selfphase

Selfphase is not a widely standardized term in scientific glossaries. In many contexts, it is used informally to refer to the phase change that a wave experiences as a result of its own intensity, a phenomenon more precisely described as self-phase modulation (SPM) in nonlinear optics.

In a Kerr-type medium, the refractive index depends on the instantaneous intensity: n = n0 + n2 I(t). As an optical pulse propagates, this intensity-dependent index imprints a time-varying nonlinear phase on the wave. For a uniform medium of length L, the nonlinear phase shift is φNL(t) ≈ k0 n2 I(t) L, where k0 is the vacuum wavenumber. The instantaneous frequency shift is δω(t) = -dφNL/dt, which can cause spectral broadening and chirping of the pulse. The overall evolution of the pulse also depends on the interplay between nonlinearity and dispersion in the medium.

Self-phase modulation is a fundamental effect in ultrafast and nonlinear optics and is central to phenomena such as supercontinuum generation and pulse compression in fiber systems. It is also exploited as a tool for measuring the nonlinear refractive index and for characterizing ultrashort pulses.

Notes and terminology: the phrase “selfphase” often appears as shorthand in informal discussions or older literature, but contemporary usage typically specifies “self-phase modulation.” It is distinct from cross-phase modulation, where the phase of one wave is modulated by the intensity of another. When used, selfphase generally refers to the same self-induced phase modulation mechanism described above.