JP6139893B2 - Plasmon quantum interferometric modulator - Google Patents

Description

  The present invention relates to a modulator using plasmons, and more particularly to a modulator that modulates plasmon intensity by an interference effect.

  In an optical communication device, an optical modulator for modulating the intensity of an input optical signal is used. As an optical modulator, for example, a Mach-Zehnder interferometer type optical modulator is conventionally known. The Mach-Zehnder interferometer type optical modulator includes an input waveguide, two arm waveguides branched from the input waveguide, and an output waveguide where the two arm waveguides merge. In the Mach-Zehnder type optical modulator, the intensity of light is controlled by changing the refractive index of at least one of the two arm waveguides, that is, by modulating the light propagation constant, thereby controlling the interference of light passing through the two arm waveguides. Modulation can be performed.

  In order to change the refractive index of the waveguide, for example, an electro-optic effect (EO effect) is used. As the waveguide material, lithium niobate (LN) having a large EO effect and a high response speed is preferably used. However, even when LN is used in the waveguide, it is necessary to configure the optical modulator with a size of about several centimeters in order to generate a refractive index change corresponding to a phase difference of π radians. Further, due to the material dispersion of LN, the modulation speed is limited to about several tens to 100 Gbps.

  Furthermore, since the optical modulator uses light, it is limited by the diffraction limit of light, and thus there is a limit to downsizing the optical modulator. Therefore, in order to increase the integration of optical communication devices, a Mach-Zehnder interferometer type modulator (called a plasmon modulator) that uses plasmons instead of light has recently been studied. The plasmon modulator is common to the above-described Mach-Zehnder optical modulator in that it includes an input waveguide, two arm waveguides, and an output waveguide. However, it is the plasmon generated from the optical signal that passes through the waveguide of the plasmon modulator, and the Mach-Zehnder type optical modulator is different in that intensity modulation is performed using interference between plasmons that have passed through the two arm waveguides. Different. Since the diffraction limit of light is not applied to plasmons, the plasmon modulator can be miniaturized beyond the diffraction limit of light.

  Non-Patent Documents 1 to 3 describe Mach-Zehnder interferometer type plasmon modulators. The plasmon modulators described in Non-Patent Documents 1 to 2 use the thermo-optic effect (TO effect) and heat two or more arm waveguides to change the plasmon propagation constant, thereby changing the two arm waveguides. Intensity modulation is performed by controlling the interference of plasmons that have passed through. In particular, Non-Patent Document 3 realizes a plasmon modulator having a small size of 60 μm.

T. Nikolajsen et al., "Surface plasmon polariton based modulators and switches operating at telecom wavelengths", Appl. Phys. Lett., 2004, Vol. 85, No. 24, pp. 5833-5835 D. Kalavrouziotis et al., "First demonstration of active plasmonic device in true data traffic conditions: ON / OFF thermo-optic modulation using a hybrid silicon-plasmonic asymmetric MZI", Optical Fiber Communication Conference (OFC) 2012, 2012, OW3E. Three S. Papaioannou et al., "WDM Switching Employing a Hybrid Silicon-Plasmonic A-MZI", European Conference and Exhibition on Optical Communication (ECOC) 2012, 2012, P2.10

  However, since the plasmon modulators described in Non-Patent Documents 1 to 3 use the TO effect, it takes time to increase and decrease the heat, and there is a limit to improving the response speed. In the optical modulator using the above-described LN, the modulation speed is about several tens to 100 Gbps, whereas the plasmon modulator described in Non-Patent Documents 1 to 3 is about several tens of Kbps. Practically, a higher modulation speed is required.

  Further, in an optoelectronic integrated chip that is expected to be realized in the future, a modulator having a small size of several μm or less is considered necessary. For this reason, the size of 60 μm of Non-Patent Document 3 is still insufficient, and further downsizing of the plasmon modulator is required.

  The present invention has been made to solve the above-described problems, and includes a plasmon modulator that can be reduced in size and capable of speeding up modulation, and an optical modulator including the plasmon modulator. The purpose is to provide.

  A first aspect of the present invention is a modulator that modulates plasmons, and an input waveguide for guiding the plasmons, and each input end thereof is connected to an output end of the input waveguide. Two arm waveguides for guiding the plasmons; an output waveguide for guiding the plasmons, the input ends of which are connected to the respective output ends of the two arm waveguides; Magnetic field generating means for generating a magnetic field in a region surrounded by two arm waveguides.

  According to a second aspect of the present invention, there is provided a modulator for modulating plasmons, wherein an input waveguide for guiding the plasmons and each input end thereof are connected to an output end of the input waveguide. Two arm waveguides for guiding the plasmons; an output waveguide for guiding the plasmons, the input ends of which are connected to the respective output ends of the two arm waveguides; Voltage applying means for applying a voltage to at least one of the two arm waveguides.

  Since the plasmon modulator according to the present invention performs modulation by applying a magnetic field or voltage to an electron wave that constitutes a plasmon generated from light, it can be made smaller than a conventional plasmon modulator. In addition, miniaturization beyond the diffraction limit of light is possible. Further, as a result of the miniaturization, it is possible to perform modulation at a higher speed than the conventional plasmon modulator.

It is a schematic diagram for demonstrating the waveform of a plasmon and an electron wave. It is a schematic diagram for demonstrating the principle of operation of this invention. It is the top view and sectional drawing of a plasmon modulator which concern on 1st Embodiment. It is the top view and perspective view of the magnetic field generation means which concern on 1st Embodiment. It is a schematic diagram for demonstrating the calculation method of the current required in order to generate (pi) phase modulation. It is a figure which shows the graph of an electric current required in order to generate (pi) phase modulation. It is a schematic diagram for demonstrating the waveform of a plasmon and an electron wave. It is a top view of the plasmon modulator which concerns on 2nd Embodiment. It is a top view of the plasmon modulator which concerns on 3rd Embodiment. It is a top view of the plasmon modulator which concerns on 4th Embodiment. It is a top view of the plasmon modulator which concerns on 5th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

(Operating principle)
First, the operation principle of the present invention will be described. It is known that when light is incident on the interface between the dielectric and the metal, free electrons in the metal collectively vibrate due to the electric field vibration of the light and propagate in the direction of the interface as a density wave with electron density. This density wave of electron density is called plasmon. Plasmons are not constrained by the diffraction limit of light, and thus can be confined in a region smaller than the wavelength of light.

  FIG. 1A is a schematic diagram showing a light waveform 1. FIG. 1B is a schematic diagram showing a waveform 2 of electrons in the metal before the incidence of light. Here, for simplification, FIG. 1B shows a state in which individual electron waves (also referred to as electron waves) are in phase (that is, a coherent state). Therefore, the waveform 1 shown in FIG. 1B is a shape in which a large number of electron waves are superimposed, and only the amplitude of one electron wave is increased.

  When light is incident on the metal, the electron density is sparse due to the electric field vibration of the incident light. Therefore, in accordance with the light waveform 1 shown in FIG. 1A, the waveform 2 of the electrons in the metal shown in FIG. The amplitude changes. FIG. 1 (c) shows a waveform 2 'of electrons in the metal after incidence of light. Thus, the envelope (waveform 1 ') of the waveform 2' of the electron changed by the incident light indicates the waveform of the plasmon that is a density wave of electron density. 1A to 1C show wavelengths different from the actual wavelengths in consideration of easy viewing. The actual electron density density wave (waveform 1 ′) has a length on the order of μm, whereas the electron wave (waveform 2 ′) has a wavelength less than a thousandth (sub-nm order, for example, About 0.5 nm). That is, one wave of the waveform 1 ′ includes one thousand or more waves of the waveform 2 ′.

  The individual electrons constituting the plasmon can undergo a phase change due to the quantum interference effect. The present invention uses the quantum interference effect for changing the phase of the quantum mechanical wave of the individual electrons constituting the plasmon, instead of using the propagation constant change due to the EO effect or the TO effect as in the conventional case for the plasmon interference. . The conventional plasmon modulator changes the propagation constant of a plasmon wave (corresponding to the waveform 1 'in FIG. 1C), which is an electron density wave. In contrast, in the present invention, the phase of the electron wave (corresponding to the waveform 2 'in FIG. 1C) is changed. Therefore, in the present invention, since the modulation target is an electron wave having a small wavelength, the modulator can be made smaller than before. Further, since the CR time constant of the circuit is reduced by reducing the size of the modulator, the modulation speed can be increased.

  The quantum interference effect used in the present invention will be described below. This quantum interference effect is also known as the Aharanov-Bohm effect. FIG. 2 is a schematic diagram of the Mach-Zehnder interferometer 3 using plasmons. The Mach-Zehnder interferometer 3 includes an input waveguide 4, two arm waveguides 5a and 5b branched from the input waveguide 4, and an output waveguide 6 where the two arm waveguides 5a and 5b merge. When a plasmon passes through such a Mach-Zehnder interferometer 3, when a magnetic field and an electric field are applied to the two arm waveguides 5a and 5b, the relationship between the wave functions of electron waves constituting the plasmon in each waveguide is as follows. It can be expressed as

[psi ₁ and [psi ₂ each two arm waveguides 5a, the electron wave wave function immediately after branches to 5b, [psi _{1 'and} [psi _2' each two arm waveguides 5a, the effect of magnetic and electric fields in 5b The wave function of the electron wave after reception, ψ ′, is the wave function of the electron wave in the output waveguide 6.

  φ is a scalar potential corresponding to the electric field, and A (x) is a vector potential corresponding to the magnetic field. The integrals of the equations (1) and (2) are integrals along the paths of the arm waveguides 5a and 5b, respectively, and the integral of the equation (3) is the area of the region surrounded by the arm waveguides 5a and 5b. is there.

  The integral of the vector potential A (x) in the equation (3) is equal to the total magnetic flux Φ penetrating the region surrounded by the arm waveguides 5a and 5b, as represented by the following equation (4).

  From the above equations (1) to (4), the wave function ψ ′ of the electron wave in the output waveguide 6 can be changed by changing at least one of the scalar potential φ and the vector potential A (x). I understand. That is, at least one of a voltage applied to the arm waveguides 5a and 5b (corresponding to the scalar potential φ) and a magnetic field in the region surrounded by the arm waveguides 5a and 5b (corresponding to the vector potential A (x)) is changed. Thus, the modulation of the electron wave can be performed.

(First embodiment)
In the present embodiment, the electron wave is modulated by changing the vector potential A (x), that is, by changing the magnetic field, in the quantum interference effect described using the equations (1) to (4). In this embodiment, the scalar potential φ component is set to 0 in equation (3). Therefore, the output electron wave is modulated by changing the vector potential A (x). Here, when the magnetic flux quantum unit h / 2e is substituted into the integral value of the equation (3), the following equation (5) is obtained from the relationship of h (hever) = h / 2π.

  Therefore, by changing the magnetic field in the region surrounded by the two arm waveguides 5a and 5b by the magnetic flux quantum unit, the phase difference cancels out the electron waves passing through the two arm waveguides 5a and 5b. A phase shift of π radians (also referred to as π phase shift) can be caused. Therefore, sufficient phase interference can be caused with very small power required for causing magnetic field fluctuations in units of magnetic flux quantum, so that the power consumption of the plasmon modulator can be greatly reduced.

  FIG. 3A is a plan view of the plasmon modulator 10 according to the present embodiment. A plasmon modulator 10 (also referred to as a plasmon quantum interference modulator) branches from an input optical waveguide 12, an input plasmon waveguide 13 connected to the input optical waveguide 12, and the input plasmon waveguide 13 in a substrate 11. Two arm waveguides 14a and 14b, an output plasmon waveguide 15 where the arm waveguides 14a and 14b merge, and an output optical waveguide 16 connected to the output plasmon waveguide 15 are provided. Each waveguide has an input end to which an optical signal or plasmon is input (incident) and an output end to which an optical signal or plasmon is output (emitted).

  The plasmon modulator 10 further includes a conductive wire 17 as a magnetic field generating means for generating a magnetic field in a region surrounded by the two arm waveguides 14a and 14b, and a current for supplying the conductive wire 17 with a current. A magnetic field control device 18.

The substrate 11 is formed using a dielectric material (for example, SiO ₂ ). The input optical waveguide 12 is a transmission path for guiding an optical signal, and is formed of a dielectric material (for example, SiO ₂ doped with impurities) having a refractive index higher than that of the substrate 11. Light is input from the input end of the input optical waveguide 12. With such a configuration, the substrate 11 serves as a clad and the input optical waveguide 12 serves as a core, and an optical signal is guided.

  The input plasmon waveguide 13 is a transmission path for guiding plasmons. The input end of the input plasmon waveguide 13 is connected to the output end of the input optical waveguide 12. The input plasmon waveguide 13 is made of a material (for example, a metal material such as gold or silver) in which plasmons are easily excited and propagated, and has a thin film shape. When an optical signal is incident on the surface of the input plasmon waveguide 13, the plasmon is excited, and the excited plasmon propagates on the surface of the input plasmon waveguide 13.

  FIG. 3B is a cross-sectional view of the plasmon modulator 10 according to the present embodiment, and is a connection portion between the input optical waveguide 12 and the input plasmon waveguide 13 (AA ′ line in FIG. 3A). A cross section of the plasmon modulator 10 is shown. The input optical waveguide 12 and the input plasmon waveguide 13 are in contact with each other with a predetermined area in the propagation direction of the optical signal and the plasmon at the connection portion. With such a configuration, a wider contact area is ensured than when the input optical waveguide 12 and the input plasmon waveguide 13 are connected to each other at the end faces, so that an optical signal passing through the input optical waveguide 12 is sufficient for the input plasmon waveguide 13. Is incident on. As a result, the plasmon is easily excited on the surface of the input plasmon waveguide 13 by the optical signal.

  The arm waveguides 14a and 14b are transmission paths for guiding plasmons, respectively. The input ends of the arm waveguides 14 a and 14 b are connected to the output end of the input plasmon waveguide 13. The arm waveguides 14a and 14b are made of a metal material (for example, gold or silver) in which plasmons are easily excited and propagated, and have a thin film shape. The plasmon propagated on the input plasmon waveguide 13 is branched into two at the portion where the input plasmon waveguide 13 is connected to the arm waveguides 14a and 14b, and is propagated on the surfaces of the arm waveguides 14a and 14b, respectively. The

  The output plasmon waveguide 15 is a transmission path for guiding plasmons. The input end of the output plasmon waveguide 15 is connected to the output end of each of the arm waveguides 14a and 14b. The output plasmon waveguide 15 is made of a material (for example, a metal material such as gold or silver) in which plasmons are easily excited and propagated, and has a thin film shape. The plasmons propagated on the arm waveguides 14 a and 14 b are merged together at a portion where the arm waveguides 14 a and 14 b are connected to the output plasmon waveguide 15, and propagated on the surface of the output plasmon waveguide 15. .

The output optical waveguide 16 is a transmission path for guiding an optical signal, and is formed of a dielectric material (for example, SiO ₂ doped with impurities) having a higher refractive index than that of the substrate 11. The input end of the output optical waveguide 16 is connected to the output end of the output plasmon waveguide 15. The plasmon propagated on the output plasmon waveguide 15 is converted into an optical signal at a connection portion between the output plasmon waveguide 15 and the output optical waveguide 16 and input to the output optical waveguide 16. With such a configuration, the substrate 11 serves as a clad and the output optical waveguide 16 serves as a core, and an optical signal is guided. Light is output from the output end of the output optical waveguide 16.

  FIG. 3C is a cross-sectional view of the plasmon modulator 10 according to the present embodiment, and is a connection portion between the output plasmon waveguide 15 and the output optical waveguide 16 (BB ′ line in FIG. 3A). A cross section is shown. The output plasmon waveguide 15 and the output optical waveguide 16 are in contact with each other with a predetermined area in the propagation direction of the optical signal and the plasmon at the connection portion thereof. With such a configuration, a wider contact area is ensured than when the output plasmon waveguide 15 and the output optical waveguide 16 are connected to each other at the end faces, so that the plasmon passing through the output plasmon waveguide 15 is converted into an optical signal and output. It becomes easy to output to the optical waveguide 16.

  The conductive wire 17 is formed using an arbitrary conductive material, and is provided in a straight line along the propagation direction of the optical signal and the plasmon. The magnetic field control device 18 is connected to the conductive wire 17, supplies a current C to the conductive wire 17, and controls the magnitude and timing of the current C. When a current C is supplied from the magnetic field control device 18 to the conductive wire 17, a magnetic field is generated around the conductive wire 17, and as a result, a magnetic field is also generated in a region surrounded by the two arm waveguides 14a and 14b. Therefore, by controlling the current C supplied from the magnetic field control device 18 to the conductive wire 17, the quantum interference effect on the electrons constituting the plasmons passing through the arm waveguides 14a and 14b can be controlled, and as a result output The intensity of the plasmon output to the plasmon waveguide 15 can be modulated.

  The conductive wire 17 as the magnetic field generating means is not limited to a linear shape as shown in FIG. 3A, but can arbitrarily generate a magnetic field in a region surrounded by the two arm waveguides 14a and 14b. The shape may be sufficient. 4A and 4B are a plan view and a perspective view showing another form of the conductive wire 17 as the magnetic field generating means. The conductive wire 17 shown in FIGS. 4A and 4B is a single-turn coil, and is provided along the two arm waveguides 14 a and 14 b in parallel to the surface of the substrate 11. When a current C is passed through the conductive wire 17, a magnetic flux Φ is generated in a region surrounded by the two arm waveguides 14a and 14b.

  In the present embodiment, the conductive wire 17 and the magnetic field control device 18 are provided separately from the substrate 11, but at least a part of the conductive wire 17 and the magnetic field control device 18 may be provided in the substrate 11.

  In the plasmon modulator 10 according to the present embodiment, a current required for phase modulation was calculated. FIG. 5 is a diagram for explaining a current calculation method. As shown in FIG. 5, it is assumed that the two arm waveguides 14a and 14 and the conductive wire 17 exist on the same plane, and a region surrounded by the two arm waveguides 14a and 14b is defined as a circle D having a radius R. I reckon. The total magnetic flux Φ in the region surrounded by the two arm waveguides 14a and 14b can be expressed by the following equation (6).

r is a coordinate in the direction perpendicular to the conductive wire 17 (the position of the conductive wire 17 is zero), and l is a coordinate in the direction along the conductive wire 17 (the center of the circle D is zero). is there. θ is an angle with respect to the center of the circle D. d is the distance between the conductive wire 17 and the arm waveguide 14 b closer to the conductive wire 17. μ is magnetic permeability (assuming 1.275 × 10 ⁻⁶ H / m). I is the value of the direct current flowing through the conductive wire 17.

  As described using the equation (5), causing the π phase shift corresponds to changing the magnetic flux in the region surrounded by the two arm waveguides 14a and 14b by the magnetic flux quantum unit h / 2e. Therefore, in Formula (6), the value of the current I necessary to cause the π phase shift can be calculated by substituting the magnetic flux quantum unit h / 2e for Φ.

  FIG. 6 is a graph showing a relationship between the radius R of the circle D and the value of I necessary for causing the π phase shift, calculated using the equation (6). The distance d between the conductive wire 17 and the arm waveguide 14b was set in three ways: 1 μm, 2 μm, and 3 μm.

  From FIG. 6, it can be seen that the larger the radius R, that is, the larger the region surrounded by the two arm waveguides 14a and 14b, the more π phase shift can be caused by a smaller current. Further, FIG. 6 shows that a π phase shift can be caused with a smaller current as the distance d between the conductive wire 17 and the arm waveguide 14b is shorter.

  Specifically, according to FIG. 6, the distance d between the conductive wire 17 and the arm waveguide 14b is 3 μm or less, the radius R is 10 μm or less, and the current value that causes the π phase shift is several. A plasmon modulator of less than mA can be realized. In this case, assuming that the resistance value of the conductive wire 17 is about several Ω, the power consumption is less than 1 mW. As described above, the plasmon modulator 10 can be configured in a very small size, and a π phase shift can be caused by a magnetic flux fluctuation of a magnetic flux quantum unit, so that power consumption can be greatly reduced.

  Since the plasmon modulator 10 according to the present embodiment modulates an electron wave having a small wavelength, the plasmon modulator 10 can be made smaller in size than the conventional plasmon modulator. Moreover, since the CR time constant as a circuit is reduced by reducing the size of the plasmon modulator, the modulation speed can be increased. Furthermore, since a π phase shift can be caused by a magnetic flux fluctuation in units of magnetic flux quantum, power consumption can be greatly reduced.

(Second Embodiment)
In the description of FIGS. 1A to 1C, it is assumed that each electron wave is in a coherent state. However, generally, at normal temperature, the phases of the electron waves are not aligned (incoherent state).

  FIG. 7A is a schematic diagram showing a waveform of electrons in the metal after the incidence of light when each electron wave is in an incoherent state. In FIG. 7A, since the phases of the individual electron waves are not aligned and do not take the shape of the waves when superimposed, the waveform 8 of the electrons is indicated by diagonal lines.

  Since the plasmon excitation occurs even when the electrons are incoherent, the waveform 7 which is the envelope of the electron waveform 8 which is the plasmon waveform is the same as the waveform 1 ′ in FIG. However, when the electrons are incoherent, the quantum interference effect associated with each electron is averaged, so that the interference intensity is reduced, that is, the intensity modulation resolution is reduced. Therefore, it is desirable to increase the coherency of electrons in order to improve the interference intensity and improve the intensity modulation resolution.

  In order to bring the electrons closer to a coherent state, the waveguide of the electron wave may be made of a superconductor. Since electrons behave as Fermi particles at room temperature, they occupy different states. On the other hand, in the superconducting state, electron pairs behave as Bose particles and Bose-Einstein condensation occurs, so that a plurality of electron pairs occupy the same state and become coherent.

  FIG. 8 is a plan view of the plasmon modulator 20 according to the present embodiment. The plasmon modulator 20 includes an input optical waveguide 12, an input plasmon waveguide 13 connected to the input optical waveguide 12, and an input superconducting waveguide 23 connected to the input plasmon waveguide 13 in the substrate 11. The two arm superconducting waveguides 24 a and 24 b branched from the input superconducting waveguide 23, the output superconducting waveguide 25 where the arm superconducting waveguides 24 a and 24 b merge, and the output superconducting waveguide 25 are connected. An output plasmon waveguide 15 and an output optical waveguide 16 connected to the output plasmon waveguide 15. Each waveguide has an input end to which an optical signal or plasmon is input (incident) and an output end to which an optical signal or plasmon is output (emitted).

  Further, the plasmon modulator 20 supplies a current to the conductive wire 17 as a magnetic field generating means for generating a magnetic field in a region surrounded by the two arm superconducting waveguides 24 a and 24 b, and the conductive wire 17. A magnetic field control device 18 for cooling and a cooling device 21 for cooling the member.

  The input optical waveguide 12, the input plasmon waveguide 13, the output plasmon waveguide 15, and the output optical waveguide 16 have the same configuration as that of the first embodiment.

  The cooling device 21 cools at least the superconductor portion of the plasmon modulator 20, that is, the input superconducting waveguide 23, the arm superconducting waveguides 24 a and 24 b, and the output superconducting waveguide 25. In order to bring a metal or compound into a superconducting state, it is necessary to cool it below a predetermined temperature that varies depending on the substance. The predetermined temperature is, for example, about 1K for Al and about 90K for YBCO. As the cooling device 21, any superconductor material constituting the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25 can be cooled to a low temperature at which the superconducting material becomes superconducting. Can be used. The cooling device 21 may be configured to cool the entire plasmon modulator 20 or may be configured to cool only a portion of the plasmon modulator 20 that is configured of at least a superconductor material. May be.

  When performing a modulation operation using the plasmon modulator 20, the cooling device 21 is operated to maintain the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25 in a superconducting state. Keep it.

  The input superconducting waveguide 23 is a transmission path for guiding plasmons propagating from the input plasmon waveguide 13. The input end of the input superconducting waveguide 23 is connected to the output end of the input plasmon waveguide 13. The input superconducting waveguide 23 is made of a superconductor material (for example, a metal such as Al, Nb, In, Sn, or a compound such as YBCO), and has a thin film shape. Plasmon propagated from the input plasmon waveguide 13 is propagated on the surface of the input superconducting waveguide 23 in a superconducting state.

  The arm superconducting waveguides 24a and 24b are transmission lines for guiding plasmons. The input ends of the arm superconducting waveguides 24 a and 24 b are connected to the output end of the input superconducting waveguide 23. The arm superconducting waveguides 24a and 24b are formed of a superconductor material (for example, a metal such as Al, Nb, In, or Sn, or a compound such as YBCO), and has a thin film shape. Plasmon propagated on the input superconducting waveguide 23 is branched into two at the portion where the input superconducting waveguide 23 is connected to the arm superconducting waveguides 24a and 24b, and the arm superconducting waveguide 24a, It propagates on the surface of 24b in a superconducting state.

  The output superconducting waveguide 25 is a transmission path for guiding plasmons. The input end of the output superconducting waveguide 25 is connected to the output end of each of the arm superconducting waveguides 24a and 24b. The output superconducting waveguide 25 is made of a superconductor material (for example, a metal such as Al, Nb, In, Sn, or a compound such as YBCO) and has a thin film shape. The plasmons propagated on the arm superconducting waveguides 24 a and 24 b are merged together at a portion where the superconducting waveguides 24 a and 24 b are connected to the output superconducting waveguide 25. Propagated on the surface in a superconducting state. Thereafter, the propagated plasmon is input from the output end of the output superconducting waveguide 25 to the input end of the output plasmon waveguide 15.

  The conductive wire 17 and the magnetic field control device 18 have the same configuration as that of the first embodiment, and generate a magnetic field in a region surrounded by the two arm superconducting waveguides 24a and 24b. By controlling the current C supplied to the conductive wire 17 from the magnetic field control device 18, the quantum interference effect of the electrons constituting the plasmons passing through the arm superconducting waveguides 24a and 24b can be controlled. The intensity of the plasmon output to the conductive waveguide 25 can be modulated.

  In the present embodiment, since the plasmons passing through the arm superconducting waveguides 24a and 24b are in a superconducting state, individual electrons constituting the plasmons are in a coherent state. Therefore, the interference intensity can be improved and the modulation resolution can be improved as compared with the first embodiment. Furthermore, in the superconducting state, the electron pairs are united to cause electron wave interference, so that a π phase shift can be performed with a magnetic flux fluctuation that is half the magnetic flux quantum unit h / 2e. As a result, the power consumption of the plasmon modulator can be further reduced as compared with the first embodiment in which the π phase shift is performed by the magnetic flux fluctuation of the magnetic flux quantum unit h / 2e.

  In superconductor materials, the excitation efficiency of plasmons when light is incident may be low. For this reason, if all the waveguides through which plasmons propagate are made of a superconductive material, the excitation efficiency of plasmons may be reduced, and the modulation efficiency as a plasmon modulator may be deteriorated. On the other hand, in this embodiment, the input plasmon waveguide 13 and the output plasmon waveguide 15 are made of a material in which plasmons are easily excited and propagated, and the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and The output superconducting waveguide 25 is made of a superconductor material. For this reason, it is possible to suppress a decrease in the excitation efficiency of plasmons and bring only a specific portion of the waveguide into a superconducting state.

  Furthermore, since the plasmon modulator 20 according to the present embodiment modulates an electron wave having a small wavelength as in the first embodiment, the size can be made smaller than that of the conventional plasmon modulator. Become. Moreover, since the CR time constant as a circuit is reduced by reducing the size of the plasmon modulator, the modulation speed can be increased.

  In this embodiment, the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25 are composed of superconductors, but it is not always necessary to make all of them superconductors. If at least a part of the waveguide through which plasmons propagate is made of a superconductor, the coherency of electrons can be improved and the interference intensity can be improved.

  In this embodiment, the plasmon waveguide is composed of a superconductor. However, it is not always necessary to use a superconductor, and the coherency of electrons can be improved and interference intensity can be improved by simply lowering the plasmon waveguide. Can be made. For example, the cooling device 21 may be further provided in the first embodiment, and the temperature of each plasmon waveguide of the plasmon modulator 10 may be lowered.

(Third embodiment)
In the second embodiment, the coherency of electrons constituting the plasmon is enhanced by configuring the waveguide through which the plasmon passes with a superconductor. On the other hand, in this embodiment, the coherent property of electrons in the waveguide is further enhanced by flowing a coherent current through the waveguide. Specifically, a coherent current is passed through a waveguide, the coherent current is amplitude-modulated by a plasmon wave, and the amplitude-modulated coherent current is modulated by a magnetic field. Thereby, the interference intensity of the quantum interference effect can be improved, and the modulation resolution can be improved.

  Here, the coherent current means that the electrons constituting the current are in a coherent state. FIG. 7B is a schematic diagram showing a waveform 9 of electrons constituting a coherent current. The waveform 9 is formed by superimposing a large number of coherent electron waves as in the waveform 1 shown in FIG. 1B, and has a shape in which only the amplitude of one electron wave is increased.

  When the plasmon having the waveform 7 shown in FIG. 7A is superimposed on the waveform 9 of the electrons constituting such a coherent current, the amplitude of the electron wave constituting the coherent current is amplified by the plasmon wave. Modulated. FIG. 7C is a schematic diagram showing a waveform 9 ′ of electrons constituting a coherent current amplitude-modulated by plasmons. The envelope (waveform 7 ') of the waveform 9' thus amplitude-modulated corresponds to the plasmon waveform 7 shown in FIG.

  In the present embodiment, modulation using the quantum interference effect is performed on electrons constituting a coherent current, not electrons constituting plasmons. As in the first and second embodiments, the phase of an electron wave having a small wavelength is changed, so that an element can be configured with a very small size and the modulation speed can be increased.

  FIG. 9 is a plan view of the plasmon modulator 30 according to the present embodiment. The plasmon modulator 30 further includes a current source 31 for flowing a current through the waveguide in addition to the configuration of the plasmon modulator 20 of the second embodiment (FIG. 8).

  The current source 31 is connected to the input plasmon waveguide 13 and the output plasmon waveguide 15, and the input plasmon waveguide 13, the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25. The direct current E is supplied to the output plasmon waveguide 15 in the direction opposite to the direction in which the plasmons travel. Since the electron wave E 'of the electrons constituting the current E travels in the opposite direction to the current E, the traveling direction of the electron wave E' is the same as the traveling direction of the plasmon.

  The input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25 have the same configuration as that of the second embodiment. Since the current E passes through the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25 that are made of a superconductor, the current E becomes a coherent current. That is, the electron wave E ′ of electrons constituting the current E is in a coherent state.

  When the plasmon propagated on the input plasmon waveguide 13 is input to the input superconducting waveguide 23, it is superimposed on the coherent electron wave E ′ flowing through the input superconducting waveguide 23. As a result, the electron wave E ′ is subjected to amplitude modulation by the plasmon wave.

  The electron wave E ′ is branched into two, passes through the arm superconducting waveguides 24 a and 24 b, and then merges with the output superconducting waveguide 25. At that time, the electric wave E ′ output to the output superconducting waveguide 25 is changed by changing the magnetic field in the region surrounded by the arm superconducting waveguides 24 a and 24 b by the conductive wire 17 and the magnetic field controller 18. The intensity of is modulated. As a result, the electron wave E ′ is in a state in which modulation information due to the quantum interference effect using the magnetic field is added in addition to the modulation information due to the plasmon.

  Thereafter, when the electron wave E ′ is input from the output superconducting waveguide 25 to the plasmon waveguide 15, it is converted into plasmon again. The electrons constituting the plasmon are in a state of being modulated by the quantum interference effect.

  In the present embodiment, since the current passing through the arm superconducting waveguides 24a and 24b is in the superconducting state, the individual electrons constituting the current are in a coherent state. Therefore, the interference intensity can be improved and the modulation resolution can be improved as compared with the first embodiment. Furthermore, in the superconducting state, the electron pairs are united to cause electron wave interference, so that a π phase shift can be performed with a magnetic flux fluctuation that is half the magnetic flux quantum unit h / 2e. As a result, the power consumption of the plasmon modulator can be further reduced as compared with the first embodiment in which the π phase shift is performed by the magnetic flux fluctuation of the magnetic flux quantum unit h / 2e.

  In superconductor materials, the excitation efficiency of plasmons when light is incident may be low. For this reason, if all the waveguides through which plasmons propagate are made of a superconductive material, the excitation efficiency of plasmons may be reduced, and the modulation efficiency as a plasmon modulator may be deteriorated. On the other hand, in this embodiment, the input plasmon waveguide 13 and the output plasmon waveguide 15 are made of a material in which plasmons are easily excited and propagated, and the input superconducting waveguide 23, the arm superconducting waveguides 24a and 24b, and Since the output superconducting waveguide 25 is made of a superconductor material, a decrease in plasmon excitation efficiency can be suppressed, and only a specific portion of the waveguide can be brought into a superconducting state.

  Furthermore, since the plasmon modulator 20 according to the present embodiment modulates an electron wave having a small wavelength as in the first embodiment, the size can be made smaller than that of the conventional plasmon modulator. Become. Moreover, since the CR time constant as a circuit is reduced by reducing the size of the plasmon modulator, the modulation speed can be increased.

  In the present embodiment, the input superconducting waveguide 23b, the arm superconducting waveguides 24a and 24b, and the output superconducting waveguide 25 are composed of superconductors, but it is not necessary to make all of them superconductors. If at least a part of the waveguide through which plasmons propagate is made of a superconductor, the coherency of electrons can be improved and the interference intensity can be improved.

(Fourth embodiment)
In the present embodiment, the scalar potential φ is changed in the quantum interference effect described using Expressions (1) to (4). That is, the electron wave is modulated by changing the electric field. In the present embodiment, the vector potential A (x) component is set to 0 in Equation (3). Therefore, the output electron wave is modulated by changing the scalar potential φ.

  FIG. 10 is a plan view of the plasmon modulator 40 according to the present embodiment. The plasmon modulator 40 eliminates the conductive wire 17 and the magnetic field control device 18 from the plasmon modulator 10 of the first embodiment (FIG. 3A), and instead applies a voltage to the arm waveguide 14a. It has a configuration including an electrode 41 as voltage applying means and a voltage control device 42 for applying a voltage to the electrode 41. Other configurations are the same as those of the plasmon modulator 10 of the first embodiment.

  The electrode 41 is an electrode formed using an arbitrary conductor material, and is provided in the vicinity of the arm waveguide 14a. The voltage control device 42 is connected to the electrode 41, applies a predetermined voltage to the electrode 41, and controls the magnitude and timing of the voltage. When a voltage is supplied from the voltage control device 42 to the electrode 41, a voltage is applied to the arm waveguide 14a existing in the vicinity thereof. Therefore, by controlling the voltage supplied from the voltage control device 42 to the electrode 41, the quantum interference effect of the plasmons passing through the arm waveguides 14a and 14b can be controlled. As a result, the output is output to the output plasmon waveguide 15. The intensity of the electron wave can be modulated.

  Also in the present embodiment, similarly to the first embodiment, since the modulation is performed on the electron wave having a small wavelength, the size can be made smaller than that of the conventional plasmon modulator. Moreover, since the CR time constant as a circuit is reduced by reducing the size of the plasmon modulator, the modulation speed can be increased.

  In FIG. 10, the electrode 41 is provided in the vicinity of the arm waveguide 14a. However, the electrode 41 may be provided in the vicinity of at least one of the arm waveguides 14a and 14b, or a plurality of electrodes 41 may be provided.

  Also in the present embodiment, as in the second embodiment, at least a part of the waveguide through which plasmons propagate may be formed of a superconductor. With such a configuration, the coherency of the electron wave constituting the plasmon is improved, so that the interference intensity of the quantum interference effect can be improved. Further, as in the third embodiment, a coherent current is allowed to flow through the waveguide, the coherent current is amplitude-modulated by plasmons, and the amplitude-modulated coherent current may be modulated by an electric field. . With such a configuration, it is possible to suppress the deterioration of plasmon propagation efficiency and improve the interference intensity of the quantum interference effect.

(Fifth embodiment)
In the present embodiment, both the scalar potential φ and the vector potential A (x) are changed in the quantum interference effect described using the expressions (1) to (4). That is, the electron wave is modulated by changing the electric field and magnetic field.

  FIG. 11 is a plan view of the plasmon modulator 50 according to the present embodiment. In addition to the plasmon modulator 10 of the first embodiment (FIG. 3A), the plasmon modulator 50 includes an electrode 41 as voltage applying means for applying a voltage to the arm waveguide 14a, and a voltage applied to the electrode 41. And a voltage control device 42 for providing. The electrode 41 and the voltage control device 42 have the same configuration as in the fourth embodiment. Other configurations are the same as those of the plasmon modulator 10 of the first embodiment.

  In the present embodiment, the magnetic field generated by the current supplied to the conductive wire 17 is used for modulation, and the voltage supplied to the electrode 41 is used supplementarily. That is, for example, when there is a difference in optical path length between the arm waveguides 14a and 14b, the voltage supplied to the electrode 41 is controlled so as to absorb the influence of the optical path length difference. Since the supplied current can be controlled only for modulation, the control can be facilitated.

  Further, in the present embodiment as well, as in the first embodiment, since the modulation is performed on the electron wave having a small wavelength, the size can be made smaller than that of the conventional plasmon modulator. Moreover, since the CR time constant as a circuit is reduced by reducing the size of the plasmon modulator, the modulation speed can be increased.

  Contrary to the present embodiment, the voltage supplied to the electrode 41 may be used for modulation, and the magnetic field generated by the current supplied to the conductive wire 17 may be used supplementarily.

  Also in the present embodiment, as in the second embodiment, at least a part of the waveguide through which plasmons propagate may be formed of a superconductor. With such a configuration, the coherency of the electron wave constituting the plasmon is improved, so that the interference intensity of the quantum interference effect can be improved. Further, as in the third embodiment, a coherent current is allowed to flow through the waveguide, the coherent current is amplitude-modulated by plasmons, and the amplitude-modulated coherent current may be modulated by an electric field. . With such a configuration, it is possible to suppress the deterioration of plasmon propagation efficiency and improve the interference intensity of the quantum interference effect.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention.

  Each of the above-described embodiments is manufactured as a planar optical waveguide (PLC) in which a waveguide is provided in the substrate. Any form of waveguide capable of propagating may be used. For example, at least a part of a waveguide that propagates an optical signal or plasmon may be formed into a wire shape (fiber shape).

10, 20, 30, 40, 50 Plasmon modulator (Plasmon quantum interference modulator)
DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Input optical waveguide 13 Input plasmon waveguide 14a, 14b Arm waveguide 15 Output plasmon waveguide 16 Output optical waveguide 17 Conductive wire (magnetic field generation means)
18 Magnetic field control device 21 Cooling device 23 Input superconducting waveguide 24a, 24b Arm superconducting waveguide 25 Output superconducting waveguide 31 Current source 41 Electrode (voltage applying means)
42 Voltage controller

Claims (7)

A modulator for modulating plasmons,
An input waveguide for guiding the plasmon;
Two arm waveguides for guiding the plasmon, each input end connected to an output end of the input waveguide;
An output waveguide for guiding the plasmon, wherein an input end is connected to an output end of each of the two arm waveguides;
Magnetic field generating means for generating a magnetic field in a region surrounded by the two arm waveguides;
A cooling device for cooling the input waveguide, the two arm waveguides, and the output waveguide;
With
At least a part of the input waveguide, the two arm waveguides, and the output waveguide is formed using a superconductor material,
The cooling device is capable of cooling to a temperature at which the superconductor material is in a superconducting state;
The modulator, wherein electrons constituting the plasmon are in a coherent state.   The magnetic field generation unit further includes a magnetic field control device for controlling the magnetic field so as to give a predetermined phase difference to an electron wave constituting the plasmon passing through each of the two arm waveguides. 2. The modulator according to 1. A region having a predetermined length from the input end of the input waveguide is formed using a material different from the superconductor material,
Modulator according to claim 1 in which a predetermined length of the area from the output end of the output waveguide, characterized in that it is formed by using a material different from that of the superconductor material. A current source for passing a current through the input waveguide, the two arm waveguides, and the output waveguide;
The flowing direction of the current modulator according to claim 1, characterized in that the direction opposite to the direction of propagation of the plasmon. An input optical waveguide connected to the input end of the input waveguide for guiding an optical signal input to the modulator;
An output optical waveguide connected to the output end of the output waveguide, for guiding an optical signal output from the modulator;
Further comprising
The plasmon is generated when the optical signal input to the modulator is incident on the input waveguide from the input optical waveguide,
The optical signal output from the modulator is generated when the plasmon is incident on the output optical waveguide from the output waveguide.
The modulator according to claim 1.   The modulator according to claim 1, further comprising a voltage applying unit configured to apply a voltage to at least one of the two arm waveguides. A modulator for modulating plasmons,
An input waveguide for guiding the plasmon;
Two arm waveguides for guiding the plasmon, each input end connected to an output end of the input waveguide;
An output waveguide for guiding the plasmon, the input end of which is connected to the output end of each of the two arm waveguides;
Voltage applying means for applying a voltage to at least one of the two arm waveguides;
A cooling device for cooling the input waveguide, the two arm waveguides, and the output waveguide;
With
At least a part of the input waveguide, the two arm waveguides, and the output waveguide is formed using a superconductor material,
The cooling device is capable of cooling to a temperature at which the superconductor material is in a superconducting state;
The modulator, wherein electrons constituting the plasmon are in a coherent state.

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