Noa Voloch

Radially symmetric nonlinear photonic crystals

Different types of quadratic, radially symmetric, nonlinear photonic crystals are presented. The modulation of the nonlinear coefficient may be a periodic or an aperiodic function of the radial coordinate, whereas the azimuthal symmetry of the crystal may be either continuous or discrete. Nonlinear interactions within these structures are studied in two orientations, transverse and longitudinal, for which the interacting beams propagate either perpendicularly or in the plane of modulation. We show that radially symmetric structures can phase match multiple arbitrary processes in any direction. We study multiple wavelength three-wave mixing interactions and multiple direction interactions and analyze spatially dependent polarization states of the generated harmonics.

Nonlinear Photonic Quasicrystals for Novel Optical Devices

Two well-known methods for the design of quasicrystal models are used to create novel nonlinear optical devices. These devices are useful for efficient three-wave mixing of several different processes, and therefore offer greater flexibility with respect to the more common periodic nonlinear photonic crystals. We demonstrate applications for polarization switching as well as multi-wavelength and multi-directional frequency doubling. The generalized dual grid method is proven to be efficient for designing photonic quasicrystals for one-dimensional collinear devices as well as elaborate two-dimensional multi-directional devices. The cut-and-project method is physically realized by sending finite-width optical beams at an irrational angle through a periodic two-dimensional nonlinear photonic crystal. This enables the creation of two simultaneous collinear optical processes that can be varied by changing the angle of the beams.

Analysis of Colinear Quasi-Phase-Matching in Nonlinear Photonic Crystals

Standard quasi-phase-matching (QPM) schemes assume exact momentum relations between the interacting beams, thus necessitating the direct use of a reciprocal lattice vector to satisfy momentum balance. Usage of finite width beams for colinear interactions permits to use a projection of the reciprocal lattice vector along the propagation direction of the beams. We analytically derive this result and exam the new options given by this projection-based QPM for the analysis and design of nonlinear optical devices.

Second harmonic generation in periodic and aperiodic transversely poled crystals

One of the greatest advances in the field of second-harmonic generation (SHG) has been brought about by the use of multi-domain crystals with periodic or aperiodic alteration of the sign of the quadratic nonlinearity. All applications involving the SHG process, however, rely on the propagation of the fundamental beam in the plane perpendicular to the ferroelectric domain walls. Here we realize a transverse geometry, when the fundamental beam propagates along the normal to the plane of nonlinearity modulation. We report on the observation of ringtype SHG and new type nonlinear diffraction patterns utilizing Z-cut samples with different types of modulation of their quadratic nonlinearity (see Fig.1): (a) rectangular periodically poled structure patterned in stoichiometric LiTaO3 (RSLT); (b) annularly poled structure in stoichiometric LiTaO3 (ASLT); (c) short-range ordered poled structure patterned in LiNbO3 (SRO-LNB); (d) nonlinear photonic octagonal quasi-crystal sructure patterned in LiNbO3 (OQC-LNB); and (e) disordered nonlinear photonic structure such as unpoled SBN (DNPS-SBN).

Raman-Nath nonlinear diffraction in second harmonic generation

In the linear optics, light beam propagating through a structure with periodic refractive index experiences either single order Bragg diffraction, when the full vectorial phase matching (PM) condition is satisfied, or multi-order Raman-Nath diffraction (RND), otherwise. Analogously, in parametric processes such as second harmonic (SH) generation light can experience nonlinear diffraction in periodically poled crystals with homogeneous linear refractive index. In this, the so called, nonlinear Bragg diffraction [1], the SH beam is emitted at a specific angle, determined by the vectorial phase-matching condition 2k1 + Gn = k2, where k1 and k2 are the respective wave-vectors of the fundamental and the second harmonic and Gn denotes the grating vector of the periodic modulation of the sign of nonlinearity [see Fig. 1(a), left]. However, if this vectorial condition is not satisfied, a multi-order nonlinear diffraction of the SH should be seen instead [see Fig. 1(a), right], in analogy to the linear Raman-Nath diffraction.

New Quasi Phase Matching Options by Lattice Projection

We experimentally demonstrate that finite width interaction of a co-linear χ(2) process inside a periodic nonlinear photonic crystal leads to new possibilities of phase matching and thus to radiation un-accounted for by regular plane-wave analysis. Article not available.