JPH08240826A - Optical clock signal regenerator - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to reproduce a clock signal from a high-speed optical signal without requiring strict requirements. [Structure] Two specific frequency components are extracted from laser light that oscillates at a single frequency. One of the extracted frequencies is changed, an optical signal data string is combined therewith, the combined optical phase is detected, and the frequency shift amount is controlled so that the phases match. The beat component of the other frequency component and the frequency component whose frequency has been shifted is used as the optical clock signal to extract the optical clock signal.

Description

Detailed Description of the Invention

[0001]

The present invention is used in optical communication. The present invention is suitable for use in an optical signal repeater. The present invention
The present invention relates to a technique for regenerating an optical clock signal based on an optical signal data train in an optical signal repeater or the like.

[0002]

2. Description of the Related Art FIG. 2 shows the configuration of a conventional optical clock signal reproducing apparatus. This FIG. 2 has been previously proposed by the applicant (Japanese Patent Application No. 6-295099, not yet published at the time of filing this application).

This optical clock signal regenerator has a frequency f
A laser diode 11 that oscillates at ₁ and a laser diode 12 that oscillates at a frequency f ₂ and an optical signal including the output light of the laser diodes 11 and 12 and including the frequency difference (f ₁ −f ₂ ) of the frequencies. Optical coupler 16 for outputting
And the optical signal correlator 1 for identifying the coincidence of the signal phase appearing in the output light of the optical coupler 17 and the optical coupler 17 to which the differential frequency of the optical coupler 16 and the optical signal data string are input.
3, a photodiode 14 for detecting the output of the optical signal correlator 13, and a control circuit 15 to which the output of the photodiode 14 is input. According to the detection output of the optical signal correlator 13, the optical signal data string The control circuit 15 controls the oscillation frequency of the laser diode 11 so that the phase difference between the optical coupler 16 and the optical coupler 16 is minimized, and the difference frequency is output from the optical coupler 17 as a reproduced optical clock signal.

The operation will be briefly described. The laser diodes 11 and 12 have optical frequencies f ₁ and f ₂ respectively.
In the single mode continuous oscillation, the difference between the optical frequencies f ₁ and f ₂ is set to be substantially equal to the optical clock signal frequency. In the configuration of FIG. 2, the laser diodes 11 and 12 are
Of at least one of the oscillation frequencies is variable by a control signal from the outside, and the oscillation frequency difference (f ₁ −
It is necessary that f ₂ ) can be adjusted. In the description below, the oscillation light frequency of the laser diode 11 is variable, and the oscillation light frequency of the laser diode 12 is fixed. The laser used in all the embodiments of the present invention described later is not limited to the laser diode as long as it oscillates at a single frequency.

The lights output from the laser diodes 11 and 12 are combined by the optical coupler 16, and the amplitude of the combined wave changes sinusoidally with 1 / | f ₁ -f ₂ | as the cycle. Laser diode 1
The combined wave of 1 and 12 is combined with the optical signal data string by the optical coupler 17, and then input to the optical signal correlator 13. However, the optical signal data string is return-to-zero (RZ)
It is intensity-modulated by a code.

The optical signal correlator 13 is a laser diode 1
It has a function of outputting the largest optical signal or the smallest optical signal when the phases of the composite wave of 1 and 12 and the optical signal data string match, and detecting the phase difference between the two. The composition is, for example, “S. Kawanishi and M. Saruwatari,“ Ne
w-type phase-locked loop using traveling-wave lase
r diode optical amplifier for very high speed opti
cal transmission, "Electron.Lett.vol.24, pp, 1452-14
53,1988 ”and“ Japanese Patent Application No. 6-295099 ”, detailed description thereof will be omitted.

The output signal of the optical signal correlator 13 is converted into an electric signal by the photodiode 14 which serves as a photodetector. The control circuit 15 monitors the output of the optical signal correlator 13 converted into an electric signal, and controls the optical oscillation frequency of the laser diode 11 so as to maximize the output. The period 1 / | f of the combined wave of the laser diodes 11 and 12 combined by the optical coupler 17 by the above operation
₁₋ f ₂ | is synchronized with the bit period of the optical signal data string,
An optical clock signal can be obtained.

The electrical signals used in the optical clock signal regenerator shown in FIG. 2 are the output of the optical signal correlator 13 and the control signal of the laser diode 11, both of which have a band of about Δf ₁ + Δf _2. Have. However, Δf ₁ and Δf ₂ are the fluctuation widths of the oscillation frequencies of the laser diodes 11 and 12, respectively. These are much smaller than the bit rate (10 GHz or higher) which is considered to be applied to the optical clock signal regenerator, and the stability of about MHz can be obtained relatively easily. Therefore, bit synchronization can be realized without using a high-speed electric signal.

[0009]

However, in this conventional technique, a variable frequency laser diode requires the following performance.

First, the spectral line width of the laser diode must be sufficiently smaller than the reciprocal of the delay time of the feedback loop. The reason for this is that if the phase of the laser changes within the delay time, correct feedback will not be applied. The delay time of the feedback loop is the time from when the optical clock signal is emitted from the variable frequency laser diode to when the feedback signal reaches the variable frequency laser diode again through the optical signal correlator. If the length of the optical fiber or wire in the middle is about 2 m in total, the delay time τ is
It will be about 10 ns. Since this reciprocal is 100 MHz, the line width requirement for the frequency tunable laser diode is at least 10 MHz or less, and in some cases 100 MHz.
KHz to 1 MHz or less may be required. Such a laser diode is not easily obtained, or even if it is obtained, it is expensive.

Secondly, the frequency modulation band of the frequency tunable laser diode must be sufficiently wider than its spectral line width. The reason is that it is necessary to control the random frequency fluctuation of the oscillating laser diode by frequency modulation. Realization of such a variable frequency laser diode is generally difficult, and the laser diode is expensive.

The present invention solves the two problems of the prior art, can perform optical clock signal regeneration with an all-optical configuration without requiring a severe performance requirement for a laser diode, and can inexpensively construct a system. An object is to provide an optical clock signal regenerator.

[0013]

The first aspect of the present invention is to:
In an optical clock signal regenerator that forms the clock signal from an optical signal data string, an optical signal oscillator that oscillates at a single frequency, and a modulator that modulates the output light of this optical signal oscillator and outputs it as modulated light, Optical filter means for selecting and outputting two specific frequency components of the output modulated light, optical frequency control means for controlling the frequency of the output light of one of the optical filter means, and output of the optical frequency control means. A first optical coupler that combines the light and the other output light of the optical filter means and outputs in two directions, and a unit for detecting the phase difference between one output light of the first optical coupler and the optical signal data string. The phase difference detection means and means for adjusting the optical frequency control means according to the detection output of the phase difference detection means to minimize the phase difference are provided, and the other output of the first optical coupler is a reproduction optical clock. Characterized in that it is outputted as a click signal.

A second aspect of the present invention is to provide an optical signal oscillator that oscillates at a single frequency, a modulator that modulates the output light of the optical signal oscillator and outputs the modulated light, and a modulator for the output modulated light. An optical filter means for selecting and outputting two specific frequency components, a first optical coupler for combining one output light and the other output light of the optical filter means and outputting in two directions, and a first optical coupler. Phase difference detecting means for detecting the phase difference between one output light of the one optical coupler and the optical signal data string, and modulation of the modulating means so that the phase difference is minimized according to the detection output of the phase difference detecting means. Means for controlling the frequency, and the other output of the first optical coupler is output as a regenerated optical clock signal.

A third aspect of the present invention is to provide an optical signal oscillator that oscillates at a single frequency, a modulator that modulates the output light of the optical signal oscillator and outputs the modulated light, and the output modulated light. The optical filter means for selecting and outputting two of the specific frequency components and the output light of one of the optical filter means and the output light of the other are multiplexed and output in two directions with their phases opposite to each other. A second optical coupler, third and fourth optical couplers that combine the output light of the opposite phase and the optical signal data string and each branch into two, and output light of one of the third and fourth optical couplers. According to the phase difference detecting means for detecting the phase difference of the phase difference detecting means and the detection output of the phase difference detecting means, the modulation frequency of the modulating means is set so that the phase difference between the outputs of the third and fourth multiplexing means is minimized. And a means for controlling the third The other output of the fourth optical coupler is characterized in that it is outputted as a regenerated optical clock signal.

A fourth aspect of the present invention is to provide an optical signal oscillator which oscillates at a single frequency, a modulator which modulates the output light of the optical signal oscillator and outputs the modulated light, and the output modulated light. Optical filter means for selecting and outputting two specific frequency components, a fifth optical coupler for branching one of the output lights of the optical filter means in two directions, and the other of the output light of the optical filter means. A sixth optical coupler that branches in two directions,
An optical frequency control means for shifting the optical frequency of one output light of the output light of the fifth optical coupler, and an optical frequency control means for multiplexing the output light of the optical frequency control means and one of the output lights of the sixth optical coupler. A seventh optical coupler, an eighth optical coupler for multiplexing the other output light of the fifth optical coupler and the other output light of the sixth optical coupler, and a fixed frequency for giving a fixed frequency Δf to the optical frequency control means. Generating means, phase difference detecting means for detecting the phase difference between the phase of the output light of the seventh optical coupler and the phase of the optical signal data string, and the phase difference is minimized according to the detection output of this phase difference detecting means. And a means for controlling the modulation frequency of the modulating means, and the other output of the eighth optical coupler is output as a regenerated optical clock signal.

A fifth aspect of the present invention is to provide an optical signal oscillator which oscillates at a single frequency, a modulator which modulates the output light of the optical signal oscillator and outputs the modulated light, and the output modulated light. Optical filter means for selecting and outputting two specific frequency components, optical frequency control means for controlling the frequency of the output light of one of the optical filter means, output light of the frequency control means and the optical filter. A second optical coupler that combines the other output light of the means and outputs the light in two directions with their phases opposite to each other, and this output light of the opposite phase and the optical signal data string are combined and each branched into two branches. The third and fourth optical couplers, the phase difference detecting means for detecting the phase difference of the output light from one of the third and fourth optical couplers, and the third and fourth optical couplers according to the detection output of the phase difference detecting means. The output of the fourth optical coupler Difference in Seki and means for adjusting said optical frequency control means so as to minimize the other output of the third or fourth optical coupler is characterized in that it is outputted as a regenerated optical clock signal.

A sixth aspect of the present invention is to provide an optical signal oscillator which oscillates at a single frequency, a modulator which modulates the output light of the optical signal oscillator and outputs the modulated light, and the output modulated light. Of two specific frequency components of the optical filter means, the first optical frequency control means for shifting the optical frequency of one output light of the optical filter means, and the first optical frequency control means. A fifth optical coupler for branching one of the output lights in two directions, a sixth optical coupler for branching the other of the output lights of the optical filter means in two directions, and one of the output lights of the fifth optical coupler. Second optical frequency control means for shifting the optical frequency of, a seventh optical coupler for multiplexing the output light of the second optical frequency control means and one of the output lights of the sixth optical coupler, and the fifth optical coupler The other output light of the coupler and the output of the sixth optical coupler An eighth optical coupler for multiplexing the other of the lights, a fixed frequency generating means for giving a fixed frequency Δf to the second optical frequency control means, a phase of the output light of the seventh optical coupler and a phase of an optical signal data string. And a means for adjusting the first optical frequency control means so as to minimize the phase difference according to the detection output of the phase difference detecting means. The other output of the optical coupler is output as a regenerated optical clock signal.

In the inventions of the third and fifth aspects, the phase difference detecting means outputs the signal data string and the output of the second optical coupler from the output light of one of the third and fourth optical couplers, respectively. It is preferable to include two optical signal correlators that detect the correlation with light and one balanced photodetector that receives the detection outputs of the two optical signal correlators.

In the inventions of the fourth and sixth aspects,
Phase difference detection means, an optical signal correlator that detects the phase difference between the phase of the output light of the seventh optical coupler and the optical signal data string, and a photodiode that converts the output of this optical signal correlator into an electrical signal, It is preferable to include a phase comparator for performing phase comparison between the output signal of the photodiode and the fixed output frequency of the fixed frequency generating means.

The optical frequency control means may include an acousto-optic modulator that shifts the frequency of the optical signal passing therethrough. The optical frequency control means includes an acousto-optic modulator that shifts the frequency of an optical signal that passes through and an optical system that allows light whose frequency is controlled to pass in the forward and reverse directions on the same path of the acousto-optic modulator. Can be included.

[0022]

In the conventional optical clock signal reproducing apparatus, when the optical clock signal is formed, the optical clock signal is formed by controlling the frequency of one of the two laser diodes. On the other hand, in the present invention, one laser diode that oscillates at a single frequency is modulated, two of the frequency components generated by the modulation are extracted by the optical filter, and the frequency of one of them is changed. Then, the optical signals of the two frequency components are combined to generate the optical signal of the beat frequency.
Then, by detecting the phase difference between the phase of the optical signal and the optical signal data string and performing loopback control to change the frequency given to the light of one frequency component so that the phase difference becomes the minimum, The clock signal is formed. Alternatively, an optical clock signal synchronized with the optical signal data string is formed by controlling the modulation frequency given to the laser diode.

[0023]

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

(First Embodiment) FIG. 1 is a block diagram showing the arrangement of an optical clock signal regenerator according to the first embodiment of the present invention.

In the first embodiment, a laser diode 21 as an optical signal oscillator that oscillates at a single frequency, a modulator 22 that modulates the output light of the laser diode 21 and outputs the modulated light, and this modulator. A sine wave signal generator 23 for giving a sine wave signal of frequency f _m to 22; an optical filter 24 for selecting and outputting two specific frequency components of the modulated light output from the modulator 22; The acousto-optic modulator 25 as an optical frequency control means for controlling the frequency of one output light, the output light of the acousto-optic modulator 25 and the other output light of the optical filter 24 are combined and output in two directions. An optical coupler 29, an optical signal data string as a phase difference detecting means for detecting a phase difference between one output light of the optical coupler 29 and the optical signal data string, and one output light of the optical coupler 29 are inputted. Phase difference detecting circuit 27 for detecting a phase difference between the output light of the coupler 30 and the optical coupler 30 in optical correlation
And according to the detection output of the phase difference detection circuit 27,
A sine wave signal generator 28 that outputs a sine wave of frequency f _AOM to control the acousto-optic modulator 25 so that the phase difference between the optical signal data string and the combined output light of the optical coupler 29 is minimized.
With. The frequency _AOM of the sine wave signal generator 28 is controlled by the output of the phase difference detection circuit 27. In this embodiment, the other output of the optical coupler 29 becomes the regenerated optical clock signal.

The operation of the first embodiment will be described.

The oscillation frequency of the laser diode 21 is set to f _0.
And The laser light is modulated by the modulator 22. A new frequency f ₀ ± nf _m (n =
1, 2, ...) occurs. The optical filter 24 outputs the f ₀ + Nf _m and f ₀ -Nf _m of these frequencies to different ports. The frequency of one of these is changed by the acousto-optic modulator 25 by f _AOM . When these are combined by the optical coupler 29, the frequency of the optical clock obtained is 2Nf _m + f _AOM . Therefore, in this embodiment, 2Nf _m + f _AOM
So they become approximately equal to the clock frequency of the optical signal to f _c, it may be set to f _m. That is,

[0028]

[Equation 1] F _m is set as follows. N is an integer determined by the modulation depth of the modulator 22 (which represents the degree of modulation and is also referred to as a modulation index), but is generally about 10 to 20,
f _m can be smaller than the clock frequency f _c.

The phase difference detection circuit 27 compares the phases of the optical signal data string and the optical clock, and controls the frequency f _AOM of the sine wave signal generator 28 so as to synchronize them, thereby synchronizing the optical signal data string. The optical clock signal can be obtained.

In this embodiment, the spectral line width of the laser diode 21 is not as strict as in the conventional example. That is, even if the oscillation frequency of the laser diode 21 changes, the frequencies of the two outputs from the optical filter 24 change in exactly the same way, and therefore the frequency of the optical clock, which is the beat frequency, is not affected at all.

(Second Embodiment) FIG. 3 shows a second embodiment. This second embodiment is used in place of the acousto-optic modulator 25 and the sine wave signal generator 28 of FIG. Another configuration of the optical frequency control performed for one output light from the optical filter 24 is shown.

In this optical frequency control configuration, lenses 31 and 32 are arranged on the input side and the output side of the acousto-optic modulator 25, and one lens 32 is arranged between the mirror 33 and the acousto-optic modulator 25. The other lens 31 is arranged at a position where it is coupled to an optical fiber 35 connected to an optical multiplexer / demultiplexer 34 composed of an optical coupler or an optical circulator. Optical fiber 35, lens 31, acousto-optic modulator 2
5, the lens 32, and the mirror 33 are arranged apart from each other by the focal length of the lens. The acousto-optic modulator 25 is controlled by the sine wave signal generator 28, modulates the optical frequency of the light passing therethrough, and operates as an acousto-optic frequency shifter.

The operation of the second embodiment is the same as that of the second embodiment, and the frequency of light is changed by the frequency of the sine wave signal generator 28. The feature of the second embodiment is that even if the frequency f _AOM of the sine wave signal generator 28 changes due to the feedback from the phase difference detecting means 27, the coupling efficiency to the optical fiber on the output side does not change, This can be realized by reflecting the light that has passed through the acousto-optic modulator 25, making it incident on the acousto-optic modulator 25 again in the opposite direction, and making a change again, as shown in FIG. In this case, the frequency of the obtained optical clock is 2Nf _m + 2f _AOM ,

[0034]

[Equation 2] And need to be set.

(Third Embodiment) FIG. 4 shows the structure of a third embodiment of the present invention. The third embodiment is characterized in that the sine wave signal generator 36 of the same frequency as the sine wave oscillator 28 controls the modulator 22 so that the beat frequency matches the clock of the optical signal data train. That is, in the third embodiment, the laser diode 21 that oscillates at a single frequency and the laser diode 21
Modulator 22 that modulates the output light of
And an optical filter 24 that selects and outputs two specific frequency components of the modulated light output from the modulator 22, and one output light and the other output light of the optical filter 24 are combined to form two directions. And an optical coupler 30 for multiplexing one output light of the optical coupler 29 and an optical signal data string.
And the phase difference detection circuit 27 that detects the phase difference between the optical signal data string and the output light of the optical coupler 29 by the output light of this optical coupler, and the phase difference is the minimum according to the detection output of this phase difference detection circuit 27. The sine wave signal generator 36 is provided as means for controlling the modulation frequency of the modulator 22 so that

The clock frequency obtained in this embodiment is the first
A 2NF _m As is apparent from the description of examples. By controlling this f _m by the feedback signal from the phase difference detection circuit 27, the optical clock can be synchronized with the optical signal data string.

(Fourth Embodiment) FIG. 5 shows the configuration of a fourth embodiment of the present invention, in which the phase difference detecting means comprises a pair of optical signal correlators 45 and 46 and a balanced photodetector 47. It is characterized by including. That is, in the fourth embodiment, the laser diode 21 that oscillates at a single frequency is used.
A modulator 22 that modulates the output light of the laser diode 21 and outputs the modulated light, and an optical filter 24 that selects and outputs two specific frequency components of the output modulated light.
, An optical coupler 51 that branches one of the output lights of the optical filter 24 in two directions, an optical coupler 52 that branches the other of the output lights of the optical filter 24 in two directions, and a light of one of the output lights of the optical coupler 51. Acousto-optic modulator 2 for acousto-optically frequency shifting as optical frequency control means for frequency shifting
5, the output light of the acousto-optic modulator 25 and the optical coupler 52.
Of the output light of the optical coupler 53, the optical coupler 54 which combines the other output light of the optical coupler 51 and the other output light of the optical coupler 52, and the acousto-optic modulator 25 with a fixed frequency Δf. And a fixed frequency oscillator 60 as a fixed frequency oscillating means for providing a signal, and an optical coupler 55 as a phase difference detecting means for detecting a phase difference between the phase of the output light of the optical coupler 53 and the phase of the optical signal data string. Optical signal correlator 56 for detecting the optical correlation of the output light of 55, and this optical signal correlator 5
A photodiode 57 for converting the output of 6 into an electric signal,
A phase comparator 58 for comparing the phase of the output fixed frequency Δf of the fixed frequency oscillator 60 and the phase of the correlation output of the optical signal correlator 56.
And a control circuit 59 that controls the sine wave signal generator 36 that applies a modulation frequency to the modulator 22 based on the output of the phase comparator 58 so that the detected phase difference is minimized.

The operation of this fourth embodiment will be described.

The two outputs from the optical filter 24 are branched by the optical couplers 51 and 52, respectively, and one of them is multiplexed by the optical coupler 54 to become an optical clock signal output. The other set of branches is subjected to acousto-optic frequency shift by one of the acousto-optic modulators 25 to change the optical frequency, and then multiplexed by the optical coupler 53. The acousto-optic modulator 25 is driven by a fixed frequency oscillator 60 that generates a fixed frequency of Δf, and changes the optical frequency of the optical coupler 51 by Δf and outputs it. However, Δf is assumed to be extremely lower than the frequency of the optical clock signal.

As a result, the intensity of the output signal of the optical coupler 27 fluctuates with a cycle of 1 / (2Nf _m + Δf). The output of the optical coupler 53 is combined with the optical signal data string by the optical coupler 55 and input to the optical signal correlator 56. The function of the optical signal correlator 56 is exactly the same as that of the fourth embodiment. In the fifth embodiment, the intensity of the output optical signal correlator 56 varies the 1 / [Δf- (f _m -f _c)] as a cycle. However, f _c is a bit rate. Therefore, when the cycle of the clock signal and the bit rate are synchronized, the fluctuation cycle of the output of the optical signal correlator 56 becomes equal to Δf. The phase comparator 58 includes an optical signal correlator 56 (photodiode 57 as a photodetector).
The output of the electric signal) is compared with the phase of the fixed frequency oscillator 60 of Δf, and the frequency of the sine wave signal generator 36 is controlled via the control circuit 59 so that the phase matches. As a result, the output of the optical coupler 54 is synchronized with the bit rate.

(Sixth Embodiment) This sixth embodiment is provided with the phase difference detecting means shown in FIG. 5, and one of the outputs of the optical filter described in the first embodiment of FIG. 1 has a frequency f _AOM. It is equipped with a configuration for making changes. That is, in the present embodiment, a laser diode 21 that oscillates at a single frequency, a modulator 22 that modulates the output light of this laser diode 21 and outputs it as modulated light, and a frequency f _m as a modulation frequency to this modulator. A sine wave signal generator 67 for providing a sine wave signal of
An optical filter 24 that selects and outputs two specific frequency components of the modulated light output from the modulator 22, and the optical filter 24.
Acousto-optic modulator 25 for controlling the frequency of one output light
And a second optical coupler 63 that multiplexes the output light of the acousto-optic modulator 25 and the other output light of the optical filter 24 and outputs them in two directions with their mutual phases being opposite phases, and the outputs of these opposite phases. The light and the optical signal data string are combined, and each is 2
Optical couplers 61 and 62 for branching, and the optical couplers 61 and 6
The optical signal correlators 46 and 47 are used as phase difference detection means for detecting the phase difference from the optical signal data string from one of the two output lights.
A balanced photodetector 47 for detecting the outputs of the optical signal correlators 46 and 47, an optical signal data string appearing in the balanced photodetector 47, and an optical coupler 63.
As a means for adjusting the frequency given to the acousto-optic modulator 25 so that the phase difference with the combined output of (1) becomes minimum (zero),
And a sine wave signal generator 28 whose oscillation frequency can be controlled from the outside.

In the operation, the operation of forming the optical clock signal is the same as that of the first embodiment, and the operation of the phase difference detecting means is the same as that of the fourth embodiment.

(Seventh Embodiment) This seventh embodiment comprises the phase difference detecting means shown in FIG. 6, and the frequency f _AOM is applied to one of the outputs of the optical filter described in the first embodiment of FIG. It is equipped with a configuration for making changes. That is, in the present embodiment, a laser diode 21 that oscillates at a single frequency, a modulator 22 that modulates the output light of this laser diode 21 and outputs it as modulated light, and a frequency f _m as a modulation frequency to this modulator. A sine wave signal generator 67 for providing a sine wave signal of
An optical filter 24 that selects and outputs two specific frequency components of the modulated light output from the modulator 22, and the optical filter 24.
An acousto-optic modulator 73 as a first optical frequency control means for shifting the optical frequency of one of the output lights, an optical coupler 51 for branching one of the output lights of the acousto-optic modulator 73 in two directions, and an optical filter. An optical coupler 52 for branching the other of the output light of 24 into two directions, an acousto-optic modulator 25 as second optical frequency control means for shifting the optical frequency of one output light of the output light of the optical coupler 51, An optical coupler 53 that combines the output light of the acousto-optic modulator 25 and one of the output lights of the optical coupler 52, and the other output light of the optical coupler 51 and the other output light of the sixth optical coupler 52 are combined. An optical coupler 54 that undulates,
A fixed frequency oscillator 60 which gives a fixed frequency Δf to the acousto-optic modulator 25, and a phase difference detecting means for detecting the phase difference between the phase of the output light of the optical coupler 53 and the phase of the optical signal data string, and the optical signal data string , An optical coupler 55 for multiplexing the output light of the optical coupler 53, an optical signal correlator 56, a photodiode 57, a phase comparator 58 for detecting a phase difference between the fixed frequency Δf and the output of the optical signal correlator 56, a phase According to the output of the control circuit 59 and the control circuit 59 to which the output of the comparator 58 is input, the acousto-optic modulator 73 is arranged to minimize the phase difference.
And a sine wave signal generator 72 for controlling the frequency applied to the. In this embodiment, the output of the optical coupler 54 is output as the regenerated optical clock signal.

In the operation, the operation of forming the optical clock signal is the same as that of the first embodiment, and the operation of the phase difference detecting means is the same as that of the fifth embodiment.

[0045]

As described above, according to the present invention, when a clock signal is regenerated from a high-speed optical signal that cannot be followed by an electric circuit, a strict requirement is imposed on the spectral line width and frequency modulation band of a laser forming an optical clock. Since it is not necessary, it is possible to realize an optical clock signal regenerator that forms an optical clock signal synchronized with an optical signal data string with an all-optical configuration, and it is possible to construct a system at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional configuration.

FIG. 3 is a diagram showing the configuration of an optical frequency control means of a second embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a third embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 6 is a block diagram showing the configuration of a fifth embodiment of the present invention.

FIG. 7 is a block diagram showing the configuration of a sixth embodiment of the present invention.

FIG. 8 is a block diagram showing the configuration of a seventh embodiment of the present invention.

[Explanation of symbols]

11, 12, 21 Laser diode 13 Optical signal correlator 14 Photodiode 15 Control circuit 16, 17 Optical coupler 22 Modulator 23, 28, 36 Sine wave signal generator 24 Optical filter 25 Acousto-optic modulator 27 Phase difference detection circuit 29 , 30 Optical coupler 31, 32 Lens 33 Mirror 34 Optical multiplexer / demultiplexer 35 Optical fiber 41, 42, 43, 44, 51, 52, 53, 54, 5
6, 61, 62, 63, 64 Optical coupler 45, 46, 56 Optical signal correlator 47 Balanced photodetector 57 Photodiode 58 Phase comparator 59 Control circuit 60 Fixed frequency oscillator 67, 71 Sine wave signal generator

Claims (10)

[Claims] 1. An optical signal oscillator (21) that oscillates at a single frequency, a modulation means (22) that modulates the output light of the optical signal oscillator and outputs the modulated light, and a specific output of this output modulated light. Optical filter means (24) for selecting and outputting two of the frequency components, optical frequency control means (25) for controlling the frequency of the output light of one of the optical filter means, and output light of the optical frequency control means And a first optical coupler (29) for combining the other output light of the optical filter means and outputting in two directions, and a phase difference between one output light of the first optical coupler and the optical signal data string is detected. And a means (28) for adjusting the optical frequency control means so as to minimize the phase difference according to the detection output of the phase difference detection means. The other output of the optical coupler is regenerated Optical clock signal reproducing apparatus characterized by being output as the clock signal. 2. An optical signal oscillator (21) which oscillates at a single frequency, a modulation means (22) which modulates the output light of this optical signal oscillator and outputs it as modulated light, and a specific output of this output modulated light. An optical filter means (24) for selecting and outputting two of the frequency components, and a first optical coupler (29) for multiplexing one output light and the other output light of this optical filter means and outputting them in two directions. And a phase difference detecting means (27, 30) for detecting a phase difference between one output light of the first optical coupler and the optical signal data string, and the phase difference is minimized according to the detection output of the phase difference detecting means. And a means (36) for controlling the modulation frequency of the modulating means so that the other output of the first optical coupler is output as a reproduced optical clock signal. 3. An optical signal oscillator (21) that oscillates at a single frequency, a modulation means (22) that modulates the output light of this optical signal oscillator and outputs it as modulated light, and a specific output of this output modulated light. Optical filter means (24) for selecting and outputting two of the frequency components and one output light and the other output light of this optical filter means are combined and output in two directions with their phases opposite to each other. A second optical coupler (43), and third and fourth optical couplers (41, 41, 41, 40) for multiplexing the output light and the optical signal data string having opposite phases to each other and branching into two.
42), a phase difference detecting means (45, 46, 47) for detecting a phase difference between the output lights of one of the third and fourth optical couplers, and the third output according to the detection output of the phase difference detecting means. And a means (36) for controlling the modulation frequency of the modulating means so that the phase difference between the outputs of the fourth multiplexing means is minimized, and the other output of the third or fourth optical coupler is a regenerated optical clock. An optical clock signal regenerator which is output as a signal. 4. An optical signal oscillator (21) that oscillates at a single frequency, a modulation means (22) that modulates the output light of this optical signal oscillator and outputs it as modulated light, and a specific output of this output modulated light. An optical filter means (24) for selecting and outputting two of the frequency components, a fifth optical coupler (51) for branching one of the output lights of the optical filter means in two directions, and an output light of the optical filter means. A sixth optical coupler (52) branching the other of the two in two directions, an optical frequency control means (25) for shifting the optical frequency of one output light of the output light of the fifth optical coupler, and the optical frequency control means A seventh optical coupler (53) for multiplexing the output light of the second optical coupler and one of the output lights of the sixth optical coupler, the other output light of the fifth optical coupler and the other output light of the sixth optical coupler. An eighth optical coupler (54) for multiplexing optical signals, and the optical frequency control A fixed frequency generating means for providing a fixed frequency Δf to the means (60), the phase difference detecting means (55, 56 for detecting a phase difference between the phase of the phase with the optical signal data string of the output light of the seventh optical coupler,
57, 58) and means (36) for controlling the modulation frequency of the modulating means so as to minimize the phase difference according to the detection output of the phase difference detecting means. An optical clock signal regenerator wherein the output is output as a regenerated optical clock signal. 5. An optical signal oscillator (21) that oscillates at a single frequency, a modulation means (22) that modulates the output light of this optical signal oscillator and outputs as modulated light, and a specific output of this output modulated light. An optical filter means (24) for selecting and outputting two of the frequency components, an optical frequency control means (25) for controlling the frequency of one output light of this optical filter means, an output light of this frequency control means and The output light of the other side of the optical filter means is combined and the phase of each other is set as the opposite phase.
The second optical coupler (63) for outputting in the direction, and the third and fourth optical couplers (61, 61, 61, 61) for multiplexing the output light and the optical signal data string having opposite phases to each other and branching into two.
62), phase difference detecting means (45, 46, 47) for detecting the phase difference between the output lights of one of the third and fourth optical couplers, and the third output according to the detection output of the phase difference detecting means. And means (65) for adjusting the optical frequency control means so as to minimize the difference in correlation between the outputs of the fourth optical coupler and the other output of the third or fourth optical coupler. An optical clock signal regenerator characterized by being output as. 6. An optical signal oscillator (21) that oscillates at a single frequency, a modulation means (22) that modulates the output light of this optical signal oscillator and outputs it as modulated light, and a specific output of this output modulated light. Optical filter means (24) for selecting and outputting two of the frequency components, first optical frequency control means (73) for shifting the optical frequency of one output light of the optical filter means, and the first optical frequency A fifth optical coupler (51) that branches one of the output lights of the control means in two directions, a sixth optical coupler (52) that branches the other of the output lights of the optical filter means in two directions, and the fifth light Second optical frequency control means (25) for shifting the optical frequency of one output light of the coupler output light, and the output light of the second optical frequency control means and one of the output lights of the sixth optical coupler are combined. A seventh optical coupler (53) that undulates, and the fifth light An eighth optical coupler (54) for multiplexing the other output light of the plastic and the other output light of the sixth optical coupler, and a fixed frequency generation means (60) for giving a fixed frequency Δf to the second optical frequency control means. ) And a phase difference detecting means (55, 56, 56) for detecting a phase difference between the phase of the output light of the seventh optical coupler and the phase of the optical signal data string.
57, 58) and means (72) for adjusting the first optical frequency control means so that the phase difference is minimized according to the detection output of the phase difference detection means. The optical clock signal regenerator is characterized in that the output of is output as a regenerated optical clock signal. 7. The two optical signal correlators for detecting the correlation between the signal data string and the output light of the second optical coupler from the output light of one of the third and fourth optical couplers, respectively. The optical clock signal regenerator according to claim 3 or 5, comprising (45, 46) and one balanced photodetector (47) for receiving the detection outputs of the two optical signal correlators. 8. The phase difference detection means electrically detects the optical signal correlator (56) for detecting the phase difference between the phase of the output light of the seventh optical coupler and the optical signal data string, and the output of this optical signal correlator. 7. The light according to claim 4, further comprising a photodiode (57) for converting into a signal, and a phase comparator (58) for phase comparison between an output signal of the photodiode and an output fixed frequency of the fixed frequency generating means. Clock signal regeneration device. 9. The optical frequency control means includes an acousto-optic modulator for shifting the frequency of an optical signal passing therethrough.
9. The optical clock signal regenerator according to any one of 5 to 8. 10. The optical frequency control means comprises an acousto-optic modulator that shifts the frequency of an optical signal that passes therethrough, and an optical device that passes light whose frequency is controlled in the forward and reverse directions on the same path of the acousto-optic modulator. 9. The optical clock signal regenerator according to claim 1, including a system.