Symmetrical Coupling Multi-Cavity Bandpass Filter for CMOS Compatible Fluorescence Detection

Integration of functional components such as excitation light source, micro-fluidic chip, optical filters, and complementary metal–oxide–semiconductor (CMOS) sensors on a single photonics chip for fluorescence detection by advanced semiconductor process, is a future technology for rapid responding, high accuracy, and handheld point-of-care diagnosis protocol in field application of daily life. We designed a CMOS compatible bandpass filter on a glass substrate based on symmetrical coupling multi-cavity (SCMC) SiN/SiO
₂
thin film stacker aimed at detection of 5-carboxylfluorescein (5-FAM), a commonly used fluorescence probe in biotechnology and medicine diagnosis. The calculation based on transfer matrix method (TMM) and 2D finite difference time domain (FDTD) algorithm, revealed that there was an optimized number of cavities in the SCMC stacker, for the transmittance in the pass band decreasing with the increment of the number of cavities while the optical density in the stop band improving with it. For a SCMC stacker with 10 resonant cavities, both the TMM and 2D FDTD calculation, figured out that the fluorescence emission and the remained excitation source should be directed to incident on the SCMC stacker with an angle less than 18° for a good passing of fluorescence emission centered at 520 nm and blocking of excitation light of a wavelength of 488 nm. It provided new insights for future design and fabrication of micro-lens array and micro-apertures array for the highly integrated photonics chip aimed at detection of fluorescence on a single chip.