Simple and effective solutions for low-cost coherent WDM-PON

This paper presents the most significant results achieved in the last two years by our group in coherent ultra-dense-WDM PON for λ-to-the-user access. Here we mostly focus on the architectures based on simple OOK-NRZ modulation format. We demonstrated the real-time implementation of our coherent receiver and we proved its compatibility with direct modulated laser (DML). Receiver sensitivities as low as -48 dBm at BER=1·10-3 for 1.25 Gb/s has been observed, showing the feasibility of a coherent ONU receiver based on devices commonly available and with limited cost. The system support quite high ODN losses and allows the λ-to-the-user approach

Coherent PON system with high-sensitivity polarization-independent receiver and no ADC/DSP

A 1.25 Gb/s ASK PON system with -51dBm sensitivity (at BER=2-103) is enabled by a polarization-independent coherent receiver that needs no DSP (nor ADC). The system just uses common DFBs and commercial electronic devices and has 52 dB dynamic range

Hitless wavelength assignment in filterless optical access networks

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

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

Electrical filter-based and low-complexity DPSK coherent optical receiver

Direct-detection of differential phase shifted keying (DPSK) optical signals is implemented either by ad hoc optical filtering or one-bit delayed optical interferometers. We show a coherent receiver where the filtering is performed in the electrical domain after down-converting the incoming signal to the baseband or to an intermediate frequency. This can be particularly advantageous whenever optical filters cannot be used or when extremely narrow filtering (sub-GHz) would be required [for example ultra-dense wavelength division multiplexing (WDM) passive optical networks]. Electrical filters can be realized more accurately than their optical counterpart. In addition, in a coherent receiver, this operation is colorless and avoids digital signal processing. We show experimentally this reduced complexity receiver and compare it with the classical one based on the delay and multiply block

Applications of narrow-filtering based on optical coherent detection

Processing of high-frequency, wide-band signals is conveniently performed in the optical domain due to availability of optical filters which intrinsically have a wide-band response. On the other end, there are several application scenarios where very sharp pass-band filtering is required. In these cases, realizing the processing in the optical domain might not be technically simple, although filters of extremely high Q-factor have been demonstrated. This paper presents the feasibility of signal processing based on very sharp electrical filtering (<; 1 GHz around 193 THz) assisted by optical down-conversion, i.e., by means of optical coherent detection. In particular, we show experimentally two applications where the filtering capability is exploited to perform signal processing: the demodulation of phase-modulated optical signals and the implementation of a chirp-managed transmission link. Other possible applications of this technique will be also discussed at the presentation

Polarization-Independent Coherent Real-Time Analog Receiver for PON Access Systems

A 1.25-Gb/s ASK passive optical network (PON) system with a -51 dBm pre-FEC sensitivity (at BER = 2 × 10-3) is enabled by a real-time polarization-independent coherent receiver (PI-RX) that needs no DSP (nor ADC). The receiver, which only makes use of common DFBs and commercially available electronic ICs, is targeted for use on a 6.25-GHz UD-WDM grid and has a 52-dB dynamic range. Measurements of the robustness of the PI-RX against backreflections and crosstalk from coexistent adjacent channels show that this preliminary implementation is suitable for UD-WDM-PON systems with frequency spacing down to 5 GHz

Real-time coherent ONU for ¿-to-the-user based on fully analogue processing of OOK signals

Using fully-analogue and commercially available electronics, we realize a real-time coherent ONU receiver for Ultra-Dense WDM-PON based on intensity-modulated signals. The receiver also requires common photonic components and has -47dBm sensitivity at FEC level.Peer Reviewe

High-power budget OFDM-PON compatible with ultra-narrow channel spacing

We demonstrate a coherent OFDM-PON based on a simplified coherent receiver, which exploits a DFB local oscillator without phase/frequency locking. We achieve ultra-narrow channel spacing (Δν = 1.6 GHz) and high-power budget (43 dB/35 dB) for 1.25/10 Gb/s