A superconducting nanowire single-photon detector based on TM0 mode absorption and detection method

Abstract

The present invention provides a superconducting nanowire single-photon detector based on TM0 mode absorption and a detection method, comprising: a directional coupler for realizing the conversion from TE0 mode to TE1 mode; a polarization rotator connected to the directional coupler for realizing the conversion from TE1 mode to TM0 mode; and a nanowire single-photon detector connected to the polarization rotator for realizing the absorption and detection of the TM0 mode. The superconducting nanowire single-photon detector based on TM0 mode absorption of the present invention has a simple structure, realizes the efficient conversion from TE0 mode to TM0 mode on the basis of SOI structure, and is quickly absorbed and detected by the nanowire single-photon detector, which not only greatly shortens the required length of the nanowire, thereby reducing the process conditions required for the production of the nanowire, but also protects the device from being damaged by the etchant, so that the working performance of the device is stable.

Description

Technical Field

[0001] The present invention belongs to the field of integrated quantum chips and relates to a superconducting nanowire single-photon detector based on TM0 mode absorption and a detection method. Background Art

[0002] Single-photon detectors with high detection efficiency have important applications in the field of photon quantum, especially some detection-based applications, such as photon quantum computing, quantum key distribution, quantum Bose sampling, loophole-free Bell experiment, etc. In the 1550nm communication band, InGaAs near-infrared avalanche diode detectors are the current mainstream detectors, but this detector has a large dark count and the detection efficiency is usually less than 30%. In addition, this detector is an independent structure outside the chip, which does not meet the development trend of miniaturization and integration.

[0003] Superconducting nanowire single photon detector (SNSPD) is a single photon detector that has developed rapidly in recent years. This detector is a highly sensitive photon detector that uses superconducting nanofilm wires for photon detection. It has the advantages of high efficiency, high counting rate, low dark count, and small time jitter. With auxiliary resonant cavity, reflector and other structures, the single photon detection efficiency in the 1550nm band can be as high as 90% or more, and the dark count is less than 100Hz. However, traditional SNSPDs all use the method of vertical fiber incidence, which does not meet the requirements of on-chip integration. In addition, the resonant cavity and other structures limit the bandwidth.

[0004] At present, a waveguide traveling wave coupling SNSPD is a better solution. It adopts the absorption mode of waveguide evanescent wave coupling. This absorption mode is transferred from off-chip to on-chip, and high absorption efficiency can be achieved without the need for a resonant cavity structure, which can well solve the defects of vertical incidence SNSPD. SNSPD based on waveguide traveling wave coupling has been realized on a variety of material systems, such as SOI, SiN, GaAs, etc., and has been applied to some important devices, such as detectors that can distinguish the number of photons, two-photon interference experiments, etc. However, in general, these SNSPDs all use quasi-transverse electric mode (TE) absorption. Due to the direction of the TE mode electric field, it usually takes tens of microns of NbN nanowires to achieve nearly 100% absorption, and these structures require the NbN film to be directly grown on the top of the waveguide, which puts forward high requirements on the manufacturing process of NbN nanowires. First, the thickness of the NbN film is only a few nanometers and the long structure leads to low yield; second, the etching process of NbN needs to be precisely controlled, otherwise over-etching will damage the upper surface of the waveguide and cause scattering loss. Summary of the invention

[0005] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide a superconducting nanowire single-photon detector and detection method based on TM0 mode absorption, which is used to solve the problems of complex structure, high process conditions and low yield of superconducting nanowire single-photon detectors in the prior art.

[0006] To achieve the above objectives and other related objectives, the present invention provides a superconducting nanowire single-photon detector based on TM0 mode absorption, comprising:

[0007] Directional coupler, used to achieve conversion from TE0 mode to TE1 mode;

[0008] A polarization rotator, connected to the directional coupler, for realizing the conversion from TE1 mode to TM0 mode;

[0009] The nanowire single-photon detector is connected to the polarization rotator and is used to realize the absorption and detection of the TM0 mode.

[0010] Optionally, the directional coupler comprises a parallel coupled line directional coupler.

[0011] Optionally, the directional coupler includes a main waveguide and a sub-waveguide arranged at intervals, the width of the main waveguide is smaller than the width of the sub-waveguide, wherein the main waveguide includes a first section, a second section and a third section connected in sequence, and the third section and the sub-waveguide are parallel and coupled to each other.

[0012] Optionally, the directional coupler has an input port, which is configured at one end of the main waveguide to input the TE0 mode into the main waveguide, and the sub-waveguide is electromagnetically coupled to the main waveguide and extracts the TE1 mode.

[0013] Optionally, the polarization rotator includes a first waveguide, a second waveguide and a third waveguide connected in sequence, and the first waveguide is connected to the directional coupler.

[0014] Optionally, the widths of the first waveguide, the second waveguide, and the third waveguide are linearly gradient.

[0015] Optionally, the nanowire single-photon detector comprises:

[0016] substrate;

[0017] An insulating layer, located on the surface of the substrate;

[0018] A waveguide, located on the surface of the insulating layer;

[0019] a covering layer, located on the insulating layer and covering the exposed surface of the waveguide;

[0020] The superconducting nanowire is located on the surface of the covering layer.

[0021] Optionally, the material of the insulating layer includes SiO2.

[0022] Optionally, the material of the covering layer includes SiO2, the distance between the upper surface of the covering layer and the upper surface of the waveguide does not exceed 50 nm, and the roughness of the covering layer is less than 1 nm.

[0023] Optionally, the superconducting nanowire is in a square wave shape with right-angle bends, and two ends of the superconducting nanowire are respectively connected to the positive and negative electrodes.

[0024] Optionally, the length of the superconducting nanowire along the TM0 transmission direction is in the range of 5-10 μm.

[0025] Optionally, the superconducting nanowire material is selected from one of NbN, NbTiN, TiN, TaN, WSi, Nb and MoGe.

[0026] The present invention also provides a detection method of a superconducting nanowire single-photon detector based on TM0 mode absorption, comprising the following steps:

[0027] Input the TE0 mode light wave through the input port of the directional coupler;

[0028] The TE0 mode is coupled from the main waveguide to the auxiliary waveguide and converted into the TE1 mode;

[0029] The TE1 mode is converted to the TM0 mode in the polarization converter;

[0030] Nanowire single-photon detectors achieve absorption and detection of the TM0 mode through the evanescent wave coupling method.

[0031] As described above, the superconducting nanowire single-photon detector based on TM0 mode absorption of the present invention has the following beneficial effects:

[0032] (1) The nanowire single-photon detector uses TM0 mode absorption. The nanowire only needs 5 μm in length to complete 100% light field absorption, which greatly shortens the required length of the nanowire. Therefore, the process conditions required for nanowire production are reduced, which can reduce costs and improve yields, achieving efficient production;

[0033] (2) The nanowires can be grown on top of the cover layer that clads the waveguide. In this way, the cover layer can act as a barrier to prevent the core waveguide from being damaged by the etchant and affecting the device performance.

[0034] (3) The overall structure of the device is simple, and it can achieve efficient conversion from TE0 mode to TM0 mode. It can be quickly absorbed and detected by SNSPD and has high working efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Shown is a schematic diagram of the top view of the structure of a superconducting nanowire single-photon detector based on TM0 mode absorption provided by the present invention.

[0036] Figure 2 Shown is a graph showing how the imaginary part of the effective refractive index of a mode in a waveguide in a superconducting nanowire single-photon detector based on TM0 mode absorption provided by the present invention varies with the waveguide width.

[0037] Figure 3 Shown is a schematic diagram of the side cross-sectional structure of a superconducting nanowire single-photon detector based on TM0 mode absorption provided by the present invention.

[0038] Figure 4 Shown is a flow chart of the detection method of the superconducting nanowire single-photon detector based on TM0 mode absorption provided by the present invention.

[0039] Component number description

[0040] 10 Substrate

[0041] 20 Insulation layer

[0042] 30 Overlay

[0043] 40 Waveguide

[0044] 401 Main waveguide

[0045] 4011 First paragraph

[0046] 4012 Second paragraph

[0047] 4013 The third paragraph

[0048] 402 Sub-waveguide

[0049] 403 First Waveguide

[0050] 404 Second Waveguide

[0051] 405 Third Waveguide

[0052] 50 Superconducting Nanowires

[0053] 61 Positive electrode

[0054] 62 Negative electrode DETAILED DESCRIPTION

[0055] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0056] It should be noted that the illustrations provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Although the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation, the form, quantity, positional relationship and proportion of each component in actual implementation can be changed at will under the premise of realizing the technical solution of this party, and the component layout form may also be more complicated.

[0057] See also Figure 1 The present invention provides a superconducting nanowire single-photon detector based on TM0 mode absorption, including a directional coupler (DC), a polarization rotator (SNSPD) and a nanowire single-photon detector (SNSPD), wherein the directional coupler is used to realize the conversion from TE0 mode to TE1 mode; the polarization rotator is connected to the directional coupler to realize the conversion from TE1 mode to TM0 mode; the nanowire single-photon detector is connected to the polarization rotator to realize the absorption and detection of the TM0 mode.

[0058] As an example, see Figure 1 , the directional coupler can be a parallel coupled line directional coupler, and the directional coupler includes a main waveguide 401 and a sub-waveguide 402 which are arranged at intervals. Specifically, the width of the main waveguide 401 is smaller than the width of the sub-waveguide 402, wherein the main waveguide 401 is in an S-shaped shape and can be divided into three sections connected in sequence, namely a first section 4011, a second section 4012 and a third section 4013. The third section 4013 is parallel to and coupled with the sub-waveguide 402, wherein the length (L4) of the third section 4013 is 13 μm. In addition, the distance (gap) between the third section 4013 of the main waveguide 401 and the sub-waveguide 402 is 0.15 μm.

[0059] It should be pointed out that in other embodiments, the length and spacing between the main waveguide 401 and the auxiliary waveguide 402 can be adjusted as needed, and the protection scope of the present invention should not be excessively limited here.

[0060] As an example, see Figure 1 The directional coupler has an input port (not shown in the figure), and the input port is configured at one end of the main waveguide 401 to input the TE0 mode into the main waveguide 401, that is, the TE0 mode is input through a port of the first section 4011, and is transmitted through the second section 4012 and the third section 4013, and is converted into the TE1 mode through the gap between the main waveguide 401 and the sub-waveguide 402. The sub-waveguide 402 is electromagnetically coupled with the main waveguide 401 and extracts the TE1 mode.

[0061] Please note that Figure 2 The directional coupler in the entire device is designed based on the mode coupling theory. When the effective refractive index of the TE0 mode in the main waveguide is equal to the effective refractive index of the TE1 mode in the sub-waveguide, the TE0 mode in the main waveguide can be efficiently coupled to the adjacent sub-waveguide. Figure 2 The dotted lines in the figure indicate that the TE0 mode and TE1 mode with the same effective refractive index correspond to the main waveguide width (W4) of 0.41 μm and the sub-waveguide width (W3) of 0.85 μm, respectively.

[0062] As an example, see Figure 1 The polarization rotator includes a first waveguide 403, a second waveguide 404 and a third waveguide 405 connected in sequence, and the first waveguide 403 is connected to the directional coupler.

[0063] As an example, see Figure 1 , the widths of the first waveguide 403, the second waveguide 404, and the third waveguide 405 are linearly gradient, that is, the cross-sectional shapes of the first waveguide 403, the second waveguide 404, and the third waveguide 405 on the horizontal plane are all trapezoidal, and each section of the waveguide gradually becomes narrower along the TE1 transmission direction.

[0064] Specifically, the length (L3) of the first waveguide 403 is 10 μm, the width (W3) of the connection part with the sub-waveguide 402 is 0.85 μm, and the width (W2) of the connection part with the second waveguide 404 is 0.7 μm; the length (L2) of the second waveguide 404 is 46 μm, and the width (W1) of the connection part with the third waveguide 405 is 0.56 μm; the length (L1) of the third waveguide 405 is 4 μm, and the width (W0) of the connection part with the waveguide 40 in the nanowire single-photon detector is 0.5 μm.

[0065] Please note that Figure 1 and Figure 2 There is mode hybridization between the TE1 mode and the TM0 mode. The waveguide width (W co ) is 0.65μm ( Figure 2The TE1 mode and the TM0 mode cannot be distinguished. Therefore, the width of the second waveguide 404 in the designed polarization rotator is reduced from 0.7μm (W2) to 0.56μm (W1), which just covers the waveguide width of 0.65μm corresponding to the mode hybridization point. At this time, the TE1 mode in the waveguide can be converted into the TM0 mode. According to calculations, when the length of L2 is 46μm, the conversion efficiency from TE1 to TM0 can reach 99%.

[0066] It should be pointed out that in other embodiments, the width and length of each section of the polarization rotator can be adjusted as needed, as long as the TE1 mode in the waveguide can be converted into the TM0 mode with a preset conversion efficiency, and the protection scope of the present invention should not be excessively limited here.

[0067] As an example, see Figure 3 The nanowire single-photon detector is designed based on a SOI structure and includes:

[0068] Substrate 10;

[0069] An insulating layer 20, located on the surface of the substrate 10;

[0070] A waveguide 40, located on the surface of the insulating layer 20;

[0071] a covering layer 30 , located on the insulating layer 20 and covering an exposed surface of the waveguide 40 ;

[0072] The superconducting nanowire 50 is located on the surface of the cover layer 30 .

[0073] As an example, the substrate 10 includes but is not limited to a silicon substrate, a magnesium oxide substrate, a germanium substrate, a gallium nitride substrate, a gallium arsenide substrate or a sapphire substrate. The nanowire single-photon detector provided by the present invention uses a silicon substrate, because silicon is a common semiconductor material with the advantages of low material cost, mature processing technology, high surface flatness, good uniformity, etc. It is easier to grow an oxide film on a silicon substrate, which is conducive to improving the yield of the nanowire single-photon detector.

[0074] As an example, the insulating layer 20 may also be a buried oxide layer, which may be made of SiO 2 material, and its thickness is preferably 2 μm.

[0075] As an example, the cover layer 30 may be a SiO2 layer, and the distance between its upper surface and the upper surface of the waveguide 40 may be 50 nm. Preferably, the cover layer 30 may be thinned by using a chemical mechanical polishing (CMP) technique, so that the distance between the upper surface of the cover layer 30 and the upper surface of the waveguide 40 is less than 50 nm, and its roughness is ensured to be less than 1 nm, thereby ensuring that the superconducting nanowire 50 deposited on the cover layer 30 is not affected, so that the device maintains good working performance.

[0076] Please note that Figure 2 and Figure 3 The nanowire single-photon detector, as the core part of the entire device, can realize efficient conversion from TE1 mode to TM0 mode. The principle is that when the distance between the upper surface of the covering layer 30 and the upper surface of the waveguide 40 is thinned to 50nm, the effective refractive index of the mode in the waveguide 40 changes with the waveguide width, so that mode hybridization occurs between the TE1 mode and the TM0 mode.

[0077] For details, please refer to Figure 3 The width (W0) of the waveguide covered by the covering layer 30 in the nanowire single-photon detector is 500 nm and the thickness is 220 nm.

[0078] As an example, see Figure 1 and Figure 3 , the superconducting nanowire 50 is in the shape of a square wave with right-angle bends, the convex end of the square wave is close to the connection between the waveguide of the polarization rotator and the waveguide of the nanowire single-photon detector, and the two extended ends of the superconducting nanowire 50 are respectively connected to the positive electrode 61 and the negative electrode 62. The length of the superconducting nanowire 50 along the TM0 transmission direction is in the range of 5-10μm. Preferably, the length of the superconducting nanowire 50 along the TM0 transmission direction is in the range of 5-6μm. The length of the superconducting nanowire 50 along the TM0 transmission direction of this embodiment is 5μm. The distance between the two parallel nanowires perpendicular to the TM0 transmission direction is 80nm, the line width of the superconducting nanowire 50 is 100nm, and the thickness is 7nm.

[0079] As an example, the material of the superconducting nanowire 50 is selected from one of NbN, TiN, TaN, WSi, Nb and MoGe. Preferably, the present invention uses NbN as the superconducting nanowire material.

[0080] See also Figure 1 and Figure 4 The present invention also provides a detection method of a superconducting nanowire single-photon detector based on TM0 mode absorption, comprising the following steps:

[0081] S1: input TE0 mode light wave through the input port of the directional coupler;

[0082] S2: TE0 mode is coupled from the main waveguide to the auxiliary waveguide and converted into TE1 mode;

[0083] S3: TE1 mode is converted to TM0 mode in the polarization converter;

[0084] S4: Nanowire single-photon detectors achieve absorption and detection of TM0 mode through evanescent wave coupling.

[0085] As an example, in step S2, see Figure 2 Based on the mode coupling theory, when the effective refractive index of the TE0 mode in the main waveguide 401 is equal to the effective refractive index of the TE1 mode in the sub-waveguide 402, the TE0 mode in the main waveguide 401 can be efficiently coupled to the adjacent sub-waveguide 402. Specifically, in this embodiment, the effective refractive index of the TE0 mode in the main waveguide 401 is equal to the effective refractive index of the TE1 mode in the sub-waveguide 402 and is both 2.24, the width of the main waveguide (W4) is 0.41 μm, the width of the sub-waveguide (W3) is 0.85 μm, and the TE0 mode is coupled from the main waveguide to the sub-waveguide and converted into the TE1 mode.

[0086] It should be pointed out that in other embodiments, the effective refractive index of the TE0 mode in the main waveguide 401 is equal to the effective refractive index of the TE1 mode in the sub-waveguide 402, and can be adjusted as needed, and the corresponding main waveguide width and sub-waveguide width are also adjusted accordingly. The protection scope of the present invention should not be excessively limited here.

[0087] As an example, in step S3, see Figure 1 and Figure 2 There is mode hybridization between the TE1 mode and the TM0 mode. The waveguide thickness (W co ) is 0.65μm ( Figure 2 We cannot distinguish the TE1 mode from the TM0 mode, so the width of the second waveguide 404 in the designed polarization rotator is reduced from 0.7μm (W2) to 0.56μm (W1), just covering the waveguide width 0.65μm corresponding to the mode hybridization point. At this time, the TE1 mode in the waveguide can be converted into the TM0 mode. According to calculations, when the length of L2 is 46μm, the conversion efficiency from TE1 to TM0 can reach 99%.

[0088] It should be noted that most silicon-based photonic devices use TE mode, especially TE0 mode, as the fundamental mode in the device. This is because the loss of TM mode is greater than that of TE mode. Therefore, TE mode is used to transmit in the waveguide in the transmission part of the device. If the detection part of the device also absorbs TE mode, due to the direction of the TE mode electric field, it usually takes a superconducting nanowire 50 of several tens of microns to complete nearly 100% absorption, and the superconducting nanowire 50 needs to be directly grown on the top of the waveguide 40, which puts forward high requirements on the manufacturing process of nanowires. First, the thickness of the nanowire film is only a few nanometers and the long structure leads to low yield; second, the etching process of the nanowire needs to be accurately controlled, otherwise over-etching will damage the upper surface of the waveguide 40, resulting in scattering loss. If the TM0 mode absorption method is adopted, not only the length of the superconducting nanowire 50 can be greatly shortened, but also the superconducting nanowire 50 can be grown on the cover layer 30 of the waveguide 40, so that the cover layer 30 can act as a barrier layer to prevent the core waveguide from being damaged by the etchant. Therefore, a polarization rotation structure is needed to convert the TE mode to the TM0 mode.

[0089] As an example, in step S4, the length of the superconducting nanowire 50 in the nanowire single-photon detector along the TM0 transmission direction only needs to be 5 μm to achieve 100% light field absorption.

[0090] As an example, the waveguide 40 in the superconducting nanowire single-photon detector based on TM0 mode absorption is a silicon waveguide.

[0091] In summary, the present invention provides a superconducting nanowire single-photon detector based on TM0 mode absorption, comprising: a directional coupler for realizing the conversion from TE0 mode to TE1 mode; a polarization rotator connected to the directional coupler for realizing the conversion from TE1 mode to TM0 mode; and a nanowire single-photon detector connected to the polarization rotator for realizing the absorption and detection of the TM0 mode. The superconducting nanowire single-photon detector based on TM0 mode absorption of the present invention has the following beneficial effects: (1) By adopting the TM0 mode absorption method, the nanowire single-photon detector only needs a length of 5 μm to complete 100% light field absorption, which greatly shortens the required length of the nanowire. Therefore, the process conditions required for nanowire production are reduced, the cost can be reduced, the yield can be improved, and efficient production can be achieved. (2) The nanowire can be grown above the covering layer of the cladding waveguide, so that the covering layer can act as a barrier layer to prevent the core waveguide from being damaged by the etchant and affecting the device performance. (3) The overall structure of the device is simple, and it can achieve efficient conversion from TE0 mode to TM0 mode. It can be quickly absorbed and detected by SNSPD and has high working efficiency.

[0092] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A superconducting nanowire single-photon detector based on TM0 mode absorption, characterized in that: include: Directional coupler, used to achieve conversion from TE0 mode to TE1 mode; A polarization rotator, connected to the directional coupler, for realizing the conversion from TE1 mode to TM0 mode; The nanowire single-photon detector is connected to the polarization rotator and is used to realize the absorption and detection of the TM0 mode.

2. The superconducting nanowire single-photon detector based on TM0 mode absorption according to claim 1, characterized in that: The directional coupler comprises a parallel coupled line directional coupler.

3. The superconducting nanowire single-photon detector based on TM0 mode absorption according to claim 2, characterized in that: The directional coupler comprises a main waveguide and a sub-waveguide which are arranged at intervals, wherein the width of the main waveguide is smaller than the width of the sub-waveguide, wherein the main waveguide comprises a first section, a second section and a third section which are connected in sequence, and the third section and the sub-waveguide are parallel to and coupled with each other.

4. The superconducting nanowire single-photon detector based on TM0 mode absorption according to claim 3, characterized in that: The directional coupler has an input port, the input port is arranged at one end of the main waveguide to input the TE0 mode into the main waveguide, and the sub-waveguide is electromagnetically coupled to the main waveguide to extract the TE1 mode.

5. The superconducting nanowire single-photon detector based on TM0 mode absorption according to claim 1, characterized in that: The polarization rotator includes a first waveguide, a second waveguide, and a third waveguide connected in sequence, and the first waveguide is connected to the directional coupler.

6. The superconducting nanowire single-photon detector based on TM0 mode absorption according to claim 5, characterized in that: The widths of the first waveguide, the second waveguide, and the third waveguide are linearly gradient.

7. The superconducting nanowire single-photon detector based on TM0 mode absorption according to claim 1, characterized in that: The nanowire single-photon detector comprises: substrate; An insulating layer, located on the surface of the substrate; A waveguide, located on the surface of the insulating layer; a covering layer, located on the insulating layer and covering the exposed surface of the waveguide; The superconducting nanowire is located on the surface of the covering layer.

8. The nanowire single-photon detector according to claim 7, characterized in that: The material of the insulating layer includes SiO2.

9. The nanowire single-photon detector according to claim 7, characterized in that: The material of the covering layer includes SiO2, the distance between the upper surface of the covering layer and the upper surface of the waveguide does not exceed 50 nm, and the roughness of the covering layer is less than 1 nm.

10. The nanowire single-photon detector according to claim 7, characterized in that: The superconducting nanowire is in a square wave shape with right-angle bends, and two ends of the superconducting nanowire are respectively connected to positive and negative electrodes.

11. The nanowire single-photon detector according to claim 7, characterized in that: The length of the superconducting nanowire along the TM0 transmission direction is in the range of 5-10 μm.

12. The nanowire single-photon detector according to claim 7, characterized in that: The material of the superconducting nanowire is selected from one of NbN, NbTiN, TiN, TaN, WSi, Nb and MoGe.

13. A detection method for a superconducting nanowire single-photon detector based on TM0 mode absorption, characterized in that: The following steps are involved: Input the TE0 mode light wave through the input port of the directional coupler; The TE0 mode is coupled from the main waveguide to the auxiliary waveguide and converted into the TE1 mode; The TE1 mode is converted to the TM0 mode in the polarization converter; Nanowire single-photon detectors achieve absorption and detection of the TM0 mode through the evanescent wave coupling method.

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