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©2017 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. We experimentally demonstrate an innovative ultradense wavelength division multiplexing (UDWDM) passive optical networks (PON) that implements the full ¿-to-the-user concept in a filterless distribution network. Key element of the proposed system is a novel class of coherent transceivers, purposely developed with a nonconventional technical approach. Indeed, they are designed and realized to avoid D/A-A/D converter stages and digital signal processing in favor of simple analog processing so that they match system, cost, and power consumption requirements of the access networks without sacrificing the overall performance. These coherent transceivers target different use case scenarios (residential, business, fixed, wireless) still keeping perfect compatibility and co-existence with legacy infrastructures installed to support gray, time division multiplexed PON systems. Moreover, the availability of coherent transceivers of different cost/performance ratios allows for deployments of different quality service grades. In this paper, we report the successful field trial of the proposed systems in a testbed where 14 UDWDM channels (and one legacy E-PON system) are transmitted simultaneously in a dark-fiber network deployed in the city of Pisa (Italy), delivering real-time and/or test traffic. The trial demonstrated filterless operations (each remote node selects individually its own UDWDM channel on a fine 6.25-GHz grid), real-time GbE transmissions (by using either fully analog or light digital signal processing), multirate transmission (1.25 and 10 Gb/s), high optical distribution network loss (18-40 dB) as well as a bidirectional channel monitoring system.

A monolithically integrated dual electroabsorption modulated laser (DEML), consisting of distributed feedback laser (DFB) and electroabsorption modulator (EAM) sections, is proposed as a transmitter in an optical network unit with phase-shift keying (PSK) modulation. The DFB is directly modulated in phase, and the EAM section is applied for mitigating the residual amplitude modulation. The DEML, as compared with external phase modulator, has advantages of low cost, simplified design, low footprint, and reasonable power consumption, thus making it attractive for an ultradense wavelength division multiplexing passive optical unit. The system is validated at 2.5 and 5 Gb/s with intradyne detection.

©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.

COCONUT project demonstrated an innovative DWDM Passive Optical Network implementing the full λ-to-the-user concept in a filterless distribution fiber network. We make use of an innovative class of coherent transceivers that exploit the advantages of coherent detection in terms of sensitivity and channel selectivity in a cost efficient manner. The different transceivers developed target different use case scenarios, showing perfect compatibility with legacy infrastructures installed. In this paper, we report the successful trial of the proposed system in a testbed where 4 different coherent transceivers (plus one legacy E-PON system) ran simultaneously, operating over 14 DWDM channels, in a dark-fiber network in the city of Pisa, delivering real-time and/or test traffic. The testbed demonstrated filterless operations, multi-rate transmission (from 1.25 to 10 Gb/s/λ), high ODN loss (18 – 40 dB) as well as a bi-directional channel monitoring system.

We experimentally demonstrate a flexible direct phase modulated DFB laser through a beat signal for UDWDM PON. Rx sensitivity of −45 dBm at BER=10−3 and channel spacing of 7.5 GHz are achieved for 5 Gb/s.

We experimentally studied the implementation of forward error correction in software defined radio access networks by means of transceivers based on USRP. We tested the system in a 2 m wireless link and obtain an improvement in the performance of 4 dB for BPSK and QPSK modulation formats and almost of 5 dB for 8-PSK when adding a Reed Solomon code (127, 123) for reducing the errors. A characterization of the USRP as transceiver is also presented.

An optical access network with LTE, optical data, and CATV signals is experimentally studied. Rx sensitivities of −27.5 dBm, −26 dBm, and −24 dBm were obtained at bitrates of 1.25 Gb/s, 2.5 Gb/s, and 10 Gb/s at BER=10−4; whereas Rx optical power of −27 dBm is needed at an EVM of 28.2% for LTE. The minimum spectral separation is also measured showing the effect of the high power CATV on the other two signals.

© 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.

Direct phase modulation of DFB is demonstrated with DPSK, DQPSK and Duobinary modulation formats and detected with an intradyne receiver based on a 120-degree hybrid. The system is tested in a 50 km fibre link with 6.25 GHz channel spacing among users in a UDWDM-PON. By using higher modulation formats, the spectral efficiency can be increased in a single carrier system without spectral shaping while achieving an Rx sensitivity of −40 dBm at BER = 10−3 for 5 Gb/s in a 2 GHz bandwidth limited DFB.

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.

We demonstrate an 8-DPSK directly phase-modulated DFB with intradyne detection in a 50 km, 6.25 GHz channel spaced UDWDM-PON. A bit rate of 7.5 Gb/s is achieved with Rx sensitivity of -31 dBm at BER=10-3.

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.

We experimentally transmitted jointly an OFDM data and LTE signal in a single wavelength within an optical access network. The LTE was centered at a frequency of 1.5GHz while OFDM was left at baseband. After characterization of the waveforms and the receiver the LTE RF power was optimized to improve the performance of the system. Both signals were properly detected with a single photodiode. Receiver sensitivities of −29dBm and −25dBm were measured at a target BER of 10−3 for BPSK OFDM and LTE respectively. The results show that the RF frequency multiplexing technique can be employed towards an access network converging both fixed and mobile data.

©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.

A 6.25GHz spaced UDWDM PON is experimentally tested with directly-phase modulated lasers, polarization scrambling and homodyne detection. Bitrates from 1.25Gb/s to 5Gb/s per λ are achieved in a 50km fibre-link serving up to 1024 users.

We experimentally demonstrate a novel low-cost transmitter based on a directly modulated DFB with phase diversity in time. A sensitivity of −38dBm at 2.5Gb/s was achieved for 6.25GHz spaced UDWDM-PON with a simple intradyne receiver having 1 photodiode per polarization.

The performance of a directly phase modulated RSOA and an equalized DFB is compared with homodyne coherent detection for udWDM-PONs. Both device produce similar signals but the receiver sensitivity improves by 1.5dB at BER=10−3 with the RSOA because of its flatter phase response and less intensity modulation residual than the DFB.

We evaluate the duty cycle in RZ coded signals in an optical access network emulated with two users at a bit rate of 10 Gb/s. An optimum duty cycle of 75% was found for a fibre link of 25 km. This value remained when increasing the launched power up to 12 dBm. The range for 1 dB penalty was between 60% and 80%. In comparison with NRZ, with the optimum duty cycle the performance in terms of the receiver sensitivity for a BER of 2×10−4 improved by almost 4.5 dB while the bandwidth between neighbour users was limited to 45 GHz.

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.

Overcome the limited modulation bandwidth of low cost uncooled To-can packaged RSOA (∼400 MHz) and operate it at 3.125 Gb/s using homodyne techniques with the optimal performance for phase modulation via measured characteristics.

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.

We propose a heterodyne receiver with a single-photodiode per polarization for ONU receiver in low-cost udWDM-PON. This grants polarization diversity operation showing a penalty of 6dB in sensitivity compared to a balanced detector.

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.

The upstream of an OFDM-PON with direct modulated lasers tuned in temperature was experimentally tested. Results demonstrate flexible bandwidth allocation, and show it constitutes an efficient strategy to cope with the differential link-loss among the users in the PON.

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

A simple and low cost method for wavelength control of economical random non-preselected independent ONU sources is shown to increase the number of users in an OFDMA-PON. The method is based on OLT monitoring and thermal tuning control; it has been validated through Monte-Carlo simulations and a probabilistic model. The minimum optical spectral gap between the ONUs wavelengths that guarantees a tolerable amount of optical beat interference has been determined through an experiment.

An OFDM-PON with a simple centralized wavelength control of low-cost non-preselected independent ONU sources is presented, dimensioned, and tested experimentally. The rejection-ratio is reduced to less than 1% increasing the cost-effectiveness of the access network.

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.

A statistical OFDM-PON was experimentally tested with flexible bandwidth allocation for proper detection of ONUs with differential link loss. Sign-labels were also added to boost the system sensitivity by 3dB.

A survey of optical transmission techniques based on Orthogonal Frequency Division Multiplexing (OFDM) is presented. The characteristics and power budget/transmission performance of these methods are evaluated on optical access networks.

A low bandwidth RSOA-based WDM-PON system operating at 10 Gb/s is enhanced by means of a correlation-sensitive MLSE. By using this receiver configuration, lower number of states is needed and about 20% longer fibre distance can be achieved than using a conventional MLSE.

We analyze by simulation the performance of the differential quadrature phase-shift keying (DQPSK) modulation format in dispersion-managed multi-span WDM optical systems at 43 Gb/s, with 50 GHz channel spacing, in the presence of fiber nonlinearity. We show that the use of maximum-likelihood sequence-estimation (MLSE) receivers significantly helps to increase tolerance to dispersion map design. We also show that the use of an MLSE algorithm which takes into account the correlation of samples allows to improve system performance, partially mitigating the impact of fiber non-linearity. Some of the results presented here hint at a possible use of similar techniques in the context of coherent systems as well.

A centralized polarization scrambling and single-PD coherent ONU Rx system is proposed and tested with two Tx and direct-phase modulated DFBs. Polarization independence at the Rx, and a sensitivity at BER=10-3 of ×45dBm with 7.5GHz channel spacing were achieved.

A simple technique is presented to improve the sensitivity of cost-effective IMDD-OFDM systems by transmitting the signal absolute value and adding a label with the sample signs. Results indicate that a boost of about 3dB is achieved.

A homodyne coherent receiver for ultra-dense WDM-PON with off the shelf components is presented. It consists of a conventional DFB, phase switched clock signal, an optical coupler instead of a 90 degrees hybrid, balanced photodetectors and digital signal processing. The phase swing for a DBPSK signal was optimized and the performance was experimentally evaluated in terms of the sensitivity for several laser linewidths. The acceptable frequency offset and clock time delay was also assessed. The results exhibit a sensitivity of -48 dBm at a BER of 10(-3) and indicate a high tolerance to phase noise. (C) 2012 Optical Society of America

This article presents ACCORDANCE, a novel optical access network architecture based on OFDMA technology and applied on a PON topology. In compliance with next generation optical access requirements, this architecture aims to outperform existing PON solutions in terms of total capacity, bandwidth allocation flexibility, number of users, and network reach. Moreover, it provides the opportunity for convergence with wireless technologies and a smooth migration path from legacy access solutions like TDMA-PONs and DSL.

A simple method for wavelength control of economical random non-preselected independent ONU source, by OLT monitoring and thermal tuning, is presented and dimensioned. It reduces the spectral overlap probability and increases the cost-effectiveness of an OFDMA-PON.