Electro-optical modulator and modulation method thereof

Abstract

The invention provides an electro-optical modulator and a modulation method thereof, the electro-optical modulator comprises a substrate, a buried oxide layer and a lithium niobate waveguide layer are sequentially stacked on the substrate, and the lithium niobate waveguide layer comprises a first optical waveguide and a second optical waveguide; the electrode layer comprises a composite traveling wave electrode and a direct-current electrode, and the direct-current electrode is arranged on one side, in the signal transmission direction, of the composite traveling wave electrode; wherein the composite traveling wave electrode comprises a metal electrode and a polymer electrode, the metal electrode is embedded into the buried oxide layer, the polymer electrode is arranged on the surface of the buried oxide layer, and the composite traveling wave electrode is arranged between the first optical waveguide and the second optical waveguide and arranged on the side faces of the first optical waveguide and the second optical waveguide respectively; wherein the direct current electrode is arranged between the first optical waveguide and the second optical waveguide. The electro-optical modulator is high in electro-optical conversion efficiency, the plasma effect caused by light field coupling is effectively avoided, and the light loss of the device is remarkably reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated microwave photonics, and in particular to an electro-optical modulator and a modulation method thereof. BACKGROUND

[0002] With the rapid development of human society towards intelligence, sensing, transmission and processing of signals become an important part of future intelligent information processing systems. Microwave photonics combines the advantages of photons and microwaves, such as high bandwidth, low loss and flexible and easy control, and is considered as one of the disruptive technologies of the next generation of information systems, and is also one of the core technologies in the fields of 6G mobile communication, cloud computing and artificial intelligence. Electro-optical modulator is a key device for realizing information electro-optical conversion, and plays an important role in microwave photonics system. Thin film lithium niobate electro-optical modulator as an important electro-optical modulator has the potential of high integration with other microwave photonics devices and broad application prospects. However, the existing thin film lithium niobate modulator generally has the problem of low electro-optical conversion efficiency, which ultimately affects the core indicators such as gain, noise figure and dynamic range of microwave photonics system. SUMMARY

[0003] (I) Technical problems to be solved

[0004] In view of the above problems, the main purpose of the present application is to provide an electro-optical modulator and a modulation method thereof, which not only solves the problem of low electro-optical conversion efficiency, but also effectively avoids the plasmonic effect caused by optical field coupling, and significantly reduces the optical loss of the device.

[0005] (II) Technical solutions

[0006] In order to achieve the above purpose, the present application provides an electro-optical modulator in the first aspect, comprising: a substrate, a buried oxide layer and a lithium niobate waveguide layer are sequentially stacked on the substrate, wherein the lithium niobate waveguide layer comprises a first optical waveguide and a second optical waveguide; an electrode layer comprising a composite traveling wave electrode and a direct current electrode, the direct current electrode being arranged on one side of the composite traveling wave electrode along the signal transmission direction; wherein the composite traveling wave electrode comprises a metal electrode and a polymer electrode, the metal electrode is embedded in the buried oxide layer, the polymer electrode is arranged on the surface of the buried oxide layer, and the composite traveling wave electrode is arranged between the first optical waveguide and the second optical waveguide, and is arranged on the side of the first optical waveguide and the second optical waveguide respectively; wherein the direct current electrode is arranged between the first optical waveguide and the second optical waveguide.

[0007] In the above scheme, the first optical waveguide and the second optical waveguide are in close contact with the polymer electrode in the composite traveling wave electrode without gap.

[0008] In the above scheme, the height of the first optical waveguide and the second optical waveguide is the same as the height of the polymer electrode; the height of the metal electrode is greater than or equal to the height of the polymer electrode.

[0009] In the above scheme, the metal electrode includes a first ground wire, a first signal wire and a second ground wire, wherein the first ground wire, the first signal wire and the second ground wire are parallel to the first optical waveguide; the first ground wire, the first signal wire and the second ground wire are parallel to the second optical waveguide.

[0010] In the above scheme, the polymer electrode includes an insulating polymer, the refractive index of the insulating polymer is lower than that of lithium niobate material, and the dielectric constant of the insulating polymer is higher than that of lithium niobate material.

[0011] In the above scheme, the lithium niobate waveguide layer further includes a beam splitter and a beam combiner, the output end of the beam splitter is connected to the input end of the first optical waveguide and the input end of the second optical waveguide; the input end of the beam combiner is connected to the output end of the first optical waveguide and the output end of the second optical waveguide.

[0012] In the above scheme, the direct current electrode includes a third ground wire, a fourth ground wire and a second signal wire; the second signal wire is arranged between the first optical waveguide and the second optical waveguide; the third ground wire and the fourth ground wire are arranged on one side of the first optical waveguide and the second optical waveguide respectively, and the third ground wire and the fourth ground wire are oppositely arranged along the second signal wire.

[0013] In the above scheme, the direct current electrode is an optical waveguide with an optical phase shift greater than 2π.

[0014] In the above scheme, the first optical waveguide and the second optical waveguide are lithium niobate ridge waveguides or lithium niobate strip waveguides.

[0015] The second aspect of the present application provides a modulation method of an electro-optical modulator, comprising: inputting an optical carrier signal through a beam splitter, and outputting the optical carrier signal into a first optical waveguide and a second optical waveguide in equal proportions; performing electro-optical interaction between a radio frequency signal loaded on a composite traveling wave electrode and the optical carrier signal in the first optical waveguide and the second optical waveguide, and modulating the radio frequency signal onto the optical carrier signal; and changing a direct current voltage loaded on a direct current electrode to regulate the refractive index of the first optical waveguide and the second optical waveguide, so that the bias point of the electro-optical modulator changes.

[0016] (Three) beneficial effects

[0017] The technical scheme of the embodiment of the present application has at least the following beneficial effects:

[0018] 1. The electro-optical modulator provided by the present application has the following beneficial effects:

[0019] 2. The electro-optic modulator provided by this invention, because the first and second optical waveguides are in direct contact with the polymer electrode, not only confines the optical field but also controls the electric field within the waveguides, thus alleviating the problem of low electro-optic conversion efficiency caused by the waveguide shielding effect. Simultaneously, because the first and second optical waveguides are far from the metal electrode, the plasma effect caused by optical field coupling can be avoided, significantly reducing the optical loss of the device. Attached Figure Description

[0020] Figure 1 A schematic top view of an electro-optic modulator according to an embodiment of the present invention is shown;

[0021] Figure 2 A schematic cross-sectional view of an electro-optic modulator according to an embodiment of the present invention is shown;

[0022] Figure 3 A schematic flowchart of a modulation method for an electro-optic modulator according to an embodiment of the present invention is shown.

[0023] [Explanation of reference numerals in the attached figures]

[0024] 1-Beam splitter; 2-Composite traveling wave electrode; 3-First optical waveguide; 4-Second optical waveguide;

[0025] 5-DC electrode; 6-Band combiner; 7-Substrate layer; 8-Buried oxide layer; 9-Polymer electrode; 10-Metal electrode. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] Figure 1 A top view of an electro-optic modulator according to an embodiment of the present invention is shown schematically. Figure 2 A cross-sectional view of an electro-optic modulator according to an embodiment of the present invention is shown schematically.

[0028] Please participate specifically. Figure 1 and Figure 2The electro-optic modulator includes: a substrate 7, on which a buried oxide layer 8 and a lithium niobate waveguide layer are sequentially stacked, wherein the lithium niobate waveguide layer includes a first optical waveguide 3 and a second optical waveguide 4; an electrode layer including a composite traveling wave electrode 2 and a DC electrode 5, wherein the DC electrode 5 is disposed on one side of the composite traveling wave electrode 2 along the signal transmission direction; wherein the composite traveling wave electrode 2 includes a metal electrode 10 and a polymer electrode 9, wherein the metal electrode 10 is embedded in the buried oxide layer 8, the polymer electrode 9 is disposed on the surface of the buried oxide layer 8, and the composite traveling wave electrode 2 is disposed between the first optical waveguide 3 and the second optical waveguide 4, and is respectively disposed on the side surfaces of the first optical waveguide 3 and the second optical waveguide 4; wherein the DC electrode 5 is disposed between the first optical waveguide 3 and the second optical waveguide 4.

[0029] For example, the substrate layer 7 can be made of materials such as quartz or silicon, and the buried oxide layer 8 can be made of materials such as silicon dioxide. The substrate layer 7 ensures the compactness and stability of the device structure. On a suitable substrate, other layers such as the buried oxide layer 8 can grow the required materials. The buried oxide layer 8 plays an important role in preventing device contamination, protecting the surface and interior of the device, and can act as a contamination barrier layer, preventing dirty substances in the environment from penetrating the sensitive device surface.

[0030] For example, the first optical waveguide 3 and the second optical waveguide 4 are lithium niobate ridge waveguides or lithium niobate strip waveguides, so that the waveguides can be selected accordingly based on the actual situation and the technical effects to be achieved.

[0031] Please continue reading. Figure 2 The electro-optic modulator chip has a first optical waveguide 3 and a second optical waveguide 4 that are parallel to each other on the lithium niobate waveguide layer. Both the first optical waveguide 3 and the second optical waveguide 4 are in close, seamless contact with the polymer electrode 9 in the composite traveling-wave electrode 2. For example... Figure 2 As shown, the heights of the first optical waveguide 3 and the second optical waveguide 4 are the same as the height of the polymer electrode 9; the height of the metal electrode 10 is greater than or equal to the height of the polymer electrode 9. By making the polymer electrode 9 and the optical waveguide the same height, they can make better contact, thereby avoiding the waveguide shielding effect in traditional electro-optic modulators, improving electro-optic overlap integration, and increasing modulation efficiency.

[0032] Please continue reading. Figure 1 Both sides of the polymer electrode 9 along the Z direction are metal electrodes 10. The metal electrodes 10 are embedded in the buried oxide layer 8, which makes the electric field more concentrated inside the optical waveguide, increases the overlap integral of the electric field and the optical field, and improves the conversion efficiency.

[0033] Specifically, the metal electrode 10 in the composite traveling wave electrode 2 includes three metal signal lines along the Z direction, namely the first ground line G1, the first signal line S1, and the second ground line G2. The three metal signal lines are parallel to the first optical waveguide 3 and the second optical waveguide 4, and are staggered with the first optical waveguide 3 and the second optical waveguide 4 along the Z direction.

[0034] In embodiments of the present invention, the polymer electrode 9 comprises an insulating polymer having a lower refractive index than lithium niobate and a higher dielectric constant than lithium niobate. For example, the polymer electrode 9 may be made of materials such as glycerol or NPS-PMMA.

[0035] In embodiments of the present invention, the material of the metal electrode 10 may be, for example, but not limited to, gold, titanium, etc.

[0036] To mitigate the waveguide shielding effect and overcome the low electro-optic conversion efficiency caused by differences in dielectric constants, this embodiment proposes to use a polymer electrode 9 and a metal electrode 10 to jointly form a composite traveling wave electrode 2. Since the polymer electrode 9 is in direct contact with the first optical waveguide 3 and the second optical waveguide 4, this structure can alleviate the waveguide shielding effect in traditional electro-optic modulators, thereby achieving high-efficiency, low-loss electro-optic modulation.

[0037] Furthermore, in the prior art, the metal electrode and the waveguide are basically in contact. However, in the embodiments of the present invention, since the metal electrode 10 is relatively far from the first waveguide 3 and the second waveguide 4, the plasma effect caused by optical field coupling can be avoided, and the optical loss of the device can be significantly reduced.

[0038] In embodiments of the present invention, such as Figure 1 As shown, the lithium niobate waveguide layer of the electro-optic modulator chip also includes a beam splitter 1 and a beam combiner 6. The output end of the beam splitter 1 is connected to the input end of the first optical waveguide 3 and the input end of the second optical waveguide 4; the input end of the beam combiner 6 is connected to the output end of the first optical waveguide 3 and the output end of the second optical waveguide 4.

[0039] Specifically, beam splitter 1 and beam combiner 6 are waveguide devices. Beam splitter 1 can achieve one input and two outputs, and can be, but is not limited to, a Y-branch, a 1×2 multimode interferometer, or a directional coupler. Beam combiner 6 is an optical beam combiner that can achieve equal power beam combining, and can be, but is not limited to, a 2×1 multimode interferometer, a Y-branch, or a directional coupler. By setting beam splitter 1, the input optical carrier signal is split into two beams with the same power, which are then modulated by the first optical waveguide 3 and the second optical waveguide 4, respectively. After being combined by beam combiner 6, a stronger beam is formed, improving signal strength and transmission speed.

[0040] In an embodiment of the present invention, the two-way splitting ratio of beam splitter 1 and beam combiner 6 can be set to 0.5:0.5.

[0041] In an embodiment of the present invention, the DC electrode 5 is disposed on one side of the composite traveling wave electrode 2 along the signal transmission direction (i.e., along the Y-axis direction), and the DC electrode 5 includes a third ground line G3, a fourth ground line G4, and a second signal line S2.

[0042] Specifically, such as Figure 1 As shown, the second signal line S2 is located between the first optical waveguide 3 and the second optical waveguide 4; the third ground line G3 and the fourth ground line G4 are respectively located on one side of the first optical waveguide 3 and the second optical waveguide 4, and the third ground line G3 and the fourth ground line G4 are arranged opposite to each other along the second signal line S2.

[0043] For example, the DC electrode 5 is an adjustable phase shifter, which can be, but is not limited to, an electro-optic phase shifter, a thermo-optic phase shifter, etc. The DC electrode 5 works together with the composite traveling wave electrode 2, and the bias point of the modulator can be adjusted by changing the voltage applied to the DC electrode 5.

[0044] As another example, the DC electrode 5 is an optical waveguide capable of achieving an optical phase shift greater than 2π.

[0045] In embodiments of the present invention, all parts of the electro-optic modulator chip, except for the composite traveling wave electrode 2 and the DC electrode 5, are connected by optical waveguides. The lithium niobate waveguide layer uses thin-film lithium niobate material, thus possessing the advantages of high electro-optic coefficient and low loss.

[0046] Based on the above description of the electro-optic modulator, this embodiment of the invention also provides a modulation method for the electro-optic modulator, which will be described in detail below.

[0047] Figure 3 A schematic flowchart of a modulation method for an electro-optic modulator according to an embodiment of the present invention is shown.

[0048] Please refer to the following for details. Figure 3 The modulation method of the electro-optic modulator specifically includes operations S1~S3.

[0049] During operation S1, the optical carrier signal input through beam splitter 1 is output proportionally to the first optical waveguide 3 and the second optical waveguide 4.

[0050] In operation S2, the radio frequency signal loaded on the composite traveling wave electrode 2 interacts electro-optically with the optical carrier signal in the first optical waveguide 3 and the second optical waveguide 4, thereby modulating the radio frequency signal onto the optical carrier signal.

[0051] In operation S3, by changing the DC voltage applied to the DC electrode 5, the refractive index of the first optical waveguide 3 and the second optical waveguide 4 is adjusted, thereby changing the bias point of the electro-optic modulator.

[0052] For example, based on the above modulation method, a thin-film lithium niobate electro-optic modulator chip is selected for modulation. For instance, a thin-film lithium niobate material with a thickness of 600 nm is used, operating in the 1550 nm band. The first optical waveguide 3, the second optical waveguide 4, and all waveguide devices are ridge waveguides with a ridge height of 300 nm. The width of the optical waveguide used to connect the various parts is 1 μm. The beam splitter 1 uses a 1×2 multimode interferometer, with the splitting ratio of the upper and lower paths set to 0.5:0.5. The composite traveling-wave electrode 2 is a metal electrode 10 containing three signal lines. The composite traveling-wave electrode 2 is composed of the metal electrode 10 and the polymer electrode 9. The metal electrode 10 is made of Au, and the polymer electrode 9 is NPS-PMMA. The DC electrode 5 has a thickness of 900 nm, and the widths of the third ground line, the fourth ground line, and the second signal line are 11 μm, with a spacing of 7 μm from the waveguide. The beam combiner 6 uses a 2×1 multimode interferometer, with the splitting ratio of the upper and lower paths set to 0.5:0.5.

[0053] By modulating the aforementioned thin-film lithium niobate electro-optic modulator chip, the optical carrier signal and radio frequency signal are modulated based on the combined action of the composite traveling wave electrode and the DC electrode, thereby overcoming the technical problems of low conversion efficiency, limited bandwidth, and difficulty in integration of lithium niobate electro-optic modulators.

[0054] In embodiments of the present invention, a composite traveling-wave electrode is formed using polymer electrodes and metal electrodes. Since the polymer electrodes are in direct contact with the lithium niobate waveguide, the electric field is controlled within the waveguide while simultaneously confining the optical field. This structure alleviates the waveguide shielding effect, thereby achieving high-efficiency, low-loss electro-optic modulation. Furthermore, because the metal electrodes are located far from the lithium niobate waveguide, plasma effects caused by optical field coupling are avoided, significantly reducing the optical loss of the device.

[0055] Those skilled in the art will understand that although the invention has been shown and described with reference to specific exemplary embodiments thereof, they should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Therefore, the scope of the invention should not be limited to the above embodiments, but should be determined not only by the appended claims, but also by their equivalents.

[0056] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electro-optic modulator, characterized by The application relates to a lithium niobate waveguide device, which comprises the following parts: a substrate (7) on which a buried oxide layer (8) and a lithium niobate waveguide layer are sequentially stacked, wherein the lithium niobate waveguide layer comprises a first optical waveguide (3) and a second optical waveguide (4); an electrode layer which comprises a composite row wave electrode (2) and a direct current electrode (5), and the direct current electrode (5) is arranged on one side of the composite row wave electrode (2) along a signal transmission direction; wherein the composite row wave electrode (2) comprises a metal electrode (10) and a polymer electrode (9), the metal electrode (10) is embedded in the buried oxide layer (8), and the polymer electrode (9) is arranged on the surface of the buried oxide layer (8), and the composite row wave electrode (2) is arranged between the first optical waveguide (3) and the second optical waveguide (4) and is arranged on the side of the first optical waveguide (3) and the second optical waveguide (4) respectively; wherein the direct current electrode (5) is arranged between the first optical waveguide (3) and the second optical waveguide (4).

2. The electro-optic modulator of claim 1, wherein, The first optical waveguide (3) and the second optical waveguide (4) are in close contact with the polymer electrode (9) in the composite row wave electrode (2) without any gap.

3. The electro-optic modulator of claim 1 or 2, wherein, The height of the first optical waveguide (3) and the second optical waveguide (4) is the same as the height of the polymer electrode (9). The height of the metal electrode (10) is greater than or equal to the height of the polymer electrode (9).

4. The electro-optic modulator of claim 1, wherein, The metal electrode (10) comprises a first ground wire, a first signal wire and a second ground wire, wherein the first ground wire, the first signal wire and the second ground wire are parallel to the first optical waveguide (3); The first ground wire, the first signal wire and the second ground wire are parallel to the second optical waveguide (4).

5. The electro-optic modulator of claim 1, wherein, The polymer electrode (9) comprises an insulating polymer, the refractive index of the insulating polymer is lower than that of lithium niobate material, and the dielectric constant of the insulating polymer is higher than that of lithium niobate material.

6. The electro-optic modulator of claim 1, wherein, The lithium niobate waveguide layer further comprises a beam splitter (1) and a beam combiner (6), the output end of the beam splitter (1) is connected with the input end of the first optical waveguide (3) and the input end of the second optical waveguide (4); The input end of the beam combiner (6) is connected with the output end of the first optical waveguide (3) and the output end of the second optical waveguide (4).

7. The electro-optic modulator of claim 1, wherein, The direct current electrode (5) comprises a third ground wire, a fourth ground wire and a second signal wire; The second signal wire is arranged between the first optical waveguide (3) and the second optical waveguide (4); The third ground wire and the fourth ground wire are arranged on one side of the first optical waveguide and the second optical waveguide respectively, and the third ground wire and the fourth ground wire are oppositely arranged along the second signal wire.

8. The electro-optic modulator of claim 1 or 7, wherein, The direct current electrode (5) is used for realizing an optical waveguide with an optical phase shift greater than 2pi.

9. The electro-optic modulator of claim 1, wherein, The first optical waveguide (3) and the second optical waveguide (4) are lithium niobate ridge waveguides or lithium niobate strip waveguides.

10. A modulation method of an electro-optic modulator, applied to the electro-optic modulator according to any one of claims 1 to 9, characterized in that, The application further relates to a lithium niobate waveguide device, which comprises the following parts: An optical carrier signal input through a beam splitter (1) is output to a first optical waveguide (3) and a second optical waveguide (4) in equal proportions; An RF signal loaded on a composite row wave electrode (2) and an optical carrier signal in the first optical waveguide (3) and the second optical waveguide (4) are subjected to electro-optical interaction, so that the RF signal is modulated on the optical carrier signal; By changing the direct current voltage loaded on the direct current electrode (5), the refractive index of the first optical waveguide (3) and the second optical waveguide (4) is regulated, so that the bias point of the electro-optic modulator is changed.

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