Apparatus and method for the generation of supercontinuum pulses

• US 9,531,153 B2
• Filed: 04/24/2014
• Issued: 12/27/2016
• Est. Priority Date: 01/19/2008
• Status: Active Grant

• Current Assignee: NKT Photonics A/S (NKT A/S)
• Original Assignee: Fianium Ltd (NKT A/S)
• Inventors: Clowes, John Redvers, Grudinin, Anatoly Borisovich, Godfrey, Ian Michael
• Primary Examiner(s): Niu, Xinning
• Application Number:
  US14/260,340
• Publication Number:
  US 20140369370A1
• Time in Patent Office: 978 Days
• US Class Current: 1/1
• CPC Class Codes: G01N 2021/6419 Excitation at two or more wavelengths
• CPC Class Codes: G01N 2021/6441 with two or more labels
• CPC Class Codes: G01N 21/6458 Fluorescence microscopy fluorescence microscopes per se G02B21/0076 and G02B21/16
• CPC Class Codes: G01N 2201/0697 Pulsed lasers
• CPC Class Codes: G02B 21/16 adapted for ultraviolet illumination ; Fluorescence microscopes G02B21/0076 takes precedence
• CPC Class Codes: G02F 1/3528 for producing a supercontinuum
• CPC Class Codes: G02F 1/353 Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
• CPC Class Codes: G02F 1/365 in an optical waveguide structure G02F1/377, G02F1/395 take precedence
• CPC Class Codes: H01S 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• 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 3/10 Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
• CPC Class Codes: H01S 3/10046 Pulse repetition rate control H01S3/11 takes precedence
• CPC Class Codes: H01S 3/1024 for pulse generation
• CPC Class Codes: H01S 3/108 using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering mode locking using a non-linear element H01S3/1112
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/2308 Amplifier arrangements, e.g. MOPA

Abstract

Optical pulse source, for generating optical supercontinuum pulses, comprising: an optical pump laser operable to generate a number of optical pump pulses at a pump pulse repetition rate; a nonlinear optical element arranged to receive optical pump pulses and configured to generate therefrom optical supercontinuum pulses; and a gating device provided between the pump laser and the nonlinear optical element and operable to selectively limit the number of optical pump pulses received by the nonlinear optical element in order to generate optical supercontinuum pulses at a user selectable repetition rate lower than the pump pulse repetition rate, wherein the optical pulse source further comprises a second gating device provided after the nonlinear optical element.

Claims

1. An optical pulse source for generating optical supercontinuum pulses, comprising:

an optical pump laser operable to generate a number of optical pump pulses at a pump pulse repetition rate;

a nonlinear optical element arranged to receive optical pump pulses and configured to generate therefrom optical supercontinuum pulses;

a gating device provided between the pump laser and the nonlinear optical element and operable to selectively limit the number of optical pump pulses received by the nonlinear optical element in order to generate optical supercontinuum pulses at a user selectable repetition rate lower than the pump pulse repetition rate;

a wavelength-tunable optical bandpass filter configured to receive at least one optical supercontinuum pulse and to wavelength filter the at least one optical supercontinuum pulse at a predetermined wavelength; and

wherein the wavelength-tunable optical bandpass filter is configured to receive a plurality of optical supercontinuum pulses in a pulse set and to wavelength filter each pulse at a respective one of a corresponding plurality of predetermined wavelengths, to thereby form a wavelength-interleaved optical continuum pulse set.

2. An optical pulse source according to claim 1 wherein the wavelength-tunable optical bandpass filter is configured to filter a plurality of the optical supercontinuum pulse sets in series to thereby form a repeating wavelength-interleaved optical supercontinuum pulse set.

3. An optical pulse source for generating optical supercontinuum pulses, comprising:

an optical pump laser operable to generate a number of optical pump pulses at a pump pulse repetition rate;

a nonlinear optical element arranged to receive optical pump pulses and configured to generate therefrom optical supercontinuum pulses;

a gating device provided between the pump laser and the nonlinear optical element and operable to selectively limit the number of optical pump pulses received by the nonlinear optical element in order to generate optical supercontinuum pulses at a user selectable repetition rate lower than the pump pulse repetition rate; and

wherein the optical pulse source further comprises a second gating device provided after the nonlinear optical element.

4. An optical pulse source according to claim 3, wherein the second gating device comprises an acousto-optical modulator, a wavelength-tunable optical bandpass filter, or an acousto-optic tunable filter.

5. An optical pulse source according to claim 3, wherein the second gating device is operable to reduce the optical intensity of one or more optical supercontinuum pulses.

6. A method of allowing a user to select the repetition rate of optical supercontinuum pulses generated by a source of optical supercontinuum pulses, comprising:

generating a number of optical pump pulses having an associated repetition rate and a duration with a pump pulse source;

gating the optical pump pulses to reduce the repetition rate;

introducing the gated optical pump pulses into a nonlinear optical element and generating therefrom optical supercontinuum pulses at the reduced repetition rate, wherein the user can select the reduced repetition rate;

where the optical supercontinuum pulses have an associated energy, and the method further comprises scaling the optical supercontinuum pulse energy by increasing the pump pulse duration as well as said gating to reduce the pump pulse repetition rate.

7. The method of claim 6, wherein scaling the energy of optical supercontinuum pulses further comprises reducing the repetition rate to less than 20 MHz and increasing the optical pump pulse duration to greater than 10 picoseconds.

8. The method of claim 7, wherein the pump pulse duration is increased to at least 200 picoseconds.

9. An optical pulse source for generating optical supercontinuum pulses, comprising:

an optical pump laser operable to generate a number of optical pump pulses at a pump pulse repetition rate;

a nonlinear optical element arranged to receive optical pump pulses and configured to generate therefrom optical supercontinuum pulses;

a gating device provided between the pump laser and the nonlinear optical element and operable to selectively limit the number of optical pump pulses received by the nonlinear optical element in order to generate optical supercontinuum pulses at a user selectable repetition rate lower than the pump pulse repetition rate; and

wherein the optical pulse source is configured to generate output optical supercontinuum pulses at a repetition rate in the range 1 MHz to 10 MHz with an energy spectral density of at least 100 picojoules per nanometer, and the optical pulse source is configured to provide an illumination source for a stimulated emission depletion (STED) microscope.

10. An optical pulse source according to claim 9, wherein the optical pulse source further comprises a controller configured to scale the energy of the optical supercontinuum pulses by reducing the pump pulse repetition rate of the optical pump laser and increasing the pump pulse duration.

11. An optical pulse source according to claim 9, wherein the optical pump pulse repetition rate is less than 20 MHz, and the optical pump pulses have a duration of at least 200 picoseconds.

12. An optical pulse source according to claim 9, wherein the STED microscope is fluorescence-based, and wherein the illumination source provides excitation illumination and stimulated emission illumination.

13. A method of allowing a user to select the repetition rate of optical supercontinuum pulses generated by a source of optical supercontinuum pulses, comprising:

generating a number of optical pump pulses having an associated repetition rate and a duration with a pump pulse source;

gating the optical pump pulses to reduce the repetition rate;

introducing the gated optical pump pulses into a nonlinear optical element and generating therefrom optical supercontinuum pulses at the reduced repetition rate wherein the user can select the reduced repetition rate; and

the method further comprising making use of the optical supercontinuum pulses to perform fluorescent lifetime imaging (FLIM), time correlated fluorescence single photon counting (TCSPC), or stimulated emission depletion (STED) microscopy.

14. The method of claim 13, wherein making use of the optical supercontinuum pulses comprises performing FLIM.

15. The method of claim 13, wherein making use of the optical supercontinuum pulses comprises performing STED microscopy.

16. The method of claim 13, wherein making use of the optical supercontinuum pulses comprises performing TCSPC.

17. The method of claim 13, comprising amplifying the gated optical pump pulses before introducing the gated optical pump pulses to the nonlinear optical element.

18. The method of claim 17, comprising amplifying the optical pump pulses before gating the optical pump pulses to reduce the repetition rate.

19. The method of claim 17, wherein amplifying the gated optical pump pulses comprises amplifying the gated optical pump pulses with an optical fiber amplifier wherein the peak power of a pulse that can be amplified is clamped, and wherein the duration of the gated optical pulses is selected such that the peak power of the gated optical pulses is within the peak power clamp.

20. The method of claim 19, wherein the duration of the gated optical pulses is hundreds of picosceconds.

21. The method of claim 20 comprising making use of the supercontinuum pulses to perform STED microscopy.

22. A method of generating optical supercontinuum pulses having increased spectral energy density, comprising:

generating a number of optical pump pulses having an associated repetition rate;

gating the optical pump pulses to reduce the repetition rate;

amplifying the gated optical pump pulses with an optical fiber amplifier wherein the pulse energy is fixed; and

introducing the amplified and gated optical pump pulses into a nonlinear optical element and generating therefrom optical supercontinuum pulses at the reduced repetition rate.

23. The method of claim 22, wherein generating the optical pump pulses comprises generating optical pump pulses with a mode locked optical fiber oscillator.