JPH07261141A - Polarization controller - Google Patents

Abstract

PURPOSE:To provide a polarization controller which controls the polarization plane of input light and is capable of sufficiently rotating the polarization plane. CONSTITUTION:A ferroelectric liquid crystal material 15 is sealed with glass substrates 16, 17 having electrodes 18, 19 and oriented films 20, 21 formed on them. A double refractive plate 14 which is arranged to align the optical axis to the optical axis of one stable state of the two stable states common to two ferroelectric liquid crystal elements 12, 13 and has the refractiveness set with a retardation omega in such a manner that the polarized light component of the incident light in the same direction as the direction of the exit light at the time of rotation of the polarized light of the incident light attains <=5% of the incident light is arranged between the ferroelectric liquid crystal elements 12, 13 arranged in such a manner that the major axes of the molecules face the same direction by impression of electric fields of the same polarities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization controller, and more particularly to a polarization controller for controlling the plane of polarization of input light.

In the fields of optical computers, optical exchangers, etc., research and development of elements utilizing polarization of light are being actively conducted. Liquid crystals are two-dimensional polarization control elements, and among them, ferroelectric liquid crystals are highly expected to be used because of their excellent properties such as high-speed response and memory.
A technique for efficiently controlling polarization is demanded for such a polarization controller.

[0003]

2. Description of the Related Art Conventionally, a polarization control element using a ferroelectric liquid crystal is known. FIG. 7 shows a configuration diagram of a conventional polarization control device using a ferroelectric liquid crystal.

The conventional polarization control device 32 has a structure in which a liquid crystal 39 is sandwiched and enclosed by glass substrates 37 and 38 having transparent electrodes 33 and 34 and alignment films 35 and 36 formed on the inner surface side.

A polarization control circuit 40 is provided on the transparent electrodes 33 and 34.
Further, a polarization control signal is supplied, and the molecular long axis direction of the liquid crystal 39 is changed according to the polarity of the polarization control signal.
The polarization plane of the incident light I is rotated and emitted.

[0006]

However, in the conventional polarization control device, the polarization of incident light is controlled by one ferroelectric liquid crystal element. In this case, the ferroelectric liquid crystal having a bookshelf structure without alignment defects is used. Even if a liquid crystal liquid crystal element is used, sufficient rotation of the plane of polarization does not occur, and when the SP conversion of polarized light is performed with this element, there is a problem in that the amount of transmitted light is significantly reduced.

The present invention has been made in view of the above points, and an object of the present invention is to provide a polarization control device capable of rotating a polarization plane sufficiently.

[0008]

FIG. 1 is a block diagram showing the principle of the present invention. The first polarization control means 1 has a predetermined retardation φ and rotates the polarization plane of light according to an external electric field.

The second polarization control means 2 is arranged in parallel with the first polarization control means 1, has the same retardation as the first polarization control means 1, and rotates the polarization plane of light according to an external electric field. Let

The compensating plate 3 is arranged in parallel between the first polarizing means and the second polarizing means, and the total retardation is the retardation φ of the first polarizing means and the second polarizing means 2.
Retardation (ω) is shown to compensate for the components of the incident light I and the emitted light F, which are orthogonal to each other, to be emitted at substantially the same level.

According to a second aspect, one surface of the first and second polarization control means 1 and 2 facing the compensating plate 3 is shared with the compensating plate.

According to a third aspect of the present invention, the first and second polarization control means 1 and 2 sandwich the ferroelectric liquid crystal 15 between the alignment films 20 and 21 and the transparent substrates 16 and 17 on which the transparent electrodes 17 and 18 are formed. It is composed of a ferroelectric liquid crystal element.

[0013]

When a ferroelectric liquid crystal element is considered as the first and second polarization means, when the polarized light perpendicular to the optical axis of the ferroelectric liquid crystal element alone passes through the ferroelectric liquid crystal element. When the phase is set to 1, the phase when polarized light parallel to the optical axis passes through this ferroelectric liquid crystal element is

[0014]

[Outer 1]

Anyway, At this time, φ becomes the retardation of the ferroelectric liquid crystal element. Similarly, considering a plate having birefringence as the compensating plate, when the phase of light polarized perpendicular to the optical axis when passing through the plate having the birefringent surface is 1, the light polarized parallel to the optical axis is assumed. When passing through this ferroelectric liquid crystal element, the phase is

[0016]

[Outside 2]

Anyway, At this time, ω becomes the retardation of the plate having birefringence. When this is expressed in a matrix, the following Expressions 1 and 2 are obtained.

[0018]

[Equation 1]

In the ferroelectric liquid crystal, if the change angle (tilt angle) of the molecular long axis due to the polarity reversal of the applied electric field is set to θ, the matrix expression M of this entire element can be expressed as in Expression 3.

[0020]

[Equation 2]

Here, the incident light is expressed in a matrix.

[0022]

[Equation 3]

Matrix expression of emitted light

[0024]

[Equation 4]

Then, the outgoing light F can be expressed by F = MI. Assuming that the light polarized in the x-axis direction is (1, 0), the light is transmitted as it is when the optical axis of the ferroelectric liquid crystal element coincides with the x-axis (when θ = 0, it is also calculated from the formula. .), The outgoing light F is expressed as in Equation 4 when the molecular long axis changes by θ.

[0026]

[Equation 5]

At this time, the amplitude of the emitted light F in the x-axis direction is 0.
Then, it is orthogonal to the polarization of the original incident light I. Change of phase of plate with birefringence

[0028]

[Outside 3]

That is, setting the retardation ω enables efficient control of polarization.

According to the second aspect, by making the surfaces of the first and second polarization control means facing the compensating plate and both surfaces of the compensating plate common, for example, the number of glass substrates for liquid crystal encapsulation. Therefore, the attenuation of light can be reduced, and the device can be thinned.

[0031]

FIG. 2 shows a block diagram of an embodiment of the present invention. The polarization control device 11 of this embodiment includes ferroelectric liquid crystal elements 12, 1
3 and a birefringent plate 14, and a ferroelectric liquid crystal element 12,
A birefringent plate 14 is sandwiched between 13 and arranged.

The ferroelectric liquid crystal elements 12 and 13 are structured such that the ferroelectric liquid crystal material 15 is sandwiched between glass substrates 16 and 17 and sealed between the glass substrates 16 and 17.

Transparent electrodes 1 are provided on the glass substrates 16 and 17, respectively.
8 and 19 are formed, and alignment films 20 and 21 are further formed on the transparent electrodes 18 and 19. Transparent electrode 18,1
A polarization control circuit 22 is connected to the polarization control circuit 22, and the polarization control circuit 22 transmits the transparent electrodes 18 and 19 in accordance with the polarization state of the emitted light.
A predetermined voltage is applied to.

Further, the ferroelectric liquid crystal elements 12 and 13 have a phase shift between the fast axis and the slow axis when light passes through the liquid crystal material 15, that is, due to their birefringence while passing through the liquid crystal. The retardation φ, which is the phase difference between the ordinary light and the extraordinary light, is φ = π / 2, and the rubbing direction R of the alignment films 20 and 21.
The tilt angle θ, which means the deflection angle in the direction of the moment of the liquid crystal molecules centered at, is processed to be θ = π / 5.

In the birefringent plate 14, the liquid crystal material 23 of smectic A is not provided with a driving electrode, and the alignment films 24 and 25 are formed.
Only the glass substrates 26 and 27 are formed so as to be enclosed. At this time, the rubbing direction of the alignment films 24 and 25 is set to R, and the retardation ω is set to ω = about −0.7.

The ferroelectric liquid crystal elements 12 and 13 are arranged so that the major axes of their molecules are oriented in the same direction by the application of electric fields of the same polarity. The optical axis of the birefringent plate 14 is arranged so as to coincide with the optical axis in one stable state of the two stable states common to the ferroelectric liquid crystal elements 12 and 13.

In this system, when the light traveling direction is the z-axis, the optical axis of the birefringent plate 14 is the x-axis, and the axis orthogonal to the z-axis and the x-axis is the y-axis, the polarization direction of the incident light is the x-axis. Positioned against the device to match.

FIG. 3 and FIG. 4 show operation explanatory diagrams of the first embodiment of the present invention. FIG. 3 is for explaining the operation when the incident light I having a polarization plane in the x direction is output as the outgoing light F without being rotated. At this time, the polarization control circuit 22 causes the ferroelectric liquid crystal element 12, A low level signal is applied to 13. At this time, θ in the equation (4) becomes θ = 0, and the incident light I
Is I = (1,0), the output light F is F = (1,0) from the equation (4).

FIG. 4 shows the incident light I having a polarization plane in the x direction
In the operation explanatory view in the case of rotating as 0 ° and outputting as the emitted light F, at this time, a high level signal is applied from the polarization control circuit 22 to the ferroelectric liquid crystal elements 12 and 13, and the molecules of the liquid crystal rotate by θ. To do.

According to this embodiment, when the intensity of the x-axis component of the transmitted light when the light polarized in the x-axis direction is transmitted as it is, the y of the transmitted light when the polarization plane is rotated is set. The transmitted light intensity of the component is 0.975. When the ferroelectric liquid crystal element was used alone, the transmitted light intensity of the y-axis component of the transmitted light when the polarization plane was rotated was 0.931. In this way, the intensity is increased from 0.931 to 0.975, and the function of rotating the polarized light is improved.

At this time, the retardation of the ferroelectric liquid crystal elements 12 and 13 is φ, the retardation of the birefringent plate 14 is ω, and the change angle of the liquid crystal molecule long axis due to the polarization reversal of the ferroelectric liquid crystal elements 12 and 13 is θ. And incident light

[0042]

[Equation 6]

That is, when the polarization plane is in the X-axis direction, the emitted light

[0044]

[Equation 7]

It is desirable that the intensity of polarized light has a polarization plane in the X-axis direction.

[0046]

[Equation 8]

That is, it is desirable to set the retardations φ and ω so that the polarization component in the same direction as the incident light becomes 5% or less of the incident light when the polarized light is rotated.

As described above, according to the present embodiment, the angle of change of the molecular long axis due to the polarity reversal of the applied electric field is small in spite of having a good molecular orientation, so that it is slightly unsuitable as an SP conversion element. The suitable one is compensated by the retardation of the two ferroelectric liquid crystal elements and the compensating plate, a sufficient conversion angle is obtained, and the conversion can be performed with high efficiency.

FIG. 5 shows a block diagram of an application example of the first embodiment of the present invention.

Incident light is supplied to the polarizing plate 23. The polarizing plate 23 transmits only S light having a predetermined polarization plane and is supplied to the polarization control device 11.

In the polarization control device 11, the S light supplied according to the control signal from the polarization control circuit 22 is transmitted as it is, or the S light is converted into P light whose polarization plane is rotated by 2 / π and emitted. Is controlled.

The light emitted from the polarization controller 11 is supplied to the polarization beam splitter 24. In the polarization beam splitter 24, if the light emitted from the polarization control device 11 is S light, it is transmitted as it is, and if it is P light, it is bent π / 2 with respect to the light incident direction and is emitted. Therefore, the S or P light emitted from the polarization beam splitter 24 is output as light modulated by the polarization controller 11.

At this time, by using the polarization control device 11 of this embodiment, the attenuation at the time of conversion from S light to P light can be reduced, and a large modulated optical signal can be obtained.

FIG. 6 shows a block diagram of the second embodiment of the present invention. In the figure, the same components as those in FIG.
The description is omitted.

In this embodiment, the ferroelectric liquid crystal element 13 of FIG.
Glass substrates 16 and 17 on the side facing the compensating plate 14
In place of the glass substrates 24 and 25 of the compensating plate 14, the glass substrates 30 and 31 sharing them are provided.

On the outer surface of the glass substrate 26, the electrodes 19 and the alignment film 21 of the ferroelectric liquid crystal element 12 are formed, and on the inner surface thereof, the alignment film 26 of the birefringent plate 14 is formed.

The electrode 16 of the ferroelectric liquid crystal element 13 and the alignment film 20 are formed on the outer surface of the glass substrate 26, and the alignment film 27 of the birefringent plate 14 is formed on the inner surface.

According to this embodiment, four glass substrates 1 are used.
Since 6, 17, 24, and 25 can be replaced by the two glass substrates 30 and 31, the number of glass substrates can be reduced, and therefore, thinning is possible and
The light attenuation can be reduced, and more efficient conversion becomes possible.

Although the birefringent plate 13 is composed of a ferroelectric liquid crystal element in the first and second embodiments, the invention is not limited to this, and it may be composed of a solid crystal having birefringence.

[0060]

As described above, according to claim 1 of the present invention, the rotation of the plane of polarization of incident light is compensated for by the first and second polarization control means and the retardations φ and ω of the compensating plate, thereby increasing the molecular length. Even if the change angle of the axis is small, the incident light can be sufficiently rotated, so that the polarization control can be performed with high efficiency.

According to the second aspect, the glass substrate for sealing the liquid crystal or the like of the first and second polarization control means is shared with both surfaces of the compensating plate, so that the glass substrate becomes unnecessary and the device is made thin. In addition to being able to reduce the light attenuation due to the glass substrate, the polarization control can be performed with high efficiency.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of a first embodiment of the present invention.

FIG. 3 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 5 is a configuration diagram of an application example of the first embodiment of the present invention.

FIG. 6 is a configuration diagram of a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st polarization control means 2 2nd polarization control means 3 Compensation plate (phi), (omega) retardation I Incident light F Emission light 12,13 Ferroelectric liquid crystal element 14 Birefringent plate 15,23 Ferroelectric liquid crystal material 16,17 , 24, 25 Glass plate 18, 19 Electrode 20, 21 Alignment film 22 Polarization control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G09G 3/36 (72) Inventor Hiroki Shirato 1015 Ueodachu, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Limited (72) Inventor Tetsuya Makino 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (3)

[Claims] 1. A first polarization control means (1) having a predetermined retardation (φ) and rotating a polarization plane of light according to an external electric field; and a first polarization control means (1) parallel to the first polarization control means (1). A second polarization control means (2), which has the same retardation (φ) as that of the first polarization control means (1) and rotates the polarization plane of light according to an external electric field; The first polarization control means (1) and the second polarization control means (2) are arranged in parallel to each other, and the retardation of the first polarization control means (1) and the second polarization control means (2). Incoming light (I) and outgoing light (F) in combination with (φ)
And a compensator (3) having a retardation (ω) for compensating so that the components orthogonal to each other are substantially the same. 2. The first and second polarization control means (1,
2. The polarization control device according to claim 1, wherein one surface of 2) facing the compensating plate (3) is shared with the compensating plate (3). 3. The first and second polarization control means (1,
2) is a transparent substrate (1) on which a ferroelectric liquid crystal (15) is formed with an alignment film (20, 21) and transparent electrodes (18, 19).
Ferroelectric liquid crystal element (12, 1) sandwiched by 6, 17)
3. The polarization control device according to claim 1, wherein the polarization control device is composed of 3).