We designed a new type of gas sensor, an optical tentacle, made of highly integrated polymer micro-ring resonators in three-dimensional space on the tiny end-facet of a multicore optical fiber. Two pairs of three polymer micro-ring resonators were hung symmetrically on both sides of three suspended micro-waveguides as the sensing units. The micro-waveguides interlace to form a three-layer nested configuration, which makes the multicore optical fiber a “tentacle” for vapors of volatile organic compounds. Both experiments and theoretical simulation confirmed that the symmetrical coupling of multiple pairs of rings with the micro-waveguide had better resonance than the single ring setup. This is because the symmetrical light modes in the waveguides couple with the rings separately. All the optical micro-components were fabricated by the two-photon lithography technology on the end facet of multicore optical fiber. The optical tentacle shows good sensitivity and reversibility. This approach can also be adopted for sensor array design on a chip. Furthermore, optical sensors that can sense vapors with multiple constituents may be achieved in the future by adding selective sensitive materials to or on the surface of the rings.
The potential of whispering-gallery-modes (WGMs) microcavities in sensing applications has been being released continuously with improvements from various aspects. Introducing smart materials and structures into the WGMs microcavities based sensing systems are an effective approach to promote their applications in real world. Here, we propose a smart grating as the coupling setup to a WGMs microcavity of polystyrene microsphere to enhance the responses to chemical and thermal stimulations. The changes of the coupling distance due to the deformation of the smart grating induce additional increments to the intrinsic wavelength shifts of the WGMs of the microcavity, which is proved to be the mechanism of the response enhancements. We use two-photon lithography based “lab on fiber” technology to realize the device and the demonstration of the response enhancements. Our results may be of great significance to the design of the WGMs microcavity based chemical and temperature sensors.
We designed and fabricated photonic molecules on the tiny end facet of a multicore optical fiber. The photonic molecules are three pairs of coupled polymer micro-ring resonators, which are stacked on the fiber in three layers. The normal mode splitting of the photonic molecules is simulated and observed experimentally. It is shown that if the absorption of vapors causes both the radii and refractive index changes of the rings, the two branches of the split resonant modes show different wavelength shifts. The photonic molecules were fabricated by the two-photon lithography technology and show good sensitivity to various organic vapors.
There is limited knowledge on the evolution of physical and chemical parameters near the surface of polymer materials at the microscopic level during glass transition, owing to the complexity of this process. For example, the distribution and evolution of the refractive index near the surface of polymer materials during glass transition are thus far unknown; however, this information is necessary for the design of optical micro‐elements based on polymer materials. Herein, a strategy is proposed to achieve the expression of the refractive index as a function of depth and temperature inside a polystyrene microsphere. The difference in the wavelength shifts between two whispering gallery modes with different radial orders is employed to detect the evolution of the refractive index during the glass transition. A model is established based on experimental observations and further confirmed by numerical simulations. It is believed that the results obtained can assist with the design of polymer optical micro‐elements and systems as well as sensing applications of whispering gallery microcavities.
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