KR100845412B1 - Wdm-pon networks with tone frequency - Google Patents

Abstract

The present invention relates to a WDM-PON network that can economically and easily perform initial installation, maintenance, maintenance and management of the WDM-PON network by assigning and modulating a unique tone frequency for each optical transmitter. A central base station device consists of a number of laser light sources and optical receivers, optical multiplexers and wide multiplexers, optical amplifiers, bandpass filters, tone frequencies with different optical wavelengths that are modulated by the addition of the tone frequency. And a monitor unit, wherein the subscriber unit includes a detachable optical branch coupling filter, a laser light source modulated by adding a tone frequency, and an optical receiver for monitoring the tone frequency.

WDM-PON, tone frequency, transfer, maintenance channel, bidirectional communication  

Description

WDM-PON NETWORKS WITH TONE FREQUENCY}

1 is for a conventional representative WDM-PON network

2 is a conventional configuration of a WDM-PON network configured as a bus network;

3 is a block diagram of a WDM-PON annular network according to an embodiment of the present invention.

4 is a diagram illustrating a function of adding a tone frequency to an optical transmitter and extracting a tone frequency from the optical receiver.

5 is an exemplary diagram of light wavelength and tone frequency allocation.

6 is a flowchart of preventing gain saturation of an optical receiver using a tone frequency.

7 is a block diagram of a subscriber-end device.

8 is an exemplary view illustrating that various types of services may be provided by one subscriber.

The present invention relates to a Passive Optical Network (PON) using Wavelength Division Multiplexing (WDM), in particular a tone frequency as well as a service signal for each laser light source used to deliver a service signal. It is about WDM-PON that can make initial installation, maintenance, maintenance and management of WDM-PON convenient, economical and safe by adding signal.

In the optical communication method using WDM, different optical wavelengths are allocated to each communication channel, and then optically multiplexed and transmitted to a destination through a single optical path, and then demultiplexed and separated into respective communication channels at the destination. This method has been widely used in backbone networks because of its large optical savings and large capacity transmission regardless of the communication protocol. Recently, however, as a large-capacity service such as IPTV has emerged, a subscriber network incorporating WDM technology has been proposed in the subscriber network.

The configuration of the conventional WDM-PON is shown in FIG. Each optical transmitter 101 in the central base station apparatus 100 in the central office (CO) has a different wavelength. The output of each transmitter is optically multiplexed through the optical multiplexer 102 and transmitted by sharing a single optical path to a remote node (RN: Remote Node) 110, and then divided by each wavelength in the remote node, thereby each subscriber-end device 103 , 104). In this case, the remote node functions optical demultiplexing for each wavelength. The uplink transmission from the subscriber station devices 103 and 104 to the central base station device 100 undergoes the reverse process.

The problem with the prior art is that the optical wavelengths assigned at each subscriber end are unknown. This creates difficulties in the initial installation and failure of the system. In order to know the optical wavelength, an expensive optical spectrum analyzer (OSA) must be used. Since the subscriber-end device 300 is located in a general home or building, etc., the user terminal should always have an OSA for installation and maintenance of the optical network unit (ONU).

In order to solve this problem, various methods based on the wavelength independent subscriber apparatus have been proposed. Firstly H. D. Kim, S.-G. Kang, and C.-H. Lee, "A low-cost WDM source with an ASE injected Fabry-Perot semiconductor laser," IEEE Photon, Technol. Lett., Vol. 12, no. 8, pp. 1067-1069, Aug. There is a method using the wavelength-locking phenomenon described in 2000.

Secondly, W. Lee, M. Y. Park, S. H. Cho, J. Lee, Ch. Kim, G. Jeong, and B. W. Kim, "Bidirectional WDM-PON based on gain-saturated reflective semiconductor optical amplifiers," IEEE Photon. Technol. Lett., Vol. 17, no. 11, pp. 2460-2462, Nov. There is a method using the semiconductor optical amplifier described in 2005. Third, N. J. Frigo, P. P. Iannone, P. D. Magill, T. E. Darcie, M. M. Downs, B. N. Desi, U. Koren, T. L. Koch, C. Dragone, H.M. Presby, and G. E. Bodeep, "A Wavelength-Division Multiplexed Passive Optical Network with Cost-shared Components," IEEE Photon, Technol. Lett., Vol. 6, no. 11, pp. 1365-1367, Nov. There is a method of feedback of a light source sent from the central base station described in 1994. These methods have the advantage of not paying special attention to the wavelength of light allocated to the subscriber end when installing or replacing the subscriber end device.

However, WDM-PON using these methods also provides the disadvantages of increased cost or limited environmental scope to ensure normal operation. Also, in reality, there are many places where a network needs to be constructed as shown in FIG. Information remains. That is, the case where a colorless light source is useful may be limited. In addition, the characteristics of the WDM-PON capable of high-capacity transmission are sometimes sacrificed to obtain the above advantages.

The present invention is to solve the above problems, and as in the prior art, it is not operating the network without the information about the wavelength assigned to each subscriber end and the light source wavelength used in each subscriber end, it is easy to use the light source wavelength information It is to operate the network using the light source wavelength information to be obtained in an economical way. The present invention can maintain the advantages, such as the variety and simplicity of the network configuration and ease of maintenance, high capacity transmission possibility of the WDM-PON.

An object of the present invention is a passive optical network (PON) using WDM, and in particular, low frequency tone frequency as well as high speed data for each laser light source used to transmit a service signal. By adding signals, WDM-PON can be configured and configured to make the initial installation, maintenance, maintenance and management of WDM-PON convenient, economical and safe.

In order to achieve the above object, the present invention provides a central base station (CO) consisting of a plurality of optical transceivers, optical multiplexers, wide area multiplexers, optical amplifiers, broadband filters, optical coupler coupler, optical transmitter and receiver, optical channel monitor. WDM optical subscriber network, characterized in that the configured subscriber end (ONU) in a single optical fiber configuration.

The present invention relates to a central base station (CO) consisting of a plurality of optical transmitters, a plurality of optical receivers, an optical multiplexer, a regional multiplexer, an optical amplifier, and a broadband filter, and a first subscriber unit comprising an optical filter, an optical transmitter, and an optical receiver. In the WDM optical subscriber network, the optical signals having a predetermined wavelength output from the plurality of optical transmitters are optically multiplexed in the optical multiplexer and the optical multiplexed. The optical signal is transmitted to the subscriber apparatus via the single optical line through the broadband filter, and the optical signal transmitted from the first subscriber unit is transmitted to the single optical line and then reversed by the wide multiplexer via the broadband filter. Multiplexed and transmitted to the plurality of optical receivers, the optical filter receives the optical signal in the single optical path, the optical signal of a predetermined wavelength assigned to the first subscriber device Block / receive and transmit to the optical receiver, and combine and transmit the optical signal of the small wavelength output from the optical transmitter into the single optical line, and each optical transmitter of the plurality of optical transmitters distinguishes the channel number of each transmitter A first tone frequency generator for modulating by adding different tone frequencies, and a second tone frequency generator for modulating by adding a predetermined tone frequency to distinguish the optical signal of the subscriber apparatus from the optical transmitter of the first subscriber device. The plurality of optical receivers and the optical receiver of the first subscriber device include an optical channel monitor unit for detecting a tone frequency in the received optical signal. It is about.

The present invention uses the tone frequency as a carrier wave in the wavelength division multiplexing optical subscriber network, modulates one of the ASK, FSK, and CDMA transmission schemes to establish a monitoring communication channel between the central base station and the plurality of optical subscriber devices. The present invention relates to a wavelength division multiplexing optical subscriber network for distinguishing channels by using a tone frequency, further comprising forming an optical monitoring channel unit.

The first subscriber device further comprises a second subscriber device for performing a first direction communication and a second direction communication in bidirectional communication with the central base station in the wavelength division multiplexing optical subscriber networks. The present invention relates to a wavelength division multiple access optical subscriber network that distinguishes channels using a tone frequency, characterized by constituting a single subscriber device.

The present invention is characterized in that in the wavelength division multiplexing optical subscriber networks, when any one of the first subscriber device and the second subscriber device communicates with the central base station, the other subscriber device maintains a standby state. The present invention relates to a wavelength division multiplexing optical subscriber network that distinguishes channels using tone frequencies.

In addition, the present invention is to add a different tone frequency to each optical transmitter located in the central base station in the WDM optical subscriber network to modulate the channel number and direction of each transmitter by zooming, and each located in the subscriber network The optical transmitter also adds different tone frequencies and modulates them so that the channel number and direction of each transmitter can be known to the central base station.

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

3 illustrates a preferred embodiment of the present invention. In an embodiment of the present invention, a central office terminal (COT) is an annular network composed of four subscriber units (ONUs). The COT divides each channel data into two signals and converts the COT_CW and COT_CCW into optical signals of predetermined wavelengths, respectively, and transmits them simultaneously in the clockwise and counterclockwise directions.

 The ONU extracts an optical signal of a predetermined wavelength allocated from the wavelength division multiplex optical signals transmitted in both directions from the COT, and selects and outputs a signal in a specific direction from the clockwise and counterclockwise optical signals. The ONU divides the signal to be transmitted to the COT into two signals, converts each signal into an optical signal having a predetermined wavelength, and transmits the signal clockwise and counterclockwise. The COT selects and outputs a specific signal from the clockwise and counterclockwise signals transmitted from the ONU.

Downlink data TX-DATA of channel 1 CH-1 is divided into clockwise CW data and counterclockwise CCW data by the switch units 303, 304, 305, and 306. Lose. Downlink CW data is transmitted to the COT-CW 301, and downlink CCW data is transmitted to the COT_CCW 302, respectively. COT-CW (Central Office Terminal-ClockWise, 301) converts the downlink CW data distributed in each channel into optical signals of predetermined wavelengths assigned to the corresponding channels, and splits the optical signals of the converted wavelengths into wavelength-multiplexed optical fibers. A wavelength division multiplexed uplink CCW optical signal transmitted in a clockwise direction through the 350 and generated in an ONU (Optical Network Unit) and transmitted in a counterclockwise direction, and uplink CCW data through an optical receiver for each channel. It converts to and transmits to the switch unit (303, 304, 305, 306) for each channel.

COT-CCW (Central Office Terminal-Counter ClockWise, 302) performs a similar function as COT-CW (301), and transmits the downlink CCW data through the optical fiber 351 through the optical conversion and wavelength division multiplexing In addition, the multiplexing and optically receiving the upstream CW optical signal transmitted in the clockwise direction is converted to the upward CW data to transmit to the switch (303, 304, 305, 306) for each channel. Each switch of the switch unit 303, 304, 305, 306 for each channel selects one of high quality data from the upstream CW data transmitted from the COT_CW 301 and the uplink CCW data transmitted from the COT_CCW 420 to the upstream data (RX-DATA). send.

The COT_CW 301 and the COT_CCW 302 are composed of an optical transmitter, an optical receiver, an optical multiplexer, a broadband multiplexer, a band separate filter, and an optical amplifier having separate wavelengths for each channel.

4 shows a functional block diagram of the COT_CW 301. The structure of the COT_CCW 302 is similar to that of the COT_CW 301, but only the difference in the transmission direction (the difference between the CW direction and the CCW direction) will be described.

The configuration of the COT_CW 301 is shown in Fig. 4A. The COT_CW 301 includes four optical transmitters 410-413, optical receivers 420-423, optical multiplexers 401, wide area multiplexers 402, optical transmitter amplifiers 403, and optical receiver amplifiers 404. And a band separation filter 405. Specific configurations of the optical transmitters 410-413 and the optical receiver are shown in FIG. 4 (b). Each transmitter is composed of a light source 412, a tone frequency generator 413, a downlink data 411 and a multiplier for synthesizing the tone frequency. The light source for each channel operates at different light wavelengths assigned for each channel.

For example, channels 1, 2, 3, and 4 are assigned different wavelengths of lamda-1, lamda-2, lamda-3, and lamda-4 and use light sources operating at the assigned wavelengths. The downlink CW data 411 to be transmitted to the ONU and a specific tone frequency 413 signal of about several tens of kHz to several tens of MHz representing the wavelength of the light source are modulated into a superimposed signal by a multiplier.

The signal shape before the downlink CW data signal 411 and the tone frequency overlap is shown in Fig. 4 (c), and the signal shape after the overlapping signal is shown in Fig. 4 (d). Each optical receiver comprises a high speed receiver 422, an optical tap coupler 423, a low speed receiver 424, and a channel monitor 425. The uplink CCW optical signal transmitted from the ONU is distributed at a small rate by the optical tap coupler 423 to be transmitted to the low speed receiver 424, and most of the remaining optical signals are transmitted to the high speed receiver 422. The high speed receiver 422 photoelectrically converts a high speed optical signal into uplink CCW data 421 and transmits the same to the switch unit of the corresponding channel.

Since the low speed receiver 424 is optimized for low speed data, it serves as a low bandpass filter electrically, so that the high speed upstream data is filtered out and detects only the low tone frequency signal. The detected tone frequency signal is input to the channel monitor circuit 425. By assigning a unique tone frequency to each optical wavelength used in WDM-PON, it is a simple and economical electronic circuit that can measure the existence of optical wavelength and the magnitude of the corresponding optical signal.

5 shows an example of allocating a tone frequency to each optical wavelength. A total of 16 tone frequencies have been allocated for the four channels. Four wavelengths are used upward (COT-> ONU) and four wavelengths are downward (ONU-> COT). In addition, two tone frequencies are allocated to each wavelength. Among the two tone frequencies, the first tone frequency is transmitted in addition to the optical signal transmitted in the clockwise direction, and the remaining second tone frequencies are added in addition to the optical signal transmitted in the counterclockwise direction.

 Accordingly, since the first and second tone frequencies indicate whether the corresponding optical signal is transmitted clockwise (CW) or counter clockwise (CCW) in the annular network, the WDM-PON This allows you to verify that the network is installed correctly during operation. In addition, the installation of the WDM-PON of the present invention facilitates the installation and maintenance / management of the WDM-PON network only by a simple instrument that can measure only the tone frequency, not an expensive optical spectrum analyzer.

The band separation filter 405 shown in FIG. 4 transmits the wavelength division multiplexed downlink optical signal transmitted from the optical transmission optical amplifier 403 to the optical path 406, and the wavelength division multiplexing transmitted from the optical path 406. It serves to transmit the uplink optical signal to the optical receiving optical amplifier 404. The uplink optical signal refers to an optical signal obtained by optically multiplexing the optical paths having different wavelengths output from each ONU.

The optical wavelengths of the uplink and downlink optical signals have different wavelength bands as shown in FIG.

The band separation filter 405 may be constituted by a lump filter having a multilayer film structure or a directional coupler using an optical fiber. Such a construction method is well known to those skilled in the art. The band separation filter 405 may be replaced by an optical circulator that outputs an input of a first port to a third port and outputs an input of a third port to a second port. The optical circulator is an optical element known to those skilled in the art as an optical element whose output varies depending on the input port.

The optical transmission amplifier 403 shown in FIG. 4 compensates for optical loss by amplifying the optical multiplexed optical signals to a sufficient size. The optical receiving amplifier 404 also greatly amplifies the signal before being demultiplexed. At this time, since the distance between the central base station (COT) and the subscriber unit (ONU) are all different, the optical signal transmitted from the ONU (310, 340 in Figure 3) close to the COT is a long distance ONU (320,330 in Figure 3) Since the transmission distance is short, the loss is small, and an optical signal having a relatively large intensity is input to the optical receiver 404, and the optical signal of the large intensity can saturate the optical receiver amplifier 404.

The saturated optical receiving amplifier lowers the amplification efficiency. There is a need for a method for preventing performance degradation of the optical receiving amplifier 404.

As yet another embodiment of the present invention, FIG. 6 illustrates a method of preventing saturation of an optical receiving amplifier using a tone frequency. The low speed receiver 424 of each channel photoelectrically converts an optical signal branched from the optical tap coupler 423 of each channel to output a tone frequency. The channel monitor 425 measures the intensity of the tone frequency and transmits it to the controller (not shown).

The operation of the controller is as follows.

As a first step, the controller receives the magnitude of the tone frequency of the N-th channel and checks whether the magnitude is a value within a preset range (601). If the magnitude of the tone frequency out of the preset range is continuously input more than a predetermined number of times, an alarm is output to the administrator.

As a second step. The amplitude of the tone frequency of the Nth channel is checked to be within a threshold range (602). In a third step, if the tone frequency is smaller than the threshold range, the Nth ONU is instructed to increase the transmit power intensity of the optical signal output. If the tone frequency is greater than the threshold range, the ONU decreases the transmit power intensity of the optical signal. (603).

 In a fourth step, when the tone frequency is within a threshold range or when the third step is completed, the channel to be examined is changed to the N + 1 th channel, and then the first step is started.

As a variation of the embodiment of Fig. 6, after performing the third step, the Nth tone frequency is measured, and the third step is repeated until the intensity of the tone frequency falls within the threshold range. After the repeating process, a fourth step is performed. This modification has the advantage of stabilizing the optical signal transmission power of the Nth ONU within a normal range in a short time.

The structure of the subscriber unit ONU is shown in FIG. The ONU 700 is divided into two communication blocks 710 and 720 that serve the same function. The first communication block 710 is responsible for clockwise communication, that is, the communication with the COT-CW, and the second communication block 720 is responsible for counterclockwise communication, that is, with the COT-CCW.

The subscriber-end device shown in FIG. 7 illustrates ONU-1 transmitting and receiving data of channel 1 transmitted from the central base station. The clockwise and counterclockwise optical signals transmitted from the channel 1 of the central base station to the ONU-1 use the same wavelength λ1 as mentioned above. When a signal is input in the clockwise direction from the central base station, λ 1 is blocked by the optical filter 712.

The ONU-1 monitors the tone frequency f1e (frequency # 1, East) indicating that the channel 1 is from the received optical signal, and then transmits uplink data in the same direction (counterclockwise).

At this time, the optical transmitter 713 is turned on, and the tone frequency of f5e generated by the frequency oscillator 714 is added to the optical transmitter 713. If a signal is first inputted counterclockwise from the central base station COT, the optical transmitter 722 is first turned on, and the optical transmitter 712 is not turned on but stays in the off state.

Subscriber devices (ONU-1, 700) are independently composed of two modules, as shown in Figure 7, each can be separated. Even if one module fails, the other module can be provided without interrupting network service, and the failed module can be repaired and replaced.

As another example of using the tone frequency, an operation channel or an optical monitoring channel (OSC) capable of transmitting data between the central base station and each subscriber station device by modulating the tone frequency in the same manner as frequency shift-keying (FSK). optical supervisory channel). Since the operation channel and the optical monitoring channel operate independently of the service channel, maintenance and operation of the network can be performed regardless of the failure of the service channel.

 As another example of use of the tone frequency, in the conventional WDM-PON or another type of PON, the operation channel cannot be configured until the service channel operates normally because the operation channel is built in the service channel band. That is, since the operation of the operation channel depends on the normal operation of the service channel, the communication protocol used for operation in the WDM-PON and the protocol used by the service channel are limited to the same protocol.

However, by using the tone frequency, a single subscriber station can configure the operating channel and the service channel independently, and thus can provide services of different protocols regardless of the communication protocol of the operating channel.

 FIG. 8 illustrates an Ethernet service and a synchronous digital hierarchy (SDH) service provided by one subscriber station. Channel 1 provides SDH service, and channel 2 provides Ethernet service.

These embodiments are intended to illustrate rather than limit the invention. It will be apparent to those skilled in the art to which this invention pertains that various changes, modifications, or adjustments to the above embodiments can be made without departing from the spirit of the invention. Therefore, the protection scope of the present invention will be limited only by the appended claims, and should be construed as including all such changes, modifications or adjustments.

The present invention relates to a WDM optical subscriber network that can easily install, maintain, maintain, and manage operations.

According to the present invention, by assigning a unique tone frequency to each optical transmitter of a WDM optical subscriber network according to the wavelength and direction, the optical wavelength can be determined in a simple and economical manner in the installation and maintenance of the optical subscriber device. Thus, there is no need for expensive devices such as optical spectrum analyzers.

According to the present invention, an optical supervisory channel (OSC) for each channel can be implemented using FSK modulation or various other modulation schemes using the tone frequency added to each optical transmitter as a carrier wave, so that even when a service channel fails, Maintenance and operation is possible.

In addition, the present invention monitors the input channel and delivers the result to each ONU when the optical amplifier is used to compensate for the loss caused when multiple ONUs are connected. It is possible.

Claims (5)

A central base station (CO) consisting of a plurality of optical transmitters, a plurality of optical receivers, an optical multiplexer, a regional multiplexer, and a broadband filter, and a first subscriber module including an optical filter, an optical transmitter, and an optical receiver, and a second subscriber module. In the WDM optical subscriber network, characterized in that a plurality of subscriber unit (ONU) is formed in an annular shape through a single optical path, Optical signals having predetermined wavelengths output from the plurality of optical transmitters are optically multiplexed in the optical multiplexer, and the optical multiplexed optical signals are passed through the single optical path through the single optical path through the first and second subscriber module. And the optical signals transmitted from the first and second subscriber modules are demultiplexed in a multiplexer through a wideband filter and transmitted to the plurality of optical receivers. The optical filter filters only an optical signal having a predetermined wavelength allocated to the subscriber device from the optical signal received by the single optical line and transmits the optical signal to the optical receiver and transmits the optical signal having a predetermined wavelength output from the optical transmitter to the single optical line. , Each optical transmitter of the plurality of optical transmitters includes a first tone frequency generator for modulating by adding different tone frequencies to distinguish channel numbers of each transmitter; The optical transmitter includes a second tone frequency generator for modulating by adding a predetermined tone frequency to distinguish an optical signal for a corresponding subscriber device; And the optical receiver and the optical receiver include an optical channel monitor configured to detect a tone frequency in the received optical signal. The first subscriber module performs a first direction communication of the single optical path, and the second subscriber device performs a second direction communication of the single optical path. Wavelength Division Multiplexer Optical Subscriber Network for Differentiating Channels Using Tone Frequency The method of claim 1, Using the tone frequency as a carrier wave, modulated by one of the ASK, FSK, CDMA transmission scheme further comprises an optical monitoring channel unit for forming a monitoring communication channel between the central base station and the plurality of subscriber devices Wavelength Division Multiplexer Optical Subscriber Network for Differentiating Channels Using Tone Frequency delete The method according to claim 1 or 2, When any one of the first subscriber module and the second subscriber module communicates with the central base station, the other subscriber module maintains the standby state. Type Optical Subscriber Network The method according to claim 1 or 2, The central base station includes a distributor for distributing downlink data for transmission to the first subscriber module and the second subscriber module; And a switch unit configured to further include a switch configured to select one of the upstream data transmitted from the first subscriber module and the second subscriber module. Subscriber network

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