Tham khảo tài liệu 'advances in optical and photonic devices part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | GaAs AlOx Nonlinear Waveguides for Infrared Tunable Generation 149 To infer Rayleigh scattering loss coefficient from these values we adapted Lacey and Payne s simple model Lacey Payne 1990 to our multilayer waveguide where the attenuation coefficient is linked to R the Fourier transform of the autocorrelation function R u through the expression ar 02 d n2 -n2 i -iR p-n2k0 cos0 d0 10 4nni 0 where n1 and n2 are the refractive indices of AlOx and GaAs respectively k0 is the wave vector in vacuum p is the propagation vector 0 is the photon scattering angle as regards as the interface and ộ d is the energy distribution of the propagating mode evaluated at the position of the different interfaces and normalized as follow w J02 y dy 1 - 11 Figure 6 illustrates the variation of the loss coefficient with the value of o2 and Lc in the case of our GaAs AlOx waveguides. The star marks the value of the loss coefficient deducted from our TEM observations and the rectangle symbolizes the value of the loss coefficient taking into account the effect of smoothing occurring through the pass of electrons in the thin foil. Our model gives a value for the propagation loss a . This value is in fair agreement with experimental data suggesting that Rayleigh scattering could be the main source of propagation losses. Fig. 6. Variation of the loss coefficient with the mean square value of roughness and the coherent length. 150 Advances in Optical and Photonic Devices 5. Experimental performances In the first reports of form-birefringent frequency conversion scattering losses did not allow the full exploitation of the huge normalized conversion efficiency. After the last technological advancements described above this is now possible in mm long devices with overall conversion efficiencies comparable to that of LiNbO3 waveguides. Current loss level still prevents the use of cm long devices which would result in even higher single-pass efficiency and make parametric oscillation .
