Multiplexing Switching Research Articles

On optical communications networks and wideband network architecture

The optical networks of today are just beginning to realize their abilities to carry a tremendous amount of information in the forms of voice, data and video signals on a single optical fiber. However, many challenges lay ahead as designers and system developers attempt to integrate an ever greater number of signals. This conglomeration of various types of signals will be transported on the existing and proposed Local Area Networks, Metropolitan Area Networks and Wide Area Networks. This paper will cover some of the Wave Division Multiplexing and optical switching presently being evaluated in various testbed locations across the United States.

Congestion reduction in transmission of video over ABR networks

In transmission of bursty traffic such as video and data, a network with a fixed capacity may have some unused bandwidth. The available bit rate (ABR) scheme in ATM networks can make use of this spare channel capacity as a lower priority service. ABR has been developed initially for delay-tolerant services such as data. The authors demonstrate how, with the help of a video transcoder, delay-sensitive services such as video may be transmitted over ABR. The transcoder further compresses the video bit stream according to the rates dictated by the network with minimum degradation to the picture quality. The video quality has been optimised by combining the classical minimum cell rate (MCR) with the subjectively acceptable minimum quality (SAMQ). The performance of two different coding formats for ABR sources, namely the constant bit rate (CBR) and variable bit rate (VBR) video input to the transcoder are compared. The authors also present techniques for further reduction of congestion at the multiplexing switches and report on the impact of the forward and backward link delays on the ABR performance with a video transcoder.

Design and implementation of ultra-low latency optical label switching for packet-switched WDM networks

An ultra-low latency, high throughput Internet protocol (IP) over wavelength division multiplexing (WDM) packet switching technology for next-generation Internet (NGI) applications has been designed and demonstrated. This method overcomes limitations of conventional optical packet switching, which require buffering of packets and synchronization of bits, and optical burst switching methods that require estimation of delays at each node and for each path. An optical label switching technique was developed to realize flexible bandwidth-on-demand packet transport on a reconfigurable WDM network. The aim was to design a network with simplified protocol stacks, scalability, and data transparency. This network will enable the NGI users to send their data applications at gigabit/second access speed with low and predictable latency (<1 /spl mu/sec per switch node), with a system capacity of beyond multi-Tb/s. Packet forwarding utilizes WDM optical headers that are carried in-band on the same wavelength and modulated out-of-band in the frequency domain.

Gain-transparent SOA-switch for high-bitrate OTDM add/drop multiplexing

We report on an all-optical interferometric optical time-division multiplexing switch that exhibits high linearity, high-switching contrast, low noise, wide bandwidth, and low crosstalk. The key element of the gain-transparent switch is a semiconductor optical amplifier (SOA), which is transparent for the data signal. However, the injection of optical control pulses in the gain wavelength region of the SOA leads to index modulations at the wavelength of the data. This variation of the refractive index can be used for interferometric switching. In the application as add/drop multiplexer, the switch has the inherent advantage of leaving the nonswitched pulses undisturbed.

A non-blocking architecture for a wavelength division multiplexing photonic switching network

The authors previously derived the condition for a non-blocking architecture in a wavelength division multiplexing (WDM) photonic switching network, i.e., the generalized parallel delta network (GPDN) [1]. GPDN is configured as a multi-stage link connection of multiple unit switches, where the hardware complexity can be adjusted by varying the number of stages according to the network size. It can provide a framework for network design of various trunk networks, access networks, and in-station networks. This paper presents an architecture for a wavelength division multiplexing photonic unit switch that is applicable to a wavelength division multiplexing photonic switching network (GPDN), and evaluates the cost. The proposed wavelength division multiplexing photonic unit switch is constructed by assuming the situation in which an optical signal is multiplexed and handled without being converted to an electrical signal and employing the wavelength division multiplexing technique. The latter is considered promising for future networks from the viewpoint of reducing hardware complexity and economizing broadband communication. The input call to the carrier is wavelength converted to the carrier corresponding to the required outlet. Then, an optical filter is used to realize spatial switching. By combining the photonic unit switches proposed here, a large-scale switching network can be constructed. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(8): 59–67, 1998

A non‐blocking architecture for a wavelength division multiplexing photonic switching network

A non‐blocking architecture for a wavelength division multiplexing photonic switching network

Analysis of a WDM packet switch with improved performance under bursty traffic conditions due to tuneable wavelength converters

For realistic traffic, i.e., bursty traffic patterns, the use of tuneable wavelength converters is recognized as essential for reducing the complexity of photonic wavelength division multiplexing (WDM) packet switches. Results are obtained from an analytical traffic model that includes buffering in the wavelength domain and accounts for bursty traffic. The theoretical model is verified by simulations and from the model we find that higher traffic loads as well as burstiness can be accepted when tuneable wavelength converters are used. Consequently, a larger throughput of the photonic packet switches is obtained and very importantly, this is achieved while keeping the number of gates needed to realize the space switches nearly constant.

Integrated multichannel optical wavelength selective switches incorporating an arrayed-waveguide grating multiplexer and thermooptic switches

A multichannel optical wavelength selective switch is investigated, which can switch signals at arbitrary wavelengths between multichannels in wavelength division multiplexing systems. It is based on the combination of an arrayed-waveguide grating (AWG) multiplexer and an array of optical space-division switches. A monolithically integrated 2/spl times/2 optical wavelength selective switch is successfully fabricated for four multiplexed signals in the 1.55 /spl mu/m wavelength region. Here, an AWG and four 2/spl times/2 thermooptic switches are laid out on a 30/spl times/60 mm/sup 2/ chip. Wavelength selective switching operations for four wavelength signals between two lines are demonstrated in a time slot of 40 ms with a switching speed of 1 ms.

Redundancy design of a wafer scale and high‐speed FFT processor

The purpose of this paper is to provide a realization of FFT processors capable of real time processing of image signals. All of the arithmetic operations in such FFT processors must be achieved with hardware technology, so that the chip size of the processor LSI is wafer scale. To realize such WSI processors, this paper introduces redundancy technology. A redundant system design is shown in which special emphasis is placed on the chip area of the interconnection lines between butterflies as follows: 1 In the design of the non-redundant FFT processor, the chip area of the interconnection lines is reduced as much as possible. 2 A redundant structure capable of recovering from defects in the interconnection lines is proposed. 3 A yield equation is derived in which the entire effect of interconnection area is considered. 4 In the redundant system design, the total redundant chip area, including the chip area for interconnection lines and multiplexing switches, is minimized. It is indicated that an FFT processor whose chip area is 120 times that of the standard LSI with 50% yield may be realized with a 6% increase in chip area but without decreasing the yield. © Scripta Technica, Inc. Syst Comp Jpn, 28(6): 18–29, 1997.

Redundancy design of a wafer scale and high-speed FFT processor

The purpose of this paper is to provide a realization of FFT processors capable of real time processing of image signals. All of the arithmetic operations in such FFT processors must be achieved with hardware technology, so that the chip size of the processor LSI is wafer scale. To realize such WSI processors, this paper introduces redundancy technology. A redundant system design is shown in which special emphasis is placed on the chip area of the interconnection lines between butterflies as follows: 1) In the design of the non-redundant FFT processor, the chip area of the interconnection lines is reduced as much as possible. 2) A redundant structure capable of recovering from defects in the interconnection lines is proposed. 3) A yield equation is derived in which the entire effect of interconnection area is considered. 4) In the redundant system design, the total redundant chip area, including the chip area for interconnection lines and multiplexing switches, is minimized. It is indicated that an FFT processor whose chip area is 120 times that of the standard LSI with 50% yield may be realized with a 6% increase in chip area but without decreasing the yield.

Free-Space Optical Crossbar-Switches for Self-Routing and Strictly Nonblocking Networks

A space-division multiplexing switch was fabricated without precise alignments using electro-photonic multichip module technologies. Design rules and fabrication processes for the switch are described. Experiments show the switch has capacity for 1-Gigabit-per-second data transmission.

FRONTIERNET: frequency-routing-type time-division interconnection network

This paper describes a photonic time division multiplexing (TDM) highway switch, called FRONTIERNET, that uses optical frequency as routing information. This switch architecture can be applied to asynchronous transfer mode (ATM) switching systems. The N/spl times/N switch consists of N tunable frequency convertors and N frequency-division-multiplexed (FDM) output buffers connected through an N/spl times/N frequency router. The router can interconnect N input highways with N output highways in a completely noninterfering way. It is possible to address each output highway uniquely by the choice of frequency (frequency routing) and each output highway can receive any given frequency from only one input. This switch architecture therefore has three advantages: its novel output buffering scheme achieves the best possible performance, there is no need for a complicated contention resolution mechanism between input highways, and there is no splitting loss of the transmitted optical power. An experimental switch with a one-cell FDM buffer was constructed. The tunable frequency convertor based on fast tunable frequency lasers can transmit high-speed optical cells to which frequencies are assigned on a cell-by-cell basis. The frequency router is an integrated-optic arrayed-waveguide grating 16/spl times/16 filter produced by using planar-lightwave-circuit (PLC) technology. The one-cell FDM output buffer based on optical fiber delay lines can store FDM cells and select only one cell at each timeslot over the output highway. A 2.5-Gb/s experimental switch was successfully operated, And an experimental FDM loop buffer was also demonstrated. This stores two cells at a data rate of 2.5 Gb/s. The bit error rate (EER) of the cells after up to 10 circulations is <10/sup -9/. The performance of the buffer in terms of the probability of cell loss and the cell wafting time in the buffer is analyzed numerically. It is concluded that fewer optical buffers are needed to satisfy the desired probability of the cell loss compared with the conventional electronic buffers. The scale of the switch can be expanded in a modular fashion in two ways using a multistage frequency router and a multistage switching network. And the multihop FRONTIERNET architecture is proposed to reduce the required frequency channels rather than the single-hop FRONTIERNET. The switch scale is also very easy to expand by connecting the frequency-router-based switching submodules.

WDM packet switch architectures and analysis of the influence of tunable wavelength converters on the performance

A detailed analytical traffic model for a photonic wavelength division multiplexing (WDM) packet switch block is presented and the requirements to the buffer size is analyzed. Three different switch architectures are considered, each of them representing different complexities in terms of component count and requirements to the components, it is shown that the number of fiber delay-lines, that form the optical buffer, can be substantially reduced by the use of tunable optical wavelength converters, thereby exploiting the wavelength domain to solve contention of optical packets. For a 16/spl times/16 switch with four wavelength channels per inlet, all at a load of 0.8, the number of delay-lines is reduced from 47 to 12 by use of tuneable optical wavelength converters. Apart from the number of delay-lines the physical buffer structure is analyzed with special attention to the possibilities offered by optics, i.e., the possibility of several outlets sharing the same physical buffer. For the three architectures presented here, a tradeoff in the buffer architectures is addressed: a buffer physically shared among an outlets requires many wavelengths internally in the switch block, whereas, architectures with buffers dedicated to each outlet require a smaller number of wavelengths.

Digitally tunable optical filters using arrayed-waveguide grating (AWG) multiplexers and optical switches

Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(/spl radic/(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel.

Use of WDM technique in SDH networks

Abstract This paper proposes the introduction of the multiwavelength technique in the three layers of a SDH-based network. In the trunk layer, wavelength division multiplexing (WDM) takes advantage of the optical parallelism in a single fiber. Cross-connection can be achieved either passively (i.e., with tunable filters) or by means of wavelength converters. The latter solution, which offers high flexibility, was implemented in a 4 × 4 optical routing element. In the junction network the feasibility of a three-station WDM self-healing ring was demonstrated. Finally, in the access network, synchronous burst access and time and wavelength division multiplexing (T/WDM) switching is proposed to offer service flexibility to the subscribers.

A novel all-optical self-routed wavelength-addressable network (SWANET)

A novel all-optical self-routed wavelength-addressable network based on a new multiwavelength routing protocol is proposed. A distributed switching network that uses a low-speed routing header provides a transparent path for the high-speed data while utilizing low-speed electronic processing of the routing header. Each data packet is preceded by a routing header composed of a serial combination of wavelengths. The number of destination addresses is dramatically increased over conventional wavelength-division multiplexing or conventional photonic packet switching networks for the same number of wavelengths or header digits, respectively. A 1/spl times/4 switching node is implemented demonstrating the switching and transmission capabilities of this wavelength-addressable network. >

A broadband ring network: multichannel optical slotted ring

This paper presents a multichannel optical ring network for broadband integrated services. The network uses a multichannel architecture with wavelength division multiplexing (WDM) and photonic packet switching devices for its access mechanism. The electronic speed bottleneck is removed out of the ring, which allows utilization of the full bandwidth for the optical fiber transmission medium. For compatibility with B-ISDN, the network uses a similar cell structure to that of an ATM based cell with a slotted ring concept. Fiber optic delay line matched filters are used as a means of address detection at the destination nodes. The network architecture is described and a design of the optical switching node is presented. A novel technique is devised in order to measure the average transfer delay of a cell in the multichannel slotted ring network. The analytical results show an excellent agreement with simulation results over a broad range of parameters. The results show that the major part of the cell transfer delay is coming from the propagation delay from a source to a destination. It is also observed that the throughput characteristic of the network depends upon the aggregated transmission capacity of the network.

Simulation driven resource allocation in ATM networks

Asynchronous Transfer Mode (ATM) traffic is characterized by a wide variety of traffic source classes. Each class of traffic has differing effects on the buffer and link capacity resources of the network. This results in a high level of complexity in predicting resource allocations for each source. The network must be managed in real-time in order to avoid congestion which tends to collapse its utilization. Network congestion requires admission control which in turn must require a measure of resource requirements from a randomly variable source. In this paper we proposed a frequency-domain probability density function convolution method for predicting the resource requirements of a source based on its input characteristics. A taxonomy and classification of sources based on measurable characteristics is also proposed. The classes of sources are simulated and the resulting requirements are compared to the prediction. A feedback mechanism is described which can result in a highly accurate and very efficient table lookup method for realtime resource allocation in ATM multiplexing switches.

FDM-channel selection filter using arrayed-waveguidegratingmultiplexer with input and output switches

A novel configuration is reported for a tunable channel-selection filter that employs an arrayed-waveguide grating (AWG) multiplexer and optical switches. The filter requires only 2(√N – 1) 1 × 2 switch elements to select one of N frequency-division-multiplexed (FDM) channels. A filter for 100 GHz-spaced 16 FDM channels is demonstrated with an AWG 16 × 16 multiplexer and six 1 × 2 switches.

NONLINEAR ORGANIC MOLECULES AND MATERIALS FOR OPTOELECTRONIC DEVICES

The development of important applications related to optical telecommunications and optical signal processing rely increasingly on nonlinear optical phenomena underlying these optical functions such as frequency conversion and modulation, amplification and emission, multiplexing and directional switching, optical logical gates, and others. This will depend on the design, elaboration and availability of new materials displaying enhanced nonlinearities to be subsequently integrated into waveguiding devices. Organic materials are noteworthy candidates in this context, provided their microscopic and macroscopic properties are properly optimized with respect to the type of application required. Among the key-factors in the development of these materials are the quasi-unlimited variety of molecular structures accessible by organic synthesis, the possibility to connect specific nonlinear properties to other kinds of functionalities which are of crucial importance for the development of commercial devices (e.g., compatibility with other materials used in integrated optical circuits such as semi-conductors), and their exceptionally large second-order, non-resonant nonlinear response. Such performances are strongly dependent on a better understanding of the ‘molecular engineering’, rules, correlating molecular structures to their nonlinear optical properties towards optimization of the microscopic second order polarizabilities β and third-order polarizabilities γ. We will present in the following some examples of the most recent developments of highly efficient nonlinear molecules, ranging from purely one-dimensional structures such as polyenes to fully three-dimensional systems, taking full advantage of the tensorial character of the microscopic or macroscopic susceptibility tensors.