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Understanding Linear Polarization and Attenuation in Optical Fibers

Learn about hybrid modes, linearly polarized waves, and attenuation in optical fibers explained with relevant examples and diagrams.

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Understanding Linear Polarization and Attenuation in Optical Fibers

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  1. n2 y=d/2 d n1 y=0 y=d/2 n2 Even solutions: Odd solutions:

  2. Linear Polarization • fiber내에서 빛이 통과할때는 Ez와 Hz성분을 모두 갖는 hybrid modes를 가진다. • 그러나 굴절률차이가 아주 작은(Δ<<1)경우에는 거의 plane polarized된 traveling waves로 보이게 된다. • 이런 waves를 linearly polarized(LP)라고 부르고, 이들은 transverse electric and magnetic field 특성을 모두 갖는다. • Lplm mode는 아래와같이 표현이 가능하다. • 2xl: max peak # along φ • M : max peak # along r

  3. Modes in step index fiber • V-number (normalized frequency) • Normalized propagation constant,b • 우측 그림에서 볼 수 있듯이 V-number가 2.405보다 작으면 single mode가 된다.

  4. Attenuation in Optical fibers • 우측 그림은 silica를 기본 물질로 사용하는 fiber의 파장에 따른 attenuation을 나타낸다. • Rayleigh scattering과 Lattice absorption에 의해서 fundamental limit이 정해진다. • 1310nm와 1550nm에서 loss의 deep이 생기는 것을 볼수 있다. • Typical optical fiber는 1550nm에서 0.2dB/km의 attenuation coefficient를 갖는다. • Ex) αdB=0.3dB/km일때 Pin=1mW이면 Pout=0.5mW가 되는 거리 L은?

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