Self Phase Modulation: Understanding Nonlinear Fibre Optics

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.