Question

Relation between the acceptance angle and numerical aperture (NA) is:

• A. acceptance angle = cos-1 (NA)
• B. acceptance angle = sin-1 (NA)
• C. acceptance angle = cosec-1 (NA)
• D. acceptance angle = tan-1 (NA)

Answer 1

Answer: (B)

acceptance angle = sin-1 (NA)

Answer 2

The numerical aperture (NA) of an optical fiber is defined as $NA = n_0 \sin \theta_a$, where $n_0$ is the refractive index of the external medium and $\theta_a$ is the acceptance angle. For light entering from air, $n_0 = 1$, thus $NA = \sin \theta_a$. Rearranging this equation to solve for the acceptance angle, we get $\theta_a = \sin^{-1}(NA)$.