Tightly trapped acoustic phonons in photonic crystal fibres as highly nonlinear artificial Raman oscillators
Tightly trapped acoustic phonons in photonic crystal fibres as highly nonlinear artificial Raman oscillators
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DOI：
10.1038/nphys1217
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发表时间：
2009-04-01
期刊：
影响因子：
19.6
通讯作者：
Russell, P. St. J.
中科院分区：
文献类型：
--
作者：
Kang, M. S.;Nazarkin, A.;Russell, P. St. J.
光和高超声波之间的相互作用可以通过严格的场约束来增强，如周期性结构材料（1）、微腔（2）、微机械谐振器（3）和光子晶体光纤（4-6）（PCF）所示。有许多弱声光相互作用的例子，例如，传统光纤中的导声波布里渊散射（7）。这种前向散射效应是由纤芯引导的光与整个光纤横截面的声共振相互作用引起的，并且在量子光学实验中被视为噪声源（8）。在这里，我们报告的观测强非线性前向散射的激光千兆赫兹的声振动，紧紧地被困在一起的小核心的二氧化硅-空气光子晶体光纤。声波以接近90度的角度在纤芯上来回反弹，形成具有平坦色散曲线和明显截止频率Ω（α）的光学声子类模式。这确保了与引导光学模式的自动相位匹配，使得在用调谐到Ω（a）的双频激光源泵浦时，产生由Ω（a）间隔的多个光学边带。强边带的数量在这种拉曼过程中增加与泵浦功率。结果指出，一类新的可设计的非线性光学器件的应用，例如，脉冲合成，频率梳发电电信和光纤激光器锁模。
Interactions between light and hypersonic waves can be enhanced by tight field confinement, as shown in periodically structured materials(1), microcavities(2), micromechanical resonators(3) and photonic crystal fibres(4-6) (PCFs). There are many examples of weak sound-light interactions, for example, guided acoustic-wave Brillouin scattering in conventional optical fibres(7). This forward-scattering effect results from the interaction of core-guided light with acoustic resonances of the entire fibre cross-section, and is viewed as a noise source in quantum-optics experiments(8). Here, we report the observation of strongly nonlinear forward scattering of laser light by gigahertz acoustic vibrations, tightly trapped together in the small core of a silica-air PCF. Bouncing to and fro across the core at close to 90 degrees to the fibre axis, the acoustic waves form optical-phonon-like modes with a flat dispersion curve and a distinct cutoff frequency Omega(a). This ensures automatic phase-matching to the guided optical mode so that, on pumping with a dual-frequency laser source tuned to Omega(a), multiple optical side bands are generated, spaced by Omega(a). The number of strong side bands in this Raman-like process increases with pump power. The results point to a new class of designable nonlinear optical device with applications in, for example, pulse synthesis, frequency comb generation for telecommunications and fibre laser mode-locking.