This PDF file contains the front matter associated with SPIE Proceedings Volume 7959, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

Worldwide, higher-order modulation formats are intensively investigated to further increase the spectral efficiency for building the next generation of high-speed metro systems. IQ-modulators, coherent receivers and electronic equalizers are hereby discussed as key devices. We report on system design issues as well as on HHI's latest achievements in developing InP based high-speed modulators and coherent receiver frontends.

As response to continuously increasing demands on transmission capacity, we describe a four-dimensional (4D) coded multicarrier/OFDM schemes suitable for metro and long-haul optical networks, which are capable to fully exploit advantages of both multicarrier/OFDM and multidimensional systems. Two multidimensional coded modulation schemes are presented in this invited paper: (i) 4D multicarrier system in which the 4D signal constellation points are imposed on orthogonal subcarriers and (ii) N-dimensional OFDM scheme. In N-dimensional OFDM, the signal constellation points are represented in matrix form by placing coordinates of signal constellation points along columns of signal matrix. We further apply 2D inverse FFT to obtain 2D array of complex numbers. Coordinates of complex numbers can be considered as I and Q channels, while coordinates of 2D array can be mapped to two orthogonal polarizations; resulting in 4D signal space. On receiver side, we use conventional polarization-diversity receiver, followed by 2D-FFT demapper. Therefore, these schemes can fully exploit advantages of OFDM, to deal with chromatic dispersion, PMD and PDL effects; and multidimensional signal constellations to improve dramatically OSNR sensitivity of conventional optical OFDM systems.

In order achieve beyond 400 Gb/s serial optical transmission using commercially available equipment, in this work, we propose the use of channel capacity achieving modulation formats. We present a method to determine the optimum signal constellation for an arbitrary dispersion map. This method can be described by the following steps. (i) Determine the probability density functions (pdfs) of the fiber-optics channel, which can be approximated by complex Gaussian function or estimated by evaluating histograms. (ii) Use the resulting pdfs to determine the optimum input distribution to achieve the channel capacity. A split-step method is presented to perform the optimization over the probabilities and mass points of input distributions. (iii) After quantizing the optimum input distribution the optimum signal constellation can be determined. We study two types of dispersion maps currently in use, which are suitable for metro and mediumhaul applications. For each of them we determine the optimum signal constellation. The numerical results demonstrate the efficiency of this method and show that the optimized signal constellation can increase the transmission distance at most by three spans against its counterpart.

This paper shows the requirements for next generation optical access (NGOA) networks and analyzes the potential of OFDM (orthogonal frequency division multiplexing) for the use in such network scenarios. First, we show the motivation for NGOA systems based on the future requirements on FTTH access systems and list the advantages of OFDM in such scenarios. In the next part, the basics of OFDM and different methods to generate and detect optical OFDM signals are explained and analyzed. At the transmitter side the options include intensity modulation and the more advanced field modulation of the optical OFDM signal. At the receiver there is the choice between direct detection and coherent detection. As the result of this discussion we show our vision of the future use of OFDM in optical access networks.

Multicolor (a.k.a. broadband) photodetector having a detection capability ranging from near ultra-violet to infrared can be useful as a common detector for various applications such as optical communication and optical interconnects etc. The capability of using single detector in receiver system for optical communication covering both data and transport systems, not only makes the total system cost lower, but it also makes easier the system vendors to reduce the inventory. We proposed detector having the detection capability ranging from 350 nm to 2000 nm, wavelengths that covers all optical communication wavelengths application. This invited paper has two-fold objectives: (a) provide a comprehensive overview of conventional photo detectors and their types, being used in today's optical communication and (b) introduce a development of broadband photodetector which authors pioneered. The features of proposed broadband detector are simple structure, low-cost, high quantum efficiency, high sensitivity, and high speed. Performance results will be presented along with its possible applications.

Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.

POFs (polymer optical fibers) gradually replace traditional communication media such as copper and glass within short distance communication systems. Primarily, this is due to their cost-effectiveness and easy handling. POFs are used in various fields of optical communication, e.g. the automotive sector or in-house communication. So far, however, only a few key components for a POF communication network are available. Even basic components, such as splices and couplers, are fabricated manually. Therefore, these circumstances result in high costs and fluctuations in components' performance. Available couplers have high insertion losses due to their manufacturing method. This can only be compensated by higher power budgets. In order to produce couplers with higher performances new fabrication methods are indispensable. A cheap and effective way to produce couplers for POF communication systems is injection molding. The paper gives an overview of couplers available on market, compares their performances, and shows a way to produce couplers by means of injection molding.

Photonic balancing - a scheme where logically opposite pulses derived from the two outputs of a delay-line demodulator for phase shift keyed (PSK) signals counter-propagate in the saturated regime of a semiconductor optical amplifier (SOA) - has been proven to enhance the receiver performance, e.g. in terms of decreased optical signal-to-noise-ratio (OSNR) requirements for a given target bit error ratio (BER). Here, we extend the photonic balancing scheme towards a new concept for a regenerative amplifier targeted at extending the reach and/or the number of subscribers in passive optical networks (PON) in order to support major operators' plans to reduce the number of central offices and access areas by approximately 90%. For a given target BER, we demonstrate experimentally (a) an 8-dB higher post-amplifier loss tolerance, (b) an extended feeder line length (75 km) combined with high splitting ratio (10 layers) for a preamplified version, and (c) high input power variation tolerance (> 30 dB burst-to-burst) in upstream direction as needed for highly asymmetric tree structures.

In this article we present a summary of the latest 100 Gbps field trials in the network of Deutsche Telekom AG with industry partners. We cover a brown field approach as alien wavelength on existing systems, a green field high speed overlay network approach and a high speed interface router-router coupling.

Nonlinearities are a performance limitation in coherent optical links, and efforts have been made to understand the tradeoffs between launch power and the penalties related to nonlinearities. Using both simulation and experimental results from our 100G testbed we investigate the use of a nonlinear phase criterion that quantifies the total nonlinear phase accumulation within a 112 Gb/s PDM-QPSK link. We examine the nonlinear effects of self-phase (SPM) and cross-phase modulation (XPM) on a 112 Gb/s PM-QPSK channel propagating between four 10 Gb/s OOK aggressor channels on a 50 GHz grid and quantify the launch power and span count scaling behavior. In order to assess the applicability of a nonlinear phase criterion on real-world links, we determine the launch power that yields a 1.5 dB OSNR penalty at a BER of 10^-3 for each configuration. This launch power then allows the identification of a Nonlinear Threshold Power (number of spans times launch power) that fully incorporates the increasing nonlinear penalties with further transmission distance. This metric allows for the determination of a set of engineering rules for deployment of 100 Gb/s PDM-QPSK in linear links with arbitrary number of spans and span distances. We find that this nonlinear threshold is constant in dispersion-compensated links. These experimental results are validated with simulations.

Flattop liquid crystal tunable optical interleavers have shown a great potential to perform in the DWDM systems. In this paper, chromatic dispersion analyses are conducted for a flattop liquid crystal tunable optical interleaver based on Combined Michelson and Gires-Tournois interferometers. In order to try to reduce the dispersion associated with the interleaver's operation, tuning capability of the liquid crystal is used to tune the chromatic dispersion spectrum. Simulation results show a 66.5% reduction in the chromatic dispersion for the simulated interleaver configuration when compared to the air filled cavities in the interleaver. This reduction is achieved without any additional components or design modifications but only with the tuning capability of the liquid crystal. Moreover, the chromatic dispersion spectrum can be tuned. This provides more freedom for designers to try to minimize the chromatic dispersion effects on the system performance.

Polarization mode dispersion is the limiting factor in todays large capacity photonic network systems since it causes intersymbol interference especially at high data rates. When polarization multiplex is employed to increase spectral efficiency, the distortions caused by polarization mode dispersion get even stronger due to the additional polarization crosstalk. Employing coherent detection these mitigations can be fully compensated with linear filters, since coherent detection delivers amplitude, phase and polarization information of the electrical field. As a drawback we have to take into account a high complexity of the receiver, causing high overall cost. At the other hand we have direct detection systems where the receiver complexity can be kept low. Furthermore maximum likelihood sequence estimation detection has been successfully demonstrated for standard direct detection systems. In a first step an advanced maximum likelihood sequence estimation detector, which is able to work in an intensity modulated polarization multiplex direct detection system, is developed. The performance of the detector is assessed by simulations and it is shown that it is capable to significantly reduce system outages. The method then is compared with a least mean squares based equalizer which is employed to compensate for signal distortions in an intensity modulated polarization multiplex coherent detection transmission system.

A technique for DPSK receiver-sensitivity improvement is demonstrated using numerical simulations. It is based on reshaping and reamplifying of received 80 Gbit/s DPSK using an SOA before a one bit delay interferometer. The SOA re-amplifies data without adding amplitude or differential phase noise due to its gain-compression. The system is tested using 2³¹-1 PRBS RZ-DPSK (NRZ-DPSK) loaded with both phase and amplitude noise. It shows 2dB (1.7dB) quality-factor improvement. The estimated BER by error-counting shows receiver-sensitivity improvement of (See manuscript)3dB in case of single-ended detection and (See manuscript)2dB ((See manuscript)2.5dB) in case of balanced-detection. This single-ended improvement is comparable to that of common DPSK balanced-detection technique.

This paper presents an overview of the requirements of the next generation dynamic mesh type reconfigurable optical add-drop multiplexer (ROADM) networks carrying optical channels at 100Gb/s and higher data rates. Liquid crystal (LC) and 1-axis Micro-Electro-Mechanical Systems (MEMS) for scalable and flexible wavelength selective switches (WSS) devices for these networks is highlighted.

The current fixed grid WDM system and ROADM node cannot provide optimum spectrum utilization and flexibility in metro networks. A solution is a flexible WDM network that can allocate optical spectrum and provision connections dynamically. In this paper, we propose and experimentally demonstrate a colorless, directionless and contentionless multi-degree ROADM node with flexible spectrum configuration for such network. Experiment results show that interdegree cross-connect and colorless, directionless add/drop operation on spectrum variable WDM signals can be achieved without incurring wavelength blocking in the node. This ROADM node enables spectrum efficient and cost efficient switching compared to fixed grid ROADM nodes.

This paper proposes an inter-domain path control system based on PCE (Path Computation Element) for large-scale photonic networks, especially for a photonic network across over multiple carrier domains. We discuss the overall architecture of multi-domain optical network control system. The system utilizes maximum flow information in path computation and Path Key scheme in signaling, which improve the load-balancing and the confidentiality of the inside information for the route computation and the path provisioning among different carriers. We also provide measured performance results for inter-domain path computation and path setups using global optimization scheme, estimating the path provisioning time at the network scale dependency with the route computation time and the signaling time. As a result, we show its applicability to a 1000-node scale photonic network.

A strategy is implemented for solving the Logical Topology Design (LTD) based on a Linear Formulation (LP) with channel interference constraints. The formulation is able to provide excellent solutions. In traditional LTD Problem there is no a-priori knowledge of channel use and once the solution has been implemented the interference cannot be avoided. Taking into consideration the effects of adjacent channel interference, we extend the traditional formulation as a set of analytical formulas as additional constraints on LTD.

Optical networks of tomorrow are expected to support the rapid growth of data services such as the broadband access, including broadband mobile access, storage area networks with long connection times and large transfer capacities, as well as data center interconnections, requiring ultra-high capacity links. Those services with differing capacities and patterns will converge in the same optical platform. The standardization bodies have reached an agreement on the format of the optical 100 Gb/s transmission. However, the large variety of services is likely to generate traffics both below 100 Gb/s as well as exceeding that maximum port speed. In order to address this demand efficiently it is necessary to consider more flexible methods of traffic allocation. One solution may be provided by a spectrum-sliced elastic optical path network (SLICE). The aim of SLICE is to efficiently allocate client traffic while performing the necessary networking functionality directly in the optical domain. Technologies and concepts employed in SLICE enable efficient utilization of network resources by providing optical paths with bandwidths ranging from 40 Gb/s to over 400 Gb/s. Basing on the concept of elastic optical path, we discuss the following concepts: path bandwidth flexibly following client traffic with capacity of 40 to 400Gb/s, grooming and aggregation performed optically: seamless aggregation of optical paths exceeding the maximum speed of a single port to form a super-wavelength optical path; sharing of resources through reduction of the overall number of required resources; distance adaptation through reduction of consumed resources by transmission margin optimization.

Requirements on photonics modeling vary significantly when aiming to design, analyze and optimize a single device, a complete transmission link or a complex network. Depending on the task at hand, different levels of detail for emulating the underlying physical characteristics and signal interactions are necessary. We present a multi-layer photonics modeling framework that addresses the different design challenges of devices, links and networks. Our discussed methodology is based on flexible optical signal representations, equipment models ranging from very detailed to high-level parametric, sophisticated numerical algorithms and means for automated parameter and technology variation and optimization. We discuss applications such as the detailed modeling on photonics integrated circuit level, the characterization of a high-speed transmission link utilizing multilevel modulation and coherent detection, the parametric analysis of transmission links and network dynamics, and the cost-optimized placement of equipment in moderately complex networks.

Due to emerging heterogeneous applications, the traffic in metro optical networks is becoming more dynamic with diverse granularities. The Flexible Optical WDM (FWDM) network architecture can support such heterogeneous line rates with finer granularities by provisioning channels with flexible spectrum allocation to leverage spectral and wavelength efficiencies. In this paper, we introduce the dynamic routing, wavelength assignment, and spectrum allocation problem for the first time. We propose an efficient greedy algorithm, and evaluate the the performance of the FWDM architecture with the conventional fixed grid WDM network architecture in terms of blocking probability and network throughput. Results show that the proposed architecture improves network blocking probability and throughput compared to fixed grid networks.

In this work, we have demonstrated a new smart grid model by our novel green photonics technology based on selforganized optical networks realizing an autonomous peer-to-peer electric power transmissions without centralized control for the power grid. In this optical network, we introduced an adaptive algorithm for concurrent peer-to-peer communications, by utilizing optical nonlinearity depending only on the signal strength passing through the network. This method is applicable for autonomous organization of functions for ad-hoc electric power distribution systems for the power grid. For this purpose, a simple optical- electrical hybrid bistable circuit composed of such as light emitting diode (LED) and photo diode (PD), has been incorporated into the network node. In the experiment, the method uses a simple, local adaptation of transmission weights at each network node, which enables self-organizing functions of the network, such as self-routing, self-optimization, self-recovery and self-protection. Based on this method, we have demonstrated experimentally a new smart grid model applicable for ad-hoc electric power distribution systems mediated by power comsumptions. In this model, electric power flow is controlled autonomously through the self-organized network nodes associated with individual power facilities having photovoltaics and electric storage devices, etc., and the nodes convert the amounts of electric power supply and/or comsumption to the light intensity values using above mentioned transmission weights at each node. As a consequence, we have experimentally demonstrated a simple shorthaul system model for ad-hoc electric power distribution with a self-organized optical network as a novel green photonics technology application for smart grid.