This thesis describes the outcome of study to investigate methods of broadband matching to photonic devices such as lasers and high speed detectors. The thesis is divided into two areas of interest relating to the design of broadband fiber optic links. The first area is the application of numerical methods and commensurate line methods to the design of compact equalisers which allow an improved transducer power gain over a wide band. It is shown that physically small equalisers can yield an improvement of 4 dB over a 2 GHz bandwidth. The second area considered is the distortion inherent in a laser diode. Detailed measurements of the second order and intermodulation products are given. A small signal perturbation analysis is presented which helps to explain the observed distortion products. The results of numerical simulation of the distortion using a state variable implementation of the full rate equations and related first, second and intermodulation equations is presented and possible methods of reducing the distortion are explored. It is shown that in principle the distortion could be reduced by pre-generating the distortion and adding an inverted form of the distortion to the transmitted signal. The distortion can then be corrected in the fiber and simulation studies suggest that an improvement of 13 dB optical or 26 dB electrical may be possible.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 115-121).

Bragg grating reflectors etched in amorphous silicon overlay films have been integrated with Ti:LiNbO3 optical waveguides. With a 12.5 mm long grating segment and an etch depth of ~ 93 nm in a 105 nm-thick silicon film, a narrow (0.05 nm) spectral bandwidth with a record high transmission dip (> 20 dB) was achieved at a wavelength of ~1542 nm for TE polarization on an x-cut, y-propagating substrate. The reflectance in the channel waveguides is found to be strongly dependent on the depth of the etched grating. The 3-dB bandwidth of 0.05 nm obtained for all tested samples is the smallest reported for waveguides in LiNbO3. The effect of the Bragg waveguide loss factor on the transmittance and reflectance spectra is investigated using a model for contra-directional coupling that includes an attenuation coefficient. The Bragg grating spectral characteristics are exploited to fabricate distributed Bragg feedback modulators (DBFM) and Bragg reflector Fabry-Perot modulators (BFPM). The sharp cut-off in transmission and reflection spectra, which is an inherent characteristic of Bragg grating, was tuned by applying voltage via the linear electrooptic effect, to produce intensity modulation. The Bragg grating based modulators consume less electric power compared to polarization intensity modulators (PIMs). The DBFM demonstrates 1/1.6 times the modulating voltage of a PIM with identical waveguide and electrode structure. The BFPM shows 1/3.3 times the modulating voltage of the PIM. No difference in the frequency response is observed among the three modulators. Comparison of the modulation sensitivity in the linear region indicates that the Bragg grating based modulators provide better sensitivity than that of the PIM with identical waveguide and electrode structure. These results indicate the potential advantage of the Bragg grating based modulators for enhanced modulation efficiency over conventional modulators. Further improvements can be expected from the optimization of the electrode design.

This thesis concerns various aspects of the durability offibre optic sensors embedded in composite. Since repair orreplacement of embedded sensors is not generally possible, thefunctional reliability of embedded sensors is one of the mostimportant prerequisites for successful use. The main researchobjective was to investigate the interaction between the sensorand the composite, and how this is affecting the mechanical andoptical sensor response. Fibre optic sensors embedded incomposite structures induce local stress concentrations whenthe composite is subjected to mechanical loads andenvironmental changes such as temperature and moisture. Acomplex transfer of stresses through the interfaces between theembedded sensor and the composite occurs and can result inlarge local stresses in the composite and a significant changein the response of the embedded sensor. These stressconcentrations make the interfaces susceptible todebonding. The sensor performance was studied experimentally andnumerically. Some basic results were generated for the EFPI andBragg grating sensors. The phase-strain response was determinedduring static and fatigue loading. The results showed that thesensors were more reliable in compression than in tensilestatic and fatigue loading. Generally, the sensor reliabilityduring loading was significantly improved for the Bragg gratingsensors over that of the EFPI sensor, as an effect of thesensor geometry. This was also demonstrated in theinvestigations on impacts. Impacts do not necessarily result indamage in the composite, but might cause debonding or otherfailure modes in the sensor area. Large, local stressconcentrations occur at several positions in the EFPI sensor,which pointed out that this sensor type was not suitable forembedded applications. The shift in focus from the sensor concept based on the EFPIsensor to that based on the Bragg grating sensor manifesteditself in several studies. The calculated deformation fieldaround an embedded optical fibre was verified in experimentsusing a high-resolution moiré interferometric technique.Furthermore, the improvement in the coating technology wasverified. A significant higher interfacial strength wasobtained with the silane-treated glass surface. The resultsindicated that at least a twofold improvement of the shearstrength was obtained. To simultaneously measure the in-plane strain components andthe temperature change, embedded Bragg grating sensors werearranged in a rosette configuration. The relationship betweenthe optical response from each sensor and the strains in thelaminate was numerically and analytically established. Damage lead to stress redistribution in the sensor region,which may influence the output from the embedded Bragg gratingsensor. The effect was numerically evaluated for interfacialdamage, and was compared to that of a sensor with undamagedinterface. The results showed that debonding might have asignificant influence, in particular for combined thermal andmechanical loading. <b>Keywords</b>: composites, fibre optic sensor, embedded, EFPIsensor, Bragg grating sensor, durability, fatigue, impact,strain measurement, interface, stress analysis

It is estimated that, between the year 2000 and 2003, thenumber of online Internet users will grow from 250 millions to500 millions. This growth results in rapidly increasing demandfor fibre-optic communication bandwidth, occurring at alllevels: from access and local area networks (LANs) tometro-area networks (MANs). A now established solution for manyapplications such as interconnects and Gigabit Ethernet is thevertical cavity surface emitting laser (VCSEL). The advantagesof VCSELs are numerous: low fabrication and coupling costs,large modulation bandwidth, array integration and tunability.VCSEL-based modules, with speed up to 2.5 Gbit/s are nowcommercially available for multimode fibre (MMF) basedapplications. However, devices operating at long wavelength andhigher transmission rates (10Gbit/s and more) will be needed inthe near future. The purpose of the work presented in this thesis was toobtain an understanding of the high-speed properties of VCSELs,in order to extend the modulation frequency at which they canbe used in fibre optical communication systems. An approach forsystematic high-speed characterisation of VCSELs is presentedand both its potential benefits and problems are discussed. Itis shown that the VCSEL dynamics, under certain conditions, canbe well described by a small number of parameters that can beextracted from small signal measurements and used forfurtheroptimisation. The calibrated small-signal modulation responsesof VCSELs have been measured and fitted to an analyticaltransfer function allowing the estimation of the resonancefrequency, damping factor and parasitic cut-off at differentbias points. This data can be used to determine the relativeimportance of different bandwidth limiting effects due todamping, thermal heating and parasitics. Small signal analysis and transmission experiments wereperformed with a large sample of VCSELs covering the variousranges of applications. Visible VCSELs and resonant cavitylight emitting diodes (RCLEDs) for very short reach plasticoptical fibre (POF) applications, 850nm datacom VCSELs forshort distance multimode fibre networks, and long wavelengthVCSELs for long haul single mode fibre transmission. <b>Keywords:</b>Semiconductor lasers, VCSEL, high-speedmodulation, fibre optic networks, datacom, RCLED, plasticoptical fibre

External modulators will become key components in fiberoptical communica- tion systems operating at 40Gbit/s andhigher bitrates. Semiconductor electro- absorption (EA)modulators are promising candidates because of their high-speed potential, and their process compatibility with thecorresponding semi- conductor laser light sources. Thetraveling-wave (TW) electrode concept for electro-opticmodulators has been used for a long time in order to resolvethe con°ict between high modulation depth and highmodulation bandwidth. Re- cently, it has been adopted for EAmodulators as well. This thesis presents the work carried out on design,fabrication and analysis of traveling-wave EA modulators(TWEAM) based on InP-InGaAsP. The lengths of TWEAM arecomparable to the lengths of their lumped counterparts. Theexperimental data of this work were analyzed in order show thatthe traveling- wave concept results in better performance evenfor short EA modulators. One key issue is the impedancematching. The low intrinsic characteristic modulator impedancehas to be matched with a corresponding load. In this case, theTW con figuration leads to a much higher bandwidth than for alumped EA modulator with the same length and the same connectedload. An InP process was developed allowing the fabrication ofTWEAM with integrated termination resistors. Experimentalmicrowave properties were ob- tained for different TWEAMgeometries. It is reported on long TWEAM that showstate-of-the-art bandwidth. A 450&amp;#956m long TWEAM reached43GHz, and 67GHz (beyond characterization limit) were indicatedfor a 250&amp;#956m device. The experimental results onmicrowave properties were compared to full-wave, and circuitmodel simulations. The analysis reveals an impedance bandwidthtrade- off for the cross sectional electrode configuration. Results of a new high-impedance design in form of asegmented TWEAM are presented. The devices were processedwithin the frame of this work and record bandwidth performanceis reported. At 50&amp;#937­ impedance a bandwidth in the90GHz region was indicated.

Wavelength Division Multiplexing Passive Optical Networks (WDM PONs) offer a great solution to satisfy the increasing demand of bandwidth. In addition, it offers a higher level of data security through virtual point to point connections. A great challenge in realizing cost-effective WDM PON is the need for a transmitter at each Optical Network Unit (ONU) with a dedicated wavelength, which overloads the total cost of the system, in addition to reducing the number of available wavelengths in the system. Remodulation scheme is an ultimate solution for these problems of WDM PONs as the downstream signal itself is remodulated with upstream data which saves the need for a laser source at the ONU side. In this thesis I propose and experimentally demonstrate a novel wavelength remodulation scheme for WDM PONs that employs Differential Phase Shift Keying (DPSK) for downstream and Return to Zero DPSK (RZ-DPSK) for upstream. The use of DPSK enhanced the system with improved receiver sensitivity and RZ-DPSK improved the tolerance toward chromatic dispersion. In addition, I investigate the Backreflection (BR) penalty resulting from beat noise of BRs with upstream signal in a bidirectional WDM PON system that uses remodulation and phase modulation as a modulation format. I experimentally demonstrate the optimal conditions to operate the system and minimize the BR penalty.

Este trabajo de tesis recoge las contribuciones aportadas en el campo de los sensores de fibra óptica en tres ámbitos de trabajo. Un sistema sensor de alta temperatura sin contacto con transductores de fibras ópticas de sílice se ha presentado. Dos topologías de "ojo abierto" y "ojo cerrado" y un algoritmo de decodificación "pirometría de banda dual" propuesto en este trabajo son las novedosas aportaciones presentadas. El sistema ha sido validado en laboratorio y en pruebas de campo de forma exitosa. Para sensores de temperatura con fibras dopadas con Erbio se ha demostrado que su máxima sensibilidad tiene lugar cuando la longitud utilizada es superior a la óptima exigida por el bombeo. Finalmente se ha modelado y validado en laboratorio una red de sensores acústicos basados en interferómetros Fabry-Perot de cavidad larga determinando a partir del modelo obtenido la fase mínima detectable y la visibilidad máxima del sistema. / The thesis collects contributions in the field of optic fibre sensors for three areas. A high temperature sensor system without contact based on silica optic fibre transducers has been submitted. Two topologies "open eye" and "closed eye" and a dual band pyrometer decoding algorithm are the submitted innovative contributions. The system has been validated successful in the laboratory and field tests so. Another contribution has been the demonstration that the maximum sensitivity for temperature sensors based on Er-doped fibres occurs when the used length is more than the optimum required by pumping. Finally a network of acoustic sensors based on Fabry-Perot fibre interferometers has been modelled and validated in the laboratory. The minimum detectable phase and maximum visibility of the system has been obtained from the proposed and validated model

Le travail effectué dans le cadre de ce mémoire nous a permis de faire des préparations chimiques de monocristaux à partir de substitution partielle de phosphore par l'arséniate dans des nouveaux composés issus de la famille de KDP . D'une part, la présence des propriétés physiques intéressantes propre au matériau NDAP fournie des résultats inédits en comparaison avec les composés étudiés dans la famille de KDP, en particulier la présence de la superconductivité à la température ambiante. Ce dernier point, paraît prometteur pour l'application de ce matériau dans divers domaines technologiques. D'autre part, l'amélioration considérable des propriétés physiques du composé KDP doublement substitué, permettant au composé KNDAP d'être un candidat potentiel pour couvrir les besoins technologiques dans le domaine de l'émission Laser, offrant ainsi de nouvelles perspectives pour des applications militaires et fondamentales.

The past decades have witnessed the development of new materials with large nonlinear optical properties, which have made them attractive candidats for a broad spectrum of breakthrough applications in the electro-optic and photonic fields (e.g., telecommunication and computing). A deeper understanding of the relationship between, on the one hand, the chemical structure and, on the other hand, the electronic and (linear and nonlinear) optical properties has proven useful for the rational design of new efficient materials. Reaching such an understanding has attracted major interest in the scientific community worldwide in both academia and industry. Therefore, the development of new efficient NLO chromophores and materials along with commercial devices of high quality is helped via the establishment of multidisciplinary research teams combining: (i) the theoretical modeling using quantum-chemical computational calculations; (ii) the organic synthesis; (iii) the optical characterization; and (iv) the device fabrication. In this dissertation, quantum-chemistry is used to evaluate the second- and third-order NLO properties of series of new chromophores and take advantage of a feedback loop with the experimental team to understand the structure-property relationships.