JP2011191107A - Optical transmission device including multichannel rotary joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical rotary joint having 0.2 dB or less deviation of a propagation loss by rotation, which performs multichannel measurement simultaneously and infinitely rotates, and also to provide an optical electromagnetic field sensor. <P>SOLUTION: This multichannel high-stability optical electromagnetic field sensor is acquired by acquiring an RF signal having a very small deviation, by compensating deviation of transmission loss generated by rotation of the optical rotary joint, by installing a feedback circuit by the use of light so that the DC level of an intensity-modulated measurement signal becomes a constant value, or providing a feedback circuit of an electric circuit, and by installing an optical multiplexer and a branching filter composed of wavelength filters above and below the optical rotary joint, and performing measurement with laser beams of different wavelengths. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is an apparatus for measuring the electric field strength of an electromagnetic wave propagating in space using a laser light source and an optical crystal, or an optical transmission apparatus for optically modulating and transmitting a received voltage from a receiving antenna. The present invention relates to an electric field sensor used as a measuring instrument for measuring characteristics of radio waves and electromagnetic noise in the field of environmental problems (electromagnetic compatibility), and a transmission device that also functions as an antenna for detecting signal radio waves of a specific frequency such as a mobile phone.

  In general, many electrical devices such as information devices such as computers, communication devices, FA devices such as robots, or controllers 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. However, there is a problem that the electric field distribution is 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. A second method and a third method using the above are being studied.

  In the second method, the detection signal detected by the diode is amplified and converted into an optical signal in addition to the light emitting diode, and the optical signal is led to the photodetector. In addition to the problem that the metal portion of a certain size exists and the shape becomes large because it is necessary, there is a drawback that the detection sensitivity of the electric field is low and the response speed is slow.

  Furthermore, the third method is a method of converting the electric field intensity into a change in intensity of transmitted light and finally demodulating it into an electric output, and is called an optical electric field sensor to distinguish it from the first and second methods. Yes. The element structure is such that a small antenna is connected, the light emitted from the optical fiber is passed through the element as parallel light through a lens, the polarization direction is rotated by the electric field in the element, and converted into light intensity modulation by the analyzer. There are a bulk type optical electric field sensor coupled to an optical fiber and a waveguide type optical electric field sensor that converts electric field intensity into optical intensity modulation by an optical waveguide provided on the element. Normally, the waveguide type optical electric field sensor is 10 times more sensitive than the bulk type optical electric field sensor, but the bulk type optical electric field sensor is smaller than the waveguide type optical electric field sensor. Since it can be detected up to a high frequency, it has been studied to use properly depending on the application.

  FIG. 6 shows a basic configuration of a conventional optical electric field sensor, and FIG. 7 shows a detailed configuration of a bulk type optical electric field sensor head used for the electric field sensor in a perspective view.

Here, the sensor head of FIG. 7 includes a polarizer 6, a wave plate 7, an analyzer 8, an electro-optic element 9, a parallel electrode 14, and an antenna 15.
The input laser beam 16 is transmitted only by a linearly polarized wave in a specific direction by the polarizer 6, and this linearly polarized wave is rotated to an arbitrary angle by the wave plate 7 and is incident on the electro-optic element 9. Here, the incident laser light rotates in the polarization direction according to the applied electric field intensity, and transmits only the polarization direction component of the analyzer 8. Using this effect, the applied electric field strength can be measured by converting the input electric field strength into light intensity modulation.

  FIG. 7 is a perspective view showing a detailed configuration of a sensor head used in a waveguide type optical electric field sensor.

  Here, in the sensor head of FIG. 7, a pair of modulation electrodes 14 ′ are installed at predetermined positions on the lithium niobate single crystal substrate 10, and are connected to the antenna 15 ′. The phase shift optical waveguide 12 branched from the incident optical waveguide 11 is coupled to one side of the pair of modulation electrodes 14 ′, and the output optical waveguide 13 is formed by joining the phase shift optical waveguide 12 on the other side. An optical fiber 2 ′ is coupled to the incident end of the incident optical waveguide 11 for incident light, and an optical fiber 3 ′ is coupled to the output end of the output optical waveguide 13 for outgoing light.

  In the waveguide type optical electric field sensor, light passing through the optical fiber 2 'from the light source 1' enters the sensor head 4 'as incident light. In the sensor head 4 ′, after incident light is incident on the incident optical waveguide 11, energy is divided by the two phase shift optical waveguides 12 and transmitted between 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 an electric field component is generated on one side of the phase shift optical waveguide 12 between the electrodes. As a result, a refractive index change occurs due to the electro-optic effect, and the phase difference corresponding to the magnitude of the applied electric field changes between the light waves propagating through the phase shift optical waveguide 12. That is, the intensity of the outgoing light emitted to the optical fiber 3 ′ through the outgoing optical waveguide 13 changes according to the applied electric field strength, and the change in the light intensity is measured by the photodetector (light receiver) 17 ′. Thus, the strength of the applied electric field can be measured.

On the other hand, as shown in FIG. 8, for the purpose of evaluating the reception characteristics of the antenna 15 '', not for electric field measurement, or for the purpose of voltage signal transmission using the high impedance input (not shown), By electrically connecting the antenna 15 ″ to be measured and the modulation electrode 14 with a high-frequency connector 18 or the like, it can be used as a voltage detection device that converts the received voltage signal of the antenna 15 ′ into a light intensity signal and transmits it.
This can be applied to both a bulk type optical electric field sensor and a waveguide type optical electric field sensor. However, the optical electric field sensor is collectively referred to as both the above-mentioned electric field measuring application and the later-described antenna measuring application.

  An optical magnetic field sensor can also be obtained by using a magnetic field detection type antenna such as a loop antenna for the waveguide type electric field sensor.

  As described above, since the optical electric field sensor and the optical magnetic field sensor are not structurally essential, they are labeled as a photoelectric magnetic field sensor.

  By the way, recently, due to the necessity of easy handling, as shown in FIG. 9, the sensor head 4 ′ ″ is optically connected to the electro-optical element end, the magneto-optical element end, or to the phase shift optical waveguide end as shown in FIG. By installing a conventional mirror 20, 20 ′, a photoelectric magnetic field sensor called a reflection type without an outgoing light side fiber has been proposed and used. In this case, the optical circulator 19 is used to separate light incident on the optical electric field sensor head and light returning from the optical electric field sensor head.

  Regarding such a reflection type photoelectric magnetic field sensor, one of the measurement contents that have attracted particular attention in the antenna performance evaluation method is the evaluation of a mobile phone MIMO antenna.

  This is a technology that aims to increase the communication speed by installing multiple antennas on one mobile phone terminal and simultaneously performing wireless communication with multiple antennas.

  For this purpose, it is necessary to evaluate the reception performance of multiple antennas simultaneously. As a method, a mobile phone terminal with multiple antennas is fixed on a turntable in an anechoic chamber, and the turntable is rotated. A general method is to measure the received radio wave intensity from a certain direction and evaluate the performance.

  In order to extract the signal from the antenna on the turntable, when using a normal coaxial cable, the rotating side and the fixed side are electrically connected by using an RF rotary joint.

  A general measurement system is shown in FIG. Radio waves are radiated from the transmission antenna 15 through the amplifier 31 from the network analyzer 32. The measured antennas 36 and 36 'receive the radio waves, and signals are returned to the network analyzer 32 from the RF rotary joint 34 fixed to the turntable 33 through the coaxial cables 35 and 35', and the antenna characteristics are evaluated.

  Here, the RF rotary joint is configured so that the two coaxial cables can be rotated while being electrically separated, and infinite rotation is possible in the same direction, so different conditions can be measured for each rotation. Measurement can be performed efficiently.

Japanese Patent Laid-Open No. 07-020159

JP 07-294575 A

JP 2000-338154 A

  As shown in FIG. 2, the inventor has previously been able to compensate for transmission loss caused by bending or stress of an optical fiber by adding an optical or electrical feedback circuit in a photoelectric magnetic field sensor. I found.

  However, in the antenna performance evaluation, when a photoelectric magnetic field sensor is used, the photoelectric magnetic field sensor head 39 is fixed on the turntable 33 as shown in FIG. Since the optical fiber is wound up by the rotation of the turntable because it is connected to the device 38, infinite rotation is impossible.

  On the other hand, optical rotary joints have been on the market for a long time, but light is propagated in space by a pair of lenses and optically coupled by rotating one side of the lens together, but the vertical axis of rotation matches precisely. It is very expensive, and the deviation of propagation loss due to rotation is about 0.5 dB, and the accuracy required for antenna measurement is within 0.2 dB, so it cannot be used.

  Also, when measuring multiple antennas to be measured at the same time, a multi-channel optical rotary joint is required, but a commercially available multi-channel optical rotary joint is more expensive, and the deviation of propagation loss exceeds 2 dB. However, there is a problem in that it cannot be corrected sufficiently and accurate and efficient measurement with light cannot be performed.

  The present invention has been made to solve such problems, and its technical problem is that the deviation of propagation loss is within 0.2 dB due to rotation, and multi-CH measurement can be performed simultaneously and infinite rotation is possible. It is to provide an optical rotary joint and a photoelectric magnetic field sensor.

  According to the present invention, by installing the feedback circuit by light so that the DC level of the intensity-modulated measurement signal becomes a constant value, or by installing the feedback circuit by electric circuit, the rotation of the optical rotary joint By compensating the deviation of the generated transmission loss, an RF signal with a very small deviation is acquired, and a multiplexer and a duplexer consisting of wavelength filters are installed above and below the optical rotary joint. By measuring, a highly stable photoelectric magnetic field sensor having multiple CHs can be obtained.

  As described above, combining a feedback circuit with an amplifier with a constant output control circuit, an optical rotary joint, a multiplexer, a demultiplexer, and a photoelectric magnetic field sensor with different wavelengths enables simultaneous measurement of multi-channel antennas and stable operation. RF output is obtained.

2 shows the configuration of two reflection type optical electric field sensors with feedback circuits, one optical rotary joint, a multiplexer, and a duplexer according to an embodiment of the present invention. 1 shows a basic configuration of a reflective optical electric field sensor with a feedback circuit. The input voltage and operation curve of the optical electric field sensor when there is no transmission loss of the optical rotary joint are shown. The input voltage and operation curve of an optical electric field sensor when the transmission loss of an optical rotary joint increases are shown. It is an example of the sensor head of a bulk type optical electric field sensor. 1 shows a configuration of a conventional transmission type optical electric field sensor. It is an example of the sensor head of a waveguide type optical electric field sensor. 1 shows a configuration of an optical electric field sensor using an external antenna. This shows the configuration of a conventional reflective optical electric field sensor. It is an example of a sensor head of a waveguide type optical electric field sensor (reflection type). It is an example of the measurement system of the conventional multi-channel antenna measurement using a coaxial cable. It is an example of the measurement example of the conventional 2CH antenna measurement which uses an optical fiber.

  EXAMPLES Examples will be given below, and the multi-CH measurement photoelectric magnetic field sensor of the present invention will be described in detail with reference to the drawings.

  Both the bulk type optical electric field sensor and the waveguide type optical electric field sensor convert the voltage applied to the parallel electrodes of the optical electric field sensor head into the light intensity modulation. The relationship is expressed as shown in FIG. .

  Incident light (FIG. 3-1) output from the light source with the optical power P0 is trigonometrically generated by the voltage between the parallel electrodes (FIG. 3-3) when passing through the optical electric field sensor head when there is no transmission loss. It changes so that it may become the transmittance | permeability of 0-100% (FIG. 3-2). The curve of this graph is called an operation curve.

  At this time, the transmittance when no voltage is applied between the parallel electrodes is called an operating point. However, when the transmittance of 50% is the operating point, the highest sensitivity can be obtained. The operating point is determined at a position of 50%.

  Here, if the voltage applied between the parallel electrodes is ± Vi, the transmittance of the optical electric field sensor head moves on the operating point AB, and the transmitted light has an average value as shown in FIG. 3-4. Is modulated light with an amplitude of 1 / 2A'B '.

  On the other hand, a transmission loss occurs due to the rotational axis mismatch of the optical rotary joint, and the incident light to the optical electric field sensor head changes from P0 to P1, as shown in FIG.

  When a voltage of ± Vi is applied between the parallel electrodes of the optical electric field sensor head as in FIG. 3, the operating curve becomes FIG. 4-2 and the operating point OP2 becomes lower than OP1, and the amplitude of the transmitted modulated light Becomes 1 / 2C'D '.

  Here, by amplifying OP2 ′ in FIG. 3-4 to OP1 ′, the amplitude 1 / 2C′D ′ can be set to 1 / 2A′B ′, and the transmission loss of the optical rotary joint can be corrected. it can.

  The operating points OP1 'and OP2' are obtained by the time average value of FIGS. 3-4 and 4-4 or the DC output by low-pass filter transmission.

  Therefore, if a gain is constantly adjusted so that the operating point OP2 becomes a constant value by installing a variable amplifier in the optical circuit or the electric circuit, the transmission loss fluctuation of the optical rotary joint can be corrected.

Furthermore, after installing multiple photoelectric magnetic field sensors with different wavelengths, combining them with a multiplexer, passing through an optical rotary joint, separating them for each wavelength again with a demultiplexer, each E / O converter Incident.
The light modulated by the E / O converter is combined and separated through the optical rotary joint in the reverse process to the incident state, and then demodulated into an RF signal by each O / E converter. .

  FIG. 1 shows a basic configuration of a system for measuring a 2CH antenna simultaneously by installing an optical rotary joint in a reflective optical electric field sensor with a feedback circuit according to an embodiment of the present invention. A multiplexer and demultiplexer are installed before and after.

  In FIG. 1, a laser light source with a feedback circuit and a detector (referred to as a controller) 38 and a photoelectric magnetic field sensor head 4 are operated at a wavelength of 1550 nm, and a controller 38 ′ and a photoelectric magnetic field sensor head 4 ′ are operated at 1530 nm. .

  In this system, the laser light emitted from the controllers 38 and 38 'is combined with light of 1550 nm and 1530 nm by the multiplexer 24, and the combined light is incident on the optical rotary joint. After that, the combined light that has passed through the optical rotary joint is again separated into 1550 nm and 1530 nm by a demultiplexer, and is incident on each E / O converter.

  Next, the radio wave transmitted from the transmitting antenna 26 is received by the antenna under measurement 36 and the antenna under measurement 36 ′, and power is input to the E / O converter 4 and the E / O converter 4 ′ connected thereto. The

  Unmodulated light having a wavelength of 1550 nm is input to the E / O converter 4, and modulated light is output by the received power input from the antenna under measurement 36. Similarly, unmodulated light having a wavelength of 1530 nm is input to the E / O converter 4 ′, and modulated light is output by electric power input from the antenna to be measured 36 ′.

  The modulated light having a wavelength of 1550 nm from the optical fiber 2 and the modulated light having a wavelength of 1530 nm from the optical fiber 2 ′ are combined in the reverse direction through the duplexer and are incident on the optical rotary joint. Thereafter, the signal is demultiplexed by passing through a multiplexer, is incident on each RF demodulation circuit, and is emitted as an RF signal of each CH. By passing through the feedback circuit at this time, the fluctuation of the transmission loss due to the deviation due to the rotation of the optical rotary joint is corrected, and a stable output can be obtained. Furthermore, since laser beams having different wavelengths are used for signal transmission, multi-channel antenna evaluation can be performed using a single optical rotary joint.

  The light source of the photoelectric magnetic field sensor is not limited to the embodiment of the present invention because the same effect can be obtained even if the orthogonally polarized waves are combined by the two light sources and the multiplexer and incident on the E / O converter.

1, 1 ', 1'',1''' light source
2, 2 ', 2'',2''', 2 '''' optical fiber 1
3, 3 ', 3''optical fiber 2
4, 4 ', 4'',4''' sensor head
5 Feedback circuit
6 Polarizer
7 Wave plate
8 Analyzer
9 Electro-optic element
10, 10 'Lithium niobate single crystal substrate
11, 11 'Incident optical waveguide
12, 12 'phase shift optical waveguide
13 Output optical waveguide
14, 14 'parallel electrode
15, 15 ', 15``, 15''' antenna
16 Laser light
17, 17 ', 17``, 17''' photodetector
18 high frequency connectors
19 Optical circulator
20,20 'reflector
31 amplifier
32 Network analyzer
33 Turntable
34 RF rotary joint
35 Coaxial cable
36,36 'Antenna under test
37 Anechoic chamber
38, 38 'Laser light source / detector (controller) with feedback circuit
39,39 'optical magnetic field sensor head

Claims (6)

  An electric field / magnetic field / voltage detection apparatus comprising an optical rotary joint in a photoelectric magnetic field sensor including a feedback circuit including a variable amplifier including a constant output control circuit.   2. The photoelectric photoelectric sensor according to claim 1, wherein linearly polarized laser light is incident on an element having an electro-optic effect, and the polarization angle changes according to the applied electric field strength. Electric field / voltage detection device characterized by that.   2. The optical electric field sensor according to claim 1, wherein an optical waveguide is formed in an element having an electro-optic effect, linearly polarized laser light is incident, and a polarization angle changes in accordance with an applied electric field strength. An electric field / voltage detection device characterized by being a waveguide type optical electric field sensor.   2. The optical electric field sensor according to claim 1, wherein a muffler-Zehnder type optical waveguide is formed in an element having an electro-optic effect, linearly polarized laser light is incident, and light intensity modulation is performed in accordance with the applied electric field intensity. An electric field / voltage detection device characterized in that it is a waveguide type optical electric field sensor utilizing the above.   5. The electric field / voltage detection device according to claim 1, wherein a plurality of the photoelectric magnetic field sensors are provided, a multiplexer and a duplexer are installed before and after the optical rotary joint, and a multi-CH antenna can be measured.   6. The magnetic field detection device according to claim 1, wherein the magnetic field detection device is an element having a magneto-optical effect.