5 Gbit/s burst-mode experiments for high split extended reach PONs X. Yin, X.Z. Qiu, B. Baekelandt, C. Me´lange, T. De Ridder, J. Bauwelinck and J. Vandewege Burst-mode (BM) experiments at 5 Gbit/s on optically ampliﬁed high split passive optical networks (PONs) with extended reach are pre- sented. The evaluated systems include a DC-coupled burst-mode receiver (BM-Rx) integrated with a BM clock data recovery (BM-CDR) circuit, an inline EDFA and two branches of BM transmit- ters (BM-Txs). High optical power budget combined with very short guard time and receiver settling time was achieved. Introduction: Worldwide, the passive optical network (PON) is one of the most massively deployed ﬁbre access technologies designed to deliver broadband content over the ‘last mile’ to customers. The current G-PONs typically offer 2.5 Gbit/s downstream and 1.25 Gbit/s upstream, shared between 32 customers over a reach of up to 20 km. The latest G.984.6 standardises a long-reach PON, shared between 128 customers over a reach of 60 km. And the ITU-T FSAN study group for XG-PON1 systems aims at 10 Gbit/s downstream and 2.5 Gbit/s upstream. To greatly simplify network architectures and further reduce costs, research attention has turned to more radical network solutions based on optically ampliﬁed, high split, extended reach PONs. An innovative broadband optical network has been devel- oped within the EU-funded FP6 IST PIEMAN project. The PIEMAN network comprises an ultra-high-capacity hybrid WDM/TDM physical layer, and integrates access and metro networks into one system. This innovative broadband optical network evolves from today’s G-PONs and supports 32 upstream and downstream wavelengths. Each wave- length channel carries 10 Gbit/s data over a 100 km reach and connects up to 512 optical network units (ONUs). EDFAs are used to overcome the path loss [1, 2]. In this Letter, we focus on burst-mode experiments based on time-domain multiple access (TDMA) on a single wavelength channel. Speciﬁc 10 Gbit/s burst-mode physical medium dependent (BM- PMD) components were needed to realise the TDMA upstream trans- mission [3]. Three fully DC-coupled 10 Gbit/s BM-PMD chips have been designed and fabricated in a 0.25 mm SiGe BiCMOS process. They are located at the optical line termination (OLT) and show advanced features. A BM transimpedance ampliﬁer (BM-TIA) performs fast gain setting and automatic gain locking in ,6 ns on a packet-by- packet basis. A BM post-ampliﬁer (BM-PA) with automatic reset gener- ation and automatic burst detection was designed for a guard time as short as 25.6 ns and a preamble of ,23.8 ns [4]. A BM clock and data recovery chip (BM-CDR) performs oversampling clock phase recovery using novel mixed analogue/digital phase picking circuitry [5]. The DC-coupled BM receiver (BM-Rx) prototype containing the BM-TIA and the BM-PA ICs was originally designed and characterised for 10 Gbit/s. To relax the very challenging BM-PMD prototype real- isation, the critical uplink integration with the BM-CDR and an EDFA was performed at 5 Gbit/s. For the ﬁrst time, this Letter presents measurement results on the upstream burst-mode operation at 5 Gbit/s of all challenging BM-PMD components made in PIEMAN, integrated in an optically ampliﬁed high split extended reach PON with a very short overhead, thus a high network transmission efﬁciency. Experimental setups: Intensive lab experiments were carried out on four conﬁgurations using the BM-Rx prototype. The BM-Rx was ﬁrst tested with a BM transmitter (BM-Tx) back-to-back (B2B) as a baseline per- formance measure. Then the BM-Rx was integrated with the BM- CDR containing a 1  16 DeMUX. With an Agilent 81250 ParBERT the upstream BER (in BM operation) was measured at one of the 16 CDR output channels, as shown in Fig. 1a. Here the BM-CDR needs a 10 GHz clock input signal. For high split extended reach PONs, at least one BM-EDFA is required at the remote node (RN) to compensate for the optical distribution network (ODN) loss of the access portion. In Fig. 1b ‘Att1’ was used to set the input signal power in front of the EDFA, where a 231 dBm level corresponds to a high splitting factor of 512. ‘Att2’ was inserted to vary the input signal power in front of the BM-Rx for the uplink BER measurements. An optical bandpass ﬁlter (OBPF) with 3 dB bandwidth of 0.3 nm was inserted to remove ampliﬁed spontaneous emission (ASE) noise generated by the EDFA. Finally, two branches of BM-Txs were built, as shown in Fig. 1c, to emulate the worst TDMA scenario: strong bursts immediately followed by weak bursts. A gated semiconductor optical ampliﬁer (SOA) was made available by the FP7 ICT Euro-FOS project, and used to increase the optical output power of the second BM-Tx, in order to generate a sufﬁciently large loud/soft ratio for this experiment. OLT 81250 ParBERT generator analyser BM-Tx BM-Rx PIN-TIA BM-PA reset BM-CDR 1x16 DeMUX 1ch. 311Mbit/s data 5 GHz data 5 Gbit/s data 10 GHz clock in Att scope ONU a BM-Tx BM-Rx PIN-TIA BM-PA reset 81250 ParBERT generator analyser 5 Gbit/s data 5 Gbit/s data (–31dBm input in 512-split case) Att1 RN- EDFA Att2 OBPF OLT ONU ODN loss feed loss b c BM-Tx1 BM-Rx PIN-TIA BM-PA reset Att1 OBPF BM-Tx2 Att2 gated SOA generator2 ParBERT generator1 analyser splitter 5 Gbit/s received data 2.5 Gbit/s data2 gating signal loud/soft ratio=15.1dB OLT ONU1 ONU2 5 Gbit/s data1 Fig. 1 Upstream burst-mode experimental setups a Conﬁguration of BM-Rx with BM-CDR b Conﬁguration of BM-Rx with EDFA c Conﬁguration of BM-Rx with two branches of BM-Txs In all the above experiments, the BM-Tx emitted repetitive packets were 2.15 or 6.55 ms long and separated by a guard time of 25.6 ns. Each packet consisted of a 25.6 ns Rx preamble followed by a PRBS 2 31 2 1 payload, except for the BM-CDR testing. In this case, as BER was measured only on one of the 16 CDR output channels after the 1  16 DeMUX, a ﬁxed PRBS 2 15 –1 payload (32 767 bits) had to be used for matching the received patterns with the emitted patterns. Moreover, 24 bits of a 1010 sequence were added after the 25.6 ns Rx pre- amble for the clock phase alignment of the BM-CDR. Note that no exter- nal time-critical control signals (such as a reset pulse) are required for any of the experiments, which is a big advantage when implementing and operating the PON uplink in burst-mode operation [6]. Experimental results: Fig. 2 shows the measured BM-BER curves for the above-mentioned four setups. The sensitivity of the pin-photodiode BM-Rx in B2B conﬁguration was 215.6 dBm (BER ¼ 10 210 ) at 5 Gbit/s. This Rx sensitivity was limited by the wide 3 dB bandwidth of the BM-TIA, originally designed for 10 GHz operation, and by the fact that the BM-Rx burst detection circuitry of the BM-PA was designed for a 215 dBm threshold level as speciﬁed for this optically ampliﬁed PON system. The measured Rx burst-to-burst dynamic range was 16.1 dB. For the BM-Rx plus BM-CDR conﬁguration, the measured BM-Rx sensitivity was 214.4 dBm and the dynamic range was larger than 14.5 dB. So the penalty caused by the BM-CDR was 1.2 dB. Note that the BM-CDR requires a 10 GHz clock input as it was designed for 10 GHz. The performance penalty caused by the BM-CDR can reasonably be expected to be lower when a 5 Gbit/s BM-CDR is used for this experiment. For evaluating the uplink optical budget in a 512-way split case, the minimum input power of the EDFA was set to 231 dBm. This rep- resents the packets generated by ONUs experiencing the maximum ODN loss of 36 dB. The EDFA gain was set to 30 dB. By adjusting ELECTRONICS LETTERS 7th January 2010 Vol. 46 No. 1