All-Normal-Dispersion Femtosecond Fiber Laser

• US 20100220751A1
• Filed: 09/18/2007
• Published: 09/02/2010
• Est. Priority Date: 09/18/2006
• Status: Active Grant

• Current Assignee: Cornell Center For Technology, Enterprise & Commercialization (Cornell University)
• Original Assignee: Cornell Center For Technology, Enterprise & Commercialization (Cornell University)
• Inventors: Buckley, Joel, Chong, Chin Yu, Wise, Frank
• Granted Patent: US 8,416,817 B2
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: H01S 2301/08 Generation of pulses with special temporal shape or frequency spectrum
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/08027 by a filter, e.g. a Fabry-Perot filter is used for wavelength setting
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• 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 modelocked fiber laser is designed to have strong pulse-shaping based on spectral filtering of a highly-chirped pulse in the laser cavity. The laser generates femtosecond pulses without a dispersive delay line or anomalous dispersion in the cavity.

Claims

1. A fiber laser for generating femtosecond duration pulses comprises a gain fiber to increase the energy of a pulse in a laser cavity, said cavity also including one or more dispersion elements, each of which provides only normal group velocity dispersion, said laser cavity at least including:

a chirping element for broadening a multiple frequency component pulse in said cavity and spreading said frequency components in said pulse apart over time; and

a spectral bandpass filter for passing a portion of said chirped pulse including only frequency components in a narrow range around a selected center frequency, thereby producing self-amplitude modulation of said pulse.

2. The fiber laser of claim 1, wherein said cavity further includes

one or more elements for producing additional self-amplitude modulation of said pulse for stabilizing the laser and assisting the laser during startup.

3. The fiber laser of claim 2, wherein said one or more elements for producing additional self-amplitude modulation of said pulse include one or more elements selected from the group comprising nonlinear polarization evolution (NPE) elements and a saturable absorber.

4. The laser of claim 1, wherein said spectral bandpass filter is selected from the group comprising an interference filter and a birefringent filter combined with a wave plate.

5. The laser of claim 1, wherein said laser cavity includes an output and said laser further comprises a pulse dechirping element connected to said output for narrowing said pulse to femtosecond duration.

6. The laser of claim 5, wherein said dechirping element comprises a pair of diffraction gratings which receive the output from said laser cavity.

7. The laser of claim 1, wherein said chirping element is selected from the group comprising a pair of diffraction gratings and a dispersive delay line.

8. The laser of claim 7, wherein said waveguide is a single mode fiber (SMF).

9. A method for shaping a pulse in a laser cavity of a fiber laser that employs a gain fiber to increase the energy of a pulse in said laser cavity to facilitate generation of femtosecond duration pulses by said laser, said cavity also including one or more dispersion elements, each of which provides only normal group velocity dispersion, said method comprising the steps of:

chirping a multiple frequency component pulse in said cavity by broadening said pulse and spreading said frequency components in said pulse apart over time; and

filtering said chirped pulse with a band pass spectral filter that passes only a portion of said chirped pulse having only frequency components in a narrow range around a selected center frequency;

thereby producing self-amplitude modulation of said pulse.

10. The method of claim 9, wherein said step of chirping the pulse comprises passing the pulse through an optical waveguide.

11. The method of claim 10, wherein said step of chirping the pulse comprises passing the pulse through a segment of single mode fiber (SMF).

12. The method of claim 9, wherein the step of filtering said chirped pulse comprises passing said chirped pulse through a band pass spectral filter selected from the group comprising an interference filter and a birefringent filter combined with a wave plate.

13. The method of claim 9, further comprising the step of producing additional self-amplitude modulation of said pulse.

14. The method of claim 13, wherein said step of producing additional self-modulation of said pulse comprises passing said pulse through one or more elements selected from the group comprising nonlinear polarization evolution (NPE) elements and a saturable absorber.

15. The method of claim 9, wherein after said pulse is shaped in said cavity, the shaped pulse is output from said cavity and passed through a dechirping element to narrow the duration of the pulse.

16. The method of claim 15, wherein said dechirping element is selected from the group comprising a pair of diffraction gratings and a dispersive delay line.