Optimization Scheme for WDM-Based Transmission Technology Selection in Future Passive Optical Networks

There is a rapidly increasing data flow between sensors and on-board processors in avionic platforms. Electro-optic (EO) sensors are moving to hyperspectral and radar to phased array to enable precision targeting, wide field of view surveillance and navigation. These trends call for next generation optical network technology which has to provide increasing high speed data transmission under harsh conditions. Recent developments go beyond simple point-to-point fiber links towards establishing optical distribution networks to deal with the data traffic [1]. A flexible and potentially low-cost implementation is the passive optical network (PON) which scales easily to increasing needs simply by upgrading the peripheral units without need to change the fiber connections and infrastructure. PONs are well established in the commercial access market with the increasing push to fiber-to-the-home (FTTH) technologies which has led to the development of a variety of low-cost devices for these networks. A key enabler in our development of an avionics PON is the reflective semiconductor optical amplifier (RSOA) which combines amplification and modulation into a single device [2]. The RSOA is a non-resonant device, thus wideband with the potential for ruggedness, especially high temperature operation with small or no need for cooling. At higher data rates up to 20 Gbps a related device, the reflective electro-absorption modulator with integrated amplification (R-SOA-EAM) can be used instead. To complete the adaptation we replaced the laser, commonly used to provide optical input power in a PON architecture with another non-resonant device, the superluminescent LED (SLED). To create upgrade flexibility we utilized wavelength division multiplexing (WDM) which allows addition and subtraction of channels without changing hardware. Coarse WDM (CWDM) was chosen over Dense WDM (DWDM) for two reasons: the large channel width (20nm) of CWDM reduces cost by relaxing fabrication tolerance and renders the use of temperature control unnecessary, thereby increasing reliability. The concept and current state of development of our optical network is described in this paper.

The potential for sharing infrastructure costs between a large number of customers and the high data rates allowed by optical fibres make passive optical networks (PONs) an attractive solution to the problem of upgrading current copper-based access networks. Optically-amplified, long reach, time division multiple access (TDMA) PONs or 'SuperPONs' offer the potential to further reduce bandwidth transport costs by enabling the direct connection of access networks and inner core networks, thereby eliminating the costs of the outer core/metro backhaul network. The use of dense wavelength division multiplexing (DWDM) could also allow sharing the same feeder fibre and PON head end equipment between a number of such TDMA SuperPONs, each working at different ITU-grid wavelengths. However, a cost effective access solution should employ a customer optical network unit (ONU), which is independent of the PON wavelength, or colorless, in order to reduce the high inventory and deployment costs of using expensive, wavelength-specified sources at the customer. In this paper we demonstrate for the first time the use of a monolithically-integrated, electroabsorption modulator-semiconductor optical amplifiers (EAM-SOAs) as a colorless ONU in a high performance DWDM SuperPON system. These compact devices offer the potential for low-cost optoelectronic integration with other ONU components together with the ability to modulate at rates up to 10Gbps and beyond. We have used this approach to investigate the feasibility of supporting up to 17 SuperPONs from a single feeder fibre and PON head end, each of 100km-reach accommodating 512 users at 2.5Gb/s or 128 at 10Gb/s.

Results of the design and performance analysis of two new algorithms for efficient and fair scheduling of variable-length frames in a wavelength division multiplexing (WDM)-passive optical network (PON) under the Stanford University aCCESS-Hybrid PON (SUCCESS-HPON) architecture are reported. The WDM-PON under the SUCCESS-HPON architecture has unique features that have direct impacts on the design of scheduling algorithms. First, an optical line terminal (OLT) uses tunable transmitters and receivers that are shared by all the optical network units (ONUs) served by the OLT to reduce the number of expensive dense WDM (DWDM) transceivers. Second, also for cost reduction, ONUs have no local DWDM light sources but use optical modulators to modulate optical continuous wave (CW) bursts provided by the OLT for upstream transmissions. Therefore, the tunable transmitters at the OLT are used for both upstream and downstream transmissions. To provide efficient bidirectional communications between the OLT and the ONUs and guarantee fairness between upstream and downstream traffic, two scheduling algorithms have been designed: 1) batching earliest departure first (BEDF); and 2) sequential scheduling with schedule-time framing (S/sup 3/F). The BEDF is based on the batch scheduling mode where frames arriving at the OLT during a batch period are stored in virtual output queues (VOQs) and scheduled at the end of the batch period. It improves transmission efficiency by selecting the frame with the earliest departure time from a batch of multiple frames, which optimizes the usage of tunable transmitters in scheduling. Considering the high complexity of the optimization process in BEDF, the S/sup 3/F based on the sequential scheduling mode has also been designed as in the original sequential scheduling algorithm proposed earlier. In S/sup 3/F, the authors use VOQs to provide memory space protection among traffic flows and a granting scheme together with schedule-time framing for both upstream and downstream traffic to reduce framing and guard band overhead. Through extensive simulations under various configurations of the tunable transmitters and receivers, it has been demonstrated that both the BEDF and S/sup 3/F substantially improve the throughput and delay performances over the original sequential scheduling algorithm, while guaranteeing better fairness between upstream and downstream traffic.

Broadband Passive Optical Access Networks

Fiber-to-the-home (FTTH) or close to it (FTTx) networks are poised to become the next major success story for optical fiber communications. Future FTTx access networks unleash the economic potential and societal benefit by opening up the first/last mile bandwidth bottleneck between bandwidth-hungry end-users and high-speed backbone networks. Owing to their longevity, low attenuation, and huge bandwidth, passive optical networks (PONs) are widely deployed to realize cost-effective FTTx access networks. Fiber has been envisioned for delivering broadband services for over 30 years. However, many roadblocks related to component and installation costs have slowed down the progress toward FTTx since it was first proposed. Currently, FTTH is being installed in many countries, but it still represents only a fraction of all deployed broadband lines (Shumate [2008]). The two major state-of-the-art PON standards IEEE 802.3ah Ethernet PON (EPON) and ITU-T G.984 Gigabit PON (GPON) consist both of a single upstream wavelength channel and a separate single downstream wavelength channel, whereby both channels are operated using time division multiplexing (TDM). EPON and GPON are expected to coexist for the foreseeable future as they evolve into next-generation PONs (NG-PONs) (Effenberger et al . [2007], Kazovsky et al . [2007]). NG-PONs can be categorized into high-speed TDM PON, wavelength division multiplexing (WDM) PON, and long-reach PON (LR-PON) (Lin [2008], Effenberger et al . [2009a]).

Elastic optical network (EON) is a promising candidate for the next generation optical transport network because of its high spectrum efficiency and flexible spectrum allocation. However, to migrate from today’s dense wavelength division multiplexing (DWDM) network to EON, optical nodes such as reconfigurable optical add/drop multiplexers (ROADMs) should be replaced with the ones with expensive flexi-grid wavelength selective switches (WSSs). Thus, whether and how today’s optical network will be evolved to EON is still under debate. Meanwhile, with the technical maturity of optical super-channels that transmit bit rates at the level of 1 Tb/s, super-channels are expected to dominate the future optical transport network because of their attractiveness of high spectrum efficiency and superior cost effectiveness. In this paper, we propose a new quasi-coarse wavelength division multiplexing (Quasi-CWDM) optical network architecture that is compatible to today’s WDM network in spectrum operation, while still maintaining the flexibility of adaptation between the bit rate and the transparent reach of an optical super-channel, but not requiring expensive flexi-grid WSSs. Specifically, the Quasi-CWDM optical network employs large fixed frequency grids, whose spacing falls between the traditional CWDM and DWDM, e.g., 200 GHz or 400 GHz. To maintain the flexibility between the bit rate and the transparent reach of an optical super-channel, different modulation formats are chosen according to channel physical distances. To minimize network hardware cost and maximize carried user traffic demand, we develop a mixed integer linear programming (MILP) model and a heuristic algorithm that can efficiently groom upper-layer IP traffic onto the optical layer by optical super-channels. We compare the design based on the Quasi-CWDM network to those based on the DWDM network and the advanced EON. It is found that the proposed Quasi-CWDM network has a much lower hardware cost than the other two types of networks, while achieving spectrum efficiency close to EON.

We address the development of mobile fronthaul (MFH) radio-over-fibre (RoF) transceivers with the capability to transport Digital RoF (D-RoF) signals for C-RAN applications. The coexistence of transport of D-RoF with legacy and the future Passive Optical Network (PON) systems, such as Next Generation PON 2 (NG-PON2) will be analysed. The preliminary experimental results of transmitting several D-RoF signals with high spectral efficiency and based on Sub-Carrier Multiplexing (SCM) techniques will be presented.

Future passive optical networks (PONs) call for more flexibility to support diversified users with various rate demands and link qualities. Using traditional time-division multiplexing (TDM), the concept of a flexible rate PON was proposed to accommodate more users with link diversity by rate adaptation. In this Letter, we reveal the PON coverage can be further extended through frequency-division multiplexing (FDM) in the presence of multiuser diversity, namely, (i) there exist users with frequency-dependent link conditions and (ii) the link conditions exhibit disparity among users. We build a mathematical model and propose an optimization algorithm based on the binary tree search to optimize diversity gain. We experimentally verify its feasibility by studying the diversity gain concerning chromatic dispersion, optical path loss, and signal-to-noise ratio (SNR) variation in a 200G-class intensity-modulation direct-detection (IM-DD) system.

Future passive optical network (PON) systems supporting more than 50 Gb/s/λ present a challenge for the use of intensity modulation direct detection (IM-DD). Since coherent technology improves the receiver sensitivity over that of IM-DD, it is a promising candidate for 100 Gb/s or higher PON systems. Introducing hardware-efficient signal processing technologies tailored to PON systems will help render coherent technology suitable for PON systems. We here review hardware-efficient signal processing technologies suitable for PON systems. We introduce two types of simplified adaptive equalization (AEQ), one which sacrifices differential group delay compensation (DGDC), and another which sacrifices some chromatic dispersion compensation but does provide DGDC. Transmission experiments on a 100 Gb/s/λ-based coherent wavelength division multiplexing (WDM) PON system showed that simplified AEQ without DGDC and with DGDC exhibited only 0.2 and 1.4 dB penalty, respectively, compared with conventional DSP. The additional penalty due to the maximum possible cumulative DGD was evaluated by numerical simulation. Conventional AEQ and the simplified AEQ with DGDC showed negligible penalty, but the simplified AEQ without DGDC showed a 1.4 dB penalty. We also introduce simplified carrier phase recovery (CPR) with interpolarization phase offset estimation, and this showed the same performance as the conventional DSP, in both experiment and simulation. Taking these results into account, 100 Gb/s/λ-based coherent WDM PON systems with the simplified AEQs in combination with the simplified CPR were shown to be able to support the loss budget required for eight ONU splits over an 80 km span of single mode fiber.

It has been recently experimentally and theoretically demonstrated that three nonlinear operation regimes can be observed in reflective semiconductor amplifiers in relation to gain saturation and, consequently, in relation to the bleaching of the modulation portion of the injected signal while the injected power increases. For moderately high-injected power, the modulation component of the signal is partially bleached, i.e., the extinction ratio (ER) is reduced. For higher input power, the modulation is exactly cancelled, i.e., the ER is almost 0 dB. Finally a further increase of injected power determines modulation inversion, with consequent eye re-opening. While the first two phenomena can be observed also in SOAs, though usually at higher injected power, the last regime is specific of RSOAs. In highly nonlinear RSOA the simultaneous presence of two waves, the incoming one and the reflected, which locally compete for gain along the device length, defines areas of strong depletion. The RSOA noise reduction capability, which has been widely exploited in passive optical networks (PON) topologies, is achieved by compressing the optical intensity fluctuations associated to the injected signal. This capability relies on the same mechanism governing gain saturation and modulation bleaching. Thus it is not surprising that the same nonlinear regimes observed in relation to gain saturation can be evidenced in relation to relative intensity noise (RIN) compression. In order to highlight this behavior and its consequences on PON design, we experimentally emulated a spectrum-sliced wavelength division multiplexing (WDM) PON topology. The impact on RIN of the injection into the RSOA and subsequent filtering actions operated by arrayed waveguide gratings (AWG) placed at the remote node and at the optical line terminal is evaluated both experimentally and by simulations. RIN measurements are performed in time domain exploiting a real time oscilloscope and in the spectral domain using an electrical spectrum analyzer in different point of the WDM PON topology to enlighten the different contributions to noise. Simulations have been also using an RSOA simple model, which has been realized with the commercial software, OptSim by RSOFT, and has been implemented by matching the data collected from the RSOA gain experimental characterization.

DOI: 10.1049/ic:20070284 ISBN: 978-3-8007-3042-1 Location: Berlin, Germany Conference date: 16-20 Sept. 2007 Format: PDF We derive the performance and critical design issues of optical-coding based centralized live PON monitoring technique allowing more than 512 clients. We consider PON geographical distribution models in our performance evaluation. (2 pages) Inspec keywords: condition monitoring; encoding; optical fibre networks Subjects: Optical fibre networks; Codes

Hybrid gigabit-passive optical network (GPON) is one of the hybrid optical networks, it integrates both Wave length Division Multiplexing (WDM) GPON and Time Division Multiplexing (TDM) GPON into a single passive network, which lowers the energy consumption, networking expenditure and boosts the data rate. In this paper, Radio over Fiber Technique of 10 GB/s GPON network architecture is implemented and verified using Quadrature Phase Shift Keying Modulation of 2.4 GHz radio frequency. Single-mode fiber of length 50 km is used to propagate the radio signals. Commercial OptiSystem simulation software is used to simulate the model. In total, 32 and 64 users are supported through this model. Based on the response of the constellation diagram, received power, eye diagram, and optical signal-to-noise ratio, the system is analyzed.

Wavelength Division Multiplexing (WDM) boosts a physical medium's carrying capacity. Light frequencies within a frequency range are assigned to incoming optical communications (wavelengths or lambdas). Dense Wavelength Division Multiplexing (DWDM) has lately acquired favor as a low-cost method of increasing the transmission capacity of existing fibre cable connections. DWDM was formerly solely used in baseband digital applications, especially in terrestrial long-distance networks and, in certain cases, metropolitan and commercial networks. The performance of DWDM components and frequency-stabilized lasers has lately skyrocketed, while their costs have plummeted. As a result, a variety of novel optical network configurations have become commercially viable. Different types of DWDM systems, such as point-to-point, tree, and ring networks, are developed based on application needs. Each of these systems needs an own set of parts. Because it provides greater management and protection measures, the ring configuration is preferred above all others. A multichannel high-speed DWDM ring with 16 channels and a channel spacing of 0.4 nm was developed in this work. Each channel has a 10 Gbps data rate. The performance optimization of the DWDM ring using various modulation techniques was discovered on the simulated ring. As a comparison, the MPAPM modulation format was employed. Different modulation formats' BER and Eye diagrams were compared and analyzed. MPAPM outperformed CRZ, NRZ, RZ, and DPSK, according to research. The Electronic Dispersion Compensation (EDC) iii technology, which includes Decision Feedback Equalizers (DFE) and Feed Forward Equalizers (FFE) equalizers, can extend the transmission distance even more.

Chapter 2 - PON Architectures Review

We propose a hybrid passive optical network (PON) architecture supporting time-division multiplexing (TDM) and dense spectrum-sliced wavelength-division multiplexing (SS-WDM) over the legacy PON infrastructure. We use a fiber Bragg grating (FBG)-based self-seeded reflective semiconductor optical amplifier (RSOA) transmitter in conjunction with a recently proposed balanced receiver (BR); identical transceiver pairs are placed at the central office and customer side. Self-seeded RSOAs obviate the need for centralized sources, providing a high power, directly modulated source. Intensity noise mitigation of this thermal source is investigated by operating the RSOA in saturation and employing the recently proposed BR. We study the optimal reflectivity for seeding that balances signal power and noise cleaning to achieve the best bit error rate (BER) possible; channel widths are comparable with dense WDM when using coherent sources.