| 摘要 |
High-quality long periodic grating (LPGs) were written in air-core photonic bandgap fibers by use of high frequency short duration CO2 laser pulses to periodically vary the size and shape of the air-holes in the holey cladding. The variation of cladding holes changes the waveguide structure, instead of the index of the materials forming the waveguide, and resonantly couples the core mode to discrete higher order or surface-like modes and then to lossy quasi-continuum of cladding and radiating modes. This mechanism is different from LPGs in solid core fibers in which the core mode is directly coupled into discrete cladding modes. The LPGs in hollow-core PBFs have unique properties such as very large PDL, very small or insensitivity to temperature, bent and external refractive index, and large strain sensitivity, and will have applications in both communication devices and sensors.
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