Tong Lin

On-chip integrated optofluidic complex refractive index sensing using silicon photonic crystal nanobeam cavities

Complex refractive index sensing is proposed and experimentally demonstrated in optofluidic sensors based on silicon photonic crystal nanobeam cavities. The sensitivities are 58 and 139 nm/RIU, respectively, for the real part (n) and the imaginary part (κ) of the complex refractive index, and the corresponding detection limits are 1.8×10(-5) RIU for n and 4.1×10(-6) RIU for κ. Moreover, the capability of the complex refractive index sensing method to detect the concentration composition of the ternary mixture is demonstrated without the surface immobilization of functional groups, which is impossible to realize with the conventional refractive index sensing scheme.

Dynamic control of the asymmetric Fano resonance in side-coupled Fabry–Pérot and photonic crystal nanobeam cavities

Fano resonance is a prevailing interference phenomenon that stems from the intersection between discrete and continuum states in many fields. We theoretically and experimentally characterize the asymmetric Fano lineshape in side-coupled waveguide Fabry–Perot and photonic crystal nanobeam cavities. The measured quality-factor of the Fano resonance before tuning is 28 100. A nanoelectromechanical systems bidirectional actuator is integrated seamlessly to control the shape of the Fano resonance through in-plane translations in two directions without sacrificing the quality-factor. The peak intensity level of the Fano resonance can be increased by 8.5 dB from 60 nW to 409 nW while the corresponding dip intensity is increased by 12.8 dB from 1 nW to 18 nW. The maximum recorded quality-factor throughout the tuning procedure is up to 32 500. Potential applications of the proposed structure include enhancing the sensitivity of sensing, reconfigurable nanophotonics devices, and on-chip intensity modulator.

Design of mechanically-tunable photonic crystal split-beam nanocavity

Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We have proposed and experimentally demonstrated a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical-quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm that provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75-nm air gap. Experimental results emphasize that the quality factor of the second-order TE mode can be as high as 1.99×10(4). Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator, and the quality factor maintains quite well even if there is a lateral offset up to 64 nm. Potentially promising applications, such as sensitive optomechanical torque sensor, local tuning of Fano resonance, all-optical-reconfigurable filters, etc., are foreseen.

Out-of-plane nano-electro-mechanical tuning of the Fano resonance in photonic crystal split-beam nanocavity

We propose and experimentally demonstrate the use of Fano resonance as a means to improve the Quality factor of photonic crystal split-beam nanocavities. The Fano resonance is triggered by the interference between the second-order quasi-transverse electric resonant mode and the leaky high-order quasi-transverse electric propagation mode of the optimized photonic crystal split-beam nanocavity. Compared with a similar photonic crystal split-beam nanocavity without asymmetric Fano lineshape, the Q-factor is increased up to 3-fold: from 1.99×104 to  5.95×104. Additionally, out-of-plane tuning of the Fano resonance is investigated by means of a Nano-Electro-Mechanical Systems based actuator. The maximum centre wavelength shift of the Fano resonance reached 116.69 pm, which is more than 4.5 times the original quasi-Full Width at Half Magnitude.

Hybrid Photonic Cavity with Metal-Organic Framework Coatings for the Ultra-Sensitive Detection of Volatile Organic Compounds with High Immunity to Humidity

Detection of volatile organic compounds (VOCs) at parts-per-billion (ppb) level is one of the most challenging tasks for miniature gas sensors because of the high requirement on sensitivity and the possible interference from moisture. Herein, for the first time, we present a novel platform based on a hybrid photonic cavity with metal-organic framework (MOF) coatings for VOCs detection. We have fabricated a compact gas sensor with detection limitation ranging from 29 to 99 ppb for various VOCs including styrene, toluene, benzene, propylene and methanol. Compared to the photonic cavity without coating, the MOF-coated solution exhibits a sensitivity enhancement factor up to 1000. The present results have demonstrated great potential of MOF-coated photonic resonators in miniaturized gas sensing applications.

Development of Miniature Camera Module Integrated With Solid Tunable Lens Driven by MEMS-Thermal Actuator

The design, fabrication, assembly, and characterization of a miniature adjustable-focus camera module driven by MEMS-thermal actuators are presented. The camera module consists of one solid tunable lens for optical power variation, two identical MEMS-thermal actuators integrated with displacement amplifiers for lens element driving, a CMOS image sensor for recording, and necessary CNC fabricated components for supporting and housing. Fully 3D-multiphysics simulations with valid material properties are performed to explore the design and, hence, optimize the performance of the system. In this paper, the fabricated MEMS-devices are clearly demonstrated, and followed by the detailed characterization of the camera module. Static characterizations of the system, including the temperature distribution on actuators, electric resistance change with temperature increase, displacement-voltage curve of actuator, and the focal length tuning capability, are tested. Dynamic response speed and imaging performance of the camera module are also covered. Results show that the designed MEMS actuator is able to provide a maximum output displacement of 135

Novel one-dimensional photonic crystal air-slotted nanobeam cavity for gas sensing

\mu \text{m}

Mode competition and hopping in optomechanical nano-oscillators

when a 10 V driving voltage is applied. Driven by the thermal actuator, the solid tunable lens presents a repeatable focal length tuning from 9.2 to 7.9 mm with precise focus control. The adjustable-focus capability of the miniature camera module is experimentally demonstrated by clearly focusing targets placed at different object distances. [2016-0072]

Alignment-mechanism design for solid tunable lenses based on Alvarez principle

We have designed a novel photonic crystal air-slotted nanobeam cavity featuring high quality factor and small mode volume. The calculated high sensitivity and response factor pave the way for precise ambient gas sensing.

Miniature electrically tunable rotary dual-focus lenses

We investigate the inter-mode nonlinear interaction in the multi-mode optomechanical nano-oscillator which consists of coupled silicon nanocantilevers, where the integrated photonic crystal nanocavities provide the coupling between the optical and mechanical modes. Due to the self-saturation and cross-saturation of the mechanical gain, the inter-mode competition is observed, which leads to the bistable operation of the optomechanical nano-oscillator: only one of the mechanical modes can oscillate at any one time, and the oscillation of one mode extremely suppresses that of the other with a side mode suppression ratio (SMSR) up to 40 dB. In the meantime, mode hopping, i.e., the optomechanical oscillation switches from one mode to the other, is also observed and found to be able to be provoked by excitation laser fluctuations.