Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Patent
1990-09-28
1992-06-09
Gonzalez, Frank
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
264 15, G02B 600
Patent
active
051214628
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of scintillating optical fibers of the type having a core of a polymer of aromatic rings doped by molecules characterized by a Stokes shift. The invention also relates to new optical fibers produced by the process.
Scintillating optical fibers are known which are particularly used for detecting high energy particles. Currently, these fibers are produced by dissolving two dopants into a core monomer to be polymerized:
one dopant for the capture of the energy of excitation, able to re-emit the energy in the form of photons of an intermediate wavelength, generally of PBD (2-phenyl-5(4-biphenylyl)-1,3,4-oxadiazole), or butyl PBD, of p-tertiaryphenyl PBD,
the other dopant for shifting toward the visible range, able to absorb these intermediate photons for re-emitting them in the visible range, generally of POPOP: (1,4-di-2-(5-phenyloxazolyl)-benzene) or of bis-MSB: (p-bis(o-methylstyryl)benzene).
However, this production and doping technique, which is presently the only one known for producing scintillating optical fibers, has three essential drawbacks.
In the first place, it does not permit production of fibers of very small diameter and the fibers obtained have in practice had a diameter greater than or equal to 500 microns. This limitation stems from the combination of two factors, one related to the ratio of the energy of the conducted light to the energy of excitation, which becomes very low for these known fibers at a diameter of 500 microns, the other residing in the drawing difficulties encountered below this diameter. As a consequence, fibers of very small diameter which have been obtained during tests using the aforementioned known technique are of poor quality, unlikely to be used as particle detectors in accelerations of the linear acceleration type, synchrotron, or in medical apparatus. The reduction of the diameter of fibers to diameters on the order of 30 to 50 microns has proven essential, either for providing particle detectors, of an acceptable size, adapted to projection accelerators which tend to excite greater and greater energy bundles, or for increasing the resolution of the known detectors particularly in the medical field.
Further, scintillating optical fibers produced by the known technique have an attenuation length which in practice is less than 2 meters, that is, beyond this length, the ratio of the quantity of light emitted from the end of the fiber to the quantity of light produced at the site by the excitation energy becomes too weak for practical use. This limit shows up in particular in the molar extinction coefficient of the material of these fibers which is on the order of 20 to 30 liters/mole.cm at 420 nm.
Finally, the known fibers used in bundles in detectors require the presence of a supplemental opaque sheath around each fiber for suppressing `diaphotic` phenomena, consisting in a delocalization of the light from the excited fiber toward the adjacent fibers, which reduces the resolution of the detector. The need for this supplemental opaque sheath increases the cost of the production process, while its burdensome nature is prejudicial to the performances of the bundles of fibers and thus of the detector.
Existing scintillating fibers and their technique for production have serious limitations, for which there is no currently known solution.
The present invention proposes to overcome the aforementioned drawbacks and to provide a solution permitting the production of scintillating optical fibers of a polymer susceptible of having diameters much lower than those of known fibers and benefitting from increased attenuation lengths, regardless of the diameter of said fibers.
One object is in particular to enable the production of quality fibers having diameters on the order of 30 to 50 microns.
Another object is in particular to permit a very significant reduction of the molar extinction coefficient of the core material of the fibers, a reduction in a ratio greater than 100.
Another object is to suppress completely the diapho
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Destruel Pierre
Fabre Jean-Paul
Farenc Jean
Leutz Heinrich
Puertolas Didier
Centre National de la Recherche Scientifique
Dutton, Jr. Harold H.
Gonzalez Frank
Organisation Europeene pour la Rechesche Nucleaire
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