JPH0639341Y2 - Optical electric field detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an improvement of an optical electric field detector using quartz as an electric field detecting element, and an optical electric field detector which is easy to manufacture and has high sensitivity. Is provided.

[Prior art]

The optical electric field detector measures the strength of the electric field by utilizing the Pockels effect, that is, the phenomenon that the refractive index of the electric field detecting element changes according to the electric field strength. Some are made of crystal.

The structure of the optical electric field detector is as shown in FIG.
The light output from 11 is incident on the polarizer 14 via the optical fiber 12 and the lens system 13, and after being linearly polarized here, the prism 16A changes the direction at a right angle to the rectangular parallelepiped crystal 15 and its optical axis direction. It is incident in the (Z-axis direction). The light transmitted through the crystal 15 changes its direction at a right angle again by the prism 16B and is incident on the light receiving unit 19 via the analyzer 17 and the optical fiber 18. Since the light incident on the crystal 15 produces an inherent phase difference in the crystal according to the electric field strength, the optical electric field detector measures the electric field strength by detecting the phase difference.

(Actual development number 59-106068 etc.).

[Problems to be solved by the invention]

When the electric field E is applied from the direction orthogonal to the optical axis direction (Z-axis direction) as shown in FIG. It is known that there is a correlation between the phase difference and the electric field strength.

On the other hand, a Z-cut crystal has a so-called natural optical rotatory property, in which the vibrating surface of Z-axis incident light rotates around the optical axis regardless of the presence or absence of an electric field, and therefore the light rotates around the optical axis while the analyzer is rotating. Proceed to the side. Therefore, it is preferable for high-sensitivity measurement to fix the analyzer according to the optical rotation angle in order to detect the maximum optical output,
Precision work is required to adjust the angle around the optical axis between the analyzer and the crystal. Therefore, if the angle adjustment is not performed correctly, there is a problem that the detected light level cannot be correctly converted into the electric field intensity or the measurement sensitivity of the electric field intensity is low.

[Means for solving problems]

The present invention has been made in view of such circumstances, and by using a crystal of a predetermined length as an electric field detection element, the analyzer can be easily attached to the crystal without being bothered to adjust the polarization wave extraction direction of the analyzer. It is an object of the present invention to provide an optical electric field detector which can be obtained and can be detected with high sensitivity.

The optical electric field detector according to the present invention comprises a light emitting unit, a polarizer for converting light output from the light emitting unit into linearly polarized light through an optical fiber and a lens system, and a linearly polarized light converted by the polarizer. It has a compensator that converts it into a circularly polarized wave, and has both ends cut perpendicular to the Z-axis direction, and the length in the Z-axis direction is 90 degrees due to the natural optical rotatory power of the polarization plane at both ends. It is a long rectangular parallelepiped that becomes an integral multiple, and when an electric field is applied while the circularly polarized wave converted by the compensating plate is transmitted in the Z-axis direction, it becomes an elliptically polarized wave and proceeds to the emission side while rotating in that state. The crystal configured as described above is provided in such a manner that one side of the short side of the surface facing the right-angled portion is in contact with the emission side of the crystal and the incident light is sequentially reflected on two side surfaces including the right-angled portion.
A prism in the shape of a right-angled isosceles triangular prism that is configured to reflect once, and a surface that faces the right-angled portion are brought into contact with the first reflection side surface of the incident elliptical polarized wave in the prism that has the same shape and is smaller than this prism. An analyzer which is provided to reflect the incident elliptically polarized wave as a linearly polarized wave on the other side surface of the prism and to emit it from the position of the other half side of the surface facing the right angle portion, and to be emitted from the prism And a light receiving section for receiving the linearly polarized wave through the lens system and the optical fiber.

[Action]

The present invention has a compensator for converting linearly polarized light converted by a polarizer into a circularly polarized wave, and a polarizing plate having both ends cut perpendicular to the Z-axis direction and having a length in the Z-axis direction at both ends. It is a long rectangular parallelepiped whose rotation angle difference due to the natural optical rotatory power of the surface is an integer multiple of 90 degrees, and when the circularly polarized wave converted by the compensating plate is subjected to an electric field while passing through in the Z-axis direction, it is elliptically polarized. Since an electric field detection element consisting of a crystal configured to travel as a wave and rotate in that state to travel to the emission side is used, it is necessary to adjust the polarization wave extraction direction when attaching the analyzer. A high-sensitivity optical electric field detector can be easily manufactured without the need.

Further, a prism in the form of a right-angled isosceles triangular prism is provided on the exit side of the crystal that serves as an electric field detection element, with one short side half of the surface facing the right-angled portion in contact with the right-angled portion. In addition to having a structure in which the light is reflected twice on the two side surfaces including,
An analyzer that has the same shape as this prism and is made smaller than this prism is provided by contacting the first reflection side surface of the incident elliptical polarized wave on the prism with the surface facing the right-angled portion in contact with the incident elliptical polarized wave. Since the polarized wave is reflected by the other side surface of the prism and is emitted from the position of the other half side of the surface facing the right angle portion, the analyzer can be placed within the rectangular range covering the prism. In addition to being able to reliably convert the elliptical polarized wave converted by the crystal in a space-friendly state into a linear polarized wave, the reflected optical path of this linear polarized wave can be made parallel to the incident elliptical polarized wave optical path, The detector can be made compact.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing an embodiment of the present invention, in which 1 denotes a light emitting part. Light from the light emitting section 1 (having a vibration component in random directions) [see FIG. 2 (a)] enters the polarizer 4 through the optical fiber 2 and the lens system 3 and is linearly polarized in one direction. [See FIG. 2 (b)], then the compensator,
For example, while being incident on an n + 1/4 wave plate (n = 0,1,2 ...) (hereinafter simply referred to as a λ / 4 plate) 5 and passing therethrough, it is circularly polarized [see FIG. 2 (c)], The circularly polarized wave is incident on the crystal 6.

The crystal 6 has both ends cut perpendicular to the Z-axis direction and is a rectangular parallelepiped that is long in the Z-axis direction. When a circularly polarized wave thereof receives an electric field while transmitting in the Z-axis direction of the crystal 6. It becomes an elliptically polarized wave [see FIG. 2 (d)], and proceeds to the emission side while rotating in that state.

On the exit side of the crystal 6, a prism 8 having a right-angled isosceles triangular prism shape is provided.
Is provided in contact with one short side half of the surface 8a facing the right angle portion, and the light incident on the prism 8 is sequentially reflected twice by the two side surfaces 8b and 8c including the right angle portion.

An analyzer 7 having the same shape as the prism 8 but smaller than the prism 8 is provided on the side surface 8b on which the elliptically polarized wave is first reflected by the prism 8 with its surface facing the right angle portion in contact. The light reflected on the side surface 8b is reflected by the analyzer 7 only in one direction of the polarized wave [see FIG. 2 (e)], and the linearly polarized wave is reflected in the other side surface 8c. The light is emitted from a position near the other short side of the surface 8a.

A lens system 9 is adhered to the light emitting portion on the other short side of the surface 8a, and the linearly polarized wave emitted from the surface 8a passes through the lens system 9 and passes through the light receiving side optical fiber 10 connected thereto. Then, it is captured by the light receiving unit 11.

The light receiving unit 11 is a photoelectric conversion element that extracts light as an electric signal,
It is equipped with a circuit that measures the amplitude of light and an arithmetic circuit that stores the correlation coefficient that indicates the relationship between the intensity level of incident light and the electric field intensity. Determine the strength of the electric field based on the amplitude.

The length of the quartz crystal 6 in the Z-axis direction is determined such that the twist angle of the vibrating surface of the polarized wave differs depending on the length and the analyzer 7 extracts the shortest radial component. That is, the twist angle of the oscillating surface of the polarized wave between the incident side end surface and the outgoing side end surface of the crystal 6 of the elliptically polarized wave is set to be an integral multiple of 90 degrees. For example,
When the wavelength of light is 0.85 μm, the crystal 6 has a length of about 8.
Those of 94 (mm) × k (k = 1,2,3 ...) are used.

The reason for defining the length of the crystal in the Z-axis direction of the optical electric field detector according to the present invention configured as above is as follows. That is, the prism 8 is attached to the crystal 6 having the above-mentioned length at a predetermined angle, and the analyzer 7 is attached to the prism 8 at a predetermined angle, that is, the sensitivity is high without adjusting the take-out angle of the analyzer. This is because the optical electric field detector can be manufactured.

More specifically, if a DC electric field acts from the X-axis direction, the circularly polarized wave in the crystal 6 becomes an elliptical polarized wave with the longest radial direction in the X-axis direction and the shortest radial direction in the Y-axis direction. Is rotated by 90 degrees while passing through in the Z-axis direction, and the X-axis direction is the shortest radial direction and the Y-axis direction is the longest radial direction on the emission side end face.
Assuming that the analyzer 7 is assembled so as to capture the component in the X-axis direction, the optical information measured by the light receiving unit 19 is the shortest radial direction of the elliptical polarized wave. That is, it is possible to perform high-sensitivity measurement that maximizes the amount of light attenuation per unit electric field strength.

When the λ / 4 plate described above is used as the compensator 5, the magnitude of the electric field applied to the electric field detecting element shown above is directly proportional to the amplitude of the linearly polarized wave emitted from the surface 8a of the prism 8, and Accurate electric field measurement is possible.

〔effect〕

As described in detail above, the optical electric field detector according to the present invention has a compensator for converting linearly polarized light converted by a polarizer into a circularly polarized wave and both ends cut perpendicularly to the Z-axis direction. The length in the Z-axis direction is a long rectangular parallelepiped whose rotation angle difference due to the natural optical rotatory property of the polarization plane at both ends is an integral multiple of 90 degrees, and the circularly polarized wave converted by the compensating plate is the Z-axis. When an electric field is received while passing through in the direction, an elliptical polarized wave is generated, and an electric field detection element consisting of a crystal configured to rotate in that state and progress to the emission side is used. In this case, a highly sensitive optical electric field detector can be easily manufactured without the need to adjust the polarization wave extraction direction.

Further, when the above-mentioned λ / 4 plate is used as the compensating plate, the magnitude of the electric field applied to the electric field detecting element and the amplitude of the linearly polarized wave emitted from the surface of the prism are directly proportional to each other, which enables more accurate electric field measurement. Become.

In particular, a prism of right-angled isosceles triangular prism is provided on the exit side of the crystal, which serves as an electric field detection element, with half of the short side of the surface facing the right-angled portion in contact with the right-angled portion. In addition to being configured to be reflected twice on two side surfaces including
An analyzer that has the same shape as this prism and is made smaller than this prism is provided by contacting the first reflection side surface of the incident elliptical polarized wave on the prism with the surface facing the right-angled portion in contact with the incident elliptical polarized wave. Since the polarized wave is reflected by the other side surface of the prism and is emitted from the position of the other half side of the surface facing the right angle portion, the analyzer can be placed within the rectangular range covering the prism. In addition to being able to reliably convert the elliptical polarized wave converted by the crystal in a space-friendly state into a linear polarized wave, the reflected optical path of this linear polarized wave can be made parallel to the incident elliptical polarized wave optical path, The detector can be made compact.

Therefore, according to the detector of the present invention, there is a practical effect that it is possible to sufficiently cope with a small installation location.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention, FIG. 2 is an explanatory view of a polarization form in the product of the present invention, FIG. 3 is a schematic view of a conventional device,
FIG. 4 is an explanatory diagram of the optical axis direction of the crystal. 6 ... Crystal, 7 ... Analyzer

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Claims (1)

[Scope of utility model registration request] 1. A light emitting section, a polarizer for converting light output from the light emitting section into linearly polarized light through an optical fiber and a lens system, and linearly polarized light converted by the polarizer into circularly polarized waves. Compensation plate and a long rectangular parallelepiped having both ends cut perpendicular to the Z-axis direction and having a length in the Z-axis direction at which the rotation angle difference due to the natural optical rotatory property of the polarization plane is an integer multiple of 90 degrees. And the circularly polarized wave converted by the compensator is Z
A crystal that is configured so that when it receives an electric field while transmitting in the axial direction, it becomes an elliptically polarized wave and proceeds to the emitting side while rotating in that state, and the surface facing the emitting side of this crystal at the right angle part. A prism having a right-angled isosceles triangular prism, which is formed by contacting one half of one short side and reflects incident light twice on two side faces including a right-angled portion, and has the same shape as this prism. The first ellipsoidal polarized wave on the prism is provided with the surface facing the right angle portion in contact with the first reflecting side surface of the incident elliptical polarized wave, and the incident elliptic polarized wave is reflected on the other side surface of the prism as a linearly polarized wave and the right angle is formed. An analyzer that emits light from the position of the other half of the short side of the surface that faces the section, and a light receiving unit that receives the linearly polarized wave emitted from the prism through the lens system and the optical fiber. Optical electric field detector to symptoms.