Study On Low Polarization Dependence Of Refractive Index Change Of Quantum Wire Material

In quantum wire material,free carriers are limited in two dimensions.This limitation makes quantum wire material have better optical properties than bulk material and quantum well material,such as easier to achieve the required particle beam inversion number of lasers and more stable temperature characteristics.The refractive index change guided by carrier concentration change in active region is the main working mechanism of all-optical switch,all-optical logic gate,wavelength converter and other optical communication devices.In order to ensure good performance of these devices in practical applications,it is required that the devices have low polarization dependence on the refractive index changes of TE mode and TM mode when carrier injection occurs.Based on the theory of semiconductor energy band and combined with the strain distribution of quantum wire material,the energy band matrix of quantum wire material is established by using the eight-band k.p theoretical model with strain,and the energy band structure is solved by using the orthogonal plane wave expansion method.On this basis,the quasi-Fermi distribution of conduction and valence bands of quantum wire,momentum matrix elements and spectral line broadening effects after carrier injection are calculated.Considering the effect of band gap shrinkage,the change of the absorption coefficient caused by the band filling effect is obtained.Furthermore,the refractive index change caused by the change of absorption coefficient is obtained by Kramers-Kronig transformation.Finally,the refractive index change caused by free carrier absorption effect is calculated,and the theoretical analysis model of refractive index change of quantum wire materials under carrier guidance is established.Based on the theoretical analysis model,the influences of wire material component,barrier material component,columnar wire diameter and free carrier concentration on refractive index change spectra of TE modes and TM modes are simulated and analyzed by MATLAB,and the physical mechanism is also analyzed.On this basis,a multi-parameter adjustment method is proposed to realize low polarization dependence of refractive index change.The quantum wire material with low polarization dependence(<1%)of refractive index change within C-band(1530nm-1565 nm)is designed.It is shown that the multi-parameter adjustment method can be used to guide the design of low polarization dependence of refractive index change of quantum wire material.