A quantum light source based on waveguide-type periodically polarized lithium niobate

Abstract

This invention discloses a quantum light source based on waveguide-type periodically polarized lithium niobate (PPLN). The quantum light source includes a laser source, an intensity modulator, a PPLN optical waveguide device, a first phase modulator, a second phase modulator, and a control and drive unit integrated into a single module. All optical components are internally connected via polarization-maintaining fibers. The intensity modulator modulates the pump light output from the laser source; the PPLN optical waveguide device converts the pump light into entangled photon pairs; the first and second phase modulators independently modulate the phases of the signal photon and the idler photon; and the control and drive unit provides system-level coordinated closed-loop control for all components. This invention, through system-level integrated innovation, achieves an all-fiber, multifunctional, dynamically tunable, and highly stable quantum light source, greatly improving the practicality and ease of use of quantum systems.

Description

Technical Field

[0001] This invention relates to the field of quantum information technology, and in particular to a quantum light source based on waveguide-type periodically polarized lithium niobate (PPLN). Background Technology

[0002] Quantum entangled light sources are a key component in cutting-edge applications such as quantum communication, quantum computing, and quantum sensing. Currently, commonly used methods for fabricating quantum entangled light sources include: spontaneous parametric down-conversion (SPDC) using nonlinear crystals, four-wave mixing, and quantum dot fabrication.

[0003] Currently, considering factors such as integration, controllability, and portability, existing quantum light source technologies still have the following significant shortcomings:

[0004] 1) Complex system and demanding environmental requirements: Traditional quantum light sources based on space optical systems contain a large number of independent optical components, requiring complex and precise optical path collimation. These systems are extremely sensitive to environmental vibrations and temperature changes, have poor stability, and are difficult to operate reliably for long periods outside of the laboratory.

[0005] 2) Low integration and separation of control functions: Existing solutions typically separate the light source generation module from the modulation module (such as intensity modulation and phase modulation), requiring users to build external optical paths to manipulate the quantum state. This not only increases the size and complexity of the system but also introduces additional fiber connection losses and instabilities, and is not conducive to system-level coordinated control.

[0006] 3) Limited functionality and poor flexibility: Most existing light source modules have fixed functions and can only produce qubits of specific shapes and states. Users cannot flexibly switch between continuous light and pulsed light modes according to application requirements, and there is also a lack of open internal interfaces to encode or shape the output quantum state in real time, which greatly limits their application in diverse quantum protocols. Summary of the Invention

[0007] This invention aims to address the technical problems of existing technologies, such as system complexity, low integration, and poor flexibility, and provides a quantum light source based on waveguide-type periodically polarized lithium niobate that is small in size, highly integrated, multifunctional, stable in performance, and easy to control.

[0008] The present invention addresses the aforementioned technical problems primarily through the following technical solution: a quantum light source based on waveguide-type periodically polarized lithium niobate, comprising:

[0009] A laser source provides the pump light signal;

[0010] An intensity modulator modulates the pump light signal.

[0011] Periodically polarized lithium niobate optical waveguide devices convert intensity-modulated pump light signals into entangled photon pairs, including signal photons and idler photons, through spontaneous parametric down-conversion;

[0012] The first phase modulator modulates the phase of the signal photons;

[0013] The second phase modulator modulates the phase of the idler photons;

[0014] The control drive unit (PCBA) is electrically connected to the laser source, intensity modulator, periodically polarized lithium niobate optical waveguide device, first phase modulator and second phase modulator, and coordinates the output state of the laser source, the modulation state of the intensity modulator, the temperature of the periodically polarized lithium niobate optical waveguide device, the modulation state of the first phase modulator and the modulation state of the second phase modulator.

[0015] The laser source, intensity modulator, periodically polarized lithium niobate optical waveguide device, first phase modulator and second phase modulator are integrated into a single module and connected internally via polarization-maintaining fiber.

[0016] Unlike traditional spatial optical coupling, this solution utilizes a fully polarization-maintaining fiber optic path for transmission, effectively improving optical transmission efficiency. The control and drive unit is configured to receive external commands and generate drive signals to control the intensity modulator and phase modulator respectively, thereby achieving dynamic tunability of the light source output shape and output quantum state. The PCBA achieves coordinated optimization of optical, electrical, and thermal aspects, ensuring the performance of the entire integrated module. For example, the modulator's drive signal may need to be synchronized with the laser's state, and the PPLN's temperature needs to be extremely stable to guarantee entanglement quality. Such coordinated control is difficult to achieve efficiently when built discretely. This integration achieves more than just a simple superposition of functions; it also results in significantly improved system stability (no environmental sensitivity to spatial optical coupling), higher efficiency (low-loss transmission through all-fiber optics), greatly enhanced ease of use (users only need an electrical interface to access complex optical functions), and smaller size and lower power consumption.

[0017] Preferably, a splitter and a variable optical attenuator are connected in series between the intensity modulator and the periodically polarized lithium niobate optical waveguide device. The input of the splitter is connected to the output of the intensity modulator. The first output of the splitter outputs the main optical signal to the input of the variable optical attenuator, and the output of the variable optical attenuator is connected to the input of the periodically polarized lithium niobate optical waveguide device. The second output of the splitter outputs a monitoring optical signal to the bias controller of the control drive unit. The bias controller generates a bias voltage based on the power of the monitoring optical signal and sends it to the intensity modulator. The bias controller automatically adjusts the bias voltage applied to the intensity modulator based on the monitoring results to actively compensate for the drift of its operating point, thereby stabilizing the extinction ratio of the output optical signal.

[0018] Preferably, the periodically polarized lithium niobate optical waveguide device is configured to generate signal photons and idler photons with mutually orthogonal polarization states through a type II spontaneous parametric down-conversion process, so as to form polarization entangled photon pairs.

[0019] Preferably, the output end of the periodically polarized lithium niobate optical waveguide device is connected to a polarization beam splitter, which outputs signal photons and idler photons with mutually orthogonal polarization states to the input end of the first phase modulator and the input end of the second phase modulator, respectively.

[0020] Preferably, the periodically polarized lithium niobate optical waveguide device includes a waveguide chip, a heat sink, a thermistor, a thermoelectric cooler, and a heat dissipation base. The waveguide chip is a waveguide-type periodically polarized lithium niobate chip. The heat sink and the thermistor are in close contact with the bottom of the waveguide chip. The cooling surface of the thermoelectric cooler is in close contact with the heat sink and the thermistor to form a heat conduction path. The upper surface of the heat dissipation base is in close contact with the heat dissipation surface of the thermoelectric cooler to form a heat conduction path. The thermistor and the thermoelectric cooler are electrically connected to the temperature controller of the control drive unit. The temperature controller accurately stabilizes the operating temperature of the PPLN optical waveguide device through closed-loop feedback to optimize the quasi-phase matching efficiency.

[0021] Preferably, the laser source outputs a continuous wave pump light signal, and the intensity modulator selectively converts the continuous wave pump light signal into pulse light with a repetition frequency on the order of gigahertz, according to the control of the control drive unit.

[0022] Preferably, the first phase modulator and the second phase modulator independently phase modulate the polarized orthogonal signal photons and idler photons to prepare or encode specific polarization-entangled Bell states.

[0023] This solution integrates an intensity modulator at the light source input, which can selectively convert continuous wave laser (CW) into controllable pulsed light, allowing users to choose from multiple optical transmission modes. An integrated phase modulator at the output allows for spectral shaping or shifting of the two output signal beams, providing open modulation functionality for practical applications.

[0024] Preferably, the single module is a plug-and-play integrated packaged module with an electrical communication interface and an optical fiber output interface.

[0025] This solution combines circuitry and optical path design. The circuit design effectively solves the problem of PPLN devices requiring external driving and temperature control, creating ideal pumping conditions. The optical path design effectively solves the power adjustment of the emission source section and improves the stability of output photon pair generation.

[0026] Compared with the prior art, the present invention has the following significant advantages:

[0027] High integration and all-fiber connectivity significantly improve stability and efficiency: This invention integrates core functions such as light source generation, intensity modulation, and phase modulation into a single module, and constructs an all-fiber optical path through internal polarization-maintaining fiber fusion splicing or coupling. This completely eliminates the collimation difficulties and environmental sensitivity issues caused by spatial optical paths, greatly improving the long-term stability, vibration resistance, and optical transmission efficiency of the light source.

[0028] Built-in multi-functional modulation greatly enhances system flexibility and ease of use: By integrating an intensity modulator and a dual-path phase modulator internally, this invention enables a single light source module to possess the ability to select the output mode (continuous / pulse) and manipulate the output quantum state (independent phase encoding). Users do not need to build complex external optical paths; they can achieve diverse function calls simply through the electrical interface, realizing "plug and play" and greatly reducing the construction threshold of quantum systems.

[0029] System-level collaborative control ensures optimal performance and reliability: The proprietary control and drive unit performs unified and collaborative closed-loop control of all optical and electronic devices within the module. In particular, the precise temperature control of the PPLN device and the automatic bias locking of the intensity modulator ensure that the entire light source system can operate in the best condition for a long time and output high-quality, high-fidelity entangled photon pairs. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a quantum light source structure based on waveguide-type periodically polarized lithium niobate according to the present invention;

[0031] Figure 2 This is a schematic diagram of a periodically polarized lithium niobate optical waveguide device according to the present invention.

[0032] In the diagram: 1. Laser source; 2. Intensity modulator; 3. Splitter; 4. Variable optical attenuator; 5. Periodically polarized lithium niobate waveguide (PPLN); 6. Polarization beam splitter; 7. First phase modulator; 8. Second phase modulator; 9. Control drive unit; 51. Waveguide chip; 52. Heat sink; 53. Thermistor; 54. Semiconductor cooler; 55. Heat sink base; 91. Temperature controller. The hollow arrows in the diagram indicate the direction of the optical signal, and the solid thin lines represent electrical connections. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0034] Example: A quantum light source based on waveguide-type periodically polarized lithium niobate, such as... Figure 1 As shown, it includes:

[0035] Laser source (LD) 1 provides continuous wave (CW) pump light signal;

[0036] Intensity modulator 2, under the control of the control drive unit, selectively converts the continuous wave pump light signal into pulse light with a repetition frequency on the order of gigahertz (GHz);

[0037] The periodically polarized lithium niobate optical waveguide device (PPLN)5 converts the intensity-modulated pump light signal into entangled photon pairs, including signal photons and idler photons with mutually orthogonal polarization states, through type II spontaneous parametric down-conversion (SPDC TYPE II).

[0038] The first phase modulator 7 modulates the phase of the signal photons;

[0039] The second phase modulator 8 modulates the phase of the idler photons; the two phase modulators are independent of each other.

[0040] The control drive unit (PCBA) 9 is electrically connected to the laser source, intensity modulator, periodically polarized lithium niobate optical waveguide device, first phase modulator and second phase modulator, and coordinates the output state of the laser source, the modulation state of the intensity modulator, the temperature of the periodically polarized lithium niobate optical waveguide device, the modulation state of the first phase modulator and the modulation state of the second phase modulator.

[0041] The laser source, intensity modulator, periodically polarized lithium niobate optical waveguide device, first phase modulator, and second phase modulator are integrated into a single module and connected internally via polarization-maintaining fiber. The single module is a plug-and-play integrated packaged module with both electrical communication and fiber optic output interfaces.

[0042] Unlike traditional spatial optical coupling, this solution utilizes a fully polarization-maintaining fiber optic path for transmission, effectively improving optical transmission efficiency. The control and drive unit is configured to receive external commands and generate drive signals to control the intensity modulator and phase modulator respectively, thereby achieving dynamic tunability of the light source output shape and output quantum state. The PCBA achieves coordinated optimization of optical, electrical, and thermal aspects, ensuring the performance of the entire integrated module. For example, the modulator's drive signal may need to be synchronized with the laser's state, and the PPLN's temperature needs to be extremely stable to guarantee entanglement quality. Such coordinated control is difficult to achieve efficiently when built discretely. This integration achieves more than just a simple superposition of functions; it also results in significantly improved system stability (no environmental sensitivity to spatial optical coupling), higher efficiency (low-loss transmission through all-fiber optics), greatly enhanced ease of use (users only need an electrical interface to access complex optical functions), and smaller size and lower power consumption.

[0043] A splitter 3 and a variable optical attenuator 4 are connected in series between the intensity modulator and the periodically polarized lithium niobate optical waveguide device. The input of the splitter is connected to the output of the intensity modulator. The first output of the optical splitter outputs the main optical signal (99%) to the input of the variable optical attenuator. The output of the variable optical attenuator is connected to the input of the periodically polarized lithium niobate optical waveguide device. The second output of the optical splitter outputs the monitoring optical signal (1%) to the bias controller of the control drive unit. The bias controller generates a bias voltage according to the power of the monitoring optical signal and sends it to the intensity modulator.

[0044] The output of the periodically polarized lithium niobate optical waveguide device is connected to a polarization beam splitter 6. The polarization beam splitter outputs signal photons and idler photons with mutually orthogonal polarization states to the input of the first phase modulator and the input of the second phase modulator, respectively.

[0045] like Figure 2As shown, the periodically polarized lithium niobate optical waveguide device has a multi-layer structure, including a waveguide chip 51, a heat sink 52, a thermistor 53, a thermoelectric cooler 54, and a heat dissipation base 55. The first layer waveguide chip is a waveguide-type periodically polarized lithium niobate chip. The second layer heat sink (e.g., a small oxygen-free copper block) and the thermistor are in close contact with the bottom of the waveguide chip to form a tight thermal conductivity contact. The heat sink is used to quickly and evenly distribute the heat of the chip, and the thermistor is used to accurately detect the real-time temperature of the waveguide chip. The third layer thermoelectric cooler (TEC) has its cooling surface in close contact with the heat sink and the thermistor to form a thermal conductivity path, which is used to actively cool or heat the waveguide chip. The upper surface of the fourth layer heat dissipation base is in close contact with the heat dissipation surface of the thermoelectric cooler to form a thermal conductivity path, which is used to efficiently conduct the waste heat generated by the TEC during operation to the module shell. The thermistor and the thermoelectric cooler are electrically connected to the temperature controller 91 of the control drive unit to form a high-precision PID closed-loop temperature control system, which can stabilize the temperature of the waveguide chip at a preset value.

[0046] The first and second phase modulators independently phase modulate polarized orthogonal signal photons and idler photons to prepare or encode specific polarization-entangled Bell states.

[0047] Thanks to its integrated functional components and coordinated control, this light source module offers highly flexible application modes. Users can send commands to the control and drive unit via the electrical interface. For example, if the intensity modulator is instructed to operate in pass-through mode (without a modulated signal), the light source outputs continuous-wave entangled photon pairs; if it is instructed to load a GHz high-frequency modulated signal, the light source outputs synchronized entangled photon pulse pairs. Similarly, users can send commands to the control and drive unit to drive the first and second phase modulators to apply independent phases to the separated signal photons and idler photons. In this way, various forms of polarization-entangled Bell states can be easily prepared, or used to implement phase encoding in quantum key distribution protocols such as BB84.

[0048] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0049] Although this document uses terms such as intensity modulator and waveguide-type periodically polarized lithium niobate extensively, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would be contrary to the spirit of the invention.

Claims

1. A waveguide-type periodically poled lithium niobate-based quantum light source, characterized by, The application relates to a polarization entangled photon source, comprising: a laser source for providing a pump light signal; an intensity modulator for intensity modulating the pump light signal; a periodically poled lithium niobate optical waveguide device for converting the intensity-modulated pump light signal into entangled photon pairs including signal photons and idler photons through spontaneous parametric down-conversion; a first phase modulator for phase modulating the signal photons; a second phase modulator for phase modulating the idler photons; a control driving unit electrically connected to the laser source, the intensity modulator, the periodically poled lithium niobate optical waveguide device, the first phase modulator and the second phase modulator, and used for cooperatively controlling the output state of the laser source, the modulation state of the intensity modulator, the temperature of the periodically poled lithium niobate optical waveguide device, the modulation state of the first phase modulator and the modulation state of the second phase modulator; the laser source, the intensity modulator, the periodically poled lithium niobate optical waveguide device, the first phase modulator and the second phase modulator are integrated in a single module, and the internal optical paths are connected through polarization maintaining optical fibers; a splitter and a variable optical attenuator are further connected in series between the intensity modulator and the periodically poled lithium niobate optical waveguide device; the input end of the splitter is connected to the output end of the intensity modulator, the first output end of the optical splitter outputs a main light signal to the input end of the variable optical attenuator, the output end of the variable optical attenuator is connected to the input end of the periodically poled lithium niobate optical waveguide device; the second output end of the optical splitter outputs a monitoring light signal to a bias controller of the control driving unit, the bias controller generates a bias voltage according to the power of the monitoring light signal and sends the bias voltage to the intensity modulator; the laser source outputs a continuous wave pump light signal, and the intensity modulator selects a working mode according to the control of the control driving unit; if the intensity modulator is instructed to work in a straight-through mode without a modulation signal, the light source outputs a continuous wave entangled photon pair; if the intensity modulator is instructed to load a high-frequency modulation signal of GHz, the light source outputs a synchronous entangled photon pulse pair.

2. The waveguide-type periodically poled lithium niobate-based quantum light source of claim 1, wherein, The periodically poled lithium niobate optical waveguide device is configured to generate the signal photons and the idler photons with mutually orthogonal polarization states through a type-II spontaneous parametric down-conversion process, so as to form a polarization entangled photon pair.

3. The waveguide-type periodically poled lithium niobate-based quantum light source of claim 2, wherein, A polarization beam splitter is connected to the output end of the periodically poled lithium niobate optical waveguide device, and the polarization beam splitter outputs the signal photons and the idler photons with mutually orthogonal polarization states to the input end of the first phase modulator and the input end of the second phase modulator respectively.

4. The waveguide-type periodically poled lithium niobate-based quantum light source of claim 1 or 2 or 3, characterized in that, The periodically poled lithium niobate optical waveguide device comprises a waveguide chip, a heat sink, a thermistor, a semiconductor refrigerator and a heat dissipation base; the waveguide chip is a waveguide type periodically poled lithium niobate chip; the heat sink and the thermistor are tightly attached to the bottom of the waveguide chip, the refrigeration surface of the semiconductor refrigerator is tightly attached to the heat sink and the thermistor to form a heat conduction path, and the upper surface of the heat dissipation base is tightly attached to the heat dissipation surface of the semiconductor refrigerator to form a heat conduction path; the thermistor and the semiconductor refrigerator are electrically connected to a temperature controller of the control driving unit respectively.

5. The waveguide-type periodically poled lithium niobate-based quantum light source of claim 2 or 3, wherein, The first phase modulator and the second phase modulator independently phase modulate the polarization-orthogonal signal photons and idler photons to prepare or encode specific polarization entangled Bell states.

6. The waveguide-type periodically poled lithium niobate-based quantum light source of claim 1, wherein, The single module is a plug-and-play integrated packaging module with an electrical communication interface and a fiber output interface.

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