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International audience; A 100 Gbit/s/λ PAM-4 fiber link with an optical budget of 30 dB and 20 km fiber reach is achieved in real time experiments. This is compliant with class A (20 dB) point to point (PtP) applications as mobile fronthaul for example, and with class N1 (29 dB) point to multipoint (PtMP) for residential market. We used an integrated externally modulated laser, an analog pre-equalizer, an optical booster amplifier and/or non-filtered preamplifier and direct detection without any digital signal processing (whether real-time or offline).

©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. An ONU transmitter for UDWDM PONs based on direct phase modulated distributed feedback lasers (DFB) through digital beat signals is proposed and experimentally tested. The amplitude and duty cycle of the modulating signal are optimized for a DPKS signal. We achieved sensitivities of -50.5 dBm, and -45 dBm for bit rates of 2.5 Gb/s, and 5 Gb/s respectively at BER = 4×10-3 with an intradyne coherent receiver.

We present a coherent ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) with enhanced spectral efficiency. The benefit of using Gaussian or Nyquist pulse-shaping filters at the transmitter is evaluated through numerical simulations and experiments. The transmitters consist of directly phase modulated distributed feedback (DFB) lasers through beat signals whose duty-cycle and amplitude are digitally adjusted. The results show that transmitting a Nyquist-shaped signal achieves a 25% spectral saving allowing to place 2.5 Gb/s/user data in 6.25 GHz channels. Furthermore, the proposed transmitter tolerates differential link-losses of 15 dB at Rx sensitivity of ¿44 dBm at BER=10¿3 with intradyne detection.

© 2016 [2016 Optical Society of America.]. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited. We demonstrate a monolithically integrated dual-output DFB-SOA, and conduct the field trial on a multi-user bidirectional coherent ultradense wavelength division multiplexing-passive optical network (UDWDM-PON). To the best of our knowledge, this is the first achievement of simplified single integrated laser-based neighboring coherent optical network units (ONUs) with a 12.5 GHz channel spaced ultra-dense access network, including both downstream and upstream, taking the benefits of low footprint and low-temperature dependence.

In this Letter, an efficient bidirectional differential phase-shift keying (DPSK)-DPSK transmission for a ultradense wavelength division-multiplexed passive optical network is proposed. A single distributed feedback laser at the optical network unit (ONU) is used both as the local laser for downlink coherent detection and the optical carrier for uplink. Phase-shift keying is generated using a low-cost reflective semiconductor optical amplifier (RSOA) at the ONU. The RSOA chip has the bandwidth of 4.7 GHz at the maximum input power and bias current. For uplink transmission, the sensitivity of the RSOA chip reaches -48.2 dBm at the level of bit error rate = 10(-3) for back-to-back, and the penalty for 50 km transmission is less than 1 dB when using polarization diversity.

Ultra-dense access network attracts people's attention recently; however, until now it is difficult to implement it commercially owing to cost, footprint, and the traditional complexity of coherent receiver. Single laser, especially integrated laser-based optical network unit (ONU) provides a potential system for simplifying the ONU. Here, we show a 2.5-Gb/s/user bidirectional transmission with 5-GHz channel spacing between uplink and downlink for ultra-dense wavelength division multiplexed. A monolithic integration on dual output dual electro-absorption modulated laser (DEML)-based ONU for “λ-to-the-user” network is demonstrated. Furthermore, bidirectional differential phase-shift keying (DPSK)-amplitude shift keying and DPSK-single side band transmission with low-footprint, monolithically integrated DEML at ONU are also tested. This work was supported by the European FP7 COCONUT Project (GA318515), Ph.D. fellowship donated by China Scholarship Council (201207040059), and the Spanish Ministry of Science and Innovation under grant TEC2011–25215 (ROMULA Project).

New technologies for ultradense WDM-PON (udWDM-PON), enabled by coherent techniques and low-cost devices, are developed for an efficient utilization of the optical spectrum, revealing that the “Wavelength-to-the-User” concept can be feasible. In this paper, an udWDM-PON with only 6.25-GHz channel spacing is implemented with conventional DFB lasers, for a splitter-based PON infrastructure with 256 ONUs. The results of the analysis of udWDM access network architecture with respect to their associated complexity, cost, and migration scenarios, exhibit the potential for higher aggregate throughput, higher split ratios, and node consolidation, when compared to competing technologies.

An UDWDM-PON with simple real-time ASK and DPSK transceivers at 6.25 GHZ channel spacing is validated in a field-trial with deployed fiber with power budget above 40 dB. This work presents final results of the Coconut European Project.

Advantages offered by coherent detection systems in access networks are not limited to the increase of power budget due to the superior sensitivity. Channel selectivity is another intriguing feature offered by coherent systems that can be exploited to enable advanced system and network functionalities for access systems. Among them, we focus here on the implementation of filterless optical networks and network reconfiguration capabilities which might be required to satisfy dynamic load balancing requests and new terminal activations. We show that in the access domain these functionalities do not require DSP-aided coherent receivers, but can be easily realized by means of simpler, fully analogue real-time coherent terminals matching the access network low-cost paradigm. This paper discusses these concepts and how they can be experimentally implemented by using a novel wavelength allocation algorithm and real-time analogue coherent transceivers based on DFB lasers, whose wavelengths are tuned by a simple temperature control.

We introduce a novel algorithm for real-time ONU activation (¿ - assignment) and reconfiguration (¿ - tuning) in WDM coherent PONs. The algorithm prevents service interruption of lighted channels and it is experimentally demonstrated by using real-time fully-analog coherent transceivers.

©2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. A bandwidth-limited distributed feedback laser directly phase modulated with a 5-Gb/s differential quadrature phase shift keying (DQPSK) signal is demonstrated in a statistical ultra-dense wavelength division multiplexing passive optical network. Optical DQPSK modulation was achieved by simply equalizing a four-level waveform. An intradyne receiver based on a 120° optical hybrid with straightforward differential decoding processing was used to detect and recover the data attaining a sensitivity of -38 dBm at BER = 10-3. Negligible penalty was observed when adding a second user at 5-GHz channel separation.

The results of the analysis of the COCONUT (“COst-effective COhereNt Ultra-dense-WDM-PON for λ-to-the-user access”) project architectures with respect to their associated cost, power consumption and migration scenarios are presented. COCONUT develops udWDM access with simplified coherent technology to allow for node consolidation, increased number of homes passed, and higher split ratios when compared to standardised technologies. COCONUT can operate in a very narrow spectral band due to the 6.25 – 12.5 GHz wavelength channel spacing and provides increased per user capacity when compared to currently deployed solutions. COCONUT technology shows 80% cost reduction when compared to a conventional coherent receiver. Also in terms of power consumption at 10G, the adopted transceiver solutions compare well to TWDM PON solution, achieving less than 2 W/Gb/s.

The statistical orthogonal frequency division multiplexing passive optical network (OFDM-PON) concept with multiband optical network units (ONUs) is experimentally tested with two users and an optical line terminal at 2.5/5 Gb/s total effective capacity with binary phase-shift keying (BPSK)/quadrature phase-shift keying (QPSK) modulation. Both downstream and uplink were measured based on intensity modulation and direct detection. The ONUs consisted of local nonpreselected wavelength distributed feedback laser sources centrally controlled to reduce overlapping probability. In addition, a radio-frequency mixing stage in the ONUs up/downconverts the user data to/from the OFDM signal, reducing the computational effort. Compared with ONUs processing the whole signal, the multiband approach presents comparable results with almost symmetrical power budgets of around 25 and 20 dB with BPSK and QPSK, respectively, which could increase up to 4.5 dB by allocating a spectral guard interval between the optical carrier and the OFDM data. Furthermore, elastic bandwidth allocation is explored, which is shown to compensate for up to 18 dB differential link loss.

We report a new scheme to support, cost efficiently, ultra-dense wavelength division multiplexing (UDWDM) for optical access networks. As validating experiment, we apply phase modulation of a reflective semiconductor optical amplifier (RSOA) at the ONU with a single DEB, and simplified coherent receiver at OFT for upstream. We extend the limited 3-dB modulation bandwidth of available uncooled To-can packaged RSOA (similar to 400 MHz) and operate it at 3.125 Gb/s with the optimal performance for phase modulation using small and large signal measurement characteristics. The optimal condition is selected at input power of 0 dBm, with 70 rnA bias condition. The sensitivities at 3.125 Gbis (at BER=10(-3)) for heterodyne and intradyne detection reach -34.3 dBm and -38.8 dBm, respectively.

A differential duobinary codification is proposed for directly phase modulating a 2GHz BW equalized DFB laser. The method was tested with homodyne coherent detection achieving 6.25Gb/s bitrate transmission with -38.5dBm Rx sensitivity at BER=10-3.

The response of a DFB was equalized with a simple RC network for modulating directly its phase and producing a BPSK signal. The system was tested with a heterodyne coherent detector at 1.25 Gb/s and 2.5 Gb/s showing a sensitivity penalty of around 1dB when compared with external phase modulation. The results indicate that the technique could be considered as a reliable low-cost ONU transmitter solution in udWDM-PONs.

A simple and low cost method for wavelength control based on centralized OLT monitoring and feedback of economical random non-preselected independent ONU sources is presented. The technique was dimensioned and experimentally tested in an OFDMA-PON with 1 Gb/s ONUs and 30 km of fibre along with the minimum optical spectral gap between consecutive ONU wavelengths. Results indicate that this method reduces the spectral overlap probability and increasing the number of users and cost-effectiveness of a PON

An access optical network based on 10Gb/s DML and R-EAM-SOA as transmitters was experimentally tested with a centralized MLSE equalizer to compensate for the chirp, dispersion and RB. Several scenarios were studied and results indicate that the fibre distance reach can be improved by 50% with the use of MLSE and FEC.

We analyze by simulation the performance of an optically amplified uncompensated duobinary system using a 64-state maximum-likelihood sequence estimation (MLSE) receiver (Rx) based on a Euclidean branch metric with variable postdetection nonlinear distortion exponent. We found that the optimum exponent depends on the accumulated dispersion, the Rx analog-to-digital converter (ADC) resolution, and signal clipping. On the other hand, we found performance to be weakly dependent on the exponent value. When using a finite number of ADC resolution bits, drastic signal clipping proved very beneficial in improving the performance of the MLSE processor. Assuming three resolution bits, with joint clipping and exponent optimization, uncompensated transmission at 10.7 Gb/s over 550 km of standard single-mode fiber could be achieved with essentially no penalty with respect to back-to-back.