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+
+//OptoElectronics and Fibre Optics Communication, by C.K Sarkar and B.C Sarkar
+//Example 8.3
+//OS=Windows 10
+////Scilab version Scilab 6.0.0-beta-2(64 bit)
+clc;
+clear;
+
+//given
+Cd=6e-12;//capacitance in farad
+Id=0;//dark current in photodiode
+B=40e6;//bandwidth in Hz
+I=2e-7;//photo current before gain in Ampere
+T=300;//temperature in kelvin
+Fn=1;
+KB=1.38*1e-23//boltzman constant in SI units
+e=1.6*10^-19//charge of an electron in columb
+//case 1:
+u=2*3.14*Cd*B;
+RL=1/u;//load resistance in ohms
+mprintf("\n Load resistance is=%.2f ohms",RL);
+
+//case 2:
+i2sh=2*(e)*B*I;// shot noise in A^2
+v=4*(KB)*T*B;
+i2th=v/RL;//thermal noise in A^2
+//if i2>i1 then
+S=I^2;
+N=i2th;
+z=S/N;
+mprintf("\n Signal to noise ratio is=%.2f",z);
+//when M=Mopt and x=0.3
+x=0.3;//lies between 0.3 to 0.5 for silicon and 0.7 to 1 for Ge
+a=4*(KB)*T;
+b=(e)*x*RL*I;
+M1=a/b;
+Mopt=M1^(1/2.3)
+S1=[(Mopt)*I]^2;//signal strength in W
+N1=[2*(e)*B*I*((Mopt)^2.3)]+[(4*(KB)*T*B)/(RL)];//noise power in W
+SbyN=S1/N1;//signal to noise ratio
+mprintf("\n Signal to noise ratio is=%.2f",SbyN);
+//the answer in book is wrong