Modulation of the second-order susceptibility in GaAs/AlAs superlattices

Abstract

The modulation of the bulk-like second-order susceptibility with quantum well disordering is calculated for a GaAs/AlAs superlattice. The calculation is based on the A⋅p form of the susceptibility, which is the more appropriate form for semiconductors, and includes the influence of the Γ15c upper conduction band set which ensures the necessary absence of inversion symmetry. The undisordered structure has the degeneracy broken between the χxyz(2) and χzxy(2) tensor elements which is restored upon disordering. The shift of the half-band gap resonance gives a maximum modulation depth Δχxyz(2)≈60 pm V−1 in the transparency window for this structure.

Nonlinear frequency conversion in semiconductor optical waveguides using birefringent, modal and quasi-phase-matching techniques

“…For the waveguides used in our experiments, DD-QPM was realized through modulation of the heterostructure bandgap, which subsequently provides a modulation in the bulk-like χ (2) x yz and χ (2) zx y coefficients when operating near a material resonance. Values for this modulation in GaAs/AlAs superlattices are predicted to be as large as those available in PPLN [42]. A precise means for post-growth control over the bandgap is essential for such a technology, which can be achieved using QWI and thereby lateral control over the heterostructure bandgap can be obtained with no substantial increase in optical losses [37].…”

“…On the other hand, a fundamental limitation with GaAs is its optical isotropy, which inhibits birefringent phase matching. To circumvent this problem, a number of techniques have been effectively used to achieve phase matching in GaAs-based waveguide structures, including form birefringence phase matching (BPM) [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], quasi-phase-matching (QPM) [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] and modal phase matching (MPM) [47][48][49][50][51][52]. Variations of some of these techniques, demonstrated experimentally and predicted theoretically, include periodic switching of nonlinearity (PSN) in GaAs/AlGaAs waveguide crystals [53,54], sublattice reversal epitaxy [55], crystal domain inversion [56,57], orientation patterned GaAs [58][59]…”

Dispersion and Modulation of the Linear Optical Properties of GaAs–AlAs Superlattice Waveguides Using Quantum-Well Intermixing

“…This requirement is most straightforwardly satisfied with a superlattice structure forming the core of a waveguide. A theoretical analysis of GaAs-AlAs superlattice structures has been previously performed for second-order [11] and third-order [12] nonlinearities which indicate a substantial modulation in the bulk-like coefficients can be obtained between an as-grown and intermixed structure. In particular, a 14:14 monolayer GaAs-AlAs superlattice was identified as near optimal for second-harmonic (SH) generation with a 1550-nm fundamental, or equivalently near degenerate parametric processes with a 775-nm pump.…”

Optical Parametric Generators and Amplifiers

“…The vector q has a direction along the direction of the χ (2) modulation and the length of |q| = l c /Λ, where Λ is the spatial modulation period. The modulation of the nonlinearity can be accomplished by periodically inverting the sign of the χ (2) susceptibility, utilizing a zigzag optical path in slabs of nonlinear material with total-internal reflection [11,35,36] or by modulating the amplitude of the second-order susceptibility by periodically modifying the material properties, for instance, by employing quantum-well intermixing in GaAs-AlAs waveguides [37][38][39]. The latter two QPM methods have rarely been used so far either because of the relatively high losses as in the case of the totalinternal-reflection geometry, or due to the small thickness of the modulation which mandates a waveguide geometry for the frequency conversion device.…”