Grenier Jason R, Fernandes Luís A, Herman Peter R
Institute for Optical Sciences, and the Department of Electrical and Computer Engineering, University of Toronto, 10 Kings College Rd., Toronto, Ontario, M5S 3G4, Canada.
Opt Express. 2013 Feb 25;21(4):4493-502. doi: 10.1364/OE.21.004493.
The positional alignment of femtosecond laser written Bragg grating waveguides within standard and coreless optical fiber has been exploited to vary symmetry and open strong optical coupling to a high density of asymmetric cladding modes. This coupling was further intensified with tight focusing of the laser pulses through an oil-immersion lens to control mode size against an asymmetric refractive index profile. By extending this Bragg grating waveguide writing into bulk fused silica glass, strong coupling to a continuum of radiation-like modes facilitated a significant broadening to over hundreds of nanometers bandwidth that blended into the narrow Bragg resonance to form into a strongly isolating (43 dB) optical edge filter. This Bragg resonance defined exceptionally steep edge slopes of 136 dB/nm and 185 dB/nm for unpolarized and linearly polarized light, respectively, that were tunable through the 1450 nm to 1550 nm telecommunication band.
利用飞秒激光写入的布拉格光栅波导在标准光纤和无芯光纤中的位置对准，来改变对称性并开启与高密度非对称包层模式的强光学耦合。通过油浸透镜对激光脉冲进行紧聚焦，以控制模式尺寸以适应非对称折射率分布，从而进一步增强了这种耦合。通过将这种布拉格光栅波导写入扩展到块状熔融石英玻璃中，与连续的辐射状模式的强耦合促成了显著的展宽，带宽超过数百纳米，该带宽与窄布拉格共振混合，形成了一个强隔离（43 dB）的光学边缘滤波器。对于非偏振光和线偏振光，这种布拉格共振分别定义了异常陡峭的边缘斜率，分别为136 dB/nm和185 dB/nm，且可在1450 nm至1550 nm电信波段内调谐。
