Optical coupler, design method therefor, and vehicle light therewith

1. An optical coupler comprising:

at least one optical coupler unit comprising:

a single optical coupler entrance face configured to face, and receive light emitted by, at least one LED during operation; and

a single optical coupler exit face shaped as a Fresnel lens with a focal point at or behind a light emitting area of the at least one LED such that the light emitted by the at least one LED during operation is emitted out of the optical coupler exit face at right angles relative to the optical coupler exit face and configured to face a lightguide entrance face of a slab lightguide, wherein a ratio of a width of the single optical coupler exit face to a width of the single optical coupler entrance is greater than 3,

the single optical coupler entrance and exit faces being configured to refract light emitted by the at least one LED during operation.

2. The optical coupler according to claim 1 , wherein a ratio of a height of the single optical coupler exit face to a height of the single optical coupler exit face is between 1 and 2.

3. The optical coupler according to claim 1 , wherein the single optical coupler entrance face is planar.

4. The optical coupler according to claim 1 , wherein the single optical coupler entrance face is concave towards the at least one LED.

5. The optical coupler according to claim 1 , wherein the single optical coupler entrance face is at a first distance from a light emitting surface of the at least one LED.

6. The optical coupler according to claim 5 , wherein the single optical coupler exit face is at a second distance from the lightguide entrance face.

7. The optical coupler according to claim 1 , wherein a contact area of the single optical coupler exit face to the lightguide entrance face is less than 10% of a full area of the single optical coupler exit face.

8. The optical coupler according to claim 1 , further comprising:

an optical coupler central line joining central points of the single optical coupler entrance and exit faces along a longitudinal dimension of the optical coupler transverse to the single optical coupler entrance and exit faces; and

optical coupler cross sections transverse to the optical coupler central line, wherein, when moving along the optical coupler central line from the single optical coupler entrance face to the single optical coupler exit face, the optical coupler cross sections monotonously transform the single optical coupler entrance face into the single optical coupler exit face.

9. The optical coupler according to claim 1 , further comprising optical coupler side faces that each have an undulating shape and join the single optical coupler entrance and exit faces along a longitudinal dimension of the optical coupler.

10. The optical coupler according to claim 1 , wherein:

the at least one optical coupler unit comprises a plurality of optical coupler units,

the at least one LED comprises a plurality of LEDs,

each optical coupler unit coupled one LED of the plurality of LEDs to a portion of the lightguide entrance face,

the single optical coupler exit face of each of the plurality of optical coupler units being arranged beside each other in their width dimension, and

dimensions of a union of the single optical coupler exit face of each of the plurality of optical coupler units match dimensions of the lightguide entrance face.

11. A vehicle light comprising:

at least one LED;

a slab light guide;

at least one optical coupler between the at least one LED and the slab light guide, the at least one optical coupler unit comprising:

at least one optical coupler unit comprising:

a single optical coupler entrance face configured to face, and receive light emitted by, at least one LED during operation, and

a single optical coupler exit face shaped as a Fresnel lens with a focal point at or behind a light emitting area of the at least one LED such that the light emitted by the at least one LED during operation is emitted out of the optical coupler exit face at right angles relative to the optical coupler exit face and configured to face a lightguide entrance face of a slab lightguide, wherein a ratio of a width of the single optical coupler exit face to a width of the single optical coupler entrance is greater than 3,

the single optical coupler entrance and exit faces being configured to refract light emitted by the at least one LED during operation; and

a housing configured to accommodate the at least one LED, the slab light guide and the at least one optical coupler.

12. The vehicle light of claim 11 , wherein the single optical coupler entrance face is one of planar or concave towards the at least one LED.

13. The vehicle light of claim 11 , wherein:

the at least one optical coupler unit comprises a plurality of optical coupler units,

the at least one LED comprises a plurality of LEDs,

wherein each optical coupler unit couples one LED of the plurality of LEDs to a portion of the single lightguide entrance face,

the single optical coupler exit face of each of the plurality of optical coupler units being arranged beside each other in their width dimension, and

dimensions of a union of the single optical coupler exit face of each of the plurality of optical coupler units match dimensions of the lightguide entrance face.

14. A method of manufacturing an optical coupler for coupling at least one LED to a slab lightguide, the method comprising:

providing a straight optical coupler;

choosing dimensions for a single optical coupler entrance face and a single optical coupler exit face based on dimensions of at least a portion of a lightguide entrance face of the slab lightguide such that at least a ratio of a width of the single optical coupler exit face to a width of the single optical coupler entrance face is greater than 3, the single optical coupler entrance face being configured to face the at least one LED and the single optical coupler exit face being configured to face the lightguide entrance face, and the single optical coupler entrance and exit faces being configured to refract light emitted by the at least one LED during operation; and

selecting a shape for optical coupler side faces joining the single optical coupler entrance and exit faces along a longitudinal dimension of the optical coupler as an undulating shape.

15. The method according to claim 14 , wherein the optical coupler further comprises:

an optical coupler central line joining central points of the single optical coupler entrance and exit faces along a longitudinal dimension of the optical coupler transverse to the single optical coupler entrance and exit faces, and

optical coupler cross sections transverse to the coupler central line, wherein the method further comprises:

when moving along the optical coupler central line from the single optical coupler entrance face to the single optical coupler exit face, the optical coupler cross sections monotonously transforming the single optical coupler entrance face into the single optical coupler exit face.

16. The method according to claim 14 , further comprising bending the optical coupler by:

bending the optical coupler central line into a curved line without compressing and stretching the optical coupler, and,

on such bending, keeping the optical coupler cross sections transverse to the optical coupler central line.