JPH05153095A - Data transmitting device - Google Patents

Abstract

PURPOSE:To execute highly reliable data transmission where noise originating from a switching operation is eliminated and a noise ratio against a signal is improved. CONSTITUTION:The output signal of a modulator 12 is converted into a microwave band by a frequency converter 13 and the output is divided into two by a hybrid 14 and respectively converted into optical signals by electric/optic converters 15 and 16 so as to be duplex-transmitted by optical fibers 17 and 18. The transmitted optical signals are returned to an intermediate frequency band by frequency converters 21 and 22 after respectively converted into electric signals by the optic/electric converters 15 and 16. Phase difference between two intermediate frequency band signals is detected by the phase detecting equipment 24 of a phase control part 23 and a phase control equipment 25 controls a phase converter 26 based on the phase difference. Thus, the phases of two intermediate frequency band output signals which are respectively outputted from the frequency converter 21 and 22 become same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission device using an optical fiber, and more particularly to a data transmission device of the type which directly transmits a microwave band radio band signal through the optical fiber.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a data transmission apparatus of this type has a modulator 12 for modulating an input data signal into a signal in an intermediate frequency band, and a modulator output from the modulator 12. A frequency converter 13 that frequency-converts a signal into a microwave band, and an electro-optical converter (E / E) that converts the microwave output from the frequency converter 13 into an optical signal.
O) 15, an optical fiber 17 for transmitting the optical signal output from the electro-optical converter 15, and an optical fiber 17
The optical-electrical converter (O / E) 19 for frequency-converting the optical signal transmitted by the optical signal into the microwave band, and the optical-electrical converter 1
9. The frequency converter 21 for returning the microwave output from 9 to the intermediate frequency band, the AGC amplifier 29 for amplifying the signal in the intermediate frequency band output from this frequency converter 21, and the amplified signal for returning to the data signal. The demodulator 30 is connected in series between the transmission signal input terminal 11 and the reception signal output terminal 31.

In the data transmission apparatus having such a configuration, the data signal input from the transmission signal input terminal 11 is applied to the modulator 1.
2 is modulated into an intermediate frequency band signal, then converted to a microwave band by a frequency converter 13, and then converted into an electric band.
It is converted into an optical signal by the optical converter (E / O) 15.
After the converted optical signal passes through the optical fiber 17, the optical signal
It is returned to the microwave band by the electric converter (O / E) 19, frequency-converted to the intermediate frequency band by the frequency converter 21, amplified by the AGC amplifier 29, and then demodulated into a data signal by the demodulator 30. To be done.

In the data transmission device using the optical fiber as described above, the wavelength of the optical signal changes depending on the input current to the laser diode used as the light emitting element of the electro-optical converter 15. It has been known. Therefore, when trying to increase the reliability of the transmission line, the electric-
It is necessary to use a high quality light emitting element used for the light converter 15, which causes a problem that the entire device becomes expensive.

For this reason, the dual transmission system has been conventionally used as a data transmission device. An example of an apparatus according to this system is shown in FIG. The same components as those of the device shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

This data transmission apparatus has a transmission signal input terminal 1
1 and the reception signal output end 31 between the transmission signal input end 11
A hybrid (branching device) that splits the input signal from
4 and two electro-optical converters 15 and 16 for converting the signals branched by the hybrid 14 into optical signals, respectively.
And optical fibers 17, 18 for transmitting the optical signals converted by the electro-optical converters 15, 16, respectively, and an opto-electric converter for converting the signals transmitted by the optical fibers 17, 18 into electric signals. 19 and 20 and a selection switch 32 whose movable contact is switched to either one of the output ends of the opto-electric converters 19 and 20.

In the data transmission device of the double transmission system, the input signal is divided into two and the respective electro-optical converters 1 are separated.
5, 16, optical fibers 17, 18, optical-electrical converter 1
9 and 20 are transmitted, and either output signal is selected by the selection switch 32.

[0008]

However, in this conventional data transmission device, the opto-electric converters 19 and 20 are used.
Since the transmission signal is shocked each time the selection switch 32 in the output section of the device operates, this causes noise to cause an error in the data signal.

The present invention has been made in view of the above problems, and an object thereof is to improve a signal-to-noise ratio without causing a shock to a data signal due to a conventional switching operation.
It is to provide a data transmission device with improved reliability.

[0010]

A data transmission device of the present invention comprises a frequency converter for frequency-converting an input data signal into a microwave band, a branching device for branching an output signal of the frequency converter into two, and a branching device for branching the output signal. And two electric-optical converters for converting the output signals of the respective devices into optical signals.
Two optical fibers that respectively transmit the optical signals output from the optical converter, two optical-electrical converters that respectively convert the optical signals transmitted by these optical fibers into electrical signals, and these optical-optical converters. Two frequency converters for frequency-converting the output signal of the electric converter into an intermediate frequency band, a phase control unit for controlling the phase so that the output signals of the two frequency converters are in phase with each other, and a local oscillation signal , A local oscillator that supplies the frequency converter directly to the other frequency converter and supplies the other frequency converter via the phase control unit, and the local oscillator that is phase-shifted to the same phase by the phase control unit. A combiner that combines the output signals of the two frequency converters,
And a demodulator for demodulating the output signal of this combiner.

Specifically, the phase controller includes a phase detector for detecting a phase difference between two intermediate frequency band output signals respectively output from the two frequency converters, and the other frequency converter. The phase shifter that changes the phase of the supplied local oscillation signal and the phase shifter are controlled based on the phase difference detected by the phase detector so that the phases of the outputs of the two frequency converters become the same phase. And a phase controller for controlling.

In the data transmission apparatus of the present invention, the input data signal is frequency-converted into the microwave band by the frequency converter and then branched into two by the branching device. Each output signal of the branching device is converted into an optical signal by two electric-optical converters, transmitted by two optical fibers, and then converted into an electric signal in a microwave band by two optical-electrical converters. To be converted. Thereafter, these electric signals are frequency-converted into intermediate frequency bands by two frequency converters, respectively, and are controlled by the phase controller so that the phases of these signals are in phase. The output signals of the two frequency converters that have been phase-shifted by the phase control unit are combined by a combiner and then demodulated to the original signal.

[0013]

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

FIG. 1 is a block diagram showing the configuration of a data transmission device according to an embodiment of the present invention. The same components as those shown in FIGS. 2 and 3 are designated by the same reference numerals and the description thereof will be omitted.

In the data transmission apparatus of this embodiment, the transmission signal input terminal 11 is provided with a modulator 12, and then a frequency converter 13,
Further, a hybrid (branching device) 14 is connected,
The hybrid 14 is designed so that the data transmission system is branched into two. Electro-optical converters 15 and 16, optical fibers 17 and 18, optical-electrical converters 19 and 20, and frequency converters 21 and 22 are connected in series to the transmission system branched by the hybrid 14, respectively. The transmission system that has been branched into two by the hybrid (combiner) 28 is integrated to combine the data. The hybrid 28 includes an AGC amplifier 29 that amplifies the output of the hybrid 28 to a certain level, and the AGC amplifier 2
A demodulator 30 for demodulating the signal amplified in 9 is connected in series, and the demodulated signal of this demodulator 30 is received signal output terminal 31.
Will be output from.

A phase controller 23 is connected between the output terminals of the frequency converters 21 and 22 to control the phases of the two so that they are in phase with each other. The phase control unit 23 includes a phase detector 24 that detects a phase difference between the intermediate frequency band output signals output from the frequency converters 21 and 22, and two phase detectors based on the phase difference detected by the phase detector 24. A phase controller 25 for controlling the output signals of the intermediate frequency band to have the same phase, and a phase shifter 26 controlled by the phase controller 25.
It consists of and. A local oscillator signal is supplied from a local oscillator 27 to the frequency converter 21 and the frequency converter 22, respectively. Here, the local oscillation signal supplied to the frequency converter 22 passes through the phase shifter 26 of the phase controller 23, and the phase is controlled by the phase shifter 26.

Next, the operation of the data transmission device having the above configuration will be described. The signal input from the transmission signal input terminal 11 is modulated into an intermediate frequency band signal by the modulator 12, frequency-converted into a microwave band signal by the frequency converter 13, and then branched into two by the hybrid 14.
Each of the two branched microwave band signals is converted into an electro-optical converter 1
After being converted into an optical signal by 5, 16, the optical fiber 1
7 and 18 are transmitted. These optical fibers 17, 1
The optical signal transmitted by 8 is converted into a microwave band signal by the optical-electrical converters 19 and 20, respectively, and then converted into an intermediate frequency band signal by the frequency converters 21 and 22. The two converted intermediate frequency band signals are combined by the hybrid 28, amplified by the AGC amplifier 29 to a certain level, demodulated by the demodulator 30, and then output from the reception signal output terminal 31.

The intermediate frequency band signal synthesized by the hybrid 28 is always synthesized in phase by the following operation of the phase controller 23.

A part of the intermediate frequency band signal output from the frequency converters 21 and 22 is input to the phase detector 24, and 2
The phase difference between the two intermediate frequency band signals is detected. FIG. 4 shows the characteristics of the phase detector 24. The phase controller 25 generates a control signal to rotate the phase shifter 26 in the direction in which the phase difference output from the phase detector 24 becomes zero. In response to this control signal, the phase shifter 26 causes the local oscillator 2
Among the local transmission signals transmitted from 7 to the frequency converters 21 and 22, the phase of the local transmission signal transmitted to the frequency converter 22 side is changed. As a result, the phase of the intermediate frequency band output signal output from the frequency converter 22 changes so as to approach the phase of the intermediate frequency band signal output from the frequency converter 21. By performing the above operation continuously, the two intermediate frequency band signals always have the same phase, and are then combined by the hybrid 28.

As described above, according to the data transmission apparatus of this embodiment, since the dual transmission system is adopted and the switch for selecting one of the two transmission systems is not required, it is different from the conventional one. The noise generated by switching could be eliminated. Further, since the output signals of the two optical-electrical converters 19 and 20 are combined in phase, the signal-to-noise ratio (C / N ratio) is improved by 3 dB as compared with the case of transmitting using one optical fiber. Was done.

[0021]

As described above, according to the data transmission apparatus of the present invention, the frequency converter for converting the frequency of the input data signal into the microwave band and the branching device for branching the output signal of the frequency converter into two. , Two electro-optical converters for converting each output signal of this branching device into an optical signal, and these two
Two optical fibers each transmitting an optical signal output from one electro-optical converter, two optical-electric converters converting each optical signal transmitted by these optical fibers into an electrical signal, and these optical fibers Frequency converters for converting the output signals of the opto-electric converters to an intermediate frequency band, a phase controller for controlling the phases so that the output signals of the two frequency converters have the same phase, and a local part The oscillation signal is directly supplied to the one frequency converter, and the other frequency converter is phase-shifted to the same phase by a local oscillator that is supplied via the phase controller and the phase controller. Since a synthesizer for synthesizing the output signals of the two frequency converters and a demodulator for demodulating the output signals of the synthesizer are provided, one of two transmission systems as in the conventional case is selected. Do Because of the selection switch is not required,
The noise generated by conventional switching can be eliminated. In addition, since the outputs of the two optical-electrical converters are combined in phase, the signal-to-noise ratio is improved compared to transmission using a single optical fiber, and a high-quality transmission line can be provided. effective.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a data transmission device of the present invention.

FIG. 2 is a block diagram showing an example of a conventional data transmission device.

FIG. 3 is a block diagram showing an example of a conventional data transmission device.

FIG. 4 is a characteristic diagram showing a relationship between a phase difference between two waveform signals and an output from a phase detector.

[Explanation of symbols]

 11 Transmission Signal Input Terminal 12 Modulator 13, 21, 22 Frequency Converter 14, 28 Hybrid 15, 16 Electric-Optical Converter 17, 18 Optical Fiber 19, 20 Optical-Electrical Converter 23 Phase Control Section 24 Phase Detector 25 Phase controller 26 Phase shifter 27 Local oscillator 29 AGC amplifier 30 Demodulator 31 Received signal output end

Claims (2)

[Claims] 1. A frequency converter that frequency-converts an input data signal into a microwave band, a branching device that branches an output signal of the frequency converter into two, and an output signal of each branching device is converted into an optical signal. Two electro-optical converters, two optical fibers that respectively transmit the optical signals output from these two electro-optical converters, and the optical signals transmitted by these optical fibers are converted into electrical signals. Two optical-electrical converters for converting, two frequency converters for frequency-converting output signals of these optical-electrical converters to an intermediate frequency band, and output signals of the two frequency converters are in phase with each other. And a local control signal that supplies a local oscillation signal directly to the one frequency converter and supplies the other frequency converter to the other frequency converter via the phase control unit. And a synthesizer for synthesizing the output signals of the two frequency converters shifted in phase by the phase control unit, and a demodulator for demodulating the output signals of the synthesizer. Data transmission equipment. 2. The phase control unit is supplied to a phase detector that detects a phase difference between two intermediate frequency band output signals respectively output from the two frequency converters, and the other frequency converter. The phase shifter that changes the phase of the local oscillation signal and the phase shifter are controlled based on the phase difference detected by the phase detector so that the outputs of the two frequency converters have the same phase. The data transmission device according to claim 1, wherein the data transmission device comprises a phase controller.