Conference Agenda

Highlight on JEOS:RP, Herve C Lefevre
Thursday, 15/Sept/2022:
3:15pm - 3:30pm

Session Chair: Gilles Pauliat, Laboratoire Charles Fabry, institut d'Optique, France
Location: Auditorium

1st floor, next to registration desk, 400 seats

Chief Science Officer at iXblue, France

Title: Comments about Dispersion of Light Waves

Session Abstract

This presentation is derived from a recent eponymous publication in JEOS-RP ( Dispersion of light waves is well known, but the subject deserves some comments. Certain classical equations do not fully respect causality; as an example, group velocity vg is usually given as the first derivative of the angular frequency ω with respect to the angular spatial frequency km (or wavenumber) in the medium, whereas it is km that depends on ω. This paper also emphasizes the use of phase index n and group index ng, as inverse of their respective velocities, normalized to 1/c, the inverse of free-space light velocity. This clarifies the understanding of dispersion equations: group dispersion parameter D is related to the first derivative of ng with respect to wavelength λ, whilst group velocity dispersion GVD is also related to the first derivative of ng, but now with respect to angular frequency ω. One notices that the term second order dispersion does not have the same meaning with λ, or with ω. In addition, two original and amusing geometrical constructions are proposed; they simply derive group index ng from phase index n with a tangent, which helps to visualize their relationship. This applies to bulk materials, as well as to optical fibers and waveguides, and this can be extended to birefringence and polarization mode dispersion in polarization-maintaining fibers or birefringent waveguides.



More about speaker

Hervé C. Lefèvre is Chief Science Officer of iXblue ( in France. He was born in 1954, in Paris. He graduated from Ecole Normale Supérieure de Saint-Cloud (France) in Physics and was awarded a Doctorate in Optics-Photonics from the University of Paris-Orsay (France) in 1979. His doctorate research was performed at Thales (formerly Thomson-CSF) Central Research Laboratory, and his thesis subject was pioneering work on the fiber-optic gyroscope.
From 1980 to 1982, he was a post-doctoral research associate at Stanford University in California, continuing R&D on the fiber-optic gyroscope. In 1982, he came back to Thales Central Research Lab and became head of the fiber-optic sensor team. In 1987, he joined Photonetics, then a start-up, and became director of R&D.
In addition to fiber-optic sensors and gyroscopes, the company developed a very successful line of test instruments and components for dense-wavelength-division-multiplexing (DWDM) optical fiber communications. As the company grew, he moved to the position of Chief Operating Officer in 1999. At the end of 2000, Photonetics was acquired by the Danish group GN-Nettest, whilst its fiber-gyro activity was spun out to create iXsea. He remained with GN- Nettest and managed its Photonics Division.
In 2004, he moved to iXcore, the parent company of iXSea, as vice president for R&D with a specific involvement in iXSea's activity, and he became Chief Science Officer of iXBlue at its creation in 2010, as a merger of iXsea with several other subsidiaries of iXcore as, for example, iXfiber making specialty fibers, and Photline making integrated optic circuits.
He has authored and coauthored nearly 80 journal and conference publications about the fiber-gyro, fiber-optic components and fiber communication test instruments, and he has been granted more than 60 patents.
He is the author of a reference book on the fiber-optic gyroscope, with a first edition published by Artech House in 1993, a second one in 2014, and a third one at the beginning of 2022. These books include detailed appendixes about the fundamentals of Optics, Fiber Optics and Integrated Optics, that use many didactic figures to provide an intuitive understanding of the subject.
He was president of the French Society of Optics (SFO) for the 2005-2007 period, and president of the European Optical Society (EOS) for the 2010-2012 period.
He is Honorary Member of SFO, and member of the International Honorary Committee of the Optical Fiber Sensor (OFS) conference.
In early 2022, he was elected member of the French Academy of Technologies.

No contributions were assigned to this session.