JP3313536B2 - Optical pulse time multiplexing control method and optical pulse time multiplexing control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an optical pulse time multiplexing control method and an optical pulse time multiplexing control device for an optical communication system modulated to have a (Return to Zero) format.

[0002]

2. Description of the Related Art The configuration of a conventional optical pulse time multiplexing apparatus is shown in FIG. In this drawing, reference numeral 100 denotes a short light pulse generation circuit that generates a short light pulse using a laser diode (LD) or the like, 101 denotes a branching circuit that branches the short light pulse into two, one system and two systems, and 102 denotes a demultiplexing circuit. A modulator for modulating the optical pulse of the first system by the transmission information signal 1, 103 is a semi-fixed delay circuit for delaying the modulated optical pulse, 104 is a first system composed of the modulator 102 and the semi-fixed delay circuit 103, and 105 is 2 Modulator for modulating the optical pulse of the system by the transmission information signal 2, 10
6 is a semi-fixed delay circuit for delaying the modulated optical pulse, 1
Reference numeral 07 denotes a two-system comprising a modulator 105 and a semi-fixed delay circuit 106, and 108 outputs an optical pulse time multiplexed signal by synthesizing an optical pulse output from the first system 104 and an optical pulse output from the second system 107. It is a multiplexing circuit.

In the optical pulse time multiplexing apparatus configured as described above, the short light pulse a as shown in FIG. Is input to the demultiplexing circuit 101 and branched into two optical waveguides. One of the branched short optical pulses is input to the first system 104, and the modulator 102 modulates the light intensity of the one short optical pulse by the transmission information signal 1 synchronized with the repetition period of the short optical pulse. , And is further delayed by the semi-fixed delay circuit 103 for a predetermined time.

The other short optical pulse is input to the second system 107, and is modulated in the modulator 105 by the transmission information signal 2 synchronized with the repetition period of the short optical pulse, as shown in FIG. The modulated short optical pulse c in the RZ format is further delayed by the semi-fixed delay circuit 106 for a predetermined time. Then, the modulated short optical pulse b from the first system and the modulated short optical pulse c from the second system 107 are input to the multiplexing circuit 108 and synthesized on the time axis. Is output. The period of the time multiplexed signal d is set to の (the repetition frequency is twice) of the repetition period of the short light pulse generated from the short light pulse generation circuit 100.

[0005] The semi-fixed delay circuit 103 and the semi-fixed delay circuit 106 need to be combined so that the period of the time multiplexed signal d becomes １ ／ of the repetition period of the short optical pulse generated from the short optical pulse generation circuit 100. Modulated short light pulse b when
Since the modulated short light pulse c needs to be located at the center between the short light pulses c and c, it is provided to adjust the time relationship between the modulated short light pulse b and the modulated short light pulse c. As described above, by time-multiplexing the optical pulse signals of the first and second systems, the transmission capacity can be doubled or more, and an efficient optical communication system can be provided.

[0006]

In the above-described conventional optical pulse time multiplexing apparatus, after adjusting the delay times of the semi-fixed delay circuit 103 and the semi-fixed delay circuit 106 so as to be optimum, the respective delay times are adjusted. Is fixed. However, the section required to generate the modulated short optical pulses b and c, that is, the output of the demultiplexing circuit 101,
In many cases, the route to the input of 8 is spatially different from each other for reasons of device configuration and manufacturing. Further, the respective path lengths are generally different in many cases.

The path of a short optical pulse is usually constructed by an optical fiber. However, since the optical fiber has a temperature characteristic that expands and contracts depending on the temperature, the length of the optical fiber is random due to the fluctuation of each environmental temperature. To fluctuate. Therefore, if the path lengths are different, the relative time between the modulated short optical pulses of the time multiplexed signal d output from the multiplexing circuit 108 fluctuates randomly. On the other hand, in order to separate the modulated short optical pulse b and the modulated short optical pulse c from the time multiplexed signal d on the receiving side, the pulse repetition frequency of the time multiplexed signal d is extracted, and the timing based on the extracted pulse repetition frequency is extracted. It is necessary to separate the modulated short optical pulse b and the modulated short optical pulse c.

However, when the pulse repetition period of the time multiplexed signal d fluctuates as described above, jitter occurs in the pulse repetition frequency, and the modulated short optical pulse b and the modulated short optical pulse c are accurately detected on the receiving side. However, there has been a problem that transmission characteristics are deteriorated, and good communication cannot be performed. Furthermore, in optical soliton communication at a transmission speed of 20 Gbps, timing jitter at the receiving end is considered to be the main cause of deterioration of transmission characteristics. However, when the error rate is limited to 10 ⁻¹⁰ due to timing jitter, the transmission In the optical time multiplexing device, the timing is 2 picoseconds (2 × 10
It is known that the error rate is degraded by one digit or more when it fluctuates ( ⁻¹² sec; 2 ps).

In consideration of the above, in order to prevent the time fluctuation of the transmitting apparatus from being reflected in the error rate, 1/5 of the bit interval is required.
It is necessary to arrange a plurality of optical pulse trains with an accuracy of 0 or less. The time fluctuation of about 2 ps corresponds to a length of about 0.4 mm in terms of fluctuation of the optical fiber length. This conversion is obtained by calculating “length of optical fiber” = “propagation time (2p
s)] × “light speed (3 × 10 ⁸ )” ÷ “propagation coefficient of optical fiber (1.47)”. However, since the expansion and contraction rate of an optical fiber protected by a commonly used nylon coating is about 3 × 10 ⁻⁵ (° C. ⁻¹ ),
For example, when two optical circuits are in the same temperature environment and there is a difference of 1 m in the length of the optical fiber, 3 × 1 in a temperature change of 1 ° C.
A fluctuation of 0 ^-5 m occurs. Further, when a temperature change of 14 ° C. occurs, the fluctuation of the optical fiber length exceeds 0.4 mm and exceeds the above-mentioned limit of the error rate, so that the transmission characteristics deteriorate.

To explain using another example, for example, two systems of optical circuits are set at different positions, and the length of an optical fiber constituting each optical fiber circuit is one.
In the case of 0 m and the same length, if a difference of 1 ° C. occurs between the surrounding temperatures accommodating the respective optical circuits, 3 × 10
^-4 m, and a temperature difference of 2 ° C., the variation in the length of the optical fibers constituting the two optical circuits is 6 × 10 ^-4 m (0.6 mm), Beyond the limit of .4 mm, the transmission characteristics deteriorate. Therefore, the conventional optical pulse time multiplexing apparatus has a problem that it cannot be operated stably without deteriorating transmission characteristics over a long period of time. Further, in order to realize optical communication having a transmission speed exceeding 20 Gbps, the above-mentioned fluctuation of the optical fiber length is more severely restricted.

An object of the present invention is to provide an optical pulse time multiplexing control method and an optical pulse time multiplexing control device which can maintain good transmission characteristics over a long period of time and operate stably.

[0012]

According to the optical pulse time multiplexing control method of the present invention, a plurality of systems of optical pulses are branched, and a repetition frequency signal of each optical pulse is extracted.
Using one repetition frequency signal of the extracted plural systems as a reference signal, and performing phase detection with each of the remaining plural systems of repetition frequency signals, and when the plurality of optical pulses are time-multiplexed, The delay time of the light pulse of the remaining system is feedback-controlled in accordance with the result of the phase detection so that the light pulses of the system are arranged at equal intervals.

In the above-described optical pulse time multiplexing control method, the optical pulse output from the optical pulse generating circuit is branched into a plurality of light pulses, and each of the branched light pulses is modulated by transmission information to transmit the plurality of light pulses. In addition, only one system is provided with phase detection means for performing the processes from the extraction to phase detection, and the light pulses of the plurality of branched systems are time-divided, The output is supplied to phase detection means provided only in the system, and the output of the phase detection means is distributed to each system and fed back to control the delay time.

Further, an optical pulse time multiplexing control device embodying the optical pulse time multiplexing control method of the present invention is an extracting means for splitting a plurality of systems of optical pulses and extracting a repetition frequency signal of each optical pulse. And a delay means capable of changing a delay time inserted in a path of each optical pulse so that when optical pulses of a plurality of systems are time-multiplexed, the optical pulses are arranged at equal intervals. A phase detector that detects a relative phase with a repetition frequency signal of the remaining plural systems, using one repetition frequency signal of the plural systems extracted by the extraction unit as a reference signal, and By providing a means for performing feedback control of the delay time by a phase detection signal output from the phase detector, the optical pulse trains of the plurality of systems are arranged at equal intervals. During is obtained so as to be multiplexed arrangement.

In the above-described optical pulse time multiplexing control apparatus, a multi-branch circuit for branching an optical pulse output of an optical pulse generation circuit into a plurality of optical pulses, and a plurality of modulators for modulating each of the plurality of branched optical pulses with transmission information. Comprising a plurality of optical pulses that are output from the plurality of modulators, an optical demultiplexer that branches the optical pulses of the plurality of systems, and the optical demultiplexer that is provided after the optical demultiplexer. And an optical multiplexer configured to perform time multiplexing by combining the optical pulses of the plurality of systems, and the propagation time of an optical line connecting the optical demultiplexer and the optical multiplexer has no adverse effect. To the extent, the optical line is shortened, an optical demultiplexer that branches the optical pulses of the plurality of systems, and an optical detector that optically detects the optical pulse branched by the optical demultiplexer. Provided, the optical demultiplexing The optical line connecting the optical detector and the optical detector is configured such that the optical line is shortened to the extent that the propagation time does not adversely affect the optical line, and only one phase detection unit from the extraction unit to the phase detector is provided. The divided plural optical pulses are time-divided and supplied to a phase detection unit provided only in one system, and the output of the phase detection unit is distributed to each system and the delay is performed. This is to be fed back to the means.

[0016]

According to the present invention, feedback control is performed so that the relative time positions of a plurality of time-multiplexed optical pulses do not fluctuate. Time multiplexing can be performed while maintaining intervals. Therefore, it is possible to construct a good optical communication system capable of maintaining transmission characteristics with a low error rate over a long period of time. The number of systems that can be time-multiplexed is not limited to two, and three or more optical pulses can be time-multiplexed stably while maintaining good transmission characteristics with a low error rate.

[0017]

1A and 1B are block diagrams of a first embodiment of an optical pulse time multiplexing control device embodying an optical pulse time multiplexing control method according to the present invention. In FIG. 1A, reference numeral 40 denotes a short light pulse generation circuit that generates a short light pulse using a laser diode (LD) or the like, and 41 denotes a demultiplexer that branches the short light pulse into two, one system and two systems. A circuit 42 for modulating an optical pulse of the first system with the transmission information signal 1; 43
Is a modulator for modulating the optical pulses of the two systems with the transmission information signal 2.

In FIG. 1B, reference numerals 1 and 3 denote semi-fixed delay circuits for respectively delaying the inputted optical pulse signals A and B by a predetermined time, and 2 denotes an optical pulse signal delayed by the semi-fixed delay circuit 1. An optical demultiplexer 4 for splitting the signal Bd into two is a semi-fixed delay circuit 3 according to a control signal applied from the outside.
An external control type variable delay circuit for delaying the optical pulse signal delayed by the external control type variable delay circuit, an optical splitter for splitting the optical pulse signal Ad delayed by the external control type variable delay circuit into two,
Is an optical multiplexer that outputs one optical pulse time multiplexed signal C by combining one optical pulse signal Bd branched by the optical demultiplexer 2 and one optical pulse signal Ad branched by the optical demultiplexer 5. It is.

Reference numerals 7 and 11 denote light receiving devices for receiving the other optical pulse signal Bd branched by the optical demultiplexer 2 or the other optical pulse signal Ad branched by the optical demultiplexer 5 and converting the same into an electric signal. Devices 8 and 12 are amplifiers for amplifying respective pulse signals converted into electric signals output from the light receivers 7 and 11;
Bandpass filters (BPF) 9 and 13 extract the repetition frequency components of the respective pulse signals amplified by the amplifiers 8 and 12, and 10 and 14 shift the phases of the frequency components extracted by the BPFs 9 and 13, respectively. A phase shifter 15 is a phase detector for detecting a relative phase of a frequency component output from the phase shifters 10 and 14, and 16 is a filter for filtering a phase detection signal output from the phase detector 15 according to a phase difference. , A low-pass filter (LPF) 17 for removing a noise component included in the phase detection signal, an amplifier 17 for amplifying the filtered signal output from the LPF 16, and 18 according to an error voltage output from the amplifier 17. This is a phase adjustment control circuit that controls the amount of delay of the external control type variable delay circuit 4.

In the optical pulse time division multiplexing control device constructed as described above, the short light pulse a as shown in FIG. 1A is continuously generated at predetermined intervals from the short light pulse generation circuit 40 shown in FIG. The short light pulse a is supplied to the branching circuit 41.
And branched into two optical waveguides. One of the branched short optical pulses is input to the first system, and the modulator 42 transmits the transmission information signal 1 synchronized with the repetition period of the short optical pulse.
Is modulated into a modulated short optical pulse A in the RZ format. The other short optical pulse that has been branched is input to the second system, and the light intensity is modulated by the modulator 43 in accordance with the transmission information signal 2 that is synchronized with the repetition period of the short optical pulse. Pulse B is set.

The modulated short optical pulse B is input to the semi-fixed delay circuit 1 shown in FIG. 1B, is delayed for a predetermined time to form an optical pulse signal Bd as shown in FIG. One of the branched optical pulse signals Bd is input to the optical multiplexer 6, and the other optical pulse signal Bd is input to the optical receiver 7. The modulated short optical pulse signal A input to the semi-fixed delay circuit 3 is delayed by a predetermined time in the semi-fixed delay circuit 3 and the externally controlled variable delay circuit 4 to become an optical pulse signal Ad as shown in FIG. Then, the light is split into two in the optical splitter 5, and one of the split optical pulse signals Ad is input to the optical multiplexer 6, and the other split optical pulse signal Ad is input to the light receiver 11.

Since the present invention automatically adjusts the phase relationship between the optical pulse signals Bd and Ad in the optical multiplexer 6, the optical receiver 7 for detecting the respective phase states is used. And 11 are output from the optical multiplexer 6
Must faithfully represent the phase relationship between the optical pulse signals Bd and Ad. However, the optical fiber between the optical demultiplexer 2 and the optical multiplexer 6, the optical demultiplexer 2 and the optical receiver 7, the optical demultiplexer 5 and the optical multiplexer 6, and the optical fiber between the optical demultiplexer 5 and the optical receiver 11 are not shown. Since the variation in length gives an error to the detection accuracy of the phase relationship between the optical pulse signal Bd and the AD in the optical multiplexer 6, it is necessary to keep the length of these optical fibers stable. 6 is nothing less than improving the accuracy of the phase detection. The following method can be considered to keep the length of the optical fiber stable.

As shown in FIG. 5, the optical demultiplexers 2 and 5, the optical multiplexer 6, and the photodetectors 7 and 11 are integrated, an optical fiber connecting them is eliminated, and an error factor of phase detection is eliminated. The optical splitters 2 and 5, the optical multiplexer 6, and the light receivers 7 and 11 are installed on the same temperature environment, and are housed on the same substrate or a case, for example, so that the optical splitter 2 and the optical multiplexer 6 Between the optical splitter 2 and the optical receiver 7, between the optical splitter 5 and the optical multiplexer 5.
The length between the optical splitter 5 and the photodetector 11 is set to 50 cm or less, thereby enabling phase detection with less error. This is a case where a nylon-coated optical fiber core wire is used. In the case of an optical fiber using a coating with a small expansion and contraction rate such as an ultraviolet curing resin, 5 m is used.
If the following conditions are satisfied, sufficient phase detection accuracy can be maintained.

Continuing the description, the optical pulse signal Ad and the optical pulse signal Bd input in the optical multiplexer 6 are combined to form an optical pulse time multiplexed signal C as shown in the figure. The pulse repetition frequency of the optical pulse time multiplexed signal C is twice the pulse repetition frequency of the optical pulse signal Ad or the optical pulse signal Bd.
The delay time of the externally-controlled variable delay circuit 4 is controlled as described later so that the optical pulse signal Bd and the optical pulse signal Bd are alternately arranged at equal time intervals.

That is, the optical pulse signal Bd received by the photodetector 7 is converted into an electric signal and then amplified by the amplifier 8, and then the pulse repetition frequency component is extracted by the BPF 9. The optical pulse signal Ad received by the optical receiver 11 is converted into an electric signal and then amplified by the amplifier 12, and then the pulse repetition frequency component is extracted by the BPF 13. After the relative phase of the pulse repetition frequency component from the BPF 9 and the pulse repetition frequency component from the BPF 13 are adjusted by the phase shifters 10 and 14, respectively, the phase detector 15 compares the positions of the two frequency components fa and fb. A phase difference is detected. (Phase shifter 10,
The adjustment of 14 will be described later. )

The output signal from the phase detector 15 is an LPF
16 and an amplifier 17 to output an error voltage. This error voltage is applied as a delay amount control signal to the external control type variable delay circuit 4 via the phase adjustment control circuit 18, whereby the relative time position between the optical pulse signal Ad and the optical pulse signal Bd fluctuates. Feedback control so that there is no Therefore, the optical pulse signals A and B
Can fluctuate, the time multiplexed signal C in which the optical pulse signals Ad are arranged in the center between the optical pulse signals Bd can be generated.

The initial adjustment of the semi-fixed delay circuits 1 and 3 and the phase shifters 10 and 14 is performed as follows. First, after setting the delay amount of the external control type variable delay circuit 4 at the center of the operation range, the optical pulse time multiplexed signal C output from the optical multiplexer 6 is observed, and the optical pulse signal Ad and the optical pulse signal Bd are observed. The delay amounts of the semi-fixed delay circuit 1 and the semi-fixed delay circuit 3 are adjusted so that the time arrangement of the above is optimized. Next, the phase shift amounts of the phase shifters 10 and 14 are adjusted so that the error voltage output from the amplifier 17 becomes zero.
With this adjustment, the phase relationship between the pulse repetition frequency component fa of the optical pulse signal Ad input to the phase detector 15 and the pulse repetition frequency component fb of the optical pulse signal Bd becomes π / 2 radians. Here, when the delay control range of the external control type variable delay circuit 4 is sufficient, the initial value of the external control type variable delay circuit 4 is set so as to optimize the time allocation even if the semi-fixed delay circuit 1 and the like are omitted. can do. Further, when the phase shift range of the phase shifters 10 and 14 is 90 ° or more, one of the phase shifters 10 and 14 can be omitted, and economy can be achieved.

The phase detector 15 is composed of a multiplier as shown in FIG. 2A, and its phase detection characteristic is as shown in FIG. That is, the phase detector 1
5, the pulse repetition frequency component fa of the light pulse Ad and the pulse repetition frequency component fb of the light pulse Bd
Is zero (a phase matching state) when the phase relationship is π / 2 and -π / 2. Therefore, it can be seen that phase detection is possible in two regions where the phase relationship between the frequency component fa and the frequency component fb is 0 to π and -π to 0.

Here, the frequency component fa and the frequency component fb
If the relative time change from the optimum value (π / 2) of the frequency component fa is θ under the condition that the phase relationship of 0 to π is θ, the error voltage is cos (π / 2 + θ), that is, −sin θ. Therefore, when the phase relationship between the optical pulse signal Ad and the optical pulse signal Bd, which are the optical pulse time multiplexed signal C, is optimal,
The error voltage of the output of the phase detector 15 becomes zero, while an error voltage occurs when the phase relationship between the optical pulse signal Ad and the optical pulse signal Bd fluctuates from the optimum value.
The error voltage has a polarity and an amplitude corresponding to the phase change direction and the time change amount.

Further, referring to FIG.
FIG. 3A shows a case where the phase relationship between the optical pulse signal Ad and the optical pulse signal Bd is optimized, and the phase difference between the optical pulse signal Ad and the optical pulse signal Bd is π / It is 2. At this time, the error voltage is set to zero as shown in the lower part. FIG. 3B shows a case where the optical fiber length fluctuates due to fluctuations in the environmental temperature and the like, and the phase relationship between the optical pulse signal Ad and the optical pulse signal Bd becomes larger than when optimal. . At this time, the phase relationship between the pulse repetition frequency component fa of the optical pulse signal Ad and the pulse repetition frequency component fb of the optical pulse signal Bd at the input of the phase detector 15 is shown in the upper part, and the error voltage is shown in the lower part. ing. This error voltage becomes negative, and the phase adjustment control circuit 18 controls the error voltage to be zero by gradually shortening the delay amount of the external control type variable delay circuit 4, as shown in FIG. To the optimal conditions.

FIG. 3 (c) shows a case where the length of the optical fiber fluctuates due to fluctuations in the environmental temperature and the like, and the phase relationship between the optical pulse signal Ad and the optical pulse signal Bd becomes smaller than the optimal case. Is shown. At this time, the pulse repetition frequency component fa of the optical pulse signal Ad at the input of the phase detector 15
A phase relationship between the pulse repetition frequency component fb and the pulse repetition frequency component fb of the optical pulse signal Bd is shown in the upper part, and an error voltage is shown in the lower part. The error voltage becomes positive, and the phase adjustment control circuit 18 controls the error voltage to be zero by gradually increasing the delay amount of the external control type variable delay circuit 4 to thereby reduce the error voltage to zero as shown in FIG. To the optimal conditions.

On the other hand, it is better to set the phase relationship between the frequency component fa and the frequency component fb to -π to 0 due to the difference in the electrical length of the electrical path from the light receiver 7 and the light receiver 11 to the phase detector 15. , The phase shifter 10 and the phase shifter 14 may be convenient. In this case, the phase relationship between the frequency component fa and the frequency component fb in the optimum state is −
π / 2. Further, the optimum value of the frequency component fa (−π /
If the relative time change from 2) is θ, the error voltage is co
s (−π / 2 + θ), that is, sin θ. Therefore, the polarity of the error voltage is opposite to the case where the phase relationship between the frequency component fa and the frequency component fb is set to 0 to π, but the control direction for increasing / decreasing the delay amount of the external control type variable delay circuit 4 is reversed. Then, it will be possible to draw in the optimum conditions.

Next, an example of the configuration of the external control type variable delay circuit 4 is shown in FIG. In this figure, 4-1 is a prism which can be moved back and forth by an actuator or the like. That is, if the prism 4-1 is retracted by a distance d as shown by a broken line, for example, due to the error voltage from the phase adjustment control circuit 18, the path of the input light Ain becomes longer by 2d, and the output light delayed by that amount. Aout is output. In this way, the prism 4- in accordance with the error voltage
By controlling 1 back and forth, it is possible to delay by a predetermined amount.

Next, FIG. 6 is a block diagram of an optical pulse time multiplexing control apparatus according to a second embodiment of the present invention which can optically time multiplex two or more systems of optical pulse signals.
In this figure, the optical pulse signal R input to the optical demultiplexer 21 is changed to the optical pulse signals 1, 2, 3,. Are time reference signals when time multiplexing is performed.
The optical pulse signal R in the Z format is applied to the optical demultiplexer 2.
In FIG. 1, one of the branched optical pulse signals R is input to the optical multiplexer 23, and the other of the branched optical pulse signals R is input to the optical receiver 24.

The optical pulse signal R input to the light receiver 24 is converted into an electric signal and amplified by the amplifier 25. Then, the pulse repetition frequency component is extracted by the BPF 26, further amplified by the amplifier 27, and distributed to N dividers (DIV) 32. Also,
The modulated RZ input to the external control type variable delay circuit 1 is
The optical pulse signal A in the format is delayed by a predetermined time in the externally controlled variable delay circuit 1 to become an optical pulse signal A1, and then branched into two in the optical demultiplexer 22-1 and branched. One optical pulse signal A1 is sent to the optical multiplexer 23, and the other optical pulse signal A1 is sent to the optical receiver 2
8-1.

The light pulse signal A1 input to the light receiver 28-1 is converted into an electric signal and amplified by the amplifier 29-1. Then, the pulse repetition frequency component is extracted by the BPF 30-1, and further the phase is shifted by the phase shifter 31-1 and input to the phase detector 33-1.
Phase detection is performed by multiplying the pulse repetition frequency component of the optical pulse signal R distributed in 2 by the pulse repetition frequency component. The output signal from the phase detector 33-1 is an LPF 34-
The error voltage is filtered by 1 and amplified by the amplifier 35-1 to obtain an error voltage 1.

The processing of the modulated optical pulse signals 2 to N input to the externally controlled variable delay circuits 2 to N in the RZ format is performed in the same manner as the optical pulse signal 1.
Error voltages 2 to N corresponding to the phase error with the optical pulse signal R are output from the amplifiers 35-2 to 35-N, respectively. The error voltages 1, 2,... N are externally controlled variable delay circuits 36-1, 36-2,.
36-N, and the optical pulse signals 1, 2,.
-The phase of N is adjusted.

By the way, the optical pulse signal R and the optical pulse signals A1 to AN inputted in the optical multiplexer 23 are combined to form an optical pulse time multiplexed signal C as shown in FIG.
It is said. The pulse repetition frequency of the optical pulse time multiplexed signal C is the optical pulse signal R or the optical pulse signal 1,
,... N times (N + 1) times the pulse repetition frequency of the optical pulse signal R and the optical pulse signals 1, 2,.
The externally-controlled variable delay circuits 1, 2,..., N are arranged at equal time intervals and their time positions are not fluctuated.
The phase amount of N is feedback-controlled. The operation of the feedback control is performed in the same manner as in the embodiment shown in FIG. 1, and the description thereof will be omitted.

Next, the externally controlled variable delay circuits 1, 2,.
..N and phase shifters 31-1, 31-2,... 31-
The initial adjustment of N will be described with reference to FIG. The optical pulse signal R and the optical pulse signals 1, 2,... N are generated as shown in FIG. ing. At the time of the initial adjustment, first, the optical pulse time multiplexed signal C output from the optical multiplexer 23 is observed, and the time arrangement of the optical pulse signals 1, 2,. External control type variable delay circuit 1,
2,... N are adjusted. In this case, assuming that the period of the optical pulse signal R is T, the optical pulse signals 1, 2,... N are 1T / (N + 1) as indicated by A1 to AN in FIG. , 2T / (N +
1),... NT / (N + 1).

Next, the amplifiers 35-1, 35-2,...
,... N output from 35-N become zero, respectively, so that the phase shifters 31-1, 31-2,.
Adjust the 31-N phase shift. With this adjustment,
The phase relationship between the optical pulse signal R converted to the optical pulse time multiplexed signal C and the optical pulse signals 1, 2,... N is 2π / (N +
1), 4π / (N + 1),... 2Nπ / (N + 1) radians, and phase detectors 33-1, 33-2,
, 33-N and the phase relationship between the pulse repetition frequency components of the optical pulse signals 1, 2,... N are respectively π / 2 radians.

Thus, control can be performed so that the relative time positions of the optical pulse signal R and the optical pulse signals 1, 2,... N do not fluctuate. Therefore, it is possible to generate a time multiplexed signal C in which the optical pulse signals 1, 2,... N are arranged at equal time intervals between the optical pulse signals R as indicated by C in FIG.

Next, the configuration of a modification of the second embodiment of the present invention is shown in FIG.
, A set of photodetectors 28, an amplifier 29, a BPF 30, a phase shifter 31,
Are commonly used. That is, the optical demultiplexer 22
An optical pulse signal A1, A2,... AN branched by -1, 22-2,. , An amplifier 29, a BPF 30, and a phase shifter 31, the repetition frequency signal is extracted and made to have a predetermined phase. Then, a relative phase with respect to the optical pulse signal R is detected by the phase detector 33, further filtered by the LPF 34, amplified by the amplifier 35, and converted into an error voltage. This error voltage is input to the distribution circuit 38 and distributed to the phase adjustment control circuit 36-1 by the distribution circuit 38 to be a signal for controlling the phase amount of the externally controlled variable delay circuit 1.

Accordingly, the control is performed so that the phase amount of the optical pulse signal 1 becomes a predetermined phase amount. As described above, any one of the phase adjustment circuits 36-1, 36-2,... 36-N of the system selected by the distribution circuit 38 so as to control the phase of the optical pulse signal of the system selected by the selection circuit 37. Crabs are distributed to supply error voltage. This makes it possible to simplify the configuration of the optical pulse time multiplexing control device. The other operation of the feedback control in this modified example is the same as that of the second embodiment, and the description thereof will be omitted.

[0044]

Since the present invention is configured as described above, feedback control can be performed so that the relative time positions of a plurality of time-multiplexed light pulses do not fluctuate, and a plurality of light pulses of a plurality of systems can be controlled. Can be time-multiplexed so that the time position of the data does not fluctuate and maintain an equal time interval. Therefore, a good optical communication system with a low error rate can be constructed over a long period of time. The number of systems that can be multiplexed is not limited to two, and optical pulse signals of three or more systems can be time-multiplexed stably while maintaining good transmission characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of an optical pulse time multiplexing control device of the present invention.

FIG. 2 is a diagram showing a phase detection characteristic of a phase detector in the optical pulse time multiplexing control device of the present invention.

FIG. 3 is a diagram for explaining a phase detection operation of a phase detector in the optical pulse time multiplexing control device of the present invention.

FIG. 4 is a diagram illustrating an example of an externally controlled variable delay circuit.

FIG. 5 is a diagram showing a structure in which two systems of an optical demultiplexer, a light receiver, and an optical multiplexer are packaged.

FIG. 6 is a block diagram of a second embodiment of the optical pulse time multiplexing control device of the present invention.

FIG. 7 is a diagram showing the timing of an optical pulse signal of the optical pulse time division multiplexing control device of the second embodiment.

FIG. 8 is a block diagram showing a configuration of a modification of the second embodiment.

FIG. 9 is a block diagram and timing chart of a conventional optical pulse time multiplexing control device.

[Explanation of symbols]

1,3,103,106 Semi-fixed delay circuit 2,5,21,22-1-22-N Optical demultiplexer 4 Externally controlled variable delay circuit 6,23 Optical multiplexer 7,11,24,28-1 -28-N light receiver 8,12,17,25,29-1 ~ 29-N, 35,3
5-1 to 35-N amplifier 9, 13, 26, 30-1 to 30-N Band-pass filter (BPF) 10, 14, 31-1 to 31-N Phase shifter 15, 33-1 to 33-N Phase detector 16, 34, 34-1 to 34-N Low-pass filter (LPF) 18, 36 Phase adjustment control circuit 32 Divider 37 Selection circuit 38 Distribution circuit 40, 100 Short optical pulse generation circuit 41, 101 Demultiplexing circuit 42, 43, 102, 105 modulator 104 1 system 107 2 system 108 multiplexing circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-107703 (JP, A) JP-A-7-38575 (JP, A) JP-A-3-117236 (JP, A) JP-A-60-1985 90443 (JP, A) JP-A-6-141002 (JP, A) JP-A-4-100016 (JP, A) JP-A-8-23303 (JP, A) (58) Fields investigated (Int. Cl. ^7, DB name) H04J 14/08 H04B 10/00 - 10/28 JICST file (JOIS)

Claims (8)

(57) [Claims] An optical pulse of a plurality of systems is branched, and a repetition frequency signal of each optical pulse is extracted.
Using one repetition frequency signal of the extracted plural systems as a reference signal, and performing phase detection with each of the remaining plural systems of repetition frequency signals, and when the plurality of optical pulses are time-multiplexed, An optical pulse time multiplexing control method, wherein the delay time of the remaining optical pulses is feedback-controlled in accordance with the result of the phase detection so that the optical pulses of the systems are arranged at equal intervals. 2. An optical pulse output from an optical pulse generating circuit is divided into a plurality of optical pulses, and each of the divided optical pulses is modulated by transmission information to be an optical pulse of the plurality of systems. 2. The optical pulse time multiplexing control method according to claim 1, wherein: 3. A phase detection device comprising only one phase detection means for performing a process from the extraction to phase detection is provided, and the plurality of branched optical pulses are time-divided to provide only the one system. 3. The optical pulse time division multiplexing control method according to claim 1, wherein an output of said phase detecting means is distributed to respective systems and fed back so as to control a delay time. 4. An extracting means for branching optical pulses of a plurality of systems and extracting a repetition frequency signal of each optical pulse, and when the optical pulses of the plurality of systems are time-multiplexed, each optical pulse is equal to each other. A delay unit that can vary the delay time inserted in each optical pulse path so as to be arranged at intervals; and a repetition frequency signal of one of a plurality of systems extracted by the extraction unit as a reference signal. A phase detector for detecting a relative phase with each of the repetition frequency signals of the remaining plural systems, and a means for feedback-controlling the delay time of the delay means with a phase detection signal output from the phase detector. The optical pulse time multiplexing control device, wherein the optical pulse trains of the plurality of systems are time-multiplexed at equal intervals. 5. A multi-branch circuit for branching an optical pulse output of an optical pulse generation circuit into a plurality of optical pulses, and a plurality of modulators for modulating each of the plurality of optical pulses with transmission information, the plurality of modulators being provided. 5. The optical pulse time division multiplexing control device according to claim 4, wherein the optical pulses of the plurality of systems are output from a device. 6. An optical demultiplexer for branching the optical pulses of the plurality of systems, respectively, and an optical demultiplexer disposed after the optical demultiplexer and time-multiplexing by synthesizing the optical pulses of the plurality of systems. An optical multiplexer, wherein the optical line is shortened to such an extent that a propagation time of an optical line connecting the optical demultiplexer and the optical multiplexer is not adversely affected. An optical pulse time multiplexing control device as described in the above. 7. An optical demultiplexer for branching the optical pulses of the plurality of systems, and an optical detector for optically detecting the optical pulses branched by the optical demultiplexer, wherein the optical demultiplexer and 7. The optical pulse time division multiplexing control device according to claim 4, wherein said optical line is shortened so as not to adversely affect the propagation time of the optical line connecting to the optical detector. 8. A phase detection section from said extraction means to a phase detector is provided in only one system, and the plurality of branched optical pulses are time-divided to provide a phase in only one system. 8. The optical pulse time multiplexing control device according to claim 4, wherein an output of the phase detection unit is supplied to a detection unit, distributed to respective systems, and fed back to the delay unit. .