(a) Sunlight subtends a half-angle of as seen from the Earth. Estimate the maximum…

PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging

What an Instrument Can See, Ch Radiance, etendue and a throughput budget that is spent

Problem

(a) Sunlight subtends a half-angle of

\theta_s = 0.267^\circ

as seen from the Earth. Estimate the maximum concentration factor

C_{\max} = n^2/\sin^2\theta_s

achievable for an absorber immersed in water,

n = 1.33

. (b) A telecom multimode fibre has a core diameter of

62.5\ \mu\mathrm{m}

and a numerical aperture

\mathrm{NA} = 0.275

, and carries light at

\lambda = 1310\ \mathrm{nm}

in air at its input face. Estimate the number of independent beams (modes) per polarisation it carries, using

N = \Xi/\lambda^2

with

\Xi = \pi A\,\mathrm{NA}^2