A Broadband Polarization Beam Splitter Based On Negative Refractive Lithium Niobate Photonic Crystal Slab

In 1968,Veselago analyzed the propagation phenomenon of electromagnetic wave in the materials with negative dielectric constant?and magnetic permeability?.Until 1987,EliYablonovitch and Sajeev John first proposed photonic crystal?PhC?,a spatial periodic dielectric structure which exists band gaps with a certain range of frequency.As an artificial microstructure formed by the periodic arrangement of the mediums with different refractive index,photonic crystal has gained more and more attentions in recent years with the properties of photonic bandgap?PBG?and photonic localization.Lithium niobate?LiNbO₃,LN?is an important nonlinear optical material with wide transmission window?400nm5500nm?,since LN is called"optical silicon"for integrated optical system,which has more applications in achieving wavelength converters,optical logic gates and computers,etc.,and especially in generating quantum polarization sources by spontaneous parametric down conversion?SPDC?.The size of traditional optical system based on LN is 1cm or larger,which limit the application in integrated optical circuits.Therefore,more and more attentions are focused on LN-based PhC.In this dissertation,we propose a polarization beam splitter?PBS?,a new kind of optical device based on photonic crystal.The research significance and theoretical background are introduced.We design a PBS,using a negative refractive PhC wedge slab based on lithium niobate.By using Rsoft CAD,we calculate the PBG structure of TE and TM polarizations by Plane Wave Expansion?PWE?.Meanwhile,we stimulate the propagation phenomenon of TE and TM polarizations in the PhC structure by Finite-Difference Time-Domain method?FDTD?.The detailed _i^rs^Te_auppwnp^hs_snoohcie^ee_llgiinaac_l ^a_cdrrt_ge ^r_ihir_e^{F r c}_zzz u^ierha_{ont aetfhh}m^s_t ^st_{d ie al} ^{c l} _o^{o oy}_{8i s l} ⁿ_gnw_di,ⁿ _{hs ig}i_h^{t t} _fatd^e_ih ^{o h}_ftiti t^nfe_{gt ei}h_nss ^t_{hrn 1} ^s _{e t}.^{p u} _fo5to^ras_{nPor 5t}f_h^{r oi}_{r a} ^e_t?^np _{Cn w} ^g_Pm4^{o a}_{Lm oB}0^{s s}_{t Ni} 0^{e fL}_oaGsn^d_-p ^oi_{sn b a}m ^lNlPbohO_{irdaraoet snanswel d}rdaraoet snanswel d 5^{w C3}_{i da} da 5^s _{a az v}0._{b p en}ⁱⁱ0^ss_{ePr od l} n_o ^b _{u BeP} m^ta_{ptnS B} ^h_wa._g^{s a}_{i g9St} ^et_ada.0hT^d_{r et ei}i h°_b^{i ot}_{T o} e_{abw hn m}ⁿ _n ⁱ_{a ie} p^s_{tdno p h}r ^L_rdwi_p ⁱ_hee n^aN_{irw eT d}c^b _ointi^nO_tEdphop ³_{ht oa} l^o _hmse_o ⁿ_na.^-_{e e fn} ^{c l}_dno ^oi_{d8T o}f ₇^{l n}_0h ^u_0nP ^e_{%Te n}p^{a m} _{B M} M r^r_mo ⁿ_tS o _frw.p^am_{a ipc}oⁿ_ntTahs^ad_{osE l}^te_{n m} ^e_{a t}d ^ar_irh ⁱⁱ_{asis ez}^ra°_npsP ^l_{iia d l}^hB_otb ^o_{ti r n}S^wl_{o T ot n}^{ie t}_ahMoi^sh_sdes_f.,K Then we compare the difference between LN-based and Si-based PBS.The absolute difference value of refractive index between LN and air is smaller than that between Si and air.Meanwhile,there occurs large reflection at the surfaces for a Si-based PhC,both can induce energy loss for Si-based Phc,and no good PBS feature can be obtained with high efficiency.Finally,we conpare the wavelength bandwidth of different thickness of LN slab.The study find that when different thickness of LN slab increases in the range of 700nm to 900nm with the interval of 50nm,the central wavelength of TE and TM polarizations shifts toward the direction of wavelength increasing.And the wavelength bandwidth is on the increase with the transmission of over 80%.