A procedure is introduced for increasing the sensitivity of measurements in integrated ring resonators beyond what has been previously accomplished. This is demonstrated by a high-frequency, phase sensitive lock to the ring resonators. A prototyped fiber Fabry-Perot cavity is used for comparison of the method to a similar cavity. The Pound-Drever-Hall (PDH) method is used as a proven, ultra-sensitive method with the exploration of a much higher frequency modulation than has been previously discussed to overcome comparatively low finesse of the ring resonator cavities. The high frequency facilitates the use of the same modulation signal to separately probe the phase information of different integrated ring resonators with quality factors of 8.2 x10^5 and 2.4 x10^5. The large free spectral range of small cavities and low finesse provides a challenge to sensing and locking the long-term stability of diode lasers due to small dynamic range and signal-to-noise ratios. These can be accommodated for by a calculated increase in modulation frequency using the PDH approach. Further, cavity design parameters will be shown to have a significant affect on the resolution of the phase-sensing approach. A distributed feedback laser is locked to a ring resonator to demonstrate the present sensitivity which can then be discussed in comparison to other fiber and integrated sensors. The relationship of the signal-to-noise ratio (S/N) and frequency range to the cavity error signal will be explored with an algorithm to optimize this relationship. The free spectral range and the cavity transfer function coefficients provide input parameters to this relationship to determine the optimum S/N and frequency range of the respective cavities used for locking and sensing. The purpose is to show how future contributions to the measurements and experiments of micro-cavities, specifically ring resonators, is well-served by the PDH method with high-frequency modulation.

In this work, we use Coherent produced 532nm cw laser as pump source, and 266nm is obtained by frequency doubling. The ring cavity of a laser is generally subject to various perturbation, and the stability of a single-mode laser can be improved by electronically locking its frequency. We use a Pound-Drever-Hall laser frequency stabilization system to control the cavity length. This method utilizes an external phase modulator to produce the sideband and is capable of detecting weak signal to get the information of cavity disturbation. Finally, the signal is dealt with electrical circuit and then feedback to a PZT to control the stabilization of the cavity length.

A procedure is introduced for increasing the sensitivity of measurements in integrated ring resonators beyond what has been previously accomplished. This is demonstrated by a high-frequency, phase sensitive lock to the ring resonators. A prototyped fiber Fabry-Perot cavity is used for comparison of the method to a similar cavity. The Pound-Drever-Hall (PDH) method is used as a proven, ultra-sensitive method with the exploration of a much higher frequency modulation than has been previously discussed to overcome comparatively low finesse of the ring resonator cavities. The high frequency facilitates the use of the same modulation signal to separately probe the phase information of different integrated ring resonators with quality factors of 8.2 x10^5 and 2.4 x10^5. The large free spectral range of small cavities and low finesse provides a challenge to sensing and locking the long-term stability of diode lasers due to small dynamic range and signal-to-noise ratios. These can be accommodated for by a calculated increase in modulation frequency using the PDH approach. Further, cavity design parameters will be shown to have a significant affect on the resolution of the phase-sensing approach. A distributed feedback laser is locked to a ring resonator to demonstrate the present sensitivity which can then be discussed in comparison to other fiber and integrated sensors. The relationship of the signal-to-noise ratio (S/N) and frequency range to the cavity error signal will be explored with an algorithm to optimize this relationship. The free spectral range and the cavity transfer function coefficients provide input parameters to this relationship to determine the optimum S/N and frequency range of the respective cavities used for locking and sensing. The purpose is to show how future contributions to the measurements and experiments of micro-cavities, specifically ring resonators, is well-served by the PDH method with high-frequency modulation.

<p>In this Thesis I report on my work done in replicating the Pound-Drever-Hall (PDH) laser stabilization technique as well as applications of PDH to microring resonators and generated Optical Frequency Combs (OFC). These works have been broken down into three sections. First, I replicated the PDH method with a continuous wave (CW) laser along with a Fabry-Pérot Cavity (FPC). Second, I applied the same technique to a 25 GHz Free Spectral Range (FSR) microring resonator fabricated in Silicon Nitride. Third, I applied the PDH technique to a high Quality Factor (Q) high Free Spectral Range (FSR) microring resonator in preparation to lock the repetition rate of two soliton combs beat together. The last experiment was for an application towards a compact optical clock system; such systems will have a wide impact on the infrastructure of our navigation and communication structures in use today.</p>

Linewidth is a measure of the frequency stability of any kind of oscillator, and it is a defining characteristic of coherent lasers. Narrow linewidth laser technology, particularly in the field of fiber-based infrared lasers, has progressed to the point where highly stable sources are commercially available with linewidths on the order of 1-100 kHz. In order to achieve a higher level of stability, the laser must be augmented by an external frequency stabilization system. This paper presents the design and operation of a frequency locking system for infrared fiber lasers. Using the Pound-Drever-Hall technique, the system significantly reduces the linewidth of an input laser with an un-stabilized linewidth of 2 kHz. It uses a high-finesse Fabry-Perot cavity, which is mechanically and thermally isolated, as a frequency reference to measure the time-varying frequency of the input laser. An electronic feedback loop works to correct the frequency error and maintain constant optical power. Testing has proven the Pound-Drever-Hall system to be highly stable and capable of operating continuously for several seconds at a time. / Master of Science

L'objet de cette thèse porte sur la conception et la réalisation de deux sources laser non linéaires accordables dans les domaines IR et UV, pour le raccordement de la sensibilité spectrale des détecteurs au moyen du radiomètre cryogénique du laboratoire commun de métrologie (LCM). La source IR est un oscillateur paramétrique optique (OPO) résonant sur les ondes pompe et signal (PRSRO), utilisant un cristal de niobate de lithium à inversion de domaines de polarisation dopé par 5% d'oxyde de magnésium (ppMgCLN). Pompé par un laser Ti:Al2O3 en anneau mono-fréquence et accordable, délivrant 500 mW de puissance utile autour de 795 nm, l'OPO possède un seuil d'oscillation de 110 mW. Une couverture spectrale continue entre 1 µm et 3.5 µm a été obtenue, avec des puissances de l'ordre du mW pour l'onde signal (1 µm à 1.5 µm) et des puissances comprises entre $20$ à $50$ mW pour l'onde complémentaire couvrant un octave de longueur d'onde IR entre 1.7 µm et 3.5 µm. La source UV est obtenue par doublage de fréquence en cavité externe du laser Ti:Al2O3, dans un cristal de triborate de lithium (LiB3O5). Un accord de phase en température à angle d'accord de phase fixé permet l'obtention d'une couverture spectrale comprise entre 390 nm et 405 nm. L'asservissement de la cavité de doublage sur la fréquence du laser Ti:Al2O3 par la méthode de Pound-Drever-Hall, ainsi qu'une adaptation de mode optimale, permet d'obtenir une puissance de 5.64 mW à 400 nm à partir de 480 mW de puissance fondamentale. / The work presented in this PhD dissertation details the strategy adopted to build two non-linear laser sources that are widely in the mid-infrared and blue-UV spectral ranges. These laser sources are needed for the traceability to SI units of coherent light irradiance measurements using a cryogenic radiometer of the using cryogenic radiometer of the Laboratoire commun de métrologie (LCM) .The infrared laser source is an optical parametric oscillator (OPO) resonating on the pump and signal wavelengths (PRSRO) and employing a periodically poled Lithium Niobate non-linear crystal doped with 5% magnesium oxide (ppMgCLN). The PRSRO is pumped by a single-frequency tunable bow-tie ring cavity Titanium-Sapphire laser (Ti:Al2O3) delivering 500 mW output power at 795 nm wavelength, , resulting in a power oscillation threshold of 110 mW. The PRSRO emission could continuously cover the spectral range from 1 µm to 3.5 µm. The level of output power achieved is of the order of 1 mW for the signal wave (1 µm to 1.5 µm) and between 20 mW and 50 mW for idler wave spanning an octave wavelength range (1.7 µm to 3.5 µm).The UV source based on the second harmonic generation on the Titanium-Sapphire tunable laser using an external enhancement cavity containing a critically phase-matched LBO non linear crystal (LiB3O5). Temperature-tuning of the phase-matching condition at a fixed crystal orientation leads to a wide tunability from 390 nm to 405 nm wavelength. The external cavity optical pathlength was actively locked to the laser frequency using a¨Pound-Drever-Hall servo, allowing to extract up to 6 mW power at 400 nm wavelength with a 480 mW pump power. Despite a perfect mode-matching efficiency, the power performance was limited by the poor nonlinear impedance matching of the resonator, due to both the weak nonlinearity of the crystal and the low incoming laser power.

L'objet de cette thèse porte sur la conception et la réalisation de deux sources laser non linéaires accordables dans les domaines IR et UV, pour le raccordement de la sensibilité spectrale des détecteurs au moyen du radiomètre cryogénique du laboratoire commun de métrologie (LCM). La source IR est un oscillateur paramétrique optique (OPO) résonant sur les ondes pompe et signal (PRSRO), utilisant un cristal de niobate de lithium à inversion de domaines de polarisation dopé par 5% d'oxyde de magnésium (ppMgCLN). Pompé par un laser Ti:Al2O3 en anneau mono-fréquence et accordable, délivrant 500 mW de puissance utile autour de 795 nm, l'OPO possède un seuil d'oscillation de 110 mW. Une couverture spectrale continue entre 1 µm et 3.5 µm a été obtenue, avec des puissances de l'ordre du mW pour l'onde signal (1 µm à 1.5 µm) et des puissances comprises entre $20$ à $50$ mW pour l'onde complémentaire couvrant un octave de longueur d'onde IR entre 1.7 µm et 3.5 µm. La source UV est obtenue par doublage de fréquence en cavité externe du laser Ti:Al2O3, dans un cristal de triborate de lithium (LiB3O5). Un accord de phase en température à angle d'accord de phase fixé permet l'obtention d'une couverture spectrale comprise entre 390 nm et 405 nm. L'asservissement de la cavité de doublage sur la fréquence du laser Ti:Al2O3 par la méthode de Pound-Drever-Hall, ainsi qu'une adaptation de mode optimale, permet d'obtenir une puissance de 5.64 mW à 400 nm à partir de 480 mW de puissance fondamentale.

Les lasers stabilisés à long terme sont utilisés dans de nombreux domaines en métrologie, leur incursion dans les applications spatiales se précise depuis quelques années, missions de physique fondamentale, géodésie... Ce travail concerne les lasers stables pour le projet LISA (détection spatiale des ondes de gravitation, mission prévue dans 10 ans); en vue de cette application spatiale, les montages doivent satisfaire plusieurs critères: compacité, stabilité mécanique, robustesse et fiabilité. Les références utilisables pour l'asservissement long terme (iode, chapitre 3) et court terme (cavité de Fabry-Pérot, chapitre 4) sont décrites, ainsi que leurs limitations principales. L'analyse et le choix de ces références de stabilisation seront couplés avec le choix des techniques de stabilisation (PDH, Tilt-Locking, Modulation Transfer). Dans les techniques de stabilisation, celle de Pound-Drever-Hall (PDH), un classique en matière de configuration, est comparée au Tilt-Locking, une technique continu et peu consommatrice en énergie, dans le cas d'une référence Fabry-Perot monolithique. Les calcules théorique pour chaque technique et chaque type de référence ammeneront à une description des sources de bruit et à une simulation des signaux d'erreur attendus. Les performances théoriques sur le long terme et les efficacités quantiques sont intercomparées. La deuxième partie, présentera les montages expérimentaux et les résultats obtenus, pour des lasers stabilisés sur Fabry-Perot et sur l'Iode moléculaire. Pour calibrer les dérives de fréquence du Fabry-Perot, sa fréquence de résonance sera mesurée par rapport à celle de la molécule, ce qui permettra de présenter des solutions obtenues analytiquement et numériquement pour l'asservissement en longueur de cette référence mécanique. En appendices, les détails de dimensionnement des bruits de LISA conduisant aux spécifications des lasers, le rappel théorique des ondes de gravitation ainsi que divers simulations de calculs effectués.