Study Of Band Gap Broadening Method And Waveguide Transmission Property Of Photonic Crystal Formed By Holographic Lithography

Since the concept of photonic crystal(PhC) was proposed in 1987,photonic crystal has attracted great attention in the fields of optical physics,condensed matter physics, electromagnetic waves and information technology.Lots of achievements related to theoretical and experimental studies have been reported and applied in some regions.For the effective application of photonic crystals,designing and fabricating photonic crystals with complete band gap in near infrared and visible region become a focus for science research in the last decade.Compared with other techniques of PhC fabrication,such as Layer-by-Layer method, semiconductor microfabrication,self-assembling approach,etc.,the process of holographic lithography(HL) is more economical,rapid,convenient and effective.In this thesis,holographic lithography,plane wave extension method(PWE) and finite difference time domain(FDTD) are used to systematically investigate the photonic crystals with large complete band gap formed by symmetrical umbrellalike beams configuration in theories.We have proposed several desiging methods to produce holograpgic PhCs and widen their complete band gaps effectively,and carried out a series of simulation study of PhC structures and their transmission properties to verify our calculation results of band gap characters.The main initiative contributions in this dissertation include following aspects:1,Beams design and PBG properties study for optimized 2D square lattice formed by HLIn holographic fabrication of photonic crystal the shape and size of the dielectric columns or particles("atoms") are determined by the isointensity surfaces of the interference field.Therefore,their photonic band gap(PBG) properties closely relate to their fabrication design.As an example,in Chapter 3 we propose two kinds of holographically formed novel two-dimensional(2D) square lattice.One is composed of pincushion columns rotated by 45°,and it is shown that this structure has complete PBGs in a wide range of dielectric contrast comparable to or even larger than those of the same lattice with square columns reported before.Theoretical analysis has revealed that a 2D lattice with circular columns connected by veins can produce large complete band gap when the radius of columns and the width of veins are properly choosen.Here we have proposed a holographic method to fabricate another similar 2D structure of irregular columns.These two kinds of PhCs can yield greater 2D complete band gaps.Moreover, the requirement for various system parameters is more relaxable in the fabrication process of PhCs with complete band gaps.We have systematically analysed the relations between these system parameters and PBGs,and derived a conclusion from these research results to give a guideline for practical fabrication.2,Structure design and PBG properties study of 2D triangular hybrid holographic latticeIn Chapter 4,we firstly carry out the study of relation between symmetry and band gap of periodic PhCs,and propose a kind of technique to change the symmetry property of photonic crystal with second exposure in holographic lithography.The theoretical analysis indicates that complete relative PBGs can be enhanced by properly lowering the symmetry property of photonic crystal lattice and choosing the size and pattern of the columns.Computations show that the optimazed normal structure has complete band gaps over wide ranges of system parameters,and the minimum dielectric constant required to open a complete band gap withΔω/ω＞1%is as low as 3.8,which is the lowest compared with the results of 2D periodic photonic crystals ever reported.These results provide a valuable guideline for realization of light transmissing efficiently in waveguide with low dielectric constant contrast.3,Holographic fabrication of 3D PhCs by interference of umbrellalike symmetrical beams and the study of their PBG propertiesGenerally,3D PhCs are more versatile than 2D PhCs.An important way to make 3D PhCs by HL is the interference of four umbrellalike symmetrical beams(IFUB) where three ambient beams(A-beams) form the same apex angleθwith a central beam (C-beam) and any two of the three A-beams also form the same angle.In Chapter 5 a theoretical investigation of the possible three-dimensional photonic crystal structures that can be created by holographic interference using the symmetric umbrellalike configuration of four plane waves is made.The irreducible Brillouin zones and the photonic band gap properties of the possible resulting crystal lattices when the apex angle is varied from 10°to nearly 180°are investigated,which will be helpful to the efficient use of this method in experiments.Moreover,we propose a holographic design of five-beam symmetric umbrella configuration and systematically analyze the band gap properties of resultant photonic crystals when the apex angle is continuously increased. The diamondlike structure with a largest relative band gap can be obtained with this recording geometry conveniently where all the beams are incident from the same half-space.This five-beam symmetric umbrella configuration provides a feasibility to relax the experiment requirements in HL and optimize PBG property of photonic crystals.4,Study of transmission properties in holographic photonic crystal waveguideIn order to study the waveguide characters of 2D holographic PhCs,we have investigated the transmission properties of the photonic crystal waveguide(PCW) which is a line defect with two 60°bends in a 2D triangular holographic PhCs in Chapter 6. Calculations have shown that for this PCW high transmission(＞90%) through sharp comers can be obtained in a wide frequency range.As far as we know,this result should be the widest frequency range with high transmission(＞90%) in the waveguide of similar 2D triangular PhCs ever reported.We have also found that the specific holographic designs of PhC have strong influence on the resonance between the two bends.This work makes holographic PhCs promising for application in the range of photonic integrated circuits and provides a guideline for optimizing the transmission property of holographic PCW. 5,Experimental demonstration of holographic fabrication of 2- and 3-D PhCsFinally,fabrication of PhC templates by HL and the PhCs with controlled defects by combination of single-photon and two-photon photopolymerization have been studied experimentally.In our experiment,we have designed several practical recording equipments and fabricated several PhCs templates.Moreover,we have introduced the line defect with an orthogonal bend in PhCs templates successfully.The work in this field may be limited by our experimental conditions,but these experimental results have proved that HL has unique advantage in fabrication of PhCs with large area and low cost, and verify that combination of holographic lithography and two-photon polymerization can be used to fabricate PhCs with defects.Arranging from photonic band gap broadening,optimization of transmission properties to the defect behavior,and from theoretical analysis to experimental demonstrations,these research works provide a systematic study in the field of holographic PhCs with fruitful achievements which have been published in a series of famous international journals,such as Optics Express.