JPS59109026A - Light modulator - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal panel type light modulator of small light loss with simple constitution by penetrating an optical fiber through the liquid crystal and exposing the core. CONSTITUTION:An optical fiber 10 is penetrated through a liquid crystal cell provided with a substrate 11, a sealing material 14 and transparent electrode films 12, 13, and the clad part 10b of the optical fiber 10 which is in contact with the liquid crystal 15 is stripped off to expose a core 10a. When a voltage is not applied to the electrode film 12, 13, the longer axes of liquid crystal molecules are arranged in the direction of optic axial of the optical fiber, and when the voltage is applied in the direction perpendicular to the optic axis. The refractive index of the liquid crystal becomes an extraordinary light refractive index etae and an ordinary light refractive index etao, respectively. The refraction index etac of the optical fiber core becomes etae>etac>etao. As the liquid crystal acts as a clad, light is transmitted in the core 10a when a voltage is applied, and not transmitted in the core 10a when a voltage is not applied. By this way, a liquid crystal panel type light modulator of small light loss can be obtained with simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to an optical modulator9, and more specifically relates to an optical modulator using liquid crystal.

(2) Disadvantages of the Prior Art As an example of a conventional optical modulator using a liquid crystal, a liquid crystal optical switch is shown in FIG. In the figure, 1 is an input optical fiber, 2 is an output optical fiber, 6 is a vertical polarizing plate that passes vertical light, 4 is a horizontal polarizing plate that passes horizontal light, and 5 and 6 are polarizing plates 3 and 4. The transparent electrode is provided on the inner surface facing the glass substrate, and a semiconductor film such as tin oxide or indium oxide, which is provided on the glass substrate by means such as vapor deposition, is usually used.

When no voltage is applied between the transparent electrodes 5 and 6, the liquid crystal 7 is oriented vertically on the vertically polarized light (fiS) side and horizontally oriented on the horizontal polarizing plate 4 side, so-called T N ( It has a twista nematic) structure. 8 is a lens that converts the light emitted from the optical fiber 1 into parallel light, and 9 is a lens that focuses the light onto the optical fiber 2. Usually, a focusing rod lens (trade name: SELFOC lens) is used. optical fiber 1
When light is made incident on the vertically polarizing plate 3 through the entire lens 8, only the vertically polarized component of this light advances to the liquid crystal 7. When no voltage is applied, the polarization direction of the light incident on the liquid crystal 7 is rotated by 90 degrees due to the TN structure, and the horizontally polarized light passes through the horizontal polarizing plate 4, is focused by the lens 9, and propagates to the output fiber 2. do. This time is what is called ON (open).

Next, when an alternating voltage of several square meters is applied between the transparent electrodes 5 and 6, the liquid crystal molecules are aligned in the upward direction of the stain due to the electric field effect, so the vertically polarized light component that has passed through the vertical polarizing plate 5 changes its polarization direction. It advances to the horizontal polarizing plate 4 with the same polarization direction without any difference.

Therefore, since it cannot pass through the horizontal polarizing plate 4, it does not propagate to the output side fiber 2. This is the 0FF (closed) state.

The conventional 0N-OFF type liquid crystal switch with the above configuration (
Although optical modulators (optical modulators) are opened and closed by external electrical control signals, they have not been put into practical use due to the following major drawbacks.

■ Increased costs due to the use of polarizing plates and focusing lenses.
Optical loss (approximately 5 dB) occurs.

■ The size is large because the liquid crystal surface is perpendicular to the optical axis.

■ The liquid crystal propagation loss is large, ranging from 2 to 37 dB/on, mainly due to scattering due to alignment fluctuations of liquid crystal molecules.

(3) Purpose of the Invention The present invention has been made to eliminate the above-mentioned drawbacks.
The present invention provides an optical modulator having a structure in which an original fiber is configured to pass through a liquid crystal, and an optical fiber core is exposed in the liquid crystal.

(4) Structure and operation of the invention The present invention will be explained below based on the drawings.

2 and 5 are cross-sectional views of an optical modulator for explaining the present invention in detail. Here, 10 indicates an optical fiber, and its configuration is a core part 1O-a and a cladding part 10-b.
It becomes. This is a substrate provided to sandwich the optical fiber 10, and is made of an insulating material such as glass. Transparent electrodes 12 and 13 made of tin oxide or the like are provided on the base plate 11 by means of vapor deposition or the like, and each has a lead? a1
6 and 17 to the outside. Reference numeral 15 is a nematic liquid crystal, which is characterized by elongated molecules arranged with their long axes unilaterally aligned. Now, in the optical fiber 10, the cladding part 10-b is peeled off at the part in contact with the liquid crystal.
The core part 10-a is in direct contact with the liquid crystal, so to speak.
The liquid crystal serves as the cladding part of the optical fiber. The above components are fixed to the sole material 14 to form an optical modulator.

The liquid crystal molecules have an elongated shape as described above, but since the rod-shaped molecules are arranged with their long sleeves facing in one direction, the electric polarizability is large in the long axis, that is, the original axis direction. Light having an electric oscillation vector in a plane including the optical axis is an extraordinary ray, and its refractive index ηe is larger than the refractive index η0 of an ordinary ray having an electric oscillation vector in a plane perpendicular to the optical axis. (It is optically positive.) Furthermore, by subjecting the wall surface to an orientation treatment such as diagonal deposition of SiOx or rubbing, the molecular axis can be made parallel to the wall surface or perpendicular to the image.

On the other hand, when an electric field is applied, the molecular axis is oriented in the direction of the electric field or in a direction perpendicular to it.

Now, in FIG. 2 and FIG. 5, the transparent conductive films 12 and 13, and if necessary, the fiber core part 10-a
Kvi, if the above-mentioned alignment treatment is performed in the fiber optical axis direction, in the state shown in FIG. 2 where no voltage is applied between the two transparent conductive films 12 and 13, the liquid crystal 1
5, the long axis of the liquid crystal molecules is aligned in the direction of the optical axis of the fiber. Therefore, the light propagating through the optical fiber core 10-a feels the extraordinary refractive index ηθ of the liquid crystal. On the other hand, when a voltage is applied between the transparent conductive films 12 and 16 as shown in FIG. You will feel the ordinary refractive index η0. Therefore, the refractive index ηC of the optical fiber core is ηe〉ηC〉ηO...
If (1) is true, then in the state of the 21st bacterium with no voltage applied, ηθ is larger than ηC, that is, the cladding (liquid crystal) part has a larger refractive index than the core part, and is non-waveguide. mode. Further voltage is applied and in the state of 1ζ Fig. 5, η
C is large (ηojj), that is, the cladding (liquid crystal) part has a smaller refractive index than the core part, and becomes a waveguide mode. In other words, an ON-OFF type optical switch, ie, an optical modulator, shown in FIG. 2 is constructed.

The basic principle of the present invention can be summarized as follows. In other words, by changing the state of the liquid crystal in response to external control signals and thereby making the refractive index felt by the optical fiber core larger or smaller than that of the core, it can be used as a non-waveguide mode or a waveguide mode. It is a method of modulating optical signals.

As optical fiber core, polystyrene, clad IPU
MA (polymethyl methacrylate).

When a liquid crystal is used as a mixture of phenylcyclohexane and biphenylcyclohexane, and a He-Nθ laser (wavelength 0.635 Atrn) is used as a light source, ηc=
1,59, ηe = t63, ηo = 1.5
Therefore, an optical modulator having the structure shown in FIG. 2 is possible.

In addition, the core is made of PMMA, which is most commonly used as a plastic fiber, and the cladding is made of fluorine polymer (wavelength α
At 655 μm, 1 a = 1.495)'f:
If using the same fiber, ηθ=1.55.
It is sufficient to select a liquid crystal with η0=1.45 or so.

Furthermore, even if a quartz fiber (particularly a core made of quartz and a plastic cladding) fy is used, ηc = 1.45, so it is possible to select a liquid crystal with ηθ = 1.50 and ηo = 1.40. As described above, it will be appreciated that the optical modulator of the present invention has the advantage of having a wide degree of freedom in design since there is room for selection of both the fiber and the liquid crystal material.

Now, as can be easily inferred from Figure 2, it is possible to easily create an array of optical fibers.

This embodiment is shown in FIG.

In FIG. 4, 20 is an optical array modulator, and the substrate 1
1. Sealing material 14. It is composed of transparent conductive films 12 and 16 provided on the inside of the substrate so as to face each other, and furthermore, an optical fiber 10.The structure is exactly the same as that shown in FIG. 2. However, since the transparent electrodes 12-15 are divided and each corresponds to an optical fiber, each electrode can independently receive a control signal from an external control circuit (not shown). Therefore, the amount of light passing through the optical fiber 10 can be modulated separately.

The ratio of the amount of light passing through the optical fiber (extinction ratio) in the ON-OFF state is somewhat large in the configurations shown in FIG. 2 or 4, and depending on the application, a larger extinction ratio may be desired. In that case, as shown in Figure 5, the optical fiber 1
This objective is achieved by providing a bend 25 at 0. Here, FIG. 5 (shows a cross-sectional view on the plane of the optical modulator. In other words, it can be confirmed from the arrow indicating the light ray shown in the optical fiber core 10-a, but it is difficult to confirm in the case of FIG. In FIG. 5, the light dissipation of the low-order mode at the time of fi OF F can be reliably achieved at the bent portion.

However, when the radius of curvature of the bent part is r and the fiber diameter is R, r/R (10...................................................(2
), the light transmittance at the bent portion decreases, so it is necessary to select an appropriate value from equation (2).

Similar to FIG. 4, FIG. 6 shows a complete array of optical modulators having the structure shown in FIG. 5. Here, 21 is an optical array modulator, which is provided inside the substrate 11 and separated by L transparent conductive films 12-1 and 1272.

......, 12-7 (the transparent conductive film provided on the opposite substrate is omitted) is connected to an external control circuit (
The amount of light passing through the optical fiber 1U is separately modulated by receiving a control signal from the optical fiber 1U (not shown).

(5) Effects of the Invention The present invention has been explained above by showing all the embodiments, but the advantages can be summarized as follows.

■ No new technology or equipment is required as the structure is exactly the same as a conventional LCD panel.

■ For the same reason, the structure is simple and manufacturing is easy.

Furthermore, since the number of parts is small, it is compact.

(3) Therefore, the cost does not increase.

■ Since optical fiber is used as the waveguide, loss is not a problem at all.

■ Easy to create arrays. Additionally, the cost increase due to arraying is determined by the number of fibers, and other parts do not contribute much to the cost increase.

■ When creating an array, there is almost no limit to the number of fibers. It can be expanded to the size of a tab or an LCD display panel.

Next, applications of the present invention will be described.

FIG. 7 shows the relationship between the electric field applied to the liquid crystal and the light transmittance of the optical fiber. Area A is in the ON state.

Region B is in an OFF state, and region B is in a state in which the amount of transmitted light changes continuously depending on the electric field. Therefore, an ON-OFF type optical switch that uses a change between A and 0 and a B-C modulator that actively uses B become possible.

Further, as the external control No. 18, temperature or the like can be used instead of the electric field applied to the liquid crystal. This utilizes the change in the refractive index of the liquid crystal that changes the YML power ratio, and the optical modulator of the present invention can be used as a temperature sensor. However, in this case, the transparent conductive film to be provided on the insulating substrate is not required.

As described above, the scope of application of the present invention is wide and its value is high.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of a conventional optical modulator using liquid crystal. FIGS. 2 and 3 are cross-sectional views showing one embodiment for explaining the principle of the optical modulator of the present invention. FIG. 4 is a perspective view showing an embodiment of the optical modulator of the present invention. FIG. 5 is a cross-sectional view showing an embodiment for explaining the principle of the variable meter of the present invention. FIG. 6 is a plan view showing an embodiment of the optical modulator of the present invention. FIG. 7 is a graph for explaining the principle f of the optical modulator of the present invention, and shows the entire relationship between the external control signal and the light transmittance. 10... Optical fiber 10-a... Optical fiber core 10-1...
... Optical fiber cladding 11 ... Base 12, 16 ... Transparent conductive film 14 ... Sole material 15 ... Liquid crystal and above Applicant Corporation Daini Seikosha No. 1 Figure No. 4 Mouth No. 9

Claims (1)

[Scope of Claims] (1) In an optical modulator whose refractive index can be changed by an external control signal, the optical modulator includes two insulating substrates provided with at least transparent conductive films, and the insulating substrate. The liquid crystal injected between the substrates, the optical fiber whose core is exposed at the part that penetrates the liquid crystal and contacts the liquid crystal, the insulating substrate and the original fiber are positioned and fixed to each other, and the liquid crystal is The optical modulation device is characterized in that the light transmittance of the optical fiber is completely changed depending on the state of the liquid crystal according to the external direction + lI r, ql + divination symbol. (2. In the optical modulator according to claim 1,
An optical modulator characterized in that an external control signal is an electric field applied to a liquid crystal through a transparent conductive film. (3) In the optical modulator according to claim 1,
An optical modulator characterized in that an atmospheric event such as temperature or pressure is used as an external control signal. (4) In the optical modulator according to claim 1,
Part or all of the substrate, transparent conductive film, and optical fiber constituting the optical modulator are subjected to alignment treatment for liquid crystal, and the direction thereof is approximately parallel to the substrate. modulator. (5) In the optical modulator according to claim 1,
An optical modulator characterized in that the optical fiber has a bent part at the part where it contacts the liquid crystal. (6) Fi--An optical modulator according to claim 1, characterized in that a plurality of optical fibers are housed in a beam ζ array.