ISSN: 2277 943 Performance Evaluation of Optical Cross Connects for Dense and Ultra Wide Wavelength Division Multiplexing Transmission Systems Ahmed Nabih Zaki Rashed Electronics and Electrical Communications Engineering Department Faculty of Electronic Engineering, Menouf 32951, Menoufia University, EGYPT Abstract Continuous growth in demand for optical network capacity and the sudden maturation of WDM technologies have fueled the development of long-haul optical network systems that transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 1 Gb/s or more. Micro-electromechanical systems devices are recognized to be the enabling technologies to build the next-generation cost-effective and reliable high capacity optical cross connects. While the promises of automatically reconfigurable networks and bit-rate-independent photonic switching are bright. This paper has presented the performance evaluation of optical cross connects for dense and ultra wide wavelength division multiplexing transmission systems., and transmission systems have been investigated under the same operating conditions. Index Terms Optical cross connect, Coupling switch, Fiber switch loss, Crosstalk, Bit error rate, and Signal quality. I. INTRODUCTION The continuous increase in the demand for broadband services will impose unprecedented demands on the transport optical layer in terms of transmission capacity and routing agility. Wavelength Division Multiplexing (WDM) is widely recognized as the preferred transport mechanism for the next generation of high capacity systems. WDM transmission experiments of 1 Tbit/s have already been reported [1]. An important step towards the implementation of end-to-end optical networks, is the realization of a reliable and simple optical cross connect (OXC) that is able to scale smoothly in order to cope with this increased transmission capacity. The cross connect throughput is defined as the product given by the number of input/output links times the number of wavelength channels per link times the bit-rate per link. Apparently, OXCs with over 1 Tbit/s throughput will be needed. OXCs in wavelength routed networks are attractive due to their reduced complexity in routing and connection set-up procedures. Various optical cross connects architectures have been proposed [2-4]. In [5], the cross connection of the various wavelength channels is implemented using space switches with either a crossbar fabric or a bus fabric, something that generates interrelation (crosstalk) between the channels. Large crossbar switches are lossy and their performance is optimum only for one wavelength channel. In this case, the designer is bound to select only one architecture (Scheme 1 in [6]) something that is not desirable due to the attributed crosstalk limitations. Space switches in the form of amplifier gate switch arrays [7] are attractive but again their complexity should be traded with performance [8] and their scalability per node is limited due to ASE accumulation to a switch size of 32 x 32 [9, 1]. In [4-6], for each delivery-and-coupling switch, a power combiner is used with number of ports equal to the number of wavelength channels something that is scaling up the passive losses for a considerable number of channels. This architecture is suitable for a large number of links populated with a small number of wavelength channels something that under utilize the fiber bandwidth. Also, it does not have broadcast capability. Rapid developments in lightwave technology offer the potential of making huge bandwidths available in a single optical fiber. It would be possible to construct multiple-access networks with fiber links of 5 Tbps using the low loss pass band (12 16 nm) of optical fibers [1]. The bottleneck to this is typically the much lower speed of the optical-electrical interface. This may however be countered using Wavelength Division Multiplexing (WDM) and all-optical switching. By operating a large number of wavelength-multiplexed channels over each optical link in the network, WDM will be able to provide a good utilization of the overall network capacity. The high speeds attainable with each WDM channel will also make it attractive for use in future applications [2-4]. WDM networks may be realized using a wavelength routing mechanism to route different lightpaths between the various nodes of the network. In this kind of wavelength routed network [5], the intermediate nodes switch optical signals from an incoming link to an outgoing one, preferably without any intermediate optical/electrical conversion. In an all-optical wavelength-routed network [9] of this type, an optical crossconnect switch (OXC) performs the routing and switching functions at each node. Note that the OXC is a switch, which will generally be controlled by the management layer while setting up or terminating lightpaths. It would therefore require less frequent and slower reconfiguration than if it were to be controlled by call traffic signaling. II. OPTICAL CROSS CONNECT ARCHITECTURE MODEL An emerging vision of the next-generation cross connects for optical networks is one that allows network reconfiguration in the optical layer (Fig. 1): provisioning and restoration in large units (e.g., the wavelength). Since the number of wavelengths per fiber has already reached hundreds today (16 wavelengths for 1 Gb/s) and is expected to 586
ISSN: 2277 943 increase, the desired port counts for such OXCs are expected to be in the thousands, where scalability is a paramount concern. Such a switch must also operate in a fully non blocking manner, where every input must be allowed to connect to every output with no restriction. In addition, insertion loss, physical size, polarization effects, and switching times are also critical considerations. Equipped with intelligent provisioning and restoration capabilities, the next-generation OXC must also meet the stringent telecommunication requirements with an operating lifetime of 2 years [1, 11]. Fig. 1. Optical cross connect architecture schematic view. An optical layer switch can be implemented using optoelectronics interfaces and high-speed electronics. Due to the advancement of state-of-theart integrated circuit (IC) technologies, multiple vendors currently offer electronics based optical switches, also known as O-e-O (Optical-electrical- Optical) switches, with a few hundred 2.5 Gb/s ports residing in several equipment bays [12-14]. These state-of-the-art switching systems provision and mesh-restore wavelengths at a granularity of 155 Mb/s to 2.5 Gb/s. They provision and mesh-restore 1 Gb/s wavelengths (OC-192) via inverse multiplexing down to the basic switch rate, with the capability of grooming such sub rate signals within a given 1 Gb/s pipe. Intelligence of this switch allows dynamic and automatic provisioning and protection as well as in-service system upgrades. Based on multiple stages of Clos structures [1, 15], these switches are also scalable to thousands of switching ports [16]. III. MODEL ANALYSIS Optical dense wavelength division multiplexing (DWDM) networks are very promising due to their large bandwidth, their large flexibility and the possibility to upgrade the existing optical fiber networks to WDM networks [17-2]. WDM has already been introduced in commercial systems. All-optical cross connects (OXC), however, have not yet been used for the routing of the signals in any of these commercial systems. Several OXC topologies have been introduced, but their use has so far been limited to field trials [21-27], usually with a small number of input output fibers and wavelength channels. The fact, that in practical systems many signals and wavelength channels could influence each other and cause significant crosstalk in the optical cross connect, has probably prevented the use of OXC s in commercial systems. For strict non blocking, the switching element (SE) for type I and type II as a function of number of cross connects N can be given by [28]: SE Type I 2N N 1 (1) SE Type II N N 1 (2) As well as the switching drive (SD) for type I and type II can be described by the following equations [28, 29]: SD Type I 2N log2 N (3) SD Type II N log2 N (4) Moreover the switching loss (SL) for type I and type II as a function of number of cross connects N can be given by [3]: SL Type I 2 N log2 N L se L fs (5) SL Type II log 2 N 3 L se 2L fs (6) Where L se is the loss per switch element and L fs is the fiber switch loss. As well as the signal to noise ratio (SNR) for type I and type II as a function of number of users N can be [31]: SNR Type I 2 XT 1 log 1 log2 N (7) SNR Type II XT 1 log 1 log2 N (8) Where XT is the crosstalk in db. Finally the bit error rate for OXC transmission systems is expressed as [32]: 2 SNR BER.exp. SNR 8, (9) IV. PERFORMANCE ANALYSIS This study has presented the performance analysis and evaluation of optical cross connect elements in dense and ultra wide transmission systems over wide range of the affecting operating parameters as shown in Table 1. Switching loss, signal to noise ratio and bit error rate are the major interesting design parameters in current research. 587
Switching Elements, SE Switching Elements, SE ISSN: 2277 943 Table 1. List of the parameters used in the simulation [1, 8, 12, 3]. Operating parameter Symbol Value Number of cross connects (DWDM) N (DWDM) 1-9 Number of cross connects (UW-WDM) N (UW-WDM) 1-6 Loss per switch element L se.5 db Crosstalk XT 5 db Fiber switch loss L fs.2 db 1.E+6 1.E+5 1.E+4 1.E+3 1 2 3 4 5 6 7 8 9 Fig. 2. Variations of switching elements versus variations of number of Cross connects in DWDM transmission systems at the 1.E+7 1.E+6 1.E+5 1.E+4 1 15 2 25 3 35 4 45 5 55 6 Fig. 3. Variations of switching elements versus variations of number of Cross connects in UW-WDM transmission systems at the 588
Switching loss, SL, db Switching Drivers, SE Switching Drivers, SE ISSN: 2277 943 1.E+7 1.E+6 1.E+5 1.E+4 1 2 3 4 5 6 7 8 9 Fig. 4. Variations of switching drivers versus variations of number of Cross connects in DWDM transmission systems at the 1.E+8 1.E+7 1.E+6 1.E+5 1 15 2 25 3 35 4 45 5 55 6 Fig. 5. Variations of switching drivers versus variations of number of Cross connects in UW-WDM transmission systems at the 25 225 2 175 15 125 1 75 5 25 1 2 3 4 5 6 7 8 9 Fig. 6. Variations of switching loss against variations of number of Cross connects in DWDM transmission systems at the 589
Signal to noise ratio, SNR, db Signal to noise ratio, SNR, db Switching loss, SL, db ISSN: 2277 943 425 4 375 35 325 3 275 25 225 1 15 2 25 3 35 4 45 5 55 6 Fig. 7. Variations of switching loss against variations of number of Cross connects in UW-WDM transmission systems at the 25 22.5 2 17.5 15 12.5 1 7.5 5 2.5 1 2 3 4 5 6 7 8 9 Fig. 8. Variations of signal to noise ratio against variations of number of Cross connects in DWDM transmission systems at the 1 9 8 7 6 5 4 3 2 1 1 15 2 25 3 35 4 45 5 55 6 Fig. 9. Variations of signal to noise ratio against variations of number of Cross connects in UW-WDM transmission systems at the 59
Bit error rate, BERx1-12 Bit error rate, BERx1-12 Bit error rate, BERx1-12 Bit error rate, BERx1-12 ISSN: 2277 943.12.1.16.14.12.8.1.6.8.4.6.4.2.2 1 2 3 4 5 6 7 8 9 Fig. 1. Variations of bit error rate against variations of number of Cross connects in DWDM transmission systems at the 1.2 1 2 1.8 1.6.8.6.4.2 1.4 1.2 1.8.6.4.2 1 2 3 4 5 6 Fig. 11. Variations of bit error rate against variations of number of Cross connects in UW-WDM transmission systems at the Based on the modeling equations analysis over wide range of the operating parameters, and the series of the Figs. (2-11), the following features are assured: i) Figs (1-4) have assured that number of cross connects in both DWDM and UW-WDM increase, this results in the increased number of switching elements and drivers for both Torous and mesh Torous transmission systems. ii) Figs. (5, 6) have indicated that as number of cross connects in both DWDM and UW-WDM increase, this results in the increased number of switching loss for both Torous and mesh Torous transmission systems. iii) As Shown in Figs. (7-11) have demonstrated that number of cross connects in both DWDM and UW- WDM increase, this results in the increased signal to noise ratio and therefore the decreased bit error rate for both Torous and mesh Torous transmission systems. IV. CONCLUSIONS In a summary, we have investigated the Torous and mesh Torous optical cross connects transmission systems with using dense wavelength and ultra wide wavelength division multiplexing techniques. Switching elements, switching drivers, and switching loss with signal to noise ratio and bit error rates are the major interesting issues. It is theoretically found that with increasing optical cross transmission connects, this results in the increased switching loss and therefore slightly change in signal to noise ratio and also slightly change in bit error rates. 591
ISSN: 2277 943 REFERENCES [1] G. R. Hill et al.: A transport network layer based on optical network elements, Journal of Lightwave Technology, vol. 11, no. 5/6, May/June 1993, pp. 667-679. [2] A. Jourdan F. Masseti, M. Garnot, G. Soulage, M.Sotom: Design and implementation of a fully reconfigurable alloptical cross connect for high capacity multi wavelength transport networks, Journal of Lightwave Technology, vol. 14, no. 6, June 1996, pp. 1198-126. [3] M. Koga et al: Design and performance of an optical path cross connect system based on the wavelength path concept, Journal of Lightwave Technology, vol. 14, no. 6, June 1996, pp. 116-1118. [4] S. Okamoto, A. Watanabe, K. Sato: Optical path cross connect node architecture for photonic transport networks, Journal of Lightwave Technology, vol. 14, no. 6, June 1996, pp. 141-1422. [5] A. Watanabe, S. Okamoto, K. Sato: Optical path crossconnect system architecture suitable for large scale expansion, Journal of Lightwave Technology, vol. 14, no. 1, Oct. 1996, pp. 2162-2172. [6] E. Iannone, R. Sabella: Optical path technologies: A comparison among different cross connect architectures, Journal of Lightwave Technology, vol. 14, no. 1, Oct. 1996, pp. 2184-2196. [7] J. Zhou, R. Cadeddu, E. Casaccia, C. Cavazzoni, M. O Mahony: Crosstalk in multi wavelength optical crossconnect networks, Journal of Lightwave Technology, vol. 14, no. 1, Oct. 1996, pp. 1423-1435. [8] M. Renaud, M. Bachmann, M. Erman: Semiconductor optical space switches, IEEE Journal of Selected Topics in Quantum Electronics, vol. 2, no. 2, June 1996, pp. 277-288. [9] G. Soulage et al: Clamped-gain SOA gates as multiwavelength space switches, OFC 95 (San Diego, CA, Feb/March 1995), paper TuD1, pp. 9-1. ; also G. Soulage et al: 4x4 space switch based on clamped-gain semiconductor optical amplifiers in 16x1 Gb/s WDM experiment, in ACTS WDM components meeting. [1] M. Gustavsson et al: Monolithically integrated 4x4 InGaAsP/InP laser amplifier gate switch arrays, Electronic Letters, vol. 28, no. 24, Nov. 1995, pp. 2223-2225. [11] L. Gillner: Transmission limitations in the all-optical network, Proc. of ECOC 96 (Oslo, Norway, Sept. 1996), paper TuB.2.3, vol. 2, pp. 39-44. [12] A. Stavdas: Design of optical multiplexer/demultiplexer for dense WDM wavelength routed networks, Ph.D. Thesis, University of London, 1995. [13] F. Tomofeyev et al: Free-space grating demultiplexer for applications in densely spaced, sub nanometer wavelengthrouted optical networks, Electronic Letters, vol. 31, no. 16, Aug. 1995, pp. 1368-137. [14] E. Churin, P. Bayvel: Coherent crosstalk and free-space wavelength routers, Electronics Letters, vol. 34, 1998, pp.1225 [15] M. Hoffmann, T. Gross, P. Kopka, E. Voges: All-silicon bistable micro-mechanical fibre switches, Electronic Letters, vol. 34, no. 2, Jan. 1998, pp. 27-28. [16] J. Sokoloff, P. Prucnal, I. Glesk, M. Kane: A terahertz optical asymmetric demultiplexer (TOAD), IEEE Photonics Technology Letters, vol. 5, no. 7, July 1993, pp. 787-79. [17] M. Eiselt, M. Ciselt, W. Pieper, H. Weber: SLALOM: Semiconductor laser amplifier in a loop mirror, Journal of Lightwave Technology, vol. 13, no. 1, Oct. 1995, pp. 299-2112. [18] A. Ellis et al: Ultra-high-speed OTDM networks using semiconductor amplifier-based processing nodes, Journal of Lightwave Technology, vol. 13, no. 5, May 1995, pp. 761-77. [19] T. Houbavlis et al: All-Optical XOR in Semiconductor Optical Amplifier-Assisted Fiber Sagnac gate, submitted to IEEE Photonics Technology Letters. [2] J. Lucek, K. Smith: All-optical signal regenerator, Optics Letters, vol. 18, no. 15, Aug. 1993, pp. 1226-1228. [21] M. Neuhauser, H. Rein, H. Wernz, A. Felder: 13 Gb/s Si bipolar preamplifier for optical front ends, Electronic Letters, vol. 29, no. 5, March 1993, pp. 492-493. [22] D. Simeonidou, R. Nejabati, G. Zervas, D. Klonidis, A. Tzanakaki, and M. J. O Mahony, Dynamic optical network architectures and technologies for existing and emerging grid services, IEEE J. Lightwave Technol., vol. 23, no. 1, pp. 3347 3357, Oct 25. [23] M. J. O Mahony, D. Simeonidou, D. K. Hunter, and A. Tzanakaki, The application of optical packet switching in future communication networks, IEEE Commun. Mag., vol. 39, no. 3, pp. 128 135, Mar. 21. [24] C. Qiao and M. Yoo, Optical burst switching (OBS) a new paradigm for an optical Internet, J. High Speed Networks, vol. 8, no. 1, pp. 69 84, 1999. [25] C. Qiao, Labeled optical burst switching for IP-over- WDM integration, IEEE Commun. Mag., vol. 38, no. 9, pp. 14 114, Sept. 2. [26] S. J. B. Yoo, Optical packet and burst switching technologies for the future photonic Internet, J. Lightwave Technol., vol. 24, no. 12, pp. 4468 4492, Dec. 26. [27] G. I. Papadimitriou, C. Papazoglou, and A. S. Pomportsis, Optical switching: switch fabrics, techniques, and architectures, J. Lightwave Technol., vol. 21, no. 2, pp. 384 45, Feb. 23. [28] I. Baldine, M. Cassada, A. Bragg, G. Karmous-Edwards, and D. Stevenson, Just-in-time optical burst switching implementation in the ATDnet all-optical networking testbed, in Proc. IEEE Globecom, San Francisco, CA, USA, vol. 5, pp. 2777 2781, Dec. 23. [29] A. A. Amin, K. Shimizu, M. Takenaka, R. Inohara, K. Nishimura, Y. Horiuchi, M. Usami, Y. Takita, Y. Kai, Y. Aoki, H. Onaka, T.Miyahara, T. Hatta, K. Motoshima, and Y. Nakano, Label-based path switching and error-free forwarding in a prototype optical burst switching node using a fast 4 4 optical switch and shared wavelength conversion, in Proc. Optical Fiber Communication Conf. (OFC), Anaheim, CA, USA, Mar. 26, paper OFO5. [3] K. Nashimoto, N. Tanaka, M. LaBuda, D. Ritums, J. Dawley, M. Raj, D. Kudzuma, and T. Vo, High-speed PLZT optical switches for burst and packet switching, in Proc. 2nd Int. Conf. on Broadband Networks (IEEE Broadnets), Boston, MA, USA, Oct. 25, vol. 2, pp. 1118 1123. [31] C. T. Politi, A. Tzanakaki, D. Klonidis, M. J. O Mahony, and I. Tomkos, Optical cross-connect architecture using waveband conversion and a passive wavelength router, 592
ISSN: 2277 943 Proc. IEE Optoelectronics, vol. 152, no. 4, pp. 215 221, Aug. 25. [32] D. Klonidis, C. Politi, R. Nejabati, M. J. O Mahony, and D. Simeonidou, OPSnet: design and demonstration of an asynchronous high speed optical packet switch, IEEE J Lightwave Technol., vol. 23, no. 1, pp. 2914 2925, Oct. 25. Author's Profile Dr. Ahmed Nabih Zaki Rashed was born in Menouf city, Menoufia State, Egypt country in 23 July, 1976. Received the B.Sc., M.Sc., and Ph.D. scientific degrees in the Electronics and Electrical Communications Engineering Department from Faculty of Electronic Engineering, Menoufia University in 1999, 25, and 21 respectively. Currently, his job carrier is a scientific lecturer in Electronics and Electrical Communications Engineering Department, Faculty of Electronic Engineering, Menoufia university, Menouf. Postal Menouf city code: 32951, EGYPT. His scientific master science thesis has focused on polymer fibers in optical access communication systems. Moreover his scientific Ph. D. thesis has focused on recent applications in linear or nonlinear passive or active in optical networks. His interesting research mainly focuses on transmission capacity, a data rate product and long transmission distances of passive and active optical communication networks, wireless communication, radio over fiber communication systems, and optical network security and management. He has published many high scientific research papers in high quality and technical international journals in the field of advanced communication systems, optoelectronic devices, and passive optical access communication networks. His areas of interest and experience in optical communication systems, advanced optical communication networks, wireless optical access networks, analog communication systems, optical filters and Sensors, digital communication systems, optoelectronics devices, and advanced material science, network management systems, multimedia data base, network security, encryption and optical access computing systems. As well as he is editorial board member in high academic scientific International research Journals. Moreover he is a reviewer member in high impact scientific research international journals in the field of electronics, electrical communication systems, optoelectronics, information technology and advanced optical communication systems and networks. His published paper in Optics and Laser Technology Journal has scored most downloaded articles in Elsevier publisher 213. 593