JPH08307390A - Method and device for multiplexing optical pulse time - Google Patents

Abstract

PURPOSE: To safely and easily extract a clock signal through a narrow band pass filter on the receiving side by transmitting a multiplexed optical pulse string obtained by superposing the optical pulse strings of respective channels at irregular time intervals. CONSTITUTION: A reference optical pulse string with an 100ps period is distributed to reference optical pulse strings for four channels having the same period and phase. The reference optical pulse strings of four channels are respectively modulated by respective optical modulators 2a to 2d corresponding to respective channels in accordance with the transmission signals of the corresponding channels. The optical pulse strings of four channels modulated by the modulators 2a to 2d are respectively delayed by optical delays 3a to 3d corresponding to respective channels. The optical pulse strings of respective channels are successively delayed in each time lag 20PS from 0PS up to 60PS. The optical pulse strings of four channels delayed by these delays 3a to 3d are coupled by a photocoupler 4 and outputted as one multiplexed optical pulse string.

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 that enables ultra-high-speed optical communication by temporally multiplexing an optical pulse train of a return zero system and transmitting it as a high-density multiplexed optical pulse train. The present invention relates to a multiplexing method and an apparatus thereof.

[0002]

2. Description of the Related Art An optical soliton pulse is formed by balancing dispersion in an optical fiber and a non-linear effect (self-phase modulation effect) in which a refractive index changes with light intensity. Therefore, this optical soliton pulse is more than 2 wavelengths below the zero-dispersion wavelength of the optical fiber so that very little dispersion occurs.
Light on the long wavelength side of about 10 nm is used. The zero-dispersion wavelength is the wavelength of light at which the dispersion value of the optical fiber is 0 ps / km / nm (ps represents p seconds), and the wavelength near 1.3 μm or 1.5 μm is zero in a normal optical fiber. It becomes a dispersion wavelength. Further, this optical soliton pulse must be strong enough so that the light intensity causes a non-linear effect, and therefore, for example, FWHM (the time during which the optical pulse lasts more than half the amplitude of the peak power) has a peak power of 10 to 15 ps. Is required to be a steep optical pulse of about 10 to 20 mW. An experiment using FWHM of this optical pulse of 1 ps or less has also been reported.

The optical soliton pulse is originally transmitted as an isolated wave, but in the optical soliton transmission, this optical pulse is transmitted as an optical pulse train having a predetermined period. At this time, since each light pulse requires a predetermined FWHM and peak power, the light pulse is transmitted or blocked according to "0" and "1" of the digital signal to thereby perform intensity modulation (amplitude modulation) depending on the presence or absence of the light pulse. Modulation) is performed. In addition, the optical pulse train in this optical soliton transmission requires a non-lighting state for a sufficient time between the optical pulses, and thus the non-return-zero method (NRZ method) is generally used for ordinary optical communication. However, it is a signal of the return zero system (RZ system).

In the electrical transmission of signals, 10
If it exceeds Gbit / s (G bits per second), the pulse width of the electric signal becomes extremely narrow, which makes it very unwieldy and impractical. However, in optical soliton transmission, at a transmission rate of 10 Gbit / s, the time interval of each optical pulse is 100 ps, so FWHM is 10 p
As a result, it is possible to secure enough time without light. Therefore, by superimposing the optical pulse train of another signal sequence on the optical pulse train of one sequence while shifting the time, the optical pulse trains of a plurality of signal sequences can be multiplexed at high density to enable ultrahigh-speed optical communication. For example, a multiplexed optical pulse train of 80 Gbit / s obtained by multiplexing 8 channels of an optical pulse train of 10 Gbit / s, or 1
A transmission experiment of a 160 Gbit / s multiplexed optical pulse train in which 6 channels are multiplexed has already been reported.

FIG. 4 shows an example of a conventional optical pulse time multiplexing apparatus for multiplexing a 4-channel optical pulse train. In this optical pulse time multiplexing device, a basic optical pulse train having a cycle of 100 ps is input to the optical distributor 1.
The optical distributor 1 converts the input 1-sequence basic optical pulse train into 4
It is an optical circuit element that distributes and outputs to the basic optical pulse train of the channel. The four-channel basic optical pulse train output from the optical distributor 1 is input to the optical coupler 4 via the optical modulators 2a to 2d and the optical delay devices 3a to 3d, respectively. Each of the optical modulators 2a to 2d is a circuit element that modulates an optical pulse train by controlling transmission or blocking of an optical pulse according to an electric transmission signal of a corresponding channel. The optical delay devices 3a to 3d are optical circuit elements that delay the optical pulse train by a predetermined delay time, and the delay time is 0 ps, 25 ps, 50 p for each channel.
s and 75 ps so that a time difference of 25 ps (a phase difference of 90 °) is sequentially generated. The optical coupler 4 is an optical circuit element that combines the input 4-channel optical pulse trains and outputs a series of multiplexed optical pulse trains.

This optical pulse time multiplexer has a period of 10
The optical modulators 2a to 2d independently modulate the 4-channel basic optical pulse train of 0 ps (10 Gbit / s), and the optical delay devices 3a to 3d sequentially perform 2 modulation.
By shifting the time by 5 ps each, the optical pulses of each channel are arranged at equal intervals during a period of 100 ps. Then, by combining these optical pulse trains with the optical coupler 4, a 40 Gbit / s multiplexed optical pulse train can be obtained. In the waveform of the multiplexed optical pulse train shown in FIG. 4, all the bits of the transmission signal are, for example, “1” for easy understanding of the description, and the optical pulses of the basic optical pulse train are all transmitted by the optical modulators 2a to 2d. The following shows the case of being performed. The same applies to the waveform of the multiplexed optical pulse train shown below.

When optical communication is performed using the above-mentioned multiplexed optical pulse train, the optical pulse train for each channel is provided on the receiving side by optical means so that the multiplexed optical pulse train has a transmission rate that is electrically easy to handle. Need to be separated.
FIG. 5 shows an example of an optical circuit that performs such separation for each channel. This optical circuit inputs the transmitted multiplexed optical pulse train to the optical distributor 6. The light distributor 6 is an optical circuit element having the same configuration as the light distributor 1 shown in FIG. The four-channel multiplexed optical pulse train output from the optical distributor 6 is an optical AND gate 7 respectively.
a to 7d.

On the receiving side, a local basic optical pulse train equivalent to the basic optical pulse train on the transmitting side, that is, a local basic optical pulse train having a period of 100 ps whose phase matches the optical pulse train of any channel of the multiplexed optical pulse train. Is generated,
This local basic optical pulse train is input to the optical distributor 8. The light distributor 8 is also the light distributor 1 shown in FIG.
It is an optical circuit element having the same configuration as. The 4-channel local basic optical pulse train output from the optical distributor 8 is input to the corresponding optical AND gates 7a to 7d via the optical delay devices 9a to 9d, respectively. Each optical delay device 9
a to 9d also have the same configuration as the optical delay devices 3a to 3d shown in FIG. 4, and the delay time is 0 ps, 25 for each channel.
It is set to ps, 50 ps, and 75 ps, respectively.

Each of the optical AND gates 7a to 7d has a multiplexed optical pulse train distributed by the optical distributor 6 and an optical delay device 9a to.
9d is an optical circuit element that obtains a logical product with a local basic optical pulse train whose time is shifted by 25 ps for each channel.
This light pulse is output only when both of these light pulse trains simultaneously have a light pulse. Therefore, from the optical AND gates 7a to 7d of each of these channels, only the optical pulse of the corresponding channel in the multiplexed optical pulse train is output, and all other optical pulses are masked. The optical pulse train can be separated for each channel. The optical pulse train separated for each channel has a transmission rate of 10 Gbit / s, which facilitates electrical signal processing. Therefore, each optical pulse sequence is converted into an electrical signal by photoelectric conversion to demodulate the original transmission signal. be able to.

Here, on the receiving side, in order to generate a local basic optical pulse train to be input to the optical distributor 8 of the optical circuit shown in FIG. 5, the period 100p synchronized with the multiplexed optical pulse train is generated.
It is necessary to generate an electrical clock signal of s (frequency 10 GHz). To stably generate such a clock signal, it is ideal to use a phase locked loop circuit as shown in FIG. This phase-locked loop circuit inputs the transmitted multiplexed optical pulse train to the optical phase comparator 10. The optical pulse train output from the semiconductor laser 11 is also input to the optical phase comparator 10. The optical phase comparator 10 is composed of an optical AND gate using a nonlinear optical effect of an optical fiber and a photoelectric conversion element, and outputs a voltage according to a phase difference between two input optical pulses, that is, a time difference between peaks of the optical pulse. It is an input / electrical output circuit element. This optical phase comparator 10
The voltage output from is input to the voltage controlled oscillator 12. The voltage controlled oscillator 12 is 10 GH depending on the input voltage.
It is an electric oscillator whose oscillation frequency changes in the vicinity of z, and outputs a pulse signal in which a steep pulse appears every oscillation cycle. The pulse signal output from the voltage controlled oscillator 12 is input to the semiconductor laser 11. The semiconductor laser 11 is driven by this pulse signal so that the FWHM is 1
It is an electric input / optical output circuit element that outputs an optical pulse train in the vicinity of 0 ps and a period of 100 ps (frequency: 10 GHz).

The phase locked loop circuit outputs from the optical phase comparator 10 when the phase of the optical pulse train emitted from the semiconductor laser 11 completely matches the optical pulse train of any channel of the multiplexed optical pulse train. Based on the voltage, the voltage controlled oscillator 12 outputs a pulse signal with a cycle of 100 ps which causes the semiconductor laser 11 to maintain the current output of the optical pulse train. When the phase of the optical pulse train emitted from the semiconductor laser 11 is shifted,
The voltage controlled oscillator 12 outputs a pulse signal whose frequency is changed so as to recover the phase shift of the optical pulse train. Therefore, this voltage controlled oscillator 12
Output a pulse signal having a period of 100 ps (frequency of 10 GHz) and a phase that matches the optical pulse train of any channel of the multiplexed optical pulse train.
If this pulse signal is used as a clock signal, a local basic optical pulse train to be input to the optical distributor 8 of the optical circuit shown in FIG. 5 can be generated based on this clock signal.

Further, there has been conventionally proposed a method of easily obtaining a clock signal for generating a local basic optical pulse train without using the above phase locked loop circuit.
That is, in the case of transmitting the 40 Gbit / s multiplexed optical pulse train, as shown in FIG. 7, for example, only the amplitude of the optical pulse P1 of the first channel is made larger than that of the optical pulses P2 to P4 of the other channels. And then transmit. In order to change only the amplitude of the optical pulse of one channel, the power distribution of the optical pulse train in the optical distributor 1 or the optical coupler 4 shown in FIG. 4 may be changed. In a normal multiplexed optical pulse train, the optical pulse trains of each channel having the same amplitude are arranged at equal intervals with a time shift, so if the modulation is ignored, the frequency component of 10 GHz (cycle 100 ps) of the basic optical pulse train is lost. However, if the amplitude of the optical pulse is increased every 100 ps in this manner, the multiplexed optical pulse train will always include the frequency component of 10 GHz. Therefore, if the electric signal obtained by photoelectrically converting this multiplexed optical pulse train is passed through a narrow band pass filter that passes only the signal component around 10 GHz, the receiving side can easily extract a 10 GHz clock signal synchronized with the multiplexed optical pulse train. can do.

[0013]

However, the method using the phase-locked loop circuit shown in FIG. 6 has an advantage that a clock signal can be stably generated, but the optical phase comparator 10 and the voltage are used. Since the controlled oscillator 12 is a complicated and expensive circuit element, there is a problem that the cost of equipment on the receiving side is significantly increased.

Further, the optical soliton pulse has a limitation that the peak power of the optical pulse must be a value within a predetermined range according to the FWHM of the optical pulse and the characteristics of the optical fiber as described above. Therefore, in the method of changing the amplitude of the optical pulse shown in FIG. 7, the difference in amplitude cannot be increased so much that the power spectrum of the frequency component of 10 GHz becomes small and the clock signal can be stably extracted. There was a problem that I could not do it.

The present invention has been made in view of the above circumstances, and transmits a multiplexed optical pulse train in which optical pulse trains of respective channels are superposed at time intervals that are not equal intervals, so that a narrow band pass is made on the receiving side. An object of the present invention is to provide an optical pulse time-multiplexing method and apparatus capable of stably and easily extracting a clock signal using a filter.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a multiplexed optical pulse train of a format in which basic optical pulse trains of a plurality of channels having the same period are sequentially superposed by shifting the time for each channel. about,
In an optical pulse time-multiplexing method in which transmission is performed by controlling transmission or blocking of each optical pulse for each channel and transmitted, at least one position in the time difference sequentially shifted for each channel is set to a period of a basic optical pulse train. The time difference is different from the time divided by the total number of channels.

The basic optical pulse trains of a plurality of channels having the same cycle and phase are modulated by controlling the transmission or blocking of the optical pulses by the optical modulators, respectively, and each of them is shorter than the cycle of the basic optical pulse trains and the channels In an optical pulse time multiplexing device that delays by an optical delay device having a different delay time for each channel and then combines the optical pulse trains of these channels by an optical coupler to multiplex the optical pulse trains of at least one channel, The delay time is set to a time different from a natural multiple of the time obtained by dividing the period of the basic optical pulse train by the total number of channels.

Further, the period of the basic optical pulse train is T0, the total number of channels is N, the unit delay time T1 is T1 <(T0 / N), and the delay multiple M is 0 ≦ M <N. In the case of an integer having a relationship of, the delay time of the optical delay device of each channel is set to T1 × M time for the delay multiple M different for each channel.

[0019]

According to the means of the present invention, the modulated basic optical pulse train is transmitted as a multiplexed optical pulse train of a format in which the time is sequentially shifted for each channel and superimposed, as in the conventional case, so that the time multiplexing is performed at high density. Ultra high speed optical communication can be performed. Moreover, this multiplexed optical pulse train is
Since the time difference between at least one channel is not completely equal, the intervals of time difference which are not equal are repeated in the cycle of the basic optical pulse train. Therefore, this multiplexed optical pulse train surely contains the frequency component of the basic optical pulse train, and by extracting the signal of this frequency component using the filter on the receiving side, it is possible to Thus, it becomes possible to stably and easily extract a clock signal having a constant phase difference, that is, a clock signal synchronized with this multiplexed optical pulse train.

The multiplexed optical pulse train may be modulated by adding the basic optical pulse train for each channel and then combining them, or may be directly applied by the channel for the multiplexed optical pulse train. . Further, in the case of applying modulation to the basic optical pulse train, first, after applying modulation, the time of the optical pulse train of each channel may be sequentially shifted, and then these optical pulse trains may be combined. It is also possible to sequentially shift the times of the basic optical pulse trains, apply modulation, and then combine them.

According to the above means, the basic optical pulse train of each channel is modulated by the optical modulator, delayed by the optical delay device and then coupled by the optical coupler so that each channel can be processed in the same manner as in the conventional case. It is possible to obtain a high-density multiplexed optical pulse train having different delay times. Moreover, in this multiplexed optical pulse train, the delay time of at least one channel does not become a time difference in which the delay time is sequentially shifted by equal intervals, so that the non-equal time intervals are repeated in the cycle of the basic optical pulse train. Therefore, this multiplexed optical pulse train surely contains the frequency component of the basic optical pulse train, and by extracting the signal of this frequency component using the filter on the receiving side, the clock signal synchronized with the multiplexed optical pulse train is stabilized. And it can be easily extracted.

A basic optical pulse train of a plurality of channels having the same cycle and phase can be generated by branching a series of basic optical pulse trains into a plurality of channels by an optical distributor. The basic optical pulse train of each channel may be delayed by the optical delay device after being modulated by the optical modulator, or may be delayed by the optical delay device and then modulated by the optical modulator. Of course, if the delay time of any one of the optical delay devices is 0, this optical delay device can be omitted.

Further, according to the above means, since the unit delay time T1 in which each channel is sequentially delayed becomes a time interval shorter than T0 / N which is a time interval of equal intervals, the channel having the longest delay time (delay Only the time interval between the optical pulse of the channel having the maximum multiple M) and the optical pulse of the channel having the delay time of 0 immediately thereafter (the channel having the delay multiple M of 0) is equal to T0 /. It becomes longer than N, and this long time interval is repeated in the cycle of the basic optical pulse train. Therefore, also in this case, the combined multiplexed optical pulse train surely includes the frequency component of the basic optical pulse train, and by extracting the signal of this frequency component using the filter on the receiving side, the multiplexed optical pulse train is obtained. It becomes possible to stably and easily extract the clock signal synchronized with.

In the case of this means, in the means, the delay time of the optical delay devices of all the channels is the time (T0) obtained by dividing the period of the basic optical pulse train by the total number of channels.
/ N) is set to a time different from a natural number multiple. The shorter the unit delay time T1 is, the larger the power spectrum of the frequency component of the basic optical pulse train can be made as the unit delay time T1 is shorter than T0 / N. Separation by channel becomes difficult. The unit delay time T1 is
If the time is not sufficiently longer than the FWHM of the light pulse,
Transmission as an optical soliton pulse becomes impossible.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a first embodiment of the present invention. FIG. 1 is a block diagram of an optical pulse time multiplexing device, and FIG. 2 is a waveform diagram of a multiplexed optical pulse train. In addition,
Constituent members having the same functions as those of the conventional example shown in FIG. 4 are designated by the same reference numerals.

In this embodiment, each is 10 Gbit / s.
An optical pulse time multiplexing device that superimposes a four-channel optical pulse train that is a modulated basic optical pulse train and output a 40 Gbit / s multiplexed optical pulse train, and an optical pulse time multiplexing method using this device will be described.

In this optical pulse time multiplexing apparatus, as shown in FIG. 1, a basic optical pulse train having a cycle of 100 ps and an FWHM of 10 ps is input to the optical distributor 1. The optical distributor 1 is an optical circuit element that combines a 3 decibel coupler to distribute an input 1-series optical pulse train into 4-channel optical pulse trains each having a power reduced to 1/4 and output the optical pulse train. The four-channel basic optical pulse train output from the optical distributor 1 is input to the optical coupler 4 via the optical modulators 2a to 2d and the optical delay devices 3a to 3d, respectively. Optical modulator 2a for each channel
2d is for transmitting an optical pulse when the bit of the transmission signal is “1” and blocking the optical pulse when the bit of the transmission signal is “0”, depending on the electrical transmission signal of the corresponding channel. , An optical circuit element that modulates a basic optical pulse train. The optical delay devices 3a to 3d of each channel are
It is an optical circuit element that delays the modulated optical pulse train by a predetermined delay time, and is set to a different delay time for each channel by changing the optical path length of the element. That is, the delay time of the optical delay device 3a of the first channel is set to 0 ps, the delay time of the optical delay device 3b of the second channel is set to 20 ps, and the delay time of the optical delay device 3c of the third channel is 40 ps. Is set, the delay time of the optical delay device 3d of the fourth channel is set to 60 ps,
A time difference of 20 ps is sequentially generated for each channel. The optical delay device 3a for the first channel is
Since the delay time is 0 ps, it can be omitted. Like the optical distributor 1, the optical coupler 4 combines 3 decibel couplers to combine the input 4-channel optical pulse trains, and the power of each optical pulse is reduced to 1/4. An optical circuit element that outputs a pulsed optical pulse train.

In the optical pulse time division multiplexer having the above-mentioned configuration, the basic optical pulse train having a cycle of 100 ps (10 Gbit / s) is first distributed by the optical distributor 1 to the basic optical pulse train of four channels having the same cycle and phase. Next, the basic optical pulse trains of these four channels are converted into the optical modulators 2a to
In 2d, each is modulated according to the transmission signal of the corresponding channel. Transmission signals are independently sent from the outside at a transmission rate of 10 Gbit / s4
It is the electrical digital signal of the channel. The 4-channel optical pulse trains modulated by the optical modulators 2a to 2d are delayed by the optical delay devices 3a to 3d of the respective channels. That is, the optical delayer 3a for the first channel delays 0 ps, the optical delayer 3b for the second channel delays 20 ps, and the optical delayer 3c for the third channel delays 40 ps. The optical delay device 3d of the fourth channel delays by 60 ps. Therefore, the optical pulse train of each channel is sequentially shifted by 20 ps for each channel. The 4-channel optical pulse trains delayed by the optical delay devices 3a to 3d are combined by the optical combiner 4 and output as a series of multiplexed optical pulse trains. The multiplexed optical pulse train thus obtained is passed through an optical fiber (not shown) and is used for ultra-high-speed optical communication in which time is densely multiplexed by optical soliton transmission.

As shown in FIG. 2, the multiplexed optical pulse train output from the optical coupler 4 has four optical pulses P1 to P4 of each channel sequentially 20 p within one cycle of 100 ps.
While appearing at time intervals shifted by s, a time interval of 40 ps occurs between the optical pulse P4 of the fourth channel and the optical pulse P1 of the first channel in the next one cycle. In FIG. 2 as well, the waveform of the multiplexed optical pulse train is shown as if all the optical pulses were transmitted by the optical modulators 2a to 2d, as in FIG. Therefore, in this multiplexed optical pulse train, the time interval between the channels is 20 p, which is shorter than 25 ps, which is the time of equal intervals when 100 ps, which is the period of the basic optical pulse train, is divided by 4 of the total number of channels.
In addition, the time interval of 40 ps without the optical pulse always appears every 100 ps of the cycle regardless of any modulation by the transmission signal.

As a result, the multiplexed optical pulse train output from the optical pulse time multiplexer of this embodiment has a length of 20 ps, which is the time interval between channels, at the end of each 100 ps cycle of the basic optical pulse train. Since a time interval without a light pulse of 40 ps having a certain length is repeated, the frequency component of 10 GHz (period 100 ps) of this basic light pulse train is included in a sufficiently large power spectrum. Therefore, if this multiplexed optical pulse train is converted into an electrical signal by the semiconductor photoelectric conversion element on the receiving side and passed through an electrical narrow band pass filter that passes only the signal component near 10 GHz, the transmitted multiplexed optical pulse is transmitted. A clock signal which always has a constant phase difference with respect to any channel of the pulse train, that is, 10G synchronized with this multiplexed optical pulse train.
The clock signal of Hz can be extracted stably and easily.

FIG. 3 shows a second embodiment of the present invention and is a block diagram of an optical pulse time multiplexing apparatus. The constituent elements having the same functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals.

Also in this embodiment, each is 10 Gbi.
An optical pulse time multiplexing device that superimposes a 4-channel optical pulse train that is a modulated t / s basic optical pulse train and outputs a 40 Gbit / s multiplexed optical pulse train, and an optical pulse time multiplexing method using this device will be described. To do.

This optical pulse time multiplexer has a period of 1
The first basic optical pulse train at 00ps and FWHM of 10ps
Is input to the optical distributor 1a. One optical pulse train output from the first optical distributor 1a is
The signal is modulated by the transmission signal in the optical modulator 2a of the first channel and input to the first optical coupler 4a. The other optical pulse train output from the first optical distributor 1a is delayed by 20 ps in the first optical delay device 5a and input to the second optical distributor 1b. One of the optical pulse trains output from the second optical distributor 1b is modulated by the transmission signal in the second channel optical modulator 2b and input to the first optical coupler 4a.
The optical pulse train output from the first optical coupler 4a is
It is input to the second optical coupler 4b.

The other optical pulse train output from the second optical distributor 1b is delayed by 20 ps in the second optical delay device 5b and input to the third optical distributor 1c. One of the optical pulse trains output from the third optical distributor 1c is modulated by the transmission signal in the optical modulator 2c of the third channel and input to the second optical coupler 4b. The optical pulse train output from the second optical coupler 4b is input to the third optical coupler 4c. The other optical pulse train output from the third optical distributor 1c is delayed by 20 ps in the third optical delay device 5c, and then modulated by the transmission signal in the optical modulator 2d of the fourth channel to generate the third optical pulse. It is input to the coupler 4c. Then, the optical pulse train output from the third optical coupler 4c becomes a multiplexed optical pulse train.

The first to third light distributors 1a to 1c are
It is composed of a 3 decibel coupler that distributes one series of optical pulse trains into two channels of optical pulse trains each having a power reduced to 1/2. Further, the first to third optical couplers 4a to 4
c is a 2-channel optical pulse train whose power is 1
It consists of a 3 dB coupler that couples to a series of optical pulse trains reduced to ½. The first to third optical delay devices 5a to 5
c is the optical delay device 3a of the first embodiment shown in FIG.
Although the configuration is the same as that of 3d to 3d, all delay times are set to 20 ps in this embodiment. The optical modulators 2a to 2d of the respective channels are the same as those of the first embodiment shown in FIG.

According to the optical pulse time division multiplexer having the above-mentioned structure, the basic optical pulse train has the first to third optical distributors 1a to 1c.
Are sequentially divided into two, and the four-channel optical pulse trains thus distributed are sequentially combined by the first to third optical couplers 4a to 4c to form one series of multiplexed optical pulse trains. Further, the optical pulse train of the first channel has a delay of 0 ps because it does not pass through the optical delay device, and the optical pulse train of the second channel has a delay of 20 ps passing through only the first optical delay device 5a and the third channel. Optical pulse train of 40 ps passes through the first and second optical delay devices 5a and 5b.
(= 20 ps × 2) is delayed, and the optical pulse train of the fourth channel is delayed by 60 ps (= 20 ps × 3) through the first to third optical delay units 5a to 5c. The optical pulse train of each of these channels is transmitted to the optical delay device 5a.
.. to 5c, the optical modulators 2a to 2 of the corresponding channels are subjected to delays with different cumulative numbers of delay times.
modulated by d.

As a result, the optical pulse time multiplexing apparatus of the present embodiment operates in the same manner as the first embodiment shown in FIG. 1 except that the order of delay and modulation of the optical pulse train in each channel is changed. It is possible to output the same multiplexed optical pulse train as that shown in FIG. 2 from the third optical coupler 4c. Therefore, also in the case of the present embodiment, if this multiplexed optical pulse train is converted into an electric signal by the semiconductor photoelectric conversion element on the receiving side and passed through an electric narrow band pass filter that passes only the signal component near 10 GHz, It is possible to stably and easily extract a 10 GHz clock signal that is synchronized with the transmitted multiplexed optical pulse train.

In each of the first and second embodiments, the case where the time multiplexing of four channels is performed has been described, but the present invention is not limited to this, and the time multiplexing of other plural channels is performed. The same can be applied to the case.
Further, in both the first and second embodiments, the transmission speed by the basic optical pulse train is set to 10 Gbit / s, but the present invention is not limited to this, and the other transmission speeds can be similarly implemented. You can Further, in the first and second embodiments, the time interval between channels of the multiplexed optical pulse train is
The period of 100 ps of the basic optical pulse train is 20 ps, which is a constant interval shorter than 25 ps, which is an equal interval when the total number of channels is divided by 4, but in the present invention, it is sufficient if at least one time interval is different from the equidistant time. .

In the first and second embodiments, only the case where the basic optical pulse trains of a plurality of channels are modulated and delayed for each channel and then combined to form a multiplexed optical pulse train will be described. However, for example, the time interval of each optical pulse is 20 ps and 4 by some means.
It is also possible to generate an optical pulse train of 0 ps and to modulate such an optical pulse train for each channel.

Further, in the above-mentioned first and second embodiments, only the case where the optical soliton transmission is performed has been described, but the present invention can be similarly implemented if the optical pulse train of the return zero system is transmitted. You can

[0042]

As is apparent from the above description, according to the optical pulse time multiplexing method and apparatus of the present invention, the amplitude of the optical pulse is not changed for each channel,
Since it is possible to reliably include the frequency component of the basic optical pulse train in the multiplexed optical pulse train, even if the receiving side does not use a complicated circuit such as a phase-locked loop circuit, it has the frequency of the basic optical pulse train and is multiplexed. The clock signal synchronized with the optical pulse train can be stably and easily extracted.

[Brief description of drawings]

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

FIG. 2 shows a first embodiment of the present invention and is a waveform diagram of a multiplexed optical pulse train.

FIG. 3 shows a second embodiment of the present invention and is a block diagram of an optical pulse time multiplexing device.

FIG. 4 is a block diagram of an optical pulse time multiplexing device, showing a conventional example.

FIG. 5 is a block diagram of an optical circuit for separating a multiplexed optical pulse train for each channel.

FIG. 6 is a block diagram of a phase locked loop circuit showing a conventional example for generating a clock signal.

FIG. 7 shows a conventional example for generating a clock signal and is a waveform diagram of a multiplexed optical pulse train.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 optical distributor 1a-1c optical distributor 2a-2d optical modulator 3a-3d optical delay device 4 optical coupler 4a-4c optical coupler 5a-5c optical delay device

Claims (3)

[Claims] 1. A multiplexed optical pulse train of a format in which basic optical pulse trains of a plurality of channels having the same cycle are sequentially superimposed on each channel by shifting the time, and modulated by controlling transmission or blocking of each optical pulse for each channel. In the optical pulse time-division multiplexing method for performing transmission by performing the above-mentioned transmission, at least one of the time differences sequentially shifted for each channel is
An optical pulse time-multiplexing method, wherein the position is set to a time difference different from the time obtained by dividing the period of the basic optical pulse train by the total number of channels. 2. A basic optical pulse train of a plurality of channels having the same period and phase is modulated by controlling transmission or blocking of an optical pulse by an optical modulator, and each is shorter than the period of the basic optical pulse train and the channel In an optical pulse time multiplexer that delays the optical pulse trains having different delay times for each channel and then combines the optical pulse trains of each channel by an optical coupler, the optical pulse time multiplexer of at least one channel An optical pulse time multiplexer, wherein the delay time is set to a time different from a natural multiple of the time obtained by dividing the cycle of the basic optical pulse train by the total number of channels. 3. The period of the basic optical pulse train is T0,
When the total number of the channels is N, the unit delay time T1 is T
1 <(T0 / N) and the delay multiple M is 0 ≦ M <N
The delay time of the optical delay device of each channel is set to a time T1 × M for a delay multiple M different for each channel, when the integer having the relationship of Optical pulse time multiplexer.