Optical Fiber Extrinsic Micro-Cavity Scanning Microscopy

Abstract

Abstract-An extrinsic Fabry-Perot cavity in optical fiber is used 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, in the limit of nearly homogeneous sample with complex permittivity having Im(ε) Real(ε). The transverse resolution is not defined by the numerical aperture NA of the fiber and consequently by the conventional Rayleigh limit (about 0.6λ/NA), but it is a function of the transverse field behavior of the electromagnetic field inside the micro-cavity. Differently, the resolution in the normal direction is limited mainly by the source bandwidth and demodulation algorithm. The system shows a compact and simple architecture. An analytical model for data interpretation is also introduced.

Synthetic holography based on scanning microcavity

“…According to the model reported in Ref. 12, the back-reflected intensity from the optical cavity can be written as:…”

“…Scanning cavity has recently attracted the interest in microscopy thanks to its very high sensitivity in nanoparticle detection and in contrast-phase imaging. 11,12 In our technique the cavity is realized by approaching a cleaved optical fiber to the surface under investigation, within a working range of tens of micrometers. The optical set-up is reported in Figure 1, where a broadband diode laser at 850 nm (bandwidth FWHM = 40 nm, operating current = 150 mA, output power = 0.6 mW) feeds a directional coupler connected to the optical probe, that has a NA ranging from 0.10 to 0.14 and a MDF equal to 5.6 µm.…”

Optomechanical reference accelerometer

“…The effective cavity reflectivity for a low-finesse external fiber micro-cavity has been studied in great detail [24,28,29]. Models are available that include the influence of angular misalignment and multiple reflections.…”

3d Super-Resolution Fluorescence Microscopy Using Cylindrical Vector Beams

“…Three-dimensional (3D) dark spots surrounded by light (bottle beams) are applied in many areas in optics, such as dark-spot optical traps for atoms [1,2] or as erase beams for super-resolution fluorescence microscopy [3][4][5][6][7]. Several methods have been used to produce 3D bottle beams that have an intensity null surrounded by light in all directions.…”