Patent Document

ORIGIN OF THE INVENTION 
     The invention described herein was made by an employee of the United States Government, and may be manufactured and used by the government for government purposes without the payment of any royalties therein and therefor. The invention was made under contract between the United States Government and employees of other entities and as such the United States Government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The invention is in the field of broadband incandescent light sources which may be used for the calibration of spectrometers and for powering optical sensors. 
     BACKGROUND OF THE INVENTION 
     The invention is in the field of broadband light sources used to calibrate spectrometers or supply light to other optical instruments for powering them or for other calibration and measurement purposes. Spectrometers are instruments which are used to determine spectral information about objects which indicate to scientists and engineers qualitative and quantitative information about the objects. Light emitting objects (which may include planets and samples from planets) emit light in the form of photons when excited by an energy source. Light in the form of photons is emitted when electrons of an object change states in distinct energy levels according to quantum theory. It is this emission which scientists and engineers sense with a spectrometer to evaluate and correlate measurements of the spectrometer with known spectral information about elements to infer the constituency of the object. The light emitting source or object may be a planet or it may be a sample taken from a planet and analyzed in a laboratory type environment on-board a space ship. 
     Spectrometers have been known for some time but those in use today are highly specialized and designed to process and measure electromagnetic radiation over a certain band of frequencies. Crude spectrometers can be made at home from cereal boxes with slits in them which admit light in a certain region of the visible spectrum to a compact disk placed at an angle with respect to the incoming light which is then refracted in spectra which can be viewed and used to infer the chemical make-up of the atmosphere. Spectrometers used on board spaceships are very sophisticated instruments and include complex calibratable gratings and electronics to accept and process light from planets and samples from planets in determining the elemental composition of an object. Spectrometers analyze the excitation of objects which have been excited by a light source. 
     Military use of spectrometers is prevalent to identify discontinuities in the surface of our own planet to infer that which is not normal for a specific location thus identifying weapons and equipment. 
     Electromagnetic radiation is denoted as such because it includes electric fields and magnetic fields which are propagated by the source of the radiation. The general equation of frequency times wavelength=speed of light governs all electromagnetic radiation such that the higher the frequency the shorter the wavelength and vice versa. 
     The spectrometers which can be used with the broadband light source of the instant invention are designed to view the entire visible light spectrum. 
     White light sources are used to calibrate spectrometers in the visible range. It is desirable, therefore, to have an output source which spans past the visible light spectrum. The visible light range includes red, orange, yellow, green, blue, indigo and violet. Some recent commentaries are now indicating that indigo should possibly not be included as a separate color as it is a combination of other colors. 
     A broadband white light source includes all components of the visible spectrum as demonstrated by early scientists such as Newton wherein white light coming from the sun was broken down into its several components with the use of a prism. 
     U.S. Pat. No. 6,796,866 which has one inventor in common with the instant application is incorporated herein by reference.  FIG. 1  is a schematic  100  of the prior art device illustrated in U.S. Pat. No. 6,796,866. There are three silicon layers  108 ,  106 ,  102  disclosed in the &#39;866 patent. The silicon substrate  202  includes a top nitride layer  204 , a bottom nitride layer  206 , and a cavity  208  which allows for the transmission of light to the window  104 . The silicon substrate  106  is a middle filament mount layer having a top nitride layer  214  and a bottom nitride layer  216 . The silicon substrate layer  108  includes a reflective top layer  242 . The spiral filament  220  is bridged across an aperture  218  in the middle substrate  106 . Contacts  220  of the filament communicate with electrical leads  222  which in turn communicate with wire bond pad  210  and wire bond lead  240 . 
     The &#39;866 patent discloses a MEMS based package which employs Ti/Pt/Au bonding rings  230 ,  232 ,  250 ,  252  to bond the bottom layer  108  to the middle layer  106  and the middle layer  106  to the top layer  102 . The bonding rings are deposited on the Si semiconductors in a facing relationship. Insulation  234  is interposed between the nitride  214  and the contact pads  232  to prevent electrical shorting between electrical leads  222  and conductive bonding rings  232 . 
     The bottom layer  108 , the middle layer  106  (silicon substrate  212 ), and the top layer  102  are bonded together. The reflective surface  242  contributes to the radiation of light through transmission window  104  in the top nitride layer  204  of the top layer  102 . 
       FIG. 2  is a schematic  200  of the prior art device illustrated in U.S. Pat. No. 6,796,866. The end contact portions  220  are connected to electrical leads  222 ,  236  according to the specification of the &#39;866 patent. It will be noticed that the spacing between the double-spirals is constant between the end portions  220  and an intermediate portion  291  all the way to the central portion  292 . The language of a double-spiral, intermediate portion  291  and the central portion  292  does not appear in the &#39;866 patent and are not extracted therefrom. It has been discovered that when the filament of the &#39;866 patent is heated from the joule heating caused by the flow of current therethrough, the filament  200  expands radially and it also expands lengthwise. 
     Actual mechanical and electrical contact may result in partial shorting of a portion of a turn of the spiral. If the turns are too close together this can happen due to some distortion of the spiral during operation or due to vibration. In an earlier design in which the space between turns was everywhere constant, the shorting tended to occur near the outer part of the spiral where distortion appeared to be most severe. 
     The filament has constant thickness. The width of the filament varies along its length as wider tabs (end contacts) and less wide outer windings and still less wide inner windings. The thermal expansion of the material differs based on joule heating which varies with the voltage applied and with the resistance (determined by cross-sectional area) of the particular part of the filament. The end contacts of the filament are wider than the windings of the filament so the end contacts or tabs have a larger cross-sectional area than the windings and so have a lower resistance than the windings and so have less joule heating for a particular operating voltage than the windings. Since both the end contacts and outer windings are wider than the inner windings, both the end contacts and outer windings run cooler than the inner windings for a particular operating voltage. The cooler metal expands less and is less flexible than the warmer inner windings. The inner windings expand along their length, following the curve out. As the inner windings tend to de-coil or unwind, their length increases and they may eventually collide with the more stationary cooler outer windings producing an electrical short path. 
       FIG. 2A  is a schematic  200 A of the prior art device illustrated in U.S. Pat. No. 6,796,866 with the tungsten coil thereof illustrated in the process of unwinding. Reference numerals  260 A,  261 A,  262 A and  263 A indicate the general location where the first and second spirals interengage each other upon heating thereof. In  FIG. 2 , reference numerals  260 ,  261 ,  262 , and  263  indicate gaps between the windings of the spirals. When the first and second spirals are heated they expand and engage as indicated by reference numerals  260 A,  261 A,  262 A and  263 A as illustrated in  FIG. 2A . 
     The shortened path then has lower resistance and draws even more current which increases the evaporation rate of the filament which decreases the lifetime because the filament narrows further until it gets to a point where it melts and opens the circuit creating an open circuit path. 
     Although the light source of the &#39;866 patent is a very efficient broadband light source its assembly is somewhat complicated and involves the deposition of the Ti/Pt/Au bonding rings on the top, middle and bottom layers and subsequent processing under vacuum or in an inert atmosphere at or near atmospheric pressure in a thermal compression binder to assemble the device together. 
     U.S. Pat. No. 5,977,707 to Koenig discloses a planar spiral made from tungsten as illustrated in  FIG. 7  thereof but the remaining claimed structure and processes are not found or suggested by the reference. 
     U.S. Pat. No. 3,604,971 to Tracy discloses a filament mounting structure for a display device which includes a plurality of helical filaments to form a display but fails to disclose a single planar double spiral as claimed. 
     Therefore, it is desirable to have an ultraminiature light source which does not short-out due to thermal expansion and vibrations of the filament and which is efficiently packaged. 
     SUMMARY OF THE INVENTION 
     An ultraminiature light source comprises a ceramic base and a generally planar double-spiral shaped tungsten filament suspended within the ceramic base. The ceramic base may be a glass or glass ceramic. A lid which is partially transparent is placed over the ceramic base. The lid may also be coated with dielectric material to selectively transfer specific radiation bands that are selective to the application. The ceramic enclosure or base includes a reflective bottom, a ledge, and a raised perimeter having a metallic surface. The ledge includes metallic surfaces embedded therein for electrical communication with the double-spiral shaped tungsten filament. The double-spiral shaped tungsten filament comprises first and second interleaved concentric spiral portions radially converging with decreasing radius and centrally joined together in a central portion. Each of the first and second spiral portions of the double-spiral shaped tungsten filament includes an end contact portion, an intermediate portion and a central portion. A feature of the aforesaid design double spiral shaped filament is that upon joule heating it lengthens and this physical feature can be used to place the filament in compression against an end stop for additional vibrational damping. 
     A first gap defined between the first and second spiral portions of the dual-spiral shaped tungsten filament and a second gap defined between the second and first spiral portions of the dual-spiral shaped tungsten filament. The first spiral portion being wound, for example, in a clockwise direction and the second spiral portion being wound in a clockwise direction with said first gap defined between the first and second spirals. The second gap defined between the second and first spiral portions being substantially constant between the intermediate portions of the spiral portions. The first gap between the end contact portion of the first spiral portion and the second spiral portion being relatively larger than the first gap between the intermediate portions of the first and second spiral portions. 
     The second gap between the end contact portion of the second spiral and the first spiral portion being relatively larger than the second gap between the intermediate portions of the second and first spiral portions. The first and second gaps near and at the central portion being relatively smaller than the gaps between the intermediate portions of the spiral portions of the double-spiral shaped filament. The end contacts of the first and second spiral portions may be brazed or affixed by other means to the metal surfaces of the ledge of the ceramic enclosure such that the double-spiral shaped tungsten filament is suspended above the reflective base. The transparent portion of the lid is soldered to the metal surfaces of the ceramic bases and forms a chamber within which the double-spiral shaped tungsten filament resides and is suspended therein. The chamber being substantially at a desired vacuum or filled with non-reactive gas for a desired specific photochemical action. 
     The process for making an ultraminiature light source is disclosed and claimed. The steps include fabricating a double-spiral ultraminiature tungsten filament from tungsten foil. Braze preform is placed over two metal contacts of a suitable chip carrier package. End contacts of the tungsten filament are positioned so as to bring them into engagement with the braze preform covering the contacts of the chip carrier package. The chip carrier package is placed with the filament positioned therein into a vacuum furnace. Preferably, the chip carrier package has a base plated with a material selected from the group of reflective refractory metal, refractory ceramic carbide, boride, and nitride. The chip carrier package is heated to approximately 800° C. under a desired vacuum and the tungsten filament is bonded to the chip carrier package by the braze preform. The chip carrier package, the tungsten filament, and the brazing are then cooled while the pressure is increased to atmospheric pressure. A solder preform is applied to the perimeter of the lid which has a transparent portion. The solder preform is nicked to create a discontinuity therein. 
     The lid has a solder preform which is tack welded over the perimeter of the lid. The solder preform of the lid is then applied over the perimeter of the chip carrier package. The chip carrier package includes an upper lip or perimeter which has a gold plating which resides over a nickel plating which interengages the solder preform. The lid with said solder affixed thereto is brought forcibly into engaging contact with the chip carrier package and placed into the furnace under a desired vacuum. The chip package is then heated under the desired vacuum to the eutectic temperature of the solder to remelt and reflow the solder to seal the chip carrier package under the desired vacuum. The chip carrier is then cooled to room temperature and restored to atmospheric pressure. 
     The ceramic chip carrier of the instant invention as described below includes a stepped profile in cross-section. The bottom of the ceramic chip carrier includes a gold plated surface which may be polished. The first step of the profile includes contacts over which the ultraminiature dual spiral filament is bridged. 
     The &#39;866 patent reference does not teach or disclose an ultraminiature dual spiral having divergent end contact portions which are brazed to a pair of contacts within the ceramic chip carrier. Nor does the &#39;866 patent teach or disclose the use of a ceramic chip carrier in combination with a commercially available lid. Nor does the &#39;866 patent teach or disclose the claimed process steps. 
     Nor does the structure of the &#39;866 patent prohibit shorting of the spirals upon thermal expansion or because of vibration. 
     The invention also discloses structure for using the light emitted from the dual spiraled tungsten filament. Specifically, an ultraminiature light conducting package comprises a dual spiraled tungsten filament having a substantially constant thickness and a carrier package having a transparent window. The dual spiraled tungsten filament is suspended within the package. A fiber optic light guide is affixed to the transparent window of the package. 
     Accordingly, it is an object of the invention to provide an ultraminiature light source which is efficiently coupled to a fiber optic guide. 
     Accordingly, it is an object of the invention to provide an ultraminiature light source which includes a double-spiral filament with divergent end contact portions. 
     Accordingly, it is an object of the invention to provide an ultraminiature light source which includes a double-spiral filament having wide end contacts which neck down to a reduced-width transitional portion which then gradually reduce down in width in the shape of a wide sweeping and tapering arc to a width maintained by the inner windings which terminate in a central portion. 
     Accordingly, it is an object of the invention to provide an ultraminiature light source in a chip carrier package which includes a ceramic base and a partially transparent lid. 
     Accordingly, it is an object of the invention to provide an ultraminiature light source whose filament maintains its integrity despite vibration and heating. 
     Accordingly, it is an object of the invention to provide an ultraminiature light source whose filament does not short between portions thereof due to thermal expansion of the tungsten, tungsten alloy or other filament material. 
     Accordingly, it is an object of the invention to use a commercially available package and lid in combination with a new process and new filament disclosed herein which is advantageous insofar as sealing of the package, simplicity of construction, ruggedness, durability and cost are concerned. 
     These and other objects will be best understood when reference is made to the Brief Description of the Drawings, Description of the Invention and Claims which follow hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of the prior art device illustrated in U.S. Pat. No. 6,796,866. 
         FIG. 2  is a schematic of the prior art device illustrated in U.S. Pat. No. 6,796,866. 
         FIG. 2A  is a schematic of the prior art device illustrated in U.S. Pat. No. 6,796,866 with the tungsten coil thereof illustrated in the process of unwinding. 
         FIG. 3  is an illustration of the double-spiral filament of the instant invention having end contact portions which are divergent from the next adjacent spiral. 
         FIG. 3A  is an illustration of the double-spiral filament of the instant invention similar to  FIG. 3  with additional reference numerals employed to indicate dimensions and radii of the filament. 
         FIG. 3B  is an enlargement of a portion of the double-spiral filament illustrated in  FIG. 3A . 
         FIG. 3C  is a perspective view of the double-spiral filament illustrated in  FIG. 3 . 
         FIG. 3D  is an illustration of the double-spiral filament of the instant invention similar to  FIG. 3  after the filament has been energized and thermal expansion of the filament has taken place. 
         FIG. 4  is an illustration of the ceramic base illustrating a reflective bottom, a ledge having contact pairs which engages the end contact portions of the spiral, and an upper perimeter or lip which is coated with metal. 
         FIG. 4A  is a quarter-sectional view of the ceramic base illustrating the reflective bottom portion, the ledge and the upper perimeter or lip. 
         FIG. 4B  is an enlarged quarter-sectional view of the ceramic base or housing illustrating the reflective layer covering the bottom of the leadless chip carrier, the nickel plating on the perimeter and the gold plating on the nickel plating. 
         FIG. 5  is a view similar to  FIG. 4  with the double-spiral element placed in the ceramic base straddling the ledge with the end contact portions mating with a respective pair of the contact pairs of the ledge. 
         FIG. 5A  is a quarter sectional view of  FIG. 5 . 
         FIG. 6  is a view of the bottom side of the lid illustrating the transparent window and the lip which mates with the upper surface of the ceramic base. 
         FIG. 6A  is a side view of the lid. 
         FIG. 6B  is an enlarged portion of  FIG. 6A  illustrating a nick in the solder preform. 
         FIG. 7  is a top view of the ultraminiature light source assembled. 
         FIG. 8  is a schematic of the steps to manufacture the ultraminiature light source. 
         FIG. 9  is a top view of the ultraminiature light source with a fiber optic guide secured to the transparent window with optical adhesive. 
         FIG. 9A  is an enlarged cross-sectional view taken along the lines  9 A- 9 A of  FIG. 9 . 
         FIG. 10  is an enlarged cross-sectional view similar to  FIG. 9A  illustrating another fiber optical guide coupling arrangement. 
         FIG. 11  is an enlarged cross-sectional view of another connector arrangement. 
         FIG. 11A  is an enlarged cross-sectional view of another connector similar to  FIG. 11  with a lens integral with the lamp package window. 
         FIG. 11B  is an enlarged cross-sectional view of a connector similar to  FIG. 11A  with the connector directly engaging and attached to the lens with adhesive, solder, braze, glass frit or welded to the package lid. 
     
    
    
     The drawings will be best understood when reference is made to the Description of the Invention and Claims which follow hereinbelow. 
     DESCRIPTION OF THE INVENTION 
       FIG. 3  is an illustration of the double-spiral element  300  of the instant invention having end contact portions  301 ,  302  which are divergent from the next adjacent spiral. By increasing the radius of the outer windings of the double-spiral, the inner windings are allowed to decoil while not contacting the outer windings or tabs so that the short path is less likely for a particular operating voltage. The net result is to allow more stable light output for a longer lifetime at a higher operating point for the filament. 
     End contact portions  301 ,  302  of the double-spiral filament contact ledge  405  of leadless chip carrier package  400  and are in electrical communication therewith. See,  FIGS. 4 and 4A , which generally represent a commercially available leadless chip carrier package such as the one illustrated and made by Kyocera Corporation of Kyoto, Japan, Kyocera Drawing Number PB-C88231-JMI. It will be noted that the leadless chip carrier package includes a plurality of gold contacts which are embedded in or deposited on the surface of the ledge. Any oppositely oriented pair of contacts may be used as they will position the double-spiral filament centrally within the chip carrier package. The double-spiral filament  300  is centrally mounted as this will maximize the light output through a correspondingly oriented window  602  in a lid  600  as illustrated in  FIGS. 6 and 7 . 
     A braze preform available from Morgan Ceramics/Wesgo Metals Incusil-ABA having 59% Ag, 27.25% Cu, 12.5% In and 1.25% Ti having a liquidus temp=715° C. covers the contacts of the leadless chip carrier. The leadless chip carrier with the filament engaging the braze preform and the contacts are then heated under a desired vacuum at approximately 800° C. until the filament is secured in place. 
     A transitional portion  303  of the filament interconnects end contact portion  301  and outer spiral portion  306  of the first spiral and a transitional portion  304  interconnects the end contact portion  302  and outer spiral portion  305  of the second spiral. It will be noticed that the end contact portions  301  and  302  are significantly larger in cross-sectional area than the transitional portions  303 ,  304 . The filament is 0.025 mm (25 μm) thick everywhere and the end contacts are approximately 0.50 mm (500 μm) wide as represented by reference numeral  354  in  FIG. 3A . Also see,  FIG. 3C , reference numeral  388 , illustrating the thickness  388  of the filament. Shoulders  330 ,  331  reduce the width of the end contact portions to the width of the transition portions  303 ,  304 . 
       FIG. 3A  is an illustration  300 A of the double-spiral filament  300  of the instant invention similar to  FIG. 3  with additional reference numerals employed to indicate dimensions and radii of the filament. 
     Referring still to  FIG. 3 , the beginning  305 A of the outer-most winding  307  of the second spiral  305  is illustrated. Reference numeral  307  represents the outer-most winding of the second spiral. Reference numeral  305 A represents the beginning of the outer-most winding  307  of the second spiral  305 . Reference numeral  306 A represents the beginning of the outer-most winding  308  of the first spiral  306 . Reference numeral  308  represents the outer-most winding of the first spiral  308 . 
     Arrow  340  is indicated in  FIG. 3  as pointing to the gap  316  (sometimes referred herein as “the second gap”) between second spiral  305  and first spiral  306  and arrow  341  is pointing toward the beginning of the gap  314  (sometimes referred herein as “the first gap”) between first spiral  306  and second spiral  305 . These arrows signify the relatively large gaps at the entrances to the interleaved first  306  and second spiral  305 .  FIG. 3D  illustrates the gaps  314 ,  316  of the filament after energization (i.e., after the application of appropriate voltage across the end contacts  301 ,  302 ) of the tungsten or tungsten alloy filament. The inner windings as discussed hereinbelow are expanded radially outward and lengthened slightly. The filament, as illustrated in  FIG. 3 , accommodates the joule heating of the filament such that the unwanted contact in the region, defined generally by reference numerals  260 ,  261 ,  262  and  263  in  FIG. 2A , is avoided and does not occur. Referring to  FIG. 3D , the fill factor may change with joule heating, but the filament should unspool evenly so the fill factor should remain mostly the same even though the output disk should grow or shrink as the filament heats or cools. 
     Referring to  FIGS. 3-3D , fill factors for the filament disclosed herein will vary depending on desired temperature of the particular filament used; however, the filament illustrated in  FIG. 3  is 25 μm thick (reference numeral  388 ,  FIG. 3C ) everywhere, has a 50% fill factor using a 50 μm spacing between spirals  305 ,  306 , and has a 50 μm winding width. The filament of  FIG. 3  operates at approximately 2200° K. for 1000 hours. The importance of the fill factor or aspect ratio has to do with the fact that the closer the windings are together the more light you can output per unit area. The spacing is determined by the amount that the filament expands due to thermal effects during operation. 
     Still referring to  FIGS. 3-3D , the inner windings are approximately about the same cross-section, and are the smallest in cross-sectional area of the filament components. This makes the hot spot of the filament generally in the middle (central portion  313 ) of the filament away from the walls of the package. Since the light comes from the middle of the package it can be easily coupled to the optical fiber attached to the window of the light source. 
     Still referring to  FIGS. 3-3D , the outer windings are tapered like a sickle as a transition from the strong end contacts  301 / 303  and  302 / 304  to the inner windings of the interleaved spirals  305 ,  306 . The outer windings  305 ,  306  are shaped like a sickle with the arc being fairly wide and sturdy to provide a strong gradual transition to the inner windings instead of going right from the end contacts directly to a narrow winding as does the structure of  FIGS. 2 and 2A . The arc supports the inner windings encouraging them to uncoil as they heat instead of just twisting off in a torquing motion at the end contact connection point. The arc distributes the stress during temperature changes and thus increases the service life. The arc also provides for the inner windings of the coil to grow outwardly. The end contacts have the greatest cross-section of the filament. In this way the end contacts create a stable base for damping filament vibration and have a lot of adhesion surface area to bind the filament to the leadless chip carrier package. The large end contact portions also provide a relatively large place to handle the filament during the assembly process. 
     Still referring to  FIGS. 3-3D , the narrower inner windings (intermediate windings  309 ,  310 ,  311 ,  312 ) have the same current as the end contact portions because the current is the same throughout all portions of the filament. The narrower inner windings have the same thickness as the end contact portions  301 ,  302  and as the inner windings&#39; cross-sectional area is smaller (than the arc, transition portions and end contacts) their relative resistance per incremental unit length is relatively higher and they joule heat more since the same current is squeezed through essentially a smaller volume which means the same number of electrons per second interact with fewer atoms generating more photons and different energy photons than are generated at the end contact portions. 
     Still referring to  FIGS. 3-3D , having the arc and designing the filament such that the outer windings are spaced apart from the inner windings (intermediate windings  309 ,  310 ,  311 ,  312 ) may decrease the fill factor somewhat but most of the light is from the inner windings so the optical fiber will couple effectively to the filament. In this arrangement the fill factor is about 50%. Filaments having fill factors greater than 50% may be used. The inner windings are approximately 50 μm wide and are spaced apart approximately 50 μm from winding to winding. 
     The second spiral  305  includes intermediate winding portions  309 ,  311  which terminate in a central portion  313  which joins second and first spirals  305 ,  306  together. The first spiral includes intermediate winding portions  310 ,  312  which also terminate in the central portion  313 . Generally the windings of the spirals  305 ,  306  are widest at the arc which comprises outer-most winding and gradually tapers to the width of the inner winding which is approximately 50 μm. 
     Referring to  FIG. 3A , the overall length  350  of the filament is approximately 8 mm (8000 μm). The radii  355  of the outer-most windings  307 ,  308  of the second and first spirals  305 ,  306 , respectively, are approximately 0.89 mm (890 μm). The radii  356  of the outer-most windings  307 ,  308  of both spirals  306 ,  305  are reduced gradually to approximately 0.68 mm (680 μm) through an arc of about 90° and the radii  357  are further reduced to 0.58 mm (580 μm) through an arc of 180°. Thereafter, the radii are further reduced. 
     The approximate length  351  between transition portions  303 ,  304  is 4.84 mm (4840 μm) for the example illustrated in  FIG. 3A . The outer diameter  352  of the filament is approximately 1.50 mm (1,500 μm) and is also illustrated in  FIG. 3A . The diameter  353  of the tungsten or tungsten alloy filament is approximately 1.15 mm (1,150 μm) at the point where the outer-most windings have swept an arc of approximately 180° from the entrance. The filament employs end contact portions  301 ,  302  which are then reduced in cross-section in transition portions  303 ,  304 . The distance  358  between the contact portions (i.e., where they are reduced by shoulders  330 ,  331  to become transition portions  303 ,  304 ) is approximately 4.84 mm (4,840 μm). The contact end portions are 1.43 mm (1,430 μm) in length as indicated by reference numeral  359 . 
     The invention is disclosed herein by way of example only and those skilled in the art will readily recognize after reading the specification that many of the dimensions stated herein may be changed without departing from the spirit and scope of the claimed invention. 
       FIG. 3B  is an enlargement  300 B of a portion of the double-spiral filament illustrated in  FIG. 3A . Reference numeral  314  represents the first gap between the first spiral  306  and the second spiral  305  at the beginning of the outer-most winding  308 . Reference numeral  315  represents the first gap between the first spiral  306  and the second spiral  305  after an arc of about 90° of the outer-most winding  308 . Reference numeral  317  represents the first gap between intermediate portions of the first spiral  306  and the second spiral  305 . Reference numeral  323  represents the termination of the first gap between the intermediate portions of the first and second spirals. The gap terminates where the spirals are joined as indicated by reference numeral  313 . 
     Still referring to  FIG. 3B , second gap  320  between intermediate portions of the second  305  and first  306  spirals is illustrated and that second gap which began as  316 ,  316 A terminates as indicated by reference numeral  324 . 
       FIG. 3C  is a perspective view  300 C of the double-spiral filament illustrated in  FIG. 3  and which illustrates the thickness  388  of 0.025 mm (25 μm) and the generally planar form of the filament which is generally represented by the reference numeral  300  in  FIG. 3 . In the future it is contemplated that a thickness of 0.050 (50 μm) may be used. 
       FIG. 4  is an illustration of the ceramic housing or base  400  illustrating a bottom  400 , a ledge  405  having contact pairs  405 A,  406  which engage the end contact portions  301 ,  302  of the spiral filament  300 , and an upper perimeter or lip  402  which is metal coated  402 B,  402 A. 
     The ceramic housing has a metallized upper lip  402 A consisting of a base coating of nickel plating  402 B with a top coating of 0.0015 mm (1.5 μm) of gold plating  402 A. 
     The bottom  404  of the housing may be polished. Alternatively, a reflective refractory metal, refractory ceramic carbide, boride, or nitride  404 A may be deposited on the bottom  404 . The bottom reflector layer provides a reflective surface  404 A to improve transmission through the transmission window  602  above, see  FIG. 7 . Alternatively, the bottom reflector layer may include a reflective metal layer  404 A which may be a Ti 200 Å/Pt 1000 Å reflective film. Silver may also be used as a reflective material. 
     Still referring to  FIG. 4 , grooves  401 ,  412 ,  409 ,  410 , are cut vertically into the sides of the leadless chip carrier  400  to allow for interconnections directly to metal contacts  411 ,  414  within the grooves from outside the leadless chip carrier. Metal contact  405 A is in electrical communication (not shown) with contact  411  within the leadless chip carrier  400 . Similarly metal contact  408  is in electrical communication (not shown) with contact  414  within the leadless chip carrier  400 . 
     Contact pairs  407 ,  408  and  406 ,  405 A are the preferred contacts over which braze preform is placed prior to placing end contact portions  301 ,  302  therein for heating to secure the filament within. Any of the contact pairs may be used as they all result in the centering of the filament within the housing and for its alignment with the window in the lid. 
       FIG. 4A  is a quarter-sectional view  400 A of the ceramic base or housing  400  illustrating the reflective bottom portion  404 A, the ledge  405  and the upper perimeter or lip  402 .  FIG. 4A  provides a good illustration of outer surface contacts  411 ,  414  for interconnection to outside devices. 
       FIG. 4B  is an enlarged portion  400 B of the quarter-sectional view  400 A of the ceramic base or housing illustrating the reflective layer  404 A covering the bottom of the leadless chip carrier, the nickel plating  402 B on the perimeter and the gold plating  402 A on the nickel plating  402 B. Reference numeral  405 B indicates a braze preform on top of contact  405 A in which end contact  301 ,  302  may be placed. The end contacts of the tungsten filament may be bonded to contacts of the chip carrier package by a suitable process such as brazing, electron beam welding, spot welding or laser welding. 
       FIG. 5  is a view  500  similar to  FIG. 4  with the double-spiral filament  300  placed in the ceramic base or housing  400  straddling the ledge  405  with the end contact portions  301 ,  302  mating with a respective pair  405 A,  406  of the contact pairs of the ledge  405 . 
       FIG. 5A  is a quarter sectional view  500 A of  FIG. 5  illustrating the braze preform securing the end contact portion  301  to contact  405 A on ledge  405  of housing  400 . End contact portion  301  is fused to the contact  405 A upon sufficient heating and subsequent cooling. 
       FIG. 6  is a view  600  of the bottom side of the lid  601  illustrating the transparent window  602  and the lip  603 A which mates with and is secured to the upper surface  402 A of the ceramic base. The lid is commercially available from Spectrum Semiconductor Materials of San Jose, Calif. part no. C-731-21-50MK100MND-GKL. The material of the lid is Kovar and includes the gold plating on top of nickel with a 80% Au/20% Sn solder preform.  FIG. 6A  is a side view  600 A of the lid  601  illustrating the lip  603 A with solder preform  603  applied over the lip. At least one notch, nick or groove  608  is cut into the solder preform  603  such that when it is secured or held into sealing engagement with gold plated surface  402 A and placed in a furnace under vacuum conditions the contents of the ceramic housing  400  and the lid  601  are evacuated. Alternatively, the ceramic housing and lid may be placed in an environment of halogen gas.  FIG. 6B  is an enlarged portion of  FIG. 6A  illustrating nick  608  in more detail. The heat of the furnace remelts and reflows the solder preform eliminating the nick and securing the lid and the chip carrier package together. 
       FIG. 7  is a top view  700  of the ultraminiature light source assembled. 
       FIG. 8  is a schematic  800  of the steps to manufacture the ultraminiature light source. The steps include fabricating a double-spiral ultraminiature tungsten filament from tungsten foil- 801 ; placing braze preform over two metal contacts of a suitable chip carrier package- 802 ; positioning end contacts of the tungsten filament into engagement with the braze preform covering the contacts of the chip carrier package- 803 ; placing the chip carrier package with the filament positioned therein into a vacuum furnace, the chip carrier package having a base plated with a material selected from the group of reflective refractory metal, refractory ceramic carbide, boride, and nitride- 804 ; heating, under desired vacuum, the chip carrier package, the tungsten filament, and the braze preform  805  at approximately 800° C. to melt the braze preform and bond the filament to the chip package; cooling the chip carrier package, the tungsten filament, and the brazing while increasing pressure to atmospheric pressure- 806 ; applying solder preform to the perimeter of a lid having a transparent portion- 807 ; nicking the solder preform to create a discontinuity therein- 808 ; applying the lid having a transparent portion and having a solder preform tack welded over the perimeter of the lid to the chip carrier package, the chip carrier includes an upper lip having a gold plating which resides over a nickel plating; holding the lid with the solder affixed thereto into engagement with the chip carrier package- 810 ; placing the chip carrier package with the lid held in place into the furnace under desired vacuum- 811 ; heating, under desired vacuum, the chip package to the eutectic temperature of solder to remelt and reflow the solder to seal the chip carrier package under the desired vacuum to create an air tight seal between the package and the lid- 812 ; and, cooling to room temperature and restoring atmospheric pressure within the furnace- 813 . 
     Alternatively, the step of placing braze preform on the contacts may be substituted with any suitable process of bonding the contacts to the chip carrier by brazing, electron beam welding, spot welding or laser welding. 
     The eutectic point referred to in the step denoted by reference numeral  812  is the point at which the liquid phase borders directly on the solid phase. The temperature that corresponds to this point is known as the eutectic temperature. 
     The step of applying solder preform to the perimeter of a lid having a transparent portion- 807 —includes the solder preform being tack welded to the window lid. The attachment of the solder preform to the lid prior to the sealing process avoids potential handling damage to the delicate 0.510 mm (510 μm) thick gold preform and reduces alignment offsets of the gold preform to the sealing surfaces. 
     The ceramic housing has a metallized upper lip consisting of a base coating of nickel plating with a top coating of 0.0015 mm (1.5 μm) of gold plating. 
     The light source disclosed herein was successfully tested at 3.125 VDC at 0.40 A yielding approximately 1.250 W at 2200° K. for approximately 1000 hours. Different filament materials operating at different voltages will produces different values. 
       FIG. 9  is a top view  900  of the ultraminiature light source with a fiber optic guide  901  secured to the transparent window  602  with optical adhesive  902 . 
       FIG. 9A  is an enlarged cross-sectional view  900 A taken along the lines  9 A- 9 A of  FIG. 9 . A gap  903  of approximately 0.58 mm (580 μm) is illustrated in  FIG. 9A  between the filament and the window  602 . 
     The advantage of the tungsten light source disclosed herein includes the fact that it provides a broad optical spectrum. This broad spectrum is accompanied by a short coherence length. It is key, therefore, to couple the light source into an optical fiber in an efficient manner. This becomes increasingly problematic when the core size of the optical fiber is small. Fibers used in optical fiber sensors may be 50 microns or smaller. Such fibers usually have a small numerical aperture number (NA) such as 0.22. This means that either the light entering the fiber must be fairly collimated or that the fiber must be close to the source if the light is not highly collimated. The tungsten light source disclosed herein radiates light in all directions although the dual spiral coils tend to concentrate the light source. In order to maximize coupling a small filament light source with dimensions approaching that of the fiber, close spacing of the fiber to the filament is required to achieve any sort of efficiency in getting the tungsten light spectrum into the fiber. 
       FIG. 10  is an enlarged cross-sectional view  1000  similar to  FIG. 9A  illustrating another fiber optic guide coupling arrangement. Connector housing  1001  fits over the packaged tungsten filament light source and the connector female receptacle  1002  is in engagement with the package. Male connector  1003  is insertable within the female connector  1002 . Male connector  1003  includes a housing portion  1004  and a resilient portion  1005  for receiving the fiber  901 . The fiber  901  is positioned in proximity to the window for good coupling to the tungsten filament. Resilient material  1005  is used to grip the fiber optic guide  901  and enables the replacement of the optic fiber  901  if necessary. 
       FIG. 11  is an enlarged cross-sectional view  1100  of another connector arrangement wherein the fiber is held in a male connector  1110 , which in turn is coupled to a female connector receptacle  1112  affixed to a lamp package mount  1113 . Optionally a lens  1120  may be used.  FIG. 11A  is an enlarged cross-sectional view  1100 A of another connector similar to  FIG. 11  with a lens integrally affixed  1121  with the lamp package window.  FIG. 11B  is an enlarged cross-sectional view  100 B of a connector similar to  FIG. 11A  with the connector directly engaging and attached to the lens by adhesive, solder, braze, or glass frit  1130 . Alternatively the lens  1120  may be welded to the package lid. 
       1100 -cross-sectional view of a coupling arrangement with an optional lens  1100 A-cross-sectional view of a coupling arrangement with a lens integral with the transparent window 
     LIST OF REFERENCE NUMERALS 
     
         
           100 —schematic of related art device in U.S. Pat. No. 6,796,866. 
           102 —top silicon substrate 
           104 —transparent window in top silicon substrate 
           106 —middle silicon substrate for mounting filament  200   
           108 —bottom silicon substrate 
           200 —filament 
           202 —silicon substrate 
           212 —silicon substrate 
           204 —top nitride layer of top substrate 
           206 —bottom nitride layer of top substrate 
           210 —wire bond pad 
           214 —top nitride layer of middle filament mounting substrate  106   
           216 —bottom nitride layer of middle filament mounting substrate 
           218 —aperture in bottom substrate 
           220 —end contacts of the spiral filament 
           222 —electrical leads 
           230 —bonding ring 
           232 —bonding ring 
           234 —insulation 
           236 —electrical leads 
           240 —wire bond lead 
           242 —reflective top layer of bottom silicon substrate  108   
           250 —bonding ring 
           252 —bonding ring 
           260 —gap 
           261 —gap 
           262 —gap 
           263 —gap 
           260 A—contact area after heating 
           261 A—contact area after heating 
           262 A—contact area after heating 
           263 A—contact area after heating 
           291 —intermediate portion 
           292 —central portion 
           300 —double-spiral filament 
           300 A—double-spiral filament with dimensions includes 
           300 B—enlarged filament portion of  FIG. 3   
           300 C—perspective view of filament 
           301 —end contact portion which sits on ledge of leadless chip carrier package 
           302 —end contact portion which sits on ledge of leadless chip carrier package 
           303 —transitional portion interconnecting end contact portion  301  and outer spiral portion  306  of the first spiral 
           304 —transitional portion interconnecting end contact portion  302  and outer spiral portion  305  of the second spiral 
           305 —second spiral 
           305 A—beginning of outer-most winding  307  the second spiral  305   
           306 —first spiral 
           306 A—beginning of outer-most winding  308  of the first spiral 
           307 —outer-most winding of the second spiral 
           308 —outer-most winding of the first spiral 
           309 —intermediate winding of the second spiral 
           310 —intermediate winding of the first spiral 
           311 —intermediate winding of the second spiral 
           312 —intermediate winding of the first spiral 
           313 —central portion joining first and second spirals 
           314 —gap between beginning portion of first spiral and second spiral 
           315 —gap between beginning portion of first spiral and second spiral where they begin to converge 
           316 —gap between beginning portion of second spiral and first spiral 
           316 A—gap between beginning portion of second spiral and first spiral where they begin to converge 
           317 —gap between intermediate portions of first and second spirals 
           320 —gap between intermediate portions of second and first spirals 
           323 —termination of gap between intermediate portions of first and second spirals 
           324 —termination of gap between intermediate portions of second and first spirals 
           340 —arrow to beginning of gap between second spiral  305  and first spiral  306   
           341 —arrow to beginning of gap between first spiral  306  and second spiral  305   
           350 —overall length of approximately 8.00 mm of the filament of the example illustrated 
           351 —approximate length of 4.84 mm between transition portions  303 ,  340  of the example illustrated 
           352 —outer diameter of approximately 1.50 mm of the filament of the example illustrated 
           353 —diameter of filament after approximately 180° arc of the example illustrated 
           354 —approximate width of 0.500 mm of the contact portions  302 ,  301  of the example illustrated 
           355 —approximate radii of 0.89 mm of the first and second spirals at the beginning of the spirals of the example of the example illustrated 
           356 —approximate radii of 0.68 mm of the first and second spirals after an approximate 90° arc of the example illustrated 
           357 —approximate radii of 0.58 mm of the first and second spirals after an approximate 180° arc of the example illustrated 
           358 —approximate distance of 4.84 mm between the contact portion of the example illustrated 
           359 —length of end contact portion 
           388 —thickness of the filament 
           400 —top plan view of a leadless chip carrier 
           400 A—quarter-sectional view of the leadless chip carrier illustrated in  FIG. 4  taken along the lines  4 A- 4 A 
           400 B—quarter-sectional view of the leadless chip carrier illustrated in  FIG. 4  further illustrating the braze preform and the reflective bottom 
           401 —side indentation of leadless chip carrier 
           402 —upper surface or perimeter of the leadless chip carrier 
           402 A—nickel plating 
           402 B—gold plating 
           404 —bottom of leadless chip carrier package 
           404 A—reflective material on the bottom of the chip carrier package 
           405 —ledge 
           405 A—contact 
           405 B—braze preform, electron welding, spot welding, laser welding 
           406 —contact 
           407 —contact 
           408 —contact 
           409 —exterior contact 
           410 —exterior contact 
           411 —exterior contact 
           412 —side indentation of leadless chip carrier package 
           500 —top plan view of a leadless chip carrier similar to view of  FIG. 4  with the filament placed therein 
           500 A—quarter-sectional view taken along the lines  5 A- 5 A of  FIG. 5   
           501 —braze preform 
           600 —bottom view of the lid  601   
           600 A—side view of the lid  601   
           600 B—enlarged portion of  FIG. 6A   
           601 —lid 
           602 —transparent window 
           603 —solder preform on bottom facing lip 
           603 A—lip 
           604 —bottom side of top cover of the lip 
           608 —nick in the solder preform  603   
           609 —top cover of lid  601   
           700 —completed assembly of the light source with the lid 
           800 —schematic of process to manufacture the light source 
           801 —fabricating a double-spiral ultraminiature tungsten filament from tungsten foil 
           802 —placing braze preform over two metal contacts of a suitable chip carrier package or electron welding, spot welding or laser welding 
           803 —positioning end contacts of the tungsten filament into engagement with the braze preform covering the contacts of the chip carrier package 
           804 —placing the chip carrier package with the filament positioned therein into a vacuum furnace, the chip carrier package having a base plated with a material selected from the group of reflective refractory metal, refractory ceramic carbide, boride, and nitride 
           805 —heating, under desired vacuum, the chip carrier package, the tungsten filament, and the braze preform at approximately 800° C. 
           806 —cooling the chip carrier package, the tungsten filament, and the brazing while increasing pressure to atmospheric pressure 
           807 —applying solder preform to the perimeter of a lid having a transparent portion 
           808 —nicking the solder preform to create a discontinuity therein 
           809 —applying the lid having a transparent portion and having a solder preform tack welded over the perimeter of the lid to the chip carrier package, the chip carrier includes an upper lip having a gold plating which resides over a nickel plating 
           810 —holding the lid with the solder affixed thereto into engagement with the chip carrier package 
           811 —placing the chip carrier package with the lid held in place into the furnace under desired vacuum 
           812 —heating, under desired vacuum, the chip package to the eutectic temperature of solder to remelt and reflow the solder to seal the chip carrier package under the desired vacuum 
           813 —cooling to room temperature and restoring atmospheric pressure within the furnace 
           900 —top view of filament within the assembled package coupled to a fiber optic guide 
           900 A—cross-sectional view taken along the lines  9 A- 9 A 
           901 —fiber optic guide 
           902 —optical adhesive 
           903 —gap between window  602  and filament 
           1000 —cross-sectional view of a connector for coupling a fiber optic guide to the assembled package 
           1001 —connector housing 
           1002 —connector female receptacle 
           1003 —male connector 
           1004 —housing of the male connector 
           1005 —resilient material gripping the fiber optic guide  901   
           1100 —cross-sectional view of a coupling arrangement with an optional lens 
           1100 A—cross-sectional view of a coupling arrangement with a lens integral with the transparent window 
           1100 B—cross-sectional view of a connector affixed directly to a lens 
           1110 —male connector 
           1112 —female connector 
           1113 —package coupling mount 
           1120 —lens 
           1121 —lens embedded in window  602   
           1130 —adhesive, solder, braze, glass frit or ultrasonic weld 
       
    
     Those skilled in the art will readily recognize that the invention has been set forth by way of examples only and that many changes may be made to the structure of the examples and to the process set forth by way of examples without departing from the spirit and scope of the claims attached hereto.

Technology Category: 5