Patent Publication Number: US-2003231843-A1

Title: Fiber optic light compressor for a curing instrument

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to concentrated light sources. More particularly, the invention relates to a concentrated light source for a dental curing light that employs a manifold fiber optic array for concentrating light from multiple illumination sources.  
       BACKGROUND OF THE INVENTION  
       [0002] Dental composites employ well-known materials, and are used in a variety of dental procedures including restoration work and teeth filling after root canal procedures and other procedures requiring drilling. Several well-known dental composites have been sold under the trade names of BRILLIANT LINE, Z-100, TPH, CHARISMA and HERCULITE &amp; BRODIGY.  
       [0003] Such composites are typically formed from liquid and powder components that are mixed together to form a paste. The paste is formed to have a consistency sufficiently workable and self-supporting to be applied to an opening or cavity in a tooth. The liquid component may typically comprise phosphoric acid and water, while the powder component may comprise ceramic materials including cordite, silica or silicium oxide. After the composite is applied to a tooth, it must be cured to form a permanent bond with the tooth.  
       [0004] Curing requires the liquid component to evaporate, causing the composite to harden. In the past, curing has been accomplished by air drying, which has the disadvantage of requiring significant time. This time can greatly inconvenience the patient. More recently, light curing has become popular in the field of dentistry as a means for decreasing curing times. According to this trend, curing lights have been developed for dental curing applications. An example of such a curing light is illustrated by U.S. Pat. No. 5,975,895, issued Nov. 2, 1999 to Sullivan, which is hereby incorporated by reference.  
       [0005] Conventional dental curing lights generally employ tungsten filament halogen lamps that incorporate a filament for generating light, a reflector for directing light and a blue filter that limits transmitted light to wavelengths in the region of 400 to 500 nanometers (nm). Light is typically directed from the filtered lamp to a light guide, which directs the light to a position adjacent to the material to be cured.  
       [0006] A problem with conventional halogen-based curing lights is that the lamp, filter and reflector degrade with time. This degradation is particularly accelerated by heat generated by the halogen lamp. For example, this heat may cause filters to blister and cause reflectors to discolor, leading to reductions in light output and curing effectiveness. While heat may be dissipated for example by the addition of a fan unit to the light, the fan adds cost and may cause other undesired effects (for example, noise). Alternate lamp technologies (for example, using Xenon and laser light sources) tend to be costly, require filtration, consume large amounts of power and generate significant heat. In particular, laser technologies have also required stringent safety precautions.  
       [0007] Light Emitting Diodes (LEDs) and Laser Diodes (LDs) appear to be good candidate curing light sources, having reasonable cost and an expected operational life of between 10 and 15 years. In addition, LEDs and LDs can be designed to produce a significant portion of light output having a frequency in the desired range of 400 to 500 nm. For example, much of the spectral radiant intensity for many blue LEDs peaks at  468  nm, producing an almost ideal bandwidth for dental curing applications.  
       [0008] To date, it has been difficult to generate sufficient power levels from LED or LD lamp designs for dental curing applications (a minimum of 800 milliwatts per square centimeter). Accordingly, it would be desirable to develop a curing light using LED or LD lamps having sufficient power to support dental curing applications.  
       SUMMARY OF THE INVENTION  
       [0009] These and other deficiencies have been solved by a novel fiber optic light compressor comprising a bundle of fiber optic strands, a plurality of individual LED and/or LD light sources, and a plurality of optical receptacles, each receptacle optically coupled to both a receiving end of a strand in the bundle of fiber optic strands and a single one of the plurality of individual light sources. Each receptacle is arranged to capture substantially all of the light energy output by its associated light source. Strands in the bundle are tightly packed in a longitudinally-oriented array, so that transmitting ends of the strands define a transmitting surface that delivers a concentrated light beam composed of energy produced by each of the plurality of light sources. In this manner, virtually all of the light energy supplied by the individual light sources is delivered to the concentrated light beam.  
       [0010] In a first embodiment of the present invention, the light receptacle comprises an optical taper having a core component relieved at a wide end of the taper in order to receive a light source. A cladding component at the wide end of the taper encapsulates the light source to help confine light energy within the taper.  
       [0011] In a second embodiment of the present invention, the light receptacle comprises a cavity having a cladding-coated surface to encapsulate the light source and to confine light energy. A polished portion of the receiving end of the fiber optic strand is inserted into a housing of the light source (for example, through a transparent bell-shaped structure of an LED or through the exit window of a LD), and fixedly attached to the light source housing using an optical epoxy. Virtually all of the energy of the light source is captured by the polished portion of the strand.  
       [0012] The optical receptacles may be positioned such that their individual centerlines are perpendicular to a centerline of the bundle, in one or more rows that are parallel to the centerline of the bundle. Each row is radially positioned around the bundle. Alternatively, the receptacles may be staggered about the centerline of the bundle to achieve a tighter physical spacing.  
       [0013] In a typical dental curing lamp application having six radial rows of light sources with thirteen individual light sources per row, a concentrated power beam is generated having a light power density in excess of 800 milliwatts per square centimeter.  
       [0014] The aforementioned objects, features and advantages will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawing, which forms an integral part thereof. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] A more complete understanding of the invention may be obtained by reading the following description of specific illustrative embodiments of the invention in conjunction with the appended drawing in which:  
     [0016] FIGS.  1 ( a ) and  1 ( b ) illustrate principles associated with launching a light beam in an optical fiber;  
     [0017]FIG. 2( a ) illustrates light reflection properties for a halogen lamp used in a prior art curing tool application;  
     [0018] FIGS.  2 ( b )- 2 ( d ) illustrate features of a prior art curing lamp light source employing multiple LEDs;  
     [0019] FIGS.  3 ( a )- 3 ( g ) illustrate several embodiments of the present invention; and  
     [0020]FIG. 4 illustrates an application of the present invention employed in a dental curing lamp.  
    
    
     [0021] In the various figures, like reference numerals designate like or similar elements of the invention.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0022] The following detailed description includes a description of the best mode or modes of the invention presently contemplated. Such description is not intended to be understood in a limiting sense, but to be an example of the invention presented solely for illustration thereof, and by reference to which in connection with the following description and the accompanying drawings one skilled in the art may be advised of the advantages and construction of the invention.  
     [0023] FIGS.  1 ( a ),  1 ( b ) illustrate a standard light transport medium in the form of an optical fiber  10 . Optical fiber  10  includes a fiber core  12 , a fiber cladding  14  and a fiber outer coating  16 . Fiber core  12  typically serves as the portion of the fiber operative to carry light, and has an index of refraction N 1 . Fiber cladding  14  serves to help confine light within the core  12 , and has an index of refraction N 2 , which is typically less than N 1 . Fiber outer coating  16  provides protection against abrasion and other potential physical damage to fiber  10 . A typical fiber  10  used for short distance application as will be herein described may have an outer diameter between 0.04 and 0.06 inches in diameter, and have about 83 percent of its cross-sectional area comprising core  12  and about 17 percent of its cross-sectional area comprising cladding  14 .  
     [0024] As illustrated in FIG. 1( a ), incident beam  22  from light source  20  moves across air medium gap  21  to strike receiving end face  9  of the fiber  10  at an angle θ 1  with respect to fiber centerline  15 . Incident beam  22  is reflected at end face  9  as reflected beam  24 , and is refracted at end face  9  as refracted beam  26 . Reflected beam  24  makes an angle θ 3  with respect to centerline  15 , and refracted beam  26  makes an angle θ 2  with respect to centerline  15 . Because end face  9  is perpendicular to centerline  15 , angle θ 3  is equal to angle θ 1 . Employing Snell&#39;s law, angle θ 2  can be determined by using the following relationship:  
       N   air * sin θ 1   =N   1 * sin θ 2   (1)  
     [0025] Where N air  is an index of refraction for air, and N 1  is the index of refraction for the fiber core.  
     [0026] Ideally, incident light from light source  20  will be fully refracted at end face  9  to enter fiber core  12 , and light reaching interface  25  between fiber core  12  and fiber cladding  14  will be reflected at interface  25 , thereby causing light to travel in a contained fashion within fiber  10 . However, if light enters fiber core  12  at a sufficiently large angle with respect to centerline  15  (as illustrated by light beam  30  refracted from incident light beam  28 ), some light (illustrated by light beam  32 ) may escape fiber core  12  and be refracted through fiber cladding  14 . The angle beyond which light cannot be fully carried within fiber core  12  is referred to as the critical angle.  
     [0027] A useful property of an optical system or element is numerical aperture (NA), which may be defined as the sine of the vertex angle of the largest cone of light that can enter or leave the system or element, multiplied by the index of refraction for the medium in which the vertex of the cone is located. In the case of optical fiber  10 , a capacity for accepting light rays from light source  20  may be represented by a numerical aperture calculated as follows:  
       NA= {square root}{square root over ( )}(( N   1 ) 2 −( N   2 ) 2 )  (2)  
     [0028] Where N 1  is the index of refraction for core  12 , and N 2  is the index of refraction for the cladding  14 .  
     [0029] For example, in a common fiber configuration for short distance fiber transmission where N 1 =1.62 and N 2 =1.52, NA=0.56, which corresponds to a maximum underlying critical angle of 34 degrees. In other words, any light supplied by light source  20  at an off-centerline incident angle θ a  in excess of the maximum underlying critical angle will not be accepted by fiber  10 . As fiber  10  accepts light up to 34 degrees off centerline  15  in any direction, the maximum acceptance angle of the fiber  10  is twice the maximum underlying critical angle, or 68 degrees.  
     [0030] As a result of various optical effects including transmissive losses within the fiber and refractive properties at the fiber boundaries, the maximum angle at which light rays will exit from a delivery end face (not shown) of fiber  10  of FIG. 1 will generally be less than the maximum underlying critical angle at which light rays are delivered by light source  20  to receiving end face  9 . For example, a fiber having a maximum underlying critical angle of 34 degrees may be limited to a maximum exit angle as small as 26 degrees. In order to avoid this loss of incident light, the maximum incident angle θ a  for light source  20  is preferably selected to be about 50 percent less than the maximum acceptance angle. For example, for a critical angle of 34 degrees in a short-range fiber  10  having a NA of 0.56, a maximum incident angle of between 18 and 25 degrees is preferred.  
     [0031]FIG. 2( a ) illustrates a conventional light source and pickup assembly  100  used in curing lights similar to the curing light disclosed by U.S. Pat. No. 5,975,895. Halogen light source  20  includes an illuminating element  20   a  which radiates and directs light to reflector  20   b , from which at least a portion of the reflected light (represented by rays  22   a ,  22   b  and  22   c ) are directed to pickup  11 . As shown in the enlarged portion of FIG. 2( a ), rays  22   b ,  22   c  are directed to fiber bundle  10 , and will be refracted into fibers in fiber bundle  10  only so long as rays  22   b ,  22   c  are not reflected beyond the critical angle for fibers in fiber bundle  10 . As can also be seen from the enlarged portion of FIG. 2( a ), at least a portion of light ray  22   a  impinges on pickup  11  in bundle support area  13  surrounding fiber bundle  10 , and is therefore not received by fiber bundle  10  at all. In this manner, much of the light energy produced by lamp  20  is either reflected away or otherwise fails to reach fiber bundle  10 .  
     [0032] FIGS.  2 ( b ) and  2 ( c ) illustrate a second light source and pickup assembly  110 . Lamp array  20  comprises a plurality of LEDs (represented, for example, by LEDs  20   d  and  20   e  of FIG. 2( b )) positioned in a semi-circular array with respect to pickup  11 . Importantly, as illustrated in FIG. 2( d ), LED  20   d  presents a viewing angle θ V , which may vary from 25 degrees to more than 80 degrees according to the specifications of the LED manufacturer. (representative LEDs are commercially available, for example, from Nichia America Corporation of Mountville, Pa.).  
     [0033] Accordingly, and as illustrated in FIGS.  2 ( c ) and ( 2   d ), LED  20   d  having viewing angle θ V  is optimally placed a distance  21  from pickup assembly  11  in order for light rays  22   d  to coincide in area with the area of fiber bundle  17   d . If placed at a greater distance, light dispersion defined by viewing angle θ V  will cause some of the rays at the periphery of light rays  22   d  to strike pickup assembly  11  outside of the area defined by fiber bundle  17   d.    
     [0034] While light rays  22   d  coincide in area with fiber bundle area  17   d , it can be seen from FIG. 2( c ) that light rays  22   e  associated with LED  20   e  strike bundle support surface  13  at an angle θ P , thereby creating an oval-shaped light beam  17   e  on surface  13 . Portions of light beam  17   e  extend beyond bundle area  17   d . Accordingly, in the light source and pickup assembly  110  illustrated by FIGS.  2 ( b )- 2 ( d ), some light generated by LEDs  20  will most likely fail to be captured by fiber bundle  10 .  
     [0035] The present invention overcomes the limitations of these prior art systems. Several aspects of the present invention are illustrated in FIGS.  3 ( a )- 3 ( g ), and will be described with reference thereto.  
     [0036] FIGS.  3 ( a ) and  3 ( b ) illustrate a fiber optic light assembly  40 . In FIG. 3( a ), a plurality of light sources  20  are each positioned near a large end  41   a  of one of a plurality of optical receptacles  41 . A small end  41   b  of each of the plurality of optical receptacles  41  is fusedly connected to a receiving end of one of a plurality of optical fiber strands  42 . Optical receptacles  41  are fixedly positioned within receiver  43 . Receiver  43  has a cavity  45  for routing fiber optic strands  42  to terminate at a transmitting surface  44 . As illustrated in FIG. 3( b ), optical fiber strands  42  are tightly and longitudinally bundled within cavity  45 . Thus, light collected from light sources  20  via optical receptacles  41  is transmitted by fiber optic strands  42  to transmitting surface  44 , and emerges in a concentrated light beam at transmitting surface  44 .  
     [0037] FIGS.  3 ( c ) and  3 ( e ) illustrate two embodiments of the optical receptacle  41  of FIGS.  3 ( a ),  3 ( b ). In FIG. 3( c ), LD  20  is coupled to a tapered optical fiber  41 , in which a core material has been removed at large end  41   a  of taper  41  to a depth  46  in order to accommodate insertion of LD  20  at large end  41   a . Cladding  41   d  remains in place over the entire distance between large end  41   a  and small end  41   b . It should be noted that, in forming a recess for LD  20  within taper  41 , one alternative to removing core material to a depth  46  to form the recess may be to extend cladding  41   d  by a length  46  to form the recess.  
     [0038] As illustrated in the embodiment of FIG. 3( c ), aperture  43   a  holds LD  20  and taper  41  in a fixed position. Cladding  41   d  extends over outer metallic cover  20   g  of the LD  20 , and serves together with base surface  20   j  to contain light emitted by LD element  20   h  so that it may be reflected into receiving surface  41   e  of the taper  41  through a window (not shown) in outer cover  20   g.    
     [0039] Taper  41  is positioned in aperture  43   a  of opaque receiver  43  so that virtually none of the light emitted by LD  20  escapes taper  41 . In addition, taper  41  guides light received from LD  20  into an interfacing fiber strand  42  such that virtually no light is directed to fiber strand  42  at an angle in excess of the critical angle for fiber strand  42 . In this manner, virtually all light energy emitted by LD element  20   h  is collected by fiber strand  42  and transmitted to transmitting surface  44 .  
     [0040] In FIG. 3( d ), LED  20  is coupled with the tapered optical fiber  41  of FIG. 3( c ) at large end  41   a . Once more, a sufficient amount of core material has been removed at large end  41   a  in order to accommodate insertion of LED  20  at large end  41   a  such that LED element  20   h  is positioned below an outer surface  43   b  of opaque receiver  43 . Again, virtually all light emitted by LED element  20   h  is collected by taper  41  and transmitted to transmitting surface  44 .  
     [0041]FIG. 3( e ) illustrates a second embodiment of optical receptacle  41 . In FIG. 3( e ), coated optical fiber  41   g  extends into cavity  43   c , which is lined by cladding  41   f . LED  20  is positioned within cavity  43   c  such that LED element  20   h  is positioned below outer surface  43   b  of receiver  43 . Fiber  41   g  pierces transparent bell-shaped structure  20   k  of LED  20  at an apex of transparent bell-shaped structure  20   k , and is fixed to transparent structure  20   k , for example, with optical epoxy  48  (commercially available, for example, from Epoxy Technology of Billenia, Mass.). Fiber end  41   h  of fiber  41   g  positioned within transparent bell-shaped structure  20   k  is highly polished in order to remove coating and cladding layers. As a result, substantially all light emitted by LED element  20   h  is collected by polished fiber end  41   h . It should be noted that one skilled in the art would be easily able to substitute other devices for the LED  20  of FIG. 3( e ) (for example, laser diodes).  
     [0042] FIGS.  3 ( f ) and  3 ( g ) illustrate an alternate configuration for fiber optic light source  40  of FIGS.  3 ( a ),  3 ( b ). In the light source  40  of FIGS.  3 ( f ) and  3 ( g ), receiver  43  is arranged to position six longitudinal rows of LEDs  20  and tapers  41 , each row radially positioned with respect to cavity  45 . This configuration of LEDs  20 , tapers  41  and fibers  42  permits a significant number of LEDs  20  to be positioned in a relatively small space (suitable, for example, for positioning within the handle of a dental curing lamp). In the configuration shown in FIGS.  3 ( f ) and  3 ( g ), six longitudinal rows of thirteen LEDs each yields a concentrated light source of 78 LEDs. This array yields an effective power density in excess of 800 milliwatts per square centimeter.  
     [0043]FIG. 4 shows the light source  40  of FIGS.  3 ( f ),  3 ( g ) incorporated in a dental curing light  50 . Light source  40  is positioned, for example, within case  51  of light  50  that case  51  may also function as a gripping handle. Case  51  contains power supply  52 , which provides power to light sources  20  via power feed cables  53 . Transmitting surface  44  of light source  40  is optically coupled at a receiving end  54  of transmitting tip  55 , which channels light emitted at transmitting surface  44  to tip end  56 , for emissions and application to polymerize a dental material.  
     [0044] It should be apparent to one skilled in the art that a great variety of configurations arranged to have a variety of numbers of LED rows and a variety of numbers of LEDs in each row are fully contemplated by the present invention. A number of other variants on this configuration are contemplated as well (for example, a radial array of LEDs in which alternating LED&#39;s in each row are offset from adjacent LEDs in the row in order to reduce the overall length of the array). Any configuration contemplating multiple solid-state light sources  20  each individually in combination with a tapered or other receptacle  41  designed to capture substantially all light emitted by the individual light source  20  and delivering the captured light to an optical fiber such that a plurality of optical fibers form a bundle that provides a concentrated light beam powered from the individual light sources  20  is contemplated by the present invention.  
     [0045] It should also be apparent to one skilled in the art that the configuration of FIGS.  3 ( f ) and  3 ( g ) may be implemented with a number of types of receptacles  41  and light sources  20 , including the preferred configuration of FIG. 3( e ).  
     [0046] While the present invention has been described at some length and with some particularity with respect to the several described embodiments, it is not intended that it should be limited to any such particulars or embodiments or any particular embodiment, but it is to be construed with references to the appended claims so as to provide the broadest possible interpretation of such claims in view of the prior art and, therefore, to effectively encompass the intended scope of the invention.