Holographic multi-waveguide system: towards implementation in wearable sensor technologies

Holographic optical elements (HOEs) are integral to advancements in optical sensing, augmented reality, solar energy harvesting, biomedical diagnostics, and many other fields, offering precise and versatile light manipulation capabilities. This study, to the best of the authors' knowledge, is the first to design and fabricate an HOE mutliwaveguide system using a thermally and environmentally stable photopolymerizable hybrid sol-gel (PHSG) for sensing applications. Using a 476.5 nm recording wavelength, 60% diffraction efficiency PHSG holographic waveguides of spatial frequency of 1720 lines/mm were successfully fabricated to function as in- and out-couplers at 632.8 nm and 700 nm wavelength, respectively. The waveguides were integrated into a polydimethylsiloxane (PDMS) microfluidic system, guiding excitation light of 632.8 nm wavelength into and extracting fluorescence light signal peaking at 700 nm from a location filled with methylene blue water solution. Further, to demonstrate the potential of the proposed optical system, four holographic waveguides were recorded by peristrophic and angular multiplexing in the same location of the material and the input beam was delivered into four spatially separated channels by total internal reflection in the sol-gel layer, thus, successfully highlighting the capabilities and advantages of HOE waveguides for parallel interrogation of multiple locations in a wearable sensor. This study demonstrates the efficiency and versatility of PHSG-based HOE waveguides, underscoring their potential to enhance photonic device design and performance across various optical applications.