JPH0918422A - Optical transceiver - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] The polarization state of the optical main signal is changed by the clock synchronized with the main signal, and the effect of polarization fluctuation is affected by the polarization component of the optical signal received through the optical fiber. Without receiving the clock, the clock is extracted and the main signal synchronized with this is reproduced. An electric / optical converter 22 receives a main signal of an electric signal and converts the main signal into a light intensity-modulated optical main signal, and a polarization scrambler 25 cyclically changes the polarization state of the optical main signal. Output to. Next, the demultiplexer 41 demultiplexes the optical signal transmitted via the optical fiber 3, and the first light receiver 42 converts the first optical signal demultiplexed by the demultiplexer into an electrical signal. Further, the polarization state detector 50 converts the change in the polarization state into an electric signal by the second optical signal demultiplexed by the demultiplexer, and the clock extraction circuit 55 changes the polarization from the output of the second photodetector 54. Extract the scramble frequency. Then, the receiver 43 reproduces the main signal based on the output of the first light receiver 42 and the clock extracted by the clock extraction circuit 55.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission / reception apparatus for polarization-scrambling an optical signal of a main signal with a clock of the signal and transmitting it by an optical fiber.

[0002]

[Prior art]

Conventional example 1. In the ultra high-speed optical time division multiplex transmission system, it becomes difficult to extract a clock in the optical receiver. Therefore, a method of transmitting the clock at a wavelength different from that of the signal has been proposed. FIG. 14 shows Y. Miyamoto et al, “D
ata and Clock WDM Transmi
session using 20 Gbit / s Ele
ctric Demultiplexer with
Waveguidepin Photodiode I
interface ”, ECOC'94, pp.755-
758 (issued in 1994).

In FIG. 14, a main signal and a clock signal are input from 1a and 1b, respectively. Electric / optical converter 2a
Converts the main signal into an optical signal of wavelength λa. The electrical / optical converter 2b converts the clock signal into an optical signal of wavelength λb.
WDM (Wavelength-Division-Multiplexing) coupler 3
Output lights from the electro-optical converters 2a and 2b are combined by a and sent to the optical fiber 3 which is a transmission path. In the optical receiver, the WDM coupler 3b demultiplexes the light having the wavelengths λa and λb and inputs the demultiplexed lights to the optical filters 5a and 5b, respectively.
The optical filter 5a has a wavelength λa, and the optical filter 5b has a wavelength λa.
b is selectively transmitted. Reference numerals 6a and 6b denote light receivers that convert an optical signal into an electric signal, and output a main signal and a clock signal, respectively. The main signal is output from 7a and the clock signal is output from 7b.

Conventional example 2. FIG. 15 shows Japanese Patent Laid-Open No. 63-1802.
32, in which the main signal and the sub signal are 1
Input from a and 1b. 2 is an electric / optical converter,
Converts the main signal into an optical signal. 9 is a polarization modulator,
The plane of polarization of the main signal is modulated in synchronization with the sub signal. The transmission line is composed of the polarization-maintaining optical fiber 30. The plane of polarization is the direction V orthogonal to the main strain direction of the polarization-maintaining optical fiber when the sub-signal is "1", and the direction parallel to the main strain direction of the polarization-maintaining optical fiber when the sub-signal is "0". It is modulated by the polarization modulator 9 to be H. In the optical receiver, the polarization beam splitter 10 demultiplexes the polarization planes into directions H and V, and the light of the polarization plane of the direction V is input to the light receiver 6a and the light of the polarization plane of the direction H is input to the light receiver 6b. To be done. The output of the light receiver 6a and the output of the light receiver 6b are combined by the adder 11 to demodulate the main signal.
The sub-signal is demodulated from the output of b.

[0005]

The conventional example 1 has a drawback in that two electric / optical converters and two light receivers are required. In addition, the transmission line must transmit two wavelengths. A component having wavelength dependency such as an optical amplifier may be inserted in the optical fiber that is the transmission path, and it is not easy to transmit two different wavelengths. In the conventional example 2, since an optical receiver that accurately transmits polarization plane information and receives an optical signal in a specific polarization direction is used, an expensive polarization-maintaining optical fiber that does not cause polarization fluctuation is essential. There was a problem. Further, there is a problem that an adder is required for demodulation of the main signal, which makes the configuration complicated.

The first purpose is to perform optical intensity modulation of the main signal and polarization scramble of the clock by using light of one wavelength,
It is to transmit the main signal and the clock without being affected by the polarization fluctuation in the optical fiber.

A second object is to scramble the polarization of an optical signal obtained by time-division-multiplexing a plurality of main signals with a clock, and transmit the optical multiplexed signal and the clock without being affected by polarization fluctuations in the optical fiber. Is.

A third object is to extract a stable clock which is hardly influenced by polarization fluctuation of an optical fiber by using a wave plate.

A fourth object is to facilitate the manufacture of a high frequency circuit for polarization scramble driving by increasing the amplitude of the signal for polarization scramble driving and lowering the driving frequency.

A fifth object is to facilitate the manufacture of a high-frequency circuit for polarization scramble driving by lowering the frequency of the signal for driving the polarization scrambler by connecting the polarization scramblers in cascade.

The sixth object is to
This is to stop the driving of the polarization scrambling and reduce the power consumption of the drive circuit for the polarization scrambling.

A seventh object is to obtain a main signal whose light intensity is modulated,
It is intended to transmit a main signal, a clock and a sub signal by polarization scrambling with a signal obtained by frequency-modulating a clock with a sub signal of a predetermined frequency.

An eighth object is to switch a sub signal having a predetermined frequency and the clock while transmitting the main signal in synchronization with the clock so that the sub signal can be transmitted while the synchronization can be maintained even if the clock runs out. It is what

[0014]

An optical transmitter / receiver according to a first aspect of the present invention comprises an electric / optical converter for receiving a main signal of an electric signal and outputting a light intensity-modulated optical signal, and an electric / optical converter. A polarization scrambler that periodically changes the polarization state of the optical signal and outputs it to the optical fiber, and a polarization scrambler that periodically changes the polarization state of the optical signal based on a clock that is synchronized with the main signal A polarization scrambler driving circuit for driving, a demultiplexer for demultiplexing the optical signal transmitted through the optical fiber, and a first demultiplexer for converting the first optical signal demultiplexed by the demultiplexer into an electrical signal. A light receiver, a polarization state detector that converts a change in polarization state into an electric signal by the second optical signal demultiplexed by the demultiplexer, and polarization based on the electric signal from the polarization state detector A clock extraction circuit for extracting a scramble frequency and reproducing a clock; It is obtained by a receiver for reproducing a main signal based on a clock output and a clock extracting circuit of the optical device is extracted.

An optical transmitter / receiver according to a second aspect of the present invention includes an electric / optical converter which receives a plurality of main signals synchronized with each other and outputs an optical main signal whose light intensity is modulated, and a plurality of optical signals from the electric / optical converter. An optical multiplexer that multiplexes the main signal in a time division manner and outputs an optical signal, a polarization scrambler that periodically changes the polarization state of the multiplexed optical signal and outputs it to an optical fiber, and a polarization scrambler. A polarization scrambler drive circuit that drives to periodically change the polarization state of the optical signal based on the clock that is synchronized with the main signal, a demultiplexer that receives and demultiplexes the optical signal from the optical fiber, and a demultiplexer. Demultiplexer that demultiplexes the first optical signal demultiplexed by the optical demultiplexer into a plurality of optical main signals, and polarized wave that converts the change in the polarization state into an electrical signal by the second optical signal demultiplexed by the demultiplexer Based on the electrical signals from the state detector and the polarization state detector, the polarization A clock extracting circuit for extracting a amble frequency and reproducing a clock, and a receiver for reproducing a plurality of optical main signals separated by an optical demultiplexer based on the clock extracted by the clock extracting circuit into a main signal. .

An optical transmitter / receiver according to a third aspect of the present invention is a polarizer that transmits only a polarized component of a fixed second direction of the demultiplexed second optical signal, and a optical signal that converts the optical signal from the polarizer into an electrical signal. And two light receivers.

An optical transmitter / receiver according to a fourth aspect of the present invention transmits the demultiplexed second optical signal with a phase difference of π / 2 between the polarized light perpendicular to the main axis and the polarized light horizontal. A four-wave plate, a polarizer that transmits only a polarization component of light from the quarter-wave plate in a certain direction, a second light receiver that converts an optical signal from the polarizer into an electric signal, and a second A wavelength plate control circuit for detecting the amplitude value of the output of the photodetector and controlling the rotation around the main axis of the quarter wavelength plate so as to increase the amplitude value is provided.

In the optical transmitter / receiver according to the fifth aspect of the invention, the optical signal has a phase difference π between polarized light perpendicular to the principal axis and polarized light horizontal to the principal axis.
1/2 wave plate with a phase difference of π
A two-wave plate, a polarizer for transmitting the second optical signal demultiplexed by the demultiplexer, and transmitting only a polarization component in a certain direction of the optical signal transmitted through the quarter-wave plate and the half-wave plate; A second photodetector for converting an optical signal from a child into an electric signal, and a quarter wave plate and a half wave plate for detecting the amplitude value of the output of the second photoreceiver and increasing the amplitude value. And a wave plate control circuit for controlling rotation around the main axis of the.

In the optical transmitter / receiver according to the sixth aspect of the present invention, the polarization scrambler converts the phase change amount π into one light wave of the orthogonal polarization component.
Is provided with a polarization scrambler drive circuit that drives with an amplitude that is an integral multiple of the voltage that can be obtained.

In the optical transmitter / receiver according to the seventh invention, an optical signal is input to a plurality of polarization scramblers cascade-connected in multiple stages and a leading polarization scrambler for receiving the optical signal from the electrical / optical converter. And a polarization scrambler drive circuit for driving the polarization scrambler by giving a delay corresponding to the time difference from the time when the optical signal is input to the own polarization scrambler.

The optical transmitter / receiver according to the eighth invention comprises a polarization scrambler drive circuit for stopping the drive of the polarization scrambler while light is not input to the polarization scrambler.

An optical transmitter / receiver according to a ninth aspect of the present invention is based on a frequency modulator which receives a sub-signal of a predetermined frequency and frequency-modulates the sub-signal by using a clock synchronized with the main signal as a carrier, based on the output of the frequency modulator. A polarization scrambler drive circuit for driving the polarization scrambler and a demodulator for demodulating the frequency-modulated sub-signal from the polarization state detector are provided.

An optical transmitter / receiver according to a tenth aspect of the present invention comprises a switcher which receives a sub-signal of a predetermined frequency and switches between a clock and the sub-signal synchronized with the main signal, and a polarization scrambler based on the output of the switcher. It is provided with a polarization scrambler driving circuit for driving and a detector for detecting the frequency of the sub-signal from the output of the polarization state detector.

[0024]

According to the first aspect of the invention, the electric / optical converter receives the main signal of the electric signal and outputs an optical signal whose optical intensity is modulated, and the polarization scrambler polarizes the optical signal from the electric / optical converter. The polarization scrambler driving circuit drives the polarization scrambler so as to periodically change the polarization state of the optical signal based on the clock synchronized with the main signal while the state is periodically changed and output to the optical fiber. . Next, the demultiplexer demultiplexes the optical signal transmitted through the optical fiber, and the first photodetector
The demultiplexed first optical signal is converted into an electric signal. Also,
The polarization state detector converts the change in the polarization state into an electrical signal by the demultiplexed second optical signal, and the clock extraction circuit determines the polarization scramble frequency based on the electrical signal from the polarization state detector. Extract and regenerate the clock. Then, the receiver reproduces the main signal based on the output of the first light receiver and the clock extracted by the clock extraction circuit.

In the second aspect of the invention, the electro-optical converter receives the plurality of main signals synchronized with each other and outputs the optical main signal whose light intensity is modulated, and the optical multiplexing device outputs the plurality of optical signals from the electro-optical converter. The main signal is time-division multiplexed and an optical signal is output. The polarization scrambler periodically changes the polarization state of the multiplexed optical signal and outputs it to the optical fiber, and the polarization scrambler drive circuit outputs the optical signal based on the clock that synchronizes the polarization scrambler with the main signal. It is driven so as to periodically change the polarization state of the signal. Next, the demultiplexer receives and demultiplexes the optical signal from the optical fiber, and the optical demultiplexer demultiplexes the demultiplexed first optical signal into a plurality of optical main signals. Further, the polarization state detector converts a change in the polarization state into an electric signal by the demultiplexed second optical signal. Then, the clock extraction circuit extracts the polarization scramble frequency based on the electric signal from the polarization state detector to regenerate the clock, and the receiver extracts a plurality of optical signals separated by the optical demultiplexer based on the extracted clock. The main signal is reproduced as the main signal.

In the third invention, the polarizer transmits only the polarized component in the fixed direction of the demultiplexed second optical signal,
The second light receiver converts the optical signal from the polarizer into an electrical signal.

In the fourth invention, the quarter wave plate transmits the demultiplexed second optical signal with a phase difference of π / 2 between the polarized light perpendicular to the principal axis and the polarized light horizontal to the main axis. The polarizer transmits only the polarized component of the light from the quarter-wave plate in a fixed direction. Then, the second photodetector converts the optical signal from the polarizer into an electric signal, and the wave plate control circuit detects the amplitude value of the output of the second photodetector to increase the amplitude value 1 /.
Rotation is controlled around the main axis of the four-wave plate.

In the fifth invention, a quarter wave plate and 1
The / 2 wave plate gives an optical signal a phase difference π / 2 and a phase difference π between the polarized light perpendicular to the main axis and the polarized light horizontal to allow transmission.
The second optical signal with the demultiplexed polarizer is 1/4 wave plate and 1 /
Only the polarized component in a certain direction of the optical signal transmitted through the two-wave plate is transmitted. Then, the second photodetector converts the optical signal from the polarizer into an electric signal, and the wave plate control circuit detects the amplitude value of the output of the second photodetector and makes it 1/4 so as to increase the amplitude value. Rotation is controlled around the main axes of the wave plate and the half wave plate.

In the sixth aspect of the invention, the polarization scrambler driving circuit drives the polarization scrambler with an amplitude that is an integral multiple of the voltage with which the phase change amount π is obtained for one light wave of the orthogonal polarization component.

In the seventh invention, a plurality of polarization scramblers cascade-connected in multiple stages are provided, and a polarization scrambler drive circuit of each stage receives the optical signal from the electro-optical converter. The polarization scrambler is driven with a delay corresponding to the time difference from the input of the optical signal to the input signal to the self-polarization scrambler.

In the eighth invention, the polarization scrambler driving circuit stops driving the polarization scrambler while light is not input to the polarization scrambler.

In the ninth invention, the frequency modulator receives the sub-signal of a predetermined frequency, frequency-modulates the sub-signal using the clock synchronized with the main signal as a carrier, and the polarization scrambler drive circuit is the frequency modulator. Drive the polarization scrambler based on the output. Then, the demodulator demodulates the frequency-modulated sub-signal from the polarization state detector.

In the tenth aspect of the invention, the switch receives the sub-signal of a predetermined frequency, switches between the clock synchronized with the main signal and the sub-signal, and the polarization scrambler drive circuit shifts the polarization based on the output of the switch. Drive the wave scrambler. Then, the detector detects the frequency of the sub signal from the output of the polarization state detector.

[0034]

【Example】

Embodiment 1 FIG. In this embodiment, polarization scrambling is carried out by a clock synchronized with the main signal and transmitted through an optical fiber, and the main signal is reproduced on the receiving side based on the clock extracted from the change in the polarization state. FIG. 1 is a block diagram showing the configuration of the optical transceiver of this embodiment. In the figure, 1
Is a main signal input terminal, 2 is an optical transmitter, 3 is an optical fiber,
Reference numeral 4 is an optical receiver, and 7 is an output terminal for the main signal.

In the optical transmitter 2, 21 is an oscillator for outputting a main clock signal, 22 is an electric / optical converter for converting the main signal into an optical signal, and 23 is a prescaler, which divides the main clock signal into integers. A clock signal for driving the polarization scrambler (hereinafter referred to as a drive clock signal) is output after the rotation. 2
Reference numeral 4 is a polarization scrambler drive circuit, and 25 is a polarization scrambler, which scrambles the output light of the electro-optical converter 22 with the output of the polarization scrambler drive circuit 24. 2
Reference numeral 51 is an optical input of the polarization scrambler 25, 252 is an optical output of the polarization scrambler 25, and 253 is a polarization scrambler drive signal.

In the optical receiver 4, 41 is a demultiplexer and 42
Is a light receiver, and 43 is a receiver. Reference numeral 50 denotes a polarization state detector that converts a change in polarization state into an electric signal, and includes a polarizer 53 and a light receiver 54. A clock extraction circuit 55 outputs a clock signal (hereinafter referred to as a reception clock signal) extracted from the change in polarization. A multiplexer 57 outputs a main clock signal that is an integral multiple of the frequency of the received clock signal.

Next, FIG. 2 shows a configuration of a peripheral circuit for driving the polarization scrambler 25 and a configuration example of the polarization scrambler 25. In the figure, 21 is an oscillator, 24 is a polarization scrambler drive circuit, 25 is a polarization scrambler, 251
Is a polarization scrambler light input, 10a and 10b are polarization beam splitters, 11 is a phase modulator, and 252 is a polarization scrambler light output.

Next, the operation will be described with reference to FIGS. 1 and 2. In FIG. 1, the electrical / optical converter 22 converts the main signal from the input terminal 1 into an optical signal by intensity modulation in synchronization with the main clock signal of the output of the oscillator 21, and converts the signal into a polarization scrambler 25.
Output to The prescaler 23 frequency-divides the main clock signal from the oscillator 21 into a frequency of 1 / integer, generates a drive clock signal for driving the polarization scrambler, and outputs the drive clock signal to the polarization scrambler drive circuit 24. However, the cycle of the drive clock signal is set to a sufficiently short cycle that is not affected by polarization fluctuation in the transmission line. In FIG. 2, the polarization scrambler 25 demultiplexes the optical signal input from the polarization scrambler optical input 251 into orthogonal polarization components by the polarization beam splitter 10a, one of the demultiplexed signals is vertical polarization, and the other is horizontal. If the polarized light is used, the vertically polarized light remains as it is.
Then, the horizontally polarized light is phase-modulated by the phase modulator 11 to be combined with the vertically polarized light by the polarization beam splitter 10b and output to the polarization scrambler light output 252.

Here, the phase modulator 11 phase-modulates the horizontally polarized light by the drive signal from the polarization scrambler drive circuit 24. For example, when a voltage is applied to the phase modulator 11 in FIG. 2, the phase of the horizontally polarized light changes, but the voltage at which the amount of phase change is π (hereinafter, half-wave voltage Vπ) is the amplitude and changes periodically. When a signal is added, the polarization state of the output light of the polarization scrambler 25 can be changed in that cycle. Therefore, if the polarization scrambler 25 is driven with the amplitude of the half-wave voltage Vπ and the cycle of the drive clock signal, the polarization scrambler 25 outputs the output light of the electro-optical converter 22, that is, the light intensity-modulated light. The polarization state of the main signal can be continuously changed in the cycle of the drive clock signal.

In the optical receiver 4, the optical signal from the optical fiber 3 is demultiplexed by the demultiplexer 41, and the photodetector 42 and the polarization state detector 5
Output to 0. The light receiver 42 performs optical / electrical conversion of the optical signal,
Output to the receiver 43. On the other hand, the polarization state detector 50
The polarizer 53 transmits only the polarization component in a specific direction to the optical signal from the demultiplexer 41, and the light receiver 54 performs optical / electrical conversion on the optical signal from the polarizer 53 to change the polarization state to an electrical signal. And outputs to the clock extraction circuit 55.

The clock extraction circuit 55 is the polarization state detector 5
The electric signal from 0 is passed through a narrow band filter incorporated in the clock extraction circuit 55 to extract a signal having the same frequency as the polarization scrambler drive clock signal of the optical transmitter 2 to generate a reception clock signal. The narrow band filter has a bandwidth that is not affected by polarization fluctuations for extracting the received clock signal. For example, a narrow band filter having a Q value (center frequency / half-value width) of about 1000 with respect to the center frequency is used. . The multiplexer 57 obtains the main clock signal by multiplying the frequency of the received clock signal by an integer. Then, based on the main clock signal and the output of the light receiver 42, the receiver 43
Reproduces the main signal and outputs it to the output terminal 7.

As described above, the polarization state of the optical main signal is changed by the clock synchronized with the optical main signal, and the clock is extracted from the polarization component of the optical signal received through the optical fiber 3. The clock can be extracted without being affected by fluctuations, and the main signal synchronized with this can be reproduced. Further, since the clock component is transmitted using the change frequency of the polarization state and the polarization state itself is not used as a signal, it is not necessary to use an expensive polarization maintaining fiber. Further, the clock extraction circuit can be composed of an electronic circuit which is simpler than the internal synchronization system which transmits and receives the main signal and the synchronization signal by modulating the light intensity.

Embodiment 2 FIG. In this embodiment, two main signals whose light intensity has been modulated are time-division multiplexed, and a clock is transmitted by polarization scrambling. FIG. 3 is a block diagram showing the configuration of the optical transceiver of this embodiment. In the optical transmitter 2 of FIG. 3, reference numeral 1a denotes an input terminal for the first main signal, 1b.
Is an input terminal for the second main signal, 22a and 22b are electrical / optical converters, 26 is an optical multiplexer, and electrical / optical converters 22a and
The optical signal from 22b is time-division-multiplexed and is configured by using, for example, an optical coupler. Next, in the optical receiving section 4, 46 is an optical demultiplexer for demultiplexing the time-division multiplexed optical signal, and for example, an optical switch or a modulator can be used. 42a and 42b are photodetectors, 43a and 43
b is a receiver, 7a is an output terminal for the reproduced first main signal, and 7b is an output terminal for the reproduced second main signal. Others are the same as those in the first embodiment, and the description thereof will be omitted.

Next, the operation will be described. In the optical transmitter 2, the electric / optical converters 22 a and 22 b are the oscillator 21.
The first and second main signals are converted into optical signals by intensity modulation in synchronism with the main clock signal output from the optical multiplexer 2
6 time-division-multiplexes the optical signals of the first main signal and the second main signal. Therefore, the transmission speed of the time division multiplexed optical signal is doubled. Then, the polarization scrambler drive circuit 24 drives the polarization scrambler 25 with the polarization scrambler drive signal 253 for the optical signal subjected to the optical time division multiplexing, and the polarization scrambler 25 causes the optical fiber 3 to operate. Output to.

Next, in the optical receiver 4, the demultiplexer 41
The polarization state detector 50 uses the polarizer 53 and the light receiver 54 to convert the optical signal from the transit optical fiber 3 into a periodic change in the optical polarization state into an electric signal. Then, as in the first embodiment, the clock extraction circuit 55 extracts the reception clock signal from the electric signal, and the multiplexer 57 generates a main clock signal that is an integral multiple of the frequency of the reception clock signal. And
An optical demultiplexer 4 is provided for demultiplexing the multiplexed optical signal from the optical fiber 3.
6 separates into a first optical main signal and a second optical main signal based on the main clock signal. In addition, the two separated optical signals are converted into electric signals by the light receiver 42a and the light receiver 42b, and the receivers 43a and 43b reproduce the first main signal and the second main signal using the main clock signal. To do. Other operations are the same as those in the first embodiment and will not be described.

In the above example, the example of optical multiplexing is two, but it is also possible to increase the degree of multiplexing, and the transmission rate of the intensity-modulated optical signal is high, but the polarization state is changed. The frequency does not have to be changed. That is, the frequency of the polarization scrambler drive signal may be the same as that in the first embodiment. Further, the clock extraction circuit 55 in the optical receiver 4 does not need to be changed.

Example 3. The present embodiment is intended to efficiently extract a stable clock from a change in the polarization state of an optical signal from an optical fiber by using a wave plate. FIG. 4 is a block diagram showing the configuration of this embodiment. In the optical receiving unit 4 in the figure, reference numeral 50 denotes a polarization state detector that converts a change in polarization state into an electric signal, and is composed of 51, 51a, 53, 54 and 56. Reference numeral 51 denotes a quarter-wave plate, which generates a phase difference of π / 2 with respect to a linear polarization state horizontal to the main axis of the quarter-wave plate and a linear polarization state perpendicular to the main axis. By rotating around the main axis of the quarter-wave plate 51, it is possible to change an arbitrary elliptical polarization into a linear polarization. However, the direction of the linearly polarized wave is determined by the elliptically polarized state of the input. 51a is 1 /
This is a four-wave plate driving device that rotates about the main axis of the quarter-wave plate 51. 56 is a wave plate control circuit, which is 1 /
The quarter-wave plate 51 is rotationally controlled via the four-wave plate driving device 51a. Others are the same as those in the first embodiment and the description thereof will be omitted.

Next, the operation will be described focusing on the polarization state detector 50. The other operations are the same as those in the first embodiment and will not be described. The optical signal from the optical fiber 3 is demultiplexed by the demultiplexer 41,
Output to the polarization state detector 50. By the way, the polarization state of the optical signal periodically changes due to the polarization scrambler. The polarization state detector 50 will be described below by focusing on the polarization state at a certain point. Is circularly polarized, for example, the quarter-wave plate 51 linearly polarizes and outputs the linearly polarized light to the polarizer 53, the polarizer 53 transmits only the polarized component in a specific direction, and the light receiver 54 outputs the optical signal from the polarizer 53. Is converted into an electric signal by optical / electric conversion, and is output to the clock extraction circuit 55. Next, the clock extraction circuit 55 extracts the reception clock signal having the same polarization scramble frequency from the output of the light receiver 54, and outputs it to the wave plate control circuit 56 and the multiplexer 57.

The wave plate control circuit 56 detects the amplitude value of the received clock signal and drives the quarter wave plate driving device 51a so that the amplitude value becomes large, and the quarter wave plate driving device 5 is driven.
1a rotates the quarter-wave plate 51 about the main axis. That is, the polarizer 5 is rotated by the rotation of the quarter-wave plate 51.
The polarization direction to 3 changes, and the amplitude of the received clock signal changes via the light receiver 54 and the clock extraction circuit 55. Then, the influence of the rotation of the quarter wave plate 51 is fed back to the wave plate control circuit 56, so that the wave plate control circuit 56 increases the amplitude of the reception clock signal so that the quarter wave plate 5
Rotation is controlled around 1 as the main axis. The control speed of the quarter-wave plate is sufficiently slower than the polarization scrambler frequency and higher than the polarization fluctuation generated in the transmission line.

Now, since the quarter-wave plate 51 can change an arbitrary elliptical polarization state into a linear polarization, for example, 1
When the quarter-wave plate 51 is rotationally controlled and the linear polarization direction is aligned with the transmission direction of the polarizer 53, the maximum amount of light is transmitted, and the photodetector 34 performs optical / electrical conversion, so that the maximum amplitude value is obtained. A clock signal is obtained. Therefore, the amplitude value of the clock signal can be maximized by the control of the wave plate control circuit 56, and the frequency component can be efficiently and surely extracted from the change in the polarization state of the light. Further, even if polarization fluctuations occur in the optical fiber 3, since the light is received by following the polarization direction of the fluctuations as described above, stable clock extraction can be performed. However, 1 /
Since the direction of the linearly polarized wave of the four-wave plate 51 is determined by the elliptical polarization state of the input, the polarization direction may not be matched with the direction in which the polarizer 53 transmits. For this reason, the efficiency of conversion into the change in light intensity cannot always be maximized by the polarizer 53.

Embodiment 4 FIG. Next, by adding a ½ wavelength plate to the configuration of FIG. 4 of the third embodiment, an example in which the efficiency of clock extraction is higher than that of the third embodiment without depending on the polarization state of the optical signal from the optical fiber 3 It is shown below. FIG. 5 shows an example in which quarter-wave plates and half-wave plates are connected in series. In the figure, reference numeral 50 denotes a polarization state detector for converting a change in polarization state into an electric signal 51, 51a. , 52, 52a, 53, 5
It consists of 4, 56. 51 is a quarter-wave plate, 51a is a quarter-wave plate driving device, 52 is a half-wave plate, and a linear polarization state is horizontal to the main axis of the half-wave plate and is a vertical polarization state. A phase difference of π is generated. Reference numeral 52a is a half-wave plate driving device, which rotates about the main axis of the half-wave plate. 56 is a wave plate control circuit, which is 1 /
The quarter-wave plate 51 is rotationally controlled through the four-wave plate driving device 51a, and the half-wave plate is driven through the half-wave plate driving device 52a.
The rotation of the wave plate 52 is controlled.

Next, the operation will be described. In the operation of the optical receiver 4, the demultiplexer 41 demultiplexes the signal from the optical fiber 3 and outputs the demultiplexed signal to the photodetector 42 and the polarization state detector 50. The light receiver 42 performs optical / electrical conversion on the optical signal and outputs it to the receiver 43. By the way, although the polarization state of the optical signal periodically changes by the polarization scrambler, focusing on the polarization state at a certain point in the description, the polarization state detector 50 detects that the demultiplexed light is circular, for example. For polarized waves, the quarter-wave plate 51 linearly polarizes, and the half-wave plate 52 polarizes the linearly polarized input light in a desired polarization direction and outputs the polarized light to the polarizer 53. 1 /
Only the polarized component of the light from the two-wave plate 52 in a certain direction is transmitted, the light receiver 54 converts the optical signal from the polarizer 53 into an electric signal, and outputs the electric signal to the clock extraction circuit 55. The clock extraction circuit 55 extracts a reception clock signal equal to the polarization scramble frequency from the output of the polarization state detector 50, that is, the output of the photodetector 54, and outputs it to the wave plate control circuit 56.

The wave plate control circuit 56 adjusts the quarter wave plate driving device 5 so that the amplitude value of the received clock signal becomes large.
1a rotates about the main axis of the quarter-wave plate 51,
The main shaft of the half-wave plate 52 is rotated by the half-wave plate driving device 52a. The control time constant for the quarter-wave plate 51 is made sufficiently longer or shorter than the control time constant for the half-wave plate 52 so as not to oscillate. And 1/4
The rotation of the wave plate 51 and the ½ wave plate 52 changes the polarization direction to the polarizer 53, the amplitude of the received clock signal changes via the light receiver 54 and the clock extraction circuit 55, and the wave plate control circuit 56 Quarter wave plates 51 and 1
The influence of the rotation of the 1/2 wave plate 52 is fed back, and the wave plate control circuit 56 increases the amplitude of the reception clock signal so that the 1/4 wave plate 51 and the 1/2 wave plate 52.
Is controlled around the spindle. The control speed of the quarter-wave plate 51 and the half-wave plate 52 is sufficiently slower than the polarization scrambler frequency and faster than the polarization fluctuation generated in the transmission line.

Since the quarter-wave plate 51 can change an arbitrary elliptical polarization state into a linear polarization and the half-wave plate 52 can change the linear polarization into a linear polarization in an arbitrary polarization direction, For example, if the quarter-wave plate 51 and the half-wave plate 52 are rotationally controlled so that the linearly polarized wave direction is aligned with the direction in which the polarizer 53 transmits, the amount of light that is transmitted becomes maximum, and the light received by the light receiver 34
Since the electric conversion is performed, the clock signal having the maximum amplitude value can be obtained. Therefore, the amplitude value of the clock signal can be maximized by the control of the wave plate control circuit 56, and the frequency component can be efficiently and surely extracted from the change in the polarization state of the light. Further, even if polarization fluctuations occur in the optical fiber 3, since the light is received by following the polarization direction of the fluctuations as described above, stable clock extraction can be performed. The above-mentioned example has a configuration in which the quarter-wave plate and the half-wave plate are added to the first embodiment, but the same applies to the second embodiment.
The same effect can be obtained if the quarter wave plate and the half wave plate are added. Further, although the 1/2 wavelength plate is arranged after the 1/4 wavelength plate, the 1/2 wavelength plate may be first.

Embodiment 5 FIG. This embodiment is a polarization scrambler 2
It is intended to double the voltage of the polarization scrambler drive signal added to 5 to halve the frequency. FIG. 6 shows the configuration of the optical transmitter 2 of this embodiment. The optical receiver 4 is the first embodiment.
Same as above and omit the explanation. In FIG. 6, 24 is a polarization scrambler drive circuit, 25 is a polarization scrambler, 251 is a polarization scrambler light input, 252 is a polarization scrambler light output, and 253 is a polarization scrambler drive signal. Others are the same as the first embodiment.

The operation of FIG. 6 will be described with reference to FIG. FIG.
In (a) and (b), the polarization scrambler drive signal 253 is shown. The amplitude values are (a) Vπ, (b) 2Vπ, and the period is 1 / f second. (C) and (d) show a cross section passing through the center of the Poincare sphere showing the state of polarization, (c) is the polarization scrambler drive signal 253 of (a), and (d) is (b). Represents the polarization state when driven by the polarization scrambler drive signal 253. In the figure, P, Q, L, and R respectively represent points on the cross section of the Poincare sphere, P and Q represent the linearly polarized state, and L and R represent the circularly polarized state. Q is +45 degrees in the phase relationship between the horizontal and vertical polarization components, and P is the phase relationship between the horizontal and vertical polarization components.
It is -45 degrees, L represents left-handed circularly polarized light, and R represents right-handed circularly polarized light.

The polarization state of the light output from the polarization scrambler 25 is P when the output of the polarization scrambler drive circuit 24, that is, the voltage applied to the phase modulator 11 in FIG. The polarization state of the light input to the phase modulator 11 is adjusted. Then, the voltage required to set the phase change amount of the horizontal polarization by the phase modulator 11 to π, that is, the half-wave voltage Vπ.
When, is added, the polarization state of the output light of the polarization scrambler 25 moves on the Poincare sphere by P, L, and Q for half a circle. When the output voltage of the polarization scrambler drive circuit 24 is changed by one cycle with an amplitude of Vπ as shown in FIG.
As shown in (c), P, L, Q, L, P, R on the Poincare sphere
Make one round trip with Q, R, and P.

On the other hand, when the output voltage of the polarization scrambler drive circuit 24 is changed by one cycle with an amplitude of 2 Vπ as shown in FIG. 7B, the polarization state is on the Poincare sphere as shown in FIG. 7D. Make two round trips. That is, when the amplitude is doubled, the polarization state changes at double speed. Using this property, the output of the polarization scrambler drive circuit 24 in the case of the first embodiment, that is, the amplitude of the polarization scrambler drive signal 253 is doubled and the frequency is halved to drive the polarization scrambler 25. As a result, the cycle of changing the polarization state of the output light of the polarization scrambler can be made the same.

When the polarization scrambler driving circuit 24 changes the polarization state by one cycle every one cycle by phase modulation, the polarization scrambler driving signal 253 having the amplitude of the half wavelength voltage Vπ is used as the polarization scrambler 25. To drive. At this time, the polarization state of the optical signal output by the polarization scrambler 25 can be regarded as non-polarized on average over a time period sufficiently longer than one cycle of phase modulation. However, the polarization scrambler drive signal 253
Depending on the waveform of, the polarization state may not become non-polarized on the time average even if the phase modulation is performed by changing one cycle. At that time, the amplitude of the polarization scrambler drive signal 253 is set to a value close to the half-wave voltage Vπ so that the polarization state becomes non-polarized in time average. For example, the polarization scrambler drive signal 25
When the waveform of 3 is a sine wave, the polarization state does not become non-polarized on the time average, so the polarization scrambler drive signal 25
The amplitude of 3 is made lower than the half-wave voltage Vπ so that the time average of the polarization state becomes non-polarized.

In the above example, the amplitude of the polarization scrambler drive signal 253 is doubled, but it is an integer multiple (N
Double). The same applies to the case where the polarization scrambler drive circuit 24 changes the polarization state by N periods by performing phase modulation for N periods by phase modulation, and the polarization scrambler drive signal 253 has an amplitude N times the half wavelength voltage Vπ. The polarization scrambler 25 is driven by. However, when the polarization state does not become non-polarized on average over a time sufficiently longer than N periods, the amplitude of the polarization scrambler drive signal 253 is a value close to N times the half-wave voltage Vπ, and the polarization state is time averaged. Is set to have non-polarized amplitude.

Further, when an optical signal is relayed using an optical amplifier, it is known that the S / N of the optical signal deteriorates if the polarization state of the optical signal is biased. Therefore, by making the polarization state time-average non-polarized as described above, deterioration of the signal-to-noise ratio can be suppressed, and long-distance relay transmission can be performed. Also, when the amplitude of the polarization scrambler drive signal is multiplied by an integer, the change frequency of the polarization state becomes a multiple, so that the frequency of the polarization scrambler drive signal can be reduced to a fraction of an integer.
Facilitates the manufacture of high frequency polarization scramblers.

Embodiment 6 FIG. In this embodiment, two polarization scramblers are connected in cascade to double the change rate of the polarization state. FIG. 8 shows the configuration of the optical transmitter 2 of this embodiment.
The light receiving unit 4 is the same as that in the first embodiment and will not be described. In FIG. 8, reference numerals 24a and 24b denote polarization scrambler drive circuits, and 25
2a and 25b are polarization scramblers, an example of which is shown in FIG. 2
Reference numeral 51a is an optical input of the polarization scrambler 25a, and 251b is an optical input of the polarization scrambler 25b. Reference numeral 27 denotes a delay circuit, which sets a delay amount equal to the time difference between the optical signal being input to the polarization scrambler 25a and the optical signal being input to the polarization scrambler 25b. Others are the same as the first embodiment.

Next, the operation will be described. The polarization scramblers 25a and 25b include the phase modulator 11 shown in FIG.
It is driven by 24b. Polarization scrambler 25a,
25b, when the voltage at which the phase change amount π of the phase modulator 11 is obtained, that is, the half-wavelength voltage is Vπ, the outputs of the polarization scrambler drive circuits 24a and 24b have amplitude values of V
π, and the repetition period is 1 / (fHz). Therefore, the polarization scramblers 25a and 25b are connected in cascade, and after being input to the polarization scrambler 25a, the polarization scrambler 2
The delay circuit 27 provides the polarization scrambler drive circuit 24b with a delay equal to the time difference until it is input to 5b.

Therefore, the phase shift amount is determined by the polarization scrambler 2
In the phase modulator 11 of 5a, π, polarization scrambler 2
In the phase modulator 11 of 5b, the sum is 2π, and the polarization state of the output light of the polarization scrambler 25b is 1
It changes in a cycle of / (2fHz), that is, a frequency of 2fHz. Therefore, in order to change the polarization state of the output light of the polarization scrambler 25b at a cycle of 1 / (2fHz), the clock cycle of the output of the polarization scrambler driving circuit 25b is set to 1 / in the example of the first embodiment. (2 fHz), that is, frequency 2 f
However, in this embodiment, the clock frequency may be half the fHz.

As described above, the polarization scrambler driving frequency can be halved because the polarization scrambler frequency is doubled by connecting the polarization scramblers in cascade. Manufacturing is easy. In the above example, two polarization scramblers are cascaded, but two or more cascaded scramblers may be cascaded. Also, the phase modulation is 0
However, it may be an integral multiple of π. Further, although the amplitude at which the phase change amount π is obtained is the drive voltage of the half-wave voltage Vπ, it may be an integral multiple of the half-wave voltage Vπ.

Example 7. In this embodiment, driving of the polarization scrambler is stopped while light is not being input, and the power consumption of the polarization scrambler drive circuit 24 is reduced. FIG. 9 shows the configuration of the optical transmitter 2 of this embodiment. The optical receiving unit 4 is the same as that of the first embodiment, and therefore its explanation is omitted. In FIG. 9, 1 is a main signal input terminal, 24 is a polarization scrambler drive circuit, and an amplifier that consumes less power when the input level is low is built in. Reference numeral 25 is a polarization scrambler, 253 is a polarization scrambler drive signal, and 28 is an AND gate. Others are the same as those in the first embodiment and the description thereof will be omitted. In FIG. 10, (a) shows a signal at the main signal input terminal 1, and (b) shows a polarization scrambler drive signal 253 output from the polarization scrambler drive circuit 25.

Next, the operation will be described with reference to FIGS. 9 and 10 focusing on lowering the power of the polarization scrambler driving circuit 24, and the other operations are the same as those in the first embodiment and will not be described. In FIG. 9, A
In the ND gate 28, the main signal shown in FIG.
When the main signal is "0", the AND gate 28 outputs "0" without passing through the output of the prescaler 23. The polarization scrambler drive circuit 24 outputs 0v to “0” of the input to the built-in amplifier, thereby
The polarization scrambler 25 is driven by the drive signal shown in (b). As the built-in amplifier, when the input level is low, an amplifier that consumes less power, for example, a class B or class C amplifier is used.

As described above, when the main signal is "0", that is, when there is no optical input, the level of the signal applied to the amplifier incorporated in the polarization scrambler drive circuit 24 is set to 0v and the drive of the polarization scrambler is stopped. Therefore, the polarization scrambler drive circuit 24 with low power consumption can be realized.

Embodiment 8 FIG. In this embodiment, a polarization scrambler driving clock signal is frequency-modulated with a sub-signal of a predetermined frequency to be transmitted. FIG. 11 is a block diagram showing the configuration of this embodiment. 1a is a main signal input terminal,
1b is a sub signal input terminal, 29a is a frequency modulator, 59 is a frequency demodulator, 7a is a main signal output terminal, and 7b is a sub signal output terminal. Others are the same as those in the first embodiment and the description thereof will be omitted.
Next, the operation will be described focusing on the transmission of the sub-signal, and the other operations are the same as those in the first embodiment and will not be described.

The frequency modulator 29a frequency-modulates the clock signal output from the prescaler 23 with the sub-signal from the sub-signal input terminal 1b, and the polarization scrambler drive circuit 24 uses the frequency-modulated clock signal to polarize the scrambler 25. To drive. Then, the polarization scrambler 25 changes the polarization state in the cycle of the drive clock and outputs it to the optical fiber 3.
The optical receiver 4 receives the optical signal from the optical fiber 3, and the demultiplexer 41, the polarizer 53, the light receiver 54, and the clock extraction circuit 55 of the optical receiver 4 extract the clock from the fluctuation of the polarization state of the optical signal. Then, the frequency demodulator 59 demodulates the frequency-modulated clock by passing the frequency component of the sub-signal with the built-in narrow-band filter to reproduce the sub-signal. Then, the sub signal is output from the sub signal output terminal 7b.

As described above, since the frequency of the clock for driving the polarization scrambler is frequency-modulated by the sub-signal, the sub-signal can be transmitted simultaneously with the main signal.

Example 9. This embodiment is intended to transmit a sub signal together with the main signal by time-divisionally switching a clock signal for driving a polarization scrambler and a sub signal of a predetermined frequency. However, the sub signal is transmitted within the time period in which the clock extraction circuit can hold the synchronization even if the clock signal is interrupted. Here, the sub signal has a small amount of information, and is a signal for monitoring and controlling the optical repeater connected to the optical fiber 3, for example.

FIG. 12 is a block diagram showing the structure of this embodiment. 1a is a main signal input terminal, 1b is a sub signal 1 input terminal, 1c is a sub signal 2 input terminal, 231 is a prescaler output, 29b is a switcher, 241 is a drive clock signal, 2
53 is a polarization scrambler drive signal, 59b is frequency f1
A detector, 59c is a frequency f2 detector, 7a is a main signal output terminal, 7b is a sub signal 1 output terminal, and 7c is a sub signal 2 output terminal. FIG.
Is a drive clock signal 241 for driving the polarization scrambler
And 231 shows the relationship between the sub-signal 1 and the sub-signal 2, where 231 is the drive clock signal of the prescaler output, 1b is the sub-signal 1,
1c is a sub signal 2, and 241 is a drive clock signal.

Next, the operation will be described with reference to FIGS. 12 and 13 focusing on the transmission of the sub-signal, and the other operations are the same as those in the first embodiment and will not be described. In FIG. 12, the switch 29b outputs the drive clock signal 241 of the prescaler output 231 of the frequency fd to the polarization scrambler drive circuit 24 when the sub signal 1 and the sub signal 2 are "0". Then, the switch 29b
When the sub signal 1 outputs "1", the output 231 of the prescaler is stopped as shown in FIG. 13, and while the sub signal 1 output 1b is "1", the driving clock signal 241 of the frequency f1 is polarized scrambler driven. Output to the circuit 24. When the sub signal 2 outputs "1" to the switch 29b, the prescaler output 231 is stopped as shown in FIG. 13, and the sub clock 2 output 1c is "1" while the drive clock signal 241 having the frequency f2 is output.
To the polarization scrambler drive circuit 24. The polarization scrambler drive circuit 24 drives the polarization scrambler 25 so as to change the polarization state in the cycle of the drive clock, and the polarization scrambler 25 outputs an optical signal to the optical fiber 3.

The optical receiver 4 receives the optical signal from the optical fiber 3 and receives the optical demultiplexer 41 and the polarizer 53 of the polarization state detector 50.
The signal 541 converted into an electric signal through the light receiver 54 is output to the frequency f1 detector 59b, the frequency f2 detector 59c, and the clock extraction circuit 55. And the frequency f1
The detector 59b uses a built-in narrow band filter to generate a frequency f
The sub signal 1 of 1 is detected and output from the sub signal 1 output terminal 7b. The frequency f2 detector 59c detects the sub signal 2 of the frequency f2 by using a built-in narrow band filter, and outputs it from the sub signal 2 output terminal 7c. Here, the clock extraction circuit 55
Uses a phase synchronization circuit that synchronizes with the frequency fd of the drive clock signal 231. When the sub signal 1 or the sub signal 2 outputs "1", the period during which "1" is maintained is within the period in which the clock extraction circuit 55 can maintain phase synchronization even if the drive clock signal 231 is interrupted. As described above, since the sub signal is transmitted by polarization scrambling while the clock extraction circuit maintains the synchronization, the sub signal can be transmitted at the same time as the main signal.

In the optical amplification repeater, the demultiplexer 41 and the polarizer 5
Similarly, the auxiliary signal can be detected by including the optical receiver 3, the light receiver 54, and the auxiliary signal demodulator 59. For example, if the sub-signal with the frequency f1 is detected, the output of the optical amplification repeater is increased, and the frequency f2 is increased.
If the sub-signal is detected, the output of the optical amplification repeater can be reduced and the optical amplification repeater can be remotely controlled.

[0077]

According to the first aspect of the invention, the polarization state of the optical main signal is changed with the clock synchronized with the optical main signal, and the clock is extracted from the polarization component of the optical signal received through the optical fiber to obtain the main signal. , The main signal can be transmitted without being affected by the polarization fluctuation in the optical fiber. Further, since the clock component is transmitted using the change frequency of the polarization state and the polarization state itself is not used as a signal, it is not necessary to use an expensive polarization maintaining fiber. Further, the clock extraction circuit can be composed of an electronic circuit which is simpler than the internal synchronization system which transmits and receives the main signal and the synchronization signal by modulating the light intensity.

In the second invention, even if the optical signal becomes high speed by increasing the multiplicity of the main signal, the frequency of the clock for driving the polarization scrambler is the same, and the multiplexing and
It can be separated and clock extraction is easy.

In the third invention, since the change of the polarization state is efficiently converted into an electric signal by using the quarter-wave plate, stable clock extraction which is not easily affected by the fluctuation of the polarization state in the optical fiber. You can

In the fourth invention, a quarter wave plate and 1
Since the change of the polarization state is converted into an electric signal more efficiently by using the / 2 wavelength plate, stable clock extraction which is hardly influenced by the fluctuation of the polarization state in the optical fiber can be performed.

In the fifth invention, when the amplitude of the polarization scrambler drive signal is multiplied by an integer, the change frequency of the polarization state becomes an integer multiple, and conversely, the frequency of the polarization scrambler drive signal is divided by an integer. No. 1 and the manufacture of a high frequency polarization scrambler is facilitated.

In the sixth aspect of the invention, since a plurality of polarization scramblers are connected in cascade to increase the changing speed of the polarization state, conversely, the polarization scrambler drive frequency can be lowered correspondingly, and the high frequency polarization scrambler can be reduced. The bra is easier to manufacture.

In the seventh invention, the power consumption can be reduced because the driving of the polarization scrambler is stopped when there is no optical input to the polarization scrambler.

In the eighth invention, the frequency of the clock for driving the polarization scrambler is frequency-modulated by the sub-signal of a predetermined frequency, so that the sub-signal can be transmitted simultaneously with the main signal.

According to the ninth aspect of the invention, since the sub-signal of a predetermined frequency is transmitted by polarization scrambling while the clock extraction circuit maintains synchronization even if the clock is interrupted, the sub-signal can be transmitted simultaneously with the main signal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical transceiver according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a polarization scrambler.

FIG. 3 is a configuration diagram of an optical transceiver according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical transceiver according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical transceiver according to a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical transmitter according to a fifth embodiment of the present invention.

FIG. 7 is a diagram showing a polarization state when the polarization scrambler of the fifth embodiment is driven.

FIG. 8 is a configuration diagram of an optical transmitter according to a sixth embodiment of the present invention.

FIG. 9 is a configuration diagram of an optical transmitter according to a seventh embodiment of the present invention.

FIG. 10 is a diagram showing a polarization scrambler drive signal according to a seventh embodiment.

FIG. 11 is a configuration diagram of an optical transceiver according to an eighth embodiment of the present invention.

FIG. 12 is a configuration diagram of an optical transmitter / receiver according to a ninth embodiment of the present invention.

FIG. 13 is a diagram showing an example in which a sub-signal according to the ninth embodiment is switched to a polarization scrambler drive clock signal and transmitted.

FIG. 14 is a configuration diagram of an optical transmitter / receiver of a first conventional example.

FIG. 15 is a configuration diagram of an optical transmitter / receiver of a second conventional example.

[Explanation of symbols]

 2 Optical transmitter 21 Oscillator 22, 22a, 22b Optical / electrical converter 24, 24a, 24b Polarization scrambler drive circuit 25, 25a, 25b Polarization scrambler 26 Optical multiplexer 27 Delay circuit 28 AND gate 29a Frequency modulator 29b Switcher 3 Optical fiber 4 Optical receiver 41 Demultiplexer 42, 42a, 42b First light receiver 43, 43a, 43b Receiver 46 Optical separation device 50 Polarization state detector 51 1/4 Wave plate 52 1 / 2 Wave plate 53 Polarizer 54 Second light receiver 55 Clock extraction circuit 56 Wave plate control circuit 57 Multiplexer 59 Demodulator 59b, 59c Detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G02F 2/00 H04J 14/00 14/04 14/06

Claims (10)

[Claims] 1. An optical transmitter / receiver having the following components. 1. 1. An electric / optical converter that receives a main signal of an electric signal and outputs an optical signal whose light intensity is modulated. 2. A polarization scrambler that periodically changes the polarization state of the optical signal from the electric / optical converter and outputs the optical signal to the optical fiber. 3. A polarization scrambler drive circuit that drives the polarization scrambler so as to periodically change the polarization state of the optical signal based on a clock that is synchronized with the main signal. 4. A demultiplexer that demultiplexes an optical signal transmitted via the optical fiber, 5. A first light receiver for converting the first optical signal demultiplexed by the demultiplexer into an electrical signal, 6. 6. A polarization state detector that converts a change in polarization state into an electric signal by the second optical signal demultiplexed by the demultiplexer. 7. A clock extraction circuit that extracts a polarization scramble frequency and regenerates a clock based on the electric signal from the polarization state detector. A receiver for reproducing the main signal based on the output of the first light receiver and the clock extracted by the clock extraction circuit. 2. An optical transmitter / receiver having the following components. 1. 1. An electrical / optical converter which receives a plurality of main signals synchronized with each other and outputs an optical main signal whose light intensity is modulated, 2. An optical multiplexer that multiplexes a plurality of optical main signals from the electrical / optical converter in a time division manner and outputs an optical signal. 3. A polarization scrambler that periodically changes the polarization state of the multiplexed optical signal and outputs it to an optical fiber. 4. A polarization scrambler drive circuit that drives the polarization scrambler so as to periodically change the polarization state of the optical signal based on a clock that is synchronized with the main signal. 5. A demultiplexer that receives and demultiplexes the optical signal from the optical fiber, 6. An optical demultiplexer that demultiplexes the first optical signal demultiplexed by the demultiplexer into a plurality of the optical main signals. 7. A polarization state detector that converts a change in polarization state into an electric signal by the second optical signal demultiplexed by the demultiplexer. 8. A clock extraction circuit that extracts a polarization scramble frequency and regenerates a clock based on the electric signal from the polarization state detector. A receiver for reproducing the plurality of optical main signals separated by an optical separation device into the main signals based on the clocks extracted by the clock extraction circuit. 3. The optical transmitter / receiver according to claim 1, wherein the polarization state detector has the following components. 1. 1. A polarizer that transmits only the polarization component in a certain direction of the second optical signal demultiplexed by the demultiplexer, Second, which converts an optical signal from the polarizer into an electric signal
Receiver of. 4. The optical transceiver according to claim 1, wherein the polarization state detector has the following components. 1. 1. A quarter-wave plate that transmits the second optical signal demultiplexed by the demultiplexer with a phase difference π / 2 between the polarized light vertical to the main axis and the polarized light horizontal to the main axis. 2. A polarizer that transmits only a polarized component in a certain direction of light from the quarter-wave plate. Second, which converts an optical signal from the polarizer into an electric signal
Light receiver of 4. A wave plate control circuit for detecting an amplitude value of the output of the second photodetector and controlling rotation about the main axis of the quarter wave plate so as to increase the amplitude value. 5. The optical transmission / reception device according to claim 1, wherein the polarization state detector has the following components. 1. The optical signal is transmitted by giving a phase difference π / 2 and a phase difference π between polarized light perpendicular to the main axis and polarized light horizontal to the main axis.
4 wave plate and 1/2 wave plate, 1. 2. A polarizer for transmitting only the polarized component in a certain direction of the optical signal transmitted through the quarter wavelength plate and the half wavelength plate for the second optical signal demultiplexed by the demultiplexer. Second, which converts an optical signal from the polarizer into an electric signal
Light receiver of 4. A wave plate control circuit for detecting an amplitude value of the output of the second photodetector and controlling rotation about the main axes of the quarter wave plate and the half wave plate so that the amplitude value becomes large. 6. The polarization scrambler drive circuit drives the polarization scrambler with an amplitude that is an integral multiple of a voltage with which a phase change amount π is obtained for one light wave of the orthogonal polarization component. The optical transceiver according to claim 1 or 2. 7. The polarization scrambler is formed by connecting a plurality of polarization scramblers in cascade connection in multiple stages, and the polarization scrambler drive circuit is provided for the polarization scrambler, and the polarization scrambler of each stage is provided. The bra drive circuit is a delay corresponding to the time difference from the input of the optical signal to the head polarization scrambler receiving the optical signal from the electric / optical converter to the input of the optical signal to the own polarization scrambler. The optical transmission / reception device according to claim 1 or 2, wherein the polarization scrambler is driven by applying the signal. 8. The polarization scrambler drive circuit is configured to stop the drive of the polarization scrambler while light is not input to the polarization scrambler. Optical transceiver. 9. A frequency modulator that receives a sub-signal of a predetermined frequency and frequency-modulates the sub-signal by using a clock synchronized with the main signal as a carrier, and a frequency-modulated sub-signal from the polarization state detector. A demodulator for demodulation, the polarization scrambler drive circuit drives the polarization scrambler based on the output of the frequency modulator, and the demodulator is the sub-signal from the polarization state detector. The optical transmission / reception device according to claim 1 or 2, wherein 10. A switcher for receiving a sub-signal of a predetermined frequency and switching between a clock synchronized with the main signal and the sub-signal, and a detector for detecting the frequency of the sub-signal from the output of the polarization state detector. And the polarization scrambler drive circuit drives the polarization scrambler based on the output of the switch, and the detector detects the sub-signal from the polarization state detector. The optical transceiver according to claim 1 or 2.