Performance Analysis of DWDM Systems with Optical Add Drop Multiplexers and Optical Cross Connects

Abstract

This thesis deals with Performance analysis of Optical Add /drop multiplexers and optical Cross connects for Dense Wavelength Division Multiplexing system. It is essential to add/remove different channels in an optical communication system. The OADM provides flexibility and greater connectivity in the optical communication system. The OXC permits the system to be reconfigured on a channel by channel basis to optimize and exchange signals pattern, facilitate growth of network and increases network survivability. The sharing of system devices like OXADM, amplifiers and ROADM is permitted by the grouping of a multiple channels on a single fiber which results in cost savings. The Optical cross add drop multiplexer provides adding/dropping function and cross connecting signals similar to OADM and OXC in the optical system. Reconfigurable add drop multiplexer enables many channels which carry data to be added/dropped from optical fiber port without the need of optical-electrical-optical conversion. The designing and investigation of OXC, OADM using MZI-techniques, OADM based on FBG-circulator and ROADM based on DCE, PLC and WSS in fiber optical communication system is presented.

Firstly, an optical system performance in terms of crosstalk with OADM based on MZI, MZI-semiconductor optical amplifier and MZI-FBG techniques placed at 20 km point of a 40 km link obtained at 8 × 10 Gbps with 0.1 nm channel spacing has been evaluated and found that with the MZI-FBG based OADM, the signal can be transmitted with very less bit error rate and improved Quality value whereas MZI-SOA based OADM shows the worst results. The dense WDM system with optical add drop multiplexer placed at 35 km point of a 70 km link has also been investigated and is found that MZI-FBG based OADM and OADM based on MZI provide better results with covered transmission distance (150km) at channel spacing of 0.1 nm and 10 Gbps bit rate without using DCF and amplifier. It is observed that the worst case is with the MZI-SOA based OADM. In addition, it is observed that the MZI-based OADM is cost effective as compared to MZI–Semiconductor optical amplifier and MZI–Fiber Bragg grating based OADM. Further, unique architecture of an OADM based on FBG-Optical circulator has also been investigated for DWDM system with different modulators like Amplitude Modulator (AM), Mach-Zehnder (MZ) and Electro absorption (EA). This investigation has been done at 40 Gbps/ channel with ultra-narrow channel spacing of 0.1 nm. The maximum distance can be achieved upto 70 km with acceptable BER performance using AM modulator. It is reduced to 50 and 30 km with MZ and EA respectively. It is also found that using Amplitude Modulator, the structure provides acceptable BER with 280 GHz maximum FBG bandwidth and 9 dB insertion loss, circulator insertion loss of 4.5 dB. Further, the investigation of DWDM system based on OXCs using MZI, MZI-Semiconductor optical amplifier and MZI-Fiber Bragg grating techniques in the presence of crosstalk at 4x10 Gbps with 0.1nm channel spacing using standard single mode fiber has been done. To examine the optical communication system performance, the influence of increase in fiber length has been investigated. It is observed that the signal can be reached with minimum bit error rate using MZI-Fiber bragg grating based OXC and MZI based OXC up to 80 km whereas, the MZI-Semiconductor optical amplifier based OXC provides poor performance. The input-output power relationship shows improvement up to -14 dBm approximately in output power for MZI based OXC and MZI-FBG based OXC. It is observed that MZI based OXC architecture is cost efficient in comparison to MZI-SOA and MZI-FBG based OXC architectures. In addition, this thesis gives an insight into the scope of integration of optical add/drop multiplexer and OXC. The performance of DWDM system using OXADM at 4 × 10 Gbps with 0.1 nm channel spacing and the effect of attenuation, insertion loss and crosstalk has been demonstrated and observed that the signal can be transmitted up to 85 km without amplification at 6 dB insertion loss with 50 dB attenuation. Further, it is analyzed that the system provides acceptable performance with maximum of −35 dB crosstalk at 70 dB insertion loss and 6 dB attenuation for the same transmitted distance. We show enhancement in distance of transmission at reduced channel spacing and high bit rate. The thesis also highlights the investigative study of the effect of crosstalk in Dynamic Reconfigurable OADM based on Dynamic Channel Equalizer obtained with channel spacing of 100GHz at 40× 10 Gbps. The dynamic power transient with dynamic channel equalizer is also studied which equalizes the power variations with a single ROADM and observed that the signal with acceptable optical output power (-40 dBm) using dynamic ROADM based on Dynamic channel equalizer can be transmitted up to maximum distance of 220 km at 15 dB crosstalk. Further, the investigation of ROADM based on the Planar light wave circuit (PLC) and Wavelength Selective Switch (WSS) with 16 channels at bit rate of 10 Gbps with 100GHz channel spacing has been carried out. The dynamic power transients caused by addition or deletion of channels are mitigated using dynamic EDFA are also studied and analyzed that the signal with acceptable optical output power (-34 dBm) using dynamic ROADM based on PLC and WSS can be transmitted up to maximum distance of 462 km using three Dynamic EDFAs. The evaluation of the number of nodes supported in optical communication system with minimum optical input power considering different topologies like bus, ring and hybrid using OADM at 10 Gb/s with 30 km distance between successive nodes in the presence of hybrid optical amplifier has been done. It is found that in bus topology, maximum numbers of 18 nodes are supported for -20 dBm signal input power. In ring topology, 30 nodes are supported for -30 dBm signal input power but in hybrid topology, at -20 dBm signals input power, the number of nodes supported for upper bus is 6 but for ring, the number of nodes supported is more than 10. We also investigated the number of nodes supported in optical network at different crosstalks with minimum optical input power for Ring, bus topologies using optical cross connects with protection schemes at 10 Gb/s in the presence of hybrid optical amplifier. It is found that in ring topology, more than 20 nodes are supported at -10 dBm input power and 8 nodes are supported at -20 dBm signal input power for -30 dB crosstalks. In bus topology, 16 nodes are supported at -10 dBm input power and 4 nodes are supported at -20 dBm input power for -30 dB crosstalks. The number of nodes supported in case of -50 dB and -70 dB crosstalks are more than 20 in both the bus and ring topologies.