L3 type film lithium niobate photonic crystal microcavity optimization method based on reverse design

Abstract

The invention provides an L3 type thin film lithium niobate photonic crystal microcavity optimization method based on reverse design, and relates to the technical field of photoelectronics, and the method comprises the following steps: S1, obtaining an initial photonic crystal microcavity; s2, randomly adjusting the radius size of an air hole on a non-coordinate axis on the initial photonic crystal microcavity based on a reverse design algorithm until a first type of photonic crystal structure corresponding to the highest Q value is adjusted; and S3, based on a Gaussian envelope function optimization principle, adjusting the displacement of the centers of the air holes located on the X coordinate axis and the Y coordinate axis on the first type of photonic crystal structure until the corresponding second type of photonic crystal structure when the Q value is the highest is adjusted. The beneficial effects of the invention are that the Q value of the photonic crystal micro-cavity is substantially improved, the L3 cavity film lithium niobate photonic crystal annular cavity with the highest Q value at present is realized, and the L3 cavity film lithium niobate photonic crystal annular cavity has the advantages of small size, low loss, high integration level and the like.

Description

Technical Field

[0001] This invention relates to the field of optoelectronics technology, and in particular to an optimization method for a microcavity of an L3-type thin-film lithium niobate photonic crystal based on reverse design. Background Technology

[0002] L3-type photonic crystal microcavities, as a typical photonic crystal structure, are formed by removing three adjacent air holes in a two-dimensional periodic photonic crystal. They enable efficient localization and manipulation of light and have broad application prospects in micro- and nano-optical devices. Lithium niobate (LiNbO3) thin films, with their excellent electro-optic, nonlinear optical, and piezoelectric properties, combined with L3-type photonic crystal microcavity structures, offer new possibilities for developing high-performance optical devices.

[0003] In the field of photonic crystal microcavity research, the Q-value is a key parameter that precisely describes the light storage capacity of a photonic crystal microcavity and also represents its optical loss. Essentially, the Q-value of a photonic crystal microcavity is positively correlated with its light storage capacity; that is, the higher the Q-value, the stronger the light storage capacity. Furthermore, as the Q-value increases, the intensity of the interaction between light and matter within the cavity also increases.

[0004] In recent years, reverse engineering has opened up new avenues for the design of photonic crystal microcavities. Guided by the target optical function, it uses optimization algorithms to solve for structural parameters in reverse. However, when applied to L3-type thin-film lithium niobate photonic crystal microcavities, this method encounters multiple challenges. The refractive index dispersion and crystal orientation differences of thin-film lithium niobate, as well as structural errors caused by manufacturing processes, significantly increase the complexity of reverse engineering. These factors must be fully considered during the optimization process to ensure that the design results are both accurate and manufacturable.

[0005] In the field of microcavity Q-value optimization, current mainstream methods are divided into two categories: traditional scanning and machine learning. While traditional scanning optimization is simple to operate and easy to understand, the electromagnetic simulation process is time-consuming and lacks comprehensive research on key parameters affecting the Q-value, resulting in low utilization of optimization parameters and difficulty in obtaining high-Q microcavities. Although machine learning algorithms can learn from large datasets and intelligently predict high-Q structures, they are limited by the fundamental microcavity Q-value. Randomly generated datasets often concentrate in the low-Q space, leading to insufficient prediction accuracy for high-Q structures.

[0006] Meanwhile, despite continuous advancements in micro- and nano-fabrication technologies, enabling the fabrication of high-precision photonic crystal microcavities, process errors cannot be completely avoided. This necessitates design methods that not only achieve high-performance optical design but also possess robustness against manufacturing errors, thereby improving device yield and stability. Traditional reverse engineering methods, however, have significant shortcomings in handling manufacturing errors and struggle to meet actual production needs. Summary of the Invention

[0007] In view of this, in order to overcome the limitations of traditional design and achieve high-performance and robust microcavity design of L3 type thin-film lithium niobate photonic crystal, embodiments of the present invention provide an optimization method for L3 type thin-film lithium niobate photonic crystal microcavities based on reverse design.

[0008] Embodiments of the present invention provide an optimization method for L3-type thin-film lithium niobate photonic crystal microcavities based on reverse design, comprising the following steps:

[0009] S1. Obtain an initial photonic crystal microcavity, wherein the initial photonic crystal microcavity is a two-dimensional periodic photonic crystal formed by setting multiple air holes on a thin-film lithium niobate plate, wherein the two-dimensional periodic photonic crystal has three missing air holes at its geometric center.

[0010] S2. Keep the air holes on the X and Y axes of the initial photonic crystal microcavity unchanged, and randomly adjust the radius of the air holes on the non-X and non-Y axes of the initial photonic crystal microcavity based on the reverse design algorithm until the first type of photonic crystal structure corresponding to the highest Q value is obtained.

[0011] S3. Keep the air holes on the non-X and non-Y coordinate axes of the first type of photonic crystal structure unchanged, and adjust the displacement of the center of the air holes on the X and Y coordinate axes of the first type of photonic crystal structure based on the Gaussian envelope function optimization principle until the second type of photonic crystal structure corresponding to the highest Q value is obtained.

[0012] Furthermore, in step S2, different radii of air holes are randomly assigned within a specified wavelength range using a reverse design algorithm until the first type of photonic crystal structure corresponding to the highest Q value is obtained.

[0013] Furthermore, the specified wavelength range is 144nm-162nm.

[0014] Furthermore, the four parameters of 144nm, 150nm, 156nm and 162nm are randomly assigned to each air hole to generate multiple crystal structures. The crystal structure corresponding to the highest Q value is selected as the first type of photonic crystal structure.

[0015] Furthermore, step S3 includes adjusting the displacement of the center of the air hole on the X-axis based on the Gaussian envelope function optimization principle and adjusting the displacement of the center of the air hole on the Y-axis based on the Gaussian envelope function optimization principle.

[0016] Furthermore, the centers of a pair of air holes that are symmetrical about the X-axis have the same displacement, and the centers of a pair of air holes that are symmetrical about the Y-axis have the same displacement.

[0017] Furthermore, among two adjacent air holes located on the X-axis and on one side of the Y-axis, one moves toward the origin and the other moves away from the origin; among two adjacent air holes located on the Y-axis and on one side of the X-axis, one moves toward the origin and the other moves away from the origin.

[0018] Furthermore, the air hole is a standard round hole.

[0019] Furthermore, the initial photonic crystal microcavity has a thickness of 300 nm, a refractive index of 2.21 near a wavelength of 1340 nm, a lattice period a of 600 nm, and an air hole radius of 162 nm.

[0020] Further, in step S3, the air holes located on the X-axis include four pairs symmetrically positioned relative to the origin, arranged sequentially along the direction away from the origin as the first pair of X-axis holes, the second pair of X-axis holes, the third pair of X-axis holes, and the fourth pair of X-axis holes. The first pair of X-axis holes are all moved 54 nm toward the origin, the second pair of X-axis holes are all moved 48 nm away from the origin, the third pair of X-axis holes are all moved 48 nm toward the origin, and the fourth pair of X-axis holes are all moved 78 nm away from the origin. The air holes located on the Y-axis include two pairs symmetrically positioned relative to the origin, arranged sequentially along the direction away from the origin as the first pair of Y-axis holes and the second pair of Y-axis holes. The first pair of Y-axis holes are all moved 54 nm toward the origin, and the second pair of Y-axis holes are all moved 30 nm away from the origin.

[0021] The beneficial effects of the technical solutions provided by the embodiments of the present invention are as follows:

[0022] This invention presents an L3-type thin-film lithium niobate photonic crystal microcavity optimization method based on reverse design. Based on a reverse design algorithm, the radii of air holes on the non-X and non-Y axes of the initial photonic crystal microcavity are randomly adjusted until the first type of photonic crystal structure corresponding to the highest Q value is randomly selected. Then, based on the Gaussian envelope function optimization principle, the displacement of the air hole centers on the X and Y axes of the initial photonic crystal microcavity is adjusted to determine the second type of photonic crystal structure corresponding to the highest Q value. Combining the first and second type of photonic crystal structures yields the optimized photonic crystal microcavity, significantly improving the Q value of the photonic crystal microcavity, for example, increasing it from the initial 1550 to 7241. Furthermore, this invention addresses the problem of difficulty and time consumption in simultaneously optimizing multiple parameters when optimizing the Q value, achieving the highest Q value currently available for an L3-type thin-film lithium niobate photonic crystal ring cavity. It possesses advantages such as small size, low loss, and high integration, and is widely used in optical communication, optical sensing, biomedicine, and quantum information fields. Attached Figure Description

[0023] Figure 1 This is a flowchart of the L3-type thin-film lithium niobate photonic crystal microcavity optimization method based on reverse design, as described in this invention.

[0024] Figure 2 This is a schematic diagram of the initial photonic crystal microcavity;

[0025] Figure 3 This is a schematic diagram showing the distribution of air holes on the non-X and non-Y coordinate axes of a type-1 photonic crystal structure.

[0026] Figure 4 This is a schematic diagram of the air hole modulation distribution on the X and Y coordinate axes of a type II photonic crystal structure;

[0027] Figure 5 This is a schematic diagram of the overall structure of the second type of photonic crystal. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings. The following description presents a preferred embodiment of the various possible embodiments of the present invention, intended to provide a basic understanding of the invention, but not intended to identify key or decisive elements of the invention or to limit the scope of protection sought.

[0029] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0030] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0031] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures. Also, it should be understood that, for ease of description, the dimensions of the various parts shown in the figures are not drawn to actual scale.

[0032] In the description of this invention, it should be noted that the circuits, electronic components and modules involved in this invention are all prior art, which can be fully implemented by those skilled in the art, and need not be elaborated upon. The content protected by this invention does not involve improvements to the internal structure and method.

[0033] It should be further noted that, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Please refer to Figure 1 The embodiments of the present invention provide an optimization method for L3-type thin-film lithium niobate photonic crystal microcavities based on reverse design, comprising the following steps:

[0035] S1. Obtain an initial photonic crystal microcavity, wherein the initial photonic crystal microcavity is a two-dimensional periodic photonic crystal formed by setting multiple air holes on a thin-film lithium niobate plate, and the two-dimensional periodic photonic crystal has three missing air holes at its geometric center.

[0036] like Figure 2 As shown, the initial photonic crystal microcavity is a traditional L3-type photonic crystal microcavity made of thin-film lithium niobate material. The air holes of the initial photonic crystal microcavity are standard circular holes. The air holes of the initial photonic crystal microcavity are arranged in multiple rows (X-axis direction) and multiple columns (Y-axis direction) in a quincunx pattern.

[0037] It should be noted that the initial photonic crystal microcavity is generally rectangular in shape, and its dimensions can be flexibly set according to the actual application scenario. For example, in this embodiment, the initial photonic crystal microcavity has a thickness of 300 nm, a refractive index of 2.21 near a wavelength of 1340 nm, a lattice period a of 600 nm, an air hole radius of 162 nm, and an initial Q value of 1550.

[0038] S2. Keep the air holes on the X and Y axes of the initial photonic crystal microcavity unchanged, and randomly adjust the radius of the air holes on the non-X and non-Y axes of the initial photonic crystal microcavity based on the reverse design algorithm until the first type of photonic crystal structure corresponding to the highest Q value is obtained.

[0039] Specifically, such as Figure 3 As shown, when adjusting the radius of the air holes (white filling holes) on the non-X coordinate axis and non-Y coordinate axis, different radius sizes are randomly assigned to different air holes within a specified wavelength range through a reverse design algorithm until the first type of photonic crystal structure corresponding to the highest Q value is obtained.

[0040] In this embodiment, different radii are assigned to different air holes within the specified wavelength range of 144nm-162nm. That is, the maximum radius of the air hole on the non-X coordinate axis and the non-Y coordinate axis is 162nm, and the minimum radius is 144nm.

[0041] It should be noted that, guided by a high Q value, the algorithm structure for determining the air hole radius on the selected non-X and non-Y coordinate axes uses multiple wavelength parameter ranges as structural parameters for inverse optimization. After iterative optimization within these wavelength parameter ranges, the optimal wavelength parameter range is selected. In this embodiment, six wavelength parameter ranges are set: [144nm, 150nm, 156nm, 162nm], [168nm, 174nm, 180nm, 186nm], [192nm, 198nm, 204nm, 210nm], [204nm, 210nm, 216nm, 222nm], [216nm, 222nm, 228nm, 234nm], and [240nm, 246nm, 252nm, 258nm]. After continuous iterative optimization, the wavelength parameter range of [144nm, 150nm, 156nm, 162nm] was determined to be optimal, with the air hole radii randomly distributed within this range on the non-X and non-Y coordinate axes. Furthermore, the four parameters of 144nm, 150nm, 156nm, and 162nm were randomly assigned to each air hole, generating multiple crystal structures. The crystal structure corresponding to the highest Q value was compared and selected as the first type of photonic crystal structure. In this embodiment, the first type of photonic crystal structure achieved a Q value improvement of 4100.

[0042] S3. Keep the air holes on the non-X and non-Y coordinate axes of the first type of photonic crystal structure unchanged, and adjust the displacement of the center of the air holes on the X and Y coordinate axes of the first type of photonic crystal structure based on the Gaussian envelope function optimization principle until the second type of photonic crystal structure corresponding to the highest Q value is obtained.

[0043] Specifically, such as Figure 4 and 5 As shown, the displacement of the center of the air hole (yellow filling hole) on the X-axis of the first type of photonic crystal structure is adjusted based on the Gaussian envelope function optimization principle, and the displacement of the center of the air hole (yellow filling hole) on the Y-axis of the first type of photonic crystal structure is adjusted based on the Gaussian envelope function optimization principle.

[0044] Among them, the centers of a pair of air holes that are symmetrical about the X-axis have the same displacement, and the centers of a pair of air holes that are symmetrical about the Y-axis have the same displacement.

[0045] Furthermore, among two adjacent air holes located on the X-axis and to one side of the Y-axis, one moves towards the origin O and the other moves away from the origin O; among two adjacent air holes located on the Y-axis and to one side of the X-axis, one moves towards the origin O and the other moves away from the origin O. The origin O is the geometric center of the initial photonic crystal microcavity.

[0046] In this embodiment, the air holes on the X-axis include four pairs symmetrically arranged relative to the origin O. Along the direction away from the origin O, they are sequentially the first pair of X-axis holes, the second pair of X-axis holes, the third pair of X-axis holes, and the fourth pair of X-axis holes. The first pair of X-axis holes are all moved 54 nm toward the origin O, the second pair of X-axis holes are all moved 48 nm away from the origin O, the third pair of X-axis holes are all moved 48 nm toward the origin O, and the fourth pair of X-axis holes are all moved 78 nm away from the origin O. The air holes on the Y-axis include two pairs symmetrically arranged relative to the origin O. Along the direction away from the origin O, they are sequentially the first pair of Y-axis holes and the second pair of Y-axis holes. The first pair of Y-axis holes are all moved 54 nm toward the origin O, and the second pair of Y-axis holes are all moved 30 nm away from the origin O.

[0047] The obtained second type of photonic crystal structure is the final optimized photonic crystal microcavity. The Q value of the optimized photonic crystal microcavity was increased from the initial Q value of 1550 of the initial photonic crystal microcavity to the final Q value of 7241, achieving a significant improvement in the Q value of the L3 type thin film lithium niobate photonic crystal microcavity.

[0048] In this document, the directional terms such as front, back, top, and bottom are defined based on the position of the components in the accompanying drawings and their relative positions to each other, solely for the purpose of clarity and convenience in expressing the technical solution. It should be understood that these are relative concepts and can vary depending on different methods of use and placement; the use of these directional terms should not limit the scope of protection claimed in this application.

[0049] Where there is no conflict, the embodiments and features described above can be combined with each other. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for optimizing the microcavity of an L3-type thin-film lithium niobate photonic crystal based on reverse design, characterized in that, Includes the following steps: S1. Obtain an initial photonic crystal microcavity, wherein the initial photonic crystal microcavity is a two-dimensional periodic photonic crystal formed by setting multiple air holes on a thin-film lithium niobate plate, wherein the two-dimensional periodic photonic crystal has three missing air holes at its geometric center. S2. Keep the air holes on the X and Y axes of the initial photonic crystal microcavity unchanged, and randomly adjust the radius of the air holes on the non-X and non-Y axes of the initial photonic crystal microcavity based on the reverse design algorithm until the first type of photonic crystal structure corresponding to the highest Q value is obtained. S3. Keep the air holes on the non-X and non-Y coordinate axes of the first type of photonic crystal structure unchanged, and adjust the displacement of the center of the air holes on the X and Y coordinate axes of the first type of photonic crystal structure based on the Gaussian envelope function optimization principle until the second type of photonic crystal structure corresponding to the highest Q value is obtained.

2. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 1, characterized in that: In step S2, different radii of air holes are randomly assigned within a specified wavelength range using a reverse design algorithm until the first type of photonic crystal structure corresponding to the highest Q value is obtained.

3. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 2, characterized in that: The specified wavelength range is 144nm-162nm.

4. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 2 or 3, characterized in that: Four parameters, 144nm, 150nm, 156nm and 162nm, were randomly assigned to each air hole to generate multiple crystal structures. The crystal structure corresponding to the highest Q value was selected as the first type of photonic crystal structure.

5. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 1, characterized in that: Step S3 includes adjusting the displacement of the center of the air hole on the X-axis based on the Gaussian envelope function optimization principle and adjusting the displacement of the center of the air hole on the Y-axis based on the Gaussian envelope function optimization principle.

6. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 5, characterized in that: The centers of a pair of air holes that are symmetrical about the X-axis have the same displacement, and the centers of a pair of air holes that are symmetrical about the Y-axis have the same displacement.

7. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 5, characterized in that: Among two adjacent air holes located on the X-axis and on one side of the Y-axis, one moves toward the origin and the other moves away from the origin; among two adjacent air holes located on the Y-axis and on one side of the X-axis, one moves toward the origin and the other moves away from the origin.

8. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 1, characterized in that: The air hole is a standard round hole.

9. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 1, characterized in that: The initial photonic crystal microcavity has a thickness of 300 nm, a refractive index of 2.21 near a wavelength of 1340 nm, a lattice period a of 600 nm, and an air hole radius of 162 nm.

10. The method for optimizing the microcavity of L3-type thin-film lithium niobate photonic crystal based on reverse design as described in claim 9, characterized in that: In step S3, the air holes on the X-axis include four pairs symmetrical about the origin, arranged sequentially along the direction away from the origin: the first pair of X-axis holes, the second pair of X-axis holes, the third pair of X-axis holes, and the fourth pair of X-axis holes. The first pair of X-axis holes are all moved 54 nm toward the origin, the second pair of X-axis holes are all moved 48 nm away from the origin, the third pair of X-axis holes are all moved 48 nm toward the origin, and the fourth pair of X-axis holes are all moved 78 nm away from the origin. The air holes on the Y-axis include two pairs symmetrical about the origin, arranged sequentially along the direction away from the origin: the first pair of Y-axis holes and the second pair of Y-axis holes. The first pair of Y-axis holes are all moved 54 nm toward the origin, and the second pair of Y-axis holes are all moved 30 nm away from the origin.

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