Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-10-28
2001-06-26
Sikder, Mohammad (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S034000, C385S035000, C385S036000
Reexamination Certificate
active
06253006
ABSTRACT:
BACKGROUND OF THE INVENTION
A) Field of the Invention
The present invention relates generally to fiber optics lighting systems and, specifically, to a fiber optics illumination device employing a plurality of optical fibers, said fibers arranged in a spaced and ordered geometrical organization, and a single optical element, for example, a lens, for receiving light from a light source, and distributing said light as a secondary source to said plurality of optical fibers in said organization.
B) Description of the Prior Art
It is well known in the field of optics that optical fibers are capable of effectively and efficiently conducting light from a common source along unequal paths to various locations remote from the light source without encountering substantial transmission losses. Because of this characteristic, there is increasing interest in the application of fiber optics to uses where space is limited. One such use is the overall illumination needs of the interior of vehicles where space is scarce or difficult-to-reach due to aerodynamic and styling considerations.
The prior art discloses various concepts that basically employ a plurality of, for example, 36 or more optical fibers formed into a bundle that is typically 5 to 10 millimeters in diameter. The prior art optical system (
FIG. 1
) consists of a light source
1
, a heat rejection filter
3
and a condenser lens
5
. The source
1
is imaged on to the entry face
7
a
of the fiber bundle
7
by condenser lens
6
. The fibers of bundle
7
when viewed from its proximal end
7
a
is seen to be composed of a plurality of fibers (
FIG. 1
a
). The fibers of bundle
7
may be made of glass or polymer fibers. The individual glass fibers consist of a core
11
surrounded by a cladding
12
, the clad fibers arranged in a circular cross-section and constrained within sheath
13
. Polymer fiber, on the other hand, may or may not have a cladding depending on the specific application and on the diameter of the polymer core. The core of a polymer fiber may be PMMA and, if clad, a fluoropolymer resin, commonly known by the DuPont trademark Teflon, is used as the cladding material. For small diameter fiber, the polymer fiber's exterior is vacuum coated with a thin film of Teflon.
Said fiber bundle
7
subsequent to entry face
7
a
is splayed into a plurality of individual fibers, forming the main optical harness, wherein their respective distal ends are separated from each other, arranged and spatially ordered into, for example, a square configuration (
FIG. 1
b
). Ferrules
9
are attached to the distal end of each fiber facilitating a means by which individual fibers of at least one additional fiber optics subharness assembly may be attached. The said subharness, in a conjoined relationship with the main harness, comprises a fiber optics harness assembly for conveying light to courtesy lights, indicator status lights and other lit devices within the vehicle.
Referring to
FIG. 2
, the fiber optics harness assembly
22
may originate at the rear of the vehicle
20
in, for example, its trunk space. Said fiber optics harness
22
is typically split into two branches
23
and
25
, each branch transporting light along opposite sides of the vehicle to the various lit devices
27
. The method, by which the individual fibers of fiber bundle
7
are separated, arranged and spatially ordered is a technical problem unique to the application.
There is known a distribution device in which the individual fibers of a fiber bundle are mechanically separated, arranged and ordered. The said device, illustrated in
FIG. 3
, is a fiber optics bundle connector
30
consisting of five major parts, to wit, a cinch ring
35
, a hollow cone
37
, a spacer
39
, a terminal block
31
and a terminal position assurance device (TPA)
33
. Cinch ring
35
is used to tightly pack the individual fibers together into a bundle
7
(
FIG. 1
a
). The hollow cone
37
and its spacer
39
, inserted therein, are used to compartmentalize and organize the individual optical fibers into an ordered spatial pattern conducive to their eventual routing destinations within the vehicle. The terminal block
31
provides for path-length equalization of the individual fibers throughout the assembly so that all of the fibers may be terminated individually in the same manner. The TPA
33
ensures that the ferrules of the terminated optical fibers are properly located, thus forming the desired fiber spatial organizaton.
Accordingly, the basic purpose of the fiber optics bundle connector
30
is to transform the fiber bundle
7
into an array of spaced and ordered individual fibers forming a two-dimensional pattern
7
b
to which one or more fiber optics subharnesses may be attached. More importantly, said arrangement positions and orients said individual fibers of the main harness such that the direction of light propagation emerging therefrom are mutually co-parallel and perpendicular to the distal face of the TPA. In said spaced arrangement and orientation, the individual fibers may be conveniently and efficiently culled and coupled to fibers of one or more fiber optics sub-harnesses, extending from the TPA in route to the various lit devices within the interior lighting system.
While this general approach may fulfill overall illumination requirements, there are major shortcomings to this approach. First, there is attendant to this method significant loss in illuminance due to the number of coupling means required. Second, there is accompanying this method a significant variation in both the luminance and luminous intensity incident on the proximal face of the individual fibers of the main optics harness. The prior art method leads to the non-uniform filling of illumination to the proximal faces of the individual fibers of the sub-harness and, hence, at their exit faces which terminate at the various lit devices. Third, the method requires a relatively large number of parts, requiring assembly, as well as the labor necessary to cull individual fibers into various apertures—a procedure which is not considered to be cost effective.
The luminous efficiencies of the prior art approach will now be discussed. Referring to
FIG. 1
, the factors affecting the level of illumination received at the distal end of an individual fiber are:
1. Total light accepted by the condenser from the lamp.
2. Reflection losses at air-glass surfaces.
3. Losses at the coupling of light source to fiber bundle
4. Internal transmittance of the fiber.
5. Angle (&agr;′) of the final Illuminating cone.
6. Losses associated with the in-tandem connection of fibers.
If the light source itself, such as a filament-based lamp, presents an area S, the total light accepted by a condenser of aperture &agr; is given by the formula
F=&pgr;BS
sin
2
&agr;
The quantity B is a measure of the luminosity of the source, S is the source area and &agr; is the semi-angle of the angular light distribution of the condenser. The source S is imaged by the condenser on the entry face of the fiber bundle, where the aperture angle is &agr;′. The linear magnification between this image and the source is given by
M=
(sin &agr;)/(sin &agr;′)
so that the magnification for areas is
S′
/(
S
)=
M
2
=[(Sin &agr;)/(sin &agr;′)]
2
The maximum value of F′ exists when the source image just fills the diameter of the entry face of the fiber bundle and sin &agr;′ has a maximum value corresponding to the numerical aperture accepted by the individual fibers of the fiber bundle. Provided the image of the light source completely fills the entry face, and the cones of light forming this image have a sin &agr;′ equal to the numerical aperture (NA) of the fibers, no increase in the amount of light from the source is possible.
When there is loss due to surface reflections, R, the fraction of light transmitted by a single surface is (1−R), and the transmittance of N surfaces is
T=
(1−
R
)
N
Now, the fraction of light transmitted by the fiber bundle
Radiant Optics Inc.
Rockey Milnamow & Katz Ltd.
Sikder Mohammad
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