Supercontinuum light source, a system and a method of measuring

Patent metadata

Field	Value
Publication number	US-9504374-B2
Application number	US-201314404748-A
Country	US
Kind code	B2
Filing date	May 30, 2013
Priority date	Jun 1, 2012
Publication date	Nov 29, 2016
Grant date	Nov 29, 2016

Abstract

A supercontinuum light source comprising an intermediate supercontinuum light source and a single mode coupling unit, an optical measurement system comprising such light source, as well as a method of measuring are described. The supercontinuum light source comprises a pulse frequency multiplier to increase the repetition rate and the single mode coupling unit is arranged to dampen and shape the spectrum from the intermediate supercontinuum light source to allow measurements with a reduced noise floor.

First claim

The invention claimed is:

1. An optical measurement system suitable for measuring at least one parameter of an object, the system comprising a supercontinuum light source and a detector for detecting light from said object,
said supercontinuum light source having a light source output and comprising an intermediate supercontinuum light source and a coupling unit, wherein said intermediate supercontinuum light source comprises:
a. a seed laser arranged to provide seed pulses with a pulse frequency F seed ,
b. a pulse frequency multiplier (PFM) arranged to multiply the seed pulses and convert F seed to pump pulses with a pulse frequency F pump where F pump is larger than F seed and F pump is at least about 150 MHz;
c. a non-linear element arranged to receive said pump pulses and convert said pump pulses to a supercontinuum light provided as an output of said non-linear element and having a supercontinuum spectrum spanning at least from about λ 1 to about λ 2 where λ 1 −λ 2 >about 500 nm,

wherein the output from the non-linear element is coupled to the coupling unit to provide an output from coupling unit, wherein the light source output comprises the output from the coupling unit, wherein
said supercontinuum light source being arranged to illuminate the object to be measured with at least part of an output of said coupling unit, said detector being arranged to receive reflected light from said object to be measured, wherein said detector has an integration time of at least about 1/F pump .

2. The optical measurement system according to claim 1 , wherein said coupling unit is arranged to dampen and/or shape said supercontinuum spectrum from said non-linear element.

3. The optical measurement system according to claim 2 , wherein said coupling unit is arranged to receive said supercontinuum light and spectrally shape it so that the output spectrum from said coupling unit is spanning from λ 3 to λ 4 , where λ 3 −λ 4 >0, λ 1 ≧λ 3 and λ 2 ≦λ 4 .

4. The optical measurement system according to claim 3 , where λ 3 −λ 4 is larger than about 100 nm.

5. The optical measurement system according to claim 3 , where λ 4 is smaller than about 1000 nm.

6. The optical measurement system according to claim 3 , where λ 3 is larger than about 1070 nm.

7. The system according to claim 3 , wherein the spectrally shaped output spectrum output from the coupling unit is different from the spectrum in the wavelength range from λ 3 to λ 4 from the intermediate supercontinuum source.

8. The optical measurement system according to claim 2 , where said coupling unit comprises at least one of the following in order to carry out said dampening:
i) misalignment or mismatch of the output from the non-linear element to the coupling unit;
ii) splice loss at the input to and/or output from the coupling unit; or
iii) a broadband attenuation filter, such as a neutral density filter or a broadband beam splitter.

9. The optical measurement system according to claim 1 , wherein said coupling unit comprises at least one of the following: a prism, a low-pass optical filter, a high-pass optical filter, a bandpass optical filter, and an optical fiber.

10. The optical measurement system according to claim 9 , wherein said coupling unit is arranged to shape the spectrum from the intermediate supercontinuum light source into a Gaussian spectrum, a double peak spectrum or a flat top spectrum.

11. The optical measurement system according to claim 9 , wherein the coupling unit comprises an optical fiber where the optical fiber is a single mode fiber.

12. The optical measurement system according to claim 1 , wherein the coupling unit comprises:
an input for coupling to the non-linear element;
a dichroic element at the input of the coupling unit, said dichroic element being arranged to transmit wavelengths below a threshold wavelength λ 5 , wherein λ 5 >λ 3 ;
at least one of the following: a prism, a low-pass optical filter, a high-pass optical filter or a bandpass optical filter; and
an optical fiber, the output of which is the output from the coupling unit.

13. The optical measurement system according to claim 12 , wherein said dichroic element is an optical fiber, said optical fiber being a step index fiber or a micro-structured fiber comprising micro-structures in the form of air or low-index glass material.

14. The optical measurement system according to claim 12 , wherein the coupling unit is a single mode coupling unit and the coupling unit comprises an optical fiber where the optical fiber is a single mode fiber.

15. The optical measurement system according to claim 1 , wherein the total optical power at the output from said coupling unit is less than about 100 mW.

16. The optical measurement system of claim 1 , wherein said seed laser is arranged to provide seed pulses with pulse duration t seed , said pulse duration t seed being longer than about 0.1 ps.

17. The optical measurement system according to claim 1 , wherein said seed laser is arranged to provide seed pulses with pulse duration t seed , wherein said pulse duration t seed is shorter than about 1 μs.

18. The optical measurement system according to claim 1 , wherein said non-linear element is an optical fiber.

19. The optical measurement system according to claim 1 , wherein said intermediate supercontinuum light source comprises a pulse compressor, such as a PBG fiber, said pulse compressor being arranged to receive the pulses from said pulse frequency multiplier (PFM) and to output time-compressed pulses to said non-linear element.

20. The optical measurement system according to claim 1 , wherein said intermediate supercontinuum light source is an incoherent light source.

21. The optical measurement system according to claim 1 , wherein the major part, such as at least about 90%, of all of the output of said coupling unit is arranged to illuminate the object.

22. The optical measurement system of claim 21 , wherein said system comprises said object, said object being a part of a human or animal body.

23. The optical measurement system according to claim 21 , wherein the detector has an integration time being longer than 50/F pump .

24. The optical measurement system according to claim 21 , wherein said measuring system is a reflection mode measurement system arranged to measure light reflected from said object, based on white light interferometry.

25. A method of measuring at least one parameter of an object to be measured, the method comprising:
a. Providing an optical measurement system of claim 1 ;
b. Illuminating the object to be measured with at least part of an output of said coupling unit, and
c. detecting light from said object by a detector.

26. The method according to claim 25 , wherein said object is a part of a human or animal body.

27. The method according to claim 25 , wherein said method is performed in connection with treatment to correct refractive eye corrections.

28. The method according to claim 25 , wherein said method comprises measuring the boundaries of the Bowman layer inside a human eye.

29. The optical measurement system according to claim 1 , wherein the coupling unit is a single mode coupling unit.

30. The method according to claim 25 , wherein the coupling unit is a single mode coupling unit.

31. An optical measurement sys

Assignees

• Nkt Photonics As

Inventors

• Thomsen Carsten L
• Andersen Thomas Vestergaard
• Feuchter Thomas

Classifications

• H01S5/0092

  for nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity · CPC title

• H01S5/0657

  Mode locking, i.e. generation of pulses at a frequency corresponding to a roundtrip in the cavity · CPC title

• G02F1/353

  Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams · CPC title

• G02F1/365

  in an optical waveguide structure (G02F1/377, {G02F1/395} take precedence) · CPC title

• A61B3/1005

  for measuring distances inside the eye, e.g. thickness of the cornea (A61B3/11 takes precedence) · CPC title