Pulsed laser sources

Patent metadata

Field	Value
Publication number	US-9653868-B2
Application number	US-201615207959-A
Country	US
Kind code	B2
Filing date	Jul 12, 2016
Priority date	Jul 25, 2003
Publication date	May 16, 2017
Grant date	May 16, 2017

Abstract

Modelocked fiber laser resonators may be coupled with optical amplifiers. An isolator optionally may separate the resonator from the amplifier. A reflective optical element on one end of the resonator having a relatively low reflectivity may be employed to couple light from the 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 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 grating to the inverse of the dispersion of the intra-cavity fiber. Frequency comb sources may be constructed from such modelocked fiber oscillators. Low dispersion and an in-line interferometer that provides feedback may assist in controlling the frequency components output from the comb source.

First claim

What is claimed is:

1. A frequency comb source comprising:
a mode-locked fiber oscillator comprising optical fiber disposed in an optical cavity;
a non-linear optical element disposed to receive pulsed output from said mode-locked fiber oscillator and to generate a supercontinuum comprising a first train of optical pulses having a first set of frequency components;
an interferometer disposed to receive said first train of optical pulses, said interferometer comprising a frequency converter comprising a nonlinear waveguide and configured to generate a second train of optical pulses having a second set of frequency components that are shifted in frequency with respect to the first set of frequency components, said second train of optical pulses temporally overlapping said first set of optical pulses, said interferometer configured to interfere at least a portion of said first train and said second train of optical pulses to generate an optical interference signal comprising beat frequencies; and
an optical detector configured to detect said optical interference signal and output said beat frequencies.

2. The frequency comb source according to claim 1 , wherein said interferometer comprises an f to 2f interferometric arrangement.

3. The frequency comb source according to claim 1 , wherein said non-linear optical element comprises a highly non-linear fiber.

4. The frequency comb source according to claim 1 , wherein said nonlinear waveguide comprises PPLN.

5. The frequency comb source according to claim 1 , wherein said nonlinear waveguide comprises a periodically poled grating section.

6. The frequency comb source according to claim 1 , further comprising an optical filter disposed upstream from said optical detector, said filter substantially transmitting portions of the supercontinuum that contribute to signals representative of said beat frequencies.

7. The frequency comb source according to claim 1 , wherein said pulsed output from said mode-locked fiber oscillator comprises frequency components having a repetition frequency, f rep , and a carrier envelope offset frequency, f ceo , said frequency comb source further comprising:
a feedback system having an input for receiving a beat frequency related to f ceo ,
said feedback system comprising a phase lock loop to compare said beat frequency related to f ceo with a reference frequency,
said feedback system connected to said mode-locked fiber oscillator to control said carrier envelope offset frequency, f ceo , based on said beat frequencies.

8. The frequency comb source according to claim 1 , said frequency comb source further comprising optical comb lines characterized by a repetition frequency, f rep , and a carrier envelope offset frequency, f ceo , said frequency comb source further comprising:
a first feedback system configured to lock at least one of the optical comb lines to an optical frequency reference.

9. The frequency comb source according to claim 8 , further comprising a second feedback system configured to control f ceo .

10. The frequency comb source according to claim 9 , wherein said second feedback system configured to control f ceo is configured to adjust a pump power for the modelocked fiber oscillator.

11. The frequency comb source according to claim 8 , further comprising an electro-mechanical transducer configured to controllably alter the cavity length of said optical cavity in response to a signal in the first feedback system.

12. The frequency comb source according to claim 1 , wherein said pulsed output from said mode-locked fiber oscillator comprises frequency components having a repetition frequency, f rep , and a carrier envelope offset frequency, f ceo ,
said optical cavity comprising an addressable intra-cavity element,
said frequency comb source further comprising a feedback system connected to said mode-locked fiber oscillator and said addressable intra-cavity element to control said carrier envelope offset frequency, f ceo ,
said addressable intra-cavity element configured to perturb said mode-locked fiber oscillator in response to feedback from said feedback system.

13. The frequency comb source according to claim 12 , wherein said addressable intra-cavity element comprises a heating element, an electro-mechanical transducer, or a piezo-electric transducer.

14. The frequency comb source according to claim 1 , wherein:
said frequency comb source is substantially fiber based,
said non-linear optical element comprises a highly non-linear fiber, and
said frequency comb source comprises coupling fibers that are spliced to the highly non-linear fiber so as to couple said supercontinuum from the highly non-linear fiber to the nonlinear waveguide.

15. The frequency comb source according to claim 1 , wherein said frequency comb source is substantially fiber based, and said frequency comb source comprises a coupling fiber attached to the non-linear waveguide for output coupling the output of said non-linear waveguide.

16. The frequency comb source according to claim 1 , wherein said optical fiber disposed in said cavity has a total length L, and said mode-locked fiber oscillator has a total dispersion in the range from −10,000 femtosec 2 /m×L to +2,500 femtosec 2 /m×L.

17. The frequency comb source according to claim 1 , wherein said mode-locked fiber oscillator has a total absolute dispersion less than about 5,000 femtosec 2 .

18. The frequency comb source according to claim 1 , wherein said nonlinear optical element is fiber based and has a dispersion in the range from −5,000 femtosec 2 /m to +2,000 femtosec 2 /m.

19. The frequency comb source according to claim 1 , wherein said optical cavity of said mode-locked fiber oscillator is configured with sufficiently low cavity dispersion such that a carrier envelope offset frequency beat signal (f ceo beat signal) having a frequency bandwidth smaller than approximately 200 kHz is obtainable from said frequency comb source.

20. The frequency comb source according to claim 1 , further comprising a fiber amplifier disposed between said mode-locked fiber oscillator and said non-linear optical element.

21. The frequency comb source according to claim 18 , further comprising an isolator disposed between said mode-locked fiber oscillator and said fiber amplifier.

22. The frequency comb source according to claim 1 , wherein said interferometer comprises a group delay compensator configured to compensate for a difference in optical path between said at least a portion of said first train and second train of optical pulses interfering in said interferometer, said group delay compensator configured to reduce said optical path difference.

23. A frequency comb source comprising:
a mode-locked fiber oscillator comprising a least two optical fibers with different dispersion characteristics disposed in an optical cavity and arranged such that said mode-locked cavity dispersion is in the range from −10,000 femtosec 2 /m×L to +2,500 femtosec 2 /m×L where L is the total intra-cavity fiber length, said mode-locked fiber oscillator configured to output pulses having a carrier envelope offset frequency f ceo ;
a non-linear optical element disposed downstream from said mode-locked fiber oscillator configured to receive pulses originating from said mode-locked fiber oscillator to generate a supercontinuum; and
an interferometer configured to generate a beat signal representative of the f ceo of said mode-locked fiber oscillator.

Assignees

• Imra America Inc

Inventors

• Fermann Martin E
• Hartl Ingmar
• Imeshev Gennady

Classifications

• H01S3/1106

  Mode locking · CPC title

• G02F1/3517

  using an interferometer · CPC title

• H01S3/0092

  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 title

• H01S3/0078

  Frequency filtering · CPC title

• H01S3/0057 Primary

  Temporal shaping, e.g. pulse compression, frequency chirping (soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108) · CPC title