Cvqkd system integrated with microcavity optical frequency comb and implementation method of optical path thereof

Abstract

The application discloses a CVQKD system based on integrated microcavity optical frequency comb, which comprises a sending end, an interference end and a receiving end. The sending end generates optical frequency comb by using an integrated microcavity, modulates entangled photon pairs, sends part of signal light and idler light to the receiving end, performs homodyne detection on the other part of signal light and idler light, records the raw code value, performs classical communication with the receiving end, sends the encrypted message, and processes the key. The interference end generates interference to the communication. The receiving end generates optical frequency comb by using an integrated microcavity, modulates entangled photon pairs, receives the idler light and signal light from the sending end, performs homodyne detection, records the raw code value, performs classical communication with the sending end, decrypts the received message, and processes the key. The application further provides an optical path implementation method of the CVQKD system based on the integrated microcavity optical frequency comb. The application solves the problems of low entanglement degree, high complexity and high power consumption of the existing entangled state continuous variable quantum key distribution system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of quantum key distribution, and relates to a CVQKD system integrated with a microcavity optical comb and an implementation method of an optical path thereof. BACKGROUND

[0002] Continuous variable quantum key distribution (CVQKD, Continuous Variable Quantum Key Distribution) loads information onto continuous variables such as phases, amplitudes and angular momentums of quantum signal pulses, realizes modulation of the quantum signal, and realizes extraction of information by using balanced homodyne measurement at a receiving end, so as to realize transmission of quantum keys. The continuous variable quantum key distribution technology based on entangled states has better noise resistance than other protocols.

[0003] At present, one of the most effective ways to prepare continuous variable quantum entanglement is to use a second-order nonlinear process [45-58], mainly to use a non-degenerate optical parametric amplifier (NOPA, Non-degenerate Optical Parametric Amplifier) to amplify and modulate signal light, idler light and pump light in different proportions from a seed light injection module, and cooperate with a multi-stage peripheral phase locking module to generate a stable entangled source. Thus, there are problems such as complex actual optical path, low locking precision of NOPA cavity length and phase, high crystal thermal effect, and low entanglement degree. SUMMARY

[0004] To achieve the above object, the application provides a CVQKD system integrated with a microcavity optical comb and an implementation method of an optical path thereof, which solves the problems of low entanglement degree, high complexity and high power consumption of the existing entangled state continuous variable quantum key distribution system.

[0005] The technical scheme adopted by the application is a CVQKD system based on an integrated microcavity optical comb, which comprises:

[0006] The sending end: uses the internal integrated microcavity to generate an optical comb, modulates entangled photon pairs in an entangled state for key distribution; sends part of the signal light and idler light to the receiving end, homodyne detects the other part of the signal light and idler light, records the raw code value, and sends it to the receiving end; performs classical communication with the receiving end, sends the encrypted message, and processes the key;

[0007] The interference end: is used for interfering with the communication between the sending end and the receiving end;

[0008] The receiving end utilizes the integrated microcavity to generate an optical frequency comb, modulates entangled photon pairs in an entangled state for key detection, receives idler light and signal light from the sending end, performs homodyne detection on the received idler light and signal light, records the naked code value at this time, performs classical communication with the sending end, decrypts the received message, and post-processes the key.

[0009] Further, the sending end and the receiving end each include a dual-color entangled source generation device based on an integrated microcavity optical frequency comb; the dual-color entangled source generation device includes an optical frequency comb generation module and an entangled source modulation module, wherein the optical frequency comb generation module includes:

[0010] The main continuous tunable laser has a working range of 1480nm-1640nm, is used to provide a main laser pump source for the system, generates a single stable frequency as a center frequency of the optical frequency comb, and has a working range of 1480nm-1640nm.

[0011] The auxiliary continuous tunable laser has a working range of 1480nm-1640nm, is used to perform thermal effect adjustment on the ring microcavity, and ensures that the finally formed optical frequency comb is maintained stable.

[0012] The main ytterbium-erbium co-doped power amplifier is used to amplify the power of the main continuous tunable laser, so as to meet the input power required by four-wave mixing of the ring microcavity.

[0013] The auxiliary main ytterbium-erbium co-doped power amplifier is used to amplify the power of the auxiliary continuous tunable laser, so as to ensure that the purpose of balancing the optical frequency comb in the ring microcavity can be achieved.

[0014] The optical isolator is used to ensure that the output light of the main ytterbium-erbium co-doped power amplifier propagates in one direction, block reflected light from the end face of the pigtail and the circulator, and protect the main ytterbium-erbium co-doped power amplifier from damage caused by impact.

[0015] The auxiliary optical isolator is used to ensure that the output light of the auxiliary main ytterbium-erbium co-doped power amplifier propagates in one direction, block reflected light from the end face of the pigtail and the circulator, and protect the auxiliary main ytterbium-erbium co-doped power amplifier from damage caused by impact.

[0016] The polarization controller is used to filter the light beam from the main continuous tunable laser, select the most suitable polarized light to input into the ring microcavity, ensure that only a single mode is input into the ring microcavity, and enable efficient four-wave mixing effect to form an optical frequency comb.

[0017] The auxiliary polarization controller is used to filter the light beam from the auxiliary main ytterbium-erbium co-doped power amplifier, select the most suitable polarized light to input into the ring microcavity, ensure that only a single mode is input into the ring microcavity, and ensure that no extra polarized light is generated, so as to provide a pure ring microcavity thermal environment.

[0018] Annular microcavity: used for receiving polarized light from polarization controller and auxiliary polarization controller, forming original optical frequency comb.

[0019] Further, the entanglement source modulation module comprises:

[0020] First frequency shaper: used for selecting two groups of photon pairs with the largest correlation from the original optical frequency comb output from the annular microcavity according to the entanglement modulation type, respectively signal photon pairs and idler photon pairs, to form a two-color entangled photon source;

[0021] Phase modulator: used for phase modulation of the entangled photon source, so that the two groups of signal light and idler light are subjected to interference operation respectively, changing the photon state, generating new frequency sidebands distributed at 1 / 2 phase difference of the original signal light and idler light, forming two-color entangled photon pairs;

[0022] Second frequency shaper: used for separating the entangled photon pairs into independent signal light and idler light, the signal light being used for transmitting end modulation key, and the idler light being used for receiving end key analysis;

[0023] Beam splitter: used for splitting the signal light into SIGNAL and SIGNAL1 two parts, the signal light SIGNAL being used for interference with idler light to generate quantum state required by the system during modulation of quantum key, and the signal light SIGNAL1 being directly transmitted to the receiving end through the channel for detection of quantum key by the receiving end.

[0024] Further, the transmitting end further comprises:

[0025] Balanced homodyne detector: used for detecting the interference light generated between the input signal light SIGNAL and idler light by homodyne detection method, extracting the quadrature amplitude component and quadrature phase component of the interference light respectively, and completing the analysis of raw code and key in the continuous extraction process;

[0026] Beam splitter: used for splitting the idler light into two parts for interference with the signal light SIGNAL and beam combination with the signal light SIGNAL1 respectively;

[0027] Amplitude modulator: used for modulating the idler light to generate frequency sideband local oscillator light;

[0028] Polarization beam splitter: used for splitting the local oscillator light signal output by the amplitude modulator into two parts while keeping the polarization state unchanged;

[0029] Faraday mirror: used for injecting the local oscillator light separated by the polarization beam splitter back into the main light path with the same polarization;

[0030] Fiber beam combiner: used for coupling the signal light SIGNAL1 and the local oscillator light into a single-mode fiber with mutually perpendicular polarization directions.

[0031] Further, the receiving end comprises:

[0032] A polarization controller for compensating the polarization of the received light transmitted over a long distance;

[0033] A fiber polarization beam splitter for separating the signal light SIGNAL1 and the local light;

[0034] A polarization beam splitter for splitting the signal light SIGNAL1;

[0035] A Faraday mirror for reflecting the split signal light back to the optical path;

[0036] A fiber optical amplifier for amplifying the local light signal;

[0037] A phase modulator for locking the local light and the signal light SIGNAL1 at different phases;

[0038] A balanced homodyne detector for detecting the local light and the signal light SIGNAL1 at different phases in a homodyne detection manner, extracting the quadrature amplitude component and the quadrature phase component of the interference light respectively, and completing the analysis of the naked code and the key in the extraction process.

[0039] The application further provides an optical path implementation method of a CVQKD system based on an integrated microcavity optical frequency comb, comprising the following steps:

[0040] Step S1, the sending end tests the quadrature components of the signal light SIGNAL and a part of the idler light field after interference by a balanced homodyne detector of a two-color entangled source generation device, and collects the alternating current signal of the balanced homodyne detector into a computer through a data acquisition card to obtain a group of naked codes; then the local light is modulated into pulsed light after being delayed by a polarization beam splitter and a Faraday mirror, the pulsed light and the signal light SIGNAL1 are coupled into an optical fiber, and are sent to the receiving end by the interference end;

[0041] Step S2, the interference end generates interference to the communication between the sending end and the receiving end;

[0042] Step S3, the polarization controller of the receiving end first compensates the polarization of the light signal transmitted over a long distance, separates the signal light SIGNAL1 and the local light through the cooperation of the fiber polarization beam splitter; the separated signal light SIGNAL1 is shot back to the main optical path after being delayed by the polarization beam splitter and the Faraday mirror; the local light is amplified by the fiber optical amplifier and then modulated by the phase modulator, and finally enters the balanced homodyne detector together with the delayed signal light SIGNAL1 to extract the quadrature components and complete the analysis of the key;

[0043] The local light is another part of the idler light which is not interfered with the signal light SIGNAL.

[0044] Further, the working process of the two-color entanglement source generating device in step S1 is as follows:

[0045] The main pump and the auxiliary pump with a frequency interval of multiple free spectral ranges are generated by a main continuous tunable laser and an auxiliary continuous tunable laser, the main pump and the auxiliary pump are amplified by amplifiers, the polarization light in the optical fiber is adjusted to linearly polarized light matching the ring microcavity by a polarization controller, then the main pump and the auxiliary pump enter the ring microcavity from the positive and negative directions respectively, and the optical frequency comb of the Kerr single soliton state is generated from the main pump light path direction through a circulator; the optical frequency comb passes through a first frequency shaper to filter out the unnecessary comb teeth, leaving two groups of sidebands, i.e., a total of four comb teeth, which are input into a phase modulator to generate new frequency sidebands, and finally the signal light and the idler light are separated from the new frequency sidebands by a second frequency shaper, and the signal light is divided into signal light SIGNAL and signal light SIGNAL1 by a beam splitter.

[0046] Further, the delay method of the local oscillator light in step S1 is as follows:

[0047] The polarization beam splitter divides the local oscillator light signal output by the amplitude modulator into two parts while keeping the polarization state unchanged; the separated local oscillator light is reflected by a Faraday mirror, and then the local oscillator light is injected back into the main light path with the same polarization by the Faraday mirror, so as to separate the local oscillator light and the signal light in time, and the local oscillator light is delayed.

[0048] The beneficial effects of the present application are as follows:

[0049] The silicon-based semiconductor processing technology is adopted, which is mature and stable in process, high in reliability and low in power consumption, and can process high-Q silicon nitride ring micro-nano resonant cavities, so that in the case of the same original laser source, a quantum entanglement source with stronger noise robustness and higher entanglement degree can be generated, and finally the CVQKD system can perform quantum key distribution at a longer distance under the same laser power, or a higher key generation rate can be achieved under the same distribution distance, which provides valuable quantum resources for the earlier popularization and landing of quantum key distribution technology. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description, and obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.

[0051] Figure 1is a silicon-based silicon nitride micro-nano resonant cavity quantum light source modulation device schematic diagram of an embodiment of the application; wherein (a) is a top view of the micro-nano resonant cavity, (b) is a straight waveguide cross section.

[0052] Figure 2 is a microcavity layout for microcavity processing.

[0053] Figure 3 is an integrated microcavity optical frequency comb CVQKD system structure schematic diagram of an embodiment of the application.

[0054] Figure 4 is an integrated microcavity optical frequency comb-based two-color entangled source generation device structure schematic diagram of an embodiment of the application.

[0055] Figure 5 is a sending end schematic diagram of an embodiment of the application.

[0056] Figure 6 is a receiving end schematic diagram of an embodiment of the application. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the application.

[0058] Embodiment 1

[0059] The embodiment provides a silicon-based silicon nitride micro-nano resonant cavity quantum light source modulation device, which comprises a straight waveguide and a silicon nitride micro-nano resonant cavity, and can provide stable and efficient entangled sources for quantum computing, quantum secure communication and the like. In the embodiment, the evolution of the wave form in the ring-shaped micro-nano resonant cavity is simulated through simulation, including dispersion curve simulation, soliton simulation, end face coupling efficiency simulation, and Q value and gap simulation, and the microcavity (micro-nano resonant cavity) structure parameters capable of meeting stable and efficient entangled source output are obtained. The specific microcavity structure parameters and materials are shown in the table. Figure 1 The inner diameter radius of the ring-shaped microcavity is 239.1 μm, the outer diameter radius is 240.75 μm, the width of the straight waveguide is 1.8 μm, the length of the straight waveguide is 4.34 mm, the gap between the straight waveguide and the ring-shaped waveguide is 0.5 μm, the length of the coupling waveguide is 300 μm, the height is H = 0.8 μm, the bottom angle is θ = 89°, and the end face width is ​​​​The waveguide has a width of 0.25 μm, the distance from the upper end of the waveguide to the top of the chip is H1=2.7 μm, and the distance from the lower end of the waveguide to the bottom of the chip is H2=4.0 μm.

[0060] Embodiment 2

[0061] In this embodiment, a silicon nitride microcavity is processed by using a micro-nano processing technology. The core technology involved includes electron beam direct writing (EBL), dielectric thin film etching (NMC), mask pattern lithography, and end face cutting and polishing. The lithography pattern and mask design necessary for microcavity processing are completed by Klayout and AutoCAD, as shown in FIG. 2. The required 525um silicon dioxide substrate, 800nm silicon nitride wafer, and tools for microcavity processing are purchased; the EBL, NMC dielectric thin film etching, and wafer slicing and cleaning processes are realized in a foundry, and the required waveguide and microcavity coupled therewith are etched on the surface of the silicon nitride, so as to realize the processing of the silicon nitride microcavity and the waveguide.

[0062] Embodiment 3

[0063] This embodiment provides a CVQKD (continuous variable quantum key distribution) system based on an integrated microcavity (micro-nano resonant cavity) optical frequency comb, as shown in Figure 3 , wherein X A (P A ) represents an amplitude component or a phase component of a signal A, vacuum represents a vacuum state signal, EPR is an entanglement source generation module, Microring Resonator in the module is a micro-ring resonant cavity, S2 and I2 are signal light 2 and idler light 2 in the entanglement source, A and B0 are equivalent to the signal light S2 and the idler light I2 respectively; T represents the transmittance of a transmission channel, X line represents channel noise, Quantum Memory represents a quantum channel storage function that may exist in an interference end Eve, B1 represents a quantum signal after eavesdropping, B2 represents a quantum signal received by a receiving end Bob, EPR1 is an entanglement source generation module, and signal light S3 and idler light I3 generated thereby are used for interferometric measurement, wherein the signal light S3 is input to a beam splitter, and the signal F0 is obtained, and the signals obtained after interference of F0 and B2 are B3 and F respectively, and the amplitude component or the phase component X B (P B). The CVQKD system mainly includes three parts: the sending end (Alice), the receiving end (Bob) and the interference end (Eve). The main functions of the sending end (Alice) are three: first, the integrated micro-nano cavity inside generates an optical frequency comb to modulate the entangled photon pairs in the entangled state for key distribution; second, the signal light is sent to Bob (interfered by Eve in the middle), the idler light is homodyne detected, and the current naked code value is recorded; third, the classical communication with Bob is carried out, the encrypted message is sent, and the key is processed. Since the classical communication part is not the design core, the implementation details are not described. The functions of Bob corresponding to the main functions of the sending end are three: first, the integrated micro-nano cavity inside generates an optical frequency comb to modulate the entangled photon pairs in the entangled state for key detection; second, the idler light from Alice is received and homodyne detected to record the current naked code value; third, the classical communication with Alice is carried out, the received message is decrypted, and the key is post-processed. The function of the interference end (Eve) is to simulate the communication eavesdropping and attack that may occur in the actual situation, and to interfere with the communication between Alice and Bob using the most effective predictable eavesdropping or attack mode. In actual processing, according to the different attack forms of Eve, it is equivalent to the corresponding channel noise.

[0064] Embodiment 4

[0065] This embodiment provides a dual-color entangled source generation device based on an integrated microcavity optical frequency comb, which is shown in Figure 4 , mainly divided into two parts: an optical frequency comb generation module and an entangled source modulation module. The optical frequency comb generation module generates a main pump and an auxiliary pump with a frequency interval of 5 FSR (Free Spectral Range) through two continuous tunable lasers, amplifies them through two amplifiers, adjusts the polarization in the optical fiber to linear polarization matching the microcavity through a polarization controller, then enters the ring micro-nano cavity from the front and back directions, and generates a Kerr single soliton state optical frequency comb from the main pump light path direction through a circulator, which enters the entangled source modulation module. First, the first frequency shaper filters out the unnecessary comb teeth, leaving two groups of sidebands with a total of 4 comb teeth, which are input to the phase modulator to generate new frequency components (sidebands). This symmetric sideband will have a higher degree of entanglement. Finally, the second frequency shaper separates S2 and I2 from the current light beam and distributes them to Alice and Bob for key distribution work. This embodiment mainly includes the following devices:

[0066] The main continuous tunable laser (Main Laser) has a working range of 1480nm~1640nm, and its main function is to provide a main laser pump source for the system to generate a single stable frequency as the center frequency of the optical frequency comb.

[0067] The main ytterbium erbium co-doped power amplifier (EDFA) is mainly used to amplify the power of the main continuous tunable laser to meet the input power required for four-wave mixing in the ring micro-nano resonator.

[0068] The optical isolator (ISO) is used to ensure that the output light of the main ytterbium erbium co-doped power amplifier propagates in one direction, blocks the reflected light from the end face of the tail fiber and the circulator, and protects the power amplifier from damage caused by impact.

[0069] The paddle-shaped mechanical polarization controller (PC) is used to filter the light beam from the main continuous tunable laser, select the most suitable polarized light to input into the ring micro-nano resonator, and ensure that only a single mode is input into the ring microcavity, which can efficiently generate four-wave mixing effect to form an optical frequency comb.

[0070] The auxiliary continuous tunable laser (Aux Laser) has a working range of 1480nm~1640nm, and its main function is to set its output frequency at a suitable distance from the main pump laser (main continuous tunable laser) through experience (program control), and set the output power slightly higher than the main pump laser, to adjust the thermal effect of the ring microcavity, and ensure that the final formed optical frequency comb can maintain stability.

[0071] The function of the auxiliary main ytterbium erbium co-doped power amplifier (EDFA1) is to amplify the power of the auxiliary pump laser (auxiliary continuous tunable laser) to ensure that the purpose of balancing the optical frequency comb in the microcavity can be achieved.

[0072] The auxiliary optical isolator (ISO1) is used to ensure that the output light of the auxiliary power amplifier (auxiliary main ytterbium erbium co-doped power amplifier) propagates in one direction, blocks the reflected light from the end face of the tail fiber and the circulator, and protects the power amplifier from damage caused by impact.

[0073] The auxiliary paddle-shaped mechanical polarization controller (PC1) is used to filter the light beam from the auxiliary pump source, select the most suitable polarized light to input into the ring micro-nano resonator, and ensure that only a single mode is input into the ring microcavity, to ensure that no extra polarized light is generated, and to provide a pure microcavity thermal environment.

[0074] The ring micro-nano resonator (i.e. ring microcavity, Microring Resonator) is a high-Q (quality factor) nonlinear material microcavity. The pump light output from the polarization controller is coupled into the microcavity through a fiber lens. Due to four-wave mixing, new frequency components are generated. When the power coupled into a certain resonant cavity of the microcavity reaches the red detuning region, the optical frequency comb in the form of a gradually emerging single soliton state will be excited. By analyzing the symmetrical teeth of the optical frequency comb, it can be found that there is entanglement. The more stable the soliton state is, the smaller the noise is, and the higher the entanglement degree is.

[0075] The first programmable filter is a frequency demultiplexer which extracts the required frequency from the signal source, i.e. from the original optical frequency comb, according to the type of entanglement modulation we need to select the two groups of photon pairs with the largest correlation, signal photons and idler photons, to form a two-color entangled photon source.

[0076] The phase modulator is used for phase modulation of the entangled photon source, so that the two groups of signal light and idler light are subjected to interference operation, the photon state is changed, a new frequency sideband is generated, which is distributed at 1 / 2 phase difference of the original signal light and idler light, and is called two-color (two-dimensional) entangled photon pairs.

[0077] The second programmable filter is also a frequency demultiplexer which separates the entangled photon pairs into independent signal light and idler light, which are used for Alice to modulate the key and Bob to analyze the key, respectively.

[0078] The beam splitter divides the signal light into two parts, SIGNAL is used for interference with idler light to generate the required quantum state during modulation of the quantum key, and SIGNAL1 is directly transmitted to Bob through the channel for Bob to detect the quantum key.

[0079] Embodiment 5

[0080] This embodiment provides an optical path implementation of an Alice sending end, and an optical path diagram thereof is as shown in Figure 5The quantum channel of the sending end of Alice has two main functions. The first function is to use a balanced homodyne detector to test the quadrature components of the signal light SIGNAL and the idler light I2 after interference, and to collect the AC signal of the detector into the computer through a data acquisition card to obtain a set of raw codes. The second function is to couple the signal light SIGNAL1 and a part of the idler light I2 (i.e. local oscillator light) into an optical fiber to facilitate compatibility with existing communication networks. The sending end uses polarization multiplexing and time division multiplexing technology, which can effectively reduce the additional noise caused by the leakage of local oscillator light (i.e. a part of idler light I2 separated by a beam splitter, locally oscillator, LO light) into the signal light path, affecting the performance of the system. A 1km single-mode optical fiber is used for time division multiplexing. In order to ensure the polarization of the LO light, a Faraday mirror (FM) is used to inject the LO light back into the main light path with the same polarization, separating the LO light and the signal light in time by 10μs. After that, the continuous LO light passes through a 40dB amplitude modulator (AM), which modulates the continuous light into pulsed light with a pulse width of 10μs and a repetition rate of 50kHz / s. The continuous signal light and pulsed LO enter the optical distance single-mode fiber through the fiber coupler, with a difference of 10μs, which can make the two light fields enter the single-mode fiber with perpendicular polarization directions.

[0081] The embodiment mainly includes the following devices:

[0082] The balanced homodyne detector (BPD) uses a homodyne detection method to detect the input mixed light, extracts the quadrature amplitude component and quadrature phase component respectively, and completes the analysis of raw codes and keys in the continuous extraction process.

[0083] The beam splitter (BS) divides the input idler light I2 into two parts, which are used for interference with SIGNAL and beam combination with SIGNAL1 respectively.

[0084] The amplitude modulator (AM) principle is to modulate the amplitude component, i.e. to modulate the I2 light to generate frequency sideband local oscillator light.

[0085] The polarization beam splitter (PBS) is essentially a beam splitter that can divide the signal into two parts while maintaining the polarization state unchanged.

[0086] Faraday mirror (FM) can ensure that the polarization state of the forward transmission light and the polarization state of the reflected light are always orthogonal under any birefringence, so it can be used to eliminate power fluctuations.

[0087] Embodiment 6

[0088] The present embodiment provides a receiving end (Bob), and a light path diagram thereof is shown as follows. Figure 6 The receiving end (Bob) device: after the local light and the signal light SIGNAL1 are transmitted through the same quantum channel, they reach the receiving end. The three-ring polarization controller first compensates the polarization of the light transmitted over a long distance back, separates the signal light SIGNAL1 and the local light through the cooperation of the fiber polarization beam splitter. Consistent with the effect of the 1km fiber and the Faraday mirror on the local light in the Alice end device, the signal light SIGNAL1 corresponds to a delay of 10μs, and the local light and the signal light SIGNAL1 will coincide in time and reach the balanced homodyne detector at the same time. Since the intensity of the local light is weakened after long-distance transmission, it does not meet the signal-to-noise ratio requirements of the balanced homodyne detector, so a fiber optical amplifier (FOA) is added to the local light path. Due to the fluorescence effect of the BOA, there will be strong broadband background light, which needs to be filtered out using a narrowband filter. By using a phase modulator (PM) in the LO light path, the local light and the signal light are locked at different phases to measure different quadrature components. When the relative phase is locked at 0(π) phase, the orthogonal phase component of the signal light field is measured, and when the relative phase is locked at π / 2, the orthogonal amplitude component of the signal light field is measured.

[0089] The above only describes the preferred embodiments of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A CVQKD system based on integrated microcavity optical frequency comb, characterized in that, The application relates to a quantum key distribution system based on an integrated microcavity optical frequency comb. The sending end comprises the following steps: generating an optical frequency comb by using an internal integrated microcavity, modulating entangled photon pairs in an entangled state for key distribution, sending part of signal light and idler light to the receiving end, performing homodyne detection on the other part of signal light and idler light, recording the naked code value, and sending the naked code value to the receiving end; performing classical communication with the receiving end, sending the encrypted message, and processing the key; The interference end is used for interfering with the communication between the sending end and the receiving end. The receiving end comprises the following steps: generating an optical frequency comb by using an internal integrated microcavity, modulating entangled photon pairs in an entangled state for key detection, receiving idler light and signal light from the sending end, performing homodyne detection on the received idler light and signal light, recording the naked code value at the moment, performing classical communication with the sending end, decrypting the received message, and post-processing the key. The sending end and the receiving end both comprise a double-color entangled source generating device based on an integrated microcavity optical frequency comb. The double-color entangled source generating device comprises an optical frequency comb generating module and an entangled source modulating module. A main continuous tunable laser is used for providing a main laser pumping source for the system, generating a single stable frequency, and serving as a center frequency of the optical frequency comb. An auxiliary continuous tunable laser is used for adjusting the thermal effect of the ring microcavity, so that the finally formed optical frequency comb can be maintained stable. A main ytterbium-erbium co-doped power amplifier is used for amplifying the power of the main continuous tunable laser, so that the input power required by four-wave mixing of the ring microcavity can be met. An auxiliary main ytterbium-erbium co-doped power amplifier is used for amplifying the power of the auxiliary continuous tunable laser, so that the purpose of balancing the optical frequency comb in the ring microcavity can be achieved. An optical isolator is used for ensuring that the output light of the main ytterbium-erbium co-doped power amplifier propagates in one direction, blocking the reflected light from the end face of the pigtail and the circulator, and protecting the main ytterbium-erbium co-doped power amplifier from being damaged due to impact. An auxiliary optical isolator is used for ensuring that the output light of the auxiliary main ytterbium-erbium co-doped power amplifier propagates in one direction, blocking the reflected light from the end face of the pigtail and the circulator, and protecting the auxiliary main ytterbium-erbium co-doped power amplifier from being damaged due to impact. A polarization controller is used for filtering the light beam from the main continuous tunable laser, selecting the most suitable polarized light to input into the ring microcavity, ensuring that only a single mode is input into the ring microcavity, and enabling efficient four-wave mixing effect to form the optical frequency comb. An auxiliary polarization controller is used for filtering the light beam from the auxiliary main ytterbium-erbium co-doped power amplifier, selecting the most suitable polarized light to input into the ring microcavity, ensuring that only a single mode is input into the ring microcavity, and ensuring that no extra polarized light is generated, so that a pure ring microcavity thermal environment is provided. The ring microcavity is used for receiving the polarized light from the polarization controller and the auxiliary polarization controller, and forming an original optical frequency comb. The entangled source modulating module comprises the following steps: The first frequency shaper is used to select two groups of photon pairs with the largest correlation from the original optical frequency comb output from the ring microcavity according to the entanglement modulation type, and the two groups of photon pairs are signal photon pairs and idler photon pairs, respectively, to form a two-color entangled photon source; The phase modulator is used for phase modulation of the entangled photon source, so that the two groups of signal light and idler light are subjected to interference operation respectively, the photon state is changed, new frequency sidebands are generated, and the new frequency sidebands are distributed at 1 / 2 phase difference of the original signal light and idler light, to form a two-color entangled photon pair; The second frequency shaper is used to separate the entangled photon pair into independent signal light and idler light, the signal light is used for modulation key at the sending end, and the idler light is used for key analysis at the receiving end. The beam splitter is used to divide the signal light into SIGNAL and SIGNAL1, the signal light SIGNAL is used for interference with the idler light to generate a quantum state required by the system, and the signal light SIGNAL1 is directly transmitted to the receiving end through the channel and is used for detection of the quantum key at the receiving end.

2. The CVQKD system based on integrated microcavity optical frequency comb according to claim 1, characterized in that, The sending end further comprises: The balanced homodyne detector is used to detect the interference light generated between the input signal light SIGNAL and the idler light in a homodyne detection manner, extracts the quadrature amplitude component and the quadrature phase component of the interference light respectively, and analyzes the raw code and the key in the continuous extraction process; The beam splitter is used to divide the idler light into two parts, which are used for interference with the signal light SIGNAL and the signal light SIGNAL1 respectively; The amplitude modulator is used to modulate the idler light to generate a frequency sideband local oscillator light; The polarization beam splitter is used for splitting the local oscillator light signal output by the amplitude modulator into two parts while keeping the polarization state unchanged; The Faraday mirror is used to inject the local oscillator light separated by the polarization beam splitter back into the main light path with the same polarization; The fiber combiner is used to couple the signal light SIGNAL1 and the local oscillator light into a single-mode fiber with perpendicular polarization directions.

3. The CVQKD system based on integrated microcavity optical frequency comb according to claim 1, characterized in that, The receiving end comprises: The polarization controller is used to compensate for the polarization of the received light transmitted over a long distance; The fiber polarization beam splitter is used to separate the signal light SIGNAL1 and the local oscillator light; The polarization beam splitter is used to split the signal light SIGNAL1; The Faraday mirror is used to reflect the split signal light back to the light path; The fiber optical amplifier is used to amplify the local oscillator light signal; The phase modulator is used to lock the local oscillator light and the signal light SIGNAL1 at different phases; The balanced homodyne detector is used to detect the local oscillator light and the signal light SIGNAL1 at different phases in a homodyne detection manner, extracts the quadrature amplitude component and the quadrature phase component of the interference light respectively, and analyzes the raw code and the key in the extraction process.

4. The optical path implementation method of the integrated microcavity optical frequency comb based CVQKD system according to claim 1 or 3, characterized in that, The method comprises the following steps: Step S1, the sending end tests the quadrature components of the signal light SIGNAL output by the double-color entangled source generation device after interference with a part of the idler light through the balanced homodyne detector, and collects the balanced homodyne detector alternating current signal into the computer through the data acquisition card to obtain a group of bare codes; then the local oscillator light is modulated into pulsed light after being delayed by the polarization beam splitter and the Faraday mirror, the pulsed light and the signal light SIGNAL1 are coupled into the optical fiber, and then transmitted to the receiving end by the interference end; Step S2, the interference end interferes with the communication between the sending end and the receiving end; Step S3, the polarization controller of the receiving end first compensates the polarization of the optical signal after long-distance transmission, separates the signal light SIGNAL1 and the local oscillator light through the cooperation of the fiber polarization beam splitter; the separated signal light SIGNAL1 is shot back to the main light path after being delayed by the polarization beam splitter and the Faraday mirror; the local oscillator light is amplified by the fiber optical amplifier and then modulated by the phase modulator, and finally enters the balanced homodyne detector together with the delayed signal light SIGNAL1 to extract the quadrature components and complete the key analysis; The local oscillator light is another part of the idler light that has not been interfered with the signal light SIGNAL.

5. The optical path implementation method of the CVQKD system based on the integrated microcavity optical frequency comb according to claim 4, characterized in that, The working process of the double-color entangled source generation device in step S1 is as follows: The main continuous tunable laser and the auxiliary continuous tunable laser generate main pump and auxiliary pump with a frequency interval of multiple free spectral ranges, the main pump and the auxiliary pump are amplified by the amplifier, the polarization light in the optical fiber is adjusted to linearly polarized light matching the ring microcavity by the polarization controller, and then enters the ring microcavity from the positive and negative directions respectively, and generates a Kerr single soliton state optical frequency comb from the main pump light path direction through the circulator; the optical frequency comb filters out the unnecessary comb teeth through the first frequency shaper, leaving two groups of sidebands, a total of four comb teeth, which are input into the phase modulator to generate new frequency sidebands, and finally the signal light and the idler light are separated from the new frequency sidebands through the second frequency shaper, and the signal light is divided into signal light SIGNAL and signal light SIGNAL1 by the beam splitter.

6. The optical path implementation method of the CVQKD system based on the integrated microcavity optical frequency comb according to claim 4, characterized in that, The delay method of the local oscillator light in step S1 is as follows: The polarization beam splitter divides the local oscillator light signal output by the amplitude modulator into two parts while keeping the polarization state unchanged; after being reflected by the Faraday mirror, the separated local oscillator light is used to inject the local oscillator light into the main light path again with the same polarization, which separates the local oscillator light and the signal light in time, and realizes the delay of the local oscillator light.

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