Surface Nanoscale Axial Photonics Microresonators Research Articles

Regulation and Liquid Sensing of Electromagnetically Induced Transparency-like Phenomena Implemented in a SNAP Microresonator.

Optical microresonators supporting whispering-gallery modes (WGMs) have become a versatile platform for achieving electromagnetically induced transparency-like (EIT-like) phenomena. We theoretically and experimentally demonstrated the tunable coupled-mode induced transparency based on the surface nanoscale axial photonics (SNAP) microresonator. Single-EIT-like and double-EIT-like (DEIT-like) effects with one or more transparent windows are achieved due to dense mode families and tunable resonant frequencies. The experimental results can be well-fitted by the coupled mode theory. An automatically adjustable EIT-like effect is discovered by immersing the sensing region of the SNAP microresonator into an aqueous environment. The sharp lineshape and high slope of the transparent window allow us to achieve a liquid refractive index sensitivity of 2058.8 pm/RIU. Furthermore, we investigated a displacement sensing phenomenon by monitoring changes in the slope of the transparent window. We believe that the above results pave the way for multi-channel all-optical switching devices, multi-channel optical communications, and biochemical sensing processing.

Fabrication of surface nanoscale axial photonics structures with electric arc discharge

The fabrication of surface nanoscale axial photonics (SNAP) microresonators, utilizing the approach of electric arc discharge (EAD), is accomplished, achieving a precision at the angstrom level. This paper thoroughly investigates the effects that discharge intensity and discharge duration have on SNAP microresonators, respectively, through the manipulation of relevant discharge parameters. The results indicate that, within a specified range of discharge intensity, a linear relationship is observed between the effective radius variation (ERV) and the discharge intensity, characterized by a slope of 0.325 nm/intensity unit. As the discharge duration is extended, the ERV gradually increases, eventually reaching a saturation value, which is inherently determined by the discharge intensity. Additionally, as the discharge intensity (or time) continues to increase, a “convex–concave–convex” shape is observed on the fiber, providing a method for fabricating bat microresonators. These discoveries derived from our study contribute toward providing a strong foundation for the progressive enhancement and refinement of EAD-based SNAP fabrication techniques.

Configurable SNAP microresonators induced by axial pre-strain-assisted CO2 laser exposure.

Flexible engineering of the complex shapes of the surface nanoscale axial photonics (SNAP) bottle microresonators (SBMs) is challenging for future nanophotonic technology applications. Here, we experimentally propose a powerful approach for the one-step fabrication of SBMs with simultaneous negative and positive radius variations, exhibiting a distinctive "bump-well-bump" profile. It is executed by utilizing two focused and symmetrical CO2 laser beams exposed on the fiber surface for only several hundred milliseconds. The spectral characteristics of different eigenmodes are analyzed, providing deep insights into the complex physical processes during the CO2 laser exposure. The shapes of the SBMs can be flexibly adjusted by the exposure time, laser power, and applied pre-strains. As a proof of this technique, the developed approach enables the efficient production of a bat SBM, ensuring a uniform field amplitude of the bat mode over the length exceeding 120 µm with 7% deviation. Our proposed technique provides a powerful technique for the efficient fabrication of SBMs with predetermined shapes, laying the groundwork for its applications on microscale optical signal processing, quantum computing, and so on.

Theory of nonlinear whispering-gallery-mode dynamics in surface nanoscale axial photonics microresonators

Theory of nonlinear whispering-gallery-mode dynamics in surface nanoscale axial photonics microresonators

Rapid and high-precision displacement sensing based on the multiple mode dip areas in a SNAP microresonator.

Whispering gallery mode (WGM) microresonators offer significant potential for precise displacement measurement owing to their compact size, ultrahigh sensitivity, and rapid response. However, conventional WGM displacement sensors are prone to noise interference, resulting in accuracy loss, while the demodulation process for displacement often exhibits prolonged duration. To address these limitations, this study proposes a rapid and high-precision displacement sensing method based on the dip areas of multiple resonant modes in a surface nanoscale axial photonics microresonator. By employing a neural network to fit the nonlinear relationship between displacement and the areas of multiple resonant dips, we achieve displacement prediction with an accuracy better than 0.03µm over a range of 200µm. In comparison to alternative sensing approaches, this method exhibits resilience to temperature variations, and its sensing performance remains comparable to that in a noise-free environment as long as the signal-to-noise ratio is greater than 25dB. Furthermore, the extraction of the dip area enables significantly enhanced speed in displacement measurement, providing an effective solution for achieving rapid and highly accurate displacement sensing.

Large-range and high-sensitivity displacement sensing based on a SNAP microresonator by multimode encoding technique

Probe-type micro-displacement sensors with a large range and high sensitivity have important applications in both aerospace and nano-lithography. However, the state-of-the-art measurement range achieved using conventional methods such as charge coupled device imaging and fiber grating demodulation is limited to only tens of micrometers. In this study, we propose and demonstrate a displacement sensing mechanism with a large range and high sensitivity for measuring linear displacements. The mechanism is based on a multimode encoding technique implemented on a surface nanoscale axial photonics (SNAP) microcavity platform. By tracking the transmittance variations of multiple axial modes and employing encoding techniques, we can determine the rough absolute position as well as the axial mode with the highest sensitivity in each region. Moreover, the selected mode for each region is exploited to accurately measure the micro-displacement with a large range and high accuracy. As a proof-of-principle experiment, the results indicate a large sensing range about 346 μm and a high sensitivity ranging up to 0.013 μm−1. Assuming that the transmittance can be resolved by 0.1%, the resolution of the measurement is about 0.1 μm.

Microresonator devices lithographically introduced at the optical fiber surface.

We present a simple lithographic method for fabrication of microresonator devices at the optical fiber surface. First, we undress the predetermined surface areas of a fiber segment from the polymer coating with a focused CO2 laser beam. Next, using the remaining coating as a mask, we etch the fiber in a hydrofluoric acid solution. Finally, we completely undress the fiber segment from coating to create a chain of silica bottle microresonators with nanoscale radius variation [surface nanoscale axial photonics (SNAP) microresonators]. We demonstrate the developed method by fabrication of a chain of five 1 mm long and 30 nm high microresonators at the surface of a 125 µm diameter optical fiber and a single 0.5 mm long and 291 nm high microresonator at the surface of a 38 µm diameter fiber. As another application, we fabricate a rectangular 5 mm long SNAP microresonator at the surface of a 38 µm diameter fiber and investigate its performance as a miniature delay line. The propagation of a 100 ps pulse with 1 ns delay, 0.035c velocity, and negligible dispersion is demonstrated. In contrast to previously developed approaches in SNAP technology, the developed method allows the introduction of much larger fiber radius variation ranging from nanoscale to microscale.

Accurate fabrication of SNAP microresonators via a femtosecond laser with multidimensional optimized parameters.

Surface nanoscale axial photonics (SNAP) microresonators with nanoscale effective radius variations (ERVs) along the optical fiber axis can be fabricated by inscribing axially oriented lines inside the fiber with a femtosecond laser. Here, we propose the multi-dimensional fabrication parameter system for the femtosecond laser fabrication of SNAP devices and systematically investigate the relationships between the introduced ERV and the multidimensionally controllable fabrication parameters. Specifically, both the qualitative and quantitative processing principles are revealed. As a proof-of-principle, by multidimensionally optimizing the fabrication parameters, we realize a SNAP microresonator with the characteristics of both small axial size and maximal ERV. The achieved ERV is almost 5 times larger than the ERV achieved with the previous unoptimized method. Our work promotes the fs laser inscription technology to be a flexible and versatile approach for fabricating the SNAP devices with ultra-high precision, ultra-low loss and high robustness.

SNAP structures fabricated by profile design of in-fiber inscribed regions with a femtosecond laser.

Fabricating a surface nanoscale axial photonics (SNAP) microresonator with a specific profile is a challenging and important issue since its advent. We propose a powerful approach for the flexible fabrication of the SNAP structures with arbitrary profiles by a femtosecond laser. Our method is to design the profile of the length distribution of the inscribed lines to match the profile of the required SNAP microresonator, and to combine it with other fabrication parameters to precisely control the radius variation of the SNAP structure. In experiments, we demonstrate the design and fabrication of the SNAP structures with the parabolic, semi-parabolic, and bat profiles. The developed approach is expected to be universal for the fabrication of complex high Q-factor SNAP structures, which lays the groundwork for exploring the versatile performances of the SNAP devices.

Efficient postprocessing technique for fabricating surface nanoscale axial photonics microresonators with subangstrom precision by femtosecond laser.

We demonstrated the subangstrom precise correction of surface nanoscale axial photonics (SNAP) micro-resonators by the femtosecond (fs) laser postprocessing technique for the first time. The internal stress can be induced by fs laser inscriptions in the fiber, causing nanoscale effective radius variation (ERV). However, the obtained ultraprecise fabrication usually undergoes multiple tries. Here, we propose a novel postprocessing technique based on the fs laser that significantly reduces the ERV errors and improves the fabrication precision without iterative corrections. The postexposure process is achieved at the original exposure locations using lower pulse energy than that in the initial fabrication process. The results show that the ERV is nearly proportional to the pulse energy of the postexposure process. The slope of the ERV versus the pulse energy is 0.07Å/nJ. The maximum of the postprocessed ERV can reach 8.0Å. The repeatability was experimentally verified by accomplishing the correction on three SNAP microresonators with the precision of 0.75Å. The developed fabrication technique with fs laser enables SNAP microresonators with new breakthrough applications for optomechanics and filters.

Tunable SNAP microresonators via internal ohmic heating

We demonstrate a thermally tunable surface nanoscale axial photonics (SNAP) platform. Stable tuning is achieved by heating a SNAP structure fabricated on the surface of a silica capillary with a metal wire positioned inside. Heating a SNAP microresonator with a uniform wire introduces uniform variation of its effective radius which results in constant shift of its resonance wavelengths. Heating with a nonuniform wire allows local nanoscale variation of the capillary effective radius, which enables differential tuning of the spectrum of SNAP structures, as well as the creation of temporary SNAP microresonators that exist only when current is applied. As an example, we fabricate two bottle microresonators coupled to each other and demonstrate differential tuning of their resonance wavelengths into and out of degeneracy with precision better than 0.2pm. The developed approach is beneficial for ultra-precise fabrication of tunable ultralow loss parity-time symmetric, optomechanical, and cavity quantum electrodynamics (QED) devices.

Fabrication of surface nanoscale axial photonics structures with a femtosecond laser.

Surface nanoscale axial photonics (SNAP) structures are fabricated with a femtosecond laser for the first time, to the best of our knowledge. The inscriptions introduced by the laser pressurize the fiber and cause its nanoscale effective radius variation. We demonstrate the subangstrom precise fabrication of individual and coupled SNAP microresonators having the effective radius variation of several nanometers. Our results pave the way to a novel ultraprecise SNAP fabrication technology based on the femtosecond laser inscription.

SNAP: Fabrication of long coupled microresonator chains with sub-angstrom precision

Based on the recently-introduced Surface Nanoscale Axial Photonics (SNAP) platform, we demonstrate a chain of 30 coupled SNAP microresonators spaced by 50 micron along an optical fiber, which is fabricated with the precision of 0.7 angstrom and a standard deviation of 0.12 angstrom in effective microresonator radius. To the best of our knowledge, this result surpasses those achieved in other super-low-loss photonic technologies developed to date by two orders of magnitude. The chain exhibits bandgaps in both the discrete and continuous spectrum in excellent agreement with theory. The developed method enables robust fabrication of SNAP devices with sub-angstrom precision.

Coupled high Q-factor surface nanoscale axial photonics (SNAP) microresonators

We experimentally demonstrate series of identical two, three, and five coupled high Q-factor surface nanoscale axial photonics (SNAP) microresonators formed by periodic nanoscale variation of the optical fiber radius. These microresonators are fabricated with a 100 μm period along an 18 μm radius optical fiber. The axial FWHM of these microresonators is 80 μm and their Q-factor exceeds 10(7). In addition, we demonstrate a SNAP microresonator with the axial FWHM as small as 30 μm and the axial FWHM of the fundamental mode as small as 10 μm. These results may potentially enable the dense integration of record low loss coupled photonic microdevices on the optical fiber platform.