Film lithium niobate electro-optical modulator based on frequency domain equalizer

Abstract

The invention relates to a film lithium niobate electro-optical modulator based on a frequency domain equalizer. The film lithium niobate electro-optical modulator comprises a first 1 * 2 multi-mode interference coupler, a first homodromous modulation area, a second homodromous modulation area, a reverse modulation area and a second 1 * 2 multi-mode interference coupler, in the first same-direction modulation area, modulation of applying a first-direction electric field to an optical signal in the first same-direction modulation area in a push-pull manner through a first ground-signal-ground traveling wave electrode; in the second homonymous modulation area, modulation of applying a first direction electric field to the optical signal in the second homonymous modulation area through a second ground-signal-ground traveling wave electrode in a push-pull manner; and in the reverse modulation region, modulation of applying a second direction electric field to the optical signal in the reverse modulation region in a push-pull manner through a third ground-signal-ground traveling wave electrode. According to the invention, large electro-optical bandwidth can be realized without using a capacitive load traveling wave electrode and extra process conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of thin-film lithium niobate electro-optic modulators, and particularly to a thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer. Background Art

[0002] The demand for massive data communication in applications such as artificial intelligence, cloud services, and 5G has promoted the development of large-bandwidth and high-efficiency electro-optic (EO) modulators. According to existing reports, a thin-film lithium niobate (TFLN) modulator based on a capacitive load traveling wave electrode (CL-TWE) can achieve a single-wave transmission rate of 400 Gbps, which shows great potential in the field of high-speed optical communication. Due to the slow-wave effect of the capacitive load traveling wave electrode of the thin-film lithium niobate modulator with an ultra-large electro-optic bandwidth, special methods are required to achieve the matching of the electro-optic rate, such as using an LNOI wafer with a quartz substrate and a wet etching process to hollow out the substrate. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer, which can achieve a large electro-optic bandwidth without using a capacitive load traveling wave electrode and additional process conditions.

[0004] The technical solution adopted by the present invention to solve its technical problems is: to provide a thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer, including: a first 1×2 multimode interference coupler, a first co-directional modulation region, a second co-directional modulation region, a reverse modulation region, and a second 1×2 multimode interference coupler; the input end of the first 1×2 multimode interference coupler is connected to an input waveguide, and the output end is connected to the input end of the first co-directional modulation region; the output end of the first co-directional modulation region is connected to the input end of the second co-directional modulation region through a first bending region; the output end of the second co-directional modulation region is connected to the input end of the reverse modulation region through a second bending region; the output end of the reverse modulation region is connected to the input end of the second 1×2 multimode interference coupler; the output end of the second 1×2 multimode interference coupler is connected to an output waveguide;

[0005] In the first co-directional modulation region, a first ground-signal-ground traveling wave electrode is used to modulate the optical signal in the first co-directional modulation region by applying an electric field in a first direction in a push-pull manner; in the second co-directional modulation region, a second ground-signal-ground traveling wave electrode is used to modulate the optical signal in the second co-directional modulation region by applying an electric field in a first direction in a push-pull manner; in the reverse modulation region, a third ground-signal-ground traveling wave electrode is used to modulate the optical signal in the reverse modulation region by applying an electric field in a second direction in a push-pull manner; wherein, the first direction is the opposite direction of the second direction;

[0006] The transmission direction of the optical signal in the first co-directional modulation region is opposite to that of the optical signal in the second co-directional modulation region; the transmission direction of the optical signal in the first co-directional modulation region is the same as that of the optical signal in the reverse modulation region.

[0007] The first co-directional modulation region includes:

[0008] A first lithium niobate waveguide, the input end of which is connected to the first output port of the output end of the first 1×2 multimode interference coupler through an interlayer coupler, and the output end of which is connected to the input end of the first bent waveguide in the first bent region through an interlayer coupler;

[0009] A second lithium niobate waveguide, the input end of which is connected to the second output port of the output end of the first 1×2 multimode interference coupler through an interlayer coupler, and the output end of which is connected to the input end of the second bent waveguide in the first bent region through an interlayer coupler;

[0010] A first straight signal electrode, which is located between the first lithium niobate waveguide and the second lithium niobate waveguide, the starting end of which is connected to a radio frequency source, and the ending end of which is connected to the starting end of the first bent signal electrode in the first bent region;

[0011] A first ground electrode, which is located on the side of the first lithium niobate waveguide where the first straight signal electrode is not provided, and is connected to the first bent ground electrode in the first bent region;

[0012] A second ground electrode, which is located between the second lithium niobate waveguide and the third lithium niobate waveguide in the second co-directional modulation region;

[0013] The first ground electrode, the first straight signal electrode, and the second ground electrode form the first ground-signal-ground traveling wave electrode; the first bent waveguide and the second bent waveguide are made of the same material.

[0014] The first bent region includes:

[0015] A first bent waveguide, the input end of which is connected to the output end of the first lithium niobate waveguide in the first co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the third lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler;

[0016] A second bent waveguide, the input end of which is connected to the output end of the second lithium niobate waveguide in the first co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the fourth lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler;

[0017] The first bent signal electrode, with its starting end connected to the end of the first straight signal electrode in the first co-directional modulation region and its ending end connected to the starting end of the second straight signal electrode in the second co-directional modulation region;

[0018] The first bent ground electrode, arranged on the outside of the first bent signal electrode and connected to the first ground electrode in the first co-directional modulation region;

[0019] Wherein, the cross section between the first bent waveguide and the second bent waveguide is connected by a cross waveguide.

[0020] The distance between the first bent signal electrode and the second ground electrode in the first co-directional modulation region, and the distance between the first bent signal electrode and the first bent ground electrode remain unchanged; the widths of the first bent signal electrode, the first straight signal electrode in the first co-directional modulation region, and the second straight signal electrode in the second co-directional modulation region are the same.

[0021] The second co-directional modulation region includes:

[0022] The third lithium niobate waveguide, with its input end connected to the first bent waveguide in the first bent region through an interlayer coupler and its output end connected to the third bent waveguide in the second bent region through an interlayer coupler;

[0023] The fourth lithium niobate waveguide, with its input end connected to the second bent waveguide in the first bent region through an interlayer coupler and its output end connected to the fourth bent waveguide in the second bent region through an interlayer coupler;

[0024] The second straight signal electrode, located between the third lithium niobate waveguide and the fourth lithium niobate waveguide, with its starting end connected to the end of the first bent signal electrode in the first bent region and its ending end connected to the starting end of the second bent signal electrode in the second bent region;

[0025] The second ground electrode, located between the second lithium niobate waveguide in the first communication modulation region and the third lithium niobate waveguide;

[0026] The third ground electrode, located between the fourth lithium niobate waveguide and the fifth lithium niobate waveguide in the reverse modulation region;

[0027] The second ground electrode, the second straight signal electrode, and the third ground electrode form the second ground-signal-ground traveling wave electrode; the materials of the first bent waveguide, the second bent waveguide, and the third bent waveguide are the same; the materials of the first bent waveguide and the fourth bent waveguide are different.

[0028] The second bent region includes:

[0029] The third bent waveguide, the input end of which is connected to the output end of the third lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the sixth lithium niobate waveguide in the reverse modulation region through an interlayer coupler;

[0030] The fourth bent waveguide, the input end of which is connected to the output end of the fourth lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the fifth lithium niobate waveguide in the reverse modulation region through an interlayer coupler;

[0031] The second bent signal electrode, the starting end of which is connected to the end of the second straight signal electrode in the second co-directional modulation region, and the end of which is connected to the starting end of the third straight signal electrode in the reverse modulation region;

[0032] The second bent ground electrode is located outside the second bent signal electrode and is connected to the second ground electrode in the first co-directional region;

[0033] Wherein, there is no cross section between the third bent waveguide and the fourth bent waveguide.

[0034] The distance between the second bent signal electrode and the third ground electrode in the reverse modulation region, and the distance between the second bent signal electrode and the second bent ground electrode remain unchanged; the widths of the second bent signal electrode, the second straight signal electrode in the second co-directional modulation region, and the third straight signal electrode in the reverse modulation region are the same.

[0035] The reverse modulation region includes:

[0036] The fifth lithium niobate waveguide, the input end of which is connected to the fourth bent waveguide in the second bent region through an interlayer coupler, and the output end of which is connected to the first input port of the input end of the second 1×2 multimode interference coupler through an interlayer coupler;

[0037] The sixth lithium niobate waveguide, the input end of which is connected to the third bent waveguide in the second bent region through an interlayer coupler, and the output end of which is connected to the second input port of the input end of the second 1×2 multimode interference coupler through an interlayer coupler;

[0038] The third straight signal electrode is located between the fifth lithium niobate waveguide and the sixth lithium niobate waveguide, the starting end of which is connected to the end of the second bent signal electrode in the second bent region, and the end is provided with a terminal resistor connected to the fourth ground electrode;

[0039] The third ground electrode is located between the fourth lithium niobate waveguide in the second co-directional modulation region and the fifth lithium niobate waveguide;

[0040] The fourth ground electrode is located on the side of the sixth lithium niobate waveguide where the third straight signal electrode is not provided, and is respectively connected to the second bent ground electrode in the second bent region and the first bent ground electrode in the first bent region;

[0041] The third ground electrode, the third straight signal electrode, and the fourth ground electrode constitute the third ground-signal-ground traveling wave electrode.

[0042] The interlayer coupler is a silicon / silicon nitride / lithium niobate interlayer coupler.

[0043] A thermo-optic phase shifter is provided on the waveguide connected to one of the two input ports at the input end of the second 1×2 multimode interference coupler.

[0044] Beneficial effects

[0045] Due to the above technical solutions, compared with the prior art, the present invention has the following advantages and positive effects: The present invention constitutes a frequency domain equalizer through the electrode parts in the first co-directional modulation region, the second co-directional modulation region, and the reverse modulation region, thereby introducing a frequency domain equalizer into the thin film lithium niobate electro-optic modulator. Therefore, a large electro-optic bandwidth can be achieved without using capacitive load traveling wave electrodes and additional process conditions. Brief description of the drawings

[0046] Figure 1 is a schematic structural diagram of a thin film lithium niobate electro-optic modulator based on a frequency domain equalizer according to an embodiment of the present invention;

[0047] Figure 2 is a schematic electrode diagram of a thin film lithium niobate electro-optic modulator based on a frequency domain equalizer according to an embodiment of the present invention;

[0048] Figure 3 is a schematic optical device diagram of a thin film lithium niobate electro-optic modulator based on a frequency domain equalizer according to an embodiment of the present invention;

[0049] Figure 4 is a process diagram of the preparation of a thin film lithium niobate electro-optic modulator based on a frequency domain equalizer according to an embodiment of the present invention;

[0050] Figure 5 is a simulation result diagram of a thin film lithium niobate electro-optic modulator based on a frequency domain equalizer according to an embodiment of the present invention. Specific embodiments

[0051] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0052] Embodiments of the present invention relate to a thin-film lithium niobate electro-optic modulator based on a frequency-domain equalizer, as Figures 1 - 3 shown, including: a first 1×2 multimode interference coupler 1, a first co-directional modulation region 2, a second co-directional modulation region 3, a reverse modulation region 4, and a second 1×2 multimode interference coupler 5; the input end of the first 1×2 multimode interference coupler 1 is connected to the input waveguide 6, and the output end is connected to the input end of the first co-directional modulation region 2; the output end of the first co-directional modulation region 2 is connected to the input end of the second co-directional modulation region 3 through a first bending region 7; the output end of the second co-directional modulation region 3 is connected to the input end of the reverse modulation region 4 through a second bending region 8; the output end of the reverse modulation region 4 is connected to the input end of the second 1×2 multimode interference coupler 5; the output end of the second 1×2 multimode interference coupler 5 is connected to the output waveguide 9.

[0053] Among them, in the first co-directional modulation region 2, a first ground-signal-ground traveling-wave electrode modulates the optical signal in the first co-directional modulation region 2 in a push-pull manner to apply an electric field in the first direction; in the second co-directional modulation region 3, a second ground-signal-ground traveling-wave electrode modulates the optical signal in the second co-directional modulation region 3 in a push-pull manner to apply an electric field in the first direction; in the reverse modulation region 4, a third ground-signal-ground traveling-wave electrode modulates the optical signal in the reverse modulation region 4 in a push-pull manner to apply an electric field in the second direction; where the first direction is the opposite direction of the second direction.

[0054] The first co-directional modulation region 2 in this embodiment includes:

[0055] A first lithium niobate waveguide 21, the input end is connected to the first output port of the output end of the first 1×2 multimode interference coupler 1 through an interlayer coupler, and the output end is connected to the input end of the first bent waveguide 71 in the first bending region 7 through an interlayer coupler;

[0056] A second lithium niobate waveguide 22, the input end is connected to the second output port of the output end of the first 1×2 multimode interference coupler 1 through an interlayer coupler, and the output end is connected to the input end of the second bent waveguide 72 in the first bending region 7 through an interlayer coupler;

[0057] A first straight signal electrode 23, located between the first lithium niobate waveguide 21 and the second lithium niobate waveguide 22, the starting end is connected to the radio frequency source, and the ending end is connected to the starting end of the first bent signal electrode 73 in the first bending region 7;

[0058] The first ground electrode 24 is located on one side of the first lithium niobate waveguide 21 where the first straight signal electrode 23 is not provided, and is connected to the first bent ground electrode 74 of the first bent region 7;

[0059] The second ground electrode 25 is located between the second lithium niobate waveguide 22 and the third lithium niobate waveguide 31 in the second co-directional modulation region;

[0060] The first ground electrode 24, the first straight signal electrode 23, and the second ground electrode 25 form the first ground-signal-ground traveling wave electrode; the first bent waveguide 71 and the second bent waveguide 72 are made of the same material, both being silicon nitride bent waveguides.

[0061] The optical signal is input into the silicon waveguide through the first silicon coupler, and then is split by the first 1×2 multimode interference coupler 1. After splitting, the two beams of light respectively pass through their respective silicon / nitride / lithium niobate interlayer couplers, so that the light is input from the silicon waveguide into the first lithium niobate waveguide 21 and the second lithium niobate waveguide 22. The optical signals in the first lithium niobate waveguide 21 and the second lithium niobate waveguide 22 are modulated in a push-pull manner by the ground-signal-ground traveling wave electrode composed of the first ground electrode 24, the second ground electrode 25, and the first straight signal electrode 23. Among them, the RF source is input in the same direction as the optical signal in a single-ended push-pull manner in the RF source input region. After passing through the first co-directional modulation region, the electrical signal and the optical signal enter the first bent region 7.

[0062] The first bent region 7 in this embodiment includes:

[0063] The first bent waveguide 71, the input end of which is connected to the output end of the first lithium niobate waveguide 21 in the first co-directional modulation region 2 through an interlayer coupler, and the output end of which is connected to the input end of the third lithium niobate waveguide 31 in the second co-directional modulation region 3 through an interlayer coupler;

[0064] The second bent waveguide 72, the input end of which is connected to the output end of the second lithium niobate waveguide 22 in the first co-directional modulation region 2 through an interlayer coupler, and the output end of which is connected to the input end of the fourth lithium niobate waveguide 32 in the second co-directional modulation region 3 through an interlayer coupler;

[0065] The first bent signal electrode 73, the starting end of which is connected to the end of the first straight signal electrode 23 in the first co-directional modulation region 2, and the end of which is connected to the starting end of the second straight signal electrode 33 in the second co-directional modulation region 3;

[0066] The first bent ground electrode 74 is arranged outside the first bent signal electrode 73 and is connected to the first ground electrode 24 in the first co-directional modulation region 2;

[0067] Among them, the cross-section between the first bent waveguide 71 and the second bent waveguide 72 is connected by a cross waveguide.

[0068] In the first bending region, the propagation directions of both the electrical signal and the optical signal are reversed by 180°.

[0069] For the optical signal, the optical signals in the first lithium niobate waveguide 21 and the second lithium niobate waveguide 22 are modulated and then respectively input into the first silicon nitride bent waveguide 71 and the second silicon nitride bent waveguide 72 through their respective silicon nitride / lithium niobate interlayer couplers. The first silicon nitride bent waveguide 71 and the second silicon nitride bent waveguide 72 cross during the 180° bending process to keep the phase modulation directions of the lithium niobate waveguides consistent before and after the 180° bending by the signal electrodes. To reduce the loss and crosstalk of the cross, a silicon nitride cross waveguide is also used in the cross-section between the first silicon nitride bent waveguide 71 and the second silicon nitride bent waveguide 72. After passing through the first silicon nitride bent waveguide 71 and the second silicon nitride bent waveguide 72, the propagation direction of the optical signal changes by 180° (i.e., the propagation direction is reversed). The optical signals in the first silicon nitride bent waveguide 71 and the second silicon nitride bent waveguide 72 are respectively input into the second co-directional modulation region 3 through their respective silicon nitride / lithium niobate interlayer couplers.

[0070] For the electrical signal, the connection between the first bent signal electrode 73 and the first straight signal electrode 23 maintains the same width, and the first bent signal electrode 73 is bent by 180°. At this time, the propagation direction of the electrical signal changes by 180°. During the bending process, the distances between the first bent signal electrode 73 and the second ground electrode 25, and between the first bent signal electrode 73 and the first bent ground electrode 74 remain unchanged.

[0071] The second co-directional modulation region 3 in this embodiment includes:

[0072] A third lithium niobate waveguide 31, whose input end is connected to the first bent waveguide 71 in the first bending region 7 through an interlayer coupler, and whose output end is connected to the third bent waveguide 81 in the second bending region 8 through an interlayer coupler;

[0073] A fourth lithium niobate waveguide 32, whose input end is connected to the second bent waveguide 72 in the first bending region 7 through an interlayer coupler, and whose output end is connected to the fourth bent waveguide 82 in the second bending region 8 through an interlayer coupler;

[0074] A second straight signal electrode 33, located between the third lithium niobate waveguide 31 and the fourth lithium niobate waveguide 32, with its starting end connected to the end of the first bent signal electrode 73 in the first bending region 7, and its ending end connected to the starting end of the second bent signal electrode 83 in the second bending region 8;

[0075] The second ground electrode 25 is located between the second lithium niobate waveguide 22 of the first communication modulation region 2 and the third lithium niobate waveguide 31;

[0076] The third ground electrode 34 is located between the fourth lithium niobate waveguide 32 and the fifth lithium niobate waveguide 41 of the reverse modulation region 4;

[0077] The second ground electrode 25, the second direct signal electrode 33, and the third ground electrode 34 form the second ground-signal-ground traveling-wave electrode; the first bending waveguide 71, the second bending waveguide 72, and the third bending waveguide 81 are made of the same material; the first bending waveguide 71 and the fourth bending waveguide 82 are made of different materials.

[0078] In the second co-directional modulation region 3, for the optical signal, since the optical signal passes through the first bending region 7, the optical signal in the first lithium niobate waveguide 21 enters the third lithium niobate waveguide 31, and the optical signal in the second lithium niobate waveguide 22 enters the fourth lithium niobate waveguide 32. The direction of the electric field applied by the first direct signal electrode 23 to the first lithium niobate waveguide 21 is the same as the direction of the electric field applied by the second direct signal electrode 33 to the third lithium niobate waveguide 31. Compared with the first lithium niobate waveguide 31, the optical signal in the third lithium niobate waveguide 33 is co-directionally modulated. Similarly, the direction of the electric field applied by the first direct signal electrode 23 to the second lithium niobate waveguide 22 is the same as the direction of the electric field applied by the second direct signal electrode 33 to the fourth lithium niobate waveguide 32. Compared with the second lithium niobate waveguide 22, the optical signal in the fourth lithium niobate waveguide 32 is co-directionally modulated. Therefore, this region is called the second co-directional modulation region.

[0079] For the electrical signal, after passing through the first bending region 7, the electrical signal remains in the same propagation direction as the optical signal. The second ground-signal-ground traveling-wave electrode composed of the second direct signal electrode 33, the second ground electrode 25, and the third ground electrode 34 modulates the optical signals in the third lithium niobate waveguide 31 and the fourth lithium niobate waveguide 32 in a push-pull manner.

[0080] The second bending region 8 in this embodiment includes:

[0081] The third bending waveguide 81, the input end of which is connected to the output end of the third lithium niobate waveguide 31 of the second co-directional modulation region 3 through an interlayer coupler, and the output end of which is connected to the input end of the sixth lithium niobate waveguide 42 of the reverse modulation region 4 through an interlayer coupler;

[0082] The fourth bending waveguide 82, the input end of which is connected to the output end of the fourth lithium niobate waveguide 32 of the second co-directional modulation region 3 through an interlayer coupler, and the output end of which is connected to the input end of the fifth lithium niobate waveguide 41 of the reverse modulation region 4 through an interlayer coupler;

[0083] The second bent signal electrode 83 has its starting end connected to the end of the second straight signal electrode 33 in the second co-directional modulation region 3, and its ending end connected to the starting end of the third straight signal electrode 43 in the reverse modulation region 4;

[0084] The second bent ground electrode 84 is located outside the second bent signal electrode 83 and is connected to the second ground electrode 25 in the first co-directional region 2;

[0085] Among them, there is no intersection section between the third bent waveguide 81 and the fourth bent waveguide 82. The third bent waveguide 81 can be a silicon nitride bent waveguide, and the fourth bent waveguide 82 can be a silicon waveguide.

[0086] In the second bent region 8, for the optical signal, the modulated optical signal in the third lithium niobate waveguide 31 enters the third bent waveguide 81 through the silicon nitride / lithium niobate interlayer coupler. The modulated optical signal in the fourth lithium niobate waveguide 32 enters the fourth bent waveguide 82 through the third silicon / silicon nitride / lithium niobate interlayer coupler. The directions of the third bent waveguide 81 and the fourth bent waveguide 82 change by 180°, and the propagation directions of the optical signals in the third bent waveguide 81 and the fourth bent waveguide 82 also reverse by 180°. Subsequently, the optical signal in the third silicon bent waveguide 81 is input into the sixth lithium niobate waveguide 42 through the silicon nitride / lithium niobate coupler, and the optical signal in the fourth bent waveguide 82 is input into the fifth lithium niobate waveguide 41 through the silicon / silicon nitride / lithium niobate coupler.

[0087] For the electrical signal, the second bent signal electrode 83 is connected to the second straight signal electrode 33 while maintaining the width unchanged, and the second bent signal electrode 83 bends by 180°. At this time, the propagation direction of the electrical signal changes by 180°. During the bending process, the distances between the second bent signal electrode 83 and the third ground electrode 34, and between the second bent signal electrode 83 and the second bent ground electrode 84 remain unchanged.

[0088] The reverse modulation region 4 in this embodiment includes:

[0089] The fifth lithium niobate waveguide 41 has its input end connected to the fourth bent waveguide 82 in the second bent region 8 through an interlayer coupler, and its output end connected to the first input port of the input end of the second 1×2 multimode interference coupler 5 through an interlayer coupler;

[0090] The sixth lithium niobate waveguide 42 has its input end connected to the third bent waveguide 81 in the second bent region 8 through an interlayer coupler, and its output end connected to the second input port of the input end of the second 1×2 multimode interference coupler 5 through an interlayer coupler;

[0091] The third straight signal electrode 43 is located between the fifth lithium niobate waveguide 41 and the sixth lithium niobate waveguide 42. Its starting end is connected to the end of the second bent signal electrode 83 in the second bending region 8, and a terminal resistor is provided at the end, which is connected to the fourth ground electrode 44;

[0092] The third ground electrode 34 is located between the fourth lithium niobate waveguide 32 in the second co-modulation region 3 and the fifth lithium niobate waveguide 41;

[0093] The fourth ground electrode 44 is located on the side of the sixth lithium niobate waveguide 42 where the third straight signal electrode 43 is not provided, and is respectively connected to the second bent ground electrode 84 in the second bending region 8 and the first bent ground electrode 74 in the first bending region 7;

[0094] The third ground electrode 34, the third straight signal electrode 43, and the fourth ground electrode 74 constitute the third ground-signal-ground traveling wave electrode.

[0095] In the reverse modulation region 4, for the optical signal, since the optical signal passes through the second bending region 8, the optical signal in the third lithium niobate waveguide 31 enters the sixth lithium niobate waveguide 42, and the optical signal in the fourth lithium niobate waveguide 32 enters the fifth lithium niobate waveguide 41. The direction of the electric field applied by the third straight signal electrode 43 to the sixth lithium niobate waveguide 42 is opposite to the direction of the electric field applied by the second straight signal electrode 33 to the third lithium niobate waveguide 31. Compared with the third lithium niobate waveguide 31, the optical signal in the sixth lithium niobate waveguide 42 is reversely modulated. Similarly, the direction of the electric field applied by the third straight signal electrode 43 to the fifth lithium niobate waveguide 41 is opposite to the direction of the electric field applied by the second straight signal electrode 33 to the fourth lithium niobate waveguide 32. Compared with the fourth lithium niobate waveguide 32, the optical signal in the fifth lithium niobate waveguide 41 is reversely modulated. Therefore, this region is called the reverse modulation region. After reverse modulation, the optical signals in the fifth lithium niobate waveguide 41 and the sixth lithium niobate waveguide 42 are respectively re-input into two different silicon waveguides through their respective silicon / nitride / lithium niobate interlayer couplers. On one of the silicon waveguides, the silicon waveguide is heated and phase-shifted by a titanium nitride thermo-optic phase shifter to calibrate the operating point of the modulator. Finally, the optical signals in the two silicon waveguides are combined and output through the second 1×2 multimode interference coupler 5.

[0096] For the electrical signal, after passing through the second bending region 8, the electrical signal remains in the same propagation direction as the optical signal. The third ground-signal-ground traveling wave electrode composed of the third straight signal electrode 43, the third ground electrode 34, and the fourth ground electrode 44 modulates the optical signals in the fifth lithium niobate waveguide 41 and the sixth lithium niobate waveguide 42 in a push-pull manner. In this embodiment, the first ground electrode 24, the second ground electrode 25, the third ground electrode 34, and the fourth ground electrode 44 are connected to the same ground electrode. A titanium nitride chip termination resistor with an impedance equal to that of the traveling wave electrode is provided at the end of the third straight signal electrode 43, and the third straight signal electrode 43 is connected to the ground electrode through this termination resistor to reduce radio frequency reflection.

[0097] The thin-film lithium niobate electro-optic modulator based on the frequency domain equalizer of this embodiment can be prepared through the following steps, as Figure 4 shown below:

[0098] Step 1, fabricate a silicon pattern on a silicon-on-insulator wafer of a high-resistance silicon substrate;

[0099] Step 2, deposit silicon nitride and etch to fabricate a silicon nitride pattern;

[0100] Step 3, bond a lithium niobate wafer, and after bonding, grind and thin the lithium niobate wafer;

[0101] Step 4, etch the lithium niobate to form a lithium niobate ridge waveguide pattern;

[0102] Step 5, deposit metal traveling wave electrodes and titanium nitride.

[0103] For a 10 mm device (the length of the traveling wave electrode and the modulation arm is 30 mm), the EO S21 electro-optic bandwidth is 210 GHz, the insertion loss is 2.55 dB, and the driving voltage is 2.36 V. As Figure 5 shown, the thin-film lithium niobate electro-optic modulator based on the frequency domain equalizer ( Figure 5 the red curve in) has a much larger bandwidth improvement compared to the conventional thin-film lithium niobate electro-optic modulator ( Figure 5 the black curve in), has the potential to achieve a single-wave 800 Gbps transmission rate, and is expected to be applied to 3.2 T optical modules.

[0104] It is not difficult to find that the present invention constitutes a frequency domain equalizer through the electrode parts in the first co-directional modulation region, the second co-directional modulation region, and the reverse modulation region, thereby introducing a frequency domain equalizer into the thin-film lithium niobate electro-optic modulator. Therefore, without using a capacitive load traveling wave electrode and additional process conditions, a large electro-optic bandwidth can be achieved.

Claims

1. A thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer, characterized in that, Comprising: A first 1×2 multimode interference coupler, a first co-directional modulation region, a second co-directional modulation region, a reverse modulation region, and a second 1×2 multimode interference coupler; The input end of the first 1×2 multimode interference coupler is connected to the input waveguide, and the output end is connected to the input end of the first co-directional modulation region; the output end of the first co-directional modulation region is connected to the input end of the second co-directional modulation region through a first bending region; the output end of the second co-directional modulation region is connected to the input end of the reverse modulation region through a second bending region; the output end of the reverse modulation region is connected to the input end of the second 1×2 multimode interference coupler; the output end of the second 1×2 multimode interference coupler is connected to the output waveguide; In the first co-directional modulation region, a first ground-signal-ground traveling-wave electrode modulates the optical signal in the first co-directional modulation region by applying an electric field in the first direction in a push-pull manner; in the second co-directional modulation region, a second ground-signal-ground traveling-wave electrode modulates the optical signal in the second co-directional modulation region by applying an electric field in the first direction in a push-pull manner; in the reverse modulation region, a third ground-signal-ground traveling-wave electrode modulates the optical signal in the reverse modulation region by applying an electric field in the second direction in a push-pull manner; wherein, the first direction is the opposite direction of the second direction; The transmission direction of the optical signal in the first co-directional modulation region is opposite to the transmission direction of the optical signal in the second co-directional modulation region; the transmission direction of the optical signal in the first co-directional modulation region is the same as the transmission direction of the optical signal in the reverse modulation region.

2. The thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer according to claim 1, characterized in that, The first co-directional modulation region includes: A first lithium niobate waveguide, the input end of which is connected to the first output port of the output end of the first 1×2 multimode interference coupler through an interlayer coupler, And the output end is connected to the input end of the first bent waveguide in the first bending region through an interlayer coupler; A second lithium niobate waveguide, the input end of which is connected to the second output port of the output end of the first 1×2 multimode interference coupler through an interlayer coupler, And the output end is connected to the input end of the second bent waveguide in the first bending region through an interlayer coupler; A first straight signal electrode, located between the first lithium niobate waveguide and the second lithium niobate waveguide, the starting end of which is connected to a radio frequency source, and the ending end of which is connected to the starting end of the first bent signal electrode in the first bending region; A first ground electrode, located on the side of the first lithium niobate waveguide where the first straight signal electrode is not provided, and is connected to the first bent ground electrode in the first bending region; A second ground electrode, located between the second lithium niobate waveguide and the third lithium niobate waveguide in the second co-directional modulation region; The first ground electrode, the first straight signal electrode, and the second ground electrode form the first ground-signal-ground traveling-wave electrode; the first bent waveguide and the second bent waveguide are made of the same material.

3. The thin-film lithium niobate electro-optic modulator based on a frequency-domain equalizer according to claim 1, wherein, The first bending region includes: The first bent waveguide, the input end of which is connected to the output end of the first lithium niobate waveguide in the first co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the third lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler; The second bent waveguide, the input end of which is connected to the output end of the second lithium niobate waveguide in the first co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the fourth lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler; The first bent signal electrode, the starting end of which is connected to the end of the first straight signal electrode in the first co-directional modulation region, and the end of which is connected to the starting end of the second straight signal electrode in the second co-directional modulation region; The first bent ground electrode, which is arranged outside the first bent signal electrode and is connected to the first ground electrode in the first co-directional modulation region; Wherein, a cross-section between the first bent waveguide and the second bent waveguide is connected by a cross waveguide.

4. The thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer according to claim 3, wherein The distance between the first bent signal electrode and the second ground electrode in the first co-directional modulation region, and the distance between the first bent signal electrode and the first bent ground electrode remain unchanged; the width of the first bent signal electrode, the width of the first straight signal electrode in the first co-directional modulation region, and the width of the second straight signal electrode in the second co-directional modulation region are the same.

5. The thin-film lithium niobate electro-optic modulator based on a frequency-domain equalizer according to claim 1, characterized in that, The second co-directional modulation region includes: The third lithium niobate waveguide, the input end of which is connected to the first bent waveguide in the first bent region through an interlayer coupler, and the output end of which is connected to the third bent waveguide in the second bent region through an interlayer coupler; The fourth lithium niobate waveguide, the input end of which is connected to the second bent waveguide in the first bent region through an interlayer coupler, and the output end of which is connected to the fourth bent waveguide in the second bent region through an interlayer coupler; The second straight signal electrode, which is located between the third lithium niobate waveguide and the fourth lithium niobate waveguide, the starting end of which is connected to the end of the first bent signal electrode in the first bent region, and the end of which is connected to the starting end of the second bent signal electrode in the second bent region; The second ground electrode, which is located between the second lithium niobate waveguide in the first communication modulation region and the third lithium niobate waveguide; The third ground electrode, which is located between the fourth lithium niobate waveguide and the fifth lithium niobate waveguide in the reverse modulation region; the second ground electrode, the second straight signal electrode, and the third ground electrode form the second ground-signal-ground traveling wave electrode; the materials of the first bent waveguide, the second bent waveguide, and the third bent waveguide are the same; the materials of the first bent waveguide and the fourth bent waveguide are different.

6. The thin-film lithium niobate electro-optic modulator based on a frequency-domain equalizer according to claim 1, wherein The The second bent region includes: The third bent waveguide, the input end of which is connected to the output end of the third lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the sixth lithium niobate waveguide in the reverse modulation region through an interlayer coupler; The fourth bent waveguide, the input end of which is connected to the output end of the fourth lithium niobate waveguide in the second co-directional modulation region through an interlayer coupler, and the output end of which is connected to the input end of the fifth lithium niobate waveguide in the reverse modulation region through an interlayer coupler; The second bent signal electrode, with its starting end connected to the end of the second straight signal electrode in the second co-directional modulation region, and its end connected to the starting end of the third straight signal electrode in the reverse modulation region; The second bent ground electrode, located outside the second bent signal electrode and connected to the second ground electrode in the first co-directional region; Wherein, there is no cross-section between the third bent waveguide and the fourth bent waveguide.

7. The thin-film lithium niobate electro-optic modulator based on a frequency-domain equalizer according to claim 6, wherein The distance between the second bent signal electrode and the third ground electrode in the reverse modulation region, and the distance between the second bent signal electrode and the second bent ground electrode remain unchanged; the widths of the second bent signal electrode, the second straight signal electrode in the second co-directional modulation region, and the third straight signal electrode in the reverse modulation region are the same.

8. The thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer according to claim 1, characterized in that, The reverse modulation region includes: The fifth lithium niobate waveguide, with its input end connected to the fourth bent waveguide in the second bent region through an interlayer coupler, and its output end connected to the first input port of the input end of the second 1×2 multimode interference coupler through an interlayer coupler; The sixth lithium niobate waveguide, with its input end connected to the third bent waveguide in the second bent region through an interlayer coupler, and its output end connected to the second input port of the input end of the second 1×2 multimode interference coupler through an interlayer coupler; The third straight signal electrode is located between the fifth lithium niobate waveguide and the sixth lithium niobate waveguide, with its starting end connected to the end of the second bent signal electrode in the second bent region, and its end provided with a termination resistor connected to the fourth ground electrode; The third ground electrode is located between the fourth lithium niobate waveguide in the second co-directional modulation region and the fifth lithium niobate waveguide; The fourth ground electrode is located on the side of the sixth lithium niobate waveguide where the third straight signal electrode is not provided, and is respectively connected to the second bent ground electrode in the second bent region and the first bent ground electrode in the first bent region; The third ground electrode, the third straight signal electrode, and the fourth ground electrode form the third ground-signal-ground traveling-wave electrode.

9. The thin-film lithium niobate electro-optic modulator based on a frequency-domain equalizer according to any one of claims 2-8, characterized in that, The interlayer coupler is a silicon / nitride / silicon-lithium niobate interlayer coupler.

10. The thin-film lithium niobate electro-optic modulator based on a frequency domain equalizer according to claim 1, characterized in that, A thermo-optic phase shifter is provided on the waveguide connected to one of the two input ports of the input end of the second 1×2 multimode interference coupler.

Images