High efficiency thin film electro-optic modulator on a silicon photonics platform

Abstract

The electro-optic modulator (100) includes a substrate (104) and an optical waveguide (106), the optical waveguide including an electro-optic thin film (102) disposed on the substrate. The optical waveguide has an input terminal (105) coupled to receive an optical signal and an output terminal (109) opposite to the input terminal. A first electrode and a second electrode (108, 110) are disposed on the substrate along opposite sides of the waveguide. A differential driver (124) has a first differential output and a second differential output (126, 128), the first differential output and the second differential output being coupled to apply a differential electrical signal between the first electrode and the second electrode, thereby modulating the polarization of the optical signal propagating in the waveguide.

Description

Cross-reference to related applications

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 543,925, filed October 12, 2023, which is incorporated herein by reference. Technical Field

[0002] This invention relates generally to optical communication devices, and more particularly to electro-optic modulators. Background Technology

[0003] The demand for high-speed connectivity in electronic systems is growing rapidly, further fueled by recent interest in AI-based platforms such as ChatGPT. These requirements can be met by photonic circuits and waveguides, in which high-speed electro-optic amplitude modulators are key components. In addition to high modulation speeds, these modulators are required to have high efficiency, i.e., low switching voltages and low optical losses. Silicon-based electro-optic modulators offer a solution for communication speeds up to approximately 128 GBd (gigabots), but this solution cannot meet all the aforementioned speed requirements of 200 GBd. Summary of the Invention

[0004] The embodiments of the present invention described below provide an improved design for an electro-optic modulator.

[0005] According to an embodiment of the present invention, an electro-optic modulator is provided, comprising a substrate and an optical waveguide including an electro-optic thin film disposed on the substrate. The optical waveguide has an input terminal coupled to receive an optical signal and an output terminal opposite to the input terminal. A first electrode and a second electrode are disposed on the substrate along opposite sides of the waveguide. A differential driver has a first differential output and a second differential output, the first differential output and the second differential output being coupled to apply a differential electrical signal between the first electrode and the second electrode, thereby modulating the polarization of the optical signal propagating in the waveguide.

[0006] In the disclosed embodiments, the optical waveguide has a waveguide axis along which an optical signal propagates, and the electro-optic thin film includes a uniaxial crystal disposed on a substrate, the crystal having a Z-axis orientation perpendicular to the substrate and a Y-axis orientation parallel to the waveguide axis.

[0007] In some embodiments, the optical signal at the input end of the optical waveguide has linear polarization, and the modulator includes a controller coupled to control a differential driver to modulate the rotation of the linear polarization of the optical signal exiting the output end of the optical waveguide. In the disclosed embodiments, the modulator includes a third electrode and a fourth electrode disposed on a substrate on opposite sides of the waveguide between the input end and the first and second electrodes, wherein the controller is coupled to apply a DC voltage between the third and fourth electrodes to adjust the input angle of the linear polarization of the optical signal prior to polarization modulation.

[0008] Alternatively or additionally, the modulator includes a third electrode and a fourth electrode disposed on a substrate along the sides of the first electrode and the second electrode, respectively, wherein the first electrode and the second electrode are disposed between the third electrode and the fourth electrode and the waveguide, wherein the third electrode and the fourth electrode are grounded, and the first electrode, the second electrode, the third electrode and the fourth electrode define a differential transmission line extending along the waveguide.

[0009] Further, or alternatively, the modulator includes an optical polarizer coupled to receive an optical signal from the output of the optical waveguide to generate an amplitude-modulated output beam in response to a differential signal and according to the modulated polarization response.

[0010] In the disclosed embodiments, the electro-optic thin film is selected from the material group consisting of lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and barium titanate (BaTiO3).

[0011] In one embodiment, the substrate comprises a silicon photonic circuit. Alternatively, the substrate comprises an electro-optic thin film.

[0012] According to embodiments of the present invention, a dual-polarization coherent modulator is also provided, comprising a substrate and at least a first electro-optic modulator and a second electro-optic modulator. Each electro-optic modulator includes an optical waveguide comprising an electro-optic thin film disposed on the substrate, and a first electrode and a second electrode disposed on opposite sides of the waveguide on the substrate. A differential driver has a first differential output and a second differential output, the first differential output and the second differential output being coupled to apply a differential signal between the first electrode and the second electrode, thereby rotating the polarization of an optical signal propagating in the waveguide. An optical polarizer is coupled to receive the optical signal from the waveguide, thereby generating an amplitude-modulated output beam. A beamsplitter is coupled to divide a coherent input beam between corresponding inputs of at least the first electro-optic modulator and the second electro-optic modulator. A combiner is coupled to combine corresponding amplitude-modulated output beams generated by at least the first modulator and the second modulator, while rotating the polarization of at least one of the amplitude-modulated output beams, to generate a combined beam comprising dual polarization.

[0013] In the disclosed embodiments, at least the first electro-optic modulator and the second electro-optic modulator include first, second, third and fourth modulators, wherein the first, second, third and fourth modulators are configured to apply in-phase modulation and quadrature modulation to each of the dual polarizations.

[0014] According to embodiments of the present invention, a method for manufacturing an electro-optic modulator is also provided. The method includes depositing an optical waveguide comprising an electro-optic thin film disposed on a substrate, and coupling the input end of the optical waveguide to receive an optical signal. A first electrode and a second electrode are deposited on the substrate along opposite sides of the waveguide. A controller is coupled to apply a differential electrical signal between the first and second electrodes, thereby modulating the polarization of the optical signal propagating in the waveguide.

[0015] According to embodiments of the present invention, a method for modulating an optical signal is further provided. The method includes providing an electro-optic modulator comprising an optical waveguide, the optical waveguide including an electro-optic thin film disposed on a substrate, and a first electrode and a second electrode disposed on opposite sides of the waveguide on the substrate. An optical signal is input to an input terminal of the optical waveguide. A differential electrical signal is applied between the first electrode and the second electrode to modulate the polarization of the optical signal propagating in the optical waveguide.

[0016] The invention will be more fully understood from the following detailed description of embodiments thereof, taken in conjunction with the accompanying drawings, in which: Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an electro-optic modulator according to an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of an electro-optic modulator according to another embodiment of the present invention; and

[0019] Figure 3 This is a schematic diagram of a dual-polarization coherent modulator according to an embodiment of the present invention. Detailed Implementation

[0020] Recently, thin-film lithium niobate (TFLN) has attracted attention as a preferred material for high-speed optical modulators due to its high bandwidth, low loss, and high efficiency, although at the cost of a larger device size. The electro-optic properties of lithium niobate (LiNbO3) allow for optical phase modulation and polarization rotation, depending on the direction of the applied electric field and the propagation direction of the optical signal relative to the crystal axis of the material. TFLN modulators have been integrated into silicon photonics platforms, but further improvements in modulator efficiency and reduction in size are still needed.

[0021] The embodiments of the invention described herein provide a novel method for polarization modulation using a TFLN waveguide on a silicon photonic circuit with differential electrical drive. The TFLN is oriented with a so-called Z-cut orientation, where the Z-axis of its crystal is perpendicular to the substrate and its Y-axis is along the waveguide axis. Electrodes on opposite sides of the waveguide are coupled to two differential outputs of a differential driver. By appropriately selecting the driving voltage, the polarization of an optical signal propagating in the waveguide can be efficiently rotated due to the proximity of both the electrodes and the waveguide, and the orientation of the TFLN's crystal axis relative to the electric field. In some embodiments, an optical polarizer at the output of the TFLN waveguide converts the polarization rotation into modulation of the optical signal's amplitude.

[0022] In addition to this type of single-channel amplitude modulation, the same principle may also be used to achieve dual-polarization coherent modulation.

[0023] As an alternative to lithium niobate, other uniaxial electro-optic materials such as lithium tantalate (LiTaO3) and barium titanate (BaTiO3) could be used. Alternatively, instead of integrating the TFLN waveguide with silicon photonic circuitry, the TFLN modulator could be used as a standalone unit, with all its passive components and phase tuners fabricated on the TFLN.

[0024] Therefore, in the disclosed embodiments, the electro-optic modulator includes a substrate and an optical waveguide including a uniaxial electro-optic thin film disposed on the substrate. Two electrodes are formed on the substrate and disposed along opposite sides of the waveguide, and a differential driver applies a differential electrical signal between the electrodes to modulate the polarization of an optical signal propagating in the waveguide. For this purpose, in some embodiments, the thin film is deposited on the waveguide such that the Z-axis orientation of the electro-optic material crystal is perpendicular to the substrate and the Y-axis orientation of the crystal is parallel to the waveguide axis.

[0025] In some embodiments, the optical signal at the optical waveguide input has linear polarization, and a differential driver is controlled to modulate the rotation of the linear polarization of the optical signal exiting the optical waveguide output. A polarizer at the optical waveguide output may be used to convert the polarization-modulated optical signal into an amplitude-modulated output beam.

[0026] In a further disclosed embodiment, the dual-polarization coherent modulator includes a substrate and at least a first electro-optic modulator and a second electro-optic modulator of the type described above, each electro-optic modulator having its own differential driver and optical polarizer to generate a corresponding amplitude-modulated output beam. A beam splitter divides the coherent input beams between the respective inputs of the electro-optic modulators, and a combiner combines the corresponding amplitude-modulated output beams while rotating the polarization of at least one of the output beams to generate a combined beam including dual polarizations. In one embodiment, four electro-optic modulators are deployed in this configuration to apply in-phase (I) and quadrature (Q) modulation to each of the dual polarizations.

[0027] Figure 1 This is a schematic top view of an electro-optic modulator 100 according to an embodiment of the present invention.

[0028] The modulator 100 includes a waveguide 106 having a waveguide axis 111. The waveguide 106 is formed, for example, by photolithography in a Z-cut thin-film lithium niobate (TFLN) layer 102 disposed on a substrate of the silicon photonic circuit 104. In this embodiment, the Y-axis and Z-axis of the Cartesian coordinate system 107 are respectively aligned with the corresponding crystal axes of the TFLN layer 102, wherein the Z-axis of the TFLN layer crystal is oriented perpendicular to the silicon photonic circuit 104, and the Y-axis of the crystal is oriented parallel to the axis 111 of the waveguide 106. (According to conventional usage in crystal optics, the Z-axis is the direction along which light rays can propagate in a uniaxial crystal without birefringence.)

[0029] Positive and negative signal electrodes 108 and 110, labeled S+ and S-, are deposited along opposite sides of waveguide 106, and ground electrodes 112 and 114, labeled G, are deposited adjacent to the signal electrodes. The signal electrodes 108 and 110, together with the ground electrodes 112 and 114, form a differential transmission line 113 extending along waveguide 106.

[0030] The modulator 100 also includes a polarizer 116 disposed on the silicon photonic circuit 104, comprising an input 118 and two outputs 120 and 122. The output 109 of the waveguide 106 is coupled to the input 118 of the polarizer 116, which guides the TE polarization mode propagating in the waveguide to the output 120 and the TM polarization mode to the output 122. (TE polarization is defined with an electric field (E-field) in the X direction, and TM polarization is defined with an E-field in the Z direction.)

[0031] A differential driver 124, comprising differential positive and negative outputs 126 and 128, drives a modulator 100 with a differential signal between the two outputs. The positive output 126 is coupled to a positive signal electrode 108, and the negative output 128 is coupled to a negative signal electrode 110. The drive circuit is closed by coupling the signal electrodes 108 and 110 to ground 130 via corresponding load resistors 132 and 134. A controller 136 applies a modulation signal to the differential driver 124, thereby generating a radio frequency (RF) electric field 138 of magnitude Ex across waveguide 106 in the X direction. In this configuration, the differential driver 124 is able to drive the differential transmission line defined by electrodes 108, 110, 112, and 114 at a high baud rate (e.g., 200 GBd or higher), while the close proximity of the signal electrodes 108 and 110 to waveguide 106 facilitates the generation of a high Ex field within the waveguide, thereby achieving strong optical modulation over a short modulation length.

[0032] In some embodiments, controller 136 includes a programmable controller programmed in software and / or firmware to perform the functions described herein. Additionally or alternatively, at least some functions of controller 136 may be implemented by hardware logic circuitry, which may be hardwired or programmable. In either case, controller 88 has a suitable interface for receiving and transmitting data and instructions from other elements of device 100 as required, and for transmitting data and instructions to other elements of device 100.

[0033] The electro-optic properties of lithium niobate (LiNbO3) are obtained from the electro-optic tensor T: [Equation 1] Where the nonzero coefficients of tensor T It has the following values: = 8.6 pm / V, = 3.4 pm / V, = 30.8 pm / V, and = 28 pm / V.

[0034] The ordinary and extraordinary refractive indices of lithium niobate (LiNbO3) are respectively... =2.21 and =2.13.

[0035] For an optical signal propagating along the Y direction in waveguide 106 under an applied electric field Ex, its refractive index ellipsoid becomes: [Equation 2]

[0036] As can be seen from Equation 2 of the refractive index ellipsoid, for a Z-tangent TFLN 102 with an electric field of 138 in the X direction, the second largest coefficient of the electro-optic tensor T is utilized. By defining new Cartesian axes X' and Z' along the diagonal directions (eliminating the cross term ZX), the refractive index ellipsoid of Equation 2 can be written as: [Equation 3]

[0037] The differential changes in refractive index along the X' and Z' axes caused by the electric field Ex can be written as: [Equation 4] as well as [Equation 5]

[0038] When the linearly polarized input beam 140 is injected into the waveguide 106 through input 105, the polarization of the optical signal propagating in the waveguide rotates due to birefringence as expressed by equations 4 and 5. Therefore, the polarization state of the optical signal at output 109 is modulated by the electric field Ex applied by the differential driver 124. This polarization-modulated optical signal is coupled to input 118 of polarizer 116, which then converts the signal into amplitude-modulated TE-polarized and TM-polarized output signals at the corresponding outputs 120 and 122. The TE-polarized and TM-polarized signals are emitted from the silicon photonic circuit 104 as corresponding output beams 142 and 144 via an edge coupler or other suitable coupler.

[0039] Modulation efficiency of electro-optic modulator 100 The modulation efficiency is defined as the voltage V across signal electrodes 108 and 110 multiplied by the length L of waveguide 106 located between the signal electrodes. The output of the modulator is "disconnected." Specifically, if the input beam 140 is TE polarized, such that the optical signal leaves the modulator through output 120 as beam 142 (without beam 144) at zero applied voltage, then applying the voltage V defined herein will rotate the original TE polarization 90° along length L to TM. Therefore, polarizer 116 guides the entire optical signal received at its input 118 to its output 122 and further to beam 144, extinguishing beam 142.

[0040] For modulator 100, modulator efficiency It can be written as: [Equation 6] Where λ is the wavelength of light propagating in waveguide 106, and d is the distance between signal electrodes 108 and 110. Since the denominator has the second largest coefficient of the electro-optic tensor T... and ordinary refractive index With extraordinary refractive index The sum of cubes, modulation efficiency The value is low (where "low" is advantageous for the modulator). As mentioned above, The combination of the lower value and the high field Ex contributes to the overall high efficiency of the modulator 100.

[0041] Figure 2 This is a schematic diagram of an electro-optic modulator 200 according to another embodiment of the present invention. Modulator 200 and modulator 100 ( Figure 1 Similarly, input polarization control has been added, as described below. For simplicity, Figure 2 Omitted Figure 1 Some of the components shown (such as elements of a differential transmission line).

[0042] Similar to modulator 100, modulator 200 includes a waveguide 206 formed in a Z-cut thin-film lithium niobate (TFLN) layer 202 disposed on silicon photonic circuit 204. In this example, the waveguide 206, having an input terminal 208 and an output terminal 210, is U-shaped. Positive signal electrode 212 and negative signal electrode 214 are disposed on opposite sides of the waveguide 206 on the TFLN layer 202. Furthermore, DC electrodes 216 and 218 are disposed on the opposite sides of the waveguide 206 between the input terminal 208 and the signal electrodes 212 and 214 on the TFLN layer 202. Modulator 200 also includes an input coupler 220, an output coupler 222, a polarizer 224, and transition couplers 226 and 228 on the silicon photonic circuit 204. Input coupler 220 and output coupler 222 include, for example, edge couplers, grating couplers, or other suitable couplers. Polarizer 224 may alternatively include a polarization beamsplitter.

[0043] Input coupler 220 is coupled to input terminal 208 of waveguide 206 via transition coupler 226. The transition coupler mode-matches the guided optical signal from silicon photonic circuit 204 to TFLN layer 202. Output terminal 210 of waveguide 206 is coupled to output coupler 222 via transition coupler 228 (similar to transition coupler 226) and further via polarizer.

[0044] Similar to modulator 100 ( Figure 1 The differential driver 236 drives the modulator 200, wherein the outputs 238 and 240 of the driver are coupled to corresponding signal electrodes 212 and 214. Similar to controller 136 ( Figure 1 The controller 241 is coupled to the differential driver 236 and DC electrodes 216 and 218.

[0045] A linearly polarized input beam 242 is received into the silicon photonic circuit 204 via input coupler 220. A guiding optical signal is transmitted to the input terminal 208 of waveguide 206 via transition coupler 226. Controller 241 applies a DC voltage to DC electrodes 216 and 218, which rotates the polarization angle of the optical signal propagating in waveguide 206 from an initial polarization angle f0 to a new fixed polarization angle f1. Polarization angle f1 sets the operating point for the RF polarization modulation of the optical signal passing between signal electrodes 212 and 214. This polarization-modulated optical signal exits waveguide 206 via output terminal 210 and is transmitted to polarizer 224 via transition coupler 228, whereby polarizer 224 converts the polarization modulation into amplitude modulation. The amplitude-modulated wave is transmitted to output coupler 222, where it exits modulator 200 as output beam 244. The overall effect of the DC voltage applied to DC electrodes 216 and 218 is to shift the amplitude modulation range of the output beam 244 for a given modulation voltage range between signal electrodes 212 and 214.

[0046] Figure 3 This is a schematic diagram of a dual-polarization coherent modulator 300 according to an embodiment of the present invention.

[0047] The dual-polarization coherent modulator 300 includes four modulators, each of which is similar to modulator 200. Figure 2 Modulators 302a, 302b, 302c, and 302d are defined by dashed lines. For clarity, only items in modulator 302a are labeled in the figure (excluding the inputs and outputs of modulators 302b-302d). All four modulators 302a-302d are formed in a Z-cut TFLN layer 304 and disposed on silicon photonic circuit 306.

[0048] Modulator 302a includes a U-shaped TFLN waveguide 308a having an input terminal 310a and an output terminal 312a. Signal electrodes 314a and 316a are disposed along opposite sides of waveguide 308a, and DC electrodes 318a and 320a are disposed along the waveguide side between the input terminal 310a and the signal electrodes. Optical input 322a of modulator 302a is coupled to input terminal 310a via transition coupler 326a. Output terminal 312a is coupled to output 332a of modulator 302a via transition coupler 328a and polarizer 330a (or alternatively, polarization beam splitter).

[0049] Differential driver 334a drives modulator 302a, and the outputs 336a and 338a of this driver are coupled to corresponding signal electrodes 314a and 316a. Similarly, differential drivers 334b-334d are coupled to drive corresponding modulators 302b-302d. Similar to controller 241 (… Figure 2 However, the controller 340 with the added channel is coupled to the differential drivers 334a-334d and the DC electrodes 318a and 320a of the modulator 302a, and is also coupled to the corresponding DC electrodes of the modulators 302b-302d.

[0050] The dual-polarization coherent modulator 300 also includes the following components integrated onto the silicon photonic circuit 306: input coupler 342 and output coupler 344 (edge ​​coupler or grating coupler), waveguide beamsplitters 346, 348, and 350, waveguide combiners 352 and 354, phase tuners 356, 358, and 360, and polarization rotator combiner 362, the functionality of which is further detailed below. A controller 340 drives the phase tuners 356, 358, and 360. Both the active and passive waveguide components of the modulator 300 are designed to maintain the transverse mode structure and coherence of both the TE polarized signal and the TM polarized signal propagating in the modulator.

[0051] The TE polarization coherent input beam 364 enters the modulator 300 through the input coupler 342. It propagates as a guide optical signal to the beam splitter 346, which splits the signal into two beams. Each split beam is further split into two beams by corresponding beam splitters 348 and 350. The resulting four optical signals propagate to the corresponding inputs 322a, 322b, 322c, and 322d of modulators 302a, 302b, 302c, and 302d.

[0052] The operation of modulator 302a will now be described by example. An optical signal transitions from input 322a of modulator 302a to waveguide 308a via transition coupler 326a. Controller 340 applies a DC voltage to DC electrodes 318a and 320a, which rotates the polarization angle of the optical signal propagating in waveguide 308a, setting the initial polarization of the guided wave. Signal electrodes 314a and 316a are driven by controller 340 and differential driver 334a using an RF signal to rotate the polarization. The optical signal exits waveguide 308a via output 312a and transition coupler 328 and enters polarizer 330a, which converts the polarization-modulated signal into an amplitude-modulated signal, which exits at modulator output 332a. Similarly, each of the remaining three modulators 302b, 302c, and 302d generates an amplitude-modulated signal exiting from the corresponding outputs 332b, 332c, and 332d.

[0053] The phases of the optical signals exiting modulators 302b and 302d are phase-shifted by corresponding phase tuners 356 and 358, resulting in a 90° phase difference with the signals exiting modulators 302a and 302b. These phase-shifted signals are paired with signals from modulators 302a and 302c in corresponding combiners 352 and 354. Combiners 352 and 354 transmit the corresponding signals indicated by arrows 366 and 368, where phase tuners 356 and 358 have generated in-phase and quadrature components. Signal 366 propagates directly to polarization rotator combiner 362, which transmits it as a TE-polarized signal. Signal 368 passes through phase tuner 360, which shifts the phase of signal 368; it then propagates to polarization rotator combiner 362, which rotates its polarization from TE to TM while transmitting the signal.

[0054] Therefore, the output beam 370 from the output coupler 344 includes both TE and TM polarizations, wherein the amplitude of each polarization, the phase shift between the two polarizations, and the ratio between the in-phase and quadrature components of the signal are determined by four modulators 302a, 302b, 302c, and 302d. The output beam 370 can be further transmitted in an optical fiber (e.g., an optical fiber connected to an additional system), thereby providing four independent communication channels in a single optical fiber.

[0055] It should be noted that the above embodiments are cited as examples, and the present invention is not limited to what has been specifically shown and described above. Rather, the scope of the present invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications of the present invention that are obvious to those skilled in the art after reading the foregoing description and are not disclosed in the prior art.

Claims

1. An electro-optic modulator, comprising: Substrate; An optical waveguide includes an electro-optic thin film disposed on the substrate, the optical waveguide having an input terminal coupled to receive an optical signal and an output terminal opposite to the input terminal; A first electrode and a second electrode are disposed on the substrate along opposite sides of the waveguide; as well as A differential driver having a first differential output and a second differential output, the first differential output and the second differential output being coupled to apply a differential electrical signal between a first electrode and a second electrode, thereby modulating the polarization of the optical signal propagating in the waveguide.

2. The modulator according to claim 1, wherein the optical waveguide has a waveguide axis, the optical signal propagates along the waveguide axis, and the electro-optic thin film comprises a uniaxial crystal disposed on the substrate, the uniaxial crystal having a crystal Z-axis oriented perpendicular to the substrate and a crystal Y-axis oriented parallel to the waveguide axis.

3. The modulator of claim 1, wherein the optical signal at the input end of the optical waveguide has linear polarization, and the modulator includes a controller coupled to control the differential driver to modulate the rotation of the linear polarization of the optical signal exiting the output end of the optical waveguide.

4. The modulator of claim 3, and comprising: A third electrode and a fourth electrode are disposed on the substrate, on opposite sides of the waveguide between the input terminal and the first and second electrodes, wherein the controller is coupled to apply a DC voltage between the third and fourth electrodes, thereby adjusting the input angle of the linear polarization of the optical signal before the modulation of the polarization.

5. The modulator of claim 1, and comprising: A third electrode and a fourth electrode are respectively disposed on the substrate along the sides of the first electrode and the second electrode, wherein the first electrode and the second electrode are disposed between the third electrode and the fourth electrode and the waveguide, wherein the third electrode and the fourth electrode are grounded, and the first electrode, the second electrode, the third electrode and the fourth electrode define a differential transmission line extending along the waveguide.

6. The modulator of claim 1 and comprising: An optical polarizer, coupled to receive the optical signal from the output of the optical waveguide, generates an amplitude-modulated output beam in response to the differential signal and according to the modulated polarization response.

7. The modulator according to any one of claims 1 to 6, wherein the electro-optic thin film is selected from the group consisting of lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and barium titanate (BaTiO3).

8. The modulator according to any one of claims 1 to 6, wherein the substrate comprises a silicon photonic circuit.

9. The modulator according to any one of claims 1 to 6, wherein the substrate comprises an electro-optic thin film.

10. A dual-polarization coherent modulator, comprising: Substrate; At least a first electro-optic modulator and a second electro-optic modulator, each electro-optic modulator comprising: An optical waveguide, including an electro-optic thin film disposed on the substrate; A first electrode and a second electrode are disposed on the substrate along opposite sides of the waveguide; A differential driver having a first differential output and a second differential output, the first differential output and the second differential output being coupled to apply a differential signal between a first electrode and a second electrode, thereby causing polarization rotation of an optical signal propagating in the waveguide; and An optical polarizer, coupled to receive the optical signal from the waveguide to generate an amplitude-modulated output beam; Beam splitter, coupled to divide a coherent input beam between corresponding inputs of the at least first electro-optic modulator and the second electro-optic modulator; and A combiner, coupled to combine corresponding amplitude-modulated output beams generated by the at least first modulator and the second modulator, while rotating the polarization of at least one of the amplitude-modulated output beams, thereby generating a combined beam including dual polarization.

11. The modulator of claim 10, wherein the at least first electro-optic modulator and the second electro-optic modulator comprise a first modulator, a second modulator, a third modulator, and a fourth modulator, wherein the first modulator, the second modulator, the third modulator, and the fourth modulator are configured to apply in-phase modulation and quadrature modulation to each of the dual polarizations.

12. A method for manufacturing an electro-optic modulator, comprising: A deposited optical waveguide is provided, the optical waveguide comprising an electro-optic thin film disposed on a substrate; The input end of the optical waveguide is coupled to receive optical signals; A first electrode and a second electrode are deposited on the substrate along opposite sides of the waveguide; as well as A coupling controller is used to apply a differential electrical signal between the first electrode and the second electrode, thereby modulating the polarization of the optical signal propagating in the waveguide.

13. The method of claim 12, wherein depositing the optical waveguide comprises: A uniaxial electro-optic thin film is deposited on the substrate, wherein the crystal Z-axis of the uniaxial electro-optic thin film is oriented perpendicular to the substrate and the crystal Y-axis is oriented parallel to the waveguide axis of the optical waveguide.

14. The method of claim 12, and comprising: A third electrode and a fourth electrode are deposited on the substrate along the sides of the first electrode and the second electrode, respectively, wherein the first electrode and the second electrode are disposed between the third electrode and the fourth electrode and the waveguide, wherein the third electrode and the fourth electrode are grounded, and the first electrode, the second electrode, the third electrode and the fourth electrode define a differential transmission line extending along the waveguide.

15. The method of claim 12, and comprising: A coupled optical polarizer is used to receive the optical signal from the output of the optical waveguide, thereby generating an amplitude-modulated output beam in response to the differential signal and according to the modulated polarization response.

16. The method according to any one of claims 12 to 15, wherein depositing the optical waveguide comprises depositing a uniaxial electro-optic thin film selected from the group consisting of lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and barium titanate (BaTiO3).

17. The method of any of claims 12-15, wherein depositing the optical waveguide comprises: The optical waveguide is formed on a silicon photonic circuit.

18. The method of any of claims 12-15, wherein depositing the optical waveguide comprises: The substrate is formed from the uniaxial electro-optic thin film.

19. A method for modulating an optical signal, the method comprising: An electro-optic modulator is provided, the electro-optic modulator including an optical waveguide, a first electrode and a second electrode, the optical waveguide including an electro-optic thin film disposed on a substrate, and the first electrode and the second electrode disposed on the substrate along opposite sides of the waveguide; The optical signal is input to the input terminal of the optical waveguide; as well as A differential electrical signal is applied between the first electrode and the second electrode to modulate the polarization of the optical signal propagating in the optical waveguide.

20. The method of claim 19, wherein inputting the optical signal comprises receiving the optical signal having linear polarization at the input end of the optical waveguide, and wherein applying the differential electrical signal comprises controlling the rotation of the linear polarization of the optical signal exiting the output end of the optical waveguide.

21. The method of claim 20, further comprising applying a DC voltage between a third electrode and a fourth electrode to adjust the input angle of the linear polarization of the optical signal prior to modulation of the polarization, the third electrode and the fourth electrode being on opposite sides of the waveguide between the input terminal and the first electrode and the second electrode.

22. The method of claim 20 or 21, and comprising: A coupled optical polarizer is used to receive the optical signal from the output of the optical waveguide, thereby generating an amplitude-modulated output beam in response to the differential signal and according to the modulated polarization response.

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