CROSSTALK ANALYSIS OF A FBG-OC BASED OPTICAL ADD-DROP MULTIPLEXER FOR WDM CROSSCONNECTS SYSTEM

7/31/2019 CROSSTALK ANALYSIS OF A FBG-OC BASED OPTICAL ADD-DROP MULTIPLEXER FOR WDM CROSSCONNECTS SYSTEM

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International Journal of Advances in Engineering & Technology, July 2012.IJAET ISSN: 2231-1963

54 Vol. 4, Issue 1, pp. 54-67

C ROSSTALK ANALYSIS OF A FBG-OC BASED O PTICAL ADD -DROP M ULTIPLEXER FOR WDM C ROSSCONNECTS SYSTEM

Nahian Chowdhury 1, Shahid Jaman 2, Rubab Amin 3, Md. Sadman Sakib Chowdhury 4

1Lecturer, Department of EEE, A.D.U.S.T, Dhaka, Bangladesh1, 2, 4 Department of EEE, Ahsanullah University of Science and Technology, Dhaka, BD

3Department of EECS, North-South University, Dhaka, Bangladesh

A BSTRACT

Theoretical analysis and numerical simulation is carried out to evaluate the performance of an Optical Add-drop multiplexer (OADM) for Wavelength Division Multiplexing (WDM) transmission system in the presence of linear crosstalk due to Fiber Bragg Gratings (FBGs) and optical circulator (OC) which can be used in OpticalCrossconnects. We analyzed here the add drop multiplexing system for multiple wavelength channels, different condition of channel presence and channel separation. We simulate the crosstalk power, signal-to crosstalk ratio (SCR) and bit error rate (BER) of the system with different number of channels presence. Here wecompared crosstalk power and SCR for multiple wavelength channels like 4, 8, 16, 32 channels consideringdifferent channel separation and drop of channels from the system. It is found that the SCR increases with thechannel separation and SCR decreases with increase of the channel Bandwidth (B). BER increases with the

number of wavelength channels due to increased in amount of crosstalk.

K EYWORDS : BER, Crosstalk depends on channel presence, FBG, OADM, OC, SCR.

I. INTRODUCTION The Optical adddrop multiplexer (OADM) is a key component for wavelength-division multiplexing(WDM). An important technical issue for OADM design is the crosstalk, which can severely degradesystem performance. Many types of OADMs have been demonstrated based on different opticaldevices. These devices include arrayed-waveguide grating multiplexers, MachZehnderinterferometers with fiber Bragg gratings (FBGs), and optical circulators with FBGs. Among them,the structures that use fiber gratings combined with circulators are attractive because of their lowinsertion loss, low crosstalk, and temperature and polarization insensitivity [1].In this paper, we demonstrate and analysis the OADM structures that exhibit low crosstalk even withmultiple wavelengths. The OADM use a simple configuration of a 3 port Optical Circulator withFBGs, depending on the requirement of ADD or DROP channel. It can be used in Optical CrossConnects to design Broad Optical Networks. WDM has already been introduced in commercialsystems.Crosstalk analyses of OXCs presented so far are generally focused on conventional OXCs [2 - 4]. All-optical cross connects (OXC), however, have not yet been used for the routing of the signals BroadOptical Networks. Several OXC topologies have been presented in previous paper, but their use hasso far been limited to field trials, usually with a small number of inputoutput fiber and/or wavelengthchannels. The fact, that in practical systems many signals and wavelength channels could influenceeach other and cause significant crosstalk in the optical cross connects.

We have analyzed the basic principle and Bandwidth of FBG, general formula of system BER. Wehave evaluated the Crosstalk power, Signal to crosstalk ratio and the mathematical expression of BER


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of FBG-OC based WDM Crossconnects system with different number of channel presence, variablechannel separation and number of input channels up to presence the effects on desire signal. TheResults are discussed in the later section.

II. SYSTEM ANALYSIS 2.1 BASIC PRINCIPLE OF F IBER BRAGG G RATINGS FBGs today constitutes an extremely important wavelength-selective all-fiber guided wavecomponent for a myriad of applications such as filtering, wavelength multiplexing, demultiplexingand signal add/drop applications to combine or separate wavelength channels in DWDM opticalcommunication systems. FBGs can be used as a wavelength selective feedback mirror to lock thelasing wavelength of a laser diode [1, 5].

A Bragg grating is a periodic perturbation of the refractive index along the waveguide formed byexposure to an intense ultraviolet optical interference pattern. For example, in an optical fiber, theexposure induces a permanent refractive index change in the core of the fiber. This resulting variationof the effective refractive index of the guided mode along an optical fiber axis, z, can be

described by:

n = nz1+vcos2z+ Where n (z) is the dc index change spatially averaged over a grating period, v is the fringevisibility of the index change, is the nominal grating period, and 2 / describes grating chirp [6].

From the Couple mode theory, In Bragg gratings (also called reflection or short-period gratings)coupling occurs between modes travelling in opposite directions and so the mode travelling in theopposite direction should have a bounce angle, = . Since the mode propagation constant isgiven by:

2 n

Where, n_eff = n sin and =n ,+n , If the two modes are identical, the result is the well known equation for Bragg reflection:

= 2n Therefore, the peak of the Bragg reflection is:

= 1+nn Finally, the power reflection is [7]:

R =k sinh Lsinh L+coshL And transmission power:

T =sinh L+coshL At the phase matching wavelength, or the Bragg grating centre wavelength, there is no wave vectordetuning and equals zero, the expression for the reflectivity and transitivity become:

R = tanh Land T = for uniform gratings.The Bandwidth of an UFBG (Uniform FBG) is [7]:


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+ kL n L For strong gratings, >> , the bandwidth is independent of the length of the grating and isproportional to the ac coupling constant.

2.2 IMPLEMENTATION OF G AUSSIAN P ULSE O R SINC PULSE Data transmission form is one of the crucial factors of the optical communication systems. TheGaussian pulse form is considered as it more accurately models the data waveforms generated inpractical optical communications systems. The Gaussian Function is [8]:

G= 1 2exp 2

Here we used sinc pulse as data transmission, which is given by:

Where, f = sample frequency; T= 1/R R= Bit Rate of the sample. 2.2.1 Analysis of Optical Bandwidth

Figure 1: Optical Bandwidth and Channel Separation

=.,For, = 0.1nmChannel Spacing f = 12.5 GHz if = 1550nm

.

Let us assume that a signal s has a Gaussian probability distribution function with a mean value m.sothe probability density function is given by:

=1 2expsm2 Now, The BER equation can then be written as [8] :

=12 01 +10 Where, Probability p(1/0) is deciding 1 when 0 is transmitted and p(0/1) is deciding 0 when 1 istransmitted


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0 1 = 1 2 exp + 2

0 1 =12

+ 2

1 0 = 1 2 exp + 2

1 0 =12 Where erfc stands for the complementary error function, defined as :

=2 exp

So, the BER is given by:

=14 + 2 + + 2 The BER depends on the decision threshold I D. In practice, I D is optimized to minimize the BER. Theminimum occurs when I D is chosen such that:

+ 2 = + 2 + ln + = +

=+ + +

+

The BER with the optimum setting of the decision threshold is obtained by :

12 2 exp /2

2 Here = Crosstalk Photocurrent when bit 1 is transmitted, and = Crosstalk Photocurrentwhen bit 0 is transmitted.

III. NOISE C ALCULATION Now, Optical receivers convert incident optical power Pin into electric current through a photodiode.The relation [9] :

Where = Average current;

= Incident power;

= Responsivity of the photodetector (A/W)

The Responsivity R can be expressed in terms of a fundamental quantity , called the quantumefficiency and defined as :

1.24 3.1 SHOT NOISE Shot noise is a manifestation of the fact that an electric current consists of a stream of electrons thatare generated at random times. The total shot noise in receiver is given [9] by:


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= 2 +2 Where = Photocurrent and = Dark current; and

B = Effective noise bandwidth of the receiver.

The quantity is the root-mean-square (RMS) value of the noise current induced by shot noise.

3.2 C ROSSTALK NOISE Crosstalk noise is consists of an electric current due to interference channels. Crosstalk can be definedas [14, 16]:

= 2 +2 The quantity is the root-mean-square (RMS) value of the noise current induced by crosstalk power.

Where, = Crosstalk Photocurrent when bit 1 is transmitted, and = Crosstalk Photocurrentwhen bit 0 is transmitted.

3.3 T HERMAL NOISE

Total Thermal noise is given by [10, 16]:

=4 Where = Load Resistance;

T = Absolute temperature and

k= Boltzmann constant,

And B = Bandwidth =

IV. AT R ECEIVER E ND

Figure 2: Receiver Design4.1 SIGNAL T O NOISE R ATIO The Signal to Noise Ratio is [10,11]:

= = + + = + +

=2 +2 +4 +

Where Ip=Photocurrent and Id=Dark current of the detector.

4.2 C ROSSTALK NOISE POWER

Where = Crosstalk noise power, can be defined as:


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This Crosstalk power is only forHere B = Channel Bandwidth an

=Reflectivity of =4.3 SIGNAL T O C ROSSTALKNow the Signal Power is given b

Where = Bragg Wavelength Now the Signal to Crosstalk rati

SCRB=Now by putting, = . , wh

B RV. R ESULTS AND DISThe theoretical analysis are preoptical WDM system based oninterference channels and Systeof channel separation and Band

Figure 3: Normalize Reflectivit

vances in Engineering & Technology, July

Vol. 4

= 2 channel, if there is 2 interference channel

d

ATIO (SCR) y:

= =

is given by:

= = =+ +

10 log R++ere = 1and =

12erfc12 2 ++USSION

sented in previous sections, following the perfoFiber Bragg gratings are evaluated with effecs SCR and BER of given number of wavelengtidth are shown.

y of uniform for Bragg wavelength 1550nm with vari

2012.ISSN: 2231-1963

Issue 1, pp. 54-67

5 exist [14,16].

rmance results of anof crosstalk due to

hs with several value

tion in Bandwidth.


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Figure 3 shows the Normalize reflectivity power as a function of wavelength with different number of Bandwidth (B). Here Bandwidth B=0.2nm=2*Rb, where Rb=Bit Rate of the sample.

Figure 4: Normalize Transitivity of uniform Bragg for 1550nm Bragg wavelength

Figure 4 shows the Transmitivity of uniform grating for 1550nm Bragg wavelength with differentBandwidth (B).

5.1 C ROSSTALK P OWER , SCR AND BER To observe crosstalk power (Pc) ,Signal to Crosstalk Ratio (SCR) and the bit error rate (BER)performance of WDM system using FBG-OC based Dmux, we stimulated previous equation. Toevaluate BER, the following system parameters are chosen here:

= 300 , = 1.38 10, = 100,

number of channelsN= 32, bit rate= 12.5 / , Channel specing D= 25 64 Channel Ban wi th= 25 The Ratio == 1 to 1.5 5.1.1 C ASE 1:

5 Channel WDM system With 1st And 5th Channel is OFF:

Figure 5: 5 channel WDM system considering 1st and 5th channel is off (Worst Case)

OFF OFF


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Here Figure 5 shows a 5 channel WDM system. The 3rd channel is interferes with 4 interferencechannels at Bandwidth 4*Rb. Here we consider 1st and 5th channel is off.

We consider worst case with the mid-channel (3rd) as the desired signal channel & others areinterference channels. After filtering the desired channel, it is obvious that there will be some portionof interference channel, which interfere in getting the actual signal. This interference produces

crosstalk

(a) (b)

Figure 6: Crosstalk (a) and SCR (b) vs m=Dch/Bch with 5 channel WDM system considering 1st and 5thchannel is off (Worst Case).

Plots of Crosstalk versus Normalized channel separation are plotted in figure 6 (a). Here crosstalk of 2interference channels enter within the signal. In this case Crosstalk Power increases with increase invalue of Bandwidth (B). It is observed that more Crosstalk is added with increase of Bandwidth (B)and Crosstalk power decreases with increase in Normalize channel separation, m= Dch/Bch). Whileseparation of channel increasing less crosstalk enters to the signal comparing previous position.Plots of SCR versus Normalized channel separation are plotted with different value of Bandwidth infigure 6 (b). Here crosstalk of 2 interference channels enter within the signal. In this case, SCRdecreases with increase in value of Bandwidth (B). Because it is observed that more Crosstalk isadded with increase of Bandwidth (B) and Crosstalk power decrease with increase of Normalizechannel separation, = / . Again, SCR increases with the channel separation increases.Because while separation of channel increasing less crosstalk enters to the signal comparing previousposition.

TABLE 1: Evaluation of Crosstalk for case 1 TABLE 2: Evaluation of SCR for Case 1

Bandwidth (B) Channel spacing (Dch) Crosstalk

2*Rb2.5*Rb3*Rb

Dch(min) = Bch = 25 GHz6.22e+0086.57e+0087.49e+008

2*Rb2.5*Rb3*Rb

Dch(max) = 25

GHz+64*df

0.80e+0080.84e+0081.82e+008

5.1.2 C ASE 2:

5 Channel WDM System with 4th Channel is OFF:

Bandwidth (B) Channel spacing (Dch) SCR

2 * Rb2.5 * Rb3 * Rb

Dch(min) = Bch = 25 GHz28.93 dB28.40 dB27.11 dB

2* Rb2.5* Rb3* Rb

Dch(max) = 25 GHz+64*df 49.33 dB48.98 dB41.25 dB


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Figure 7: 5 channel WDM system considering 4th channel is off

Figure 7 shows a 5 channel WDM system. The 3rd channel is interferes with 4 interference channelsat Bandwidth 4*Rb. Here we Consider 4th channel is off.

(a) (b)

Figure 8: Crosstalk (a) and SCR (b) vs m=Dch/Bch with 5 channel WDM system considering 4th channel isoff.

Plots of Crosstalk versus Normalized channel separation are plotted considering 4th channel is off infigure 8 (a). Here crosstalk of 3 interference channels enter within the signal. In this case, Crosstalk Power increases with increase in value of Bandwidth (B).In figure 8 (b) considering 4th channel is off, here crosstalk of 3 interference channels enter within thesignal. In this case SCR decreases with increase in value of Bandwidth (B) Again, SCR increases withthe channel separation increases. Because of disappear of 4th channel less crosstalk power is enterwithin the mid channel as 3rd channel

TABLE 3: Crosstalk Evaluation for Case 2Bandwidth (B) Channel spacing (Dch) Crosstalk

2*Rb2.5*Rb3*Rb

Dch(min)=Bch=25 GHz3.27e+0083.43e+0084.01e+008

2*Rb2.5*Rb3*Rb

Dch(max)=25GHz+64*df

0.42e+0080.45e+0080.98e+008

OFF


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TABLE 4: Evaluation of Signal to Crosstalk Ratio for Case 2Bandwidth (B) Channel spacing (Dch) SCR

2*Rb2.5*Rb3*Rb

Dch(min)=Bch=25 GHz35.36 dB34.90 dB33.34 dB

2*Rb2.5*Rb3*Rb

Dch(max) = 25 GHz+64*df 55.79 dB55.03 dB47.42 dB

5.2 C ROSSTALK VS. m W ITH DIFFERENT C HANNEL BANDWIDTH (B)Figure 9 (a) and Figure 9 (b) are evaluating the Crosstalk Power against Normalized ChannelSeparation m=(Dch/Bch) for the mid-channel at the worst case scenario with different ChannelBandwidth B=2Rb to 4Rb for 5 & 9 Channel WDM System having 4 & 8 interference channelrespectively.

(a) (b)

Figure 9: Crosstalk Power vs Ratio m with different Channel Bandwidth (BW) for 4 interference channels (a)and 8 interference channels (b).

Plots of Crosstalk versus Normalized channel separation are plotted with different channel Bandwidth(B) for 5 channels WDM system in figure 11.For 9 channel WDM system, the crosstalk power decreases with the channel separation increases.Because while separation of channel increasing less crosstalk enters to the signal comparing previousposition. Nevertheless, the value of crosstalk power is higher for 9 channel WDM system than 5Channel WDM System.

5.2.1 D ISCUSSION

We observed in the case of 4 & 8 Interference channels that more Crosstalk occurs in 8 interferencechannel rather than 4 interference channels with same Bandwidth (B) and same Normalized ChannelSeparation m. However, with 16 interference channels, crosstalk does not change so much and with32 interference channels, considerations are negligible.


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5.3 SCR V S. m W ITH DIFFERENT C HANNEL BANDWIDTH (B)

(a) (b)Figure 10: Signal-to-Crosstalk Ratio (SCR) vs. Normalized Channel separation m with different Channel

Bandwidth (B) with 4 interference channels (a) and 8 interference channels (b).

5.3.1 D ISCUSSION

We observed in the case of 4 & 8 Interference channels that SCR is lower in 8 interference channelrather than 4 interference channels with same Bandwidth (B) and same Normalized channelseparation m. with 16 interference channels, SCR does not change so much and with 32 interferencechannels, considerations are negligible.

5.4 SCR V S m W ITH DIFFERENT VALUE O F BIT R ATE (R B) A T BER

Figure 11: Signal-to-Crosstalk-ratio (SCR) vs. Normalized Channel Separation m at BER 10 of a WDMsystem FBG based DMUX with different value of Bit Rate Rb. where m=Dch/Bch.

The Plots of Signal-to-Crosstalk-ratio (SCR) vs. Normalized Channel Separation m at BER 10 -12 areshown in figure 11 with different value of Bit Rate (Rb).

In this figure, Bit rate is varied from 15Gbps to 30 Gbps.

It is noticed that with increase in Bit Rate (Rb), there is increase in SCR with respect to different

values of m=Dch/Bch.


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5.5 BER VS. SCR W ITH D IFFERENT BANDWIDTH (B)

Figure 12: Bit-error-rate (BER) vs. Signal-to-Crosstalk-ratio (SCR) at the receiver end of a WDM system FBGbased DMUX with different number of m. where m=Dch/Bch.

Fig 12 shows the BER against Signal to crosstalk ratio (SCR) for the channel positioned 3rd with thedifferent value of the Bandwidth (B) with 4 number of interference channels. In this configuration,BER increases with increase in Bandwidth (B) and BER decreases with SCR. It is observed that lessBER found with more SCR for 5 wavelength channels.

5.6 BER V S. SCR W ITH DIFFERENT VALUE O F m

Here Figure 13 shows the BER against Signal to crosstalk ratio (SCR) for the channel positioned 3rdwith the different value of the Ratio (m) of Channel spacing (Dch) and Channel Bandwidth (Bch)with 4 number of interference channels

Figure 13: Bit-error-rate (BER) vs. Signal-to-Crosstalk-ratio (SCR) at the receiver end of a WDM system FBGbased DMUX with different number of m. where m=Dch/Bch.

In this configuration, BER increases with the Ratio m increases and SCR increases. It is observed thatmore BER found with more SCR for 4 interference channels.

VI. C ONCLUSION

Crosstalk and the BER performance of FBG-OC based WDM system are evaluated and differentfactors that are affected the magnitude of crosstalk and BER in the OADM system also analyzed. We


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International Journal of AdIJAET

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found in analysis that BER is inproblem of such kind of OADBandwidth (B) of the channel inchannels. Here we have given soFurther works can be carriedOptical Pre-Amplifier and Amlimitations in the WDM system.

ACKNOWLEDGEMENTS The authors would like to thank

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AUTHORS

Nahian Chowdhury received hisfrom Ahsanullah University of ScieHe is currently working as a LectTechnology, Bangladesh. He hasfields of interest include Opticalnetworks, Optoelectronic and Photo

vances in Engineering & Technology, July

Vol. 4

reased with the number of wavelength channelsis that Crosstalk and BER are also increase

creases. However, BER is not affected with morme of our outcome results from all analysis.ut with amplifier-induced crosstalk in a WDlifier, there should have some ASE noise and

Prof. Dr. Satya Prasad Majumder, BUET for sup

ragg Gratings (BT Laboratories, Martlesham Heath I

mder, Bit error rate and crosstalk performance in optnal of Optical Networking, Vol. 6, No. 3, March 200rthier, Roel Baets, Crosstalk Analysis Of Multiwawave Technology, Vol. 17, No. 8, August 1999.

a SATO, Optical Switching Devices Using Nonlineon Wavelength Integration and Manipulation, IPA

r Optic Communication Systems, Third Edition (Jo

ld Meltz, Fiber Bragg Grating Technology Fundanology, Vol. 15, No. 8, August 1997.shi and Srinivas Talabattula, Analytical Method toInstrument, J. Instrum. Soc. India 37(4) 297-308.Communications (McGraw-Hill, 1991).ber Communication (Prentice-Hall, 1985).. Nolasco Pinto, T. Almeida, Performance DegradatiNetworks Using Optical Add Drop Multiplexers B, Vol.3, No.2, Setembro 2000.and Wanyi Gu, Coherent And Incoherent Cross

wave Technology, Vol. 17, No. 5, May 1999.al Enabling Technologies for WDM systems, N

on of Fiber Bragg Grating sensors, Institute of Photo07745 Jena, Germany.mad Rezaul Karim, Crosstalk Modeling and AnalysConnects for WDM Networks, IEEE 978-1-4244-45

. Frigo, Mark D. Feuer, A Taxonomical consideratioetwork Communications, 3:4,327-333, 2001;20

n the Netherlands.e performance of optical cross connect based on fibnal Journal of Computer Science & Information Te

umar N. Sivarajan, Optical Networks (MorganN 1-55860-655-6)

achelors Degree in Electrical and Electronic Enginnce and Technology (AUST), Dhaka, Bangladesh inrer of EEE in Atish Dipankar University of Scienc

International Journal paper based on GSM network fiber communication, Digital communication, O

nics.

2012.ISSN: 2231-1963

Issue 1, pp. 54-67

increases. The mainsignificantly as thethan 16 wavelength

network. With anIntraband crosstalk

rvising us.

swich, UK; Academic

ical cross connect with.elength Optical Cross

ar Fiber-Optic GratingP Books 2 (2005) pp.

n Wiley & Sons, Inc.

entals and Overview,

stimate the Bandwidth

n Due To Crosstalk Inased On Fiber Bragg

alk In WDM Optical

kia Research Center,

nic Technology -IPHT

is of FBG OC-Based7-9, 2009.

n of Optical Add/Drop1 Kluwer Academic

er bragg grating underhnology (IJCSIT) Vol

Kaufmann Publishers,

ering2011.e and. Hisptical


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Shahid Jaman received his Bachelors Degree in Electrical and Electronic Engineering fromAhsanullah University of Science and Technology, Dhaka, Bangladesh in 2011. He is currentlyworking as a Maintenance engineer in Samah Razor Blade Ind. Ltd. He has one internationalJournal. His fields of interest include optical communication, Digital communication and VLSIdesign.

Rubab Amin received BSc degree with the distinction Summa Cum Laude in Electronics &Telecommunications Engineering from the department of Electrical Engineering & ComputerScience of North South University, Dhaka, Bangladesh in 2011.

Md. Sadman Sakib Chowdhury received his Bachelor of Science in Electrical & ElectronicEngineering from Ahsanullah University of Science & Technology in 2011.He is currentlyworking in Biotech Services. His area of choice for further study includes Optical

Communication and Bio-photonics.

CROSSTALK ANALYSIS OF A FBG-OC BASED OPTICAL ADD-DROP MULTIPLEXER FOR WDM CROSSCONNECTS SYSTEM

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Transcript of CROSSTALK ANALYSIS OF A FBG-OC BASED OPTICAL ADD-DROP MULTIPLEXER FOR WDM CROSSCONNECTS SYSTEM