Interféromètre de Mach-Zehnder

thumb|Principe de l'interféromètre de Mach-Zehnder. L'interféromètre de Mach-Zehnder est un interféromètre optique créé en 1891 et 1892 par Ludwig Mach - fils d'Ernst Mach - et Ludwig Zehnder, dont le principe est très proche de celui de l'interféromètre de Michelson. Il est constitué de deux miroirs et de deux miroirs semi-réfléchissants. Comme le montre le schéma ci-contre, un faisceau de lumière cohérente est divisé en deux, puis ces deux faisceaux sont alors recombinés à l'aide d'un miroir semi-réfléchissant. Ils vont donc pouvoir interférer entre eux. La figure d'interférences ainsi obtenue permet de réaliser des mesures très précises sur la source de lumière et sur tout échantillon transparent placé sur le trajet d'un des deux faisceaux. On peut par exemple mesurer un défaut de parallélisme des faces d'une lame de verre, ou encore un défaut de planéité ou de sphéricité. Outre l'application classique destinée à la mesure qui repose essentiellement sur une vision ondulatoire de la

Limitations of Proximity Lithography Printing

Krishnaparvathy Puthankovilakam

Photolithography is one of the earliest technologies used to transfer patterns to a substrate. It is also known as optical lithography since it uses light to transfer the pattern. The main exposure techniques exist in the industry are projection printing, contact printing, and proximity printing. Projection printing technology uses optical elements between mask and wafer to project the feature on the mask to the wafer. This is very expensive and delivers the highest resolution. In contact printing, the mask and wafer are in contact with each other and in proximity printing, the mask is kept at some proximity distance away from the wafer. Proximity printing is an easy and cost effective printing technique because the damage to the mask will be less and also no optical elements between mask and wafer are used. The main drawback of the proximity printing is the diffraction effect caused by the proximity gap between mask and wafer, which limits the resolution. The main objective of this thesis is to study the limitations of proximity printing and to increase its resolution. To study the limitations, different types of design strategies and verification methods are used in the thesis. First is the simulation technique which is performed with GenISys Layout LAB. This is specially designed for proximity printing. The software gives the aerial image and final resist pattern as output. The most interesting and important aspect is the second verification technique which is the experimental setup. A measurement setup has been built to study the light propagation from different masks and to study the aerial image at different proximity gaps. The setup is known as High Resolution Interference Microscopy (HRIM). The setup is basically a Mach- Zehnder interferometer having different light sources, sample plane and reference arm which are used according to the samples. The final verification is achieved using the mask aligner. Both the simulation and experiments are carried out using a special illumination optics called MO exposure optics from Süss MicroOptics. The thesis mainly focuses on the rule based optical proximity correction a technique which is a simple method for mass production. Correction structures are designed for one dimensional and two dimensional features in amplitude masks. Adding lines near the edge to improve the edge slope will be discussed as the one dimensional correction. The different intensity cutting planes and the comparison between simulation and experimental results will be discussed along with that. A unified correction structure is designed to solve corner rounding problem and will be studied as the two dimensional study. The structure is defined to print different line widths at single proximity gap on single exposure. Usually, all the structures in the amplitude mask are studied with their aerial image intensities at different proximity gaps. But, here the study extends to phase evaluation also. The measurement technique can measure both intensity and phase evolution from the mask structures. Phase evolution from amplitude correction features will be discussed and how the phase modulates the intensity patterns is also studied. The role of fundamental principles like phase singularities, phase shifts are also discussed to find its effects on proximity printing structures. The study also leads to the intensity and phase propagation from phase shifting mask (PSM) . The structure evaluated is a group of corners in PSM.

EPFL2017

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Olivier Boris Scherler

One method for locating extrasolar planets is to observe the lateral movement of a star in the sky caused by a planet in orbit around it. In order to detect this displacement, the angular position of the star has to be measured with high accuracy. This technique is called astrometry. The Very Large Telescope Interferometer (VLTI) is operated by the European Southern Observatory and located at the Paranal Observatory in Chile. The purpose of the PRIMA instrument (Phase Referenced Imaging and Micro-arcsecond Astrometry) of the VLTI is to perform high-resolution astrometric measurements and high-resolution imaging of faint stars using white light interferometry, by combining the light collected by two telescopes. In order to allow the detection of extrasolar planets, the astrometric measurement has to be performed with micro-arcsecond accuracy. In astrometric mode the PRIMA instrument observes two targets at the same time: the object of scientific interest, and a bright reference star. The angular position of the science object relative to the reference star is obtained by monitoring the differential optical path travelled by the light of each object in two separate white-light interferometers. The aim of this work was to develop a high-resolution laser metrology based on superheterodyne interferometry, with an accuracy of 5 nm over a differential optical path of 100 mm. Moreover the laser source had to be stabilised on an absolute frequency reference, in order to ensure the long-term stability and calibration required to achieve the target performance. Superheterodyne interferometry allowed the direct measurement of the differential optical path using two heterodyne interferometers working with two different frequency shifts. The differential phase measurement between the two interferometers was obtained by electronic mixing of the two heterodyne signals, leading to the differential optical path needed for the astrometric measurement

Institut de Microtechnique, Université de Neuchâtel2006

A fibre optic and machine learning based health monitoring system for superconducting power applications in modern supergrids

Arooj Akbar

The concerns for climate change and the transition to renewables is increasing the relevance of superconducting applications: High Temperature Superconductor (HTS) cables for efficient power transmission, superconducting magnets for nuclear fusion, superconducting fault current limiters (SFCLs) for HVDC grid protection and superconducting compact generators for wind turbines, to name a few. However, to tap into the full potential of HTS applications, the main problem of hotspots needs to be addressed. Hotspots are localized points of heating, which can arise in HTS devices mainly due to the intrinsic inhomogeneity of critical current along the superconductor length. The motivation behind this thesis, was to develop a health monitoring technique for a SFCL device under the European union project FastGrid. This device required a fast hotspot detection time of 10 ms in order to timely open the DC breaker in order to protect the device. During the course of this thesis an extremely fast and economical optical fibre sensing based hotspot detection technique has been developed and patented. The technique uses the Mach-Zehnder Interferometer (MZI) and is an efficient and economical way to detect hotspots in HTS applications. Due to the MZI sensitivity being a composite of strain sensitive and temperature sensitive contributions, the MZI gives an instantaneous response to a hotspot (within 10 ms), because of the quick strain transfer to the optical fibre. The research carried out under this thesis has involved experimentation on HTS tapes (10 cm to 1 m in length). The technique has also been integrated and tested with a SFCL pancake prototype with long lengths of conductor (12 m and 17 m). The thesis has also focused on finite element modelling to better understand the MZI sensitivity. The experimentation and modelling together, has enabled a better understanding of the MZI response to hotspots and the challenges of using MZI for HTS health monitoring. Due to the extremely high sensitivity of the MZI , the MZI output signal can also manifest the environmental noise caused by mechanical vibrations, bubbling in the cryostat and temperature variations, along with the response to heating in the sample. This presents the problems of false alarms and indiscernible response to hotspots. The work done for this thesis has also focused substantially on finding a suitable data analysis technique to supplement the MZI method. A discrete wavelet transform (DWT) based feature extraction together with a machine learning based classification for reliable quench detection has been developed in the course of this work with very encouraging results . This is an important development for the MZI technique as it significantly impacts and improves the MZI reliability and practicality for HTS applications. Additionally, this is also of substantial importance to the progress of HTS applications in the industry, especially the power sector which continues to evolve with the shift towards renewables and will rely more on HTS applications like SFCLs and HTS cables. With a reliable hotspot detection technique like the MZI, we can facilitate mass adoption of such HTS applications.

EPFL2022