JP2000115075A - Dispersion compensator for bidirectional transmission and optical communication system using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion compensator for bidirectional transmission which actualizes more economical optical transmission of high quality and an optical communication system which uses it. SOLUTION: Wave-multiplexed signal light 1-1 of an up line which is inputted to a 1st optical circulator 3-1 is amplified by an Er-added optical fiber 7-1, demultiplexed to wavelength bands by a WDM(wavelength demultiplexing) filter 9-1, reflected by chirped grating elements 10-1 and 2, returned to the WDM filter 9-1 and multiplexed, and returned to the 1st optical circulator 3-1 and outputted. Wavelength-multiplexed signal 2-1 of a down line which is inputted to a 2nd optical circulator 3-2 is amplified by an Er-added optical fiber 7-2, demultiplexed to wavelength bands by a WDM filter 9-2, reflected by chirped grating elements 10-3 and 4, returned to the WDM filter 9-2 and multiplexed, and returned to the 2nd optical circulator 3-2 and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion compensator for bidirectional transmission for compensating chromatic dispersion when transmitting wavelength-division multiplexed signal light in uplink and downlink, and an optical communication system using the same. More specifically, the present invention relates to a bidirectional transmission dispersion compensator that realizes more economical and high-quality optical transmission and an optical communication system using the same.

[0002]

2. Description of the Related Art In recent years, with the rapid development of optical fiber amplifiers in the 1.55 μm band, high-speed and large-capacity information is transmitted by wavelength multiplexing transmission using several or several tens of signal lights in the 1.55 μm band. Research and development of systems for long-distance transmission have become active. As a configuration method of such a system, a single-mode optical fiber having a zero-demultiplexing characteristic of 1.3 μm is used for a transmission line, and a signal light of 1.55 μm band is wavelength-multiplexed to several or several tens of waves in this transmission line. A method of transmitting the wavelength-division multiplexed signal light has been studied. A problem in transmitting the wavelength multiplexed signal light over a long distance is chromatic dispersion. That is, when the input signal light propagates through an optical fiber having a large dispersion value over a long distance, the output signal light deteriorates. Therefore, it is necessary to compensate for chromatic dispersion and make the dispersion value zero. As a method of compensating for the chromatic dispersion of the optical fiber in the 1.55 μm band, a method of inserting a dispersion compensating fiber into a transmission line, a method of propagating a wavelength multiplexed signal light to a Bragg grating fiber connected in cascade, and a method of respectively providing a desired delay There has been proposed a method of compensating for chromatic dispersion by allowing reflection after giving time.

On the other hand, a method of bidirectionally transmitting wavelength-division multiplexed signal light having a different wavelength band between an uplink and a downlink using the above-described chromatic dispersion compensation method has been studied. FIG. 9 shows an example. This optical communication system has terminal relay units 112-1 and 112-2 at both ends, and an intermediate relay unit 113-112 between these terminal relay units 112-1 and 112-2.
, 113-2,... Are provided. Then, the plurality of transmitters 10 are provided in the terminal relay unit 112-1 (112-2).
0-1 to 100-n (102-1 to 102-m) and a plurality of receivers 101-1 to 101-m (103-1 to 103)
-N), and the wavelength division multiplex transmission and reception of the signal light in the different wavelength bands between the relay stations at both ends. For example, the transmitters 100-1 to 100-n operate at wavelengths of 1.53 μm to 1.
Transmits several or a dozen or so signal lights at 0.8 nm intervals in the range of 544 μm, and the transmitters 102-1 to 102-m transmit signals at 0.8 nm intervals in the wavelength range of 1.545 μm to 1.56 μm. Transmits wave or dozens of signal lights.

[0004] The signal lights of the respective wavelengths are multiplexed by a WDM filter 104-1 (104-3; hereinafter, the direction in parentheses is the opposite direction), and a single-mode optical fiber transmission line 105-1 (several tens km) is used. 106-s), dispersion-compensated by the dispersion compensating fiber 107-1 (108-s), and then the optical fiber amplifier 109-1 (110-s).
After amplification by the WDM filter 111-1 (111-
r), and the single mode optical fiber transmission line 10
5-2 (105-r) and the intermediate relay unit 113-1
(113-q; not shown). Then, the signal is demultiplexed by the WDM filter 111-2 (111-q; not shown) of the intermediate relay unit 113-1 (113-q; not shown).
Similarly, after the chromatic dispersion is compensated by the dispersion compensating fiber 107-2 (107-q; not shown), the optical fiber amplifier 10-2
9-2 (109-q; not shown), the signal light power is amplified, multiplexed by a WDM filter 111-3 (111-p; not shown), and the single mode optical fiber transmission line 10
It is sent to the next intermediate relay unit 113-2 (113-p; not shown) through 5-3 (106-q; not shown). After passing through a plurality of intermediate repeaters in this way, the signal finally reaches the terminal repeater 112-2 (112-1) at the opposite end, is demultiplexed by the WDM filter 111-r (111-1), and dispersion-compensated. The fiber is guided to the single-mode optical fiber transmission line 105-s (106-1) through the fiber 107-s (108-1) and the optical fiber amplifier 109-s (110-1), and thereafter, to the WDM filter 104-4. The receivers 103-1 to 103-n (101-1 to 10-3) receive the signal light of each wavelength, demultiplexed into the respective wavelengths in (104-2).
1-m).

In the above system, the single mode optical fiber transmission lines 105-1 to 105-s, 106-1 to 106-1
The length of 106-s is set to be about 50 km to 100 km, and several to several tens of intermediate relay units are used.

However, in this system configuration, a dispersion compensating fiber and an optical fiber amplifier are used independently for the uplink and the downlink, so that the system becomes very expensive. Therefore, as a method of reducing the price of the above system, the configuration method of FIGS.
No. 917.

First, the configuration method shown in FIG. 10 is a method in which optical circulators 120 and 123 are arranged on both sides of one dispersion compensator 121, and this dispersion compensator 121 is used for both upstream signal light and downstream signal light. is there. This makes it possible to reduce the total amount of dispersion compensating fibers and reduce the mounting space as compared with the case of FIG. 9 in which dispersion compensators are separately provided for each of the upstream signal light and the downstream signal light. 1
Reference numerals 24, 125, 126, and 127 are optical amplifiers, and 128 is a single mode optical fiber.

Next, in the configuration method shown in FIG. 11, optical multiplexers / demultiplexers 129-1 and 129-2 are arranged on both sides of one dispersion compensator 121 instead of an optical circulator, and the dispersion compensator 121 is moved up. This is a method for sharing signal light and downlink signal light.

[0009]

However, the methods shown in FIGS. 10 and 11 have the following problems.

(1) Signal light having different wavelength bands must be wavelength-division multiplex-transmitted to the upstream line and the downstream line. The wavelength band may have a bandwidth of 10 nm to 80 nm. In order to transmit a wavelength-division multiplexed signal light having such a wide bandwidth as described above, the dispersion compensator 121 is required to have a very wide band and a small dispersion slope. However, at present, it is difficult to realize a wideband dispersion compensator as described above, and as a result, chromatic dispersion is accumulated by passing through a large number of intermediate repeaters while chromatic dispersion cannot be completely compensated. The signal light causes waveform distortion and is deteriorated, so that high-quality optical transmission cannot be realized.

(2) Since the optical fiber amplifier cannot be shared between the upstream line and the downstream line, it is difficult to drastically reduce the cost.

(3) Terminal relay units 112-1 and 112-2
If the distance extends from several hundred km to several thousand km, the chromatic dispersion described in (1) becomes extremely large, and the method of sharing one dispersion compensator for upstream signal light and downstream signal light cannot be used. .

It is an object of the present invention to provide a bidirectional transmission dispersion compensator which solves the above problems and realizes more economical and high-quality optical transmission, and an optical communication system using the same. .

[0014]

In order to achieve the above object, a bidirectional transmission dispersion compensator according to the present invention is provided with a first optical circulator having a plurality of ports, and the first optical circulator is provided with a first port. It is assumed that the upstream wavelength-division multiplexed signal light is input, a first Er-doped optical fiber is connected to a second port which is a forward direction of the first port, and pumping light is injected into the first Er-doped optical fiber, This first Er
One input terminal of a WDM coupler for demultiplexing and extracting upstream and downstream signal light is connected to the added optical fiber, and the upstream signal light is divided into a plurality of wavelength bands at the upstream output terminal of the WDM coupler. Connect the first WDM filter to wave,
By connecting a chirped grating element that delays and reflects the signal light according to the wavelength to each demultiplexing output terminal of the first WDM filter, each reflected signal light is multiplexed by the first WDM filter. And returns to the second port of the first optical circulator via the WDM coupler and the first Er-doped optical fiber, and is output from the third port in the forward direction of the second port as wavelength-division multiplexed signal light of the uplink. A second optical circulator having a plurality of ports is provided, and a wavelength multiplexed signal light of a downlink is input to a first port of the second optical circulator, and the forward direction of the first port is provided. The second Er-doped optical fiber is connected to the second port, and pump light is injected into the second Er-doped optical fiber. Connect the other input terminal of the coupler, connecting the second WDM filter for demultiplexing a signal light downlink to downlink the output terminal of the WDM coupler into a plurality of wavelength bands,
By connecting a chirped grating element that delays and reflects the signal light according to the wavelength to each demultiplexing output terminal of the second WDM filter, the reflected signal light is multiplexed by the second WDM filter. The light returns to the second port of the second optical circulator via the WDM coupler and the second Er-doped optical fiber, and is output from the third port, which is a forward direction of the second port, as a wavelength-division multiplexed signal light. It is configured as follows.

The chirped grating element may reflect the input signal light in the wavelength band with a longer delay time as the signal light has a shorter wavelength.

The first and second Er-doped optical fibers may be configured so that pumping light of 0.98 μm or 1.48 μm propagates from one or both directions, respectively.

A second WDM is provided between the WDM coupler (referred to as a first WDM coupler) and the first and second WDM filters.
A DM coupler is inserted, an upstream output end of the first WDM coupler is connected to one input end of the second WDM coupler, and a downstream output end of the first WDM coupler is connected to the other end of the second WDM coupler. Connected to an input end to form a loop, an up-link output end of the second WDM coupler is connected to the first WDM filter, and a down-link output end of the second WDM coupler is connected to the second WDM filter. You may.

Further, the dispersion compensator for bidirectional transmission of the present invention is provided with a first optical circulator having at least four ports, and inputs the upstream wavelength multiplexed signal light to the first port of the first optical circulator. A first WDM filter that splits the signal light of the uplink into a plurality of wavelength bands is connected to a second port that is a forward direction of the first port, and each of the split output terminals of the first WDM filter is connected to the first WDM filter. By connecting a chirped grating element that reflects and delays the signal light according to the wavelength, each reflected signal light is multiplexed by the first WDM filter and returns to the second port of the first optical circulator. And a second optical circulator having at least four ports is provided. Downlink wavelength multiplexed signal light is input to a first port of the second optical circulator. A second WDM filter for splitting the downlink signal light into a plurality of wavelength bands is connected to a second port which is a forward direction of the first port, and each demultiplexing output terminal of the second WDM filter is connected. By connecting a chirped grating element that delays and reflects the signal light according to the wavelength, the reflected signal lights are multiplexed by the second WDM filter and are connected to the second port of the second optical circulator. It is configured to return, and an Er-doped optical fiber is provided between a third port, which is a forward direction of the second port of the first optical circulator, and a third port, which is a forward direction of the second port of the second optical circulator. At the same time, pumping light is injected into the Er-doped optical fiber, and upstream wavelength-division multiplexed signal light is output from a fourth port in the forward direction of the third port of the second optical circulator. , In which the first optical third port fourth port than downlink wavelength-multiplexed signal light comprising a forward circulator is to be outputted.

The Er-doped optical fiber may be configured so that pumping light of 0.98 μm or 1.48 μm propagates from one direction or both directions.

Further, the dispersion compensator for bidirectional transmission according to the present invention is provided with a first optical circulator having a plurality of ports, and inputs an upstream wavelength multiplexed signal light to the first port of the first optical circulator. A first Er-doped optical fiber is connected to a second port, which is a forward direction of the first port, and pumping light is injected into the first Er-doped optical fiber. A first port of a third optical circulator having a first port is connected to a second port which is a forward direction of the first port, and a first WDM filter for splitting an upstream signal light into a plurality of wavelength bands is connected to the second port. By connecting a chirped grating element that delays and reflects the signal light according to the wavelength to each demultiplexing output terminal of the first WDM filter, the reflected signal light is converted to the first WD. A second optical circulator having a plurality of ports is provided so as to be multiplexed by a filter and returned to the second port of the third optical circulator, and a downlink wavelength multiplexed signal is provided to the first port of the second optical circulator. Light is to be input, a second Er-doped optical fiber is connected to a second port that is a forward direction of the first port, and pumping light is injected into the second Er-doped optical fiber,
A third port in the forward direction of the second port of the third optical circulator is connected to the second Er-doped optical fiber, and return light of the upstream wavelength-division multiplexed signal light passes through the second Er-doped optical fiber. The second optical circulator is configured to be output from a third port which is a forward direction of the second port, and a fourth port which is a forward direction of the third port of the third optical circulator is provided with a downlink signal. A second WDM filter for splitting light into a plurality of wavelength bands is connected,
By connecting a chirped grating element that delays and reflects the signal light according to the wavelength to each of the demultiplexing output terminals of the DM filter, the reflected signal light is converted into the second W signal.
The light is multiplexed by the DM filter and returns to the fourth port of the third optical circulator. From the first port in the forward direction of the fourth port, the first optical circulator passes through the first Er-doped optical fiber. It is configured such that it is output as upstream wavelength-division multiplexed signal light from a third port in the forward direction of two ports.

The first and second Er-doped optical fibers may be configured so that pumping light of 0.98 μm or 1.48 μm propagates from one direction or both directions, respectively.

A coupler for extracting a part of the signal light is provided in the propagation path of the wavelength-division multiplexed signal light of the upstream line and the downstream line, and the coupler has a light receiving element for receiving a part of the signal light and converting it to an electric signal. A drive circuit may be provided for connection and controlling the optical power of the excitation light according to the electric signal.

The chirped grating element may have a fiber type structure or a waveguide type structure.

Further, the optical communication system of the present invention uses any one of the above-described dispersion compensators for bidirectional transmission, and the upstream and downstream wavelength multiplexed signal light input to the dispersion compensator for bidirectional transmission is used. , Each of which is composed of at least four signal lights having different wavelengths and transmitted through a single-mode optical fiber of at least 40 km.

The information transmission rate of the wavelength multiplexed signal light in the uplink and the downlink is at least 2.4 Gb /
It may be s.

[0026] The wavelengths of the upstream and downstream wavelength-division multiplexed signal lights may be in the range of 1.53 µm to 1.61 µm.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the dispersion compensator for bidirectional transmission according to the present invention is provided with an optical circulator 3-1 having three ports, and an upstream line is connected to a first port of the optical circulator 3-1. The Er-doped optical fiber 7-1 is connected to a second port, which is a forward direction of the first port, and the Er-doped optical fiber (EDF) 7-1 is connected.
Pump light having a wavelength of 0.98 μm is injected from the pump light source 4-1 into the Er-doped optical fiber 7-1, and one of the WDM couplers 8 that separates and extracts the upstream signal light and the downstream signal light. And a WDM filter 9-1 for demultiplexing the signal light of the up-link into a plurality of wavelength bands is connected to an up-link output end of the WDM coupler 8, and each demultiplexing of the WDM filter 9-1 is performed. Chirped grating elements 10-1 and 10-10 which reflect signal light at an output end with a delay according to the wavelength
-2 are connected, and the third port of the optical circulator 3-1 is connected to the upstream line.

The dispersion compensator for bidirectional transmission has three
An optical circulator 3-2 having two ports is provided, a down line is connected to a first port of the optical circulator 3-2, and an Er-doped optical fiber 7-2 is connected to a second port in the forward direction of the first port. Connect with this Er
0.98 μm wavelength from the excitation light source 4-2 to the added optical fiber
And the other input terminal of the WDM coupler 8 is connected to the Er-doped optical fiber 7-2.
A WDM filter 9-2 for demultiplexing the down-link signal light into a plurality of wavelength bands is connected to the down-link output terminal of the coupler 8, and the demultiplex output terminals of the WDM filter 9-2 convert the signal light according to the wavelength. The chirped grating elements 10-3 and 10-4 that reflect with a delay are connected to each other, and the third port of the second optical circulator 3-2 is connected to the downstream line.

On the uplink, wavelength-division multiplexed signal light having wavelengths λ1 to λm is transmitted. The upstream wavelength-multiplexed signal light input to the first port of the optical circulator 3-1 propagates in the order of arrows 1-1, 1-2, 1-3, 1-4, 1-5, and 1-6. Then, the signal is output from the third port of the optical circulator 3-1. During that time, chromatic dispersion compensation and two optical amplifications are performed to output signal light.

The wavelength division multiplexed signal light of wavelengths λn to λz is transmitted on the down line. Downlink wavelength-division multiplexed signal light input to the first port of the optical circulator 3-2 propagates in the order of arrows 2-1, 2-2, 2-3, 2-4, 2-5, and 2-6. Then, the signal is output from the third port of the optical circulator 3-2. During that time, chromatic dispersion compensation and two optical amplifications are performed to output signal light.

The wavelength-division multiplexed signal light input at arrows 1-1 and 2-1 has propagated through a single-mode optical fiber having a zero-dispersion wavelength of 1.3 μm for at least 40 km. The wavelength-division multiplexed signal light output in 2-6 has the chromatic dispersion compensated and the optical power amplified.

Hereinafter, the dispersion compensator for bidirectional transmission will be described in detail.

First, the wavelength division multiplexed signal light (wavelength λ
1 to λm, for example, signal light having a wavelength range of 1.53 μm to 1.545 μm) is signal light that has propagated through a single mode optical fiber for at least 40 km, and causes attenuation of optical power and chromatic dispersion. The signal light of arrow 1-1 is
The light enters the first port of the optical circulator 3-1 and is guided to the second port, where the excitation light source 4-1 (wavelength 0.98 μm
Doped optical fiber 7 through a coupler 11-1 (coupling circuit for coupling the pumped light to the Er doped optical fiber 7-1) together with the pumping light (arrow 5-1) from the band or the 1.48 μm band semiconductor laser. -1, propagated inside, amplified,
It is taken out as indicated by an arrow 1-2. Thereafter, the signal light is incident on the WDM coupler 8 so that arrows 1-3.
And is guided to the WDM filter 9-1.
On the other hand, most of the pump light is absorbed by the Er-doped optical fiber 7-1 and contributes to amplification of the signal light, but the unabsorbed pump light is absorbed by the Er-doped optical fiber 7 as indicated by arrows 5-2 and 5-3. -2, the wavelength multiplexed signal light of the downlink (arrow 2)
-1). Further, an excitation light source 4-2 (a semiconductor laser having a wavelength of 0.98 μm band or 1.48 μm band)
Are not absorbed by the Er-doped optical fiber 7-2 out of the excitation light (arrow 6-1) from the arrows 6-2 and 6-3.
As described above, the light propagates through the Er-doped optical fiber 7-1 to contribute to amplification of the wavelength-multiplexed signal light in the uplink.

The signal light (arrows 1-3) guided to the WDM filter 9-1 has two wavelength bands, for example, wavelengths λ1 to λ1.
λ4 band and wavelength λ5 to λ8 band (wavelength λ1 to λ3 band, wavelength λ4 to λ6 band, wavelength λ1 to λ6 band and wavelength λ
7 to λ12 band). Wavelength λ
The signal light in the 1 to λ4 band propagates through the chirped grating element (chirped grating fiber or chirped grating waveguide) 10-1 as indicated by an arrow 1-3-1. The light propagates through the chirped grating element 10-2 as indicated by an arrow 1-3-3.

Here, λ1 <λ2 <λ3 <... <λ7 <λ
Assuming that the signal wavelength is 8, the signal light of the wavelength λ1 propagates through the chirped grating element 10-1 to the farthest and is reflected, returns as indicated by the arrow 1-3-2, and generates the longest delay time, thereby causing the WDM filter 9--1. They are multiplexed by 1. Wavelength λ
The signal lights of 2, λ3, λ4 are sequentially propagated through the chirped grating element 10-1 and reflected (the signal light of wavelength λ4 is reflected closest), and arrows 1-3.
-2, successively increasing the delay time,
The signals are multiplexed by the filter 9-1. Similarly, wavelengths λ5 to λ8
The band signal light is transmitted to the chirped grating element 10-.
The signals propagate, propagate, reflect, and return backward so as to successively cause a large delay time in the signal 2 and are multiplexed by the WDM filter 9-1.

The signal light in the wavelength λ1 to λ4 band and the wavelength λ5
The signal light obtained by multiplexing the signal light in the λ8 band with the WDM filter 9-1 propagates as indicated by an arrow 1-4, is coupled to the Er-doped optical fiber 7-1 by the WDM coupler 8, and is indicated by an arrow 1-5.
Propagates through the Er-doped optical fiber 7-1 as shown in FIG.
Amplified, guided from the second port to the third port of the optical circulator 3-1 and output as indicated by an arrow 1-6,
It is transmitted to the next repeater not shown.

Next, wavelength-division multiplexed signal light (wavelength λ)
n to λz, for example, signal light in a wavelength range of 1.546 μm to 1.56 μm) is signal light that has propagated at least 40 km through the single mode optical fiber, and causes attenuation of optical power and chromatic dispersion. The signal light of arrow 2-1 is
The light enters the first port of the optical circulator 3-2, is guided to the second port, and is coupled with the excitation light (arrow 6-1) from the excitation light source 4-2 (couples the excitation light to the Er-doped optical fiber 7-). 2 through a coupling circuit for coupling to
The light propagates through the r-doped optical fiber 7-2, is amplified, and
It is taken out like -2. Then, this signal light is W
By being incident on the DM coupler 8, it is demultiplexed as indicated by the arrow 2-3 and guided to the WDM filter 9-2. In addition,
The signal light indicated by the arrow 2-1 is also amplified by the pump light indicated by the arrow 5-3 propagating through the Er-doped optical fiber 7-2. It is lower than the amplification degree obtained by propagating in the optical fiber 7-2.

The signal light (arrow 2-3) guided to the WDM filter 9-2 has two wavelength bands, for example, wavelengths λ9 to λ9.
λ12 band and wavelength λ13 to λ16 band (wavelength λ9 to λ
11 bands, wavelengths λ12 to λ14, and wavelengths λ9 to λ1
The signal light having a wavelength of λ9 to λ12 is split into a chirped grating element (a chirped grating fiber or a chirped grating waveguide) 10-3 by an arrow 2. The signal light having the wavelength λ13 to λ16 band propagates through the chirped grating element 10-4 as indicated by an arrow 2-3-3. Here, λ9 <λ1
Assuming that 0 <λ11 <... <λ15 <λ16, the signal light of the wavelength λ9 propagates to the farthest in the chirped grating element 10-3 and is reflected, as in the case of the above-described uplink. The signal returns as shown in 3-2, generates the largest delay time, and is multiplexed by the WDM filter 9-2. The signal light of wavelength λ16 is applied to the chirped grating element 1
The light propagates through 0-4, is reflected closest, propagates back, and is multiplexed by the WDM filter 9-2. Thus, the chirped grating elements 10-3, 10-4
In the signal light propagated and reflected in the inside and returned to the WDM filter 9-2 again, the signal light having the wavelength λ9 has the largest delay time, and the delay time occurring in the order of the wavelengths λ10, λ11. Become. This compensates for chromatic dispersion.

The signal light in the wavelength λ9 to λ12 band and the wavelength λ1
The signal light obtained by multiplexing the signal light in the 3 to λ16 band with the WDM filter 9-2 propagates as indicated by an arrow 2-4, and
The light is coupled to the Er-doped optical fiber 7-2 by the coupler 8, propagates through the Er-doped optical fiber 7-2 as indicated by an arrow 2-5, is amplified again, and is amplified from the second port to the third port of the optical circulator 3-2. And output as shown by the arrow 2-6 and transmitted to the next repeater (not shown).

As described above, in this dispersion compensator for bidirectional transmission, the optical components are shared between the uplink and the downlink, so that the number of optical components can be significantly reduced and the cost can be reduced. . Further, by sharing the optical amplifier, the optical amplification can be performed more efficiently, and a high gain can be achieved by two times of the optical amplification, that is, going and returning. Further, since the pump light source is also used, high efficiency and high gain can be achieved. In the most important chromatic dispersion compensation, appropriate dispersion compensation can be performed for each wavelength, so that an extremely small dispersion slope characteristic can be obtained. That is, multi-relay transmission of 10 or more can be easily realized. Further, even if the wavelength range to be used is widened, it is possible to easily cope with a wide band by increasing N of one input N output of the WDM filter 9-1 to 3, 4, 5,. Note that the optical power of the uplink signal light and the optical power of the downlink signal light can be basically controlled by adjusting the optical power of the pump light sources 4-1 and 4-2. In addition, in the configuration of FIG. 1, the wavelength of the signal light can use the wavelength range of 1.53 μm to 1.61 μm, and a wider band optical communication system can be constructed.

Next, a second embodiment of the present invention will be described.

As shown in FIG. 2, the dispersion compensator for bidirectional transmission uses the WDM coupler 8 used in the configuration of FIG.
The WDM coupler 8-1 is connected to both output terminals to form a loop, and a WDM coupler 8-2 is provided so as to be coupled to the loop. One input N output (N = 2) WDM at output end
Filters 9-1 and 9-2 are connected.

The operation of the bidirectional transmission dispersion compensator of FIG. 2 is different from that of FIG. 1 in the following point. WDM coupler 8
-1 wavelength-division multiplexed signal light (arrow 1-1)
3) and the wavelength-division multiplexed signal light of the downlink (arrows 2-3)
The light is further demultiplexed by the WDM coupler 8-2, and arrows 1-3A,
The WDM filters 9-1 and 9-
2 and are split into respective wavelength bands by the WDM filters 9-1 and 9-2, propagate through the chirped grating elements 10-1, 10-2, 10-3, and 10-4, and are reflected. , Back-propagating to the WDM filters 9-1 and 9
2, the signals are multiplexed, propagate as indicated by arrows 1-3B and 2-3B, are demultiplexed by the WDM coupler 8-2, and
4, 2-4, and further demultiplexed by the WDM coupler 8-1 to be Er-doped optical fibers 7-1 and 7-2, respectively.
Return to The upstream wavelength multiplexed signal light propagates as indicated by an arrow 1-5, and the optical circulator 3- as indicated by an arrow 1-6.
1 is output from the third port. The wavelength-division multiplexed signal light of the downstream line propagates as indicated by an arrow 2-5, and is output from the third port of the optical circulator 3-2 as indicated by an arrow 2-6.

Next, a third embodiment of the present invention will be described.

As shown in FIG. 3, the dispersion compensator for bidirectional transmission is an optical circulator 12 having four ports.
-1, an upstream line is connected to a first port of the optical circulator 12-1, a WDM filter 9-1 is connected to a second port which is a forward direction of the first port, and the WDM filter 9-1 is connected to the upstream port. The chirped grating elements 10-1 and 10-2 are respectively connected to the respective demultiplexing output terminals of the optical circulator 12 and the optical circulator 12 having four ports.
-2 is provided, a down line is connected to a first port of the optical circulator 12-2, a WDM filter 9-2 is connected to a second port which is a forward direction of the first port, and the WDM filter 9-2 is connected. The chirped grating elements 10-3 and 10-4 are connected to the respective demultiplexing output terminals of the optical circulator 12-1, and a third port in the forward direction of the second port of the optical circulator 12-1 and a second port of the optical circulator 12-2. Is connected to the third port in the forward direction by an Er-doped optical fiber 7, and pump light having a wavelength of 0.98 μm and 1.48 μm from the pump light sources 4-1 and 4-2 is supplied to the Er-doped optical fiber 7. Inject the optical circulator 12
The fourth port, which is the forward direction of the third port of -1, is connected to the down line, and the fourth port, which is the forward direction of the third port of the optical circulator 12-2, is connected to the up line.

The wavelength division multiplexed signal light of wavelengths λ1 to λm is transmitted on the up line, and the wavelength multiplexed signal light of wavelengths λn to λz is transmitted on the down line. The upstream wavelength multiplexed signal light (arrow 1-1) input to the first port of the optical circulator 12-1 is guided from the second port of the optical circulator 12-1 as shown by the arrow 1-2, and the WDM filter 9 −
1 is input. The signal light demultiplexed by the WDM filter 9-1 has a delay time in each of the chirped grating elements 10-1 and 10-2 as in the case of FIG.
The light is returned to the DM filter 9-1, multiplexed, extracted as indicated by an arrow 1-3, and guided from the second port to the third port of the optical circulator 12-1. Similarly, the wavelength-division multiplexed signal light (arrow 2-1) input to the first port of the optical circulator 12-2 is guided as indicated by an arrow 2-2, demultiplexed by a WDM filter 9-2, and Each of the chirped grating elements 10-3 and 10-4 generates a delay time, returns to the WDM filter 9-2, is multiplexed, extracted as indicated by an arrow 2-3, and is extracted by the optical circulator 12-2.
From the second port to the third port.

Uplink wavelength multiplexed signal light (arrows 1-3)
Is Er in which the excitation light (arrows 5-2 and 6-2) is propagating.
The light is amplified by propagating in the added optical fiber 7, is output from the third port of the optical circulator 12-2 through the fourth port as shown by an arrow 1-6, and is transmitted to the next repeater (not shown). . Similarly, the wavelength-division multiplexed signal light of the downlink (arrow 2-3) is converted to the pump light (arrow 5-2, arrow 5-2).
6-2) propagates through the Er-doped optical fiber 7 in which the light is amplified, and the optical circulator 12- is amplified.
Arrow 2-6 from the third port to the fourth port
And transmitted to the next repeater (not shown).

In this dispersion compensator for bidirectional transmission, the wavelength multiplexed signal light of the upstream line and the downstream line propagates through one Er-doped optical fiber 7 to be commonly amplified. With this configuration, in order to control the optical power of the uplink and downlink signal light, the pumping light power is mainly adjusted.To control the optical power of both signal lights completely independently, For example, an optical variable attenuator may be inserted on the fourth port side of the optical circulators 12-1 and 12-2.

Next, a fourth embodiment of the present invention will be described.

As shown in FIG. 4, the dispersion compensator for bidirectional transmission is a third optical circulator 12 having four ports instead of the WDM coupler 8 used in the configuration of FIG.
The Er-doped optical fiber 7-1 is connected to the first port of the optical circulator 12-3, the WDM filter 9-1 is connected to the second port, and the E port is connected to the third port.
r-doped optical fiber 7-2 is connected, and WD is connected to the fourth port.
The M filter 9-2 is connected.

The wavelength-division multiplexed signal light of the upstream line input to the first port of the optical circulator 3-1 is indicated by arrows 1-1 and 1-1.
The light propagates in the order of 1-2, 1-3, 1-4, 1-5, and 1-6, and is output from the third port of the optical circulator 3-2. Downlink wavelength multiplexed signal light input to the first port of the optical circulator 3-2 is indicated by arrows 2-1 and 2-2-1.
The light propagates in the order of 2, 2-3, 2-4, 2-5, and 2-6, and is output from the third port of the optical circulator 3-1.

In this configuration, the signal light of the up-link and the down-link both pass through the two Er-doped optical fibers 7-1 and 7-2, so that a high gain characteristic can be realized.

The bidirectional transmission dispersion compensator of FIG. 5 is obtained by adding an optical power control mechanism to the bidirectional transmission dispersion compensator of FIG. That is, the coupler 13-1 is provided on the first port side of the optical circulator 3-1.
The light receiving element 14-1 is connected to the
2, a coupler 13-2 is provided on the first port side, and the light receiving element 14-2 is connected to the coupler 13-2.

A part of the wavelength-division multiplexed signal light (optical power in the range of 1/10 to 1/100) propagated on the up line and the down line is taken out by couplers 13-1 and 13-2 and received by light receiving element 14-1. , 14-2, and converts the electric signals into drive circuits 15-1, 15 for the excitation light sources 4-1 and 4-2.
The power of the excitation light is adjusted by feeding back to -2. Thereby, the Er-doped optical fibers 7-1 and 7-
The optical power of the signal light is controlled by changing the amplification degree in step 2.

An optical filter is inserted into the light receiving surfaces of the light receiving elements 14-1 and 14-2 so that only the signal light of a specific wavelength of the wavelength multiplexed signal light can be detected, or the coupler 13-
By making the wavelength selectivity of 1, 13-2 narrow, the optical power can be controlled with higher accuracy. Further, wavelengths (1.51 μm, 1.52 μm, 1.62) different from the wavelengths of the wavelength multiplexed signal light from the uplink and the downlink.
μm), and the monitoring signals are taken out by the couplers 13-1 and 13-2 and are received by the light receiving element 14-.
1, 14-2 may receive light.

The dispersion compensator for two-way transmission shown in FIG. 6 is obtained by adding an optical power control mechanism to the dispersion compensator for two-way transmission shown in FIG. That is, the coupler 13-is connected to the Er-doped optical fiber 7.
1 and 13-2 are provided, and the light receiving elements 14-1 and 14-2 are connected to the couplers 13-1 and 13-2. 16
Is a circuit having a comparison circuit for the light reception signal and a drive circuit for the excitation light source. The output signal of the circuit 16 is used as the excitation light source 7-
1 or the optical power of the excitation light source 7-2 is adjusted.

Next, an optical communication system using the bidirectional transmission dispersion compensator of the present invention will be described. As shown in FIG. 7, the optical communication system includes an uplink wavelength multiplex transmitter 17 and a downlink wavelength multiplex receiver 20, an uplink wavelength multiplex receiver 18, and a downlink wavelength multiplex transmitter 19.
, 23-2, 23-2,..., 23-
n is a multi-relay transmission system. .., 21-n, 22-1, 1-2 at least 40 km between the transceiver and the repeater.
2-2,..., 22-n are interposed.

Uplink wavelength-division multiplexed signal light using the wavelengths λ1 to λm is transmitted from the uplink wavelength-division multiplexing transmitter 17, and this signal light is transmitted to the single mode optical fiber 21-1.
To the repeater 23-1, and the repeater 23-1
Performs optical amplification and chromatic dispersion compensation. Further, the signal light propagates through the single mode optical fiber 21-2 and reaches the repeater 23-2, where the optical amplification and the chromatic dispersion compensation are performed. Hereinafter, the same is repeated, and finally, the signal light reaches the wavelength-division multiplexing receiver 18 for the uplink,
The signal light of each wavelength is received, and the information signal is reproduced.

On the other hand, from the wavelength division multiplexing transmitter 19 for the downlink, a wavelength division multiplexed signal light of the wavelength λn to λz is transmitted, and this signal light is transmitted to the single mode optical fiber 2.
2-n to reach the repeater 23-n, where the repeater 2
At 3-n, optical amplification and chromatic dispersion compensation are performed. Thereafter, the same is repeated, and finally, the signal light reaches the wavelength-division multiplexing receiver 20 for downlink, the signal light of each wavelength is received, and the information signal is reproduced.

As described above, in the repeater, the optical amplification and the chromatic dispersion compensation of the wavelength multiplexed signal light of the uplink and the downlink are realized by one dispersion compensator for bidirectional transmission. This optical communication system is a very economical and simple system, and can realize high gain amplification and very small dispersion slope characteristics. Further, even if the number of multiplexed wavelengths increases, chromatic dispersion compensation can be performed with high accuracy.

The optical communication system of FIG. 8 is configured using the dispersion compensator for bidirectional transmission of the present invention. This optical communication system is obtained by incorporating the dispersion compensator for bidirectional transmission of the present invention into the system of FIG. In the terminal relay unit, a transmission path from the wavelength-division multiplexing transmitter 17 for the uplink and a transmission path to the wavelength-division multiplexing receiver 20 for the downlink are connected to the 4-port optical circulator 3-1 and the 4-port optical circulator 3-1. The Er-doped optical fiber 7 is connected to a three-port optical circulator 3-2, and a common transmission line is taken out of the optical circulator 3-2.
In the intermediate repeater, three-port optical circulators are alternately connected in different forms, so that chromatic dispersion compensators for performing chromatic dispersion compensation on the uplink and the downlink are alternately formed. In the figure, the chromatic dispersion compensator shown above the transmission line is for the uplink, and the chromatic dispersion compensator shown below the transmission line is for the downlink.

In this optical communication system, the optical amplification and the chromatic dispersion compensation in the terminal relay unit and the intermediate relay unit are shared between the uplink and the downlink. That is, the number of optical amplifiers and the number of chromatic dispersion compensators are only half as compared with the system of FIG. Accordingly, the number of optical components can be significantly reduced.

In the optical communication system shown in FIGS. 7 and 8,
Each information transmission rate can use at least 2.4 Gb / s, and furthermore, 10 Gb / s and 40 Gb / s.
s can also be used. Further, the wavelength interval is set to 0.
Using 1 nm, 0.2 nm, 0.4 nm, 0.8 nm, etc., 4, 6, 8, 10, 1
Six waves, 24 waves, 32 waves, 40 waves, or the like can be used. The number of relays is 10 or more, the transmission distance is 400 km or more, and the Er-doped optical fibers 7, 7-1 and 7-2 are made of silica glass, fluoride glass or tellurite glass. You can use the base type, connect the same type to the cascade,
The different types described above can be used in a cascade. Further, as a method of flattening the gain in the used wavelength band, chirped grating elements 10-1 to 10-4 are used.
The optical filter that attenuates the signal light in the above-mentioned wavelength band by a desired value may be inserted into the one that propagates the signal light having a wavelength of about 1.53 μm. Alternatively, a part of the chromatic dispersion compensator (WDM couplers 8, 8-1, 8-2, WDM filter 9
-1, 9-2, optical circulator 12-3, etc.
An optical circuit for suppressing the gain near the wavelength of 1.53 μm may be inserted between these optical components.

[0065]

The present invention exhibits the following excellent effects.

(1) Optical amplification and chromatic dispersion compensation can be shared between the uplink and the downlink. In particular, even if the number of multiplexed wavelengths is increased and the used wavelength band is widened, sufficient optical amplification can be performed and chromatic dispersion compensation can be performed.

(2) The number of optical components can be significantly reduced as compared with the prior art. In particular, since optical components can be shared for optical amplification and chromatic dispersion compensation, the number of optical components can be greatly reduced.

(3) Even if 10 or more relay units are provided in multiple stages,
The chromatic dispersion slope does not increase.

(4) The light source for excitation can be shared by the two optical amplifiers.

(5) At an optical transmission speed of 2.4 Gb / s or more, wavelength multiplexing transmission of at least 4 channels can be performed on both the upstream and downstream lines, with a relay interval of at least 40 km, and multiple relays of 10 or more relays. Transmission can take place.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a dispersion compensator for bidirectional transmission according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a dispersion compensator for bidirectional transmission according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a dispersion compensator for bidirectional transmission according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a dispersion compensator for bidirectional transmission according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of a dispersion compensator for bidirectional transmission according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram of a dispersion compensator for bidirectional transmission according to a sixth embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical communication system using the dispersion compensator for bidirectional transmission of the present invention.

FIG. 8 is a configuration diagram of an optical communication system using the dispersion compensator for bidirectional transmission of the present invention.

FIG. 9 is a configuration diagram of a conventional optical communication system for bidirectional transmission.

FIG. 10 is a configuration diagram of a conventional optical communication system for bidirectional transmission.

FIG. 11 is a configuration diagram of a conventional optical communication system for bidirectional transmission.

[Explanation of symbols]

3-1, 3-2, 12-1, 12-2, 12-3 Optical circulator 4-1, 4-2 Excitation light source 7, 7-1, 7-2 Er-doped optical fiber 8, 8-1, 8 -2 WDM coupler 9-1, 9-2 WDM filter 10-1, 10-2, 10-3, 10-4 Chirped grating element 14-1, 14-2 Light receiving element

Continued on the front page (72) Inventor Hiroyuki Nakano 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in the Information and Communication Division, Hitachi, Ltd. 5F072 AB09 AK06 KK07 RR01 YY17 5K002 BA04 BA05 BA21 CA09 CA13 DA02 DA42 FA01

Claims (13)

[Claims] 1. A first optical circulator having a plurality of ports is provided. Uplink wavelength multiplexed signal light is input to a first port of the first optical circulator, and a first optical circulator is provided in a forward direction of the first port. A WDM that connects a first Er-doped optical fiber to two ports, injects pumping light into the first Er-doped optical fiber, and separates and separates upstream and downstream signal lights into the first Er-doped optical fiber. One input terminal of the coupler is connected, and a first WDM filter for splitting an upstream signal light into a plurality of wavelength bands is connected to an upstream output terminal of the WDM coupler. By connecting each of the chirped grating elements that delay the signal light according to the wavelength and reflect it at the output end, each reflected signal light is multiplexed by the first WDM filter and The signal returns to the second port of the first optical circulator via the WDM coupler and the first Er-doped optical fiber, and is output from the third port in the forward direction of the second port as wavelength-division multiplexed signal light of the uplink. A second optical circulator having a plurality of ports is provided, and a wavelength multiplexed signal light of a downlink is input to a first port of the second optical circulator, and a second optical circulator is provided in the forward direction of the first port. A second Er-doped optical fiber is connected to the port, and pump light is injected into the second Er-doped optical fiber. The other input end of the WDM coupler is connected to the second Er-doped optical fiber. A second WDM filter is connected to the down-link output terminal to split the down-link signal light into a plurality of wavelength bands. By connecting the extended and reflected chirped grating elements to each other, the reflected signal light is multiplexed by the second WDM filter and passes through the WDM coupler and the second Er-doped optical fiber to form the second light. A dispersion compensator for bidirectional transmission, wherein the dispersion compensator is configured to return to a second port of the circulator and output as a wavelength-division multiplexed signal light from a third port in a forward direction of the second port. 2. The chirped grating element,
2. The dispersion compensator for bidirectional transmission according to claim 1, wherein the signal light in the input wavelength band is reflected with a longer delay time as the signal light has a shorter wavelength. 3. The apparatus according to claim 1, wherein the first and second Er-doped optical fibers are configured such that pumping light of 0.98 μm or 1.48 μm propagates from one direction or both directions, respectively. Or the dispersion compensator for bidirectional transmission according to 2. 4. A second WDM coupler is inserted between the WDM coupler (referred to as a first WDM coupler) and the first and second WDM filters, and an uplink output terminal of the first WDM coupler is connected to the second WDM coupler. A second WDM coupler is connected to one input terminal and a downstream output terminal of the first WDM coupler is connected to the other input terminal of the second WDM coupler to form a loop. 4. The dispersion for bidirectional transmission according to claim 1, wherein an output terminal is connected to said first WDM filter, and a downstream output terminal of said second WDM coupler is connected to said second WDM filter. Compensator. 5. A first optical circulator having at least four ports, wherein an upstream wavelength multiplexed signal light is input to a first port of the first optical circulator, and the forward direction of the first port is provided. A second port is connected to a first WDM filter for demultiplexing the upstream signal light into a plurality of wavelength bands, and a chirp that delays and reflects the signal light according to the wavelength at each demultiplexing output terminal of the first WDM filter. By connecting the respective grating elements, each of the reflected signal lights is multiplexed by the first WDM filter and returns to the second port of the first optical circulator, and the second signal port has at least four ports. A two-optical circulator is provided, and a wavelength-division multiplexed signal light of a downlink is input to a first port of the second optical circulator. A second port is connected to a second WDM filter for demultiplexing the downlink signal light into a plurality of wavelength bands, and the signal light is delayed and reflected according to the wavelength at each branch output terminal of the second WDM filter. By connecting each of the chirped grating elements, each of the reflected signal lights is multiplexed by the second WDM filter and returns to the second port of the second optical circulator. An Er-doped optical fiber is connected between a third port, which is a forward direction of the second port, and a third port, which is a forward direction of the second port of the second optical circulator, and excitation light is supplied to the Er-doped optical fiber. Inject,
Uplink wavelength-multiplexed signal light is output from a fourth port in the forward direction of the third port of the second optical circulator,
A dispersion compensator for bidirectional transmission, characterized in that a wavelength-division multiplexed signal light of a downlink is output from a fourth port which is a forward direction of a third port of the first optical circulator. 6. The Er-doped optical fiber has a width of 0.98 μm or 1.48 μm from one direction or both directions, respectively.
6. The dispersion compensator for bidirectional transmission according to claim 5, wherein said pump light is configured to propagate. 7. A first optical circulator having a plurality of ports, an upstream wavelength multiplexed signal light is input to a first port of the first optical circulator, and a first optical circulator is provided in a forward direction of the first port. A first Er-doped optical fiber is connected to two ports, and pump light is injected into the first Er-doped optical fiber, and a first port of a third optical circulator having four ports is connected to the first Er-doped optical fiber. Then, a first WDM filter for splitting the signal light of the uplink into a plurality of wavelength bands is connected to a second port which is a forward direction of the first port, and a signal is output to each split output terminal of the first WDM filter. By connecting each of the chirped grating elements that delays and reflects light in accordance with the wavelength, each of the reflected signal lights is multiplexed by the first WDM filter and the third optical circuit A second optical circulator having a plurality of ports is provided so as to return to the second port of the circulator, and the wavelength multiplexed signal light of the downlink is input to the first port of the second optical circulator. A second Er-doped optical fiber is connected to a second port, which is a forward direction of the port, and pumping light is injected into the second Er-doped optical fiber. The third port, which is the forward direction of the port, is connected, and the return light of the wavelength multiplexed signal light of the upstream line becomes the forward direction of the second port of the second optical circulator via the second Er-doped optical fiber. A second WDM filter configured to be output from a third port and configured to split a downlink signal light into a plurality of wavelength bands to a fourth port in the forward direction of the third port of the third optical circulator. And a chirped grating element for delaying and reflecting the signal light in accordance with the wavelength according to the wavelength is connected to each demultiplexing output terminal of the second WDM filter, so that the reflected signal light is transmitted to the second WDM filter. Return to the fourth port of the third optical circulator, and from the first port in the forward direction of the fourth port via the first Er-doped optical fiber, the second port of the first optical circulator A dispersion compensator for bidirectional transmission, characterized in that the dispersion compensator is configured to be output as upstream wavelength-division multiplexed signal light from a third port in the forward direction. 8. The pump device according to claim 7, wherein the first and second Er-doped optical fibers are configured such that pumping light of 0.98 μm or 1.48 μm propagates from one direction or both directions. The dispersion compensator for bidirectional transmission according to the above. 9. A coupler for extracting a part of the signal light in a propagation path of the wavelength-division multiplexed signal light in the uplink and the downlink, and a light receiving part for receiving a part of the signal light and converting it into an electric signal. The dispersion compensator for bidirectional transmission according to any one of claims 1 to 8, further comprising a drive circuit that connects the elements and controls the optical power of the excitation light according to the electric signal. 10. The dispersion compensator for bidirectional transmission according to claim 1, wherein said chirped grating element has a fiber type structure or a waveguide type structure. 11. A bidirectional transmission dispersion compensator according to claim 1, wherein at least one of the uplink and downlink wavelength multiplexed signal light input to the bidirectional transmission dispersion compensator is at least one. An optical communication system comprising four signal lights having different wavelengths and being transmitted through a single-mode optical fiber of at least 40 km. 12. The information transmission speed of the uplink and downlink wavelength multiplexed signal light is at least 2.4 G each.
The optical communication system according to claim 11, wherein b / s is set. 13. The optical communication system according to claim 11, wherein the wavelengths of the wavelength multiplexed signal light of the uplink and the downlink are included in a range of 1.53 μm to 1.61 μm.