JPH01918A - light modulation element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light modulation element that modulates the intensity of light.

[Conventional technology]

In recent years, optical communication systems using optical fibers have reached the stage of practical use, and development of optical systems consisting of basic components, ie, a light source, a transmission path, and a light receiver, is progressing. In addition to the above-mentioned basic components, the development of optical switches, optical modulation elements, etc. is strongly desired in order to realize more sophisticated optical systems.

Optical switches are used for switching in the event of failures in optical transmission lines or light receiving/emitting elements, and for future optical exchange. (1) Mechanical type.

It can be divided into (2) electro-optical type, (3) acousto-optical type, (4) magneto-optical type, (5) thermo-optical type, (6) method using molecular orientation, etc.

As an optical switch, an optical switch is considered in which several ports are provided in a PLZT waveguide layer and the optical path is switched using a change in the refractive index of PLZT due to voltage application. This type of optical switch is described in, for example, Technical Research Report of the Institute of Electronics and Communication Engineers, OQE 84-16. (1984) No. 57
There are some listed on pages.

Various types of traveling wave type optical modulation elements using LiNb○3 waveguides have been studied. As an example of this type of optical modulation element, for example, Journal of the Institute of Electronics and Communication Engineers Vol. 69 (1986) No. 1
Some of them are listed on page 41.

[Problem that the invention seeks to solve]

Among these conventionally developed light modulation elements, only one with a response of 1
High-speed devices below μS utilize changes in the refractive index of materials associated with electro-optic and magneto-optic effects. but,
Since these refractive index changes are within a few percent, it has only been possible to mainly modulate the intensity of light propagating within the waveguide.

An object of the present invention is to provide an optical modulation element with a simple configuration that operates without using a waveguide.

[Means for solving problems]

In the present invention, the above object is achieved by constructing an optical modulation element by utilizing the fact that the continuous change in the Meissner property in the mixed region of the second type superconductor corresponds to the change in the optical refractive index. do.

[Effect]

When light is irradiated onto a superconducting material, the light is reflected by the Meissner effect.The zero-order, temperature, and current.

When the substance is transferred to a normal conduction state by a magnetic field or the like, the Meissner effect disappears and the amount of reflected light decreases. In a type 2 superconductor, superconductivity (Meissner property) and normal conductivity coexist in the mixed region, and this can be continuously changed by the applied magnetic field. In other words, it is possible to continuously change the amount of reflected light in the mixed region. Furthermore, by appropriately selecting the thickness of the superconductor, it is possible to arbitrarily set the range of change in the amount of reflected light or transmitted light, in other words, the dynamic range of modulation.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained using FIG. 1. In FIG. 1, numeral 10 indicates a thin film of a superconductor formed on a transparent substrate 20. It is a substance that exhibits complete conductivity and complete diamagnetism when cooled, and is divided into type 1 and type 2 depending on its magnetic properties. In the type 1 superconductor shown in Figure 2(a), when a magnetic field H is applied, the critical value H
At c, the completely diamagnetic state (Meissner state) is broken and a transition to the normal conduction state occurs. These include Pb, I
In the type 2 superconductor shown in FIG. 2(b), which has many single-element metals such as n and Sn, the magnetic field is applied = 2. lX10” (
The magnetic flux line vortex quantized by Wb) enters and becomes a mixed state. When the magnetic field is further strengthened, the state transitions to a normal conduction state at the upper critical magnetic field Hc x. Many of these materials include alloys and compound materials such as NbTi and NbaSn. In the Meissner state, light is reflected on the surface of a superconductor like the reflection of electromagnetic waves in a perfect conductor.

The operation of the light modulation element of the present invention will be explained using FIG. 6.
In the figure, 10 is a superconductor, 20 is a substrate, 100 is incident light,
110 represents reflected light, 120 represents transmitted light, and the second
As shown in figure (b), in a type 2 superconductor, the applied magnetic field H
When H (Hc t), the superconductor is in the Meissner state. Therefore, the incident light 100, which is an electromagnetic wave, cannot enter the inside of the superconductor 10 and is reflected, and the reflected light 110 becomes the maximum. This is set as the OFF state. By increasing the applied magnetic field H, Hc 1<
When H< He z, a mixed state occurs, and the incident light 100 begins to enter the inside of the superconductor. At this time, transmitted light 1
20 appears, and the reflected light 110 gradually decreases. When the applied magnetic field is further increased so that HCZ<H, the state becomes normal conduction, the Meissner property disappears, and the reflected light 110 becomes the minimum and the transmitted light 120 becomes the maximum. This is set to the on state. Intensity modulation of incident and emitted light can be performed using continuous changes in the amount of transmitted light and reflected light between the on state and the off state.

Changes in reflectance and transmittance between the on state and the off state can be changed by changing the thickness of the superconductor. This will be explained below using the amount of transmitted light as an example.

The magnetic field penetration depth λB of the superconductor is λa = (m/e”μons)”/z (1)
It is expressed as In this case, m represents the mass of the electron, -e represents the charge of the electron, μ0 represents the magnetic permeability in vacuum, and ns/2 represents the density of the superconducting electron pair. Since light is an electromagnetic wave,
The light penetration depth λB is λ82λB.

Now, let the film thickness of the superconductor be d, and the amount of transmitted light in the off state'
Think about rant. d) When λB, T'ozt=
It is 0. As d is gradually reduced, transmitted light begins to appear when d2λS, and Tozz>O.

If d is further reduced, ToLi becomes 21 when d(λB). The relationship between T o t i and d is shown in FIG. 4(a).

In the on state, the superconductor is in a normal conduction state, so the Meissner effect does not occur, so the light penetration depth λ, is λ,〉λ
It becomes B. The relationship between the film thickness d and the amount of transmitted light T on is as shown in Figure 4 (b). At this time, the extinction ratio (Toll/T
att ) has the characteristics as shown in Figure 4(c), and d=d
The maximum value is taken at o. Generally, a light modulation element with a large extinction ratio is desired, so the film thickness of the superconductor should be
is preferable, and if it is desired to set the extinction ratio depending on the application, it can be done by changing the thickness of the superconductor. At this time, if 0 < d < d o, T on is larger than do < d, so the power of the light source can be small.

Although the case where transmitted light is used is shown here, it is also possible to use one reflected light. At that time, change the angle of incidence.
By separating the optical axes of incident light and reflected light, it is possible to realize a light modulation element that utilizes both transmitted light and reflected light and in which the respective lights do not interfere with each other.

In practical optical modulation elements, in addition to the configurations shown in FIGS. 1 and 3, a waveguide layer and a protective layer are often used in combination.

The main points of the present invention are that a type 2 superconductor is used and the state change of the mixed region is used to modulate the intensity of light; Penetration depth λB
(2λs<2−n), and the extinction ratio can be changed by changing the film thickness.

Furthermore, since it can be realized without using a waveguide type, intensity modulation of light having different wavelengths is also possible. Furthermore, since devices using superconductors, such as Josephson devices, operate at high speed, the switching time in the optical modulation device of the present invention is the rise and fall of the magnetic field.

The rise and fall times of such a magnetic field can be made much shorter than the high voltage switching time required for conventional Pockels cells, so the optical modulation element can operate at high speed.

FIG. 5 shows an embodiment of a method of operating a light modulation element of the invention. In the figure, 10 is a superconductor, 20 is a substrate, 30 is a magnetic field generator, 31 is a power source, 32 is a switch, 33 is a variable resistor, and 100 is incident light. When the switch 32 is closed, the magnetic field generator 30 A current flows and a magnetic field H can be applied to the superconductor 10. The magnitude of the applied magnetic field H can be changed by adjusting the current flowing through the magnetic field generating section 30 using a variable resistor. With this configuration, intensity modulation of the incident light 100 can be performed according to the operating principle described above.

Figure 6 shows the critical conditions for superconductors. The inside of the volume represented by temperature T and magnetic field H2 and current I shown in the figure is in a superconducting state, and the outside is in a normal conducting state. Conditions vary depending on temperature, magnetic field, and current magnitude. Although the embodiment shown in FIG. 5 shows the case in which the optical modulation element is operated only by a magnetic field, it is also possible to operate it in combination with temperature and current. If the critical temperature Tc is very large, the superconductor can be
By heating to around c, it becomes possible to operate with a small magnetic field. A similar effect can be obtained by changing the current flowing through the superconductor. Furthermore, when keeping the external magnetic field constant, changing the temperature or current changes the critical conditions, producing the same effect as relatively increasing or decreasing the applied magnetic field, making it possible to operate the optical modulation element. becomes.

FIG. 7 shows an embodiment of a method for operating the light modulation element of the present invention using light as a heat source. In the figure, 10 represents a superconductor, 2o represents a substrate, 21 represents a light absorption film, 100 represents incident light, and 200 represents control light for operating a switch. The light absorption film 21 does not absorb the incident light 100 but can absorb the control light 200. Specifically, (1) the intensity of the control light 200 is made sufficiently strong compared to the incident light 100;

(2) Changing the wavelengths of two lights, etc. In such a configuration, when the intensity of the control light 200 is changed, the amount of light absorbed changes and the temperature of the light absorption film 21 changes, so that the temperature of the superconductor 10 can be controlled by heat conduction.

If this is done near the critical temperature Tc, it becomes possible to operate the optical modulation element.

FIG. 8 shows an embodiment of a method for operating the optical modulation element of the present invention by utilizing the fact that light is an electromagnetic wave.

In the figure, 10 is a superconductor, 20 is a substrate, and 22 is a waveguide layer 10.
0 represents incident light, and 200 represents control light. Since light is an electromagnetic wave, an optical switch can be operated by using a magnetic field H (H) HC1. FIG. 8(a) shows a case where the optical axis of the control light 200 is changed from that of the incident light 100 and the control light 200 is made to enter obliquely. The light modulation element can be operated by adjusting the intensity of the control light 200. FIG. 8(b) shows an embodiment in which the control light is not directly incident on the superconductor. The control light 200 is transmitted through a waveguide layer 22 provided adjacent to the superconductor 10.
Go inside. At this time, the electromagnetic field of the control light 200 is y = k o! It penetrates into the superconductor 10 by a penetration depth γ expressed by (2). here k
o represents the wave number of the control light 200 in vacuum, N represents the isolateral refractive index of the waveguide layer 22, and n represents the refractive index of the superconductor 10, respectively.

If γ is made larger than the film thickness of the superconductor 1o, the control light 20
The light modulation element of the present invention can be operated with an electromagnetic field of zero. This configuration allows uniform operation over a wide area. Furthermore, when used in a mode in which the control light in the waveguide layer becomes a standing wave, the magnetic field strength is distributed sinusoidally in the plane, and regions with high and low Meissner characteristics appear alternately. Similar to the acousto-optic effect caused by surface acoustic waves,
It is also possible to use it as a diffraction grating with a refractive index distribution.

When the embodiment shown in FIGS. 7 and 8 is actually used as a light modulation element, a light source, a control system, etc. are required. In the embodiment shown in FIG. 8(b), it is also possible to change the waveguide mode by using a buffer layer between the waveguide M22 and the superconductor 10.

The gist of the present invention is to operate a light modulation element by changing the state of a superconductor using light as a heat source or using its electromagnetic field.

FIG. 9 is a block diagram of an optical attenuator using the optical modulation element of the present invention. In FIG. 9, the control section 70 can change the strength of the magnetic field applied to the optical modulation element 60. If the intensity of the incident light 100 is 0, then the intensity of the transmitted light 120 is O<I
-c-<I (I-axe I.

can be changed continuously within the range. Here, I 1lln and I wax represent the amount of transmitted light when the superconductor of the light modulation element 60 is in the Meissner state and the normal conduction state, respectively.

FIG. 10 shows an embodiment of an optical amplifier using the optical modulation element of the present invention. Intensity information of the signal light 130 detected by the detection section 80 is input to the control section 70, and the light modulation element 60 is operated. Assuming that the incident light 100 is DC light with sufficiently greater intensity than the signal light 130, the transmitted light 120 is an amplified version of the signal light 130. The multiplication factor can be set by the control unit 70 and the intensity of the incident light 100.

With the same configuration, the multiplier can also be used as a calculator by intensity modulating the incident light 100. Furthermore, by changing the wavelengths of the incident light 100 and the signal light 130, it is also possible to use it as a wavelength converter.

FIG. 11 is an example of an optical amplifier that operates directly with light. As the light modulation element 60, the one shown in FIGS. 9 and 10 is used. The function is the same as the optical amplifier explained in FIG. Since it does not include an electrical circuit system, it is expected to be resistant to noise and operate at high speed.

Since the light modulating element of the present invention utilizes the state change of the second type superconductor, if this is considered as a change in the optical refractive index, a waveguide type light modulating element can also be constructed.

Superconducting materials suitable for carrying out the present invention are preferably those that (1) exhibit superconductivity at room temperature, and (2) those whose interaction strength with light changes significantly due to transition. NbTi is a conventionally known material system.

Alloy systems such as Nb5Sn have a low Tc (<30K) and are electrically conductive even in a normal conduction state, so the strength of interaction with light does not change significantly. In addition to these, La-
Oxide-based superconducting materials represented by Ba-Cu-○ and Y-Ba-Cu-○ systems have a high Tc <(>77K) and are insulators in the normal conduction state, so they are difficult to absorb light due to transition. There is a large change in the interaction between

〔Effect of the invention〕

According to the present invention, since the interaction with light accompanying continuous state changes in the mixed state of the second type superconductor is utilized, an optical modulation element with a large refractive index change and a simple configuration can be realized.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the light modulation element of the present invention,
Figure 2 is a diagram showing the B-H characteristics of the superconductor, Figure 3 is a schematic diagram showing the operation of the light modulation element, and Figure 4 is the relationship between the extinction ratio of the light modulation element and the film thickness of the superconductor. Fig. 5 is a schematic diagram showing an example of controlling a light modulation element by a magnetic field, Fig. 6 is a schematic diagram showing the critical conditions of a superconductor, and Fig. 7 is a diagram showing light modulation using light as a heat source. FIG. 8 is a block diagram showing an example of controlling a light modulation element using the electromagnetic field of light. FIG. FIG. 10 is a block diagram of an optical attenuator using the optical modulation element of the present invention, and FIG. 11 is a block diagram of an optical amplifier that operates directly with light. 1o... Superconductor, 20... Substrate, 21... Light absorption film, 22... Waveguide layer, 30... Magnetic field generation part, 31
...Power source, 32...Switch, 60...Optical switch, 70...Control unit, 8o...Detection unit, 100...
・Incoming light, 110...Reflected light, 120...Transmitted light,
130...Signal light, 200th 1st Snake 10...Oden Sonzanno...Basic desire # λ mouth (^) (b) Whole power 0jiH Yu 3 mouth 100... Input le 110...・Tatsu #gen + 20...Nine is the ninth taku thousand mouth 5 ■ 35...1 combination 7 Figure 2 DO Fu 8 n (b) 9th village 10th 8 ω

Claims (1)

[Scope of Claims] 1. An optical modulation element that modulates the intensity of light, characterized in that it uses a type 2 superconductor whose state changes between superconductivity and normal conduction. 2. In claim 1, the state change of the superconductor is caused by one or any combination of the temperature of the superconductor, the current flowing through the superconductor, and the magnetic field applied to the superconductor. A light modulation element characterized by having a means for performing an intensity modulation operation. 3. In claim 2, in addition to the intensity-modulated first light, a second light is guided to a light modulation element, and the second light is generated using a heat source or its electromagnetic field. A light modulation element characterized by operating as follows. 4. An optical modulation element according to any one of claims 1 to 3, characterized in that it comprises at least a substrate and a superconductor thin film. 5. A light modulation element according to claim 4, characterized in that a transparent substrate is used.