Fiber-coupled quantum dot single-photon source array and preparation method thereof

Abstract

The present invention discloses a fiber-coupled quantum dot single-photon source array and a method for preparing the same, belonging to the field of semiconductor single-photon sources. The array comprises: an i-type GaAs substrate, a first contact layer, a second contact layer, and a third contact layer arranged from bottom to top, the second contact layer having a quantum dot layer for generating single photons; a long waveguide and an arc-shaped grating prepared on the second and third contact layers; a one-dimensional photonic crystal mirror prepared on the waveguide on the side away from the grating, wherein the waveguide is connected to the grating; an air slot prepared below the waveguide and the grating; a table prepared on the upper surface of the third contact layer on the side of the grating away from the waveguide; and a polished optical fiber array mounted on the upper surface of the table. The fiber-coupled quantum dot single-photon source array of the present invention can be more conveniently and effectively coupled with other quantum optical circuits.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor single-photon sources, and in particular relates to a fiber-coupled quantum dot single-photon source array and a preparation method thereof. Background Art

[0002] With the demise of Moore's Law, the development of traditional electronic chips has been limited to a certain extent. The ever-increasing demand for computing requires us to find new computing methods with higher speeds and lower power consumption. This has led to the emergence of photons as information media, creating quantum optical chips that offer an alternative to traditional electronic chips. These chips offer the advantages of high speed and low energy consumption. Quantum optical chips can be applied to fields such as quantum communications, a crucial future application scenario.

[0003] Similar to the integrated circuits used in traditional electronic chips, photonic quantum chips also require the construction of a suitable integrated optical circuit, which mainly includes a quantum light source, a quantum random number generator, quantum entanglement coding technology, and single-photon detection technology. Among them, quantum light sources include quasi-single-photon sources, probabilistic single-photon sources, and deterministic single-photon sources. The former two have the disadvantage of high multi-photon content and low single-photon purity, while deterministic single-photon sources have excellent single-photon purity, making them excellent single-photon sources.

[0004] Currently, there are many approaches to using deterministic single-photon sources, such as single atoms, diamond color centers, and quantum dots. Performance indicators for single-photon sources include single-photon purity, homogeneity, and collection efficiency. Single-photon sources generated using III-V semiconductor quantum dots have relatively good performance indicators. However, optical circuits made from III-V semiconductors experience significant loss of light generated by quantum dots due to the material's high refractive index. While silicon, a commonly used material in integrated optics, boasts low loss, it is not possible to grow quantum dots with similarly good performance, making it impossible to obtain a single-photon source with such high performance indicators. Currently, passive silicon-based optical integrated circuit technology is highly mature in integrated optics, so resolving its light source issue is crucial. One approach is to transfer single photons generated by semiconductor quantum dots to silicon-based optical integrated circuits.

[0005] The current method for transferring single photons generated by semiconductor quantum dots to other optical integrated circuits is to couple the single photons generated in the III-V semiconductor quantum dots with single-mode optical fibers for collection, and ultimately transfer the single photons to the desired location via the optical fibers. A major challenge with this approach is how to effectively transmit the photons generated by the quantum dots from the planar structure and couple them into the optical fiber. This challenge arises because the optical fiber mode does not match the subwavelength mode of the nanowaveguide, resulting in many different implementation methods for this approach. First, an optical waveguide is made on the surface of a III-V semiconductor near the quantum dots using micro-nano processing technology. Next, one method is to use the evanescent wave above the optical waveguide for coupling, and gently place the single-mode optical fiber on the top of the waveguide to couple the single photons into the optical fiber. However, this method has restrictions on the position of the structure, and it has high requirements for the optical fiber and needs to be customized; the second method is to make the end face of the waveguide into a tapered gradient tip waveguide, and collect the single photons generated by the quantum dots into the optical fiber through this end face waveguide. This method is more efficient than the previous method, and is simpler, more convenient, and lower in cost. The disadvantage is that the structure needs to be made at the edge of the sample, and the tapered area needs to be relatively long to meet the insulation conditions. Summary of the Invention

[0006] In order to solve the problems in the prior art, the present invention provides a fiber-coupled quantum dot single-photon source array and a preparation method thereof.

[0007] The technical solutions of the present invention are as follows:

[0008] In a first aspect, the present invention discloses a method for preparing a fiber-coupled quantum dot single-photon source array, comprising the following steps:

[0009] A III-V semiconductor structure with semiconductor quantum dots is prepared, wherein the III-V semiconductor structure comprises, from bottom to top, an i-type GaAs substrate, a first contact layer, a second contact layer, and a third contact layer; the second contact layer comprises a quantum dot layer for generating single photons; the second contact layer and the third contact layer are etched to form two symmetrically arranged grooves, wherein the grooves comprise a first segment and a second segment connected to each other, the first segments of the two grooves being parallel to each other, and the unetched area therebetween serving as a waveguide; the second segments of the two grooves are at an angle within a range of 30-40 degrees, and the third contact layer is etched at the unetched area between the second segments of the two grooves to form a grating consisting of a plurality of arcuate slits, wherein the protruding ends of the arcuate slits face away from the waveguide, and the main diffraction order emission angle of the grating is 8-9 degrees; and then, the grating is formed at a position away from the waveguide. A second contact layer and a third contact layer are etched on the waveguide on one side of the grating to form a one-dimensional photonic crystal mirror; a table is formed on the upper surface of the third contact layer on the side of the grating away from the waveguide; the first contact layer below the waveguide and the grating is etched to form an air groove, which serves as the cladding of the waveguide and is used to meet the total reflection condition of the waveguide; when a single photon is coupled from the waveguide to the grating and diffracts, the air groove can also reflect the diffracted single photon to prevent the single photon from entering the i-type GaAs substrate; an optical fiber array with a polished end face is installed on the upper surface of the table so that light emitted through the optical fiber array can enter the grating; wherein, in order to increase the contact area between the optical fiber array and the table, the optical fiber array is placed horizontally, and the angle between the polished end face of the optical fiber array and the horizontal plane is generally 20 to 50 degrees.

[0010] In a second aspect, the present invention discloses a fiber-coupled quantum dot single-photon source array prepared by the method.

[0011] In a third aspect, the present invention discloses a single photon transfer method using the fiber-coupled quantum dot single photon source array, comprising the following steps:

[0012] First, connect the external fiber optic beam splitter to the fiber optic array, and then connect the external laser and optical circuit to the fiber optic beam splitter respectively; the fiber optic beam splitter will not affect the laser light emitted by the laser; when a single photon is transmitted from the fiber optic array to the fiber optic beam splitter, the fiber optic beam splitter will input the single photon into the optical circuit; turn on the laser, the laser emits a laser, and the laser passes through the fiber optic beam splitter and enters the fiber optic array. The laser is transmitted along the arrangement direction of the optical fibers in the fiber optic array. When the laser is transmitted to the polished end face, the laser is reflected and emitted from the fiber optic array. The laser emitted from the fiber optic array enters the grating of the corresponding photon unit. When the laser enters the grating, due to diffraction, the laser will be decomposed into laser beams in different directions. The laser beam transmitted along the waveguide arrangement direction is coupled into the waveguide, and the laser beam coupled into the waveguide illuminates When the single photon hits the quantum dot layer in the waveguide, the quantum dot layer is excited to produce a single photon, which propagates in all directions in the waveguide. When the single photon hits the one-dimensional photonic crystal mirror, the one-dimensional photonic crystal mirror reflects the single photon. After reflection by the one-dimensional photonic crystal mirror, the single photon continues to propagate in the waveguide. When the single photon propagates to the side of the waveguide close to the grating, the single photon is coupled from the waveguide to the grating, and the single photon diffracts on the grating. Some of the diffracted single photons are emitted from the grating. The single photons whose emission angle is within the main diffraction order emission angle range of the grating propagate to the polished end face of the optical fiber array and are reflected by the polished end face. After reflection, the single photon enters the optical fiber array and propagates along the arrangement direction of the optical fiber, thereby entering the optical fiber beam splitter. The single photon is output from the optical fiber beam splitter and enters the optical circuit, completing the transfer of the single photon.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention uses electron beam lithography, ultraviolet lithography, dry etching, wet etching and other methods for micro-nano fabrication, forming an air groove, a waveguide, a one-dimensional photonic crystal mirror, a grating and a table on the sample. The air groove is arranged below the waveguide and the grating, which meets the total reflection condition of the waveguide and overcomes the problem of no cladding in the sample when the waveguide and the grating are coupled. At the same time, when a single photon is coupled from the waveguide to the grating and diffracts, the air groove can also reflect the diffracted single photon, preventing the single photon from entering the i-type GaAs substrate. Therefore, with the air groove, the diffracted single photon moving downward will hit the air boundary of the air groove and be reflected. After reflection, there is a certain possibility that it will enter the optical fiber array, which also improves the single photon collection rate to a certain extent. The one-dimensional photonic crystal mirror is arranged on the waveguide on the side away from the grating, which can reflect the single photon generated by the quantum dot in the waveguide, thereby promoting the coupling of the single photon into the grating. The grating is shallowly etched, its depth not reaching the quantum dot layer, and its main diffraction order emission angle is 8-9 degrees, essentially perpendicular to the grating plane. This grating can couple single photons within the waveguide plane to a plane perpendicular to the waveguide, with relatively high transmission efficiency. Furthermore, the grating is curved, focusing the emitted light spot and shaping the beam into a Gaussian shape, significantly increasing the coupling efficiency with the optical fiber array mounted on the table. Similarly, the end faces of the optical fiber array mounted on the table are polished to a customized angle of 20-50 degrees. Within this angle range, the optical fiber array effectively transmits single photons into the optical fiber, improving the coupling efficiency between single photons from the grating and the optical fiber array. The table is placed on the sample surface on one side of the grating and has a thickness of 5-10 μm. This thickness prevents the optical fiber array from contacting and damaging the grating and other components during coupling. The table design of the present invention fully utilizes the various properties of photoresist, resulting in a relatively ingenious design. The waveguide, grating, one-dimensional photonic crystal mirror, air groove, table, and fiber array designed on the sample work together to couple single photons generated by the quantum dot single-photon source through the grating and fiber array, enabling transfer to other optical circuits. Finally, the grating of the present invention can be fabricated at any location within the sample connected to the waveguide, thus overcoming the fiber placement issues of existing techniques. Furthermore, the present invention's unique design of the grating and fiber array allows for more convenient and efficient coupling with other quantum optical circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a main view of the stack structure of an epitaxially grown III-V semiconductor structure with semiconductor quantum dots;

[0016] Figure 2 This is a cross-sectional view of the III-V semiconductor structure after processing the grating, waveguide and one-dimensional photonic crystal mirror;

[0017] Figure 3 This is a top view of the III-V semiconductor structure after processing the grating, waveguide and one-dimensional photonic crystal mirror;

[0018] Figure 4 This is a cross-sectional view of the III-V semiconductor structure after the mesa and air groove are processed;

[0019] Figure 5 is a cross-sectional view of a fiber-coupled quantum dot single-photon source array;

[0020] Figure 6 This is a top view of multiple photon units in a fiber-coupled quantum dot single-photon source array;

[0021] Figure 7 It is a flow chart of the method for preparing a fiber-coupled quantum dot single-photon source array.

[0022] In the figure, 1. p-type GaAs contact layer; 2. i-type GaAs contact layer; 3. i-type Al 0.3 Ga 0.7 As contact layer; 4. InAs quantum dot layer; 5. i-type GaAs contact layer; 6. n-type GaAs contact layer; 7. n-type Al 0.6 Ga 0.4 As contact layer; 8.i-type Al 0.6 Ga 0.4 As contact layer; 9. i-type GaAs substrate; 10. Grating; 11. Air channel; 12. Waveguide; 13. One-dimensional photonic crystal mirror; 14. Air slot; 15. Mesa; 16. Fiber array. DETAILED DESCRIPTION

[0023] The present invention will be further described and illustrated below in conjunction with specific embodiments. The embodiments are merely illustrative of the present disclosure and do not limit its scope. The technical features of the various embodiments of the present invention may be combined accordingly, provided that there is no conflict between them.

[0024] In order to facilitate understanding of the present invention, some terms are introduced below.

[0025] First of all, a waveguide is a transmission line similar to a pipe. There is a refractive index difference between the inside and outside of the waveguide. Light that meets a specific angle will be totally reflected at the side wall of the waveguide. Therefore, the light will be confined by the waveguide and will not diverge. This specific angle is also the numerical aperture of the waveguide.

[0026] A grating is a periodic optical micro-nanostructure. Due to the periodic change of the refractive index, this optical structure can change the propagation angle of the light beam reaching the grating. Combining the grating with a waveguide can emit the light in the waveguide perpendicular to the sample surface.

[0027] A fiber array is a collection of multiple optical fibers customized by channel count, light collection angle, and wavelength. The fibers in the substrate and pressure plate are stripped of their coating and polished to a specific angle as needed. The spacing between fibers is 127µm or 250µm. Optical fibers operate on similar principles to waveguides. The core is surrounded by a cladding and coating, each with different refractive indices. Similar to waveguides, these layers can confine light within the core, achieving total internal reflection.

[0028] Electron beam lithography is a technique that uses high-energy focused electrons for photolithography. These electrons act directly on electron-sensitive photoresist, ultimately forming the desired pattern. Due to its short wavelength, electron beam lithography has very high resolution and can achieve line widths of several nanometers. The application of electron beam lithography can couple quantum dots into waveguides, collect single photons emitted by the quantum dots through gratings, and transmit them nearly vertically to an optical fiber array outside the sample surface for collection. This allows the integration of quantum dot single-photon sources into arbitrary optical circuits.

[0029] Dry etching is a commonly used isotropic etching method. It is a process of removing solid thin films by chemically reacting with neutral substances in the ground state or excited state. At low pressure, a corresponding plasma is generated in the gas. At the same time, a magnetic induction coupling coil is added to the equipment to enhance the downward directionality of the plasma. These plasma gas flows react with the sample surface and produce volatile substances. The volatile substances are subsequently carried away in the vacuum environment, and the etching is finally completed.

[0030] Wet etching is an anisotropic etching method that mainly uses specific acidic or alkaline solutions to perform corrosion.

[0031] The present invention will be described in further detail below with reference to the accompanying drawings:

[0032] The present invention uses various micro-nano processing methods to manufacture gratings 10, waveguides 12, one-dimensional photonic crystal mirrors 13 and tables 15 on a semiconductor structure with quantum dots, and then uses a translation stage to align and fix the optical fiber array 16 to form an optical fiber coupled quantum dot single photon source array, thereby achieving the goal of optical fiber coupling. Figure 7 As shown, the specific implementation steps for preparing a fiber-coupled quantum dot single-photon source array are as follows:

[0033] Step 1: Use epitaxial growth method to grow III-V semiconductor materials with quantum dots, such as Figure 1 As shown, the III-V semiconductor structure includes, from bottom to top, an i-type GaAs substrate 9, an i-type Al 0.6 Ga 0.4 As contact layer 8, n-type Al 0.6 Ga0.4 As contact layer 7, n-type GaAs contact layer 6, i-type GaAs contact layer 5, InAs quantum dot layer 4, i-type Al 0.3 Ga 0.7 As contact layer 3, i-type GaAs contact layer 2 and p-type GaAs contact layer 1; i-type Al 0.6 Ga 0.4 As contact layer 8 and n-type Al 0.6 Ga 0.4 The As contact layer 7 constitutes the first contact layer, the n-type GaAs contact layer 6, the i-type GaAs contact layer 5 and the InAs quantum dot layer 4 constitute the second contact layer, and the i-type Al 0.3 Ga 0.7 As contact layer 3, i-type GaAs contact layer 2 and p-type GaAs contact layer 1 constitute the third contact layer; the InAs quantum dot layer 4 is used to generate single photons, which is formed by lattice mismatch between InAs and GaAs layers and can generate single photons under laser excitation of corresponding wavelengths, such as Figure 1 As shown in the main view, the thickness of the p-type GaAs contact layer 1 is 30-50nm, the thickness of the i-type GaAs contact layer 2 is 3-10nm, the thickness of the i-type Al0.3Ga0.7As contact layer 3 is 50-60nm, the thickness of the InAs quantum dot layer 4 is 10-20nm, the thickness of the i-type GaAs contact layer 5 is 40-50nm, the thickness of the n-type GaAs contact layer 6 is 30-40nm, and the thickness of the n-type Al 0.6 Ga 0.4 The thickness of the As contact layer 7 is 200-250 nm, and the i-type Al 0.6 Ga 0.4 The thickness of the As contact layer 8 is 900-1000 nm, and the n-type Al 0.6 Ga 0.4 As contact layer 7 and i-type Al 0.6 Ga 0.4 The As contact layer is a sacrificial layer, that is, a part of the air groove 14. The thickness of the i-type GaAs contact layer 9 is 300-500 μm, and it is a substrate structure of Group III-V semiconductor material and has no role in micro-nanostructure.

[0034] Step 2: Use electron beam lithography and dry etching technology to first make the waveguide 12, one-dimensional photonic crystal mirror 13 and grating 10, then make the table 15; finally use wet etching technology to make the air groove 14; thereby achieving the scattering of the light emitted by the quantum dots in the waveguide plane to the outside of the plane, such as Figure 2 and Figure 3 As shown, the specific preparation method is as follows:

[0035] 1) Prepare the array structure of the waveguide 12, the one-dimensional photonic crystal mirror 13 and the grating 10:

[0036] 1.1) Spin-coat AR-P 6200.13 electron beam photoresist (positive photoresist) on the upper surface of the p-type GaAs contact layer 1;

[0037] 1.2) Using electron beam lithography, the desired pattern is transferred to the spin-coated photoresist. The desired pattern is the structural array of the waveguide 12, the structural array of the one-dimensional photonic crystal mirror 13 and the array structure of the grating 10 designed according to the physical principles of electrodynamics and waveguide optics. They constitute an array structure as a whole, that is, a photonic unit, such as Figure 3 As shown;

[0038] 1.3) Using a developer to remove the exposed pattern on the photoresist, the developer is a special developer of the AR-P 6200 series;

[0039] 1.4) Transferring the photoresist pattern to the III-V semiconductor material covered by the photoresist by dry etching;

[0040] Specifically: Figure 3 As shown, the second contact layer and the third contact layer are etched to form two symmetrically arranged grooves, which are air channels 11. The grooves include a first section and a second section connected to each other. The first sections of the two grooves are parallel to each other, and the unetched area between them serves as a waveguide 12. The second sections of the two grooves are at a certain angle of 30-40 degrees. The third contact layer is etched to different depths in the unetched area between the second sections of the two grooves to form a grating 10 composed of multiple arc-shaped slits, with the protruding ends of the arc-shaped slits facing away from the waveguide 12. The second contact layer and the third contact layer are then etched on the waveguide 12 on the side away from the grating 10 to form a one-dimensional photonic crystal mirror 13. The method for forming a one-dimensional photonic crystal mirror 13 is as follows: first, a second contact layer and a third contact layer are etched on the waveguide away from the grating side to prepare a photonic crystal hole, and then a plurality of photonic crystal holes are formed along the arrangement direction of the waveguide. These photonic crystal holes are arranged in a row according to a certain period. All photonic crystal holes constitute a one-dimensional photonic crystal mirror. The radius of the photonic crystal hole is 70 to 80 nm, the distance between the centers of two adjacent photonic crystal holes is 200 to 240 nm, and the number of photonic crystal holes is 20 to 40.

[0041] 1.5) Residual photoresist after dry etching of the III-V semiconductor material is removed; a waveguide 12, a one-dimensional photonic crystal mirror 13, and a grating 10 are formed, wherein the width of the waveguide 12 is 350 to 480 nm; the period of the grating 10 is 300 to 400 nm, the grating ring width (i.e., the width of the slits) is 150 to 250 nm, and the number of arcuate slits in the grating 10 is 10 to 20.

[0042] In a specific embodiment of the present invention, the period of the grating 10 is 365 nm, the grating ring width is 182.5 nm, and the number of arc-shaped slits in the grating 10 is 11.

[0043] 2) Preparation of table 15:

[0044] 2.1) Spin-coating SU-8 2010 UV photoresist (negative photoresist) on the upper surface of the p-type GaAs contact layer 1 on the side of the grating 10 away from the waveguide 12;

[0045] 2.2) Overlaying the mesa pattern onto the SU-8 2010 UV photoresist on the III-V semiconductor material by UV lithography;

[0046] 2.3) Remove the unnecessary part of the SU-8 photoresist with a developer to form a mesa 15, and obtain Figure 4 wherein the developer is a special developer for the SU-8 2000 series; the height of the table 15 is 5 to 10 um.

[0047] 3) Preparation of air groove 14:

[0048] After the terraces 15 are formed, the III-V semiconductor material is wet-etched in a hydrofluoric acid solution to form air grooves 14 .

[0049] In a specific embodiment of the present invention, the wet etching uses a 1:20 hydrofluoric acid solution, which can selectively etch n-type Al 0.6 Ga 0.4 As contact layer 7 and i-type Al 0.6 Ga 0.4 As contact layer 8 Al 0.6 Ga 0.4 As will not corrode other GaAs contact layers and quantum dot layers. The hydrofluoric acid solution enters the n-type Al from the air channel 11 and the one-dimensional photonic crystal mirror 13 generated after dry etching. 0.6 Ga 0.4 As contact layer 7 and i-type Al 0.6 Ga 0.4The As contact layer 8 is eventually etched to create a nearly square air slot 14. This air slot 14 is located below the waveguide 12 and grating 10, ensuring total internal reflection of the waveguide 12. Furthermore, when single photons are coupled from the waveguide into the grating and diffract, the air slot 14 reflects the diffracted single photons, preventing them from entering the i-type GaAs substrate 9. Therefore, with the air slot 14, diffracted single photons moving downward will strike the air boundary of the air slot 14 and reflect, with a certain probability of entering the optical fiber array 16. This improves the single photon collection rate to a certain extent. Without the air slot 14 below the grating 10, diffracted single photons moving downward would enter and be absorbed by the i-type GaAs substrate 9, reducing the number of collected single photons and the single photon collection rate. Because SU-8 2010 is resistant to a 1:20 hydrofluoric acid solution, the mesa 15 is not corroded.

[0050] During fabrication, smooth waveguide and grating sidewalls are crucial. Therefore, the present invention employs methods such as low-temperature development to achieve this effect. Smooth sidewalls help improve light transmission and grating efficiency. Furthermore, the fabrication of grating 10 requires an electron beam lithography overlay process, where overlay accuracy is crucial. The electron beam lithography instrument used in the present invention can achieve overlay accuracy of several nanometers.

[0051] So far, completed Figure 4 The structure shown in the figure is made, and the functions of each part are as follows:

[0052] The grating 10 is a shallowly etched grating. "Shallowly etched" because the depth of the grating does not reach the InAs quantum dot layer 4, this shallowly etched grating couples light within the plane of the waveguide 12 to a plane perpendicular to the waveguide 12, resulting in relatively high transmission efficiency. One of the important parameters of the grating 10 is its exit angle, defined as the angle between the angle of light emitted from the grating and the normal to the grating plane. The exit angle of a grating typically ranges from 0 to 90°. Due to grating diffraction, light diffracted from the grating has diffraction orders, which are divided into primary and secondary orders. The primary order has the highest light intensity, while the secondary orders are weaker. The grating used in the present invention has a primary order exit angle of approximately 8°, meaning that the primary order exit angle is 8 to 9 degrees, essentially perpendicular to the grating plane. In addition, by making the grating into a micro-elliptical arc shape, the outgoing light spot can be focused and the light beam can be shaped into a Gaussian shape, greatly increasing the coupling efficiency with the optical fiber. In general inventions, when quantum dots are coupled to optical fibers without using micro-lenses, the overall coupling efficiency is extremely low, less than 5%. The theoretical coupling efficiency of the present invention can reach up to 60% to 70%.

[0053] The one-dimensional photonic crystal mirror 13 is arranged on the waveguide away from the side of the grating. It is a periodic structure formed by air holes arranged in one direction. It can allow light in certain waveguide modes to be transmitted from one end to the other, that is, it has a bandwidth. If light that is not within its bandwidth is transmitted to one end, it will be directly reflected. By designing the radius of the air holes and the period of arrangement, the single photons generated by the quantum dots in the waveguide 12 can be reflected.

[0054] The waveguide 12 includes a p-type GaAs contact layer 1, an i-type GaAs contact layer 2, an i-type Al 0.3 Ga 0.7 The semiconductor structure of the As contact layer 3, InAs quantum dot layer 4, i-type GaAs contact layer 5, and n-type GaAs contact layer 6 is used to transmit light and requires a surrounding medium with a suitable refractive index to function properly. Therefore, a corresponding air groove 14 is made to wrap around the waveguide 12. The air groove 14 is a groove structure made by wet etching to meet the total reflection condition of the waveguide 12.

[0055] The air channel 11 is an air region formed by dry etching and is used to satisfy the total reflection condition of the waveguide 12;

[0056] The table 15 is made of SU-8 photoresist, taking advantage of the photosensitive properties of the photoresist and the high resolution of SU-8. After undergoing 95°C pre-baking, exposure, development, and 95°C post-baking, the SU-8 essentially loses its viscosity and hardens, meeting the requirements of the present invention as a table 15 for placing the optical fiber array. Furthermore, SU-8 does not lose thickness in the presence of hydrofluoric acid. The thickness used in the present invention is approximately 5 to 10 μm. This thickness is intended to prevent the optical fiber array from colliding with and damaging components such as the grating during coupling. The table used in the present invention is an innovative design that fully utilizes the various properties of the photoresist, making it a relatively ingenious design.

[0057] Step 3: After completing Figure 4 After the preparation shown in FIG. 1 , it is necessary to install a polished optical fiber array 16 on the upper surface of the table 15 so that the light emitted through the optical fiber array 16 can enter the grating structure; wherein the angle between the end face of the polished optical fiber and the horizontal plane is 20 to 50 degrees; the preparation of the optical fiber coupled quantum single photon source array is completed to obtain the following Figure 5 The fiber-coupled quantum single-photon source array is shown.

[0058] Specifically, when installing the fiber array 16, it is necessary to use a multi-axis translation stage, a rotary translation stage, a storage stage, etc. to find the optimal coupling position on the table 15. Among them, the multi-axis translation stage can be controlled to move back and forth by a knob to adjust the position of the fiber array, the rotary translation stage can adjust the fiber array to be parallel to the plane where the grating is located, and the storage stage is used to place the sample. At the same time, the system also includes a camera for real-time observation of the position of the coupled fiber array and a corresponding computer. After adjusting each translation stage to find the optimal coupling position, the fiber array 16 is fixed to the table 15 with low-temperature resistant glue, such as Figure 5 The optical fiber array 16 of the present invention is made of 9 optical fibers with their coating removed, and can be purchased from the market.

[0059] In a specific embodiment of the present invention, the optical fiber array 16 is composed of an optical fiber and a substrate cladding. The optical fiber is placed in the substrate cladding. The optical fiber in the substrate cladding is an optical fiber with the coating removed. There are a total of 9 fibers, corresponding to the five arrays of single-photon sources and the two double-ended alignment devices. The five arrays of single-photon sources match the five optical fibers used to transmit single photons to other optical circuits, and the two double-ended alignment devices match the remaining four optical fibers. These four optical fibers are used to align the coupling work. Since there is an angle between the light beam emitted by the grating and the normal to the waveguide plane, the optical fiber array needs to be polished at an angle. The standard polishing angles are 0°, 8°, 42.5°, and 45°. The polishing angle used in the present invention is a customized 41°, which is also affected by the refractive index of the substrate cladding and the refractive index of the core. The 41° angle allows light to be effectively transmitted to the core, improving the coupling efficiency between the light in the grating and the optical fiber array.

[0060] like Figure 6 As shown, the grating 10, waveguide 12, and one-dimensional photonic crystal mirror 13 form a photon unit. Multiple photon units are arranged in the same direction and parallel to each other on a III-V semiconductor structure. The arrangement of the photon units is perpendicular to the direction in which the first section of the groove is formed. The number of photon units is equal to the number of optical fibers in the optical fiber array 16 used to transmit single photons to other optical circuits. Light emitted from a fiber enters a photon unit, and similarly, single photons coupled out of the photon unit also enter the fiber.

[0061] The present invention can be coupled with any optical circuit that requires single photons as quantum light sources, and its operation is simple and stable. The single photon transfer method using the fiber-coupled quantum dot single photon source array of the present invention works as follows:

[0062] First, connect an external fiber optic splitter to the fiber array. Then, select a laser with an appropriate wavelength (around 900nm). Then, connect the external laser and the optical circuit to the fiber optic splitter. The fiber optic splitter does not affect the laser light emitted by the laser. When a single photon is transmitted from the fiber array to the fiber optic splitter, the fiber optic splitter inputs the single photon into the optical circuit.

[0063] Turn on the laser and emit it. The laser passes through the fiber beam splitter and enters the fiber array 16. The laser is transmitted along the arrangement direction of the optical fibers in the fiber array 16. When the laser reaches the polished end face, the laser is reflected and emitted from the fiber array 16. The laser emitted from the fiber array 16 enters the grating 10 of the corresponding photon unit, that is, the laser emitted from one optical fiber enters the grating 10 of the corresponding photon unit. The laser incident on the grating 10 will undergo diffraction and the laser will be decomposed into laser beams in different directions. The laser beam transmitted along the waveguide arrangement direction is coupled to the waveguide 12. When the laser beam coupled to the waveguide 12 irradiates the InAs quantum dot layer 4 in the waveguide 12, the InAs quantum dot layer 4 is excited to generate single photons. The single photons propagate in all directions in the waveguide. When the single photons hit the one-dimensional photonic crystal mirror 13, The one-dimensional photonic crystal mirror 13 reflects the single photon. After being reflected by the one-dimensional photonic crystal mirror 13, the single photon continues to propagate in the waveguide 12. When the single photon propagates to the side of the waveguide 12 close to the grating 10, due to diffraction, the single photon is coupled from the waveguide 12 to the grating 10. After diffraction, some single photons are emitted from the grating 10. The single photons with an emission angle within the main diffraction order emission angle range of the grating 10 propagate to the polished end face of the optical fiber array 16 and are reflected by the polished end face. After reflection, the single photon enters the optical fiber array 16, that is, the single photon emitted from a grating 10 enters the optical fiber corresponding to the photon unit where the grating 10 is located, thereby entering the optical fiber array 16; the single photon entering the optical fiber array 16 propagates along the arrangement direction of the optical fiber, thereby entering the optical fiber splitter, and the single photon is output from the optical fiber splitter and enters the optical circuit, completing the transfer of the single photon.

[0064] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they are not to be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the spirit of the present invention, and all such variations and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a fiber-coupled quantum dot single-photon source array, characterized in that: The following steps are involved: Preparing a III-V semiconductor structure with semiconductor quantum dots, the III-V semiconductor structure comprising, from bottom to top, an i-type GaAs substrate, a first contact layer, a second contact layer, and a third contact layer; the second contact layer having a quantum dot layer for generating single photons; The second and third contact layers are etched to form two symmetrically arranged grooves, each groove including a first segment and a second segment connected to each other. The first segments of the two grooves are parallel to each other, and the unetched area between them serves as a waveguide. The second segments of the two grooves are angled at a certain angle of 30-40 degrees. The third contact layer is etched to different depths in the unetched area between the second segments of the two grooves to form a grating composed of multiple arcuate slits, with the protruding ends of the arcuate slits facing away from the waveguide, and the main diffraction order emission angle of the grating is 8-9 degrees. The second and third contact layers are then etched on the waveguide on the side away from the grating to form a one-dimensional photonic crystal mirror. forming a mesa on an upper surface of the third contact layer on a side of the grating away from the waveguide; Etching the first contact layer below the waveguide and the grating to form an air slot. The air slot serves as the waveguide's cladding to satisfy the waveguide's total internal reflection condition. When a single photon is coupled from the waveguide into the grating and diffracted, the air slot can also reflect the diffracted single photon, preventing the single photon from entering the i-type GaAs substrate. An optical fiber array with polished end faces is mounted on the upper surface of the table so that light emitted from the optical fibers in the optical fiber array can enter the grating; wherein the angle between the polished end faces of the optical fiber array and the horizontal plane is 20 to 50 degrees.

2. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, wherein: The method for forming the one-dimensional photonic crystal mirror is: First, a second contact layer and a third contact layer are etched on the waveguide away from the grating side to prepare a photonic crystal hole. Then, multiple photonic crystal holes are formed along the arrangement direction of the waveguide. All the photonic crystal holes constitute a one-dimensional photonic crystal mirror. The radius of the photonic crystal hole is 70 to 80 nm, the distance between the centers of two adjacent photonic crystal holes is 200 to 240 nm, and the number of photonic crystal holes is 20 to 40.

3. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 2, wherein: The grating, the waveguide connected to the grating, and the one-dimensional photonic crystal mirror on the waveguide constitute a photon unit. The III-V semiconductor structure is provided with multiple photon units arranged in the same direction and parallel to each other. The arrangement direction of the multiple photon units is perpendicular to the opening direction of the first section of the groove. The number of photon units is equal to the number of optical fibers in the optical fiber array used to transmit single photons. The optical fibers correspond one-to-one to the photon units, and light emitted from one optical fiber enters one photon unit. The width of the waveguide is 350 to 480 nm, the number of the arc-shaped slits is 10 to 20, the width of the arc-shaped slits is 150 to 250 nm, and the distance between two adjacent arc-shaped slits is 300 to 400 nm.

4. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, wherein: The first contact layer includes i-type Al from bottom to top 0.6 Ga 0.4 As contact layer and n-type Al 0.6 Ga 0.4 As contact layer; the second contact layer includes an n-type GaAs contact layer, an i-type GaAs contact layer and an InAs quantum dot layer from bottom to top; the third contact layer includes an i-type Al 0.3 Ga 0.7 As contact layer, i-type GaAs contact layer and p-type GaAs contact layer; among them, i-type Al 0.6 Ga 0.4 The thickness of the As contact layer is 900-1000 nm, and the n-type Al 0.6 Ga 0.4 The thickness of the As contact layer is 200-250nm, the thickness of the n-type GaAs contact layer is 30-40nm, the thickness of the i-type GaAs contact layer is 40-50nm, the thickness of the InAs quantum dot layer is 10-20nm, and the thickness of the i-type Al 0.3 Ga 0.7 The thickness of the As contact layer is 50-60 nm, the thickness of the i-type GaAs contact layer is 3-10 nm, the thickness of the p-type GaAs contact layer is 30-50 nm, and the thickness of the i-type GaAs substrate is 300-500 μm.

5. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, wherein: The steps of forming the mesa include: SU-8 photoresist is coated on the upper surface of the third contact layer on one side of the grating structure, and then the SU-8 photoresist is pre-baked, exposed, developed and post-baked to finally form a mesa with a thickness of 5 to 10 μm.

6. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, wherein: The grooves, gratings and one-dimensional photonic crystal mirrors are all prepared by dry etching; the air grooves are prepared by wet etching.

7. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 6, characterized in that: The air tank was prepared using a 1:20 hydrofluoric acid solution.

8. A fiber-coupled quantum dot single-photon source array prepared by the method of claim 1.

9. The fiber-coupled quantum dot single-photon source array according to claim 8, characterized in that: The grating, the waveguide connected to the grating, and the one-dimensional photonic crystal mirror on the waveguide constitute a photon unit. The III-V semiconductor structure has multiple photon units arranged in the same direction and parallel to each other. The arrangement direction of the multiple photon units is perpendicular to the opening direction of the first section of the groove. The number of photon units is equal to the number of optical fibers in the optical fiber array used to transmit single photons. The optical fibers correspond one-to-one to the photon units, and light emitted from one optical fiber enters one photon unit.

10. A single photon transfer method using the fiber-coupled quantum dot single photon source array according to claim 9, characterized in that: The following steps are involved: First, connect an external fiber optic beam splitter to the fiber array, and then connect an external laser and an optical circuit to the fiber optic beam splitter. When a single photon is transmitted from the fiber array to the fiber optic beam splitter, the fiber optic beam splitter inputs the single photon into the optical circuit. Turn on the laser, the laser emits laser light, and the laser light passes through the fiber beam splitter and enters the fiber array. The laser light is transmitted along the arrangement direction of the optical fibers in the fiber array. When the laser light is transmitted to the polished end face, the laser light is reflected and emitted from the fiber array. The laser light emitted from the fiber array enters the grating of the corresponding photon unit. The laser light incident on the grating will undergo diffraction, and the laser light will be decomposed into laser beams in different directions. The laser light beam transmitted along the arrangement direction of the waveguide is coupled into the waveguide. When the laser light beam coupled into the waveguide is irradiated on the quantum dot layer in the waveguide, the quantum dot layer is excited to generate single photons. The single photons propagate in all directions in the waveguide. When the single photon collides with the one-dimensional photon When a single photon is reflected by a crystal mirror, the one-dimensional photonic crystal mirror reflects the single photon. After being reflected by the one-dimensional photonic crystal mirror, the single photon continues to propagate in the waveguide. When the single photon propagates to the side of the waveguide close to the grating, the single photon is coupled from the waveguide to the grating. The single photon diffracts on the grating. Some of the single photons after diffraction are emitted from the grating. The single photons with an emission angle within the main diffraction order emission angle range of the grating propagate to the polished end face of the optical fiber array and are reflected by the polished end face. After reflection, the single photon enters the optical fiber of the optical fiber array and propagates along the arrangement direction of the optical fiber, thereby entering the optical fiber beam splitter. The single photon is output from the optical fiber beam splitter and enters the optical circuit, completing the transfer of the single photon.

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