JPH02107034A - Light time-division multiplexing system - Google Patents

Abstract

PURPOSE:To reduce the costs of optical transmitter, and to eliminate the inter- bit interference of optical multiple signal by branching a repetitive optical pulse train in a light area, then multiplexing an encoded optical data signal. CONSTITUTION:A clock signal 1 is inputted to an optical pulse train generator 3, the optical pulse trains are repeatedly sent to an optical fiber 6, and branched to optical fibers 6a to 6m. Data signals (a) to (m) (electric signals) are respectively inputted to photoconverters 4a to 4m, and light is encoded. By setting the length of optical fibers 6a to 6m and 7a to 7m so that the phase of the optical output signal of the optical modulators 4a to 4m may be delayed by a prescribed time, the time-divided/multiplexed optical signal can be obtained in the output of a photocoupler 5. Thus, since the light can be time-divided and multiplexed by using a single optical pulse train generator, the light time-dividing/ multiplexing transmitter can be made inexpensive, the optical wavelength of the respective bits of the multiple optical signal in made the same, the interference based on the wavelength dispersion between the respective bits can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tarok signal branching system and an optical pulse train generation system in an optical time division multiplexing system.

[Conventional technology]

Conventionally, the optical time division multiplexing method has been described in Electronics Letters, Volume 23. Number 5 (1987
), pages 208 to 209 (Electronic
s Letters, Vo Q, 23, Na
5 (1987) pp. 208-209).

In the conventional system, a clock signal is branched into multiplexed signals (m signals) in the electrical domain, and each of the m branch signals is delayed and then input to m optical pulse train generators. Each of these m optical pulse trains has m Ti
: RZ (return two) by LiNb0δ switch
Optical intensity modulation is performed using a return-to-zero (return-to-zero) code, and then m data optical signals are time-division multiplexed by an optical coupler.

FIG. 3 shows the configuration of a conventional optical time division multiplexing system (multiplexing number m). In this conventional example, optical pulse train generators 38-3m and optical modulators 48-4m.

Hikari Kabra5. It is composed of optical fibers 7a to 7m and 8.

The input signals are clock signal 1 and data signal a (2
a) to data signal m (2m). The clock signal is branched into m signals in the electrical domain and input to m optical pulse train generators 38 to 3m.

At this time, an appropriate delay time τ is given to the m clock electrical signals for multiplexing at a subsequent stage.

98 to 9m indicate delay circuits.

Optical pulse trains of frequencies io are output from the optical pulse train generators 38 to 3m, input to optical modulators 4a to 4m, respectively, and sent to RZ double signal optical fibers 78 to 7m. These optical signals are processed by an optical coupler 5 at a bit rate mfo
(b/s) NRZ signal.

In this method, 1 m of optical pulse train generators are required to branch the clock signal 1 in the electrical domain. Further, in general, these m optical pulse trains have different optical wavelengths.

For this reason, when multiplexed optical signals are transmitted through long-distance optical fibers, the propagation time differs between each bit, resulting in bit-to-bit interference and significant deterioration of transmission characteristics.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, a clock signal is branched into m multiplexed signals in the electrical domain, and each branched signal is given a delay time and then input to m mode clock lasers. Therefore, m mode-locked lasers are required to be multiplexed, making the optical transmitter extremely expensive. Also,
When multiplexed optical signals are transmitted over long-distance optical fibers, the optical wavelengths of the m mode-locked lasers generally differ, so they are affected by the dispersion of the optical fibers, and the phase of the multiplexed optical signals at the optical receiving end is greatly disturbed. There's a problem.

SUMMARY OF THE INVENTION An object of the present invention is to reduce the cost of an optical transmitter and to eliminate bit-to-bit interference of an optical multiplexed signal due to differences in optical wavelength between optical pulse train generators.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a repetitive optical pulse train generated using one optical pulse train generator is branched into m pieces (m is the number of multiplexed pulses), and each is encoded and multiplied by RZ. This method employs a method in which signals are generated, each of which is given an appropriate delay time, and then combined using an optical coupler or the like to perform time division multiplexing.

As the optical pulse train generator, a method using a mode-locked semiconductor laser or a semiconductor laser operating in a gain-switched state can be cited as an easy-to-implement method.

Furthermore, since the optical pulse train is split into m parts, each branch signal is attenuated to 1/m or less (in the case of equal distribution).
. If this point becomes a problem, an optical multiplier is used before or after the optical modulator or after the optical coupler.

[Operation] A single optical pulse train generator used for optical time division multiplexing branches an optical pulse train into m multiplexed pulse trains in the optical region. Each of these branched signals is encoded into m RZ times signals by an optical modulator. Therefore, it is sufficient to use only one optical pulse train generator, and a low-cost optical multiplex transmitter can be constructed. Furthermore, since the optical signal has a single generation source, the optical wavelength of each bit of the multiplexed optical signal is also the same. Therefore, even in long-distance optical fiber transmission, interference based on chromatic dispersion between bits is eliminated.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 shows the basic configuration of an embodiment of the present invention.

The embodiment shown in this figure is shown for the number of multiplexes m.

The optical time division multiplexing method uses an optical pulse train generator 3 and an optical modulator 4.
a, 4b,...4m, optical coupler 5. optical fiber 6.6
It is composed of a, 6b, -6m, 7a, 7b, -7m, and 8. The input signals are clock signal 1 (frequency fo) and data signals a (2a) to data signals m (2m).

FIG. 2 shows the signal waveforms of each part in this optical multiplexing system. In FIG. 2, 1:4 multiplexing is used as an example.

The lock signal 1 (frequency jo) as shown in FIG. 2A is input to the optical pulse train generator 3, and a repeating optical pulse train as shown in FIG. It is assumed that this optical pulse train has a frequency fo and a pulse width of approximately ], /4 fo or less than 1/4 fo.

The optical pulse train in the optical fiber 6 is branched into optical fibers 68 to 6m, and input to optical modulators 4a to 4m, respectively.

A data signal a"m (electrical signal) is input to each of the optical modulators 48 to 4m, and a digital signal 11 + F I
The light is encoded according to JO11. As a result, the optical outputs of the optical modulators 48 to 4m are RZ multiplied signals with a duty ratio of 1/4, and are sent to the optical fibers 7a to 7b.

The optical fibers 68-6m, 7a-7m are connected so that the RZ multiplied signal phase of the output of the optical modulators 48-4m is delayed by 1/4fo time at the time of input to the optical coupler 5.
By setting the length of , an NRZ signal of mfo (b/s) can be obtained at the output of the optical coupler 5.

In FIG. 1, a mode-locked laser or a semiconductor laser operating in a gain-switched state can be used as the optical pulse train generator 3.

As the optical modulators 48 to 4m, a directional coupler type optical switch, a Matsuha-Zehnder type optical switch, a light absorption type modulator, etc. can be used as those that are advantageous for high-speed operation.

According to the embodiment shown in FIG.
Since optical time division multiplexing can be performed using only one transmitter, the cost of the optical time division multiplexing transmitter can be reduced. Also, light (,
Since the source of No. 1 is single, the optical wavelength of each bit of the multiplexed optical signal is also the same, and even in long-distance optical fiber transmission, interference based on wavelength dispersion between each bit is eliminated. be.

FIG. 4 shows a second embodiment of the invention. The basic configuration is the same as that in FIG. 1, with an optical amplifier 10 inserted after the optical pulse train generator 3.

In the present invention, since the output of the optical pulse generator 3 is branched into m signals, each branch signal is attenuated. For example, considering the case of equal distribution, the branch No. 4d power will be 1/m or less.

Optical amplifier 10 can compensate for this attenuation. The optical amplifier 10 may be inserted at each preceding stage of the optical modulators 4a to 4m, that is, to each part of the optical fibers 68 to 6b.

Moreover, each subsequent stage of the optical modulators 4a to 4m, that is, each part of the optical fibers 78 to 7m may be used. Furthermore, optical coupler 5
It may be inserted after the .

〔Effect of the invention〕

Since the present invention is configured as described above, it has the effects described below.

Since optical time division multiplexing can be performed using only one optical pulse train generator, the cost of the optical time division multiplexing transmitter can be reduced. In addition, since the optical signal has a single source, the optical wavelength of each bit of the multiplexed optical signal is the same, and even in long-distance optical fiber transmission, interference due to chromatic dispersion between each bit is eliminated. . Furthermore, by adding an optical amplifier to the device used in this method, it is possible to compensate for the drop in power due to branching in the optical domain and achieve high output.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of an embodiment of the present invention, and FIG. 2 is a schematic diagram of No. 48 waveforms of various parts in the embodiment of the present invention.
FIG. 3 is a block diagram of a conventional example, and FIG. 4 is a block diagram of a second embodiment of the present invention. 1... Clock signal, 2a-2m... Data signal,
3゜38~3m...Optical pulse train generator, 48~4m・
... Optical modulator, 5... Optical coupler. Circulation letter 5 Closing map sunny day part

Claims (1)

[Claims] 1. Consisting of an optical pulse train generator, an optical modulator, and an optical coupler, after splitting a repeated optical pulse train generated at a clock signal frequency in an optical domain, the optical signal is encoded by the optical modulator. An optical time division multiplexing method characterized in that data signals are multiplexed by the optical coupler. 2. The optical time division multiplexing system according to claim 1, wherein a mode-locked laser is used as the optical pulse train generator. 3. The optical time division multiplexing system according to claim 1, wherein a semiconductor laser operating in a gain-switched state is used as the optical pulse train generator. 4. The optical time division multiplexing system according to claim 1, further comprising an optical amplifier provided between the optical pulse train generator and the optical modulator. 5. The optical time division multiplexing system according to claim 1, further comprising an optical amplifier provided between the optical modulator and the optical coupler. 6. The optical time division multiplexing system according to claim 1, wherein an optical amplifier is provided at a stage subsequent to the optical coupler.