JP2006129327A - Wavelength multiplexed transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accomplish a wavelength multiplexed transmission system in which influences of XPM are eliminated and noise is not caused in a data signal and a video signal in a single-core optical fiber transmission system which is used conventionally. <P>SOLUTION: In a wavelength multiplexed transmission system of the present invention, when transmitting a data signal and a video signal of different wavelengths while superimposing them on one optical fiber, the signals are transmitted by providing a means for attenuating the data signal or a data signal in the multiplexed signal of the data signal and video signal for a predetermined amount. As a means for attenuating the data signal for the predetermined amount, the data signal is attenuated by an optical attenuator or the like before superimposing the video signal and the data signal, or attenuated by the optical attenuator or the like after superimposing the video signal and the data signal. Furthermore, the video signal and the data signal are superimposed and the superimposed signal is then branched and attenuated. According to the present invention, it is possible to suppress the production of coherent noise to a signal due to cross-phase modulation (XPM) wherein light power is highly strengthened and it becomes obvious as a distance of optical transmission is made longer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wavelength division multiplexing transmission system for transmitting data signals and video signals having different wavelengths superimposed on a single optical fiber.

  2. Description of the Related Art In recent years, with the progress of information communication networks, wavelength multiplex transmission systems that superimpose and transmit signals of different wavelengths on one optical fiber, such as a CATV optical transmission system and an FTTH optical transmission system, have been proposed. This is because the output of the optical amplifier can be increased and the NF (Noise Figure) can be reduced, and an analog video signal can be transmitted on the FTTH due to the appearance of an optical transmitter of an external modulation system. Is mentioned.

  Of these, the CATV optical transmission system frequency-multiplexes broadcast waves of up to about 77 channels in a transmission band of 70 to 770 MHz, converts them into optical signals, and transmits them. There are two types of CATV optical transmission systems: a direct modulation system and an external modulation system.

  The CATV optical transmission system based on the direct modulation system modulates the current of a semiconductor laser (LD) with a video signal, and directly modulates and outputs the optical signal (see, for example, Patent Document 1). In the direct modulation method, the spread of the optical spectrum occurs due to a phenomenon called LD chirping, and the influence of light dispersion is likely to occur, but it can be configured at low cost. On the other hand, a CATV optical transmission system based on an external modulation system does not perform modulation with an LD, but performs signal modulation using an external modulation element, which is excellent in chirping characteristics, but requires an external modulator. However, it is more expensive than the direct modulation method in terms of cost (see, for example, Patent Document 2).

  In addition, the FTTH optical transmission system has a concept of using optical fiber for the access section to each subscriber and creating a high-speed information communication environment. A passive branch device (optical coupler) is provided in the middle of the optical fiber transmission line. Thus, for example, an optical wiring configuration using a PON (Passive Optical Network), which is a star-type network in which the transmission path is branched into 2 to 32, is configured (see, for example, Patent Document 3).

JP-A 63-169836 Japanese Patent Laid-Open No. 2004-120753 JP-A-6-177840

  By the way, the conventional techniques as described above have the following problems to be solved.

  That is, a phenomenon called cross-phase modulation (XPM) often occurs when a data signal and a video signal amplified by an optical amplifier are superimposed on a single optical fiber and transmitted. In some cases, coherent noise occurs in the signals of each other. In particular, when the video signal is an analog system, the noise of the received video appears significantly due to the influence of the data signal. The effect of XPM increases as the optical power incident on the optical fiber increases and as the optical fiber becomes longer. Therefore, if the optical fiber becomes longer and the optical power becomes higher with the development of the information communication network, the influence of the XPM becomes a problem that cannot be ignored.

  In order to avoid the above problems, a two-fiber optical fiber transmission system that transmits video signals and data signals through separate optical fibers is also conceivable. However, the transmission path requires a large number of optical fibers, which is expensive in terms of cost. This is not preferable because it becomes complicated and complicated from the viewpoint of the system configuration.

  The present invention realizes a wavelength division multiplexing transmission system that eliminates the influence of XPM and does not generate noise in each of a data signal and a video signal in a conventionally used single-core optical fiber transmission system.

  In order to solve the above-described problems, the present invention has the following configuration.

  That is, according to the present invention, as a first aspect, in a wavelength division multiplexing transmission system for transmitting a video signal and a data signal having different wavelengths superimposed on a single optical fiber, means for attenuating the data signal by a predetermined amount is provided. It is characterized by transmitting.

  According to a second aspect, in the first aspect, means for attenuating the data signal is provided before the video signal and the data signal are superimposed by a multiplexing optical coupler.

  Furthermore, as a third aspect, in the first aspect or the second aspect, an optical attenuator or an optical attenuating fiber is used as means for attenuating the data signal.

  As a fourth aspect, in the third aspect, the optical attenuator or the optical attenuation fiber attenuates a data signal having a wavelength of 1.49 μm.

Furthermore, as a fifth aspect, in a wavelength division multiplexing transmission system for transmitting a video signal and a data signal having different wavelengths superimposed on a single optical fiber, the video signal and the data signal are superimposed by a multiplexing optical coupler. Means for attenuating the combined signal is provided.
As a sixth aspect, in the fifth aspect, a means for attenuating only the data signal of the combined signal is provided.

Furthermore, as a seventh aspect, in the sixth aspect, an optical attenuator or an optical attenuating fiber is used as means for attenuating only the data signal.
As an eighth aspect, in the seventh aspect, the optical attenuator or optical attenuation fiber attenuates a data signal having a wavelength of 1.49 μm.
Further, as a ninth aspect, in any one of the fifth to eighth aspects, the means for attenuating the combined signal superimposes the video signal and the data signal by a combining optical coupler. It is provided immediately after.

  According to a tenth aspect, in the wavelength division multiplexing transmission system in which the video signal and the data signal having different wavelengths are superimposed and transmitted on one optical fiber, the video signal and the data signal are superimposed by the multiplexing optical coupler. The combined signal is branched and attenuated by a branching optical coupler.

  Furthermore, as an eleventh aspect, in the tenth aspect, the demultiplexing optical coupler is provided immediately after the video signal and the data signal are superimposed by the multiplexing optical coupler.

  According to the present invention, it is possible to provide a wavelength division multiplexing transmission system in which the influence of XPM is eliminated by attenuating a data signal by a predetermined amount and no noise is generated in each of the data signal and the video signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration example showing a first embodiment of a wavelength division multiplexing transmission system of the present invention. Referring to FIG. 1, a wavelength division multiplexing transmission system 1 according to the present invention includes an optical modulator 4 connected to a broadcast receiving facility 2 by a cable 31 such as a coaxial cable in order to transmit a video signal. And an optical amplifier 6 connected by an optical fiber 51, and an optical coupler 7 for multiplexing connected by this optical amplifier 6 and an optical fiber 52.

  On the other hand, in order to transmit data signals, GE-PON (Gigabit Ether-Passive Optical Network) center connected to devices 8 such as various servers and Internet host facilities and a cable 32 such as UTP cable (Unshielded Twisted Pair Cable). The GE-PON center side device 9 and the multiplex optical coupler 7 are connected to the GE-PON center side device 9 by the optical fiber 53. An optical attenuator 10 is inserted as means for attenuating the data signal in the middle of the optical fiber 53 between the coupler 7.

  The multiplexing optical coupler 7 is connected to a demultiplexing optical coupler (wavelength filter) 11 by a long-distance transmission optical fiber 54, and receives an optical image by an optical fiber 55 by a GE-PON subscriber side device 12 and an optical fiber 56. It is connected to the machine 13. Further, the GE-PON subscriber side device 12 is connected to a personal computer (PC), a switching hub (SW-HUB) or the like (not shown) by a cable 33 such as a UTP cable, and the optical video receiver 13 is also connected by a cable 34 such as a coaxial cable. It is connected to a video receiving facility (not shown).

  The operation of the wavelength division multiplexing transmission system 1 of the present embodiment having the above-described configuration will be described. First, the video signal from the broadcast receiving facility 2 is transmitted through the cable 31 and is modulated into an optical signal by the optical modulator 4, The light is input to the optical amplifier 6 through the optical fiber 51. The video signal amplified by the optical amplifier 6 is input to the multiplexing optical coupler 7. On the other hand, data signals from various devices 8 such as various servers and Internet host equipment are transmitted by the cable 32 and input to the GE-PON center side device 9.

  When this data signal has an optical output power intensity of +2.5 dBm, for example, the data signal needs to be −2 dBm or less so that XPM does not occur in the signal in which the video signal and the data signal are superimposed. There is. Therefore, as a means for attenuating the data signal, an optical attenuator 10 is provided in the middle of the transmission path consisting of the optical fiber 53 between the GE-PON center side device 9 and the multiplexing optical coupler 7 to attenuate the data signal. In this way, XPM is not generated in the signal in which the video signal and the data signal are superimposed, so that noise is not generated in each of the video signal and the data signal.

  In this embodiment, an example in which an optical attenuator is used as a means for attenuating a data signal is described. However, an optical attenuating fiber may be used instead of the optical attenuator. The optical attenuator and the optical attenuating fiber used at this time preferably have a function of mainly attenuating a wavelength of 1.49 μm in order to use a signal having a wavelength of 1.49 μm.

  Next, a second embodiment of the wavelength division multiplexing transmission system of the present invention will be described. FIG. 2 is a configuration example showing a second embodiment of the wavelength division multiplexing transmission system of the present invention. Hereinafter, the same portions as those described in FIG. 1 are denoted by the same numbers.

  In FIG. 2, a wavelength division multiplexing transmission system 1 according to the present invention first includes an optical modulator 4 connected to a broadcast receiving facility 2 by a cable 31 to transmit a video signal, and the optical modulator 4 and an optical fiber 51. An optical amplifier 6 connected, and an optical coupler 7 for multiplexing which is also connected to the optical amplifier 6 by an optical fiber 52. On the other hand, in order to transmit data signals, devices such as various servers and Internet host equipment The GE-PON center side device 9 connected by the class 8 and the cable 32, and the above-described multiplexing optical coupler 7 connected by the GE-PON center side device 9 and the optical fiber 53, In the second embodiment, multiplexing is performed in the middle of the long-distance transmission optical fiber 54 connected to the multiplexing optical coupler 7, that is, immediately after the multiplexing optical coupler 7. Optical attenuator 10 is inserted as a means for attenuating the combined signal by the optical coupler 7.

  Here, the optical attenuator 10 attenuates the combined signal as described above, but a data signal having a wavelength of 1.49 μm which has a large influence on the occurrence of XPM in the combined signal. It is preferable that only the material is attenuated. Although the insertion position of the optical attenuator 10 is not particularly limited, it is desirable that the optical attenuator 10 be provided immediately after the multiplexing optical coupler 7 as much as possible because the influence of XPM increases as the transmission distance of the optical signal increases.

  The multiplexing optical coupler 7 is connected to the demultiplexing optical coupler 11 by the long-distance transmission optical fiber 54 via the optical attenuator 10, and the GE-PON subscriber-side device 12 and the optical fiber 56 by the optical fiber 55. Thus, the optical video receiver 13 is connected. Further, the GE-PON subscriber side device 12 is connected to a personal computer (PC), a switching hub (SW-HUB) or the like (not shown) by a cable 33, and the optical video receiver 13 is connected to a video receiving facility or the like (not shown) by a cable 34. Has been.

  In the second embodiment, attenuation is applied so that the data signal is -2 dBm or less among the signals after superimposing the video signal and the data signal. In this way, XPM is not generated in the signal in which the video signal and the data signal are superimposed as in the first embodiment described with reference to FIG. 1, and therefore no noise is generated in the video signal and the data signal. It becomes like this.

  In this embodiment, an example in which an optical attenuator is used as a means for attenuating a data signal is described. However, an optical attenuating fiber is used instead of the optical attenuator as in the first embodiment. May be. The optical attenuator and the optical attenuating fiber used at this time preferably have a function of mainly attenuating the wavelength of 1.49 μm because the data signal uses a signal having a wavelength of 1.49 μm. .

  Furthermore, a third embodiment of the wavelength division multiplexing transmission system of the present invention will be described. FIG. 3 is a structural example showing a third embodiment of the wavelength division multiplexing transmission system of the present invention. In FIG. 3, a wavelength division multiplexing transmission system 1 according to the present invention includes an optical modulator 4 connected to a broadcast receiving facility 2 by a cable 31 and an optical modulator 4 and an optical fiber 51 to transmit a video signal. An optical amplifier 6 connected, and an optical coupler 7 for multiplexing which is also connected to the optical amplifier 6 by an optical fiber 52. On the other hand, in order to transmit data signals, devices such as various servers and Internet host equipment The GE-PON center side apparatus 9 connected to the class 8 by the cable 32, and the above-described multiplexing optical coupler 7 connected to the GE-PON center side apparatus 9 by the optical fiber 53. , A branching optical coupler (a coupler that splits the optical output power regardless of the wavelength) 14 is disposed immediately after the multiplexing optical coupler 7, and is disposed in the optical fiber 54. And to attenuate a signal after being superimposed multiplexing optical coupler 7 before performing long distance transmission that example 4 branches off.

  This is because one of the causes for the occurrence of XPM is that the transmission by the optical fiber becomes longer, but the signal obtained by superimposing the video signal and the data signal is transmitted by the long distance optical fiber. The signal is previously attenuated by branching so that XPM does not occur. For example, as shown in FIG. 3, the signal is branched into four by the branching optical coupler 14 immediately after the multiplexing optical coupler 7, and then each branched signal is transmitted by the optical fiber 54 over a long distance. The signal after long-distance transmission is divided into, for example, 16 branches for each closure 15 and transmitted to various devices (not shown). Even if it does in this way, since no XPM is generated, noise is not generated in each of the video signal and the data signal.

  The number of branches of the branching optical coupler is not particularly limited, and an optimal number of branches may be selected as appropriate in order to obtain a target attenuation.

It is a figure showing 1st embodiment of this invention. It is a figure showing 2nd embodiment of this invention. It is a figure showing 3rd embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wavelength multiplexing transmission system 2 ... Broadcast receiving equipment 4 ... Optical modulator 6 ... Optical amplifier 7 ... Optical coupler 8 for multiplexing 8 Equipment 9 ... GE-PON Center side device 10 ... Optical attenuator 11 ... Demultiplexing optical coupler 12 ... GE-PON subscriber side device 13 ... Optical video receiver 14 ... Branching optical coupler 15 ... closure

Claims (11)

  A wavelength division multiplexing transmission system for transmitting video signals and data signals having different wavelengths superimposed on a single optical fiber, wherein the data signals are transmitted by being provided with means for attenuating a predetermined amount.   2. The wavelength division multiplexing transmission system according to claim 1, further comprising means for attenuating the data signal before superimposing the video signal and the data signal by a multiplexing optical coupler.   3. The wavelength division multiplexing transmission system according to claim 1, wherein an optical attenuator or an optical attenuating fiber is used as means for attenuating the data signal.   4. The wavelength division multiplexing transmission system according to claim 3, wherein the optical attenuator or the optical attenuation fiber attenuates a data signal having a wavelength of 1.49 [mu] m.   In a wavelength division multiplexing transmission system for transmitting a video signal and a data signal having different wavelengths superimposed on a single optical fiber, a means for attenuating the combined signal after the video signal and the data signal are superimposed by a multiplexing optical coupler A wavelength division multiplexing transmission system.   6. The wavelength division multiplexing transmission system according to claim 5, further comprising means for attenuating only the data signal of the combined signal.   7. The wavelength division multiplexing transmission system according to claim 6, wherein an optical attenuator or an optical attenuating fiber is used as means for attenuating only the data signal.   8. The wavelength division multiplexing transmission system according to claim 7, wherein the optical attenuator or the optical attenuation fiber attenuates a data signal having a wavelength of 1.49 [mu] m.   The means for attenuating the combined signal is provided immediately after the video signal and the data signal are superimposed by an optical coupler for combining, 9. The claim according to any one of claims 5 to 8, Wavelength multiplex transmission system.   In a wavelength division multiplexing transmission system in which video signals and data signals having different wavelengths are superimposed and transmitted on a single optical fiber, the multiplexed signal after the video signal and data signal are superimposed by a multiplexing optical coupler A wavelength division multiplexing transmission system characterized in that it is branched and attenuated by a coupler. 11. The wavelength division multiplexing transmission system according to claim 10, wherein the demultiplexing optical coupler is provided immediately after the video signal and the data signal are superimposed by the multiplexing optical coupler.

Images