Integrated chemical vapor sensor based on thin wall capillary coupled porous glass microsphere optical resonator

Abstract

a b s t r a c tA miniaturized chemical vapor sensor probe was developed using a porous glass microsphere (PGM) as the alignment-free optical microresonator. The porous microsphere was placed inside a thin wall silica capillary tube that was fusion-spliced to an optical fiber. The whispering gallery modes (WGMs) of the microsphere were excited by the evanescent field of the light propagating inside the capillary thin wall. Adsorption of chemical vapor molecules into the pores led to a refractive index change of the PGM and thus the resonance wavelength shift of the WGMs. To facilitate the in-taking of chemical vapor molecules into the PGM, a micro window was opened at the backend of the capillary tube using femtosecond laser micromachining. Ethanol vapor was used to demonstrate the probe for chemical vapor sensing. With a miniaturized size, integrated structure and reflection mode of operation, the proposed probe may find useful in many practical applications such as environmental monitoring and biomedical sensing.

Applications of Optical Microcavity Resonators in Analytical Chemistry

“…Many early resonator geometries were simple structures such as spheres (16, 20, 30–33), toroids (17, 34), discs (19, 35–37), and rings (38–40). More recently, geometries including tubes (41–43), capillaries (44–48), bubbles (49), and knots (50) have also found utility. Figure 2 provides an overview of established sensor geometries.…”

“…Baseline separation of five volatile organic compounds (VOCs) was achieved in less than 2 min with a detection limit <100 ng. In addition to capillary-and ring-based gas detection systems, porous glass microspheres are also promising for gas detection applications (43). …”

Whispering Gallery Mode Optical Microresonators: Structures and Sensing Applications

“…first proposed a thin‐walled capillary coupler with optical fiber tail. The coupler operated in reflective mode and provided robust mechanical support for the microsphere resonator, as shown in Figure a . Then in 2015, members of the group proposed a porous chemical vapor sensor probe glass microsphere (PGM) resonator to detect the concentration of ethanol vapor, and it had a detection limit of about 20 ppm, as shown in Figure b .…”

“…a) Microscopic image of different fabrication steps of fiber‐like thin‐walled capillary coupler. Reproduced with permission . Copyright 2015, Elsevier B.V. b) Schematic and microscopic images of porous glass microresonator.…”

Whispering-Gallery Mode Resonators for Detecting Cancer

“…Optical resonator types are defined by their geometries and materials. The examples of geometries range from the heavily used mirroring [ 37 , 67 , 80 , 81 , 82 ] to microspheres [ 27 , 83 , 84 , 85 ], microgoblets [ 86 ], disks [ 21 , 80 , 87 ], microbubbles [ 88 , 89 ], microtoroids [ 90 ], and bottles [ 20 ]. Resonators generally utilize dielectric material.…”