JP2003318826A - Optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce degradation of signal light even when the number of nodes in a system is increased by minimizing narrow down of a band of a transmission spectrum by multi-stage passage of a multiplexer and a demultiplexer. <P>SOLUTION: In this optical transmission system constituted so that a wavelength multiplex signal light in which signal lights with a plurality of wavelength are wavelength multiplexed is transmitted between a transmission node and a reception node to be connected via an optical fiber transmission line, inserting one or more nodes including the multiplexer that multiplexes the signal light of each wavelength in the transmission node, having a demultiplexer that demultiplexes the wavelength multiplex signal light into the signal light with each wavelength in the reception node and inserting one or more nodes including the demultiplexer that demultiplexes the wavelength multiplex signal lights to the signal lights with each wavelength and the multiplexer that multiplexes the signal lights with each wavelength in the optical fiber transmission line, the multiplexers and the demultiplexers with central wavelength coincident with regulated wavelength of each signal light and the multiplexers and the demultiplexers with central wavelength slightly deviated from the regulated wavelength of each signal light are mixed and arranged as a plurality of multiplexers and demultiplexers to be arranged in the optical transmission system. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission system for wavelength-multiplexing and transmitting signal lights having a plurality of different wavelengths.
In particular, the present invention relates to an optical transmission system in which a plurality of optical add / drop nodes that add / drop signal light of a predetermined wavelength are placed in an optical transmission path.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration example of a conventional optical transmission system. In the figure, a transmitting node 10 and a receiving node 20
Is an optical fiber transmission line 30 and an optical add / drop node 40.
Connected via.

The transmitting node 10 has different wavelengths λ1.
To optical transmitters 11-1 to 11-n that output signal lights of λn
A multiplexer 12 that multiplexes the signal lights of the respective wavelengths, and an optical amplifier 13 that amplifies the multiplexed wavelength-multiplexed signal light and sends it to the optical fiber transmission line 30. The specified wavelength of the signal light output from each optical transmitter is on a predetermined wavelength grid. The optical amplifier 13 is appropriately used depending on the loss condition of the optical fiber transmission line 30, and is omitted when the loss is small.

The optical add / drop node 40 includes an optical amplifier 41 for amplifying the wavelength multiplexed signal light transmitted through the optical fiber transmission line 30, and a demultiplexer for demultiplexing the wavelength multiplexed signal light into signal lights of respective wavelengths. 42 and the signal light of each wavelength is dropped (drop)
At the same time, the optical add / drop adders 43-1 to 43-which add (add) the replacement signal light or pass the signal light as it is
n, a multiplexer 44 that multiplexes the signal light of each wavelength output from each optical add / drop multiplexer, and an optical amplifier 45 that amplifies the multiplexed wavelength-multiplexed signal light and sends it to the optical fiber transmission line 30. It is composed of The optical amplifiers 41 and 45 are appropriately used depending on the loss situation of the front and rear optical fiber transmission lines 30, and are omitted when the loss is small.

The receiving node 20 includes an optical fiber transmission line 30.
An optical amplifier 21 for amplifying the wavelength-multiplexed signal light transmitted via the optical path, a demultiplexer 22 for demultiplexing the wavelength-multiplexed signal light into signal light of each wavelength, and an optical receiver 23 for receiving the signal light of each wavelength. −
1 to 23-n. The optical amplifier 21
Is appropriately used according to the loss condition of the optical fiber transmission line 30, and is omitted when the loss is small.

With such a configuration, for example, the signal light of wavelength λ1 transmitted from the optical transmitter 11-1 of the transmission node 10 has an optical add / drop multiplexer 43-of a certain optical add / drop node 40-.
1 at the same time, the signal light of wavelength λ1 transmitted from the optical add / drop node 40 is newly added, passes through the optical add / drop multiplexer 43-1 of the other optical add / drop node 40, and is received by the receiving node 20. Is received by the optical receiver 23-1. In addition,
The wavelength at which the signal light is added / dropped can be arbitrarily set at each optical add / drop node.

[0007]

In the conventional optical transmission system, the multiplexer 12 of the transmitting node 10, the demultiplexer 42 and the multiplexer 44 of the optical add / drop node 40, and the demultiplexer 22 of the receiving node 20 are The center wavelength that maximizes the transmittance and the specified wavelength of each signal light are matched as much as possible. That is, the center wavelengths of the multiplexer and the demultiplexer are λ1 to λn with respect to the specified wavelengths λ1 to λn of the respective signal lights.

The solid line shown in FIG. 6 is one of the transmission spectra (center wavelength 1554.94 nm) of the arrayed-waveguide diffraction grating used when demultiplexing and multiplexing the wavelength-multiplexed signal light. The arrayed-waveguide diffraction grating can demultiplex wavelength-multiplexed signal light all at once, and can also collectively demultiplex signal light of each wavelength. The shape is the same for each transmission wavelength. Here, the value that maximizes the transmittance is standardized to 1, and the vicinity of the central wavelength is flatter than the Gaussian profile.

By the way, since the signal light propagating in the conventional optical transmission system passes through a large number of multiplexers and demultiplexers corresponding to the number of optical add / drop nodes, the signal light increases as the number of optical add / drop nodes increases. The pass band of light is narrowed. For example, in an optical transmission system consisting of a transmitting node, 13 optical add / drop nodes, and a receiving node, the total number of multiplexers / demultiplexers through which signal light passes is 28 (transmitting node: 1 optical branch Insertion node: 2 × 13, receiving node: 1). An example of the transmission spectrum by the multipass (28 pass) of the multiplexer and the demultiplexer is shown by the broken line in FIG. In this way, the spectrum shape is narrowed and ripples occur near the center wavelength. Therefore, strict wavelength stability is required for the signal light wavelength, but it is not easy to achieve with the conventional technology.
It is one of the major factors that deteriorate the transmission quality.

Further, since the spectrum width (full width at half maximum) at which the intensity is half the maximum value of the transmission spectrum is also narrowed, the sideband (modulation component) of the modulated signal light is greatly reduced, which also causes transmission. Quality deteriorates.

The present invention provides a stable optical transmission system that minimizes the narrowing of the transmission spectrum band due to multiple passes of a multiplexer and demultiplexer, and that causes little signal light degradation even if the number of nodes in the system increases. The purpose is to provide.

[0012]

The present invention transmits a wavelength-multiplexed signal light in which signal lights of a plurality of wavelengths are wavelength-multiplexed between a transmitting node and a receiving node connected via an optical fiber transmission line. The transmission node is provided with a multiplexer that multiplexes the signal lights of the respective wavelengths, and the receiving node is provided with a demultiplexer that demultiplexes the wavelength-multiplexed signal light into the signal lights of the respective wavelengths. 1 including a demultiplexer for demultiplexing the wavelength-division multiplexed signal light into signal light of each wavelength and a multiplexer for multiplexing the signal light of each wavelength
In an optical transmission system in which one or more nodes are inserted, as a plurality of multiplexers and demultiplexers arranged in the optical transmission system, those having a central wavelength that matches the specified wavelength of each signal light, and each signal light It is characterized in that those having a center wavelength slightly deviated from the prescribed wavelength of are mixed and arranged.

The demultiplexer and the multiplexer having the center wavelength slightly deviated from the specified wavelength of each signal light have a deviation in the positive direction and the negative direction with respect to the specified wavelength of the signal light.

The respective numbers of multiplexers and demultiplexers having a center wavelength that matches the specified wavelength of each signal light and a center wavelength that slightly deviates from the specified wavelength of each signal light are It is assumed to have a normal distribution on the wavelength axis.

It is assumed that the demultiplexer and the multiplexer of the node inserted in the optical fiber transmission line have their center wavelengths deviated in the positive and negative directions with respect to the specified wavelength of the signal light.

[0016]

1 shows an embodiment of the optical transmission system of the present invention. In the figure, the transmission node 10 and the reception node 20 are connected via an optical fiber transmission line 30 and an optical add / drop node 40.

The basic configuration of the transmitting node 10, the receiving node 20, and the optical add / drop node 40 of this embodiment is shown in FIG.
The configuration is similar to that of the conventional configuration shown in FIG. 2, but for the specified wavelength of the signal light, the multiplexer 12 'of the transmission node 10, the demultiplexer 42' and the multiplexer 44 'of the optical add / drop node 40, and the reception The feature is that the center wavelength of the demultiplexer 22 'of the node 20 is intentionally shifted. For example, with respect to the specified wavelength λ1 of the signal light, the center wavelengths of the multiplexer / demultiplexer are λ1, λ1 ± α, λ1 ±
Those that become β, λ1 ± γ, ... are mixed and arranged. Note that α ≠ β ≠ γ, and β = 2α, γ = 3α, and the like.

FIG. 2 shows an example of frequency distribution of a multiplexer / demultiplexer used in an optical transmission system. Here, the transmitting node 1
When the total number of multiplexers / demultiplexers from 0 to the receiving node 20 is 28, 8 multiplexers / demultiplexers whose center wavelength matches the specified wavelength (1554.94 nm) and the center wavelength is ± α from the specified wavelength.
An example is shown in which 6 units each have a deviation of (nm), 3 units each have a deviation of ± 2α (nm), and 3 units each have a deviation of ± 3α (nm). The transmission spectrum of each multiplexer / demultiplexer is shown in FIG. The value that maximizes the transmittance is 1
Have been standardized. Moreover, although the profile of each spectrum is the same, it is a spectrum that is translated in accordance with the center wavelength.

The transmission spectrum when a total of 28 stages of the multiplexer / demultiplexer having such variations in the center wavelength are passed is as shown by the solid line in FIG. For comparison, a broken line shows a transmission spectrum in the case of using a conventional multiplexer / demultiplexer in which the center wavelength is substantially equal to the specified wavelength. As shown here, compared to the conventional transmission spectrum, the spectrum in the vicinity of the specified wavelength has a wider band and the ripple is eliminated. Furthermore, the full width at half maximum is also widened. As a result, sufficient transmission quality can be secured even when strict wavelength stability cannot be obtained for the signal light wavelength. Further, since the full width at half maximum is also expanded, the side band of the signal light is not largely cut, and stable transmission quality can be secured.

When an arrayed-waveguide diffraction grating is used as a multiplexer / demultiplexer, conventionally, the center wavelength shifts to only one direction side (long wavelength side or short wavelength side) with respect to the signal light wavelength, and the signal light Transmission loss sometimes increased. In the configuration of the present invention, since the center wavelength of the multiplexer / demultiplexer is varied around the specified wavelength of the signal light, even if the signal light wavelength is stabilized at the specified wavelength, the transmission loss will not increase. Absent.

By the way, the frequency distribution with respect to the central wavelength of the multiplexer / demultiplexer shown in FIG. 2 assumes a normal distribution on the wavelength axis around the specified wavelength, but is limited to the normal distribution or the bilaterally symmetrical distribution. It is not something that will be done. For example, in the example of FIG. 2, if the overall balance is not greatly disturbed, 6 are shifted by + α (nm) with respect to the specified wavelength, + 2α (n
m) The number of shifts may be three, the number of shifts of −α (nm) may be five, and the number of shifts of −α (nm) may be four. When using a multiplexer / demultiplexer whose center wavelength has a normal distribution centered on the specified wavelength, select a value corresponding to the manufacturing yield of the arrayed waveguide diffraction grating as its standard deviation, and use it in an optical transmission system. A large number of multiplexers / demultiplexers can be economically selected.

Further, in the optical transmission system, the arrangement of the multiplexer / demultiplexers whose center wavelengths are respectively deviated from the specified wavelength by a predetermined value is arbitrary. For example, the frequency distribution shown in FIG. 2 may be the distribution distribution from the transmitting node 10 to the receiving node 20 as it is. Alternatively, as the demultiplexer 42 'and the multiplexer 44' of one optical add / drop node 40, one having a center wavelength deviated from the specified wavelength by + α (nm) and -α, for example.
It is also possible to use pairs that are offset by (nm).
However, their absolute values do not necessarily have to be equal. The center wavelength of the multiplexer / demultiplexer between adjacent optical add / drop nodes is arbitrarily selected. However, as the demultiplexer and the multiplexer in at least one optical add / drop node, the deviation of the center wavelength from the specified wavelength is used. By selecting ones that are substantially symmetrical, the layout design of the entire optical transmission system becomes easy.

As the multiplexer and demultiplexer, in addition to the above arrayed waveguide diffraction grating, a dielectric multilayer film filter, a fiber grating type filter, an etalon type filter, or a filter using an acousto-optic effect is used. Can be used.

Further, the node inserted in the optical fiber transmission line of the optical transmission system is not limited to the optical add / drop node as long as it includes the demultiplexer and the multiplexer, and for example, the wavelength division multiplexed signal light is demultiplexed. It may be an optical amplification relay node or the like that amplifies and amplifies each wavelength.

[0025]

As described above, in the optical transmission system of the present invention, the multiplexer and the demultiplexer having the center wavelengths matching the specified wavelength of each signal light, and the wavelengths slightly different from the specified wavelength of each signal light. By arranging the multiplexers and demultiplexers having deviated center wavelengths together, it is possible to minimize the narrowing of the transmission spectrum due to the multistage passage of the multiplexers and demultiplexers.
Even if the number of nodes increases, signal light deterioration can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an optical transmission system of the present invention.

FIG. 2 is a diagram showing an example of frequency distribution of a multiplexer / demultiplexer used in an optical transmission system.

FIG. 3 is a diagram showing a transmission spectrum of each multiplexer / demultiplexer.

FIG. 4 is a diagram showing a transmission spectrum when a total of 28 stages of light passes through the multiplexer / demultiplexer.

FIG. 5 is a diagram showing a configuration example of a conventional optical transmission system.

FIG. 6 is a diagram showing a transmission spectrum when a total of 28 stages of the multiplexer / demultiplexer in the conventional configuration are passed.

[Explanation of symbols]

10 Sending node 11 Optical transmitter 12,12 'multiplexer 13 Optical amplifier 20 receiving node 21 Optical amplifier 22,22 'duplexer 23 Optical receiver 30 optical fiber transmission line 40 Optical add / drop node 41,45 Optical amplifier 42, 42 'duplexer 43 Optical add / drop multiplexer 44,44 'Combiner

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Takahashi             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 5K102 AA01 AA36 AD01 KA01 KA42                       PC03 PC05 PC07 PH11 PH45                       PH47 PH48

Claims (6)

[Claims] 1. A configuration for transmitting wavelength-multiplexed signal light in which signal lights of a plurality of wavelengths are wavelength-multiplexed, between a transmission node and a reception node connected via an optical fiber transmission line, the transmission node A multiplexer for multiplexing the signal lights of the respective wavelengths, and a demultiplexer for demultiplexing the wavelength-multiplexed signal light into the signal lights of the respective wavelengths at the receiving node, and the wavelength-multiplexed signal in the optical fiber transmission line. An optical transmission system in which at least one node including a demultiplexer for demultiplexing light into signal light of each wavelength and a multiplexer for multiplexing signal light of each wavelength is inserted, the optical transmission system being arranged in the optical transmission system. Multiple multiplexers and demultiplexers that have a center wavelength that matches the specified wavelength of each signal light and those that have a center wavelength slightly deviated from the specified wavelength of each signal light Optical transmission system characterized by. 2. The optical transmission system according to claim 1, wherein the demultiplexer and the multiplexer having a center wavelength slightly deviated from the specified wavelength of each signal light are in the positive direction with respect to the specified wavelength of the signal light. An optical transmission system characterized by having a negative shift. 3. The optical transmission system according to claim 1, wherein the multiplexer and the demultiplexer each have a center wavelength that matches a specified wavelength of each signal light and a center wavelength that is slightly deviated from the specified wavelength of each signal light. The optical transmission system is characterized in that the respective numbers are normally distributed on the wavelength axis with respect to the specified wavelength of the signal light. 4. The optical transmission system according to claim 1, wherein the demultiplexer and the multiplexer of the node inserted in the optical fiber transmission line have respective center wavelengths with respect to the specified wavelength of the signal light. An optical transmission system having a difference between a positive direction and a negative direction. 5. The optical transmission system according to claim 1, wherein the node inserted into the optical fiber transmission line is an optical add / drop node that drops / adds signal light of a predetermined wavelength. Optical transmission system. 6. The optical transmission system according to claim 1, wherein the demultiplexer and the multiplexer are an arrayed waveguide diffraction grating, a dielectric multilayer film filter, or a fiber grating type filter, An optical transmission system characterized by being an etalon type filter or a filter using an acousto-optic effect.