Self-organized nonlinear gratings for ultrafast nanophotonics

Abstract

Modern nonlinear optical materials allow light of one wavelength be efficiently converted into light at another wavelength. However, designing nonlinear optical materials to operate with ultrashort pulses is difficult, because it is necessary to match both the phase velocities and group velocities of the light. Here we show that self-organized nonlinear gratings can be formed with femtosecond pulses propagating through nanophotonic waveguides, providing simultaneous group-velocity matching and quasi-phase-matching for second harmonic generation. We record the first direct microscopy images of photo-induced nonlinear gratings, and demonstrate how these waveguides enable simultaneous χ (2) and χ (3) nonlinear processes, which we utilize to stabilize a laser frequency comb. Finally, we derive the equations that govern self-organized grating formation for femtosecond pulses and explain the crucial role of group-velocity matching. In the future, such nanophotonic waveguides could enable scalable, reconfigurable nonlinear optical systems. arXiv:1806.07547v1 [physics.optics]

Impact of Nonlinear Kerr Effect on the Focusing Performance of Optical Lens with High-Intensity Laser Incidence

“…According to the nonlinear optics, the Kerr effect is a nonlinear optical effect occurring when the highly intense light is interacting with crystals, glasses, gases or other media. Under the light field strength E(ω) of a high-power laser with angular frequency ω, the total polarization of a nonlinear optical medium up to the third order is described by [14] P(ω) = P (1)…”

“…where P (1) and χ (1) are the first-order linear polarization and susceptibility, respectively; P (3) and χ (3) are the third-order nonlinear polarization and susceptibility, respectively, which also represent the Kerr effect; and ε 0 is the permittivity of free space. By comparing the constitutive equation D(ω) = ε(ω)E(ω) and the polarization relationship D(ω) = ε 0 E(ω) + P(ω), we have the dielectric constant of a nonlinear optical material described by…”

“…where the linear portion of refractive index n 0 is given by n 0 = 1 + χ (1) . when the nonlinear item 3χ (3) E(ω) 2 /(4n 0 ) in the square root is much less than unit one, we obtain the approximate but simplified expression of refractive index…”

“…In the near future, laser power will reach 10 PW or even 100 PW, and laser intensity will exceed the order of 10 23 W/cm 2 . This technology provides a powerful experimental means for the autonomous and controllable research of extreme physical state in the laboratory and in the research field of inertial confinement fusion (ICF) [1,2], which is a process where nuclear fusion reactions are initiated by high-power lasers and compressing a fuel target, typically in the form of a pellet that most often contains a mixture of deuterium and tritium. Meanwhile, the impact of the nonlinear optical effect of materials on the working performance of optical components has become one of the non-negligible considerations of scientists and engineers.…”

Optically Probed Time Dynamics of χ(2) Grating Inscription in SiN Waveguides

“…Unfortunately, Si3N4 does not exhibit second order nonlinear optical properties due to its amorphous nature. Yet, recently several groups showed a build-up in time of a second harmonic (SH) when a pulsed high power pump is coupled in an Si3N4 waveguide [1][2][3]. This phenomenon, referred to as all-optical poling, is explained by the growth of an harmonic space-charge modulated χ (2) grating which quasi-phase matches the pump and its SH [4].…”