Implementation of GEPON Optical Network Unit Small form factor. Transceiver

Transcription

1 Implementation of GEPON Optical Network Unit Small form factor Transceiver Yao-Ling Cheng*, Yi-Hsiung Lin, Yu-Chen Yu Opto-Electronic & Systems Laboratories/Industrial Technology Research Institute OES/ITRI, W310, Rm. 936, Bldg. 51, 195 Section 4, Chung Hsing Rd. Chutung, Hsinchu, Taiwan 310, R.O.C. ABSTRACT This paper describes a brand-new bidirectional optical transceiver module wit h Small form factor (SFF) dimensions for Optical Network Unit (ONU) specification in Gigabit Ethernet Passive Optical Network (GEPON). The discussion is addressed on optical component characterize, burst mode driving technique and burst mode phenomena measurement. The feasibility of burst mode ONU optical transceiver module for GEPON application has also been demonstrated. Keywords: SFF, ONU, GEPON, burst mode 1. INTRODUCTION GEPON is expected to be an ultimate solution for broadband access because of fiber unlimited bandwidth characteristic, low infrastructure deploying cost, bandwidth efficiency utilize and network service extended capability. This kind of application meets a transmission distance of 10km~20km and complete FTTC, FTTB or FTTH. GEPON ONU transceiver owns burst mode transmission ability for upstream data processing and Ethernet Internet Protocol data net working for downstream. Related standard association still deals with these issues and provides regulation. This paper shows a preliminary GEPON ONU transceiver module and verifies burst mode character with current standard specifications [1]. Bidirectional dual wavelengths optical component source demand, burst-mode driving technique, ONU implementation and burst mode transmitter testing results are also demonstrated. This paper presents a standard beforehand GEPON ONU transceiver and related parameters especially burst mode items are discussed and tested. 2. EXPERIMENTAL SETUP The GEPON ONU transceiver module is designed and completed as shown in fig.1. PON s are attractive for delivery of high bandwidth data directly to the home. Figure 2 shows the typical point -to-multipoint structure of a PON [2]. The

2 transceiver module package outline and footprint are based on the industry standard 2 * 10 Pin-Through -Hole (PTH) SFF module. The transceiver module package outline and footprint are based on the industry standard 2 * 10 Pin-Through -Hole (PTH). The transceiver module comprises a burst mode optical transmitter, continuous mode optical receiver. The 1.31 µm wavelength light is used for transmitting the signals from user s homes to a central office (CO). On the other hand, digital (voice/data) signals are transmitted from the CO to the user s homes with 1.49 µm light respectively.. By the way, upstream power penalty due to branches and simultaneously transmission on/off performance challenges light source and driving technique. To achieve all criteria, an GEPON ONU transceiver module owns a bidirectional dual wavelengths OSA, a burst mode laser diode driver (LDD), a continues mode limiting amplifier (LA) and system burst mode control mechanisms all compact integrated as illustration in fig nm CO OLT 1310 nm 1.3/1.49µ m WDM SMF HP- 8591E OC-2 4 Error Detector ONU1 ONU ODN (1 -N Splitter) Fig.1 The ONU SFF type transceiver with pigtail fiber Fig2. The measure setup of the GEPON ONU transceiver module 3. RESULTS AND DISCUSSION In GEPON architecture, a PON consists of an optical line terminal (OLT) at the CO, distribution fiber, optical distribution network (ODN) and an ONU at the subscriber s location. The maximum range of the network is 20 km and 32 physical ONU s can be support ed. Communication from the CO towards the subscribers is entitled downstream traffic (package signals are sent over the network at a wavelength of nm), the opposite direction is called upstream traffic using Time Division Multiple Access (TDMA) transmit signals towards CO at a wavelength of 1310 nm. Specific time slots are allocated for the transmission and reception of data by a subscriber, a precise and efficient timing management is inevitable. Furthermore, the user must turn on as fast as possible to transmit data immediately to raise efficiency of time utility rate. In between two data burst, the ONU Tx must keep silent and may not launch any optical power into the channel and avoid disturbing signals transmitted by other ONU s. In order to keep the upstream transmission efficiency high, the ONU Tx must be able to switch on/off the laser within a few nanosecond or bits preceding the upstream data [3]. In other words, the transmitter in the upstream direction must turn on/off quickly enough to be equal to the burst envelope signal. In the IEEE 802.3ah standard, there are two parameters, T ON and T OFF, to

3 define the ONU PMD tune on/ turn off time. They are both 64 ns for GEPON. In this subject, the main problem is whether the laser driver s ability can drive the laser to the bias level in a succinct duration. Figure 4 shows the burst envelope signal (upper pattern sequence in the figure) that enables the bias level (lower pattern sequence in the figure) is applied to enable the driver to test the transmitter actual T ON timing. The turn on and turn off of the burst are showed in Fig. 5 and Fig. 6. According to the IEEE 802.3ah GEPON standard, the delay of modulation signal has to be as long as 64- ns in 1.25 Gb/s to let the transmitter turn on fully. In addition, the transmitter just needs 64 ns in 1.25 Gb/s to turn off completely. Base on the analysis results, the bias level is reached within 12 pre-bias bits (9.6 ns).the disabling of the bias takes about 10 ns. The measured results in the system are as follows: Table 1.The Transmitter /receiver performances of the GEPON SFF ONT module are shown in Fig.7 and Fig. 8. The sensitivity of the receiver was 26 dbm. ONU Transceiver TxRx Module PD TIA LA CDR DATA OUT 1310 nm 1490 nm WDM Bidi LD BM LDD DATA IN CDR: Clock & Data Recovery TIA: Transimpedance Amp : Continue-mode Control BM: Burst-mode Control LA: Limiting Amp PD: Photo Diode LDD: Laser Diode Driver LD: Laser Diode Fig.3 Feature function blocks of ONU transceiver Fig.4 The External controls to measure T ON and T OFF timing measurement Figure 5 T on timing measurement Figure 6 T off timing measurement.

4 Figure 7 The Tx performances of the GEPON SFF ONT module. Figure 8 The Rx performances of the GEPON SFF ONT module with a transmitter turn on. Parameter Unit Specifications Bit rate (upstream/downstream) Gb/s 1.25/1.25 Transmission mode Tx: burst, Rx: continuous Operating wavelength nm Tx: / Rx: Bi-directional transmission 1-fibre WDM Transmission distance km 20 Mean launched power range Mean launch power of OFF transmitter dbm dbm < -60 Minimum extinction ratio db >10 Maximum spectral width nm < 3 (@1310nm) Burst Transmitter turn ON / OFF time ns <10/10 Bit error ratio Minimum sensitivity dbm -26 (Typ.) Minimum overload dbm -2 (Typ.) Table 1. The Specifications of the GEPON ONU transceiver module

5 4. CONCLUSION This paper performs a standard beforehand GEPON ONU burst mode transceiver design and presents a burst mode testing issue which defined in IEEE 802.3ah standard [1]. Important Burst mode Parameters such as laser turn on/off timing(= 9.6/10 ns) and driving methodology are deeply discussed. REFERENCES 1. IEEE802.3ah Gigabit Ethernet passive optical networks (GPON): Physical media dependent (PMD) layer specification, June, (2004). 2. G. Kramer, and G. Pesavento, Ethernet passive optical network: Building a next-generation optical access network, IEEE Commum. Mag., 40, 66-73,.(2002). 3. J. Segarra, and J. Prat, Optical Burst Switched Passive Access Network, ICTON, Mo. D2.6, , (2003). *yaoling@itri.org.tw; phone ; fax