Study On All-optical Bistability With Low Threshold And Band-rejection Filter With High Extinction Ratio

The dispersion equations of the dielectric slab waveguide,symmetrical metalcladding waveguide(SMCW),multi-layer slab waveguide,and multi-layer SMCW are firstly deduced and discussed,respectively.In the following,the reflectivity of the prism-waveguide structure is inferred by the distribution of the transverse electric field in each layer.These processes aim to analyze the property of the SMCW from a perspective of the waveguide principle.In addition,the ultrahigh-order mode(UHM),excited in the SMCW,whose guiding layer is extended to a submillimeter scale is also discussed.According to the dispersion equations,a further deduction can get conclusions that the UHM owns characteristics,including polarization-independent,high quality factor,high sensitivity,and slow light.It is believed that this SMCW can be widely used in optoelectronic devices,sensors,etc.A SMCW,whose guiding layer is inserted with Kerr nonlinear medium,based alloptical bistable configuration is proposed.Since the interaction of the oscillating wave with the Kerr nonlinear medium induces field enhancement effect,a slight change of incident beam intensity leads to a variation of the dielectric constant of the Kerr nonlinear medium.Rest on this,the polarized-independent all-optical bistability with an ultra-low threshold intensity can be achieved.It is also found that the threshold intensity is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium.In addition,the criterion for the existence of optical bistability is derived,which can be utilized to calculate the minimum threshold intensity in this structure.A prism-waveguide cascaded coupling system based band-rejection filter(BRF)is proposed.The system consists of an equilateral trapezium prism and a deposited multilayer structure.The radiative and intrinsic dampings matching condition can be well met by properly regulating the light extinction coefficient of the guiding layer and the thickness of the coupling layer.Under this condition,a series of resonant dips is realized in the reflectivity wavelength spectrum.Owing to the fact that the module of reflectivity is less than one,and the reflectivity of the cascaded coupling system is the square of a normal prism-waveguide structure,which assists in further reducing the reflectivity of the rejected frequency.To acquire a free spectral range(FSR)that is broad enough to cover the Raman spectrum scattered from the frequently used sample,the thickness of the guiding layer in the system is reduced to a micrometer scale.According to the numerical calculation,the beam intensity in the FSR is mostly reflected with an insertion loss.This system can be used in Raman signal processing to de-noising the elastic scattering background.