Two-dimensional photonic crystal laser

Abstract

Provided is a two-dimensional photonic crystal laser that is capable of scanning a laser beam and emitting the laser beam without the laser beam being attenuated by an electrode. A two-dimensional photonic crystal laser 1 is formed by sandwiching, between a first electrode 181 and a second electrode 182, a layered body 10 which has an active layer 13 and a two-dimensional photonic crystal layer 15 in which different-refractive index regions 152 are arranged periodically in a two-dimensional pattern on a plate-shaped base material 151, the regions 152 having refractive indices different from that of the base material 151. The first electrode 181 is divided into a plurality of partial electrodes 1811. The second electrode 182 is a frame-like electrode which has a frame-like section 1821 formed of a conductor, and in which a window section 1822, which is an inner-side space of the frame-like section 1821, is arranged to oppose the region encompassing the plurality of partial electrodes 1811. A lens 19 that covers the entirety of the window section 1822 is provided on the side of the second electrode 182 opposite from the layered body 10.

Description

[Technical field]

[0001] The present invention relates to a two-dimensional photonic crystal laser that amplifies light by using a two-dimensional photonic crystal. [Background technology]

[0002] A two-dimensional photonic crystal laser includes an active layer, a two-dimensional photonic crystal layer, and a pair of electrodes sandwiching them. The active layer emits light in a specific emission wavelength band when carriers (holes, electrons) are injected from the electrodes. The two-dimensional photonic crystal layer has a structure in which modified refractive index areas with a different refractive index from that of a plate-shaped base material are periodically arranged in a two-dimensional pattern. The modified refractive index areas are made of voids (air) formed in the base material, or a material different from the base material. In general, a first cladding layer made of a semiconductor is provided between one electrode (referred to as the "first electrode") and the active layer, and a second cladding layer made of a semiconductor is provided between the two-dimensional photonic crystal layer and the other electrode (referred to as the "second electrode").

[0003] In such a two-dimensional photonic crystal laser, of the light generated in the active layer, only light of a predetermined wavelength corresponding to the periodic length of the arrangement of the modified refractive index areas is amplified in the two-dimensional photonic crystal layer and oscillates into a laser, and a laser beam is emitted from the surface of the two-dimensional photonic crystal layer.

[0004] Patent Documents 1 and 2 describe a two-dimensional photonic crystal laser with a variable emission direction of a laser beam (hereinafter referred to as a "variable emission direction two-dimensional photonic crystal laser"). Such a variable emission direction two-dimensional photonic crystal laser is a light source that can be suitably used for forming characters and figures by scanning a laser beam in a laser printer, a laser display, etc.

[0005] In the variable emission direction two-dimensional photonic crystal laser described in Patent Document 1 (hereinafter referred to as the "first conventional example"), the second electrode is divided into multiple pieces and provided on the surface of the second cladding layer (the surface opposite the two-dimensional photonic crystal layer), with a gap provided between each divided electrode (each electrode is referred to as a "partial electrode"). In addition, a lens is provided facing the surface of the second cladding layer. The first electrode is provided so as to cover the entire surface of the first cladding layer (the surface opposite the active layer).

[0006] According to the first conventional example, a current is injected into a part of the active layer (hereinafter, referred to as a "current injection region") by passing a current between one of the partial electrodes or between adjacent partial electrodes and the first electrode, and light is generated in the current injection region. As a result, a laser oscillates in a region of the two-dimensional photonic crystal layer corresponding to the current injection region, and a laser beam is emitted from the two-dimensional photonic crystal layer in a direction perpendicular to the layer. The laser beam emitted from the two-dimensional photonic crystal layer passes between the partial electrodes and through the lens and is emitted to the outside. Here, the laser beam is refracted at different angles depending on the position where it enters the lens, so the traveling direction of the laser beam emitted to the outside differs depending on the position where it enters the lens and further the position of the current injection region on which the position is determined. Therefore, by changing the partial electrode that supplies a current to change the position of the current injection region, the traveling direction of the laser beam can be changed, and the laser beam can be scanned.

[0007] In the variable emission direction two-dimensional photonic crystal laser (second conventional example) described in Patent Documents 2 and 3, the modified refractive index area is arranged at a position shifted from the lattice point of a two-dimensional lattice such as a square lattice or a rectangular lattice in the two-dimensional photonic crystal layer. The shift of the position of the modified refractive index area from the lattice point at each lattice point is specified by a parameter called modulation phase. In one example, the modified refractive index area is shifted at the same distance at each lattice point in a different azimuth angle direction, and the phase of this azimuth angle corresponds to the modulation phase. The inside of the two-dimensional photonic crystal layer is virtually divided into a plurality of oscillation regions, and in the same oscillation region, the phase difference of the azimuth angle (phase difference of the modulation phase) between adjacent lattice points has the same value, and between different oscillation regions, the phase difference has a different value. The second electrode is a partial electrode provided corresponding to each of the plurality of oscillation regions. The first electrode is a transparent electrode provided so as to cover the entire surface of the first cladding layer, and the laser beam is emitted from the first electrode side. In the second conventional example, no lens is provided.

[0008] According to the second conventional example, by supplying a current between one of a plurality of partial electrodes and the first electrode, light is generated in a region of the active layer corresponding to the one partial electrode (current injection region), and laser oscillation occurs in a region of the two-dimensional photonic crystal layer corresponding to the one partial electrode (oscillation region). The laser beam travels in a direction inclined by an angle determined by the modulation phase from a direction perpendicular to the two-dimensional photonic crystal layer. Therefore, by changing the partial electrode supplying a current to change the oscillation region, the modulation phase changes, and the traveling direction of the laser beam can be changed, thereby making it possible to scan the laser beam. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2005-277219 A [Patent Document 2] International Publication No. WO2014 / 136607 [Patent Document 3] U.S. Patent Publication US2016 / 0248224 [Patent Document 4] JP 2008-243962 A Summary of the Invention [Problem to be solved by the invention]

[0010] In the first conventional example, the laser beam is emitted to the outside only between the partial electrodes, and part of the laser beam is blocked by the partial electrodes. In the second conventional example, the laser beam is emitted to the outside through the transparent electrodes, but the light transmittance of the transparent electrodes is generally not 100%, so the laser beam is attenuated by the transparent electrodes.

[0011] The problem to be solved by the present invention is to provide a variable emission direction two-dimensional photonic crystal laser that can scan a laser beam and emit the laser beam without being attenuated by electrodes. [Means for solving the problem]

[0012] A first aspect of the present invention, which has been made to solve the above problems, is a two-dimensional photonic crystal laser comprising a laminate sandwiched between a first electrode and a second electrode, the laminate having an active layer and a two-dimensional photonic crystal layer in which modified refractive index areas having a refractive index different from that of a plate-shaped base material are periodically arranged in a two-dimensional pattern, the laminate comprising: The first electrode is divided into a plurality of partial electrodes, the second electrode is a frame-shaped electrode having a frame-shaped portion made of a conductor, and a window portion, which is a space inside the frame-shaped portion, is disposed opposite to a region that envelops the plurality of partial electrodes, a lens provided on a surface of the second electrode opposite to the laminate or on a surface of the laminate facing the second electrode so as to cover the window portion; It is characterized by:

[0013] In the two-dimensional photonic crystal laser of the first embodiment, by passing a current between one or adjacent ones of the plurality of partial electrodes constituting the first electrode (the region in which these exist is called the "current supply region") and the second electrode, a current is injected into a current injection region, which is a region of the active layer corresponding to the current supply region, and light is generated in the current injection region. As a result, laser oscillation occurs in the region of the two-dimensional photonic crystal layer corresponding to the current injection region, and a laser beam is emitted from the two-dimensional photonic crystal layer in a direction perpendicular to the layer, and passes through the window part of the second electrode and the lens to be emitted to the outside of the two-dimensional photonic crystal laser. Here, since the laser beam is refracted at a different angle depending on the position where it enters the lens, the traveling direction of the laser beam emitted to the outside differs depending on the position where it enters the lens and further the position of the current supply region, which is the basis for determining the position. Therefore, by changing the partial electrode that supplies a current to change the position of the current injection region, the traveling direction of the laser beam can also be changed, and the laser beam can be scanned.

[0014] The lens may be provided on the side of the second electrode opposite to the laminate, or on the surface of the laminate on the second electrode side. When the lens is provided on the surface of the laminate on the second electrode side, the lens is preferably formed integrally with the laminate. This allows the size of the two-dimensional photonic crystal laser to be reduced. Such a lens integral with the laminate can be produced by processing the surface of the laminate on the second electrode side by a method such as etching.

[0015] The current injection region in the active layer is not the same size as the current supply region in the first electrode. In the present invention, the window portion of the second electrode is disposed opposite the region that envelops the plurality of partial electrodes, so that the outer shape of the frame portion of the second electrode is larger than the current supply region in the first electrode, and the current flows from the first electrode to the second electrode so as to spread in the in-plane direction of the active layer. Therefore, the current injection region is larger than the current supply region.

[0016] According to the two-dimensional photonic crystal laser of the first aspect, the laser beam emitted from the two-dimensional photonic crystal layer passes through the window portion of the second electrode, i.e., the space inside the frame-shaped portion where no conductor is present, and therefore the laser beam can be emitted without attenuation.

[0017] In the two-dimensional photonic crystal laser of the first aspect, it is desirable that the interval between adjacent partial electrodes is set so that a partial current injection region, which is a region where a current is injected from each of the plurality of partial electrodes into the active layer, overlaps with a part of a partial current injection region where a current is injected from a partial electrode adjacent to the partial electrode into the active layer. As a result, one current injection region that is not divided into multiple regions is formed in the active layer, and a coherent laser beam can be obtained by amplifying light emitted from this one current injection region in the two-dimensional photonic crystal layer. The overlapping of the partial current injection regions formed by adjacent partial electrodes in this way can be realized by performing a simulation and setting parameters such as the distance between the first electrode (partial electrode) and the active layer, the distance between the active layer and the second electrode, the distance between the partial electrodes, and the area of ​​the second electrode.

[0018] In the two-dimensional photonic crystal laser of the first aspect, it is desirable that the lens is arranged at a distance 0.5 to 2 times the focal length of the lens from the two-dimensional photonic crystal layer. By arranging the lens at a distance close to the focal length of the lens from the two-dimensional photonic crystal layer in this manner, it is possible to prevent the diameter of the laser beam passing through the lens from expanding.

[0019] In the two-dimensional photonic crystal laser of the first aspect, The two-dimensional photonic crystal layer is The modified refractive index area has two partial modified refractive index areas, A coupling coefficient κ of 180° diffracted light in which light propagating within the two-dimensional photonic crystal layer is diffracted in a 180° direction by the modified refractive index area 180 and the coupling coefficient of the 90° diffracted light in the 90° direction -κ90 The absolute value of the difference between (|κ 180 -(-κ 90 )|=|κ 180 +κ 90 |) is 100cm -1 It is desirable that the shapes of the two partial modified refractive index areas are set so as to be as follows.

[0020] Here, the coupling coefficient is a parameter that indicates the intensity of the diffracted light, and can take either a positive or negative value. 180 is a one-dimensional coupling coefficient (Hermitian component) that represents the interaction between the in-plane guided light that is guided in one direction and the in-plane guided light that is reflected by the modified refractive index area and changes its direction of travel by 180° (diffracted by 180°). κ 90 is a two-dimensional coupling coefficient that represents the interaction between the in-plane guided light that is guided in one direction and the light whose propagation direction is changed by 90° by the modified refractive index area. These κ 180 and κ 90 is determined based on the shape of the modified refractive index area. 180 and -κ 90 The absolute value of the difference between |κ 180 +κ 90 As | approaches 0, the intensity of the interference light between the 180° diffracted light and the 90° diffracted light becomes weaker, which suppresses the effect of confining the light within the two-dimensional photonic crystal layer, and therefore the intensity of the laser beam emitted outside the two-dimensional photonic crystal laser can be increased. Therefore, as described above, |κ 180 +κ 90 | is 100cm -1 It is desirable to do the following:

[0021] In the two-dimensional photonic crystal laser of the first aspect, it is preferable to further provide a reflecting portion made of an electrically insulating material and reflecting a laser beam between the plurality of partial electrodes (gaps between adjacent partial electrodes). This allows the laser beam emitted from the two-dimensional photonic crystal layer to the first electrode side to be reflected by the reflecting portion and the partial electrodes and emitted from the window portion of the second electrode, thereby improving the light emission efficiency.

[0022] A second aspect of the present invention is a two-dimensional photonic crystal laser comprising a laminate sandwiched between a first electrode and a second electrode, the laminate having an active layer and a two-dimensional photonic crystal layer having modified refractive index areas arranged two-dimensionally in a plate-like base material, the modified refractive index areas being different from that of the base material, The first electrode is divided into a plurality of partial electrodes, the second electrode is a frame-shaped electrode having a frame-shaped portion made of a conductor, and a window portion, which is a space inside the frame-shaped portion, is disposed opposite to a region that envelops the plurality of partial electrodes, the two-dimensional photonic crystal layer is arranged such that the modified refractive index areas form a two-dimensional standing wave to form a resonant state of a predetermined wavelength and modulate with a predetermined modulation phase Ψ at each lattice point of a basic two-dimensional lattice having a periodicity determined so as not to emit light of the wavelength to the outside, The modulation phase Ψ is a function of the wavelength λ L The wave vector of light k↑=(k x , k y ), the effective refractive index n eff , a predetermined angle θ, and an azimuth angle φ from a predetermined reference line of the basic two-dimensional lattice, x , g' y )=(k x ±|k↑|(sinθcosφ) / n eff , k y ±|k↑|(sinθsinφ) / n eff ) and the position vector r↑ of each lattice point, Ψ=r↑·G'↑, and the angle θ differs depending on the position within the two-dimensional photonic crystal layer. It is characterized by:

[0023] In the two-dimensional photonic crystal laser of the second embodiment, by passing a current between the second electrode and one or adjacent ones of the partial electrodes constituting the first electrode (the region in which these exist is called the "current supply region" as in the first embodiment), a current is injected into a current injection region, which is a portion of the active layer, and light is generated in the current injection region. This causes laser oscillation by light of the specified wavelength in a region of the two-dimensional photonic crystal layer corresponding to the current injection region (called the "light amplification region"), generating a laser beam. Here, the specified wavelength need only be within the wavelength range of the light generated in the active layer.

[0024] The laser beam thus generated is emitted from the two-dimensional photonic crystal layer at an inclination angle (the angle between the normal to the two-dimensional photonic crystal layer and the traveling direction of the laser beam) according to the modulation phase of the two-dimensional photonic crystal layer in the optical amplification region, passes through the window of the second electrode, and is emitted to the outside of the two-dimensional photonic crystal laser. This inclination angle is determined by the modulation phase Ψ at each lattice point in the optical amplification region. Since the angle θ that defines the modulation phase differs depending on the position in the two-dimensional photonic crystal layer, the traveling direction of the laser beam can be changed by changing the position of the current injection region by changing the partial electrode into which the current is injected. Therefore, the laser beam can be scanned.

[0025] Up to this point, the reciprocal lattice vector G'↑ in the modulation phase Ψ=r↑·G'↑ has been described as being independent of the position in the two-dimensional photonic crystal layer. However, as described in Patent Document 3, the reciprocal lattice vector G'↑ may be defined as a function G'(x, y)↑ that depends on the position in the two-dimensional photonic crystal layer. In this case, as described below, G'↑(x, y) can be defined using the tilt angle θ(x, y) and azimuth angle φ(x, y) of the laser beam to be emitted from a position (x, y) in the two-dimensional photonic crystal layer (strictly speaking, a "position in the plane" of the two-dimensional photonic crystal layer), and further the modulation phase Ψ(x, y) at the position (x, y) can be defined. That is, sinθ x(x)=sinθ(x, y)cosφ(x, y), and sinθ y The angle θ expressed as (y)=sinθ(x, y)sinφ(x, y) x (x) and θ y If (y) is defined, the reciprocal lattice vector G'(x, y)↑ is G'(x, y)↑=(g' x (x), g' y (y))=(k x ±|k↑|sinθ x (x) / n eff , k y ±|k↑|sinθ y (y) / n eff ) and the modulation phase Ψ(x, y) is

number

[0026] By arranging each modified refractive index area in the two-dimensional photonic crystal layer by modulating it with the modulation phase Ψ(x, y) shown in formula (1) at each lattice point of the basic two-dimensional lattice, a laser beam having a tilt angle and azimuth angle close to the tilt angle θ(x, y) and azimuth angle φ(x, y) that define the modulation phase of the two-dimensional photonic crystal layer in the optical amplification area can be obtained. In particular, if the modulation phase Ψ(x, y) is defined using the same tilt angle θ(x, y) and azimuth angle φ(x, y) in a certain optical amplification area, a laser beam having the tilt angle θ(x, y) and azimuth angle φ(x, y) can be obtained from that optical amplification area.

[0027] According to the two-dimensional photonic crystal laser of the second embodiment, the laser beam emitted from the two-dimensional photonic crystal layer passes through the window portion of the second electrode, i.e., the space inside the frame-shaped portion where no conductor is present, and therefore the laser beam can be emitted without attenuation.

[0028] In the two-dimensional photonic crystal laser of the second aspect, the modified refractive index area is arranged at each lattice point at the same distance from the lattice point, and the modulation phase for each lattice point is set by the difference in the angle between the direction of the shift and a reference line.

[0029] Alternatively, in the two-dimensional photonic crystal laser of the second aspect, the modified refractive index areas are arranged at each lattice point so as to be shifted in the same direction from the lattice point, and the modulation phase for each lattice point is set depending on the difference in the shift distance. Here, a direction that is 180° different from a certain direction corresponds to the "same direction" as the certain direction.

[0030] As yet another example, in the two-dimensional photonic crystal laser of the second embodiment, the modified refractive index areas are arranged at each lattice point, and the modulation phase for each lattice point is set by the difference in area of ​​each modified refractive index area.

[0031] In the two-dimensional photonic crystal laser of the second aspect, as in the first aspect, it is desirable that the spacing between adjacent partial electrodes is set so that a partial current injection region, which is a region where current is injected from each of the plurality of partial electrodes into the active layer, overlaps with a part of a partial current injection region where current is injected into the active layer from a partial electrode adjacent to the partial electrode.

[0032] Furthermore, in the two-dimensional photonic crystal laser of the second embodiment, similarly to the first embodiment, it is desirable to further provide a reflective portion between the plurality of partial electrodes (gaps between adjacent partial electrodes) made of an electrically insulating material and which reflects the laser beam. Effect of the Invention

[0033] According to the present invention, it is possible to obtain a variable emitting direction two-dimensional photonic crystal laser that can scan a laser beam and emit the laser beam without being attenuated by electrodes. [Brief description of the drawings]

[0034] [Figure 1] 1 is a schematic configuration diagram showing a first embodiment of a two-dimensional photonic crystal laser according to the present invention. [Diagram 2] 1 is a perspective view showing a two-dimensional photonic crystal layer, a first electrode, and a second electrode of the two-dimensional photonic crystal laser of the first embodiment. [Diagram 3] FIG. 2 is a plan view showing an example of a two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser of the first embodiment. [Figure 4] FIG. 4 is a plan view showing another example of the two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser according to the first embodiment. [Figure 5A] FIG. 2 is a plan view showing an example of the shape and arrangement of partial electrodes that configure a first electrode in the two-dimensional photonic crystal laser of the first embodiment. [Figure 5B] FIG. 4 is a plan view showing another example of the shape and arrangement of the partial electrodes that configure the first electrode in the two-dimensional photonic crystal laser of the first embodiment. [Figure 6A] 3A and 3B are diagrams showing examples of partial current injection regions and current injection regions when current is injected into an active layer from a plurality of adjacent partial electrodes in the two-dimensional photonic crystal laser of the first embodiment. [Figure 6B] FIG. 4 is a diagram showing an example in which a current injection region is moved by changing a partial electrode into which a current is injected in the two-dimensional photonic crystal laser of the first embodiment. [Figure 7A] FIG. 2 is a diagram showing an example of the propagation direction of a laser beam generated when current is injected into an active layer from a plurality of adjacent partial electrodes in the two-dimensional photonic crystal laser of the first embodiment. [Figure 7B] FIG. 2 is a diagram showing an example in which the laser beam is moved by changing the partial electrode into which a current is injected in the two-dimensional photonic crystal laser of the first embodiment, thereby changing the propagation direction of the laser beam that has passed through a lens. [Figure 8]FIG. 2 is a diagram showing the relationship between the direction of movement of a current injection region and the direction of movement (scanning) of a laser beam in the two-dimensional photonic crystal laser of the first embodiment. [Figure 9] FIG. 2 is a diagram showing an example in which a plurality of current injection regions are formed when current is injected into an active layer from a plurality of adjacent partial electrodes in the two-dimensional photonic crystal laser of the first embodiment. [Figure 10A] FIG. 4 is a diagram for explaining calculation conditions for determining the spacing between partial electrodes in the two-dimensional photonic crystal laser of the first embodiment. [Figure 10B] 1 is a graph showing the results of calculations of the relationship between the distance w from an end of a partial electrode and the current density ratio i1 / i0 for each of multiple values ​​of the depth d from the partial electrode in the two-dimensional photonic crystal laser of the first embodiment. [Figure 10C] 4 is a graph showing the relationship between the depth d from the partial electrode and the distance we from the end of the partial electrode when the current density ratio i 1 / i 0 becomes 1 / e2 in the two-dimensional photonic crystal laser of the first embodiment. [Figure 11] FIG. 13 is a diagram showing parameters for determining a coupling coefficient that represents the state of optical interference in a two-dimensional photonic crystal layer. [Figure 12A] 13 is a graph showing the results of calculating the difference in coupling coefficient representing the interference between 180° diffracted light and 90° diffracted light due to differences in distance in the x and y directions between the first partial modified refractive index area and the second partial modified refractive index area. [Figure 12B] 13 is a graph showing the results of calculating the difference in coupling coefficient, which represents the interference between 180° diffracted light and 90° diffracted light, due to differences in the ratio of the filling rates of the first partial modified refractive index area and the second partial modified refractive index area. [Figure 12C] 13 is a graph showing the results of calculating the difference in coupling coefficient representing the interference between 180° diffracted light and 90° diffracted light due to the difference in flatness between the first partial modified refractive index area and the second partial modified refractive index area. [Figure 13A] FIG. 4 is a schematic configuration diagram showing a modified example of the two-dimensional photonic crystal laser of the first embodiment. [Figure 13B] FIG. 4 is a schematic configuration diagram showing another modified example of the two-dimensional photonic crystal laser of the first embodiment. [Figure 14] FIG. 2 is a schematic configuration diagram showing a second embodiment of a two-dimensional photonic crystal laser according to the present invention. [Figure 15A] FIG. 11 is a plan view showing an example of a two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser according to the second embodiment. [Figure 15B] 15B is a plan view showing the position of the center of gravity of the modified refractive index area in the two-dimensional photonic crystal layer shown in FIG. 15A. [Figure 16A] FIG. 11 is a diagram showing an example of the propagation direction of a laser beam generated when current is injected into an active layer from a plurality of adjacent partial electrodes in the two-dimensional photonic crystal laser of the second embodiment. [Figure 16B] FIG. 11 is a diagram showing an example of how a laser beam moves and the traveling direction of the laser beam changes by changing the partial electrode into which a current is injected in the two-dimensional photonic crystal laser of the second embodiment. [Figure 17] FIG. 11 is a plan view showing the position of the center of gravity of a modified refractive index area in an example of a configuration in which the same deviation azimuth angle is set within the same deviation azimuth angle setting area having a plurality of lattice points adjacent in the x direction, and different deviation azimuth angles are set among different deviation azimuth angle setting areas, which is a modified example of the second embodiment. [Figure 18] FIG. 13 is a plan view showing the position of the center of gravity of a modified refractive index area in an example of a configuration in which the shift distance in the x direction is modulated by the modulation phase, which is a modified example of the second embodiment. [Figure 19] FIG. 13 is a plan view showing a two-dimensional photonic crystal layer in an example of a configuration in which the area of ​​the planar shape of a modified refractive index area is modulated by a modulation phase, which is a modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] 1 to 19, an embodiment of an emission direction variable two-dimensional photonic crystal laser (hereinafter simply referred to as "two-dimensional photonic crystal laser") according to the present invention will be described. Note that, for convenience, the terms "upper" and "lower" are used below when describing the relative positional relationship between the components of the two-dimensional photonic crystal laser, but these terms do not limit the orientation of the two-dimensional photonic crystal laser.

[0036] (a) Two-dimensional photonic crystal laser of the first embodiment (a-1) Configuration of the two-dimensional photonic crystal laser according to the first embodiment 1, the two-dimensional photonic crystal laser 1 of the first embodiment has a structure in which a laminate 10, which will be described later, is sandwiched between a first electrode 181 and a second electrode 182. In addition, a lens 19 is provided on the side of second electrode 182 opposite to laminate 10.

[0037] 1, laminate 10 is obtained by laminating substrate 11, first cladding layer 121, active layer 13, carrier block layer 14, two-dimensional photonic crystal layer 15, second cladding layer 122, and contact layer 16. First electrode 181 is provided on the upper surface of contact layer 16, and second electrode 182 is provided on the lower surface of substrate 11.

[0038] The active layer 13 emits light in a specific emission wavelength band when holes and electrons are injected into it. The active layer 13 may be, for example, a multiple-quantum well (MQW) in which a large number of thin films made of indium gallium arsenide (InGaAs) and thin films made of gallium arsenide (GaAs) are alternately stacked.

[0039] 2 and 3, the two-dimensional photonic crystal layer 15 is configured by a plate-shaped base material 151 having modified refractive index areas 152, the modified refractive index areas 152 having a refractive index different from that of the base material 151, arranged two-dimensionally and periodically within the base material 151. The modified refractive index areas 152 are typically configured by forming holes (refractive index ≈ 1) in the base material 151. Instead of forming holes, the modified refractive index areas 152 may be formed by embedding a member (modified refractive index member) having a refractive index different from that of the base material 151 in the base material 151.

[0040] In this embodiment, a large number of modified refractive index areas 152 are arranged in a square lattice pattern in the base material 151. In addition, in this embodiment, one modified refractive index area 152 is formed by combining two partial modified refractive index areas, a first partial modified refractive index area 1521 and a second partial modified refractive index area 1522. The first partial modified refractive index area 1521 is elliptical, and the second partial modified refractive index area 1522 is circular. The major axis of the ellipse of the first partial modified refractive index area 1521 is arranged so as to face a direction inclined at 45° with respect to a line connecting the nearest lattice points of the square lattice.

[0041] For convenience of drawing, only 70 modified refractive index areas 152 are depicted in FIG. 3, but in reality, many more modified refractive index areas 152 are provided in the two-dimensional photonic crystal layer 15 .

[0042] The configuration of the modified refractive index area 152 given here is an example, and each modified refractive index area 152 may be composed of only one hole or modified refractive index member, or may be composed of three or more holes or modified refractive index members. The shape of the modified refractive index area or each partial modified refractive index area is not limited to the above example. For example, as shown in FIG. 4, modified refractive index areas 152A composed of one hole having a planar shape of an equilateral triangle can be periodically arranged in a two-dimensional shape. By using a modified refractive index area having a noncircular planar shape such as an equilateral triangle, it is possible to suppress the loss of light due to interference in the two-dimensional photonic crystal. The modified refractive index area 152 composed of the first partial modified refractive index area 1521 and the second partial modified refractive index area 1522 shown in FIG. 2 and FIG. 3 also has a noncircular planar shape as a whole, so that the loss of light due to interference can be suppressed.

[0043] Typically, n-type semiconductors are used for the substrate 11 and the first cladding layer 121, and p-type semiconductors are used for the carrier block layer 14, the base material 151 of the two-dimensional photonic crystal layer 15, the second cladding layer 122, and the contact layer 16. As a result, in the laminate 10, a diode is formed in which a p-type semiconductor is arranged on the first electrode 181 side and an n-type semiconductor is arranged on the second electrode 182 side with the active layer 13 in between, and holes are injected from the first electrode 181 side and electrons are injected from the second electrode 182 side into the active layer 13. As a specific example, n-type GaAs can be used for the substrate 11, n-type aluminum gallium arsenide (AlGaAs) can be used for the first cladding layer 121, p-type AlGaAs can be used for both the carrier block layer 14 and the second cladding layer 122, and p-type GaAs can be used for the contact layer 16.

[0044] Conversely to the above example, it is also possible to use p-type semiconductors for the substrate 11 and the first cladding layer 121, and n-type semiconductors for the carrier block layer 14, the base material 151, the second cladding layer 122, and the contact layer 16. However, since n-type semiconductors are cheaper than p-type semiconductors, in order to reduce material costs, it is preferable to use an n-type semiconductor for the substrate 11, which needs to be thicker than the other layers, as in the above example.

[0045] Furthermore, the positions of active layer 13 and two-dimensional photonic crystal layer 15 may be reversed from those shown in Fig. 1. However, since each layer is fabricated in order on substrate 11 during the manufacture of two-dimensional photonic crystal laser 1, it is preferable to provide active layer 13 closer to substrate 11 (the side fabricated first) than two-dimensional photonic crystal layer 15 having holes (modified refractive index regions) as shown in Fig. 1, because this allows active layer 13 to be fabricated precisely without being affected by unevenness due to the presence of holes.

[0046] It is desirable to set the thickness of each layer constituting laminate 10 so that the combined thickness L2 of each layer (substrate 11 and first cladding layer 121) located closer to second electrode 182 than active layer 13 is sufficiently larger than the combined thickness L1 of each layer (carrier block layer 14, two-dimensional photonic crystal layer 15, second cladding layer 122, contact layer 16) located closer to first electrode 181 than active layer 13. The reason for this will be described later together with the explanation of the operation of two-dimensional photonic crystal laser 1.

[0047] As shown in Figs. 5A and 5B, the first electrode 181 is divided into a number of partial electrodes 1811 made of a conductor. The partial electrodes 1811 are arranged in a line in the example of Fig. 5A, and are arranged to be distributed two-dimensionally in the example of Fig. 5B. The planar shape of the partial electrodes 1811 is rectangular in the example of Fig. 5A and square in the example of Fig. 5B, but is not limited to these shapes. Each partial electrode 1811 is connected to one electrode (positive electrode when the contact layer 16 is made of a p-type semiconductor) of a DC power supply 92 via a switch 91 provided for each partial electrode 1811. For example, a field effect transistor can be used as the switch 91. Note that the wiring including the switch 91 and the DC power supply 92 are not components of the two-dimensional photonic crystal laser 1.

[0048] The distance between partial electrodes 1811 will be described later together with the explanation of the operation of two-dimensional photonic crystal laser 1.

[0049] In reality, the partial electrodes 1811 are provided in greater numbers than those shown in Figures 5A and 5B. For example, in the example shown in Figure 5A, several hundred partial electrodes 1811 can be arranged in each of the vertical and horizontal directions of the figure, and in the example shown in Figure 5B, several hundred partial electrodes 1811 can be arranged in each of the vertical and horizontal directions of the figure.

[0050] A reflective layer (reflecting portion) 17 made of an electrically insulating material that reflects a laser beam is provided on the upper surface of contact layer 16 between the partial electrodes 1811 and on the end of the upper surface, which is a portion where partial electrodes 1811 are not provided. The partial electrodes 1811 also have the role of reflecting the laser beam. The reflective layer 17 is intended to increase the light emission efficiency by reflecting the laser beam emitted from the two-dimensional photonic crystal layer 15 toward the first electrode 181 and causing it to exit from window portion 1822 of second electrode 182.

[0051] 2, the second electrode 182 has a frame-shaped portion 1821 made of a conductor and a window portion 1822 which is a space inside the frame-shaped portion 1821. The window portion 1822 is disposed opposite to a region that envelops the multiple partial electrodes 1811 of the first electrode 181. The second electrode 182 is connected to the other electrode of the DC power supply 92 (the negative electrode when the substrate 11 is made of an n-type semiconductor).

[0052] In this embodiment, lens 19 is a plano-convex lens having one convex surface and the other flat surface. Instead of a plano-convex lens, a lens having both convex surfaces may be used. Alternatively, a concave lens may be used as lens 19. Lens 19 is located at a distance L from two-dimensional photonic crystal layer 15 that is 0.5 to 2 times the focal length f of lens 19. LP It is preferable that the lens 19 and the laser beam source 14 are spaced apart from each other by a distance equal to the focal length f of the lens 19, and it is more preferable that the lens 19 and the laser beam source 14 are spaced apart by a distance equal to the focal length f of the lens 19. This can prevent the diameter of the laser beam that has passed through the lens 19 from expanding.

[0053] Furthermore, instead of the lens 19 exemplified above, a lens or prism (in this application, prisms are also included in the lens) in which either or both of the surface curvature and focal length are variable by electrical control, such as an electrowetting lens or a liquid crystal lens, may be used. In this case, a control unit is used that performs electrical control to change the surface curvature and / or focal length of the lens.

[0054] (a-2) Operation of the two-dimensional photonic crystal laser of the first embodiment The operation of the two-dimensional photonic crystal laser 1 of the first embodiment will be described with reference to FIGS.

[0055] When using this two-dimensional photonic crystal laser 1, of the switches 91 provided for each partial electrode 1811, one or more switches 91A connected to one or more adjacent partial electrodes 1811 (the one or more adjacent partial electrodes 1811 are referred to as a "partial electrode group 1811A", and the region in which the partial electrode group 1811A exists is referred to as a "current supply region 21". See FIG. 6A) are turned ON. In the example shown in FIG. 6A, the switches 91 of the four partial electrodes 1811 included in the partial electrode group 1811A are turned ON, but this number is not limited.

[0056] As a result, a current flows between one or more partial electrodes 1811 constituting the partial electrode group 1811A and the second electrode 182, and holes are supplied from each partial electrode 1811 and electrons are supplied from the second electrode 182 into the laminate 10. When a current flows from the partial electrode group 1811A, the current flows so as to slightly expand in a direction parallel to the active layer 13 as it flows from each partial electrode 1811 toward the second electrode 182. Therefore, when the distance between adjacent partial electrodes 1811 is smaller than a certain threshold value, a partial current injection region 221, which is a region where a current is injected from each partial electrode 1811 to the active layer 13, overlaps with a part of the partial current injection region 221 of the current injected from the adjacent partial electrode 1811. As a result, an integrated current injection region 22 is formed in the active layer 13 (FIG. 6A).

[0057] In the active layer 13, light having a predetermined wavelength range determined by the material of the active layer 13 is generated in the current injection region 22. Of this light, light having a wavelength corresponding to the period of the modified refractive index regions 152 in the two-dimensional photonic crystal layer 15 is amplified in a region (light amplification region) of the two-dimensional photonic crystal layer 15 corresponding to the current injection region 22, and lasing occurs. Then, the laser beam LB is emitted in a direction perpendicular to the two-dimensional photonic crystal layer 15, passes through the window portion 1822 of the second electrode 182, and enters the lens 19 (FIG. 7A). The laser beam LB is refracted in a direction according to the position at which it enters the lens 19, and is emitted to the outside of the two-dimensional photonic crystal laser 1 in a direction tilted from the direction perpendicular to the two-dimensional photonic crystal layer 15.

[0058] The direction of the laser beam LB emitted outside the two-dimensional photonic crystal laser 1 changes as follows by changing the partial electrode 1811 into which a current is injected. For example, as shown in FIG. 6B, among the four partial electrodes 1811 constituting the partial electrode group 1811A shown in FIG. 6A, the switch 91 of the leftmost partial electrode 1811 in the same figure is turned OFF, and the switch 91 of the partial electrode 1811 adjacent to the right, which had the switch 91 turned OFF in FIG. 6A, is newly turned ON. As a result, the current supply region 21 moves to the right by the amount of one partial electrode 1811, and accordingly, the current injection region 22 and the light amplification region in the active layer 13 also move to the right. Then, the entry position of the laser beam LB emitted from the two-dimensional photonic crystal layer 15 into the lens 19 also moves to the right (FIG. 7B). As a result, the laser beam LB is refracted in a direction different from that in FIG. 7A according to the difference in the entry position, and is emitted to the outside of the two-dimensional photonic crystal laser 1 in a different tilt direction.

[0059] As described above, by changing the partial electrodes 1811 included in the partial electrode group 1811A to move the current injection region 22, the inclination direction of the laser beam LB emitted from the lens 19 to the outside of the two-dimensional photonic crystal laser 1 changes, so that the laser beam LB can be scanned as shown in Fig. 8. At that time, the laser beam LB passes through the window portion 1822 of the second electrode 182 before entering the lens 19, so that the laser beam LB can be emitted without being attenuated by the second electrode 182.

[0060] FIG. 8 shows the laser beam LB moving one-dimensionally, but if the partial electrodes 1811 are arranged two-dimensionally as shown in FIG. 5B, the laser beam LB can be moved two-dimensionally.

[0061] As described above, when a lens whose surface curvature and / or focal length are variable by electrical control or the like is used, the laser beam LB can be scanned by electrically switching the partial electrodes 1811 included in the partial electrode group 1811A and changing the surface curvature and / or focal length of the lens. In general, the response speed when electrically switching the partial electrodes 1811 included in the partial electrode group 1811A is faster than the response speed when changing the surface curvature and focal length of the lens. In consideration of this point, for example, the partial electrodes 1811 arranged one-dimensionally are electrically switched to the partial electrodes 1811 included in the partial electrode group 1811A to repeatedly scan the laser beam LB in one direction, and the surface curvature and / or focal length of the lens are changed to scan the laser beam LB in a direction different from the one direction (for example, a direction perpendicular to the one direction), thereby scanning the laser beam LB two-dimensionally.

[0062] 6A and 6B, a case where the interval between adjacent partial electrodes 1811 is smaller than a certain threshold has been described, but when the interval between adjacent partial electrodes 1811 is larger than a certain threshold, the partial current injection regions 221 of the current injected from each partial electrode 1811 do not overlap with each other, and a plurality of divided current injection regions 22 are formed in the active layer 13 (FIG. 9). When divided current injection regions 22 are formed in this way, laser oscillation with low coherence (incoherent) occurs in the two-dimensional photonic crystal layer 15. In contrast, as shown in FIGS. 6A and 6B, by setting the interval between adjacent partial electrodes 1811 so that a single current injection region 22 is formed, a laser beam with high coherence (coherent) can be obtained.

[0063] The interval between the partial electrodes 1811 can be appropriately determined by performing a preliminary experiment or a simulation. As an example, a simulation was performed as follows under the conditions shown in FIG. 10A. In this simulation, the interval (gap) between the partial electrodes 1811 is w p In this case, at a position of a depth (distance in a direction perpendicular to the active layer 13) d sufficiently smaller than the distance from one partial electrode 1811 to the second electrode 182, a ratio of a current density i1 at a position B1 parallel to the active layer 13 and at a distance w away from the position B0 on ​​the opposite side of the partial electrode 1811 to a current density i0 at a position B0 intersecting with a perpendicular line h from the end of the partial electrode 1811 was obtained as i1 / i0. Specifically, the distance between the partial electrode 1811 and the second electrode 182 was set to (154+d) μm, d was within a range of 3.5 to 12.5 μm, and w was within a range of 0 to 65 μm. The width of the partial electrode 1811 was set to 30 μm, but this value has little effect on the calculation results.

[0064] The calculation results are shown in FIG. 10B. Regardless of the value of the distance d, the current density ratio i1 / i0 decreases as w increases, that is, as the distance from the end of the partial electrode 1811 increases. When this i1 / i0 reaches a certain value (1 / e 2 The range over which the current spreads is defined as the range greater than i1 / i0=1 / e for each distance d.2 The value of the distance w when e The results are shown in Figure 10C. The data obtained was approximated by a linear function, w e =3.819d+14.309.

[0065] Using the results of this calculation, when the active layer 13 is located at a depth d from the partial electrodes 1811, the distance w between the partial electrodes 1811 is p 2w e As a result, at the depth position of the active layer 13, the partial current injection regions 221 formed by the two partial electrodes 1811 are spaced apart from each other by a distance w e Since the current injection regions 221 extend beyond the upper limit, the partial current injection regions 221 overlap each other. Therefore, an integrated current injection region 22 can be formed, and a coherent laser beam can be obtained.

[0066] The smaller the size of each partial electrode 1811, the more precisely the position of the current injection region 22 can be set, and the more precisely the tilt direction of the laser beam can be controlled. For example, when the partial electrodes 1811 are arranged one-dimensionally as shown in FIG. 5A, the size of each partial electrode 1811 is set so that the current injection region 22 includes 10 to 50 partial electrodes 1811, and the position of the current injection region 22 moves by 2 to 10% of the area of ​​the current injection region 22 with one ON / OFF operation of the switch 91. Similarly, when the partial electrodes 1811 are arranged two-dimensionally as shown in FIG. 5B, the size of each partial electrode 1811 can be set so that 10 to 50 partial electrodes 1811 are arranged per side of the rectangular current injection region 22.

[0067] The size of current injection region 22 and the number of switches 91 to be turned on simultaneously, which determines the size of current injection region 22, are determined so as to obtain the required optical output depending on the application of two-dimensional photonic crystal laser 1. For example, when used for sensing applications such as LiDAR (Laser Imaging Detection and Ranging), an optical output of 1 W to several tens of W is required for pulsed light, and accordingly, the size of current injection region 22 is preferably within the range of a rectangle (including a square) with one side measuring 10 μm to 500 μm. When used for applications such as laser processing, an optical output of the order of 100 W to 1,000 W is required, and accordingly, the size of current injection region 22 is preferably within the range of a rectangle with one side measuring 1 mm to 1 cm.

[0068] (a-3) Design of two-dimensional photonic crystal layers to adjust optical output In the two-dimensional photonic crystal laser 1, the size of the current injection region 22 and other factors are designed so as to obtain an optical output suited to the application. One of the targets of such design is the configuration of the two-dimensional photonic crystal layer. An example of such a design will be described below.

[0069] It has been known that in a two-dimensional photonic crystal laser, the intensity of light in the two-dimensional photonic crystal layer is increased by increasing the interference of light caused by the diffraction of light propagating in the two-dimensional photonic crystal layer by the modified refractive index region, while the output of light emitted to the outside of the two-dimensional photonic crystal may be decreased if the interference is too strong, since the light is easily trapped in the two-dimensional photonic crystal. Therefore, the two-dimensional photonic crystal laser described in Patent Document 4 uses a two-dimensional photonic crystal layer in which one modified refractive index region, which is made of two holes or a member having a refractive index different from that of the base material, that is, a main modified refractive index region (corresponding to the first partial modified refractive index region 1521 in this embodiment) and a sub modified refractive index region (corresponding to the second partial modified refractive index region 1522 in this embodiment), is periodically arranged in a two-dimensional shape. In this two-dimensional photonic crystal laser, the positions of the main modified refractive index region and the sub modified refractive index region are set so that the interference light between the diffracted light diffracted in a 180° direction by the main modified refractive index region and the diffracted light diffracted in a 180° direction by the sub modified refractive index region, among the light propagating within the two-dimensional photonic crystal layer, is strengthened or weakened according to the purpose.

[0070] In this specification, the two-dimensional photonic crystal layer is designed taking into consideration the interference between the diffracted light (180° diffracted light) diffracted in the 180° direction by two partial modified refractive index areas (first partial modified refractive index area 1521 and second partial modified refractive index area 1522) and the diffracted light (90° diffracted light) diffracted in the 90° direction. Specifically, as shown in Fig. 11, one of the two orthogonal directions in which the lattice points of the square lattice are most adjacently arranged is the x direction, and the other is the y direction, and the distance d x , d y , the ratio f1 / f2 of the filling rates f1 and f2 of the two partial modified refractive index areas (the ratio of the volume of each partial modified refractive index area to the entire two-dimensional photonic crystal layer 15), and the flattening rates c1 and c2 of the two partial modified refractive index areas (the length in the longest direction in the planar shape of the partial modified refractive index area is L L , the length perpendicular to that direction is L s Then, c = 1-(L s / L LBy appropriately changing these parameters, the diffraction efficiency |κ of the 180° diffracted light in each of the two partial modified refractive index areas can be set. 180 | and the diffraction efficiency of 90° diffracted light |-κ 90 | changes, and accordingly, the strength of the interference between the 180° diffracted light and the 90° diffracted light by the two partial modified refractive index areas changes, so the intensity of the laser beam emitted to the outside of the two-dimensional photonic crystal laser also changes. 180 and -κ 90 is a parameter that represents the intensity of diffracted light, called the coupling coefficient, and can take either a positive or negative value. 180 and -κ 90 The absolute value of the difference between |κ 180 +κ 90 As | approaches 0, the intensity of the interference light between the 180° diffracted light and the 90° diffracted light becomes weaker, thereby suppressing the effect of confining the light within the two-dimensional photonic crystal layer.

[0071] In order to increase the intensity of the laser beam emitted from a two-dimensional photonic crystal laser, the difference in the coupling coefficients |κ 180 -(-κ 90 )|=|κ 180 +κ 90 It is preferable that | is close to 0. Therefore, with respect to the two-dimensional photonic crystal layer 15 shown in FIG. 11, (a) the distance d x (d x =d y (b) the ratio of filling rates f1 / f2, and (c) the difference in flatness c1-c2 are different. 180 +κ 90 In each calculation, the first partial modified refractive index area 1521 was a perfect circle (c1=0) or an ellipse (c1≠0) having a major axis in a direction inclined at 45° to the x direction, and the second partial modified refractive index area 1522 was a perfect circle (c2=0). xwas set to 0.262a in (b) and (c), f1 / f2 was set to 1.33 in (a) and (c), and c1 was changed in each calculation. Note that, when the shape of the modified refractive index area does not have rotational symmetry as shown in FIG. 11, the two-dimensional coupling coefficients representing the reflection (90° diffraction) with respect to the straight line y=-x and the reflection (90° diffraction) with respect to the straight line y=x may take different values. In such a case, at least one of the two-dimensional coupling coefficients and κ 180 Difference of |κ 180 -(-κ 90 )|=|κ 180 +κ 90 It is desirable that | is close to 0, and both two-dimensional coupling coefficients are κ 180 It is more desirable that the difference between the ray and the reflection be close to 0. In the calculation, the reflection (90° diffraction) on the line y=x is expressed as k 90 It was decided.

[0072] The calculation results are shown in FIG. 12A for (a), FIG. 12B for (b), and FIG. 12C for (c). x (=d y ) is in the range of 0.258a to 0.266a and c1 is in the range of 0.50 to 0.60, |κ 180 +κ 90 | is 100cm -1 In (b), by setting c1 within a certain range (for example, when f1 / f2=1.5, c1 is set within the range of 0.55 to 0.65) in the entire range of f1 / f2 (1.17 to 1.67) in which the calculation was performed, |κ 180 +κ 90 | is 100cm -1 In (c), by setting c1 within a certain range (for example, when c2=0, c1 is set within the range of 0.50 to 0.60), |κ 180 +κ 90 | is 100cm -1 It is possible to suppress it to the value below. By performing calculations like the above example, the distance, filling rate, and flattening rate of the first partial modified refractive index area 1521 and the second partial modified refractive index area 1522 can be designed.

[0073] (a-4) Modification of the two-dimensional photonic crystal laser of the first embodiment A modification of the two-dimensional photonic crystal laser of the first embodiment will be described with reference to FIGS. 13A and 13B.

[0074] The two-dimensional photonic crystal laser 1A shown in FIG. 13A has a laminate 10A instead of the laminate 10 in the above-mentioned two-dimensional photonic crystal laser 1. In the laminate 10A, a lens 19A is formed at a position facing a window portion 1822 on the surface on the second electrode 182 side. No lens is provided on the opposite side of the second electrode 182. The lens 19A is obtained by processing the surface of the substrate 11A into a Fresnel lens shape. The Fresnel lens is obtained by dividing an ordinary lens into concentric regions, and while maintaining the shape of the curved surface on one surface (the surface of the substrate 11A in this modification), thinning the thickness of the region between the concentric circles to a predetermined value or less to give the surface a saw-tooth shape. The configuration of the two-dimensional photonic crystal laser 1A other than the points described above is the same as that of the above-mentioned two-dimensional photonic crystal laser 1.

[0075] In the two-dimensional photonic crystal laser 1B shown in FIG. 13B, a laminate 10B is provided instead of the laminate 10 in the two-dimensional photonic crystal laser 1. A lens 19B is formed at a position facing the window portion 1822 on the surface of the second electrode 182 side of the laminate 10B. No lens is provided on the opposite side of the second electrode 182. The lens 19B is a lens called a metalens, which is provided with a lens function by processing the surface of the substrate 11B with an accuracy equal to or less than the wavelength of the laser beam and appropriately forming a microstructure (metasurface) capable of controlling the phase of transmitted light within the surface. The metalens can be considered to be almost flat, and can be made sufficiently thin. The other configurations of the two-dimensional photonic crystal laser 1B are the same as those of the two-dimensional photonic crystal laser 1 described above.

[0076] According to the two-dimensional photonic crystal lasers 1A and 1B of the present modified examples, the size of the two-dimensional photonic crystal laser can be made smaller than when lens 19 separate from laminate 10 is provided.

[0077] In the above-mentioned two-dimensional photonic crystal laser 1, reflection layers (reflectors) 17 for reflecting a laser beam are provided between the partial electrodes 1811 and at the ends of the upper surface of contact layer 16. Instead, a distributed Bragg reflector made of a conductive semiconductor material may be provided between two-dimensional photonic crystal layer 15 and partial electrode 1811. The positional relationship between the distributed Bragg reflector and second cladding layer 122 and contact layer 16 is not particularly important. This allows the laser beam emitted from two-dimensional photonic crystal layer 15 to the first electrode 181 side to be reflected by the distributed Bragg reflector and emitted from window portion 1822 of second electrode 182, thereby improving the light emission efficiency. The distributed Bragg reflector may be formed of a periodic structure in which layers made of doped GaAs and layers made of doped AlAs are alternately stacked, for example.

[0078] In addition to the above, those skilled in the art can further modify the two-dimensional photonic crystal laser of the first embodiment and its modifications within the scope of the present invention.

[0079] (b) Two-dimensional photonic crystal laser according to the second embodiment (b-1) Configuration of the two-dimensional photonic crystal laser according to the second embodiment 14, the two-dimensional photonic crystal laser 2 of the second embodiment differs from the two-dimensional photonic crystal laser 1 of the first embodiment in that it includes a laminate 30 including a two-dimensional photonic crystal layer 35 having a different configuration from the two-dimensional photonic crystal layer 15 in the two-dimensional photonic crystal laser 1 of the first embodiment, and in that it does not include a lens 19. Apart from these two points, the two-dimensional photonic crystal laser 2 of the second embodiment has a common configuration with the two-dimensional photonic crystal laser 1 of the first embodiment. Therefore, a description of the common configuration will be omitted, and the configuration of the two-dimensional photonic crystal layer 35 will be described below.

[0080] As shown in Fig. 15A, the two-dimensional photonic crystal layer 35 has modified refractive index areas 352 arranged in a plate-shaped base material 351 as follows. In the example shown in Fig. 15A, the planar shape of the modified refractive index area 352 is composed of one equilateral triangle, but the shape of the modified refractive index area 352 in the second embodiment is not limited to this example. In Fig. 15A, the modified refractive index area 352 actually provided in the two-dimensional photonic crystal layer 35 is shown by a solid line, a square lattice, which is a basic two-dimensional lattice, is shown by a dashed line, and a state in which the center of gravity of the modified refractive index area 352V is virtually arranged at the lattice point of the square lattice is shown by a dashed line. Moreover, Fig. 15B shows the square lattice (dotted line) and the position of the center of gravity (black circle) of the actual modified refractive index area 352.

[0081] In this two-dimensional photonic crystal layer 35, the distance (magnitude of positional shift s) between the lattice point and the center of gravity of the actual modified refractive index area 352 is the same for all lattice points, and the direction of the shift is modulated as follows. If the lattice constant of a square lattice is a, the position vector r↑ of each lattice point is expressed by an integer m in the orthogonal coordinate system. x , m y Using r↑=(m x a, m y a). The x direction is the direction of the reference line, the design value of the inclination angle of the laser beam is θ, and the azimuth angle from the reference line is φ. In this case, the wave vector k↑ is k↑=(π / a, π / a), and the reciprocal lattice vector G'=(g' x , g' y )teeth

number

number

[0082] Therefore, in the two-dimensional photonic crystal laser 2 of the second embodiment, the position in the two-dimensional photonic crystal layer 35 (position vector r↑=(m x a, m y For each of a), the deviation azimuth angle Ψ is set so that the value of the inclination angle θ in equation (3) is different. For example, as shown in FIG. 15B, the difference ΔΨ in the deviation azimuth angle Ψ between the modified refractive index areas 352 adjacent to each other in the x direction is x The offset azimuth angle Ψ at each position is set so that increases by δ in the x direction. A plurality of partial electrodes 1811 are provided so as to be aligned in the x direction.

[0083] (b-2) Operation of the two-dimensional photonic crystal laser according to the second embodiment When using the two-dimensional photonic crystal laser 2 of the second embodiment, as in the first embodiment, by turning on one or more of the switches 91A of the partial electrodes 1811 constituting the partial electrode group 1811A among the switches 91 provided for each partial electrode 1811, a current is passed between the one or more partial electrodes 1811 and the second electrode 182, and a current is injected into the current injection region 22 that is a part of the active layer 13. As a result, in the active layer 13, light having a predetermined wavelength range is generated in the current injection region 22, and among this light, light having a wavelength corresponding to the period of the modified refractive index regions 152 in the two-dimensional photonic crystal layer 15 is amplified in a region (light amplification region) of the two-dimensional photonic crystal layer 35 corresponding to the current injection region 22, and laser oscillation occurs. The laser beam LB is emitted to the outside of the two-dimensional photonic crystal laser 2 in a direction inclined by an inclination angle corresponding to the angle θ that defines the deviation azimuth angle Ψ in the light amplification region of the two-dimensional photonic crystal layer 35 (FIG. 16A). In the two-dimensional photonic crystal layer 35 of the example shown in Figures 15A and 15B, the angle θ that defines the misalignment azimuth angle Ψ varies depending on the position within one optical amplification region, so the inclination angle of the laser beam LB is approximately the average value of the angle θ within the optical amplification region.

[0084] When the partial electrode 1811 into which current is injected is changed, the position of the current injection region 22 moves, and accordingly the region in which light is amplified in the two-dimensional photonic crystal layer 35 also moves. This changes the range of values ​​of the misalignment azimuth angle Ψ and the angle θ that defines it in the light amplification region, and therefore the inclination angle of the laser beam LB also changes (FIG. 16B). This changes the inclination angle of the laser beam LB emitted to the outside of the two-dimensional photonic crystal laser 2, making it possible to scan the laser beam LB. Furthermore, when the laser beam LB is emitted to the outside of the two-dimensional photonic crystal laser 2, it passes through the window portion 1822 of the second electrode 182. Therefore, the laser beam LB can be emitted without being attenuated by the second electrode 182.

[0085] (b-3) Modification of the two-dimensional photonic crystal laser of the second embodiment A modified example of the second embodiment will be described. For example, in the example shown in Figures 15A and 15B, the angle θ defining the misalignment azimuth Ψ is set to a different value between all lattice points adjacent in the x direction, but as shown in Figure 17, the two-dimensional photonic crystal layer 35 may be divided into misalignment azimuth setting regions 231, 232, 233... each having a plurality of lattice points in the x direction, and the angle θ may be set to the same value within the same misalignment azimuth setting region 231, 232, 233, while the angle θ may be set to different values ​​between different misalignment azimuth setting regions 231, 232, 233.

[0086] In the example shown in Figures 15A and 15B, a square lattice is used as the basic two-dimensional lattice, but other two-dimensional lattices such as a rectangular lattice or a triangular lattice may be used as the basic two-dimensional lattice. For example, when a rectangular lattice with lattice constants a1 and a2 is used as the basic two-dimensional lattice, the reciprocal lattice vector G' = (g' x , g' y )teeth

number

number

[0087] In addition, when the basic two-dimensional lattice is a triangular lattice with lattice constant a, the position vector r↑ of the lattice point is expressed as r↑=(m1a+(1 / 2)m2a, (3 1 / 2 / 2)m2a), and the reciprocal lattice vector G' = (g' x , g' y )teeth

number

number

number

number

[0088] In the example shown in FIG. 15B, the distance s between the lattice point and the center of gravity of the actual modified refractive index area 352 is the same at all lattice points, and the shift direction (shift azimuth angle) is modulated. However, as shown in FIG. 18, the shift direction is the same at all lattice points (x direction), and the distance s is expressed as s=s max cosΨ. In this case, |s| is 0 and the maximum value s max As in the example shown in FIG. 15B, the modulation phase Ψ can be set to different values ​​by setting the angle θ to different values ​​depending on the lattice point. This allows the angle of the emitted laser beam to be changed by moving the position of the current injection region into the active layer, thereby moving the position of the optical amplification region, thereby scanning the laser beam.

[0089] Alternatively, as shown in FIG. 19, the center of gravity of the modified refractive index area 352 may be located at the lattice points of a basic two-dimensional lattice, and the area S of the planar shape of each modified refractive index area 352 may be determined to be S=S0+S'cosΨ by the modulation phase Ψ. In this case, the area S is modulated between the minimum value (S0-S') and the maximum value (S0+S'). As in the example shown in FIG. 15B, the modulation phase Ψ can be set to different values ​​by setting the angle θ to different values ​​depending on the lattice point. This allows the position of the current injection region into the active layer to be moved, thereby moving the position of the optical amplification region, thereby scanning the emitted laser beam.

[0090] As described in Patent Document 3, when using the modulation phase Ψ(x, y) obtained from the reciprocal lattice vector G'(x, y)↑ that depends on the position in the two-dimensional photonic crystal layer, the modulation phase Ψ(x, y) can be obtained specifically as follows. For example, when the basic two-dimensional lattice is a square lattice with lattice constant a, each component g' of the reciprocal lattice vector G'(x, y)↑ can be obtained as follows: x (x) and g' y (y) is

number

number

[0091] Using the modulation phase Ψ(x, y) thus obtained, at each lattice point in the two-dimensional photonic crystal, the direction and magnitude of the shift in the position of the modified refractive index area from the lattice point, or the area of ​​the modified refractive index area, etc., can be modulated according to the position (x, y) of the lattice point, in a manner similar to the examples shown in Figures 15 to 19.

[0092] In particular, by applying the example shown in Fig. 17, different tilt angles θ(x, y) and / or azimuth angles φ(x, y) are set for each of the shift azimuth angle setting regions 231, 232, 233..., and the same tilt angle θ(x, y) and azimuth angle φ(x, y) are set within the same shift azimuth angle setting region 231, 232, 233.... In this way, by injecting a current so that one of the shift azimuth angle setting regions 231, 232, 233... becomes a light amplification region, a laser beam having the tilt angle θ(x, y) and azimuth angle φ(x, y) set in the shift azimuth angle setting region can be obtained. Note that, although the shift direction of the position of the modified refractive index region from the lattice point is modulated in Fig. 17, the same applies when modulating using other parameters such as the magnitude of the shift or the area of ​​the modified refractive index region.

[0093] Even when the basic two-dimensional lattice is another two-dimensional lattice such as a rectangular lattice or a triangular lattice, the modulation phase Ψ(x, y) can be obtained from the reciprocal lattice vector G'(x, y)↑, which depends on the position within the two-dimensional photonic crystal layer, by using a similar calculation.

[0094] In two-dimensional photonic crystal laser 2 , similarly to two-dimensional photonic crystal laser 1 , a distributed Bragg reflector may be provided between two-dimensional photonic crystal layer 15 and partial electrode 1811 instead of reflecting layer 17 .

[0095] It will be understood by those skilled in the art that further modifications can be made by combining the modifications of the second embodiment described above.

[0096] The present invention is not limited to the above first embodiment, second embodiment, and modified examples, and further modifications are possible. [Explanation of symbols]

[0097] 1, 1A, 1B, 2...2D Photonic Crystal Lasers 10, 30...Laminate 11, 11A, 11B...Board 121…First cladding layer 122…Second cladding layer 13…Active layer 14…Carrier block layer 15, 35...2D photonic crystal layer 151, 351...Base material 152, 152A, 352...Modified refractive index areas 1521...First partial modified refractive index region 1522…Second partial modified refractive index region 16…Contact layer 181...1st electrode 1811…Partial electrode 1811A…Partial electrode group 182…Second electrode 1821…Frame-shaped part 1822…Window section 19, 19A, 19B…Lens 21…Current supply area 22...Current injection region 221…Partial current injection region 231…Azimuth setting area 352V… Virtually arranged modified refractive index areas 91, 91A…Switch 92…DC power supply

Claims

1. A two-dimensional photonic crystal laser comprising a laminate sandwiched between a first electrode and a second electrode, the laminate having an active layer and a two-dimensional photonic crystal layer having modified refractive index areas, the modified refractive index of which is different from that of a plate-shaped base material, periodically arranged in a two-dimensional manner, The first electrode is divided into a plurality of partial electrodes, the second electrode is a frame-shaped electrode having a frame-shaped portion made of a conductor, and a window portion, which is a space inside the frame-shaped portion, is disposed opposite to a region that envelops the plurality of partial electrodes, a lens provided on a surface of the second electrode opposite to the laminate or on a surface of the laminate facing the second electrode so as to cover the window portion; A two-dimensional photonic crystal laser.

2. 2. The two-dimensional photonic crystal laser according to claim 1, wherein the lens is formed integrally with the laminate on a surface of the laminate facing the second electrode.

3. 3. The two-dimensional photonic crystal laser according to claim 1, wherein the spacing between adjacent partial electrodes is set so that a partial current injection region, which is a region in which current is injected into the active layer from each of the plurality of partial electrodes, overlaps with a portion of a partial current injection region in which current is injected into the active layer from a partial electrode adjacent to the partial electrode.

4. 4. The two-dimensional photonic crystal laser according to claim 1, wherein the lens is disposed at a distance of 0.5 to 2 times the focal length of the lens from the two-dimensional photonic crystal layer.

5. 5. The two-dimensional photonic crystal laser according to claim 1, wherein the lens is variable in either one or both of the surface curvature and the focal length.

6. The two-dimensional photonic crystal layer is The modified refractive index area has two partial modified refractive index areas, A coupling coefficient κ of 180° diffracted light in which light propagating within the two-dimensional photonic crystal layer is diffracted in a 180° direction by the modified refractive index area 180 and the coupling coefficient of the 90° diffracted light in the 90° direction -κ 90 The absolute value of the difference between |κ 180 +κ 90 | is 100cm -1 The shapes of the two partial modified refractive index areas are set as follows:

6. The two-dimensional photonic crystal laser according to claim 1, wherein the first and second photonic crystals are arranged in a first plane.

7. The two-dimensional photonic crystal laser according to any one of claims 1 to 6, further comprising a reflective portion between the plurality of partial electrodes, the reflective portion being made of an electrically insulating material and capable of reflecting a laser beam.

8. A two-dimensional photonic crystal laser comprising a laminate sandwiched between a first electrode and a second electrode, the laminate having an active layer and a two-dimensional photonic crystal layer having modified refractive index areas arranged two-dimensionally in a plate-like base material, the modified refractive index areas having a refractive index different from that of the base material, The first electrode is divided into a plurality of partial electrodes, the second electrode is a frame-shaped electrode having a frame-shaped portion made of a conductor, and a window portion, which is a space inside the frame-shaped portion, is disposed opposite to a region that envelops the plurality of partial electrodes, The two-dimensional photonic crystal layer has a wavelength λ L A resonance state of the wavelength λ is formed. L are arranged by modulating with a predetermined modulation phase Ψ at each lattice point of a basic two-dimensional lattice having a periodicity determined so as not to emit light of The modulation phase Ψ is a function of the wavelength λ L The wave vector of light k↑=(k x , k y ), the effective refractive index n eff , a predetermined angle θ, and an azimuth angle φ from a predetermined reference line of the basic two-dimensional lattice, x , g' y )=(k x ±|k↑|(sinθcosφ) / n eff , k y ±|k↑|(sinθsinφ) / n eff ) and the position vector r↑ of each lattice point, the angle θ is expressed as Ψ=r↑·G'↑, and the angle θ differs depending on the position in the two-dimensional photonic crystal layer. A two-dimensional photonic crystal laser.

9. The reciprocal lattice vector G'↑ is expressed by the inclination angle θ(x, y) and the azimuth angle φ(x, y) of the laser beam to be emitted from the position (x, y) in the two-dimensional photonic crystal layer, x (x)=sinθ(x, y)cosφ(x, y), and sinθ y Using (y) = sinθ(x, y) sinφ(x, y), the position function G'(x, y)↑ = (g' x (x), g' y (y))=(k x ±|k↑|sinθ x (x) / n eff , k y ±|k↑|sinθ y (y) / n eff ), The modulation phase Ψ is a function of the position [0010] …(1) 9. The two-dimensional photonic crystal laser according to claim 8, characterized in that it is defined as follows:

10. 10. The two-dimensional photonic crystal laser according to claim 8 or 9, characterized in that the spacing between adjacent partial electrodes is set so that a partial current injection region, which is a region in which current is injected into the active layer from each of the plurality of partial electrodes, overlaps with a portion of a partial current injection region in which current is injected into the active layer from a partial electrode adjacent to the partial electrode.

11. The two-dimensional photonic crystal laser according to any one of claims 8 to 10, further comprising a reflecting portion between the plurality of partial electrodes, the reflecting portion being made of an electrically insulating material and reflecting the laser beam.

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