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1 Introduction Starting from the optical fiber communication occurs , FTTH access networks have been regarded as the inevitable direction of future development is the ultimate solution for broadband access. Many programs in the FTTH, which PON (Passive Optical Network) has aroused much concern as the current main optical access means. We know that PON technology in the years experienced APON, BPON to the current EPON, GPON. And with the Ethernet technology in metro networks in the spread and development of broadband access technology, people pay more attention to 1Gbit / s over broadband PON technology, the EPON, GPON. GPON is standardized by the ITU work, the main objective is to achieve 1Gbit / s access rate above. GPON frame structure is not based on any specified type of format, but a variety of user signals based on the original format of the package, so GPON bandwidth utilization, support a more substantial business advantage, while it also increases the system complexity, and GPON system more stringent requirements on the device, so its relatively high cost of the system. EPON is to cheap and easy transmission of Ethernet PON structure technology and combine it with a single Ethernet frame to transmit a variety of business, which makes simple economic EPON technology very popular. And EPON has the same transmission TDM, IP data and video broadcast capability, which for video broadcasting, is by extending the third wavelength (1550nm) to achieve, as RFoverlay. To save fiber resources and reduce the ONU (optical network unit) cost of the client, usually three to single fiber transmission technology to achieve such a comprehensive business transfer, which is the so-called Triplex. At the same time the client can send and receive analog and digital receiver modules became three to FTTH system requires a key module. This is the description of this Module. Introduced two RF overlay EPON EPON system consists of OLT (Optical Line Termination), ONU (Optical NetworkUnit) and optical fiber modules, the system using the Ethernet protocol. Optical Distribution Unit of the passive optical splitter device to OLT optical signals assigned to each ONU, an EPON OLT system can have 1 and 16 ~ 32 ONU. We call the signal from the OLT to the ONU for the downlink signal, ONU to the OLT signal for the uplink signal, PON up / down signal is generally used TDMA / TDM technology, TDM downlink signal by way of broadcasting, OLT will TDM bit streams Send to a feeder fiber, the optical splitter to power by the shunt, broadcasting to all of the ONU, each ONU can only remove part of the ONU-specific time slots in the information. In the upstream direction is more to the point, transmission is more complex, it uses time division multiple access (TDMA) by the passive optical splitter coupled to the information each ONU to transmit to the feeder fiber and the OLT, which makes it up access methods for the burst type. This brings a range of issues, such as optical signal burst firing, burst receiver, burst synchronization, ranging, dynamic bandwidth allocation and other issues. So-called RF overlayEPON, is on the Ethernet access network (EAN) standard IEEE802.3ah work with G.983.3 wavelength agreement provides that the data channel works in 1490 ± 10nm (downlink) and 1310 ± 50nm (upstream) wavelength, and CATV channels work in 1555 ± 5nm wavelength. EPON is the original system, by adding a wavelength to transmit CATV RF signals. PON downstream signal broadcasting work is also the best way to transmit CATV signals, so by adding a wavelength EPON in the CATV signal to transmit the video is the most cost-effective access technology. However, CATV analog receiver optical power requirement is relatively high (range normally required for the-8dBm ~ +2 dBm), the EPON system link loss is 26dB, so it is necessary to increase the central office to CATV EDFA 17dBm optical signal amplification to more than This makes fiber stimulated Brillouin scattering (SBS), self-phase modulation (SPM) and stimulated Raman scattering (SRS) and other nonlinear effects can occur [1], resulting in deterioration of system performance indicators. But the FTTH optical path analysis and system testing shows that for the three-passive optical network, the appropriate optical design program with minimal overhead to achieve optimal system performance, it can 20KM transmission distance and the splitting ratio was 1:32 in the BPON, EPON, GPON systems to achieve triple-play (TriplePlay) operations [2]. RF overlayPON system architecture shown in Figure 1, the client, a three-module that can implement all of the photoelectric conversion ONU side. 3 RF overlay EPON performance of the three modules required to Can see from the above description , PON downstream direction of continuous access mode for the uplink burst, so EPON system performance requirements of the three to the module are as follows: 1) PON TDMA upstream to point to multiple ways that work when one user, other users in the off state, but this time there are certain optical power output, the optical power that for the leaky power. Leaky power there will be interference on the central office OLT, in order to reduce the interference, the first requirement Leaky power as small as possible, it also requires upstream optical transmitter extinction ratio to be high. Leaky EPON system power requirements to less than-45dBm, extinction ratio greater than 9dB. 2) To improve the upstream bandwidth utilization, PON Burst Mode Transmitter on the opening / closing time provisions were made. EPON agreement module on / off time less than 512ns. 3) for CATV video signals, the state radio and television industry standard provides: cable system carrier to noise ratio (C / N) 43dB, the second beat combination than (C / CSO) 54dB, Cubic beat ratio (C / CTB) 54dB [4]. This indicator should be allocated in various parts of the system, so the performance requirements of CATV optical receiver is much larger than these values. In general, required optical receiver C / N 50dB, nonlinear indicators C / CSO 60 dB, C / CTB 65 dB. 4) EPON system, the user segment of the digital receiver sensitivity requirements than-26dBm. 5) As the three-module in the client, the work environment may be very bad, so the three-module to be cheap, stable performance and high reliability. 43 to the Module First of three to the device (Triplexer) selection of three modules to the core of the device is the device, which was completed for sub-wave / combiner and the modules required for photoelectric conversion. Therefore the device has the following three requirements: 1) known by the model described in the previous The e-commerce company in China offers quality products such as Multi Head Laser Manufacturer , Disco Laser Light Manufacturer, and more. For more , please visit Rgy Laser today!
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