JPS61121030A - Voltage sensor of optical waveguide type - Google Patents

Abstract

PURPOSE:To extend the measurement range while keeping the measurement accuracy at a high value by forming plural light intensity modulating circuits, which have electrodes to which a voltage to be measured is impressed, on a substrate having the electrooptic effect and giving various phase shift to output light intensity characteristics of these light intensity modulating circuits preliminarily. CONSTITUTION:A Y-shaped optical waveguide 50 for input is provided on a substrate 1, and two output-side optical waveguides are connected to optical waveguides 21 and 31 for input of two Mach-Zehnder type optical waveguides 20 and 30. The light inputted to the optical waveguide 50 is branched equally into two and is inputted to Mach-Zehnder type optical waveguides 20 and 30, and these input lights have intensities modulated in accordance with the applied voltage and are outputted from output-side optical waveguides 22 and 32. Phase shifting electrodes 25a, 25b, 35a, and 35b and electrodes 26a, 26b, 36a, and 36b for applying voltages to be measured are formed on branch optical waveguides 23, 24, 33, and 34 of Mach-Zehnder type optical waveguides 20 and 30.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention According to the present invention, when a voltage to be measured is applied to an electrode of a light intensity modulation circuit formed on a substrate having an electro-optic effect, light is In a leading wave type voltage sensor where the output light intensity of the intensity modulation circuit changes, is it on the board? The present invention is characterized in that two optical intensity modulation circuits are provided, and different phase shifts are given to these optical intensity modulation circuits in advance. The light intensity modulation circuit is, for example, a Matsuhatsu Enda type optical S wavepath.

The invention will be described in detail below in accordance with the following table of contents.

(1) Background of the invention (1゜1) Technical field (1, 2) Description of the prior art (2) Summary of the invention (2, 1) Purpose of the invention (2, 2) Structure and effects of the invention (3) Implementation Explanation of examples (3, 1) Structure and voltage measurement principle of leading wave type voltage sensor (3, 2) Voltage measurement Vt position (3, 3) Modifications (1, Name of the invention (1, 1) Technical field This invention The present invention relates to an optical waveguide type voltage sensor, and more particularly relates to a voltage sensor that utilizes the fact that the phase of light propagating through a leading wavepath formed in an optical material having an electro-optic effect changes with the application of a voltage.

(1, 2) Description of Prior Art In recent years, with the progress of optical application technology, research and development of various optical sensors have been actively conducted.

Optical sensors have the characteristics that light or optical fibers are not affected by electromagnetic induction and can maintain high electrical insulation, so they can be used to make measurements in areas that were previously impossible to measure. Measurement is possible.

An example of a conventional optical waveguide type voltage sensor is shown in FIG. This is called a push-pull type voltage sensor. 'IX 2-cut LiNb with optical effect
By thermally diffusing Ti onto the surface of the O3 substrate (1),
Matsuhatsu Enda type optical waveguide (10
) is formed. Matsuha Tsuenda type optical waveguide (10
) is the output leading waveguide where the large-blade leading waveguide (11), two branching leading waveguides (13) (141) branched from it at equal angles, and the branching optical waveguides (13) and (14) join together. (12) Branch leading waveguide (
13) Each pair of phase shift electrodes (15a) (15b) and m measuring voltage application electrodes (16a) (16b) are formed by, for example, depositing AI so that a portion thereof overlaps (14). It is formed. 1m (15a) of these
There is S! between ~(ieb) and the substrate (1). A buffer layer (as shown) made of Oz or the like is provided.

FIG. 2 shows the relationship between the voltage applied between the electrodes (16a) and (16b) and the intensity of light output from the output leading waveguide (12). The light transmitted to the input optical waveguide (11) is equally branched and propagated to two branch leading waveguides (13) and (14), and is combined and outputted by the output leading waveguide (12). If no voltage is applied between E h (15a) (15b) and (16a) (16b), the light input to the optical waveguide (11) will be output from the optical waveguide (12) with the same intensity. be done.

Let us consider a case where no voltage is applied between the phase shift electrodes (15a) (15b1).

When a voltage is applied between the electrodes (16a) and (16b) through the terminal (18), the branched optical waveguide (13) (
14) the refractive index of the part increases depending on the applied voltage,
On the other hand, it decreases. Therefore, the optical waveguides (13) (14
) The phase of light propagating in one optical waveguide advances and lags in the other optical waveguide. Lights with different phases pass through the output leading wavepath (
12), the output light intensity changes depending on the phase difference between the two combined lights. Branch leading waveway (13)
When the phase difference between the two lights propagating through (14) becomes exactly π, the output light intensity becomes zero. The applied voltage at this time is called a half-wavelength voltage ■π. 74 Vi (16a
The relationship between the voltage applied to H16b) and the output light intensity is the second
Indicated by dashed lines in the figure.

The phase shifting electrodes (15a) (15b) are used to shift the curve shown by the chain line in FIG. 2 to the curve shown by the solid line. Electrode (15a) through terminal (17)
A voltage for phase shift 1 to Vπ/2 is applied between (15b).

The voltage applied between the electrodes (16a) and (16b) is measured using the portion with good linearity shown by the thick line in FIG. In this way, since a linear approximation of the output light intensity characteristic is used, the measurement range of the voltage to be measured inevitably becomes narrow.

For example, when the relative error with respect to Vπ is 1%, the measurement range is −Vπ/4 to Vπ/4, and if the relative error is to be further reduced, the measurement range must be further narrowed L7.

(2) Summary of the invention.

(2,1) Purpose of the Invention The object of the present invention is to widen the measurement range while maintaining high measurement accuracy in a leading wave type voltage sensor υ.

(2, 2) Structure and Effect of the Invention The leading wave type voltage generator according to the present invention has a plurality of light intensity modulation circuits each having an electrode to which a wave modulation voltage is applied, on a substrate that produces an electro-optic effect. It is noted that these light intensity modulation circuits are given different phase shifts in advance to their output light intensity characteristics.
be a sign.

A plurality of light intensity modulation circuits are formed on the substrate, and the voltage to be measured is applied to one pole of all of these light intensity modulation circuits. Since these light intensity modulation circuits are given different phase shifts in advance, the plurality of light intensity modulation circuits share a plurality of different measurement ranges, and the measurement range as a whole is expanded.

(3) Description of Examples (3,1) Structure and Voltage Measurement Principle of Optical Waveguide Voltage Sensor In Fig. 3, two Matsuhatsu Enda type optical waveguides (20) ( 30) is formed. The input leading waveguide, branch leading waveguide, and output optical waveguide of the Mach-Zehnder optical waveguide (20) are designated by symbols (21), (23N24), and (22), respectively.
It is shown in Corresponding parts of the optical waveguide (30) are indicated by symbols (31), (33), (34), and (32), respectively. These two Matsuhatsu Enda type optical waveguides +201 (30) have exactly the same configuration, and their half wavelength? 'Fi catty is also set equally.

1) Is there an input Y on the board? A nine-prong type optical waveguide (50) is provided, and its two output side leading waveguides are input leading waveguides (21) of two Mach-Zehnder type optical waveguides (20) and (30).
031). The light input to the optical waveguide (50) is equally split into two parts and input to the Mach-Zehnder type optical waveguides (20) and (30), where the light is intensity modulated according to the applied voltage and then sent to the output leading waveguide ( 22) (32)
is output from. These output lights are referred to as output lights I and ■.

Branch leading waveguide (2) of Matsuha Tsuenda type optical waveguide (20)
3024) There is a phase shift electrode (2Sa) on each
(25b) and measured voltage application dose Kx (26a)
(26b) is formed. Similarly, the other Mach-Zehnder type optical waveguide (30) is also provided with electrodes (35a) (3Sb) and (36a) (36b) for phase shifting and for applying a voltage to be measured.

A phase shift voltage is applied between the terminals (17). This voltage is between E 'N (25a) (2Sb) and (35a
) (35b), these electrodes are connected to the terminal (17) by a wiring pattern so that a voltage of opposite polarity is applied between the terminals (35b).

Between the electrodes (26a) (26b) and (36a) (36b
), these Ti poles are connected to the terminal (18) by a wiring pattern so that the voltage to be measured applied between the terminals (18) is applied with the same polarity.

For example, the substrate (1) is cut by 2-cut 1-iNboa,
The leading waveguide is formed by thermal diffusion of Ti, and the electrodes and the like are formed by vapor deposition of A/.

FIG. 4 shows the characteristics of the output light intensity in the circuit shown in FIG. 3. A voltage of 3vπ/4 is applied between the terminals (11), a phase shift of 3■π/4 is applied to the output light, and a phase shift of -3■π/4 is given in advance to the output light ■. There is.

Of these output light intensity curves, a portion with good linearity used for voltage training is shown by a thick line.

As can be seen from FIG. 4, there are four parts where the mouth line approximation can be performed, and these cover the measurement range from -■π to Vπ. In other words, when the relative error to Vπ is 1%,
A measurement range of π to ■π can be achieved, which is actually four times the conventional measurement range.

Which of these four approximate straight lines represents the voltage applied between the terminals (18) can be determined by the two output lights ■ and ■.
can be determined by the intensity level. For example, when the applied voltage is from 1π to -■π/2, the intensity of the completed output is between the lower limit level SL and the upper limit level SH, and the intensity of the output light (2) is equal to or higher than the upper limit level 88. Therefore, under these conditions, the voltage applied to the gutter is -■π~
-Vπ/2, and its actual value can be found from the n-line approximation of the intensity curve of the output light T. Output completed, ■
The intensity level condition is that the applied voltage is 1■π to -Vπ/2,
-■π/2~0.0~vπ/2 and ■π/2~Vπ are different depending on the range, so which of the four approximate straight lines should be used depends on the level condition. It is uniquely determined by

The level conditions are summarized as follows.

Table 1: Here, H represents a state where the output light is above the upper limit level 88, M represents a state where the output light is between the upper limit level SH and the lower limit level SL, and represents a state where the output light is below the lower limit level SL. There is. It will be understood that the applied voltage can be determined based on the output light intensity at the M level.

(3,21 Voltage constant device Figure 5 shows an example of a voltage measuring device using the above-mentioned optical wave type voltage hinger.Input light is applied to the substrate (1) through the input optical fiber (60). Y-shaped leading waveguide for input (
50) The measured voltage is applied across the terminals (18). Phase shift voltage 3■π/4 is terminal (17)
It is applied in advance in between. The intensity is modulated by the voltage to be measured, and two Mach-Zehnder type optical waveguides (201 (
The output lights (2) and (3) outputted from 30) are guided to a location through output optical fibers (61) and (62), respectively, through which an internal measurement path is provided.

The output lights I and ■ are output from photoelectric conversion elements (63) and (64), respectively.
) are converted into electrical signals representing these output light intensities. These electrical signals are then passed through a level discrimination circuit (65
)(66). Level discrimination circuit (65) (6
6) have the above-mentioned upper and lower limit levels 5l-1 and SL, respectively.
S is set, and a signal indicating which level of H, M, or L the output light intensities (■, ■) belong to is output. This signal is sent to the logic circuit (67), and it is determined to which range of the approximate straight line it belongs based on the logic in Table 1 mentioned above. The switching circuit (68) includes photoelectric conversion elements (63) (64).
) are input, and one of these signals is selected according to the determination result of the logic circuit (67) and sent to the voltage determination circuit (69). Voltage determination circuit'
1j! 1 (69) is the logic circuit (6
One approximation MI determined by the judgment result of 7)! By comparing the input optical intensity signal with the input optical intensity signal, the trained voltage is determined and output.

(3, 3) Modification FIG. 6 shows a modification. No phase shift electrode is provided here. Instead, a Mach-Zehnder type optical waveguide (201 (30) branch leading waveguide (24H3
3) wide portions (27N37) are formed respectively, thereby achieving a phase shift of ±3■π/4,
The same intensity characteristics of the output light as shown in FIG. 4 are q.

On the other hand, a narrow portion may be provided in the branch leading wavepath.

In Figures 3 and 6, one input light is equally branched and guided to two Mach-Zehnder type optical waveguides, but the two input lights are input to two Mach-Zehnder type optical waveguides separately. It's okay.

By increasing the number of light intensity modulation circuits formed on the substrate, it becomes possible to perform measurements with much higher precision.

FIG. 7 shows the output light intensity characteristics when three light intensity modulation circuits are provided. The output lights of the three light intensity modulation circuits are represented by output lights I, ■, and ■, respectively. A phase shift of 2V:'C/3 is given to the output completion, a phase shift of Vπ is given to the output light (2), and a phase shift of 122π/3 is given to the output light (2).

Since there are a total of six approximate straight lines within the measurement range of the applied voltage -Vπ to ■π, the relative error is 0.95% or less. The level conditions for which of the six approximate straight lines should be selected are shown in the table below.

Margin below Table 2

[Brief explanation of drawings]

Figure 1 is a perspective view showing the conventional leading wave type voltage.
The figure is a graph showing the output light intensity characteristics of this voltage sensor. FIG. 3 is a perspective view showing an example of the optical waveguide voltage sensor according to the present invention, and FIG. 4 is a graph showing the output light intensity characteristics of this voltage sensor. FIG. 5 is a configuration diagram showing a voltage measuring device using a voltage sensor according to the present invention. FIG. 6 is a non-trAm diagram of another embodiment of the present invention. FIG. 7 is a graph showing output light intensity characteristics when three light intensity modulation circuits are used. (1)... Substrate, (20) (21)... Mach-Zehnder type optical waveguide, (25a) (25bH35a) (3S
b)...Phase shift electrode, (26aH26b) (3
6a) (36b)...Electrode for applying voltage to be measured, (27
037)...Wide part for phase shift. Patent applicant Tateishi? Iiii Co., Ltd. 1”i-1Σ-
-i -i-

Claims (2)

[Claims] (1) A plurality of light intensity modulation circuits each having an electrode to which a voltage to be measured is applied is formed on a substrate having an electro-optic effect, and these light intensity modulation circuits have different output light intensity characteristics in advance. Optical waveguide voltage sensor with phase shift. (2) The optical waveguide type voltage sensor according to claim (1), wherein the optical intensity modulation circuit is a Mach-Zehnder type optical waveguide.