KR100962773B1 - Variable optical attenuator of liquid crystal - Google Patents

Abstract

The present invention is disclosed for a liquid crystal variable light attenuator. Liquid crystal tunable optical attenuator according to the present invention is an optical fiber formed of silica or a polymer for transmitting light; A waveguide connected to the optical fiber to receive and transmit light; A liquid crystal panel provided at a predetermined portion of the waveguide to transmit light; An optical branching unit for dividing the entire light intensity transmitted through the liquid crystal panel into a predetermined intensity; And a control unit for controlling the liquid crystal panel to detect the intensity of the light transmitted through the light splitter and to adjust the detected light transmission amount.

The liquid crystal variable light attenuator according to the present invention can perform a real-time light attenuation online by constructing a feedback system in a circuit using a liquid crystal cell.

Liquid crystal, optical attenuator, waveguide, optical fiber

Description

Liquid Crystal Variable Light Attenuator {VARIABLE OPTICAL ATTENUATOR OF LIQUID CRYSTAL}

1 is a view schematically showing the configuration of a liquid crystal variable optical attenuator according to the present invention.

2 is a view showing an embodiment of a liquid crystal cell applied to the light modulation portion in the liquid crystal variable light attenuator according to the present invention.

Figure 3 is a view showing an application example using a liquid crystal variable light attenuator produced by the present invention.

<Description of the symbols for the main parts of the drawings>

101 --- Light attenuation part 102 --- Control part

103 --- Fiber 104 --- Waveguide

105 --- Liquid Crystal Panel 106 --- Optical Branch

107 --- collimator 108 --- light receiver

109 --- converter 110 --- detector

111 --- Differential amplifier 112 --- Drive

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal variable attenuator, and more particularly, to a liquid crystal variable attenuator capable of performing optical attenuation online in real time by constructing a feedback system in a circuit using a liquid crystal cell.

With the recent increase in demand and interest in optical communication, expectations and roles for not only the overall system but also each optical communication component constituting it are very important.

At the same time, various researches are being conducted on new optical devices that can secure high-performance, low-cost and high reliability. Due to these influences, interest in polymer optical devices and liquid crystal optical devices, in addition to silica optical devices, has recently increased, and actual commercial products have been introduced.

In general, the optical attenuator serves to attenuate the intensity of the input optical signal, and the variable optical attenuator refers to an optical attenuator that can externally control the attenuation of the optical signal in an electrical or mechanical manner.

Conventional variable optical attenuators include opto-mechanical optical attenuators, optical attenuators using micro electro mechanical systems (MEMS), thermo-optic optical waveguide optical attenuators, and the like.

An opto-mechanical optical attenuator uses two optical fibers to separate two optical fibers at a narrow interval and mechanically move a variable absorption filter or shield between them to absorb or block some of the light, It uses a method of changing the intensity of transmitted light by aligning two optical fibers side by side and adjusting the spacing between the optical fibers.

However, these optical-mechanical optical attenuators have very good characteristics such as optical attenuation range of more than 50 dB, small insertion loss and linearity of 0.1 dB, but the device is large and the operation speed is slow in seconds. There are disadvantages.

The optical attenuator fabricated with microelectromechanical systems (MEMS) shares the excellent operating characteristics of the optical-mechanical optical attenuator, while at the same time operating speed is very fast and small in microseconds. However, it is a disadvantage that it is difficult to integrate with other optical waveguide elements.

Thermo-optic variable attenuators are implemented using the operating characteristics of thermo-optic modulators or thermo-optic switches and can be used in integrated optical circuits. So far, a thermo-optical variable optical attenuator using silica or polymer has been announced, and the optical attenuation can be precisely controlled with millisecond operation speed, polarization independence and power of several hundred mW or less. It shows the function.

In particular, an optical attenuator using an asymmetric Y-branch optical switch has a similar digital operation in which the optical attenuation is continuously reduced according to an external driving signal such as an optical-mechanical optical attenuator or a microelectromechanical system optical attenuator, resulting in saturation. In recent years, active research has been carried out as it has various advantages such as showing digital-likeoperational characteristics, widening the light attenuation range to 30dB or more, and making manufacturing easier by increasing the tolerance in the manufacturing process. have.

The variable optical attenuator using the thermo-optical device according to the prior art includes an optical modulator comprising an asymmetrical Y-shaped branch waveguide and a driving electrode for power application, a main output port and a main output port for transmitting the attenuation output from the optical modulator. It consists of a monitor port that extracts and monitors a part of it, and a dummy drain port that separates part of the input optical power in a curved form from the Y-shaped branch waveguide.

The optical attenuator of the prior art configured as described above is composed of one asymmetrical Y branch and a driving electrode, and according to the mode evolutionary principle, the output intensity decreases according to the applied power, and the output light is fed back to stabilize the output.

However, the thermo-optic variable optical attenuator of the prior art consumes a relatively large amount of power due to the nonlinear change in the optical attenuation with respect to the external applied power. There is a problem that the efficiency is greatly reduced.

An object of the present invention is to provide a liquid crystal variable optical attenuator capable of performing optical attenuation in real time on-line by constructing a feedback system in a circuit using a liquid crystal cell.

In order to achieve the above object, a liquid crystal variable attenuator according to the present invention,

An optical fiber formed of silica or polymer to transmit light;

A waveguide connected to the optical fiber to receive and transmit light;

A liquid crystal panel provided at a predetermined portion of the waveguide to transmit light;                     

An optical branching unit for dividing the entire light intensity transmitted through the liquid crystal panel into a predetermined intensity;

It is characterized in that it comprises a control unit for controlling the liquid crystal panel in order to detect the intensity of the light transmitted from the optical splitter, and to adjust the detected light transmission amount.

Here, in particular, both sides of the liquid crystal panel is characterized in that the collimator is further provided to transmit with parallel light.

Here, in particular, the control unit includes a light receiving unit for receiving the light detected by the optical branch;

A converter for converting the intensity of the received light into a current / voltage;

A detector which detects an error by comparing the voltage difference of the detected light with a standard voltage;

A differential amplifier for giving a differential amplification according to the detected error signal;

Its characteristics are that it includes a drive unit driven according to the differentially amplified voltage compared to the standard voltage.

According to the present invention, it is possible to configure the feedback system in a circuit using the liquid crystal cell to perform optical attenuation online in real time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view schematically showing the configuration of a liquid crystal variable optical attenuator according to the present invention. As shown in the drawing, the liquid crystal variable optical attenuator according to the present invention is largely composed of two regions, the optical attenuator 101 and the controller 102, so that all of them can be organically fed back. network) is connected.                     

First, the light attenuator 101 includes a single mode type waveguide 104 connected to an incident fiber made of silica or a polymer, a liquid crystal panel 105 through which light passes, and an optical branch part ( 106, an optical fiber 103 connected to a waveguide 104.

The control unit 102 includes a light receiving unit 108 for receiving the light detected by the optical branch unit 106; A conversion unit (109) for converting the intensity of the received light into current / voltage; A detection unit (110) for detecting an error by comparing the detected voltage difference with the standard voltage; A differential amplifier (111) for giving a differential amplification according to the detected error signal; Compared with the standard voltage, the driving unit 112 is driven according to the differentially amplified voltage.

The liquid crystal variable optical attenuator according to the present invention configured as described above operates as follows.

First, the light input to the optical fiber 103 on the input side passes through a liquid crystal cell while traveling in a single mode waveguide 104, and in the optical branch 106, 1/10 of the total light intensity. Light corresponding to the branched portion is introduced into the light receiving unit 108.

The current / voltage converter 109 converts the current / voltage value according to the detected light intensity, and then detects the voltage difference of the detected light in comparison with the standard voltage and introduces the detected voltage into the detector 110.

Then, the differential amplifier 111 performs differential amplification according to the detected error value, and the amplified current / voltage signal is transmitted to the driver 112. Here, the driver 112 applies a predetermined voltage to the liquid crystal cell of the liquid crystal panel 105 according to the given signal, and the transmittance of the liquid crystal cell changes according to the applied voltage.

Therefore, at a predetermined voltage, the transmittance is always constant. When the voltage applied to the liquid crystal cell varies according to the intensity of light input, the transmittance is obtained according to the applied voltage.

This cycle is done on-line continuously in real time, giving you complete power control. In this case, when a liquid crystal cell having a gentle I-V curve is used, the response speed is rather lowered, but the accuracy is increased.

This can be adjusted within an appropriate range through an optimized liquid crystal cell design. In particular, when using a PDLC having applicability as a light shutter, it is possible to efficiently attenuate the transmitted light by adjusting the scattering degree of light according to an applied voltage.

In addition, the use of a polymer matrix can have an advantage in refractive index matching with an optical waveguide, and can eliminate the use of a polarizer and an alignment film which are essentially required in a liquid crystal cell. It has excellent advantages in terms of cell process simplification and light utilization efficiency.

FIG. 2 is a diagram illustrating an embodiment of a liquid crystal cell applied to an optical modulation part in a liquid crystal variable optical attenuator according to the present invention. As shown in FIG. 2, when voltage is applied to the liquid crystal panel 105 by the driver 112 of the controller 102, the liquid crystal cell rises along the direction of the electric field and transmits the light passing through the collimator as it is. do. If the voltage is not applied, the arrangement of molecules in the liquid crystal cell becomes irregular, so that light is not transmitted by scattering of light.

Here, the liquid crystal simultaneously has a regular molecular arrangement such as liquidity and solid crystals. In addition, when the voltage is applied while having optical anisotropy, the molecular arrangement of the liquid crystal is changed along the direction of the electric field.

Therefore, by applying a voltage to change the arrangement of the liquid crystal cell in accordance with the direction of the electric field to adjust the transmitted light.

Herein, the liquid crystal cell has an appropriate refractive index (about 1.8) matching between two glass covers or plastic substrates formed with a transparent electrode (ITO) (refractive index of about 2.0). It is formed into a structure in which an anti-reflective coating is formed and a polymer dispersed liquid crystal (refractive index of about 1.55) is injected.

In addition, by considering the refractive index of the material used in the optical waveguide (Optical waveguide), by matching the refractive index of the multilayer film appropriately (minimal optical loss due to internal scattering can be minimized.

In addition, a smooth I-V curve is required in the liquid crystal variable attenuator, which can be adjusted according to an appropriate liquid crystal cell design. The liquid crystal modes that can be used include 90-degree TN, VAN, and PDLC, but PDLC is most applicable and can be optimized according to the appropriate design according to the mode.

In addition, the liquid crystal variable attenuator device according to the present invention is not limited to a single channel shown as an example, and theoretically, N multi-channel arrays are possible, and the electrode design of the liquid crystal cell is improved. Through multiplexing device manufacturing also has the advantage that can be simply produced.

3 is a view showing an application example using a liquid crystal variable light attenuator manufactured by the present invention. As shown therein, the variable optical attenuator has various applications, and is a core device that is used in many system elements that require the introduction of constant light intensity, such as the amplifier end, the front end of the receiver, and the demultiplexer end.

The embodiment of the present invention shows an example applied to the end of the demultiplexer. A variable optical attenuator element is placed at each of the demultiplexer output stages to uniformly adjust the intensity of the light separated for each wavelength, and attenuates individually according to the light intensity of each port. To be input to the receiver.

As described above, the present invention introduces a liquid crystal cell into a variable optical attenuator and configures a feed-back system in a circuit, thereby providing a new type of optical attenuation in real time on-line. It can be said to be an element of.

In addition, by using a liquid crystal cell (cell) there is no reliability problem of long time use, there is an advantage that there is no big problem in the stability of the device. By manufacturing one liquid crystal cell, it is possible to easily manufacture multi-channel devices according to the appropriate electrode pattern design, thereby simplifying the process and securing price competitiveness.

Accordingly, the liquid crystal variable optical attenuator according to the present invention has wide applicability in the field of optical communication such as the front end of a receiver, the end of an optical amplifier, and the end of a demultiplexer.

Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the liquid crystal variable light attenuator according to the present invention may perform a real-time light attenuation online by constructing a feedback system in a circuit using a liquid crystal cell.

Claims (3)

An optical fiber formed of silica or a polymer to transmit light; A waveguide connected to the optical fiber to receive and transmit light; A liquid crystal panel provided in the waveguide to transmit light; An optical branching part which splits a part of the light transmitted through the liquid crystal panel; And A control unit which detects the intensity of light branched from the optical branch and controls the liquid crystal panel to adjust the light transmittance of the liquid crystal panel based on the detected intensity of the light; Liquid crystal tunable optical attenuator comprising a. The method of claim 1, Both sides of the liquid crystal panel further comprises a collimator, the liquid crystal variable light attenuator, characterized in that the transmission through parallel light. The method of claim 1, The control unit includes a light receiving unit for receiving the light detected by the optical branch; A converter for converting the intensity of the received light into a current / voltage; A detector which detects an error by comparing the voltage difference of the detected light with a standard voltage; A differential amplifier for differential amplification according to the detected error signal; And a driving unit driven according to the differentially amplified voltage compared to the standard voltage.

Images