Hybrid integrated optical fiber coupling superconducting nanowire single-photon detector and implementation method

Abstract

The invention discloses a hybrid integrated optical fiber coupling superconducting nanowire single-photon detector and an implementation method. The detector is directly integrated on the end face of an optical fiber, each layer of superconducting nanowire single-photon detector comprises a superconducting nanowire, electrodes at the two ends and a lower-layer optical cavity, the center of the nanowire is aligned with a fiber core of the optical fiber, and the uppermost layer is integrated with the optical cavity and a reflector; wherein the projections of the nanowires of the same detector are parallel to each other, the nanowires of different detectors are mutually orthogonal in pairs, and the polarization-insensitive superconducting nanowire single-photon detector is obtained after packaging. Or the nanowire projections of each layer of detector are parallel to each other, and the superconductive nanowire single-photon detector with high absorptivity is obtained after packaging. Or all layers of detectors and reflectors are integrated into optical cavities with different thicknesses, and the wide-spectrum superconducting nanowire single-photon detector with multiple central wavelengths is obtained after packaging. According to the invention, a high-performance and multifunctional superconducting nanowire single-photon detector is realized through a hybrid integration process.

Description

Technical Field

[0001] The invention relates to a superconducting nanowire single-photon detector and an implementation method thereof, and in particular discloses a hybrid integrated optical fiber coupled superconducting nanowire single-photon detector and an implementation method thereof. Background Art

[0002] Superconducting nanowire single photon detector (SNSPD) is the detector with the best comprehensive performance in the infrared band. It has been widely used in quantum communication, deep space exploration, single photon laser radar, biological microscopic imaging and other fields. Optical fiber has become the main transmission method in communication due to its wide transmission bandwidth, low signal attenuation and strong anti-interference ability. Therefore, optical fiber is widely used to couple signal light into the detector. The optical signal is transmitted in the optical fiber in the form of a plane wave. When the plane wave is obliquely incident on the medium plane, the plane S_λ formed by the wave vector k and the normal vector n of the plane is defined as the incident plane. When the electric field component of the plane wave is perpendicular to the incident plane, it is called plane wave TE polarization or S polarization light. If the two are parallel to each other, it is called plane wave TM polarization or P polarization light. The meandering wire structure of the traditional SNSPD is equivalent to a nano grating, so the detector has the characteristic of polarization sensitivity, and its absorption rate for P polarization light is greater than that for S polarization light. In the quantum secure communication scenario, polarization-sensitive detectors will increase the bit error rate due to the drift of the polarization state of photons during propagation in optical fibers. Polarization-insensitive single-photon detectors are currently a major research hotspot. In 2008, SN Dorenbos et al. verified in "Superconducting single photon detectors with minimized polarization dependence" that the polarization sensitivity of SNSPD can be reduced by using two orthogonal winding nanowire structures or spiral structures. However, the center of this structure is a corner or spiral core that cannot respond to photons, and the light absorption rate is low. In 2018, XL Hu et al. designed a Peano curve structure SNSPD based on fractal theory in "Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity". The polarization extinction ratio dropped to 1.1, but due to the large number of corners in the structure, the current crowding effect was obvious, the superconducting critical current of the device was compressed, and the quantum efficiency was not saturated. In 2019, R. Xu et al. demonstrated in "Demonstration of polarization insensitive superconducting nanowire single-photon detector with Si compensation" that the polarization extinction ratio of the device was reduced to 1.1. layer》 proposed to use high refractive index material Si to cover NbN nanowires, so as to improve the nanowire's absorption rate of S-polarized light by reducing the difference in dielectric constant between the nanowires and the surrounding filling materials. The maximum detection efficiency at 1550nm was measured to be 61%, and the polarization extinction ratio was 1.09. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention provides a hybrid integrated optical fiber coupled superconducting nanowire single photon detector and an implementation method thereof.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] The present invention provides a hybrid integrated optical fiber coupled superconducting nanowire single-photon detector, wherein the superconducting nanowire single-photon detector is directly integrated into the end face of an optical fiber component, and the superconducting nanowire single-photon detector comprises a plurality of superconducting nanowire single-photon detector components, wherein the superconducting nanowire single-photon detector components comprise superconducting nanowires and electrodes connected to both ends of the nanowires and a lower optical cavity, wherein the nanowire portion of each layer of superconducting nanowire single-photon detector components is aligned with the core of the optical fiber; wherein: the nanowire projections of the same superconducting nanowire single-photon detector component are parallel to each other, and the nanowires of different superconducting nanowire single-photon detectors are mutually orthogonal in pairs; or, the nanowire projections of each layer of superconducting nanowire single-photon detector components overlap; or, each layer of superconducting nanowire single-photon detectors and reflectors are integrated with optical cavities of different thicknesses.

[0006] Furthermore, a reflector assembly is integrated on the upper side of the topmost superconducting nanowire single-photon detector assembly, and the reflector assembly includes a reflector and an optical cavity. The superconducting nanowire single-photon detector assembly, the optical fiber assembly, and the reflector assembly are prepared separately. The number of superconducting nanowire single-photon detector assemblies is four. After the probe station selects the superconducting nanowire single-photon detector assemblies with saturated quantum efficiency, four of them are selected and rotated 0°, 45°, 90°, and 135° respectively and transferred to the end face of the optical fiber assembly. Finally, the reflector assembly is transferred and packaged to obtain a polarization-insensitive superconducting nanowire single-photon detector.

[0007] Furthermore, a reflector assembly is integrated on the upper side of the topmost superconducting nanowire single-photon detector assembly. The superconducting nanowire single-photon detector assembly, optical fiber assembly, and reflector assembly are prepared separately. There are four layers of superconducting nanowire single-photon detector assemblies. The nanowire projections of the superconducting nanowire single-photon detector assembly overlap. There are four types of electrodes with offset angles of 0°, 45°, 90°, and 135°, respectively. After the probe station selects the superconducting nanowire single-photon detection with saturated quantum efficiency, one of each type is selected to transfer the nanowires in overlapping and stacked manner to the end face of the optical fiber assembly, and finally the reflector assembly is transferred and packaged to obtain a superconducting nanowire single-photon detector with high absorption rate.

[0008] Furthermore, a reflector assembly is integrated on the upper side of the topmost superconducting nanowire single-photon detector component unit, and the superconducting nanowire single-photon detector component, optical fiber component, and reflector component are prepared separately. The number of superconducting nanowire single-photon detector components is four, and each layer of superconducting nanowire single-photon detectors and reflectors are respectively integrated with optical cavities of different thicknesses, and after packaging, superconducting nanowire single-photon detectors with a variety of central wavelengths or wide spectra are obtained.

[0009] Furthermore, the system detection efficiency of the detector is equal to the product of the three efficiencies:

[0010]

[0011] in, is the system detection efficiency, is the coupling efficiency, For the absorption efficiency, is the quantum efficiency; the coupling efficiency of the optical fiber end directly coupled to the detector is 100%, and 100% quantum efficiency can be achieved by designing the thickness of the superconducting film and the width of the nanowire. The detection efficiency of the system is determined by the absorption efficiency.

[0012] Furthermore, the absorption efficiency is:

[0013]

[0014] in, is the period of the nanowire, is the nanowire thickness, is the time-averaged resistance dissipation of NbN, is the time-averaged Poynting power density of the incident wave.

[0015] Furthermore, the superconducting nanowire single-photon detector assembly is picked up with a PDMS stamp and then transferred to the thermal release material. The superconducting nanowire single-photon detector assembly and the optical fiber end face are aligned and fitted under a microscope. Finally, the thermal release tape is removed after being heated to lose its stickiness. The superconducting nanowire single-photon detector assembly is retained on the optical fiber end face due to the van der Waals force, thereby realizing the transfer and combination of the superconducting nanowire single-photon detector assembly.

[0016] The present invention also provides a method for realizing the above-mentioned hybrid integrated optical fiber-coupled superconducting nanowire single-photon detector, wherein each layer of superconducting nanowire single-photon detector components are first processed separately. When a reflector component is included, the reflector component is also processed separately first, and then made into a patch structure, and finally transferred to the end face of the optical fiber component and uniformly packaged to realize hybrid integration at the micro-nano scale.

[0017] The method comprises the following steps:

[0018] Step 1: Separate and prepare each component;

[0019] The preparation method of the superconducting nanowire single-photon detector assembly is as follows: growing a superconducting film on a thermally oxidized silicon wafer, growing a device electrode, etching a nanowire pattern in the center, etching a superconducting film and silicon oxide on the periphery of the structure, etching the substrate on the lower side of the device to make the device suspended, and the SiO2 under the superconducting film is simultaneously used as an optical cavity to enhance absorption;

[0020] The preparation method of the reflector assembly is as follows: growing a metal adhesion structure on a thermally oxidized silicon wafer, growing a reflector pattern, etching the silicon oxide around the structure, etching the substrate on the lower side so that the reflector is suspended, and the SiO2 under the metal film simultaneously serves as an optical cavity to enhance absorption;

[0021] The preparation method of the optical fiber component comprises: cleaning the optical fiber end face and growing an electrode on the optical fiber end face.

[0022] Step 2: Unified packaging;

[0023] The unified packaging method for each component is: pick up the required component, then transfer it to the heat release material, align and fit the component and the optical fiber end face under a microscope, and finally remove it after heating to make the heat release tape lose its stickiness. The component is retained on the optical fiber end face due to the van der Waals force, thus realizing the transfer and combination of the component.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This method directly integrates superconducting nanowire single-photon detectors on the end face of the optical fiber, which avoids the loss and uncertainty of far-field coupling, such as alignment errors caused by deformation during cooling, and has an integrated and simple structure, resulting in a small thermal load on the system.

[0026] 2. This method separates and processes the superconducting nanowire single-photon detector component, the reflector component, and the optical fiber component, and then makes them into a patch structure. Finally, the hybrid integration of micro-nano scale is realized on the end face of the optical fiber through methods such as PDMS transfer, which avoids the problem of poor quality of superconducting film caused by lattice mismatch between substrate and superconducting material or uneven substrate when preparing the detector, which affects the detector performance, ensures the yield rate, and is easy for large-scale production;

[0027] 3. The polarization-insensitive superconducting nanowire single-photon detector obtained by this method can reduce the anisotropy of the meandering nanowires and achieve polarization-insensitive characteristics by integrating multiple groups of orthogonal superconducting nanowire single-photon detectors. It can be applied to quantum communication to reduce the bit error rate, and to single-photon time-of-flight imaging to improve the imaging quality and detection distance.

[0028] 4. The integrated multi-layer SNSPD structure in this method can achieve a system detection efficiency infinitely close to 100% SNSPD, which is expected to promote the development of basic quantum science research such as quantum light source calibration and quantum candela definition, and be applied to quantum key distribution, deep space communication, infrared detection imaging and other scenarios;

[0029] 5. This method can control the central wavelength of the superconducting nanowire single-photon detector by controlling the thickness of the optical cavity, and can realize superconducting nanowire single-photon detectors with different central wavelengths or single-photon detectors with wide spectrum response. The former can be applied to a variety of scenarios, such as 532nm band detectors can be widely used in communications and imaging in underwater environments, 850nm band detectors can be used in short-distance optical communications, biomedical imaging, etc., 1310nm and 1550nm bands can be used in optical fiber communications, etc. The latter can be used in astronomical spectral observations, fluorescence spectral lifetime, Raman spectroscopy measurement, quantum light source characterization, wavelength division multiplexing quantum communications, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of a hybrid integrated fiber-coupled superconducting nanowire single-photon detector;

[0031] Figure 2 is a schematic diagram of the SNSPD components;

[0032] Figure 3 is a schematic diagram of the reflector assembly;

[0033] Figure 4 It is a schematic diagram of the structure of the near-field coupled polarization-insensitive SNSPD device at the end face of the optical fiber;

[0034] Figure 5 This is a schematic diagram of the structure of the fiber end face near-field coupled high absorption efficiency SNSPD device;

[0035] Figure 6 It is a schematic diagram of a method for realizing a hybrid integrated fiber-coupled superconducting nanowire single-photon detector;

[0036] Figure 7 This is the simulation result of the relationship between the absorption rate of a single-layer SNSPD device and the width of the superconducting nanowire photosensitive surface;

[0037] Figure 8 This is the simulation result of the relationship between the absorption rate of a single-layer SNSPD device and the thickness of the superconducting nanowire;

[0038] Fig. 9 is the simulation result of the absorptivity of the nanowire to S-polarized and P-polarized light;

[0039] Fig.10 These are the absorptivity simulation results for single-, double-, triple-, and quad-layer devices;

[0040] Fig.11 It is the simulation result of the absorption rate of superconducting nanowire single-photon detectors in different central bands;

[0041] Fig.12 This is the simulation result of the absorptivity of a superconducting nanowire single-photon detector with a wide spectrum response.

[0042] Markings in the figure: 1- optical fiber core; 2- optical fiber cladding; 3- NbN superconducting nanowire; 4- SiO2 optical cavity; 5- reflector; 6- gold electrode; 7- Si; 8- SNSPD component one; 9- reflector component; 10- SNSPD component two; 11- SNSPD component three; 12- SNSPD component four; 13- SNSPD component five; 14- SNSPD component six; 15- SNSPD component seven; 16- SNSPD component eight. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0044] like Figure 1 As shown, a hybrid integrated fiber-coupled superconducting nanowire single-photon detector includes a SNSPD component, an optical fiber component, and a reflector component. The nanowire single-photon detector is directly integrated at the end face of the optical fiber component, and the superconducting nanowire single-photon detector includes a plurality of superconducting nanowire single-photon detector components. The superconducting nanowire single-photon detector component includes a superconducting nanowire and electrodes connected to both ends of the nanowire and a lower optical cavity. The nanowire portion of each layer of the superconducting nanowire single-photon detector component is aligned with the core of the optical fiber.

[0045] The present invention first separates and prepares each component, and the separated and prepared SNSPD components are as follows: Figure 2 As shown, the separated and prepared reflector components are as follows Figure 3 As shown, after unified packaging, different packaging methods can realize at least the following four single-photon detectors with different functions.

[0046] Among them, the structure of the fiber end face near-field coupling polarization-insensitive SNSPD device is as follows: Figure 4 As shown. In the device, the nanowire projections of the same superconducting nanowire single-photon detector assembly are parallel to each other, and the nanowires of different superconducting nanowire single-photon detectors are mutually orthogonal. This embodiment is described by taking two groups of orthogonal superconducting nanowire single-photon detector assemblies as an example. The upper side of the topmost superconducting nanowire single-photon detector assembly is integrated with a reflector assembly 9, and the number of superconducting nanowire single-photon detector assemblies is four layers, namely Figure 4As shown in the figure, SNSPD component 1 8 and its gold electrode 6 and lower SiO2 optical cavity 4, SNSPD component 2 10 and its gold electrode 6 and lower SiO2 optical cavity 4, SNSPD component 3 11 and its gold electrode 6 and lower SiO2 optical cavity 4, SNSPD component 4 12 and its gold electrode 6 and lower SiO2 optical cavity 4, after the superconducting nanowire single-photon detector components with saturated quantum efficiency are selected on the probe station, four of them are selected and rotated 0°, 45°, 90° and 135° respectively and transferred to the end face of the optical fiber component, the optical fiber component includes an optical fiber core 1, an optical fiber cladding 2 and an end face gold electrode 6, the nanowire parts of each layer of the superconducting nanowire single-photon detector components are aligned with the core of the optical fiber, and finally the reflector component 9 is transferred and packaged to obtain a polarization-insensitive superconducting nanowire single-photon detector.

[0047] Polarization Extinction Ratio (PER) is commonly used to evaluate the polarization sensitivity of a device: , is the maximum system detection efficiency of the device, The PER is the minimum system detection efficiency of the device. The closer it is to 1, the more uniform the device's absorption of light with different polarizations is, i.e., it is polarization-insensitive.

[0048] like Fig. 9 As shown in the figure, the nanowire is equivalent to a nanograting and has polarization-sensitive properties, so the absorption rate of S-polarized light is greater than the absorption rate of P-polarized light. The orthogonal structured nanowires can evenly absorb the two polarized lights, thereby offsetting the polarization-sensitive properties, and the absorption rate of multiple groups of orthogonal nanowires is higher.

[0049] Among them, the structure of the fiber end face near-field coupling high system detection efficiency SNSPD device is as follows Figure 5 As shown. In this device, the nanowire projections of each layer of superconducting nanowire single-photon detector units overlap. A reflector assembly 9 is integrated on the upper side of the top layer of superconducting nanowire single-photon detector units. In this embodiment, the number of superconducting nanowire single-photon detector units is four layers, namely Figure 5 As shown in the figure, SNSPD component five 13 and its gold electrode 6 and the lower SiO2 optical cavity 4, SNSPD component six 14 and its gold electrode 6 and the lower SiO2 optical cavity 4, SNSPD component seven 15 and its gold electrode 6 and the lower SiO2 optical cavity 4, SNSPD component eight 16 and its gold electrode 6 and the lower SiO2 optical cavity 4, the nanowire projections of the superconducting nanowire single-photon detector assembly overlap, and the electrodes are divided into four types, namely 0°, 45°, 90°, and 135°. One of each type is selected to transfer the nanowires in overlapping and stacked manner to the end face of the optical fiber assembly, and finally the reflector assembly 9 is transferred and packaged to obtain a superconducting nanowire single-photon detector with a system detection efficiency close to 100%.

[0050] The system detection efficiency of the fiber end face near-field coupled high absorption efficiency SNSPD device is equal to the product of the three efficiencies: , is the system detection efficiency, is the coupling efficiency, For absorption efficiency, The packaging method of the present invention can achieve lossless coupling of incident light, that is, the coupling efficiency is 100%. By designing the thickness of the superconducting film and the width of the nanowire, the saturated quantum efficiency can be achieved, that is, the quantum efficiency is 100%. Therefore, the system detection efficiency of the structure is determined by the absorption efficiency. , is the period of the nanowire, is the nanowire thickness, is the time-averaged resistance dissipation of NbN, is the time-averaged Poynting power density of the incident wave.

[0051] like Figure 7 As shown in the figure, for SMF 28e optical fiber with a core diameter of 9.2μm, when the incident light is S polarized, when the width of the NbN meander line is 90nm, the period is 270nm, and the thickness is 5nm, the larger the width of the photosensitive surface, the higher the absorption rate. When the width is greater than 15um, the growth rate of the absorption rate slows down and approaches saturation. Figure 8 As shown in the figure, when the width of the photosensitive surface of nanowires with the same width and period is 15μm, the thicker the superconducting nanowire, the greater the absorption rate, and the absorption rate reaches a maximum of 99.6% at 18nm. However, since the thickness of superconducting nanowires is inversely proportional to the quantum efficiency, in order to ensure the saturation of quantum efficiency, nanowires are usually prepared with 4nm-8nm thick films, so at least four layers are required to achieve an absorption rate close to 100%.

[0052] Each layer of superconducting nanowire single photon detectors and reflectors are integrated with optical cavities of different thicknesses, and after packaging, superconducting nanowire single photon detectors with multiple central wavelengths or wide spectra are obtained. The superconducting nanowire single photon detectors with different central wavelength bands are as follows: Fig.11 As shown in FIG. 1 , it can be seen that the hybrid integration method achieves a central wavelength absorption efficiency of nearly 100% in the 1064nm, 1550nm, and 2000nm bands. Fig.12 As shown, it can be seen that the hybrid integrated fiber-coupled superconducting nanowire single-photon detectors with five different central wavelengths can achieve an absorption efficiency of more than 88% in the 1000nm-2000nm band.

[0053] The method of first separating and preparing each component and then packaging it uniformly is as follows Figure 6As shown. The preparation method of assembling SNSPD components is: growing superconducting film on thermally oxidized silicon wafer, growing device electrodes, etching the central nanowire pattern, etching the superconducting film and silicon oxide around the structure, etching Si7 on the substrate on the lower side of the device to make the device suspended, and SiO2 under the superconducting film is also used as an optical cavity to enhance absorption; the preparation method of the reflector component is: growing a metal adhesion structure on a thermally oxidized silicon wafer, growing a reflector pattern, etching silicon oxide around the structure, etching Si on the substrate on the lower side to make the reflector suspended, and SiO2 under the metal film is also used as an optical cavity to enhance absorption; the preparation method of the optical fiber component is: cleaning the optical fiber end face, and growing electrodes on the optical fiber end face. The assembly method of each component is: picking up the required component with a PDMS stamp, then transferring it to the thermal release material, aligning and bonding the component and the optical fiber end face under a microscope, and finally removing it after heating to make the thermal release tape lose its stickiness, while the component is retained on the optical fiber end face due to van der Waals force, realizing the transfer and combination of the component.

[0054] Superconducting thin film materials are NbN, NbTiN, W x Si 1-x etc. (preferably NbN superconducting nanowire 3 in this embodiment), the thickness is generally 4nm-8nm, and the width of the superconducting nanowire is generally 50nm-200nm; the metal adhesion structure material is Ti, Ni, and the thickness is generally 5nm-20nm; the reflector material is Au, Ag (the reflector 5 can be a metal reflector such as Au, Ag, Al, etc., or a Bragg reflector with a relatively high period number can be used instead of the metal film), and the thickness is generally 100nm-200nm; the refractive index of SiO24 on the thermally oxidized silicon wafer is between 1.4 and 1.5, the thickness of the thermal oxide layer on the thermally oxidized silicon substrate of the SNSPD component is 1 / 2 of the equivalent wavelength of the incident wavelength therein, and the thickness of the thermal oxide layer on the thermally oxidized silicon substrate of the reflector component is 1 / 4 of the equivalent wavelength of the incident wavelength therein.

[0055] The complete process flow of growing superconducting film is to clean the substrate and grow superconducting film by magnetron sputtering. The complete process flow of growing superconducting film, metal adhesion structure, reflector and electrode is to evenly coat LOR10B and AZ1500 photoresist on the substrate (photoresist can also choose other photoresists in the AZ series or SU-8 photoresist, etc., and the thickness of the photoresist can be controlled by adjusting the rotation speed), laser direct writing exposure pattern, develop in orthogonal developer, grow metal film by magnetron sputtering or electron beam evaporation, soak in acetone to strip the photoresist, soak in alcohol and water for cleaning. The process flow of etching SiO2 is to evenly coat AZ4620 photoresist, laser direct writing exposure etching pattern, develop in orthogonal developer, wet etch SiO2 with buffered oxide etchant (BOE) or dry etch SiO2 with CF4. The etching method of etching Si is wet etching with TMAH solution or KOH solution, or dry etching with SF6. The thermal release material is polydimethylsiloxane (PDMS).

[0056] In this embodiment, the specific preparation method of the optical fiber end face near-field coupled polarization-insensitive SNSPD device includes:

[0057] 1. Preparation of optical fiber components: fix a stainless steel mask with 8 electrode patterns on the end face of SMF 28e optical fiber, and sequentially grow 10nm Ti and 150nm Au through electron beam evaporation equipment to transfer the electrode pattern to the end face of the optical fiber to obtain an optical fiber component, in which the eight electrodes are divided into four groups, the opposite electrodes form one group, one end reads the signal and the other end is grounded, and the optical fiber type can be single-mode, multi-mode, polarization-maintaining fiber and other types;

[0058] 2. Preparation of SNSPD components: (1) Take a thermally oxidized silicon wafer substrate with a SiO2 thickness of 1 / 2 of the equivalent wavelength of the incident light of 1550nm. Due to process error, the actual measurement is 520nm, which is recorded as substrate one; (2) Grow a 5nm thick superconducting NbN film on substrate one by magnetron sputtering, with a square resistance of 300Ω / sq; (3) Transfer the electrode pattern to the film by photolithography (laser direct writing) and magnetron sputtering (or electron beam evaporation) in sequence, where the lower layer of the electrode is a 10nm Ti adhesion layer and the upper layer is a 100nm Ti adhesion layer. Au; (4) Prepare nanowire structure by electron beam exposure and reactive ion etching. The line width of a single nanowire is 90nm, the period is 270nm, and the photosensitive surface is 15μm*15μm; (5) Etch the NbN film around the device with CHF3 / SF6 mixed gas by photolithography (laser direct writing) and reactive ion etching to separate the signal input and output ends; (6) Etch SiO2 around the device by immersing it in BOE solution, and then etch Si6 under the device with SF6 gas until the device is completely suspended; (7) Select the device with saturated quantum efficiency in the 1.5K probe station; (8) Take 4 devices as SNSPD component one, SNSPD component two, SNSPD component three, and SNSPD component four;

[0059] 3. Preparation of reflector assembly: (1) Take a thermally oxidized silicon wafer substrate with SiO2 thickness of 1 / 4 of the equivalent wavelength of the incident light. Due to process error, the actual measured value is 253nm, which is recorded as substrate 2; (2) Transfer the reflector pattern to substrate 2 by photolithography (laser direct writing) and electron beam evaporation in sequence, where the lower layer of the reflector is a 10nm Ti adhesion layer and the upper layer is a 150nm Ag reflector; (3) Etch the SiO2 around the reflector and the lower layer Si by the above method to obtain a suspended reflector assembly;

[0060] 4. Packaging: Pick up SNSPD component 1 with a PDMS stamp, and then transfer it to the heat-release PDMS (or other tapes with heat-release effect) to turn the electrode of the device on the component to the side away from PDMS, and then align the electrodes of the device and the end face of the optical fiber component to fit, and then heat to make the PDMS lose its viscosity, while SNSPD component 1 is retained on the end face of the optical fiber due to the van der Waals force, and then SNSPD component 2, SNSPD component 3, and SNSPD component 4 are rotated 45°, 90°, and 135° respectively and transferred to the end face of the optical fiber component, and finally the reflector is transferred to complete the packaging;

[0061] 5. Connect the optical fiber end face electrode and the electrode on the PCB board through silver glue wire (the connection between the optical fiber end face electrode and the electrode on the PCB board can also be connected through wire bonding technology), and then fix the PCB board in the GM refrigerator through a copper block. Test at 1.5K, and read the RF signal of the response pulse through the low-temperature coaxial line.

[0062] In this embodiment, the specific preparation method of the optical fiber end face near-field coupling high system detection efficiency SNSPD device is similar to the specific preparation method of the optical fiber end face near-field coupling polarization-insensitive SNSPD device mentioned above. The SNSPD component in the above method is replaced by a SNSPD with nanowires in the same direction and electrodes in four directions to achieve a system detection efficiency close to 100%. Specifically, there are four types of electrodes on the device, with offset angles of 0°, 45°, 90°, and 135°, respectively, to obtain four types of SNSPD components, whose superconducting nanowire structures and substrate SiO2 thicknesses are exactly the same, recorded as SNSPD component five (electrode offset angle 0°), SNSPD component six (electrode offset angle 45°), SNSPD component seven (electrode offset angle 90°), and SNSPD component eight (electrode offset angle 135°); wherein the superconducting nanowire structure is designed to be in the same direction to ensure the uniformity of the nanowires after exposure by the electron beam evaporation process, and at the same time satisfy that when the incident light is TE polarized light, the four-layer components can achieve optimal absorption, thereby achieving an overall high absorption efficiency; such as Fig.10 As shown in the figure, by this method of hybrid integration of 4-layer SNSPD devices on the optical fiber end face, the absorption rate can reach 99.4%.

[0063] In this embodiment, the specific preparation method of the SNSPD device with multiple central bands coupled to the optical fiber end face near field is similar to the specific preparation method of the SNSPD device with high system detection efficiency coupled to the optical fiber end face near field. The thickness of the lower SiO2 optical cavity of the SNSPD component and the reflector component in the above method is replaced with 1 / 2 and 1 / 4 of the equivalent wavelength of the required central band in SiO2, respectively.

[0064] In this embodiment, the specific preparation method of the optical fiber end face near-field coupling wide spectrum response SNSPD device is similar to the specific preparation method of the optical fiber end face near-field coupling multiple central band SNSPD device. The SNSPD device with wide spectrum response can be obtained by combining the SiO2 thickness of the SNSPD component and the reflector component in the above method to replace 1 / 2 and 1 / 4 of the equivalent wavelength of a specific band in SiO2.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A hybrid integrated fiber-coupled superconducting nanowire single-photon detector, characterized in that: The superconducting nanowire single-photon detector is directly integrated into the end face of the optical fiber component, and the superconducting nanowire single-photon detector includes a plurality of superconducting nanowire single-photon detector components, and the superconducting nanowire single-photon detector components include superconducting nanowires and electrodes connected to both ends of the nanowires and a lower optical cavity, and the nanowire portion of each layer of superconducting nanowire single-photon detector components is aligned with the core of the optical fiber; wherein: the nanowire projections of the same superconducting nanowire single-photon detector component are parallel to each other, and the nanowires of different superconducting nanowire single-photon detectors are orthogonal to each other; or, the nanowire projections of each layer of superconducting nanowire single-photon detector components overlap; or, each layer of superconducting nanowire single-photon detectors and reflectors are integrated with optical cavities of different thicknesses.

2. The hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to claim 1, characterized in that: A reflector assembly is integrated on the upper side of the topmost superconducting nanowire single-photon detector assembly, and the reflector assembly includes a reflector and an optical cavity. The superconducting nanowire single-photon detector assembly, the optical fiber assembly, and the reflector assembly are prepared separately. There are four layers of superconducting nanowire single-photon detector assemblies. After the probe station selects the superconducting nanowire single-photon detector assemblies with saturated quantum efficiency, four of them are selected and rotated 0°, 45°, 90°, and 135° respectively and transferred to the end face of the optical fiber assembly. Finally, the reflector assembly is transferred and packaged to obtain a polarization-insensitive superconducting nanowire single-photon detector.

3. The hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to claim 1, characterized in that: A reflector assembly is integrated on the upper side of the topmost superconducting nanowire single-photon detector assembly. The superconducting nanowire single-photon detector assembly, optical fiber assembly, and reflector assembly are prepared separately. There are four layers of superconducting nanowire single-photon detector assemblies. The nanowire projections of the superconducting nanowire single-photon detector assembly overlap. There are four types of electrodes with offset angles of 0°, 45°, 90°, and 135°, respectively. After the probe station selects the superconducting nanowire single-photon detection with saturated quantum efficiency, one of each type is selected to transfer the nanowires to the end face of the optical fiber assembly in an overlapping and stacked manner, and finally the reflector assembly is transferred and packaged to obtain a superconducting nanowire single-photon detector with high absorption rate.

4. The hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to claim 1, characterized in that: A reflector assembly is integrated on the upper side of the topmost superconducting nanowire single-photon detector component unit. The superconducting nanowire single-photon detector component, optical fiber component, and reflector component are prepared separately. The number of superconducting nanowire single-photon detector components is four. Each layer of superconducting nanowire single-photon detectors and reflectors are respectively integrated with optical cavities of different thicknesses. After packaging, superconducting nanowire single-photon detectors with a variety of central wavelengths or wide spectra are obtained.

5. The hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to claim 3, characterized in that: The system detection efficiency of the detector is equal to the product of the three efficiencies: ； in, is the system detection efficiency, is the coupling efficiency, For the absorption efficiency, is the quantum efficiency; the coupling efficiency of the optical fiber end directly coupled to the detector is 100%, and 100% quantum efficiency can be achieved by designing the thickness of the superconducting film and the width of the nanowire. The detection efficiency of the system is determined by the absorption efficiency.

6. The hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to claim 5, characterized in that: The absorption efficiency is: ； in, is the period of the nanowire, is the nanowire thickness, is the time-averaged resistance dissipation of NbN, is the time-averaged Poynting power density of the incident wave.

7. The hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to claim 1, characterized in that: The superconducting nanowire single-photon detector assembly is picked up with a PDMS stamp and then transferred to the thermal release material. The superconducting nanowire single-photon detector assembly and the optical fiber end face are aligned and fitted under a microscope. Finally, the thermal release tape is heated to lose its stickiness and then removed. The superconducting nanowire single-photon detector assembly is retained on the optical fiber end face due to the van der Waals force, thereby realizing the transfer and combination of the superconducting nanowire single-photon detector assembly.

8. The method for realizing the hybrid integrated fiber-coupled superconducting nanowire single-photon detector according to any one of claims 1 to 7, characterized in that: Each layer of superconducting nanowire single-photon detector components is first processed separately. When a mirror component is included, the mirror component is also processed separately first, and then made into a patch structure, and finally transferred to the end face of the optical fiber component and packaged uniformly to achieve hybrid integration at the micro-nano scale.

9. The method according to claim 8, characterized in that The steps include: Step 1: Separate and prepare each component; The preparation method of the superconducting nanowire single-photon detector assembly is as follows: growing a superconducting film on a thermally oxidized silicon wafer, growing a device electrode, etching a nanowire pattern in the center, etching a superconducting film and silicon oxide on the periphery of the structure, etching the substrate on the lower side of the device to make the device suspended, and the SiO2 under the superconducting film is simultaneously used as an optical cavity to enhance absorption; The preparation method of the reflector assembly is as follows: growing a metal adhesion structure on a thermally oxidized silicon wafer, growing a reflector pattern, etching the silicon oxide around the structure, etching the substrate on the lower side so that the reflector is suspended, and the SiO2 under the metal film simultaneously serves as an optical cavity to enhance absorption; The preparation method of the optical fiber assembly comprises: cleaning the end face of the optical fiber and growing an electrode on the end face of the optical fiber; Step 2: Unified packaging; The unified packaging method for each component is: pick up the required component, then transfer it to the heat release material, align and fit the component and the optical fiber end face under a microscope, and finally remove it after heating to make the heat release tape lose its stickiness. The component is retained on the optical fiber end face due to the van der Waals force, thus realizing the transfer and combination of the component.

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