Adjustable mid-infrared super-continuum generator using a tunable femtosecond oscillator

• US 9,601,899 B2
• Filed: 01/05/2015
• Issued: 03/21/2017
• Est. Priority Date: 01/07/2014
• Status: Active Grant

• Current Assignee: Thorlabs Incorporated
• Original Assignee: Thorlabs Incorporated
• Inventors: Salem, Reza, Fendel, Peter, Cable, Alex
• Primary Examiner(s): TANINGCO, MARCUS H
• Application Number:
  US14/589,509
• Publication Number:
  US 20150288133A1
• Time in Patent Office: 806 Days
• US Class Current: 1/1
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/59 Transmissivity G01N21/25 takes precedence
• CPC Class Codes: G02B 21/0032 Optical details of illumination, e.g. light-sources, pinholes, beam splitters, slits, fibers G02B21/0036 - G02B21/008; means for illumination of specimens in general G02B21/06
• CPC Class Codes: G02B 21/0076 arrangements using fluorescence or luminescence
• CPC Class Codes: G02B 21/361 Optical details, e.g. image relay to the camera or image sensor G02B21/364 takes precedence; illumination details G02B21/06 and subgroups
• CPC Class Codes: G02B 2207/114 Two photon or multiphoton effect
• 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 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

A super-continuum system including: a fiber laser configured to output a pulse having a center wavelength; a first nonlinear waveguide configured to shift the wavelength of the pulse from the fiber laser; a first fiber amplifier of at least one stage configured to amplify the output from the first nonlinear waveguide; and a second nonlinear waveguide configured to spectrally broaden the output from the first fiber amplifier.

Claims

1. A super-continuum system comprising:

a mode-locked fiber laser with an optical bandwidth corresponding to a transform limited pulse duration of less than 1 ps and a pulse repetition rate of more than 1 MHz configured to output a pulse having a center wavelength;

a first nonlinear waveguide configured to shift the wavelength of the pulse from the mode-locked fiber laser;

a first fiber amplifier of at least one stage configured to amplify the output from the first nonlinear waveguide and further configured to output femtosecond pulses by using the interplay between the dispersion and nonlinearity in the first fiber amplifier; and

a second nonlinear waveguide with a zero-dispersion point that is close to the center wavelength of the pulses exiting the first fiber amplifier configured to spectrally broaden the output from the first fiber amplifier by self-phase modulation.

2. The system of claim 1, wherein the first nonlinear waveguide shifts the output wavelength from the mode-locked fiber laser to a wavelength longer than 1700 nm and shorter than 2800 nm.

3. The system of claim 2, wherein the first fiber amplifier operates in the wavelength region between 1700 nm and 2800 nm.

4. The system of claim 1, wherein the second nonlinear waveguide is fabricated from a material with some transparency in the mid-infrared region.

5. The system, of claim 1, wherein the second nonlinear waveguide has anomalous dispersion at the center wavelength of the pulses exiting the first fiber amplifier.

6. The system of claim 1, further comprising a second fiber amplifier configured to boost the power from the mode-locked fiber laser and to control the amount of wavelength shift.

7. The system of claim 1, further comprising a first polarization controller for controlling an amount of wavelength shift through a Raman soliton self-frequency shifting process.

8. The system of claim 1, further comprising a first dispersive element configured to create a desired amount of chirp on the pulse entering the second fiber amplifier.

9. The system of claim 1, further comprising a second polarization controller configured to adjust the polarization state of the pulses entering the first fiber amplifier.

10. The system of claim 1, further comprising a second dispersive element configured to adjust the amount of chirp on the pulse entering the second nonlinear waveguide.

11. The system of claim 1, further comprising a third polarization controller to adjust the polarization state of the pulses entering the second nonlinear waveguide.

12. The system of claim 1, further comprising a third nonlinear waveguide placed between the first fiber amplifier and the second nonlinear waveguide to shift the wavelength of the output from the first fiber amplifier.

13. The system of claim 1, further comprising a splitter after the second fiber amplifier for splitting the output of the mode-locked fiber laser into a first path and a second path, the output on the first path is coupled to the first nonlinear waveguide and the light from the first fiber amplifier is combined with the output of the second path and coupled to the second nonlinear waveguide, in order to seed the second nonlinear waveguide with two different wavelengths.

14. The system of claim 1, further comprising a splitter after the mode-locked fiber laser for splitting the output of the mode-locked fiber laser into a first path and a second path, the output on the first path is coupled to the first nonlinear waveguide and the light from the first fiber amplifier is combined with the output of the second path and coupled to the second nonlinear waveguide, in order to seed the second nonlinear waveguide with two different wavelengths.

15. The system of claim 14, further comprising a variable delay line on the first path or on the second path.

16. The system of claim 14, further comprising a third fiber amplifier on the second path.

17. The system of claim 1, further comprising a band-pass filter configured to select a spectral band in the output pulse.

18. A method for operating super-continuum system that comprises a mode-locked fiber laser with an optical bandwidth corresponding to a transform limited pulse duration of less than 1 ps and a pulse repetition rate of more than 1 MHz configured to output a pulse having a center wavelength;

a first nonlinear waveguide configured to shift the wavelength of the pulse from the mode-locked fiber laser;

a first fiber amplifier with at least one stage configured to amplify the output from the first nonlinear waveguide and further configured to output femtosecond pulses by using the interplay between the dispersion and nonlinearity in the first fiber amplifier; and

a second nonlinear waveguide with a zero-dispersion point that is close to the center wavelength of the pulses exiting the first fiber amplifier configured to spectrally broaden the output from the first fiber amplifier by self-phase modulation, the method comprising;

receiving a feedback from, via a feedback loop filter, the output of the first fiber amplifier or the output of the second nonlinear waveguide; and

dynamically adjusting peak power, energy, wavelength or polarization of the pulse entering the second nonlinear waveguide based on the feedback.

19. A spectroscopy system, comprising:

a mode-locked fiber laser with an optical bandwidth corresponding to a transform limited pulse duration of less than 1 ps and a pulse repetition rate of more than 1 MHz configured to output a pulse having a center wavelength;

a first nonlinear waveguide configured to shift the wavelength of the pulse from the mode-locked fiber laser;

a first fiber amplifier of at least one stage configured to amplify the output from the first nonlinear waveguide and further configured to output femtosecond pulses by using the interplay between the dispersion and nonlinearity in the first fiber amplifier;

a second nonlinear waveguide with a zero-dispersion point that is close to the center wavelength of the pulses exiting the first fiber amplifier configured to spectrally broaden the output from the first fiber amplifier by self-phase modulation;

a sample processing unit configured to direct the light output from the super-continuum system to pass through or reflect off a sample; and

a spectrometer or interferometer configured to analyze the light that passes through, reflects off or is scattered by the sample.

20. A method for increasing the spectral coverage of a spectroscopy system that comprises:

a mode-locked fiber laser with an optical bandwidth corresponding to a transform limited pulse duration of less than 1 ps and a pulse repetition rate of more than 1 MHz configured to output a pulse having a center wavelength;

a first nonlinear waveguide configured to shift the wavelength of the pulse from the mode-locked fiber laser;

a first fiber amplifier of at least one stage configured to amplify the output from the first nonlinear waveguide and further configured to output femtosecond pulses by using the interplay between the dispersion and nonlinearity in the first fiber amplifier;

a second nonlinear waveguide with a zero-dispersion point that is close to the center wavelength of the pulses exiting the first fiber amplifier configured to spectrally broaden the output from the first fiber amplifier by self-phase modulation;

a sample processing unit configured to direct the light output from the super-continuum system to pass through or reflect off a sample; and

a spectrometer or interferometer configured to analyze the light that passes through, reflects off or is scattered by the sample, the method comprising;

performing multiple spectral measurements while adjusting one or more parameters of the super-continuum spectrum.