Future Optical Access Networks Research Articles

Minimising nonlinear Raman crosstalk in future network overlays on legacy passive optical networks

There is a desire to overlay future optical access networks onto legacy passive optical networks (PONs) to provide increasingly advanced services by filling empty wavelength bands of legacy gigabit rate PONs. Nonlinear Raman crosstalk from new wavelengths onto legacy RF video services (1550–1560 nm band) and onto the legacy digital downstream at 1490 nm, however, can limit the number and the launch power of new wavelengths. As an example, straightforward physical-layer adjustments at the optical line terminal that increase the number of new, 10 Gbit/s channels launched in the 1575–1580 nm band by a factor of 16 without increasing the Raman penalty on the video signal are illustrated. A physical-layer (RF) filter modifies the on–off-keyed signal feeding each 10 Gbit/s transmitter, suppressing the RF Raman crosstalk on the video signal by 9 dB while incurring a power penalty on each 10 Gbit/s link of <0.5 (2.0) dB with (without) forward error correction. The previous Raman mitigation work used non-standard line-coding to shape the 10 Gbit/s electrical spectrum. In addition, polarisation-interleaving of new wavelengths lowers the worst-case RF DC crosstalk by ∼3 dB in fibres and it limits and stabilises DC crosstalk in low polarisation mode dispersion fibre links.

Real-time Digital Signal Processing for Optical OFDM-Based Future Optical Access Networks

In this paper, key aspects associated with realizing real-time digital signal processing (DSP)-based optical transceivers for use in future optical access networks are considered. The fundamental principles of optical orthogonal frequency division multiplexing (OOFDM)-based transceivers and their associated DSP implementation are presented. This is followed by an extensive review of the real-time DSP implemented in the end-to-end OOFDM transceivers experimentally demonstrated over the past several years.

Power Budget Analysis of Colorless Hybrid WDM/TDM-PON Scheme Using Downstream DPSK and Re-modulated Upstream OOK Data Signals

Hybrid wavelength-division multiplexed/time-division multiplexed passive optical access networks (WDM/TDM-PONs) combine the advance features of both WDM and TDM PONs to provide a cost-effective access network solution. We demonstrate and analyze the transmission performances and power budget issues of a colorless hybrid WDM/TDM-PON scheme. A 10-Gb/s downstream differential phase shift keying (DPSK) and remodulated upstream on/off keying (OOK) data signals are transmitted over 25 km standard single mode fiber. Simulation results show error free transmission having adequate power margins in both downstream and upstream transmission, which prove the applicability of the proposed scheme to future passive optical access networks. The power budget confines both the PON splitting ratio and the distance between the Optical Line Terminal (OLT) and Optical Network Unit (ONU).

A Silicon Differential Receiver With Zero-Biased Balanced Detection for Access Networks

We present an optimized differential receiver in silicon with a minimized footprint and balanced zero-biased Ge photodiodes. The receiver integrates a delay-line with a 2×4 multimode interferometer 90° hybrid and two balanced photodiodes for differential quadrature phase-shift keying demodulation. Two receivers are tested, for 10 and 20 Gb/s operation, and well opened eye-diagrams and symbol constellations are obtained with error vector magnitude values as low as 12.5% and 19.57%, respectively. The results confirm the potential of integrated silicon receivers to become key building blocks for future passive optical access networks based on advanced modulation formats.

Dynamic Software-Defined Resource Optimization in Next-Generation Optical Access Enabled by OFDMA-Based Meta-MAC Provisioning

In order to address a diverse and demanding set of service and network drivers, several technology candidates with inherent physical layer (PHY) differences are emerging for future optical access networks. To overcome this PHY divide and enable both cost and bandwidth efficient heterogeneous technology co-existence in future optical access, we propose a novel Orthogonal Frequency Division Multiple Access (OFDMA)-based “meta-MAC”, which encapsulates PHY variations and enables fair inter-technology bandwidth arbitration. The new software-defined meta-MAC is envisioned to work on top of constituent MAC protocols, and exploit virtual OFDMA subcarriers as both finely granular and scalable bandwidth assignment units. We introduce important OFDMA meta-MAC design principles, and propose an elaborate three-stage dynamic resource provisioning scheme that satisfies the key requirements. The performance benefits of the meta-MAC concept and the proposed dynamic resource provisioning schemes in terms of spectrum management flexibility and support of diverse services are verified via real-time traffic simulation, confirming the attractiveness of the new approach for future optical access systems.

Combining DPSK and duobinary for the downstream in 40-Gb/s long-reach WDM-PONs

We propose and demonstrate combining differential phase-shift keying (DPSK) and duobinary transmission for the downstream in 40-Gb/s long-reach wavelength division multiplexed-passive optical networks (WDM-PONs) in order to provide robust transmission performance in the backhaul section and simple detection at the ONUs. DPSK is deployed in the trunk span as it provides stronger robustness to fiber nonlinearity. Duobinary is used in the access span where its higher chromatic dispersion tolerance relieves the need for dispersion compensation. All-optical multichannel modulation format conversion from DPSK to duobinary is realized in the local exchange in a single delay interferometer to reduce system cost. Single and multi-channel 80-km long-reach DPSK transmission and up to 5-km duobinary access transmission are experimentally demonstrated at 40Gb/s. The proposed approach shows great potential for future high data rate optical access networks.

Experiments on a 10 Gb/s Fast-Settling High-Sensitivity Burst-Mode Receiver With On-Chip Auto-Reset for 10G-GPONs [Invited

This paper presents a 10 Gb/s avalanche-photodiode-based DC-coupled reshaping and reamplifying (2R) burst-mode receiver with on-chip auto-reset generation and multiple data rate support, designed for 10G-GPONs. A short 2R settling time of 75 ns (150 ns for lower-rate operation), a high receiver sensitivity of -31.3 dBm, and a large loud/soft ratio of 25.3 dB are demonstrated at 2.5/5/10 Gb/s in burst-mode operation. Allowing multi-rate operation without external reset signals, it shows great potential for use in emerging symmetric 10G-GPON systems and allows for more flexible future optical access networks.

Scalable and Spectrally Efficient Long-Reach Optical Access Networks Employing Frequency Interleaved Directly Detected Optical OFDM

Extending the reach of traditional passive optical networks (PONs) to 100 km and increasing the split ratio beyond 1:64 are promising solutions in future optical access networks. These systems can accommodate increased users at longer distances potentially at low cost. With the increasing demand for higher bandwidths, current networks may soon require that bit rates upgrade to 100 Gb/s and beyond. However, the traditional on-off-keyed PON cannot be scaled up to such bit rates, as very high-speed opto-electronic devices are required that are still maturing. Therefore, to provide a comprehensive solution to these scalability issues of existing PONs, we propose a spectrally efficient (4 bit/s/Hz) 100 Gb/s long-reach PON based on 64 quadrature amplitude modulation (QAM) and frequency interleaved directly detected optical orthogonal-frequency-division multiplexing. We show that the proposed system may operate effectively over 100 km of single mode fiber with a 1024-way split and a receiver bandwidth of 25 GHz. It is also shown that the system can be provisioned to support even higher numbers of users (e.g., 2048, 4096, etc.) simply by varying the order of QAM with little compromise in bit rates. Moreover, the effects of various link parameters such as laser linewidths, fiber dispersion, filter profiles, etc. are also investigated for proper link dimensioning.

A Novel MAMSK-OFDM Technology for Next-Generation Optical Access Networks

We have proposed a novel multiamplitude minimum shift keying orthogonal frequency-division-multiplexing (MAMSK-OFDM) technology for the optical access network. In our experiment, the 5-Gb/s 2AMSK-OFDM signal and 2.5-Gb/s upstream on-off keying (OOK) signal are transmitted over 20-km single-mode fiber (SMF) successfully. We further compare the MAMSK-OFDM signal with 4-quadrature amplitude modulation (4QAM)/8QAM-OFDM and MSK-OFDM signals, and the results show the prospect of this technology in future optical access networks.

Future Optical Access Network and Spectral M-Ary ASK OCDM as Its Key Technology

This paper presents spectral multi-level (M-ary) amplitude shift keying (ASK) optical code-division-multiplexing (OCDM) as a key technology for future optical access network. A novel transmitter configuration to achieve flexible scalability that is required in future optical access network is proposed. The transmitter employs pre-biasing circuits and dummy data input. Pre-biasing circuits enable us to achieve high tolerance to multiple access interference by compensating for the nonlinearity of the M-ary ASK and increase the number of multiplexed binary data streams. By inputting the dummy data into the transmitter so that the total number of multiplexed binary data streams including those that actually accommodate users/services and the dummy streams remains constant, the number of users/services can be increased up to the total number of data streams without changing the parameters for pre-biasing. Therefore, the proposed transmitter can flexibly enhance the scalability of the spectral M-ary ASK OCDM. The formulas for calculating the bit error rate characteristics are described when using the conventional and proposed transmitters. The feasibility of the proposed transmitter is verified theoretically using the established formulas.

A WDM-Based Future Optical Access Network and Support Technologies for Adapting the User Demands' Diversity

We propose the network on demand concept to yield the optical access network system that well handles the diversity in user demands and support technologies such as module and devices configuration. In this proposal, the network accommodation equipment, such as OLT needed for each service, is installed ‘virtually’ using WDM, and the physical rate can adapt to the user-demanded service rate by using the WDM parallel transmission technique. It well handles the diversity in user demands/services and lowers system power consumption.

Multi-wavelength optical transmitter based on time-domain modulation of directly modulated wavelength-swept light

A multi-wavelength optical transmitter that employs time-domain modulation of directly modulated wavelength-swept light is proposed. This scheme offers the simplicity and flexibility needed for future optical access networks based on high spectral density wavelength division multiplexing. A proof-of-concept demonstration of the generation and selective detection of four-channel 1.25 Gbit/s signals is shown.

A Design of WDM/TDM-PON Provisioning for Future Optical Access Network Upgrade

In this paper, we propose a PON-based access network based on conventional TDM-PON architecture for the smooth, economical and effective transition to the future optical access network. We also propose a dynamic MAC protocol for wavelength channel and bandwidth allocation in the TDM-PON subscriber networks, which can provide enhanced network scalability and flexibility, and greater adaptability to the increasing number of subscribers in TDM-PON. In the proposed dynamic MAC protocol, several key functions are manifested, such as multiple wavelength channel utilization and dynamic allocation of multiple time-slots to a user depending on SLA between OLT and ONUs to meet QoS requirements. A dedicated control channel is used for delivering the request and status information between OLT and ONUs. We evaluate the performances of the proposed MAC protocol thru a statistical queuing analysis and numerical simulations. In addition, through simulations using various traffic models we verify the superior performance of the proposed approach by comparing it with conventional TDM-PONs.

Multiple-Length Variable-Weight Optical Orthogonal Codes for Supporting Multirate Multimedia Services in Optical CDMA Networks

Future optical code division multiple access (CDMA) networks should be designed for multirate and fully integrated multimedia services. In the conventional schemes, multilength optical orthogonal codes (OOCs) are designed to support multirate systems, while variable-weight OOCs are designed to support differentiated quality of service (QoS) for multimedia applications. In this paper, a novel class of optical signature codes; multiple-length variable-weight optical orthogonal codes (MLVW-OOC) is proposed for supporting multirate and integrated multimedia services in optical CDMA networks. The proposed MLVW-OOC has features that are easy to construct variable-weight codes and expanded to multiple-length codes. A construction method for designing MLVW-OOCs up to three levels of codes is discussed. The designed MLVW-OOCs can support differentiated requirements on data rates and QoS for several types of services in the networks. A code analysis for obtaining the value of cross-correlation constraints or multiple access interference (MAI) computation for several levels of codes is also suggested. The cross-correlation constraints of the proposed codes are better than the conventional codes such as multilength OOCs. Finally, the bit error probability performance of the two-level MLVW-OOC is evaluated analytically. The results show that the proposed MLVW-OOC can provide differentiated bit error probability performances for several combinations of data rates and QoS.

Options for future optical access networks

Optical access technology is now standardized, commercially available, and being deployed in some countries. In general, technology continues to develop, and optical access is no exception. New optical access technologies are now being widely reported; the technical trends are WDM, 10 Gb/s, and longer reach/higher splits. It is also important to take account of the evolution from installed legacy in possible future optical access standards

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

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.