Two-dimensional photonic crystal laser

Abstract

Provided is a two-dimensional photonic crystal laser capable of transmitting a laser light-based signal at a high S / N ratio. A two-dimensional photonic crystal laser (10) is provided with: an active layer (11); a two-dimensional photonic crystal layer (12) having a two-dimensional photonic crystal structure in which different refractive index sections (122), which are sites having a different refractive index from that of the base material, are periodically arranged in a two-dimensional manner in a plate-shaped base material (121) laminated on the active layer (11) directly or via another layer, and having a plurality of current injection regions (1201, 1202) having mutually different resonance frequencies; and a current injection unit (divided electrode (172)) that injects a signal current into each of the plurality of current injection regions (1201, 1202), the signal current having a ratio of current intensities of the plurality of current injection regions (1201, 1202) that varies over time.

Description

Technical Field

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

[0002] With the popularity of portable information terminals in recent years, the so-called "Internet of Things" in which various objects such as cars are connected to the Internet will continue to become popular in the future, and the frequency resources of the wireless bands used for communication may be exhausted. As one of the countermeasures, the use of lasers for wireless communication (called "free-space optical communication") is being studied. Such free-space optical communication is envisioned to be applied to, for example, communication between base stations of mobile phones, communication between the ground and satellites, or communication between satellites. In order to realize such free-space optical communication, a laser light source with a large output power and a small expansion angle of the emitted laser beam is required. As a candidate for such a laser light source, a two-dimensional photonic crystal laser can be listed (for example, refer to non-patent document 1).

[0003] A two-dimensional photonic crystal laser comprises an active layer and a two-dimensional photonic crystal layer, and a pair of electrodes sandwiching them. The active layer emits light in a specific wavelength band by injecting carriers (holes and electrons) from the electrode pair. The two-dimensional photonic crystal layer has a structure in which different refractive index portions, each with a different refractive index, are periodically arranged two-dimensionally on a plate-like base material. The different refractive index portions are formed by holes (air) formed in the base material or a member made of a different material from the base material. In such a two-dimensional photonic crystal laser, of the light generated by the active layer, only light of a predetermined resonant frequency, determined by the length of the period (period length) in which the different refractive index portions are arranged in the two-dimensional photonic crystal layer, the area ratio (volume ratio if the thickness direction is also considered), and the refractive index of the base material, resonates within the two-dimensional photonic crystal layer and oscillates, emitting laser light from the surface of the two-dimensional photonic crystal layer. Here, the resonant wavelength within the two-dimensional photonic crystal layer is determined by the period length, but even if the resonant wavelength is the same, the resonant frequency will also be different if the average refractive index of the two-dimensional photonic crystal layer as a whole is different. The volume of the different refractive index portion affects the average refractive index of the entire two-dimensional photonic crystal layer, and thus also affects the resonance frequency.

[0004] In non-patent document 1, as an initial experiment in free-space optical communication, a current obtained by superimposing a signal current with an amplitude of 0.1A on a DC bias current of 2.5A flowing between a pair of electrodes of a two-dimensional photonic crystal laser is described. The intensity of the laser light emitted from the two-dimensional photonic crystal laser is detected using a detector 1.1m away from the laser. This experiment confirmed that the intensity of the laser light was modulated corresponding to the amplitude modulation of the current. In other words, the amplitude-modulated current, which is an electrical signal, is converted by the two-dimensional photonic crystal laser into an intensity-modulated optical signal, which can be received by the detector as a receiver.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-243962

[0008] Patent Document 2: International Publication No. WO2017 / 150387

[0009] Non-patent literature

[0010] Non-Patent Literature 1: S. Ishimura et al., “Proposal and Demonstration of Free-Space Optical Communication Using Lens-Free Photonic-Crystal Surface-Emitting Laser,” Proceedings European Conference Optical Community (France), published by the European Physical Society, 2022, Th3A.7 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] In free-space optical communication, in order to achieve long-distance communication, it is required to use a laser with an optical output power of more than 1W, and in order to communicate large amounts of information, it is required to use a high modulation frequency of more than 1GHz. In the two-dimensional photonic crystal laser described in non-patent document 1, the optical output power can be made more than 1W, but if the modulation frequency is increased, it is difficult to increase the amplitude of the signal current input to the laser, and the conversion efficiency from the internal signal current of the laser to the signal light is also reduced. As a result, it is impossible to fully increase the modulation amplitude of the intensity of the laser, that is, the intensity of the optical signal received by the detector as a receiver. Therefore, the signal / noise ratio (S / N ratio) of the optical signal cannot be fully improved.

[0013] An object of the present invention is to provide a two-dimensional photonic crystal laser capable of transmitting a laser signal with a high S / N ratio.

[0014] Solutions for solving problems

[0015] The two-dimensional photonic crystal laser of the present invention, which has been developed to solve the above-mentioned problems, comprises:

[0016] a) active layer;

[0017] b) a two-dimensional photonic crystal layer having a two-dimensional photonic crystal structure in which portions having a refractive index different from that of the base material, i.e., different refractive index portions, are two-dimensionally periodically arranged within a plate-like base material stacked directly or via other layers on the active layer, and having a plurality of current injection regions having mutually different resonant frequencies; and

[0018] c) A current injection unit that injects a signal current into each of the plurality of current injection areas, wherein a ratio of current intensities between the plurality of current injection areas changes with time.

[0019] In the two-dimensional photonic crystal laser of the present invention, the two-dimensional photonic crystal layer is divided (not physically but virtually) into multiple current injection regions, so that the resonant frequency of each current injection region is different. As mentioned above, in a two-dimensional photonic crystal laser, the period length of the configuration of the different refractive index portion, the volume fraction of the different refractive index portion, the refractive index of the base material, etc. are generally determined. Therefore, by making the period length, volume fraction, refractive index of the base material, etc. of each of the multiple current injection regions different (further specific examples are described later), the resonant frequency in each current injection region becomes a different value. If the current injection portion injects a signal current into each of these multiple current injection regions, the signal current is introduced into the region of the active layer directly or across other layers opposite to these current injection regions, and each region of the active layer generates light of different intensities corresponding to the magnitude of the signal current. In the two-dimensional photonic crystal layer, light of different intensities is introduced from the active layer according to each current injection region. In the present invention, since the intensity ratio of the signal current between the current injection regions changes over time, the intensity ratio of the light between the current injection regions also changes over time.

[0020] In the present invention, the resonant frequencies of each current injection region are different from each other, but if light is introduced into multiple current injection regions at the same time, the current injection regions do not form different resonant states, but form a basic resonant state in the entire two-dimensional photonic crystal layer, and resonate at one resonant frequency. Hereinafter, the resonant frequency of the basic resonant state formed in the entire two-dimensional photonic crystal layer is referred to as the "full resonant frequency". The full resonant frequency is determined by the resonant frequency of each current injection region determined according to the period length, volume ratio, etc. as described above, and the magnitude of the current density injected according to each current injection region (corresponding to the intensity of the light introduced from the active layer). According to the magnitude of the current density (the intensity of light), the weighting of the contribution of the resonant frequency of each current injection region is different, so that the full resonant frequency becomes a value closer to the resonant frequency of the current injection region with a large current density than the current injection region with a small current density. For example, in a two-dimensional photonic crystal layer having two current injection regions, namely a first current injection region having a first resonant frequency and a second current injection region having a second resonant frequency, the greater the ratio of the current density of the current injected into the first current injection region to the current density of the current injected into the second current injection region, the closer the full resonant frequency is to the first resonant frequency, and the smaller the current density ratio is, the closer it is to the second resonant frequency.

[0021] In the present invention, a signal current that varies over time is injected into multiple current injection regions in a two-dimensional photonic crystal layer having such characteristics, each with a different magnitude. This imparts temporal variation to the overall resonant frequency. For example, if a current with a waveform having a peak corresponding to half a sine wave cycle is used as a signal representing "1," and a current of zero is used as a signal representing "0," then the signal current, which is a current of this waveform superimposed on a DC current of the same magnitude with different amplitudes for each current injection region, will have a different temporal variation in the magnitude of the current density in each current injection region, with half a sine wave cycle as one cycle. Consequently, the overall resonant frequency also varies over time. In this way, the laser light emitted from the two-dimensional photonic crystal laser of the present invention is imparted with temporal variation in the frequency of the light (note, this is not the frequency of the light intensity variation, but the frequency of the light as a wave).

[0022] The optical signal of a laser beam having such a time-varying frequency can be detected with a high S / N ratio using known methods such as the delayed self-homodyne method (compared to the case of non-patent document 1 in which the intensity of the light is modulated). The delayed self-homodyne method is a method in which a signal (in the present invention, an optical signal having the time-varying frequency of the light) is divided into two, one of which is delayed by a predetermined delay time, and then the two signals are mixed to extract the frequency difference component. This method is known as a method capable of high-speed frequency discrimination. Furthermore, in the present invention, the optical signal detection method is not limited to the delayed self-homodyne method, and other methods may also be used.

[0023] Typically, the resonant frequency of each current injection region can be set based on the period length of the two-dimensional lattice and / or the volume of the different refractive index portion on the basis of configuring the different refractive index portion into a two-dimensional lattice. In the two-dimensional lattice in which the different refractive index portion is configured, square lattice, triangular lattice, rectangular lattice, rhombic lattice, etc. can be used. The shorter the period length, the higher the resonant frequency. In addition, when the refractive index of the different refractive index portion is smaller than that of the mother material, the larger the volume, the higher the resonant frequency. When the refractive index of the different refractive index portion is larger than that of the mother material, the smaller the volume, the higher the resonant frequency. However, if the form of the two-dimensional lattice (square lattice, triangular lattice, etc.) is different in each current injection region, a basic resonant state cannot be formed in the overall structure of the two-dimensional photonic crystal layer. Therefore, a two-dimensional lattice of the same form is used in each current injection region.

[0024] Alternatively, the resonant frequency of each current injection region can be adjusted by forming the base material and / or the different refractive index portion from different materials for each current injection region, thereby setting the average refractive index of each region to a different value. In this case, it is easier to manufacture the base material by forming the base material from a different material for each current injection region, while making all the different refractive index portions into holes (of the same material).

[0025] Furthermore, by varying the DC current (the DC component of the signal current) injected into each current injection region as part of the signal current, the average refractive index of each current injection region can be varied, thereby also setting the resonant frequency of each current injection region. The larger the DC component of the signal current injected into the current injection region, the greater the time-averaged heat generation, thereby increasing the temperature of the current injection region. Therefore, the average refractive index of each current injection region can be adjusted based on the magnitude of the DC component of the signal current. The smaller the average refractive index, the higher the resonant frequency.

[0026] In the two-dimensional photonic crystal laser of the present invention, it is preferred that

[0027] Modulate the above signal current at a specified modulation frequency,

[0028] Furthermore, the difference between the maximum resonant frequency and the minimum resonant frequency among the resonant frequencies of the plurality of current injection regions is greater than the modulation frequency.

[0029] In the two-dimensional photonic crystal laser of the present invention, the following structure may also be adopted:

[0030] The signal current injected into two current injection areas among the plurality of current injection areas is a current obtained by superimposing a time-varying current on a direct current, the time-varying current having either a waveform in which the current value maintains a positive or negative value or a waveform in which the current value maintains zero according to each predetermined modulation cycle.

[0031] In the two current injection regions, the time-varying currents are in opposite phases (in other words, the other one is -1 times the phase of the other one).

[0032] By using this signal current, data represented by a binary value can be transmitted for each modulation cycle: a waveform maintaining a positive or negative current value of the time-varying current is set to "1," and a waveform maintaining a zero current value is set to "0." Furthermore, the DC current can have the same or different values ​​for each current injection region. By setting this DC current to a different value for each current injection region, the resonant frequency of each current injection region can be set as described above.

[0033] Alternatively, in the two-dimensional photonic crystal laser of the present invention, the following structure may also be adopted:

[0034] The signal current injected into one of the plurality of current injection regions is a current obtained by superimposing a time-varying current on a direct current having a first magnitude, the time-varying current having either a waveform in which the current value maintains a positive or negative value or a waveform in which the current value maintains zero according to each predetermined modulation period.

[0035] The signal current injected into another current injection region among the plurality of current injection regions is a direct current with a second magnitude.

[0036] In this case, data represented by a binary value, where a waveform maintaining a positive or negative current value of the time-varying current is set to "1" and a waveform maintaining a current value of zero is set to "0," may be transmitted for each modulation cycle. Furthermore, the first magnitude and the second magnitude related to the DC current may be the same or different. The resonant frequency of each current injection region may also be set based on these magnitudes.

[0037] Effects of the Invention

[0038] According to the present invention, a two-dimensional photonic crystal laser capable of transmitting a laser signal with a high S / N ratio can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a perspective view showing one embodiment of the two-dimensional photonic crystal laser of the present invention.

[0040] Figure 2It is a schematic plan view showing the structure of a two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser according to the present embodiment, and a partially enlarged view showing an enlarged square region indicated by a solid line in the schematic plan view.

[0041] Figure 3 This is a partially enlarged view showing another example of the structure of the two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser according to this embodiment.

[0042] Figure 4 This is a partially enlarged view showing still another different example of the structure of the two-dimensional photonic crystal layer in the two-dimensional photonic crystal laser according to this embodiment.

[0043] Figure 5 It is a perspective view showing a modified example of the shape of the electrodes in the two-dimensional photonic crystal laser according to the present embodiment.

[0044] Figure 6 This is a perspective view showing another modified example of the shape of the electrodes in the two-dimensional photonic crystal laser according to this embodiment.

[0045] Figure 7 This is a schematic diagram of the structure of an information transmission and reception system using the two-dimensional photonic crystal laser according to this embodiment.

[0046] Figure 8 This is a graph showing the results of simulations of temporal changes in the frequency of laser light obtained when a signal current obtained by superimposing a sinusoidal high-frequency current on a direct current is injected into the two-dimensional photonic crystal laser of this embodiment.

[0047] Figure 9 This is a graph showing the relationship between the modulation frequency of the high-frequency current and the amplitude of the frequency change of the laser light obtained by simulation when a signal current is injected in which a sinusoidal high-frequency current is superimposed on a direct current in the two-dimensional photonic crystal laser of this embodiment.

[0048] Figure 10 This is an optical microscope photograph of the two-dimensional photonic crystal laser produced in this embodiment, taken from the upper surface (output electrode) side.

[0049] Figure 11 This is a graph showing the results of measuring the temporal change in the frequency of laser light obtained when a signal current obtained by superimposing a sinusoidal high-frequency current on a direct current was injected into the two-dimensional photonic crystal laser fabricated in this embodiment.

[0050] Figure 12This is a graph showing the results of measuring the temporal variation in the amplitude of the intensity of laser light obtained when a signal current obtained by superimposing a sinusoidal high-frequency current on a direct current was injected into the two-dimensional photonic crystal laser fabricated in this embodiment.

[0051] Figure 13 This is a graph showing an example (Specific Example 1) of a signal current injected into the two-dimensional photonic crystal laser according to the present embodiment to provide information of “1” and “0”.

[0052] Figure 14 This is a graph showing the results of simulations of temporal changes in the intensity of laser light obtained in Specific Example 1.

[0053] Figure 15 This is a graph showing the results of simulations of temporal changes in the frequency of the laser light obtained in Specific Example 1.

[0054] Figure 16 This is a graph showing the results of obtaining a signal obtained by the delayed self-homodyne method in Specific Example 1 through simulation.

[0055] Figure 17 This is a graph showing another example (Specific Example 2) of the signal current injected into the two-dimensional photonic crystal laser of this embodiment to provide information of “1” and “0”.

[0056] Figure 18 This is a graph showing the results of simulations of temporal changes in the intensity of laser light obtained in Specific Example 2.

[0057] Figure 19 This is a graph showing the results of simulations of temporal changes in the frequency of the laser light obtained in Specific Example 2.

[0058] Figure 20 This is a graph showing the results of obtaining a signal obtained by the delayed self-homodyne method in Specific Example 2 through simulation.

[0059] Figure 21 This is a graph showing the results of simulations of the relationship between the modulation frequency and the amplitude of the temporal variation in the intensity of the laser light, obtained in the modified example of Specific Example 2 and the reference example.

[0060] Figure 22 This is a graph showing the results of measuring the relationship between the modulation frequency and the amplitude of the temporal change in the intensity of the laser light for the two-dimensional photonic crystal laser fabricated in this embodiment.

[0061] Figure 23This is a graph showing the results of simulations of the difference in the relationship between the modulation frequency and the amplitude of the temporal variation in laser intensity based on the ratio of the magnitudes of the DC currents injected into the two current injection regions, obtained in a modified example of Specific Example 2. DETAILED DESCRIPTION

[0062] use Figures 1 to 23 An embodiment of the two-dimensional photonic crystal laser of the present invention will be described.

[0063] (1) Configuration of the Two-Dimensional Photonic Crystal Laser of the Present Embodiment

[0064] like Figure 1 As shown, the two-dimensional photonic crystal laser 10 of this embodiment has a structure in which an emission-side electrode 171, a substrate 16, a first cladding layer 141, an active layer 11, a spacer layer 13, a two-dimensional photonic crystal layer 12, a second cladding layer 142, and a splitting electrode 172 are stacked in this order. However, the order of the active layer 11 and the two-dimensional photonic crystal layer 12 can also be reversed to the above order. In addition, Figure 1 In order to show the shape of the split electrode 172, the split electrode 172 is depicted at a position away from the second cladding layer 142, but in reality the split electrode 172 is in contact with the lower surface of the second cladding layer 142. Figure 1 In the figure, the emission-side electrode 171 is represented as the upper side, and the split electrode 172 is represented as the lower side. In the following description, the expressions "upper" and "lower" are also used for convenience, but the orientation of the two-dimensional photonic crystal laser 10 during use is not limited to these. The following describes the structure of each layer and electrode. First, the layer having the same structure as the existing two-dimensional photonic crystal laser is described. Then, the structure of the two-dimensional photonic crystal layer 12 and the two sets of electrodes (the emission-side electrode 171 and the split electrode 172) having the structure unique to the present invention is specifically described.

[0065] The active layer 11 emits light in a predetermined wavelength range by injecting charges into it due to the current flowing between the emission-side electrode 171 and the split electrode 172. The active layer 11 can be made of, for example, InGaAs / AlGaAs multiple quantum wells (emission wavelength: 935-945 nm).

[0066] The first cladding layer 141 and the second cladding layer 142 have the function of injecting charges from the emission-side electrode 171 and the splitting electrode 172, and have the function of suppressing the leakage of the in-plane guided light guided parallel to the two-dimensional photonic crystal layer 12 from the layer. In order to achieve the former function, for example, an n-type semiconductor (e.g., n-type Al 0.37 Ga 0.63 As), a p-type semiconductor (e.g., p-type Al0.37 Ga 0.63 As).

[0067] The spacer layer 13 is provided to allow holes injected from the split electrode 172 to pass through and be introduced into the active layer 11, and to inhibit electrons injected from the emission-side electrode 171 from passing through the active layer 11 (thereby, the electrons are combined with the holes closer to the emission-side electrode 171 than the active layer 11). The material of the spacer layer 13 can be, for example, p-type Al 0.45 Ga 0.55 As.

[0068] To maintain the overall mechanical strength of the two-dimensional photonic crystal laser 10 and to ensure that the distance between the emission-side electrode 171 and the active layer 11 is greater than the distance between the splitting electrode 172 and the active layer 11, the substrate 16 is sufficiently thick compared to the other layers. For the same reasons as for the first cladding layer 141, an n-type semiconductor is used as the material for the substrate 16.

[0069] The emission-side electrode 171 is an annular electrode made of a conductive material. As described later, the inner side of the annular ring of the emission-side electrode 171 functions as a window 1710 through which the laser beam oscillated by the two-dimensional photonic crystal layer 12 passes.

[0070] The split electrode 172 is formed of a conductive material and is an electrode formed by splitting a disk-shaped member having a diameter smaller than the outer diameter (diameter) of the ring of the emission-side electrode 171 into two. One of the two electrodes is referred to as the first split electrode 1721, and the other is referred to as the second split electrode 1722. The split electrode 172 functions as the above-mentioned current injection portion. In the present embodiment, the above-mentioned disk-shaped member is divided into two equal parts, but either the first split electrode 1721 or the second split electrode 1722 can be made larger than the other. In addition, in the present embodiment, a split electrode 172 divided into two is used, but a split electrode divided into three or more can also be used.

[0071] The two-dimensional photonic crystal layer 12 is as follows Figure 2 As shown in FIG. 1 , as will be described later, a different refractive index portion 122 having a different refractive index from a plate-like base material 121 is disposed thereon. The base material 121 is made of a p-type semiconductor (e.g., p-type GaAs), similar to the second cladding layer 142 and the spacer layer 13. Typically, the different refractive index portion 122 uses holes, but a member having a different refractive index from that of the base material 121 may be used instead of holes.

[0072] The two-dimensional photonic crystal layer 12 is provided with a first current injection region 1201 and a second current injection region 1202 that are virtually divided into two (not physically divided) in the in-plane direction.

[0073] The first current injection region 1201 and the second current injection region 1202 are respectively provided directly above the first split electrode 1721 and the second split electrode 1722, and are regions having substantially the same shape and size as the first split electrode 1721 and the second split electrode 1722. The current flowing between the first split electrode 1721 and the emission-side electrode 171 expands in the in-plane direction as it moves from the first split electrode 1721 toward the emission-side electrode 171. However, by making the substrate 16 sufficiently thicker than the second cladding layer 142, the current flowing in the two-dimensional photonic crystal layer 12 hardly expands beyond the in-plane range of the first split electrode 1721, but flows within the first current injection region 1201 (it should be noted that the current flowing in the first split electrode 1721 is substantially the same as the first split electrode 1721). Figure 1 In order to clearly indicate a thinner layer, substrate 16 is shown as having a thickness several times that of second cladding layer 142. However, in reality, substrate 16 has a thickness ranging from several dozen to over a hundred times that of second cladding layer 142. For the same reason, the current flowing between second split electrode 1722 and emission-side electrode 171 flows within second current injection region 1202 at the location of two-dimensional photonic crystal layer 12. Thus, the magnitude of the current flowing in first current injection region 1201 and second current injection region 1202, respectively, can be independently controlled using first split electrode 1721 and second split electrode 1722.

[0074] In this embodiment, a component formed by combining two holes, such as an elliptical cylindrical first refractive index portion 1221 and a smaller cylindrical second refractive index portion 1222 (a component having a refractive index different from that of the base material 121 may also be used as described above) is used as a refractive index portion 122. By using a refractive index portion combining two holes or components in this manner, it is possible to suppress the localization of light in a portion of the two-dimensional photonic crystal layer 12, thereby forming a resonant state of light within a wider range within the two-dimensional photonic crystal layer 12 and causing the laser beam to oscillate (for example, see Patent Documents 1 and 2). In addition, the shapes of the first refractive index portion 1221 and the second refractive index portion 1222 are not limited to this example, and various shapes may be used (for example, both are elliptical cylindrical, both are cylindrical, either or both are triangular prism or quadrangular prism, etc.). In addition, a refractive index portion may be formed by only one hole or component, or by three or more holes or components.

[0075] In the present embodiment, one anisotropic refractive index portion 122 is disposed at each lattice point of a square lattice in any one of the first current injection region 1201 and the second current injection region 1202 (a set is disposed by combining the first anisotropic refractive index portion 1221 and the second anisotropic refractive index portion 1222). Let the period length of the square lattice in the first current injection region 1201 be a1, and the period length of the second current injection region 1202 be a2. a2 is smaller than a1 (a2 < a1). Thus, by setting the period lengths in the first current injection region 1201 and the second current injection region 1202 to different values, when currents are respectively injected into the first current injection region 1201 and the second current injection region 1202, among the light generated by the currents in the active layer 11, the light corresponding to the resonance frequency determined by the period length of each region resonates, and the resonance frequencies in these respective regions become different values. Specifically, the resonance frequency of the second current injection region 1202 with a shorter period length is larger than the resonance frequency of the first current injection region 1201. <00,00205>Instead of (or together with) the case where the anisotropic refractive index portions 122 are disposed with different period lengths between the first current injection region 1201 and the second current injection region 1202 as in the above example, anisotropic refractive index portions 122 with different volume ratios may be disposed. Here, the volume ratio refers to the ratio of the volume occupied by the anisotropic refractive index portion 122 in the volume defined by the product of the unit lattice (a square with a lattice length of a × a) of the two-dimensional lattice (a square lattice in this example) in which the anisotropic refractive index portion 122 is disposed and the thickness of the two-dimensional photonic crystal layer 12. Figure 3 An example showing that anisotropic refractive index portions 122 with different volume ratios are disposed between the first current injection region 1201 and the second current injection region 1202 is shown. In this example, let the volume ratio of the anisotropic refractive index portion 122 disposed in the first current injection region 1201 be V1, and the volume ratio of the anisotropic refractive index portion 122 disposed in the second current injection region 1202 be V2. It is set that V2 is greater than V1 (V2 > V1). In this case, the resonance frequency of the second current injection region 1202 with a larger volume ratio is larger than the resonance frequency of the first current injection region 1201.

[0077] It is also possible to make both the period length and the volume ratio different values between the first current injection region 1201 and the second current injection region 1202.

[0078] [[ID=II]]In the examples described so far, the anisotropic refractive index portions 122 are disposed in a square lattice shape, but the anisotropic refractive index portions 122 may also be disposed at the lattice points of two-dimensional lattices in other forms such as a triangular lattice shape, a rectangular lattice shape, and a rhombic lattice shape. However, in each current injection region, the anisotropic refractive index portions 122 are disposed at the lattice points of two-dimensional lattices in the same form.

[0079] Instead of making the period lengths or volume ratios (or both) different between the first current injection region 1201 and the second current injection region 1202 as in the above example, the refractive index of the base material 121 in each region may be made different. Figure 4 An example of using base materials 1211 and 1212 with different refractive indices between the first current injection region 1201 and the second current injection region 1202 is shown. In this example, the refractive index of the base material 1211 of the first current injection region 1201 is set to n1, and the refractive index of the base material 1212 of the second current injection region 1202 is set to n2, and n2 is set to be smaller than n1 (n2<n1). In this case, the resonance frequency of the second current injection region 1202 with a smaller refractive index is greater than the resonance frequency of the first current injection region 1201. In addition, instead of the refractive index of the base material, or together with the refractive index of the base material, the refractive index of the different refractive index portion 122 can be made different between the first current injection region 1201 and the second current injection region 1202. However, in this case, it is necessary to use a component with a refractive index different from that of the base material 121 as the different refractive index portion 122 instead of using a hole in at least one current injection region. Therefore, as Figure 4 It is easier to manufacture by making the refractive index (material) of the base material 121 different in each current injection area as in the example.

[0080] Alternatively, as a method of making the refractive index of the base material different in each current injection region, for example, the current density of the direct current flowing in each current injection region may be made different, thereby making each current injection region have a different temperature.

[0081] Furthermore, in the examples described so far, two current injection areas (a first current injection area 1201 and a second current injection area 1202) are set, but on the basis of using a split electrode divided into three or more as described above, three or more current injection areas can be set corresponding to these electrodes, and the different refractive index portion 122 can be configured in each current injection area with a different period length or a different volume ratio.

[0082] In the examples described so far, the electrodes facing the emission side electrodes 171 are set as the split electrodes 172, but it is also possible to Figure 5 As shown in FIG, the emission side electrode 171 is divided into two (or more than three) electrodes (in the example of the figure, the first emission side divided electrode 1711 and the second emission side divided electrode 1712), and current is independently injected from these electrodes into different current injection areas. In this case, the electrodes opposite to the emission side electrode 171 (1721, 1722) can be set as follows Figure 5As shown in the figure, the undivided counter electrode 1723 can also be set to the same side as ( Figure 1 ) The same split electrode 172. In addition, the shape of the emission side electrode 171 and the counter electrode 1723 (or their split electrodes) is not limited to the above-mentioned shape. Figure 1 and Figure 5 In the embodiment, the emission-side electrode 171 is in a circular ring shape with both the outer edge and the inner edge (the outer edge of the window 1710) being circular, but the outer edge and the inner edge do not need to be the same shape. Figure 6 As shown, an emission-side electrode 171 (first emission-side segmented electrode 1711 and second emission-side segmented electrode 1712) having a circular inner edge (outer edge of window 1710) and a square outer edge may also be used.

[0083] (2) Operation of the Two-Dimensional Photonic Crystal Laser of This Embodiment

[0084] Next, the operation of the two-dimensional photonic crystal laser 10 of this embodiment will be described. When the two-dimensional photonic crystal laser 10 is used, the signal current generator 211 (see FIG. 21 ) generates a signal current by using the power supplied from the power supply (not shown). Figure 7 ) generates a first signal current whose magnitude varies with time in a predetermined waveform and a second signal current whose waveform varies with time differently from the first signal current. The first signal current is then caused to flow between the emitting-side electrode 171 and the first split electrode 1721, while the second signal current is caused to flow between the emitting-side electrode 171 and the second split electrode 1722 (independently of the first split electrode 1721 side).

[0085] A first signal current is introduced into a region of the active layer 11 that is opposite the first current injection region 1201 of the two-dimensional photonic crystal layer 12 (via the spacer layer 13). This region of the active layer 11 generates light of an intensity corresponding to the magnitude of the signal current, and this light is directed into the first current injection region 1201. Similarly, a second signal current is introduced into a region of the active layer 11 that is opposite the second current injection region 1202 of the two-dimensional photonic crystal layer 12. This region of the active layer 11 generates light of an intensity corresponding to the magnitude of the signal current, and this light is directed into the second current injection region 1202.

[0086] As a result, the two-dimensional photonic crystal layer 12 forms a fundamental resonant state throughout its entirety, resonating at a full resonant frequency. The full resonant frequency is a frequency between the resonant frequencies of the first and second current injection regions 1201 and 1202, respectively, determined by the period length and / or volume fraction of the different refractive index portion 122, and is determined by weighting the intensity of light introduced into the first and second current injection regions 1201 and 1202, respectively. This resonance generates laser light. The generated laser light is emitted from the surface of the two-dimensional photonic crystal layer 12 through various layers such as the spacer layer 13 and the window 1710 of the emission-side electrode 171, toward the exterior of the two-dimensional photonic crystal laser 10.

[0087] Here, the first signal current and the second signal current change with time in different waveforms, respectively, and thus the ratio of the intensities of the light respectively introduced into the first current injection region 1201 and the second current injection region 1202 also changes with time. Therefore, the weighted change of the intensity of the light between the two current injection regions changes with time, and the full resonance frequency also changes with time. Therefore, by setting the first signal current and the second signal current to waveforms corresponding to certain information (a specific example will be described later), the information can be transmitted in the form of a time variation of the full resonance frequency through the laser L emitted from the two-dimensional photonic crystal laser 10. In addition, using a detector 221 and a computer 222 (refer to Figure 7 ) etc., and upon receiving the laser light L, outputs a modulation signal (a specific example will be described later) corresponding to the temporal variation in the frequency of the laser light L, thereby enabling the reception of the aforementioned information. Therefore, an information transmission and reception system 20 can be constructed by a transmitter 21 including the two-dimensional photonic crystal laser 10 of this embodiment and the like, and a receiver 22 including the detector 221 and the like.

[0088] (3) Specific examples

[0089] Furthermore, several specific examples will be used for explanation.

[0090] (3-1) Common structures in specific examples

[0091] Here, the volume fraction of the different-refractive-index portion 122 is set to 11% in both the first current injection region 1201 and the second current injection region 1202 (the volume fraction of the first different-refractive-index portion 1221 is 7%, and the volume fraction of the second different-refractive-index portion 1222 is 4%). The period length is set so that the difference between the first current injection region 1201 and the second current injection region 1202 is 0.005%, 0.010%, or 0.015% (depending on the example). The period length a1 on the first current injection region 1201 side is set to 276 nm. Both the first current injection region 1201 and the second current injection region 1202 are semicircular in shape with a diameter of 500 μm. In addition, since the difference between the period lengths a1 and a2 is small, errors may occur in the distance between each different refractive index portion 122 (= period length) during production. However, since different refractive index portions 122 are arranged with hundreds of periods to more than 1000 periods in each current injection area, such a small difference in period length can be formed if the average value of the entire current injection area is viewed.

[0092] (3-2) Preliminary simulation and experiment

[0093] For a two-dimensional photonic crystal laser 10 having a two-dimensional photonic crystal layer 12 having a two-dimensional periodic structure of this example, a preliminary simulation was conducted to examine the case of injecting a signal current in which a sinusoidal high-frequency current was superimposed on a direct current. In this simulation, the magnitude of the direct current injected into the first current injection region 1201 and the second current injection region 1202 was set to 1.5 A, the maximum amplitude of the high-frequency current was set to 100 mA, and the high-frequency currents were set to be in opposite phases between the first current injection region 1201 and the second current injection region 1202 (i.e., the magnitude of one was -1 times the magnitude of the other). The frequency (modulation frequency) of the high-frequency current was set to 2 GHz. Therefore, the difference Δf (16 GHz, 32 GHz, or 48 GHz) between the resonant frequencies of the first current injection region 1201 and the second current injection region 1202 was sufficiently greater than the modulation frequency of the signal current.

[0094] The results of this simulation, such as Figure 8 As shown, when the value of Δf is arbitrary, the frequency of the laser light emitted by the two-dimensional photonic crystal laser 10 is determined by the magnitude of the DC current ( Figure 8 The vertical axis of the signal current (with the frequency set to 0 (origin)) changes in magnitude in a sinusoidal manner over time with the same period (or modulation frequency). Figure 8For comparison, the results of simulations are also shown for the case where the first current injection region 1201 and the second current injection region 1202 are set to the same two-dimensional periodic structure, that is, when Δf is 0, but the time variation of the laser frequency is not seen in this comparative example.

[0095] Furthermore, for the case where Δf is 48 GHz, multiple simulations were performed in the modulation frequency range of 500 MHz to 20 GHz to determine the amplitude of the time variation of the laser frequency. The results are shown in Figure 9 It can be seen that the frequency of the laser light changes with time, with a peak value near 5 GHz and an amplitude exceeding 1 GHz in a range where the modulation frequency is smaller than 5 GHz.

[0096] Next, the process of manufacturing the two-dimensional photonic crystal laser 10 of this embodiment and performing the Figure 8 Shown are the results of a simulation of the same experiment. Figure 10 FIG. 1 shows an optical microscope photograph of the two-dimensional photonic crystal laser 10 produced in this experiment, taken from the upper surface (emission-side electrode 171). Figure 6 The first emission side split electrode 1711 and the second emission side split electrode 1712 are shaped as shown. The first emission side split electrode 1711 and the first electrode pad 311 are connected by a wire made of gold, and the second emission side split electrode 1712 and the second electrode pad 312 are also connected by the same wire. Figure 10 Cannot be observed in. Figure 6 . ) is connected to the ground pad 32, and the ground pad 32 is grounded. The two-dimensional photonic crystal layer 12 (in Figure 10 Cannot be observed in. Figure 2 ). The period length a1 of the square lattice of the first current injection region 1201 is set to a1=a0+Δa / 2, and the period length a2 of the second current injection region 1202 is set to a2=a0-Δa / 2, and a0=278nm, Δa=0.8×10 -4 a0 (the difference between a1 and a2 is 0.008%). Due to the difference in these period lengths, the difference Δf between the resonance frequencies of the first current injection region 1201 and the second current injection region 1202 becomes 26 GHz.

[0097] A signal current consisting of a superposition of a high-frequency current with a frequency (modulation frequency) of 1.2 GHz and an amplitude of 0.11 A, and a direct current of 1.5 A, with opposite phases between the first and second emission-side split electrodes 1711 and 1712, was injected between the first and second emission-side split electrodes 1711 and 1712 and the counter electrode 1723. The results of measuring the temporal variation of the frequency of the laser light emitted by the two-dimensional photonic crystal laser 10 are shown in FIG. Figure 11 As shown in the simulation results, the laser frequency changes sinusoidally over time. The amplitude of the frequency change over time is approximately 0.6 GHz.

[0098] In addition, the amplitude of the laser intensity was measured (note that this is different from the amplitude of the time variation of the frequency mentioned above). The results are as follows: Figure 12 As shown, almost no temporal variation occurs. As described above, in the two-dimensional photonic crystal laser 10 of this embodiment, it is possible to suppress the variation in the amplitude of the intensity of the laser light and to impart periodic temporal variation to the frequency of the laser light.

[0099] (3-3) Specific example 1

[0100] Next, as a specific example 1, the use of Figure 13 The example of the high frequency current used in the previous simulation is replaced by the signal current obtained by superimposing the binary information current of "1" and "0" on the direct current. In this example, a sine wave (amplitude I smax ) in which a waveform that changes over time for a half cycle that maintains a positive value represents "1", and a waveform that does not change over time represents "0". In correspondence with the sequence of "1" or "0" information to be transmitted, a time-varying current having such a "1" or "0" waveform is superimposed on the magnitude I according to each modulation cycle (Δt). DC The first signal current is obtained by using a half-cycle of the sine wave as the modulation period of the first signal current, and the modulation frequency is set to 2 GHz. The second signal current is obtained by superimposing the waveform of the time-varying current "1" or "0" in the first signal current on the phase opposite to the first signal current, that is, on the basis of positive and negative inversion. DC Obtained from the direct current.

[0101] The injection of Δf=48 GHz into the two-dimensional photonic crystal laser 10 of the above example was performed. Figure 13 The simulation results of the first signal current and the second signal current are shown as follows Figure 14As shown in the figure, although the intensity of the emitted laser light fluctuates slightly during the period when the "1" signal is transmitted, there is no significant temporal variation in intensity. Even if one were to detect "0" and "1" signals based on such laser light intensity, it would be difficult to do so with a high S / N ratio.

[0102] On the other hand, Figure 15 As shown in FIG, the time variation of the frequency of the emitted laser light is observed to be significantly reduced during the period of time when the “1” signal is sent. When the time variation of the frequency of the laser light within one modulation cycle of sending the “1” signal ( Figure 15 When the area of ​​the downward peak indicated by the diagonal line is estimated, the time variation of the laser frequency is equivalent to a phase variation of 3π / 4 during one modulation cycle of the signal current compared to the case without such a variation. In the presence of such a phase variation, if a delayed self-homodyne method is performed to cause interference between the laser output signal delayed by one cycle and the original signal, the following is shown: Figure 16 As shown, in the intensity of the obtained delayed interference light, the time variation of the intensity of the original laser light can be observed ( Figure 14 ) corresponds to a significant temporal variation in intensity that is not observed in the "1" and "0" signals. By acquiring this temporal variation in intensity, it is possible to receive a sequence of "1" or "0" information sent from the two-dimensional photonic crystal laser 10. The amplitude of the intensity variation of this delayed interference light exceeds 1W, which can improve the S / N ratio compared to the case of detecting the intensity variation of the laser itself. In addition, the magnitude of the phase change within one modulation cycle is preferably in the range of π / 2 to 3π / 2, and most preferably π.

[0103] (3-4) Specific example 2

[0104] Next, for Figure 17 The first signal current shown uses the amplitude I corresponding to the binary information of "1" and "0" similar to that of the specific example 1. smax The current waveform is superimposed on the size I DC The current obtained by the DC current and the second signal current only use the magnitude I without time change DC The same simulation as in Example 1 was performed for the case of a DC current. As a result, the intensity of the emitted laser light was as follows: Figure 18 As shown in FIG, although the variation of the time period in which the “1” signal is sent is greater than that of Example 1 ( Figure 14 ) is slightly larger, but the magnitude of its variation is one order of magnitude smaller than the magnitude of the intensity variation obtained by the delayed self-homodyne method described later. Figure 19 As shown, the frequency of the emitted laser light is close to that of Example 1 ( Figure 15The delayed interference light signal obtained by interfering the laser output signal with the original signal after delaying it by one cycle is also as shown in FIG. Figure 20 Shown and specific example 1 ( Figure 16 ) Similarly, significant time changes in intensity corresponding to changes in the signals of "1" and "0" are obtained, and intensity changes can be detected with a high S / N ratio.

[0105] (3-5) Modification of Specific Example 2

[0106] In Example 2, the frequency of the laser light varies with time, and as Figure 18 As shown, the intensity of the laser also changes with time. Below, a simulation is performed to find the amplitude of the time variation of the laser intensity while changing the modulation frequency of the first signal current. For simplicity, the first signal current is set to be a high-frequency current of a sinusoidal wave superimposed on a direct current, and the second signal current is set to be only a direct current. For the case of Δf = 48 GHz, the relationship between the modulation frequency obtained by simulation and the amplitude of the time variation of the laser intensity is shown in Figure 21 For reference, the simulation results for the case where the first current injection region 1201 and the second current injection region 1202 are configured as the same two-dimensional periodic structure, that is, the case of Δf = 0 GHz, are also shown. In this modification of Specific Example 2, the amplitude of the temporal variation in laser intensity is larger at all modulation frequencies compared to the reference example, further improving the S / N ratio.

[0107] In particular, the amplitude decreases temporarily with a peak value near 5 GHz as the modulation frequency increases, but further reaches a peak value near 17 GHz on the high modulation frequency side from near 12 GHz (in Figure 21 The peak value (indicated by the downward arrow in the figure) becomes higher. This means that in the modified example of Specific Example 2, information can be transmitted at a higher modulation frequency, that is, the amount of information per unit time transmitted at a high S / N ratio can be increased. For example, the modulation frequency at an amplitude of -3dB is 9.0 GHz in the reference example, but 19.5 GHz in the modified example of Specific Example 2.

[0108] In addition, the two-dimensional photonic crystal laser 10 produced in this embodiment was subjected to the same Figure 21 The simulation experiment shown is as follows. In this experiment, in addition to Δa = 1.6 × 10 -4 Except for a0 (the difference Δf between the resonance frequencies of the first current injection region 1201 and the second current injection region 1202 is 52 GHz), the same Figures 10 to 12The experiment shown in the figure uses a two-dimensional photonic crystal laser 10 with the same structure. As for the injected current, a direct current of 1.6A is set between the first emission side split electrode 1711 and the counter electrode 1723, and a high-frequency current with an amplitude of 0.06A is superimposed on the direct current of 1.6A between the second emission side split electrode 1712 and the counter electrode 1723. The relationship between the frequency (modulation frequency) of the high-frequency current and the amplitude of the time variation of the laser intensity is measured. The results are shown in Figure 22 . Figure 22 The dashed curve shown in the figure represents the simulated value for a reference example in which the different refractive index portions 122 are arranged with the same period length (a0 = 278 nm) throughout the two-dimensional photonic crystal layer 12, and Δf = 0. The modulation frequency at which the amplitude of the temporal variation in laser intensity is -3 dB is approximately 6.5 GHz in the reference example. In contrast, this embodiment achieves a modulation frequency of 10 GHz or higher, enabling information to be transmitted at a higher frequency.

[0109] The increase in the amplitude of the temporal variation in laser intensity in the high modulation frequency band is believed to be caused by a phenomenon known as photon / photon resonance. In the two-dimensional photonic crystal laser 10, by setting a resonant frequency difference Δf between the first current injection region 1201 and the second current injection region 1202, in addition to the aforementioned basic resonant state that generates laser oscillation at all resonant frequencies, there are also higher-order resonant states with different electric field distributions and longer resonant wavelengths (lower resonant frequencies). Since the loss in the higher-order resonant state is greater than that in the basic resonant state, oscillation is generally not achieved. However, if a signal current with a modulation frequency equivalent to the resonant frequency difference between the two resonant states is injected into only one of the first current injection region 1201 and the second current injection region 1202, weak coupling (photon / photon resonance) occurs between the basic resonant state and the higher-order resonant state, thereby improving the efficiency of converting the signal current into signal light.

[0110] The amplitude of the temporal variation in the intensity of the laser light based on such a modulation frequency further varies depending on the ratio of the DC current injected into the first current injection region 1201 and the second current injection region 1202. Figure 23 The simulation results shown in FIG. 1 show that if the magnitude of the DC current injected into the second current injection region 1202 is DC2 Divide by the magnitude I of the DC current (after removing the high-frequency current) injected into the first current injection region 1201 DC1 The obtained value I DC2 / I DC1 The simulation is performed for the three cases where the ratio is 0.67 (2 / 3), 1, and 1.5. Figure 23 As shown, I DC2 / IDC1 As the value increases, the amplitude of the temporal variation in the intensity of the laser light in a region where the modulation frequency is high (particularly 20 GHz or higher) can be increased.

[0111] In the examples described so far, a sine wave or a waveform corresponding to half a sine wave cycle was used as part of the waveform of the signal current. However, any waveform shape, such as a rectangular wave or a triangular wave, can be used as long as it can maintain a positive or negative value. Furthermore, in Specific Example 1, the current superimposed on the DC current in the second signal current is set to -1 times the first signal current, but other factors (including positive factors) may also be used.

[0112] While the embodiments and variations of the two-dimensional photonic crystal laser of the present invention have been described above, the present invention is not limited to these embodiments and variations and is capable of further variations. Furthermore, two or more of the multiple configurations described in the embodiments and variations may be used in combination, or one or more of the multiple configurations described in the embodiments and variations may be used in combination with other configurations.

[0113] [Way]

[0114] Those skilled in the art will appreciate that the above exemplary embodiments are specific examples of the following aspects.

[0115] (Item 1) A two-dimensional photonic crystal laser according to one embodiment of the present invention includes:

[0116] a) active layer;

[0117] b) a two-dimensional photonic crystal layer having a two-dimensional photonic crystal structure in which portions having a refractive index different from that of the base material, i.e., different refractive index portions, are two-dimensionally periodically arranged within a plate-like base material stacked directly or via other layers on the active layer, and having a plurality of current injection regions having mutually different resonant frequencies; and

[0118] c) A current injection unit that injects a signal current into each of the plurality of current injection areas, wherein a ratio of current intensities between the plurality of current injection areas changes with time.

[0119] (Item 2) In the two-dimensional photonic crystal laser of Item 2, in the two-dimensional photonic crystal laser of Item 1, the plurality of current injection regions are periodically arranged in a two-dimensional lattice of the same form with different period lengths.

[0120] (Item 3) In the two-dimensional photonic crystal laser of Item 3, in the two-dimensional photonic crystal laser of Item 1 or Item 2, the plurality of current injection regions are periodically arranged in a two-dimensional lattice of the same form with different volume ratios in the different refractive index portions.

[0121] (Item 4) In the two-dimensional photonic crystal laser of Item 4, in the two-dimensional photonic crystal laser of any one of Items 1 to 3, the base material of the plurality of current injection regions and the materials of either or both of the different refractive index portions are different from each other.

[0122] (Item 5) In the two-dimensional photonic crystal laser of Item 5, in the two-dimensional photonic crystal laser of any one of Items 1 to 4, the magnitudes of the DC components of the signal currents in the plurality of current injection regions are different from each other.

[0123] (Item 6) The two-dimensional photonic crystal laser of Item 6 is the two-dimensional photonic crystal laser of any one of Items 1 to 5,

[0124] Modulate the above signal current at a specified modulation frequency,

[0125] A difference between a maximum resonant frequency and a minimum resonant frequency among the resonant frequencies of the plurality of current injection regions is greater than the modulation frequency.

[0126] (Item 7) The two-dimensional photonic crystal laser of Item 7 is the two-dimensional photonic crystal laser of any one of Items 1 to 6,

[0127] The signal current injected into two current injection areas among the plurality of current injection areas is a current obtained by superimposing a time-varying current on a direct current, the time-varying current having either a waveform in which the current value maintains a positive or negative value or a waveform in which the current value maintains zero according to each predetermined modulation cycle.

[0128] In the two current injection regions, the time-varying currents are in opposite phases to each other.

[0129] (Item 8) The two-dimensional photonic crystal laser of Item 8 is the two-dimensional photonic crystal laser of any one of Items 1 to 6,

[0130] The signal current injected into one of the plurality of current injection regions is a current obtained by superimposing a time-varying current on a direct current having a first magnitude, the time-varying current having either a waveform in which the current value maintains a positive or negative value or a waveform in which the current value maintains zero according to each predetermined modulation period.

[0131] The signal current injected into another current injection region among the plurality of current injection regions is a direct current having the same magnitude as the direct current.

[0132] (Item 9) In the two-dimensional photonic crystal laser of Item 9, in the two-dimensional photonic crystal laser of any one of Items 1 to 8, the aforementioned different refractive index portion is formed by combining two holes or components having a refractive index different from that of the aforementioned base material.

[0133] (Item 10) An information transmission and reception system according to one embodiment of the present invention comprises:

[0134] A transmitter comprising the two-dimensional photonic crystal laser according to any one of items 1 to 9; and

[0135] The receiver includes a photodetector that receives the laser light emitted by the two-dimensional photonic crystal laser and outputs a modulation signal that is a signal corresponding to a temporal change in the frequency of the laser light.

[0136] (Item 11) A transmitter for an information transmission and reception system according to one embodiment of the present invention includes the two-dimensional photonic crystal laser according to any one of Items 1 to 9.

[0137] Description of Reference Numerals

[0138] 10…Two-dimensional photonic crystal laser

[0139] 11…Active layer

[0140] 12…2D photonic crystal layer

[0141] 1201…first current injection region

[0142] 1202…Second current injection region

[0143] 121, 1211, 1212…base material

[0144] 122…different refractive index portion

[0145] 1221…first different refractive index portion

[0146] 1222…Second anisorefractive index portion

[0147] 13…Spacer layer

[0148] 141…first coating layer

[0149] 142…Second coating layer

[0150] 16...Substrate

[0151] 171…Emission side electrode

[0152] 1710…Window

[0153] 1711…First emission-side split electrode

[0154] 1712…Second emission side split electrode

[0155] 172…Split electrode

[0156] 1721…First dividing electrode

[0157] 1722…Second split electrode

[0158] 1723…Counter electrode

[0159] 20…Information sending and receiving system

[0160] 21…Transmitter

[0161] 211…Signal current generator

[0162] 22…Receiver

[0163] 221…Detector

[0164] 222…Computer

[0165] 311…first electrode pad

[0166] 312…second electrode pad

[0167] 32…Ground pad

[0168] L…Laser

Claims

1. A two-dimensional photonic crystal laser comprising: a) active layer; b) a two-dimensional photonic crystal layer having a two-dimensional photonic crystal structure in which portions having a refractive index different from that of the base material, i.e., different refractive index portions, are two-dimensionally periodically arranged within a plate-like base material stacked directly or via other layers on the active layer, and having a plurality of current injection regions having mutually different resonant frequencies; and c) A current injection unit that injects a signal current into each of the plurality of current injection areas, wherein a ratio of current intensities between the plurality of current injection areas changes with time.

2. The two-dimensional photonic crystal laser according to claim 1, wherein: The plurality of current injection regions are periodically arranged in the different refractive index portion in a two-dimensional lattice having the same form and with different period lengths.

3. The two-dimensional photonic crystal laser according to claim 1, wherein: The plurality of current injection regions are periodically arranged in the different refractive index portion in a two-dimensional lattice having the same form and at different volume ratios.

4. The two-dimensional photonic crystal laser according to claim 1, wherein: The base material of the plurality of current injection regions and the materials of either or both of the different refractive index portions are different from each other.

5. The two-dimensional photonic crystal laser according to claim 1, wherein: The magnitudes of the DC components of the signal currents in the plurality of current injection regions are different from each other.

6. The two-dimensional photonic crystal laser according to claim 1, wherein: modulating the signal current at a prescribed modulation frequency, A difference between a maximum resonant frequency and a minimum resonant frequency among the resonant frequencies of the plurality of current injection regions is greater than the modulation frequency.

7. The two-dimensional photonic crystal laser according to claim 1, wherein: The signal current injected into two current injection areas among the plurality of current injection areas is a current obtained by superimposing a time-varying current on a direct current, the time-varying current having either a waveform in which the current value maintains a positive or negative value or a waveform in which the current value maintains zero according to each predetermined modulation cycle. In the two current injection regions, the time-varying currents are in opposite phases to each other.

8. The two-dimensional photonic crystal laser according to claim 1, wherein: The signal current injected into one of the plurality of current injection regions is a current obtained by superimposing a time-varying current on a direct current having a first magnitude, the time-varying current having either a waveform in which the current value maintains a positive or negative value or a waveform in which the current value maintains zero according to each predetermined modulation period. The signal current injected into another current injection region among the plurality of current injection regions is a direct current having a second magnitude.

9. The two-dimensional photonic crystal laser according to claim 1, wherein: The different refractive index portion is formed by combining two holes or two members having a refractive index different from that of the base material.

10. An information transceiver system comprising: A transmitter comprising the two-dimensional photonic crystal laser according to any one of claims 1 to 9; and The receiver includes a photodetector that receives the laser light emitted by the two-dimensional photonic crystal laser and outputs a modulation signal that is a signal corresponding to a temporal change in the frequency of the laser light. 11 . A transmitter for an information transmission and reception system, comprising the two-dimensional photonic crystal laser according to claim 1 .

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