A device and method for generating polarization entanglement sources based on multi-period polarization nonlinear crystals
By realizing multiple nonlinear processes in a single crystal through a multi-period polarized nonlinear crystal, and combining filtering and beam splitting systems, the problems of low yield of entangled photon pairs and complex optical paths in the prior art are solved, and the generation of a highly efficient non-degenerate polarization entangled source is realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV
- Filing Date
- 2026-04-30
- Publication Date
- 2026-06-30
AI Technical Summary
In the prior art, the yield of polarization entangled photon pairs generated by type II spontaneous parametric downconversion of a single crystal is low, the collection efficiency of entangled photon pairs generated by the SPDC process of a cross-crystal is low, and the Sagnac ring method has a complex optical path that is difficult to adjust, which cannot meet the requirements of non-degenerate entangled sources.
By employing a multi-period polarized nonlinear crystal, an optical path is designed and polarization and phase are adjusted using a phase modulator. Multiple nonlinear processes are realized in a single crystal using the multi-period polarized crystal, and combined with a filtering and beam splitting system, a non-degenerate polarization entangled source is formed.
This improved the yield of entangled photon pairs, simplified the optical path structure, and enabled the efficient generation of non-degenerate polarization entangled sources.
Smart Images
Figure CN122307987A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of nonlinear optics and quantum optics, and in particular to a polarization entanglement source generation device and method based on a multi-period polarized nonlinear crystal. Background Technology
[0002] Photons are widely used entanglement carriers because of their weak interaction with the surrounding environment, low decoherence, and ease of propagation. Among the many degrees of freedom in photon entanglement, polarization entanglement has significant advantages. Currently, the most common method for generating polarization entangled sources is through the spontaneous parametric downconversion (SPDC) process in a second-order nonlinear crystal. In this process, a high-frequency photon is converted into two low-frequency photons through second-order nonlinear optical interactions. Energy and momentum conservation must be satisfied in this process. Adjusting the crystal angle can lead to walk-off phenomena, which limits the efficiency of the nonlinear process. Later, another phase-matching method, namely quasi-phase matching (QPM), was proposed. By precisely designing its polarization period, flexible control of the reciprocal lattice vector can be achieved. There are three existing ways to realize photon polarization entangled sources: the first is through the second-order spontaneous parametric downconversion (SPDC) of a single crystal, i.e., using type II birefringent phase matching (BPM); the second is through the SPDC process of a cross crystal, where two type I BPM nonlinear crystals are aligned at 90° to each other and then attached, resulting in a polarization entangled photon pair forming a cone; the third is through the Sagnac ring method.
[0003] However, for the first method, which generates a polarization-entangled source through type II spontaneous parametric downconversion using a single crystal, only the photon pairs at the intersection of the two cones are polarization-entangled, resulting in a low yield of entangled photon pairs. For the second method, which generates a polarization-entangled source through type I spontaneous parametric downconversion using a cross-crystal, typically only a portion of the cone is collected for use, also leading to a low yield of entangled photon pairs. For the third method, which generates a polarization-entangled source using a Sagnac ring, although the yield of entangled photon pairs is high, the overall optical path is complex and difficult to adjust. Furthermore, the photon pairs generated by the above schemes are nearly degenerate, which cannot meet the requirements of some scenarios for non-degenerate (i.e., signal light and parametric light wavelengths are different) entangled sources. Therefore, it is necessary to provide a non-degenerate polarization-entangled source with a simple structure and high yield. Summary of the Invention
[0004] Purpose of the invention: The purpose of this invention is to provide a device and method for generating polarization entanglement sources based on multi-period polarized nonlinear crystals.
[0005] Technical solution: The polarization entanglement source generation device based on a multi-period polarization nonlinear crystal described in this invention includes, from left to right, a light source (Pump), a half-wave plate (HWP), and a phase modulator. The system includes an aspherical lens f1, a multi-period polarized nonlinear crystal QPM, an aspherical lens f2, a filter system LP, a beam splitter DM, and coupling systems C1 and C2; the light source Pump emits light from the left side, which passes sequentially through a half-wave plate HWP and a phase modulator. After the aspherical lens f1, the multi-periodic polarized crystal QPM, and the aspherical lens f2 are adjusted for polarization and phase, they are focused onto the center of the crystal, generating two SPDC processes simultaneously. Then, the converted signal light and parametric light are collimated, filtered by the filtering system LP, and finally separated by the beam splitting system DM. The two beams form a non-degenerate polarization entangled source.
[0006] Furthermore, the phase modulator It includes two quarter-wave plates (QWP) and one half-wave plate (HWP), and the relative phase of the generated entangled states is adjusted by adjusting the phase of the pump light.
[0007] Furthermore, the multi-period polarized crystal QPM allows for multiple flexible nonlinear processes to be performed in a single crystal. By calculating and selecting an appropriate period, various non-degenerate conversion processes can be implemented in the same crystal under the same light source pump.
[0008] Furthermore, the period selection of the multi-period polarized crystal QPM satisfies the following formula:
[0009]
[0010] in, , , These represent the momentum of the pump light, signal light, and idler light, respectively. The reciprocal lattice vectors introduced by the periodic structure;
[0011]
[0012] Where m, n, p... are non-zero integers. , , ...for different cycles.
[0013] Furthermore, the filtering system LP includes a long-pass filter for separating the pump light from the parametric light, which is transmitted through the filtering system LP.
[0014] Furthermore, the beam splitting system DM includes a dichroic mirror for separating signal light of different wavelengths from idler light, and the signal light is transmitted through the beam splitting system DM.
[0015] Furthermore, the coupling systems C1 and C2 use collimators to collect light of two wavelengths into the optical fiber for subsequent testing.
[0016] The polarization entanglement source generation method based on a multi-period polarization nonlinear crystal described in this invention is used to emit light from the left side of a light source (Pump), which then passes sequentially through a half-wave plate (HWP) and a phase modulator. After the aspherical lens f1, the multi-periodic polarized crystal QPM, and the aspherical lens f2 are adjusted for polarization and phase, they are focused onto the center of the crystal, generating two SPDC processes simultaneously. Then, the converted signal light and parametric light are collimated, filtered by the filtering system LP, and finally separated by the beam splitting system DM, so that the two beams ultimately form a non-degenerate polarization entangled source.
[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The present invention provides a new method for generating photon polarization entanglement sources. It utilizes multi-period polarized nonlinear crystals as frequency conversion materials, designs optical paths, realizes entanglement sources with polarization as the entanglement dimension, and solves a series of engineering problems such as temperature control and assembly in entanglement source experiments. Ultimately, it can improve the yield of entangled photon pairs while eliminating the need for complex optical path construction. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the structure of the present invention;
[0019] Figure 2 This is a schematic diagram of a dual-period polarized nonlinear crystal structure.
[0020] Figure 3 This is a schematic diagram of a dual-period polarized nonlinear crystal that simultaneously satisfies process 1 and process 2. Detailed Implementation
[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.
[0022] like Figure 1 As shown, the polarization entanglement source generation device based on a multi-period polarization nonlinear crystal of the present invention includes, from left to right, a light source (Pump), a half-wave plate (HWP), and a phase modulator. The system includes an aspherical lens f1, a multi-period polarized nonlinear crystal QPM, an aspherical lens f2, a filter system LP, a beam splitter DM, and coupling systems C1 and C2; the light source Pump emits light from the left side, which passes sequentially through a half-wave plate HWP and a phase modulator. After the aspherical lens f1, the multi-periodic polarized crystal QPM, and the aspherical lens f2 are adjusted for polarization and phase, they are focused onto the center of the crystal, generating two SPDC processes simultaneously. Then, the converted signal light and parametric light are collimated, filtered by the filtering system LP, and finally separated by the beam splitting system DM. The two beams form a non-degenerate polarization entangled source.
[0023] The phase modulator It includes two quarter-wave plates (QWP) and one half-wave plate (HWP), and the relative phase of the generated entangled states is adjusted by adjusting the phase of the pump light;
[0024] The half-wave plate (HWP) is used to modulate the polarization of the pump light;
[0025] The aspherical lens f1 focuses the pump light into the parametric downconversion unit;
[0026] The aspherical lens f2 collimates the outgoing parametric downconversion light;
[0027] The filtering system LP includes a long-pass filter for separating the pump light from the parametric light, which is transmitted through the filtering system LP.
[0028] The beam splitting system DM includes a dichroic mirror for separating signal light and idler light of different wavelengths, and the signal light is transmitted through the beam splitting system DM;
[0029] The coupling systems C1 and C2 use collimators to collect light of two wavelengths into the optical fiber for subsequent testing.
[0030] Multi-period polarized crystals (QPMs) allow for multiple flexible nonlinear processes within a single crystal, enabling compact and integrated devices. In this architecture, by computationally selecting an appropriate period, various non-degenerate conversion processes can be implemented in the same crystal under the same light source pump.
[0031] The period selection of the multi-period polarized crystal QPM satisfies the following formula:
[0032]
[0033] in, , , These represent the momentum of the pump light, signal light, and idler light, respectively. The reciprocal lattice vectors introduced by the periodic structure;
[0034]
[0035] Where m, n, p... are non-zero integers. , , ...for different cycles.
[0036] like Figure 2 As shown, taking a two-period structure as an example, and These are two different periods. Under the same pump light, the crystal can simultaneously satisfy process 1 and process 2, such as... Figure 3 As shown, the following equations are satisfied simultaneously:
[0037]
[0038] A specific implementation is as follows: A polarization entanglement source is generated using a 532nm wavelength light source to produce a signal photon (s) with a wavelength of 1550nm and an idler photon (i) with a wavelength of 810nm. We use a lithium niobate crystal; for simplicity, we only consider the collinear process and only take... and .
[0039] That is, the following equation must be satisfied:
[0040]
[0041] Further transformed into:
[0042]
[0043] And both cycles must meet the following conditions. (where l is an integer), so that crystals can be manufactured.
[0044] Substitute the parameters of lithium niobate crystals at 298 K:
[0045] =532 nm, =1550 nm, =810 nm;
[0046] = 2.32318, = 2.234237;
[0047] = 2.211026, = 2.13788;
[0048] = 2.253867, = 2.174708.
[0049] Finally obtained
[0050]
[0051] At this point, the test is performed. If the value is close to an integer, the crystal can be manufactured and used.
[0052] Entanglement detection methods:
[0053] By connecting the photons collected by the coupling systems C1 and C2 to the polarization entanglement characterization module, parameters such as the yield and contrast of the entangled source can be characterized.
[0054] The polarization entanglement source generation method based on a multi-period polarization nonlinear crystal described in this invention is used to emit light from the left side of a light source (Pump), which then passes sequentially through a half-wave plate (HWP) and a phase modulator. After the aspherical lens f1, the multi-periodic polarized crystal QPM, and the aspherical lens f2 are adjusted for polarization and phase, they are focused onto the center of the crystal, generating two SPDC processes simultaneously. Then, the converted signal light and parametric light are collimated, filtered by the filtering system LP, and finally separated by the beam splitting system DM, so that the two beams ultimately form a non-degenerate polarization entangled source.
[0055] This invention proposes a novel method for generating photon polarization entanglement sources, namely, a polarization entanglement source based on a multi-period polarization nonlinear crystal, and provides the design principle and optical path structure using a dual-period crystal as an example.
Claims
1. A polarization entanglement source generation device based on a multi-period polarization nonlinear crystal, characterized in that, From left to right: Pump (light source), HWP (half-wave plate), and phase modulator. The system includes an aspherical lens f1, a multi-period polarized nonlinear crystal QPM, an aspherical lens f2, a filter system LP, a beam splitter DM, and coupling systems C1 and C2; the light source Pump emits light from the left side, which passes sequentially through a half-wave plate HWP and a phase modulator. After the aspherical lens f1, the multi-periodic polarized crystal QPM, and the aspherical lens f2 are adjusted for polarization and phase, they are focused onto the center of the crystal, generating two SPDC processes simultaneously. Then, the converted signal light and parametric light are collimated, filtered by the filtering system LP, and finally separated by the beam splitting system DM. The two beams form a non-degenerate polarization entangled source.
2. The polarization entanglement source generation device based on a multi-period polarized nonlinear crystal according to claim 1, characterized in that, The phase modulator It includes two quarter-wave plates (QWP) and one half-wave plate (HWP), and the relative phase of the generated entangled states is adjusted by adjusting the phase of the pump light.
3. The polarization entanglement source generation device based on a multi-period polarization nonlinear crystal according to claim 1, characterized in that, The multi-period polarized crystal QPM allows for multiple flexible nonlinear processes to be performed in a single crystal. By selecting an appropriate period, various non-degenerate conversion processes can be implemented in the same crystal under the same light source pump.
4. The polarization entanglement source generation device based on a multi-period polarization nonlinear crystal according to claim 1, characterized in that, The period selection of the multi-period polarized crystal QPM satisfies the following formula: in, , , These represent the momentum of the pump light, signal light, and idler light, respectively. The reciprocal lattice vectors introduced by the periodic structure; Where m, n, p... are non-zero integers. , , ...for different cycles.
5. The polarization entanglement source generation device based on a multi-period polarization nonlinear crystal according to claim 1, characterized in that, The filtering system LP includes a long-pass filter for separating the pump light from the parametric light, which is transmitted through the filtering system LP.
6. The polarization entanglement source generation device based on a multi-period polarization nonlinear crystal according to claim 1, characterized in that, The beam splitting system DM includes a dichroic mirror used to separate signal light and idler light of different wavelengths, and the signal light is transmitted through the beam splitting system DM.
7. The polarization entanglement source generation device based on a multi-period polarization nonlinear crystal according to claim 1, characterized in that, The coupling systems C1 and C2 use collimators to collect light of two wavelengths into the optical fiber for subsequent testing.
8. A method for generating a polarization entanglement source based on a multi-period polarization nonlinear crystal, characterized in that, Used to direct light from the left side of the pump, which then passes sequentially through a half-wave plate (HWP) and a phase modulator. After the aspherical lens f1, the multi-periodic polarized crystal QPM, and the aspherical lens f2 are adjusted for polarization and phase, they are focused onto the center of the crystal, generating two SPDC processes simultaneously. Then, the converted signal light and parametric light are collimated, filtered by the filtering system LP, and finally separated by the beam splitting system DM, so that the two beams ultimately form a non-degenerate polarization entangled source.