A large fiber sensor network for an acoustic neutrino telescope

The scientific prospects of detecting neutrinos with an energy close or even higher than the GKZ cut-off energy has been discussed extensively in literature. It is clear that due to their expected low flux,the detection of these ultra-high energy neutrinos (Eν > 1018 eV) requires a telescope larger than 100km3. Acoustic detection may provide a way to observe these ultra-high energy cosmic neutrinos, as sound that they induce in the deep sea when neutrinos lose their energy travels undisturbed for many kilometers. To realize a large scale acoustic neutrino telescope, dedicated technology must be developed that allows for a deep sea sensor network. Fiber optic hydrophone technology provides a promising means to establish a large scale sensor network with the proper sensitivity to detect the small signals from the neutrino interactions

Fiber Bragg grating sensors

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

Fiber optic hydrophones for acoustic neutrino detection

Cosmic neutrinos with ultra high energies can be detected acoustically using hydrophones. The detection of these neutrinos may provide crucial information about then GZK mechanism. The flux of these neutrinos, however, is expected to be low, so that a detection volume is required more than a order of magnitude larger than what has presently been realized. With a large detection volume and a large number of hydrophones, there is a need for technology that is cheap and easy to deploy. Fiber optics provide a natural way for distributed sensing. In addition, a sensor has been designed and manufactured that can be produced cost-effectively on an industrial scale. Sensitivity measurements show that the sensor is able to reach the required sea-state zero level. For a proper interpretation of the expected bipolar signals, filtering techniques should be applied to remove the effects of the unwanted resonance peaks

Fiber interferometer combining sub-nm displacement resolution with miniaturized sensor head

The presented interferometer concept enables high-accuracy target displacement measurement in difficult accessible locations and the development of small fiber optic sensor to measure other physical parameters e.g. pressure, vibration, gravity force, etc.. Furthermore, this configuration is basically insensitive to disturbances to the lead fiber between the passive sensor head and the measurement system including the electro-optical parts and the detection interferometer. Two test setups are built and tested to demonstrate the feasibility of high-speed measurement up to 50 kHz, low system drift of ~0.5 nm over 500 s and a low displacement noise level down to 2.8 pm/√ Hz

Fiber optic hydrophones for acoustic neutrino detection

Cosmic neutrinos with ultra high energies can be detected acoustically using hydrophones. The detection of these neutrinos may provide crucial information about then GZK mechanism. The flux of these neutrinos, however, is expected to be low, so that a detection volume is required more than a order of magnitude larger than what has presently been realized. With a large detection volume and a large number of hydrophones, there is a need for technology that is cheap and easy to deploy. Fiber optics provide a natural way for distributed sensing. In addition, a sensor has been designed and manufactured that can be produced cost-effectively on an industrial scale. Sensitivity measurements show that the sensor is able to reach the required sea-state zero level. For a proper interpretation of the expected bipolar signals, filtering techniques should be applied to remove the effects of the unwanted resonance peaks

Special optical fiber design to reduce reflection peak distortion of a FBG embedded in inhomogeneous material

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