An Optimum Design Of 3x3 Optical Switch Based On Integrated MZI

Table 1The comparison and optimum result of thethickness of the waveguide according to InsertionLoss and Extinction Ratio of the Proposedstructure

Thickness

width(µm)Switching

State

Output

Port

I.L.(dB) Ex.R.(dB)

7.5

State 1

Out 1 -1.93-11.07Out 2 -13.01

Out 3 -5.27

State 2

Out 1 -18.23-17.43Out 2 -0.80

Out 3 -8.44

State 3

Out 1 -12.51-19.22Out 2 -19.58

Out 3 -0.362

8.0

State 1

Out 1 -0.70-11.9Out 2 -12.6

Out 3 -10.3

State 2

Out 1 -23.0-22.67Out 2 -0.34

Out 3 -11.7

State 3

Out 1 -23.0-22.94Out 2 -21.4

Out 3 -0.06

8.5

State 1

Out 1 -0.57-12.89Out 2 -12.51

Out 3 -13.46

State 2

Out 1 -15.68-14.43Out 2 -1.249

Out 3 -6.861

State 3

Out 1 -9.546-7.277Out 2 -5.543

Out 3 -2.269

The simulation results show good performance forthis structure. Table 1 shows the insertion loss(I.L.), and the extinction ratio (Ex.R.) of theproposed optical switch. Insertion loss of a switchis a part of power that is lost and has to be low forgood performance and the extinction ratio is theratio of output power in ON state to output powerin OFF state. Insertion loss and extinction ratiothat are the important parameters for opticalswitching can be calculated by these equations:

I.L.(dB)=

in

out

PP

10log10 (2)

Ex.R.(dB)=

high

low

PP

10log10 (3)

Where outP and inP are the output and input powerand highP and lowP show the higher and sum oflower levels in output in both state of ON andOFF[5]. As shown in Table 1, the output results ofthe device are acceptable for a good performanceof all-optical switch.With choosing the exactreflecting index, this structure can work as 3x3Switch Based On Integrated Mach-ZehnderInterferometer. In the future, with the materialsthat can have higher nonlinearity the outputs of thestructure can increase to have an all-optical switchwithout any complicated materials or structure.

3 Analyze the influence of Electro-Optic

The influence of Electro-Optic refer to changes inthe refractive index of material induced by theapplication of an external electric field, whichtherefore modulates the optical properties , theapplied field is not the electric field of any lightwave, but separate external field[8]. Ordinarilyalteration in the refractive index are Slightly. Theinfluence of electro-optic are categorizedaccording to first and second order effects. Therefractive index n have been taken as a function ofapplied electric field E, that is n=n(E), so it can beexpand this as a Taylor series in E. The newrefractive index n’ would be:

n’= n + a1 E + a 2 E 2 + ... (4)

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ISSN: 1109-2742 357 Issue 6, Volume 9, June 2010

Where the coefficients a1 , and a 2 are called thelinear electro-optic effect and second orderelectro-optic effect coefficients. The change in ndue to the first E term is called the Pockels effect.The change in n due to the second E 2 term iscalled the Kerr effect, and the coefficient a 2 isgenerally written as λK, where K is called the Kerrcoefficient.In the case of the Pockels effect, the preciseeffect of the applied electric field depends onthe crystal structure and symmetry of thematerial under consideration. main contributionto birefringence to electro-optical crystal is dueto Kerr’s effect, it means[12]:

∆n p <<∆n k

The Kerr electro-optical effect consists in the factthat, under the influence of an electric field, anoptical anisotropy with an induced optical axisappears. The axis is directed along the appliedelectric field. When light radiation passes througha sample located in the electric field, a phasedifference φ appears between the orthogonallypolarized light components [10]:

ϕ = 222 KlEnl πλπ

=∆ (5)

Where n∆ is the induced birefringence; l is thelength of the optical path in the zone of fieldapplication; in the zone of field application; λ isthe light wavelength; E , V/m, is the electric fieldstrength; and K, m/V 2 , is the Kerr coefficient ofthe material. Assuming that the electric field isuniform, the field strength E can be expressed viathe applied voltage oV and the distance betweenthe electrodes d . Expression (1) then takes theform:

ϕ = 2πBl 2oV / d 2 (6)

The Pockles effect expressed in this equation:

Ean 2=∆ (7)

This is an over-simplification because in reality itmust be consider the effect of an applied fieldalong a particular crystal direction on therefractive index for light with a given propagationdirection and polarization[8].

Fig.4 The index ellipsoid showing the principalaxes of the dielectric (x,y,z) and thecorresponding refractive indices(n x , n y , n z )

3.1 Electric impermeability, indexellipsoid, dielectric constant andrefractive index

In many optical fibre applications, such asinterferometry, the effective refractive index ofthe guided modes is of great interest. In the caseof electro-optic responses, it is often moreinformative to know how the refractive indexresponds to an incident electric field than tocompletely understand the non-linear polarisation.The electric displacement field is defined by therelation:

=ε0+ (8)

where is the electric field, ε0 is the permittivityof free space, and is the dipole moment per unitvolume or polarisation density. The electricdisplacement field can be expressed in terms ofthe electric polarisability as:

=ε0 1+ = (9)where is the electric permittivity.



The electric impermeability switch =0 can beused to construct the index ellipsoid i.e.

1=∑ij jiij xxη , ,=1,2,3, (10)

where ijη are the elements of the impermeabilityswitch . The index ellipsoid and the electricimpermeability tensor can be used to describedielectrics and anisotropic materials such ascrystals. The principal axes of the ellipsoid are theprincipal optical axes of the dielectric and thedimensions along these axes are the correspondingrefractive indices (see Fig.4). In the case of opticalfibre where the propagation direction or axis of thefibre may be assigned to the z direction, or axis, ofthe index ellipsoid and then the dimensions alongthe x and y axis are the refractive indices for x andy polarised modes. i.e.

xη =xεε 0 = 2

1xn

, and yη =yεε0 = 2

1

yn(11)

The presence of a DC electric field will alter theindex ellipsoid so that elements of the indexellipsoid become a function of the electric field i.eΕijη . To include the non-linear response the

electric impermeability switch can be expanded ina Taylor’s series about E=0 as follows.

lkijklkijkijij sr ΕΕ+Ε+=Ε ηη )( , ,,,=1,2,3 (12)

Where )0(ijij ηη = ,k

ijijkr

Ε∂∂

=η

,lk

ijijklK

ΕΕ∂

∂=

η2

21

and the derivatives are evaluated at E=0. Thesummation notation over repeated indices isimplied and the ijkr and ijklK coefficients arecalled the Pockels and Kerr coefficientsrespectively.

4 ConclusionsAn optimum 3x3 optical switch based on

Mach-Zehnder interferometer was successfullydesigned using OptiBPM, for switching opticalsignal with wavelength 1300nm. The couplingefficiency of the 3x3 optical switch designed canbe controlled by changing the voltage applied tothe electrode region. When no voltage is applied,the switch acts as a passive optical switch in whichthe coupling efficiency is 100%. When switchingvoltage is applied to the electrode region of the

3x3 optical switch, on coupling occurs where theoptical signal is switched to the same outputwaveguide. With this electro-optic effect, the 3x3optical switch can act as an electro-optic switch toswitch optical signal to desired output port.



( a )

( b )

Fig. 5 (a) Beam propagation simulation and the normalized output power of the proposed structure in the first state ofthe switching operation.(b)The output power vs. Iterations in the first state according to the effect of changingthe voltage -8.0V.



( c )

( d )

Fig. 6 (c) Beam propagation simulation and the normalized output power of the proposed structure in the secondstate of the switching operation.(d)The output power vs. Iterations in the second state according to the effectof changing the voltage 0.0V.



( e )

( f )

Fig.7 (e) Beam propagation simulation and the normalized output power of the proposed structure in the third stateof the switching operation.(f)The output power vs. Iterations in the third state according to the effect ofchanging the voltage 8.0V.



Acknowledgment:This work is sponsored by National UniversityMalaysia-Universiti Kebangsaan Malaysia(UKM), throughout grand no: UKM-AP-ICT-17-2009, 01-01-02-SF0493. The authors would like tothank the project leader and appreciate hiskindness, valuable assistance, and financialsupport.

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T. F. Krauss, “Demonstration of an integratedoptical switch in a silicon photonic crystaldirectional coupler” Physics E, vol. 41 pp. 1111-1114, 2009.

[2].Chuan-Tao Zheng Chun-Sheng Ma, Xin Yan, Xian-Yin Wang, Da-Ming Zhang “Analysis of responsecharacteristics for polymer directional couplerelectro-optic switches,” Optics Communications,vol. 281 pp. 5998-6005, 2008.

[3].Chuan-Tao Zheng, Chun-Sheng Ma, Xin Yan,Xian-Yin Wang, Da-Ming Zhang, “ Simulationand optimization of polymer directional couplerelectro-optic switch with push-pull electrodes,”Optics Communications, vol. 281, pp. 3695-3702,2008.

[4].N. Naim, R. Ngah, T. Prakoso, S. Sarnin, H. AbdulRahman, Z. Ghassemlooy “Modelling of All-Optical Symmetric Mach-Zehnder Switch withAsymmetric Coupler”IEEE International RF andMicrowave Con. 352-356, December 2-4, 2008.

[5].Rahim Ghayour, Ahmad Naseri Taheri, andMohammad Taghi Fathi, “Integrated Mach-Zehnderbased 2x2 all-optical switch using nonlinear two-mode interferometer waveguide,” Applied Optics,vol. 47, pp. 632-638,2008.

[6].Ghanshyam Singh, R. P. Yadav, Vijay Janyani, andAranab Ray,”Design of 2x2 Optoelectronic SwitchBased on MZI and Study the Effect of ElectrodeSwitching Voltages” World Academy of Science,Engineering and Technology 39 2008.

[7].Binming Liang, Qu Li, Gagjun Liu, Guoliang Jin,“Nonlinear directional coupler with variablecoupling coefficient and variable nonlinearrefractive index coefficient,” OpticsCommunications, vol. 274, pp. 447-451, 2005.

[8].S.O.Kasap ”Optoelectronics and Photonics:Principles and Practices” 294-2001

[9].Moh. S.Ab. Rahman , Khaled. M. Shaktur, R.Mohammad ” An Electro-Optic 3x3 Switch BasedOn Integrated Mach-Zehnder Interferometer” 8thWSEAS International Con.Penang, Malaysia,March 23-25, 2010.

[10].A.A. Vetrov, A.A. Lipovskii, D.K. Tagantsev ” AHighly Sensitive Technique for easurementsof theKerr Electrooptic Coefficient in Glasses and GlassCeramics” Instruments and ExperimentalTechniques, Vol. 45, No. 4, 2002.

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An Optimum Design Of 3x3 Optical Switch Based On Integrated MZI