KR100742653B1 - Fiber link monitoring scheme in bidirectional wdm-pon using ase-injected fp-ld - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high density wavelength division multiplex passive optical subscriber network system. In particular, the apparatus employs periodicity of Arranged Waveguide Grating (AWG), and places a reflector in each ONU (Optical Network Unit) to remotely monitor an optical path. It is about. In case of using a conventional fiber Bragg grating (FBG), each ONU uses a FBG corresponding to its own wavelength, but there is no mutual compatibility between ONUs. However, the present invention provides a reflector independent of the wavelength allocated to each channel. By using it, the compatibility between ONUs makes it easy to install the system and significantly reduces the number of maintenance ONUs. In addition, by using a light source of a different band from the transmission and reception signal, there is no interference, the ONU power is turned off, there is an advantage that can detect the line failure even when there is no optical signal.

WDM-PON, AWG, optical line surveillance, bidirectional optical subscriber network, high density wavelength division    

Description

FIBER LINK MONITORING SCHEME IN BIDIRECTIONAL WDM-PON USING ASE-INJECTED FP-LD} Bidirectional wavelength division multiplexing using a laser immersed in an incoherent light source

1 is a configuration diagram of a bidirectional high density WDM-PON system using a laser light source immersed in a conventional non-coherent light source.

2 is a block diagram of a high-density WDM-PON system having a light path monitoring device of the present invention.
3 shows periodic frequency transmission characteristics of 1 * N AWG.

4 is a structural diagram of an ONU having a light path monitoring reflector according to the present invention;

Figure 5 is an illustration of a device capable of monitoring the signal for monitoring the optical path according to the present invention.

6 is an exemplary diagram showing a spectrum of a downlink signal for each channel measured according to an exemplary embodiment of the present invention.

7 is an exemplary view showing a spectrum of an uplink signal for each channel measured according to an exemplary embodiment of the present invention.

8 is an exemplary view showing a spectrum of a monitoring signal according to the loss of the optical path measured according to an embodiment of the present invention.

 Exemplary view of the measurement result of the optical surveillance signal.

* Explanation of symbols for the main parts of the drawings

Tx: Optical Transmitter

Rx: optical receiver

AWG: Arrayed Waveguide Grating

BLS: incoherent broadband light source

SMF: Fiber Optic

ONU: Optical Network Unit

130, 135, 150, 155, 320, 325: wavelength division (WDM) coupler (separate and combine A, B band / C band)

160: A / B band wavelength division coupler

190: 1/90 tap coupler

191, 192: Optical splitter for monitoring signal monitor

330, 335: A band reflection filter

The present invention relates to a Dense wavelength division multiplexing passive optical network (WDM-PON) system, in particular subscriber side light in WDM-PON using a light source immersed in incoherent light. The present invention relates to a state monitoring device.

Recently, the telecommunications industry considers FTTH (Fiber To The Home) to be the ultimate solution for the rapidly expanding broadcast, Internet, and multimedia services, and it is easy to maintain, maintain, and manage optical networks. Passive optical subscriber network (PON) is adopted. Passive optical subscriber network is a structure in which one optical fiber is connected from the central base station (CO) to the remote node (RN), and then each individual optical fiber is connected from the RN to each subscriber. There is an advantage that can be significantly reduced for fiber cable installation. Among the passive optical subscriber networks, the wavelength division multiplexing passive optical subscriber network (WDM-PON) is capable of transmitting a large amount of data by assigning different wavelengths to subscribers and having excellent security. In addition, it is easy to improve the performance by narrowing the channel interval or increasing the transmission speed for each channel in accordance with the increase in demand for more subscribers and services.

However, these high-density WDM-PON systems require light sources with different wavelengths, and each light source requires high wavelength accuracy and stabilization of the oscillation wavelength, so that expensive DDM WP-PON systems, such as DFB LD (Distributed Feedback Laser Diode), There is a problem of using a light source. Recently, a low-cost light source capable of solving such a problem is known from Korean Patent (10-0325687) 'Light source for wavelength division multiplexing optical communication using a Fabry-Perot laser diode wavelength-immersed in the injected non-coherent light'. In addition, the WDM-PON system using the above light source is disclosed in the Republic of Korea Patent (10-0496710) 'bidirectional wavelength division multiplex passive optical network using a light source wavelength-immersed in the injected non-coherent light'.

In order to efficiently manage the network in the above system, the present invention needs to be able to monitor the state of the optical path and up and down signals in the CO. In two-way communication, the link is broken because the transceiver of one of the up and down signals does not operate or the loss of the optical path increases. Conventional WDM line monitoring is a method of directly monitoring the uplink signal using only a tap, and it is possible to know only whether an optical signal is normally received, and there is a disadvantage in that it is not a transmitter problem or a problem of the line itself. In addition, even when using optical time domain reflectometry (OTDR), which is commonly used for line monitoring, there is a problem in that subscriber line information is not known in the RN.

The present invention has been proposed to solve the above problems, in a bidirectional wavelength division multiplex passive optical network using a light source immersed in incoherent light, using a light source and a LED light source of a different band as a signal source and It is to provide a system for monitoring low cost, stable and reliable real time optical path.

Another object of the present invention is to immediately find out whether the problem of the optical fiber itself or the transceiver of the subscriber end when bidirectional optical communication failure occurs to shorten the system recovery time.

In order to achieve the above object, the present invention provides a wavelength dividing coupler (160) for combining down-light signals and supervisory signals in CO and B-, C-bands and other monitoring A-bands used for up-down optical signals. The AWG 220 is located at a remote node for splitting the multiplexed optical signal and the monitoring light at each wavelength, and the A-band reflectors 330 and 335 selectively reflecting the monitoring light at the ONU. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic diagram illustrating a bidirectional high density WDM-PON system using a light source whose wavelength is locked to an incoherent light source equipped with a light ray monitoring device, according to a first embodiment of the present invention. 191, CO 100 including the monitoring signal light source 185, RN 200, and ONU 300 including the monitoring signal reflectors 330 and 335.

3 is a diagram illustrating the frequency transmission characteristics of 1 * N AWG, and shows transmission characteristics based on a free spectral range (FSR). As shown in Fig. 1, an optical signal having a wavelength corresponding to λ _A1 , λ _B1 , λ _C1 , ... is output, and a port N emits light having a wavelength of λ _AN , λ _BN , λ _CN , ... do. At this time, each wavelength relationship is as follows.

λ _BN = m * FSR + λ _AN, λ _BN = n * FSR + λ _AN --------------------------- Formula [1] .

N = 1, 2, ..., N

Where FSR: Free Spectral Range of AWG, m, n is a nonzero integer.

The B-band incoherent light source 181 located in the CO 100 is spectrally divided by wavelength by 1 * N AWG 140 and injected into the optical transmitters 110 and 115 through the WDM coupler 130 and 135. do. At this time, the oscillation wavelength of the optical transmitter is automatically submerged in the wavelength of the injected light.

Downlink signals λ _B1 ,..., Λ _BN coming from the optical transmitters 110 and 115 pass through the WDM coupler as the inverse of the B-band incoherent light source path, and are then multiplexed in the AWG to allow the WDM coupler 150 and the circular. Passed through the radar 175, it is coupled to the monitoring light source LED by the A / B band optocoupler 160. The combined downlink signals λ _B1 ,..., Λ _BN and the supervisory light source λ _A are combined with the C-band incoherent light source λ _C by the WDM coupler 155.

Downlink signals output from the WDM coupler 155 (B band optical signal, A band monitoring light source, C band incoherent light source) are 10% branched from the tap coupler 190 to the down signal monitor optical splitter 192. 90% is demultiplexed from the 1 * N remote node 200 via the optical cable and delivered to each ONU 300. A (λ _A1 , ..., λ _AN ), B (λ _B1 , ..., λ _BN ), C (λ _C1 , ..., λ _CN ) band lights that are brought to the optical subscriber end are WDM couplers 320,325 C-band non-coherent light is reflected and injected into the optical transmitter (340, 345). On the other hand, the A and B band light passes through the WDM coupler 320 and 325 and the monitoring light λ _A1 ,..., Λ _AN are reflected by the A band reflectors 330 and 335 to go upward. It is input to the receivers 350 and 355.

On the other hand, the wavelength-locked light source λ _C1 from the optical transmitter 340 is combined with the reflected supervisory light λ _A1 and the WDM coupler 320 so that the uplink signals (λ _A2 , ..., λ _AN ) of different wavelengths are provided at the AWG 220 located at RN. And monitoring light (λ _C2 ,..., Lambda _CN ). The multiplexed upstream signals pass through the optical cable 210, and then in the 2 * 2 tap coupler 190, some (1%) go to the optical splitter 191, which can monitor the optical path and upstream signal, while the remaining 99% is WDM. Only the C band optical signal is separated from the coupler 155 and demultiplexed by different wavelengths in the 1 * N AWG 140 through the circulator 170 and the WDM coupler 150 and input to each receiver.

On the other hand, by monitoring the optical splitter (191, 192) can detect the up and down signal state for each channel, in particular, by dividing the spectrum of the optical splitter 192 in the spectrum of the optical splitter 191, the loss of each subscriber line line in the CO accurately You can calculate.

4 is a structural diagram of an ONU having a light path monitoring reflector according to the present invention, wherein the optical signals λ _A1 , λ _B1 , and λ _C1 branched from the first port of the 1 * N AWG of the remote node to the optical subscriber device are optical After passing through the adapter 301, the C band incoherent light λ _C1 is reflected by the WDM coupler 320 and injected into the optical transmitter 340. The λ _A1 and λ _B1 optical signals pass through the WDM coupler 320 to reach the A-band reflector 330, where the monitoring light λ _A1 is reflected and the B-band downlink signal λ _B1 is the optical receiver 350. Is entered. The oscillation wavelength of the optical transmitter 340 is immersed in the injected spectral partitioned incoherent optical wavelength (λ _C1 ). The uplink optical signal λ _C1 is coupled to the monitoring signal light λ _A1 reflected from the WDM optical coupler 320 and then transmitted to the remote node through the optical adapter 301.

FIG. 5 shows a wavelength tunable filter or an OSA (Optical Spectrum Analyzer) with a typical square ratio that can be connected to an optical splitter (191, 192) of a WDM-PON system equipped with a light path monitoring device for channel monitoring. .

FIG. 6 illustrates a spectrum measured by using an OSA in an optical splitter for a channel-specific downlink signal measured according to an exemplary embodiment of the present invention. For convenience, we have 4 channels. In the spectrum, it can be seen that there are downward ASE (Amplified Spontaneous Emission) light sources (A-band: for monitoring, C-band: injection locking for upstream signal) and four downlink signals (B-band).

FIG. 7 is a spectrum measured by connecting the channel monitor of FIG. 5 to the optical splitter of optical fiber No. 191. The four signals of part A are monitoring signals showing that each line state is normal. The B signal is a downward signal (about 35 dB) returned by Rayleigh backscatter from the fiber.

FIG. 8 is a line monitoring signal examined by changing an optical path loss to 0 dB (A), 1.2 dB (B), and 2.5 dB (C) using an optical attenuator. You can see dB and 5 dB increase.

As described above, it is possible to estimate the optical line loss by looking at the degree to which the monitoring signal decreases, and when the optical monitoring signal size is normal and there is no uplink signal, the optical path is normal, but the optical transmitter at the subscriber end operates. If not. And when the subscriber unplugs the patch. All downstream signals are returned 4% of the optical connector cross section for easy detection. If the optical path is disconnected before reaching the remote node, the line monitoring signal and the uplink signal disappear all over the channel.

Meanwhile, the present invention uses optical signals of different bands up and down, and the signal for monitoring also uses light sources of different bands from up and down signals. In the example of FIG. 5, the supervisory signal uses an E-band, the downlink signal uses a C-band, and the uplink signal uses an L-band. The band may be selectively changed according to embodiments and other bands S- and O-bands may be used.

The present invention described above is not limited to the described embodiments and drawings, and various changes or modifications can be made within the scope without departing from the spirit and technical scope of the present invention. It will be apparent to those having the above, therefore, a simple change according to the embodiment of the present invention will not be able to escape the scope of the present invention.

As described above, the present invention uses the periodic transmission characteristics of the AWG, and the ONU of the subscriber end is compatible with each other by using the same reflector regardless of the channel wavelength and is easy to install and maintain. Do.

In addition, it provides line-by-channel line monitoring of high density WDM-PON system using incoherent light source injection to FP-LD, and can monitor up-down optical transmitter status as well as line failure. Therefore, it is possible to improve the reliability of the optical subscriber network, there is an advantage that can provide a stable high-quality transmission service.

Claims (6)

An apparatus for monitoring a light path of a two-way Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) system including a central base station (CO), a remote node (RN), and a subscriber access unit (ONU), An optical splitter located at the CO, branched from a transmission optical fiber, the optical splitter capable of monitoring a portion of a supervisory signal or a multiplexed Wavelength Division Multiplexing (WDM) signal; A light emitting diode (LED) located in the CO and generating an A-band signal, which is a monitoring signal for monitoring a light path; WDM coupler located at the CO and distributing and combining the A-band signal and the B-band signal, which is a downlink signal, having a common port, a reflection port and a transmission port, and the A-band signal is input to the reflection port and the B- When the band signal is input to the transmission port, both the A-band signal and the B-band signal are output to the common port, and reversibly, when the A-band signal and the B-band signal are input to the common port, A first WDM coupler for outputting an A-band signal and a B-band signal to the transmission port, respectively; And A second WDM coupler positioned at the CO and ONU and distributing and combining the A / B-band signal and the C-band signal that is an uplink signal; And A reflector positioned in the ONU and reflecting only the A-band signal among the A-band signal and the B-band signal output from the second WDM coupler. Ray monitoring device of the bidirectional WDM-PON system comprising a. 2. The Fabry-Perot laser diode (FP-LD) according to claim 1, wherein the CO includes an arrayed waveguide grating (AWG) having periodic transmission characteristics as an optical multiplexer / demultiplexer, and is wavelength-locked as an incoherent light source. Ray monitoring device of the bidirectional WDM-PON system comprising a. The bidirectional WDM-PON system according to claim 1, wherein the reflector includes a WDM thin-film filter type reflector reflecting all A-band signals such that supervisory signals of all channels from the optical multiplexer / demultiplexer are reflected. Ray monitoring device. delete The optical splitter of claim 1, wherein the optical splitter may monitor one or more of a downlink data signal, a broadband downlink non-coherent light source, and a downlink supervisory light source, and uplink one or more of an uplink data signal or a line supervisory signal. The optical line monitoring device of a bidirectional WDM-PON system, comprising a 2 * 2 splitter that can be detected. The apparatus of claim 1, wherein the optical splitter is connected to a channel monitor including one of a variable wavelength filter and an optical spectrum analyzer (OSA) to monitor the optical path.

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