Lensing Schemes for Coupling Improvement



. When the emitting area of the source is smaller than the core area of fiber, the power coupling efficiency becomes poor. In order to improve the coupling efficiency miniature lens is placed between source and fiber. Microlens magnifies the emitting area of source equal to core area. The power coupled increases by a factor equal to magnification factor of lens.
. Important types of lensing schemes are :
1. Rounded  end fiber.
2. Spherical – surfaced LED and Spherical-ended fiber.
3. Taper ended fiber.
4. Non imaging microsphere.
5. Cylinderical lens.
6. Imagine sphere.
       Fig. 1 shows the lensing schemes.
. There are some drawbacks of using lens.
1. Complexity increases.
2. Fabrication  and handling difficulty.
3. Precise mechanical alignments needed.



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