FREQUENCY COMB SOURCE WITH LARGE COMB SPACING

• US 20120133931A1
• Filed: 11/29/2010
• Published: 05/31/2012
• Est. Priority Date: 11/29/2010
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: FERMANN, Martin, HARTL, Ingmar
• Granted Patent: US 8,571,075 B2
• Time in Patent Office: Days
• US Class Current: 356/300
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G02F 1/3528 for producing a supercontinuum
• CPC Class Codes: G02F 1/365 in an optical waveguide structure G02F1/377, G02F1/395 take precedence
• CPC Class Codes: H01S 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/08054 Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115
• CPC Class Codes: H01S 3/0809 Two-wavelenghth emission
• CPC Class Codes: H01S 3/10046 Pulse repetition rate control H01S3/11 takes precedence
• CPC Class Codes: H01S 3/105 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity lengthH01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1118 Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
• CPC Class Codes: H01S 3/1618 ytterbium

Abstract

A frequency comb laser providing large comb spacing is disclosed. At least one embodiment includes a mode locked waveguide laser system. The mode locked waveguide laser includes a laser cavity having a waveguide, and a dispersion control unit (DCU) in the cavity. The DCU imparts an angular dispersion, group-velocity dispersion (GVD) and a spatial chirp to a beam propagating in the cavity. The DCU is capable of producing net GVD in a range from a positive value to a negative value. In some embodiments a tunable fiber frequency comb system configured as an optical frequency synthesizer is provided. In at least one embodiment a low phase noise micro-wave source may be implemented with a fiber comb laser having a comb spacing greater than about 1 GHz. The laser system is suitable for mass-producible fiber comb sources with large comb spacing and low noise. Applications include high-resolution spectroscopy.

Claims

1. A mode locked waveguide laser system, comprising:

a mode locked waveguide laser comprising a laser cavity having a waveguide;

an intra-cavity beam emitted from said waveguide;

a dispersion control unit (DCU) disposed in said cavity and in an optical path of said intra-cavity beam, wherein said laser cavity is configured in such a way that said intra-cavity beam is redirected to said waveguide after traversing at least said DCU,

wherein said DCU imparts angular dispersion, and group-velocity dispersion (GVD) to said intra-cavity beam during propagation in said cavity, and imparts a spatial chirp to said redirected beam, wherein said DCU is capable of producing net GVD in a range from a positive value to a negative value.

2. The mode locked waveguide laser system according to claim 1, wherein said mode locked waveguide laser comprises a mode locked fiber laser.

3. The mode locked waveguide laser system according to claim 1, wherein said DCU comprises a diffraction grating and a lens system.

4. The mode locked waveguide laser system according to claim 1, wherein said DCU comprises a lens system, and further comprises a prism or grism.

5. The mode locked waveguide laser system according to claim 1, wherein said DCU comprises one or more of a diffraction grating, prism, grism, and angled waveguide endface, and further comprises one or more of an optical lens and mirror.

6. The mode locked waveguide laser system according to claim 1, further comprising:

means for control of the carrier envelope offset frequency of said mode locked waveguide laser.

7. The mode locked waveguide laser system according to claim 6, wherein said means for carrier envelope offset frequency control comprises an optical element and a mechanism for translating said optical element along an axis.

8. The mode locked waveguide laser system according to claim 1, wherein said mode locked waveguide laser is configured as a soliton laser.

9. The mode locked waveguide laser system according to claim 1, wherein said mode locked waveguide laser operates at a repetition rate greater than about 1 GHz.

10. The mode locked waveguide laser system according to claim 1, wherein said mode locked waveguide laser is configured to operate at dual wavelengths simultaneously, and wherein said DCU is configured to provide a wavelength separation of said dual wavelengths.

11. The mode locked waveguide laser system according to claim 10, wherein said waveguide laser comprises a fiber laser, and said waveguide laser is configured to provide a different repetition rate for each of said dual wavelengths.

12. The mode locked waveguide laser system according to claim 11, wherein said mode locked laser is further configured for multi-heterodyne spectroscopy.

13. The mode locked waveguide laser system according to claim 11, wherein said mode locked waveguide laser comprises a split mirror.

14. The mode locked waveguide laser system according to claim 1, further comprising:

a spectral broadening stage.

15. The mode locked waveguide laser system according to claim 1, further comprising:

a repetition rate multiplier.

16. The mode locked waveguide laser system according to claim 1, further comprising:

an optical modulator providing a pulse train with a mark/space ratio>

2;

at least one fiber amplifier; and

one or more spectral broadening stages downstream from said mode locked waveguide laser.

17. The mode locked waveguide laser system according to claim 1, wherein said mode locked waveguide laser is configured such that a temporal bandwidth of said mode locked waveguide laser is limited, at least in part, by said spatial chirp.

18. The mode locked waveguide laser system according to claim 1, wherein said DCU is configured to displace at least one optical element of said DCU so as to adjust said net GVD to a value within said range.

27. The mode locked waveguide laser system according to claim 1, wherein said mode locked waveguide laser comprises a highly rare earth doped gain fiber.

29. A mode locked waveguide laser system according to claim 1, wherein said waveguide laser is configured as a ring laser or with a Fabry-Perot cavity.

30. A mode locked waveguide laser system according to claim 1, comprising:

an additional electronic feedback circuit configured to stabilize said comb laser output power.

19. A tunable fiber frequency comb system configured as an optical frequency synthesizer, said tunable comb system comprising:

a fiber comb laser;

a comb controller to control said comb laser, and to provide a tunable comb spacing;

a quantum cascade laser generating an optical output at substantially a single optical frequency corresponding to a wavelength in the mid to far IR wavelength range;

a frequency broadening stage receiving an output of said fiber comb laser, said frequency broadening stage configured to produce spectral overlap with said optical output spectrum of said quantum cascade laser;

a comb line selector to select and isolate at least one comb line from said fiber comb laser, said comb having a comb spacing greater than about 250 MHz;

a feedback loop to lock said output optical frequency of said quantum cascade laser to said selected comb line, whereby the optical frequency of said quantum cascade laser becomes a function of the tunable comb spacing.

20. The tunable fiber frequency comb system configured as an optical frequency synthesizer according to claim 19, wherein said comb line selector comprises one or both of an RF filter and an optical filter.

21. The tunable fiber frequency comb system configured as an optical frequency synthesizer according to claim 19, wherein said feedback loop is configured to selectively adjust a temperature or operating current of said quantum cascade laser.

22. A high resolution spectroscopy system, comprising,

a fiber comb laser having a repetition rate greater than about 1 GHz;

an optical sub-system disposed downstream from said fiber comb laser, and configured to optically resolve the individual comb lines from said comb system, said optical sub-system comprising;

at least one or both of a diffraction grating and a VIPA, and a one or two dimensional detector array, the individual elements of the detector array being spaced in such a way that each element is sensitive to an optical frequency band approximately equal to the comb line spacing.

23. The high resolution spectroscopy system according to claim 22, said frequency comb system further comprising:

a tunable comb spacing, a tunable carrier envelope offset frequency, or both.

24. The high resolution spectroscopy system according to claim 22, further comprising:

at least one reference laser and at least one detector configured for measuring the instantaneous optical frequencies of said comb system.

25. A low phase noise micro-wave source comprising:

a fiber comb laser with a comb spacing greater than about 1 GHz;

a reference laser;

a first detector to measure a first micro-wave beat signal between a line of said comb laser and the optical reference laser;

a sub-system to measure a carrier envelope offset frequency of said fiber comb laser, said sub-system receiving an output from said comb laser, and producing an output signal (CEO) representative of said carrier envelope offset frequency;

a mixer receiving said first micro-wave beat signal and said output signal (CEO) and generating a second beat signal;

a comb controller to control said comb laser, said comb controller receiving said second beat signal, wherein a portion of said comb controller is configured to phase lock said second beat signal to a micro-wave reference with modulation of the comb laser spacing;

a second detector providing a low phase noise micro-wave output signal.

26. A low phase noise micro-wave source according to claim 25, comprising:

an additional electronic feedback circuit configured to stabilize said comb laser output power.

28. The low phase noise micro-wave source according to claim 25, wherein said fiber comb laser comprises a highly rare earth doped gain fiber.