Answer:
[tex]i_{cr} = 71.27^{\circ}[/tex]
[tex]\alpha_{cr} = 29.01^{\circ}[/tex]
Given:
refractive index of core, [tex]n_{core} = 1.51[/tex]
refractive index of clad, [tex]n_{clad} = 1.43[/tex]
Explanation:
Critical angle can be defined as the incidence angle which results in the refraction angle being equal to [tex]90^{\circ}[/tex] at that angle of incidence.
For Total Internal Reflection to occur, the incidence angle must be greater than the critical angle.
Now, we know that the critical angle, [tex]\theta_{cr}[/tex] is given by:
[tex]sin\theta_{cr} = \frac{n_{clad}}{n_{core}}[/tex]
[tex]\theta_{cr} = sin^{- 1}(\frac{n_{clad}}{n_{core}})[/tex]
[tex]\theta_{cr} = sin^{- 1}(\frac{1.43}{1.51}) = sin^{- 1}(0.947) = 71.27^{\circ}[/tex]
[tex]i_{cr} = \theta_{cr} = 71.27^{\circ}[/tex]
Now, for [tex]\alpha_{cr}[/tex]:
[tex]\frac{sin\gamma_{cr}}{sin\alpha_{cr}} = \frac{1}{n_{core}}[/tex]
[tex]sin\alpha_{cr}= sin(90^{\circ} - 71.27^{\circ})\times 1.51[/tex]
[tex]sin\alpha_{cr}= sin(18.734^{\circ})\times 1.51[/tex]
[tex]\alpha_{cr}= sin^{- 1}0.485 = 29.01^{\circ}[/tex]