CN113985629A - Folding capacitive load electrode structure, electro-optical modulator and preparation method thereof - Google Patents
Folding capacitive load electrode structure, electro-optical modulator and preparation method thereof Download PDFInfo
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Abstract
The invention provides a folding capacitive load electrode structure, an electro-optic 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-main signal electrode-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 bent part to connect the first main ground electrode with the second main ground electrode; the electro-optical modulator comprises an electrode structure and a lithium niobate waveguide structure, and 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; loading T-shaped electrodes are arranged on two sides of the waveguide; by adopting the folding capacitive load electro-optical modulator, a parasitic coupling slot line mode can be inhibited to the maximum extent, so that the electro-optical modulator can work in a push-pull mode efficiently, and the transmission loss and return loss of an electric signal are reduced.
Description
Technical Field
The invention relates to the technical field of optical communication and integrated optical modulation, in particular to a folding capacitive load electrode structure, an electro-optical modulator and a preparation method thereof.
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 manufacturing electro-optical modulators. The advent of thin film lithium niobate platforms pushed the performance and integration specifications of lithium niobate modulators to a new height. By dry etching the lithium niobate thin film layer, the optical waveguide with low loss and high refractive index contrast can be obtained. Due to the lithium niobate waveguide with strong optical limitation, the modulation efficiency is greatly improved to 2V/cm. As shown in fig. 1, which is a schematic diagram of a lithium niobate thin-film electro-optical modulator based on a common coplanar waveguide transmission line structure, the electro-optical bandwidth is mainly limited by the microwave loss of the electrode, which is caused by the current crowding effect due to the small gap between the signal electrode and the ground electrode. FIG. 2 is a schematic diagram of a Mach-Zehnder 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 tens of μm; in order to realize 50 omega impedance matching, the width of the main signal electrode is increased, so that the current distribution is more uniform and is not easy to gather at the edge of the electrode, and the microwave loss is reduced.
The publication number CN113325612A (2021-08-31 on the publication date) provides a thin-film lithium niobate electro-optic modulator and a preparation method thereof, 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 guide; the thin-film lithium niobate optical signal guide comprises a Mach-Zehnder structure; respectively arranging a traveling wave signal electrode and a traveling wave grounding electrode at two sides of each optical signal guide arm of the Mach-Zehnder structure, and arranging a capacitance load type T-structure electrode for modulating optical signals in the optical signal guide arms between the traveling wave signal electrode and the traveling wave grounding electrode; hollow isolation structures used 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 thin-film lithium niobate electro-optical modulator realizes low driving voltage, low microwave loss and large electro-optical bandwidth under a silicon-based substrate.
However, in the electro-optical modulator adopting the mach-zehnder structure, because the difference between the lengths of the inner and outer slots is large when the periodic load electrode structure is bent at a right angle, signals in two gaps are not synchronous any more in a time domain, 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 type capacitive load electrode structure, an electro-optical modulator and a preparation method thereof, aiming at overcoming the defects of large 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 foldable capacitive load electrode structure, comprising a main signal electrode, a first main ground electrode, and a second main ground electrode, wherein the first main ground electrode-main signal electrode-second main ground electrode form a G-S-G coplanar waveguide transmission line, which comprises a straight transmission line portion and a curved transmission line portion; in the straight transmission line part, two sides of a main signal electrode are connected with loading T-shaped electrodes, and one side between a first main ground electrode and a main signal electrode and one side between a second main ground electrode and the main signal electrode are connected with the loading T-shaped electrodes; the transmission line part is bent, and the main signal electrode is provided with a plurality of air bridges at the bent part to connect the first main ground electrode with the second main ground electrode.
In the technical scheme, the air bridge is arranged above the bent part of the main signal electrode to connect the first main ground electrode and the second main ground electrode, so that the phases of electromagnetic waves at discontinuous parts can be the same, the parasitic capacitance of the air bridge is minimized, the excitation of a parasitic coupling slot line mode is inhibited to the maximum 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 beneficial to 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 applied to different waveguides are opposite all the time, and the direction of the electric field applied to the same waveguide is unchanged all the time, and the foldable capacitive load electro-optic modulator works in a push-pull mode to inhibit a slot line mode.
Preferably, 2n corner structures are arranged at the bent position of the main signal electrode, wherein n is a positive integer, the 2 nth corner structure and the 2n-1 st corner structure are the same as a positive or reverse right-angle corner, and the 2 nth corner structure and the 2n +1 st corner structure have opposite corner directions; the air bridge is arranged above the corner structure of the main signal electrode.
Preferably, the main signal electrodes include 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 bent 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 disposed 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 arranged above the corner structure, and the chamfer and the air bridge are matched for use, so that the slot line mode is jointly inhibited, and the microwave loss and the return loss caused by the 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 erected above the first electrode chamfer and the second electrode chamfer respectively, and the air bridges are connected with the first main ground electrode and the second main ground electrode respectively.
Preferably, the loaded 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 foldable capacitive load electro-optical modulator, including the foldable capacitive load electrode structure, and a lithium niobate waveguide structure, where the lithium niobate waveguide structure is disposed on the foldable 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 waveguides are arranged between the loaded T-shaped electrodes respectively arranged on the first straight main signal electrode and the second main ground electrode, and between the loaded T-shaped electrodes respectively arranged on the second straight main signal electrode and the first main ground 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 borne by the first waveguide and the second waveguide are always opposite, and the direction of the electric field borne by the same waveguide is always unchanged, so that the electro-optical modulator efficiently works in a push-pull mode, and a slot line mode is inhibited.
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 connected in sequence; the first straight waveguide is arranged between loading T-shaped electrodes which are respectively arranged on the first main ground electrode and the first straight main signal electrode; the second straight waveguide is arranged between loading T-shaped electrodes which are respectively arranged on a second main ground electrode and a second straight main signal electrode; the third straight waveguide is arranged between loading T-shaped electrodes which are respectively arranged on the first straight main signal electrode and the second main ground electrode; the fourth straight waveguide is arranged between the loaded T-shaped electrodes respectively arranged on the second straight main signal electrode and the first main ground electrode.
Preferably, the first curved waveguide is communicated with the second curved waveguide, and the part of the first curved waveguide communicated with the second curved waveguide constitutes an X-shaped crossed 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 signal is split by the optical splitter after being input into the input waveguide, and then respectively enters the first waveguide and the second waveguide, and then enters the optical combiner from the first waveguide and the second waveguide to be combined, and finally enters 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 following steps:
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 combined substrate obtained in the step S1;
s3: preparing coplanar metal electrodes on the lithium niobate thin film combined substrate obtained in the step S2 to form a folding type capacitive load electrode structure consisting of two ground electrodes and a signal electrode;
s4: preparing an insulating medium layer as a support of the air bridge on the lithium niobate thin film combined substrate obtained in the step S3;
s5: on the lithium niobate thin film combined substrate obtained in step S4, an air bridge structure is prepared, which connects the two ground electrodes in the folded capacitive load electrode structure and does not contact the signal electrode.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that: the folded capacitive load electro-optic modulator is composed of a folded capacitive load electrode structure and a lithium niobate waveguide structure, the folded capacitive load electrode structure can enable the electromagnetic wave phases at discontinuous positions to be the same, meanwhile, the parasitic capacitance of an air bridge is minimized, and the excitation of a parasitic coupling slot line mode is restrained to the maximum extent; the waveguides in the lithium niobate waveguide structure are always arranged between the loading T-shaped electrodes, the directions of electric fields borne by the two waveguides are always opposite, and the direction of the electric field borne by the same waveguide is always unchanged, so that the electro-optic modulator efficiently works in a push-pull mode, a slot line mode is inhibited, the transmission loss and return loss of electric signals are reduced, and the performance of the electro-optic 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 lithium niobate thin-film electro-optic modulator based on a periodic capacitive load electrode structure.
Fig. 3 is a schematic diagram of the structure of the folded capacitive load electrode in embodiment 1.
Fig. 4 is a partial view of the air bridge portion of the folded capacitive load electrode structure of example 1.
Fig. 5 is a schematic diagram of a structure of a folded capacitive load electrode in embodiment 2.
Fig. 6 is a partial view of the 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 chip of a folded capacitive-loading electro-optic modulator in example 3.
Fig. 8 is a schematic diagram of a folded capacitive load electro-optic modulator folded once in embodiment 3.
Fig. 9 is a partial view of a folded capacitive-load electro-optic modulator folded once in embodiment 3.
Fig. 10 is a schematic diagram of a folded capacitive-load electro-optic modulator folded twice in embodiment 4.
Fig. 11 is a partial view of a folded capacitive-load electro-optic modulator folded twice in embodiment 4.
FIG. 12 is the S of the folded capacitive load electro-optic modulator of example 4 using the conventional direct turning and using the chamfer and air bridge structure11Parameter change is compared with the graph.
FIG. 13 is the S of the folded capacitive load electro-optic modulator of example 4 using normal direct turning and using chamfer and air bridge structure21Parameter change is compared with the graph.
Fig. 14 is a flow chart of a method of making a folded capacitive loaded electro-optic modulator.
Wherein, 1-lithium niobate thin film layer, 11-input waveguide, 111-first waveguide, 1111-first straight waveguide, 1112-second straight waveguide, 1113-first curved waveguide, 1114-third curved waveguide, 1115-fifth straight waveguide, 112-second waveguide, 1121-third straight waveguide, 1122-fourth straight waveguide, 1123-second curved waveguide, 1124-fourth curved waveguide, 1125-sixth straight waveguide, 12-optical beam splitter, 13-optical beam combiner, 14-output waveguide, 2-coplanar waveguide transmission line layer, 21-main signal electrode, 211-first straight main signal electrode, 212-first curved main signal electrode, 2121-first electrode chamfer, 2122-second electrode chamfer, 213-second straight main signal electrode, 214-second curved main signal electrode, 2141-third electrode chamfer, 2142-fourth electrode chamfer, 215-third straight main signal electrode, 22-first main ground electrode, 23-second main ground electrode, 31-first air bridge, 32-second air bridge, 33-third air bridge, 34-fourth air bridge, 35-fifth air bridge, 36-sixth air bridge, 37-seventh air bridge, 38-eighth air bridge, 4-loaded T-electrode, 5-substrate material.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
the technical solution of the present 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 foldable 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 first main signal electrode 21, and the second main ground electrode 23 form a G-S-G coplanar waveguide transmission line 2, which includes a straight transmission line portion and a curved transmission line portion; in the straight transmission line part, two sides of a main signal electrode 21 are connected with loading T-shaped electrodes, and one side between a first main ground electrode 22 and a second main ground electrode 23 and the main signal electrode 21 is connected with the loading T-shaped electrodes; wherein, the transmission line part is bent, the main signal electrode 21 is provided with a plurality of air bridges at the bent part 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 2 nth corner structure and the 2n-1 st corner structure are both a forward or reverse right-angle corner, and the 2 nth corner structure and the 2n +1 st corner structure have opposite corner directions; the air bridge is positioned over the corner structure of the main signal electrode 21.
In this embodiment, the electrode structure is a folding capacitive load electrode structure that is folded once, that is, n is 1, and the number of the corner structures is 2.
In the specific implementation process, the air bridge is arranged 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 phases of electromagnetic waves at discontinuous parts can be the same, the parasitic capacitance of the air bridge is minimized, the excitation of a parasitic coupling slot line mode is inhibited to the maximum 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 beneficial to realizing low driving voltage and miniaturized packaging at the same time.
Example 2
Referring to fig. 5-6, the present embodiment provides a foldable capacitive load electrode structure, wherein a chamfer is formed at an 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, there are 4 air bridges, which are respectively installed above the first electrode chamfer 2121 and the second electrode chamfer 2122, and the air bridges are respectively connected to the first main ground electrode 22 and the second main ground electrode 23. 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 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 of the second electrode chamfer 2122, one end of the fourth air bridge 34 is connected with the first main ground electrode 22, and the other end is connected with the second main ground electrode 23.
In a specific implementation, 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 path difference between the two slit spaces can be shortened. The electromagnetic waves at the discontinuous parts can be made to have the same phase by using the air bridges for connection, and the slot line mode can be suppressed.
The embodiment uses the least air bridge, inhibits the excitation of a 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 and the air bridge together to suppress the slot line mode, thereby minimizing the microwave loss and the return loss caused by the 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, this embodiment provides a folded capacitive loading electro-optic modulator, which is a folded once two-segment type folded capacitive loading electro-optic modulator, and includes a folded once-folded capacitive loading electrode structure and a lithium niobate waveguide structure, where n is 1, and the lithium niobate waveguide structure is disposed on the folded capacitive loading electrode structure; the lithium niobate waveguide structure comprises a first waveguide 111 and a second waveguide 112; the first waveguide 111 is installed between the loaded T-shaped electrodes 4 respectively arranged on the first main ground electrode 22 and the first straight main signal electrode 211, and between the loaded T-shaped electrodes 4 respectively arranged 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 disposed on the first straight main signal electrode 211 and the second main ground electrode 23, and between the loading T-shaped electrodes 4 respectively disposed 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 which is subjected to etching processing; a substrate material 5 is arranged below the lithium niobate thin film layer 1, and the substrate material 5 comprises silicon, quartz, lithium niobate and sapphire, or a multilayer material consisting of the above materials and a silicon dioxide buried oxide 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 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 disposed 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 respectively arranged on the second main ground electrode 23 and the second straight main signal electrode 212; the third straight waveguide 1121 is installed between the loading T-shaped electrodes 4 respectively disposed on the first straight main signal electrode 211 and the second main ground electrode 23; the fourth straight waveguide 1122 is installed between the loaded T-electrodes 4 respectively disposed on the second straight main signal electrode 212 and the first main ground electrode 22. Wherein, the main electric field component between the loaded T-shaped electrodes 4 is consistent with the Z-axis direction of the X-cut lithium niobate film, so the strongest electro-optic coefficient r of the lithium niobate material can be utilized33。
In this embodiment, the lithium niobate waveguide structure further includes an input waveguide 11, an optical splitter 12, an optical combiner 13, and an output waveguide 14; after being input into the input waveguide 11, the optical signal is split by the optical splitter 12 and enters the first waveguide 111 and the second waveguide 112, and after entering the optical combiner 13 from the first waveguide 111 and the second waveguide 112 for optical combining, the optical signal enters the output waveguide 14.
In this embodiment, the first curved waveguide 1113 is communicated with the second curved waveguide 1123, and the part of the first curved waveguide 1113 communicated with the second curved waveguide 1123 constitutes an X-shaped cross waveguide.
In the implementation process, after the 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 passes through the first curved waveguide1113 and the second curved waveguide 1123 are connected to form an X-shaped cross, so that the loss caused by diffraction of light when the first waveguide 111 and the second waveguide 112 are crossed can be reduced, the first waveguide 111 and the second waveguide 112 are always positioned between the loading T-shaped electrodes 4, the directions of electric fields applied to the first waveguide 111 and the second waveguide 112 are always opposite, and the direction of the electric field applied to the same waveguide is always unchanged, so that the folded capacitive load electro-optic modulator works in a push-pull mode, and a slot line mode is suppressed. Amount of phase change of the first waveguide 111
And the amount of phase change of the second waveguide 112
Respectively as follows:
wherein n iseIs the refractive index of extraordinary ray, r33The strongest electro-optic coefficient of lithium niobate material, EzIs the electric field component along the Z-axis direction of the lithium niobate crystal, and lambda is the wavelength of the optical signal, L1Is the total length, L, of the first straight waveguide 1111 and the second straight waveguide 11122The total length of the third straight waveguide 1121 and the fourth straight waveguide 1122; l is1And L2The total length of the effective electro-optical interaction. The invention greatly shortens the length of the device by folding the lithium niobate waveguide and the coplanar waveguide transmission line, and is beneficial to simultaneously realizing low driving voltage and miniaturized packaging. The direction of an 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 crossed positions of the two waveguides are connected through an X-shaped cross structure so as to realize low loss and low crosstalk.
Example 4
Referring to fig. 8-11, the present embodiment provides a folded capacitive loading electro-optic modulator, which is a three-stage folded capacitive loading electro-optic modulator with n being 2, 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 to the second straight main signal electrode 213, and the other end is connected to the second curved main signal electrode 214; the fourth electrode fillet 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 fillet 2141, 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 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 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 disposed above the end of the fourth electrode fillet 2142, one end of the eighth air bridge 38 is connected to the first main ground electrode 22, and the other end is connected to 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 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 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, and 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, the fourth straight waveguide 1122, the fourth curved waveguide 1124 and the sixth straight waveguide 1125 being connected in series.
In this embodiment, the third curved waveguide 1114 is in communication with the fourth curved waveguide 1124, and the 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 installed between the loaded T-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 transmission performance of the curved-surface coplanar waveguide transmission line can be remarkably improved by using the structure of the electrode chamfer and the air bridge, and as shown in fig. 10 and 11, the reflection coefficient S of the structure is adopted within the frequency band of 1 GHz-67 GHz11Keeping below-15 dB, the transmission coefficient S21 increases significantly and is smoother, which means that the slot line pattern is effectively suppressed.
Example 5
The embodiment provides a method for manufacturing a folding capacitive load electro-optical modulator, which is used for manufacturing the folding capacitive load electro-optical modulator according to the embodiment, and includes the following steps:
s1: the required lithium niobate waveguide structure is prepared on the 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 process in this embodiment includes the use of stepper, contact lithography, electron beam direct writing, and laser direct writing.
S2: and depositing a low-refractive-index insulating medium buffer layer on the lithium niobate thin film combined 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 and electronic glue.
S3: and (4) 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 type capacitive load electrode structure consisting of two earth electrodes and a signal electrode.
S4: and (4) preparing an insulating medium layer as a support of the air bridge by adopting the processes of 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 insulating dielectric layer may be made of silicon dioxide, silicon nitride, aluminum oxide, titanium dioxide, insulating photoresist, or a combination thereof.
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-optic modulator; the air bridge connects the two ground electrodes in the folded capacitive load electrode structure and does not contact the signal electrode. In this embodiment, when the substrate material 5 of the lithium niobate thin film combined substrate is silicon, the substrate around the electrode may be removed by wet etching, or a trench may be prepared around the electrode by an etching process to the silicon substrate, and a part of the silicon substrate may be removed by isotropic etching.
In addition, in the invention, metal wire bonding technology can be used to replace the air bridge structure so as to realize the contact connection of the two ground electrodes and not to contact with the signal electrode.
The terms describing positional relationships in the drawings are for illustrative purposes only and are not to be construed as limiting the patent;
it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A folded capacitive load electrode structure, comprising a main signal electrode (21), a first main ground electrode (22), a second main ground electrode (23), wherein the first main ground electrode (22) -main signal electrode (21) -second main ground electrode (23) form a G-S-G coplanar waveguide transmission line (2), the G-S-G coplanar waveguide transmission line (2) comprising a straight transmission line portion and a curved transmission line portion; in the straight transmission line part, two sides of a main signal electrode (21) are connected with loading T-shaped electrodes, and one side between a first main ground electrode (22) and a second main ground electrode (23) and the main signal electrode (21) is connected with the loading T-shaped electrodes; the transmission line part is bent, and a plurality of air bridges are erected at the bent part of the main signal electrode (21) to connect the first main ground electrode (22) with the second main ground electrode (23).
2. The folded capacitive load electrode structure of claim 1, wherein the main signal electrode (21) is provided with 2n corner structures at the bending position, where n is a positive integer, and the 2n corner structure and the 2n-1 corner structure are the same as a forward or reverse right-angle corner, and the 2n corner structure and the 2n +1 corner structure have opposite corner directions; the air bridge is arranged above the corner structure of the main signal electrode (21).
3. The folded capacitive load electrode structure of claim 2, wherein said 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 bent 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 of the corner structure.
4. The folded capacitive load electrode structure of claim 3, wherein said at least 4 air bridges are respectively disposed above said first and second electrode chamfers (2121, 2122) and are respectively connected to said first and second main ground electrodes (22, 23).
5. The folded capacitive load electrode structure according to claim 1, wherein the laterally disposed loaded T-electrodes (4) of the main signal electrode (21), the first main ground electrode (22) and the second main ground electrode (23) are respectively disposed oppositely.
6. A folded capacitive load electro-optic modulator, comprising the folded capacitive load electrode structure of any one of claims 1 to 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 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) and between the loading T-shaped electrodes (4) respectively arranged 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 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 (212) and the first main ground electrode (22).
7. The folded capacitive-loaded electro-optic modulator of claim 6,
the first waveguide (111) comprises a first straight waveguide (1111), a first bent 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 loading T-shaped electrodes (4) respectively arranged on a first main ground electrode (22) and a first straight main signal electrode (211);
the second straight waveguide (1112) is arranged between loading T-shaped electrodes (4) which are respectively arranged on a second main ground electrode (23) and a second straight main signal electrode (212);
the third straight waveguide (1121) is installed between loading T-shaped electrodes (4) which are 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 loaded T-shaped electrodes (4) respectively arranged on the second straight main signal electrode (212) and the first main ground electrode (22).
8. The folded capacitive load electro-optic modulator of claim 7, wherein the first curved waveguide (1113) is in communication with a second curved waveguide (1123), the portion of the first curved waveguide (1113) in communication with the second curved waveguide (1123) constituting 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 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 an optical splitter (12), and respectively enter the first waveguide (111) and the second waveguide (112), and then enter the optical combiner (13) from the first waveguide (111) and the second waveguide (112) for optical combination, and then enter the output waveguide (14).
10. A method of making a folded capacitive loaded 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 combined substrate obtained in the step S1;
s3: preparing coplanar metal electrodes on the lithium niobate thin film combined substrate obtained in the step S2 to form a folding type capacitive load electrode structure consisting of two ground electrodes and a signal electrode;
s4: preparing an insulating medium layer on the folding capacitive load electrode structure of the lithium niobate thin film combined substrate obtained in the step S3 as a support of an air bridge;
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 electro-optic modulator; the air bridge connects the two ground electrodes in the folded capacitive load electrode structure and does not contact the signal electrode.
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| US20140369637A1 (en) * | 2012-02-15 | 2014-12-18 | Fraunhofer-Gesellschaft zur Förderung der angewand ten Forschung e.V. | Electro-optic modulators |
| US20180003893A1 (en) * | 2014-12-19 | 2018-01-04 | Fraunhofer-Gesellschaft zur Förderung der angewand ten 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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| US20140369637A1 (en) * | 2012-02-15 | 2014-12-18 | Fraunhofer-Gesellschaft zur Förderung der angewand ten Forschung e.V. | Electro-optic modulators |
| US20180003893A1 (en) * | 2014-12-19 | 2018-01-04 | Fraunhofer-Gesellschaft zur Förderung der angewand ten Forschung e.V. | Electro-optical modulator |
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