Functional lasing microcapillaries for surface-specific sensing

Dual-parameter sensing of refractive index and pressure by dual-polarization microresonators

We propose a dual-polarization microring resonator that can simultaneously measure refractive index and pressure. Since the transverse electric (TE) mode and the transverse magnetic (TM) mode of a silicon waveguide have different energy distributions, TE and TM polarization have significant differences in sensitivity to environmental refractive index and pressure changes. Different responses to external refractive index and pressure changes can be obtained by simultaneously exciting TE and TM modes in a microring resonator. The refractive index sensitivities obtained in the experiment were 132.97 and 40.54 nm/RIU; the pressure sensitivities were 1.41 and 1.59 pm/KPa, respectively. By inversion of the second-order sensitivity matrix, it is verified that the effective refractive index and pressure response can be obtained simultaneously through a single measurement to realize the dual-parameter sensing of the surrounding refractive index and the pressure of the device structure.

Coexistence of transmission mechanisms for independent multi-parameter sensing in a silica capillary-based cascaded structure

The coexistence of transmission mechanisms, including Fabry-Perot (FP), Mach-Zehnder (MZ), and anti-resonant (AR), is demonstrated via a silica capillary-based cascaded structure. The analysis for MZ shows that one pathway is formed by the beam refracted into the silica capillary cladding from the air core, rather than being transmitted into the cladding directly at the splicing interface. Using the ray optics method, the two coexistence conditions are derived for FP and MZ, and for FP, MZ and AR, respectively. The existence percentages of the three mechanisms can be obtained using the fast Fourier transform. Finally, the coexistence of multiple transmission mechanisms is applied for independent multi-parameter sensing with the FP-based temperature sensitivity of 10.0 pm/°C and AR-based strain sensitivity of 1.33 nm/N. The third mechanism MZ interference can assist in verifying changes in both the temperature and axial strain. This shows the possibility to optimize the transmission spectra for independent multi-parameter sensing by tailoring the existence percentages of different mechanisms.

Hyperboloid-Drum Microdisk Laser Biosensors for Ultrasensitive Detection of Human IgG

Whispering gallery mode (WGM) microresonators have been used as optical sensors in fundamental research and practical applications. The majority of WGM sensors are passive resonators that require complex systems, thereby limiting their practicality. Active resonators enable the remote excitation and collection of WGM-modulated fluorescence spectra, without requiring complex systems, and can be used as alternatives to passive microresonators. This paper demonstrates an active microresonator, which is a microdisk laser in a hyperboloid-drum (HD) shape. The HD microdisk lasers are a combination of a rhodamine B-doped photoresist and a silica microdisk. These HD microdisk lasers can be utilized for the detection of label-free biomolecules. The biomolecule concentration can be as low as 1 ag mL^-1 , whereas the theoretical detection limit of the biosensor for human IgG in phosphate buffer saline is 9 ag mL^-1 (0.06 a_M ). Additionally, the biosensors are able to detect biomolecules in an artificial serum, with a theoretical detection limit of 9 ag mL^-1 (0.06 a_M ). These results are approximately four orders of magnitude more sensitive than those for the typical active WGM biosensors. The proposed HD microdisk laser biosensors show enormous detection potential for biomarkers in protein secretions or body fluids.