Hybrid Mach-Zehnder interferometer manufactured by femtosecond laser multiscan technique

Pablo Roldán Varona,David Pallarés Aldeiturriaga,José Miguel López Higuera,Luis Rodríguez Cobo

doi:10.1117/12.2538813

Pablo Roldán Varona, David Pallarés Aldeiturriaga + Show 2 more

Open Access

https://doi.org/10.1117/12.2538813

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Publication Date: Aug 28, 2019
Citations: 2	License type: other-oa

Affiliation: Universidad de Cantabria, Instituto de Salud Carlos III

Abstract

In this paper, a 6 mm hybrid Mach-Zehnder Interferometer (MZI) has been manufactured within a standard optical fiber using multiscan inscription with femtosecond laser. This technique allows the employ of cladding waveguides (CWG) as sensing arms for the interferometer. Refracted Near Field (RNF) profilometry and Quantitative Phase Microscopy (QPM) consistently suggest that CWG exhibit a smooth Type I refractive index change (RIC) that increases with the number of scans. This makes the scan number a potential way to control the coupling and Free Spectral Range (FSR) of the manufactured MZI. Its combination with a fiber Bragg grating (FBG) inscribed in the core makes possible to discriminate between different parameters.

Highlights

The use of femtosecond lasers as a means of direct inscription of components through three-dimensional structures inside the bulk volume of transparent materials has been a great opportunity in terms of simplicity and flexibility for the micromachining of materials [1]
Mach-Zehnder Interferometers are based on the optical path difference (OPD) that arises when the light is divided into two different optical paths: one is set as reference and the other acts as the sensor element (CWG)
In order to eliminate the spherical aberration of the fiber itself, this is placed between a slide and a coverslip, depositing an index-matching oil between both [4]

Summary

INTRODUCTION

The use of femtosecond lasers as a means of direct inscription of components through three-dimensional structures inside the bulk volume of transparent materials has been a great opportunity in terms of simplicity and flexibility for the micromachining of materials [1] It has a special interest in the design of optical fiber sensors (OFS) for its potential application in multiple scenarios. Due to its simple design, the use of interferometers, especially the MZI, has traditionally been done using air cavities, fiber tapers, long-period fiber gratings (LPGs) or waveguides formed by fs laser-based RI changes [3] In this work, it is proposed a hybrid MZI (combines a FBG in the core) through the manufacture of waveguides formed by multiple inscriptions, using the above-mentioned RI changes by fs laser. After each scan, the sample position moves slightly on the perpendicular axis to both the laser beam propagation axis and waveguide longitudinal axis (Figure 1b)

Sensor design

Cladding waveguide

MZI and FBG

CONCLUSIONS