KR100404517B1 - Optical Communication System using 4 Wavelength Circulator Add/Drop Type Wavelength Division Multiplexing - Google Patents

Abstract

The present invention is to install a wavelength pass add / drop optical module in the optical path connected between the existing transmitting station or base station and the receiving station or repeater 4 wavelength circulator add to expand the communication range without the addition of the optical path and repeater The present invention relates to an optical communication system using a / drop type wavelength division multiplexer, and more particularly, to an optical communication system comprising: a first wavelength division multiplexer for dividing / mixing a first wavelength and a second wavelength; A circulator connected to the first wavelength division multiplexer and transmitting the wavelengths inputted through two different ports through a specified path without mutual interference; A second wavelength division multiplexer, coupled to the first wavelength division multiplexer, for splitting the third wavelength in a communication line of the second wavelength; And a slave unit coupled to the circulator and the second wavelength division multiplexer, the slave unit comprising a third wavelength division multiplexer for splitting / mixing the first wavelength, the second wavelength, and the third wavelength. Therefore, according to the present invention, by installing a slave unit in the optical path connected to the base unit and the master unit of the repeater, the existing base station and the master unit can communicate without distortion or loss of signal, and can communicate with each other between the slave units. It works.

Description

Optical Communication System using 4 Wavelength Circulator Add / Drop Type Wavelength Division Multiplexing}

The present invention relates to an optical communication system using a four-wavelength circulator add / drop type wavelength division multiplexer, and more particularly, to a wavelength pass add / drop type in an optical path connected between an existing transmitting station or base station and a receiving station or repeater. The present invention relates to an optical communication system using a four-wavelength circulator add / drop type wavelength division multiplexer capable of widening a communication range without installing an optical fiber and a repeater by installing an optical module.

Recently, due to the progress of the mobile communication service, the general consumer is a non-demand region, ranging from mountainous wallpaper and remote islands that the mobile communication service could not reach, as well as underground spaces and apartment complexes remaining in the blind spot due to poor radio wave environment in the urban area. I want a higher quality service. However, in order to meet these demands, constructing and operating a base station at a high cost in a low-traffic area deteriorates the management account of the mobile operator and wastes national resources due to the inefficiency of the investment. Accordingly, there is a demand for a method that can secure coverage and improve call quality as a concept different from existing mobile communication systems. Advanced countries are actively reviewing relay systems using CATV networks, and considering the topographical characteristics of Korea, where more than 80% of the land is mountainous and hilly, the line-of-sight between base stations and relay stations The use of microwave or laser relay systems that need to be secured is very limited.

1 is a schematic configuration diagram of a conventional optical communication system, in which a conventional optical communication system 100 includes a base station 110 and a repeater 120, and the repeater 120 is again a master unit 125. ) And slave units 125a to 125d. In addition, although only one master unit 125 is illustrated in FIG. 1, three master units 125 may be connected to each base station 110, and four slave units 125a to 125d may be connected to each master unit 125. Can be.

The base station 110 serves as a bridge connecting the switching center (not shown) and the mobile terminal, a wired network connecting the base station 110 and the switching station, a wireless network connecting the mobile terminal and the base station 110 and the like. It consists of antenna, transmitter, receiver, and power supply for wireless connection, and is in charge of matching function so that they can be interconnected.

The master unit 125 of the repeater 120 is connected to the base station 110, and the slave units 125a to 125d are linked to the master unit 125 by an optical cable. Here, the optical communication from the base station 110 to the master unit 125 uses a wavelength of 1310 nm, and the optical communication from the master unit 125 to the base station 110 uses a wavelength of 1550 nm. Since the optical communication system 100 transmits and receives radio waves by using an optical cable, it is possible to implement excellent call quality that can communicate with minimal radio wave loss. Considering that the service range of the base station 110 is within about 1.5 km in the downtown area and about 5 km in the suburban area, the optical communication system 100 may have a maximum of 12 slave units in a base station 110 in a radius of 20 km. It can be installed in a short time, so it can serve a wide range of areas.

In such an optical communication system 100, by realizing a high-tech information communication network, a signal from one place in a subscriber network such as CATV or FITL (Fiber In To Loop) is distributed to several places or vice versa. A multiplexing device that combines this is necessary. Such a multiplexing device is not as simple as in the case of conventional communication cables and can be realized by a special device, that is, an optical coupler. In a very simple case, an optical coupler is commercially available, which can be from 1 x 2 (that is, splitting a signal into two channels) to 32 x 32 (that is, receiving 32 channels and then splitting them back into 32 channels). In the early days of optical communication, a complicated communication network configuration in which an optical fiber and an optical cable channel was expanded without using an optical coupler became a simple communication network by using an optical coupler. There are various types of couplers according to the information communication network configuration, such as a star coupler, a directional coupler and a tree coupler.

In addition, a wavelength division multiplexing device (WDM), which is used as one of a special coupler and divides the wavelength of light (signal), is used. For example, WDM separates 1310nm wavelength from 1550nm wavelength and inputs two different signals with different wavelengths, transmits them through one channel or fiber optic cable, and receives the integrated signal and separates them into two signals. Play a role. The mechanism of the WDM function is a grating method using the principle that the refraction and reflection change according to the wavelength, and a dichroic coating method using the principle that the specific wavelength passes through the filter but reflects other wavelengths. There is this.

However, such a conventional optical communication system has various problems. First, in the conventional optical communication system, since the network is constructed in a 1: 1, 1: 2, 1: 3 manner according to the installation and expandability of the master unit and the slave unit, the repeater demand has already reached the saturation state, and the slave unit is added. If you want to build it is inconvenient to establish a separate optical cable. In addition, the cost for the expansion of the optical cable is added to increase the cost burden of the carrier. Second, since the slave units are controlled by the master unit without being controlled by the base station, communication between the slave units is not free. Of course, communication between the slave units is also possible, but to realize this, additional equipment must be implemented in the slave unit. Third, the multiplexing method using the optical coupler is difficult to vary the wavelength and has a disadvantage of large and small losses during transmission depending on the branching ratio. It is difficult to adapt to a fluid environment because a fixed specific wavelength is used to distribute or combine desired wavelengths using an optocoupler.

Accordingly, the present invention has been made to solve the conventional problems as described above, the object of the present invention is a wavelength pass add / drop type 4 wavelength in an optical communication system using a conventional 1: 1 method 1310nm, 1550nm WDM The present invention provides an optical communication system using a four-wavelength circulator add / drop type wavelength division multiplexer to provide a low cost optical communication service without installing an additional optical cable by installing a slave unit composed of optical modules.

1 is a schematic configuration diagram of a conventional optical communication system,

2 is a schematic configuration diagram of an optical communication system according to the present invention;

3 is an internal configuration diagram of the slave unit of FIG. 2,

4A and 4B are conceptual views illustrating the internal structure and the optical path of the circulator used in the present invention.

5 is a signal flow diagram illustrating a connection relationship and a wavelength flow of a slave unit according to the present invention.

♣ Explanation of symbols for the main parts of the drawing ♣

210,500: base station 220,590: master unit

230, A: first slave unit 240, B: second slave unit

250: optical cable 510,550: first WDM

320,520,560: Circulator 530,570: Second WDM

540,580: Third WDM

In order to achieve the above object, the present invention provides a mobile communication service in a shaded / square area where radio waves do not reach, and an optical communication system for providing a high quality communication service by connecting a base station and a master unit to widen the communication range. And a plurality of slave units positioned between the master unit and the base unit and the master unit to communicate with each other, and independently communicate with each other without control of the base station and the master unit. A first wavelength division multiplexer for splitting / mixing two wavelengths; A circulator connected to the first wavelength division multiplexer and transmitting the wavelengths inputted through two different ports through a specified path without mutual interference; A second wavelength division multiplexer, coupled to the first wavelength division multiplexer, for splitting the third wavelength in a communication line of the second wavelength; And a third wavelength division multiplexer coupled to the circulator and the second wavelength division multiplexer, the third wavelength division multiplexer for splitting / splitting the first wavelength, the second wavelength, and the third wavelength, and the third wavelength division multiplexer of one slave unit. The first wavelength division multiplexer of the other slave unit is configured to be connected.

According to the present invention, the slave unit is connected between the base station and the master unit so that the slave units can communicate with each other, and the slave unit is installed on the existing optical line without the additional optical line. Therefore, the communication range can be widened and stable communication reliability can be realized. That is, the existing base station and the master unit is to communicate as it is, and the slave unit can communicate with each other independently. In addition, wavelength blocking to prevent interference of adjacent wavelengths is controlled so that the isolation ratio is approximately 60 dB using a fiber type or microlens type filter in each line. In some cases, the isolation ratio can be changed freely in the range of 25 to 60 dB.

Hereinafter, exemplary embodiments of an optical communication system using a four-wavelength circulator add / drop type wavelength division multiplexer according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a schematic configuration diagram of an optical communication system 200 according to the present invention. The optical communication system 200 includes a base station 210, a master unit 220, and slave units 230 and 240, respectively. The component of is connected with the optical cable 250. Here, although only two slave units 230 and 240 are shown, it is obvious to those skilled in the art that a plurality of slave units 230 and 240 may be connected according to the application environment of the present invention.

The base station 210 serves as a bridge connecting the switching center (not shown) and the mobile terminal, a wired network connecting the base station 210 and the switching station, a wireless network connecting the mobile terminal and the base station 210, and the like. It consists of antenna, transmitter, receiver, and power supply for wireless connection, and is in charge of matching function so that they can be interconnected. Since the components of the base station 210 are known to those skilled in the art, the detailed description is not provided herein.

The repeater minimizes transmission disturbances that occur when receiving the reception band signal and the shadow / square area (for example, buildings, department stores, malls, underground parking lots, subways, tunnels, etc.) where the coverage of the base station 210 cannot be secured smoothly. As a means for covering the above, it is to amplify the bidirectional signal to provide high quality service of a general base station level in a shadow area. The repeater consists of a master unit 220 and a slave unit 230, 240, the master unit 220 of the repeater is connected to the base station 210, a slave unit between the base station 210 and the master unit 220 230 and 240 are linked by optical cables. Repeaters may be used to cover shadows / squares in service areas or to extend coverage.

The base station 210 and the master unit 220 communicates using the existing method as it is. That is, the wavelength used when communicating from the base station 210 to the master unit 220 is 1310 nm, and the wavelength used when communicating from the master unit 220 to the base station 210 is 1550 nm. Also, in general, the wavelength used when communicating from the first slave unit 230 to the second slave unit 240 is 1510 nm, and used when communicating from the second slave unit 240 to the first slave unit 230. The wavelength to be used is 1310 nm, but the transmission wavelength can be set differently (for example, wavelengths of 1510 and 1530 nm). That is, the wavelength that can be used for communication between the slave units 230 and 240 may be freely selected and used within the range of 1300 to 1700 nm. The first slave unit 230 is directly connected to the base station 210 and the optical cable 250, the second slave unit 240 to the first slave unit 230 and the master unit 220 and the optical cable 250 It is connected.

3 is an internal configuration diagram of the slave unit of FIG. 2, wherein the slave unit 300 includes three WDMs 310, 330, and 340 and one circulator 320. Here, since the first slave unit 230 and the second slave unit 240 have the same configuration, only one slave unit 300 will be described. However, among the components of the first slave unit 230 and the second slave unit 240, the input direction and output direction of the circulator (that is, a port for inputting a wavelength and a port for outputting a wavelength) are opposite to each other. to be.

The first WDM 310 is an optical fiber type or microlens filter wavelength division multiplexer and performs a function of dividing / mixing a specific wavelength. That is, the WDM performs a function of adding a signal to be transmitted from each node or dropping a signal to be received. The optical communication method using WDM allocates light of different wavelengths to up and down signals and transmits them through the same optical fiber, which is almost similar to the frequency division multiplexing method of an electrical signal. In this method, by installing a wavelength multiplexing circuit at both ends of the optical cable and separating and extracting the up and down signals due to the difference in wavelength, communication can be carried out so that there is little leakage and mixing on the opposite side even if the optical cable is reflected in the middle. For example, a 1310 nm wavelength is separated from a 1550 nm wavelength, two separate signals are inputted at different wavelengths and transmitted through one channel, or an optical cable, and the integrated signal is received and then two wavelength divided multiplexers are used. Separate by signal. In addition, one optical cable can simultaneously send signals in opposite directions using a bidirectional coupler.

To implement optical communication using WDM smoothly, high gain and flat optical amplifiers, lasers that maintain accurate wavelengths, multiplexers and demultiplexers that combine or separate multiple wavelengths, and optical filters with low crosstalk are required. Modulation techniques for long distance transmission and distributed compensation techniques to further speed up a single channel are required.

Amplifying the weak signal without photoelectric conversion and restoring it to the original signal form is an indispensable element in high-speed optical communication. An erbium doped fiber amplifier (EDFA) is mainly used. Important variables for EDFA are gain flatness and output. If there is a gain difference depending on the wavelength, if the multi-stage amplification is performed, the power difference between the channels increases, and the signal of the other channel is weak because the amplifier output is saturated by the large signal. Therefore, it is desirable to select and communicate with a channel to be multiplexed by selecting a place where the gain of the amplifier is flat.

In addition, in order to maintain a constant wavelength spacing of each channel, there must be a laser diode (LD) operating at a desired wavelength, and a technique for continuously monitoring the wavelength of each LD and controlling it to not change is required. For this purpose, it is preferable to use LD (for example, Multiquantumwell DFB LD) which can select a wavelength of 40 channels or more at 0.8 nm intervals, and to determine the intensity of transmitted light by using an interferometer that transmits only for a wavelength of a predetermined interval. The current wavelength position of the method is adopted and used.

The method of implementing an arrayed waveguide grating (AWG) as a power line communication (PLC) circuit is a method of multiplexing optically combining wavelengths of multiple channels, each of which is modulated at a transmitter, or demultiplexing, which separates multiple transmitted channels by wavelength. As the number of channels increases, it is cheaper than other methods, and it is widely used in that it can be mass-produced once a specification is set. Therefore, it is very useful when branching / combining at an intermediate node or when the number of channels to be branched / combined increases. On the other hand, when the number of branching / coupling is small, a method using a fiber grating (Fiber Grating) manufactured to reflect only a specific wavelength is preferable. In addition, although optical loss was the main factor limiting the transmission distance in the optical communication around 1310 nm, as the EDFA is applied, chirp and dispersion of the LD are emerging as important factors for limiting the transmission distance. The chirp is a phenomenon in which the wavelength changes instantaneously with the change of the input current when LD is directly modulated, which causes the wavelength to become wider and the pulse is distorted according to transmission. In order to accomplish this, long-distance transmission uses a method of externally modulating a light source emitted from the LD without directly modulating the LD. A Mach-Zehnder interferometer mainly using LiNbO ₃ is used to realize such a modulation scheme.

The circulator 320 is connected to the first WDM 310 and performs a function of separating and demultiplexing bidirectional signals or merging remultiplexed bidirectional signals. The circulator 320 is an irreversible passive element composed of three or more ports. For example, when composed of three ports, the light component having a circulation structure such that the light input to the first port is output only to the second port and the light input to the second port is output only to the third port. The circulator 320 is applied to an optical fiber amplifier or bidirectional communication applied to a wavelength division multiplexing system. The internal structure and the optical path of the general circulator 320 will be described in detail with reference to FIGS. 4A and 4B.

The second WDM 330 is connected to the first WDM 310 and an external specific wavelength, and functions to multiplex or demultiplex the wavelength branched from the first WDM 310 and the external wavelength. Here, the second WDM 330 divides a desired wavelength in a communication line having a specific wavelength by using a spacing Spacing FiberBiconical Tapered (FBT) type or a bandpass filter WDM. In the present invention, 1510 nm is used by dividing the 1550 nm communication line. In addition, a wavelength band of 1510 nm / 1530 nm or 1480 nm / 1550 nm may be selected and used according to a communication environment. That is, the second WDM can be freely selected and used in the wavelength range of 1400 to 1700 nm. Other functions are the same as the first WDM 310.

The third WDM 340 is connected to the circulator 320 and the second WDM 330 and performs a function of splitting / mixing a specific wavelength. Here, the third WDM 340 uses an optical fiber type or microlens filter WDM, and only the connection relationship is different, and other functions are the same as the first WDM 310.

4A and 4B are conceptual views illustrating an internal structure and an optical path of the circulator 400 used in the present invention. More specifically, FIG. 4A illustrates an optical path traveling from the first port to the second photo. 4b shows an optical path traveling from the second port to the third port. The circulator 400 includes a first polarization beam splitter (hereinafter referred to as 'PBS') 410, a first prism 420, a Faraday Rotator 430, and a crystal rotor ( Quartz 45 ° Rotator) 440, the second PBS 450 and the second prism 460. Here, the functional description of each component of the circulator 400 will be omitted, and the description will be given based on the optical path.

First, an optical path traveling from the first port to the second port will be described with reference to FIG. 4A. The unpolarized light (━━) incident from the first port is separated into the s-polarized beam (------) and the p-polarized beam (━--━) through the first PBS 410. The s-polarized beam is reflected through the first prism 420 and rotated through the Faraday rotor 430 and the crystal rotor 440 to become a p-polarized beam. The p-polarized beam separated by the first PBS 410 is rotated through the Faraday rotor 430 and the crystal rotor 440 like the s-polarized beam to become the s-polarized beam, and through the second prism 460 The reflection is coupled to the p-polarized beam in the second PBS 450 and output to the second port.

Next, an optical path traveling from the second port to the third port will be described with reference to FIG. 4B. The optical path from the second port to the third port runs in the opposite direction to the path shown in FIG. 4A. However, since the Faraday rotor 430 is an irreversible rotor, even if light incident in the reverse direction is rotated by 45 ° by the crystal rotor 440, it is compensated by the Faraday rotor 430 so that the polarization state does not change. The PBS 410 is output to the third port.

Hereinafter, an operation relationship of an optical communication system using a four-wavelength circulator add / drop type wavelength division multiplexer according to the present invention will be described in more detail with reference to the accompanying drawings.

5 is a signal flow diagram illustrating a connection relationship and a wavelength flow of a slave unit according to the present invention.

First, before describing the operation of the present invention, an optical communication system in which two slave units A and B are connected between the base station 500 and the master unit 590 is constructed. Here, the slave unit installed close to the base station 500 among the two slave units is called the second slave unit B. The slave unit installed close to the first slave unit A and the master unit 590 is referred to as a second slave unit B. FIG. . In addition, the wavelength transmitted from the base station 500 to the master unit 590 is 1310 nm, the wavelength transmitted from the master unit 590 to the base station 500 is 1550 nm, and the first slave unit A to the second slave unit B The wavelength transmitted to) is 1510 nm and the wavelength transmitted from the second slave unit B to the first slave unit A is 1310 nm. Here, the communication wavelengths between the base station 500 and the master unit 590 and the second slave unit B and the first slave unit A using the same wavelength are used to distinguish each other from the base station 500 and the master. Assume that the communication wavelength between the units 590 is 1310Anm, and the communication wavelength between the second slave unit B and the first slave unit A is 1310Bnm.

First, looking at the path of the wavelength traveling from the base station 500 to the master unit 590, in order to communicate from the base station 500 to the master unit 590, it must pass through the slave unit in the middle, from the base station 500 The output 1310Anm is branched by the first WDM 510 of the first slave unit A and applied to the first port of the circulator 520. The wavelength input to the first port of the circulator 520 is output to the second port along the light path shown in FIG. 4A, and the detailed description of the light path from the first port to the second port is described in FIG. 4A. Since it is described in detail in the part, it is not described here. 1310Anm passing through the circulator 520 is combined through the third WDM is applied to the first WDM 550 of the second slave unit (B). 1310Anm applied to the second slave unit B is transmitted to the master unit through the same process as the first slave unit A.

Second, looking at the path of the wavelength from the master unit 590 to the base station 500, 1550nm applied from the master unit 590 is divided by the third WDM (580) of the second slave unit (B) 2 is input to the WDM 570. The 1550 nm input to the second WDM 570 is demultiplexed and combined by the first WDM 550 and then applied to the third WDM 540 of the first slave unit A. FIG. The 1550 nm applied to the first slave unit A is transmitted to the base station through the same process as the second slave unit B.

Third, looking at the path of the wavelength traveling from the first slave unit A to the second slave unit B, the communication wavelength from the first slave unit A to the second slave unit B uses 1510 nm. 1510/1550 40nm Spacing FBT type WDM is used to split 1510nm into 1550nm lines. The 1510 nm divided by the second WDM 530 of the first slave unit A is applied to the first WDM 550 of the second slave unit B through the third WDM 540, and then the second WDM Multiplexed by 570. The second slave unit B extracts 1510 nm multiplexed by the second WDM 570 to use for communication.

Fourth, looking at the path of the wavelength traveling from the second slave unit (B) to the first slave unit (A), the communication wavelength from the second slave unit (B) to the first slave unit (A) uses 1310Bnm. 1310Bnm is used as an input wavelength through one port (eg, the third port) of the circulator 560 of the second slave unit B. After passing through the circulator 560 of the second slave unit B, the 1310 nm is combined by the first WDM 550 to pass through the third WDM 540 of the first slave unit A, and then the first slave. It is input to the circulator 520 of the unit A. The wavelength input to the second port of the circulator 520 is output to the third port, and a detailed description of the optical path from the second port to the third port is described in detail in the description of FIG. 4B. Do not explain.

As described above, according to the present invention, the base station and the master unit, the first slave unit and the second slave unit are communicated at four wavelengths by dividing and combining three wavelengths by WDM and adding a communication line by a circulator. can do. Here, it is desirable to adjust the isolation ratio to about 25 to 60 dB using a fiber type filter to break the wavelength at which 1310 nm is transmitted to the 1550 nm line or 1550 nm to the 1310 nm line. Accordingly, in the present invention, 1310 nm, 1510 nm, and 1550 nm can be used to communicate independently of each other. The isolation ratio between each wavelength is at least -12dB, the isolation ratio per channel is at least -25dB, and the isolation ratio to prevent interference between 1310nm and 1550nm is -25dB or more, and the insertion loss of each wavelength is set to 2.2dB or less. . Further, the bandwidth of 1310 nm is ± 10 nm, and the bandwidth of 1510 nm and 1550 nm is ± 7 nm.

The above description is only for explaining one embodiment, and the present invention is not limited to the above-described embodiment and can be variously changed within the scope of the appended claims. For example, the shape and structure of each component specifically shown in the embodiment of the present invention may be modified.

As described above, according to the optical communication system using the four-wavelength circulator add / drop type wavelength division multiplexer according to the present invention, the conventional base station and the master unit are provided by installing a slave unit in an optical path connected to the master unit of the base station and the repeater. Can communicate without distortion or loss of signal, and can communicate with each other between slave units.

In addition, by installing a wavelength pass add / drop optical module in an optical path connected between an existing transmitting station or base station and a receiving station or repeater, the communication range can be expanded at a low price without the addition of the optical path and repeater. .

Claims (6)

In the optical communication system that provides a high quality communication service by connecting the base station and the master unit to provide a mobile communication service in the shaded / square area that the radio waves do not reach, and to extend the communication range, Located between the base station and the master unit includes a plurality of slave units for mutually communicating the communication wavelength of the base station and the master unit, and independently communicate with each other without control of the base station and the master unit, The slave unit A first wavelength division multiplexer for dividing / mixing an input first wavelength and a second wavelength; A circulator connected to the first wavelength division multiplexer and transmitting a wavelength input to two different ports through a designated path without mutual interference; A second wavelength division multiplexer, coupled to the first wavelength division multiplexer, for splitting a third wavelength in a communication line of the second wavelength; And A third wavelength division multiplexer coupled to the circulator and the second wavelength division multiplexer, the third wavelength division multiplexer dividing / splitting the first wavelength, the second wavelength, and the third wavelength; And the third wavelength division multiplexer of one slave unit and the first wavelength division multiplexer of the other slave unit are connected to each other to form an optical communication system using a four wavelength circulator add / drop type wavelength division multiplexer. The optical communication system according to claim 1, wherein the first wavelength is 1310 nm, the second wavelength is 1550 nm, and the third wavelength is 1510 nm. delete The method of claim 1, wherein the second wavelength division multiplexer adjusts the isolation ratio using an optical fiber type or microlens filter wavelength division multiplexer, The isolation ratio is an optical communication system using a four-wavelength circulator add / drop type wavelength division multiplexer characterized in that it is adopted in the range of 25 ~ 60dB. delete [5] The optical communication system of claim 4, wherein the second wavelength division multiplexer selects and uses a specific wavelength in a range of 1400 nm to 1700 nm.