JP2008224716A - Ac modulation noise compensating method for optical output signal of liquid crystal optical component, and ac modulation noise compensation type liquid crystal optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of compensating AC modulation noise, and AC modulation noise compensation type liquid crystal optical component. <P>SOLUTION: The AC modulation noise compensation type liquid crystal optical component having a liquid crystal cell controlling the quantity of transmitted light by rotating a plane of polarization of incident linearly polarized light according to a liquid crystal drive signal as an AC electric signal includes a polarization plane rotator which rotates the plane of polarization of incident light reversely to the liquid crystal cell according to a given signal to project the incident linearly polarized light toward the liquid crystal cell, and a signal waveform computing element which inputs the liquid crystal drive signal, generates a compensation electric signal causing the polarization plane rotator to have an amount of rotation of the plane of polarization corresponding to intensity-modulation noise generated at the liquid crystal cell when the liquid crystal drive signal rises or falls, and supplies the signal to the polarization plane rotator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal optical component that modulates the intensity of an optical signal using liquid crystal, and more particularly to a liquid crystal optical component that drives liquid crystal with an AC electrical signal.

  As a technique for adjusting the intensity of an optical signal using liquid crystal, there are those disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2001-13477) and Patent Document 2 (Japanese Patent Laid-Open No. 2005-202271).

  A liquid crystal optical attenuator disclosed in Patent Document 1 passes through a polarization separating means for separating light incident from the outside into P-polarized light and S-polarized light, a liquid crystal element on which P-polarized light and S-polarized light are incident, and the liquid crystal element. Polarization combining means for combining and emitting P-polarized light and S-polarized light, applying a 10 KHz sine wave voltage (AC electrical signal) to the liquid crystal element, and controlling the amount of light transmitted through the liquid crystal element by the applied voltage value Is.

Patent Document 2 discloses an optical waveguide type liquid crystal variable optical attenuator in FIGS. 1 and 2 and paragraphs 0012 to 0014 of the specification. The variable optical attenuator includes a main core 1, a sub-core 4 that is disposed in proximity to the main core 1 and filled with liquid crystal that contacts the alignment films 7 </ b> A and 7 </ b> B, and the sub-core 4 opposite to the main core 1. The amount of light energy transferred from the main core 1 to the sub-core 4 is controlled by changing the refractive index of the liquid crystal according to the voltage applied to the electrodes. The light intensity on the output side of the core 1 is modulated.
JP 2001-13477 A JP-A-2005-202271

  Among the optical components using liquid crystal, when the liquid crystal element is driven by an AC electric signal like the liquid crystal optical attenuator described in Patent Document 1, the orientation of the liquid crystal molecules is changed at the rise and fall of the AC electric signal. By swinging back from the direction when the voltage is applied to the direction when the applied voltage is cut off, the polarization plane of the light beam after passing through the liquid crystal cell is instantaneously rotated toward the direction when no voltage is applied. As a result, intensity modulation occurs in the output optical signal and is superimposed as noise, which may degrade signal transmission characteristics. This is the same as that described in Patent Document 2 in which the refractive index of the liquid crystal is controlled by voltage.

  In particular, in a normally-on variable optical attenuator in which the amount of attenuation increases according to the drive voltage amplitude, it is necessary to increase the drive voltage (AC amplitude) applied to the liquid crystal cell in order to obtain a large amount of attenuation. Since AC modulation noise increases with the drive voltage and the signal transmission characteristics may deteriorate, there is a problem that a large variable range that can be used in the variable optical attenuator cannot be secured.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to realize a method for compensating for AC modulation noise and a liquid crystal optical component of AC modulation noise compensation type. .

The AC modulation noise compensation type liquid crystal optical component of the present invention is an AC modulation noise compensation type having a liquid crystal cell that controls the amount of transmitted light by rotating the plane of polarization of linearly polarized light that is incident according to a liquid crystal drive signal that is an AC electrical signal. In liquid crystal optical components,
A polarization plane rotator that rotates a polarization plane of incident light in a direction opposite to the liquid crystal cell according to a given signal, and emits incident linearly polarized light toward the liquid crystal cell;
The liquid crystal driving signal is input, and a compensation electric signal is generated that causes the polarization plane rotator to generate a rotation amount of a polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and the polarization An AC modulation noise compensation type liquid crystal optical component comprising a signal waveform calculator for supplying to a surface rotator.

An AC modulation noise compensation type liquid crystal optical component according to another aspect of the present invention includes an AC liquid crystal cell having a liquid crystal cell that controls the amount of transmitted light by rotating the plane of polarization of linearly polarized light that is incident according to a liquid crystal drive signal that is an AC electrical signal. In modulation noise compensation type liquid crystal optical components,
A polarization plane rotator that rotates a polarization plane of incident light in a direction opposite to the liquid crystal cell in response to a given signal with respect to the light emitted from the liquid crystal cell;
The liquid crystal driving signal is input, and a compensation electric signal is generated that causes the polarization plane rotator to generate a rotation amount of a polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and the polarization It has a signal waveform calculator supplied to the surface rotator.

An AC modulation noise compensation method for an optical output signal of a liquid crystal optical component according to the present invention includes a liquid crystal cell that controls the amount of transmitted light by rotating the polarization plane of incident linearly polarized light in accordance with a liquid crystal drive signal that is an AC electrical signal. In an AC modulation noise compensation method for an optical output signal of a liquid crystal optical component performed by an AC modulation noise compensation type liquid crystal optical component,
A polarization plane rotator that rotates the polarization plane of incident light in a direction opposite to the liquid crystal cell according to a given signal and emits the incident linearly polarized light toward the liquid crystal cell,
From the liquid crystal drive signal, generate a compensation electric signal for causing the polarization plane rotator to generate a rotation amount of the polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and rotating the polarization plane It supplies to a container.

An AC modulation noise compensation method for an optical output signal of a liquid crystal optical component according to another embodiment of the present invention is a liquid crystal that controls the amount of transmitted light by rotating the polarization plane of incident linearly polarized light according to a liquid crystal drive signal that is an AC electrical signal. In an AC modulation noise compensation method for an optical output signal of a liquid crystal optical component performed by an AC modulation noise compensation type liquid crystal optical component having a cell,
For the light emitted from the liquid crystal cell, a polarization plane rotator is provided that rotates the polarization plane of the incident light in a direction opposite to the liquid crystal cell according to a given signal.
From the liquid crystal drive signal, generate a compensation electric signal for causing the polarization plane rotator to generate a rotation amount of the polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and rotating the polarization plane It supplies to a container.

  In the present invention, the polarization plane of the light beam before transmission through the liquid crystal cell is rotated by the compensation electrical signal generated from the liquid crystal drive signal by the signal waveform calculator, so that after the liquid crystal cell transmission occurs at the rise and fall of the liquid crystal drive signal. The polarization plane rotation of the light beam is canceled, and AC modulation noise superimposed on the output optical signal is removed.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. This embodiment comprises an input side fiber collimator 1, a polarization separator 2, a polarization plane rotator 3, a liquid crystal cell 4, a polarization synthesizer 5, an output side fiber collimator 6, a signal waveform calculator 7 and an AC signal source 12. ing.

  The polarization separator 2 separates the light beam input from the input side fiber collimator 1 into two polarized beams of normal light and abnormal light orthogonal to each other. As an example, it will be described below that the liquid crystal cell 4 operates in the TN mode.

  The liquid crystal cell 4 rotates the plane of polarization determined by the amplitude of the liquid crystal drive signal 11 which is an AC electric signal output from the AC signal source 12 with respect to the input light beam. For example, when the amplitude of the applied AC electrical signal is 0, the polarization plane rotates 90 degrees, and the rotation angle of the polarization plane decreases as the AC electrical signal amplitude increases.

  The light beam that has passed through the liquid crystal cell 4 is combined by a backward polarization combiner 5 and coupled to an output side fiber collimator 6. The above configuration is the same as that of a conventional liquid crystal optical component.

  The polarization plane rotator 3 serving as a characteristic component of the present invention rotates the polarization plane of the light beam that has passed through the polarization separator 2 in accordance with the compensation electric signal 10 applied from the signal waveform calculator 7.

  The signal waveform calculator 7 includes a linear calculator, an integral calculator, and the like, and generates a compensation electrical signal 10 from the input liquid crystal drive signal 11. The polarization separator 2, the polarization synthesizer 5, and the polarization plane rotator 3 use ferroelectric crystals such as rutile oxide and lithium niobate, respectively.

  Next, the operation of the polarization plane rotator 3 will be described with reference to time charts shown in FIGS. 2 (a), 2 (b), and 2 (c).

  In general, when a liquid crystal drive signal 11 having a finite rise and fall time, as shown in FIG. 2A, is applied to the liquid crystal cell 4, the liquid crystal cell 4 at the rise and fall of the liquid crystal drive signal 11 The polarization plane rotates in the light beam after transmission, and accordingly, as shown in FIG. 2B, intensity modulation noise is superimposed on the output optical signal.

  The signal waveform calculator 7 receives the liquid crystal drive signal 11 and generates a compensation electric signal 10 as shown in FIG. The compensation electric signal 10 corresponds to the intensity modulation noise amount shown in FIG. 2B and is output to the polarization plane rotator 3. The polarization plane rotator 3 performs polarization plane rotation opposite to the rotation direction of the polarization plane by the liquid crystal cell 4, and the rising edge of the liquid crystal drive signal 11 is applied by applying the compensation electric signal 10 to the polarization plane rotator 3. In addition, the polarization plane rotation opposite to and equal to the polarization plane rotation of the light beam after passing through the liquid crystal cell 4 occurs at the time of falling.

  As described above, in this embodiment, the rotation of the polarization plane (intensity modulation noise) in the liquid crystal cell 4 generated in synchronization with the liquid crystal drive signal 11 is caused to occur by the polarization plane rotator 3 in an opposite phase and an equal amount of polarization plane. It is possible to prevent the occurrence of AC intensity modulation noise that has been offset by the rotation of the signal and superimposed on the output optical signal.

  Other examples of the present invention include the following.

  Although the basic configuration is as described above, the polarization rotator can be disposed behind the liquid crystal cell 4 or can be separately disposed at the positions of the two light beams of abnormal light and normal light. is there.

  In addition, the input side fiber collimator 1, the output side fiber collimator 6, the polarization separator 2, the polarization synthesizer 5, and the polarization plane rotator 3 of the above embodiment may be configured to be integrated in a planar optical waveguide in a hybrid or monolithic manner. .

  In addition, the present invention has been described by taking the liquid crystal cell of TN mode operation as an example, but the liquid crystal drive signal is also applied to the AC modulation noise in the liquid crystal cell driven in the operation mode other than the TN mode operation such as the ECB mode. The compensation signal is synthesized based on the phase difference in the light beam before passing through the liquid crystal cell instead of the rotation angle of the polarization plane (phase difference between two orthogonal polarization components parallel or perpendicular to the optical axis direction of the polarization separator). By controlling, it is possible to compensate for AC modulation noise.

It is explanatory drawing of a structure of one Example of this invention. It is a figure for demonstrating operation | movement of the Example of this invention, (a) is an example of a liquid-crystal drive signal, (b) is an example of AC intensity modulation noise superimposed on the output optical signal of an optical component. (C) is an example of the compensation electric signal applied to the polarization plane rotator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input side fiber collimator 2 Polarization separator 3 Polarization surface rotator 4 Liquid crystal cell 5 Polarization synthesizer 6 Output side fiber collimator 7 Signal waveform calculator 12 AC signal source

Claims (4)

In an AC modulation noise compensation type liquid crystal optical component having a liquid crystal cell that rotates a polarization plane of linearly polarized light that is incident according to a liquid crystal drive signal that is an AC electric signal and controls a transmitted light amount,
A polarization plane rotator that rotates a polarization plane of incident light in a direction opposite to the liquid crystal cell according to a given signal, and emits incident linearly polarized light toward the liquid crystal cell;
The liquid crystal driving signal is input, and a compensation electric signal is generated that causes the polarization plane rotator to generate a rotation amount of a polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and the polarization An AC modulation noise compensation type liquid crystal optical component comprising a signal waveform calculator for supplying to a surface rotator. In an AC modulation noise compensation type liquid crystal optical component having a liquid crystal cell that rotates a polarization plane of linearly polarized light that is incident according to a liquid crystal drive signal that is an AC electric signal and controls a transmitted light amount,
A polarization plane rotator that rotates a polarization plane of incident light in a direction opposite to the liquid crystal cell in response to a given signal with respect to the light emitted from the liquid crystal cell;
The liquid crystal driving signal is input, and a compensation electric signal is generated that causes the polarization plane rotator to generate a rotation amount of a polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and the polarization An AC modulation noise compensation type liquid crystal optical component comprising a signal waveform calculator for supplying to a surface rotator. Light output signal of liquid crystal optical component performed by AC modulation noise compensation type liquid crystal optical component having a liquid crystal cell that controls the amount of transmitted light by rotating the polarization plane of incident linearly polarized light according to the liquid crystal drive signal that is an AC electric signal In the AC modulation noise compensation method of
A polarization plane rotator that rotates the polarization plane of incident light in a direction opposite to the liquid crystal cell according to a given signal and emits the incident linearly polarized light toward the liquid crystal cell,
From the liquid crystal drive signal, generate a compensation electric signal for causing the polarization plane rotator to generate a rotation amount of the polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and rotating the polarization plane A method of compensating for an AC modulation noise of an optical output signal of a liquid crystal optical component. Light output signal of liquid crystal optical component performed by AC modulation noise compensation type liquid crystal optical component having a liquid crystal cell that controls the amount of transmitted light by rotating the polarization plane of incident linearly polarized light according to the liquid crystal drive signal that is an AC electric signal In the AC modulation noise compensation method of
For the light emitted from the liquid crystal cell, a polarization plane rotator is provided that rotates the polarization plane of the incident light in a direction opposite to the liquid crystal cell according to a given signal.
From the liquid crystal drive signal, generate a compensation electric signal for causing the polarization plane rotator to generate a rotation amount of the polarization plane corresponding to intensity modulation noise generated in the liquid crystal cell at the time of rising and falling, and rotating the polarization plane A method of compensating for an AC modulation noise of an optical output signal of a liquid crystal optical component.

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