WO2017214791A1

WO2017214791A1 - Polarization entangled photon pair generation method and apparatus

Info

Publication number: WO2017214791A1
Application number: PCT/CN2016/085540
Authority: WO
Inventors: 柏艳飞; 张臣雄
Original assignee: 华为技术有限公司
Priority date: 2016-06-13
Filing date: 2016-06-13
Publication date: 2017-12-21
Also published as: CN108604037B; CN108604037A

Abstract

A polarization entangled photon pair generation method and apparatus, falling within the technical field of optical communications. The method comprises: dividing a beam of input photons into two beams of photons with the same energy, converting the two beams of photons into TE mode polarization photon pairs with the same polarization state, then converting one of the TE mode polarization photon pairs into a TM mode polarization photon pair, and further obtaining a polarization entangled photon pair by superposing the TE mode polarization photon pair and the TM mode polarization photon pair. The present invention breaks through the shortcoming in the prior art that a polarization entangled photon pair is only generated in a conical beam overlapping area, and the generated TE mode and TM mode polarization photon pairs are fully used to generate the polarization entangled photon pair, thereby improving the generation efficiency of the polarization entangled photon pair; moreover, the energies of the TE mode and TM mode polarization photon pairs are the same, and thus the brightness of an entangled light source is relatively high. In addition, the apparatus is simple in structure and can be solidified in a silicon-based optical waveguide chip, and the phase is relatively stable.

Description

Method and device for generating polarization entangled photon pair

Technical field

The present invention relates to the field of optical communication technologies, and in particular, to a method and an apparatus for generating a polarization entangled photon pair.

Background technique

Quantum entanglement is the most important resource in quantum information processing. It is a special quantum state in a composite system composed of multiple particles. Entanglement sources in quantum entanglement include photons, electrons, ions, and the like. Since the coherence of photons is better, entangled photons become a common source of quantum entanglement. Photons have different degrees of freedom, such as polarization degrees of freedom, path degrees of freedom, angular momentum degrees of freedom, etc. Each degree of freedom can be used to encode information. Polarization entangled photons based on polarization degrees of freedom are widely used in quantum information processing because polarization degrees of freedom can be flexibly manipulated by wave plates.

At present, the optical waveguide of SOI (Silicon On Insulator) is mainly used. Based on the third-order nonlinearity of silicon material, the pump photon generates a spontaneous four-wave mixing process to generate correlated photon pairs. However, in the silicon wire waveguide, due to the large birefringence effect of the TE mode (Transsverse Electric mode) and the TM mode (Transsverse Magnetic mode), the TE mode polarized photon pair is more efficient than the TM mode. The generation efficiency of polarized photon pairs is large, resulting in almost all of the polarized photon pairs generated in the silicon waveguides being TE mode polarized photon pairs. In order to obtain a polarization entangled photon pair, a method of generating a polarized photon pair needs to be improved.

Figure 1 shows a method for generating a polarization entangled photon pair based on a spontaneous parametric down-conversion process of a second-order nonlinear crystal. Referring to Figure 1, when a short beam of pump photons is incident on a second-order nonlinear crystal, the photons undergo a spontaneous parametric down-conversion process, which splits into two lower-energy photons. The two photons are polarized photons in the horizontal direction and the polarized photons in the vertical direction, and the outgoing directions of the two photons are in the direction indicated by the two cones in Fig. 1, and the two conical overlapping regions Photon pair Superimposed as a polarization entangled photon pair.

In the process of implementing the present invention, the inventors have found that the prior art has at least the following problems:

A photon pair in only two conical overlapping regions can produce a polarization entangled photon pair, and photons in other regions cannot be utilized, resulting in a lower efficiency of the polarization entangled photon pair and a lower luminance of the entangled source. Moreover, the structure of the device is complicated, and all the methods using the bulk optical method require fine adjustment of the optical path and unstable phase.

Summary of the invention

In order to solve the problems of the prior art, embodiments of the present invention provide a method and an apparatus for generating a polarization entangled photon pair. The technical solution is as follows:

In a first aspect, a device for generating a polarization entangled photon pair is provided, the device comprising: a beam splitter, a photon pair generating module, a fundamental mode conversion module, and a polarization converter;

The beam splitter includes an input end, a first output end, and a second output end, the beam splitter splitting the photon beam input by the input end into a first photon beam and a second photon beam having the same energy, a photon beam is output through the first output end, and the second photon beam is output through the second output end;

The photon pair generating module includes a first photon pair generating unit and a second photon pair generating unit, the first photon pair generating unit is connected to the first output end, and can trigger the first photon beam to generate a first TE a pair of modulo polarized photons, the second photon pair generating unit being coupled to the second output end, capable of triggering the second photon beam to generate a second TE mode polarized photon pair;

The basic mode conversion module includes a first fundamental mode conversion unit and a second fundamental mode conversion unit, and the first fundamental mode conversion unit is connected to the first photon pair generating unit, and is capable of polarizing the first TE mode Converting to a first TE fundamental mode polarized photon pair, the second fundamental mode converting unit being coupled to the second photon pair generating unit, capable of converting the second TE mode polarized photon pair into a second TE fundamental mode polarizing Photon pair

The polarization converter includes a first polarization conversion unit and a second polarization conversion unit, the first polarization conversion unit being coupled to the first fundamental mode conversion unit, capable of polarizing photons of the first TE fundamental mode Coupled to the second polarization conversion unit, the second polarization conversion unit is coupled to the second fundamental mode conversion unit, capable of converting the first TE fundamental mode polarization photon pair into a first TM fundamental mode polarization a photon pair, and superimposing the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair as a polarization entangled photon pair, and outputting the polarization entangled photon pair.

The TE mode polarized photon pair and the TM mode polarized photon pair generated in the present invention are all used to generate polarization entangled photon pairs, and the polarization entangled photon pair has high efficiency, and the energy of the TE mode polarized photon pair and the TM mode polarized photon pair. Similarly, the polarization entangled photon pair obtained by the two has higher luminance when used as an entangled light source. Further, the device of the present invention has a simple structure and can be cured in a silicon-based optical waveguide chip such that the phase of the generated polarization entangled photon pair is stabilized.

In conjunction with the first aspect, in a first possible implementation of the first aspect, the beam splitter is a Y-beam splitter. It not only enriches the form of the beam splitter, but also enables a processed photon to be accurately divided into two photons of the same energy.

In conjunction with the first aspect, in a second possible implementation of the first aspect, the beam splitter is a multimode interferometer, the multimode interferometer further comprising a multimode waveguide region, the multimode waveguide region connection The input end, the first output end, and the second output end. It not only enriches the form of the beam splitter, but also enables a processed photon to be accurately divided into two photons of the same energy.

In a second possible implementation manner of the first aspect, in the third possible implementation manner of the first aspect, the beam splitter, the photon pair generating module, and the fundamental mode conversion Both the module and the polarization converter are comprised of a silicon dioxide cladding and silicon nanowires.

In conjunction with the third possible implementation of the first aspect, in a fourth possible implementation manner of the first aspect, the silicon nanowires in the photon pair generating module are curved and surrounded by a silicon dioxide cladding layer, and The first photon pair generating unit and the second photon pair generating unit have the same structure of the silicon nanowires, so that photon pairs having the same polarization state can be generated through the first photon pair generating unit and the second photon pair generating unit.

In conjunction with the fourth possible implementation of the first aspect, in a fifth possible implementation manner of the first aspect, the silicon nanowires of the first photon pair generating unit and the second photon pair generating unit are both Spiral distribution.

In conjunction with the third possible implementation of the first aspect, in a sixth possible implementation manner of the first aspect, the silicon nanowires in the basic mode conversion module are tapered, so that the upper and lower light can be The TE modes in the waveguide are converted to different fundamental modes.

In conjunction with the sixth possible implementation of the first aspect, in a seventh possible implementation manner of the first aspect, the width of the silicon nanowires in the first fundamental mode conversion unit is smaller than the second fundamental mode conversion unit The width of the silicon nanowires.

In conjunction with the first aspect, in an eighth possible implementation of the first aspect, the polarization converter is an asymmetric directional coupler based polarization converter.

In a second aspect, a method for generating a polarization entangled photon pair is provided, the method applying the polarization entangled photon pair generating device of the first aspect, the method comprising:

The beam splitter splits the photon beam input by the input end into a first photon beam and a second photon beam of the same energy, and the first output end transmits the first photon beam to the first photon pair a generating unit, the first photon pair generating unit triggering the first photon beam to generate a first TE mode polarized photon pair, and transmitting the first TE mode polarized photon pair to the first fundamental mode converting unit The second output transmits the second photon beam to the second photon pair generating unit, and the second photon pair generating unit triggers the second photon beam to generate a second TE mode polarized photon pair, and Transmitting a second TE mode polarized photon pair to the second fundamental mode conversion unit;

The first fundamental mode conversion unit converts the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, and transmits the first TE fundamental mode polarized photon pair to the first polarization conversion unit The second fundamental mode conversion unit converts the second TE mode polarized photon pair into a second TE fundamental mode polarized photon pair, and transmits the second TE fundamental mode polarized photon pair to the second polarization conversion unit;

The first polarization conversion unit couples the first TE fundamental mode polarized photon pair to the second polarization conversion unit, and the second polarization conversion unit converts the first TE fundamental mode polarization photon pair to a TM fundamental mode polarized photon pair and the first TM fundamental mode polarized photon pair and the second TE The fundamental mode polarized photon pairs are superimposed as polarization entangled photon pairs, and the polarization entangled photon pairs are output.

The beneficial effects brought by the technical solutions provided by the embodiments of the present invention are:

By dividing one input photon into two photons of the same energy and converting the two photons into TE mode polarized photon pairs having the same polarization state, one of the TE mode polarized photon pairs is converted into a TM mode polarized photon. Yes, the polarization entangled photon pair is further obtained by superimposing the TE mode polarized photon pair and the TM mode polarized photon pair. The invention breaks through the deficiency of the polarization entangled photon pair in the prior art only in the overlapping region of the conical beam, and the generated TE mode and the TM mode polarized photon pair are all used to generate the polarization entangled photon pair, and the polarization entangled photon pair is improved. The efficiency of the generation, and the energy of the TE mode and the TM mode polarized photon pair are the same, and thus the brightness of the entangled light source is high. In addition, the device has a simple structure and can be cured in a silicon-based optical waveguide chip, and the phase is relatively stable.

DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the present invention. Other drawings may also be obtained from those of ordinary skill in the art in light of the inventive work.

1 is a method of generating a prior art polarization entangled photon pair provided by the present invention;

2 is a schematic structural diagram of a device for generating a polarization entangled photon pair according to an embodiment of the present invention;

3 is a schematic structural view of a Y-type beam splitter according to another embodiment of the present invention;

4 is a schematic structural view of a multimode interferometer according to another embodiment of the present invention;

FIG. 5 is a schematic structural view of an optical waveguide according to another embodiment of the present invention; FIG.

6 is a schematic structural diagram of a polarization converter according to another embodiment of the present invention;

FIG. 7 is a flow chart of a method for generating a polarization entangled photon pair according to another embodiment of the present invention.

Wherein, the reference numerals are: 1, a beam splitter; 11, an input terminal; 12, a first output terminal; 13, a second output terminal; 14, a multimode waveguide region; 2. a photon pair generating module; Photon pair generation a second photon pair generating unit; 3. a fundamental mode conversion module; 31, a first fundamental mode conversion unit; 32, a second fundamental mode conversion unit; 4. a polarization converter; 41, a first polarization conversion unit; 42. A second polarization conversion unit.

detailed description

The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

Referring to FIG. 2, an embodiment of the present invention provides a device for generating a polarization entangled photon pair, the device comprising: a beam splitter 1, a photon pair generating module 2, a fundamental mode conversion module 3, and a polarization converter 4.

The beam splitter 1 includes an input end 11, a first output end 12 and a second output end 13, and the beam splitter 1 splits the photon beam input from the input end 11 into a first photon beam and a second photon beam of the same energy. The first photon beam is output through the first output terminal 12, and the second photon beam is output through the second output terminal 13;

The photon pair generating module 2 includes a first photon pair generating unit 21 and a second photon pair generating unit 22, the first photon pair generating unit 21 being connected to the first output terminal 12, the first photon pair generating unit 21 being capable of triggering the first The photon beam generates a first TE mode polarized photon pair and transmits the generated first TE mode polarized photon pair; the second photon pair generating unit 22 is coupled to the second output 13 and the second photon pair generating unit 22 is capable of triggering The second photon beam generates a second TE mode polarized photon pair and transmits the generated second TE mode polarized photon pair. In this embodiment, the first TE mode polarized photon pair and the second TE mode polarized photon pair have the same Correlated photon pairs of polarization states, the two are identical, only the transmission paths are different;

The fundamental mode conversion module 3 includes a first fundamental mode conversion unit 31 and a second fundamental mode conversion unit 32, and the first fundamental mode conversion unit 31 is connected to the first photon pair generation unit 21 for receiving the first photon pair generation unit 21 Generating a first TE mode polarized photon pair and converting the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, thereby transmitting a first TE fundamental mode polarized photon pair; and a second fundamental mode conversion unit 32 is connected to the second photon pair generating unit 22 for receiving the second TE mode polarized photon pair generated by the second photon pair generating unit 22, and converting the second TE mode polarized photon pair into the second TE mode polarized photon And, in turn, transmitting a second TE fundamental mode polarized photon pair;

The polarization converter 4 includes a first polarization conversion unit 41 and a second polarization conversion unit 42, which is connected to the first fundamental mode conversion unit 31 for receiving the first transmission of the first fundamental mode conversion unit 31. The TE fundamental mode polarizes the photon pair and couples the first TE fundamental mode polarized photon pair to the second polarization unit; the second polarization conversion unit 42 is coupled to the second TE fundamental mode polarized photon pair for receiving the second fundamental mode The second TE fundamental mode polarized photon pair transmitted by the polarization conversion unit 32, the effective polarization of the first TE fundamental mode polarized photon pair in the first polarization conversion unit 41 and the TM fundamental mode polarized photon pair in the second deflection conversion unit 42 When the rates are equal, the first TE fundamental mode polarized photon pair is converted into a first TM fundamental mode polarized photon pair, and the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair are superimposed into polarization entangled photons. Then, the polarization entangled photon pair is output.

In one embodiment of the invention, referring to Figure 3, the beam splitter 1 can be a Y-beam splitter. When the beam splitter 1 is a Y-type beam splitter, the positional relationship of the input terminal 11, the first output terminal 12 and the second output terminal 13 in the Y-type beam splitter is as shown in FIG.

In another embodiment of the invention, referring to Figure 4, the beam splitter 1 can also be a multimode interferometer. When the beam splitter 1 is a multimode interferometer, the multimode interferometer includes an input terminal 11, a first output terminal 12, a second output terminal 13 and a multimode waveguide region 14, the multimode waveguide region 14 being connected to the input terminal 11, The first output terminal 12 and the second output terminal 13 are provided. The width and length of the multimode waveguide region 14 are set as desired to ensure that the light field achieves a 50/50 splitting effect, i.e., the input photon beam can be split into first and second photon beams of the same energy.

In this embodiment, the generating device for the polarization entangled photon pair shown in FIG. 2 may be an optical waveguide. Generally, the optical waveguide is mainly composed of a silicon dioxide cladding layer and silicon nanowires. Therefore, the beam splitting shown in FIG. The photon pair generation module 2, the fundamental mode conversion module 3, and the polarization converter 4 are each composed of a silicon dioxide cladding layer and silicon nanowires. Correspondingly, the input end 11, the first output end 12 and the second output end 13 of the beam splitter 1 are also composed of a silicon dioxide cladding and silicon nanowires; the first photon pair included in the photon pair generating module 2 The generating unit 21 and the second photon pair generating unit 22 are also composed of a silicon dioxide cladding layer and silicon nanowires; the first fundamental mode converting unit 31 and the second fundamental mode converting unit 32 included in the fundamental mode converting module 3 are also composed of two The silicon oxide cladding layer and the silicon nanowires are formed; the first polarization conversion unit 41 included in the polarization converter 4 The second polarization conversion unit 42 is also composed of a silicon dioxide cladding layer and silicon nanowires. Generally, the light beam in the optical waveguide is mainly transmitted along the silicon nanowire. In order to visually display the transmission path of the light beam in the optical waveguide, as shown in FIG. 5, the silicon nanowires constituting the functional modules in the device are shown in the optical waveguide chip. Distribution.

When the generating device of the polarization entangled photon pair shown in FIG. 2 is an optical waveguide, the silicon nanowires in the photon pair generating module 2 are curved and surrounded in the silicon dioxide cladding layer, and the structure is compact and the length meets the design requirement, so that the light beam is in the photon. When the generating module 2 is transmitted, the spontaneous four-wave mixing process of the silicon nanowire waveguide can be used to generate a TE mode polarized photon pair. In order to ensure that the polarized photon pairs generated by the first photon pair generating unit 21 and the second photon pair generating unit 22 have the same polarization state, the silicon nanowires in the first photon pair generating unit 21 and the second photon pair generating unit 22 have the same size. And symmetrically distributed. As shown in FIG. 5, the silicon photon in the first photon pair generating unit 21 and the second photon pair generating unit 22 are symmetrically distributed and spiral, of course, the first photon pair generating unit 21 and the second photon pair generating unit 22 The shape of the silicon nanowires may also be other shapes, which is not specifically limited in this embodiment.

In this embodiment, the silicon nanowires in the fundamental mode conversion module 3 are tapered, the width of the silicon nanowires in the first fundamental mode conversion unit 31 is gradually tapered, and the silicon nanometers in the second fundamental mode conversion unit 32 are tapered. The width of the line is gradually thickened, so that the first fundamental mode conversion unit 31 becomes a fine optical waveguide, and the second fundamental mode conversion unit 32 becomes a thick waveguide. Of course, the width of the silicon nanowires in the first fundamental mode conversion unit 31 can be Gradually thickening, the width of the silicon nanowires in the second fundamental mode conversion unit 32 may be tapered such that the first fundamental mode conversion unit 31 becomes a coarse optical waveguide and the second fundamental mode conversion unit 32 becomes a fine optical waveguide. In short, it is only necessary to ensure that the thicknesses of the two optical waveguides in the fundamental mode conversion module 3 are different. In the present embodiment, the width of the silicon nanowires in the fundamental mode conversion module 3 is determined by the width of the silicon nanowires in the polarization converter 4, specifically, the width of the silicon nanowires in the first polarization conversion unit 41 is determined. The width of the silicon nanowires in the first fundamental mode conversion unit 31, and the width of the silicon nanowires in the second polarization conversion unit 42 determine the width of the silicon nanowires in the second fundamental mode conversion unit 32, when in the polarization converter 4 As the width of the silicon nanowires changes, the width of the silicon nanowires in the fundamental mode conversion module 3 needs to be redesigned as needed.

When the first photon pair generating unit 21 transmits the generated first TE mode polarized photon pair to the first base In the mode conversion unit 31, the first fundamental mode conversion unit 31 converts the mode of the first TE mode deflection photon pair into a corresponding fundamental mode according to the width of the self silicon nanowire, and obtains the first TE fundamental mode polarized photon pair. When the second photon pair generating unit 22 transmits the generated second TE mode polarized photon pair to the second fundamental mode converting unit 32, the second fundamental mode converting unit 32 sets the second TE mode according to the width of the self silicon nanowire. The mode of the polarized photon pair is converted to the corresponding fundamental mode, resulting in a second TE fundamental mode polarized photon pair. Since the optical waveguides corresponding to the first fundamental mode conversion unit 31 and the second fundamental mode conversion unit 32 are different, the first TE fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair obtained after the conversion are also different.

In the present embodiment, the polarization converter 4 is a polarization converter of an asymmetric directional coupler, and the length and width of the silicon nanowires in the first polarization conversion unit 41 and the second polarization conversion unit 42 are also different. In one embodiment of the present invention, the length of the silicon nanowires in the first polarization conversion unit 41 may be smaller than the length of the silicon nanowires in the second polarization conversion unit 42, and the silicon nanowires in the first polarization conversion unit 41 The width is smaller than the width of the silicon nanowires in the second polarization conversion unit 42, at which time the first polarization conversion unit 41 does not output a polarization entangled photon pair, which can serve as a test port, and the second polarization conversion unit 42 serves as an output terminal to output polarization entanglement. Photon pair. In another embodiment of the present invention, the length of the silicon nanowires in the first polarization conversion unit 41 may be greater than the length of the silicon nanowires in the second polarization conversion unit 42, and the silicon nanometers in the first polarization conversion unit 41 The width of the line is greater than the width of the silicon nanowires in the second polarization conversion unit 42. At this time, the first polarization conversion unit 41 outputs a polarization entangled photon pair as an output terminal, and the second polarization conversion unit 42 does not output a polarization entangled photon pair. As a test port.

In the present embodiment, based on the polarization converter of the asymmetric directional coupler, when the width of the silicon nanowires in the first polarization conversion unit 41 and the second polarization conversion unit 42 satisfies certain conditions, the first polarization conversion unit 41 can be made Corresponding to the first TE fundamental mode polarized photon pair in the optical waveguide and the second TM polarization converting unit 42 corresponding to the second TM fundamental mode polarized photon pair in the optical waveguide, the effective refractive index is equal, and according to the coupled mode theory, the finer light can be The TE fundamental mode polarized photon pair in the waveguide is coupled into the coarser optical waveguide and converted into a TM fundamental mode polarized photon pair in the coarser optical waveguide, while the TE fundamental mode polarized photon pair in the coarser optical waveguide still propagates therein. . The TE fundamental mode can be expressed as a TE ₀ mode, and the TM fundamental mode can be expressed as a TM ₀ mode. For example, as shown in (a) of FIG. 6, the length of the coupling region is 36.8 um, and when the TE ₀ mode in the thin optical waveguide is equal to the effective refractive index of the TM ₀ mode in the coarse optical waveguide, the fine optical waveguide can be The TE ₀ mode photon pair is coupled into the coarse optical waveguide, and the TE ₀ mode photon pair in the coarse optical waveguide still propagates in the coarse optical waveguide. Figure 6 (b) is a cross-sectional view of the polarization converter, where w1 is the width of the thin optical waveguide, w2 is the width in the coarse optical waveguide, and g is the distance between the thin waveguide and the thick waveguide, h is The height of the thick and thin optical waveguide. W1 may be 330 nm, w2 may be 600 nm, g may be 100 nm, and h may be 250 nm. Of course, in practical applications, the above structural parameters may be specifically designed according to requirements, and are not limited to the above listed data, as long as the fine optical waveguide is satisfied. The TE ₀ mode in the middle is equal to the effective refractive index of the TM ₀ mode in the coarse optical waveguide, and the length of the coupling region needs to ensure that most of the TE ₀ mode in the thin optical waveguide is converted into the TM ₀ mode in the thick waveguide.

In this embodiment, the first photon pair generating unit 21, the first fundamental mode converting unit 31, and the first polarizing converting unit 41 may constitute an on-path optical waveguide, and the second photon pair generating unit 22 and the second fundamental mode converting unit may be configured. 32 and the second polarization conversion unit 42 constitute a lower optical waveguide. By adding a metal electrode to the upper optical waveguide and the lower optical waveguide, after applying a voltage, the relative phase of the photons in the upper and lower waveguides can be adjusted by using the photothermal effect, and the polarization entangled state is |ψ>=a|TE, TE> +be ^iθ |TM, TM> polarization entangled photon pairs. Where ψ is the polarization entangled state, θ is the relative phase, a and b are arbitrary parameters, and a and b satisfy the normalization condition |a| ² +|b| ² =1.

The device provided by the embodiment of the present invention divides one input photon into two photons of the same energy, and converts the two photons into TE-mode polarized photon pairs having the same polarization state, thereby polarizing one of the TE modes. The photon pair is converted into a TM mode polarized photon pair, and the polarization entangled photon pair is further obtained by superimposing the TE mode polarized photon pair and the TM mode polarized photon pair. The invention breaks through the deficiency of the polarization entangled photon pair in the prior art only in the overlapping region of the conical beam, and the generated TE mode and the TM mode polarized photon pair are all used to generate the polarization entangled photon pair, and the polarization entangled photon pair is improved. The efficiency of the generation, and the energy of the TE mode and the TM mode polarized photon pair are the same, and thus the brightness of the entangled light source is high. In addition, the device has a simple structure and can be cured in a silicon-based optical waveguide chip, and the phase is relatively stable.

The method for generating a polarization entangled photon according to the above-mentioned FIG. 2, the embodiment of the present invention provides a method for generating a polarization entangled photon. Referring to FIG. 7, the method flow provided by the embodiment includes:

701. The beam splitter divides the photon beam input at the input end into a first photon beam and a second photon beam having the same energy, and the first output end transmits the first photon beam to the first photon pair generating unit, and the first photon pair generates The unit triggers the first photon beam to generate a first TE mode polarized photon pair, and transmits the first TE mode polarized photon pair to the first fundamental mode conversion unit, and the second output transmits the second photon beam to the second photon pair generating unit The second photon pair generating unit triggers the second photon beam to generate a second TE mode polarized photon pair, and transmits the second TE mode polarized photon pair to the second fundamental mode converting unit.

702. The first fundamental mode conversion unit converts the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, and transmits the first TE fundamental mode polarized photon pair to the first polarization conversion unit, and the second fundamental mode conversion The unit converts the second TE mode polarized photon pair into a second TE fundamental mode polarized photon pair and transmits the second TE fundamental mode polarized photon pair to the second polarization converting unit.

703. The first polarization conversion unit couples the first TE fundamental mode polarization photon pair into the second polarization conversion unit, and the second polarization conversion unit converts the first TE fundamental mode polarization photon pair into the first TM fundamental mode polarization photon pair. And superimposing the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair into a polarization entangled photon pair, and outputting a polarization entangled photon pair.

Taking the generating device of the polarization entangled photon pair as an example of the optical waveguide, the above process of generating the polarization entangled photon pair based on the optical waveguide is as follows:

In the first step, the pump photons are input from the off-chip into the SOI optical chip, and are split into two photon beams of the same energy through the beam splitter and transmitted to the upper and lower optical waveguides.

In the second step, the third-order nonlinearity of the silicon wire waveguide is used to generate a spontaneous four-wave mixing process, and the upper and lower optical waveguides respectively generate TE-mode polarized photon pairs having the same polarization state.

In the third step, the tapered optical waveguide converts the mode of the TE mode polarized photon pair into a fundamental mode TE ₀ mode in the coarse and fine optical waveguide.

In the fourth step, the TE ₀ mode photon in the thin waveguide is converted into the TM ₀ mode photon in the thick waveguide by using a polarization converter, and the TE ₀ mode photon pair in the coarse waveguide and the converted TM ₀ mode photon pair are superposed. The polarization entangles the pair of photons, which in turn outputs a pair of polarization entangled photons.

The method provided by the embodiment of the present invention divides one input photon into two photons of the same energy, and converts the two photons into TE-mode polarized photon pairs having the same polarization state, thereby polarizing one of the TE modes. The photon pair is converted into a TM mode polarized photon pair, and the polarization entangled photon pair is further obtained by superimposing the TE mode polarized photon pair and the TM mode polarized photon pair. The invention breaks through the deficiency of the polarization entangled photon pair in the prior art only in the overlapping region of the conical beam, and the generated TE mode and the TM mode polarized photon pair are all used to generate the polarization entangled photon pair, and the polarization entangled photon pair is improved. The efficiency of the generation, and the energy of the TE mode and the TM mode polarized photon pair are the same, and thus the brightness of the entangled light source is high. In addition, the device has a simple structure and can be cured in a silicon-based optical waveguide chip, and the phase is relatively stable.

It should be noted that the device for generating a polarization entangled photon pair provided by the above embodiment is only exemplified by the division of the above functional modules when generating a polarization entangled photon pair. In practical applications, the function may be allocated according to needs. The different functional modules are completed, that is, the internal structure of the polarization entangled photon pair generating device is divided into different functional modules to complete all or part of the functions described above. In addition, the apparatus for generating a polarization entangled photon pair provided by the above embodiment is the same as the embodiment of the method for generating a polarization entangled photon pair. The specific implementation process is described in detail in the method embodiment, and details are not described herein again.

A person skilled in the art may understand that all or part of the steps of implementing the above embodiments may be completed by hardware, or may be instructed by a program to execute related hardware, and the program may be stored in a computer readable storage medium. The storage medium mentioned may be a read only memory, a magnetic disk or an optical disk or the like.

The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalents, improvements, etc., which are within the spirit and scope of the present invention, should be included in the protection of the present invention. Within the scope.

Claims

A device for generating a polarization entangled photon pair, characterized in that the device comprises: a beam splitter, a photon pair generating module, a fundamental mode conversion module and a polarization converter;

The beam splitter includes an input end, a first output end, and a second output end, the beam splitter splitting the photon beam input by the input end into a first photon beam and a second photon beam having the same energy, a photon beam is output through the first output end, and the second photon beam is output through the second output end;

The photon pair generating module includes a first photon pair generating unit and a second photon pair generating unit, the first photon pair generating unit is connected to the first output end, and can trigger the first photon beam to generate a first TE a pair of modulo polarized photons, the second photon pair generating unit being coupled to the second output end, capable of triggering the second photon beam to generate a second TE mode polarized photon pair;

The basic mode conversion module includes a first fundamental mode conversion unit and a second fundamental mode conversion unit, and the first fundamental mode conversion unit is connected to the first photon pair generating unit, and is capable of polarizing the first TE mode Converting to a first TE fundamental mode polarized photon pair, the second fundamental mode converting unit being coupled to the second photon pair generating unit, capable of converting the second TE mode polarized photon pair into a second TE fundamental mode polarizing Photon pair

The polarization converter includes a first polarization conversion unit and a second polarization conversion unit, the first polarization conversion unit being coupled to the first fundamental mode conversion unit, capable of coupling the first TE fundamental mode polarization photon pair to In the second polarization conversion unit, the second polarization conversion unit is connected to the second fundamental mode conversion unit, and is capable of converting the first TE fundamental mode polarization photon pair into a first TM fundamental mode polarization photon pair. And superposing the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair into a polarization entangled photon pair, and outputting the polarization entangled photon pair.
The device of claim 1 wherein said beam splitter is a Y-beam splitter.
The apparatus according to claim 1, wherein said beam splitter is a multimode interferometer, said multimode interferometer further comprising a multimode waveguide region, said multimode waveguide region connecting said input end, said The first output end and the second output end are described.
The apparatus according to any one of claims 1 to 3, wherein the beam splitter, the photon pair generating module, the fundamental mode conversion module, and the polarization converter are all packaged by silicon dioxide. The layer is composed of silicon nanowires.
The apparatus according to claim 4, wherein the silicon nanowires in the photon pair generating module are curved to surround the silicon dioxide cladding, and the first photon pair generating unit and the second photon pair The structure of the silicon nanowires in the generating unit is the same.
The apparatus according to claim 5, wherein the silicon photon of the first photon pair generating unit and the second photon pair generating unit are spirally distributed.
The apparatus according to claim 4, wherein the silicon nanowires in the fundamental mode conversion module are tapered.
The apparatus according to claim 7, wherein a width of the silicon nanowires in the first fundamental mode conversion unit is smaller than a width of the silicon nanowires in the second fundamental mode conversion unit.
The apparatus of claim 1 wherein said polarization converter is a polarization converter based on an asymmetric directional coupler.
A method for generating a polarization entangled photon pair, wherein the method uses the polarization entangled photon pair generating device according to any one of claims 1 to 9, the method comprising:

The beam splitter splits the photon beam input by the input end into a first photon beam and a second photon beam of the same energy, and the first output end transmits the first photon beam to the first photon pair a generating unit, the first photon pair generating unit triggering the first photon beam to generate a first TE mode polarized photon pair, and The first TE mode polarized photon pair is transmitted to the first fundamental mode conversion unit, and the second output transmits the second photon beam to the second photon pair generating unit, the second photon pair Generating unit triggers the second photon beam to generate a second TE mode polarized photon pair, and transmits the second TE mode polarized photon pair to the second fundamental mode conversion unit;

The first fundamental mode conversion unit converts the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, and transmits the first TE fundamental mode polarized photon pair to the first polarization conversion unit The second fundamental mode conversion unit converts the second TE mode polarized photon pair into a second TE fundamental mode polarized photon pair, and transmits the second TE fundamental mode polarized photon pair to the second polarization conversion unit;

The first polarization conversion unit couples the first TE fundamental mode polarized photon pair to the second polarization conversion unit, and the second polarization conversion unit converts the first TE fundamental mode polarization photon pair to A TM fundamental mode polarized photon pair, and the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair are superimposed into a polarization entangled photon pair, and the polarization entangled photon pair is output.