JP2003008550A - Wdm optical transmitter and wdm optical transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a WDM optical transmitter that applies orthogonal polarized wavelength multiplexing to optical signals to multiplex many more optical wavelengths and can be simply realized at a low cost. SOLUTION: The WDM optical transmitters are respectively provided with a PBS (polarized wave multiplex coupler) 54 that applies orthogonal polarized wave multiplexing to two optical signals (e.g. λ1 and λ2) as a set among a plurality of optical signals with different wavelengths λ1-λm, a DCF(dispersion compensation fiber) 56 that compensates a dispersion of one set of the multiplexed optical signals, and an optical amplifier 58 that amplifies a set of the compensated optical signals. A multiplexer 60 multiplexes the amplified optical signals of each set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a WDM (Wavelength Dielectric) which multiplexes and transmits a plurality of optical signals having different wavelengths.
The present invention relates to a WDM optical transmission device and a WDM optical transmission method that perform orthogonal polarization wavelength division multiplexing.

[0002]

2. Description of the Related Art At present, a method of narrowing a wavelength interval in a wavelength division multiplexing transmission method and transmitting more optical signals is actively developed for the purpose of increasing the capacity. A WDM optical transmitter of this type is shown in FIG. 3 and will be described. FIG. 3 is a block diagram showing the configuration of a conventional WDM optical transmitter.

The WDM optical transmitter 10 shown in FIG.
The wavelengths of the optical signals of the odd number (ODD) channel and the even number (EVEN) channel are respectively amplified, the dispersion values are compensated and multiplexed, and then multiplexed and transmitted in the order of the channel numbers. On the side, a plurality of optical transmission circuits 11 each equipped with an optical laser, a plurality of optical amplifiers 13 connected to these optical transmission circuits 11, and these optical amplifiers 13
And a multiplexer 17 connected by a DCF (dispersion compensating fiber) 15, and a plurality of optical transmitter circuits 1 each equipped with an optical laser on the optical signal processing side of even channels.
2, a plurality of optical amplifiers 14 connected to these optical transmission circuits 12, and a multiplexer 18 connected to these optical amplifiers 14 by a DCF 16, and CPL (connected to each multiplexer 17 and 18) The optical coupler) 20 is provided.

In such a configuration, the odd-numbered channel optical signals emitted from the respective optical transmission circuits 11 are amplified by the respective optical amplifiers 13 and input to the multiplexer 17 via the respective DCFs 15. Is combined with. Similarly, the even-numbered channel optical signals emitted from the respective optical transmission circuits 12 are amplified by the respective optical amplifiers 14, and the respective DCFs 16 are amplified.
Is input to the multiplexer 18 and is multiplexed there. The optical signals from the multiplexers 17 and 18 are multiplexed by the CPL 20 and then transmitted to the optical fiber transmission line.

CPL2 is obtained by such wavelength multiplexing processing.
An example of the polarization direction and the optical spectrum of the optical signal output from 0 is shown in FIG. In FIG. 4, the wavelength λ1 of the optical signal of the first odd-numbered channel, the wavelength λ2 of the first even-numbered channel, ... The wavelength λn of the n-th even-numbered channel are arranged and multiplexed in this order, and each wavelength interval is 0.4 nm. .

However, when the wavelength spacing is narrowed as described above, deterioration due to crosstalk between adjacent channels and non-linear effects (FWM, XPM, etc.) in the transmission line becomes large, and the transmitted optical signal deteriorates. As a method of improving this deterioration, a wavelength multiplexing system of orthogonal polarization has been proposed in which the polarization of the odd-numbered channels and the polarization of the even-numbered channels of all WDM signals are orthogonalized and multiplexed, and good transmission performance has been obtained. (OF
C'98 PD12 ”320Gb / s WDM Transmission (64 ×
5Gb / s) over 7200km using Large ModeFiberSpans and
Chirped Return-to-Zero Signals ”) A WDM optical transmitter of the orthogonal polarization wavelength division multiplexing system is shown in Fig. 5 and explained. It is a block diagram which shows the structure of a transmitter.

A WDM optical transmitter 30 shown in FIG. 5 has a plurality of optical transmitter circuits 31 each having an optical laser mounted on the optical signal processing side of an odd channel, and a plurality of optical transmitter circuits 31 connected to these optical transmitter circuits 31. A polarization-maintaining optical amplifier 33 and a polarization-maintaining multiplexer 37 connected to the polarization-maintaining optical amplifier 33 by a polarization-maintaining DCF (polarization-maintaining dispersion compensating fiber) 15 are provided. A plurality of optical transmission circuits 32 each having an optical laser mounted on the optical signal processing side of the even channel.
And a plurality of polarization-maintaining optical amplifiers 34 connected to these optical transmission circuits 32, and a polarization-maintaining multiplexer 38 connected to these polarization-maintaining optical amplifiers 34 by a polarization-maintaining DCF 36. PB provided and connected to each multiplexer 37 and 38
An S (polarization multiplexing coupler) 40 is provided.

However, each optical transmission circuit 31 and each polarization preserving optical amplifier 33 are connected by a polarization preserving fiber, and similarly, the polarization preserving multiplexer 37 and PBS 40, each optical transmission circuit 32 and each polarization. Conservation type optical amplifier 34, polarization conservation type multiplexer 38 and PB
S40 is also connected by a polarization maintaining fiber.

In such a configuration, the odd-numbered channel optical signals emitted from the respective optical transmission circuits 31 are amplified by the respective polarization-maintaining optical amplifiers 33, and polarized via the respective polarization-maintaining DCFs 35. It is input to the wave preservation type multiplexer 37,
It is multiplexed here. Similarly, the even-numbered channel optical signals emitted from the respective optical transmission circuits 32 are amplified by the respective polarization-preserving optical amplifiers 34, and are transmitted through the respective polarization-preserving DCFs 36 to the polarization-preserving multiplexer 38. It is input to and multiplexed here. The optical signals from the multiplexers 37 and 38 are orthogonally polarized and wavelength-multiplexed by the PBS 40 and then transmitted to the optical fiber transmission line.

FIG. 6 shows an example of the polarization direction and optical spectrum of the optical signal output from the PBS 40 by such orthogonal polarization wavelength division multiplexing processing. In FIG. 6, the wavelength λ1 of the optical signal of the first odd channel, the wavelength λ2 of the first even channel,
The wavelength λ2n of the n-th even channel is arranged in this order and orthogonally multiplexed, and each wavelength interval is 0.2 nm. That is, since the polarized waves between all the wavelengths are orthogonal to each other, it is possible to make all the wavelength intervals narrower.

An apparatus for performing this kind of orthogonal polarization wavelength division multiplexing is disclosed in Japanese Patent Laid-Open No. 8-18536. As for the contents of this publication, when the description in the abstract is cited, a polarization control means is provided between the optical transmitter and the optical multiplexing means, and a polarization separating means is provided between the optical demultiplexing means and the optical receiver in the wavelength region. The wavelength spacing between the output lights of the optical transmitter is set to be smaller than the minimum wavelength spacing at which the suppression ratio at which crosstalk can be ignored is obtained by the optical demultiplexing means, and
The polarization directions of the output lights having the adjacent wavelengths are made substantially orthogonal by the polarization control means.

[0012]

However, the conventional WDM
In the optical transmitter, the orthogonal polarization wavelength division multiplexing WDM optical transmitter 30 shown in FIG. 5 needs to multiplex signals in a state in which polarization is maintained for each wavelength. There is a problem that the configuration is complicated as compared with the WDM optical transmitter 10 of the system. In addition, many polarization-maintaining optical amplifiers 33 and 34 and polarization-maintaining dispersion compensating fiber 3 are provided.
5, 36 and multiplexers 37, 38 are included.
Since the devices of these constituent elements 33 to 38 are special types, there is a problem that it is difficult to realize and mass-produce the WDM optical transmitter 50. Therefore, the practical use of this kind of orthogonal polarization wavelength division multiplexing system has not been realized yet.

Also, in Japanese Patent Laid-Open No. 18536/1996, it is necessary to multiplex signals while maintaining polarization for each wavelength. Therefore, a polarization preserving multiplexer such as a polarization preserving device. However, there is a problem that the device is difficult to realize and the cost is high.

The present invention has been made in view of the above point, and by performing orthogonal polarization wavelength division multiplexing, more optical wavelengths can be multiplexed and can be realized simply and at low cost. WDM optical transmitter and W
It is an object to provide a DM optical transmission method.

[0015]

In order to solve the above problems, a WDM optical transmitter according to the present invention is a WDM optical transmitter that performs orthogonal polarization wavelength division multiplexing processing. A multiplexing unit that multiplexes two optical signals as one set with orthogonal polarizations; a compensating unit that compensates the dispersion value of the multiplexed one set of optical signals;
Each group is provided with an amplifying means for amplifying a pair of optical signals, and a multiplexing means for multiplexing the amplified optical signals of each group.

Further, the WDM optical transmitter of the present invention is characterized in that the optical signal frequency at the time of emitting the optical signal is determined so that the wavelength intervals of the optical signals multiplexed by the multiplexing means become equal.

Further, the WDM optical transmitter of the present invention narrows the wavelength interval of the optical signals in the groups whose polarizations are orthogonal to each other in the optical signals multiplexed by the multiplexing means so that the optical signals between the groups are Is characterized in that the frequency of the optical signal at the time of emitting the optical signal is determined so that the wavelength interval of is wide.

Further, the WDM optical transmission method of the present invention is a WDM optical transmission method for transmitting an optical signal by performing orthogonal polarization wavelength division multiplexing processing, wherein among a plurality of optical signals having different wavelengths,
It is characterized in that two optical signals are set as one set and their polarizations are orthogonalized to each other, and the multiplexed optical signals of each set are multiplexed and transmitted.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a WDM according to an embodiment of the present invention.
It is a block diagram which shows the structure of an optical transmitter.

The WDM optical transmitter 50 shown in FIG. 1 performs orthogonal polarization wavelength division multiplexing processing, and a set of optical signals of adjacent odd and even channels (for example, wavelengths λ1 and λ).
2) is emitted, a pair of optical transmission circuits 51 and 52 equipped with an optical laser that emits an optical signal, and a PB connected to these optical transmission circuits 51 and 52 with a polarization maintaining fiber.
An S (polarization multiplex coupler) 54 and an optical amplifier 58 connected to the PBS 54 by a DCF (dispersion compensation fiber) 56.
And a multiplexer 6 connected to each of the optical amplifiers 58 as well as a circuit including a half of the total number m of optical signal channels.
It is configured with 0.

However, the circuit at the forefront in the figure is the first and second circuits.
The optical signals of the channels (wavelengths are λ1 and λ2) are emitted, and the optical signals of the third and fourth channels (wavelengths are λ3 and λ4) ... (Wavelength is λm−1, λm).

In such a structure, first, the optical signals of the adjacent wavelengths λ1 and λ2 emitted from the optical transmission circuits 51 and 52 of the first and second channels are polarized by the PBS 54. The waves are combined in the orthogonal state. The DCF 56 compensates the dispersion value of each of the two orthogonal polarization multiplexed signals, and then the optical amplifier 58 amplifies the signals to a constant optical signal power. The amplified optical signal and another optical signal which has been similarly orthogonally polarized and multiplexed one by one are multiplexed by the multiplexer 60.

As described above, according to the WDM optical transmitter of the embodiment, since the optical signals of the adjacent channels are orthogonally polarized and wavelength-multiplexed for each set, the conventional wavelengths as shown in FIG. 3 are used. It is possible to reduce the non-linear interaction between adjacent channels, as compared with a multiplexing system, and to realize an increase in transmission distance and an increase in the number of wavelength multiplexes by narrowing the channel spacing.

Further, it can be realized easily and at low cost as compared with the conventional apparatus of the orthogonal polarization wavelength division multiplexing system as shown in FIG. The reason for this is that the number of dispersion compensating fibers and optical amplifiers is halved because it compensates and amplifies the dispersion of orthogonal polarization wavelength-multiplexed optical signals, and many polarization-maintaining optical amplifiers and polarization-maintaining dispersion amplifiers are used. This is because it is not necessary to use the compensation fiber and the multiplexer.

As another embodiment, as shown in FIG. 2, two adjacent wavelengths (λ1 and λ) that are orthogonal polarization multiplexed are provided.
2, .lamda.3 and .lamda.4, ..., .lamda.m-1 and .lamda.m) are narrowed (for example, 0.2 nm), and the wavelength intervals between each pair are wide (for example, .lamda.2 and .lamda.3, .lamda.4 and .lamda.5 ... .4n
m) It may be set. In this setting, the frequency of the optical laser emission light of each optical transmission circuit 51, 52 is 25 GHz for each pair of optical signals and 50 GHz for each pair of optical signals.
It can be realized by

In addition, if such a setting can be made, two adjacent wavelengths (λ1 and λ2, λ3 and λ) that are orthogonal polarization multiplexed are provided.
, ..., λm−1 and λm), the channel spacing is determined by the nonlinear interaction (FWM, XP) between adjacent channels during transmission.
(M, etc.) is reduced, so that it can be made narrower than between λ2 and λ3 (λ4 and λ5, ...) In which the orthogonality of polarization is not maintained.

By thus narrowing the wavelength interval of the adjacent channels whose polarizations are orthogonal to each other, more wavelengths can be multiplexed as compared with the conventional wavelength multiplexing system.

If all the wavelength intervals are made equal, it is effective in an optical transmission system that does not require a large number of wavelengths such as 64 waves. This is because when the number of wavelengths is small, even if the wavelength intervals are equal, the intervals can be widened by that amount, which reduces the nonlinear interaction (FWM, XPM, etc.) between adjacent channels during transmission. Therefore, the characteristics can be improved.

[0030]

As described above, according to the present invention,
Therefore, by performing orthogonal polarization wavelength division multiplexing, more optical wavelengths can be multiplexed, and at the same time, it can be realized easily and at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a WDM optical transmitter according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a polarization direction and an optical spectrum of an optical signal transmitted from a WDM optical transmitter according to another embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional WDM optical transmitter.

FIG. 4 is a diagram showing an example of a polarization direction and an optical spectrum of an optical signal transmitted from the conventional WDM optical transmitter.

FIG. 5 is a WD to which a conventional orthogonal polarization wavelength division multiplexing method is applied.
It is a block diagram which shows the structure of the M optical transmitter.

FIG. 6 is a diagram showing an example of a polarization direction and an optical spectrum of an optical signal transmitted from a WDM optical transmitter to which the conventional orthogonal polarization wavelength division multiplexing method is applied.

[Explanation of symbols]

10, 30, 50 WDM optical transmitter 11, 12, 31, 32, 51, 52 Optical transmitter circuit 13, 14, 58 Optical amplifier 15, 16, 56 DCF (dispersion compensation fiber) 17, 18, 60 Multiplexer 20 CPL (optical coupler) 33, 34 Polarization-maintaining optical amplifier 35, 36 Polarization-maintaining DCF (polarization-maintaining dispersion compensating fiber) 37, 38 Polarization-maintaining multiplexer 40, 54 PBS (polarization-multiplexing coupler) )

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Claims (4)

[Claims] 1. A WDM optical transmitter that performs orthogonal polarization wavelength division multiplexing processing, wherein one of two optical signals is selected from a plurality of optical signals having different wavelengths.
Multiplexing means for orthogonally multiplexing the polarized waves as a group, and compensating means for compensating for the dispersion value of the multiplexed one set of optical signals,
WDM light comprising: each set of amplification means for amplifying the one set of compensated optical signals, and multiplexing means for multiplexing the amplified set of optical signals of each set. Transmitter. 2. The WDM optical transmitter according to claim 1, wherein the optical signal frequency at the time of emitting the optical signal is determined so that the wavelength intervals of the optical signals multiplexed by the multiplexing means become equal. 3. In the optical signals multiplexed by the multiplexing means, the wavelength intervals of the optical signals in the groups whose polarizations are orthogonal to each other are narrowed, and the wavelength intervals of the optical signals between the groups are widened. The WDM optical transmitter according to claim 1, wherein an optical signal frequency at the time of emitting the optical signal is determined. 4. A WDM optical transmission method for performing an orthogonal polarization wavelength division multiplexing process to transmit an optical signal, wherein two optical signals among a plurality of optical signals having different wavelengths
A WDM optical transmission method characterized in that polarized waves are orthogonalized and multiplexed as a set, and the multiplexed optical signals of each set are multiplexed and transmitted.