JPH0221273A - Optical apparatus - Google Patents

Abstract

PURPOSE:To achieve a lowering of measuring errors by absorbing a change in pressure within a closed container housing a measuring part. CONSTITUTION:A closed container 10 housing a sensor head as measuring part made up of optical parts 3-6 is provided with a communication hole 22 piercing both inside and outside and a bellows 24 is mounted at an external opening part. As the bellows 24 is made of an expansively deformable material, the capacity of an internal space of the container 10 is allowed to change and the bellows 24 is deformed expansively according to a pressure change to keep a pressure within the container 10 almost the same as an external pressure. A cover section 26 covering the bellows 24 is arranged integral with the container 10 and a hole 27 is made as being communicating with the outside so that a pressure of an external space reaches the outer circumference of the bellows 24. This can improve variation in the output associated with a temperature change thereby enabling lowering of measuring errors effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical device equipped with an optical element having an electric or magneto-optical effect, and in particular to an improvement of the optical device in which measurement errors due to temperature changes can be advantageously reduced. It is related to the structure that was created.

(Prior art) Traditionally, lithium niobate (LiNb0z)
Optical devices such as optical modulators and optical voltage sensors that utilize the electrical or magneto-optical effects of crystals such as these are known. Since these optical devices that utilize electricity or magneto-optical effects use light as a signal medium, they can electrically isolate signals, and optical signal transmission lines are free from electrostatic induction and It is recognized that it has the characteristic that it is hardly affected by electromagnetic induction. The electric or magneto-optical effect is a phenomenon in which the refractive index of the element changes depending on the strength of the applied electric or magnetic field, modulating the transmitted light. It is used to modulate light and measure voltage.

Incidentally, an optical voltage sensor as shown in FIG. 1, for example, is known as a device that utilizes such an electro-optic effect. In addition, in this FIG. 1, 1 is a light source, 2
is an optical fiber, 3 is an electro-optic crystal such as 1NbO3,
4a is a polarizer, 4b is an analyzer, 5 is a λ/4 plate, 6 is a fiber collimator, 7 is a light receiver, 8 is an electrode provided on the opposing surface of the electro-optic crystal 3, and these optical components 3 ~6 constitute a sensor head which is a measurement site.

When a Pockels element such as 1Nb03 is used as the electro-optic crystal 3, the light emitted from the light source 1 passes through the polarizer 4a to become linearly polarized light, and further passes through the electro-optic crystal 3 to become elliptically polarized light. becomes. Further, this elliptically polarized light passes through the λ/4 plate 5 and the analyzer 4b, and the amount of light is changed according to its ellipticity. The amount of light is determined by the electrode 8 provided on the electro-optic crystal 3.
By measuring the amount of light, the voltage to be measured can be determined.

In addition, in order to prevent measurement errors caused by moisture, dust, dirt, etc. on the optical path and to ensure reliability, the sensor head of such a photovoltaic sensor is generally airtight and It has a structure in which it is housed in a liquid-tightly sealed container 10.

However, in an optical device having a structure in which a sensor head including an optical element having such an electric (magneto) optical effect, for example a crystal such as LiNb0z or LiTaO3, is housed in a closed container, the sensor head is Due to changes in the environmental temperature, the output characteristics become extremely unstable.
In particular, such optical devices have excellent insulation resistance and noise resistance characteristics, and are therefore suitable for use in the power field. Since the device is used over a wide temperature range of about 80° C., changes in output characteristics due to changes in the environmental temperature have been a major problem.

(Problem to be solved) Here, the present invention has been made against the background of the above-mentioned circumstances, and the problem to be solved is:
An object of the present invention is to provide an improved optical device in which measurement errors due to changes in ambient temperature can be advantageously reduced in an optical device equipped with an optical element having an electric or magneto-optical effect.

(Solution Means) In order to solve this problem, the present invention includes:
In an optical device including an optical element that modulates transmitted light according to the strength of an electromagnetic field applied from the outside, a measurement site including at least the optical element is housed in a sealed container, and the container A feature of the container is that it is provided with a pressure absorption mechanism that absorbs changes in pressure within the container by allowing changes in volume within the container.

(Specific structure and effects of the invention) That is, the present invention is based on the inventor's experiments on an optical device having a sensor head in which a measurement part including an optical element is housed in a sealed container as described above. After further investigation, it became clear that the output characteristics of such a device, that is, the changes in the characteristics of the optical element, were not simply due to the influence of temperature factors.

More specifically, in such an optical device, a pressure change is applied to a sensor head housed in a closed container based on expansion/contraction of the air inside the container due to temperature change. It was observed that the value reached a change of about 0.8 to 1.2 atm with respect to a temperature change of -20 to 80°C. On the other hand, for example, as shown in FIG. 2, a communication hole is provided in the sealed container 10 of the sensor head in the optical device as shown in FIG. When the pressure inside the container 10 was changed by injecting air into the container 10 or sucking air out from the container 10 using the pressurizing device 12, the output characteristics were as shown in FIG. As if (to change, that is, electro-optic crystal (3)
It has been found that the properties of the material change significantly under the influence of pressure factors. In addition, in Figure 2, 14
．． 14 are lead wires for applying a voltage to be measured between the electrodes (8, 8), respectively.

The present invention has been made based on such knowledge, and the optical device according to the present invention is equipped with a pressure absorption mechanism that can allow a change in volume within the container, and the pressure absorption mechanism is The mechanism can absorb pressure fluctuations within the container and maintain the pressure within the container approximately constant.

Therefore, in the optical device according to the present invention, pressure changes inside the container due to expansion and contraction of air due to temperature changes can be eliminated, and therefore, among changes in the output characteristics of the sensor due to temperature changes, Pressure factors can be almost completely avoided, and the measurement accuracy and reliability can be advantageously improved.

(Examples) Hereinafter, in order to clarify the present invention more specifically, examples of the present invention will be described in detail with reference to the drawings.

First, FIG. 4 shows an optical voltage sensor as a specific example of the optical device according to the present invention. In the photovoltage sensor shown in FIG. 4, the parts constituting the measurement system are the same as those of the photovoltage sensor shown in FIG. By assigning the reference numeral , a detailed explanation thereof will be omitted.

That is, in the optical voltage sensor in this example,
A communication hole 22 is provided to penetrate the wall of the closed container IO, which is constituted by the optical components 3 to 6 and houses a sensor head as a measurement site, inside and outside. A bellows 24 is attached to the outer opening of the through hole 22, and the internal space of the container 10 is communicated with the bellows 24, so that the internal space of the container 10 is connected to the internal space of the bellows 24. It is also configured to include.

Here, the bellows 24 is made of an elastic or flexible material with excellent heat resistance, such as fluororesin, and is easily expandable and deformable. Since the bellows 24 is attached to the outer opening of the communication hole 22, a change in the volume of the internal space of the container 10 in which the sensor head is housed can be allowed based on the expansion and contraction of the bellows 24. In other words, in response to changes in the pressure inside the container 10, the bellows 24 is expanded and contracted based on the pressure difference with the outside space, so that the pressure inside the container 10 is changed to the outside pressure. This means that the change can be absorbed.

In addition, in the optical voltage sensor in this embodiment, a cover part 26 that covers the bellows 24 is attached to the container 10.
is integrally provided, and the bellows 24 is protected by the cover portion 26.

Of course, the cover portion 26 is provided with a through hole 27 that communicates with the external space, so that the pressure of the external space can be applied to the outer peripheral surface of the bellows 24.

Then, using a photovoltage sensor with such a structure,
As shown in FIG. 5, the sensor head (container 10) is housed in a constant temperature bath 28.
The photovoltage sensor output was measured when the temperature inside was changed from -20 to 80°C. Note that, as is well known, such a photovoltage sensor output is performed by guiding the electrical signal output from the photoreceiver 7 to an AC component detector 30 and a DC component detector 32, respectively, and detecting the desired signal component there. After the signal is taken out, the division circuit 34 performs calculations to obtain an output signal as a result of compensating for variations in the amount of light in the optical transmission path.

In addition, in such measurements, a Pockels element (LiNb0z crystal) is used as the electro-optic crystal 3, and L is used as the light source 1.
Measurements were made using an ED and a PIN photodiode as the light receiver 7, respectively, and applying a voltage of 60V (501(z)) between the electrodes 8 and 8 from the AC stabilized power supply 36.

Further, in making such measurements, as a comparative example, similar output measurements were also made for a photovoltage sensor equipped with a container 10 with a constant volume as shown in FIG. 1. In addition, in the optical voltage sensor having such a conventional structure, during the above-mentioned measurement, the thermostatic chamber 28 in which the container 10 is placed is used.
Pressure fluctuations from 0.8 to 1.2 atm were observed within the container 10 as the temperature changed from -20 to 8 degrees Celsius.

The measurement results for this example and the conventional example are also shown in FIG. In addition, in FIG. 6, the output value of the photovoltage sensor is shown as the output value at a temperature of 25°C in the device of this embodiment, and the output value at a temperature of 25°C in the device of the comparative example.
The output values at a temperature of 5°C were each expressed as a reference output fluctuation rate.

It is clear from FIG. 6 that in the optical voltage sensor of the device of this embodiment, output fluctuations due to temperature changes can be improved and measurement errors can be effectively reduced.

Therefore, in the optical voltage sensor having such a structure, since the internal pressure fluctuation can be avoided while ensuring the airtightness of the container 10, moisture, dust, dirt, etc. in the sensor head can be prevented. Measurement errors caused by environmental temperature changes can be effectively reduced while ensuring sufficient prevention of adverse effects caused by environmental temperature changes, thereby advantageously improving the usability and reliability of the device. It is.

Although one embodiment of the present invention has been described in detail above, this is a literal illustration, and the present invention is not to be construed as being limited only to this specific example.

For example, the cover portion 26 protecting the bellows 24 is not absolutely necessary.

In addition, the pressure absorption mechanism may be any mechanism as long as it can absorb pressure fluctuations within the container 1O, and may be configured with a diaphragm (elastic thin film) in the form of a flat membrane or bag, for example. It is also possible to construct it not by deformation but by a piston structure or the like.

Further, in the above embodiment, an example was shown in which the present invention was applied to a photovoltage sensor using a Pockels element, which is an electro-optical element, but various other elements having an electric or magneto-optical effect, For example, the present inventor has confirmed that even in Faraday elements, changes in optical characteristics occur due to pressure fluctuations, and therefore, optical The present invention can also be advantageously applied to various optical devices such as modulators, voltage sensors, and magnetic sensors.

In addition, although not listed, the present invention can be implemented in embodiments with various changes, modifications, improvements, etc., based on the knowledge of those skilled in the art, and such embodiments are not limited to the present invention. It goes without saying that any of these are included within the scope of the present invention as long as they do not depart from the spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the structure of an example of a conventional optical voltage sensor. Fig. 2 is a perspective view for explaining an experimental method conducted to measure sensor output fluctuations due to changes in pressure inside the container, and Fig. 3 shows measurement results obtained in such an experiment. It is a graph. FIG. 4 is an explanatory diagram showing the structure of a photovoltage sensor according to an embodiment of the present invention.
The figure is an explanatory diagram for explaining an experimental method conducted to measure output fluctuations due to temperature changes of such an optical voltage sensor, and FIG. 6 is a graph showing measurement results obtained in such an experiment. be. 3: Electro-optic crystal 4a: Polarizer 4b Two analyzers 5: λ/4 plate 6: Fiber collimator 7: Light receiver 8: Electrode IO: Container 22: Communication hole 24: Bellows

Claims (1)

[Claims] In an optical device including an optical element that modulates transmitted light according to the strength of an electromagnetic field applied from the outside, a measurement site including at least the optical element is housed in a sealed container, and the container 1. An optical device comprising a pressure absorption mechanism that absorbs pressure changes within the container by allowing volume changes within the container.