What does the coupling efficiency equation? $\eta = (pf / ps) =(NA)^2$ signify where pf is the power coupled to the source ps source power.
1 Answer
  1. The coupling efficiency is defined as a measure of amount of power emitted from an optical source that can be coupled into a fiber.

    $\therefore$ Coupling efficiency

    $ɳ_c = \frac{P_{fiber}}{P_{source}}$


    $P_{fiber}$ is the power coupled into the fiber

    $P_{source}$ is the power emitted from source

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  1. The coupling efficiency also depends on the type of fiber.

  2. Many suppliers offer optical sources along with a short fiber already coupled to the source.

  3. This small section of fiber that comes along with the source is called as “flylead” or “pigtail”.

  4. case 1:

    If the source radius (rs)< fiber core radius (a) then

    $$ɳ_c = \frac{P_f}{P_s} = (NA)^2$$

    $$NA = sin θ_a$$

    $P_s$ = power emitted from the source

    $= π^2.r_s^2.B_0$

    $B_0$ is the Axial radiance

6. Case II:


$P_f =(\frac{a}{r_s} )^2.P_s .(NA)^2$

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