CN116009292A - Polarization independent electro-optic modulator based on thin film lithium niobate multimode waveguide - Google Patents
Polarization independent electro-optic modulator based on thin film lithium niobate multimode waveguide Download PDFInfo
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Abstract
The invention discloses a polarization-independent electro-optic modulator based on a thin film lithium niobate multimode waveguide, which comprises a silicon substrate layer, an oxygen-buried layer, a lithium niobate layer and a metal electrode positioned on the lithium niobate layer. The X-cut thin film based lithium niobate layer comprises an input and output straight waveguide, an input and output end mode converter, a multimode beam splitter, a multimode waveguide phase shift arm and a multimode beam combiner. When TE is 0 When a mode is input from any input straight waveguide, the modulation principle is the same as that of a traditional Mach-Zehnder electro-optic modulator; and TE (TE) 0 Modulo the same transmission path, when TM 0 When the mode is input, the mode is converted into a first-order transverse electric mode (TE) through an input end mode converter 1 Mode, implementing TE through multimode beam splitter 1 Mode 3dB beam splitting, modulation in multimode waveguide phase shift arm, interference output via multimode beam combiner, and final conversion to TM via output mode converter 0 And (5) outputting a module. The invention effectively expands the electro-optic modulationThe application range of the light modulator solves the modulation problem of light with different polarization modes.
Description
Technical Field
The invention relates to the field of integrated optoelectronic devices, in particular to a polarization independent electro-optic modulator based on a thin film lithium niobate multimode waveguide.
Background
Electro-optic modulator technology is a modulation technique that superimposes an electrical signal carrying information on a carrier light wave. The light modulation can change certain parameters of the light wave, such as amplitude, frequency, phase, polarization state, duration and the like, according to a certain rule. Electro-optic modulators are realized by the electro-optic Effect of materials, wherein the refractive index change of a material based on the Pockels Effect (Pockels Effect) is proportional to the electric field, the coefficient of which is related to the electro-optic coefficient of the material.
The lithium niobate material has the advantages of high electro-optic coefficient and low loss in C wave band, and is the preferred material for electro-optic modulator. Meanwhile, the problems of small waveguide refractive index difference of the traditional lithium niobate material are solved by the occurrence of the lithium niobate thin film and the breakthrough of the etching technology, stronger mode restriction can be realized, and the method is a solution of a next generation photon integrated circuit. The modulator based on the thin film lithium niobate material has great application value in the future optical communication field as a next generation modulator with low modulation voltage, high modulation bandwidth and low insertion loss.
The current electro-optical modulator basically modulates the TE fundamental mode, and the polarization state of the light wave needs to be strictly controlled from the beginning of the light wave passing through the grating input device, so that the interference of light in other polarization modes on the required TE polarized light is prevented, the modulation efficiency and the modulation signal quality are affected, and the light wave in other polarization states cannot be effectively utilized.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention discloses a polarization independent electro-optic modulator based on a thin film lithium niobate multimode waveguide. Through analysis from the optical electromagnetic wave theory level, the modulator structure is designed and optimized, so that light waves in TM or TE polarization states can be effectively utilized and modulated, the problem of polarization control is solved, and the application range of the electro-optical modulator is widened.
In order to achieve the above object, the present invention adopts the following structure:
a polarization independent electro-optic modulator based on a thin film lithium niobate multimode waveguide comprises a silicon substrate layer, an oxygen buried layer, a lithium niobate layer and a metal layer which are sequentially laminated from bottom to top; forming a thin film lithium niobate optical waveguide on the X-cut lithium niobate layer by an etching technology, wherein the thin film lithium niobate optical waveguide comprises an input straight waveguide, an input end mode converter, a multimode beam splitter, a first S-bend waveguide, a multimode waveguide phase shift arm, a second S-bend waveguide, a multimode beam combiner, an output end mode converter and an output straight waveguide which are connected in sequence; the multimode waveguide phase shift arm is provided with a metal traveling wave electrode, and the metal traveling wave electrode comprises: the metal traveling wave signal electrodes of the periodically arranged T-shaped structure metal electrodes are respectively connected to two sides of the silicon substrate, the metal traveling wave grounding electrodes of the periodically arranged T-shaped structure metal electrodes are respectively connected to one side of the silicon substrate, and a cavity is formed by etching part of the silicon substrate. Specifically, the metal traveling wave signal electrodes, of which two sides are respectively connected with a group of periodically arranged T-shaped structure metal electrodes, are positioned between two arms of the multimode waveguide phase shift arm, and the two metal traveling wave grounding electrodes, of which one side is connected with a group of periodically arranged T-shaped structure metal electrodes, are positioned outside the two arms of the multimode waveguide phase shift arm, so that the whole Mach-Zehnder modulation structure is symmetrically arranged.
In a further embodiment, the input and output mode converters are identical in structure, enabling a narrower end TM 0 Die and wider end TE 1 Mode interconversion with TE 0 The die remains unchanged. Narrower end waveguide width W of the mode converter 1 Less than TM 0 Mode and TE 1 Mode hybridization width of mode and support TE 0 ，TM 0 A mode. The wider end waveguide width W of the mode converter 2 Greater than TM 0 Mode and TE 1 Mode hybridization width. Length L of mode converter 1 Determined by mode evolution theory to achieve narrower-end TM 0 Die and wider end TE 1 Complete coupling of the modes.
In a further embodiment, the multimode beam splitter has the same structure as the multimode beam combiner, and is composed of a 2×2 multimode interference structure and two groups of input/output gradual taper, wherein the width W of the multimode interference structure 4 And length L 3 Determined by multimode dry self-imaging theory, when TE 0 Or TE (TE) 1 When the mode is input from one port, TE can be realized simultaneously 0 Or TE (TE) 1 3dB splitting of the mode. The tail end width W of the input/output gradual change cone 2 And W is 5 Greater than TM 0 Mode and TE 1 Mode hybridization width, avoiding mode conversion of light through gradual taper.
In a further embodiment, the modulator material is selected from thin film lithium niobate, including a silicon substrate layer, an oxygen-buried layer, a lithium niobate layer and a metal electrode above the lithium niobate layer, which are sequentially stacked from bottom to top, and the upper cladding layer may be selected from a material with a smaller refractive index, such as air. The T-structure metal electrode, the metal traveling wave grounding electrode and the metal traveling wave signal electrode are all made of gold.
In a further embodiment, the multimode waveguide phase shift arms on two sides of the metal traveling wave signal electrode are ridge multimode waveguides, and two ends of the multimode waveguide phase shift arm are connected with the S-bend waveguide through a gradual taper, so that TE is achieved 0 Mode and TE 1 The dies are transferred adiabatically, respectively. Lithium niobate below electrodes on two sides of the multimode waveguide phase shift arm is not etched, so that metal absorption loss is reduced.
In a further embodiment, the modulation region portion has a width W of the multimode waveguide phase shift arm 6 Requiring computational optimization to guarantee for TE 0 Mode and TE 1 When the light of the modes is modulated, half-wave voltages of the two modes can be equal, and the width is as small as possible, so that the simultaneous high-efficiency modulation of different polarized lights is realized.
In a further embodiment, in the modulation area part, structural parameters of a metal traveling wave electrode containing a T-structure metal electrode and a multimode waveguide phase shift arm are optimized by using full-wave three-dimensional electromagnetic simulation software for analyzing microwave engineering problems based on an electromagnetic field finite element method, so that TE is realized 0 Mode and TE 1 The mode realizes lower microwave and light wave loss at the same time, lower half-wave voltage, and the refractive index of the microwave group is designed to be between that of the multimode waveguide TE by adopting partial etching of the silicon substrate 0 Mode and TE 1 And in the middle of the refractive indexes of the mode groups, the refractive index mismatch of the microwave and the optical wave is reduced, so that the two modes simultaneously achieve larger electro-optic bandwidth modulation. The metal traveling wave electrode is a gold electrode and comprises two thicknesses, wherein the first is a T-structure metal electrode with the thickness of 200nm and the second is a metal traveling wave grounding electrodeThe thickness of the electrode and the metal traveling wave signal main electrode is 1.1 mu m.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a polarization independent electro-optic modulator based on a thin film lithium niobate multimode waveguide by utilizing the electro-optic effect of the thin film lithium niobate crystal and the principle that a plurality of transverse electric modes of the multimode waveguide can be modulated simultaneously. When TE is 0 When a mode is input from any input straight waveguide, the modulation principle is the same as that of a Mach-Zehnder electro-optic modulator on a traditional X-cut film lithium niobate platform; when TM 0 When the mode is input, the mode is converted into TE through the mode converter at the input end 1 Mode, implementing TE through multimode beam splitter 1 Mode 3dB beam splitting, modulating the mode in the multimode waveguide phase shift arm, interfering output via multimode beam combiner, and converting to TM via output mode converter 0 And (5) outputting a module. Therefore, the invention can realize simultaneous modulation of TE polarization and TM polarization light, provides a new scheme for realizing the polarization-independent electro-optical modulator, effectively expands the application range of the electro-optical modulator and solves the modulation problem of light with different polarization modes.
Drawings
FIG. 1 is a schematic diagram of the overall structure of a polarization independent electro-optic modulator based on a thin film lithium niobate multimode waveguide in accordance with the present invention;
FIG. 2 is a graph of the equivalent refractive index change for different modes as a function of waveguide width.
FIG. 3 is a TE having a wavelength of 1.55. Mu.m 0 Light field transmission patterns when light is input at the narrower end of the mode converter in the invention.
FIG. 4 is a TM pattern with a wavelength of 1.55. Mu.m 0 Light is converted to TE in the present invention at the narrower end input of the mode converter 1 And a light field transmission diagram of mode output.
FIG. 5 is a TE having a wavelength of 1.55. Mu.m 0 Light field transmission diagram of light at the input of the multimode beam splitter in the invention.
FIG. 6 is a TE having a wavelength of 1.55. Mu.m 0 Spectral output of light at the input of the multimode beam splitter in the present invention.
FIG. 7 is a TM pattern with a wavelength of 1.55. Mu.m 0 The light is converted into TE by the mode converter in the invention 1 Light field patterns transmitted at the multimode beam splitter after mode.
FIG. 8 is a TE having a wavelength of 1.55. Mu.m 1 Spectral output of light at the input of the multimode beam splitter in the present invention.
FIG. 9 is a schematic cross-sectional view of a modulation region according to the present invention.
FIG. 10 is a graph of the light field distribution at static voltage and RF mode field at 100GHZ calculated by COMSOL and HFSS simulations.
Fig. 11 is a graph of the characteristic impedance of the traveling wave electrode calculated by simulation in the present invention, with the dashed line being the 50 ohm position.
FIG. 12 is a graph showing the results of simulated calculation of refractive index of a modulator microwave group according to the present invention, with dashed lines representing multimode waveguide TE 0 Mode and TE 1 Group refractive index of the mode light waves.
FIG. 13 shows a simulated calculated modulator TE according to the present invention 0 Mode and TE 1 And (5) a modular electro-optic bandwidth result graph.
In the figure, 1, an input straight waveguide, 2, an input end mode converter, 3, an input gradual change cone of a multimode beam splitter, 4, an output gradual change cone of the multimode beam splitter, 5, a multimode beam splitter, 6, a first S-bend waveguide, 7, an input gradual change cone of a multimode waveguide phase shift arm, 8, a multimode waveguide phase shift arm, 9, a metal traveling wave ground electrode, 10, a metal traveling wave signal electrode, 11, an output gradual change cone of a multimode waveguide phase shift arm, 12, a second S-bend waveguide, 13, an input gradual change cone of a multimode beam combiner, 14, a multimode beam combiner, 15, an output gradual change cone of the multimode beam combiner, 16, an output end mode converter, 17, an output straight waveguide, 18, a T-structure metal electrode, 19, a small hole, 20, a lithium niobate layer, 21, a buried oxide layer, 22, a silicon substrate layer and 23.
Detailed Description
The invention is further illustrated in the following figures and examples.
Example 1
Referring to fig. 1, a schematic overall structure of a polarization independent electro-optical modulator based on a thin film lithium niobate multimode waveguide is shown, wherein a platform of the modulator is an X-cut thin film lithium niobate, and the input straight waveguide 1, the output straight waveguide 17, the input mode converter 2, and the output mode converter are describedThe device 16, the multimode beam splitter 5, the first S curved waveguide 6, the second S curved waveguide 12, the input gradual taper 7 of the multimode waveguide phase shift arm, the output gradual taper 11 of the multimode waveguide phase shift arm, the multimode waveguide phase shift arm 8 and the multimode beam combiner 14 can be etched on a thin film lithium niobate platform by using an inductive coupling plasma etching technology after exposure by electron beams or photoetching, and the metal electrode comprises a metal traveling wave grounding electrode 9 and a metal traveling wave signal electrode 10, and can be obtained by coating a film by an electron beam evaporation mode. When TM 0 When a mode is input from a certain port, it is converted into TE by the input mode converter 2 1 Mode, TE is realized through multimode beam splitter 5 1 Mode 3dB beam splitting; when TE is 0 When the modes are input from the same port, the modes are kept unchanged through the input end mode converter 2, and 3dB beam splitting is completed in the same multimode beam splitter 5. In the modulation region, a metal traveling wave grounding electrode 9 is positioned outside two arms of the multimode waveguide phase shift arm 8, a metal traveling wave signal electrode 10 is positioned between the two arms of the multimode waveguide phase shift arm 8, and TE 0 Mode and TE 1 The direction of the mode electric field is the same as the direction of the optical axis of the lithium niobate, and according to the electro-optic effect of the lithium niobate, the refractive index of the lithium niobate crystal can be changed by changing the voltage on the electrode, thereby the transmitted TE 0 Mode and TE 1 The phases of the analog optical wave signals are effectively modulated at the same time. Phase modulated TE 0 Mode and TE 1 The mode optical wave signal is interferometrically output at the multimode combiner 14, wherein TE 1 The mode is converted to TM by the output mode converter 16 0 Mould, TE 0 The mode remains unchanged.
Referring to fig. 9, all etched waveguide structures in the present invention use a high refractive index material thin film lithium niobate as a core layer, the thickness of the thin film lithium niobate layer 20 is 400nm, the etching depth is 200nm, an air low refractive index upper cladding layer and a buried oxide layer 21 with a thickness of 3 μm are adopted, and the substrate is a silicon substrate 22. The selected thin film lithium niobate is X-cut lithium niobate, and the waveguide direction is Y-axis direction of lithium niobate.
The working principle of the invention is TE 0 Or TM 0 Mode light from width w 1 Input straight waveguide (1) input of =0.8μm, transmitted to input mode converter 2, te 0 Mode is maintained constant and low loss transmission in input mode converter 2, while TM 0 The mode light is converted into TE by the input mode converter 2 1 The mode is retransmitted to the multimode beam splitter 5. As can be seen from the change of the equivalent refractive index of the different modes according to the change of the waveguide width in FIG. 2, the width w 0 Near =1.25 [ mu ] m, TM 0 Mode and TE 1 Mode hybridization occurs, and the width of the input end of the mode converter is selected from the left to the right at the position to be w 1 =0.8μm, output width w 2 =2.5 [ mu ] m, select length L 1 =300 μm satisfies TM 0 Mode and TE 1 Conversion of the modes is efficient. TE (TE) 0 Or TE (TE) 1 The mode is split into 3dB by the multimode beam splitter 5, and the width of the other side of the input gradual change cone 3 on the multimode beam splitter 5 is w 3 =2.8 [ mu ] m, length L 2 =50μm, width of multimode interference structure w 4 =8μm, long L 3 =169.5 μm to achieve lower insertion loss of the multimode beam splitter 5. Multimode interference structure output width and w on multimode beam splitter 3 The same, its output gradually changing cone 4 output width w 5 =1.5 μm, the width selection needs to be greater than the mode hybridization width w 0 Length L 4 =200 μm to achieve adiabatic transfer. TE (TE) 0 Or TE (TE) 1 The mode light is transmitted again by a first S-bend waveguide 6 of width 1.5 μm and then passes through a length L 5 =250μm, width from w 5 Gradual change of =1.5 [ mu ] m to w 6 An input taper 7 of the multimode waveguide phase shift arm of =2.35 μm enters the multimode waveguide phase shift arm 8. The width of the metal traveling wave grounding electrode 9 is 223 mu m, the width of the metal traveling wave signal electrode 10 is 73 mu m, the length of the metal traveling wave grounding electrode and the signal electrode is 0.8cm, the height of the metal traveling wave electrode is 1.1 mu m, the height of the T-structure metal electrode 18 is 200nm, and the etching removal depth w is carried out from the small hole 19 between the T-structure metal electrodes 18 9 Silicon substrate=28 μm to achieve refractive index matching. The width of the multimode waveguide 8 between the metallic traveling wave ground and the signal electrode is w 6 =2.35 [ mu ] m, the width is defined by TE 0 Or TE (TE) 1 The mode is determined by the condition that the modes have the same half-wave voltage. The distance w between the T-shaped metal electrodes 18 on two sides of the multimode waveguide 8 =4.6 μm, waveguide to T-structure metal electrode 18Distance w 7 =1.125 μm. The length of the part from the T-structure metal electrode 18 to the metal traveling wave main electrode is h=19 mu m, the width is t=5 mu m, the length of the T-structure metal electrode 18 in a state parallel to the straight waveguide is r=47 mu m, the width is s=3 mu m, the distance between the two T-structure metal electrodes 18 on the same side is c=3 mu m, and the length of the small hole 19 between the T-structure metal electrodes 18 is l=36 mu m, and the width is w=13 mu m. The microwave signal is applied to one end of the metal traveling wave electrode, and is transmitted in the same direction as the light propagation direction, and the other end of the metal traveling wave electrode is externally connected with a 50 ohm load. Modulated TE 0 Or TE (TE) 1 The light of the modes is interfered by a multimode combiner 14 connected by a second S-bend waveguide 12 to output, TE 0 Or TE (TE) 1 Mode re-passes through the output mode converter 16 and the output straight waveguide 17 to TE 0 Or TM 0 And (5) mode output.
Numerical simulation of optical waves by time domain finite difference method (Finite Difference Time Domain, FDTD), FIG. 3 shows the design at TE 0 When light having a mode and a wavelength of 1.55 μm is inputted, the transmission efficiency is 99.97% in the case of the electric field amplitude distribution of light transmission in the input side mode converter 2. FIG. 4 shows the design at TM 0 When light having a mode and a wavelength of 1.55 μm is inputted, the mode conversion efficiency is 99.91% in the case of the electric field amplitude distribution of light transmission in the input side mode converter 2. FIG. 5 shows the design at TE 0 The electric field amplitude distribution of the light transmission in the multimode beam splitter 5 at the input of the light having a mode and a wavelength of 1.55 μm. FIG. 6 shows the design TE 0 The spectral response of the two port outputs when the mode light is input to the multimode beam splitter 5, the peak insertion loss is-3.03 dB, and the two port output deviation is 0.003dB. FIG. 7 shows the design at TM 0 When light with a mode and a wavelength of 1.55 μm is input, the light is converted into TE by the input end mode converter 2 1 After the mode, the electric field amplitude distribution of the light transmission in the multimode beam splitter 5. FIG. 8 shows the design TE 1 The spectral response of the two port outputs when the mode light is input to the multimode beam splitter 5, the peak insertion loss is-3.07 dB, and the two port output deviation is 0.089dB.
The invention uses the electromagnetic wave, frequency domain (ewfd) interface and HFSS electromagnetic simulation of COMSOL softwareThe simulation of the modulation region photoelectric performance was performed by the real software, and the optical field distribution and the RF mode field distribution with the frequency of 100GHZ under static voltage calculated by the COMSOL and HFSS simulation are shown in fig. 10. Solving the electric field intensity inside the electro-optic material according to the electro-optic material characteristics and the structural size of the designed modulator, and calculating the TE under the waveguides and electrodes with different sizes 0 Mode and TE 1 Optical wave loss of the mode, group refractive index, and half-wave voltage required. Device structure modeling is carried out by using HFSS software, so that structural parameters of a traveling wave electrode with a T structure and a multimode waveguide phase shift arm are optimized, and TE is finally realized at the same time 0 Mode and TE 1 The mode is lower in microwave and light wave loss, the half-wave voltage is lower, and the refractive index of the microwave group is designed to be between that of the multimode waveguide TE by adopting partial etching of the silicon substrate 0 Mode and TE 1 And in the middle of the refractive indexes of the mode groups, the refractive index mismatch of the microwave and the optical wave is reduced, so that the two modes simultaneously achieve larger electro-optic bandwidth modulation. Simulation results show that when the modulator length is taken to be 0.8cm, the half-wave voltage values of both modes are 2.64V. TE (TE) 0 The effective refractive index of the mode is 1.818, the group refractive index is 2.23, TE 1 The effective index of the mode is 1.759 and the group index is 2.28, as shown in fig. 12, the microwave index is between the indices of the two light wave modes. The matching value of the characteristic impedance obtained by the simulation was about 51 ohms, as shown in fig. 11. The 3dB electro-optic bandwidth of both modes is greater than 110GHz and TE 1 The electro-optic bandwidth of the mode is slightly greater than TE 0 The electro-optic bandwidth of the mode, as shown in FIG. 13, is due to TE at high frequency bands (e.g., above 80 GHz) 1 The refractive index of the mode is more matched with that of the microwave.
While the embodiments have been described above, other variations and modifications will occur to those skilled in the art once the basic inventive concepts are known, and it is therefore intended that the foregoing description and drawings illustrate only embodiments of the invention and not limit the scope of the invention, and it is therefore intended that the invention not be limited to the specific embodiments described, but that the invention may be practiced with their equivalent structures or with their equivalent processes or with their use directly or indirectly in other related fields.
Claims (8)
1. The polarization independent electro-optic modulator based on the thin film lithium niobate multimode waveguide is characterized by comprising a silicon substrate layer (22), an oxygen buried layer (21) and a lithium niobate layer (20) which are sequentially stacked from bottom to top, wherein a T-structure metal electrode (18), a metal traveling wave signal electrode (10) and a metal traveling wave grounding electrode (9) are arranged above the lithium niobate layer (20); forming a thin film lithium niobate optical waveguide on the X-cut lithium niobate layer (20) by an etching technology, wherein the thin film lithium niobate optical waveguide comprises an input straight waveguide (1), an input end mode converter (2), a multimode beam splitter (5), a first S-shaped bent waveguide (6), an input gradual change cone (7) of a multimode waveguide phase shift arm, a multimode waveguide phase shift arm (8), an output gradual change cone (11) of the multimode waveguide phase shift arm, a second S-shaped bent waveguide (12), a multimode beam combiner (14), an output end mode converter (16) and an output straight waveguide (17) which are connected in sequence; a metal traveling wave electrode is arranged around the multimode waveguide phase shift arm (8), and the metal traveling wave electrode comprises: the two sides of the metal traveling wave signal electrode are respectively connected with a group of periodically arranged T-shaped structure metal electrodes (18), the one side of the metal traveling wave grounding electrode is connected with a group of periodically arranged T-shaped structure metal electrodes (18), and the silicon substrate layer (22) is partially etched through small holes (19) at the lithium niobate layer (20) to form a cavity (23); specifically, the metal traveling wave signal electrodes (10) of which two sides are respectively connected with a group of periodically arranged T-shaped structure metal electrodes (18) are positioned between the two arms (8) of the multimode waveguide phase shift arm, the metal traveling wave grounding electrodes (9) of which one side is connected with a group of periodically arranged T-shaped structure metal electrodes (18) are positioned at the outer sides of the two arms of the multimode waveguide phase shift arm (8), and the whole Mach-Zehnder modulation structure is arranged up and down and symmetrically left and right.
2. Polarization-independent electro-optic modulator based on thin-film lithium niobate multimode waveguide according to claim 1, characterized in that the input-side mode converter (2) and the output-side mode converter (16) are identical in structure for realizing a narrower-side TM 0 Die and wider end TE 1 Mode interconversion with TE 0 The die remains unchanged; the narrower end waveguide width W of the input end mode converter (2) 1 Less than TM 0 Mode and TE 1 Mode hybridization width of mode and support TE 0 ，TM 0 Mode, the wider end waveguide width W of the input end mode converter (2) 2 Greater than TM 0 Mode and TE 1 Mode hybridization width; length L of the input-side mode converter (2) 1 Determined by mode evolution theory to achieve narrower-end TM 0 Die and wider end TE 1 Complete coupling of the modes.
3. The polarization-independent electro-optic modulator based on the thin-film lithium niobate multimode waveguide according to claim 1, characterized in that the multimode beam splitter (5) has the same structure as the multimode beam combiner (14), and consists of a 2×2 multimode interference structure and two groups of input-output gradual taper, and the width W of the interference structure of the multimode beam splitter 4 And length L 3 Determined by multimode interference self-imaging theory, when TE 0 Or TE (TE) 1 When the mode is input from one port, TE is realized simultaneously 0 Or TE (TE) 1 3dB splitting of the mode, the input taper (3) end width W of the multimode beam splitter 2 And the tail end width W of an output gradual change cone (4) of the multimode beam splitter 5 Greater than TM 0 Mode and TE 1 The mode hybridization width prevents light from mode conversion through the gradual change cone, and the structure of the output gradual change cone (15) of the multimode beam combiner and the structure of the input gradual change cone (3) of the multimode beam splitter are identical and symmetrically placed, and the structure of the input gradual change cone (13) of the multimode beam combiner and the structure of the output gradual change cone (4) of the multimode beam splitter are identical and symmetrically placed.
4. The polarization independent electro-optic modulator of claim 1, wherein the modulator material is selected from the group consisting of X-cut thin film lithium niobate on insulator, comprising a silicon substrate layer (22), a low refractive index buried oxide layer (21), a high refractive index lithium niobate ridge core layer (20), and a lower refractive index air overclad.
5. The polarization-independent electro-optic modulator of claim 1,the method is characterized in that multimode waveguide phase shift arms (8) at two sides of a metal traveling wave signal electrode (10) are ridge multimode waveguides, and two ends of the multimode waveguide phase shift arms (8) are respectively connected with a first S-bend waveguide (6) and a second S-bend waveguide (12) through an input gradual change cone (7) of the multimode waveguide phase shift arms and an output gradual change cone (11) of the multimode waveguide phase shift arms, so that TE is realized 0 Mode and TE 1 The modes are transmitted in an adiabatic mode respectively, and the input gradual change cone (7) of the multimode waveguide phase shift arm and the output gradual change cone (11) of the multimode waveguide phase shift arm are completely identical in structure and are symmetrically arranged; lithium niobate below the metal electrodes on two sides of the multimode waveguide phase shift arm (8) is not etched, so that metal absorption loss is reduced.
6. Polarization-independent electro-optic modulator based on a thin-film lithium niobate multimode waveguide according to any of claims 1-6, characterized in that in the modulation region part the width W of the multimode waveguide phase-shift arm (8) 6 Require assurance of TE 0 Mode and TE 1 When the light of the modes is modulated, half-wave voltages of the two modes are equal, and the width is as small as possible, so that the simultaneous high-efficiency modulation of different polarized lights is realized.
7. Polarization-independent electro-optic modulator based on thin-film lithium niobate multimode waveguide according to claim 1, characterized in that in the modulation region section, the structural parameters of the metallic traveling wave electrode containing T-structured metallic electrode (18) and multimode waveguide phase shift arm (8) are optimized to TE by using full-wave three-dimensional electromagnetic simulation software based on electromagnetic field finite element method analysis of microwave engineering problem 0 Mode and TE 1 The mode realizes lower microwave and light wave loss at the same time, lower half-wave voltage, etches the silicon substrate partially, designs the refractive index of the microwave group to be between that of the multimode waveguide TE 0 Mode and TE 1 And in the middle of the refractive indexes of the mode groups, the refractive index mismatch of the microwave and the optical wave is reduced, so that the two modes simultaneously achieve larger electro-optic bandwidth modulation.
8. The polarization independent electro-optic modulator based on thin film lithium niobate multimode waveguide according to claim 1, wherein the metal electrode material is gold, comprising two thicknesses, the first being a T-structured metal electrode (18) with a thickness of 200nm, the second being a metal traveling wave ground electrode (9) and a metal traveling wave signal electrode (10) with a thickness of 1.1 μm.
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| CN116560119A (en) * | 2023-06-25 | 2023-08-08 | 华中科技大学 | Silicon-based thin film lithium niobate broadband electro-optic modulator chip based on traveling wave electrode structure |
| CN116560119B (en) * | 2023-06-25 | 2023-09-19 | 华中科技大学 | Silicon-based thin film lithium niobate broadband electro-optic modulator chip based on traveling wave electrode structure |
| CN116520494A (en) * | 2023-06-28 | 2023-08-01 | 之江实验室 | Silicon nitride waveguide TE0/TE1 broadband mode converter |
| CN116760479A (en) * | 2023-08-14 | 2023-09-15 | 浙江九州量子信息技术股份有限公司 | Film lithium niobate phase decoding photon chip and quantum key distribution system |
| CN116760479B (en) * | 2023-08-14 | 2023-11-24 | 浙江九州量子信息技术股份有限公司 | Film lithium niobate phase decoding photon chip and quantum key distribution system |
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