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Design and characterization of planar waveguide new optical add and drop multiplexer by using beam propagation method simulator.

Introduction

Upgrading telecommunication networks to increase their capacity is becoming increasingly important due to the rapid increase in network traffic. Wavelength division multiplexing (WDM) provides a new dimension for solving capacity and flexibility problems. Arrayed waveguide grating (AWG) is one of the most important components in WDM systems to split the wavelength to different unit. It has many advantages, including small size, high reliability, easy integration and low cost. AWGs can be used to realize multiple functions, such as wavelength multi/demultiplexers, wavelength routers, channel monitors, optical add/drop multiplexer (OADM), and optical cross connect (OXC). Ever since its invention in 1980s, AWG is being studied around the world (China Papers, 2010). The wavelength operational of OADM is depend to the type the types of AWG used. Instead of AWG, the demultiplexer based on the WDM coupler is also be used as the wavelength splitting element in the OADM. Here the coupled mode theory and evanescent field is important parameter in determining the efficiency of device that will be fabricated. The physical properties (length and width) of the device is also be influenced.

The term "mode coupling' addresses one of at least three different means of power transfer. These include coupling modes of distinct waveguides by evanescent fields, coupling modes in the same waveguide by longitudinally homogeneous perturbations, and co- and contradirectional coupling by longitudinally inhomogeneous, usually periodical perturbations (Universitat Obnasbruck, 2008).

Coarse WDMs (CWDM) is the economical solution that is proposed after DWDM and WDM to reduce the standard of the previous system. The system is not requiring the high performance and very rigid specification such as super cooled laser source and super narrowband filter as the WDM requirement instead. CWDM perform two functions. First, they filter the light, ensuring only the desired wavelengths are used. Second, they multiplex or demultiplex multiple wavelengths, which are used on a single fiber link. The difference lies in the wavelengths, which are used. In CWDM space, the 1310-band and the 1550-band are divided into smaller bands, each only 20-nm wide. In the multiplex operation, the multiple wavelength bands are combined (i.e. muxed) onto a single fiber. In a demultiplex operation, the multiple wavelength bands are separated (i.e. demuxed) from a single fiber. The used wavelengths are defined by the International Telecommunications Union; reference ITU G.694.2 for the ITU CWDM Wavelength Grid. Note: as of June 2002, eighteen center wavelengths, from 1270 nm to 1610 nm, were listed (Fiberdyne, 2003; Rahman, 2005).

An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF). This is a type of optical node, which is generally used for the construction of optical telecommunications networks. "Add" and "drop" here refer to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of optical cross-connect. A traditional OADM consists of three stages: an optical demultiplexer, an optical multiplexer, and between them a method of reconfiguring the paths between the optical demultiplexer, the optical multiplexer and a set of ports for adding and dropping signals. The optical demultiplexer separates wavelengths in an input fiber onto ports. The reconfiguration can be achieved by a fiber patch panel or by optical switches which direct the wavelengths to the optical multiplexer or to drop ports. The optical multiplexer multiplexes the wavelength channels that are to continue on from demultipexer ports with those from the add ports, onto a single output fiber.

All the light paths that directly pass an OADM are termed cut-through lightpaths, while those that are added or dropped at the OADM node are termed added/dropped lightpaths. An OADM with remotely reconfigurable optical switches (for example 1x2) in the middle stage is called a reconfigurable OADM (ROADM). Ones without this feature are known as fixed OADMs. While the term OADM applies to both types, it is often used interchangeably with ROADM.

Physically, there are several ways to realize an OADM. There are a variety of demultiplexer and multiplexer technologies including thin film filters, fiber Bragg gratings with optical circulators, free space grating devices and integrated planar Arrayed waveguide gratings. The switching or reconfiguration functions range from the manual fiber patch panel to a variety of switching technologies including MEMS, Liquid crystal and thermo optic switches in planar waveguide circuits.

Although both have add/drop functionality, OADMs are distinct from add-drop multiplexers. The former function in the photonic domain under wavelength-division multiplexing, while the latter are implicitly considered to function in the traditional SONET/SDH networks.

The focus of this paper is the design, simulation and characterization of optical cross add drop multiplexers based on planar waveguide which operate in two CWDM wavelength. Fiber to the home (FTTH) has been developing rapidly in recent years and will become a major technology for next generation broadband access networks. An waveguide based OADM has many advantages including small size, high reliability and low cost. The commonly used wavelengths for CWDM has spacing of 20 nm. Because of the wide wavelength spacing, it is difficult to produce satisfactory results with a conventional AWG design.

Design:

The increase in capacity beyond than 10 Gbps of data transmission has been limiting the use of coaxial cable as a medium for data transmission. In this case, fiber-optic technology has become an option to meet the demand for broadband transmission. With the implementation of WDM in optical fiber technology has become a medium of transmission without the limit and offers many advantages including high capacity, high speed, long distance data transmission capabilities and the quality of the received signal is better. The information transmitted in the optical domain is transferred through the line point to point SONET equipment / SDH to form a ring and mesh networks topology.

In this network the needs of devices to implement add and drop function and path routing are performed by OADM and OXC devices respectively. Both devices have large applications in the optical world and have a similar basic structure, but both have different characteristics (Rahman, 2001). OADM control signals of different wavelengths at each base, while the OXC will operate the same wavelengths (Mutafungwa, 2000; Eldada, 2000; Rahman, 2004). As a result, the devices are used at different locations with different functions. Device manufacturers conspired set used OADM in the ring network while OXC was used in the mesh network. However, the evolution of communication in the world today has directed two features of these devices be integrated together to form a hybrid device. Topology migration and network security issues in the ring network have inspired the existence of a device that can perform all the functions addresses by OADM and OXC called OXADM (Rahman, 2008; Rahman, 2008; Rahman, 2008; Rahman, 2006; Rahman, 2006). OXADM is the first in its class that combines the features of OADM and OXC devices. With the embedding of new features such as multiplexing and 'U' turn routing have extended the function and are not challenging by any existing devices yet. Moreover, all OXADM signal processing carried out in the optical domain.

The design of OADM is cascaded with multiplexer to perform the full OADM function. The basic block diagram of semi complete device is shown in Figure 1(a) and full complete OADM device is shown in Figure 1 (b). In actual application our proposed device will be cascaded with multiplexer to accumulate all signal in one output port.

[FIGURE 1 OMITTED]

Simulation Result:

The new architecture of OADM is designed by using Beam propagation method tool (BPM) and the results of optical field propagation are shown in Figure 2 and Figure 3 respectively for two different operating wavelength; 1610 nm and 1590 nm.

The input signal is injected into input port and the output power is measured to each of output ports. The measured power of every output port for each OADM function is shown in Table 1 and Figure 4. Then the parameter of Crosstalk and Directivity are further calculated. The results are shown in Figure 5 and Figure 6. The coupling area is a significant part of the device architecture. The length will determine the wavelength selection.

Result and Discussion

OADM has performed four function for every operating wavelength such as drop, add, pass though and path exchange. Table 1 shows the measurement of each output port during the OADM performing its function. The Directivity of a channel is the maximum signal from that channel measured at any other than the selected channel within any clear window for all polarization states, referenced to the incident signal level. According to Figure 5, the minimum value of crosstalk is 9.6 dB. The Adjacent Crosstalk of a channel is the highest transmission within an adjacent passband referenced to the lowest transmission within the selected channel passband. The highest and lowest transmissions are determined for any (possibly different) polarization states within each passband. Referring to Figure 6, the minimum value of Directivity is 9.2 dB.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

References

China Papers, 2010. Planar Waveguide Devices Based on Novel Arrayed Waveguide Gratings for Wavelength Division Multiplexing and Access Networks. http://www.china-papers.com/?p=117564

Universitat Obnasbruck. 2008. Coupled Mode Theory. http://wwwhome.math.utwente.nl/~hammerm/Wmm_Manual/cmt.html

Fiberdyne, 2003. Introduction to Coarse Wavelength Division Multiiplexing (CWDM). http://www.fiberdyne.com/products/pdf/cwdmintro.PDF

Rahman, M.S.A. and Sahbudin Shaari, 2005, Modeling of New Structure of CWDM Waveguide Based Multiplexer and Demultiplexer, Proceeding 2005 IEEE National Symposium on Microelectronics, pp: 361-366, pub. IEEE Malaysia Section.

Rahman, M.S.A. and S. Shaari, 2001. Design and Characteristics of Wavelength Demultiplexer Based on Tilted in Glass Waveguide, Proceedings 2001 IEEE National Symposium on Microelectronics, pp: 370-374, pub. IEEE Malaysia Section.

Tzanakaki, A., I. Zacharopoulus, I. Tomkos, 2003. Optical add/drop multiplexers and optical cross-connects for wavelength routed network, ICTON, pp: 41-46.

Mutafungwa, E., 2000. An improved wavelength-selective all fiber cross-connect node, IEEE Journal of Applied Optics, pp: 63-69.

Eldada, L. and J.V. Nunen, 2000. Architecture and performance requirements of optical metro ring nodes in implementing optical add/drop and protection functions, Telephotonics Review.

Rahman, M.S.A., S. Shaari, 2004. Modeling of planar lightwave circuit OADM for CWDM", Proceeding 2004 Postgraduate Conference, pp: 116-120.

Rahman, M.S.A., S. Sulaiman, K. Mat and B.C. Ng, 2008. The Hybrid Protection Scheme in Hybrid OADM/OXC/MUX. Australian Journals of basic Applied Science, 2(4): 968-976.

Rahman, M.S.A., 2008. First Experimental on OXADM restoration scheme Using Point-to-Point Configuration. Journal of Optical Communication, JOC (German), 29(3): 174-177.

Rahman, M.S.A., 2008. Highlighting on Multiplex Restoration Scheme in Optical Cross add and Drop Multiplexer (OXADM). Journal of Optical Communication, JOC (German), 29(4): 205-208.

Rahman, M.S.A., S. Shaari, 2006. OXADM restoration scheme: Approach to optical ring network protection", IEEE International Conference on Networks. pp: 371-376.

Rahman, M.S.A., H. Husin, A.A. Ehsan, S. Shaari, 2006. Analytical modeling of optical cross add and drop multiplexing switch", Proceeding 2006 IEEE International Conference on Semiconductor Electronics, pub. IEEE Malaysia Section, pp: 290-293.

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

Mohammad Syuhaimi Ab-Rahman

Spectrum Technology Research Group (SPECTECH) Department of Electrical, Electronics and Systems Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia 43600 UKM Bangi, Selangor, Malaysia
Table 1: Measurement of each output port during the OADM performing
its function.

                         Drop       Output     Output     Drop
                         1590 nm    1590 nm    1610 nm    1610 nm

Wavelength   Operation   Output 1   Output 2   Output 3   Output4

1610 nm      Drop        7.98E-04   1.67E-03   7.52E-02   6.34E-01
             Transmit    4.80E-03   1.79E-03   7.65E-01   6.50E-03
             Exchange    1.63E-03   1.79E-03   5.91E-02   1.26E-02
             Add         3.82E-03   1.90E-04   6.51E-01   7.02E-02

1590 nm      Drop        6.36E-01   2.31E-02   2.96E-02   4.92E-05
             Transmit    4.45E-02   7.51E-01   3.23E-02   2.57E-04
             Exchange    4.15E-02   4.69E-02   2.78E-02   1.99E-02
             Add         1.21E-02   6.50E-01   5.63E-05   2.51E-04

                         Exchange   Exchange
                         1590 nm    1610 nm

Wavelength   Operation   Output 5   Output 6

1610 nm      Drop        2.25E-02   9.74E-03
             Transmit    4.12E-04   9.10E-03
             Exchange    7.68E-03   5.60E-01
             Add         4.66E-03   1.25E-02

1590 nm      Drop        5.61E-04   2.31E-04
             Transmit    3.20E-03   7.47E-04
             Exchange    4.99E-01   6.52E-03
             Add         5.61E-03   4.69E-04
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Title Annotation:Original Article
Author:Ab-Rahman, Mohammad Syuhaimi
Publication:Advances in Natural and Applied Sciences
Article Type:Technical report
Geographic Code:9MALA
Date:Apr 1, 2011
Words:2120
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