Monday, December 1, 2014

TOMORROW! Seminar: "Self-phase modulation in lithium niobate waveguides" by Dr. Roland Schiek 12.2.14/11:00am-12:00pm/ CREOL 103

Seminar: "Self-phase modulation in lithium niobate waveguides" by Dr. Roland Schiek
Tuesday, December 2, 2014 11:00 AM to 12:00 PM
CREOL Room 103

Dr. Roland Schiek
Ostbayerische Technische Hochschule Regensburg
Regensburg, Germany

Self-phase modulation in lithium niobate waveguides with cascaded quadratic and cubic nonlinearities is characterized by comparison of amplitude and phase of input and output pulse envelopes and spectra. Cubic nonlinear susceptibility coefficients of lithium niobate were determined from the measured nonlinear phase shifts. 
In non-centrosymmetric crystals typical cubic nonlinear effects like soliton propagation, modulational instability and supercontinuum generation are observed at power levels well below the expected values corresponding to the cubic nonlinear susceptibility. Responsible is a cascading of the quadratic non-linearity which mimics the third-order nonlinearity. Often considered relevant only close to phase-matching of the quadratic mixing, it was recently pointed out that the cascaded nonlinearity dominates the third-order nonlinearity in a much wider range. The most basic experimental evidence of a cubic nonlinearity is self-phase modulation (SPM). The first measurements of SPM in pure cubic nonlinear fibers needed long interaction lengths and were performed only in the spectral domain. Therefore, the most distinguished characteristic of SPM, the similarity of the variation in time of both, the pulse intensity and the nonlinear phase shift were not observed directly. With a measurement of the complex pulse envelope of pulses propagating in lithium niobate (LiNbO3) waveguides in addition to spectral measurements a complete characterization of SPM was performed in only cm-long samples. The contribution of different orders of the dielectric nonlinearity to the non-linear refraction could be identified and separated for a wide phase-mismatch range because the cubic nonlinearity is independent of the phase-mismatch in contrast to the changing cascaded quadratic nonlinearity. For specific geometries the cascaded nonlinearity dominates the cubic nonlinearity also far from phase-matching. By comparing quadratic and cubic contributions important elements of the cubic nonlinear susceptibility tensor of lithium niobate at wavelengths of 1.32mm and 1.55mm were determined.

For additional information:
Dr. Demetrios Christodoulides


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