Thin film lithium tantalate electro-optical modulator with efficient thermo-optical bias point control

Abstract

The utility model discloses a film lithium tantalate electro-optical modulator with efficient thermo-optical bias point control, which is of an MZM type structure, is arranged on an LTOI material platform and comprises an input waveguide, a light beam splitter, a modulation electrode area, a bias electrode area, a light beam combiner and an output waveguide. The output end of the input waveguide is connected with the input end of the light beam splitter; the output end of the light beam splitter is divided into two paths, and the two paths are respectively connected with an upper arm and a lower arm in the modulation electrode area through waveguides; in the modulation electrode area, the waveguide passing through the upper arm is connected with the first 90-degree bent waveguide, and is connected with the bias electrode area through the 180-degree bent waveguide; the waveguide passing through the bias electrode area is connected to the input end of a light beam combiner through a second 90-degree bent waveguide and a waveguide of a lower arm in the modulation electrode area; the output end of the light beam combiner is connected with the input end of the output waveguide.

Description

Technical Field

[0001] This invention relates to the field of electro-optic modulator technology, specifically to a thin-film lithium tantalate electro-optic modulator with high-efficiency thermo-optic bias point control. Background Technology

[0002] Lithium tantalate (LiTaO3) is a high-performance material that has attracted much attention due to its excellent acousto-optic and electro-optic properties, wide optical transmission window (covering 240 nm to 5.5 μm), and excellent resistance to photodamage. Lithium tantalate possesses a near-ideal stoichiometric composition, resulting in weaker photorefractive effects and DC drift characteristics compared to lithium niobate. Furthermore, it maintains low loss (0.2 dB / cm) and good optical stability even at high temperatures (-40℃ to 85℃) and high power (hundreds of milliwatt-level lasers). In recent years, advancements in ion implantation and smart slicing technologies have enabled the industry to fabricate high-performance thin-film lithium tantalate (LTOI) optical wafers. These wafers bond lithium tantalate, with thicknesses ranging from several hundred nanometers, to a silicon + silicon oxide substrate using bonding technology. The resulting thin-film lithium tantalate optical waveguide structures exhibit stronger optical confinement, higher electro-optic modulation efficiency, and the ability to integrate devices and chips on a large scale.

[0003] In recent years, research institutions and enterprises have shown a significant increase in their attention to LTOI materials. Besides its widespread application in acoustic filter chips, it has also demonstrated remarkable capabilities in electro-optic modulation. Compared to thin-film lithium niobate (LNOI), LTOI offers lower wafer manufacturing costs due to its high-volume applications in acoustics. LTOI possesses a linear electro-optic coefficient comparable to LNOI, a femtosecond-level electro-optic response rate, low optical transmission loss, and a similar optical refractive index, enabling the fabrication of high-bandwidth electro-optic modulators. Furthermore, due to the higher atomic weight of tantalum compared to niobium, LTOI has fewer lithium defect dislocations, a closer stoichiometric ratio of tantalum to lithium (closer to 50%), and less lattice damage during argon-ion etching of waveguides. These factors contribute to LTOI's superior electrostatic drift and damage resistance compared to LNOI, resulting in greater long-term operational stability.

[0004] For electro-optic modulation devices fabricated from LNOI and LTOI materials, the modulation region waveguide is parallel to the crystal's y-axis, and the polarization direction of the light propagating within the waveguide is along the material's z-axis (also known as the c-axis), corresponding to the e-ray. Since the thermo-optic coefficient of lithium tantalate's e-ray is only 1 / 7 to 1 / 8 that of lithium niobate, the power consumption of the thermo-optic biaser in lithium tantalate modulators is significantly higher than that in lithium niobate modulators. This can cause power consumption to exceed the specified limits in many applications. Utility Model Content

[0005] This utility model aims to overcome the shortcomings of the existing technology and provides the following solution:

[0006] A high-efficiency thermo-optical bias point controlled thin-film lithium tantalate electro-optic modulator, wherein the thin-film lithium tantalate electro-optic modulator is an MZM type structure and is disposed on an LTOI material platform, comprising: an input waveguide, an optical beam splitter, a modulation electrode region, a bias electrode region, an optical beam combiner, and an output waveguide;

[0007] The output end of the input waveguide is connected to the input end of the optical beam splitter;

[0008] The output of the optical beam splitter is divided into two paths, which are connected to the upper and lower arms in the modulation electrode region respectively through waveguides.

[0009] In the modulation electrode region, the waveguide of the upper arm is connected to the first 90° bent waveguide, and the 180° bent waveguide is connected to the bias electrode region.

[0010] The waveguide passing through the bias electrode region is connected to the input end of the optical combiner via a second 90° bent waveguide and the waveguide of the lower arm in the modulation electrode region.

[0011] The output end of the optical beam combiner is connected to the input end of the output waveguide.

[0012] Preferably, in the LTOI material platform:

[0013] The substrate silicon thickness is 300μm-900μm;

[0014] The buried oxide layer material is silicon dioxide or BCB low refractive index light-transmitting material, with a thickness of 2μm-20μm;

[0015] The thin-film lithium tantalate device layer is an x-tangential thin film with a thickness of 200nm-1000nm.

[0016] Preferably, the MZM-type structure is located in the thin-film lithium tantalate device layer of the LTOI material platform;

[0017] The LT optical waveguide is either a ridge-type optical waveguide or a strip-type optical waveguide, and the etching depth does not exceed the total thickness of the LT.

[0018] The LT optical waveguide is covered with a silicon oxide cladding with a thickness of 500 nm-2 μm;

[0019] A metal resistive layer is disposed above the cladding silicon oxide. The metal resistive layer consists of a resistive portion and leads. The resistive portion has a rectangular block structure and is made of Ti, TiN, or TaN. The metal layer has a resistance of 30Ω-1000Ω, a thickness of 50nm-300nm, a length of 10μm-300μm, and a width of 1μm-10μm. The leads are connected to both sides of the resistive portion and are made of Au or Cu. The leads have a thickness of 300nm-10μm, a length of 50μm-500μm, and a width of 50μm-500μm.

[0020] Preferably, the structure of the modulation electrode region adopts a GSG-type traveling wave electrode structure.

[0021] Preferably, the electrode in the bias electrode region is a thermal bias electrode, which is composed of a silicon layer, a buried oxide layer, an LT waveguide layer, a silicon oxide layer and a metal resistor layer in sequence.

[0022] The metal resistive layer and waveguide of the bias electrode region are both arranged along the z-direction of the crystal.

[0023] The bending profiles of the first 90° bending waveguide, the second 90° bending waveguide, and the 180° bending waveguide are either circular arc or Euler bending, with bending radii greater than 50 μm.

[0024] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0025] This invention utilizes two sets of 90° curved waveguides to rotate the thermal bias electrode and the corresponding waveguide transmission direction by 90°, so that the e-light transmitted in the waveguide is converted into o-light transmission. This significantly reduces the thermally controlled power consumption by utilizing the high o-light thermo-optic coefficient of LT material (increasing it by an order of magnitude). Attached Figure Description

[0026] To more clearly illustrate the technical solution of this utility model, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of this utility model;

[0028] Figure 2 This is a schematic diagram of the thermal bias electrode structure of this utility model. Detailed Implementation

[0029] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0030] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example

[0032] In this embodiment, as Figure 1 As shown, a high-efficiency thermo-optical bias point controlled thin-film lithium tantalate electro-optic modulator is disclosed. The thin-film lithium tantalate electro-optic modulator has an MZM type structure and is disposed on an LTOI material platform. It includes: an input waveguide, an optical beam splitter, a modulation electrode region, a bias electrode region, an optical beam combiner, and an output waveguide.

[0033] The output end of the input waveguide is connected to the input end of the optical beamsplitter; the output end of the optical beamsplitter is divided into two paths, which are connected to the upper arm and lower arm in the modulation electrode region respectively through waveguides; in the modulation electrode region, the waveguide of the upper arm is connected to the first 90° bent waveguide, and the 180° bent waveguide is connected to the bias electrode region; the waveguide through the bias electrode region is connected to the input end of the optical beam combiner through the second 90° bent waveguide and the waveguide of the lower arm in the modulation electrode region; the output end of the optical beam combiner is connected to the input end of the output waveguide.

[0034] In the LTOI material platform: the substrate silicon thickness is 300μm-900μm; the buried oxide layer material is silicon oxide or BCB or other low refractive index transparent materials, with a thickness of 2μm-20μm; the device layer is an x-tangential thin film with a thickness of 200nm-1000nm.

[0035] The MZM-type structure is located on the thin-film lithium tantalate device layer (LT waveguide layer) of the LTOI material platform. The LT waveguide is either a ridge waveguide or a strip waveguide, with an etching depth not exceeding the total thickness of the LT. A cladding silicon oxide layer with a thickness of 500 nm-2 μm is placed above the LT waveguide. A metal resistor layer is placed above the cladding silicon oxide layer, consisting of a resistor portion and leads. The resistor portion is a rectangular block structure, made of common on-chip resistor materials such as Ti, TiN, or TaN. This resistor portion is located directly above the LT waveguide and is isolated by silicon oxide to prevent direct contact with the lead. The contact is used for thermal tuning of the LT optical waveguide. The metal layer has a resistance of 30Ω-1000Ω, a thickness of 50nm-300nm, a length of 10μm-300μm, and a width of 1μm-10μm. The pins are connected to both sides of the resistor and are made of highly conductive metals such as Au or Cu. The pins have a thickness of 300nm-10μm, a length of 50μm-500μm, and a width of 50μm-500μm. The pin dimensions are designed to facilitate easy connection with gold wires or probes for chip testing and device packaging.

[0036] In this embodiment, the LT waveguide is a ridge waveguide or a strip waveguide, and the etching depth does not exceed the total thickness of the LT, but must be greater than 0. A cladding silicon oxide layer covers the LT waveguide, with a thickness between 500 nm and 2 μm. The thickness cannot be too thin, otherwise it will cause strong absorption of the optical field within the waveguide; it also cannot be too thick, otherwise the distance between the LT waveguide and the titanium resistor will be too great, leading to a decrease in thermo-optical tuning efficiency. A typical thickness is 1 μm. A metal layer is disposed above the cladding silicon oxide layer. In this embodiment, the metal layer is made of titanium. The resistance of the titanium resistor is between 30 and 1000 ohms, typically with a thickness of 50-300 nm, a length of 50-300 μm, and a width of 1-10 μm. Titanium can also be replaced with other metal materials with comparable resistivity, such as TaN or TiN.

[0037] The modulation electrode region adopts a GSG-type traveling wave electrode structure.

[0038] In this embodiment, the electrode structure parameters need to be designed to match impedance, optical-microwave group velocity, and radio frequency loss in order to enable the device to have a high electro-optic modulation bandwidth.

[0039] The electrodes in the bias electrode region are thermally biased electrodes, which are composed of a silicon layer, a buried oxide layer, an LT optical waveguide layer, a silicon oxide layer, and a metal resistive layer in sequence. The metal resistive layer and the waveguide direction in the bias electrode region are both arranged along the z-direction of the crystal. The bending lines of the first 90° bending waveguide, the second 90° bending waveguide, and the 180° bending waveguide are circular arc or Euler bending type, and the bending radius is greater than 50μm.

[0040] In this embodiment, the electrode in the bias electrode region is a thermally biased electrode, such as... Figure 2As shown, the structure is composed of a silicon layer, a buried oxide layer, an LT waveguide layer, a silicon oxide layer, and a metal resistor layer in sequence. In this embodiment, the metal resistor layer in the bias electrode region is made of titanium and gold. The metal resistor and waveguide are both positioned along the z-direction of the crystal, and can have an angle with the z-axis of the crystal, but cannot exceed 30°. The modulation electrode region and the bias electrode region are connected by a 90° curved arc waveguide with a bending radius exceeding 50μm to reduce optical bending loss. The bending shape can be a conventional linear shape such as a circular arc or an Euler bend. The waveguide connecting the bias electrode region to the +z and -z directions is a 180° curved arc waveguide with a bending radius exceeding 50μm to reduce optical bending loss. The bending shape can be a conventional linear shape such as a circular arc or an Euler bend. Then, it is connected to one input end of the optical combiner through a second 90° curved waveguide with a bending radius exceeding 50μm to reduce optical bending loss. The bending shape can be a conventional linear shape such as a circular arc or an Euler bend.

[0041] The embodiments described above are merely preferred embodiments of the present utility model and are not intended to limit the scope of the present utility model. Any modifications and improvements made to the technical solutions of the present utility model by those skilled in the art without departing from the spirit of the present utility model should fall within the protection scope defined by the claims of the present utility model.

Claims

1. A high efficiency thermooptic bias point controlled thin film lithium tantalate electro-optic modulator, characterized by, The thin film lithium tantalite electro-optical modulator is an MZM type structure, is arranged on an LTOI material platform, and comprises an input waveguide, an optical beam splitter, a modulation electrode area, a bias electrode area, an optical beam combiner and an output waveguide. An output end of the input waveguide is connected with an input end of the optical beam splitter. Output ends of the optical beam splitter are divided into two paths, and are connected with an upper arm and a lower arm in the modulation electrode area through waveguides respectively. In the modulation electrode area, a waveguide passing through the upper arm is connected with a first 90° bending waveguide, and is connected with the bias electrode area through a 180° bending waveguide. A waveguide passing through the bias electrode area is connected with a waveguide of the lower arm in the modulation electrode area through a second 90° bending waveguide to an input end of the optical beam combiner. An output end of the optical beam combiner is connected with an input end of the output waveguide.

2. The high efficiency thermal-optic bias point controlled thin film lithium tantalate electro-optic modulator of claim 1, wherein, In the LTOI material platform: The thickness of the substrate silicon is 300 μm-900 μm; The buried oxygen layer material is silicon oxide or BCB low refractive transparent material, and the thickness is 2 μm-20 μm; The thin film lithium tantalate device layer is x-cut thin film, and the thickness is 200 nm-1000 nm.

3. The high efficiency thermal-optic bias point controlled thin film lithium tantalate electro-optic modulator of claim 1, wherein, The MZM type structure is located on the thin film lithium tantalate device layer of the LTOI material platform; The LT optical waveguide is a ridge type optical waveguide or a strip type optical waveguide, and the etching depth does not exceed the total thickness of LT; A cladding silicon oxide is arranged above the LT optical waveguide, and the thickness is 500 nm-2 μm; A metal resistance layer is arranged above the cladding silicon oxide, and the metal resistance layer is composed of a resistance part and a pin; the resistance part is a rectangular block structure, the material is Ti, TiN or TaN, the resistance of the metal layer is 30 Ω-1000 Ω, the thickness is 50 nm-300 nm, the length is 10 μm-300 μm, and the width is 1 μm-10 μm; the pin is connected with two sides of the resistance part, the material is Au or Cu, the thickness of the pin is 300 nm-10 μm, the length is 50 μm-500 μm, and the width is 50 μm-500 μm.

4. The high efficiency thermal-optic bias point controlled thin film lithium tantalate electro-optic modulator of claim 1, wherein, The structure of the modulation electrode area adopts a GSG type traveling wave electrode structure.

5. The high efficiency thermal-optic bias point controlled thin film lithium tantalate electro-optic modulator of claim 1, wherein, The electrode of the bias electrode area adopts a thermal bias electrode, which is composed of a silicon layer, a buried oxygen layer, an LT optical waveguide layer, a silicon oxide layer and a metal resistance layer in sequence; The metal resistance layer and the waveguide direction of the bias electrode area are placed along the z direction of the crystal; The bending line type of the first 90° bending waveguide, the second 90° bending waveguide and the 180° bending waveguide is circular arc or Euler bending type, and the bending radius is greater than 50 μm.

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