Differential 8-APSK monolithically integrated dual-EML transmitter for flexible coherent PONs

© 2019 Optical Society of America. One print or electronic copy of this version author final draft, 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 experimentally demonstrate a simultaneous amplitude and phase modulation of a monolithically integrated dual electro-absorption modulated laser. The proposed technique combines a 4-ary direct phase modulation with a two-level amplitude modulation obtaining an 8-ary amplitude phase shift keying external-modulator-free transmitter (Tx). Its performance was tested up to 7.5 Gb/s in a 25 km single-mode fiber link with intradyne coherent detection. A receiver sensitivity of -42.5¿¿dBm was achieved at a forward error correction limit bit error ratio =4×10-3. The results show that the proposed system can be an efficient flexible Tx for next-generation passive optical networks.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

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

Transmission impairments mitigation in next generation coherent optical access networks

Worldwide, the coherent technologies have revolutionized the optical communication systems, significantly increasing the capacity of the fiber channel owing to transmission of advanced modulation formats and effective mitigation of propagation impairments. However, the actual commercial solutions for long-haul core/backbone networks are still complex and costly, and therefore hardly feasible for deployment in optical access networks. In particular, the main limitations arise from the customer premises equipment whose cost, footprint and power consumption may be kept down. Thus, the optimal solutions for next generation coherent optical access are required to achieve high performance but at lower complexity and cost, since in the access scenario the cost-effectiveness takes more relevance over achieving the best system performance. The research described in this thesis primarily aims at the development of the customer equipment “namely the coherent transceiver” for a passive optical access network that implements the novel wavelength-to-the-user concept by serving hundreds of users (e.g., 256 users) with dedicated wavelengths allocated in ultra-narrow optical grid. The proposed access network features complexity-reduced coherent technologies by leveraging photonic integration, commercial low-cost lasers and optics, and consumer electronics. To this end, the thesis investigates on the main transmission impairments that affect signal integrity from source to destination in the access network, and proposes novel and enhanced mitigation strategies by either low-complexity digital signal processing or analog hardware design. The covered topics spread over both the optical transmitter and the coherent receiver subsystems. Simplified optical modulation is addressed by direct phase modulation of semiconductor lasers profiting from the laser chirp. Digital pre-equalization of non-ideal frequency response from electronic/photonic devices “such as lasers, amplifiers and data converters” is investigated, focusing on the tolerance to quantization noise from digital-to-analog converters with limited resolution. Hardware-efficient strategies for optical carrier recovery based on differential phase detection are explored in two scenarios: homodyne receivers aided by digital signal processing, or fully analog heterodyne receivers. Finally, to deal with the critical polarization matching in coherent systems, simplified architectures for polarization-independent coherent receivers using low-cost optics and simpler receiver front-end are investigated.A nivel mundial, las tecnologías coherentes han revolucionado los sistemas de comunicaciones ópticas, aumentando significativamente la capacidad del canal de fibra gracias a la transmisión de formatos de modulación avanzados y a la mitigación efectiva de las degradaciones en la propagación. Sin embargo, las soluciones comerciales actuales para redes troncales de largo alcance siguen siendo complejas y costosas y, por lo tanto, difícilmente viables para su implementación en redes ópticas de acceso. En particular, las principales limitaciones surgen del equipo de usuario cuyo coste, tamaño y consumo de energía deben mantenerse bajos. Por lo tanto, las soluciones óptimas para las redes ópticas de acceso coherentes de nueva generación deben lograr un alto rendimiento pero con menor complejidad y coste, ya que en el escenario de acceso la relación coste-eficiencia toma más relevancia que lograr el mejor rendimiento del sistema. La investigación descrita en esta tesis se enfoca principalmente en el desarrollo del equipo de usuario, es decir, el transceptor coherente¿, para una red óptica pasiva de acceso que implementa el nuevo concepto de longitud de onda al usuario, al servir a cientos de usuarios (e.g., 256 usuarios) con longitudes de onda dedicadas y asignadas en una rejilla óptica ultra estrecha. La red de acceso propuesta implementa tecnologías coherentes de complejidad reducida al aprovechar la integración fotónica, láseres y dispositivos ópticos comerciales y de bajo coste, y electrónica de consumo. Con tal fin, la tesis investiga las principales degradaciones en la transmisión que afectan la integridad de la señal desde la fuente hasta el destino en la red de acceso, y propone nuevas y mejoradas estrategias de mitigación usando tanto procesamiento digital de señales de baja complejidad como diseño de hardware analógico. Los temas tratados abarcan desde el transmisor óptico hasta los subsistemas del receptor coherente. La modulación óptica simplificada se aborda mediante modulación directa de fase de láseres de semiconductor, aprovechando el chirp del láser. Se investiga la pre-ecualización digital de la respuesta frecuencial no ideal de dispositivos electrónicos/fotónicos tales como láseres, amplificadores y conversores de datos, centrándose en la tolerancia al ruido de cuantificación de los conversores digital-analógico con resolución limitada. Las estrategias para la recuperación de la portadora óptica basadas en la detección diferencial de fase y eficientes en hardware, se exploran en dos escenarios: receptores homodinos asistidos por procesamiento digital de señales, o receptores heterodinos completamente analógicos. Finalmente, para hacer frente al crítico ajuste de la polarización en sistemas coherentes, se investigan arquitecturas simplificadas para receptores coherentes independientes de la polarización utilizando óptica de bajo coste y un front-end óptico del receptor más simple.Postprint (published version

Coherent UD-WDM RoF Fronthaul network with D-EML transmitter and phase-noise robust receiver

This work proposes and tests a simplified coherent uplink architecture for ultra-dense coherent analog mobile Fronthaul with phase noise cancellation based on single sideband modulation of a dual-EML. Results show optical channel spacings of only 1.5 GHz and error-free signal recovery with Δν Tb = 1.2% and 3% with reaching power as low as −46dBm for 100 Mbit/s and −38 dBm for 1 Gbit/s using QPSK modulation.This work was supported by the Spanish Comisión Interministerial de Ciencia y Tecnología (CICYT) Project Versatile Coherent Dual Optical Network (VERSONET) under Grant RTI2018-097051 and in part by the Grant “Proyectos de I+D+i” under Grant PID2019-107885GB- C31.Peer ReviewedPostprint (author's final draft

LUT-Free carrier recovery for intradyne optical DPSK receivers in UDWDM-PON

We present an LUT-free feed-forward carrier recovery architecture in intradyne optical DPSK receivers that reduces ~41% DSP hardware resources and 61% required process clocks with 85% less power consumption in real-time operation on FPGA with data at 1.25Gbps. © 2018 IEEE.Peer ReviewedPostprint (published version

Optimized differential detection-based optical carrier recovery for intradyne 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 optical carrier recovery based on differential detection that reduces required DSP hardware resources. Results show -55dBm sensitivity for BER=10-3 and high tolerance against fast LO frequency dithering, with DPSK data at 1.25Gbps.Peer ReviewedPostprint (published version

Differential 8-APSK monolithically integrated dual-EML transmitter for flexible coherent PONs

© 2019 Optical Society of America. One print or electronic copy of this version author final draft, 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 experimentally demonstrate a simultaneous amplitude and phase modulation of a monolithically integrated dual electro-absorption modulated laser. The proposed technique combines a 4-ary direct phase modulation with a two-level amplitude modulation obtaining an 8-ary amplitude phase shift keying external-modulator-free transmitter (Tx). Its performance was tested up to 7.5 Gb/s in a 25 km single-mode fiber link with intradyne coherent detection. A receiver sensitivity of -42.5¿¿dBm was achieved at a forward error correction limit bit error ratio =4×10-3. The results show that the proposed system can be an efficient flexible Tx for next-generation passive optical networks.Peer Reviewe

Coherent ultra-dense WDM-PON enabled by complexity-reduced digital transceivers

© 2020 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 worksCoherent technologies, along with digital signal processing (DSP), have revolutionized optical communication systems, significantly increasing the capacity of the fiber channel owing to transmission of advanced modulation formats and mitigation of propagation impairments. However, commercial solutions for high-capacity core networks are too complex and costly, and therefore hardly feasible, for access networks with high terminal density, where cost, power budget, and footprint are the main limiting factors. This article analyzes the key enabling techniques to implement a complexity-reduced coherent transceiver (CoTRX) by exploiting photonic integration, simplified optical modulation, low-cost DFB lasers, consumer electronics, and low-complexity DSP. Bulk optical modulators are replaced by direct amplitude-and-phase modulation of an integrated electro-absorption modulated laser (EML) with a smaller footprint, generating up to 8-ary modulation formats. Hardware-efficient DSP algorithms for the coherent transmitter and receiver, including pulse-shaping for direct phase modulation, differential detection for optical phase recovery, and digital pre-emphasis with enhanced tolerance to quantization noise, are investigated to face the challenges imposed by low-cost photonic and electronic devices, such as strong phase noise, wavelength drifts, severe bandwidth limitation, and low resolution data converters. Through numerical simulations and real-time experiments, the results indicate that this new class of CoTRX enables effective implementation of wavelength-to-the-user PON with dedicated 1.25-20 Gb/s per user, in an ultra-dense 6.25-25 GHz spaced WDM optical grid, with >30 dB loss budget, outperforming the current competing technologies for access networks.This work was supported in part by the Spanish Project FLIPER (TEC2015-70835), and the FPU program from the Education Ministry of Spain (FPU12/06318).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 Reviewe