JPH10154962A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost in which a diffusion compensation fiber is used in common by a plurality of optical receivers. SOLUTION: In a passive optical network consisting of an optical transmitter 2-1, a 1st optical fiber 4-1-0, a star coupler 5-1-1, a plurality of optical fibers (4-1-1-4-1-M-N) and a plurality of optical receivers (7-1-1-7-1-N), a diffusion compensation fiber 3-1 is provided between the optical transmitter 2-1 and the 1st optical fiber 4-1-0, and the diffusion compensation amount of the diffusion compensation fiber 3-1 is selected to be inverse diffusion amount -D of a mean wavelength diffusion amount D of the optical fiber used between the optical transmitter and a plurality of the optical receiver so as to allow a plurality of the optical receivers to use the diffusion compensation fiber in common and then the cost is reduced.

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 compensating chromatic dispersion in an optical fiber by using a dispersion compensating device. The present invention relates to an optical transmission system (hereinafter, referred to as a passive optical network) in which a dispersion compensation fiber is shared by a plurality of optical receivers.

[0002]

2. Description of the Related Art In an optical transmission system using an optical fiber having chromatic dispersion, "Dispersion-Induced Composite" is used.
e Second-Order Distortion at 1.55 μm ", (IEEE P
HOTONICS TECHNOLOGY LETTERS, Vol.3, pp.59-61,
As described in 1991), a signal waveform after transmission through an optical fiber is distorted due to chromatic dispersion of the optical fiber. The signal waveform distortion after optical fiber transmission is caused by wavelength dependence of the optical fiber propagation speed due to wavelength fluctuation of a light source such as a semiconductor laser called wavelength chirping. When an analog signal such as an image is used as a signal source due to signal waveform distortion due to chromatic dispersion, a problem arises in that the transmission distance is limited from the viewpoint of satisfying required distortion characteristics (composite secondary distortion and the like).
In addition, when transmitting an optical pulse such as a digital signal, the width of the optical pulse is widened at the output end of the optical fiber, so that the pulse interval of the optical fiber input optical signal is limited, and the transmission band is limited. . For the latter, see "Analysis Dyanamic Spect."
ral Width of Dynamic-Single-Mode (DSM) Laser and R
elated Transmission Bandwidth of Single-Mode Fiber
s ", (IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol.QE-2
1, pp. 292-297, 1985).

In order to reduce the amount of signal waveform distortion due to optical fiber chromatic dispersion, the total amount of chromatic dispersion in the entire optical transmission system can be reduced by reducing wavelength chirping, using a dispersion compensating device, applying a dispersion shift fiber, and the like. Need to measure.

[0004] 1.55 μm which enables very low loss and optical amplification
In long-distance optical transmission in the m-band, a method of compensating for the amount of chromatic dispersion generated in an optical fiber using a dispersion compensating device is applied. And transmitted over 2000 km ("10 Gbit / s dispersion-compensated
transmission over 2245km conventional fibers i
na recirculating loop "(ELECTRONICS LETTERS, Vol.
31, pp. 375-376, 1995)).

[0005] However, the application of dispersion compensation devices to passive optical networks has not been sufficiently discussed. However, "Study of 128 optical distribution system of 150ch AM / QAM hybrid signal" (IEICE technical report OCS94-2, pp.9-15, 1994-05)
Discloses an optical transmission system using a dispersion-shifted fiber in which the wavelength of zero dispersion is shifted from 1.3 μm to 1.55 μm, instead of the ordinary dispersion fiber.
However, in an optical transmission system in which a dispersion-shifted fiber is applied to one optical subscriber line, there is a problem that the cost increases. Here, a fiber having no dispersion at the optical signal wavelength is referred to as a zero dispersion fiber.

[0006]

As described above, in the optical subscriber transmission line, since a large number of users are connected, reduction of equipment cost is the most important issue. When a dispersion compensating fiber is used to reduce the chromatic dispersion of an optical fiber in each optical subscriber transmission line, there is a problem that the cost increases. In addition, there is a problem that the design becomes complicated because the amount of dispersion compensation differs in each optical transmission line.

A first object of the present invention is to eliminate the above-mentioned problems and to realize fiber dispersion compensation at low cost. A second object of the present invention is to provide a design method in a case where the amount of dispersion compensation differs in each optical transmission line.

[0008]

According to the present invention, an optical signal transmitted from an optical transmitter through a first optical fiber, which is a common optical transmission line, is branched by a star coupler and passed through a plurality of second optical fibers. In an optical transmission system (passive optical network) that distributes light to a plurality of optical receiving devices,
A dispersion compensating fiber is installed between the optical transmitter and the star coupler, and the inverse dispersion of the average value D of the chromatic dispersion between the optical transmitter and each optical receiver-D is set as the dispersion compensation amount of the dispersion compensating fiber. Thus, the above object is achieved by sharing the dispersion compensating fiber with a plurality of optical receivers.

In the present invention, the length of the dispersion compensating fiber can be shortened by using a zero dispersion fiber (called a dispersion shift fiber in the 1.5 μm band) in the passive optical network.

Further, according to the present invention, in a transmission system using a multi-stage star coupler, an upstream signal transmission system, and a bidirectional transmission system, it is possible to obtain an appropriate dispersion compensation amount and an installation position of a dispersion compensation fiber.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 is a diagram illustrating the configuration of an optical transmission system according to Embodiment 1 of the present invention. In FIG. 1, an optical transmission device 2-1 sends an optical fiber 4-1-1 as a common optical transmission line.
0 is transmitted to the star coupler 5-1-1.
The optical transmission device 2-1 has a configuration in which the light is distributed to N optical receiving devices by 1-1 to 5-M-P and optical fibers 4-1-1 to 4-1-MN. A dispersion compensating fiber 3-1 is provided between the optical transmission device 2-1 and the optical fiber 4-1-0.
And the inverse dispersion of the average value of the chromatic dispersion between the optical receivers 7-1-1 to 7-1-N is used as the compensation amount of the dispersion compensating fiber 3-1, and the dispersion compensating fiber 3-1 is shared. Things.

Hereinafter, the configuration will be described in detail. FIG. 1 shows an optical transmission device 2-1 for converting an input signal into an optical signal, a dispersion compensating fiber 3-1 for compensating for chromatic dispersion, and an optical transmission device 2-1 and a star coupler 5-1-1. And an optical fiber 4-1-0, which serves as a common optical transmission line, and an optical fiber 4-1.
Connect star couplers 5-1-1-1 to 5-1-1-MP for optically distributing the output light from 1-0 to each optical receiver, and between star couplers and between star couplers and optical receivers Optical fibers 4-1-1-1 to 4-1-1-M-N and optical amplifiers 6-1-1-0 and 6-1-1-1-1 for compensating for optical signal power reduced by optical branching by the star coupler. 1 ...
And N optical receivers 7-1-1 through 7-1-N for converting optical signals into respective electric signals. The number and length of the star couplers, the number of branches, and the number and length of the optical fibers that connect between the star couplers and between the star coupler and the optical receiver differ depending on the installation positions of the star coupler and the optical receiver.

The dispersion compensation amount of the dispersion compensating fiber is set as follows. The optical signal input to the optical receiver 7-1-1 in FIG. 1 is subjected to chromatic dispersion (dispersion amount D0 +) by the optical fibers 4-1-1-0, 4-1-1-1 to 4-1-1-M-1. D11 + ... + D
M1). Hereinafter, similarly, the other optical receivers 7-1-2
The amount of chromatic dispersion of the optical fiber is also determined for the optical signal input to 7-1-N, and the value differs depending on the optical fiber that passes from the optical transmitter to each optical receiver. Optical transmitting device and each optical receiving device 7-1-1 to 7-1-1
The inverse dispersion amount -D of the average value D of the wavelength dispersion amount generated in the optical fiber between 1 and N is set as the dispersion compensation amount of the dispersion compensating fiber 3-1.

[0014]

[Table 1]

An example of a method of measuring and setting a dispersion compensation amount in an actual optical transmission system will be described below according to signal processing. The amount of chromatic dispersion generated in the optical fiber can be obtained from the light wavelength and the optical fiber length. A short optical pulse signal is transmitted from an optical transmitter, and the optical fiber length can be measured from the transmitted optical pulse signal and the time delay of a reflected return optical pulse signal from the optical receiver (Optical T).
ime Domain Reflectrometry method). In the embodiment shown in FIG. 1, the optical pulse signal transmitted from the optical transmitter is optically branched by the star coupler, passes through optical fibers having different lengths from the star coupler to each optical receiver, and is reflected at each optical receiver. Is done. The optical pulse signal reflected by each optical receiving device is optically multiplexed again by the star coupler, and returns to the optical transmitting device as reflected light. By measuring the average value of the time delay of the optical signal transmitted from the optical transmitter and the reflected return optical signal from each optical receiver, the average optical fiber length from the optical transmitter to each optical receiver can be calculated. Desired. From the obtained average optical fiber length, the average amount of chromatic dispersion D between the optical transmitting device and each optical receiving device was obtained,
The inverse dispersion amount -D is set to the dispersion compensation amount of the dispersion compensating fiber.

In this embodiment, a dispersion compensating fiber is installed between the optical transmitting device 2-1 and the star coupler 5-1-1, and the optical transmitting device 2-1 and each of the optical receiving devices 7-1-1 to 7-1-1. By setting the inverse dispersion amount of the average value of the chromatic dispersion amount between 1 and N as the dispersion compensation amount of the dispersion compensating fiber, the distortion amount of the optical signal input to each optical receiving device can be averaged, The dispersion compensating fiber 3-1 is connected to N optical receivers 7-1-1 through 7-1-1.
1-N can be shared and cost can be reduced.

In this embodiment, the installation position and quantity of the dispersion compensating fiber can be designed and selected according to the cost, the amount of signal distortion in each optical receiver, and the like.

(Embodiment 2) FIG. 2 is a diagram illustrating the configuration of an optical transmission system according to Embodiment 2 of the present invention. In FIG. 2, the output light from the optical transmission device 2-2 is composed of components 00 to 1
K, ..., and N optical receivers 7-2-1 through 7-2
-N.

Hereinafter, the configuration 00 will be described as an example. The configuration 00 is composed of a dispersion compensating fiber 3-2-0-0, a star coupler 5-2-2-0-0, an optical fiber 4-2-2-C0 serving as a common optical transmission line, and a configuration between the components 00-11 and 00-1K. It consists of optical fibers 4-2-0-1 to 4-2-0-K to be connected.

[0020]

[Table 2]

[0021]

[Table 3]

As shown in Table 2, the dispersion compensating fiber 3-2-
In the case of 0-0, the amount of chromatic dispersion (D00 + D01 to D00 + D) generated in each optical transmission line of the optical fiber connecting the optical fiber 4-2-C0 and the components 00-11 to 00-1K.
0K) is defined as the amount of inverse dispersion of the average value (D00 + ΣD0i / K). Similarly, in each of the other configurations 11 to 1K,..., The respective dispersion compensating fibers have the inverse dispersion of the average value of the chromatic dispersion in the optical fiber branched by the star coupler and the optical fiber branched by the star coupler as shown in Table 3. Is the dispersion compensation amount. With this configuration, the cost can be reduced by sharing a plurality of dispersion compensating fibers, and the wavelength between the optical transmitting device and each of the receiving devices 7-2-1 to 7-2-N can be compared with the embodiment shown in FIG. Dispersion differences can be reduced.

In addition, the installation position of the dispersion compensating fiber depends on the cost, the amount of signal distortion in each optical receiver, and the like.
The quantity can be designed and selected.

(Embodiment 3) FIG. 3 is a diagram illustrating the configuration of an optical transmission system according to Embodiment 3 of the present invention. In FIG. 3, the optical output from the optical transmitter 2-3 is transmitted through the optical fiber 4-3, and the optical output is transmitted to N optical receivers 7-3-1 to 7-3-N by the star coupler 5-3. In the distributed configuration, the dispersion compensating fiber is installed between the optical transmitter 2-3 and the star coupler 5-3, and the optical fiber between the star coupler 5-3 and the optical receivers 7-3-1 to 7-3-N is provided. Is shown as an example in which dispersion shift fibers 9-1 to 9-N are used. The dispersion compensating fiber 3-3 compensates for the amount of chromatic dispersion of the optical fiber 4-3, which is a common optical transmission line. The optical transmitter 2-3 and each of the optical receivers 7-3-1 to 7-3-7 are used together with the dispersion compensating fiber 3-3 and the dispersion shift fibers 9-1 to 9-N for transmitting the output light from the star coupler 5-3. -
Between 3-N, the amount of chromatic dispersion can be made zero,
An optical signal without distortion can be received. Further, similarly to the first and second embodiments, the dispersion compensating fiber 3-3 can be shared by N optical receivers.

In this embodiment, the star coupler has only one stage connection. However, as in the first and second embodiments, a configuration in which a plurality of star couplers are connected in series and in parallel can be used. 3-3, dispersion shift fiber 9-2. The configuration can be shared by a large number of optical receiving devices.

(Embodiment 4) Although all of the above embodiments have been described by taking only downlink signals as an example, up-down bidirectional communication may be used. FIG. 4 shows an embodiment in which the same wavelength is used for bidirectional (upper and lower) optical signals. In the fourth embodiment, an optical transmission line, an optical transmission device, and a reception device are optically coupled by an optical coupler, and a dispersion compensating fiber 3-4, a star coupler 5-4, an optical fiber transmission line 4-4-1,. , 4-4-
The case where N is shared is shown. Hereinafter, the configuration will be described separately for an uplink signal and a downlink signal.

The downstream optical signal transmitted from the optical transmitter 7-4-0 is input to the dispersion compensating fiber 3-4 via the optical coupler 11-4-0. The output optical signal from the dispersion compensating fiber is distributed to N optical fiber transmission lines 4-4-1,..., 4-4-N by a star coupler.
4-1..., 11-4-N N Optical Receivers 8-4
-1, ..., 8-4-N.

On the other hand, N optical transmitters 2-4-0,.
Optical signal transmitted from the optical coupler 11-4-
,..., 4-4-N are transmitted through N optical fiber transmission lines 4-4-1,. The optical signals transmitted through the optical fiber are multiplexed by the star coupler 5-4 and input to the dispersion compensating fiber 3-4. Dispersion compensation 3-
Output optical signals from the four fibers are received by the optical receiver 7-4-0 via the optical coupler 11-4-0.

In the dispersion compensating fiber, the inverse dispersion amount -D of the average value D of the chromatic dispersion amount generated in each of the optical fiber transmission lines 4-4-1,... By setting the amount of dispersion compensation, the N sets of optical transmitters and optical receivers can share the dispersion compensating fiber, and if they are rubbed, the reduction can be achieved. Further, it is possible to average the difference in the amount of chromatic dispersion generated in each optical fiber transmission line.

In the fourth embodiment, the configuration is such that the star couplers are connected in one stage. However, the configuration may be such that the star couplers are connected in multiple stages, so that the dispersion compensating fiber can be shared by a larger number of optical transmission / reception devices.

(Embodiment 5) Embodiment 5 in which two sets of optical transmission systems for upstream signals and optical transmission systems for downstream signals are used.
Is shown in FIG. The fifth embodiment corresponds to a case where different wavelengths are used for the upper and lower optical signals, or a case where the upper and lower signals are transmitted through separate optical fibers from the viewpoint of the transmission band.

Optical transmitter 2-5-D, dispersion compensating fiber 3
-5-D, Star coupler 5-5-D, Optical receiver 7-5-D
,..., 7-5-D-N are for downlink signals, and the optical transmitters 2-5-U-1,.
-UN, star coupler 5-5-U, dispersion compensating fiber 3
-5-U and the optical receiving device 7-5-U are for upstream signals. In the case of a downlink signal, the dispersion compensation amount of the dispersion compensating fiber is set to a value -D for compensating the average value D of the dispersion amount between the optical transmitter and each optical receiver. The same applies to the uplink signal, which is set to a value -D * for compensating the average value D * of the dispersion amount between each optical transmitter and the optical receiver.

As in the first and second embodiments, an optical amplifier may be provided as appropriate, or a configuration in which star couplers are connected in multiple stages may be adopted. However, when an optical amplifier is installed, the amplification directions are opposite for upstream and downstream.

[0034]

According to the present invention, in an optical transmission system (passive optical network) composed of a plurality of optical receivers for one optical transmitter, an optical fiber is generated between an optical transmitter and each optical receiver. By installing a dispersion compensating fiber having an inverse dispersion amount of the average value of the chromatic dispersion amount on a common optical transmission line in a plurality of optical receivers, the dispersion compensating fiber can be shared, and the cost in the optical transmission system Was reduced.

Further, with the above-described configuration, it was possible to provide a second object of the present invention, that is, a design method in which the amount of dispersion compensation differs in each optical transmission line.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an optical transmission system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an optical transmission system according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of an optical transmission system according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of an optical transmission system according to a fourth embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration of an optical transmission system that is Embodiment 5 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Input signal, 2 ... Optical transmission device, 3 ... Dispersion compensation fiber, 4 ... Optical fiber, 5 ... Star coupler, 6 ... Optical amplifier, 7 ... Optical receiving device, 8 ... Output signal, 9 ... Dispersion shift fiber.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/135 10/13 10/12 10/02 10/20

Claims (12)

[Claims] 1. An optical transmitter for converting an input electric signal into an optical signal, a first optical fiber for transmitting output light from the optical transmitter, and an N-branch output light of the first optical fiber (where N is 2 or more). (The natural number of
Optical transmission system, comprising: a star coupler that performs output, N second optical fibers that transmit output light from the star coupler, and N optical receiving devices that respectively convert output light of the second optical fiber into electric signals. 2. The optical transmission system according to claim 1, wherein the first optical fiber has dispersion at the wavelength of the optical signal, and a dispersion compensating fiber is provided between the optical transmitter and the star coupler. 2. An optical transmission device for converting an input electric signal into an optical signal, a first optical fiber for transmitting output light from the optical transmission device, and N output branches of the first optical fiber (where N is 2 or more). (The natural number of
Optical transmission system, comprising: a star coupler that performs output, N second optical fibers that transmit output light from the star coupler, and N optical receiving devices that respectively convert output light of the second optical fiber into electric signals. 2. The optical transmission system according to claim 1, wherein the first optical fiber is a zero dispersion fiber at a wavelength of the optical signal, and a dispersion compensating fiber is provided between the optical transmitter and the star coupler. 3. The optical transmission system according to claim 1, wherein the inverse dispersion amount -D of the average dispersion amount D of the sum of chromatic dispersion amounts of the first optical fiber and the second optical fiber is dispersion-compensated. An optical transmission system, wherein a fiber dispersion compensation amount is used. 4. The optical transmission system according to claim 1, wherein a dispersion compensating fiber having an inverse dispersion amount of the chromatic dispersion amount of the first optical fiber is provided between the optical transmitter and the star coupler. An optical transmission system comprising a zero dispersion fiber at the wavelength of an optical signal. 5. An optical transmitter for converting an input electric signal into an optical signal, a first optical fiber for transmitting output light from the optical transmitter, and a first optical fiber for branching output light of the first optical fiber into a plurality of rows. Dan 1
A row star coupler, and at least one M-th P-th row (M is 2) that branches at least one row of output light from the first-stage first-row star coupler.
The above natural number, P is a natural number) In an optical transmission system including a star coupler and a plurality of optical receivers for converting output light from the first to M-th stage P-row star couplers into electric signals, An optical transmission system, wherein the fiber has dispersion at the wavelength of the optical signal, and a dispersion compensating fiber is provided between the optical transmission device and the first-stage first-row star coupler. 6. The optical transmission system according to claim 5, wherein the inverse dispersion amount -D of the average dispersion amount D of the chromatic dispersion amount between the optical transmitting device and each of the plurality of optical receiving devices is defined as the dispersion compensation amount of the dispersion compensating fiber. An optical transmission system characterized by: 7. The optical transmission system according to claim 5, wherein a dispersion compensating fiber having an inverse chromatic dispersion of the first optical fiber is inserted between the optical transmitting device and the first-stage first-row star coupler. An optical transmission system, wherein an optical fiber constituting an optical fiber network for distributing output light from a first-stage first-row star coupler to a plurality of optical receiving devices is a zero-dispersion fiber at a wavelength of an optical signal. . 8. The optical transmission system according to claim 5, wherein a dispersion compensating fiber is inserted into a part or all of the optical fibers connecting between the star couplers. 9. The optical transmission system according to claim 1, wherein an optical amplifier is inserted in the optical transmission line. 10. An N signal converter (N) for converting an input signal into an optical signal.
Is a natural number of 2 or more), N first optical fibers that transmit output light from the optical transmitter, a star coupler that multiplexes output light of the first optical fiber, and a star coupler. An optical transmission system comprising: a second optical fiber that transmits the output light of the second optical fiber; and an optical receiving device that converts the output light of the second optical fiber into an electric signal, wherein the second optical fiber disperses at the wavelength of the optical signal. An optical transmission system comprising: a dispersion compensating fiber provided between the optical receiver and the star coupler. 11. The optical transmission system according to claim 10, wherein the inverse dispersion amount -D of the average dispersion amount D of the sum of the chromatic dispersion amounts of the first optical fiber and the second optical fiber is calculated as the dispersion compensation amount of the dispersion compensating fiber. An optical transmission system, characterized in that: 12. An optical transmission system using the optical transmission system according to claim 1 for downlink signal transmission, and using the optical transmission system according to claim 10 or 11 for uplink signal transmission.