JP2005236897A - Optical transmission system and optical transmission apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission system and optical transmission apparatus, capable of flexibly dealing with the changes in the situation of laying an optical fiber so as to improve operating convenience. <P>SOLUTION: In an optical transmission system for transmitting, via an optical transmission zone, wherein a plurality of optical signals can be accommodated, an optical signal which is modulated into an analog signal by a radio frequency signal used for wireless zone communication in a mobile communications system, wavelengths of two or more optical signals, among the plurality of optical signals, are made different from each other. Namely, different wavelengths are used for an uplink and a downlink in the optical transmission zone. Thus, if a number of optical fibers are available, the optical fibers are assigned to the links, respectively so that apparatus costs are reduced. When the number of optical fibers is not enough, the number of optical fibers is reduced by wavelength multiplexing. Thus, flexible system operation can be realized, while keeping an optical transmission apparatus as it is. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical transmission system that transmits an optical signal modulated with an analog signal such as a radio signal via an optical fiber, and an optical transmission device used in the optical transmission system. In particular, the present invention relates to an optical transmission system in which an optical signal is intensity-modulated and transmitted by a radio frequency signal used in a radio section of a mobile communication system such as IMT-2000.

  In recent years, communication systems that transmit analog signals as analog have been reviewed. In particular, an optical analog transmission system using an optical fiber has attracted attention, and is applied as a relay system in a CATV (Cable Television) network or a mobile communication network. In particular, a system applied to a mobile phone network is called a ROF (Radio Over Fiber) system.

  Application of the ROF system to a mobile communication network based on various standards such as a CDMA (Code Division Multiple Access) system represented by IMT-2000 or a TDMA (Time Division Multiple Access) system has been studied. The ROF system realizes long-distance transmission by transmitting an optical signal modulated by an analog signal in a radio band (for example, 2 GHz band).

  In this type of system, a device that exchanges analog signals with a base station is referred to as a master station device. A device installed in a remote dead zone or the like via an optical fiber and sending / receiving an analog signal to / from the master station device is called a slave station device. The transmission direction from the master station device to the slave station device is referred to as downlink, and the reverse is referred to as uplink.

  By the way, in the existing ROF system, the number of optical fibers connecting the master station device and the slave station device is fixed. That is, when using light of the same wavelength for both the downlink and the uplink, two optical fibers are used. When one optical fiber is used, the wavelength is different between the downlink and the uplink, and the optical signal of each link is multiplexed / separated by a wavelength poly-polymerization optical distributor provided in the apparatus.

  However, the status of optical fiber laying in the transmission section (number, quality, capital investment conditions, etc.) is fluid. For example, if an own optical fiber can be laid in a section using an optical fiber borrowed from another business operator, the operation cost is reduced, and a sufficient number of optical fibers can be used. The reverse is also possible. In this way, the number of optical fibers that can be used in the transmission section may change due to user needs and cost circumstances. In the existing ROF system, it is difficult to flexibly cope with such a situation, and some countermeasures are awaited because it causes inconveniences such as unnecessary consumption of operation costs.

  In a situation where the number of optical fibers is insufficient, the cost of the apparatus becomes high, but the cost of the transmission line can be reduced by using an apparatus incorporating a wavelength multi-polymerization light distributor. However, even if an environment where an optical fiber can be used abundantly is prepared from this situation, the benefits cannot be enjoyed, and an expensive apparatus must be used. Conversely, in a situation where the transmission line cost is low, an inexpensive single wavelength optical transmission device may be used. However, if the transmission line cost increases from this situation, the system operation cost must be increased accordingly.

A related technique is disclosed in Patent Document 1 below. This document discloses general matters that can be the basis of an ROF system.
Japanese Patent Laid-Open No. 9-200840 (paragraph numbers [0009] to [0011], FIG. 1)

As described above, in the existing ROF system, the number of optical fibers in the transmission section is fixedly determined by the installed optical transmission apparatus (master station apparatus and slave station apparatus). Therefore, it is necessary for the device manufacturer to manufacture various types of optical transmission devices in which the number of optical fibers consumed is changed, and excessive equipment investment is forced. In addition, the number of optical fibers cannot be changed after the installation of the optical transmission apparatus, and this cannot be dealt with even if the installation status of the optical fiber changes after the start of operation.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical transmission system and an optical transmission apparatus that can flexibly cope with changes in the installation status of optical fibers, thereby improving convenience in operation. Is to provide.

  In order to achieve the above object, according to one aspect of the present invention, an optical transmission section that can accommodate a plurality of optical signals, an optical signal that is analog-modulated by a radio frequency signal used in radio section communication of a mobile communication system. In the optical transmission system for transmitting via the optical signal, there is provided an optical transmission system characterized in that two or more of the plurality of optical signals have different wavelengths.

  By taking such a measure, if an optical fiber can be used abundantly in the optical transmission section, an optical fiber may be assigned to each individual optical signal. If the resource cost increases from this situation, for example, an optical multiplexer / demultiplexer may be used to share one optical fiber with optical signals having different wavelengths. Moreover, the same optical transmission device can be used before and after the change of the situation. That is, it is not necessary to replace the optical transmission device according to the change of the situation. Therefore, it is possible to flexibly cope with a change in the installation status of the optical fiber, and it is possible to improve the convenience in operation.

  ADVANTAGE OF THE INVENTION According to this invention, the optical transmission system and optical transmission apparatus which can respond flexibly to the change of the installation condition of an optical fiber, and aimed at the improvement in the convenience on operation can be provided.

[First Embodiment]
FIG. 1 is a functional block diagram showing a first embodiment of an optical transmission system according to the present invention. The system of FIG. 1 is provided to assist a mobile communication system such as a cellular phone network, and expands a service area developed by a base station apparatus CT using an optical fiber F. This type of system is known as a ROF (Radio Over Fiber) system. In FIG. 1, a master station 10 and a slave station 11 as an optical transmission apparatus are arranged to face each other via an optical transmission section. Downlink and uplink optical fibers F are respectively provided in the optical transmission section. That is, the optical transmission section can accommodate a plurality of optical signals.

  In FIG. 1, a radio frequency signal (hereinafter referred to as an RF signal) transmitted from the base station apparatus CT is taken into the master station 10 via a coaxial cable (not shown). In the master station 10, the RF signal is given to a laser diode (LD) 10b via an RF coupler 10a. The laser diode 10b generates intensity-modulated light corresponding to the analog waveform of the RF signal. This intensity-modulated light is transmitted to the slave station 11 via the optical fiber F in the downlink.

  In the slave station 11, the intensity-modulated light is converted into an electric signal by a photodiode (PD) 11a, thereby reproducing an analog RF signal. The reproduced RF signal is radiated from the antenna ANT to the space via the transmission amplifier and is received by the portable terminal TT.

  On the other hand, the RF signal transmitted from the portable terminal TT is received by the slave station 11 and applied to the laser diode 11b. The laser diode 11b generates intensity-modulated light corresponding to the analog waveform of the RF signal. This intensity-modulated light is transmitted to the master station 10 via the optical fiber F in the uplink.

  In the master station 10, the intensity-modulated light is converted into an electric signal by the photodiode 10c, and an analog RF signal is reproduced. The reproduced RF signal is given to the base station apparatus CT via the RF coupler / distributor 10a.

  Incidentally, in the first embodiment, the oscillation wavelengths of the laser diodes 10b and 11b are made different from each other. Specifically, for example, the oscillation wavelength of the laser diode 10b is set to the 1.3 μ band, and the oscillation wavelength of the laser diode 11b is set to the 1.5 μ band.

  With such a configuration, when the communication carrier lays the optical fiber F on its own, the optical fiber F is provided for each link when there is sufficient resources in the optical transmission section without a shortage of resources. Can be used. Therefore, the apparatus cost can be reduced and the initial capital investment can be suppressed. On the other hand, when an optical line is rented from another company, it may be as shown in FIG.

  FIG. 2 is a diagram showing a modification of the system of FIG. In the system of FIG. 2, optical multiplexers / demultiplexers 12 are installed at both ends of an optical transmission section, and one optical fiber F is shared by optical signals λ1 and λ2 having different wavelengths. Thereby, the number of optical fibers F can be reduced as compared with FIG. Accordingly, although the cost of the optical multiplexer / demultiplexer 12 is required, the number of optical fibers F can be reduced to reduce the operation cost of the optical fiber borrowing fee.

  FIG. 3 is a functional block diagram showing an existing optical transmission system for comparison. In FIG. 3, the same wavelength is used for both the downlink and the uplink. Therefore, an optical multiplexer / demultiplexer cannot be used, and two optical fibers F are always required in the optical transmission section.

  On the other hand, in the first embodiment, the optical signal that is analog-modulated by the radio frequency signal used for radio section communication of the mobile communication system is transmitted through the optical transmission section that can accommodate a plurality of optical signals. In the transmission system, the wavelengths of two or more of the plurality of optical signals are made different from each other. That is, different wavelengths are used for the uplink and the downlink in the optical transmission section. Thus, the system configurations of FIGS. 1 and 2 can be used properly according to the optical fiber installation conditions.

  That is, in the first embodiment, the optical multiplexer / demultiplexer 12 can be arbitrarily provided by making the transmission wavelengths of the optical transmission devices facing each other across the optical transmission section different from each other. As a result, the number of optical fibers used can be freely changed without replacing the optical transmission device itself. That is, even if there is no problem at the beginning of system operation, the number of optical fibers can be reduced when the number of installed optical fibers is gradually tightened, and the system configuration can be changed in stages. As a result, the network configuration can be changed efficiently. From these facts, it is possible to flexibly cope with a change in the installation status of the optical fiber, and it is possible to provide an optical transmission system that is improved in operational convenience.

[Second Embodiment]
FIG. 4 is a functional block diagram showing a second embodiment of the optical transmission system according to the present invention. 4, parts that are the same as those in FIG. 1 are given the same reference numerals, and only different parts will be described here. In FIG. 4, an optical repeater 13 is newly provided as an optical transmission apparatus. This optical repeater 13 can connect a plurality (two in FIG. 4) of slave stations 11 on the downlink side. As a result, there are a plurality of optical transmission sections. That is, one optical transmission section is formed between the master station 10 and the optical repeater 13, and one optical transmission section is formed between the optical repeater 13 and each slave station 11.

  The optical signal λ1 transmitted from the laser diode 10b of the master station 10 is temporarily returned to the RF signal by the photodiode 13a of the optical repeater 13. This RF signal is input to one of the laser diodes (without a sign) via the RF coupler 13c, and returned to the optical signal again. This optical signal is transmitted to one of the slave stations 11. On the other hand, the optical signal transmitted from the slave station 11 via the uplink passes through the optical repeater 13 and is transmitted to the master station 10 by the optical signal λ2. By providing the optical repeater 13, the distance of the optical transmission section can be extended or the number of slave stations 11 can be increased.

  In the second embodiment, different wavelengths are used in the uplink and the downlink in the optical transmission section between the master station 10 and the optical repeater 13. Thereby, the effect similar to 1st Embodiment can be acquired in the said area.

[Third Embodiment]
FIG. 5 is a functional block diagram showing a third embodiment of the optical transmission system according to the present invention. 5, parts common to FIG. 4 are given the same reference numerals, and only different parts will be described here. In FIG. 5, the optical repeater 13 includes a laser diode 13d and a photodiode 13e on the downlink side. The laser diode 13d generates an optical signal having a wavelength λ1, and the photodiode 13e receives an optical signal having a wavelength λ2.

  The system shown in FIG. 5 uses different wavelengths in the uplink and downlink in each optical transmission section between the optical repeater 13 and each slave station 11 shown in FIG. In the section, the same effect as that of the first embodiment can be obtained. In particular, since the number of optical fibers F required for four in the section can be reduced to two, the cost reduction effect according to the tightness of resources is great.

[Fourth Embodiment]
FIG. 6 is a functional block diagram showing a fourth embodiment of the optical transmission system according to the present invention. In FIG. 6, parts that are the same as those in FIG. 4 are given the same reference numerals, and only different parts will be described here.

  The system of FIG. 6 is configured to perform two-system sector division in the uplink of the optical transmission section between the master station 10 and the optical repeater 13. That is, the optical repeater 13 includes laser diodes 13b and 13f for uplink transmission, and the master station 10 includes photodiodes 10c and 10d for uplink reception. These diodes are provided at both ends of the sectorized uplink section. The laser diode 13f and the photodiode 10d make a pair to transmit / receive an optical signal having the wavelength λ1. The laser diode 13b and the photodiode 10c make a pair to transmit / receive an optical signal having the wavelength λ2. The optical signal λ1 is used for transmission of the 0 system signal, and the optical signal λ2 is used for transmission of the 1 system signal.

  The same effect as that of the first embodiment can also be obtained by the above configuration. Particularly, in the fourth embodiment, the number of optical fibers in the sector-divided link section can be freely changed, and the flexibility in system operation can be further improved.

  In addition, this invention is not limited to the said embodiment as it is. For example, a cheaper optical coupler or optical circulator may be used instead of the optical multiplexer / demultiplexer 12. Further, the present invention can be embodied by modifying the constituent elements without departing from the spirit of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a functional block diagram showing a first embodiment of an optical transmission system according to the present invention. The functional block diagram which shows 2nd Embodiment of the optical transmission system concerning this invention. The functional block diagram which shows the existing optical transmission system for a comparison. The functional block diagram which shows 2nd Embodiment of the optical transmission system concerning this invention. The functional block diagram which shows 3rd Embodiment of the optical transmission system concerning this invention. The functional block diagram which shows 4th Embodiment of the optical transmission system concerning this invention.

Explanation of symbols

  CT: base station apparatus, F: optical fiber, ANT ... antenna, TT ... mobile terminal, 10 ... master station, 10a ... RF coupler, 10b, 11b, 13b, 13d, 13f ... laser diode, 10c, 10d, 11a , 13a, 13e ... photodiode, 11 ... slave station, 12 ... optical multiplexer / demultiplexer, 13 ... optical repeater, 13c ... RF multiplexer / demultiplexer

Claims (4)

In an optical transmission system for transmitting an optical signal, which is analog-modulated by a radio frequency signal used for radio section communication of a mobile communication system, through an optical transmission section capable of accommodating a plurality of optical signals,
An optical transmission system characterized in that two or more of the plurality of optical signals have different wavelengths. In an optical transmission system comprising a plurality of optical transmission devices for transmitting an optical signal analog-modulated by a radio frequency signal used for radio section communication of a mobile communication system, through the optical transmission section,
An optical transmission system characterized in that transmission wavelengths of optical transmission apparatuses that exchange optical signals with each other across the optical transmission section are different from each other in the optical transmission section. In an optical transmission system comprising a plurality of optical transmission devices for transmitting an optical signal analog-modulated by a radio frequency signal used for radio section communication of a mobile communication system, through the optical transmission section,
When a plurality of optical signals are sent from one of a pair of optical transmission devices arranged across the optical transmission section to the other optical transmission device, two or more of the plurality of optical signals are transmitted. An optical transmission system characterized by having different wavelengths. In an optical transmission device used in an optical transmission system for transmitting an optical signal, which is analog-modulated by a radio frequency signal used for radio section communication of a mobile communication system, through an optical transmission section capable of accommodating a plurality of optical signals,
An optical transmission apparatus comprising optical transmission means for transmitting a plurality of optical signals having different wavelengths from each other in the optical transmission section.

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