Application Gallery

In modern biosensing technologies, sensors based on optical resonant structures have attracted considerable attention due to their high sensitivity and label-free detection capability. As a representative nanoscale photonic element, resonant grating structures enable high-precision sensing by monitoring shifts in the resonance peaks of their reflection or transmission spectra in response to subtle variations in the surrounding refractive index. This property makes them highly attractive for applications in biomolecular recognition, environmental monitoring, and medical diagnostics. In this case study, following the work of *Cunningham et al.[^1]*, a representative resonant biosensor grating is modeled and simulated, and its optical response characteristics are analyzed.

Integrated photonics has become a key enabling technology in areas such as optical communications, sensing, and signal processing. Among various photonic devices, microring resonators are widely used in applications such as filtering, modulation, and nonlinear optics due to their compact footprint, high quality factor, and excellent wavelength-selective properties. In this case, we design and simulate a microring resonator with a center wavelength of 1.55 um and a free spectral range (FSR) of 3200 GHz.

Optical microcavities based on optical waveguides typically have a high quality factor and can be applied in various fields such as optical filters, lasers, and modulators. This case aims to analyze the resonance spectrum of a 1D Bragg grating microcavity based on an optical waveguide. Using the FDTD method, the resonant frequencies and quality factor Q are calculated too. By increasing the dimensions of the central structure of the Bragg grating, a defect is introduced that enables the occurrence of transmission resonance within the stopband of the Bragg structure.

The whispering gallery modes of a microdisk use the total internal reflection (TIR) of light to confine the light within the microdisk to achieve light enhancement. The whispering gallery mode of a microdisk has a high quality factor and a small mode volume, so it is a frontier and popular field of current optical research. In this case, we hope to find the first- and second-order whispering gallery modes of GaN cylinders.

Generally, in the simulation of high-Q resonant cavities, the field amplitude obtained is inaccurate. The reason is that the loss rate in the high-Q resonant cavity is slow. If the simulation time is not long enough, the field in the cavity will not decay to 0 at the end of the simulation. At this time, the amplitude of the mode field in the cavity needs to be corrected to obtain the final actual amplitude. This case constructs a photonic crystal resonant cavity structure to demonstrate how to correct the field amplitude when the simulation time of a high-Q resonant cavity is insufficient.