JPH01163677A - Signal addition system by optical element - Google Patents

Abstract

PURPOSE:To compensate a variation component due to the temperature of a polarization plane maintaining fiber for two light beams by detouring light for temperature compensation by an electrooptic effect element, entering light for signal addition into the electrooptic effect element, and converting those two light beams photoelectrically. CONSTITUTION:The circular polarized light lambda1 for signal addition and light lambda2 for temperature compensation are branched into two directions by a beam splitter 3 to guide the light lambda1 to a filter 4, a Pockels effect element 1a, and a beam splitter 5 and the light lambda2 to a filter 5, reflecting plates 7 and 8, and the splitter 5. Then the splitter 5 multiplexes the elliptic polarized light of the light lambda1 and light lambda2 and the composite wave is inputted to a reception part 9 through a B-phase addition part and a C-phase addition part and converted photoelectrically. The phase difference between the component of the light lambda1 and the component of the light lambda2 is detected according to the converted signal and only phase-modulated components which are added by the respective addition part are detected with high accuracy according to the phase difference.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a signal addition method using an optical element, and more specifically, an electro-optic effect element that changes the phase of transmitted light according to the amount of electricity measured. are placed at multiple measurement points,
The present invention relates to a signal addition method for transmitting the above-mentioned phase change through a polarization-maintaining fiber to obtain a vector sum of measured electrical quantities.

<Conventional technology> Conventionally, transformers and capacitors were mainly used to extract signals from wiring. These devices have problems with insulation, which is a serious problem in the power transmission and distribution sector, which handles high voltage and large amounts of power.

Furthermore, the zero-phase component is used when detecting ground faults, disconnections, etc. in power transmission and distribution systems. To measure this zero-phase component, each phase component is extracted by electromagnetic induction between the power transmission and distribution line and the transformer, or by the connection between the power transmission and distribution line and the capacitor, and the following formula [
However, the zero-sequence component is only about 0.01% of the rated value, and the output level is very low. There are also variations. Further, since the transformer is large and heavy, it has the disadvantage that it is difficult to install it on a pole. Since capacitors are connected to power transmission and distribution lines, problems arise due to increased capacitance of the system and insulation of the capacitors.

Therefore, a signal addition method using optical elements is attracting attention as a means of measuring each phase component separately from the power transmission and distribution lines.

Conventionally, the signal addition method using optical elements consists of a polarization-maintaining fiber (10) that guides incident light (specifically, circularly polarized light) and the polarization-maintaining fiber (10), as shown in FIG.
0) are connected in series by A, B.

A Pockels effect element (2
0) and a receiving section (30).

The operation of the above signal addition method is as follows.

Circularly polarized light (Pl) is guided to a polarization maintaining fiber (10) and input to a first Pockels effect element 20).

And in the first Pockels effect element (20),
A phase difference corresponding to the voltage Va of the A-phase transmission and distribution line is added to the circularly polarized light to generate elliptically polarized light (Pa), which is then transferred to a polarization-maintaining fiber (
10). Next, the second Pockels effect element (
20), the elliptically polarized light (P
A phase difference is added to a) to generate elliptically polarized light (pb), which is input to the polarization maintaining fiber (10).

Next, in the third Pockels effect element (20),
A phase difference is further added to the modulated signal from the first Pockels effect element (20) according to the voltage Vc of the C-phase transmission and distribution line to generate elliptically polarized light (Pc), which is then transmitted to the polarization-maintaining fiber (10). incident.

Then, the elliptically polarized light (Pc) from the polarization preserving fiber (10) is photoelectrically converted by a photodiode.

By inputting this converted signal to an amplifier or the like, the zero-sequence voltage V shown in equation (I) above is obtained. The zero-sequence voltage corresponding to is extracted.

<Problems to be Solved by the Invention> However, the phase angle of the polarization preserving fiber (10) varies greatly depending on the temperature. Specifically, a 1 m long polarization maintaining fiber (10) fluctuates by π (radians) per 1°C. Due to this fluctuation component, there is a problem that the addition result from each Pockels effect element (20), that is, the zero-sequence voltage in the above example cannot be detected with high accuracy.

Therefore, in order to compensate for this fluctuation component, in the conventional signal addition method, the ambient temperature of the polarization preserving fiber (10) is kept constant, or after photoelectric conversion, a differential amplifier is used to compensate for the polarization preserving fiber (10). ), but there are problems such as drift errors in the differential amplifier, and optical signals are on the order of several thousand angstroms, so it is easy to cancel errors that occur during optical transmission. It is impossible to prevent this with electric circuits alone.

Purpose of the Invention The present invention was made in view of the above problems, and provides an optical system that compensates for the temperature fluctuation component caused by the polarization preserving fiber with high precision and enables the addition result of measured voltages to be detected with high precision. The purpose of this invention is to provide a signal addition method using elements.

Means and operation for solving the above problems> In order to achieve the above object, the signal addition method using an optical element of the present invention is capable of maintaining two lights of different wavelengths for signal addition and temperature compensation in the same plane of polarization. The light for signal addition and temperature compensation is transmitted through a fiber, and the light for signal addition and temperature compensation is split at the entrance of the electro-optic effect element. The light for signal addition and the light for temperature compensation are photoelectrically converted by detouring from the element, and the phase difference between the two lights is detected based on this converted value.
Based on this phase difference, the error due to the temperature characteristics of the polarization preserving fiber is compensated for and the phase change added by the electro-optical element is detected.

More specifically, electro-optic effect elements that change the phase of transmitted light according to the amount of electricity to be measured are placed at multiple measurement points, and the phase change is transmitted through a polarization preserving fiber to change the amount of electricity to be measured. When calculating the vector sum,
Two lights of different wavelengths for signal addition and compensation are guided from the same polarization maintaining fiber to the entrance of the electro-optic effect element, and the signal addition light is made incident on the electro-optic element. On the other hand, the compensation light is made to bypass the electro-optic effect element.

In other words, since the light for signal addition passes through the polarization-preserving fiber and the electro-optic effect element, a phase difference is added by the electro-optic effect element, and the phase changes gradually due to the influence of the ambient temperature of the polarization-preserving fiber. do.

Since the compensation light only passes through the polarization maintaining fiber, the phase of the compensation light changes gradually due to the influence of the ambient temperature.

Then, by photoelectrically converting the two lights, for example, and detecting the phase difference between the two lights, that is, the fluctuation component (phase difference) based on the influence of the temperature of the polarization preserving fiber, It is possible to compensate for errors due to the temperature characteristics of the polarization preserving fiber.

Therefore, it is possible to compensate for fluctuations based on the temperature characteristics of the polarization-maintaining fiber, and it is possible to perform phase difference modulation with high precision on the light for signal addition.

<Example> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.

FIG. 1 shows a signal addition system using optical elements as an embodiment of the present invention, in which Pockels effect elements (1a) (1, b) (18
), and the signal adders of each phase are connected by a polarization preserving fiber (2). The signal adders for each phase have the same configuration, and the A phase will be explained.

The A-phase signal addition section includes a polarization-maintaining fiber (2) that guides two lights consisting of signal addition light (wavelength λ1) and temperature compensation light (wavelength λ2), and a polarization-maintaining fiber (
The first beam splitter (3) splits the two lights from 2) into two directions, and of the two lights from the first beam splitter (3), only the light for signal addition (λ1) is transmitted. A first filter (4), a Pockels effect element (1a) that applies a phase change to the transmitted light from the first filter (4) according to the phase voltage Va, and generates elliptically polarized light; and an ellipse from the Pockels effect element (1a). Of the two lights from the second beam splitter (5) that splits polarized light into two directions and the first beam splitter (3), the light for temperature compensation (λ2)
a second filter (6) that only transmits the temperature compensation light (λ2); a reflection plate (7) that reflects the temperature compensation light (λ2) from the second filter (6); λ2
) to the second beam splitter (5), and a receiving section (9) that receives the composite wave after passing through the B and C phases.

To explain in more detail, the Pockels effect element (l
a), (lb), and (lc) are first-order electro-optic effect elements, which apply an electric field to circularly polarized light (λ1) for signal addition to elliptically polarize it. Then, the effects of electric fields corresponding to the voltages Va, Vb, and Vc of the A, B, and C phases are applied, and a phase difference is sequentially added to the signal addition light (λ1).

The polarization-maintaining fiber (2) is a single-mode fiber in which polarization is preserved from the input end to the output end, and the Pockels effect element (1a) receives circularly polarized light (
λ1), and each Pockels effect element (L
The elliptically polarized light modulated by a), (lb), and (lc) is input to the Pockels effect element of the next phase or the receiving section (9) while preserving the plane of polarization.

The first beam splitter (3) splits two lights from the polarization maintaining fiber (2) into two directions.

Note that it is also possible to use a half mirror instead of the beam splitter.

The first filter (4) transmits only the signal addition light (λ1) of the two lights from the first beam splitter, and the second filter (6) transmits the two lights from the first beam splitter. Among the lights, only the temperature compensation light (λ2) is transmitted.

The reflector (7) uses a mirror and reflects the temperature compensation light (λ2) from the second filter (6) in the direction of the reflector (8). 8) transfers the temperature compensation light (λ2) from the reflector (7) to the second beam splitter (5).
).

The second beam splitter (5) is similar to the first beam splitter (3), and transmits the elliptically polarized light (λ1) for signal addition from the Pockels effect element (1a), and also reflects it. Temperature compensation light from plate (8) (
λ2) is reflected and guided to the polarization maintaining fiber (2).

The receiving section (9) includes a photodetector (91) that photoelectrically converts the transmitted light from the A-phase, B-phase, and C-phase signal addition sections, and a photodetector (91) that converts the signals from the photodetector (91) into light for signal addition ( A filter (92) separates the temperature compensation light (λ1) component and the temperature compensation light (λ2) component, and the Pockels effect element (l
a) An adder circuit (93) that detects only phase change components due to (lb) and (lc).

The operation of the signal addition method using the optical element having the above configuration is as follows.

= 11− circularly polarized light for signal addition (λ1) and light for temperature compensation (λ
2) is guided to the first beam splitter (3) through the polarization maintaining fiber (2), and the first beam splitter (
3), the light is split into two directions, and on one side, only the signal addition light (λ1) is transmitted through the first filter (4).
A phase difference corresponding to the phase voltage *a of the A phase is added by the Pockels effect element (1a), and the second beam splitter (
5). The light split by the first beam splitter (3) passes through the second filter (6), where only the temperature compensation light (λ2) is transmitted, and the light is passed through the two reflectors (7).
(8) leads to the second beam splitter (5). Then, the signal addition light (λ1) and the temperature compensation light (λ2) are combined in the second beam splitter (5) and are input into the polarization maintaining fiber (2).

Next, the composite wave from the polarization preserving fiber (2) is guided to the B-phase signal addition section, and a phase change corresponding to the B-phase voltage vb is added by the Pockels effect element (1b).
Furthermore, a phase change corresponding to the phase voltage Vc of the C phase is added in the C phase adder.

Next, in the receiving section (9), a photodetector (9
1) photoelectrically converts the transmitted light from the A-phase, B-phase, and C-phase signal addition sections, and converts the signal from the photodetector (91) into a light (λ1) component for signal addition using a filter (92). , and the temperature-compensating light (λ2) component, and the adder circuit (93) reverses the phase difference of the separated signals and adds them, thereby reducing the gradual polarization-preserving fiber (2) due to temperature changes. The influence of phase fluctuations is removed, and only the phase change component due to the Pockels effect element (la) (lb) (IC) is detected.

To summarize the above, circularly polarized light (λ1) for signal addition and light (λ2) for temperature compensation are sent to the first beam splitter (3).
The light for signal addition (λ1) is split into two directions at the first filter (4) → Pockels effect element (1a) → second beam splitter (5).
The light split by the beam splitter (3) is guided through the second filter (6) -> the reflection plate (7) -> the reflection plate (8) -> the second beam splitter (5). Then, in the second beam splitter (5), the elliptically polarized light of the signal addition light (λ1) and the temperature compensation light (λ2) are combined 13 - into a B-phase adder - a C-phase adder - The synthesized wave is incident on the receiving section (9), where the synthesized wave is photoelectrically converted, and further, based on the converted signal, the components of the light (λ1) for signal addition and the light (λ2) for temperature compensation are converted. Since the phase difference with the component can be detected, only the phase modulation component added in each adder can be detected with high precision based on this phase difference.

or more zero-sequence voltage*. As explained above, the same applies to zero-sequence current. It is also applicable to magnetic fields and other quantities of electricity, in which case electro-optical elements such as Faraday rotators are used.

<Effects of the Invention> As described above, according to the signal addition method using the optical element of the present invention, the combined wave of signal addition light and temperature compensation light from the polarization preserving fiber is branched, and The light is incident on the electro-optic effect element, and the temperature-compensating light is bypassed through the electro-optic effect element, and the two lights are photoelectrically converted. By doing so, the fluctuation component of the two lights due to the temperature of the polarization-maintaining fiber is reduced. By compensating for this fluctuation component, the phase modulation component added by the electro-optic effect element can be detected with high precision, which is a unique effect.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an apparatus for implementing a signal addition method using an electro-optical element as an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a signal addition method using a conventional electro-optical element. (la), (lb), (lc) --- Pockels effect element, (2) --- polarization preserving fiber, (3) --- first beam splitter-1 (4) --- first filter , (5)...Second beam splitter-1 (6)...Second filter, (7) (8)...Reflection plate

Claims (1)

[Claims] 1. Change in phase of transmitted light according to the amount of electricity measured We conducted multiple measurements of electro-optic effect elements that give Placed at a fixed point, the above phase change is maintained at a polarization plane. The amount of electricity is measured by transmitting it through existing fibers. The signal addition method that calculates the vector sum of waveforms for signal addition and temperature compensation. Preserves the same polarization plane for two lights with different lengths Transmitted by fiber, electro-optic effect For signal addition and Branch the light for temperature compensation and add the light for signal addition. When light enters the electro-optic effect element, The light for temperature compensation is converted into an electro-optic effect element. light and temperature compensation for signal addition. Photoelectrically convert the compensation light and convert it into this converted value. The phase difference between the two lights is detected based on the Temperature of polarization preserving fiber based on difference Electro-optical element by compensating for errors due to characteristics It is possible to detect the phase change added by Signal addition using an optical element characterized by method.