Graphene-based optical sub-system

Abstract

The present disclosure provides an optical sub-system for a passive, mode-locked laser optical system. The optical sub-system may include a graphene-based saturable absorber and an optical device configured to control dispersion properties of the laser optical system. The graphene-based saturable absorber may be supported by the optical device.

Claims

1. An optical sub-system for a passive, mode-locked laser optical system, the optical sub-system providing an all-in-one saturable absorber mirror with a dispersion compensation function, the optical sub-system comprising: a graphene-based saturable absorber; and an optical device comprising a multilayer dispersive mirror configured to control dispersion properties of the laser optical system, wherein the graphene-based saturable absorber is deposited on a surface of the optical device, and wherein the optical device is mounted on a mount allowing rotation of the optical device about an axis to change an angle of incidence onto the optical device and allow additional tuning of laser parameters including a wavelength of a light pulse.

2. An optical sub-system according to claim 1, wherein the graphene-based saturable absorber comprises at least one of: graphene, a graphene derivative, carbon nanotubes and functionalized graphene, and/or wherein the graphene-based saturable absorber is configured to be voltage controlled, wherein the graphene-based saturable absorber is a graphene-based capacitor or supercapacitor.

3. An optical system, comprising: an optical sub-system providing an all-in-one saturable absorber mirror with a dispersion compensation function for a passive, mode-locked laser optical system, the optical sub-system comprising: a graphene-based saturable absorber; and an optical device comprising a multilayer dispersive mirror, the optical device configured to control dispersion properties of the laser optical system, wherein the graphene-based saturable absorber is deposited on a surface of the optical device, and wherein the optical device is mounted on a mount allowing rotation of the optical device about an axis to change an angle of incidence onto the optical device and allow additional tuning of laser parameters including a wavelength of a light pulse; and the optical system further comprising: a laser gain medium doped with a transition metal ion dopant.

4. An optical system according to claim 3, wherein the laser gain medium is a single crystal or wherein the laser gain medium is polycrystalline.

5. An optical system according to claim 4, wherein when the crystal has a cubic structure, it is crystallographically orientated in such a way that the propagation vector of the light pulse is predominantly directed along one of the [100], [010], or crystallographic axes of the crystal or wherein when the crystal has a wurtzite structure, it is crystallographically orientated in such a way that the propagation vector of the light pulse is predominantly directed along the optical axis of the crystal, the optical axis being the [0001] crystallographic axis.

6. An optical system according to claim 3, wherein the transition metal ion dopant is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu or wherein the transition metal ion dopant is selected from the group consisting of Cr2+ and Fe2+.

7. An optical system according to claim 3, wherein said laser gain medium comprises a host material selected from the group consisting of: sulfide, selenide, mixed selenide-sulfide, telluride and corundum.

8. An optical system according to claim 3, wherein said host material is selected from ZnS, ZnSe, ZnTe, CdS, CdSe and CdTe.

9. An optical system according to claim 3, wherein said laser gain medium is a II-VI compound having the formula MX, where M is a divalent cation selected from the group consisting of Mg, Zn, and Cd, or a combination of these and X is a divalent anion selected from the group consisting of S, Se and Te, or a combination of these or wherein the laser gain medium is Ti:sapphire.

10. An optical system according to claim 3, wherein the laser gain medium is a chromium doped zinc sulfide (Cr:ZnS) crystal, or a chromium doped zinc selenide (Cr:ZnSe) crystal.

11. A passively mode-locked laser resonator, comprising: an optical system comprising: an optical sub-system providing an all-in-one saturable absorber mirror with a dispersion compensation function for a passive, mode-locked laser optical system, the optical sub-system comprising; a graphene-based saturable absorber; and an optical device comprising a multilayer dispersive mirror, the optical device configured to control dispersion properties of the laser optical system, wherein the graphene-based saturable absorber is deposited on a surface of the optical device, and wherein the optical device is mounted on a mount allowing rotation of the optical device about an axis to change an angle of incidence onto the optical device and allow additional tuning of laser parameters including a wavelength of a light pulse; and the optical system further comprising: a laser gain medium doped with a transition metal ion dopant, and the passively mode-locked laser resonator further comprising: a set of mirrors forming a cavity, the laser gain medium being provided within the cavity; a plurality of dispersive elements; and an optical Kerr element, wherein the optical Kerr element is the laser gain medium, or is provided as a separate element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A preferred embodiment of the present invention will now be described in greater detail by way of example only and with reference to the accompanying figures in which:

(2) FIG. 1 shows a Cr:ZnS femtosecond laser with a dispersion-compensating graphene-based self-starting optical sub-system;

(3) FIG. 2 shows a modified version of the system of FIG. 1;

(4) FIG. 3 shows an optical spectrum of the output of the system; and

(5) FIG. 4 shows an optical sub-system comprising a graphene-based capacitor or supercapacitor acting as voltage-controlled saturable absorber, deposited on an optical device with dispersion control capability, wherein the optical sub system is transmissive (FIG. 4(a)) or reflective (FIG. 4(b)).

DETAILED DESCRIPTION

(6) The laser system 10 shown in FIG. 1 generates laser pulses of a few tens of femtoseconds at a wavelength near 2.4 m.

(7) A CW Er-fiber laser was used as a pump source 12. The laser provided up to 5 W of polarized pump emission at 1.61 m.

(8) The system 10 comprises a common X-folded astigmatically compensated four-mirror cavity, having a total length of about 2.9 m and equivalent arm length ratio of 3:2. A 2.5 mm thick passively-cooled Cr:ZnS active element 18 is positioned at Brewster angle between the concave cavity mirrors 16 and 22 having radius of curvature (ROC) of 50 and 75 mm, respectively.

(9) The cavity mode is focused to a graphene saturable absorber 26 by a chirped concave mirror 24 with ROC=150 mm. The graphene saturable absorber 26 is deposited directly on the surface of the flat high-reflector mirror (by chemical vapor deposition on a copper substrate) thus forming the graphene-based saturable absorber mirror. The graphene saturable absorber 26 is mounted on a supporting element 25 which is connected to the chirped mirror 24.

(10) Compensation of the group-delay dispersion was achieved by a double reflection (on a round trip) from a chirped high reflectance concave mirror 24.

(11) The laser output 30 was coupled out of the system by output coupler 28.

(12) FIG. 2 is similar to FIG. 1, except that the compensation of the group-delay dispersion is achieved by one single reflection from a chirped high reflectance mirror 32. The output coupler 28 is set in a folding position in order to ensure only one reflection from the chirped mirror 32. The laser thus emitted two beams 30, 34 and the measured output power is a sum of both beams.

(13) FIG. 3 shows the optical spectrum of the output of the system.

(14) FIG. 4 shows an optical sub-system comprising a graphene-based capacitor or supercapacitor acting as voltage-controlled saturable absorber, deposited on an optical device with dispersion control capability.

(15) As shown in FIG. 4(a), the capacitor or supercapacitor comprises two polished bulk substrate plates 1, 2 which can be made from, for example, YAG, Sapphire, BaF.sub.2, or CaF.sub.2, which are transparent at the laser operation wavelength and which have a thickness of typically one to a few millimeters (or any length necessary to provide dispersion management inside the laser resonator). The substrate plates introduce a desired amount of dispersion at the laser operation wavelength.

(16) Alternatively, as shown in FIG. 4(b), one of the graphene electrodes can be transfer printed onto a dielectric mirror (4), dispersion compensation mirror, or output coupler mirror, which will act as one of the substrates.

(17) On the substrate plates are provided voltage controlled graphene electrodes. Such electrodes can have a form of two monolayer large-area graphene electrodes, each synthesized via chemical vapor deposition and transfer printed onto the above substrate plate.

(18) The spacing 3 between the two graphene electrodes can be filled, for example, with an electrolyte (supercapacitor) or a dielectric (capacitor).

(19) The following clauses set out features of the invention which may not presently be claimed in this application, but which may form the basis for future amendment or a divisional application.

(20) 1. An optical system comprising: a passively mode-locked short pulse laser resonator comprising of the cavity forming set of mirrors and dispersive elements, supplied with an excitation pump beam and causing a resonator laser beam, a transition-metal doped laser crystal including an optical Kerr element, and the graphene based device, which acts simultaneously as a saturable absorber mirror with dispersion compensation function to achieve self-starting mode locking and to control the pulse temporal, spectral, and phase properties, wherein: said transition metal ion dopant acts as an active laser light emitting optical center; excitation pump beam means associated with the gain medium for pumping the gain medium; cavity forming means surrounding the gain medium to form a resonant laser cavity; including an optical Kerr element means either associated with the Kerr-Lens producing effect inside the laser crystal or a separate from the laser crystal optical Kerr element inside the laser resonator; graphene based means comprising at least one of graphene, a graphene derivative, carbon nanotubes and functionalized graphene; self-starting means that short pulses start to form without external force at the moment of switching on the pump beam; a multilayer dispersive mirror means a dielectric or semiconductor based highly or partially reflective multilayer Bragg-reflector mirror of the type of Gires-Tournois or chirped mirror.

(21) 2. An optical system according to clause 1, wherein said laser crystal is a chromium doped zinc sulfide (Cr:ZnS) crystal;

(22) 3. An optical system according to clause 1, wherein said laser crystal is a chromium doped zinc selenide (Cr:ZnSe) crystal;

(23) 4. An optical system according to clause 1, wherein said laser crystal is selected from the group consisting of sulfide, selenide, mixed selenide-sulfide, telluride and corundum host materials.

(24) 5. An optical system according to clause 4 wherein the transition metal ion dopant is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu.

(25) 6. An optical system according to clause 5, wherein said laser crystal is a II-VI compound having the formula MX, where M is a divalent cation selected from the group consisting of Mg, Zn, and Cd, or a combination of these and X is a divalent anion selected from the group consisting of S, Se and Te, or a combination of these.

(26) 7. An optical system according to clause 6, wherein said host material is selected from ZnS, ZnSe, ZnTe, CdS, CdSe and CdTe.

(27) 8. An optical system according to clause 8 wherein the transition metal ion is selected from the group consisting of Cr.sup.2+ and Fe.sup.2+.

(28) 9. An optical system according to clause 5, wherein said laser crystal is a Ti:sapphire.

(29) 10. An optical system according to any preceding clause, wherein said gain medium is a polycrystalline material.

(30) 11. An optical system according to any of clauses 1 to 10, wherein said gain medium is a single-crystalline material.

(31) 12. An optical system according to clause 1, wherein the distance between the graphene based mirror and dispersive mirror of said device is adjustable.

(32) 13. An optical system according to clause 1, wherein the angle of incidence of the intra-cavity signal laser beam on the dispersive mirror of the said device is adjustable.

(33) 14. An optical system according to clause 1, wherein the laser resonator forming output coupling mirror is graphene based with both saturable and partial dispersion compensation function.

(34) 15. An optical system according to clause 1, wherein the said graphene based device is comprised of the graphene based saturable absorber mirror consisting of a single or more graphene or graphene based layers is supported on the facet of a dispersion-controlling mirror.

(35) 16. An optical system according to clause 1, wherein the said graphene based device is comprised of the graphene based saturable absorber mirror consisting of a single or more graphene or graphene based layers is supported on the facet of the output dispersion-controlling mirror.

(36) 17. An optical system according to clause 1, wherein the said dispersive elements may also include a plate (of tenths to few millimeters thick) of sapphire, yttrium aluminum garnet, calcium fluoride, barium fluoride or other material transparent in the wavelength of interest and providing substantial dispersion-compensating function in the cavity.

(37) 18. An optical system according to clause 1, wherein the said dispersive element is comprised of a graphene based saturable absorber mirror with a focusing dispersion-controlling mirror, such device being preferably manufactured and aligned as a single unit prior to final assembly.

(38) 19. An optical system according to clause 1, wherein the said dispersive element is comprised of a graphene based saturable absorber mirror with a pair of Gires-Tournois mirrors with adjustable angle of incidence to achieve desired operation wavelength and dispersion, such device being preferably manufactured and aligned as a single unit prior to final assembly.

(39) 20. An optical system according to clause 2, wherein the said laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along one of the crystallographic axes of the crystal [100], [010], or [001].

(40) 21. An optical system according to clause 3, wherein the said laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along one of the crystallographic axes of the crystal [100], [010], or [001].

(41) 22. An optical system according to clause 1, wherein said laser crystal is a chromium doped zinc sulfide (Cr:ZnS) crystal of the wurtzite structure;

(42) 23. An optical system according to clause 22, wherein the said laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along the optical axis of the crystal (crystallographic axis [001]).

(43) 24. An optical system according to clause 5, wherein the said cubic laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along one of the crystallographic axes of the crystal [100], [010], or [001].

(44) 25. An optical system according to clause 5, wherein the said wurtzite laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along the optical axis of the crystal (crystallographic axis [001]).

(45) 26. An optical system according to clause 6, wherein the said cubic laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along one of the crystallographic axes of the crystal [100], [010], or [001].

(46) 27. An optical system according to clause 6, wherein the said wurtzite laser crystal is crystallographically orientated in such a way that the propagation vector of the light pulse is directed along the optical axis of the crystal (crystallographic axis [001]).

(47) 28. An optical sub-system for a passive, mode-locked laser optical system, the optical sub-system comprising; a graphene-based saturable absorber; and a partially transparent output coupling mirror; wherein the graphene-based saturable absorber is supported by the output coupling mirror.

(48) 29. An optical sub-system according to clause 28, wherein the graphene-based saturable absorber is deposited on a surface of the output coupling mirror.

(49) 30. An optical sub-system according to clause 28, wherein the graphene-based saturable absorber is held spatially separated from the output coupling mirror by a supporting mechanism which is connected to the output coupling mirror.

(50) 31. An optical sub-system according to clause 28, wherein the graphene-based saturable absorber is deposited on a mirror.

(51) 32. An optical sub-system according to clause 30 or 31, wherein the supporting mechanism is adjustable such that the distance between the graphene-based saturable absorber and the output coupling mirror is variable.

(52) 33. An optical sub-system according to any of clauses 28 to 32, wherein the output coupling mirror is mounted on a mount allowing rotation of the output coupling mirror about an axis.

(53) 34. An optical sub-system according to any of clauses 28 to 33, wherein the graphene-based saturable absorber comprises at least one of: graphene, a graphene derivative, carbon nanotubes and functionalized graphene.

(54) 35. An optical sub-system according to any of clauses 28 to 34, further comprising an active gain medium, wherein the optical sub-system is provided integrally with or connected to and the active laser gain medium.

(55) It should be apparent that the foregoing relates only to the preferred embodiments of the present application and the resultant patent. Numerous changes and modification may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.