The high-quality whispering gallery mode micro-cavity can significantly enhance the interaction between light and matter, and has a wide range of applications in the fields of low threshold nonlinear optics, quantum electrodynamics, photomechanical mechanics, and biosensing. The whispering gallery mode optical microcavity based on the dielectric crystal substrate has unique advantages such as high nonlinear coefficient (second or third order), wide transparent window, low intrinsic absorption, almost no impurity emission, etc., in constructing the optical frequency comb, the next generation Classical or quantum entangled light sources, quantum information processing chips, portable tunable light sources, etc. show important scientific significance and good commercial prospects. However, using existing manual or mechanical polishing techniques, it is difficult to obtain micro-scale, small-sized, high-quality optical microcavities on crystal chips.
Chinese Academy of Sciences, Shanghai Institute of Optics and Fine Mechanics, State Key Laboratory of Intense Field Laser Physics, Lin Jintian, etc. cooperated with the State Key Laboratory of Modern Optical Instruments of Zhejiang University, and proposed a crystal-based high-quality whispering-laser-based optical microcavity based on femtosecond laser writing. The new recipe for preparation [Sci. Rep. 5, 8072 (2015)].
The solution uses a lithium niobate film/silica/lithium tantalate substrate sandwich structure material as a sample (as shown in FIG. 1 ), and a micro-column is prepared on the sample by water-assisted femtosecond laser etching; Using a focused ion beam (FIB) to grind the edge of the micro-cylinder to reduce the roughness of the edge; in order to expand the refractive index difference between the micro-cavity and the surrounding environment, the silicon dioxide layer is etched into small pillars to form a suspended lithium niobate. Microplate; Finally, the microdisk cavity is subjected to high temperature treatment. The prepared lithium niobate thin film microcavity is shown in Fig. 2(a). After measurement, the quality factor of the crystal microcavity reached 2.5×105 at the 1550 nm band (see Fig. 2(b)). The microcavity is pumped using a narrow-band tunable laser with a single longitudinal mode, and a significant second harmonic signal is obtained with a normalized conversion efficiency of 1.35×10-5/mW [arXiv: 1405.6473 (2014)]. Figure 2(c) shows a microcavity side view that generates the second harmonic of purple.
Due to the insensitivity of the preparation technology to the properties of the crystal material, it is expected that a high-quality whispering gallery mode optical microcavity can be prepared on a variety of dielectric crystals, and the application of the microcavity in nonlinear optics and quantum optics can be promoted.
The study was supported by the national major scientific research program and the National Natural Science Foundation.
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