Laser-based light source

1. A laser-based light source comprising at least one laser, at least one optical fiber, at least one conversion device and at least one detector, wherein the at least one laser is adapted to emit laser light with a laser peak emission wavelength, wherein the at least one optical fiber is adapted to guide the laser light such that the laser light is received at a first surface of the at least one conversion device, wherein the conversion device is adapted to convert at least a part of the laser light to converted light, wherein a peak emission wavelength of the converted light is in a longer wavelength range than the laser peak emission wavelength, wherein the at least one optical fiber is further adapted to receive from the conversion device and to guide back in the direction of the at least one laser a part of the converted light, and wherein the detector is arranged to detect at least a part of the back guided converted light.

2. The laser-based light source according to claim 1 , wherein the at least one optical fiber comprises at least a first light guiding structure with a first numerical aperture and at least a second light guiding structure with a second numerical aperture with respect to an optical axis of the at least one optical fiber, and wherein the detector is arranged to receive the part of the back guided converted light which is received by the at least one optical fiber from the conversion device at an angle with respect to the optical axis which is bigger than a first boundary angle with respect to the optical axis, wherein the first boundary angle is defined by the smaller of the first numerical aperture and the second numerical aperture.

3. The laser-based light source according to claim 2 , wherein the detector is arranged to receive the part of the back guided converted light which is received by the at least one optical fiber from the conversion device at an angle with respect to the optical axis which is bigger than a second boundary angle with respect to the optical axis, wherein the second boundary angle is defined by the bigger of the first numerical aperture and the second numerical aperture.

4. The laser-based light source according to claim 2 , wherein the at least one optical fiber is a double cladded optical fiber, wherein the first light guiding structure is a core of the double cladded optical fiber, wherein the second light guiding structure is an inner cladding of the double cladded optical fiber and wherein the double cladded optical fiber further comprises an outer cladding.

5. The laser-based light source according to claim 4 , wherein a first refractive index of the core is bigger than a second refractive index of the inner cladding, and wherein the second refractive index of the inner cladding is bigger than a third refractive index of the outer cladding.

6. The laser-based light source according to claim 5 , wherein the first numerical aperture of the core is smaller than the second numerical aperture of the inner cladding.

7. The laser-based light source according to claim 6 , wherein the laser-based light source is arranged such that the laser light is received by the core within a first range of angles smaller than the first boundary angle defined by the first numerical aperture such that the laser light is guided to the conversion device within the core, and wherein the laser-based light source is arranged such that a part of the converted light is received by the core or the inner cladding within a second range of angles bigger than the first boundary angle such that this part of the converted light is back guided to the detector within the core and the inner cladding, and wherein the detector is arranged to receive this part of the back guided converted light at an angle with respect to the optical axis which is bigger than the first boundary angle.

8. The laser-based light source according to claim 7 , wherein the laser-based light source is arranged such that a part of the converted light is received by the core or the inner cladding within a third range of angles such that this part of the converted light is back guided to the detector within the core and the inner cladding, wherein the third range of angles is bigger than a second boundary angle defined by the second numerical aperture and wherein the detector is arranged to receive this part of the back guided converted light at an angle with respect to the optical axis which is bigger than the second boundary angle and smaller than a maximum angle defined by the first refractive index of the core and the third refractive index of the outer cladding.

9. The laser-based light source according to claim 7 , wherein the laser-based light source comprises a first optical device and a second optical device, wherein the first optical device is arranged to focus the laser light to the core such that the laser light is received by the core within the first range of angles, and wherein the second optical device is arranged such that at least a part of the converted light is focused to the core or the inner cladding such that this part of the converted light is received by the core or the inner cladding at an angle which is bigger than a second boundary angle defined by the second numerical aperture.

10. The laser-based light source according to claim 5 , wherein the first numerical aperture of the core is bigger than the second numerical aperture of the inner cladding.

11. The laser-based light source according to claim 1 , wherein the laser-based light source comprises at least one controller arranged to receive detector signals from the detector, and wherein the at least one controller is arranged to provide control signals to control the at least one laser based on the received detector signals.

12. The laser-based light source according to claim 11 , wherein the at least one controller being arranged to switch off the at least one laser if an intensity of the back guided converted light measured by the detector is below a predetermined threshold value.

13. The laser-based light source according to claim 5 , wherein the inner cladding is further arranged such that laser light reflected at the first surface of the conversion device, but not the converted light, is absorbed in order to reduce the intensity of back guided reflected laser light received by the core or the inner cladding at bigger angles than the first boundary angle.

14. A vehicle headlight comprising at least one laser-based light source according to claim 1 .

15. A lighting system comprising at least one vehicle headlight according to claim 14 and at least one light emission control device, wherein the light emission control device is adapted to submit control signals to the at least one vehicle headlight.