Comparative study of quantitative phase imaging techniques for refractometry of optical waveguides

Abstract

A comparative study of quantitative phase imaging techniques for refractometry of optical waveguides is presented. Three techniques were examined: a method based on the transport-of-intensity equation, quadri-wave lateral shearing interferometry and digital holographic microscopy. The refractive index profile of a SMF-28 optical fiber was thoroughly characterized and served as a gold standard to assess the accuracy and precision of the phase imaging methods. Optical waveguides were inscribed in an Eagle2000 glass chip using a femtosecond laser and used to evaluate the sensitivity limit of these phase imaging approaches. It is shown that all three techniques provide accurate, repeatable and sensitive refractive index measurements. Using these phase imaging methods, we report a comprehensive map of the photosensitivity to femtosecond pulses of Eagle2000 glass. Finally, the reported data suggests that the phase imaging techniques are suited to be used as precise and non-destructive refractive index shift measuring tools to study and control the inscription process of optical waveguides.

Nonlinear increase, invisibility, and sign inversion of a localized fs-laser-induced refractive index change in crystals and glasses

“…This methodology, described in detail in ref. 63 , was carried out to recover the refractive index change (Δn) of the waveguides from the phase image. Accordingly, Δn measurements were considered to be exact within a 2% error margin or better.…”

Polychromatic digital holographic microscopy: a quasicoherent-noise-free imaging technique to explore the connectivity of living neuronal networks

“…The polychromatic setup was assembled from a commercial transmission Mach-Zehnder interferometer-based DHM (DHM T-1003, Lyncée Tec), described previously. 26,27 The genuine internal coherent light source of the DHM was bypassed by a tunable wavelength laser system, consisting of a supercontinuum white-light laser (SWLL) (SuperK EXR-20, NKT Photonics) coupled with a multiwavelength acousto-optic tunable filter (AOTF) (SuperK SELECT VIS-nIR, NKT Photonics), injected in the microscope with a delivery optical fiber (OF) (FD7-PM, NKT Photonics), as shown in Fig. 1(a).…”

Direct Inscription of on-surface waveguides in polymers using a mid-ir fiber laser

“…The camera is a wave-front analyzer that uses lateral shearing interferometry (QWLSI) to yield a quantitative phase image of transparent objects [18]. A methodology similar to the one described in a previous report [19] was implemented to recover the index contrast profiles of the waveguides from the phase map. In order to obtain quantitative phase images of the cross section of the waveguides [20], transverse slices were cut from the 30 mm long sample and polished down to a thickness of 80 μm or less.…”