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Refractive Index Modulation And Waveguide Construction By Ion Irradiation In Several Optical Materials

Posted on:2019-02-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:C ChenFull Text:PDF
GTID:1318330545453593Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
Integrated optical circuit,a highly integrated optical system,is composed of several functional elements,such as micro light sources,optical switches,beam splitters,directional couplers,modulators and micro detectors.It enables sending,receiving,transmitting,and processing of optical signals in a chip scale.Compared with the conventional optical system,integrated optical circuit is smaller in volume,lighter in weight,lower in cost,and more stable in performance.Optical waveguide,the basic element of integrated optical circuit,is constituted by a relatively high refractive index region surrounded by relatively low refractive index regions.Usually,they have geometries in wide variety and sizes of micron or even sub-micron scale that is comparable to the wavelength of light.Based on the total internal reflection,the light field is enclosed inside the waveguide region and can only be transmitted in a specific direction.Owing to the extremely tiny space of the waveguide region,the power density of the internal light field is easy to reach a high level.As a consequence,some of the optical properties of substrate materials,such as nonlinearity and laser characteristics,will have better performance in the guiding structures.The quality of the waveguide is related to the performance of the whole integrated optical circuit.Therefore,the fabrication of high quality waveguides is of extraordinary significance.Appropriate substrate material should be selected for waveguide fabrication,which is necessary to have wonderful optical,physical and chemical properties,like high transmittance,high damage threshold,high temperature durability,corrosion resistance and anti-deliquescence.The frequently used materials contain single crystals,transparent ceramics,optical glasses,semiconductors and organic polymers.Furthermore,the fabrication technique must be applicable for the selected substrate material;only in this way can the ideal guiding structure be achieved.The basic principle of waveguide producing is to induce the modification of the refractive index in the substrate material,so that the refractive index of the waveguide region is greater than that of the surrounding environment.At present,the relatively mature approaches for waveguide fabrication include thin film deposition,epitaxial growth,metal ion diffusion,ion exchange,ion implantation or ion irradiation,pulsed laser inscription and so on.Ion implantation and ion irradiation have not only applicability for most kinds of materials,but also strong flexibility and controllability.However,the mechanism of the two methods is not exactly the same in waveguide formation.Generally speaking,ion implantation changes the refractive index of the substrate,mainly depending on the structural damage caused by elastic collision between the target nuclei and incident ions at the end of projected range.This damage usually results in a partial drop of refractive index and the formation of an optical barrier.The waveguide is located between the barrier and the surface of the sample.The Ion adopted by ion irradiation has relative atomic mass over 6,and energy more than 1 MeV/amu.In this case,the incident energy is mainly deposited on the material through the inelastic collision between the ions and electrons in the target material,causing the electronic damage and leading to the change of the refractive index.This book mainly studies the ion implantation and ion irradiation on the modification of refractive index in several optical materials.The planar optical waveguides are formed through bombarding the sample surfaces by ions with proper type,energy and dose.Combined with other surface patterning technologies,for example,femtosecond laser ablation and diamond blade dicing,two-dimensional ridge waveguides and the three-dimensional branch waveguides are further obtained.The guiding characteristics of waveguides,such as propagation modes and propagation losses,as well as functional properties related to substrate materials,such as fluorescence features,up conversion emissions and nonlinear frequency conversions,are respectively characterized.According to the energy depositions of ion implantation or ion irradiation,the refractive index distributions for waveguides are reconstructed reasonably.The propagations of light field in waveguides are simulated and compared with the measured results.We have explored a new method of modulating the refractive index of lithium niobate crystal,that is,the electronic energy deposition in the process of argon ion irradiation.By adjusting the energy of the incident ions,an optical barrier could be created at a variable depth.On this basis,the surface type waveguides and embedded cladding like waveguides were successfully constructed with different thicknesses.In the experiment,we utilized the second order nonlinear polarization effect of certain crystals,to realize efficient output of the generated second harmonic from waveguides,through different phase matching methods,including birefringence phase matching and non-critical phase matching,and under two regimes of continuous wave and pulse laser.The specific contents of this book contain:On the surface of Nd:SLG and Nd:SGG disordered crystals,ridge waveguides with relatively smooth sidewalls were manufactured,using 15 MeV carbon ion irradiation combined with diamond dicing.The guided modes and propagation losses were measured from 633 nm visible light to 4 ?m infrared band,showing fine light limitations and excellent guiding characteristics of the obtained ridges.In addition,it is found that the fluorescence properties of neodymium ions are retained in the waveguide to a large extent,providing the possibility for waveguide laser generation.On the surface of erbium and ytterbium co-doped phosphate glass,ridge waveguide structures with different width were fabricated,using femtosecond laser ablation and 15 MeV carbon ion irradiation.The mode distributions and propagation losses were measured at the wavebands of 633 and 1064 nm.The refractive index profile near the sample surface was reconstructed,according to the situation of ion energy deposition.Under the excitation of 980 nm laser,the upconversion emission of green and red fluorescence was realized in the ridge-shaped erbium ytterbium co-doped phosphate glass waveguide.On the surface nonlinear potassium titanyl phosphate(KTP)crystal,high quality(sidewall roughness of approximately 2 nm)and low loss(propagation loss about 1dB·cm-1)ridge optical waveguide were manufactured,using 15 MeV carbon ion irradiation combined with precision diamond dicing process.The waveguide modes at 532 and 1064 nm waveguides were measured,and the refractive index distribution of the ridge waveguide was reconstructed.The effect of carbon ion irradiation on the nonlinearity of KTP crystal is analyzed by the comparison of Raman scattering spectra.On the condition of type II birefringence phase matching,frequency doubled green light was effectively output from the waveguides.Under the pump of 1064 nm pulse laser,the maximum second harmonic output power and light conversion efficiency are up to 110.9 W and 12.4%respectively.In the nonlinear potassium titanyl arsenate(KTA)crystal,ridge waveguides and Y-branch waveguide beam splitters were achieved with different specifications,using 15 MeV oxygen ion implantation combined with femtosecond laser ablation technology.The propagation characteristics of the waveguides were studied at the wavebands of 633 and 808 nm.It is found that the output light power of the waveguide varied with the input light polarization,and the splitting ratio of the beam splitter was determined by the alignment of the incident beam.After stepwise annealing treatments,the propagation losses of the waveguide were significantly reduced and the guiding performances were greatly improved.The modulation of the refractive index of lithium niobate(LiNb03)crystal has been actualized through the electron energy deposition of argon(Ar)ion irradiation.By changing the incident energy of ions,the surface waveguides were obtained with different specifications.A cladding-like waveguide buried below the surface was constructed,using multi-energy irradiation.The propagation characteristics of the waveguides,as well as frequency doubling performance under non-critical phase matching,were studied at the wavelength of 1064 nm.According to the variation of electronic stopping power with the depth,the ordinary and extraordinary refractive index distributions were reasonably rebuilt for the waveguides.
Keywords/Search Tags:integrated optical circuit, optical waveguide, ion implantation, ion irradiation, femtosecond laser ablation, diamond dicing, ridge waveguide, branch waveguide, fluorescence, up conversion emission, second harmonic
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