WO2009016586A1

WO2009016586A1 - Tir collimator with improved uniformity

Info

Publication number: WO2009016586A1
Application number: PCT/IB2008/053035
Authority: WO
Inventors: Elvira J. M. Paulussen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-08-02
Filing date: 2008-07-29
Publication date: 2009-02-05
Also published as: TW200925511A

Abstract

A collimator is presented. The collimator comprises a first portion (209) for collimating a first part of the light into a first light beam and a second portion (211) for collimating a second part of the light into a second light beam, wherein the intensity distribution of the first light beam along a centre line perpendicular to the direction of propagation of said first light beam comprises two spaced apart intensity peaks, and the intensity distribution of the 5 second light beam along a centre line perpendicular to the direction of propagation of said secondlight beam comprises one intensity peak. Embodiments comprising a paraboloidal outer reflective portion and a torus lens are disclosed.

Description

TIR collimator with improved uniformity

FIELD OF THE INVENTION

The present invention relates to a collimator for collimating incoming light comprising a first portion for collimating a first part of the light into a first light beam and a second portion for collimating a second part of the light into a second light beam.

TECHNICAL BACKGROUND

Compound parabolic concentrators (CPCs) are well known as collimators in lighting applications where e.g. light emitting diodes are used as light sources. Such components can either be hollow or solid. A hollow CPC has a reflective coating, whilst a solid CPC can have a reflective coating or be based on total internal reflection. A CPC has a small input end where light from a LED is introduced, and a large output end where collimated light exits the CPC.

To achieve a high degree of collimation, the CPC has to be considerably long. To reduce the total length, the CPC can be replaced by a shorter collimator, which has a larger output angle, and a lens for providing additional collimation. The total combination

(collimator + lens) will be much shorter compared to a single CPC with the same collimation angle.

However, such combination of collimator and lens result in a less uniform light intensity distribution compared to conventional CPCs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvement of the above techniques and prior art. More particularly, it is an object of the present invention to provide a small collimator resulting in an improved light intensity distribution. The above objective is provided according to a first aspect of the invention by a collimator for collimation of incoming light, comprising a first portion configured such that it is capable of collimating a first part of the light into a first light beam and a second portion configured such that it is capable of collimating a second part of the light into a second light beam, wherein the intensity distribution of the first light beam along a centre line perpendicular to the direction of propagation of said first light beam comprises two spaced apart intensity peaks, and the intensity distribution of the second light beam along a centre line perpendicular to the direction of propagation of said second light beam comprises one intensity peak. The collimator is advantageous in that two different portions can be individually adjusted in order to provide a more uniform light intensity distribution.

The first and second portion may be configured such that the first light beam and the second light beam are superimposed so as to form a single, uniform collimated intensity distribution.

The first and second portion may be configured such that the first light beam is centred with respect to the optical axis of said collimator, and the first and second portion may be configured such that the second light beam is centred with respect to the optical axis of said collimator, which is advantageous in that the collimated light is aligned with the collimator.

The first and second portion may be configured such that the two spaced apart intensity peaks of the intensity distribution of the first light beam are symmetrical with respect to the optical axis of said collimator, and such that the intensity peak of the intensity distribution of the second light beam is symmetrical with respect to the optical axis of said collimator which is advantageous in that the collimated light is symmetrically aligned with the collimator. The collimator may further comprise an exit window for mounting external optical components. Thus, the collimator may be easily integrated in more complex arrangements.

One of said first portion or second portion may be an outer reflective portion and the other of said first portion or second portion may be an inner refractive portion, which is advantageous in that the collimator is a compact component.

The reflective portion may reflect light under total internal reflection, which is advantageous in that no losses will occur due to reflection.

The refractive portion may comprise a lens pair, which is advantageous in that the size of the collimator is reduced. The refractive portion may comprise aspheric lenses, which is advantageous in that optical aberrations are reduced.

The reflective portion may comprise a paraboloid shape, which is advantageous in that light may be reflected efficient. The refractive portion may comprise a torus lens, which is advantageous in that a complex beam profile may be formed.

According to a second aspect of the invention, a lighting device is provided comprising a light source and a collimator according to the first aspect of the invention. The advantages of the first aspect of the invention are also applicable for this second aspect of the invention.

Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

Fig. 1 shows a basic setup of a collimator according to the present invention and a light source.

Fig. 2 is a sectional view of a collimator according to a first embodiment of the invention.

Fig. 3 is a diagram showing the intensity distributions of the first light beam and the second light beam. Fig. 4 shows a simulated example of a uniform light intensity distribution formed by the intensity distributions of the first light beam and the second light beam.

Fig. 5 is a sectional view of a collimator according to a second embodiment of the invention.

Fig. 6 shows a lighting device having a collimator according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 shows a collimator 1 having a light entry side 3 and a light exit side 5. The collimator is centred along its optical axis Z. A small light source, e.g. a light emitting diode (LED) 7 is positioned adjacent to the light entry side 3. The LED 7 emits divergent light towards the light entry side 3 of the collimator 1, and the light is collimated by the collimator 1 and extracted out from the light exit side 5.

As shown in fig. 2, a collimator 201 has an outer reflective portion 209 and an inner refractive portion 211. Both portions extends from a light entry side 203 to a light exit side 205. The reflective portion 209 and the refractive portion 211 are arranged symmetrically around the optical axis Z. The shape of the reflective portion 209 is described by a portion of a parabola rotated around the optical axis Z. The reflective portion 209 extends from a starting point T on the optical axis Z to an end point E, and the shape can mathematically be described by fiy) = ay² + by + c , T ≤ f(y) ≤ E , where y is the height of the collimator 201 measured from the optical axis Z and a, b, c are constants.

The refractive portion 211 comprises one lens 213 arranged at the light entry side 203, and one lens 215 arranged at the light exit side 205.

The light emitted from a LED 207 is incident on both the reflective portion 209 and the refractive portion 211. The reflective portion 209 collimates a first portion of light into a first light beam by total internal reflection, and the refractive portion 211 collimates a second portion of light into a second light beam by refraction. The first light beam and the second light beam have different light intensity distributions, and the light intensity distribution of all light collimated by the collimator 201 is a superposition of the first light beam and the second light beam.

In fig. 3, two such different light intensity distributions 17, 23 are shown. One light intensity distribution 17 along a centre line perpendicular to the direction of propagation comprises two spaced apart intensity peaks 19, 21. The intensity peaks 19, 21 are symmetrical with respect to the optical axis Z of said collimator 201 of fig. 2, such that the corresponding light beam has a hole in its centre. The other light intensity distribution 23 along a centre line perpendicular to the direction of propagation comprises one intensity peak 25. The intensity peak 25 is symmetrical with respect to the optical axis Z of said collimator 201, such that the corresponding light beam fills the hole of the other light beam.

In a first embodiment, as shown in fig. 2, the reflective portion 209 is adjusted to collimate the light beam having two peaks 19, 21 in the intensity distribution. The refractive portion is adjusted to collimate the light beam having one single peak 25 in the intensity distribution. In order to form a light beam having two peaks 19, 21 in the intensity distribution, the shape of the parabola is shifted. Keeping the starting point T and the end point E the same, the constant c is changed to instead be c + Ac. For example, having /O) = ay² + by + c and a = 1.3169, b = -8.6887, and c = 41.501, the reflective portion 9 provides a light intensity distribution comprising one centre aligned peak. Having c instead set to c + Ac, and Ac = 0.2 enough shift is achieved to create a hole in the centre of the light distribution. To achieve a more uniform total light intensity distribution of the collimated light, the hole in the centre is filled by the refractive part 211. In this embodiment, the refractive part 211 is designed as two aspheric lenses 213, 215.

In fig. 4, a graphical illustration of simulations of the first embodiment is shown. The reflective portion 209 provides a collimated light beam. In Cl, the corresponding intensity distribution is shown, taken along a centre line perpendicular to the direction of propagation. The refractive portion 211 provides a collimated light beam profile with an intensity distribution as shown in chart C2. The two light beams are superimposed to form a resulting uniform collimated light beam, having an intensity distribution as shown in chart C3. The full width of the half maximum value (FWHM) fl of the gap between the two peaks in the intensity distribution shown in Cl is equal (or close to equal) to the FWHM value f2 of the peak in the intensity distribution shown in C2.

In another embodiment, the intensity distribution of two spaced apart peaks 19, 21 is achieved by displacing the light source 207 with relation to the collimator. In this embodiment, the LED 207 is placed on the optical axis of the collimator but farther from the collimator 201.

Fig. 5 shows a further embodiment, wherein the reflective portion 309 is adjusted to collimate the light beam so that the corresponding intensity distribution 23 has one single peak 25. The refractive portion 311 is adjusted to collimate the light beam so that the corresponding intensity distribution 17 has two peaks 19, 21. The shape of the reflective portion 309 is therefore changed so that only one intensity peak 25 is provided. To achieve a more uniform total light intensity distribution of the collimated light, the refractive portion 311 provides a hole in the centre of the intensity distribution 17 that is filled by the light beam of the reflective portion 309. In this embodiment, the refractive part 311 is designed as a torus lens 327. The torus lens 327 is rotated around the optical axis Z of the collimator 301 and faces the light exit side 305. The refractive portion has also a flat cone angle 329 facing the light entry side 303. However, this could also be a torus lens, a spherical lens or an aspherical lens. The two light beams, corresponding to the reflective portion 309 and the refractive portion 311, are superimposed to form a resulting uniform collimated light beam. Again referring to fig. 4, the full width of the half maximum value (FWHM) fl of the gap between the two peaks in the intensity distribution shown in Cl is equal (or close to equal) to the FWHM value f2 of the peak in the intensity distribution shown in C2.

In a further embodiment, the refractive portion 311 is adjusted in order to provide two intensity peaks 19, 21, e.g. by using a torus lens 327. The shape of the parabola of the reflective portion 309 is shifted by changing the constant c to instead be c - Ac . The shape of the intensity peak resulting from the reflective portion 309 will then comprise a narrow peak superposed on a broader peak. Thus, the intensity peak comprises a saddle point on each side of the maximum intensity value.

Returning to fig. 1, the exit side 5 of the collimator 1 is flat and can be used to mount an external optical component (not shown). The external component can e.g. be a liquid crystal scatterer in order to enable active beam width control.

In fig. 6, a lighting device 90 is shown. The lighting device 90 has a LED light source 7, connected to a control unit 94 for supplying power to the light source 7. The lighting device has also a collimator 1, 201, 301 for collimating the light emitted from the LED 7.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

CLAIMS:

1. A collimator for collimation of incoming light, comprising a first portion (209, 309) configured such that it is capable of collimating a first part of the light into a first light beam and a second portion (211, 311) configured such that it is capable of collimating a second part of the light into a second light beam, wherein - the intensity distribution of the first light beam along a centre line perpendicular to the direction of propagation of said first light beam comprises two spaced apart intensity peaks (19, 21), and the intensity distribution of the second light beam along a centre line perpendicular to the direction of propagation of said second light beam comprises one intensity peak (25).

2. A collimator according to claim 1, wherein the first and second portion (209, 309, 211, 311) are configured such that the first light beam and the second light beam are superimposed so as to form a single, uniform collimated intensity distribution.

3. A collimator according to any one of claims 1 or 2, wherein the first and second portion (209, 309, 211, 311) are configured such that the first light beam is centred with respect to the optical axis (Z) of said collimator.

4. A collimator according to any one of claims 1-3, wherein the first and second portion (209, 309 211, 311) are configured such that the second light beam is centred with respect to the optical axis (Z) of said collimator.

5. A collimator according to any one of claims 1-4, wherein the first and second portion (209, 309, 211, 311) are configured such that the two spaced apart intensity peaks

(19, 21) of the intensity distribution of the first light beam are symmetrical with respect to the optical axis (Z) of said collimator.

6. A collimator according to any one of claims 1-5, wherein the first and second portion (209, 309, 211, 311) are configured such that the intensity peak (25) of the intensity distribution of the second light beam is symmetrical with respect to the optical axis (Z) of said collimator.

7. A collimator according to any one of claims 1-6, wherein the collimator (201, 301) further comprises an exit window (5, 205, 305) for mounting external optical components.

8. A collimator according to any one of claims 1-7, wherein one of said first portion or second portion (209, 309, 211, 311) is an outer reflective portion (209, 309) and the other of said first portion or second portion is an inner refractive portion (211, 311).

9. A collimator according to claim 8, wherein the reflective portion (209, 309) reflects light under total internal reflection.

10. A collimator according to any one of claims 8-9, wherein the refractive portion (211, 311) comprises at least one lens.

11. A collimator according to any one of claims 8-10, wherein the refractive portion (211, 311) comprises at least one aspheric lens.

12. A collimator according to any one of claims 8-11, wherein the reflective portion (209, 309) comprises a paraboloid shape.

13. A collimator according to any one of claims 8-12, wherein the refractive portion (211, 311) comprises a torus lens.

14. A lighting device comprising a light source (7) and a collimator (1) according to any of claims 1-13.