JPH06222307A - Branched interference type optical waveguide - Google Patents

Abstract

PURPOSE:To provide the branched interference type optical waveguide which eliminates antenna parts and electrode parts for an electric field sensor by a branched interference type optical modulator and can be constituted of only the pure optical parts without including metals. CONSTITUTION:This branched interference type optical waveguide consists of a first Y-branched optical waveguide which is formed on a ferroelectric substance substrate having an electrooptical effect and branches incident light to two, two phase shifts optical waveguides 1 which are connected to the branched two optical waveguides and a second Y-branched-optical waveguide for joining these two phase shift optical waveguides. A part 2 of at least one phase shift optical waveguide of the two phase shift optical waveguides is subjected to polarization inversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control device for controlling incident light by means of an optical waveguide, and particularly to measurement of radio wave noise generated from an electric circuit and radio wave noise in a measurement environment, high power equipment and power transmission line. The present invention relates to a branch interference type optical waveguide used for measurement of an electric field generated.

[0002]

2. Description of the Related Art At present, the most frequently used electric field sensor for EMC uses an antenna and measures the intensity of radio waves sensed by the antenna to measure noise. However, when this method is used, a coaxial cable must be connected between the antenna and the measuring device. This coaxial cable itself causes noise of several dB, which causes a measurement error.

As a method of preventing the generation of noise from such a coaxial cable, a method of using an optical fiber cable as a means for propagating electric field information from an antenna and reducing an error due to measurement noise generated during measurement can be considered. .

FIG. 1 shows an optical waveguide used as a concrete method thereof. As the waveguide 1, a branching interference type optical waveguide (switch) is used, which splits the incident laser light into two laser lights equally and then multiplexes the two laser lights.

Normally, a branching interferometer type optical modulator applies reciprocal electric fields to the branched optical waveguides and shifts the phase of laser light passing through the two optical waveguides by π / 2 to combine them. Cancel each other's laser light by the phase difference,
It has a structure in which the laser light intensity on the emission optical waveguide is set to "0".

Therefore, electric field information (voltage) from the antenna
Is given to the electrode part of this branching interferometric optical modulator, the intensity of the laser light emitted from the branching interferometric optical modulator changes linearly with the applied electric field, so that the antenna It becomes possible to transmit the electric field strength of the above by the optical fiber.

[0007]

However, in the above-described method, impedance matching with the antenna is difficult, and the characteristics of the electrodes of the branching interferometric optical modulator are deteriorated or the electric field is disturbed by the presence of an electric field. Occurs.

Further, in this method, the presence of the electrodes often poses a problem in the same manner as described above even when the electric field of the high power device is measured.

An object of the present invention is to eliminate the antenna part and electrode part for the electric field sensor by the branch interferometer type optical modulator as described above, and to construct the branch interferometer type optical waveguide which can be constituted by only pure optical parts containing no metal. To provide.

[0010]

According to the present invention, there is provided a first Y-branch optical waveguide which is formed on a ferroelectric substrate having an electro-optical effect and which splits incident light into two. Two phase shift optical waveguides connected to the two optical waveguides and a second Y-branch optical waveguide for merging the two phase shift optical waveguides.
A branching interference type optical waveguide is obtained in which a part of at least one of the two phase shifting optical waveguides is polarization-inverted.

[0011]

The electric field applied to the branched interferometric optical modulator is applied in the crystal axis direction of the LiNbO ₃ crystal used.

Since the direction of the electric field applied to this crystal axis determines the direction of the phase to be changed, in the ordinary branching interferometer type optical modulator, it is installed in the vicinity of the optical waveguide in each of the optical waveguides branched into two. With the electrodes, opposite electric fields are applied to cause changes in the refractive index in opposite directions due to the electro-optic effect, and the phase difference is set to π / 2.

Therefore, when the electrode portion of the commonly used branch interferometric optical modulator is simply removed, the electric fields applied to the two branched optical waveguides are in the same direction with respect to the crystal axis. Lights that are phase-shifted in the same phase are combined and laser light that is simply phase-modulated is emitted as output light, and the electric field strength can only be measured by determining the phase shift. That is, in this case, the light intensity cannot be changed by the electric field.

On the other hand, when the branched interference type optical waveguide of the present invention is used, the electric field applied to the two branched optical waveguides is one in the same direction with respect to the crystal axis, and the other has the opposite electric field. Since they are applied in the opposite directions, a refractive index change in the opposite direction occurs between them and a phase shift occurs.
That is, in this case, the electric field applied to the branch interference type optical waveguide makes it possible to change the intensity of the laser beam passing through this optical waveguide.

[0015]

Embodiments of the present invention will be described in detail below with reference to the drawings.

As an example of the present invention, Z-cut Li
Using NbO ₃ crystal substrate, the width is 8μm and the depth is 6μ
The m optical waveguide 1 was formed by Ti thermal diffusion in a branch interference form. Here, the length of the branch straight line portion between the optical waveguide 1 and the polarization-inverted optical waveguide portion 2 was 25 mm, and the distance between the branch straight line portions was 20 μm.

Further, the branch interferometer type optical modulator is
₂ was deposited to about 0.5 μm, and one portion of the optical waveguide branched into two was exposed by photoresist patterning and SiO ₂ etching.

Next, in a WET oxygen atmosphere, 1000
After heat treatment was performed at 2 ° C. for 2 hours and after heating was completed, the mixture was naturally cooled in an electric furnace. In this way, the polarization inversion part of the optical waveguide was created. The SiO ₂ remaining on the crystal surface was removed with a buffer etching solution.

The branch interference type optical waveguide manufactured in this manner is provided with an optical fiber (polarization plane holding fiber on the incident side,
The emission side was a single mode fiber and the wavelength of the propagating laser light was 1.31 μm), and the intensity of the emitted laser light was measured outside the measurement environment. In addition, this measurement is 50 MH
z. Furthermore, the level meter bandwidth is 7.5.
It was set to kHz.

When the electric field strength of the electric field sensor in this embodiment was measured in this manner, it was 150 dBμV / m
It was confirmed that the linearity was exhibited up to 60 dBμV / m.

It was also found that the electric field intensity detectable by this electric field sensor was about 60 dBμV / m (about 1 mV / m). This value is 10 times or more improved in sensitivity as compared with the conventional electric field sensor using bulk LiNbO ₃ .

Further, since this electric field sensor does not use an electrode, an antenna or the like, it is a very small element with little transmission noise.

[0023]

As described above, according to the present invention, the antenna section and the electrode section for the electric field sensor by the branch interference type optical modulator are deleted, and the branch interference type is formed only by the pure optical parts containing no metal. Since the optical waveguide can be configured, its sensitivity can be significantly improved as compared with the conventional optical waveguide, and the size of the element and the transmission noise can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a branching interference type optical modulator of an embodiment of the present invention.

[Explanation of symbols]

 1 Optical waveguide 2 Optical waveguide part with polarization reversed

Claims (2)

[Claims] 1. A first Y-branch optical waveguide which is formed on a ferroelectric substrate having an electro-optical effect and which splits incident light into two, and a second Y-branch optical waveguide connected to the two branched optical waveguides.
One phase shift optical waveguide and a second Y-branch optical waveguide for merging these two phase shift optical waveguides, and a part of at least one of the two phase shift optical waveguides. A branched interference type optical waveguide characterized by being polarization-inverted. 2. An electric field sensor using the branch interference type optical waveguide according to claim 1.