Photonic crystal self-collimation sensor

Application of photonic-crystal-based nonlinear ring resonators for realizing an all-optical comparator

Optical comparators can play crucial roles in the all-optical digital circuits required for optical calculation and optical processing. A typical digital comparator is a logic circuit that can compare two binary codes and show the results by activating one of its three output ports. In this paper, a photonic crystal (PhC)-based structure was proposed for designing a 1-bit all-optical comparator. The proposed structure was designed using nonlinear ring resonators inside PhCs. Optical intensity of ${1}\,\,{\rm W/}\unicode{x00B5} {{\rm m}^2}$1W/µm² at the input ports is required for the proper operation of the proposed structure. For the final structure, the maximum rise time obtained was about 4 ps.

Applications and developments of on-chip biochemical sensors based on optofluidic photonic crystal cavities

Photonic crystal (PC) cavities, which possess the advantages of compactness, flexible design, and suitability for integration in a lab-on-a-chip system, are able to distinguish slight variations in refractive index with only a small amount of analyte. Combined with the newly proposed optofluidic technology, PC-cavity devices stimulate an emerging class of miniaturized and label-free biochemical sensors. In this review, an overview of optofluidic PC cavities based biochemical sensors is presented. First, the basic properties of the PC, as well as the sensing principle of the PC cavity, are discussed. Second, the applications of the sensors in detecting gas, liquid, and biomolecule concentrations are reviewed, with a focus on their structures, sensing principles, sensing properties, advantages, and disadvantages. Finally, the current challenges and future development directions of optofluidic PC-cavity-based biochemical sensors are discussed.

Higher Q factor and higher extinction ratio with lower detection limit photonic crystal-parallel-integrated sensor array for on-chip optical multiplexing sensing

We introduce an alternative method to establish a nanoscale sensor array based on a photonic crystal (PhC) slab, which is referred to as a 1×4 monolithic PhC parallel-integrated sensor array (PhC-PISA). To realize this function, four lattice-shifted resonant cavities are butt-coupled to four output waveguide branches, respectively. By shifting the first to the two closest neighboring holes around the defect, a high Q factor over 1.5×10⁴ has been obtained. Owing to the slightly different cavity spacing, each PhC resonator shows an independent resonant peak shift as the refractive index changes surrounding the resonant cavity. The specific single peak with a well-defined extinction ratio exceeds 25 dB. By applying the finite-difference time-domain (FDTD) method, we demonstrate that the sensitivities of each sensor in PhC-PISA S₁=60.500  nm/RIU, S₂=59.623  nm/RIU, S₃=62.500  nm/RIU, and S₄=51.142  nm/RIU (refractive index unit) are achieved, respectively. In addition, the negligible crosstalk and detection limit as small as 1×10^-4 have been observed. The proposed sensor array as a desirable platform has great potential to realize optical multiplexing sensing and high-density monolithic integration.

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.

Experimentally simulating quantum walks with self-collimated light

In self-collimated photonic crystal, periodically arranged air holes of sub-wavelength scale provide flattened equi-frequency curves perpendicular to the ΓM direction, which allow light or photons propagating in a quasi-uniform medium without diffraction. Here we for the first time experimentally simulate four-step single-photon discrete time quantum walks with classical light in such a photonic crystal chip fabricated on silicon-on-insulator. Similarities between theoretical expectations and experimental results are higher than 0.98. The functional area is compact and can be extended to construct more complicated linear quantum circuits.

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 planar self-collimating photonic crystals

Self-collimation in photonic crystals has received a lot of attention in the literature, partly due to recent interest in silicon photonics, yet no performance metrics have been proposed. This paper proposes a figure of merit (FOM) for self-collimation and outlines a methodical approach for calculating it. Performance metrics include bandwidth, angular acceptance, strength, and an overall FOM. Two key contributions of this work include the performance metrics and identifying that the optimum frequency for self-collimation is not at the inflection point. The FOM is used to optimize a planar photonic crystal composed of a square array of cylinders. Conclusions are drawn about how the refractive indices and fill fraction of the lattice impact each of the performance metrics. The optimization is demonstrated by simulating two spatially variant self-collimating photonic crystals, where one has a high FOM and the other has a low FOM. This work gives optical designers tremendous insight into how to design and optimize robust self-collimating photonic crystals, which promises many applications in silicon photonics and integrated optics.

Lateral cavity photonic crystal surface emitting laser based on commercial epitaxial wafer

A lateral cavity photonic crystal surface emitting laser (LC-PCSEL) with airholes of cone-like shape etched near to the active layer is fabricated. It employs only a simple commercial epitaxial wafer without DBR and needs no wafer bonding technique. Surface emitting lasing action at 1575 nm with power of 1.8 mW is observed at room temperature, providing potential values for mass production of electrically driven PCSELs with low cost. Additionally, Fano resonance is utilized to analyze aperture equivalence of PC, and energy distribution in simplified laser structure is simulated to show oscillation and transmission characteristics of laser.