Fig. 3: Measuring the transmissive directions of the scattered light from the photonic chip.

a Schematic of the experimental set-up for the transmissive BFP imaging. b, c The photos of the photonic chip and a coverslip when a light beam passes through, which show that light field can be generated at the surface of the photonic chip. d, f Transmission BFP images of the photonic chip under normal incidence with a light-emitting diode (LED) beam, the incident wavelengths are selected as 640 and 750 nm. The color scale encodes the experimental transmission power (normalized) of the bottom and top multilayer. The bottom panels of d, f are the case where the bottom multilayer of the photonic chip was removed, to demonstrate the role of bottom multilayer. Comparisons between top and bottom panels of d, f shows that the bottom multilayer can enhance the intensity of the transmissive light from the photonic chip. The red-dashed circle represents the position with NA = 0.7 (for a regular air objective used in the darkfield and TIR imaging experiments) and the black one NA = 1 (corresponding to the TIR angle), the oil-immersed objective’s numerical aperture (NA) is marked with a red-solid circle (NA = 1.49). The orientation of the polarizer is marked with a solid arrow on d, f. e, g Quantitatively demonstrating the angular distribution of the transmissive light from the photonic chip. The NA of the horizontal axis is corresponding to transmission angle θ (NA = n × sin(θ), n is the refractive of the oil). The intensity of the transmissive light within low NA (<0.7) is about 1.5% (or 1.6%), meaning that the direct transmission of the scattered light from the photonic chip is very weak.