Light source

1. A light source arranged to output light at a first wavelength, the light source comprising:

a luminescent concentrator having a slab-shaped geometry with a width to thickness ratio of greater than 7:1, the luminescent concentrator comprising:

an input port arranged to receive light and define a first area;

an output port arranged to transmit light and define a second area which is smaller than the first area;

surfaces arranged to direct light inside the luminescent concentrator to the output port;

wherein the luminescent concentrator further comprises lumophores arranged to receive light at a second wavelength and emit light at the first wavelength; and

a pump light supply coupled to the input port and arranged to illuminate the input port with light at the second wavelength.

2. The light source as claimed in claim 1 wherein the luminescent concentrator has a length to width ratio of greater than 10:1.

3. The light source as claimed in claim 1 wherein the luminescent concentrator has a thickness of less than 1 millimeter.

4. The light source as claimed in claim 1 wherein the luminescent concentrator has a width of less than 20 millimeters.

5. The light source as claimed in claim 1 wherein the luminescent concentrator has a length of less than 5 meters.

6. The light source as claimed in claim 1 wherein the emitted light at the second wavelength has a maximum luminance of less than 100 watts per square millimeter per steradian.

7. The light source as claimed in claim 1 wherein the lumophore is a fluorophore or a phosphor.

8. The light source as claimed in claim 1 wherein the luminescent concentrator comprises Cerium-doped YAG.

9. The light source as claimed in claim 1 wherein the light supply is a planar LED array.

10. A luminescent concentrator system comprising:

the light source of claim 1 ; and

an optical coupler comprising:

a first port arranged to couple with an output port of the luminescent concentrator and define a first area;

a second port defining a second area having an aspect ratio different to the first area; and

a substantially adiabatic taper arranged to guide light from the first port to the second port.

11. The luminescent concentrator system as claimed in claim 10 wherein the aspect ratio of the second area is less than the aspect ratio of the first area.

12. The luminescent concentrator system as claimed in claim 10 having a fishtail shape.

13. The luminescent concentrator system as claimed in claim 10 arranged such that light is guided along the substantially adiabatic taper by internal reflection.

14. The luminescent concentrator system as claimed in claim 10 wherein the optical coupler is passive.

15. A luminescent concentrator system comprising:

a light source of claim 1 and further comprising:

an optical coupler having:

a first port arranged to couple with the output port of the luminescent concentrator, wherein the first port defines a first area with a first aspect ratio;

a second port that defines a second area having a second aspect ratio that is different than the first aspect ratio; and

an adiabatic taper arranged to guide the light from the first port to the second port.

16. A method of processing light, the method comprising the following steps:

receiving the light at a first wavelength with a luminescent concentrator having a slab-shaped geometry with a width to thickness ratio of greater than 7:1 and a first port that defines a first area through which the light is received;

converting the light to a second wavelength; and

directing the light at the second wavelength to a second port of the luminescent concentrator that defines a second area which is smaller than the first area;

receiving the light at the second wavelength from the second port with an optical coupler having a longitudinal adiabatic taper and a third port; and

directing the light at the second wavelength using the longitudinal adiabatic taper to the third port that has an aspect ratio that is different than the aspect ratio of the second port.

17. The method as claimed in claim 16 wherein the first wavelength is in the range 450 to 495 nanometers and the second wavelength is in the range 570 to 590 nanometers.

18. The method as claimed in claim 16 wherein the step of converting the light to a second wavelength is performed by a fluorophore.