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Fabrication of high-Q lithium niobate microresonators using femtosecond laser micromachining.

Lin J, Xu Y, Fang Z, Wang M, Song J, Wang N, Qiao L, Fang W, Cheng Y - Sci Rep (2015)

Bottom Line: We report on fabrication of high-Q lithium niobate (LN) whispering-gallery-mode (WGM) microresonators suspended on silica pedestals by femtosecond laser direct writing followed by focused ion beam (FIB) milling.The micrometer-scale (diameter ~82 μm) LN resonator possesses a Q factor of ~2.5 × 10(5) around 1550 nm wavelength.The combination of femtosecond laser direct writing with FIB enables high-efficiency, high-precision nanofabrication of high-Q crystalline microresonators.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China [2] University of Chinese Academy of Sciences, Beijing 100049, China.

ABSTRACT
We report on fabrication of high-Q lithium niobate (LN) whispering-gallery-mode (WGM) microresonators suspended on silica pedestals by femtosecond laser direct writing followed by focused ion beam (FIB) milling. The micrometer-scale (diameter ~82 μm) LN resonator possesses a Q factor of ~2.5 × 10(5) around 1550 nm wavelength. The combination of femtosecond laser direct writing with FIB enables high-efficiency, high-precision nanofabrication of high-Q crystalline microresonators.

No MeSH data available.


Related in: MedlinePlus

(a) SEM image of a cylindrical post formed after femtosecond laser ablation; (b) and (c) SEM images of two cylindrical posts with diameters of 55 μm and 33 μm, respectively, after the FIB milling; (d) SEM image (top view) of the 55-μm diameter microresonator after the chemical etching and annealing.Inset in (d): side view of the microresonator, showing the freestanding edge of the LN microresonator.
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f2: (a) SEM image of a cylindrical post formed after femtosecond laser ablation; (b) and (c) SEM images of two cylindrical posts with diameters of 55 μm and 33 μm, respectively, after the FIB milling; (d) SEM image (top view) of the 55-μm diameter microresonator after the chemical etching and annealing.Inset in (d): side view of the microresonator, showing the freestanding edge of the LN microresonator.

Mentions: The details on the fabrication of LN microresonator can be found in Methods. The thicknesses of the LN thin film and silica layer were 700 nm and 2 μm, respectively. Briefly speaking, we first fabricated a cylindrical post with a diameter of ~59 μm and a total height of ~15 μm (corresponding to a cutting depth of 12 μm into the LN substrate beneath the silica), which is shown in Fig. 2(a), by femtosecond laser micromachining. Since the roughness on the laser ablated sidewall of the cylindrical post is on the order of a few tens of nanometers, which is too poor for high-Q microresonator application, FIB milling was used to smooth the periphery of the cylindrical post. The FIB milling was operated twice, beginning with a coarse milling and followed with a fine one. In the coarse milling, a 30-keV ion beam with a beam current of 4 nA was used to polish the periphery; whereas in the fine milling, the beam current was reduced to 1 nA. The milling was stopped at a depth of 3 μm from the top surface. The total FIB milling process took ~15 min. After the FIB milling, the diameter of the microresonator was reduced to 55 μm. Most importantly, the LN microresonator shows a highly smooth edge, as evidenced in its scanning electron microscope (SEM) image (Fig. 2(b)). Figure 2(c) shows another cylindrical post with a smaller diameter of 33 μm after the FIB milling. In principle, microresonators of diameters below 10 μm can be fabricated using our technique. It should be noted that the FIB process frequently induces the creation of lattice defects (i.e., vacancies and atomic nuclei), leading to the formation of amorphous material due to keV ion beam side dose or lateral ion straggle at the periphery of the microresonator. However, such defects are not critical in our experiments, since no free carrier is involved in the nonlinear generation process.


Fabrication of high-Q lithium niobate microresonators using femtosecond laser micromachining.

Lin J, Xu Y, Fang Z, Wang M, Song J, Wang N, Qiao L, Fang W, Cheng Y - Sci Rep (2015)

(a) SEM image of a cylindrical post formed after femtosecond laser ablation; (b) and (c) SEM images of two cylindrical posts with diameters of 55 μm and 33 μm, respectively, after the FIB milling; (d) SEM image (top view) of the 55-μm diameter microresonator after the chemical etching and annealing.Inset in (d): side view of the microresonator, showing the freestanding edge of the LN microresonator.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308694&req=5

f2: (a) SEM image of a cylindrical post formed after femtosecond laser ablation; (b) and (c) SEM images of two cylindrical posts with diameters of 55 μm and 33 μm, respectively, after the FIB milling; (d) SEM image (top view) of the 55-μm diameter microresonator after the chemical etching and annealing.Inset in (d): side view of the microresonator, showing the freestanding edge of the LN microresonator.
Mentions: The details on the fabrication of LN microresonator can be found in Methods. The thicknesses of the LN thin film and silica layer were 700 nm and 2 μm, respectively. Briefly speaking, we first fabricated a cylindrical post with a diameter of ~59 μm and a total height of ~15 μm (corresponding to a cutting depth of 12 μm into the LN substrate beneath the silica), which is shown in Fig. 2(a), by femtosecond laser micromachining. Since the roughness on the laser ablated sidewall of the cylindrical post is on the order of a few tens of nanometers, which is too poor for high-Q microresonator application, FIB milling was used to smooth the periphery of the cylindrical post. The FIB milling was operated twice, beginning with a coarse milling and followed with a fine one. In the coarse milling, a 30-keV ion beam with a beam current of 4 nA was used to polish the periphery; whereas in the fine milling, the beam current was reduced to 1 nA. The milling was stopped at a depth of 3 μm from the top surface. The total FIB milling process took ~15 min. After the FIB milling, the diameter of the microresonator was reduced to 55 μm. Most importantly, the LN microresonator shows a highly smooth edge, as evidenced in its scanning electron microscope (SEM) image (Fig. 2(b)). Figure 2(c) shows another cylindrical post with a smaller diameter of 33 μm after the FIB milling. In principle, microresonators of diameters below 10 μm can be fabricated using our technique. It should be noted that the FIB process frequently induces the creation of lattice defects (i.e., vacancies and atomic nuclei), leading to the formation of amorphous material due to keV ion beam side dose or lateral ion straggle at the periphery of the microresonator. However, such defects are not critical in our experiments, since no free carrier is involved in the nonlinear generation process.

Bottom Line: We report on fabrication of high-Q lithium niobate (LN) whispering-gallery-mode (WGM) microresonators suspended on silica pedestals by femtosecond laser direct writing followed by focused ion beam (FIB) milling.The micrometer-scale (diameter ~82 μm) LN resonator possesses a Q factor of ~2.5 × 10(5) around 1550 nm wavelength.The combination of femtosecond laser direct writing with FIB enables high-efficiency, high-precision nanofabrication of high-Q crystalline microresonators.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China [2] University of Chinese Academy of Sciences, Beijing 100049, China.

ABSTRACT
We report on fabrication of high-Q lithium niobate (LN) whispering-gallery-mode (WGM) microresonators suspended on silica pedestals by femtosecond laser direct writing followed by focused ion beam (FIB) milling. The micrometer-scale (diameter ~82 μm) LN resonator possesses a Q factor of ~2.5 × 10(5) around 1550 nm wavelength. The combination of femtosecond laser direct writing with FIB enables high-efficiency, high-precision nanofabrication of high-Q crystalline microresonators.

No MeSH data available.


Related in: MedlinePlus