All-in-one integrated polymer waveguide with phase-shifted Bragg grating for enhanced fluorescence detection

Polymer waveguide is remarkable in integrated photonic biosensing due to its low loss in visible wavelength and easy integration in microfluidics system. In this paper, we proposed a polymer waveguide-based optofluidic chip for all-in-one fluorescent detection, featuring an on-chip light source and fluorescence filtering. A phase-shifted Bragg grating (PS-BG) waveguide is introduced for the first time as an excitation filter in fluorescent microscopy, just letting the excitation wavelength pass through. In the middle region, a slot waveguide with field enhancement serves as sensing region to enable intense light-sample interactions for improving the yield of fluorescence. The PS-BG can also reflect the back-propagating fluorescence back to the front light-collecting direction, thereby enhancing the light collection efficiency. At the end of the waveguide, another Bragg grating is designed to only allow fluorescence to pass through while reflecting the excitation light back, further enhancing the effectiveness of the excitation light. Detailed numerical analysis shows that the fluorescence excitation efficiency of the chip can be enhanced by a factor of 1.7, and the total fluorescence collection efficiency can reach up to 49.67% at the excitation wavelength of 578 nm and fluorescence wavelength of 668 nm. The proposed on-chip fluorescence collection system holds potential applications for miniaturized and portable devices for biomedical fluorescence detection.