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Brillouin-Based Distributed Temperature and Strain Sensors
Published in Arthur H. Hartog, An Introduction to Distributed Optical Fibre Sensors, 2017
Self-phase modulation (SPM), on the other hand, is an effect caused by the non-linearity of the refractive index that responds slightly to the square of the electric field, i.e. in proportion to optical power. This would be of no consequence if the probe power were constant; however, it is modulated in some way, usually as a pulse. This means that the refractive index is slightly higher in the centre of the pulses than outside it. The phase velocity of the pulse is therefore reduced slightly as the intensity is increased; therefore, the leading edge of the pulse experiences a small positive frequency shift, and the trailing edge, a negative frequency shift. These effects are cumulative along the fibre, and it is the derivative of the optical power across the pulse that causes the phase modulation. As a result, the effect of SPM is exacerbated as the spatial resolution is made finer, for a given peak power. The reader is referred to the Section 3.3.3.5 of Chapter 3 on frequency-diverse C-OTDR for a discussion of means of alleviating the effect of SPM.
Relay-Assisted FSO Communications
Published in Z. Ghassemlooy, W. Popoola, S. Rajbhandari, Optical Wireless Communications, 2019
Z. Ghassemlooy, W. Popoola, S. Rajbhandari
Nonlinear effects, such as self-phase modulation (SPM), which results from the Kerr nonlinearity, are commonly used terms in fibre optics communication systems. Note that the refractive index of the transmission medium can only depend quadratically on the field, i.e., on the intensity I, as given by [73]: n=n+n2I
Optical transmission
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Michel Joindot, Michel Digonnet
When a signal propagates through an optical fiber, through the Kerr effect it causes a change Δn in the refractive index of the fiber material. In turn, this modification of the medium property reacts on the signal by changing its velocity and thus its phase. This nonlinear effect is known as self-phase modulation (SPM). For a signal of power P, the index perturbation Δn is expressed as
Visible to mid-infrared supercontinuum generated in novel GeS2–Ga2S3–CsI step-index fibre
Published in Journal of Modern Optics, 2019
Wenyong Wei, Xuefeng Peng, Shixun Dai, Yingying Wang, Min Xie, Chenfeng Yang, Guangtao Li, Peilong Yang
The transmission of light waves in an optical fibre can be expressed by Maxwell’s equations. In general, a slowly varying envelope is used to approximate the value of the rapidly varying component in an electric field for further simplification. In the time coordinate system (delay coordinate system) for moving the group velocity of the pulse, the optical envelope function A(z,T) is expressed by Schrödinger equation (26): where α denotes the loss coefficient and the third term represents the wavelength dispersion effect (including the high-order mode dispersion). The entire right-hand side includes the nonlinear effects, such as self-phase modulation (SPM), four-wave mixing, self-sharpening, and stimulated Raman scattering.