arXiv subjects

Ni Yao

Publications and source records attributed to Ni Yao.

24 records · Page 2Linked to original sources

arXiv2020

Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber

A lithium niobate on insulator ridge waveguide allows constructing high-density photonic integrated circuits thanks to its small bending radius offered by the high index contrast. Meanwhile, the significant mode-field mismatch between an optical fiber and the single-mode lithium niobate waveguide leads to low coupling efficiencies. Here, we demonstrate, both numerically and experimentally, that the problem can be solved with a tapered single mode fiber of an optimized mode field profile. Numerical simulation shows that the minimum coupling losses for the TE and TM mode are 0.32 dB and 0.86 dB, respectively. Experimentally, though without anti-reflection coating, the measured coupling losses for TE and TM mode are 1.32 dB and 1.88 dB, respectively. Our technique paves a way for a broad range of on-chip lithium niobate applications.

physics.optics↗

arXiv2018

Enhancement of the Monolayer WS2 Exciton Photoluminescence with a 2D-Material/Air/GaP In-Plane Microcavity

Light-matter interaction with two-dimensional materials gained significant attention in recent years leading to the reporting of weak and strong coupling regimes, and effective nano-laser operation with various structures. Particularly, future applications involving monolayer materials in waveguide-coupled on-chip integrated circuitry and valleytronic nanophotonics require controlling, directing and optimizing photoluminescence. In this context, photoluminescence enhancement from monolayer transition-metal dichalcogenides on patterned semiconducting substrates becomes attractive. It is demonstrated in our work using focussed-ion-beam-etched GaP and monolayer WS2 suspended on hexagonal-BN buffer sheets. We present a unique optical microcavity approach capable of both efficient in-plane and out-of-plane confinement of light, which results in a WS2 photoluminescence enhancement by a factor of 10 compared to the unstructured substrate at room temperature. The key concept is the combination of interference effects in both the horizontal direction using a bull's-eye-shaped circular Bragg grating and in vertical direction by means of a multiple reflection model with optimized etch depth of circular air-GaP structures for maximum constructive interference effects of the applied pump and expected emission light.

physics.app-ph↗

arXiv2018

Ultrasensitive hybrid optical skin

Electronic skin, a class of wearable electronic sensors that mimic the functionalities of human skin, has made remarkable success in applications including health monitoring, human-machine interaction and electronic-biological interfaces. While electronic skin continues to achieve higher sensitivity and faster response, its ultimate performance is fundamentally limited by the nature of low-frequency AC currents in electronic circuitries. Here we demonstrate highly sensitive optical skin (O-skin) in which the primary sensory elements are optically driven. The simple construction of the sensors is achieved by embedding glass micro/nanofibers (MNFs) in thin layers of polydimethylsiloxane (PDMS). Enabled by the highly sensitive power-leakage response of the guided modes from the MNF upon external stimuli, our optical sensors show ultrahigh sensitivity (1870/kPa), low detection limit (7 mPa) and fast response (10 microseconds) for pressure sensing, significantly exceeding the performance metrics of state-of-the-art electronic skins. Electromagnetic interference (EMI)-free detection of high-frequency vibrations, wrist pulse and human voice are realized. Moreover, a five-sensor optical data glove and a 2x2-MNF tactile sensor are demonstrated. Our results pave the way toward wearable optical devices ranging from ultrasensitive flexible sensors to optical skins.

physics.app-ph↗

arXiv2018

Lithium niobate micro-disk resonators of quality factors above 10^7

We report on fabrication of crystalline lithium niobate microresonators with quality factors above 10^7 as measured around 770 nm wavelength. Our technique relies on femtosecond laser micromachining for patterning a mask coated on the lithium niobate on insulate (LNOI) into a microdisk, followed by a chemo-mechanical polishing process for transferring the disk-shaped pattern to the LNOI. Nonlinear processes including second harmonic generation and Raman scattering have been demonstrated in the fabricated microdisk.

physics.app-ph↗

arXiv2018

Simultaneous generation of four-wave mixing and stimulated Raman scattering in coupled lithium niobate microdisks mediated by second harmonic generation

High quality lithium niobate thin film microresonators provide an ideal platform for on-chip nonlinear optics applications. However, the phase matching condition for efficient parametric process sets a high requirement for fabrication control. Here we demonstrate a photonic molecular structure composed of two strongly coupled lithium niobate microdisks of different diameters fabricated using femtosecond laser micromachining and focused ion beam milling. With a continuous wave excitation, rich nonlinear optical processes including cascaded four-wave mixing and stimulated Raman scattering were observed around the second harmonic wavelength. Our results indicate that the coupled microdisks form a superior system for nonlinear optical process.

physics.optics↗

arXiv2017

Fabrication of high quality factor lithium niobate double-disk using a femtosecond laser

We demonstrate fabrication of a high quality factor lithium niobate double-disk whispering-gallery microcavity using femtosecond laser assisted ion beam milling. Using this method, two vertically stacked 30-um-diameter disks with a 200-nm-gap are fabricated. With our device, an optical quality factor as high as 1.2*10^5 is demonstrated. Our approach is scalable to fabricate multiple disks on a single chip.

physics.app-ph↗