Abstract
We demonstrate the potential of birefringence-based, all-optical, ultrafast conversion between the transverse modes in integrated optical waveguides by modelling the conversion process by numerically solving the multi-mode coupled nonlinear Schroedinger equations. The observed conversion is induced by a control beam and due to the Kerr effect, resulting in a transient index grating which coherently scatters probe light from one transverse waveguide mode into another. We introduce birefringent phase matching to enable efficient all-optically induced mode conversion at different wavelengths of the control and probe beam. It is shown that tailoring the waveguide geometry can be exploited to explicitly minimize intermodal group delay as well as to maximize the nonlinear coefficient, under the constraint of a phase matching condition. The waveguide geometries investigated here, allow for mode conversion with over two orders of magnitude reduced control pulse energy compared to previous schemes and thereby promise nonlinear mode switching exceeding efficiencies of 90% at switching energies below 1 nJ.
Highlights
Efficient all-optical switching based on a number of nonlinear effects is a research topic of high interest [1]
The optically induced long-period gratings (OLPG) induced via the Kerr effect in waveguides arises from the multimode interference intensity pattern caused by the beating of two control beam modes, that propagate with different phase velocities
A central advantage of the novel scheme is that it circumvents the experimentally observed cross-talk due to nonlinear polarization rotation when working at the same wavelength for control and probe beam [12]
Summary
Efficient all-optical switching based on a number of nonlinear effects is a research topic of high interest [1]. We show low-power, cross-talk free all-optical conversion of transverse modes in integrated waveguides by numerically modeling the nonlinear interaction between the involved pump and probe beam modes. Compared to earlier work [11,12,13] the small modal areas inherent to integrated waveguides are coming at the cost of an increased group velocity mismatch of the involved modes of up to two orders of magnitude This is more than compensated by a much higher effective nonlinearity, which substantially reduces the necessary pulse energy for all-optical mode conversion. In the calculations presented here, we have selected Si3N4, due to its availability with loss as low as 0.1 dB/m [14] and a transparent wavelength range from 400 nm to about 2.3 μm, making Si3N4 an experimentally widely used material for nonlinear optics [15,16,17,18,19]
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