JP2006033686A - Single-core two-way communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-core two-way communication system capable of suppressing the deterioration of transmission characteristics caused by a Raman amplification effect in a subscriber optical communication system wherein two-way optical communication is performed by a single core optical fiber. <P>SOLUTION: A single-core two-way communication system comprises: a master station for transmitting a plurality of downlink data signals to a slave station and receiving a plurality of uplink data signals from the slave station; the slave station for transmitting the plurality of uplink data signals to the master station and receiving the plurality of downlink data signals from the master station; and a pair of optical branching filters provided between one terminal of a single core optical fiber and the master station and between the other terminal and the slave station for transmitting the plurality of downlink signals and the plurality of uplink signals via the single core optical fiber, respectively. The master station includes a means for transmitting a dummy signal of which the bits are inverted from a data signal and the wavelength is proximate to the data signal, in addition to an analog modulated video signal and the digital modulated data signal, and the slave station uses a wavelength selection filter to receive and demodulate the data signal separately from the dummy signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical communication system. More specifically, the present invention relates to an optical terminator (master station) in a switching center and a subscriber terminal accommodating device (slave station) accommodating a plurality of subscriber premises terminals. And a single-fiber bidirectional communication system for performing bidirectional optical communication through this single-fiber optical fiber.

  In order to respond to the demands for communication diversity and high speed, opticalization of the subscriber network, which is the basis of the communication infrastructure, is being promoted. In order to realize all-optical subscriber systems, it is indispensable to economically provide services currently provided by existing metal wires using optical fibers. As a method for this purpose, there is a PDS (Passive Double Star) optical subscriber transmission method. In this method, a center station C (OSU: Optical Subscriber Unit) has a plurality of slave units (ONU: Optical Network Unit) provided via an optical star coupler (SC) that is a passive component. Since a station is accommodated, a plurality of slave stations can be efficiently accommodated, and therefore, development is being advanced energetically.

In the conventional system, a two-core optical fiber was used as the transmission line, but in recent years, communication and video distribution were performed using a single-fiber optical fiber for the purpose of economicalizing the FTTH (Fiber To The Home) service. The structure which implement | achieves is proposed (for example, refer patent document 1, 2).
JP-A-5-183520 JP-A-8-23309

  In a conventional network, a data signal with a wavelength of 1.49 μm and a video signal with a wavelength of 1.55 μm are transmitted through the same optical fiber, and the wavelength of the data signal with a wavelength of 1.49 μm and the video signal with a wavelength of 1.55 μm is transmitted. Since the difference is only 0.06 μm, there is a problem that the video signal light having a wavelength of 1.55 μm is subjected to Raman amplification by the data signal light having a wavelength of 1.49 μm, and noise is generated in the video signal.

  FIG. 3 shows the wavelength characteristics of Raman gain generated by an optical signal having a wavelength of 1.49 μm. Due to the characteristics of Raman amplification in the silica-based fiber, the maximum gain occurs at about 1.59 μm, which is about 0.1 μm away from the optical signal having the wavelength of 1.49 μm, which is the excitation light, but the wavelength that is the wavelength of the video signal It can be seen that there is a considerable Raman gain even in the vicinity of 1.55 μm. As a result, a phenomenon occurs in which a data signal having a wavelength of 1.49 μm becomes excitation light and a video signal having a wavelength of 1.55 μm is amplified, and noise is generated in the video signal.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a single-fiber bidirectional communication system capable of suppressing deterioration of transmission characteristics due to a Raman amplification effect in a subscriber optical communication system that performs bidirectional optical communication with a single optical fiber. To do.

In order to achieve the above object, the present invention is a single-fiber bidirectional communication system that performs bidirectional communication through a single optical fiber, which transmits a plurality of downlink data signals to a slave station, and a plurality of uplink data signals from the slave station , A slave station that transmits a plurality of uplink data signals to the master station, and receives a plurality of downlink data signals from the master station, between one end of a single optical fiber and the master station and others A pair of optical multiplexers / demultiplexers that are respectively provided between the terminal and the slave station and allow a plurality of downlink signals and a plurality of uplink signals to be transmitted through the single optical fiber, and the master station is analog-modulated In addition to the video signal and the digitally modulated data signal, the data signal and the bit are inverted, and includes means for transmitting a dummy signal whose wavelength is close to that of the data signal. Providing fiber bidirectional communication system, characterized by receiving demodulated separately from the dummy signal No..
In the single-core bidirectional communication system of the present invention, it is preferable that the wavelength difference between the downstream dummy signal and the downstream data signal is in the range of 0.1 nm to 10 nm.
In the single-core bidirectional communication system of the present invention, the downstream dummy signal is preferably on the longer wavelength side than the downstream data signal.

  According to the single-core bidirectional communication system of the present invention, Raman amplification occurs between a data signal and a video signal having a slight wavelength difference, for example, a Raman amplification in which a downstream data signal having a wavelength of 1.49 μm affects a video signal having a wavelength of 1.55 μm. Can be erased with a dummy signal that has been bit-inverted, so that the influence of Raman amplification can be avoided and there is an advantage that good transmission quality can be obtained.

  In the single-core bidirectional communication system of the present invention, a signal light source generating a data signal having a wavelength of 1.49 μm (downlink signal A) is a signal having the same optical power and a wavelength of 0.1 to 10 nm, 1. A dummy signal (downstream signal A ′) in which the bit of the 1.49 μm data signal is inverted is combined with the 1.49 μm data signal, and then combined with a video signal (downstream signal B) of a wavelength of 1.55 μm, Transmit through fiber.

  On the receiving side, the downstream signal B, the downstream signal A, and the downstream signal A ′ are demultiplexed by the wavelength filter, and only the downstream signal A ′ is blocked from the downstream signal A and the downstream signal A ′ by the wavelength selection filter. The light is received by the light receiving device.

  When performing such bidirectional optical communication, the Raman amplification effect is exerted on the downlink signal B when the downlink signal A is ON, and the Raman amplification effect is not exerted on the downlink signal B when the downlink signal A is OFF. . On the other hand, since the downstream signal A ′ is turned on when the downstream signal A is OFF, this downstream signal A ′ exerts a Raman amplification effect on the downstream signal B, and conversely, when the downstream signal A is ON. Since the downstream signal A ′ is OFF, the downstream signal A ′ exerts a Raman amplification effect on the downstream signal B.

  In general, the Raman amplification coefficient becomes maximum when the wavelengths of the pumping light and the amplified light are about 100 nm apart (in the case of a wavelength of 1.55 μm band), and the gain gradually decreases regardless of whether the wavelength is nearer or farther than that. Since the signal A and the signal A ′ have different wavelengths, the effect of Raman amplification on the signal B is different. However, when the wavelengths are close to each other, almost the same Raman gain can be obtained. Accordingly, the closer the wavelengths of the signal A and the signal A ′ are, the better. However, if the wavelength is too close, it is difficult to separate the signal A and the signal A ′ on the receiving side. Limited by the resolution of the separation filter. Conversely, if the wavelengths of the signal A and the signal A ′ are separated, separation on the light receiving side is easy, but the difference in the effect of Raman amplification on the signal B is greatly different, and the influence of noise due to Raman amplification. There is a problem that the effect of removing is reduced.

  Here, when the absolute value of the wavelength difference between the signal A and the signal A ′ is the same, it is desirable that the wavelength of the signal A ′ is set longer than the wavelength of the signal A. This is because the Raman gain is gradually reduced on the shorter wavelength side than the maximum gain wavelength, whereas the gain is relatively steeply reduced on the longer wavelength side.

  As described above, regardless of the ON / OFF state of the downstream signal A, the signal B continuously receives the Raman amplification effect, and thus is not subject to power fluctuations due to the presence or absence of the Raman amplification effect. That is, deterioration of the video signal is avoided.

  1 and 2 are block diagrams showing an embodiment of the single-core bidirectional communication system of the present invention. FIG. 1 is a block diagram showing the overall configuration of the system. FIG. 2 is an Ethernet (registered trademark) passive optical network ( Hereinafter, this is referred to as “E-PON.”) It is a configuration diagram showing configurations of a station apparatus and an E-PON subscriber apparatus. In these drawings, reference numeral 1 is an optical fiber, 2 is a master station, 3 is a slave station, 4 is a broadcast (video) processing unit, 5 is a communication (data) processing unit, and 6 is an optical multiplexer / demultiplexer on the master station side. 8 is an optical transmitter, 9 is an optical amplifier, 10 is a star coupler, 11 is an optical amplifier, 12 is a switching hub, 13 is a device for an E-PON station, and 14 is a star. A coupler, 15 is a wavelength division multiplexing filter serving as an optical multiplexer / demultiplexer on the slave station side, 16 is a video-optical network unit (hereinafter referred to as V-ONU) which is a subscriber line terminating device, and 17 is an E-PON subscriber. Device, 18 is a 1.3 μm receiver, 19 is a 1.49 μm transmitter, 20 is a 1.495 μm transmitter, 21 is an optical coupler, 22 and 23 are WDM couplers, 24 is a 1.3 μm transmitter, and 25 is 1 .49μm receiver, 26 is 1.495μm blocking film It is.

  This one-core two-way communication system transmits a plurality of downlink data signals to a slave station 3 through a single optical fiber 1 and receives a plurality of uplink data signals from the slave station 3. A slave station 3 that transmits a plurality of downlink data signals from the master station, and is provided between one end of the single optical fiber 1 and the master station and between the other end and the slave station, respectively. It comprises a wavelength multiplexing filter 6 and a wavelength multiplexing filter 15 as a pair of optical multiplexers / demultiplexers that enable transmission of a plurality of downstream signals and a plurality of upstream signals through the optical fiber 1. In addition to the generated video signal and the digitally modulated data signal, the data signal and the bit are inverted, and a 1.495 μm transmitter 20 for transmitting a dummy signal whose wavelength is close to that of the data signal is included. It is characterized in that the received separated and demodulated data signal and dummy signal using a 1.495μm cutoff filter 26 which is a wavelength selective filter.

  In the example shown in FIGS. 1 and 2, the video signal transmitted from the master station 2 to the slave station 3 through the optical fiber 1 is an optical signal having a wavelength of 1.55 μm. Of the data signals between the master station 2 and the slave station 3, the downlink data signal uses an optical signal with a wavelength of 1.49 μm, the uplink data signal uses an optical signal with a wavelength of 1.3 μm, and the downlink data signal And a dummy signal transmitted to the slave station 3 side using a wavelength of 1.495 μm. In this example, the wavelength difference (absolute value) between the downstream data signal (wavelength 1.49 μm) and the dummy signal (wavelength 1.495 μm) is about 5 nm.

  The master station 2 includes a broadcast (video) processing unit 4 for sending a video signal having a wavelength of 1.55 μm to the slave station 3 side, and a communication (data) processing unit 5 for exchanging data signals with the slave station 3. In addition, the video signal from the broadcast (video) processing unit 4, the downstream data signal from the communication (data) processing unit 5, and the dummy signal are combined and sent to the optical fiber 1, and from the slave station 3 through the optical fiber 1. It comprises a wavelength multiplexing filter 6 as an optical multiplexer / demultiplexer that sends an upstream data signal sent to the station side to a communication (data) processing unit 5.

The broadcast (video) processing unit 4 mixes and distributes various received signals such as satellite broadcast (BS, CS) and terrestrial waves, and an optical signal (wavelength 1.55 μm). An optical transmitter 8 that transmits the video signal, an optical amplifier 9 that amplifies the video signal, a star coupler 10 that branches the amplified light into a number of ports (for example, 16 branches), and a branch side port. And a plurality of optical amplifiers 11.
The communication (data) unit 5 includes a switching hub 12 and an E-PON station device 13, and the switching hub 12 can be connected to the Internet.

  The slave station 3 includes a wavelength multiplexing filter 15, a V-ONU 16 that is a subscriber line termination device, and an E-PON subscriber device 17. The slave station 3 is provided in each subscriber's home, and a star coupler 14 is provided on the subscriber side of the optical fiber 1 so that the slave station 3 is connected to each branch side port of the star coupler 14. It has become.

  As shown in FIG. 2, the E-PON station device 13 on the parent station side includes a 1.3 μm receiver 18 that receives an uplink data signal having a wavelength of 1.3 μm transmitted from the child station 3 side, and A 1.49 μm transmitter 19 for transmitting a downstream data signal having a wavelength of 1.49 μm to be transmitted to the station 3 side, and a dummy signal having bits inverted with the same optical power as the downstream data signal, using a light source having a wavelength of 1.495 μm. 1.95 μm transmitter 20, optical coupler 21 for combining the downlink data signal transmitted from 1.49 μm transmitter 19 and the dummy signal transmitted from 1.495 μm transmitter 20, and this E-PON station apparatus 13 and a WDM coupler 22 interposed between the optical fiber 1 and the optical fiber 1.

  The E-PON subscriber unit 17 on the slave station side transmits a 1.3 μm transmitter 24 for transmitting an uplink data signal having a wavelength of 1.3 μm to be transmitted to the master station 2 and an uplink data signal transmitted from the master station 2 as a dummy. A 1.49 μm receiver 25 that receives the signal after passing through a 1.495 μm blocking filter 26 that blocks the signal, and a WDM coupler 22 interposed between the E-PON subscriber device 17 and the optical fiber 1. It is prepared for.

  In the single-fiber bidirectional communication system according to the present example, a video signal is placed on an optical signal having a wavelength of 1.55 μm, a data signal is placed on an optical signal having a wavelength of 1.49 μm, and multiplexed by a wavelength multiplexing filter. Transmit to. At this time, the E-PON station internal device 13 uses the wavelength 1.495 μm transmitter 20 to multiplex the dummy signal whose bit is inverted with the same optical power as the downlink data signal with the downlink data signal of the wavelength 1.49 μm. Then, the data is transmitted to each subscriber station 3 on the subscriber side through the optical fiber 1. On the slave station 3 side, only the downlink data signal having the wavelength of 1.49 μm is received by using the wavelength 1.495 μm cutoff filter 26 in the E-PON subscriber device 17.

  In this way, when a downlink data signal having a wavelength of 1.49 μm, which causes Raman amplification in a video signal having a wavelength of 1.55 μm, is sent from the master station 2 to the slave station 3 side, a wavelength (1. 495 μm) and a dummy signal whose bit is inverted with the same optical power is combined with the downlink data signal and sent to the subscriber station 3 on the subscriber side through the optical fiber 1, so that the downstream signal is turned on / off. Regardless, the video signal is constantly subjected to the Raman amplification effect, and thus is not subject to power fluctuations due to the presence or absence of the Raman amplification effect. Therefore, the influence of Raman amplification can be avoided and good transmission quality can be obtained.

In this example, the optical coupler 21 (3 dB coupler) is used for multiplexing the wavelength 1.49 μm data signal and the wavelength 1.495 μm dummy signal, but a wavelength multiplexer can be used instead.
Further, a wavelength multiplexer can be used in place of the wavelength 1.495 μm cutoff filter 26.

It is a block diagram which shows one Embodiment of the single core bidirectional | two-way communication system of this invention. It is a block diagram which shows the structure of the apparatus for E-PON stations and the apparatus for E-PON subscribers in the system of FIG. It is a graph which shows the wavelength characteristic of the Raman gain which generate | occur | produces with the optical signal of wavelength 1.49 micrometer in a silica type optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Master station, 3 ... Slave station, 4 ... Broadcast (video) processing part, 5 ... Communication (data) processing part, 6 ... Wavelength multiplexing filter, 7 ... Mixing / distribution part, 8 ... Optical transmission 9 ... Optical amplifier, 10 ... Star coupler, 11 ... Optical amplifier, 12 ... Switching hub, 13 ... E-PON station equipment, 14 ... Star coupler, 15 ... Wavelength multiplexing filter, 16 ... V-ONU, 17 ... E-PON subscriber equipment, 18 ... 1.3 [mu] m receiver, 19 ... 1.49 [mu] m transmitter, 20 ... 1.495 [mu] m transmitter, 21 ... Optical coupler, 22, 23 ... WDM coupler, 24 ... 1.3 [mu] m transmission 25 ... 1.49 μm receiver, 26 ... 1.495 μm blocking filter.

Claims (3)

  A single-fiber bidirectional communication system that performs bidirectional communication through a single optical fiber, a master station that transmits a plurality of downlink data signals to a slave station and receives a plurality of uplink data signals from the slave station, and the master station A slave station that transmits a plurality of uplink data signals and receives a plurality of downlink data signals from a master station, and is provided between one end of a single optical fiber and the master station and between the other end and the slave station, A pair of optical multiplexers / demultiplexers that allow a plurality of downstream signals and a plurality of upstream signals to be transmitted through the single optical fiber, wherein the master station adds an analog-modulated video signal and a digital-modulated data signal And means for transmitting a dummy signal whose bit is inverted with respect to the data signal and whose wavelength is close to that of the data signal. The slave station receives the data signal separately from the dummy signal using a wavelength selection filter, and receives and recovers the data signal. Fiber bidirectional communication system, characterized by.   The single-core bidirectional communication system according to claim 1, wherein a wavelength difference between the downstream dummy signal and the downstream data signal is in a range of 0.1 nm to 10 nm. The single-core bidirectional communication system according to claim 1 or 2, wherein the downstream dummy signal is on a longer wavelength side than the downstream data signal.

Images