Light source device and control method

Abstract

This light source device is provided with: a light source that outputs light; a reflection unit that has a control signal input unit and is configured so as to be able to control the distribution of angles at which incident light is reflected on the basis of the control signal; and a diffraction lattice that splits the light outputted from the light source, enters the reflection part, and returns at least a portion of the light reflected by the reflection part to the light source, an optical resonator is formed by the light source and the reflection part, and the bandwidth of the light returned from the diffraction lattice to the light source is controlled by controlling the distribution of the angles of the light reflected by the reflection part on the basis of a control signal.

Description

Technical Field

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

[0002] Patent Document 1 describes a Littman / Metcalf type external resonator semiconductor laser. In the external resonator semiconductor laser of Patent Document 1, a wide spectrum (bandwidth) is achieved by replacing the end mirror with a concave mirror and setting the radius of curvature equal to the distance between the concave mirror and the diffraction grating.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent No. 7,245,642 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] In the external cavity semiconductor laser described above, the curvature radius of the concave mirror is fixed. In such a structure, the bandwidth of the light returning from the diffraction grating to the light source cannot be arbitrarily adjusted.

[0008] One embodiment of the present invention has been made in view of the above circumstances, and provides a light source device and a control method capable of arbitrarily adjusting the bandwidth of light returning from a diffraction grating to the light source.

[0009] Means used to solve problems

[0010] (1) A light source device according to one embodiment of the present invention comprises: a light source that outputs light; a reflecting portion that has an input portion for a control signal and is configured to control the distribution of angles of reflection of incident light based on the control signal; and a diffraction grating that splits light output from the light source and causes the light to be incident on the reflecting portion, and causes at least a portion of the light reflected at the reflecting portion to return to the light source, wherein an optical resonator is formed by the light source and the reflecting portion, and outputs light that returns to the light source, and the bandwidth of the light returned from the diffraction grating to the light source is controlled by controlling the distribution of angles of the light reflected at the reflecting portion based on the control signal.

[0011] In a light source device according to one embodiment of the present invention, light output from a light source is split at a diffraction grating and incident on a reflecting portion. Furthermore, at least a portion of the light reflected at the reflecting portion returns from the diffraction grating to the light source. In such a light source device, the reflecting portion can control the distribution of angles of light reflection based on a control signal, and control the bandwidth of light returning from the diffraction grating to the light source by controlling the distribution of the angles. According to such a structure, the distribution of angles of light reflection at the reflecting portion can be changed by changing the control signal, thereby changing the bandwidth of light returning from the diffraction grating to the light source. That is, according to a light source device according to one embodiment of the present invention, the bandwidth of light returning from the diffraction grating to the light source can be arbitrarily adjusted.

[0012] (2) In the light source device described in (1) above, the reflecting portion may include a spatial light modulator, wherein the spatial light modulator controls the distribution of angles at which incident light is reflected by displaying a modulation pattern based on a control signal. In this manner, by using the spatial light modulator as the reflecting portion, the bandwidth of light returning from the diffraction grating to the light source can be easily and accurately adjusted.

[0013] (3) In the light source device described in (1) above, the reflecting portion may be configured to include a variable curvature reflector, wherein the variable curvature reflector controls the distribution of angles of reflection of incident light by changing the radius of curvature based on a control signal. In this way, by using the variable curvature reflector to change the radius of curvature, the bandwidth of light returning from the diffraction grating to the light source can be appropriately adjusted. In addition, in the variable curvature reflector, compared to a case where the distribution of reflection angles is controlled by a modulation pattern, such as in a spatial light modulator, the bandwidth of light can be easily adjusted because there is no need to consider the influence of polarized light or unmodulated light.

[0014] (4) In the light source device described in (1) above, the reflecting portion may be configured to include: a reflector, and a variable focus lens disposed between the diffraction grating and the reflector, wherein the variable focus lens controls the distribution of the angle of reflection of the incident light by changing the focal length of the variable focus lens based on a control signal. In this way, by using the variable focus lens to change the focal length of the variable focus lens, the bandwidth of the light returning from the diffraction grating to the light source can be appropriately adjusted. In addition, in such a structure, compared with a case where the distribution of the reflection angle is controlled by a modulation pattern, such as a spatial light modulator, since there is no need to consider the influence of polarized light or unmodulated light (this need not be considered except when using a polarization-sensitive element such as a liquid crystal), the bandwidth of the light can be easily adjusted.

[0015] (5) In the light source devices described in (1) to (4) above, the light source may output light corresponding to the injected current, and the bandwidth of the light returning from the diffraction grating to the light source may be dynamically controlled by varying the injected current and the control signal over time. This configuration allows for more flexible adjustment of the light bandwidth depending on the usage scenario.

[0016] (6) In the light source devices described in (1) to (5) above, the reflecting portion and the diffraction grating may be arranged so that the center of curvature of the reflecting surface of the reflecting portion coincides with the center of the light beam incident on the diffraction grating. With such a configuration, the paths of the light before and after reflection on the reflecting surface of the reflecting portion tend to be the same, thereby widening the bandwidth of the light returning from the diffraction grating to the light source.

[0017] (7) The light source device described in (1) to (6) above may further include a control signal generating unit that generates a second control signal based on a measurement result of light output from the light source device. In this manner, by measuring the light returning from the diffraction grating to the light source and feeding back the measurement result, a new control signal (second control signal) can be generated, thereby taking into account the actual measurement result and easily adjusting the light bandwidth to a more desired value.

[0018] (8) A control method according to one embodiment of the present invention includes: outputting light from a light source toward a diffraction grating; and inputting a control signal for controlling the angular distribution of light reflected from the reflective portion into a reflective portion into which the light split by the diffraction grating enters. According to this control method, the bandwidth of light returning from the diffraction grating to the light source can be arbitrarily adjusted.

[0019] (9) In the light source device described in (1) to (4) above, the light source unit including the light source may be configured to include: an excitation light source that outputs excitation light; and a gain fiber that is an optical fiber having a gain corresponding to the excitation light. According to such a structure, it is possible to switch between laser oscillation and spontaneous emission amplification by adjusting the power of the excitation light. In addition, in the light source unit, by using a gain fiber having a gain corresponding to the excitation light, the light is confined in the gain fiber as a narrow space, which makes it easier to produce nonlinear effects. Such nonlinear effects are more easily produced by using a highly nonlinear fiber as the gain fiber. Examples of nonlinear effects include self-phase modulation, cross-phase modulation, modulation instability, stimulated Raman scattering, stimulated Brillouin scattering, four-wave mixing, and supercontinuum generation. By utilizing these nonlinear effects, for example, the spectrum can be further expanded, thereby increasing the degree of freedom in controlling the spectrum of light.

[0020] (10) The light source device described in (1) to (7) or (9) above may further include an optical fiber for guiding the light output from the diffraction grating. In this manner, due to the structure in which the light output from the diffraction grating is guided through the optical fiber, the light is confined within the optical fiber, making it easier to produce nonlinear effects. Such nonlinear effects are more easily produced by using highly nonlinear optical fibers as the optical fibers. By utilizing nonlinear effects, for example, the spectrum can be further expanded, thereby increasing the degree of freedom in controlling the light spectrum.

[0021] Effects of the Invention

[0022] According to one embodiment of the present invention, the bandwidth of light returning from the diffraction grating to the light source can be arbitrarily adjusted. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram schematically showing a light source device according to the first embodiment.

[0024] Figure 2 A diagram showing an example of a modulation pattern displayed on a spatial light modulator.

[0025] Figure 3 It is a diagram for explaining a first operation example of the light source device.

[0026] Figure 4It is a diagram for explaining a second operation example of the light source device.

[0027] Figure 5 It is a diagram for explaining a third operation example of the light source device.

[0028] Figure 6 It is a diagram for explaining a fourth operation example of the light source device.

[0029] Figure 7 This is a diagram schematically showing a light source device according to a second embodiment.

[0030] Figure 8 This is a diagram schematically showing a light source device according to a fourth embodiment.

[0031] Figure 9 This is a diagram schematically showing a light source device according to a fifth embodiment.

[0032] Figure 10 This is a diagram schematically showing a light source device according to a sixth embodiment.

[0033] Figure 11 It indicates the use of Figure 10 Diagram of the interferometric measurement of the light source setup shown.

[0034] Figure 12 It is used Figure 10 Flowchart of interferometric measurement of the light source device shown.

[0035] Figure 13 It is a diagram for explaining interference measurement using the light source device of the seventh embodiment.

[0036] Figure 14 This is a diagram schematically showing a light source device according to the eighth embodiment.

[0037] Figure 15 This is a diagram schematically showing a light source device according to a ninth embodiment. DETAILED DESCRIPTION

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same or corresponding parts are given the same reference numerals, and repeated descriptions are omitted.

[0039] Figure 1 This figure schematically illustrates a light source device 1 according to the first embodiment. Light source device 1 is an external cavity laser (ECL). Light source device 1 is, for example, a Littmann-type external cavity laser, and employs a structure in which first-order light from a diffraction grating is reflected by a mirror and returned to the semiconductor laser.

[0040] like Figure 1As shown, the light source device 1 includes a light source unit 10 , a current controller 20 , a temperature controller 30 , a lens 40 , a diffraction grating 50 , a spatial light modulator 60 (reflecting section), a drive circuit 70 , and a PC 80 .

[0041] The light source unit 10 is configured to include a light source 11 and an LD mount 12. The light source 11 is, for example, a semiconductor laser (LD: Laser Diode) that outputs light having a natural emission spectrum with a center wavelength of 850 nm. The light source 11 may also be, for example, a Fabry-Perot type semiconductor laser. The end face of the light source 11 on the side coupled to the external resonator (the side in the light output direction) may also be anti-reflection coated. The light source 11 is fixed to the LD mount 12. The LD mount 12 may also be a mount with a TEC (Thermo-Electric Cooler). In the light source device 1, an optical resonator is formed by the light source 11 and the spatial light modulator 60 (described later). In the light source device 1, light is output and returns to the light source 11 through the external resonator.

[0042] The current controller 20 supplies current to the light source 11 via the LD holder 12, causing the light source 11 to emit light. Specifically, the light source 11 emits light in accordance with the current (injected current) supplied from the current controller 20. The light source 11 generates laser oscillation in accordance with the supplied (injected) current value, or operates below the oscillation threshold.

[0043] The temperature controller 30 supplies current to the TEC provided on the LD holder 12 to control the heat absorption (or heat dissipation) of the TEC, thereby maintaining the temperature of the light source 11 constant via the TEC.

[0044] The lens 40 is a lens (e.g., a collimating lens) that efficiently couples the light output from the light source 11 to the light source 11 as it returns through the diffraction grating 50 and the spatial light modulator 60 (which makes one complete rotation within the external resonator). When the light emitted from the light source 11 is significantly diffused, the beam diameter and divergence angle can be adjusted by the lens 40. Furthermore, the light transmitted through the lens 40 may or may not be parallel light. The position of the lens 40 can also be fixed to a position where high light output is achieved, independent of the focal length of the modulation pattern (phase pattern) displayed on the spatial light modulator 60.

[0045] The diffraction grating 50 separates the light mixed with various wavelengths output from the light source 11 and makes the light incident on the spatial light modulator 60, and returns at least a portion of the light reflected by the spatial light modulator 60 to the light source 11. The diffraction grating 50 separates the light for each wavelength, with the first-order light heading toward the spatial light modulator 60 and the zero-order light being output.

[0046] The spatial light modulator 60 controls the angular distribution of incident light reflection by displaying a modulation pattern based on a control signal (described later). The spatial light modulator 60 is, for example, a reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM). The modulation pattern (phase pattern) is generated by the PC 80, input from the PC 80 to the driver circuit 70, and displayed on the spatial light modulator 60 based on a control signal from the driver circuit 70. Thus, the control signal input from the driver circuit 70 to the spatial light modulator 60 is a signal related to the display of the modulation pattern.

[0047] The spatial light modulator 60 displays a lens pattern as a modulation pattern, for example. As the lens pattern, for example, a Fresnel lens pattern (Fresnel lens pattern) may also be used. Hereinafter, in this embodiment, the lens pattern is described as a Fresnel lens pattern, but the lens pattern may also be an aspherical lens pattern, etc. The curvature radius of the Fresnel lens pattern is a value twice the focal length. The curvature radius 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, the focal length of the Fresnel lens pattern as the modulation pattern is changed, thereby changing the curvature radius of the Fresnel lens pattern, and the angular distribution of the light reflected from the spatial light modulator 60 is changed. When the angular distribution of the light reflected from the spatial light modulator 60 is changed, the consistency of the paths of the light before and after the reflection from the spatial light modulator 60 is changed. In the spatial light In the modulator 60, the higher the degree of consistency between the radius of curvature of the Fresnel lens pattern and the distance between the spatial light modulator 60 and the diffraction grating 50, the wider the wavelength band in which the paths of the light before and after the reflection of the spatial light modulator 60 are consistent (the wavelength band with high coupling efficiency with the light source 11). By controlling the angular distribution of the reflected light based on the control signal in the spatial light modulator 60, the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be controlled. That is, in the spatial light modulator 60, the expansion of the 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 expansion of the spectrum without moving or aligning the optical parts. In addition, the bandwidth of the light returning to the light source 11 depends on, for example, the wavelength dependence of the coupling efficiency with the light source 11 and the emission spectrum of the light source 11.

[0048] When the spatial light modulator 60 is a reflective liquid crystal spatial light modulator, the phase modulation performed by the spatial light modulator 60 is strongly affected by polarized light. The spatial light modulator 60 is configured so that the polarization direction in which phase modulation can be performed becomes Figure 1The x-direction or y-direction in the spatial light modulator 60 (i.e., the direction parallel to the reflection surface 60a of the spatial light modulator 60). The spatial light modulator 60 can also be configured so that the reflection surface 60a is parallel to the reflection surface of the diffraction grating 50, or it can be configured so that it is not parallel. The polarization direction of the spatial light modulator 60 that can perform phase modulation is, for example, consistent with the linear polarization direction of the light output from the light source 11. In addition, in the spatial light modulator 60, the optical system can be adjusted or the position of the modulation pattern can be adjusted in such a way that the normal extending from the center of the modulation pattern passes through the center of the light beam on the diffraction grating 50. The spatial light modulator 60 and the diffraction grating 50 can also be configured so that the center of curvature of the reflection surface 60a of the spatial light modulator 60 is consistent with the center of the light beam of the light incident on the diffraction grating 50. More specifically, the spatial light modulator 60 and the diffraction grating 50 may be arranged so that, when the radius of curvature of the reflecting surface 60a of the spatial light modulator 60 is changed, the locus of the center of curvature intersects with the center of the light beam incident on the diffraction grating 50. The center of curvature of the reflecting surface 60a of the spatial light modulator 60 refers to the center of curvature of the modulation pattern displayed on the spatial light modulator 60.

[0049] The spatial light modulator 60 can also display a predetermined surface shape correction pattern by overlapping the modulation pattern as needed. The surface shape correction pattern here refers to a pattern that corrects the shape of the reflecting surface 60a of the spatial light modulator 60. The spatial light modulator 60 can also further display a pattern that corrects the aberrations generated in the optical system by overlapping. In addition, the spatial light modulator 60 can also display a modulation pattern (Fresnel lens pattern) with different focal distances in the x-direction and the y-direction. In this case, for example, by optimizing the focal distance in the y-direction, the coupling efficiency of the light returning to the light source 11 can be improved. In addition, in the spatial light modulator 60, it is also possible to change only the focal distance in the x-direction and perform the above-mentioned control of the bandwidth of the light (spectrum expansion control).

[0050] In the spatial light modulator 60, there is a problem that unmodulated light appears as 0th order light. As a countermeasure to such a problem, it is also possible to Figure 2 As shown, as the modulation pattern displayed on the spatial light modulator 60, a pattern in which a blazed diffraction grating pattern is superimposed on a Fresnel lens pattern is used. Figure 2 5 shows a blazed diffraction lattice pattern 501 and a pattern 502 in which the blazed diffraction lattice pattern is superimposed on a Fresnel lens pattern. In this case, the first-order light diffracted by superimposing the blazed diffraction lattice pattern on the Fresnel lens pattern 502 can also be used as light returning to the light source 11.

[0051] Next, first to sixth operation examples will be described as operation examples of the light source device 1 .

[0052] Figure 3 1 is a diagram illustrating a first operation example of the light source device 1. Figure 3 As shown in (a), in the first operation example, the spatial light modulator 60 displays a modulation pattern in which the curvature radius of the Fresnel lens pattern is set to ∞ (plane mirror). In this case, the display Figure 3 A modulation pattern 503 of a uniform image as shown in (a). Figure 3 (b) shows the simulation result of the frequency band of the output light of the light source device 1 when the curvature radius of the Fresnel lens pattern is set to ∞. Figure 3 As shown in (b), when the curvature radius of the Fresnel lens pattern is set to ∞, the wavelength band in which the paths of the light before and after the reflection of the spatial light modulator 60 are consistent (the wavelength band with high coupling efficiency with the light source 11) becomes narrower. Figure 3 In the example (b), the bandwidth of light output from the light source device 1 is approximately 500 kHz. The spread of the oscillation spectrum depends on the gain frequency characteristics of the light source 11, the nonlinear behavior of the laser oscillation, and the bandwidth of the light returning to the light source 11.

[0053] Figure 4 1 is a diagram illustrating a second operation example of the light source device 1. Figure 4 In the second operation example shown in (a), the curvature radius of the Fresnel lens pattern displayed on the spatial light modulator 60 is set to be the same as the distance between the spatial light modulator 60 and the diffraction grating 50. In this case, the display Figure 4 The modulation pattern 504 of the convex lens with a focal length of 45 mm is shown in (a). In the spatial light modulator 60, only the area where the light reaches is phase modulated. Figure 4 The modulation pattern 504 shown in (a) exhibits a Fresnel lens pattern only in a limited area (the center area in the figure). When the radius of curvature of the Fresnel lens pattern is set to the same as the distance between the spatial light modulator 60 and the diffraction grating 50, the light beam expands from the center of curvature. Therefore, upon reflection from the spatial light modulator 60, all wavelength components return along the same path as their original path. In other words, the wavelength dependence of the diffraction angle at the diffraction grating 50 is eliminated by the spatial light modulator 60. Figure 4 (b) shows the simulation result of the frequency band of the output light of the light source device 1 when the curvature radius of the Fresnel lens pattern is set to be the same as the distance between the spatial light modulator 60 and the diffraction grating 50. Figure 4 As shown in (b) of FIG. 5 , when the curvature radius of the Fresnel lens pattern is set to be the same as the distance between the spatial light modulator 60 and the diffraction grating 50 , the bandwidth of the light returning to the light source 11 becomes extremely wide.

[0054] Figure 51 is a diagram illustrating a third operation example of the light source device 1. Figure 5 In the third operation example shown in (a), the curvature radius of the Fresnel lens pattern displayed on the spatial light modulator 60 is set to be larger than the distance between the spatial light modulator 60 and the diffraction grating 50. In this case, the display Figure 5 A modulation pattern 505 of a convex lens with a focal length of 55 mm, for example, as shown in (a). Figure 5 (b) shows the simulation result of the frequency band of the output light of the light source device 1 when the curvature radius of the Fresnel lens pattern is set to be larger than the distance between the spatial light modulator 60 and the diffraction grating 50. Figure 5 As shown in (b), when the radius of curvature of the Fresnel lens pattern is set to be larger than the distance between the spatial light modulator 60 and the diffraction grating 50, the bandwidth of the light returning to the light source 11 is wider than that in the first operating example and narrower than that in the second operating example. In other words, a spectrum expansion intermediate between the first and second operating examples is achieved.

[0055] Figure 6 1 is a diagram illustrating a fourth operation example of the light source device 1. Figure 6 In the fourth operation example shown in (a), the modulation pattern of the convex curved mirror (convex mirror) is displayed in the spatial light modulator 60. In this case, the display Figure 6 , for example, a modulation pattern 506 of a concave lens with a focal length of 45 mm, as shown in (a). When such a modulation pattern is displayed, the difference in the diffraction angle of the diffraction grating for each wavelength increases through the convex mirror, so that the wavelength band that can be directly returned to the light source 11 can be narrowed, and a narrower bandwidth can be achieved compared to the case where the radius of curvature is set to ∞ as in the first action example. In addition, the smaller the absolute value of the radius of curvature of the convex mirror, the smaller the width of the wavelength dependence of the coupling efficiency. In addition, when the diameter of the light beam of each wavelength is small enough on the reflecting surface (in the case of a few pixels), the intensity of the 0th order light can be reduced by displaying the diffraction grating pattern outside the column corresponding to the center wavelength (the pixel string in the y direction), thereby further narrowing the frequency band of the light. The direction of the diffraction grating pattern is, for example, set to the direction that diffracts the light in the y direction. The column corresponding to the center wavelength can also be multiple columns.

[0056] A fifth operating example of the light source device 1 will be described. In this fifth operating example, the injection current supplied from the current controller 20 to the light source 11 is set below the threshold current. In this case, the light source 11 does not generate laser oscillation and operates in the amplified spontaneous emission (ASE) region. Furthermore, since ASE is unpolarized light, a linear polarizer may be provided within the optical resonator formed by the light source 11 and the spatial light modulator 60.

[0057] The sixth operating example of the light source device 1 will be described. In this sixth operating example, the bandwidth (spectral spread) of the light returning from the diffraction grating 50 to the light source 11 is dynamically controlled by varying the injection current supplied by the current controller 20 to the light source 11 and the control signal supplied by the drive circuit 70 to the spatial light modulator 60 over time. Varying the control signal over time is, for example, equivalent to dynamically and continuously switching the modulation patterns of the first to fourth operating examples described above.

[0058] Next, the effects of the light source device 1 according to the first embodiment will be described.

[0059] The light source device 1 includes: a light source 11 that outputs light; a reflecting portion (spatial light modulator 60) having an input portion for a control signal and configured to control the distribution of angles of reflection of incident light based on the control signal; and a diffraction grating 50, which splits the light output from the light source 11 and makes it incident on the spatial light modulator 60, and returns at least a portion of the light reflected by the spatial light modulator 60 to the light source, forms an optical resonator by the light source 11 and the spatial light modulator 60, outputs light returned to the light source 11, controls the distribution of angles of light reflected by the spatial light modulator 60 based on the control signal, and thereby controls the bandwidth of the light returning from the diffraction grating 50 to the light source 11.

[0060] In the light source device 1 of the present embodiment, the light output from the light source 11 is split by the diffraction grating 50 and is incident on the spatial light modulator 60. Furthermore, at least a portion of the light reflected by the spatial light modulator 60 returns from the diffraction 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 of light reflection based on a control signal, and to control the bandwidth of the light returning from the diffraction grating 50 to the light source 11 by controlling the distribution of angles. According to such a structure, by changing the control signal, the distribution of angles of light reflection on the spatial light modulator 60 can be changed, thereby changing the bandwidth of the light returning from the diffraction grating 50 to the light source 11. That is, according to the light source device 1 of the present embodiment, the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be arbitrarily adjusted.

[0061] The spatial light modulator 60 can also control the distribution of the angles at which incident light is reflected by displaying a modulation pattern based on a control signal. Thus, by using the spatial light modulator 60 as a reflector, the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be easily and accurately adjusted.

[0062] Light source 11 can also output light corresponding to the injected current, so that the injected current and the control signal vary over time, thereby dynamically controlling the bandwidth of the light returning from diffraction grating 50 to light source 11. This structure allows for more flexible adjustment of the light bandwidth according to the usage scenario.

[0063] As an example of application scenarios, consider the field of optical communications, such as evaluating how the performance of coherent communication systems and optical components varies with the optical bandwidth, and the impact of dynamic changes in optical bandwidth. Alternatively, consider reducing temporal coherence to mitigate speckle noise in imaging using coherent light. Application scenarios are not limited to the above.

[0064] Alternatively, the spatial light modulator 60 and the diffraction grating 50 may be arranged so that the center of curvature of the reflection surface 60a of the spatial light modulator 60 coincides with the center of the light beam incident on the diffraction grating 50. With such a configuration, the paths of the light before and after reflection on the reflection surface 60a of the spatial light modulator 60 tend to become the same, and the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be widened.

[0065] Next, refer to Figure 7 , a light source device 1A according to a second embodiment will be described. Figure 7 The following description mainly focuses on the configurations that differ from the light source device 1 of the first embodiment, and descriptions of the same configurations are omitted (this also applies to the third to seventh embodiments described later).

[0066] Figure 7 The light source device 1A shown has, as a reflector, a phase-type SLM 160, which uses a segmented deformable mirror (Segmented Deformable Mirror) with a reflective surface as a pixel structure. In such a phase-type SLM 160, since the optical path length changes by shifting the reflective portion of the pixel, the phase modulation is less susceptible to the influence of polarized light. When using the phase-type SLM 160, the angle distribution of the incident light reflection is controlled based on the control signal from the drive circuit 170, and the bandwidth of the light returning from the diffraction grating 50 to the light source 11 is thereby controlled, similar to the light source device 1 described above.

[0067] Next, the light source device of the third embodiment is described. The light source device of the third embodiment has a reflecting surface connected by a continuous membrane as a reflecting portion. Such a reflecting portion can also be constructed to include a continuous deformable mirror, for example. The continuous deformable mirror deforms the reflecting surface through an actuator array located behind the reflecting surface, thereby performing spatial phase modulation. The configuration of the actuator array of such a phase-type SLM can also be, for example, a square array or a hexagonal array. In such a phase-type SLM, phase modulation is not easily affected by polarized light, and the generation of unmodulated light such as that seen in a spatial light modulator with a pixel structure is suppressed. In addition, since the reflecting surface is connected to each other by a continuous membrane, a phase-folded pattern cannot be displayed. Therefore, a lens pattern without phase folding can also be used as a modulation pattern. When displaying the desired pattern, it is necessary to determine the control matrix (or influence function matrix).

[0068] In the case where a phase-type SLM using a continuous deformable mirror is used as a reflecting part, the layout of the actuator array of the phase-type SLM can also be radial, for example. In such a phase-type SLM, phase modulation is not easily affected by polarized light, and the generation of unmodulated light such as that seen in a spatial light modulator having a pixel structure is suppressed. In the modulation pattern in this case, the center of the pattern is the same as the center of the device. When the modulation pattern is operated, for example, as a variable curvature mirror, a lens pattern without phase folding can also be displayed. When displaying the desired pattern, it is necessary to determine the control matrix (or influence function matrix).

[0069] Next, refer to Figure 8 , a light source device 1B according to a fourth embodiment will be described. Figure 8 Schematic diagram of a light source device 1B according to a fourth embodiment. Figure 8As shown, the light source device 1 has a variable curvature mirror (VCM) 260 as a reflecting portion. The variable curvature mirror 260 controls the distribution of the angles at which incident light is reflected by physically changing the radius of curvature of the reflecting surface based on a control signal from the driving circuit 270. The variable curvature mirror 260 can be changed into both a concave mirror and a convex mirror. As examples of the variable curvature mirror 260, for example, a mirror that changes the pressure of the fluid behind the mirror, a mirror that actuates an actuator behind the mirror, a mirror that utilizes thermal expansion, a mirror that utilizes electrostatic force, and the like can be considered. In such a variable curvature mirror 260, it is not easily affected by polarized light, and the generation of unmodulated light such as that seen in a spatial light modulator having a pixel structure is suppressed.

[0070] By changing the radius of curvature using the variable curvature mirror 260, the bandwidth of the light returning from the diffraction grating 50 to the light source can be appropriately adjusted. Furthermore, compared to a spatial light modulator, for example, where the distribution of reflection angles is controlled by a modulation pattern, the variable curvature mirror 260 does not need to consider the effects of polarized light or unmodulated light, making it possible to easily adjust the bandwidth of light.

[0071] Next, refer to Figure 9 , a light source device 1C according to a fifth embodiment will be described. Figure 9 Schematic diagram of a light source device 1C according to the fifth embodiment. Figure 9 As shown, light source device 1C includes a variable focus lens 361 and a plane mirror 362 (reflecting mirror) as a reflecting unit. Variable focus lens 361 controls the angular distribution of reflected incident light by varying its focal length based on a control signal from drive circuit 370. Variable focus lens 361 can also be positioned between diffraction grating 50 and plane mirror 362, preferably as close to plane mirror 362 as possible.

[0072] In such a structure, the light split by the diffraction grating 50 is incident on the plane mirror 362 via the variable focus lens 361, and the light reflected by the plane mirror 362 returns to the light source 11 via the variable focus lens 361 and the diffraction grating 50. Since the light returning to the light source 11 passes through the variable focus lens 361 twice, the focal length and the main plane are calculated to correspond to the operation mode (control of the distribution of the angle of light reflection). In addition, such a structure can correspond to both concave mirrors and convex mirrors. As the variable focus lens 361, for example, the following forms can be considered: a lens that changes the shape of an object sealed with liquid, a lens that utilizes the deformation of the liquid interface, a lens that utilizes the electro-optical effect, a lens that utilizes liquid crystal, etc. In such a structure, phase modulation is not easily affected by polarized light, and is also not easily affected by unmodulated light. However, when using an element that is sensitive to polarized light, such as liquid crystal, it is necessary to consider the influence of polarized light and unmodulated light.

[0073] In this way, by using the variable-focus lens 361 and changing the focal length of the variable-focus lens 361, the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be appropriately adjusted. Furthermore, in this configuration, compared to, for example, a spatial light modulator that controls the distribution of the reflection angles of the modulation pattern, there is no need to consider the effects of polarized light or unmodulated light (except when using a polarization-sensitive element such as liquid crystal), making it possible to easily adjust the bandwidth of light.

[0074] Next, refer to Figure 10 , a light source device 1D according to a sixth embodiment will be described. Figure 10 It is a diagram schematically showing a light source device 1D according to the sixth embodiment. Figure 10 The light source device 1D shown includes, in addition to the configuration of the light source device 1 of the first embodiment, an objective lens 90, an optical fiber 100, and a spectrometer (e.g., a spectrum analyzer) 110. These additional configurations are used to monitor light from the end face of the light source 11 that is not coupled to an external resonator.

[0075] 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 the optical fiber 100 via the objective lens 90. Furthermore, the light is input to the 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 result to the PC 80. Furthermore, the PC 80 generates a modulation pattern that feeds back the measurement result of the optical spectrum analyzer 110 and outputs it to the drive circuit 70. The modulation pattern that feeds back the measurement result is displayed on the spatial light modulator 60 based on the control signal from the drive circuit 70. Thus, in the light source device 1D, a new control signal (second control signal) that feeds back the measurement result is generated based on the measurement result of the light returning from the diffraction grating 50 to the light source 11, whose bandwidth is controlled based on the original control signal (first control signal). In this case, the optical spectrum analyzer 110, the PC 80, and the drive circuit 70 correspond to a control signal generation unit.

[0076] In this way, by measuring the light returning from the diffraction grating 50 to the light source 11 and feeding back the measurement result, a new control signal (second control signal) is generated, thereby making it possible to more easily adjust the light bandwidth to a more desired value taking into account the actual measurement result.

[0077] Figure 11 It indicates the use of Figure 10 FIG. 1 is a diagram showing an example of interferometry using the light source device 1D shown in FIG. In this interferometry, interferometry is performed using light output from the light source 11 of the light source device 1D. Figure 11 The illustrated measurement object 606 is a measurement object (sample) in this interferometry. Figure 11 The CMOS camera 609 shown is the detector in this interferometry measurement. Figure 11 The objective lens 601 , pinhole 602 , lens 603 , beam splitter 604 , reference mirror 605 , lens 607 , and lens 608 are shown as interferometers in the present interferometry.

[0078] Light output from light source 11 passes through objective lens 601 and pinhole 602 and reaches lens 603. Objective lens 601 and pinhole 602 function as a spatial filter. Light passes through lens 603 and becomes parallel light. The parallel light passed through lens 603 reaches beam splitter 604 and is split into light that directly passes through and reaches measurement object 606, and light that is reflected and reaches reference mirror 605. Light reflected from measurement object 606 is reflected by beam splitter 604, passes through lenses 607 and 608 that constitute a 4f system, and is detected by CMOS camera 609. Furthermore, light from reference mirror 605 passes through beam splitter 604, lenses 607 and 608, and is detected by CMOS camera 609.

[0079] In the interferometer described above, the optical path length from lens 607 to reference mirror 605 and the optical path length from lens 607 to measurement object 606 both coincide with the focal length of lens 607. Furthermore, the optical path length from lens 608 to CMOS camera 609 coincides with the focal length of lens 608.

[0080] Reference Figure 12 ,illustrate Figure 10 The interferometry process of the light source device 1D is shown. Figure 12 It is used Figure 11 Flowchart of interferometric measurement of the light source device 1D shown.

[0081] like Figure 12 As shown, first, pre-processing is performed (step S1). In the pre-processing, the temperature control of the TEC placed on the LD fixture 12 is started by the temperature controller 30. In addition, only the surface shape correction pattern is displayed on the spatial light modulator 60. In addition, the reciprocal of the curvature radius of the Fresnel lens pattern as the modulation pattern of the spatial light modulator 60 is set to 0. In this way, by setting the reciprocal of the curvature radius as a parameter, it is easy to process in any case where the curvature radius is positive (in the case of a concave mirror) and negative (in the case of a convex mirror), and the processing of the curvature radius: ∞ is canceled. In addition, the target value of the spectrum expansion (bandwidth) is set.

[0082] Next, a current exceeding the oscillation threshold is injected into the light source 11 via the current controller 20, causing the light source 11 to generate laser oscillation (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).

[0083] Next, the optical spectrum analyzer 110 measures the spectrum of the light (output light) returning to the light source 11 (step S4). Then, it is determined whether the spread (bandwidth) of the spectrum is close to a desired value (step S5).

[0084] When it is determined in step S5 that the spread of the spectrum is close to the desired value, for example, the PC 610 calculates the surface shape of the measurement object 606 based on the image acquired by the CMOS camera 609 (step S6 ).

[0085] If it is determined in step S5 that the spread of the spectrum is not close to the expected value, it is determined whether the spread of the spectrum is larger than the expected value (step S7).

[0086] If it is determined in step S7 that the spectrum expansion is greater than the expected value, a determination is made as to whether the reciprocal of the radius of curvature has reached a lower limit (step S8). The lower limit of the reciprocal of the radius of curvature may be, for example, (-1 / the distance between the spatial light modulator 60 and the diffraction grating 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 radius of curvature has not reached the lower limit, the reciprocal of the radius of curvature is decreased (step S9), and the process of step S3 is repeated.

[0087] If it is determined in step S7 that the spectrum expansion is not greater than the expected value, it is determined whether the reciprocal of the radius of curvature has reached an upper limit (step S10). The upper limit of the reciprocal of the radius of curvature may be, for example, (+1 / the distance between the spatial light modulator 60 and the diffraction grating 50).

[0088] If it is determined in step S10 that the upper limit has been reached, it is determined whether the injected current is greater than or equal to the threshold current (step S11). If it is determined in step S11 that the injected current is greater than or equal to the threshold current, the injected current is set to less than or equal to the threshold current, and the inverse of the curvature radius is set to 0 (step S12), and the process is repeated from step S3. If it is determined in step S11 that the injected current is not greater than or equal to the threshold current, the process of step S6 is performed.

[0089] If it is determined in step S10 that the upper limit has not been reached, the inverse of the curvature radius is increased (step S13 ), and the process is restarted from step S3 .

[0090] Next, refer to Figure 13 , a light source device 1E according to a seventh embodiment will be described. Figure 13 This figure illustrates interferometry using a light source device 1E according to the seventh embodiment. Using the light source device 1E, interferometry can be performed in the same manner as the light source device 1D according to the sixth embodiment described above. The light source device 1E differs from the light source device 1D described above in that the spectrum is measured (monitored) on the output light side used for interferometry.

[0091] That is, the light source device 1E, as a structure for measuring a spectrum, includes: a beam splitter 750, an objective lens 760, an optical fiber 770, and a spectrometer (e.g., an optical spectrum analyzer) 120. The beam splitter 750 is disposed between the diffraction grating 50 and the objective lens 601. The output light from the diffraction grating 50 reaches the beam splitter 750 and is split into light that directly transmits 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 via the objective lens 760. Then, this light is 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 that reflects the measurement results of the optical spectrum analyzer 120 and outputs it to the drive circuit 70. The modulation pattern that reflects the measurement results is displayed on the spatial light modulator 60 based on a control signal from the drive circuit 70. In this manner, by measuring the spectrum on the output light side for interference measurement, feedback control of the control signal can be performed in the same manner as in the sixth embodiment.

[0092] Next, refer to Figure 14 , a light source device 1F according to an eighth embodiment will be described. Figure 14 It is a diagram schematically showing a light source device 1F according to the eighth embodiment. Figure 14 The light source device 1F shown has the same basic structure as the light source device 1 of the first embodiment, but differs from the light source device 1 in that a light source unit 10F is provided instead of the light source unit 10 .

[0093] The light source unit 10F is configured to include: a light source 11 (excitation light source), an LD fixture 12, a lens 13, an optical fiber 14, and a gain fiber 15. The light source 11 and the LD fixture 12 have the same structure as the light source 11 and the LD fixture 12 of the light source unit 10 of the first embodiment. The light source 11 is a light source that outputs excitation light that excites the gain fiber 15, for example, an LD. The lens 13 is a lens that focuses the excitation light output from the light source 11 to the incident end 14a of the optical fiber 14. The optical fiber 14 is an optical fiber that guides the excitation light incident from the incident end 14a to the gain fiber 15. The output end 14b of the optical fiber 14 is connected to the incident end 15a of the gain fiber 15. The optical fiber 14 can also be, for example, a single-mode optical fiber.

[0094] The gain fiber 15 is a fiber amplifier having a gain corresponding to the excitation light incident from the incident end 15a via the optical fiber 14. The gain fiber 15 is, for example, a double-clad fiber in which a rare earth element is doped in the optical fiber core. In this case, the gain fiber 15 obtains optical gain by induced emission from the rare earth element. As the rare earth element, Yb (ytterbium) or Er (erbium) or the like can also be used. The gain fiber 15 can also be a single-mode gain fiber. By using a single-mode gain fiber, nonlinearity can be improved and spatial mode selection can be performed. In addition, the gain fiber 15 can also be a highly nonlinear fiber.

[0095] A fiber Bragg grating may be formed in the gain fiber 15. Furthermore, the gain fiber 15 and the optical fiber 14 may be connected via another optical fiber (not shown), and a fiber Bragg grating may be formed in the other optical fiber. Furthermore, the gain fiber 15 and the optical fiber 14 may be connected via, for example, a WDM (Wavelength Division Multiplexing) coupler.

[0096] In a structure with such a gain fiber 15, it is possible to switch between laser oscillation and spontaneous emission amplification by adjusting the power of the excitation light. Furthermore, in the light source unit 10F, by using a gain fiber 15 with a gain corresponding to the excitation light, the light is confined within the narrow space of the gain fiber 15, increasing the optical power and facilitating the generation of nonlinear effects. As light travels back and forth multiple times within the optical resonator, the nonlinear effects can be accumulated, generating even greater nonlinear effects. Such nonlinear effects are more easily generated by using a highly nonlinear fiber as the gain fiber 15. Examples of nonlinear effects include self-phase modulation, cross-phase modulation, modulation instability, stimulated Raman scattering, stimulated Brillouin scattering, four-wave mixing, and supercontinuum generation. By utilizing these nonlinear effects, for example, further broadening the spectrum, the degree of freedom in spectral control of light is increased.

[0097] Next, refer to Figure 15 , a light source device 1G according to a ninth embodiment will be described. Figure 15 It is a diagram schematically showing a light source device 1G according to a ninth embodiment. Figure 15The basic structure of the light source device 1G shown is the same as that of the light source device 1 of the first embodiment, but differs from the light source device 1 in that it includes a lens 151 and an optical fiber 152. The lens 151 and the optical fiber 152 are provided on the path along which light output from the diffraction grating 50 travels.

[0098] The lens 151 is a coupling lens for coupling the light output from the diffraction grating 50 to the optical fiber 152 .

[0099] Optical fiber 152 guides the light output from diffraction grating 50, i.e., the light coupled through lens 151. Optical fiber 152 guides light incident from input end 152a, causing the light to exit from output end 152b. Optical fiber 152 can also be a single-mode optical fiber. Using a single-mode optical fiber can enhance nonlinearity and enable spatial mode selection. Furthermore, optical fiber 152 can also be a highly nonlinear optical fiber.

[0100] In this way, according to the structure in which the light output from the diffraction lattice 50 is guided through the optical fiber 152, the light is confined in the optical fiber 152, and a nonlinear effect is easily generated. In such a structure, the light passes through the optical fiber 152 only once, so it is easy to predict the spectrum after the nonlinear effect is generated, and the ease of control is improved. Such a nonlinear effect is more easily generated by using a high nonlinear optical fiber as the optical fiber 152. By utilizing the nonlinear effect, for example, further expanding the spectrum, etc., the degree of freedom of spectral control of the light is increased. In addition, such a structure with an optical fiber for guiding the light output from the diffraction lattice 50 is not limited to Figure 15 For example, the following method can also be used Figure 11 As shown in FIG. 1 , the optical fiber 100 is provided with a structure for guiding light emitted from the end face (rear end face) of the light source 11 that is not coupled to the external resonator. Figure 14 The connection between the optical fiber 14 and the gain fiber 15 is inserted into a WDM coupler or the like to extract light and includes an optical fiber for guiding the extracted light. All structures are the same in that they include an optical fiber for guiding the light output from the diffraction grating 50.

[0101] Description of Reference Signs

[0102] 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G…light source device, 11…light source, 50…diffraction grating, 60…spatial light modulator (reflection part), 60a…reflection surface, 152…optical fiber, 260…variable curvature reflector, 361…variable focus lens, 362…plane reflector (reflection mirror).

Claims

1. A light source device, wherein: have: a light source, which outputs light; a reflecting portion having an input portion for a control signal and configured to control the distribution of angles at which incident light is reflected based on the control signal; and a diffraction grating that splits the light output from the light source and makes it incident on the reflecting portion, and returns at least a part of the light reflected by the reflecting portion to the light source, The light source and the reflector form an optical resonator, and output light returning to the light source. By controlling the angular distribution of the light reflected by the reflecting portion based on the control signal, the bandwidth of the light returning from the diffraction grating to the light source is controlled.

2. The light source device according to claim 1, wherein: The reflecting unit is configured to include a spatial light modulator, The spatial light modulator controls the distribution of the angles of reflection of the incident light by displaying a modulation pattern based on the control signal.

3. The light source device according to claim 1, wherein: The reflecting part is configured to include a variable curvature reflecting mirror. The variable curvature mirror controls the distribution of the angle at which the incident light is reflected by changing the radius of curvature based on the control signal.

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

5. The light source device according to any one of claims 1 to 4, wherein: The light source outputs light corresponding to the injected current, By varying the injection current and the control signal over time, the bandwidth of light returning from the diffraction grating to the light source is dynamically controlled.

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 center of a beam of light incident on the diffraction grating.

7. The light source device according to any one of claims 1 to 4, wherein: The device further includes a control signal generating unit configured to generate the second control signal based on a measurement result of light output from the light source device.

8. A method for controlling a light source device, in, include: outputting light from the light source toward the diffraction lattice; as well as A control signal for controlling the angular distribution of the light reflected by the diffraction grating is input to the reflecting portion on which the light split by the diffraction grating is incident.

9. The light source device according to any one of claims 1 to 4, wherein: The light source unit including the light source includes: an excitation light source that outputs excitation light; and a gain fiber that is an optical fiber having a gain corresponding to the excitation light.

10. The light source device according to any one of claims 1 to 4, wherein: The invention further includes an optical fiber for guiding the light output from the diffraction grating.

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