WO2022266962A1

WO2022266962A1 - Electrically driven single-photon source

Info

Publication number: WO2022266962A1
Application number: PCT/CN2021/102200
Authority: WO
Inventors: 刘进; 耿巍
Original assignee: 华为技术有限公司
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2022-12-29
Also published as: CN117015913A

Abstract

An electrically driven single-photon source (100), comprising an electrical injection laser (10) and a cavity two-level structure (20), the cavity two-level structure (20) having only one quantum dot (O); the cavity two-level structure (20) is located on the light emergent side of the electrical injection laser (10), and the optical center of the cavity two-level structure (20) is aligned with the optical center of the electrical injection laser (10); the cavity two-level structure (20) is used for generating a single photon under the action of pump light emitted by the electrical injection laser (10), and the direction in which the single photon is emitted is parallel to the direction in which the pump light is emitted. The described electrically driven single-photon source (100) combines the electrical injection laser (10) with the cavity two-level structure (20) so as to form a novel hardware structure, and generates the single-photon source (100) by means of hybrid integration, which can improve the overall level of integration of the device. Moreover, with the described electrically driven single-photon source (100), the quality and collection efficiency of a single photon can be optimized by changing the structure of the cavity two-level structure (20) and the electrical injection laser (10).

Description

An electrically driven single photon source

technical field

The present application relates to the technical field of semiconductor photonic devices, in particular to an electrically driven single photon source.

Background technique

According to the description of quantum optics, light not only has the characteristics of electromagnetic waves, but also exhibits the motion behavior of particles. "Photon" is the smallest unit of this quantified electromagnetic field. Up to now, there are three main mechanisms used by single photon sources: using an atom-like dual-level system to generate a single photon source, using a light intensity attenuator to attenuate laser pulses to generate a single photon source, and using a nonlinear principle to generate a single photon source . Since only the first of the above-mentioned mechanisms is a non-probability-produced "deterministic" single-photon source, the development of a single-photon source prepared by this preparation method has greater practical significance.

At present, the first method for preparing a single photon source mainly adopts two driving forms of light driving (photoluminescence) or electric driving (electroluminescence). Among them, optical drive is the current mainstream method. The quality of single photons generated by this driving method is better, but it has disadvantages in terms of device complexity and integration. The traditional path is difficult to achieve large-scale; , but has natural disadvantages such as high noise and poor photon quality.

Therefore, how to provide a high-efficiency, high-integration single-photon source that can produce high-quality photons is an urgent technical problem to be solved.

Contents of the invention

The present application provides an electrically driven single photon source to provide a single photon source with high efficiency, high integration and the ability to produce high-quality photons.

The present application provides an electrically driven single photon source, which includes an electrical injection laser and a cavity two-level structure. Among them, the electrical injection laser is used to generate pumping light, and there is only one quantum dot in the two-level structure of the cavity, and the two-level structure of the cavity is used to provide a resonant cavity and a two-level structure for generating a single photon. Specifically, the cavity two-level structure is located on the light-emitting side of the electrical injection laser, and the optical center of the cavity two-level structure is aligned with the optics of the electrical injection laser. The pump light emitted by the electrical injection laser is incident on the two-level structure of the cavity to excite the electrons in the quantum dots in the two-level structure of the cavity from a low energy level to a high energy level; when the electrons transition back to a low energy level, the quantum dots are released in the direction away from the electrical injection laser single photon. Since only one quantum dot is contained in the electrically driven single photon source provided by the present application, only one photon is emitted for each pulse, and the purity is better. It is worth noting that, in the electrically driven single-photon source provided by the present application, the pumping light emitted by the electrical injection laser emits in a direction parallel to that of the single photons emitted by the cavity two-level structure. In other words, the cavity two-level structure is located in the light-emitting direction of the pump light. This structural setting allows the pump light to directly act on the two-level structure of the cavity, thereby improving the excitation efficiency of the two-level structure of the cavity by the electric injection laser, so as to increase the yield of single photons.

The electrically driven single photon source provided by this application combines the electrical injection laser with the cavity two-level structure to form a new hardware structure. The single photon source is generated by hybrid integration, which can improve the overall integration of the device. It should be understood that the electrically driven single photon source provided by the present application can adjust the wavelength and polarization of the quantum dot light by changing the material and size of the two-level structure of the cavity and the shape, period, duty cycle, etching depth and other parameters of the resonant cavity. As well as beam shape and direction, so as to optimize the quality and collection efficiency of single photons. At the same time, by changing the shape and material of the resonant cavity in the electrical injection laser, the wavelength, output direction and polarization state of the laser can be adjusted, so that the quality and collection efficiency of single photons can be optimized.

When setting up the specific structure of the electric injection laser and the cavity two-level structure, the electric injection laser can be a vertical surface emitting laser or other laser structures, and the cavity two-level structure can be a cavity quantum dot. As for the cavity quantum dot, a two-dimensional Or self-assembled semiconductor quantum dots or other cavity quantum dots in a three-dimensional cavity. The details can be set according to requirements, which will not be repeated here. Exemplarily, the electrical injection laser is a DBR (distributed bragg reflector, distributed Bragg reflector) laser, and the cavity two-level structure is a grating structure.

When specifically setting the structure of the DBR laser and the grating structure, there are at least the following specific implementations:

In a specific embodiment, the cross-section of the DBR laser on the first plane is elliptical, and the first plane is perpendicular to the arrangement direction of the DBR laser and the grating structure; and the cross-section of the grating structure on the second plane is elliptical, and the second The plane is parallel to the first plane. In other words, the first plane and the second plane are arranged in parallel, and both are perpendicular to the arrangement direction of the DBR laser and the grating structure. It is worth noting that the long axis of the section of the grating structure on the second plane and the long axis of the section of the DBR laser on the first plane have two configurations, perpendicular to each other and parallel to each other.

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 long axis of the elliptical 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 on the first plane; the grating structure has the first resonant light and the second resonant light with orthogonal polarization states, and the polarization direction of the first resonant light is parallel to the elliptical cross-section of the grating structure on the second plane The major axis of the second resonant light is parallel to the minor axis of the elliptical cross-section of the grating structure in the second plane. A quantum dot in the second energy level of the cavity has a wavelength λ ₀ corresponding to its second energy level.

When the difference between the wavelength λ ₀ corresponding to the second energy level of the quantum dot and the wavelength λ ₁ ' of the first resonant light of the cavity two-level structure is smaller than the threshold, the polarization direction of the generated single photon is parallel to the long axis of the grating structure. At this time, there are two arrangements for the long axis of the section of the cavity two-level structure on the second plane and the long axis of the section of the electric injection laser on the first plane:

Mode 1: When the two major axes of the cavity two-level structure and the electric injection laser are perpendicular to each other, the wavelength λ of the _first laser light emitted by the electric injection laser is equal to the wavelength λ of the first resonant light of the cavity two-level structure ₁ '.

Mode 2: When the two major axes of the cavity two-level structure and the electrical injection laser are parallel to each other, the wavelength λ of the _second laser light emitted by the electrical injection laser is equal to the wavelength λ of the first resonant light of the cavity two-level structure ₁ '.

It is worth noting that the threshold is half the full width at half maximum of the quantum dot emission spectrum.

When the difference between the wavelength λ ₀ corresponding to the second energy level of the quantum dot and the wavelength λ ₂ ' of the second resonant light of the cavity two-level structure is smaller than the threshold, the polarization direction of the generated single photon is parallel to the short axis of the grating structure. At this time, the long axis of the cross-section of the cavity two-level structure on the second plane and the long axis of the cross-section of the electric injection laser on the first plane also have two arrangements:

Method 1: When the two major axes of the cavity two-level structure and the electric injection laser are perpendicular to each other, the wavelength λ of the _second laser light emitted by the electric injection laser is equal to the wavelength λ of the second resonant light of the cavity two-level structure ₂ ';

Mode 2: When the two major axes of the cavity two-level structure and the electric injection laser are parallel to each other, the wavelength λ of the _first laser light emitted by the electric injection laser is equal to the wavelength λ of the second resonant light of the cavity two-level structure ₂ '.

In general, this specific embodiment enables the electrically driven single-photon source provided in the present application to generate a single-photon light source through resonant excitation.

Of course, in order to improve the quality of the single photon source produced by the electrically driven single photon source provided by this application, it can be set that the electrically driven single photon source provided by this application also includes a polarization filter and a wavelength filter, and the polarization filter and the wavelength filter It is located on the side of the cavity two-level structure away from the electric injection laser. It is worth noting that since the electrical injection laser emits two lasers, the polarization filter can be used to filter the laser light with different polarization and the same wavelength as the single photon, and at the same time, the wavelength filter can be used to pass the laser light with the same polarization and different wavelength as the single photon. A single-photon source with high brightness and high identity is obtained.

In another specific embodiment, the cross section of the DBR laser on the first plane is circular, and the first plane is perpendicular to the arrangement direction of the DBR laser and the grating structure; the cross section of the grating structure on the second plane is circular, and the second plane 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 wavelengths of the first laser and the second laser are both λ; the grating structure has a first resonant light and a second resonant light, and the first The wavelengths of the resonant light and the second resonant light are both λ', and λ' is greater than λ.

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

Of course, in order to improve the quality of the single photon source produced by the electrically driven single photon source provided in this application, the electrically driven single photon source provided by this application can be configured to further include a wavelength filter, and the wavelength filter is set at the cavity two-level structure away from One side of the electrical injection laser is used to filter out the first laser light and the second laser light emitted by the electrical injection laser, so that a high-brightness single-photon source can be obtained.

When specifically setting the internal structure of the DBR laser, the DBR laser includes a DBR resonator, the DBR resonator includes a central layer and a plurality of structure pairs, and a part of the structure pairs in the plurality of structure pairs is located on the side of the center layer towards the two-level structure of the cavity. Part of the structure pair is located in the center layer away from the cavity two-level structure; each structure pair in the plurality of structure pairs includes a first structure layer and a second structure layer made of different materials, and the second structure layer is located away from the center of the first structure layer layer side.

It is worth noting that when setting the number of structure pairs on both sides of the center layer, it should be noted that the number of structure pairs on the side of the center layer facing the cavity two-level structure is less than the number of structure pairs on the side of the center layer facing away from the cavity two-level structure The number is so that the laser light emitted by the DBR laser is sent from the second structure to the first structure until it hits the cavity two-level structure.

When specifically setting the grating structure in the cavity two-level structure, the grating structure can be set to include a substrate, a grating layer on the side of the substrate away from the DBR laser, and a transparent medium layer on the side of the grating layer away from the substrate. It is worth noting that the grating layer has a resonant cavity, and quantum dots are arranged in the resonant cavity. As for the transparent medium layer, it can be a specific structural layer, or a vacuum or air layer, which can be set according to requirements, and will not be repeated here.

Description of drawings

Figure 1a is a schematic diagram of the principle of using a dual-level system to generate a single-photon light source;

Figure 1b is a schematic diagram of the principle of using a light intensity attenuator to attenuate a laser pulse to generate a single-photon light source;

Figure 1c is a schematic diagram of the principle of generating a single-photon light source using the nonlinear principle;

FIG. 2 is a schematic structural diagram of an electrically driven single photon source provided in an embodiment of the present application;

Fig. 3 is the specific structural diagram of the electrical injection laser in the electrically driven single photon source shown in Fig. 2;

Fig. 4 is the enlarged schematic diagram of place D in Fig. 3;

FIG. 5 is a cross-sectional view of the electrical injection laser provided in the embodiment of the present application in the first plane P;

Fig. 6 is a simulation diagram of the first laser and the second laser formed by adopting the structures shown in Fig. 3 to Fig. 5 and corresponding parameters;

Fig. 7 is a specific structural diagram of the cavity two-level structure in the electrically driven single photon source shown in Fig. 3;

FIG. 8 is a cross-sectional view of the grating layer provided by the embodiment of the present application at the second plane Q;

Fig. 9 is a schematic diagram of the first type of electrically driven single photon source provided by the embodiment of the present application;

Fig. 10 is a wavelength relationship diagram of the structure in Fig. 9;

Fig. 11 is a second schematic diagram of the electrically driven single photon source provided by the embodiment of the present application;

Fig. 12 is a wavelength relationship diagram of the structure in Fig. 11;

Fig. 13 is a schematic diagram of the third type of electrically driven single photon source provided by the embodiment of the present application;

Fig. 14 is a wavelength relationship diagram of the structure in Fig. 13;

Fig. 15 is a schematic diagram of the third type of electrically driven single photon source provided by the embodiment of the present application;

Fig. 16 is a wavelength relationship diagram of the structure in Fig. 15;

Fig. 17 is another cross-sectional view of the electrical injection laser provided in the embodiment of the present application in the first plane P;

FIG. 18 is another cross-sectional view of the grating layer at the second plane Q provided by the embodiment of the present application.

detailed description

In order to facilitate the understanding of the electrically driven single photon source provided by the embodiment of the present application, the relevant technical background is firstly introduced.

A "photon" is the smallest unit of quantification of an electromagnetic field. It is defined as having energy hν, 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, single photons have revolutionized several new and traditional fields of science, including:

a) The field of quantum communication: using a single photon as a qubit for transmission in self-use space or optical fiber. The quality of the single-photon light source has a decisive impact on key yield and photon coherence.

b) The field of quantum computing: massively parallel computations using linear interactions of single or entangled photons. Whether a single-photon light source can generate "on-demand" photons is one of the prerequisites for the success of quantum computing.

c) Field of Metrology: Superdiffraction-limited imaging of biological samples using single photons. Characteristics such as brightness and monochromaticity of individual photons play a decisive role in imaging quality.

d) Other basic experiments: For example, in the verification of Bell's inequality in quantum mechanics and the search for gravitational waves, single photons also play a huge role.

Up to now, there are three main ways to prepare single photon sources:

The first way: use an atomic-like dual-level system to generate a single-photon light source, as shown in Figure 1a, when an electron spontaneously decays from an excited state to a ground state, a photon is released at the same time. It is worth noting that the single-photon sources prepared by this mechanism include certain atoms, molecules, color centers, and quantum dots. Single-photon sources prepared in this way are the only light sources that emit "deterministic" single-photons.

The second way: use a light intensity attenuator to weaken the laser pulse, so as to obtain a single photon in a single pulse with a certain probability, as shown in Figure 1b. Since the number of photons contained in each pulse conforms to the Poisson distribution, the ratio of the probability of obtaining multi-photons to single-photons is P _(>1) /P ₍₁₎ ≈<n>/2, where <n> is each Average number of photons contained in a pulse. Therefore, although this method is simple and feasible, in order to obtain a single photon source, the light intensity must be reduced to a minimum, which results in most of the pulses being empty, which greatly limits the efficiency of this method to prepare a single photon source.

The third way: using the nonlinear principle to generate a single-photon light source. Specifically, as shown in Figure 1c, a single photon pair is generated under a certain probability, and one of the single photons is used to predict the other single photon. It is worth noting that this mechanism usually uses the interaction of the pump laser with the nonlinear material to produce spontaneous parametric down-conversion (SPDC) or spontaneous four-wave mixing (SFWM) phenomenon, thereby converting the pump photon into two coherent photons. However, the single-photon source produced by this preparation method also has probabilistic defects, and is usually larger in size. Compared with the single-photon source produced by the first preparation method, the integration degree is not high.

Since only the first of the above-mentioned methods is a "deterministic" single-photon source generated non-probably, the development of such a single-photon source has greater practical significance. At present, there are mainly two driving forms of this photon source, namely light driving (photoluminescence) and electric driving (electroluminescence). In comparison, the electric drive method is more suitable for large-scale preparation. There are mainly two types of electrically driven single photon sources in the prior art, as follows:

One electric drive method is direct electric excitation. Specifically, an electrode structure is added to the DBR (distributed bragg reflector, distributed Bragg reflection) cavity structure, and n-type and p-type doping are performed separately, and the electric injection method is used to provide carriers. , the carrier then transitions and produces a single photon. However, the photons generated by this driving method are not only poor in identity, but also have low purity of single photons. Generally speaking, the quality of photons formed by this driving method is poor.

Another electric driving method is: process the laser and the cavity two-level structure on the same chip, and indirectly use the laser to excite the cavity two-level structure. Since the active region of the laser is on the same plane as the two-level structure, that is, the plane where the quantum dots are located, this method excites the two-level structure horizontally through the laser, and emits single photons vertically. This emission direction cannot effectively separate the pump light emitted by the laser from the single-photon signal by non-wavelength filtering, so only non-resonant excitation can be used, resulting in poor identity of the single-photon light source. It should be understood that in this driving mode, the laser source is a quantum dot laser, and there must be enough quantum dots in the active region of the laser to ensure luminous efficiency; however, there must be a small enough quantum dots at the single photon source to ensure single photon purity. However, it is difficult to ensure precise control of the quantum dot density on the same sample, which results in poor quality of single-photon light source.

Based on the above application scenarios, an embodiment of the present application provides an electrically driven single photon source to provide a single photon source with high efficiency, high integration and the ability to produce high-quality photons.

The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

The terms used in the following examples are for the purpose of describing particular examples only, and are not intended to limit the application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "said", "above", "the" and "this" are intended to also Expressions such as "one or more" are included unless the context clearly dictates otherwise.

Reference to "one embodiment" or "some embodiments" or the like in this specification means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in other embodiments," etc. in various places in this specification are not necessarily All refer to the same embodiment, but mean "one or more but not all embodiments" unless specifically stated otherwise. The terms "including", "comprising", "having" and variations thereof mean "including but not limited to", unless specifically stated otherwise.

FIG. 2 is an electrically driven single photon source 100 provided in the embodiment of the present 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, and the resonant cavity There is only one quantum dot O inside. Specifically, the cavity two-level structure 20 is located on the light-emitting side of the electrical injection laser 10 , and the optical center of the cavity two-level structure 20 is aligned with the optical center of the electrical injection laser 10 . Exemplarily, as shown in FIG. 2, the axis line L1 of the electrical injection laser 10 is collinear with the axis line L2 _of the cavity _two -level structure 20, that is, the optical center of the cavity two-level structure 20 and the electrical injection The optical centers of the lasers 10 are aligned. It should be understood that the electrical injection laser 10 in the electrically driven single photon source 100 provided by the present application can generate pumping light. The electrons in the quantum dot O in the level structure 20 change from a low energy level to a high energy level; when the electrons transition back to a low energy level, the quantum dot O releases a single photon in the direction away from the electrical injection laser 10 . Since the electrically driven single photon source 100 provided in the present application contains only one quantum dot O, only one photon is emitted per pulse, and the purity is better.

It is worth noting that, in the electrically driven single photon source 100 provided by the embodiment of the present application, the outgoing direction of the pump light emitted by the electrical injection laser 10 is parallel to the outgoing direction of the single photon emitted by the cavity two-level structure 20 . In other words, the cavity two-level structure 20 is located in the light emitting direction of the pumping light. However, this structural setting allows the pump light to directly act on the two-cavity level structure, thereby improving the excitation efficiency of the electric injection laser 10 on the two-cavity level structure 20, so as to increase the yield of single photons.

The electrically driven single photon source 100 provided in the embodiment of the present application combines the electrical injection laser 10 and the cavity two-level structure 20 to form a new hardware structure, and realizes the electrically pumped single photon source through hybrid integration, thereby improving the The overall integration of the device. At the same time, the electrically driven single photon source 100 provided in the embodiment of the present application combines the advantages of both electric driving and optical driving, avoids the respective shortcomings of the two driving methods, and can also improve photon quality and yield.

Specifically, when setting the electrically driven single photon source 100 provided by the embodiment of the present application, by changing the material and size of the cavity two-level structure 20 and parameters such as the shape, period, duty cycle, and etching depth of the resonant cavity, The wavelength, polarization, and beam shape and direction of quantum dot O luminescence can be adjusted to optimize the quality and collection efficiency of single photons. At the same time, by changing the shape and material of the resonant cavity in the electrical injection laser 100 provided by the embodiment of the present application, the wavelength, emission direction and polarization state of the laser can be adjusted, so that the quality and collection efficiency of single photons can be optimized.

When assembling the electrically driven single photon source 100 provided by the embodiment of the present application, please continue to refer to the structure shown in FIG. 2 , and stack the electrical injection laser 10 and the cavity two-level structure 20 at a certain interval by flip-chip packaging. , and ensure optical center alignment. It is worth noting that an insulating layer made of a transparent material may be provided between the electrical injection laser 10 and the cavity two-level structure 20 according to requirements, which will not be repeated here.

Specifically, when preparing the electrically driven single photon source 100 provided by the embodiment of the present application, a substrate layer and a driving structure for driving the electrical injection laser 10 need to be provided. The preparation material of the substrate layer can be selected as Si (Silicon), SiO ₂ (Silicon Dioxide) or SOI (Silicon On Insulator). As shown in FIG. 2 , a first electrode 40 is formed on one side of the substrate 30 , an electrical injection laser 10 is formed on a side of the first electrode 40 away from the substrate 30 , and an electrical injection laser 10 is formed on a side away from the first electrode 40 A second electrode 50 is provided. It should be noted that a power source 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 source 60 form a driving structure of the electrical injection laser 10 . Exemplarily, the power supply 60 is respectively connected to the first electrode 40 and the second electrode 50 through gold contacts.

Please continue to refer to the structure shown in FIG. 4 , the arrangement direction of the electrical injection laser 10 and the cavity two-level structure 20 is perpendicular to the substrate 30 . Here, in order to facilitate the description of the positional relationship between the electrical injection laser 10, the cavity two-level structure 20 and other structures, the plane where the substrate 30 is located is the horizontal plane, and the arrangement direction of the electrical injection laser 10 and the cavity two-level structure 20 is vertical. straight direction. It should be understood that when the electrically driven single photon source 100 provided in the embodiment of the present application is applied, whether the plane where the substrate 30 is located is a horizontal plane can be set according to requirements, which is not limited here.

Of course, in the electrically driven single photon source 100 provided in the embodiment of the present application, the electrical injection laser 10 can be a vertical-cavity surface-emitting laser (VCSEL) or other laser structures, so as to provide Two-level structure 10 laser. The cavity two-level structure 20 may be a cavity quantum dot O structure. As for cavity quantum dot O structures, self-assembled semiconductor quantum dot O or other cavity quantum dot O structures in 2D or 3D cavities can be used to provide resonant cavities and energy levels that generate single photons. Exemplarily, the electrical injection laser 10 may be selected as a DBR (distributed bragg reflector, distributed Bragg reflector) laser, and the cavity two-level structure 20 is a grating structure.

In the following, the electrical injection laser 10 is a GaAs (gallium arsenide)/AlGaAs (aluminum gallium arsenide) DBR laser, and the cavity two-level structure 20 is a shallow-etched two-dimensional cavity structure (grating structure), and the center of the grating structure resonator is GaAs quantum dot O; at the same time, the two structures of the electrical injection laser 10 and the cavity two-level structure 20 are coupled by flip-chip packaging" as an example, specifically introducing the implementation method of the electrically driven single photon source 100 provided by the embodiment of the present application . It should be pointed out that the electrically driven single photon source 100 provided in the embodiment of the present application is not limited to the materials, structures (dimensions) and coupling methods in the example.

Implementation Mode 1

FIG. 3 is a specific structural diagram of the electrical injection laser 10 in the electrically driven single photon source 100 shown in FIG. 2 . It should be understood that the electrical injection laser 10 is a DBR laser. It is worth noting that the DBR laser also has a resonant cavity inside. After the external excitation energy enters the resonant cavity, it will oscillate in the resonant cavity under the action of each driving structure as shown in Figure 2 to generate resonant light. It is emitted by the DBR laser in the form of laser light. FIG. 4 is an enlarged schematic diagram at D in FIG. 3 , the electrical injection laser 10 includes a DBR resonator M, and the DBR resonator M specifically includes a GaAs central layer 11 and a plurality of 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 facing away from the cavity two-level structure 20 side. Each structure pair in the first structure pair 12 and the second structure pair 13 includes a GaAs layer and an AlGaAs layer, and the AlGaAs layer is located on a side of the GaAs layer away from the GaAs central layer 11 . It is worth noting that when setting the number of structure pairs on both sides of the GaAs central layer, it should be noted that the number of the first structure pair 12 is smaller than the number of the second structure pair 13, so that the laser light emitted by the DBR laser is controlled by the second structure pair 13 Sent in the direction of the first structure pair 12 .

The resonant wavelength _λtotal of the DBR laser is mainly determined by the thickness d ₁ of the GaAs central layer in the vertical direction, so the wavelength and thickness usually satisfy _λtotal ≈d ₁ xn _GaAs , where n _GaAs is the refractive index of the GaAs central layer material. In other words, the thickness of the GaAs central layer when setting

Meanwhile, the thickness of each GaAs layer

The thickness of each AlGaAs layer

FIG. 5 is a cross-sectional view of the electrical injection laser 10 in FIG. 3 in a first plane P. As shown in FIG. The first plane P is perpendicular to the arrangement direction of the electrical injection laser 10 and the cavity two-level structure 20 shown in FIG. 2 . Please continue to refer to FIG. 5 , and illustrate by taking the first plane P located in the AlGaAs layer as an example, and the cross section of the AlGaAs layer is elliptical. It should be noted that on a plane parallel to the first plane P, the cross section of the GaAs layer is also elliptical, which is not shown here.

By adjusting the radius of the DBR cavity M, the resonance wavelength can be fine-tuned. In other words, the resonance wavelength of the DBR laser is proportional to the radius of the DBR cavity M. Theoretically, when the radius of the resonator M is infinite, the resonance wavelength of the DBR laser is equal to _λtotal . Therefore, for a finite radius of the resonator M, the resonance wavelength is smaller than _λtotal . Since the cross-section of the DBR resonator M in the first plane P is elliptical, and the elliptical cross-section has a major axis and a minor axis, therefore, the major axis radius r and the short axis _of the DBR resonator M cross-section in the first plane P Shaft radius r ₂ different dimensions. Based on this, by controlling the major-axis radius r ₁ and the minor-axis radius r ₂ , 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.

Specifically, the 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 long axis of the elliptical 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 section of the DBR laser on the first plane P; the wavelength of the first laser is λ ₁ , and the wavelength of the second laser is λ ₂ . It should be understood that the wavelength λ1 of the first laser is slightly different from the wavelength _λ2 of the _second laser, and both λ1 and _λ2 are smaller than _λtotal _. In the specific setting, adjust the structural parameters such as the length of the major axis and the minor axis of the elliptical cross-section of the DBR laser in the first plane P, the thickness and quantity of each film layer in the DBR resonator M, and the refractive index of the selected structure, which can be The adjustment of the first laser light and the second laser light emitted by the laser is realized. At the same time, through this adjustment, most of the light generated by the DBR laser can be emitted upwards, thereby improving the excitation efficiency.

For ease of understanding, for example, it is defined that the polarization direction of the first laser light is parallel to the X axis, and the polarization direction of the second laser light is parallel to the Y axis.

A parameter design scheme of a DBR laser is now provided:

FIG. 6 is a simulation diagram of the first laser and the second laser formed by adopting the structures shown in FIGS. 3 to 5 and the parameters in the above table. As shown in Figure 6, the wavelength shows only the first laser light whose polarization direction is parallel to the X direction at 874.972; the wavelength shows only the second laser light whose polarization direction is parallel to the Y direction at 875.62. In other words, the wavelength λ ₁ of the first laser light generated by the DBR laser formed using the structural parameters in the above table = 874.97nm, and the wavelength λ ₂ = 875.62nm of the second laser light.

FIG. 7 is a specific structural diagram of the cavity two-level structure 20 in the structure shown in FIG. 3 . Specifically, the cavity two-level structure 20 is a shallow etched two-dimensional cavity structure. Exemplarily, the shallow etched two-dimensional cavity structure is a grating structure. The cavity two-level structure 20 can be specifically set to include a substrate 21 and a grating layer 22 disposed on the side of the substrate 21 away from the DBR laser. The grating layer 22 has a resonant cavity, and the resonant cavity is provided with quantum dots O (shown in black in the figure) ball shown). Exemplary, the substrate 21 is made of SiO ₂ (silicon dioxide) or SOI (silicon on insulator) material; the distance between the quantum dot O and the surface of the grating layer 22 can be set to 90nm as shown in FIG. It includes a main part and a plurality of ring-shaped raised parts, the thickness of the main part can be set to 60nm as shown in FIG. 7 , and the thickness of the raised part can be set to 120nm as shown in FIG. 7 . Of course, the structural parameters of the grating layer 22 are not limited to those shown in FIG. 7 , and can be changed according to requirements.

In addition, a transparent medium layer (not shown in FIG. 7 ) can also be provided on the side of the grating layer 22 in the cavity two-level structure 20 away from the substrate 21. The transparent medium layer can be a specific structural layer, or it can be a vacuum or air layer.

In order to realize that most of the light generated by the cavity two-level structure 20 can be emitted away from the DBR laser, thereby improving the emission efficiency, after the resonant wavelength _λtotal ' is determined, the grating structure needs to be adjusted according to the resonant wavelength _λtotal ' and the emission direction Sure. It is worth noting that the grating structure needs to satisfy the following equation:

Where: n _eff is the effective refractive index of the grating layer; Λ is the period of the grating layer; n _C is the refractive index of the transparent medium layer; θ is the angle between the photon emission direction and the vertical direction in the resonant cavity of the grating layer. n _C is the refractive index of the transparent medium layer covering the grating layer, and the value is 1 when the transparent medium layer is a vacuum or an air layer.

It is worth noting that n _eff is determined by the etching depth of the grating layer and the duty ratio (ratio of the width of the unetched part to the period Λ of the grating).

FIG. 8 is a cross-sectional view of the grating layer 22 in FIG. 7 at the second plane Q, and the second plane Q is parallel to the first plane P. Referring to FIG. Please continue to refer to FIG. 8, the cross-section of the grating structure on the second plane Q is elliptical. In other words, the first plane P and the second plane Q are arranged in parallel, and both are perpendicular to the electrical injection shown in FIG. The arrangement direction of the laser 10 and the cavity two-level structure 20 .

Since the resonant wavelength λ _total ' of the grating structure is related to the diameter of the most central part, and the most central part of the grating structure is elliptical, and the major axis dimension of the ellipse is r ₁ ', and the minor axis dimension is r ₂ ', Therefore, the grating structure emits slightly different wavelengths of light in the direction parallel to the major axis and in the direction parallel to the minor axis.

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 long axis of the elliptical section of the grating structure on the second plane Q, and the polarization direction of the second resonant light is The polarization direction is parallel to the minor axis of the elliptical section of the second plane Q; the wavelength of the first resonant light is λ ₁ ', and the wavelength of the second resonant light is λ ₂ '. It should be understood that the wavelength λ ₁ ′ of the first resonant light is slightly different from the wavelength λ ₂ ′ of the second resonant light, and both λ ₁ ′ and λ ₂ ′ are smaller than λ _total ’. 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.

It is worth noting that the quantum dot O in the cavity two-level structure 20 has a wavelength λ ₀ corresponding to its two-level energy.

When the difference between the wavelength λ ₀ corresponding to the second energy level of the quantum dot O and the wavelength λ ₁ ' of the first resonant light of the cavity two-level energy level structure 20 is less than the threshold value, the polarization direction of the generated single photon is parallel to the long axis of the grating structure . In other words, the first resonant light exists in the resonant cavity M. At this time, the long axis of the section of the cavity two-level structure 20 on the second plane Q and the long axis of the section of the electrical injection laser 10 on the first plane P have two arrangements:

Mode one: the structure shown in Figure 9, when the cavity two-level structure 20 and the two major axes of the electrical injection laser 10 are perpendicular to each other, the wavelength λ ₁ of the first laser in the laser light emitted by the electrical injection laser 10 is equal to the cavity The wavelength λ ₁ ′ of the first resonant light of the two-level structure 20 is specifically shown in FIG. 10 .

Mode two: the structure shown in Figure 11, when the cavity two-level structure 20 and the two major axes of the electric injection laser 10 are parallel to each other, the wavelength λ of the _second laser in the laser light emitted by the electric injection laser 10 is equal to the cavity The wavelength λ ₁ ′ of the first resonant light of the two-level structure 20 is specifically shown in FIG. 12 .

When the difference between the wavelength λ ₀ corresponding to the second energy level of the quantum dot O and the wavelength λ ₂ ' of the second resonant light of the cavity two-level structure 20 is less than the threshold value, the polarization direction of the generated single photon is parallel to the short axis of the grating structure . In other words, the second resonant light exists in the resonant cavity M. At this time, the long axis of the section of the cavity two-level structure 20 on the second plane Q and the long axis of the section of the electrical injection laser 10 on the first plane P also have two arrangements:

1) structure as shown in Figure 13, when the cavity two level structure 20 and the two major axes of the electric injection laser 10 are perpendicular to each other, the wavelength λ of the _second laser in the laser light emitted by the electric injection laser 10 is equal to the cavity two The wavelength λ ₂ ' of the second resonant light of the energy level structure 20, specifically as shown in Figure 14;

2) structure as shown in Figure 15, when two major axes of cavity two energy level structure 20 and electric injection laser 10 are parallel to each other, the wavelength λ ₁ of the first laser in the laser light emitted by electric injection laser 10 is equal to cavity two energy The wavelength λ ₂ ′ of the second resonance light of the stage structure 20 is specifically shown in FIG. 16 .

Likewise, the threshold is half the full width at half maximum of the quantum dot emission spectrum. In other words, λ ₁ ′ and λ ₂ ′ are equal to or close to the wavelength corresponding to the second energy level of the quantum dot O.

Please continue to refer to the structure shown in FIG. 8 . In FIG. 8 , there is a gap between each ring-shaped raised portion and the central portion, and each ring-shaped raised portion and a gap form a structure pair. Exemplarily, the number of the structure pairs is 12. Along the radial direction, the size of each structure pair is exemplarily set to 340 nm, wherein the interval is exemplarily set to 100 nm. Of course, it can also be set to other sizes according to requirements, which will not be repeated here.

In order to improve the quality of the single photon source produced by the electrically driven single photon source 100 provided in the present application, it can be set that the electrically driven single photon source 100 provided in the present application also includes a polarization filter and a wavelength filter (not shown in the figure). The polarization filter and the wavelength filter are arranged on the side of the cavity two-level structure 20 away from the electrical injection laser 10 . It is worth noting that since the electrical injection laser emits two lasers, the polarization filter can be used to filter the laser light with different polarization and the same wavelength as the single photon, and at the same time, the wavelength filter can be used to filter the laser light with the same polarization and different wavelength as the single photon. A single-photon source with high brightness and high identity can be obtained.

Implementation mode two

The difference between Embodiment 2 and Embodiment 1 is that, as shown in FIG. The cross-sectional view in plane Q is circular. The electrically driven single-photon source provided in the embodiment of the present application can generate a single-photon light source through non-resonant excitation.

Please continue to refer to FIG. 17 , the cross-section of the DBR resonator M in the first plane P is circular, and the radius of the circular cross-section is the same as r everywhere. Based on this, compared with the electrical injection laser 10 shown in FIG. 5 , the electrical injection laser 10 shown in FIG. 17 emits the same wavelength of laser light in the direction parallel to the long axis and the direction parallel to the short axis.

Specifically, the 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 on the first plane P, and the polarization direction of the second laser is parallel to the DBR laser on the Y direction of a plane P. Since the section of the DBR resonator M is circular, the wavelengths of the first laser and the second laser are both λ. In the specific setting, adjust the structural parameters such as the radius of the circular section of the DBR laser in the first plane P, the thickness and quantity of the inner film layer of the DBR resonator M, and the refractive index of the selected structure, so as to realize the output of the first laser and the Adjustment of the second laser. At the same time, through this adjustment, most of the light generated by the DBR laser can be emitted upwards, thereby improving the excitation efficiency.

A parameter design scheme of a DBR laser is now provided:

Please continue to refer to FIG. 18 , the section of the grating structure on the second plane Q is circular. In other words, the first plane P and the second plane Q are arranged in parallel, and both are perpendicular to the arrangement direction of the DBR laser and the grating structure. Since the resonant wavelength λ _total ' of the grating structure is related to the diameter of the most central part, and the most central part of the grating structure is a circle with a radius r, so comparing the structure shown in Figure 8, the structure shown in Figure 18 The wavelength of light emitted by the middle grating structure in the direction parallel to the major axis and the direction parallel to the minor axis is the same.

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 laser light is parallel to the grating structure In the Y direction of the second plane Q, the wavelength of the first resonant light and the wavelength of the second resonant light are both λ'.

It should be noted that in the embodiment of the present application, it is necessary to control the difference between λ' and the wavelength corresponding to the second energy level of the quantum dot O to be smaller than the threshold value, and the threshold value is half the full width at half maximum of the spectrum emitted by the quantum dot. In other words, λ' is equal to or close to the wavelength corresponding to the second energy level of the quantum dot O. At the same time, it is necessary to ensure that the wavelength λ' is greater than the wavelength λ, so that the electrical injection laser 10 shown in Figure 2 can be non-resonant with the cavity two-level structure 20, so that the quantum Point O produces photons.

Please continue to refer to FIG. 18 . In FIG. 18 , there is a gap between each ring-shaped raised portion and the central portion, and each ring-shaped raised portion and a gap form a structural pair. Exemplarily, the radius r' of the central part is selected as 490 nm, and the number of structure pairs is 12. And along the radial direction, the size of each structure is exemplarily set to 340 nm, wherein the interval is exemplarily set to 100 nm. Of course, it can also be set to other sizes according to requirements, which will not be repeated here.

Of course, in order to improve the quality of the single photon source produced by the electrically driven single photon source provided by the present application, the electrically driven single photon source provided by the present application may also include a wavelength filter, which is arranged in the cavity two-level structure 20 The side away from the electrical injection laser 10 is used to filter out the first laser light and the second laser light, so that a high-brightness single-photon source can be obtained.

Apparently, those skilled in the art can make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the embodiments of the present application. In this way, if the modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and equivalent technologies, the present application also intends to include these modifications and variations.

Claims

An electrically driven single photon source, characterized in that it comprises an electrical injection laser and a cavity two-level structure, the cavity two-level structure has only one quantum dot; the cavity two-level structure is located at the electrical injection laser The light output side, and the optical center of the cavity two-level structure is aligned with the optical center of the electrical injection laser, and the cavity two-level structure is used to generate a single photons, and the emission direction of the single photon is parallel to the emission direction of the pump light.
The electrically driven single photon source according to claim 1, wherein the electrical injection laser is a distributed Bragg reflection DBR laser, and the cavity two-level structure is a grating structure.
The electrically driven single photon source according to claim 2, wherein the section of the DBR laser on the first plane is elliptical, and the first plane is perpendicular to the arrangement direction of the DBR laser and the grating structure; The section of the grating structure on the second plane is elliptical, and the second plane 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 long axis of the elliptical section of the DBR laser on the first plane, and the first The polarization directions of the two lasers are parallel to the short axis of the elliptical section of the DBR laser on 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 long axis of the elliptical section of the grating structure on the second plane, the The polarization direction of the second resonant light is parallel to the minor axis of the elliptical section of the grating structure on the second plane.
The electrically driven single photon source according to claim 3, wherein the wavelength corresponding to the second energy level of the quantum dot in the second energy level of the cavity is λ 0 , and the wavelength corresponding to the second energy level of the quantum dot The difference between λ 0 and the wavelength λ 1 ′ of the first resonant light of the cavity two-level structure is smaller than a threshold value, and the threshold value is half of the full width at half maximum of the spectrum emitted by the quantum dot.
The electrically driven single photon source according to claim 4, wherein the long axis of the section of the cavity two-level structure on the second plane is the same as the long axis of the section of the electric injection laser on the first plane are perpendicular to each other, and the wavelength λ 1 of the first laser light emitted by the electrical injection laser is equal to the wavelength λ 1 ′ of the first resonant light of the cavity two-level structure; or,

The long axis of the section of the cavity two-level structure on the second plane is parallel to the long axis of the section of the electric injection laser on the first plane, and the second laser in the laser light emitted by the electric injection laser The wavelength λ 2 is equal to the wavelength λ 1 ′ of the first resonant light of the cavity two-level structure.
The electrically driven single photon source according to claim 3, wherein the wavelength corresponding to the second energy level of the quantum dot in the second energy level of the cavity is λ 0 , and the wavelength corresponding to the second energy level of the quantum dot The difference between λ 0 and the wavelength λ 2 ′ of the second resonant light of the cavity two-level structure is smaller than a threshold value, and the threshold value is half of the full width at half maximum of the spectrum emitted by the quantum dot.
The electrically driven single photon source according to claim 6, wherein the long axis of the section of the cavity two-level structure on the second plane is the same as the long axis of the section of the electric injection laser on the first plane are perpendicular to each other, and the wavelength λ 2 of the second laser light emitted by the electrical injection laser is equal to the wavelength λ 2 ′ of the second resonant light of the cavity two-level structure; or,

The long axis of the section of the cavity two-level structure on the second plane is parallel to the long axis of the section of the electric injection laser on the first plane, and the wavelength λ of the first laser in the emitted laser is equal to The wavelength λ 2 ′ of the second resonant light in the cavity two-level structure.
The electrically driven single photon source according to claim 5 or 7, further comprising a polarization filter and a wavelength filter, the polarization filter and the wavelength filter are both arranged in the cavity two-level structure On the side away from the electrical injection laser, the polarization filter is used to filter the laser light with the same wavelength and different polarization from the single photon, and the wavelength filter is used to filter the laser light with the same polarization as the single photon and different wavelength.
The electrically driven single photon source according to claim 2, wherein the section of the DBR laser on the first plane is circular, and the first plane is perpendicular to the arrangement direction of the DBR laser and the grating structure; The cross section of the grating structure on the second plane is circular, and the second plane is parallel to the first plane;

The DBR laser is used to generate a first laser and a second laser with orthogonal polarization states, and the wavelengths of the first laser and the second laser are both λ;

The grating structure has a first resonant light and a second resonant light, the wavelengths of the first resonant light and the second resonant light are both λ', and the λ' is greater than the λ.
The electrically driven single photon source according to claim 9, further comprising a wavelength filter, the wavelength filter is arranged on the side of the cavity two-level structure away from the electrical injection laser to filter out the first laser and the second laser.
The electrically driven single photon source according to any one of claims 2-10, wherein the DBR laser comprises a DBR resonator, and the DBR resonator comprises a central layer and a plurality of structure pairs, a plurality of the structures The centering part of the structure pairs is located on the side of the central layer facing the cavity two-level structure, and part of the structure pairs is located on the central layer away from the cavity two-level structure; each of the multiple structure pairs A structure pair includes a first structure layer and a second structure layer made of different materials, and the second structure layer is located on a side of the first structure layer away from the central layer.
The electrically driven single photon source according to claim 11, wherein the number of structure pairs located on the side of the central layer facing the cavity two-level structure is less than that on the side of the central layer facing away from the cavity two-level structure The number of pairs of structures on one side of the structure.
The electrically driven single photon source according to any one of claims 2-12, wherein the grating structure comprises a second substrate, a grating layer arranged on the side of the second substrate away from the DBR laser and a transparent medium layer located on the side of the grating layer away from the substrate, the grating layer has a resonant cavity, and the quantum dots are arranged in the resonant cavity.