Coherent ONU based on 850 µm-long cavity-RSOA for next-generation ultra-dense access network

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.Peer ReviewedPostprint (published version

Simple single-laser coherent transceiver based on low-cost D-EML for edge networks

In this work we demonstrate single-laser, D-EML based coherent transceivers which transmit and simultaneously receive optical single sideband modulations through a phase noise cancelling scheme, leading to phase-noise and frequency-detuning clean signals. We use QPSK and 16-QAM modulations over a 500 Mbaud signal, reaching 1 Gbps and 2 Gbps respectively, with sensitivities as low as -53 and -40 dBm with unmodulated local oscillator, respectively, and -35 dBm for QPSK with modulated local oscillator, achieving high sensitivity coherent UD-WDM for analog radio over fiber and mobile fronthaul over passive optical networks.This work was supported in part by the Spanish Ministry of Science and Innovation, Versatile Optical Coherent Network (VERSONET), under Grant RTI2018-097051; and in part by the European Union’s Horizon Europe Research and Innovation Programme under the Marie Sklodowska-Curie Grant, enabling virtualized wireless and optical coexistence (EWOC), under Agreement 101073265. (Corresponding author: Miquel Masanas.)Peer ReviewedPostprint (author's final draft

Fast wavelength thermal tuning of DFB lasers for ultra dense WDM-PONs

Thermal tunability for distributed feedback lasers is generally done at slow tuning speed. We study laser current boosting and implement a pre-equalization stage for short wavelength jump, improving the tuning time to the half. A wider jump is also done under a more practical context.This work was supported in part by the Spanish Comision Interministerial de Ciencia y Tecnologia (CICYT) Project Versatile Coherent Dual Optical Network (VERSONET) under Grant RTI2018-097051.Peer ReviewedPostprint (author's final draft

UDWDM-PON using low-cost coherent transceivers with limited tunability and heuristic DWA

A new Passive Optical Network (PON) for access, making use of Ultra Dense Wavelength Division Multiplexing (UDWDM) by densely spacing channels at few GHz, and introducing the “wavelength-to-the-user” concept, is proposed. The key challenge will be developing low-cost coherent transceivers, providing an excellent selectivity while avoiding filters, and furnishing high sensitivity, which will allow high splitting ratios, large number of users and long distance reach. The Optical Distribution Network (ODN) at the outside plant is based on splitters and kept compatible with legacy systems. Optical Network Unit (ONU) designs realized with coherent transceivers using one or two lasers are presented and the corresponding Optical Line Terminal (OLT) architectures are introduced. The ONUs at customer premises own lasers with limited thermal tunability and their wavelengths are randomly distributed in a band. By using heuristic Dynamic Wavelength Assignment (DWA) schemes and extending the original working band, the required optical band is obtained and optimized. In activation processes, ONU acceptances up to 99.9% are achieved. Furthermore, in operation scenario under indoors and also under outdoors environmental conditions, ONU blocking probabilities below 0.1% and ONU availability ratios (OARs) up to 99.9% are demonstrated. The PON is dimensioned according to the number of deployed users and system reach; moreover, power safety and also fiber nonlinearities constraints are evaluated, illustrating the characteristics of the projected network. Finally, the coexistence with legacy networks is discussed.Peer ReviewedPostprint (author's final draft

Simplified carrier recovery for intradyne optical PSK receivers in udWDM-PON

©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.We present an optimized carrier recovery architecture based on differential detection for coherent optical receivers that substantially reduces the required DSP hardware resources, aimed at cost-effective transceivers for access networks applications. The proposed architecture shares the 1-symbol complex correlation required for differential phase detection within both the frequency estimation and the phase recovery blocks of the receiver DSP, thus lowering the energy consumption of the digital coherent receiver and increasing the tolerance against fast wavelength drifts of the lasers. We prototyped the proposed carrier recovery in a commercial field-programmable gate array (FPGA) for real-time evaluation with differential phase shift keying (DPSK) data at 1.25 Gb/s. The optical transmission system implemented direct-phase modulation of commercial DFB lasers, 25 km of single-mode fiber, and a coherent intradyne receiver with low-cost optical front-end based on 3×3 coupler and three photodiodes providing phase-diversity operation. Results show high performance in real time for DPSK, achieving -55 dBm sensitivity at BER = 10 -3 in a 6.25 GHz spaced ultra-dense wavelength-division multiplexing grid, high tolerance to optical phase noise, and enhanced mitigation of the fast wavelength drifts from lasers enabled by feedforward DSP correction and feed-back local oscillator automatic tuning.Peer ReviewedPostprint (author's final draft

First demonstration and field trial on multi-user UDWDM-PON full duplex PSK-PSK with single monolithic integrated dual-output-DFB-SOA based ONUs

© 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.Peer ReviewedPostprint (author's final draft

Optimization of Rayleigh-limited WDM-PONs with reflective ONU by MUX positioning and optimal ONU gain

In this work, the influence of the distribution element position and the reflective optical network unit (ONU) gain in wavelength-division-multiplexing passive optical networks are reported. After the theoretical and experimental analysis, it is determined that the best crosstalk-to-signal ratio is achieved if the multiplexer is placed either in the ONU or optical light termination vicinity, and the ONU gain has a new optimum value depending on the position. Also, it is demonstrated that Rayleigh backscattering is generally irrelevant in downstream transmission.Peer ReviewedPostprint (published version

15-dB differential link-loss UDWDM-PON with direct beat phase modulated DFBs

©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.IEEE A 15 dB differential link-loss ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) with two optical network units (ONU) spectrally spaced 6.25 GHz is experimentally implemented and tested. The ONU transmitters consist of direct phase modulated distributed feedback lasers (DFB) through a digital beat signal, whose amplitude and duty cycle are optimized for maximum phase variations, avoiding the need for an analogue equalizer. We achieved receiver sensitivities of -53 dBm, -50.5 dBm, and -45 dBm for bit rates of 1.25 Gb/s, 2.5 Gb/s, and 5 Gb/s respectively at BER = 4·10 -3 with an intradyne coherent receiver.Peer ReviewedPostprint (author's final draft

Field-Trial of a high-budget, filterless, lambda-to-the-user, UDWDM-PON enabled by an innovative class of low-cost coherent transceivers

©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.Peer ReviewedPostprint (author's final draft

Simple intradyne PSK system for UDWDM-PON

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 90º 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.Peer ReviewedPostprint (published version