Actively mode-locked fiber laser with controlled chirp output

• US 6,590,910 B2
• Filed: 09/24/2001
• Issued: 07/08/2003
• Est. Priority Date: 09/22/2000
• Status: Expired due to Fees

• Current Assignee: Calmar Optcom, Inc.
• Original Assignee: Calmar Optcom, Inc.
• Inventors: Lin, Hong
• Primary Examiner(s): Ip, Paul
• Assistant Examiner(s): Nguyen, Phillip
• Application Number:
  US09/969,124
• Publication Number:
  US 20020071454A1
• Time in Patent Office: 652 Days
• Field of Search: 372/18, 372/20, 385/27, 385/37, 356/350
• US Class Current: 372/18
• CPC Class Codes: H01S 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/107 using electro-optic devices, e.g. exhibiting Pockels or Kerr effect H01S3/1061, H01S3/1063, H01S3/1065 take precedence
• CPC Class Codes: H01S 3/1109 Active mode locking
• CPC Class Codes: H01S 3/137 for stabilising of frequency

Abstract

Mode-locked fiber lasers with an active feedback control of the frequency chirp and a mechanism for adjusting the dispersion of the output pulses.

Claims

1. A device, comprising:

a fiber ring to circulate optical energy, said fiber ring having a first fiber portion and a second fiber portion that have opposite signs in chromatic dispersion;

a fiber gain portion in said fiber ring which is responsive to optical pumping by light at a pump wavelength to produce an optical gain at a laser wavelength different from said pump wavelength;

a dispersion control unit in said fiber ring to modify a dispersion of an optical pulse in said fiber ring in response to a dispersion control signal;

an optical modulator in said fiber ring responsive to a modulator control signal to modulate a property of said optical pulse at a modulation frequency to lock different optical modes in said fiber ring; and

an output coupler in said fiber ring to couple a portion of optical energy at said laser wavelength to produce a pulsed laser output.

2. The device as in claim 1, further comprising:

an optical detector coupled to receive a portion of said pulsed laser output to produce a detector signal;

a chirp circuit coupled to said optical detector to process said detector signal to determine a difference between a frequency chirp of said pulsed laser output and a desired frequency chirp and to produce a chirp-error signal; and

a feedback circuit coupled to said chirp circuit to produce said modulator control signal according to said chirp-error signal for reducing said difference.

3. The device as in claim 1, wherein said property includes an optical phase.

4. The device as in claim 1, wherein said property includes an optical amplitude.

5. The device as in claim 1, wherein said property includes both an optical phase and an optical amplitude.

6. The device as in claim 1, wherein said optical modulator includes an amplitude modulator that modulates an amplitude of said optical pulse and a phase modulator that modulates a phase of said optical pulse.

7. The device as in claim 1, wherein said dispersion control unit includes a reflective optical grating.

8. The device as in claim 1, wherein said fiber ring is polarization maintaining.

9. The device as in claim 1, wherein chromatic dispersions of said first and said second fiber portions and said dispersion control unit are balanced to produce optical solitons in said pulsed laser output.

10. The device as in claim 1, further comprising a feedback control loop that produces said modulator control signal to control said frequency chirp of each pulse in response to a measurement of said pulsed laser output.

11. A device, comprising:

a fiber ring to circulate optical energy, said fiber ring having a first fiber portion and a second fiber portion that have opposite signs in chromatic dispersion;

a fiber gain portion in said fiber ring which is responsive to optical pumping by light at a pump wavelength to produce an optical gain at a laser wavelength different from said pump wavelength;

an optical modulator in said fiber ring responsive to a modulator control signal to modulate a property of said optical pulse at a modulation frequency to lock different optical modes in said fiber ring;

an output coupler in said fiber ring to couple a portion of optical energy at said laser wavelength to produce a pulsed laser output; and

a dispersion control unit in a path of said pulsed laser output to modify a dispersion of said pulsed laser output in response to a dispersion control signal to bias a frequency chirp of each pulse in said pulsed laser output to a desired fixed value.

12. The device as in claim 11, further comprising a feedback control loop that produces said modulator control signal to control said frequency chirp of each pulse in response to a measurement of said pulsed laser output.

13. The device as in claim 12, wherein said feedback loop includes:

an optical detector coupled to receive a portion of said pulsed laser output passing through said dispersion control unit to produce a detector signal;

a chirp circuit coupled to said optical detector to process said detector signal to determine a difference between a frequency chirp of said pulsed laser output and a desired frequency chirp and to produce a chirp-error signal; and

a feedback circuit coupled to said chirp circuit to produce said modulator control signal according to said chirp-error signal for reducing said difference.

14. The device as in claim 11, wherein said property includes an optical phase.

15. The device as in claim 11, wherein said property includes an optical amplitude.

16. The device as in claim 11, wherein said property includes both an optical phase and an optical amplitude.

17. The device as in claim 11, wherein said dispersion control unit includes a reflective optical grating.

18. The device as in claim 11, wherein said fiber ring is polarization maintaining.

19. The device as in claim 11, wherein chromatic dispersions of said first and said second fiber portions and said dispersion control unit are balanced to produce optical solitons in said pulsed laser output.

20. A device, comprising:

a polarizing beam splitter (PBS);

a polarization-maintaining fiber loop having an input terminal coupled to one facet of said PBS to receive light in a selected polarization reflected from said PBS and an output terminal coupled to another facet of said PBS to output light in said selected polarization that transmits through said PBS;

an optical isolator in said fiber loop to circulate said light directing from said input terminal to said output terminal and to suppress light in directing from said output terminal to said input terminal;

a fiber segment having a first terminal and a second terminal, said first terminal coupled to said PBS to receive light from said output terminal of said fiber loop and to deliver light to said PBS a portion of which is reflected by said PBS into said input terminal of said fiber loop;

a Faraday rotator reflector coupled to said second terminal to reflect light with a rotation of polarization by about 90 degrees, wherein said fiber ring, said fiber segment, and said Faraday rotator reflector form a laser resonator;

a fiber gain portion in said fiber segment which is responsive to optical pumping by light at a pump wavelength to produce an optical gain at a laser wavelength different from said pump wavelength;

an optical modulator in said fiber loop responsive to a modulator control signal to modulate a property of said light at a modulation frequency to lock different modes in said laser resonator to produce laser pulses,

wherein said fiber loop has a sign of dispersion that is opposite to a sign of dispersion in an optical path between said Faraday rotator reflector and said PBS,

said fiber ring having a first fiber portion and a second fiber portion that have opposite signs in chromatic dispersion;

an output coupler in said laser resonator to couple a portion of optical energy at said laser wavelength to produce a pulsed laser output; and

a dispersion control unit in said fiber segment to modify a dispersion of light in said laser resonator in response to a dispersion control signal to control a frequency chirp of said pulsed laser output.

21. The device as in claim 20, further comprising a feedback control loop that produces said modulator control signal to control said frequency chirp in response to a measurement of said pulsed laser output.

22. The device as in claim 21, wherein said feedback loop includes:

an optical detector coupled to receive a portion of said pulsed laser output passing through said dispersion control unit to produce a detector signal;

a chirp circuit coupled to said optical detector to process said detector signal to determine a difference between a frequency chirp of said pulsed laser output and a desired frequency chirp and to produce a chirp-error signal; and

a feedback circuit coupled to said chirp circuit to produce said modulator control signal according to said chirp-error signal for reducing said difference.

23. The device as in claim 20, wherein a chromatic dispersion of said fiber loop and a chromatic dispersion of said optical path between said Faraday rotator reflector and said PBS are balanced to produce optical solitons in said pulsed laser output.

24. A method, comprising;

causing a location of an optical coupler to be selected in an optical path within a mode-locked fiber laser to produce output pulses with a frequency chirp, wherein the optical path within the fiber laser includes a first fiber portion and a second fiber portion that have opposite signs in chromatic dispersion;

causing an adjustable dispersion unit in the optical path within the fiber laser to be adjusted to modify a chromatic dispersion in the output pulses to bias the frequency chirp of the output pulses near a desired frequency chirp; and

causing a phase of an optical modulation on optical energy in the fiber laser to be dynamically adjusted in response to a measured frequency chirp of the output pulses to reduce a deviation of the measured frequency chirp from the desired frequency chirp.