Lee K S, Erdogan T
School of Electrical and Computer Engineering, Sung Kyun Kwan University, Suwon 440-746, Korea.
Appl Opt. 2000 Mar 20;39(9):1394-404. doi: 10.1364/ao.39.001394.
Whereas core-mode reflection and core-mode-to-radiation-mode coupling in tilted fiber Bragg gratings is well understood, as is coupling between a core mode and higher-order core and cladding modes in untilted gratings, here we analyze in detail the coupling among core modes and cladding modes in reflective and transmissive tilted fiber gratings. We show that strong coupling between an LP(01) core mode and the exact (1m) cladding modes occurs in a transmissive tilted grating for nearly any tilt angle except angles close to 90 degrees, whereas the LP(01)-to-(lm) cladding mode coupling (l not equal 1) is appreciable only for tilt angles just below 90 degrees (approximately 88 degrees). In a reflective grating, strong coupling between the LP(01) core mode and the exact (1m) cladding modes occurs only for angles less than approximately 5 degrees, whereas coupling to (1m) cladding modes for m > 1 occurs only for angles greater than approximately 5 degrees. Coupling among bound core modes exhibits a similar behavior, except that in general the coupling is stronger. Experimentally we show coupling to both higher-order bound core modes and cladding modes in a transmissive tilted grating at visible and near-infrared wavelengths.
虽然倾斜光纤布拉格光栅中的纤芯模式反射和纤芯模式到辐射模式的耦合已得到充分理解，未倾斜光栅中的纤芯模式与高阶纤芯和包层模式之间的耦合也是如此，但在此我们详细分析反射型和透射型倾斜光纤光栅中纤芯模式与包层模式之间的耦合。我们表明，对于几乎任何倾斜角（除了接近90度的角度），在透射型倾斜光栅中，LP(01)纤芯模式与精确的(1m)包层模式之间都会发生强耦合，而LP(01)到(lm)包层模式的耦合（l不等于1）仅在略低于90度（约88度）的倾斜角时才明显。在反射型光栅中，LP(01)纤芯模式与精确的(1m)包层模式之间仅在小于约5度的角度时发生强耦合，而对于m>1的(1m)包层模式的耦合仅在大于约5度的角度时发生。束缚纤芯模式之间的耦合表现出类似的行为，只是一般来说耦合更强。通过实验，我们展示了在可见和近红外波长下，透射型倾斜光栅中与高阶束缚纤芯模式和包层模式的耦合。
