JPS62270926A - Total reflection type optical modulation element - Google Patents

Abstract

PURPOSE:To obtain an optical modulation element of a high speed and a high contrast by using a non-linear optical substance layer having a non-linear optical effect, bringing an incident light to this layer to transmission or total reflection, based on a voltage impression or a light irradiation, and obtaining modulated light beams. CONSTITUTION:The titled optical modulation element is constituted by making a non-linear optical substance layer 2 having a refractive index nII, and other layer (adjacent layer) 1 having a refractive index nI(>=nII) adhere closely to each other. In this case, the refractive index nI is roughly constant without being influenced by a light beam, but the refractive index nII shows such as variation as an expression nII=n0-n2I in accordance with an intensity I of a radiated light beam. In this regard, n0 denotes a refractive index in case when light beams are not radiated, and n2 denotes a coefficient for determining a ratio of a variation of the refractive index corresponding to a light radiation, and n0 and n2 are different by a kind of the non-linear optical substance layer 2. In this constitution, as for a modulation of a light beam Iin which has been made incident on the non-linear optical substance layer 2 through the adjacent layer 1, the incident light beam Iin is brought to transmission or total reflection, and a modulated light Iout is obtained, by radiating suitably a control light Iout having a prescribed intensity to its incident surface.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Summary] The present invention is a total reflection type light modulation element that utilizes a change in refractive index due to a nonlinear optical effect, and is a total reflection type optical modulation element that utilizes a change in refractive index due to a nonlinear optical effect. A high-speed, high-contrast light modulation element is realized by using the optical material fJffl and transmitting or totally reflecting the light incident on this layer based on voltage application or light irradiation to obtain modulated light. It is.

[Industrial application field]

The present invention utilizes refractive index changes due to nonlinear optical effects,
The present invention relates to a total reflection type light modulation element that modulates incident light by transmitting or totally reflecting it.

Currently, with the advancement of optical communication and optical information processing technology, the modulation speed of current optical modulators is becoming unable to keep up.
Optical modulators with a frequency of 10 GHz or higher are desired. On the other hand, a spatial light modulator is a two-dimensional array of light modulators.
) and light-light control elements that control light with light are currently being actively researched because they are essential devices for future optical systems.

[Conventional technology]

Conventionally, high-speed optical modulators use multiple quantum wells, which are made by periodically stacking two types of m-v compounds, and perform optical modulation by utilizing the difference in light absorption due to the Franz-Kelditssch effect. It is known what has been done.

Furthermore, as a spatial light modulator, there is one that uses liquid crystal and switches the path of light by utilizing the phase change caused by voltage application.

Regarding light-light control elements, no promising elements that can be put into practical use have yet appeared.

[For production]

Light that is incident on the surface of the nonlinear optical material layer (or near the interface between that layer and its adjacent layer) at an angle less than the critical angle for total reflection is hardly reflected by that surface and is transmitted as it is. Therefore, if a predetermined voltage is applied (or light is irradiated) to the nonlinear optical material layer, its refractive index changes nonlinearly, and the critical angle decreases accordingly. Then, since the incident angle becomes larger than the critical angle, the light that has been in the transmitted state suddenly switches to the totally reflected state. Conversely, if the voltage application (or light irradiation) is stopped in the total reflection state, the state is switched to the transmission state. By appropriately switching between transmission and total reflection in this way,
Modulated light can be obtained.

Therefore, in the present invention, since the traveling direction of light is largely switched between transmitted light and totally reflected light, a sufficient on/off ratio (several 10
%) is obtained, that is, the contrast is increased. In addition, since the refractive index is directly changed by voltage application or light irradiation, the modulation speed is fast (1o
ops~lns, about 10 ps for light irradiation).

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 (al is a schematic configuration diagram showing a first embodiment of the present invention. This embodiment consists of a nonlinear optical material layer 2 with a refractive index nli and another layer with a refractive index nI (≧nII). (hereinafter referred to as an adjacent layer) 1 are in close contact with each other.Here, the refractive index nz is almost constant without being affected by light, but the refractive index nl is the same as the irradiated light. Depending on the intensity ■, the following equation fl) shows a change.

nH=i10-n, I...11) Equation (11), no is the refractive index when no light is irradiated, and n2 is a coefficient that determines the rate of change in the refractive index in response to light irradiation. .

n01nZ differs depending on the type of nonlinear optical material layer 2.

In the above configuration, the modulation of the light 1 in that has entered the nonlinear optical material layer 2 via the adjacent layer 1 is achieved by appropriately irradiating the incident surface with control light I cont of a predetermined intensity, so that the incident light I in is transmitted. Or, by total reflection, modulated light■. . , (transmitted light IL, reflected light 1.). This modulation will be specifically explained below.

First, as shown in FIG. 1 (bl), if the angle of incidence of the incident light I in on the interface between the nonlinear optical material layer 2 and the adjacent layer 1 is α, and the critical angle of total reflection at the interface is α6, then This critical angle α is determined by the following formula (
2) is expressed as follows.

Here, the refractive index n is equal to no (that is, nTi when no light is irradiated), and the light intensity I is the incident light
, , and the control light I cont, so I=I
If rn ” I co++t is replaced, equation (3) is obtained.

From the above formula (3), the critical angle α. changes depending on the sum of the incident lights 1 and 7 and the control light 1 cant, and this sum (■,
7+Icarat) becomes smaller. Therefore, the incident light 1. , while keeping the incident angle α of l1fi+Ic0. , L by decreasing the critical angle α. If you increase , it will become as shown in FIG. 1(C). That is, reflected light 1. , appears very strongly due to total reflection when α, <α, but suddenly decreases when α0>α, and conversely, the transmitted light , becomes large. Critical angle α.

On the other hand, if you make it smaller, the opposite phenomenon to the above will occur.

Therefore, the critical angle α. By appropriately changing the angle of incidence near the incident angle α, the transmitted light It or the reflected light I can be turned on or off. For example, the critical angle α. is the angle of incidence α(
= constant) to become smaller than I ir+ ” I c
If the threshold value of ent is 1th, then α in equation (3). By setting = α, as shown in the figure (dl), the incident light 1 rn can be expressed as the darkness value IL
Set it to a constant value slightly smaller than h, and in this state I
Control light ■ such that Lh〈■,,, (constant) +I eoltL. 1 to overlap the above incident light 1 in.

Then, the critical angle α at this time. is smaller than the angle of incidence α, so the incident light! In is totally reflected, and as shown in Fig. 1 [
As shown in C), the reflected light I,... increases rapidly, while the transmitted light IL rapidly decreases. That is, Fig. 1<d
As shown in i, the above control light 1 cont is converted into incident light 1i
, (= constant) and by exceeding the threshold
The reflected light I can be turned on and the transmitted light rt can be turned off, and the control light ■. . If fi, is returned to zero, the reflected light 11
can be turned off and transmitted light I can be turned on. In this way, by simply changing the control light 1co□, the reflected light 1r
,Transmitted light! , can be turned on and off freely.

- As an example, the nonlinear optical material layer 2 may be made of GaAs (thickness
102 people) and Gao, ? A f! A multiple quantum well (
If the total film thickness is approximately 2.4.17 l11), then n
z = 2 Xl0-'cm2/W, and I in+
α when I coat=9mW/(10μm)
c# becomes 70°. Therefore, the incident light is 1.11 (< 9
mW/ (10 μm) 2) is irradiated at a constant angle of incidence α = 70', and a control light ■ is applied to this. By superimposing ont appropriately, summer in+I cant<9mW/(10μm
) 2 to turn off the reflected light 11 (transmitted light ■
, on), while I in ” I cor+t >
9 mW/(10 μm)2, the reflected light 1. can be turned on (transmitted light 1., turned off).

Next, FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention. In this embodiment, a nonlinear optical material layer 12 and an adjacent layer 1
1 in close contact with Ti, for example, in the film thickness direction.
Snug % Translucent electrode made of Au etc. 13.14
are placed facing each other. Note that the nonlinear optical material layer 12 is a material whose refractive index changes greatly by applying a voltage in the film thickness direction.

In the embodiment shown in FIG. 1, 1 inch of incident light is converted into control light
. . However, in this embodiment, according to the application of the voltage between the electrodes 13 and 14,
By changing the refractive index of the nonlinear optical material layer 12, the modulated light I. uL (Reflected light I,...

Transmitted light +1) is obtained. That is, the critical angle α is determined by the refractive index change due to the voltage application.

As a result, as shown in FIG. 1 fcl, (d), the reflected light 1. Alternatively, the transmitted light (■) can be turned on or off.

FIG. 3 is a schematic configuration diagram showing a third embodiment of the present invention. In this embodiment, a nonlinear optical material layer 12 whose refractive index changes greatly when a voltage is applied in the in-plane direction is used, and an adjacent layer 21 is brought into close contact with the nonlinear optical material layer 12, and a pair of electrodes 23. 24 are arranged. In the figure, the electrodes 23, 24 are similar to the embodiment shown in FIG.
A voltage V is applied between them to cause a change in the refractive index, thereby reducing the critical angle α. Change the reflected light! , or the transmitted light ■ can be turned on or off.

As described above, in each of the above embodiments, 1 inch of incident light is irradiated with other light (Figure 1) or voltage is applied (Figures 2 and 3).
Accordingly, it is transmitted or totally reflected to produce modulated light■. , are obtained. Therefore, the traveling direction of light is transmitted light 1. And reflected light! , and therefore a sufficient on/off ratio (on the order of several tens of percent) is obtained, that is, the contrast is extremely high. Furthermore, since the refractive index is directly changed by voltage application or light irradiation, the modulation speed is fast (100 ps for voltage application to about 10 ps for 1 nss light irradiation).

Note that in the embodiment shown in FIG. 1, the incident light I8. ．．
and control light■. . , . A modulator can be configured. Here, each image of the array or matrix may be turned on and off using a TFT, and in this way, driving can be simplified. Therefore, the present invention can be widely applied to optical information processing systems, optical switching equipment, and the like.

In addition, the above-mentioned nonlinear optical material layer 2.12.22 includes:
■-■ Or multiple quantum well of II-VI compound, or MNA, MNMSDAN,
PNP, merocyanine pigment, S tyry 1-py
Single crystals, polycrystals, or polymers of organic substances including tidinium cyanine dye, diacetylene, polydiacetylene, etc. can be used. The above-mentioned multiple quantum well has, for example, M B E (
? It can be formed by Iorecular Beam Etching). Further, the above-mentioned organic crystal can be produced by, for example, the Bridgman method, the zone melt method, the vapor phase growth method, the ion blating method, or the like. For cyanine dyes and diacetylene materials, the Langmuir-Prodgett method can also be used.

Further, as the nonlinear optical material layer 2.12.22, a thin layer 31 made of an insulator or a semiconductor and another thin layer made of a metal or a semiconductor with high electrical conductivity, as shown in FIG. A nonlinear optical thin film 30 formed by periodically laminating layers 32 may also be used. Conventionally, it has been known that in organic crystals such as polydiacetylene, the nonlinear optical effect increases as the spread of π electrons increases.

By analogy with this, even in inorganic materials, if highly nonlocalized electron clouds are created periodically, high nonlinearity can be obtained. Therefore, if the configuration shown in FIG. 4 is adopted, wide-spread electric clouds are periodically arranged within the film, and a large nonlinear optical effect similar to that of the organic crystal described above can be obtained.

The above thin 1iif31 has a-3i: H, a-S
iNx: Hla-SiOx: H,a-SiCx
: Semiconductor such as H, or W○×, MoOx, Ir
ox, VOx, TaOx, NbOX%MnO
Transition metal oxides such as x can be used.

In addition to general metals, the thin film 32 also includes semiconductors with high electrical conductivity, such as the above a-3i: Hla-Si
Nx: Highly doped semiconductors such as H, oxygen vacancies (Va
cancy) at a high concentration (e.g. x<2.7)
Alternatively, the above oxide doped with H, Na, etc. (for example, tungsten bronze) can be used.

Here, the thin layer 31 is a-SiNx: HXFJ film 32
An example of a film forming method using W (tungsten) will be described. Each layer is grown by plasma CVD. At this time, a-5iNx, H is 20% SiH4 diluted with hydrogen.
Using gas and NH3 gas, the flow rate ratio (NNn, /N5
=H, ) 2. Produced under the conditions of gas pressure 0.2 Torr, RF power 100 W, and substrate temperature 250'C.

W is grown by introducing WF6 gas into the chamber and subjecting it to plasma decomposition. The laminated film is grown by alternately switching these gases. It is desirable that the thickness of each layer is from several to several hundred, and the total thickness is from several thousand to several μm.

Alternatively, as shown in FIG. 4(b), a striped thin film 42 made of the same material as the thin film 32 may be sandwiched between two thin films 41 similar to the thin film 31 from both directions. In the nonlinear optical thin film 40 having such a configuration, the electron cloud is confined in the in-plane direction, so that the spread of the electron cloud can be controlled over a wide range.

Furthermore, as shown in FIG. 4(C), a thin film 52 made of the same material as the thin film 32 is replaced with a thin film 51 made of the same material as the thin film 31 but different from each other.
It may be configured such that it is sandwiched between a and 51b. For example, thin film 5
Electron-donating a-SiNx:H is used for 1a, and electron-accepting a-SiOx: is used for the other thin film 51b.
H can be used. In the nonlinear optical thin film 50 having such a configuration, a large nonlinear optical effect is obtained, and since the inversion symmetry of the film structure is destroyed, second-order nonlinearity occurs. Note that the thin film 5 in FIG. 4(C)
2 in a striped shape, the striped thin film 62 is formed into different types of thin films 61a, 61a,
It is also possible to have a configuration sandwiched between 61b. If you do this,
As described above, second-order nonlinearity can be obtained, and the spread of the electron cloud can be controlled over a wide range as in FIG. 4 (bl).

Finally, the adjacent layers 1.11.2 shown in FIGS.
As the material 1, for example, a-5iNxOy:H having a variable refractive index from 1.2 to 3.3 can be used.

This film was formed by plasma CVD at a substrate temperature of 200 to 300℃.
It can be formed at 00°C.

〔Effect of the invention〕

As explained above, according to the present invention, by using a total reflection type light modulation element using a nonlinear optical material layer, both the modulation speed and contrast are high, and the light modulator, spatial light modulator, and light - It is possible to realize a light modulation element that can be easily applied to a light control element and the like.

[Brief explanation of drawings]

Fig. 1 (al is a schematic configuration diagram showing the first embodiment of the present invention, Fig. 1 fbl is the state of the incident light 1 inch, control light ■, o7 modulated light ■, according to the same embodiment) Figure 1 (C
1 is the reflected light 11 and the transmitted light It and the critical angle α according to the same example. A diagram showing the relationship between the above reflected light I and transmitted light 1t and the light intensity (1:n+lco□)
2 is a schematic configuration diagram showing the second embodiment of the present invention, FIG. 3 is a schematic configuration diagram showing the third embodiment of the present invention, and FIG. 4 (a ) to (dl are schematic cross-sectional views showing examples of nonlinear optical thin films that can be used as nonlinear optical material layers according to each of the above embodiments. 1.1121...adjacent layer, 2.12.22... - Nonlinear optical material layer, 13.14.
23.24... Electrode, 30.40.50.60... Nonlinear optical thin film, I i
n...incident light, Icont...control light, Iout...modulated light, ■,...reflected light, ■L...transmitted light.

Claims (1)

[Claims] 1) A nonlinear optical material layer (2, 12, 22) whose refractive index changes nonlinearly by voltage application or light irradiation, or the nonlinear optical material layer and other materials in contact with the nonlinear optical material layer. A total reflection type light modulation element consisting of layers (1, 11, 21), which transmits or totally reflects light incident on the nonlinear optical material layer according to the voltage application or the light irradiation to obtain modulated light. 2) Electrodes (
13, 14), and the voltage is applied between the electrodes, the total reflection type light modulation element according to claim 1. 3) A pair of slit-shaped electrodes (23, 24) are provided on one surface of the nonlinear optical material layer, and the voltage is applied between the electrodes. Total reflection type light modulation element. 4) A pair of slit-shaped electrodes are provided on the surface of the other layer that is in contact with the nonlinear optical material layer, and the voltage is applied between the electrodes. Total reflection type light modulation element. 5) The total reflection type light modulation element according to any one of claims 2 to 4, wherein the electrodes are arranged in an array. 6) The total reflection type light modulation element according to any one of claims 2 to 4, wherein the electrodes are arranged in a matrix. 7) Claim 5 or 6, characterized in that voltage application to each electrode is controlled using a TFT.
Total internal reflection type light modulation element as described in 2. 8) The total reflection type light modulation element according to claim 1, wherein the light irradiation is performed using external control light in addition to the incident light. 9) The nonlinear optical material layer is a III-V compound or II
-VI compound multi-quantum well, the total internal reflection type light modulation device according to any one of claims 1 to 8. 10) The nonlinear optical material layer is MNA, MNMA, DA.
N, PNP, merocyanine pigment, Styry1-py
a single crystal containing any one of ridinium cyanine dye, diacetylene, and polydiacetylene;
9. The total reflection type light modulation element according to any one of claims 1 to 8, which is made of polycrystal or polymer. 11) The nonlinear optical material layer is a nonlinear optical thin film (30 , 40, 50, 60), the total reflection type optical modulation element according to any one of claims 1 to 8. 12) The thin layer made of an insulator or semiconductor is a-
Si:H, a-SiNx:H, a-SiOx:H, a-
12. The total reflection type light modulation element according to claim 11, characterized in that it is made of at least one of SiCx:H. 13) The thin layer made of an insulator or semiconductor is WO
x, MoOx, IrOx, VOx, TaOx, NbOx
, MnOx. 14) The semiconductor with high electrical conductivity is a-Si:H, a-SiNx:H, a-SiOx:H,
The total internal reflection type optical modulation according to any one of claims 11 to 13, characterized in that at least one semiconductor of a-SiCx:H is highly doped. element. 15) The semiconductor with high electrical conductivity is WOx, MoO
x, IrOx, VOx, TaOx, NbOx, MnOx
The total reflection type according to any one of claims 11 to 13, characterized in that the oxygen vacancies in at least one of the oxides are highly concentrated. Light modulation element. 16) The semiconductor with high electrical conductivity is WOx, MoO
x, IrOx, VOx, TaOx, NbOx, MnOx
H, Li, K, Na in at least one oxide of
, OH, and doped with at least one of OH.