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The detection of ultra high energetic cosmic neutrinos provides a unique means to search for extragalactic sources that accelerate particles to extreme energies. It allows to study the neutrino component of the GZK cut-off in the cosmic ray energy spectrum and the search for neutrinos beyond this limit. Due to low expected flux and small interaction cross-section of neutrinos with matter large experimental set-ups are needed to conduct this type of research. Acoustic detection of cosmic rays may provide a means for the detection of ultra-high energetic neutrinos. Using relative low absorption of sound in water, large experimental set-ups in the deep sea are possible that are able to detect these most rare events, but it requires highly sensitive hydrophones as the thermo-acoustic pulse originating from a particle shower in water has a typical amplitude as low as a mPa. It has been shown in characterisation measurements that the fibre optic hydrophone technology as designed and realised at TNO provides the required sensitivity. Noise measurements and pulse reconstruction have been conducted that show that the hydrophone is suited as a particle detector.

A brief overview of fiber Bragg grating based sensor technology from sensor head, read out unit and commercial applications is given. Fiber Bragg grating based sensor systems are becoming mature rapidly. Components for commercial pressure sensors and temperature sensors are available and slowly getting accepted. However, many advantages of the fiber Bragg grating as sensor are still not fully recognized by a wider audience. Properties such as the ability for distributed sensing, small size, light weight, immune for electromagnetic interference and resistance to harsh environments are examples of the advantages of fiber Bragg grating based sensors.

Applying an inhomogeneous lateral load to an FBG will result in distortion of the reflection spectrum due to the Poisson effect. A solution based on a special fiber is proposed and first results are shown.

Sinds de ontdekking van kosmische straling zijn veel verchillende detectoren ontwikkeld om dit fenomeen te onderzoeken. Nieuw in het rijtje is de optische hydrofoonsensor, waarmee naar hoogenergetisache neutrino's gespeurd kan worden.

During the last decades, the use of optical fiber for sensing applications has gained increasing acceptance because of its unique properties of being intrinsically safe, unsusceptible to EMI, potentially lightweight and having a large operational temperature range. Among the different Fiber Optic sensor types, Fiber Bragg Grating (FBG) is most widely used for its unique multiplexing potential and the possibility of embedding in composite material for Structural Health Monitoring. When the fiber is embedded in an inhomogeneous environment, typically a material composed of filler and base material of different stiffness, local stiff material will generate extra lateral load to the fiber. Via the Poisson effect, this will be converted to a local axial strain. The narrow and sharp peak in the reflection spectrum of an FBG sensor relies on the constant periodicity of the grating. An inhomogeneous axial strain distribution will result in distortion or broadening of the FBG reflection spectrum. For the FBG strain sensitivity of about 1.2pm/με, the spectral distortion can be disastrous for strain measurements. A fiber design to tackle this critical problem is presented. Finite Element Modeling is performed to demonstrate the effectiveness of the solution. Modeling with different configurations has been performed to verify the influence of the design. The deformation of the core in the special fiber depends on the design. For a particular configuration, the core deformation in the axial direction is calculated to be a factor of 10 lower than that of a standard fiber. The first prototype fiber samples were drawn and the manufacturing of FBG in this special fiber using the phase mask method was demonstrated successfully. © 2014 SPIE.

An overview of a fiber Bragg based sensor system, developed for in-vivo vascular pressure and temperature sensing, is presented. The focus is on sensor miniaturization and interrogator optimization to reach a viable sensor system.

We present a detailed characterization of a set of microring resonators with bent radii of 1.5 μm, fabricated in silicon-on-insulator technology. Results are in good agreement with the universal relations for coupling between microresonators and dielectric waveguides.

A robust fibre optic flow sensor has been developed to measure liquid or gas flows at ambient temperatures up to 300°C and pressures up to 100 bar. While such environmental conditions are typical in pressurized steam systems in the oil and gas industry (downhole and surface), wider applications are envisaged. The flow sensor uses a specially-designed bluff body to generate vortex-induced pressure fluctuations as a function of flow. The pressure fluctuations result in mechanical strain fluctuations in the sensor plate which is attached to the bluff-body. This is detected by means of a Fibre Bragg Grating (FBG). The frequency of the pressure fluctuations is proportional to the flow velocity and is measured by analyzing the spectrum of the FBG sensor signal. Flow velocity measurements ranging from ~1 m/s to ~25 m/s have been demonstrated. Special mechanical design, gluing and packaging processes have been developed to enable applications at high temperatures and high pressures (HPHT). Although the working principle is the same as for conventional vortex flow meters, this flow sensor does not require electronics, which is a great advantage at high temperatures. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Silicon based SOI PICs are finding new applications in the field of sensing. Since Silicon does not produce light, to deploy these sensors in real-world applications a fiber-chip connection is required. In this work we detail the fabrication of V-grooves for fiber attachment to the chip, including the design, (hard) masking and the etching process. Our results show that V-groove attached fibre is an optimized solution for SOI based sensor PICs.

It is a well studied process [1, 2] that energy deposition of cosmic ray particles in water that generate thermo-acoustic signals. Hydrophones of sufficient sensitivity could measure this signal and provide a means of detecting ultra-high energetic cosmic neutrinos. We investigate optical fiber-based hydrophone technology that could potentially have several advantages over conventional hydrophones based on piezo ceramics. Optical fibers offer a natural way to create a distributed sensing system in which several sensors are attached to a single fiber. The detection system in this case would consist of several sensors, an erbium doped fiber and an interferometric interogator. Next to the advantage of having multiple sensors on a single fiber, this technology has a low power consumption, small size and low weight. Maybe even more important, fiber optics technology provides a cost-effective and straightforward way to implement a large number of hydrophones. An investigation has been carried out to study the feasibility of using fiber based hydrophones in an application for cosmic ray particle detection. We find that the hydrophone technology as explained in this paper offers the proper sensitivity as required to detect low signals orginating from the cosmic rays.

The DARWIN mission aims to detect weak infra-red emission lines from distant orbiting earth-like planets using nulling interferometry. This requires filtering of wavefront errors using single mode waveguides operating at a wavelength range of 6.5-20 μm. This article describes the optical design of the fibers, the manufacturing protocol, the packaging for operating at cryogenic environment and various optical characterisations performed. The latter includes investigation on the effect of gold and silver absorption coatings, anti-reflection coating, fiber length on higher order mode suppression and attenuation of the fibers.

A compact, mass producible Silicon On Insulator (SOI) based pressure sensor consisting of a folded Micro Ring Resonator (MRR) on a circular diaphragm is successfully designed, fabricated and characterized. An application of pressure deflects the diaphragm, causing stress in the MRR, which elongates the waveguide length and changes the effective refractive index of the guided mode. This results in a shift in its resonant wavelengths, which represents the applied pressure. This integrated device is successfully fabricated and a linear dependence between the resonance wavelength shift and the applied pressure at a constant temperature is measured. Such a pressure sensor finds applications in environments in which only minimal invasion is tolerated.

A compact, mass producible Silicon On Insulator (SOI) based pressure sensor consisting of a folded Micro Ring Resonator (MRR) on a circular diaphragm is successfully designed, fabricated and characterized [1-3]. The MRR is designed to be single mode for TE polarized light at 1550 nm. The folded MRR has a total length of 1500 μm which is folded to cover an area of 50X400 μm2 and has a guide-width of 450 nm. The circular diaphragm having a diameter of 1350 μm and a thickness of 15 μm is fabricated by reactive ion etching from the substrate side. Light is coupled into the MRR through the “in” port and measured at the “through” port using grating couplers. An application of pressure deflects the membrane, causing stress in the MRR, which in turn changes the effective refractive index the waveguide [4]. This results in a shift in its resonant wavelengths, which represent the applied pressure. Figure 1A shows the measured linear dependence between the resonance wavelength shift and the applied pressure at a constant temperature. Figure 1 B shows a SEM image of part of the membrane with MRR and Figure 1 C shows a schematic of the folded MRR. Such a pressure sensor finds applications in environments in which only minimal invasion is tolerated, such as in medical instrumentation.