CN112835214A - Lithium niobate thin film electro-optical modulator - Google Patents
Lithium niobate thin film electro-optical modulator Download PDFInfo
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 111
- 239000010409 thin film Substances 0.000 title claims abstract description 89
- 230000003287 optical effect Effects 0.000 claims abstract description 60
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- 239000000463 material Substances 0.000 claims description 18
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- 238000004806 packaging method and process Methods 0.000 claims description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 9
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 claims description 6
- 239000010453 quartz Substances 0.000 claims description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 4
- 239000011521 glass Substances 0.000 claims description 4
- 239000003292 glue Substances 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- 239000010703 silicon Substances 0.000 claims description 4
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052594 sapphire Inorganic materials 0.000 claims description 3
- 239000010980 sapphire Substances 0.000 claims description 3
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 3
- 239000002210 silicon-based material Substances 0.000 claims description 2
- 239000000835 fiber Substances 0.000 claims 2
- 230000009286 beneficial effect Effects 0.000 abstract description 6
- 238000005452 bending Methods 0.000 description 6
- 239000010408 film Substances 0.000 description 6
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
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- 239000004065 semiconductor Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
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- Crystallography & Structural Chemistry (AREA)
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- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
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Abstract
The invention discloses a lithium niobate thin film electro-optical modulator, wherein the input end and the output end of a lithium niobate thin film optical waveguide are arranged on the bottom edge of a chip of the lithium niobate thin film electro-optical modulator, and the input end and the output end of the lithium niobate thin film optical waveguide are respectively connected with an optical waveguide in a modulation area by adopting a 90-degree bent optical waveguide. And secondly, the connection between the coplanar traveling wave electrode in the modulation region and the electrode input port or the electrode output port only passes through a section of transition electrode without a 90-degree turning transition electrode. The innovative structure can place the input optical fiber and the output optical fiber on the bottom edge of the tube shell of the electro-optical modulator to further reduce the length of the electro-optical modulator, and can reduce the microwave signal loss caused by a 90-degree turning transition electrode in a traveling wave electrode, thereby being beneficial to improving the modulation bandwidth of the electro-optical modulator.
Description
Technical Field
The invention can be applied to the technical fields of optical fiber communication, optical fiber sensing, microwave photonics, quantum communication and the like, and particularly relates to a lithium niobate thin-film electro-optic modulator.
Background
The optical modulator is widely applied to the technical fields of optical fiber communication, optical fiber sensing, microwave photonics, quantum communication and the like, is a core photoelectric component in a photoelectric module, and is used for realizing the key functions of loading an electric signal on an optical signal and carrying out low-loss transmission by using an optical fiber. The external modulator utilizing the lithium niobate crystal linear electro-optic effect principle has the outstanding advantages of low chirp coefficient, high modulation bandwidth, high switch extinction ratio and the like, and has important application in an optical fiber signal transmission system.
The lithium niobate electro-optical modulator chip manufactured by adopting the traditional technical scheme on the lithium niobate blocky body material has the advantages of good stability, low optical insertion loss, mature manufacturing process and the like. With the continuous improvement of the requirements of the optical fiber signal transmission system on the performance of the photoelectric module such as miniaturization, low power consumption, high reliability and the like, the disadvantages of the traditional lithium niobate electro-optical modulator in the aspects of volume, power consumption and the like restrict the application of the lithium niobate electro-optical modulator in the new technology of the optical fiber communication system.
In recent years, with the maturity of large-size and high-quality lithium niobate thin-film materials, the lithium niobate thin-film electro-optic modulator chip manufactured on a lithium niobate thin-film wafer by using a CMOS (complementary metal oxide semiconductor) process has the characteristics that the optical waveguide refractive index difference is large, the optical waveguide size is small, the microwave refractive index is low, the characteristic impedance is high and the like, which are obviously superior to the traditional lithium niobate electro-optic modulator chip. The characteristics can realize the obvious reduction of the device length and the half-wave voltage of the lithium niobate thin film electro-optic modulator chip and the great improvement of the modulation bandwidth.
However, whether the electro-optical modulator is made of a conventional lithium niobate bulk material or a novel lithium niobate thin-film material, the basic structures of the chip and the device are the schematic structures as shown in fig. 1, that is:
(a) the optical fibers are respectively arranged on the left side and the right side of the chip of the electro-optical modulator and are coupled and bonded with the optical waveguide structure in the chip to form an input end or an output end of an optical signal of the electro-optical modulator;
(b) after the optical fiber penetrates out of the left side and the right side of the tube shell of the electro-optical modulator, a sheath structure is generally required to be manufactured so as to protect the optical fiber and improve the mechanical reliability of an optical fiber port;
(c) in order to facilitate the connection of the traveling wave electrode and the radio frequency connector, an electrode input port and an electrode output port on the electro-optical modulator chip are respectively positioned at the bottom edge of the electro-optical modulator chip, so that a 90-degree turning transition structure is needed to be used for respectively connecting the coplanar waveguide electrode in the modulation region with the electrode input port and the electrode output port.
Therefore, the traditional lithium niobate electro-optical modulator structure design scheme is adopted, and the problems that the structure is based on a lithium niobate blocky material or a lithium niobate thin film material are as follows:
(a) because the input optical fiber or the output optical fiber needs to be placed on the left side or the right side of the electro-optical modulator chip and the device, and the port of the device tube shell needs to use the sheath to protect the optical fiber, the total length of the lithium niobate electro-optical modulator is increased, and the miniaturization of the device is not facilitated;
(b) the 90-degree turning transition electrode on the chip of the electro-optical modulator inevitably increases microwave signal loss, such as transmission loss and bending loss, and is not beneficial to realizing high modulation bandwidth of the electro-optical modulator.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a lithium niobate thin-film electro-optical modulator, which is innovative in that: firstly, the input end and the output end of the lithium niobate thin-film optical waveguide are placed at the bottom edge of the lithium niobate thin-film electro-optical modulator chip, and the input end and the output end of the lithium niobate thin-film optical waveguide are respectively connected with the optical waveguide in the modulation area by adopting the 90-degree bent optical waveguide. And secondly, the connection between the coplanar traveling wave electrode in the modulation region and the electrode input port or the electrode output port only passes through a section of transition electrode without a 90-degree turning transition electrode.
The innovative structure can place the input optical fiber and the output optical fiber on the bottom edge of the electro-optical modulator tube shell to further reduce the length of the electro-optical modulator, and can reduce the microwave signal loss caused by a 90-degree turning transition electrode in the traveling wave electrode, thereby being beneficial to improving the modulation bandwidth of the electro-optical modulator.
In order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows:
a lithium niobate thin film electro-optic modulator comprising: the device comprises a substrate wafer, a lithium niobate thin film substrate, an optical waveguide, a buffer layer thin film, a traveling wave electrode, a crystal carrier block, an optical fiber, a micro-strip circuit ceramic plate, a matching resistance ceramic plate, a packaging tube shell and a radio frequency connector;
the optical waveguide comprises an input end straight waveguide, a 90-degree bent waveguide, a modulation region waveguide and an output end straight waveguide, wherein the input end straight waveguide and the output end straight waveguide are respectively arranged at the bottom edge of the lithium niobate thin film substrate and are respectively connected with the modulation region waveguide through the 90-degree bent waveguide;
the traveling wave electrode comprises an input end electrode, a transition area electrode, a modulation area electrode and an output end electrode, wherein the input end electrode and the output end electrode are respectively arranged on the left side and the right side of the lithium niobate thin film substrate and are respectively connected with the modulation area electrode through the transition area electrode;
and the crystal carrier block with the optical fiber is coupled and bonded with the input end straight waveguide and the output end straight waveguide, and penetrates out of a port at the bottom edge of a packaging tube shell of the lithium niobate thin-film electro-optic modulator.
In a preferred embodiment, the substrate wafer provides mechanical support for the lithium niobate thin film substrate, and the material of the substrate wafer is any one of lithium niobate, lithium tantalate, silicon, quartz and sapphire.
In a preferred embodiment, the thickness of the substrate wafer 1 can be selected from 0.2mm to 2 mm.
In a preferred embodiment, the lithium niobate thin film substrate is placed on a substrate wafer, and the lithium niobate material constituting the lithium niobate thin film substrate is an optical grade crystal with single crystal quality, the tangential direction of the crystal is X-cut, and the thickness is 0.1 μm to 10 μm.
In a preferred embodiment, the optical waveguide is fabricated in a lithium niobate thin film substrate, the modulation region waveguide is a mach-zehnder intensity modulator optical waveguide, and the mach-zehnder intensity modulator optical waveguide includes: the input end Y-branch waveguide, the double-arm straight waveguide for realizing the electro-optic modulation function and the output end Y-branch waveguide;
the input end straight waveguide is vertical to the bottom edge of the lithium niobate thin film substrate, and the light wave is transmitted from the bottom edge of the lithium niobate thin film substrate to the middle part along the waveguide structure;
a section of 90-degree bent waveguide is arranged between the input end straight waveguide and the input end Y-branch waveguide and used for connecting the two sections of optical waveguide structures;
the input end Y-branch waveguide is used for realizing the beam splitting of light waves and is respectively connected with two arms of the double-arm straight strip waveguide, and the double-arm straight strip waveguide is used for realizing electro-optic modulation;
the tail end of the double-arm straight waveguide is connected with the Y-branch waveguide at the output end and is used for combining light waves transmitted in the double-arm straight waveguide;
the other section of 90-degree bent waveguide is arranged between the output end Y-branch waveguide and the output end straight waveguide and is used for guiding the light beam into the output end straight waveguide;
the straight waveguide at the output end is perpendicular to the bottom edge of the lithium niobate thin film substrate, and the light waves are transmitted from the middle part of the lithium niobate thin film substrate to the bottom edge along the waveguide structure.
In a preferred embodiment, the thickness of the travelling wave electrode is between 0.1 μm and 30 μm.
In a preferred embodiment, each section of the input terminal electrode, the transition region electrode, the output terminal electrode and the modulation region electrode is a group of coplanar waveguide electrode structures composed of 2 Ground electrodes (Ground) and 1 Signal electrode (Signal); the signal electrodes in the modulation region electrodes are placed in the middle of the double-arm straight waveguide, and the 2-branch ground electrodes are respectively placed on the outer sides of the double-arm straight waveguide, so that a push-pull electrode structure is formed.
In a preferred embodiment, the buffer layer thin film is placed above the lithium niobate thin film substrate and used for isolating the traveling wave electrode placed right above the optical waveguide, the thickness of the buffer layer thin film is 0.1 μm to 2 μm, and the thin film material is silicon oxide or aluminum oxide.
In a preferred embodiment, the crystal carrier block is made of one of lithium niobate, lithium tantalate, glass, quartz and silicon materials, and is provided with a groove or a circular hole for placing the optical fiber.
In a preferred embodiment, the optical fiber is a single-mode non-polarization-maintaining optical fiber or a single-mode polarization-maintaining optical fiber, and is fixed in the circular hole or the groove of the crystal carrier block by using ultraviolet curing glue.
Compared with the prior art, the invention has the beneficial effects that:
(1) the optical waveguide structure provided by the invention can change the placement position of the optical fiber from the left side and the right side of the traditional lithium niobate electro-optic modulator into the bottom edge, can obviously reduce the length of the lithium niobate electro-optic modulator, and is very beneficial to the miniaturization of devices;
(2) the optical waveguide structure provided by the invention can save a 90-degree bent transition electrode in a traveling wave electrode, reduce microwave loss caused by electrode bending and is beneficial to further increasing the modulation bandwidth of the electro-optical modulator.
Drawings
FIG. 1: the structure of the traditional electro-optical modulator based on the X-cut lithium niobate blocky material or the lithium niobate thin film is shown schematically;
FIG. 2-1: the invention provides a structural schematic diagram of an optical waveguide in a lithium niobate thin film electro-optic modulator chip;
FIG. 2-2: the invention provides a cross section schematic diagram of a modulation region in a lithium niobate thin film electro-optic modulator chip;
FIGS. 2 to 3: the invention provides a complete structure schematic diagram of a lithium niobate thin film electro-optic modulator;
in the figure, the names corresponding to the respective marks are: 1. a substrate wafer; 2. a lithium niobate thin film substrate; 3. An optical waveguide; 3-1, input end straight waveguide; 3-2, 90 ° curved waveguides; 3-3, modulation region waveguide; 3-3-1, an input end Y-branch waveguide; 3-3-2, double-arm straight waveguide; 3-3-3, an output end Y-branch waveguide; 3-4, output end straight waveguide; 4. a buffer layer film; 5. a traveling wave electrode; 5-1, input terminal electrode; 5-2, transition region electrodes; 5-3, an output end electrode; 5-4, 90 ° bend transition electrodes; 5-5, modulation region electrodes; 6. a crystal carrier; 7. an optical fiber; 8. a microstrip circuit ceramic board; 9. matching a resistive ceramic plate; 10. packaging the tube shell; 11. A radio frequency connector.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when used in this specification the singular forms "a", "an" and/or "the" include "specify the presence of stated features, steps, operations, elements, or modules, components, and/or combinations thereof, unless the context clearly indicates otherwise.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The principle of the lithium niobate thin film electro-optical modulator provided by the invention is as follows:
titanium diffusion or annealing proton exchange technology is mostly adopted for manufacturing the optical waveguide on the traditional lithium niobate bulk material crystal, and the refractive index difference of the formed optical waveguide is generally in the order of 0.01, so that the bending loss of the optical waveguide is large when the bending radius is small. In an integrated optical device, in order to reduce the bending loss of an optical waveguide, the refractive index difference of a waveguide structure is often selected to be increased so as to improve the constraint capacity of the optical waveguide on optical wave energy and reduce the leakage of the optical wave energy. Different from the optical waveguide in the lithium niobate material, the refractive index difference of the optical waveguide in the lithium niobate film can reach 0.7-1.2, and the constraint capacity to the optical wave energy is much higher than that of the optical waveguide in the lithium niobate material, so that the optical waveguide structure with small bending radius can be manufactured.
For reference and comparison, fig. 1 shows a schematic diagram of a conventional electro-optic modulator based on X-cut lithium niobate bulk material or thin film.
In the conventional structure, the substrate wafer 1 is a lithium niobate wafer, and the input end straight waveguide and 3-1 and the output end straight waveguide 3-5 are respectively placed on the left side and the right side of the substrate wafer 1 and are respectively coupled and bonded with the crystal carrier block 6 on which the optical fiber 7 is placed. The optical fibers 7 are led out from the left and right sides of the package 10, respectively.
In the traditional structure, an input end electrode 5-1 and an output end electrode 5-3 are respectively arranged at the bottom edge of a substrate wafer 1 and are connected with a modulation electrode 5-3 through a 90-degree bent transition electrode 5-4. The radio frequency connector 11 is arranged at the bottom edge of the packaging tube shell and is connected with the input terminal electrode 5-1 through the microstrip circuit ceramic board 8.
Fig. 2 shows a lithium niobate thin-film electro-optical modulator provided by the present invention, which includes: the chip comprises a substrate wafer 1, a lithium niobate thin film substrate 2, an optical waveguide 3, a buffer layer thin film 4, a traveling wave electrode 5, a crystal carrier block 6, an optical fiber 7, a micro-strip circuit ceramic plate 8, a matching resistance ceramic plate 9, a packaging shell 10 and a radio frequency connector 11.
An input end straight waveguide 3-1 and an output end straight waveguide 3-5 in the optical waveguide 3 are respectively arranged at the bottom edge of the lithium niobate thin film substrate 2, instead of the left side and the right side in the traditional lithium niobate electro-optical modulator chip structure, and are respectively connected with the modulation region waveguide 3-3 through a 90-degree bent waveguide 3-2. An input end electrode 5-1 and an output end electrode 5-3 in the traveling wave electrode 5 are respectively arranged on the left side and the right side of the lithium niobate thin film substrate 2 and are respectively connected with the modulation region electrode 5-3 through a transition region electrode 5-2. And the crystal carrier block 6 provided with the optical fiber 7 is coupled and bonded with the input end straight waveguide 3-1 and the output end straight waveguide 3-5 and penetrates out of a port at the bottom edge of the packaging tube shell 10 of the lithium niobate thin film electro-optic modulator.
The substrate wafer 1 can provide mechanical support for the lithium niobate thin film substrate 2, and the material of the substrate wafer can be any one of lithium niobate, lithium tantalate, silicon, quartz, sapphire and the like. The thickness of the substrate wafer 1 can be selected to be 0.2mm to 2mm, and considering that the crystal carrier 5 is usually selected to be a glass round tube with a diameter of 1.8mm, the thickness of the substrate wafer 1 is preferably 1 mm.
The lithium niobate thin film substrate 2 is placed on the substrate wafer 1, and the lithium niobate material forming the lithium niobate thin film substrate 2 is an optical grade crystal with single crystal quality, the tangential direction of the crystal is X-cut, and the thickness is 0.1-10 μm. The crystal tangent direction of the lithium niobate thin film substrate 2 is preferably X-cut Y-transfer in consideration of utilizing the maximum electro-optic coefficient of lithium niobate crystal.
The optical waveguide 3 is manufactured in the lithium niobate thin film substrate 2, and an optical waveguide structure capable of locally restricting light beams can be formed by adopting process methods such as local doping, local coating, ridge waveguide etching and the like. The optical waveguide 3 includes: the optical waveguide comprises an input end straight waveguide 3-1, a 90-degree bent waveguide 3-2 connected with the input end straight waveguide, a Mach-Zehnder intensity modulator optical waveguide, a 90-degree bent waveguide 3-2 connected with an output end straight waveguide and an output end straight waveguide 3-4.
Wherein the Mach-Zehnder intensity modulator optical waveguide includes: an input end Y-branch waveguide 3-3-1, a double-arm straight waveguide 3-3-2 for realizing electro-optic modulation function, and an output end Y-branch waveguide 3-3-3.
The input end straight waveguide 3-1 is vertical to the bottom edge of the lithium niobate thin film substrate 2, and the light wave is transmitted from the bottom edge of the lithium niobate thin film substrate 2 to the middle part along the waveguide structure;
the 90-degree bent waveguide 3-2 is arranged between the input end straight waveguide 3-1 and the input end Y-branch waveguide 3-3-1 and is used for connecting the two sections of optical waveguide structures;
the input end Y-branch waveguide 3-3-1 is used for realizing the beam splitting of light waves and is respectively connected with two arms of the double-arm straight waveguide 3-3-2, and the double-arm straight waveguide 3-3-2 is used for realizing the electro-optic modulation;
the tail end of the double-arm straight strip waveguide 3-3-2 is connected with the output end Y-branch waveguide 3-3-3 and used for combining light waves transmitted in the double-arm straight strip waveguide 3-3-2;
the other section of 90-degree bent waveguide 3-2 is arranged between the output end Y branch waveguide 3-3-3 and the output end straight waveguide 3-4 and used for guiding light beams into the output end straight waveguide 3-4;
the output end straight waveguides 3-4 are perpendicular to the bottom edge of the lithium niobate thin film substrate 2, and the light waves are transmitted from the middle part of the lithium niobate thin film substrate 2 to the bottom edge along the waveguide structure.
The traveling wave electrode 5 is in a coplanar waveguide structure. The traveling-wave electrode 5 includes: the device comprises an input end electrode 5-1, a transition region electrode 5-2, an output end electrode 5-3 and a modulation region electrode 5-5, wherein each section of electrode is a group of coplanar waveguide electrode structures consisting of 2 Ground electrodes (Ground) and 1 Signal electrode (Signal). The thickness of the travelling wave electrode 4 is 0.1 to 30 μm.
The input end electrode 5-1 and the output end electrode 5-3 are respectively arranged on the left side and the right side of the lithium niobate thin film substrate 2, but not on the bottom of the traditional lithium niobate electro-optical modulator chip structure, and are respectively connected with the modulation area electrode 5-5 through the transition area electrode 5-2.
The input end electrode 5-1, the transition region electrode 5-2, the output end electrode 5-3 and the modulation region electrode 5-5 are all of coplanar waveguide structures;
wherein, a signal electrode in the modulation region electrode 5-5 is arranged in the middle of the double-arm straight waveguide 3-3-2, and 2 ground electrodes are respectively arranged at the outer sides of the double-arm straight waveguide 3-3-2 to form a push-pull electrode structure;
wherein, the width of the signal electrode in the modulation area electrode 5-3 is 10 μm to 100 μm, the distance between the right edge of the signal electrode in the modulation area electrode 5-3 and the left edge of the right side ground electrode is 10 μm to 30 μm, and the distance between the left edge of the signal electrode in the modulation area electrode 5-3 and the right edge of the left side ground electrode is 10 μm to 30 μm;
wherein, the width of the signal electrode in the input end electrode 5-1 and the output end electrode 5-3 is not less than the width of the signal electrode in the modulation electrode 5-3;
a section of transition region electrode 5-2 is respectively arranged among the input end electrode 5-1, the output end electrode 5-3 and the modulation electrode 5-3, and is used for realizing the transition from the electrode structure size of the input end electrode 5-1, the electrode structure size of the output end electrode 5-3 to the electrode structure size of the modulation electrode 5-3 and the transition of characteristic impedance in each part of the electrode structure;
if the width of the signal electrode of the input end electrode 5-1 and the width of the signal electrode of the output end electrode 5-3 are larger than the width of the signal electrode of the modulation electrode 5-3, the signal electrode of the transition area electrode 5-2 adopts a conical structure, namely the width of the signal electrode is linearly widened from the width of the signal electrode of the modulation electrode 5-3 to the width of the signal electrode of the input end electrode 5-1 and the width of the signal electrode of the output end electrode 5-3;
if the width of the signal electrode of the input end electrode 5-1 and the width of the signal electrode of the output end electrode 5-3 are equal to the width of the signal electrode of the modulation electrode 5-3, the width of the signal electrode of the transition area electrode 5-2 is consistent with the width of the signal electrode of the modulation electrode 5-3;
different from the traveling wave electrode structure in the traditional lithium niobate electro-optical modulator chip, the traveling wave electrode 5 in the invention does not contain a 90-degree bent electrode.
The buffer layer film 4 is arranged above the lithium niobate film substrate 2 and used for isolating the traveling wave electrode 5 arranged right above the optical waveguide 3 and avoiding the light energy absorption of the traveling wave electrode 5 on the optical waveguide 3. The thickness of the buffer layer film 4 is 0.1-2 μm, and the film material is silicon oxide or aluminum oxide.
The crystal carrying block 6 can be one of lithium niobate, lithium tantalate, glass, quartz, silicon and other materials, and is provided with a groove with a shape of a round hole or a square groove, a semicircular groove, a V-shaped groove and the like for placing an optical fiber. The optical fiber 7 is a single-mode non-polarization-maintaining optical fiber or a single-mode polarization-maintaining optical fiber and is fixed in a circular hole or a groove of the crystal carrying block 6 by using ultraviolet curing glue. After polishing, the crystal carrier block 6 penetrated with the optical fiber 7 is respectively bonded with the input end straight waveguide 3-1 and the output end straight waveguide 3-4 by using ultraviolet curing glue, and the optical fiber 7 is led out from the packaging tube shell 10 to form an input port and an output port of light waves.
The micro-strip circuit ceramic plate 8 is arranged between the radio frequency connector 11 on the packaging tube shell 10 and the input end electrode 5-1 of the traveling wave electrode 5 and is used for realizing the input of microwave signals.
The matching resistance ceramic plate 9 is arranged at the output end electrode 5-3 of the traveling wave electrode 5 and used for absorbing microwave signals.
The lithium niobate thin-film electro-optical modulator is only an embodiment of the invention, and the scheme can be applied to a strength modulator and is also applicable to other types of lithium niobate thin-film electro-optical modulators, such as a phase modulator, a polarization controller, a polarization switch, a polarization scrambler, an optical switch, a QPSK modulator and the like. In the structure of the lithium niobate thin-film electro-optic modulator described in the embodiment of the present invention, the structure of the present invention can be used regardless of the presence or absence of the buffer layer thin film.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A lithium niobate thin film electro-optic modulator, comprising: the device comprises a substrate wafer (1), a lithium niobate thin film substrate (2), an optical waveguide (3), a buffer layer thin film (4), a traveling wave electrode (5), a crystal carrier block (6), an optical fiber (7), a micro-strip circuit ceramic plate (8), a matching resistance ceramic plate (9), a packaging tube shell (10) and a radio frequency connector (11);
the optical waveguide (3) comprises an input end straight waveguide (3-1), a 90-degree bent waveguide (3-2), a modulation region waveguide (3-3) and an output end straight waveguide (3-4), wherein the input end straight waveguide (3-1) and the output end straight waveguide (3-5) are respectively placed on the bottom edge of the lithium niobate thin film substrate (2) and are respectively connected with the modulation region waveguide (3-3) through the 90-degree bent waveguide (3-2);
the traveling wave electrode (5) comprises an input end electrode (5-1), a transition area electrode (5-2), a modulation area electrode (5-5) and an output end electrode (5-3), wherein the input end electrode (5-1) and the output end electrode (5-3) are respectively arranged on the left side and the right side of the lithium niobate thin film substrate (2) and are respectively connected with the modulation area electrode (5-3) through the transition area electrode (5-2);
and the crystal carrier block (6) provided with the optical fiber (7) is coupled and bonded with the input end straight waveguide (3-1) and the output end straight waveguide (3-5), and the optical fiber (7) penetrates out from a port at the bottom edge of a packaging tube shell (10) of the lithium niobate thin-film electro-optic modulator.
2. The lithium niobate thin film electro-optic modulator of claim 1,
the substrate wafer (1) provides mechanical support for the lithium niobate thin film substrate (2), and the material of the substrate wafer is any one of lithium niobate, lithium tantalate, silicon, quartz and sapphire.
3. The lithium niobate thin film electro-optic modulator of claim 2, wherein the thickness of the substrate wafer 1 is selected from 0.2mm to 2 mm.
4. The lithium niobate thin-film electro-optical modulator according to claim 1, wherein the lithium niobate thin-film substrate (2) is placed on a substrate wafer (1), and the lithium niobate material constituting the lithium niobate thin-film substrate (2) is an optical-grade crystal having a single crystal quality, a crystal tangent of which is an X-cut, and a thickness of which is 0.1 μm to 10 μm.
5. The lithium niobate thin film electro-optic modulator of claim 1,
the optical waveguide (3) is manufactured in a lithium niobate thin film substrate (2), the modulation region waveguide (3-3) is a Mach-Zehnder intensity modulator optical waveguide, and the Mach-Zehnder intensity modulator optical waveguide comprises: an input end Y-branch waveguide (3-3-1), a double-arm straight waveguide (3-3-2) for realizing electro-optic modulation function, and an output end Y-branch waveguide (3-3-3);
the input end straight waveguide (3-1) is vertical to the bottom edge of the lithium niobate thin film substrate (2), and the light wave is transmitted from the bottom edge of the lithium niobate thin film substrate (2) to the middle part along the waveguide structure;
a section of 90-degree bent waveguide (3-2) is arranged between the input end straight waveguide (3-1) and the input end Y-branch waveguide (3-3-1) and used for connecting the two sections of optical waveguide structures;
the input end Y-branch waveguide (3-3-1) is used for realizing the beam splitting of light waves and is respectively connected with two arms of the double-arm straight waveguide (3-3-2), and the double-arm straight waveguide (3-3-2) is used for realizing electro-optic modulation;
the tail end of the double-arm straight strip waveguide (3-3-2) is connected with the output end Y-branch waveguide (3-3-3) and used for combining light waves transmitted in the double-arm straight strip waveguide (3-3-2);
the other section of 90-degree bent waveguide (3-2) is arranged between the output end Y-branch waveguide (3-3-3) and the output end straight waveguide (3-4) and used for guiding light beams into the output end straight waveguide (3-4);
the straight waveguide (3-4) at the output end is vertical to the bottom edge of the lithium niobate thin film substrate (2), and the light wave is transmitted from the middle part of the lithium niobate thin film substrate (2) to the bottom edge along the waveguide structure.
6. The lithium niobate thin-film electro-optic modulator according to claim 1, wherein the traveling wave electrode (5) has a thickness of 0.1 μm to 30 μm.
7. The lithium niobate thin-film electro-optic modulator according to claim 1, wherein each section of the input electrode (5-1), the transition region electrode (5-2), the output electrode (5-3) and the modulation region electrode (5-5) is a group of coplanar waveguide electrode structures consisting of 2 ground electrodes and 1 signal electrode; wherein, the signal electrode in the modulation region electrode (5-5) is arranged in the middle of the double-arm straight waveguide (3-3-2), and the 2-branch ground electrodes are respectively arranged at the outer sides of the double-arm straight waveguide (3-3-2) to form a push-pull electrode structure.
8. The lithium niobate thin film electro-optic modulator of claim 1,
the buffer layer thin film (4) is arranged above the lithium niobate thin film substrate (2) and used for isolating the traveling wave electrode (5) arranged right above the optical waveguide (3), the thickness of the buffer layer thin film (4) is 0.1-2 mu m, and the thin film material is silicon oxide or aluminum oxide.
9. The lithium niobate thin-film electro-optic modulator according to claim 1, wherein the crystal carrier block (6) is one of lithium niobate, lithium tantalate, glass, quartz, and silicon material, and has a groove or a circular hole for placing an optical fiber.
10. The lithium niobate thin-film electro-optic modulator according to claim 1, wherein the optical fiber (7) is a single-mode non-polarization-maintaining fiber or a single-mode polarization-maintaining fiber, and is fixed in the groove or the circular hole of the crystal carrier block (6) by using ultraviolet curing glue.
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