Femtosecond second-harmonic generation in AlGaAs Bragg reflection waveguides: theory and experiment

Abstract

The impact of third-order nonlinearities including self-phase modulation and two-photon absorption on the efficiency of the second-harmonic generation is numerically investigated using the split-step Fourier method in phase-matched Bragg reflection waveguides. Also using the same technique, the adverse effects of group velocity mismatch and group velocity dispersion of the interacting frequencies on the efficiency of the nonlinear process are examined and contrasted for optimal sample design. Using an optimized structure, we report efficient femtosecond second-harmonic generation in monolithic AlGaAs Bragg reflection waveguides for a type II nonlinear interaction. For a 190 fs pulsed pump around 1555 nm with an average power of 3.3 mW, a peak second-harmonic power of 25.5 W is measured in a sample with a length of 1.1 mm. The normalized conversion efficiency of the process is estimated to be 2.0ϫ 10 4 % W −1 cm −2. Pump depletion is clearly observed when operating at the phase-matching wavelength.

Pulsed- and continuous-wave difference-frequency generation in AlGaAs Bragg reflection waveguides

“…where ⌬␤ = ␤ p − ␤ s − ␤ DF is the wave number mismatch; v g,i is the group velocity; ␤ 2,i is the GVD parameter; is the spatial nonlinear overlap factor; ␣ 0,i is the linear loss coefficient; ␣ 2,i and n 2,i are effective TPA and SPM coefficients of the structure, respectively; and A eff,i ͑3͒ is the thirdorder effective area [17]. The pulse envelope is normalized such that the harmonic power P i can be expressed as P i = ͉A i ͉ 2 .…”

“…where c is vacuum speed of light and d eff is the effective second-order nonlinear coefficient [17]. In parametric processes involving ultrashort optical pulses, first-and second-order modal dispersions can considerably influence the efficiency of the nonlinear interaction.…”

“…Second-order modal dispersion properties can also have degrading effects on the efficiency of the nonlinear interaction. Of particular importance is the GVD, which manifests itself in the pulse broadening, hence reducing the pulse peak power [17]. The presence of ͑3͒ , including TPA and SPM, under high pump power condition can further affect the efficiency of DFG.…”

“…TPA and SPM are power dependent, and their effects on the ͑2͒ process become significant when the operating peak power is high [16,17]. The effects of dispersion and ͑3͒ on femtosecond secondharmonic generation of BRWs have been previously reported in [17]. However their effects on DFG have not been reported yet.…”

Design methodology for efficient frequency conversion in Bragg reflection lasers

“…Recently, the use of Bragg reflection waveguides (BRWs) as a means of phase matching second-order nonlinearity [5] has shown high conversion efficiencies in both short pulse [6] and CW [7] second-harmonic generation (SHG). Conversion efficiency over 10;000% ∕ W cm 2 was achieved using picosecond pulses.…”