A Method and System for Mixed Transmission of Wireless Optical Quantum Key and Data

Abstract

The present invention relates to a method and system for wireless optical quantum key and data mixed transmission. The method includes: Step S1: The laser light source of the sending device uses OOK modulation, and the generated modulated optical signal includes: a strong optical signal and a weak optical signal; the weak optical signal is further subjected to polarization modulation to carry key information; the polarization state of the strong optical signal is not changed and its original polarization state is maintained; the mixed transmission signal is obtained and sent; Step S2: The receiving device includes four optical detection paths. When receiving the mixed transmission signal, the transmitted data and the initial key are demodulated according to the number and response state of the optical detection paths that generate responses within each symbol period. Specifically, when receiving the strong optical signal, at least three optical detection paths will generate signal responses; when receiving the weak optical signal, at most only one optical detection path generates a signal response, and at this time, decoding is performed according to this response to obtain the quantum key. The method provided by the present invention saves the cost of the mixed transmission system and reduces the interference of communication signals on quantum signals.

Description

Technical Field

[0001] The present invention relates to the fields of communications and data encryption, and in particular to a method and system for mixed transmission of wireless optical quantum keys and data. Background Art

[0002] Wireless optical communication technology can effectively support data transmission in complex indoor scenarios, outdoor vehicle networks, underwater robots, underwater sensor networks, and other technologies, thereby promoting the development of the Internet of Everything (IoE) in the 6G all-space, all-scenario network. Compared to traditional communication methods such as radio frequency or underwater acoustic waves, wireless optical communication has attracted widespread attention from researchers both domestically and internationally in recent years due to its abundant spectrum resources, support for gigabit-per-second data rates, low transmission latency, strong anti-interference capabilities, and low cost.

[0003] To ensure the secure transmission of wireless optical communication data, quantum key distribution (QKD), a technology that has been theoretically proven to be absolutely secure, can be considered. This technology allows for secure key distribution between senders and receivers, combined with one-time pad encryption to achieve confidential communication.

[0004] Actual wireless optical communication systems typically use LEDs or LDs as light sources. The light they emit is highly directional, requiring precise alignment and rapid tracking of the optical paths between the sender and receiver. To achieve secure communication, the current traditional approach involves adding dedicated equipment for quantum key distribution (QKD). This also requires additional equipment for alignment and tracking of the QKD link's transmitter and receiver, which undoubtedly increases the cost and implementation complexity of the entire wireless optical communication system. Therefore, it is necessary to consider transmitting the quantum key and communication data over the same link to save costs. Existing research on mixed transmission of quantum keys and data often borrows the concept of mixed transmission in optical fiber communications, employing wavelength division multiplexing (WDM) to achieve this. However, because the intensity of classical optical communication signals is far greater than the extremely weak light used in QKD, this mixed transmission method inevitably generates strong interference in the QKD link and places high demands on the color separation performance of the dichroic mirrors at the receiving end. Therefore, reducing the interference of communication signals on quantum signals has become an urgent issue. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method and system for wireless optical quantum key and data mixed transmission.

[0006] The technical solution of the present invention is: a wireless optical quantum key and data mixed transmission method, comprising:

[0007] Step S1: The laser light source of the transmitting device uses OOK modulation, i.e., on-off modulation. The generated modulated optical signal includes: a weak optical signal corresponding to an information bit of 0 and a strong optical signal corresponding to an information bit of 1. The weak optical signal is further subjected to polarization modulation to carry the key information. The strong optical signal is not polarized and remains in its original polarization state. The mixed transmission signal is obtained and sent.

[0008] Step S2: The receiving device includes four optical detection paths. When receiving the mixed transmission signal, the transmitted data and the initial key are demodulated according to the number and response status of the optical detection paths that generate responses within each symbol period: when receiving a strong optical signal, at least three of the optical detection paths will generate signal responses; when receiving a weak optical signal, at most only one of the optical detection paths generates a signal response. At this time, decoding is performed according to this response to obtain the initial key.

[0009] Compared with the prior art, the present invention has the following advantages:

[0010] The present invention discloses a method for mixed transmission of wireless optical quantum key and data. By synchronously controlling the optical intensity emitted by the light source and the working state of the polarization modulator, the polarization state and the signal state can be completely distinguished without causing aliasing. At the same time, the polarization modulator only modulates the weak light and does not modulate the strong light; and the strong optical signal for communication and the weak optical signal carrying the key are distinguished in time, which not only saves the cost of the mixed transmission system but also reduces the interference of the communication signal on the quantum signal. Description of the Drawings

[0011] Figure 1 It is a flowchart of a method for mixed transmission of wireless optical quantum key and data in an embodiment of the present invention;

[0012] Figure 2 It is a schematic structural diagram of a transmitting device in an embodiment of the present invention;

[0013] Figure 3 It is a schematic structural diagram of a receiving device in an embodiment of the present invention;

[0014] Figure 4 It is a diagram of the experimental results of the screening key rate obtained by using the present method for transmission in an embodiment of the present invention;

[0015] Figure 5 It is a diagram of the experimental results of the quantum bit error rate obtained by using the present method for transmission in an embodiment of the present invention. Detailed Embodiments

[0016] The present invention provides a method for mixed transmission of wireless optical quantum key and data, which mixes and transmits the quantum key and communication data on the same optical link and the same wavelength channel, saving the cost of the mixed transmission system and reducing the interference of the communication signal on the quantum signal.

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention through specific embodiments in conjunction with the accompanying drawings.

[0018] Embodiment 1

[0019] As Figure 1 shown, a method for mixed transmission of wireless optical quantum key and data provided by an embodiment of the present invention includes the following steps:

[0020] Step S1: The laser light source of the transmitting device uses OOK modulation, that is, on-off modulation. The generated modulated optical signal includes: a weak optical signal corresponding to an information bit of 0 and a strong optical signal corresponding to an information bit of 1; the weak optical signal is further subjected to polarization modulation to carry the key information; the polarization of the strong optical signal is not changed, and its original polarization state is maintained; the mixed transmission signal is obtained and sent.

[0021] The laser light source of the embodiment of the present invention uses OOK modulation, so that two optical signals with different intensities can be generated: a weak optical signal corresponding to an information bit of "0" and a strong optical signal corresponding to an information bit of "1". The intensity of the weak optical signal after attenuation by the attenuation sheet is only at the single-photon level. Subsequently, the polarization modulator modulates the polarization of the weak optical signal according to the polarization modulator control signal sequence generated by the mixed transmission signal generation module to carry the key information; for the strong optical signal, the polarization modulator does not change its polarization, so as to maintain its original polarization state; finally, the transmitting device sends out the generated mixed transmission signal.

[0022] In this step, the distribution of the quantum key adopts the BB84 protocol based on polarization coding. After the optical signal passes through the vertical polarizer, photons with non-vertical polarization states will be filtered out, so that all the photons reaching the polarization modulator are vertically polarized photons; after the polarization modulator modulates the vertically polarized photons, four polarization states of photons are transmitted: horizontal, vertical, left-handed and right-handed.

[0023] Step S2: The receiving device includes four optical detection paths. When receiving the mixed transmission signal, the transmitted data and the initial key are demodulated according to the number and response status of the optical detection paths that generate responses within each symbol period: when receiving the strong optical signal, at least three optical detection paths will generate signal responses; when receiving the weak optical signal, at most only one optical detection path generates a signal response, and at this time, decoding is performed according to this response to obtain the initial key.

[0024] To detect photons in four states emitted by the transmitting end, the receiving device is designed with four optical detection paths. When the mixed transmission signal arrives at the receiving device, if a strong light signal "1" is received, at this time, due to the strong light intensity and a sufficient number of photons, about half of the photons will pass through the beam splitter and half will be reflected. Most of the photons on the measurement basis optical path that matches the photon polarization state will pass through the polarization beam splitter or be reflected by the polarization beam splitter and reach the photon detectors at the corresponding positions; the photons on the measurement basis optical path that do not match the photon polarization state will continue to be split in half by the polarization beam splitter and then enter the photon detectors. Therefore, when the strong light "1" symbol arrives, at least three of the four photon detectors of the receiving device will generate pulse counts, and the counts are relatively large. When the weak light "0" symbol arrives, since the weak light signal has only a single photon, it will either pass through the beam splitter or be reflected by the beam splitter, and finally can only reach one photon detector. Therefore, at most only one detector will generate a pulse count. When receiving the mixed transmission signal, the receiving device can determine the "1" and "0" of the communication according to the number of detectors that generate pulse counts in each symbol period, and obtain the corresponding quantum key according to the pulse count that appears in the photon detector that receives the "0" symbol.

[0025] The present invention discloses a method for mixed transmission of wireless optical quantum key and data. By synchronously controlling the light intensity emitted by the light source and the output signal of the polarization modulator, the polarization state and the signal state can be completely distinguished and no aliasing will occur. At the same time, the polarization modulator is used to modulate only the weak light and does not modulate the strong light; and the strong light signal for communication and the weak light signal carrying the key are distinguished in time, which not only saves the cost of the mixed transmission system but also reduces the interference of the communication signal on the quantum signal.

[0026] Embodiment 2

[0027] As Figure 2 and Figure 3 shown, the embodiment of the present invention provides a wireless optical quantum key and data mixed transmission system, including the following modules:

[0028] Transmitting device 1, including: a mixed transmission signal generation module 11, a single-photon signal preparation module 12, and a polarization state modulation module 13, which are used to perform polarization modulation on the weak light signal in the modulated optical signal so that it carries key information and send the mixed transmission signal;

[0029] Among them, the mixed transmission signal generation module 11 generates the modulation electrical signal required for traditional communication and the polarization modulator control signal required for quantum key distribution, and inputs them into the single-photon signal preparation module 12 and the polarization modulation module 13 respectively;

[0030] The single-photon signal preparation module 12 includes a coherent light source 121 and an attenuation sheet 122. The coherent light source 121 generates two optical signals with different intensities, namely a weak optical signal 0 and a strong optical signal 1, based on the modulated electrical signal generated by the hybrid transmission signal generation module 11. The intensity of the weak optical signal becomes at the single-photon level after passing through the attenuation sheet 122.

[0031] The polarization modulation module 13 includes a vertical polarizer 131 and a polarization modulator 132. The vertical polarizer 131 filters out photons with non-vertical polarization states emitted by the single-photon preparation module 12, so that all photons reaching the polarization modulator 132 are vertically polarized photons. When sending the strong optical signal 1, the polarization modulator does not work, and the strong light maintains its original polarization state. When sending the weak optical signal 0, the polarization modulator 132 modulates the vertically polarized photons based on the polarization modulator control signal generated by the hybrid transmission signal generation module 11 to complete the key loading process, thereby realizing the synthesis of communication data and quantum key.

[0032] The receiving device 2 includes four polarization optical detection paths for receiving the hybrid transmission signal and decoding the weak optical electrical signal therein to obtain the quantum key. Specifically, it includes:

[0033] The first polarization optical detection path includes a power splitter 21, a first polarization beam splitter 22, and a first photon detector 23. The first photon detector 23 is used to receive the optical signal after the hybrid transmission signal passes through the power splitter 21 and the first polarization beam splitter 22.

[0034] The second polarization optical detection path includes a second photon detector 24 for receiving the optical signal reflected by the first polarization beam splitter 22.

[0035] The third polarization optical detection path includes a quarter-wave plate 25, a second polarization beam splitter 26, and a third photon detector 27. The optical signal reflected by the power splitter 21 passes through the quarter-wave plate 25 and is then reflected by the second polarization beam splitter 26 to reach the third photon detector 27.

[0036] The fourth polarization optical detection path includes a fourth photon detector 28 for receiving the optical signal passing through the second polarization beam splitter 26.

[0037] The receiving device can demodulate the communication signal according to the number of optical paths where the photon detector generates a response within each symbol period, and can demodulate the corresponding received key according to the detection optical path that generates a response during the time period where the "0" code is located.

[0038] To test the performance of the wireless optical quantum key and data hybrid transmission system provided by the present invention, a quantum key and communication data hybrid transmission experiment was carried out in a 15-meter water tank. The experimental results are as Figure 4 and Figure 5As shown, where the abscissa represents the horizontal, vertical, right-handed and left-handed states corresponding to the four optical detection channels respectively. In the experiment, the light intensity ratio corresponding to the communication signal "1" code and "0" code is about 11:1. Under the condition that the pulse repetition frequency at the sending end is 125KHz, the finally obtained average screening key rate is 24.88Kbps, and the quantum bit error rate (QBER) is 0.1079, meeting the security standard (under a simple intercept and resend attack, the bit error rate below 0.25 meets the security standard, and below 0.1 meets the absolute security standard); the communication rate is 12.5Kbps and the bit error rate is 0. The experimental results verify the feasibility of the proposed wireless optical quantum key and data mixed transmission method, and prove that the proposed wireless optical quantum key and data mixed transmission system has good performance.

[0039] The above embodiments are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of the present invention shall be covered within the scope of the present invention.

Claims

1. A method for mixed transmission of wireless optical quantum key and data, characterized in that, Including: Step S1: The laser light source of the transmitting device uses OOK modulation, i.e., on-off modulation. The generated modulated optical signal includes: a weak optical signal corresponding to an information bit of 0 and a strong optical signal corresponding to an information bit of 1. The weak optical signal is further subjected to polarization modulation to carry the key information. The polarization of the strong optical signal is not changed, and its original polarization state is maintained. The mixed transmission signal is obtained and sent. Step S2: The receiving device includes four optical detection paths. When receiving the mixed transmission signal, the transmitted data and the initial key are demodulated according to the number and response status of the optical detection paths that generate responses within each symbol period. When receiving the strong optical signal, at least three of the optical detection paths will generate signal responses. When receiving the weak optical signal, at most only one of the optical detection paths generates a signal response. At this time, decoding is performed according to this response to obtain the initial key.

2. The wireless optical quantum key and data mixed transmission method according to claim 1, wherein The quantum key distribution uses the BB84 protocol based on polarization coding to transmit photons in four polarization states, including: horizontal, vertical, left-handed, and right-handed.

3. A wireless optical quantum key and data mixed transmission system, characterized in that, Including a transmitting device and a receiving device, where The transmitting device includes: a mixed transmission signal generation module, a single-photon signal preparation module, and a polarization state modulation module, which are used to perform polarization modulation on the weak optical signal in the modulated optical signal to carry the quantum key and send the mixed transmission signal. Among them, the mixed transmission signal generation module generates a modulation electrical signal required for traditional communication and a polarization modulator control signal required for quantum key distribution, and inputs them into the single-photon signal preparation module and the polarization modulation module respectively. The single-photon signal preparation module includes: a coherent light source and an attenuation sheet. Among them, the coherent light source can generate two optical signals with different intensities based on the modulation electrical signal: a weak optical signal 0 and a strong optical signal 1. After passing through the attenuation sheet, the output intensity of the weak optical signal is at the single-photon level. The polarization modulation module includes: a vertical polarizer and a polarization modulator. Among them, the vertical polarizer filters out photons with non-vertical polarization states emitted by the single-photon preparation module, so that all photons reaching the polarization modulator are vertically polarized photons. When sending the weak optical signal 0, the polarization modulator is used to modulate the vertically polarized photons, and their polarization states are adjusted to horizontal, vertical, left-handed, and right-handed states according to the BB48 protocol to complete the key loading process. The receiving device includes: four polarization optical detection paths, which are used to receive the mixed transmission signal and decode the weak optical electrical signal therein to obtain the quantum key.

4. The wireless optical quantum key and data mixed transmission system according to claim 3, characterized in that, Among them, The first polarization optical detection path includes: a power splitter, a first polarization beam splitter, and a first photon detector. Among them, the first photon detector is used to receive the optical signal after the mixed transmission signal passes through the power splitter and the first polarization beam splitter. The second polarization optical detection path includes: a second photon detector, which is used to receive the optical signal reflected by the first polarization beam splitter. The third polarized light detection path includes: a quarter-wave plate, a second polarization beam splitter, and a third photon detector. Among them, the optical signal reflected from the power beam splitter passes through the quarter-wave plate, is reflected by the second polarization beam splitter, and reaches the third photon detector; The fourth polarized light detection path includes: a fourth photon detector that receives the optical signal transmitted through the second polarization beam splitter.

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