Two-dimensional photonic crystal laser

Abstract

A two-dimensional photonic crystal laser (10) is provided with an active layer (11) and a two-dimensional photonic crystal layer (12) in which, in a plate-shaped base member (121), different refractive index regions (122) having a refractive index different from that of the base member (121) are arranged in a square lattice shape with a periodic length a in a first direction and in a second direction that is different from the first direction by 90°. The different refractive index regions (122): include n (n is a natural number) partial region pairs each comprising a pair of two partial regions (1221, 1222) which have the same shape and are positioned in a manner shifting from each other by +0.25a or -0.25a in the first direction and +0.25a or -0.25a in the second direction; and are composed of a basic region in which 2n partial regions (1221, 1222) included in the n partial region pairs are connected without overlapping each other and without a gap, or a deformation region deformed from the basic region by, in some or all of the n partial region pairs, adding an additional region (1224) to either or both of the two partial regions (1221, 1222) and / or removing a removal region (1223) from either or both of the two partial regions (1221, 1222).

Description

Two-dimensional photonic crystal laser

[0001] The present invention relates to a two-dimensional photonic crystal laser (also known as a "two-dimensional photonic crystal surface-emitting laser") that amplifies light using a two-dimensional photonic crystal.

[0002] In recent years, two-dimensional photonic crystal lasers have attracted attention as semiconductor lasers that can achieve high optical output. A two-dimensional photonic crystal laser has a two-dimensional photonic crystal layer in which regions with different refractive indices are periodically arranged on a plate-shaped base material, and an active layer which is an emitting layer. The regions with different refractive indices consist of voids formed in the base material or components made of materials different from the base material (components with different refractive indices). In a two-dimensional photonic crystal laser, when an electric current is injected into the active layer, only the light whose wavelength (depending on the refractive index in the two-dimensional photonic crystal layer) corresponds to the period of the region with different refractive indices is amplified from the light generated in the active layer, causing laser oscillation, and is emitted as a laser beam in a direction perpendicular to the two-dimensional photonic crystal layer. Because two-dimensional photonic crystal lasers emit light from the surface of the two-dimensional photonic crystal layer (surface emission), they have a larger emission area than conventional edge-emitting semiconductor lasers, and have the advantage of being able to easily increase optical output while maintaining single-mode oscillation.

[0003] Patent documents 1 and 2 describe a two-dimensional photonic crystal laser having a two-dimensional photonic crystal layer having a square lattice-like periodic structure in which pairs of different refractive index regions, each consisting of two different refractive index regions, are periodically arranged in a certain direction (referred to as the "x direction") with a period length a, and in a direction 90° different from the x direction (referred to as the "y direction") with the same period length a. Hereinafter, the two different refractive index regions constituting each pair of different refractive index regions will be referred to as the "first different refractive index region" and the "second different refractive index region." In each pair of different refractive index regions, the first different refractive index region and the second different refractive index region are positioned offset from each other in directions inclined by 45° with respect to the x and y directions. The magnitude of the positional offset between the first and second different refractive index regions is within the range of 0.15a to 0.35a in the x and y directions, respectively.

[0004] In the two-dimensional photonic crystal lasers described in Patent Documents 1 and 2, of the in-plane propagating light of wavelength a (= period length) that propagates within the two-dimensional photonic crystal layer in a direction parallel to the layer, 180° diffracted light, which is diffracted (reflected) in the first different refractive index region and changes its propagation direction by 180°, and 180° diffracted light, which is diffracted in the second different refractive index region and changes its propagation direction by 180°, are weakened by interference. In a typical two-dimensional photonic crystal laser, repeated diffraction in the 180° direction causes the light to become localized in a part of the two-dimensional photonic crystal layer. However, in the two-dimensional photonic crystal lasers described in Patent Documents 1 and 2, localization of light is suppressed by weakening the 180° diffracted light through interference, and the laser beam can be emitted from a wide area within the two-dimensional photonic crystal layer. As a result, the two-dimensional photonic crystal lasers described in Patent Documents 1 and 2 can achieve laser oscillation over a large area and in a single mode.

[0005] The two-dimensional photonic crystal laser described in Patent Document 2 further reduces the localization of light by adjusting the positional relationship, shape, and / or size of the first and second different refractive index regions. This is achieved by interfering the light, which has been weakened by the interference of 180° diffracted light diffracted in the first and second different refractive index regions as described above, with 90° diffracted light diffracted in the first and second different refractive index regions, whose propagation direction changes by 90°, thereby further suppressing the localization of light. In addition, the two-dimensional photonic crystal laser described in Patent Document 2 includes a light reflection layer provided between one of the pair of electrodes that inject current into the active layer and the two-dimensional photonic crystal layer, and the laser beam is emitted on the opposite side from the reflection layer as viewed from the active layer and the two-dimensional photonic crystal layer. These configurations allow for an even greater increase in optical output. Furthermore, by adjusting the phase change when light is reflected by the light-reflecting layer, it becomes possible to appropriately set the intensity of diffraction that returns to the in-plane propagating light via the outgoing light. This further expands the difference in loss between the fundamental mode, which has a single antinode of an electric field in the plane, and the higher-order modes, which have multiple antinodes of electric fields in the plane, thereby selectively amplifying the fundamental mode. Alternatively, instead of providing a light-reflecting layer, one of the pair of electrodes may be made to function as the light-reflecting layer.

[0006] Japanese Patent Publication No. 2008-243962, International Publication No. WO2022 / 181722

[0007] In the two-dimensional photonic crystal lasers described in Patent Documents 1 and 2, it is necessary to form two regions with different refractive indices (a first region with different refractive indices and a second region with different refractive indices) for each lattice point in a square lattice. Therefore, it is necessary to reduce the area of ​​each region with different refractive indices, which requires advanced technology for fabrication.

[0008] Furthermore, when two regions with different refractive indices are composed of materials with different refractive indices, the difference in refractive index with the base material is smaller than in the case of a void. As a result, the intensity of the 90° diffracted light, which is diffracted indirectly via light propagating obliquely because the polarization directions before and after diffraction are orthogonal, becomes relatively weaker than the intensity of the 180° diffracted light, which is diffracted light due to direct diffraction without a change in polarization direction. Therefore, there is a risk that the balance between these 180° and 90° diffracted lights will be disrupted.

[0009] The problem that this invention aims to solve is to provide a two-dimensional photonic crystal laser that can achieve laser oscillation over a large area and in a single mode, and that can be easily manufactured.

[0010] The two-dimensional photonic crystal laser according to the present invention, which was developed to solve the above problems, comprises: a) an active layer; b) a two-dimensional photonic crystal layer provided on one surface side of the active layer, wherein regions with different refractive indices from the base material are arranged in a square lattice pattern within a plate-shaped base material with a period length a in the first direction and the same period length a in the second direction at a 90° angle to the first direction; and c) a pair of electrodes provided so as to sandwich the active layer and the two-dimensional photonic crystal layer in the stacking direction, wherein the regions with different refractive indices have n (n is a natural number) pairs of subregions, each consisting of two pairs of identically shaped subregions positioned offset from each other by +0.25a or -0.25a in the first direction and +0.25a or -0.25a in the second direction, and the 2n subregions of the n pairs of subregions are connected to each other without overlapping and without gaps, forming a basic region, or In some or all of the n pairs of sub-regions, an additional region is added to one or both of the two sub-regions, and / or a removal region is removed from one or both of the two sub-regions, thereby transforming the basic region.

[0011] The active layer and the two-dimensional photonic crystal layer may be in direct contact, or an intervening layer may be present between them. The same applies between the active layer and one of the pair of electrodes, and between the two-dimensional photonic crystal layer and the other electrode.

[0012] Hereafter, the two subregions of a given pair of subregions will be referred to as the "first subregion" and the "second subregion."

[0013] In each of the n pairs of subregions, the second subregion is positioned offset from the first subregion by +0.25a or -0.25a in the first direction and +0.25a or -0.25a in the second direction. That is, using "+" and "-" to represent directions that are 180° apart in the first and second directions, the second subregion is positioned offset from the first subregion by one of the following directions: "+0.25a in the first direction and +0.25a in the second direction", "+0.25a in the first direction and -0.25a in the second direction", "-0.25a in the first direction and +0.25a in the second direction", or "-0.25a in the first direction and -0.25a in the second direction". Note that since the first and second subregions have the same shape, the "offset" described here refers to the offset between the entire first subregion and the entire second subregion, but it can also be viewed as the offset between the area centers of the first subregion and the area centers of the second subregion.

[0014] The phrase "the 2n subregions of n pairs of subregions are connected without overlapping and without gaps" means that not only in individual pairs of subregions, but all 2n subregions of the entire region of different refractive indices are connected without overlapping and without gaps. However, this does not mean that one subregion is directly connected to all of the remaining (2n-1) subregions; rather, two of the 2n subregions are connected directly or indirectly through other subregions. When n is 2 or greater, two subregions belonging to the same subregion pair are also connected directly or indirectly through other subregions.

[0015] In the region of different refractive indices, vacancies formed in the base material or members with different refractive indices are used, similar to conventional two-dimensional photonic crystals. The members with different refractive indices may have a refractive index lower than that of the base material, or a refractive index higher than that of the base material.

[0016] In the two-dimensional photonic crystal laser according to the present invention, in each of the n pairs of sub-regions, the first and second sub-regions in the different refractive index regions are shifted by 0.25a in the first direction and 0.25a in the second direction. As a result, the wavelength of the light generated when a current is injected from a pair of electrodes into the active layer within the two-dimensional photonic crystal layer matches the period length a. Consequently, the light propagating in the first and second directions is weakened by interference between the 180° diffracted light from the first sub-region and the 180° diffracted light from the second sub-region. Therefore, similar to the two-dimensional photonic crystal lasers described in Patent Documents 1 and 2, localization of light within the two-dimensional photonic crystal layer is suppressed, and the laser beam can be emitted from a wide area within the two-dimensional photonic crystal layer, thereby enabling laser oscillation over a large area and in a single mode.

[0017] Hereinafter, the region in which an additional region is added to the first partial region and / or a removal region is removed from the first partial region will be referred to as the "first deformed partial region," and the region in which an additional region is added to the second partial region and / or a removal region is removed from the second partial region will be referred to as the "second deformed partial region." When the two-dimensional photonic crystal laser according to the present invention comprises a two-dimensional photonic crystal layer having such deformed regions, the intensity of interference between the light weakened by interference between the 180° diffracted light diffracted at 180° in the first deformed partial region and the 180° diffracted light diffracted at 180° in the second deformed partial region, and the 90° diffracted light whose propagation direction is changed by 90° (90° diffracted) after being diffracted in the first and second deformed partial regions, respectively, can be adjusted. This is equivalent to adjusting the positional relationship, shape, and / or size of the first different refractive index region and the second different refractive index region in the two-dimensional photonic crystal laser described in Patent Document 2.

[0018] According to the two-dimensional photonic crystal laser of the present invention, the different refractive index region consists of a basic region in which all 2n subregions are connected without overlapping or gaps, or a deformed region obtained by deforming the basic region as described above. As a result, the different refractive index region as a whole is composed of a single region that is not separated. Therefore, the size of each vacancy or different refractive index member constituting the different refractive index region can be increased compared to the case where a pair of different refractive index regions consisting of two different refractive index regions described in Patent Documents 1 and 2 is used, thereby making it easier to manufacture a two-dimensional photonic crystal laser.

[0019] As mentioned above, voids or members with different refractive indices can be used in the regions with different refractive indices. Members with different refractive indices have the advantage of a higher heat dissipation effect than voids, which releases heat generated in the two-dimensional photonic crystal layer to the outside. Furthermore, when voids are used in the regions with different refractive indices, there is a risk that the material of the other layer may penetrate into the voids when other layers are fabricated after the two-dimensional photonic crystal layer containing the voids has been manufactured, unintentionally reducing the refractive index difference between the base material and the regions with different refractive indices. In contrast, when members with different refractive indices are used, it is possible to prevent unintended material from penetrating into the regions with different refractive indices by forming the members with different refractive indices in the two-dimensional photonic crystal layer before fabricating other layers.

[0020] As described above, different refractive index members have advantages that voids do not, but small different refractive index members are even more difficult to manufacture than small voids. In contrast, according to the present invention, the area occupied by a single different refractive index member can be increased, making it easy to manufacture.

[0021] Furthermore, because the difference in refractive index between the different refractive index member and the base material is smaller than that between the void and the base material, there is a problem in that the intensity of the 90° diffracted light is relatively weaker than the intensity of the 180° diffracted light. Therefore, when two different refractive index members are used as described in Patent Documents 1 and 2, depending on their shapes, the balance between the 180° diffracted light and the 90° diffracted light may be disrupted. In contrast, according to the present invention, as described above, the area occupied by a single different refractive index member can be increased, making manufacturing easier. This increases the degree of freedom in designing the shape of the different refractive index member, preventing the balance between the 180° diffracted light and the 90° diffracted light from being disrupted, and making it possible to more reliably obtain single-mode laser oscillation over a large area.

[0022] When the region with different refractive indices is a deformation region, it is preferable that the area of ​​the added region or the removed region be 20% or less of the area of ​​the basic region, and more preferably 10% or less. This prevents the effect of interference and attenuation between the 180° diffracted light in the first deformation region and the 180° diffracted light in the second deformation region from becoming too small.

[0023] Preferably, the aforementioned different refractive index regions have a shape in which an additional region is added to one of the two subregions and a removal region is removed from the other in at least one pair of subregion pairs. This clarifies the difference in shape between the two subregions within a pair of subregion pairs, making it easier to set the intensity of the 180° diffracted light, and allowing the effective coupling coefficient determined by the interference with the 90° diffracted light to be adjusted to an appropriate value. Here, the effective coupling coefficient is a coefficient that represents the strength of the combined interaction between the in-plane guided light propagating within the two-dimensional photonic crystal layer and the 180° diffracted light obtained by its 180° diffraction, and the interaction between the in-plane guided light and the 90° diffracted light obtained by its 90° diffraction. The effective coupling coefficient is obtained using a one-dimensional coupling coefficient that represents the strength of the interaction between the in-plane guided light and the 180° diffracted light, and a two-dimensional coupling coefficient that represents the strength of the interaction between the in-plane guided light and the 90° diffracted light.

[0024] The anisotropic refractive index region includes a first sub-region and a second sub-region, which are two sub-regions of one pair of sub-region pairs among the n pairs of sub-region pairs, and two sub-regions of another pair of sub-region pairs among the n pairs of sub-region pairs, which are two regions of the same shape arranged symmetrically with respect to a straight line passing through the area centers of the first sub-region and the second sub-region, and the area centers of the two regions are separated by 0.25a in the first direction and 0.25a in the second direction, and the third sub-region and the fourth sub-region are connected to the second sub-region without overlapping with the second sub-region and without having a gap therebetween. In this way, the light diffracted by 180° in the first sub-region and the second sub-region is weakened by interference, and the light diffracted by 180° in the third sub-region and the fourth sub-region is also weakened by interference, so that the localization of light as a whole in the two-dimensional photonic crystal layer can be further suppressed. In addition, since there are a plurality of sub-region pairs, the effective coupling coefficient can be set to a more suitable value.

[0025] The two-dimensional photonic crystal laser according to the present invention can further have a reflective layer provided between the two-dimensional photonic crystal layer and one of the pair of electrodes, or formed of one of the pair of electrodes. Thereby, the output of the light emitted from the surface of the two-dimensional photonic crystal laser opposite to the side provided with the reflective layer can be increased. Further, by adjusting the reflection phase in the light reflection layer, it is possible to appropriately control the diffraction intensity that returns to the in-plane guided light again through the emitted light, thereby further expanding the loss difference between the fundamental mode having a single electric field antinode in the plane and the higher-order mode having a plurality of electric field antinodes in the plane.

[0026] According to the present invention, a two-dimensional photonic crystal laser capable of realizing laser oscillation over a large area and in a single mode and being easily manufactured can be obtained.

[0027] Perspective view (a) showing a first embodiment of a two-dimensional photonic crystal laser according to the present invention, and a plan view (b) of a two-dimensional photonic crystal layer included in the two-dimensional photonic crystal laser. Plan view showing an enlarged example of a birefringence region, which is a basic region, of the two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser of the first embodiment. Plan view showing an example of a birefringence region that is a deformed region deformed from the shape of the basic region shown in FIG. 2. Plan view showing an example of a birefringence region further deformed from the deformed region shown in FIG. 3. Schematic diagram showing light (a) diffracted by 180° and light (b) diffracted by 90° in the birefringence region of the two-dimensional photonic crystal laser of the first embodiment. Graph showing the results of calculating the value of R, which is a parameter related to the difference in emission coefficients between the fundamental mode and the first higher-order mode, and the value of I, which is a parameter related to the emission coefficient of the fundamental mode, for various examples in which the mode of deformation of the birefringence region is different, in the two-dimensional photonic crystal laser of the first embodiment. Plan view showing the birefringence region in the two-dimensional photonic crystal laser of the second embodiment. Diagram showing two deformation examples of the birefringence region in the two-dimensional photonic crystal laser of the second embodiment. Graph showing the results of calculating the values of R and I for various examples in which the mode of deformation of the birefringence region is different, in the two-dimensional photonic crystal laser having the birefringence region shown in FIGS. 7 and 8.

[0028] Embodiments of a two-dimensional photonic crystal laser according to the present invention will be described with reference to FIGS. 1 to 9.

[0029] (1) Configuration of the two-dimensional photonic crystal laser of the first embodiment The two-dimensional photonic crystal laser 10 of the first embodiment has a configuration in which a first electrode (also a reflective layer) 171, 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 are laminated in this order, as shown in FIG. 1(a). However, the order of the active layer 11 and the two-dimensional photonic crystal layer 12 may be reversed from the above. In FIG. 1(a), for convenience, the first electrode 171 is shown on the lower side and the second electrode 172 is shown on the upper side, but the orientation of the two-dimensional photonic crystal laser 10 during use is not limited to that shown in this figure. Hereinafter, the configurations of the electrodes and each layer will be described.

[0030] The active layer 11 emits light having a predetermined wavelength range when charge is injected from the first electrode 171 and the second electrode 172. For the material of the active layer 11, for example, InGaAs / AlGaAs multiple quantum wells (emission wavelength range: 935 to 945 nm in vacuum) can be used.

[0031] As shown in Figure 1(b), the two-dimensional photonic crystal layer 12 is formed by arranging regions with different refractive indices 122, which have refractive indices different from those of the base material 121, in a square lattice within a plate-shaped base material 121, with a period length a in a first direction (hereinafter referred to as the "x direction") and the same period length a in a second direction (hereinafter referred to as the "y direction") which is 90° different from the first direction. Here, the period length a is the value obtained by converting the wavelength of light generated in the active layer 11 to the wavelength within the two-dimensional photonic crystal layer 12 (by dividing the wavelength in vacuum by the effective refractive index perceived by light within the two-dimensional photonic crystal layer 12).

[0032] Each individual differential refractive index region 122 consists of a pair of subregions, as shown in Figures 1(b) and 2, comprising a first subregion 1221 and a second subregion 1222 which has the same shape as the first subregion 1221 but is offset from the first subregion 1221 by 0.25a in the x direction and 0.25a in the y direction. The first subregion 1221 and the second subregion 1222 are connected without overlapping and without any gaps between them. In this specification, the differential refractive index region 122 consisting of the first subregion 1221 and the second subregion 1222 connected in this manner is referred to as the "basic region". In this example, the first subregion 1221 and the second subregion 1222 have two opposing sides of a rectangle transformed into curves of the same shape, and the first subregion 1221 is provided with a convex curve C11 that is directed so as to be convex when viewed from the subregion, and a concave curve C12 that is directed so as to be concave when viewed from the subregion. Similarly, the second sub-region 1222 is provided with a convex curve C21 and a concave curve C22. The concave curve C12 of the first sub-region 1221 and the convex curve C21 of the second sub-region 1222 coincide, thereby connecting the first sub-region 1221 and the second sub-region 1222 without overlapping or having any gaps.

[0033] Furthermore, in the first embodiment, the shape of the region with different refractive indices can be deformed from the shape of the basic region. In the example shown in Figure 3, the region with different refractive indices 122A is a deformed region having a shape in which the removal region 1223 is removed from the first partial region 1221 in the basic region, and the addition region 1224 is added to the second partial region 1222. In this specification, the regions obtained by partially removing and adding from the first partial region 1221 and the second partial region 1222 are defined as the first deformed partial region 1221A and the second deformed partial region 1222A, respectively. In the first deformed partial region 1221A, the convex curve C11 is shorter than that of the first partial region 1221, and in the second deformed partial region 1222A, the concave curve C22 is longer than that of the second partial region 1222. In this way, the convex curve C11 and concave curve C22, whose lengths have been changed from those of the basic region, are connected at one end and at the other end with straight lines, and the region with different refractive indices 122A is defined by these two straight lines, the convex curve C11, and the concave curve C22. In the first deformed subregion 1221A and the second deformed subregion 1222A, a removal region 1223 and an addition region 1224 are provided at positions close to these two straight lines, respectively. Let L1 = (1-c)L0 be the length of the convex curve C11 in the first deformed subregion 1221A, and L2 = (1+c)L0 be the length of the concave curve C22 in the second deformed subregion 1222A. For each sub-region, if we define D as the ratio of the area of ​​the sub-region added or removed by the deformation of the convex curve C11 and the concave curve C22 to the area of ​​the sub-region before deformation, then the deformation rate of the first deformed sub-region 1221A is D = -0.5c, and the deformation rate of the second deformed sub-region 1222A is D = +0.5c.

[0034] The differential refractive index region 122B shown in Figure 4 is a deformation region having a first deformation sub-region 1221B, which is formed by adding an additional region 1225 to the negative x and negative y directions of the first deformation sub-region 1221A in the differential refractive index region 122A, and a second deformation sub-region 1222B, which is formed by adding an additional region 1226 to the positive x and positive y directions of the second deformation sub-region 1222A in the differential refractive index region 122A. The span of the differential refractive index region 122A in a direction inclined at 45° with respect to both directions, such that both the x and y directions move from negative to positive, is 0.5a × 2 1 / 2(See Figure 3) In contrast, the span of the different refractive index region 122B in the same direction is (0.5a + Δd) × 2 1 / 2 This is defined by the following: Here, Δd can take on either a positive or negative value. When Δd is positive, it means that the added regions 1225 and 1226 are added, whereas when Δd is negative, it means that the removal regions are removed from the first deformed subregion 1221A and the second deformed subregion 1222A in the different refractive index region 122A, respectively. Combining this deformation due to the change in the span length with the deformation of the convex curve C11 and concave curve C22 described above, the deformation rate of the first deformed subregion 1221B is D = -0.5c + Δd / (0.5a), and the deformation rate of the second deformed subregion 1222B is D = +0.5c + Δd / (0.5a).

[0035] The base material 121 is made of a p-type semiconductor for injecting holes from the first electrode 171 into the active layer 11 through the two-dimensional photonic crystal layer 12. For example, p-type GaAs can be used as the p-type semiconductor for the base material 121. The different refractive index regions 122, 122A, and 122B are each formed by a single vacancy or a single different refractive index member made of a material different from the base material 121. For example, InGaP, a p-type semiconductor, can be used as the material for the different refractive index member. When electrons are injected from the first electrode 171, the base material 121 and the different refractive index members constituting the different refractive index regions 122, 122A, and 122B are made of n-type semiconductors.

[0036] The first cladding layer 141 is made of a p-type semiconductor (or an n-type semiconductor when electrons are injected from the first electrode 171) for the same reasons as the material of the two-dimensional photonic crystal layer 12. On the other hand, the second cladding layer 142 is made of an n-type semiconductor (or a p-type semiconductor when holes are injected from the second electrode 172 when electrons are injected from the first electrode 171) in order to inject electrons from the second electrode 172 into the active layer 11. For example, the first cladding layer 141 is made of p-type Al 0.37 Ga 0.63 As is used, and n-type Al is used in the second cladding layer 142. 0.37 Ga 0.63 As can be used in each case.

[0037] The substrate 16 is made sufficiently thicker than the other layers in order to maintain the overall mechanical strength of the two-dimensional photonic crystal laser 10. The material of the substrate 16 is an n-type semiconductor (a p-type semiconductor when holes are injected from the second electrode 172), similar to the second cladding layer 142, and can be, for example, n-type GaAs.

[0038] The spacer layer 13 is provided to allow holes injected from the first electrode 171 to pass through and be introduced into the active layer 11, while suppressing electrons injected from the second electrode 172 from passing through the active layer 11 (therefore, they do not combine with holes on the side of the first electrode 171 rather than the active layer 11). In the first embodiment, the spacer layer 13 has an i-type (intrinsic semiconductor) Al on the active layer 11 side. 0.45 Ga 0.55 A two-layer structure is used, in which a 25 nm thick layer made of As is placed on the two-dimensional photonic crystal layer 12 side is a 90 nm thick layer made of i-type GaAs.

[0039] The first electrode (which also serves as a reflective layer) 171 is made of a conductive metal and is provided on the entire surface of the first cladding layer 141 opposite to the two-dimensional photonic crystal layer 12. The first electrode 171 has the role of injecting holes (or electrons) into the active layer 11, as well as acting as a reflective layer that reflects the laser beam emitted from the two-dimensional photonic crystal layer 12 toward the first electrode 171.

[0040] The second electrode 172 has a structure in which the center of a conductive metal plate is hollowed out. The hollowed-out portion of the plate-like member is called the window portion 1722, and the portion of the plate-like member that remains is called the frame portion 1721.

[0041] (2) Operation of the two-dimensional photonic crystal laser of the first embodiment By applying a predetermined voltage between the first electrode 171 and the second electrode 172, a current is injected from both electrodes into the active layer 11. As a result, light emission having a wavelength within a predetermined wavelength band corresponding to the material of the active layer 11 is generated from the active layer 11. The light emission thus generated is selectively amplified in the two-dimensional photonic crystal layer 12 by resonance of light with a resonant wavelength corresponding to the period length a of the square lattice (details will be described in the next paragraph), and laser oscillation occurs.

[0042] When resonance occurs, the light of the resonant wavelength propagating in the x and y directions within the two-dimensional photonic crystal layer 12 is diffracted by 180° in the first subregion 1221 and the second subregion 1222, or in the first deformed subregion 1221A (or 1221B) and the second deformed subregion 1222A (or 1222B), respectively. The light diffracted by 180° in these two (deformed) subregions is then weakened by interference (see Figure 5(a) for the case of the first subregion 1221 and the second subregion 1222. The thick lines in the figure indicate 180° diffraction). As a result, localization of light within the two-dimensional photonic crystal layer 12 is suppressed, and laser oscillation can be performed over a wide area within the two-dimensional photonic crystal layer 12. This makes it possible to generate a high-power laser beam. Note that while Figure 5(a) shows how light propagating in the positive x and y directions is diffracted by 180°, light propagating in the negative direction is also diffracted by 180°.

[0043] The 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 electrode 171 is reflected by the first electrode (which also serves as a reflective layer) 171 and directed toward the second electrode 172, and then emitted to the outside through the window portion 1722. On the other hand, the laser beam emitted towards the second electrode 172 is emitted directly to the outside through the window portion 1722. At this time, by setting the distance between the surface of the two-dimensional photonic crystal layer 12 on the first electrode 171 side and the surface of the first electrode 171 on the two-dimensional photonic crystal layer 12 side to 1 / 2 times the wavelength of the laser beam or an integer multiple thereof, the laser beam reflected by the first electrode (which also serves as a reflective layer) 171 and the laser beam emitted from the two-dimensional photonic crystal layer 12 toward the second electrode 172 side can be made to interfere, further increasing the output of the laser beam emitted to the outside.

[0044] More precisely, in addition to the interference due to the 180° diffraction described above, light of the resonant wavelength propagating in the x - direction and y - direction within the two - dimensional photonic crystal layer 12 is diffracted by 90° in the first deformed partial region 1221A (or 1221B) and the second deformed partial region 1222A (or 1222B), respectively, and the interference of the diffracted lights (see Fig. 5(b). The thick lines in the figure indicate 90° diffraction) occurs within the two - dimensional photonic crystal layer 12. According to Patent Document 2, by approaching the real part R of the effective coupling coefficient resulting from the interference of these 180° diffracted light and 90° diffracted light to 0, it is shown that it is possible to expand the difference in the radiation coefficients between the fundamental mode having a single electric - field antinode in the plane and the higher - order mode having a plurality of electric - field antinodes in the plane. By setting the imaginary part I of the above - mentioned effective coupling coefficient to an appropriate value, it is shown that the radiation coefficient of the fundamental mode can be adjusted to a value suitable for laser oscillation (details of R and the radiation coefficient will be described later). When the two - dimensional photonic crystal layer 12 has the first deformed partial region 1221A (the same as above) and the second deformed partial region 1222A (the same as above), the values of the above - mentioned effective coupling coefficients R and I can be continuously controlled. As a result, a large difference in the radiation coefficients between the fundamental mode and the higher - order mode can be obtained, and large - area single - mode oscillation can be realized. Hereinafter, an explanation including a specific calculation example will be given.

[0045] Generally, in a two - dimensional photonic crystal laser, the efficiency of emitting a laser beam to the outside is indicated by an index called the radiation coefficient. The radiation coefficient refers to the ratio of the light radiated in the direction perpendicular to the two - dimensional photonic crystal layer by diffraction during the propagation of the light existing as a guided - wave mode in the two - dimensional photonic crystal layer per unit length. As described in Patent Document 2, in a two - dimensional photonic crystal in which regions of different refractive indices are arranged in a square lattice, in the resonant state called "mode A" with the lowest energy, the radiation coefficient α of the fundamental mode v0 and the radiation coefficient α of the first higher - order mode having a wavelength (double the wave number) half that of the fundamental mode v1 are respectively represented by. Therefore, the difference in the radiation coefficients Δα between the fundamental mode and the first higher - order mode v =(α v1 -α v0 ) is This is the result. R and I are respectively R=Re[(κ 1D +κ 2D- )exp(-iθ PC )] …(4) I=Im[(κ 1D +κ 2D- )exp(-iθ PC )] …(5) is the real and imaginary parts of the effective coupling coefficients mentioned above. Here, "Re[]" and "Im[]" mean the real and imaginary parts of the formulas in the brackets, respectively. κ 1D This coefficient, called the one-dimensional coupling coefficient, represents the interaction between in-plane guided light propagating in the x and y directions within the two-dimensional photonic crystal layer 12 and the light diffracted by 180°. Also, κ 2D- θ is a coefficient called the two-dimensional coupling coefficient, which represents the interaction between in-plane guided light propagating in the positive and negative x directions and light diffracted at 90° in the negative and positive y directions (i.e., opposite in sign to the in-plane guided light) (similarly, the interaction between in-plane guided light propagating in the positive and negative y directions and light diffracted at 90° in the negative and positive x directions). PC This represents the added phase when in-plane guided light guiding in the negative x direction is diffracted through the emitted light into in-plane guided light guiding in the positive x direction. L represents the diameter of the inscribed circle in the area where light emission occurs when current is injected into the active layer 11. μ is a coefficient that indicates the strength with which in-plane guided light propagating in the x and y directions is coupled to each other via emitted light that is emitted perpendicular to the two-dimensional photonic crystal layer 12.

[0046] The parameter κ included in R, as described above, 1D κ 2D- and θ PC This parameter is determined by the planar shape of the different refractive index regions (wherein μ is mainly determined by the phase difference between the light emitted directly from the two-dimensional photonic crystal layer 12 to the outside and the light reflected by the reflective layer and emitted to the outside). From equation (1), the emission coefficient α of the fundamental mode is v0 This is mainly determined by the magnitude of the imaginary part I of the effective coupling coefficient, where I is an appropriate value (as a guideline, |I| ≤ 30 cm). -1 By designing the shape of the different refractive index regions to be such that ), an emissivity coefficient α of an appropriate size for laser oscillation can be obtained.v0 This can be achieved. And the difference in the emission coefficient Δα v The larger this value, the more efficient it is to emit the fundamental mode laser beam while preventing the mixing of higher-order modes (first higher-order mode and higher-order modes of even higher order). From equation (3), the smaller the absolute value of R|R|, the greater the difference in the emission coefficient Δα. v As |R| becomes larger, the efficiency of emitting the fundamental mode laser beam can be increased by designing the shape of the different refractive index region so that |R| becomes smaller. As a guideline, |R| ≤ 30 cm -1 Therefore, even in a large oscillation region of 3 mm in diameter within the two-dimensional photonic crystal layer 12, single-mode oscillation consisting only of fundamental modes can be realized.

[0047] Therefore, calculations were performed to determine the values ​​of |R| and |I| for the different refractive index regions 122, 122A, and 122B in the two-dimensional photonic crystal laser 10 of the first embodiment. In these calculations, various examples were considered in which the value of c, which is a parameter that defines the length of the convex curve C11 and the concave curve C22 as described above, and the value of Δd, which is a parameter that defines the span length as described above, are different. When c=0 and Δd=0, it corresponds to the different refractive index region 122; when c≠0 and Δd=0, it corresponds to the different refractive index region 122A; and when c≠0 and Δd≠0, it corresponds to the different refractive index region 122B. Calculations were performed with c in the range of -0.2 to +0.2 and Δd in the range of 0 to +0.05a (therefore, the different refractive index region 122B is when additional regions 1225 and 1226 are added). In this case, the deformation rate of the first deformation region 1221A or 1221B is -10% to +10%, and the deformation rate of the second deformation region 1222A or 1222B is 0% to +20%. The refractive index of the base material 121 is 3.55, and the refractive index of the different refractive index regions 122, 122A, and 122B is 3.26.

[0048] The calculation results are shown in Figure 6 (Note that in Figure 6, either |R| or |I| is 50 cm). -1 (Calculation data exceeding this value are omitted from the illustration.) Due to differences in the values ​​of c and Δd, |R| and |I| can take various values, but in most cases |R| ≤ 30 cm -1and |I| ≤ 30cm -1 It satisfies these conditions, and as mentioned above, it can achieve single-mode oscillation consisting only of the fundamental mode even in a large oscillation region with a diameter of 3 mm.

[0049] In the two-dimensional photonic crystal laser 10 of the first embodiment, the differential refractive index region 122 is composed of a single, unseparated region, where the first partial region 1221 and the second partial region 1222 are connected without overlap and without any gaps between the two partial regions. Therefore, the size of each vacancy or differential refractive index member constituting the differential refractive index region 122 can be increased compared to the case where a pair of differential refractive index regions consisting of two differential refractive index regions described in Patent Documents 1 and 2 is used, thereby making it easier to manufacture the two-dimensional photonic crystal laser 10. In particular, since it is more difficult to manufacture small differential refractive index members than to manufacture small vacancies, using large differential refractive index members as in the first embodiment significantly contributes to facilitating the manufacture of the two-dimensional photonic crystal laser 10. These effects are similar when using differential refractive index regions 122A and 122B, which are deformable regions.

[0050] Furthermore, when designing the structure of the different refractive index regions, the degree of design freedom can be increased by adding the different refractive index region composed of a single region of the first embodiment as a candidate, along with the different refractive index region pairs described in Patent Documents 1 and 2.

[0051] When using the deformable regions, namely the different refractive index regions 122A and 122B, it is also possible to continuously change the values ​​of |R| and |I| during the design phase, which has the added benefit of making it easy to determine the optimal conditions for achieving single-mode laser oscillation.

[0052] Furthermore, when using the different refractive index region 122A, the first deformed portion region 1221A is obtained by removing the removal region 1223 from the first portion region 1221, and the second deformed portion region 1222A is obtained by adding the addition region 1224 to the first portion region 1221. This clearly distinguishes the shape differences between the first deformed portion region 1221A and the second deformed portion region 1222A, allowing for the setting of appropriate |R| and |I| values.

[0053] (3) Second Embodiment The two-dimensional photonic crystal laser of the second embodiment has the same configuration as the two-dimensional photonic crystal laser of the first embodiment, except for the region of different refractive indices. The region of different refractive indices of the two-dimensional photonic crystal laser of the second embodiment will be described below.

[0054] Figure 7 shows the different refractive index regions 122C of the two-dimensional photonic crystal laser of the second embodiment. Similar to the different refractive index regions 122 described above, these different refractive index regions 122C are arranged in a square lattice within the base material 121 with period lengths a in the x and y directions, respectively.

[0055] The shape of the region with different refractive indices 122C will now be described. In the region with different refractive indices 122C, a first rectangular subregion 1221C and a second rectangular subregion 1222C, which are identical in shape to each other, are positioned offset by +0.25a in the x direction and +0.25a in the y direction, such that each side of the rectangle is inclined at 45° with respect to the x and y directions, and one of the shorter sides touches each other. The first subregion 1221C and the second subregion 1222C constitute the first subregion pair. Furthermore, the third subregion 1231 and the fourth subregion 1232 are located symmetrically with respect to a line passing through the area center of the first subregion 1221C (the "+" mark shown within the first subregion 1221C in Figure 7; the "+" marks shown within other subregions indicate the area center of that region) and the area center of the second subregion 1222C (the line shown as a dashed line in Figure 7). The area centers of the third subregion 1231 and the fourth subregion 1232 are separated by 0.25a in the x-direction and 0.25a in the y-direction. These third subregions 1231 and the fourth subregion 1232 constitute the second subregion pair. These four subregions are connected without overlapping or gaps. In the example shown in Figure 7, the midpoint of the line segment connecting the area center of the third subregion 1231 and the area center of the fourth subregion 1232 coincides with the area center of the second subregion 1222C, but they do not have to coincide.

[0056] The combined length of the long side of the first subregion 1221C and the long side of the second subregion 1222C is (0.5a + Δd) × 2 1 / 2 (Half of this length is the length of the longer side in each of these two subregions). In this embodiment, several examples are used in which Δd differs within the range of -0.05a to +0.05a (including 0). This means that the first subregion 1221C and the second subregion 1222C are deformed by a deformation rate D within the range of -10% to +10%. The length of the shorter side of the first subregion 1221C and the second subregion 1222C is (0.10a) × 2 1 / 2 The lengths of the shorter sides of the third subregion 1231 and the fourth subregion 1232 are (0.15a) × 2 1 / 2Therefore, these shorter sides are not deformed. In the example shown in Figure 7, the length c of the longer sides of the third sub-region 1231 and the fourth sub-region 1232 is the same as the length of the longer side of the second sub-region 1222C, but it can be changed within the range of 0.16a to 0.30a. Therefore, the longer sides of the third sub-region 1231 and the fourth sub-region 1232 may be shorter (Figure 8(a)) or longer (Figure 8(b)) than the longer side of the second sub-region 1222C. In the example shown in Figure 8, the shorter sides of the second sub-region 1222C, the third sub-region 1231, and the fourth sub-region 1232 that are furthest from the first sub-region 1221C are aligned in a straight line, but other arrangements are also possible. For example, the areas may be arranged such that the shorter sides closer to the first sub-region 1221C are aligned in a straight line, or the areas of the second sub-region 1222C, the third sub-region 1231, and the fourth sub-region 1232 may be arranged so that their area centers are aligned in a straight line parallel to their shorter sides.

[0057] For a two-dimensional photonic crystal laser 10 having such a different refractive index region 122C, the value of |R| was calculated along with the value of |I|. The refractive index of the base material 121 was assumed to be 3.55, and the refractive index of the different refractive index region 122C was assumed to be 3.26.

[0058] The calculation results are shown in Figure 9 (Note that in Figure 9, either |R| or |I| is 50 cm). -1 (Calculation data exceeding this value are not shown in the figure.) Due to differences in the values ​​of c and Δd, R can take on various values, but in most cases |R| ≤ 30 cm -1 and |I| ≤ 30cm -1 It satisfies these conditions, and as mentioned above, it can achieve single-mode oscillation consisting only of the fundamental mode even in a large oscillation region with a diameter of 3 mm.

[0059] The two-dimensional photonic crystal laser of the second embodiment provides the same effects as the two-dimensional photonic crystal laser of the first embodiment, which includes different refractive index regions 122 consisting of a basic region. That is, not only the light diffracted by 180° in the first subregion 1221C and the second subregion 1222C, but also the light diffracted by 180° in the third subregion 1231 and the fourth subregion 1232, respectively, is weakened by interference, so that the localization of light within the two-dimensional photonic crystal layer 12 can be suppressed as a whole. In addition, the presence of multiple subregion pairs allows for more precise adjustment of the real part R and imaginary part I of the effective coupling coefficient during the design phase.

[0060] (4) Modifications The embodiments of the two-dimensional photonic crystal laser according to the present invention have been described above, but it goes without saying that the present invention is not limited to the above embodiments. In particular, the shape of the different refractive index regions can be modified in various ways within the scope of the present invention, other than those of the above embodiments. In addition, although the number of partial region pairs was set to one pair (first embodiment) or two pairs (second embodiment) in the above embodiments, different refractive index regions having three or more partial region pairs may also be used.

[0061] It is also possible to modify components other than those in the different refractive index region. For example, in the above embodiment, the first electrode 171 also serves as a reflective layer, but a reflective layer may be provided separately from the first electrode 171. When such a reflective layer is provided between the two-dimensional photonic crystal layer 12 and the first electrode 171, it is made of a conductive material. On the other hand, when the reflective layer is provided on the opposite side of the two-dimensional photonic crystal layer 12 from the perspective of the first electrode 171, the material of the first electrode 171 is a material that can transmit the generated laser beam (for example, indium tin oxide (ITO) when the laser beam is visible light). Furthermore, the reflective layer may be omitted (the first electrode 171 does not serve as a reflective layer, and no other reflective layer is provided).

[0062] The layers other than the active layer 11, the two-dimensional photonic crystal layer 12, the first electrode 171, and the second electrode 172 may be omitted as appropriate, or other layers may be added as needed. Furthermore, the materials of each layer are not limited to those listed above.

[0063] [Embodiments] It will be apparent to those skilled in the art that the exemplary embodiments described above are specific examples of the following embodiments.

[0064] (Section 1) The two-dimensional photonic crystal laser according to Section 1 comprises: a) an active layer; b) a two-dimensional photonic crystal layer provided on one surface side of the active layer, wherein regions with different refractive indices from the base material are arranged in a square lattice within a plate-shaped base material, with a period length a in the first direction and the same period length a in the second direction at a 90° angle to the first direction; and c) a pair of electrodes provided so as to sandwich the active layer and the two-dimensional photonic crystal layer in the stacking direction, wherein the regions with different refractive indices have n (n is a natural number) pairs of subregions, each consisting of two pairs of identically shaped subregions positioned offset from each other by +0.25a or -0.25a in the first direction and +0.25a or -0.25a in the second direction, and the 2n subregions of the n pairs of subregions are connected to each other without overlapping and without gaps, or In some or all of the n pairs of sub-regions, an additional region is added to one or both of the two sub-regions, and / or a removal region is removed from one or both of the two sub-regions, thereby forming a modified region that is deformed from the basic region.

[0065] (Paragraph 2) The two-dimensional photonic crystal laser according to Paragraph 2 is the two-dimensional photonic crystal laser according to Paragraph 1, wherein the different refractive index region is made of a member whose refractive index is different from that of the base material.

[0066] (Article 3) The two-dimensional photonic crystal laser according to Article 3 is a two-dimensional photonic crystal laser according to Article 1 or Article 2, wherein the area of ​​the added region or the removed region is 20% or less of the area of ​​the basic region.

[0067] (Article 4) The two-dimensional photonic crystal laser according to Article 4 is a two-dimensional photonic crystal laser according to any one of Articles 1 to 3, wherein the different refractive index regions have a shape in which an additional region is added to one of the two subregions and a removal region is removed from the other, in at least one pair of subregion pairs.

[0068] (Clause 5) The two-dimensional photonic crystal laser according to Clause 5 is a two-dimensional photonic crystal laser according to any one of Clauses 1 to 4, wherein the different refractive index regions include a first subregion and a second subregion which are two subregions having one pair of subregions from the n pairs of subregions, and a third subregion and a fourth subregion which are two subregions having the other pair of subregions from the n pairs of subregions which are identical in shape and are positioned symmetrically with respect to a line passing through the area center of the first subregion and the area center of the second subregion, with their area centers separated by 0.25a in the first direction and 0.25a in the second direction, and which do not overlap with the second subregion and are connected to the second subregion without any gap between them.

[0069] (Clause 6) The two-dimensional photonic crystal laser according to Clause 6 is a two-dimensional photonic crystal laser according to any one of Clauses 1 to 5, further comprising a reflective layer provided between the two-dimensional photonic crystal layer and one of the pair of electrodes, or consisting of one of the pair of electrodes.

[0070] 10...2D photonic crystal laser 11...Active layer 12...2D photonic crystal layer 121...Base material 122, 122A, 122B, 122C...Different refractive index regions 1221, 1221C...First partial region 1221A, 1221B...First deformed partial region 1222, 1222C...Second partial region 1222A, 1222B...Second deformed partial region 1223...Removal region 1224, 1225, 1226...Additional region 1231...Third partial region 1232...Fourth partial region 13...Spacer layer 141...First cladding layer 142...Second cladding layer 16...Substrate 171...First electrode 172...Second electrode 1721...Frame portion 1722...Window portion C11, C21...Convex curve C12, C22...concave curve

Claims

1. a) an active layer; b) a two-dimensional photonic crystal layer provided on one surface side of the active layer, wherein regions with different refractive indices from the base material are arranged in a square lattice within a plate-shaped base material, with a period length a in the first direction and the same period length a in the second direction at a 90° angle to the first direction; c) a pair of electrodes provided so as to sandwich the active layer and the two-dimensional photonic crystal layer in the stacking direction, wherein the regions with different refractive indices have n (n is a natural number) pairs of subregions, each consisting of two pairs of identically shaped subregions positioned offset from each other by +0.25a or -0.25a in the first direction and +0.25a or -0.25a in the second direction, and the 2n subregions of these n pairs of subregions are connected to each other without overlapping and without gaps, or, A two-dimensional photonic crystal laser comprising a deformed region formed by deforming the basic region, in part or all of the n pairs of subregions, by adding an additional region to one or both of the two subregions, and / or by removing a removal region from one or both of the two subregions.

2. The two-dimensional photonic crystal laser according to claim 1, wherein the region with different refractive indices is made of a member with a refractive index different from that of the base material.

3. The two-dimensional photonic crystal laser according to claim 1 or 2, wherein the area of ​​the added region or the removed region is 20% or less of the area of ​​the basic region.

4. The two-dimensional photonic crystal laser according to claim 1 or 2, wherein the different refractive index regions have a shape in which an additional region is added to one of the two subregions and a removal region is removed from the other in at least one pair of subregion pairs.

5. The two-dimensional photonic crystal laser according to claim 1 or 2, wherein the different refractive index regions comprise a first subregion and a second subregion, which are two subregions of one pair of subregions among the n pairs of subregions, and a third subregion and a fourth subregion, which are two subregions of the other pair of subregions among the n pairs of subregions, which are identical in shape and are positioned symmetrically with respect to a line passing through the area center of the first subregion and the area center of the second subregion, with their area centers separated by 0.25a in the first direction and 0.25a in the second direction, and which do not overlap with the second subregion and are connected to the second subregion without any gap between them.

6. The two-dimensional photonic crystal laser according to claim 1 or 2, further comprising a reflective layer provided between the two-dimensional photonic crystal layer and one of the pair of electrodes, or consisting of one of the pair of electrodes.

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