Lijun Huang

Refractive index sensing utilizing parallel tapered nano-slotted photonic crystal nano-beam cavities

We demonstrate refractive index sensing using parallel tapered nano-slotted photonic-crystal nano-beam cavities with three-dimensional (3D) finite-difference time-domain (3D-FDTD) simulation. The electric field of the cavity mode is strongly concentrated in the slot region leading to a large light–matter overlap, which is expected to add a significant contribution to sensitivity, and thus we present high refractive-index sensitivity of more than 600  nm/refractive index units. Additionally, the quality (Q)-factor in the proposed design is theoretically investigated, and through tapering the diameter of the pores outside the Bragg mirrors in nano-beam cavities and the width of the adjacent nano-slots, an optimal Q-factor of 11770 is obtained. A high figure of merit (FOM=4637) of the designed model has been obtained. We anticipate that this geometry is potentially an ideal platform for refractive-index based bio-sensing.

Design Low Crosstalk Ring-Slot Array Structure for Label-Free Multiplexed Sensing

We theoretically demonstrate a low crosstalk ring-slot array structure used for label-free multiplexed sensing. The proposed sensors array is based on an array of three ring-slot and input/output line defect coupling waveguides. Each ring-slot cavity has slightly different cavity spacing and different resonant frequency. Results obtained using two dimensional finite-difference time-domain (2D-FDTD) simulation indicate that the resonant frequencies of each sensor unit in response to the refractive index variations are independent. The refractive index sensitivity is 134 ∼ 145.5 nm/RIU (refractive index unit) and the Q factors more than 104 can be achieved. The calculated detect limit lower than 1.13 × 10−4 RIU is obtained. In addition, an extremely small crosstalk lower than −25.8 dB is achieved among the array of three ring-slot cavities. The results demonstrate that this multiplexed sensor array is a promising platform for integrated optical devices and enables highly parallel label-free detection.

Optimization of One Dimensional Photonic Crystal Elliptical-Hole Low-Index Mode Nanobeam Cavities for On-Chip Sensing

We report the design of one dimensional photonic crystal nanobeam cavities with elliptical holes that is fully encapsulated in the water environment and can confine the light in the low index region. The proposed structure, based on the principle of gentle confinement of the electromagnetic field, is designed by tapering the width of the host photonic crystal waveguide away from the center of the cavity while keeping other parameters constant. With elliptical-hole low-index mode nanobeam cavities and tapered waveguide widths, through three dimensional finite-difference time-domain simulations, large band-gap and high reflectivity are achieved to confine the optical mode. Also, the electric field is confined in the elliptical holes, which helps to enhance the sensitivity. The simulation results demonstrate that we achieve the highest quality factor of 1.35 × 105 when 15 taper segments and 15 additional mirror segments are placed on both sides of the host waveguide. A sensitivity of 390 nm/RIU (refractive index unit) and mode volume of 2.23 (λres/nsi)3 are achieved in the water environment, thus showing exceptionally good on-chip sensing properties with respect to high sensitivity, small footprints and masses.

Multiplexed Simultaneous High Sensitivity Sensors with High-Order Mode Based on the Integration of Photonic Crystal 1 × 3 Beam Splitter and Three Different Single-Slot PCNCs

We simulated an efficient method for the sensor array of high-sensitivity single-slot photonic crystal nanobeam cavities (PCNCs) on a silicon platform. With the combination of a well-designed photonic crystal waveguide (PhCW) filter and an elaborate single-slot PCNC, a specific high-order resonant mode was filtered for sensing. A 1 × 3 beam splitter carefully established was implemented to split channels and integrate three sensors to realize microarrays. By applying the three-dimensional finite-difference-time-domain (3D-FDTD) method, the sensitivities calculated were S1 = 492 nm/RIU, S2 = 244 nm/RIU, and S3 = 552 nm/RIU, respectively. To the best of our knowledge, this is the first multiplexing design in which each sensor cite features such a high sensitivity simultaneously.

A potential candidate design for nanosecond-order delay based on high-group index four rows optimized air holes line-defect photonic crystal waveguide

Abstract In order to meet the demand of ultra-high optical delay within a limited transmission distance, a high-group index line-defect photonic crystal waveguide (PCW) is designed. By adjusting the parameters of holes adjacent to the defect, a high constant group index about 680 and the corresponding flat bandwidth approximately 0.4 nm are obtained. Group velocity dispersion in the flat-band slow light region is in the order of 109 ps2/km, which is non-negligible. Thus, the pulse broadening caused by dispersion that limits the transmission distance of the pulse in PCW is evaluated through broaden factor (BF). Considering the limitation of BF, a highest time delay up to 70.9 ps for 24 μm delay line is obtained. Assuming return-to-zero modulation format, the above optimized delay line supports a bit rate of the signal up to 12.9 bit/s. The study provides an important approach for realizing large time delay with small size using line-defect PCW.

Double-layered photonic crystal slabs with guided-mode resonance as a high-sensitivity biosensor and application for single nanoparticle detection

Double-layered guided-mode resonance (GMR) biosensor is designed to achieve an ultra-high sensitivity of 937.64 nm/RIU based on photonic crystal slabs. In addition, we demonstrate a theoretical study of such high-performance sensor for single nanoparticle detection.