An optical Kerr signal has been simulated for GaAs/AlAs multilayer cavity structures by using the self-consistent transfer matrix method. Enhancement of the Kerr signal intensity was clearly demonstrated for the cavity mode (λ∼1504 nm) owing to the strong optical field in the multilayer cavity. The Kerr signal intensity can be further enhanced with the use of a higher nonlinear refractive index only for the half-wavelength (λ/2) cavity layer. We propose a GaAs/AlAs multilayer structure with the λ/2 cavity layer containing InAs quantum dots embedded in strain-relaxed barriers for an ultrafast optical Kerr gate switch with extremely low switching energy.

The enhanced optical Kerr effect in a GaAs/AlAs multilayer cavity has been studied by numerical simulation using the self-consistent transfer matrix method. The simulated Kerr signal intensity of the cavity mode ( $ 1504 nm) markedly increases with increasing multilayer period because of the high quality factor (Q) of the multilayer cavity. The simulation results reveal that Kerr signal intensity increases in proportion to Q 4 , which is well explained by the enhanced nonlinear phase shift owing to (1) the large refractive index change induced by the strong internal optical field of the pump light and (2) the long photon lifetime of the probe light in the multilayer cavity.

A strong enhancement of two-photon absorption (TPA) has been demonstrated in a 30-period GaAs/AlAs multilayer with a GaAs halfwavelength (/2) cavity layer. In order to measure the time-resolved TPA signals, we successfully developed a selective etching process using an etch-stopper structure consisting of 5-nm-thick AlAs and 200-nm-thick Al 0:3 Ga 0:7 As double layers for removing the GaAs substrate. An analysis of the observed TPA results reveals that the average light intensity of the multilayer cavity is 41 times larger than that of a GaAs bulk sample. The obtained enhancement factor is in good agreement with the simulated value (45 times larger), which is determined from the simulated light intensity distribution by the conventional transfer matrix method.

Optical Kerr signals of GaAs/AlAs multilayer cavities with various quality factor (Q) were measured by an optical pump and probe technique with ultrashort pulses. Although the light intensity is enhanced in the cavities by Q, light power is restricted by the narrower spectrum of the cavity mode than that of the input ultrashort pulse. The measured Kerr signals showed larger dependence on the quality factor than that expected by simple consideration for the field enhancement effect by cavities. It seems that the nonlinear phase shift in the cavity is enhanced by the photon life time in addition to the field enhancement. This indicates that multilayer cavities are useful for enhancement of the optical Kerr signals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical Kerr response for a short‐input‐pulse of a GaAs/AlAs multilayer cavity which has a narrow cavity mode width was measured by an optical pump and probe technique. We observed a strong asymmetric temporal profile of the optical Kerr signal in the vicinity of Δt = 0. The initial rising time of the signal was 1.0 ps for Δt < 0, while the decay time was 0.25 ps for Δt > 0. The asymmetric profile of the Kerr signal was analyzed with the pulse shapes of the pump and probe pulses in the cavity. We found that the decay of the Kerr signal for Δt > 0 was faster than that of the profile explained by the pump and probe pulses. This suggests that the strong asymmetric profile of the Kerr signal was occurred by the strong phase shift due to the higher order term of the susceptibility. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)