SURFACE EMISSIONING LASER WITH TWO-DIMENSIONAL PHOTONIC CRYSTAL

Abstract

Surface-emitting laser with a two-dimensional photonic crystal, comprising: a two-dimensional photonic crystal (123) comprising a plate-shaped base member (121) and regions with a modified refractive index (122), wherein the regions with a modified refractive index (122) have a refractive index different from that of the plate-shaped base member (121) and are arranged two-dimensionally and periodically in the base member (121); an active layer (11) provided on one side of the two-dimensional photonic crystal (123); and a first electrode (15X, 15A) and a second electrode (16, 16A), which arrange the two-dimensional photonic crystal (123) and the active layer (11) sandwich-like between them for supplying current to the active layer (11), wherein the second electrode (16, 16A) covers an area equal to or wider than the first electrode (15X, 15A),wherein the first electrode (15X, 15A) is configured to supply the active layer (11) with a current at a different density depending on an in-plane position at the first electrode (15X, 15A), wherein the first electrode (15X, 15A) has a square shape and comprises two regions (15A11, 15A12) with a square first conductive region (15A11) formed near the center and a second conductive region (15A12) formed around the first conductive region (15A11), wherein the first conductive region (15A11) is made of a homogeneous conductor, and wherein the second conductive region (15A12) has a network-like conductor.

Description

TECHNICAL AREA

[0001] The present invention relates to a semiconductor laser and in particular a surface-emitting laser with a two-dimensional photonic crystal for amplifying light using a two-dimensional photonic crystal. BACKGROUND OF THE INVENTION

[0002] Semiconductor lasers offer many advantages: for example, they are small and inexpensive, have low energy consumption and a long lifespan, and have found widespread use in a variety of fields, such as light sources for optical recording, communication, laser displays, laser printers, and laser pointers. However, laser processing requires lasers with an optical output power exceeding 1 W. Currently, semiconductor lasers in practical use do not achieve this output power for the reasons described later. Therefore, gas lasers, such as carbon dioxide gas lasers, are currently used instead of semiconductor lasers in laser processing.

[0003] The reason for the low optical output power of currently used semiconductor lasers is as follows. To increase the optical output power of the semiconductor laser, it is preferable for the laser beam emitted from the laser element to have a large cross-sectional area (emission area). On the other hand, to increase processing accuracy, it is preferable for the spot of the laser beam directed onto a workpiece to have a small cross-sectional area (spot area). Thus, ideally, it is desirable for the laser beam emitted from a laser source to reach the workpiece without spreading. However, with semiconductor lasers, as the emission area increases, the spreading angle of the laser beam also increases, and wavefront distortion of the laser light occurs.When wavefront distortion of the laser light occurs, it becomes difficult to obtain a small spot area, even when the light is focused using an optical system. Therefore, with currently used semiconductor lasers, it is difficult to achieve an optical output power of 1 W or more while maintaining a small spread angle.

[0004] More recently, Noda and Liang, who are among the inventors of the present application, developed a surface-emitting laser with a two-dimensional photonic crystal, which has the following properties: an optical output power of 1.5 W and a beam spreading angle of 3° or less (non-patent literature 1 and 2). The surface-emitting laser with a two-dimensional photonic crystal comprises: a two-dimensional photonic crystal with a plate-shaped base member and regions with a modified refractive index, wherein the regions with a modified refractive index have a refractive index different from that of the plate-shaped base member and are arranged periodically in this member; and an active layer.In a surface-emitting laser with a two-dimensional photonic crystal, when an electric current is injected into the active layer, only light of a predetermined wavelength, corresponding to the periodicity of regions with a modified refractive index, is amplified from the light generated in the active layer. This induces laser oscillation, resulting in the emission of a laser beam perpendicular to the two-dimensional photonic crystal. The surface-emitting laser with a two-dimensional photonic crystal emits light (surface emission light) from a specific region within the two-dimensional photonic crystal. Therefore, this laser has a larger emission area than an end-surface emitting semiconductor laser, which can improve the output power and reduce the spreading angle.Various two-dimensional photonic crystals are conventionally known, comprising regions with a modified refractive index having different planar shapes (circle, regular triangle, etc.), arrangements (triangular lattice, square lattice, etc.), or other parameters. In the surface-emitting lasers with two-dimensional photonic crystals described in non-patent literature 1 and 2, the regions with a modified refractive index, which have a planar shape in the form of a right-angled triangle, are arranged at the lattice points of a square lattice parallel to the orthogonal sides of the region with a modified refractive index, thereby increasing the optical output power compared to conventional surface-emitting lasers with two-dimensional photonic crystals. LIST OF NON-PATENT LITERATURE

[0005] [Non-patent literature 1] Kazuyoshi Hirose and five other authors in: "Wattclass high-power, high-beam-quality photonic-crystal lasers", Nature Photonics (UK), 8, pp. 406–411, issue of 13 April 2014. [Non-patent literature 2] National University Corporation Kyoto University and Hamamatsu Photonics KK in: "Watt-class high-power photonic-crystal lasers: achieved leading the world – watt-class high output with high-beam quality achieved through surface emitting laser first in the world" [Online] website of the National University Corporation Kyoto University [accessed on August 11, 2014] from the Internet<http: / / www.kyotou.ac.jp / ja / news_data / h / h1 / news6 / 2014 / documents / 140414_1 / 01.pdf> April 10, 2014. SUMMARY OF THE INVENTIONAL PROBLEM

[0006] To improve the properties of surface-emitting lasers with two-dimensional photonic crystals, conventional investigations have so far focused solely on the configuration of these two-dimensional crystals. However, the laser of a semiconductor laser arises from an interaction between light emission from the active layer and amplification within the two-dimensional photonic crystal. No conventional study has focused on this relationship.

[0007] One problem to be solved by the present invention is to provide, taking into account the interaction between light emission from the active layer and amplification in the two-dimensional photonic crystal, a surface-emitting laser with a two-dimensional photonic crystal which improves the properties of the light to be emitted, in particular the output power. SOLUTION TO THE PROBLEM

[0008] The inventors in question have thoroughly investigated the configuration of an electrode for injecting charges into the active layer of a surface-emitting laser with a two-dimensional photonic crystal. The inventors discovered, and based the present invention on this, that by providing a distribution of the charge (carrier) density of the active layer depending on the in-plane position, an amplification effect is achieved that differs from that observed when the charge density of the active layer in the two-dimensional photonic crystal is uniform.

[0009] A surface-emitting laser with a two-dimensional photonic crystal according to the present invention, which is designed to solve the aforementioned problem, is a surface-emitting laser with a two-dimensional photonic crystal comprising: a two-dimensional photonic crystal comprising a plate-shaped base member and regions with a modified refractive index, wherein the regions with a modified refractive index have a refractive index different from that of the plate-shaped base member and are arranged two-dimensionally and periodically in the base member; an active layer which is provided on one side of the two-dimensional photonic crystal; and a first electrode and a second electrode, which are arranged sandwich-like between the two-dimensional photonic crystal and the active layer for supplying current to the active layer, wherein the second electrode covers an area equal to or wider than the first electrode, wherein the first electrode is formed to supply the active layer with a current at a different density depending on an in-plane position at the first electrode.

[0010] To emit light in a plane, a surface-emitting laser with a two-dimensional photonic crystal typically uses two electrodes. These electrodes sandwich the two-dimensional photonic crystal and the active layer between them. One electrode is made of a transparent material on the light-emitting side, while the other is made of an opaque (reflective) material, or the light-emitting electrode is smaller than the other. The active layer and the two-dimensional photonic crystal are located within an area that is equal to or wider than these electrodes (wider than the larger electrode if they differ in size).Thus, a current (charges) flowing between these electrodes is injected into a sub-region of the active layer (hereinafter referred to as the "charge injection region"). In a case where one of the electrodes is smaller than the other, the charge injection region is essentially similar to that of the smaller electrode, depending on the electrode areas and the distance between them.

[0011] In the surface-emitting laser with a two-dimensional photonic crystal according to the present invention, the smaller first electrode (narrower region) supplies current to the active layer at different densities depending on its in-plane position. This allows the charge densities in the charge injection region of the active layer to exhibit different values ​​depending on the in-plane position. Consequently, a distribution of light emission intensities is formed in the active layer depending on the in-plane position. In the two-dimensional photonic crystal, this distribution of light emission intensity causes an amplification effect, which differs from that observed when the charge density in the active layer is uniform.

[0012] As a measure to increase the optical output power of a surface-emitting laser with a two-dimensional photonic crystal, a configuration can be adopted in which the first electrode is designed to supply current to the active layer, with the distribution exhibiting the highest density in the center of the in-plane position. Thus, light emission with a maximum intensity distribution in the center of the charge injection region of the active layer occurs. The amplification of such emitted light in the two-dimensional photonic crystal facilitates laser oscillation in a fundamental mode and can reduce useless laser oscillation in higher modes. Therefore, the overall optical output power can be increased.

[0013] In contrast to the example mentioned above, in a case of selective oscillation of the laser in the higher modes of the active layer, current with a high density distribution can be supplied to positions that differ from the center in the in-plane position at the first electrode.

[0014] To supply current with varying densities to the active layer depending on the in-plane position at the first electrode, the first electrode can be configured with a conductor in a mesh form. For example, the thicknesses or spacings of the conductors in such a mesh-like conductor can be varied depending on their position, resulting in different conductor area ratios within the mesh. This allows for the generation of a current density distribution that varies depending on the in-plane position at the first electrode.

[0015] To achieve global current distribution across the entire first electrode via the network-like first electrode, it is desirable that no local current distribution dependent on the thickness and spacing of the network conductors develops. This requires that the spacing between the network conductors be 1.4 times or less wider than the current propagation L. C in the active layer. On the other hand, in order to reduce the current density or to create such a periodic distribution in a case where a locally periodic current distribution is permissible, the spacing of the network lines can be 1.4 times or more wider. Here, the current propagation L CIn the active layer, a value representing the size of a region where a current propagates from a point at the first electrode towards the second electrode in the plane of the active layer is defined by the distance from the center to the end of the region. The current propagation L C is essentially equal to the charge carrier distribution length in the active layer.

[0016] For example, the difference in current density depending on the in-plane position in the mesh-like first electrode can be formed by a mesh containing regions with different conductor area ratios. In this case, the mesh is designed to gradually reduce the area ratio of each region with increasing distance from the center of the first electrode's in-plane position. This results in light emission with an intensity distribution whose maximum lies in the center, within the charge injection region of the active layer. This light emission is amplified in the two-dimensional photonic crystal, thereby facilitating the occurrence of laser oscillation in the fundamental mode. Furthermore, in this case, the region encompassing the center can consist of only one conductor.

[0017] Alternatively, the difference in current density depending on the in-plane position in the mesh-like first electrode can be generated by varying the thickness and spacing of the mesh lines to continuously change the conductor area ratio in the mesh as a function of position. In this case, the mesh is designed to gradually reduce the conductor area ratio with increasing distance from the center of the first electrode's in-plane position, thereby causing light emission with an intensity distribution whose maximum lies in the center of the charge injection region in the active layer. This light emission is amplified in the two-dimensional photonic crystal, thus facilitating the occurrence of fundamental-mode laser oscillation.

[0018] In a case of selective oscillation of the laser in a higher mode in such a mesh-like first electrode, the area ratio of the conductor can be set to the maximum at a position other than the center of the in-plane position of the first electrode.

[0019] Another specific form of the first electrode for supplying current to the active layer with varying densities depending on its in-plane position is an electrode comprising ring-shaped conductors in a concentric circular arrangement and a connecting element for electrically linking the ring-shaped conductors together. The center of the concentric circles can be a space without a conductor. Alternatively, a non-ring-shaped (typically circular) conductor can be positioned at the center. In this specific form, a concentric circular current density distribution can be achieved by varying the width and / or spacing of the ring-shaped conductors depending on their distance from the center.To facilitate the occurrence of fundamental-mode laser oscillation, the widths of the ring-shaped conductors can be narrowed and / or the spacing widened with increasing distance from the center of the in-plane position at the first electrode. In the case of selective higher-mode oscillation, a different width and / or spacing may be used. Similar to the spacing between the mesh lines in the mesh-like first electrode, it is desirable for the ring-shaped conductors to be closely spaced to establish a global current distribution across the entire first electrode. To reduce the current density or to establish a local and periodic current distribution, a wider spacing is desirable.

[0020] Another specific form of the first electrode for supplying current at varying densities to the active layer, depending on its in-plane position, involves dividing the first electrode into regions comprising electrically isolated subelectrodes. In this specific form, different power sources are connected to the respective subelectrodes, and voltages applied between the subelectrodes and the second electrode are adjusted, thereby controlling the current densities in the respective regions. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0021] According to the present invention, the first electrode is configured to supply the active layer with a current of varying densities depending on its in-plane position, thereby enabling a different distribution of charge densities to be formed in the charge injection region of the active layer, depending on its position. This configuration can improve the properties, in particular the optical output power, of laser light that is to be amplified in the two-dimensional photonic crystal and emitted externally. BRIEF DESCRIPTION OF THE FIGURES

[0022] Fig. 1A and Fig. Figure 1B shows perspective views of an embodiment of a surface-emitting laser with a two-dimensional photonic crystal according to the present invention.

[0023] Fig. 2A and Fig. Figure 2B is a perspective view or a top view showing an example of a two-dimensional photonic crystal in the surface-emitting laser with a two-dimensional photonic crystal according to the present embodiment.

[0024] Fig. Figure 3 is a schematic diagram showing a charge injection region in the active layer of the surface-emitting laser with a two-dimensional photonic crystal according to the present embodiment in comparison with a two-dimensional photonic crystal.

[0025] Fig. Figure 4 is a top view showing a configuration of a first electrode in a surface-emitting laser with a two-dimensional photonic crystal according to a first embodiment.

[0026] Fig. 5A and Fig. Figure 5B are graphs showing charge density distributions of the active layer according to the first embodiment; here, they show Fig. 5A a middle part of the active layer and Fig. 5B shows a peripheral part of the active layer.

[0027] Fig. Figure 6 is a top view showing the central part and the peripheral part of the active layer in the first embodiment.

[0028] Fig. 7A and Fig. Figures 7B are graphs showing results of the calculation of threshold gain differences ∆α in the first embodiment, wherein Fig. 7A the difference depending on the ratio L i / L of length L i one side of a first conductive area to the length L = 200 μm of one side of the first electrode and Fig. 7B the difference as a function of L in a case of L i / L = 0.5 indicates.

[0029] Fig. 8A to Fig. Figures 8E are graphs, each showing a result of the calculation of the difference in the charge density distribution of the active layer as a function of the distance L2 between the network leads of the first electrode in the first embodiment.

[0030] Fig. 9A to Fig. Figures 9F are graphs, each showing a result of the calculation of the difference in the charge density distribution of the active layer as a function of the width L1 of the network line of the first electrode in the first embodiment.

[0031] Fig. 10A to Fig. Figure 10C are top views showing three modified examples of first electrodes according to the first embodiment.

[0032] Fig. Figure 11 is a top view showing another modified example of the first electrode according to the first embodiment.

[0033] Fig. 12A and Fig. 12B are graphs showing the results of the calculation of the threshold gain difference ∆α in the example of Fig. 11 show; Fig. 12A shows the difference as a function of the ratio w p / L of width w p the Gaussian charge density distribution to the length L = 200 μm of one side of the first electrode and Fig. 12B shows the difference as a function of L in a case of w p / L = 0.25.

[0034] Fig. Figure 13 is a top view showing another modified example of the first electrode according to the first embodiment.

[0035] Fig. Figure 14 is a top view showing a configuration of a first electrode in a surface-emitting laser with a two-dimensional photonic crystal according to a second embodiment.

[0036] Fig. Figure 15 is a top view showing a configuration of a first electrode in a surface-emitting laser with a two-dimensional photonic crystal according to a third embodiment.

[0037] Fig. Figure 16 is a top view showing a modified example of the first electrode in the surface-emitting laser with a two-dimensional photonic crystal according to the third embodiment. DESCRIPTION OF EXECUTION FORMS

[0038] With reference to Fig. 1 to Fig. Section 16 describes embodiments of surface-emitting lasers with a two-dimensional photonic crystal according to the present invention. Three embodiments are described in broad terms below. First, a configuration common to all embodiments is described. Then, the configurations characteristic of each embodiment are described, primarily with reference to the configuration of a first electrode. [Versions][Common configuration of the versions]

[0039] A surface-emitting laser 10X with a two-dimensional photonic crystal of each embodiment has a configuration in which a first electrode 15X , a first cladding layer 141 , an active layer 11 , an intermediate layer 13 , a layer 12 of a two-dimensional photonic crystal, a second cladding layer142 and a second electrode 16 stacked in this order ( Fig. 1) The sequence of the active layer 11 and the layer 12 The order for a two-dimensional photonic crystal can be the reverse of the order above. To illustrate, show Fig. 1 the first electrode 15X on the upper side, while the second electrode 16 shown on the lower side. However, in practice, the orientation of the surface-emitting laser is different. 10X The two-dimensional photonic crystal in any embodiment is not limited to the one shown in this diagram. A description of the layer and electrode configurations follows.

[0040] The active layer 11 receives charges which originate from the first electrode 15X and the second electrode 16are injected to emit light with a predetermined wavelength band. In the present embodiment, the material of the active layer is... 11 An InGaAs / AlGaAs multiple quantum well (light emission wavelength band: 935 to 945 nm) is used. However, within the scope of the present invention, the material is not limited to this. The active layer 11 It has a square shape with a thickness of approximately 2 μm, and one side of the square has the same or a greater length than that of the second electrode. 16 or 16A , which will be described later. Within the scope of the present invention, the dimension of the active layer is 11 not limited to this; another shape, such as a circular or hexagonal shape, can also be used for the layer.

[0041] The layer 12 of the two-dimensional photonic crystal, as for example in Fig. 2 shows an arrangement in which areas 122 with a modified refractive index, with a refractive index that differs from that of a plate-shaped base member 121 The difference lies in the base member 121 are arranged periodically. In the present embodiment, the material of the base member is 121 GaAs, but is not limited to this in the present invention. In the present embodiment, the areas are 122 with modified refractive index air holes (air or vacuum). An alternative can be used which is made of a material (with a refractive index) which differs from that of the base member. 121 is different. In the present embodiment, the areas are 122with a modified refractive index, which have a planar shape in the form of a right-angled triangle, arranged at the respective grid points of a square grid parallel to the orthogonal sides. The grid constant a of the square grid was determined based on 287 nm set, corresponding to the wavelength in the light emission wavelength band in the active layer 11 taking into account the refractive index in the layer 12 from a two-dimensional photonic crystal. Alternatively, another configuration can be used in which the shapes of the regions 122 with a modified refractive index, circular, regularly triangular or similarly shaped, and in which the arrangement of the areas 122 with a modified refractive index, it is a triangular grating. The planar shape of the basal member 121 is the same as that of the active layer 11, and the thickness is approximately 300 nm. In Fig. There are six vertical and six horizontal areas. 122 The modified refractive index is shown. In reality, there are more areas. 122 with a modified refractive index than the number shown in the diagram.

[0042] The intermediate layer 13 , which does not constitute an essential component of the present invention, is provided to the active layer 11 and the layer 12 to connect two-dimensional photonic crystals made of different materials. In the present embodiment, the material of the intermediate layer is 13 AlGaAs. However, the material is suitably varied according to the materials of the active layer. 11 and the layer 12 from a two-dimensional photonic crystal.

[0043] The first electrode15X It has a configuration that is specific to each embodiment. The details of the first electrode's configuration 15X are described for each embodiment. Fig. 1 is the detailed configuration of the first electrode 15X The outer shape is omitted and only the outer form is shown. The material and overall size of the first electrode are shown here. 15X described which the embodiments have in common. In the present embodiment, the material of the first electrode is 15X a p-type semiconductor and is not transparent to laser light (in the present embodiment a wavelength of 940 nm in a vacuum) emitted by the surface-emitting laser 10X is emitted with a two-dimensional photonic crystal. The first electrode 15X As a whole, it has a square shape, with the length L of one side being approximately 200 μm, and is smaller than the active layer.11 and the two-dimensional photonic crystal 123 To connect the first electrode 15X A reflective layer (not shown), made of a metal that is opaque to laser light, is provided around an insulator. The reflective layer serves to align with the first electrode. 15X to work together to benefit from the surface-emitting laser 10X to reflect laser light generated with a two-dimensional photonic crystal and the light from the second electrode 16 to emit outwards.

[0044] In the Fig. In example 1A, the second electrode is shown. 16 The second electrode is made of indium tin oxide (ITO), which is an n-type semiconductor transparent to laser light. However, the material is not limited to this in the present invention; for example, indium zinc oxide (IZO) can be used instead. 16It has a square shape, with each side having a length of approximately 800 μm, and it has a planar dimension which is equal to or slightly smaller than that of the active layer. 11 and the base member 121 the shift 12 of the two-dimensional photonic crystal. Instead of using such a transparent electrode, a second electrode can be used. 16A use which are in Fig. The second electrode is shown in 1B. 16A It features a configuration with a plate-shaped square element made of a metal that is opaque to laser light, with a central portion of the element cut out to form a square shape. The hollow portion remaining after cutting the plate-shaped element serves as a window. 161A designated and the remaining plate-shaped element is called a frame 162AThe square of the plate-shaped member has (outside the frame) 162A ) one side of 800 μm. The square of the window 161A It has a side of 600 μm. In this example, the surface-emitting laser emits light. 10X Laser light generated by a two-dimensional photonic crystal through the window 161A through it and is emitted to the outside.

[0045] The first cladding layer 141 and the second cladding layer 142 , which do not constitute essential components of the present invention, have the function of being the first electrode 15X and the active layer 11 or the second electrode 16 and the layer 12 to connect the two-dimensional photonic crystal and inject current from the first electrode 15X and the second electrode 16 into the active layer 11to facilitate this. To achieve these functions, a p-type semiconductor was chosen as the material for the first cladding layer. 141 an n-type semiconductor was used and was chosen as the material for the second cladding layer. 142 used. The first cladding layer 141 It has a two-layer structure, consisting of a layer made of p-GaAs and a layer made of p-AlGaAs, in order starting from the side of the first electrode. 15X ; likewise, the second cladding layer 142 a two-layer structure consisting of a layer made of n-GaAs and a layer made of n-AlGaAs, in order starting from the side of the second electrode. 16 (None of the two-layer structures are shown). Also regarding the first cladding layer. 141 and the second cladding layer 142It should be noted that the materials used in the present invention are not limited to those described above. The planar dimensions of the first cladding layer 141 and the second cladding layer 142 are the same as those of the active layer 11 and the base member 121 the shift 12 of a two-dimensional photonic crystal. The thickness of the first cladding layer. 141 is 2 μm and the thickness of the second cladding layer 142 The thickness is 200 μm. Thus, the active layer lies 11 much closer to the first electrode 15X than at the second electrode 16 Accordingly, a charge injection area exhibits 111 ( Fig. 3) in the active layer 11 a planar shape and a size similar to that of the first electrode 15X on. The two-dimensional photonic crystal 123 is larger than the first electrode 15XTherefore, this crystal is larger than the charge injection area. 111 the active layer 11 ( Fig. 3).

[0046] The operation of the surface-emitting laser will now begin. 10X Described using a two-dimensional photonic crystal. Between the first electrode 15X and the second electrode 16 A predetermined voltage is applied. The method for applying the voltage depends on the mode of the first electrode. 15X Each embodiment differs; the details are described for each embodiment. Applying voltage draws current from both electrodes into the charge injection area. 111 the active layer 11 injected. Thus, the charge injection area is filled. 111 Charges are injected to cause the emission of light with a wavelength in a predetermined wavelength band from the charge injection area.111 to effect the charge density distribution and the light emission intensity distribution in the charge injection region. 111 are described for each embodiment. From the resulting emission of light, light with a wavelength corresponding to the lattice constant a of the square lattice in the two-dimensional photonic crystal is selectively produced. 123 The light is amplified, resulting in laser oscillation. The oscillating laser light is emitted from the side of the second electrode. 16 emitted outwards.

[0047] Each embodiment is described below, primarily with regard to its characteristic configuration. [First embodiment – ​​mesh-shaped electrode]

[0048] In a surface-emitting laser with a two-dimensional photonic crystal of a first embodiment, a first electrode was 15A with a configuration which is in Fig. As shown in section 4, the first electrode is inserted. 15A In an overall view, it has a square shape and comprises two areas, which are a square-shaped first conductive area. 15A11 , which is formed near the center, and a second conductive area 15A12 , which surrounds the first conductive area 15A11 is formed around it. The first conductive area 15A11 It is made from a homogeneous conductor (p-type semiconductor). However, the second conductive area exhibits 15A12 a net-like conductor. Areas between the network lines 15A2 are with intermediate conductor sections made from an insulator 15A3 filled. As material for the intermediate pipe sections. 15A3 SiN was used. The conductor of the first conductive area 15A11 and the conductor, which manages the network lines 15A2 in the second conductive area 15A12The resulting structures are integrally formed and electrically interconnected, and are therefore equipotential. Such a network-like electrode can be fabricated using a typical lithography process.

[0049] In the present embodiment, the length L i (one side) of the square, which has the flat shape of the first conductive area 15A11 The carrier diffusion length in the active layer is set to 100 μm. 11 is estimated by calculation to be 2.5 μm; the size of the current propagation L C is assumed to be essentially equal to the carrier diffusion length, and the distance L2 between the network lines 15A2 in the second conductive area 15A12 was set to 3.0 μm, approximately 1.2 times wider than L C The width L1 of the power line 15A2 was set to 1.25 μm.

[0050] One result of the calculation of the charge density distribution, which is in the charge injection area 111 the active layer 11 in the surface-emitting laser with a two-dimensional photonic crystal of the first embodiment, is in Fig. 5A and Fig. Figure 5B shows the current propagation L in the calculation. C The distance L2 between the network lines is set to 2.5 μm, equal to the charge carrier distribution length. 15A2 1.2 times larger than L C . Fig. Figure 5A shows the charge density distribution at a central part. 1111 (see Fig. 6) in the charge injection area 111 , which corresponds to the first conductive area 15A11 corresponds, and Fig. Figure 5B shows the charge density distribution in a peripheral part 1112 the same Fig. 6), which leads to the second conductive area 15A12 corresponds. In the graphs of Fig. 5A and Fig. 5B will be the position of the middle part. 1111 The x-axis is taken from the center. The ordinate axis is normalized, so that the value of the center (the origin of the x-axis of the graph of) Fig. 5A) of the middle part 1111 which has the value one. As shown in these graphs, in the middle part 1111 and in the peripheral part 1112 Essentially uniform charge densities are formed. This occurs across the entire charge injection area. 111 the charge density distribution, in which the charge density distribution at the middle part 1111 is twice as large as that of the peripheral part 1112 The formation of such a charge density distribution causes the emission of light with the intensity distribution in which the maximum occurs at the central part 1111 in the charge injection area 111This light emission is located in the two-dimensional photonic crystal. 123 This enhances the laser's ability to oscillate in the fundamental mode. This reduces useless laser oscillation in a higher mode, thereby increasing the overall optical output power.

[0051] To verify the facilitation of laser oscillation in the fundamental mode, the threshold gain difference Δα was calculated in the first embodiment. The threshold gain difference Δα is obtained by subtracting the threshold gain of the fundamental mode oscillation from the threshold gain of the oscillation in the next higher mode, which has fewer antinodes and nodes than those present in the fundamental mode. The threshold gain in each oscillation mode represents the laser oscillation intensity in that mode and means that the larger the threshold gain difference Δα, the easier it is for laser oscillation to occur in the fundamental mode.

[0052] First, a result of the calculation of the threshold gain difference ∆α is given in a case where, as described above, the length of one side of the first electrode L = 200 μm and L iexhibits different values ​​in a range from 0 to 200 μm, including the value of 100 μm described above, in a graph of Fig. 7A shows the abscissa axis of this graph. i The graph shows the data for L. i / L = 1 not according to the present embodiment, but according to a conventional laser with a two-dimensional photonic crystal, the first electrode of which is made from a uniform conductive plate which is homogeneous as a whole. The data of L i / L = 0 shows that the first electrode is made from a mesh-like electrode with a uniform conductor density. According to this graph, it can be understood that in the case with the first conductive region made from the homogeneous conductor and the second conductive region mesh-like, and L i For L ≠ 0 and 1, the threshold gain difference Δα is greater than in the conventional case with L.i / L = 1, and that laser oscillation occurs readily in the fundamental mode. In the Fig. In the data shown in 7A, the threshold gain difference ∆α is greatest in a case with L i / L = 0.5, i.e., in the case mentioned above with L i = 100 μm and L = 200 μm.

[0053] Next, a result of the calculation of the threshold gain difference ∆α in a case with L will be presented. i / L = 0.5 and different values ​​of L in the graph of Fig. Figure 7B shows that, according to this graph, in a region of L greater than 300 μm, the threshold gain difference Δα decreases as the value of L increases. Conversely, the area of ​​the entire first electrode increases as the value of L increases. This is advantageous for achieving high laser output power. Based on the calculated values ​​of Δα shown in Fig. 7B were obtained, a value of 2.4 W was obtained when calculating the laser light output power, in a case of the highest value of L with L = 600 μm (L i = 300 μm) from values ​​of ∆α equal to or greater than the value of ∆α in the conventional example (L i / L = 1) in Fig. 7A. This calculated value of optical output power is higher than experimental values ​​of the lasers with two-dimensional photonic crystals described in non-patent literature 1 and 2 (although there are differences between the calculated value and the experimental values).

[0054] So far, the case has been described where the distance L2 between the network lines 15A2 in the second conductive area 15A12 the first electrode 15A 3.0 μm. In Fig. 8A to Fig. 8E are results of the calculation of the charge density in the peripheral part 1112 in the active layer 11Examples with different distances L2 are shown. The width L1 of each network line. 15A2 was reduced to 0.50 L c μm. The distance L2 was set to 0.50 L. c μm in Fig. 8A set, to 0.80 L c μm in Fig. 8B, to 1.20 L c μm in Fig. 8C ( Fig. 8C is therefore a reproduction of Fig. 5B), to 1.40 L c μm in Fig. 8D and on 2.00 L c μm in Fig. 8E. According to these calculations, the charge density distribution in the peripheral part is 1112 almost uniformly in the cases of Fig. 8A to Fig. 8C, while in the case of Fig. 8D a slight periodic fluctuation corresponding to the period of the power lines 15A2 This is shown, although the range of variation is limited to less than 5%. In contrast, in the case of Fig. 8E – with a distance L2 approximately 1.4 times wider than the current propagation L C– the width of the periodic fluctuation of the charge density distribution is large, exceeding 10%. This applies to the case of equal widths L1 of the network lines. 15A2 The charge density is lower the greater the distance L2 is.

[0055] Fig. 9A to Fig. 9F each show a result of the calculation of the charge density in the peripheral part. 1112 in the active layer 11 In examples with different widths L1, for the case of equal distances L2 of the network lines 15A2 The distance L2 between the network lines 15A2 was reduced to 1.20 L c μm. The width L1 was set to 0.50 L. c μm in Fig. 9A set (thus, Fig. 9A a reproduction of Fig. 5B and Fig. 8C), to 0.32 L c μm in Fig. 9B, to 0.20 L c μm in Fig. 9C, to 0.16 L c μm in Fig. 9D, to 0.12 L c μm in Fig. 9E and to 0.08 Lc μm in Fig. 9F. According to these calculations, the charge density distribution in the peripheral part is given by... 1112 , that the charge density is lower the smaller the width L1 of the power line 15A2 is.

[0056] As described above, when specifying the difference in the distances L2 and / or widths L1 of the network lines 15A2 in the first electrode 15A The charge density is lower the lower the area ratio of the conductor (the line) in the network. Therefore, by adjusting this distance L2 and / or this width L1, the charge density at the corresponding position in the active layer can be changed. 11 be defined.

[0057] Instead of the single conductor in the aforementioned example, the first conductive area can be 15A11 from a network with a larger conductor area ratio than the second conductive area 15A12be manufactured, for example with a greater width L1 of the power line than the second conductive area 15A12 ( Fig. 10A) or with the same width L1, but a smaller width L2. Alternatively, three or more conductive areas (a first conductive area) are possible. 15A11 , a second conductive area 15A12 , a third conductive area 15A13 ...) should be provided to determine the conductor area ratio from the center to the periphery of the first electrode. 15A to gradually become smaller ( Fig. 10B). As another example, a configuration may be provided in which a square-shaped first conductive area 15A11 with the highest conductor area ratio in the middle of a first electrode 15A A second conductive area is provided. 15A12 with the next higher conductor area ratio in contact with the sides of the square of the first conductive area 15A11is provided and a third conductive area 15A13 with a lower conductor area ratio than these two conductive areas in contact with the corners of the square of the first conductive area 15A11 is provided ( Fig. 10C).

[0058] As in Fig. As shown in Figure 11, starting from the center of the in-plane position of the first electrode 15A towards the outside, the area of ​​each intermediate line section 15A3 gradually increase. In this example, the distances L2 between the network lines 15A2 Regardless of the in-plane position, the same value is displayed, and the width L1 varies continuously, gradually decreasing with distance from the center of the in-plane position. At the center of the in-plane position, the width L1 is equal to the distance L2, and the intermediate guide areas 15A3are not present. According to this configuration, the conductor area ratio in the first electrode changes. 15A Essentially continuous, gradually decreasing with increasing distance from the center of the in-plane position. In the charge injection area 111 the active layer 11 , in which from such a first electrode 15A When current is injected, the charge density gradually decreases from the center of the in-plane position towards the outer edge; likewise, the intensity of the light emission gradually decreases from the center of the in-plane position towards the outer edge. Such an intensity distribution according to the position of the light emission is more similar to the Gaussian distribution than the distribution in the other cases cited above as examples. Thus, laser oscillation in the fundamental mode readily occurs.

[0059] Fig. 12A and Fig. Figures 12B each show a graph representing the result of the calculation of the threshold gain difference ∆α in the example of Fig. 11. Here, it is assumed that the Gaussian distribution of charge density with width w p in the charge injection area 111 is trained. Fig. 12A L was set to 200 μm, and w p / L was taken as the abscissa axis of the graph. In Fig. 12B was w p / L was set to 0.25, and L was taken as the abscissa axis. In Fig. 12A are data with w p / L = 0 not according to the present embodiment, but according to the conventional laser with a two-dimensional photonic crystal, in which a uniform charge density is formed in the active layer by the plate-shaped first electrode. It can be understood that all data according to the present embodiment, which are in Fig. Figure 12A shows a larger threshold gain difference Δα than the conventional case with w p / L = 0, and that laser oscillation in the fundamental mode occurs easily. According to the graph of Fig. In section 12B, in a region where L is greater than 400 μm, the threshold gain difference Δα decreases as L increases. Conversely, the area of ​​the entire first electrode increases as L increases. This is advantageous for increasing the laser output power. Based on the calculated values ​​of Δα, which are shown in Fig. 12B was obtained when calculating the laser light output power, resulting in a value of 8 W in the case of the largest value of L with L = 2200 μm from values ​​of ∆α equal to or greater than the value of ∆α in the conventional example of Fig. 12A. The calculated value of the optical output power is higher than the calculated value in a case where the charge density is determined by only two values ​​using the aforementioned first conductive region. 15A11 and second conductive area 15A12 is being discontinued.

[0060] Fig. Figure 13 shows an example of the first electrode. 15A for selectively oscillating the laser in a higher mode. In this example, the square-shaped first electrode was used. 15A first conductive areas 15A11 near two diagonally aligned corners of the four corners of the square, a conductive area was provided, and the remaining area was allocated to a second conductive area. 15A12 set, which has a lower conductor area ratio than the first conductive areas 15A11This structure forms a distribution in which the current density is located near the center of the planar shape of the first electrode. 15A The current density is low and high near the two corners. The injection of current with such a distribution into the active layer 11 This leads to the fact that in the active layer 11 The generated light becomes standing waves in the higher mode, where a node is located near the center and the antinodes are located near the position corresponding to the two corners on the diagonal in the two-dimensional photonic crystal. 123 correspond. Thus, the laser oscillates in the higher mode. [Second embodiment – ​​concentric circular electrode]

[0061] A surface-emitting laser with a two-dimensional photonic crystal according to a second embodiment uses a first electrode 15Bwith a configuration in which ring-shaped conductors 15B1 are provided in a concentric manner, and in which the boundaries of the ring-shaped conductor 15B1 by means of ring-shaped insulators 15B2 are isolated from each other, as in Fig. Figure 14 shows that a circular ladder is located in the center of the concentric circle. 15B0 provided. The circular ladder 15B0 and the ring-shaped ladders 15B1 are via a linear conductor 15B3 electrically connected. The width of the ring-shaped conductor 15B1 was set to establish a ratio to the width of the ring-shaped insulator. 15B2 The current density distribution is such that it decreases with increasing distance from the center. This results in a current density distribution where the density increases with the distance of the electrode from the center of the first electrode. 15B gets smaller. [Third embodiment – ​​split electrodes]

[0062] In a surface-emitting laser with a two-dimensional photonic crystal according to a third embodiment, a first electrode was 15C used with a configuration which is in Fig. Figure 15 shows a first electrode. 15C In an overall view, it has a square shape and comprises two areas, which are a square-shaped first conductive area. 15C11 , which is formed near the center, and a second conductive area 15C12 , which surrounds the first conductive area 15C11 It is formed around it. An insulating area. 15C21 , made from an insulator which is linear like the four sides of a square, is at the boundary between the first conductive area 15C11 and the second conductive area 15C12provided. In this structure, the first conductive area is active. 15C11 and the second conductive area 15C12 than the subelectrodes mentioned above. The first electrode 15C includes a linear connection area 15C31 , which is made from a conductor extending from a corner of the square of the first conductive area 15C11 on the diagonal of the square of the second conductive area 15C12 extends and a corner of the second conductive area 15C12 reached. On both sides of the line of the connection area. 15C31 is an insulating area 15C21 provided. The first electrode 15C It can be produced using a typical lithography process.

[0063] The surface-emitting laser with a two-dimensional photonic crystal according to the third embodiment applies a first voltage V1 between the first conductive region.15C11 and the second electrode 16 on, while applying a second voltage V2 lower than the first voltage V1 between the second conductive area 15C12 and the second electrode 16 is applied. During the application, the first conductive area 15C11 via the connection area 15C31 connected to a first power source (not shown), while the second conductive area 15C12 directly connected to a second power source (not shown), which is different from the eleventh power source. The first conductive area 15C11 and the second conductive area 15C12 are above the insulating area 15C21 They are electrically separated from each other, as described above. This allows different voltages to be applied to the respective areas. Such a voltage application forms a charge injection area. 111 the active layer 11a charge density distribution in which the density in the middle part 1111 is higher than that in the peripheral part 1112 From the charge injection area 111 This results in light emission with an intensity distribution whose intensity reaches a maximum in the middle part. 1111 exhibits this. This emitted light is contained within the two-dimensional photonic crystal. 123 This enhances the laser oscillation to facilitate laser oscillation in a fundamental mode. This reduces useless laser oscillation in a higher mode, thereby increasing the overall optical output power.

[0064] The first electrode 15C According to the third embodiment, starting from the center towards the periphery, three or more conductive areas can be defined (the first conductive area). 15C11 , the second conductive area 15C12 , the third conductive area 15C13 ...) include ( Fig. 16) In the case of the provision of three or more conductive areas, all boundaries between the conductive areas and insulating areas must be 15C21 , 15C22 ... provided. In conductive areas other than the outermost one, there are connection areas. 15C31 and 15C32 ... provided. The conductive areas (subelectrodes) are connected to various power sources. Reference symbol list 10X Surface-Emitting Laser with Two-Dimensional Photonic Crystal 11 Active shift 111 Charge injection area 1111 Middle part 1112 Peripheral part 12 layers of a two-dimensional photonic crystal 121 Basic member 122 areas with modified refractive index 123 Two-dimensional photonic crystal 13 Intermediate shift 141 First Cladding Layer 142 Second Cladding Layer 15A, 15B, 15C, 15X First electrode 15A11, 15C11 First conductive area 15A12, 15C12 Second conductive area 15A13, 15C13 Third conductive area 15A2 power line 15A3 Intermediate line area 15B0 Circular conductor 15B1 Ring-shaped conductor 15B2 Ring-shaped insulator 15B3 Linear conductor 15C21, 15C22 Insulating area 15C31, 15C32 connection area 16, 16A Second electrode 161A Window 162A frame

Claims

[1] Surface-emitting laser with two-dimensional photonic crystal, comprising: a two-dimensional photonic crystal comprising a plate-shaped base member and regions with a modified refractive index, wherein the regions with a modified refractive index have a refractive index different from that of the plate-shaped base member and are arranged two-dimensionally and periodically in the base member; an active layer which is provided on one side of the two-dimensional photonic crystal; and a first electrode and a second electrode, which are arranged sandwich-like between the two-dimensional photonic crystal and the active layer for supplying current to the active layer, wherein the second electrode covers an area equal to or wider than the first electrode, wherein the first electrode is formed to supply the active layer with a current at a different density depending on an in-plane position at the first electrode. [2] Surface-emitting laser with a two-dimensional photonic crystal according to claim 1, wherein the first electrode is configured to supply the current to the active layer, wherein the distribution has a highest density in a center of the in-plane position. [3] Surface-emitting laser with a two-dimensional photonic crystal according to claim 1 or 2, wherein the first electrode comprises a conductor which is formed in a mesh form. [4] Surface-emitting laser with a two-dimensional photonic crystal according to claim 3, wherein a distance between conductors of the mesh is 1.4 times or less wider than a current propagating in an in-plane direction of the active layer. [5] Surface-emitting laser with a two-dimensional photonic crystal according to claim 3 or 4, wherein the first electrode has regions with different area ratios of the conductor in the mesh. [6] Surface-emitting laser with a two-dimensional photonic crystal according to claim 5, wherein the area ratio in each of the regions gradually decreases with distance of a position from the center of the in-plane position of the first electrode. [7] Surface-emitting laser with a two-dimensional photonic crystal according to claim 6, wherein a central region in the first electrode consists only of the conductor. [8] Surface-emitting laser with a two-dimensional photonic crystal according to claim 3 or 4, wherein the area ratio of the conductor in the mesh of the first electrode changes continuously depending on a position. [9] Surface-emitting laser with a two-dimensional photonic crystal according to claim 8, wherein the area ratio of the conductor in the mesh gradually decreases with distance of a position from the center of the in-plane position of the first electrode. [10] Surface-emitting laser with a two-dimensional photonic crystal according to claim 1 or 2, wherein the first electrode comprises ring-shaped conductors in a concentric circular arrangement and a connecting part for electrically connecting the ring-shaped conductors to each other. [11] Surface-emitting laser with a two-dimensional photonic crystal according to claim 1 or 2, wherein the first electrode is divided into regions, the regions comprising subelectrodes which are electrically isolated from each other. [12] Surface-emitting laser with a two-dimensional photonic crystal according to claim 11, wherein different power sources are connected to the respective subelectrodes.