Differential electro-optic modulator, optical modulation system and integrated optical chip

Abstract

This application provides a differential electro-optic modulator, an optical modulation system, and an integrated optical chip. In this differential electro-optic modulator, a first input electrode and a second input electrode constitute a first differential transmission line electrode, and a first output electrode, a second output electrode, and a third output electrode constitute a second differential transmission line electrode. A first modulation electrode is connected to the first output electrode, a second modulation electrode is connected to the second output electrode, and a third modulation electrode is connected to the third output electrode. Therefore, this differential electro-optic modulator can be driven by a differential driver, eliminating the need for mounting DC blocking capacitors and enabling a wider operating bandwidth, thereby broadening the applicable bandwidth range. Furthermore, since the air bridge is located above the connection portion, there is no need to connect the second input electrode and the second output electrode inside the electrode conversion portion, thus not affecting the routing of the first waveguide and the second waveguide, thereby reducing the fabrication difficulty of the differential electro-optic modulator.

Description

Technical Field

[0001] The embodiments of this application relate to, but are not limited to, the field of integrated optoelectronics, and particularly to a differential electro-optic modulator, an optical modulation system, and an integrated optical chip. Background Technology

[0002] Among related technologies, electro-optic modulators based on thin-film lithium niobate (TFLN) offer advantages such as large bandwidth, low driving voltage, and low insertion loss, while also possessing the potential for mass production. Therefore, they are receiving increasing attention from industry and academia. Most current TFLN modulators employ a single-ended push-pull structure, where the modulation electrode is a ground-signal-ground coplanar waveguide (CPW) structure. This type of TFLN modulator uses a single-ended driver, requiring a DC blocking capacitor to be installed between the driver and the TFLN modulator to address the DC drift issue. However, installing a DC blocking capacitor between the driver and the TFLN modulator reduces the bandwidth of the TFLN modulator, thus affecting its applicable bandwidth range. Summary of the Invention

[0003] This application provides a differential electro-optic modulator, an optical modulation system, and an integrated optical chip, which can have a wider operating bandwidth, thereby expanding the applicable bandwidth range.

[0004] On one hand, this application provides a differential electro-optic modulator, including: an electrode switching section, including a first input electrode, a second input electrode, a first output electrode, a second output electrode, a third output electrode, a connecting section, and an air bridge; the second output electrode is located between the first output electrode and the third output electrode; the first input electrode is connected to the first output electrode and the third output electrode through the connecting section; the second input electrode is connected to the second output electrode through the air bridge; the air bridge is located above the connecting section; the first input electrode and the second input electrode constitute a first differential transmission line electrode; the first output electrode, the second output electrode, and the third output electrode... The output electrode constitutes a second differential transmission line electrode; the optical modulation section includes a first modulation electrode, a second modulation electrode, a third modulation electrode, a first waveguide, and a second waveguide. The second modulation electrode is located between the first modulation electrode and the third modulation electrode, the first waveguide is located between the first modulation electrode and the second modulation electrode, and the second waveguide is located between the second modulation electrode and the third modulation electrode. The first modulation electrode is connected to the first output electrode, the second modulation electrode is connected to the second output electrode, and the third modulation electrode is connected to the third output electrode. The first modulation electrode, the second modulation electrode, and the third modulation electrode constitute a third differential transmission line electrode.

[0005] On the other hand, embodiments of this application also provide an optical modulation system, including an electrical chip and a differential electro-optic modulator as described above, wherein: the electrical chip includes a first output terminal and a second output terminal, the first output terminal is connected to the first input electrode, and the second output terminal is connected to the second input electrode; the electrical chip is used to output a first modulation signal to the first input electrode through the first output terminal, and to output a second modulation signal to the second input electrode through the second output terminal, wherein the first modulation signal and the second modulation signal constitute a pair of differential signals.

[0006] On the other hand, embodiments of this application also provide an integrated optical chip, including: a laser for emitting continuous light; and a differential electro-optic modulator as described above, coupled to the laser, for receiving the continuous light emitted by the laser, and for modulating the continuous light emitted by the laser and outputting modulated light.

[0007] In this embodiment, the first and second input electrodes in the electrode conversion section constitute a first differential transmission line electrode, and the first, second, and third output electrodes constitute a second differential transmission line electrode. In the optical modulation section, the first modulation electrode is connected to the first output electrode, the second modulation electrode is connected to the second output electrode, and the third modulation electrode is connected to the third output electrode. Furthermore, the first waveguide in the optical modulation section is located between the first and second modulation electrodes, and the second waveguide is located between the second and third modulation electrodes. Therefore, the differential electro-optic modulator of this embodiment can be driven by a differential driver, eliminating the need for DC blocking capacitors and enabling a wider operating bandwidth, thereby expanding the applicable bandwidth range. Additionally, since the air bridge is located above the connection section, there is no need to connect the second input and second output electrodes inside the electrode conversion section, thus not affecting the routing of the first and second waveguides, thereby reducing the fabrication difficulty of the differential electro-optic modulator. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the structure of a TFLN modulator in related technologies;

[0009] Figure 2 yes Figure 1 The diagram shows a schematic cross-sectional view of the TFLN modulator.

[0010] Figure 3 This is a schematic diagram of the structure of a differential electro-optic modulator provided in an embodiment of this application;

[0011] Figure 4 This is a schematic diagram of the structure of a differential TFLN modulator in related technologies;

[0012] Figure 5 yes Figure 4 The diagram shows a schematic cross-sectional view of the differential TFLN modulator.

[0013] Figure 6 This is a schematic diagram of another differential TFLN modulator in related technologies;

[0014] Figure 7 yes Figure 6 The diagram shows a schematic cross-sectional view of the differential TFLN modulator.

[0015] Figure 8 This is a schematic diagram of another differential TFLN modulator in related technologies;

[0016] Figure 9 yes Figure 8 The diagram shows a schematic cross-sectional view of the differential TFLN modulator.

[0017] Figure 10This is a partial structural schematic diagram of the air bridge and support portion in the differential electro-optic modulator provided in the embodiments of this application;

[0018] Figure 11 This is a schematic diagram showing the orientation of the air bridge and the connecting part in the case where the optical modulation section provided in this application does not have a T-shaped track electrode;

[0019] Figure 12 This is a schematic diagram showing the orientation of the air bridge and the connecting part in the case where the optical modulation section has a T-shaped track electrode, as provided in the embodiments of this application.

[0020] Figure 13 This is a schematic diagram of another differential electro-optic modulator provided in the embodiments of this application;

[0021] Figure 14 yes Figure 13 Schematic diagram of the process section along the middle AA;

[0022] Figure 15 yes Figure 13 Schematic diagram of the process section along the middle BB;

[0023] Figure 16 This is a schematic diagram of the structure of an optical modulation system provided in an embodiment of this application;

[0024] Figure 17 This is a simulation result diagram of the S21 parameter of the electrode conversion unit provided in the embodiment of this application;

[0025] Figure 18 This is a simulation result diagram of the S11 parameter of the electrode conversion unit provided in the embodiment of this application. Detailed Implementation

[0026] To make the objectives, technical methods, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] It should be noted that in the description of the specification, claims and the above drawings, if the terms "first", "second" or the like are used for the purpose of distinguishing technical features, they should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0028] Currently, optical chip material systems include silicon photonics, indium phosphide (InP), and transducer-float (TFLN). Among these, silicon photonics modulators have a bandwidth of less than 70 GHz, which does not meet the application requirements of 200 GBaud and above. InP modulators have a bandwidth limit of approximately 110 GHz, but their production capacity and yield are limiting factors for their application. TFLN modulators, on the other hand, have advantages such as large bandwidth, low drive voltage, and low insertion loss, and also possess mass production potential, thus attracting increasing attention from industry and academia. Most current TFLN modulators adopt a single-ended push-pull structure, meaning the modulation electrodes are GSG coplanar waveguide structures, such as... Figure 1 and Figure 2 As shown, this TFLN modulator includes a GSG-type electrode structure 10 and a waveguide structure 11, wherein the polarization directions of the two waveguides are in the same direction. The polarization directions of the waveguides and the electric field directions E of the electrodes are in the same and opposite directions, respectively, forming a push-pull drive. However, this TFLN modulator requires a single-ended driver, which easily leads to DC drift. To solve the DC drift problem, a common approach is to mount a DC blocking capacitor between the driver and the TFLN modulator. However, mounting a DC blocking capacitor between the driver and the TFLN modulator reduces the bandwidth of the TFLN modulator, thus affecting its bandwidth applicability.

[0029] To enable TFLN modulators to have a wider operating bandwidth and thus broaden their bandwidth application range, this application provides a differential electro-optic modulator, an optical modulation system, and an integrated optical chip. The differential electro-optic modulator includes an electrode switching section and an optical modulation section. In the electrode switching section, a first input electrode and a second input electrode constitute a first differential transmission line electrode, and a first output electrode, a second output electrode, and a third output electrode constitute a second differential transmission line electrode. In the optical modulation section, a first modulation electrode is connected to a first output electrode, a second modulation electrode is connected to a second output electrode, and a third modulation electrode is connected to a third output electrode. Furthermore, in the optical modulation section, a first waveguide is located between the first and second modulation electrodes, and a second waveguide is located between the second and third modulation electrodes. This differential electro-optic modulator can be driven using a differential driver, eliminating the need for mounting DC blocking capacitors, thus enabling a wider operating bandwidth and broadening its bandwidth application range. Additionally, since the air bridge is located above the connecting section, there is no need to connect the second input electrode and the second output electrode inside the electrode switching section, thus not affecting the routing of the first and second waveguides, thereby reducing the fabrication difficulty of the differential electro-optic modulator.

[0030] The embodiments of this application will be further described below with reference to the accompanying drawings.

[0031] See Figure 3 , Figure 3This is a schematic diagram of the structure of a differential electro-optic modulator provided in an embodiment of this application. Figure 3 In this differential electro-optic modulator 300, there are an electrode switching section 310 and an optical modulation section 320, wherein:

[0032] The electrode conversion unit 310 includes a first input electrode 311, a second input electrode 312, a first output electrode 313, a second output electrode 314, a third output electrode 315, a connecting part 316, and an air bridge 317. The second output electrode 314 is located between the first output electrode 313 and the third output electrode 315. The first input electrode 311 is connected to the first output electrode 313 and the third output electrode 315 through the connecting part 316. The second input electrode 312 is connected to the second output electrode 314 through the air bridge 317, which is located above the connecting part 316. The first input electrode 311 and the second input electrode 312 constitute a first differential transmission line electrode, and the first output electrode 313, the second output electrode 314, and the third output electrode 315 constitute a second differential transmission line electrode.

[0033] The optical modulation unit 320 includes a first modulation electrode 321, a second modulation electrode 322, a third modulation electrode 323, a first waveguide 324, and a second waveguide 325. The second modulation electrode 322 is located between the first modulation electrode 321 and the third modulation electrode 323. The first waveguide 324 is located between the first modulation electrode 321 and the second modulation electrode 322. The second waveguide 325 is located between the second modulation electrode 322 and the third modulation electrode 323. The first modulation electrode 321 is connected to the first output electrode 313. The second modulation electrode 322 is connected to the second output electrode 314. The third modulation electrode 323 is connected to the third output electrode 315.

[0034] In related technologies, schemes using differential TFLN modulators have also been proposed. For example... Figure 4 and Figure 5 As shown, Figure 4 This is a schematic diagram of a differential TFLN modulator proposed in related technologies. Figure 5 This is a schematic diagram of the process cross-section of the differential TFLN modulator. Figure 4 and Figure 5The differential TFLN modulator includes a GSG-type electrode structure 40 and a waveguide structure 41, where the polarization directions of the two waveguides are in the same direction. The S+ and S- signals are a pair of differential signals with the same amplitude and a 180° phase difference. The polarization directions of the waveguides and the electric field directions E of the electrodes are in the same and opposite directions, respectively, forming a differential drive. Although this differential TFLN modulator does not require a DC blocking capacitor between it and the differential driver, simply changing the electrodes from GSG to GSGSG halves the modulation efficiency of the phase shifter. To maintain the same modulation depth, the length of the phase shifter needs to be doubled, leading to greater RF losses and thus reducing the bandwidth. Therefore, this differential TFLN modulator cannot effectively widen its operating bandwidth.

[0035] like Figure 6 and Figure 7 As shown, Figure 6 This is a schematic diagram of another differential TFLN modulator proposed in related technologies. Figure 7 This is a schematic diagram of the process cross-section of the differential TFLN modulator. Figure 6 and Figure 7 The differential TFLN modulator includes an SS-type electrode structure 60 and a waveguide structure 61, wherein the two waveguides have opposite polarization directions, namely polarization direction 1 and polarization direction 2. The S+ and S- signals are a pair of differential signals with the same amplitude and a phase difference of 180°. The polarization directions of the waveguides and the electric field directions E of the electrodes are in the same and opposite directions, respectively, constituting differential drive. Although this differential TFLN modulator does not require a DC blocking capacitor between itself and the differential driver, the waveguides of this differential TFLN modulator need to be polarized, increasing the difficulty of fabrication.

[0036] like Figure 8 and Figure 9 As shown, Figure 8 This is a schematic diagram of another differential TFLN modulator proposed by related technologies. Figure 9 This is a schematic diagram of the process cross-section of the differential TFLN modulator. Figure 8 and Figure 9The differential TFLN modulator includes a balun structure 80, an S-S+S- type electrode structure 81, and a waveguide structure 82. The balun structure 80 includes an S+S- differential input electrode 83 and an S-S+S- differential output electrode 84. The S+S- differential signal is input from the S+S- differential input electrode 83 to the balun structure 80 and converted into an S-S+S- differential signal output. In this differential TFLN modulator, the S- input electrode of the balun structure 80 is connected to two S- output electrodes via a first metal 85, and the S+ input electrode is connected to the S+ output electrode via a second metal 86. The second metal 86 is located below the first metal 85 and embedded within the substrate. SiO2 dielectric is filled between the S- input electrode and the second metal 86. The two waveguides in the waveguide structure 82 have the same polarization direction, polarization direction 1 and polarization direction 2, respectively. The polarization directions of the waveguides and the electric field directions E of the electrodes are in the same and opposite directions, respectively, constituting differential drive. Although this differential TFLN modulator does not require a DC blocking capacitor between itself and the differential driver, the second metal 86 is embedded within the substrate, resulting in a close distance between it and the S-input electrode. Furthermore, the space between the second metal 86 and the S-input electrode is filled with a SiO2 dielectric (a conventional filler), which easily leads to a large parasitic capacitance between them. This degrades the high-frequency performance of the differential TFLN modulator, reducing its operating bandwidth. In addition, because the second metal 86 is embedded within the substrate, its close proximity to the waveguide not only affects the waveguide routing, increasing fabrication complexity, but may also lead to additional optical absorption loss, further increasing the overall loss of the differential TFLN modulator.

[0037] Compared with the aforementioned related technologies, in the differential electro-optic modulator 300 provided in this application embodiment, the first input electrode 311 and the second input electrode 312 in the electrode switching section 310 constitute the first differential transmission line electrode, and the first output electrode 313, the second output electrode 314, and the third output electrode 315 constitute the second differential transmission line electrode. In the optical modulation section 320, the first modulation electrode 321 is connected to the first output electrode 313, the second modulation electrode 322 is connected to the second output electrode 314, and the third modulation electrode 323 is connected to the third output electrode 315. Furthermore, the first waveguide 324 in the optical modulation section 320 is located between the first modulation electrode 321 and the second modulation electrode 322, and the second waveguide 325 is located between the second modulation electrode 322 and the third modulation electrode 323. Therefore, the differential electro-optic modulator 300 in this application embodiment can be driven by a differential driver, does not require mounting a DC blocking capacitor, and can have a wider operating bandwidth, thereby expanding the bandwidth application range. In addition, since the air bridge 317 is located above the connecting part 316, it is not necessary to connect the second input electrode 312 and the second output electrode 314 inside the electrode conversion part 310. Therefore, it will not affect the routing of the first waveguide 324 and the second waveguide 325, thereby reducing the fabrication difficulty of the differential electro-optic modulator 300.

[0038] In some embodiments, reference Figure 3 The electrode conversion unit 310, comprising a first input electrode 311, a second input electrode 312, a first output electrode 313, a second output electrode 314, and a third output electrode 315, can achieve the purpose of converting a coplanar stripline (CPS) to a coplanar waveguide (CPW). This allows the S+S- differential signal transmitted on the CPS (i.e., the first differential transmission line electrode formed by the first input electrode 311 and the second input electrode 312) to be converted into the S-S+S- differential signal transmitted on the CPW (i.e., the second differential transmission line electrode formed by the first output electrode 313, the second output electrode 314, and the third output electrode 315). This facilitates the modulation of optical signals transmitted in the first waveguide 324 and the second waveguide 325 using the S-S+S- differential signal transmitted on the CPW. In other embodiments, the first output electrode 313, the second output electrode 314, and the third output electrode 315 may also be slow-wave electrodes of the same type as the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323. In this case, better impedance continuity can be obtained.

[0039] In some embodiments, the connecting portion 316 may be integrally formed with the first input electrode 311, the first output electrode 313, and the third output electrode 315, or it may be formed by extending outward from the first input electrode 311. Alternatively, it may be a component independent of the first input electrode 311, the first output electrode 313, and the third output electrode 315. The appropriate selection can be made according to the actual application, and no specific limitation is made here. In one embodiment, the connecting portion 316 may be made of materials such as gold, silver, or conductive transparent oxide, and no specific limitation is made here.

[0040] In example Figure 8 In related technologies, the bridging metal between the two S+ electrodes of the balun structure is located below the electrode region where the pad is located. This is limited by the spacing requirements of the TFLN waveguide and the electrode thickness. Furthermore, the close proximity between the top-layer CPW and the bottom-layer bridging metal easily introduces additional parasitic capacitance. In addition, if the TFLN waveguide passes through the bottom-layer metal of the balun structure region, it may cause additional optical loss. In this embodiment, an air bridge 317 is used to bridge the second input electrode 312 and the second output electrode 314. Since the air bridge 317 is located above the connection portion 316 and above the traces of the CPS electrode (i.e., the first differential transmission line electrode) and the CPW electrode (i.e., the second differential transmission line electrode), the distance between the air bridge 317 and the CPW electrode is relatively large. Therefore, it not only reduces the generation of parasitic capacitance but also avoids additional optical loss and does not affect the waveguide routing in the differential electro-optic modulator. In some embodiments, the air bridge 317 can be made of gold; no specific limitation is made here.

[0041] In some embodiments, reference Figure 3 In the optical modulation unit 320, the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323 are arranged parallel to each other. When electrical signals are applied to the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323, a first electric field is generated between the first modulation electrode 321 and the second modulation electrode 322, and a second electric field is generated between the second modulation electrode 322 and the third modulation electrode 323. A first waveguide 324 and a second waveguide 325 are respectively connected to a beam splitter P1 and a beam combiner P2. The first waveguide 324, the second waveguide 325, the beam splitter P1, and the beam combiner P2 form a Mach-Zehnder interferometer (MZI), which can convert phase modulation of light into intensity modulation. In some embodiments, the beam splitter P1 and the beam combiner P2 can be either a 1x2 or a 2x2 structure; no specific limitation is made here.

[0042] In some embodiments, both the first waveguide 324 and the second waveguide 325 are TFLN waveguides. In other embodiments, the first waveguide 324 and the second waveguide 325 may also be made of electro-optic materials such as BTO (BaTiO3, barium titanate), LTOI (Lithium Tantalate on Insulator), LiTaO3 (lithium tantalate), and PZT (Pb(Zr,Ti)O3, lead zirconate titanate), and this application does not limit this. The first waveguide 324 is disposed between the first modulation electrode 321 and the second modulation electrode 322, and the second waveguide 325 is disposed between the second modulation electrode 322 and the third modulation electrode 323. The effective refractive index of the first waveguide 324 is controlled by the modulation electric field between the first modulation electrode 321 and the second modulation electrode 322, and the effective refractive index of the second waveguide 325 is controlled by the modulation electric field between the second modulation electrode 322 and the third modulation electrode 323. The continuous light emitted by the laser can be input from beam splitter P1 to the first waveguide 324 and the second waveguide 325. When differential electrical signals are applied to the first modulation electrode 321 and the second modulation electrode 322, and differential electrical signals are also applied to the second modulation electrode 322 and the third modulation electrode 323, the first waveguide 324 will be in the first electric field generated by the first modulation electrode 321 and the second modulation electrode 322, and the second waveguide 325 will be in the second electric field generated by the second modulation electrode 322 and the third modulation electrode 323. At this time, part of the continuous light transmitted in the first waveguide 324 will be modulated by the first electric field, and another part of the continuous light transmitted in the second waveguide 325 will be modulated by the second electric field. Then, the modulated continuous light in the first waveguide 324 and the modulated continuous light in the second waveguide 325 will be converged and output by beam combiner P2.

[0043] In some embodiments, such as Figure 10As shown, the electrode conversion unit 310 also includes a support unit 318, which is disposed below the air bridge 317 and serves to support the air bridge 317. The support unit 318 can be formed of a dielectric material with a low dielectric constant, such as silicon dioxide (SiO2), benzocyclobutene (BCB), etc., and can be appropriately selected according to the actual application scenario, without specific limitation here. In some embodiments, the dielectric thickness of the support unit 318 is greater than 1 μm, for example, the dielectric thickness of the support unit 318 can be 1.5 μm or 2 μm, etc., and can be appropriately selected according to the actual application scenario, without specific limitation here. In some embodiments, the support unit 318 can be selected as a dielectric material with a lower dielectric constant (e.g., BCB dielectric material with a dielectric constant of 2.6) and has a thicker thickness (e.g., a dielectric thickness greater than 1 μm), thereby better reducing the influence of parasitic capacitance and improving the RF transmission performance of the electrode conversion unit 310.

[0044] In some embodiments, such as Figure 3 As shown, the first modulation electrode 321 is provided with a first T-shaped track electrode 326, the second modulation electrode 322 is provided with a second T-shaped track electrode 327, the first T-shaped track electrode 326 and the second T-shaped track electrode 327 are arranged opposite to each other, and the first waveguide 324 is located between the first T-shaped track electrode 326 and the second T-shaped track electrode 327; the second modulation electrode 322 is also provided with a third T-shaped track electrode 328, the third modulation electrode 323 is provided with a fourth T-shaped track electrode 329, the third T-shaped track electrode 328 and the fourth T-shaped track electrode 329 are arranged opposite to each other, and the second waveguide 325 is located between the third T-shaped track electrode 328 and the fourth T-shaped track electrode 329. When a differential electrical signal is applied to the first modulation electrode 321 and the second modulation electrode 322, a first electric field is generated between the first T-shaped track electrode 326 and the second T-shaped track electrode 327. When a differential electrical signal is also applied to the second modulation electrode 322 and the third modulation electrode 323, a second electric field is generated between the third T-shaped track electrode 328 and the fourth T-shaped track electrode 329. At this time, a portion of the continuous light transmitted in the first waveguide 324 will be modulated by the first electric field between the first T-shaped track electrode 326 and the second T-shaped track electrode 327, and another portion of the continuous light transmitted in the second waveguide 325 will be modulated by the second electric field between the third T-shaped track electrode 328 and the fourth T-shaped track electrode 329.

[0045] In some embodiments, the impedance of the third differential transmission line electrode, consisting of the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323, is matched with the impedance of the second differential transmission line electrode, consisting of the first output electrode 313, the second output electrode 314, and the third output electrode 315. For example, assuming the impedance of the third differential transmission line electrode is ZMod and the impedance of the second differential transmission line electrode is Z2, then Z2 = ZMod. Therefore, the transmission reflection of the differential electrical signal between the electrode conversion unit 310 and the optical modulation unit 320 can be reduced, thereby reducing signal integrity problems caused by impedance mismatch.

[0046] In some embodiments, the electrode switching unit 310 and the optical modulation unit 320 may be along a first direction (e.g., Figure 3 The air bridge 317 and the connecting part 316 can also be set along the direction indicated by the middle arrow.

[0047] In some cases, when the first input electrode 311 and the second input electrode 312 in the electrode conversion unit 310 receive differential electrical signals of the same amplitude but opposite direction (e.g., S+S- differential electrical signals), the first output electrode 313, the second output electrode 314, and the third output electrode 315 need to output corresponding differential electrical signals of the same amplitude but opposite direction (e.g., S-S+S- differential electrical signals). However, since there may be differences between the length of the air bridge 317 and the path lengths of the S+ and S- signals, setting both the air bridge 317 and the connecting part 316 along the first direction may cause the phase of the S+ and S- signals to deviate by 180° in the high-frequency part. In this case, the air bridge 317 can be set to form a first angle with the first direction, and the connecting part 316 can be set to form a second angle with the first direction. The first angle and the second angle can be the same or different, and can be appropriately set according to the actual application scenario. No specific limitation is made here. By setting the air bridge 317 at a first angle to the first direction and setting the connecting part 316 at a second angle to the first direction, the length difference between the length of the air bridge 317 and the path lengths of the S+ and S- signals can be reduced. This, to a certain extent, can prevent phase deviation of the differential electrical signals output by the first output electrode 313, the second output electrode 314, and the third output electrode 315. (Reference) Figure 11 and Figure 12 As shown, Figure 11 This is a schematic diagram showing the orientation of the air bridge 317 and the connecting part 316 when the optical modulation unit 320 does not have a T-shaped track electrode. Figure 12 This is a schematic diagram showing the orientation of the air bridge 317 and the connecting portion 316 when the optical modulation unit 320 has a T-shaped track electrode. Figure 11 and Figure 12As can be seen, the air bridge 317 can be positioned at a first angle θ1 with the first direction, and the connecting part 316 can be positioned at a second angle θ2 with the first direction. This design can, to a certain extent, prevent phase deviation of the differential electrical signals output by the first output electrode 313, the second output electrode 314, and the third output electrode 315.

[0048] In some embodiments, reference Figure 13 As shown, the differential electro-optic modulator 300 also includes a pad portion 330 and an impedance transformation portion 340. The pad portion 330 is connected to the electrode conversion portion 310 through the impedance transformation portion 340. The pad portion 330 is used to connect external electrical chips, and the impedance transformation portion 340 is used to match the impedance between the pad portion 330 and the electrode conversion portion 310. It should be noted that the impedance of the fourth differential transmission line electrode of the pad portion 330 and the impedance of the first differential transmission line electrode of the electrode conversion portion 310 are generally not the same. Therefore, in this embodiment, the fifth differential transmission line electrode of the impedance transformation portion 340 is used to match the impedance between the fourth differential transmission line electrode of the pad portion 330 and the first differential transmission line electrode of the electrode conversion portion 310, which can effectively reduce the signal integrity problem caused by the impedance mismatch between the fourth differential transmission line electrode of the pad portion 330 and the first differential transmission line electrode of the electrode conversion portion 310. For example, assuming the impedance of the fourth differential transmission line electrode of the pad portion 330 is Z1 and the impedance of the first differential transmission line electrode of the electrode conversion portion 310 is Z2, then the fifth differential transmission line electrode of the impedance conversion portion 340 can gradually transition the impedance Z1 to the impedance Z2, thereby achieving impedance matching between the fourth differential transmission line electrode of the pad portion 330 and the first differential transmission line electrode of the electrode conversion portion 310.

[0049] In some embodiments, the pad portion 330 includes a first pad 331 and a second pad 332, which constitute a fourth differential transmission line electrode. The first pad 331 and the second pad 332 have the same shape and size, which can be determined according to the specific wire bonding or flip-chip configuration, and may be polygonal or circular, etc., without specific limitation here. In some embodiments, the impedance of the first pad 331 and the second pad 332 can be set between 65Ω and 70Ω, and can be appropriately set according to the actual application, without specific limitation here.

[0050] In some embodiments, the impedance transformation section 340 includes a first impedance transformation electrode 341 and a second impedance transformation electrode 342, which constitute a fifth differential transmission line electrode; a first pad 331 is connected to a first input electrode 311 through the first impedance transformation electrode 341, and a second pad 332 is connected to a second input electrode 312 through the second impedance transformation electrode 342; the pad section 330, the impedance transformation section 340, the electrode transformation section 310, and the optical modulation section 320 are arranged along the first direction, and the differential impedance of the fifth differential transmission line electrode gradually changes along the first direction.

[0051] In some embodiments, when the differential impedance of the fourth differential transmission line electrode (i.e., the impedance of the first pad 331 and the second pad 332) is greater than the differential impedance of the first differential transmission line electrode (i.e., the impedance of the first input electrode 311 and the second input electrode 312), the differential impedance of the fifth differential transmission line electrode (i.e., the impedance of the first impedance transformation electrode 341 and the second impedance transformation electrode 342) gradually decreases from large to small along the first direction; that is, the value of the differential impedance of the fifth differential transmission line electrode gradually decreases from the value of the differential impedance of the fourth differential transmission line electrode to the value of the differential impedance of the first differential transmission line electrode. In another embodiment, when the differential impedance of the fourth differential transmission line electrode is less than the differential impedance of the first differential transmission line electrode, the differential impedance of the fifth differential transmission line electrode gradually increases from small to large along the first direction; that is, the value of the differential impedance of the fifth differential transmission line electrode gradually increases from the value of the differential impedance of the fourth differential transmission line electrode to the value of the differential impedance of the first differential transmission line electrode. In this way, the impedance transformation unit 340 can achieve impedance matching between the fourth differential transmission line electrode and the first differential transmission line electrode, thereby reducing signal integrity problems caused by impedance mismatch.

[0052] refer to Figure 14 and Figure 15 As shown, Figure 14 yes Figure 13 Schematic diagram of the process section along the middle AA. Figure 15 yes Figure 13 A schematic diagram of the process cross-section along the BB axis. The differential electro-optic modulator 300 includes a semiconductor substrate 301, an oxide buried layer 302, a TFLN waveguide 303, an oxide upper cladding 304, a first modulation electrode 321, a second modulation electrode 322, a third modulation electrode 323, a pad electrode 305, a first electrode transition electrode 306, a second electrode transition electrode 307, an air bridge 317, a support portion 318, and an electrode window region 308. The TFLN waveguide 303 includes a first waveguide 324, a second waveguide 325, a beam splitter P1, and a beam combiner P2. Figure 14 In the diagram, pad electrode 305 corresponds to the second pad 332. Figure 14 The first electrode conversion unit electrode 306 in the middle corresponds to the second input electrode 312. Figure 14 The second electrode conversion section electrode 307 in the middle corresponds to the second output electrode 314.

[0053] The semiconductor substrate 301 can be made of quartz or silicon. An oxide buried layer 302, disposed above the semiconductor substrate 301, can be made of silicon dioxide (SiO2), and its thickness can be between 2 μm and 10 μm; this embodiment does not impose a specific limitation. A TFLN waveguide 303, disposed above the oxide buried layer 302, can have a thickness between 400 nm and 600 nm; this embodiment does not impose a specific limitation. An oxide overcladding layer 304, disposed above the TFLN waveguide 303, can be made of silicon dioxide (SiO2). The first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323 are disposed within the oxide cladding 304 and above the TFLN waveguide 303. They can be made of materials such as gold, silver, or conductive transparent oxides. The thickness of the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323 can be appropriately set according to actual application requirements, for example, it can be set to 1 μm. The oxide cladding 304 (also called the SiO2 buffer layer) located between the TFLN waveguide 303 and the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323 has a thickness between 100 nm and 800 nm to reduce the light absorption loss of the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323. The pad electrode 305, the first electrode conversion electrode 306, and the second electrode conversion electrode 307 are disposed on the same plane and within the oxide cladding 304. All three electrodes are spaced a certain distance from the TFLN waveguide 303 to avoid affecting the optical transmission loss of the TFLN waveguide 303. This distance can be appropriately set according to actual application requirements, for example, it can be greater than 800 nm. An air bridge 317 spans between the first electrode conversion electrode 306 and the second electrode conversion electrode 307 and can be made of gold. A support portion 318 is disposed between the air bridge 317 and the oxide cladding 304 and can be made of dielectric materials such as SiO2 or BCB. The thickness of this support portion 318 can be appropriately set according to actual application requirements, for example, it can be greater than 1 μm. The electrode window region 308 is a region cut out in the oxide cladding 304 corresponding to the position of each electrode, used to realize electrical connection between each electrode, such as for electrical connection between air bridge 317 and first electrode conversion part electrode 306, second electrode conversion part electrode 307, and for electrical connection between pad electrode 305 and external electrical chip, etc.

[0054] Reference Figure 16As shown in the embodiments of this application, an optical modulation system 1600 is also provided. This optical modulation system includes an electrical chip 1610 and a differential electro-optic modulator 300 as described in any of the preceding embodiments. The electrical chip 1610 includes a first output terminal 1611 and a second output terminal 1612. The first output terminal 1611 is connected to a first input electrode 311, and the second output terminal 1612 is connected to a second input electrode 312. The electrical chip 1610 is used to output a first modulation signal to the first input electrode 311 through the first output terminal 1611, and to output a second modulation signal to the second input electrode 312 through the second output terminal 1612. In some embodiments, the electrical chip 1610 can be a differential driver chip, so the first modulation signal and the second modulation signal can constitute a pair of differential signals. Specifically, the first modulation signal can be an S+ differential signal, in which case the second modulation signal is an S- differential signal; or, the first modulation signal can be an S- differential signal, in which case the second modulation signal is an S+ differential signal.

[0055] In the differential electro-optic modulator 300, the first input electrode 311 and the second input electrode 312 in the electrode switching section 310 constitute the first differential transmission line electrode, and the first output electrode 313, the second output electrode 314, and the third output electrode 315 constitute the second differential transmission line electrode. In the optical modulation section 320, the first modulation electrode 321 is connected to the first output electrode 313, the second modulation electrode 322 is connected to the second output electrode 314, and the third modulation electrode 323 is connected to the third output electrode 315. Furthermore, the first waveguide 324 in the optical modulation section 320 is located between the first modulation electrode 321 and the second modulation electrode 322, and the second waveguide 325 is located between the second modulation electrode 322 and the third modulation electrode 323. Therefore, in the optical modulation system 1600 of this application embodiment, there is no need to mount a DC blocking capacitor between the differential electro-optic modulator 300 and the electrical chip 1610 used for differential driving, which can have a wider operating bandwidth and thus broaden the bandwidth application range. Furthermore, the second input electrode 312 in the electrode conversion section 310 is connected to the second output electrode 314 via an air bridge 317 located above the connecting section 316. This reduces the parasitic capacitance generated inside the electrode conversion section 310, thereby mitigating the degrading effect of parasitic capacitance on the operating bandwidth of the differential electro-optic modulator 300. Moreover, since the air bridge 317 is located above the connecting section 316, it is not necessary to connect the second input electrode 312 and the second output electrode 314 inside the electrode conversion section 310. Therefore, it does not affect the routing of the first waveguide 324 and the second waveguide 325, thereby reducing the fabrication difficulty of the differential electro-optic modulator 300.

[0056] In some embodiments, such as Figure 16As shown, when the differential electro-optic modulator 300 further includes a pad portion 330 and an impedance transformation portion 340, the first output terminal 1611 is connected to the first input electrode 311 via the first pad 331 and the first impedance transformation electrode 341, and the second output terminal 1612 is connected to the second input electrode 312 via the second pad 332 and the second impedance transformation electrode 342. In this case, the output impedance of the electro-optic chip 1610 matches the impedance of the pad portion 330.

[0057] In some embodiments, the electrical chip 1610 and the differential electro-optic modulator 300 can be interconnected via wire bonding or flip-chip bonding. Specifically, the first output terminal 1611 and the first pad 331, and the second output terminal 1612 and the second pad 332 are interconnected via wire bonding; or, the first output terminal 1611 and the first pad 331, and the second output terminal 1612 and the second pad 332 are interconnected via flip-chip bonding.

[0058] In some embodiments, the optical modulation system 1600 further includes a resistor matching section 1620, which is connected to the optical modulation section 320 and is used to connect the optical modulation section 320 to an external power supply. In some embodiments, the resistor matching section 1620 may include a first resistor 1621, a second resistor 1622, and a third resistor 1623, wherein the first resistor 1621 is connected to the first modulation electrode 321 and is used to connect the first modulation electrode 321 to an external power supply; the second resistor 1622 is connected to the second modulation electrode 322 and is used to connect the second modulation electrode 322 to an external power supply; and the third resistor 1623 is connected to the third modulation electrode 323 and is used to connect the third modulation electrode 323 to an external power supply.

[0059] In some embodiments, the first resistor 1621, the second resistor 1622, and the third resistor 1623 in the resistor matching section 1620 can be used to reduce reflected radio frequency signals and to power on the power chip 1610. The resistance value of the first resistor 1621 is equal to the resistance value of the third resistor 1623, and is twice the resistance value of the second resistor 1622. For example, assuming the resistance value of the first resistor 1621 is R1, the resistance value of the second resistor 1622 is R2, and the resistance value of the third resistor 1623 is R3, then R1 = 2R2 = R3. The total resistance value of the first resistor 1621, the second resistor 1622, and the third resistor 1623 is equal to the impedance value of the optical modulation section 320, i.e., ZMod = R2 + R1 / / R3, where R1 / / R3 represents the parallel impedance of the first resistor 1621 and the third resistor 1623. An external power supply can power the electrical chip 1610 through the first resistor 1621, the second resistor 1622, and the third resistor 1623. Specifically, the external power supply is transmitted through the first resistor 1621, the second resistor 1622, and the third resistor 1623 to the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323, respectively. Then, it is transmitted to the first output electrode 313, the second output electrode 314, and the third output electrode 315, respectively. Next, it is transmitted to the first input electrode 311 and the second input electrode 312, and finally to the electrical chip 1610 through the first pad 331 and the second pad 332, thus powering the electrical chip 1610. It should be noted that the voltage value of the external power supply can be flexibly configured according to the power supply requirements of the electrical chip 1610; no specific limitation is made here.

[0060] In some embodiments, when the optical modulation system 1600 is working, the differential S+S- signal is input from the input side of the electrical chip 1610. After being linearly amplified by the electrical chip 1610, it is transmitted to the first pad 331 and the second pad 332 through the first output terminal 1611 and the second output terminal 1612. At this time, the amplified differential S+S- signal is transmitted to the optical modulation unit 320 through the pad part 330, the impedance transformation part 340, and the electrode conversion part 310 in sequence. At this time, the differential S+S- signal has been converted into a differential S-S+S- signal after being converted by the electrode conversion part 310. The S- signal is transmitted in the first modulation electrode 321 and the third modulation electrode 323, and the S+ signal is transmitted in the second modulation electrode 322. It should be noted that the polarity of the first modulation electrode 321, the second modulation electrode 322, and the third modulation electrode 323 in the optical modulation section 320 is not singular. It can be S-S+S- or S+S-S+. No specific limitation is made here. These two methods are not fundamentally different in the structural design of the differential electro-optic modulator. They are only related to the polarity of the differential signal on the input side of the electrical chip 1610.

[0061] Reference Figure 17 and Figure 18 As shown, Figure 17 This is a simulation result diagram of the S21 parameter of the electrode conversion unit provided in the embodiment of this application. Figure 18 This is a simulation result diagram of the S11 parameters of the electrode conversion section provided in the embodiment of this application. Specifically, when simulating the S21 and S11 parameters of the electrode conversion section, the differential impedance of the first and second input electrodes in the electrode conversion section is set to Z1 = 45Ω, the impedance of the first, second, and third output electrodes in the electrode conversion section is set to Z2 = 45Ω, the first angle between the air bridge and the first direction is θ1 = 0°, the second angle between the connecting part and the first direction is θ2 = 0°, and the support part below the air bridge is made of BCB material with a thickness of 6μm. Figure 17 and Figure 18 The graph shown can be seen as, with Figure 8 Compared with the related technical solutions shown, the solution provided in this application embodiment has better performance, specifically in the following aspects: in the frequency range of 0 to 200 GHz, the S21 loss is lower and there is no dip in the bandwidth; the S11 reflection is smaller, and the overall value is less than -20 dB.

[0062] In addition, this application embodiment also provides an integrated optical chip, which includes a laser and a differential electro-optic modulator 300 as in any of the preceding embodiments, wherein the laser is used to emit continuous light; the differential electro-optic modulator 300 is coupled to the laser, used to receive the continuous light emitted by the laser, and used to modulate the continuous light emitted by the laser and output modulated light.

[0063] In the differential electro-optic modulator 300, the first input electrode 311 and the second input electrode 312 in the electrode switching section 310 constitute the first differential transmission line electrode, and the first output electrode 313, the second output electrode 314, and the third output electrode 315 constitute the second differential transmission line electrode. In the optical modulation section 320, the first modulation electrode 321 is connected to the first output electrode 313, the second modulation electrode 322 is connected to the second output electrode 314, and the third modulation electrode 323 is connected to the third output electrode 315. Furthermore, the first waveguide 324 in the optical modulation section 320 is located between the first modulation electrode 321 and the second modulation electrode 322, and the second waveguide 325 is located between the second modulation electrode 322 and the third modulation electrode 323. Therefore, in the integrated optical chip of this application embodiment, the differential electro-optic modulator 300 can be driven by a differential driver, eliminating the need for mounting DC blocking capacitors, and thus achieving a wider operating bandwidth, thereby broadening the applicable bandwidth range. Furthermore, the second input electrode 312 in the electrode conversion section 310 is connected to the second output electrode 314 via an air bridge 317 located above the connecting section 316. This reduces the parasitic capacitance generated inside the electrode conversion section 310, thereby mitigating the degrading effect of parasitic capacitance on the operating bandwidth of the differential electro-optic modulator 300. Moreover, since the air bridge 317 is located above the connecting section 316, it is not necessary to connect the second input electrode 312 and the second output electrode 314 inside the electrode conversion section 310. Therefore, it does not affect the routing of the first waveguide 324 and the second waveguide 325, thereby reducing the fabrication difficulty of the differential electro-optic modulator 300.

[0064] The structural embodiments described above are merely illustrative, and the units described as separate components may or may not be physically separate. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0065] The above is a detailed description of the preferred embodiments of this application. However, this application is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this application. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A differential electro-optic modulator, characterized in that, include: An electrode conversion unit includes a first input electrode, a second input electrode, a first output electrode, a second output electrode, a third output electrode, a connecting part, and an air bridge. The second output electrode is located between the first output electrode and the third output electrode. The first input electrode is connected to the first output electrode and the third output electrode through the connecting part. The second input electrode is connected to the second output electrode through the air bridge, which is located above the connecting part. The first input electrode and the second input electrode constitute a first differential transmission line electrode, and the first output electrode, the second output electrode, and the third output electrode constitute a second differential transmission line electrode. An optical modulation section includes a first modulation electrode, a second modulation electrode, a third modulation electrode, a first waveguide, and a second waveguide. The second modulation electrode is located between the first modulation electrode and the third modulation electrode. The first waveguide is located between the first modulation electrode and the second modulation electrode. The second waveguide is located between the second modulation electrode and the third modulation electrode. The first modulation electrode is connected to the first output electrode. The second modulation electrode is connected to the second output electrode. The third modulation electrode is connected to the third output electrode. The first modulation electrode, the second modulation electrode, and the third modulation electrode constitute a third differential transmission line electrode.

2. The differential electro-optic modulator according to claim 1, characterized in that, The electrode conversion unit also includes a support unit disposed below the air bridge for supporting the air bridge.

3. The differential electro-optic modulator according to claim 1, characterized in that, The electrode conversion section and the optical modulation section are arranged along a first direction, the air bridge is arranged at a first angle to the first direction, and the connecting section is arranged at a second angle to the first direction.

4. The differential electro-optic modulator according to claim 1, characterized in that, The differential electro-optic modulator further includes a pad section and an impedance transformation section. The pad section is connected to the electrode conversion section through the impedance transformation section. The pad section is used to connect an external electrical chip, and the impedance transformation section is used to match the impedance between the pad section and the electrode conversion section.

5. The differential electro-optic modulator according to claim 4, characterized in that, The pad section includes a first pad and a second pad, which together form a fourth differential transmission line electrode; the impedance transformation section includes a first impedance transformation electrode and a second impedance transformation electrode, which together form a fifth differential transmission line electrode; the first pad is connected to the first input electrode through the first impedance transformation electrode, and the second pad is connected to the second input electrode through the second impedance transformation electrode. The pad portion, the impedance transformation portion, the electrode conversion portion, and the optical modulation portion are arranged along a first direction, and the differential impedance of the fifth differential transmission line electrode gradually changes along the first direction.

6. The differential electro-optic modulator according to claim 1, characterized in that, The first modulation electrode is provided with a first T-shaped track electrode, the second modulation electrode is provided with a second T-shaped track electrode, the first T-shaped track electrode and the second T-shaped track electrode are arranged opposite to each other, and the first waveguide is located between the first T-shaped track electrode and the second T-shaped track electrode; The second modulation electrode is further provided with a third T-shaped track electrode, and the third modulation electrode is provided with a fourth T-shaped track electrode. The third T-shaped track electrode and the fourth T-shaped track electrode are arranged opposite to each other, and the second waveguide is located between the third T-shaped track electrode and the fourth T-shaped track electrode.

7. An optical modulation system, characterized in that, Includes an electrical chip and a differential electro-optic modulator as described in any one of claims 1 to 6, wherein: The electrical chip includes a first output terminal and a second output terminal, wherein the first output terminal is connected to the first input electrode and the second output terminal is connected to the second input electrode; The electrical chip is used to output a first modulation signal to the first input electrode through the first output terminal, and to output a second modulation signal to the second input electrode through the second output terminal, wherein the first modulation signal and the second modulation signal constitute a pair of differential signals.

8. The optical modulation system according to claim 7, characterized in that, The optical modulation system further includes a resistor matching section, which is connected to the optical modulation section and is used to connect the optical modulation section to an external power supply.

9. The optical modulation system according to claim 8, characterized in that, The resistor matching section includes a first resistor, a second resistor, and a third resistor, wherein: The first resistor is connected to the first modulation electrode and is used to connect the first modulation electrode to an external power supply. The second resistor is connected to the second modulation electrode and is used to connect the second modulation electrode to an external power supply; The third resistor is connected to the third modulation electrode and is used to connect the third modulation electrode to an external power source.

10. An integrated optical chip, characterized in that, include: Lasers are used to emit continuous light; The differential electro-optic modulator as described in any one of claims 1 to 6 is coupled to the laser and is used to receive continuous light emitted by the laser and to output modulated light after modulating the continuous light emitted by the laser.

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