Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-05-10
2003-02-18
Sikder, Mohammad (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S032000, C362S300000, C362S301000, C362S302000
Reexamination Certificate
active
06522807
ABSTRACT:
TECHNICAL FIELD
This invention pertains to efficient reflective coupling of collimated light into the input end of a light guide.
BACKGROUND
FIG. 1
schematically depicts the way in which light is conventionally emitted into the input end of a light guide of the type disclosed in U.S. Pat. Nos. 4,615,579; 4,750,798; 4,787,708; 4,834,495; or, 4,850,665. An elongate (i.e. non-point) light source such as an arc-type metal halide light bulb
10
mounted in a socket
12
is slidably inserted through an aperture
14
in a paraboloidal collimator
16
. The circumferential rim at the wide end of collimator
16
is flanged as shown at
18
. A mating circumferential flange
20
is provided around the input end of hollow prism light guide
22
. Flanges
18
,
20
are connected together to mechanically couple collimator
16
to the input end of light guide
22
. When light bulb
10
is energized, light rays emitted by the bulb's arc portion
24
are reflected and collimated by collimator
16
toward the input end of light guide
22
which confines the rays and distributes them uniformly along the light guide.
Prism light guides work best when the input light is collimated within a half angle of about 30°. This requirement limits the range of suitable light sources, because the efficiency with which light can be emitted into the input end of the light guide decreases rapidly as the size of the light bulb increases. Arc-type metal halide light bulbs of the type shown in
FIG. 1
are reasonably practical light sources for illuminating light guides, due to their high efficiency, compact size and reasonably long lamp life.
The maximum efficiency with which prior art paraboloidal collimator
16
can couple collimated light into light guide
22
depends on the ratio of the light guide's diameter “D”, to the length “L” of the light bulb's arc. For a typical prior art D:L ratio of about 6:1, reflector efficiencies of about 70% can be achieved. Thus, about 30% of the light emitted by light bulb
10
is typically lost, in the sense that it does not enter the input end of light guide
22
. It is desirable to reduce the ratio D:L, since this would enable the use of larger, higher output, more efficient metal halide arc lamps. But, even modest reductions in the ratio D:L substantially reduce the efficiency with which light emitted by the light bulb can be collimated and coupled into the input end of the light guide. For example, a D:L ratio of about 4:1 typically yields a light guide input coupling efficiency of only about 50%, meaning that about 50% of the light emitted by the light bulb is lost, in the sense that it does not enter the input end of the light guide as collimated light.
This invention overcomes the coupling efficiency problems associated with conventional light guide systems. For example, the invention permits efficient collimation and coupling of light emitted by a one kW metal halide light bulb having a 12,000 hour rated life into a 25 cm diameter light guide. Such systems are advantageous in general lighting situations in which high efficiency linear lighting is required and in which maintenance of multiple point source or fluorescent fixtures is problematic.
SUMMARY OF INVENTION
The invention provides a reflector for reflecting light emitted by an elongate light source into the input end of a light guide having a light guide diameter “D”. All embodiments of the invention incorporate a collimating reflector having a narrow apertured end through which the light source is insertably positionable; and, a wide apertured end having a diameter exceeding “D”, through which light is emitted into the light guide. All embodiments of the invention also incorporate an “output end” annular reflector, or an “input end annular reflector, or both.
The output end annular reflector has a wide apertured end which circumferentially surrounds the collimating reflector near its wide apertured end, and a narrow apertured end which circumferentially surrounds the input end of the light guide. The input end annular reflector has a narrow apertured end through which the light source is insertably positionable, and a wide apertured end which circumferentially surrounds the collimating reflector near its narrow apertured end. All of the reflectors are cylindrically symmetrical about a common longitudinal axis. Light rays emitted by the light source which pass to the collimating reflector are reflected by the collimating reflector and produce an output light beam having a beam width which varies as a function of distance along the aforementioned axis. The light guide's input end is positioned at a selected distance along the axis at which the output light beam has a minimum beam width value.
Advantageously, the input end annular reflector further has a curved surface, such that, in any cross-sectional plane containing the aforementioned axis, the curved surface defines a first arc on one side of the axis, and, a second arc on an opposed side of the axis. The first arc has a first centre of curvature located on the one side of the axis, and further located within a cylinder which is symmetrical about the axis and which has a diameter not greater than the diameter of the collimating reflector's narrow apertured end. The second arc has a second centre of curvature located on the opposed side of the axis and further located within the aforementioned cylinder.
The collimating reflector is preferably an off-axis paraboloidal cross-section, cylindrically symmetrical reflector having a focal point f. The output end annular reflector preferably forms a spherical arc section having a center of curvature near the collimating reflector's focal point f. The light source is typically a metal halide light bulb having a light emitting arc having one end near the focal point f and an opposed end near the narrow apertured end of the collimating reflector.
REFERENCES:
patent: 2179161 (1939-11-01), Rambusch et al.
patent: 4241382 (1980-12-01), Daniel
patent: 4615579 (1986-10-01), Whitehead
patent: 4750798 (1988-06-01), Whitehead
patent: 4755918 (1988-07-01), Pristash et al.
patent: 4787708 (1988-11-01), Whitehead
patent: 4834495 (1989-05-01), Whitehead
patent: 4850665 (1989-07-01), Whitehead
patent: 63 092909 (1988-09-01), None
patent: WO 00/53972 (2000-09-01), None
The Photonics Dictionary, 45th ed., 1999, Laurin Publ. Co. Inc., Pittsfield, MA, p. D-26, definition of “collimated radiation”.
Buckingham Stephen W.
Sikder Mohammad
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