Pulsed laser sources

• US 7,649,915 B2
• Filed: 03/10/2006
• Issued: 01/19/2010
• Est. Priority Date: 07/25/2003
• Status: Expired due to Fees

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin E., Imeshev, Gennady, Hartl, Ingmar
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): FORDE, DELMA ROSA
• Application Number:
  US11/372,859
• Publication Number:
  US 20060198398A1
• Time in Patent Office: 1,411 Days
• Field of Search: 372/18, 372/28, 372/21, 372/30, 372/32, 372/20, 372/31, 372/23
• US Class Current: 372/18
• CPC Class Codes: G02F 1/3517 using an interferometer
• CPC Class Codes: G02F 1/3528 for producing a supercontinuum
• CPC Class Codes: H01S 3/0014 Monitoring arrangements not otherwise provided for photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108
• CPC Class Codes: H01S 3/0078 Frequency filtering
• 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 3/067 Fibre lasers
• 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 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/10 Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
• 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 3/1053 Control by pressure or deformation
• CPC Class Codes: H01S 3/106 by controlling devices placed within the cavity H01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1067 using pressure or deformation
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1106 Mode locking
• 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 3/1616 thulium

Abstract

Various embodiments include modelocked fiber laser resonators that may be coupled with optical amplifiers. An isolator may separate the laser resonator from the amplifier, although certain embodiments exclude such an isolator. A reflective optical element on one end of the resonator having a relatively low reflectivity may be employed to couple light from the laser resonator to the amplifier. Enhanced pulse-width control may be provided with concatenated sections of both polarization-maintaining and non-polarization-maintaining fibers. Apodized fiber Bragg gratings and integrated fiber polarizers may be also be included in the laser cavity to assist in linearly polarizing the output of the cavity. Very short pulses with a large optical bandwidth may be obtained by matching the dispersion value of the fiber Bragg grating to the inverse of the dispersion of the intra-cavity fiber. Frequency comb sources may be constructed from such modelocked fiber oscillators. In various exemplary embodiments, low dispersion and an in-line interferometer that provides feedback, assist in controlling the frequency components output from the comb source.

Claims

1. A frequency comb source for producing a frequency comb, said frequency comb source comprising:

a mode-locked fiber oscillator having a resonant cavity comprising an optical fiber having a length, L, said resonant cavity supporting a plurality of optical modes, wherein said mode-locked fiber oscillator is pumped with at least one pump laser diode, said mode-locked fiber oscillator mode-locking said plurality of optical modes to produce a mode-locked optical signal, said mode-locked optical signal comprising frequency components of said comb;

a feedback system for controlling a carrier envelope offset frequency of said mode-locked fiber oscillator, wherein said feedback system comprises an element configured to control a pump current of said pump diode in response to a feedback signal representative of a beat signal frequency; and

a substantially non-linear optical element having sufficient optical non-linearity to generate additional frequency components in said frequency comb, wherein said mode-locked fiber oscillator has a total dispersion less than about 10,000 femtosec²/m×

L, said total dispersion and said feedback system thereby reducing frequency noise.

2. The frequency comb source of claim 1, wherein said mode-locked fiber oscillator comprises first and second dispersive optical elements selected to have positive and negative dispersion, respectively.

3. The frequency comb source of claim 1, wherein said dispersion of said mode-locked fiber oscillator is less than or equal to about 5,000 femtosec².

4. The frequency comb source of claim 1, further comprising:

a coupler to separate at least a portion of said frequency components into a plurality of high frequency components and a plurality of low frequency components; and

a frequency converter to increase the frequency of said low frequency components to substantially match the high frequency components,

wherein said frequency converter comprises a periodically poled material.

5. The frequency comb source of claim 4, wherein said periodically poled material comprises Lithium Niobate crystal (PPLN).

6. The frequency comb source of claim 1, further comprising:

a coupler to separate at least a portion of said frequency components into a plurality of high frequency components and a plurality of low frequency components; and

at least one element disposed in an optical path said coupler, said at least one element configured to increase spectral or temporal overlap between different pulses propagating within said coupler or along said optical path.

7. The frequency comb source of claim 1, wherein said mode-locked fiber oscillator comprises a fiber grating configured to limit at least one of a spectral width and a cavity dispersion.

8. The frequency comb source of claim 1, wherein said non-linear element comprises a highly non-linear optical fiber.

9. The frequency comb source of claim 8, wherein said highly non-linear fiber comprises a Bismuth-oxide based optical glass with a non-zero dispersion value, and wherein said highly non-linear fiber limits Raman generation.

10. The frequency comb source of claim 8, wherein said non-linear fiber has approximately zero dispersion or a flattened dispersion profile at an emission wavelength of said oscillator.

11. The frequency comb source of claim 8, wherein a length of said non-linear fiber is sufficiently short to substantially preserve coherence of said frequency components.

12. The frequency comb source of claim 1, wherein said substantially non-linear optical element comprises a holey optical fiber or a silica optical fiber.

13. The frequency comb source of claim 1, further comprising first and second piezo-electric transducers configured to adjust the repetition rate of said oscillator.

14. The frequency comb source of claim 1, wherein said dispersion is in the range of about −

20,000 femtosecond² to about +5000 femtosecond².

19. The frequency comb source of claim 1, further comprising a cladding-pumped fiber amplifier amplifying an output from said mode-locked fiber oscillator.

20. The frequency comb source of claim 19, wherein said amplifier is substantially nonlinear, and said nonlinear amplifier provides spectral broadening.

21. The frequency comb source of claim 19, wherein an output of said cladding pumped amplifier is optically connected to a non-linear fiber that provides spectral broadening.

22. The frequency comb source of claim 19, wherein an output of said cladding pumped amplifier is optically connected to said substantially non-linear element.

23. The frequency comb source of claim 1, wherein said non-linear element comprises a portion of a cladding pumped non-linear amplifier that provides spectral broadening.

24. The frequency comb source of claim 1, further comprising means for limiting noise of said frequency comb source, said means comprising at least one element to reduce a total dispersion of said mode-locked fiber oscillator cavity to a value substantially less than an absolute dispersion of any cavity element of said fiber oscillator cavity.

15. A frequency comb source for producing a frequency comb, said frequency comb source comprising:

a mode-locked fiber oscillator having a resonant cavity comprising an optical fiber having a length, L, said resonant cavity supporting a plurality of optical modes, wherein said oscillator comprises a fiber grating, said mode-locked fiber oscillator mode-locking said plurality of optical modes to produce a mode-locked optical signal, said mode-locked optical signal comprising frequency components of said comb;

a feedback system for controlling a carrier envelope offset frequency of said mode-locked fiber oscillator, wherein said feedback system comprises a heating element configured to control a temperature of said fiber grating; and

a substantially non-linear optical element having sufficient optical non-linearity to generate additional frequency components in said frequency comb, wherein said mode-locked fiber oscillator has a total dispersion less than about 10,000 femtosec²/m×

L, said total dispersion and said feedback system thereby reducing frequency noise.

16. A frequency comb source for producing a frequency comb, said frequency comb source comprising:

a mode-locked fiber oscillator having a resonant cavity comprising an optical fiber having a length, L, said resonant cavity supporting a plurality of optical modes, wherein said oscillator comprises a fiber grating, said mode-locked fiber oscillator mode-locking said plurality of optical modes to produce a mode-locked optical signal, said mode-locked optical signal comprising frequency components of said comb;

a feedback system for controlling a carrier envelope offset frequency of said mode-locked fiber oscillator, wherein said feedback system comprises a transducer configured to control a pressure applied to said fiber grating; and

a substantially non-linear optical element having sufficient optical non-linearity to generate additional frequency components in said frequency comb, wherein said mode-locked fiber oscillator has a total dispersion less than about 10,000 femtosec²/m×

L, said total dispersion and said feedback system thereby reducing frequency noise.

17. A frequency comb source for producing a frequency comb, said frequency comb source comprising:

a mode-locked fiber oscillator having a resonant cavity comprising an optical fiber having a length, L, said resonant cavity supporting a plurality of optical modes, said mode-locked fiber oscillator mode-locking said plurality of optical modes to produce a mode-locked optical signal, said mode-locked optical signal comprising frequency components of said comb;

a feedback system for controlling a carrier envelope offset frequency of said mode-locked fiber oscillator, wherein said feedback system is configured to modulate a repetition rate of said mode-locked fiber oscillator in response to a feedback signal representative of a beat signal frequency; and

a substantially non-linear optical element having sufficient optical non-linearity to generate additional frequency components in said frequency comb, wherein said mode-locked fiber oscillator has a total dispersion less than about 10,000 femtosec²/m×

L, said total dispersion and said feedback system thereby reducing frequency noise.

18. A frequency comb source for producing a frequency comb, said frequency comb source comprising:

a mode-locked fiber oscillator having a resonant cavity comprising an optical fiber having a length, L, said resonant cavity supporting a plurality of optical modes, said mode-locked fiber oscillator mode-locking said plurality of optical modes to produce a mode-locked optical signal, said mode-locked optical signal comprising frequency components of said comb;

a feedback system for controlling a carrier envelope offset frequency of said mode-locked fiber oscillator, wherein said feedback system comprises multiple feedback loops, said feedback loops configured in such a way that decouples a variation in both a repetition rate and carrier envelope offset frequency, said variation being caused in response to a stimulus applied to said mode-locked fiber oscillator; and

a substantially non-linear optical element having sufficient optical non-linearity to generate additional frequency components in said frequency comb, wherein said mode-locked fiber oscillator has a total dispersion less than about 10,000 femtosec²/m×

L, said total dispersion and said feedback system thereby reducing frequency noise.