集成光波導ppt課件(存儲版)
【正文】 then LncnnLnvnLn22112121c r i t i c a lt ?????????????????????????() The critical angle ray travel time is: ????????21nnL14 Multimode Distortion The total delay is 2211 )(nnnL????????? ?This is the modal pulse spread per unit length in a multimode waveguide. We can write it as cnnLtt a x i a lc r i t i c a l 1221 ???() 112121 nnnnnL ???????? ????????? ?15 Multimode Distortion 221nL????????? ? 1L ????????? ?to get )( 121nnn ???Use the fractional refractive index change () Modal Pulse Spread If n1 and n2 are nearly equal 16 Multimode Distortion 212NAL ???????? ?Finally, in terms of the numerical aperture the modal spread can be expressed as: () Modal Pulse Spread 1 2N A n??17 DISPERSION AND DISTORTION IN THE SLAB WAVEGUIDE 22m o dD is p e rs iv e M u lt i eD is to rt io n D is to rt io nL L L? ? ?? ? ?? ? ? ?? ? ? ? ? ???? ? ? ? ? ?? ? ? ?? ? ? ? ? ?? ? ? ?The total pulse spread is given by: 18 167。 ???? ??????? ge f f MncL5 6 Waveguide Dispersion Mode Chart ?? = ?2 ?1 For a fixed d ( slab thickness), neff varies with ?. Thus, different wavelengths from the same source travel at different speeds. This yields pulse spreading. This is waveguide dispersion. 7 Waveguide Dispersion Since n1 and n2 also vary with wavelength, material dispersion exists in addition to waveguide dispersion. The total dispersive pulse spread is the sum of the two. That is: ? ? ? ? ?? ????? gMML/? 因為材料色散 M有可能為負值(例如在石英玻
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