This thesis investigates the generation and radio-over-fibre (RoF) transport of unlicensed 60 GHz millimetre-wave (mm-wave) frequency band. The investigated benefits of transmission schemes applicable for the mm-wave generation include optical carrier suppression (OCS), optical frequency multiplication (OFM) and remote heterodyne detection (RHD). For the in-door cabling of the mm-wave transmission, a low-cost polymer optical fibre (POF) along with bend-insensitive single mode fibre (BI-SMF) has been investigated for short-range networks. Transporting mm-wave generated signals over POF and BI-SMF cables based on OCS scheme showed results with the highest spectral efficiency and least inter-symbol interference over a 2.5 Gbit/s data delivery. Based on this thesis analysis, OCS simulation of POF showed the most reliable power penalty performance and receiver sensitivity at 30-m whilst the BI-SMF fiber produced equal observations at 150-m and more. In observing the free space links of delivering the RoF signal, the attenuation on the received signal power for both POF and BI-SMF was insignificant but expected, as the simulation assumed complete and total collimation of the light beams onto the aperture of the photodetector. OCS scheme for mm-wave generation and transport was explored based on the cost effectiveness of using one external modulator compared to other generation schemes that utilised more than one external modulator. OFM scheme was simulated to transport LTE and Wi-Fi signals along with 60 GHz RF band through both SMF and MMF-POF/BI-SMF cables. OFM transport scheme produced the highest attenuation on LTE, Wi-Fi and mm-wave signals carrying 100 Mbit/s data as simulated POF lengths increased. The best performance POF length was observed at 10-m. The application of offset launch technique at the coupling of SMF and POF showed insignificant improvement on signal bandwidth. The free space OFM transmission also demonstrated negligible change to the received signal power. This reinforces the attributes of deploying OWC system in an in-door environment. In other investigation, the simulated successful delivery of mm-wave signal using RHD scheme modulated and transported 10 Gbit/s data signal over POF and BI-SMF cables. Additional observed unrecorded result also showed BI-SMF cable maintained a 2% reduction of received power for 450-m fiber cable from 150-m. The attributes to RHD includes its low operating power system application and delivery of localised 60 GHz signal for uplink RoF transmission. The conceptualised design of Gigabit data delivery for indoor customer applications either through POF or BI-SMF cable, transporting various wireless channels has been presented in this thesis for the design of a robust next generation Broadband access network to reinforce the fiber-inside-the-home (FiTH) deployment.

Q-switched operation of a holmium-doped fluoride fiber laser at 1.2 mu m wavelength induced by a semiconductor saturable absorber mirror (SESAM) is reported. 650 ns pulses with 0.13 mu J pulse energy at a repetition rate of 260 kHz were obtained.

Cladding pumped single-frequency Yb3+-doped fiber amplifiers at 976 nm were investigated. Over 4 W output power was obtained and further power scaling can be achieved by reducing the cladding diameter of the Yb3+-doped fiber.

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The focus of this thesis is on the development of sensing devices based on optical fiber sensors, specifically optical Fiber Bragg Gratings (FBG), using laser microfabrication methods. FBG is a type of optical fibers whose spectral response is affected by applied strain and temperature. As a result, it can be calibrated for the measurement of physical parameters manifesting themselves in the changes of strain or temperature. The unique features of optical fiber sensors such as FBGs have encouraged the widespread use of the sensor and the development of optical fiber-based sensing devices for structural measurements, failure diagnostics, thermal measurements, pressure monitoring, etc. These features include light weight, small size, long-term durability, robustness to electromagnetic disturbances, and resistance to corrosion. Despite the encouraging features, there are some limitations and challenges associated with FBGs and their applications. One of the challenges associated with FBGs is the coupling of the effects of strain and temperature in the optical response of the sensors which affects the reliability and accuracy of the measurements. Another limitation of FBGs is insensitivity to the index of refraction of their surrounding medium. In liquids, the index of refraction is a function of concentration. Making FBGs sensitive to the index of refraction and keeping their thermal sensitivity intact enable optical sensors with the capability of the simultaneous measurement of concentration and temperature in liquids. Considering the unique features of FBGs, embedding of the sensors in metal parts for in-situ load monitoring is a cutting-edge research topic. Several industries such as machining tools, aerospace, and automotive industries can benefit from this technology. The metal embedding process is a challenging task, as the thermal decay of UV-written gratings can starts at a temperature of ~200 oC and accelerates at higher temperatures. As a result, the embedding process needs to be performed at low temperatures. The objective of the current thesis is to move forward the existing research front in the area of optical fiber sensors by finding effective solutions to the aforementioned limitations. The approaches consist of modeling, design, and fabrication of new FBG-based sensing devices. State-of-the-art laser microfabrication methods are proposed and implemented for the fabrication of the devices. Two approaches are adopted for the development of the FBG-based sensing devices: the additive method and the subtractive method. In both methods, laser direct microfabrication techniques are utilized. The additive method deals with the deposition of on-fiber metal thin films, and the subtractive method is based on the selective removal of materials from the periphery of optical fibers. To design the sensing devices and analyze the performance of the sensors, an opto-mechanical model of FBGs for thermal and structural monitoring is developed. The model is derived from the photo-elastic and thermo-optic properties of optical fibers. The developed model can be applied to predict the optical responses of a FBG exposed to structural loads and temperature variations with uniform and non-uniform distributions. The model is also extended to obtain optical responses of superstructure FBGs in which a secondary periodicity is induced in the index of refraction along the optical fiber. To address the temperature-strain coupling in FBGs, Superstructure FBGs (SFBG) with on-fiber metal thin films are designed and fabricated. It is shown that SFBGs have the capability of measuring strain and temperature simultaneously. The design of the sensor with on-fiber thin films is carried out by using the developed opto-mechanical model of FBGs. The performance of the sensor in concurrent measurement of strain and temperature is investigated by using a customized test rig. A laser-based Direct Write (DW) method, called Laser-Assisted Maskless Microdeposition (LAMM), is implemented to selectively deposit silver thin films on optical fibers and fabricate the superstructure FBGs. To attain thin films with premium quality, a characterization scheme is designed to study the geometrical, mechanical, and microstructural properties of the thin films in terms of the LAMM process parameters. A FBG, capable of measuring concentration and temperature of liquids is developed, and its performance is tested. Femtosecond laser micromachining is successfully implemented as a subtractive method for the sensor fabrication. For this purpose, periodic micro-grooves are inscribed in the cladding of regular FBGs so as to increase their sensitivity to the concentration of their surrounding liquid while keeping their thermal sensitivity intact. This type of sensors has the potential for applications in biomedical research, in which the in-situ measurement of the properties of biological analytes is required. Another accomplishment of this thesis is the development of FBG sensors embedded in metal parts for structural health monitoring using low temperature embedding processes. In this regard, the opto-mechanical model is extended to predict the optical response of the embedded FBGs. The embedding process involves low temperature casting, on-fiber thin film deposition, and electroplating methods. The performance of the embedded sensors is evaluated in structural loading and thermal cycling.

The focus of this thesis is on the development of sensing devices based on optical fiber sensors, specifically optical Fiber Bragg Gratings (FBG), using laser microfabrication methods. FBG is a type of optical fibers whose spectral response is affected by applied strain and temperature. As a result, it can be calibrated for the measurement of physical parameters manifesting themselves in the changes of strain or temperature. The unique features of optical fiber sensors such as FBGs have encouraged the widespread use of the sensor and the development of optical fiber-based sensing devices for structural measurements, failure diagnostics, thermal measurements, pressure monitoring, etc. These features include light weight, small size, long-term durability, robustness to electromagnetic disturbances, and resistance to corrosion. Despite the encouraging features, there are some limitations and challenges associated with FBGs and their applications. One of the challenges associated with FBGs is the coupling of the effects of strain and temperature in the optical response of the sensors which affects the reliability and accuracy of the measurements. Another limitation of FBGs is insensitivity to the index of refraction of their surrounding medium. In liquids, the index of refraction is a function of concentration. Making FBGs sensitive to the index of refraction and keeping their thermal sensitivity intact enable optical sensors with the capability of the simultaneous measurement of concentration and temperature in liquids. Considering the unique features of FBGs, embedding of the sensors in metal parts for in-situ load monitoring is a cutting-edge research topic. Several industries such as machining tools, aerospace, and automotive industries can benefit from this technology. The metal embedding process is a challenging task, as the thermal decay of UV-written gratings can starts at a temperature of ~200 oC and accelerates at higher temperatures. As a result, the embedding process needs to be performed at low temperatures. The objective of the current thesis is to move forward the existing research front in the area of optical fiber sensors by finding effective solutions to the aforementioned limitations. The approaches consist of modeling, design, and fabrication of new FBG-based sensing devices. State-of-the-art laser microfabrication methods are proposed and implemented for the fabrication of the devices. Two approaches are adopted for the development of the FBG-based sensing devices: the additive method and the subtractive method. In both methods, laser direct microfabrication techniques are utilized. The additive method deals with the deposition of on-fiber metal thin films, and the subtractive method is based on the selective removal of materials from the periphery of optical fibers. To design the sensing devices and analyze the performance of the sensors, an opto-mechanical model of FBGs for thermal and structural monitoring is developed. The model is derived from the photo-elastic and thermo-optic properties of optical fibers. The developed model can be applied to predict the optical responses of a FBG exposed to structural loads and temperature variations with uniform and non-uniform distributions. The model is also extended to obtain optical responses of superstructure FBGs in which a secondary periodicity is induced in the index of refraction along the optical fiber. To address the temperature-strain coupling in FBGs, Superstructure FBGs (SFBG) with on-fiber metal thin films are designed and fabricated. It is shown that SFBGs have the capability of measuring strain and temperature simultaneously. The design of the sensor with on-fiber thin films is carried out by using the developed opto-mechanical model of FBGs. The performance of the sensor in concurrent measurement of strain and temperature is investigated by using a customized test rig. A laser-based Direct Write (DW) method, called Laser-Assisted Maskless Microdeposition (LAMM), is implemented to selectively deposit silver thin films on optical fibers and fabricate the superstructure FBGs. To attain thin films with premium quality, a characterization scheme is designed to study the geometrical, mechanical, and microstructural properties of the thin films in terms of the LAMM process parameters. A FBG, capable of measuring concentration and temperature of liquids is developed, and its performance is tested. Femtosecond laser micromachining is successfully implemented as a subtractive method for the sensor fabrication. For this purpose, periodic micro-grooves are inscribed in the cladding of regular FBGs so as to increase their sensitivity to the concentration of their surrounding liquid while keeping their thermal sensitivity intact. This type of sensors has the potential for applications in biomedical research, in which the in-situ measurement of the properties of biological analytes is required. Another accomplishment of this thesis is the development of FBG sensors embedded in metal parts for structural health monitoring using low temperature embedding processes. In this regard, the opto-mechanical model is extended to predict the optical response of the embedded FBGs. The embedding process involves low temperature casting, on-fiber thin film deposition, and electroplating methods. The performance of the embedded sensors is evaluated in structural loading and thermal cycling.

In this study, we will discuss the fabrication detail about the capillary optical fiber and microstructured optical fiber (MOF) from the preform manufacture to the drawing process and apply our capillary optical fiber in a temperature sensor device. First, we discuss the influence of the drawing parameters contribution for the fiber, and we will introduce how to design a preform and discuss how to keep our fibre geometry in drawing process by controlling the drawing parameters. For better fiber products, we need to make some important improvements such as fixing the preform geometry and designing the preform pressure or vacuum input path before the fiber drawing process. In the fiber drawing we want to control the fiber inner diameter and make the interval between three capillary tube disappear. We will solve these problems by different preform making methods or drawing tower hardware design and drawing parameter control. Now we can successfully make single ring hole MOFs by the capillary tube sealed method. But the hole structure is not as good as expectation. We will try to design a pressure and vacuum input device to replace the capillary tube sealed method. And help us to make better and more different MOF structures. We also used our capillary optical fiber to be a temperature sensor. We will describe the principle and the sensing sensitivity of our sensing device in this study. Our temperature sensing device shows a linear relationship between the temperature and operation wavelength, and the sensing sensitivity is 0.038nm/¢XC

No description available.