Rapid optical interrogation of flowing cells or particles is a powerful tool in the field of biomedical diagnostics. Determination of size and composition of fast-flowing cells, with diameters in the range of 2-15 μm, often require complex open-space optics and expensive highspeed cameras. In this work, a method to overcome these challenges by using a hydrodynamic flow-based microfluidic platform coupled with on-chip integrated fiber optics is reported. The lab-scale portable device developed uses a combination of on-chip lensed and nonlensed optical fibers for precision illumination. The narrow light beam produced by the lensed fiber (f ¼ 150 μm) enables precise optical analysis with high sensitivity. A planar arrangement of optical fibers at various angles facilitates multi-parametric analysis from a single point of interrogation. As proof of concept, the laboratory-scale portable bench-top prototype is used to measure fluorescence signals from CD4 immunostained cells and human blood samples. The performance of microfluidic flow analyzer is also compared to the conventional Guava® easyCyte 8HT flow cytometer.

This work demonstrates an interferometric technique to estimate the reflected powers from dielectric interfaces and the reflection coefficient using the Fresnel equation for measurement of the refractive index (RI) of liquid samples. It uses low-coherence common-path optical interferometry that is commonly used for optical imaging. A uniquely designed optical fiber tip generating a high-quality non-diffractive Bessel beam probes liquid samples in a glass container non-invasively. The light reflected from different interfaces of the container is recollected by the same optical fiber tip. The reflected beams interfere with the reference beam generated at the fiber tip itself. This interference spectrum is further processed using fast-Fourier transform to measure reflected powers from the respective interfaces. The acquired powers are used to solve the Fresnel equation to find RI of liquid samples. As a proof of concept, experiments have been performed on several liquid samples including turbid media such as blood. This non-invasive interferometric technique could also be an ideal example confirming the Fresnel equation for reflection of light. Unlike other optical fiber-based RI sensors, this technique does not require temperature compensation. The method can be employed for inspection of the production process in terms of RI in pharmaceutical and chemical process plants, etc.

We demonstrate the excitation and detection of whispering gallery modes in optical microresonators using a "point-and-play", fiber-based, optical nano-antenna. The coupling mechanism is based on cavity-enhanced Rayleigh scattering. Collected spectra exhibit Lorentzian dips, Fano shapes, or Lorentzian peaks, with a coupling efficiency around 13%. The spectra are characterized by the coupling gap, polarization, and fiber tip position. The coupling method is simple, low-cost and, most importantly, the Q-factor can be maintained at 10 8 over a wide coupling range, thereby making it suitable for metrology, sensing, or cavity quantum electrodynamics (cQED) experiments.

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