Patent ID: 12199671

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, embodiments of the invention will be described in conjunction with the accompanying drawings.FIG.1is a block diagram of the configuration of an optical transmission system1according to a first embodiment of the invention. The optical transmission system1includes an optical communication device2A (a first optical communication device), an optical communication device2B (a second optical communication device), an optical transmission path3, and an FBG-DCM4(a first FBG-DCM).

The optical transmission path3includes an optical fiber31and an optical amplifier32. The optical fiber31is a transmission medium for optical signals, and for example an SSMF (Standard Single Mode Fiber) is used. The optical amplifier32amplifies optical signals. The configuration shown in the optical transmission path3is an example only, and the optical amplifier32may be inserted in the middle of the optical fiber31or a device other than the optical amplifier32such as an optical switch and a regenerative repeater may be connected to the optical fiber31or inserted in the middle of the optical fiber31.

The FBG-DCM4is a wavelength dispersion compensation device and provided between the optical communication device2A and the optical transmission path3. The FBG-DCM4is connected to the optical communication device2A and the optical transmission path3through the optical fiber.

The optical communication device2A includes an optical transmitting unit5. The optical transmitting unit5is connected to the FBG-DCM4through the optical fiber. The optical transmitting unit5includes an electrical signal generating unit51and an optical signal generating unit52. The electrical signal generating unit51encodes the transmission data as an information source, converts the encoded transmission data into an electrical signal, and outputs the signal to the optical signal generating unit52. The optical signal generating unit52converts the electrical signal output by the electrical signal generating unit51into an optical signal and outputs the optical signal to the optical fiber connected to the optical transmitting unit5.

The optical communication device2B includes an optical receiving unit6. The optical receiving unit6is connected to the optical transmission path3. The optical receiving unit6includes an optical signal receiving unit61and an electrical signal processing unit62. The optical signal receiving unit61receives an optical signal transmitted through the optical transmission path3, converts the received optical signal into an electrical signal, and outputs the signal to the electrical signal processing unit62. The electrical signal processing unit62decodes the electrical signals output by the optical signal receiving unit61and restores the transmission data.

Processing According to First Embodiment

FIG.2is a flowchart for illustrating the flow of processing steps carried out by the optical transmission system1according to the first embodiment. The electrical signal generating unit51encodes transmission data and converts the encoded transmission data into an electrical signal to generate the electrical signal. The electrical signal generating unit51outputs the generated electrical signal of the transmission data to the optical signal generating unit52(step S1). The optical signal generating unit52obtains the electrical signal output by the electrical signal generating unit51. The optical signal generating unit52converts the obtained electrical signal into an optical signal. The optical signal generating unit52outputs the optical signal obtained by the conversion to the optical fiber connected to the optical transmitting unit5(step S2).

The FBG-DCM4obtains an optical signal output by the optical communication device2A. The FBG-DCM4performs wavelength dispersion compensation on the obtained optical signal. The FBG-DCM4outputs, to the optical transmission path3, the optical signal after the wavelength dispersion compensation (step S3). The optical signal output by the FBG-DCM4is amplified by the optical amplifier32and then input to the optical communication device2B (step S4).

The optical signal receiving unit61receives the input optical signal. The optical signal receiving unit61converts the received optical signal into an electrical signal and outputs the resulting signal to the electrical signal processing unit62(step S5). The electrical signal processing unit62obtains the electrical signal output by the optical signal receiving unit61. The electrical signal processing unit62decodes the obtained electrical signal and restores the transmission data (step S6).

Effects According to First Embodiment

Now, effects brought about by the optical transmission system1according to the first embodiment will be described with reference toFIGS.3to5.FIG.3is a block diagram of an optical transmission system200. In the optical transmission system200, a DCF140is used instead of the FBG-DCM4in the configuration of the optical transmission system1, and the DCF140is inserted between the optical transmission path3and the optical communication device2B.FIG.4is a block diagram of an optical transmission system300. In the optical transmission system300, the FBG-DCM4is inserted between the optical transmission path3and the optical communication device2B. InFIG.3andFIG.4, the same elements as those in the optical transmission system1are designated by the same reference characters.

FIG.5is a table showing the relation among transmission power, loss in transmission, and received power in the optical transmission system200, the optical transmission system300, and the optical transmission system1. The transmission power inFIG.5is the power of the optical signal generated and output by the optical signal generating unit52of the optical communication device2A. The received power inFIG.5is the power of the optical signal that is received by the optical signal receiving unit61of optical communication device2B. In the table shown inFIG.5, the loss in the optical transmission path3is “10 dB” and the loss in the DCF140is “5 dB”, and the loss in the FBG-DCM4is “3 dB”.

In the example shown in the row of item number 1, the transmission power of the optical transmission system200is set to “0 dBm”, this is because the upper limit for the input optical power must be “0 dBm” for the SSMF optical fiber31and the DCF140of the optical transmission path3in order to reduce the nonlinear optical effect.

In the example shown in the row of item number 2, the transmission power in the optical transmission system300is also set to “0 dBm”, but the FBG-DCM4is not inserted on the side of the optical communication device2A which outputs the optical signal in the optical transmission system300. Therefore, similarly to the optical transmission system200, the upper limit for the input optical power must be “0 dBm” in order to reduce the nonlinear optical effect.

In contrast, as shown in the row of item number 3, in the optical transmission system1, the FBG-DCM4is inserted closer to the optical communication device2A. Specifically, in the optical transmission system1, the FBG-DCM4is inserted in the stage preceding the optical transmission path3. This allows the optical power to be increased during transmission by the optical communication device2A, and therefore the power is set to “3 dBm”.

As can be seen from comparison between the value “−15 dBm” in the “received power” in the row of item number 1 and the values “−13 dBm” and “−10 dBm” in the rows of item numbers 2 and 3, the received power obtained using the FBG-DCM4is higher than the power obtained using DCF140. As can be seen from comparison between the value “−13 dBm” in the “received power” in the row of item number 2 and the value “−10 dBm” in the “received power” in the row of item number 3, the optical transmission system1having the FBG-DCM4provided closer to the optical communication device2A can provide greater transmission power, and therefore the received power can be greater. Therefore, the resulting received power can be greater using the FBG-DCM4than using the DCF140. When the FBG-DCM4is inserted on the optical signal transmission side, even greater power is received.

The rows of item numbers 4 and 5 show the minimum necessary transmission power in comparison when the minimum light receiving sensitivity of the optical signal receiving unit61of the optical communication device2B is “−30 dBm. As shown in the row of item number 4, in the optical transmission system200, when the transmission power of the optical signal generated by the optical signal generating unit52is set to “−16 dBm”, the power received at the optical signal receiving unit61is “−31 dBm” which is less than the minimum light receiving sensitivity “−30 dBm”. Therefore, in the optical transmission system200, the transmission power of the optical signal generated by the optical signal generating unit52must be set to at least “−15 dBm” in order to satisfy the minimum light receiving sensitivity.

In contrast, as shown in the row of item number 5, in the optical transmission system1according to the first embodiment, even when the transmission power of the optical signal generated by the optical signal generating unit52is set to “−13 dBm”, the received power at the optical signal receiving unit61is “−26 dBm”, which satisfies the minimum light receiving sensitivity. Therefore, when the transmission power of the optical signal generated by the optical signal generating unit52is at least “−17 dBm”, the minimum light receiving sensitivity of the optical signal receiving unit61can be satisfied. Therefore, the optical transmission system1according to the first embodiment can satisfy the minimum light receiving sensitivity of the optical signal receiving unit61with smaller transmission power than that of the optical transmission system200.

In the optical transmission system1according to the first embodiment, the optical communication device2A outputs an optical signal. The optical communication device2B receives the optical signal output by the optical communication device2A and transmitted through the optical transmission path3. The FBG-DCM4is inserted between the optical communication device2A and the optical transmission path3, receives the optical signal output by the optical communication device2A, performs wavelength dispersion compensation on the received optical signal, and outputs the resulting signal to the optical transmission path3.

As the FBG-DCM4is inserted, the waveform distortion attributable to wavelength dispersion can be compensated while suppressing the nonlinear optical effects if the transmission power of the optical signal is increased. Since the power of the optical signal to be transmitted can be increased, the OSNR can be improved. Therefore, the quality of received signals can be improved and the transmission distance can be increased. As described above, when the minimum light receiving sensitivity is determined, the minimum light receiving sensitivity can be secured with less transmission power by using the FBG-DCM4than by using the DCF140. In this way, the minimum light receiving sensitivity can be achieved with reduced transmission power. As the FBG-DCM4is inserted closer to the optical communication device2A which includes the optical transmitting unit5, the optical signal can be transmitted with greater transmission power, which improves the quality of received signals.

Second Embodiment

FIG.6is a block diagram of an optical transmission system1aaccording to a second embodiment of the invention. The optical transmission system1aincludes optical communication devices2C-1and2C-2, an FBG-DCM4-α (a first FBG-DCM), a4-β (a second FBG-DCM), and optical transmission paths3-α and3-β.

The FBG-DCMs4-α and4-β have the same configuration as the FBG-DCM4according to the first embodiment. The optical transmission paths3-α and3-β have the same configuration as the optical transmission path3according to the first embodiment.

The optical communication device2C-1includes an optical transmitting/receiving unit7-1. The optical transmitting/receiving unit7-1includes an electrical signal generating unit51-1, an optical signal generating unit52-1, an optical signal receiving unit61-1, and an electrical signal processing unit62-1. The optical communication device2C-2includes an optical transmitting/receiving unit7-2. The optical transmitting/receiving unit7-2includes an electrical signal generating unit51-2, an optical signal generating unit52-2, an optical signal receiving unit61-2, and an electrical signal processing unit62-2.

The electrical signal generating units51-1and51-2have the same configuration as the electrical signal generating unit51according to the first embodiment. The optical signal generating units52-1and52-2have the same configuration as the optical signal generating unit52according to the first embodiment. The optical signal receiving units61-1and61-2have the same configuration as the optical signal receiving unit61according to the first embodiment. The electrical signal processing units62-1and62-2have the same configuration as the electrical signal processing unit62according to the first embodiment.

The optical signal generating unit52-1of the optical communication device2C-1is connected to the optical signal receiving unit61-2of the optical communication device2C-2through the FBG-DCM4-aand the optical transmission path3-a. The path through the FBG-DCM4-aand the optical transmission path3-aserves as a transmission path from the optical communication device2C-1to the optical communication device2C-2.

The optical signal generating unit52-2of the optical communication device2C-2is connected to the optical signal receiving unit61-1of the optical communication device2C-1through the FBG-DCM4-13and the optical transmission path3-13. The path through the FBG-DCM4-13and the optical transmission path3-13serves as a transmission path from the optical communication device2C-2to the optical communication device2C-1.

In other words, in the optical transmission system1aaccording to the second embodiment, the optical communication devices2C-1and2C-2respectively have the optical transmitting/receiving units7-1and7-2each including the optical transmitting unit5and the optical receiving unit6according to the first embodiment in an integrated manner and are configured to transmit and receive optical signals from each other.

Therefore, the optical transmission system1aaccording to the second embodiment performs the same processing as that performed by the optical transmission system1according to the first embodiment shown inFIG.2by the combination of the electrical signal generating unit51-1, the optical signal generating unit52-1, the FBG-DCM4-a, the optical transmission path3-a, the optical signal receiving unit61-2, and the electrical signal processing unit62-2. The optical transmission system1aaccording to the second embodiment performs the same processing as that performed by the optical transmission system1according to the first embodiment shown inFIG.2by the combination of the electrical signal generating unit51-2, the optical signal generating unit52-2, the FBG-DCM4-13, the optical transmission path3-13, the optical signal receiving unit61-1, and the electrical signal processing unit62-1.

Effects According to Second Embodiment

Now, effects brought about by the optical transmission system1aaccording to the second embodiment will be described with reference toFIGS.7and8.FIG.7is a block diagram of the optical transmission system200a. In the optical transmission system200a, DCFs140-aand140-13are used instead of the FBG-DCMs4-aand4-13in the configuration of optical transmission system1a. The DCF140-ais inserted between the optical transmission path3-aand the optical communication device2C-2, and the DCF140-13is inserted between the optical transmission path3-13and the optical communication device2C-1. InFIG.7, the same elements as those of the optical transmission system1ashown inFIG.6are designated by the same reference characters.

FIG.8is a table showing the relation between the transmission power, the loss in transmission, and the received power in the optical transmission system200aand the optical transmission system1a. The transmission power inFIG.8refers to the power of the optical signal generated and output by the optical signal generating unit52-1of the optical communication device2C-1or the optical signal generating unit52-2of the optical communication device2C-2. The received power inFIG.8refers to the power of the optical signal received by the optical signal receiving unit61-2of optical communication device2C-2or the optical signal receiving unit61-1of the optical communication device2C-1. In the table shown inFIG.8, the loss through the optical transmission paths3-α and3-β is “10 dB”, the loss through the DCFs140-α and140-β is “5 dB”, and the loss through the FBG-DCMs4-α and4-β is “3 dB”.

Item numbers 1 and 2 show the minimum necessary transmission power for each of the optical signal receiving units61-1and61-2in comparison for the minimum light receiving sensitivity is “−30 dBm”. As shown in the row of item number 1, in the optical transmission system200a, when the transmission power of the optical signals generated by the optical signal generating units52-1and52-2is set to “−16 dBm”, the received power at the optical signal receiving units61-2and61-2opposed to each other is “−31 dBm”, which indicates that the minimum light receiving sensitivity “−30 dBm” cannot be satisfied. Therefore, in the optical transmission system200a, in order to satisfy the minimum light receiving sensitivity, the power of the optical signal generated by each of the optical signal generating units52-1and52-2must be at least “−15 dBm”.

In contrast, as shown in the row of item number 2, in the optical transmission system1aaccording to the second embodiment, when the transmission power of the optical signal generated by each of the optical signal generating units52-1and52-2is “−13 dBm”, the received power at each of the optical signal receiving units61-2and61-1is “−26 dBm”, and therefore the minimum light receiving sensitivity can be satisfied. Therefore, when the transmission power of each of the optical signals generated by the optical signal generating units52-1and52-2is at least “−17 dBm”, the minimum light receiving sensitivity for the optical signal receiving units61-2and61-1can be satisfied. Therefore, the optical transmission system1aaccording to the second embodiment can satisfy the minimum light receiving sensitivity for the optical signal receiving units61-2and61-1with smaller transmission power than that of the optical transmission system200a.

In the optical transmission system1aaccording to the second embodiment described above, the optical communication device2C-1outputs an optical signal. The optical communication device2C-2receives the optical signal output by the optical communication device2C-1and transmitted by the optical transmission path3-a. The optical communication device2C-2outputs an optical signal. The optical communication device2C-1receives the optical signal output by the optical communication device2C-2and transmitted by the optical transmission path3-β.

In the optical transmission system1a, the FBG-DCM4-α is inserted between the optical communication device2C-1and the optical transmission path3-α, receives an optical signal output by the optical communication device2C-1, performs wavelength dispersion compensation on the received optical signal, and outputs the resulting signal to the optical transmission path3-α. The FBG-DCM4-β is inserted between the optical communication device2C-2and the optical transmission path3-β, receives the optical signal output by the optical communication device2C-2, performs wavelength dispersion compensation on the received optical signal, and outputs the resulting signal to the optical transmission path3-β.

The insertion of the FBG-DCMs4-α and4-β allows the waveform distortion attributable to wavelength dispersion to be compensated while reducing nonlinear optical effects when the power of each of the optical signal's output by the optical communication devices2C-1and2C-2is increased. Since the power of each of the optical signals output by the optical communication devices2C-1and2C-2can be increased, the OSNR can be improved. As a result, the quality of received signals can be improved and the transmission distance can be increased. As described above, when the minimum light receiving sensitivity is determined, the minimum light-receiving sensitivity can be achieved with less transmission power than the case of using the DCFs140-α and140-β. The FBG-DCMs4-α and4-β are inserted in positions closer to the optical signal generating units52-1and52-2of the optical communication devices2C-1and2C-2, so that optical signals with greater transmission power can be transmitted, and therefore the quality of received signals can be improved.

Third Embodiment

FIG.9is a block diagram of the configuration of an optical transmission system1baccording to a third embodiment of the invention. The elements according to the third embodiment which are the same as those of the optical transmission system1according to the first embodiment shown inFIG.1are designated by the same reference characters, and different elements will be described. The optical transmission system1bincludes N optical communication devices2A-1,2A-2, . . . ,2A-N, a wavelength division multiplexing multiplexer8, an FBG-DCM4, an optical transmission path3, a wavelength division multiplexing demultiplexer9, and N optical communication devices2B-1,2B-2, . . . ,2B-N. Here, N is an integer of two or more. The number of the optical communication devices2A-1to2A-N and the number of the optical communication devices2B-1to2B-N are equal.

The optical communication devices2A-1to2A-N each have the same configuration as that of the optical communication device2A according to the first embodiment. The optical communication devices2A-1to2A-N each transmit optical signals with different wavelengths from each other. The optical communication devices2B-1to2B-N each have the same configuration as that of the optical communication device2B according to the first embodiment. In the following description, functional units of the optical communication devices2A-1to2A-N and2B-1to2B-N that correspond to the functional units of the optical communication devices2A and2B are designated by the reference characters of these functional units with the branch numbers. For example, the functional unit of the optical communication device2A-1which corresponds to the electrical signal generating unit51of the optical communication device2A is indicated as an electrical signal generating unit51-1.

The wavelength division multiplexing multiplexer8has N input ports and one output port. The wavelength division multiplexing multiplexer8is, for example, a WDM-MUX (Wavelength Division Multiplexing-Multiplexer). The N input ports of the wavelength division multiplexing multiplexer8are connected with the optical communication devices2A-1to2A-N respectively through optical fibers. The output port of the wavelength division multiplexing multiplexer8is connected with the FBG-DCM4through the optical fiber. The wavelength division multiplexing multiplexer8obtains N optical signals with different wavelengths from each other output by the optical communication devices2A-1to2A-N. The wavelength division multiplexing multiplexer8converts the N optical signals with different wavelengths from each other into optical signals with N different wavelengths. The wavelength division multiplexing multiplexer8multiplexes the converted optical signals with the N different wavelengths from each other. In this way, the wavelength division multiplexing multiplexer8generates a multiplexed signal.

The wavelength division multiplexing demultiplexer9includes one input port and N output ports. The wavelength division multiplexing demultiplexer9is, for example, a WDM-DEMUX (Wavelength Division Multiplexing-Demultiplexer). An optical transmission path3is connected to the input port of the wavelength division multiplexing demultiplexer9. The N output ports of the wavelength division multiplexing demultiplexer9are connected with the optical communication devices2B-1to2B-N through optical fibers. The wavelength division multiplexing demultiplexer9obtains the multiplexed signal transmitted through the optical transmission path3. The wavelength division multiplexing demultiplexer9splits the obtained multiplexed signal on a wavelength basis.

The wavelength division multiplexing demultiplexer9outputs the N optical signals with different wavelengths from each other obtained by demultiplexing to the optical communication devices2B-1to2B-N connected to the output ports. The N different wavelengths from each other are output from the output ports associated in advance. The N input ports of the wavelength division multiplexing multiplexer8and the N output ports of the wavelength division multiplexing demultiplexer9are associated in advance on a one-to-one basis. For example, assume that the first input port of the wavelength division multiplexing multiplexer8is associated with the first output port of the wavelength division multiplexing demultiplexer9. In this case, the wavelength division multiplexing multiplexer8converts an optical signal obtained from the first input port into a signal with a prescribed wavelength. Therefore, the wavelength division multiplexing demultiplexer9is previously set to split the optical signal with the prescribed wavelength and output the resulting signal to the first output port.

Processing According to Third Embodiment

FIG.10is a flowchart for illustrating the flow of processing steps performed by the optical transmission system1baccording to the third embodiment. The electrical signal generating units51-1to51-N of the optical communication devices2A-1to2A-N encode transmission data and convert the encoded transmission data into electrical signals to generate the electrical signals. The electrical signal generating units51-1to51-N output the generated electrical signals of the transmission data to the optical signal generating units52-1to52-N connected therewith (step Sb1).

The optical signal generating units52-1to52-N obtain the electrical signals of the transmission data output by the electrical signal generating units51-1to51-N. The optical signal generating units52-1to52-N convert the obtained electrical signals into optical signals. In this case, the optical signal generating units52-1to52-N generate optical signals with different wavelengths from each other. The optical signal generating units52-1to52-N output the optical signals obtained by the conversion to the wavelength division multiplexing multiplexer8(step Sb2).

The wavelength division multiplexing multiplexer8obtains the N optical signals with the different wavelengths from each other output by the optical signal generating units52-1to52-N. The wavelength division multiplexing multiplexer8converts the N optical signals with the different wavelengths from each other into optical signals with different N wavelengths from each other. The wavelength division multiplexing multiplexer8multiplexes the converted optical signals with the N different wavelengths to generate a multiplexed signal. The wavelength division multiplexing multiplexer8outputs the generated multiplexed signal to the FBG-DCM4(step Sb3). The FBG-DCM4obtains the multiplexed signal. The FBG-DCM4performs wavelength dispersion compensation on the obtained multiplexed signal. The FBG-DCM4outputs the multiplexed signal after the wavelength dispersion compensation to the optical transmission path3(step Sb4). The multiplexed signal transmitted from the FBG-DCM4is input to the wavelength division multiplexing demultiplexer9through the optical transmission path3(step Sb5).

The wavelength division multiplexing demultiplexer9receives the input multiplexed signal. The wavelength division multiplexing demultiplexer9splits the received multiplexed signal on a wavelength-basis. The wavelength division multiplexing demultiplexer9outputs the N optical signals obtained by the demultiplexing from the output ports associated with the wavelengths of the N optical signals to the optical communication devices2B-1to2B-N (step Sb6).

The optical signal receiving units61-1to61-N receive and obtain the optical signals output by the wavelength division multiplexing demultiplexer9. The optical signal receiving units61-1to61-N convert the obtained optical signals into electrical signals and output the signals to the electrical signal processing units62-1to62-N (step Sb7). The electrical signal processing units62-1to62-N obtain the electrical signals output by the optical signal receiving units61-1to61-N. The electrical signal processing units62-1to62-N decode the obtained electrical signals and restore the transmission data (step Sb8).

Another Exemplary Configuration According to Third Embodiment

FIG.11is a block diagram of the configuration of an optical transmission system1cas another exemplary configuration according to the third embodiment. InFIG.11, the same elements as those of the optical transmission system1bshown inFIG.9are designated by the same reference characters, and different elements will be described.

The optical transmission system1cincludes optical communication devices2A-1to2A-N, N optical communication devices2B-1to2B-N, an optical transmission path3, N FBG-DCMs4-1to4-N, a wavelength division multiplexing multiplexer8and a wavelength division multiplexing demultiplexer9.

The N FBG-DCMs4-1to4-N are connected, through optical fibers, to the optical communication devices2A-1to2A-N and the N ports of the wavelength division multiplexing multiplexer8. In the optical transmission system1c, the optical signals with different wavelengths from one another output by the optical communication devices2A-1to2A-N are individually compensated for wavelength dispersion. The wavelength division multiplexing multiplexer8obtains the N wavelength-dispersion compensated optical signals with different wavelengths from one another. The wavelength division multiplexing multiplexer8converts the N obtained optical signals with different wavelengths from one another into optical signals with different wavelengths from one another. The wavelength division multiplexing multiplexer8multiplexes the converted optical signals and outputs the resulting signal to the optical transmission path3.

In the optical transmission system1band the optical transmission system1cin the other exemplary configuration described above according to the third embodiment, the wavelength division multiplexing multiplexer8is connected to the plurality of optical communication devices2A-1to2A-N and generates a multiplexed signal by wavelength division multiplexing the plurality of optical signals with different wavelengths from one another output by the optical communication devices2A-1to2A-N. The wavelength division multiplexing multiplexer8outputs the generated multiplexed signal to the optical transmission path3. The wavelength division multiplexing demultiplexer9is connected to the plurality of optical communication devices2B-1to2B-N. The wavelength division multiplexing demultiplexer9receives the multiplexed signal output by wavelength division multiplexing multiplexer8. The wavelength division multiplexing demultiplexer9splits the received multiplexed signal on a wavelength basis and outputs the resulting signals to the plurality of optical communication devices2B-1to2B-N.

In the optical transmission systems1band1c, the FBG-DCM4is inserted between the wavelength division multiplexing multiplexer8and the optical transmission path3, receives the optical signals output by the wavelength division multiplexing multiplexer8, performs wavelength dispersion compensation on the received optical signals, and outputs the resulting signals to the optical transmission path3. Alternatively, a plurality of FBG-DCMs4-1to4-N is inserted between the plurality of optical communication devices2A-1to2A-N and the wavelength division multiplexing multiplexer8and receive the optical signals output by the optical communication devices2A-1to2A-N, perform wavelength dispersion compensation on the received optical signals, and output the resulting signals to the wavelength division multiplexing multiplexer8.

Since the FBG-DCM4or the FGB-DCMs4-1to4-N are inserted, waveform distortion attributable to wavelength dispersion can be compensated while reducing non-linear optical effects when the transmission power of the optical signal is increased. In particular, since the FBG-DCM has a limited wavelength range for wavelength dispersion compensation, the compensation effect can be increased by individually carrying out wavelength dispersion compensation rather than carrying out wavelength dispersion compensation on the waveform multiplexed signals together at a time. Since the power of the transmission optical signals can be increased, the OSNR can be improved. Therefore, the quality of received signals can be improved and the transmission distance can be increased. In the optical transmission systems1band1c, the FBG-DCMs4and4-1to4-N are inserted in positions closer to the optical communication devices2A-1to2A-N, so that optical signals can be transmitted with greater transmission power, which can further improve the quality of received signals.

Fourth Embodiment

FIG.12is a block diagram of the configuration of an optical transmission system1daccording to a fourth embodiment of the invention. According to the fourth embodiment, the same elements as those of the optical transmission system1aaccording to the second embodiment shown inFIG.6and the optical transmission system1baccording to the third embodiment shown inFIG.9are designated by the same reference characters, and different elements will be described.

The optical transmission system1dincludes N optical communication devices2C-1-1,2C-1-2, . . . ,2C-1-N, wavelength division multiplexing multiplexer/demultiplexers10-1and10-2, N optical communication devices2C-2-1,2C2, . . . ,2C-2-N, optical transmission paths3-α and3-β, and FBG-DCMs4-α and4-β.

The optical communication devices2C-1-1to2C-1-N have the same configuration as the optical communication device2C-1according to the second embodiment. The optical communication devices2C-1-1to2C-1-N output optical signals with different wavelengths from one another. The optical communication devices2C-2-1to2C-2-N have the same configuration as the optical communication device2C-2according to the second embodiment. The optical communication devices2C-2-1to2C-2-N output optical signals with different wavelengths from one another. The optical communication devices2C-1and2C-2according to the second embodiment have the same configuration, and therefore the optical communication devices2C-1-1to2C-1-N and2C-2-1to2C-2-N have the same configuration. In the following description, the functional units of the optical communication devices2C-1-1to2C-1-N and2C-2-1to2C-2-N which correspond to the functional units of the optical communication devices2C-1and2C-2are designated by the same reference characters followed by branch numbers. For example, the functional unit of the optical communication device2C-1-1which corresponds to the optical transmitting/receiving unit7-1of the optical communication device2C-1is indicated as an optical transmitting/receiving unit7-1-1.

The wavelength division multiplexing multiplexer/demultiplexer10-1includes a wavelength division multiplexing multiplexer8-1and a wavelength division multiplexing demultiplexer9-1as shown inFIG.13. The wavelength division multiplexing multiplexer8-1has the same configuration as the wavelength division multiplexing multiplexer8according to the third embodiment. The wavelength division multiplexing demultiplexer9-1has the same configuration as the wavelength division multiplexing demultiplexer9according to the third embodiment.

The N input ports of the wavelength division multiplexing multiplexer8-1are connected with the optical signal generating units52-1-1to52-1-N of the optical communication devices2C-1-1to2C-1-N. The output port of the wavelength division multiplexing multiplexer8-1is connected with the FBG-DCM4-α.

The input port of the wavelength division multiplexing demultiplexer9-1is connected with the optical transmission path3-β. The N output ports of the wavelength division multiplexing demultiplexer9-1are connected with the optical signal receiving units61-1-1to61-1-N of the optical communication devices2C-1-1to2C-1-N.

The wavelength division multiplexing multiplexer/demultiplexer10-2has the same configuration as the wavelength division multiplexing multiplexer/demultiplexer10-1and includes the wavelength division multiplexing multiplexer8-2corresponding to the wavelength division multiplexing multiplexer8-1and the wavelength division multiplexing demultiplexer9-1corresponding to the wavelength division multiplexing demultiplexer9-2.

The N input ports of the wavelength division multiplexing multiplexer8-2are connected with the optical signal generating units52-2-1to52-2-N of the optical communication devices2C-2-1to2C-2-N. The FBG-DCM4-β is connected to the output port of the wavelength division multiplexing multiplexer8-2.

The input port of the wavelength division multiplexing demultiplexer9-2is connected with the optical transmission path3-α. The N output ports of the wavelength division multiplexing demultiplexer9-2are connected with the optical signal receiving units61-2-1to61-2-N of the optical communication devices2C-2-1to2C-2-N.

The optical signal generating units52-1-1to52-1-N of the optical communication devices2C-1-1to2C-1-N are connected to the wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1, to the wavelength division multiplexing demultiplexer9-2of wavelength division multiplexing multiplexer/demultiplexer10-2through the FBG-DCM4-α and the optical transmission path3-α, and to the optical signal receiving units61-2-1to61-2-N of the optical communication devices2C-2-1to2C-2-N through the wavelength division multiplexing demultiplexer9-2. The paths formed by these connections serve as transmission paths shown in solid lines from the optical communication devices2C-1-1to2C-1-N to the optical communication devices2C-2-1to2C-2-N.

The optical signal generating units52-2-1to52-2-N of the optical communication devices2C-2-1to2C-2-N are connected to the wavelength division multiplexing multiplexer8-2of the wavelength division multiplexing multiplexer/demultiplexer10-2, to the wavelength division multiplexing demultiplexer9-1of the wavelength division multiplexing multiplexer/demultiplexer10-1through the FBG-DCM4-β and the optical transmission path3-β, and to the optical signal receiving unit61-1-1to61-1-N of the optical communication devices2C-1-1to2C-1-N through the wavelength division multiplexing demultiplexer9-1. The paths formed by these connections serve as the transmission paths shown in dashed lines from the optical communication devices2C-2-1to2C-2-N to the optical communication devices2C-1-1to2C-1-N.

Therefore, the optical transmission system1daccording to the fourth embodiment performs the same processing as that carried out by the optical transmission system1baccording to the third embodiment shown inFIG.10by the combination of the electrical signal generating units51-1-1to51-1-N and the optical signal generating units52-1-1to52-1-N of the optical communication devices2C-1-1to2C-1-N and the combination of the wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1, the FBG-DCM4-α, the optical transmission path3-α, and the wavelength division multiplexing demultiplexer9-2of the wavelength division multiplexing multiplexer/demultiplexer10-2, and the optical signal receiving units61-2-1to61-2-N and the electrical signal processing units62-2-1to62-2-N of the optical communication devices2C-2-1to2C-2-N.

The optical transmission system1daccording to the fourth embodiment performs the same processing as that carried out by the optical transmission system1B according to the third embodiment shown inFIG.10by the combination of the electrical signal generating units51-2-1to51-2-N and the optical signal generating units52-1-2to52-2-N of the optical communication devices2C-2-1to2C-2-N and the combination of the wavelength division multiplexing multiplexer8-2of the wavelength division multiplexing multiplexer/demultiplexer10-2, the FBG-DCM4-β, the optical transmission path3-β, the wavelength division multiplexing demultiplexer9-1of the wavelength division multiplexing multiplexer/demultiplexer10-1, and the optical signal receiving units61-1-1to61-1-N and the electrical signal processing units62-2-1to62-2-N of the optical communication devices2C-1-1to2C-1-N.

Another Exemplary Configuration According to Fourth Embodiment

FIG.14is a block diagram of the configuration of an optical transmission system1eas another exemplary configuration according to the fourth embodiment. InFIG.14, the same elements as those of the optical transmission system1dshown inFIG.12are designated by the same reference characters, and different elements will be described.

The optical transmission system1eincludes optical communication devices2C-1-1to2C-1-N, N optical communication devices2C-2-1to2C-2-N, and optical transmission paths3aand313, N FBG-DCMs4-α-1to4-α-N, N FBG-DCMs4-β-1to4-β-N, and wavelength division multiplexing multiplexer/demultiplexers10-1and10-2.

The N FBG-DCMs4-α-1to4-α-N are connected to the optical signal generating units52-1-1to52-1-N of the optical communication devices2C-1-1to2C-1-N and the N ports of the wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1through optical fibers.

The N FBG-DCMs4-β-1to4-β-N are connected to the optical signal generating units52-2-1to52-2-N of the optical communication devices2C-2-1to2C-2-N and the N ports of the wavelength division multiplexing multiplexer8-2of the wavelength division multiplexing multiplexer/demultiplexer10-2through optical fibers.

In the optical transmission system1e, the FBG-DCMs4-α-1to4-α-N individually perform wavelength dispersion compensation on optical signals with different wavelengths from one another output by the optical communication devices2C-1-1to2C-1-N. The wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1obtains the N wavelength dispersion compensated optical signals with different wavelengths from one another. The wavelength division multiplexing multiplexer8-1converts the N obtained optical signals with different wavelengths from one another into optical signals with different wavelengths from one another. The wavelength division multiplexing multiplexer8-1multiplexes the optical signals obtained by the conversion and outputs the resulting signal to the optical transmission path3-α.

In the optical transmission system1e, the optical signal generating units52-2-1to52-2-N of the optical communication devices2C-2-1to2C-2-N output optical signals with different wavelengths from one another. The FBG-DCMs4-β-1to4-β-N individually compensate for the wavelength dispersion of the optical signals with the different wavelengths. The wavelength division multiplexing multiplexer8-2of the wavelength division multiplexing multiplexer/demultiplexer10-2obtains the N wavelength dispersion compensated optical signals with the different wavelengths from one another. The wavelength division multiplexing multiplexer8-2converts the N obtained optical signals with the different wavelengths from one another into optical signals with different wavelengths from one another. The wavelength division multiplexing multiplexer8-2multiplexes the converted optical signals and outputs the resulting signal to the optical transmission path3-β.

In the optical transmission system1dand the optical transmission system1eaccording to the other exemplary configuration according to the fourth embodiment described above, the wavelength division multiplexing multiplexer8-1is connected to the plurality of optical communication devices2C-1-1to2C-1-N to perform the wavelength division multiplexing of a plurality of optical signals output by the optical communication devices2C-1-1to2C-1-N and output the resulting signal. The wavelength division multiplexing multiplexer8-2is connected to the plurality of optical communication devices2C-2-1to2C-2-N to perform the wavelength division multiplexing of a plurality of optical signals output by the devices2C-2-1to2C-2-N and output the resulting signal. The wavelength division multiplexing demultiplexer9-1is connected to the plurality of optical communication devices2C-1-1to2C-1-N. The wavelength division multiplexing demultiplexer9-1receives the multiplexed signal output by the wavelength division multiplexing multiplexer8-2. The wavelength division multiplexing demultiplexer9-1splits the received multiplexed signal on a wavelength-basis and outputs the resulting signals to the plurality of optical communication devices2C-1-1to2C-1-N. The wavelength division multiplexing demultiplexer9-2is connected to the plurality of optical communication devices2C-2-1to2C-2-N. The wavelength division multiplexing demultiplexer9-2receives the multiplexed signal output by wavelength division multiplexing multiplexer8-1. The wavelength division multiplexing demultiplexer9-2splits the received multiplexed signal on a wavelength-basis and outputs the resulting signals to the plurality of optical communication devices2C-2-1to2C-2-N.

In the optical transmission system1d, the FBG-DCM4-α is inserted between the wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1and the optical transmission path3-α to receive the optical signal output by the wavelength division multiplexing multiplexer8-1. The FBG-DCM4-α performs wavelength dispersion compensation on the received optical signal and outputs the resulting signal to the optical transmission path3-α. The FBG-DCM4-β is inserted between the wavelength division multiplexer8-2and the optical transmission path3-13to receive the optical signal output by the wavelength division multiplexer8-2. The FBG-DCM4-β performs wavelength dispersion compensation on the received optical signal and sends the resulting signal to the optical transmission path3-β.

In the optical transmission system1e, the plurality of FBG-DCMs4-α-1to4-α-N is inserted between the plurality of optical communication devices2C-1-1to2C-1-N and the wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1to receive the optical signals output by the optical communication devices2C-1-1to2C-1-N. The plurality of FBG-DCMs4-α-1to4-α-N performs wavelength dispersion compensation on the received optical signals and output the resulting signals to the wavelength division multiplexing multiplexer8-1. The plurality of FBG-DCMs4-β-1to4-β-N is inserted between the plurality of optical communication devices2C-2-1to2C-2-N and the wavelength division multiplexing multiplexer8-2to receive optical signals output by the optical communication devices2C-2-1to2C-2-N. The plurality of FBG-DCMs4-β-1to4-β-N performs wavelength dispersion compensation on the received optical signals and output the resulting signals to the wavelength division multiplexing multiplexer8-2.

Since the FBG-DCMs4-α,4-α-1to4-α-N,4-β, and4-β-1to4-β-N are inserted, waveform distortion attributable to wavelength dispersion can be compensated while reducing nonlinear optical effects when the power of the optical signals transmitted by the optical communication devices2C-1-1to2C-1-N and2C-2-1to2C-2-N are increased. In particular, since the FBG-DCM has a limited wavelength range for wavelength dispersion compensation, the compensation effect can be improved by performing wavelength dispersion compensation on each individual signal to improve the compensation effect rather than performing wavelength dispersion compensation on a wavelength division multiplexed optical signal at a time. Since the optical communication devices2C-1-1to2C-1-N and2C-2-1to2C-2-N can increase the power of the optical signals to be transmitted, the OSNR can be improved. As a result, the quality of received signals can be improved and the transmission distance can be increased. The FBG-DCMs4-α,4-α-1to4-α-N,4-β, and4-β-1to4-β-N are inserted in positions closer to the optical signal generating units52-1-1to52-1-N of the optical communication devices2C-1-1to2C-1-N and the optical signal generating units52-2-1to52-2-N of the optical communication devices2C-2-1to2C-2-N, so that the optical signals can be transmitted with greater transmission power, which can further improve the quality of received signals.

Note that in the section including the FBG-DCM4-α, the optical transmission path3-α, the FBG-DCM4-β, and the optical transmission path3-β in the optical transmission system1aaccording to the second embodiment and the optical transmission system1daccording to the fourth embodiment and in the section including the optical transmission paths3-α and3-13in the optical transmission system1eas the other exemplary configuration according to the fourth embodiment, the path shown in solid lines and the path shown in dashed lines may be a path multiplexed with different wavelengths in a single optical fiber path rather than as two physically different paths.

In the case of the optical transmission system1aaccording to the second embodiment, a configuration for wavelength multiplexing and splitting is required. Therefore, for example, in the optical transmission system1daccording to the fourth embodiment, instead of the N optical communication devices2C-1-1to2C-1-N, one optical communication device2C-1must be connected to the wavelength division multiplexing multiplexer/demultiplexer10-1, and instead of the N optical communication devices2C-2-1to2C-2-N, one optical communication device2C-2must be connected to the wavelength division multiplexing multiplexer/demultiplexer10-2.

In order to provide paths with different wavelengths, the wavelength division multiplexing multiplexer/demultiplexers10-1and10-2are configured to allocate different wavelengths to the paths from the wavelength division multiplexing multiplexer8-1of the wavelength division multiplexing multiplexer/demultiplexer10-1to the wavelength division multiplexing demultiplexer9-2of the wavelength division multiplexing multiplexer/demultiplexer10-2and from the wavelength division multiplexing multiplexer8-2of the wavelength division multiplexing multiplexer/demultiplexer10-2to the wavelength division multiplexing demultiplexer9-1of the wavelength division multiplexing multiplexer/demultiplexer10-1.

In order to perform wavelength division multiplexing for each transmission/reception path in a single optical fiber path, the FBG-DCM4-α performs wavelength dispersion compensation on optical signals generated by the optical signal generating units52-1and52-1-1to52-1-N of the optical communication devices2C-1and2C-1-1to2C-1-N. Then, the FBG-DCM4-β performs wavelength dispersion compensation on optical signals generated by the optical signal generating units52-2and52-2-1to52-2-N of the optical communication devices2C-2and2C-2-1to2C-2-N.

In the optical transmission systems1,1a,1b,1c,1d, and1eaccording to the first to fourth embodiments described above, an external measurement device may be connected in the optical communication devices2B,2C-1,2C-2,2B-1to2B-N,2C-1-1to2C-1-N, and2C-2-1to2C-2-N on the receiving side, so that the user can check the quality of received signals. The optical communication devices2B,2C-1,2C-2,2B-1to2B-N,2C-1-1to2C-1-N, and2C-2-1to2C-2-N on the receiving side may detect the quality of received signals and provide feedback on the result to the transmitting side. In this way, the user can check changes in the quality of received signals before and after the insertion of the FBG-DCMs4,4-1to4-N,4-α,4-β,4-α-1to4-α-N, and4-β-1to4-β-N.

The optical communication devices2A,2B,2A-1to2A-N,2B-1to2B-N,2C-1,2C-2,2C-1-1to2C-1-N,2C-2-1to2C-2-N according to the above-described embodiments may be implemented by computers. In such a case, the program to realize their functions may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read and executed by the computer system. The term “computer system” herein includes the OS and hardware such as peripheral devices.

The “computer-readable recording medium” refers to a portable medium such as a flexible disk, an optical magnetic disk, a ROM, and a CD-ROM, and other storage devices such as a hard disk which are built in a computer system. The “computer-readable recording medium” may also include an element for dynamically retaining a program for a short period of time such as a communication line when the program is transmitted over a network such as the Internet or a communication line such as a telephone line, or an element for retaining a program for a prescribed time period such as a volatile memory inside a server or a computer system that serves as client in that case. The program may be used to implement some of the above-described functions or may also be combined with a program already recorded in the computer system to implement the above-mentioned functions or a programmable logic device such as an FPGA (Field Programmable Gate Array) may be used to implement the functions.

The embodiments of the invention have been described in detail with reference to the drawings, but the specific configurations are not limited by the embodiments, and designs and the like within the gist of the invention are encompassed by the invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to long-distance optical fiber communication with wavelength dispersion.

REFERENCE SIGNS LIST

1Optical transmission system2A,2B Optical communication device3Optical transmission path4FBG-DCM5Optical transmitting unit6Optical receiving unit31Optical fiber32Optical amplifier51Electrical signal generating unit52Optical signal generating unit61Optical signal receiving unit62Electrical signal processing unit