Wide Band Magneto Optical Modulators in Advanced High Speed Optical Communication Systems

7/31/2019 Wide Band Magneto Optical Modulators in Advanced High Speed Optical Communication Systems

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INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH, VOLUME 1, ISSUE 5, JUNE 2012 ISSN 2277-8616

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IJSTR2012www.ijstr.org

Wide Band Magneto-Optical Modulators InAdvanced High Speed Optical Communication

SystemsAhmed Nabih Zaki Rashed

AbstractThe technology involves a new type of compact device based on magneto-optics in a fiber micro modulator. This type of modulatorallows the user to inter manipulate and control the propagation of the incoming light. The operation mechanism uses external magnetic field tomanipulate Fe micro particle in order to cause modulation of an optical signal that propagates along an optical waveguide. This paper haspresented yttrium iron garnet (YIG) and lithium niobate (LiNbO3) which are examined for use as a wideband magneto-optic modulator. Awideband YIG modulator has recently been developed which represents a great improvement over other magneto -optic modulators.

Index Terms Magneto-optic modulation, Faraday rotation Effect, LiNbO3, YIG, and Ultra fast magnetic f ield.

1.INTRODUCTIONOver the last several years, the demand for high bandwidthnetworking has dramatically increased, encouraging thecontinued development of high-speed electrical and opticaldevices. In particular, the realization of high bandwidth, lowpower, efficient modulators plays a fundamental role in theimprovement of integrated optical systems and networks.Contemporary optical modulation devices rely primarily onelectro-optic (EO) interaction in nonlinear materials. Byexploiting the Pockels effect, the electric field associated witha high-speed electrical signal is employed to modulate anoptical beam. However, in recent years, there has been anemergence of a new class of photonic devices based on themagneto-optic (MO) effect [1, 2]. These devices utilize theFaraday effect, in which the magnetic field associated with anelectrical signal modulates an optical beam. Such magneto-photonic devices offer high bandwidth modulation andswitching capabilities comparable to those based on the EOeffect. The recent interest in such technology is stimulated bycurrent advances in the growth of a variety of MO materials,namely rare-earth iron garnets [3]. High-quality magneticgarnet films are readily available in a variety of forms and canbe grown by epitaxial or sputter methods for particularapplications. Such films have a large Faraday rotation, lowabsorption in the near infrared, and a low saturationmagnetization. Furthermore, their optical properties can beeasily manipulated by doping, such as the substitution ofbismuth in yttrium iron garnets [4].

Research into the application of rare-earth iron garnets hasresulted in the development of a variety of unique MO photonic

devices, such as resonant/non resonant modulatorspolarization sensitive beam deflectors, switches, and isolatorsIn spite of these benefits, MO device technology is still in itsinfancy and has not yet been fully explored for integrated highspeed optical technology. Magneto photonic devices to datehave relied on the propagation of light waves through the MOmaterial. As the light beam travels through the MO medium, itsplane of polarization is rotated according to the Faraday effec[5], resulting in a polarization modulation. However, thetransmission arrangement presents difficulties associated withthe MO material such as optical absorption of the light beamas it propagates through the interaction region, as well asinherent birefringence. To observe a maximum MO effect, it isdesirable to have a MO material with large Faraday rotation

negligible birefringence, and very little absorption. Of thevarious MO materials available, bismuth-substituted yttriumiron garnet (Bi-YIG) is often chosen for the backbone of avariety of MO devices as it has a very large MO interaction [6].Optical modulators have become indispensible in manyapplications or optical instruments. Light interacts with mattersin various macroscopic ways. The most commonly knownphenomenon include electro-optical (EO) effect, acoustooptical (AO) effect, and magneto-optical (MO) effect. AOmodulators and EO modulators have already found manyapplications, and state-of-the-art modulators are alreadycommercially available. However, AO modulator inherentlysuffers from slow modulation speed. Although EO modulator iscapable of fast modulation [7], it requires a relatively high

accuracy on the alignment in free-space applications. MOeffect, on the other hand, finds its application only as an opticaisolator so far. Although there have been many researches onMO modulators in integrated optics [8], the possibility of a free-space MO modulator has not been widely investigated. TheMO modulator can not only work as an intensity modulatowhen combined with two linear polarizer, but can also work asa polarization rotator alone. In the present study, magnetooptic materials have unique physical properties that offer theopportunity of constructing devices with many speciafunctions not possible from other photonic devices. The mostsignificant of these properties are that the linear magneto-opticeffect can produce circular birefringence and that, unlike other

______________________

Ahmed Nabih Zaki RashedElectronics and Electrical Communications EngineeringDepartment Faculty of Electronic Engineering, Menouf

32951, Menoufia University, [email protected]:-E
mailto:[email protected]:[email protected]:[email protected]


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optical effects in dielectric media, it is nonreciprocal. Allpractical magneto-optic devices exploit one or both of thesetwo properties. Important applications of these devices includepolarization control, optical isolation, optical modulation, andmagneto-optic recording. The basic principles of magneto-optic modulator effects are considered in this study.

2.MAGNETO-OPTICAL MODULATOR SCHEMATIC VIEWAs the internet and modern communications becomesincreasingly prevalent across the globe, all-optic networks. Inrecent years, for the sake of satisfying high speedtransmission and exchange of optical-message through fiber-optic networks, optical switch has been significantly improvedas an important element for optical communication bycontinuous widely research [9].

Fig. 1. Basic Construction of MO Modulator under study.

As shown in Fig. 1, the proposed structure of MO modulatorbased on a microwave micro strip line with a polarizationsensitive MO active medium and fiber optic continuous wave(CW) light delivery. As the requirement from the opticalcommunication technique, it should be characterized as lowcrosstalk, low insert loss, short switching time and lowpolarization sensitivity together with special requirement onextinction ratio, switch scale and dimension. As the factors thatwill affect the optical switch parameters, it consists of thequality of separate units technical index (transmissivity,

rotation angle etc.) and also the quality of units final assemblyand adjusting1.So far, a variety of optical switches have beendeveloped. In comparison to the various other opticalswitches, the magneto-optic switch based on Faraday rotationeffect for light consists of special optical route including a typeof high-quality magneto-optic material YIG crystal, a novelswitch of generating pico second-order electrical pulses andFaraday rotator configuration with ultrafast magnetic field. It isfeatured as low insertion loss, low crosstalk, high switchingspeed and small bulky size. Using the polarization andFaraday Effect of magneto-optic crystal, the magneto-opticswitch can hold the function of all-optical switching, which isneeded in all-optical communication networks [10].

3.THEORETICAL MODEL ANALYSISWhen a transparent material is placed in a magnetic field andlinearly polarized light is passed through it along the directionof the magnetic field, the emerging light is found to remainlinearly polarized, but with a net rotation in degree, of theplane of polarization that is proportional to both the thickness din mm, of the sample and the strength of the magnetic field Bin Tesla, along traveling direction, according to the empiricalrelation [11]:

,180

dVB Degree (1)

Where V is the Verdet constant for the material. The Verdeconstant is both temperature and wavelength dependent. TheFaraday Effect is similar to optical activity. The difference isthat optical activity doesnt require an externally appliedmagnetic field to rotate the light polarization and it onlydepends on the traveling length and material concentrationThe modulation depth, Mp can be expressed in terms of pulseduration in psec, and angle of rotation in degree, by using

MATLAB curve fitting program as the following formula [12]: 285 100032.0)(100765.01021.0 xxMp (2

The transmittance of MO modulator Tm, can be expressed as:

5.0cos2mT (3The signal to noise ratio (SNR) of MO modulator can beexpressed as the following formula [13]:

eBWq

rPSNR

02log10

, (4)

Where r is the reflection coefficient, BWe is the electricabandwidth, P0 is the laser power, q is the electron charge, and is the its modulator responsivity. The bit error rate (BERessentially specifies the average probability of incorrect bit

identification. In general. The higher the received SNR, thelower the BER probability will be. The bit error rate (BER) isrelated to the signal to noise ratio (SNR) as follows [12, 13]:

,22

15.0

SNRerfBER (5

Moreover the refractive index of the LiNbO3, and YIG are casunder the Sellemier equation as the following [14, 15]:

2102

92

87

265

2

4321

2

)(

B

B

MBB

MBB

MBBMBBn

(6

The set of parameters is dimensionally adjusted for LiNbO3as: B1Li=5.35583, B2Li=4.629x10-7, B3Li=0.100473B4Li=3.862x10-8, B5Li=0.20692, B6Li=-0.89x10-8, B7Li=100

B8Li=2.657x10-5, B9Li=11.34927, B10Li=0.015334, andM=(T-T0)(T+570.82). While the set of parameters isdimensionally adjusted for YIG as: B1YIG=0.00987B2YIG=1.43567x10-11, B3YIG=0.10765x10-3B4YIG=0.00532x10-8, B5YIG=0.0541, B6YIG=10.4329x10-9B7YIG=1234, B8YIG=0.05437x10-7, B9YIG=14927B10YIG=0.00384, and M=(T-T0)(T+590.54). Thus the previousequation can be simplified as the following formula:

210

29

2

78

256

2

3412

2

B

B

B

B

BBn

(7

Where B12=B1+(B2M), B34=B3+(B4M); B56=B5+(B6M), andB78=B7+(B8M). In the general case, if the device operationefficiency, 1, the inductance L and internal electricaresistance Re of MO modulator, we have [16]:

62

2

0nLc

L

m

(8

eR 60nLc m

(9

Where Lm is the modulator length, c is speed of light, 0 is thefree space permeability, is the spectral linewidth of the lasediode, and n is the refractive index of the selected materiabased MO modulator.


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4.SIMULATION RESULTS AND PERFORMANCE ANALYSISWe have deeply investigated the recent advances of wideband magneto optical modulators in advanced high speedoptical communication systems over wide range of theaffecting operating parameters as shown in Table 1.

Table 1: Proposed operating parameters for magneto-optical modulators.

Parameter DefinitionValue andunit

T=T0Ambienttemperature=roomtemperature

300 K

Pulse duration 100 psec

d Modulator thickness5 mm 25mm

B Magnetic field intensity

0.1

web/mm21web/mm2

Operating signalwavelength

1.3 m

V

Verdet constant forLiNbO3

4.54x10-6rad/A

Verdet constant for YIG5.65x10-6rad/A

Q Electron charge 1.6x10-19C

BWe Electrical bandwidth 1 MHz

P0 Laser power 1 mWatt

Modulator responsivity 0.4 A/Watt

r Reflection coefficient0.55 at =1.3m

Spectral linewidth of

optical source0.1 nm

C Speed of light 3x108 m/sec

Lm Modulator length50 mm 100mm

0 Free space permeability 4x10-7 H/m

Device operationefficiency

0.9

Based on the model equations analysis of MO modulatorassumed set of the operating parameters, and the set of theseries of the Figs. (2-12), the following facts are assured:- Figs. (2-4) have assured that angle of rotation increases withincreasing MO modulator thickness and applied magnetic fieldintensity for both materials based MO modulator devices. We

have indicated that YIG MO modulator has presented higheangle of rotation than LiNbO3 MO modulator at the sameoperating conditions.- Figs. (5-7) have demonstrated that modulation depthincreases with increasing MO modulator thickness and appliedmagnetic field intensity for both materials based MO modulatodevices. As well as we have observed that YIG MO modulatohas presented higher modulation depth compared to LiNbO3MO modulator at the same operating conditions.- As shown in Fig. 8 has indicated that modulatotransmittance increases with increasing MO modulatothickness and applied magnetic field intensity for bothmaterials based MO modulator devices. We have indicatedthat YIG MO modulator has presented higher transmittance

than LiNbO3 MO modulator under the same considerations.- Figs. (9, 10) have demonstrated that SNR increases andBER decreases with increasing MO modulator thickness andapplied magnetic field intensity for both materials based MOmodulator devices. As well as we have observed that YIG MOmodulator has presented higher SNR and lower BERcompared to LiNbO3 MO modulator at the same operatingconditions.- As shown in Figs. (11, 12) have assured that modulatorinductance and resistance decrease with increasing MOmodulator length for both materials based MO modulatodevices. As well as we have observed that YIG MO modulatohas presented lower resistance and inductance compared toLiNbO3 MO modulator at the same operating conditions.


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5.CONCLUSIONSThe Faraday effect or Faraday rotation is a magneto-opticalphenomenon, or an interaction between light and a magneticfield. The rotation of the plane of polarization is proportional tothe intensity of the component of the magnetic field in thedirection of the beam of light. It is observed that the increasedapplied magnetic field intensity and MO thickness, resulting in

the increased angle of rotation, modulation depth,transmittance, signal to noise ratio, and the decreased bit errorrate for both materials based MO modulators under the sameconsiderations. It is theoretically found that YIG based MOmodulator has presented the highest angle of rotation,modulation depth, transmittance, and signal to noise ratio, andthe lowest bit error rate, inductance and resistance circuitvalues under the same operating conditions. Therefore thismade YIG based MO modulator is the best candidatesselected materials for wide bandwidth and high speedapplications in advanced optical communication systems.

REFERENCES[1] Abd El-Naser A. Mohammed, Ahmed Nabih Zaki Rashed

and Mohamoud M. A. Eid, Rapid Progress of A ThermaArrayed Waveguide Grating Module for DenseWavelength Division Multiplexing Applications, AdvancedScience Letters, Vol. 5, No. 1, pp. 56-63, Jan. 2012.

[2] S. E. Irvine and A. Y. Elezzabi, Modeling of High Speed

MO Beam Deflection, IEEE J. Quantum Electron., Vol38, No. 2, pp. 14281435, Oct. 2002.[3] D. Young and C. S. Tsai, GHz Bandwidth Magneto Optic

Interaction in Yttrium Iron Garnet Gadolinium GalliumGarnet Waveguide Using Magnetostatic Forward VolumeWaves, Appl. Phys. Lett., Vol. 53, No. 3, pp. 169616981988.

[4] Abd El-Naser A. Mohammed, Gaber E. S. M. El-Abyad, AbdEl-Fattah A. Saad, and Ahmed Nabih Zaki Rashed, HighTransmission Bit Rate of A thermal Arrayed WaveguideGrating (AWG) Module in Passive Optical Networks,IJCSIS International Journal of Computer Science andInformation Security, Vol. 1, No. 1, pp. 13-22, May 2009.


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[5] H. Dtsch, P. Hertel, B. Lhrmann, S. Sure, H. P. Winkler,and M. Ye, Applications of Magnetic Garnet Films inIntegrated Optics, IEEE Trans. Magn., Vol. 28, No. 3, pp.29792984, Sept. 1992.

[6] S. E. Irvine and A. Y. Elezzabi, A miniature BroadbandBismuth Substituted Yttrium Iron arnet Magneto OpticModulator, J. Phys. D, Vol. 36, No. 3, pp. 22182221,2003.

[7] A. Prabhakar and D. D. Stancil, Wideband OpticalModulation Via the Magneto Optic Interaction in Abismuth-Luetriu Iron Garnet Film, Appl. Phys. Lett., Vol.71, No. 2, pp. 151153, 1997.

[8] C. S. Tsai, Integrated Acousto Optic and Magneto OpticDevices for Optical Information Processing, Proc. IEEE,Vol. 84, No. 3, pp. 853869, June 1996.

[9] F. Zhou, H. Lu, Z. Cao, and Q. Shen, Electro OpticPolymer Light Modulator Based on Attenuated TotalReflection, Proc. SPIE, Vol. 49, No. 5, pp. 395398,2002.

[9] J. Bremer, V. Vaicikauskas, F. Hansteen, and O. Hundrei,Influence of Surface Plasmons on the Faraday Effect inBismuth Ssubstituted Yttrium Iron Garnet Films, J. Appl.

Phys., Vol. 89, No. 1, pp. 61776182, 2001.[10] Abd El-Naser A. Mohammed, Abd El-Fattah A. Saad, and

Ahmed Nabih Zaki Rashed, Matrices of the Thermal andSpectral Variations for the fabrication Materials Based

Arrayed Waveguide Grating Devices, InternationalJournal of Physical Sciences, Vol. 4, No. 4, pp. 205-211,April 2009.

[11] Abd El-Naser A. Mohammed, Mohamed A. metawee,Ahmed Nabih Zaki Rashed, and Amina E. M. El-NabawyUnguided Nonlinear Optical Laser Pulses Propagate inWaters With Soliton Transmission Technique,International Journal of Multidisciplinary Sciences andEngineering (IJMSE), Vol. 2, No. 1, pp. 1-10, March 2011.

[12] Abd El-Naser A. Mohammed, Ahmed Nabih Zaki Rashed,

and Mohammed S. F. Tabour TransmissionCharacteristics of Radio over Fiber (ROF) MillimeterWaveSystems in Local Area Optical Communication Networks,International Journal of Advanced Networks andApplications, Vol. 2, No. 6, pp. 876-886, May/June 2011.

[13] M. Caldwell and E. Yeatman, Surface Plasmon SpatialLight Modulators Based On Liquid Crystal, Appl. Opt., vol.31, pp. 38803891, 1992.

[14] Abd El-Naser A. Mohammed, Abd El-Fattah A. Saad, andAhmed Nabih Zaki Rashed, Estimated OptimizationParameters of Arrayed Waveguide Grating (AWG) for C-Band Applications, International Journal of PhysicalSciences, Vol. 4, No. 4, pp. 149-155, April 2009.

[15] Abd El-Naser A. Mohammed, Abd El-Fattah A. Saad, and

Ahmed Nabih Zaki Rashed, Thermal SensitivityCoefficients of the Fabrication Materials Based A thermalArrayed Waveguide Grating (AWG) in Wide Area DenseWavelength Division Multiplexing Optical Networks,International Journal of Engineering and Technology(IJET), Vol. 1, No. 2, pp. 131-139, June 2009.

[16] Ahmed Nabih Zaki Rashed, Ultra High Speed LiNbO3and Polymer Electrooptic Modulators in Lightwave Optical

Access Communication Networks, International Journalof Advanced Science and Technology, Vol. 35, pp. 41-60,Oct. 2011.

Author's Profile

Dr. Ahmed Nabih Zaki Rashed was born inMenouf city, Menoufia State, Egypt country in23 July, 1976. Received the B.Sc., M.Sc.and Ph.D. scientific degrees in theElectronics and Electrical CommunicationsEngineering Department from Faculty o

Electronic Engineering, Menoufia Universityin 1999, 2005, and 2010 respectively.

Currently, his job carrier is a scientific lecturer in Electronicsand Electrical Communications EngineeringDepartment,Faculty of Electronic Engineering, Menoufiauniversity, Menouf, postal Menouf city code: 32951, EGYPTHis scientific master science thesis has focused on polymerfibers in optical access communication systems. Moreover hisscientific Ph. D. thesis has focused on recent applications inlinear or nonlinear passive or active in optical networks. Hisinteresting research mainly focuses on transmission capacitya data rate product and long transmission distances opassive and active optical communication networks, wirelesscommunication, radio over fiber communication systems, and

optical network security and management. He has publishedmany high scientific research papers in high quality andtechnical international journals in the field of advancedcommunication systems, optoelectronic devices, and passiveoptical access communication networks. His areas of interestand experience in optical communication systems, advancedoptical communication networks, wireless optical accessnetworks, analog communication systems, optical filters andSensors, digital communication systems, optoelectronicsdevices, and advanced material science, networkmanagement systems, multimedia data base, networksecurity, encryption and optical access computing systems. Heis a reviewer member and also editorial board member in highquality scientific research international journals in the field of

Electronics, Electrical communication and advanced opticacommunication systems and networks. His personal electronicmail (E-mail:[email protected]).

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Wide Band Magneto Optical Modulators in Advanced High Speed Optical Communication Systems

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