The ANTARES collaboration is building a deep sea neutrino telescope in the Mediterranean Sea. This detector will cover a sensitive area of typically 0.1 km 2 and will be equipped with about 1000 optical modules. Each of these optical modules consists of a large area photomultiplier and its associated electronics housed in a pressure resistant glass sphere. The design of the ANTARES optical module, which is a key element of the detector, has been finalized following extensive R&D studies and is reviewed here in detail.
ANTARES is a project leading towards the construction and deployment of a neutrino telescope in the deep Mediterranean Sea. The telescope will use an array of photomultiplier tubes to detect the Cherenkov light emitted by muons resulting from the interaction with matter of high energy neutrinos. In the vicinity of the deployment site the ANTARES collaboration has performed a series of in-situ measurements to study the change in light transmission through glass surfaces during immersions of several months. The average loss of light transmission is estimated to be only ∼ 2% at the equator of a glass sphere one year after deployment. It decreases with increasing zenith angle, and tends to saturate with time. The transmission loss, therefore, is expected to remain small for the several year lifetime of the ANTARES detector whose optical modules are oriented downwards. The measurements were complemented by the analysis of the 210 Pb activity profile in sediment cores and the study of biofouling on glass plates. Despite a significant sedimentation rate at the site, in the 0.02 -0.05 cm · yr −1 range, the sediments adhere loosely to the glass surfaces and can be washed off by water currents. Further, fouling by deposits of light-absorbing particulates is only significant for surfaces facing upwards.
A 1550 nm DWDM planar external cavity laser (ECL) is demonstrated to provide low phase/frequency noise, narrow linewidth, and low RIN. The cavity includes a semiconductor gain chip and a planar lightwave circuit waveguide with Bragg grating, packaged in a 14-pin butterfly package. This planar ECL laser is designed to operate under vibration and in harsh environmental conditions. The laser shows linewidth ≤ 2.6 kHz, phase/frequency noise comparable with that of long cavity fiber lasers, RIN ≤ -147dB/Hz at 1kHz, and power ≥ 10mW. Performance is suitable for various high performance fiber optic sensing systems, including interferometric sensing in Oil and Gas, military/security and other applications, currently served mostly by costly and less reliable laser sources.Keywords: planar external cavity laser, phase noise, linewidth, relative intensity noise, fiber optic sensing, butterfly package, seismic exploration, remote interferometric sensing. IntroductionHigh performance, fiber optic distributed interferometric technology was developed over the past 15 years for obtaining high quality dynamic measurements, but it has only recently moved into the deployment stage. Due to the technology's historically high cost, applications fall mostly into military surveillance or remote sensing in severe environments (sub-sea or subsurface for the oil and gas industry). These applications are now moving toward cost/performance optimization as the technology matures. Other more cost sensitive applications, which include distributed structural monitoring, large area and perimeter surveillance, seismic monitoring, and communications systems security, are now gaining the benefits of this optimization, and these applications are much larger in terms of market size.
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