7 research outputs found
Optical Methods in Sensing and Imaging for Medical and Biological Applications
The recent advances in optical sources and detectors have opened up new opportunities for sensing and imaging techniques which can be successfully used in biomedical and healthcare applications. This book, entitled ‘Optical Methods in Sensing and Imaging for Medical and Biological Applications’, focuses on various aspects of the research and development related to these areas. The book will be a valuable source of information presenting the recent advances in optical methods and novel techniques, as well as their applications in the fields of biomedicine and healthcare, to anyone interested in this subject
New photonic architectures and devices for generation and detection of sub-THz and THz waves
The development of high-quality and reliable devices in the THz frequency region to fill the existing technological gap has become a major concern. This is chiefly motivated by the need of a widespread exploitation of the extensive variety of identified applications in this frequency region by a wide range of users, including the non-scientific community. The photonic approaches used for these purposes offer important and exclusive advantages over other existing alternatives, which have as a main representative the all-electronic technology, especially in terms of frequency range coverage, possibility of photonic distribution using optical fibers, weight and Electromagnetic Interference (EMI) immunity. Nevertheless, the optical techniques have traditionally provided with worse performance in terms of phase noise, tunability and dynamic range (in generation), and conversion ratio (in detection) when compared to state-of-theart all-electronic THz technology. The work accomplished in this thesis focuses on the design, development and validation of new photonic architectures and devices for both generation and detection of sub-THz and THz waves which overcome the drawbacks of optical techniques at this frequency region while maintaining all their advantages. In this thesis, several photonic sub-THz and THz generation systems have been developed using Difference Frequency Generation (DFG) architectures in which the DFG source is provided by an Optical Frequency Comb Generator (OFCG) and optical mode selection. Different devices and techniques are investigated for each part of the system before arriving to the final high performance synthesizer. Passively Mode-Locked Laser Diodes (PMMLDs) are firstly evaluated as integrated OFCG. An improved design of the OFCG is achieved with a scheme based on a Discrete Mode (DM) laser under Gain- Switching (GS) regime and optical span expansion by the use of a single Electro- Optical (EO) phase modulator. As optical mode selection, both high selective optical filtering and Optical Injection Locking (OIL) are used and evaluated. A commercial 50 GHz photodiode (PD) and an n-i-pn-i-p superlattice THz photomixer are employed as photodetector for Optical to THz conversion. The final reported system consists on an OFCG based on GS, OIL as mode selection strategy and an n-i-pn-i-p superlattice photomixer. This synthesizer offers a wide frequency range (60-140 GHz), readily scalable to a range between 10 GHz and values well above 1 THz. Quasi-continuous tunability is offered in the whole frequency range, with a frequency resolution of 0.1 Hz at 100 GHz that can be straightforwardly improved to 0.01 Hz at 100 GHz and 0.1 Hz at 1 THz. The measured FWHM at 120 GHz is <10 Hz, only limited by the measurement instrumentation. The system offers excellent frequency and power stability with frequency and power deviations over 1 hour of 5 Hz and 1.5 dB, respectively. These values are also limited by both the accuracy and uncertainty of the measurement setup. The performance achieved by this photonic sub-THz and THz synthesizer for most figures of merit matches or even surpasses those of commercial stateof- the-art all-electronic systems, and overcomes some of their characteristics in more than one million times when compared to commercial state-of-the-art photonic solutions. The detection part of this thesis explores the use of photonic architectures based on EO heterodyne receivers and the key devices that encompass these architectures: photonic Local Oscillators (LOs) and EO mixers. First results are developed at microwave frequencies (<15 GHz) using an Ultra-Nonlinear Semiconductor Amplifier (XN-SOA) as EO mixer and a GS based photonic LO. It is demonstrated how this LO device based on GS provides with a significant improvement in the performance of the overall EO receiver when compared to a traditional linearly modulated LO. Furthermore, this detection architecture is validated in an actual application (photonic imaging array), featuring scalability, flexibility and reasonable conversion ratios. After this, an EO heterodyne receiver is demonstrated up to frequencies of 110 GHz. The photonic LO employed is the abovementioned photonic sub- THz synthesizer developed in this thesis, while the EO mixer is an np-i-pn quasi ballistic THz detector. The first fabricated sample of this novel device is used, which is optimized for homodyne/heterodyne detection. The resulting sub-THz EO heterodyne receiver has conversion ratios around -75 dB. It works under zero-bias conditions, which together with the photonic distribution of the LO offers a high potential for remote detection of sub-THz and THz waves. In summary, new photonic architectures and devices are able to provide with state-of-the-art performance for generation of sub-THz and THz waves. In the case of EO heterodyne detection at sub-THz and THz frequency regions, photonic techniques are improving their performance and are closer to offer an alternative to all-electronic detectors. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------El desarrollo de dispositivos fiables y de alta calidad en el rango frecuencial
de Terahercios (THz) con el fin de cubrir el actual vacío tecnológico se ha convertido
en una importante inquietud científica. Esto está principalmente motivado por la
necesidad de explotar el gran número de aplicaciones identificadas en esta región
frecuencial por un gran número de usuarios, incluyendo a usuarios no científicos.
El enfoque fotónico empleado para estos propósitos ofrece importantes y
exclusivas ventajas sobre otras alternativas existentes, que tienen como principal
representante a la tecnología electrónica, especialmente en términos de rango
de frecuencia de funcionamiento, posibilidad de distribución fotónica con fibras
ópticas, peso, e inmunidad electromagnética. No obstante, las técnicas fotónicas
tradicionalmente han ofrecido peores prestaciones en términos de ruido de fase,
sintonía y rango dinámico (en generación) y ratio de conversión (en detección)
con respecto a la tecnología electrónica de THz en el estado del arte. El trabajo
realizado en esta tesis se centra en el diseño, desarrollo y validación de nuevas
arquitecturas y componentes fotónicos tanto para generación como detección de
ondas de sub-THz y THz que permitan solucionar las desventajas de las técnicas
ópticas manteniendo todas sus ventajas.
En esta tesis, varios sistemas de generación de sub-THz y THz han sido
desarrollados utilizando arquitecturas Difference Frequency Generation (DFG)
en las que la fuente DFG es proveída por un Optical Frequency Comb Generator
(OFCG) y selección de modos ópticos. Diferentes dispositivos y técnicas
son investigados para cada parte del sistema hasta conseguir un sintetizador
de altas prestaciones. Passively Mode-Locked Laser Diodes (PMMLDs) son inicialmente evaluados como OFCG integrados. Un diseño mejorado del OFCG
es conseguido mediante el uso de un esquema basado en un láser Discrete Mode
(DM) bajo régimen Gain Switching (GS) y expansión del ancho de banda óptico
mediante el uso de un modulador de fase Electro-Óptico (EO). Como estrategia
de selección de modos ópticos, tanto filtrado óptico altamente selectivo como
Optical Injection Locking (OIL) son usados y evaluados. Un fotodiodo comercial
de ancho de banda 50 GHz y un fotomezclador de THz de superred n-i-pn-i-p
son empleados.
El sistema de generación final que se presenta en esta tesis consiste en
un OFCG basado en GS, OIL como técnica de selección de modos ópticos y
un fotomezclador de THz de superred n-i-pn-i-p. Este sintetizador ofrece un
rango de funcionamiento de 60 a 140 GHz, directamente escalable a un rango
entre 10 GHz y valores más allá de un THz. Sintonía cuasi-continua es ofrecida
en todo el rango de frecuencia de operación, con una resolución en frecuencia
de 0.1 Hz a 100 GHz que puede ser directamente escalable a 0.01 Hz a 100 GHz y 0.1 Hz a 1 THz. El ancho de línea a 3-dB de la señal a 120 GHz es menor de
10 Hz, solo limitada por la instrumentación de medida. El sistema ofrece una
excelente estabilidad en potencia y frecuencia, con desviaciones sobre una hora
de operación de 1.5 dB y 5 Hz, respectivamente. Estos valores también están
limitados por la precisión e incertidumbre de la instrumentación de medida.
Las prestaciones conseguidas por este sintetizador fotónico de sub-THz
y THz para la mayoría de figuras de mérito, igualan o superan aquellas de las
mejores soluciones comerciales electrónicas en el estado del arte, y supera algunas
de estas características en más de un millón de veces en el caso de soluciones
fotónicas comerciales en el estado del arte.
La parte de detección de esta tesis explora el uso de arquitecturas fotónicas
basadas en receptores EO heterodinos y los componentes clave que forman estas
arquitecturas: Oscilador Local (OL) fotónico y mezcladores EO. Los primeros
resultados son desarrollados en el entorno de microondas (<15 GHz) usando un
amplificador de semiconductor óptico ultra no lineal (XN-SOA) como mezclador
EO y un OL fotónico basado en GS. Se demuestra como este OL basado en GS
ofrece una mejora significativa de las prestaciones del receptor con respecto al
uso de OL fotónicos tradicionales basados en modulación lineal. Además, esta
arquitectura de detección es validada en una aplicación real (imaging array
fotónico), ofreciendo escalabilidad, flexibilidad y ratios de conversión razonables.
Tras esto, un receptor EO heterodino es demostrado hasta frecuencias de 110 GHz. El OL fotónico empleado es el sintetizador de altas prestaciones
presentado en esta tesis, mientras que el mezclador EO es un nuevo detector de
THz: el np-i-pn cuasi-balístico. La primera muestra fabricada de estos nuevos
dispositivos, especialmente diseñados y optimizados para detección homodina
y heterodina, es empleada. El receptor EO heterodino resultante ofrece ratios
de conversión de -75 dB. Este dispositivo es capaz de trabajar sin alimentación,
lo que unido a la distribución fotónica del OL, ofrece un gran potencial para
detección remota de ondas de sub-THz y THz.
En resumen, las nuevas arquitecturas y dispositivos fotónicos presentados
en esta tesis son capaces de ofrecer prestaciones en el estado del arte para
generación de ondas de sub-THz y THz. En el caso de detectores EO heterodinos
en frecuencias de sub-THz y THz, las técnicas fotónicas están mejorando sus
prestaciones significativamente y están cada vez más cerca de ofrecer una
alternativa a detectores electrónicos en el estado del arte
Smoking and Second Hand Smoking in Adolescents with Chronic Kidney Disease: A Report from the Chronic Kidney Disease in Children (CKiD) Cohort Study
The goal of this study was to determine the prevalence of smoking and second hand smoking [SHS] in adolescents with CKD and their relationship to baseline parameters at enrollment in the CKiD, observational cohort study of 600 children (aged 1-16 yrs) with Schwartz estimated GFR of 30-90 ml/min/1.73m2. 239 adolescents had self-report survey data on smoking and SHS exposure: 21 [9%] subjects had “ever” smoked a cigarette. Among them, 4 were current and 17 were former smokers. Hypertension was more prevalent in those that had “ever” smoked a cigarette (42%) compared to non-smokers (9%), p\u3c0.01. Among 218 non-smokers, 130 (59%) were male, 142 (65%) were Caucasian; 60 (28%) reported SHS exposure compared to 158 (72%) with no exposure. Non-smoker adolescents with SHS exposure were compared to those without SHS exposure. There was no racial, age, or gender differences between both groups. Baseline creatinine, diastolic hypertension, C reactive protein, lipid profile, GFR and hemoglobin were not statistically different. Significantly higher protein to creatinine ratio (0.90 vs. 0.53, p\u3c0.01) was observed in those exposed to SHS compared to those not exposed. Exposed adolescents were heavier than non-exposed adolescents (85th percentile vs. 55th percentile for BMI, p\u3c 0.01). Uncontrolled casual systolic hypertension was twice as prevalent among those exposed to SHS (16%) compared to those not exposed to SHS (7%), though the difference was not statistically significant (p= 0.07). Adjusted multivariate regression analysis [OR (95% CI)] showed that increased protein to creatinine ratio [1.34 (1.03, 1.75)] and higher BMI [1.14 (1.02, 1.29)] were independently associated with exposure to SHS among non-smoker adolescents. These results reveal that among adolescents with CKD, cigarette use is low and SHS is highly prevalent. The association of smoking with hypertension and SHS with increased proteinuria suggests a possible role of these factors in CKD progression and cardiovascular outcomes