A thin film lithium niobate electro-optic modulator chip and a modulation method thereof

Abstract

The disclosure provides a thin film lithium niobate electro-optic modulator chip and a modulation method thereof. The chip comprises, from bottom to top, a substrate layer, a buried oxide layer, a lithium niobate waveguide layer, and an electrode layer. The upper surface of the lithium niobate waveguide layer comprises first and second parallel optical waveguides. The electrode layer comprises a composite traveling wave electrode and a direct current electrode. The composite traveling wave electrode is a T-shaped distributed traveling wave electrode structure, arranged between the first and second optical waveguides and on the side surfaces of the first and second optical waveguides. The direct current electrode is arranged between the first and second optical waveguides and downstream of the composite traveling wave electrode in the signal transmission direction. The chip has high conversion efficiency and increased bandwidth, and overcomes the technical problem of difficult integration.

Description

Technical Field

[0001] This disclosure relates to the field of integrated microwave photonics technology, specifically to a thin-film lithium niobate electro-optic modulator chip and its modulation method. Background Technology

[0002] As human society rapidly advances towards intelligence, signal perception, transmission, and processing are crucial components of future integrated intelligent information processing systems. Microwave photonics technology, combining the high bandwidth and low loss of photons with the flexible and easily controllable advantages of microwaves, is considered a disruptive technology for next-generation information systems and a core technology in applications such as 6G mobile communication, cloud computing, and artificial intelligence. However, microwave photonics systems suffer from low conversion efficiency in the microwave-to-light conversion process, including modulation efficiency of the electric field controlling the light field and quantum efficiency of photoelectric conversion. These efficiencies ultimately determine core indicators such as system gain, noise figure, and dynamic range. Electro-optic modulators are core devices for realizing electro-optic conversion in microwave photonics systems. Thin-film lithium niobate electro-optic modulators are an important type of electro-optic modulator, capable of high integration with other microwave photonic devices and possessing broad application prospects. However, existing thin-film lithium niobate modulators all suffer from low electro-optic conversion efficiency. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] In view of the above problems, this disclosure provides a thin-film lithium niobate electro-optic modulator chip and its modulation method, so as to at least partially solve the technical problems of low conversion efficiency, limited bandwidth and difficulty in integration of traditional lithium niobate electro-optic modulators.

[0005] (II) Technical Solution

[0006] This disclosure provides a thin-film lithium niobate electro-optic modulator chip, comprising: a substrate layer, a buried oxide layer, a lithium niobate waveguide layer, and an electrode layer, stacked sequentially from bottom to top; the upper surface of the lithium niobate waveguide layer includes a first optical waveguide and a second optical waveguide that are parallel to each other; the electrode layer includes a composite traveling-wave electrode and a DC electrode; the composite traveling-wave electrode is a T-shaped distributed traveling-wave electrode structure, disposed between the first optical waveguide and the second optical waveguide and on the sides of the first optical waveguide and the second optical waveguide; the DC electrode is disposed between the first optical waveguide and the second optical waveguide, and is located downstream of the composite traveling-wave electrode in the signal transmission direction.

[0007] According to an embodiment of this disclosure, the composite traveling-wave electrode comprises: a coplanar traveling-wave electrode and a conductive polymer material; the coplanar traveling-wave electrode comprises three metal signal lines, which are respectively a first ground line, a first signal line, and a second ground line. The three metal signal lines are parallel to the first optical waveguide and the second optical waveguide, and are staggered with the first optical waveguide and the second optical waveguide. Each of the metal signal lines has a plurality of metal interfaces equally spaced on one side of the first optical waveguide and / or the second optical waveguide; the conductive polymer material fills the space between each of the metal interfaces and the first optical waveguide and the second optical waveguide, and is rectangular in shape, forming a T-shaped microstructure with the metal interfaces.

[0008] According to an embodiment of this disclosure, the upper surface of 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 ends of the first optical waveguide and the second optical waveguide; the input end of the beam combiner is connected to the output ends of the first optical waveguide and the second optical waveguide.

[0009] According to embodiments of this disclosure, the two-way splitting ratio of the beam splitter and the beam combiner is set to 0.5:0.5.

[0010] According to an embodiment of this disclosure, the DC electrode includes: a third ground line, a fourth ground line, and a second signal line; the second signal line is located between the first optical waveguide and the second optical waveguide; the third ground line and the fourth ground line are respectively located on one side of the first optical waveguide and the second optical waveguide, and are opposite to the position of the second signal line.

[0011] According to embodiments of this disclosure, the DC electrode is an optical waveguide capable of achieving an optical phase shift greater than 2π.

[0012] According to embodiments of this disclosure, the substrate layer is made of quartz or silicon; the buried oxide layer is made of silicon dioxide.

[0013] According to embodiments of this disclosure, the height of the conductive polymer material is the same as the height of the first optical waveguide and the second optical waveguide, and the height of the coplanar traveling wave electrode is greater than or equal to the height of the conductive polymer material.

[0014] According to embodiments of this disclosure, the first optical waveguide and the second optical waveguide are lithium niobate ridge waveguides or lithium niobate strip waveguides.

[0015] The second aspect of this disclosure provides a modulation method for a thin-film lithium niobate electro-optic modulator chip, applied to the thin-film lithium niobate electro-optic modulator chip, comprising: inputting an optical carrier signal through a beam splitter and outputting it proportionally to a first optical waveguide and a second optical waveguide; loading a radio frequency (RF) signal onto a composite traveling-wave electrode, wherein the RF signal interacts with the optical carrier signal in the first and second optical waveguides using an electro-optic effect, thereby modulating the RF signal onto the optical carrier signal to achieve modulation; changing the DC voltage loaded on a DC electrode to regulate the refractive index of the first and second optical waveguides, thereby changing the bias point at which the modulator chip operates.

[0016] (III) Beneficial Effects

[0017] 1. The thin-film lithium niobate electro-optic modulator chip provided in this disclosure, because the first and second optical waveguides are in direct contact with the conductive polymer material, not only confines the optical field but also controls the electric field within the waveguides, fundamentally avoiding 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 coplanar traveling wave electrode, the plasma effect caused by optical field coupling can be avoided, significantly reducing the optical loss of the device.

[0018] 2. The thin-film lithium niobate electro-optic modulator chip provided in this disclosure avoids current accumulation caused by the skin effect of high-frequency electromagnetic fields by setting a T-shaped microstructure, thereby reducing the ohmic loss of radio frequency signals in the electrodes and achieving high bandwidth. Attached Figure Description

[0019] To gain a more complete understanding of this disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, wherein:

[0020] Figure 1 The thin-film lithium niobate electro-optic modulator chip described in this disclosure is illustrated schematically.

[0021] Explanation of reference numerals in the attached figures:

[0022] 1-Band splitter;

[0023] 2-Composite traveling wave electrode;

[0024] 3-First optical waveguide;

[0025] 4-Second optical waveguide;

[0026] 5-DC electrode;

[0027] 6- Bundle combiner;

[0028] 7-Substrate layer;

[0029] 8-Buried oxide layer;

[0030] 9-Conductive polymer materials;

[0031] 10-Coplanar traveling wave electrode. Detailed Implementation

[0032] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0035] Figure 1 The schematic illustration shows a thin-film lithium niobate electro-optic modulator chip provided in an embodiment of the present disclosure, wherein the upper left corner is a cross-sectional view of the composite traveling wave electrode 2, and the lower right corner is a top view of a portion of the composite traveling wave electrode 2.

[0036] The chip consists of, from bottom to top, a substrate layer 7, a buried oxide layer 8, a lithium niobate waveguide layer, and an electrode layer.

[0037] The lithium niobate waveguide layer includes a first optical waveguide 3 and a second optical waveguide 4 that are parallel to each other; the electrode layer includes a composite traveling wave electrode 2 and a DC electrode 5; the composite traveling wave electrode 2 is a T-shaped distributed traveling wave electrode structure, located between the first optical waveguide 3 and the second optical waveguide 4 and on the sides of the first optical waveguide 3 and the second optical waveguide 4; the DC electrode 5 is located between the first optical waveguide 3 and the second optical waveguide 4, downstream of the composite traveling wave electrode 2 in the signal transmission direction.

[0038] In this embodiment, except for the composite traveling wave electrode 2 and the DC electrode 5, all other parts are connected by optical waveguides. The lithium niobate waveguide layer uses thin-film lithium niobate material, thus possessing the advantages of large bandwidth and fast tuning.

[0039] Furthermore, the composite traveling wave electrode 2 includes: a coplanar traveling wave electrode 10 and a conductive polymer material 9; the coplanar traveling wave electrode 10 includes three metal signal lines, namely a first ground line, a first signal line and a second ground line, respectively. 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. Each metal signal line has multiple metal interfaces evenly spaced on one side relative to the first optical waveguide 3 and / or the second optical waveguide 4; the conductive polymer material 9 is filled between each metal interface and the first optical waveguide 3 and the second optical waveguide 4, and is rectangular in shape, forming a T-shaped microstructure with the metal interfaces.

[0040] The conductive polymer material 9 can be, but is not limited to, polymethyl methacrylate (PMMA) and other materials; the coplanar traveling wave electrode 10 can be, but is not limited to, gold, titanium and other materials.

[0041] To avoid waveguide shielding effects and overcome the problem of low electro-optic conversion efficiency caused by differences in dielectric constants, this disclosure proposes to use a conductive polymer material 9 and a coplanar traveling wave electrode 10 to jointly form a composite traveling wave electrode 2. Since the conductive polymer material 9 is in direct contact with the first optical waveguide 3 and the second optical waveguide 4, this structure can perfectly avoid the waveguide shielding effect in traditional electro-optic modulators, thereby achieving high-efficiency, low-loss electro-optic modulation. Furthermore, because the coplanar traveling wave electrode 10 is far from the waveguide, the plasma effect caused by optical field coupling can be avoided, significantly reducing the optical loss of the device.

[0042] The T-shaped microstructure formed by the metal interface and the conductive polymer material 9 provides more surface area for the coplanar traveling wave electrode 10, thereby increasing the effective conductor area, reducing the equivalent resistance, reducing ohmic loss, improving bandwidth, and avoiding current accumulation caused by the skin effect of high-frequency electromagnetic fields.

[0043] In this embodiment, the upper surface of the lithium niobate waveguide layer 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 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 second optical waveguide 4.

[0044] 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.

[0045] Furthermore, the splitting ratio of the two beams of beam splitter 1 and beam combiner 6 is set to 0.5:0.5.

[0046] In this embodiment, the DC electrode 5 includes: a third ground line, a fourth ground line, and a second signal line; the second signal line is located between the first optical waveguide 3 and the second optical waveguide 4; the third ground line and the fourth ground line are located on both sides of the first optical waveguide 3 and the second optical waveguide 4, respectively, and are opposite to the position of the second signal line.

[0047] 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.

[0048] Furthermore, the DC electrode 5 is an optical waveguide capable of achieving an optical phase shift greater than 2π.

[0049] In this embodiment, the substrate 7 is made of quartz or silicon; the buried oxide layer 8 is made of silicon dioxide.

[0050] 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 to prevent dirty substances in the environment from penetrating the sensitive device surface.

[0051] In this embodiment, the height of the conductive polymer material 9 is the same as the height of the first optical waveguide 3 and the second optical waveguide 4, and the height of the coplanar traveling wave electrode 10 is greater than or equal to the height of the conductive polymer material 9. Because the conductive polymer material 9 and the optical waveguide are at 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.

[0052] In this embodiment, 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.

[0053] Another aspect of this disclosure provides a modulation method for a thin-film lithium niobate electro-optic modulator chip, applicable to, for example... Figure 1 The thin-film lithium niobate electro-optic modulator chip shown specifically includes:

[0054] The optical carrier signal is input through beam splitter 1 and output proportionally to the first optical waveguide 3 and the second optical waveguide 4;

[0055] A radio frequency (RF) signal is loaded onto the composite traveling wave electrode 2. The RF signal interacts with the optical carrier signal in the first optical waveguide 3 and the second optical waveguide 4 using the electro-optic effect, thereby modulating the RF signal onto the optical carrier signal to achieve modulation.

[0056] By changing the DC voltage applied to the DC electrode 5, the refractive indices of the first optical waveguide 3 and the second optical waveguide 4 are adjusted, thereby changing the bias point at which the modulator chip operates.

[0057] The modulation method of the thin-film lithium niobate electro-optic modulator chip provided in this embodiment is based on the combined action of the composite traveling wave electrode 2 and the DC electrode 5 to modulate the optical carrier signal and the radio frequency signal, thereby overcoming the technical problems of low conversion efficiency, limited bandwidth, and difficulty in integration of lithium niobate electro-optic modulators.

[0058] Example 1:

[0059] The substrate layer 7, the buried oxide layer 8, the lithium niobate waveguide layer and the electrode layer, wherein the electrode layer includes a composite traveling wave electrode 2 and a DC electrode 5, and the upper surface of the lithium niobate waveguide layer includes a first optical waveguide 3, a second optical waveguide 4, a beam splitter 1 and a beam combiner 6.

[0060] The substrate 7 is made of silicon, and the buried oxide layer 8 is made of silicon dioxide.

[0061] The thin-film lithium niobate electro-optic modulator chip uses a 600nm thick thin-film lithium niobate material and operates in the 1550nm band. The first optical waveguide 3, the second optical waveguide 4, and all waveguide devices are ridge waveguides with a ridge height of 300nm. The width of the optical waveguides used to connect the various parts is 1μm.

[0062] 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.

[0063] The composite traveling wave electrode 2 is a coplanar traveling wave electrode 10 containing three signal lines, arranged from top to bottom as ground-signal-ground, with a T-shaped distributed traveling wave electrode structure. The composite traveling wave electrode 2 is composed of the coplanar traveling wave electrode 10 and a conductive polymer material 9. The coplanar traveling wave electrode 10 is made of Au, and the conductive polymer material 9 is made of PMMA.

[0064] 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 between them and the waveguide.

[0065] 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.

[0066] This disclosure utilizes a conductive polymer material 9 and a coplanar traveling-wave electrode 10 to form a composite traveling-wave electrode 2. Since the conductive polymer material 9 is in direct contact with the lithium niobate waveguide, the electric field is controlled within the waveguide while simultaneously confining the optical field. This structure fundamentally avoids the waveguide shielding effect, thereby achieving high-efficiency, low-loss electro-optic modulation. Furthermore, because the coplanar traveling-wave electrode 10 is far from the lithium niobate waveguide, plasma effects caused by optical field coupling are avoided, significantly reducing the device's optical loss. Simultaneously, this disclosure employs a metal interface and the conductive polymer material 9 to form a T-shaped microstructure. These T-shaped microstructures, together with the coplanar traveling-wave electrode 10, avoid current accumulation caused by the skin effect of high-frequency electromagnetic fields, reducing the equivalent resistance and decreasing ohmic loss, thereby increasing bandwidth.

[0067] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0068] Although this disclosure has been shown and described with reference to specific exemplary embodiments thereof, those skilled in the art will understand that various changes in form and detail may be made to this disclosure without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. Therefore, the scope of this disclosure should not be limited to the above embodiments, but should be defined not only by the appended claims, but also by their equivalents.

Claims

1. A thin-film lithium niobate electro-optic modulator chip, characterized in that, include: The substrate layer, buried oxide layer, lithium niobate waveguide layer and electrode layer are stacked sequentially from bottom to top; The upper surface of the lithium niobate waveguide layer includes a first optical waveguide and a second optical waveguide that are parallel to each other. The electrode layer includes a composite traveling wave electrode and a DC electrode; The composite traveling wave electrode is a T-shaped distributed traveling wave electrode structure, disposed between the first optical waveguide and the second optical waveguide and on the sides of the first optical waveguide and the second optical waveguide; The composite traveling wave electrode comprises: a coplanar traveling wave electrode and a conductive polymer material; The coplanar traveling wave electrode includes three metal signal lines, namely a first ground line, a first signal line, and a second ground line. The three metal signal lines are parallel to the first optical waveguide and the second optical waveguide, and are staggered with the first optical waveguide and the second optical waveguide. Each metal signal line has multiple metal interfaces evenly spaced on one side of the first optical waveguide and / or the second optical waveguide. The conductive polymer material is filled between each of the metal interfaces and the first and second optical waveguides, and is rectangular in shape, forming a T-shaped microstructure with the metal interfaces. The DC electrode is located between the first optical waveguide and the second optical waveguide, downstream of the composite traveling wave electrode in the signal transmission direction.

2. The thin-film lithium niobate electro-optic modulator chip according to claim 1, characterized in that, The upper surface of the lithium niobate waveguide layer also includes: Beam splitters and beam combiners; The output of the beam splitter is connected to the input of the first optical waveguide and the second optical waveguide; The input end of the beam combiner is connected to the output ends of the first optical waveguide and the second optical waveguide.

3. The thin-film lithium niobate electro-optic modulator chip according to claim 2, characterized in that, The two-way splitting ratio of the beam splitter and the beam combiner is set to 0.5:0.

5.

4. The thin-film lithium niobate electro-optic modulator chip according to claim 1, characterized in that, The DC electrode includes: Third ground wire, fourth ground wire, and second signal line; The second signal line is located between the first optical waveguide and the second optical waveguide; The third ground line and the fourth ground line are located on one side of the first optical waveguide and the second optical waveguide, respectively, and are opposite to the position of the second signal line.

5. The thin-film lithium niobate electro-optic modulator chip according to claim 1, characterized in that, The DC electrode is an optical waveguide capable of achieving an optical phase shift greater than 2π.

6. The thin-film lithium niobate electro-optic modulator chip according to claim 2, characterized in that, The substrate layer is made of quartz or silicon; the buried oxide layer is made of silicon dioxide.

7. The thin-film lithium niobate electro-optic modulator chip according to claim 1, characterized in that, The height of the conductive polymer material is the same as the height of the first optical waveguide and the second optical waveguide, and the height of the coplanar traveling wave electrode is greater than or equal to the height of the conductive polymer material.

8. The thin-film lithium niobate electro-optic modulator chip according to claim 1, characterized in that, The first optical waveguide and the second optical waveguide are lithium niobate ridge waveguides or lithium niobate strip waveguides.

9. A modulation method for a thin-film lithium niobate electro-optic modulator chip, applied to the thin-film lithium niobate electro-optic modulator chip as described in any one of claims 1 to 8, characterized in that, include: The optical carrier signal is input through a beam splitter and output proportionally to the first and second optical waveguides; A radio frequency (RF) signal is loaded onto a composite traveling wave electrode. The RF signal interacts with the optical carrier signal in the first and second optical waveguides using an electro-optic effect, thereby modulating the RF signal onto the optical carrier signal to achieve modulation. By changing the DC voltage applied to the DC electrode, the refractive indices of the first and second optical waveguides are adjusted, thereby changing the bias point at which the modulator chip operates.

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