JPH05216076A - Optical deflection device - Google Patents

Abstract

PURPOSE:To provide the optical deflection device which can be driven by a low voltage and can be made two-dimensional and small in size. CONSTITUTION:This deflection device is constituted of a polarization rotating device 13 capable of rotating the polarization of input signal light 12 which is linearly polarized light by 90 deg. according to control signals and the deflector 14 for changing over the output direction of the signal light according to the polarization state. The deflector 14 is constituted of three sheets of transparent substrates 15, 16, 17 and is formed with saw tooth-shaped grids 18, 19 facing opposite directions on both sides of the central transparent substrate 17. The saw tooth-shaped grids are formed of double refractive materials. Liquid crystals 20, 21 which are homogeneously oriented in parallel with inscribed lines and have double refractiveness are respectively held between the transparent substrates 15, 16, 17 so that the input signal light 12 is parallel shifted according to the control signal of the polarization rotating device 13 and the optical path of the output signal 22 is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflector for switching the optical path of signal light in a spatial connection of light applied to optical switching or the like.

[0002]

2. Description of the Related Art Optical switching is an important basic technique in optical information processing and optical switching for realizing optical spatial connection by utilizing incoherence and parallelism of light. one of.

The functions required for this optical switching include a shutter function for controlling transmission and blocking of signal light, and an optical deflection technique for controlling the traveling direction of light, that is, an optical path changing function. Here, for changing the optical path in the optical deflection technique, there are methods such as changing the output angle of the signal light or shifting the optical path in parallel, which is appropriately selected depending on the system configuration.

Among these, as a technique for shifting the optical path in parallel, one based on the electro-optical effect is known. Electro-optical deflection by the electro-optical effect is realized by combining an electro-optical switch and a birefringent prism, a mirror or the like. Here, the electro-optical switch is a liquid crystal,
Alternatively, it is a device that uses ceramics or the like to modulate the intensity, angle, polarization direction, etc. of light by electrical input, and includes so-called spatial light modulators and the like. In electro-optical deflection, the polarization direction of signal light is changed by this electro-optical switch.

On the other hand, in the birefringent prism, the input light can be separated into ordinary light and extraordinary light by its birefringent action.
The ordinary light and the extraordinary light have their optical paths deviated by an amount corresponding to the retardation value of the material forming the birefringent prism. Therefore, the polarization plane of the signal light, which is linearly polarized light, is made to correspond to the ordinary light or the extraordinary light with respect to the birefringent prism, and the polarization direction of the signal light is rotated by π / 2 by the electro-optical switch to switch between the ordinary light and the extraordinary light. This enables optical path shift, that is, optical path conversion.

As described above, the electro-optical deflection is a method of shifting the optical path by the amount of birefringence by using a birefringent material such as calcite. This method allows high-speed deflection in principle, but the shift amount of the optical path is determined by the retardation value of the birefringent material. Generally, the birefringence of an optical material is small, and a thick birefringent material is required to obtain a large optical path shift amount. Therefore, the mounting volume becomes large and the material cost such as calcite becomes high. There was a flaw.

Further, a mechanical method has been studied in which a reflecting mirror or the like is formed in the device and the emitting angle of the signal light is changed by rotating the reflecting mirror.
There is a problem in that it is difficult to make a micro mirror and the reliability of the rotation drive unit.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical deflecting device which can be reduced in size and cost.

[0009]

The structure of an optical deflecting device according to the present invention that achieves the above object is a polarization rotating device for rotating the polarization direction of incident signal light, and an input light from the polarization rotating device. A deflecting device for parallel-shifting and outputting according to the polarization direction is provided, and the deflecting device is composed of one transparent substrate located at the center and two transparent substrates arranged on both sides of the transparent substrate, and On both sides of the transparent substrate, the sawtooth gratings facing in opposite directions, the sawtooth gratings are made of a birefringent material, and the transparent substrate at the center and the two transparent substrates on both sides are in between. It holds a liquid crystal, the liquid crystal is homogeneously aligned, and the liquid crystal has birefringence, and the refractive index of either the major axis or the minor axis thereof forms a sawtooth grating on both sides of the central transparent substrate. The optical axis direction of the material Characterized in that it coincides with the optical axis and the vertical refractive index.

[0010]

In the optical deflector having the above structure, the signal light can be parallel-shifted by controlling the polarization state of the input signal.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an optical deflecting device according to the present embodiment, and FIG. 2 is an enlarged view of a main part of FIG. 1, and is an operation diagram showing a deflected state of signal light in a sawtooth grating.

As shown in these figures, the optical deflecting device 11 according to this embodiment includes a polarization rotating device 13 capable of rotating the polarization of the input signal light 12 which is a linearly polarized light by 90 ° in accordance with a control signal. The deflecting device 14 is configured to switch the output direction of the signal light according to the polarization state. The deflecting device 14 is composed of three transparent substrates 15, 16 and 17, and saw-tooth saw-toothed gratings 18 and 19 facing in opposite directions are formed on both side surfaces of the central transparent substrate 17.

The sawtooth gratings 18 and 19 are made of the same material and have the same shape characteristics such as pitch and taper angle.
Only that direction is reversed. In FIG. 1, the sawtooth gratings 18 and 19 are inscribed in the direction perpendicular to the paper surface. The saw-toothed gratings 18 and 19 are made of a uniaxially oriented material having birefringence, and the refractive index in the optical axis direction is smaller than the refractive index in the direction perpendicular to the optical axis. The direction is the same as the optical axis direction of the constituent material.

Liquid crystals 20 and 21 are held between each of the three transparent substrates 15, 16 and 17. Liquid crystal 20, 2
1 is homogeneously aligned parallel to the scribe lines of the sawtooth gratings 18 and 19, and the alignment directions of the liquid crystals 20 and 21 are the same.
It is the same as the ruled line direction of the sawtooth gratings 18 and 19.

The liquid crystals 20 and 21 have the same optical characteristics and have birefringence, and the refractive index in the major axis direction is larger than the refractive index in the minor axis direction. The materials of the liquid crystals 20 and 21 or the sawtooth gratings 18 and 19 are selected so that the refractive indices of the liquid crystals 20 and 21 in the long axis direction are the same as the refractive indexes of the sawtooth gratings 18 and 19 in the optical axis direction. ..

Further, the deflecting device 14 is arranged so that the alignment directions of the liquid crystals 20 and 21 are the same as the polarization direction of the input signal light 12 which is linearly polarized light. At this time, the polarization direction of the input signal light 12 is equal to the ruled line direction of the sawtooth gratings 18 and 19,
It is also equal to the optical axis direction of the material forming the saw-toothed gratings 18, 19.

FIG. 2 shows a portion of the sawtooth grid of the deflection device 14 in FIG. Further, FIG. 3 shows a state in which the liquid crystal molecules 20 a are aligned in parallel with the sawtooth lattice 19.

The operation of the optical deflector according to the present invention will be described below with reference to FIG. Sawtooth grating 19 through liquid crystal 20
Due to the taper of the sawtooth grating, the input signal light 12 incident on is refracted into the sawtooth grating 19 under the condition generally expressed by the following equation (1). n ₁ · sin θ ₁ = n ₂ · sin θ ₂ (1)

In the equation (1), n ₁ is the liquid crystal 20.
Is the effective refractive index of n, and n ₂ is the refractive index of the material forming the sawtooth grating 19. Further, θ ₁ is a sawtooth grid 19
Is the incident angle of the input signal light 12 with respect to, which is equal to the taper angle of the sawtooth grating 19.

Θ ₂ is the emission angle of the input signal light 12 with respect to the taper normal of the sawtooth grating 19. On the other hand, the signal light emitted from the saw-toothed grating 18 through the transparent substrate 17 and emitted from the saw-toothed grating 18 is refracted into the liquid crystal 21 under the condition represented by the equation (2). n ₃ · sin θ ₃ = n ₄ · sin θ ₄ (2)

In the above equation (2), n ₃ is the refractive index of the material forming the sawtooth grating 18, and n ₄ is the effective refractive index of the liquid crystal 21. Further, θ ₃ is the incident angle of the signal light with respect to the sawtooth grating 18, and θ ₄ is the outgoing angle of the signal light with respect to the taper perpendicular of the sawtooth grating. Where 2
Since the two saw-toothed gratings 18 and 19 have the same shape (cross-sectional shape, pitch, etc.) and have the same material and orientation direction, n ₂ = n ₃ , and the optical characteristics of the liquid crystals 20 and 21, And the orientation directions are the same, n ₁ = n ₄
Becomes

An object of the optical polarization device according to the present invention is to change the optical path of the signal light according to the control signal, and the switching is performed by rotating the polarization plane of the input signal light which is linearly polarized light (rotation by 90 °). ), Do not allow or control.

First, consider a case where the polarization plane of the input signal light 12 is not rotated by the polarization rotation device 13. For this purpose when the orientation of the polarization direction and the liquid crystal 20 of the signal light 12 as described above matches the refractive index n ₁ of the liquid crystal 20 feels the signal light 12, the refractive index n ₁ long axis direction of the liquid crystal 20 ‖ The refractive index of the saw-toothed grating 19 that the signal light 12 feels is the refractive index n ₂ ∥ of the material forming the saw-toothed grating 19 in the optical axis direction.

Here, the refractive index n ₁ of the liquid crystal 20 in the major axis direction
Since the material of the liquid crystal 20 or the sawtooth grating 19 is set so that ‖ and the refractive index n ₂ ‖ of the sawtooth grating 19 in the optical axis direction are matched, in this case, n ₁ ‖ = n ₂ ‖ That is, n ₁ = n ₂ . Therefore, the input signal light 12 is the same as if the sawtooth grating 19 were not present, and the input signal light 12 goes straight.

Furthermore, since the same thing is established at the interface between the sawtooth grating 18 and the liquid crystal 21, the output signal light 22 output from the sawtooth grating 18 becomes a straight signal light 23 that travels straight.

On the other hand, when the polarization state of the input signal light is rotated by 90 ° by the polarization rotation device, the polarization direction of the input signal 12 is parallel to the minor axis direction of the liquid crystal 20, so that the sawtooth grating 19 and the liquid crystal are aligned. At the boundary with 20, the refractive index n ₁ of the liquid crystal 20 which the input signal light 12 feels is the refractive index n ₁ ⊥ in the minor axis direction.
become.

Since the liquid crystal 20 has a refractive index anisotropy, n ₁ ‖ ≠ n ₁ ⊥, and n ₁ ‖> n ₁ ⊥, so that the polarization plane of the signal light does not rotate. , The effective refractive index is reduced by the refractive index anisotropy Δn ₁ (n ₁ ‖-n ₁ ⊥) of the liquid crystal 20. On the other hand, the effective refractive index of the sawtooth grating 19 which the input signal light 12 feels is the refractive index n ₂ ⊥ in the direction perpendicular to the optical axis direction, and since the sawtooth grating material has birefringence, it is in the optical axis direction. N ₂ ‖ and n ₂ ⊥ are different from _{each other.}
Since ‖ ≠ n ₂ ⊥ and n ₂ ‖ <n ₂ ⊥, the refractive index sensed by the input signal light 12 is Δn ₂ (n ₂ ⊥-n ₂ ‖ compared to when the polarization plane of the signal light is not rotated. ) Only increase.

From the above, the input signal light 12 is deflected at the interface between the liquid crystal 20 and the saw-toothed grating 19 to an angle θ ₂ (≠ θ ₁ ) which is determined by a large difference in refractive index [Δn ₁ + Δn ₂ ]. The deflected signal light is refracted again at the interface between the sawtooth grating 18 and the liquid crystal 21. In this case, n ₂ = n ₃ and n ₁ = n ₄ , and the sawtooth grating 18 and
Since the taper angles of 19 are the same, θ ₂ = θ ₃ and θ ₁ = θ ₄ , and the output signal light 22 is output as the deflection signal light 24 that is shifted in parallel with the straight traveling signal light 23. To do.

In this way, by rotating the polarization direction of the input signal light 12 according to the control signal by the polarization rotation device 13, it becomes possible to change the output angle of the input signal light 12, and the output signal light 22. It is possible to change the optical path of.

The shift amount of the output signal light is mainly determined by the taper angle θ ₁ and the refractive indices n‖ and n⊥ (n _e , n ₀ ) of the liquid crystal, and the refractive indices n‖ and n⊥ of the sawtooth grating, and the output. Each may be selected according to the required value of the shift amount.

For example, in the case of electro-optical deflection using a birefringent material such as calcite, the shift amount is determined by the retardation value of the birefringent material, and therefore a large refractive index anisotropy is required to obtain a large shift amount. It is necessary to use a material or to increase the thickness of the birefringent material, which increases the difficulty of obtaining a material with good crystallinity such as calcite, and causes problems such as an increase in mounting volume and an increase in cost. It becomes apparent.

In the optical deflector according to the present invention, the refractive index anisotropies of both the liquid crystal and the saw-toothed grating material can be added and effectively used, so that a large difference in refractive index can be effectively realized and a large shift amount can be obtained. You can If the amount of shift is the same, it is possible to make the thickness of the deflecting device the same as or thinner than that of calcite, making it smaller and less expensive than conventional optical path changing devices that use birefringent materials such as calcite. Is possible.

In FIG. 2, the refractive index anisotropies of the liquid crystals 20 and 21 and the sawtooth gratings 18 and 19 are shown by the liquid crystal 20 and 2.
1 is n‖> n⊥, and sawtooth gratings 18 and 19 are n‖ <n
I explained in ⊥. However, the liquid crystals 20, 21 and the sawtooth grating 1
The polarities of the refractive index anisotropies in 8 and 19 may satisfy the following relationships, and the optical deflector according to the present invention is not limited to the above relationships. The refractive index in the major axis direction of the liquid crystal is larger than the refractive index in the minor axis direction, the optical axis direction of the sawtooth lattice-constituting material coincides with the direction of the ruled line of the grating, and the refractive index of the lattice-constituting material in the optical axis direction is It is smaller than the refractive index in the direction perpendicular to the optical axis. (The above description) The refractive index of the liquid crystal in the major axis direction is smaller than the refractive index in the minor axis direction, and the optical axis direction of the sawtooth lattice-constituting material coincides with the ruled line direction of the lattice. Has a refractive index greater than that in the direction perpendicular to the optical axis. The refractive index of the liquid crystal in the major axis direction is larger than the refractive index in the minor axis direction, the optical axis direction of the saw-toothed grating constituent material is orthogonal to the grating line direction, and the refractive index of the grating constituent material in the optical axis direction is It is larger than the refractive index in the direction perpendicular to the optical axis. The refractive index of the liquid crystal in the major axis direction is smaller than the refractive index in the minor axis direction, and the optical axis direction of the sawtooth lattice constituent material and the direction of the ruled line of the grating are orthogonal to each other, and the refractive index of the lattice constituent material in the optical axis direction is It is smaller than the refractive index in the direction perpendicular to the optical axis.

As described above, the shift amount of the output signal light is determined by the shape parameter of the sawtooth grating or the like which constitutes this device,
And the characteristic parameters of the liquid crystal and the like.

However, when the shape of the sawtooth grating 17 is small, the analysis effect becomes remarkable, and so-called high-order light is generated, so that the analysis effect is reduced and crosstalk occurs.

Therefore, in order to blazed the input signal light 12 in a specific direction, the saw-toothed grating to be formed may be a blazed diffraction grating. The blazed condition of this blazed diffraction grating is represented by the following equation (3). d · sin (θ ₂ −θ ₁ ) = m · λ (m = 1, 2 ...) (3)

Here, d is the pitch of the blazed diffraction grating, λ is the wavelength of the signal light, and m is the order. Expressions (1), (2) and (3) for the wavelength λ of the input signal light 12
By satisfying the formula, the blazed light shifted by a desired amount is output.

As described above, by optimizing the grating pitch d in addition to the shape and characteristic parameters, it is possible to obtain output light with high diffraction efficiency and no crosstalk.

Typical examples of the liquid crystal used in the light deflecting device of the present invention include nematic liquid crystal used in liquid crystal displays and the like, which exhibit birefringence.
There is no limitation on the kind as long as homogeneous alignment is possible, and for example, ferroelectric liquid crystal may be used.

The material is not limited to liquid crystal, and any type of birefringent material can be used as long as it can be formed on a sawtooth grating or a blazed grating in a uniaxially oriented structure.

In FIG. 1, saw-toothed gratings 18, 1
Although 9 is shown as a structure different from that of the central transparent substrate 17, the transparent substrate 17 may be directly processed into a sawtooth shape, or may be processed into a sawtooth shape after laminating silicon oxide or the like, or a sawtooth shape. It is also possible to stack the processed plates.

When the saw-toothed gratings 18 and 19 and the transparent substrate 17 have different configurations, it is desirable that the refractive indices of the two are the same, but even if they do not match, the saw-toothed grating 19 inputs to the saw-toothed grating 18. In that case, the signal light is only parallel-shifted, and there is no particular problem.

As the material of the sawtooth lattice, for example, Li
Examples include birefringent substrate materials such as NbO ₃ and quartz, organic polymer materials, and the like, which may be selected in consideration of matching with the refractive index of the liquid crystal used, workability, and the like.

The polarization rotation device 13 may have any function as long as it has a function of rotating the polarization of the input signal light by 90 ° in accordance with the control signal. For example, as a configuration example,
There is a configuration using a TN type liquid crystal cell twisted by 90 °. In this case, the polarization plane of the input signal rotates 90 ° when no voltage is applied, and the polarization plane does not rotate when voltage is applied.
A desired polarization rotation device can be constructed.

Even if a ferroelectric liquid crystal is used as the liquid crystal, the function of rotating the polarization plane can be realized, and in particular, in this case, there is an advantage that it is not necessary to continuously apply the voltage because of the memory property.

[0046]

As described above, in the optical deflecting device of the present invention, an output is made with a simple structure without providing an electrically or mechanically movable part, and without using a birefringent material such as calcite. Since the signal light can be parallel-shifted, the optical switch can be downsized and the cost can be reduced.
Further, by using the liquid crystal device as the polarization rotation device, it is possible to reduce the entire voltage, and the effect is great in realizing the optical switch.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical deflecting device according to an embodiment.

FIG. 2 is an operation diagram showing a deflected state of signal light in a sawtooth grating portion.

FIG. 3 is an alignment state diagram of a sawtooth lattice and liquid crystal molecules.

[Explanation of symbols]

 11 Optical Deflection Device 12 Input Signal Light 13 Polarization Rotation Device 14 Deflection Device 15, 16, 17 Transparent Substrate 18, 19 Sawtooth Grating 20, 21 Liquid Crystal 20a Liquid Crystal Molecule 22 Output Signal Light 23 Linear Signal Light 24 Deflection Signal Light

Claims (2)

[Claims] 1. A polarization rotation device for rotating the polarization direction of incident signal light, and a deflection device for parallelly shifting and outputting the input light from the polarization rotation device according to the polarization direction, and The deflecting device is composed of one transparent substrate located at the center and two transparent substrates arranged on both sides of the transparent substrate, and on both sides of the central transparent substrate, there are saw-toothed gratings facing in opposite directions. The sawtooth grating is formed of a birefringent material, and the central transparent substrate and the two transparent substrates on both sides each hold a liquid crystal therebetween, and the liquid crystal is homogeneously aligned and the liquid crystal is birefringent. And the refractive index of either the major axis or the minor axis thereof matches the refractive index of the material forming the sawtooth gratings on both sides of the central transparent substrate in the optical axis direction or in the direction perpendicular to the optical axis. Characteristic light deflection device. 2. The optical deflector according to claim 1, wherein the sawtooth grating is a blazed diffraction grating.