An electrically driven single photon source

Abstract

An electrically driven single photon source (100) comprises an electrically injected laser (10) and a cavity two-level structure (20), the cavity two-level structure (20) only having one quantum dot (O); the cavity two-level structure (20) is located on the light emitting side of the electrically injected laser (10), and the optical center of the cavity two-level structure (20) is aligned with the optical center of the electrically injected laser (10); the cavity two-level structure (20) is used to generate a single photon under the action of the pump light emitted by the electrically injected laser (10), and the emission direction of the single photon is parallel to the emission direction of the pump light. The electrically driven single photon source (100) combines the electrically injected laser (10) and the cavity two-level structure (20) to form a new hardware structure, and generates the single photon source (100) through hybrid integration, so that the overall integration of the device can be improved. Moreover, the electrically driven single photon source (100) can optimize the quality and collection efficiency of the single photon by changing the structure of the cavity two-level structure (20) and the electrically injected laser (10).

Description

Technical Field

[0001] This application relates to the field of semiconductor photonic device technology, and in particular to an electrically driven single-photon source. Background Technology

[0002] According to quantum optics, light not only possesses the characteristics of electromagnetic waves but also exhibits particle-like motion. The "photon" is the smallest unit of this quantized electromagnetic field. Currently, single-photon sources are mainly generated using three mechanisms: utilizing atomic-like two-level systems, using light intensity attenuators to reduce laser pulses, and utilizing nonlinear principles. Since only the first mechanism is a non-probabilistic, "deterministic" single-photon source, developing single-photon sources using this method has significant practical implications.

[0003] Currently, the first method for preparing single-photon sources mainly employs two driving methods: optical driving (photoluminescence) or electrical driving (electroluminescence). Among them, optical driving is the mainstream method, which produces single photons of good quality, but it has disadvantages in terms of device complexity and integration, and traditional approaches are difficult to scale up. Although electrical driving has high integration, it has inherent disadvantages such as high noise and poor photon quality.

[0004] Therefore, how to provide a high-efficiency, highly integrated single-photon source capable of producing high-quality photons is an urgent technical problem to be solved. Summary of the Invention

[0005] This application provides an electrically driven single-photon source, which offers a high-efficiency, highly integrated single-photon source capable of producing high-quality photons.

[0006] This application provides an electrically driven single-photon source, comprising an electrically injected laser and a cavity two-level structure. The electrically injected laser generates pump light, and the cavity two-level structure contains only one quantum dot, serving as the resonant cavity and two-level structure for generating a single photon. Specifically, the cavity two-level structure is located on the emission side of the electrically injected laser, and its optical center is optically aligned with the laser. The pump light emitted by the electrically injected laser is incident on the cavity two-level structure, exciting electrons in the quantum dot to transition from a low energy level to a high energy level. When an electron transitions back to a low energy level, the quantum dot releases a single photon away from the laser. Because the electrically driven single-photon source provided in this application contains only one quantum dot, each pulse emits only one photon, resulting in good purity. Notably, the emission direction of the pump light emitted by the electrically injected laser in the electrically driven single-photon source provided in this application is parallel to the emission direction of the single photon emitted by the cavity two-level structure. In other words, the cavity two-level structure is located in the direction of pump light emission. This structural arrangement allows the pump light to act directly on the cavity two-level structure, thereby improving the excitation efficiency of the cavity two-level structure by the electrically injected laser and thus increasing the single-photon yield.

[0007] The electrically driven single-photon source provided in this application combines an electrically injected laser with a cavity two-level structure to form a novel hardware structure. By generating a single-photon source through hybrid integration, the overall integration density of the device can be improved. It should be understood that the electrically driven single-photon source provided in this application can adjust the wavelength, polarization, and beam shape and direction of quantum dot emission by changing the material and size of the cavity two-level structure, as well as the shape, period, duty cycle, and etching depth of the resonant cavity, thereby optimizing the quality and collection efficiency of the single photon. Simultaneously, by changing the shape and material of the resonant cavity in the electrically injected laser, the wavelength, emission direction, and polarization state of the laser can be adjusted, thereby optimizing the quality and collection efficiency of the single photon.

[0008] When setting the specific structure of the electrically injected laser and the cavity two-level structure, the electrically injected laser can be a vertical-plane emitting laser or other laser structure, while the cavity two-level structure can be a cavity quantum dot. The cavity quantum dot can be a self-assembled semiconductor quantum dot or other cavity quantum dot within a two-dimensional or three-dimensional cavity. The specific configuration can be tailored to requirements and will not be elaborated further here. For example, the electrically injected laser is a DBR (distributed bragg reflector) laser, and the cavity two-level structure is a grating structure.

[0009] When specifically configuring the DBR laser and grating structure, at least the following specific implementation methods exist:

[0010] In one specific embodiment, the DBR laser has an elliptical cross-section in the first plane, which is perpendicular to the alignment direction of the DBR laser and the grating structure; and the grating structure has an elliptical cross-section in the second plane, which is parallel to the first plane. In other words, the first and second planes are arranged parallel to each other and both are perpendicular to the alignment direction of the DBR laser and the grating structure. It is worth noting that the major axis of the grating structure in the second plane and the major axis of the DBR laser in the first plane can be configured either perpendicularly or parallel to each other.

[0011] Specifically, the DBR laser is used to generate a first laser and a second laser with orthogonal polarization states. The polarization direction of the first laser is parallel to the major axis of the elliptical cross-section of the DBR laser in the first plane, and the polarization direction of the second laser is parallel to the minor axis of the elliptical cross-section of the DBR laser in the first plane. The grating structure has a first resonant light and a second resonant light with orthogonal polarization states. The polarization direction of the first resonant light is parallel to the major axis of the elliptical cross-section of the grating structure in the second plane, and the polarization direction of the second resonant light is parallel to the minor axis of the elliptical cross-section of the grating structure in the second plane. The quantum dot in the cavity two-level has a wavelength λ0 corresponding to its two levels.

[0012] When the difference between the wavelength λ0 corresponding to the second energy level of the quantum dot and the wavelength λ1' of the first resonant light of the cavity two-level structure is less than a threshold, the polarization direction of the generated single photon is parallel to the long axis of the grating structure. At this time, the long axis of the cavity two-level structure in the second plane and the long axis of the electrically injected laser in the first plane can be arranged in two ways:

[0013] Method 1: When the cavity two-level structure is perpendicular to the two major axes of the electrically injected laser, the wavelength λ1 of the first laser emitted by the electrically injected laser is equal to the wavelength λ1' of the first resonant light of the cavity two-level structure.

[0014] Method 2: When the cavity two-level structure is parallel to the two major axes of the electrically injected laser, the wavelength λ2 of the second laser emitted by the electrically injected laser is equal to the wavelength λ1' of the first resonant light of the cavity two-level structure.

[0015] It is worth noting that the threshold is half the full width at half maximum (FWHM) of the spectrum emitted by the quantum dot.

[0016] When the difference between the wavelength λ0 corresponding to the second energy level of the quantum dot and the wavelength λ2' of the second resonant light of the cavity two-level structure is less than a threshold, the polarization direction of the generated single photon is parallel to the short axis of the grating structure. At this time, the major axis of the cavity two-level structure in the second plane and the major axis of the electrically injected laser in the first plane also have two possible arrangements:

[0017] Method 1: When the cavity two-level structure is perpendicular to the two major axes of the electrically injected laser, the wavelength λ2 of the second laser emitted by the electrically injected laser is equal to the wavelength λ2' of the second resonant light of the cavity two-level structure.

[0018] Method 2: When the cavity two-level structure is parallel to the two major axes of the electrically injected laser, the wavelength λ1 of the first laser emitted by the electrically injected laser is equal to the wavelength λ2' of the second resonant light of the cavity two-level structure.

[0019] It is worth noting that the threshold is half the full width at half maximum (FWHM) of the spectrum emitted by the quantum dot.

[0020] In summary, this specific implementation enables the electrically driven single-photon source provided in this application to generate a single-photon source through resonant excitation.

[0021] Of course, to improve the quality of the single-photon source generated by the electrically driven single-photon source provided in this application, the electrically driven single-photon source can also include a polarization filter and a wavelength filter, which are located on the side of the cavity two-level structure away from the electrically injected laser. It is worth noting that since the electrically injected laser emits two laser beams, the polarization filter can be used to filter out the laser beam with a different polarization but the same wavelength as the single photon, while the wavelength filter can be used to filter out the laser beam with the same polarization but a different wavelength as the single photon, thereby obtaining a single-photon source with high brightness and high indistinguishability.

[0022] In another specific embodiment, the DBR laser has a circular cross-section in the first plane, which is perpendicular to the alignment direction of the DBR laser and the grating structure; the grating structure has a circular cross-section in the second plane, which is parallel to the first plane; the DBR laser is used to generate a first laser and a second laser with orthogonal polarization states, both with wavelengths of λ; the grating structure has a first resonant light and a second resonant light, both with wavelengths of λ', and λ' is greater than λ.

[0023] In this specific embodiment, the wavelength λ of the laser emitted by the DBR laser is smaller than the wavelength λ' of the resonant light of the grating structure, which enables the electrically driven single-photon source provided in this application to generate a single-photon source through non-resonant excitation.

[0024] Of course, in order to improve the quality of the single photon source generated by the electrically driven single photon source provided in this application, the electrically driven single photon source provided in this application may also include a wavelength filter. The wavelength filter is located on the side of the cavity two-level structure away from the electrically injected laser to filter out the first laser and the second laser emitted by the electrically injected laser, thereby obtaining a high-brightness single photon source.

[0025] When specifically setting the internal structure of a DBR laser, the DBR laser includes a DBR resonant cavity, which includes a central layer and multiple structure pairs. Among the multiple structure pairs, some structure pairs are located on the side of the central layer facing the cavity two-level structure, and some structure pairs are located on the side of the central layer away from the cavity two-level structure. Each of the multiple structure pairs includes a first structure layer and a second structure layer made of different materials, and the second structure layer is located on the side of the first structure layer away from the central layer.

[0026] It is worth noting that when setting the number of structure pairs on both sides of the central layer, the number of structure pairs on the side of the central layer facing the cavity level structure should be less than the number of structure pairs on the side of the central layer away from the cavity level structure, so that the laser emitted by the DBR laser is emitted from the second structure pair towards the first structure pair until it hits the cavity level structure.

[0027] When specifically configuring the grating structure in the cavity two-level structure, the grating structure can include a substrate, a grating layer disposed on the side of the substrate facing away from the DBR laser, and a transparent dielectric layer disposed on the side of the grating layer facing away from the substrate. It is worth noting that the grating layer has a resonant cavity, within which quantum dots are disposed. The transparent dielectric layer can be a specific structural layer, or it can be a vacuum or air layer, depending on the requirements; further details will not be provided here. Attached Figure Description

[0028] Figure 1a This is a schematic diagram illustrating the principle of generating a single-photon source using a two-level system.

[0029] Figure 1b A schematic diagram illustrating the principle of using an intensity attenuator to reduce laser pulses in order to generate a single-photon source;

[0030] Figure 1c A schematic diagram illustrating the principle of generating a single-photon light source using nonlinearity.

[0031] Figure 2 This application provides a schematic diagram of the structure of an electrically driven single-photon source according to an embodiment of the present application.

[0032] Figure 3 for Figure 2 The diagram shows the specific structure of the electrically injected laser in the electrically driven single-photon source.

[0033] Figure 4 for Figure 3 Enlarged view of point D in the middle;

[0034] Figure 5 A cross-sectional view of an electrically injected laser provided in an embodiment of this application within a first plane P;

[0035] Figure 6 To adopt Figures 3 to 5The simulation diagrams of the first and second lasers formed by the structure and corresponding parameters shown are shown.

[0036] Figure 7 for Figure 3 The diagram shows a detailed structural diagram of the cavity two-level structure in the electrically driven single-photon source.

[0037] Figure 8 A cross-sectional view of the grating layer at the second plane Q provided in an embodiment of this application;

[0038] Figure 9 This is a first schematic diagram of an electrically driven single-photon source provided in an embodiment of this application;

[0039] Figure 10 for Figure 9 Wavelength relationship diagram of the structure in the middle;

[0040] Figure 11 This is a second schematic diagram of an electrically driven single-photon source provided in an embodiment of this application;

[0041] Figure 12 for Figure 11 Wavelength relationship diagram of the structure in the middle;

[0042] Figure 13 This is a third schematic diagram of an electrically driven single-photon source provided in an embodiment of this application;

[0043] Figure 14 for Figure 13 Wavelength relationship diagram of the structure in the middle;

[0044] Figure 15 This is a third schematic diagram of an electrically driven single-photon source provided in an embodiment of this application;

[0045] Figure 16 for Figure 15 Wavelength relationship diagram of the structure in the middle;

[0046] Figure 17 Another cross-sectional view of the electrically injected laser provided in the first plane P according to an embodiment of this application;

[0047] Figure 18 Another cross-sectional view of the grating layer at the second plane Q provided in the embodiments of this application. Detailed Implementation

[0048] To facilitate understanding of the electrically driven single-photon source provided in the embodiments of this application, the relevant technical background will be introduced first.

[0049] A photon is the smallest unit of quantified electromagnetic field. It is defined as having energy hν and traveling at the speed of light c in a vacuum, where h is Planck's constant and ν is the frequency of the electromagnetic field. Since John F. Clauser first used the cascade transition effect in calcium atoms to generate single-photon pairs in 1974, a single photon has had a revolutionary impact on many new and traditional scientific fields, including:

[0050] a) Quantum communication: Using single photons as qubits, transmitted in self-contained space or optical fibers. The quality of the single-photon source has a decisive impact on key yield and photon coherence.

[0051] b) Quantum computing: using linear interactions of single or entangled photons for massive parallel computations. Whether a single-photon source can produce "on-demand" photons is one of the prerequisites for the success of quantum computing.

[0052] c) Metrology: Super-diffraction-limited imaging of biological samples using single photons. The brightness and monochromaticity of a single photon have a decisive influence on the image quality.

[0053] d) Other fundamental experiments: Single photons also play a significant role in areas such as verifying Bell's inequality in quantum mechanics and searching for gravitational waves.

[0054] To date, there are three main methods for preparing single-photon sources:

[0055] The first method: Utilizing a two-level system similar to atoms to generate a single-photon source, specifically as follows... Figure 1a As shown, when an electron spontaneously decays from an excited state to the ground state, it simultaneously releases a photon. It is noteworthy that single-photon sources prepared using this mechanism include certain atoms, molecules, color centers, and quantum dots. Single-photon sources prepared in this way are the only type of light source capable of emitting a "definite" single photon.

[0056] The second method involves using an intensity attenuator to reduce the laser pulse, thereby increasing the probability of obtaining a single photon within a single pulse. Specifically, as shown below... Figure 1b As shown. Since the number of photons in each pulse follows a Poisson distribution, the ratio of the probability of obtaining multiple photons to the probability of obtaining single photons is P. (>1) / P (1) ≈ <n> / 2, where, <n>This represents the average number of photons contained in each pulse. Therefore, although this method is simple and easy to implement, to obtain a single-photon source, the light intensity must be reduced to a minimum, which results in most pulses being empty, thus greatly limiting the efficiency of this method in preparing single-photon sources.

[0057] The third method: Utilizing nonlinear principles to generate single-photon light sources. Specifically, as follows... Figure 1c As shown, single-photon pairs are generated with a certain probability, and one single photon is used to predict the other. It is worth noting that this mechanism typically utilizes the interaction between the pump laser and a nonlinear material to produce spontaneous parametric down-conversion (SPDC) or spontaneous four-wave mixing (SFWM), thereby converting the pump photon into two coherent photons. However, single-photon sources produced by this method also suffer from probabilistic defects and are typically larger in size, resulting in lower integration compared to single-photon sources produced by the first method.

[0058] Of the aforementioned methods, only the first method produces a non-probabilistic, "deterministic" single-photon source, making its development of such a source of greater practical significance. Currently, this type of photon source primarily employs two driving methods: optical driving (photoluminescence) and electrical driving (electroluminescence). Comparatively, electrical driving is more suitable for large-scale fabrication. Existing electrically driven single-photon sources mainly fall into two categories, as detailed below:

[0059] One electrically driven method is direct electrical excitation. Specifically, electrode structures are added to a DBR (distributed Bragg reflector) cavity structure, and n-type and p-type doping is performed respectively. Charge carriers are provided using electrical injection, and these charge carriers then transition to generate single photons. However, the photons generated by this driving method not only have poor indistinguishability but also low purity. In general, the photon quality formed by this driving method is poor.

[0060] Another electrically driven method involves fabricating the laser and cavity two-level structure on the same chip, indirectly using the laser to excite the cavity two-level structure. Since the active region of the laser and the two-level structure are on the same plane—the plane where the quantum dots are located—this method excites the two-level structure laterally by the laser, while single photons are emitted longitudinally. This emission direction cannot effectively separate the pump light emitted by the laser from the single-photon signal using non-wavelength filtering, thus requiring non-resonant excitation, resulting in poor indistinguishability of the single-photon source. It should be understood that in this driving method, the laser source is a quantum dot laser, requiring a sufficient number of quantum dots in the active region to ensure luminous efficiency; however, the single-photon source requires a sufficiently small number of quantum dots to ensure the purity of the single photons. However, it is difficult to precisely control the quantum dot density on the same sample, resulting in poor quality of the single-photon source.

[0061] Based on the above application scenarios, this application provides an electrically driven single-photon source to provide a high-efficiency, highly integrated single-photon source capable of producing high-quality photons.

[0062] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0063] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions "a," "an," "the," "the," "the," and "this" are intended to also include expressions such as "one or more," unless the context clearly indicates otherwise.

[0064] References to "one embodiment" or "some embodiments" as used in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0065] Figure 2 An electrically driven single-photon source 100 is provided as an embodiment of this application. The electrically driven single-photon source 100 includes an electrically injected laser 10 and a cavity two-level structure 20. The cavity two-level structure 20 has a resonant cavity containing only one quantum dot O. Specifically, the cavity two-level structure 20 is located on the light-emitting side of the electrically injected laser 10, and the optical center of the cavity two-level structure 20 is aligned with the optical center of the electrically injected laser 10. For example, as... Figure 2 As shown, the axis L1 of the electrically injected laser 10 is collinear with the axis L2 of the cavity two-level structure 20, meaning that the optical center of the cavity two-level structure 20 is aligned with the optical center of the electrically injected laser 10. It should be understood that the electrically injected laser 10 within the electrically driven single-photon source 100 provided in this application can generate pump light. This pump light, emitted from the electrically injected laser 10, strikes the cavity two-level structure 20, exciting electrons in the quantum dot O within the cavity two-level structure 20 from a low energy level to a high energy level. When the electron transitions back to a low energy level, the quantum dot O releases a single photon in the direction away from the electrically injected laser 10. Since the electrically driven single-photon source 100 provided in this application contains only one quantum dot O, each pulse emits only one photon, resulting in good purity.

[0066] It is worth noting that in the electrically driven single-photon source 100 provided in this application embodiment, the emission direction of the pump light emitted by the electrically injected laser 10 is parallel to the emission direction of the single photon emitted by the cavity level structure 20. In other words, the cavity level structure 20 is located in the emission direction of the pump light. This structural arrangement allows the pump light to directly act on the cavity level structure, thereby improving the excitation efficiency of the electrically injected laser 10 on the cavity level structure 20 and thus increasing the yield of single photons.

[0067] The electrically driven single-photon source 100 provided in this application embodiment combines an electrically injected laser 10 with a cavity two-level structure 20 to form a novel hardware structure. This hybrid integration approach achieves an electrically pumped single-photon source, thereby improving the overall integration density of the device. Furthermore, the electrically driven single-photon source 100 provided in this application embodiment combines the advantages of both electrical and optical driving methods, avoiding the drawbacks of each, and can also improve photon quality and yield.

[0068] Specifically, when setting up the electrically driven single-photon source 100 provided in this application embodiment, by changing the material and size of the cavity two-level structure 20, as well as the shape, period, duty cycle, etching depth, and other parameters of the resonant cavity, the wavelength, polarization, beam shape, and direction of the quantum dot O emission can be adjusted, thereby optimizing the quality and collection efficiency of the single photon. Simultaneously, by changing the shape and material of the resonant cavity in the electrically injected laser 100 provided in this application embodiment, the wavelength, emission direction, and polarization state of the laser can be adjusted, thereby optimizing the quality and collection efficiency of the single photon.

[0069] When assembling the electrically driven single-photon source 100 provided in the embodiments of this application, please continue to refer to Figure 2 The structure shown stacks the electrically injected laser 10 and the cavity two-level structure 20 at certain intervals using a flip-chip packaging method, ensuring optical center alignment. It is worth noting that an insulating layer made of transparent material can be placed between the electrically injected laser 10 and the cavity two-level structure 20 as needed; this will not be elaborated further here.

[0070] Specifically, in fabricating the electrically driven single-photon source 100 provided in this application embodiment, a substrate layer and a driving structure for driving the electrically injected laser 10 need to be provided. The substrate layer can be, for example, made of Si (silicon), SiO2 (silicon dioxide), or SOI (silicon-on-insulator). Figure 2 As shown, a first electrode 40 is formed on one side of the substrate 30, an electrically injected laser 10 is formed on the side of the first electrode 40 opposite to the substrate 30, and a second electrode 50 is provided on the side of the electrically injected laser 10 opposite to the first electrode 40. Notably, a power supply 60 is connected between the first electrode 40 and the second electrode 50, and the first electrode 40, the second electrode 50, and the power supply 60 form the driving structure of the electrically injected laser 10. For example, the power supply 60 is connected to the first electrode 40 and the second electrode 50 respectively via gold contacts.

[0071] Please continue to refer to this. Figure 4 In the structure shown, the electrically injected laser 10 and the cavity two-level structure 20 are arranged perpendicular to the substrate 30. For ease of description of the positional relationships of the electrically injected laser 10, the cavity two-level structure 20, and other structures, the plane containing the substrate 30 is considered horizontal, and the arrangement direction of the electrically injected laser 10 and the cavity two-level structure 20 is considered vertical. It should be understood that when applying the electrically driven single-photon source 100 provided in the embodiments of this application, whether the plane containing the substrate 30 is horizontal can be set according to requirements and is not limited here.

[0072] Of course, in the electrically driven single-photon source 100 provided in this application embodiment, the electrically injected laser 10 can be a vertical-cavity surface-emitting laser (VCSEL) or other laser structure to provide laser for pumping the upper cavity two-level structure 10. The cavity two-level structure 20 can be a cavity quantum dot O structure. As for the cavity quantum dot O structure, self-assembled semiconductor quantum dots O or other cavity quantum dot O structures in a two-dimensional or three-dimensional cavity can be used to provide a resonant cavity and energy levels for generating single photons. For example, the electrically injected laser 10 can be selected as a DBR (distributed Bragg reflector) laser, and the cavity two-level structure 20 can be a grating structure.

[0073] The following example illustrates the implementation method of the electrically driven single-photon source 100 provided in this application: "The electrically injected laser 10 is a GaAs (gallium arsenide) / AlGaAs (aluminum gallium arsenide) DBR laser, the cavity two-level structure 20 is a shallowly etched two-dimensional cavity structure (grating structure), and the center of the grating structure resonant cavity is a GaAs quantum dot O; simultaneously, the electrically injected laser 10 and the cavity two-level structure 20 are coupled through a flip-chip package." It should be noted that the electrically driven single-photon source 100 provided in this application is not limited to the materials, structures (sizes), and coupling methods in the example.

[0074] Implementation Method 1

[0075] Figure 3 for Figure 2 The diagram shows a detailed structure of the electrically injected laser 10 in the electrically driven single-photon source 100. It should be understood that this electrically injected laser 10 is a DBR laser. It is worth noting that the DBR laser also has an internal resonant cavity; after external excitation energy enters the resonant cavity, it will... Figure 2 Under the action of the various driving structures shown, oscillations occur in the resonant cavity to generate resonant light, which is eventually emitted by the DBR laser in the form of laser light. Figure 4 for Figure 3 The enlarged schematic diagram at point D shows that the electrically injected laser 10 includes a DBR resonant cavity M, which specifically includes a GaAs central layer 11 and multiple structure pairs. Specifically, multiple stacked first structure pairs 12 are located on the side of the GaAs central layer 11 facing the cavity two-level structure 20, and multiple stacked second structure pairs 13 are located on the side of the GaAs central layer 11 away from the cavity two-level structure 20. Each structure pair 12 and 13 includes a GaAs layer and an AlGaAs layer, with the AlGaAs layer located on the side of the GaAs layer away from the GaAs central layer 11. It is noteworthy that when setting the number of structure pairs on both sides of the GaAs central layer, the number of first structure pairs 12 should be less than the number of second structure pairs 13, so that the laser emitted by the DBR laser is emitted from the second structure pairs 13 towards the first structure pairs 12.

[0076] The resonant wavelength λ of the DBR laser 总 The wavelength is mainly determined by the thickness d1 of the GaAs central layer in the vertical direction, therefore the wavelength and thickness usually satisfy λ. 总 ≈d1xn GaAs , where n GaAs is the refractive index of the GaAs core layer material. In other words, it represents the thickness of the GaAs core layer at the time of setup. Meanwhile, the thickness of each GaAs layer Thickness of each AlGaAs layer

[0077] Figure 5 for Figure 3 A cross-sectional view of the electrically injected laser 10 within a first plane P. This first plane P is perpendicular to... Figure 2 The arrangement of the electrically injected laser 10 and the cavity two-level structure 20 is shown. Please refer to [reference needed]. Figure 5 Taking the first plane P located in the AlGaAs layer as an example, the cross-section of the AlGaAs layer is elliptical. It is worth noting that the cross-section of the GaAs layer is also elliptical in the plane parallel to the first plane P, but it is not shown here.

[0078] The resonant wavelength can be fine-tuned by adjusting the radius of the DBR resonant cavity M. In other words, the resonant wavelength of a DBR laser is directly proportional to the radius of the DBR resonant cavity M. Theoretically, when the radius of the resonant cavity M is infinite, the resonant wavelength of the DBR laser is equal to λ. 总 Therefore, for a finite-sized resonant cavity M with a radius of less than λ, the resonant wavelength is less than λ. 总 Since the cross-section of the DBR resonator M within the first plane P is elliptical, and this elliptical cross-section has a major axis and a minor axis, the major axis radius r1 and the minor axis radius r2 of the DBR resonator M within the first plane P are different. Based on this, by controlling the major axis radius r1 and the minor axis radius r2, the wavelength of the laser emitted by the DBR laser in the direction parallel to the major axis and the direction parallel to the minor axis can be slightly different.

[0079] Specifically, a DBR laser can generate a first laser and a second laser with orthogonal polarization states. The polarization direction of the first laser is parallel to the major axis of the elliptical cross-section of the DBR laser in the first plane P, and the polarization direction of the second laser is parallel to the minor axis of the elliptical cross-section of the DBR laser in the first plane P. The wavelength of the first laser is λ1, and the wavelength of the second laser is λ2. It should be understood that the wavelengths λ1 and λ2 of the first and second lasers are slightly different, and both λ1 and λ2 are less than λ2. 总 In specific setups, adjusting structural parameters such as the lengths of the major and minor axes of the elliptical cross-section within the first plane P of the DBR laser, the thickness and number of each film layer within the DBR resonant cavity M, and the refractive index of the selected structure can adjust the output of the first and second laser beams. Simultaneously, this adjustment allows for the emission of most of the light generated by the DBR laser upwards, thereby improving excitation efficiency.

[0080] For ease of understanding, for example, the polarization direction of the first laser is defined as parallel to the X-axis, and the polarization direction of the second laser is defined as parallel to the Y-axis.

[0081] Here is a parameter design scheme for a DBR laser:

[0082]

[0083] Figure 6 To adopt Figures 3 to 5 The simulation diagrams of the first and second lasers formed by the structure shown and the parameters in the table above are presented. Figure 6 The data shown indicates that at a wavelength of 874.972 nm, only the first laser beam with a polarization direction parallel to the X direction exists; and at a wavelength of 875.62 nm, only the second laser beam with a polarization direction parallel to the Y direction exists. In other words, the first laser beam generated by the DBR laser with the structural parameters in the table above has a wavelength of λ1 = 874.97 nm, and the second laser beam has a wavelength of λ2 = 875.62 nm.

[0084] Figure 7 for Figure 3 The diagram shows a specific structural diagram of the cavity two-level structure 20. Specifically, the cavity two-level structure 20 is a shallowly etched two-dimensional cavity structure. Exemplarily, this shallowly etched two-dimensional cavity structure is a grating structure. Specifically, the cavity two-level structure 20 can be configured to include a substrate 21 and a grating layer 22 disposed on the side of the substrate 21 facing away from the DBR laser. The grating layer 22 has a resonant cavity, and quantum dots O (shown as small black spheres in the diagram) are disposed within the resonant cavity. Exemplarily, the substrate 21 is formed from SiO2 (silicon dioxide) or SOI (silicon-on-insulator) material; the distance between the quantum dots O and the surface of the grating layer 22 can be as follows: Figure 7 As shown, the grating layer 22 is set to 90nm, comprising a main body and multiple annular protrusions. The thickness of the main body can be set as follows: Figure 7 As shown in the figure, the thickness of the protrusion at 60nm can be set as follows: Figure 7 The 120nm shown is an example. Of course, the structural parameters of the grating layer 22 are not limited to... Figure 7 The content shown can be changed as needed.

[0085] In addition, a transparent dielectric layer may be provided on the side of the grating layer 22 facing away from the substrate 21 in the cavity two-level structure 20. Figure 7 (Not shown in the image), the transparent medium layer can be a specific structural layer, or a vacuum or air layer.

[0086] To ensure that most of the light generated by the cavity two-level structure 20 is emitted away from the DBR laser, thereby improving emission efficiency, the resonant wavelength λ is determined. 总 After that, the grating structure needs to be based on the resonant wavelength λ. 总 The emission direction is used to determine the grating structure. It is worth noting that the grating structure must satisfy the following equation:

[0087]

[0088] Where: n eff n is the effective refractive index of the grating layer; Λ is the period of the grating layer; n C θ is the refractive index of the transparent dielectric layer; θ is the angle between the photon emission direction and the vertical direction in the resonant cavity of the grating layer. C This is the refractive index of the transparent dielectric layer covering the grating layer. When the transparent dielectric layer is a vacuum or an air layer, this value is 1.

[0089] It is worth noting that n eff It is determined by the etching depth of the grating layer and the duty cycle (the ratio of the width of the unetched portion to the grating period Λ).

[0090] Figure 8 for Figure 7 A cross-sectional view of the middle grating layer 22 at the second plane Q, which is parallel to the first plane P. Please refer to [reference needed]. Figure 8 The grating structure has an elliptical cross-section in the second plane Q. In other words, the first plane P and the second plane Q are arranged parallel to each other and both perpendicular to the plane. Figure 2 The arrangement direction of the electrically injected laser 10 and the cavity two-level structure 20 shown.

[0091] Due to the resonant wavelength λ of the grating structure 总 The diameter of the central part is related to the grating structure, and the central part is elliptical with a major axis of r1' and a minor axis of r2'. Therefore, the wavelength of the light emitted from the grating structure in the direction parallel to the major axis is slightly different from that in the direction parallel to the minor axis.

[0092] Specifically, the grating structure has a first resonant light and a second resonant light with orthogonal polarization states. The polarization direction of the first resonant light is parallel to the major axis of the elliptical cross-section of the grating structure in the second plane Q, and the polarization direction of the second resonant light is parallel to the minor axis of the grating structure in the elliptical cross-section of the second plane Q. The wavelength of the first resonant light is λ1', and the wavelength of the second resonant light is λ2'. It should be understood that the wavelengths λ1' and λ2' of the first and second resonant lights are slightly different, and both λ1' and λ2' are less than λ. 总 For ease of understanding, for example, the polarization direction of the first resonant light is parallel to the X-axis, and the polarization direction of the second resonant light is parallel to the Y-axis.

[0093] It is worth noting that the quantum dot O in the cavity two-level structure 20 has a wavelength λ0 corresponding to its two levels.

[0094] When the difference between the wavelength λ0 corresponding to the second level of quantum dot O and the wavelength λ1' of the first resonant light of cavity two-level structure 20 is less than a threshold, the polarization direction of the generated single photon is parallel to the long axis of the grating structure. In other words, there is a first resonant light within the resonant cavity M. At this time, the long axis of the cavity two-level structure 20 in the second plane Q and the long axis of the electrically injected laser 10 in the first plane P have two possible arrangements:

[0095] Method 1: For example Figure 9 As shown in the diagram, when the cavity two-level structure 20 is perpendicular to the two major axes of the electrically injected laser 10, the wavelength λ1 of the first laser emitted by the electrically injected laser 10 is equal to the wavelength λ1' of the first resonant light of the cavity two-level structure 20, as detailed below. Figure 10 As shown.

[0096] Method 2: For example Figure 11 As shown in the diagram, when the cavity two-level structure 20 is parallel to the two major axes of the electrically injected laser 10, the wavelength λ2 of the second laser emitted by the electrically injected laser 10 is equal to the wavelength λ1' of the first resonant light of the cavity two-level structure 20, as specifically... Figure 12 As shown.

[0097] It is worth noting that the threshold is half the full width at half maximum (FWHM) of the spectrum emitted by the quantum dot.

[0098] When the difference between the wavelength λ0 corresponding to the second level of quantum dot O and the wavelength λ2' of the second resonant light of cavity two-level structure 20 is less than a threshold, the polarization direction of the generated single photon is parallel to the short axis of the grating structure. In other words, there is a second resonant light inside the resonant cavity M. At this time, the major axis of the cross-section of the cavity two-level structure 20 in the second plane Q and the major axis of the cross-section of the electrically injected laser 10 in the first plane P also have two possible arrangements:

[0099] 1) such as Figure 13 As shown in the diagram, when the cavity two-level structure 20 is perpendicular to the two major axes of the electrically injected laser 10, the wavelength λ2 of the second laser emitted by the electrically injected laser 10 is equal to the wavelength λ2' of the second resonant light of the cavity two-level structure 20, as detailed below. Figure 14 As shown;

[0100] 2) such as Figure 15 As shown in the diagram, when the two major axes of the cavity two-level structure 20 and the electrically injected laser 10 are parallel to each other, the wavelength λ1 of the first laser emitted by the electrically injected laser 10 is equal to the wavelength λ2' of the second resonant light of the cavity two-level structure 20, as detailed below. Figure 16 As shown.

[0101] Similarly, the threshold is half the full width at half maximum (FWHM) of the spectrum emitted by the quantum dot. In other words, λ1' and λ2' are equal to or close to the wavelengths corresponding to the two energy levels of quantum dot O.

[0102] Please continue to refer to this. Figure 8 The structure shown. Figure 8 Each annular protrusion is spaced from the central portion, and each annular protrusion and a spacer form a structural pair. For example, the number of structural pairs is 12. In the radial direction, the dimension of each structural pair is, for example, set to 340 nm, where the spacer is, for example, set to 100 nm. Of course, other dimensions can be used as needed, which will not be elaborated here.

[0103] To improve the quality of the single-photon source generated by the electrically driven single-photon source 100 provided in this application, the electrically driven single-photon source 100 may further include a polarization filter and a wavelength filter (not shown in the figure). The polarization filter and wavelength filter are located on the side of the cavity two-level structure 20 opposite to the electrically injected laser 10. It is worth noting that since the electrically injected laser emits two laser beams, the polarization filter can filter out the laser beam with a different polarization but the same wavelength as the single photon, while the wavelength filter filters out the laser beam with the same polarization but a different wavelength as the single photon, thereby obtaining a single-photon source with high brightness and high indistinguishability.

[0104] Implementation Method 2

[0105] The difference between Implementation Method 2 and Implementation Method 1 lies only in that, for example Figure 17 The cross-sectional view of the electrically injected laser 10 shown in the first plane P is circular, and, as... Figure 18 The cross-sectional view of the cavity two-level structure 20 shown in the second plane Q is circular. The electrically driven single-photon source provided in this embodiment can generate a single-photon source through non-resonant excitation.

[0106] Please continue to refer to this. Figure 17 The DBR resonant cavity M has a circular cross-section within the first plane P, and the radius of this circular cross-section is the same (r) at all points. Based on this, a comparison is made... Figure 5 The electrically injected laser 10 shown is... Figure 17 The electrically injected laser 10 shown emits lasers with the same wavelength in the direction parallel to the long axis and in the direction parallel to the short axis.

[0107] Specifically, a DBR laser can generate a first laser and a second laser with orthogonal polarization states. The polarization direction of the first laser is parallel to the X-direction of the DBR laser in the first plane P, and the polarization direction of the second laser is parallel to the Y-direction of the DBR laser in the first plane P. Since the cross-section of the DBR resonator M is circular, the wavelengths of both the first and second lasers are λ. In specific settings, adjusting structural parameters such as the radius of the circular cross-section of the DBR laser in the first plane P, the thickness and number of layers in the DBR resonator M, and the refractive index of the selected structure can adjust the emitted first and second lasers. Simultaneously, through this adjustment, most of the light generated by the DBR laser can be emitted upwards, thereby improving the excitation efficiency.

[0108] Here is a parameter design scheme for a DBR laser:

[0109]

[0110] Please continue to refer to this. Figure 18 The grating structure has a circular cross-section in the second plane Q. In other words, the first plane P and the second plane Q are arranged parallel to each other and both are perpendicular to the alignment direction of the DBR laser and the grating structure. Because the resonant wavelength λ of the grating structure... 总 'It is related to the diameter of the part at the very center, and the very center of the grating structure is circular with a radius of r, so the comparison...' Figure 8 The structure shown. Figure 18 In the structure shown, the wavelength of the light emitted from the grating structure in the direction parallel to the long axis is the same as that in the direction parallel to the short axis.

[0111] Specifically, the grating structure has a first resonant light and a second resonant light with orthogonal polarization states. The polarization direction of the first resonant light is parallel to the grating structure in the X direction of the second plane Q, and the polarization direction of the second resonant light is parallel to the grating structure in the Y direction of the second plane Q. The wavelengths of the first resonant light and the second resonant light are both λ'.

[0112] It is important to note that in this embodiment, the difference between λ' and the wavelength corresponding to the second energy level of quantum dot O needs to be less than a threshold value, which is half the full width at half maximum (FWHM) of the emitted spectrum of the quantum dot. In other words, λ' is equal to or close to the wavelength corresponding to the second energy level of quantum dot O. At the same time, it is necessary to ensure that wavelength λ' is greater than wavelength λ, so that... Figure 2 The electrically injected laser 10 shown can be non-resonant with the cavity two-level structure 20, so that the quantum dot O in the resonant cavity of the cavity two-level structure 20 generates photons.

[0113] Please continue to refer to this. Figure 18 , Figure 18 Each annular protrusion is spaced from the central portion, and each annular protrusion and a spacer form a structure pair. For example, the radius r' of the central portion is chosen to be 490 nm, and the number of structure pairs is 12. Furthermore, the dimension of each structure is, for example, set to 340 nm in the radial direction, with the spacer, for example, set to 100 nm. Of course, other dimensions can be used as needed, which will not be elaborated here.

[0114] Of course, in order to improve the quality of the single photon source generated by the electrically driven single photon source provided in this application, the electrically driven single photon source provided in this application may also include a wavelength filter. The wavelength filter is located on the side of the cavity two-level structure 20 away from the electrically injected laser 10 to filter out the first laser and the second laser, thereby obtaining a high-brightness single photon source.

[0115] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.< / n> < / n>

Claims

1. An electrically driven single photon source, characterized in that The device includes an electrically injected laser and a cavity two-level structure, wherein the cavity two-level structure has only one quantum dot; the cavity two-level structure is located on the light-emitting side of the electrically injected laser, and the optical center of the cavity two-level structure is aligned with the optical center of the electrically injected laser; the cavity two-level structure is used to generate single photons under the action of pump light emitted by the electrically injected laser, and the emission direction of the single photon is parallel to the emission direction of the pump light.

2. The electrically driven single-photon source as described in claim 1, characterized in that, The electrically injected laser is a distributed Bragg reflector (DBR) laser, and the cavity two-level structure is a grating structure.

3. The electrically driven single-photon source as described in claim 2, characterized in that, The DBR laser has an elliptical cross-section in the first plane, which is perpendicular to the alignment direction of the DBR laser and the grating structure; the grating structure has an elliptical cross-section in the second plane, which is parallel to the first plane. The DBR laser is used to generate a first laser and a second laser with orthogonal polarization states. The polarization direction of the first laser is parallel to the major axis of the elliptical cross-section of the DBR laser in the first plane, and the polarization direction of the second laser is parallel to the minor axis of the elliptical cross-section of the DBR laser in the first plane. The grating structure has a first resonant light and a second resonant light with orthogonal polarization states. The polarization direction of the first resonant light is parallel to the major axis of the elliptical cross section of the grating structure in the second plane, and the polarization direction of the second resonant light is parallel to the minor axis of the elliptical cross section of the grating structure in the second plane.

4. The electrically driven single-photon source as described in claim 3, characterized in that, The wavelength corresponding to the second energy level of the quantum dot in the cavity two-level structure is λ0, and the difference between the wavelength λ0 corresponding to the second energy level of the quantum dot and the wavelength λ1' of the first resonant light of the cavity two-level structure is less than a threshold value, which is half the half width at half maximum (FWHM) of the spectrum emitted by the quantum dot.

5. The electrically driven single-photon source as described in claim 4, characterized in that, The major axis of the cavity two-level structure in the second plane is perpendicular to the major axis of the electrically injected laser in the first plane, and the wavelength λ1 of the first laser emitted by the electrically injected laser is equal to the wavelength λ1' of the first resonant light of the cavity two-level structure; or, The major axis of the cavity two-level structure in the second plane is parallel to the major axis of the electrically injected laser in the first plane, and the wavelength λ2 of the second laser emitted by the electrically injected laser is equal to the wavelength λ1' of the first resonant light of the cavity two-level structure.

6. The electrically driven single-photon source as described in claim 3, characterized in that, The wavelength corresponding to the second energy level of the quantum dot in the cavity two-level structure is λ0, and the difference between the wavelength λ0 corresponding to the second energy level of the quantum dot and the wavelength λ2' of the second resonant light of the cavity two-level structure is less than a threshold value, which is half the half width at half maximum (FWHM) of the spectrum emitted by the quantum dot.

7. The electrically driven single-photon source as described in claim 6, characterized in that, The major axis of the cavity two-level structure in the second plane is perpendicular to the major axis of the electrically injected laser in the first plane, and the wavelength λ2 of the second laser emitted by the electrically injected laser is equal to the wavelength λ2' of the second resonant light of the cavity two-level structure; or, The major axis of the cavity two-level structure in the second plane is parallel to the major axis of the electrically injected laser in the first plane, and the wavelength λ1 of the first laser emitted is equal to the wavelength λ2' of the second resonant light in the cavity two-level structure.

8. The electrically driven single-photon source as described in claim 5 or 7, characterized in that, It also includes a polarization filter and a wavelength filter. Both the polarization filter and the wavelength filter are located on the side of the cavity two-level structure away from the electrically injected laser. The polarization filter is used to filter laser light with a different polarization but the same wavelength as the single photon, and the wavelength filter is used to filter laser light with the same polarization but a different wavelength as the single photon.

9. The electrically driven single-photon source as described in claim 2, characterized in that, The DBR laser has a circular cross-section in the first plane, which is perpendicular to the alignment direction of the DBR laser and the grating structure; the grating structure has a circular cross-section in the second plane, which is parallel to the first plane. The DBR laser is used to generate a first laser and a second laser with orthogonal polarization states, both of which have a wavelength of λ. The grating structure has a first resonant light and a second resonant light, both of which have a wavelength of λ', and the wavelength of λ' is greater than that of λ.

10. The electrically driven single-photon source as described in claim 9, characterized in that, It also includes a wavelength filter, which is located on the side of the cavity two-level structure away from the electrically injected laser, to filter out the first laser and the second laser.

11. The electrically driven single-photon source according to any one of claims 2-10, characterized in that, The DBR laser includes a DBR resonant cavity, which includes a central layer and multiple structure pairs. Some of the structure pairs are located on the side of the central layer facing the cavity two-level structure, while some of the structure pairs are located on the central layer away from the cavity two-level structure. Each of the plurality of structural pairs includes a first structural layer and a second structural layer made of different materials, wherein the second structural layer is located on the side of the first structural layer opposite to the central layer.

12. The electrically driven single-photon source as described in claim 11, characterized in that, The number of structure pairs located on the side of the central layer facing the cavity two-level structure is less than the number of structure pairs located on the side of the central layer away from the cavity two-level structure.

13. The electrically driven single-photon source according to any one of claims 2-12, characterized in that, The grating structure includes a second substrate, a grating layer disposed on the side of the second substrate opposite to the DBR laser, and a transparent dielectric layer located on the side of the grating layer opposite to the substrate. The grating layer has a resonant cavity, and the quantum dot is disposed in the resonant cavity.

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