We report on fabrication of microresonators of high quality (high-Q) factors in both glass and crystalline materials by femtosecond laser 3D micromachining. Based on this novel approach, we obtained high-Q microresonators of non-in-plane geometries in glass materials such as fused silica and Nd: glass and demonstrated lasing at a pump power as low as 69 microwatts. We also fabricated on-chip microresonators of sub-100 μm diameters in crystalline materials including calcium fluoride and lithium niobate, and demonstrated efficient second harmonic generation using the high-Q lithium niobate microresonator. Furthermore, femtosecond laser 3D micromachining allows direct integration of the microresonators with other functional microcomponents, such as a microfluidic mixer and a microheater, leading to compact microdevices with enhanced functionalities. Our technique opens new avenues for fabricating high-Q microresonators with either 2D or 3D geometries on various types of dielectric materials.
We report on fabrication of three-dimensional (3D) high-quality (Q) whispering-gallery-mode microcavities by femtosecond laser micromachining. The main fabrication procedures include the formation of on-chip freestanding microdisk through selective material removal by femtosecond laser pulses, followed by surface smoothing processes (CO2 laser reflow for amorphous glass and focused ion beam (FIB) sidewall milling for crystalline materials) to improve the Q factors. Fused silica microcavities with 3D geometries are demonstrated with Q factors exceeding 106. A microcavity laser based on Nd:glass has been fabricated, showing a threshold as low as 69μW via free space continuous-wave optical excitation at the room temperature. CaF2 crystalline microcavities with Q factor of ~4.2×104 have also been demonstrated. This technique allows us to fabricate 3D high-Q microcavities in various transparent materials such as glass and crystals, which will benefit a broad spectrum of applications such as nonlinear optics, quantum optics, and bio-sensing.