JPH11331095A - Wide band optical signal transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable wide band optical signal transmission without exchanging a current erbium doped fiber amplifier(EDFA) by connecting a second optical amplifier to an optical transmission medium for amplifying the second optical signal of another band transmitted by the same optical transmission medium. SOLUTION: Optical fiber sections 7A-7(K+1) and EDFS 9A-9K amplify and transmit multiplexed optical signals on 1545 nm band. Then, additional plural laser sources 1(N+1)-1(N+M) are connected to modulators 3(N+1) to 3(N+M) and its output is connected to a multiplexer 5A. In this case, amplifiers 15A-15K are connected between the ends of respective optical fibers 7A-7K and the heads of the next optical fibers 7(A+1) to 7(K+1). The multiplexer 5A multiplexes an inputted modulated signal into signal on 1,585 nm. The amplifiers 15A-15K have 1,585 nm band as a passing band and amplify this multiplexed signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical transmission system,
More specifically, wideband multi-channel wavelength division multiplexing (WD)
M) Regarding the system.

[0002]

BACKGROUND OF THE INVENTION Dense wavelength division multiplexing (DWSM) is used in fiber optic transmission systems to transmit data and voice signals over a single optical transmission fiber. Commercially available DWDM systems commonly use a conventional erbium-doped fiber amplifier (EDFA) as an interrupter to amplify signals that are lost due to attenuation in the fiber. EDFA is 154
Around 5 nm (here referred to as the 1545 band, which extends from approximately 1528 to approximately 1562 nm, 34
in the optical signal band, which is concentrated in the optical signal band (which is the passband of nm). Consequently, to accommodate the maximum number of multiplexed signals, the channels must be narrowly delimited in the passband. As a result, a practical WDM system requires 8 GHz with a channel space of 50 GHz.
0 channels can be transmitted, so that the full capacity of the system is 2.5 Gbit / s for each channel
Operating at 200 Gbit / s (or if each channel is 10 Gbit / s,
800 Gbit / s).

If a larger number of channels are to be accommodated within this bandwidth, a channel space of 5
It may be less than 0 GHz (0.4 nm).
However, when the channel space becomes 50 GHz or less, a nonlinear effect such as four-photon mixing obtains a high gain, thereby deteriorating system performance.

FIG. 1 shows that EDFAs 1528 and 15
A typical DWDM system with a bandwidth provided between 62 nm and a capacity of n channels will be described.
The system outputs n to n high-speed modulators 3A-3N.
Laser sources 1A-1N. The signal that modulates the laser signal is data and / or digitized audio.
Typical modulators are either of the integrated electroabsorption type or of an external device electroabsorption type. The laser source and the modulator together form an n-channel transponder.

[0005] Between 1528 and 1562 nm (1545)
The optical signal provided by the transponder, which spans the nm band), is multiplexed by the dense wavelength division multiplexer 5. The multiplexed signal is applied to the optical fiber 7A.

[0006] The fiber and / or its connection device and / or the multiplexer 5 creates a loss where the optical signal transmitted by the fiber is attenuated to a predetermined power level, typically -20 dBm per channel. To amplify the signal, an erbium-doped fiber amplifier (EDFA) 9A-9K
Is used. When the signal is amplified by the amplifier 9A, it is transmitted to the fiber 7B, and the amplification and transmission are repeated until the final section 7 (K + 1). ED
A plot of the FA passband is illustrated in FIG.

At the end of the transmission path, a signal is input to the input of a demultiplexer 11. Demultiplexer 1
The reference numeral 1 designates modulated signals (channels) of various wavelengths forming a multiplexed signal in different receivers 13A-13N.
And enter it separately. With EDFA spacing typically between 50 and 100 km, the system can sometimes include additional features such as add / drop capabilities.

In order to increase the number of channels, that is, to increase the capacity of the transmission fiber, the bandwidth of the system limited by the EDFA bandwidth (1545 nm band) must be expanded. The double bandwidth fiber amplifier (DBFA) invented by the inventor and described in a U.S. patent application Ser. No. 09 / 026,657 filed on Feb. 20, 1998, uses a conventional EDFA. Double the bandwidth provided can be provided. However, in order to improve the quality of the DWDM transmission system from the conventional EDFA bandwidth to the DBFA bandwidth, it is necessary to dispose of the existing EDFA and replace it with a DBFA at uneconomic cost.

[0009]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a broadband optical signal transmission system.

[0010]

SUMMARY OF THE INVENTION In accordance with an embodiment of the present invention, there is no need to replace existing EDFAs,
The same optical fiber is used to transmit DWDM optical signals in both the nm band and the longer wavelength 1585 nm band. From 1545 nm, 1545
Current DW to include both
To extend the DM bandwidth, a new 1585 nm band amplifier is used.

A new optical coupler, referred to herein as an add / drop filter, is used to connect the multiplexed signal band to the optical fiber and to separate the multiplexed signal from the optical fiber. As a result, new amplifiers can amplify optical signals in the 1585 nm band, while current EDFAs can amplify optical signals in the 1545 nm band.

The modulated optical signals in the 1585 nm band form another plurality of channels transmitted by optical fibers similar to those in the 1545 nm band. Therefore, a channel space of 50 GHz
, Or the total number of channels that can be transmitted by the system can be substantially doubled, eg, to approximately 160, without replacing the current EDFA. Thus, the cost of expansion is significantly reduced.

According to an embodiment of the present invention, a method for transmitting a wideband wavelength division multiplexed signal comprises the steps of: transmitting a wavelength division multiplexed signal on said combined signal having said different discrete bandwidths in separate amplifiers each having a different bandwidth. Separately amplifying the amplified signals, and transmitting all amplified optical signals of different different bandwidths through the same optical fiber.

The method of transmitting a broadband wavelength division multiplex signal uses a current wavelength division multiplex transmission system. Wherein the current system multiplexes the plurality of first input optical signals into a lower bandwidth signal and adds the first multiplexed optical signal to an initial portion of the fiber optic transmission line that includes the lower bandwidth optical amplifier; And a multiplexer for applying the first multiplexed optical signal to an input of the demultiplexer.

[0015] A method of transmitting a wideband wavelength division multiplexed signal using current wavelength division multiplexing transmission systems comprises the steps of: Multiplexing the second multiplexed optical signal into the first transmission system, and passing the lower bandwidth signal from the first optical fiber transmission line to the lower bandwidth optical amplifier. Passing the second multiplexed optical signal from an optical fiber transmission line to an amplifier having a different bandwidth; connecting each amplified signal to an optical fiber of a longer transmission line for further transmission; Demultiplexing each of the different bandwidth signals into a plurality of second output optical signals.

According to another embodiment, a broadband optical signal transmission system amplifies a first optical signal in one band transmitted by (a) at least one optical transmission medium and (b) an optical transmission medium. A first optical amplifier connected to the optical transmission medium, and (c) connected to the optical transmission medium to amplify a second optical signal in another band transmitted by the same optical transmission medium. A second optical amplifier; and (d) at least one demultiplexer for separating the optical signal transmitted by the optical transmission medium and for outputting the separated optical signal to each output.

A method for amplifying a broadband optical signal formed by multiplexed optical signals in two bands in a current fiber optic transmission line having a current amplifier, the current amplifier comprising a signal in only one of the two bands. And directing the signal in the other of the two bands to an auxiliary amplifier that can amplify the signal in the other of the two bands, bypassing the current amplifier.

Preferably, one of the two bands is a 1545 nm band and the other of the two bands is a 1585 nm band.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more readily understood by considering the following detailed description in conjunction with the accompanying drawings.

FIG. 3 illustrates a broadband optical transmission system according to an embodiment of the present invention. Laser source 1A-1
N, modulators 3A-3N, multiplexer 5, demultiplexer 11, and receivers 13A-13N are connected as in the prior art. Similarly, fiber optic sections (or any optical transmission media) 7A-7 (K + 1) and EDFAs 9A-9K amplify and transmit the multiplexed optical signal in the 1545 nm band illustrated in FIG.

However, additional multiple laser sources 1 (N
+1) -1 (N + M) is the modulator 3 (N + 1) -3 (N +
M), the output of which is connected to the input of the multiplexer 5A. The output of the multiplexer 5A is connected to a first input of an optical fiber 7A in the manner described below.

An amplifier 15 having the properties described below
A-15K is connected between the end of each optical fiber 7A-7K and the head of the next optical fiber 7 (A + 1) -7 (K + 1).

The multiplexer 5A multiplexes the modulated signal input thereto into a signal at 1585 nm. The signal has a wavelength of approximately 1565nm to 1605nm. Amplifiers 15A to 15K have a 1585 nm band as a pass band, and amplify the multiplexed signal.

At the end of the transmission path, the signal in the 1585 nm band is separated from the signal in the 1545 nm band. The signal in the 1585 nm band is
Added to demultiplexer 11A, demultiplexer 11A separates their outputs and corresponding modulated signals from modulators 3 (N + 1) -3 (N + M) and adds them to separate output channels so that they 13
(N + 1) -13 (N + M).

The amplifier has a passband as illustrated in the plot of FIG.

The same fiber optic medium, which effectively doubles the capacity of the fiber optic link, is an all-optical signal channel in the 1545 nm band described in FIG. 2 and another in the 1585 nm band described in FIG. It will be clear that all optical signal channels can be transmitted. Prior art EDFAs
Since it is used continuously as part of this embodiment, it does not need to be replaced, thus saving money. However, in some devices, multiplexers 5 and 5
It may be preferable to combine A with a single multiplexer and / or a single demultiplexer and / or to combine demultiplexers 11 and 11A with a single multiplexer and / or a single demultiplexer. Should be noted.

Multiplexer and optical fiber, optical fiber and demultiplexer, optical fiber and amplifier 9A-
Band-dependent couplers / decouplers preferably add / drop filters 17A-17 (K + 1), 17I and 1 to connect the 9K inputs and outputs, respectively.
Used in the form of 70. Filter 17I is used to connect multiplexers 5 and 5A to fiber section 7A, and filter 17O is used to connect the last section 7 (K + 1) of fiber to the inputs of demultiplexers 11 and 11A. Filters 17A-17 (K + 1) are used to connect the fiber sections to the inputs and outputs of amplifiers 9A-9K and 15A-15K. Each of the filters can combine the multiplexed signals in the two bands into one optical stream and combine the combined optical streams into 154
Split into two multiplexed signals in each of the 5 nm and 1585 nm bands.

FIG. 5 shows the filters 17I and 17A-17.
An add / drop filter that can be used as either (K + 1) or 170 is described. One form of this filter is described in the inventor's U.S. patent application filed Feb. 20, 1998 (application no.
6,657), which is incorporated herein by reference. The filter includes a standard passband filter for the 1545 nm band, which passes the 1545 nm band signal in both directions. It is sent to the common port 21 and the add / drop port 23 and may be received therefrom. Regarding the use of signals in the 1585 nm band, the filter is
The signal in the m-band is reflected, and the signal can be collected at the bidirectional passport 25.
Similarly, signals in the 1585 nm band applied to passport 25 are reflected to the common port.

Therefore, the addition / drop filter can receive signals in the 1545 nm and 1585 nm bands at the common port 21 and divide these signals into separate bands. Add / drop port 23
A 1545nm signal appears on the passport 25 and a 1585nm signal appears on the passport 25.
nm signal appears. The filter combines the signal in the 1585 nm band that appears at passport 25 with the 1545 nm band.
And transmits the combined signal to the common port 21.

Another add / drop filter capable of performing band separation and combination may be used in place of the described filter.

As described above, the addition / drop filter 17
I combines the signals in the respective bands received from the outputs of multiplexers 5 and 5A and connects the combined signals to fiber optic section 7A. Summing / drop filter 17A filters the combined signal at 1545 nm.
And 1585 nm bands and connect them to the respective inputs of amplifiers 9A and 15A. Thus, the amplifiers 9A and 15A receive the optical signal in the band that can be amplified.

Similarly, the output signals of amplifiers 9A and 15A are combined in add / drop filter 17B in a manner similar to that of add / drop filter 17I. The combined signal is connected to the input of fiber optic section 7B. In a similar manner, a summing / dropping filter separates and combines optical signals along the transmission route. In the communication route, the amplifier amplifies the signal in each band.

The final section 7 of the optical fiber (K +
At the end of 1), add / drop filter 17O
Separates the signals into separate bands and applies them to the inputs of respective demultiplexers 11 and 11A whose channels are split as described above.

In certain designs, the length of the fiber optic sections 7A and / or 7 (K + 1) is
Note that it may be zero. In such a case, the output of multiplexer 5 can be connected to the input of amplifier 9A, and the output of multiplexer 5A can be connected to the input of amplifier 15A. Further, the output of the amplifier 9K is
The output of the amplifier 15K can be connected to the input of the demultiplexer 11A while being connected to the input of the demultiplexer 11.

The amplifiers 15A-15K can be of a design as shown in FIG. This design constitutes an embodiment of the invention as disclosed in the aforementioned inventor's U.S. Patent Application Serial No. 09 / 026,657, which is incorporated herein by reference. This structure is 980 nm or 1480
Includes a high power pump laser (e.g., power greater than 150 mW) in nm, which is 980/15
An erbium-doped amplified spontaneous emission (ASE) generator 26 is pumped by a 50 nm optical coupler 24. AS
E generator 26 has a back ASE reflected by fiber Bragg grating 27. The grating 27 that reflects the back ASE back to the generator 26 saturates it and effectively generates the forward transfer ASE. This large amount of ASE having a peak at about 1532 nm passes through the optical coupler 24 and is absorbed by the second amplifier 29. The second amplifier 29 outputs 1 to the signal input to the input port INPUT.
Gives the gain at 585 nm.

The gain of the structure described above is 20d
A BDM gain of B or higher is shown to be achieved in the laboratory prototype. If more gain is needed, a second pump laser 31 is connected to the generator 26 via an optical coupler 33. Pump laser 31 should generate an optical signal at either 980 or 1480 nm.

The input isolator 35 and the output isolator 37 are connected in series to the input port INPUT and the output port OUTPUT, respectively, to protect the amplifier from lasing due to back reflection. Amplifier 1
The final passband of the above described amplifier, which can constitute each of 5A-15K, is illustrated in FIG.

The multiplexers and demultiplexers can be formed by commercially available thin film filters, waveguides or bicone fusion techniques.

Thus, the present invention allows the use of the installed base of a DWDM system. By using the bypass configuration of the amplifier for 1585 nm signals described herein, the system can be enhanced to have twice the capacity without waste and minimal cost.

In practicing the present invention, it will be appreciated that it is not necessary to stick to the exact band wavelengths as described, and that the present invention is applicable to other bands and bandwidths. .

Persons understanding the present invention may conceive of alternative embodiments and modifications using the principles described herein. All such embodiments and modifications are considered to be within the spirit and scope of the invention, as defined in the claims set forth herein.

[Brief description of the drawings]

FIG. 1 is a block diagram of a system according to the prior art.

FIG. 2 is a graph relating to the passband of an amplifier used in the system of FIG. 1;

FIG. 3 is a block diagram of a system according to the present invention.

FIG. 4 is a graph relating to a pass band of a second amplifier used in the system of FIG. 3;

FIG. 5 shows an addition / addition used in an embodiment of the present invention.
It is a schematic diagram of a drop filter.

FIG. 6 is a block diagram of an amplifier used in the system of FIG.

[Explanation of symbols]

1A-1 (N + M) Laser source 3A-3 (N + M) Modulator 5, 5A Multiplexer 7A-7 (K + 1) Optical fiber 9A-9K Amplifier 11, 11A Demultiplexer 13- 13 (N + M) Receiver 15A-15K Amplifier 17I, 17A-17 (K + 1), 17O Addition / drop filter 19 Standard passband filter 21 Common port 22 Pump laser 23 Addition / Drop port 24 Optical coupler 25 Pass port 26 ASE generator 27 Fiber Bragg grating 29 Second amplifier 31 Pump laser 33 Optical coupler 35, 37 Isolator

Claims (28)

[Claims] 1. A first optical transmission medium coupled to an optical transmission medium for amplifying a first optical signal in one band transmitted by the optical transmission medium. (C) a second optical amplifier connected to the optical transmission medium for amplifying a second optical signal in another band transmitted by the same optical transmission medium; and (d) the optical transmission. A broadband optical signal transmission system including at least one demultiplexer for separating optical signals transmitted by a medium and for providing separated optical signals to respective outputs. 2. The system according to claim 1, including at least one add / drop filter for connecting the optical amplifier to the optical transmission medium. 3. In order to multiplex a plurality of input optical signals,
3. The system according to claim 2, further comprising at least one multiplexer for applying a multiplexed optical signal to an input of an optical amplifier in each of one band and another band. 4. In order to multiplex a plurality of input optical signals,
And further including at least one multiplexer for adding the multiplexed optical signal to the optical transmission line by means of an input summing / dropping filter, each input of the first and second optical amplifiers in a separate said one band and another band. 3. The system according to claim 2, further comprising a summing / dropping filter for connecting an optical transmission line to the transmission line. 5. The at least one demultiplexer comprises:
3. The system according to claim 2, including a pair of demultiplexers having respective inputs connected to receive output signals directly from the first and second optical amplifiers. 6. The at least one demultiplexer comprises:
The downstream optical transmission medium and the downstream optical amplifier make the first
3. The system according to claim 2, including a pair of demultiplexers having respective inputs connected to receive an output signal from the second optical amplifier. 7. The at least one demultiplexer comprises:
5. The system according to claim 4, including a pair of demultiplexers having respective inputs connected to receive output signals directly from the first and second optical amplifiers. 8. The at least one demultiplexer comprises:
The downstream optical transmission medium and the downstream optical amplifier make the first
5. The system according to claim 4, including a pair of demultiplexers having respective inputs connected to receive an output signal from the second optical amplifier. 9. The apparatus of claim 9, further comprising an add / drop filter for connecting the output of the first and second amplifiers to a transmission medium, wherein the output add / drop filter connects an end of the transmission medium to at least one demultiplexer. Item 2
Pertaining to the system. 10. The at least one demultiplexer includes a first demultiplexer for receiving an optical signal in one band from an output port of the output summing / dropping filter and another output port of the output summing / dropping filter. ,
The system according to claim 9, including a second demultiplexer for receiving an optical signal in another band. 11. The at least one demultiplexer includes a downstream optical transmission medium and a downstream optical amplifier.
3. The system according to claim 2, having an input connected to receive an output signal from the first and second optical amplifiers. 12. The downstream optical transmission medium comprises an optical fiber, and the summing / dropping filter includes a first and a second light in one and another band respectively at each end of the optical transmission medium except the last optical transmission medium. A summing / drop filter connecting the respective outputs of the first and second optical amplifiers to respective inputs of the optical transmission medium except the first optical transmission medium; and at least one multiplexer Is connected to a first input of each of the first and second optical amplifiers in each of said one and another bands, wherein the last output optical signal of the first and second optical amplifiers is at least The system according to claim 11, connected to an input of one demultiplexer. 13. The system according to claim 12, wherein the output optical signal of the at least one multiplexer is directly connected to a first input of each of the first and second optical amplifiers. 14. The system according to claim 12, wherein the last output optical signals of the first and second optical amplifiers are directly connected to an input of at least one demultiplexer. 15. The system according to claim 12, wherein the output optical signal of the at least one multiplexer is connected to the first optical fiber by a summing / drop filter. 16. The final output optical signals of the first and second optical amplifiers are connected by a summing / drop filter to the input end of the last optical fiber, and the output end of the last optical fiber is connected by a summing / drop filter. 2. The device of claim 1, wherein the device is connected to at least one demultiplexer.
Pertaining to the system. 17. A first multiplexer device for receiving a plurality of first input optical signals and for outputting a combined optical signal for transmitting the first optical signal in a first optical band. A transmission system for a first optical band; and (b) a transmission including a plurality of first optical amplifiers and a plurality of optical fibers for amplifying a combined optical signal in the first optical band transmitted by the plurality of optical fibers. (C) a second multiplexer device for receiving a plurality of second input optical signals and for connecting a combined optical signal for transmitting the second optical signal in the second optical band to the transmission system; A) a plurality of second optical amplifiers parallel to the plurality of first optical amplifiers for amplifying the combined optical signal in the second optical band transmitted by the plurality of optical fibers; A wavelength dependent coupler that further combines the combined signals of the bands and adds them to the input of the optical fiber; and further separates the combined signals into first and second bands and separates them into respective first and second optical signal amplifiers. A broadband optical signal transmission system comprising, in addition to an input, a wavelength dependent decoupler optionally applied to a respective input of the demultiplexer. 18. The system according to claim 17, wherein the coupler and the decoupler are sum / drop filters. 19. The system according to claim 17, wherein the first and second optical bands are optical bands centered nominally at 1545 nm and 1585 nm, respectively. 20. A bidirectional common port for receiving an input signal, a bidirectional add / drop port for transmitting a 1545 nm signal passing through a 1545 nm optical filter, and a 1545 nm passband optical filter input at the common port. The filter includes a bidirectional 1545 nm passband optical filter that includes a bidirectional passport that receives a reflected optical signal that does not pass through and a bidirectional passport that receives an optical signal outside the 1545 nm passband, such that they are reflected to a common port. 19. The system according to claim 18, wherein the 1545 nm band signal reflected at the summing / dropping port is combined. 21. The first optical amplifier is an erbium-doped fiber amplifier; the second optical amplifier includes a first erbium-doped amplified spontaneous emission (ASE) generator; An ASE) generator comprising: (i) means for applying a high power optical signal at either 980 nm or 1480 nm to the first ASE generator; and (ii) reflecting back ASE back to the first ASE generator. An input through the Bragg grating, comprising: a Bragg grating reflector connected to the first ASE generator; and (iii) a second ASE generator receiving the output signal from the first ASE generator and transmitting the output signal to the output. 18. The system according to claim 17, including an input for applying a signal to the first ASE generator. 22. The apparatus of claim 2, further comprising an isolator connected in series between the input and the Bragg grating reflector.
The system according to 1. 23. The system according to claim 22, further comprising means for applying a second optical signal at either 980 nm or 1480 nm to the first ASE generator. 24. A method for transmitting a wideband wavelength division multiplexed signal using a current wavelength division multiplexing transmission system, wherein the current system transmits a plurality of first input optical signals to a lower bandwidth signal. A multiplexer for adding a first multiplexed optical signal to an initial portion of an optical fiber transmission line including a lower bandwidth optical amplifier, and further adding the first multiplexed optical signal to an input of a demultiplexer; Multiplexing the bi-multiplexed optical signal into a second multiplexed optical signal in a band different from the band of the lower bandwidth signal; connecting the second multiplexed optical signal to the first transmission system; Passing the bandwidth signal from the first optical fiber transmission line to a lower bandwidth optical amplifier; and transmitting the second multiplexed optical signal to the optical fiber. From the input to an amplifier having a different bandwidth; connecting each amplified signal to a longer transmission line optical fiber for further transmission; and A method for transmitting a broadband wavelength division multiplexed signal comprising demultiplexing into a second output optical signal. 25. A separate amplifier, each having a different bandwidth, separately amplifying the wavelength division multiplexed signal in the combined signal having the different bandwidths; Transmitting all of the amplified optical signals having the same bandwidth. 26. The method according to claim 25, wherein the wavelength division multiplexed signals are in the 1585 nm and 1545 nm bands. 27. A method for amplifying a broadband optical signal formed of multiplexed signals in two bands in a current fiber optic transmission line including a current amplifier capable of amplifying only signals in one of the two bands. A method for amplifying a broadband optical signal comprising directing a signal in the other of the two bands to an auxiliary amplifier that can amplify a signal in the other of the two bands, avoiding current amplifiers. 28. One of the two bands is 1545
nm band, the other of the two bands being 1585 nm
28. The method according to claim 27, which is a band.