JPS62198769A - Optical fiber type voltage sensor - Google Patents

Abstract

PURPOSE:To greatly improve optical loss by providing an optical fiber for output at specific distance from an optical fiber for input where linear polarized light is incident. CONSTITUTION:The polarization plane maintaining type optical fiber 9 for input and the multimode type optical fiber 10 for output are arranged on one end surface of a self-convergence type rod lens 2 via one birefringent material 3, and a Pockels material 5, a 1/8-wavelength plate 6, and a reflection plate 7 are arranged on the other end surface of the lens 2. The optical fiber 9 is arranged right above the optical axis of the lens 2 and the optical fiber 10, on the other hand, is arranged at distance of ordinary-extraordinary light separation width in the ordinary-extraordinary light separating direction of the birefringent material. The linear polarized light is incident on the optical fiber 9 from a semiconductor laser 12 and shifted in phase corresponding to a voltage applied from an electrode 4 before returning the optical fiber 10 by being reflected by the reflecting plate 7, so that ordinary light and extraordinary light are polarized and separated. The extraordinary light has its phase shift converted into intensity variation by the birefringent material 3 and is converged on the optical fiber 10 and propagated therein, thereby obtaining variation in the quantity of light proportional to the level of the voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical fiber type voltage sensor using the Pockels effect.

Conventional technologies such as BSO, Li NbO3, Zn S, etc. Optical fiber voltage sensors, which optically measure the voltage of high-voltage power transmission lines using the optical crystal Nohockels effect, have excellent insulation properties and electromagnetic induction noise, and can be used using resistor voltage division methods, capacitor voltage division methods, etc. Since it has many advantages over electrical measurement methods, it has been actively developed in recent years.

FIG. 2 shows a conventional example of an optical fiber type voltage sensor that utilizes the Pockels effect. For bidirectional use, a birefringent material (rutile plate) 3 is placed between the output optical fiber 1 and one end of the self-focusing rod lens 2 to provide a polarization separation function. At the other end of the focusing rod lens 2, there is a Pockels material (in this conventional example, L i N b O3 single crystal) 5 having an electrode 4 and a 1/3 wavelength plate 6 .
, and a reflecting plate 7 are arranged to constitute a reflective optical system. There is a splitter 8 in front of the input/output optical fiber 117j, which passes the light gin from the input optical fiber 9 to the input/output optical fiber 1, and also passes the light gin from the input/output optical fiber 1 in the opposite direction. Light eout' (i-branched to output optical fiber 1o).

To explain the principle of operation, the light ein emitted from the input/output optical fiber 1 becomes linearly polarized light by the rutile flat plate 3.
After passing through the Pockels material 5 and the 1/3 wavelength plate 6, it is reflected by the mirror 7, and after passing through the 1/3 wavelength plate 6 and the Pockels material 6 again, it is polarized and separated by the rutile flat plate 3, and is used for both input and output. The light is received by fiber 1. The refractive index of the Pockels material 5 changes depending on the electric field, but since the rate of change differs depending on the polarization direction, the phase of the light passing therethrough changes and becomes elliptically polarized light. This change in polarization is separated by a rutile flat plate 3, which is an analyzer, and converted into a change in intensity.

Here, the optical phase difference Δφ that the light passing through the Pockels material 5 receives due to the electric field is proportional to the applied electric field strength E. In other words, Δφ=kE However: Constant of proportionality...
...(1).

Also, by reciprocating the 1/3 wavelength plate, the light beam is
It receives a phase difference of 2. Therefore, the output intensity in this case is p oc 1-5in (Δφ) , old, , , , (2), and when Δφ is small, p cc 1~Δφ=1−kE −0−,0
, -<3), and a change in the amount of light proportional to the electric field strength E can be obtained.

Problems to be Solved by the Invention In the conventional example, since the input/output optical fiber 1 is used in both directions, a splitter 8 is required to branch the signal light eout.
Since the light passes through the splitter 8 twice, once at the input and once at the output, a total optical loss of edB or more occurs at the half mirror 11 in the splitter 8, the coupling site of the optical components, etc.

In addition, since the branch 8 is required, the cost is high;
High reliability cannot be obtained due to the increase in the number of parts.

Furthermore, in this conventional example, since the light passes through the birefringent material 3 twice, loss e dB due to two polarization separations cannot be avoided.

Means for Solving the Problems In order to solve the above problems, the present invention uses a semiconductor laser as a light source and connects an input polarization maintaining optical fiber and an output multimode optical 7-eyeper to a self-focusing type. Placed on one end surface of the rod lens via a piece of birefringent material,
A material having a Pockels effect, a 1/8 wavelength plate, and a reflection plate are disposed on the other end surface of the self-focusing rod lens, and the input polarization-maintaining optical fiber is connected to the other end surface of the self-focusing rod lens. The output multimode optical fiber is arranged on the optical axis, and the ordinary light and extraordinary light of the birefringent material are connected to the output multimode optical fiber from the position of the input polarization preserving optical fiber with respect to the optical axis of the focusing rod lens. In the separation direction,
The light beams are placed at positions separated by the separation width between the ordinary light and the extraordinary light.

Function: With the above configuration, the light emitted from the input polarization-maintaining optical fiber becomes linearly polarized light, eliminating the need for polarization separation on the input side and avoiding 3 dB optical loss. Since the output optical fiber, which has a relatively larger core diameter than the input optical fiber, is used exclusively for output, it is possible to reduce the coupling loss of light between the person and the output, and also eliminates the need for a splitter, which reduces the large optical loss. We can expect wide-ranging improvements. Furthermore, since the oscillation wavelength range of the semiconductor laser used as the light source is generally very narrow, several nanometers, it is possible to improve measurement accuracy.

Embodiment FIG. 1 is a configuration diagram showing an embodiment of the optical fiber type voltage sensor of the present invention, and the same parts as in the conventional example are given the same numbers.

The major difference from the conventional example is that the output optical fiber 1o is placed at a position away from the position of the input optical fiber 9 in the polarization separation direction of the birefringent material 3 only during polarization separation, and the input and output optical fibers are separated. Therefore, there is no need for a turnout.

Next, the principle of operation of the sensor according to the present invention will be explained. The linearly polarized light emitted from the semiconductor laser 12 enters the polarization eigenaxis of the input polarization-maintaining optical fiber arranged on the optical axis of the self-focusing rod lens 2 . As a result, the light propagates through the optical fiber while maintaining linear polarization and enters the birefringent material 3 made of a rutile plate or the like. The input polarization-maintaining optical fiber 9 is connected so that the linearly polarized light incident at this time becomes ordinary light.
By adjusting the rotation axis of the output end face around the fiber axis, the light passes through the birefringent material 3 with almost no loss, becomes a parallel light at the self-focusing lens 2, and the Pockels materials 6 and 1
After passing through the /8 wavelength plate 6, it is reflected by the reflection plate 7, and the 1/8 wavelength is reflected again.
The light passes through the 8-wavelength plate 6 and the Pockels material 6 and enters the birefringent material 3 again. Since the light undergoes a phase change corresponding to the voltage applied from the electrode 4 when passing through the Pockels material 5, it also undergoes a phase change corresponding to the voltage applied from the electrode 4.
Since the light becomes elliptically polarized due to the phase difference of four wavelengths, the light that enters the birefringent material 3 again is polarized and separated into ordinary light and extraordinary light, resulting in two light beams. Of these two light beams, the extraordinary light passes through the birefringent material 3, the phase change is converted into an intensity change, and the light is focused on the output multimode optical fiber and propagated, increasing the amount of light proportional to the voltage intensity. You can get change.

Note that although a single crystal of rutile is used as the birefringent material, for example, calcite can also be used.

In addition, the rutile plate is cut out at an angle with respect to the optical axis in order to separate the two polarized acids at an angle.
In order to effectively separate polarized light according to the optical fiber spacing,
What is necessary is to design the angle with the optical axis and the thickness of the rutile flat plate.

In this embodiment, the 1/8 wavelength plate was placed between the Pockels material and the mirror, but the operation remains the same no matter where it is placed between the birefringent material and the mirror.

In this example, in order to self-concentrate the input optical fiber, the output 9 fibers are placed on the optical axis, and the input optical fiber is placed at a position separated by the polarization separation width in the polarization separation direction of the birefringent material. It's okay.

Note that the Pockels material is not limited to L I N b Os, but also those having the Pockels effect (for example, KDP).

ADP, LfTaO3, Zn5e, ZnS, crystal, etc.)
It goes without saying that the positions of the electrodes are different depending on whether the transverse modulation method is used or the vertical modulation method.

Effects of the Invention As described above, according to the present invention, the output light from the input polarization-maintaining optical fiber becomes linearly polarized light, eliminating the need for polarization separation on the input side and avoiding 3 dB optical loss. In addition to this, an output multimode optical fiber with a larger core diameter than the input optical fiber (polarization maintaining optical fiber core diameter is 10 μm or less, multimode optical fiber has a core diameter of 50 μm or more) is used for output only. Therefore, optical coupling loss between input and output can be reduced, and a splitter is not required, so a significant improvement in optical loss can be expected.

Furthermore, the half-maximum eclipse of the oscillation wavelength of the semiconductor laser used as a light source is generally several Hm, which is much narrower than that of a light-emitting diode (several 10 nm - 10° nm or more), making it possible to improve measurement accuracy. This is the result.

[Brief explanation of drawings]

7. Lifetime enjoyment of 1M1 juice and 10 benefits +ry-t-kaniri. FIG. 2 is a block diagram of a lever-type voltage sensor, and FIG. 2 is a block diagram of a conventional sensor length. 9... Input polarization preserving optical fiber, 10.
...Multimode optical fiber for output, 12...
... Semiconductor laser, 3 ... Birefringent material, 2
・・・・・・Self-focusing rod lens, 5・・・・・・
Pockels material, 6...1/8 wavelength plate, 4...
...Electrode, 7...Reflector. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] A semiconductor laser is used as a light source, and an input polarization-maintaining optical fiber and an output multimode optical fiber are placed on one end face of a self-focusing rod lens via a piece of birefringent material, and A material having a Pockels effect, a 1/8 wavelength plate, and a reflection plate are arranged on the other end surface of the focusing rod lens, and the input polarization maintaining optical fiber is placed on the optical axis of the self-focusing rod lens. and the output multimode optical fiber is arranged from the position of the input polarization preserving optical fiber with respect to the optical axis of the focusing rod lens in the direction of ordinary and extraordinary light separation of the birefringent material. , an optical fiber type voltage sensor arranged at a position separated by the ordinary light and extraordinary light separation width.