Micro-mechanical film lithium niobate electro-optical device

Abstract

Optical devices made of thin film lithium niobate and fabrication thereof are provided. In some embodiments, an optical device includes a substrate and an optical waveguide disposed on the substrate. The optical waveguide includes lithium niobate. The optical waveguide has a central ridge extending laterally along the substrate. A pair of electrodes is disposed on opposite sides of the central ridge of the optical waveguide.

Description

[0001] This application is a divisional application of the patent application with application number 201780063035.1, titled "Micromechanical Thin-Film Lithium Niobate Electro-Optic Device", filed by the present applicant on August 11, 2017. The entire content of the parent case is incorporated into this divisional application by reference.

[0002] Cross - Reference to Related Applications

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 374,226, filed on August 12, 2016, which is incorporated herein by reference in its entirety. Background Art

[0004] Embodiments of the present invention relate to optical waveguides, and more particularly to optical devices fabricated from thin-film lithium niobate (LN). Summary of the Invention

[0005] According to embodiments of the present disclosure, a method of fabricating an optical waveguide is provided. A first resist is deposited on a lithium niobate film. A second resist is deposited on the first resist in a first pattern. The first resist is patterned according to the first pattern. The lithium niobate film is etched to transfer the first pattern from the first resist to the lithium niobate film.

[0006] In some embodiments, the lithium niobate film has a thickness of about 1 μm or less. In some embodiments, the lithium niobate film has a thickness of about 700 nm or less. In some embodiments, the lithium niobate film has a thickness of about 400 nm or less.

[0007] In some embodiments, the lithium niobate film is disposed on an insulator. In some embodiments, the refractive index of the insulator is less than the refractive index of the lithium niobate film. In some embodiments, the insulator includes silicon dioxide.

[0008] In some embodiments, the insulator is disposed on a carrier. In some embodiments, the carrier includes lithium niobate. In some embodiments, the carrier includes silicon. In some embodiments, the carrier includes quartz. In some embodiments, the carrier includes silicon dioxide. In some embodiments, the carrier includes sapphire.

[0009] In some embodiments, the first resist comprises amorphous silicon. In some embodiments, the first resist comprises silicon dioxide. In some embodiments, the first resist comprises silicon nitride. In some embodiments, the first resist comprises aluminum oxide. In some embodiments, the first resist comprises titanium dioxide. In some embodiments, the hardness of the first resist is greater than the hardness of the second resist. In some embodiments, the first resist is deposited by chemical vapor deposition. In some embodiments, the first resist is deposited by plasma enhanced chemical vapor deposition. In some embodiments, the first resist is p-doped. In some embodiments, the first resist has a thickness of about 800 nm.

[0010] In some embodiments, the second resist comprises a polymer. In some embodiments, the polymer comprises a flowable oxide. In some embodiments, the polymer comprises FOX-16. In some embodiments, the second resist is deposited by spin coating. In some embodiments, depositing the second resist includes lithographically patterning the second resist according to a first pattern. In some embodiments, the second resist is lithographically patterned by electron beam lithography.

[0011] In some embodiments, the first resist is etched by dry etching. In some embodiments, the first resist is etched by reactive ion etching. In some embodiments, the reactive ion etching is inductively coupled plasma reactive ion etching. In some embodiments, the reactive ion etching uses Ar + plasma.

[0012] In some embodiments, the lithium niobate film is etched by dry etching. In some embodiments, the lithium niobate film is etched by reactive ion etching. In some embodiments, the reactive ion etching is inductively coupled plasma reactive ion etching. In some embodiments, the reactive ion etching uses Ar + plasma.

[0013] In some embodiments, the method includes removing the first resist from the lithium niobate film. In some embodiments, removing the first resist from the lithium niobate film includes exposing the first resist to a potassium hydroxide solution. In some embodiments, the potassium hydroxide solution is a 30% solution. In some embodiments, the first resist is exposed to the potassium hydroxide solution at about 80 °C for about 2 minutes.

[0014] In some embodiments, the method includes patterning an electrode on an insulator. In some embodiments, the electrode is patterned by electron beam lithography. In some embodiments, the electron beam lithography includes PMMA lift-off. In some embodiments, the electrode comprises a metal. In some embodiments, the electrode comprises gold.

[0015] In some embodiments, the method includes patterning electrodes on a lithium niobate film. In some embodiments, the electrodes are patterned by electron beam lithography. In some embodiments, the electron beam lithography includes PMMA lift-off. In some embodiments, the electrodes comprise a metal. In some embodiments, the electrodes comprise gold.

[0016] In some embodiments, the lithium niobate film is monolithic.

[0017] According to another embodiment of the present disclosure, an electro-optic device is provided. The device includes a substrate. An optical waveguide is disposed on the substrate. The optical waveguide comprises lithium niobate. The optical waveguide has a central ridge extending laterally along the substrate. An electrode pair is disposed on opposite sides of the central ridge of the optical waveguide.

[0018] In some embodiments, the central ridge has a width of about 1 μm or less. In some embodiments, the central ridge has a width of about 900 nm or less. In some embodiments, the central ridge has a width of about 500 nm. In some embodiments, the central ridge has a width of about 400 nm.

[0019] In some embodiments, the optical waveguide includes legs extending outward from the central ridge along a first side of the substrate between the first side of the substrate and the electrodes. In some embodiments, the height of the legs is less than the height of the central ridge. In some embodiments, the height of the legs is less than or equal to half of the height of the central ridge. In some embodiments, the legs have a height of about 300 nm.

[0020] In some embodiments, the lithium niobate is a crystal and is arranged such that the x-axis of its crystal lattice extends substantially perpendicular to the first side of the substrate. In some embodiments, the lithium niobate is monolithic.

[0021] In some embodiments, the central ridge has a thickness of about 1 μm or less. In some embodiments, the central ridge has a thickness of about 700 nm or less. In some embodiments, the central ridge has a thickness of about 400 nm or greater. In some embodiments, the central ridge has a thickness of about 400 nm.

[0022] In some embodiments, the substrate is an insulator. In some embodiments, the refractive index of the insulator is less than the refractive index of the optical waveguide. In some embodiments, the insulator comprises silica.

[0023] In some embodiments, the device includes a carrier, and the substrate is disposed on the carrier. In some embodiments, the carrier comprises lithium niobate. In some embodiments, the carrier comprises silicon. In some embodiments, the carrier comprises quartz. In some embodiments, the carrier comprises silica. In some embodiments, the carrier comprises sapphire.

[0024] In some embodiments, the electrodes comprise a metal. In some embodiments, the electrodes comprise gold. In some embodiments, the pair of electrodes is adapted to modulate an optical mode of an optical waveguide when a voltage is applied across the pair of electrodes.

[0025] In some embodiments, the optical waveguide comprises a substantially semi-circular bend. In some embodiments, the substantially semi-circular bend has a radius of about 50 μm or less. In some embodiments, the substantially semi-circular bend has a radius of about 20 μm. In some embodiments, the substantially semi-circular bend has a radius of about 5 μm.

[0026] In some embodiments, each of the pair of electrodes has a length of about 1 mm or less.

[0027] In some embodiments, the optical waveguide is disposed along a substantially serpentine path defined by a plurality of arcuate segments. In some embodiments, the arcuate segments are substantially semi-circular. In some embodiments, each of the arcuate segments has a radius of less than about 50 μm. In some embodiments, each of the arcuate segments has a radius of about 20 μm. In some embodiments, each of the arcuate segments has a radius of about 5 μm. In some embodiments, each of the arcuate segments is separated by about 1 mm or less.

[0028] In some embodiments, the pair of electrodes is separated by about 3.5 μm.

[0029] In some embodiments, the optical waveguide is disposed along a substantially circular path. In some embodiments, the optical waveguide is disposed on a first side of a substrate to form a ring resonator. In some embodiments, the optical waveguide is disposed on a first side of a substrate to form a racetrack resonator. In some embodiments, the optical waveguide is disposed on a first side of a substrate to form a Mach-Zehnder interferometer.

[0030] In some embodiments, the device is adapted to shift a resonant wavelength by an applied voltage. In some embodiments, the device is adapted to provide velocity matching. In some embodiments, the device is adapted to provide electro-optic modulation.

[0031] The present invention also includes the following items:

[0032] 1. A method, the method comprising:

[0033] Depositing a first resist on a lithium niobate film;

[0034] Depositing a second resist on the first resist in a first pattern;

[0035] Patterning the first resist according to the first pattern;

[0036] Etch the lithium niobate film to transfer the first pattern from the first resist to the lithium niobate film.

[0037] 2. The method according to item 1, wherein the lithium niobate film has a thickness of about 1 μm or less.

[0038] 3. The method according to item 2, wherein the lithium niobate film has a thickness of about 700 nm or less.

[0039] 4. The method according to item 3, wherein the lithium niobate film has a thickness of about 400 nm or less.

[0040] 5. The method according to item 1, wherein the lithium niobate film is disposed on an insulator.

[0041] 6. The method according to item 5, wherein the refractive index of the insulator is less than the refractive index of the lithium niobate film.

[0042] 7. The method according to item 5, wherein the insulator comprises silicon dioxide.

[0043] 8. The method according to item 5, wherein the insulator is disposed on a carrier.

[0044] 9. The method according to item 8, wherein the carrier comprises lithium niobate.

[0045] 10. The method according to item 8, wherein the carrier comprises silicon.

[0046] 11. The method according to item 8, wherein the carrier comprises quartz.

[0047] 12. The method according to item 8, wherein the carrier comprises silicon dioxide.

[0048] 13. The method according to item 8, wherein the carrier comprises sapphire.

[0049] 14. The method according to item 1, wherein the first resist comprises amorphous silicon.

[0050] 15. The method according to item 1, wherein the first resist comprises silicon dioxide.

[0051] 16. The method according to item 1, wherein the first resist comprises silicon nitride.

[0052] 17. The method according to item 1, wherein the first resist comprises aluminum oxide.

[0053] 18. The method according to item 1, wherein the first resist comprises titanium dioxide.

[0054] 19. The method according to item 1, wherein the hardness of the first resist is greater than the hardness of the second resist.

[0055] 20. The method according to item 1, wherein the first resist is deposited by chemical vapor deposition.

[0056] 21. The method according to item 20, wherein the first resist is deposited by plasma-enhanced chemical vapor deposition.

[0057] 22. The method according to item 1, wherein the first resist is p-doped.

[0058] 23. The method according to item 1, wherein the first resist has a thickness of about 800 nm.

[0059] 24. The method according to item 1, wherein the second resist comprises a polymer.

[0060] 25. The method according to item 22, wherein the polymer comprises a flowable oxide.

[0061] 26. The method according to item 23, wherein the polymer comprises FOX-16.

[0062] 27. The method according to item 1, wherein the second resist is deposited by spin coating.

[0063] 28. The method according to item 1, wherein depositing the second resist comprises:

[0064] lithographically patterning the second resist according to the first pattern.

[0065] 29. The method according to item 26, wherein the second resist is lithographically patterned by electron beam lithography.

[0066] 30. The method according to item 1, wherein the first resist is etched by dry etching.

[0067] 31. The method according to item 1, wherein the first resist is etched by reactive ion etching.

[0068] 32. The method according to item 31, wherein the reactive ion etching is inductively coupled plasma reactive ion etching.

[0069] 33. The method according to item 31, wherein the reactive ion etching uses Ar + plasma.

[0070] 34. The method according to item 1, wherein the lithium niobate film is etched by dry etching.

[0071] 35. The method according to item 1, wherein the lithium niobate film is etched by reactive ion etching.

[0072] 36. The method according to item 35, wherein the reactive ion etching is inductively coupled plasma reactive ion etching.

[0073] 37. The method according to item 35, wherein the reactive ion etching uses Ar + plasma.

[0074] 38. The method according to item 1, the method further comprising:

[0075] Removing the first resist from the lithium niobate film.

[0076] 39. The method according to item 36, wherein removing the first resist from the lithium niobate film comprises:

[0077] Exposing the first resist to a potassium hydroxide solution.

[0078] 40. The method according to item 39, wherein the potassium hydroxide solution is a 30% solution.

[0079] 41. The method according to item 39, wherein the first resist is exposed to the potassium hydroxide solution at about 80 °C for about 2 minutes.

[0080] 42. The method according to item 1, wherein the lithium niobate film is disposed on an insulator, the method further comprising:

[0081] Patterning an electrode on the insulator.

[0082] 43. The method according to item 42, wherein the electrode is patterned by electron beam lithography.

[0083] 44. The method according to item 43, wherein the electron beam lithography includes PMMA lift-off.

[0084] 45. The method according to item 42, wherein the electrode contains a metal.

[0085] 46. The method according to item 45, wherein the electrode contains gold.

[0086] 47. The method according to item 1, the method further comprising:

[0087] Patterning an electrode on the lithium niobate film.

[0088] 48. The method according to item 47, wherein the electrode is patterned by electron beam lithography.

[0089] 49. The method according to item 48, wherein the electron beam lithography includes PMMA lift-off.

[0090] 50. The method according to item 47, wherein the electrode comprises a metal.

[0091] 51. The method according to item 50, wherein the electrode comprises gold.

[0092] 52. The method according to item 1, wherein the lithium niobate film is monolithic.

[0093] 53. An apparatus, the apparatus comprising:

[0094] A substrate having a first side;

[0095] An optical waveguide disposed on the first side of the substrate, the optical waveguide comprising lithium niobate and having a central ridge;

[0096] An electrode pair disposed on the first side of the substrate such that the central ridge of the optical waveguide extends between the electrode pair.

[0097] 54. The apparatus according to item 53, wherein the optical waveguide further comprises:

[0098] Legs extending outward from the central ridge along the first side of the substrate between the first side of the substrate and the electrode.

[0099] 55. The apparatus according to item 53, wherein the central ridge has a width of about 1 μm or less.

[0100] 56. The apparatus according to item 53, wherein the central ridge has a width of about 900 nm or less.

[0101] 57. The apparatus according to item 53, wherein the central ridge has a width of about 500 nm.

[0102] 58. The apparatus according to item 53, wherein the central ridge has a width of about 400 nm.

[0103] 59. The apparatus according to item 54, wherein the height of the legs is less than the height of the central ridge.

[0104] 60. The apparatus according to item 59, wherein the height of the legs is less than or equal to half of the height of the central ridge.

[0105] 61. The apparatus according to item 59, wherein the legs have a height of about 300 nm.

[0106] 62. The device according to item 53, wherein the lithium niobate is a crystal and is arranged such that the x-axis of its lattice extends substantially perpendicular to the first side of the substrate.

[0107] 63. The device according to item 53, wherein the central ridge has a thickness of about 1 μm or less.

[0108] 64. The method according to item 63, wherein the central ridge has a thickness of about 700 nm or less.

[0109] 65. The device according to item 63, wherein the central ridge has a thickness of about 400 nm or more.

[0110] 66. The device according to item 63, wherein the central ridge has a thickness of about 400 nm.

[0111] 67. The device according to item 53, wherein the substrate is an insulator.

[0112] 68. The device according to item 67, wherein the refractive index of the insulator is less than the refractive index of the optical waveguide.

[0113] 69. The device according to item 67, wherein the insulator comprises silicon dioxide.

[0114] 70. The device according to item 53, the device further comprising:

[0115] A carrier, on which the substrate is disposed.

[0116] 71. The device according to item 70, wherein the carrier comprises lithium niobate.

[0117] 72. The device according to item 70, wherein the carrier comprises silicon.

[0118] 73. The device according to item 70, wherein the carrier comprises quartz.

[0119] 74. The method according to item 70, wherein the carrier comprises silicon dioxide.

[0120] 75. The method according to item 70, wherein the carrier comprises sapphire.

[0121] 76. The device according to item 53, wherein the electrode comprises a metal.

[0122] 77. The device according to item 76, wherein the electrode comprises gold.

[0123] 78. The device according to item 53, wherein the pair of electrodes is adapted to modulate the optical mode of the optical waveguide when a voltage is applied across the pair of electrodes.

[0124] 79. The device according to item 53, wherein the optical waveguide comprises a substantially semi-circular bend.

[0125] 80. The device according to item 79, wherein the substantially semi-circular bend has a radius of about 50 μm or less.

[0126] 81. The device according to item 79, wherein the substantially semi-circular bend has a radius of about 20 μm.

[0127] 82. The device according to item 79, wherein the substantially semi-circular bend has a radius of about 5 μm.

[0128] 83. The device according to item 53, wherein each of the pair of electrodes has a length of about 1 mm or less.

[0129] 84. The device according to item 53, wherein the optical waveguide is arranged along a substantially serpentine path defined by a plurality of arcuate segments.

[0130] 85. The device according to item 84, wherein the arcuate segments are substantially semi-circular.

[0131] 86. The device according to item 84, wherein each of the arcuate segments has a radius of less than about 50 μm.

[0132] 87. The device according to item 84, wherein each of the arcuate segments has a radius of about 20 μm.

[0133] 88. The device according to item 84, wherein each of the arcuate segments has a radius of about 5 μm.

[0134] 89. The device according to item 84, wherein the arcuate segments are each separated by about 1 mm or less.

[0135] 90. The device according to item 53, wherein the pair of electrodes is separated by about 3.5 μm.

[0136] 91. The device according to item 53, wherein the optical waveguide is arranged along a substantially circular path.

[0137] 92. The device according to item 53, wherein the optical waveguide is arranged on the first side of the substrate to form a ring resonator.

[0138] 93. The device according to item 53, wherein the optical waveguide is disposed on the first side of the substrate to form a racetrack resonator.

[0139] 94. The device according to item 53, wherein the optical waveguide is disposed on the first side of the substrate to form a Mach-Zehnder interferometer.

[0140] 95. The device according to item 53, the device being adapted to shift a resonant wavelength by an applied voltage.

[0141] 96. The device according to item 53, the device being adapted to provide velocity matching.

[0142] 97. The device according to item 53, the device being adapted to provide electro-optic modulation. Description of the Drawings

[0143] Figure 1 is a cross-sectional view of an electro-optic modulator according to an embodiment of the present disclosure.

[0144] Figure 2A -B is a SEM image of a fabricated racetrack resonator-based modulator according to an embodiment of the present disclosure.

[0145] Figure 3 is a graph of transmittance versus wavelength, illustrating the measured optical transmission spectrum of a modulator and its Lorentzian fit according to an embodiment of the present disclosure.

[0146] Figure 4 is a graph of electro-optic response versus frequency, illustrating the frequency response of a modulator according to an embodiment of the present disclosure.

[0147] Figure 5A -E is a schematic diagram of an optical device, sequentially illustrating the steps of a method for manufacturing a device according to an embodiment of the present disclosure.

[0148] Figure 6 is a cross-sectional view of a waveguide according to an embodiment of the present disclosure.

[0149] Figure 7 is a plan view of an exemplary modulator layout according to an embodiment of the present disclosure.

[0150] Figure 8 is a plan view of an exemplary modulator layout illustrating the RF phase.

[0151] Figure 9 is a plan view of an exemplary modulator layout according to an embodiment of the present disclosure, illustrating the RF phase.

[0152] Figure 10Cross-sectional view of an exemplary waveguide according to an embodiment of the present disclosure.

[0153] Figure 11 Cross-sectional view of an exemplary waveguide according to an embodiment of the present disclosure.

[0154] Figure 12 Perspective view of an ion-diffused LN waveguide next to an etched LN waveguide according to an embodiment of the present disclosure.

[0155] Figure 13 Schematic diagram of an exemplary device layout including a thin-film LN waveguide and an RF electrode according to an embodiment of the present disclosure.

[0156] Figure 14 Pseudo-color scanning electron microscope (SEM) image of a modulator based on racetrack and ring resonators according to an embodiment of the present disclosure.

[0157] Figure 15 Pseudo-color scanning electron microscope (SEM) image of a modulator based on a Mach-Zehnder interferometer according to an embodiment of the present disclosure.

[0158] Figure 16 Close-up SEM image of an exemplary metal electrode and an associated optical waveguide according to an embodiment of the present disclosure.

[0159] Figure 17 Cross-sectional view of the simulated optical transverse electric (TE) mode distribution (mode profile) and RF electric field of a waveguide according to an embodiment of the present disclosure.

[0160] Figure 18 Graph of wavelength versus normalized transmittance in a racetrack resonator according to an embodiment of the present disclosure.

[0161] Figure 19 Graph of DC compensation (offset) versus resonance shift in a racetrack resonator according to an embodiment of the present disclosure.

[0162] Figure 20 Graph of optical transmittance versus DC compensation in a Mach-Zehnder interferometer according to an embodiment of the present disclosure.

[0163] Figure 21 Schematic diagram of an instrument for testing the eye diagram of a device according to the present disclosure.

[0164] Figure 22 Graph of the modulation frequency of a racetrack resonator versus the electro-optic coefficient S 21 of the present disclosure.

[0165] Figure 23 is a graph of the modulation frequency of a Mach-Zehnder interferometer according to an embodiment of the present disclosure with respect to the electro-optic coefficient S 21 of.

[0166] Figure 24A -F is the eye diagram of a racetrack resonator and a Mach-Zehnder interferometer according to an embodiment of the present disclosure.

[0167] Figure 25A -B is the eye diagram of a Mach-Zehnder interferometer according to an embodiment of the present disclosure. Detailed Embodiments

[0168] The conversion of information from the electrical domain to the optical domain is a core process in modern communication, data center operations, and optical-assisted ranging applications. Such conversion can be achieved in electro-optic devices, where the applied DC / AC voltage causes corresponding changes in the characteristics of the optical field, such as intensity or phase.

[0169] This document provides integrated thin-film lithium niobate (LN) devices for electro-optic applications, which include waveguides and racetrack resonators. This document also provides methods for the design and fabrication of electro-optic modulators that convert voltage signals into optical intensity or phase modulation.

[0170] A variety of resonator-based lithium niobate electro-optic devices are provided, which include racetrack or ring resonators fabricated on thin-film lithium niobate. The resonant wavelength is shifted by the applied voltage. Such devices can be used for compact high-speed electro-optic modulators and switches.

[0171] Similarly, a variety of Mach-Zehnder interferometer (MZI)-based thin-film lithium niobate electro-optic devices are provided. Speed matching for electro-optic modulation on such thin-film lithium niobate substrates is provided. Such devices can be used for low-loss, low-voltage, and high-speed electro-optic modulators and switches.

[0172] The physical principle of electro-optic conversion in the devices according to the embodiments of the present disclosure is based on χ (2) (Pockels) effect, where the material refractive index changes proportionally to the applied external electric field. This effect can also be used for bulk LN modulators. The integrated methods described herein reduce the device footprint, improve the device efficiency, and enable new design paradigms. Due to the high confinement of the guided optical modes in various embodiments, tight bends of the waveguides and resonators are possible. Tight bends allow the fabrication of ring resonators with a radius of less than 20 microns.

[0173] The micron-scale photonic structures on LN fabricated according to the embodiments of the present disclosure exhibit improved properties suitable for on-chip electro-optic devices. Improvements have been made for modulators, footprint, energy cost per bit, and electro-optic bandwidth.

[0174] As described above, the modulator according to the present disclosure exhibits a reduced size of approximately 20 μm across due to the high confinement of the optical mode. An alternative design relying on a bulk LN modulator is approximately 10 cm across. Reducing the device size enables new designs for optical waveguides and electrical contacts. The bulk LN modulator suffers from radio frequency (RF) propagation losses and is limited by RF and optical phase matching conditions. In contrast, the microstructured thin-film LN technology according to the present disclosure enables micro-ring resonator photonic structures that are effective and much smaller than the wavelength of the RF field, thus eliminating the limitations on RF losses and phase matching conditions.

[0175] Compared to alternative bulk LN modulators, the microstructured LN modulator also consumes significantly less energy per bit of information processed. Reducing the size of the electrical pads results in a smaller capacitance (C), and thus reduces the amount of energy (Es = 1 / 2CV 2 ) required to effect switching. While the energy consumption of alternative bulk LN modulators is in the range of 10 pJ / bit, the device according to the present disclosure achieves an energy consumption of approximately 1 fJ / bit.

[0176] Reference Figure 1 depicts, in cross-section, an exemplary electro-optic modulator according to an embodiment of the present disclosure. The modulator structure 100 includes a lithographically patterned LN optical waveguide 101 disposed on a substrate 102. In some embodiments, the substrate 102 comprises silica. In some embodiments, electrical contact pads 103, 104 are located around the waveguide 101 to form a capacitor. In some embodiments, the waveguide 101 includes a central ridge 105, the flanks of which are outer legs 106, 107 that extend outward from the central ridge 105 and are disposed beneath the contact pads 103, 104. In some embodiments, the waveguide 101 is coupled to an LN micro-ring or racetrack-shaped optical microcavity. In some embodiments, the electrical contact pads are placed around the optical cavity to form a capacitor.

[0177] Reference Figure 2A -B, an optical resonator according to an embodiment of the present disclosure includes a circular ridge waveguide 201 that supports an optical whispering gallery mode (WGM). Optical access to the resonator is achieved by placing a straight bus ridge waveguide 202 in the vicinity of the resonator 201. Although in the depicted exemplary embodiment the resonator 201 is substantially racetrack-shaped, it should be understood that the techniques described herein are applicable to the design and fabrication of resonators of various shapes, including racetrack-shaped and ring-shaped. In some embodiments, electrical contact pads 203, 204 are placed around the optical cavity to form a capacitor.

[0178] Reference Figure 3, which illustrates the measured optical transmission spectrum (shown as circles) of a 20-μm ring modulator according to an embodiment of the present disclosure and its Lorentzian fit (shown as a solid line). The loaded optical quality factor is approximately 5700. The resonant frequency of the WGM is highly sensitive to the refractive index of the waveguide. When a voltage is applied between the contact pads, the shift in the resonance frequency of the cavity causes a change in the laser transmittance.

[0179] Reference Figure 4 , which illustrates the frequency response of a 20-μm ring modulator according to an embodiment of the present disclosure, showing a -3 dB electro-optic bandwidth greater than 40 GHz. The theoretical response is depicted as a smooth curve.

[0180] Now referring to FIG. 5, a method of manufacturing a device according to an embodiment of the present disclosure is illustrated. In some embodiments, a combination of photolithography and Ar + plasma dry etching is used to fabricate waveguides, resonators, or other optical devices, as described below.

[0181] Reference Figure 5A , a sub-micron (400 - 700 nm) LN thin film 501 is bonded on top of a lower-index insulator 502 to form an LNOI structure 503. In some embodiments, the insulator 502 comprises silicon dioxide. In some embodiments, the insulator 502 is disposed on a carrier 504. In some embodiments, the carrier 504 comprises LN. In some embodiments, the carrier 504 comprises silicon. In some embodiments, the carrier 504 comprises quartz. A first resist layer 505 is deposited on the thin film 501. In some embodiments, the first resist layer 505 comprises amorphous silicon or silicon dioxide. In other embodiments, the first resist layer 505 comprises silicon nitride, aluminum, or aluminum oxide (aluminum(III) oxide) or titanium dioxide. In some embodiments, the first resist layer 505 is deposited by plasma-enhanced chemical vapor deposition (PECVD). In other embodiments, the first resist layer 505 is deposited by sputtering, electron beam evaporation, or thermal evaporation. In some embodiments, the first resist layer 505 is p-doped. In some embodiments, for example, in certain embodiments where the first resist layer 505 comprises silicon, the first resist layer 505 has a thickness of approximately 800 nm.

[0182] Reference Figure 5B, a second resist layer 506 is deposited on the first resist layer 505. In some embodiments, the second resist layer comprises a polymer. In some embodiments, the polymer is a flowable oxide. In some embodiments, the polymer is hydrogen silsesquioxane (HSQ). In some embodiments, the polymer is FOX-16. In some embodiments, the first resist layer 505 comprises a photoresist based on poly(methyl methacrylate) (PMMA), poly(methylglutaramide) (PMGI), novolak (DNQ / Novolac), SU-8, OSTE polymer, Ma-N photoresist, Shipley photoresist, SPR photoresist, or ZEP photoresist. In some embodiments, the polymer is deposited by spin coating. After depositing the second resist layer 506, it is lithographically patterned. In some embodiments, the lithographic patterning includes electron beam lithography. In some embodiments, the lithographic patterning includes a photoresist process.

[0183] Reference Figure 5C , after patterning the second resist layer 506, the pattern is transferred to the first resist layer 505, thereby patterning the first resist layer according to the pattern. In some embodiments, the pattern is transferred from the second resist layer 506 to the first resist layer 505 by reactive ion etching (RIE). In some embodiments, the RIE is inductively coupled plasma (ICP) RIE. The remaining portions 507...508 of the first resist layer 505 serve as a hard mask for the dry etching of the LN thin film 501. In some embodiments, the dry etching is performed by reactive ion etching (RIE). In some embodiments, the RIE is electron cyclotron resonance (ECR) RLE. In some embodiments, the RIE uses Ar + plasma.

[0184] Reference Figure 5D , in some embodiments, the remaining portions 507...508 of the first resist layer 505 are removed, leaving the waveguide 509. In some embodiments, the removal is performed by exposure to a potassium hydroxide solution (KOH). In some embodiments, the KOH solution is 30%. In some embodiments, the exposure is performed at about 80 °C for about 2 minutes.

[0185] Reference Figure 5E, in some embodiments, electrodes 510...511 are patterned around waveguide 509. In some embodiments, electron beam lithography is used to pattern electrodes 510...511. In some embodiments, a PMMA lift-off process is used. In some embodiments, electrodes 510...511 are metallic. In some embodiments, electrodes 510...511 comprise gold. In some embodiments, electrodes 510...511 comprise titanium. In some embodiments, electrodes 510...511 comprise layers of gold and titanium. In some embodiments, electrodes 510...511 comprise a titanium layer of about 15 nm and a gold layer of about 300 nm.

[0186] The fabrication process described above provides a waveguide structure with minimal surface roughness and controllable scattering loss by using a two-step transfer process. As described above, the pattern is transferred from a soft polymer photoresist to a hard material to create a hard mask with smooth edges. The pattern is then smoothly transferred to the thin film LN using the hard mask. In contrast, alternative waveguides that rely on ion implantation in bulk LN have large optical modes and are not suitable for bends or fine structures as described herein. Alternative waveguides fabricated from LN without the two-step transfer process described herein lack smooth edges and thus exhibit high optical losses. The techniques of the present disclosure produce waveguides with smooth edges and exhibit an optical quality factor Q of at least 100,000, and in some embodiments at least 1,000,000.

[0187] As described above, in some embodiments, a hard mask and a soft polymer resist are used. In some embodiments, the hardness of the hard mask is greater than the hardness of the soft polymer resist. Hardness can be measured using various well-known tests, including, for example, Vickers, Brinell, Rockwell, Meyer, or Leeb tests.

[0188] Reference Figure 6 , depicts an exemplary electro-optic modulator in cross-section according to an embodiment of the present disclosure. Modulator structure 600 includes an optical waveguide 601 disposed on a substrate 602. In some embodiments, substrate 602 comprises silica. In some embodiments, electrodes 603, 604 are located around waveguide 601 to form a capacitor. In some embodiments, waveguide 601 includes a central ridge 605, the sides of which are outer legs 606, 607 that extend outward from central ridge 605 and are disposed beneath contact pads 603, 604. In some embodiments, substrate 602 has a height of about 350 nm.

[0189] In some embodiments, the ridge 605 of the waveguide 601 has a width of approximately 500 nm. In some embodiments, the ridge 605 of the waveguide 601 has a width of approximately 400 nm. In other embodiments, the ridge 605 of the waveguide 601 has a width less than approximately 1 μm. The narrow width of the ridge 605 of the waveguide 601 provides good confinement of the optical mode and enables tight bending of the waveguide. Moreover, the narrow width enables the electrodes 603, 604 to be positioned closely, which reduces power consumption and improves efficiency. In some embodiments, the waveguide is bent to a radius of approximately 20 μm. In some embodiments, the ridge 605 of the waveguide 601 has a height of approximately 350 nm. In some embodiments, the ridge 605 of the waveguide 601 has a height of approximately 200 nm.

[0190] Some embodiments include outer legs 606, 607, while some embodiments do not include outer legs 606, 607. When present, the outer legs 606, 607 assist in the propagation of the electric field. In particular, by extending beneath the electrodes 603, 604, the voltage drop across the air is minimized. However, the addition of the legs 606, 607 reduces the confinement of the optical mode to the ridge 605. Additionally, the legs 606, 607 increase the minimum bending radius of the waveguide 601. Generally, where the height of the legs 606, 607 is approximately half or less of the height of the ridge 605, the confinement remains high enough for the applications discussed herein.

[0191] As shown, the optical waveguide 601 is made of an x-cut LN crystal such that the x-axis of the LN lattice extends substantially perpendicular to the substrate outwardly. As described above, the LN crystal exhibits electro-optic birefringence. Although the fabrication techniques described herein are orientation-agnostic, the x-cut enables the electrodes to be disposed on either side of the ridge 605 such that the orientation of the resulting electric field is substantially parallel to the substrate 602 and substantially perpendicular to the waveguide 601. In some embodiments, the z-axis of the LN crystal is oriented in the same direction as the electric field.

[0192] In contrast, alternative waveguides that rely on ion implantation in bulk LN to form waveguides have a large optical mode of approximately 5 μm and are not suitable for bending or fine structures as described herein. Additionally, since the waveguide is embedded in the bulk, the electrodes cannot be disposed on either side of the waveguide.

[0193] Alternative waveguides fabricated from z-cut LN crystals require electrodes to be disposed above and below the waveguide. Stacking electrodes beneath the LN waveguide results in a more expensive and complex fabrication process. Moreover, the large electrodes involved result in a large capacitance.

[0194] Reference Figure 7, illustrates an exemplary modulator layout in accordance with embodiments of the present disclosure. Electrode pairs 701...705 are disposed on either side of waveguide 706. Waveguide 706 is arranged along a serpentine path having a plurality of arcuate segments 707. In some embodiments, the serpentine path includes a plurality of substantially linear portions 708 connected in pairs by arcuate segments 707. In some embodiments, the arcuate segments are substantially semi-circular. In some embodiments, the semi-circular bend has a radius of about 5 μm. In other embodiments, the semi-circular bend has a radius of about 20 μm. In some embodiments, the waveguide has a width of about 500 nm. In some embodiments, the semi-circular bends are separated by less than about 1 mm. In such embodiments, the length of each electrode is less than about 1 mm. Generally, to facilitate phase matching, each electrode is less than the wavelength of the RF microwave propagating in the circuit. In some embodiments, each electrode is less than 1 / 4 of the wavelength of the RF microwave propagating in the circuit.

[0195] Reference Figures 8 - 9 , illustrates the phase matching in accordance with embodiments of the present disclosure. In an electro-optic modulator, RF and optical phase matching are important considerations when the total wire length is comparable to or longer than the wavelength of the RF microwave. Reference Figure 8 , illustrates an exemplary waveguide 801. The flanks of waveguide 801 are electrodes 802, 803, subjecting it to an electric field. The orientation of the electric field can be reversed at intervals 811...817. In the illustrated example, the electric field experienced by the optical field flips sign every half wavelength as it propagates along the electrode. Thus, the orientation of the electric field can cancel some or all of the electro-optic shift in the waveguide.

[0196] To address this problem in a large straight waveguide, such as the exemplary 10 cm long waveguide illustrated, phase matching is required. Modulation is achieved by matching the phase velocities of the electrical and optical waves such that the optical field experiences the same electrical phase along the entire waveguide. However, such phase matching requires specially designed electrodes and compromises other design objectives, such as capacitance.

[0197] Reference Figure 9 , depicts Figure 7 waveguide 706. As further discussed above, waveguide 706 includes bends 707. Because the waveguide includes tight bends, the RF propagation length along electrode 701 can be reduced to less than 1 / 4 of the RF wavelength even while the total waveguide length remains the same. In such embodiments, the optical field experiences an electric field as it propagates through the waveguide. It should be understood that the indicated polarities are merely exemplary and that various effects can be achieved by manipulation of the electric field in accordance with the present disclosure.

[0198] As described above, alternative LN waveguides are too wide to bend. This results in long straight waveguides that require long electrodes. The length poses a major limitation to the modulator design. The phase of the optical wave and the voltage must be matched. In addition, the electrical propagation loss over long distances at high frequencies must be considered.

[0199] The fabrication techniques described herein allow for the generation of very narrow waveguides that enable the re-design of the device topology. Since the waveguides according to the present disclosure can be bent with a tight radius, the electrode size can be significantly reduced. This eliminates the above limitations and enables higher efficiency, better performance, higher speed, lower energy consumption, and a smaller footprint. In some embodiments, the short electrodes described herein allow the modulator to operate at frequencies of about 40 GHz or higher.

[0200] The techniques described herein are applicable to a wide range of integrated electro-optic devices based on thin-film LN devices, including modulators, switches, and linear modulators based on Mach-Zehnder interferometers. In the case of using waveguide-based interferometers instead of microresonators, the same fabrication method can be applied, enabling a much larger optical operation bandwidth. Due to much better optical confinement, the contact electrodes can be placed closer to each other than in alternative bulk LN modulators, thus reducing the modulation voltage. In addition, the small bend radius allows for routing the waveguides and reducing the overall RF propagation length and the electronic capacitance, making ultra-high-speed and low-power-consuming modulators possible. The same device configuration can also be applicable to optical switches with a high on / off ratio and low insertion loss. Different from the plasma dispersion effect in silicon and the quantum-confined Stark effect in indium phosphide, the Pockels effect is inherently linear. High-speed linear modulators can be constructed without expensive signal post-processing, which is crucial in analog circuits and communications.

[0201] Now referring to Figures 10 - 11 , the microwave transmission line velocity matching is illustrated in a cross-sectional view of an exemplary waveguide according to the present disclosure. Alternative LN modulators do not support velocity matching because the microwave dielectric constant of LN is very high (∼28). This results in a low microwave group velocity compared to the light guided on the LN chip. In alternative modulators, a low dielectric constant SiO2 buffer layer can be used to increase the microwave group velocity, which results in a reduced modulation efficiency. In the thin-film design as described herein, since the optical mode is confined in the LN thin film, the substrate does not need to have a high dielectric constant. Thus, the bulk substrate can be a low RF-index material such as Si, quartz, silica, sapphire, or a combination thereof, such that the optical and microwave group velocities can be perfectly matched.

[0202] In Figure 10In [the structure], the LN waveguide 1001 has a high dielectric constant, resulting in a high refractive index (about 5). The optical index of the optical mode 1002 is about 2.2. As a result, velocity matching is difficult. As described above, in various exemplary embodiments, the electrode 1003 can be gold.

[0203] In Figure 11 [the structure], the LN waveguide 1101 is disposed on the SiO2 layer 1104, which is in turn disposed on the substrate wafer 1105. In various embodiments, the substrate can be silicon, quartz, silica, sapphire, or a combination thereof. The optical index of the optical mode 1102 is about 2.2. The SiO2 layer 1104 and the substrate 1105 (e.g., silicon) have a low refractive index (3.4 for silicon, 2.0 for quartz and silica, 3.0 - 3.3 for sapphire), so the optical and microwave velocities can be matched. As described above, in various exemplary embodiments, the electrode 1003 can be gold.

[0204] Due to the improved modulation efficiency obtained through shorter electrodes and better velocity matching, a higher bandwidth (about 100 GHz or higher) with a lower drive voltage (about 2 V or lower) can be obtained compared to alternative methods.

[0205] As described above, LN exhibits a wide bandgap (high transparency) and a large second-order (χ2) electro-optic coefficient (about 30 pm / V). Compared with silicon and indium phosphide (InP), the χ2 process in LN linearly changes its refractive index on the femtosecond time scale with the applied electric field. The efficiency of this process is determined by the overlap of the optical and electric fields. Alternative ion-diffused LN waveguides suffer from a low refractive index contrast (Δn < 0.02) between the core and the cladding, resulting in a large optical modal volume and bending radius. As a result, the photon structure is large, and the radio frequency (RF) electrodes must be placed far from the optical mode to prevent harmful waveguide propagation losses, thus significantly reducing the electro-optic switching efficiency.

[0206] Referring to Figure 12 , an ion-diffused LN waveguide 1201 is shown approximately to scale beside an etched LN waveguide embedded in SiO2 1202. Regions 1203, 1204 indicate the approximate waveguide cores in each device. The larger refractive index contrast in the etched waveguide allows for stronger light confinement.

[0207] Referring to Figure 13 , an exemplary device layout including a thin-film LN waveguide and an RF electrode is provided according to an embodiment of the present disclosure. Metal vias and bridges are fabricated to enable modulation on both sides of the device. The inset shows an exemplary device cross-section, illustrating the gold electrode layer 1301, the LN layer 1302, and the SiO2 layer 1303. The exemplary device 1300 includes a racetrack resonator 1304 and a Mach-Zehnder interferometer 1305 (partially depicted).

[0208] As described herein, an exemplary device such as device 1300 exhibits a single-crystalline LN photonic structure with sub-micron optical confinement, a small bend radius (<20 μm), and low propagation loss. In various embodiments, the single-crystalline LN is directly formed into nanoscale waveguides. Waveguides are defined on a thin-film LN substrate on insulator using electron beam lithography, and subsequently dry-etched in an Ar + plasma using a deposited Si hard mask, as further described above. The refractive index contrast between the LN core and the silica (SiO2) cladding is Δn = 0.67, which is more than an order of magnitude higher than that of alternative ion-diffused LN waveguides.

[0209] Now referring to Figure 14 , a modulator based on racetrack and ring resonators according to an embodiment of the present disclosure is shown. The ring resonator 1401 and the racetrack resonator 1402 include thin-film LN waveguides fabricated as further described above.

[0210] Now referring to Figure 15 , a modulator based on a Mach-Zehnder interferometer according to an embodiment of the present disclosure is shown. The interferometer 1501 includes thin-film LN waveguides fabricated as further described above.

[0211] Referring to Figure 16 , a close-up SEM image of an exemplary metal electrode and an associated optical waveguide is provided.

[0212] Referring to Figure 17 , a cross-sectional view of the simulated optical transverse electric (TE) mode distribution (E z component) and the RF electric field (shown by the arrows) for an exemplary waveguide according to the present disclosure is provided. In this exemplary embodiment, the x-cut LN is most sensitive to the horizontal component of the electric field (E z ). In this figure, h corresponds to the LN waveguide height; w corresponds to the waveguide width; s corresponds to the LN plate thickness; and g corresponds to the metal electrode gap.

[0213] In the numerical simulation overlap between the corresponding optics and the electric field, the optical waveguide has a top width w = 900 nm, a rib height h = 400 nm, and a plate thickness s = 300 nm. To maximize the in-plane electric field (Ez), the optical waveguide is sandwiched between a signal and a ground electrode with a gap of g = 3.5 μm. The SiO2 cladding is used to further enhance this overlap by increasing the dielectric constant of the surrounding medium to match the high dielectric constant of LN (about 28).

[0214] This example includes a series of fabricated nanophotonic LN devices, including nanowaveguides, ring resonators, racetrack resonators, and Mach-Zehnder interferometers (MZIs). The propagation loss of various exemplary structures is about 3 dB / cm or less. The propagation loss is limited by the etch roughness and is about 2 dB / cm or less in some exemplary structures. The exemplary MZI and racetrack structures described herein have low on-chip insertion losses of about 2 dB or less and about 1 dB or less, respectively. Some exemplary structures exhibit additional coupling losses of about 5 dB / facet or less.

[0215] The height-confined optical mode allows for maximizing the electro-optic modulation efficiency by placing gold micro RF electrodes close to the LN waveguide. As further discussed above, these exemplary devices utilize an x-cut LN configuration where the transverse electric (TE) optical mode and the in-plane electric field (Ez) interact through the highest electro-optic tensor component (r 33 ) of the LN. The waveguide geometry and the micro RF electrode position facilitate an optimal overlap between the optical and electric fields while minimizing bending losses and metal-induced absorption losses.

[0216] Now referring to Figure 18 , the measured transmission spectrum of an exemplary high-Q (∼50,000) racetrack resonator is shown in a plot of wavelength versus normalized transmittance. A large frequency shift is shown under an applied DC voltage.

[0217] Now referring to Figure 19 , the linear resonant wavelength shift of an exemplary racetrack resonator is shown as a function of DC voltage, with error bars. The measured tuning efficiency is 7.0 pm / V.

[0218] Now referring to Figure 20 , the optical transmittance of an exemplary 2-mm-long MZI modulator is plotted versus the applied DC voltage. The half-wave voltage (V π ) of 9 V and the voltage-length product of 1.8 V-cm are indicated.

[0219] As shown, effective and linear electro-optic tuning is provided in the racetrack modulator and the micro MZI modulator. Figure 18Shows the transmission spectrum of a racetrack resonator with a loaded quality (Q) factor of ~50,000. When a voltage is applied, the change in refractive index changes the effective optical path length of the resonator, resulting in a resonance frequency shift. The electric fields on the two racetrack arms are aligned in the same direction, such that the modulations on the two arms add up. The measured electro-optic efficiency is 7.0 pm / V, with good linearity, and no visible change in the resonance extinction ratio and linewidth. The MZI modulator is a balanced interferometer with two 50:50 Y splitters and two optical paths. The applied voltage induces a phase delay in one arm and a phase advance in the other arm, which in turn changes the output intensity through interference at the Y-combiner. The minimum voltage required to fully switch the output between on and off is defined as the half-wave voltage (V π ). Measured from a 2-mm long MZI modulator, V π is 9 V, and the extinction ratio is 10 dB. This corresponds to a voltage-length product of 1.8 V-cm, which is an order of magnitude better than alternative bulk LN devices.

[0220] Reference Figure 21 , depicts an exemplary setup for testing the eye diagram. The dashed line represents the signal path for electro-optic bandwidth measurement. The tunable laser 2101 probes the device under test 2102. The device under test (DUT) 2102 is observed through a scope 2103 using a pseudo-random binary sequence (PRBS) 2103. The vector network analyzer (VNA) 2104 is in turn coupled to the electrical probe 2105.

[0221] Reference Figure 22 , illustrates the electro-optic bandwidth (S 21 parameter) of an exemplary racetrack resonator with Q of ~8000. The corresponding 3-dB bandwidth is 30 GHz.

[0222] Reference Figure 23 , illustrates the electro-optic bandwidth (S 21 parameter) of an exemplary 2-mm long MZI. The corresponding 3-dB bandwidth is 15 GHz.

[0223] Referring to FIG. 24, provides eye diagrams of racetrack-shaped ( Figure 24A -C) and MZI ( Figure 24D -F) modulators with data rates up to 40 Gbps and 22 Gbps. All eye diagrams are measured using a 2 7 -1 PRBS in a non-return-to-zero scheme, with an electrical drive of 5.66 V PP . For the racetrack resonator and MZI, the extinction ratios are 3 dB and 8 dB, respectively.

[0224] Referring to FIG. 25, provides 12.5 Gbps ( Figure 25A ) and 22 Gbps ( Figure 25BEye diagram of the MZI modulator in ( ), where the device is heated by 20 °C. The extinction ratio is 8 dB.

[0225] As shown, the LN devices according to the present disclosure exhibit a high electro-optic bandwidth (S 21 parameter), which is characterized using a network analyzer and a high-speed photodiode (as Figure 21 shown). For a racetrack resonator modulator with a Q-factor of 8000, a 3 dB electro-optic bandwidth of 30 GHz was measured (as Figure 22 shown). This value is limited by the cavity-photon lifetime of the resonator (about 6 ps). The lifetime-limited bandwidth was confirmed by testing additional resonators with Q of 5700 and 18000.

[0226] The resulting 3 dB bandwidths were 40 GHz and 11 GHz, respectively. The Q-factor was designed from the intrinsic value by controlling the distance between the RF electrode and the optical waveguide. It is estimated that the intrinsic RC bandwidth limit of the racetrack modulator exceeds 100 GHz.

[0227] For an exemplary 2 mm long MZI device with direct capacitance modulation, the measured electro-optic 3 dB bandwidth was about 15 GHz (as Figure 23 shown). This is limited by the RC constant due to the large capacitance (about 0.2 pF) caused by the use of a longer RF electrode. In this example, the measured bandwidth is limited by the 50 Ω impedance of the network analyzer driver because the on-chip resistance is small (<10 Ω).

[0228] This platform supports data transmission rates up to 40 Gbps. Figure 24 shows the non-return-to-zero (NRZ) open eye diagrams of both the racetrack and MZI modulators at various data rates obtained with a 2 pp -1 (pseudo) random binary sequence at 5.66 V. 7 Due to the high signal quality, these devices can operate at a data rate 1.5 times their 3 dB bandwidth, which corresponds to 40 Gbps and 22 Gbps for the racetrack and MZI devices, respectively. The measured extinction ratios of these modulators are 3 dB and 8 dB, and the power consumptions (CV 2 / 4) are 240 fJ / bit and 1.6 pJ / bit, respectively.

[0229] Due to the low thermo-optic coefficient of LN (3.9×10 -5 K -1 ), the MZI modulator maintains the stable thermal properties of its bulk counterpart. Figure 25 illustrates the eye diagrams across a range of ΔT = 20 °C. The MZI modulator is able to maintain an open eye diagram at a maximum data rate of 22 Gbps without any feedback to compensate for temperature drift (open-loop configuration).

[0230] The micron-scale LN modulators described herein have high bandwidth, excellent linearity, low voltage, and good temperature stability. The high dielectric constant (ε RF ~28) of LN dictates that the RF field in LN propagates much slower than the optical field (ε opt ~4), resulting in a performance compromise between bandwidth and drive voltage. In the thin-film monolithic LN approach described herein, phase matching can be achieved because the electric field is mainly located in low-dielectric SiO2 (ε opt ~4) and easily propagates at a group velocity nearly the same as that of light. The thin-film micro-MZI modulator has a phase-matched RF transmission line architecture, enabling simultaneous achievement of ultra-high bandwidth (>60 GHz) and low modulation voltage (~1 V), and thus can be directly driven by CMOS circuits.

[0231] Active microresonators and low-loss waveguides enable chip-scale photonic circuits to be densely integrated with switches, filters, and nonlinear wavelength sources operating in a wide wavelength range (from visible light to mid-infrared). In addition, micro-ring modulators with an ultra-compact footprint (as small as 30 μm × 30 μm) are attractive for data center applications where real estate is at a premium. The high-performance monolithic LN nanophotonic platform described herein provides a practical and cost-effective solution to meet the growing demands of next-generation data centers and metro and long-haul optical communications.

[0232] The description of the various embodiments of the present invention has been given for purposes of illustration, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terms used herein are chosen in order to best explain the principles of the embodiments, the practical application, or the technical improvement of the technology seen in the market, or to enable other ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A device, the device comprising: A substrate having a first side; A lithium niobate optical waveguide disposed on the first side of the substrate, the optical waveguide comprising: A central ridge; and Legs extending outward from the central ridge along the first side of the substrate, Wherein the central ridge consists essentially of undoped lithium niobate, The device further comprises an electrode pair disposed on the first side of the substrate such that each leg of the optical waveguide extends from the central ridge towards one of the electrode pair, Wherein the optical waveguide comprises a substantially semi-circular bend having a radius of about 50 μm or less.

2. The device according to claim 1, wherein the central ridge has a width of about 1 μm or less.

3. The device according to claim 1, wherein the height of the legs is less than the height of the central ridge.

4. The device according to claim 3, wherein the height of the legs is less than or equal to half of the height of the central ridge.

5. The device according to claim 3, wherein the legs have a height of about 300 nm.

6. The device according to claim 1, wherein the lithium niobate is crystalline and is arranged such that the x-axis of its lattice extends substantially perpendicular to the first side of the substrate.

7. The device according to claim 1, wherein the central ridge has a thickness of about 1 μm or less.

8. The device according to claim 7, wherein the central ridge has a thickness of about 400 nm or more.

9. The device according to claim 1, wherein the substrate is an insulator.

10. The device according to claim 9, wherein the refractive index of the insulator is less than the refractive index of the optical waveguide.

11. The device according to claim 9, wherein the insulator comprises silicon dioxide.

12. The device according to claim 1, the device further comprising: A carrier, the substrate being disposed on the carrier.

13. The device according to claim 12, wherein the carrier comprises lithium niobate, silicon, quartz, silicon dioxide or sapphire.

14. The device according to claim 1, wherein the electrodes comprise metal.

15. The device according to claim 14, wherein the electrodes comprise gold.

16. The device according to claim 1, wherein the electrode pair is adapted to modulate the optical mode of the optical waveguide when a voltage is applied across the electrode pair.

17. The device according to claim 1, wherein each of the electrode pair has a length of about 1 mm or less.

18. The device according to claim 1, wherein the electrodes of the electrode pair are separated by about 3.5 μm.

19. The device according to claim 1, wherein the optical waveguide is disposed along a substantially circular path.

20. The device according to claim 1, wherein the optical waveguide is disposed on the first side of the substrate to form a ring resonator.

21. The device according to claim 1, wherein the optical waveguide is disposed on the first side of the substrate to form a racetrack resonator.

22. The device according to claim 1, wherein the optical waveguide is disposed on the first side of the substrate to form a Mach-Zehnder interferometer.

23. The device according to claim 1, wherein the device is adapted to shift the resonant wavelength by an applied voltage.

24. The device according to claim 1, wherein the device is adapted to provide velocity matching.

25. The device according to claim 1, wherein the device is adapted to provide electro-optic modulation.

26. The device according to claim 1, wherein at least a portion of each leg is disposed beneath a respective one of the electrodes.

27. A device comprising: a substrate having a first side; a lithium niobate optical waveguide disposed on the first side of the substrate, the optical waveguide comprising: a central ridge; and legs extending outwardly from the central ridge along the first side of the substrate, wherein the central ridge consists essentially of undoped lithium niobate, the device further comprising an electrode pair disposed on the first side of the substrate such that each leg of the optical waveguide extends from the central ridge towards one of the electrode pair, wherein the optical waveguide is disposed along a substantially serpentine path defined by a plurality of arcuate segments, wherein each of the arcuate segments has a radius of less than about 50 μm.

28. The device according to claim 27, wherein the arcuate segments are substantially semi-circular.

29. The device according to claim 27, wherein the arcuate segments are each separated by about 1 mm or less.

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