A photonic front-end processor in a WDM ATM multicast switch

Dense wavelength-division multiplexing (DWDM) technology has provided tremendous transmission capacity in optical fiber communications. However, switching and routing capacity is still far behind transmission capacity. This is because most of today's packet switches and routers are implemented using electronic technologies. Optical packet switches are the potential candidate to boost switching capacity to be comparable with transmission capacity. In this paper, we present a photonic asynchronous transfer mode (ATM) front-end processor that has been implemented and is to be used in an optically transparent WDM ATM multicast (3M) switch. We have successfully demonstrate the front-end processor in two different experiments. One performs cell delineation based on ITU standards and overwrites VCI/VPI optically at 2.5 Gb/s. The other performs cell synchronization, where cells from different input ports running at 2.5 Gb/s are phase-aligned in the optical domain before they are routed in the switch fabric. The resolution of alignment is achieved to the extent of 100 ps (or 1/4 bit). An integrated 1×2 Y-junction semiconductor optical amplifier (SOA) switch has been developed to facilitate the cell synchronizer     

Design and performance of an optical path cross-connect systembased on wavelength path concept

This paper describes the system design and performance of an optical path cross-connect (OPXC) system based on wavelength path concept. The (OPXC) is designed to offer 16 sets of input and output fiber ports with each fiber transporting eight multiwavelength signals for optical paths. Each optical path has a capacity of 2.5 Gb/s. Consequently, the total system throughput is 8×16×2.5=320 Gb/s and the OPXC features high modularity and expandability for switch components. By exploiting planar lightwave circuit (PLC) technologies, four sets of (8×16) delivery-and-coupling-type optical switches (DC-switches) are developed for the 320 Gb/s throughput OPXC system. The DC-switch offers the average insertion-loss of 12.6 dB and ON/OFF ratio of 42.1 dB. The PLC arrayed-waveguide gratings are confirmed to successfully demultiplex the eight directly modulated signals, multiplexed at a spacing of 1 nm, with a crosstalk of under -25 dB. Eight wavelength-division multiplexing signals, directly modulated at 2.5 Gb/s, are confirmed to be transported over 330 km via a cross-connection node in the test-bed system that simulates five-node network. The experimental performances demonstrated In this paper ensures full scale implementation of the proposed optical path cross-connect system with 320 Gb/s throughput and high integrity     

Coherent-to-incoherent light conversion for optical correlators

The authors present a novel coherent-to amplified spontaneous emission (ASE) converter based on SOA's cross-gain modulation (XGM) in a counterpropagating configuration. Experimental characterizations of the ASE converter with bit-error rate (BER) measurements at 2.5 and 5 Gb/s are shown. The device capabilities are exploited in a delay lines optical recognizer at 2.5 Gb/s. Recognition is based on a coherent-to-incoherent light conversion followed by a fiber array correlation filter. Experimental evidence here reported shows performance improvement in comparison with a scheme which adopts a standard telecom source     

Experimental and analytical evaluation of packaged 4×4InGaAsP/InP semiconductor optical amplifier gate switch matrices foroptical networks

Packaged 4×4 semiconductor optical amplifier gate switch arrays have been studied experimentally and analytically. Experimentally, a dynamic range of the input power to the switch of more than 20 dB was obtained at 622 Mb/s with less than 2 dB power penalty. Wavelength division multiplexing transmission with four channels at 622 Mb/s each through the same path was successfully demonstrated. The switch was also evaluated in an installed fiber network, where a 2.5 Gb/s signal was transmitted through three cascaded switch routes and 160 km fiber. A numerical time-domain model incorporating an electrical filter in the receiver confirmed the experimental results. It furthermore indicated that residual reflections between the different waveguide sections within the switch and at the chip facets may degrade the performance of the switch     

Client-configurable eight-channel optical add/drop multiplexerusing micromachining technology

A client-configurable optical add/drop multiplexer (OADM) is demonstrated using a micromachined 8×6 matrix switch. The matrix switch can be configured to add/drop any of the eight input channels from/to any of the six add/drop ports. For the switching fabric, the insertion loss is 2~3 dB for the dropped channels and 8~9 dB for the added channels by using the backsides of the micromirror switches. The switching extinction ratio is over 40 dB, the crosstalk between channels is less than -40 dB, and they are equipment-limited in this experiment     

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.     

An optical packet switch based on WDM technologies

Dense wavelength-division multiplexing (DWDM) technology offers tremendous transmission capacity in optical fiber communications. However, switching and routing capacity lags behind the transmission capacity, since most of today's packet switches and routers are implemented using slower electronic components. Optical packet switches are one of the potential candidates to improve switching capacity to be comparable with optical transmission capacity. In this paper, we present an optically transparent asynchronous transfer mode (OPATM) switch that consists of a photonic front-end processor and a WDM switching fabric. A WDM loop memory is deployed as a multiported shared memory in the switching fabric. The photonic front-end processor performs the cell delineation, VPI/VCI overwriting, and cell synchronization functions in the optical domain under the control of electronic signals. The WDM switching fabric stores and forwards cells from each input port to one or more specific output ports determined by the electronic route controller. We have demonstrated with experiments the functions and capabilities of the front-end processor and the switching fabric at the header-processing rate of 2.5 Gb/s. Other than ATM, the switching architecture can be easily modified to apply to other types of fixed-length payload formats with different bit rates. Using this kind of photonic switch to route information, an optical network has the advantages of bit rate, wavelength, and signal-format transparencies. Within the transparency distance, the network is capable of handling a widely heterogeneous mix of traffic, including even analog signals.     

Lossless 1×4 laser diode optical gate switch

The fabrication of a compact 1×4 laser diode (LD) optical gate switch for the 1.3 μm band, comprising five LD optical gate submodules and a 1×4 planar lightwave circuit, is described. The switch exhibited a lossless switching function and polarization sensitivities of 0.5-1.1 dB, with operation currents of 45 to 55 mA. At operation currents of 120 mA, the switch exhibited positive gains of 9.0 to 10.2 dB. No power penalty was detected for nonreturn-to-zero (NRZ) transmissions of up to 2 Gb/s at -10 dBm input levels, when a narrowband optical filter for spontaneous emission reduction was used     

Large-scale WDM star-based photonic ATM switches

This paper describes the large-scale photonic asynchronous transfer mode (ATM) switching systems being developed in NTT Laboratories. It uses wavelength division multiplexing (WDM) techniques to attack 1 TB/s throughput. The architecture is a simple star with modular structure and effectively combines optical WDM techniques and electrical control circuits. Recent achievements in important key technologies leading to the realization of large-scale photonic ATM switches based on the architecture are described. We show that we can obtain a 320 Gb/s system that can tolerate the polarization and wavelength dependencies of optical devices. Our experiments using rack-mounted prototypes demonstrate the feasibility of our architecture. The experiments showed stable system operation and high-speed WDM switching capability up to the total optical bandwidth of 12.8 nm, as well as successful 10 Gb/s 4×4 broadcast-and-select and 2.5 Gb/s 16×16 wavelength-routing switch operations     

2×2 buffered switch fabrics for traffic routing, merging, andshaping in photonic cell networks

An approach to optical packet switching is discussed, which uses small, simplified optical elements for traffic routing, merging, and shaping. The elements are constructed from 2×2 switches and optical delay lines, and may be implemented in a variety of technologies. They are designed for use with deflection routing, and even when using only six switches in a module, a deflection probability of 2.8×10^-7 is possible with a load of 0.8. The modules may also be used as 2×1 mergers where a deflection probability of 10^-12 is possible with six switches and a total load of 0.8. The BER performance of the modules is simulated with respect to crosstalk, with even relatively poor switch devices of -18.5 dB isolation yielding a power penalty of less than 1 dB. A networking strategy radically different from today's is discussed, driven by the need to reduce hardware, software and operating costs     

Capacity Scaling in a Multihost Wavelength-Striped SOA-Based Switch Fabric

The scaling of the capacity of a semiconductor- optical-amplifier-based switch carrying wavelength-striped data is assessed under packet timescale reconfiguration for short- reach high-capacity data interconnects. Off-the-shelf components are used with a low-complexity control layer to demonstrate high-capacity end-to-end packet routing. The impact of increasing the aggregate data rate and the number of connections made to the switch fabric is assessed in terms of the power penalty and dynamic range for a broadcast and select architecture. Studies with up to ten wavelength-multiplexed data channels with an aggregate capacity of 100 Gb/s are shown to give sufficient margin for even higher aggregate data rates and for the additional splitter stages, which would enable 8times8 connectivity in a single stage. Further increases in connectivity are anticipated with higher performance commercially available transmitters and receivers. Multipath routing is assessed with three hosts simultaneously transmitting wavelength-striped data packets over the same switch fabric to reveal a penalty in the range of 0.3-0.6 dB due to multi- path crosstalk and a modest penalty in the range of 0.4-1.2 dB that was incurred through dynamic routing. A route to terabit-per- second switch performance in a single-stage low-complexity switch fabric is identified.     

High-level fluctuation tolerant optical receiver for optical packetswitch and WDM cross-connect

This paper proposes a high-level fluctuation tolerant optical receiver for optical packet switches and WDM cross-connects. We describe the tolerance of an experimental receiver to packet-level fluctuation and coherent crosstalk. The sensitivity of the experimental receiver was -26.9 dBm for the packet receiver configuration and -32.7 dBm for the WDM cross-connect configuration at the bit rate of 10 Gb/s. In the setup for level-fluctuating packet reception, the power-penalties of 1.1 and 4.6 dB were observed with 6 and 10 dB of fluctuation, respectively. As a WDM cross-connect, the sensitivity penalties of the receiver under the coherent crosstalk powers of -15 and -12 dB were 2.5 and 6.5 dB, respectively     

Optical TDM sorting networks for high-speed switching

The general time-space-time switching problem in telecommunications requires the use of multichannel time slot interchangers. We propose two multichannel time slot sorters which sort N² time-division multiplexed (TDM) optical inputs, arranged as N frames with N time slots per frame using O(Nlog²N) optical switch elements. The TDM optical inputs are sorted in place without expanding the space-time fabric into a space-division switch. The hardware components used are 2×2 optical switches (LiNbO₃ directional couplers) and optical delay lines connected in a feedforward fashion. Two space-time variants of the spatial odd-even merge algorithm are used to design the sorters. By maintaining the number of shift-exchange operations invariant at each stage, the proposed sorters use fewer switches than previously proposed sorters using switches with feedback line delays. The use of local control at each 2×2 switch makes the proposed sorters more practical for high-speed optical inputs than Benes-based time slot permuters with global control and high latency, which affects interframe distance. Both time slot sorters support pipelining of input frames and sorted outputs are available at each time slot after an initial frame delay. The proposed sorters find practical application in the time-domain equivalents of space-division, nonblocking, self-routing packet switches using the sort-banyan architecture, such as the Starlite switch, Sunshine switch, etc     

All-Optical Self-Routing Latching Switch Based on Active Mach–Zehnder Interferometer

A new architecture for an all-optical self-routing packet switch is reported. The control signals are optical pulses which can be easily extracted from the packet header. The experimental results at 40 Gb/s show a low power penalty and an on-off contrast ratio higher than 9 dB     

A growable packet (ATM) switch architecture: design principles andapplication

The problem of designing a large high-performance, broadband packet of ATM (asynchronous transfer mode) switch is discussed. Ways to construct arbitrarily large switches out of modest-size packet switches without sacrificing overall delay/throughput performance are presented. A growable switch architecture is presented that is based on three key principles: a generalized knockout principle exploits the statistical behaviour of packet arrivals and thereby reduces the interconnect complexity, output queuing yields the best possible delay/throughput performance, and distributed intelligence in routing packets through the interconnect fabric eliminates internal path conflicts. Features of the architecture include the guarantee of first-in-first-out packet sequence, broadcast and multicast capabilities, and compatibility with variable-length packets, which avoids the need for packet-size standardization. As a broadband ISDN example, a 2048×2048 configuration with building blocks of 42×16 packet switch modules and 128×128 interconnect modules, both of which fall within existing hardware capabilities, is presented     

A 1.8 Gb/s GaAs optoelectronic universal switch LSI withmonolithically integrated photodetector and laser driver

A high-speed monolithic optical interface switch LSI is developed using a GaAs MSM photodetector and large-scale integrated electric circuits. This LSI operates universally as a 1.8 Gb/s optical-input/optical-output four-channel time-division switch, a 1.8 Gb/s optical-input/electrical-output 1:4 demultiplexer, a 2.0 Gb/s electrical-output 4:1 multiplexer, and a 2.8 Gb/s electrical-input/electrical-output 4×4 space-division switch. It uses a new multistage 2×2 switch block with small hardware and high-speed operation. It can be expanded to a 16×16 optical-input/optical-output time-division switch operating at up to 1.8 Gb/s for broadband-ISDN     

High-density micromachined polygon optical crossconnects exploitingnetwork connection-symmetry

Optical-layer crossconnects with high port count appear to be emerging as key elements for provisioning and restoration in future wavelength-division-multiplexed networks. We demonstrate here a means of achieving high-density optical crossconnects utilizing free-space micromachined optical switches that exploit connection-symmetry in core-transport networks. The micromachined polygon switches proposed here are strictly nonblocking. Measured insertion losses of 3.1-3.5 dB for a 16×16 (8×8 bidirectional) switch suggest the promise of scaling to large port count     

Crosstalk measurements of integrated high-speedTi:LiNbO3 Δβ-reversal switching circuits

Directional coupler crosstalk was measured at multigigahertz frequencies using an optical sampling method for improved sensitivity. At both 2- and 4-GHz switching frequency, the crosstalk in both switch states of the coupler was ⩽-19 dB for an element of a 1×4 switch array intended for time-division-multiplexing applications. The authors also report measurements of intercoupler crosstalk for this switch array     

Hybrid optical switch using passive polymer waveguides andsemiconductor optical amplifiers

Optical switching can be performed by using optical amplifiers combined with a passive waveguiding network. Recently, most of the effort in optical amplifier switch modules have been focused on monolithic switches in which the entire device is fabricated on an InP substrate together with the semiconductor optical amplifiers (SOA's). In this paper, we investigate the use of SOA's with passive polymer waveguides to make hybrid switches of varying sizes. The optical amplifiers serve dual purposes, gating the signal and amplifying the signal. Amplification is needed in order to offset the losses associated with the passive waveguide elements as well as the losses from component misalignments in the switch module. Our analysis finds the largest switch module size that can be made with the architecture used. We also calculate the maximum number of switch modules which can be cascaded in order to retain a bit-error rate (BER) under 10^-9