Two-dimensional photonic crystal surface-emitting laser

Abstract

A two-dimensional photonic crystal surface-emission laser (10) includes a two-dimensional photonic crystal layer (12) formed by periodically arranging, in a plate-shaped base material (121), a different-refractive-index region (122) having a different refractive index from that of the base material (121); an active layer (11) provided on one surface side of the two-dimensional photonic crystal layer (12); and a reflection layer (15) provided on the other surface side of the two-dimensional photonic crystal layer (12) in a manner separated from the two-dimensional photonic crystal layer (12) or on the side of the active layer (11) opposite to the two-dimensional photonic crystal layer (12), wherein a distance d between the surfaces of the two-dimensional photonic crystal layer (12) and the reflection layer (15) facing each other is set so that a radiation coefficient difference Δα v =(α v1 ‑α v0 ) is 1 cm ‑1 or more, where α v is a radiation coefficient of a first high-order mode having the second smallest loss among the light amplified by the two-dimensional photonic crystal layer (12), and α v1 is a radiation coefficient of a fundamental mode having the smallest loss. v0 ​

Description

Technical Field

[0001] This invention relates to a two-dimensional photonic crystal surface-emitting laser that uses a two-dimensional photonic crystal to amplify light. Background Technology

[0002] Semiconductor lasers offer numerous advantages, including small size, low cost, low power consumption, and long lifespan, leading to their widespread adoption in a wide range of fields such as optical recording light sources, communication light sources, laser displays, laser printers, and laser pointers. However, the field of laser processing requires lasers with an output of at least 100W and a narrow beam divergence angle, which currently unavailable in semiconductor lasers. Therefore, gas lasers, such as carbon dioxide lasers, are currently used instead of semiconductor lasers in laser processing.

[0003] In recent years, two-dimensional photonic crystal surface-emitting lasers (SPEAS) have attracted attention as semiconductor lasers expected to achieve high light output while maintaining a narrow beam divergence angle. A SPEAS comprises a two-dimensional photonic crystal layer formed by periodically arranging regions of different refractive indices (within the refractive index of the substrate) in a plate-like substrate, and an active layer serving as the light-emitting layer. Typically, the regions of different refractive indices are formed by voids in the substrate. In a SPEAS, when a current is injected into the active layer, the light generated in the active layer is amplified only by light of a predetermined wavelength corresponding to the period of the regions of different refractive indices, resulting in laser oscillation, and is emitted as a laser beam in a direction perpendicular to the two-dimensional photonic crystal layer. Since SPEAS emits light from a fixed area within the two-dimensional photonic crystal layer (surface emission), it has advantages over conventional end-emitting semiconductor lasers, such as a larger emission area and easier increase in light output.

[0004] Patent Document 1 describes a two-dimensional photonic crystal surface-emitting laser with a two-dimensional photonic crystal layer. This two-dimensional photonic crystal layer is formed by periodically arranging pairs of anomalous refractive index regions—two planar regions of different areas with different planar shapes—at a predetermined distance on a plate-shaped substrate, in a square lattice configuration with a period length 'a' longer than the predetermined distance. Hereinafter, the one with the larger planar area constituting the anomalous refractive index region pair is referred to as the "primary anomalous refractive index region," and the smaller one as the "secondary anomalous refractive index region." Furthermore, in the square lattice where the lattice points of the anomalous refractive index region pair are arranged at a period length 'a', one of the two mutually orthogonal directions is designated as the "x-direction," and the other as the "y-direction."

[0005] In the structure of Patent Document 1, the distance (denoted as d) in the x-direction from the primary anisorefractive index region to the secondary anisorefractive index region is...x The distance in the y direction (denoted as d) and the distance in the y direction. y When both wavelengths are 0.25λ, the difference in optical path length between light with wavelength (depending on the refractive index within the two-dimensional photonic crystal layer) λ, which is reflected by the primary anisotropic region and has a 180° change in direction, and light reflected by the secondary anisotropic region and has a 180° change in direction, is 0.5λ, which is weakened by interference. Regarding the case of light reflected in the 180° direction, after repeated reflection, the light will locally exist in a portion of the two-dimensional photonic crystal layer. In addition to the oscillation of the fundamental mode caused by light with wavelength λ, oscillations of higher-order modes with different wavelengths and spatial distributions than the fundamental mode also occur simultaneously, contributing to the increase in beam divergence angle. Therefore, by adopting the above structure, light can locally exist in a portion of the two-dimensional photonic crystal layer, and even if the area of ​​the two-dimensional photonic crystal layer is increased to some extent (for example, setting the radius of the inscribed circle of the region containing the anisotropic regions to 300μm to 500μm), single-mode oscillation in the fundamental mode can be maintained.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2008-243962 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In the two-dimensional photonic crystal surface-emitting laser described in Patent Document 1, as mentioned above, the effect of light reflection in the 180° direction is reduced by using regions of different refractive indices. Therefore, even if the area of ​​the two-dimensional photonic crystal layer is increased to some extent, oscillations in a single mode (single wavelength) consisting of the fundamental mode can be maintained. However, in the two-dimensional photonic crystal layer, diffraction occurs, causing the light's direction of travel to change by 90° due to the periodically arranged regions of different refractive indices (90° diffraction), and diffraction occurs in the direction perpendicular to the two-dimensional photonic crystal layer (emitted light). If the area of ​​the two-dimensional photonic crystal layer is further increased, these diffractions will cause light to be locally contained within a portion of the two-dimensional photonic crystal. As a result, oscillations in higher-order modes (other wavelengths) are more likely to occur, and consequently, the beam angle diverges.

[0011] The problem to be solved by the present invention is to provide a two-dimensional photonic crystal surface-emitting laser capable of realizing the oscillation of a single wavelength laser.

[0012] Solution for solving the problem

[0013] The two-dimensional photonic crystal surface-emitting laser of the present invention, which addresses the above-mentioned problems, is characterized by having:

[0014] a) A two-dimensional photonic crystal layer, which is formed by periodically arranging regions with different refractive indices than the refractive index of the substrate in a plate-shaped substrate;

[0015] b) An active layer disposed on one side of the two-dimensional photonic crystal layer; and

[0016] c) A reflective layer, which is disposed separately from the two-dimensional photonic crystal layer on the other side of the two-dimensional photonic crystal layer, or disposed on the side of the active layer opposite to the two-dimensional photonic crystal layer.

[0017] The distance between the opposing surfaces of the two-dimensional photonic crystal layer and the reflective layer is set such that the difference in emissivity Δα v =(α v1 -α v0 ) is 1cm -1 The above refers to the difference in radiation coefficient Δα. v The radiative coefficient α of the first higher-order mode with the second smallest loss in the light amplified by the two-dimensional photonic crystal layer is... v1 Subtract the radiation coefficient α of the basic mode with minimum loss v0 The value obtained.

[0018] Here, the radiation coefficient refers to the proportion of light in a two-dimensional photonic crystal layer that is diffracted in a direction perpendicular to the two-dimensional photonic crystal layer during the waveguided phase of a unit length.

[0019] In a two-dimensional photonic crystal surface-emitting laser, the interaction between the waveguide light (in-plane guided light) within the two-dimensional photonic crystal layer and the outgoing light emitted from the two-dimensional photonic crystal layer in a direction perpendicular to it affects the radiation coefficient α of each mode of the fundamental mode and the first higher-order mode. v0 and α v1 The value of . Furthermore, a reflective layer is provided separately from the two-dimensional photonic crystal layer. The emitted light is generated by interfering light emitted from the two-dimensional photonic crystal layer to the opposite side of the reflective layer (referred to as "first emitted light") with light emitted from the two-dimensional photonic crystal layer to the reflective layer side and reflected by the reflective layer (referred to as "second emitted light"). This allows the magnitude of the interaction between the in-plane guided light and the emitted light to be set according to the distance between the opposing surfaces of the two-dimensional photonic crystal layer and the reflective layer (inter-surface distance). Therefore, the radiation coefficient α of the basic mode can be set according to the magnitude of this inter-surface distance. v0 The radiation coefficient α of the first higher-order mode v1 The value of this can also be used to set the radiation coefficient difference Δα.v =(α v1 -α v0 The value of ).

[0020] By dividing the radiation coefficient difference Δα according to the size of the inter-face distance in this way... v When set to a positive value, the light (non-laser) of the first higher-order mode tends to leak in a direction perpendicular to the two-dimensional photonic crystal layer, compared to the fundamental mode. Therefore, when the gain of the active layer is uniform in-plane, the fundamental mode is selectively enhanced through resonance within the two-dimensional photonic crystal layer, oscillating to produce a single-wavelength laser composed of the fundamental mode.

[0021] Furthermore, if a current is further injected into the active layer while the laser oscillation in the basic mode has been generated, the carriers in the active layer will be consumed in the region of high intensity of the basic mode light, resulting in non-uniformity in the in-plane gain distribution. However, generally speaking, if the difference in the radiation coefficient Δα... v 1cm -1 Therefore, even if non-uniformity occurs in the gain distribution, the above-mentioned stable single-wavelength laser oscillation can still be maintained.

[0022] If the inter-plane distance is changed, the phase difference θ between the first emitted light and the second emitted light... ref The angle varies from -180° to +180°. The interaction between the in-plane guided wave and the outgoing wave is relative to the phase difference θ. ref The phase difference θ increases and decreases in a sinusoidal manner. ref The further away from 0° (closer to +180° or -180°), the smaller the interaction. At this point, because the coupling effect of multiple in-plane guided wavelights through the outgoing light is weakened, the in-plane guided wavelights propagate independently in each direction, making leakage more likely in the vertical direction. As a result, the radiation coefficient α of the fundamental mode and higher-order modes... v0 and α v1 and its radiation coefficient difference Δα v Both increase. Therefore, if the aforementioned radiation coefficient difference Δα is realized... v The phase difference θ of the lower limit value ref Let it be ±θ lim (θ lim If the phase difference θ > 0), then make the phase difference θ ref Less than -θ lim or greater than +θ lim The size of the distance between surfaces can be determined by the method.

[0023] For the reflective layer, a distributed Bragg reflector (DBR), such as that used in vertical resonator surface-emitting lasers (VCSELs), can be used. Alternatively, one of a pair of electrodes for injecting current into the active layer can be formed using a material that reflects the second emitted light, and that electrode can be used as the reflective layer.

[0024] The anisotropic region can also be composed of a region with a refractive index different from that of the base material, but it is preferable to form a pair of anisotropic regions by separately arranging a first anisotropic region and a second anisotropic region with different planar shapes and areas. By using such a pair of anisotropic regions to appropriately set the positional relationship between the first and second anisotropic regions, the light whose direction of travel changes by 180° after being reflected by the anisotropic region pair can be weakened through interference. Furthermore, by also adjusting the sizes of the first and second anisotropic regions, light whose direction of travel changes by 180° in the anisotropic region pair can be weakened together through interference with light whose direction of travel changes by 90° in the anisotropic region pair, resulting in more complete in-plane disappearance interference. Therefore, in addition to the inter-plane distance, the magnitude of the interaction between the in-plane guided light and the emitted light can be set according to the positional relationship and / or the size of the first and second anisotropic regions, thereby also setting the radiation coefficient difference Δα. v The value of .

[0025] The interplanar distance between the opposing surfaces of the two-dimensional photonic crystal layer and the reflective layer can be determined by the thickness of the intermediate layer disposed between these two layers. Such an intermediate layer can be, for example, a cladding layer made of p-type or n-type semiconductor. The cladding layer serves to transport holes or electrons injected into the active layer from an electrode located on the outer side (opposite to the two-dimensional photonic crystal layer) of the reflective layer (or constituting the reflective layer), and also serves to suppress the leakage of in-plane guided light (in a form other than emitted light) from the two-dimensional photonic crystal layer.

[0026] With this coating layer, the two-dimensional photonic crystal surface-emitting laser according to the present invention preferably has the following structure. That is, in the two-dimensional photonic crystal surface-emitting laser according to the present invention, it is preferred that...

[0027] It also includes a first coating layer and a second coating layer, which are two coating layers disposed in a manner that sandwiches the two-dimensional photonic crystal layer and the active layer. The first coating layer is disposed between the two-dimensional photonic crystal layer and the reflective layer and is made of a p-type semiconductor or an n-type semiconductor. When viewed from the two-dimensional photonic crystal layer, the second coating layer is disposed on the opposite side of the reflective layer side, and the second coating layer is made of a semiconductor having charge carriers with opposite polarities to those of the first coating layer.

[0028] The product of the thickness and refractive index of the layer located between the first coating layer and the second coating layer, excluding the two-dimensional photonic crystal layer, is greater than the product of the thickness and refractive index of the two-dimensional photonic crystal layer.

[0029] In a two-dimensional photonic crystal surface-emitting laser, the product of the thickness and refractive index of each layer refers to the effective optical path length of light in the direction perpendicular to the layer within that layer. By making the effective thickness and refractive index product (i.e., the optical path length in the vertical direction) of the layers located between the first and second cladding layers (excluding the two-dimensional photonic crystal layer) larger than the product of the thickness and refractive index of the two-dimensional photonic crystal layer (as above), compared to the opposite case, the proportion of light distributed in the two-dimensional photonic crystal layer is reduced. The coupling effect of multiple in-plane guided wavelights through the outgoing light is weakened, so the in-plane guided wavelights propagate independently in each direction, making leakage more likely in the vertical direction. As a result, the radiation coefficient α of the fundamental mode and higher-order modes... v0 and α v1 and its radiation coefficient difference Δα v All increase. Therefore, by setting the thickness and refractive index of each layer between the first and second cladding layers as described above, the difference in radiation coefficient Δα v The larger the wavelength, the easier it is to generate oscillations in the fundamental mode, thereby enabling the laser of a single wavelength to oscillate more stably.

[0030] Furthermore, between the first and second cladding layers, in addition to the two-dimensional photonic crystal layer and the active layer, there may be one or more other layers. In the presence of such other layers, the term "layers other than the two-dimensional photonic crystal layer" refers to multiple layers composed of the active layer and the one or more other layers. In this case, the "product of the thickness and refractive index of the layers other than the two-dimensional photonic crystal layer" is equivalent to calculating the product of the thickness and refractive index of each of these multiple layers and summing the values ​​of these products.

[0031] As one of the aforementioned "other layers," a guiding layer can be disposed between the first cladding layer and the second cladding layer, which, when viewed from the active layer, is disposed on the side opposite to the two-dimensional photonic crystal layer. The guiding layer has the following function: reducing the proportion of in-plane guided light distributed in the two-dimensional photonic crystal layer, thereby weakening the coupling effect of multiple in-plane guided light beams through the outgoing light.

[0032] The effects of the invention

[0033] According to the present invention, a two-dimensional photonic crystal surface-emitting laser capable of oscillating a single wavelength of laser light can be obtained. Attached Figure Description

[0034] Figure 1 This is a perspective view (a) showing a first embodiment of the two-dimensional photonic crystal surface-emitting laser according to the present invention, and a top view (b) showing the two-dimensional photonic crystal layer provided by the two-dimensional photonic crystal surface-emitting laser.

[0035] Figure 2 This illustrates how the coefficient μ, representing the magnitude of the interaction between the in-plane guided wavelight and the outgoing light during 180° diffraction, and the difference in emissivity Δα, are calculated for the two-dimensional photonic crystal surface-emitting laser of the first embodiment. v A chart showing the results obtained from the relationship.

[0036] Figure 3 This is an enlarged top view (a) showing the pair of heterorefringent index regions of the two-dimensional photonic crystal surface-emitting laser of the first embodiment, and the calculation of the one-dimensional coupling coefficient κ for several examples with different parameters δa and 2x shown in (a). 1D With the two-dimensional coupling coefficient κ 2D- The real part Re(κ) of the sum 1D +κ 2D- ) and imaginary part Im(κ) 1D +κ 2D- The results obtained are shown in graph (b).

[0037] Figure 4 This illustrates how, in a two-dimensional photonic crystal surface-emitting laser according to the first embodiment, the phase difference θ between the first and second emitted beams is calculated. ref A graph showing the results obtained from the relationship between the coefficients μ.

[0038] Figure 5 This illustrates how the phase difference θ of a two-dimensional photonic crystal surface-emitting laser, according to the first embodiment, is calculated. ref A graph showing the results obtained from the relationship between the threshold gain difference and the threshold gain difference.

[0039] Figure 6This is a graph showing the results obtained by calculating the current-laser output characteristics of the two-dimensional photonic crystal surface-emitting laser of the first embodiment.

[0040] Figure 7 This is a graph showing the results obtained by calculating the oscillation spectrum of the two-dimensional photonic crystal surface-emitting laser of the first embodiment.

[0041] Figure 8 This is a graph showing an example of the spectrum of naturally emitted light from a two-dimensional photonic crystal surface-emitting laser according to the first embodiment.

[0042] Figure 9 This is a perspective view illustrating a second embodiment of the two-dimensional photonic crystal surface-emitting laser according to the present invention.

[0043] Figure 10 This illustrates how, in a second embodiment of a two-dimensional photonic crystal surface-emitting laser, the proportion Γ of light existing in the two-dimensional photonic crystal layer and the active layer respectively during operation is calculated. pc and Γ act A chart of the results obtained.

[0044] Figure 11 This example illustrates how the phase difference θ between the first and second emitted beams is calculated using a two-dimensional photonic crystal surface-emitting laser (with a guide layer thickness of 300 nm) according to the second embodiment. ref A graph showing the results obtained from the relationship between the coefficients μ.

[0045] Figure 12 This illustrates a two-dimensional photonic crystal surface-emitting laser with a guide layer thickness of 300 nm and a phase difference θ, according to the second embodiment. ref (For the example of 0°) A graph showing the results obtained by calculating the current-laser output characteristics.

[0046] Figure 13 This illustrates a two-dimensional photonic crystal surface-emitting laser with a guide layer thickness of 300 nm and a phase difference θ, according to the second embodiment. ref (For example, 0°) A graph showing the results obtained by calculating the oscillation spectrum.

[0047] Figure 14 This is a three-dimensional view of a modified two-dimensional photonic crystal surface-emitting laser. Detailed Implementation

[0048] use Figures 1 to 14 This invention will be used to illustrate the implementation of the two-dimensional photonic crystal surface-emitting laser.

[0049] [1] Structure of the two-dimensional photonic crystal surface-emitting laser of the first embodiment

[0050] like Figure 1 As shown in (a), the two-dimensional photonic crystal surface-emitting laser 10 of the first embodiment has a structure formed by stacking a first electrode 171, a reflective layer 15, a first cladding layer 141, a two-dimensional photonic crystal layer 12, a spacer layer 13, an active layer 11, a second cladding layer 142, a substrate 16, and a second electrode 172 in the order described. However, the order of the active layer 11 and the two-dimensional photonic crystal layer 12 may be reversed. Figure 1 In (a), for convenience, the first electrode 171 is shown as the lower side and the second electrode 172 as the upper side, but the direction of the two-dimensional photonic crystal surface-emitting laser 10 in use is not limited to the direction shown in this figure. The structure of the electrodes and each layer will be described below.

[0051] By injecting charge from the first electrode 171 and the second electrode 172, the active layer 11 emits light with a predetermined wavelength range. In the first embodiment, the material of the active layer 11 is InGaAs / AlGaAs multiple quantum well (emission wavelength range: 935-945 nm), and the thickness of the active layer 11 is set to 90 nm.

[0052] like Figure 1 As shown in (b), the two-dimensional photonic crystal layer 12 is formed by arranging regions with different refractive indices than the refractive index of the parent material 121 in a square lattice within a plate-shaped parent material 121. Considering the influence of the refractive index of the regions with different refractive indices 122 on the overall refractive index of the two-dimensional photonic crystal layer 12, the period length a of the square lattice is set to 278 nm, corresponding to the wavelength within the emission wavelength range of the active layer 11. The parent material 121 is made of p-type GaAs, with the same planar dimensions as the active layer 11, and a thickness of 160 nm. The period length a can be appropriately varied according to the material of the parent material 121 and the emission wavelength range in the active layer 11.

[0053] The anisotropic refractive index region pair 122 includes a first anisotropic refractive index region 1221 and a second anisotropic refractive index region 1222. In the first embodiment, both the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222 utilize regions formed by pores formed in the base material 121. The planar shape of the first anisotropic refractive index region 1221 is elliptical, and the planar shape of the second anisotropic refractive index region 1222 is circular. The area of ​​the planar shape of the first anisotropic refractive index region 1221 is larger than the area of ​​the planar shape of the second anisotropic refractive index region 1222. The centroids of the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222 within an anisotropic refractive index region pair 122 are offset by the same distance δa in two directions, namely the x-direction and the y-direction, where the lattice points of the square lattice are arranged with a period length a. Similar to the invention described in Patent Document 1, it is preferable that the magnitude of their offset δa is set in the range of 0.15a to 0.35a in both the x-direction and the y-direction. The minor axis of the ellipse of the first anisotropic region 1221 is inclined at 45° with respect to the x and y directions, and the centroid of the second anisotropic region 1222 is located on the extension of this minor axis (which is the straight line y = x on the plane with the x and y directions as coordinate axes). Details regarding the lengths of the major and minor axes of the ellipse of the first anisotropic region 1221 and the diameter of the second anisotropic region 1222 are explained in Section [3-2]. Alternatively, a single anisotropic region can be used instead of a pair of anisotropic regions 122. Furthermore, within the anisotropic regions (pair), a component with a refractive index different from that of the parent material 121 can be used instead of a void.

[0054] The reflective layer 15 reflects laser light incident from the two-dimensional photonic crystal layer 12 through the first cladding layer 141. In the first embodiment, a distributed Bragg reflector (DBR) is used. The DBR used in the first embodiment is a laser beam formed by Al... 0.1 Ga 0.9 The first layer, composed of As with a thickness of 68 nm, and the second layer, composed of Al... 0.9 Ga 0.1 The laser is formed by alternately stacking 14 layers of a second layer, each 78 nm thick, made of As. The thicknesses of the first and second layers are set such that the sum of the thicknesses of the first and second layers is half the wavelength of the incident laser within the medium. With this structure, the optical path difference between laser light reflected by one first layer and laser light reflected by another first layer is an integer multiple of the wavelength, thus the reflected light is enhanced through interference (the same applies to laser light reflected by one second layer and laser light reflected by another second layer).

[0055] The first cladding layer 141 is made of a p-type semiconductor to inject holes from the first electrode 171 into the active layer 11 (the reason for setting the material of the parent material 121 of the two-dimensional photonic crystal layer 12 as p-type GaAs, which is a p-type semiconductor, is the same). In the first embodiment, p-type Al was used as the material of the first cladding layer 141. 0.37 Ga 0.63 However, other p-type semiconductors may also be used. The thickness of the first cladding layer 141 is determined to be a value within the range of 930 nm to 1030 nm in the first embodiment, but is not limited to this in the present invention. This thickness corresponds to the distance d between the opposing surfaces of the two-dimensional photonic crystal layer 12 and the reflective layer 15. Details of the method for determining the inter-surface distance (thickness of the first cladding layer 141) d are described in Section [3-1].

[0056] The second cladding layer 142 is made of an n-type semiconductor to inject electrons from the second electrode 172 into the active layer 11. In the first embodiment, n-type Al was used as the material for the second cladding layer 142. 0.37 Ga 0.63 However, other n-type semiconductors may also be used. The thickness of the second cladding layer 142 is not particularly limited; in the first embodiment, it is set to 1100 nm.

[0057] The substrate 16 is made of a material that is sufficiently thick compared to the other layers to maintain the overall mechanical strength of the two-dimensional photonic crystal surface-emitting laser 10. In the first embodiment, this thickness is set to 150 μm (150,000 nm). For the same reasons as the second cladding layer 142, the substrate 16 is made of an n-type semiconductor. In the first embodiment, it is made of n-type GaAs, but other n-type semiconductors may also be used.

[0058] The spacer layer 13 is provided to suppress the introduction of holes injected from the first electrode 171 into the active layer 11 and to suppress the passage of electrons injected from the second electrode 172 through the active layer 11 (thereby coupling with holes at a position closer to the first electrode 171 than the active layer 11). In the first embodiment, regarding the spacer layer 13, an Al material of type I (intrinsic semiconductor) is used, disposed on the active layer 11 side. 0.45 Ga 0.55 A spacer layer 13 is a double-layer structure consisting of a 25 nm thick As layer and a 90 nm thick layer of i-type GaAs disposed on the side of the two-dimensional photonic crystal layer 12.

[0059] The first electrode 171 is circular in shape and is disposed in the two-dimensional photonic crystal layer 12 within a narrower area than the region where the two-dimensional photonic crystal is formed. The second electrode 172 has a structure obtained by hollowing out the center of a circular metal plate material. The hollowed-out portion of the plate-shaped member is called the window portion 1722, and the remaining portion of the plate-shaped member is called the frame portion 1721. Furthermore, in Figure 1 In (a), the first electrode 171 is shown in a way that it moves downward from the reflective layer 15 in order to represent the first electrode 171, but in reality the first electrode 171 is in contact with the lower surface of the reflective layer 15.

[0060] [2] Operation of the two-dimensional photonic crystal surface-emitting laser in the first embodiment

[0061] Next, the operation of the two-dimensional photonic crystal surface-emitting laser 10 according to the first embodiment will be described. A predetermined voltage is applied between the first electrode 171 and the second electrode 172, and current is injected into the active layer 11 from both electrodes. This generates light emission from the active layer 11, with a wavelength within a predetermined wavelength range corresponding to the material of the active layer 11. The light emission generated in this way is selectively amplified within the two-dimensional photonic crystal layer 12 due to resonance with light at a resonant wavelength corresponding to the period length a of the square lattice, thereby performing laser oscillation. Furthermore, as in the example described above where the thickness of each layer is set, the distance between the first electrode 171 and the active layer 11 is made sufficiently close compared to the distance between the second electrode 172 and the active layer 11, so that the range of light emission generated by injecting current into the active layer is approximately equal to the shape of the first electrode 171.

[0062] An oscillating laser beam is emitted from both surfaces of the two-dimensional photonic crystal layer 12 in directions perpendicular to the two-dimensional photonic crystal layer 12. The laser beam emitted towards the first cladding layer 141 (the second emitted beam) is reflected by the reflective layer 15, passes through the two-dimensional photonic crystal layer 12, and heads towards the second cladding layer 142. Furthermore, this second emitted beam interferes with the laser beam emitted directly towards the second cladding layer 142 of the two-dimensional photonic crystal layer 12 (the first emitted beam) to generate an emitted beam, which is emitted outward from the window 1722 of the second electrode 172. Here, the state of the emitted beam depends on the phase difference θ between the first and second emitted beams, determined by the inter-surface distance. ref Furthermore, the emitted light's radiation coefficient α of the fundamental mode is affected by its interaction with the in-plane guided wavelight within the two-dimensional photonic crystal layer 12. v0 The radiation coefficient α of the first higher-order mode v1 The difference in radiation coefficient Δα causes an impact in order to obtain a single wavelength laser of the basic mode. v (=α v1 -α v0The larger the value, the better. Therefore, in order to obtain a single-wavelength laser in the basic mode, the inter-plane distance needs to be appropriately designed. The design of the inter-plane distance and the associated anisotropic refractive index region are explained below.

[0063] [3] Details of the design of the two-dimensional photonic crystal surface-emitting laser of the first embodiment

[0064] [3-1] Design example of inter-surface distance (thickness of the first covering layer 141) d

[0065] The design of the inter-plane distance will now be explained in detail using the case where the regions with different refractive indices are arranged in a square lattice, as in the two-dimensional photonic crystal layer 12 of the first embodiment.

[0066] In a two-dimensional photonic crystal in which regions of different refractive indices are arranged in a tetragonal lattice, the radiation coefficient α is expressed by the following [number 1] based on the theoretical formula for the complex intrinsic frequency of the lowest-energy photon band, known as "mode A". v .

[0067] [Number 1]

[0068]

[0069] (1) In the formula, R is the real part of the effective coupling coefficient and I is the imaginary part of the effective coupling coefficient, which is expressed by the following formula.

[0070] R = Re[(κ] 1D +κ 2D -)exp(-1θ PC )] …(2)

[0071] I=Im[(κ 1D +κ 2D -)exp(-iθ PC )] …(3)

[0072] In equations (2) and (3), κ 1D It is a one-dimensional coupling coefficient (Hermitian component), which represents the interaction between an in-plane guided wave along one direction and an in-plane guided wave whose direction of travel has changed by 180° (180° diffraction) after being reflected by a region of different refractive index. κ 2D - is the two-dimensional coupling coefficient representing reflection (90° diffraction) relative to the line y = -x. This two-dimensional coupling coefficient represents the interaction between in-plane guided wave light traveling along one direction and light whose direction of travel has changed by 90° after passing through a region of different refractive indices. Furthermore, the two-dimensional coupling coefficient representing reflection (90° diffraction) relative to the line y = x is denoted by κ.2D+ This indicates that these κ... 1D κ 2D -and κ 2D +Calculated based on the shape of the anisotropic refractive index regions (in the first embodiment, the positional relationship and shape of the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222 in the anisotropic refractive index region pair 122). θ PC θ represents the additional phase when an in-plane guided waveguide beam pointing negatively in the x-direction is diffracted by the outgoing light into an in-plane guided waveguide beam pointing positively in the x-direction. This is assuming the midpoint between the centroids of the first and second heterorefringent regions is located at the center of the unit lattice. PC Approximately 165°. Furthermore, μ in equation (1) is the non-Hermitian coupling coefficient when the in-plane guided wavelights couple with each other through the outgoing light, which depends on the interference phase difference θ between the first and second outgoing light, determined according to the inter-plane distance d. ref The following formula can be used for approximation.

[0073] μ = μ noref (1+cos(θ ref ))…(4)

[0074] Where, μ noref This is the value of μ in the absence of a reflective layer. Δk represents the shift of the wavenumber in wavenumber space from the origin Γ point towards Γ-M, which is equivalent to the resonant wavenumber generated in a two-dimensional photonic crystal of finite size. Furthermore, in equation (1), |I| and |Δk| are approximated as values ​​that are sufficiently small compared to |R| and |μ|.

[0075] For example, when the diameter of the inscribed circle of the region emitting light by injecting current into the active layer is L (e.g., the region is a circle with a diameter of L or a square with a side length of L), the resonant wavenumber Δk0 of the fundamental mode when the light emission resonates in the two-dimensional photonic crystal layer 12 is π / L, and the resonant wavenumber Δk1 of the first higher-order mode is 2π / L. If these Δk0 and Δk1 are substituted into equation (1), the radiation coefficient α of the fundamental mode is... v0 The radiation coefficient α of the first higher-order mode v1 become

[0076] [Number 2]

[0077]

[0078]

[0079] Therefore, the difference in radiation coefficient Δα v =(α v1 -α v0 )become

[0080] [Number 3]

[0081]

[0082] As mentioned above, μ and R in equation (7) include κ based on the shape of the heterorefringent region. 1D and κ 2D- and the phase difference θ based on the thickness (inter-surface distance) d and refractive index of the first cladding layer 141. ref Therefore, κ is determined based on the shape of the region with different refractive indices. 1D and κ 2D- Based on this, if we want to make the difference in radiation coefficient Δα in equation (7) v Become 1cm -1 The above methods determine the phase difference θ ref Then the thickness (interfacial distance) d of the first covering layer 141 can be set. Furthermore, in equation (7), if R is set to 0 cm... -1 (or a value sufficiently small compared to μ), then Δα v It is inversely proportional to μ, therefore, regardless of the value of the diameter L, there exists in equation (7) that makes the difference in radiation coefficient Δα... v 1cm -1 The range of μ values ​​above, and therefore, according to equation (4), there must exist a corresponding phase difference θ. ref The value of μ. For example, in the case of L = 10 mm, if the value of μ is set to 14.8 cm. -1 The following can then convert Δα v Set to 1cm -1 That's all. However, through theoretical calculations, Δα v The upper limit is 3 1 / 2 μ is given, therefore in order to give Δα v Set to 1cm -1 In the above, μ needs to be 3. -1 / 2 cm -1 above.

[0083] [3-2] Design of 122 in the region of different refractive indices

[0084] As clearly stated in equation (7), the closer R is to 0 cm -1 Then the difference in radiation coefficient Δα v The larger the value, the easier it is to oscillate and produce a single wavelength of laser light. Figure 2 The chart shows the results for L = 3 mm and R = 0 cm. -1 And R = 200cm -1 In various situations, with μ ranging from 0 to 300 cm -1 Calculate the radiation coefficient difference Δα within the rangev The results obtained. According to the graph, R = 0 cm regardless of the value of μ. -1 The difference in radiation coefficient Δα under the condition v Both are greater than R = 200cm -1 The difference in radiation coefficient Δα under the condition v Height. R is 0cm. -1 This means that the light that has been diffracted at 180° and the light that has been diffracted at 90° in the region of different refractive indices cancel each other out through interference, thereby preventing the local presence of light in a part of the two-dimensional photonic crystal.

[0085] Therefore, it is best to make R as close to 0cm as possible. -1 The shape of the anisotropic refractive index region (anisotropic refractive index region to 122) is designed in a manner that... Figure 3 In the example shown in (a), with the lattice constant a set to 278 nm, the major axis diameter of the first anisotropic refractive index region 1221 set to 124.8 nm, the minor axis diameter of the first anisotropic refractive index region 1221 set to (52.6 + 2x) nm, and the diameter of the second anisotropic refractive index region 1222 set to (67.3 - 2x) mm, for a total of 15 cases, the values ​​of 2x are varied in three ways within the range of 3.0 to 6.1 nm, and the positional offsets δa of the anisotropic refractive index regions in the x and y directions of the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222 in 122 are varied in five ways between 0.264 a and 0.280 a, respectively. 1D +κ 2D- The real part Re(κ) 1D +κ 2D- ) and imaginary part Im(κ) 1D +κ 2D- The value of ). The positions of the first anisotropic refractive index region 1221 and the second anisotropic refractive index region 1222 are defined by the position of the centroid of their planar shapes. In Figure 3 The example in (b) shows μ = 74 cm -1 (θ ref In the case of 70°, when δa = 0.276a and 2x = 4.6nm in 15 cases, Re(κ) 1D +κ 2D- ) and Im(κ 1D +κ 2D- The value of ) is closest to 0, and the value of R expressed by equation (2) is also closest to 0. Therefore, it is preferred to set δa=0.276a and 2x=4.6nm.

[0086] [3-3]μ and Δα v Calculation example

[0087] Next, after using Re(κ) to make Re(κ) 1D +κ 2D- ) and Im(κ 1D +κ 2D- The method that is closest to 0 determines the different refractive index regions of δa and 2x. For example, in the case of 122, this will result in a phase difference θ between the first and second emitted light beams. ref The result obtained by calculating μ while changing (i.e., changing the inter-face distance d) is in Figure 4 The chart shows that the threshold gain difference (compared to the radiation coefficient difference Δα) will be calculated. v Similarly, the results obtained for the parameter representing the ease of laser oscillation of the basic mode relative to the first higher-order mode are as follows: Figure 5 As shown in (a) and (b). Regarding the threshold gain difference, the first electrode 171 is set to have a diameter L = 1 mm ( Figure 5 The calculations were performed using either a 3mm circle (as in case (a)) or a 3mm circle (as in case (b)) and assuming that current was injected into the entire region of the active layer corresponding to that circle. From these graphs, it is known that as θ... ref As μ moves away from 0° towards either positive or negative, it decreases. Figure 4 In either case L = 1 mm or 3 mm, the threshold gain difference increases. Figure 5 (a) and (b) indicate that it is easy to emit laser light of a single wavelength.

[0088] In particular, according to equation (4), by using |θ ref Setting the angle to 90° or higher allows the value of μ with a reflective layer to be the same as the value without a reflective layer (μ). noref Below this value, the threshold gain difference can be increased compared to the case without a reflective layer. However, at |θ... ref When |θ| = 180°, the first and second reflected rays disappear due to interference. Therefore, |θ| = 180°. ref | Set to less than 180°.

[0089] [3-4] Example of Calculating Oscillation Spectra

[0090] Next, for a lattice constant of a = 279 nm, parameters for the anisotropic refractive index region 122 of δa = 0.256 a, 2x = 5.6 nm, and the phase difference θ between the first and second emitted beams, the following parameters are considered. ref -90° (μ=88cm) -1 The current-laser output characteristics and oscillation spectrum were calculated for a region with a diameter L of 3 mm where a two-dimensional photonic crystal is formed. The threshold gain difference under this condition was 1.27 cm⁻¹. -1 The calculation results of the current-laser output characteristics are then applied in... Figure 6 The chart shows that the oscillation spectrum is in Figure 7 The diagram is shown. Regarding the current-laser output characteristics, calculations were performed for both cases where the current was supplied uniformly and cases where the current was supplied non-uniformly to the region where the two-dimensional photonic crystal was formed. However, since there is almost no difference between them, in Figure 6 All calculation results are superimposed and displayed without distinction.

[0091] As in Figure 6 As shown in the graph, when the current exceeds the threshold (approximately 30A), the laser output increases linearly with increasing current. The oscillation spectrum was calculated up to a maximum current of 200A, but a single wavelength oscillation spectrum was obtained for all current values.

[0092] [3-5] Methods for determining μ and R through experiments

[0093] As explained in Section [3-1] above, the difference in radiation coefficient Δα v The real part R, which depends on the effective coupling coefficient, and the coefficient μ, which represents the magnitude of the interaction between the in-plane guided wavelight and the outgoing light during 180° diffraction, are given by R and μ, which depend on the phase difference θ. ref One-dimensional coupling coefficient κ 1D and the two-dimensional coupling coefficient κ 2D- When the one-dimensional and two-dimensional coupling coefficients are unknown, R and μ can be determined experimentally as follows.

[0094] In the two-dimensional photonic crystal surface-emitting laser 10, spontaneous emission (not laser emission) is generated by injecting a current smaller than that used to generate laser oscillation. This spontaneous emission includes light originating from band A, which is a photonic band and contributes to laser oscillation, as well as light originating from band C, whose polarization direction is the same as that of band A emission and is detrimental to laser oscillation due to high loss. Therefore, a polarizer is arranged on the second electrode 172 to allow the polarized light of bands A and C to pass through (in the direction of the straight line y = -x on a graph with x and y directions as coordinate axes), and the spectrum of the spontaneous emission is measured. An example of the measured spontaneous emission spectrum is shown below. Figure 8 As shown in the figure. In this natural emission spectrum, wavelengths λ originating from band A were observed. A (Same wavelength as laser), with a half-value width Δλ A The peak originates from the wavelength λ with C. C and each has a half-value width Δλ C The peaks. Based on these λ... A , Δλ A , λ C , Δλ C Find R and μ.

[0095] [Number 4]

[0096]

[0097]

[0098] Here, n g It is the group refractive index (calculated by dividing the speed of light c by the group velocity v of the light beam). g (Defined by the value obtained).

[0099] [4] Two-dimensional photonic crystal surface-emitting laser of the second embodiment

[0100] like Figure 9 As shown, the two-dimensional photonic crystal surface-emitting laser 10A of the second embodiment has a structure formed by stacking a first electrode 171, a reflective layer 15, a first cladding layer 141, a two-dimensional photonic crystal layer 12, a spacer layer 13, an active layer 11, a guiding layer 18, a second cladding layer 142, a substrate 16, and a second electrode 172 in the order described.

[0101] Among these layers, the guiding layer 18 is a layer absent in the two-dimensional photonic crystal surface-emitting laser 10 of the first embodiment. The guiding layer 18 is disposed between the first cladding layer 141 and the second cladding layer 142, and when viewed from the active layer 11, it is positioned on the side opposite to the two-dimensional photonic crystal layer 12. The guiding layer 18 has the following function: reducing the proportion of in-plane guided light distributed in the two-dimensional photonic crystal layer 12, thereby weakening the coupling effect of multiple in-plane guided light beams through the emitted light. In this embodiment, the guiding layer 18 is made of Al, which is an n-type semiconductor. 0.15 Ga 0.85 It is made of As (refractive index 3.45). The thickness of the guiding layer 18 is set to a value between 80 and 400 nm based on the setting value of the distance d between the opposing surfaces of the two-dimensional photonic crystal layer 12 and the reflective layer 15 (the inter-surface distance).

[0102] The two-dimensional photonic crystal layer 12 has the same structure as in the first embodiment (see reference). Figure 1 (b) Here, the period length a of the square lattice is 278 nm, and the fill factor of the anisotropic region 122 (the proportion of the volume occupied by the anisotropic region 122 within the two-dimensional photonic crystal layer 12) is 8%. The refractive index of p-type GaAs, the material of the parent material 121, is 3.55, and the refractive index of air, the material of the anisotropic region 122, is approximately 1. Based on these dimensions and the refractive indices of each material, the overall refractive index of the two-dimensional photonic crystal layer 12 is 3.42.

[0103] The structures of the first electrode 171, reflective layer 15, first cladding layer 141, spacer layer 13, active layer 11, second cladding layer 142, substrate 16, and second electrode 172 are the same as those in the first embodiment. Specifically, considering the layer between the first cladding layer 141 and the second cladding layer 142, the active layer 11 is an InGaAs / AlGaAs multi-quantum-well structure with an average refractive index of 3.49 and a thickness of 90 nm. Furthermore, the spacer layer 13 comprises i-type Al... 0.45 Ga 0.55 The structure consists of a 25 nm thick layer of As and a 90 nm thick layer of i-type GaAs, with an average refractive index of 3.49.

[0104] Based on these parameters, the product of the thickness and refractive index of the two-dimensional photonic crystal layer 12 is 547.2 nm. On the other hand, the product of the thickness and refractive index of the layers other than the two-dimensional photonic crystal layer 12 located between the first cladding layer 141 and the second cladding layer 142—namely, the spacer layer 13, the active layer 11, and the guide layer 18 (the sum of these three values ​​obtained by calculating the product of thickness and refractive index for each of these three layers separately) falls within the range of 991.5 to 2095.5 nm depending on the thickness of the guide layer 18. Therefore, regardless of the range in which the latter value falls, the latter value is always larger than the former value.

[0105] Furthermore, the materials and thicknesses of the layers listed here are examples, and can be appropriately varied within a range where the product of the thickness and refractive index of the spacer layer 13, the active layer 11, and the guide layer 18 is greater than the product of the thickness and refractive index of the two-dimensional photonic crystal layer 12.

[0106] For the two-dimensional photonic crystal surface-emitting laser 10A of the second embodiment, the proportion Γ of light existing in the two-dimensional photonic crystal layer 12 during operation is calculated. pc The ratio Γ of light present in the active layer 11 act The calculations were performed for four cases: the thickness of the guide layer 18 is 80nm, 200nm, 300nm, and 400nm. The calculation results are presented in... Figure 10 As shown in the diagram. Meanwhile, when calculating for the case where the bootstrap layer 18 is absent, Γ pc Γ is 0.222. act The value is 0.065. Based on these calculations, it is known that, in the presence of the guide layer 18, compared to the absence of the guide layer 18, the greater the thickness of the guide layer 18, the higher the Γ value. pc ( Figure 10The smaller the value of the black circle (marked in black), the smaller the proportion of in-plane guided light confined within the two-dimensional photonic crystal layer 12. Consequently, the coupling effect between multiple in-plane guided light beams through the outgoing light is weakened, leading to independent propagation of the in-plane guided light in each direction, making it prone to leakage in directions perpendicular to the two-dimensional photonic crystal layer 12. It is assumed that as a result, the greater the thickness of the guiding layer 18, the higher the radiation coefficient α of the fundamental mode and higher-order modes. v0 and α v1 The larger the value, the greater the difference in radiation coefficient Δα. v It also increases, thus making it easier to obtain oscillations of a single wavelength of laser light. Furthermore, although Γ act The difference decreases slightly as the thickness of the guide layer 18 increases, but the difference based on the presence or absence of the guide layer 18 or its thickness is not like Γ. pc That was so remarkable.

[0107] Next, for the two-dimensional photonic crystal surface-emitting laser 10A of the second embodiment, while keeping the phase difference θ between the first emitted light and the second emitted light... ref The result obtained by changing the coefficient μ, which represents the magnitude of the interaction between the in-plane guided wavelight and the outgoing light during 180° diffraction, is... Figure 11 As shown in the figure. In this calculation, the thickness of the guide layer 18 is set to 300 nm. If this calculation result is compared with the result obtained by performing the same calculation in the first embodiment... Figure 4 In contrast, it is considered that even if the phase difference θ of μ is not sufficiently suppressed in the first embodiment... ref In the second embodiment, the value of μ can also be suppressed within a range of approximately -60° to +60°, thereby reducing the radiation coefficient difference Δα. v It becomes larger, thus making it easier to oscillate and produce a single wavelength of laser light.

[0108] Next, for the second embodiment, the current-laser output characteristics and oscillation spectrum are calculated. In these calculations, the thickness of the guiding layer 18 is set to 300 nm, and the phase difference θ is... ref The value is set to 0°. However, in this calculation, the two-dimensional photonic crystal layer used is a two-dimensional photonic crystal layer with the same heterorefringence region pair 122 as the two-dimensional photonic crystal layer 12 in the first embodiment, with δa set to 0.259a and 2x set to 3.0 nm. The difference in radiation coefficient Δα in this case... v It is 1.33cm -1 The calculation results of the current-laser output characteristics are then applied in... Figure 12 The diagram shows the calculation results of the oscillation spectrum in... Figure 13 As shown in the figure. Based on these calculations, it can be confirmed that in the second embodiment, even θ ref A value of 0° is used to suppress the difference in radiation coefficient Δα.v Even under unfavorable conditions, it is possible to obtain a single wavelength laser within a range where the injected current is up to 200A and the output is up to 170W.

[0109] In the example described up to this point as the second embodiment, by providing a guiding layer 18 between the active layer 11 and the second cladding layer 142, the product of the thickness and refractive index of the layers located between the first cladding layer 141 and the second cladding layer 142, excluding the two-dimensional photonic crystal layer 12, is made larger than the product of the thickness and refractive index of the two-dimensional photonic crystal layer 12. However, the value of their product can also be set by other methods. For example, by making the sum of the thicknesses of the layers located between the first cladding layer 141 and the second cladding layer 142, excluding the two-dimensional photonic crystal layer 12, larger than the thickness of the two-dimensional photonic crystal layer 12, the condition for the value of the product of thickness and refractive index can be easily satisfied even without using a material whose refractive index is extremely large (in the case of layers other than the two-dimensional photonic crystal layer 12) or extremely small (in the case of the two-dimensional photonic crystal layer 12) compared to other layers.

[0110] Furthermore, by using a material with a lower refractive index than the parent material 121, the refractive index of the two-dimensional photonic crystal layer 12 can be made lower than that of other layers, thereby easily satisfying the aforementioned condition regarding the product of thickness and refractive index. For example, if the fill factor is 8%, the same as in the second embodiment described above, and the material of the parent material 121 is changed from GaAs to Al... 0.1 Ga 0.9 As, then it can make Γ pc The value decreased by about 50%.

[0111] [5] Other

[0112] In the description up to this point, along with the first and second embodiments described above, variations derived from these embodiments have been described (e.g., using a heterorefractive index region instead of a heterorefractive index region pair 122, using a component with a refractive index different from that of the base material 121 instead of a hole as a heterorefractive index region (pair), etc.), but the present invention is not limited to these embodiments and variations, and various further variations are possible.

[0113] For example, in the first and second embodiments described above, the shape of the first electrode 171 is circular, but it can also be square. Figure 14Other shapes, such as ), are also possible. Alternatively, the first electrode 171 may be shaped such that its length in one of the two directions (the directions represented by the lines y = x and y = -x on a graph with x and y as coordinate axes) in the region where current is injected into the active layer is 45° relative to the x and y directions of the square lattice in the two-dimensional photonic crystal layer 12, is shorter than its length in the other direction. For example, the two-dimensional coupling coefficient κ described in section [3-1] above... 2D- With κ 2D+ When the absolute value of the difference is generated, the first higher-order mode is likely to exist locally in the direction of the straight line y = -x in the two directions. Therefore, in such cases, by setting the region to a shape in which the length in the direction in which the first higher-order mode exists is shorter than the length in the other direction, the laser oscillation of the first higher-order mode can be suppressed more reliably.

[0114] Explanation of reference numerals in the attached figures

[0115] 10: Two-dimensional photonic crystal surface-emitting laser; 11: Active layer; 12: Two-dimensional photonic crystal layer; 121: Mother material; 122: Pair of anisotropic refractive index regions; 1221: First anisotropic refractive index region; 1222: Second anisotropic refractive index region; 13: Spacer layer; 141: First cladding layer; 142: Second cladding layer; 15: Reflective layer; 16: Substrate; 171: First electrode; 172: Second electrode; 1721: Frame portion; 1722: Window portion; 18: Guide layer.

Claims

1. A two-dimensional photonic crystal surface-emitting laser, characterized in that, have: a) A two-dimensional photonic crystal layer, which is formed by periodically arranging regions with different refractive indices than the refractive index of the substrate in a plate-shaped substrate; b) An active layer disposed on one side of the two-dimensional photonic crystal layer; and c) A reflective layer, which is disposed separately from the two-dimensional photonic crystal layer on the other side of the two-dimensional photonic crystal layer, or disposed on the side of the active layer opposite to the two-dimensional photonic crystal layer. The distance between the opposing surfaces of the two-dimensional photonic crystal layer and the reflective layer is set such that the difference in emissivity Δα v =(α v1 -α v0 ) is 1cm -1 The above refers to the difference in radiation coefficients Δα. v The radiative coefficient α of the first higher-order mode with the second smallest loss in the light amplified by the two-dimensional photonic crystal layer is... v1 Subtract the radiation coefficient α of the basic mode with minimum loss v0 The value obtained.

2. The two-dimensional photonic crystal surface-emitting laser according to claim 1, characterized in that, In the two-dimensional photonic crystal layer, The regions with different refractive indices are arranged in a tetragonal lattice. Use R = Re[(κ) 1D +κ 2D- )exp(-iθ PC The phase difference θ between the first and second emitted beams ref The non-Hermitian coupling coefficient μ when the in-plane guided wavelights couple with each other through the outgoing light, and the diameter L of the inscribed circle of the range of light emission caused by injecting current into the active layer, are expressed by the following [number 5] to represent the radiation coefficient difference Δα. v , where, regarding the R = Re[(κ 1D +κ 2D- )exp(-iθ PC Using a one-dimensional coupling coefficient κ] 1D Two-dimensional coupling coefficient κ 2D- And the additional phase θ when the in-plane guided wavelight pointing negatively in the x-direction is diffracted by the outgoing light into the in-plane guided wavelight pointing positively in the x-direction. PC This means that the first emitted light is emitted from the two-dimensional photonic crystal layer to the opposite side of the reflective layer, and the second emitted light is emitted from the two-dimensional photonic crystal layer to the reflective layer and is reflected by the reflective layer. [Number 5] 3. The two-dimensional photonic crystal surface-emitting laser according to claim 2, characterized in that, The diameter L of the inscribed circle is 1 mm or more.

4. The two-dimensional photonic crystal surface-emitting laser according to claim 2 or 3, characterized in that, The phase difference θ ref The absolute value is greater than 90° and less than 180°.

5. The two-dimensional photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, The anisotropic region is composed of anisotropic region pairs, which are regions formed by separately arranging a first anisotropic region and a second anisotropic region with different planar shapes and areas.

6. The two-dimensional photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, It also includes electrodes for injecting current into the active layer. The regions with different refractive indices are arranged in a square lattice with a defined period. The shape of the electrode is configured such that the length in one of the two directions in which the region into which the current is injected is tilted by 45° relative to the lattice points of the square lattice arranged in the periodic manner is shorter than the length in the other direction.

7. The two-dimensional photonic crystal surface-emitting laser according to claim 1 or 2, characterized in that, It also includes a first coating layer and a second coating layer, which are two coating layers disposed in a manner that sandwiches the two-dimensional photonic crystal layer and the active layer. The first coating layer is disposed between the two-dimensional photonic crystal layer and the reflective layer and is made of a p-type semiconductor or an n-type semiconductor. When viewed from the two-dimensional photonic crystal layer, the second coating layer is disposed on the opposite side of the reflective layer side, and the second coating layer is made of a semiconductor having charge carriers with opposite polarities to those of the first coating layer. The product of the thickness and refractive index of the layer located between the first coating layer and the second coating layer, excluding the two-dimensional photonic crystal layer, is greater than the product of the thickness and refractive index of the two-dimensional photonic crystal layer.

8. The two-dimensional photonic crystal surface-emitting laser according to claim 7, characterized in that, The sum of the thicknesses of the layers located between the first coating layer and the second coating layer, excluding the two-dimensional photonic crystal layer, is greater than the thickness of the two-dimensional photonic crystal layer.

9. The two-dimensional photonic crystal surface-emitting laser according to claim 7, characterized in that, The refractive index of the two-dimensional photonic crystal layer is lower than that of the layers other than the two-dimensional photonic crystal layer located between the first cladding layer and the second cladding layer.

10. The two-dimensional photonic crystal surface-emitting laser according to claim 7, characterized in that, A guiding layer is provided between the first coating layer and the second coating layer, and when viewed from the active layer, the guiding layer is disposed on the side opposite to the two-dimensional photonic crystal layer.

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