Tunable filter

Abstract

Provided is a tunable filter, wherein a first angle-variable mirror is configured so that some wavelength components among a plurality of wavelength components included in diffracted light are reflected by a first reflection surface. A second angle variable mirror is configured so that some wavelength components among the plurality of wavelength components included in the diffraction light are incident on a first reflection surface and object light is reflected by a second reflection surface. The object light is one of input light and diffracted light. A second angle-variable mirror is arranged such that a wavelength component incident on the first reflection surface can be changed by changing the angle of the second reflection surface. The first angle-variable mirror is arranged such that the ratio of the reflected light outputted from the tunable filter from among the reflected light from the first reflection surface can be changed by changing the angle of the first reflection surface.

Description

Tunable wavelength filter

[0001] The present disclosure relates to tunable filters.

[0002] 2. Description of the Related Art Conventionally, optical communication networks using wavelength division multiplexing (WDM) optical communication technology are known, and wavelength tunable filters are installed in the optical communication networks to remove noise, for example.

[0003] A known tunable filter includes a diffraction grating and a variable-angle mirror (see, for example, Patent Document 1). The diffraction grating spatially separates multiple wavelength components contained in input light. The variable-angle mirror is disposed downstream of the diffraction grating. Depending on the angle of the reflecting surface of the variable-angle mirror, some of the multiple wavelength components are selectively guided to and output through an output optical fiber.

[0004] U.S. Patent Publication No. 2008 / 0085119

[0005] There is a demand for miniaturization of optical communication devices such as optical transceivers that incorporate tunable filters. Such optical communication devices are generally equipped with optical power attenuators to adjust signal strength. To miniaturize optical communication devices, it is conceivable to integrate the optical systems of the tunable filter and the optical power attenuator into a single optical system. Therefore, the inventors are considering providing the tunable filter with an amplitude variable function.

[0006] In order to provide a wavelength tunable filter with an amplitude variable function, it is possible to use a biaxial variable-angle mirror as the variable-angle mirror, in other words, to provide two rotation axes on the reflecting surface of the variable-angle mirror. The biaxial variable-angle mirror is configured as, for example, a MEMS (Micro-electrical-mechanical system) mirror.

[0007] However, biaxial variable-angle mirrors are typically larger than single-axis variable-angle mirrors due to their more complex structure. Therefore, MEMS-type biaxial variable-angle mirrors require a high drive voltage to change the angle of their reflecting surfaces, necessitating a booster circuit. The need for this booster circuit can be a factor hindering the miniaturization of optical communication devices.

[0008] One way to avoid the need for a boost circuit is to reduce the weight of the biaxial tiltable mirror. However, reducing the weight of the tiltable mirror reduces the resonant frequency of the tiltable mirror. If the resonant frequency is low, the biaxial tiltable mirror may vibrate significantly due to the impact caused by inserting or removing a cable into or from optical communication equipment. Such vibrations may lead to malfunctions in optical transmission. In other words, a decrease in the resonant frequency may have an undesirable effect on the stability of communication.

[0009] Therefore, according to one aspect of the present disclosure, it is desirable to provide a novel wavelength tunable filter that has an amplitude variable function and a configuration with excellent impact resistance.

[0010] According to one aspect of the present disclosure, there is provided a tunable filter for selectively outputting some wavelength components from among a plurality of wavelength components contained in input light, the tunable filter including an output section, a diffraction grating, a first variable-angle mirror, and a second variable-angle mirror.

[0011] The output unit is configured to output a portion of the wavelength components. The diffraction grating is disposed in a propagation path of the input light. The diffraction grating is configured to spatially separate the multiple wavelength components included in the input light and output them as diffracted light.

[0012] The first variable-angle mirror has a first reflecting surface whose angle can be changed, and is configured to reflect, at the first reflecting surface, some of the wavelength components contained in the diffracted light from the diffraction grating.

[0013] The second variable-angle mirror has a second reflecting surface whose angle can be changed. The second variable-angle mirror is provided on a propagation path of the object light. The object light is one of the input light and the diffracted light. The second variable-angle mirror is configured to reflect the object light with the second reflecting surface so that some wavelength components of the multiple wavelength components contained in the diffracted light are incident on the first reflecting surface. The second variable-angle mirror is positioned so that the wavelength components that are incident on the first reflecting surface as some wavelength components can be changed by changing the angle of the second reflecting surface.

[0014] The first angle-variable mirror is positioned so that the proportion of reflected light from the first reflecting surface corresponding to some wavelength components that is output from the wavelength-variable filter through the output section can be changed by changing the angle of the first reflecting surface.

[0015] This tunable filter allows amplitude tuning using the first variable-angle mirror and wavelength tuning using the second variable-angle mirror, thereby reducing the disadvantages (e.g., a decrease in resonant frequency) that would occur if both amplitude and wavelength tuning were achieved using only one variable-angle mirror.

[0016] Therefore, according to one aspect of the present disclosure, it is possible to provide a novel wavelength tunable filter having an amplitude variable function and a configuration with excellent impact resistance.

[0017] According to one aspect of the present disclosure, the first variable-angle mirror may be a variable-angle mirror having only one rotation axis along the first reflecting surface as the rotation axis of the first reflecting surface, and the second variable-angle mirror may be a variable-angle mirror having only one rotation axis along the second reflecting surface as the rotation axis of the second reflecting surface.

[0018] By using two uniaxial angle-variable mirrors to achieve amplitude and wavelength tuning, it is possible to provide a novel wavelength tunable filter with an amplitude tuning function that has a configuration with excellent impact resistance.

[0019] According to one aspect of the present disclosure, the first and second variable-angle mirrors may be arranged such that the rotation axis of the first variable-angle mirror is orthogonal to the rotation axis of the second variable-angle mirror. By arranging the rotation axes of the first and second reflecting surfaces orthogonal to each other, it is possible to change the amplitude and wavelength independently of each other in the tunable filter.

[0020] According to one aspect of the present disclosure, the second angle-variable mirror can be positioned such that the diffracted light is displaced relative to the first reflecting surface in a first direction in accordance with the angle of the second reflecting surface, the first direction being a direction in which multiple wavelength components are spatially separated in the diffracted light.

[0021] The first variable-angle mirror can be positioned such that, depending on the angle of the first reflecting surface, reflected light from the first reflecting surface is displaced relative to the output section in a second direction perpendicular to the first direction.

[0022] By arranging the first and second angle variable mirrors in this way, the amplitude and wavelength can be changed independently of each other in the wavelength tunable filter.

[0023] According to one aspect of the present disclosure, the first variable-angle mirror may be provided in the propagation path of the diffracted light downstream from the diffraction grating, and the second variable-angle mirror may be provided in the propagation path of the input light upstream from the diffraction grating.

[0024] By arranging the first and second angle variable mirrors in this way, it is possible to configure an amplitude variable wavelength filter using a relatively simple optical system.

[0025] 4A is a block diagram showing the configuration of a wavelength tunable filter and a controller; FIG. 4B is a diagram conceptually showing the optical configuration of the wavelength tunable filter; FIG. 4C is an explanatory diagram related to intensity (in other words, amplitude) adjustment; FIG. 4A is a diagram showing an example of the configuration of a first angle variable mirror, and FIG. 4B is a diagram showing an example of the configuration of a second angle variable mirror.

[0026] 10...wavelength tunable filter, 11...input / output section, 12...collimator, 15...diffraction grating, 17...first angle variable mirror, 17A...reflecting surface, 19...second angle variable mirror, 19A...reflecting surface, 30...controller, 111...input optical fiber, 115...output optical fiber, C1...rotation axis, C2...rotation axis

[0027] Exemplary embodiments of the present disclosure will now be described with reference to the drawings.

[0028] The tunable filter 10 of this embodiment shown in Fig. 1 is provided to filter optical signals in a transmission path of the optical signals in a wavelength division multiplexing (WDM) network. The tunable filter 10 is configured to output, as output light, some wavelength components out of multiple wavelength components contained in input light, which is an optical signal input to the tunable filter 10. This tunable filter 10 is disposed within the housing of an optical communication device such as an optical transceiver.

[0029] The tunable filter 10 is configured as a bandpass filter capable of changing the signal passband. The tunable filter 10 is further configured to be capable of changing the intensity of the output light, in other words, the amplitude. That is, the tunable filter 10 of this embodiment is configured as a tunable filter having an amplitude variable function.

[0030] 2, the wavelength tunable filter 10 includes an input / output unit 11, a collimator 12, a diffraction grating 15, a first angle-variable mirror 17, and a second angle-variable mirror 19. The first angle-variable mirror 17 has a reflecting surface 17A whose angle can be changed. The second angle-variable mirror 19 has a reflecting surface 19A whose angle can be changed.

[0031] 1, the tunable filter 10 is configured to be able to change the angles of the reflecting surfaces 17A and 19A individually under the control of a controller 30. The controller 30 is configured to be able to control the wavelength and intensity (in other words, amplitude) of the output light from the tunable filter 10 by controlling the angles of the reflecting surfaces 17A and 19A.

[0032] More specifically, the tunable filter 10 includes an input optical fiber 111 and an output optical fiber 115 as the input / output unit 11. The collimator 12 includes an input collimator 121 and an output collimator 125.

[0033] The input collimator 121 is provided in the propagation path of the input light from the input optical fiber 111. The collimator 121 is configured to collimate the input light from the input optical fiber 111. The input light propagates along the xy plane shown in Fig. 2. The z-axis shown in Fig. 2 is perpendicular to the xy plane.

[0034] The output collimator 125 is provided in the propagation path of the output light output from the wavelength tunable filter 10 through the output optical fiber 115. The collimator 125 is configured to collimate the output light propagating to the output optical fiber 115.

[0035] The diffraction grating 15 is disposed on the propagation path of the input light. The diffraction grating 15 is a transmission type diffraction grating. The diffraction grating 15 is configured to spatially separate multiple wavelength components contained in the input light and output them as diffracted light.

[0036] According to this embodiment, the diffraction grating 15 spatially separates multiple wavelength components in a direction perpendicular to the z-axis shown in Fig. 2. The diffraction grating 15 has input and output surfaces parallel to the z-axis. Input light is incident on the input surface of the diffraction grating 15. Each of the multiple wavelength components contained in the input light propagates downstream from the output surface of the diffraction grating 15 at an angle (diffraction angle) according to the angle of incidence and wavelength.

[0037] First variable-angle mirror 17 is provided downstream of diffraction grating 15, i.e., on the propagation path of the diffracted light from diffraction grating 15. First variable-angle mirror 17 is configured to selectively receive and reflect, at reflecting surface 17A, some wavelength components among a plurality of spatially separated wavelength components contained in the diffracted light. Of the plurality of wavelength components contained in the diffracted light, the wavelength components that are incident on reflecting surface 17A as the some wavelength components are wavelength components whose diffraction angle with respect to diffraction grating 15 is a predetermined angle. Here, reflecting surface 17A may be understood to be a region of the reflecting surface of first variable-angle mirror 17 that is effectively used for outputting an optical signal through output optical fiber 115.

[0038] The second variable-angle mirror 19 is provided on the propagation path of the input light upstream of the diffraction grating 15. The second variable-angle mirror 19 is configured to reflect the input light propagating from the input optical fiber 111 through the collimator 121 toward the diffraction grating 15. The second variable-angle mirror 19 is configured as a uniaxial variable-angle mirror having only one rotation axis C2 of the reflecting surface 19A, the rotation axis C2 being along the reflecting surface 19A.

[0039] The rotation axis C2 of the second variable-angle mirror 19 is parallel to the z-axis. That is, the second variable-angle mirror 19 is configured so that the reflecting surface 19A can be rotated around the z-axis. This rotation changes the angle of the reflecting surface 19A.

[0040] The angle of incidence of the input light with respect to the input surface of the diffraction grating 15 is controlled by the angle of the reflecting surface 19A of the second angle-variable mirror 19. As the angle of incidence changes, the diffraction angles of the multiple wavelength components contained in the diffracted light also change.

[0041] That is, the propagation direction of each of the multiple wavelength components output as diffracted light from the output surface of diffraction grating 15 changes depending on the angle of reflecting surface 19A of second angle-variable mirror 19. As the angle of reflecting surface 19A changes, the diffracted light is displaced relative to reflecting surface 17A of first angle-variable mirror 17 in the wavelength dispersion direction in which the multiple wavelength components are spatially separated. The angle of reflecting surface 19A of second angle-variable mirror 19 is controlled by controller 30 to an angle according to the signal passband to be realized.

[0042] In response to this angle control, second variable-angle mirror 19 reflects the input light at reflecting surface 19A so that, of the multiple wavelength components contained in the diffracted light, some wavelength components corresponding to the signal pass band to be realized are incident on reflecting surface 17A of first variable-angle mirror 17. In this way, second variable-angle mirror 19 is positioned so that, by changing the angle of reflecting surface 19A, the wavelength components that are incident on reflecting surface 17A of first variable-angle mirror 17, of the multiple wavelength components contained in the input light, can be changed.

[0043] As described above, among the multiple wavelength components contained in the diffracted light, wavelength components in a band corresponding to the angle of the reflecting surface 19A of the second angle-variable mirror 19 are selectively incident on the reflecting surface 17A of the first angle-variable mirror 17. These wavelength components are reflected by the reflecting surface 17A, and propagate as output light through the diffraction grating 15, the second angle-variable mirror 19, and the collimator 125 to the output optical fiber 115, and are output from the wavelength-variable filter 10 through the output optical fiber 115 as an output section.

[0044] The first angle-variable mirror 17 is configured as a single-axis angle-variable mirror having only one axis, the rotation axis C1 of the reflecting surface 17A, which is aligned with the reflecting surface 17A. The rotation axis C1 of the first angle-variable mirror 17 is perpendicular to the z-axis. In other words, the first angle-variable mirror 17 is configured so that the reflecting surface 17A can rotate around the rotation axis C1 perpendicular to the z-axis. This rotation changes the angle of the reflecting surface 17A.

[0045] Here, the angle of the reflecting surface 17A with respect to the xy plane is referred to as the elevation angle. As the elevation angle of the reflecting surface 17A changes, the propagation path of the reflected light from the reflecting surface 17A, i.e., the output light, to the output optical fiber 115 changes in the z-axis direction.

[0046] 3, the propagation path of the output light relative to the end face 115A of the output optical fiber 115 is displaced in the z-axis direction, which is perpendicular to the chromatic dispersion direction, depending on the angle of the reflecting surface 17A. The optical coupling rate of the output light reflected by the reflecting surface 17A of the first angle-variable mirror 17 to the output optical fiber 115 changes due to the relative change in the propagation path of the output light relative to the end face 115A.

[0047] That is, depending on the angle of the reflecting surface 17A, the proportion of the light reflected by the reflecting surface 17A that is guided into the output optical fiber 115 and output from the wavelength-tunable filter 10 changes. As a result, the intensity, in other words, the amplitude, of the output light that passes through the output optical fiber 115 and is output from the wavelength-tunable filter 10 changes.

[0048] The angle of the reflecting surface 17A of the first angle-variable mirror 17 is controlled by the controller 30 to an angle according to the intensity (in other words, amplitude) of the output light to be realized. By this angle control, the first angle-variable mirror 17 operates to change the proportion of the reflected light from the reflecting surface 17A, which contains the wavelength component to be output from the wavelength-variable filter 10, that is optically coupled with the output optical fiber 115 and output from the wavelength-variable filter 10 through the output optical fiber 115.

[0049] As shown in Fig. 4A, the first variable-angle mirror 17 is configured as a MEMS mirror whose reflective surface 17A can rotate around a rotation axis C1, in other words, can be tilted. As shown in Fig. 4B, the second variable-angle mirror 19 is configured as a MEMS mirror whose reflective surface 19A can rotate around a rotation axis C2, in other words, can be tilted.

[0050] 4A includes a plate 171 having a reflecting surface 17A and a frame 175 surrounding the outer periphery of the plate 171. The plate 171 is rectangular and is connected to the frame 175 inside the frame 175 so as to be rotatable about a rotation axis C1. The plate 171 has comb electrodes 171A on two sides parallel to the rotation axis C1.

[0051] The frame 175 has a rectangular shape, and when connected to the plate 171, surrounds the periphery of the plate 171. The frame 175 has comb electrodes 175A having a shape complementary to the comb electrodes 171A at positions facing the comb electrodes 171A provided on the plate 171, i.e., on two inner sides parallel to the rotation axis C1.

[0052] The plate 171 is connected to the frame 175 so that comb electrodes 171A provided on two sides of the plate 171 and comb electrodes 175A provided on two inner sides of the frame 175 are interdigitated with a small gap between them. The electrostatic force generated between the comb electrodes 171A and 175A causes the plate 171 to rotate around a rotation axis C1 relative to the frame 175.

[0053] With this configuration, the first variable angle mirror 17 is configured as a MEMS variable angle mirror in which the reflecting surface 17A can rotate or tilt around the rotation axis C1. However, the configuration of the first variable angle mirror 17 is not limited to this.

[0054] 4B , the second variable-angle mirror 19 has a configuration similar to that of the first variable-angle mirror 17, rotated 90 degrees. The second variable-angle mirror 19 includes a plate 191 having a reflecting surface 19A, and a frame 195.

[0055] The plate 191 is connected to the frame 195 so as to be rotatable around the rotation axis C2. The plate 191 has comb electrodes 191A on two sides parallel to the rotation axis C2. The plate 191 is connected to the frame 195 so as to be rotatable around the rotation axis C2 inside the frame 195.

[0056] The frame 195 is a rectangular frame that, when connected to the plate 191, surrounds the periphery of the plate 191. The frame 195 has comb electrodes 195A that have a shape complementary to the comb electrodes 191A at positions facing the comb electrodes 191A provided on the plate 191, i.e., on two inner sides parallel to the rotation axis C2.

[0057] The plate 191 is connected to the frame 195 so that a comb electrode 191A provided on the plate 191 and a comb electrode 195A provided on the inner side of the frame 195 are interdigitated with a small gap between them. The electrostatic force generated between the comb electrodes 191A and 195A causes the plate 191 to rotate around a rotation axis C2 relative to the frame 195.

[0058] With this configuration, the second variable-angle mirror 19 is configured as a MEMS-type variable-angle mirror in which the reflecting surface 19A can rotate or tilt around the rotation axis C2. However, the configuration of the second variable-angle mirror 19 is not limited to this.

[0059] The configuration of the tunable filter 10 of this embodiment has been described above. As mentioned above, there is a demand for miniaturization of optical communication equipment such as optical transceivers. Conventionally, optical transceivers are provided with an optical power attenuator in addition to the tunable filter 10. In contrast, the tunable filter 10 of this embodiment has an amplitude variable function, and therefore does not require an optical power attenuator to be installed in the optical communication equipment. Therefore, the tunable filter 10 of this embodiment is useful for miniaturizing optical communication equipment.

[0060] The above-described wavelength tunable filter 10 uses two variable-angle mirrors having mutually orthogonal rotation axes C1 and C2, i.e., a first variable-angle mirror 17 and a second variable-angle mirror 19, to control the incidence of an optical signal of a selected wavelength on the reflecting surface 17A and to control the proportion of this optical signal optically coupled to the output optical fiber 115. The first variable-angle mirror 17 and the second variable-angle mirror 19 are each single-axis variable-angle mirrors having only one rotation axis, and are not dual-axis variable-angle mirrors having two rotation axes.

[0061] 4A and 4B, as the weight of the MEMS mirror increases, the driving voltage also increases. A MEMS mirror having two rotation axes has a complex structure and is heavier than a MEMS mirror having only one rotation axis.

[0062] Therefore, an additional boost circuit may be required to drive a MEMS mirror with two rotation axes. This boost circuit may be a factor that hinders miniaturization of the wavelength tunable filter. One way to avoid the need for a boost circuit is to reduce the weight of the MEMS mirror, but reducing the weight will result in a decrease in the resonant frequency of the MEMS mirror.

[0063] A decrease in the resonant frequency reduces the shock resistance of the tunable filter and reduces the stability of communication. For example, shocks caused by plugging or unplugging a cable to an optical communication device that includes a tunable filter can cause vibrations in the MEMS mirror, potentially resulting in unstable communication.

[0064] According to this embodiment, the wavelength-tunable filter 10 is constructed using two uniaxial angle-variable mirrors as described above, and therefore, it is possible to suppress a decrease in the resonant frequency of the angle-variable mirrors, and it is also possible to suppress a decrease in impact resistance due to a decrease in the resonant frequency.

[0065] Therefore, according to this embodiment, it is possible to provide a novel wavelength tunable filter 10 having an amplitude variable function and a configuration with excellent shock resistance.

[0066] [Other Embodiments] The present disclosure is not limited to the above-described embodiment and can employ various aspects. In the above-described embodiment, single-axis variable-angle mirrors are used as the first variable-angle mirror 17 and the second variable-angle mirror 19. However, if the required size can be achieved and / or if necessary for other optical path control, variable-angle mirrors having two or more rotation axes may be used for one or both of the first variable-angle mirror 17 and the second variable-angle mirror 19.

[0067] One significant feature of the above-described wavelength tunable filter 10 is that wavelength selection and amplitude adjustment are realized by separate angle variable mirrors (first angle variable mirror 17 and second angle variable mirror 19).

[0068] In the wavelength tunable filter 10 of the above embodiment, a fixed mirror with a fixed reflective surface may be disposed in place of the variable angle mirror at the position corresponding to the first variable angle mirror 17. The first variable angle mirror 17 may be provided in the propagation path of the light reflected by the fixed mirror.

[0069] In this case, the first angle-variable mirror 17 can be provided at a position closer to the output optical fiber 115 than the diffraction grating 15. The first angle-variable mirror 17 can receive the reflected light from the fixed mirror at a reflecting surface 17A. The first angle-variable mirror 17 can control the optical coupling rate of the reflected light to the output optical fiber 115 by changing the angle of the reflecting surface 17A.

[0070] As another example, in the wavelength-tunable filter 10 of the above embodiment, a fixed mirror with a fixed reflecting surface may be disposed in place of the second angle-variable mirror 19. The second angle-variable mirror 19 may be disposed downstream of the diffraction grating 15, on the propagation path of the diffracted light between the diffraction grating 15 and the first angle-variable mirror 17. In this case, the angle of the reflecting surface 19A of the second angle-variable mirror 19 can be controlled so that the wavelength component to be output, among the multiple wavelength components contained in the diffracted light, is selectively incident on the reflecting surface 17A of the first angle-variable mirror 17.

[0071] However, as in the above-described embodiment, if the first variable-angle mirror 17 is provided in the propagation path of the diffracted light downstream of the diffraction grating 15 and the second variable-angle mirror 19 is provided in the propagation path of the input light upstream of the diffraction grating 15, it is possible to realize a wavelength-tunable filter 10 with an amplitude-tunable function using a simple optical system without a fixed mirror.

[0072] The function of one component in the above embodiments may be distributed among multiple components. The functions of multiple components may be integrated into one component. Part of the configuration of the above embodiments may be omitted. At least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. All aspects included in the technical idea identified from the wording of the claims are embodiments of the present disclosure.

Claims

1. A wavelength-tunable filter for selectively outputting some wavelength components out of a plurality of wavelength components contained in input light, comprising: an output unit for outputting the some wavelength components; a diffraction grating arranged in a propagation path of the input light and configured to spatially separate the plurality of wavelength components contained in the input light and output them as diffracted light; a first variable-angle mirror having a first reflecting surface whose angle can be changed and configured to reflect, at the first reflecting surface, the some wavelength components out of the plurality of wavelength components contained in the diffracted light from the diffraction grating; and a second variable-angle mirror having a second reflecting surface whose angle can be changed and arranged in a propagation path of object light which is one of the input light and the diffracted light, and configured to reflect, at the second reflecting surface, the object light out of the plurality of wavelength components contained in the diffracted light so that the some wavelength components are incident on the first reflecting surface, wherein the second variable-angle mirror is arranged so that the wavelength components incident on the first reflecting surface as the some wavelength components can be changed by changing the angle of the second reflecting surface, The first angle-variable mirror is arranged so that, by changing the angle of the first reflecting surface, a proportion of the reflected light from the first reflecting surface corresponding to the some wavelength components that is output from the wavelength-variable filter through the output unit can be changed.

2. A wavelength tunable filter according to claim 1, wherein the first angle-variable mirror is an angle-variable mirror having only one rotation axis along the first reflecting surface as the rotation axis of the first reflecting surface, and the second angle-variable mirror is an angle-variable mirror having only one rotation axis along the second reflecting surface as the rotation axis of the second reflecting surface.

3. A wavelength tunable filter according to claim 2, wherein the first variable angle mirror and the second variable angle mirror are arranged so that the rotation axis of the first variable angle mirror is perpendicular to the rotation axis of the second variable angle mirror.

4. A wavelength-tunable filter according to any one of claims 1 to 3, wherein the second angle-variable mirror is arranged so that the diffracted light is displaced relative to the first reflecting surface in a first direction in which the multiple wavelength components are spatially separated, depending on the angle of the second reflecting surface; and the first angle-variable mirror is arranged so that the reflected light from the first reflecting surface is displaced relative to the output section in a second direction perpendicular to the first direction, depending on the angle of the first reflecting surface.

5. A wavelength tunable filter according to any one of claims 1 to 4, wherein the first angle variable mirror is provided in the propagation path of the diffracted light downstream of the diffraction grating, and the second angle variable mirror is provided in the propagation path of the input light upstream of the diffraction grating.

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