Ultrashort-pulse source with controllable multiple-wavelength output

• US 6,154,310 A
• Filed: 11/21/1997
• Issued: 11/28/2000
• Est. Priority Date: 11/21/1997
• Status: Expired due to Term

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Galvanauskas, Almantas, Harter, Donald J., Wong, Ka K.
• Primary Examiner(s): Lee, John D.
• Application Number:
  US08/975,679
• Time in Patent Office: 1,103 Days
• Field of Search: 359/326-332, 359/341, 385/15, 385/39, 385/45, 385/46, 385/48, 385/122, 372/21, 372/22
• US Class Current: 359/328
• CPC Class Codes: G01B 9/02007 Two or more frequencies or sources used for interferometric measurement using only beat G01B9/02003
• CPC Class Codes: G01B 9/02014 by using pulsed light
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence
• CPC Class Codes: G02F 1/3132 of directional coupler type
• CPC Class Codes: G02F 1/3137 with intersecting or branching waveguides, e.g. X-switches and Y-junctions
• CPC Class Codes: G02F 1/335 having an optical waveguide structure
• CPC Class Codes: G02F 1/395 in optical waveguides
• CPC Class Codes: G02F 2201/124 interdigital
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108

Abstract

A multiple-wavelength ultrashort-pulse laser system includes a laser generator producing ultrashort pulses at a fixed wavelength, and at least one and preferably a plurality of wavelength-conversion channels. Preferably, a fiber laser system is used for generating single-wavelength, ultrashort pulses. An optical split switch matrix directs the pulses from the laser generator into at least one of the wavelength conversion channels. An optical combining switch matrix is disposed downstream of the wavelength-conversion channels and combines outputs from separate wavelength-conversion channels into a single output channel. Preferably, waveguides formed in a ferroelectric substrate by titanium indiffusion (TI) and/or proton exchange (PE) form the wavelength-conversion channels and the splitting and combining matrices. Use of the waveguide allows efficient optical parametric generation to occur in the wavelength-conversion channels at pulse energies achievable with a mode-locked laser source. The multiple-wavelength laser system can replace a plurality of different, single-wavelength laser systems. One particular application for the system is a multi-photon microscope, where the ability to select the ultrashort-signal wavelength of the laser source accommodates any single fluorescent dye or several fluorescent dyes simultaneously. In its simplest form, the system can be used to convert the laser wavelength to a more favorable wavelength. For example, pulses generated at 1.55 μm by a mode-locked erbium fiber laser can be converted to 1.3 μm for use in optical coherence tomography or to 1.04-1.12 μm for amplification by a Yterbium amplifier, allowing amplification of pulses which can be used in a display, printing or machining system.

Claims

1. An ultrashort pulse generator for generating ultrashort optical pulses at a plurality of different wavelengths, comprising:

an ultrashort optical pulse source generating ultrashort optical pulses;

a plurality of wavelength conversion channels for converting a wavelength of said ultrashort optical pulses to said different wavelengths, each of said wavelength conversion channels comprising an optical waveguide and including an optical parametric generation portion for parametrically generating said ultrashort optical pulses at at least one of said different wavelengths.

2. The ultrashort pulse generator according to claim 1, wherein the optical waveguide in each of said wavelength conversion channels is formed in a substrate comprising a periodically-poled ferroelectric optical material.

3. The ultrashort pulse generator according to claim 2, wherein said periodically-poled ferroelectric optical material is one of:

lithium niobate, lithium tantalate, and KTP.

4. The ultrashort pulse generator according to claim 1, wherein each of said wavelength conversion channels converts the wavelength of said ultrashort optical pulses as a function of at least one of:

a temperature of the wavelength conversion channel;

a wavelength of light pumped into said wavelength conversion channel; and

a periodic-poling period of an electric field in said wavelength conversion channel.

5. The ultrashort pulse generator according to claim 1, wherein said ultrashort optical pulse source is a mode-locked laser.

6. The ultrashort pulse generator according to claim 5, wherein said mode-locked laser is an erbium-doped fiber laser.

7. The ultrashort pulse generator according to claim 1, wherein said ultrashort optical pulse source is a mode-locked Ti:

sapphire laser or a mode-locked Cr;

Forsterite laser.

8. The ultrashort pulse generator according to claim 1, wherein each of said wavelength conversion channels further comprises at least one harmonic generator for generating ultrashort optical pulses whose wavelength is shorter than the wavelength of the ultrashort optical pulses generated by said ultrashort optical pulse source.

9. The ultrashort pulse generator according to claim 1, further comprising an optical splitter for directing the energy of said ultrashort optical pulses from said ultrashort optical pulse source into at least one of said wavelength conversion channels.

10. The ultrashort pulse generator according to claim 9, wherein said optical splitter comprises a switching waveguide, having a first refractive index, connecting a single input optical waveguide to n optical waveguides of said wavelength conversion channels, where n is an integer greater than 1, said switching waveguide including n regions of different refractive index for guiding optical pulses from said single input optical waveguide to respective ones of said n optical waveguides.

11. The ultrashort pulse generator according to claim 10, wherein said switching waveguide is formed in a ferroelectric optical material by titanium indiffusion, and said n regions of different refractive index are formed by proton exchange.

12. The ultrashort pulse generator according to claim 10, wherein the energy of ultrashort optical pulses received from said single input optical waveguide is distributed substantially equally among a plurality of said n optical waveguides.

13. The ultrashort pulse generator according to claim 10, wherein said optical splitter further comprises a 1×

n directional coupler for directing the energy of ultrashort optical pulses received from said single input optical waveguide into any single one or any combination of said n regions of different refractive index, whereby the energy of the ultrashort optical pulses received from said single input optical waveguide is guided into any single one or any combination of said n optical waveguides.

14. The ultrashort pulse generator according to claim 13, wherein said 1×

n directional coupler comprises n acousto-optic devices for generating surface acoustic waves capable of deflecting ultrashort optical pulses received at said single input optical waveguide into respective ones of said n optical waveguides.

15. The ultrashort pulse generator according to claim 14, wherein said n acousto-optic devices are interdigital transducers.

16. The ultrashort pulse generator according to claim 13, wherein said 1×

n directional coupler comprises n electro-optic devices capable of deflecting ultrashort optical pulses received at said single input optical waveguide into respective ones of said n optical waveguides.

17. The ultrashort pulse generator according to claim 16, wherein said n electro-optic devices are electro-optic induced gratings.

18. The ultrashort pulse generator according to claim 9, further comprising an optical combiner for directing ultrashort optical pulses in each of said wavelength conversion channels into a single output waveguide.

19. The ultrashort pulse generator according to claim 18, wherein said optical combiner comprises:

an output waveguide; and

n optical directional couplers, where n is an integer greater than 1, each of which respectively couples one of n optical waveguides of said wavelength conversion channels to said output waveguide, wherein application of a voltage to one of said n optical directional couplers couples ultrashort optical pulses propagating in a corresponding one of said n optical waveguides into said output waveguide.

20. The ultrashort pulse generator according to claim 19, wherein ultrashort optical pulses from a plurality of said n optical waveguides propagate in said output waveguide simultaneously.

21. The ultrashort pulse generator according to claim 19, wherein said output waveguide comprises n axially extending portions each having a different refractive index, wherein ultrashort optical pulses coupled into said output waveguide from an optical waveguide i propagate substantially in axially extending portions 1 through i, where i is an integer from 1 to n, such that ultrashort optical pulses of different wavelengths propagate in said output waveguide substantially in a single mode.

22. The ultrashort pulse generator according to claim 19, wherein said output waveguide is formed in a ferroelectric optical material by at least one of titanium indiffusion and proton exchange.

23. The ultrashort pulse generator according to claim 1, further comprising an ultrashort-pulse amplifier upstream of said wavelength conversion channels for amplifying said ultrashort optical pulses.

24. The ultrashort pulse generator according to claim 23, wherein said ultrashort-pulse amplifier is an erbium fiber amplifier.

25. The ultrashort pulse generator according to claim 1, further comprising an ultrashort-pulse amplifier downstream of said wavelength conversion channels, wherein said ultrashort-pulse amplifier is one of:

a Ytterbium fiber amplifier and a Ytterbium YAG amplifier.

26. An ultrashort pulse generator for generating ultrashort optical pulses at a plurality of different wavelengths, comprising:

a mode-locked laser generating ultrashort optical pulses; and

a wavelength conversion section including an optical parametric generation portion and including a waveguide-based optical switching section connecting a single input optical waveguide to n output optical waveguides, where n is an integer greater than 1, including acousto-optical or electro-optical means for effecting switching of optical pulses from said single input optical waveguide to respective ones of said n output optical waveguides.

27. The ultrashort pulse generator according to claim 26, wherein said wavelength conversion section is formed in a periodically-poled ferroelectric optical material.

28. The ultrashort pulse generator according to claim 27, wherein said wavelength conversion section converts the wavelength of said ultrashort optical pulses as a function of at least a periodic-poling period of said ferroelectric material.

29. A multi-wavelength ultrashort-pulse generator, comprising:

a laser for generating ultrashort optical pulses at a single wavelength;

a plurality of wavelength conversion channels for converting said ultrashort optical pulses to a plurality of respective different wavelengths; and

an optical switch for switching ultrashort optical pulses from any one or any combination of said wavelength conversion channels into a single output channel.

30. The multi-wavelength ultrashort-pulse generator according to claim 29, wherein each of said wavelength conversion channels includes an optical parametric generation portion which parametrically generates the ultrashort optical pulses.

31. An ultrashort pulse generator for generating ultrashort optical pulses at a plurality of different wavelengths, comprising:

an ultrashort optical pulse source generating ultrashort optical pulses;

an optical pump for generating pump pulses at a pump wavelength;

an optical waveguide for converting a wavelength of said ultrashort optical pulses to said different wavelengths, said optical waveguide including;

a first harmonic generation section responsive to said ultrashort optical pulses, for generating harmonic ultrashort optical pulses at a harmonic wavelength;

an optical parametric generation section responsive to the harmonic ultrashort optical pulses and the pump pulses, for parametrically generating signal ultrashort optical pulses at a signal wavelength and idler ultrashort optical pulses at an idler wavelength;

a second harmonic generation section responsive to the signal ultrashort optical pulses, for generating first output ultrashort optical pulses at a first wavelength; and

a third harmonic generation section responsive to said idler ultrashort optical pulses, for generating second output ultrashort optical pulses at a second wavelength, said optical waveguide transmitting third output ultrashort optical pulses at said pump wavelength; and

an ultrashort-pulse amplifier downstream of said optical waveguide, for amplifying ultrashort optical pulses at a wavelength different from a wavelength of said ultrashort optical pulses generated by said ultrashort optical pulse source.

32. The ultrashort pulse generator according to claim 31, wherein said ultrashort-pulse amplifier is one of:

a Ytterbium fiber amplifier and a Ytterbium YAG amplifier.

33. An ultrashort pulse generator for generating ultrashort optical pulses at a plurality of different wavelengths, comprising:

an ultrashort optical pulse source generating ultrashort optical pulses;

an optical pump for generating pump pulses at a pump wavelength; and

an optical waveguide for converting a wavelength of said ultrashort optical pulses to said different wavelengths, said optical waveguide including;

a first harmonic generation section responsive to said ultrashort optical pulses, for generating harmonic ultrashort optical pulses at a harmonic wavelength;

an optical parametric generation section responsive to the harmonic ultrashort optical pulses and the pump pulses, for parametrically generating signal ultrashort optical pulses at a signal wavelength and idler ultrashort optical pulses at an idler wavelength;

a second harmonic generation section responsive to the signal ultrashort optical pulses, for generating first output ultrashort optical pulses at a first wavelength; and

a third harmonic generation section responsive to said idler ultrashort optical pulses, for generating second output ultrashort optical pulses at a second wavelength, said optical waveguide transmitting third output ultrashort optical pulses at said pump wavelength.

34. The ultrashort pulse generator according to claim 33, wherein said first, second and third harmonic generation sections are second-harmonic generators.

35. The ultrashort pulse generator according to claim 33, wherein said optical waveguide is formed in a substrate comprising a periodically-poled ferroelectric optical material.

36. The ultrashort pulse generator according to claim 35, wherein said periodically-poled ferroelectric optical material is one of:

lithium niobate, lithium tantalate, and KTP.

37. The ultrashort pulse generator according to claim 33, wherein said ultrashort optical pulse source is a mode-locked laser.

38. The ultrashort pulse generator according to claim 37, wherein said mode-locked laser is an erbium-doped fiber laser.

39. The ultrashort pulse generator according to claim 33, further comprising an ultrashort-pulse amplifier upstream of said optical waveguide for amplifying said ultrashort optical pulses.

40. The ultrashort pulse generator according to claim 39, wherein said ultrashort-pulse amplifier is an erbium fiber amplifier.

41. The ultrashort pulse generator according to claim 33, wherein each of said first, second and pump wavelengths corresponds to one of red, green and blue light.