δ θ of the emitted light can be maintained at substantially 0.1 degrees. This can suppress a change in the resolution of scanning due to the emission angle θ. Further, since the beam width Δ θ of the outgoing light is 0.1 °, high resolution can be maintained regardless of the outgoing angle θ.

In the above example, the reflectance is at the local maximum point P_LMIs monotonically decreased on the long wavelength side, but the reflectance does not need to be at the maximum point P_LMThe long wavelength side of (a) must monotonically decrease. Fig. 14 is a diagram showing the reflection spectrum of another chirped DBR according to the present embodiment corresponding to an incident angle of Φ ═ 0 °. In the example shown in fig. 14, the reflection spectrum includes a local maximum point P in a wavelength band in which the reflectance is 95% or more_LM1And a maximum point P on the long wavelength side thereof_LM2And at the maximum point P_LM1Long wavelength side of and a maximum point P_LM2Short wavelength side inflection point P of₁To the inflection point P₃. In the reflection spectrum, the reflectivity is at the maximum point P_LM1Long wavelength side of and a maximum point P_LM2The short wavelength side of (a) is first decreased and then increased with an increase in wavelength. I.e. the reflectivity is at the point of maximum P_LM1Is not monotonically decreasing. Reflectivity at the maximum point P_LM2Monotonically decreases on the long wavelength side. In this case, the reflectance is also gradually, more specifically, stepwise decreased with an increase in the incident angle Φ in an extremely high wavelength band in which the reflectance is about 99.5% to 99.9%. The wavelength range is approximately 940nm or more and approximately 1000nm or less.

As described above, in the slow light waveguide 10 according to the present embodiment, the dependency of the beam width Δ θ of the outgoing light on the outgoing angle θ can be suppressed. Further, even if the emission angle θ changes, the beam width Δ θ of the emitted light can be kept narrow. This effect can be obtained when at least one of the mirror 30 and the mirror 40 in the slow light waveguide 10 has the following reflection spectrum. The reflection spectrum includes 1 maximum point and the 1 st inflection point and the 2 nd inflection point on the longer wavelength side than the maximum point in a wavelength band in which the reflectance is 90% or more corresponding to an incident angle where Φ is 0 °. The wavelength of the 1 st inflection point is shorter than the wavelength of the 2 nd inflection point. The wavelength λ of the light 22 propagating through the optical waveguide layer 20 is a wavelength equal to or higher than the maximum point and equal to or lower than the 1 st inflection point. This wavelength band may be included in a wavelength band of 0.8 μm or more and 1.2 μm or less that can be used for the LiDAR system described above, for example. One of the mirror 30 and the mirror 40 may show such a reflection spectrum, or both of the mirror 30 and the mirror 40 may show such a reflection spectrum. In the example shown in fig. 2, light is emitted from the mirror 30 and reflected by the mirror 40, but the present invention is not limited to this example. The light may be reflected by the mirror 30 and emitted from the mirror 40, or may be emitted from both the mirror 30 and the mirror 40.

In the present embodiment, the peak point P is located at the maximum point P of the specific reflection spectrum_LMAn inflection point is provided on the long wavelength side so that the change of the reflectance with respect to the change of the incident angle phi becomes gentle, and a region in which the reflectance changes gently is used. Therefore, the wavelength λ of the light 22 propagating in the optical waveguide layer 20 is the maximum point P_LM1 st inflection point P₁A wavelength represented by the following formula.

[ number 3]

(P_LM+P₁)/2＜λ＜P₁ (3)

< application example >

Fig. 15 is a diagram showing an example of the configuration of an optical scanning device 100 in which elements such as a beam splitter 90, a waveguide array 10A, a phase shifter array 80A, and a light source 130 are integrated on a circuit substrate (e.g., a chip). The light source 130 may be a light emitting element such as a semiconductor laser. The light source 130 in this example emits light of a single wavelength in free space at a wavelength λ. The optical splitter 90 branches light from the light source 130 and introduces the light into waveguides in the plurality of phase shifters. In the example shown in fig. 15, an electrode 62A and a plurality of electrodes 62B are provided on the chip. A control signal is supplied from the electrode 62A to the waveguide array 10A. Control signals are sent from the plurality of electrodes 62B to the plurality of phase shifters 80 in the phase shifter array 80A, respectively. The electrode 62A and the plurality of electrodes 62B may be connected to a control circuit, not shown, that generates the control signal. The control circuit may be provided on the chip shown in fig. 15 or on another chip in the optical scanning apparatus 100.

As shown in fig. 15, by integrating all the components on a chip, a wide range of light scanning can be realized with a small-sized apparatus. For example, all the components shown in fig. 15 can be integrated on a chip of about 2mm × 1 mm.

Fig. 16 is a schematic diagram showing a case where a beam of laser light or the like is irradiated from the optical scanning apparatus 100 to a far field and 2-dimensional scanning is performed. The 2-dimensional scan is performed by moving the beam spot 310 in the horizontal and vertical directions. For example, a 2-dimensional distance measurement image can be acquired by combining with a known TOF (Time Of Flight) method. The TOF method is a method of measuring a distance by calculating a time of flight of light by irradiating laser light and observing reflected light from an object.

Fig. 17 is a block diagram showing an example of the configuration of the LiDAR system 300 as an example of a light detection system capable of generating such a distance measurement image. The LiDAR system 300 is equipped with an optical scanning device 100, a light detector 400, signal processing circuitry 600, and control circuitry 500. The photodetector 400 detects light emitted from the optical scanning apparatus 100 and reflected from the object. The light detector 400 may be, for example, an image sensor having sensitivity to the wavelength λ of light emitted from the optical scanning apparatus 100, or a photodetector including a light receiving element such as a photodiode. The photodetector 400 outputs an electrical signal corresponding to the amount of received light. The signal processing circuit 600 calculates the distance to the object based on the electric signal output from the photodetector 400, and generates distance distribution data. The distance distribution data is data representing a 2-dimensional distribution of distances (i.e., a range image). The control circuit 500 is a processor that controls the optical scanning apparatus 100, the photodetector 400, and the signal processing circuit 600. The control circuit 500 controls the timing of irradiation of the light beam from the optical scanning apparatus 100 and the timing of exposure and signal reading of the photodetector 400, and instructs the signal processing circuit 600 to generate a ranging image.

In the 2-dimensional scan, the frame rate for obtaining the range image can be selected from, for example, 60fps, 50fps, 30fps, 25fps, 24fps, and the like, which are generally used for moving images. Further, if the application to the in-vehicle system is considered, the higher the frame rate, the more frequently the distance measurement image is acquired, and the obstacle can be detected with high accuracy. For example, when traveling at 60km/h, images can be acquired at a frame rate of 60fps for approximately 28cm of vehicle movement. At a frame rate of 120fps, images can be acquired for each approximately 14cm of vehicle movement. At a frame rate of 180fps, an image can be acquired for approximately 9.3cm of vehicle movement.

The time required to acquire 1 range image depends on the speed of the beam sweep. For example, in order to obtain an image with a resolution of 100 × 100 at 60fps, it is necessary to perform beam scanning with 1 spot at 1.67 μ s or less. In this case, the control circuit 500 controls emission of the light beam by the optical scanning device 100 and signal accumulation/readout by the photodetector 400 at an operation speed of 600 kHz.

Example of application to light-receiving apparatus

The light scanning apparatus of the present disclosure can also be used as a light receiving apparatus in substantially the same configuration. The light receiving device includes the same waveguide array 10A as the light scanning device, and a 1 st adjusting element that adjusts the direction of light that can be received. Each 1 st mirror 30 of the waveguide array 10A transmits light incident from the 3rd direction to the opposite side of the 1 st reflecting surface. Each optical waveguide layer 20 of the waveguide array 10A propagates the light transmitted through the 1 st mirror 30 in the 2 nd direction. The 1 st adjusting element changes at least 1 of the refractive index and thickness of the optical waveguide layer 20 and the wavelength of light in each waveguide element 10, thereby changing the direction of light that can be received. Further, in the case where the light receiving device includes the plurality of phase shifters 80 or 80a and 80b, which are the same as the light scanning device, and the 2 nd adjusting element that changes the phase difference of the light output from the plurality of waveguide elements 10 through the plurality of phase shifters 80 or 80a and 80b, respectively, the direction of the light that can be received can be changed in 2 dimensions.

For example, a light receiving device in which the light source 130 in the light scanning device 100 shown in fig. 15 is replaced with a receiving circuit can be configured. If light of wavelength lambda is directed towards the waveguide arrayIncident on column 10A, the light is sent out through the phase shifter array 80A toward the beam splitter 90, and finally collected at a location and sent to the receiving circuit. The intensity of the light collected to the one position can be said to represent the sensitivity of the light receiving device. The sensitivity of the light receiving device can be adjusted by the adjusting elements incorporated into the waveguide array and the phase shifter array 80A, respectively. In the light receiving device, for example, in fig. 4, the directions of wave vectors (thick arrows in the drawing) are opposite. The incident light has a light component in the direction in which the waveguide elements 10 extend (X direction in the figure) and a light component in the direction in which the waveguide elements 10 are arranged (Y direction in the figure). The sensitivity of the light component in the X direction can be adjusted by the adjustment element incorporated in the waveguide array 10A. On the other hand, the sensitivity of the light component in the alignment direction of the waveguide elements 10 can be adjusted by the adjustment element incorporated into the phase shifter array 80A. According to the phase difference delta phi of the light when the sensitivity of the light receiving device is maximum and the refractive index n of the optical waveguide layer 20_wAnd thickness d, theta and alpha shown in FIG. 4₀. This enables the direction of light incidence to be determined.

The above embodiments can be combined as appropriate.

Finally, the above optical devices are summarized as the following items.

The optical device according to item 1 includes: a 1 st mirror having a 1 st reflecting surface and extending in a 1 st direction; a 2 nd mirror having a 2 nd reflecting surface opposed to the 1 st reflecting surface and extending in the 1 st direction; and an optical waveguide layer located between the 1 st mirror and the 2 nd mirror to propagate light along the 1 st direction. The transmittance of the 1 st mirror is higher than that of the 2 nd mirror. A reflection spectrum of at least one of the 1 st mirror and the 2 nd mirror corresponding to light incident from a normal direction of a reflection surface is: the wavelength band having a reflectance of 90% or more includes a maximum point, and a 1 st inflection point and a 2 nd inflection point which are located on a longer wavelength side than the maximum point.

In this optical device, the reflectance of at least one of the 1 st mirror and the 2 nd mirror gradually decreases as the incident angle of light increases. This can suppress a beam width of light emitted from at least one of the 1 st mirror and the 2 nd mirror from changing depending on an emission angle.

The optical device according to item 2 is: in the optical device according to item 1, a wavelength at the 1 st inflection point is shorter than a wavelength at the 2 nd inflection point. The wavelength λ of the light propagating in the optical waveguide layer is a wavelength that is equal to or longer than the maximum point and equal to or shorter than the 1 st inflection point.

In this optical device, the reflectance of at least one of the 1 st mirror and the 2 nd mirror decreases in a stepwise manner as the incident angle of light increases. This can suppress the beam width of the outgoing light from varying depending on the outgoing angle.

The optical device according to item 3 is: the optical device according to claim 1 or 2, wherein the wavelength band is included in a range from 0.8 μm to 1.2 μm.

The light device can be adapted for use in a LiDAR system.

The optical device according to item 4 is: in the optical device according to any one of items 1 to 3, at least one of the 1 st mirror and the 2 nd mirror includes a distributed bragg reflector having a stacked structure.

In this optical device, the same effects as those of the optical device according to any one of items 1 to 3 can be obtained.

The optical device according to item 5 is: in the optical device according to item 4, the distributed bragg reflector is a chirped DBR.

In this optical device, the same effects as those of the optical device according to item 4 can be obtained.

The optical device according to item 6 is: in the optical device according to item 1, the 1 st mirror has the reflection spectrum.

In this optical device, it is possible to suppress a beam width of light emitted from the 1 st mirror from varying depending on an emission angle.

Industrial applicability

The optical scanning device and the optical receiving device in the present disclosure can be used for applications such as a laser radar system mounted on a vehicle such as an automobile, a UAV, or an AGV.

Description of reference numerals:

10 waveguide element and optical waveguide

11 optical waveguide

10A waveguide array

15. 15a, 15b, 15c, 15m grating

20 optical waveguide layer

22 dielectric member

30 st mirror

40 nd 2 reflection mirror

30es exit surface

30s 1 st reflecting surface

40s 2 nd reflecting surface

51 dielectric layer

62A, 62B, 62A, 62B electrode

73 multiple partition walls

80 phase shifter

80A phase shifter array

90 optical splitter

100 optical scanning device

111 connection region

112 non-connecting region

110 waveguide array driving circuit

130 light source

210 phase shifter array driving circuit

310 beam spot

400 photo detector

500 control circuit

600 signal processing circuit