A lithium niobate electro-optic modulator based on multi-dimensional dynamic tunable and a preparation method and application thereof

Abstract

This invention relates to a multidimensional dynamically tunable lithium niobate electro-optic modulator, its fabrication method, and its applications. The lithium niobate electro-optic modulator includes, from bottom to top, a substrate layer, a lithium niobate film layer, and a lithium niobate waveguide, and further includes, from bottom to top, an isolation layer, a thermo-optical tuning layer, and a global tuning electrode disposed above the lithium niobate waveguide. A two-dimensional photonic crystal is disposed on the upper surface of the lithium niobate waveguide. The two-dimensional photonic crystal is a hexagonal close-packed array of air holes, and periodic slots are arranged in the air hole array to form a grating. Interdigitated electrodes are disposed on both sides of the lithium niobate waveguide. The thermo-optical tuning layer is made of vanadium oxide and consists of several parallel stripes perpendicular to the light propagation direction. The lithium niobate electro-optic modulator of this invention can achieve tuning in three dimensions: wavelength, modulation depth, and polarization state control, and is suitable for multi-channel reconfigurable optical networks.

Description

Technical Field

[0001] This application relates to the field of electro-optic modulator technology, and in particular to a multidimensional dynamically tunable lithium niobate electro-optic modulator, its fabrication method, and its application. Background Technology

[0002] The lithium niobate electro-optic modulator is a core device that utilizes the linear electro-optic effect (Pockell effect) of lithium niobate crystals to achieve high-speed modulation of optical signals. Its working principle can be summarized as follows: when an external electric field is applied, the refractive index of lithium niobate changes linearly (…). Electro-optic modulators convert electrical signals into intensity / phase / frequency modulations of optical signals using a Mach-Zehnder interferometer (MZI) or phase modulation structure. While traditional lithium niobate modulators are irreplaceable in high-speed modulation, they face three fundamental challenges: 1. Fixed operating wavelength, unable to respond to channel switching requirements in wavelength division multiplexing (WDM) systems; 2. Fast electro-optic tuning speed but narrow tuning range, suitable only for fine-tuning; 3. Limited multi-functional integration, with filtering, modulation, and routing functions implemented by discrete components, resulting in high insertion loss and severe crosstalk. The multi-dimensional dynamic tunability of lithium niobate electro-optic modulators integrates electro-optic tuning (high-speed), thermo-optic tuning (broadband), and photonic crystal grating (filtering) on ​​a single chip. This not only solves the industry dilemma of the incompatibility between high-speed and broadband tuning but also provides a hardware foundation for defining future scenarios such as optical networks, quantum optical chips, and intelligent sensing.

[0003] To achieve wavelength tunability in lithium niobate electro-optic modulators, traditional approaches mainly rely on two types of techniques: electro-optic fine-tuning and thermo-optic tuning. However, both have significant limitations. First, electro-optic fine-tuning directly adjusts the refractive index using the electro-optic effect of lithium niobate by applying a DC bias voltage to the Mach-Zehnder modulator arm to change the interference phase, but it cannot cover multiple channel spacings. Second, thermo-optic tuning mainly utilizes the thermo-optic effect of lithium niobate or its coating layer, integrating a metal microheater to heat the waveguide and change its thermal emissivity. This approach suffers from low efficiency, easy introduction of insertion loss, and high crosstalk.

[0004] The optical switching device in US Patent US20190253776A1 is primarily based on the vanadium dioxide (VO2) phase transition mechanism. It achieves binary switching (on / off state) of the optical path by triggering an insulator-metal phase transition via electro / optical pulses, essentially a discrete high-speed optical switching mechanism. Although the optical switching device structure in this patent contains waveguides and photonic crystal gratings, and also includes materials such as vanadium dioxide, it cannot achieve multi-dimensional dynamic tunability. The main reasons are: 1. Thermo-optical tuning relies on the VO2 phase transition, only providing a step change in refractive index (discontinuous), and the metallic state introduces high losses; 2. Electro-optical tuning is completely absent; the electrodes are only used to trigger the phase transition, without integrating electro-optical materials (such as lithium niobate) for refractive index fine-tuning; 3. The photonic crystal only serves as a static waveguide enhancement structure and does not work in conjunction with the phase transition mechanism to achieve dynamic bandgap modulation. Therefore, the optical switching device structure in this patent is limited to high-speed switching functionality and cannot support multi-dimensional operation that combines continuous wavelength tuning with signal modulation. Summary of the Invention

[0005] The primary objective of this invention is to overcome the problem that existing lithium niobate electro-optic modulators cannot simultaneously achieve electro-optic tuning and thermo-optic tuning, and to provide a multi-dimensional dynamically tunable lithium niobate electro-optic modulator.

[0006] A further objective of this invention is to provide a method for fabricating a multidimensional dynamically tunable lithium niobate electro-optic modulator.

[0007] Another object of the present invention is to provide an application of the above-mentioned lithium niobate electro-optic modulator.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A multidimensional dynamically tunable lithium niobate electro-optic modulator includes a substrate layer, a lithium niobate film layer and a lithium niobate waveguide arranged sequentially from bottom to top, and also includes an isolation layer, a thermo-optic tuning layer and a global tuning electrode arranged from bottom to top above the lithium niobate waveguide.

[0010] The upper surface of the lithium niobate waveguide is provided with a two-dimensional photonic crystal, which is a hexagonal close-packed air hole array, and periodic slot lines are set in the air hole array to form a grating.

[0011] The lithium niobate waveguide has interdigitated electrodes on both sides;

[0012] The thermo-optical tuning layer is made of vanadium oxide and consists of several parallel stripes perpendicular to the direction of light propagation.

[0013] Through research, the inventors of this invention discovered that the specific photonic crystal, grating, and thermo-optical tuning layer in the lithium niobate electro-optic modulator of this invention can achieve tuning in three dimensions—wavelength, modulation depth, and polarization state—through thermo-optical and electro-optical dual physical fields, making it suitable for multi-channel reconfigurable optical networks.

[0014] The principle is as follows: Photonic crystals can block the propagation of specific wavelengths through the photonic bandgap effect. The bandgap edge has a high group refractive index, and the minute refractive index change induced by the vanadium oxide phase transition in the thermo-optical tuning layer is significantly amplified by the bandgap edge, achieving broadband wavelength tuning. The air-hole array in the photonic crystal can generate differentiated photonic bandgap for TE and TM modes, thereby achieving polarization-state controlled tuning. Gratings, through their periodic structure, generate polarization-dependent diffraction (e.g., tilted gratings) or mode coupling (e.g., subwavelength gratings), which can selectively enhance the coupling efficiency of TE and TM modes, thus achieving polarization-state controlled tuning. Combined with the thermo-optical tuning layer, wavelength tuning can be achieved. The thermo-optical tuning layer, on the one hand, can switch the waveguide-grating coupling state through the vanadium oxide phase transition, thereby achieving modulation depth tuning; on the other hand, relying on the temperature-dependent refractive index change of vanadium oxide, this change works synergistically with the bandgap edge effect of the photonic crystal to jointly achieve wavelength tuning.

[0015] Furthermore, the lithium niobate electro-optic modulator of the present invention has low insertion loss, high bandwidth and high coupling efficiency.

[0016] Preferably, the substrate layer comprises, from bottom to top, a supporting substrate and an intermediate buried oxide layer.

[0017] More preferably, the material of the supporting substrate is at least one of Si, SiC, sapphire, lithium niobate, quartz or diamond.

[0018] More preferably, the thickness of the supporting substrate is 100~600 μm.

[0019] More preferably, the material of the intermediate buried oxide layer is at least one of silicon dioxide, silicon nitride, or aluminum oxide.

[0020] More preferably, the thickness of the intermediate buried oxygen layer is 0.1~10 μm.

[0021] Preferably, the thickness of the lithium niobate film is 100~1200 nm.

[0022] Preferably, the lithium niobate waveguide is a ridge-type lithium niobate waveguide.

[0023] Preferably, the lithium niobate waveguide has a width of 0.1~10 μm and a height of 50~1000 nm.

[0024] Preferably, the lattice constant of the two-dimensional photonic crystal is 300~1000 nm.

[0025] Preferably, no air hole is provided at the center of the two-dimensional photonic crystal.

[0026] Preferably, the air holes in the air hole array are circular in shape.

[0027] Preferably, the depth of the air holes in the air hole array is 200~400 nm.

[0028] More preferably, the depth of the air holes in the air hole array is 200~250 nm. Controlling the depth of the air holes within this range results in a lithium niobate electro-optic modulator with higher wavelength tuning range, modulation depth, polarization extinction ratio, bandwidth, and coupling efficiency, as well as lower insertion loss.

[0029] Preferably, the aperture of the air holes in the air hole array is 100~300 nm.

[0030] More preferably, the air holes in the air hole array have the same aperture or the aperture varies from 100 nm to 300 nm along the light propagation direction.

[0031] More preferably, the gradient change is 10~100 nm / mm.

[0032] Preferably, the spacing between the air holes in the air hole array is 100~500 nm.

[0033] Preferably, the grating is a Bragg grating.

[0034] Preferably, the periodic grooves are perpendicular to the direction of light propagation.

[0035] Preferably, the material of the isolation layer is at least one of alumina, silicon dioxide, silicon nitride, calcium fluoride, or hafnium silicate.

[0036] Preferably, the thickness of the isolation layer is 10~50 nm.

[0037] Preferably, the surface roughness of the isolation layer is <1 nm.

[0038] Preferably, the width of the stripes is 200~400 nm.

[0039] Preferably, the spacing between the stripes is 300~1500 nm.

[0040] More preferably, the spacing between the stripes is 300~600 nm. Controlling the spacing between two adjacent stripes in the thermo-optical tuning layer within this range results in a lithium niobate electro-optic modulator with higher wavelength tuning range, modulation depth, polarization extinction ratio, bandwidth, and coupling efficiency, as well as lower insertion loss.

[0041] Preferably, the spacing of the stripes is 1 to 3 times the lattice constant of the two-dimensional photonic crystal.

[0042] Preferably, the thickness of the thermo-optical tuning layer is 50~400 nm.

[0043] Preferably, the phase transition temperature threshold of the vanadium oxide is 65~70℃.

[0044] Preferably, the global tuning electrode is an ITO transparent electrode.

[0045] Preferably, the transmittance of the global tuning electrode is greater than 90%.

[0046] Preferably, the resistivity of the global tuning electrode is less than 1×10⁻⁶. -3 Ω·cm.

[0047] Preferably, the global tuning electrode covers the thermo-optical tuning layer.

[0048] Preferably, the thickness of the global tuning electrode is 50~500 nm.

[0049] Preferably, the material of the interdigitated electrode is at least one of gold or graphene.

[0050] More preferably, the interdigitated electrode is a composite structure of gold and graphene, with the graphene covering the surface of the gold.

[0051] More preferably, the thickness of the graphene is 1~5 nm.

[0052] Preferably, the width of the interdigitated electrode is 100~300 nm.

[0053] Preferably, the period of the interdigitated electrodes matches the lattice constant of the photonic crystal.

[0054] Preferably, the interdigitated electrodes are finger-shaped or comb-shaped.

[0055] Preferably, the spacing between the interdigitated electrodes is 200~500 nm.

[0056] A method for fabricating a multidimensional dynamically tunable lithium niobate electro-optic modulator includes the following steps:

[0057] S1. A lithium niobate film is formed above the substrate layer;

[0058] S2. A lithium niobate waveguide is formed above the lithium niobate film layer;

[0059] S3. The upper surface of the lithium niobate waveguide is etched to form a hexagonal close-packed air hole array, thereby forming a two-dimensional photonic crystal. Periodic grooves are etched in the air hole array to form a grating.

[0060] S4. An isolation layer is formed above the lithium niobate waveguide layer;

[0061] S5. A thermo-optical tuning layer is formed above the isolation layer;

[0062] S6. Fabricate the global tuning electrode and interdigitated electrode.

[0063] Preferably, the specific process of step S1 is as follows: a lithium niobate film layer on an insulator (the structure of which specifically includes a supporting substrate, an intermediate buried oxide layer and a top layer of bonded lithium niobate film) is provided, and then ultrasonically cleaned with acetone, ethanol and water in sequence, and dried.

[0064] Preferably, the specific process of step S2 is as follows: spin-coating a layer of electron beam photoresist on the lithium niobate thin film layer, forming a lithium niobate waveguide pattern by electron beam exposure, and then etching the lithium niobate waveguide pattern formed by electron beam exposure.

[0065] More preferably, the etching process is at least one of reactive ion etching, dry etching, wet etching, or femtosecond laser etching.

[0066] More preferably, the etching power is 100~400 W and the etching bias voltage is 50~400 V.

[0067] Preferably, the specific process of step S3 is as follows: the upper surface of the lithium niobate waveguide is etched by focused ion beam or dry etching to form a hexagonal close-packed air hole array, thereby forming a two-dimensional photonic crystal, and then periodic grooves are etched in the air hole array to form a grating.

[0068] More preferably, the aperture size of the hexagonal close-packed structure can be monitored in real time through secondary electronic imaging.

[0069] More preferably, the period of the grating is designed according to the Bragg condition.

[0070] Preferably, the periodic grooves are perpendicular to the direction of light propagation.

[0071] Preferably, in step S3, the center of the two-dimensional photonic crystal is not etched with air holes.

[0072] Preferably, the specific process of step S4 is as follows: an isolation layer is formed on the lithium niobate waveguide by a non-conformal deposition process.

[0073] More preferably, the non-conformal deposition process is at least one of evaporation or tilting sputtering.

[0074] Preferably, the specific process of step S5 is as follows: vanadium oxide is grown on the isolation layer by magnetron sputtering, pulsed laser deposition or sol-gel method, and the stripe pattern of vanadium oxide is prepared by nanoimprinting technology.

[0075] Preferably, the specific process of step S6 is as follows: a global tuning electrode is prepared on the thermo-optical tuning layer by electron beam evaporation, magnetron sputtering or sol-gel method; interdigitated electrodes are prepared on both sides of the lithium niobate waveguide by photolithography, magnetron sputtering or evaporation method.

[0076] This invention also protects the application of the above-mentioned lithium niobate electro-optic modulator in multi-channel reconfigurable optical networks.

[0077] Compared with the prior art, the beneficial effects of the present invention are:

[0078] The lithium niobate electro-optic modulator of the present invention uses a specific photonic crystal, grating and thermo-optic tuning layer to achieve tuning in three dimensions: wavelength, modulation depth and polarization state control through thermo-optic and electro-optic dual physical fields, which is suitable for multi-channel reconfigurable optical networks.

[0079] Furthermore, the lithium niobate electro-optic modulator of the present invention has low insertion loss, high bandwidth and high coupling efficiency. Attached Figure Description

[0080] Figure 1 This is a schematic diagram of the structure of the lithium niobate electro-optic modulator in Example 1.

[0081] Figure 2 A schematic diagram showing the etching process to form a ridge-shaped lithium niobate waveguide layer on the surface of a lithium niobate film.

[0082] Figure 3 A schematic diagram showing the etching of a photonic crystal and grating structure on the upper surface of a lithium niobate waveguide;

[0083] Figure 4 A schematic diagram of the fabrication of an isolation layer on a lithium niobate waveguide;

[0084] Figure 5 A schematic diagram showing the fabrication of a thermo-optical tuning layer on an isolation layer;

[0085] Figure 6 A schematic diagram showing the fabrication of an ITO transparent electrode on a thermo-optical tuning layer;

[0086] Figure 7 A schematic diagram showing the fabrication of interdigitated electrodes on both sides of a lithium niobate waveguide;

[0087] Figure 8 This is a SEM image of the lithium niobate electro-optic modulator of Example 1;

[0088] Figure 9This is a schematic diagram of the light spot transmission of the lithium niobate electro-optic modulator in Example 1. Detailed Implementation

[0089] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0090] Example 1

[0091] This embodiment provides a multidimensional dynamically tunable lithium niobate electro-optic modulator, the structure of which is as follows: Figure 1 As shown, it includes a substrate layer 1, a lithium niobate film layer 2 and a lithium niobate waveguide 3 arranged sequentially from bottom to top, and also includes an isolation layer 4, a thermo-optical tuning layer 5 and a global tuning electrode 6 arranged above the lithium niobate waveguide 3 from bottom to top.

[0092] The upper surface of the lithium niobate waveguide 3 is provided with a two-dimensional photonic crystal 31, which is a hexagonal close-packed air hole array. No air hole is set in the center of the two-dimensional photonic crystal 31 (to serve as a dielectric pillar). Periodic grooves are set in the air hole array to form a grating 32, and the periodic grooves are perpendicular to the light propagation direction.

[0093] The lithium niobate waveguide 3 has interdigitated electrodes 7 on both sides, with the interdigitated fingers of the interdigitated electrodes 7 pointing towards the lithium niobate waveguide 3.

[0094] The material of the isolation layer 4 is aluminum oxide, and the material of the thermo-optical tuning layer 5 is vanadium oxide. The thermo-optical tuning layer 5 is composed of several parallel stripes, and the stripes are perpendicular to the direction of light propagation.

[0095] The substrate layer, from bottom to top, includes a supporting substrate 11 and an intermediate buried oxide layer 12.

[0096] The supporting substrate 11 is made of Si and has a thickness of 400 μm; the intermediate buried oxide layer 12 is made of SiO2 and has a thickness of 2 μm; and the lithium niobate film layer 2 has a thickness of 500 nm.

[0097] The lithium niobate waveguide 3 is a ridge-type lithium niobate waveguide with a width of 2 μm and a height of 400 nm. The lattice constant of the two-dimensional photonic crystal 31 is 300 nm. The air holes in the air hole array are circular in shape, with a depth of 200 nm, an aperture of 200 nm, and a spacing of 100 nm. The grating 32 is a Bragg grating.

[0098] The thickness of the isolation layer 4 is 20 nm, and the surface roughness of the isolation layer 4 is 0.5 nm;

[0099] The thickness of the thermo-optical tuning layer 5 is 200 nm, the width of the stripes is 300 nm, the spacing between two adjacent stripes is 500 nm, and the phase transition temperature threshold of vanadium oxide is 65℃.

[0100] The global tuning electrode 6 is an ITO transparent electrode, with a transmittance of 92% and a resistivity of 5×10⁻⁶. -4 Ω·cm, the global tuning electrode 6 is covered with a thermo-optical tuning layer 5, and the thickness of the global tuning electrode 6 is 300 nm;

[0101] The interdigitated electrode 7 is a composite structure of gold and graphene, with graphene covering the surface of gold. The graphene thickness is 2 nm. The period of the interdigitated electrode 7 is 300 nm. The shape of the interdigitated electrode 7 is finger-like. The spacing of the interdigitated electrode 7 is 500 nm. The width of the interdigitated electrode 7 is 200 nm.

[0102] The fabrication method of the lithium niobate electro-optic modulator in this embodiment includes the following steps:

[0103] (1) Provide a lithium niobate film layer on an insulator (the structure of which specifically includes a supporting substrate, an intermediate buried oxide layer and a top layer of bonded lithium niobate film), and ultrasonically clean it for 5 minutes each with acetone, ethanol and deionized water to remove oil stains from the film surface, and then dry it in an oven at 80°C for 10 minutes.

[0104] (2) A layer of electron beam photoresist is spin-coated onto the lithium niobate film, and a lithium niobate waveguide pattern is formed by electron beam exposure. Then, reactive ion etching is used to etch the waveguide pattern formed by electron beam exposure to form a lithium niobate waveguide (e.g., Figure 2 As shown), the etching power is 200 W, and the bias voltage is adjusted to 60 V;

[0105] (3) A hexagonal close-packed circular air hole array is formed on the upper surface of the lithium niobate waveguide by dry etching, thereby forming a two-dimensional photonic crystal. The air hole is not etched in the center of the two-dimensional photonic crystal. Then, periodic grooves are etched in the circular air hole array to form a grating (e.g., Figure 3 As shown), the period of the grating is designed according to the Bragg condition, and the periodic grooves are perpendicular to the direction of light propagation; the hexagonal close-packed structure allows for real-time monitoring of the aperture size through secondary electron imaging.

[0106] (4) An isolation layer is formed above the lithium niobate waveguide by tilting sputtering (e.g., Figure 4 As shown in the figure, the tilting sputtering method can effectively avoid the alumina particles covering the inside of the photonic crystal pores;

[0107] (5) Vanadium oxide is grown on the isolation layer by pulsed laser deposition, and a striped pattern of vanadium oxide is prepared by nanoimprinting technology. The stripes are perpendicular to the light propagation direction to obtain a thermo-optical tuning layer (e.g., Figure 5 (as shown)

[0108] (6) Fabrication of ITO transparent electrodes on thermo-optical tuning layers by electron beam evaporation (e.g. Figure 6 As shown), interdigitated electrodes (such as those shown) are fabricated on both sides of a lithium niobate waveguide using photolithography. Figure 7 (As shown).

[0109] The lithium niobate electro-optic modulator of this embodiment was characterized by SEM and simulated, and the results are as follows: Figures 8-9 As shown. From Figure 9 It can be seen that the beam distribution of the lithium niobate electro-optic modulator in Example 1 is uniform.

[0110] Example 2

[0111] This embodiment provides a lithium niobate electro-optic modulator, which differs from Embodiment 1 in that the depth of the air holes in the air hole array is 250 nm.

[0112] The preparation method of the lithium niobate electro-optic modulator in this embodiment is the same as that in Embodiment 1.

[0113] Example 3

[0114] This embodiment provides a lithium niobate electro-optic modulator, which differs from Embodiment 1 in that the depth of the air holes in the air hole array is 300 nm.

[0115] The preparation method of the lithium niobate electro-optic modulator in this embodiment is the same as that in Embodiment 1.

[0116] Example 4

[0117] This embodiment provides a lithium niobate electro-optic modulator, which differs from Embodiment 1 in that the spacing between two adjacent stripes in the thermo-optic tuning layer is 600 nm.

[0118] The preparation method of the lithium niobate electro-optic modulator in this embodiment is the same as that in Embodiment 1.

[0119] Example 5

[0120] This embodiment provides a lithium niobate electro-optic modulator, which differs from Embodiment 1 in that the spacing between two adjacent stripes in the thermo-optic tuning layer is 900 nm.

[0121] The preparation method of the lithium niobate electro-optic modulator in this embodiment is the same as that in Embodiment 1.

[0122] The lithium niobate electro-optic modulators of Examples 2-5 were subjected to SEM characterization and simulation tests. The test results were similar to those of the lithium niobate electro-optic modulator of Example 1.

[0123] Comparative Example 1

[0124] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that: the upper surface of the lithium niobate waveguide does not have a two-dimensional photonic crystal; and no thermo-optic tuning layer is provided.

[0125] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0126] Step (3) is changed to: etching periodic grooves on the upper surface of the lithium niobate waveguide to form a grating. The period of the grating is designed according to the Bragg condition, and the periodic grooves are perpendicular to the direction of light propagation.

[0127] Step (5) is not performed.

[0128] Comparative Example 2

[0129] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that the upper surface of the lithium niobate waveguide does not have a two-dimensional photonic crystal.

[0130] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0131] Step (3) is changed to: etching periodic grooves on the upper surface of the lithium niobate waveguide to form a grating. The period of the grating is designed according to the Bragg condition, and the periodic grooves are perpendicular to the direction of light propagation.

[0132] Comparative Example 3

[0133] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that it does not have a grating.

[0134] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0135] Step (3) is changed to: forming a hexagonal close-packed circular air hole array on the upper surface of the lithium niobate waveguide by dry etching, thereby forming a two-dimensional photonic crystal, and the air hole is not etched in the center of the two-dimensional photonic crystal.

[0136] Comparative Example 4

[0137] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that it does not have a thermo-optic tuning layer.

[0138] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0139] Step (5) is not performed.

[0140] Comparative Example 5

[0141] This comparative example provides a comparative lithium niobate electro-optic modulator, which differs from Example 1 in that the material of the thermo-optic tuning layer is strontium titanate.

[0142] The fabrication method of the comparative lithium niobate electro-optic modulator differs from that of Example 1 in that:

[0143] Step (5) is changed to: growing strontium titanate on the isolation layer by pulsed laser deposition, and preparing the stripe pattern of strontium titanate by nanoimprinting technology, with the stripes perpendicular to the light propagation direction, to obtain the thermo-optical tuning layer;

[0144] Performance testing

[0145] 1. Wavelength tuning range

[0146] Wavelength tuning range refers to the maximum range of wavelength tuning achievable by the modulator through the application of an electrical signal (voltage / current), expressed in wavelength (nm). The wavelength tuning ranges of the lithium niobate electro-optic modulators in each embodiment and the comparative lithium niobate electro-optic modulators in each comparative example were tested, and the results are shown in Table 1. The test method is as follows: The test instruments include a tunable laser, an RF signal generator, an optical power meter / spectrum analyzer, a polarization controller, a temperature controller, a DC power supply, and fiber optic patch cords / optical couplers. The test steps are as follows:

[0147] 1) Initialization and parameter setting

[0148] Turn on all equipment and preheat for 30 minutes (to ensure laser power and modulator temperature are stable). Set the modulator bias voltage: Apply bias through the DC power supply to make the modulator operate at the "linear operating point" (between the minimum and maximum transmission points of the MZI modulator, which can be determined by scanning the bias voltage and monitoring the output optical power). Set the drive signal: The RF signal generator outputs a sine wave (frequency 10 GHz) with an amplitude twice that of the modulator's half-wave voltage. Set the laser initial parameters: wavelength starting point (1520 nm), output power stable (to avoid power fluctuations affecting the test, the input optical power can be fixed to the modulator's rated value using an attenuator).

[0149] 2) Wavelength scanning and parameter monitoring

[0150] The laser wavelength was gradually increased to the endpoint (1610 nm) in fixed step sizes (0.1 nm), with a 5-second pause at each step (to ensure system stability). At each wavelength, the following parameters were recorded: modulated output optical power, extinction ratio, and modulation depth.

[0151] 3) Threshold determination and wavelength tuning range calculation

[0152] Set performance thresholds: extinction ratio ≥ 20 dB (ensuring signal contrast); modulation depth ≥ 80% (ensuring significant modulation effect); output optical power fluctuation ≤ 1 dB (ensuring transmission stability). Select all wavelengths that meet the above thresholds and determine the minimum wavelength λ. min and maximum wavelength λ max The formula for calculating the wavelength tuning range (Δλ) is: .

[0153] 2. Modulation depth

[0154] Modulation depth refers to a parameter that measures the strength of the modulation of an optical signal by a modulator. It is the ratio of the maximum change in light intensity after modulation to the average light intensity (usually expressed as a percentage or decibels). The modulation depth of the lithium niobate electro-optic modulators in each embodiment and the comparative lithium niobate electro-optic modulators in each comparative example were tested, and the results are shown in Table 1. The test method is as follows: The test instruments include a single-mode laser, a signal generator (outputting a sine / square wave electrical signal), a lithium niobate modulator, a photodetector, and an oscilloscope. The test steps are as follows:

[0155] 1) Optical path setup. The laser output light is coupled into the modulator, the modulator electrodes are connected to the modulated electrical signal (such as a 1kHz sine wave) output by the signal generator, the output light is connected to the photodetector, and the detector signal is connected to the oscilloscope.

[0156] 2) Record the extreme values ​​of light intensity. Read the maximum value of the modulated light intensity (I) on an oscilloscope. max ) and minimum value (I min The calculation method is the modulation depth. .

[0157] 3. Polarization extinction ratio

[0158] The polarization extinction ratio is defined as the ratio (in dB) of the intensity of the dominant polarization state (e.g., TE mode) to the intensity of the orthogonal polarization state (e.g., TM mode) in the modulator output light, reflecting the modulator's ability to maintain polarization states. The polarization extinction ratios of the lithium niobate electro-optic modulator in the test example and the comparative lithium niobate electro-optic modulators in each example are shown in Table 1. The test method is as follows: The test instruments include a single-mode laser, a polarization controller, a lithium niobate modulator, a polarization analyzer (or polarimeter), and an optical power meter. The test steps are as follows:

[0159] 1) Optical path setup. The laser output light is adjusted to the modulator's main polarization state (such as TE mode) by a polarization controller, and then coupled into the modulator. The output of the modulator is connected to a polarization analyzer.

[0160] 2) Measure the intensity of polarized light. Measure the main polarization state (BPS) in the output light using a polarization analyzer.I para ) and orthogonal polarization states ( I perp Optical power. Polarization extinction ratio ( PER The formula for calculating ) is .

[0161] 4. Insertion loss

[0162] The insertion loss of the lithium niobate electro-optic modulators in each embodiment and the comparative lithium niobate electro-optic modulators in each comparative example was tested, and the results are shown in Table 1. The test method is as follows: The test instruments include a single-mode laser, an optical power meter, an optical fiber patch cord, and a lithium niobate modulator (with an optical fiber interface). The test steps are as follows:

[0163] 1) Calibrate the optical path. The laser output light is directly connected to an optical power meter via an optical fiber to record the input power. P in (It is necessary to ensure stable coupling between the optical fiber and the power meter.)

[0164] 2) Connect the modulator. Connect the laser output fiber to the modulator input, and the modulator output fiber to an optical power meter to record the output power. P out (The modulator is not powered on and is in a "shoot-through" state). Among these, the insertion loss ( IL The calculation formula for ) is as follows: .

[0165] 5. Modulation bandwidth

[0166] Modulation bandwidth refers to the frequency range within which a modulator can effectively transmit the modulated signal, and is usually expressed as 3dB bandwidth (i.e., the range at which the modulated signal power drops to its maximum). (Frequency). The modulation bandwidth of the lithium niobate electro-optic modulators of each embodiment and the comparative lithium niobate electro-optic modulators of each comparative example were tested, and the results are shown in Table 1. The test method is as follows: The test instruments include a narrow linewidth laser, a lithium niobate modulator, a vector network analyzer (VNA), a photodetector (with a bandwidth higher than that of the modulator under test), and an RF amplifier. The test steps are as follows:

[0167] 1) Optical path setup. The laser output light is coupled into the modulator, and the modulator's RF electrode is connected to the signal output terminal (PORT1) of the vector network analyzer; the modulator output light is connected to the photodetector, and the detector's electrical signal output terminal is connected to the receiver terminal (PORT2) of the vector network analyzer.

[0168] 2) Calibration system. Before connecting to the modulator, calibrate the RF path of the VNA using a calibration kit (to remove losses from cables and connectors).

[0169] 3) Frequency sweep test. Set the frequency sweep range of the VNA (100kHz~50GHz), measure the electro-optical transmission coefficient (S21 parameter) at different frequencies, record the curve of signal power change with frequency, and find the frequency point corresponding to the S21 parameter dropping by 3dB from the maximum value of the low frequency band. This frequency is the 3dB bandwidth of the modulator.

[0170] 6. Coupling efficiency

[0171] Coupling efficiency is defined as the percentage (expressed as a percentage) of the optical power incident on the modulator input that is successfully coupled into the modulator waveguide. It is a key parameter for measuring the degree of matching between light and waveguide. The coupling efficiency of the lithium niobate electro-optic modulators in each embodiment and the comparative lithium niobate electro-optic modulators in each comparative example were tested, and the results are shown in Table 1. The test method is as follows: The test instruments include a single-mode laser, an optical power meter, fiber optic patch cords, a lithium niobate modulator (bare waveguide end face), and a microscopic adjustment frame (for controlling the alignment of the fiber and waveguide). The test steps are as follows:

[0172] 1) Measure the total incident power. The laser output light is directly connected to an optical power meter via an optical fiber, and the fiber output power is recorded. P total (i.e., the total power incident on the modulator end face).

[0173] 2) Alignment and Coupling: Align the fiber end face with the modulator waveguide input end using a micro-adjustment fixture (adjust lateral, longitudinal, and angular deviations). Connect the modulator output waveguide to another fiber (or directly receive the signal using a power meter), and record the output power after coupling into the waveguide. P coupled Coupling efficiency ( η The formula for calculating ) is .

[0174] Table 1 Results of each performance test

[0175]

[0176] As shown in Table 1, the lithium niobate electro-optic modulators of Examples 1-5 have a wavelength tuning range of 14.5 nm and above, a modulation depth of 87% and above, a polarization extinction ratio of 40 dB and above, an insertion loss of 1.2 dB and below, a bandwidth of 85 GHz and above, and a coupling efficiency of 85% and above. This indicates that the lithium niobate electro-optic modulator of the present invention can achieve tuning in three dimensions: wavelength, modulation depth, and polarization state control. Furthermore, the lithium niobate electro-optic modulator of the present invention exhibits low insertion loss, high bandwidth, and high coupling efficiency.

[0177] Comparative Example 1, without a two-dimensional photonic crystal and a thermo-optical tuning layer, produces a lithium niobate electro-optic modulator that cannot achieve tuning in three dimensions: wavelength, modulation depth, and polarization state. It also suffers from high insertion loss, low bandwidth, and low coupling efficiency.

[0178] Comparative Example 2, without a two-dimensional photonic crystal, produces a lithium niobate electro-optic modulator that can only achieve tuning in one dimension of modulation depth, and has high insertion loss, low bandwidth, and low coupling efficiency.

[0179] Comparative Example 3, without a grating, produces a lithium niobate electro-optic modulator that can only achieve tuning in one dimension of modulation depth, and has high insertion loss, low bandwidth, and low coupling efficiency.

[0180] Comparative Example 4 without a thermo-optical tuning layer and Comparative Example 5 with vanadium titanate replacing the thermo-optical tuning layer both produced comparative lithium niobate electro-optic modulators that could only achieve tuning in one dimension of polarization state control, and had high insertion loss, low bandwidth, and low coupling efficiency.

[0181] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A multidimensional dynamically tunable lithium niobate electro-optic modulator, characterized in that, It includes a substrate layer (1), a lithium niobate film layer (2) and a lithium niobate waveguide (3) arranged sequentially from bottom to top, and also includes an isolation layer (4), a thermo-optical tuning layer (5) and a global tuning electrode (6) arranged above the lithium niobate waveguide (3) from bottom to top. The upper surface of the lithium niobate waveguide (3) is provided with a two-dimensional photonic crystal (31), which is a hexagonal close-packed air hole array, and periodic slot lines are set in the air hole array to form a grating (32). The lithium niobate waveguide (3) has interdigitated electrodes (7) on both sides. The thermo-optical tuning layer (5) is made of vanadium oxide and consists of several parallel stripes, which are perpendicular to the direction of light propagation. No air hole is provided at the center of the two-dimensional photonic crystal (31); The spacing of the stripes is 1 to 3 times the lattice constant of the two-dimensional photonic crystal (31); The period of the interdigitated electrode (7) matches the lattice constant of the photonic crystal (31).

2. The lithium niobate electro-optic modulator based on multidimensional dynamic tunable as described in claim 1, characterized in that, The depth of the air holes in the air hole array is 200~400nm.

3. The lithium niobate electro-optic modulator based on multidimensional dynamic tunable as described in claim 1, characterized in that, The aperture of the air holes in the air hole array is 100~300nm.

4. The lithium niobate electro-optic modulator based on multidimensional dynamic tunable as described in claim 1, characterized in that, The grating (32) is a Bragg grating.

5. The lithium niobate electro-optic modulator based on multidimensional dynamic tunable as described in claim 1, characterized in that, The material of the isolation layer (4) is at least one of alumina, silicon dioxide, silicon nitride, calcium fluoride or hafnium silicate.

6. The lithium niobate electro-optic modulator based on multidimensional dynamic tunable as described in claim 1, characterized in that, The spacing between the stripes is 300~1500nm.

7. The lithium niobate electro-optic modulator based on multidimensional dynamic tunable as described in claim 1, characterized in that, The thickness of the thermo-optical tuning layer (5) is 50~400nm.

8. A method for fabricating a multidimensional dynamically tunable lithium niobate electro-optic modulator as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. A lithium niobate film is formed above the substrate layer; S2. A lithium niobate waveguide is formed above the lithium niobate film layer; S3. The upper surface of the lithium niobate waveguide is etched to form a hexagonal close-packed air hole array, thereby forming a two-dimensional photonic crystal. Periodic grooves are etched in the air hole array to form a grating. S4. An isolation layer is formed above the lithium niobate waveguide; S5. A thermo-optical tuning layer is formed above the isolation layer; S6. Fabricate the global tuning electrode and interdigitated electrode.

9. The application of the multidimensional dynamically tunable lithium niobate electro-optic modulator according to any one of claims 1 to 7 in a multi-channel reconfigurable optical network.

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