All-Optical High-Resolution On-Chip Pressure Sensing Method Based on Tunable Liquid-Core/Liquid-Cladding Waveguide

In various application fields of microfluidic technology, precise pressure control within microchannels is crucial for achieving the functionality of lab-on-a-chip systems, particularly in the emerging field of organoids-on-chips. However, fluid propulsion can only be achieved through external devices, and the complex microchannel structures, along with inevitable pressure drops, make it extremely challenging to measure and control fluid pressure at specific positions within the microfluidic chip. This study proposes an all-optical on-chip pressure sensing method based on tunable liquid-core/liquid-cladding ( $\text{L}^{{2}}\vphantom {^{\int }}$ ) waveguides. The varying degrees of bending deformation in the $\text{L}^{{2}}$ waveguide within the sensing chip can readily characterize changes in local pressure within the tested channel, thereby establishing a sensing mechanism through the measurement of waveguide losses. Experimental results demonstrate that this pressure measurement method has a theoretical resolution of 0.14 mbar and a measured conservative resolution of 1.32 mbar. Furthermore, it exhibits advantages in terms of sensitivity, linear range, accuracy, real-time capability, integration, and adaptability. More importantly, compared with conventional solid-state devices, this method allows for liquid-based flexible reconstructions, enabling customized adjustment of sensing performance. When the required measuring pressure is reduced from 400 to 300 mbar, sensitivity can be increased by 67.3% through waveguide reconstruction. When the required measuring pressure increases from 300 to 400 mbar, waveguide reconstruction can reduce nonlinearity error by 68%, maintaining linearity within a wider pressure range. This study offers a reliable research tool for the development of microfluidic technology and significantly expands the application potential of liquid-based sensor devices.