Non-local spatial light field imaging system

Abstract

The application discloses a non-local spatial light field imaging system, comprising: an entangled light source preparation module, including a PPKTP entangled source based on a Sagnac interferometer; a trigger light path, including a first wave plate, a polarization beam splitter and a single-photon avalanche diode connected in sequence; an idler light path, including a first Sagnac interferometer, a spatial light modulator, a second Sagnac interferometer and a 4f system; and a coincidence imaging module, including a second wave plate, a third Sagnac interferometer, an enhanced charge-coupled device and a coincidence counting unit. The application provides a feasible system for measuring a three-dimensional quantum spatial light field, has the function of realizing non-local quantum state measurement in the z direction, realizes non-local imaging and tomographic measurement of the quantum light field on a single ICCD detection plane, obtains three-dimensional spatial wave function information, and has the advantages of high precision and wide z direction measurement range.

Description

Technical Field

[0001] This application relates to the field of quantum information technology, and specifically to a nonlocal spatial light field imaging system. Background Technology

[0002] Nonlocal imaging is a novel imaging technique based on quantum optics principles. Its core lies in utilizing non-classical light sources with quantum correlation properties, such as entangled photon pairs, to extract object information through triggered or coincident measurements, thus possessing imaging capabilities that surpass classical limits. Typical nonlocal imaging schemes include ghost imaging and probeless photon imaging. These methods do not require direct detection of photons interacting with the object; instead, they reconstruct object information by measuring photons in another entangled optical path and analyzing the correlation between the two. These methods fully leverage the nonlocal properties of quantum entanglement, freeing the information acquisition process from classical limitations such as "field-of-view resolution" in traditional imaging, and exhibiting unique advantages in low-light and high-noise environments.

[0003] However, most existing nonlocal quantum imaging systems focus on acquiring two-dimensional intensity distributions or projected images of objects. Their imaging process essentially compresses a three-dimensional object into a two-dimensional plane for recording, lacking the ability to perform tomographic measurements of the light field itself along the propagation direction (z-direction). This makes it impossible to reconstruct the complete amplitude and phase evolution of the light field in three-dimensional space, hindering its extension to direct observation and visualization of the dynamic wave function of quantum states. The 2013 paper "Real-Time Imaging of Quantum Entanglement," published in *Science Reports*, Volume 3, No. 1914, significantly improved the signal-to-noise ratio and contrast of the imaging using an enhanced charge-coupled device (ICCD) and nonlocal triggering measurements. It also achieved real-time imaging measurements of the influence of a photon and its entangled photons, breaking through the bottleneck of real-time imaging of photon entanglement. However, direct entanglement observation or imaging in the z-direction has not yet been achieved. The paper "Diffraction-Limited Plenoptic Imaging with Correlated Light," published in Volume 119, Issue 243602 of *PHYSICAL REVIEW LETTERS* in 2017, demonstrated that correlation-limited plenoptic imaging can maintain or even improve resolution at higher degrees of freedom, pushing imaging to the fundamental limit set by the wave nature of light. It achieved a seven-fold increase in depth of field while maintaining diffraction-limited imaging resolution. While achieving a certain degree of three-dimensional quantum imaging, it requires multiple measurements and extensive correlation calculations, and is fundamentally limited by the diffraction properties of light and numerical aperture, preventing further expansion of information acquisition in the z-direction. This restricts a deeper understanding and direct observation of the essential behavior of quantum light fields, and also limits the application potential of quantum imaging in three-dimensional sensing, high-dimensional quantum information processing, and other fields. Summary of the Invention

[0004] This application provides a nonlocal spatial light field imaging system, which aims to solve the problems mentioned in the background art, realize the acquisition of the evolution information of the entire light field on a single ICCD detection plane, and complete the spatial entangled light field tomography measurement.

[0005] In one embodiment, this application provides a non-local spatial light field imaging system, comprising: The entangled light source preparation module includes a PPKTP entangled source based on a Sagnac interferometer, which is used to generate polarization-based entangled photon pairs and separate the entangled photon pairs into signal photons and idler photons; The trigger optical path includes a first waveplate, a polarization beamsplitter, and a single-photon avalanche diode connected together. The first waveplate and the polarization beamsplitter form a polarization projection system for selecting the projection of signal photons onto different polarization substrates. The single-photon avalanche diode is used to receive the signal photons selected by the polarization projection system and convert them into electrical signals for output. The idler optical path includes a first Sagnac interferometer, a spatial light modulator, a second Sagnac interferometer, and a 4f system. The first Sagnac interferometer splits the idler photons based on orthogonal polarization. The spatial light modulator receives and modulates the two split beams. The second Sagnac interferometer combines the two modulated beams into one. The 4f system processes and outputs the combined beam. The coincidence imaging module includes a second waveplate, a third Sagnac interferometer, an enhanced charge-coupled device (ECD), and a coincidence counting unit. The second waveplate projects the output beam of the 4f system onto a predetermined polarization base before it enters the third Sagnac interferometer. The third Sagnac interferometer splits the beam into two parallel beams and outputs them to the ECD. The coincidence counting unit receives the signal output by the single-photon avalanche diode and uses the arrival of the signal photon as a gating signal to trigger the ECD through coincidence measurement.

[0006] In an optional embodiment, the entangled light source fabrication module further includes: The system comprises a first half-wave plate, a dichroic mirror, and several reflectors. The pump light, after being adjusted by the first half-wave plate, is reflected by the dichroic mirror into the PPKTP entangled source based on the Sagnac interferometer. The first half-wave plate is used to adjust the polarization of the incident pump light to balance the clockwise and counterclockwise pump light power within the PPKTP entangled source based on the Sagnac interferometer. Signal photons output from the PPKTP entangled source based on the Sagnac interferometer pass through the dichroic mirror and, after being oriented by the several reflectors, enter the trigger light path. Idle photons output from the PPKTP entangled source based on the Sagnac interferometer are oriented by another correspondingly configured reflector and then enter the idler light path.

[0007] In one alternative, the first waveplate is a half-wave plate or a quarter-wave plate.

[0008] In one alternative, the PPKTP entanglement source based on the Sagnac interferometer is a loop consisting of two broadband mirrors, a dual-wavelength polarization beam splitter, and a periodically polarized potassium titanyl phosphate crystal, with a dual-wavelength half-wave plate disposed within the loop.

[0009] In an alternative embodiment, the idler optical path further includes: The second half-wave plate is positioned between the first Sagnac interferometer and the spatial light modulator. The horizontally polarized beam output from the first Sagnac interferometer is adjusted to a vertically polarized beam by the second half-wave plate before entering the spatial light modulator for modulation. The vertically polarized beam output from the first Sagnac interferometer is adjusted by the spatial light modulator and then reversed by the second half-wave plate to be adjusted to a horizontally polarized beam. Finally, the two beams are oriented by a mirror and then enter the second Sagnac interferometer for beam combining.

[0010] In one alternative embodiment, the idler photon output of the entangled light source preparation module is connected to the input of the idler optical path via a single-mode optical fiber of a predetermined length.

[0011] In one alternative, the second waveplate is a half-wave plate or a quarter-wave plate.

[0012] In an alternative embodiment, the coincidence imaging module further includes: A lens is positioned between the second waveplate and the third Sagnac interferometer. The output beam of the 4f system is first adjusted by the second waveplate, then focused by the lens, and finally enters the third Sagnac interferometer.

[0013] In one alternative embodiment, the first, second, and third Sagnac interferometers each consist of a polarization beam splitter and two mirrors.

[0014] In one alternative, the 4f system includes two lenses and a small aperture disposed between the two lenses.

[0015] The beneficial effects of this application are: This application provides a practical system for measuring three-dimensional quantum space light fields. It has the function of non-local quantum state measurement in the z-direction, realizes non-local imaging and tomographic measurement of quantum light fields on a single ICCD detector plane, and obtains its three-dimensional space wave function information. It also has the advantages of high accuracy and wide measurement range in the z-direction. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the composition and optical path of a non-localized spatial light field imaging system according to an embodiment of this application; Figure 2 This is a schematic diagram of direct observation of a three-dimensional quantum light field based on polarization tomography in one embodiment of this application; Figure 3 This is a schematic diagram of a silicon-based liquid crystal (SLM) structure.

[0018] Labels for each item in the figure: 100. Entangled light source preparation module; 101. PPKTP entangled source based on Sagnac interferometer; 102. First half-wave plate; 200. Trigger optical path; 201. First wave plate; 300. Irregular optical path; 301. First Sagnac interferometer; 302. Second Sagnac interferometer; 303. Second half-wave plate; 400. Coincidence imaging module; 401. Third Sagnac interferometer; 402. Coincidence counting unit; 403. Second wave plate; M, mirror; BM, broadband mirror; PPKTP, periodically polarized potassium titanate phosphate crystal; PBS, polarization beam splitter; D-PBS, dual-wavelength polarization beam splitter; HWP, half-wave plate; QWP, quarter-wave plate; D-HWP, dual-wavelength half-wave plate; DM, dichroic mirror; SPAD, single-photon avalanche photodiode; SLM, spatial light modulator; ICCD, enhancement-coupled device; lens; iris, pinhole. Detailed Implementation

[0019] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application. Similarly, the following examples are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0023] Based on the principles of quantum optics, the light field to be measured (idle light) is separated from its entangled signal photons (signal light). Utilizing the inherent non-local correlation properties of entangled photon pairs, and based on the principle of coincidence measurement, measurement events for the light field are selected by choosing the signal photons. This method spatially separates the detection of the target light field from its state preparation, and allows for the selection of measurement basis vectors through the manipulation of the signal photons. After constructing a virtual diffraction process using digital phase conjugation technology on the idler light, the signal photons are used as the gating signal to trigger the measurement. Complete projection measurements of the idler light field on a fixed plane are performed to obtain information about its quantum state under specific basis vectors. This allows for direct observation of the entanglement and dynamic wave function during the propagation of the idler light field.

[0024] Entangled two-photon states are key to achieving correlated photon-triggered imaging, typically prepared via spontaneous parametric downconversion (SPDC) at low gain. In the imaging system, the entangled photon pair is split into a signal photon and an idler photon, each entering a separate optical path. The strong correlation between the two photons allows the detection of one photon to trigger the measurement of the other. Therefore, after determining the quantum state, the detection of the signal photon can be used to filter out the corresponding idler photon information, thereby achieving nonlocal correlated imaging.

[0025] The standard method for characterizing quantum states is quantum state tomography, typically involving multiple tomographic measurements performed on a fixed measurement plane, known as projection measurements. Each measurement probes a specific aspect of a possible state. A specific measurement of a quantum system corresponds to a Hermitian operator whose eigenstates form a set of orthogonal bases. A "projection measurement" of the system projects its state onto one of the eigenstates of this base, and the eigenvalue is used as the measurement result. A complete quantum state is established by performing a series of projection measurements on different bases. In quantum optics, this technique has been successfully applied to characterize degrees of freedom such as photon polarization states, orbital angular momentum states, and spatial mode states. Taking polarization degrees of freedom as an example, for this two-dimensional quantum system, a set of unbiased orthogonal bases (complementary orthogonal bases, where for any state vector of one orthogonal base, the probability of obtaining any specific result when measured on the other orthogonal base is the same. This basis selection allows for obtaining maximum information with minimal measurements) is typically chosen to achieve complete measurement. Examples include horizontal polarization (H), vertical polarization (V), diagonal polarization (D), anti-diagonal polarization (A), left-handed circular polarization (L), and right-handed circular polarization (R) as measurement bases. Through statistical analysis of the measurement results, the mathematical description of the quantum state (e.g., density matrix) is reconstructed. Combining the selectivity and labeling capabilities of nonlocal imaging, the construction of the idler beam projection base can be achieved by modulating spatially separated and entangled signal beams.

[0026] Normally, projection measurements can only be performed on a fixed plane. To measure in three dimensions, it usually means that the detector needs to be moved, which will introduce larger systematic errors and affect the measurement accuracy.

[0027] Based on this, this application employs digital phase conjugation technology to simulate the diffraction process of the light field, achieving full propagation domain field distribution reconstruction within a single observation plane. Based on Fresnel diffraction theory, by loading a specific phase in the frequency domain and performing a Fourier transform, the light field distribution at any propagation distance can be accurately reconstructed. Combining the aforementioned nonlocal imaging and quantum state tomography principles, loading a digital propagation phase onto idler photons enables tomographic measurement and imaging of the spatial light field at arbitrary propagation positions within a fixed plane.

[0028] In some implementations, please refer to Figure 1 This application provides a non-local spatial light field imaging system, comprising: The entangled light source preparation module 100 includes a PPKTP entangled source 101 based on a Sagnac interferometer, which is used to generate polarization-based entangled photon pairs and separate the entangled photon pairs into signal photons and idler photons; The trigger optical path 200 includes a first waveplate 201, a polarization beam splitter PBS, and a single-photon avalanche diode SPAD connected in series. The first waveplate 201 and the polarization beam splitter PBS form a polarization projection system, which is used to select the projection of signal photons on different polarization substrates. The single-photon avalanche diode SPAD is used to receive the signal photons selected by the polarization projection system and convert them into electrical signals for output. The idler optical path 300 includes a first Sagnac interferometer 301, a spatial light modulator (SLM), a second Sagnac interferometer 302, and a 4f system. The first Sagnac interferometer 301 splits the idler photons based on orthogonal polarization. The SLM receives and modulates the two split beams. The second Sagnac interferometer combines the two modulated beams into one. The 4f system processes and outputs the combined beam. The coincidence imaging module 400 includes a second waveplate 403, a third Sagnac interferometer 401, an enhancement charge-coupled device (ICCD), and a coincidence counting unit 402. The second waveplate 403 projects the output beam of the 4f system onto a predetermined polarization base and then into the third Sagnac interferometer 401. The third Sagnac interferometer 401 splits the beam into two parallel beams and outputs them to the ICCD. The coincidence counting unit receives the signal output by the single-photon avalanche diode (SPAD) and then uses the arrival of the signal photon as a gating signal to trigger the ICCD through coincidence measurement.

[0029] In this embodiment, the entangled light source preparation module 100 employs the SPDC process of a PPKTP entangled source 101 based on a Sagnac interferometer to generate high-fidelity polarization-based entangled photon pairs. As an example, a continuous-wave 780 nm laser (TOPTICA Photonics TA pro_025154) is first frequency-doubled (SHG) through a periodically polarized potassium titanyl phosphate crystal (PPKTP) to generate 390 nm frequency-doubled light as pump light. As an example, the entangled photon pair is generated in a 10 mm long type II PPKTP crystal, with the crystal temperature controlled at the temperature corresponding to the 780 nm degenerate wavelength. Physically, this involves generating a 390 nm polarization-based entangled photon pair. The photon is converted into a 780 nm... Photon and a 780 nm Photon. The output state of the polarization-entangled degenerate photon pair generated at this time can be written as: Entangled photon pairs generated by pump light in different clockwise directions are separated into signal photons and idler photons by a dual-wavelength polarization beam splitter (D-PBS), which then enter the trigger optical path and the idler optical path, respectively. Figure 1 The trigger optical path 200 and the idler optical path 300 are shown. Signal photons enter the trigger optical path 200, and idler photons enter the idler optical path 300.

[0030] In the trigger optical path 200, the signal photon first passes through a polarization projection system composed of a first waveplate 201 and a polarization beam splitter PBS, enabling the selection of projection onto different polarization substrates. By adjusting the angle of the first waveplate 201, the projection substrate can be set to... , , , , or These are mutually unbiased orthogonal bases. Therefore, density matrices corresponding to different Bell states can be generated through local operations on the first waveplate. For example, inserting a... HWP can transform the original Bell state represented by equation (4-1) into: This control method allows us to freely select the projection of the signal photon in a specific polarization state as the trigger signal, and non-locally select the corresponding idler photon in the idler optical path. The selected signal photon is received by a single-photon avalanche diode SPAD (LBTEK SPD500A-FC), which converts the optical signal into an electrical signal and outputs a coincidence counting unit 402 (HydraHarp 400 M). The arrival of the photon is used as the trigger signal through coincidence measurement, and this signal is used as the external trigger gating to control the enhancement-mode charge-coupled device (ICCD, PI-MAX4).

[0031] The spatial light field modulation of the idler optical path 300 employs a dual Sagnac ring structure to achieve beam splitting and combining based on polarization, and combines this with a spatial light modulator (SLM) to complete complex amplitude modulation and digital propagation phase loading of the light field. As an example, idler photons are first injected into the first Sagnac interferometer 301. At the PBS, the photons are split based on orthogonal polarization: |H> photons are transmitted through the PBS, propagating counterclockwise along the loop, and returning to the PBS while still being transmitted through the outgoing interferometer. |V> photons are reflected through the PBS, propagating clockwise along the loop, and returning to the PBS while still being reflected through the outgoing interferometer. Here, by adjusting the tilt angles of the two mirrors M, the outgoing beams can be separated in parallel, achieving the physical effect of separating the beams by |H> and |V>. The two separated beams are then respectively incident on the spatial light modulator (SLM) for modulation, performing precise complex amplitude modulation and loading of the digital propagation phase. The two modulated beam components are combined in the second Sagnac interferometer 302. The physical process is the reverse of the loop in the first Sagnac interferometer 301. The parallel beams |H> and |V> are combined into one beam by adjusting the tilt angle of the mirror. After being processed by the 4f system, the photons of the combined beam enter the coincidence imaging module and are focused by the lens onto the ICCD detection surface in the coincidence imaging module 400.

[0032] In the coincidence imaging module 400, the beam is split by the third Sagnac interferometer 401 to achieve the double-slit effect. The third Sagnac interferometer 401 splits the beam into two parallel beams. The starting point of the output polarization beam splitter PBS is the same as the starting point of the double slits, and the beam spacing is the same as the double slit spacing. The second waveplate 403 placed in front of the third Sagnac interferometer 401, combined with the polarization beam splitter PBS in the third Sagnac interferometer 401, forms a polarization analyzer-like structure that can project the beam onto other polarization bases, thereby realizing polarization selection in the quantum double-slit experiment. Thus, the two parallel beams output from the third Sagnac interferometer 401 are completely equivalent to the beam state after passing through the two slits in the quantum double-slit interference experiment, and the evolution information of the entire light field can be obtained on a single observation plane by adjusting the digital propagation phase.

[0033] Please see Figure 2 Figure (a) is a schematic diagram of direct observation of a three-dimensional quantum light field based on polarization tomography, as shown in one example of this application. Specifically, Figure (a) is a schematic diagram of the spatial wave function visualization of the quantum light field, illustrating the direct observation of the quantum light field based on polarization tomography. The entangled Bell state light field was obtained through polarization tomography measurements at different z-direction positions, thus revealing the propagation and evolution of the entire quantum light field. Figure (b) shows the measurement results visualized in Figure (a) using a parametric sphere. The longitudes of points on the sphere's surface are... Color coding, latitude Encoded by brightness. Each point on the sphere corresponds to an isospin profile of the polarization vector in three-dimensional real space (dark towards the south pole, spin down; bright towards the north pole, spin up). Figure (c) shows the two-dimensional measurement results of part of the propagation distance, which shows the propagation distances of 4.3... And 10.0 The results of two-dimensional polarization-spatial mode vector measurement of the light field are compared with the complete tomographic measurement results under an unbiased orthogonal polarization basis. It is evident that the spatial mode degree of freedom and polarization degree of freedom of the double-slit interference light field based on orthogonal polarization exhibit classical entanglement (mathematically expressed as the inseparability of different degrees of freedom of light into a product), and can be considered a vector structure. The propagation of this structure in the light field results in a change in the interference area, thus allowing for more in-depth analysis and the acquisition of more information in the z-direction. Combined with the manipulation of the digital propagation phase, complete polarization tomographic measurement of the light field can obtain complete polarization-spatial mode information, acquiring the three-dimensional spatial wave function of the quantum light field. This application provides a practical system for measuring three-dimensional quantum spatial light fields, possessing the capability to achieve non-local quantum state measurement in the z-direction, while also offering advantages such as high accuracy and a wide measurement range in the z-direction.

[0034] In one example, the spatial light modulator is a silicon-based liquid crystal (SLM), with the structure shown below. Figure 3 As shown, a liquid crystal layer is sandwiched between two transparent alignment films, which are attached to a transparent electrode layer and covered with a planar glass substrate. The bottom is a silicon substrate, and the top is an active matrix circuit directly connected to the pixelated metal electrodes. This circuit controls the orientation of liquid crystal molecules at each pixel. Its core working principle is based on the electric field-controlled birefringence effect of nematic liquid crystal materials to achieve pixel-level dynamic phase modulation. Therefore, the polarization direction of the incident light needs to be aligned with the optical axis of the liquid crystal molecules to ensure that the incident light propagates entirely in the form of e-rays, achieving the set modulation effect. Otherwise, an inappropriate polarization direction will cause a rapid decrease in modulation efficiency and introduce uncontrollable additional modulation. In this example, the SLM-based method requires the incident light to be in the |H> state. Therefore, the idler optical path of this application also includes: a second half-wave plate 303, which is disposed between the first Sagnac interferometer 301 and the spatial light modulator (SLM). The horizontally polarized beam output by the first Sagnac interferometer 301... The beam is adjusted to vertical polarization by the second half-wave plate 303. The beam is then modulated by the spatial light modulator (SLM). Furthermore, the vertically polarized beam |H> output from the first Sagnac interferometer 301, after being adjusted by the SLM, is redirected from its reverse direction and then passed through the second half-wave plate 303 to become a horizontally polarized beam. Finally |H>、 After the two beams are oriented by a reflecting mirror M, they enter the second Sagnac interferometer 302 to achieve beam combining. Thus, by utilizing a clever optical path design, the beams of the first Sagnac interferometer 301 are first adjusted to be |H> light through the same second half-wave plate 303 to meet the incident requirements of the SLM. Then, the original |H> light is modulated and reversed to be converted into |V> light to meet the beam combining requirements of the second Sagnac interferometer 302.

[0035] In one example, the entangled light source preparation module 100 further includes: a first half-wave plate 102, a dichroic mirror DM, and several reflecting mirrors M; the pump light is adjusted by the first half-wave plate 102 and then reflected by the dichroic mirror DM into the PPKTP entangled source 101 based on the Sagnac interferometer. The first half-wave plate 102 is used to adjust the polarization of the incident pump light to balance the pump light power in the clockwise and counterclockwise directions within the PPKTP entangled source 101 based on the Sagnac interferometer. After the signal photons output from the PPKTP entangled source 101 based on the Sagnac interferometer pass through the dichroic mirror DM, they are oriented by several reflecting mirrors M and then enter the trigger light path 200. The idler photons output from the PPKTP entangled source based on the Sagnac interferometer are oriented by another correspondingly configured reflecting mirror M and then enter the idler light path 300.

[0036] In some implementations, the first waveplate may be a half-wave plate (HWP) or a quarter-wave plate (QWP). The second waveplate may be a half-wave plate (HWP) or a quarter-wave plate (QWP).

[0037] In some implementations, the Sagnac interferometer-based PPKTP entangled source can be a loop consisting of two broadband mirrors, a dual-wavelength polarization beamsplitter (D-PBS), and a periodically polarized potassium titanyl phosphate crystal, with a dual-wavelength half-wave plate disposed within the loop. Pump light, after being focused, is injected into the Sagnac interferometer-based PPKTP entangled source, which consists of a Sagnac interferometer loop composed of two broadband mirrors and a dual-wavelength (390 nm / 780 nm) polarization beamsplitter (D-PBS).

[0038] In some implementations, the idler photon output of the entangled light source preparation module 100 is connected to the input of the idler optical path 300 via a single-mode fiber 102 of a predetermined length. The single-mode fiber 102 serves as an optical delay line to match the electrical delay response of the trigger signal in the trigger optical path 200. This ensures that the photons detected by the single-photon avalanche diode (SPAD) and the photons arriving at the ICCD from the idler optical path 300 originate from the same entangled pair, thereby ensuring that each photon recorded by the ICCD is gated by the corresponding trigger photon, guaranteeing the accuracy of signal acquisition.

[0039] In some embodiments, the coincidence imaging module 400 further includes: The lens is positioned between the second waveplate 403 and the third Sagnac interferometer 401. The output beam of the 4f system is first adjusted by the second waveplate 403, then focused by the lens before entering the third Sagnac interferometer 401. This focusing not only increases the power density but, more importantly, enables a Fourier transform, allowing observation of the spatial domain information of the optical field after loading the digital propagation phase in the frequency domain—that is, the reconstructed propagated optical field distribution.

[0040] In some implementations, the 4f system includes two lenses and an iris aperture positioned between the two lenses. The beam is spatially filtered through the 4f system, utilizing the iris aperture placed at the focal point within the 4f system to filter out higher-order components generated by SLM modulation.

[0041] This application provides a practical method for measuring three-dimensional quantum space light fields, which can realize the function of non-local quantum state measurement in the z direction, realize non-local imaging and tomographic measurement of quantum light fields on a single ICCD detector plane, obtain its three-dimensional space wave function information, and has the advantages of high accuracy and wide measurement range in the z direction.

[0042] The above are merely some embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A non-local spatial light field imaging system, characterized in that, include: The entangled light source preparation module includes a PPKTP entangled source based on a Sagnac interferometer, which is used to generate polarization-based entangled photon pairs and separate the entangled photon pairs into signal photons and idler photons; The trigger optical path includes a first waveplate, a polarization beamsplitter, and a single-photon avalanche diode connected together. The first waveplate and the polarization beamsplitter form a polarization projection system for selecting the projection of signal photons onto different polarization substrates. The single-photon avalanche diode is used to receive the signal photons selected by the polarization projection system and convert them into electrical signals for output. The idler optical path includes a first Sagnac interferometer, a spatial light modulator, a second Sagnac interferometer, and a 4f system. The first Sagnac interferometer splits the idler photons based on orthogonal polarization. The spatial light modulator receives and modulates the two split beams. The second Sagnac interferometer merges the two modulated beams into one beam. The 4f system processes and outputs the merged beam. and The coincidence imaging module includes a second waveplate, a third Sagnac interferometer, an enhanced charge-coupled device (ECD), and a coincidence counting unit. The second waveplate projects the output beam of the 4f system onto a predetermined polarization base before it enters the third Sagnac interferometer. The third Sagnac interferometer splits the beam into two parallel beams and outputs them to the ECD. The coincidence counting unit receives the signal output by the single-photon avalanche diode and uses the arrival of the signal photon as a gating signal to trigger the ECD through coincidence measurement.

2. The non-local spatial light field imaging system according to claim 1, characterized in that, The entangled light source preparation module also includes: The system comprises a first half-wave plate, a dichroic mirror, and several reflectors. The pump light, after being adjusted by the first half-wave plate, is reflected by the dichroic mirror into the PPKTP entangled source based on the Sagnac interferometer. The first half-wave plate is used to adjust the polarization of the incident pump light to balance the clockwise and counterclockwise pump light power within the PPKTP entangled source based on the Sagnac interferometer. The signal photons output from the PPKTP entangled source based on the Sagnac interferometer penetrate the dichroic mirror and, after being oriented by the several reflectors, enter the trigger light path. The idler photons output from the PPKTP entangled source based on the Sagnac interferometer are oriented by another correspondingly configured reflector and then enter the idler light path.

3. The non-local spatial light field imaging system according to claim 1, characterized in that: The first waveplate is a half-wave plate or a quarter-wave plate.

4. The non-local spatial light field imaging system according to claim 1, characterized in that: The PPKTP entanglement source based on the Sagnac interferometer consists of a loop composed of two broadband mirrors, a dual-wavelength polarization beam splitter, and a periodically polarized potassium titanium phosphate crystal, with a dual-wavelength half-wave plate disposed within the loop.

5. The non-local spatial light field imaging system according to claim 1, characterized in that, The idler optical path also includes: The second half-wave plate is positioned between the first Sagnac interferometer and the spatial light modulator. The horizontally polarized beam output from the first Sagnac interferometer is adjusted to a vertically polarized beam by the second half-wave plate before entering the spatial light modulator for modulation. The vertically polarized beam output from the first Sagnac interferometer is adjusted by the spatial light modulator and then reversed by the second half-wave plate to be adjusted to a horizontally polarized beam. Finally, the two beams are oriented by a mirror and then enter the second Sagnac interferometer for beam combining.

6. The non-local spatial light field imaging system according to claim 1, characterized in that: The idler photon output terminal of the entangled light source preparation module is connected to the input terminal of the idler optical path via a single-mode optical fiber of a predetermined length.

7. The non-local spatial light field imaging system according to claim 1, characterized in that: The second waveplate is a half-wave plate or a quarter-wave plate.

8. The non-local spatial light field imaging system according to claim 1, characterized in that, Also includes: A lens is positioned between the second waveplate and the third Sagnac interferometer. The output beam of the 4f system is first adjusted by the second waveplate, then focused by the lens, and finally enters the third Sagnac interferometer.

9. The non-local spatial light field imaging system according to claim 1, characterized in that: The first, second, and third Sagnac interferometers each consist of a polarization beam splitter and two mirrors.

10. The non-local spatial light field imaging system according to claim 1, characterized in that: The 4f system includes two lenses and a small aperture disposed between the two lenses.

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