Patent Description:
The following relates to the illumination arts, phosphor wheel arts, optical interference filter manufacturing arts, and related arts.

Some known phosphor based light sources use a yellow phosphor which is excited by a blue LED or laser. In order to create white light, additional blue light is provided and mixed with the yellow light in the right proportions in order to create white light with a desired color temperature. A known approach is to employ a yellow phosphor layer that converts only a fraction of the blue light, while the remainder of the blue light transmits through the yellow phosphor layer without conversion and thereby mixes with the converted yellow light. The thickness of the yellow phosphor layer is chosen to tune to a desired ratio of direct blue light and converted yellow light in the mixture.

<CIT>, <CIT>, <CIT>, <CIT> and <CIT> all show different variations of lighting apparatuses/illumination systems comprising phosphor conversion components. However, the present application disclose some improvements herein.

In one disclosed aspect, a white light source is disclosed, comprising a light source and a phosphor conversion component. The light source emits short wavelength light peaked at a peak wavelength of <NUM> nanometers or shorter. The phosphor conversion component includes a light conversion layer comprising a phosphor effective to convert the short wavelength light to converted light. The light conversion layer includes light passages comprising openings or passage material that does not comprise the phosphor and is light transmissive for the short wavelength light. The light conversion layer further has a thickness that is at least three times a light penetration depth of the short wavelength light in the light conversion layer. The light source is disposed respective to the phosphor conversion component so as to illuminate the light conversion layer with the emitted short wavelength light and to pass the short wavelength light through the light passages.

In some embodiments the light transmissive substrate comprises light scattering particles. In some embodiments the light transmissive substrate comprises a light transmissive plate. In some embodiments the light source emits said short wavelength light as a collimated light beam directed normal to a surface of the light transmissive plate. In some embodiments the phosphor conversion component comprises: a reflective substrate that is reflective for the short wavelength light and for the converted light; and said light conversion layer disposed on the reflective substrate; wherein the light source is disposed respective to the phosphor conversion component so as to illuminate the light conversion layer with the emitted short wavelength light and to pass the short wavelength light through the light passages and reflect from the reflective substrate back through the light passages. In some embodiments the phosphor conversion component comprises a phosphor wheel including a disk arranged to rotate about a central axis of the disk and said light conversion layer disposed on at least a periphery of the disk. In some embodiments the light passages have a lateral dimension that is less than or equal to <NUM> times the peak wavelength of the short wavelength light. In some embodiments the peak wavelength is <NUM> nanometers or shorter. In some embodiments the converted light has a peak wavelength of <NUM> nanometers or longer.

In another disclosed aspect, a phosphor conversion component comprises a substrate and a light conversion layer disposed on the substrate. The light conversion layer comprises a phosphor effective to convert short wavelength light having a peak wavelength of <NUM> nanometers or shorter to converted light. The light conversion layer includes light passages comprising openings or passage material that does not comprise the phosphor and is light transmissive for the short wavelength light. The light conversion layer further has a thickness that is at least three times a light penetration depth of the short wavelength light in the light conversion layer.

In some embodiments the substrate is a light-transmissive substrate that is light transmissive for the short wavelength light. In some embodiments the light transmissive substrate comprises light scattering particles. In some embodiments the light transmissive substrate comprises a light transmissive plate. In some embodiments the substrate is a reflective substrate that is reflective for the short wavelength light and for the converted light. In some embodiments the phosphor conversion component comprises a phosphor wheel including a disk arranged to rotate about a central axis of the disk and said light conversion layer disposed on at least a periphery of the disk. In some embodiments the light passages have a lateral dimension that is less than or equal to <NUM> times the peak wavelength of the short wavelength light. In some embodiments the converted light has a peak wavelength of <NUM> nanometers or longer.

In another disclosed aspect, a white light generation method is disclosed. Short wavelength light peaked at a peak wavelength of <NUM> nanometers or shorter is emitted. The short wavelength light is passed through at least a light conversion layer of a phosphor conversion component. The light conversion layer comprises a phosphor that converts the short wavelength light to converted light. The light conversion further has a thickness that is at least three times a light penetration depth of the short wavelength light in the light conversion layer. Furthermore, the light conversion layer has light passages comprising openings or passage material that does not comprise the phosphor and is light transmissive for the short wavelength light whereby a portion of the short wavelength light passes through the light passages without being converted to converted light. White light is output, comprising a mixture of the converted light and the portion of the short wavelength light that passes through the light passages without being converted to converted light.

In some embodiments the phosphor conversion component further includes a reflective substrate and the passing of the short wavelength light through at least the light conversion layer of the phosphor conversion component further comprises reflecting the converted light and the portion of the short wavelength light that passes through the light passages without being converted to converted light off the reflective substrate. In some embodiments the phosphor conversion component comprises a phosphor wheel and the method further comprises rotating the phosphor wheel about an axis during the emitting, passing, and outputting operations.

Known white light sources employing a blue light emitter in conjunction with a yellow phosphor have certain disadvantages. The phosphor thickness is designed to simultaneously optimize both the fraction of primary light that passes through the substrate without being converted and the fraction of primary light that is converted by the phosphor layer. This can limit flexibility of the design, as thinning the phosphor layer to increase the primary light that is passed concurrently reduces generation of the converted light; and likewise, increasing the thickness of the phosphor layer to decrease the primary light that is passed concurrently increases generation of the converted light. Furthermore, the passage of the primary light through the phosphor layer may alter characteristics of the primary light, e.g. by partial absorption of the primary light. Such absorption reduces efficiency and, if it is wavelength-dependent, changes the color content of the primary light. In particular, it is common for shorter wavelength light components to be preferentially absorbed over longer wavelength light components, which can reduce the "blueness" of the primary light. The interrelatedness of the various device parameters on the primary and converted light outputs can make it difficult to maintain lighting characteristics from one manufacturing run to the next, such as color temperature or color rendering, or to reliably manufacture white light devices with different characteristics in different runs (e.g. one run providing warm white light at <NUM> and the next providing cold white light at <NUM>).

These problems can be overcome by providing separate light sources for exciting the yellow phosphor and for mixing blue light to produce the final output white light. However, this approach requires a second short wavelength light source, or alternatively requires optics such as a beam splitter for splitting the light from a single short wavelength light source into two optical paths, thus increasing complexity and cost.

In white light sources disclosed herein, a light conversion layer comprising phosphor is provided, and is modified as disclosed herein to further have light passages comprising openings or passage material that does not comprise the phosphor and is light transmissive for the short wavelength light. In this approach, a single light source illuminates the light conversion layer with short wavelength (e.g. blue) light. The short wavelength light is converted to converted light (e.g. yellow light) by the phosphor, except at the light passages - at these passages the short wavelength light passes through so as to mix some short wavelength (e.g. blue) light with the converted (e.g. yellow) light. In a blue/yellow white light source of this design, the mixture (in appropriate proportions) of blue light passing through the light passages and yellow light converted by the phosphor creates white light.

In one manufacturing approach, a partially transparent phosphor is created by having phosphor applied to a substrate surface in such a manner that there are areas with phosphor applied and other areas (the short wavelength light passages) where there is no phosphor applied. For a given blue light source and given light conversion layer with a given phosphor and at a given thickness, the fill factor (that is, the ratio of phosphor covered area to total area) determines the blue/yellow ratio which controls the whiteness of the light and color temperature. Typically, the fill factor will be in the range of <NUM>% to <NUM>% in order to create white light with the desired color temperature. Advantageously, other properties of the device such as the spectrum of the blue light source and/or the type of phosphor can be adjusted independently to further optimize the white light characteristics. In one contemplated approach, the light conversion layer with light passages is fabricated by applying the phosphor uniformly and then etching areas off using wet chemical etching, laser ablation, or the like to remove the layer at the light passages. In the case of wet chemical etching, the pattern of light passages can be defined using photolithographic techniques.

Such a white light source may be advantageously deployed in (by way of nonlimiting illustrative example) projectors using transmissive phosphor wheels, reflective phosphor wheels, projectors using light transmissive microdisplays (e,g. LCD based), reflective microdisplays such as DLP and LCOS (reflective liquid crystal on silicon). For lighting applications the patterned light conversion layer can be applied directly to an LED or laser, or can be applied to an auxiliary substrate/external filter depending on the architecture.

In some contemplated embodiments, by choosing the size (i.e. aperture) of the short wavelength light passages through the light conversion layer, a designed amount of light diffraction is introduced into the short wavelength light passing through so as to form a desired output spatial distribution for the short wavelength light. In some embodiments, the spatial distribution of the short wavelength light is designed to be close to the spatial distribution of the yellow phosphor light (which is typically an approximately Lambertian spatial distribution). An approximately Lambertian spatial distribution for the blue light can be achieved, in some embodiments, by using sufficiently small-area apertures so as to introduce large-angle diffraction components. As a further variant, it is contemplated to form the light passages with a distribution of sizes and/or dimensions, preferably with the variously sized/dimensioned light passages interspersed over the area of the layer. In this design, the spatial distribution of the short wavelength light is effectively a weighted superposition of the spatial distributions achieved by the variously sized/dimensioned light passages, with the weights controlled by the ratios of the various sizes/dimensions. More generally, the goal in some embodiments is to produce the effect of diffusing the blue light to a desired degree which facilitates mixing with the yellow converted light. (Alternatively, this can be achieved by the addition of a downstream diffuser element).

With reference now to <FIG>, a white light source comprises a light source <NUM> emitting short wavelength light <NUM> which is peaked at a peak wavelength of <NUM> nanometers or shorter. The illustrative light source <NUM> comprises a planar substrate <NUM>, e.g. a printed circuit board (PCB), on which is disposed an array of light emitting diodes (LEDs) <NUM> which emit the short wavelength light <NUM>; however, other types of light sources emitting suitable short wavelength light may be used, e.g. a semiconductor laser, an incandescent light source, or so forth. A phosphor conversion component <NUM> includes a light conversion layer <NUM> comprising a phosphor effective to convert the short wavelength light <NUM> to converted light <NUM>. The illustrative phosphor conversion component <NUM> includes a light transmissive substrate <NUM>, e.g. a glass plate, sapphire plate, transparent plastic plate, or so forth, on which the light conversion layer <NUM> is disposed. The illustrative white light source of <FIG> has the short wavelength light <NUM> impinging on the side of the phosphor conversion component <NUM> on which the light conversion layer <NUM> is disposed. However, it is alternatively contemplated to arrange the white light source so that the short wavelength light impinges on the substrate side of the phosphor conversion component <NUM> and passes through the light-transmissive substrate <NUM> to reach the light conversion layer <NUM>. In the illustrative example of <FIG>, the phosphor conversion component <NUM> is a plate, and the light source <NUM> emits the short wavelength light <NUM> as a collimated light beam that is directed normal to a surface of the light transmissive plate.

As best seen in <FIG> and <FIG>, which show a plan view (<FIG>) and side sectional view (<FIG>) of the phosphor conversion component <NUM> of the white light source of <FIG>, the light conversion layer <NUM> includes light passages <NUM> comprising openings or passage material that does not comprise the phosphor and is light transmissive for the short wavelength light <NUM>. The light source <NUM> is disposed respective to the phosphor conversion component <NUM> so as to illuminate the light conversion layer <NUM> with the emitted short wavelength light <NUM> and to pass the short wavelength light <NUM> through the light passages <NUM>. This produces mixed light <NUM> comprising a mixture of the short wavelength light <NUM> that passes through the light passages <NUM> and the converted light <NUM>.

The light source <NUM> emits the short wavelength light <NUM> peaked at a peak wavelength of <NUM> nanometers or shorter. While the LED array <NUM> is illustrated, more generally the light source <NUM> may comprise a monochromatic laser light source emitting monochromatic light at an emission line of <NUM> nanometers or shorter, or may comprise an LED, incandescent lamp, or other polychromatic light source emitting over a visible spectrum that is peaked at a peak wavelength of <NUM> nanometers or shorter. The wavelength of <NUM> nanometers approximately corresponds to the transition from green light to yellowish light. Mixing strongly green light with phosphor emission in the yellow range (i.e. the converted light <NUM>) is likely to produce relatively poor quality white light <NUM>; hence, in some preferred embodiments the light source <NUM> emits short wavelength light peaked at a peak wavelength of <NUM> nanometers or shorter (e.g., monochromatic light at an emission line of <NUM> nanometers or shorter, or polychromatic light over a visible spectrum that is peaked at a peak wavelength of <NUM> nanometers or shorter). The wavelength of <NUM> nanometers approximately corresponds to the transition from blue light to green light; hence, employing the light source <NUM> emitting with this specified shorter wavelength characteristic provides more pure bluish light which mixes with the phosphor emission (i.e. converted light <NUM>) to produce a better quality of white light <NUM>. It should be noted that in the case of a polychromatic short wavelength light source it is contemplated for the total spectrum of the short wavelength light to comprise the aforementioned visible spectrum further extending into the near ultraviolet - such ultraviolet light is not visible to the human eye. Similarly, in the case of a monochromatic light source (e.g. a laser), the output may be at multiple lines some of which may be in the ultraviolet and hence outside of the visible range.

The converted light <NUM> is output by the phosphor of the light conversion layer <NUM> energized by the short wavelength light <NUM>. For a white light source design, the converted light <NUM> preferably has a peak wavelength of <NUM> nanometers or longer, corresponding tothe green, yellow, orange, and red visible spectral regions. In a blue/yellow design the converted light <NUM> is preferably yellowish light, e.g. in the spectral range of roughly <NUM>-<NUM> nanometers. In an alternative blue/green/red design, the converted light <NUM> may have two peaks: a first peak at roughly <NUM>-<NUM> nanometers corresponding to greenish light, and a second peak at roughly <NUM> nanometers or longer corresponding to reddish light. In some such embodiments, the phosphor of the light conversion layer <NUM> suitably includes separate green and red phosphors in proportions chosen to provide the desired green/red light ratio. These are merely illustrative examples, and the precise phosphor composition and the precise spectral composition of the short wavelength light <NUM> may be chosen to provide white light <NUM> of a desired color temperature, color rendering index (CRI), or other desired spectral and/or "whiteness" characteristics.

The light conversion layer <NUM> has a thickness t as indicated in <FIG>. The light conversion layer <NUM> is of sufficient thickness so that substantially all of the short wavelength light <NUM> that impinges on the light conversion layer <NUM> is converted to converted light <NUM>, and/or is partially absorbed by the light conversion layer <NUM>. In this case, substantially no short wavelength light passes through the light conversion layer <NUM>. To quantify this, the light penetration depth δ of the light conversion layer <NUM> is defined as the depth at which the initial light intensity of the short wavelength light <NUM> decreases to <NUM>/e ≈ <NUM>,<NUM> of its initial value. This definition of the light penetration depth δ is a conventional definition constructed on the basis of a conventional model of light absorption in which the light intensity at a distance x into the layer is given as I = I<NUM>eαx where δ = <NUM>/α. Using these conventions, if the light conversion layer <NUM> has a thickness of 3δ then it attenuates the initial short wavelength light <NUM> to under <NUM>% of its initial intensity. This is deemed to constitute substantially all of the short wavelength light <NUM> that impinges on the light conversion layer <NUM> being converted (or absorbed) by the light conversion layer <NUM>. According to the claims, the light conversion layer <NUM> has a thickness of at least 3δ, and accordingly the blending of the short wavelength light <NUM> and the converted light <NUM> is controlled (almost) entirely by a ratio R of the total area of the light passages <NUM> compared with the total area of the light conversion layer <NUM> (including the light passages <NUM>). To take a limiting case, R = <NUM> corresponds to having no light passages <NUM>; while, R = <NUM> corresponds to the total area of the light passages <NUM> being one-half of the total area of the light conversion layer <NUM>. It will be appreciated that as the R increases this corresponds to a greater fraction of the short wavelength light <NUM> passing through the light passages <NUM> and a smaller fraction of that light being converted to converted light <NUM>. Advantageously, the ratio R is entirely controlled by the geometry of the array of light passages <NUM> (their number or density, and their size) which can be precisely controlled by suitable techniques such as photolithographic wet or dry etching.

To obtain homogenous white light <NUM>, the short wavelength light <NUM> that passes through the light passages <NUM> and the converted light <NUM> should be well-mixed (i.e. well-blended). Various approaches can be employed to promote blending or mixing of the short wavelength light <NUM> that passes through the light passages <NUM> and the converted light <NUM>. In one approach, the light passages <NUM> are relatively small and closely spaced. The light passages <NUM> may optionally have lateral size (e.g. diameter in the illustrative case of light passages <NUM> with circular cross-section) that is small enough to produce diffraction of the short wavelength light <NUM> passing through the light passages <NUM> In some embodiments, the light passages <NUM> have a lateral dimension that is less than or equal to <NUM> times the peak wavelength to obtain stronger and/or higher angle diffraction. (In other embodiments, larger-diameter light passages are employed such that no diffraction is obtained, or insufficient diffraction is obtained to provide the desired spatial distribution, and a downstream diffuser or other added optics is provided to shape the light distribution). Depending upon the formation process for forming the light passages <NUM>, they may have roughened sidewalls that further promote light scattering and consequent blending. As another option, the light-transmissive substrate <NUM> can include light scattering particles (e.g., Al<NUM>O<NUM> particles dispersed in a glass or plastic substrate), have a roughened backside surface, have a backside surface coated with a light-scattering layer, or otherwise be configured as a light diffuser plate. This approach is typically most effective with the orientation shown in <FIG> in which the short wavelength light <NUM> impinges on the light conversion layer <NUM>, so that the white light <NUM> then passes through the light-diffusing substrate <NUM>. As yet another contemplated approach, the light passages <NUM> may be filled with passage material that does not comprise the phosphor and is light transmissive for the short wavelength light <NUM>, and which passage material also includes light scattering particles (e.g., scattering by reflection and/or refractive effects). For example, the passage material may be a transparent epoxy filler in which reflective Al<NUM>O<NUM> particles are dispersed so as to scatter the short wavelength light <NUM> passing through the epoxy-filled light passages <NUM>.

With reference to <FIG>, another embodiment is described, in which a white light source <NUM> emitting the short wavelength light <NUM> peaked at a peak wavelength of <NUM> nanometers or shorter (and in some embodiments is peaked at a peak wavelength of <NUM> nanometers or shorter) is in the form of a laser <NUM>, and a phosphor conversion component <NUM> is in the form of a rotating reflective phosphor wheel <NUM> having the light conversion layer <NUM> disposed on a reflective substrate <NUM> that is reflective for the short wavelength light <NUM> and for the converted light. In the reflective configuration, the light source <NUM> is disposed respective to the phosphor conversion component <NUM> so as to illuminate the light conversion layer <NUM> with the emitted short wavelength light <NUM> and to pass the short wavelength light <NUM> through the light passages <NUM> and reflect from the reflective substrate <NUM> back through the light passages <NUM>. The illustrative phosphor conversion component <NUM> comprises a phosphor wheel <NUM> including a disk <NUM> arranged to rotate about a central axis <NUM> of the disk, and the light conversion layer <NUM> is disposed on at least a portion of the disk, namely in an outer annular region of the disk <NUM> in the illustrative example of <FIG>. The metal disk or "wheel" <NUM> may, by way of nonlimiting illustration, be made of copper, a copper alloy, an aluminum alloy, silver-coated glass, or so forth. The light conversion layer <NUM> is attached to or coated on an outer perimeter of the wheel <NUM>, that is, disposed at or near the outer rim of the wheel <NUM>. In operation the metal wheel <NUM> is rotated about the central axis <NUM>, for example, by connecting a motor shaft of a motor (not shown) to the central axis <NUM> and operating the motor to rotate the phosphor wheel <NUM> in an illustrated clockwise direction CW (counterclockwise rotation is also contemplated). Simultaneously with the rotation, the laser <NUM> applies the short wavelength light <NUM> to a local region - this is diagrammatically indicated in <FIG> by the laser <NUM> applying an illustrative pump laser beam spot L. As the metal wheel <NUM> rotates the portion of the annular light conversion layer <NUM> located at the spot L changes, so as to limit (or spread) the generated heat. This can allow for higher power operation. <FIG> diagrammatically shows a side sectional view. In the illustrative optical configuration the short wavelength light <NUM> is applied at an angle and the resulting white light <NUM> is emitted at a reflective angle as seen in <FIG>. Other configurations are contemplated, e.g. using mirrors, lenses, and/or other optical components to configure the light paths. Due to the angled light incidence and reflection the thickness of the light conversion layer <NUM> should be sufficiently thin to permit short wavelength light <NUM> that passes through the light passages <NUM> to reflect back through the (same) passages. In some embodiments it is contemplated to facilitate this by configuring the light passages <NUM> as elongated slots or slits in the light conversion layer <NUM>, with the long direction of the slots or slits aligned with the angle of incidence/reflection.

The illustrative phosphor conversion element <NUM> formed as a phosphor wheel <NUM> employs a reflective configuration with reflective substrate <NUM>. However, it will be appreciated that a light transmissive phosphor wheel may be similarly constructed by replacing the reflective substrate <NUM> with the light transmissive substrate <NUM> of the embodiment of <FIG>. This alternative light transmissive phosphor wheel embodiment has an advantage in that the short wavelength light <NUM> can be applied normal to the surface of the phosphor wheel so that the white light <NUM> is transmitted light that passes through the phosphor wheel (with some fraction being converted to converted light <NUM> as described with reference to <FIG>).

In addition to, or in place of, heat load spreading by way of rotation in the case of the rotating phosphor wheel <NUM> of <FIG>, other cooling mechanisms may be provided, which may also be applicable for the static embodiments of <FIG>. For example, the substrate <NUM>, <NUM> may be made of a thermally conductive material. In the case of a reflective substrate, a thermally conductive metal plate may be used to remove or spread the heat. For a light-transmissive substrate, a thermally conducting transparent polymer material is contemplated to improve heat removal or spreading. Additionally or alternatively, other mechanisms for cooling the light conversion layer <NUM> may be provided, such as liquid cooling, thermoelectric cooling (applicable for stationary or rotating phosphors for high fluence applications), addition of a dedicated heat sink optionally with forced air cooling, or so forth. Depending upon the application, the light source <NUM>, <NUM> could be pulsed in time to provide cooling intervals, with the pulsing being at a frequency and duty cycle chosen to be amenable for the particular application.

Claim 1:
A phosphor conversion component (<NUM>;<NUM>) comprising:
a light conversion layer (<NUM>) comprising a phosphor effective to convert short wavelength light (<NUM>) having a peak wavelength of <NUM> nanometers or shorter to converted light (<NUM>);
wherein the light conversion layer (<NUM>) includes light passages (<NUM>) comprising openings or passage material that does not comprise the phosphor and is light transmissive for the short wavelength light (<NUM>);
characterized in that
the light conversion layer (<NUM>) has a thickness that is at least three times a light penetration depth (<NUM>) of the short wavelength light in the light conversion layer.