Topological laser and manufacturing method thereof

Abstract

The invention discloses a topological laser and a manufacturing method. The topological laser comprises an active layer, a topological normal condition photonic crystal and a topological non-normal condition photonic crystal, wherein the topological normal condition photonic crystal and the topological non-normal condition photonic crystal adopt one-dimensional topological photonic crystals; the active layer is a perovskite quantum layer, and a limiting effect can be generated at a spliced boundary, so that an interface state is limited between two photonic crystals. According to the invention, photoetching-free, high-directivity and low-threshold single-mode laser emission can be realized; the technology difficulty and the preparation cost can be reduced, and a way is laid for realizing an efficient topology laser working in the whole visible spectrum range.

Description

Technical Field

[0001] The present invention relates to semiconductor laser technology, and in particular to a topological laser requiring no photolithography and a manufacturing method thereof. Background Art

[0002] The concept of topological photonics, characterized by global topological invariants of photon wave functions in the optical dispersion band, has been used in recent years to design optical cavities that are resistant to manufacturing defects and to demonstrate a variety of topological microlasers that can operate in the infrared. The cavity design of these lasers relies on the excitation of boundary states (such as edge states or corner states) at the interface of photonic structures in different topological stages. The difference in topological invariants at the interface defines the boundary states. Typical edge / corner emitting topological lasers based on one-dimensional chains or two-dimensional arrays of semiconductor resonators have poor directionality, are difficult to couple, have complex designs, and are limited to infrared operation. Recently, topological lasers based on topological bulk states and topological vertical cavity laser arrays have solved the problems of directionality and outcoupling, but have not improved the design complexity and the ability to obtain short emission wavelengths. The currently proposed topological vertical emitting lasers still face a problem: when the device operates in the microwave range, extremely high-precision lithography processes are required to achieve microwave resonance, which poses a huge challenge to domestic lithography processes. Summary of the Invention

[0003] To address the aforementioned issues in the prior art, the present invention proposes a lithography-free topological laser based on the SSH model and its fabrication method. This approach employs a novel optical field confinement method and a novel mode selection mechanism, eliminating the need for lithography and reducing the emission threshold while achieving stable vertically emitting single-mode lasing. By leveraging the topological invariance of one-dimensional photonic crystals, the effects of process errors on the laser are reduced. Furthermore, the use of lithography is avoided, reducing process costs.

[0004] One object of the present invention is to propose a topological laser, characterized in that: it includes an active layer; a topologically trivial photonic crystal formed on one side of the active layer, the topologically trivial photonic crystal is a one-dimensional unit cell array, including a plurality of unit cells periodically arranged with the same lattice constant, each unit cell includes a first intermediate layer and a first covering layer located on both sides of the first intermediate layer, the refractive index of the first intermediate layer is less than the refractive index of the first covering layers on both sides, and the height of the first intermediate layer is greater than the sum of the heights of the first covering layers on both sides, so that the band gap of the topologically trivial photonic crystal is opened, and the Zak phase of the first energy band is 0; the topologically non-trivial A topological non-trivial photonic crystal is formed on the other side of the active layer, the topological non-trivial photonic crystal is a one-dimensional unit cell array, including a plurality of unit cells periodically arranged with the same lattice constant, each unit cell including a second intermediate layer and second covering layers on both sides of the second intermediate layer, the refractive index of the second intermediate layer is greater than the refractive index of the second covering layers on both sides, and the height of the second intermediate layer is less than the sum of the heights of the second covering layers on both sides, so that the band gap of the topological non-trivial photonic crystal is opened, and the Zak phase of the first energy band is π; wherein the active layer, the topological non-trivial photonic crystal and the topological non-trivial photonic crystal constitute a resonant cavity.

[0005] Preferably, the active layer is realized by a CsPbBr3 perovskite quantum dot film.

[0006] Preferably, for optically pumped lasers, stable laser wavelength tuning is achieved by selecting a sample with a continuously varying active layer thickness.

[0007] Preferably, the topological laser is constructed by splicing a topologically trivial state with a bandgap and a topologically nontrivial state. Interface states of a certain frequency are generated at the splicing site. The optical field of the interface state is highly immune to local perturbations of the structure, such as uneven thickness of the quantum dot film, thereby reducing the impact of defects in the processed layers of the quantum dot film on the single-mode characteristics of the laser.

[0008] Preferably, the first intermediate layer is SiO2, and the first covering layers on both sides are TiO2.

[0009] Preferably, the second intermediate layer is TiO2, and the second covering layers on both sides are SiO2.

[0010] Preferably, the first intermediate layer and the second intermediate layer are arranged at intervals, wherein the first covering layer is composed of half of the second intermediate layer on one side of the topological trivial state photonic crystal; and the second covering layer is composed of half of the first intermediate layer on one side of the topological non-trivial state photonic crystal.

[0011] According to the purpose of the present invention, a method for manufacturing a topological laser is also proposed, comprising the following steps: 1) periodically alternating electron beam evaporation deposition of high refractive index layers and low refractive index layers; 2) arranging a topological trivial photonic crystal and a topological non-trivial photonic crystal, wherein the topological trivial photonic crystal includes a plurality of unit cells periodically arranged with the same lattice constant, each unit cell includes a first intermediate layer and a first covering layer located on both sides of the first intermediate layer, the first intermediate layer is the low refractive index layer, and the first covering layer is composed of half of the high refractive index layer; the topological non-trivial photonic crystal includes a plurality of unit cells periodically arranged with the same lattice constant, each unit cell includes a second intermediate layer and a second covering layer located on both sides of the second intermediate layer, the second intermediate layer is the high refractive index layer, and the second covering layer is composed of half of the low refractive index layer; 3) the topological trivial photonic crystal and the topological non-trivial photonic crystal are spliced ​​together to form a boundary at the splicing; 4) replacing the high refractive index layer at the boundary with a perovskite quantum dot film to realize an active layer.

[0012] Preferably, the high refractive index layer is TiO2, and the low refractive index layer is SiO2.

[0013] The topological edge state laser based on the SSH model of the present invention includes: a topological trivial state photonic crystal and a topological non-trivial state photonic crystal, and a one-dimensional topological photonic crystal is used; for the optically pumped laser, the active layer is a perovskite quantum layer, and no part needs to be photolithographically processed. The topological non-trivial state photonic crystal and the topological trivial state photonic crystal each include a plurality of unit cells arranged periodically with the same lattice constant. The two sides of each unit cell are rectangles of the same height, and the middle is a rectangle of different heights. When the refractive index of the middle rectangle is less than the refractive index of the rectangles on both sides, and the height is greater than the sum of the heights of the rectangles on both sides, the band gap is opened, and the Zak phase of the first band is 0. This band structure is called a topological trivial state, forming a topological trivial state photonic crystal. When the refractive index of the middle rectangle is greater than that of the rectangles on both sides, and its height is less than the sum of the heights of the rectangles on both sides, the band gap is opened. At this time, the Zak phase of the first energy band is π. This band structure is called a topological non-trivial state, forming a topological non-trivial photonic crystal. Both photonic crystals have open energy bands and have the same band structure. The topological trivial state photonic crystal and the topological non-trivial state photonic crystal are spliced ​​together, forming a boundary at the splicing point, forming a resonant cavity. For optically pumped lasers, when the pump light is incident on the laser resonant cavity, the light in the boundary state will be confined at the boundary, and the photons generated by the active layer will reflect back and forth within the boundary, resulting in lasing.

[0014] The wavelength range of the one-dimensional topological edge-state laser is consistent with the gain region of the selected perovskite film. Adjusting the thickness of the gain medium in the active layer adjusts the gain region, and thus the wavelength range of the topological edge-state laser. Unlike conventional semiconductor lasers, the optical field confinement does not rely on the waveguide layer. Based on the SSH model deposition structure, the optical field can be strongly confined in the perpendicular plane direction.

[0015] Topological edge state lasers are highly immune to local perturbations. When the interface states exist in the photonic band gap, changes in the quantum dot film thickness will not destroy the single-mode characteristics of the topological edge state laser.

[0016] Advantages of the present invention

[0017] Based on topological band physics, this invention proposes a new resonant cavity construction mechanism and addresses practical application challenges with its design approach. The advantages of the proposed topological edge-state laser, which satisfies the one-dimensional SSH model in its longitudinal structure, include: The new resonant cavity construction mechanism enables lithography-free, highly directional, low-threshold, narrow-linewidth single-mode vertical laser emission, significantly reducing process complexity and fabrication costs. The invention is robust to local perturbations in multilayer structures and is particularly well-suited for quantum dot lasers, overcoming the typical problems of poor uniformity, aggregation, and luminescence quenching associated with thick quantum dot films. This paves the way for highly efficient topological lasers operating across the entire visible spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic structural diagram of Example 1 of a topological edge state laser satisfying a one-dimensional SSH model in its longitudinal structure according to the present invention.

[0019] Figure 2 Schematic diagram of a one-dimensional topological photonic crystal according to Example 1 of the topological edge state laser of the present invention; wherein (a) is a schematic diagram of a topological non-trivial state photonic crystal and a topological trivial state photonic crystal, (b) is a schematic diagram of the energy bands of the topological non-trivial state and topological trivial state photonic crystals. (c) is a schematic diagram of the normalized electric field distribution along the z-axis within the corresponding unit cells of the first two optical bands of the topological non-trivial state and topological trivial state photonic crystals.

[0020] Figure 3 This is a graph of the quality factors of various modes supported by the laser resonant cavity of Example 1 of the topological edge state laser of the present invention.

[0021] Figure 4 This is a diagram of the electric field distribution of the edge state mode supported by the laser resonant cavity of Example 1 of the topological edge state laser of the present invention.

[0022] Figure 5In the first embodiment of the topological edge state laser of the present invention, a tunable single-mode laser emission wavelength is obtained by exciting perovskite quantum dot films of different thicknesses. DETAILED DESCRIPTION

[0023] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0024] Example 1

[0025] like Figure 1 As shown, this example utilizes optical pumping excitation. The topological edge state laser based on the one-dimensional SSH model includes an active layer, and topologically trivial photonic crystals and topologically non-trivial photonic crystals located on either side of the active layer. The topologically trivial photonic crystals and topologically non-trivial photonic crystals are constructed using one-dimensional photonic crystals. The topologically non-trivial photonic crystals and topologically non-trivial photonic crystals are constructed by periodically depositing layers of high-refractive index and low-refractive index materials. The active layer is made of a perovskite CsPbBr3 quantum dot film. By varying the thickness of the active layer material, the gain range varies. The topologically trivial photonic crystal and the topologically non-trivial photonic crystal are spliced ​​together, forming a boundary at the splice to form the laser resonant cavity. The topological edge state laser based on the longitudinal SSH structure does not rely on a waveguide layer to confine the light field. Due to its topological properties, the edge state light field can be strongly confined in the perpendicular plane direction. In this embodiment, the edge state mode to be excited has a high quality factor and a narrow spectral linewidth. When external excitation light enters the laser resonator, the generated light is effectively fed back into the laser resonator due to the optical field confinement effect caused by band inversion, resulting in lasing at the operating wavelength. In this example, the laser's luminous area and output power are determined by the area of ​​the active layer.

[0026] Figure 2(a) shows a topological non-trivial photonic crystal and a topological trivial photonic crystal, each comprising a plurality of one-dimensional unit cell arrays arranged periodically with the same lattice constant. In which, the topological trivial photonic crystal includes a plurality of unit cells arranged periodically with the same lattice constant, each unit cell includes a first intermediate layer and a first covering layer located on both sides of the first intermediate layer, the refractive index of the first intermediate layer is less than the refractive index of the first covering layers on both sides, and the height of the first intermediate layer is greater than the sum of the heights of the first covering layers on both sides, so that the band gap of the topological trivial photonic crystal is opened, and the Zak phase of the first energy band is 0 at this time; the topological non-trivial photonic crystal is a one-dimensional unit cell array, including a plurality of unit cells arranged periodically with the same lattice constant, each unit cell includes a second intermediate layer and a second covering layer located on both sides of the second intermediate layer, the refractive index of the second intermediate layer is greater than the refractive index of the second covering layers on both sides, and the height of the second intermediate layer is less than the sum of the heights of the second covering layers on both sides, so that the band gap of the topological non-trivial photonic crystal is opened, and the Zak phase of the first energy band is π; wherein the active layer, the topological trivial photonic crystal and the topological non-trivial photonic crystal constitute a resonant cavity. In actual production, topological trivial photonic crystals and topological non-trivial photonic crystals can be made by alternating electron beam evaporation deposition of high refractive index materials and high refractive index materials, wherein in a single unit cell of the topological trivial photonic crystal, the middle layer is formed by low refractive index material, and the covering layers on both sides are respectively composed of half of the adjacent high refractive index material, while in a single unit cell of the topological non-trivial photonic crystal, the middle layer is formed by high refractive index material, and the covering layers on both sides are respectively composed of half of the adjacent low refractive index material, so that the height of the low refractive index layer is smaller than the height of the high refractive index. In this way, high and low refractive index layers can be alternately deposited by electron beam evaporation deposition and other methods, and then the topological trivial photonic crystal and the topological non-trivial photonic crystal are spliced ​​to form a boundary at the splicing point. Finally, the perovskite quantum dot layer is used as the active layer to replace the high refractive index layer at the boundary to form the entire laser resonant cavity. This can simplify the structure and production difficulty of the device. The band structures of topological trivial photonic crystals and topological non-trivial photonic crystals are as follows: Figure 2 (b) As shown in the left figure, the normalized electric field distribution along the z-axis in the corresponding unit cells of the first and second energy bands is as follows: Figure 2 (c) As shown in the left figure; when the refractive index of the middle layer is greater than the refractive index of the two covering layers, and the height is less than the sum of the heights of the two covering layers, the band gap is opened, the Zak phase of the first band is π, and the photonic crystal undergoes band inversion. This band structure is called a topological non-trivial state, forming a topological non-trivial state photonic crystal; its band structure is as shown Figure 2 (b) As shown in the right figure, the normalized electric field distribution along the z-axis in the corresponding unit cells of the first and second energy bands is as follows: Figure 2 (c) As shown in the right figure.

[0027] In a specific example, the laser resonant cavity is composed of periodic TiO2 layers and SiO2 layers. Specifically, the lattice period constant is set to a = 132nm, the TiO2 layer height is set to d1 = 62nm, and the SiO2 layer height is set to d2 = 70nm. Through full-wave simulation, the quality factors of different modes existing in the above laser resonant cavity are calculated, such as Figure 3 As shown. Among them, the edge state mode has the highest quality factor and has the best confinement effect in the laser resonant cavity. The smaller the quality factor of the bulk mode, the worse the light field confinement effect. This characteristic is conducive to achieving final single-mode lasing, and this characteristic is independent of the size of the laser resonant cavity. The previous perovskite quantum dot laser resonant cavity can support multiple modes, and because of their similar quality factors, they lack an intrinsic mode selection mechanism, making it difficult to achieve stable single-mode lasing. The topological laser mode selection mechanism of the present invention does not depend on the size of the laser resonant cavity, and can maintain stable single-mode emission while increasing the light-emitting area of ​​the device and increasing the output power.

[0028] The intrinsic electric field of the edge state of the topological laser in the above embodiment is as follows: Figure 4 As shown in Figure 2, we can see a laser light field distribution that is strongly confined within the laser resonator.

[0029] Figure 5 The emission wavelength of the topological edge state laser of the above embodiment changes with the thickness of the active layer. When the thickness of the perovskite quantum dot film increases, the emission wavelength shifts to the left.

[0030] Through the analysis of the examples, the advantages of the topological edge state laser based on the longitudinal SSH model proposed in the present invention can be demonstrated: the new light field confinement mechanism can realize single-mode vertical laser emission without lithography, high directionality, low threshold, and narrow linewidth.

Claims

1. A topological laser, characterized in that: include active layer; A topologically trivial photonic crystal is formed on one side of the active layer, wherein the topologically trivial photonic crystal is a one-dimensional unit cell array, including a plurality of unit cells periodically arranged with the same lattice constant, each unit cell including a first intermediate layer and first covering layers located on both sides of the first intermediate layer, wherein the refractive index of the first intermediate layer is less than the refractive index of the first covering layers on both sides, and the height of the first intermediate layer is greater than the sum of the heights of the first covering layers on both sides, so that the band gap of the topologically trivial photonic crystal is opened, and at this time, the Zak phase of the first energy band is 0; A topological non-trivial photonic crystal is formed on the other side of the active layer, wherein the topological non-trivial photonic crystal is a one-dimensional unit cell array, including a plurality of unit cells periodically arranged with the same lattice constant, each unit cell including a second intermediate layer and second cover layers located on both sides of the second intermediate layer, the refractive index of the second intermediate layer is greater than the refractive index of the second cover layers on both sides, and the height of the second intermediate layer is less than the sum of the heights of the second cover layers on both sides, so that the band gap of the topological non-trivial photonic crystal is opened, and at this time the Zak phase of the first energy band is π; The active layer, the topological trivial state photonic crystal and the topological non-trivial state photonic crystal constitute a resonant cavity.

2. The topological laser according to claim 1, characterized in that: The active layer is realized by a CsPbBr3 perovskite quantum dot film.

3. The topological laser according to claim 1, characterized in that: The first intermediate layer is SiO2, and the first covering layers on both sides are TiO2.

4. The topological laser according to claim 1, characterized in that: The second intermediate layer is TiO2, and the first covering layers on both sides are SiO2.

5. A method for manufacturing a topological laser according to claim 1, characterized in that: The following steps are involved: 1) Periodic alternating electron beam evaporation deposition of high refractive index layers and low refractive index layers; 2) providing a topologically trivial photonic crystal and a topologically non-trivial photonic crystal, wherein the topologically trivial photonic crystal comprises a plurality of unit cells periodically arranged with the same lattice constant, each unit cell comprising a first intermediate layer and first covering layers located on both sides of the first intermediate layer, the first intermediate layer being the low refractive index layer, and the first covering layer being composed of half of the high refractive index layer; and the topologically non-trivial photonic crystal comprises a plurality of unit cells periodically arranged with the same lattice constant, each unit cell comprising a second intermediate layer and second covering layers located on both sides of the second intermediate layer, the second intermediate layer being the high refractive index layer, and the second covering layer being composed of half of the low refractive index layer; 3) The topological trivial state photonic crystal and the topological non-trivial state photonic crystal are spliced ​​together to form a boundary at the splicing point; 4) The high refractive index layer at the boundary is replaced by a perovskite quantum dot film to realize the active layer.

6. The method for manufacturing a topological laser according to claim 5, wherein: The high refractive index layer is TiO2, and the low refractive index layer is SiO2.

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