44 research outputs found
Spectral Interferometry with Frequency Combs
In this review paper, we provide an overview of the state of the art in linear interferometric techniques using laser frequency comb sources. Diverse techniques including Fourier transform spectroscopy, linear spectral interferometry and swept-wavelength interferometry are covered in detail. The unique features brought by laser frequency comb sources are shown, and specific applications highlighted in molecular spectroscopy, optical coherence tomography and the characterization of photonic integrated devices and components. Finally, the possibilities enabled by advances in chip scale swept sources and frequency combs are discussed
Characterisation of Optical Fibers Using Dual-Comb Swept-Wavelength Interferometry
The growth in data traffic coupled with trends in internet use will result in a requirement for interfaces of the network to reach Tb/s data rate in the future. Considering this, novel transmission techniques that can increase the date rate with orders of magnitude must be considered. One such example is space-division multiplexing (SDM) fibers. Application of novel fibers and SDM components in communication systems is always coupled with limitations and distortions of the signal due to crosstalk, dispersion, differential mode group delay (DMGD) and other effects. They can be calculated, studied and partially mitigated if the transfer function of the fiber under test is known. Thus, it is essential to characterize the fiber\u27s and other component\u27s transfer matrix using fast and accurate measurement techniques. Moreover, these characterisation measurements can be used for building channel models, which can assist in simulations of the transmission and estimation of ultimate system performance.In this thesis various techniques for SDM devices characterisation are described and a novel method based on dual-comb spectroscopy and swept-wavelength interferometry is proposed and evaluated. The presented technique, dual-comb swept-wavelength interferometry (DC-SWI), is studied in terms of capabilities, advantages and limitations with application on different devices under test. This experimental scheme is also used for characterisation of a coupled-core fiber, where the transfer function and DMGD values were extracted.Furthermore, different channel models describing the properties of SDM fiber links are briefly reviewed and discussed
A novel technique of optical frequency sweep linearization of a DFB laser for high resolution FMCW reflectometry
13301甲第4407号博士(学術)金沢大学博士論文本文Full 以下に掲載:1.Journal of Engineering and Applied Sciences (JEAS) 10(8) pp.3817-3522 MAY 2015. ARPN. 共著者:NOR AZLINAH BINTI MD LAZAM, Koichi Iiyama, Takeo Maruyama, Yosuke Kimura and Nguyen Van Tu 2.International Journal of Electrical and Electronics Engineering Research (IJEEER) 5(6) pp.1-10 DEC 2015. TRANS-STELLAR. 共著者:NOR AZLINAH BINTI MD LAZAM, Akihiro Igarashi, Nakamoto Atsushi, Takeo Maruyama and Koichi Iiyam
Chirped-pulse phase-sensitive optical time domain reflectometry
El mundo actual funciona gracias a las grandes infraestructuras que dotan de energía y transporte seguros a sus ciudadanos. Dichas infraestructuras (presas, diques, gaseoductos, oleoductos, puentes, líneas de ferrocarril, carreteras…) típicamente presentan grandes dimensiones y es especialmente difícil monitorizar su buen funcionamiento y su salud estructural además de protegerlas de posibles amenazas. Los sensores distribuidos de fibra óptica son una solución fiable y rentable para esta problemática, ya que permiten medir vibraciones, deformaciones y temperatura a lo largo de todos los puntos de una fibra óptica estándar de comunicaciones.
Los sensores de fibra óptica basados en scattering Rayleigh son particularmente útiles cuando las medidas deben ser realizadas en tiempo real, como por ejemplo en la detección y caracterización de vibraciones. En esta tesis, se ha realizado un estudio acerca de distintas soluciones y alternativas a las limitaciones de la tecnología OTDR. Se ha propuesto una nueva técnica, derivada de ésta, que ofrece unas prestaciones que superan notablemente a las de los sistemas OTDR tradicionales.
Para ello, en primer lugar, se ha procedido a realizar un estudio en profundidad de los fundamentos y el estado del arte de las técnicas de monitorización basadas en Reflectometría Óptica en el Dominio del Tiempo (OTDR, por sus siglas en inglés) y, en particular, sobre la implementación sensible a la fase, también conocida como OTDR. Se ha estudiado la limitación en rango y resolución de los sistemas OTDR principalmente asociada a la aparición de efectos no lineales como la inestabilidad de modulación. Actualmente, un OTDR tradicional presenta una resolución máxima del orden de los 10 metros para un rango de medida del orden de pocas decenas de km (si no se aplica ningún tipo de técnica de amplificación distribuida). Además de estudiar esta limitación y a qué es debida, se han propuesto dos técnicas para mitigar los efectos perjudiciales de la MI. En primer lugar, se ha realizado un estudio del efecto de la forma de los pulsos ópticos empleados en el sensor en la traza retrodispersada en un OTDR. Se ha podido comprobar cómo los pulsos triangulares o gaussianos presentan mayor robustez que los pulsos rectangulares, tradicionalmente empleados, frente a la MI. En segundo lugar, se ha propuesto una técnica basada en el concepto de Amplificación de Pulsos Chirpeados (CPA, por sus siglas en inglés), que ha permitido desarrollar un OTDR con resoluciones milimétricas. Hasta el momento ningún OTDR había podido llegar a tales resoluciones, lo que abre un nuevo abanico de aplicaciones a la tecnología OTDR donde se requiera alta resolución espacial en la medida.
También se ha estudiado la otra gran limitación de este tipo de sensores: su comportamiento no lineal ante una perturbación. Actualmente, salvo que se implementen técnicas de recuperación de fase o barridos en longitud de onda que implican más complejidad, coste y tiempo de medida, no es posible realizar medidas cuantificables de temperatura o deformaciones. Del mismo modo, tampoco se pueden realizar medidas acústicas reales. En este trabajo, en primer lugar, se propone emplear la técnica de Reconstrucción de Fase empleando Diferenciación Óptica Ultrarápida (PROUD, por sus siglas en inglés) para recuperar el campo complejo de una señal OTDR. Con esta medida, el sensor pasaría a comportarse de forma lineal sin la complejidad intrínseca de los métodos tradicionales de detección de fase. En segundo lugar, y de aquí viene el nombre de esta tesis doctoral, se propone el uso de pulsos chirpeados en los sensores OTDR. La nueva técnica llamada Chirped-Pulse OTDR, ha permitido la medida de forma lineal de cambios de temperatura y deformaciones, en un único disparo y sin la necesidad de realizar barridos en frecuencia o implementar detección coherente. A lo largo de este trabajo, se han alcanzado resoluciones de 0.5mK/4n y se ha demostrado la posibilidad de hacer medidas acústicas reales. También se han estudiado las limitaciones de esta técnica y propuesto varias soluciones. Se ha demostrado que el ruido de fase del láser empleado en el sistema, puede ser mitigado con esta nueva técnica. Además, se ha propuesto el uso de amplificación distribuida basada en scattering Raman estimulado para alcanzar rangos de medida mayores, hasta 75 km con una resolución espacial de 10 m
Design of an FPGA Based High-Speed Data Acquisition System for Frequency Scanning Interferometry Long Range Measurement
Frequency Scanning Interferometry (FSI) has become a popular method for long-range, target based, distance measurements. However, the cost of developing such systems, particularly the electronic components required for high-speed data acquisition, remains a significant concern. In this paper, we present a cost-effective, FPGA-based real-time data acquisition system specifically designed for FSI, with a focus on long absolute distance measurements. Our design minimizes the use of third-party intellectual property (IP) and is fully compatible with the Xilinx FPGA 7 series families. The hardware employs a 160 MS/s, 16-bit dual-channel ADC interfaced to the FPGA via a Low Voltage Differential Signal (LVDS). The proposed system incorporates an external sampling clock, referred to as the K- clock, which linearizes the laser's tuning rate, enabling optical measurements to be sampled at equal optical frequency intervals rather than equal time intervals. Additionally, we present the design of a high-speed, 160 MS/s ADC module for the front-end analogue signal interface and the LVDS connection to the chosen FPGA. We demonstrate that the digitized data samples can be efficiently transmitted to a PC application via a USB interface for further processing
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Advances in Swept-Wavelength Interferometry for Precision Measurements
Originally developed for radar applications in the 1950s, swept-wavelength interferometry (SWI) at optical wavelengths has been an active area of research for the past thirty years, with applications in fields ranging from fiber optic telecommunications to biomedical imaging. It now forms the basis of several measurement techniques, including optical frequency domain reflectometry (OFDR), swept-source optical coherence tomography (SS-OCT), and frequency-modulated continuous-wave (FMCW) lidar. In this thesis, I present several novel contributions to the field of SWI that include improvements and extensions to the state of the art in SWI for performing precision measurements. The first is a method for accurately monitoring the instantaneous frequency of the tunable source to accommodate nonlinearities in the source tuning characteristics. This work extends the commonly used method incorporating an auxiliary interferometer to the increasingly relevant cases of long interferometer path mismatches and high-speed wavelength tuning. The second contribution enables precision absolute range measurements to within a small fraction of the transform-limited range resolution of the SWI system. This is accomplished through the use of digital filtering in the time domain and phase slope estimation in the frequency domain. Measurements of optical group delay with attosecond-level precision are experimentally demonstrated and applied to measurements of group refractive index and physical thickness. The accuracy of the group refractive index measurement is shown to be on the order of 10-6, while measurements of absolute thicknesses of macroscopic samples are accomplished with accuracy on the order of 10 nm. Furthermore, subnanometer uncertainty for relative thickness measurements can be achieved. For the case of crystalline silicon wafers, the achievable uncertainty is on the same order as the Si-Si bond length, opening the door to potential thickness profiling with single atomic monolayer precision. Thirdly, I demonstrate a novel implementation of SWI in the form of an SS-OCT system for performing quantitative measurements of spatially resolved refractive index contrast. This system relies on the depth-sectioning capability of SWI to isolate Fresnel reflectivity variations at an interface of interest within an optical sample. A motivating application for this quantitative index contrast measurement, volume lithography of photosensitive polymers, is also discussed in detail. This discussion includes the first demonstration of two-dimensional optical waveguide arrays fabricated in photosensitive polymers by means of holographic lithography
Coherent Rayleigh time domain reflectometry:novel applications for optical fibre sensing
Owing to the advantages of the optical fibre, such as lightweight, small size, low cost and immunity to electromagnetic interferences, the fibre sensors have been applied in diverse fields and the scientific research on fibre sensing keeps improving to meet new industrial demands. In this thesis, a novel distributed fibre sensor based on coherent Rayleigh scattering is investigated to realise best accuracy measurements. Coherent Rayleigh scattering is found to be essentially assimilated to a random walk process, thus its statistical properties are theoretically analysed based on the mature theory on random walk. Then the spectral characteristics of the Rayleigh backscattered light is investigated for different incident pulse shapes. The spectral distribution of the trace amplitude turns out to be identical to the spectrum of the incident pulse. Meanwhile, a theoretical model is proposed to describe the coherent Rayleigh trace in time and frequency domains. Experiments are carried out to validate the theoretical analysis and the proposed model. Then the statistical properties and the visibility of the coherent Rayleigh traces obtained by experiment and simulation are investigated for different detection bandwidth. The minimum 3 dB bandwidth required to resolve all features of a coherent Rayleigh intensity trace is determined to be 3 times larger than the bandwidth of the incident rectangular pulse. Then coherent Rayleigh scattering is applied to distributed sensing using the optical time domain reflectometry technique. The working principle is explained by the restorability of the Rayleigh trace in time domain and by a spectral shift in frequency domain. The temperature sensitivity is calculated over a wide range from 300 K down to 4.5 K based on the thermo-optic effect and the thermal expansion of the silica fibre. The experimental results in a standard fibre with acrylate coating and a fibre specially coated with ORMOCER® confirm the high temperature sensitivity (over 1 GHz/K) and demonstrate a temperature resolution in the milliKelvin range even under cryogenic conditions. The fibre with the ORMOCER® coating exhibits a higher temperature sensitivity at room temperature than the acrylate coated fibre due to the extra strain induced by the temperate change in the coating and a more stable sensing behaviour because the polymers forming the coating stabilise the mechanical and thermal responses of the fibre. The sensors based on coherent Rayleigh scattering are also applied to retrieve the phase birefringence distribution along polarisation-maintaining and standard single mode fibres. The minimum detectable birefringence reaches 3×10¿7 when the spatial resolution is 2 m and even smaller value can be resolved using longer optical pulses. In addition, this birefringence measurement is capable of distributed temperature and strain sensing in a PANDA and an elliptical-core polarisation-maintaining fibres since the birefringence is sensitive to environmental variations. The experimental results demonstrate that this method is one order of magnitude more sensitive than a fibre sensor based on Brillouin scattering. Moreover, discriminated temperature and strain sensing is realised by a combination of this birefringence measurement and a standard COTDR sensor. This thesis is concluded by a discussion of further research directions on coherent Rayleigh scattering based distributed sensing
Fiber Optic Sensors in Chemical and Biological Applications
The Special Issue "Fiber Optic Sensors in Chemical and Biological Applications” gathers recent original papers. The subjects of the papers cover a broad range of optical fiber chemical sensors and biosensors applied for regulation in bioreactors, to novel concepts of intrinsic optical fiber sensors
Enabling Technology in Optical Fiber Communications: From Device, System to Networking
This book explores the enabling technology in optical fiber communications. It focuses on the state-of-the-art advances from fundamental theories, devices, and subsystems to networking applications as well as future perspectives of optical fiber communications. The topics cover include integrated photonics, fiber optics, fiber and free-space optical communications, and optical networking