HK1177981A - Light source - Google Patents

Description

Light source

The application is a divisional application of Chinese patent application with the invention name of 'microwave light source with solid dielectric waveguide', application date of 2011, 5, 16 and application number of 200880131995.8.

Technical Field

The invention relates to a light source for a lamp driven by microwaves.

Background

It is known to excite a discharge in a bulb to produce light. Typical examples are sodium discharge lamps and fluorescent tube lamps. The latter uses mercury vapor that generates ultraviolet radiation. This, in turn, excites the phosphor to produce visible light. Such lamps are more efficient than tungsten lamps in consuming lumens of light emitted per watt of electricity. However, they still have the disadvantage that electrodes are required in the lamp. Because they carry the current required for discharge, they deteriorate and eventually fail.

We have developed electrodeless bulb lamps as shown in our patent application No. PCT/GB2006/002018 for lamps (our "' 2018 lamp"), patent application PCT/GB2005/005080 for bulbs for lamps and patent application PCT/GB2007/001935 for matching circuits for microwave driven lamps. They all relate to electrodeless lamps which excite a light-emitting plasma in a bulb by using microwave energy. Earlier proposals involving the use of airwaves to couple microwave energy into the bulb have been proposed, for example by Fusion Lighting Corporation in their U.S. Pat. No.5,334,913. If an air waveguide is used, the lamp volume is large because the physical dimensions of the waveguide are a fraction of the wavelength of the microwaves in air. This is not a problem for e.g. street lamps, but makes this type of lamp unsuitable for many applications. For this reason, our' 2018 lamp uses a dielectric waveguide, which considerably reduces the wavelength at the operating frequency of 2.4 GHz. Such lamps are suitable for use in household appliances such as rear projection televisions.

Approximately 8 years ago, we employed the founder of LuximInc ("Luxim") with a counselor agreement by the stockholder in the microwave-excited light industry. On 31/7/2000, Luxim filed U.S. provisional patent application No 60/222,028, which was subsequently granted, via appropriate procedures, U.S. Pat. No. 6,737,809 ("Luxim patent"). The abstract is as follows:

a Dielectric Waveguide Integrated Plasma Lamp (DWIPL) having a body consisting essentially of at least one dielectric material having a dielectric constant greater than about 2 and having a shape and dimensions such that the body resonates in at least one resonant mode when microwave energy of an appropriate frequency is coupled into the body. A bulb located in a cavity within the body contains a fill gas that forms a light emitting plasma when receiving energy from the resonating body. "

We believe this is the first disclosure for coupling microwave energy into a solid dielectric waveguide in an electrodeless bulb. At that time, attention was focused on the significant reduction in size that can be achieved by using a solid medium. We are in the ceramic field as such related to this project. The ceramic selected is alumina.

Our U.S. patent No 6,666,739 is older in date than the advisor protocol described above. Its abstract is as follows:

"the lamp is comprised of a hollow tubular body having a closed end and an open end. The body is a sintered ceramic material. A window is sealed over the open end, the window and the body being bonded by a layer of frit. The window is sapphire. A particulate charge of inert gas and excitable material is sealed within the body. In use, the lamp is subjected to RF electromagnetic radiation to heat the lamp to 1000 ℃, so that it emits visible light via sapphire ".

Not only is the alumina opaque in the form of use, but the waveguide is also silvered to provide boundary conditions for the resonant electric field within the waveguide. In the Luxim patent it is proposed that light should be emitted via a sapphire window.

Since the above cooperation we have not appreciated any suggestion of using a solid dielectric waveguide that does not use a separate bulb (typically of quartz) to enclose microwave excitable material in a recess in an opaque waveguide (typically of alumina) or in an integrated device that is close to a recess in an opaque waveguide and encloses a transparent window of microwave excitable material.

In pursuit of our improvements in microwave-excited light technology, Andrew new invented another way to combine the bulb and waveguide into a single component.

Therefore, we filed our patent application No 0722548.5 on 16/11/2007, which is referred to herein as our first LER (light emitting resonator) patent application. It describes a visible light source of a lamp driven by a microwave source having:

●, which is transparent to visible light, and opaque to microwaves, and resonates upon microwave excitation,

● a filler material capable of being excited by microwave energy to form a plasma that emits visible light, and

● an antenna within the housing positioned for plasma induced excitation of the microwave resonance formed within the housing, the antenna having a connector extending out of the housing for coupling to a microwave source.

Our first LER, which was first conceived of a larger housing with thinner walls and an antenna in an enclosed space containing a filler, in the development of our first LER we developed our second LER, where the enclosed space was smaller and the antenna was located within the material of the housing.

Therefore, we filed on 23/5/2008 our patent application No 0809471.6, which is referred to herein as our second LER (light emitting resonator) patent application. It describes a visible light source to be driven by microwave energy, the light source having:

● A solid plasma container, the material of which is transparent or opaque so that light can pass through it, the plasma container having a sealed space therein,

● surrounds a Faraday cage of the plasma vessel, which cage is at least partially light-transmissive, so that light is transmitted out of the plasma vessel, while being closed to microwaves,

● in a space of material capable of being excited by microwave energy to form a light-emitting plasma therein, and

● an antenna disposed within the plasma container for emitting plasma-inducing microwave energy toward the fill, the antenna having:

● connectors extending out of the plasma container to couple to a microwave energy source; this arrangement allows light from the plasma in space to pass through the plasma vessel and radiate out of the plasma vessel via the cage.

We now further improve LER and related technologies, and Andrew Neate and BarriePreston jointly establish the present invention, which provides the advantage of LER in lamps using our' 2018 bulb.

Disclosure of Invention

According to the present invention, there is provided a light source comprising:

● A light-transmitting waveguide of solid dielectric material having

●, surrounding the waveguide,

● bulb cavity within the waveguide and Faraday cage, an

● antenna cavity in the waveguide and Faraday cage, an

● bulb having a microwave excitable fill, the bulb being contained in a bulb cavity; wherein

● A Faraday cage includes:

● a solid portion extending across the back of the lucent waveguide to a transverse extent of the lucent waveguide; and

● a clamp that clamps the solid portion and the waveguide together and connects the solid portion to the optically transparent front of the faraday cage;

● the solid portion is reflective for directing light forward;

● the lucent waveguide and the solid portion of the waveguide are complementary in shape for emitted light to focus;

●, the light-transmissive front portion of the Faraday cage includes a mesh-like metallic element or a light-transmissive conductive coating.

As used in this specification:

by "optically transparent" is meant that the material from which the component described as being optically transparent is formed is transparent or translucent.

The lamp using such a light source has advantages over the lamp of the' 809 patent in that: light radiating laterally from the bulb can be collected and utilized as well as axial light. In the' 809 patent, only axial light from one end of the bulb may be utilized.

Typically, the waveguide is dimensioned such that microwave resonance occurs with the cavity at maximum field for optimal excitation of the filler. In a preferred embodiment, the waveguide has a circular cross-section and is dimensioned such that the half-waves extend diametrically therein.

Preferably, the envelope of the bulb and the lucent waveguide are of the same material.

As in the' 809 patent, the bulb cavity may be open, depending on the surface of the waveguide. However, we prefer to place the bulb deeper into the waveguide. Both aspects can be achieved by:

1. a hole is provided into the waveguide over half its depth, a bulb is inserted into the hole, and a plug of the same material as the waveguide is used to close the hole. Although not necessary, it is possible to enclose the plug to the waveguide, preferably by conveniently fixing the plug to the waveguide through a local fusion point;

2. the waveguide is provided in two halves which when closed together provide a bulb cavity. The two halves need not be equal nor symmetrically identical, and the two halves may be point fused together.

Where the crucible (crucible) and plug are of glass material, the plug and crucible or halves of the latter may be held or sealed together by local fusion of the plug material at the step and/or countersink (counter-bore) as the case may be. When they are ceramic materials, they are held or sealed together by local fusion of the glass frit. The local fusion can be performed by a laser.

In either case, the bulb may be unconstrained within the cavity. Preferably, however, it is fixable relative to the cavity. This is suitably achieved by spot-fusing the shaft portion of the bulb in a correspondingly sized hole extending from the cavity.

A faraday cage may be used to hold the bulb in its cavity.

In one particular embodiment:

● holding the bulb in the cavity by a tube of dielectric material;

● the open surface of the cavity is the back surface of the lucent waveguide and the tube is held by a portion of the faraday cage;

● the bulb has an extension at the inner end of the tube;

● tubes provide antenna cavities;

● and

● the light-transmissive front portion of the Faraday cage includes a mesh-like metallic element or a light-transmissive conductive coating.

These features may be utilized separately or together.

The faraday cage may comprise at least one aperture for locally increasing light transmission therethrough. Preferably, the aperture is no larger than 1/10 the free space wavelength of the microwaves in the crucible. Typically, the aperture is no more than 1/10 x 12.24cm, i.e. 12.24mm, for operation at 2.45GHz, and no more than 6.12mm for 5.8 GHz.

It is envisaged that the plasma crucible is of quartz or a sintered transparent ceramic material, although other materials are suitable. In particular, the ceramic material may be transparent or translucent.

An example of a suitable translucent ceramic is polycrystalline alumina and an example of a transparent ceramic is polycrystalline yttrium aluminum garnet — YAG. Other possible materials are aluminum nitride and single crystal sapphire.

Preferably, the material of the bulb and the material of the waveguide have the same coefficient of thermal expansion, which can be achieved by conveniently making them of the same material. Nevertheless, the bulb may run hotter than the cavity, particularly when it has a lower thermal conductivity, and it is preferable to provide a void for expansion of the bulb. Niobium, quartz have a low thermal conductivity compared to alumina.

Although the antenna is typically placed in the antenna cavity and secured there by other mechanical constraints in the light source, it is envisaged that the antenna may be secured in the waveguide, for example by: the waveguide material around the antenna is melted, closing the cavity.

Preferably, the lamp also comprises the microwave source and the matching circuit as a single integrated structure.

Drawings

To assist in understanding the invention, various specific embodiments thereof will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic perspective view of a bulb of a lamp having a light source, an optically transparent waveguide and a microwave source according to the parent application of the present divisional application;

FIG. 2 is a cross-sectional side view of the bulb and lucent waveguide of FIG. 1;

FIG. 3 is an end view of the lucent waveguide;

FIG. 4 is an exploded view of another lucent waveguide; and

FIG. 5 is an end view of another waveguide;

FIG. 6 is a perspective view of another light source of the parent of the present divisional application;

FIG. 7 is a cross-sectional view of the light source shown in FIG. 6 mounted to the reflector 120 at the focal point;

FIG. 8 is a view similar to FIG. 7 of a light source according to the present divisional application.

Detailed Description

Referring to the drawings, FIG. 1 shows a generalized representation of a parent lamp 1, the lamp 1 including an oscillator and amplifier source 2 of microwave energy, which typically operates at 2.45 or 5.8GHz or other frequencies within the ISM band. The source delivers microwaves via a matching circuit 3 to an antenna 4, the antenna 4 extending into a cavity 5 in a lucent waveguide 6. The lucent waveguide is quartz and has a central cavity 7 which houses a bulb 8. The bulb is a sealed quartz tube 9 and is filled with an inert gas and a microwave excitable material, which radiates visible light when excited by microwaves. The bulb has a stem 10, which stem 10 is received in a stem bore 11 extending from a central cavity. The waveguide is transparent and light from the bulb can leave the waveguide in any direction, influenced by any reflective surface. The microwaves cannot leave the waveguide, which is bounded on its surface by a faraday cage. Generally, a faraday cage includes: an ITO coating 12 on the front surface of the waveguide; a light reflective coating 10 on the rear surface of the waveguide, the light reflective coating 10 being typically silver and having a silicon monoxide coating 13; and a wire mesh 14 contacting the ITO and light reflective coating and grounded, the wire mesh extending around the sides of the waveguide between the front and back surfaces. The light may pass through a wire mesh for collection and use.

The shape and size of the waveguide is such that a maximum electric field is established at the bulb when driven by a selected microwave frequency. This dimension is believed to be within the ability of those skilled in the art in view of the dielectric constant of the quartz of the waveguide.

One physical configuration of a light source comprising a bulb and a waveguide is shown in fig. 2 and 3. The quartz waveguide 21 is a whole body with holes 22 starting from one surface 23. The hole extends with a maximum diameter 24 to approximately 60% of the thickness of the waveguide for receiving the bulb body 25, and then continues with a clearance diameter 26 for receiving the shaft 27 of the bulb. The plug 28 fills the bore hole over the bulb top and is secured by fusion 29 (e.g., by laser sealing) of the waveguide and plug material at the aperture 30 of the hole. In this regard, the laser is focused on the bond wire 31 at the aperture between the plug and the waveguide and traverses around the bond wire to locally melt the quartz, which rapidly re-condenses to secure the plug within the waveguide. If the fusion is continuous around the plug, a seal is formed. On the opposite surface 32, a similar laser operation is performed when the rod-shaped portion protrudes from the rod-shaped hole. The surfaces 23, 33 are then polished, if necessary, to remove any splash marks. Thus, the waveguide is formed integrally with the bulb.

It should be noted that such material sealing is only possible when both the bulb envelope and the waveguide are of quartz. When they are light-transmissive polycrystalline alumina, a glass frit is introduced at the seal and the frit melts, fixes and seals the parts.

A faraday cage can then be placed. Although the antenna and its cavity are shown as coaxial in fig. 1, in fig. 2 the cavity 33 of the present embodiment is arranged eccentrically.

Another physical structure is shown in fig. 4 and 5. The waveguide 41 has two complementary portions 42, 33. They have mating surfaces 44, 45 in which recesses 46, 47 are provided which are equivalent to the bore 22 and shaft extension 26. The bulb 48 is placed in a recess in one part and the shaft 49 is laser fixed 50 at its distal end to the recess, where the thermal stress used is expected to be minimal. The other part is added around the periphery of the joining surfaces of the two parts, so that the two parts are laser sealed 51 together. They will be polished flat so that once they are brought together, the two-part construction of the waveguide will not affect its function as a microwave resonant waveguide. Thus, the waveguide is once again integral with the bulb.

Although the above embodiments have been described as being quartz, i.e. both the bulb and the waveguide are quartz, they may be of other materials. In particular as transparent or at least translucent material or as made transparent or at least translucent material: fused silica, sapphire, polycrystalline alumina (PCA), Yttrium Aluminum Garnet (YAG), and aluminum nitride.

The invention is not intended to be limited to the details of the above-described embodiments. For example, while the figures show a waveguide that is cylindrical in shape and equal in length and diameter and an antenna cavity that is generally on the central axis of the waveguide, the length to diameter ratio may be varied so that they are short and thick or long and thin. Likewise, the antennas may be arranged eccentrically as shown in fig. 2. The antenna may be sealed, i.e. the cavity is sealed with the antenna in place, or the cavity may be opened and the antenna inserted.

The waveguide may also have other different geometries, such as cubic, and again the dimensions are chosen to be suitable for resonance. In fact, it is not necessary to drive the waveguide resonantly.

Referring to fig. 6 and 7, the light source of the master case is shown having a short, thick, circular quartz waveguide 101 of 50.8mm diameter and 35mm height. A 5mm diameter hole 103 extends centrally from the rear surface 102 into the waveguide, projecting within 5mm of the front surface 104 of the waveguide. It has a 6mm countersink (counter bore)105 extending 15 mm. In the hole 103 is positioned a 5mm diameter quartz electrodeless bulb 106, i.e. a' 2018 bulb, having a body 107 of 15mm and a stem 108 of 5mm length and 2mm diameter. A 15mm long quartz tube 109 is received in the counter bore and a rod is received in its bore 110. With the tube flush with the rear surface 102 of the waveguide, the bulb is fixed.

An aluminum ground layer 112 contacts the rear surface to secure the tube 109 and thus the bulb. An antenna 113 extends centrally and is insulated therefrom, the antenna 113 protruding into the hole 110 to supply microwaves from a not-shown driving circuit to form a resonance in the waveguide and the light-emitting plasma in the bulb.

A mesh-like metal foil 115 around the circumference 114 of the waveguide and extending from the waveguide forms a faraday cage 116 together with the ground plane. A hole 117 in the foil is centrally aligned with the end of the bulb to allow unobstructed emission of axial light from the bulb. Most of the radiated light passes through the mesh foil at the circumference 114. The clip 118 secures the back ground layer 112 and the waveguide together while connecting the back ground layer to the mesh foil. The foil on the circumference is crimped 119 to the foil on the front surface.

The light source is mounted at the focal point of a reflector 120 shown partially in fig. 7.

Turning to fig. 8, a light source of the present division is shown in which the waveguide 211 has a parabolic shape with an additional back ground layer 212. This directs the light emitted by the bulb towards the waveguide. The back ground layer has a clamp 213 at its front edge 214, the clamp 213 clamping the waveguide within the back ground layer and clamping across a wire mesh 215 in front of the waveguide such that it is clamped between the back ground layer and the waveguide via edge 216. A wire mesh completes the faraday cage of the light source. It has a similar position of the tube through its bulb.

In an alternative, not shown, the bulb is received in an open cavity in the waveguide and is held there by a wire mesh.

Claims (14)

1. A light source, comprising:

● an optically transparent waveguide of solid dielectric material having:

●, surrounding the waveguide,

● bulb cavity within the waveguide and the Faraday cage, an

● antenna recess in the waveguide and the Faraday cage, an

● a bulb having a microwave excitable fill, the bulb being received in the bulb cavity;

wherein

● A Faraday cage includes:

● a solid portion extending across the back of the lucent waveguide to a transverse extent of the lucent waveguide; and

● a clamp that clamps the solid portion and the waveguide together and connects the solid portion to the optically transparent front of the faraday cage;

● the solid portion is reflective for directing light forward;

● the lucent waveguide and the solid portion of the waveguide are complementary in shape for emitted light to focus;

●, the light-transmissive front portion of the Faraday cage includes a mesh-like metallic element or a light-transmissive conductive coating.

2. The light source of claim 1, wherein:

● the waveguide is dimensioned to allow microwave resonance with the cavity at a location of maximum field strength;

● the waveguide has a circular cross-section and is dimensioned such that the half-waves extend diametrically therein.

3. A light source as claimed in any preceding claim, wherein the cladding of the bulb and the lucent waveguide are of the same material.

4. A light source as claimed in any preceding claim, wherein the bulb cavity is open at a surface of the lucent waveguide.

5. A light source according to any one of the preceding claims, wherein said bulb cavity is closed, preferably by a plug of solid dielectric material fixed to said lucent waveguide.

6. A light source according to any preceding claim, wherein the lucent waveguide has two portions, one or both portions having a cavity formed at a common joining surface of the two portions, preferably the two portions being fixed together.

7. A light source as claimed in any preceding claim, wherein the bulb is unconstrained within the cavity.

8. A light source as claimed in any preceding claim, wherein the bulb is fixed in the cavity.

9. A light source as claimed in any preceding claim, wherein the envelope of the bulb, plug (where provided) and waveguide are of glass material and are fixed or sealed together by local fusion of the material or by local fusion of the glass feedstock material.

10. The light source of claim 4, wherein:

● holding the bulb in the cavity by a tube of dielectric material;

● the surface of the cavity open is a rear surface of the lucent waveguide and the tube is held by a portion of the Faraday cage;

● the bulb has an extension at the inner end of the tube; and

● the tube provides the antenna cavity.

11. A light source as claimed in any preceding claim, wherein the faraday cage comprises at least one aperture for locally increasing light transmission therethrough, the aperture being no greater than 1/10 of the free space wavelength of the microwaves in the crucible.

12. A light source as claimed in any preceding claim, wherein the lucent waveguide is of quartz or polycrystalline alumina or polycrystalline yttrium aluminium garnet or aluminium nitride or single crystal sapphire.

13. A light source as claimed in any preceding claim, in combination with a separate reflector to reflect light emitted from the lucent crucible in a particular direction.

14. A light source as claimed in any preceding claim in combination as a lamp with a microwave drive circuit comprising:

● a microwave source; and

● matching circuits.