Broadband generation of mid IR, coherent continua with optical fibers

• US 8,971,358 B2
• Filed: 03/08/2012
• Issued: 03/03/2015
• Est. Priority Date: 03/14/2011
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin, Hartl, Ingmar
• Primary Examiner(s): Rodriguez, Armando
• Application Number:
  US13/415,374
• Publication Number:
  US 20120236314A1
• Time in Patent Office: 1,090 Days
• Field of Search: 372/6, 372/18, 372/19, 372/21, 372/25
• US Class Current: 372/6
• 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 3/10 Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating

Abstract

Coherent and compact supercontinuum light sources for the mid IR spectral regime are disclosed and exemplary applications thereof. The supercontinuum generation is based on the use of highly nonlinear fibers or waveguides. In at least one embodiment the coherence of the supercontinuum sources is increased using low noise mode locked short pulse sources. Compact supercontinuum light sources can be constructed with the use of passively mode locked fiber or diode lasers. Wavelength tunable sources can be constructed using appropriate optical filters or frequency conversion sections. Highly coherent supercontinuum sources further facilitate coherent detection schemes and can improve the signal/noise ratio in lock in detection schemes.

Claims

1. A coherent supercontinuum source, comprising:

a low-noise fiber-based pulsed source arranged in combination with a highly non-linear material, said low-noise fiber-based source comprising a mode locked fiber oscillator, said fiber-based pulse source generating an output comprising short optical pulses having a pulse width <

1 ps at a central wavelength >

1700 nm, said highly non-linear material receiving said output from said low-noise fiber-based pulse source and generating a coherent supercontinuum having a spectral bandwidth of at least one-half octave between two −

30 dB points; and

a low-noise pump source to pump said low-noise fiber-based pulsed source,

wherein said supercontinuum is characterized by having a first order nearest neighbor coherence value of at least 0.7 at two locations within said spectral bandwidth.

2. The coherent supercontinuum source according to claim 1, wherein said continuum covers a spectral bandwidth larger than 1 octave measured between two −

30 dB points.

3. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a highly nonlinear silica fiber comprising a core region with a Germania concentration >

10 mole %.

4. The coherent supercontinuum source according to claim 3, wherein said highly nonlinear silica fiber is dispersion flattened with a dispersion value <

|10| ps²/km in a spectral range within ±

100 nm of the central wavelength of said fiber-based pulsed source.

5. The coherent supercontinuum source according to claim 3, wherein said highly nonlinear fiber has a W refractive index profile.

6. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a photonic crystal fiber.

7. The coherent supercontinuum source according to claim 6, wherein said photonic crystal fiber is silica based and comprises a core region with a Germania concentration >

10 mole %.

8. The coherent supercontinuum source according to claim 1, wherein said low-noise pump source comprises at least one single-frequency seed source.

9. The coherent supercontinuum source according to claim 1, wherein said low-noise pump source comprises a seed source nearly free of any longitudinal mode structure.

10. The coherent supercontinuum source according to claim 1, wherein said low-noise pump source comprises a seed source that generates amplified spontaneous emission.

11. The coherent supercontinuum source according to claim 1, wherein an output of said pump source is injected into the core of a gain fiber within said mode locked fiber oscillator.

12. The coherent supercontinuum source according to claim 1, wherein said low-noise fiber-based source comprises a passively mode locked fiber oscillator based on a Tm, Tm:

Ho, or a Ho doped fiber.

13. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material is selected from SF-6, bismuth, lead, tellurite, fluoride, fluorotellurite or chalcogenide glass fiber.

14. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a soft or heavy metal oxide glass fiber.

15. The coherent supercontinuum source according to claim 14, wherein said highly nonlinear fiber is non-silica fiber, and is dispersion flattened with a dispersion value <

|100| ps²/km in a spectral range within ±

100 nm of the central wavelength of said laser source.

16. The coherent supercontinuum source according to claim 1, wherein said low-noise fiber based source produces pulses with a pulse width <

300 fs.

17. The coherent supercontinuum source according to claim 1, wherein said low-noise fiber-based source produces pulses with a pulse width <

100 fs.

18. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a periodically poled nonlinear crystal waveguide.

19. The coherent supercontinuum source according to claim 1, said supercontinuum source exhibits high phase coherence at least at two spectral points within said continuum, said two spectral points separated by at least one-half octave.

20. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a high numerical aperture photonic crystal fiber (PCF) having a core and a single layer of air holes at least partially surrounding said core.

21. The coherent supercontinuum source according to claim 1, wherein said coherence is measurable by RF beat signal with a S/N ratio of at least 10 dB when measured with an RF frequency analyzer at 100 kHz resolution, measurable with an f-2f interferometer.

22. The supercontinuum source according to claim 1, wherein a spectrum of said supercontinuum comprises multiple spectral lines, and said coherence is characterizable with a detectable RF beat signal between a single frequency laser output and an individual frequency line separated within said supercontinuum spectrum by at least 0.5 octave from said central wavelength, said RF beat signal having a S/N ratio of at least about 10 dB measurable with an RF frequency analyzer at about 100 kHz resolution.

23. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a highly nonlinear fiber.

24. The coherent supercontinuum source according to claim 23, wherein said highly nonlinear material has a normal dispersion value at the central wavelength of said fiber-based pulsed source.

25. The coherent supercontinuum source according to claim 1, wherein said highly nonlinear material comprises a soft or heavy metal oxide glass fiber, and said fiber has a normal dispersion value at the central wavelength of said fiber-based pulsed source.

26. A coherent supercontinuum source comprising;

a fiber-based laser source generating short optical pulses, said fiber-based source generating an output at a central wavelength >

1700 nm, said short optical pulses comprising a pulse width <

10 ps;

a nonlinear waveguide for self-frequency shifting the output of said fiber-based source to frequency shifted output wavelengths >

2200 nm; and

a highly nonlinear material receiving pulses having said frequency shifted output wavelengths and generating said coherent supercontinuum therewith,

wherein said coherent supercontinuum generated with said highly nonlinear material is characterized by having a spectral bandwidth of at least one-half octave between two −

30 dB points and a first order nearest neighbor coherence value of at least 0.7 at two locations within said spectral bandwidth.