Nonlinear Optics: Effects and Devices
In this work we are interested in frequency conversion in materials with engineered second order nonlinearity for application in formation of novel light sources, wave front shaping and all optical signal processing.
Nonlinear Photonic crystals are nonlinear optical materials that maintain a constant refractive index but exhibit spatially periodic reversal of the sign of their second-order nonlinearity. This modulation of the nonlinearity provides a mechanism enabling to synchronize phases of co-propagating electromagnetic waves such that they can efficiently exchange energy. In this way it is possible to convert optical beam with given frequency into one or more beams at different frequencies. Meanwhile, the wave front of these generated beams can be controlled and modified by engineering the second-order nonlinear coefficient in precise patterns. All these functions are highly desired in all-optical signal processing and nonlinear photonic devices.
In Laser Physics Center, we have recently developed an advanced electric-poling technique for fabrication of high-quality periodic, quasi-periodic and randomized nonlinear photonic structures in ferroelectric crystals. With these crystals, we have realized broadband optical frequency conversion with conversion efficiencies that are at least one-order of magnitude higher than previously recorded.
Fig. 1(a) Electric-field poling through liquid electrodes; (b) Schematic of typical experimental setup. (c) The recorded image of the generated beams at new frequencies in a short-range ordered nonlinear photonic crystal
We also invented a novel technique of nonlinear microscopy that utilizes the presence of nonlinear optical responses localized at the interface separating oppositely oriented second-order nonlinear coefficient. We demonstrated that tightly focused infrared beam leads to a strong emission of the Čerenkov second harmonic signal only when the interface is illuminated. In this way, it enables direct 3D imaging of the ferroelectric domains inside the nonlinear photonic crystal with high contrast as well as sub-diffraction limit resolution.
Fig. 2 Nonlinear photonic structures imaged by the nonlinear Cerenkov second harmonic microscopy
- Y. Sheng et al., Three-dimensional ferroelectric domain visualization by Čerenkov-type second harmonic generation Opt. Express 18, 16539 (2010).
- Y. Sheng, et al., Čerenkov-type second-harmonic generation with fundamental beams of different polarizations Opt. Lett. 35, 1317 (2011).
- K. Kalinowski, et al., Wavelength and position tuning of Cerenkov second-harmonic generation in optical superlattice, Appl. Phys. Lett. 99, 181128 (2011).
- Y. Sheng et al., Broadband second harmonic generation in one-dimensional randomized nonlinear photonic crystal, Appl. Phys. Lett. 99, 031108 (2011).
- K. Kalinowski, et al., Parametric wave interaction in one-dimensional nonlinear photonic crystal with randomized distribution of second-order nonlinearity, Appl. Phys. B, 109 557-566 (2012).
- Y. Sheng, V. Roppo, K. Kalinowski, W. Krolikowski, The role of a localized modulation of χ(2) in Cerenkov second harmonic generation in nonlinear bulk medium, Opt. Lett. 37, 3864--3866 (2012).