Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2001-12-17
2004-04-20
Strecker, Gerard (Department: 2862)
Optical waveguides
Optical fiber waveguide with cladding
C385S031000, C065S378000, C065S385000, C065S392000, C065S394000, C065S485000
Reexamination Certificate
active
06724963
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to illuminating optical fibers and manufacturing processes to produce optical fibers having patterned light diffusion sites along the length of the fibers.
2. Information Disclosure Statement
The radiation emitted by a laser beam source can be coupled into an optical fiber of suitable dimensions and optical properties wherein the light can be transported with no significant losses over very long distances. Today's state of the art fibers have found broad application in the fields of telecommunication, optical inspection, medical therapy, laser applications and many more. The fabrication processes are well understood and optical fibers are manufactured in large quantities at high quality providing lifetimes up to over one million hours.
Optical fibers rely on total internal reflection at the interface between the fiber core and the surrounding cladding to contain the light within the core of the fiber. The light guiding effect occurs in optical fibers where cores are much larger than the wavelength of the incident light. For light guiding to occur, the refractive index of the fiber cladding must be lower than the refractive index of the fiber core. A light ray incident to the fiber core's end under an angle sufficiently small relative to the fiber axis can enter the fiber and is refracted according Snell's law into a certain angle. It then hits the interface between fiber core and cladding and is, assuming the angle of incidence to the surface is sufficiently large, totally reflected back into the core. If no bends occur that exceed a critical curvature, the light cannot leave the fiber core and is thus guided through the fiber until it reaches the end. If the core is small, typically in the range of a few multiples of the wavelength of the radiation that is to be coupled into the fiber, the light guiding effect can be easier understood in terms of a wave guiding.
The fiber is an optical system wherein light propagation is possible only in distinct Eigenmodes. These modes can be excited by incident light and then propagated through the fiber. All light guiding effects in optical fibers share a common feature, the optical field is not completely confined to the fiber core. Slight parts of the radiation lap into the fiber cladding; known as an “evanescent field” to people skilled in the art. This evanescent field does not necessarily contribute to the damping of the fiber, but it can significantly influence the guiding and mode properties.
Since it is possible to couple into fibers the radiation of high power light sources, such as diodes and laser beams, one can think of applying specially manufactured illuminating fibers in a wide variety of applications.
Normally the goal of the fiber manufacturing process is to minimize the fiber's intrinsic losses. Illuminating fibers show a different behavior than conventional fibers, because their optical loss is not usually as small as possible but well defined over the length of the fiber. This is realized by manufacturing the fiber in such a manner that a certain amount is coupled out of the fiber's radiation guiding core and is diffused into the fiber cladding, from where it is scattered. The fiber cladding appears to be illuminated. Illuminating fibers of this simple kind can be manufactured in several ways.
For polymer cladded fibers, one method treats the fiber chemically while still uncoated so that the core's surrounding becomes rough and thus diffuses a certain part of the light being totally reflected at the core/cladding interface. This method has several disadvantages. It is a very rough method and can only be slightly regulated, thus the illumination effect will vary strongly with the length of the fiber. The technique cannot be used with glass cladded fibers.
Another method utilizes the scattering effect of several substances added to the basic material from which the fiber is manufactured. This permits a very homogeneous doping of the fiber core. Similarly, the polymer cladding can contain a dopant material, from which parts of the evanescent field are scattered so the fiber appears illuminated. This method can produce a uniform diffusion, but does not permit a patterned diffusion along the fibers length.
Although uses for illuminating fibers are suggested in the prior art, few discuss the use of partially diffusing fibers as an economical means to achieve the desired end products.
U.S. Pat. No. 3,508,589 describes luminous textile products made luminous by incorporating optical fibers, which have been enhanced to “frustrate total reflection”. Methods discussed are the disruption of the internal reflecting surfaces by roughening the surface of the unsheathed core by etching, grit blasting or abrading. It would be economically advantageous be able to produce the patterned diffusive properties at the time the fiber was manufactured. The methods described could not be used for a glass cladded fiber.
Since state of the art fibers have uniform scattering rates according to their fabrication process, a necessary requirement to realize the above mentioned applications is a manufacturing method to produce long lengths of diffusing optical fibers with tailored properties, especially concerning their scatter rates.
U.S. Pat. No. 5,737,472 describes an optical fiber with multiple point lateral illumination. The method that the invention proposes is treating a fiber of length on the order of several meters, to produce an appearance of uniformity or quasi-continuous luminosity. The illumination is accomplished by numerous, closely spaced degradations on the fiber surface. The number and size of the degradation are a function of their distance from the illumination source. The degradations are obtained by sandblasting or attack by an aerosol solvent. The patent describes several methods of maintaining uniform illumination. These include changing the sandblaster characteristics as a function of fiber length and using a photocell to measured the intensity of perceived light at the sandblast site, which controls the speed of the fiber. In one embodiment of the invention, the optical fiber includes several treated areas separated by non-treated areas. The invention illustrates a spool-to-spool (fixed length) post-draw process and is not suitable for very long lengths of fibers.
U.S. Pat. No. 5,905,837 describes a method to controllably tap and distribute light propagating through an optical fiber. The invention comprises an optical fiber having multiple cross-sectional regions each having a different index of refraction. When light passing through the fiber reaches the interface where the refractive index changes, the light traversing the fiber is diverted out of the optical fiber through the side of the fiber. Refractive regions and reflective layers help to direct light out of the fibers. Prisms may advantageously be applied to the exit side of the fiber to focus the light for use. The invention primarily relies on dispersive elements in the optical fiber material, reflective elements and prisms. The reflective and prismatic elements are not derived from the fiber itself. It does not suggest the advantageous treatments of the cladding or combinations of core and cladding. The patent does not describe or suggest a continuous in-line operation integrated into the production of the fiber.
U.S. Pat. No. 5,781,679 describes an apparatus for tapping and dispersing light from an optical fiber. The invention comprises mirrors constructed from the optical fiber itself through a series of micro-cutting, masking, coating and refilling operations. Dispersive elements are added to the refilling material before it is placed within the cut region of the fiber. The cut and refilled regions act as a tap allowing diffused light to exit the optical fiber. The invention does not describe or suggest producing the light-dispersing fiber in a continuous process nor does it discuss the treatment of a fiber cladding for enhanced illumination effects.
BJ Associates
CeramOptec Industries Inc.
Skutnik Bolesh J.
Strecker Gerard
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