CN113985629B - Folding capacitive load electrode structure, electro-optic modulator and preparation method thereof - Google Patents
Folding capacitive load electrode structure, electro-optic modulator and preparation method thereof Download PDFInfo
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- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
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- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
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Abstract
The invention provides a folding capacitive load electrode structure, an electro-optical modulator and a preparation method thereof, wherein the electrode structure comprises a main signal electrode, a first main ground electrode, a second main ground electrode and a plurality of air bridges; the first main ground electrode, the main signal electrode and the second main ground electrode form a G-S-G coplanar waveguide transmission line; the main signal electrode is provided with a plurality of air bridges at the bending position to connect the first main ground electrode and the second main ground electrode; the electro-optic modulator comprises an electrode structure and a lithium niobate waveguide structure, wherein the waveguide structure is arranged on the folding capacitive load electrode structure; the lithium niobate waveguide structure comprises a first waveguide and a second waveguide; the two sides of the waveguide are provided with loading T-shaped electrodes; the adoption of the folding capacitive load electro-optical modulator can furthest inhibit the parasitic coupling slot line mode, so that the electro-optical modulator can efficiently work in a push-pull mode, thereby reducing the transmission loss and the return loss of electric signals.
Description
Technical Field
The present invention relates to the field of optical communication technology and integrated optical modulation technology, and more particularly, to a folding capacitive load electrode structure, an electro-optical modulator, and a method of manufacturing the same.
Background
The high-speed and low-power consumption electro-optical modulator is a core device for realizing high-speed information conversion in optical interconnection. Among them, lithium niobate is the most popular material for making electro-optic modulators. The advent of thin film lithium niobate platforms has pushed the performance and integration scale of lithium niobate modulators to a new height. By dry etching the lithium niobate thin film layer, an optical waveguide with low loss and high refractive index contrast can be obtained. Thanks to this lithium niobate waveguide with strong optical confinement, the modulation efficiency is greatly improved to 2V/cm. As shown in fig. 1, the electro-optic bandwidth of the lithium niobate thin film electro-optic modulator based on the common coplanar waveguide transmission line structure is mainly limited by the microwave loss of the electrode, which is caused by the current concentration effect caused by the small gap between the signal electrode and the ground electrode. FIG. 2 is a schematic diagram of a Mach-Zehnder type lithium niobate thin film electro-optic modulator based on a periodic capacitive load electrode structure in which the gap between the main signal electrode and the main ground electrode is greatly increased by several tens of μm; in order to realize 50 omega impedance matching, the width of the main signal electrode is also increased, so that the current distribution is more uniform, aggregation is not easy to occur at the edge of the electrode, and the reduction of microwave loss is facilitated.
The publication No. CN113325612A (publication No. 2021-08-31) proposes a thin film lithium niobate electro-optic modulator and a preparation method, wherein the thin film lithium niobate electro-optic modulator comprises a silicon substrate, an oxygen-buried layer and a lithium niobate layer which are arranged from bottom to top, and the upper surface of the lithium niobate layer is etched to form a thin film lithium niobate optical signal conductor; the thin film lithium niobate optical signal guide comprises a Mach-Zehnder structure; the method comprises the steps that traveling wave signal electrodes and traveling wave grounding electrodes are respectively arranged on two sides of each optical signal guide arm of a Mach-Zehnder structure, and capacitive load type T-shaped structure electrodes for modulating optical signals in the optical signal guide arms are arranged between the traveling wave signal electrodes and the traveling wave grounding electrodes; and hollow isolation structures for reducing the effective refractive index of the microwave signals are arranged on the two sides and below each optical signal guide arm of the Mach-Zehnder structure. The electro-optic modulator realizes a thin film lithium niobate electro-optic modulator with low driving voltage, low microwave loss and large electro-optic bandwidth under a silicon substrate.
However, in the electro-optical modulator adopting the Mach-Zehnder structure, the periodic load electrode structure has large difference between the lengths of the inner and outer slots when bent at right angles, signals in two slots in the time domain are not synchronous any more, a slot line mode is generated, and the electro-optical modulator has large microwave loss and low performance.
Disclosure of Invention
The invention provides a folding capacitive load electrode structure, an electro-optical modulator and a preparation method thereof, which are used for overcoming the defects of high microwave loss and low performance of the electro-optical modulator caused by a slot line mode in the prior art.
In order to solve the technical problems, the technical scheme of the invention is as follows:
in a first aspect, the present invention provides a folded capacitive load electrode structure, including a main signal electrode, a first main ground electrode, and a second main ground electrode, where the first main ground electrode, the main signal electrode, and the second main ground electrode form a G-S-G coplanar waveguide transmission line, including a straight transmission line portion and a curved transmission line portion; the direct transmission line part is connected with the loading T-shaped electrode at two sides of the main signal electrode, and the loading T-shaped electrode is connected at one side between the first main ground electrode and the main signal electrode and one side between the second main ground electrode and the main signal electrode; and the main signal electrode is provided with a plurality of air bridges at the bending position to connect the first main ground electrode and the second main ground electrode.
In the technical scheme, the air bridge is erected above the bending part of the main signal electrode to connect the first main ground electrode and the second main ground electrode, so that the electromagnetic wave phases at the discontinuous parts are the same, the parasitic capacitance of the air bridge is minimized, the excitation of a parasitic coupling slot line mode is restrained to the maximum extent, the microwave loss and the return loss are reduced, and the performance of the electro-optic modulator is improved; the folding electrode structure design can greatly shorten the length of the device, and is favorable for realizing low driving voltage and miniaturized packaging at the same time; when the waveguide is introduced to be matched with the electrode structure of the technical scheme for use, the waveguide is arranged between the loading T-shaped electrodes, so that the directions of electric fields received by different waveguides are always opposite, and the directions of electric fields received by the same waveguide are always unchanged, thereby enabling the folding capacitive load electro-optical modulator to work in a push-pull mode and inhibiting a slot line mode.
Preferably, the bending part of the main signal electrode is provided with 2n corner structures, wherein n is a positive integer, the 2n corner structure and the 2n-1 corner structure are the same as a positive or reverse right-angle corner, and the corner directions of the 2n corner structure and the 2n+1 corner structure are opposite; the air bridge is mounted over the corner structure of the main signal electrode.
Preferably, the main signal electrode includes a first straight main signal electrode, a first curved main signal electrode, a second straight main signal electrode, a first electrode chamfer and a second electrode chamfer; one end of the first electrode chamfer is connected with the first straight main signal electrode, and the other end of the first electrode chamfer is connected with the first bent main signal electrode; one end of the second electrode chamfer is connected with the first bending main signal electrode, and the other end of the second electrode chamfer is connected with the second straight main signal electrode. The first electrode chamfer and the second electrode chamfer are arranged outside the corner structure.
In the technical scheme, the first electrode chamfer and the second electrode chamfer arranged on the outer side of the corner structure can reduce the path difference of the groove between the main signal electrode and the main ground electrode; the air bridge is erected above the corner structure, and the chamfer and the air bridge are matched to jointly inhibit a slot line mode, so that microwave loss and return loss caused by discontinuity at the corners of the main signal electrode, the first main ground electrode and the second main ground electrode are minimized.
Preferably, the number of the air bridges is at least 4, the air bridges are respectively erected above the first electrode chamfer and the second electrode chamfer, and the air bridges are respectively connected with the first main ground electrode and the second main ground electrode.
Preferably, the loading T-shaped electrodes arranged on the sides of the main signal electrode, the first main ground electrode and the second main ground electrode are respectively arranged oppositely.
In a second aspect, the present invention provides a folded capacitive load electro-optic modulator, including the folded capacitive load electrode structure, and a lithium niobate waveguide structure disposed on the folded capacitive load electrode structure; the lithium niobate waveguide structure comprises a first waveguide and a second waveguide; the first waveguide is arranged between the loading T-shaped electrodes respectively arranged on the first main ground electrode and the first straight main signal electrode, and between the loading T-shaped electrodes respectively arranged on the second main ground electrode and the second straight main signal electrode; the second waveguide is installed between the loading T-shaped electrodes respectively arranged on the first straight main signal electrode and the second main electrode, and between the loading T-shaped electrodes respectively arranged on the second straight main signal electrode and the first main electrode.
In the technical scheme, the first waveguide and the second waveguide are always positioned between the loading T-shaped electrodes, the directions of electric fields received by the first waveguide and the second waveguide are always opposite, and the directions of electric fields received by the same waveguide are always unchanged, so that the electro-optical modulator can efficiently work in a push-pull mode, and a slot line mode is restrained.
Preferably, the first waveguide comprises a first straight waveguide, a first curved waveguide and a second straight waveguide which are connected in sequence; the second waveguide comprises a third straight waveguide, a second bent waveguide and a fourth straight waveguide which are sequentially connected; the first straight waveguide is arranged between the loading T-shaped electrodes respectively arranged on the first main ground electrode and the first straight main signal electrode; the second straight waveguide is arranged between the loading T-shaped electrodes respectively arranged on the second main ground electrode and the second straight main signal electrode; the third straight waveguide is arranged between the loading T-shaped electrodes respectively arranged on the first straight main signal electrode and the second main electrode; the fourth straight waveguide is installed between loading T-shaped electrodes respectively arranged on the second straight main signal electrode and the first main electrode.
Preferably, the first curved waveguide is in communication with the second curved waveguide, and a portion of the first curved waveguide in communication with the second curved waveguide constitutes an X-shaped cross waveguide.
Preferably, the lithium niobate waveguide structure further comprises an input waveguide, an optical beam splitter, an optical beam combiner and an output waveguide; the optical signals are input into the input waveguide and then split through the optical beam splitter, enter the first waveguide and the second waveguide respectively, enter the beam combiner from the first waveguide and the second waveguide to combine, and enter the output waveguide.
In a third aspect, the present invention further provides a method for manufacturing a folded capacitive load electro-optic modulator, including the steps of:
s1: preparing a lithium niobate waveguide structure on a lithium niobate thin film substrate;
s2: depositing a silicon dioxide buffer layer on the lithium niobate thin film composite substrate obtained in the step S1;
s3: preparing a coplanar metal electrode on the lithium niobate thin film combined substrate obtained in the step S2 to form a folding capacitive load electrode structure consisting of two ground electrodes and a signal electrode;
s4: preparing an insulating medium layer serving as a support of an air bridge on the lithium niobate thin film combined substrate obtained in the step S3;
s5: and (3) preparing an air bridge structure on the lithium niobate thin film combined substrate obtained in the step S4, wherein the air bridge is connected with two ground electrodes in the folding capacitive load electrode structure and is not contacted with the signal electrode.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that: the folding capacitive load electro-optic modulator consisting of the folding capacitive load electrode structure and the lithium niobate waveguide structure is adopted, the folding capacitive load electrode structure can enable the electromagnetic wave phases at the discontinuous positions to be the same, meanwhile, the parasitic capacitance of the air bridge is minimized, and the excitation of the parasitic coupling slot line mode is restrained to the greatest extent; the waveguide in the lithium niobate waveguide structure is always arranged between the loading T-shaped electrodes, the directions of electric fields received by the two waveguides are always opposite, and the directions of electric fields received by the same waveguide are always unchanged, so that the electro-optical modulator can efficiently work in a push-pull mode, a slot line mode is restrained, the transmission loss and the return loss of electric signals are reduced, and the performance of the electro-optical modulator is improved.
Drawings
Fig. 1 is a schematic diagram of a lithium niobate thin film electro-optic modulator based on a common coplanar waveguide transmission line structure.
Fig. 2 is a schematic diagram of a mach-zehnder type lithium niobate thin film electro-optic modulator based on a periodic capacitive load electrode structure.
Fig. 3 is a schematic diagram of a folded capacitive load electrode structure in embodiment 1.
Fig. 4 is a partial view of an air bridge portion of a folded capacitive load electrode structure of example 1.
Fig. 5 is a schematic diagram of a folded capacitive load electrode structure in embodiment 2.
Fig. 6 is a partial view of an air bridge and chamfer structure of the folded capacitive load electrode structure of example 2.
Fig. 7 is a schematic cross-sectional view of a modulation region of a folded capacitive load electro-optic modulator chip of embodiment 3.
Fig. 8 is a schematic diagram of a folded capacitive load electro-optic modulator of embodiment 3 folded once.
Fig. 9 is a partial view of the folded capacitive load electro-optic modulator of embodiment 3 folded once.
Fig. 10 is a schematic diagram of a folded capacitive load electro-optic modulator folded twice in example 4.
Fig. 11 is a partial view of the folded capacitive load electro-optic modulator of example 4 folded twice.
FIG. 12 is a diagram of an S-shaped capacitive load electro-optic modulator employing a common direct corner and employing a chamfer and air bridge structure in example 4 11 Parameter variation versus graph.
FIG. 13 is a diagram of an S-shaped capacitive load electro-optic modulator employing a common direct corner and employing a chamfer and air bridge structure in example 4 21 Parameter variation versus graph.
Fig. 14 is a flow chart of a method of making a folded capacitive load electro-optic modulator.
The air-bridge comprises a 1-lithium niobate thin film layer, 11-input waveguide, 111-first waveguide, 1111-first straight waveguide, 1112-second straight waveguide, 1113-first bent waveguide, 1114-third bent waveguide, 1115-fifth straight waveguide, 112-second waveguide, 1121-third straight waveguide, 1122-fourth straight waveguide, 1123-second bent waveguide, 1124-fourth bent waveguide, 1125-sixth straight waveguide, 12-optical splitter, 13-optical combiner, 14-output waveguide, 2-coplanar waveguide transmission line layer, 21-main signal electrode, 211-first straight main signal electrode, 212-first bent main signal electrode, 2121-first electrode chamfer, 2122-second electrode chamfer, 213-second straight main signal electrode, 214-second bent main signal electrode, 2141-third electrode chamfer, 2142-fourth electrode chamfer, 215-third straight main signal electrode, 22-first main electrode, 23-second main electrode, 31-first air bridge, 32-second air bridge, 33-third straight main signal electrode, 212-first bent main signal electrode, 214-second bent main signal electrode chamfer, 214-bent main signal electrode, 214-bent main electrode, 35-bent air bridge, and air bridge 5-air bridge, and air bridge substrate, and air bridge.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
the technical scheme of the invention is further described below with reference to the accompanying drawings and examples.
Example 1
Referring to fig. 3-4, the present embodiment provides a folded capacitive load electrode structure, which includes a main signal electrode 21, a first main ground electrode 22, and a second main ground electrode 23, wherein the first main ground electrode 22-the main signal electrode 21-the second main ground electrode 23 form a G-S-G coplanar waveguide transmission line 2, and includes a straight transmission line portion and a curved transmission line portion; wherein, the straight transmission line part, the two sides of the main signal electrode 21 are connected with the loading T-shaped electrode, and one side between the first main ground electrode 22 and the second main ground electrode 23 and the main signal electrode 21 is connected with the loading T-shaped electrode; wherein the transmission line part is bent, and the main signal electrode 21 is provided with a plurality of air bridges at the bending position to connect the first main ground electrode 22 and the second main ground electrode 23;
in this embodiment, the main signal electrode 21 is provided with 2n corner structures, where n is a positive integer, the 2n corner structure and the 2n-1 corner structure are the same as a forward or reverse right-angle corner, and the corner directions of the 2n corner structure and the 2n+1 corner structure are opposite; the air bridge is bridged over the corner structure of the main signal electrode 21.
In this embodiment, the electrode structure is a folded capacitive electrode structure that is folded once, i.e., n=1, and the corner structures are provided with 2.
In the specific implementation process, the air bridge is erected above the corner structure of the main signal electrode to connect the first main ground electrode and the second main ground electrode, so that the electromagnetic wave phases at the discontinuous positions are the same, meanwhile, the parasitic capacitance of the air bridge is minimized, the excitation of a parasitic coupling slot line mode is restrained to the greatest extent, the microwave loss and the return loss are reduced, and the performance of the electro-optical modulator is improved; the folding electrode structure design can greatly shorten the length of the device, and is favorable for realizing low driving voltage and miniaturized packaging at the same time.
Example 2
Referring to fig. 5-6, the present embodiment provides a folding capacitive load electrode structure, and a chamfer is formed on the outer side of the corner structure.
In this embodiment, the main signal electrode 21 includes a first straight main signal electrode 211, a first curved main signal electrode 212, a second straight main signal electrode 213, a first electrode chamfer 2121, and a second electrode chamfer 2122; one end of the first electrode chamfer 2121 is connected with the first straight main signal electrode 211, and the other end is connected with the first bent main signal electrode 212;
one end of the second electrode chamfer 2122 is connected to the first curved main signal electrode 212, and the other end is connected to the second straight main signal electrode 213.
In this embodiment, 4 air bridges are respectively arranged above the first electrode chamfer 2121 and the second electrode chamfer 2122, and the first main ground electrode 22 and the second main ground electrode 23 are respectively connected to the air bridges. As shown in fig. 4, a first air bridge 31 is disposed above the initial position of the first electrode chamfer 2121, one end of the first air bridge 31 is connected to the first main ground electrode 22, and the other end is connected to the second main ground electrode 23; a second air bridge 32 is arranged above the tail end of the first electrode chamfer 2121, one end of the second air bridge 32 is connected with the first main ground electrode 22, and the other end of the second air bridge is connected with the second main ground electrode 23; a third air bridge 33 is arranged above the initial position of the second electrode chamfer 2122, one end of the third air bridge 33 is connected with the first main ground electrode 22, and the other end of the third air bridge 33 is connected with the second main ground electrode 23; a fourth air bridge 34 is arranged above the tail end of the second electrode chamfer 2122, and one end of the fourth air bridge 34 is connected with the first main ground electrode 22, and the other end of the fourth air bridge is connected with the second main ground electrode 23.
In a specific implementation process, the first electrode chamfer 2121 and the second electrode chamfer 2122 are disposed outside the corner structure of the first curved main signal electrode 212, so that the spatial path difference of two gaps can be shortened. By connecting the two parts by using an air bridge, the electromagnetic wave phases at the discontinuous parts can be identical, and the slot line mode can be restrained.
The embodiment uses the least air bridge, inhibits the excitation of the parasitic coupling slot line mode to the maximum extent, and simultaneously minimizes the parasitic capacitance of the air bridge; the present invention uses the chamfer structure in combination with the air bridge to jointly suppress the slot line mode, thereby minimizing microwave loss and return loss due to discontinuity at the corners of the main signal electrode 21, the first main ground electrode 22 and the second main ground electrode 23.
Example 3
Referring to fig. 5-6, the present embodiment provides a folded capacitive load electro-optic modulator, which is a folded capacitive load electro-optic modulator with two sections, and includes a folded capacitive load electrode structure and a lithium niobate waveguide structure, wherein the folded capacitive load electrode structure and the lithium niobate waveguide structure are folded once when n=1 as proposed in embodiment 1, and the lithium niobate waveguide structure is disposed on the folded capacitive load electrode structure; the lithium niobate waveguide structure includes a first waveguide 111 and a second waveguide 112; the first waveguide 111 is installed between the loading T-shaped electrodes 4 respectively provided on the first main ground electrode 22 and the first straight main signal electrode 211, and between the loading T-shaped electrodes 4 respectively provided on the second main ground electrode 23 and the second straight main signal electrode 212; the second waveguide 112 is installed between the loading T-shaped electrodes 4 respectively provided on the first straight main signal electrode 211 and the second main ground electrode 23, and between the loading T-shaped electrodes 4 respectively provided on the second straight main signal electrode 212 and the first main ground electrode 22.
In this embodiment, the electro-optical modulator further includes a lithium niobate thin film layer 1, and the lithium niobate waveguide structure is disposed on the lithium niobate thin film layer 1. The lithium niobate thin film layer 1 can be an X-cut, Y-cut or Z-cut lithium niobate crystal subjected to etching processing; a substrate material 5 is further arranged below the lithium niobate thin film layer 1, and the substrate material 5 comprises silicon, quartz, lithium niobate and sapphire, or a multi-layer material formed by the materials and a silicon dioxide oxygen burying layer.
In this embodiment, as shown in fig. 7, the first waveguide 111 includes a first straight waveguide 1111, a first curved waveguide 1113, and a second straight waveguide 1112 connected in order; the second waveguide 112 includes a third straight waveguide 1121, a second curved waveguide 1123, and a fourth straight waveguide 1122 connected in sequence; the first straight waveguide 1111 is installed between the loading T-shaped electrodes 4 respectively provided on the first main ground electrode 22 and the first straight main signal electrode 211; the second straight waveguide 1112 is installed between the loading T-shaped electrodes 4 provided on the second main ground electrode 23 and the second straight main signal electrode 212, respectively; the third straight waveguides 1121 are arranged on the first straight main signal electrodes respectively211 and the loaded T-shaped electrode 4 on the second main ground electrode 23; the fourth straight waveguide 1122 is mounted between the loaded T-shaped electrodes 4 disposed on the second straight main signal electrode 212 and the first main ground electrode 22, respectively. Wherein the main electric field component between the loading T-shaped electrodes 4 is consistent with the Z-axis direction of the X-cut lithium niobate film, and the strongest electro-optic coefficient r of the lithium niobate material can be utilized 33 。
In this embodiment, the lithium niobate waveguide structure further includes an input waveguide 11, an optical beam splitter 12, an optical beam combiner 13, and an output waveguide 14; the optical signal is input into the input waveguide 11, split by the optical splitter 12, enter the first waveguide 111 and the second waveguide 112 respectively, enter the optical combiner 13 from the first waveguide 111 and the second waveguide 112, and enter the output waveguide 14.
In this embodiment, the first curved waveguide 1113 is in communication with the second curved waveguide 1123, and the portion of the first curved waveguide 1113 in communication with the second curved waveguide 1123 constitutes an X-shaped cross waveguide.
In a specific implementation process, after an optical signal passes through the optical input waveguide 11, the optical signal enters the first waveguide 111 through the first output end of the input waveguide 11 and enters the second waveguide 112 through the second output end of the input waveguide 11, and the first curved waveguide 1113 and the second curved waveguide 1123 are connected to form an X-shaped cross, so that loss caused by diffraction of light when the first waveguide 111 and the second waveguide 112 cross can be reduced, the first waveguide 111 and the second waveguide 112 are always located between the loading T-shaped electrodes 4, the directions of electric fields received by the first waveguide 111 and the second waveguide 112 are always opposite, and the directions of electric fields received by the same waveguide are always unchanged, so that the folding capacitive load electro-optical modulator works in a push-pull mode and suppresses a slot line mode. Phase change amount of the first waveguide 111And the phase change amount of the second waveguide 112 +.>The method comprises the following steps of:
wherein n is e Is the refractive index of extraordinary ray, r 33 The strongest electro-optic coefficient of the lithium niobate material, E z Lambda is the wavelength of the optical signal, L, for the electric field component along the Z-axis direction of the lithium niobate crystal 1 L is the total length of the first straight waveguide 1111 and the second straight waveguide 1112 2 Is the total length of the third straight waveguide 1121 and the fourth straight waveguide 1122; l (L) 1 And L 2 For an effective overall length of electro-optic interaction. The invention greatly shortens the device length by folding the lithium niobate waveguide and the coplanar waveguide transmission line, and is favorable for simultaneously realizing low driving voltage and miniaturized packaging. The direction of the electric field received by the same waveguide after being folded is unchanged, the modulation depth is accumulated along with the length of each section of photoelectric interaction, and the crossing parts of the two waveguides are connected through an X-shaped crossing structure, so that low loss and low crosstalk are realized.
Example 4
Referring to fig. 8-13, the present embodiment provides a folded capacitive load electro-optic modulator, which is a folded capacitive load electro-optic modulator with n=2, folded twice and three sections, and further includes a second curved main signal electrode 214, a third electrode chamfer 2141, a fourth electrode chamfer 2142, and a third straight main signal electrode 215; one end of the third electrode chamfer 2141 is connected with the second straight main signal electrode 213, and the other end is connected with the second curved main signal electrode 214; the fourth electrode chamfer 2142 has one end connected to the second curved main signal electrode 214 and the other end connected to the third straight main signal electrode 215.
In this embodiment, a fifth air bridge 35 is disposed above the initial position of the third electrode chamfer 2141, and one end of the fifth air bridge 35 is connected to the first main ground electrode 22, and the other end is connected to the second main ground electrode 23; a sixth air bridge 36 is arranged above the tail end of the third electrode chamfer 2141, one end of the sixth air bridge 36 is connected with the first main ground electrode 22, and the other end of the sixth air bridge is connected with the second main ground electrode 23; a seventh air bridge 37 is arranged above the initial position of the fourth electrode chamfer 2142, one end of the seventh air bridge 37 is connected with the first main ground electrode 22, and the other end is connected with the second main ground electrode 23; an eighth air bridge 38 is arranged above the tail end of the fourth electrode chamfer 2142, and one end of the eighth air bridge 38 is connected with the first main ground electrode 22, and the other end of the eighth air bridge is connected with the second main ground electrode 23.
In this embodiment, a loading T-shaped electrode 4 is disposed between the second main ground electrode 23 and the third straight main signal electrode 215, and the plurality of loading T-shaped electrodes 4 are disposed on the second main ground electrode 23 and the third straight main signal electrode 215 respectively; a loading T-shaped electrode 4 is arranged between the third straight main signal electrode 215 and the first main ground electrode 22, and the loading T-shaped electrodes 4 are respectively and oppositely arranged on the third straight main signal electrode 215 and the first main ground electrode 22;
in this embodiment, the first waveguide 111 further includes a third curved waveguide 1114 and a fifth straight waveguide 1115, where the second straight waveguide 1112, the third curved waveguide 1114 and the fifth straight waveguide 1115 are sequentially connected; the second waveguide 112 further includes a fourth curved waveguide 1124 and a sixth straight waveguide 1125, and the fourth straight waveguide 1122, the fourth curved waveguide 1124, and the sixth straight waveguide 1125 are sequentially connected.
In this embodiment, the third curved waveguide 1114 is in communication with the fourth curved waveguide 1124, and a portion of the third curved waveguide 1114 in communication with the fourth curved waveguide 1124 forms an X-shaped cross waveguide.
In this embodiment, the fifth straight waveguide 1115 is installed between the loading T-shaped electrodes 4 oppositely disposed on the second main ground electrode 23 and the third straight main signal electrode 215, respectively; the sixth straight waveguide 1125 is mounted between the loading T-shaped electrodes 4 oppositely disposed on the third straight main signal electrode 215 and the first main ground electrode 22, respectively.
In the specific implementation process, the structure using the electrode chamfer and the air bridge can remarkably improve the transmission performance of the coplanar waveguide transmission line with the curved surface, as shown in fig. 12 and 13, in the frequency band of 1 GHz-67 GHz, the reflection coefficient S of the structure is adopted 11 Below-15 dB, the transmission coefficient S21 increases significantly and is smoother, meaning that the slotline mode is effectively suppressed.
Example 5
Referring to fig. 14, the present embodiment provides a method for manufacturing a folded capacitive load electro-optic modulator, which is used for manufacturing the folded capacitive load electro-optic modulator described in the above embodiment, and includes the following steps:
s1: the required lithium niobate waveguide structure is prepared on an insulator lithium niobate thin film substrate through a photoetching process, and comprises an input waveguide 11, an output waveguide 14, a first waveguide 111, a second waveguide 112, an X-shaped crossed waveguide, an optical beam splitter 12 and an optical beam combiner 13. The photolithography etching process in this embodiment includes the use of a stepper, a contact-type lithography machine, electron beam direct writing, and laser direct writing.
S2: and (3) depositing a low-refractive-index insulating medium buffer layer on the lithium niobate thin film composite substrate obtained in the step (S1). The low-refractive-index insulating medium buffer layer can be made of low-refractive-index insulating medium materials such as silicon dioxide, silicon nitride, silicon oxynitride, ultraviolet photoresist, deep ultraviolet photoresist, electronic glue and the like.
S3: and (2) preparing a metal electrode on the lithium niobate thin film combined substrate obtained in the step (S2) by adopting photoetching, metal deposition and metal stripping processes to form a folding capacitive load electrode structure consisting of two ground electrodes and a signal electrode.
S4: and (3) preparing an insulating medium layer serving as an air bridge support by adopting processes such as deposition, exposure, development and the like on the folding capacitive load electrode structure of the lithium niobate thin film combined substrate obtained in the step (S3). In this embodiment, the material of the insulating dielectric layer may be silicon dioxide, silicon nitride, aluminum oxide, titanium dioxide, insulating photoresist, or a combination of the above materials.
S5: preparing an air bridge structure on the insulating medium layer of the lithium niobate thin film combined substrate obtained in the step S4 by adopting photoetching, metal deposition and metal stripping processes to obtain a folding capacitive load electro-optical modulator; the air bridge connects two ground electrodes in the folded capacitive electrode structure and is not in contact with the signal electrode. In this embodiment, when the substrate material 5 of the lithium niobate thin film composite substrate is silicon, the substrate around the electrode may be removed by wet etching, or the trench may be prepared to the silicon substrate around the electrode by an etching process, and a part of the silicon substrate may be removed by isotropic etching.
In addition, in the present invention, the air bridge structure may be replaced with a metal wire bonding technique to achieve contact bonding of the two ground electrodes without contact with the signal electrode.
The terms describing the positional relationship in the drawings are merely illustrative, and are not to be construed as limiting the present patent;
it is to be understood that the above examples of the present invention are provided by way of illustration only and not by way of limitation of the embodiments of the present invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.
Claims (10)
1. A folding capacitive load electrode structure, which is characterized by comprising a main signal electrode (21), a first main ground electrode (22) and a second main ground electrode (23), wherein the first main ground electrode (22) -the main signal electrode (21) -the second main ground electrode (23) form a G-S-G coplanar waveguide transmission line (2), and the G-S-G coplanar waveguide transmission line (2) comprises a straight transmission line part and a curved transmission line part; wherein, the two sides of the main signal electrode (21) are connected with the loading T-shaped electrode, and one side between the first main ground electrode (22) and the second main ground electrode (23) and the main signal electrode (21) is connected with the loading T-shaped electrode; wherein the transmission line part is bent, and the main signal electrode (21) is provided with a plurality of air bridges at the bending position to connect the first main ground electrode (22) with the second main ground electrode (23).
2. The folding capacitive load electrode structure according to claim 1, characterized in that the main signal electrode (21) is provided with 2n corner structures at the bending position, wherein n is a positive integer, and the 2n corner structure and the 2n-1 corner structure are both positive or reverse right angle corners, and the corner directions of the 2n corner structure and the 2n+1 corner structure are opposite; the air bridge is mounted over the corner structure of the main signal electrode (21).
3. The folding capacitive load electrode structure of claim 2, wherein the main signal electrode (21) comprises a first straight main signal electrode (211), a first curved main signal electrode (212), a second straight main signal electrode (213), a first electrode chamfer (2121) and a second electrode chamfer (2122);
one end of the first electrode chamfer (2121) is connected with the first straight main signal electrode (211), and the other end of the first electrode chamfer is connected with the first bent main signal electrode (212);
one end of the second electrode chamfer (2122) is connected with the first bending main signal electrode (212), and the other end of the second electrode chamfer is connected with the second straight main signal electrode (213);
the first electrode chamfer (2121) and the second electrode chamfer (2122) are disposed outside the corner structure.
4. The folding capacitive load electrode structure according to claim 3, characterized in that at least 4 air bridges are provided, which are respectively erected above the first electrode chamfer (2121) and the second electrode chamfer (2122), and which are respectively connected to the first main ground electrode (22) and the second main ground electrode (23).
5. The folding capacitive load electrode structure according to claim 1, characterized in that the loading T-shaped electrodes (4) provided at the sides of the main signal electrode (21), the first main ground electrode (22) and the second main ground electrode (23) are respectively provided opposite to each other.
6. A folded capacitive load electro-optic modulator comprising the folded capacitive load electrode structure of any one of claims 1-5, and a lithium niobate waveguide structure disposed on the folded capacitive load electrode structure;
the lithium niobate waveguide structure comprises a first waveguide (111) and a second waveguide (112);
the first waveguide (111) is arranged between the loading T-shaped electrodes (4) respectively arranged on the first main ground electrode (22) and the first straight main signal electrode (211), and between the loading T-shaped electrodes (4) respectively arranged on the second main ground electrode (23) and the second straight main signal electrode (213);
the second waveguide (112) is installed between the loading T-shaped electrodes (4) respectively arranged on the first straight main signal electrode (211) and the second main ground electrode (23), and between the loading T-shaped electrodes (4) respectively arranged on the second straight main signal electrode (213) and the first main ground electrode (22).
7. The folding capacitive load electro-optic modulator of claim 6, wherein,
the first waveguide (111) comprises a first straight waveguide (1111), a first curved waveguide (1113) and a second straight waveguide (1112) which are connected in sequence;
the second waveguide (112) comprises a third straight waveguide (1121), a second curved waveguide (1123) and a fourth straight waveguide (1122) which are connected in sequence;
the first straight waveguide (1111) is installed between the loading T-shaped electrodes (4) respectively arranged on the first main ground electrode (22) and the first straight main signal electrode (211);
the second straight waveguide (1112) is arranged between the loading T-shaped electrodes (4) respectively arranged on the second main ground electrode (23) and the second straight main signal electrode (213);
the third straight waveguide (1121) is installed between loading T-shaped electrodes (4) respectively arranged on the first straight main signal electrode (211) and the second main ground electrode (23);
the fourth straight waveguide (1122) is installed between the loading T-shaped electrodes (4) respectively provided on the second straight main signal electrode (213) and the first main ground electrode (22).
8. The folded capacitive load electro-optic modulator of claim 7, wherein the first curved waveguide (1113) communicates with the second curved waveguide (1123), and wherein a portion of the first curved waveguide (1113) that communicates with the second curved waveguide (1123) constitutes an X-shaped cross waveguide.
9. The folded capacitive load electro-optic modulator of claim 6, wherein the lithium niobate waveguide structure further comprises an input waveguide (11), an optical splitter (12), an optical combiner (13), and an output waveguide (14); the optical signals are input into the input waveguide (11) and then split through the optical beam splitter (12), enter the first waveguide (111) and the second waveguide (112) respectively, enter the optical beam combiner (13) from the first waveguide (111) and the second waveguide (112) to combine the beams, and enter the output waveguide (14).
10. A method of making a folded capacitive load electro-optic modulator of claim 8, comprising the steps of:
s1: preparing a lithium niobate waveguide structure on a lithium niobate thin film substrate;
s2: depositing a low-refractive-index insulating medium buffer layer on the lithium niobate thin film composite substrate obtained in the step S1;
s3: preparing a coplanar metal electrode on the lithium niobate thin film combined substrate obtained in the step S2 to form a folding capacitive load electrode structure consisting of two ground electrodes and a signal electrode;
s4: preparing an insulating medium layer serving as a support of an air bridge on the folding capacitive load electrode structure of the lithium niobate thin film combined substrate obtained in the step S3;
s5: preparing an air bridge structure on the insulating medium layer of the lithium niobate thin film combined substrate obtained in the step S4 to obtain a folding capacitive load electrooptical modulator; the air bridge connects two ground electrodes in the folded capacitive electrode structure and is not in contact with the signal electrode.
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| CN112904599A (en) * | 2021-04-07 | 2021-06-04 | 华中科技大学 | High-speed modulator |
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| DE102014119195B4 (en) * | 2014-12-19 | 2016-10-06 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Electro-optical modulator |
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| CN112904599A (en) * | 2021-04-07 | 2021-06-04 | 华中科技大学 | High-speed modulator |
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| 孙时豪 等.高性能硅和铌酸锂异质集成薄膜电光调制器(特邀).红外与激光工程.2021,第50卷(第7期),第1-3页. * |
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