Optical fiber coupling quantum dot single photon source array and preparation method thereof

Abstract

The invention discloses an optical fiber coupling quantum dot single photon source array and a preparation method thereof, and belongs 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 which are arranged from bottom to top, wherein the second contact layer is internally provided with a quantum dot layer for generating single photons; the long-strip-shaped waveguide and the arc-shaped grating are prepared on the second contact layer and the third contact layer, the one-dimensional photonic crystal mirror is prepared on the side, away from the grating, of the waveguide, and the waveguide is connected with the grating; the air slot is prepared below the waveguide and the grating; the mesa is prepared on the upper surface of the third contact layer on one side, far away from the waveguide, of the grating; and the ground optical fiber array is arranged on the upper surface of the table board. The optical fiber coupling quantum dot single photon source array can be more conveniently and effectively coupled with other quantum optical loops.

Description

Technical Field

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

[0002] With the failure of Moore's Law, the development of traditional electronic chips has been restricted to a certain extent, and the ever-evolving computing needs require us to find a new computing method with higher speed and lower loss. As a result, photons were born as information media, forming optical quantum chips that replace traditional electronic chips. This type of optical quantum chip has the advantages of high speed and low energy consumption. The optical quantum chip can be applied to fields such as quantum communication, which is a very important application scenario in the future.

[0003] Similar to the integrated circuits used in traditional electronic chips, photonic quantum chips also need to build a suitable integrated optical circuit, which mainly includes quantum light source, 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 components and low single photon purity, while deterministic single photon sources have good single photon purity and are good single photon sources.

[0004] At present, there are many schemes for the use of deterministic single-photon sources, such as using single atoms, diamond color centers, quantum dots, etc. The performance indicators of single-photon sources include single-photon purity, homogeneity, collection efficiency, etc. The single-photon source generated by III-V semiconductor quantum dots has relatively good performance indicators. However, the optical circuit made of III-V semiconductors has a large loss of light generated by quantum dots due to the high refractive index of the material. Although silicon-based materials commonly used in integrated optics have the characteristics of low loss, they cannot grow quantum dots with the same good performance, so single-photon sources with good performance indicators cannot be obtained. At present, in integrated optics, passive silicon-based optical integrated circuit technology is very mature in terms of process, so it is very important to solve its light source problem. Transferring single photons generated by semiconductor quantum dots to silicon-based optical integrated circuits is one method.

[0005] The current method of transferring single photons generated by semiconductor quantum dots to other optical integrated circuits is to couple and collect single photons generated in III-V semiconductor quantum dots with single-mode optical fibers, and finally transfer the single photons to where they are needed through optical fibers. A major challenge of this solution is how to effectively transmit the photons generated by quantum dots from the planar structure and couple them into the optical fiber. The reason for this challenge is that the mode of the optical fiber does not match the sub-wavelength mode of the nanowaveguide, so there are many different ways to implement this solution. First, an optical waveguide is made on the surface of the 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 photon 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 the waveguide on this end face. This method is more efficient than the previous method, and is simpler, more convenient and less costly. 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 solution of the present invention is 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 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 therebetween serves as a waveguide; the second sections of the two grooves form a certain angle within a range of 30-40 degrees, and the third contact layer is etched at the unetched area between the second sections of the two grooves to form a grating composed of a plurality of arc-shaped slits, wherein the protruding ends of the arc-shaped slits face in a direction 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; an air groove is formed by etching the first contact layer below the waveguide and the grating, and the air groove serves as a cladding of the waveguide 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 at the same time, the angle between the polished end face in 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 the 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 is emitted into the grating of the corresponding photon unit. When the laser is emitted onto 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. The laser beam coupled into the waveguide illuminates When the single photon is irradiated onto the quantum dot layer in the waveguide, the quantum dot layer is excited to generate 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, and the single photon reflected by the one-dimensional photonic crystal mirror 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 single photons after diffraction are emitted from the grating. 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 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 adopts electron beam lithography, ultraviolet lithography, dry etching, wet etching and other methods for micro-nano processing, and forms an air slot, a waveguide, a one-dimensional photonic crystal mirror, a grating and a table on the sample, wherein the air slot is arranged below the waveguide and the grating, satisfies the total reflection condition of the waveguide, and overcomes the problem that there is 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 slot can also reflect the diffracted single photon to prevent the single photon from entering the i-type GaAs substrate, so after the air slot is provided, the diffracted and downwardly moving single photon will hit the air boundary of the air slot and reflect, and there is a certain possibility of entering the optical fiber array after reflection, which also improves the collection rate of single photons to a certain extent. The one-dimensional photonic crystal mirror is arranged on the waveguide away from the grating side, and 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 a shallow etched grating, the depth of which does not reach the quantum dot layer, and the main diffraction order emission angle is 8 to 9 degrees, that is, basically perpendicular to the grating plane. Such a grating can couple single photons in the waveguide plane to the plane perpendicular to the waveguide, and has a relatively high transmission efficiency; in addition, the grating is made into an arc shape, which can focus the emission spot and shape the light beam into a Gaussian shape, greatly increasing the coupling efficiency with the optical fiber array installed on the table. Similarly, the end face of the optical fiber array installed on the table is grinded, and the grinding angle is customized to 20 to 50 degrees. The optical fiber array within such an angle range can effectively transmit single photons to the optical fiber, and also improve the coupling efficiency between the single photons in the grating and the optical fiber array. The table is set on the sample surface on one side of the grating, and its thickness is 5 to 10um. This thickness can prevent the optical fiber array from hitting the grating and other devices and damaging them when coupling the optical fiber array with the grating. The various characteristics of the photoresist are fully utilized when making the table in the present invention, which is a relatively ingenious design. Through the combined action of the waveguide, grating, one-dimensional photonic crystal mirror, air groove, table and optical fiber array designed on the sample, the single photon generated by the quantum dot single photon source is finally coupled to the optical fiber array through the grating, so that it can be transferred to other optical circuits. Finally, the grating of the present invention can be made at any position connected to the waveguide in the sample, thus overcoming the problem of the specificity of the optical fiber position in the prior art. At the same time, the present invention also specially designs the grating and optical fiber array, so that it can be more conveniently and effectively coupled with other quantum optical circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a front view of a stacked structure of an epitaxially grown III-V semiconductor structure with semiconductor quantum dots;

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

[0018] Figure 4 It is a cross-sectional view of the III-V semiconductor structure after the table 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 It 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 a 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. table; 16. optical fiber array. DETAILED DESCRIPTION

[0023] The present invention is further described and illustrated below in conjunction with specific embodiments. The embodiments are merely exemplary of the present disclosure and do not define the scope of limitation. The technical features of each embodiment of the present invention may be combined accordingly without conflicting with each other.

[0024] In order to facilitate the 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 inside and outside 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 the numerical aperture of the waveguide.

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

[0027] Fiber array is a kind of multi-fiber array customized according to the number of channels, light collection angle, and light wavelength. The coating layer is removed from the fiber part in the substrate and the pressure plate. The fiber is also ground into a certain angle according to the requirements. The spacing between the fibers is 127um or 250um. The optical fiber is a device with similar principles to the waveguide. The middle part of the optical fiber is the core, and the outside of the core is the cladding and coating from the inside to the outside. The refractive index between the core and the cladding is different. Similar to the waveguide, it can bind light in the core to achieve total reflection.

[0028] Electron beam lithography is a technology that uses high-energy focused electrons for lithography. These electrons act directly on electron-sensitive photoresists to eventually form the desired pattern. Due to its short wavelength, electron beam lithography has a very high resolution and can achieve a line width of several nanometers. The application of electron beam lithography can couple quantum dots to waveguides, collect single photons emitted by quantum dots through gratings, and emit them nearly vertically to the optical fiber array outside the sample surface for collection. In this way, it is possible to combine quantum dot single photon sources with any optical circuit.

[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. The corresponding plasma is generated in the gas at low pressure. 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 taken away in the subsequent vacuum environment, and finally the etching is completed.

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

[0031] The present invention is further described in detail below in conjunction with 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 table tops 15 on semiconductor structures 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 the 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 front view, the thickness of the p-type GaAs contact layer 1 is 30 to 50 nm, the thickness of the i-type GaAs contact layer 2 is 3 to 10 nm, the thickness of the i-type Al0.3Ga0.7As contact layer 3 is 50 to 60 nm, the thickness of the InAs quantum dot layer 4 is 10 to 20 nm, the thickness of the i-type GaAs contact layer 5 is 40 to 50 nm, the thickness of the n-type GaAs contact layer 6 is 30 to 40 nm, 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 to 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 slot 14. The thickness of the i-type GaAs contact layer 9 is 300-500 um, which is a substrate structure of III-V semiconductor materials and has no effect on micro-nano structures.

[0034] Step 2: Use electron beam lithography and dry etching technology to first make the waveguide 12, the one-dimensional photonic crystal mirror 13 and the grating 10, and then make the table 15; finally use wet etching technology to make the air groove 14; thereby scattering 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 to transfer the desired pattern onto the spin-coated photoresist, the desired pattern is a structural array of waveguides 12, a structural array of one-dimensional photonic crystal mirrors 13 and an array structure of gratings 10 designed according to physical principles such as electrodynamics and waveguide optics, which constitute an array structure as a whole, that is, a photon 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 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 therebetween 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 at the unetched area between the second sections of the two grooves to form a grating 10 composed of a plurality of arc-shaped slits, and the protruding ends of the arc-shaped slits face in a direction away from the waveguide 12. Then, the second contact layer and the third contact layer are 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 a waveguide away from a 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, and 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.

[0041] 1.5) Residual photoresist after dry etching on 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 slit) is 150 to 250 nm, and the number of arc 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 ultraviolet 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) The mesa pattern is overlaid 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 The structure shown; wherein the developer is a special developer for SU-8 2000 series; the height of the table 15 is 5 to 10um.

[0047] 3) Preparation of air slot 14:

[0048] After the terrace 15 is formed, the III-V group semiconductor material is wet-etched in a hydrofluoric acid solution to form an air groove 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 Al2O3 through 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 0.4As contact layer 8, finally corroded to produce an approximately square air slot 14, the corroded air slot 14 is located below the waveguide 12 and the grating 10 to meet the total reflection condition of the waveguide 12; at the same time, when a single photon is coupled from the waveguide to the grating and diffracted, the air slot 14 can also reflect the diffracted single photon to prevent the single photon from entering the i-type GaAs substrate 9, so after the air slot 14, the diffracted and downward moving single photon will hit the air boundary of the air slot 14 and reflect, and there is a certain possibility of entering the optical fiber array 16 after reflection, which also improves the collection rate of single photons to a certain extent. If there is no air slot 14 located below the grating 10, the diffracted and downward moving single photon will enter the i-type GaAs substrate 9 and be absorbed by the i-type GaAs substrate 9, then the number of collected single photons will be reduced, and the collection rate of single photons will be reduced. Since SU-8 2010 is resistant to 1:20 hydrofluoric acid solution, the table 15 will not be corroded.

[0050] During the production, smooth waveguide sidewalls and grating sidewalls are very important, so the present invention adopts methods such as low temperature development to achieve this effect, and smooth sidewalls help improve light transmission and grating efficiency. In addition, the production of the grating 10 requires an overlay step of electron beam lithography, in which overlay accuracy is very important, and the overlay accuracy of the electron beam lithography instrument used in the present invention can reach a few 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 shallow etched grating. The reason for the shallow etched grating is that the depth of the grating does not reach the InAs quantum dot layer 4. The shallow etched grating is used to couple the light in the waveguide 12 plane to the plane perpendicular to the waveguide 12, and has a relatively high transmission efficiency. One of the important parameters of the grating 10 is its exit angle. The definition of the grating exit angle is the angle between the angle of the grating exit and the normal line of the grating plane. Generally, the exit angle of the grating is between 0 and 90 degrees. Due to the existence of grating diffraction, the light diffracted from the grating has diffraction orders. The diffraction orders are divided into main diffraction orders and sub-diffraction orders. The main diffraction order has the highest light intensity, and the sub-diffraction order is weaker. The main diffraction order exit angle of the grating used in the present invention is about 8 degrees, that is, the main diffraction order exit angle of the grating is 8 to 9 degrees. That is, it is basically 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, which greatly increases the coupling efficiency with the optical fiber. In general inventions, when quantum dots and optical fibers are coupled without using a micro-lens method, the overall coupling efficiency is extremely low, less than 5%. The coupling efficiency of the present invention can theoretically reach up to 60% to 70%.

[0053] The one-dimensional photonic crystal mirror 13 is arranged on the waveguide away from the grating side. 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 end, 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, and an i-type Al 0.3 Ga 0.7 The semiconductor structure of the As contact layer 3, the InAs quantum dot layer 4, the i-type GaAs contact layer 5 and the n-type GaAs contact layer 6 is used to transmit light and requires a medium with a suitable refractive index around it to work properly, so a corresponding air groove 14 is made to wrap the waveguide 12. The air groove 14 is a groove structure made by wet etching, which is used 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, which utilizes the photosensitive characteristics of the photoresist and the high resolution of SU-8. After 95°C pre-baking, exposure, development and 95°C post-baking, SU-8 basically loses its viscosity and hardens, meeting the needs of the table 15 for placing the optical fiber array of the present invention. In addition, SU-8 does not reduce its thickness under hydrofluoric acid. The thickness used in the present invention is about 5 to 10um. The purpose of setting this thickness is to prevent the optical fiber array from hitting devices such as gratings and damaging them when coupling the optical fiber array with the grating. The table used in the present invention is an innovative design, which makes full use of the various characteristics of the photoresist and is a more 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 rotational translation stage, a storage stage, etc. to find the best coupling position on the table 15. Among them, the multi-axis translation stage can be controlled to move forward and backward by a knob to adjust the position of the fiber array, the rotational 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 best coupling position, fix the fiber array 16 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 9 optical fibers in total, 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, the waveguide 12 and the one-dimensional photonic crystal mirror 13 form a photon unit. There are multiple photon units on a III-V semiconductor structure. The multiple photon units are arranged in the same direction and are 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 16 for transmitting single photons to other optical circuits. Light emitted from an optical fiber enters a photon unit, and similarly, the single photon coupled out of the photon unit also enters the optical fiber.

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

[0062] First, connect the external fiber beam splitter to the fiber array, then select a laser of the appropriate wavelength (around 900nm), and then connect the external laser and the optical circuit to the fiber beam splitter respectively; the fiber beam splitter will not affect the laser light emitted by the laser; when a single photon is transmitted from the fiber array to the fiber beam splitter, the fiber beam splitter will input the single photon into the optical circuit;

[0063] Turn on the laser, the laser emits laser, and 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 fiber in the fiber array 16. When the laser is transmitted to the polished end face, the laser is reflected and emitted from the fiber array 16. The laser emitted from the fiber array 16 is emitted into 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, and the single photon reflected by the one-dimensional photonic crystal mirror 13 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 beam splitter, and the single photon is output from the optical fiber beam splitter and enters the optical circuit, completing the transfer of the single photon.

[0064] The above-mentioned embodiments only express several implementation modes of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope 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: 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 has 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 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 therebetween serves as a waveguide; the second sections of the two grooves are at a certain angle of 30-40 degrees, and the third contact layer is etched at different depths at the unetched area between the second sections of the two grooves to form a grating composed of a plurality of arc-shaped slits, wherein the protruding ends of the arc-shaped slits face away from the waveguide, and the main diffraction order emission angle of the grating is 8-9 degrees; and then the second contact layer and the third contact layer are etched on the waveguide away from the grating to form a one-dimensional photonic crystal mirror; forming a table on the upper surface of the third contact layer on the side of the grating away from the waveguide; Etching the first contact layer below the waveguide and the grating to form an air groove, the air groove serves as the cladding of the waveguide to meet the total reflection condition of the waveguide; when a single photon is coupled from the waveguide to the grating and diffracted, 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 polished end faces is installed on the upper surface of the table, so that light emitted through the optical fibers in the optical fiber array can enter the grating; wherein the angle between the polished end faces in 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, characterized in that: The method of forming the one-dimensional photonic crystal mirror is: First, a second contact layer and a third contact layer are etched on a waveguide away from a 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. 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, 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. A plurality of photon units arranged in the same direction and parallel to each other are formed on the III-V semiconductor structure. The arrangement direction of the plurality of 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 for transmitting single photons. The optical fibers correspond to the photon units one by one, 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 slits is 10 to 20, the width of the arc slits is 150 to 250 nm, and the distance between two adjacent arc slits is 300 to 400 nm.

4. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, characterized in that: The first contact layer includes i-type Al 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, from bottom to top, an n-type GaAs contact layer, an i-type GaAs contact layer and an InAs quantum dot layer; the third contact layer includes, from bottom to top, 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 900-1000nm, 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 um.

5. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, characterized in that: 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 table with a thickness of 5 to 10 um.

6. The method for preparing a fiber-coupled quantum dot single-photon source array according to claim 1, characterized in that: The groove, grating and one-dimensional photonic crystal mirror are all prepared by dry etching; the air groove is 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. There are multiple photon units arranged in the same direction and parallel to each other on the III-V semiconductor structure. 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 for transmitting single photons. The optical fibers correspond to the photon units one by one, 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 of claim 9, characterized in that: The following steps are involved: First, an external fiber beam splitter is connected to the fiber array, and then an external laser and an optical circuit are connected to the fiber beam splitter respectively; when a single photon is transmitted from the fiber array to the fiber beam splitter, the fiber beam splitter inputs the single photon into the optical circuit; Turn on the laser, the laser emits laser, and the laser passes through the fiber beam splitter and enters the fiber array. The laser is transmitted along the arrangement direction of the optical fiber in the fiber array. When the laser is transmitted to the polished end face, the laser is reflected and emitted from the fiber array. The laser emitted from the fiber array enters the grating of the corresponding photon unit. The laser incident on the grating 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. When the laser beam coupled to the waveguide irradiates the quantum dot layer in the waveguide, the quantum dot layer is excited to produce single photons. The single photons propagate in all directions in the waveguide. When the single photons collide with the one-dimensional photons Crystal mirror, the one-dimensional photonic crystal mirror reflects the single photon, and the single photon reflected by the one-dimensional photonic crystal mirror 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 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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