Periodically oriented crystal as polarization entangled photon bright source
By alternately stacking birefringent phase matching crystals to form a periodic crystal structure, the problem of the existing polarization entangled photons on the source is solved, and a high-brightness and high-entangled polarized entangled photon bright source is achieved, which simplifies the setting and adjustment process.
Patent Information
- Application Number
- CN202411740654.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-11-30
- Filing Date
- 2024-11-29
- Publication Date
- 2025-05-30
AI Technical Summary
Existing polarization entangled photons have spatial and/or time domain walk-off effects on sources, resulting in non-optimal entanglement and complexity, cost, and adjustment difficulty when weighing brightness and entanglement purity.
Multiple birefringent phase-matched crystals are alternately stacked to form a periodic crystal structure, and bonded with near-refractive index-matched optical epoxy resin to form a high brightness and high entanglement polarized entangled photon bright source.
The bright source of high-quality entangled photons is achieved, reducing the trade-off between brightness and entangled purity, avoiding additional compensation elements, and simplifying the setup and adjustment process.
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Figure CN120065598A_ABST
Abstract
Description
[0001] Cross - reference to related applications
[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 604,664, filed on November 30, 2023. The disclosure of U.S. Provisional Patent Application No. 63 / 604,664 is incorporated herein by reference. Technical field
[0003] The present disclosure generally relates to light sources, and more particularly to periodically - oriented crystals as bright sources of polarization - entangled photons. Background art
[0004] All currently available sources of polarization - entangled photon pairs suffer from spatial and / or temporal walk - off effects because, within the birefringent crystals used to generate the photon pairs, photons with horizontal polarization behave differently from photons with vertical polarization. The spatial walk - off effect means different emission angles for different polarizations, while the temporal walk - off effect describes different arrival times of different polarizations at the detector. Both of these effects lead to non - optimal entanglement because the different polarizations become distinguishable. Typically, these effects increase with increasing crystal length. On the other hand, when using thin crystals, the brightness of the source (the number of pairs generated per time) is affected. Thus, there is a trade - off between brightness and entanglement purity. This can be partially avoided by using compensating elements (birefringent crystals) that cancel the walk - off effect. However, these elements increase the complexity, cost, loss, and difficulty of adjustment of the setup.
[0005] Since 1999, pairs of orthogonally - oriented crystals have been used as ultra - bright sources of polarization - entangled photons [1 - 2]. Nonlinear crystals are cut and polished to form identical crystal pairs, whose optical axis orientations are optimized for a specific pump wavelength to achieve spontaneous down - conversion of entangled photon pairs. Then, a pair of identical crystals are oriented with respect to each other such that the planes containing their optical axes and the pump beam are rotated 90 degrees with respect to each other, i.e., about the surface normal of the crystal entrance face, which balances the walk - off effect and increases entanglement. Finally, the pair of crystals are optically contacted together. While the crystal pair can improve the brightness and entanglement of a single crystal, the design of such a crystal pair requires a trade - off between brightness and entanglement because the way to improve one degrades the other. A key feature of the crystal pair is the optical contact between the two crystals, which is a delicate process and cannot be scaled up to multiple thin crystals.
[0006] Therefore, there has long been a need for a technical solution that can provide a bright source of high - quality entangled photons while minimizing the need for a trade - off between brightness and entanglement purity. Summary of the invention
[0007] One embodiment of the present disclosure provides a crystal stack as a bright source of polarization-entangled photons, comprising: a plurality of first birefringent phase-matching crystals having a first optical axis; and a corresponding plurality of second birefringent phase-matching crystals having a second optical axis; wherein the plurality of first and second crystals are alternately stacked to form a periodic crystal structure, and the first optical axis is offset from the second optical axis by a desired angle.
[0008] One embodiment of the present invention provides a system for generating a bright source of polarization-entangled photons, comprising: a laser configured to generate polarized laser light; a plurality of first birefringent phase-matching crystals having a first optical axis; and a corresponding plurality of second birefringent phase-matching crystals having a second optical axis; wherein the plurality of first and second crystals are alternately stacked to form a periodic crystal structure, and the first optical axis is offset from the second optical axis by a desired angle; and the crystal stack is configured to output polarization-entangled photons when receiving the polarized laser light from the laser. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 An example of three pairs of periodically oriented crystals according to an embodiment is shown.
[0010] Figure 2 A system for generating a bright source of polarization-entangled photons according to an embodiment is shown. DETAILED DESCRIPTION
[0011] The description of the illustrative embodiments in accordance with the principles of the present disclosure is intended to be read in conjunction with the accompanying drawings, which are considered to be a part of the entire written description. In the description of the embodiments disclosed herein, any reference to direction or orientation is merely for the convenience of description and is not intended to limit the scope of the present disclosure in any way. Related terms, such as "below", "above", "horizontal", "vertical", "above", "below", "upper", "lower", "top" and "bottom" and their derivatives (e.g., "horizontally", "downwardly", "upwardly", etc.) should be construed to refer to the orientation subsequently described or shown in the drawings discussed. These relative terms are for descriptive convenience only and do not require the device to be constructed or operated in a particular orientation unless explicitly stated. Terms such as "attached", "attached to", "connected", "coupled", "interconnected", etc. refer to such a relationship in which structures are directly or indirectly fixed or attached to each other through intermediate structures, and the attached or relationship can be movable or rigid, unless otherwise explicitly described. In addition, the features and advantages of the present disclosure are illustrated by reference to the exemplary embodiments. Therefore, the present disclosure should not be construed as being limited to the exemplary embodiments showing some possible non-limiting combinations of features, which may exist alone or in other combinations of features; the scope of the present disclosure is defined by the appended claims.
[0012] The present invention describes the presently contemplated best mode of carrying out the invention. This description is not to be understood in a limiting sense, but rather is provided by way of example only, presented for illustrative purposes with reference to the drawings, to inform one of ordinary skill in the art of the advantages and construction of certain embodiments. In the various views of the drawings, like reference numerals denote like or similar parts.
[0013] It should be noted that the disclosed embodiments are merely examples of many useful applications of the innovative teachings herein. In general, statements in the specification of this application do not necessarily limit any of the various claimed disclosures. Additionally, some statements may apply to some inventive features but not to others. In general, unless otherwise stated, without loss of generality, a singular element may be plural and vice versa.
[0014] The present disclosure describes a method of fabricating a compensated thin crystal stack without the strict requirements of optical contact. The periodically oriented crystal stacks described in this patent provide an elegant solution to the above problems, as they combine the advantages of thin crystals (good entanglement) and thick crystals (high brightness). The stack of multiple crystal pairs relies on a near refractive index-matched optically transparent epoxy resin to achieve a construction of more than 2 crystals without the spatial separation and interference stabilization required for a free-space construction [3]. The preferred embodiment starts with 2N (where N is an integer greater than 1) independent birefringent phase-matching crystals with thicknesses between 50 and 500 microns, then assembles the uncoated crystals with a 90-degree rotation of the optical axis between each crystal, and bonds them with a near refractive index-matched optical epoxy resin. The assembled stack has an AR coating for the wavelength of interest on the outer layer interacting with air. Figure 1 An example of such a periodically oriented crystal stack is shown. In this example, the stacked crystal structure 100 includes 3 pairs of periodically oriented crystals. Crystal 110 has an optical axis (OA) 112, and crystal 120 has an optical axis 122 oriented at an angle with respect to the optical axis 112. Crystals 110 and 120 are stacked alternately as shown (i.e., 110, 120, 110, 120, 110, 120). According to one embodiment, the outer surfaces S1 and S7 can be AR coated for a specific wavelength. According to one embodiment, the crystal interfaces S2, S3, S4, S5, and S6 are bonded with a transparent refractive index-matching epoxy resin.
[0015] The entanglement quality increases with the reduction of the single-layer thickness, while the brightness increases with the increase in the number of layers. For a large number of thin layers, both the temporal and / or spatial walk-off effects are fully compensated inside the crystal, making additional compensation elements redundant and thus avoiding the drawbacks described in the background art section. This works because of the alternating polarization of the layers, and photons see the same average walk-off regardless of their polarization. The emitted photon pairs are strongly entangled over the entire emission cone, greatly facilitating the alignment process and improving the measure of entanglement, such as Bell tests.
[0016] According to one embodiment, the stacked crystal structure 100 can be used in a system for generating a bright source of polarization-entangled photons. Figure 2 An example system is shown. The system 200 includes a laser source 210 configured to generate a polarized laser beam 220. The laser beam is directed to the stacked crystal structure 100, and the stacked crystal structure outputs polarized entangled photons.
[0017] Although the present disclosure has been described in detail with respect to the several embodiments and has a certain particularity, it does not mean that the present disclosure should be limited to any such details or embodiments or any specific embodiment, but rather should be understood to provide the broadest possible interpretation in view of the related art. Thus, it can effectively cover various embodiments herein. In addition, the above describes various embodiments foreseen by the inventors, for which descriptions enabling the implementation of the invention can be obtained, although modifications to the present disclosure not currently foreseen may represent equivalents thereof.
[0018] References:
[0019] [1].Kwiat, Paul G., et al. “Ultrabright source of polarization-entangled photons,” Physical Review A 60.2 (1999): R773.
[0020] [2].Kwiat, Paul G., Phillippe H. Eberhard, and Andrew G. White. “Ultra-bright source of polarization-entangled photons,” U.S. Patent No. 6,424,665. 23 Jul. 2002.
[0021] [3].Hardy,Lucien.“Source of photons with correlated polarisations andcorrelated directions,”Physics Letters A161.4(1992):326-328.
Claims
1. A crystal stack as a bright source of polarization-entangled photons, comprising: a plurality of first birefringent phase-matched crystals having a first optical axis; and a corresponding plurality of second birefringent phase-matched crystals having a second optical axis; The plurality of first crystals and the plurality of second crystals are alternately stacked to form a periodic crystal structure, wherein the first optical axis is offset from the second optical axis by a desired angle.
2. The crystal stack according to claim 1, wherein: The first crystal and the second crystal are bonded together by a near-index-matched optical epoxy.
3. The crystal stack according to claim 1, wherein: The first crystal and the second crystal have a thickness of 50-500 μm.
4. The crystal stack according to claim 1, wherein: The first optical axis is offset from the second optical axis by 90 degrees.
5. The crystal stack according to claim 1, wherein: The periodic crystal structure includes a wavelength-specific AR coating on the end faces of the stack that interact with air.
6. A system for generating a bright source of polarization-entangled photons, comprising: a laser configured to generate polarized laser light; a plurality of first birefringent phase-matched crystals having a first optical axis; and a corresponding plurality of second birefringent phase-matched crystals having a second optical axis; wherein the plurality of first crystals and the plurality of second crystals are alternately stacked to form a periodic crystal structure, wherein the first optical axis is offset from the second optical axis by a desired angle; and The crystal stack is configured to output polarization-entangled photons upon receiving the polarized laser light from the laser.
7. The system according to claim 6, wherein: The first crystal and the second crystal are bonded together by a near-index-matched optical epoxy.
8. The system according to claim 6, wherein: The first crystal and the second crystal have a thickness of 50-500 μm.
9. The system according to claim 6, wherein: The first optical axis is offset from the second optical axis by 90 degrees.
10. The system according to claim 6, wherein: The periodic crystal structure includes a wavelength-specific AR coating on the end faces of the stack that interact with air.