Multiphoton Nanosculpting of Optical Resonant and Nonresonant Microsensors on Fiber Tips

Abstract

This work presents a multiphoton nanosculpting process that is employed to fabricate three-dimensional (3D) mechanically assisted optical resonant and nonresonant microsensors on fiber tips. The resonant microsensor consists of a complex 3D optical cavity design with submicron resolution and advanced micromechanical features including a hinged, multipositional mirror, a 3D spring body to displace this mirror without deforming it, and adhesive-retaining features for sealing the cavity. These features represent a breakthrough in the integration and fabrication capabilities of micro-optomechanical systems. The demonstrated dynamic optical surface enables directional thin-film deposition onto obscured areas. We leverage the rotation of the dynamically movable mirror to deposit a thin reflective coating onto the inner surfaces of a Fabry–Pérot cavity (FPC) with curved geometry. The reflective coating in conjunction with the dynamically rotatable mirror greatly improves the quality factor of the FPC and enables a new class of highly integrated multipurpose sensor systems. A unique spring body FPC on an optical fiber tip is used to demonstrate pressure sensing with a sensitivity of 38 ± 7 pm/kPa over a range of −80 to 345 kPa. The nonresonant microsensor consists of microblades that spin in response to an incident flow. Light exiting the core of the optical fiber is reflected back into the fiber core at a flow-dependent rate as the blades pass by. The fiber tip flow sensor operates successfully over a range of 9–25 LPM using nitrogen gas and achieves a linear response of 706 ± 43 reflections/LPM over a range of 10.9–12 LPM. The nanostructuring technology presented in this work offers a path forward for utilizing 3D design freedom in micromechanically enhanced optical and optofluidic systems to facilitate versatile processing and advantageous geometries beyond the current state-of-the-art.

3D Printing of Glass Micro-Optics with Subwavelength Features on Optical Fiber Tips

“…The light injected from the fiber core interferes with the cavity, and a portion of the light will be reflected back to the fiber. If we use a broadband light source as an input and collect the reflection spectrum of the Fabry–Pérot interferometer, the wavelength of a dip of the interference pattern λ m is given by λ m = 2 n L m where n is the refractive index of the medium within the cavity, L is the length of the cavity, and m is the order of the interference dip . If the length of the cavity remains unchanged during the measurement and we always track the same order of the interference dip, L and m are constant.…”

“…where n is the refractive index of the medium within the cavity, L is the length of the cavity, and m is the order of the interference dip. 17 If the length of the cavity remains unchanged during the measurement and we always track the same order of the interference dip, L and m are constant. By differentiating eq 2 with respect to n, we can get…”

“…Furthermore, these 3D-printed glass structures show exceptional resistance to many chemicals. We have demonstrated a fiber-tip refractive index sensor capable of robust measurement of the refractive index of aggressive organic solvents, in which polymer counterparts ,, would suffer from swelling and deformation. The small sensor sampled a liquid volume of only a picoliter.…”

“…However, the small area and delicate nature of the optical fiber tip make it challenging to apply standard microfabrication processes optimized for planar substrates. To overcome these challenges, researchers have proposed several approaches that are tailored for fabrication on fiber tips, such as chemical etching, , electron-beam lithography, , focused ion-beam milling, , nanoimprint lithography, , self-guiding photopolymerization, 3D μ-printing technology, and 3D direct laser writing (DLW). , Among these approaches, 3D DLW is particularly attractive because it enables the fabrication of arbitrary 3D structures with submicrometer resolution and complex designs. A plethora of intricate fiber-tip microstructures has been manufactured using the 3D DLW technique, and applications in beam shaping and sensing have been demonstrated. − However, these fiber-tip devices were made of polymers, which are known to swell and deform upon exposure to many organic solvents.…”

“…To overcome these challenges, researchers have proposed several approaches that are tailored for fabrication on fiber tips, such as chemical etching, 7 , 8 electron-beam lithography, 9 , 10 focused ion-beam milling, 4 , 11 nanoimprint lithography, 12 , 13 self-guiding photopolymerization, 14 3D μ-printing technology, 15 and 3D direct laser writing (DLW). 16 , 17 Among these approaches, 3D DLW is particularly attractive because it enables the fabrication of arbitrary 3D structures with submicrometer resolution and complex designs. A plethora of intricate fiber-tip microstructures has been manufactured using the 3D DLW technique, and applications in beam shaping and sensing have been demonstrated.…”