Air and dielectric bands photonic crystal microringresonator for refractive index sensing

On-chip simultaneous measurement of humidity and temperature using cascaded photonic crystal microring resonators with error correction

We present the design, fabrication, and characterization of cascaded silicon-on-insulator photonic crystal microring resonators (PhCMRRs) for dual-parameter sensing based on a multiple resonances multiple modes (MRMM) technique. Benefitting from the slow-light effect, the engineered PhCMRRs exhibit unique optical field distributions with different sensitivities via the excitation of dielectric and air modes. The multiple resonances of two distinct modes offer new possibilities for enriching the sensing receptors with additional information about environmental changes while preserving all essential properties of traditional microring resonator based sensors. As a proof of concept, we demonstrate the feasibility of extracting humidity and temperature responses simultaneously with a single spectrum measurement by employing polymethyl methacrylate as the hydrophilic coating, obtaining a relative humidity (RH) sensitivity of 3.36 pm/%RH, 5.57 pm/%RH and a temperature sensitivity of 85.9 pm/°C, 67.1 pm/°C for selected dielectric mode and air mode, respectively. Moreover, the MRMM enriched data further forges the capability to perform mutual cancellation of the measurement error, which improves the sensing performance reflected by the coefficient of determination (R²-value), calculated as 0.97 and 0.99 for RH and temperature sensing results, respectively.

Compact Slot Microring Resonator for Sensitive and Label-Free Optical Sensing

A novel all-pass slot microring resonator (SMRR), intended for label-free optical biosensing based on silicon-on-insulator platforms, is proposed. The sensor consists of a bent asymmetric directional coupler and an asymmetric-slot microring waveguide. The appropriate slot width of 140 nm is identified by the three-dimensional finite-difference time-domain (3D-FDTD) method for better light-matter interaction in applications. According to numerical calculations, the SMRR sensor with a footprint of 10 µm × 10 µm has a concentration sensitivity of 725.71 pm/% for sodium chloride (NaCl) solutions. The corresponding refractive index sensitivity is 403 nm/RIU (refractive index unit), which is approximately six times greater than that of traditional microring resonator sensors. A low detection limit of 0.129% is also achieved. This SMRR is an excellent candidate for label-free optical biosensors due to its compact structure and excellent sensing capability.

Controlling of spatial modes in multi-mode photonic crystal nanobeam cavity

We numerically and experimentally present the characteristics of disturbed spatial modes (air mode and dielectric mode) in multi-mode photonic crystal nanobeam cavity (PCNC) in the mid-infrared wavelength range. The results show that the resonance wavelength of the spatial modes can be controlled by modifying the size, period and position of the central periodical mirrors in PCNC, achieving better utilization of the spectrum resource. Additionally, side coupling characteristics of PCNC supporting both air and dielectric modes are investigated for the first time. This work serves as a proof of design method that the spatial modes can be controlled flexibly in PCNC, paving the way to achieve integrated multi-function devices in a limited spectrum range.

Nanorod photonic crystal ring resonators

In this study, we shed light on the properties of a photonic ring resonator made up of a closed array of circular dielectric nanorods arranged periodically in a background material. This type of resonator can reach high-quality factors (Q-factor) for specific transverse-magnetic (TM)-like modes, while maintaining a small footprint. We validate this by full 3D finite difference time domain simulations. The properties of the mode most interesting for applications are determined for various parameters of the resonator for the material parameters of GaN. This study provides design guidelines for the realization of this type of photonic nano-resonator and proposes and analyses two practical implementations.

Photonic crystal microring resonator for label-free biosensing

A label-free optical biosensor based on a one-dimensional photonic crystal microring resonator with enhanced light-matter interaction is demonstrated. More than a 2-fold improvement in volumetric and surface sensing sensitivity is achieved compared to conventional microring sensors. The experimental bulk detection sensitivity is ~248nm/RIU and label-free detection of DNA and proteins is reported at the nanomolar scale. With a minimum feature size greater than 100nm, the photonic crystal microring resonator biosensor can be fabricated with the same standard lithographic techniques used to mass fabricate conventional microring resonators.

Slow light in mass-produced, dispersion-engineered photonic crystal ring resonators

We present experimental results of photonic crystal ring resonators (PhCRRs) fabricated on the CMOS-compatible, silicon-on-insulator platform via 193-nm deep-UV lithography. Our dispersion-engineering design approach is compared to experimental results, showing very good agreement between theory and measurements. Specifically, we report a mean photonic band-edge wavelength of 1546.2 ± 5.8 nm, a 0.2% variation from our targeted band-edge wavelength of 1550 nm. Methods for the direct calculation of the experimental, discrete dispersion relation and extraction of intrinsic quality factors for a highly-dispersive resonator are discussed. A maximum intrinsic quality factor of ≈83,800 is reported, substantiating our design method and indicating that high-throughput optical lithography is a viable candidate for PhCRR fabrication. Finally, through comparison of the mean intrinsic quality and slowdown factors of the PhCRRs and standard ring resonators, we present evidence of an increase in light-matter interaction strength with simultaneous preservation of microcavity lifetimes.

Hybrid plasmonic–photonic whispering gallery mode resonators for sensing: a critical review

In this review we present the state of the art and the most recent advances in the field of optical sensing with hybrid plasmonic–photonic whispering gallery mode (WGM) resonators.