Quantum key distribution decoder, decoding method, and chip

Abstract

The application relates to a quantum key distribution decoder, a decoding method and a chip, the quantum key distribution decoder comprising a high-speed intensity modulator and an interferometer, wherein: the high-speed intensity modulator is used for receiving optical signal pulses and has a pulse output port, the high-speed intensity modulator is used for regulating the received optical signal pulses to one arm of the interferometer through the regulation of the pulse output port; and the interferometer is used for carrying out interference decoding on the optical signal pulses regulated by the high-speed intensity modulator. According to the quantum key distribution decoding scheme provided by the application, by adding a high-speed intensity modulator in front of a traditional interferometer, the front and rear pulse time sequences are interfered by regulating the pulse output port, each optical signal pulse is not divided into two parts, the intrinsic 3dB loss is avoided, and the system code rate is improved.

Description

Technical Field

[0001] This application relates to the field of quantum communication technology, and in particular to a quantum key distribution decoder, decoding method, and chip. Background Technology

[0002] Currently, the fundamental principles of quantum mechanics guarantee the unconditional security of quantum key distribution at the cost of prohibiting the amplification of quantum states. Over the past few years, with the proposal and experimental optimization of protocols such as BB84, decoy state, measurement device-independent (MDI-QKD), and two-field key distribution (TF-QKD), the secure communication distance and key generation rate of quantum key distribution systems have achieved breakthrough improvements.

[0003] Although MDI-QKD and TF-QKD protocols have developed rapidly in recent years, with transmission distances exceeding 400 kilometers, these protocols have high requirements. The photons emitted by both communicating parties must be identical in frequency, polarization, and time delay, making their practical implementation relatively complex. In contrast, traditional point-to-point BB84 QKD systems, based on time-phase or polarization coding, consist of a transmitter and a receiver, without a central measurement terminal. These systems are simple to operate and highly suitable for short-range QKD (Quantum Key Distribution) communication within 200 km. Currently, mainstream commercial and quantum communication networks are also primarily point-to-point.

[0004] Light waves, as information carriers, have advantages over traditional electrical signals, such as resistance to electromagnetic interference, low transmission loss, and large capacity. Currently, in quantum key distribution systems, optical quantum signals are mainly encoded using time-phase coding and polarization coding. Polarization coding is suitable for spatial transmission, while time-phase coding is more suitable for transmission in optical fibers. Moreover, the aforementioned protocols can all be implemented in optical fiber systems using time-phase coding.

[0005] However, in point-to-point protocols based on time-phase coding, the current receiver decoder consists of only a single unbalanced interferometer. This requires splitting each optical pulse in two, adjusting the time delay of one path to align the timing of successive pulses, and finally performing interferometric decoding. This results in an intrinsic 3dB loss. This intrinsic 3dB loss affects the code generation rate of the system, hindering further improvements in code generation. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this application provides a novel quantum key distribution decoding scheme. In this scheme, the receiver decoder includes not only an interferometer but also a high-speed intensity modulator. By adjusting the pulse output port, the optical signal pulse is modulated to one of the two arms of the interferometer, eliminating the need to split the optical signal pulse in two and avoiding the intrinsic 3dB loss.

[0007] According to a first aspect of this application, a quantum key distribution decoder is provided, characterized in that it includes a high-speed intensity modulator and an interferometer, wherein:

[0008] The high-speed intensity modulator is used to receive optical signal pulses and has a pulse output port. The high-speed intensity modulator, by adjusting its pulse output port, modulates the received optical signal pulses to one of the two arms of the interferometer; and

[0009] The interferometer is used to perform interference decoding on optical signal pulses modulated by the high-speed intensity modulator.

[0010] The high-speed intensity modulator is used for:

[0011] The single-pulse optical signal is modulated to a fixed arm in the interferometer; and / or

[0012] The first pulse of the dual-pulse optical signal is modulated to one arm of the interferometer with a delay line, and the second pulse is modulated to one arm of the interferometer without a delay line.

[0013] The high-speed intensity modulator is also used for:

[0014] The difference between the intensity of the optical signal pulse modulated to one arm of the interferometer with a delay line and the intensity of the optical signal pulse modulated to the other arm of the interferometer without a delay line is modulated to be less than a preset threshold.

[0015] The high-speed intensity modulator includes a phase modulation region, which is used to control the received optical signal pulses.

[0016] The delay line of the interferometer is a multimode wide waveguide and / or a gradually curved waveguide.

[0017] According to a second aspect of this application, a method for decoding using the quantum key distribution decoder described in the first aspect is provided, characterized in that it includes:

[0018] The received optical signal pulse is modulated to one of the two arms of the interferometer using the high-speed intensity modulator; and

[0019] The interferometer performs interference decoding on the optical signal pulses modulated by the high-speed intensity modulator.

[0020] The step of modulating the received optical signal pulse to one of the two arms of the interferometer via the high-speed intensity modulator includes:

[0021] The single-pulse optical signal is modulated to a fixed arm in the interferometer;

[0022] The first pulse of the dual-pulse optical signal is modulated to one arm of the interferometer with a delay line, and the second pulse is modulated to one arm of the interferometer without a delay line.

[0023] The step of modulating the first pulse of the dual-pulse optical signal to one arm of the interferometer with a delay line and modulating the second pulse to one arm of the interferometer without a delay line includes:

[0024] The difference between the intensity of the optical signal pulse modulated to one arm of the interferometer with a delay line and the intensity of the optical signal pulse modulated to the other arm of the interferometer without a delay line is modulated to be less than a preset threshold.

[0025] According to a third aspect of this application, a chip is provided, characterized in that the chip includes a decoder as described in the first aspect; or,

[0026] The chip includes a processor for performing the method as described in the second aspect.

[0027] The chip includes a thin-film lithium niobate photonic chip.

[0028] According to the quantum key distribution decoding scheme provided in this application, by adding a high-speed intensity modulator in front of the traditional interferometer, the timing of the preceding and following pulses can be interfered with by adjusting the pulse output port. This eliminates the need to split each optical signal pulse in two, avoids the intrinsic 3dB loss, and helps to improve the system code rate. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings, without exceeding the scope of protection claimed by this application.

[0030] Figure 1 This is a schematic diagram of a point-to-point quantum key distribution decoder in existing technology.

[0031] Figure 2 This is a schematic diagram of a quantum key distribution decoder according to an embodiment of this application.

[0032] Figure 3 This is an image of a high-speed intensity modulator according to one embodiment.

[0033] Figure 4 Is adopted Figure 2 The flowchart shown illustrates the decoding method performed by the quantum key distribution decoder. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Figure 1 This is a schematic diagram of a point-to-point quantum key distribution decoder in existing technology. For example... Figure 1 As shown, in the prior art, point-to-point quantum key distribution decoders only include an interferometer, such as a 2x2 unbalanced interferometer, which includes a 2x2 beam splitter. According to some embodiments, the beam splitter is composed of a multi-mode interferometer (MMI) and / or a directional coupler (DC).

[0036] exist Figure 1 In the quantum key distribution decoder shown, the interferometer splits the received optical signal pulse in two. One half follows the arm of the interferometer without delay lines, corresponding to the upper arm, while the other half follows the arm with delay lines, corresponding to the lower arm. Then, the timing of the preceding and following pulses is aligned before interference decoding. However, because each optical signal pulse is split in two... Figure 1 The quantum key distribution decoder shown has an intrinsic 3dB loss, which affects the code generation rate of the system.

[0037] for Figure 1 To address the problems of the quantum key distribution decoder shown, according to one aspect of this application, a new quantum key distribution decoder is provided, such as... Figure 2 As shown. In Figure 2 In this quantum key distribution decoder, in addition to an interferometer, a high-speed intensity modulator is also included, positioned in front of the interferometer. According to some embodiments, the high-speed intensity modulator has the following structure: Figure 3 As shown. According to some embodiments, the high-speed intensity modulator includes a beam splitter and a phase modulation region.

[0038] According to some embodiments, the high-speed intensity modulator acts as a path router for time pulses, determining whether the optical signal pulse is output from the upper or lower arm by adjusting its pulse output port. In other words, it modulates the received optical signal pulse to one of the two arms of the interferometer, rather than splitting the optical signal pulse in two. The interferometer then performs interference decoding upon receiving the optical signal pulse modulated by the high-speed intensity modulator.

[0039] According to some embodiments, the optical signal pulses may include single-pulse optical signals and double-pulse optical signals, such as Z-based single pulses and X-based double pulses. Specifically, for single-pulse optical signals, the high-speed intensity modulator modulates them to a fixed arm of the interferometer, for example, to an arm of the interferometer without a delay line or to an arm of the interferometer with a delay line; for double-pulse optical signals, the high-speed intensity modulator modulates the first pulse to an arm of the interferometer with a delay line and the second pulse to an arm of the interferometer without a delay line.

[0040] According to some embodiments, the optical signal pulse can be modulated through the phase modulation region of a high-speed intensity modulator, that is, the arm of the interferometer can be determined for the optical signal pulse to travel through.

[0041] According to some embodiments, in the process of modulating optical signal pulses, the high-speed intensity modulator can modulate the intensities of the two output beams to be equivalent when there are two output beams. For example, the output intensity of the optical pulse that does not pass through the delay line of the interferometer can be modulated to be equivalent to the intensity of the optical pulse that passes through the delay line of the interferometer. Specifically, the intensity of the optical signal pulse modulated to the arm of the interferometer with the delay line can be modulated to be equal to the intensity of the optical signal pulse modulated to the arm of the interferometer without the delay line, or the difference between the two can be modulated to be less than a preset threshold. By modulating the intensities of the two output beams to be equivalent, the interference visibility is improved. According to some embodiments, the intensity of the two output beams can be modulated to be equivalent through the phase modulation region of the high-speed intensity modulator.

[0042] According to some embodiments, delay lines may suffer from loss issues, such as process deviations leading to slightly higher losses. For the design of the delay line in an interferometer, the first priority is to reduce losses. This can be achieved by designing multimode wide waveguides and / or tapered waveguides. Furthermore, the bending radius should be as large as possible during design to avoid polarization mode switching caused by the anisotropic properties of lithium niobate. According to some embodiments, the delay line can employ a time-delay adjustable structure to adjust the time delay.

[0043] exist Figure 2 In the quantum key distribution decoder, the electrode part consists of GSG (Ground-Signal-Ground) traveling wave high-speed electrodes and thermally modulated electrodes. The GSG traveling wave electrodes are used for high-speed modulation, and the thermally modulated electrodes are used for bias point control and phase control of the unbalanced interferometer.

[0044] exist Figure 2 Based on this application, and according to another aspect of this application, a method is provided that employs... Figure 2 The method shown is for decoding using a quantum key distribution decoder. For example... Figure 4 As shown, the method includes the following steps.

[0045] Step S401: The received optical signal pulse is modulated to one of the two arms of the interferometer using the high-speed intensity modulator; and

[0046] Step S402: The optical signal pulses modulated by the high-speed intensity modulator are subjected to interference decoding by the interferometer.

[0047] According to some embodiments, the high-speed intensity modulator acts as a path router for time pulses, determining whether the optical signal pulse is output from the upper or lower arm by adjusting its pulse output port. In other words, it modulates the received optical signal pulse to one of the two arms of the interferometer, rather than splitting the optical signal pulse in two. The interferometer then performs interference decoding upon receiving the optical signal pulse modulated by the high-speed intensity modulator.

[0048] According to some embodiments, the optical signal pulses may include single-pulse optical signals and double-pulse optical signals, such as Z-based single pulses and X-based double pulses. Specifically, for single-pulse optical signals, the high-speed intensity modulator modulates them to a fixed arm of the interferometer, for example, to an arm of the interferometer without a delay line or to an arm of the interferometer with a delay line; for double-pulse optical signals, the high-speed intensity modulator modulates the first pulse to an arm of the interferometer with a delay line and the second pulse to an arm of the interferometer without a delay line.

[0049] Thus, step S401 specifically includes:

[0050] Step S4011: Modulate the single-pulse optical signal to one fixed arm in the interferometer;

[0051] Step S4012: The first pulse of the dual-pulse optical signal is modulated to one arm of the interferometer with a delay line, and the second pulse is modulated to one arm of the interferometer without a delay line.

[0052] According to some embodiments, in the process of modulating optical signal pulses, the high-speed intensity modulator can modulate the intensities of the two output beams to be equivalent when there are two output beams. For example, the output intensity of the optical pulse that does not pass through the delay line of the interferometer can be modulated to be equivalent to the intensity of the optical pulse that passes through the delay line of the interferometer. Specifically, the intensity of the optical signal pulse modulated to the arm of the interferometer with the delay line can be modulated to be equal to the intensity of the optical signal pulse modulated to the arm of the interferometer without the delay line, or the difference between the two can be modulated to be less than a preset threshold. By modulating the intensities of the two output beams to be equivalent, the interference visibility is improved. According to some embodiments, the intensity of the two output beams can be modulated to be equivalent through the phase modulation region of the high-speed intensity modulator.

[0053] Thus, step S4012 specifically includes: modulating the difference between the intensity of the optical signal pulse modulated to one arm of the interferometer with a delay line and the intensity of the optical signal pulse modulated to the other arm of the interferometer without a delay line to be less than a preset threshold.

[0054] exist Figure 2 Based on this application, and according to another aspect of this application, a chip is provided that integrates... Figure 2 The quantum key distribution decoder shown is shown.

[0055] Existing fiber-optic unbalanced interferometers suffer from phase jitter due to environmental temperature and stress disturbances, requiring methods such as vibration isolation, temperature control, and active compensation to stabilize the phase jitter. Integrating the quantum key distribution decoder onto a chip avoids these drawbacks.

[0056] According to some embodiments, thin-film lithium niobate exhibits excellent linear second-order electro-optic properties. Combined with semiconductor micro / nano fabrication technology, it can realize ultra-low-loss optical waveguides, enabling the on-chip integration of a series of high-speed electro-optic modulators and optical waveguides. Waveguide loss can be below 0.1 dB / cm, modulator bandwidth can reach over 50 GHz, and half-wave voltage is less than 2 V.

[0057] The quantum key distribution decoder achieves on-chip integration of the optical system using a thin-film lithium niobate optical chip, forming a thin-film lithium niobate optical chip. Utilizing the excellent electro-optical properties and low-loss characteristics of lithium niobate, a high-performance chip-based integration of the quantum key distribution decoder is realized.

[0058] According to some embodiments, on-chip integration of quantum key distribution decoders can also be achieved using other photonic integration materials, such as InP, Si, SiN, SiO2, etc.

[0059] According to some embodiments, the quantum key distribution decoder chip designed according to the present invention may include a 2x2 Mach-Zehnder high-speed intensity modulator and a 2x2 unbalanced interferometer. The 2x2 Mach-Zehnder high-speed intensity modulator acts as a path router for time pulses, determining whether the pulse is output on the upper or lower arm. The 2x2 unbalanced interferometer is used to align the timing of the two pulses from the upper and lower arms, and finally perform interference decoding at the beam splitter. Based on this design, routing on single-pulse or dual-pulse paths is achieved, avoiding 3dB optical loss and improving the system code rate.

[0060] exist Figure 4 Based on this application, and according to another aspect, a chip is provided that includes a processor, the processor being configured to perform... Figure 4 The method described.

[0061] Compared to existing fiber optic receiver systems, chip loss primarily stems from device loss, end-face loss, and electrode metal absorption loss. If waveguide loss is reduced to below 0.1 dB / cm, optimizing the delay line and beam splitter design can achieve device loss of less than 0.5 dB. Currently, end-face loss is less than 0.7 dB / facet; using wedge-shaped fibers with special mode-matching or photonics wire bonding technology can further reduce end-face coupling loss. Electrode metal absorption loss can be reduced to negligible levels by increasing the GSG electrode spacing or placing the electrodes on the waveguide capping layer. In summary, through technological optimization, loss levels similar to traditional fiber optic decoders, less than 1 dB, can be achieved while avoiding the intrinsic 3 dB loss during interferometric decoding.

[0062] According to the quantum key distribution decoder, decoding method and chip provided in this application, by adding a high-speed intensity modulator in front of the traditional interferometer, the timing of the preceding and following pulses can be interfered with by adjusting the pulse output port. This eliminates the need to split each optical signal pulse in two, avoids the intrinsic 3dB loss, and helps to improve the system code rate.

[0063] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A quantum key distribution decoder, characterized in that, Includes a high-speed intensity modulator and an interferometer, wherein: The high-speed intensity modulator is used to receive optical signal pulses and has a pulse output port. The high-speed intensity modulator, by adjusting its pulse output port, modulates the received optical signal pulses to one of the two arms of the interferometer; and The interferometer is used to perform interference decoding on optical signal pulses modulated by the high-speed intensity modulator. The high-speed intensity modulator is used for: The single-pulse optical signal is modulated to a fixed arm in the interferometer; and / or The first pulse of the dual-pulse optical signal is modulated to one arm of the interferometer with a delay line, and the second pulse is modulated to one arm of the interferometer without a delay line. The high-speed intensity modulator is also used for: The difference between the intensity of the optical signal pulse modulated to one arm of the interferometer with a delay line and the intensity of the optical signal pulse modulated to the other arm of the interferometer without a delay line is modulated to be less than a preset threshold. The high-speed intensity modulator includes a phase modulation region, which is used to control the received optical signal pulses.

2. The decoder as described in claim 1, characterized in that, The delay line of the interferometer is a multimode wide waveguide and / or a gradually curved waveguide.

3. A method for decoding using the quantum key distribution decoder as described in claim 1 or 2, characterized in that, include: The high-speed intensity modulator modulates the received optical signal pulses to one of the two arms of the interferometer. as well as The interferometer performs interference decoding on the optical signal pulses modulated by the high-speed intensity modulator.

4. The method as described in claim 3, characterized in that, The step of modulating the received optical signal pulse to one of the two arms of the interferometer via the high-speed intensity modulator includes: The single-pulse optical signal is modulated to a fixed arm in the interferometer; The first pulse of the dual-pulse optical signal is modulated to one arm of the interferometer with a delay line, and the second pulse is modulated to one arm of the interferometer without a delay line.

5. The method as described in claim 4, characterized in that, The step of modulating the first pulse of the dual-pulse optical signal to one arm of the interferometer with a delay line and modulating the second pulse to one arm of the interferometer without a delay line includes: The difference between the intensity of the optical signal pulse modulated to one arm of the interferometer with a delay line and the intensity of the optical signal pulse modulated to the other arm of the interferometer without a delay line is modulated to be less than a preset threshold.

6. A chip, characterized in that, The chip includes the decoder as described in claim 1 or 2; or... The chip includes a processor for performing the method as described in any one of claims 3 to 5.

7. The chip as described in claim 6, characterized in that, The chip includes a thin-film lithium niobate photonic chip.

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