Infrared imaging of fixed-cells through micro-cavity fiber optic scanning microscopy

Noninvasive, lens-free microscopy methods helps biologists to measure quantitative contrast phase imaging without damaging the cells. An extrinsic scanning micro-cavity in optical fiber is proposed to achieve surface imaging at infrared wavelengths. The micro-cavity is realized by approaching a single mode fiber with a numerical aperture NA to a sample and it is fed by a low-coherence source. The measurement of the reflected optical intensity provides a map of the sample reflectivity, whereas from the analysis of the reflected spectrum in the time/spatial domain, we disentangle the topography and contrast phase information. The latter describes the contrast variation of the reflected spectrum from the cavity due to changes in topography and surface refractive index. The interference of diffracted waves defines the transverse field behavior of the electromagnetic field inside the micro-cavity, affecting in this way the transverse resolution, that is not defined by the numerical aperture NA of the fiber and consequently by the conventional Rayleigh limit (about 0.6λ/NA). The resolution in the normal direction is limited mainly by the source bandwidth and demodulation algorithm. The system shows a compact and simple architecture.