Light-emitting element

Abstract

This light-emitting element (1) comprises comb-teeth electrodes (13, 14) on a surface of a substrate (10) composed of a liquid crystal that includes a rare-earth element that serves as a light-emission center. The comb-teeth electrodes (13, 14) are formed on zinc oxide thin films (11, 12) that are formed on the substrate (10).

Description

[Technical Field]

[0001] The present invention relates to a light-emitting device that uses a rare earth element as a luminescent center. [Background technology]

[0002] Rare-earth element luminescence centers have little non-radiative decay and are capable of emitting light in the communication wavelength band, so they are applied to various optical communication devices such as highly efficient lasers and amplifiers. In recent years, technology has been established to fabricate optical waveguides and resonators containing rare-earth elements on silicon substrates, and research and development is also underway to use them as light sources in on-chip optical integrated circuits (Non-Patent Document 1). However, because rare-earth element luminescence centers are difficult to control using an external electric field, it has been necessary to introduce a separate modulator to perform optical control such as intensity modulation.

[0003] One method for dynamically controlling the emission characteristics of rare earth elements is to use vibrational strain (Non-Patent Document 2). Non-Patent Document 2 reports a method for controlling emission wavelength using vibrational strain by processing a solid crystal containing a rare earth element into a cantilever-shaped oscillator structure. However, fabricating the cantilever structure requires three-dimensional processing using an ion beam, making it difficult to fabricate a large number of elements at once. This makes it difficult to integrate elements and increase the scale required for application to on-chip optical integrated circuits. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] X. [Non-patent document 2] R. Ohta,et al.,“Rare-Earth-Mediated Optomechanical System in the Reversed Dissipation Regime”,Physical Review Letters,126,047404,2021 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a light-emitting element that can modulate the emission wavelength and emission intensity of the emission center and can be easily applied to optical integrated circuits. [Means for solving the problem]

[0006] The light-emitting device of the present invention is characterized in that it has a comb-shaped electrode on the surface of a solid material containing a rare earth element that serves as a light-emitting center. [Effects of the Invention]

[0007] In the present invention, a comb-shaped electrode is provided on the surface of a solid material containing a rare earth element that serves as the luminescence center, and by applying an electric signal to the comb-shaped electrode, it is possible to modulate the luminescence wavelength and luminescence intensity of the luminescence center. Furthermore, the present invention facilitates the integration and large-scale scale of elements required for application to optical integrated circuits. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing the configuration of a light emitting device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of a comb electrode according to a first embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing a spectrum of a transmission signal between comb-tooth electrodes. [Figure 4] FIG. 4 is a diagram showing the relationship between the frequency of the electrical signal applied to the comb-tooth electrode and the optical absorption spectrum of erbium. [Figure 5] FIG. 5 is a diagram showing the change over time in the intensity of light output from the light emitting element. [Figure 6] FIG. 6 is a perspective view showing the configuration of a light emitting device according to a second embodiment of the present invention. [Figure 7] FIG. 7 is a perspective view showing the configuration of a light emitting device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Principle of the Invention] When a comb-shaped electrode is placed on a solid material with piezoelectric properties and an AC voltage is applied to the electrode, an elastic wave is generated on the surface of the solid material at a frequency corresponding to the spacing of the comb teeth. In this invention, we propose a structure that can control the light emission from rare earth element luminescence centers using this surface elastic wave.

[0010] For example, solid materials containing rare earth elements such as erbium (Er) are often non-piezoelectric materials, but by forming an oriented piezoelectric film, it is possible to generate surface acoustic waves. The strain and thermal effects of the surface acoustic waves make it possible to modulate the emission wavelength and intensity of the luminescence center. By creating a vibration resonance mechanism with a concave-convex structure on the surface of the solid material whose wavelength and period match the wavelength of the surface acoustic wave, it is possible to confine the surface acoustic wave and increase the strain effect of the surface acoustic wave. Furthermore, by removing part of the piezoelectric film or incorporating an optical waveguide or optical resonator, it is possible to improve the light extraction efficiency and luminous efficiency.

[0011] The structure of the present invention can be fabricated by ordinary semiconductor processes such as photolithography and metal deposition, and is characterized by its ease of integration of elements and large scale, which are required for application to optical integrated circuits.

[0012] [First Example] Hereinafter, examples of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following examples.

[0013] Fig. 1 is a perspective view showing the configuration of a light-emitting device according to this embodiment. The light-emitting device 1 comprises a substrate 10 made of yttrium silicate (Y2SiO5) crystals doped with Er, which serves as the luminescent center, zinc oxide (ZnO) thin films 11 and 12 each having a thickness of 500 µm formed on the substrate 10, and comb-shaped electrodes 13 and 14 made of a metal such as aluminum (Al) and having a thickness of 50 nm formed on the surfaces of the ZnO thin films 11 and 12. Reference numeral 100 in Fig. 1 denotes light output from the light-emitting device 1.

[0014] 2 is a plan view of the comb-tooth electrode 13. The comb-tooth electrode 13 has two opposing comb-shaped electrode portions 131 and 132. The electrode portions 131 and 132 are provided with a plurality of electrode fingers 133 and 134 that protrude toward the opposing electrode portion, respectively. The width W of the electrode fingers 133 and 134 is 500 μm, and the distance D between the electrode fingers 133 and 134 is 4 μm.

[0015] Similarly, comb-tooth electrode 14 has two opposing comb-shaped electrode portions 141 and 142. Electrode portions 141 and 142 are provided with a plurality of electrode fingers 143 and 144 that protrude toward the opposing electrode portion, respectively. As with comb-tooth electrode 13, electrode fingers 143 and 144 have a width of 500 μm and are spaced 4 μm apart.

[0016] To fabricate the light-emitting device 1 shown in Figure 1, a ZnO thin film is formed on a substrate 10, and comb-tooth electrodes 13 and 14 are formed on the ZnO thin film. The ZnO thin film is oriented in the c-axis direction. Finally, the ZnO thin film between the comb-tooth electrodes 13 and 14 is removed by wet etching to separate the ZnO thin film 11 below the comb-tooth electrode 13 from the ZnO thin film 12 below the comb-tooth electrode 14. It is possible to extract output light from the light-emitting device 1 from the area where the ZnO thin film has been removed, or to input excitation light into the area where the ZnO thin film has been removed.

[0017] The transmission spectrum of the electrical signal between the comb-tooth electrodes 13 and 14 is shown in Figure 3. The transmission spectrum in Figure 3 was obtained by applying an AC signal from an external power source between the electrode portions 131 and 132 of the comb-tooth electrode 13 to generate surface acoustic waves, and then detecting the electrical signal between the electrode portions 141 and 142 of the comb-tooth electrode 14. Although the comb-tooth electrodes 13 and 14 are electrically isolated, signal propagation was confirmed at frequencies of 200 MHz, 580 MHz, 950 MHz, and 1.3 GHz. The signal propagation indicates that the electrical signals at these frequencies were converted into surface acoustic waves by the comb-tooth electrode 13.

[0018] Next, we evaluated the changes in the optical properties of Er that occur when surface acoustic waves are excited. Figure 4 shows the relationship between the frequency of the electrical signal applied to the comb-tooth electrode 13 and the absorption spectrum of Er. The excitation light irradiated on the light-emitting element 1 can be light that resonates with the luminescence center. In this example, excitation light with a frequency of 195.117 THz to 195.123 THz was irradiated on the light-emitting element 1 from an external light source, and the frequency of the AC signal applied to the comb-tooth electrode 13 from an external power source was changed from 210 MHz to 190 MHz.

[0019] The example in Figure 4 shows that the optical absorption intensity decreases as the color goes from white to black, and that the optical absorption of 195.120 THz decreases significantly when the frequency of the signal applied to the comb-tooth electrode 13 matches 200 MHz. The results in Figure 4 show that the emission intensity of Er can be controlled by an electrical signal by using surface acoustic waves.

[0020] 5 shows the change over time in the intensity of light output from the light-emitting element 1 when an electrical signal in which a carrier wave with a carrier frequency of 200 MHz is intensity-modulated by a rectangular wave with a period of 60 seconds is applied to the comb-tooth electrode 13. When a voltage of approximately 10.8 V was applied to the comb-tooth electrode 13, intensity-modulated light emission of approximately 8.2 dB was confirmed.

[0021] [Second Example] 6 is a perspective view showing the configuration of a light-emitting device according to a second embodiment of the present invention. The light-emitting device 1a of this embodiment comprises a substrate 10, a ZnO thin film 15 formed on the substrate 10, comb-shaped electrodes 16 and 17 made of a metal such as Al formed on the surface of the ZnO thin film 15, and Bragg reflectors 18 and 19 (vibration resonance mechanisms) made of a metal such as Al formed on the surface of the ZnO thin film 15 to surround the comb-shaped electrodes 16 and 17.

[0022] In this example, curved comb-tooth electrodes 16 and 17 were formed on the same substrate 10 and ZnO thin film 15 as in the first example. The comb-tooth electrode 16 has two comb-shaped electrode portions 161 and 162 facing each other. The electrode portions 161 and 162 are provided with a plurality of electrode fingers 163 and 164 that protrude toward the opposing electrode portion, respectively. Similarly, the comb-tooth electrode 17 has two comb-shaped electrode portions 171 and 172 facing each other. The electrode portions 171 and 172 are provided with a plurality of electrode fingers 173 and 174 that protrude toward the opposing electrode portion, respectively.

[0023] In this example, Bragg reflectors 18 and 19 are formed by arranging a plurality of thin metal wires on the outer sides of comb-tooth electrodes 16 and 17 on the surface of ZnO thin film 15. The width of the thin metal wires is the same as the width of electrode fingers 163, 164, 173, and 174. The spacing between the thin metal wires is the same as the spacing between electrode fingers 163 and 164 and the spacing between electrode fingers 173 and 174.

[0024] Surface acoustic waves generated by applying an electric signal to the comb-tooth electrodes 16 or 17 are reflected by the Bragg reflectors 18, 19 and gather in the center of the substrate surrounded by the Bragg reflectors 18, 19. In this embodiment, the Bragg reflectors 18, 19 can confine the surface acoustic waves, so the Q value, which indicates the confinement performance, can be increased, and the distortion effect of the surface acoustic waves can be made greater than in the first embodiment. With the above configuration, this embodiment makes it possible to improve the modulation amplitude of light and reduce the applied voltage.

[0025] In this embodiment, a Bragg reflector made of thin metal wires is used as a vibration resonance mechanism for spatially confining surface acoustic waves, but this is not limited to this and various other vibration resonance mechanisms can be applied.

[0026] [Third Example] 7 is a perspective view showing the configuration of a light-emitting element according to a third embodiment of the present invention. The light-emitting element 1b of this embodiment has a thin-wire optical waveguide 20 made of silicon nitride (Si3N4) formed on the surface of the substrate 10 between the comb-tooth electrodes 13 and 14 of the first embodiment. The optical waveguide 20 has a width of 1 μm and a thickness of 500 nm.

[0027] In the structure of this embodiment, a portion of the light propagating through the optical waveguide 20 seeps into the substrate 10, thereby achieving efficient optical excitation of Er near the substrate surface. It is also possible to extract the output light of the light-emitting element 1b via the optical waveguide 20. Furthermore, in this embodiment, the output light can be guided via the optical waveguide 20 to other optical elements, such as a demultiplexer or detector, on the same chip as the light-emitting element 1b, thereby realizing a structure suitable for application to optical integrated circuits.

[0028] In this embodiment, a thin-wire optical waveguide is used as the optical waveguide, but it is also possible to use optical waveguides or optical resonators of various other shapes. In the second embodiment, the ZnO thin film 15 between the comb-tooth electrodes 16 and 17 may be removed, and an optical waveguide or an optical resonator may be formed on the surface of the substrate 10 between the comb-tooth electrodes 16 and 17 .

[0029] In the first to third embodiments, a ZnO thin film, which is a piezoelectric film, was formed on a Y2SiO5 crystal to control the light emission of Er, but the present invention is not limited to a specific crystal, a specific piezoelectric film, or a specific rare earth element. Furthermore, in the first to third embodiments, comb-tooth electrodes with linear and curved electrode fingers were used, but the present invention is not limited to comb-tooth electrodes with a specific shape. Furthermore, in the first to third embodiments, two electrodes are provided, as in the examples of comb-tooth electrodes 13 and 14 or comb-tooth electrodes 16 and 17, but a single comb-tooth electrode may be used because a surface acoustic wave can be generated if an excitation electrode is provided.

[0030] Some or all of the above embodiments may be described as, but are not limited to, the following supplementary notes.

[0031] (Note 1) The light-emitting device of the present invention has a comb-shaped electrode on the surface of a solid material containing a rare earth element that serves as the luminescence center.

[0032] (Supplementary Note 2) In the light-emitting device according to Supplementary Note 1, the comb-tooth electrode is formed on the surface of a piezoelectric film formed on the solid material.

[0033] (Supplementary Note 3) The light-emitting device according to Supplementary Note 1 further includes a vibration resonance mechanism formed on the surface of the solid material so as to surround the comb-teeth electrode and configured to reflect surface acoustic waves from the comb-teeth electrode.

[0034] (Supplementary Note 4) In the light-emitting device according to Supplementary Note 3, the comb-tooth electrode and the vibration resonance mechanism are formed on the surface of a piezoelectric film formed on the solid material.

[0035] (Supplementary Note 5) The light-emitting device according to Supplementary Note 1 further comprises an optical waveguide or an optical resonator on the surface of the solid material.

[0036] (Appendix 6) In the light-emitting element described in Appendix 5, the comb-tooth electrode is formed on the surface of a piezoelectric film formed on the solid material, and the optical waveguide or the optical resonator is formed on the surface of the solid material in a region where a portion of the piezoelectric film near the comb-tooth electrode has been removed.

[0037] (Appendix 7) The light-emitting element described in Appendix 1 further includes a vibration resonance mechanism formed on the surface of the solid material so as to surround the comb-teeth electrode and configured to reflect surface acoustic waves from the comb-teeth electrode, and an optical waveguide or an optical resonator formed on the surface of the solid material.

[0038] (Appendix 8) In the light-emitting device described in Appendix 7, the comb-tooth electrode and the vibration resonance mechanism are formed on the surface of a piezoelectric film formed on the solid material, and the optical waveguide or the optical resonator is formed on the surface of the solid material in a region where a portion of the piezoelectric film near the comb-tooth electrode has been removed. [Industrial Applicability]

[0039] The present invention can be applied to a light-emitting device. [Explanation of symbols]

[0040] 1, 1a, 1b...light-emitting element, 10...substrate, 11, 12, 15...zinc oxide thin film, 13, 14, 16, 17...comb-tooth electrode, 18, 19...Bragg reflector, 20...thin-wire optical waveguide, 131, 132, 141, 142, 161, 162, 171, 172...electrode portion, 133, 134, 143, 144, 163, 164, 173, 174...electrode fingers

Claims

1. A light-emitting device characterized by comprising a comb-shaped electrode on the surface of a solid material containing a rare earth element that serves as a light-emitting center.

2. 2. The light-emitting device according to claim 1, The light-emitting element is characterized in that the comb-teeth electrode is formed on the surface of a piezoelectric film formed on the solid material.

3. 2. The light-emitting device according to claim 1, A light-emitting device further comprising a vibration resonance mechanism formed on the surface of the solid material so as to surround the comb-teeth electrode and configured to reflect surface acoustic waves from the comb-teeth electrode.

4. 4. The light-emitting device according to claim 3, The light-emitting element is characterized in that the comb-tooth electrode and the vibration resonance mechanism are formed on the surface of a piezoelectric film formed on the solid material.

5. 2. The light-emitting device according to claim 1, The light-emitting device further comprises an optical waveguide or an optical resonator on the surface of the solid material.

6. 6. The light-emitting device according to claim 5, the comb-tooth electrode is formed on a surface of a piezoelectric film formed on the solid material, The light-emitting device is characterized in that the optical waveguide or the optical resonator is formed on the surface of the solid material in a region where a part of the piezoelectric film near the comb-teeth electrode has been removed.

7. 2. The light-emitting device according to claim 1, a vibration resonance mechanism formed on the surface of the solid material so as to surround the comb-teeth electrode and configured to reflect surface acoustic waves from the comb-teeth electrode; A light-emitting device further comprising an optical waveguide or an optical resonator formed on the surface of the solid material.

8. 8. The light-emitting device according to claim 7, the comb-tooth electrode and the vibration resonance mechanism are formed on a surface of a piezoelectric film formed on the solid material, The light-emitting device is characterized in that the optical waveguide or the optical resonator is formed on the surface of the solid material in a region where a part of the piezoelectric film near the comb-teeth electrode has been removed.

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