May 3, 2016

Michael Maria

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Project title,ESR1: Establishment of connection between noise and usefulness of Super-Continuum (SC) in clinical applications such as Optical Coherence Tomography (OCT)

Investigate the potential of Super-Continuum light source for Optical Coherence Tomography in Dermatology. Understand what are the particular challenge for Ultra-High Resolution Optical Coherence Tomography and how to fully exploit Super-Continuum light for medical imaging.


Current projects and research areas

  • Ultra-High Resolution Optical Coherence Tomography (UHR-OCT)
  • Noise Characterization in OCT
  • Master-Slave Interferometry
  • Skin imaging using OCT at 1300 nm
  • Supercontinuum light source

Motivation

Optical Coherence Tomography (OCT) is nowadays a daily tool for Ophtalmologist, and it is slowly admitted as a very interesting tool for Dermatologists. Ultra-High Resolution (UHR) images of skin provide to doctors a fast reliable non-invasive diagnostic possibility. Using a Super-Continuum (SC) light source for OCT offers an ultra-broadband spectrum around 1300 nm which end up as the best compromise between depth penetration of light in skin and axial resolution.

Currently, I am working on developing a UHR spectrometer-based OCT system using a SC light source centered at 1270 nm using a bandwidth of 400 nm. I am more specifically working on the noise performance of such a system and also on the issue of non-linearity arising form the interferometer. Considering the first point, a good understanding of noise impact into the OCT image provide information on how to improve the SC itself and also how to optimally use it in terms of OCT input setting. Regarding the non-linearity issue, it is crucial to perfectly control and compensate for them in order to reach UHR-OCT specifications. Non-linearity issue includes the dispersion in the system, the data resampling or the non-linear swept in fast tunable laser.


Professional experience

  • March 2014 – March 2017
    Marie Curie Early stage  researcher (UBAPHODESA, FP7-PEOPLE-2013-ITN, 607627) at NKT Photonics A/S (DK) and University of Kent (UK).
  • April 2013 – September 2013
    Industrial Master Thesis at Thales Research and Technology (III-V Lab) – Palaiseau (Paris -France).
    Development of very high power laser diode emitting at 975nm, with high wall plug efficiency, wavelength stabilization for fiber laser pumping based on III-V Semiconductors
  • June 2012 – August 2012
    Internship at M1 Level at the University of Barcleona (UB) in the Applied Optics Laboratory.
    Development of a control code for microscope platform synchronised with a modulated femtosecond laser for direct writing

Education

  • September 2009 – September 2013
    MSc in Optics at the advanced national college of applied science and technology (ENSSAT – Rennes I University) in Lannion (France) and BarcelonaTech University (Barcelona – Spain) for a student exchange of one semester with the Master in Photonics.
  • September 2007 – August 2009
    French ”Prep School” in Math, Physics and Chemistry at Lycée Pierre Mendes France in La Roche-sur-Yon (France).
  • June 2007
    French Baccalaureat with honors

Publications

Article

  • A. Bradu, M. Maria and A. Gh. Podoleanu, ”Demonstration of tolerance to dispersion of Master-Slave Interferometry”, Opt. Express. 23(11), 14148-14161 (2015).

Abstract:
A theoretical model is developed for the Master/Slave interferometry (MSI) that is used to demonstrate its tolerance to dispersion left uncompensated in the interferometer when evaluating distances and thicknesses. In order to prove experimentally its tolerance to dispersion, different lengths of optical fiber are inserted into the interferometer to introduce dispersion. It is demonstrated that the sensitivity profile versus optical path difference is not affected by the length of fiber left uncompensated. It is also demonstrated that the axial resolution is constant within the axial range, close to the expected theoretical resolution determined by the optical source bandwidth. Then the thickness of a glass plate is measured several times in the presence of dispersion and errors in measurements are evaluated using the MSI method and the conventional Fourier transformation (FT) based method using linearized/calibrated data. The standard deviation for thickness results obtained with the MSI is more than 5 times smaller than the standard deviation for results delivered by the conventional, FT based method.

  • S. Rivet, M. Maria, A. Bradu, T. Feuchter, L. Leick and A. Gh. Podoleanu, ”Complex Master-Slave Interferometry”, Opt. Express. 24(3), 2885-2904 (2016).

Abstract:
A general theoretical model is developed to improve the novel Spectral Domain Interferometry method denoted as Master/Slave (MS) Interferometry. In this model, two functions, g and h are introduced to describe the modulation chirp of the channeled spectrum signal due to nonlinearities in the decoding process from wavenumber to time and due to dispersion in the interferometer. The utilization of these two functions brings two major improvements to previous implementations of the MS method. A first improvement consists in reducing the number of channeled spectra necessary to be collected at Master stage. In previous MSI implementation, the number of channeled spectra at the Master stage equated the number of depths where information was selected from at the Slave stage. The paper demonstrates that two experimental channeled spectra only acquired at Master stage suffice to produce A-scans from any number of resolved depths at the Slave stage. A second improvement is the utilization of complex signal processing. Previous MSI implementations discarded the phase. Complex processing of the electrical signal determined by the channeled spectrum allows phase processing that opens several novel avenues. A first consequence of such signal processing is reduction in the random component of the phase without affecting the axial resolution. In previous MSI implementations, phase instabilities were reduced by an average over the wavenumber that led to reduction in the axial resolution.

Conference, workshop and summer school

  • Metrology 2015 (Photonics Europe 2015 – Munich) – Oral Presentation

Title: Novel dispersion-tolerant interferometry method for accurate measurements of thicknesses
Authors: Michael Maria, Adrian Bradu, Thomas Feuchter, Lasse Leick and Adrian Gh. Podoleanu
Abstract:
We demonstrate that the recently proposed master-slave interferometry method is able to provide true dispersion free depth profiles in a spectrometer-based set-up that can be used for accurate displacement measurements in sensing and optical coherence tomography. The proposed technique is based on correlating the channelled spectra produced by the linear camera in the spectrometer with previously recorded masks. As such technique is not based on Fourier transformations (FT), it does not require any resampling of data and is immune to any amounts of dispersion left unbalanced in the system. In order to prove the tolerance of technique to dispersion, different lengths of optical fiber are used in the interferometer to introduce dispersion and it is demonstrated that neither the sensitivity profile versus optical path difference (OPD) nor the depth resolution are affected. In opposition, it is shown that the classical FT based methods using calibrated data provide less accurate optical path length measurements and exhibit a quicker decays of sensitivity with OPD.

  • Danish Optical Society annual meeting (Odense) – Oral Presentation

Title: Novel dispersion-tolerant interferometry method for accurate measurements of thicknesses
Authors: Michael Maria, Adrian Bradu, Thomas Feuchter, Lasse Leick and Adrian Gh. Podoleanu

  • Bios 2016 (Photonics West 2016 – San Francisco) – Poster Presentation

Title: Broadband Master-Slave Interferometry using a super continuum light source
Authors: Michael Maria, Adrian Bradu, Thomas Feuchter, Lasse Leick and Adrian Gh. Podoleanu
Abstract:
We report on a demonstration of a broadband master-slave interferometry system (MSI) using a supercontinuum light source. Principleof MSI based in channeled spectrum comparison , is extended to to optical source with bandwidth close to 100 nm around 830 nm. A-scan and B-scan of phantom multi-layer object and finger nail are presented and compared with conventional Fourier Domain (FD-OCT) image produced with and without calibration. MSI insensitivity to dispersion from the interferometer and no needs of camera calibration help to handle very broad spectrum with minimum software compensation of system non-linearity. MSI B-scans present constant axial resolution over the entire depth range while conventional (calibrated and uncalibrated) FD-OCT methods are limited by the effect of dispersion. Data calibration improves axial resolution but only over a small depth rangefor conventional FD-OCT.