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
CREOL Room 103
Dr. Roland Schiek
Ostbayerische Technische
Hochschule Regensburg
Regensburg, Germany
Abstract:
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
407-882-0074
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