Lecture

Self Phase Modulation: Understanding Nonlinear Fibre Optics

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In course

PHYS-607: Nonlinear fibre optics

Presentation of the different sources of optical nonlinearities in an optical fibre ...

Description

This lecture covers the concept of self phase modulation (SPM) in nonlinear fibre optics, where an intensity-varying wave can induce a phase shift on itself due to the Kerr effect. The instructor explains the accumulated phase of the wave, the nonlinear coefficient, maximum phase shift, spectral broadening, instantaneous frequency, chirp, induced nonlinear chirp, and the impact of SPM on pulse shape and frequency. Through examples and equations, the lecture delves into how SPM affects the pulse shape, inducing negative chirp near the leading edge and positive chirp as intensity grows. The frequency shift to the red with increasing intensity and to the blue with decreasing intensity is also discussed.

Instructors (2)

Luc Thévenaz

Luc Thévenaz received in 1982 the M.Sc. degree in astrophysics from the Observatory of Geneva, Switzerland, and in 1988 the Ph.D. degree in physics from the University of Geneva, Switzerland. He developed at this moment his field of expertise, i.e. fibre optics. In 1988 he joined the Swiss Federal Institute of Technology of Lausanne (EPFL) where he currently leads a research group involved in photonics, namely fibre optics and optical sensing. Research topics include Brillouin-scattering fibre sensors, nonlinear fibre optics, slow & fast light and laser spectroscopy in gases. His main achievements are: - the invention of a novel configuration for distributed Brillouin fibre sensing based on a single laser source, resulting in a high intrinsic stability making for the first time field measurements possible, - the development of a photoacoustic gas trace sensor using a near infra-red semiconductor laser, detecting a gas concentration at the ppb level, - the first experimental demonstration of optically-controlled slow & fast light in optical fibres, realized at ambient temperature and operating at any wavelength since based on stimulated Brillouin scattering. The first negative group velocity of light was also realized in optical fibres using this approach. In 1991, he visited the PUC University in Rio de Janeiro, Brazil where he worked on the generation of picosecond pulses in semiconductor lasers. In 1991-1992 he stayed at Stanford University, USA, where he participated in the development of a Brillouin laser gyroscope. He joined in 1998 the company Orbisphere Laboratories SA in Neuchâtel, Switzerland, as Expert Scientist to develop gas trace sensors based on photoacoustic laser spectroscopy. In 1998 and 1999 he visited the Korea Advanced Institute of Science and Technology (KAIST) in Daejon, South Korea, where he worked on fibre laser current sensors. In 2000 he co-founded the spin-off company Omnisens that is developing and commercializing advanced photonic instrumentation. In 2007 he visited Tel Aviv University where he studied the all-optical control of polarization in optical fibres. During winter 2010 he stayed at the University of Sydney where he studied applications of stimulated Brillouin scattering in chalcogenide waveguides. In 2014 he stayed at the Polytechnic University of Valencia where he worked on microwave applications of stimulated Brillouin scattering. He was member of the Consortium in the FP7 European Project GOSPEL "Governing the speed of light", was Chairman of the European COST Action 299 "FIDES: Optical Fibres for New Challenges Facing the Information Society" and is author or co-author of some 480 publications and 12 patents. He is now Coordinator of the H2020 Marie Skłodowska-Curie Innovative Training Networks FINESSE (FIbre NErve Systems for Sensing). He is co-Executive Editor-in-Chief of the journal "Nature Light: Science & Applications" and is Member of the Editorial Board (Associate Editor) for the journal "APL Photonics" & "Laser & Photonics Reviews". He is also Fellow of both the IEEE and the Optical Society (OSA).

Official source

Related concepts (32)

Nonlinear optics

Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers. Above the Schwinger limit, the vacuum itself is expected to become nonlinear.

Frequency modulation

Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude.

Self-phase modulation

Self-phase modulation (SPM) is a nonlinear optical effect of light–matter interaction. An ultrashort pulse of light, when travelling in a medium, will induce a varying refractive index of the medium due to the optical Kerr effect. This variation in refractive index will produce a phase shift in the pulse, leading to a change of the pulse's frequency spectrum. Self-phase modulation is an important effect in optical systems that use short, intense pulses of light, such as lasers and optical fiber communications systems.

Frequency domain

In mathematics, physics, electronics, control systems engineering, and statistics, the frequency domain refers to the analysis of mathematical functions or signals with respect to frequency, rather than time. Put simply, a time-domain graph shows how a signal changes over time, whereas a frequency-domain graph shows how the signal is distributed within different frequency bands over a range of frequencies. A frequency-domain representation consists of both the magnitude and the phase of a set of sinusoids (or other basis waveforms) at the frequency components of the signal.

Kerr effect

The Kerr effect, also called the quadratic electro-optic (QEO) effect, is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index change is directly proportional to the square of the electric field instead of varying linearly with it. All materials show a Kerr effect, but certain liquids display it more strongly than others. The Kerr effect was discovered in 1875 by Scottish physicist John Kerr.

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