An electro-optic modulator

Abstract

The application provides an electro-optical modulator, belonging to the technical field of electro-optical modulation. The electro-optical modulator comprises a Mach-Zehnder interference optical path and an electrode assembly. The Mach-Zehnder interference optical path comprises a first branch waveguide and a second branch waveguide. The electrode assembly comprises a radio frequency electrode and a direct current bias electrode. The radio frequency electrode and the direct current bias electrode are integrally formed or separately arranged. Because the first direct current bias voltage V1 and the second direct current bias voltage V2 with the same electric field direction and different voltages are respectively loaded on the first branch waveguide and the second branch waveguide, the phase change caused by the direct current drift generated on the first branch waveguide and the second branch waveguide is mutually offset after the beam combining waveguide of the Mach-Zehnder interference optical path, and the generated direct current drift is inhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electro-optical modulation, and particularly relates to an electro-optical modulator. BACKGROUND

[0002] Electro-optical devices are often used in optical fiber communication systems to control optical signals. Generally, these electro-optical devices include at least one optical waveguide made of and / or generated in an electro-optical material. When an electric field is generated in the electro-optical material, the refractive index of the optical waveguide will change, thereby the optical signal propagating therein can be changed. Commonly used electro-optical devices employed in communication systems include electro-optical modulators, optical switches, optical couplers, etc.

[0003] High-performance electro-optical modulators are very important components in the field of optical communication and optical signal processing, and in recent years, thin-film lithium niobate electro-optical modulators have attracted widespread attention. However, the DC drift phenomenon in the thin-film lithium niobate electro-optical modulator is considered to be caused by the free-moving charges in the substrate or cladding material under the action of an external field, such as K + , Na + , OH - , defects, alkali metal impurities, etc. At the same time, the lithium niobate material itself has a photorefractive effect, which will generate induced charges, thereby causing DC drift. In the lithium niobate electro-optical modulator, DC drift will cause the working point of the modulator to be unstable, and seriously affect the performance of the modulator. SUMMARY

[0004] The purpose of the present application is to solve the problem of DC drift in the existing lithium niobate electro-optical modulator, and thus a new electro-optical modulator is proposed.

[0005] The present application provides an electro-optical modulator, comprising:

[0006] a Mach-Zehnder interference optical path comprising a first branch waveguide and a second branch waveguide;

[0007] an electrode assembly comprising a radio frequency electrode and a direct current bias electrode, the radio frequency electrode and the direct current bias electrode being integrally formed or separately provided,

[0008] wherein the first branch waveguide and the second branch waveguide are respectively loaded with first and second direct current bias voltages V1 and V2 having the same electric field direction and different voltages.

[0009] The electro-optical modulator described above, wherein:

[0010] The radio frequency electrode and the direct current bias electrode are integrally formed by a biasing device.

[0011] The electro-optical modulator described above, wherein:

[0012] The first branch waveguide and the second branch waveguide are also respectively loaded with a radio frequency signal.

[0013] The electro-optical modulator, wherein:

[0014] When the radio frequency electrode and the direct current bias electrode are separately arranged, the number of the direct current bias electrodes is four,

[0015] The first branch waveguide and the second branch waveguide are both provided with two direct current bias electrodes on both sides.

[0016] The electro-optical modulator, wherein:

[0017] The radio frequency electrode includes a radio frequency signal electrode and two radio frequency ground electrodes, the radio frequency signal electrode is arranged between the first branch waveguide and the second branch waveguide, and the two radio frequency ground electrodes are arranged on both sides of the first branch waveguide and the second branch waveguide and away from the radio frequency signal electrode.

[0018] The electro-optical modulator, wherein:

[0019] The first direct current drift and the second direct current drift generated by the first direct current bias voltage V1 and the second direct current bias voltage V2 respectively conform to a predetermined curve.

[0020] The electro-optical modulator, wherein:

[0021] In the predetermined curve, by adjusting the size of the first direct current bias voltage V1 and the second direct current bias voltage V2 loaded, the difference between the first direct current drift and the second direct current drift tends to zero.

[0022] The present application also provides another electro-optical modulator, comprising:

[0023] A Mach-Zehnder interference optical path, comprising a first branch waveguide and a second branch waveguide;

[0024] An electrode assembly, comprising a radio frequency electrode and a direct current bias electrode, the radio frequency electrode and the direct current bias electrode being separately arranged;

[0025] The first branch waveguide or the second branch waveguide is loaded with a direct current bias voltage V3,

[0026] The region loaded with the direct current bias voltage V3 does not contain a cladding; or

[0027] The region loaded with the direct current bias voltage V3 is provided with a high conductivity material.

[0028] The present application also provides still another electro-optical modulator, comprising:

[0029] A Mach-Zehnder interference optical path, comprising a first branch waveguide and a second branch waveguide;

[0030] An electrode assembly, comprising a radio frequency electrode;

[0031] The first branch waveguide or the second branch waveguide is provided with an electromechanical control device.

[0032] Any one of the above electro-optical modulators, wherein:

[0033] The electro-optical modulator comprises a bulk lithium niobate modulator or a thin film lithium niobate modulator.

[0034] Effects and advantages of the present application

[0035] The electro-optical modulator comprises a Mach-Zehnder interference optical path and an electrode assembly, the Mach-Zehnder interference optical path comprises a first branch waveguide and a second branch waveguide, and the electrode assembly comprises a radio frequency electrode and a direct current bias electrode, which are integrally formed or separately provided. Because the first direct current bias voltage V1 and the second direct current bias voltage V2 with the same electric field direction and different voltages are respectively loaded on the first branch waveguide and the second branch waveguide, the phase changes caused by the direct current drifts generated on the first branch waveguide and the second branch waveguide are mutually offset after passing through the beam combining waveguide of the Mach-Zehnder interference optical path, and the generated direct current drifts are suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a structural schematic diagram of a first electro-optical modulator of an embodiment of the present application.

[0037] Figure 2 is a predetermined curve schematic diagram after loading a direct current bias voltage in the embodiment of the present application.

[0038] Figure 3 is a structural schematic diagram of a radio frequency electrode of the first electro-optical modulator of the embodiment of the present application.

[0039] Figure 4 is a structural schematic diagram of a direct current bias electrode in the first electro-optical modulator of the embodiment of the present application.

[0040] Figure 5 is a structural schematic diagram of a second electro-optical modulator in the embodiment of the present application.

[0041] Figure 6 is a structural schematic diagram of a third electro-optical modulator in the embodiment of the present application.

[0042] Figure 7 is a structural schematic diagram of a fourth electro-optical modulator in the embodiment of the present application.

[0043] Figure 8 is a structural schematic diagram of a fifth electro-optical modulator in the embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application provides an electro-optical modulator in combination with the embodiments and drawings.

[0045] <Embodiment>

[0046] Figure 1 is a structural schematic diagram of a first electro-optical modulator of the embodiment of the present application.

[0047] As shown in Figure 1 , the first electro-optical modulator 100 provided by the embodiment of the present application includes a substrate 10, a Mach-Zehnder interference optical path 20 and an electrode assembly 30.

[0048] The substrate 10 includes a substrate and a silicon dioxide buffer layer arranged in sequence. The substrate can be a silicon substrate or other substrates such as quartz.

[0049] The Mach-Zehnder interference optical path 20 is arranged on the substrate 10 and includes an input main waveguide 21, a first branch waveguide 22, a second branch waveguide 23 and an output main waveguide 24. An optical signal is input along the input main waveguide 21 and is split at a Y-shaped splitting waveguide to generate a first optical signal and a second optical signal. The first optical signal is transmitted along the first branch waveguide 22, and the second optical signal is transmitted along the second branch waveguide 23. After modulation and biasing by the electrode assembly 30, the first optical signal and the second optical signal are combined at a Y-shaped combining waveguide and then enter the output main waveguide 24.

[0050] The electrode assembly 30 includes a radio frequency electrode 31 and a direct current bias electrode 32, Figure 1 The radio frequency electrode 31 and the direct current bias electrode 32 are arranged separately. The first optical signal and the second optical signal passing through the Y-shaped splitting waveguide are first modulated by a radio frequency signal loaded on the radio frequency electrode 31 and then biased by a direct current bias voltage loaded on the direct current bias electrode 32.

[0051] Specifically, the radio frequency electrode 31 includes a radio frequency signal electrode and two radio frequency ground electrodes. The radio frequency signal electrode is arranged between the first branch waveguide 22 and the second branch waveguide 23, and the two radio frequency ground electrodes are arranged on both sides of the first branch waveguide 22 and the second branch waveguide 23 and away from the radio frequency signal electrode.

[0052] The number of the direct current bias electrode 32 is four, which are arranged on both sides of the first branch waveguide 22 and the second branch waveguide 23. In the embodiment, the direct current bias electrode 32 includes two direct current bias signal electrodes and two direct current bias ground electrodes. Figure 1In the embodiment, the electric field direction of the first DC bias voltage V1 loaded on the first branch waveguide 22 is from the positive pole to the negative pole, i.e. the electric field direction is downward. The electric field direction of the second DC bias voltage V2 loaded on the second branch waveguide 23 is also from the positive pole to the negative pole, i.e. the electric field direction on the second branch waveguide 23 is the same as that on the first branch waveguide 22, but the voltage value is different. In other embodiments, the first DC bias voltage V1 and the second DC bias voltage V2 loaded on the first branch waveguide 22 and the second branch waveguide 23 respectively can also have the electric field direction upward. Therefore, in the embodiment, as long as the electric field directions of the two DC bias voltages loaded on the first branch waveguide 22 and the second branch waveguide 23 are the same and the voltage values are different, the embodiment is applicable.

[0053] In the embodiment, the first DC bias voltage V1 and the second DC bias voltage V2 with the same electric field direction and different voltage values are loaded on the first branch waveguide 22 and the second branch waveguide 23 respectively, and the first DC drift and the second DC drift simultaneously generated by the first DC bias voltage V1 and the second DC bias voltage V2 are made to conform to the predetermined curve.

[0054] Figure 2 is a schematic diagram of the predetermined curve after the DC bias voltage is loaded in the embodiment of the application.

[0055] As shown in Figure 2 , the abscissa of the predetermined curve is the first DC bias voltage V1 and the second DC bias voltage V2 loaded on the first branch waveguide 22 and the second branch waveguide 23 respectively, and the DC bias voltage V of the operating point, and the ordinate is the DC drift generated by the corresponding DC bias voltage. By adjusting the voltage values of the first DC bias voltage V1 loaded on the first branch waveguide 22 and the second DC bias voltage V2 loaded on the second branch waveguide 23, and determining the DC bias voltage V of the operating point in the differential form, i.e. V=V1-V2, the DC bias voltage V of the operating point is usually biased at the quadrature point (i.e. at the bias phase π / 2). It can be seen that Figure 2 by adjusting the voltage values of the loaded first DC bias voltage V1 and the second DC bias voltage V2, so that the difference between the first DC drift generated by the loaded first DC bias voltage V1 and the second DC drift generated by the loaded second DC bias voltage V2 becomes smaller and smaller, and finally tends to zero, i.e. after passing through the Y-shaped beam combining waveguide, the phase change caused by the DC drift generated by the two simultaneously is mutually offset after the beam combining through the Y-shaped beam combining waveguide, so as to suppress the DC drift.

[0056] Figure 3 is a structure schematic diagram of the radio frequency electrode of the first electro-optical modulator in the embodiment of the application.

[0057] As shown in Figure 3As shown, the electro-optic modulator 100 of this embodiment includes a substrate 11, a silicon dioxide buffer layer 12, a lithium niobate waveguide core layer 2, a radio frequency electrode 31, and a cladding layer 40 arranged sequentially from bottom to top.

[0058] The substrate 11 and the silicon dioxide buffer layer 12 are the base 10 in this embodiment, and the lithium niobate waveguide core layer 2 is disposed above the silicon dioxide buffer layer 12.

[0059] The radio frequency (RF) electrode 31 comprises three metal electrodes, for example, all three metal electrodes can be copper electrodes. The middle electrode located above the lithium niobate waveguide core layer 2 is the RF signal electrode, and the metal electrodes located on both sides of the RF signal electrode are RF ground electrodes. The RF electrode 31 is used to load an RF signal to change the refractive index of the optical signal, thereby changing the output light intensity of the optical signal.

[0060] Figure 4 This is a schematic diagram of the DC bias electrode in the first type of electro-optic modulator according to an embodiment of the present invention.

[0061] like Figure 4 As shown, the electro-optic modulator 100 of this embodiment includes a substrate 11, a silicon dioxide buffer layer 12, a lithium niobate waveguide core layer 2, a DC bias electrode 32, and a cladding layer 40 arranged sequentially from bottom to top.

[0062] Four DC bias electrodes 32 are arranged sequentially above the lithium niobate waveguide core layer 2. DC bias voltages V1 and V2 are applied to the DC bias electrodes 32, and the DC bias voltage V corresponding to the operating point is obtained in a differential form.

[0063] Figure 5 This is a schematic diagram of the structure of the second type of electro-optic modulator in this embodiment of the invention.

[0064] like Figure 5 As shown, the second electro-optic modulator 200 in this embodiment of the invention includes a substrate 10, a Mach-Zehnder interference optical path 20, and an electrode assembly 230. In this embodiment of the invention, components identical to those in the first electro-optic modulator 100 are given the same reference numerals, and different components are renumbered; the same applies to the electro-optic modulators described below.

[0065] In electrode assembly 230, the radio frequency (RF) electrode and the DC bias electrode are integrally formed, thereby simultaneously applying the RF signal and the DC bias voltage to the first branch waveguide 22 and the second branch waveguide 23. In this embodiment, a biaser in the prior art is used to combine the RF electrode and the DC bias electrode. The RF electrode adopts a GSSG transmission line structure, and the RF electrodes are arranged from top to bottom as a first RF ground electrode, a first RF signal electrode, a second RF signal electrode, and a second RF ground electrode. When the first RF signal is applied to the first RF signal electrode, and the electrical signal of the first DC bias voltage V1 is input to the biaser, a first output signal containing both is output; when the second RF signal is applied to the second RF signal electrode, and the electrical signal of the second DC bias voltage V2 is input to the biaser, a second output signal containing both is output. Figure 5 In the first branch waveguide 22 and the second branch waveguide 23, a first DC bias voltage V1 and a second DC bias voltage V2 with the same electric field direction but different voltage values ​​are simultaneously applied. Therefore, the phase changes caused by the DC drift generated simultaneously in the first branch waveguide 22 and the second branch waveguide 23 are canceled out by the Y-shaped beam combiner waveguide, thereby suppressing the DC drift caused by the applied DC bias voltages V1 and V2. The DC drift generated by the second electro-optic modulator 200 in this embodiment after applying DC bias voltages V1 and V2 also conforms to the same principle. Figure 2 The predetermined curve shown will not be described in detail here.

[0066] Figure 6 This is a schematic diagram of the structure of the third type of electro-optic modulator in this embodiment of the invention.

[0067] like Figure 6 As shown, the structure of the third electro-optic modulator 300 in this embodiment is similar to that of the first electro-optic modulator 100, including a substrate 10, a Mach-Zehnder interference optical path 20, and an electrode assembly 330. The electrode assembly 330 includes a radio frequency electrode 31 and a DC bias electrode 331. The radio frequency electrode 31 and the DC bias electrode 331 are separately disposed. The only difference is that either the first branch waveguide 22 or the second branch waveguide 23 of the Mach-Zehnder interference optical path 20 is loaded with a DC bias voltage V3, and no silicon dioxide cladding is disposed in the region where the DC bias voltage V3 is loaded (i.e., Figure 6 The dashed area in the figure does not contain a silicon dioxide cladding, that is, there is no silicon dioxide cladding below the DC bias electrode 331, which can avoid the interference of impurity charges in the silicon dioxide cladding on the applied DC bias voltage V3.

[0068] Figure 7 This is a schematic diagram of the structure of the fourth type of electro-optic modulator in this embodiment of the invention.

[0069] like Figure 7As shown, the structure of the fourth electro-optic modulator 400 in this embodiment is similar to that of the third electro-optic modulator 300, including a substrate 10, a Mach-Zehnder interference optical path 20, and an electrode assembly 430. The electrode assembly 430 includes a radio frequency electrode 31 and a DC bias electrode 431. A DC bias voltage V3 is applied to either the first branch waveguide 22 or the second branch waveguide 23 of the Mach-Zehnder interference optical path 20. The only difference is that a high-conductivity material is also provided below the silicon dioxide cladding of the DC bias electrode 431. Adding a high-conductivity material can increase conductivity, thereby releasing the charge accumulated due to the applied DC bias voltage V3 and suppressing the DC drift caused by the applied DC bias voltage V3.

[0070] Figure 8 This is a schematic diagram of the structure of the fifth electro-optic modulator in this embodiment of the invention.

[0071] like Figure 8 As shown, the fifth electro-optic modulator 500 provided in this embodiment includes a substrate 10, a Mach-Zehnder interference optical path 20, a radio frequency electrode 31, and an electromechanical control device 501. The Mach-Zehnder interference optical path 20 includes a first branch waveguide 22 and a second branch waveguide 23. The radio frequency electrode 31 adopts a GSG transmission line structure. In this embodiment, the fifth electro-optic modulator 500 sets the electromechanical control device 501 on either the first branch waveguide 22 or the second branch waveguide 23. It utilizes the piezoelectric effect of lithium niobate to change the material polarization and refractive index, replacing the DC bias electrode, thereby reducing energy consumption and suppressing DC drift.

[0072] The five electro-optic modulators provided in the embodiments of the present invention include thin-film lithium niobate electro-optic modulators or bulk lithium niobate electro-optic modulators, which suppress DC drift by applying a DC bias voltage or by using electromechanical control.

[0073] The method for fabricating the electro-optic modulator provided in this embodiment can employ existing lithium niobate etching and electrode fabrication processes, such as electron beam lithography, reactive ion etching, PECVD (plasma-enhanced chemical vapor deposition), ultraviolet lithography, metal lift-off, and pre-annealing. In the pre-annealing process, the temperature and time can be set to 550°C and 3 hours, respectively, with slow cooling in a tube furnace to reduce defects, release stress, and make the lattice of the lithium niobate waveguide core layer 2 more uniform, thereby suppressing DC drift caused by defects.

[0074] The foregoing is considered as illustrative only of the principles of the application. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the application to the exact construction and practice described. Accordingly, all suitable modifications and equivalents should be considered as falling within the scope of the application as defined by the claims that follow.

Claims

1. An electro-optic modulator, characterized in that, include: The Mach-Zehnder interferometer optical path includes a first branch waveguide and a second branch waveguide; An electrode assembly includes a radio frequency electrode and a DC bias electrode, wherein the radio frequency electrode and the DC bias electrode are integrally formed or separately disposed. Wherein, the first branch waveguide and the second branch waveguide are respectively loaded with a first DC bias voltage V1 and a second DC bias voltage V2 with the same electric field direction but different voltages; There are four DC bias electrodes, which are respectively loaded on both sides of the first branch waveguide and the second branch waveguide; The electric field direction of the first DC bias voltage V1 applied to the first branch waveguide is from the positive terminal to the negative terminal; The electric field direction of the second DC bias voltage V2 applied to the second branch waveguide is from the positive terminal to the negative terminal.

2. The electro-optic modulator according to claim 1, characterized in that: The radio frequency electrode and the DC bias electrode are integrally formed by a biaser.

3. The electro-optic modulator according to claim 2, characterized in that: Radio frequency signals are also loaded onto the first branch waveguide and the second branch waveguide, respectively.

4. The electro-optic modulator according to claim 1, characterized in that: When the radio frequency electrode and the DC bias electrode are set separately, the number of DC bias electrodes is four, and two DC bias electrodes are provided on both sides of the first branch waveguide and the second branch waveguide.

5. The electro-optic modulator according to claim 4, characterized in that: The radio frequency electrode includes a radio frequency signal electrode and two radio frequency ground electrodes; the radio frequency signal electrode is disposed between the first branch waveguide and the second branch waveguide. The two radio frequency grounding electrodes are respectively disposed on both sides of the first branch waveguide and the second branch waveguide and are far away from the radio frequency signal electrode.

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