Distributed Light Intensity Modulator

Abstract

The present application discloses a distributed light intensity modulator, comprising: a substrate, and a splitter element, an optical waveguide, and a light combining element connected in sequence and arranged on the substrate; a driving electrode, which is arranged on the substrate and includes a plurality of sub-driving electrodes arranged at intervals; an optical waveguide passes through the sub-driving electrodes in sequence; and at least one voltage bias electrode, which is at least partially arranged at intervals from the sub-driving electrodes. The length of each sub-driving electrode is much smaller than the total length of a conventional modulator of this type. In each sub-driving electrode, the propagation of the optical signal can be approximately synchronized with the propagation of the electrical signal. The walk-off phenomenon between the photoelectric signals is minimized. By using a voltage bias electrode arranged between each sub-driving electrode as an anti-crosstalk device for shielding the crosstalk between the sub-driving electrodes, the modulation bandwidth can be increased and the driving voltage can be reduced simultaneously, so that the modulator can reduce the zero drift phenomenon and prevent the crosstalk problem between the sub-driving electrodes caused by increasing the modulation bandwidth and reducing the driving voltage.

Description

Technical Field

[0001] The present application relates to the field of light modulation technology, and in particular to a distributed light intensity modulator. Background Art

[0002] High-speed electro-optic modulation has very wide and important applications, such as optical communication, microwave optoelectronics, laser beam deflection, wavefront modulation, etc. Electro-optic modulators are modulators made using the electro-optic effect of certain electro-optic crystals, such as lithium niobate crystals (LiNbO3), gallium arsenide crystals (GaAs) and lithium tantalate crystals (LiTaO3). The electro-optic effect means that when a voltage is applied to an electro-optic crystal, the refractive index of the electro-optic crystal will change, resulting in changes in the characteristics of the light wave passing through the crystal, thereby achieving modulation of the phase, amplitude, intensity and polarization state of the optical signal.

[0003] However, in the light modulation process, it is difficult to achieve low driving voltage and high modulation bandwidth modulation at the same time. Summary of the invention

[0004] The main purpose of the present application is to provide a distributed light intensity modulator to achieve modulation with low driving voltage and high modulation bandwidth.

[0005] Based on this, an embodiment of the present application provides a distributed light intensity modulator, comprising: a substrate, and a splitter element, an optical waveguide, and a light combining element connected in sequence and arranged on the substrate; a driving electrode, arranged on the substrate, comprising a plurality of sub-driving electrodes arranged at intervals; the optical waveguide passes through the sub-driving electrodes in sequence; and at least one voltage bias electrode, at least partially spaced apart from the sub-driving electrode.

[0006] Optionally, the driving electrode is a coplanar waveguide structure.

[0007] Optionally, the same electrical signal is applied to the sub-driving electrodes.

[0008] Optionally, the electrical signals applied to the adjacent sub-driving electrodes have a delay, wherein the delay duration is the time required for the optical signal to be transmitted from the starting end of the previous sub-driving electrode to the starting end of the next adjacent sub-driving electrode.

[0009] Optionally, the optical waveguide includes a plurality of modulation sections and a plurality of bending sections connected between the modulation sections, wherein a bending direction of the bending section is toward a previous modulation section connected to the bending section.

[0010] Optionally, the modulation part includes a first sub-modulation part and a second sub-modulation part, wherein light propagation directions inside the first sub-modulation part and the second sub-modulation part are opposite.

[0011] Optionally, the first sub-modulation part passes through the sub-driving electrode and / or the voltage bias electrode; the second sub-modulation part passes through the voltage bias electrode and / or the sub-driving electrode.

[0012] Optionally, the first sub-modulation section is parallel to the second sub-modulation section, and optical signal propagation directions in the first sub-modulation section and the second sub-modulation section are opposite.

[0013] Optionally, the voltage bias electrode includes: a voltage bias electrode, to which a bias voltage is applied, and a first ground electrode and a second ground electrode located on both sides of the voltage bias electrode; the driving electrode includes: a driving signal electrode, to which a driving signal is applied, and a third ground electrode and a fourth ground electrode located on both sides of the driving signal electrode.

[0014] Optionally, the optical waveguide includes a first modulation arm and a second modulation arm, wherein the first modulation arm is arranged between the voltage bias electrode and the first ground electrode, and is arranged between the drive signal electrode and the third ground electrode, and the second modulation arm is arranged between the voltage bias electrode and the second ground electrode, and is arranged between the drive signal electrode and the fourth ground electrode.

[0015] This application has the following beneficial effects:

[0016] The driving electrode is set as a distributed driving electrode. Since the driving electrode is distributed, the length of the driving electrode of each part is much smaller than the total length of the equivalent traditional modulator of this type, and the driving signal voltage of each part is also much smaller than the driving signal voltage of the equivalent traditional modulator. In the driving electrode of each part, the propagation of the optical signal can reach approximately synchronous propagation or even synchronous propagation with the electrical signal. The walk-off phenomenon between the photoelectric signals is minimized, and the upper limit of the modulation bandwidth is increased. At the same time, since the driving electrode is changed from a traditional one-segment driving electrode to a distributed multi-segment driving electrode, the driving voltage required to be applied to each electrode is also greatly reduced. The voltage bias electrode is set between each sub-driving electrode, and the electrical signal applied to the voltage bias electrode is different from that to each sub-driving electrode, and each voltage bias electrode includes a ground wire, so it can be used as an anti-crosstalk device for shielding the crosstalk between the sub-driving electrodes. Therefore, the modulation bandwidth can be increased and the driving voltage can be reduced simultaneously, and the modulator can reduce the zero drift phenomenon and prevent the crosstalk problem between the sub-driving electrodes caused by increasing the modulation bandwidth and reducing the driving voltage. Therefore, the modulation performance of the optical modulator is greatly improved.

[0017] The electrical signals applied to each sub-driving electrode are the same, and the same electrical signal is applied to each part of the driving electrode, which is equivalent to resetting the electrical signal when the electrical signal propagates along each part of the driving electrode, greatly reducing the loss of the electrical signal and greatly improving the modulation efficiency. The grounding wire groups are respectively arranged between the sub-driving electrodes, wherein the sub-driving electrodes are arranged on the parallel parts with the same optical signal propagation direction, and the grounding wire groups are arranged on the parallel parts with the opposite optical signal propagation direction to the parallel parts where the sub-driving electrodes are arranged, which can greatly reduce the crosstalk between the sub-driving electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of this application are used to provide a further understanding of this application, so that other features, purposes and advantages of this application become more obvious. The schematic embodiment drawings and their descriptions of this application are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0019] Figure 1 is a schematic diagram of a distributed light intensity modulator according to an embodiment of the present application;

[0020] Figure 2 is a partial cross-sectional schematic diagram of a distributed light intensity modulator according to an embodiment of the present application;

[0021] Figure 3 FIG. 4 is a schematic diagram of another distributed light intensity modulator according to an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present application. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] As described in the background art, there is often a trade-off between the driving voltage and the modulation bandwidth. The electro-optic effect is usually weak in the electro-optic medium, so a low driving voltage requires a sufficiently long waveguide to accumulate sufficient electro-optic effect. However, the inventors have found through research that there is a group velocity mismatch between the light wave and the driving electrical signal, which will cause a serious walk-off phenomenon between the light wave and the driving electrical signal after long-distance transmission, severely limiting the modulation bandwidth. In addition, a long optical waveguide also requires a long driving electrode, which, due to the resistance loss of the electrode material, leads to a large microwave driving signal propagation loss, which ultimately limits the possibility of further reducing the driving voltage. This serious design trade-off problem exists in almost all traveling-wave-based optoelectronic modulators, severely limiting the performance of the device.

[0025] Ideally, for a lithium niobate modulator, no voltage and voltage represent the maximum and minimum output light intensity, i.e., signal 1 and signal 0, respectively. However, due to the material properties of lithium niobate, even in the absence of an external voltage, the two arms of the Mach-Zehnder Interferometer (MZI) have a phase difference, resulting in the output light intensity being between the maximum and minimum values ​​when no voltage is applied and when voltage is applied. This is the zero-point voltage drift phenomenon. At the same time, as the bandwidth increases, the crosstalk problem between multiple signals becomes more and more significant. Ultimately, it will make it difficult to continue to reduce the driving voltage.

[0026] Based on the inventor's research, the present invention provides a distributed light intensity modulator. Figure 1 As shown, the optical modulator includes: a substrate 60, and a splitter element 10, an optical waveguide 20, and a light combining element 30 that are sequentially connected and arranged on the substrate 60; a driving electrode 40, which is arranged on the substrate 60 and includes a plurality of sub-driving electrodes 41 that are arranged at intervals, and the optical waveguide 20 sequentially passes through the sub-driving electrodes 41; at least one voltage bias electrode 50, at least a part of the voltage bias electrodes 50 are spaced apart from the sub-driving electrodes 41, specifically, at least one voltage bias electrode 50 can be arranged between two sub-driving electrodes 41, and the arrangement order of the voltage bias electrode 50 and the sub-driving electrode 41 can be any order.

[0027] Due to the group velocity mismatch between the optical wave and the driving electrical signal, a serious optical wave-driving point signal walk-off phenomenon will occur after long-distance transmission, which seriously limits the driving voltage and bandwidth. Therefore, in this embodiment, the driving electrode 40 is set as a distributed driving electrode 40. Since the driving electrode 40 is distributed, the length of each sub-driving electrode 41 is much smaller than the total length of the modulator. In each sub-driving electrode 41, the propagation of the optical signal can achieve approximately synchronous propagation or even synchronous propagation with the electrical signal. The walk-off phenomenon between the photoelectric signals is minimized, and the upper limit of the modulation bandwidth is increased. In addition, since the lithium niobate modulator has a zero drift phenomenon, a voltage bias electrode 50 is set between the sub-driving electrodes 41, and a bias voltage is applied to the voltage bias electrode 50 to modulate the phase difference on the modulation arm. As the modulation bandwidth increases, the crosstalk problem between multiple signals becomes more and more significant. When the driving electrode 40 includes a plurality of sub-driving electrodes 41 arranged at intervals, the crosstalk problem exists not only in the signals between the channels, but also between each electrode of each sub-electrode. In this embodiment, a voltage bias electrode 50 is arranged between each sub-driving electrode 41. The voltage bias electrode 50 is different from the electrical signal applied to each sub-driving electrode 41, and each voltage bias electrode 50 includes a bottom line, so it can be used as an anti-crosstalk device for shielding the crosstalk between the sub-driving electrodes 41. Therefore, the modulation bandwidth can be increased and the driving voltage can be reduced simultaneously, and the modulator can reduce the zero drift phenomenon and prevent the crosstalk problem between the sub-driving electrodes 41 caused by increasing the modulation bandwidth and reducing the driving voltage. Therefore, the modulation performance of the optical modulator is greatly improved.

[0028] As an exemplary embodiment, the optical modulator may be a lithium niobate crystal (LiNbO3) optical modulator, a gallium arsenide crystal (GaAs) optical modulator, or a lithium tantalate crystal (LiTaO3) optical modulator. In this embodiment, the lithium niobate crystal optical modulator is taken as an example for description. Figure 2 As shown in the partial cross-sectional view of the optical modulator, the optical waveguide 20 and the driving electrode 40 are located on the surface of the substrate 60 , and a bonding layer 70 may be further provided between the substrate 60 and the optical waveguide 20 and the driving electrode 40 .

[0029] As an exemplary embodiment, the voltage bias electrode 50 includes: a voltage signal electrode, to which a bias voltage is applied, and a first ground electrode and a second ground electrode located on both sides of the voltage bias electrode; the driving electrode includes: a driving signal electrode, to which a driving signal is applied, and a third ground electrode and a fourth ground electrode located on both sides of the driving signal electrode. The optical waveguide 20 includes a first modulation arm 24 and a second modulation arm 25, wherein the first modulation arm 24 is arranged between the voltage bias electrode and the first ground electrode, and between the driving signal electrode and the third ground electrode, and the second modulation arm 25 is arranged between the voltage bias electrode and the second ground electrode, and between the driving signal electrode and the fourth ground electrode.

[0030] As an exemplary embodiment, the light splitting element 10 can use a Y-branch beam splitting optical waveguide, and the light combining element 30 can use a Y-branch beam combining optical waveguide. One end of the light splitting element 10 is connected to a single-mode optical fiber for optical signal input, and the other end is connected to the first modulation arm 24 and the second modulation arm 25 respectively with the Y branch. The Y branch at one end of the light combining element 30 is connected to the first modulation arm 24 and the second modulation arm 25 respectively, and the other end is connected to a single-mode optical fiber for optical signal output. Specifically, the input optical signal is divided into two equal or similar beams at a Y branch after passing through a section of single-mode optical fiber, and transmitted through the first modulation arm 24 and the second modulation arm 25 respectively. The first modulation arm 24 and the second modulation arm 25 are made of electro-optical materials, and their refractive index changes with the magnitude of the applied voltage, so that the two optical signals produce a phase difference when they arrive at the second Y branch. If the optical path difference of the two optical signals is an integer multiple of the wavelength, the coherence of the two optical signals is enhanced; if the optical path difference of the two optical signals is 1 / 2 of the wavelength, the two optical signals are coherently offset, and the modulator output is very small. Therefore, the optical signal can be modulated by controlling the voltage of the electrical signal on the driving electrode 40 .

[0031] As an exemplary embodiment, the driving electrode 40 includes N sub-driving electrodes 41 arranged at intervals along the optical waveguide 20, wherein N ≥ 2. Figure 1 As shown. The driving electrode 40 is divided into N parts, each part has a shorter length L, and the final effective driving length is N*L. In this embodiment, the electrical signals applied to each sub-driving electrode 41 are the same, and the same electrical signal is applied to each part of the driving electrode 40, which is equivalent to resetting the electrical signal when the electrical signal propagates along each part of the driving electrode 40, greatly reducing the loss of the electrical signal and greatly improving the modulation efficiency.

[0032] In order to better match the electrical signals on each sub-driving electrode 41, so that the modulation of the optical signal on each sub-driving electrode 41 is as similar as possible, in this embodiment, the electrical signals applied to the adjacent sub-driving electrodes 41 have a delay, wherein the delay duration is the time required for the optical signal to be transmitted from the starting end of the previous sub-driving electrode 41 to the starting end of the next adjacent sub-driving electrode 41. As an exemplary embodiment, assuming that the electrical signal applied to the first sub-driving electrode 41 is V1(t), the time required for the optical signal to be transmitted from the nth sub-driving electrode 41 to the starting end of the n+1th sub-driving electrode 41 is T n , where n=1, 2, ..., N-1 represents the number of sub-driving electrodes 41. The electric signal applied to each sub-driving electrode 41 is expressed as follows:

[0033]

[0034] Due to the delay in the propagation of the electrical signal and the optical signal applied to the adjacent sub-driving electrodes 41 before the distributed driving electrode 40, each part of the sub-driving electrodes 41 has the same electrical signal, which is equivalent to resetting the electrical signal when the electrical signal propagates along each part of the sub-driving electrodes 41, greatly reducing the loss of the electrical signal and significantly improving the modulation efficiency.

[0035] In the present embodiment, the driving electrode 40 is a coplanar waveguide structure, which can be exemplarily a GSG coplanar waveguide line, or other RF transmission lines such as a CPW or CPWG coplanar waveguide line, wherein G is a ground electrode and S is a signal electrode (the coplanar waveguide structure can also use other phase modulation units). An unmodulated constant light source is input from the entrance end, and after passing through the optical splitter 10, it is equally divided into two beams of light with equal or similar light intensities, which enter the first modulation arm 24 and the second modulation arm 25 respectively. The first modulation arm 24 and the second modulation arm 25 simultaneously pass through the driving electrode 40 area of ​​the coplanar waveguide structure, and the time for the optical signal to pass through the two adjacent sub-driving electrodes 41 in the first modulation arm 24 and the second modulation arm 25 is the same, that is, the lengths of the two sub-driving electrodes 40 are equal. One end of the sub-driving electrode 41 is the input area of ​​the electrical signal, and the other end is coupled to an external microwave terminal blocker (RFterminator) or a microwave terminal blocker circuit (on-chip circuit). After passing through the multi-segment sub-driving electrodes 41, the first modulation arm 24 and the second modulation arm 25 are combined into the same optical waveguide 20 by a light combining element 30 and then output. As an exemplary embodiment, the impedance of the sub-driving electrode 41 is the same as or similar to the impedance of the electrical signal input end, for example, it can be 50Ω; the propagation speed of the electrical signal in the driving electrode 40 is the same as or similar to the speed of light in the optical waveguide 20; the resistance loss of the electrical signal transmitted in the driving electrode 40 is as low as possible. In this embodiment, the material of the driving electrode 40 can be a high-conductivity and low-resistance material such as gold, silver, copper, aluminum, and graphene.

[0036] As an exemplary embodiment, the optical waveguide includes a plurality of modulation sections 21 and a plurality of bends 22 connected between the modulation sections 21, wherein the bending direction of the bends 22 is toward the previous modulation section 21 connected to the bends 22. Exemplarily, the optical waveguide starts from the first modulation section 21, and the bending direction of the first bend 22 connected to the first modulation section 21 is toward the first modulation section 21, so that the extension direction of the second modulation section 21 connected to the first bend 22 is toward the first modulation section 21, and after the plurality of modulation sections 21 are connected to the plurality of bends 22, the shape formed is roughly "S"-shaped or a "snake" extending back and forth. As an exemplary embodiment, the modulation section 21 includes a first sub-modulation section 211 and a second sub-modulation section 212, wherein the light propagation directions inside the first sub-modulation section 211 and the second sub-modulation section 212 are different. Exemplarily, the extension direction of the first sub-modulation section 211 can be the "forward" direction of the optical waveguide, and the extension direction of the second sub-modulation section 212 can be the "reciprocal" direction of the optical waveguide.

[0037] The first sub-modulation unit 211 passes through the sub-driving electrode 41, and the second sub-modulation unit 212 passes through the voltage bias electrode 50. Those skilled in the art should understand that the first sub-modulation unit 211 may also pass through the voltage bias electrode 50, and the second sub-modulation unit 212 may also pass through the sub-driving electrode 41. In this embodiment, the arrangement positions of the voltage bias electrode 50 and the sub-driving electrode 41 are not limited. For example, Figure 1 As shown, the first sub-modulation part 211 and the second sub-modulation part 212 are arranged at intervals along the Y direction of the substrate surface, and the sub-driving electrode 41 is arranged at intervals from the voltage bias electrode 50. Since there is crosstalk between the sub-driving electrodes when the modulation bandwidth is increased and the driving voltage is reduced simultaneously (using a plurality of spaced sub-driving electrodes), the voltage bias electrodes are arranged at intervals between the sub-driving electrodes along the Y direction of the substrate surface, so that the modulator can reduce the zero drift phenomenon and prevent the crosstalk problem between the sub-driving electrodes caused by increasing the modulation bandwidth and reducing the driving voltage while increasing the modulation bandwidth and reducing the driving voltage simultaneously, and the modulation performance of the optical modulator can be greatly improved.

[0038] As another exemplary embodiment, in order to prevent crosstalk between the sub-driving electrodes, Figure 3 As shown, a grounding wire group 80 may be provided between each sub-driving electrode. In this embodiment, the grounding wire group 80 may include a first grounding wire, a second grounding wire and a third grounding wire, wherein the first modulation arm 24 is located between the second grounding wire and the first grounding wire, and the second modulation arm 25 is located between the second grounding wire and the third grounding wire. Since there may be a crosstalk problem between each sub-driving electrode 41, adding three grounding wires between two sub-driving electrodes 41 can greatly reduce the crosstalk between the sub-driving electrodes 41.

[0039] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A distributed light intensity modulator, characterized in that: include: A substrate, and a light splitting element, an optical waveguide, and a light combining element which are arranged on the substrate and connected in sequence; A driving electrode, disposed on the substrate, comprising a plurality of sub-driving electrodes arranged at intervals; A voltage bias electrode, disposed between the sub-driving electrodes; at least one voltage bias electrode, at least partially spaced apart from the sub-driving electrode; The driving electrode is a coplanar waveguide structure; The optical waveguide includes a plurality of modulation sections and a plurality of bending sections connected between the modulation sections, wherein the bending direction of the bending section is toward the previous modulation section connected to the bending section; The modulation part includes a first sub-modulation part and a second sub-modulation part, wherein the light propagation directions inside the first sub-modulation part and the second sub-modulation part are opposite; The first sub-modulation section passes through the sub-driving electrode or the voltage bias electrode; The second sub-modulation section passes through the voltage bias electrode or the sub-driving electrode; The first sub-modulation part and the second sub-modulation part pass through different electrodes.

2. The distributed light intensity modulator according to claim 1, characterized in that: The same electrical signal is applied to the sub-driving electrodes.

3. The distributed light intensity modulator according to claim 2, characterized in that: The electrical signals applied to the adjacent sub-driving electrodes have a delay, wherein the delay duration is the time required for the optical signal to be transmitted from the starting end of the previous sub-driving electrode to the starting end of the next adjacent sub-driving electrode.

4. The distributed light intensity modulator according to claim 1, characterized in that: The first sub-modulation section is parallel to the second sub-modulation section, and optical signals in the first sub-modulation section and the second sub-modulation section propagate in opposite directions.

5. The distributed light intensity modulator according to claim 1, characterized in that: The voltage bias electrode comprises: a voltage bias electrode to which a bias voltage is applied, and a first ground electrode and a second ground electrode located at both sides of the voltage bias electrode; The driving electrode includes a driving signal electrode to which a driving signal is applied, and a third ground electrode and a fourth ground electrode located at both sides of the driving signal electrode.

6. The distributed light intensity modulator according to claim 5, characterized in that: The optical waveguide includes a first modulation arm and a second modulation arm, wherein the first modulation arm is arranged between the voltage bias electrode and the first ground electrode, and is arranged between the drive signal electrode and the third ground electrode, and the second modulation arm is arranged between the voltage bias electrode and the second ground electrode, and is arranged between the drive signal electrode and the fourth ground electrode.

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