JPH1144721A - Sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensing device capable of reducing the cost and power consumption and being miniaturized by using a linear polarized light source, and using a normal single-mode optical fiber as a transmission line. SOLUTION: The light emitted from a light source 46 and transmitted on an input side single-mode optical fiber 10 is separated into two perpendicular polarized components by polarizing separator 13. The polarized components are fed to two reflection type light modulators 11, 12 respectively. The AC voltage induced on an antenna 15 is concurrently applied to two light modulators 11, 12. Two polarized components are modulated respectively, and the modulated light is polarization-synthesized and guided to a light detector 47 through an output side single-mode optical fiber 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a sensing device that converts electromagnetic waves into optical signals and detects the signals. This type of sensing device can detect a signal radio wave used for wireless communication and broadcasting, and can also detect the strength and frequency of a radio wave in the EMC field, and can also detect electromagnetic noise.

[0002]

2. Description of the Related Art With the development of information networks, the use density of radio waves, which is a main information transmission medium, has increased, and has spread to higher frequency bands. In a communication system, fusion between an optical fiber transmission line, which is relatively easy to operate at a high frequency, and wireless communication is progressing.

Also, many electronic devices such as information devices and communication devices such as computers, FA devices such as robots, and control devices for automobiles always have a risk of malfunctioning due to the influence of electromagnetic waves coming from the outside. In order to take measures against extraneous electromagnetic waves, it is important to accurately measure the electromagnetic waves generated by each device or device. Therefore, a sensing device has been developed that can connect an antenna rod to an optical modulator to directly convert an electromagnetic wave into an optical signal and detect the intensity and frequency of the optical signal to measure the electromagnetic wave.

FIG. 4 shows an example of the configuration of a conventional sensing device. FIG. 5 shows a configuration of a reflection type optical modulator used in the sensing device. In the drawing, a broken line with an arrow indicates a direction in which light is propagated (the same applies hereinafter). A lithium niobate crystal is used as a substrate 81, on which an input / output optical waveguide 85, a phase shift optical waveguide 84 and a reflecting section 8 are formed by titanium diffusion.
6, a reflection type branching interference type optical waveguide 6 and a modulation electrode 82 having a divided structure are formed. The AC voltage induced by the antenna 44 is guided to the modulation electrode 82 and applied to the phase shift optical waveguide 84. The light from the light source 46 is the optical fiber 4
8, through the optical circulator 72 and the optical fiber 49, enter the input / output optical waveguide 85 of the reflection type optical modulator 42, and
Energy is split into two phase-shifted optical waveguides 84,
The light is reflected by the reflecting portion 86 and is again emitted to the optical fiber 49 through the input / output optical waveguide 85. At this time, the optical fiber 4
The intensity of the outgoing light to be output to the phase shift optical waveguide 84
Change in intensity according to the AC voltage applied to the antenna 4.
4 can detect the intensity and frequency of a radio wave applied to the radio wave 4, a signal included in the radio wave, and the like.

[0005]

In the above-mentioned conventional sensing device, a polarization maintaining optical fiber is used as the optical fiber 48 because the optical modulator operates only for a fixed polarization component. This is because, when a normal single mode optical fiber is used, the polarization state changes due to distortion, temperature change, etc., so that the power of the light modulated by the optical modulator fluctuates. However, polarization-maintaining optical fibers are more expensive than ordinary single-mode optical fibers.

When the distance from the optical modulator connected to the antenna to the terminal device including the light source and the photodetector is long and the optical fiber 48 is long, two linearly polarized light sources are combined as a light source to generate random polarized light. A configuration using a single mode optical fiber as a transmission line is described in Japanese Patent Application No. 7-322938. However, this configuration requires two linearly polarized light sources, so that the device becomes very expensive, and the power consumption and the shape become large.

[0007] An object of the present invention is to provide a sensing device which can use one linearly polarized light source and which can use a normal single-mode optical fiber as a transmission line, thereby being able to reduce the cost, the power consumption, and the size. Is to do.

[0008]

In order to solve the above-mentioned problems, a sensing device according to the present invention comprises an antenna for inducing an alternating voltage in response to an electromagnetic wave, light generating means for generating linearly polarized light, A light separating unit that separates the light into a plurality of polarized light components, and a light modulating unit that modulates the plurality of polarized light components according to the AC voltage to generate a plurality of modulated lights,
An output stage for generating a device output according to the plurality of modulated lights.

Preferably, the output stage includes a light combining means for combining the plurality of modulated lights to generate a combined light, and a light detecting means for detecting the combined light and generating the output of the device.

The light modulating means includes a plurality of light modulators connected in parallel between the light separating means and the light synthesizing means, wherein the plurality of light modulators receive the plurality of polarized light components respectively, and It is preferable that an AC voltage is applied simultaneously.

Preferably, the AC voltage is applied in synchronization with the plurality of optical modulators.

Preferably, an optical path between the light separating means and the light synthesizing means has a difference in optical path length between those passing through different optical modulators of at most 1 m.

Preferably, an optical path between the light separating means and the light synthesizing means has an optical path loss difference of at most 3 dB between those passing through different optical modulators.

[0014] An optical attenuator may be inserted in the optical path between the light separating means and the light combining means to limit the difference in loss of the optical path between those passing through different optical modulators to at most 3 dB.

Each of the plurality of light modulators is a reflection type light modulator configured so that incident light is internally reflected and returns to the incident end, and the light separating means and the light synthesizing means are a single light modulator. It may be constituted by a separation / synthesizer.

An optical circulator may be inserted between each of the light generating means and the light detecting means and the light separating / combining device.

The light generating means and the optical circulator may be connected by an input-side single-mode optical fiber transmission line, and the light detecting means and the optical circulator may be connected by an output-side single-mode optical fiber transmission line.

[0018]

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

FIG. 1 shows a configuration of a sensing device according to an embodiment of the present invention. The light source 46, the photodetector 47, and the optical circulator 72 are the same as those of the conventional sensing device of FIG. The light emitted from the optical circulator 72 is separated into two polarization components orthogonal to each other by the polarization separator 13, and is incident on the two reflection type optical modulators 11 and 12, respectively. Here, each of the reflection type optical modulators 11 and 12 has the same configuration as that shown in FIG. 5, and terminals 16 and 17 of the respective modulation electrodes.
Are connected in parallel to the output terminal of the dipole antenna 15.

The light source 46 functions as light generating means and generates linearly polarized light such as laser light. The linearly polarized light emitted from the light source 46 passes through the single mode optical fiber 10 and is converted into two mutually orthogonal polarized light components by the polarization separator 13. At this time, the polarization separator 13 functions as a light separation unit. The polarization directions of the two polarization components are adjusted and the reflection type optical modulators 11 and 12 are adjusted.
Incident on.

The AC voltage induced in the antenna 15 is simultaneously applied to the electrodes of the reflection type optical modulators 11 and 12. In accordance with the AC voltage induced in the antenna 15, the reflection type optical modulators 11 and 12 cause the incident lights 18 and 1 composed of two polarization components to be incident.
9 are simultaneously modulated to generate two outgoing lights 20 and 21 which are respectively modulated lights. The reflection type optical modulators 11 and 12 together constitute an optical modulation unit.

Further, the outgoing lights 20 and 21 are supplied to the polarization separator 13.
Are polarized and synthesized. At this time, the polarization separator 13 functions as a light combining unit. Since the polarization splitter 13 functions as a light splitting unit or a light synthesizing unit, it can be regarded as a light splitting / synthesizing unit. The combined light polarized and combined by the polarization separator 13 enters the optical circulator 72, and enters the photodetector 47 via the single mode optical fiber 30. In the path of light emission from the polarization separator 13, the polarization separator 13, the optical circulator 72, the single mode optical fiber 30, and the photodetector 47 are collectively referred to as an output stage here.

Note that the signals received by the antenna 15 are synchronously applied to the two reflection type optical modulators 11 and 12,
The lines 22 and 23 connecting the antenna 15 and the terminals 16 and 17 are set to have substantially the same length. Further, the optical path lengths passing through the two reflective optical modulators 11 and 12 are set to be substantially equal to each other so that the modulated outgoing lights 20 and 21 are also synthesized in synchronization. Here, the modulation frequency is about 20 MHz, and the allowable value of the phase shift is 1 /
If the wavelength is 10 wavelengths or less, the difference in optical fiber length is required to be 1 m or less.

In the sensing device shown in FIG. 1, when the polarization state changes due to distortion or temperature change in the single-mode optical fiber transmission line 10, the optical power ratio between the incident lights 18 and 19 changes, but the sum is constant. . Therefore, if the insertion loss of the reflection type optical modulators 11 and 12 is almost the same, the power of the light incident on the photodetector 47 is constant. Here, the difference in optical path loss between the optical path passing through the reflective optical modulator 11 and the optical path passing through the reflective optical modulator 12 is set to at most 3 dB. An optical attenuator may be inserted in the optical path so as to compensate for the difference in insertion loss between the optical modulators 11 and 12, and the difference in optical path loss may be adjusted to at most 3 dB.

As described above, the sensing device of FIG.
Since two linearly polarized light sources can be used and a normal single mode optical fiber can be used as a transmission line, cost reduction, power consumption reduction, and size reduction can be achieved.

FIG. 2 shows a sensing device according to another embodiment of the present invention. In this sensing device, ordinary transmission-type light modulators 31 and 32 are used as light modulators. FIG. 3 shows an example of a transmission optical modulator that can be used in this sensing device. Light incident on the incident optical waveguide 51 is split into two phase-shifted optical waveguides 52 and 53, passes through the modulating electrode 54 and merges with the output optical waveguide 55, and interferes with each other to be output as intensity-modulated light.

Further, a passive resonance circuit 33 is formed between the output terminal of the antenna 44 and the electrodes of the transmission type optical modulators 31 and 32 to increase the voltage applied to the electrodes in a specific frequency range to increase the sensitivity. Is increasing.

In FIG. 2, the outgoing light composed of linearly polarized light, such as laser light from a light source 46, is applied to a single mode optical fiber 1.
The light passes through 0 and becomes two polarization components orthogonal to each other by the polarization separator 13 and enters the transmission type optical modulators 31 and 32. The transmissive light modulators 31 and 32 respectively modulate the two polarization components according to the AC voltage induced by the antenna 44 and emit a plurality of modulated lights. Outgoing lights from the two optical modulators 31 and 32 are combined by the polarization combiner 25 and pass through the single mode optical fiber 30 to enter the photodetector 47.

Also in this sensing device, a constant light power is incident on the photodetector irrespective of the polarization state of the light passing through the single mode optical fiber 10, so that the device can be constituted by one light source.

In the above description, an example in which one linearly polarized light is separated into two polarization components orthogonal to each other by the polarization separator 13 has been described. However, three or more polarization components are separated and a corresponding number of optical modulators are used. It can be similarly implemented by using.

In the embodiment shown in FIG. 1, a device having both functions may be constructed and used in place of the polarization separator 13 and the optical circulator 72 functioning as an optical separator / combiner.

[0032]

As described above, according to the present invention, one linearly polarized light source can be used, and a normal single-mode optical fiber is used as a transmission line to reduce the cost, power consumption, and size. A sensing device capable of performing the above is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a sensing device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a sensing device according to another embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a transmission type optical modulator used in the sensing device of FIG. 2;

FIG. 4 is a diagram showing a configuration of a conventional sensing device.

FIG. 5 is a diagram showing a configuration of a reflection type optical modulator used in the sensing device of FIG. 4;

[Explanation of symbols]

 Reference Signs List 46 light source 47 photodetector 10 input-side single-mode optical fiber 11, 12, 42 reflection-type optical modulator 13 polarization separator 15, 44 antenna 25 polarization combiner 30 output-side single-mode optical fiber 31, 32 transmission-type optical modulator 33 Resonance circuit 72 Optical circulator 81 Substrate 85 Input / output optical waveguide 84, 52, 53 Phase shift optical waveguide 82, 54 Modulation electrode

Claims (10)

[Claims] An antenna for inducing an AC voltage in response to an electromagnetic wave; a light generating means for generating linearly polarized light; a light separating means for separating the linearly polarized light into a plurality of polarization components; A sensing device, comprising: a light modulation unit that modulates a plurality of polarization components to generate a plurality of modulated lights; and an output stage that generates a device output according to the plurality of modulated lights. 2. The output stage includes: a light combining unit that combines the plurality of modulated lights to generate a combined light; and a light detection unit that detects the combined light and generates the device output. The sensing device as described. 3. The light modulating means includes a plurality of light modulators connected in parallel between the light separating means and the light combining means, and the plurality of light modulators receive the plurality of polarization components, respectively. The sensing device according to claim 2, wherein the AC voltage is applied simultaneously. 4. The sensing device according to claim 3, wherein the AC voltage is applied in synchronization with the plurality of optical modulators. 5. The sensing device according to claim 3, wherein an optical path between the light separating means and the light synthesizing means has an optical path length difference of at most 1 m between those passing through different optical modulators. 6. The sensing device according to claim 4, wherein an optical path between the light separating means and the light combining means has a difference in loss of the optical path between those passing through different optical modulators of at most 3 dB. 7. An optical attenuator for limiting a difference in loss of an optical path between light passing through different optical modulators to at most 3 dB is inserted in an optical path between the light separating means and the light combining means. 3. The sensing device according to 3. 8. Each of the plurality of light modulators is a reflection type light modulator configured so that incident light is internally reflected and returns to an incident end, and the light separating unit and the light combining unit are a single unit. The sensing device according to any one of claims 3 to 7, wherein the sensing device is configured by a light separating / combining device. 9. The sensing device according to claim 8, wherein an optical circulator is inserted between each of said light generating means and said light detecting means and said light separating / combining device. 10. The light generating means and the optical circulator are connected by an input-side single-mode optical fiber transmission line, and the light detecting means and the optical circulator are connected by an output-side single-mode optical fiber transmission line. 9. The sensing device according to 9.