Nano laser construction method and device based on optical singularity

Abstract

The present invention discloses a nano-laser construction method and device based on an optical singularity. The present invention embeds a needle-tip structure into a resonant cavity, and utilizes the optical singularity existing at the tip of the needle-tip structure to extremely localize the electric field in the resonant cavity near the tip, thereby realizing a nano-laser with extremely localized space, and its mode volume can break through the optical diffraction limit. The nano-laser device based on the optical singularity of the present invention can be prepared by etching an active layer, and the mode volume of the optical singularity laser can be further reduced by using an atomic layer deposition method. The nano-laser device of the present invention has the advantages of small mode volume and high controllability; and is independent of metal, and has the advantages of small thermal effect, high stability, low energy consumption and high coherence. The present invention can be applied to fields such as communication, computing, imaging, sensing, detection, and exploration of the interaction between light and matter in extreme light field localization.

Description

Technical Field

[0001] The invention relates to semiconductor laser technology, and in particular to a nano laser construction method and device based on optical singularity. Background Art

[0002] Since the advent of lasers in 1960, localizing light fields in dimensions such as time, frequency, momentum or space to achieve higher-performance lasers has always been the core driving force behind the development of laser physics and devices. The new high-performance lasers spawned by this have also profoundly promoted the progress of modern science and technology. For example, extremely localized light fields in the time dimension can produce ultrafast attosecond lasers (2023 Nobel Prize in Physics), and extremely localized light fields in the frequency dimension can produce frequency-stable lasers required to build precision interferometers, making gravitational wave detection possible (2017 Nobel Prize in Physics).

[0003] In terms of spatial dimension, nanolaser confines the light field to a very small area, whose size is close to or smaller than its lasing wavelength in three dimensions, achieving extreme spatial localization of the light field. The construction of this localized light field not only enables nanolaser to have the characteristics of small size, low energy consumption and high speed, but also opens up a new way to study the interaction between light and matter in a strongly confined system.

[0004] At the turn of the century, the invention of semiconductor micro-nano lasers, including micro-disk lasers, photonic crystal defect lasers, and nanowire lasers, reduced the characteristic size of lasers to the order of a vacuum wavelength. In lasers, the gain medium amplifies photons by stimulated emission, so the size of the laser is limited by the optical diffraction limit, and the minimum scale is at the order of a wavelength.

[0005] In order to break through the optical diffraction limit and obtain a smaller laser, scientists proposed the concept of plasmon nanolaser in 2003. Plasmon nanolaser breaks through the optical diffraction limit by amplifying plasmons through stimulated radiation rather than amplifying photons. The characteristic scale of its resonant cavity can be reduced to one tenth of the vacuum wavelength, reaching the characteristic scale of electronic devices. In 2009, plasmon nanolaser was realized for the first time in the world. Although plasmon nanolaser can break through the optical diffraction limit, the free electron oscillation it uses will be accompanied by metal absorption loss, which will inevitably bring about problems such as high energy consumption and low coherence, affecting the performance of nanolaser. Summary of the invention

[0006] Due to the above problems of nano lasers, new construction methods and new devices of nano lasers that do not rely on metals and break through the optical diffraction limit will be of great significance to the development of nano lasers. The present invention applies the needle-tip structure to the construction of nano lasers by utilizing the optical singularity of the electric field at the tip of the needle-tip structure, and proposes a construction method, device and device preparation method of nano lasers based on the optical singularity, as well as a method and device to further enhance the localization of the light field.

[0007] In a first aspect of the present invention, a nano-laser construction method based on optical singularity is proposed, comprising the following steps:

[0008] S1. Select any resonant cavity and obtain the electric field distribution of its eigenmode;

[0009] S2, select any needle-tip structure and embed the needle-tip structure into the resonant cavity;

[0010] There is an optical singularity at the tip of the needle-shaped structure, and the optical field is extremely localized in the tip area of ​​the needle through the coupling of the optical singularity mode and the eigenmode of the resonant cavity;

[0011] S3. By pumping the active region embedded in the resonant cavity of the needle-like structure, extremely spatially localized nanolaser is achieved.

[0012] Optionally, the calculation method of the eigenmode electric field distribution in step S1 can be numerical simulation calculation, analytical analysis and the like; the needle-shaped structure in step S2 is a single needle-shaped structure (such as Figure 1 As shown), the bow-tie structure with two needle tips facing each other (as shown Figure 2 As shown) or more structures with opposite needle tips; the pumping described in step S3 is optical pumping or electrical pumping, and the active region can be located at any position in the resonant cavity embedded in the needle tip structure.

[0013] Mode volume is one of the important indicators for measuring laser miniaturization and can be expressed as Here ε(r) represents the dielectric constant at the spatial position r, E(r) represents the electric field at the spatial position r, and the mode volume reflects the volume occupied by the mode in space. The mode volume of the nanolaser based on optical singularity constructed by the above method can break the diffraction limit.

[0014] When the above method is specifically implemented, the resonant cavity may be a nanocavity, and the needle-tip structure may be a nanostructure.

[0015] In a second aspect of the present invention, a nano laser device based on an optical singularity is proposed, comprising a nano cavity and a needle-point structure embedded in the nano cavity. An active region exists in the nano cavity or the needle-point structure, an optical singularity exists at the tip of the needle-point structure, and an optical singularity mode is coupled with an eigenmode of the resonant cavity.

[0016] Preferably, the nanocavity and the needle-tip structure are both composed of an active region, and the wavelength range of the nanolaser device based on the optical singularity can be adjusted by selecting the material of the active region to adjust the gain region range. The wavelength range can range from visible, near-infrared, communication band, mid-infrared light band to terahertz band. For example, materials such as GaN can be selected for the visible light band, and materials such as InGaAs, InGaAsP and InAlGaAs can be selected for the communication band.

[0017] Optionally, the active region includes but is not limited to: semiconductor materials, single-layer quantum wells, multi-layer quantum wells, quantum dots, two-dimensional materials or dye molecules. Preferably, the active region is an active layer composed of materials such as multi-layer quantum wells.

[0018] Optionally, the nanocavity may be a corner nanocavity, a photonic crystal defect cavity, or the like.

[0019] Optionally, the needle tip structure may be a bow-tie structure with two needle tips facing each other or a single needle tip structure, and the shape of the needle tip includes but is not limited to a triangular prism, a tetrahedron, a cone, and the like.

[0020] Optionally, the nanocavity and the needle-tip structure are made of active materials. Preferably, the needle-tip structure is a bow-tie structure with two needle tips facing each other, and the distance between the two needle tips can be as small as 20 nm, or even smaller.

[0021] Optionally, the nanocavity and the needle-tip structure are composed of an active material and a dielectric layer on the surface of the structure. The distance between the two needle-tip tips of the bow-tie structure can be further reduced to 2 nm, or even smaller.

[0022] In the third aspect of the present invention, a method for preparing a nano laser device based on an optical singularity is proposed, comprising: etching an active layer according to a pattern formed by a nano cavity and a needle-shaped structure embedded in the nano cavity to obtain a nano laser device based on an optical singularity.

[0023] In some embodiments of the present invention, the method for preparing the above-mentioned nano-laser device based on optical singularity comprises the following steps:

[0024] 1) Preparing a mask layer on the active layer;

[0025] 2) drawing an etching pattern consisting of the nanocavity and the needle-shaped structure embedded in the nanocavity by computer-aided design;

[0026] 3) The etched pattern is transferred to the mask layer through photolithography technology, and then further transferred to the active layer.

[0027] The material of the active layer is selected according to the wavelength range of the nano-laser device to be prepared, for example, the communication band can be InGaAs, InGaAsP and InAlGaAs etc. The thickness of the active layer is preferably 200nm.

[0028] Optionally, the mask layer may be made of materials such as silicon dioxide.

[0029] In a fourth aspect of the present invention, a method for further reducing the mode volume of the nano-laser device based on an optical singularity is proposed, wherein the nano-laser device comprises a nano-cavity and a bow-tie structure with two needle tips facing each other embedded in the nano-cavity, and a dielectric layer (such as Figure 3 As shown in FIG. 1 ). The distance between the two tips of the bow-tie structure can be reduced by atomic layer deposition growth. The optical singularity mode is mainly concentrated between the two tips of the bow-tie structure. The mode volume depends on the distance between the tips. Therefore, the mode volume of the above-mentioned nano-laser device based on optical singularity can be further reduced.

[0030] The thickness of the dielectric layer can be controlled at the atomic scale, enabling a bow-tie structure tip gap as small as 1 nm.

[0031] In the fifth aspect of the present invention, a nano-laser device based on optical singularity with smaller mode volume is proposed, including a nano-cavity and a bow-tie structure with two needle tips facing each other embedded in the nano-cavity, wherein the nano-cavity and the bow-tie structure are composed of an active layer and a dielectric layer on the surface of the structure.

[0032] The active layer etching method can be used to obtain a bow-tie structure with a gap of 10nm. The atomic layer deposition method can achieve conformal growth of dielectric materials and accurately control the gap size. As the thickness of the deposited atomic layer increases, the gap size at the bow-tie tip decreases and the pattern volume decreases. The thickness of the film formed by atomic layer deposition can be controlled at the atomic scale, and a bow-tie tip gap as small as 1nm can be achieved.

[0033] Optionally, the dielectric layer may be TiO 2 、Al 2 O 3 、SiO 2 MgF 2 A material with a refractive index greater than that of the regions above and below the device.

[0034] Advantages of the present invention:

[0035] 1. The nano-laser construction method of the present invention can realize nano-laser whose mode volume breaks through the diffraction limit without relying on metal.

[0036] 2. The method of reducing the volume of the nano-laser mode of the present invention uses atomic layer deposition technology and has high controllability.

[0037] 3. The nano laser device of the present invention does not need to use metal materials, and the laser device has small thermal effect, high stability, low energy consumption and high coherence.

[0038] 4. The nano laser device of the present invention has a small mode volume, a short lifetime of spontaneously emitted photons, and a fast modulation speed, and can be used for communication and computing.

[0039] 5. The nano-laser device of the present invention has a large electric field energy density at the needle tip, and the lasing wavelength is sensitive to changes in the environment, and can be used for sensing and detection.

[0040] 6. The nano-laser device of the present invention has a highly localized electric field at the needle tip, which can be applied to imaging and the exploration of the interaction between light and matter in extreme light field localization. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the nano-laser construction method based on the optical singularity in the needle tip structure of the present invention.

[0042] Figure 2 It is a schematic diagram of the nano-laser construction method based on the optical singularity in the bow-tie structure of the present invention.

[0043] Figure 3 It is a schematic diagram of the method of the present invention for further reducing the volume of the optical singular point laser mode.

[0044] Figure 4 Schematic diagram of the structure of a nano-laser device based on an optical singular point prepared in an embodiment of the present invention, wherein (a) is a three-dimensional stereogram, (b) is a three-dimensional enlarged diagram, (c) is a cross-sectional diagram, and (d) is a top view.

[0045] Figure 5 The scanning electron microscope images of the nano-laser device based on optical singularity prepared in an embodiment of the present invention, wherein (a) is a top view of the device, and (b) is an enlarged stereoscopic image of the center of (a).

[0046] Figure 6 This is a simulation diagram of the variation of the mode volume of a nano-laser device based on optical singularity with the tip spacing according to an embodiment of the present invention.

[0047] Figure 7Schematic diagram of an optical singular point nano-laser device with a smaller mode volume according to an embodiment of the present invention, wherein (a) is a cross-sectional view and (b) is an enlarged view of the bow-tie structure.

[0048] Figure 8 Scanning electron microscope images of an optical singular point nanolaser device with a smaller mode volume prepared in an embodiment of the present invention, wherein (a) is a top view of the device, (b) is an enlarged stereoscopic image of the center of (a), and (c) is a top view of the tip gap of (b).

[0049] Fig. 9 Figure 1 is a graph showing the lasing results of an optical singular point nanolaser device with a smaller mode volume prepared in an embodiment of the present invention, wherein (a) is a normalized spectrum graph, (b) is an input-output power curve graph and a line width variation graph in logarithmic coordinates, (c) is a spectrum graph showing that the line width narrows as the power increases, and (d) is a graph showing the variation of the second-order linked function with power.

[0050] Fig.10 The simulated real-space electric field distribution diagram of the optical singular point nanolaser device with a smaller mode volume prepared in an embodiment of the present invention, where (a) is the electric field mode distribution diagram of the nanocavity, (b) is the electric field mode distribution diagram of the central bow-tie structure, and (c) is the intensity distribution diagram at the dotted line in (b).

[0051] Fig.11 Time-resolved spontaneous emission photon lifetime diagram of an optical singular point nano-laser device with a smaller mode volume and a structureless substrate prepared in an embodiment of the present invention.

[0052] Description of the main component symbols in the accompanying drawings:

[0053] 1-InP substrate; 2-InGaAsP multi-quantum well active layer; 3-corner nanocavity; 4-bow-tie structure; 5-TiO 2 film. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described below through specific embodiments with reference to the accompanying drawings.

[0055] In this embodiment, a bow-tie structure is embedded in a corner nanocavity to realize a nanolaser based on an optical singularity, whose mode volume exceeds the diffraction limit, and the mode volume is further reduced by an atomic layer deposition method.

[0056] like Figure 4As shown, the nanolaser device based on optical singularity of this embodiment includes an InP substrate 1 and an InGaAsP multi-quantum well active layer 2, and the active layer includes a corner nanocavity 3 and a bow-tie structure 4. The corner nanocavity 3 is composed of two sets of photonic crystals twisted at a certain angle in the same layer of semiconductor material, which can confine the light field to the central area of ​​the corner nanocavity. The bow-tie structure 4 is composed of two triangular prism-shaped dielectric nanostructures with opposite sharp corners. Embedded in this area, the light field can be further confined between the two sharp corners, and the mode volume breaks through the diffraction limit. The atomic layer deposition method can reduce the spacing between the sharp corners, thereby further reducing the mode volume of the laser. This method can confine the light field to a scale of 1nm.

[0057] In this embodiment, a silicon dioxide mask layer is first prepared on an InP substrate 1 and an InGaAsP multi-quantum well active layer 2, and a photoresist is spin-coated on the surface; the desired etching pattern is drawn using computer-aided design (CAD), and the etched pattern includes a corner nanocavity with a 3.89° angle and a bow-tie structure with a tip gap of about 20nm embedded in the center, and the entire pattern side length is about 4μm. Subsequently, the designed pattern is transferred to the photoresist using an electron beam exposure technique to complete the preliminary transfer process. Next, the pattern is first transferred to the silicon dioxide mask layer using an inductively coupled plasma etching technique, and further transferred to an InGaAsP multi-quantum well layer with a thickness of 200nm. After completing these steps, the InP substrate is etched with diluted hydrochloric acid to form a suspended structure, which can better localize the light field in the vertical direction. Figure 5 (a) shows the scanning electron microscope image of the device obtained by the above method. Figure 5 (b) shows the bow-tie structure with a tip spacing of approximately 20 nm in the center of the device. Figure 6 The 3D full-wave simulations in show that the mode volume corresponding to this tip spacing exceeds the diffraction limit and can be further reduced as the bow-tie tip spacing decreases.

[0058] In order to reduce the bow-tie tip spacing and thus reduce the mode volume, this embodiment uses an atomic layer deposition method to realize TiO 2 Conformal growth of thin film 5, allowing precise control of bow-tie tip spacing and mode volume, Figure 7 Schematic diagram of a device that further reduces the mode volume in this embodiment. TiO formed by atomic layer deposition 2 The thickness of the film 5 can be controlled at the atomic scale, enabling bow-tie tip gaps as low as 1 nm. Figure 8 (a) is a scanning electron microscope image of the reduced mode volume device of this embodiment, in which the corner nanocavity is formed by rotating two sets of triangular lattices with a period of 465nm and a hole diameter of 170nm by 3.89°; Figure 8(b) is a magnified SEM image of the corresponding center, showing the bow-tie tip gap after the device atomic layer deposition; Figure 8 (c) shows that the bow-tie tip gap after atomic layer deposition can be controlled to (1.7±1.0) nm.

[0059] The above nanolaser device was optically pumped at room temperature, and the lasing behavior of the device was experimentally characterized, including the nonlinear phase transition in the input-output power curve, the linewidth narrowing effect, and the second-order correlation function (g (2) (τ)) evolution. Fig. 9 (a) shows the normalized spectrum of the device at different pump intensities, and single-mode laser is observed to appear with the increase of pump power. Fig. 9 (b) shows the corresponding input-output power curve and line width change curve. The input-output power curve in logarithmic coordinates presents an S-shape, indicating the phase transition from spontaneous emission to stimulated emission. According to the definition of quantum threshold, the laser threshold is determined to be 26 kW cm -2 ; The line width change curve reflects that the line width of the cavity mode will decrease rapidly when the threshold is exceeded. Fig. 9 (c) shows three spectra corresponding to pump powers below, close to, and above the lasing threshold, which clearly illustrate the linewidth narrowing effect. The highest laser quality factor calculated from the spectra is 13200. Fig. 9 In (d) use g (2) (τ) characterizes the statistical properties of the device's output light field, further confirming its lasing behavior. When close to the laser threshold, the emitted photons exhibit super-Poisson distribution characteristics (g (2) (τ=0)>1). When the photon emission is above the threshold, the photon emission evolves from super-Poisson distribution to Poisson distribution, indicating that the coherent light is emitted (g (2) (τ=0)=1).

[0060] Fig.10 (a) and (b) show the simulated electric field distribution of the cavity mode, indicating that there is an extremely localized electric field distribution in the tip gap of the bow-tie structure. Figure 6 The 3D full-wave simulation in shows that the lasing mode corresponding to the tip spacing of 1.7nm has a wavelength of about 0.0005λ 3 Extremely small mode volume, smaller than the optical diffraction limit (λ / 2n) 3 One sixth of . Fig.10 (c) depicts the intensity distribution of the dotted line in (b), highlighting the local electric field distribution at the atomic scale.

[0061] Fig.11The time-resolved spontaneous emission photon lifetimes of nanolasers and structureless substrates are demonstrated, indicating an enhancement in the spontaneous emission rate of photons. The spontaneous emission photon lifetime of the nanolaser device based on optical singularities is 23ps, while that of the structureless substrate is 1350ps, corresponding to a Purcell factor of 58.

[0062] The analysis of the experimental results of the embodiments shows the advantages of the nano-laser based on optical singularity proposed in the present invention: it is independent of metal materials and the mode volume exceeds the diffraction limit.

[0063] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.

Claims

1. A nano-laser construction method based on optical singularity, comprising the following steps: S1. Select a resonant cavity, which is a nanocavity, and obtain the electric field distribution of its eigenmode; S2. Select a needle tip structure, wherein the needle tip structure is a bow-tie structure with two needle tips facing each other or a single needle tip structure, and embed the needle tip structure into the resonant cavity; There is an optical singularity at the tip of the needle-shaped structure, and the optical field is extremely localized in the tip area of ​​the needle through the coupling of the optical singularity mode and the eigenmode of the resonant cavity; S3. By pumping the active region embedded in the resonant cavity of the needle-like structure, extremely spatially localized nanolaser is achieved.

2. The nano-laser construction method according to claim 1, characterized in that: The calculation method of the eigenmode electric field distribution in step S1 is numerical simulation calculation or analytical analysis; the pumping in step S3 is optical pumping or electrical pumping, and the active area is located at any position in the resonant cavity embedded in the needle-tip structure.

3. A nano laser device based on an optical singularity, comprising a nano cavity and a needle-shaped structure embedded in the nano cavity, characterized in that: The needle tip structure is a bow-tie structure with two needle tips facing each other or a single needle tip structure; an active area exists in the nano cavity or the needle tip structure, an optical singularity exists at the tip of the needle tip structure, and the optical singularity mode is coupled with the intrinsic mode of the nano cavity.

4. The nano laser device according to claim 3, characterized in that: The nanocavity is a corner nanocavity or a photonic crystal defect cavity.

5. The nano laser device according to claim 3, characterized in that: The active region is a semiconductor material, a single-layer quantum well, a multi-layer quantum well, a quantum dot, a two-dimensional material or a dye molecule.

6. The nano laser device according to claim 3, characterized in that: The nanocavity and the needle-tip structure are made of active materials, and the distance between the two needle-tip tips of the bow-tie structure is less than or equal to 20 nm.

7. The nano laser device according to claim 3, characterized in that: The nanocavity and needle-tip structure are composed of active materials and a dielectric layer on the surface of the structure, and the distance between the two needle-tip tips of the bow-tie structure is less than or equal to 2nm.

8. The nano-laser device according to claim 7, characterized in that: The dielectric layer is TiO2, Al2O3, SiO2 or MgF2.

9. A method for preparing a nano laser device based on an optical singularity, wherein the nano laser device comprises a nano cavity and a needle tip structure embedded in the nano cavity, wherein the needle tip structure is a bow tie structure with two needle tips facing each other or a single needle tip structure; an active region exists in the nano cavity or the needle tip structure, an optical singularity exists at the tip of the needle tip structure, and a mode of the optical singularity is coupled with an eigenmode of the nano cavity, wherein the preparation method comprises: According to the pattern formed by the nano cavity and the needle-point structure, active layer etching is performed to obtain a nano laser device based on optical singularity.

10. The preparation method according to claim 9, characterized in that: The following steps are involved: 1) Preparing a mask layer on the active layer; 2) drawing an etching pattern consisting of the nanocavity and the needle-shaped structure embedded in the nanocavity by computer-aided design; 3) The etched pattern is transferred to the mask layer through photolithography technology, and then further transferred to the active layer.

11. The preparation method according to claim 9 or 10, characterized in that: The preparation method further comprises: growing a dielectric layer on the surface of the etched active layer structure by using atomic layer deposition.

12. A method for reducing the mode volume of a nano laser device based on an optical singularity, the nano laser device comprising a nano cavity and a needle tip structure embedded in the nano cavity, the needle tip structure being a bow tie structure with two needle tips facing each other, an active region existing in the nano cavity or the bow tie structure, an optical singularity existing at the tip of the needle tip structure, and the optical singularity mode coupling with the intrinsic mode of the nano cavity; a dielectric layer is grown on the structural surface of the nano laser device by atomic layer deposition, so that the distance between the two tips of the bow tie structure is reduced, thereby reducing the mode volume of the nano laser device.

13. Application of the nano-laser device based on optical singularity according to any one of claims 3 to 8 in the fields of communication, computing, imaging, sensing, detection and exploration of the interaction between light and matter in extreme light fields.

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