Light source device and control method

Abstract

To arbitrarily adjust the band width of light returned to a light source from a diffraction grating.SOLUTION: A light source device 1 comprises: a light source 11 which outputs light; a reflection unit (spatial light modulator 60) which has an input unit of a control signal and is configured to be able to control the distribution of an angle of reflection of incident light on the basis of the control signal; and a diffraction grating 50 which splits light output from the light source 11 to make the light incident on the spatial light modulator 60 and returns at least a portion of the light reflected in the spatial light modulator 60 to the light source. An optical resonator is formed by the light source 11 and the spatial light modulator 60. The band width of the light returned to the light source 11 from the diffraction grating 50 is controlled by controlling the distribution of the angle of the light reflected in the spatial light modulator 60 on the basis of the control signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the present invention relates to a light source device and a control method. [Background technology]

[0002] Patent Document 1 describes a Littman / Metcalf type external cavity semiconductor laser. In the external cavity semiconductor laser of Patent Document 1, the end mirror is changed to a concave mirror, and the radius of curvature of the concave mirror is changed to a circular mirror. Occasionally By making the distance between the grating equal to the wavelength, a wide spectrum (bandwidth) can be obtained. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 7,245,642 Summary of the Invention [Problem to be solved by the invention]

[0004] In the external cavity semiconductor laser described above, the radius of curvature of the concave mirror is fixed. Occasionally The bandwidth of the light returned from the grating to the light source cannot be adjusted arbitrarily.

[0005] One aspect of the present invention has been made in view of the above circumstances, Occasionally A light source device and a control method are provided that are capable of arbitrarily adjusting the bandwidth of light returned from a grating to a light source. [Means for solving the problem]

[0006] (1) A light source device according to one aspect of the present invention includes a light source that outputs light, a reflector that has an input unit for a control signal and is configured to be able to control the distribution of angles at which the incident light is reflected based on the control signal, and a circuit that splits the light output from the light source and causes it to be incident on the reflector, and returns at least a portion of the light reflected by the reflector to the light source. Occasionally and a grating, and an optical resonator is formed by the light source and the reflecting section, and the light returned to the light source is output, and the angular distribution of the light reflected by the reflecting section is controlled based on a control signal, thereby forming a circular Occasionally The bandwidth of the light returned from the grating to the light source is controlled.

[0007] In the light source device according to one aspect of the present invention, light output from a light source is circulated. Occasionally The light is split by the grating and enters the reflector. At least a part of the light reflected by the reflector is Occasionally In such a light source device, the reflecting section is configured to be able to control the distribution of angles at which light is reflected based on a control signal, and the reflected light is reflected by controlling the distribution of angles. Occasionally The bandwidth of the light returned from the grating to the light source is controlled. With this configuration, by changing the control signal, the distribution of the angles at which the light is reflected at the reflecting section is changed, and the reflected light is Occasionally The bandwidth of the light returned from the grating to the light source can be changed. Occasionally The bandwidth of the light returned from the grating to the light source can be adjusted arbitrarily.

[0008] (2) In the light source device described in (1) above, the reflecting section may be configured to include a spatial light modulator, and the spatial light modulator may control the distribution of angles at which the incident light is reflected by displaying a modulation pattern based on a control signal. In this way, by using a spatial light modulator as the reflecting section, it is possible to easily and accurately Occasionally The bandwidth of the light returned from the grating to the light source can be adjusted.

[0009] (3) In the light source device described in (1) above, the reflecting section may be configured to include a variable curvature mirror, and the variable curvature mirror may control the distribution of angles at which the incident light is reflected by changing the radius of curvature based on a control signal. In this way, by changing the radius of curvature using the variable curvature mirror, Occasionally The bandwidth of the light returned from the grating to the light source can be appropriately adjusted. Furthermore, the variable curvature mirror does not require consideration of the effects of polarization or unmodulated light, as opposed to controlling the distribution of reflection angles using a modulation pattern, such as in a spatial light modulator, making it easier to adjust the bandwidth of the light.

[0010] (4) In the light source device described in (1) above, the reflecting portion comprises a mirror and a reflector. Occasionally and a variable-focus lens provided between the grating and the mirror, and the variable-focus lens may control the distribution of angles at which the incident light is reflected by changing the focal length of the variable-focus lens based on a control signal. Occasionally The bandwidth of the light returned from the grating to the light source can be appropriately adjusted. Furthermore, in this configuration, the influence of polarization or unmodulated light does not need to be taken into consideration (unless a polarization-sensitive element such as a liquid crystal is used), unlike when the distribution of reflection angles is controlled by a modulation pattern such as a spatial light modulator, and therefore the bandwidth of the light can be easily adjusted.

[0011] (5) In the light source device described in (1) to (4) above, the light source outputs light according to the injection current, and the injection current and the control signal are changed over time to generate a circuit. Occasionally The bandwidth of the light returned from the grating to the light source may be dynamically controlled, allowing for more flexible adjustment of the bandwidth of the light depending on the application scenario.

[0012] (6) In the light source device described in (1) to (5) above, the center of curvature of the reflecting surface of the reflecting portion and the rotation OccasionallyThe reflecting part and the diffracting part are arranged so that the beam center of the light incident on the grating coincides with the beam center of the light incident on the grating. Occasionally With this configuration, the path of light before and after reflection on the reflecting surface of the reflecting portion tends to be the same, Occasionally The bandwidth of the light returned from the grating to the light source can be increased.

[0013] (7) The light source device according to any one of (1) to (6) above may further include a control signal generating unit that generates a second control signal based on the measurement result of the light output from the light source device. Occasionally The light returned from the grating to the light source is measured, the measurement results are fed back, and a new control signal (second control signal) is generated, making it easier to adjust the bandwidth of the light to a more desired value, taking into account the actual measurement results.

[0014] (8) A control method according to one aspect of the present invention includes: Occasionally Light is output to the grating and Occasionally and inputting a control signal to a reflecting portion onto which the light dispersed by the grating is incident, the control signal controlling the angular distribution of the light reflected by the reflecting portion. Occasionally The bandwidth of the light returned from the grating to the light source can be adjusted arbitrarily. [Effects of the Invention]

[0015] According to one aspect of the present invention, Occasionally The bandwidth of the light returned from the grating to the light source can be adjusted arbitrarily. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram schematically illustrating a light source device according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing an example of a modulation pattern displayed on a spatial light modulator. [Figure 3] 5A and 5B are diagrams illustrating a first operation example of the light source device. [Figure 4]10A and 10B are diagrams illustrating a second operation example of the light source device. [Figure 5] 10A and 10B are diagrams illustrating a third operation example of the light source device. [Figure 6] 10A and 10B are diagrams illustrating a fourth example of operation of the light source device. [Figure 7] FIG. 10 is a diagram schematically illustrating a light source device according to a second embodiment. [Figure 8] FIG. 10 is a diagram schematically illustrating a light source device according to a fourth embodiment. [Figure 9] FIG. 10 is a diagram schematically illustrating a light source device according to a fifth embodiment. [Figure 10] FIG. 10 is a diagram schematically illustrating a light source device according to a sixth embodiment. [Figure 11] 11A and 11B are diagrams illustrating interference measurement using the light source device shown in FIG. 10. [Figure 12] 11 is a flowchart of interference measurement using the light source device shown in FIG. [Figure 13] 13A and 13B are diagrams illustrating interference measurement using a light source device according to a seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0018] FIG. 1 is a diagram schematically illustrating a light source device 1 according to a first embodiment. The light source device 1 is an external cavity laser (ECL). The light source device 1 is, for example, a Littman type external cavity laser, Occasionally The primary light from the grating is reflected by a mirror and returned to the semiconductor laser.

[0019] As shown in FIG. 1, the light source device 1 includes a light source unit 10, a current controller 20, a temperature controller 30, a lens 40, and a condenser. OccasionallyThe device includes a grating 50, a spatial light modulator 60 (a reflecting portion), a driving circuit 70, and a PC 80.

[0020] The light source unit 10 includes a light source 11 and an LD mount 12. The light source 11 is a semiconductor laser (LD: Laser Diode) that outputs light having a spontaneous emission spectrum with a center wavelength of, for example, 850 nm. The light source 11 may be, for example, a Fabry-Perot type semiconductor laser. An anti-reflection coating may be applied to the end face of the light source 11 on the side coupled to the external resonator (the light output side). The light source 11 is mounted on the LD mount 12. The LD mount 12 may be a mount equipped with a TEC (Thermo-Electric Cooler). In the light source device 1, an optical resonator is formed by the light source 11 and a spatial light modulator 60 (described later). The light source device 1 outputs light that has passed through the external resonator and returned to the light source 11.

[0021] The current controller 20 is configured to supply a current to the light source 11 via the LD mount 12, causing the light source 11 to output light. That is, the light source 11 outputs light according to the current (injected current) supplied from the current controller 20. The light source 11 either generates laser oscillation or operates below the oscillation threshold according to the value of the supplied (injected) current.

[0022] The temperature controller 30 is configured to supply a current to the TEC attached to the LD mount 12 to control the heat absorption (or heat radiation) of the TEC, and to keep the temperature of the light source 11 constant via the TEC.

[0023] The lens 40 rotates the light emitted from the light source 11. OccasionallyThis is a lens (for example, a collimating lens) that efficiently couples the light back to the light source 11 after passing through the grating 50 and the spatial light modulator 60 (after making one revolution inside the external resonator). The light emitted from the light source 11 diverges widely, and the lens 40 adjusts the beam diameter and divergence angle of the light. The light that passes through the lens 40 may or may not be parallel light. The position of the lens 40 may be fixed at a position where high optical output can be obtained, regardless of the focal length of the modulation pattern (phase pattern) displayed on the spatial light modulator 60.

[0024] times Occasionally The grating 50 is configured to separate the light output from the light source 11, which is a mixture of various wavelengths, and to make the light incident on the spatial light modulator 60, and to return at least a portion of the light reflected by the spatial light modulator 60 to the light source 11. Occasionally The grating 50 separates the light into wavelengths, and the first-order light is directed to a spatial light modulator 60, while the zero-order light is extracted as output light.

[0025] The spatial light modulator 60 controls the distribution of angles at which incident light is reflected by displaying a modulation pattern based on a control signal (described later). The spatial light modulator 60 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM). The modulation pattern (phase pattern) is generated in the PC 80, input from the PC 80 to the drive circuit 70, and displayed on the spatial light modulator 60 based on the control signal from the drive circuit 70. In this way, the control signal input from the drive circuit 70 to the spatial light modulator 60 is a signal related to the display of the modulation pattern.

[0026] The spatial light modulator 60 displays, for example, a lens pattern as a modulation pattern. For example, a Fresnel lens pattern may be used as the lens pattern. In the following, in this embodiment, the lens pattern will be described as a Fresnel lens pattern, but the lens pattern may be an aspherical lens pattern or the like. The radius of curvature of the Fresnel lens pattern is twice the focal length. The radius of curvature is a positive value in the case of a concave mirror and a negative value in the case of a convex mirror. The focal length is a positive value in the case of a convex lens and a negative value in the case of a concave lens. In the spatial light modulator 60, by changing the focal length of the Fresnel lens pattern, which is the modulation pattern, the radius of curvature of the Fresnel lens pattern changes, and the angular distribution of the light reflected by the spatial light modulator 60 changes. When the angular distribution of the light reflected by the spatial light modulator 60 changes, the degree of coincidence of the paths of the light before and after reflection by the spatial light modulator 60 changes. In the spatial light modulator 60, the radius of curvature of the Fresnel lens pattern and the spatial light modulator 60-times change. Occasionally The closer the correspondence to the distance between the gratings 50, the wider the wavelength band in which the paths of the light before and after reflection in the spatial light modulator 60 match (the wavelength band in which the coupling efficiency to the light source 11 is high). In this way, in the spatial light modulator 60, the angular distribution of the reflected light is controlled based on the control signal, thereby Occasionally The bandwidth of the light returned from the grating 50 to the light source 11 can be controlled. That is, in the spatial light modulator 60, the spread of the optical spectrum can be controlled by changing the focal length of the Fresnel lens pattern. In this way, the spatial light modulator 60 can control the spread of the optical spectrum without moving or aligning optical components. Note that the bandwidth of the light returned to the light source 11 is determined by, for example, the wavelength dependency of the coupling efficiency to the light source 11, the emission spectrum of the light source 11, and the like.

[0027] When the spatial light modulator 60 is a reflective liquid crystal spatial light modulator, the phase modulation by the spatial light modulator 60 is strongly affected by polarization. The spatial light modulator 60 is arranged so that the polarization direction that can be phase modulated is the x direction or y direction in FIG. 1 (i.e., the direction parallel to the reflecting surface 60a of the spatial light modulator 60). The spatial light modulator 60 is arranged so that the reflecting surface 60a and the polarized light Occasionally The spatial light modulator 60 may be arranged so as to be parallel to the reflecting surface of the grating 50, or may not be arranged so as to be parallel to the reflecting surface of the grating 50. The polarization direction that can be phase-modulated in the spatial light modulator 60 is made to coincide with the linear polarization direction of the light output from the light source 11, for example. In addition, in the spatial light modulator 60, the normal extending from the center of the modulation pattern is made to coincide with the linear polarization direction of the light output from the light source 11. Occasionally The optical system may be adjusted or the modulation pattern position may be adjusted so that the beam of light passes through the center of the grating 50. Occasionally The grating 50 has a center of curvature corresponding to the reflecting surface 60a of the spatial light modulator 60 and a center of curvature corresponding to the reflecting surface 60a of the spatial light modulator 60. Occasionally The spatial light modulator 60 and the grating 50 may be arranged so that the beam center of the light incident on the grating 50 coincides with each other. Occasionally The grating 50 is a trajectory of the center of curvature when the radius of curvature of the reflecting surface 60a of the spatial light modulator 60 is changed, and a rotation Occasionally The grating 50 may be disposed so as to intersect with the beam center of the light incident on the grating 50. Note that the center of curvature of the reflecting surface 60a of the spatial light modulator 60 is the center of curvature of the modulation pattern displayed on the spatial light modulator 60.

[0028] The spatial light modulator 60 may display a predetermined surface shape correction pattern superimposed on the modulation pattern as necessary. The surface shape correction pattern here is a pattern that corrects the shape of the reflecting surface 60a of the spatial light modulator 60. The spatial light modulator 60 may further superimpose a pattern that corrects aberrations generated in the optical system. The spatial light modulator 60 may also display a modulation pattern (Fresnel lens pattern) with different focal lengths in the x and y directions. In this case, the coupling efficiency of light returning to the light source 11 can be increased by optimizing the focal length in the y direction, for example. Note that the spatial light modulator 60 may control the bandwidth of light (control the spread of the optical spectrum) described above by changing only the focal length in the x direction.

[0029] The spatial light modulator 60 has a problem in that unmodulated light appears as zero-order light. To address this problem, a Fresnel lens pattern with a blazed pattern is used as the modulation pattern displayed on the spatial light modulator 60, as shown in FIG. Occasionally A pattern in which a grid pattern is superimposed may also be used. Occasionally A grid pattern 501 and a Fresnel lens pattern with blazed patterns Occasionally A pattern 502 is shown in which a grid pattern is superimposed. In this case, a blazed grid pattern is superimposed on the Fresnel lens pattern. Occasionally The pattern 502 is a grid pattern. Occasionally The reflected primary light may be returned to the light source 11.

[0030] Next, first to sixth operation examples of the light source device 1 will be described.

[0031] FIG. 3 is a diagram illustrating a first operation example of the light source device 1. As shown in FIG. 3(a), in the first operation example, the spatial light modulator 60 displays a modulation pattern in which the radius of curvature of the Fresnel lens pattern is ∞ (flat mirror). In this case, a modulation pattern 503 of a uniform image as shown in FIG. 3(a) is displayed. FIG. 3(b) is a simulation result showing the bandwidth of the output light of the light source device 1 when the radius of curvature of the Fresnel lens pattern is ∞. As shown in FIG. 3(b), when the radius of curvature of the Fresnel lens pattern is ∞, the wavelength band in which the paths of light before and after reflection in the spatial light modulator 60 match (the wavelength band with high coupling efficiency to the light source 11) becomes narrower. In the example of FIG. 3(b), the bandwidth of the light output from the light source device 1 is approximately 500 kHz. The spread of the oscillation spectrum is determined by the gain-frequency characteristics of the light source 11, the nonlinear behavior of laser oscillation, the bandwidth of the light returned to the light source 11, and the like.

[0032] 4A and 4B are diagrams illustrating a second operation example of the light source device 1. In the second operation example shown in FIG. 4A, in the spatial light modulator 60, the radius of curvature of the Fresnel lens pattern is Occasionally A modulation pattern that is the same as the distance between the gratings 50 is displayed. In this case, a modulation pattern 504 of a convex lens with a focal length of 45 mm, for example, as shown in FIG. 4(a) is displayed. Since the spatial light modulator 60 only needs to perform phase modulation in the area where light hits, the modulation pattern 504 shown in FIG. 4(a) displays a Fresnel lens pattern only in a limited area (the central area in the figure). The radius of curvature of the Fresnel lens pattern is the same as the radius of curvature of the spatial light modulator 60. Occasionally If the distance between the gratings 50 is the same as the distance between the gratings 50, the light beam spreads from the center of curvature, and all wavelength components are reflected by the spatial light modulator 60 and return to the same path as the original path. Occasionally Grid 50 times Occasionally The wavelength dependency of the angle is cancelled by the spatial light modulator 60. FIG. 4(b) shows the case where the radius of curvature of the Fresnel lens pattern is changed by the spatial light modulator 60. Occasionally4(b) shows the simulation results showing the bandwidth of the output light from the light source device 1 when the radius of curvature of the Fresnel lens pattern is set to be the same as the distance between the gratings 50. As shown in FIG. 4(b), Occasionally For the same distance between gratings 50, the bandwidth of the light returned to the light source 11 is very wide.

[0033] 5A and 5B are diagrams illustrating a third operation example of the light source device 1. In the third operation example shown in FIG. 5A, in the spatial light modulator 60, the radius of curvature of the Fresnel lens pattern is Occasionally A modulation pattern larger than the distance between the gratings 50 is displayed. In this case, a modulation pattern 505 of a convex lens with a focal length of 55 mm, for example, as shown in FIG. 5(a) is displayed. FIG. 5(b) shows a case where the radius of curvature of the Fresnel lens pattern is 60 times the spatial light modulator. Occasionally 5B is a simulation result showing the bandwidth of the output light of the light source device 1 when the radius of curvature of the Fresnel lens pattern is set to be larger than the distance between the gratings 50. As shown in FIG. 5B, when the radius of curvature of the Fresnel lens pattern is set to be larger than the distance between the gratings 50, the spatial light modulator 60-fold is set to be larger than the distance between the gratings 50. Occasionally When the distance between the gratings 50 is increased, the bandwidth of the light returned to the light source 11 is wider than in the first operational example and narrower than in the second operational example, i.e., a spectral spread intermediate between the first and second operational examples is obtained.

[0034] FIG. 6 is a diagram illustrating a fourth operation example of the light source device 1. In the fourth operation example shown in FIG. 6(a), a modulation pattern of a convex curved mirror (convex mirror) is displayed in the spatial light modulator 60. In this case, a modulation pattern 506 of a concave lens with a focal length of 45 mm, for example, as shown in FIG. 6(a) is displayed. When such a modulation pattern is displayed, the convex mirror rotates the light. Occasionally Circulation per wavelength by grating OccasionallySince the difference in angle is increased, the wavelength band that can return straight to the light source 11 is narrowed, and an even narrower bandwidth can be achieved than when the radius of curvature is set to ∞ as in the first operation example. Note that the smaller the absolute value of the radius of curvature of the convex mirror, the narrower the width of the wavelength dependency of the coupling efficiency. Note that when the beam diameter of each wavelength is sufficiently small on the reflecting surface (about a few pixels), the beam is not circulated in any direction other than the row (a series of pixels in the y direction) corresponding to the central wavelength. Occasionally By displaying a grating pattern and reducing the intensity of the zero-order light, the light band can be further narrowed. Occasionally The orientation of the grating pattern is such that the light is rotated in the y direction, for example. Occasionally The row corresponding to the center wavelength may be a plurality of rows.

[0035] A fifth operation example of the light source device 1 will be described. In the fifth operation example, the injection current supplied from the current controller 20 to the light source 11 is set to a threshold current or less. In this case, the light source 11 does not oscillate laser light and operates in the amplified spontaneous emission (ASE) region. Since the ASE is unpolarized, a linear polarizer may be provided in the optical resonator formed by the light source 11 and the spatial light modulator 60.

[0036] A sixth operation example of the light source device 1 will be described. In the sixth operation example, the injection current supplied to the light source 11 by the current controller 20 and the control signal supplied to the spatial light modulator 60 by the drive circuit 70 are each changed over time, thereby Occasionally It dynamically controls the bandwidth (spread of the optical spectrum) of the light returned from the grating 50 to the light source 11. Changing the control signal over time corresponds to, for example, dynamically and continuously switching the modulation patterns in the first to fourth operation examples described above.

[0037] Next, the effects of the light source device 1 according to the first embodiment will be described.

[0038] The light source device 1 includes a light source 11 that outputs light, a reflecting section (spatial light modulator 60) that has an input section for a control signal and is configured to be able to control the distribution of angles at which the incident light is reflected based on the control signal, and a circuit that splits the light output from the light source 11 and makes it incident on the spatial light modulator 60, while returning at least a portion of the light reflected by the spatial light modulator 60 to the light source. Occasionally The light source 11 and the spatial light modulator 60 form an optical resonator, and the light returned to the light source 11 is output, and the angular distribution of the light reflected by the spatial light modulator 60 is controlled based on a control signal, thereby forming a circular Occasionally The bandwidth of the light returned from the grating 50 to the light source 11 is controlled.

[0039] In the light source device 1 according to this embodiment, light output from the light source 11 is circulated. Occasionally The light is dispersed by the grating 50 and enters the spatial light modulator 60. At least a part of the light reflected by the spatial light modulator 60 is then reflected by the Occasionally The light is returned from the grating 50 to the light source 11. In such a light source device 1, the spatial light modulator 60 is configured to be able to control the distribution of angles at which the light is reflected based on a control signal, and the rotation is controlled by controlling the distribution of the angles. Occasionally The bandwidth of the light returned from the grating 50 to the light source 11 is controlled. In this configuration, by changing the control signal, the distribution of angles at which the light is reflected from the spatial light modulator 60 is changed, and the rotation Occasionally It is possible to change the bandwidth of the light returned from the grating 50 to the light source 11. That is, according to the light source device 1 of this embodiment, Occasionally The bandwidth of the light returned from the grating 50 to the light source 11 can be adjusted arbitrarily.

[0040] The spatial light modulator 60 may control the distribution of angles at which the incident light is reflected by displaying a modulation pattern based on a control signal. In this way, by using the spatial light modulator 60 as a reflecting section, it is possible to easily and accurately reflect the incident light. Occasionally The bandwidth of the light returned from the grating 50 to the light source 11 can be adjusted.

[0041] The light source 11 outputs light according to the injection current, and the injection current and the control signal are changed over time to generate a circuit. Occasionally It is also possible to dynamically control the bandwidth of the light returned from the grating 50 to the light source 11. With this configuration, the bandwidth of the light can be adjusted more flexibly depending on the usage scene.

[0042] Possible application scenarios here include, for example, in the field of optical communications, evaluating how the performance of a coherent communication system or optical component changes depending on the optical bandwidth, or evaluating the impact of dynamic changes in the optical bandwidth. Alternatively, possible application scenarios include reducing temporal coherence in imaging using coherent light to reduce speckle noise. Note that application scenarios are not limited to the above.

[0043] The center of curvature of the reflecting surface 60a of the spatial light modulator 60 and the rotation Occasionally The spatial light modulator 60 and the diffraction grating 50 are aligned so that the beam center of the light incident on the diffraction grating 50 coincides with the beam center of the light incident on the diffraction grating 50. Occasionally A grating 50 may be disposed. With such a configuration, the paths of light before and after reflection on the reflecting surface 60a of the spatial light modulator 60 tend to be the same, Occasionally The bandwidth of the light returned from the grating 50 to the light source 11 can be increased.

[0044] Next, a light source device 1A according to a second embodiment will be described with reference to Fig. 7. Fig. 7 is a diagram schematically showing the light source device 1A according to the second embodiment. Note that in the following description, configurations different from the light source device 1 according to the first embodiment will be mainly described, and descriptions of common configurations will be omitted (the same applies to the third to seventh embodiments, which will be described later).

[0045] The light source device 1A shown in FIG. 7 has a phase-type SLM 160 that uses a segmented deformable mirror as a reflecting section, where the reflecting surface is structurally separated into pixels. This type of phase-type SLM 160 utilizes the fact that the reflecting part of the pixel translates to change the optical path length, so it is less susceptible to the influence of polarization on phase modulation. Even when using a phase-type SLM 160, it is possible to control the distribution of angles at which incident light is reflected based on a control signal from a drive circuit 170, thereby reducing the amount of light reflected. Occasionally The light source device 1 is similar to the light source device 1 described above in that it controls the bandwidth of the light returned from the grating 50 to the light source 11 .

[0046] Next, a light source device according to a third embodiment will be described. The light source device according to the third embodiment has a reflecting surface connected by a single continuous film as a reflecting unit. Such a reflecting unit may be configured, for example, to include a continuous deformable mirror. A continuous deformable mirror performs spatial phase modulation by deforming the reflecting surface using an actuator array behind the reflecting surface. The actuator array of such a phase-type SLM may be arranged, for example, in a square array or a hexagonal array. Such a phase-type SLM is less susceptible to polarization effects in phase modulation and suppresses the generation of unmodulated light, as seen in spatial light modulators with pixel structures. Since the reflecting surfaces are connected to each other by a continuous film, a phase-folded pattern cannot be displayed. Therefore, a lens pattern without phase folding may be used as the modulation pattern. To display a desired pattern, a control matrix (or influence function matrix) must be determined.

[0047] When a phase-type SLM using a continuous deformable mirror is used as the reflector, the actuator array layout of the phase-type SLM may be, for example, radial. Such a phase-type SLM is less susceptible to polarization effects in phase modulation, and suppresses the generation of unmodulated light, as seen in spatial light modulators with pixel structures. In this case, the modulation pattern has the same pattern center as the device center. When the modulation pattern is operated as, for example, a variable curvature mirror, a lens pattern without phase wrapping may be displayed. To display a desired pattern, a control matrix (or influence function matrix) must be determined.

[0048] Next, a light source device 1B according to a fourth embodiment will be described with reference to FIG. 8. FIG. 8 is a schematic diagram illustrating the light source device 1B according to the fourth embodiment. As shown in FIG. 8, the light source device 1 includes a variable curvature mirror (VCM) 260 as a reflector. The variable curvature mirror 260 controls the distribution of angles at which incident light is reflected by physically changing the radius of curvature of the reflecting surface based on a control signal from a drive circuit 270. The variable curvature mirror 260 can be changed into both a concave mirror and a convex mirror. Possible embodiments of the variable curvature mirror 260 include, for example, one that changes the pressure of a fluid behind the mirror, one that operates an actuator behind the mirror, one that utilizes thermal expansion, and one that utilizes electrostatic force. Such a variable curvature mirror 260 is less susceptible to polarization and suppresses the generation of unmodulated light, which is common in spatial light modulators with a pixel structure.

[0049] In this way, by changing the radius of curvature using the variable curvature mirror 260, Occasionally It is possible to appropriately adjust the bandwidth of the light returned to the light source from the grating 50. Furthermore, in the variable curvature mirror 260, compared to controlling the distribution of reflection angles by a modulation pattern such as a spatial light modulator, it is not necessary to consider the influence of polarized light or unmodulated light, and therefore the bandwidth of the light can be easily adjusted.

[0050] Next, a light source device 1C according to a fifth embodiment will be described with reference to FIG. 9. FIG. 9 is a diagram schematically showing the light source device 1C according to the fifth embodiment. As shown in FIG. 9, the light source device 1C has a variable-focus lens 361 and a plane mirror 362 (mirror) as a reflecting section. The variable-focus lens 361 controls the distribution of angles at which incident light is reflected by changing the focal length of the variable-focus lens 361 based on a control signal from a drive circuit 370. The variable-focus lens 361 controls the distribution of angles at which incident light is reflected by the rotation Occasionally It may be provided between the grating 50 and the plane mirror 362 and as close to the plane mirror 362 as possible.

[0051] In such a configuration, Occasionally The light dispersed by the grating 50 passes through a variable focus lens 361 and is incident on a plane mirror 362, and the light reflected by the plane mirror 362 passes through the variable focus lens 361 and the plane mirror 362. Occasionally The light returned to the light source 11 passes through the grating 50 and is returned to the light source 11. Because the light returned to the light source 11 passes through the variable-focus lens 361 twice, the composite focal length and principal plane are determined, and the focal length and the operating mode (control of the distribution of angles at which the light is reflected) are associated. This configuration is also compatible with both concave and convex mirrors. Possible configurations of the variable-focus lens 361 include those that change the shape of an object containing a liquid, those that utilize deformation of the liquid interface, those that utilize the electro-optic effect, and those that utilize liquid crystal. This configuration is less susceptible to the effects of polarization on phase modulation and to the effects of unmodulated light. However, when using a polarization-sensitive element such as liquid crystal, the effects of polarized light and unmodulated light must be taken into consideration.

[0052] In this way, by using the variable-focus lens 361 to change the focal length of the variable-focus lens 361, OccasionallyIt is possible to appropriately adjust the bandwidth of the light returned from the grating 50 to the light source 11. Furthermore, in this configuration, compared to controlling the distribution of reflection angles using a modulation pattern such as a spatial light modulator, it is not necessary to consider the influence of polarized light or unmodulated light (this need not be taken into account except in the case where a polarization-sensitive element such as a liquid crystal is used), and therefore the bandwidth of the light can be easily adjusted.

[0053] Next, a light source device 1D according to a sixth embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram schematically illustrating the light source device 1D according to the sixth embodiment. The light source device 1D shown in Fig. 10 includes an objective lens 90, an optical fiber 100, and a spectroscope (e.g., an optical spectrum analyzer) 110 in addition to the configuration of the light source device 1 according to the first embodiment. These additional components are for monitoring light from an end face of the light source 11 that is not coupled to the external resonator.

[0054] That is, in the light source device 1D, for example, light from an end face that is not coupled to an external resonator is coupled to an optical fiber 100 by an objective lens 90. Then, the light is input to an optical spectrum analyzer 110 via the optical fiber 100. The optical spectrum analyzer 110 measures the spectrum of the input light and outputs the measurement results to a PC 80. Then, the PC 80 generates a modulation pattern by feeding back the measurement results in the optical spectrum analyzer 110, and outputs the generated modulation pattern to a driving circuit 70. The modulation pattern by feeding back the measurement results is displayed on the spatial light modulator 60 based on a control signal from the driving circuit 70. In this way, in the light source device 1D, a circuit whose bandwidth is controlled based on the original control signal (first control signal) is generated. Occasionally A new control signal (second control signal) is generated based on the measurement result of the light returned from the grating 50 to the light source 11. In this case, the optical spectrum analyzer 110, the PC 80, and the driver circuit 70 constitute a control signal generator.

[0055] In this way, OccasionallyThe light returned from the grating 50 to the light source 11 is measured, the measurement results are fed back, and a new control signal (second control signal) is generated, making it easier to adjust the bandwidth of the light to a more desired value, taking into account the actual measurement results.

[0056] FIG. 11 is a diagram illustrating an example of interferometry using the light source device 1D shown in FIG. 10. In this interferometry, the interferometry is performed using light output from the light source 11 of the light source device 1D. A measurement object 606 shown in FIG. 11 is a measurement object (sample) in this interferometry. A CMOS camera 609 shown in FIG. 11 is a detector in this interferometry. An objective lens 601, a pinhole 602, a lens 603, a beam splitter 604, a reference mirror 605, a lens 607, and a lens 608 shown in FIG. 11 are an interferometer in this interferometry. A PC 610 performs predetermined processing based on the image acquired by the CMOS camera 609.

[0057] Light output from the light source 11 passes through an objective lens 601 and a pinhole 602 and reaches a lens 603. The objective lens 601 and the pinhole 602 function as a spatial filter. The light is collimated by the lens 603. The light collimated by the lens 603 reaches a beam splitter 604 and is split into light that passes directly to a measurement object 606 and light that is reflected and reaches a reference mirror 605. The light reflected by the measurement object 606 is reflected by the beam splitter 604, passes through lenses 607 and 608 that constitute a 4f system, and is detected by a CMOS camera 609. The light from the reference mirror 605 passes through the beam splitter 604, passes through lenses 607 and 608, and is detected by the CMOS camera 609.

[0058] In the above interferometer, the optical path length from the lens 607 to the reference mirror 605 and the optical path length from the lens 607 to the measurement object 606 both match the focal length of the lens 607. In addition, the optical path length from the lens 608 to the CMOS camera 609 matches the focal length of the lens 608.

[0059] The process of interference measurement using the light source device 1D shown in Fig. 10 will be described with reference to Fig. 12. Fig. 12 is a flowchart of interference measurement using the light source device 1D shown in Fig. 11.

[0060] As shown in FIG. 12, first, pre-processing is performed (step S1). In pre-processing, the temperature controller 30 starts temperature control of the TEC attached to the LD mount 12. Also, only the surface shape correction pattern is displayed on the spatial light modulator 60. Also, the reciprocal of the radius of curvature of the Fresnel lens pattern, which is the modulation pattern of the spatial light modulator 60, is set to 0. In this way, by using the reciprocal of the radius of curvature as a parameter, it becomes easy to handle both the case where the radius of curvature is positive (in the case of a concave mirror) and the case where it is negative (in the case of a convex mirror), and it is possible to eliminate the handling of the radius of curvature: ∞. Also, a target value for the spread (bandwidth) of the optical spectrum is set.

[0061] Next, the current controller 20 injects a current equal to or greater than the oscillation threshold into the light source 11, causing the light source 11 to oscillate (step S2). Next, a modulation pattern (phase pattern) in which the surface shape correction pattern and the Fresnel lens pattern with the set curvature radius are superimposed is displayed on the spatial light modulator 60 (step S3).

[0062] Next, the optical spectrum analyzer 110 measures the spectrum of the light (output light) returned to the light source 11 (step S4). Then, it is determined whether the spread (bandwidth) of the optical spectrum is close to a desired value (step S5).

[0063] If it is determined in step S5 that the spread of the optical spectrum is close to the desired value, then, for example, in the PC 610, the surface shape of the measurement object 606 is calculated from the image acquired by the CMOS camera 609 (step S6).

[0064] If it is determined in step S5 that the spread of the optical spectrum is not close to the desired value, it is determined whether or not the spread of the optical spectrum is greater than the desired value (step S7).

[0065] If it is determined in step S7 that the spread of the optical spectrum is greater than the desired value, it is determined whether the reciprocal of the radius of curvature has reached its lower limit (step S8). The lower limit of the reciprocal of the radius of curvature is, for example, (-1 / Occasionally The distance between the lattice 50 and the curvature radius may be set to the lower limit (the distance between the lattice 50 and the curvature radius 50). If it is determined in step S8 that the lower limit has been reached, the process of step S6 is performed. If it is determined in step S8 that the reciprocal of the curvature radius has not reached the lower limit, the reciprocal of the curvature radius is decreased (step S9), and the process is performed again from step S3.

[0066] If it is determined in step S7 that the spread of the optical spectrum is not greater than the desired value, it is determined whether the reciprocal of the radius of curvature has reached its upper limit (step S10). The upper limit of the reciprocal of the radius of curvature is, for example, (+1 / spatial light modulator 60 and Occasionally distance between the grid 50).

[0067] If it is determined in step S10 that the upper limit has been reached, it is determined whether the injection current is equal to or greater than a threshold current (step S11). If it is determined in step S11 that the injection current is equal to or greater than the threshold current, the injection current is set to equal to or less than the threshold current, and the reciprocal of the radius of curvature is set to 0 (step S12), and the process is repeated from step S3. If it is determined in step S11 that the injection current is not equal to or greater than the threshold current, the process of step S6 is performed.

[0068] If it is determined in step S10 that the upper limit has not been reached, the reciprocal of the radius of curvature is increased (step S13), and the process is repeated from step S3.

[0069] Next, a light source device 1E according to a seventh embodiment will be described with reference to Fig. 13. Fig. 13 is a diagram illustrating interference measurement using the light source device 1E according to the seventh embodiment. By using the light source device 1E, interference measurement can be performed in the same way as the light source device 1D according to the sixth embodiment described above. Here, the light source device 1E differs from the light source device 1D in that the light spectrum is measured (monitored) on the output light side used for interference measurement.

[0070] That is, the light source device 1E includes, as components for measuring the optical spectrum, a beam splitter 750, an objective lens 760, an optical fiber 770, and a spectroscope (for example, an optical spectrum analyzer) 120. The beam splitter 750 is Occasionally It is provided between the grating 50 and the objective lens 601. Occasionally The output light from the grating 50 reaches the beam splitter 750 and is split into light that passes through the beam splitter 750 and reaches the objective lens 601, and light that is reflected and reaches the objective lens 760. The light reflected by the beam splitter 750 is coupled to the optical fiber 770 by the objective lens 760. The light is then input to the optical spectrum analyzer 120 via the optical fiber 770. The optical spectrum analyzer 120 measures the spectrum of the input light and outputs the measurement results to the PC 710. The PC 710 then generates a modulation pattern by feeding back the measurement results from the optical spectrum analyzer 120 and outputs the generated modulation pattern to the driver circuit 70. The modulation pattern by feeding back the measurement results is displayed on the spatial light modulator 60 based on a control signal from the driver circuit 70. In this way, feedback control of the control signal can be performed, as in the sixth embodiment, by measuring the optical spectrum on the side of the output light used for interferometry. [Explanation of symbols]

[0071] 1,1A,1B,1C,1D,1E…Light source device, 11…Light source, 50…times Occasionally Grating, 60... spatial light modulator (reflecting portion), 60a... reflecting surface, 260... variable curvature mirror, 361... variable focus lens, 362... plane mirror (mirror).

Claims

1. a light source that outputs light; a reflecting unit having an input unit for a control signal and configured to be able to control the distribution of angles at which incident light is reflected based on the control signal; a diffraction grating that separates the light output from the light source and causes the light to be incident on the reflecting section, and returns at least a portion of the light reflected by the reflecting section to the light source, an optical resonator is formed by the light source and the reflector, and light returned to the light source is output; A light source device in which the bandwidth of light returned from the diffraction grating to the light source is controlled by controlling the angular distribution of light reflected at the reflecting portion based on the control signal.

2. the reflecting section includes a spatial light modulator, 2. The light source device according to claim 1, wherein the spatial light modulator controls a distribution of angles at which the incident light is reflected by displaying a modulation pattern based on the control signal.

3. the reflecting section includes a variable curvature mirror, 2. The light source device according to claim 1, wherein the variable curvature mirror controls a distribution of angles at which the incident light is reflected by changing a radius of curvature based on the control signal.

4. the reflecting unit includes a mirror and a variable-focus lens provided between the diffraction grating and the mirror, 2. The light source device according to claim 1, wherein the variable-focus lens controls a distribution of angles at which the incident light is reflected by changing a focal length of the variable-focus lens based on the control signal.

5. the light source outputs light in accordance with an injection current; 5. The light source device according to claim 1, wherein the bandwidth of the light returned from the diffraction grating to the light source is dynamically controlled by changing the injection current and the control signal over time.

6. The light source device according to any one of claims 1 to 4, wherein the reflecting portion and the diffraction grating are arranged so that the center of curvature of the reflecting surface of the reflecting portion coincides with the beam center of the light incident on the diffraction grating.

7. 5. The light source device according to claim 1, further comprising a control signal generation section that generates the second control signal based on a measurement result of the light output from the light source device.

8. outputting light from a light source toward a diffraction grating; inputting a control signal to a reflecting portion onto which the light dispersed by the diffraction grating is incident, the control signal controlling the angular distribution of the light reflected by the reflecting portion.

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