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A limitation of standard brightfield microscopy is its low contrast images, especially for thin specimens of weak absorption, and biological species with refractive indices very close in value to that of their surroundings. We demonstrate, using a planar photonic chip with tailored angular transmission as the sample substrate, a standard brightfield microscopy can provide both darkfield and total internal reflection (TIR) microscopy images with one experimental configuration. The image contrast is enhanced without altering the specimens and the microscope configurations. This planar chip consists of several multilayer sections with designed photonic band gaps and a central region with dielectric nanoparticles, which does not require top-down nanofabrication and can be fabricated in a larger scale. The photonic chip eliminates the need for a bulky condenser or special objective to realize darkfield or TIR illumination. Thus, it can work as a miniaturized high-contrast-imaging device for the developments of versatile and compact microscopes.

Conventional total internal reflection fluorescence (TIRF) microscopy requires either an oil-immersed objective with high numerical aperture or a bulky prism with high refractive index to generate the evanescent waves that work as the illumination source for fluorophores. Precise alignment of the optical path is necessary for optimizing the imaging performance of TIRF microscopy, which increases the operation complexity. In this Letter, a planar photonic chip composed of a dielectric multilayer and a scattering layer is proposed to replace the TIRF objective or the prism. The uniform evanescent waves can be excited under uncollimated incidence through this chip, which simplifies the alignment of the optical configurations and provides shadowless illumination. Due to the separation of the illumination and detection light paths, TIRF microscopy can have a large field-of-view (FOV).

Spectral characterization plays an important role in both scientific research and industrial applications. There is now growing demand for spectrometers that offer advantages such as miniaturized size, high efficiency, and high spectral resolution. In this work, a planar photonic chip containing dielectric multilayers with a photonic band gap that has tailored dispersion relations is proposed for rapid spectral measurement applications by taking advantage of its ability to load low-loss Bloch surface waves (BSWs). When this chip is attached to a dispersive prism, the spectral resolution will not be reduced even if the size of the prism used in the spectrometer is reduced. On the contrary, the resolution can be improved because of the angular dispersion power of the low-loss BSWs, thus promoting the miniaturization of spectrometers. Spectra from various sources, including laser, white light, fluorescent emission, and even Raman scattering light sources, are characterized using the compact planar photonic chips. The spectral resolution achieved can be as high as 0.6 nm.

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