2. We will now model the coupling of light from a laser to an optical fibre. Ass

Question

2. We will now model the coupling of light from a laser to an optical fibre. Assume that you have a 1550 nm wavelength laser that is emitting a collimated Gaussian beam that has a beam waist radius of 2 mm. You need to couple this into a Corning SMF-28 optical fibre which has a mode-field diameter of 10.4 um (this is equivalent to twice the beam waist radius) or equivalently a numerical aperture of 0.14 (this is calculated fromthe 99% beam power angle). a) Calculate the lens focal length required to couple the light from the laser to the fibre, assuming that distances x1 and x2 are zero. What aperture diameter should the lens have. [4 points]

Explanation / Answer

im coupling 1550nm output from a single-mode lensed optical fiber to a standard SMF using a pair of collimating lenses, matched to the NA of the respective fibers. However, I find that by increasing the separation between the two lenses (where light is collimated) from ~10cm to 45cm improves the coupling efficiency by as much as 30%. As far as I know, increasing the separation distance should only increase losses.

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