Showing papers on "Wavelength-division multiplexing published in 1995"

Routing and wavelength assignment in all-optical networks

Abstract: Considers routing connections in a reconfigurable optical network using WDM. Each connection between a pair of nodes in the network is assigned a path through the network and a wavelength on that path, such that connections whose paths share a common link in the network are assigned different wavelengths. The authors derive an upper bound on the carried traffic of connections (or equivalently, a lower bound on the blocking probability) for any routing and wavelength assignment (RWA) algorithm in such a network. The bound scales with the number of wavelengths and is achieved asymptotically (when a large number of wavelengths is available) by a fixed RWA algorithm. The bound can be used as a metric against which the performance of different RWA algorithms can be compared for networks of moderate size. The authors illustrate this by comparing the performance of a simple shortest-path RWA (SP-RWA) algorithm via simulation relative to the bound. They also derive a similar bound for optical networks using dynamic wavelength converters, which are equivalent to circuit-switched telephone networks, and compare the two cases. Finally, they quantify the amount of wavelength reuse achievable in large networks using the SP-RWA via simulation as a function of the number of wavelengths, number of edges, and number of nodes for randomly constructed networks as well as de Bruijn networks. They also quantify the difference in wavelength reuse between two different optical node architectures. >

Four-photon mixing and high-speed WDM systems

Abstract: The trend toward higher bit rates in lightwave communications has increased interest in dispersion-shifted fiber to minimize dispersion penalties. At the same time optical amplifiers have increased interest in wavelength multiplexing. These two methods of increasing system capacity, if used together, can result in severe degradation due to fiber nonlinearity. This paper discusses the impact of the principal nonlinearity, four-photon mixing, and describes strategies that allow simultaneous use of high bit rates and WDM. >

Transmission characteristics of arrayed waveguide N/spl times/N wavelength multiplexer

Abstract: To realize practical wavelength division multiplexing (WDM) systems, a high-performance N/spl times/N wavelength multiplexer is introduced that is based on an arrayed-waveguide grating. Its transmission characteristics are theoretically derived and experimentally confirmed. A prototype is constructed using the previously proposed techniques that attain low insertion loss and polarization independent operation. It has 16 channels (N=16) with a spacing of 0.8 mn, or 100 GHz, in the 1.55-/spl mu/m band. Frequency relation between input and output ports, free spectral range, and passband width are determined. A demonstration of IM-DD pulse transmission shows that there is no degradation of bit error rate resulting from the finite passband width and crosstalk of the multiplexer. It is confirmed that the multiplexer can realize highly reliable N-channel WDM and WDM-based N/spl times/N interconnect optical networks. >

A heuristic wavelength assignment algorithm for multihop WDM networks with wavelength routing and wavelength re-use

Abstract: Presents a heuristic algorithm for effectively assigning a limited number of wavelengths among the access stations of a multihop network wherein the physical medium consists of optical fiber segments which interconnect wavelength-selective optical switches. Such a physical medium permits the limited number of wavelengths to be re-used among the various fiber links, thereby offering very high aggregate capacity. Although the optical connectivity among the access station can be altered by changing the states of the various optical switches, the resulting optical connectivity pattern is constrained by the limitation imposed at the physical level. The authors also study two routing schemes, used to route requests for virtual connections. The heuristic is tested on a realistic traffic model, and the call blocking performance of new requests for virtual connections is studied through extensive simulations and compared against the blocking performance of an ideal infinite capacity centralized switch (lowest possible call blocking caused exclusively by congestion on the finite capacity user input/output links, never by the switch fabric itself). Surprisingly, the authors find that, for a wide range of parameters, the blocking performance of the lightwave network is almost the same as that of the ideal centralized switch. From these results, they conclude that the heuristic algorithm is effective and the routing scheme is efficient. >

Polarization-independent all-fiber wavelength-division multiplexer based on a Sagnac interferometer.

Abstract: An all-fiber wavelength-division multiplexer (WDM) based on the nonreciprocity of the birefringence to the polarization states is proposed. The transfer function of a Sagnac interferometer is wavelength dependent if the loop birefringence of the interferometer consists of both circular and linear parts. Theoretical analysis shows that the output characteristics of this WDM are similar to those of a fiber taper-based device. Both the bandwidth and the peak wavelength of the new WDM can be tuned by changing the loop birefringence. Experimental prototypes exhibit a channel isolation greater than 25 dB with peak passband insertion loss of less than 1 dB.

An all-fiber dense wavelength-division multiplexer/demultiplexer using photoimprinted Bragg gratings

Abstract: A wavelength multiplexing/demultiplexing device is fabricated and used to drop/insert a single wavelength channel from/into a multiple wavelength transmission link with 100 GHz channel-spacing at 1550 nm. The device consists of an all-fiber Mach-Zehnder interferometer with photoinduced Bragg gratings. The following performances were measured: extraction/coupling efficiency =99.4%, excess loss 20 dB, and return loss >23 dB. >

WDM systems with unequally spaced channels

Abstract: Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A method is discussed to find non-uniform channel separations for which no four-wave mixing product is superimposed on any of the transmitted channels, therefore suppressing FWM crosstalk. The residual crosstalk, due to channel power depletion only, is analytically evaluated for intensity-modulated repeaterless wavelength-division-multiplexed (WDM) systems and compared to experimental results. The theory includes the effect of the channel depletion on the amplitude of each phase-matched FWM wave. The probability of error is evaluated including the statistics of the pattern dependent channel depletion. The BER curve computed for an 8-channel WDM system is found to be in good agreement with experimental results. In the experiment, repeaterless transmission of eight 10 Gb/s WDM channels over 137 km (11 Tb/s-km) of dispersion-shifted fiber was demonstrated and error-free operation was achieved over a wide range of input powers using unequally spaced channels. The same system with equally spaced channels could not achieve a probability of error lower than 10/sup -6/. The use of unequal channel spacing allowed fiber input power to be increased by as much as 7 dB, which could be translated into a fivefold increase of the bit rate per channel (and therefore of the system capacity), or to an increase in the system length of about 30 km. >

Two-dimensional optoelectronic tune-switch

Abstract: A communications switch for switching telecommunications signals from input wavelength division multiplexed (WDM) optical fibers to output WDM optical fibers is disclosed. A two-dimensional optoelectronic switch is also described which uses tunable lasers and optical diffractive elements to switch a matrix of input/output gigabaud channels without blocking. As the channels proceed through the switch they are spatially switched among one another first within rows, then within columns, and then again within rows in the matrix. The two-dimensional optoelectronic tune-switch (2DOTS) can realize the functionality of the nonblocking three-stage Clos switch for input/output ports carrying several gigabit/s data streams.

Bragg grating-based laser sensors systems with interferometric interrogation and wavelength division multiplexing

Abstract: We describe the use of fiber Bragg grating based lasers as sensors. An interferometric detection technique is presented for interrogating laser wavelength shifts due to measurand induced laser cavity strain with high resolution from both single-mode and multimode lasers. The principle of integrating multiple sensors to form an array is demonstrated using a wavelength division multiplexing approach. >

LARnet, a local access router network

Abstract: A novel local access network, LARNet, is proposed and demonstrated. A multifrequency laser, whose wavelength COMB94 is matched to that of a passive waveguide router in the remote node, is used as a downstream signal source. A 1.3-/spl mu/m commercially available LED provides the upstream signal. LARNet solves a major problem of WDM networks, the spectral alignment between the optical wavelengths of different channels. Furthermore. The expensive components are shared among all subscribers. Our measurements indicate that aggregate rates of 2 Gbps downstream and 155 Mbps upstream are feasible. >

The design of a European optical network

Abstract: This paper presents a number of design issues under consideration in the development of an all-optical network linking major centers in Europe. The proposed network is characterized by spanning a large geographical area, the diameter is in excess of 3000 km, but with a relatively small number of nodes (20). The study combines aspects of two optical network projects funded by the European Commission: COST 239-ultra-high capacity optical transmission networks and RACE 2028: multiwavelength transport network. The network uses multiwavelength technology and combines wavelength selection and space switching to achieve signal routing. One of the objectives of the study is to understand the extent to which transparency can be achieved in such a large network. For example the effect of using amplifiers to achieve transparency is to provide extremely long fiber paths in which non-linear effects may become significant and effectively limit the number of wavelengths that can be employed; this limit may be at conflict with the number of wavelengths required from a traffic viewpoint. The paper therefore considers capacity requirements, transmission limitations and node and network architecture issues. It is concluded that partitioning of the network may be necessary to maximize transparency and suggestions are made as to how this might be achieved. >

Efficient access to optical bandwidth wavelength routing on directed fiber trees, rings, and trees of rings

Abstract: We address efficient access to bandwidth in WDM (wavelength division multiplexing) optical networks. We consider tree topologies, ring topologies, as well as trees of rings. These are topologies of concrete practical relevance for which undirected underlying graph models have been studied before by P. Raghavan and E. Upfal (1993). As opposed to previous studies (A. Aggarwal et al., 1993; R. Pankaj, 1992; P. Raghavan and E. Upfal, 1993), we consider directed graph models. Directedness of fiber links is dictated by physical directedness of optical amplifiers. For trees, we give a polynomial time routing algorithm that satisfies requests of maximum load L/sub max/ per fiber link using no more than 15L/sub max//8/spl les/15OPT/8 optical wavelengths. This improves a 2L/sub max/ scheme that is implicit by P. Raghavan and E. Upfal by extending their undirected methods to our directed model. Alternatively stated, for fixed W wavelength technology, we can load the network up to L,, 8W/15 rather than W/2. In engineering terms, this is a so called "6.66% increase of bandwidth" and it is considered substantial. For rings, the approximation factor is 2OPT. For trees of rings, the approximation factor is 15OPT/4. Technically, optical routing requirements give rise to novel coloring paradigms. Our algorithms involve matchings and multicolored alternating cycles, combined with detailed potential and averaging analysis.

Multiwavelength simultaneous monitoring circuit employing arrayed-waveguide grating

Abstract: A multiwavelength simultaneous monitoring circuit capable of precise discrimination of wavelengths of a WDM (Wavelength Division Multiplexed) signal including multiplexed wavelength waves, and suitable for optical integrated circuits having large resistance to vibration. It includes a reference optical source, an AWG (Arrayed-waveguide grating) having periodic center transmission wavelength (or crossover wavelengths) corresponding to the wavelength spacing between multiplexed waves of the WDM signal, a first wavelength error detector for generating a wavelength error signal of an RF signal (reference optical signal) with respect to a zero-cross wavelength on the basis of a ratio between the levels of the RF signal outputted from two output waveguides of the AWG, a control circuit for locking the zero-cross wavelength to the wavelength of the RF signal in response to the wavelength error signal, and a second wavelength error detector for generating wavelength error signals of the multiplexed waves of the WDM signal by detecting signal levels of respective wavelength signals of the WDM signal outputted from each pair of output ports of the AWG.

Wavelength-division multiplexing with femtosecond pulses

Abstract: We demonstrate wavelength-division multiplexing with a single broadband femtosecond source by slicing the 3.7-THz spectral bandwidth of 85-fs laser pulses into 16 channels that are modulated individually.

Multi-channel optical fiber communication system

Abstract: A significant part of signal-to-noise degradation in WDM optical fiber communications, due to Raman crosstalk, is found to be deterministic in nature. Shaping of amplifier output to offset depletion of high frequency channels improves signal capacity by an order of magnitude.

Application of planar lightwave circuit platform to hybrid integrated optical WDM transmitter/receiver module

Abstract: The authors have fabricated an optical WDM module with a simple configuration using a PLC platform together with a spot-size converted LD (SS-LD) and a waveguide PD (WG-PD). Since the module can be formed simply by flip-chip bonding of the SS-LD and the WG-PD, this configuration reduces the number of components, and thus helps achieve a cost reduction.

Tunable add/drop optical filter providing arbitrary channel arrangements

Abstract: A novel add/drop optical filter providing arbitrary channel arrangements between two input wavelength division multiplexing (WDM) signals and two output WDM signals is presented. This device can have useful applications in WDM optical communication systems. >

Wavelength division optical multiplexing elements.

Abstract: The present invention relates to methods and apparatus for wavelength division multiplexing (WDM) using arrays of optical filtering elements to create a desired wavelength passband in an optical filter. In one aspect of the invention, an optical demultiplexer is formed using an input waveguide, such as a planar waveguide or an optical fiber, coupled to plural output waveguides. Each output waveguide includes a wavelength selective configuration of optical filtering elements formed within a contiguous portion of the waveguide forming an optical channel-selective filter having spectral regions having an optical transmission passband and spectral regions of low transmissivity. Exemplary optical filtering elements are Bragg gratings formed into an optical filter which transmits a characteristic wavelength band.

Unidirectional amplification for bi-directional transmission using wavelength-division multiplexing

Abstract: A device in accordance with the invention uses a novel four-port wavelength-division multiplexing (WDM) filter and a single erbium-doped optical amplifier (EDFA) to implement a dual wavelength bi-directional (single fiber) optical amplifier module. A system using an amplifier module in accordance with the invention, advantageously allows communication network managers to simultaneously reduce the cost of signal amplification hardware across a fiber optic network, increase fiber utilization, simplify field installation and maintenance operations, and maintain adherence to conventional protection philosophies such as 'one system per fiber'.

40 Gbit/s all-optical demultiplexing using a monolithically integrated Mach-Zehnder interferometer with semiconductor laser amplifiers

Abstract: The authors demonstrate all-optical error-free demultiplexing of 10, 20 and 40 Gbit/s to 5 Gbit/s data signals by using a monolithically integrated Mach-Zehnder interferometer with two semiconductor laser amplifiers.

Ring network communication structure on an optical carrier and reconfigurable node for said structure

Abstract: In a ring network communication structure for communication on an optical carrier (3A, 3B), a plurality of nodes (2A, ..., 2E) are interconnected by means of connections comprising at least a first (3A) and a second (3B) optical carrier, such as an optical fibre. Transmission occurs on the ring according to a WDM scheme, by utilising a first wavelength (λ₁) for communication in one direction on the first carrier (3A) of said pair, while communication in the opposite direction occurs by employing a second wavelength (λ₂) on the other optical carrier (3B). In the presence of a failure on one of the connections, the nodes adjacent (2B, 2C) to the failed connection reconfigure themselves to ensure the continuation of communication on the alternative path provided by the ring, by utilising the first wavelength (λ₁) on the second carrier (3B) and the second wavelength (λ₂) on the first carrier (3A). Preferential application to SDH optical fibre ring networks.

WDM receiver by monolithic integration of an optical preamplifier, waveguide grating router and photodiode array

Abstract: A high performance monolithic WDM receiver is demonstrated. The chip receives eight optical channels spaced by 200 GHz. An optical amplifier at the input of the device boosts the incoming signal. A fibre insertion DC responsivity of 0.5 A/W and crosstalk below -20 dB are achieved. The receiver has a small signal bandwidth of 3.5 GHz.

An all-optical wavelength-converter with semiconductor optical amplifiers monolithically integrated in an asymmetric passive Mach-Zehnder interferometer

Abstract: An all-optical wavelength-converter based on monolithic integration of a Mach-Zehnder interferometer and integrated semiconductor optical amplifiers was demonstrated. This device exhibited high stability, penalty-free conversion at 5 Gbit/s (at a BER of 10/sup 9/), no-excess penalty after a transmission over 60 km on standard fiber, and low signal-polarization dependency. The device operated in a 26-nm-wide optical window. >

Optical-filter array, optical transmitter and optical transmission system

Abstract: An optical transmitter provided by the present invention comprises: a light source; a band-pass filter for filtering a light generated by the light source; a light splitting means for splitting a light output by the band-pass filter into at least two split lights; an optical receiving unit for converting one of the split lights into an electrical signal having a level proportional to the intensity of the split light; and a control means for receiving the electrical signal for use in controlling the wavelength of the light source so as to sustain the intensity of the split light at a fixed value. With the configuration described above, fluctuations in wavelength occurring on the transmitter side can be reduced. On the top of that, by applying this optical transmitter to a WDM system, a system cold start can be done with ease.

On a Possibility of Wavelength-Domain-Multiplication Memory Using Quantum Boxes

Abstract: A new use of quantum boxes for wavelength-domain-multiplication optical memory applications is proposed. Persistent spectral-hole burning mechanism based on photo-creation of electron-hole pairs and their spatial separation by carrier tunneling is described. We discuss the feasibility of its application to optical data storage with emphasis on the memory duration and the multiplexing factor, that is, the possible number of bits stored in a laser-beam spot following the discussion by Moerner and Levenson.

Combined spatial- and time-division-multiplexing scheme for fiber grating sensors with drift-compensated phase-sensitive detection.

Abstract: A combined spatial- and time-division-multiplexing topology with drift-compensated high-resolution wavelength-shift detection is reported for fiber Bragg grating sensors. An eight-element grating sensor array is demonstrated based on this topology. A resolution of ~1.2 μe over a range of ~1.5 me with a measurement bandwidth of 30 Hz (~0.22 μɛ/Hz) has been achieved for quasi-static strain measurement.

Expandable wavelength division multiplexed optical communications systems

Abstract: The present invention provides wavelength division multiplexed optical communication systems configured for expansion with additional optical signal channels. In one embodiment, the WDM system comprises N source lasers for producing N optical signal channels, each channel having a unique wavelength where N is a whole number greater than or equal to 2. An optical multiplexer module having N+x inputs, where x is a whole number greater than or equal to 1, optically communicates with each of the N source lasers. The N+x input ports of the multiplexer are configured such that the N input ports are optically coupled to the N source lasers and the x input ports are supplemental ports not optically coupled to the N source lasers. An optical transmission path optically communicates with the multiplexer for carrying a multiplexed optical signal comprising the N optical signal channels. N optical channel selecting modules are provided, each selecting module including a Bragg grating configured to select a unique optical channel wavelength. An optical splitter module optically communicates with the optical transmission path and the optical channel selecting modules. The optical splitter includes N+y output ports, where y is a whole number greater than or equal to 1. The N+y output ports are configured such that each of the N output ports is optically coupled to one of the N optical channel selecting modules and the y output ports are supplemental ports not optically coupled to the N optical channel selecting modules.

Wavelength division multiplexed optical fiber transmission equiptment

Abstract: The present invention provides a wavelength division multiplexed optical fiber transmission equipment which can increase the number of channels of the WDM signal by reducing a required bandwidth of optical signals while suppressing an interference between signals caused by four-wave mixing. A WDM optical transmitting terminal comprises five or more optical transmitters and the wavelengths of optical signals from the optical transmitters are set such that the spacing between the wavelengths of two signals is re-used as the spacing between the wavelengths of other two signals separated by the above signals by two or more waves and there is no periodicity in the channel spacing s. For instance, the wavelengths of the optical signals are set as shown in FIG. 1. As the result, deterioration in the transmission characteristics of the optical signals can be effectively reduced and, at the same time, the maximum number of channels of the WDM signal can be increased. To the WDM optical transmitting terminal is added polarization state controllers for controlling the state of polarization such that the states of polarizations of adjacent signals cross each other at an output of the WDM optical transmitting terminal.

Passively aligned holographic wdm

Abstract: A passively aligned optical interconnect is described for use as a wavelenth division multiplexer (WDM) and demultiplexer. The device makes use of silicon waferboard for a low cost interconnect. Computer generated holograms are used to effect the multiplexing/demultiplexing as well as focusing of the beams. In an alternative embodiment, the device is used as a beam splitter for monochromatic light. In yet another embodiment, the device is used to spatially separate the polarization states of light.