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diff --git a/3638/CH21/EX21.1/Ex21_1.jpg b/3638/CH21/EX21.1/Ex21_1.jpg
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diff --git a/3638/CH21/EX21.1/Ex21_1.sce b/3638/CH21/EX21.1/Ex21_1.sce
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+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.1
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+nf=1.51;//refractive index of film
+ns=1.50;//refractive index of substrate
+nc=1.0;//refractive index of cover
+d=4e-6;//thickness of film in m
+lambda0=0.6e-6;//Wavelength in m
+ne1=1.50862;//Corresponding effective refractive index for core
+ne2=1.5046;//Corresponding effective refractive index for cladding
+k0=2*(%pi)/lambda0;//free space wave number in rad/m
+//Let A be the period of perturbation in m
+
+A=lambda0/(ne1-ne2);
+mprintf("\n A= %.1f um",A/1e-6);//Division by 10^(-6) to convert into um
+
+d1=d+1/(k0*sqrt(ne1^2-ns^2))+1/(k0*sqrt(ne1^2-nc^2));//Effective waveguide thickness for mode 1 in m
+mprintf("\n d1= %.3f um",d1/1e-6);//Division by 10^(-6) to convert into um
+d2=d+1/(k0*sqrt(ne2^2-ns^2))+1/(k0*sqrt(ne2^2-nc^2));//Effective waveguide thickness for mode 2 in m
+mprintf("\n d2= %.3f um",d2/1e-6);//Division by 10^(-6) to convert into um
+//Assuming h=0.01um in expression for k, we get:
+k=%pi/lambda0*0.01e-6*sqrt(((nf^2-ne1^2)*(nf^2-nc^2))/d1*d2*ne1*ne2);//Coupling coefficient in m^-1
+mprintf("\n k=%.3f cm^(-1)",k*1e2);//Multiplying by 10^2 to convert into cm^(-1)
+//The answers vary due to round off error
+L=%pi/(2*k);//Length for complete power transfer in m
+mprintf("\n L=%.2f cm",L/1e2);//Division by 10^2 to convert into cm
+//The answers vary due to round off error
diff --git a/3638/CH21/EX21.2/Ex21_2.jpg b/3638/CH21/EX21.2/Ex21_2.jpg
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index 000000000..9f5edd149
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+++ b/3638/CH21/EX21.2/Ex21_2.jpg
diff --git a/3638/CH21/EX21.2/Ex21_2.sce b/3638/CH21/EX21.2/Ex21_2.sce
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index 000000000..2539437db
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+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.2
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+nf=1.51;//refractive index of film
+ns=1.50;//refractive index of substrate
+nc=1.0;//refractive index of cover
+d=4e-6;//thickness of film in m
+lambda0=0.6e-6;//Wavelength in m
+ne1=1.50862;//Corresponding effective refractive index for core
+ne2=1.5046;//Corresponding effective refractive index for cladding
+//Let A be the period of perturbation in m
+
+
+//Case (i):
+A=100e-6;
+K=2*%pi/A;
+k=0.598e2;//coupling coefficient in m^-1 (from previous example)
+T=2*%pi/lambda0*(ne1-ne2)-K;//Phase mismatch in m^-1
+y=sqrt(k^2+(T/2)^2);//Resultant of k and T in m^-1
+
+mprintf("\n For A=100 um:");
+P2max=(k/y)^2;//Maximum power that gets transferred between the modes
+mprintf("\n P2max= %.1e",P2max);
+L=%pi/(2*y);//Distance for maximum power transfer in m
+mprintf("\n L=%.1f um\n",L/1e-6);//Division by 10^(-6) to convert into um
+//The answers vary due to round off error
+
+
+//Case (ii):
+A=148e-6;
+K=2*%pi/A;
+k=0.598e2;//coupling coefficient in m^-1 (from previous example)
+T=2*%pi/lambda0*(ne1-ne2)-K;//Phase mismatch in m^-1
+y=sqrt(k^2+(T/2)^2);//Resultant of k and T in m^-1
+
+mprintf("\n For A=148 um:");
+P2max=(k/y)^2;//Maximum power that gets transferred between the modes
+mprintf("\n P2max= %.1e",P2max);
+L=%pi/(2*y);//Distance for maximum power transfer in m
+mprintf("\n L=%.1f mm",L/1e-3);//Division by 10^(-6) to convert into mm
+
diff --git a/3638/CH21/EX21.3/Ex21_3.jpg b/3638/CH21/EX21.3/Ex21_3.jpg
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index 000000000..cd5d9dd30
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diff --git a/3638/CH21/EX21.3/Ex21_3.sce b/3638/CH21/EX21.3/Ex21_3.sce
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index 000000000..5482ad427
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+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.3
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+lambdac=0.6e-6;//Wavelength in m
+//Let A be perturbation of length in m
+A=149.3e-6;
+L=2.63e-2;//Length of the periodic waveguide in m
+
+DeltaLambda=0.8*A*lambdac/L;//Bandwidth of the wavelength filter in m
+mprintf("\n DeltaLambda= %.1f nm",DeltaLambda/1e-9);//Division by 10^(-9) to convert into nm
diff --git a/3638/CH21/EX21.4/Ex21_4.jpg b/3638/CH21/EX21.4/Ex21_4.jpg
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diff --git a/3638/CH21/EX21.4/Ex21_4.sce b/3638/CH21/EX21.4/Ex21_4.sce
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index 000000000..eb99462b7
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@@ -0,0 +1,12 @@
+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.4
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+va=5.96e3;//Velocity of the acoustic wave
+Lb=2e-3;//Beat length in m
+
+f=va/Lb;//Acoustic frequency in Hz for Theta=0 degrees
+mprintf("\n f=%.2f MHz",f/1e6);//Division by 10^6 to convert into MHz
diff --git a/3638/CH21/EX21.5/Ex21_5.jpg b/3638/CH21/EX21.5/Ex21_5.jpg
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index 000000000..3c25a140c
--- /dev/null
+++ b/3638/CH21/EX21.5/Ex21_5.jpg
diff --git a/3638/CH21/EX21.5/Ex21_5.sce b/3638/CH21/EX21.5/Ex21_5.sce
new file mode 100644
index 000000000..ba0104265
--- /dev/null
+++ b/3638/CH21/EX21.5/Ex21_5.sce
@@ -0,0 +1,14 @@
+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.5
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+va=5.96e3;//Velocity of the acoustic wave
+Lb=1.7e-3;//Beat length in m
+Theta=13.5;//Angle between acoustic wave and the light waves
+
+f=va/(Lb*sind(Theta));//Acoustic frequency in Hz
+mprintf("\n f=%.2f MHz",f/1e6);//Division by 10^6 to convert into MHz
+//The answers vary due to round off error
diff --git a/3638/CH21/EX21.6/Ex21_6.jpg b/3638/CH21/EX21.6/Ex21_6.jpg
new file mode 100644
index 000000000..2dd98f612
--- /dev/null
+++ b/3638/CH21/EX21.6/Ex21_6.jpg
diff --git a/3638/CH21/EX21.6/Ex21_6.sce b/3638/CH21/EX21.6/Ex21_6.sce
new file mode 100644
index 000000000..c307626a9
--- /dev/null
+++ b/3638/CH21/EX21.6/Ex21_6.sce
@@ -0,0 +1,24 @@
+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.6
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+nf=1.51;//refractive index of film
+ns=1.50;//refractive index of substrate
+nc=1.0;//refractive index of cover
+d=4e-6;//thickness of film in m
+lambda0=0.6e-6;//Wavelength in m
+ne1=1.50862;//Corresponding effective refractive index for core
+ne2=1.5046;//Corresponding effective refractive index for cladding
+//Let A be the perturbation of length in m
+A=6e-6;
+
+//Rearranging the terms of the equation 'ne1-lambda0/A=ns*cos(Thetas0)', we get:
+Thetas0=acosd((ne1-lambda0/A)/ns);
+mprintf("\n Thetas0 = %.1f degrees",Thetas0);
+
+//Rearranging the terms of the equation 'ne2-lambda0/A=ns*cos(Thetas1)', we get:
+Thetas1=acosd((ne2-lambda0/A)/ns);
+mprintf("\n Thetas1 = %.1f degrees",Thetas1);
diff --git a/3638/CH21/EX21.7/Ex21_7.jpg b/3638/CH21/EX21.7/Ex21_7.jpg
new file mode 100644
index 000000000..1359f7cb9
--- /dev/null
+++ b/3638/CH21/EX21.7/Ex21_7.jpg
diff --git a/3638/CH21/EX21.7/Ex21_7.sce b/3638/CH21/EX21.7/Ex21_7.sce
new file mode 100644
index 000000000..11306e0c5
--- /dev/null
+++ b/3638/CH21/EX21.7/Ex21_7.sce
@@ -0,0 +1,24 @@
+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.7
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+nf=1.51;//refractive index of film
+ns=1.50;//refractive index of substrate
+nc=1.0;//refractive index of cover
+d=4e-6;//thickness of film in m
+lambda0=0.6e-6;//Wavelength in m
+ne1=1.50862;//Corresponding effective refractive index for core
+ne2=1.5046;//Corresponding effective refractive index for cladding
+//Let A be the perturbation of length in m
+A=0.2e-6;
+
+//Rearranging the terms of the equation 'ne1-lambda0/A=ns*cos(Thetas0)', we get:
+Thetas0=acosd((ne1-lambda0/A)/ns);
+mprintf("\n Thetas0 = %.1f degrees",Thetas0);
+
+//Rearranging the terms of the equation 'ne2-lambda0/A=ns*cos(Thetas1)', we get:
+Thetas1=acosd((ne2-lambda0/A)/ns);
+mprintf("\n Thetas1 = %.1f degrees",Thetas1);
diff --git a/3638/CH21/EX21.8/Ex21_8.jpg b/3638/CH21/EX21.8/Ex21_8.jpg
new file mode 100644
index 000000000..6ff3e8a65
--- /dev/null
+++ b/3638/CH21/EX21.8/Ex21_8.jpg
diff --git a/3638/CH21/EX21.8/Ex21_8.sce b/3638/CH21/EX21.8/Ex21_8.sce
new file mode 100644
index 000000000..2ee948662
--- /dev/null
+++ b/3638/CH21/EX21.8/Ex21_8.sce
@@ -0,0 +1,26 @@
+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.8
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+//Since the peak reflectivity of fiber is 0.98,
+R=0.98;//Reflection coefficient of fiber
+L=1e-3;//Length of interaction in m
+lambda0=1092e-9;//Central wavelength in m
+neff=1.46;//Corresponding value of effective index in LP01 mode
+
+//Now, (tanh(k*L))^2=R
+//Rearranging terms, we get:
+k=atanh(sqrt(R))/L;//Corresponding coupling coefficient in m^(-1)
+mprintf("\n k=%.3f mm^(-1)",k/1e3);//Dividing by 10^3 to convert into mm^(-1)
+//The answers vary due to round off error
+
+//Let A be the perturbation of length in m
+A=lambda0/(2*neff);
+mprintf("\n A=%.2f um",A/1e-6);//Division by 10^(-6) to convert into um
+
+DeltaLambda=lambda0*A/L;//Corresponding bandwidth in m
+mprintf("\n DeltaLambda=%.2f nm",DeltaLambda/1e-9);//Division by 10^(-9) to convert into nm
+//The answers vary due to round off error
diff --git a/3638/CH21/EX21.9/Ex21_9.jpg b/3638/CH21/EX21.9/Ex21_9.jpg
new file mode 100644
index 000000000..8b8e05dfd
--- /dev/null
+++ b/3638/CH21/EX21.9/Ex21_9.jpg
diff --git a/3638/CH21/EX21.9/Ex21_9.sce b/3638/CH21/EX21.9/Ex21_9.sce
new file mode 100644
index 000000000..b4ffd2f6e
--- /dev/null
+++ b/3638/CH21/EX21.9/Ex21_9.sce
@@ -0,0 +1,26 @@
+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 21.9
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+//Since the peak reflectivity of fiber is 0.85,
+R=0.85;//Reflection coefficient of fiber
+L=1e-2;//Length of interaction in m
+lambda0=1.55e-6;//Central wavelength in m
+neff=1.46;//Corresponding value of effective index in LP01 mode
+
+//Now, (tanh(k*L))^2=R
+//Rearranging terms, we get:
+k=atanh(sqrt(R))/L;//Corresponding coupling coefficient in m^(-1)
+mprintf("\n k=%.3f m^(-1)",k);//The answer provided in the textbook is wrong
+
+//Let A be the perturbation of length in m
+A=lambda0/(2*neff);
+mprintf("\n A=%.2f nm",A/1e-9);//Division by 10^(-9) to convert into nm
+//The answers vary due to round off error
+
+DeltaLambda=lambda0^2/(%pi*neff*L)*sqrt((k*L)^2+(%pi)^2);//Corresponding bandwidth in m
+mprintf("\n DeltaLambda=%.2f nm",DeltaLambda/1e-9);//Division by 10^(-9) to convert into nm
+//The answer provided in the textbook is wrong