High spectral purity microwave sources based on optical resonators

L'optique constitue aujourd'hui une solution performante pour la réalisation de sources très pures en hyperfréquences, en particulier grâce à l'approche de l'oscillateur électro-optique (OEO). La pureté spectrale de ces sources est essentielle pour les applications spatiales, militaires et pour la métrologie du temps et des fréquences. Durant cette thèse, nous avons réalisé et étudié différents types d'OEO à résonateur optique en vue d'optimiser le bruit de phase de ce système. Nous avons en particulier orienté nos travaux vers une approche originale utilisant un anneau résonant fibré (ARF) passif. Ce type de résonateur présente en effet des coefficients de qualité optiques supérieurs à 109 pour des longueurs de fibre restant relativement faibles (L ~ 10 m) et facilement intégrables dans un support planaire. En parallèle, nous avons mené un travail important sur les oscillateurs à base de résonateurs optiques 3D. Concernant l'OEO à ARF, des progrès spectaculaires ont pu être obtenus grâce à une meilleure compréhension des phénomènes de bruit intrinsèques à ce système. Les deux types de bruit prépondérants étaient la conversion du bruit du laser (FM et AM) en bruit de phase RF par différentes non-linéarités (dont la photodiode) et le déclenchement d'effets non-linéaires optiques à l'intérieur du résonateur. Le contrôle de ces effets a permis en particulier d'éliminer des remontées importantes de bruit sur le spectre de l'oscillateur, et d'atteindre un niveau de bruit de phase de -128 dBc/Hz à 10 kHz de la porteuse à 10.2 GHz en utilisant un OEO à base d'un ARF passif de 100 mètres de longueur, optimisé et immunisé contre les effets non-linéaires optiques.Optics represents an elegant and reliable solution to generate high spectral purity microwave signals, especially the approach using the optoelectronic oscillator (OEO). The spectral purity of these sources is very important for space and military applications and also for time and frequency domain metrology. During this thesis, we have fabricated and studied many types of resonator based OEO in order to optimize the system phase noise. We have especially investigated an original approach using a passive fiber ring resonator (FRR). This resonator type can feature optical quality factors higher than 109 when only few meters of optical fibers are used (L ~ 10 m) and it can be easily integrated in a planar setup. Moreover, we have performed an important work on 3D WGM resonators based oscillators. In the FRR based OEO, spectacular progresses have been achieved thanks to a good understanding of the system intrinsic noise phenomena. Actually, we have found that the most important noise parameters were the laser FM and AM noise conversion into RF phase noise by means of different nonlinearities in the system (like the photodiode nonlinearity), but also by the generation of nonlinear optical effects inside the resonator. By controlling these effects, we have been able to reduce the OEO phase noise level and to reach a -128 dBc/Hz noise level at 10 kHz offset frequency from a 10.2 GHz carrier. This has been achieved using an OEO based on a 100m-long passive FRR, which has been optimized and immunized against different nonlinear optical effects

Frequency stability of a wavelength meter and applications to laser frequency stabilization

Interferometric wavelength meters have attained frequency resolutions down to the MHz range. In particular, Fizeau interferometers, which have no moving parts, are becoming a popular tool for laser characterization and stabilization. In this article, we characterize such a wavelength meter using an ultra-stable laser in terms of relative frequency instability $\sigma_y(\tau)$ and demonstrate that it can achieve a short-term instability $\sigma_y(1 s) \approx 2{\times}10^{-10}$ and a frequency drift of order $10$ MHz/day. We use this apparatus to demonstrate frequency control of a near-infrared laser, where a frequency instability below $3{\times}10^{-10}$ from 1 s to 2000 s is achieved. Such performance is for example adequate for ions trapping and atoms cooling experiments.Comment: 5 pages, 4 figure

Compact Yb+^+ optical atomic clock project: design principle and current status

We present the design of a compact optical clock based on the $^2S_{1/2} \rightarrow ^2D_{3/2}$ 435.5 nm transition in $^{171}$Yb$^+$. The ion trap will be based on a micro-fabricated circuit, with surface electrodes generating a trapping potential to localize a single Yb ion a few hundred $\mu$m from the electrodes. We present our trap design as well as simulations of the resulting trapping pseudo-potential. We also present a compact, multi-channel wavelength meter that will permit the frequency stabilization of the cooling, repumping and clear-out lasers at 369.5 nm, 935.2 nm and 638.6 nm needed to cool the ion. We use this wavelength meter to characterize and stabilize the frequency of extended cavity diode lasers at 369.5 nm and 638.6 nm.Comment: 7 pages, 5 figures. Proc. of the 8th FSM 2015, Potsdam, Germany. To be published in IOP Journal of Physics: Conference Serie

Oscillateur Optoélectronique à Base de Résonateur à Mode de Galerie à Très Fort Facteur de Qualité

National audienceLes sources de fréquences à haute pureté spectrale ont toujours fait l'objet d'intenses travaux de recherches compte tenu de leur importance dans plusieurs domaines d'applications. En effet, des telles sources sont largement utilisées dans les systèmes de communications, les radars, les satellites, la métrologie temps-fréquence et dans différentes autres applications où un signal électromagnétique est généré, reçu et traité. Une solution élégante utilisant l'optique pour stabiliser un oscillateur microonde a été démontrée il y une vingtaine d'années [1]. Cette solution, baptisée oscillateurs optoélectroniques (OEO), consiste en l'utilisation d'un élément de retard optique (ex. ligne à retard optique, résonateur optique, etc.) afin de montée en facteur de qualité dans le système de génération de fréquence. En utilisant cette architecture d'OEO avec une ligne à retard optique de 16km de longueur, un signal microonde à 10 GHz ayant un niveau de bruit de phase de -163 dBc/Hz à 7KHz de la porteuse a été démontré [2] [3]. Malgré ces résultats, l'OEO basé sur une ligne à retard optique reste volumineux et difficile à stabiliser thermiquement et mécaniquement. L'idée de remplacer la ligne à retard optique par un résonateur optique a permis de réduire considérablement la taille de l'OEO [2]. On peut notamment citer les mini-résonateurs optiques à mode de galerie (WGM) ayant des diamètres millimétriques et permettant d'atteindre des facteurs de qualité optiques (QOpt) au-delà de 10 9 [3-6]. Actuellement, différentes études théoriques et expérimentales sont menées dans notre laboratoire afin d'améliorer les performances d'un OEO stabilisé sur des résonateurs WGM fabriqués dans notre laboratoire (voir Figure 1). Ces études nous ont permis jusqu'au là de démontrer des niveaux de bruit de phase de l'ordre de -93dBc/Hz et de -90dBc/Hz à une fréquence d'offset de 10kHz de deux porteuses microondes à 6.35 GHz et 12.7GHz respectivement [7]. Ces résultats sont très encourageants et nous visons actuellement d'atteindre des niveaux de bruit plus faibles. Nos études d'amélioration des performances de l'OEO sont aujourd'hui menées sur trois principaux axes: le procès de fabrication des résonateurs WGM avec divers matériaux optiques (CaF2, MgF2, BaF2, LiF etc.) pour la montée en facteur de qualité, le système de couplage de l'onde optique au résonateur et finalement le système stabilisation type Pound-Drever-Hall de la longueur d'onde du laser sur un résonateur optique [9]. Ces études, une fois validées, devraient nous permettre de démontrer un OEO avec des performances à l'état de l'art

Résonateurs optiques à modes de galerie appliqués aux oscillateurs et aux peignes de fréquences

National audienceRésumé Nous avons fabriqué par procédés de polissage des résonateurs optique à modes de galerie en utilisant différents matériaux cristallins (CaF2 et MgF2). Ces résonateurs ont pour finalité première de générer un signal microonde ultra-stable issu d'un oscillateur opto-électronique (OEO). Puis, en s 'appuyant sur les non-linéarités de Kerr, nous générons différents peignes de fréquences optiques dans les résonateurs

SIMVASTATIN TREATMENT AMELIORATES DIABETIC TYPE 2 CONDITIONS THROUGH LOWERING THE CONCENTRATION OF PLASMA ICAM LEVELS

Diabetes type 2 is associated with other diseases including cardiovascular diseases. Obesity is a link between diabetes and cardiovascular diseases and associated with insulin resistance. Statins are used to reduce lipids and to lower the risk of cardiovascular diseases. The objective of the present study was to explore the effect of statin treatment on plasma levels of ICAM among diabetics. The study design was a prospective cohort clinical study. The study included 62 diabetic patients who were recruited from the Diabetes/Endocrine Clinics of the Prince Rashed Hospital. Data were collected from participants through a prepared questionnaire and laboratory findings of lipid profiles, glucose and ICAM levels. Study findings showed no significant variations between study and control groups at baseline level. At the end of the experiment, in study group, there were significant changes in some biochemical parameters such as ICAM level (p=0.005), cholesterol (0.019), and TG (0.025). The mean difference of study and control groups showed that significant variations were observed for the following variables ICAM (p<0.005), cholesterol (p=0.008), TG (p<0.005), and HDDL (p<0.005). Taken together, the present study showed that simvastatin therapy benefits diabetic patients even without hyperlipidemia through decreasing levels of ICAM-1, which have an inflammatory action and increase insulin resistance. It can be concluded that simvastatin is insulin sensitizer and works as anti-inflammatory agent

SIMVASTATIN TREATMENT AMELIORATES DIABETIC TYPE 2 CONDITIONS THROUGH LOWERING THE CONCENTRATION OF PLASMA ICAM LEVELS

Diabetes type 2 is associated with other diseases including cardiovascular diseases. Obesity is a link between diabetes and cardiovascular diseases and associated with insulin resistance. Statins are used to reduce lipids and to lower the risk of cardiovascular diseases. The objective of the present study was to explore the effect of statin treatment on plasma levels of ICAM among diabetics. The study design was a prospective cohort clinical study. The study included 62 diabetic patients who were recruited from the Diabetes/Endocrine Clinics of the Prince Rashed Hospital. Data were collected from participants through a prepared questionnaire and laboratory findings of lipid profiles, glucose and ICAM levels. Study findings showed no significant variations between study and control groups at baseline level. At the end of the experiment, in study group, there were significant changes in some biochemical parameters such as ICAM level (p=0.005), cholesterol (0.019), and TG (0.025). The mean difference of study and control groups showed that significant variations were observed for the following variables ICAM (p<0.005), cholesterol (p=0.008), TG (p<0.005), and HDDL (p<0.005). Taken together, the present study showed that simvastatin therapy benefits diabetic patients even without hyperlipidemia through decreasing levels of ICAM-1, which have an inflammatory action and increase insulin resistance. It can be concluded that simvastatin is insulin sensitizer and works as anti-inflammatory agent

Why do Saudi Nurses Leave Bedside Nursing: Findings from a Pilot Study

Aim: To explore the salient factors that account for Saudi nurses leaving bedside nursing to work in other fields of nursing.   Method: A non-experimental descriptive quantitative design was used to answer the research question of this pilot study. A valid and reliable questionnaire was used as an instrument for data collection. A snowball / purposive sample was used to collect the data from 46 Saudi nurses who had left bedside nursing in three hospitals in the Aseer region in southwest of Saudi Arabia. Data were analyzed by a professional statistician using descriptive statistics.   Findings: The salient factors for Saudi nurses’ decision to leave bedside nursing that were identified included: income (including allowances and financial incentives), administrative regulations, job satisfaction, and other miscellaneous factors   Conclusion: Although this pilot study has several limitations, the findings indicate that health care planners and policy staff, and nursing leaders in the Kingdom of Saudi Arabia need to develop strategies to address the issues expressed by Saudi nurses in regard to bedside nursing, particularly the need to improve (a) financial allowances and incentive systems, (b) the bedside work environment (e.g., by decreasing weekly working hours), and (c) the image of bedside Saudi nurses in the eyes of Saudi society.   Keywords: Saudi Nurses, Pilot Study, Bedside Nursing &nbsp

Pesticide use and opportunities of exposure among farmers and their families: cross-sectional studies 1998-2006 from Hebron governorate, occupied Palestinian territory

<p>Abstract</p> <p>Background</p> <p>Adverse health effects caused by pesticide exposure have been reported in occupied Palestinian territory and the world at large. The objective of this paper is to compare patterns of pesticide use in Beit-U'mmar village, West Bank, between 1998 and 2006.</p> <p>Methods</p> <p>We studied two populations in Beit-U'mmar village, comprised of: 1) 61 male farmers and their wives in 1998 and 2) 250 male farmers in 2006. Both populations completed a structured interview, which included questions about socio-demographic factors, types of farming tasks, as well as compounds, quantities, and handling of pesticides. Using the 1998 population as a reference, we applied generalized linear regression models (GLM) and 95% confidence intervals (CI) in order to estimate prevalence differences (PD) between the two populations.</p> <p>Results</p> <p>In 1998, farmers used 47 formulated pesticides on their crops. In 2006, 16 of these pesticides were still in use, including five internationally banned compounds. There were positive changes with less use of large quantities of pesticides (>40 units/year) (PD -51; CI -0.60, -0.43), in applying the recommended dosage of pesticides (PD +0.57; CI +0.48, +0.68) and complying with the safety period (PD +0.89; CI+0.83, +0.95). Changes also included farmers' habits while applying pesticides, such as less smoking (PD -0.20; CI-0.34, -0.07) and eating at the work place (PD -0.33; CI-0.47, -0.19). No significant changes were found from 1998 to 2006 regarding use of personal protective equipment, pesticide storage, farmers' habits after applying pesticides, and in using some highly hazardous pesticides.</p> <p>Conclusions</p> <p>The results were based on two cross-sectional surveys and should be interpreted with caution due to potential validity problems. The results of the study suggest some positive changes in the handling of pesticides amongst participants in 2006, which could be due to different policy interventions and regulations that were implemented after 1998. However, farm workers in Beit -U'mmar village are still at risk of health effects because of ongoing exposure to pesticides. To the best of our knowledge, no studies on long-term changes in pesticide use have been reported from developing countries.</p