J. Camilo Velasquez

Bio: J. Camilo Velasquez is an academic researcher from Polytechnic University of Catalonia. The author has contributed to research in topics: Wavelength-division multiplexing & Passive optical network. The author has an hindex of 5, co-authored 15 publications receiving 69 citations.

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

Abstract: A new passive optical network (PON) for access, making use of ultra-dense wavelength division multiplexing (UDWDM) by densely spacing channels by a few gigahertz and introducing the "wavelength-to-the-user" concept, is proposed. The key challenge will be developing low-cost coherent transceivers that provide an excellent selectivity while avoiding filters and furnishing high sensitivity, which will allow high splitting ratios, large numbers of users, and long-distance reach. The optical distribution network (ODN) at the outside plant is based on splitters and is 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 the customer premises have lasers with limited thermal tenability, 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 scenarios under indoor and also under outdoor 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 non-linearities constraints are evaluated, illustrating the characteristics of the projected network. Finally, the coexistence with legacy networks is discussed.

Coherent Ultra-Dense WDM-PON Enabled by Complexity-Reduced Digital Transceivers

Abstract: Coherent 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.

7.5 Gb/s direct DFB phase modulation with 8-DPSK for 6.25 GHz spaced coherent UDWDM-PONs

Abstract: 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.

Direct PSK-ASK Modulation for Coherent udWDM

Abstract: By means of pulse shaping, direct laser modulation reveals as an efficient low-cost option for future coherent ultra-dense-WDM-PON access systems, achieving sensitivities below −40 dBm with channel spacings of 6.25 GHz only.

Direct beat phase modulated DFB for flexible 1.25–5 Gb/s coherent UDWDM-PONs

Abstract: 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.

Laser Diode Modulation And Noise

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Coherent Access: A Review

Abstract: In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Passive Optical Networks Progress: A Tutorial

Abstract: For many years, passive optical networks (PONs) have received a considerable amount of attraction regarding their potential for providing broadband connectivity to almost every citizen, especially in remote areas where fiber optics can attract people to populate regions that have been abandoned. Error-free connectivity without dropouts can offer new opportunities to communicate, earn money and enjoy cultural events. Transmission speeds are multigigabit with distances of a few tens of kilometers; these specifications were previously reserved for high-speed and long-haul backbone networks. PONs can also support a new class of applications, such as accurate time transfer or distributed fiber sensing and follow new trends in open networking. An outline of past and current standards and standards that have been proposed for the latest generation of multigigabit PONs is provided.

Bidirectional wavelength-division multiplexing transmission over installed fibre using a simplified optical coherent access transceiver

Abstract: High-speed broadband services require optical fibres in access networks, in which multiple subscribers are connected to service providers, to satisfy the continuously growing bandwidth demand. The primitive signaling scheme used in access networks enables the use of low-cost equipment but diminishes the bandwidth available to end-users. Thus, current technology will be unable to support future broadband demands. Coherent communication systems offer significantly improved power- and bandwidth-efficiency, but require fundamental simplifications to become economically viable for access networks. Here, we demonstrate a promising simplified coherent receiver exhibiting a robust performance against polarisation fluctuations over an installed fibre network. It enables the realisation of high-order modulation formats and offers high sensitivities, achieving a four-fold increase in the supported number of subscribers and approximately doubling the transmission distance compared to the recently standardized access technology. The proposed solution indicates that digital coherent technology can be feasible and transform the access networks, enabling ubiquitous new services and applications with uncontended, multi-gigabits/user broadband connections.

Field-Trial of a High-Budget, Filterless, $\lambda$ -to-the-User, UDWDM-PON Enabled by an Innovative Class of Low-Cost Coherent Transceivers

Abstract: We experimentally demonstrate an innovative ultradense wavelength division multiplexing (UDWDM) passive optical networks (PON) that implements the full $\lambda \text {-to-the-user}$ 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 $\text{6.25}\text{-}\text {GHz}$ grid), real-time GbE transmissions (by using either fully analog or light digital signal processing), multirate transmission ( $\text{1.25}\; \text{and}\; \text{10}\,\text {Gb/s}$ ), high optical distribution network loss (18–40 dB) as well as a bidirectional channel monitoring system.