Question

What is the acceptance cone angle of a multimode optical fiber assuming that light is passing through some coupling oil at the LED driver source end and that oil has refractive index about that of olive oil, where 1) the core is high-index flint glass and the cladding is Plexiglas 2) the core is crown class and the clad is soda lime glass?

Answer 1

Solution:

The refractive index of the olive oil, n =1.47

The acceptance angle θmax can be found by following formula,

n*sinθ_max = √( n_core² - n_clad²) -----------------------------------------------------------------(1)

n = refractive index of the medium through which light eneters the fiber,

n_core = refractive index of the core,

n_clad = refractive index of the cladding

Part (1)

Refractive index of high index flint glass n_core = 1.75 and is used as a core.

Refractive index of Plexiglas n_clad = 1.49                                                                                    

Using the equation (1), we get,

n*sinθ_max = √[ n_core² - n_clad²]

1.47* sinθ_max = √[ 1.75² – 1.49²]                                                                                                    

sinθ_max = √[ 1.75² – 1.49²]/1.47

sinθ_max = 0.62437

θ_max = sin^-1(0.62437)

θ_max = 38.64^o

Thus the acceptance cone angle is 38.64^o

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part (2)

Refractive index of crown glass n_core = 1.52 and is used as a core.

Refractive index of soda lime glass n_clad = 1.518                                                                                 

Using the equation (1), we get,

n*sinθ_max = √[ n_core² - n_clad²]

1.47* sinθ_max = √[ 1.52² – 1.518²]                                                                                                  

sinθ_max = √[ 1.52² – 1.518²]/1.47

sinθ_max = 0.053026

θ_max = sin^-1(0.053026)

θ_max = 3.04^o

Thus the acceptance cone angle is 3.04^o