Added(A)/Deleted(D) following books

 A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap10.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap2.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap3.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap4.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap5.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap6.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap7.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap8.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/chap9.ipynb
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/screenshots/Sc1.png
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/screenshots/sc2.png
A  Optical_Fiber_Communication_System_by_Dr._M.K._Raina/screenshots/sc3.png

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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Ch-8 : Optical Sources"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.1 Pg: 335"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The total carrier recombination lifetime =24 ns\n",
+      "\n",
+      " The internal power =30.66 mW\n",
+      "\n",
+      " the answer is wrong in textbook\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi\n",
+    "from __future__ import division\n",
+    "tr=40## rediative life time in ns\n",
+    "tnr=60## nonrediative life time in ns\n",
+    "i=35*10**-3## drive current in amp\n",
+    "y=0.85*10**-6## wavelength in m\n",
+    "h=6.626*10**-34## plank constant\n",
+    "c=3*10**8## the speed of light in m/s\n",
+    "e=1.602*10**-19## charge\n",
+    "t=tr*tnr/(tr+tnr)## total carrier recombination lifetime ns\n",
+    "ni=t/tr## internal quantam efficiency\n",
+    "pi=(ni*h*c*i)/(e*y)## internal power in watt\n",
+    "p_int=pi*10**3## internal power in mW\n",
+    "print \"The total carrier recombination lifetime =%d ns\"%( t)#\n",
+    "print \"\\n The internal power =%0.2f mW\"%( p_int)#\n",
+    "print \"\\n the answer is wrong in textbook\""
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.2 Pg: 335"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The total carrier recombination lifetime =18.75 ns\n",
+      "\n",
+      " The peak emission wavelength =1.09 um\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi\n",
+    "from __future__ import division\n",
+    "tr=30## rediative life time in ns\n",
+    "tnr=50## nonrediative life time in ns\n",
+    "i=40*10**-3## drive current in amp\n",
+    "pi=28.4*10**-3## internal power in watt\n",
+    "h=6.626*10**-34## plank constant\n",
+    "c=3*10**8## the speed of light in m/s\n",
+    "e=1.602*10**-19## charge\n",
+    "t=tr*tnr/(tr+tnr)## total carrier recombination lifetime ns\n",
+    "ni=t/tr## internal quantam efficiency\n",
+    "y=(ni*h*c*i)/(e*pi)## peak emission wavelength in m\n",
+    "print \"The total carrier recombination lifetime =%0.2f ns\"%( t)#\n",
+    "print \"\\n The peak emission wavelength =%0.2f um\"%( y*10**6)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.3 Pg: 336"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The external power efficiency =0.39 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi\n",
+    "from __future__ import division\n",
+    "nx=3.6## refractive index\n",
+    "Fn=0.68## transmission factor\n",
+    "pe_pi=(Fn)/(4*nx**2)#\n",
+    "pi_p=0.3#\n",
+    "nep=pe_pi*pi_p## external power efficiency\n",
+    "print \"The external power efficiency =%0.2f %%\"%( nep*100)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.4 Pg: 337"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The coupling efficiency =2.25 %\n",
+      "\n",
+      " The loss =16.48 db\n",
+      "\n",
+      " The loss in decibels relative to Pint=45.24 db\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi,log\n",
+    "from __future__ import division\n",
+    "n=3.6## core refractive index\n",
+    "NA=0.15## numerical aperture\n",
+    "nc=NA**2## coupling efficiency\n",
+    "l_s=-10*log(nc)/log(10)## loss in db\n",
+    "pe_pi=0.023*0.0013## from ex 8.3\n",
+    "pc=-10*log(pe_pi)/log(10)## loss in decibels relative to Pint\n",
+    "print \"The coupling efficiency =%0.2f %%\"%( nc*100)#\n",
+    "print \"\\n The loss =%0.2f db\"%( l_s)#\n",
+    "print \"\\n The loss in decibels relative to Pint=%0.2f db\"%( pc)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.5 Pg: 337"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The optical power coupled into the fiber =7.19 uW\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "r=45*10**-6## radius in m\n",
+    "NA=0.3## numerical aperture\n",
+    "rd=40## radiance\n",
+    "A=3.14*(r*100)**2## area in cm**2\n",
+    "pe=3.14*(1-r)*A*rd*NA**2## optical power coupled into the fiber\n",
+    "Pe=pe*10**4## optical power coupled into the fiber uW\n",
+    "print \"The optical power coupled into the fiber =%0.2f uW\"%( Pe)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.6 Pg: 337"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The percentage of overall efficiency =0.37 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "pc=150*10**-6## coupling power W\n",
+    "p=20*10**-3*2## optical power W\n",
+    "npc=pc/p## overall efficiency\n",
+    "Npc=npc*100## percentage of overall efficiency\n",
+    "print \"The percentage of overall efficiency =%0.2f %%\"%( Npc)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.7 Pg: 338"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The number of longitudinal modes =300000.00\n",
+      "\n",
+      " The frequency separation of the modes =2.00 GHz\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "n=1.5## refractive index\n",
+    "L=0.05## crystal length in m\n",
+    "y=0.5*10**-6## wavelength in m\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "q=2*n*L/y## the number of longitudinal modes\n",
+    "df=c/(2*n*L)## frequency separation of the modes in Hz\n",
+    "Df=df/10**9## frequency separation of the modes in GHz\n",
+    "print \"The number of longitudinal modes =%0.2f\"%( q)#\n",
+    "print \"\\n The frequency separation of the modes =%0.2f GHz\"%( Df)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.8 Pg: 338"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The wavelength of optical emission  =0.87 um\n",
+      "\n",
+      " The frequency separation of the modes =59 GHz\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "Eg=1.43## bandgap energy in eV\n",
+    "dy=0.15*10**-9#\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "y=1.24/Eg## in um\n",
+    "y1=y*10**-6## wavelength of optical emission in m\n",
+    "df=(c*dy)/(y1**2)## the line width in Hz\n",
+    "Df=df/10**9## the line width in GHz\n",
+    "print \"The wavelength of optical emission  =%0.2f um\"%( y)#\n",
+    "print \"\\n The frequency separation of the modes =%d GHz\"%( Df)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.9 Pg: 338"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The crystal length =151.52 um\n",
+      "\n",
+      " The the number of longitudinal modes =1283\n",
+      "\n",
+      " answer is wrong in textbook\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "n=3.6## refractive index\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "y=0.85*10**-6## wavelength in m\n",
+    "df=275*10**9## frequency separation of the modes in Hz\n",
+    "L=c/(2*n*df)## crystal length in m\n",
+    "L1=L*10**6## crystal length in um\n",
+    "q=2*n*L/y## the number of longitudinal modes\n",
+    "print \"The crystal length =%0.2f um\"%( L1)#\n",
+    "print \"\\n The the number of longitudinal modes =%d\"%( q)#\n",
+    "print \"\\n answer is wrong in textbook\""
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.10 Pg: 339"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The external power efficiency =13.00 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "nt=0.20## total efficiency\n",
+    "Eg=1.43## bandgap energy in eV\n",
+    "V=2.2## applied voltage in volts\n",
+    "nep=(nt*Eg)/V## external power efficiency\n",
+    "Nep=nep*100## percentage of external power efficiency\n",
+    "print \"The external power efficiency =%0.2f %%\"%( Nep)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.11 Pg: 339"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The divergence angle =48.91 degree \n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import sqrt\n",
+    "from __future__ import division\n",
+    "h=0.35*10**-3## irradiance W/cm**2\n",
+    "po=0.45*10**-3## power output in watt\n",
+    "d=1.5## separation distance in cm\n",
+    "x=sqrt((4*po)/(3.14*d**2*h))## divergence angle in radians\n",
+    "X=(x*180)/3.14## divergence angle in degree\n",
+    "print \"The divergence angle =%0.2f degree \"%( X)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.12 Pg: 339"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The irradiance =14.44 mwatt/cm**2 \n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi\n",
+    "from __future__ import division\n",
+    "ni=0.09## normal efficiency\n",
+    "d=2*2.54## separation distance in cm\n",
+    "x=0.2## divergence angle in radians\n",
+    "vf=2.0## forward voltage in volts\n",
+    "i_f=65*10**-3## forward current in amp\n",
+    "pi=vf*i_f## input power in Watt\n",
+    "po=ni*pi## output power in Watt\n",
+    "H=4*po/(3.14*d**2*x**2)## irradiance in watt/cm**2\n",
+    "H1=H*1000## irradiance in mwatt/cm**2\n",
+    "print \"The irradiance =%0.2f mwatt/cm**2 \"%( H1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.13 Pg: 340"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The internal quantam efficiency =93.46 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "tr=3.5## relative life time in ms\n",
+    "tnr=50## nonrelative life time in ms\n",
+    "ni=tnr/(tr+tnr)## internal quantam efficiency\n",
+    "print \"The internal quantam efficiency =%0.2f %%\"%( ni*100)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.14 Pg: 340"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The optical power coupled into optical fiber =0.80 mW \n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi,sin\n",
+    "from __future__ import division\n",
+    "ni=0.15## internal quantam efficiency\n",
+    "vf=2.0## forward voltage in volts\n",
+    "i_f=15*10**-3## forward current in amp\n",
+    "x=25## acceptance angle in degree\n",
+    "pi=vf*i_f## input power in Watt\n",
+    "po=ni*pi## output power in Watt\n",
+    "NA=(sin(x*3.14/180))#\n",
+    "nc=NA**2## numerical aperture\n",
+    "pf=nc*po## optical power coupled into optical fiber in w\n",
+    "print \"The optical power coupled into optical fiber =%0.2f mW \"%( pf*1000)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.15 Pg: 340"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The rediative life time =182 ns\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "tnr=10## nonrediative life time in ns\n",
+    "n_inj=0.80## injection efficiency\n",
+    "n_ex=0.60## extraction efficiency\n",
+    "nt=0.025## total efficiency\n",
+    "nr=nt/(n_inj*n_ex)## non rediative life time in ns\n",
+    "tr=((1/nr)-1)*tnr## rediative life time in ns\n",
+    "print \"The rediative life time =%d ns\"%( tr)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.16 Pg: 341"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The bandwidth =11.67 MHz\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "tr=30*10**-9## rise time in s\n",
+    "Bw=0.35/tr## bandwidth in Hz\n",
+    "print \"The bandwidth =%0.2f MHz\"%( Bw/10**6)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.17 Pg: 341"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The  divergence angle =0.02 radians\n",
+      "\n",
+      " The  divergence angle =0.92 degree\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "y=630*10**-9## operating wavelength in m\n",
+    "w=25*10**-6## spot size in m\n",
+    "x=2*y/(3.14*w)## divergence angle in radians\n",
+    "x1=x*180/3.14##  divergence angle in degree\n",
+    "print \"The  divergence angle =%0.2f radians\"%( x)#\n",
+    "print \"\\n The  divergence angle =%0.2f degree\"%( x1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.18 Pg: 341"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The  energy =2.25 electron volts\n",
+      "\n",
+      " The energy =0.12 electron volts\n",
+      "\n",
+      " The energy =0.52 electron volts\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "y1=550*10**-3## peak of eyes response in um\n",
+    "y2=10.6## standard wavelength in um\n",
+    "y3=2.39## predominant IR line of He-Ne laser in um\n",
+    "E1=1.24/y1## energy in electron volts\n",
+    "E2=1.24/y2## energy in electron volts\n",
+    "E3=1.24/y3## energy in electron volts\n",
+    "print \"The  energy =%0.2f electron volts\"%( E1)#\n",
+    "print \"\\n The energy =%0.2f electron volts\"%( E2)#\n",
+    "print \"\\n The energy =%0.2f electron volts\"%( E3)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.19 Pg: 342"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The  cut off wavelength =885 nm\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "Eg=1.4## energy in electron volts\n",
+    "y=1.24/Eg## cut off wavelength in um\n",
+    "y1=y*1000## cut off wavelength in nm\n",
+    "print \"The  cut off wavelength =%d nm\"%( y1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.20 Pg: 342"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The  divergence angle =0.15 radians\n",
+      "\n",
+      " The  divergence angle =8.76 degree\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "y=1200*10**-9## operating wavelength in m\n",
+    "w=5*10**-6## spot size in m\n",
+    "x=2*y/(3.14*w)## divergence angle in radians\n",
+    "x1=x*180/3.14##  divergence angle in degree\n",
+    "print \"The  divergence angle =%0.2f radians\"%( x)#\n",
+    "print \"\\n The  divergence angle =%0.2f degree\"%( x1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.21 Pg: 342"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 17,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The  acceptance angle =14.03 degree\n",
+      "\n",
+      " The coupling efficiency =5.88 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import pi,asin\n",
+    "from __future__ import division\n",
+    "n1=1.48## core refractive index\n",
+    "n2=1.46## cladding refractive index \n",
+    "NA=sqrt(n1**2-n2**2)## numerical aperture\n",
+    "xa=(asin(NA))*(180/pi)## acceptance angle in degree\n",
+    "nc=NA**2## coupling efficiency\n",
+    "print \"The  acceptance angle =%0.2f degree\"%( xa)#\n",
+    "print \"\\n The coupling efficiency =%0.2f %%\"%( nc*100)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.22 Pg: 343"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The frequency separation =0.27 GHz\n",
+      "\n",
+      " The energy separation =1.13 meV\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "n=3.66## for GaAs\n",
+    "L=150*10**-6## cavity length in m\n",
+    "dv=c/(2*n*L)##frequency separation in Hz\n",
+    "dv1=dv/10**12## frequency separation in GHz\n",
+    "h=6.64*10**-34## plank constant\n",
+    "q=1.6*10**-19## charge of an electron\n",
+    "dE=(h*dv)/q## energy separation eV\n",
+    "print \"The frequency separation =%0.2f GHz\"%( dv1)#\n",
+    "print \"\\n The energy separation =%0.2f meV\"%( dE*1000)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.23 Pg: 343"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The conversion efficiency =1 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "po=2*10**-3## optical power in watts\n",
+    "I=100*10**-3## current in amp\n",
+    "V=2## applied voltage in volt\n",
+    "pe=I*V## electrical power in watts\n",
+    "n=(po/pe)*100## conversion efficiency\n",
+    "print \"The conversion efficiency =%d %%\"%( n)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.24 Pg: 343"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The wavelength =0.87 um\n",
+      "\n",
+      " The width =39 GHz\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "h=6.64*10**-34## plank constant\n",
+    "Eg=1.43## gap energy in eV\n",
+    "y=(1.24*10**-6)/Eg## wavelength in m\n",
+    "dy=0.1*10**-9## in m\n",
+    "df=(dy*c)/y**2## width in Hz\n",
+    "print \"The wavelength =%0.2f um\"%( y*10**6)#\n",
+    "print \"\\n The width =%d GHz\"%( df/10**9)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.25 Pg: 344"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The total carrier recombination lifetime =19.57 ns\n",
+      "\n",
+      " The internal quantam efficiency =0.78 \n",
+      "\n",
+      " The internal power =2.60 mW\n",
+      "\n",
+      " The power emitted =1.86 mW\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "tr=25## rediative life time in ns\n",
+    "tnr=90## nonrediative life time in ns\n",
+    "i=3.5*10**-3## drive current in amp\n",
+    "y=1.31*10**-6## wavelength in m\n",
+    "h=6.625*10**-34## plank constant\n",
+    "c=3*10**8## the speed of light in m/s\n",
+    "e=1.6*10**-19## charge\n",
+    "t=tr*tnr/(tr+tnr)## total carrier recombination lifetime ns\n",
+    "ni=t/tr## internal quantam efficiency\n",
+    "pi=(ni*h*c*i)/(e*y)## internal power in watt\n",
+    "p_int=pi*10**3## internal power in mW\n",
+    "P=p_int/(ni*(ni+1))## power emitted in mW\n",
+    "print \"The total carrier recombination lifetime =%0.2f ns\"%( t)#\n",
+    "print \"\\n The internal quantam efficiency =%0.2f \"%( ni)#\n",
+    "print \"\\n The internal power =%0.2f mW\"%( p_int)#\n",
+    "print \"\\n The power emitted =%0.2f mW\"%( P)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.26 Pg: 344"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The external efficiency =10.30 %\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "nt=0.18## total efficiency\n",
+    "Eg=1.43## band gape energy eV\n",
+    "V=2.5## appied voltage in volt\n",
+    "n_ex=(nt*(Eg/V))*100## external efficiency\n",
+    "print \"The external efficiency =%0.2f %%\"%( n_ex)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.27 Pg: 345"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The cavity length =149 um\n",
+      "\n",
+      " The number of longitudinal modes =1233\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import floor\n",
+    "from __future__ import division\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "n=3.6## for GaAs\n",
+    "df=278*10**9## separation in Hz\n",
+    "y=0.87*10**-6## wavelength in m\n",
+    "L=c/(2*n*df)## cavity length in m\n",
+    "l=L*10**6## cavity length in um\n",
+    "L1=floor(l)*10**-6## cavity length in m\n",
+    "q=(2*n*L1)/y## number of longitudinal modes\n",
+    "print \"The cavity length =%d um\"%( l)#\n",
+    "print \"\\n The number of longitudinal modes =%d\"%( q)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.28 Pg: 345"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The coupling efficiency =0.06\n",
+      "\n",
+      " The loss =12.33 decibels\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import log,sin\n",
+    "from __future__ import division\n",
+    "ac=14## acceptance angle in degree\n",
+    "nc=(sin(ac*3.14/180))**2## coupling efficiency\n",
+    "l_s=-10*log(nc)/log(10)## loss in decibels\n",
+    "print \"The coupling efficiency =%0.2f\"%( nc)#\n",
+    "print \"\\n The loss =%0.2f decibels\"%( l_s)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:8.29 Pg: 346"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "The frequency separation =81 GHz\n",
+      "\n",
+      " The wavelength separation =0.20 nm\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "c=3*10**8## speed of light in m/s\n",
+    "n=3.7## for GaAs\n",
+    "L=500*10**-6## cavity length in m\n",
+    "y=850*10**-9##\n",
+    "df=c/(2*n*L)##frequency separation in Hz\n",
+    "df1=df/10**9## frequency separation in GHz\n",
+    "dy=(y*y)/(2*L*n)## wavelength in m\n",
+    "dy1=dy*10**9## wavelength in nm\n",
+    "print \"The frequency separation =%d GHz\"%( df1)#\n",
+    "print \"\\n The wavelength separation =%0.2f nm\"%( dy1)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}