JP2007316004A - Light source device for orthogonally polarized light, and electric field sensor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-reliability light source for orthogonally polarized light that prevents beat noise with a light detector band, when the power is turned on, and to provide a high-reliability and stable electric field sensor that uses the same. <P>SOLUTION: In the light source for orthogonally polarized light, comprising two light sources 1, 2 for emitting linearly polarized beams with substantially equal strength values and different wavelength values from each other and an optical connector 5 for substantially orthogonalized two linearly polarized beams, emitted from the two light sources and then compositing the two beams, a means is provided for making the start-up times of the two light sources different from each other, by arranging a power supply circuit 7 for sequentially starting up the two light sources 1, 2 with time differences. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an orthogonally polarized light source device that synthesizes and emits two linearly polarized lights with their polarization planes orthogonal to each other, and an electric field sensor for measuring or detecting electromagnetic waves using the light source device, and mainly relates to EMC (electromagnetic wave). The present invention relates to an electric field sensor that is used as a measuring instrument for radio waves and electromagnetic noise in the field of the environment / electoromagnetic compatibility, and also functions as an antenna for detecting signal radio waves of a specific frequency such as broadcast radio waves.

  In general, many electric devices such as information devices such as computers and communication devices, FA devices such as robots, and control devices such as automobiles and railways are always at risk of being adversely affected by external electromagnetic noise. It is known.

  Therefore, in the recent EMC field, it is important to accurately measure the magnitude of electromagnetic noise that adversely affects the external electromagnetic environment or the noise generated by the electrical equipment itself.

  Conventionally, in order to measure the electromagnetic noise described above, three technical methods as described below are applied.

  The first technique is to receive electromagnetic noise using a normal antenna and guide it to a measuring instrument using a coaxial cable. In the second method, electromagnetic noise is received using an antenna, the received signal is detected, converted to an optical signal, and guided to a measuring instrument via an optical fiber. Further, the third method converts an electric field strength change of electromagnetic noise into a light intensity change by using an optical element configured to change the intensity of transmitted light according to the applied electric field strength, The light source and the photodetector connected to the measuring device are connected by an optical fiber.

  Of these, the first method is the most common, but there is a problem that the electric field distribution may be disturbed due to the presence of an electric cable such as a coaxial cable, or there is a risk of noise mixing in the middle of the cable. At present, the second method and the third method using optical fibers are mainly used.

  In the second method, after detecting with a diode, V / F conversion is performed to convert the obtained voltage into a frequency change amount, and the light-emitting diode is modulated with this signal to be converted into an optical signal, and the optical fiber is used. Although it is led to the photodetector, the sensor head requires an electric circuit and a battery, so there is a problem that a metal part of a certain size exists and the shape becomes large. The detection sensitivity is low and the response speed is slow.

  In the third method, a crystal having an electro-optic effect is used as a sensor head for converting electric field intensity into intensity change of transmitted light, and the transmitted light is modulated by a voltage induced by a small antenna connected to the electrode. . As the element structure, the light emitted from the optical fiber is passed through the crystal as parallel light by a lens, the polarization state is changed by the electric field induced in the crystal, passed through the analyzer, and then coupled to the optical fiber again. There are a bulk type element and a waveguide type element that constitutes an optical element by an optical waveguide provided on a crystal. Usually, the detection sensitivity of the waveguide type element is 10 times or more higher than that of the bulk type element. In general, a lithium niobate single crystal having a large electro-optic constant is used as a substrate crystal for an electric field sensor of a waveguide element.

  FIG. 4 is a diagram showing a basic configuration of an electric field sensor using a sensor head using a conventional waveguide element, and FIG. 5 is a perspective view showing a detailed configuration of the sensor head.

  In FIG. 5, in the sensor head 4, a pair of modulation electrodes 14 are installed at predetermined positions on the lithium niobate single crystal substrate 10 cut out perpendicular to the c-axis, and these modulation electrodes 14 are connected to the antenna 15 (FIG. 4). Connected). A phase shift optical waveguide 12 branched from the incident optical waveguide 11 is formed on each crystal surface below the pair of modulation electrodes 14, and the two phase shift optical waveguides 12 are merged on the output side to output the optical waveguide 13. Is formed. A polarization plane holding fiber 21 is coupled to the incident end of the incident optical waveguide 11 for incident light, and a single mode fiber 22 is connected to the outgoing end of the output optical waveguide 13 for outgoing light.

  In FIG. 4, in the electric field sensor, light passing through the polarization plane holding fiber 21 from the light source 1 connected to the power source 3 is incident on the sensor head 4 as incident light. In the sensor head 4, after incident light is incident on the incident optical waveguide 11 as shown in FIG. 5, energy is divided by the two phase shift optical waveguides 12 and propagates under the pair of modulation electrodes 14. Here, when an electric field is applied from the outside, a voltage is induced to the pair of modulation electrodes 14 by the antenna 15, and electric field components opposite to each other in the depth direction are generated in the phase shift optical waveguide 12. As a result, a refractive index change occurs due to the electro-optic effect, and a phase difference corresponding to the magnitude of the applied electric field is generated between the light waves propagating through the phase-shifted optical waveguide 12. An intensity change corresponding to the phase difference occurs. That is, the intensity of the outgoing light emitted to the single mode fiber 22 through the outgoing optical waveguide 13 changes according to the applied electric field strength, and the light intensity change is converted into an electrical signal by the photodetector 6. By measuring the intensity of the electric signal, the intensity of the applied electric field can be measured, and a radio signal can be detected from the electric signal.

  By the way, recently, in order to pursue economic efficiency, it is required to use a single-mode fiber as the incident optical fiber for the sensor head 4 instead of the polarization-maintaining fiber 21, so that the polarization plane fluctuates during transmission through the optical fiber. In order to compensate for the operational disadvantage caused by the above, as shown in Patent Document 1, a configuration in which two linearly polarized light sources are combined with a light source has been proposed.

  FIG. 6 is a diagram showing a basic configuration of such a conventional electric field sensor. This electric field sensor connects two light sources 1 and 2 that emit linearly polarized light to a power source 3, and a relatively short polarization plane holding fiber that holds a plane of polarization between the light sources 1 and 2 and the optical coupler 5. The sensor head 4 and the optical coupler 5 are further coupled by a single mode fiber 25.

  In the case of this configuration, the two linearly polarized lights emitted from the two light sources 1 and 2 pass through the polarization-maintaining fibers 23 and 24 and are synthesized by the optical coupler 5 so that the polarization planes are orthogonal to each other. The light passes through the mode fiber 25 while maintaining a relationship in which the planes of polarization are orthogonal to each other and enters the sensor head 4. For this reason, at the incident end of the sensor head 4, the orthogonal relationship of the planes of polarization is substantially maintained regardless of the state of the single mode fiber 25. Thus, the same effect as that obtained when a polarization maintaining fiber is used is obtained.

  The light sources 1 and 2 and the optical coupler 5 here and the pair of polarization plane holding fibers 23 and 24 coupled between them are collectively referred to as an orthogonal polarization light source device.

Japanese Patent No. 3627204

  In the case of the electric field sensor shown in FIG. 6 described above, if the wavelength difference between the two light sources in the orthogonal polarization light source device is large, the above-described polarization orthogonal relationship is deteriorated. Conversely, if the wavelength difference is small, the wavelength difference is accommodated by interference. It is known that noise of a certain frequency, that is, noise called beat noise is generated in an optical signal.

  This beat noise is extremely strong, and often destroys equipment connected to the subsequent stage including the photodetector. Usually, in order to avoid these, the wavelength difference of the light source used is increased to some extent, and the frequency of beat noise generation is selected to be sufficiently higher than the band of the photodetector.

  However, if the wavelength difference of the light source is too large, the orthogonality of the polarization planes cannot be maintained as described above, so that the wavelength difference is in the proximity of about 5 nm or less.

  However, in reality, when the light source is turned on, the light source rises depending on the ambient temperature and the characteristics specific to the light source until the wavelength is stabilized, and therefore, the rise method varies. FIG. 7 is a diagram illustrating an example of a change in the wavelength of the light source after power-on when the light source is a semiconductor laser. As shown in FIG. 7, in the state where the wavelengths are close to each other, there is a state where the wavelengths of the two light sources are close to or coincide with each other at the time of start-up, so that they are the same wavelength, or the wavelengths are closer than necessary. Therefore, it is unavoidable that beat noise is generated in the band of the photodetector. In other words, conventionally, when the wavelengths of two light sources in a stable state are kept close to each other, there is a risk that the beat noise generated at the start-up will cause destruction of equipment connected to the subsequent stage including the photodetector. there were.

  Accordingly, an object of the present invention is to provide a highly reliable orthogonally polarized light source device that does not generate beat noise in the photodetector band when the power is turned on, and a stable and highly reliable electric field sensor using the same. It is in.

  In order to solve the above-described problems, the orthogonally polarized light source device of the present invention has two light sources that emit linearly polarized light having substantially the same intensity and different wavelengths, and two linearly polarized light emitted from the two light sources. In the orthogonal polarization light source device comprising an optical coupler that synthesizes wavefronts substantially orthogonal to each other, means for making the activation times of the two light sources different from each other is provided.

  Further, a power supply circuit that sequentially activates the two light sources with a difference in activation time may be provided.

  The two light sources may be semiconductor lasers.

  Of the two light sources, a light source having a long wavelength may be activated first.

  An electric field sensor according to the present invention includes the orthogonally polarized light source device according to the present invention, a photodetector, an antenna, a sensor head that modulates transmitted light by a voltage induced in the antenna, and the orthogonal to the sensor head. An incident optical fiber that supplies outgoing light from the polarized light source device, and an outgoing optical fiber that guides light modulated by the sensor head to the photodetector.

  In the present invention, the start-up time is differentiated so that the wavelengths of the two linearly polarized light sources do not approach each other at the start-up, so that beat noise is not generated in the photodetector band when the power is turned on. A high orthogonal polarization light source device can be obtained, and a stable and highly reliable electric field sensor using the light source device can be obtained.

  Embodiments of an orthogonally polarized light source device and an electric field sensor using the same according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram showing a basic configuration of an embodiment of an orthogonally polarized light source device according to the present invention. Referring to FIG. 1, the orthogonally polarized light source device of the present embodiment includes two light sources 1 and 2 that emit two linearly polarized lights having substantially the same intensity of emitted light and different wavelengths, and the two light sources. A time difference starting power supply circuit 7 that sequentially drives with a difference in starting time, an optical coupler 5 that combines the two linearly polarized lights so that their polarization planes are orthogonal to each other, and light emitted from the light sources 1 and 2 are optical couplers, respectively. 5 and relatively short polarization plane holding fibers 23 and 24 led to 5. In the present embodiment, semiconductor lasers are used as the light sources 1 and 2.

  In general, in semiconductor lasers, the larger the amount of current that flows, the longer the wavelength shifts to the longer wavelength side, so the wavelength until the current at start-up stabilizes from the shorter wavelength side to the longer wavelength side as shown in FIG. It will change. Also, the frequency of occurrence of beat noise is expressed by equation (1).

f = C / (λ1) −C / (λ2) (1)
f: beat noise frequency, C: speed of light, λ1: wavelength of light source 1, λ2: wavelength of light source 2,
(Λ2> λ1)

  In the present embodiment, the band of the photodetector is 100 k to 10 GHz. At this time, it is necessary to design the beat noise generated by the light sources 1 and 2 to be 10 GHz or more. However, since the sensitivity of the photodetector exists at 10 GHz or more, in this embodiment, it is 60 GHz or more. Corresponding to this, the wavelength of the light source 1 was set to 1550.0 nm, and the wavelength of the light source 2 was set to 1550.5 nm. The beat noise frequency f at this time is 62.4 GHz. Each of the light sources 1 and 2 uses a semiconductor laser whose wavelength is stabilized within 3 seconds after activation.

  FIG. 2 is a diagram showing the transition of the light source wavelength when the time difference activation power supply circuit 7 is turned on in the present embodiment. When the power is turned on, the time difference activation power supply circuit 7 first drives the light source 2 on the long wavelength side. The light source 2 emits light and stabilizes at the rated wavelength (1550.5 nm) within 3 seconds while changing the wavelength from the short wavelength side to the long wavelength side.

  After a few seconds after the wavelength of the light source 2 is stabilized, the light source 1 is driven and stabilized at the rated wavelength (1550.0 nm). By operating in this way, no beat noise was observed.

  In this orthogonally polarized light source device, the linearly polarized light emitted from the light sources 1 and 2 passes through the polarization plane holding fibers 23 and 24, respectively, so that the polarization state is maintained, and the polarization planes are orthogonal to each other by the optical coupler 5. After that, the signals propagate through the single mode fiber 25 while maintaining the orthogonal polarization planes.

  In this embodiment, the start time difference of the time difference start power supply circuit 7 can be determined by the rising characteristics of a light source such as a semiconductor laser to be used. In the case of a semiconductor laser, at least the wavelength of the light source on the long wavelength side is stable. It can be time to do. If the wavelength difference is always greater than or equal to the set value at the time of start-up, a time shorter than that may be set. If the light source 2 having a long wavelength is activated first and the rising slopes of the wavelengths of the light source 1 and the light source 2 are the same, for example, the activation time difference may be about 10 ms or more.

  Moreover, the method of providing the starting time difference of the time difference starting power supply circuit 7 in the present embodiment may be a simple delay circuit used in a general electric circuit provided in the power supply unit on the starting side of one light source.

  FIG. 3 shows a basic configuration of an embodiment of an electric field sensor according to the present invention in which the orthogonally polarized light source of the present embodiment is mounted as a light source. The basic configuration of the electric field sensor of the present embodiment is the same as that of the conventional electric field sensor shown in FIG. 6 except for the power source unit of the light source. However, the electric field sensor of this embodiment has sufficient stability and reliability because no beat noise is generated at the time of activation. Further, in this electric field sensor, since there is no influence of the beat noise at the time of start-up, the wavelength difference between the two light sources can be set smaller by design than the conventional electric field sensor. In such a setting, since the orthogonal state of the polarization planes of the two linearly polarized lights is kept long in the optical fiber, the length of the single mode fiber 25 coupled to the incident side of the orthogonally polarized light source device is made longer than the conventional one. It can be made longer.

  As described above, according to the present invention, a stable and highly reliable orthogonally polarized light source device that does not generate beat noise in the photodetector band when the power is turned on is obtained, and stable and reliable using the device. A highly efficient electric field sensor can be obtained.

  Also, when a light source other than a semiconductor laser, for example, two solid-state laser light sources, is used as an orthogonally polarized light source, the wavelength difference can be less than the set value due to instability at the time of startup, so that the transmission wavelength is stabilized. By using the present invention with the time set as the above-described start time difference, a stable and highly reliable orthogonally polarized light source device can be obtained.

  In the orthogonally polarized light source device of the present invention, as a means for making the activation times of the two light sources different from each other, for example, a delay in one of the current drive circuits of the two semiconductor lasers is provided in addition to providing the activation time difference in the power supply portion. It is needless to say that a circuit may be provided, and the location where the delay circuit is installed and the type of the delay circuit can be selected according to the purpose and application of the light source device.

  In addition, when the light emitted from the two light sources is combined by the optical coupler with the polarization planes orthogonal to each other, in the above embodiment, the light is guided using the polarization plane holding fiber. You may lead to the coupler.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the basic composition of one Embodiment of the orthogonal polarization light source device by this invention. The figure which shows transition of the light source wavelength when the power supply of a time difference starting power supply circuit is turned on. The figure which shows the basic composition of one Embodiment of the electric field sensor by this invention. The figure which shows the basic composition of the electric field sensor using the sensor head by the conventional waveguide type element. The perspective view which shows the detailed structure of the sensor head used for an electric field sensor. The figure which shows the basic composition of the conventional electric field sensor which combined two linearly polarized light sources. The figure which shows an example of the mode of the wavelength change of the light source after power activation in the case of using the semiconductor laser as the light source in the conventional orthogonal polarization light source device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Light source 3 Power supply 4 Sensor head 5 Optical coupler 6 Photo detector 7 Time difference starting power supply circuit 10 Lithium niobate single crystal substrate 11 Incident optical waveguide 12 Phase shift optical waveguide 13 Output optical waveguide 14 Modulating electrode 15 Antenna 21, 23, 24 Polarization plane maintaining fiber 22, 25, 26 Single mode fiber

Claims (5)

  Orthogonal polarized light comprising two light sources that emit linearly polarized light having substantially the same intensity and different wavelengths, and an optical coupler that combines the two linearly polarized light emitted from the two light sources with their polarization planes substantially orthogonal to each other. An orthogonally polarized light source device, characterized in that means for making the activation times of the two light sources different from each other is provided in the light source device.   2. The orthogonally polarized light source device according to claim 1, further comprising a power supply circuit that sequentially activates the two light sources with a difference in activation time.   The orthogonally polarized light source device according to claim 1 or 2, wherein the two light sources are semiconductor lasers.   The orthogonally polarized light source device according to any one of claims 1 to 3, wherein a light source having a long wavelength is activated first among the two light sources.   5. The orthogonally polarized light source device according to claim 1, a photodetector, an antenna, a sensor head that modulates transmitted light by a voltage induced in the antenna, and the orthogonal to the sensor head An electric field sensor comprising: an incident optical fiber that supplies outgoing light from a polarized light source device; and an outgoing optical fiber that guides light modulated by the sensor head to the photodetector.

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