Feature Issue on
Optical Access Networks (OAN) The passive optical network (PON) is
an optical fiber based network architecture, which can provide much higher bandwidth
in the access network compared to traditional copper-based networks. Incorporating
wavelength-division multiplexing (WDM) in a PON allows one to support much higher
bandwidth compared to the standard PON, which operates in the "single-wavelength
mode" where one wavelength is used for upstream transmission and a separate one is
used for downstream transmission. We present a comprehensive review of various
aspects of WDM-PONs proposed in the literature. This includes enabling device
technologies for WDM-PONs and network architectures, as well as the corresponding
protocols and services that may be deployed on a WDM-PON. The WDM-PON will become a
revolutionary and scalable broadband access technology that will provide high
bandwidth to end users.

/pdf/wavelength-division-multiplexed-passive-optical-network-wdm-428jyy569l.pdf

Wavelength-division-multiplexed passive optical network (WDM-PON) technologies for broadband access: a review (Invited)

The main bandwidth bottleneck in today's networks is in the access segment. To address that bottleneck, broadband fiber access technologies such as passive optical networks (PONs) are an indispensable solution. The industry has selected time-division multiplexing (TDM) for current PON deployments. To satisfy future bandwidth demands, however, next-generation PON systems are being investigated to provide even higher performance. In this paper, we first review current TDM-PONs; we designate them as generation C. Next, we review next-generation PON systems, which we categorize into C+1 and C+2 generations. We expect C+1 systems to provide economic near-term bandwidth upgrade by overlaying new services on current TDM-PONs. For the long term, C+2 systems will provide more dramatic system improvement using wavelength division multiplexing technologies. Some C+2 architectures require new infrastructures and/or equipment, whereas others employ a more evolutionary approach. We also review key enabling components and technologies for C+1 and C+2 generations and point out important topics for future research.

/pdf/next-generation-optical-access-networks-41pmztcn8d.pdf

Next-Generation Optical Access Networks

Long-Reach optical access is a promising proposal for future access networks. This technology can enable broadband access for a large number of customers in the access/metro area, while decreasing capital and operational expenditures for the network operator. First, the paper reviews the evolutionary path of access networks and shows the drivers from technology and business perspectives for high bandwidth and low cost. A variety of research challenges in this field is reviewed, from optical components in the physical layer to the control and management issues in the upper layers. We discuss the requisites for optical sources, optical amplifiers, and optical receivers when used in networks with high transmission rate (10 Gbps) and large power attenuation (due to large split, transmission over 100 km and beyond, and propagation), and the key topological structures that allow to guarantee physical protection (tree-and-branch, ring-and-spur). Then, some relevant demonstrations of Long-Reach Optical Access Networks developed worldwide by different research institutes are presented. Finally, Dynamic Bandwidth Allocation (DBA) algorithms that allow to mitigate the effect of the increased control-plane delay in an extended-reach network are investigated.

Long-reach optical access networks: A survey of research challenges, demonstrations, and bandwidth assignment mechanisms

We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture that allows for incremental upgrade from single-channel time-division multiple-access PONs in order to provide higher bandwidth in the access network. Various dynamic-wavelength and bandwidth-allocation algorithms (DWBAs) for wave-division multiplexed PON are presented; they exploit both interchannel and intrachannel statistical multiplexing in order to achieve better performance, especially when the load on various channels is not symmetric. Three variants of the DWBA are presented, and their performance is compared. While the first variant incurs larger idle times (and, hence, poor performance), the other two algorithms achieve better but different performance with critical dissimilarities. Our analysis also focuses on the fair assignment of excessive bandwidth in the upstream direction to highly loaded optical network units. We compare the performance of DWBA to another algorithm that relies on static-channel allocation. Furthermore, a study is presented wherein the number of wavelengths increases, and a comparison with interleaved polling with adaptive cycle time is shown. We use extensive simulations throughout this paper

Dynamic Wavelength and Bandwidth Allocation in Hybrid TDM/WDM EPON Networks

A novel ultrahigh-speed electro-optic polarization modulator is introduced. The modulator uses a mode converter and a static polarization controller to change the output polarization state in a circular path, following a great circle, around the Poincare sphere. Any two states on the Poincare sphere can be connected. The mode converter is constructed using an AlGaAs ridge waveguide combined with slow-wave travelling wave electrodes. The travelling wave electrodes are designed to match the velocity of the electrical modulating signal, the data signal, to the optical carrier signal over a broad frequency range. This modulator demonstrates a 3 dB bandwidth in excess of 40 GHz. The polarization modulator exhibits extremely low differential group delay, on the order of a few 10s of femto-seconds, and low drive voltage, on the order of 5 V.

/pdf/40-ghz-electro-optic-polarization-modulator-for-fiber-optic-1496dl1fi2.pdf

40 GHz electro-optic polarization modulator for fiber optic communications systems

In this paper, the authors propose a next-generation hybrid WDM/TDM optical access network architecture called Stanford University aCCESS or SUCCESS. This architecture provides practical migration steps from current-generation time-division multiplexing (TDM)-passive optical network (PONs) to future WDM optical access networks. The architecture is backward compatible for users on existing TDM-PONs, while simultaneously capable of providing upgraded high-bandwidth services to new users on DWDM-PONs through advanced WDM techniques. The SUCCESS architecture is based on a collector ring and several distribution stars connecting the CO and the users. A semipassive configuration of the Remote Nodes (RNs) enables protection and restoration, making the network resilient to power failures. A novel design of the OLT and DWDM-PON ONUs minimizes the system cost considerably: 1) tunable lasers and receivers at the OLT are shared by all ONUs on the network to reduce the transceiver count and 2) the fast tunable lasers not only generate downstream data traffic but also provide DWDM-PON ONUs with optical CW bursts for their upstream data transmission. Results from an experimental system testbed support the feasibility of the proposed SUCCESS architecture. Also, simulation results of the first SUCCESS DWDM-PON MAC protocol verify that it can efficiently provide bidirectional transmission between the OLT and ONUs over multiple wavelengths with a small number of tunable transmitters and receivers.

/pdf/success-a-next-generation-hybrid-wdm-tdm-optical-access-sapu9cdf5u.pdf

SUCCESS: a next-generation hybrid WDM/TDM optical access network architecture

We demonstrate error-free packet-over-WDM transmission using a fast-tunable transmitter and novel packet receiver The transmitter tunes fine (08 nm) and wide (/spl sim/30 nm) within 15 ns, while the receiver receives unframed packets by bit-synchronizing in 40 ns

Performance demonstration of a fast-tunable transmitter and burst-mode packet receiver for HORNET

We propose and demonstrate a novel 4-level DD-PolSK system with LiNbO/sub 3/-based phase modulator and alternative allocation of constellations, which lead to a greatly simplified transceiver architecture. A 5 Gb/s (2.5 GS/s) testbed has been build to demonstrate the feasibility of the 4-PolSK transceiver.

4-level direct-detection polarization shift-keying (DD-PolSK) system with phase modulators

The HORNET architecture is a packet-over-wavelength-division-multiplexing ring network that utilizes fast-tunable packet transmitters and wavelength routing to enable it to scale cost-effectively to ultrahigh capacities. In this paper, we present the HORNET architecture and a novel control-channel-based media access control protocol. The survivability of the architecture is demonstrated with an experimental laboratory testbed. Mathematical analysis of the architecture shows that the wavelength routed network can scale to relatively large sizes ranging between 30 and 50 nodes, depending on the component performance. This is true even for arrangements that do not contain high-power optical amplifiers in every node.

Demonstration and system analysis of the HORNET architecture

In summary, we have demonstrated, for the first time to our knowledge, a gain-clamped discrete Raman amplifier in the S-band The device achieves peak net gain over 22 dB, and a gain variation of only 03 dB for signal input power ranging from -20 dBm to 27 dBm Unlike conventional gain-clamping designs, an extinction ratio between signal and lasing wavelength of over 30 dB is achieved This new technique suppresses instability due to randomly-polarized ASE and double Rayleigh scattering (DRS) (hence noise figure) for small signal input power under high pump power, as well as power surges due to transient effects in Raman amplifiers This promises a viable technology to provide gain bands not currently available from traditional doped fiber amplifiers

E.S. Hu

Papers

SUCCESS: a next-generation hybrid WDM/TDM optical access network architecture

Performance demonstration of a fast-tunable transmitter and burst-mode packet receiver for HORNET

4-level direct-detection polarization shift-keying (DD-PolSK) system with phase modulators

Demonstration and system analysis of the HORNET architecture

Gain-clamped S-band discrete Raman amplifier