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Waveguide based advances optical add and drop multiplexer (AOADM) for CWDM application.

Introduction

Coupling Length is defined as the active area where the signals are alternately migrate from one waveguide to another waveguide. This can be achieved by designing a fundamental of coupling waveguide architecture as shown in Figure 1. Then the coupling length will determine according to the coupling profile that is generated automatically from the BPM software used. The detail of exact coupling length selection is shown in Figure 2.

Four wavelengths of CWDM are injected to the input port. Due to the evanescent field and two very closed waveguide the signal will be migrate to another waveguide alternately. Due to different of wavelength used, propagation constant and wave number has make the signal oscillation and distance of coupling has become different and finally the signal can be separated (Figure 3). For example in this case wavelength of 1510 nm and 1530 nm together exit from one output port while 1550 nm and 1570 nm exit from other output port. Thus the selection point of coupling length has been determined successfully.

The best and effective point to separate the wavelength is when the signals are engrouped into two parts, Valley and Pulse. The bigger area of this part contributes more efficient of signal separation. The leakage can be avoid and finally improved the value of crosstalk and directivity. This two parameters are important to be controlled to enable the signal can travel longer.

The knowledge of couple mode theory and wavelength separation point determination has been translated to many designs of new optical device. Tilted grating demultiplexer, CWDM WDM coupler, CWDM OADM, 2x3 Optical Moderator, MultiRatio Optical Splitter (MROS) and etc. have shown their vast application in optical communication system (Ab-Rahman,and Shaari 2001; Ab-Rahman and Shaari 2004; Ab-Rahman and Shaari 2005; Ab-Rahman et al. 2011; Ab-Rahman et al. 2009; Ab-Rahman & Wahab 2009; Ab-Rahman & Zaman 2009; Ab-Rahman 2011). As a conclusion, the knowledge of couple mode theory with some creativity is the key of new era of optical device innovation.

Design:

The AOADMs are new optical switching devices which have an asymmetrical architecture and can perform bi-directional functions similar to existing devices such as OXADM, conventional OADMs and OXCs (Tzanakaki, A., 2003). The AOADM are located in the nodes, which have more than two switching directions in ring networks. The function of AOADM is to flexibility switch the wavelengths among the different input and output ports. However 'Accumulation' is the most interesting feature and differentiates the OXADM from other devices such as AOADM, ROADMs, TRNs, OADMs, OXNs and OXCs (Ab-Rahman, M.S., 2006; Eldada, L., 2000; Mutafungwa, E., 2000). AOADM provide capability to add and drop function and cross connecting traffic in the network which is the characteristic of OADM and OXC. Basically, AOADM consists of three main subsystems which are a wavelength selective demultiplexer, a switching subsystem and a wavelength multiplexer. AOADM is a newly upgraded device that can function as a node in both ring and mesh topology. Each AOADM is expected to handle at least two distinct wavelength channel each with granularities of 2.5 Gbps or higher. The signals can then be re-routed to any output port or/and an accumulation function can be performed which multiplexes all signals onto one path and then exit from any output port of interest.

The AOADM node focuses on providing functionally such as transport, multiplexing, routing, supervision, termination and survivability in the optical layer with ring and mesh topologies. There are eight ports for add and drop functions, which are controlled by four lines of MEMs switch. The other four lines of MEMs switches are used to control the wavelength routing function between two different paths (see Figure 1a).The functions of AOADM include node termination, drop and add, routing, multiplexing and also providing mechanism of restoration for point-to-point, ring and mesh metropolitan and also customer access network in FTTH. The concept is similar to OXADM function offered as reported in (Ab-Rahman, M.S., 2006; Ab-Rahman, M.S., 2007; Ab-Rahman, M.S., 2006; Ab-Rahman, M.S., et al, 2006; Ab-Rahman, M.S., et al, 2009; Ab-Rahman, M.S., 2009; Ab-Rahman, M.S., 2008). In ring architecture, AOADM perform as a node and the function is similar to the parallel connection add drop multiplexer (ADM) in which the drop port of one ADM is connected to Add port and vice versa (Ab-Rahman, M.S., 2008). The architecture is depicted in Figure 1b.

[FIGURE 1 OMITTED]

Figure 2 shows the architecture of AOADM waveguide device. It consists of two input ports, two output port with four terminal for add operation and four terminal for drop operation. Basically the design is based the Couple Mode Theory (CMT) and Beam propagation method (BPM) is used to simulate the device. Waveguide thickness is set at 6 [micro]m. The device dimension is 90 mm (length) x 1.2 mm (width). Eight coupling area is needed to achieved 4 wavelength CWDM AOADM.

[FIGURE 2 OMITTED]

Result and Discussion

Figure 3 shows the signal propagation profile for every function of AOADM. The design in Figure 2 is simulate using Opti_BPM software a product of Optiwave Corporation. The output power is measured for every output port with the signal is measured at every interested port and the leakage signal is measured at other output port. The characterization of device is determined by considering the interested signals and leakages and has been discussed in Figure 4 until Figure 8. The most important parameter of this characterization is directivity (measured in decibel, dB) and Crosstalk (measured in decibel, dB).

[FIGURE 3 OMITTED]

Figure 4 shows the signal distribution at every output port for each single operation of AOADM. The interested signal si significant can be seen from the graph and other signals with small amplitude are the leakages. The comparison output signal for every AOADM function is shown in Figure 5. The minimum output signal is 34% and the maximum is 73%. The leakages distribution is shown in Figure 6 with the maximum is 13 % of the total injected signal. The values form Figure 6 is used to calculate the Directivity (Figure 7) and Crosstalk (Figure 8). According to Figure 7 and Figure 8 the minimum values for both graph is 6 dB and can be accepted for optical communication purpose.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Reference

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Ab-Rahman, M.S. and H.F.A. Wahab, 2009. New Design of 1x3 Wavelength Demultiplexer Based on Tilted Grating in Glass Waveguide for First Window Operating Wavelength. Australian Journals of Basic Applied Science, 3(3): 2607-2613.

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Corresponding Author: Mohammad Syuhaimi Ab-Rahman, Spectrum Technology Research Group (SPECTECH), Department of Electrical, Electronic & Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,43600 Bangi, Malaysia, 43600 Bandar Baru Bangi, Selangor

Mohammad Syuhaimi Ab-Rahman

Spectrum Technology Research Group (SPECTECH), Department of Electrical, Electronic & Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,43600 Bangi, Malaysia, 43600 Bandar Baru Bangi, Selangor
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Title Annotation:Original Article
Author:Ab-Rahman, Mohammad Syuhaimi
Publication:Advances in Natural and Applied Sciences
Article Type:Report
Geographic Code:9MALA
Date:Nov 1, 2011
Words:1800
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