JP2006345287A - Radio wave receiving optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave receiving optical transmission system having a wide dynamic range also adaptable to intensive radio wave signals with raising the sensitivity. <P>SOLUTION: The radio wave receiving optical transmission system comprises: optical sources 20a, 20b for generating no-modulation lights; a single mode optical fiber 18b for transmitting the no-modulation signals; a plurality of optical modulators for modulating the no-modulation signals with electric signals; an antenna 11 for receiving radio waves; a filter 12; a divider 13 for dividing a signal passed through the filter into a plurality of signals; an electric amplifier 14a for amplifying at least one of the divided signals and inputting it to the optical modulators; single mode optical fibers 18d, 18c for transmission modulated lights by the optical modulators; and an O/E converter for converting the transmitted modulated lights to electric signals. The system is set so that the electric signals having mutually different intensities are applied to the plurality of optical modulators. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a sensing device that detects or measures an electric field using an optical modulator, or receives an electric wave using an optical modulator, converts it into an optical signal, transmits it, and then converts it again into an electrical signal. More particularly, the present invention relates to a radio wave reception / transmission system including an optical modulator using a branching interference type optical waveguide suitable for use in a radio wave relay apparatus for broadcasting and communication.

  There are several types of radio wave receiving / optical transmission devices provided with a conventional optical modulator based on a branched interference type optical waveguide. For example, it is shown in patent documents 1-5. The most basic conventional configuration example is shown in FIG. In FIG. 4, 41 is an antenna for receiving radio waves, 42 is an optical modulator using a branched interference optical waveguide, 43a is a polarization maintaining optical fiber, 43b is a single mode optical fiber, 44 is a light source that emits unmodulated light, 45 Is an O / E converter. An electric signal received by the antenna 41 is applied to the optical modulator 42. Light emitted from the light source 44, transmitted through the polarization maintaining optical fiber 43a, and incident on the optical modulator 42 is modulated by the received signal. The modulated light is transmitted through the single mode optical fiber 43b and enters the O / E converter 45, and the received signal is detected.

  With such a configuration, a device that receives radio waves, converts them into optical signals, transmits them, and converts them back into electric signals is used as a radio wave relay device or an electric field sensing device.

JP 9-015280 A JP-A-9-008737 JP 9-159707 A Japanese Patent Laid-Open No. 10-068750 JP 2003-107418 A

  In the radio wave reception / optical transmission apparatus as described above, an electric amplifier or the like is inserted in the input portion of the optical modulator in order to obtain the necessary sensitivity when the received signal is weak. However, when an electric amplifier is used to increase sensitivity as described above, distortion such as third-order intermodulation occurs when the received signal strength increases. As a result, when a strong radio wave is received, the received signal cannot be transmitted without significant deterioration due to the distortion.

  Therefore, an object of the present invention is to provide a radio wave reception / optical transmission system having a wide dynamic range that can cope with a strong radio wave signal while increasing sensitivity.

  In the radio wave reception / optical transmission system of the present invention, a plurality of optical modulators are used, the received signals from the antenna are distributed by the distributor, and applied through an electric amplifier, whereby different intensities are applied to the optical modulators described above. The received signal is set to be applied. These modulated optical signals are detected by an O / E converter, and an optimum signal with less distortion is selected and output.

  Also, the distribution ratio of the received signal distributed by the distributor is set so as to be greatly different, and a strong signal with a high distribution ratio is passed through an electric amplifier and input to the optical modulation by making it a stronger signal. On the other hand, a weak signal with a low distribution ratio can be transmitted without distortion even when an excessive radio wave signal is input by directly inputting it to the optical modulator.

  As described above, a wide dynamic range is achieved by setting an optical modulator corresponding to various radio wave signal intensities inputted and setting the input signal intensity thereto.

  That is, in the radio wave reception / optical transmission system of the present invention, a light source that generates unmodulated light, an optical fiber that transmits the unmodulated light, and a plurality of optical modulators that modulate the unmodulated light with an electrical signal; An antenna that receives radio waves, an input filter that passes a target frequency component of the received electrical signal, a distributor that distributes the signal that has passed through the input filter into a plurality, and at least one of the distributed At least one electric amplifier for amplifying and inputting two signals to the optical modulator, an optical fiber for transmitting the modulated light modulated by the optical modulator, and converting the transmitted modulated light into an electrical signal In the radio wave reception / optical transmission system including the O / E converter, the electrical signals having different intensities are applied to the plurality of optical modulators.

  In the radio wave reception / optical transmission system of the present invention, a light source that generates unmodulated light, an optical fiber that transmits the unmodulated light, and a plurality of optical modulators that modulate the unmodulated light with an electrical signal; An antenna that receives radio waves, an input filter that passes a target frequency component of the received electrical signal, a distributor that distributes the signal that has passed through the input filter into a plurality, and at least one of the distributed At least one electric amplifier for amplifying and inputting two signals to the optical modulator, an optical fiber for transmitting the modulated light modulated by the optical modulator, and converting the transmitted modulated light into an electrical signal In the radio wave reception / optical transmission system including the O / E converter, an electrical signal is applied to at least one of the plurality of optical modulators through the electrical amplifier, At least one of the number of light modulators may be set so that an electrical signal is directly applied from the distributor.

  Further, in the radio wave reception / optical transmission system of the present invention, it may be set such that two or more electric signals having different strengths are distributed by the distributor.

  The radio wave reception / optical transmission system of the present invention may further include a polarization coupler for distributing unmodulated light transmitted by an optical fiber to the plurality of optical modulators.

  In the radio wave reception / optical transmission system of the present invention, the power for driving the electric amplifier can be supplied by optical power feeding.

  In the radio wave reception / optical transmission system according to the present invention, an optimum signal is selected from a plurality of received signals modulated by the plurality of optical modulators and detected by the O / E converter after being transmitted through the optical fiber. A function of selecting and outputting a received signal may be provided.

  As described above, according to the present invention, there is provided a radio wave reception / light transmission system having a wide dynamic range in which a permissible range of receivable power is expanded while maintaining high sensitivity and capable of dealing with strong radio wave signals. It becomes possible to provide.

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

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration example of a radio wave reception / optical transmission system according to the present invention. 11 is an antenna that receives radio waves, 12 is a filter, 13 is a distributor, 14a and 14b are electrical amplifiers, 15a and 15b are sensor heads composed of optical modulators, 16 is an optical power feeding unit, and 17 is polarization. Couplers 18a, 18b, 18c, and 18d are single mode optical fibers, 19 is a light source for optical power supply, 20a and 20b are light sources that generate unmodulated light, 21 is a polarizing prism, and 22a and 22b are O / E converters. , 23a and 23b are electric amplifiers, 24a and 24b are distributors, 25a and 25b are detectors, 26 is a control circuit, and 27 is an RF selector switch. Here, of the lines connecting the blocks, a thick line represents a light path made of an optical fiber, and an arrow in a circle shown in the vicinity thereof represents a polarization direction. Moreover, the line of normal thickness has shown the path | route through which an electrical signal passes. And the arrow of one direction shown along these paths represents the direction through which electricity or light flows.

  Regarding the operation of this system, first, an optical power feeding method will be described. The light generated by the light source 19 for power supply installed at the transmission point is transmitted to the reception point of the radio wave by the single mode optical fiber 18a, converted into electric power at the optical power supply unit 16, and the electric amplifiers 14a and 14b. To be supplied. Here, the optical power source 19 is a semiconductor laser having a wavelength of 1.48 μm and an output of 200 mW. The optical power feeding unit 16 is configured using a photodiode and a booster circuit.

  Next, optical modulation by radio waves, optical transmission, and electrical signal reproduction will be described. A radio wave received by the antenna 11 passes through a filter 12 that passes a signal in the reception band, enters a distributor 13, and powers two signals: a signal having most of the received power and a signal having only a part of the received power. Is distributed. As the distributor 13, a directional coupler or the like can be used.

  Thereafter, a signal having most of the received power of the radio wave is input to the electric amplifier 14a, amplified, and input to the sensor head 15a. On the other hand, a signal having only a part of the received power is input to the sensor head 15b via the electric amplifier 14b having a small amplification degree. At this time, a variable gain amplifier may be used as the electrical amplifier.

Next, the configuration of the sensor heads 15a and 15b will be described with reference to FIG. FIG. 2A is a block diagram showing the configuration of the sensor head. Each of the sensor heads 15a and 15b includes a resonance circuit 37 and an optical modulator 38 using a branch interference type optical waveguide made of a LiNbO ₃ crystal. The structure of the optical modulator 38 is shown in a perspective view in FIG. 31a and 31b are optical fibers made of either polarization maintaining optical fibers or single mode optical fibers, 35 is a LiNbO ₃ substrate, 32a and 32b are input / output optical waveguides, 33a and 33b are phase shift optical waveguides, and 34a and 34b are A modulation electrode, to which an electrical signal is applied via a resonance circuit. The input non-modulated light passes through the optical modulator 38 and is intensity-modulated by the electric signals applied to the modulation electrodes 34a and 34b.

  Next, a method of supplying unmodulated light to the sensor heads 15a and 15b will be described with reference to FIG. The light sources 20a and 20b are semiconductor lasers and output linearly polarized waves having a wavelength of about 1.55 μm. Here, the two wavelengths are slightly different so that the frequency component due to the beat between the two wavelengths goes out of the reception band. The optical output is 100 mW, and these optical outputs are combined by the polarization prism 21 and then transmitted to the reception point of the radio wave by the single mode optical fiber 18 b and input to the polarization coupler 17.

  The polarization coupler 17 performs an operation of separating input light into two orthogonal polarization components. The two polarized light components output at this time have the same light intensity. The reason for this is that when attention is focused on one polarization component emitted from the polarization coupler 17, the intensity of the component having the wavelength generated by the light source 20a is changed by changing the refractive index of the single mode optical fiber 18b. This is because the intensity of the component having the wavelength generated by the other light source 20b is changed by an equal amount in the reverse direction even if is changed. This is because the linearly polarized light from the light source 20a and the linearly polarized light from the light source 20b are orthogonal when input to the single mode optical fiber 18b.

  In this way, the two outputs of the obtained polarization coupler 17 are guided to the sensor heads 15a and 15b by the polarization maintaining fiber. In the sensor head 15a, light intensity modulation is performed by the electric signal obtained by amplifying the signal having the most of the received power distributed by the distributor 13 by the electric amplifier 14a, and in the sensor head 15b, Light intensity modulation is performed by an electric signal obtained by amplifying the signal having only a part of the received power distributed by the distributor 13 by the electric amplifier 14b.

  The optical outputs of the sensor heads 15a and 15b are transmitted through the single mode optical fibers 18c and 18d, respectively, and are converted into electric signals at the transmission points by the O / E converters 22a and 22b, respectively.

  The converted electrical signals are amplified by the electrical amplifiers 23a and 23b and then input to the distributors 24a and 24b, respectively.

  The electric signals input to the distributors 24a and 24b are distributed, respectively, one output is input to the detectors 25a and 25b, and the other electric signal is input to the RF changeover switch 27.

  The signals detected by the detectors 25a and 25b are input to the control circuit 26. The control circuit 26 measures the received power from the respective detection outputs, determines which of the outputs of the distributors 24a and 24b is suitable, and performs RF switching. Switch 27 is switched. In addition, it is effective to suppress chattering when switching is determined.

  The means for feeding an electric amplifier by the above-described optical power feeding, the means for using an orthogonal polarized light source as an unmodulated light source, and the means for demultiplexing unmodulated light by a polarization coupler are disclosed in Patent Documents 2, 3, and 4, respectively. It is shown.

  In the present embodiment, when the signal of the radio wave is weak, the received signal is greatly amplified and high sensitivity is obtained by selecting the optical signal modulated by the sensor head 15a applied to the electrode of the optical modulator, When the signal of the radio wave is strong, the generation of distortion such as third-order intermodulation can be suppressed by selecting the optical signal modulated by the sensor head 15b applied to the electrode of the optical modulator without much amplification of the received signal. .

  Further, the distribution ratio of the distributor 13 and the amplification degrees of the electric amplifiers 14a and 14b can be set in accordance with the target radio signal intensity range. Further, as a method for feeding the electric amplifier, not only the optical feeding as in the above embodiment but also a battery or a solar battery can be used.

(Embodiment 2)
FIG. 3 is a block diagram showing the configuration of another embodiment of the radio wave reception / optical transmission system according to the present invention. The basic configuration is the same as that of the embodiment shown in FIG. 1, and the only difference is the electric amplifier inserted in FIG. 1 for a signal having only a part of the received power output from the distributor 13. 14b is not inserted.

  In this way, by eliminating the electrical amplifier at the front stage of the sensor head 15b, it is possible to reduce the power at the reception point, and it is possible to deal with a higher power radio signal, and to eliminate the influence of distortion of the electrical amplifier. Can do.

  In the radio wave reception / photoelectric transmission system according to the present invention, power is not transmitted to the reception point through the power line, and lightning damage at the reception point can be effectively prevented. In addition, since the reception point and the transmission point are connected by optical transmission, signal degradation due to the transmission is negligible, and it is easy to increase the distance between the reception point and the transmission point.

  Furthermore, in the radio wave reception / photoelectric transmission system of the present invention, a compensation method for polarization fluctuations required by using a single mode optical fiber, that is, a method of combining and using the polarization of two light sources orthogonally, and A highly practical system is realized by combining two optical modulators that operate with different signal intensities and a method that effectively uses two lights separated by a polarization coupler.

  As an example, it has been found from field experiment results that it is suitable for relaying terrestrial digital TV broadcast radio waves.

1 is a block diagram showing a configuration of a radio wave reception / optical transmission system according to an embodiment of the present invention. The figure which shows the structure of a sensor head. FIG. 2A is a block diagram showing the configuration of the sensor head. FIG. 2B is a perspective view showing a structure of an optical modulator using a branched interference type optical waveguide. The block diagram which shows the structure of the electromagnetic wave reception and optical transmission system by another embodiment of this invention. The figure which shows an example of the conventional electromagnetic wave reception and optical transmission apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Antenna 12 Filter 13 Divider 14a, 14b Electric amplifier 15a, 15b Sensor head 16 Optical power feeding part 17 Polarization coupler 18a, 18b, 18c, 18d Single mode optical fiber 19 Light source 20a, 20b for optical power supply Light source 21 Polarizing prism 22a, 22b O / E converters 23a, 23b Electric amplifiers 24a, 24b Dividers 25a, 25b Detector 26 Control circuit 27 RF change-over switches 31a, 31b Optical fibers 32a, 32b Input / output optical waveguides 33a, 33b Phase shift optical waveguides 34a, 34b Modulating electrode 35 LiNbO ₃ substrate 37 Resonant circuit 38 Optical modulator

Claims (6)

  A light source that generates unmodulated light, an optical fiber that transmits the unmodulated light, a plurality of optical modulators that modulate the unmodulated light with an electrical signal, an antenna that receives radio waves, and the received electrical signal An input filter that passes the target frequency component, a distributor that distributes the signal that has passed through the input filter into a plurality, and an amplifier that amplifies at least one distributed signal and inputs the amplified signal to the optical modulator Radio wave reception and optical transmission comprising at least one electrical amplifier, an optical fiber that transmits the modulated light modulated by the optical modulator, and an O / E converter that converts the transmitted modulated light into an electrical signal In the system, the radio wave reception / optical transmission system is set so that electric signals having different intensities are applied to the plurality of optical modulators.   A light source that generates unmodulated light, an optical fiber that transmits the unmodulated light, a plurality of optical modulators that modulate the unmodulated light with an electrical signal, an antenna that receives radio waves, and the received electrical signal An input filter that passes the target frequency component, a distributor that distributes the signal that has passed through the input filter into a plurality, and an amplifier that amplifies at least one distributed signal and inputs the amplified signal to the optical modulator Radio wave reception and optical transmission comprising at least one electrical amplifier, an optical fiber that transmits the modulated light modulated by the optical modulator, and an O / E converter that converts the transmitted modulated light into an electrical signal In the system, an electrical signal is applied to at least one of the plurality of light modulators through the electrical amplifier, and at least one of the plurality of light modulators is directly connected to the distributor. A radio wave reception / optical transmission system configured to receive a contact signal.   The radio wave reception / optical transmission system according to claim 1 or 2, wherein two or more electric signals having different intensities are distributed by the distributor.   4. The radio wave reception / optical transmission system according to claim 1, further comprising a polarization coupler for distributing unmodulated light transmitted by the optical fiber to the plurality of optical modulators.   5. The radio wave reception / optical transmission system according to claim 1, wherein electric power for driving the electric amplifier is supplied by optical power feeding. 6.   A function of selecting and outputting one optimum received signal from the plurality of received signals detected by the O / E converter after being modulated by the plurality of optical modulators and transmitted through the optical fiber; The radio wave reception / optical transmission system according to any one of claims 1 to 5,

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