Reproduction de : Thèse de doctorat : Physique. Option optoélectronique : Metz : 2002. / Titre provenant de l'écran-titre. Notes bibliographiques.

This thesis with the research development in design and modeling of the lithium niobate (LiNbO₃) optical waveguides. In particular, the material and modal properties of the titanium (Ti)-indiffusion and annealed proton-exchange (APE) are investigated thoroughly. By linking the relation of the design and fabrication parameters with modal properties of the LiNbO₃ waveguides, a comparative study on modaling and characterization of diffused optical waveguides is presented. First we investigate the diffusion, exchange, and annealing processes analytically and numerically. Through comparing different models of index change with concentration of the related species such as titanium and hydrogen, the material properties can be calculated. The accuracy and the scope of validity for the analytical methods are also investigated. Some important fabrication and design parameters are abstracted and used for calculating the index distribution of the optical waveguides. Then, by applying a rigorous finite difference method, the modal properties of the diffused waveguides, such as modal profile, effective index, and coupling loss with the standard fiber, can be calculated. The modal properties of the optical waveguides directly link to the fabrication parameters of corresponding waveguides. Based on modal properties of optimized waveguides, the device performances of the related devices can be easily obtained. Based on the analysis of general LiNbO₃ optical waveguides, the detail material and modal properties of the titanium-indiffusion and APE LiNbO₃ optical waveguides are further investigated. Their fabrication processes are reviewed and typical process parameters are given. Furthermore, by comparing with measurement results of the titanium-diffusion and APE LiNbO₃ optical waveguides made in McMaster University, the relation between the waveguide modal performance and design parameters is built through some effective methods and ready to be applied in the design of optical devices. Finally, we reconstruct the refractive index distribution of the optical waveguides by using the measurement results of modal properties. / Thesis / Master of Engineering (ME)

This dissertation is divided into two separate parts covering my research in two different fields of optics. Part I consists of chapters 1-3 and covers experiments on periodically poled lithium niobate while Part II consists of chapters 4-6 and covers various spectroscopic methods designed for the application of in vivo blood analysis. Chapter 1 serves as a brief introduction to periodically poled lithium niobate and its fabrication process. In chapter 2, the key results of Part I, derived from a series of experiments on poling of thinned lithium niobate, are presented. Building upon these experiments, chapter 3 concludes Part I with a study on poling of crystal ion sliced lithium niobate. Part II begins with chapter 4, which describes a spectroscopic approach for non-invasive blood analysis in vivo. In chapter 5, experiments analyzing aqueous glucose solutions with mid-infrared and Raman spectroscopy are discussed. Chapter 6 concludes this dissertation with the design and demonstration of a innovative stimulated Raman spectroscopy system. In Part I, ferroelectric poling fabrication procedures were developed, optimized, and implemented for periodic poling of thinned lithium niobate. The free-standing samples of thickness from 500 μm down to 25 μm were thinned by chemical mechanical planarization and annealed before poling. Domain structure was investigated as a function of sample thickness using Raman, scanning electron, atomic force, and optical microscopy, and broadening of poled domains was consistently found to vary with sample thickness in a strong linear correlation. Domain broadening was reduced by 38% as the thickness of the poled sample was reduced from 500 to 25 μm. Micro Raman probe measurements showed a thickness-dependent contrast in Raman active mode intensity between poled and unpoled regions, with the thinner samples having a higher intensity contrast. To explore poling on even thinner free-standing samples, crystal ion sliced lithium niobate thin films of 10 μm in thickness were fabricated. Chemical mechanical planarization of the ion-implanted layer and annealing was performed to prepare the thin films for poling. Ferroelectric poling of the crystal ion sliced samples was attempted, but unsuccessful, suggesting that alternative fabrication processes may be necessary for poling of crystal ion sliced thin films. In Part II, several disparate experiments were conducted to progress towards a common overarching goal of developing a spectroscopic method for non-invasive whole blood analysis and metabolite monitoring. A portable visible and near-infrared spectroscopy system for in vivo blood spectral identification was developed and demonstrated in a clinical setting. A custom-designed clip attached the illumination and collection optics to opposite sides of the patients’ fifth fingertip, and applied gentle pressure, gradually pushing a small quantity of blood away from the measurement site, and inducing a time-dependent change in the effective path length of blood. Time-dependent visible and near-infrared spectra were measured from the collected transmitted and scattered light. A maximum likelihood model was developed to leverage the time-dependent spectral component and identify the spectrum of blood, isolating it from that of surrounding tissue. A second set of experiments were conducted to develop a model for predicting glucose concentrations from measured mid-infrared transmission and spontaneous Raman scattering spectra. Partial least squares regression models were trained, validated, and tested on the spectra of aqueous 0-10 mM glucose solutions measured by both spectroscopic modalies. The models proved to be accurate predictors of glucose concentration as the mean squared error of the model based on mid-infrared spectra ranged from 0.10 - 0.74 mM, and that of the Raman-based model ranged from 0.26 - 0.93 mM. Finally, an LED-based stimulated Raman system was innovated to improve upon the relatively weak spontaneous Raman signal in a cost-effective manner. Stimulated Raman gain using a broadband LED Stokes source was demonstrated in the measuring of vibrational spectra of aqueous 0-10 mM glucose solutions. Scattered light was detected via photomultiplier tube and measured using either a photon counter or a lock-in amplifier in two alternative versions of the system. Both stimulated and spontaneous Raman spectra were collected with each instrument for a total of four measurement modalities. The stimulated Raman spectra measured with the photon counter showed up to 100% higher intensity for some glucose modes compared to the corresponding spontaneous Raman spectra, but also had significantly greater noise. For the spectra measured with the lock-in amplifier, the glucose modes of the stimulated Raman spectra were only 20-30% higher in intensity than those of the spontaneous Raman spectra, but had similar levels of noise. Partial least squares regression models based on spectra measured by each modality were developed and compared. The model based on stimulated Raman spectra measured with the lock-in amplifier had the strongest predictive power of all modalities and predicted the concentrations of the aqueous 0-10 mM glucose solutions with a mean squared error as low as 9.96x10-4 mM, an order of magnitude lower than that of the model based on spontaneous Raman spectra.

Selectively erbium (Er) doped titanium (Ti) in-diffused optical waveguide amplifiers on lithium niobate (LiNbO3) substrate have been fabricated and characterized in the wavelength regime around λ = 1.53μm using counter-directional pumping at λP = 1.48μm. LiNbO3 waveguide amplifiers are desirable for providing gain in optical circuit chips through integration with other optical elements on a single substrate. A prerequisite for achieving useful gain rests on the optimization of overlap between the incident guided optical signal mode distribution and the evolving emission from excited Er ions. The extent of overlap can be controlled by adjusting fabrication parameters. Fabrication parameters for Er-doped Ti in-diffused waveguide amplifiers of useful optical gain have been optimized by diffusing selective patterns of vacuum-deposited 17nm-thick erbium film at 1100˚C for 100 hours into LiNbO3, and integrating with 7μm-wide single mode straight channel waveguides formed by diffusing 1070Å thick titanium film into the LiNbO3. Small-signal gain characterization was carried out with a -30 dBm of transmitted input signal power at λS=1531nm with counter-directionally launched pump power ranging between 0 to 119mW at λP=1488nm, using TM polarization for both the signal and pump beams. At a maximum launched pump power of 119mW, a signal enhancement of 8.8dBm for 25mm-long erbium doped region, and 11.6dBm for 35mm-long erbium doped region were obtained. The corresponding calculated net gain values are 1.8dB and 2.8dB, for the 25mm-long and 35mm-long Er-doped regions, respectively.

A chalcogenide glass (arsenic-trisulfide, As2S3) optical waveguide is vertically integrated onto titanium-diffused lithium-niobate (Ti:LiNbO3) waveguides to add optical feedback paths and to create more compact optical circuits. Lithium-niobate waveguides are commonly used as building blocks for phase and amplitude modulators in high speed fiber communication networks due to its high electrooptic coefficient and low mode coupling loss to single-mode optical fibers. Although it can easily be modulated using an RF signal to create optical modulators, it lacks the intrinsic trait to create optical feedback loops due to its low core-to-cladding index contrast. Ring resonators are main building blocks of many chip-scale optical filters that require these feedback loops and are already demonstrated with other material systems. We have, for the first time, incorporated As2S3 as a guiding material on Ti:LiNbO3 and fabricated s-bends and ring resonators. We have examined As2S3-on-Ti:LiNbO3 waveguides at simulation, microfabrication, and optical characterization levels.

Aluminum nitride (AlN) thin films were deposited on Z-cut LiNbO3 substrates using the reactive RF magnetron sputtering in this thesis. By means of the analyses of XRD, SEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power of 165W and substrate temperature of 400¢J. The piezoelectric bi-layers structure of SAW devices was then fabricated. The interdigital transducers (IDTs) were fabricated on bi-layers structure. The AlN thin film thickness of piezoelectric bi-layers structure was varied in order to discuss its effects on SAW devices. From the experimental results, it reveals that the center frequency of SAW filters increases with the increased AlN thin films thickness. It means that the SAW velocity increases as the AlN thin films thickness increases. The effects of bi-layers structure on SAW devices can be discussed in detail by measuring the parameters of SAW devices like insertion loss (IL), electromechanical coupling coefficient (K2) and the temperature coefficient of delay (TCD).

Programmable two-port polarization independent electro-optically wavelength tunable filters based on asymmetric Mach-Zehnder structure in LiNbO3 substrate have been developed for 1.55 µm application. The operation principle is based on Mach-Zehnder interference and TE↔TM polarization conversion. Fabrication parameters for channel waveguides, polarization converters and bandpass filters have been optimized. Straight channel waveguides 7 µm in width were produced by diffusing 1116 Å thick Ti into LiNbO3 substrate at 1035°C for 10 hours. Single mode guiding has been realized for both TE and TM polarization. Insertion loss of 2.9 dB for TE polarization input and 3.3 dB for TM polarization input were achieved on a 46 mm long sample. Single sideband programmable polarization mode converters were produced with 16 electrode sets, each containing 64 grating periods. Programmability was achieved by applying spatially periodic weighted independent voltages to interdigital electrode sets, and controlled electronically via a personal computer through a digital-to-analog converter array chip. Maximum conversion efficiency of more than 99% was realized for both TM→TE and TE→TM, and was observed at 1530.48 nm. Two-port polarization independent electro-optically tunable wavelength filters were produced based on the results obtained above. The 3 dB bandwidth is 1.1 nm and the nearest side lobes to the main transmission are down by about 9 dB for uniform coupling. Side lobes are reduced to about 20 dB below peak transmission after apodization, and the 3 dB bandwidths increased to ~ 1.3 nm as a result. Seven channels (channel -4, -2, -1, 0, +1, +2 and +4) were selectable by programming the voltages on each electrode set. Channel spacing is 1.1~1.2 nm. The tuning ranges from 1524.04 to 1533.56 nm. Fiber-to-fiber insertion loss of the filter at center frequency is 4.3 dB for TE input and 4.2 dB for TM input. The polarization dependent loss is < 0.5 dB for all selectable channels. The temporal response to a 21 V step change in applied voltages was measured to be 586 ns for the 10%-90% rise time and 2.308 µs for the 90%-10% fall time. This research work provides a convenient scheme for making programmable two-port tunable bandpass filters and ROADMs.

Reproduction : Thèse de doctorat : Génie Physique : Metz : 1991. / Titre provenant de l'écran-titre. Notes bibliographiques. Index.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 125 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 121-125).

Two collimated laser beams, wavelength O-514 μm are overlapped within a crystal of heavily iron doped lithium niobate to form a one-dimensional volume holographic grating, a few mm long, designed to behave as a highly selective filter at near infra-red wavelengths. A novel recording geometry is described and a variety of diagnostic experiments are undertaken to determine the main characteristics of the grating. A filter fabricated using this method is used to obtain single mode operation from a 1-55 μm semiconductor laser. The historical survey of holography contained in chapter one emphasizes the dynamic properties and applications of photorefractive recording materials. Standard results of two mathematical theories, kinematic and coupled-wave, are used in chapter two to predict the properties of a Bragg grating when replayed with infra-red light. Chapter three details the recording materials suitable for an infra-red filter, followed by a discussion on the concept of 'scaling'. The recording mechanism of iron doped lithium niobate, including its fixing and erasure process, is presented in chapter four as a basis for selecting the most advantageous crystal characteristics. Mathematical models describing the complex dynamic recording process in iron doped lithium niobate are introduced in chapter five. A novel recording geometry involving the use of two prisms is critically described in chapter six, from initial conception to final implementation. The performance of the grating as an infra-red filter is assessed in chapter seven by measuring the angular response of the transmitted and diffracted beams at a wavelength of 1-152 microns. Chapter eight discusses the applications for volume holographic filters, with particular reference to one example. In chapter nine general conclusions are drawn and future directions for research are suggested. A number of appendices are also included.