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diff --git a/3638/CH12/EX12.1/Ex12_1.sce b/3638/CH12/EX12.1/Ex12_1.sce
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+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 12.1
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given
+lambda=0.8e-6;//wavelength of light in m
+n=3.5;//refractive index of Si
+e=1.6e-19;//electronic charge in C
+h=6.626e-34;//Planck's constant in SI Units
+c=3e8;//speed of electrons in m/s
+alpha=1e5;//average loss coefficient per unit length of resonator in m^(-1)
+w=20e-6;//width of depletion layer in m
+R=((n-1)/(n+1))^2;//Reflection coefficient of uncoated Si
+mprintf("\n R=%.2f",R);
+//Assuming all e-h pairs contribute to photo current i.e. zeta=1
+eta=(1-R)*(1-exp(-alpha*w));//Corresponding quantum efficiency
+mprintf("\n eta=%.1f",eta);
+v=c/lambda;//frequency corresponding to given wavelength in Hz
+rho=eta*e/(h*v);//corresponding responsivity in A/W
+mprintf("\n rho=%.2f A/W",rho);//The answers vary due to round off error
diff --git a/3638/CH12/EX12.2/Ex12_2.jpg b/3638/CH12/EX12.2/Ex12_2.jpg
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diff --git a/3638/CH12/EX12.2/Ex12_2.sce b/3638/CH12/EX12.2/Ex12_2.sce
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+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 12.2
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given 
+rho=0.5;//responsitivity of Si PIN detector in A/W
+Vb=20;//reverse bias voltage across the detector in V
+//Case (i):
+Rl=100;//load resistor in ohms
+Pmax=Vb/(rho*Rl);//maximum value of optical power P falling on the photodetector in W
+mprintf("\n For Rl=100 Ohm:");
+mprintf("\n Pmax=%.1f mW",Pmax/1e-3)//Division by 10^(-3) to convert into mW
+mprintf("\n Vr/P = %.1f mV/mW",rho*Rl);//Bias voltage per unit power in mV/mW
+//Case (ii):
+Rl=10e3;//load resistor in ohms
+Pmax=Vb/(rho*Rl);//maximum value of optical power P falling on the photodetector in W
+mprintf("\n For Rl=10 kOhm:");
+mprintf("\n Pmax=%.1f mW",Pmax/1e-3)//Division by 10^(-3) to convert into mW
+//Bias voltage per unit power in V/mW :
+mprintf("\n Vr/P = %.1f V/mW",rho*Rl/1e3);//Division by 10^3 to convert into V/mW
diff --git a/3638/CH12/EX12.3/Ex12_3.jpg b/3638/CH12/EX12.3/Ex12_3.jpg
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diff --git a/3638/CH12/EX12.3/Ex12_3.sce b/3638/CH12/EX12.3/Ex12_3.sce
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+//Introduction to Fiber Optics by A. Ghatak and K. Thyagarajan, Cambridge, New Delhi, 1999
+//Example 12.3
+//OS=Windows XP sp3
+//Scilab version 5.5.2
+clc;
+clear;
+//given 
+epsilon=10.5e-13;//permittivity of Si in F/cm
+d=500e-4;//diameter of Si detector in cm
+w=20e-4;//width of depletion layer in cm
+A=%pi*((d/2)^2);//Area of detector in cm^2
+Cd=epsilon*A/d;//Junction capacitance in F
+mprintf("\n The junction capacitance Cd=%f pF",Cd/1e-12);//division by 10^(-12) to convert into pF 
+//The answer provided in the textbook is wrong