Light source device

Abstract

The light source device includes: a light source outputting light; a spatial light modulator having an input unit for a control signal and configured so as to be able to control the distribution of the angle of reflection of incident light on the basis of the control signal; a diffraction grating that splits the light output from the light source and enters the spatial light modulator, and returns at least a portion of the light reflected by the spatial light modulator to the light source; and a pinhole through which only a portion of the light returned from the diffraction grating in a spatially dispersed state passes. Thus, in the light source device, an optical resonator is formed including the light source and the spatial light modulator, and light returned to the light source through the pinhole is output.

Description

Technical Field

[0001] One aspect of the present invention relates to a light source device. Background Technology

[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 obtained by changing the end face mirror to a concave mirror and making its radius of curvature equal to the distance between the concave mirror and the diffraction grating.

[0003] Existing technical documents

[0004] Patent documents

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

[0006] The technical problem that the invention aims to solve

[0007] Here, in the aforementioned external resonator semiconductor laser, since the light split by the diffraction grating is returned by the end mirror and coupled with a single-mode LD (Laser Diode) or the like to limit the wavelength, the elements that can be used as light sources are limited.

[0008] One aspect of the present invention was made in view of the above-mentioned circumstances, and aims to provide a light source device that does not limit the elements used as light sources.

[0009] Technical means to solve the problem

[0010] (1) A light source device according to one aspect of the present invention includes: a light source for outputting light; a reflective section having an input section for a control signal and configured to control the distribution of the angle of reflection of incident light based on the control signal; a diffraction grating for splitting light output from the light source and incident on the reflective section, and for returning at least a portion of the light reflected by the reflective section to the light source; and a spatial filter for allowing only a portion of the light returning from the diffraction grating in a spatially dispersed state to pass through. Thus, in the light source device 1, an optical resonator is formed by including the light source and the reflective section, and light returning to the light source through the spatial filter is output.

[0011] In one aspect of the light source apparatus of the present invention, light output from the light source is split by a diffraction grating and incident on a reflective section. Then, at least a portion of the light reflected by the reflective section returns from the diffraction grating to the light source. Here, a spatial filter is provided between the diffraction grating and the light source, allowing only a portion of the light returning from the diffraction grating in a spatially dispersed state to pass through, and the light returning to the light source through this spatial filter is output. Thus, by providing a spatial filter between the diffraction grating and the light source, the wavelength of the light returning to the light source and output is limited. Since the spatial filter has a wavelength-limiting function, a wavelength-limiting function is not required for the light source (or the optical fiber added within the optical resonator, etc.), and various light sources can be used. As described above, according to one aspect of the present invention, a light source apparatus that does not limit the elements used as a light source can be provided.

[0012] (2) In the light source device described in (1) above, the spatial filter can be a pinhole, a transmission mask, one or more slits, or a single-mode fiber. With such a structure, only a portion of the spatially dispersed light can be allowed to pass through appropriately.

[0013] (3) The light source device described in (1) or (2) above may also include a focusing lens that focuses the light returning from the diffraction grating, and a spatial filter is disposed at the focusing point of the focusing lens. With such a structure, the wavelength can be appropriately limited by the spatial filter.

[0014] (4) In the light source apparatus described in (1) to (3) above, the bandwidth of the light returning from the diffraction grating can also be controlled by controlling the distribution of the angle of light reflected in the reflective part based on the control signal. With this structure, by changing the control signal, the distribution of the angle of light reflection in the reflective part changes, and the bandwidth of the light returning from the diffraction grating to the light source can be changed. That is, with this structure, the bandwidth of the light returning from the diffraction grating to the light source can be arbitrarily adjusted.

[0015] The effects of the invention

[0016] According to one aspect of the present invention, it is possible to provide a light source device that does not limit the elements used as light sources. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the light source device of this embodiment.

[0018] Figure 2 This is a diagram showing an example of a modulation pattern displayed on a spatial light modulator.

[0019] Figure 3 This is a diagram illustrating the wavelength limiting function of a single-mode LD.

[0020] Figure 4This is a diagram illustrating a modified spatial filter.

[0021] Figure 5 This is a diagram illustrating a modified spatial filter. Detailed Implementation

[0022] Hereinafter, this embodiment will be described in detail with reference to the accompanying drawings. Furthermore, identical or equivalent parts are labeled with the same symbols in each drawing, and repeated descriptions are omitted.

[0023] Figure 1 This is a schematic diagram illustrating the light source device 1 according to the first embodiment. The light source device 1 is an externally resonant laser (ECL). For example, the light source device 1 is a Littman type externally resonant laser, configured to cause the primary light of the diffraction grating to be reflected by a mirror and returned to the semiconductor laser.

[0024] like Figure 1 As shown, the light source device 1 includes a light source unit 10, a current controller 20, a temperature controller 30, a lens 40 (condenser lens), a diffraction grating 50, a spatial light modulator 60 (reflector), a driving circuit 70, a PC 80, a lens 91, and a pinhole 92 (spatial filter).

[0025] The light source unit 10 is configured to include a light source 11 and an LD support 12. The light source 11 is, for example, a semiconductor laser (LD) that outputs light with a naturally emitted spectrum centered at 850 nm. The light source 11 can be, for example, a Fabry-Perot type semiconductor laser. The center wavelength of the light output by the light source 11 only needs to be between 10 nm and 3 mm. An anti-reflective coating can be applied to the end face of the side of the light source 11 that is coupled to the external resonator (the light output direction side). The light source 11 is mounted on the LD support 12. The LD support 12 can be a support with a TEC (Thermo-Electric Cooler). In the light source device 1, an optical resonator is formed by including the light source 11 and the spatial light modulator 60 (described below). In the light source device 1, light returning to the light source 11 via the external resonator (light returning to the light source 11 through the pinhole 92) is output.

[0026] The current controller 20 is a structure that supplies current to the light source 11 via the LD support 12, causing the light source 11 to output light. That is, the light source 11 outputs light corresponding to the current (injected current) supplied from the current controller. The light source 11 causes laser oscillation or operates below the oscillation threshold according to the supplied (injected) current value.

[0027] The temperature controller 30 controls the heat absorption (or heat dissipation) of the TEC by supplying current to the TEC equipped on the LD bracket 12, thereby maintaining the temperature of the light source 11 at a certain structure through the TEC.

[0028] Lens 40 is a lens that efficiently couples the light emitted from light source 11 to pinhole 92 as it returns through diffraction grating 50 and spatial light modulator 60 (which orbits once within an external resonator). That is, lens 40 functions as a focusing lens that concentrates the light returning from diffraction grating 50 onto pinhole 92. The light emitted from pinhole 92 is significantly broadened, and the beam diameter and divergence angle are adjusted by lens 40. The position of lens 40 can be fixed to achieve high light output regardless of the focal distance of the modulation pattern (phase pattern) displayed on spatial light modulator 60.

[0029] The diffraction grating 50 is a structure that splits the mixed light of various wavelengths output from the light source 11 and directs it to the spatial light modulator 60, so that at least a portion of the light reflected by the spatial light modulator 60 returns to the light source 11. In the diffraction grating 50, the light is split according to each wavelength, the first-order light is directed toward the spatial light modulator 60, and the zero-order light is extracted as the output light.

[0030] The spatial light modulator 60 has a control signal input section, which controls the distribution of the angle of reflection of incident light by displaying a modulation pattern based on the control signal. The spatial light modulator 60 is, for example, a spatial light modulator (SLM) of a reflective liquid crystal on silicon (LCOS). The modulation pattern (phase pattern) is generated in the PC80 and input from the PC80 to the driving circuit 70, and is displayed in the spatial light modulator 60 based on the control signal from the driving circuit 70. Thus, the control signal input from the driving circuit 70 to the spatial light modulator 60 is the signal involved in the display of the modulation pattern.

[0031] The spatial light modulator 60 displays a lens pattern as a modulation pattern, for example. A Fresnel lens pattern can be used, for example. Hereinafter, this embodiment will be described using a Fresnel lens pattern as an example, but other lens patterns, such as aspherical lens patterns, may also be used. The radius of curvature of the Fresnel lens pattern is, for example, twice the focal distance. The radius of curvature is positive for a concave mirror and negative for a convex mirror. The focal distance is positive for a convex lens and negative for a concave lens. In the spatial light modulator 60, by changing the focal distance of the Fresnel lens pattern used as the modulation pattern, the radius of curvature of the Fresnel lens pattern changes, and the angular distribution of the light reflected from the spatial light modulator 60 changes. When the angular distribution of the light reflected from the spatial light modulator 60 changes, the consistency of the light path before and after reflection in the spatial light modulator 60 changes. In the spatial light modulator 60, the higher the 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 region (the wavelength region with high coupling efficiency to the light source 11) in the spatial light modulator 60 where the paths of light before and after reflection are consistent. Thus, in the spatial light modulator 60, by controlling the distribution of the angle of the reflected light based on a control signal, 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, by changing the focal distance of the Fresnel lens pattern, the spectral expansion can be controlled. Thus, the spatial light modulator 60 can control the spectral expansion without the need for movement or alignment of optical components. Furthermore, the bandwidth of the light returning to the light source 11 is determined, for example, by the wavelength dependence of the coupling efficiency to the light source 11, the emission spectrum of the light source 11, and the wavelength dependence of the transmittance of spatial filters such as the pinhole 92 (e.g., the transmittance of spatial filters at various wavelengths of the light returning from the diffraction grating 50 to the light source 11).

[0032] In the case of a spatial light modulator for a reflective liquid crystal, the phase modulation based on the spatial light modulator 60 is strongly affected by polarized light. The spatial light modulator 60 is configured such that the polarization direction capable of phase modulation is... Figure 1The spatial light modulator 60 can be configured such that the x-direction or y-direction (i.e., the direction parallel to the reflecting surface 60a in the spatial light modulator 60) is parallel to or not parallel to the reflecting surface in the diffraction grating 50. The polarization direction capable of phase modulation in the spatial light modulator 60 is, for example, aligned with the linear polarization direction of the light output from the light source 11. Furthermore, in the spatial light modulator 60, the optical system or the position of the modulation pattern can be adjusted such that the normal extending from the center of the modulation pattern passes through the beam center of the light on the diffraction grating 50. The spatial light modulator 60 and the diffraction grating 50 can be configured such that the center of curvature of the reflecting surface 60a of the spatial light modulator 60 coincides with the beam center of the light incident on the diffraction grating 50. More specifically, the spatial light modulator 60 and the diffraction grating 50 can also be configured such that the trajectory of the center of curvature of the reflecting surface 60a of the spatial light modulator 60, under varying curvature radius, intersects the beam center of the light incident on the diffraction grating 50. Furthermore, 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.

[0033] The spatial light modulator 60 can also display a pattern that overlaps a predetermined surface shape correction pattern with a modulation pattern, as needed. Here, the surface shape correction pattern is a pattern that corrects the shape on the reflecting surface 60a of the spatial light modulator 60. The spatial light modulator 60 can also display patterns that correct aberrations generated in the optical system. Furthermore, the spatial light modulator 60 can also display modulation patterns (Fresnel lens patterns) with different focal distances in the x and y directions. 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. Furthermore, in the spatial light modulator 60, the aforementioned control of the light bandwidth (spectral expansion control) can be performed by only changing the focal distance in the x direction.

[0034] In the spatial light modulator 60, there is a problem where unmodulated light appears as zero-order light. As a countermeasure to this problem, such as... Figure 2 As shown, as a modulation pattern displayed on the spatial light modulator 60, a pattern that overlaps the blazed diffraction grating pattern with the Fresnel lens pattern can be used. Figure 2 In the diagram, we have blazed diffraction grating pattern 501 and pattern 502 that overlaps the blazed diffraction grating pattern with the Fresnel lens pattern. In this case, the first-order light diffracted by pattern 502, which overlaps the blazed diffraction grating pattern with the Fresnel lens pattern, can be set as the light returning to the light source 11.

[0035] The pinhole 92 is a spatial filter that limits the wavelength of light returning to the light source 11 by allowing only a portion of the light returning from the diffraction grating 50 in a spatially dispersed (separated by each wavelength) state to pass through. Here, the spatial filter can function as a unit that acts as a mask with a spatially distributed light transmittance. Alternatively, the spatial filter could be a unit including the pinhole 92 and the lens 40; however, here the pinhole 92 is used as the spatial filter. The pinhole 92 is, for example, located at the focusing point of the lens 40. The pinhole 92 is a shield with a circular aperture 92a, and it is a spatial filter that allows only light of the wavelength corresponding to the spatial position of the aperture 92a to pass through, preventing other wavelengths from passing through. The diameter of the aperture 92a of the pinhole 92 can, for example, be less than 1 mm. Furthermore, the size of the aperture 92a of the pinhole 92 can be set according to the specifications of the lens 40.

[0036] Furthermore, the light returning to the light source 11 through the pinhole 92 is reflected by the light source 11 and passes through the pinhole 92 (spatial filter) again. However, when it is focused on the light source 11, it is not in a dispersed state, so the wavelength is not limited when it passes through the pinhole 92 again.

[0037] A lens 91 is disposed between the light source 11 and the pinhole 92. Light emitted from the light source 11 travels towards the pinhole 92 through the lens 91. Light returning from the diffraction grating 50 travels towards the pinhole 92 through the lens 40.

[0038] Next, the effects of the light source device 1 in this embodiment will be explained.

[0039] The light source device 1 includes: a light source 11 for outputting light; a spatial light modulator 60 having an input section for a control signal and configured to control the distribution of the angle of reflection of incident light based on the control signal; a diffraction grating 50 that splits the light output from the light source 11 and incident it onto the spatial light modulator 60, and causes at least a portion of the light reflected by the spatial light modulator 60 to return to the light source 11; and a pinhole 92 that allows only a portion of the light returning from the diffraction grating 50 in a spatially dispersed state to pass through. Thus, in the light source device 1, an optical resonator is formed by including the light source 11 and the spatial light modulator 60, and the light returning to the light source 11 through the pinhole 92 is output.

[0040] In the light source device 1 of this embodiment, light output from the light source 11 is split by the diffraction grating 50 and incident on the spatial light modulator 60. Then, 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. Here, a pinhole 92 is provided between the diffraction grating 50 and the light source 11, allowing only a portion of the light returning from the diffraction grating 50 in a spatially dispersed state to pass through, and the light returning to the light source 11 through the pinhole 92 is output. Thus, by providing the pinhole 92 as a spatial filter between the diffraction grating 50 and the light source 11, the wavelength of the light returning to the light source 11 and being output is limited. Since the pinhole 92 has a wavelength-limiting function, a wavelength-limiting function is not required for the light source 11 (or for optical fibers added within the optical resonator, etc.), and various light sources 11 can be used. As described above, according to this embodiment, a light source device 1 that does not limit the components used as the light source 11 can be provided.

[0041] Figure 3 This diagram illustrates the wavelength limitation function of a single-mode LD. For example... Figure 3 As shown, when a single-mode LD311 is used as a light source, the wavelength of the light is limited by coupling the light returning from the diffraction grating 50 with the single-mode LD311. Thus, in a structure that gives the light source a wavelength-limiting function, the type of light source is limited. Regarding this point, as described above, in the light source device 1 of this embodiment, since the pinhole 92 has a wavelength-limiting function, a wavelength-limiting function is not required for the light source, and therefore the element used as a light source is not limited.

[0042] In the light source device 1, by employing a pinhole 92 as a spatial filter, it is possible to appropriately allow only a portion of the spatially dispersed light to pass through. That is, only the wavelength component of the light corresponding to the position of the hole 92a of the pinhole 92 passes through the pinhole 92, thus it is possible to appropriately limit only the light to the wavelength component corresponding to the hole 92a of the pinhole 92.

[0043] The light source device 1 includes a lens 40 that focuses the light returning from the diffraction grating 50, and a pinhole 92 (specifically, an aperture 92a of the pinhole 92) can be disposed at the focusing point of the lens 40. With this structure, wavelength can be appropriately limited using the pinhole 92.

[0044] In the light source device 1, the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be controlled by controlling the distribution of the angle of light reflected from the spatial light modulator 60 based on a control signal. According to this structure, by changing the control signal, the distribution of the angle of light reflection in the spatial light modulator 60 changes, thereby changing the bandwidth of the light returning from the diffraction grating 50 to the light source 11. That is, according to this structure, the bandwidth of the light returning from the diffraction grating 50 to the light source 11 can be arbitrarily adjusted.

[0045] The above description illustrates this embodiment, but the present invention is not limited to the above embodiment. For example, using a pinhole 92 (see...) Figure 1 This example, ), is used to illustrate spatial filters, but it is not limited to this. Figure 4 As shown, the spatial filter can also be a transmission mask 192. Similar to the pinhole 92 described above, the transmission mask 192 allows only a portion of the light returning from the diffraction grating 50 in a spatially dispersed state to pass towards the light source 11. The transmission mask 192 is, for example, rectangular, with a rectangular transmission region 192a formed in its central portion. In this structure, only the wavelength component of light corresponding to the position of the transmission region 192a of the transmission mask 192 passes through the transmission mask 192, thus appropriately limiting only the wavelength component of light corresponding to the transmission region 192a of the transmission mask 192. Furthermore, the shape of the transmission region 192a is not limited to a rectangle; for example, by setting a shape that matches the shape of the emitting end of the light source 11, the light utilization efficiency can be improved.

[0046] For example, when you want to use a spatial filter to achieve the same effect as the single-mode LD311 mentioned above (refer to...) Figure 3 With the same wavelength limiting function, a rectangular transmission mask 192 can be placed at the focusing point of lens 40. In this case, the size and shape of the transmission region 192a of the transmission mask 192 can be the same as the emission opening 311a of the single-mode LD (see reference). Figure 3 The size and shape of the transmission area 192a in the transmission mask 192 are consistent. In addition, the size of the transmission area 192a in the transmission mask 192 can be set according to the specifications of the lens 40.

[0047] In addition, such as Figure 5 As shown, the spatial filter can also be a single-mode fiber 292. Similar to the pinhole 92 or transmission mask 192 described above, the single-mode fiber 292 allows only a portion of the light returning from the diffraction grating 50 in a spatially dispersed state to pass towards the light source 11. The single-mode fiber 292 propagates only light of a predetermined wavelength component. With such a single-mode fiber 292, wavelength limitation can be appropriately achieved.

[0048] If you want to use the above-mentioned pinhole 92 to achieve the same wavelength limiting function as single-mode fiber 292, you can place the pinhole 92 at the focusing point of lens 40, and make the size of the hole 92a of the pinhole 92 greater than or less than three times the mode field diameter of single-mode fiber 292.

[0049] Furthermore, in structures where optical fibers are incorporated within optical resonators, such as those incorporating spatial filters like the aforementioned pinhole 92 or transmission mask 192, wavelength limitation is not required for the fiber. Therefore, fibers other than single-mode fibers, such as highly nonlinear fibers, can be used. By using highly nonlinear fibers, nonlinear effects are readily generated. 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 extended, increasing the degrees of freedom in spectral control of light.

[0050] Furthermore, the spatial filter can also be composed of one or more slits (not shown). Using such slits, only a portion of the light returning from the diffraction grating 50, which is spatially dispersed, can pass towards the light source 11. Thus, wavelength limitation can be appropriately achieved.

[0051] Explanation of symbols

[0052] 1…light source device, 11…light source, 40…lens (condenser lens), 50…diffraction grating, 60…spatial light modulator (reflector), 92…pinhole (spatial filter), 192…transmission mask (spatial filter), 292…single-mode fiber (spatial filter).

Claims

1. A light source device, characterized in that, include: A light source that outputs light; A reflective section having an input section for a control signal and configured to control the distribution of the angle of reflection of incident light based on the control signal; The light emitted from the light source is split and incident on the reflector, and at least a portion of the light reflected by the reflector returns to the diffraction grating of the light source; and A spatial filter that allows only a portion of the light returning from the diffraction grating in a spatially dispersed state to pass through. An optical resonator is formed by including the light source and the reflector, and light returning from the light source through the spatial filter is output.

2. The light source device as described in claim 1, characterized in that, The spatial filter is a pinhole, a transmission mask, one or more slits, or a single-mode fiber.

3. The light source device as described in claim 2, characterized in that, It also includes a focusing lens that focuses the light returning from the diffraction grating. The spatial filter is positioned at the focusing point of the focusing lens.

4. The light source device according to any one of claims 1 to 3, characterized in that, The bandwidth of the light returning from the diffraction grating to the light source is controlled by controlling the distribution of the angle of the light reflected from the reflective part based on the control signal.

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