Method and device for substantially eliminating optical damage in lithium niobate devices

Abstract

An integrated optical device includes a substrate. A waveguide includes a lithium niobate. A TiO.sub.2 coating is disposed at least in part over a longitudinal surface of the waveguide as a coated waveguide supported by the substrate. A silicon oxide substantially can cover and surround the waveguide in cross section over a longitudinal direction of said waveguide as an optical cladding. A method for substantially eliminating optical damage in lithium niobate devices is also described.

Claims

1. An integrated optical device comprising: a substrate; a waveguide core comprising a lithium niobate disposed on said substrate; and a TiO.sub.2 coating having a thickness from about 1 nm to about 1000 nm disposed at least in part over a longitudinal surface of said waveguide core as a coated waveguide core supported by said substrate; and wherein a photorefractive effect in said waveguide core is substantially eliminated by said TiO2 coating.

2. The integrated optical device of claim 1, wherein said waveguide core is supported by a silicon substrate.

3. The integrated optical device of claim 1, wherein said waveguide core is supported by a silicon oxide substrate.

4. The integrated optical device of claim 1, wherein said waveguide core is supported by a lithium niobate substrate.

5. The integrated optical device of claim 1, wherein said waveguide core is supported by a sapphire substrate.

6. The integrated optical device of claim 1, wherein said TiO.sub.2 coating comprises a thin-layer of TiO.sub.2 having a thickness between about 1 nm and 1000 nm.

7. The integrated optical device of claim 1, wherein said TiO2 coating is disposed between said waveguide core and a silicon oxide substrate.

8. The integrated optical device of claim 1, further comprising a silicon oxide cladding disposed over a top surface of said waveguide core.

9. The integrated optical device of claim 1, further comprising a silicon oxide cladding disposed over said TiO.sub.2 coating.

10. The integrated optical device of claim 1, wherein said waveguide core comprises a ring resonator.

11. The integrated optical device of claim 9, wherein a wavelength of a cavity resonance remains substantially unaffected for optical power up to about 6.1 w inside the resonator.

12. The integrated optical device of claim 9, wherein said ring resonator comprises an optical Q up to about 4×10.sup.5, wherein a photorefractive effect is substantially eliminated by said TiO2 coating.

13. The integrated optical device of claim 1, comprising a device cross section of a bottom surface of said waveguide core disposed on a SiO.sub.2 substrate, said TiO.sub.2 coating substantially covering a top surface of said waveguide core, and a TiO.sub.2 coating top surface exposed to an air.

14. The integrated optical device of claim 1, comprising a device cross section of a bottom surface of said waveguide core disposed on a SiO.sub.2 substrate, said TiO.sub.2 coating substantially covering a top surface of said waveguide core, and a TiO.sub.2 top surface covered by SiO.sub.2 layer.

15. The integrated optical device of claim 1, comprising a device cross section of a TiO.sub.2 coating disposed between a SiO.sub.2 substrate and said waveguide core.

16. The integrated optical device of claim 1, comprising a device cross section of a bottom surface of said waveguide core disposed on a SiO.sub.2 substrate, and said TiO.sub.2 coating is disposed on at least a right side or a left side of said waveguide core, wherein a SiO.sub.2 layer or an air covers a top surface of said waveguide core.

17. The integrated optical device of claim 1, wherein a SiO.sub.2 surrounds said device in cross section.

18. An integrated optical device comprising: a substrate; a waveguide core comprising a lithium niobate disposed on said substrate; a TiO.sub.2 coating having a thickness from about 1 nm to about 1000 nm disposed at least in part over a surface of said waveguide core on at least either of a top surface of said waveguide core or a bottom surface of said waveguide core; and a silicon oxide substantially covers and surrounds the waveguide core in cross section over a longitudinal direction of said waveguide core as an optical cladding; and wherein a photorefractive effect in said waveguide core is substantially eliminated by said TiO.sub.2 coating.

19. A method for substantially eliminating optical damage in lithium niobate devices comprising: providing a substrate; performing at least one of: fabricating a waveguide core comprising a lithium niobate on said substrate, and depositing a TiO.sub.2 coating having a thickness from about 1 nm to about 1000 nm over at least a part of a side along a longitudinal length of said waveguide core, or depositing a TiO.sub.2 coating over at least a portion of said substrate and fabricating said waveguide core on said TiO.sub.2 coating; thereby substantially eliminating a photorefractive effect in said lithium niobate waveguide core.

20. An integrated optical device comprising: a substrate; a waveguide core comprising a lithium niobate; and a coating having a thickness from about 1 nm to about 1000 nm disposed at least in part over a longitudinal surface of said waveguide core as a coated waveguide core supported by said substrate, said coating comprising at least one of: a silicon (Si), a zinc oxide (ZnO), a zirconium dioxide (ZrO.sub.2), a tin oxide (SnO.sub.2), and an indium tin oxide (ITO); and wherein a photorefractive effect in said waveguide core is substantially eliminated by said coating.

21. An integrated optical device comprising: a substrate; a waveguide core comprising a lithium niobate disposed on said substrate; a TiO.sub.2 coating disposed at least in part over a longitudinal surface of said waveguide core as a coated waveguide core supported by said substrate; and comprising a device cross section of a bottom surface of said waveguide core disposed on a SiO.sub.2 substrate, said TiO.sub.2 coating substantially covering a top surface of said waveguide core, and a TiO.sub.2 top surface covered by SiO.sub.2 layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features of the application can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles described herein. In the drawings, like numerals are used to indicate like parts throughout the various views.

(2) FIG. 1A is a drawing showing a legend of materials which follow in FIG. 1B to FIG. 1E;

(3) FIG. 1B is a drawing showing a cross section of a waveguide including a coating of a thin-layer of titanium oxide on a surface of lithium niobate according to the Application;

(4) FIG. 1C is a drawing showing a three dimensional cross section of the waveguide of FIG. 1B;

(5) FIG. 1D is a drawing showing a cross section of another type of waveguide including a coating of a thin-layer of titanium oxide on a surface of lithium niobate according to the Application;

(6) FIG. 1E is a drawing showing a three dimensional cross section of the waveguide of FIG. 1D;

(7) FIG. 2A is a drawing showing a legend of materials which follow in FIG. 2B to FIG. 2K;

(8) FIG. 2B is a drawing showing an exemplary ridge-like waveguide geometry;

(9) FIG. 2C is a drawing showing another exemplary ridge-like waveguide geometry;

(10) FIG. 2D is a drawing showing an exemplary waveguide structure where the titanium oxide layer can be placed beneath the LN layer;

(11) FIG. 2E is a drawing showing another exemplary waveguide structure where the titanium oxide layer can be placed beneath the LN layer;

(12) FIG. 2F is a drawing showing an exemplary waveguide structure which can be partially covered with titanium oxide;

(13) FIG. 2G is a drawing showing another exemplary waveguide structure which can be partially covered with titanium oxide;

(14) FIG. 2H is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide;

(15) FIG. 2I is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide;

(16) FIG. 2J is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide;

(17) FIG. 2K is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide.

(18) FIG. 3A is a drawing showing a schematic diagram of the waveguide cross section of an exemplary fabricated devices used for the experimental verification;

(19) FIG. 3B is a drawing showing a simulated optical mode field profile of the fundamental quasi-TE guided mode in the TiO.sub.2-cladded LiNbO.sub.3 waveguide of FIG. 3A;

(20) FIG. 3C is a drawing showing a scanning electron microscopic image of a fabricated microring resonator;

(21) FIG. 3D is a graph showing a cavity resonance of a bare lithium niobate microring resonator without the titanium oxide cladding;

(22) FIG. 3E is a graph showing a cavity resonance of a lithium niobate microring resonator with titanium oxide cladding according to FIG. 3A.

(23) FIG. 4A is a graph showing a laser-scanned transmission spectrum of a cavity resonance when the optical power changes inside the microring resonators for a bare lithium niobate microring resonator without titanium oxide cladding;

(24) FIG. 4B is a graph showing a laser-scanned transmission spectrum of a cavity resonance when the optical power changes inside the microring resonators for a lithium niobate microring resonator with a titanium oxide cladding;

(25) FIG. 5A is a graph showing the resonance shift (relative to 1542 nm) vs. temperature curve for both a TiO.sub.2 cladded and an intrinsic LN device;

(26) FIG. 5B is a graph showing curve fitted to data of the zoom box of FIG. 5A;

(27) FIG. 5C is a graph showing normalized transmission with no cladding;

(28) FIG. 5D is a graph showing normalized transmission with a TiO.sub.2 cladding;

(29) FIG. 5E is a graph showing input laser power for the graph of FIG. 5C;

(30) FIG. 5F is a graph showing input laser power for the graph of FIG. 5D;

(31) FIG. 6A is a drawing showing a legend of materials which follow in FIG. 6B to FIG. 6I;

(32) FIG. 6B shows an exemplary waveguide with TiO.sub.2 cladding supported by a silicon oxide substrate (SiO.sub.2 included in our definition of silicon oxide);

(33) FIG. 6C shows the structure of FIG. 6B with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide);

(34) FIG. 6D shows an exemplary waveguide with TiO.sub.2 cladding supported by a buried oxide on a silicon substrate;

(35) FIG. 6E shows the structure of FIG. 6D with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide);

(36) FIG. 6F shows an exemplary waveguide with TiO.sub.2 cladding supported by a buried oxide on a lithium niobate substrate;

(37) FIG. 6G shows the structure of FIG. 6F with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide);

(38) FIG. 6H shows an exemplary waveguide with TiO.sub.2 cladding supported by a sapphire substrate;

(39) FIG. 6I shows the structure of FIG. 6H with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide).

(40) FIG. 7A is a drawing showing a legend of materials which follow in FIG. 7B to FIG. 7D;

(41) FIG. 7B shows an exemplary commercially available Lithium niobate-on-insulator wafer;

(42) FIG. 7C shows another exemplary Lithium niobate-on-insulator wafer; and

(43) FIG. 7D shows an exemplary lithium niobate-on-sapphire wafer.

DETAILED DESCRIPTION

(44) In the description, other than the bolded paragraph numbers, non-bolded square brackets (“[ ]”) refer to the citations listed hereinbelow.

Definitions

(45) Silicon Oxide—A silicon oxide includes a silicon monoxide and the more common silicon dioxide (SiO.sub.2), such as can be used for a substrate or cladding for an optical integrated structure.

(46) Cross section—The cross section views include a variety of layers, coatings, and/or a cladding. It is understood that at least one face surface of the cross section view is typically not covered or coated where the face of the cross section is in the optical transmission path.

(47) Longitudinal direction (longitudinal direction of a waveguide)—The longitudinal direction of a waveguide is the long direction of the travel of light through the waveguide. For a straight waveguide, the longitudinal direction is about perpendicular (“into or out of the page”) to the cross section view. The longitudinal direction of a ring resonator is along the circumference (direction of travel of light in the ring).

(48) Integrated device—integrated optical devices, including integrated optoelectronic devices, photonic integrated circuits (PIC), and planar lightwave circuits. An integrated waveguide, and a ring resonator as described hereinbelow, are but two examples of integrated devices.

(49) Supported by the substrate—Supported by the substrate is used to indicate that the waveguide coated or clad by TiO.sub.2 is directly or indirectly physically or mechanically supported by the substrate as an integrated device. The waveguide coated or clad by TiO.sub.2 can be disposed directly on the substrate, or there can be any suitable number and type or types of intermediate layers between the waveguide coated or clad by TiO.sub.2 and the substrate. Also, with reference to a substrate at the “bottom” of the structure, the TiO.sub.2 coating can be above the waveguide (e.g. FIG. 2B), or below the waveguide (e.g. FIG. 2D). For example, the TiO.sub.2 coating can be disposed between the bottom of the LN waveguide and a SiO.sub.2 layer on top of the substrate (e.g. FIG. 2E). Note that in some structures according to the Application, the LN waveguide is disposed on (typically bonded to, where the LN waveguide is etched from a LN layer) a low index layer (e.g. SiO.sub.2) which is on the substrate (e.g. a Si or LN substrate).

(50) An integrated waveguide, for example, typically has a cross section at either end of the planar waveguide. The cross section of a ring resonator applies both to the optical path of the ring, as well as a portion of a side of the ring resonator which typically tangentially optically couples to another, typically about linear or about straight waveguide (which can also include a slight curve to follow the ring shape, as shown, for example, in FIG. 3C).

(51) Fabricating the waveguide—The LN waveguide of the Application is typically etched from a LN layer, such as an LN layer provided on a commercial wafer which is supplied with one or more layers already bonded to a substrate. Typically, the LN layer from which the LN waveguide is fabricated is bonded to the substrate, or is bonded to another layer which is bonded directly or indirectly to the substrate. Any suitable LN waveguide fabrication method can be used. In structures where the waveguide is fabricated over the TiO.sub.2 coating, the waveguide can be attached or bonded to the TiO.sub.2 coating. Or, a LN layer can be attached to the TiO.sub.2 coating and the waveguide then fabricated from the LN layer, typically by any suitable lithography technique and etching.

(52) This Application is in three parts. Part 1 describes the problem of optical damage caused by the photorefractive effect. Part 2 describes the new solution of the Application, where a thin-layer of titanium oxide TiO.sub.2 substantially eliminates the photorefractive effect in thin-film lithium niobate. Part 3 describes verification experiments.

(53) Part 1—Optical Damage Caused by the Photorefractive Effect

(54) As described hereinabove, lithium niobate (LN) is a workhorse material system for the photonics industry and for photonics research and development. LN has a wide range of useful properties including electro-optic effect, optical nonlinearities, acousto-optic effect, piezoelectricity that have found broad applications such as high-speed signal modulation in lightwave communications, frequency conversion in commercial lasers, signal filtering in RF/microwave electronics [1, 2, 3, 4], to name a few.

(55) Unfortunately, LN exhibits a strong photorefractive effect that induces optical damage when the optical intensity becomes significant inside the material [5]. Photorefractive-induced optical damage has become the major challenge for the application of LN devices in the high-power regime. In the prior art, to mitigate this issue, the LN crystal has either to be doped with certain ions (such as Mg) via a sophisticated doping process to increase the threshold of optical damage [6], or to be processed via a complicated day-long “optical cleaning” procedure at elevated temperature above 180° C. [7].

(56) Part 2—A Thin-Layer of Titanium Oxide TiO.sub.2 Substantially Eliminates the Photorefractive Effect in Thin-Film Lithium Niobate

(57) A new approach to substantially eliminate the photorefractive effect in thin-film lithium niobate is described in detail hereinbelow. We realized that the photorefractive effect can be quenched by coating the lithium niobate with a thin-layer of material. We realized, for example, that a thin-layer of titanium oxide TiO.sub.2 substantially eliminates the photorefractive effect in thin-film lithium niobate. A thin-layer of titanium oxide TiO.sub.2 having a thickness from about 1 nm to about 1000 nm can be used.

(58) FIG. 1A to FIG. 1E show exemplary structures to substantially eliminate the photorefractive effect in thin-film lithium niobate according to the Application. FIG. 1A is a drawing showing a legend of materials which follow in FIG. 1B to FIG. 1E. FIG. 1B is a drawing showing a cross section of a waveguide including a coating of a thin-layer of titanium oxide on the surface of lithium niobate according to the Application. FIG. 1C is a drawing showing a three dimensional cross section of the waveguide of FIG. 1B. FIG. 1D is a drawing showing a cross section of another type of waveguide including a coating of a thin-layer of titanium oxide on the surface of lithium niobate according to the Application. FIG. 1E is a drawing showing a three dimensional cross section of the waveguide of FIG. 1D.

(59) A thin-film LN photonic waveguide sits on a silicon oxide layer, such as an SiO.sub.2 substrate. A thin-layer of titanium oxide is directly coated on the surface of LN waveguide. Above the whole waveguide structure, the top cladding can be either air (FIG. 1B and FIG. C) or silicon oxide (FIG. 1D and FIG. 1E) or another low-index medium. The crystal orientation of the LN layer can be either x-cut, z-cut, or y-cut. Titanium oxide cladding has been used to engineer the thermo-optic properties of silicon and silicon nitride photonic waveguides [8, 9, 10, 11]. However, to our best understanding, titanium oxide cladding has never been applied to address the photorefractive effect.

(60) FIG. 2A to FIG. 2K show more exemplary variations of waveguide structures to substantially eliminate the photorefractive effect in thin-film lithium niobate according to the Application.

(61) FIG. 2A is a drawing showing a legend of materials which follow in FIG. 2B to FIG. 2K. FIG. 2B is a drawing showing an exemplary ridge-like waveguide geometry. FIG. 2C is a drawing showing another exemplary ridge-like waveguide geometry. FIG. 2D is a drawing showing an exemplary waveguide structure where the titanium oxide layer can be placed beneath the LN layer. FIG. 2E is a drawing showing another exemplary waveguide structure where the titanium oxide layer can be placed beneath the LN layer. FIG. 2F is a drawing showing an exemplary waveguide structure which can be partially covered with titanium oxide. FIG. 2G is a drawing showing another exemplary waveguide structure which can be partially covered with titanium oxide. FIG. 2H is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide. FIG. 2I is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide. FIG. 2J is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide. FIG. 2K is a drawing showing yet another exemplary waveguide structure which can be partially covered with titanium oxide. As long as the thin titanium oxide layer has direct contact with an adequate portion of the surface of the LN waveguide, the new method will work to substantially eliminate the photorefractive effect in thin-film lithium niobate, by coating the LN waveguide with a thin-layer of certain material that will quench the photorefractive effect.

(62) Part 3—Experimental Verification

(63) FIG. 3A to FIG. 3E show experimental verification of the new structures and method to substantially eliminate the photorefractive effect in thin-film lithium niobate of the Application. FIG. 3A is a drawing showing a schematic diagram of the waveguide cross section of exemplary fabricated devices used for the experimental verification. The waveguide structure of FIG. 3A is the same as shown in FIG. 1B. FIG. 3B is a drawing showing a simulated optical mode field profile of the fundamental quasi-TE guided mode in the TiO.sub.2-cladded LiNbO.sub.3 waveguide of FIG. 3A. FIG. 3C is a drawing showing a scanning electron microscopic image of a fabricated microring resonator. FIG. 3D is a graph showing a cavity resonance of a bare lithium niobate microring resonator without the titanium oxide cladding. FIG. 3E is a graph showing a cavity resonance of a lithium niobate microring resonator with titanium oxide cladding according to FIG. 3A.

(64) Example—A LN microring fabricated device according to FIG. 3A has a layer thickness of H=600 nm, etched down by 410 nm with h=190 nm, and a sidewall angle of θ=75°. The microring and the coupling waveguide have a waveguide width of W=1.8 and 1.2 μm, respectively. A 120-nm-thick TiO.sub.2 layer was deposited on top surface of the LN waveguide via physical vapor deposition (The current thickness of the titanium oxide layer was chosen to suppress the thermo-optic sensitivity, but to eliminate the photorefractive effect, other thickness of the TiO.sub.2 layer could also be used as well.) The simulated optical mode profile (FIG. 3B), in which the optical mode is primarily confined inside the LN waveguide core. As shown in FIG. 3D, before coating with a TiO.sub.2 cladding, the LN microring resonator exhibits an intrinsic and loaded optical Q of 6.55×10.sup.5 and 5.72×10.sup.5, respectively, in the telecom band around 1540 nm. After coating with the TiO.sub.2 cladding, the optical Q of the micro-ring remains nearly intact, as shown in FIG. 3E, with an intrinsic and loaded optical Q of 5.43×10.sup.5 and 4.19×10.sup.5, respectively. This example shows the high quality of TiO.sub.2 layer deposition.

(65) FIG. 4A and FIG. 4B show the laser-scanned transmission spectrum of a cavity resonance when the optical power changes inside the microring resonators. The laser was scanned back and forth across the cavity resonance and the light transmission from the resonators was monitored.

(66) FIG. 4A is a graph showing normalized transmission for a bare LN microring resonator without the titanium oxide cladding, where the transmission spectrum is dramatically distorted, and the resonance wavelength is significantly shifted when the optical power increases inside the resonator. This is a combined effect of therm-optic nonlinear effect and photorefractive effect.

(67) FIG. 4B is a graph showing normalized transmission for the LN microring resonator with a titanium oxide cladding. The transmission spectrum remains nearly intact and the wavelength position of the cavity resonance remains fixed even when the optical power increases to about 6.1 W inside the cavity, indicating that both the thermo-optic nonlinear effect and the photorefractive effect are eliminated in the resonator.

(68) Example—To test the temperature sensitivity of the devices, the device temperature was changed, and the wavelength drift of the cavity resonance was monitored.

(69) FIG. 5A to FIG. 5F show the experimental results. FIG. 5A is a graph showing the resonance shift (relative to 1542 nm) vs. temperature curve for both TiO.sub.2 cladded and intrinsic LN device. FIG. 5B is a graph showing curve fitted to data of the zoom box of FIG. 5A. The discrepancy between data and fitted curve is caused by higher order thermo-optic coefficient (TOC). FIG. 5C is a graph showing normalized transmission with no cladding. FIG. 5D is a graph showing normalized transmission with a TiO.sub.2 cladding. FIG. 5E and FIG. 5F show the input on-chip power curve for intrinsic and cladded LN devices. FIG. 5E is a graph showing input laser power for the graph of FIG. 5C. FIG. 5F is a graph showing input laser power for the graph of FIG. 5D.

(70) As shown in the red curve of FIG. 5A, the cavity resonance of the bare LN microring depends linearly with temperature with a slope of 52.9 pm/K. In contrast, the temperature dependence is significantly suppressed in the TiO.sub.2 added LN microring, as shown clearly by the green curve in FIG. 5A. As shown in FIG. 5B, the slope of temperature dependence decreases to zero at room temperature, leaving a slight quadratic dependence on temperature, with only about 30 pm for temperature in the range between 15 and 25° C.

(71) Of particular interest is that the TiO.sub.2 cladding modifies dramatically the nonlinear optical behavior of the microring resonator. To show this feature, the optical power launched into the resonator was increased. As shown in FIG. 5C, when the input optical power was increased from −24 dBm to −4 dBm. A significant nonlinearity-induced bistability appeared in the bare LN microring without the TiO.sub.2 cladding. This phenomenon arises from a combined effect of thermo-optic nonlinearity and the photorefractive effect, where the latter also shifts the overall cavity resonance towards blue. In strong contrast, in the TiO.sub.2-cladded LN microring, the Lorentzian shape of the cavity resonance remains nearly intact (substantially unaffected) for optical power up to about 8 dBm, indicating a negligible effect of thermo-optic nonlinearity. In particular, intriguingly, the overall cavity resonance wavelength remains constant (as indicated by the dashed line), implying a complete quenching of the photorefractive effect.

(72) In summary, we have demonstrated TiO.sub.2-cladded LN ring resonators with optical Q up to about 4×10.sup.5, cancelled first-order thermo-optic effect at room temperature, and quenched photorefraction. The significantly enhanced temperature stability and power handling capability of the demonstrated LN/TiO.sub.2 hybrid athermal devices shows great potential for stable and highly efficient operation of electro-optic signal processing and high power nonlinear photonics. Note that ring resonators of any suitable Q can be used, including ring resonators having a Q of up to about 4×10.sup.5 the relatively high Q of a LN ring resonator made possible by the new TiO.sub.2 cladding according to the Application.

(73) More generally, beyond the experimental implementations described hereinabove for TiO.sub.2-cladded LN ring resonators, the new method and device for substantially eliminating optical damage in lithium niobate devices applies to any suitable type of lithium niobate devices, typically in the form of integrated optical devices and integrated optoelectronic devices, including photonic integrated circuits (PIC) and planar lightwave circuits.

(74) Substrates—A variety of substrates can be used for the method and device for substantially eliminating optical damage in lithium niobate devices as described hereinabove according to the Application. FIG. 6A to FIG. 6I show several more exemplary structural configurations. FIG. 6A is a drawing showing a legend of materials which follow in FIG. 6B to FIG. 6I. FIG. 6B shows an exemplary waveguide with TiO.sub.2 cladding supported by a silicon oxide substrate (SiO.sub.2 included in our definition of silicon oxide). FIG. 6C shows the structure of FIG. 6B with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide). FIG. 6D shows an exemplary waveguide with TiO.sub.2 cladding supported by a buried oxide on a silicon substrate. FIG. 6E shows the structure of FIG. 6D with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide). FIG. 6F shows an exemplary waveguide with TiO.sub.2 cladding supported by a buried oxide on a lithium niobate substrate. FIG. 6G shows the structure of FIG. 6F with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide). FIG. 6H shows an exemplary waveguide with TiO.sub.2 cladding supported by a sapphire substrate. FIG. 6I shows the structure of FIG. 6H with an additional layer of SiO.sub.2 over the TiO.sub.2 cladding (on top of the TiO.sub.2 cladded waveguide).

(75) FIG. 7A to FIG. 7D show exemplary commercially available wafers and exemplary wafers using during laboratory verification implementations. Commercial wafers, such as lithium-niobate-on-insulator wafers, are available for example, from NANOLN, of Jinan, P. R. China, are typically supplied as, for example, about 3″ or 4″ wafers. FIG. 7A is a drawing showing a legend of materials which follow in FIG. 7B to FIG. 7D. FIG. 7B shows an exemplary commercially available Lithium niobate-on-insulator wafer. FIG. 7C shows another exemplary Lithium niobate-on-insulator wafer. FIG. 7D shows an exemplary lithium niobate-on-sapphire wafer.

(76) Manufacturing and Fabrication

(77) The waveguide of the Application can be fabricated from a LN layer bonded directly or indirectly to the substrate by any suitable method. Typically, the waveguide is etched by any suitable lithography and/or etching method.

(78) A TiO.sub.2 coated waveguide of the new method and device for substantially eliminating optical damage in lithium niobate devices of the application, can be manufactured and/or fabricated by any suitable technique. During implementation experiments, the TiO.sub.2 coating was created by deposition. The TiO.sub.2 layer can be deposited by any suitable methods such as, for example, physical vapor deposition (PVD), chemical vapor deposition (CVD) (including some variants such as PECVD LPCVD PACVD), liquid phase deposition (LPD) (including sol-gel, dip-coating, spinning coating), atomic layer deposition (ALD), photopatterned self-assembled monolayer, flame hydrolysis deposition, and oxidation of deposited titanium layer.

(79) Note that in some integrated structures, such as, for example, FIG. 2D, FIG. 2E, there can be a TiO.sub.2 layer below the waveguide layer (i.e. between the waveguide and the substrate). Note also, that for many types of substrates, there is also a low index layer (e.g. SiO.sub.2) disposed between either the waveguide and the substrate, or in some structures, the TiO.sub.2 clad structure and the waveguide. For example, a LN waveguide formed directly over a LN substrate would not have useable waveguide light guiding properties, because both the waveguide and substrate would have the same refractive properties.

(80) Alternative Coatings to the TiO.sub.2 coating—The following materials are believed to be alternatives for the TiO.sub.2 coating: silicon (Si), zinc oxide (ZnO), zirconium dioxide (ZrO.sub.2), tin oxide (SnO.sub.2), indium tin oxide (ITO). These materials possess properties similar to TiO.sub.2, and as such, are also useful to minimize or to substantially eliminate the photorefractive effect to some extent for a LN waveguide, in the same way as the TiO.sub.2 coating described hereinabove.

(81) Software for designing, modeling, and analyzing waveguides including a coating of a thin-layer of titanium oxide on the surface of lithium niobate according to the Application can be provided on a computer readable non-transitory storage medium. A computer readable non-transitory storage medium as non-transitory data storage includes any data stored on any suitable media in a non-fleeting manner. Such data storage includes any suitable computer readable non-transitory storage medium, including, but not limited to hard drives, non-volatile RAM, SSD devices, CDs, DVDs, etc.

(82) It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

REFERENCES

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