Polarization maintaining quantum frequency conversion device and wavelength conversion method

Abstract

The invention discloses a polarization maintaining quantum frequency conversion device and a wavelength conversion method, and relates to the technical field of light modulation. Comprising a polarization beam splitting device, an optical rotation device, a first off-axis parabolic mirror plated with a metal reflecting film, a nonlinear crystal and a second off-axis parabolic mirror plated with a metal reflecting film. The polarization beam splitting device is used for splitting the pump light and the signal light into a first light beam and a second light beam; the optical rotation device is used for turning the polarization direction of the light beam; the first off-axis parabolic mirror is used for coupling the first light beam to the nonlinear crystal, collimating the second light beam and the output light and then inputting the second light beam and the output light to a polarization beam splitting device; the second off-axis parabolic mirror is used for coupling the second light beam to the nonlinear crystal, collimating the first light beam and the output light and then inputting the collimated light to the polarization beam splitting device; and the nonlinear crystal is used for performing nonlinear transformation on the first light beam or the second light beam to generate output light.

Description

Technical Field

[0001] The present application relates to the field of light modulation technology, and in particular to a polarization-maintaining quantum frequency conversion device and a wavelength conversion method. Background Art

[0002] In the field of atomic and molecular optics, in order to carry out research on quantum networks and distributed quantum computing, it is usually necessary to realize the information transmission of quantum bits through the polarization state of photons. However, when different atomic and molecular systems absorb or emit photons, their specific energy level structure determines that they can only interact with photons of specific wavelengths, and the wavelengths of photons required by different atomic and molecular systems may vary greatly. If you want to connect different atomic and molecular systems through photons with fixed polarization states, you need to achieve the conversion of the wavelength of photons with unchanged polarization states within a wide band, that is, to achieve the conversion of the frequency of photons with unchanged polarization states within a wide band. Summary of the invention

[0003] Based on the above problems, the present application provides a polarization-maintaining quantum frequency conversion device, which can realize the conversion of the wavelength of photons with unchanged polarization state within a wide band.

[0004] The embodiments of the present application disclose the following technical solutions: The first aspect of the present application discloses a polarization-maintaining quantum frequency conversion device, the device comprising: a polarization beam splitting device, an optical rotation device, a first off-axis parabolic reflector coated with a metal reflective film, a nonlinear crystal and a second off-axis parabolic reflector coated with a metal reflective film; The polarization beam splitting device, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector form an annular structure; the annular structure provides annular paths with opposite propagation directions for a light beam in a vertical polarization state and a light beam in a horizontal polarization state; The polarization beam splitting device is used to separate the pump light and the signal light into a first light beam and a second light beam; the first light beam is a light beam in a vertical polarization state, and the second light beam is a light beam in a horizontal polarization state; The optical rotator is used to change the polarization direction of the light beam; The first off-axis parabolic reflector is used to couple the first light beam to the nonlinear crystal, and collimate the second light beam and the output light before inputting them into the polarization beam splitting device; The second off-axis parabolic reflector is used to couple the second light beam to the nonlinear crystal, and collimate the first light beam and the output light before inputting them into the polarization beam splitting device; The nonlinear crystal is used to perform nonlinear transformation on the first light beam or perform nonlinear transformation on the second light beam to generate the output light.

[0005] In an optional implementation, the polarization beam splitting device, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector form a ring structure, specifically: Taking the polarization beam splitting device as the starting point, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector are placed in sequence in a counterclockwise direction; The first off-axis parabolic reflector and the second off-axis parabolic reflector are distributed on both sides of the polarization beam splitting device; the nonlinear crystal is placed on the opposite side of the polarization beam splitting device; The optical rotator is placed between the polarization beam splitting device and the first off-axis parabolic reflector, or between the polarization beam splitting device and the second off-axis parabolic reflector.

[0006] In an optional implementation, the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 45 degrees.

[0007] In an optional implementation, the polarization beam splitting device is any one of a polarization beam splitter PBS, a Glan prism, a Wollaston prism and a polarization shifter.

[0008] In an optional implementation, the optical rotation device is any one of a half-wave plate, a Fresnel rhombus phase retarder with pi phase delay, and a polarization regulator; and the polarization regulator is composed of a quarter-wave plate and a target reflector.

[0009] In an optional implementation, if the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 90 degrees, the device further includes: a first reflector and a second reflector; The polarization beam splitting device, the first reflector, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector form the annular structure; The first reflector is used to reflect the first light beam, the second light beam and the output light; The second reflector is used to reflect the first light beam, the second light beam and the output light.

[0010] In an optional implementation, if the optical rotator is a half-wave plate or a Fresnel rhombus phase retarder with pi phase delay; the polarization beam splitting device, the first reflector, the optical rotator, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector form the annular structure, including: Taking the polarization beam splitting device as the starting point, the first reflector, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector are sequentially placed in a counterclockwise direction; The first off-axis parabolic reflector and the second off-axis parabolic reflector are distributed on both sides of the polarization beam splitting device; The first reflector and the second reflector are distributed on both sides of the polarization beam splitting device; The optical rotation device is placed between the first reflector and the first off-axis parabolic reflector, or between the second reflector and the second off-axis parabolic reflector; The nonlinear crystal is placed on the opposite side of the polarization beam splitting device.

[0011] In an optional implementation, if the optical rotator is a polarization regulator, the polarization regulator is composed of a quarter wave plate and a target reflector, the polarization beam splitting device, the first reflector, the optical rotator, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector form the annular structure, specifically: Taking the polarization beam splitting device as the starting point, the first reflector, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector, and the second reflector are sequentially placed in a counterclockwise direction; The first off-axis parabolic reflector and the second off-axis parabolic reflector are distributed on both sides of the polarization beam splitting device; The first reflector and the second reflector are distributed on both sides of the polarization beam splitting device; The nonlinear crystal and the polarization adjuster are both placed on the opposite sides of the polarization beam splitting device, and the polarization adjuster is between the polarization beam splitting device and the nonlinear crystal.

[0012] In an optional implementation, the device further includes: a first dichroic mirror and a second dichroic mirror; the pump light and the signal light are input to the polarization beam splitting device after being processed by the first dichroic mirror and the second dichroic mirror; The dichroic mirror combination formed by the first dichroic mirror and the second dichroic mirror is further used to split the pump light, the output light, and the signal light based on wavelength.

[0013] A second aspect of the present application discloses a wavelength conversion method, the method comprising: Determining the wavelength of the pump light based on the wavelength of the signal light and the wavelength of the output light; The pump light and the signal light are input into a polarization-maintaining quantum frequency conversion device to generate the output light; the polarization-maintaining quantum frequency conversion device is the device described in any one of the first aspects.

[0014] Compared with the prior art, this application has the following beneficial effects: The polarization-maintaining quantum frequency conversion device in the present application includes two off-axis parabolic reflectors coated with metal reflective films. Since the metal reflective film can achieve high-efficiency reflection of light with wavelengths ranging from ultraviolet 0.2μm to infrared 20μm, the off-axis parabolic reflector coated with the metal reflective film can reflect light of multiple wavelengths in a wide band, and can couple and collimate light of different wavelengths. Therefore, through these two off-axis parabolic reflectors, linear polarized light of different wavelengths (the first light beam or the second light beam) can be well coupled into the nonlinear crystal, and the chromatic aberration problem existing when light beams of different wavelengths are coupled into the nonlinear crystal can be eliminated as much as possible; linear polarized light of different wavelengths (the first light beam, the second light beam and the output light) can also be collimated and input into the polarization beam splitting device, and the working performance of the polarization beam splitting device can be minimized. At the same time, the polarization beam splitting device, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector in the device form a ring structure, which is equivalent to forming a Sagnac ring optical path, and has the advantages of phase self-stability and low loss.

[0015] Therefore, the polarization-maintaining quantum frequency conversion device disclosed in the present application fully combines the advantages of the Sagnac annular optical path and the off-axis parabolic reflector coated with a metal reflective film, and can achieve wavelength conversion with unchanged polarization state in the ultraviolet to infrared light range. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 A schematic diagram of the structure of a polarization-maintaining quantum frequency conversion device provided in an embodiment of the present application; Figure 2 A schematic structural diagram of another polarization-maintaining quantum frequency conversion device provided in an embodiment of the present application; Figure 3 A schematic diagram of the structure of another polarization-maintaining quantum frequency conversion device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In the field of atomic and molecular optics, in order to carry out research on quantum networks and distributed quantum computing, it is usually necessary to realize the information transmission of quantum bits through the polarization state of photons. However, when different atomic and molecular systems absorb or emit photons, their specific energy level structure determines that they can only interact with photons of specific wavelengths, and the wavelengths of photons required by different atomic and molecular systems may vary greatly. If you want to connect different atomic and molecular systems through photons with fixed polarization states, you need to achieve the conversion of the wavelength of photons whose polarization states remain unchanged within a wide band.

[0019] Based on the above problems, the present application provides a polarization-maintaining quantum frequency conversion device, which can realize the conversion of the wavelength of photons with unchanged polarization state within a wide band.

[0020] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] The components that the polarization-maintaining quantum frequency conversion device in the present application must include are: a first dichroic mirror, a second dichroic mirror, a polarization beam splitting device, an optical rotation device, a first off-axis parabolic reflector coated with a metal reflective film, a nonlinear crystal and a second off-axis parabolic reflector coated with a metal reflective film.

[0022] The polarization beam splitting device is any one of a polarization beam splitter PBS, a Glan prism, a Wollaston prism and a polarization shifter.

[0023] The optical rotation device is any one of a half-wave plate, a Fresnel rhombus phase retarder with pi phase delay, and a polarization regulator; and the polarization regulator is composed of a quarter-wave plate and a target reflector.

[0024] Among them, the first off-axis parabolic reflector and the second off-axis parabolic reflector can both be off-axis parabolic reflectors with an off-axis angle of 45 degrees; they can also both be off-axis parabolic reflectors with an off-axis angle of 90 degrees; or one can be an off-axis parabolic reflector with an off-axis angle of 45 degrees and the other can be an off-axis parabolic reflector with an off-axis angle of 90 degrees.

[0025] It is understandable that when different types of devices are selected, the structure of the polarization-maintaining quantum frequency conversion device in the present application is not exactly the same. For ease of understanding, the specific structure of the polarization-maintaining quantum frequency conversion device and the propagation process of light of different wavelengths in the polarization-maintaining quantum frequency conversion device are described in detail below in conjunction with specific embodiments.

[0026] Embodiment 1:

[0027] In the polarization-maintaining quantum frequency conversion device of the first embodiment, the polarization beam splitting device is a polarization beam splitter, the optical rotation device is a half-wave plate, and the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 45 degrees.

[0028] Figure 1 A schematic diagram of the structure of a polarization-maintaining quantum frequency conversion device provided in an embodiment of the present application. Figure 1 As shown, the polarization-maintaining quantum frequency conversion device includes: a first dichroic mirror (dichroic mirror 1), a second dichroic mirror (dichroic mirror 2), a polarization beam splitter, a half-wave plate, a first off-axis parabolic reflector (off-axis parabolic reflector 1) coated with a metal reflective film, and a nonlinear crystal. Figure 1 The off-axis parabolic reflector includes a periodically poled nonlinear crystal of a waveguide and a second off-axis parabolic reflector (off-axis parabolic reflector 2) coated with a metal reflective film.

[0029] Figure 1 The relative position relationship of the components in the device shown is: along the transmission direction of the pump light incident on the polarization-maintaining quantum frequency conversion device, the dichroic mirror 1, the dichroic mirror 2 and the polarization beam splitter are placed in sequence.

[0030] Starting from the polarization beam splitter, off-axis parabolic reflector 1, nonlinear crystal, and off-axis parabolic reflector 2 are placed in a counterclockwise direction. Off-axis parabolic reflector 1 and off-axis parabolic reflector 2 are distributed on both sides of the polarization beam splitting device; the nonlinear crystal is placed on the opposite side of the polarization beam splitter. The half-wave plate is placed between the polarization beam splitter and off-axis parabolic reflector 2.

[0031] right Figure 1 For the polarization beam splitter in the embodiment, the polarization state of the light beam reflected by the polarization beam splitter is a vertical polarization state, and the polarization state of the light beam passing through the polarization beam splitter is a horizontal polarization state. Figure 1The cutting direction of the periodically polarized nonlinear crystal determines that the polarized light coupled to the nonlinear crystal should be a beam of vertical polarization state.

[0032] It should be noted that whether the half-wave plate is placed between the polarization beam splitter and the off-axis parabolic reflector 2 or between the polarization beam splitter and the off-axis parabolic reflector 1 depends on the cutting direction of the periodically polarized nonlinear crystal. Those skilled in the art can determine the polarization states of the pump light and the signal light required for the nonlinear crystal to perform nonlinear transformation according to the cutting direction of the periodically polarized nonlinear crystal, and further determine whether the half-wave plate is placed between the polarization beam splitter and the off-axis parabolic reflector 2 or between the polarization beam splitter and the off-axis parabolic reflector 1.

[0033] A polarization beam splitter is an optical device that can separate or combine light beams with different polarization states. Those skilled in the art can determine whether the polarization state of the light beam transmitted from the polarization beam splitter is a horizontal polarization state or a vertical polarization state by selecting the material and structure of the polarization beam splitter.

[0034] Figure 1 The polarization-maintaining quantum frequency conversion device in the quantum network can generate the photons required for the interconnection between solid-state storage nodes and nodes in any communication band in the quantum network. Generally speaking, the wavelength of the light beam required for solid-state storage is 580nm, and the wavelength of the light beam required for information communication is 1550nm. In the frequency conversion process, the polarization state needs to be kept unchanged or only undergo unitary transformation.

[0035] Combination Figure 1 Taking difference frequency conversion as an example, if you want to convert the wavelength of photons from 580nm to 1550nm, you need a pump light with a wavelength of 927nm. Then use the light with a wavelength of 927nm as the pump light and the light with a wavelength of 580nm as the signal light. Input the pump light and the signal light into Figure 1 The device in can convert light with a wavelength of 1550nm (output light).

[0036] Specifically, the spot sizes of the pump light with a wavelength of 927nm and the signal light with a wavelength of 580nm are adjusted so that the pump light can pass through dichroic mirror 1 and dichroic mirror 2, and be combined with the signal light reflected by dichroic mirror 2 to obtain an initial combined light beam; after the initial combined light beam is incident on the polarization beam splitter, the light beam in the vertical polarization state in the initial combined light beam is reflected to obtain a first light beam, and the light beam in the horizontal polarization state in the initial combined light beam is transmitted to obtain a second light beam.

[0037] The first light beam, i.e., the light beam in the vertical polarization state, is transmitted in the counterclockwise direction to the off-axis parabolic reflector 1, which couples the first light beam into the nonlinear crystal to generate an output light of 1550nm (difference frequency signal light); the output light transmitted in the counterclockwise direction and the first light beam are recorded as the third light beam; the third light beam is transmitted to the off-axis parabolic reflector 2, and is collimated by the off-axis parabolic reflector 2 and then input into the half-wave plate, which converts the polarization state of the third light beam from the vertical polarization state to the horizontal polarization state to obtain the fourth light beam; the fourth light beam is transmitted to the off-axis parabolic reflector 2, and the third light beam is collimated by the off-axis parabolic reflector 2 and then input into the half-wave plate, and the half-wave plate converts the polarization state of the third light beam from the vertical polarization state to the horizontal polarization state to obtain the fourth light beam; It is transmitted to dichroic mirror 2 through the polarization beam splitter. Dichroic mirror 2 reflects the signal light with a wavelength of 580nm in the fourth light beam. The remaining 927nm pump light and 1550nm output light in the fourth light beam are transmitted to dichroic mirror 1 through dichroic mirror 2. The 1550nm output light in the fourth light beam is reflected by dichroic mirror 1, and the 927nm pump light passes through dichroic mirror 1. At this point, the three different wavelengths of pump light (927nm), signal light (580nm) and output light (1550nm) are separated.

[0038] The second light beam, i.e., the light beam in the horizontal polarization state, is transmitted to the half-wave plate in the clockwise direction, and the half-wave plate transforms the polarization state of the second light beam from the horizontal polarization state to the vertical polarization state to obtain the fifth light beam; the fifth light beam is transmitted to the off-axis parabolic reflector 2, and the off-axis parabolic reflector 2 couples the fifth light beam into the nonlinear crystal to generate an output light (difference frequency signal light) of 1550nm; the output light transmitted in the clockwise direction and the fifth light beam are used as the sixth light beam; the sixth light beam is transmitted to the off-axis parabolic reflector 1, and is collimated by the off-axis parabolic reflector 1 and then input into the polarization beam splitter , is reflected by the polarization beam splitter and input into the dichroic mirror 2. The dichroic mirror 2 reflects the signal light with a wavelength of 580nm in the sixth light beam. The remaining 927nm pump light and 1550nm output light in the sixth light beam are transmitted to the dichroic mirror 1 through the dichroic mirror 2. The 1550nm output light in the sixth light beam is reflected by the dichroic mirror 1, and the pump light with a wavelength of 927nm is transmitted through the dichroic mirror 1. At this point, the three different wavelengths of pump light (927nm), signal light (580nm) and output light (1550nm) are separated.

[0039] In order to couple the 580nm signal light and the 927nm pump light into the nonlinear crystal at the same time, it is necessary to adjust the spot size before entering the polarization beam splitter and keep the light parallel or nearly parallel. The key to waveguide coupling is that the mode field of the off-axis parabolic reflector focusing spot must match the mode field of the waveguide propagation in the nonlinear crystal. The mode field of the focusing spot can be adjusted by adjusting the spot size incident on the off-axis parabolic reflector.

[0040] It should be emphasized that Figure 1The polarization beam splitter, off-axis parabolic reflector 1, nonlinear crystal, off-axis parabolic reflector 2, and half-wave plate in the present application form a ring structure similar to the Sagnac ring optical path. Since the Sagnac ring optical path itself has the advantages of phase self-stabilization and low loss, Figure 1 The optical path also has the advantages of phase self-stabilization and low loss.

[0041] Embodiment 2: In the polarization-maintaining quantum frequency conversion device in the second embodiment, the polarization beam splitting device is a polarization beam splitter, the optical rotation device is a half-wave plate, and the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 90 degrees. When the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 90 degrees, the second embodiment also includes the first reflector and the second reflector.

[0042] Figure 2 A schematic diagram of the structure of another polarization-maintaining quantum frequency conversion device provided in an embodiment of the present application. Figure 2 As shown, the polarization-maintaining quantum frequency conversion device includes: a first dichroic mirror (dichroic mirror 1), a second dichroic mirror (dichroic mirror 2), a polarization beam splitter, a first reflector (reflector 1), a first off-axis parabolic reflector (off-axis parabolic reflector 1) coated with a metal reflective film, and a nonlinear crystal ( Figure 2 The mirror comprises a periodically polarized nonlinear crystal including a waveguide), a second off-axis parabolic reflector (off-axis parabolic reflector 2) coated with a metal reflective film, a half-wave plate and a second reflector (mirror 2).

[0043] Figure 2 The relative position relationship of the components in the device shown is: along the transmission direction of the pump light incident on the device, the dichroic mirror 1, the dichroic mirror 2 and the polarization beam splitter are placed in sequence.

[0044] Starting from the polarization beam splitter, reflector 1, off-axis parabolic reflector 1, periodically polarized nonlinear crystal, off-axis parabolic reflector 2 and reflector 2 are placed in sequence in a counterclockwise direction.

[0045] The off-axis parabolic reflector 1 and the off-axis parabolic reflector 2 are arranged on both sides of the polarization beam splitter; the reflector 1 and the reflector 2 are arranged on both sides of the polarization beam splitter. The half-wave plate is arranged between the polarization beam splitter and the off-axis parabolic reflector 2.

[0046] It should be noted that Figure 2The off-axis parabolic reflector 1 and the off-axis parabolic reflector 2 used in the invention are off-axis parabolic reflectors with an off-axis angle of 90 degrees, so two plane reflectors (reflector 1 and reflector 2) are required to change the propagation directions of the first light beam, the second light beam and the output light beam. The first reflector is used to reflect the first light beam, the second light beam and the output light; the second reflector is used to reflect the first light beam, the second light beam and the output light.

[0047] right Figure 2 For the polarization beam splitter in the embodiment, the polarization state of the light beam reflected by the polarization beam splitter is a vertical polarization state, and the polarization state of the light beam passing through the polarization beam splitter is a horizontal polarization state. Figure 2 The cutting direction of the periodically polarized nonlinear crystal determines that the polarized light coupled to the nonlinear crystal should be a beam of vertical polarization state.

[0048] It should be noted that whether the half-wave plate is placed between the reflector 2 and the off-axis parabolic reflector 2, or between the reflector 1 and the off-axis parabolic reflector 1, depends on the cutting direction of the periodically polarized nonlinear crystal. Those skilled in the art can determine the polarization states of the pump light and the signal light required when the nonlinear crystal performs nonlinear transformation according to the cutting direction of the periodically polarized nonlinear crystal, and further determine the position of the half-wave plate.

[0049] Figure 2 The polarization-maintaining quantum frequency conversion device in the quantum network can generate the photons required for interconnecting the ion trap nodes and the solid-state storage nodes in the quantum network. The following is a process of converting the 370nm photons emitted by the spontaneous radiation of the ytterbium ion with a mass number of 171 to the 580nm wavelength required for solid-state storage to illustrate this implementation example. Figure 2 The wavelength of the signal light in the ytterbium ion is 370nm, and the wavelength of the output light is 580nm. The spin state of the ytterbium ion and the polarization state of the 370nm photon emitted by spontaneous radiation are in an entangled state, so the polarization state needs to be kept unchanged or only undergo unitary transformation during the frequency conversion process.

[0050] Combination Figure 2 Taking difference frequency conversion as an example, if you want to convert light with a wavelength of 370nm to light with a wavelength of 580nm, the required pump light wavelength is 1018nm. Use the light with a wavelength of 370nm as the signal light and the light with a wavelength of 1018nm as the pump light. Input the pump light and signal light into Figure 2 The device in can convert the output light with a wavelength of 580nm.

[0051] Specifically, the spot sizes of the pump light with a wavelength of 1018nm and the signal light with a wavelength of 370nm are adjusted so that the pump light can pass through the dichroic mirror 1 and the dichroic mirror 2, and be combined with the signal light reflected by the dichroic mirror 2 to obtain an initial combined light beam; after the initial combined light beam is incident on the polarization beam splitter, the light beam with a vertical polarization state in the initial combined light beam is reflected to obtain a first light beam, and the light beam with a horizontal polarization state in the initial combined light beam is transmitted to obtain a second light beam.

[0052] The first light beam, i.e., the light beam in the vertical polarization state, is transmitted to the reflector 1 in the counterclockwise direction. The reflector 1 reflects the first light beam to the off-axis parabolic reflector 1. The off-axis parabolic reflector 1 couples the first light beam to the nonlinear crystal to generate an output light of 580nm (difference frequency signal light). The output light of 580nm transmitted in the counterclockwise direction and the first light beam are recorded as the third light beam. The third light beam is transmitted to the off-axis parabolic reflector 2, and is collimated by the off-axis parabolic reflector 2 and then input to the half-wave plate. The half-wave plate converts the polarization state of the third light beam from the vertical polarization state to the horizontal polarization state to obtain the fourth light beam. The fourth light beam is transmitted to the reflector Mirror 2, after being reflected by reflector 2, the fourth light beam is transmitted to polarization beam splitter, the fourth light beam is transmitted to dichroic mirror 2 through polarization beam splitter, dichroic mirror 2 reflects the signal light with a wavelength of 370nm in the fourth light beam, the remaining 1018nm pump light and 580nm output light in the fourth light beam are transmitted to dichroic mirror 1 through dichroic mirror 2, the 580nm output light in the fourth light beam is reflected by dichroic mirror 1, and the 1018nm pump light is transmitted through dichroic mirror 1. At this point, the three different wavelengths of pump light (1018nm), signal light (370nm) and output light (580nm) are separated.

[0053] The second light beam, i.e., the light beam in the horizontal polarization state, is transmitted to the reflector 2 in the clockwise direction, and the reflector 2 reflects the second light beam to the half-wave plate, and the half-wave plate transforms the polarization state of the second light beam from the horizontal polarization state to the vertical polarization state to obtain the fifth light beam; the fifth light beam is transmitted to the off-axis parabolic reflector 2, and the off-axis parabolic reflector 2 couples the fifth light beam into the nonlinear crystal to generate an output light of 580nm (difference frequency signal light); the output light of 580nm transmitted in the clockwise direction and the fifth light beam are used as the sixth light beam; the sixth light beam is transmitted to the off-axis parabolic reflector 1, and is collimated by the off-axis parabolic reflector 1 and then transmitted to the reflector 1, reflector 1 reflects the sixth light beam to the polarization beam splitter, and the sixth light beam is reflected by the polarization beam splitter and then transmitted to dichroic mirror 2, which reflects the signal light with a wavelength of 370nm in the sixth light beam, and the remaining 1018nm pump light and 580nm output light in the sixth light beam are transmitted to dichroic mirror 1 through dichroic mirror 2, and the 580nm output light in the sixth light beam is reflected by dichroic mirror 1, and the 1018nm pump light is transmitted through dichroic mirror 1. At this point, the three different wavelengths of pump light (1018nm), signal light (370nm) and output light (580nm) are separated.

[0054] In order to couple the 580nm signal light and the 1018nm pump light into the nonlinear crystal at the same time, it is necessary to adjust the spot size before entering the polarization beam splitter and keep the light parallel or nearly parallel.

[0055] It should be emphasized that Figure 2 The polarization beam splitter, reflector 1, off-axis parabolic reflector 1, nonlinear crystal, off-axis parabolic reflector 2, half-wave plate and reflector 2 form a ring structure, which is similar to the Sagnac ring optical path. Since the Sagnac ring optical path itself has the advantages of phase self-stabilization and low loss, the present application Figure 2 The optical path also has the advantages of phase self-stabilization and low loss.

[0056] Embodiment three: In the polarization-maintaining quantum frequency conversion device in the third embodiment, the polarization beam splitting device is a polarization beam splitter, the optical rotation device is a polarization regulator (composed of a quarter wave plate and a target reflector), and the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 90 degrees. Similar to the second embodiment, when the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 90 degrees, the third embodiment also includes a first reflector and a second reflector.

[0057] Figure 3 A schematic diagram of the structure of another polarization-maintaining quantum frequency conversion device provided in an embodiment of the present application. Figure 3As shown, the polarization-maintaining quantum frequency conversion device includes: a first dichroic mirror (dichroic mirror 1), a second dichroic mirror (dichroic mirror 2), a polarization beam splitter, a first reflector (reflector 1), a first off-axis parabolic reflector (off-axis parabolic reflector 1) coated with a metal reflective film, and a nonlinear crystal ( Figure 3 The invention comprises a periodically polarized nonlinear crystal including a waveguide), a second off-axis parabolic reflector (off-axis parabolic reflector 2) coated with a metal reflective film, a second reflector and a polarization regulator (composed of a quarter-wave plate and reflector 3); reflector 3 is the target reflector in this application.

[0058] Figure 3 The relative position relationship of the components in the device shown is: along the transmission direction of the pump light incident on the device, the dichroic mirror 1, the dichroic mirror 2 and the polarization beam splitter are placed in sequence.

[0059] Starting from the polarization beam splitter, reflector 1, off-axis parabolic reflector 1, nonlinear crystal, off-axis parabolic reflector 2 and reflector 2 are placed in sequence in a counterclockwise direction.

[0060] The off-axis parabolic reflector 1 and the off-axis parabolic reflector 2 are distributed on both sides of the polarization beam splitter; the reflector 1 and the reflector 2 are distributed on both sides of the polarization beam splitter.

[0061] The nonlinear crystal and the polarization adjuster are both placed on opposite sides of the polarization beam splitter, and the polarization adjuster is between the polarization beam splitter and the nonlinear crystal.

[0062] It should be noted that Figure 3 The off-axis parabolic reflector 1 and the off-axis parabolic reflector 2 used in the invention are off-axis parabolic reflectors with an off-axis angle of 90 degrees, so two plane reflectors (reflector 1 and reflector 2) are required to change the propagation directions of the first light beam, the second light beam and the output light beam. The first reflector is used to reflect the first light beam, the second light beam and the output light; the second reflector is used to reflect the first light beam, the second light beam and the output light.

[0063] right Figure 3 For the polarization beam splitter in the embodiment, the polarization state of the light beam reflected by the polarization beam splitter is a vertical polarization state, and the polarization state of the light beam passing through the polarization beam splitter is a horizontal polarization state. Figure 3 The cutting direction of the periodically polarized nonlinear crystal determines that the polarized light coupled to the nonlinear crystal should be a beam of vertical polarization state.

[0064] Figure 3The polarization-maintaining quantum deviation conversion device in the quantum network can generate photons required for interconnection between ion trap nodes and nodes in any communication band in the quantum network. The following is a process of converting the wavelength of 370nm photons emitted by spontaneous radiation of ytterbium ions with a mass number of 171 to the wavelength of 1550nm required for communication wavelength to illustrate this embodiment. Figure 3 The wavelength of the signal light in the transmission is 370nm, and the wavelength of the output light is 1550nm. The spin state of the ytterbium ion and the polarization state of the 370nm photon emitted by spontaneous radiation are in an entangled state, so the polarization state needs to be kept unchanged or only undergo unitary transformation during the frequency conversion process.

[0065] Combination Figure 3 Taking difference frequency conversion as an example, if you want to convert light with a wavelength of 370nm to light with a wavelength of 1550nm, the required pump light wavelength is 485nm. That is, the light with a wavelength of 370nm is used as the signal light, and the light with a wavelength of 485nm is used as the pump light. The pump light and the signal light are input into Figure 3 The device in can convert the output light with a wavelength of 1550nm.

[0066] Specifically, the spot sizes of the pump light with a wavelength of 485nm and the signal light with a wavelength of 370nm are adjusted so that the pump light can pass through dichroic mirror 1 and dichroic mirror 2, and be combined with the signal light reflected by dichroic mirror 2 to obtain an initial combined light beam; after the initial combined light beam is incident on the polarization beam splitter, the light beam with a vertical polarization state in the initial combined light beam is reflected to obtain a first light beam, and the light beam with a horizontal polarization state in the initial combined light beam is transmitted to obtain a second light beam.

[0067] The first light beam, i.e., the light beam in the vertical polarization state, is transmitted to the reflector 1 in the counterclockwise direction, and the reflector 1 reflects the first light beam to the off-axis parabolic reflector 1, and the off-axis parabolic reflector 1 couples the first light beam into the nonlinear crystal to generate an output light of 1550nm (difference frequency signal light); the output light of 1550nm transmitted in the counterclockwise direction and the first light beam are recorded as the third light beam; the third light beam is transmitted to the off-axis parabolic reflector 2, and is collimated by the off-axis parabolic reflector 2 and then transmitted to the reflector 2, and the reflector 2 reflects the third light beam to the polarization beam splitter, and the polarization beam splitter reflects the third light beam to the polarization adjuster. Specifically, the polarization beam splitter reflects the third light beam to the polarization The quarter wave plate in the regulator, the light beam is transmitted through the quarter wave plate and then transmitted to the reflector 3, and then reflected by the reflector 3 and transmitted to the quarter wave plate again, and then transmitted through the quarter wave plate, so that the polarization regulator converts the polarization state of the third light beam from a vertical polarization state to a horizontal polarization state to obtain a fourth light beam; the fourth light beam is transmitted through the polarization beam splitter to the dichroic mirror 2, and the dichroic mirror 2 reflects the signal light with a wavelength of 370nm in the fourth light beam, and the remaining 485nm pump light and 1550nm output light in the fourth light beam are transmitted to the dichroic mirror 1 through the dichroic mirror 2, and the 1550nm output light in the fourth light beam is reflected by the dichroic mirror 1, and the 485nm pump light is transmitted through the dichroic mirror 1. At this point, the three different wavelengths of pump light (485nm), signal light (370nm) and output light (1550nm) are separated.

[0068] The second light beam, i.e., the light beam in the horizontal polarization state, is transmitted to the polarization adjuster in the clockwise direction, passes through the quarter wave plate in the polarization adjuster and then is transmitted to the reflector 3, and then is reflected by the reflector 3, and then passes through the quarter wave plate, which is equivalent to passing through a half wave plate, that is, after the light of the second light beam passes through the polarization adjuster, the polarization state is converted from the horizontal polarization state to the vertical polarization state, and the fifth light beam is obtained; the fifth light beam is reflected by the polarization beam splitter to the reflector 2, and the reflector 2 reflects the fifth light beam to the off-axis parabolic reflector 2, and the off-axis parabolic reflector 2 couples the fifth light beam to the nonlinear crystal to generate an output light (difference frequency signal light) of 1550nm; the output light of 1550nm transmitted in the clockwise direction and the fifth light beam are used as the sixth light beam; The sixth light beam is transmitted to the off-axis parabolic reflector 1, and is collimated by the off-axis parabolic reflector 1 and then transmitted to the reflector 1. The reflector 1 reflects the sixth light beam to the polarization beam splitter. After being reflected by the polarization beam splitter, the sixth light beam is input to the dichroic mirror 2. The dichroic mirror 2 reflects the signal light with a wavelength of 370nm in the sixth light beam. The remaining 485nm pump light and 1550nm output light in the sixth light beam are transmitted to the dichroic mirror 1 through the dichroic mirror 2. The 1550nm output light in the sixth light beam is reflected by the dichroic mirror 1, and the pump light with a wavelength of 485nm passes through the dichroic mirror 1. At this point, the three different wavelengths of pump light (485nm), signal light (370nm) and output light (1550nm) are separated.

[0069] It should be emphasized that Figure 3 The polarization beam splitter, reflector 1, off-axis parabolic reflector 1, nonlinear crystal, off-axis parabolic reflector 2, polarization regulator and reflector 2 form a ring structure, which is similar to the Sagnac ring optical path. Since the Sagnac ring optical path itself has the advantages of phase self-stabilization and low loss, the present application Figure 3 The optical path also has the advantages of phase self-stabilization and low loss.

[0070] For ease of understanding, schematic diagrams of the structures of three polarization-maintaining quantum frequency conversion devices with different structures are provided in Example 1, Example 2, and Example 3. Although the specific structures of the polarization-maintaining quantum frequency conversion devices in the three embodiments are different, the design ideas are the same. Compared with Example 2 and Example 3, Example 1 does not include reflector 1 and reflector 2, and has a simpler structure and lower loss.

[0071] It can be seen from the introduction of the above embodiments that the wavelengths of the pump light, signal light and output light differ greatly. When light beams of different wavelengths are transmitted in a polarization-maintaining quantum frequency conversion device, it involves the process of simultaneously coupling the signal light and the pump light into the nonlinear crystal, and coupling the output light out of the nonlinear crystal. In the above coupling process, if an objective lens or an aspherical mirror is used for coupling, severe chromatic aberration effects will occur, reducing the coupling effect. Especially when ultraviolet light and infrared light are involved, the refractive index of optical glass in the ultraviolet band rises sharply, the chromatic aberration problem is serious, and it is difficult to use.

[0072] In order to solve the chromatic aberration problem, this application uses an off-axis parabolic reflector for coupling, and a metal film is plated on the surface of the off-axis parabolic reflector. The metal film can reflect a wide wavelength of light from ultraviolet 0.2μm to infrared 20μm; the off-axis parabolic reflector converges light by reflection, and there is no need to consider the problem of chromatic aberration when using a lens. Therefore, the optical path in this application realizes wide-band polarization-maintaining quantum frequency conversion through a simple optical path design.

[0073] It is understandable that the positions of the two dichroic mirrors in each of the aforementioned embodiments can be swapped, as long as the three different wavelengths of light, namely, pump light, signal light, and output light, are separated. Although the functions of the first dichroic mirror in each of the aforementioned embodiments are to transmit the pump light and reflect the output light, and the functions of the second dichroic mirror are to transmit the pump light, transmit the output light, and reflect the signal light. However, in some optional implementations, the first dichroic mirror can also transmit the pump light and reflect the signal light, and the second dichroic mirror can transmit the pump light and the signal light and reflect the output light, that is, by coating the two dichroic mirrors with film layers of different parameters, the beam splitting of the three different wavelengths of light, namely, the pump light, the signal light, and the output light, can be achieved. That is, the present application does not limit the specific function of each dichroic mirror in the dichroic mirror combination formed by the first dichroic mirror and the second dichroic mirror, and does not limit the specific parameters of the reflective film and the transmissive film coated on each dichroic mirror. What is defined in the present application is that the dichroic mirror combination formed by the first dichroic mirror and the second dichroic mirror can realize spectral splitting of pump light, output light and signal light based on wavelength.

[0074] It can be understood that the nonlinear transformation method in each of the above embodiments is not limited to difference frequency. After determining the wavelength of the signal light, the wavelength of the output light and the nonlinear crystal, the wavelength of the pump light can also be determined by sum frequency or frequency doubling.

[0075] It is understandable that, through the polarization-maintaining quantum frequency conversion device described in the above embodiments, those skilled in the art can obtain output light of more wavelengths. In the specific use process, it is sufficient to select appropriate parameters of each device in the polarization-maintaining quantum frequency conversion device based on the wavelength of the signal light, the wavelength of the output light, and the wavelength of the pump light, and this content will not be repeated in this application.

[0076] It can be understood that the polarization beam splitter used in the aforementioned embodiments is a three-wavelength polarization beam splitter, which can separate or combine three light beams of different wavelengths and different polarization states.

[0077] Based on the polarization-maintaining quantum frequency conversion device disclosed in the above embodiment, the present application also discloses a wavelength conversion method. The wavelength conversion method disclosed in the present application is implemented based on the polarization-maintaining quantum frequency conversion device disclosed in the above embodiment, and the wavelength conversion method includes: The first step: based on the wavelength of the signal light and the wavelength of the output light, determine the wavelength of the pump light; then based on the wavelength of the signal light, the wavelength of the output light and the wavelength of the pump light, determine the nonlinear crystal. This process is well known to those skilled in the art and will not be described in detail here.

[0078] The second step is to design the size of the input light spot and select the focal length of the off-axis parabolic reflector so that the light spot focused by the off-axis parabolic reflector matches the waveguide mode, thereby achieving the purpose of coupling.

[0079] The third step is to input the pump light and the signal light into a polarization-maintaining quantum frequency conversion device to generate the output light.

[0080] Based on the polarization-maintaining quantum frequency conversion device and wavelength conversion method provided in the aforementioned embodiments, the present application also provides a computer-readable storage medium, on which a computer program is stored, which, when executed by a processor, implements some or all of the steps in the aforementioned wavelength conversion method.

[0081] Based on the polarization-maintaining quantum frequency conversion device and wavelength conversion method provided in the above embodiments, the present application further provides an electronic device, including: a memory having a computer program stored thereon; A processor is used to execute the computer program in the memory to implement part or all of the steps in the wavelength conversion method provided in the above embodiment.

[0082] It should be noted that each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the method embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The method embodiment described above is merely schematic, in which the units described as separate components may or may not be physically separated, and the components indicated as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

[0083] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A polarization-maintaining quantum frequency conversion device, characterized in that: The device comprises: a polarization beam splitting device, an optical rotation device, a first off-axis parabolic reflector coated with a metal reflective film, a nonlinear crystal and a second off-axis parabolic reflector coated with a metal reflective film; The polarization beam splitting device, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector form an annular structure; the annular structure provides annular paths with opposite propagation directions for a light beam in a vertical polarization state and a light beam in a horizontal polarization state; The polarization beam splitting device is used to separate the pump light and the signal light into a first light beam and a second light beam; the first light beam is a light beam in a vertical polarization state, and the second light beam is a light beam in a horizontal polarization state; The optical rotator is used to change the polarization direction of the light beam; The first off-axis parabolic reflector is used to couple the first light beam to the nonlinear crystal, and collimate the second light beam and the output light before inputting them into the polarization beam splitting device; The second off-axis parabolic reflector is used to couple the second light beam to the nonlinear crystal, and collimate the first light beam and the output light before inputting them into the polarization beam splitting device; The nonlinear crystal is used to perform nonlinear transformation on the first light beam or perform nonlinear transformation on the second light beam to generate the output light.

2. The device according to claim 1, characterized in that The polarization beam splitting device, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector form a ring structure, specifically: Taking the polarization beam splitting device as the starting point, the first off-axis parabolic reflector, the nonlinear crystal, and the second off-axis parabolic reflector are placed in sequence in a counterclockwise direction; The first off-axis parabolic reflector and the second off-axis parabolic reflector are distributed on both sides of the polarization beam splitting device; the nonlinear crystal is placed on the opposite side of the polarization beam splitting device; The optical rotator is placed between the polarization beam splitting device and the first off-axis parabolic reflector, or between the polarization beam splitting device and the second off-axis parabolic reflector.

3. The device according to claim 2, characterized in that The first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 45 degrees.

4. The device according to claim 2, characterized in that The polarization beam splitting device is any one of a polarization beam splitter PBS, a Glan prism, a Wollaston prism and a polarization shifter.

5. The device according to claim 2, characterized in that The optical rotation device is any one of a half-wave plate, a Fresnel rhombus phase retarder with pi phase delay, and a polarization regulator; the polarization regulator is composed of a quarter-wave plate and a target reflector.

6. The device according to claim 2, characterized in that If the first off-axis parabolic reflector and the second off-axis parabolic reflector are both off-axis parabolic reflectors with an off-axis angle of 90 degrees, the device further comprises: a first reflector and a second reflector; The polarization beam splitting device, the first reflector, the optical rotation device, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector form the annular structure; The first reflector is used to reflect the first light beam, the second light beam and the output light; The second reflector is used to reflect the first light beam, the second light beam and the output light.

7. The device according to claim 6, characterized in that If the optical rotator is a half-wave plate or a Fresnel rhombus phase retarder with pi phase delay; the polarization beam splitting device, the first reflector, the optical rotator, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector form the annular structure, including: Taking the polarization beam splitting device as the starting point, the first reflector, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector are sequentially placed in a counterclockwise direction; The first off-axis parabolic reflector and the second off-axis parabolic reflector are distributed on both sides of the polarization beam splitting device; The first reflector and the second reflector are distributed on both sides of the polarization beam splitting device; The optical rotation device is placed between the first reflector and the first off-axis parabolic reflector, or between the second reflector and the second off-axis parabolic reflector; The nonlinear crystal is placed on the opposite side of the polarization beam splitting device.

8. The device according to claim 6, characterized in that If the optical rotator is a polarization regulator, the polarization regulator is composed of a quarter wave plate and a target reflector, the polarization beam splitting device, the first reflector, the optical rotator, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector and the second reflector form the annular structure, specifically: Taking the polarization beam splitting device as the starting point, the first reflector, the first off-axis parabolic reflector, the nonlinear crystal, the second off-axis parabolic reflector, and the second reflector are sequentially placed in a counterclockwise direction; The first off-axis parabolic reflector and the second off-axis parabolic reflector are distributed on both sides of the polarization beam splitting device; The first reflector and the second reflector are distributed on both sides of the polarization beam splitting device; The nonlinear crystal and the polarization adjuster are both placed on the opposite sides of the polarization beam splitting device, and the polarization adjuster is between the polarization beam splitting device and the nonlinear crystal.

9. The device according to any one of claims 1 to 8, characterized in that The device further comprises: a first dichroic mirror and a second dichroic mirror; the pump light and the signal light are input to the polarization beam splitting device after being processed by the first dichroic mirror and the second dichroic mirror; The dichroic mirror combination formed by the first dichroic mirror and the second dichroic mirror is used to split the pump light, the output light, and the signal light based on wavelength.

10. A wavelength conversion method, characterized in that: The method comprises: Determining the wavelength of the pump light based on the wavelength of the signal light and the wavelength of the output light; The pump light and the signal light are input into a polarization-maintaining quantum frequency conversion device to generate the output light; the polarization-maintaining quantum frequency conversion device is the device according to any one of claims 1 to 9.

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