JP2012137542A - Transmitter and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter and a communication system capable of enhancing a transfer rate of data.SOLUTION: An LED element 10, as a transmitter, comprises a light emitting section 130 and a plurality of modulating sections 120. The modulating sections 120 each include a modulation electrode layer 106 and a moth-eye structure layer 105, each connected to a signal input power source 121. Voltage is applied to the modulation electrode layer 106 and an n-side electrode 103 to generate a changing electric field in a material of the moth-eye structure layer 105. The electric field changes a refractive index of the moth-eye structure layer 105 to modulate light from the light emitting section 130. The plurality of modulating sections 120 modulate light emitted from the same light emitting section 130 according to respective different signals.

Description

  The present invention relates to a transmitter and a communication system.

  In recent years, a white LED using a combination of a short wavelength LED element made of a nitride semiconductor and a phosphor has been put into practical use, and the white LED is expected as a light source for future illumination. Unlike incandescent bulbs and fluorescent lamps, which are conventional illumination light sources, white LEDs can modulate light at a relatively high speed, and are expected to be applied to visible light communication utilizing this feature. Research projects aiming to construct information communication networks in offices and homes such as the Internet through visible light communication of 1 to 10 Mbps from lighting devices are being actively promoted in Japan and overseas.

  Also, as this type of visible light communication device, a device that drives a blue light excitation type white LED based on a drive current signal generated based on transmission data and outputs a visible light signal to a receiver is proposed. ing. In Patent Document 1, this visible light communication device generates a multi-tone drive current signal by adding a rising pulse at the rising edge of transmission data and adding a falling pulse at the falling edge of transmission data. It is described that a multi-tone drive means is provided.

JP 2010-103979 A

  However, the broadband communication by the present optical fiber etc. has reached 1000 Mbps, and compared with this, it is difficult to say that the transfer rate in the configuration using the light of the conventional LED or incandescent bulb is sufficient.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a transmitter and a communication system capable of improving the total data transfer rate. In this specification, “total transfer rate” refers to the overall data transfer rate considering both the transfer rate by a single transmitter and the capacity to operate multiple transmitters in parallel. means.

  In order to solve the above-mentioned problems, a transmitter according to the present invention includes at least one light-emitting unit and a plurality of modulation units that modulate light emitted from at least one light-emitting unit. A plurality of modulation means having a structure including a material in which convex portions are periodically formed, and an electric field adjustment unit that generates an electric field that changes in the material and changes a refractive index of the material. At least two modulate light radiated from the same light emitting section based on different signals.

  According to such a configuration, the electric field adjusting unit changes the refractive index to change the light amount at the same speed as the change in the refractive index. The plurality of modulation means modulate light emitted from the common light emitting unit.

The light includes a plurality of wavelengths, and at least two of the modulation means may have different periods in which the concave portions or the convex portions are formed according to any of the plurality of wavelengths.
In each of the plurality of modulation means, the period in which the concave portion or the convex portion is formed may be longer than the optical wavelength of the light modulated by the modulation means and smaller than the coherent length of the light modulated by the modulation means. .

  In addition, a communication system according to the present invention includes the above-described transmitter and a receiver having a demodulator that demodulates light emitted from a plurality of modulation means for each modulation means.

  The receiver may include a plurality of light receiving elements that detect light emitted from the plurality of modulation means, and at least two of the plurality of light receiving elements may detect light emitted from different modulation means.

  The transmitter and communication system of the present invention can improve the overall total data transfer rate by improving the data transfer rate and transfer capacity.

It is a schematic diagram which shows the outline of a structure of the communication system which concerns on this invention. It is a schematic diagram which shows the outline of a structure of the LED element of FIG. It is sectional drawing in the III-III line of FIG. It is explanatory drawing which shows the diffraction effect of the light in the interface of a different refractive index, (a) shows the state reflected in an interface, (b) shows the state which passes an interface. It is explanatory drawing which shows the diffraction effect | action of the light radiate | emitted from the moth-eye structure layer of FIG. It is a figure which shows typically the positional relationship of the LED element of FIG. 1, and a CCD camera. It is a schematic diagram which shows the modification of the modulation | alteration means of FIG.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing an outline of a configuration of a communication system according to the present invention. The communication system according to the present invention includes an LED element 10 and a receiver 20. As will be described later, the LED element 10 functions as a transmitter or a transmitter. A DC power supply 30 is connected to the LED element 10, and the DC power supply 30 supplies power to the LED element 10.

  2 and 3 schematically show the configuration of the LED element 10. 3 is a cross-sectional view taken along line III-III in FIG.

  As shown in FIG. 3, the LED element 10 includes a SiC substrate 101 and a semiconductor stacked unit 110 formed on one surface of the SiC substrate 101. The semiconductor stacked unit 110 includes a buffer layer 111, an n-type GaN layer 112, a multiple quantum well active layer 113, an electron block layer 114, and a p-type GaN layer 115 in this order from the SiC substrate 101 side. A p-side electrode 102 is formed on the P-type GaN layer 115, and an n-side electrode 103 is formed on the n-type GaN layer 112.

The SiC substrate 101 is made of single crystal 6H-type SiC to which N and B are added. When excited by ultraviolet light, the SiC substrate 101 emits visible light of a light bulb color including a plurality of wavelengths by donor-acceptor pair emission. The SiC substrate 101 emits light with a wavelength of 500 nm to 750 nm having a peak at 500 nm to 650 nm, for example. In the present embodiment, the SiC substrate 101 is adjusted to emit light having a peak wavelength of 580 nm. The doping concentration of B and N in the SiC substrate 101 is 10 ¹⁵ / cm ³ to 10 ¹⁹ / cm ³ . Here, the SiC substrate 101 can be excited by light of 408 nm or less.

  The buffer layer 111 is made of GaN. In the present embodiment, the buffer layer 111 is grown at a lower temperature than the n-type GaN layer 112 and the like. The n-type GaN layer 112 as the first conductivity type layer is formed on the buffer layer 111 and is made of n-GaN. The multiple quantum well active layer 113 as a light emitting layer is formed on the n-type GaN layer 112, is composed of GaInN / GaN, and emits ultraviolet light by recombination of electrons and holes.

  The electron block layer 114 is formed on the multiple quantum well active layer 113 and is made of p-AlGaN. The p-type GaN layer 115 as the second conductivity type layer is formed on the electron block layer 114 and is made of p-GaN. The buffer layer 111 to the p-type GaN layer 115 are formed by epitaxial growth of a group III nitride semiconductor. In addition, when a voltage is applied to the first conductive type layer and the second conductive type layer at least including the first conductive type layer, the active layer, and the second conductive type layer, the active layer is formed by recombination of electrons and holes. The layer structure of the semiconductor layer is arbitrary as long as it emits light.

  The p-side electrode 102 as the anode electrode is formed on the p-type GaN layer 115, and the surface on the p-side GaN layer 115 side forms a reflecting surface 102a. The p-side electrode 102 has a high reflectance with respect to light emitted from the multiple quantum well active layer 113. The p-side electrode 102 preferably has a reflectance of 80% or more with respect to light emitted from the multiple quantum well active layer 113. In the present embodiment, the p-side electrode 102 is made of, for example, an Ag-based or Rh-based material, and is formed by a vacuum deposition method, a sputtering method, a CVD (Chemical Vapor Deposition) method, or the like.

  The n-side electrode 103 as a cathode electrode is formed on the exposed n-type GaN layer 112 by etching the n-type GaN layer 112 from the p-type GaN layer 115. The n-side electrode 103 is made of, for example, Ti / Al / Ti / Au, and is formed by a vacuum deposition method, a sputtering method, a CVD method, or the like.

  This LED element 10 is of a flip chip type, and light is mainly extracted from the back surface (upper surface in FIG. 3) of SiC substrate 101. As described above, in the LED element 10, the SiC substrate 101, the semiconductor stacked unit 110, and the p-side electrode 102 constitute the light emitting unit 130.

A transparent conductive film 104 and a moth-eye structure layer as a structure are provided on the light extraction surface of the SiC substrate 101 (that is, the surface opposite to the surface on which the semiconductor stacked portion 110 is formed, the upper surface in FIG. 3). 105 are formed in this order. The transparent conductive film 104 has a well-known configuration, and is formed, for example, by being deposited by an electron beam evaporation method.
On the moth-eye structure layer 105, a plurality of modulation electrode layers 106 are formed. The plurality of modulation electrode layers 106 have shapes that do not contact each other. The modulation electrode layer 106 is preferably transparent to light emitted from the SiC substrate 101, and for example, ITO (Indium Tin Oxide) can be used. The modulation electrode layer 106 may be made of other materials as long as the sheet resistance is smaller than that of the moth-eye structure layer 105.

  On the modulation electrode layer 106, a refractive index adjusting pad 107 is provided. The pad 107 is a refractive index modulation electrode and can be made of, for example, Ti / Au, and is formed by a vacuum deposition method, a sputtering method, a CVD method, or the like.

  As shown in FIGS. 2 and 3, one modulation electrode layer 106 and a portion corresponding to the modulation electrode layer 106 in the moth-eye structure layer 105 (that is, the modulation electrode layer in the moth-eye structure layer 105). 106 and a portion sandwiched between the transparent conductive film 104) constitutes a modulation section 120 as modulation means. As described above, the modulation unit 120 includes the modulation electrode layer 106 and the moth-eye structure layer 105. In the example of FIG. 2, a total of 16 modulation units 120 arranged in 4 rows and 4 columns are provided, and FIG. 3 shows a cross section of four of these modulation units 120. In each modulation unit 120, the moth-eye structure layer 105 is periodically formed with convex portions 105a protruding outward, that is, on the side opposite to the SiC substrate 101, and each of the modulation electrode layers 106 has the convex portions 105a. It is formed corresponding to the formed part.

The moth-eye structure layer 105 is made of a piezoelectric material, and for example, it is preferable to use a material that is transparent to visible light, such as KTP (KTiOPO ₄ : potassium titanyl phosphate), LiNbO ₃ , LiNbO ₃ . The shape of each convex part 105a can be made into the shape which diameter-reduces toward tips, such as a cone and a polygonal pyramid. Note that the tip of each convex portion 105a may have a pointed shape or a shape that is not pointed. In the present embodiment, a light diffraction effect can be obtained by each of the convex portions 105a arranged periodically.

In the present embodiment, in each modulation unit 120, each convex portion 105a is a virtual triangular lattice with a predetermined cycle so that the center is the position of the apex of an equilateral triangle in plan view (the same direction as in FIG. 2). It is formed in alignment with the intersection of The period of each convex part 105a differs for every modulation part 120.
Here, the light emitted from the SiC substrate 101 includes a plurality of wavelengths, and the modulation unit 120 is configured to modulate light of different wavelengths included in each of the lights. In order to realize this configuration, the period of the convex portion 105a in each modulation unit 120 is determined corresponding to a specific wavelength that the modulation unit 120 modulates. The period of the convex part 105a is larger than the optical wavelength of the light modulated by the modulating part 120 and smaller than the coherent length of the light. Specifically, the period of the convex portion 105a is greater than twice the optical wavelength of the light and is equal to or less than half the coherent length.

Here, the period refers to the distance between the peak positions of the depths of the adjacent convex portions 105a. The optical wavelength means a value obtained by dividing the actual wavelength by the refractive index. Furthermore, the coherent length corresponds to a distance until the periodic vibrations of the waves cancel each other and the coherence disappears due to the difference in the individual wavelengths of the photon group having a predetermined spectral width. The coherent length lc is approximately lc = (λ ² / Δλ), where λ is the wavelength of light and Δλ is the half width of the light.

  Each modulation unit 120 is connected to a signal input power source 121. One pole of the signal input power supply 121 is connected to the modulation electrode layer 106 via the pad 107, and the other pole is connected to the n-side electrode 103. The signal input power supply 121 controls a voltage applied between the modulation electrode layer 106 and the n-side electrode 103 based on a signal to be transmitted. In this way, each of the modulation units 120 modulates light.

  The LED element 10 configured as described above emits ultraviolet light from the multiple quantum well active layer 113 when a forward voltage is applied to the p-side electrode 102 and the n-side electrode 103. Of the ultraviolet light, the light traveling toward the p-side electrode 102 is reflected by the reflecting surface 102 a of the p-side electrode 102 and travels toward the SiC substrate 101. Most of the ultraviolet light emitted from the multiple quantum well active layer 113 is directly or indirectly incident on the SiC substrate 101.

  The SiC substrate 101 emits light bulb-colored visible light when excited by ultraviolet light. When a voltage is applied to the n-side electrode 103 and the pad 107 as a refractive index modulation electrode to generate an electric field in the moth-eye structure layer 105, the refractive index of the material of the moth-eye structure layer 105 changes. Here, since the pad 107 and the modulation electrode layer 106 are provided for each modulation section 120, the refractive index of the material of the moth-eye structure layer 105 changes independently for each modulation section 120.

Here, as shown in FIG. 4A, when light is reflected at the interface of the moth-eye structure layer 105 from the Bragg diffraction condition, the condition that the reflection angle θ _ref should satisfy with respect to the incident angle θ _in is ,
d · n1 · (sin θ _in −sin θ _ref ) = m · λ (1)
It is. Here, n1 is the refractive index of the medium on the incident side, λ is the wavelength of the incident light, and m is an integer. In the present embodiment, n1 is the refractive index of the moth-eye structure layer 105.

On the other hand, as shown in FIG. 4B, from the Bragg diffraction condition, when light is transmitted at the interface of the moth-eye structure layer 105, the condition that the transmission angle θ _out should satisfy with respect to the incident angle θ _in is:
d · (n1 · sin θ _in −n2 · sin θ _out ) = m ′ · λ (2)
It is. Here, n2 is the refractive index of the medium on the exit side, and m ′ is an integer. In the present embodiment, n2 is the refractive index of air. That is, when the refractive index of the moth-eye structure layer 105 changes, the light transmission condition changes.

In order for the reflection angle θ _ref and the transmission angle θ _out that satisfy the diffraction conditions of the above equations (1) and (2) to exist, the period of each convex portion 105a is the optical wavelength inside the element (λ / n1 ) Or (λ / n2). The generally known moth-eye structure has a period set smaller than (λ / n1) or (λ / n2), and there is no diffracted light. And the period of each convex part 105a must be smaller than the coherent length which light can maintain the property as a wave, and it is preferable to set it as the half or less of coherent length. By setting it to half or less of the coherent length, the intensity of reflected light and transmitted light by diffraction can be secured.

As shown in FIG. 5, among the light isotropically emitted from the SiC substrate 101 in the LED element 10, the light incident on the moth-eye structure layer 105 at the incident angle θ _in is a reflection angle that satisfies the above formula (1). The light is reflected by θ _ref and transmitted at a transmission angle θ _out that satisfies the above equation (2). Here, when the incident angle θ _in is greater than the total reflection critical angle, the intensity of the reflected light is strong. The reflected light is reflected by the reflecting surface 102a of the p-side electrode 102 and is incident on the moth-eye structure layer 105 again, but is incident at an incident angle θ _{in that} is different from the incident angle θ _{in when} it is incident first. The transmission characteristics are different from the incident conditions.

  Thus, the convex portions 105a are formed with a period longer than the optical wavelength of the light modulated by each modulation unit 120 and smaller than the coherent length of the light, and on the diffraction surface of the moth-eye structure layer 105 on which each convex portion 105a is formed. By providing the reflecting surface 102a that reflects the reflected light and re-enters the diffractive surface, the light that is incident at an angle exceeding the total reflection critical angle can also be extracted outside the element by using the diffractive action. .

When a voltage is applied to the n-side electrode 103 and the pad 107 to generate an electric field in the moth-eye structure layer 105, the refractive index of the material of the moth-eye structure layer 105 changes for each modulation unit 120. In the present embodiment, since the moth-eye structure layer 105 has piezoelectricity, the refractive index can be changed efficiently using the Pockels effect. When the refractive index of the moth-eye structure layer 105 changes, n2 in the above equation (2) changes and the diffraction transmission condition changes. Thereby, when the LED element 10 emits light, the potential of the pad 107 can be changed for each modulation unit 120, and the amount of light extracted from the LED element 10 can be changed independently for each modulation unit 120.
Thus, the LED element 10 functions as a transmitter or a transmitter, and the pad 107 and the modulation electrode layer 106 function as a refractive index modulation electrode. The pad 107, the modulation electrode layer 106, and the n-side electrode 103 function as an electric field adjustment unit that changes the refractive index of the material of the moth-eye structure layer 142.

  Thereby, when the LED element 10 emits light, the potential of each pad 107 can be changed, and the amount of light extracted from the LED element 10 can be changed for each modulator 120. Therefore, light can be modulated in accordance with the electric field generated in the moth-eye structure layer 105, and the conventional method of adjusting and modulating the amount of electrons and holes injected from the n-side electrode 103 and the p-side electrode 102 is used. However, the modulation speed can be remarkably improved.

  Moreover, since the n-side electrode 103 is used for one of the pair of electrodes for applying a voltage to the moth-eye structure layer 105, the number of electrodes provided in the LED element 10 can be reduced. Of course, the p-side electrode 102 may be used instead of the n-side electrode 103 depending on the form of the LED element 10, and a pair of refractive index modulators are used separately from the anode electrode and the cathode electrode. An electrode may be provided.

Furthermore, since the plurality of modulation units 120 perform modulation using light emitted from the same light emitting unit 130, it is not necessary to provide the light emitting units 130 independently for each modulation unit 120, and the configuration and the manufacturing process are simplified. In addition, the cost can be reduced.
In addition, since many layers are provided in common for the plurality of modulation units 120, the configuration and the manufacturing process can be further simplified. In the example of FIG. 3, in addition to the light emitting unit 130, the n-side electrode 103, the transparent conductive film 104, and the moth-eye structure layer 105 are provided in common for the plurality of modulation units 120.

  In addition, since the moth-eye structure layer 105 is sandwiched between a pair of layers having a smaller sheet resistance than the moth-eye structure layer 105, an electric field can be reliably generated in the moth-eye structure layer 105. Furthermore, in this embodiment, since the moth-eye structure layer 105 and the modulation electrode layer 106 are made of the same group III nitride semiconductor as that of the semiconductor stacked portion 110, the device can be manufactured relatively easily.

  Returning to FIG. 1, the configuration of the receiver 20 will be described. The receiver 20 includes a CCD camera 21 as light detection means. The CCD camera 21 includes a plurality of light receiving elements and a lens that refracts incident light and guides the incident light to the light receiving elements, and these light receiving elements detect light La to Ld emitted from each modulation unit 120. With such a configuration, the CCD camera 21 detects the light emitted from each of the modulation units 120 for each modulation unit 120.

  FIG. 6 schematically shows the positional relationship between the LED element 10 and the CCD camera 21. The CCD camera 21 is arranged at a position where all the modulation units 120 of the LED element 10 can be photographed. The distance between the LED element 10 (or the modulation unit 120) and the CCD camera 21 is determined according to the resolution of the CCD camera 21. That is, the light emitted from each of the modulation units 120 may be a distance that can be independently detected by different light receiving elements of the CCD camera 21.

As illustrated in FIG. 1, the receiver 20 includes a demodulator 22 that demodulates a signal represented by light detected by the CCD camera 21 for each modulation unit 120. Since the configuration of the demodulator 22 is well known to those skilled in the art, the description of the specific configuration is omitted. The demodulator 22 may be provided as a part of the CCD camera 21 or may be provided outside the receiver 20.
As described above, the receiver 20 spatially decomposes and demodulates the signal light from the modulation unit 120 that modulates light based on each signal, thereby demodulating the spatially superimposed signal. Each can be played back separately.

In the present embodiment, the period of the convex portion 105 a can be set to 500 nm for a certain modulation unit 120. The wavelength of light modulated by the modulation unit 120 is 450 nm, and the refractive index of the group III nitride semiconductor layer is 2.4. Therefore, the optical wavelength is 187.5 nm. Moreover, since the half width of the light emitted from the multiple quantum well active layer 113 is 63 nm, the coherent length of the light is 3214 nm. In other words, in the modulation unit 120, the period of each convex portion 105a is greater than twice the corresponding optical wavelength and less than or equal to half the coherent length.
It should be noted that the period of the convex portion 105a in the other modulation unit 120 can be determined as appropriate by those skilled in the art based on the above description and the wavelength to be modulated by each modulation unit 120.

Moreover, in this embodiment, each convex part 105a is formed in a cone shape. Specifically, each convex portion 105a has a base end portion with a diameter of 200 nm and a depth of 250 nm.
The moth-eye structure layer 105 as a structure is preferably made of a material having a large Pockels effect. Specifically, it is preferable to have piezoelectricity, and more preferably an isotropic crystal. In the present embodiment, a light diffraction effect can be obtained by each of the convex portions 105a arranged periodically.

  In the first embodiment, the p-side electrode 102 forms the reflecting surface 102a. However, even if the reflecting surface 102a does not function or does not exist, the moth-eye structure layer 105 is used. The amount of light extracted from the LED element 10 changes due to the electric field generated in the. In short, the moth-eye structure layer 105 and an electric field adjusting unit that changes the refractive index by generating an electric field in the material of the moth-eye structure layer 105 may be provided.

  In the above embodiment, the moth-eye structure layer 105 is formed of AlN. However, as shown in FIG. 7, for example, n-type GaN layers 105x and AlN layers 105y may be alternately stacked. Good. In this case, since the electric field generated in each AlN layer 105y becomes strong, the refractive index change of the moth-eye structure layer 105 can be increased. For the modulation of light, it is preferable to change the refractive index of the moth-eye structure layer 105 using the Pockels effect. However, although the amount of change in the refractive index is smaller than that of the Pockels effect, the refractive index is changed using the Kerr effect. You can also

  Moreover, in the said embodiment, although what provided the refractive index modulation structure in the LED element 10 was shown, it is set as the refractive index modulator which does not have the light emission part 130 by omitting the multiple quantum well active layer 113 grade | etc.,. You can also This refractive index modulator can modulate the light transmitted through the refractive index modulator. For example, when used in combination with a light emitter such as an incandescent light bulb, the light emitted from the light emitter can be modulated. .

  In the first embodiment, the SiC substrate 101 is shown as a single crystal 6H type SiC to which N and B are added so as to emit a light bulb. For example, 6H to which Al, N and B are added is shown. White light may be emitted as type SiC, or white light may be emitted as a two-layer structure of 6H type SiC to which N and B are added and 6H type SiC to which N and Al are added.

  In the first embodiment, the LED element 10 is of a flip chip type, but it is needless to say that the LED element 10 may be a face up type. In addition, although the moth-eye structure layer 105 is shown in which the convex portions 105a are periodically formed, the concave portions may be periodically formed. Further, for example, the convex portion or the concave portion may be formed in a prismatic shape and aligned with the intersection of the virtual square lattice at a predetermined period. Furthermore, the convex portion or the concave portion may be a polygonal pyramid shape such as a triangular pyramid shape or a quadrangular pyramid shape, and it is needless to say that a specific detailed structure can be appropriately changed.

Further, in the first embodiment, the LED element 10 includes only a single light emitting unit 130, and all of the 16 modulation units 120 modulate light emitted from the same light emitting unit 130. As a modification, The LED element may include a plurality of light emitting units, and the transmitter may include a plurality of LED elements. Even with such a configuration, if at least two of the modulation means modulate the light emitted from the common light emitting unit, the configuration and the manufacturing process can be simplified and the cost can be reduced.
Further, the number of modulation units 120 is not limited to 16 as long as it is plural, and may be at least two. For example, when there are two, at least two of the light receiving elements of the CCD camera 21 may detect light emitted from different modulation units 120.

  Further, in the first embodiment, the period of the convex portion 105a in each modulation unit 120 is different for each specific wavelength modulated by the modulation unit 120. However, as a modification, not all modulations are necessary. It is not necessary for the periods in the unit 120 to be different, and it is sufficient that the periods in the at least two modulation units 120 are different.

Furthermore, the period of the convex part 105a may be the same for all the modulation parts 120. In this case, since light having the same wavelength (or the same wavelength range) is emitted from all the modulation units 120, the distance between the LED element 10 (or the modulation unit 120) and the CCD camera 21) Needs to be determined according to the resolution of the CCD camera 21.
The plurality of modulators 120 may modulate light based on different signals, respectively, or some or all of the modulators 120 may modulate light based on the same signal.

  In the first embodiment, the light detection means is configured by the CCD camera 21, but the light detection means may not be a CCD camera, and a phototransistor, a photodiode, a photo diode having an operation speed corresponding to the modulation speed of the modulation unit 120. An IC or the like can be used.

  In the first embodiment, the distance between the LED element 10 and the receiver 20 (or the distance between the modulation unit 120 and the CCD camera 21) is determined according to the resolution of the CCD camera 21, but as a modified example, This distance may exceed the resolution of the CCD camera 21. That is, it may exceed the range of distance that each of the modulation units 120 can recognize independently from each light receiving element of the CCD camera 21. Even in such a case, since the period of the convex portion 105a in each modulation unit 120 is different, the wavelength of the emitted light is different for each modulation unit 120, and the light from each modulation unit 120 is distinguished based on the wavelength. can do. In this case, the LED element 10 has a configuration in which the modulation units 120 that emit the same wavelength are not adjacent to each other (that is, a configuration in which the wavelengths of light emitted from the modulation units 120 that are adjacent to each other are different). Any distance may be used as long as the modulating units 120 that emit light can be distinguished from each other in the CCD camera 21. As the light detection means, a CCD camera equipped with a light receiving element for detecting light of different wavelengths may be used, and an optical filter that passes a specific wavelength before each light receiving element of the CCD camera is used. Also good.

10 LED element (transmitter), 20 receiver, 21 CCD camera, 22 demodulator, 30 DC power supply, 101 SiC substrate, 102 p-side electrode, 102a reflecting surface, 103 n-side electrode (electric field adjusting unit), 104 transparent conductive Film, 105 moth-eye structure layer (structure), 105a convex part, 105x n-type GaN layer, 105y AlN layer, 106 modulation electrode layer (electric field adjustment part), 107 pad (electric field adjustment part), 110 semiconductor lamination part, 111 Buffer layer, 112 n-type GaN layer, 113 multiple quantum well active layer, 114 electron block layer, 115 p-type GaN layer, 120 modulation unit (modulation means), 121 signal input power supply, 130 light emitting unit, θ _in incident angle, θ _out transmission angle, θ _ref reflection angle.

Claims (5)

At least one light emitting unit;
A plurality of modulating means for modulating light emitted from the at least one light emitting unit;
A structure including a material in which concave portions or convex portions are periodically formed on the surface;
A plurality of modulation means, including an electric field adjusting unit that generates an electric field that changes in the material and changes a refractive index of the material,
At least two of the modulation means modulate the light emitted from the same light emitting unit based on different signals. The light includes a plurality of wavelengths;
2. The transmitter according to claim 1, wherein the at least two of the modulation units have different periods in which the concave portion or the convex portion are formed according to any of the plurality of wavelengths.   The period in which the concave portion or the convex portion is formed in each of the plurality of modulation means is larger than an optical wavelength of light modulated by the modulation means and smaller than a coherent length of light modulated by the modulation means. Or the transmitter of 2. The transmitter according to any one of claims 1 to 3,
A communication system comprising: a receiver having a demodulator that demodulates light emitted from the plurality of modulation means for each of the modulation means. The receiver includes a plurality of light receiving elements that detect the light emitted from the plurality of modulation means,
The communication system according to claim 4, wherein at least two of the plurality of light receiving elements detect light emitted from the different modulation units.

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