semiconductor laser device

Abstract

Semiconductor laser device comprising: several semiconductor laser units (LDC) that can be controlled independently; and a spatial light modulator (SLM) optically coupled to a group of the plurality of semiconductor laser units (LDC), wherein each of the semiconductor laser units (LDC) comprises an active layer (4), a pair of cladding layers (2, 7) surrounding the active layer (4), and a diffraction grating layer (6) optically coupled to the active layer (4), wherein the plurality of semiconductor laser units (LDC) output laser beams along respective thickness directions, wherein the spatial light modulator (SLM) comprises a liquid crystal layer (LC), a reflection film (23) provided on a side opposite to the semiconductor laser unit (LDC) with respect to the liquid crystal layer (LC), a plurality of pixel electrodes (21) arranged two-dimensionally, and a common electrode (25) which surrounds the liquid crystal layer (LC) together with the pixel electrode (21), wherein a laser beam (LB) emitted from each of the semiconductor laser units (LDC) is incident on the spatial light modulator (SLM) and is modulated according to a state of the liquid crystal layer (LC) based on the pixel electrodes (21), wherein the laser beam (LB) reflected and modulated by the reflection film (23) of the spatial light modulator (SLM) is output from a light emission surface of each of the semiconductor laser units (LCD) to the outside again through each of the semiconductor laser units (LCD), and wherein the semiconductor laser device (LCD) further comprises a 1 / 4 wavelength plate (26) arranged between a group of the active layers (4) of the plurality of semiconductor laser units (LCD) and the reflection film (23), and a polarizing plate (27) arranged between the group of active layers (4) of the plurality of semiconductor laser units (LCD) and the light emitting surface.

Description

Technical area

[0001] The present invention relates to a semiconductor laser device functioning as a spatial light modulation light source. State of the art

[0002] In recent years, stereoscopic display of an integral photography system has been known (see Non-Patent Literature 1 and Non-Patent Literature 2). In this type of stereoscopic display, a liquid crystal display panel is arranged such that a plurality of pixels are arranged on the back of a lenticular lens. Light rays emitted from respective liquid crystal display panels belonging to the same lenticular lens travel at different angles. Therefore, by giving an appropriate image to each of the liquid crystal display panels, it is possible to give a desired image for each angle, enabling stereoscopic display based on an integral photography system. Citation list

[0003] US 2006 / 0 261 337 A1 relates to a display device with an illumination component. WO 2014 / 175 447 A1 relates to a surface-emitting laser element. US 2002 / 0 145 687 A1 relates to thin and lightweight displays. JP 2002-55 322 A relates to a liquid crystal display.

[0004] US 5 301 201 A relates to optical communication systems with semiconductor lasers. Non-patent literature [Non-Patent Reference 1] Lippmann, “Integral photography,” Scientific American, August 1911 issue, p. 164 [Non-Patent Literature 2] Ernst Lueder “3D Displays”, John Wiley & Sons, 2012, pp. 185-214 Summary of the inventionTechnical problem

[0005] However, in the case of a semiconductor laser device that combines a liquid crystal panel with a lenticular lens, it is necessary to provide a large number of liquid crystal display panels corresponding to a large number of viewing points. Therefore, as the entire system becomes larger in size, it is difficult to direct multiple beams of light required for forming a stereoscopic image into the pupil, and consequently, a problem arises in that a natural stereoscopic image cannot be obtained.

[0006] The invention is designed in view of such situations, and an object of the invention is to provide a semiconductor laser device which is also applicable to the formation of a natural stereoscopic image. Solution to the problem

[0007] In order to solve the problem described above, a first semiconductor laser device is provided, which is a semiconductor laser device having a plurality of semiconductor laser units that can be independently driven and a spatial light modulator optically coupled to a group of the plurality of semiconductor laser units, (1) wherein each of the semiconductor laser units comprises an active layer, a pair of cladding layers surrounding the active layer, and a diffraction grating layer optically coupled to the active layer, the plurality of semiconductor laser units outputting laser beams along respective thickness directions, (2) wherein the spatial light modulator comprises a liquid crystal layer, a reflection film provided on a side opposite to the semiconductor laser unit with respect to the liquid crystal layer, a plurality of pixel electrodes arranged two-dimensionally, and a common electrode,which encloses the liquid crystal layer together with the pixel electrode, (3) wherein a laser beam emitted from each of the semiconductor laser units is incident on the spatial light modulator and modulated according to a state of the liquid crystal layer based on the pixel electrodes, wherein the laser beam reflected and modulated by the reflection film of the spatial light modulator is output from a light-emitting surface of each of the semiconductor laser units to the outside again through each of the semiconductor laser units, and (4) wherein the semiconductor laser device further comprises a 1 / 4 wavelength plate arranged between a group of the active layers of the plurality of semiconductor laser units and the reflection film, and a polarizing plate arranged between the group of the active layers of the plurality of semiconductor laser units and the light-emitting surface.

[0008] According to this semiconductor laser device, a laser beam output from the semiconductor laser unit, which is a surface-emitting laser element, is emitted along the thickness direction, is reflected by the reflection film of the spatial light modulator, undergoes phase modulation in the liquid crystal layer, and is output to the outside through the polarizing plate. Therefore, the direction of a laser beam output from the polarizing plate, which undergoes phase modulation, is different for each pixel according to the intensity of the modulation in the liquid crystal layer. A laser beam to be emitted from the semiconductor laser unit to the outside without passing through the spatial light modulator can be suppressed by the polarizing plate.That is, for a laser beam passing through the 1 / 4 wavelength plate twice, being incident on the spatial light modulator and reflected, the phase of the laser beam is reversed, and consequently, its polarization azimuth is rotated by 90 degrees. Consequently, the laser beam passes through the polarization plate.

[0009] That is, if the polarization azimuth of the laser beam in the active layer is set as the first direction (A), a polarization azimuth (B) transmitted through the polarizing plate is perpendicular to the first direction (A), and the laser beam cannot directly pass through a wavelength plate. On the other hand, the laser beam that has passed through the 1 / 4 wavelength plate twice has the polarization azimuth (B) perpendicular to the first direction (A) in a case where there is no liquid crystal layer and can pass through the polarizing plate. A bias voltage is applied between the pixel electrode and the common electrode, and thus only a polarization component whose phase is adjusted by the liquid crystal layer passes through the polarizing plate.

[0010] Meanwhile, it is preferable that a width of each of the pixel electrodes be equal to or less than half the width of each of the semiconductor laser units. The width of the pixel electrode is smaller than the width of each of the semiconductor laser units, and two or more pixel electrodes are arranged corresponding to a single semiconductor laser unit. Thereby, light generated by each semiconductor laser unit travels to and returns from the spatial light modulator and is then two-dimensionally phase-modulated for each pixel of the spatial light modulator. Consequently, it is possible to control a beam pattern for each semiconductor laser unit. Therefore, a signal is applied to a spatial light modulator driving circuit to apply a peak beam having a direction controlled as an output beam pattern, and thus it is possible to output the peak beam in any direction for each semiconductor laser unit.

[0011] At this time, an array period L of the semiconductor laser unit is set equal to or less than half the diameter of the pupil of an eye, and thus, it is possible to form a natural stereoscopic image of an integral system. At this time, a maximum diffraction angle Φ of the tip beam in any direction from each semiconductor laser unit can be represented by Φ≈λ / d using a pixel width d of the spatial light modulator and a wavelength λ. Therefore, it is necessary to appropriately set a small d to obtain a desired Φ.

[0012] Meanwhile, in the example described above, the peak beam is output in any direction for each semiconductor laser unit. However, it is possible to obtain any beam pattern for each semiconductor laser unit as long as the pixel pitch d has an appropriate value and to obtain multiple beams in any direction for each semiconductor laser unit. In this case, the beams in multiple directions are obtained simultaneously in parallel, and thus, it is possible to increase the number of viewpoints when displaying and forming a natural stereoscopic image. Alternatively, it is possible to increase a frame rate by setting the same number of viewpoints.

[0013] In a second semiconductor laser device, the plurality of semiconductor laser units include a first semiconductor laser unit that outputs a laser beam having a first wavelength, a second semiconductor laser unit that outputs a laser beam having a second wavelength, and a third semiconductor laser unit that outputs a laser beam having a third wavelength, and the first, second, and third wavelengths are different from each other.

[0014] According to this semiconductor laser device, laser beams having three or more types of wavelengths are used and hence it is possible to produce a stereoscopic image having different colors.

[0015] In a third semiconductor laser device, the plurality of semiconductor laser units include a fourth semiconductor laser unit that outputs a laser beam having a fourth wavelength, a fifth semiconductor laser unit that outputs a laser beam having a fifth wavelength, and a sixth semiconductor laser unit that outputs a laser beam having a sixth wavelength, and the first, second, third, fourth, fifth, and sixth wavelengths are different from each other.

[0016] According to this semiconductor laser device, laser beams having six or more types of wavelengths can be used and hence it is possible to produce a stereoscopic image having further different colors. Advantageous effects of the invention

[0017] According to the invention, it is possible to provide a semiconductor laser device which is also applicable to the generation of a natural stereoscopic image. Brief description of the drawings Fig. 1 is a diagram illustrating a longitudinal sectional configuration of a semiconductor laser device according to a first embodiment. Fig. 2 is a diagram illustrating a longitudinal sectional configuration of a semiconductor laser device according to a second embodiment Fig. 3 is a diagram illustrating a longitudinal sectional configuration of a semiconductor laser device according to a third embodiment. Fig. 4 is a diagram showing a perspective view ( Fig. 4(A)) of the semiconductor laser device and a plan view ( Fig. 4 (B)) of a semiconductor laser unit as a unit element. Fig. 5 is a plan view of a diffraction grating layer. Description of embodiments

[0018] A semiconductor laser device according to an embodiment will be described below. The same components are denoted by the same reference numerals and symbols, and repeated descriptions are omitted.

[0019] Fig. 1 is a diagram illustrating a longitudinal sectional configuration of a semiconductor laser device according to a first embodiment.

[0020] The semiconductor laser device comprises a plurality of semiconductor laser chips LDC(N) (N is a natural number: Fig. Figure 1 illustrates a case where N = 1, 2, 3), each of which is formed by a compound semiconductor, and a spatial light modulator (SLM) optically coupled to a group of semiconductor laser chips LDC(N). Although the semiconductor laser chips LDC(N) are shown as completely separate chips in the drawing, they may be formed on a common substrate, and an isolation structure may be provided between the chips. In both a case of complete separation and a case of isolation separation, each of the semiconductor laser chips LDC(N) functions as a semiconductor laser unit.

[0021] The LDC semiconductor laser chip includes a light-emitting layer with an active layer 4, a pair of cladding layers 2 and 7 sandwiching the light-emitting layer, and a diffraction grating layer 6 optically coupled to the light-emitting layer. Meanwhile, the light-emitting layer includes the active layer 4 and light guide layers 3 and 5 sandwiching the active layer when necessary. Each LDC semiconductor laser chip includes a semiconductor substrate 1. The thickness direction of the semiconductor substrate 1 is defined as the Z-axis, and two directions perpendicular to the Z-axis are defined as the X-axis and the Y-axis, respectively.

[0022] It is assumed that semiconductor layers are sequentially epitaxially grown on the surface of the semiconductor substrate 1 in the Z-axis direction during the fabrication of the semiconductor laser device. In this case, in a case where the -Z-axis direction is set as the upward direction, the lower cladding layer 2, the light-emitting layers (the light guide layer 3, the active layer 4, and the light guide layer 5), the diffraction grating layer 6, the upper cladding layer 7, and a contact layer 8 are sequentially formed on the semiconductor substrate 1. A drive electrode E3 is formed on the surface of the semiconductor substrate 1 on the +Z-axis side, and an electrode E2 is formed on the surface of the contact layer 8 on the -Z-axis side.These electrodes E3 and E2 are a drive electrode, and each of the drive electrodes has a plurality of openings having a stripe shape or a mesh shape spread over the entire surface of the semiconductor substrate, or is formed by a transparent electrode.

[0023] When a current is supplied between the drive electrode E3 and the second electrode E2 of each of the semiconductor laser chips LDC from a laser drive circuit L-DR, the light-emitting layers independently emit light. That is, when a drive current is supplied between the drive electrode E3 and the second electrode E2, recoupling occurs between electrons and holes within the active layer 4, and the active layer 4 emits light. Carriers contributing to light emission and the emitted light are efficiently confined between the light guide layers 3 and 5 and the cladding layers 2 and 7 arranged on the upper and lower sides.

[0024] A laser beam LB generated in the light-emitting layer propagates through the diffraction grating layer 6, and the diffraction grating layer 6 emits the laser beam in a direction perpendicular to the thickness direction, i.e., the Z-axis direction. The laser beam emitted from the diffraction grating layer 6 travels in the +Z-axis direction and is incident on the spatial light modulator SLM through the cladding layer 2 and the semiconductor substrate 1.

[0025] The spatial light modulator SLM is attached to the array of semiconductor laser chips LDC, so that the laser beam LB output along the thickness direction of the diffraction grating layer 6 is input into the spatial light modulator. The laser beam is incident on a liquid crystal layer LC through a transparent electrode composed of a common electrode 25 and a pixel electrode 21 of the spatial light modulator SLM. The positions of these electrodes can be interchanged, and the pixel electrode 21 can also be configured as a transparent electrode. The spatial light modulator SLM modulates the phase of the laser beam LB for each minute region by a drive voltage applied between the pixel electrode and the common electrode, reflects the phase-modulated laser beam, and outputs the reflected laser beam to the outside through the semiconductor laser chip.

[0026] The laser beams LB output from the respective spatial light modulators SLM are superimposed on each other in a state where their phases are adjusted for each minute area, thereby forming different laser beam patterns. Far-field images of the superimposed laser beams LB can, for example, form special characters.

[0027] In this semiconductor laser device, a beam direction can be changed by the spatial light modulator SLM, and a plurality of deflected laser beams are incident on the pupil of an eye. Since the plurality of laser beams are incident on the pupil of the eye, a width L (array period) of the semiconductor laser chip LDC in the X-axis direction is set to be equal to or less than 2.5 mm. Furthermore, a width d (pitch pitch) of the pixel electrode 21 of the spatial light modulator SLM in the X-axis direction is set to be equal to or less than 60 μm to obtain the actual sweep angle of the beam.

[0028] The semiconductor laser device is arranged on the semiconductor laser chip LDC and further includes a spatial light modulator drive circuit S-DR (including a row selection circuit and a column selection circuit) that selectively applies a drive voltage between the pixel electrode and the common electrode arranged at desired addresses. These selection circuits are provided on the semiconductor laser chip, and thus, it is possible to control the spatial light modulator without installing a large-sized external wiring group.

[0029] The spatial light modulator SLM includes the transparent common electrode 25, the plurality of transparent pixel electrodes 21, and the liquid crystal layer LC disposed between the common electrode 25 and the pixel electrodes 21. The common electrode 25 is formed on a transparent substrate TS. The liquid crystal layer LC is formed of nematic liquid crystal, ferroelectric liquid crystal, or the like. A driving current is supplied from the driving circuit to the semiconductor laser chip constituting a semiconductor laser element through the driving electrode. Thereby, the laser beam LB is output from the light-emitting layer, reaches the liquid crystal layer LC through the pixel electrodes 21 of the spatial light modulator, undergoes phase modulation in the liquid crystal layer LC, is reflected by a reflection mirror or a reflection film 23, and is output to the outside through the common electrode 25.The common electrode 25 is connected to a fixed potential (ground), and the pixel electrodes 21 are connected to the row selection circuit through a switching element and a row line. A column line extends from the column selection circuit and is connected to a control terminal of the switching element. The switching element is a field-effect transistor. In this case, the control terminal serves as the gate of the transistor.

[0030] In the spatial light modulator, in a case where a specific address (x, y) is specified, an ON signal is output to the column line of the x coordinate from the column selection circuit, and a desired potential is applied to the row line of the y coordinate from the row selection circuit. In this case, a driving voltage is applied between the pixel electrode 21 and the common electrode 25 at the address (x, y), and a refractive index of the liquid crystal layer changes, thereby changing the length of a light path and adjusting the phase of the laser beam. Meanwhile, in the spatial light modulator, a row direction and a column direction are determined subjectively and are mutually interchangeable directions. The magnitude of the driving voltage is determined depending on an output potential from the row selection circuit and an output potential from the column selection circuit.However, in a case where phase control is performed more precisely, for example, a variable resistor may be connected for each switching element and the value of the variable resistor may be controlled by a selection circuit having the same configuration.

[0031] Meanwhile, a memory device and a drive circuit for the spatial light modulator may be provided. The memory device measures a phase distribution of the spatial light modulator in advance so that a device outputs a desired pattern even if the phase of the spatial light modulator varies in a plane during manufacturing of the semiconductor laser device, and corrects the phase distribution. The drive circuit generates a drive voltage applied to each pixel electrode through the selection circuit based on data stored in the memory device.That is, the semiconductor laser device may include the memory device that measures a phase distribution of the spatial light modulator in advance, stores an initial phase correction value for correcting the in-plane phase variation based on a measured value, and applies a different initial phase to each pixel electrode of the spatial light modulator. In other words, the semiconductor laser device includes the memory device (not shown) that stores an initial correction value of a drive voltage for each pixel electrode. The drive voltage is applied from a control device (not shown) to the row selection circuit and the column selection circuit of the spatial light modulator drive circuit S-DR, but the drive voltage and the initial correction value are stored in the memory device.A reference phase distribution and the measured phase distribution are compared, and the drive voltage value corresponding to a phase difference for each pixel can be set to the initial correction value. In a case where the drive voltage with the initial correction value is applied to the pixel electrode, the reference phase distribution is realized. To obtain a desired phase distribution, a desired drive voltage can be superimposed on the drive voltage corresponding to the initial correction value.

[0032] Furthermore, the semiconductor laser device may include a memory device and a correction circuit. The memory device measures the intensity of a light output in advance with respect to each phase of the spatial light modulator, assuming that a polarization state is disturbed due to the penetration of the liquid crystal, resulting in a change in the intensity of the output light obtained by the penetration of a polarizing plate, and corrects the intensity of the output light. The correction circuit corrects a drive current applied to the semiconductor laser chip LDC for each phase pattern based on data stored in the memory device.In other words, the semiconductor laser device may include a correction circuit (not shown) for correcting a drive current for each semiconductor laser chip and a memory device (not shown) that stores a correction value of a current value for correcting a drive current applied to the semiconductor laser chip LDC for each phase pattern of all pixels included in a region corresponding to each semiconductor laser chip. Consequently, it is possible to correct a drive current for each semiconductor laser chip LDC at each moment (within each frame) according to a phase pattern of all pixels corresponding to each semiconductor laser chip LDC, and to realize a uniform distribution of the amount of light that is not affected by the disturbance of a polarization state due to liquid crystal penetration.

[0033] Meanwhile, although the correction using the memory device has been described above, a configuration may be adopted in which a unit that monitors the output of each semiconductor laser chip LDC and a feedback circuit for performing feedback control according to the monitored output value are provided instead of the memory device.

[0034] A laser beam output from the diffraction grating layer 6 in the thickness direction reaches the liquid crystal layer LC through the common electrode 25 (or the pixel electrode 21 in a case where its position is replaced by the pixel electrode). A dielectric constant (refractive index) of the liquid crystal layer LC changes depending on a voltage to be applied to the pixel electrode 21. Consequently, the length of a light path of the liquid crystal layer LC with respect to the laser beam changes, and a phase changes. The phase of the laser beam LB, which reciprocates while passing through the liquid crystal layer LC, is modulated for each pixel electrode 21. Therefore, it is possible to perform wavefront control for each minute region and form a desired variable laser beam pattern by the superposition of wavefronts.

[0035] Meanwhile, a transparent insulation film (anti-reflection film) 9 made of SiO 2or SiNx is formed on the drive electrode E3. A 1 / 4 wavelength plate 26 of the spatial light modulator SLM, a transparent substrate TS, and the common electrode 25 are arranged on the transparent insulation film 9. A frame-shaped spacer 24 for holding the liquid crystal is provided on the common electrode 25, and the interior of the spacer 24 is filled with the liquid crystal layer LC. The reflection film 23 is formed on the spacer 24 and the liquid crystal layer LC, and the plurality of pixel electrodes 21 are arranged on the reflection film 23 through the protective film 22. The pixel electrodes 21 are arranged between the substrate 20 and the protective film 22.When forming the pixel electrodes 21 and the like, it is preferable to form the pixel electrodes 21 on the substrate 20 made of a semiconductor, cover the protective film 22 with the pixel electrodes 21 so that the surfaces of the pixel electrodes are flattened, form the reflection film 23 on the protective film 22, and turn the substrate, which is an intermediate product, over and place it on the frame-shaped spacer 24. Meanwhile, a suitable alignment film is provided on the upper and lower surfaces of the liquid crystal layer LC.

[0036] The laser beam LB reflected by the reflection film 23 on the liquid crystal layer LC is output to the outside through the common electrode 25 and the semiconductor laser chip LDC. Furthermore, a distance t1 between (an intermediate position in the thickness direction) the diffraction grating layer 6 and the contact layer 8 is set so that the laser beam LB reflected by the exposed surface of the contact layer 8 in the semiconductor laser chip and the light directly directed to the spatial light modulator SLM from the diffraction grating layer 6 are amplified. That is, the distance t1 can satisfy the following relationship. 2xt1=λxN or 2xt1=λx(N+1 / 2) where λ denotes the wavelength of a laser beam and N is set to be an integer.

[0037] The light-emitting layer is formed by the active layer 4 and the light guide layers 3 and 5 sandwiching the active layer, and the contact layer 8 is provided if necessary. The semiconductor laser chip includes a laser beam generation region LD in which the active layer 4 is formed. The diffraction grating layer 6 is disposed in the laser beam generation region LD and emits the laser beam LB in the thickness direction of the diffraction grating layer 6. The spatial light modulator SLM is mounted on the laser beam generation region LD. In a case of this structure, it is possible to miniaturize the device by disposing the spatial light modulator SLM on the laser beam generation region LD.

[0038] Meanwhile, the drive electrode E3 is arranged on the surface of the semiconductor substrate 1 on the +Z side. The semiconductor laser device is a semiconductor laser device that includes the semiconductor laser chip LDC and the spatial light modulator SLM optically coupled to the semiconductor laser chip LDC, modulates the laser beam LB output along the thickness direction of the semiconductor laser chip LDC by the spatial light modulator SLM, and outputs the modulated laser beam to the outside. The semiconductor laser chip LDC includes the active layer 4, the pair of cladding layers 2 and 7 sandwiching the active layer 4, the diffraction grating layer 6 optically coupled to the active layer 4, and the drive electrode E3 arranged between the cladding layer 2 on the spatial light modulator SLM side and the spatial light modulator SLM, and used to supply a current to the active layer 4.

[0039] Meanwhile, a three-dimensional orthogonal XYZ coordinate system is provided. However, in a case where the thickness direction of the semiconductor laser chip LDC is set as the Z-axis direction and a plane parallel to an interface between the semiconductor laser chip LDC and the spatial light modulator SLM is set as the XY plane, the drive electrode E3 is arranged within the XY plane. Furthermore, the drive electrode E3 has a plurality of openings when viewed from the Z-axis direction, and the drive electrode E3 has a non-periodic structure, but it may also be formed by a transparent electrode such as indium tin oxide (ITO).

[0040] A metal such as Ag or Au can be used as the material of a conductive region constituting the drive electrode, but the conductive region can also be formed by diffusing impurities with a higher concentration than that of the semiconductor substrate 1 into the semiconductor substrate. Meanwhile, a transparent electrode such as ITO, ZnO, graphene, or Ag nanowire can also be used as the material of the drive electrode. However, since a series resistance material is more preferable, it is preferable to use an opaque metal material with a stripe-shaped or mesh-shaped opening instead of the transparent electrode.

[0041] The transparent insulation film 9 is formed on the drive electrode. The spatial light modulator SLM is provided on the drive electrode E3. In this case, the row selection circuit and the column selection circuit, which are not shown in the drawing, are arranged outside the drive electrode E3, and thus, appropriate connection wiring is performed from the circuits to the pixel electrode and the common electrode. In addition, the electrode E2 is configured to transmit part or all of the laser beam LB. Regarding the electrode E2, it is also possible to adopt the same structure as that of the drive electrode E3.

[0042] The diffraction grating layer 6 has, for example, a structure in which triangular shapes are arranged in a square grating shape, and diffracts linearly polarized light in a vertical direction. At this time, when a polarization transmission axis of the linearly polarized light output from the diffraction grating layer 6 is set as axis A, a polarization transmission axis of the polarizing plate 27 is set in a direction (referred to as axis B) perpendicular to axis A. Furthermore, a fast axis of the 1 / 4-wavelength plate is set in a direction rotated by 45 degrees from axis A. The polarization azimuth of a laser beam that is incident on the spatial light modulator SLM through the 1 / 4-wavelength plate 26 and passes through the 1 / 4-wavelength plate 26 again in the opposite direction while traveling to and returning from the spatial light modulator SLM is rotated by 90 degrees.That is, in a case where the laser beam LB is incident on the 1 / 4 wavelength plate 26 as linearly polarized light having a first polarization direction (axis A), the laser beam passes through the 1 / 4 wavelength plate twice and then changes into linearly polarized light having a second polarization direction (axis B) rotated by 90 degrees with respect to the first polarization direction.

[0043] Therefore, when one polarization direction in the polarizing plate 27 is made to correspond to the second polarization direction (axis B), only a laser beam going to and returning from the spatial light modulator SLM passes through the polarizing plate 27, and components of other polarization directions are blocked by the polarizing plate 27. Therefore, noise components that have not been modulated based on the liquid crystal layer LC are removed from an output image, and thus, contrast is improved. Meanwhile, the position of the common electrode 25 can be replaced by the position of the 1 / 4 wavelength plate 26.

[0044] Fig. 5 is a top view of the diffraction grating layer.

[0045] The diffraction grating layer 6 described above is formed, for example, by a base layer 6A and regions 6B with different refractive indexes. The region 6B with different refractive indexes is embedded in the base layer 6A to have a predetermined depth and has a different refractive index from that of the base layer. A planar shape of the region 6B with different refractive indexes is shown as a circular shape, but it may also be another shape such as a triangular shape or an elliptical shape. To increase the intensity of a specific polarization direction, the planar shape may be, for example, a shape that does not have 90-degree rotational symmetry. To obtain linearly polarized light, the planar shape may be, for example, an isosceles triangle shape, a right-angled triangle shape, or an isosceles right-angled triangle shape.The different refractive index region 6B is arranged at the position of a lattice point of a square grating, but may be arranged at the position of a lattice point of a triangular grating. The diffraction grating layer 6 has a periodic structure in which a refractive index changes two-dimensionally by embedding the different refractive index region, and thus functions as a diffraction grating and also functions as a photonic crystal layer. In the drawing, the periodic structure in which perfect round holes are arranged in a square lattice shape is used. However, a periodic structure in which triangular holes are arranged in a square lattice shape can be used, and a semiconductor laser element functions as a surface-emitting laser.

[0046] Meanwhile, a material of the laser element described above will be described.

[0047] As an example of a material of a semiconductor laser element constituting the laser beam generation region LD, the semiconductor substrate 1 is formed of GaAs, the lower cladding layer 2 is formed of AlGaAs, the lower light guide layer 3 is formed of AlGaAs, the active layer 4 is formed of a multiple quantum well structure MQW (barrier layer: AlGaAs / potential well layer: InGaAs), the upper light guide layer 5 is formed of AlGaAs which is a lower layer and GaAs which is an upper layer, the upper cladding layer 7 is formed of AlGaAs, and the contact layer 8 is formed of GaAs.

[0048] Regarding the diffraction grating layer (phase modulation layer, refractive index modulation layer) 6, the base layer 6A is formed of GaAs and the different refractive index region (embedded layer) 6B embedded in the base layer 6A is formed of AlGaA.

[0049] Meanwhile, impurities of the first conductivity type (N-type) or impurities of the second conductivity type (P-type) are added to each layer (the concentration of impurities is 1×10 17 up to 1×10 21 / cm 3), so that the semiconductor substrate 1 may be set to an N-type, the lower cladding layer 2 may be set to an N-type, the lower light guide layer 3 may be set to an I-type, the active layer 4 may be set to an I-type, the lower layer of the upper light guide layer 5 may be set to a P- or I-type, the upper layer thereof may be set to an I-type, the diffraction grating layer 6 may be set to an I-type, the upper cladding layer 7 may be set to a P-type, and the contact layer 8 may be set to a P-type. Meanwhile, a region to which no impurities are intentionally added is set to natural (I-type). The concentration of I-type impurities is equal to or less than 1×10 16 / cm 3 .

[0050] In addition, for example, the thickness of the semiconductor substrate 1 can be set to 150 µm (80 µm to 350 µm), the thickness of the lower cladding layer 2 can be set to 2×10 3 nm (1×10 3 nm to 3×10 3 nm), the thickness of the lower light guide layer 3 can be set to 150 nm (0 nm to 300 nm), the thickness of the active layer 4 can be set to 30 nm (10 nm to 100 nm), the thickness of the lower layer of the upper light guide layer 5 can be set to 50 nm (10 nm to 100 nm), the thickness of the upper layer thereof can be set to 50 nm (10 nm to 200 nm), the thickness of the diffraction grating layer 6 can be set to 100 nm (50 nm to 200 nm), the thickness of the upper cladding layer 7 can be set to 2×10 3 nm (1×10 3 nm to 3×10 3 nm), and the thickness of the contact layer 8 can be set to 200 nm (50 nm to 500 nm). Meanwhile, the values ​​in parentheses are preferred values.

[0051] In addition, an energy band gap of the cladding layer is set larger than an energy band gap of the light guide layer, and the energy band gap of the light guide layer is set larger than an energy band gap of the potential well layer of the active layer 4. In AlGaAs, it is possible to easily change an energy band gap and a refractive index by changing a composition ratio of Al. In Al x Ga 1-xAs, when a composition ratio X of Al with a small atomic radius is relatively decreased (increased), an energy band gap is decreased (increased) with a positive correlation therewith. When InGaAs is formed by mixing In with a large atomic radius with GaAs, an energy band gap is decreased. That is, a composition ratio of Al of the cladding layer is larger than a composition ratio of Al of the light guide layer, and the composition ratio of Al of the light guide layer is equal to or larger than that of the barrier layer (AlGaAs) of the active layer. The composition ratio of Al of the cladding layer is set to 0.2 to 0.4, and is set to 0.3 in this example. The composition ratio of Al of the barrier layer in the light guide layer and the active layer is set to 0.1 to 0.15, and is set to 0.1 in this example.Meanwhile, in order to suppress the leakage of electrons from the active layer, a layer with a thickness of approximately 10 nm to 100 nm can be inserted between the conductive layer and the second conductivity type (p-type) cladding layer with the same Al composition as the cladding layer.

[0052] Meanwhile, the different refractive index region having a columnar shape in the diffraction grating layer 6 may be configured as a gap, and gas such as air, nitrogen, or argon may be sealed in the gap. Furthermore, in the diffraction grating layer 6, the different refractive index region 6B is arranged at the position of the lattice point of the square grating or the triangular grating in the XY plane. An interval between vertical and horizontal raster lines in the square grating has a value obtained by dividing a wavelength of a laser beam by an equivalent refractive index, and is particularly preferably set to 300 nm. The different refractive index region may be arranged at the position of the lattice point in the triangular grating instead of the position of the lattice point of the square grating.An interval between horizontal and inclined raster lines in a case of the triangular grating is obtained by dividing a wavelength of a laser beam by an equivalent refractive index and further dividing by sin60°, and is particularly preferably set to about 350 nm.

[0053] If unit vectors of orthogonal coordinates are set on x and y in a case of a square lattice with a lattice interval a, meanwhile, basis translation vectors satisfy the relations of a 1 =ax and a 2 =ay, basis vectors of a reciprocal lattice satisfy the relations b 1 =(2π / a)y and b 2 =(2π / a)x with respect to the basis translation vectors a 1 and a 2 . If a Γ-point in a photonic band of a photonic crystal, that is, a wavenumber vector k=nb 1 +mb 2(n and m are arbitrary integers), a resonance mode (standing wave in the XY plane) is obtained in which a grating interval a is equal to a wavelength λ.

[0054] Furthermore, the above-described common electrode and pixel electrode are formed of ITO or ZnO in a case where the electrodes are configured as transparent electrodes. Such materials are transparent to a laser beam and can transmit the laser beam.

[0055] In addition, the above-mentioned reflection film 23 is formed of a single-layer film or a multilayer mirror of a metal such as aluminum, and the multilayer mirror is configured by alternately stacking a high refractive index material layer (referred to as nH) and a low refractive index material layer (referred to as nL) having a relatively low refractive index with respect to the high refractive index material layer. The material of the high refractive index material layer (nH) includes at least one material (for example, Ta 2 O 5 ) selected from an oxide group (insulator group) containing Ta 2 O 5 , TiO 2 , Nb 2 O 5 , HfO 2 and the like. The low refractive index (nL) material layer comprises at least one material (for example, SiO 2 ) selected from an insulator group comprising SiO 2 , MgF2 and the like. An optical film thickness of each of the high refractive index (nH) material layer and the low refractive index (nL) material layer is set to one-quarter of a wavelength λ of a laser beam. The following types of stacked structures of these dielectric layers are considered. (1): A first structure is a structure in which a set (A) composed of the low refractive index (nL) material layer and the high refractive index (nH) material layer is repeatedly stacked m times. In this case, the total number of layers is 2×A×m. Here, m is a natural number. Meanwhile, the bottom layer is designated as the low refractive index (nL) material layer. (2): A second structure is a structure in which the above-described set (A) is repeatedly stacked m times, and the low refractive index (nL) material layer is further stacked on the high refractive index (nH) material layer disposed on the top surface. In this case, the total number of layers is 2×Axm+1. (3): In the structure of (1) or (2) described above, it is also possible to adopt a structure in which the positions of the high refractive index (nH) material layer and the low refractive index (nL) material layer are exchanged. In the case of the structure of (3), the bottom layer is the high refractive index (nH) material layer.

[0056] Finally, the semiconductor laser element described above is briefly described.

[0057] In the manufacture of the semiconductor laser element, each compound semiconductor layer uses a metal organic chemical vapor deposition (MOCVD) method. Although the crystal growth is performed on a (001) surface of the semiconductor substrate 1, the invention is not limited thereto. In the manufacture of a laser element using AlGaAs, a growth temperature of AlGaAs is 500°C to 850°C. In an experiment, a growth temperature of 550°C to 700°C is adopted. In the growth, trimethylaluminum (TMA) is used as the Al raw material, trimethylgallium (TMG) and triethylgallium (TEG) are used as the gallium raw materials, and arsine (AsH 3 ) is used as As raw material, disilane (Si 2 H 6) is used as a raw material for N-type impurities, and diethylzinc (DEZn) is used as a raw material for P-type impurities. TMA, TMG, and arsine are used in the growth of AlGaAs. TMG and arsine are used in the growth of GaAs, but TMA is not used. InGaAs is fabricated using TMG, trimethylindium (TMI), and arsine. An insulating film can be formed by sputtering a target using the constituent material of the insulating film as a raw material.

[0058] That is, the semiconductor laser element is formed by forming the N-type cladding layer (AlGaAs) 2 on the N-type semiconductor substrate (GaAs) 1, forming the light guide layer (AlGaAs) 3, the multiple quantum well structure (InGaAs / AlGaAs) 4, and the light guide layer (GaAs / AaGaAs) 5, and epitaxially growing the base layer (GaAs) 6A serving as a photonic crystal layer using a metal organic chemical vapor deposition (MOCVD) method.

[0059] Next, to achieve alignment after epitaxial growth, a SiN layer is formed on the base layer 6A by a plasma CVD (PCVD) method, and a resist is formed on the SiN layer. Furthermore, an alignment mask is formed by exposing and developing the resist, etching the SiN layer using the resist as a mask, and partially leaving the SiN layer. The remaining resist is removed.

[0060] Next, another resist is applied to the base layer 6A, and a two-dimensional minute pattern is drawn on the resist by an electron beam drawing device based on an alignment mask and is developed, thereby forming the two-dimensional minute pattern on the resist. After that, the two-dimensional minute pattern is transferred to the base layer 6A with a depth of approximately 100 nm by dry etching using the resist as a mask, thereby forming a hole, and the resist is removed. The depth of the hole is 100 nm. A compound semiconductor serving as the different refractive index region 6B (AlGaAs) is regrown in the hole to have a depth equal to or greater than the depth of the hole.Next, the upper cladding layer (AlGaAs) 7 and the contact layer (GaAs) 8 are sequentially formed by MOCVD, and a suitable electrode material is formed on the upper and lower surfaces of the substrate by a vapor deposition method or a sputtering method, thereby forming the first and second electrodes. Furthermore, an insulating film may be formed on the upper and lower surfaces of the substrate by a sputtering method or the like, if necessary.

[0061] In a case where the diffraction grating layer 6 is provided below the active layer, the diffraction grating layer may be formed on the lower cladding layer before the active layer and the lower light guide layer are formed.

[0062] In manufacturing the semiconductor laser element, the 1 / 4 wavelength plate 26 is disposed on the semiconductor substrate 1 through the insulating film 9, and the polarizing plate 27 is disposed on the surface of the contact layer 8. Meanwhile, in a case where the drive electrode E3 is formed on the semiconductor substrate 1, patterning is performed on the semiconductor substrate 1 using a photolithography method.

[0063] As described above, according to the device described above, light generated by the active layer is modulated by the diffraction grating layer and is oscillated in a two-dimensional single mode, and a part of the oscillated light is secondarily diffracted by the diffraction grating layer and incident on the liquid crystal layer as a plane wave. Since liquid crystal has refractive index anisotropy, an equivalent refractive index in a direction parallel to the light output changes depending on the rotation angle thereof. At this time, since a physical length of the liquid crystal layer is fixed, the length of a light path changes in association with a change in the refractive index. Therefore, when a plane wave is incident on the liquid crystal layer from below, it is possible to change the length of the light path for each pixel.In other words, when the plane wave is incident on the liquid crystal layer from below, its phase can be changed for each pixel, and thus, the shape of the emission wavefront can be controlled. In this way, a laser beam oscillating in a two-dimensional single mode is incident on the liquid crystal layer as a plane wave, and a wavefront phase-modulated for each pixel is obtained as the light output from below.

[0064] Fig. 4 is a diagram showing a perspective view ( Fig. 4(A)) of the semiconductor laser device and a plan view ( Fig. 4 (B)) of a semiconductor laser unit as a unit element.

[0065] The plurality of semiconductor laser chips LDCs are arranged two-dimensionally within the XY plane and can be independently driven. Since the spatial light modulator SLM is arranged on the back of each of the semiconductor laser chips LDCs, a laser beam is emitted toward a specific direction from each of the semiconductor laser chips LDCs. For example, if 4x4 = 16 pixel electrodes 21 are arranged in one semiconductor laser chip LDC and the width of the semiconductor laser chip LDC in the X-axis direction is assumed to be L, the width of the pixel electrode 21 in the X-axis direction is d, and the relationship of L≥4xd is established. Meanwhile, the dimensions thereof in the Y-axis direction are the same as those in the X-axis direction.

[0066] A first laser beam LB, output from a semiconductor laser chip LDC, is incident on the right eye (R-eye) of an observer, and a second laser beam LB, output from another semiconductor laser chip LDC, is incident on the left eye (L-eye) of the observer. Since the laser beam LB incident on the right eye and the laser beam LB incident on the left eye can be controlled independently, it is possible to create a stereoscopic image.

[0067] Fig. 2 is a diagram illustrating a longitudinal sectional configuration of a semiconductor laser device according to a second embodiment.

[0068] In this semiconductor laser device, a plurality of semiconductor laser chips (semiconductor laser units) LDC include a first semiconductor laser unit LDC(1) that outputs a laser beam LB having a first wavelength (red), a second semiconductor laser unit LDC(2) that outputs a laser beam LB having a second wavelength (green), and a third semiconductor laser unit LDC(3) that outputs a laser beam LB having a third wavelength (blue). The first, second, and third wavelengths are different from each other, and three or more types of wavelengths can be used.

[0069] According to this semiconductor laser device, laser beams having three or more types of wavelengths are used, and hence it is possible to produce a stereoscopic image having different colors by superimposing the laser beams on each other.

[0070] Fig.3 is a diagram illustrating a longitudinal sectional configuration of a semiconductor laser device according to a third embodiment.

[0071] In this semiconductor laser device, a plurality of semiconductor laser chips (semiconductor laser units) LDC include a fourth semiconductor laser unit LDC(4) that outputs a laser beam LB having a fourth wavelength (cyan), a fifth semiconductor laser unit LDC(5) that outputs a laser beam LB having a fifth wavelength (magenta), and a sixth semiconductor laser unit LDC(6) that outputs a laser beam LB having a sixth wavelength (yellow), in addition to the semiconductor laser units in the second embodiment. The first, second, third, fourth, fifth, and sixth wavelengths are different from each other, and six or more types of wavelengths can be used.

[0072] According to this semiconductor laser device, laser beams having six or more types of wavelengths can be used and hence it is possible to produce a stereoscopic image having further different colors.

[0073] As described above, the semiconductor laser device described above is a semiconductor laser device having a plurality of semiconductor laser units LDC that can be independently driven and a spatial light modulator SLM that is optically coupled to a group of the plurality of semiconductor laser units LDC, and includes the following elements. (1) Each of the semiconductor laser units LDC includes an active layer 4, a pair of cladding layers 2 and 7 between which the active layer 4 is sandwiched, and a diffraction grating layer 6 optically coupled to the active layer 4, and the plurality of semiconductor laser units LDC outputs laser beams along the respective thickness directions. (2) The spatial light modulator SLM includes a liquid crystal layer LC, a reflection film 23 provided on a side opposite to the semiconductor laser unit LDC with respect to the liquid crystal layer LC, a plurality of pixel electrodes 21 arranged two-dimensionally, and a common electrode that sandwiches the liquid crystal layer LC between the common electrode and the pixel electrodes 21. A width d of each of the pixel electrodes 21 is equal to or less than half a width L of each of the semiconductor laser units LDC. (3) A laser beam emitted from each of the semiconductor laser units LDC is incident on the spatial light modulator SLM, is modulated according to the state of the liquid crystal layer LC on the base of the pixel electrodes 21, and is reflected by the reflection film 23 of the spatial light modulator SLM. The modulated laser beam is outputted from a light emission surface (the surface of the polarizing plate 27 on the -Z-axis side) of each of the semiconductor laser units LDC to the outside again through each of the semiconductor laser units LDC. (4) The semiconductor laser device includes a 1 / 4 wavelength plate (phase difference plate) 26 disposed between a group of active layers 4 of the plurality of semiconductor laser units LDC and the reflection film 23, and a polarizing plate 27 disposed between the group of active layers 4 of the plurality of semiconductor laser units LDC and the light-emitting surface. A polarizing plate 27 is provided and covers all of the semiconductor laser units LDC, but may be separate from each semiconductor laser unit.

[0074] According to this semiconductor laser device, a laser beam output from the semiconductor laser unit LDC, which is a surface-emitting laser element, is emitted along the thickness direction, is reflected by the reflection film 23 of the spatial light modulator SLM, undergoes phase modulation in the liquid crystal layer LC, and is output to the outside through the polarizing plate 27. Therefore, the direction of a laser beam output from the polarizing plate, which undergoes phase modulation, is different for each pixel according to the modulation intensity of the liquid crystal layer LC. A laser beam to be emitted to the outside from the semiconductor laser unit LDC without passing through the spatial light modulator SLM can be suppressed by the polarizing plate 27.That is, for a laser beam passing through the 1 / 4 wavelength plate 26 twice, being incident on the spatial light modulator SLM and reflected, the phase of the laser beam is reversed, and consequently, its polarization azimuth is rotated by 90 degrees. Consequently, the laser beam passes through the polarization plate 27.

[0075] That is, when the polarization azimuth of the laser beam in the active layer 4 is set to a first direction (A), a polarization azimuth (B) transmitted through the polarizing plate 27 is perpendicular to the first direction (A), and the laser beam cannot directly pass through a wavelength plate. On the other hand, the laser beam that has passed through the 1 / 4 wavelength plate twice has the polarization azimuth (B) perpendicular to the first direction (A) in a case where there is no liquid crystal layer LC and can pass through the polarizing plate 27. A bias voltage is applied between the pixel electrode 21 and the common electrode 25, and thus only a polarization component whose phase is adjusted by the liquid crystal layer LC passes through the polarizing plate 27.

[0076] The width of the pixel electrode is smaller than that of each semiconductor laser unit, and two or more pixel electrodes are arranged corresponding to a single semiconductor laser unit. Thus, light generated by each semiconductor laser unit LDC travels to and returns from the spatial light modulator SLM, and is then two-dimensionally phase-modulated for each pixel of the spatial light modulator SLM. Consequently, it is possible to control a beam pattern for each semiconductor laser unit LDC. Therefore, a signal is applied to a spatial light modulator driving circuit S-DR to apply a peak beam having a direction controlled as an output beam pattern, and thus it is possible to output the peak beam in any direction for each semiconductor laser unit LDC.At this time, an array period L of the semiconductor laser unit LDC is set equal to or less than half the diameter of the pupil of an eye, and thus, it is possible to form a natural stereoscopic image of an integral system. At this time, a maximum diffraction angle Φ of the tip beam in any direction from each semiconductor laser unit LDC can be represented by Φ≈λ / d using a pixel pitch d of the spatial light modulator SLM and a wavelength λ. Therefore, it is necessary to appropriately set a small d to obtain a desired Φ.

[0077] Meanwhile, in the above-described example, the peak beam is output in any direction for each semiconductor laser unit LDC. However, it is possible to obtain any beam pattern for each LDC as long as the pixel pitch d has an appropriate value, and to obtain multiple beams in any direction for each semiconductor laser unit LDC. In this case, the beams in multiple directions are obtained simultaneously in parallel, and thus, it is possible to increase the number of viewpoints when displaying and forming a natural stereoscopic image. Alternatively, it is possible to increase a frame rate by setting the same number of viewpoints.

[0078] Meanwhile, a 90-degree polarization rotation of the liquid crystal layer LC can be performed in a state without bias, and a 0-degree polarization rotation thereof can be performed. In either case, it is possible to perform adjustment to a desired polarization azimuth by applying a bias voltage to the pixel electrode. List of reference symbols SLM SPATIAL LIGHT MODULATOR LDC semiconductor laser chip (semiconductor laser unit) 4 ACTIVE LAYER 2, 7 SHELL LAYER 6 DIFFRICTION GRATE LAYER

Claims

[1] Semiconductor laser device comprising: several semiconductor laser units (LDC) that can be controlled independently; and a spatial light modulator (SLM) optically coupled to a group of several semiconductor laser units (LDC), wherein each of the semiconductor laser units (LDC) comprises an active layer (4), a pair of cladding layers (2, 7) enclosing the active layer (4), and a diffraction grating layer (6) which is optically coupled to the active layer (4), wherein the plurality of semiconductor laser units (LDC) output laser beams along respective thickness directions, wherein the spatial light modulator (SLM) comprises a liquid crystal layer (LC), a reflection film (23) provided on a side opposite to the semiconductor laser unit (LDC) with respect to the liquid crystal layer (LC), a plurality of pixel electrodes (21) arranged two-dimensionally, and a common electrode (25) which surrounds the liquid crystal layer (LC) together with the pixel electrode (21), wherein a laser beam (LB) emitted from each of the semiconductor laser units (LDC) is incident on the spatial light modulator (SLM) and is modulated according to a state of the liquid crystal layer (LC) on the basis of the pixel electrodes (21), wherein the laser beam (LB) reflected and modulated by the reflection film (23) of the spatial light modulator (SLM) is output from a light emission surface of each of the semiconductor laser units (LCD) again through each of the semiconductor laser units (LCD) to the outside, and wherein the semiconductor laser device (LCD) further comprises a 1 / 4 wavelength plate (26) arranged between a group of the active layers (4) of the plurality of semiconductor laser units (LCD) and the reflection film (23), and a polarizing plate (27) arranged between the group of active layers (4) of the plurality of semiconductor laser units (LCD) and the light emitting surface. [2] A semiconductor laser device according to claim 1, wherein a width of each of said pixel electrodes (21) is equal to or less than a half width of each of said semiconductor laser units (LDC). [3] A semiconductor laser device according to claim 1 or 2, wherein the plurality of semiconductor laser units (LDC) comprise a first semiconductor laser unit (LDC) that outputs a laser beam (LB) having a first wavelength, a second semiconductor laser unit (LDC) that outputs a laser beam (LB) having a second wavelength, and a third semiconductor laser unit (LDC) that outputs a laser beam (LB) having a third wavelength, and where the first, second and third wavelengths are different from each other. [4] A semiconductor laser device according to claim 3, wherein the plurality of semiconductor laser units (LDC) comprise a fourth semiconductor laser unit (LDC) that outputs a laser beam (LB) with a fourth wavelength, a fifth semiconductor laser unit (LDC) that outputs a laser beam (LB) having a fifth wavelength, and a sixth semiconductor laser unit (LDC) outputting a laser beam (LB) having a sixth wavelength, and where the first, second, third, fourth, fifth and sixth wavelengths are different from each other.

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