JPH036465B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage measuring device that applies polarization of light, and particularly provides a method of dividing an electro-optic crystal into multiple parts in order to lower the measurement voltage.

An example of the configuration of an optical voltage measuring device is shown in FIG. 1a. In the configuration shown in FIG. 1a, a polarizer 2, an electro-optic crystal 3, a λ/4 wavelength plate 4, and an analyzer 5 are arranged along the traveling direction of light from a light source 1, and a voltage to be measured is applied to the electro-optic crystal 3. It has a measured source 6 that supplies Of these, the polarizer 2 converts the light from the light source 1 into linearly polarized light, and the electro-optic crystal 3 phase modulates the linearly polarized light into elliptically polarized light. That is, the electro-optic crystal 3 has a refractive index of nx, ny (refractive index for linearly polarized light in the X direction and linearly polarized light in the Y direction) when the voltage to be measured is zero volts,
For an applied voltage of V volts, the refractive index is nx-
Changes to kV・nY+kV (k: constant). When linearly polarized light in the _x1 direction is divided into spectral components in the X and Y directions, the refractive index in the become. The analyzer 5 is disposed orthogonal to the polarizer 2 and is used to intensity-modulate the elliptically polarized light.

Now, if the optical power incident on polarizer 2 is Pin, and the loss at the measurement part is l, then the output optical power
The relationship between Pout and the voltage to be measured Vin is as shown in equation (1) when the λ/4 wavelength plate 4 is not provided.

Pout=l·Pin Sin ² (π/2Vin/Vπ) (1) Here, Vπ is a value determined by the crystal and its used orientation, which is called a half-wave voltage. In order to use the region of equation (1) with good linearity, the λ/4 wavelength plate 4 is used to obtain the λ/4 point as shown in Figure 1b.
functions as an optical bias. When the λ/4 wavelength plate 4 is inserted in equation (1), the following equation is obtained.

Pout=l·Pin Sin ² (π/2·Vin/Vπ+π/4) 1/2l·Pin [1+Sin (πVin/Vπ)] In the region of πVin/Vπ<<1, equation (2) is obtained.

Pout≒1/2l・Pin [1+πVin/Vπ] ...(2) The relationship of equation (2) is shown in FIG. The optical signal output from the analyzer is converted into an electrical signal using an element such as a PIN photodiode.

Voltage measurement is performed based on the principle described above, and in this case, the electro-optic crystal 3 is KDP,
ADP LiNbC ₃ , LiTaO ₃ , Bi ₁₂ SiO ₂₀ , Bi ₁₂ GeO ₂₀
etc. are available. And it has no natural birefringence, no polarization processing or unnecessary. Bi ₁₂ SiO ₂₀ (bismuth silicon oxide) and Bi ₁₂ GeO ₂₀ (bismuth germanium oxide) are most suitable because of their poor hygroscopicity and good temperature stability. An example is shown in FIG.

Figure 3a shows a single crystal plate of Bi ₁₂ SiO ₂₀ with a thickness of 3 mm.
This shows the characteristics of input voltage versus output voltage when a conventional optical voltage measuring device is constructed using
Shows good linearity from 5V to 80V, measurement range is 5V
~80V.

However, the lowest measurable voltage (output sensitivity) of this voltage measuring device is about 1 to 5V. This is because the half-wave voltage of an electro-optic crystal plate generally used in an optical voltage measuring device is as high as several thousand volts.
On the other hand, in order to solve the problem of not being able to measure low voltages, it is possible to improve the measurement sensitivity by stacking a large number of electro-optic crystals, but simply increasing the number of electro-optic crystals will not cause absorption or reflection. There are disadvantages such as an increase in light loss due to the spread of the luminous flux and an increase in the size of the structure, so it is necessary to make each electro-optic crystal plate thin and stack it. However, if thin electro-optic crystal plates are placed as close as possible, the electrodes and lead wires of each crystal plate will be close together in a narrow space, which may cause creeping discharge or shoot out when a high voltage is applied. Due to different problems caused by this, it was only possible to measure the low input voltage region as shown in FIG. 3b.

The present invention provides an optical voltage measuring instrument that is free from such drawbacks and can stably measure a wide voltage range from low voltages to high voltages.

The present invention will be explained in detail below based on the drawings. FIG. 4 shows one specific example of the present invention. In FIG. 4, transparent electrodes 7, 7' (for example,
After forming In ₂ O ₃ ), the leads 8 and 8' are bonded with conductive paste. After that, the entire structure is covered with a transparent resin 9. Electro-optical element 1 manufactured in this way
In order to closely stack the resin 9, it is necessary to form the resin 9 as thin as possible and have a uniform thickness.
Methods for forming such thin resin films include the dipping method, the spin coating method using a spinner, and the vapor deposition method, but the dipping method and the rotary method have the drawbacks of producing in-plane film thickness distribution and damaging the thin crystal plate. There is.

However, polyparaxylylene formed by vapor deposition is produced by evaporating the raw material diparaxylylene.
This is a method in which the monomer is thermally decomposed and then deposited on a substrate at room temperature.A uniform film with a thickness of 1 to several tens of micrometers can be formed, and no external force is applied to the substrate, so the electro-optical element of the present invention can be manufactured. This is the most suitable way to do so. Furthermore, polyparaxylylene has high insulation resistance (10 ¹⁶ - 10 ¹⁷ Ωcm), high breakdown voltage (800V/μm - 2kV/10μm), and extremely low moisture permeability (~1g/(mi1) (100in). ² )
(24 hours)), it is most suitable for reducing leakage current between adjacent electrodes and leads in a narrow space, and for preventing creeping discharge and shot, as in the present invention.

The element 10 thus manufactured is assembled as an optical voltage measuring device as shown in FIG. In FIG. 5, reference numeral 11 indicates light emitting elements 12 and 12', and optical fibers 13 and 13' indicate rod lenses that convert light into parallel beams.

Here, the polarity of the leads is wired so that adjacent surfaces of each element have the same polarity. Even with such polarity, if the optical axes (fast axis and slow axis) of the crystal plates are arranged alternately and oppositely, sensitivity can be improved in proportion to the number of laminated plates.

FIGS. 6a and 6b show other specific examples. A large number of electro-optic crystals 3 with transparent electrodes 7, 7' formed on both sides are made of a conductive and adhesive paste 14 (for example, a paste of Ag, Au, Pt, etc.).
Then, each of them is adhered to metal supports 15 and 15' so that they are in close contact with each other as shown in Fig. a. Figure b is a view of this from above. Here, grooves may be cut in the support in order to keep the distance between each crystal plate constant. Leads 8, 8' for voltage application are taken out from supports 15, 15'. In Fig. 6, the gap between each crystal plate is drawn large, but in reality it is a narrow gap of less than 100 μm.

Next, if the whole is placed in a vacuum chamber and coated with polyparaxylylene, all gaps and conductive parts will be completely covered, so if this is used in the optical system shown in Fig. 5, It is possible to obtain exactly the same effect as in the specific example shown in . Note that FIGS. 4 to 6 are some specific examples, and the invention is not limited to these drawings; the point is that electro-optic crystal plates having transparent electrodes and coated with an insulating resin are laminated. In particular, the invention lies in the use of polyparaxylene.

Examples of the invention using Bi ₁₂ SiO ₂₀ will be described below. Note that a similar effect was obtained with Bi ₁₂ GeO ₂₀ .

Bi ₁₂ SiO ₂₀ single crystal with a thickness of 200 μm and an area of 5 × 5 mm ²
Both sides were optically polished and transparent electrodes of In ₂ O ₂ were formed on both sides. Divide this into three groups and lead (Al) as shown in Figure 4.
Voltage measuring device A, which is made by laminating 10 elements coated with polyparaxylylene to a thickness of 10 μm after attaching the foil). After gluing the 10 elements to a Cu support with Ag paste, the whole is coated with polyparaxylylene to a thickness of 10 μm. A voltage measuring device B using an element coated with polyparaxylylene and a voltage measuring device C comprising 10 elements not coated with polyparaxylylene were laminated via an epoxy spacer with a thickness of about 300 μm.

The sensitivity of all A, B, and C measuring instruments is 1 compared to the conventional one.
It became possible to measure up to 100-500mV for ~5V. The maximum measured voltage was 500 V with measuring instruments A and B due to the improved insulation properties due to the polyparaxylylene coating. Furthermore, the optical path length occupied by BSO could be kept to about 3 mm. Furthermore, it was confirmed that the input resistance was 10 ¹⁰ Ω or more relative to DC, and that it operated effectively as a measuring instrument that did not disturb the signal source.

On the other hand, in the case of conventional C measuring instruments in which polyparaxylylene is not coated, the total length is more than 6 mm and the loss due to the spread of transmitted light is A. , B increased about 5 times. On the other hand, if the spacer was made of Mylar with a thickness of about 50 μm, the loss would be reduced, but since the transparent electrode and lead parts were not completely insulated, the voltage that could be stably measured was at most about 100 V. Another drawback was that when humidity was high, leakage current increased and the input resistance decreased to about 10 ⁸ Ω.

As described above, the optical voltage measuring device according to the present invention uses polyparaxylylene as a method of laminating a large number of electro-optic crystals, thereby suppressing optical loss without increasing the overall length and achieving high input impedance. This enables stable measurements from low to high voltages.

[Brief explanation of the drawing]

Figures 1a and 1b are diagrams of the principle of an optical voltage measuring device, with Figure 1a showing the configuration and Figure 1b showing the characteristics.
Fig. 2 is a diagram of the optical output Pout with respect to the voltage input Vin which changes over time, and Figs. 4 shows a configuration example of an electro-optic effect element according to the present invention, FIG. 5 shows a configuration example of a voltage measuring device according to the present invention, and FIG. 6 shows an example of the configuration of an electro-optic effect element according to the present invention. FIG. 6a shows a side view and FIG. 6b shows a plan view of another example of the structure of the effect element. 1... Light from a light source, 2... Polarizer, 3... Crystal plate, 4... Wave plate, 5... Analyzer, 6... Power supply, 7, 7'... Transparent electrode, 8, 8' ...Reed,
9...Transparent insulating film, 10...Electro-optical element, 11
...Light source, 12,12'...Optical fiber, 13,
13'... Rod lens, 14... Conductive adhesive,
15,15'...metallic support.

Claims (1)

[Scope of Claims] 1. A polarizer, a laminated electro-optic crystal plate, a wavelength plate, and an analyzer arranged along the traveling direction of light, each of which has a transparent electrode, and An optical voltage measuring device characterized by being coated with polyparaxylylene. 2. The optical voltage measuring device according to claim 1, wherein the electro-optic crystal plate is made of bismuth silicon oxide (Bi ₁₂ SiO ₂₀ ) or bismuth germanium oxide (Bi ₁₂ GeO ₂₀ ).