Optical frequency comb spectroscopy (OFCS) combines two previously exclusive features, i.e., wide optical bandwidth and high spectral resolution, enabling precise measurements of entire molecular bands and simultaneous monitoring of multiple gas species in a short measurement time. Moreover, the equidistant mode structure of frequency combs enables efficient coupling of the comb power to enhancement resonant cavities, yielding high detection sensitivities. Different broadband detection methods have been developed to exploit the full potential of frequency combs in spectroscopy, based either on Fourier transform spectroscopy or on dispersive elements.There have been two main aims of the research presented in this thesis. The first has been to improve the performance of mechanical Fourier transform spectrometers (FTS) based on frequency combs in terms of sensitivity, resolution and spectral coverage. In pursuit of this aim, we have developed a new spectroscopic technique, so-called noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS), and achieved a shot-noise-limited sensitivity and low ppb (parts-per-billion, 10−9) CO2 concentration detection limit in the near-infrared range using commercially available components. We have also realized a novel method for acquisition and analysis of comb-based FTS spectra, a so-called sub-nominal resolution method, which provides ultra-high spectral resolution and frequency accuracy (both in kHz range, limited only by the stability of the comb) over the broadband spectral range of the frequency comb. Finally, we have developed an optical parametric oscillator generating a frequency comb in the mid-infrared range, where the strongest ro-vibrational molecular absorption lines reside. Using this mid-infrared comb and an FTS, we have demonstrated, for the first time, comb spectroscopy above 5 μm, measured broadband spectra of several species and reached low ppb detection limits for CH4, NO and CO in 1 s.The second aim has been more application-oriented, focused on frequency comb spectroscopy in combustion environments and under atmospheric conditions for fast and sensitive multispecies detection. We have demonstrated, for the first time, cavity-enhanced optical frequency comb spectroscopy in a flame, detected broadband high temperature H2O and OH spectra using the FTS in the near-infrared range and showed the potential of the technique for flame thermometry. For applications demanding a short measurement time and high sensitivity under atmospheric pressure conditions, we have implemented continuous-filtering Vernier spectroscopy, a dispersion-based spectroscopic technique, for the first time in the mid-infrared range. The spectrometer was sensitive, fast, robust, and capable of multispecies detection with 2 ppb detection limit for CH4 in 25 ms. / Optisk frekvenskamspektroskopi (OFCS) kombinerar två tidigare icke förenliga egenskaper, dvs. ett brett optiskt frekvensområde med en hög spektral upplösning, vilket möjliggör noggranna mätningar av hela molekylära absorptionsband och detektion av flera gaser samtidigt med en kort mättid. Eftersom frekvenskammar har en regelbunden struktur med jämnt separerade laser moder kan man effektivt koppla kammen till en optisk kavitet och därmed möjliggöra frekvenskamsdetektion med hög känslighet. Olika metoder har utvecklats för att utnyttja frekvenskammarnas fulla potential för spektroskopi, baserad på antingen Fouriertransform-spektroskopi eller dispersiva element.Forskningen som presenteras i denna avhandling har haft två huvudmål. Det första har varit att förbättra prestandan hos mekaniska Fourier-transformspektrometrar (FTS) baserat på frekvenskammar med avseende på känslighet, upplösning och spektral täckning. I strävan efter detta har vi utvecklat en ny spektroskopisk teknik, benämnd brusimmun kavitetsförstärkt optisk frekvenskamspektroskopi (NICE-OFCS), och uppnått en hagelbrusbegränsad känslighet och detektionsgränser ner till låga ppb koncentrationer (miljarddelar, 10−9) för CO2 i det när-infraröda frekvensområdet enbart med användning av kommersiellt tillgängliga komponenter. Vi har också utvecklat en ny metod för insamling och analys av kambaserade FTS-spektra, som betecknas ha sub-nominell upplösning. Metoden gör det möjligt att uppnå ultrahög spektral upplösning och hög frekvensnoggrannhet (båda i kHz-området, endast begränsad av kammens stabilitet) över kammens hela frekvensområde. Slutligen har vi utvecklat en optisk parametrisk oscillator som genererar en frekvenskam i det mid-infraröda frekvensområdet, där de starkaste rotations-vibrationsmolekylära absorptionslinjerna finns. Med hjälp av denna kam och en FTS har vi för första gången demonstrerat frekvenskamspektroskopi över 5 μm. Vi har detekterat bredbandsspektra av flera molekylära gaser och har, för mättider på 1 s, uppnått detektionsgränser ner till låga ppb halter för CH4, NO och CO.Det andra syftet har varit mer applikationsorienterat: att använda frekvenskamspektroskopi i förbränningsmiljö och under atmosfäriska förhållanden för snabb och känslig multiämnesdetektion. Vi har för första gången demonstrerat kavitetsförstärkt optisk frekvenskamspektroskopi i en flamma, där vi har detekterat högtemperaturspektra av H2O och OH i det när-infraröda området med användning av FTS och visat teknikens potential för termometrisk karakterisering av flammor. För applikationer som kräver en kort mättid och hög känslighet under atmosfäriska förhållanden har vi utvecklat ett detektionssystem baserat på Vernier-spektroskopi med kontinuerlig filtrering, vilket är en dispersionsbaserad teknik, för första gången i det mid-infraröda frekvensområdet. Det befanns att spektrometern var känslig, snabb, robust och kapabel till multiämnesdetektion med en detektionsgräns på 2 ppb för CH4 för korta mättider (25 ms).

The short-term jitter and longer-term wander of the frequency sweep profile of a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) laser at 1550 nm used in optical coherence tomography (OCT) and other sensing applications is characterized in this work. The VT-DBR has demonstrated success in source-swept OCT (SSOCT), performing both intensity and phase-sensitive OCT. The purpose of this paper is to investigate one of the unique aspects of the VT-DBR laser that makes it successful in OCT: the stability of the linear optical frequency sweep. A highly stable linear optical frequency sweep implies benefits for further fiber sensing applications including fiber Bragg grating and spectroscopy sensors. Short-term jitter measurements of the optical frequency sweep are taken using a 3-cavity 100 GHz free spectral range solid etalon, an athermal fiber Bragg grating, a molecular-based gas absorption reference cell, and a Mach-Zehnder interferometer. These four optical filters are used to convert time fluctuations into intensity fluctuations that can be measured by high speed optical receivers. Short term jitter values on the order of 0.5 – 0.6 pm RMS (63 – 82 MHz RMS) are typical values in the VT-DBR lasers systems characterized in this work. This level of jitter is compelling for OCT and fiber-sensing applications. Longer-term wander is characterized using a multiple-gas absorption reference cell. The long term stability and temperature insensitivity of the absorption cell is ideal for long-term wander characterization of the laser frequency sweeps. Wander values on the order of 2.6 pm of wavelength shift over an 8 hour time frame are reported in this work. The slope of the frequency versus time function of the laser sweep, on the order of 100 MHz/sample, is found to deviate by no more than 0.03% over the same 8 hour time frame. Both the long term wavelength shift and consistency of the slope indicate that these sources will perform well in OCT and fiber sensing applications. Mechanisms responsible for short-term jitter and longer- term wavelength wander likely include contributions from the laser source itself and from the high speed electronic drive circuitry that creates the wavelength ramp. Investigation of ambient temperature’s influence on the wavelength wander is also highlighted in the work.

Le Groupe de recherche en appareillage médical de Sherbrooke possède une expertise unique dans la conception de scanners à tomographie d’émission par positrons. Le fonctionnement de la tomographie d’émission par positrons repose sur la détection de photons d’annihilation colinéaires par un agencement de cristaux scintillateurs, photodétecteurs, convertisseurs temps-numérique et électronique de traitement. Une partie du groupe de recherche s’oriente vers l’utilisation des matrices de photodiodes à avalanches opérées en mode Geiger, afin d’obtenir une meilleure résolution temporelle du système et un seuil de détection plus faible que les générations précédentes,ce qui permet de détecter les premiers photons émis par le cristal scintillateur. Le convertisseur temps-numérique (TDC) développé se veut un bloc polyvalent et réutilisable mesurant des intervalles de temps avec grande précision. Son développement cible des applications de détection monophotoniques avec estampilles temporelles comme la tomographie optique dffuse, les caméras 3D ou la tomographie d’émission par positrons. Il s’intègre ici dans un circuit intégré en CMOS 130 nm assemblé verticalement avec plusieurs gaufres et dédié à la détection en tomographie d’émission par positron. La méthodologie de conception du convertisseur temps-numérique s’inspire d’une approche en signaux mixtes avec suprématie du numérique. En simulation, le TDC développé arbore une résolution de 14,5 ps, une non-linéarité différentielle de 1 bits de poids faible, une non-linéarité intégrale de 2,2 bits de poids faible, une fréquence de conversion de 11,1 millions d’échantillons par seconde, une plage dynamique de 5 ns, une puissance moyenne consommée en moyenne de 4,5 mW et une taille de 0,029 mm². Un mécanisme pour améliorer la résolution du TDC a été intégré dans un exemplaire du TDC. Son utilisation a permis d’obtenir une résolution de 12,6 ps sur un exemplaire du circuit fabriqué. Ces travaux ont permis d’explorer l’architecture en oscillateur vernier avec anneaux et d’en faire ressortir plus clairement les avantages, les inconvénients et les écueils à surveiller lors de la conception.

La communauté de la chimie atmosphérique souffre d'un manque de mesures rapides, fiables résolues spatialement et temporellement pour un large éventail de molécules réactives (radicaux tels que NO2, OH, BrO, IO, etc). En raison de leur forte réactivité, ces molécules contrôlent largement la durée de vie et la concentration de nombreuses espèces clés dans l'atmosphère, et peuvent avoir un impact important sur le climat. Les concentrations de ces radicaux sont extrêmement faibles (ppbv ou moins) et très variable dans le temps et dans l'espace, ce qui impose un véritable défi lors de la détection. Dans la première partie de cette thèse, un spectromètre UV robuste, compacte et transportable est développé, exploitant la technique ML-CEAS pour mesurer à des niveaux très faibles (pptv et même en dessous) des molécules réactives d'importance atmosphérique, en particulier, les radicaux d'oxyde d'halogènes, afin de répondre aux besoins émergents. La technique ML-CEAS est basée sur le couplage d'un laser femtoseconde à blocage de modes à une cavité optique de haute finesse, qui agit comme un piège à photons pour augmenter l'interaction entre la lumière et l'échantillon de gaz intracavité. Cela permet d'améliorer fortement la sensibilité d'absorption. La limite de détection obtenue pour le radical IO est de 20 ppqv pour un temps d'acquisition de 5 minutes, ce qui est un résultat impressionnant. Dans la deuxième partie de cette thèse, une nouvelle technique spectroscopique est développée appelée effet Vernier, qui est également basé sur l'interaction entre un laser femtoseconde à blocage de mode et une cavité optique de haute finesse. Cette technique fournit une sensibilité de détection similaire à la technique ML-CEAS, mais l'avantage est que le nombre des éléments spectraux est donné par la finesse de la cavité optique et donc peut atteindre plusieurs dizaines de milliers. De plus, cette configuration simplifie le montage expérimental par la suppression du spectrographe qui est remplacé par une simple photodiode. Le temps d'acquisition d'un spectre peut être aussi réduit à moins d' 1 ms.

This thesis proposes and demonstrates Time to Digital Converters (TDC) with high resolution realized in 65-nm digital CMOS. It is used as a phase detector in all digital PLL working with 5GHz DCO and 20MHz reference input for radio transmitters. Two kinds of high resolution TDC are designed on schematic level including Vernier TDC and parallel TDC. The Sensed Amplifier Flip Flop (SAFF) is implemented with less than 1ps sampling window to avoid metastability. The current starved delay elements are adopted in the TDC and the conversion resolution is equal to the difference of the delay time from these delay elements. Furthermore, the parallel TDC is realized on layout and finally achieves the resolution of 3ps meanwhile it consumes average power 442μW with 1.2V power supply. Measured integral nonlinearity and differential nonlinearity are 0.5LSB and 0.33LSB respectively.

This dissertation presents the novel creation of a surface relief fiber Bragg grating on the flat surface of a D-shaped optical fiber. In order to produce an efficient surface relief grating the grating must be etched into the surface of the glass fiber close to the core. A short etch that removes the cladding above the core is performed in order to decrease the core-to-flat distance and allow the light to interact with the grating on the flat surface. Due to the unique D-shape of the optical fiber the mechanical integrity of the fiber remains high even after the fabrication process. For traditional fiber Bragg gratings the index modulation occurs in the core of the optical fiber. While this method can produce highly reflective gratings they are not well suited for many sensing applications. For example, the operating temperature range is limited to a few hundred degrees Celsius before the index modulation returns to a more uniform index profile. Also because the gratings are created in the core of the fiber, interaction with the surrounding environment is limited. The surface relief fiber Bragg grating created for this work overcomes some of the sensing challenges of traditional gratings. The major accomplishments of this dissertation show a dramatic increase in operating temperature to over 1000 degrees Celsius, the ability to measure multi-dimensional bend, the ability to measure material changes around the fiber such as chemical concentration, and the ability to use a Vernier effect to dramatically increase the sensors sensitivity. In addition to the sensing applications of this work a more thorough understanding of the reflection and transmission properties of the surface relief grating is also presented. Implementation of the transfer matrix method for simulation of the gratings is also shown to be a fast and accurate modeling tool for predicting the grating response.

Insight Photonic Solutions Inc. has continued to develop their patented VT-DBR laser design; these wavelength tunable lasers promise marked image-quality and acquisition time improvements in SS-OCT applications. To be well suited for SS-OCT, tunable lasers must be capable of producing a highly linear wavelength sweep across a tuning range well-matched to the medium being imaged; many different tunable lasers used in SS-OCT are compared to identify the optimal solution. This work electrically and spectrally characterizes two completely new all-semiconductor VT-DBR designs to compare, as well. The Neptune VT-DBR, an O-band laser, operates around the 1310 nm range and is a robust solution for many OCT applications. The VTL-2 is the first 1060 nm VT-DBR laser to be demonstrated. It offers improved penetration through water over earlier designs which operate at longer wavelengths (e.g. - 1550 nm and 1310 nm), making it an optimal solution for the relatively deep imaging requirements of the human eye; the non-invasive nature of OCT makes it the ideal imaging technology for ophthalmology. Each laser has five semiconductor P-N junction segments that collectively enable precise akinetic wavelength-tuning (i.e. - the tuning mechanism has no moving parts). In an SS-OCT system utilizing one of these laser packages, the segments are synchronously driven with high speed current signals that achieve the desired wavelength, power, and sweep pattern of the optical output. To validate the laser’s fast tuning response time necessary for its use in SS-OCT, a circuit model of each tuning section is created; each laser section is modeled as a diode with a significant lead inductance. The dynamic resistance, effective capacitance, and lead inductance of this model are measured as a function of bias current and the response time corresponding to each bias condition is determined. Tuning maps, spectral linewidths, and side-mode suppression ratio (SMSR) measurements important to SS-OCT performance are also collected. Measured response times vary from 700 ps to 2 ns for the Neptune and 1.2 to 2.3 ns for the VTL-2. Linewidth measurements range from 9 MHz to 124 MHz for the Neptune and 300 kHz to 2 MHz for the VTL-2. SMSR measurements greater than 38 dB and 40 dB were observed for the Neptune and VTL-2, respectively. Collectively, these results implicate the VT-DBR lasers as ideal tunable sources for use in SS-OCT applications.

In my master's tehsis I'm dealin with the methods used for non-invasive blood pressure measurement. For realization of a virtual blood pressure meter in LabVEW I have chosen the oscillometric method. Algorithm determining systolic and diastolic blood pressure is based on the relatively easy detection of maximum amplitude oscillations (corresponds with a mean arterial pressure), when thelimiting valuesof blood pressure are in a specific ratio with a maximum amplitude of oscillation. In LabVIEW was solved loading of signal from the measure card and processing pressure curve into a form suitable for the detection of the peak oscillations. The program calculates the limits of arterial pressure and mean heart rate too. Linking the virtual device with the blood pressure sensor Vernier BPS-BTA then makes up komplex for capturing the blood pressure via oscillatory method.

This thesis describes supramolecular approaches to porphyrin nanorings. Cyclic porphyrin arrays resemble natural light harvesting systems, and it is of interest to probe the photophysical effects of bending the porphyrin aromatic π-system. A general overview of the synthesis and photophysical properties of porphyrins and their arrays is carried out in Chapter 1. The electronic structure of porphyrins is examined, and how conformational effects in oligomers, such as inter-porphyrin torsional angle and backbone bending influence the π-conjugation pathway. The structures of light harvesting complexes are discussed. Chapter 2 describes the design and synthesis of a complementary 12-armed template designed to coordinate linear porphyrin oligomers in the correct conformation for cyclisation to give a cyclic porphyrin dodecamer. Chapter 3 demonstrates two approaches to a cyclic porphyrin dodecamer ring. Firstly, a classical templating approach using the 12-armed template is described. The limitations of this approach in the quest for larger nanorings are discussed. Vernier templating, which utilises a mismatch in the number of binding sites between a ligand and its receptor is introduced as a general strategy to the synthesis of large nanorings. This is demonstrated by the synthesis of cyclic dodecamer from a linear porphyrin tetramer and a hexadentate template via a figure-of-eight intermediate. The general utility of the Vernier method to large nanorings is explored in Chapter 4 with steps towards the synthesis of a cyclic tetracosamer, consisting of 24 porphyrin subunits. In preliminary experiments, an improved route to the cyclic porphyrin octamer is described. Finally, the photophysical properties of the nanoring series are explored in Chapter 5 as a function of size and conformation. Femtosecond photoluminescence spectroscopy shows that even in cyclic dodecamer, exciton delocalisation over the entire porphyrin backbone occurs on a sub-picosecond timescale, and parallels are drawn with the dynamics of natural light harvesting complexes.

<p dir="ltr">Optical frequency combs have revolutionized metrology and advanced other fields such as RF photonics and astronomy. While powerful, they can be bulky, expensive, and difficult to manufacture. This tends to limit uses in real-world scenarios. Within the last decade or so, coherent frequency combs have begun to be generated in millimeter-scale, CMOS fabrication-compatible nonlinear crystals. These so-called “microcombs” have led to hopes of overcoming deployability constraints of more traditional bulk combs.</p><p dir="ltr">One of the first applications for \textit{bulk} frequency combs after their explosion in 2000 was the optical atomic clock. It promised extreme long-term time stability better than that of the Cesium clock that currently defines the SI second. More recently, interest in a fully portable optical atomic clock has grown. Such a device could reliably keep time even without the aid of GPS references, and potentially with greater accuracy than current GPS synchronization can provide.</p><p dir="ltr">Frequency combs have also been used to sample electrical signals more rapidly than traditional electronics can accomplish. This has been used to achieve dramatically increased effective frequency bandwidths for signal detection architectures. One can imagine how this capability would be beneficial in a portable (microcomb-driven) form: a lightweight, comb-enhanced receiver able to capture a broadband snapshot of its surrounding electromagnetic environment could be a powerful tool.</p><p dir="ltr">Timekeeping and RF photonics are the primary applications of microcombs focused upon here. I will attempt to roughly summarize important concepts and highlight relevant work in both subjects in the Introduction. Then I will move a step closer to the hands-on lab work that has largely kept me preoccupied over the last several years and describe important or commonly-employed Methods for experiments. A collection of three journal manuscripts (two published, and the third recently submitted) will follow in the Publications chapter, highlighting some experimental results. Finally, I will conclude with a brief Outlook.</p>