JPH0720159A - Photoelectric field sensor - Google Patents

Abstract

PURPOSE:To enhance the measurement accuracy of a photoelectric field sensor by making the base, to which optical components are secured, of such material as having the linear expansion coefficient substantially equal to that of the optical components, thereby retarding generation of stress in the optical components even upon vibration of the sensor or the ambient temperature variation. CONSTITUTION:A polarizer 4, a quarter wavelength plate 5, an electrooptical crystal 6, and an analyzer 7 are bonded through a silicon based adhesive 16 onto a base 15 made of BK 7 glass. The quarter wavelength plate 5 has main aligned with that of the crystal 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical electric field sensor using an electro-optic crystal.

[0002]

2. Description of the Related Art An optical electric field sensor which measures an electric field by utilizing the electro-optic effect (Pockels effect) of an electro-optic crystal has a high electrical insulation property because it uses an optical fiber for signal transmission. Since it is possible to configure a measurement system that is less susceptible to noise, it has been receiving attention in recent years.

FIG. 5 is a block diagram showing a conventional optical electric field sensor using an electro-optic crystal, and FIG. 6 shows the directions of the principal axes of the optical components used in FIG. In FIG. 5, 1
Is a light source including a light emitting diode, 2 is a light transmitting fiber for transmitting the light from the light source 1, 3 is a light transmitting lens for making the light emitted from the light transmitting fiber 2 into a substantially parallel beam, and 4 is a light transmitting lens. A polarizer 5 for converting the light emitted from the optical lens 3 into a linearly polarized wave E _o gives a phase difference π / 2 to the linearly polarized wave E _o 1
/ 4 wavelength plate, 6 analyzer electro-optic crystal to give the light passing through the phase difference Γ proportional to the measured electric field (Pockels element) 7 for detecting light E _x of the electric field vector of the principal axis direction, the 8 A light receiving fiber for condensing the light detected by the analyzer 7 on the light receiving fiber 9, 10 is a photoelectric converter including a photodiode for converting the light transmitted by the light receiving fiber into an electric signal, and 11 is an electric An amplifier for amplifying a signal to obtain an electric signal I _x , 12 is a _low- pass filter for obtaining a DC signal I _xd from the electric signal I _x , 13 is an AC signal subtracting the DC signal I _xd from the electric signal I _{x Numeral} 14 is a subtracter for obtaining I _xa , and 14 is a divider for dividing the AC signal I _xa by the DC signal I _xd to obtain the output signal I.

The principal axes of the respective optical components in FIG. 6 are such that the polarizer 4 is vertical, the quarter-wave plate 5 and the electro-optic crystal 6 are inclined 45 ° from the horizontal, and the analyzer is arranged horizontally. Here, the electric field vector of the light passing through the polarizer 4 is E
_o and the electric field vector in the principal axis direction of the quarter-wave plate 5 is E
_Assuming that _ox and E _oy are 1/4 wave plate 5 and electro-optic crystal 6,
The electric field vectors E _ox and E _oy of the light passing through are (Γ + π /
The phase difference of 2) occurs. Next, the operation of the optical electric field sensor shown in FIGS. 5 and 6 will be described. The electric field vector E _x of the light detected by the analyzer 7 is

[0005]

[Equation 1] Electrical signals I _x according to the electric field vector E _x is

[0006]

[Expression 2] I _x = | E _x | ² = | E _o | ² (1 + sin Γ) / 2 (2) Expression (2) DC signal I _{xd of the} low-pass filter 12 based on the electric signal I _x
Is

[0007]

Equation 3] ^{_{I xd = | E o | 2}} /2 ... (3) an expression, an AC signal I _xa is the output of the subtracter 13,

[0008]

## EQU4 ## Since I _xa = I _x −I _xd = | E _o | ² (sin Γ) / 2 (4), the output signal I from the divider 14 is

[0009]

[Equation 5] Becomes Here, the phase difference Γ proportional to the measured electric field is sufficiently small.

[0010]

[Equation 6] An output signal I proportional to the electric field to be measured can be obtained in a range where the above can be approximated.

Such a conventional optical electric field sensor has a vibration and
When the temperature changes, stress is generated in optical components such as the polarizer 4, the quarter-wave plate 5, the electro-optic crystal 6, and the analyzer 7. This stress has a problem that the output signal of the sensor changes because it affects the photoelastic effect.

For example, in the quarter wave plate 5, when a phase difference K occurs in the azimuth of the principal axis due to the elastic effect of stress, 1
A phase difference of (Γ + π / 2 + K) occurs in the electric field vectors E _ox and E _oy of the light that has passed through the / 4 wavelength plate 5 and the electro-optic crystal 6. Therefore, the electric signal I _x ′ due to the electric field vector E _x ′ of the light detected by the analyzer 7 is

[0013]

[Expression 7] I _x ′ = | E _x ′ | ² = | E _o | ² {1 + sin (Γ + K)} / 2 (7) Since the output signal I ′ at the divider 14 is

[0014]

## EQU8 ## I '= sin (Γ + K) (8) Therefore, the output signal I ′ obtained by the equation (8) is different from the output signal I obtained by the equation (5).

[0015]

[Equation 9] A ratio error change represented by In FIG. 7, the phase difference K '
Shows the ratio error change Δε due to [deg]. As can be seen from FIG. 7, the conventional optical electric field sensor has a problem that it is difficult to improve the measurement accuracy because the ratio error greatly changes with a slight phase difference change K ′.

[0016]

As described above, in the conventional optical electric field sensor, when stress occurs in the optical component due to vibration or temperature change, the sensor output changes due to the stress, and the measurement accuracy is improved. There was a problem that it was difficult. Therefore, an object of the present invention is to provide an optical electric field sensor in which the measurement accuracy is less likely to decrease even when subjected to vibration or temperature change.

[0017]

In order to achieve the above object, in the present invention, a polarizer, a quarter-wave plate, an electro-optic crystal and an analyzer are arranged in a substantially straight line with respect to the traveling direction of light. Then, in the optical electric field sensor for measuring the electric field by utilizing the electro-optical effect of the light transmitted through these optical components, the quarter wavelength plate and the optical crystal are arranged so that their principal axes substantially coincide with each other, and There is provided an optical electric field sensor characterized in that an optical component is fixed to a pedestal having a linear expansion coefficient substantially equal to that of the optical component with an elastic adhesive. In addition,
The pedestal is preferably made of glass, titanium, or ceramic, and the elastic adhesive is preferably a silicon-based adhesive.

[0018]

Since the optical components such as the polarizer, the quarter-wave plate, the electro-optic crystal and the analyzer are fixed to the pedestal, it is possible to prevent the relative positions of the optical components from being displaced due to vibration. The pedestal is made of a material having a coefficient of linear expansion almost equal to that of the optical component, and the optical component is fixed to the pedestal by an elastic adhesive. Therefore, the degree of expansion and contraction of the optical component and the pedestal due to the temperature change are substantially equal, and the stress generated in the optical component can be greatly reduced. Further, the quarter-wave plate and the electro-optic crystal are arranged so that their principal axes substantially coincide with each other. Therefore, even if the optical component fixed to the pedestal via the elastic adhesive rotates around the optical axis due to a change in the ambient temperature, the influence on the sensor output is negligible.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. It should be noted that the same parts as the conventional ones are given the same numbers and the description thereof is omitted. As shown in FIG. 1, the polarizer 4, the quarter-wave plate 5, the electro-optic crystal 6, and the analyzer 7 are arranged on a pedestal 15 in a substantially straight line with respect to the traveling direction of light emitted from a light source (not shown). Placed on the silicone adhesive 16
It is fixed to the pedestal 15 by. The quarter-wave plate 5 and the electro-optic crystal 6 are arranged so that their optical axes coincide with each other.

In the traveling direction of the light passing through the analyzer 7, FIG.
As shown in FIG.
Is connected to a photoelectric converter 10 by a light receiving fiber 9, and the photoelectric converter 10 is connected to an amplifier 11. The amplifier 11 is connected to the low-pass filter 12, the output of the low-pass filter 11 is transmitted to the subtractor 13 and the divider 14, and the output of the subtractor 13 is transmitted to the divider 14. Is configured.

The adhesive 16 is an elastic adhesive and has a size of several tens of μm.
It is applied to a thickness of 100 μm. The silicon-based adhesive that constitutes the adhesive 16 has excellent heat resistance and long-term reliability.
On the other hand, the pedestal 15 is made of a material whose coefficient of linear expansion is almost the same as that of the optical component. BK7 glass is generally used as a material for the polarizer 4, the quarter-wave plate 5 and the analyzer 7, and the linear expansion coefficient of the BK7 glass is 7.2 × 10 ^-6 /
℃. The coefficient of linear expansion of the electro-optic crystal 6 such as Bi ₁₂ GeO ₂₀ is 10 × 10 ^-6 / ° C. Therefore,
As the material of the pedestal 15, titanium (linear expansion coefficient 8.4 × 10 ⁻⁶ / ° C.) or ceramic (linear expansion coefficient 8) having the same BK7 glass as the optical component or a linear expansion coefficient close to BK7 glass is used.
˜9 × 10 ⁻⁶ / ° C.) is used.

Next, the operation of this embodiment will be described. Optical components such as the polarizer 4, the quarter-wave plate 5, the electro-optic crystal 6, and the analyzer 7 are fixed to the pedestal 15 with an adhesive 16.
Therefore, even if the optical electric field sensor is subjected to vibration, the adhesive 16 acts as a cushion and reduces the occurrence of stress on the optical component due to the vibration.

Further, since the optical components and the pedestal 15 have almost the same linear expansion coefficient, even if the optical electric field sensor receives a temperature change, the expansion and contraction of the optical components and the pedestal 15 are similar, so that the stress generated in the optical components is large. Is reduced to.

In the embodiment, by increasing the thickness of the adhesive 16 between the optical component and the pedestal 15, the optical component may rotate, but the change in the ratio error caused by this may be sufficiently ignored. It is a level.

For example, as shown in FIG. 2, it is assumed that the polarizer 4 rotates by θ degrees with time. At this time, the electric signal I _x ″ by the electric field vector E _x ″ of the light detected by the analyzer 7 is

[0026]

[Number 10] _{I x "= | E x"} | 2 = | E o | from ^{2 · (1+ cos2θ · sinΓ)} / 2 ... (10) be a formula, the output signal I at the divider 14 "

[0027]

[Equation 11] I ″ = cos2θ · sin Γ Equation (11) is obtained. Therefore, the output signal I ″ obtained by the equation (11) is obtained from the output signal I obtained by the equation (5).

[0028]

[Equation 12] A ratio error change represented by

FIG. 3 shows changes in the ratio error depending on the rotation angle θ '[degree]. As shown in FIG. 3, even if the rotation angle θ ′ [degree] is slightly increased, the change in the ratio error is small enough to be negligible for the optical electric field sensor whose measurement accuracy is 1% to 3%.

As described above, according to the present embodiment, even if the optical voltage sensor is vibrated or the ambient temperature changes, the optical component is fixed to the pedestal having substantially the same linear expansion coefficient by the silicon adhesive. Therefore, the stress generated in the optical component can be significantly reduced, and the phase difference of light caused by vibration or temperature change is not generated, and the change in the ratio error can be reduced to a negligible value. Therefore, there is an effect that the measurement accuracy of the optical voltage sensor is improved.

The present embodiment is not limited to the above-mentioned configuration, and the arrangement order of the optical components is as shown in FIG. 4, in which the polarizer 4, the electro-optic crystal 6, the quarter-wave plate 5, the analyzer are arranged. Even if changed to 7, the same effect can be obtained.

[0032]

As described above, according to the present invention, the quarter-wave plate and the electro-optic crystal are arranged so that their principal axes are substantially coincident with each other, and elastically bonded to the pedestal having a linear expansion coefficient substantially equal to that of the optical component. Since the optical component is fixed with the agent, it is possible to provide an optical electric field sensor that is not easily affected by vibration and temperature change and has improved measurement accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an optical electric field sensor showing an embodiment of the present invention.

FIG. 2 is a vertical sectional view of the optical electric field sensor shown in FIG.

FIG. 3 is a relationship diagram between a rotation angle of an optical component and a change in ratio error.

FIG. 4 is a configuration diagram of a main part of an optical electric field sensor showing another embodiment of the present invention.

FIG. 5 is a block diagram of an optical electric field sensor.

FIG. 6 is a configuration diagram of a main part of a conventional optical electric field sensor.

FIG. 7 is a diagram showing the relationship between phase difference and change in ratio error.

[Explanation of symbols]

4 ... Polarizer, 5 ... Quarter wave plate, 6 ... Electro-optic crystal, 7
… Analyzer, 15… Pedestal, 16… Adhesive

Claims (3)

[Claims] 1. A polarizer, a quarter-wave plate, an electro-optic crystal, and an analyzer are arranged substantially in a straight line with respect to the traveling direction of light, and the electro-optic effect of light transmitted through these optical parts is utilized. In the optical electric field sensor for measuring an electric field, the ¼ wavelength plate and the optical crystal are arranged so that their principal axes substantially coincide with each other, and the optical component has a linear expansion coefficient substantially equal to that of the optical component. An optical electric field sensor, wherein the optical electric field sensor is fixed by an elastic adhesive. 2. The optical electric field sensor according to claim 1, wherein the pedestal is made of glass, titanium, or ceramics. 3. The optical electric field sensor according to claim 1, wherein the elastic adhesive is a silicon-based adhesive.