Abstract
Flexible epoxy waveguide Bragg gratings are fabricated on a low-modulus TPX™ polymethylpentene polyolefin substrate for an easy to manufacture and low-cost optomechanical sensor pad providing exceedingly multipurpose application potentials. Rectangular EpoCore negative resist strip waveguides are formed employing standard UV mask lithography. Highly persistent Bragg gratings are inscribed directly into the channel waveguides by permanently modifying the local refractive indices through a well-defined KrF excimer laser irradiated +1/-1 order phase mask. The reproducible and vastly versatile sensing capabilities of this easy-to-apply optomechanical sensor pad are demonstrated in the form of an optical pickup for acoustic instruments, a broadband optical accelerometer, and a biomedical vital sign sensor monitoring both respiration and pulse at the same time.
Highlights
Optical sensor principles continuously gain increasing interest in mechanical sensing applications since they feature inherent electromagnetic immunity in harsh environments as well as precise, multipurpose, and multiplexing measurement capabilities [1,2,3,4]
The reproducible and vastly versatile sensing capabilities of this easy-to-apply optomechanical sensor pad are demonstrated in the form of an optical pickup for acoustic instruments, a broadband optical accelerometer, and a biomedical vital sign sensor monitoring both respiration and pulse at the same time
Optical sensor technology based on Bragg gratings (BGs) is an ever-growing, popular, and robust tool of choice for various mechanical sensing tasks such as long-term structural health monitoring in general [5,6,7], strain sensing of composite materials in particular [8,9], and even biomedical vital sign monitoring [10,11,12]
Summary
Optical sensor principles continuously gain increasing interest in mechanical sensing applications since they feature inherent electromagnetic immunity in harsh environments as well as precise, multipurpose, and multiplexing measurement capabilities [1,2,3,4]. An elementary Bragg grating comprises a periodic refractive index (RI) modulation inside an optical waveguide core. The narrow-band reflection signal resulting from constructive interference of the reflected waveguide mode at the periodic Bragg grating planes is defined as the. Neff represents the effective refractive index of the supported optical waveguide mode,. Λ refers to the grating period and m is an integer describing the order of the optical grating’s reflection [13,14]. The exact Bragg wavelength is intriguingly sensitive to environmental conditions either altering neff or Λ providing the Bragg grating’s sensor signal. Bragg gratings feature a single fiber connection together for both input and output signal light paths only, being superior to Sensors 2019, 19, 4101; doi:10.3390/s19194101 www.mdpi.com/journal/sensors
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