Variable Optical Attenuator

Abstract

To enhance a response speed in a technique for changing a light amount of light to be output.SOLUTION: A variable optical attenuator comprises a spatial phase modulation element, a first optical transmission part, a second optical transmission part, and a control part. The spatial phase modulation element has a plurality of lattice elements each of which has a base part and a light reflection surface. According to a pitch and a displacement amount of a pattern of displacement to the base part of the plurality of lattice elements, phase modulation is executed to the light radiated to the light reflection surface of each lattice element, for generating diffraction light. The first optical transmission part transmits the first light, and emits the first light toward the light reflection surface of each lattice element. The second light transmission part transmits the second light by receiving the second light which is diffraction light being different from 0-th diffraction light generated by the phase modulation to the first light by the spatial phase modulation element. The control part controls displacement of the plurality of lattice elements to the base part, for increasing and reducing a light amount of the second light entering the second optical transmission part from the spatial phase modulation element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a variable optical attenuator and an optical switch. [Background technology]

[0002] BACKGROUND ART Conventionally, in the field of optical communication technology, devices using MEMS (Micro Electro Mechanical Systems) elements as optical control elements are known (for example, Patent Documents 1 and 2, etc.).

[0003] Known devices that use this MEMS element include optical attenuators (also called variable optical attenuators), which change the rate at which the amount of input light decreases from the amount of output light (also called the reduction rate) by changing the angle of reflection of light by changing the tilt angle of a mirror placed in part of the MEMS element, and devices that switch whether or not to emit output light in response to input light (also called optical switches).

[0004] A variable optical attenuator uses, for example, a MEMS element (also called a MEMS mirror) in which two optical fibers, a collimator lens, and a mirror are arranged. Specifically, light emitted from one of the two optical fibers, the input optical fiber, passes through the collimator lens, is reflected by the MEMS mirror, passes through the collimator lens again, and is coupled to the other optical fiber, the output optical fiber. Here, by controlling the tilt amount of the MEMS mirror, the irradiation position of the light with respect to the end of the output optical fiber is shifted, thereby generating a coupling loss of the light to the output optical fiber and adjusting the rate of reduction in the amount of light.

[0005] In an optical switch, for example, in a configuration similar to that of a variable optical attenuator, the tilt amount of the MEMS mirror is controlled to switch between irradiating and not irradiating light onto the end of the output optical fiber, thereby switching between output and not outputting light through the output optical fiber. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-85869 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-85870 Summary of the Invention [Problem to be solved by the invention]

[0007] However, to change the light intensity reduction rate in a variable optical attenuator using a MEMS mirror, or to switch the light output on and off in an optical switch using a MEMS mirror, it is necessary to mechanically tilt a single MEMS mirror.

[0008] For this reason, it takes a certain amount of time, such as 1 millisecond or more, to change the light intensity reduction rate in a variable optical attenuator using a MEMS mirror, or to switch on / off the light output in an optical switch using a MEMS mirror. Therefore, it is not easy to change the light intensity reduction rate multiple times in a variable optical attenuator using a MEMS mirror, or to switch on / off the light output multiple times in an optical switch using a MEMS mirror, in a very short time.

[0009] Therefore, there is room for improvement in terms of increasing the response speed when changing the rate of reduction of the light amount in a variable optical attenuator and when switching on and off the output of light in an optical switch.

[0010] That is, in the technology for changing the amount of light output by variable optical attenuators and optical switches, there is room for improvement in terms of increasing response speed.

[0011] The present invention has been made in view of the above-mentioned problems, and has an object to increase the response speed in a technique for changing the amount of light to be output. [Means for solving the problem]

[0012] To solve the above problems, a variable optical attenuator according to a first aspect includes a spatial phase modulator, a first optical transmission section, a second optical transmission section, and a control section. The spatial phase modulator has a plurality of grating elements, each having a base section and a light-reflecting surface, and generates diffracted light by performing phase modulation on light irradiated onto the light-reflecting surface of each of the plurality of grating elements according to the pattern pitch and amount of displacement of the plurality of grating elements relative to the base section. The first optical transmission section transmits a first light and outputs the first light toward the light-reflecting surface of each of the plurality of grating elements. The second optical transmission section receives second light, which is diffracted light different from the zero-order diffracted light generated by the phase modulation of the first light by the spatial phase modulator, and transmits the second light. The control section controls the displacement of the plurality of grating elements relative to the base section to increase or decrease the amount of the second light incident on the second optical transmission section from the spatial phase modulator. The control unit adjusts the rate of reduction in the amount of the second light incident on the second light transmission section from the spatial phase modulation element by changing the pitch of the displacement pattern and thereby shifting the position at which the second light is irradiated relative to the end of the second light transmission section.

[0014] No. 2 The variable optical attenuator according to the present invention comprises: 1 of A variable optical attenuator according to an embodiment, wherein the plurality of grating elements each extend along a first direction, have the light reflecting surface, and include a plurality of first reflecting portions arranged along a second direction perpendicular to the first direction, and are provided with a first optical element portion located between the first light transmitting portion and the spatial phase modulator and converting the cross-sectional shape of the light beam of the first light from a circular shape to an elongated shape along the second direction, thereby irradiating the first light onto the light reflecting surface of each of the plurality of first reflecting portions.

[0015] No. 3 The variable optical attenuator according to the present invention comprises: 1 of A variable optical attenuator according to the aspect, wherein the plurality of grating elements each have the light reflecting surface and include a plurality of second reflecting portions arranged in a matrix, and the first light from the first optical transmission portion is irradiated onto the light reflecting surface of each of the plurality of second reflecting portions.

[0016] No. 4 The variable optical attenuator according to the aspect of the present invention comprises first to second 3The variable optical attenuator according to any one of the above aspects includes a light absorber that is positioned on the optical path of the zero-order diffracted light generated by the spatial phase modulation element in response to the irradiation of the first light onto the plurality of grating elements, and that absorbs the light. [Effects of the Invention]

[0021] 1st to 3rd 4 In any of the variable optical attenuators according to the above aspects, for example, by controlling the displacement of the plurality of grating elements relative to the base portion, it is possible to increase or decrease the intensity of diffracted light incident from the spatial phase modulator to the second optical transmission portion. This makes it possible to quickly switch, for example, the ratio of the amount of light transmitted through the second optical transmission portion to the amount of light transmitted through the first optical transmission portion. As a result, it is possible to increase the response speed of the variable optical attenuator when changing the amount of light to be output.

[0022] No. 4 According to the variable optical attenuator according to this aspect, for example, the problem of zero-order diffracted light entering the second optical transmission section due to reflection or the like within the variable optical attenuator is less likely to occur. This can improve the accuracy of switching the ratio of the amount of second light transmitted through the second optical transmission section to the amount of first light transmitted through the first optical transmission section. Therefore, the accuracy of changing the amount of light output from the variable optical attenuator can be improved. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of the configuration of a variable optical attenuator according to the first embodiment. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of the configuration of the variable optical attenuator according to the first embodiment. [Figure 3] FIG. 3 is a diagram schematically illustrating an example of the configuration of the variable optical attenuator according to the first embodiment. [Figure 4] FIG. 4 is a plan view showing a schematic example of the configuration of a grating light valve applied to a spatial phase modulation element. [Figure 5]FIG. 5 is a cross-sectional view showing a schematic example of the configuration of a grating light valve applied to a spatial phase modulation element. [Figure 6] FIG. 6 is a cross-sectional view showing a schematic example of the configuration of a grating light valve applied to a spatial phase modulation element. [Figure 7] FIG. 7 is a diagram showing an example of the operation of a grating light valve applied to a spatial phase modulation element. [Figure 8] FIG. 8 is a diagram showing an example of the operation of a grating light valve applied to a spatial phase modulation element. [Figure 9] FIG. 9 is a diagram showing an example of the operation of a grating light valve applied to a spatial phase modulation element. [Figure 10] FIG. 10 is a diagram schematically illustrating an example of the configuration of a variable optical attenuator according to the second embodiment. [Figure 11] FIG. 11 is a plan view showing a schematic example of the configuration of a flat light valve applied to a spatial phase modulation element. [Figure 12] FIG. 12 is a cross-sectional view showing a schematic example of the configuration of one reflecting element and its surrounding area in a flat light valve applied to a spatial phase modulation element. [Figure 13] FIG. 13 is a cross-sectional view showing a schematic example of the configuration of one reflecting element and its surrounding area in a flat light valve applied to a spatial phase modulation element. [Figure 14] FIG. 14 is a diagram schematically illustrating an example of the configuration of the optical switch according to the third embodiment. [Figure 15] FIG. 15 is a diagram schematically illustrating an example of the configuration of the optical switch according to the third embodiment. [Figure 16] FIG. 16 is a diagram schematically illustrating an example of the configuration of the optical switch according to the fourth embodiment. [Figure 17] FIG. 17 is a diagram schematically illustrating an example of the configuration of the optical switch according to the fourth embodiment. [Figure 18] FIG. 18 is a diagram schematically illustrating an example of the configuration of the optical switch according to the fifth embodiment. [Figure 19] FIG. 19 is a diagram schematically illustrating an example of the configuration of the optical switch according to the fifth embodiment. [Figure 20] FIG. 20 is a diagram schematically illustrating an example of the configuration of the optical switch according to the sixth embodiment. [Figure 21] FIG. 21 is a diagram schematically illustrating an example of the configuration of the optical switch according to the sixth embodiment. [Figure 22] FIG. 22 is a diagram schematically illustrating an example of the configuration of the optical switch according to the seventh embodiment. [Figure 23] FIG. 23 is a diagram schematically illustrating an example of the configuration of the optical switch according to the seventh embodiment. [Figure 24] FIG. 24 is a diagram schematically illustrating an example of the configuration of the optical switch according to the eighth embodiment. [Figure 25] FIG. 25 is a diagram schematically illustrating an example of the configuration of the optical switch according to the eighth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] Various embodiments of the present invention will be described below with reference to the accompanying drawings. The components described in these embodiments are merely examples and are not intended to limit the scope of the present invention. In the drawings, parts having similar configurations and functions are designated by the same reference numerals, and redundant explanations will be omitted in the following description. Furthermore, in the drawings, the dimensions and numbers of each part are exaggerated or simplified as necessary for ease of understanding. Each figure includes a right-handed XYZ Cartesian coordinate system to explain the positional relationships of each element. Here, the X and Y axes extend along the diffraction grating surface (also referred to as the grating surface) P0 of the spatial phase modulator 4, 4A (described later), and the Z axis extends along the normal to the grating surface P0. In the following description, the direction of the arrowhead is referred to as the + (plus) direction, and the opposite direction is referred to as the - (minus) direction.

[0027] Unless otherwise specified, expressions indicating relative or absolute positional relationships (e.g., "in one direction," "along one direction," "parallel," "orthogonal," "center," "concentric," "coaxial," etc.) not only express that positional relationship exactly, but also express a state in which there is a relative displacement in terms of angle or distance within a range in which tolerance or equivalent functionality is obtained. Expressions indicating an equal state (e.g., "identical," "equal," "homogeneous," etc.) not only express a state in which there is strict quantitative equality, but also express a state in which there is a difference in which tolerance or equivalent functionality is obtained, unless otherwise specified. Expressions indicating shape (e.g., "square shape" or "cylindrical shape," etc.) not only express the shape exactly geometrically, but also express a shape with, for example, concaves and convexes and chamfers, within a range in which equivalent effects are obtained. The expressions "comprise," "include," "have," "includes," "includes," or "have" of one component are not exclusive expressions that exclude the presence of other components. Unless otherwise specified, "above" and "below" may include cases where two elements are in contact as well as cases where two elements are separated. Unless otherwise specified, "moving in a specific direction" may include not only moving parallel to this specific direction, but also moving in a direction that has a component in this specific direction.

[0028] 1. First Embodiment <1-1. Configuration of variable optical attenuator> 1 to 3 are diagrams each showing a schematic configuration example of a variable optical attenuator 100 according to the first embodiment. Fig. 1 shows a schematic configuration example of the variable optical attenuator 100 when viewed in a plane in the +Y direction, with respect to parts other than the control unit 10. Fig. 2 shows a schematic configuration example of the variable optical attenuator 100 when viewed in a plane in the +X direction, with respect to parts other than the control unit 10. Fig. 3 shows a schematic configuration example of the variable optical attenuator 100 when viewed in a plane in the -X direction, with respect to parts other than the control unit 10.

[0029] In FIGS. 1 and 2, the optical path of the first light L1, which is the path along which the first light L1 described below travels, is indicated by an arrow drawn with a dashed line. More specifically, the optical paths at the center and both ends of the light beam of the first light L1 are indicated by arrows drawn with a dashed line. In FIGS. 1 and 3, the optical path of the second light L2, which is the path along which the second light L2 described below travels, is indicated by an arrow drawn with a two-dot chain line. More specifically, the optical paths at the center and both ends of the light beam of the second light L2 are indicated by arrows drawn with a two-dot chain line. In FIG. 1, the optical path of the third light L3, which is the path along which the third light L3 described below travels, is indicated by an arrow drawn with a dashed line. More specifically, the optical paths at the center and both ends of the light beam of the third light L3 are indicated by arrows drawn with a dashed line.

[0030] The variable optical attenuator 100 is a device that can reduce the amount of light that is incident from outside the variable optical attenuator 100 (also referred to as incident light or input light) and output the reduced light to the outside of the variable optical attenuator 100.

[0031] As shown in FIGS. 1 to 3 , the variable optical attenuator 100 includes a first optical transmission section 1, a spatial phase modulation element 4, a second optical transmission section 5, and a control section 10. In the first embodiment, the variable optical attenuator 100 also includes a first optical element section 3. The variable optical attenuator 100 also includes an optical system 2. Here, for example, the first optical transmission section 1, the spatial phase modulation element 4, the second optical transmission section 5, the first optical element section 3, and the optical system 2 are fixed by various structures so that their relative positions and postures are constant. In the example of FIGS. 1 to 3 , light emitted from the first optical transmission section 1 passes through the optical system 2 and the first optical element section 3 in this order and is irradiated onto the spatial phase modulation element 4. Light generated by the spatial phase modulation element 4 passes through the first optical element section 3 and the optical system 2 in this order and is incident on the second optical transmission section 5, etc.

[0032] <<First optical transmission section 1>> The first optical transmission unit 1 is a section that transmits light (also referred to as first light) L1. The first optical transmission unit 1 transmits, for example, incident light (input light) incident from outside the variable optical attenuator 100 as the first light L1. For example, light having a wavelength λ is used as the first light L1. An optical fiber or the like is used as the first optical transmission unit 1. The optical fiber has, for example, a core and a cladding that has a lower refractive index than the core and is positioned so as to cover the periphery of the core. The optical fiber used in the first optical transmission unit 1 can transmit the first light L1 along the longitudinal direction within the core. Furthermore, the first optical transmission unit 1 emits the first light L1 toward the spatial phase modulation element 4. For example, the first light L1 is emitted at a predetermined divergence angle from a longitudinal end (also referred to as a first end) 1e of the optical fiber constituting the first optical transmission unit 1.

[0033] <<Optical system 2>> The optical system 2 is located between the first optical transmission unit 1, the second optical transmission unit 5, and the first optical element unit 3. The optical system 2 converts the first light L1 emitted from the first end 1e of the optical fiber at a predetermined divergence angle into parallel light. A cross section of this parallel light perpendicular to the light propagation direction is, for example, circular. An optical lens such as a collimator lens is used as the optical system 2. The first light L1 converted into parallel light by the optical system 2 enters the first optical element unit 3.

[0034] <<First optical element portion 3>> The first optical element section 3 is located between the first light transmission section 1 and the spatial phase modulation element 4. The first optical element section 3 is also located between the spatial phase modulation element 4 and the second light transmission section 5. In the examples of FIGS. 1 to 3, the optical system 2 and the first optical element section 3 are arranged in this order between the first light transmission section 1 and the second light transmission section 5 and the spatial phase modulation element 4.

[0035] The first optical element unit 3 converts the cross-sectional shape of the first light L1 beam from a circular shape to an elongated shape and irradiates the first light L1 beam onto the spatial phase modulator 4. Here, the elongated shape in the cross-sectional shape of the first light L1 beam is an elongated shape along the +X direction as a second direction, which will be described later. As a result, the first light L1 beam whose cross-sectional shape is an elongated shape along the +X direction as the second direction is irradiated onto the spatial phase modulator 4. The cross-sectional shape of the beam of light is the shape of a cross section of the beam of light perpendicular to the traveling direction of the light.

[0036] Furthermore, the first optical element unit 3 converts the light generated by the spatial phase modulation element 4 into parallel light having a circular cross section and emits it toward the second optical transmission unit 5. The light generated by the spatial phase modulation element 4 may be second light L2, which will be described later, or third light L3, which will be described later.

[0037] For example, an optical lens such as a cylinder lens (also called a cylindrical lens) is applied to the first optical element portion 3. The cylinder lens has, for example, a semi-cylindrical shape (also called a semi-cylindrical shape).

[0038] <<Spatial Phase Modulator 4>> The spatial phase modulation element 4 performs phase modulation on the first light L1. This allows the spatial phase modulation element 4 to generate diffracted light toward the second light transmission section 5, for example. For example, a grating light valve, which is a type of optical phase array, as shown in FIGS. 4 to 6 is applied to the spatial phase modulation element 4. FIG. 4 is a plan view schematically showing an example of the configuration of a grating light valve applied to the spatial phase modulation element 4. FIG. 4 also shows a schematic view of a portion of the configuration of the grating light valve. FIGS. 5 and 6 are cross-sectional views schematically showing an example of the configuration of a grating light valve. FIGS. 7 to 9 are diagrams schematically showing an example of the operation of a grating light valve applied to the spatial phase modulation element 4. In Figures 4 to 9, the first direction along the main surface (also called the first main surface) F1 on the +Z direction side of the substrate 41s that constitutes the grating light valve is the +Y direction, the second direction along the first main surface F1 and perpendicular to the +Y direction is the +X direction, and the third direction along the normal to the first main surface F1 is the -Z direction.

[0039] The grating light valve has, for example, a base portion 41 and a plurality of ribbon-shaped portions (also called ribbons) 42.

[0040] The base portion 41 has, for example, a substrate 41s and an electrode (also referred to as a first reference electrode) 41e. The substrate 41s is, for example, a plate-shaped substrate such as a silicon substrate. The first reference electrode 41e is located along a first main surface F1 of the substrate 41s. The first reference electrode 41e is, for example, a metal film formed on the first main surface F1 of the substrate 41s.

[0041] The plurality of ribbons 42 are located on the first main surface F1 of the substrate 41s. Each of the plurality of ribbons 42 has an elongated ribbon-like shape extending along the +Y direction as a first direction. For example, as shown in FIG. 4, each ribbon 42 has a rectangular shape with a longitudinal direction along the +Y direction as a first direction and a lateral direction along the +X direction as a second direction. The length (also referred to as width) of each ribbon 42 in the lateral direction is set to, for example, approximately 2.0 micrometers (μm) to 25.5 μm. The length of each ribbon 42 in the longitudinal direction is set to, for example, approximately 1 millimeter (mm) to 3 mm. The plurality of ribbons 42 are not in contact with each other, and a small gap exists between two adjacent ribbons 42 among the plurality of ribbons 42.

[0042] A fine structure made of, for example, an amorphous silicon nitride film or the like is applied to each ribbon 42. The plurality of ribbons 42 are aligned along the +X direction, which is the second direction. The number of the plurality of ribbons 42 is set to, for example, about 100 to 4000.

[0043] Each ribbon 42 has, for example, a long, narrow strip-shaped reflective portion (also referred to as a first reflective portion) 42r as a grating element, and a connecting portion 42c. In other words, the grating light valve has, for example, a base portion 41 and a plurality of first reflective portions 42r as a plurality of grating elements. In each ribbon 42, the first reflective portion 42r is located in the center in the +Y direction as a first direction, and the connecting portions 42c are located at both ends in the +Y direction as the first direction. In other words, in each ribbon 42, the first connecting portion 42c, the first reflective portion 42r, and the second connecting portion 42c are located in this order in the +Y direction as a first direction.

[0044] Each of the multiple first reflecting portions 42r extends along the +Y direction as a first direction. The multiple first reflecting portions 42r are arranged along the +X direction as a second direction. Each of the multiple first reflecting portions 42r has a surface that specularly reflects light (also referred to as a light reflecting surface). The light reflecting surface is located, for example, on the side of the first reflecting portion 42r opposite to the base portion 41. The light reflecting surface is a surface parallel to the XY plane. Here, for example, the surface of each ribbon 42 is configured to be coated with a thin film of a metal such as aluminum that specularly reflects light. As a result, for example, the surface of the first reflecting portion 42r of each ribbon 42 functions as a light reflecting surface. The light reflecting surface of each of the multiple first reflecting portions 42r is irradiated with the first light L1 that has been emitted from the first optical transmission unit 1 and passed through the optical system 2 and the first optical element unit 3. In other words, the first optical transmission unit 1 emits the first light L1 toward the light reflecting surface of each of the multiple first reflecting units 42r. The light reflecting surface of each of the first reflecting units 42r can reflect the first light L1. The thin metal film that forms the surface of the first reflecting unit 42r of each ribbon 42 functions as an electrode (also referred to as a first movable electrode).

[0045] The connecting portion 42c is a portion connected to the base portion 41. For example, as shown in Fig. 5, each ribbon 42 includes a connecting portion 42c connected to the base portion 41 at both ends in the Y direction. In other words, each ribbon 42 is connected to the first main surface F1 of the base portion 41 at both ends in the Y direction. In further other words, both ends of each first reflecting portion 42r are connected to the base portion 41 via the connecting portion 42c.

[0046] Here, the multiple first reflecting portions 42r face the base portion 41 with the space S1 between them. More specifically, each first reflecting portion 42r faces the first reference electrode 41e of the base portion 41 with the space S1 between them. In other words, the first reference electrode 41e of the base portion 41 faces the multiple first reflecting portions 42r. From another perspective, the ribbon 42, which is a structure including the first reflecting portion 42r and two connecting portions 42c connecting both ends of the first reflecting portion 42r to the base portion 41, is installed over the substrate 41s so as to straddle the first reference electrode 41e without contacting the first reference electrode 41e.

[0047] Each ribbon 42 is flexible. Here, for example, when a potential difference is applied between the first reflecting portion 42r, which functions as a first movable electrode, and the first reference electrode 41e, an electrostatic force is generated between the first reflecting portion 42r and the first reference electrode 41e, attracting the first reflecting portion 42r to the first reference electrode 41e. This electrostatic force causes the ribbon 42 to bend. FIG. 5 illustrates the ribbon 42 in an unbent state (also referred to as an initial state), and FIG. 6 illustrates the ribbon 42 in a bent state. As shown in FIGS. 5 and 6, the ribbon 42 is displaced in the Z direction by bending. Here, for example, based on the position of the first reflecting portion 42r in the initial state in which the ribbon 42 is unbent, bending the ribbon 42 causes the first reflecting portion 42r to be displaced in the −Z direction, which serves as a third direction.

[0048] The grating light valve displaces the first reflecting portions 42r by an amount corresponding to a signal from the control unit 10, by bending the ribbon 42 with an electrostatic force corresponding to the signal. The grating light valve has, for example, a CMOS (Complementary Metal Oxide Semiconductor) driver (not shown) or the like for individually applying a potential to each of the plurality of first reflecting portions 42r in response to the signal from the control unit 10.

[0049] In the first embodiment, for example, the control unit 10 can adjust the potential difference applied between the first reflecting portion 42r and the first reference electrode 41e for each of the multiple ribbons 42, thereby bending the ribbon 42 using the electrostatic force between the first reflecting portion 42r and the first reference electrode 41e, and controlling the displacement of the first reflecting portion 42r relative to the base portion 41.

[0050] For example, a first potential serving as a fixed reference, such as 0 volts (V) to −12 V, is applied to the first reference electrode 41e, and a second potential equal to or greater than the first potential is applied to each of the multiple first reflecting portions 42r. The second potential is set, for example, so that the difference (potential difference) between the second potential and the first potential is a desired potential difference within a predetermined range, such as 0 V to 25 V. For example, the second potential is variable. For example, different second potentials are applied to the multiple first reflecting portions 42r. This allows the amount of displacement of the first reflecting portions 42r to be freely varied among the multiple ribbons 42. After the ribbon 42 is deflected by an electrostatic force corresponding to the potential difference applied between the first reflecting portion 42r and the first reference electrode 41e, when the potential difference applied between the first reflecting portion 42r and the first reference electrode 41e becomes substantially zero, the ribbon 42 returns to its initial, undeflected state due to the elastic force of the ribbon 42. At this time, the displacement amount of the first reflecting portion 42r returns to zero.

[0051] 7 illustrates a reference state (also referred to as the reference state) in which the displacements of the multiple first reflecting portions 42r in the multiple ribbons 42 are equal and zero. In this case, the light-reflecting surfaces of the multiple first reflecting portions 42r are positioned along the grating plane P0, and the grating light valve functions as a mirror. Here, the grating plane P0 of the grating light valve is an imaginary plane that extends along the XY plane. In FIG. 7, the grating plane P0 is indicated by a straight line segment drawn with a thin two-dot chain line, and the normal line L0 to the grating plane P0 is indicated by a straight line segment drawn with a thin one-dot chain line.

[0052] Here, when the first light L1 is irradiated onto the plurality of first reflecting portions 42r, specularly reflected light (also referred to as fourth light) L4 corresponding to the first light L1 is emitted from the plurality of first reflecting portions 42r. Regarding this state, in FIG. 7, an example of the optical path of the first light L1 is schematically shown by an arrow drawn with a dashed line, and an example of the optical path of the fourth light L4, which is the path along which the fourth light L4 travels, is schematically shown by an arrow drawn with a broken line. Here, as shown in FIG. 7, the angle (also referred to as the angle of incidence or the first angle) formed between the path (also referred to as the first optical path) Lp1 of the first light L1 along the direction in which the first light L1 travels as it is irradiated onto the grating light valve serving as the spatial phase modulator 4 functioning as a mirror and the normal L0 to the grating surface P0 is defined as θ1. Furthermore, the angle (also referred to as the specular reflection angle or the fourth angle) formed between the path (also referred to as the fourth optical path) Lp4 of the specularly reflected light (fourth light) L4, which is emitted by specularly reflecting the first light L1 off the grating light valve (spatial phase modulator 4) functioning as a mirror, and the normal L0 of the grating surface P0 is θ4. Here, as shown in FIG. 7, if the first optical path Lp1 is tilted in a counterclockwise direction around a virtual rotation axis parallel to the Y axis with respect to the normal L0, the incident angle θ1 is considered to be a positive angle. If the fourth optical path Lp4 is tilted in a clockwise direction around a virtual rotation axis parallel to the Y axis with respect to the normal L0, the fourth angle θ4 is considered to be a positive angle. In this case, the incident angle (first angle) θ1 and the specular reflection angle (fourth angle) θ4 are the same.

[0053] 8 and 9 each illustrate a state in which the displacement of the first reflecting portions 42r changes periodically in the X direction so that the plurality of first reflecting portions 42r form a sawtooth pattern, and the grating light valve functions as a blazed diffraction grating. In FIGS. 8 and 9, the grating plane P0 is indicated by a straight line segment drawn with a thin, two-dot chain line, and the normal line L0 of the grating plane P0 is indicated by a straight line segment drawn with a thin, one-dot chain line. Also, for convenience, each of FIGS. 8 and 9 includes the grating pitch Δ (also referred to as the grating pitch), which is the period of displacement in the +X direction (the second direction) of the blazed diffraction grating, and the depth Φ (also referred to as the blaze depth) of the sawtooth pattern of the blazed diffraction grating in the -Z direction (the third direction). 8 and 9, an example of the optical path of the first light L1 is schematically shown by an arrow drawn with a dashed line, an example of the optical path of the second light L2 (described later) is schematically shown by an arrow drawn with a dashed line, and Fig. 9 shows an example of the optical path of the third light L3 (described later) by an arrow drawn with a dashed line.

[0054] The grating pitch Δ is the same but the blaze depth Φ is different between the state shown in Figure 8 and the state shown in Figure 9. The grating light valve can function as a blazed diffraction grating with a variable grating pitch Δ and blaze depth Φ, for example, by controlling the amount of deflection of the multiple ribbons 42 by controlling the second potential applied to each of the multiple first reflecting portions 42r. In other words, the grating light valve can function as a blazed diffraction grating with a different grating pitch Δ and blaze depth Φ by changing the amount of displacement of each of the multiple first reflecting portions 42r relative to the base portion 41.

[0055] In the first embodiment, as shown in FIGS. 1 and 2 , the first light L1, whose cross-sectional shape has been converted into an elongated shape by the first optical element unit 3, is irradiated onto the light-reflecting surfaces of the plurality of first reflecting portions 42r serving as the plurality of grating elements. More specifically, the first light L1, whose cross-sectional shape has been converted into an elongated shape by the first optical element unit 3, is irradiated onto the central portions in the +Y direction (the first direction) of the plurality of first reflecting portions 42r serving as the plurality of grating elements. In other words, the first light L1, whose cross-sectional shape has been converted into an elongated shape by the first optical element unit 3, is irradiated onto the plurality of first reflecting portions 42r serving as the plurality of grating elements. Therefore, the first light L1, whose cross-sectional shape has been converted into an elongated shape by the first optical element unit 3, is irradiated onto a linear or band-like region that is approximately centered in the −Y direction (the first direction) of the plurality of first reflecting portions 42r serving as the plurality of grating elements.

[0056] Here, the blazed diffraction grating can generate diffracted light by applying phase modulation to the irradiated light in accordance with the grating pitch Δ of the sawtooth pattern and the blaze depth Φ. Therefore, the grating light valve can apply phase modulation to the light (specifically, the first light L1) irradiated onto the light-reflecting surface of each of the first reflecting portions 42r in accordance with the pitch and amount of displacement of the first reflecting portions 42r relative to the base portion 41 as the grating elements. This allows the grating light valve to generate diffracted light. The pitch of the displacement pattern is the repetition period in the +X direction, which is the second direction of the displacement of the first reflecting portions 42r relative to the base portion 41, and corresponds to the grating pitch Δ.

[0057] Now, let us assume that the blaze depth Φ of a grating light valve serving as a spatial phase modulator 4 functioning as a blazed diffraction grating is set to half the wavelength λ of the first light L1 (=λ / 2). Here, as shown in Fig. 8, the angle (incidence angle or first angle) formed between the path (first optical path) Lp1 of the first light L1 irradiated onto the grating light valve serving as a spatial phase modulator 4 functioning as a blazed diffraction grating along the direction in which the first light L1 travels and the normal L0 to the grating surface P0 is defined as θ1. Furthermore, the grating light valve serving as a blazed diffraction grating applies phase modulation to the first light L1, resulting in diffracted light (also referred to as second light) L2. The angle (also referred to as the first exit angle or second angle) formed between the path (also referred to as the second optical path) Lp2 of the second light L2 along the direction in which the second light L2 travels and the normal L0 to the grating surface P0 is defined as θ2. The diffracted light as the second light L2 is a diffracted light of a desired order other than the zeroth-order diffracted light. Here, as shown in Fig. 8, if the first optical path Lp1 is inclined in a direction rotating counterclockwise around a virtual rotation axis parallel to the Y axis with respect to the normal line L0, the incident angle θ1 is a positive angle, and if the second optical path Lp2 is inclined in a direction rotating clockwise around a virtual rotation axis parallel to the Y axis with respect to the normal line L0, the first exit angle θ2 is a positive angle. In this case, the relationship between the incident angle (first angle) θ1 and the first exit angle (second angle) θ2 is expressed by the following equation (1), using the wavelength λ of the first light L1 and the grating pitch Δ.

[0058] θ2=(λ / Δ)+θ1 ···(1).

[0059] Here, as shown in Fig. 8, in a grating light valve serving as a spatial phase modulator 4 functioning as a blazed diffraction grating, if the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2), the diffraction efficiency will be maximized. In other words, the amount of second light L2 relative to the amount of first light L1 will be maximized. In Fig. 8, to show the relationship in light amount between the first light L1 and the second light L2, the dashed-dotted arrow indicating the first optical path Lp1 and the dashed-two-dotted arrow indicating the second optical path Lp2 are both drawn with the same thickness.

[0060] 1 and 3, the second light L2 generated by the grating light valve serving as the spatial phase modulation element 4 passes through the first optical element unit 3 and the optical system 2 in this order and is incident on the second light transmission unit 5. At this time, the second light L2 generated by the spatial phase modulation element 4 is converted into parallel light having a circular cross section by the first optical element unit 3, and the second light L2 converted into parallel light is collected by the optical system 2 and incident on a second end 5e (described later) of the second light transmission unit 5. Here, the first exit angle (second angle) θ2 of the second light L2 is set so that the second light L2 enters the second light transmission unit 5. In other words, the grating pitch Δ that defines the first exit angle (second angle) θ2 is set to a predetermined value corresponding to the wavelength λ of the first light L1 so that the second light L2 enters the second light transmission unit 5.

[0061] On the other hand, as shown in FIG. 9, in a grating light valve functioning as a spatial phase modulator 4 as a blazed diffraction grating, when the blaze depth Φ deviates from half the wavelength λ (=λ / 2) of the first light L1, the diffraction efficiency decreases. As a result, the amount of second light L2 decreases relative to the amount of first light L1. In this case, the amount of zero-order diffracted light (also referred to as third light) L3 generated in the grating light valve functioning as a spatial phase modulator 4 as a blazed diffraction grating increases. In FIG. 9, to show the relationship in light amount among the first light L1, second light L2, and third light L3, the dashed-dotted arrow indicating the first light path Lp1 is drawn with the thickest thickness, the dashed-dotted arrow indicating the second light path Lp2 is drawn with a medium thickness, and the dashed-dotted arrow indicating the third light path Lp3 is drawn with the thinnest thickness. Here, for example, when the grating pitch Δ of the sawtooth pattern is constant, if the amount of light of the first light L1 is constant, the amount of light of the second light L2 decreases and the amount of light of the third light L3 increases depending on the deviation from half the value (=λ / 2) of the wavelength λ of the first light L1 at the blaze depth Φ.

[0062] Here, as shown in FIG. 9, the zeroth-order diffracted light (third light) L3 generated by phase-modulating the first light L1 using the grating light valve (spatial phase modulator 4) functioning as a blazed diffraction grating is referred to as a path Lp3 of the third light L3 along the traveling direction of the third light L3 (also referred to as a third optical path). The angle formed by the path Lp3 and the normal L0 to the grating surface P0 is referred to as θ3 (also referred to as a second exit angle or third angle). Here, as shown in FIG. 9, if the third optical path Lp3 is tilted in a clockwise direction about a virtual rotation axis parallel to the Y-axis with respect to the normal L0, the incident angle θ3 is a positive angle. In this case, the incident angle (first angle) θ1 and the second exit angle (third angle) θ3 are the same. In other words, the first optical path Lp1 of the first light L1 and the third optical path Lp3 of the third light L3 are rotationally symmetric with respect to the normal L0 to the grating surface P0.

[0063] 1, the third light L3 generated by the grating light valve serving as the spatial phase modulation element 4 passes through the first optical element unit 3 and the optical system 2 in this order and does not enter the second end 5e of the second light transmission unit 5. In other words, for example, the second light L2 enters the second light transmission unit 5, but the third light L3 does not enter the second light transmission unit 5. At this time, the third light L3 generated by the grating light valve serving as the spatial phase modulation element 4 is converted into parallel light having a circular cross section by the first optical element unit 3, and the third light L3 converted into parallel light is focused by the optical system 2 at a position different from the second end 5e, which will be described later, of the second light transmission unit 5.

[0064] <<Second optical transmission section 5>> The second light transmission section 5 is a section that transmits incident light. Light emitted from the spatial phase modulation element 4 in response to irradiation of the first light L1 onto each light reflecting surface of the plurality of first reflecting sections 42r in the spatial phase modulation element 4 is incident on the second light transmission section 5. In the first embodiment, second light L2 emitted from the spatial phase modulation element 4 in response to irradiation of the first light L1 is incident on the second light transmission section 5. Here, second light L2, which is diffracted light different from the zero-order diffracted light generated by phase modulation of the first light L1 by the spatial phase modulation element 4, is incident on the second light transmission section 5. In this case, the second light transmission section 5 transmits the incident second light L2.

[0065] The second optical transmission section 5 transmits the second light L2 as light to be emitted to the outside of the variable optical attenuator 100 (also referred to as emitted light or output light). In this case, the first light L1 transmitted by the first optical transmission section 1 and the second light L2 transmitted by the second optical transmission section 5 each have the same wavelength λ. As with the first optical transmission section 1, an optical fiber or the like is applied to the second optical transmission section 5. The optical fiber applied to the second optical transmission section 5 has an end section (also referred to as a second end section) 5e in the longitudinal direction to which the second light L2 is incident, and can transmit the second light L2 along the longitudinal direction within the core.

[0066] <<Control unit 10>> The control unit 10 can control the operation of the spatial phase modulation element 4. Specifically, the control unit 10 can control the displacement of a plurality of first reflecting portions 42r as a plurality of grating elements relative to the base portion 41 of the spatial phase modulation element 4. The control unit 10 can increase or decrease the amount of second light L2 incident on the second light transmission unit 5 from the grating light valve as the spatial phase modulation element 4 by controlling the displacement of the plurality of first reflecting portions 42r relative to the base portion 41. This makes it possible to quickly switch, for example, the ratio of the amount of second light L2 transmitted by the second light transmission unit 5 to the amount of first light L1 transmitted by the first light transmission unit 1. Therefore, the variable optical attenuator 100 can improve the response speed when changing the amount of light to be output.

[0067] For example, in a grating light valve serving as a spatial phase modulator 4 functioning as a blazed diffraction grating, the control unit 10 controls the amount of displacement of the plurality of first reflecting portions 42r relative to the base portion 41 while maintaining the pitch of the displacement pattern of the plurality of first reflecting portions 42r relative to the base portion 41, thereby increasing or decreasing the amount of second light L2 incident on the second light transmitting unit 5 from the grating light valve serving as the spatial phase modulator 4. Here, maintaining the pitch of the displacement pattern corresponds to maintaining the grating pitch Δ that defines the repeated sawtooth-shaped displacement pattern. Controlling the amount of displacement of the plurality of first reflecting portions 42r relative to the base portion 41 corresponds to controlling the blaze depth Φ that defines the depth of the repeated sawtooth-shaped displacement pattern.

[0068] Specifically, for example, as shown in Figures 8 and 9, the control unit 10 can increase or decrease the amount of second light L2 incident on the second optical transmission unit 5 from the grating light valve as the spatial phase modulation element 4 by controlling the grating light valve as the spatial phase modulation element 4 functioning as a blazed diffraction grating to adjust the blaze depth Φ while maintaining the grating pitch Δ.

[0069] Here, for example, if the relationship between the blaze depth Φ and the ratio of the amount of the second light L2 transmitted through the second light transmission unit 5 to the amount of the first light L1 transmitted through the first light transmission unit 1 is known in advance, the blaze depth Φ can be adjusted by the control unit 10 to control the ratio of the amount of the second light L2 transmitted through the second light transmission unit 5 to the amount of the first light L1 transmitted through the first light transmission unit 1. The ratio of the amount of the second light L2 transmitted through the second light transmission unit 5 to the amount of the first light L1 transmitted through the first light transmission unit 1 may be defined, for example, by a value obtained by dividing the amount of the second light L2 by the amount of the first light L1, or by a value obtained by dividing the difference between the amount of the first light L1 and the amount of the second light L2 by the amount of the first light L1. For example, the value obtained by dividing the difference between the light intensity of the first light L1 and the light intensity of the second light L2 by the light intensity of the first light L1 corresponds to the rate of decrease (also called the reduction rate) from the light intensity of the first light L1 transmitted by the first optical transmission section 1 to the light intensity of the second light L2 transmitted by the second optical transmission section 5.

[0070] The control unit 10 is configured to include, for example, a processor such as a CPU (Central Processing Unit), a memory and a storage unit, or an FPGA (Field Programmable Gate Array). The storage unit may be, for example, a non-volatile storage medium that stores a program executable by the CPU or the like. The control unit 10 controls the operation of the spatial phase modulation element 4 in response to, for example, a signal or information from a control device 200 external to the variable optical attenuator 100. The signal or information input from the control device 200 to the control unit 10 includes, for example, a signal or information indicating the amount of displacement of each first reflecting portion 42r relative to the base portion 41 of the spatial phase modulation element 4.

[0071] The control device 200 may be, for example, a personal computer having a CPU, a storage unit, or other such various computers. The control device 200 generates information indicating the amount of displacement of each first reflecting portion 42r relative to the base portion 41 of the spatial phase modulation element 4, in accordance with the surface shape (specifically, the grating pitch Δ and the blaze depth Φ, etc.) of the blazed diffraction grating, which corresponds to the ratio of the amount of the second light L2 transmitted through the second light transmission unit 5 to the amount of the first light L1 transmitted through the first light transmission unit 1 in the variable optical attenuator 100. Here, the relationship between the ratio of the amount of the second light L2 transmitted through the second light transmission unit 5 to the amount of the first light L1 transmitted through the first light transmission unit 1 and the blaze depth Φ can be determined, for example, by calculation using a formula related to the phase modulation of light by a blazed diffraction grating, simulation, or experiment using the configuration of the variable optical attenuator 100.

[0072] Incidentally, for example, in the variable optical attenuator using the MEMS mirror described in the background art, the rate of decrease in the amount of output light relative to the amount of input light is adjusted by adjusting the tilt amount of the MEMS mirror, which is larger than that of the first reflecting portion 42r in the variable optical attenuator 100 according to the first embodiment. In contrast, in the variable optical attenuator 100 according to the first embodiment, for example, each of the multiple first reflecting portions 42r as multiple grating elements is minute, so the amount of displacement can be controlled quickly and accurately. This allows, for example, the amount of output light to be changed quickly and accurately.

[0073] Furthermore, for example, in the variable optical attenuator using a MEMS mirror described in the background art, the tilt amount of the MEMS mirror is controlled to shift the position where light is irradiated onto the end of the output optical fiber, thereby adjusting the reduction rate of the amount of output light relative to the amount of input light. For this reason, for example, when irradiating light onto the edge of the end of the output optical fiber, fluctuations in the amount of light near the outer edge of the light beam irradiated onto the end of the output optical fiber make it difficult to control the reduction rate of the amount of output light relative to the amount of input light. Therefore, in the variable optical attenuator using a MEMS mirror described in the background art, the range in which the reduction rate of the amount of output light relative to the amount of input light can be controlled with high precision is limited. In contrast, the variable optical attenuator 100 according to the first embodiment can reduce the amount of second light L2 incident on the second optical transmission unit 5 relative to the amount of first light L1, for example, without moving the position where the second light L2 is irradiated onto the second end 5e of the second optical transmission unit 5. This makes it possible to set a wide range in which the rate of decrease in the amount of the second light L2 as output light relative to the amount of the first light L1 as input light can be controlled with high precision.

[0074] <<Modification of the First Embodiment>> In the first embodiment, the amount of second light L2 incident on the second light transmission section 5 from the grating light valve serving as the spatial phase modulation element 4 was increased or decreased by adjusting the blaze depth Φ while maintaining the grating pitch Δ in the grating light valve serving as the spatial phase modulation element 4. Alternatively, the grating pitch Δ in the grating light valve serving as the spatial phase modulation element 4 may be changed to shift the irradiation position of light on the second end 5e of the second light transmission section 5 (e.g., the end of the optical fiber on the output side), thereby adjusting the reduction rate of the amount of output light relative to the amount of input light. In this case, although it remains difficult to control the reduction rate of the amount of output light relative to the amount of input light due to fluctuations in the amount of light near the outer edge of the light beam irradiated on the second end 5e of the second light transmission section 5, compared to, for example, the variable optical attenuator using a MEMS mirror described in the background art, this has the advantage of being able to quickly change the amount of output light. 1, the variable optical attenuator 100 may include a light-absorbing object (also referred to as a light absorber) 6 located on the optical path of the zeroth-order diffracted light (third light L3) generated by a grating light valve serving as the spatial phase modulation element 4 in response to irradiation of the first light L1 onto the plurality of first reflecting portions 42r. This reduces the likelihood of the zeroth-order diffracted light entering the second optical transmission unit 5 due to reflection or the like within the variable optical attenuator 100. This may improve the accuracy of switching the ratio of the amount of the second light L2 transmitted by the second optical transmission unit 5 to the amount of the first light L1 transmitted by the first optical transmission unit 1. Therefore, the variable optical attenuator 100 may improve the accuracy of changing the amount of output light.

[0075] 1, an example of an area where the light absorber 6 is disposed is surrounded by a rectangle drawn with thin two-dot chain lines. For example, a black body using chromium or the like can be used as the light absorber 6. The light absorber 6 is fixed to the first light transmission part 1, the second light transmission part 5, etc. by various structures, for example.

[0076] <1-2. Summary of the First Embodiment> As described above, in the variable optical attenuator 100 according to the first embodiment, for example, the control unit 10 can increase or decrease the amount of second light L2 incident on the second light transmission unit 5 from the grating light valve serving as the spatial phase modulation element 4 by controlling the displacement of the plurality of first reflecting units 42r relative to the base unit 41. This makes it possible to quickly switch, for example, the ratio of the amount of second light L2 transmitted through the second light transmission unit 5 to the amount of first light L1 transmitted through the first light transmission unit 1. Therefore, in the variable optical attenuator 100, the response speed in changing the amount of light to be output can be increased.

[0077] <2. Other embodiments> The present invention is not limited to the first embodiment described above, and various modifications and improvements can be made without departing from the gist of the present invention.

[0078] <2-1. Second embodiment> In the first embodiment, for example, the spatial phase modulation element 4 may be changed to a spatial phase modulation element 4A in which a planar light valve, which is a type of optical phase array, is applied instead of the grating light valve.

[0079] Fig. 10 is a diagram schematically illustrating an example of the configuration of a variable optical attenuator 100A according to the second embodiment. In Fig. 10, as in Fig. 1, an example of an optical path of the first light L1 is indicated by an arrow drawn with a dashed line, an example of an optical path of the second light L2 is indicated by an arrow drawn with a dashed line, and an example of an optical path of the third light L3 is indicated by an arrow drawn with a dashed line. Specifically, the optical paths at the center and both ends of the light beam of the first light L1 are indicated by arrows drawn with a dashed line, the optical paths at the center and both ends of the light beam of the second light L2 are indicated by arrows drawn with a dashed line, and the optical paths at the center and both ends of the light beam of the third light L3 are indicated by arrows drawn with a dashed line.

[0080] The variable optical attenuator 100A is based on the variable optical attenuator 100 according to the first embodiment, except that the spatial phase modulation element 4 is changed to a spatial phase modulation element 4A to which a planar light valve is applied, and the first optical element unit 3 is deleted. The first optical transmission unit 1, spatial phase modulation element 4A, second optical transmission unit 5, and optical system 2 are fixed, for example, by various structures so that their relative positions and orientations are constant.

[0081] Here, the first light L1 emitted from the first light transmission unit 1 is converted into parallel light by the optical system 2, and the first light L1 converted into parallel light is irradiated onto the spatial phase modulation element 4A. The second light L2 in the form of parallel light generated by the spatial phase modulation element 4A is collected by the optical system 2 and incident on the second end 5e of the second light transmission unit 5. The third light L3 in the form of parallel light generated by the spatial phase modulation element 4A is collected by the optical system 2 at a position different from the second end 5e of the second light transmission unit 5.

[0082] FIG. 11 is a plan view schematically illustrating an example of the configuration of a planar light valve used in the spatial phase modulator 4A. FIG. 11 shows a portion of the configuration of the planar light valve. FIGS. 12 and 13 are cross-sectional views each schematically illustrating an example of the configuration of one reflecting element 44 and its surrounding area in a planar light valve used in the spatial phase modulator 4A. In FIGS. 11 to 13, a first direction along a main surface (also referred to as a second main surface) F2 on the +Z direction side of a substrate 43s constituting the planar light valve is the +Y direction; a second direction along the second main surface F2 and perpendicular to the +Y direction is the +X direction; and a third direction along a normal to the second main surface F2 is the -Z direction. For convenience, support members 44s, which will be described later, are omitted from illustration in FIGS. 12 and 13.

[0083] The planar light valve serving as the spatial phase modulation element 4A has, for example, a base portion 43 and a plurality of reflecting elements 44.

[0084] The base portion 43 has, for example, a substrate 43s and an electrode (also referred to as a second reference electrode) 43e. The substrate 43s may be, for example, a plate-shaped substrate such as a silicon substrate. The second reference electrode 43e is located along the second main surface F2 of the substrate 43s. The second reference electrode 43e may be, for example, a metal film formed on the second main surface F2 of the substrate 43s. The second reference electrode 43e may be, for example, an electrode provided for each reflective element 44, or may be an electrode common to the multiple reflective elements 44.

[0085] The plurality of reflective elements 44 are arranged in a matrix. More specifically, the plurality of reflective elements 44 are arranged in a matrix on the second main surface F2 of the substrate 43s. In the planar light valve, for example, M reflective elements 44 are arranged in the +Y direction and N reflective elements 44 are arranged in the +X direction. Here, M and N are natural numbers, and each of M and N is, for example, a numerical value ranging from several hundred to several thousand.

[0086] Each of the plurality of reflective elements 44 includes a second reflective portion 44r and a support portion 44s. In other words, the planar light valve has a plurality of second reflective portions 44r arranged in a matrix, for example, as a plurality of lattice elements. In the examples of Figures 11 to 13, each of the plurality of reflective elements 44 includes a fixed reflective portion 44f.

[0087] 11 to 13, the fixed reflector 44f is a planar, substantially rectangular portion fixed to the substrate 43s, and has a substantially circular opening in the center. The surface (also referred to as the upper surface) of the fixed reflector 44f facing the +Z direction has, for example, a light reflecting surface (also referred to as the fixed light reflecting surface) that specularly reflects light.

[0088] The second reflecting portion 44r has a light reflecting surface (also referred to as a movable light reflecting surface) that specularly reflects light. The light reflecting surface is located, for example, on the side of the second reflecting portion 44r opposite to the base portion 43. The light reflecting surface is a surface parallel to the XY plane. For example, the surface of each second reflecting portion 44r is configured to be covered with a thin film of a metal such as aluminum that specularly reflects light. As a result, for example, the surface of each second reflecting portion 44r opposite to the base portion 43 functions as a light reflecting surface. In the second embodiment, the first light L1 from the first optical transmission portion 1 is irradiated onto the light reflecting surface of each of the multiple second reflecting portions 44r. The light reflecting surface of each second reflecting portion 44r can reflect the first light L1.

[0089] The support portions 44s are flexible, support the second reflector 44r at multiple locations, and are connected to the base portion 43. The support portions 44s may have a microstructure made of, for example, an amorphous silicon nitride film. The support portions 44s may be formed, for example, by a portion of a cross-shaped structure (also referred to as a cross-shaped structure). In this case, the cross-shaped structure has a central portion that constitutes a portion of the −Z direction surface (also referred to as a back surface) of the second reflector 44r, and four end portions that serve as the support portions 44s that are bridged between the second reflector 44r and the base portion 43. The surface of the cross-shaped structure is coated with a thin metal film such as aluminum. This thin metal film functions as an electrode (also referred to as a second movable electrode). In other words, the second reflector 44r functions as a second movable electrode.

[0090] Here, the second reflecting portion 44r faces the base portion 43 across the space S1A. Each second reflecting portion 44r faces the second reference electrode 43e of the base portion 43 across the space S1A. In other words, the second reference electrode 43e of the base portion 43 faces each second reflecting portion 44r. The support portion 44s supports the second reflecting portion 44r without contacting the second reference electrode 43e, for example. Therefore, for example, bending of the support portion 44s can cause the second reflecting portion 44r to be displaced relative to the base portion 43, as shown in FIGS. 12 and 13 .

[0091] Here, for example, by applying a potential difference between the second reflecting portion 44r, which functions as a second movable electrode, and the second reference electrode 43e, an electrostatic force is generated between the second reflecting portion 44r and the second reference electrode 43e, which attracts the second reflecting portion 44r to the second reference electrode 43e. This electrostatic force causes the support portion 44s to bend.

[0092] The planar light valve as the spatial phase modulation element 4A, for example, deflects the support portion 44s by an electrostatic force according to a signal from the control portion 10, thereby displacing the second reflecting portion 44r by an amount according to the signal.

[0093] For example, the control unit 10 can adjust the potential difference applied between the second reflector 44r and the second reference electrode 43e for each of the plurality of reflecting elements 44 to deflect the support portion 44s by electrostatic force between the second reflector 44r and the second reference electrode 43e, thereby controlling the displacement of the second reflector 44r relative to the base portion 43. In other words, the control unit 10 can control the displacement of the plurality of second reflectors 44r as the plurality of lattice elements relative to the base portion 43. Note that, for example, after the support portion 44s is deflected by electrostatic force corresponding to the potential difference applied between the second reflector 44r and the second reference electrode 43e, when the potential difference applied between the second reflector 44r and the second reference electrode 43e becomes substantially zero, the elastic force of the support portion 44s causes the support portion 44s to return to an undeflected state. At this time, the displacement of the second reflector 44r returns to zero.

[0094] Here, the displacement amounts of the multiple second reflectors 44r aligned along the +Y direction are controlled to be the same. In other words, the displacement amounts of the multiple second reflectors 44r aligned in a matrix are controlled by treating each row of multiple second reflectors 44r aligned along the Y direction as a single unit. Therefore, for example, the planar light valve can function as a blazed diffraction grating by periodically changing the displacement amounts of the second reflectors 44r in the +X direction in a manner similar to the states of the grating light valve described above shown in FIGS. 8 and 9. The planar light valve as the spatial phase modulator 4A can function as a blazed diffraction grating with a variable grating pitch Δ and blaze depth Φ by controlling the amount of deflection of the multiple support portions 44s, for example, by controlling the potential applied to the second movable electrodes of the multiple second reflectors 44r. In other words, by changing the amount of displacement of each of the plurality of second reflecting portions 44r relative to the base portion 43, the flat light valve can function as a blazed diffraction grating with different grating pitches Δ and blaze depths Φ.

[0095] As described above, a blazed diffraction grating can generate diffracted light by applying phase modulation to irradiated light in accordance with the grating pitch Δ of the sawtooth pattern and the blaze depth Φ. Therefore, the planar light valve serving as the spatial phase modulator 4A can generate diffracted light by applying phase modulation to light (specifically, the first light L1) irradiated onto the light-reflecting surface of each of the second reflecting portions 44r in accordance with the pitch and amount of displacement of the second reflecting portions 44r as grating elements relative to the base portion 41. The pitch of the displacement pattern is the repetition period in the +X direction, which is the second direction of displacement of the second reflecting portions 44r relative to the base portion 43, and corresponds to the grating pitch Δ.

[0096] Therefore, even when a spatial phase modulation element 4A employing a planar light valve is employed, similarly to the first embodiment, the control unit 10 can increase or decrease the amount of second light L2 incident on the second light transmission unit 5 from the planar light valve serving as the spatial phase modulation element 4A by controlling the displacement of the plurality of second reflecting units 44r relative to the base unit 43. This makes it possible to quickly switch, for example, the ratio of the amount of second light L2 transmitted by the second light transmission unit 5 to the amount of first light L1 transmitted by the first light transmission unit 1. Therefore, the variable optical attenuator 100A can have an increased response speed when the amount of output light is changed.

[0097] For example, in a planar light valve serving as a spatial light modulator 4A functioning as a blazed diffraction grating, the control unit 10 controls the amount of displacement of the plurality of second reflecting portions 44r relative to the base portion 43 while maintaining the pitch of the displacement pattern of the plurality of second reflecting portions 44r relative to the base portion 43, thereby increasing or decreasing the amount of second light L2 incident on the second light transmitting portion 5 from the planar light valve serving as the spatial light modulator 4A. Here, maintaining the pitch of the displacement pattern corresponds to maintaining the grating pitch Δ that defines the repeated sawtooth-shaped displacement pattern. Controlling the amount of displacement of the plurality of second reflecting portions 44r relative to the base portion 43 corresponds to controlling the blaze depth Φ that defines the depth of the repeated sawtooth-shaped displacement pattern. Therefore, as in the first embodiment described above, the control unit 10 controls the planar light valve as the spatial phase modulation element 4A functioning as a blazed diffraction grating to adjust the blaze depth Φ while maintaining the grating pitch Δ, thereby increasing or decreasing the amount of second light L2 incident on the second optical transmission unit 5 from the planar light valve as the spatial phase modulation element 4A functioning as a blazed diffraction grating.

[0098] Here, for example, the shape of each of the plurality of second reflecting portions 44r is not limited to a disk shape, and may be various plate shapes such as a plate shape with rectangular upper and lower surfaces.

[0099] 10, the variable optical attenuator 100A according to the second embodiment may include a light absorber 6 located on the optical path of the zeroth-order diffracted light (third light L3) generated by the planar light valve serving as the spatial phase modulator 4A in response to irradiation of the first light L1 onto the plurality of second reflecting portions 44r. The light absorber 6 absorbs the light. For example, the light absorber 6 is disposed at a location where the third light L3 is focused by the optical system 2. This reduces the likelihood of the zeroth-order diffracted light entering the second optical transmission unit 5 due to reflection or the like within the variable optical attenuator 100A. This can improve the accuracy of switching the ratio of the amount of the second light L2 transmitted through the second optical transmission unit 5 to the amount of the first light L1 transmitted through the first optical transmission unit 1. This can improve the accuracy of changing the amount of output light in the variable optical attenuator 100A.

[0100] <2-2. Third embodiment> The variable optical attenuator 100 according to the first embodiment may be modified into an optical switch 300 in which the control unit 10 is replaced with a control unit 10A that controls the operation of the spatial phase modulation element 4 different from the control unit 10, as shown in FIGS. 14 and 15.

[0101] 14 and 15 are diagrams each schematically illustrating an example of the configuration of an optical switch 300 according to the third embodiment. In FIGS. 14 and 15, as in FIG. 1, an example of the optical path of the first light L1 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the first light L1 are indicated by an arrow drawn with a dashed line. In FIG. 14, as in FIG. 1, an example of the optical path of the second light L2 is indicated by an arrow drawn with a two-dot chain line. More specifically, the center and each end optical path of the light beam of the second light L2 are indicated by an arrow drawn with a dashed line. In FIG. 15, an example of the optical path of the fourth light L4 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the fourth light L4 are indicated by an arrow drawn with a dashed line.

[0102] The control unit 10A has a configuration similar to that of the control unit 10 according to the first embodiment, for example, and can control the operation of the spatial light modulation element 4. Specifically, the control unit 10A can control the displacement of the plurality of first reflecting portions 42r relative to the base portion 41 of a grating light valve serving as the spatial light modulation element 4. The control unit 10A can then control the presence or absence of light entering the second light transmission unit 5 from the grating light valve serving as the spatial light modulation element 4 by controlling the displacement of each of the plurality of first reflecting portions 42r relative to the base portion 41. This allows, for example, rapid switching between the presence or absence of light entering the second light transmission unit 5 from the spatial light modulation element 4. This can therefore increase the response speed of the optical switch 300 in changing the amount of light to be output.

[0103] In the third embodiment, the control unit 10A can switch between the presence and absence of incidence of the second light L2 from the grating light valve serving as the spatial phase modulation element 4 to the second optical transmission unit 5 by controlling the displacement of each of the multiple first reflecting units 42r relative to the base unit 41.

[0104] For example, as shown in Figure 8, in a grating light valve serving as a spatial phase modulation element 4 functioning as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value corresponding to the wavelength λ of the first light L1 so that the second light L2 is incident on the second light transmission section 5, and the blaze depth Φ is set to half the value of the wavelength λ of the first light L1 (= λ / 2) (also referred to as the first state), and the second light L2 is incident on the second light transmission section 5 from the grating light valve serving as the spatial phase modulation element 4.

[0105] 7, in a state where the displacement amounts of the multiple first reflecting portions 42r are equal and zero (reference state), the grating light valve serving as the spatial phase modulation element 4 functions as a mirror and does not generate the second light L2 but generates specularly reflected light (fourth light) L4. Therefore, the second light L2 is not incident on the second optical transmission section 5 from the grating light valve serving as the spatial phase modulation element 4.

[0106] In this case, for example, the control unit 10A can switch the state of the spatial light modulation element 4 between a first state in which the spatial light modulation element 4 functions as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value, and the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2), and a reference state in which the displacement amounts of the first reflecting portions 42r are equal and zero, by controlling the displacement of each of the first reflecting portions 42r relative to the base portion 41. This allows switching between a state in which the second light L2 is incident on the second light transmission unit 5 from a grating light valve serving as the spatial light modulation element 4 as shown in Fig. 14 and a state in which the second light L2 is not incident on the second light transmission unit 5 from a grating light valve serving as the spatial light modulation element 4 as shown in Fig. 15.

[0107] In the case shown in Figure 15, the fourth light L4 generated by the grating light valve as the spatial phase modulation element 4 is converted into parallel light having a circular cross-sectional shape by the first optical element part 3, and this parallel light converted into fourth light L4 is focused by the optical system 2 at a position different from the second end 5e of the second optical transmission part 5.

[0108] 15, the optical switch 300 according to the third embodiment may include a light absorber 6 that is located on the optical path of specularly reflected light (fourth light L4) generated by a grating light valve serving as the spatial phase modulation element 4 in response to irradiation of the first light L1 onto the plurality of first reflecting portions 42r, and that absorbs the light. For example, the light absorber 6 is disposed at a location where the fourth light L4 is collected by the optical system 2. This reduces the likelihood of the fourth light L4 entering the second optical transmission unit 5 due to reflection or the like within the optical switch 300.

[0109] Furthermore, for example, the control unit 10A may change the grating pitch Δ in a grating light valve functioning as a blazed diffraction grating as the spatial phase modulation element 4, thereby changing the angle (second angle) θ2 formed between the second optical path Lp2 of the second light L2 generated in the grating light valve and the normal L0 to the grating surface P0. In this way, the control unit 10A may switch between a state in which the second light L2 is incident on the second light transmission unit 5 from the grating light valve as the spatial phase modulation element 4, and a state in which the second light L2 is not incident on the second light transmission unit 5 from the grating light valve as the spatial phase modulation element 4.

[0110] <2-3. Fourth embodiment> In the third embodiment, for example, the spatial phase modulation element 4 may be changed to a spatial phase modulation element 4A in which a planar light valve, which is a type of optical phase array, is used instead of the grating light valve. From another perspective, the variable optical attenuator 100A according to the second embodiment may be changed to an optical switch 300A in which the control unit 10 is replaced with a control unit 10A that controls the operation of the spatial phase modulation element 4A different from the control unit 10, as shown in Figures 16 and 17.

[0111] 16 and 17 are diagrams each schematically illustrating an example of the configuration of an optical switch 300A according to the fourth embodiment. In FIGS. 16 and 17, as in FIGS. 14 and 15, an example of the optical path of the first light L1 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the first light L1 are indicated by an arrow drawn with a dashed line. In FIG. 16, as in FIG. 14, an example of the optical path of the second light L2 is indicated by an arrow drawn with a two-dot chain line. More specifically, the center and each end optical path of the light beam of the second light L2 are indicated by an arrow drawn with a dashed line. In FIG. 17, as in FIG. 15, an example of the optical path of the fourth light L4 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the fourth light L4 are indicated by an arrow drawn with a dashed line.

[0112] The optical switch 300A is based on the optical switch 300 according to the third embodiment, except that the spatial phase modulation element 4 is changed to a spatial phase modulation element 4A that employs a planar light valve, and the first optical element unit 3 is deleted. The first light transmission unit 1, spatial phase modulation element 4A, second light transmission unit 5, and optical system 2 are fixed, for example, by various structures so that their relative positions and orientations are constant.

[0113] 16 and 17, the first light L1 emitted from the first light transmission unit 1 is converted into parallel light by the optical system 2, and the first light L1 converted into parallel light is irradiated onto the spatial phase modulation element 4A. Also, as shown in Fig. 16, the second light L2 in the form of parallel light generated by the spatial phase modulation element 4A is collected by the optical system 2 and incident on the second end 5e of the second light transmission unit 5. Also, as shown in Fig. 17, the fourth light L4 in the form of parallel light generated by the spatial phase modulation element 4A is collected by the optical system 2 at a position different from the second end 5e of the second light transmission unit 5.

[0114] Even when a spatial phase modulation element 4A employing a planar light valve is employed, the control unit 10A can control, for example, the operation of the spatial phase modulation element 4, as in the third embodiment. Specifically, the control unit 10A can control the displacement of the plurality of second reflecting portions 44r relative to the base portion 43 of the planar light valve serving as the spatial phase modulation element 4A. The control unit 10A can then control the presence or absence of light entering the second light transmission unit 5 from the planar light valve serving as the spatial phase modulation element 4A by controlling the displacement of each of the plurality of second reflecting portions 44r relative to the base portion 43. This allows, for example, rapid switching between the presence or absence of light entering the second light transmission unit 5 from the spatial phase modulation element 4A. Therefore, the response speed of the optical switch 300A in changing the amount of light output can be increased.

[0115] In the fourth embodiment, similarly to the third embodiment, the control unit 10A controls the displacement of each of the second reflecting portions 44r relative to the base portion 43 to switch between the presence and absence of the second light L2 entering from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5. For example, by controlling the displacement of each of the second reflecting portions 44r relative to the base portion 43, the control unit 10A can switch the state of the spatial phase modulation element 4A between a first state in which the spatial phase modulation element 4A functions as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value, and the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2), and a reference state in which the displacement amounts of the second reflecting portions 44r are equal and zero. This allows switching between a state in which the second light L2 is entering from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5 as shown in FIG. 16 and a state in which the second light L2 is not entering from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5 as shown in FIG. 17.

[0116] 17, the optical switch 300A according to the fourth embodiment may include a light absorber 6 that is located on the optical path of specularly reflected light (fourth light L4) generated by the planar light valve serving as the spatial phase modulation element 4A in response to irradiation of the first light L1 onto the plurality of second reflecting portions 44r, and that absorbs the light. For example, the light absorber 6 is disposed at a location where the fourth light L4 is collected by the optical system 2. This reduces the likelihood of the fourth light L4 entering the second optical transmission unit 5 due to reflection or the like within the optical switch 300A.

[0117] <2-4. Fifth embodiment> In the above third embodiment, for example, as shown in Figures 18 and 19, the second optical transmission section 5 may be arranged so that the second light L2 is not incident thereon, but the fourth light L4 is incident thereon and transmits the fourth light L4.

[0118] 18 and 19 are diagrams each schematically illustrating an example of the configuration of an optical switch 300B according to the fifth embodiment. In FIGS. 18 and 19, as in FIGS. 14 and 15, an example of the optical path of the first light L1 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the first light L1 are indicated by an arrow drawn with a dashed line. In FIG. 18, as in FIG. 15, an example of the optical path of the fourth light L4 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the fourth light L4 are indicated by an arrow drawn with a dashed line. In FIG. 19, as in FIG. 14, an example of the optical path of the second light L2 is indicated by an arrow drawn with a two-dot chain line. More specifically, the center and each end optical path of the light beam of the second light L2 are indicated by an arrow drawn with a two-dot chain line.

[0119] The optical switch 300B has a configuration in which the arrangement of the second optical transmission section 5 is changed based on the optical switch 300 according to the third embodiment.

[0120] Even when the above configuration is adopted, the control unit 10A can switch between the incidence and non-incidence of light from the grating light valve serving as the spatial phase modulation element 4 to the second light transmission unit 5 by controlling the displacement of each of the plurality of first reflecting units 42r relative to the base unit 41. This makes it possible to quickly switch between the incidence and non-incidence of light from the spatial phase modulation element 4 to the second light transmission unit 5, for example. Therefore, the response speed of the optical switch 300B in changing the amount of light to be output can be increased.

[0121] In the fifth embodiment, the control unit 10A controls the displacement of each of the plurality of first reflecting portions 42r relative to the base portion 41, thereby switching between the presence and absence of the fourth light L4 entering from the grating light valve serving as the spatial phase modulation element 4 to the second light transmission portion 5. For example, by controlling the displacement of each of the plurality of first reflecting portions 42r relative to the base portion 41, the control unit 10A can switch the state of the spatial phase modulation element 4 between a reference state in which the displacement amounts of the plurality of first reflecting portions 42r are equal and zero, and a first state in which the spatial phase modulation element 4 functions as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value, and the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2). This switches the state between a state in which the fourth light L4 is entering from the grating light valve serving as the spatial phase modulation element 4 to the second light transmission portion 5 as shown in FIG. 18 and a state in which the fourth light L4 is not entering from the grating light valve serving as the spatial phase modulation element 4 to the second light transmission portion 5 as shown in FIG. 19.

[0122] 19, the optical switch 300B according to the fifth embodiment may include a light absorber 6 that is located on the optical path of diffracted light (second light L2) generated by a grating light valve serving as the spatial phase modulation element 4 in response to irradiation of the first light L1 onto the plurality of first reflecting portions 42r, and that absorbs the light. For example, the light absorber 6 is disposed at a location where the second light L2 is focused by the optical system 2. This reduces the likelihood of the second light L2 being incident on the second optical transmission unit 5 due to reflection or the like within the optical switch 300B.

[0123] <2-5. Sixth embodiment> In the fifth embodiment, for example, the spatial phase modulation element 4 may be changed to a spatial phase modulation element 4A in which a planar light valve, which is a type of optical phase array, is applied instead of the grating light valve. From another perspective, in the fourth embodiment, for example, as shown in Figures 20 and 21, the second optical transmission unit 5 may be arranged so that the second light L2 is not incident thereon, but the fourth light L4 is incident thereon and the second optical transmission unit 5 transmits the fourth light L4.

[0124] 20 and 21 are diagrams each schematically illustrating an example of the configuration of an optical switch 300C according to the sixth embodiment. In FIGS. 20 and 21, as in FIGS. 16 and 17, an example of the optical path of the first light L1 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the first light L1 are indicated by an arrow drawn with a dashed line. In FIG. 20, as in FIG. 17, an example of the optical path of the fourth light L4 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the fourth light L4 are indicated by an arrow drawn with a dashed line. In FIG. 21, as in FIG. 16, an example of the optical path of the second light L2 is indicated by an arrow drawn with a two-dot chain line. More specifically, the center and each end optical path of the light beam of the second light L2 are indicated by an arrow drawn with a two-dot chain line.

[0125] The optical switch 300C is based on the optical switch 300B according to the fifth embodiment, except that the spatial phase modulation element 4 is changed to a spatial phase modulation element 4A employing a planar light valve, and the first optical element unit 3 is deleted. The first light transmission unit 1, spatial phase modulation element 4A, second light transmission unit 5, and optical system 2 are fixed, for example, by various structures so that their relative positions and orientations are constant.

[0126] 20 and 21, the first light L1 emitted from the first light transmission unit 1 is converted into parallel light by the optical system 2, and the first light L1 converted into parallel light is irradiated onto the spatial phase modulation element 4A. Also, as shown in Fig. 20, the fourth light L4 in the form of parallel light generated by the spatial phase modulation element 4A is collected by the optical system 2 and incident on the second end 5e of the second light transmission unit 5. Also, as shown in Fig. 21, the second light L2 in the form of parallel light generated by the spatial phase modulation element 4A is collected by the optical system 2 at a position different from the second end 5e of the second light transmission unit 5.

[0127] Even when a spatial phase modulation element 4A employing a planar light valve is employed, the control unit 10A can control, for example, the operation of the spatial phase modulation element 4, as in the fifth embodiment. Specifically, the control unit 10A can control the displacement of each of the second reflecting portions 44r relative to the base portion 43 of the planar light valve serving as the spatial phase modulation element 4A. The control unit 10A can then control the presence or absence of light entering the second light transmission unit 5 from the planar light valve serving as the spatial phase modulation element 4A. This allows, for example, the rapid switching between the presence or absence of light entering the second light transmission unit 5 from the spatial phase modulation element 4A. This can therefore increase the response speed of the optical switch 300C in changing the amount of light output.

[0128] In the sixth embodiment, similarly to the fifth embodiment, the control unit 10A controls the displacement of each of the second reflecting portions 44r relative to the base portion 43, thereby switching between the presence and absence of the fourth light L4 entering from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5. For example, by controlling the displacement of each of the second reflecting portions 44r relative to the base portion 41, the control unit 10A can switch the state of the spatial phase modulation element 4A between a reference state in which the displacement amounts of the second reflecting portions 44r are equal and zero, and a first state in which the spatial phase modulation element 4A functions as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value, and the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2). This switches the state between a state in which the fourth light L4 is entering from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5 as shown in FIG. 20 and a state in which the fourth light L4 is not entering from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5 as shown in FIG. 21.

[0129] 21, the optical switch 300C according to the sixth embodiment may include a light absorber 6 that is located on the optical path of diffracted light (second light L2) generated by the planar light valve serving as the spatial phase modulation element 4A in response to irradiation of the first light L1 onto the plurality of second reflecting portions 44r, and that absorbs the light. For example, the light absorber 6 is disposed at a location where the second light L2 is focused by the optical system 2. This reduces the likelihood of the second light L2 being incident on the second optical transmission unit 5 due to reflection or the like within the optical switch 300B.

[0130] <2-6. Seventh embodiment> In the third embodiment, for example, as shown in FIGS. 22 and 23, a third optical transmission section 7 that receives the fourth light L4 and transmits the fourth light L4 may be added.

[0131] 22 and 23 are diagrams each schematically illustrating an example of the configuration of an optical switch 300D according to the seventh embodiment. In FIGS. 22 and 23, as in FIGS. 14 and 15, an example of the optical path of the first light L1 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the first light L1 are indicated by an arrow drawn with a dashed line. In FIG. 22, as in FIG. 14, an example of the optical path of the second light L2 is indicated by an arrow drawn with a two-dot chain line. More specifically, the center and each end optical path of the light beam of the second light L2 are indicated by an arrow drawn with a dashed line. In FIG. 23, as in FIG. 15, an example of the optical path of the fourth light L4 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the fourth light L4 are indicated by an arrow drawn with a dashed line.

[0132] The optical switch 300D is based on the optical switch 300 according to the third embodiment, and further includes a third optical transmission section 7 that is different from the second optical transmission section 5. Here, for example, the first optical transmission section 1, the spatial phase modulation element 4, the second optical transmission section 5, the first optical element section 3, the optical system 2, and the third optical transmission section 7 are fixed by various structures so that their relative positions and postures are constant.

[0133] The third light transmission section 7 is a section that transmits incident light. Light emitted from the spatial phase modulation element 4 in response to irradiation of each light reflecting surface of the plurality of first reflecting sections 42r in the spatial phase modulation element 4 with the first light L1 is incident on the third light transmission section 7. In the seventh embodiment, fourth light L4 emitted from the spatial phase modulation element 4 in response to irradiation of the first light L1 by the spatial phase modulation element 4 is incident on the third light transmission section 7. In this case, the third light transmission section 7 transmits the incident fourth light L4.

[0134] In the seventh embodiment, the second optical transmission unit 5 transmits the second light L2 as light to be output to the outside of the optical switch 300D (also referred to as first output light or first output light), and the third optical transmission unit 7 transmits the fourth light L4 as light to be output to the outside of the optical switch 300D (also referred to as second output light or second output light). Similar to the first optical transmission unit 1 and the second optical transmission unit 5, an optical fiber or the like is applied to the third optical transmission unit 7. The optical fiber applied to the third optical transmission unit 7 has a longitudinal end (also referred to as a third end) 7e into which the fourth light L4 is incident, and can transmit the fourth light L4 along the longitudinal direction within the core. Here, for example, the third end 7e is disposed at a location where the fourth light L4 is collected by the optical system 2.

[0135] In the seventh embodiment, the control unit 10A controls the displacement of each of the plurality of first reflecting units 42r relative to the base unit 41, thereby switching between a state (also referred to as a first incident state) in which light (specifically, the second light L2) is incident from the grating light valve serving as the spatial phase modulation element 4 to the second light transmission unit 5 and a state (also referred to as a second incident state) in which light (specifically, the fourth light L4) is incident from the grating light valve serving as the spatial phase modulation element 4 to the third light transmission unit 7. This allows for rapid switching between a state in which light is incident from the grating light valve serving as the spatial phase modulation element 4 to the second light transmission unit 5 and a state in which light is incident from the grating light valve serving as the spatial phase modulation element 4 to the third light transmission unit 7, for example, by controlling the displacement of the plurality of first reflecting units 42r relative to the base unit 41. This therefore increases the response speed of the optical switch 300D in changing the amount of light to be output.

[0136] Here, for example, the control unit 10A can switch the state of the spatial phase modulation element 4 between a first state in which the spatial phase modulation element 4 functions as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value, and the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2), and a reference state in which the displacements of the first reflecting portions 42r are equal and zero, by controlling the displacement of each of the first reflecting portions 42r relative to the base portion 41. This switches the state between a state in which the second light L2 is incident on the second light transmission unit 5 from the grating light valve serving as the spatial phase modulation element 4 as shown in Fig. 22 and a state in which the second light L2 is not incident on the second light transmission unit 5 from the grating light valve serving as the spatial phase modulation element 4 and the fourth light L4 is incident on the third light transmission unit 7 from the grating light valve serving as the spatial phase modulation element 4 as shown in Fig. 23.

[0137] Furthermore, for example, the control unit 10A may change the grating pitch Δ in a grating light valve functioning as a blazed diffraction grating as the spatial phase modulation element 4, thereby changing the angle (second angle) θ2 between the second optical path Lp2 of the second light L2 generated in the grating light valve and the normal L0 to the grating surface P0, thereby switching between the first and second incident states. Here, the first incident state is a state in which light (specifically, the second light L2) is incident from the grating light valve as the spatial phase modulation element 4 to the second light transmission unit 5. The second incident state is a state in which light (specifically, the second light L2) is not incident from the grating light valve as the spatial phase modulation element 4 to the second light transmission unit 5, but light (specifically, the second light L2) is incident from the grating light valve as the spatial phase modulation element 4 to the third light transmission unit 7.

[0138] <2-7. Eighth embodiment> In the seventh embodiment, for example, the spatial phase modulation element 4 may be changed to a spatial phase modulation element 4A to which a planar light valve, which is a type of optical phase array, is applied instead of the grating light valve.

[0139] 24 and 25 are diagrams each schematically illustrating an example of the configuration of an optical switch 300E according to the eighth embodiment. In FIGS. 24 and 25, as in FIGS. 22 and 23, an example of the optical path of the first light L1 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the first light L1 are indicated by an arrow drawn with a dashed line. In FIG. 24, as in FIG. 22, an example of the optical path of the second light L2 is indicated by an arrow drawn with a two-dot chain line. More specifically, the center and each end optical path of the light beam of the second light L2 are indicated by an arrow drawn with a dashed line. In FIG. 25, as in FIG. 23, an example of the optical path of the fourth light L4 is indicated by an arrow drawn with a dashed line. More specifically, the center and each end optical path of the light beam of the fourth light L4 are indicated by an arrow drawn with a dashed line.

[0140] The optical switch 300E is based on the optical switch 300D according to the seventh embodiment, except that the spatial phase modulation element 4 is changed to a spatial phase modulation element 4A employing a planar light valve, and the first optical element unit 3 is deleted. Here, for example, the first light transmission unit 1, spatial phase modulation element 4A, second light transmission unit 5, optical system 2, and third light transmission unit 7 are fixed by various structures so that their relative positions and orientations are constant.

[0141] 24 and 25, the first light L1 emitted from the first light transmission part 1 is converted into parallel light by the optical system 2, and the first light L1 converted into parallel light is irradiated onto the spatial phase modulation element 4A. Also, as shown in Fig. 24, light in the form of parallel light generated by the spatial phase modulation element 4A (specifically, the second light L2) is collected by the optical system 2 and incident on the second end 5e of the second light transmission part 5. Also, as shown in Fig. 25, light in the form of parallel light generated by the spatial phase modulation element 4A (specifically, the fourth light L4) is collected by the optical system 2 and incident on the third end 7e of the third light transmission part 7.

[0142] Even when the spatial phase modulation element 4A employing a planar light valve is employed, similarly to the seventh embodiment, the control unit 10A controls the displacement of each of the plurality of second reflecting portions 44r relative to the base portion 43 to switch between a state (first incident state) in which light (specifically, the second light L2) is incident from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5 and a state (second incident state) in which light (specifically, the fourth light L4) is incident from the planar light valve serving as the spatial phase modulation element 4A to the third light transmission portion 7. This allows rapid switching between a state in which light is incident from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission portion 5 and a state in which light is incident from the planar light valve serving as the spatial phase modulation element 4A to the third light transmission portion 7 by controlling the displacement of the plurality of second reflecting portions 44r relative to the base portion 43. Therefore, the optical switch 300E can improve the response speed in changing the amount of light to be output.

[0143] Here, for example, the control unit 10A can switch the state of the spatial phase modulation element 4A between a first state in which the spatial phase modulation element 4A functions as a blazed diffraction grating, the grating pitch Δ is set to a predetermined value, and the blaze depth Φ is set to half the wavelength λ of the first light L1 (=λ / 2), and a reference state in which the displacements of the second reflecting portions 44r are equal and zero, by controlling the displacement of each of the first reflecting portions 42r relative to the base portion 41. This allows switching between a state in which the second light L2 is incident from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission member 5 as shown in Fig. 24 and a state in which the second light L2 is not incident from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission member 5 and the fourth light L4 is incident from the planar light valve serving as the spatial phase modulation element 4A to the third light transmission member 7 as shown in Fig. 25.

[0144] In addition, for example, the control unit 10A may change the grating pitch Δ in the planar light valve serving as the spatial phase modulation element 4A functioning as a blazed diffraction grating to change the angle (second angle) θ2 formed between the second optical path Lp2 of the second light L2 generated in the planar light valve and the normal L0 to the grating surface P0, thereby switching between the first and second incident states. Here, the first incident state is a state in which light (specifically, the second light L2) is incident from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission unit 5. The second incident state is a state in which the second light L2 is not incident from the planar light valve serving as the spatial phase modulation element 4A to the second light transmission unit 5, and light (specifically, the second light L2) is incident from the planar light valve serving as the spatial phase modulation element 4A to the third light transmission unit 7.

[0145] <2-8.Other> In each of the above embodiments, for example, each of the first light transmission section 1, the second light transmission section 5, and the third light transmission section 7 is not limited to a single optical fiber and may be a light guide. The light guide may have, for example, a configuration in which a plurality of optical fibers are bundled together, or may have a configuration in which light is transmitted by reflecting light on the inner circumferential surface of a bendable tubular member, or may have a configuration in which light is transmitted inside a single bendable linear light-transmitting member. The bendable tubular member may be formed of, for example, acrylic resin or the like.

[0146] In each of the above embodiments, for example, at least a part of the functions of the control unit 10 may be provided in a device external to the variable optical attenuators 100 and 100A, or at least a part of the functions of the control unit 10A may be provided in a device external to the optical switches 300, 300A, 300B, 300C, and 300E. The external device may be, for example, the control device 200.

[0147] It goes without saying that all or part of the components constituting the above-described various embodiments and the above-described various modifications can be combined as appropriate within the scope of not causing any contradiction. [Explanation of symbols]

[0148] 1 First optical transmission section 10,10A control section 100,100A Variable Optical Attenuator 2 Optical system 3. First optical element section 300, 300A, 300B, 300C, 300E Optical Switch 4,4A Spatial Phase Modulator 41,43 Base 42r 1st reflection section 44r 2nd reflector 5 Second optical transmission section 6. Light absorber 7 Third optical transmission section L1 1st light L2 2nd light L3 Third Light L4 4th light

Claims

1. a spatial phase modulation element having a plurality of grating elements each having a base portion and a light reflecting surface, and which generates diffracted light by performing phase modulation on light irradiated onto the light reflecting surface of each of the plurality of grating elements in accordance with a pattern pitch and a displacement amount of the plurality of grating elements relative to the base portion; a first light transmitting section that transmits a first light and emits the first light toward the light reflecting surfaces of the plurality of grating elements; a second light transmitting section that receives second light, the second light being diffracted light different from zero-order diffracted light generated by phase modulation of the first light by the spatial phase modulation element, and transmits the second light; a control unit that increases or decreases the amount of the second light that is incident on the second optical transmission unit from the spatial phase modulation element by controlling displacement of the plurality of grating elements with respect to the base unit, The control unit adjusts the rate of reduction in the amount of the second light incident on the second optical transmission section from the spatial phase modulation element by changing the pitch of the displacement pattern to shift the position at which the second light is irradiated with respect to the end of the second optical transmission section.

2. 2. A variable optical attenuator according to claim 1, the plurality of grating elements each include a plurality of first reflecting portions that extend along a first direction, have the light reflecting surface, and are aligned along a second direction perpendicular to the first direction; a first optical element portion located between the first optical transmission portion and the spatial phase modulation element, and converting a cross-sectional shape of a beam of the first light from a circular shape to an elongated shape along the second direction, so that the first light is irradiated onto the light reflecting surfaces of each of the plurality of first reflecting portions.

3. 2. A variable optical attenuator according to claim 1, the plurality of grating elements each include a plurality of second reflecting portions that have the light reflecting surface and are arranged in a matrix, The first light from the first optical transmission section is irradiated onto the light reflecting surface of each of the plurality of second reflecting sections.

4. A variable optical attenuator according to any one of claims 1 to 3, a light absorber that is positioned on an optical path of zero-order diffracted light generated by the spatial phase modulation element in response to irradiation of the first light onto the plurality of grating elements, and that absorbs light.

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