Optical chip and quantum key distribution system for quantum key distribution

Abstract

This paper proposes an optical chip for quantum key distribution, and a quantum key distribution system based on this optical chip. This optical chip can meet the encoding requirements of multiple protocols with a simple, stable, and easily controllable optical path structure. It also allows encoding processes based on different protocols to have low optical loss and provides chip control capabilities with low power consumption.

Description

Technical Field

[0001] The present invention relates to the field of quantum secure communication, and in particular to an optical chip for quantum key distribution, and a quantum key distribution system implemented based on the optical chip. Background Art

[0002] Quantum key distribution, based on the quantum uncertainty principle, is a practical quantum communication technology that has been theoretically proven to be unconditionally secure. It offers the ultimate solution to the increasingly serious issue of information security. As quantum communication advances towards engineering, scalability, and high performance, the requirements for practical applications are increasing, including stability, reliability, manufacturability, testability, acquisition cost, and operational maintenance costs. Existing devices suffer from various performance flaws and imperfections, which are increasingly hindering the rapid industrialization of quantum communication. The development and evolution of mainstream communication equipment today are focused on three key areas: 1) smaller size and lower cost; 2) lower power consumption and green communication; and 3) improved stability, reliability, and broad environmental adaptability. To address these challenges, the universal solution is to continuously increase product integration. By integrating electronic, optoelectronic, and optical components, this reduces internal interconnect complexity, reduces size, and lowers power consumption. Furthermore, packaging technologies can be used to improve mechanical and climatic adaptability. Therefore, the demand for comprehensive integration of optical, optoelectronic, electronic, and data processing functions in quantum communication products is becoming increasingly urgent, attracting the attention and attention of research institutions and leading industry companies both domestically and internationally.

[0003] However, existing quantum key distribution schemes are usually designed based on non-optical chip implementation methods, and there may be some problems in directly implementing them in an optical chip manner. For example, in traditional quantum key distribution systems for time phase encoding, a scheme combining equal-arm interferometers and unequal-arm interferometers is adopted. However, when this scheme is directly used to implement optical chips, due to the great technical difficulties in etching a long arm length difference on the chip, the etching process for long arm length differences on small chips is difficult, the layout is difficult, the etching consistency is poor, the attenuation is large, and once etched, the arm length difference setting value cannot be significantly adjusted. Therefore, it is difficult to obtain a satisfactory optical chip for time phase encoding quantum key distribution systems.

[0004] Meanwhile, with the development of QKD protocols, a new phase-coded protocol, TF-QKD, was proposed in 2018. Compared to the existing BB84 protocol, TF-QKD requires more coding and modulation, and places stricter demands on chip attenuation control. Furthermore, achieving compatibility between BB84 and TF-QKD requires careful design to simultaneously meet the requirements of the different protocols. Summary of the Invention

[0005] In response to this problem, the present invention discloses an optical chip that can be implemented in the form of a silicon-based integrated chip, and a quantum key distribution system implemented based on the optical chip. With the help of the unique optical chip design proposed by the present invention, the deficiencies caused by the limitations of the etching process can be avoided, allowing a simple, stable and easy-to-control chip optical path structure to meet the coding requirements under various protocols including the BB84 protocol and the TF-QKD protocol on optical signals in the form of continuous light and pulsed light, and prepare corresponding quantum states; at the same time, in the encoding process corresponding to various protocols, low optical loss is allowed on the optical signal, which is extremely beneficial for optical chip design and parameter testing and calibration. In addition, the optical chip according to the present invention also allows the chip control function to be provided with low power consumption. Thus, an optical chip with low power consumption and capable of realizing multiple coding functions is realized.

[0006] Specifically, a first aspect of the present invention relates to an optical chip for quantum key distribution, comprising a first intensity modulation module, a second intensity modulation module, and a first phase modulation module, and forming a first optical signal input interface, a second optical signal input interface, and a first optical signal output interface;

[0007] The first and second optical signal input interfaces are configured to allow optical signals to be input into the optical chip;

[0008] The first optical signal output interface is configured to allow an optical signal to be output from the optical chip;

[0009] The first intensity modulation module is configured to perform intensity modulation on the optical signal input via the first optical signal input interface so that optical signals in different quantum states satisfy a preset light intensity relationship;

[0010] The second intensity modulation module is configured to perform intensity modulation on an optical signal input via the second optical signal input interface or an optical signal output by the first intensity modulation module, so as to implement decoy state coding on the optical signal;

[0011] The first phase modulation module is configured to perform phase modulation on the optical signal to implement phase encoding on the optical signal.

[0012] Furthermore, the first and / or second intensity modulation module includes an equal-arm interferometer having two multimode interference couplers, a first and a second arm formed between the two multimode interference couplers, and a phase modulator arranged on the first and / or second arm.

[0013] Furthermore, a phase shifter is provided on the first and / or second arm of the equal-arm interferometer for finding the optimal working point of the equal-arm interferometer.

[0014] Preferably, the phase modulator is a carrier dispersion phase modulator, and / or the phase shifter is a thermally tuned phase shifter.

[0015] Furthermore, the optical chip of the present invention further includes a synchronization optical path for performing power control on the synchronization optical signal; and / or an attenuation monitoring module for attenuating the optical signal output by the first optical signal output interface to a preset level.

[0016] Furthermore, the attenuation monitoring module includes an adjustable attenuator and a fifth multimode interference coupler;

[0017] The adjustable attenuator is configured to allow attenuation of the optical signal;

[0018] The fifth multimode interference coupler is configured to split the optical signal output by the adjustable attenuator to form an optical chip output optical signal and an output light intensity monitoring optical signal, wherein the output light intensity monitoring optical signal is used to allow monitoring of the light intensity of the optical chip output optical signal.

[0019] Preferably, the fifth multimode interference coupler is a 2*2 multimode interference coupler; and the attenuation monitoring module also includes a monitoring photodiode, which is configured to be connected to the fifth multimode interference coupler to allow monitoring of the attack light reversely injected into the optical chip through the first optical signal output interface.

[0020] Furthermore, the synchronization optical path includes an adjustable attenuator and a sixth multimode interference coupler; the adjustable attenuator is configured to allow the power of the synchronization optical signal to be controlled; the sixth multimode interference coupler is configured to split the synchronization optical signal output by the adjustable attenuator to form a synchronization optical output signal and a synchronization optical monitoring signal, and the synchronization optical monitoring signal is used to allow the light intensity of the synchronization optical output signal to be monitored.

[0021] Furthermore, the optical chip of the present invention is further formed with an output light intensity monitoring interface, a synchronization light input interface and a synchronization light output interface;

[0022] The output light intensity monitoring interface is configured to allow the output light intensity monitoring optical signal to be output from the optical chip;

[0023] The synchronization optical input interface is configured to allow the synchronization optical signal to be input into the optical chip;

[0024] The synchronization optical output interface is configured to allow a synchronization optical signal to be output from the optical chip.

[0025] Furthermore, the optical chip of the present invention may further include a third intensity modulation module, and when the optical signal input to the optical chip via any one of the first and second optical signal input interfaces is continuous light,

[0026] One of the first, second and third intensity modulation modules is configured to allow the optical signal to be chopped to convert continuous light into pulsed light;

[0027] Another one of the first, second and third intensity modulation modules is configured to allow decoy state encoding of the optical signal;

[0028] Another one of the first, second and third intensity modulation modules is configured to enable switching of the optical signal between reference optical pulses and quantum optical pulses.

[0029] Furthermore, the third intensity modulation module includes an equal-arm interferometer having two multimode interference couplers, a first and a second arm formed between the two multimode interference couplers, and a phase modulator arranged on the first and / or second arm.

[0030] Furthermore, a phase shifter is provided on the first and / or second arm of the equal-arm interferometer in the third intensity modulation module, for finding the optimal working point of the equal-arm interferometer.

[0031] Preferably, in the equal-arm interferometer of the third intensity modulation module, the phase modulator is a carrier dispersion phase modulator, and / or the phase shifter is a thermally tuned phase shifter.

[0032] Furthermore, the first intensity modulation module, the second intensity modulation module and the first phase modulation module are sequentially connected in series; and,

[0033] The optical chip further includes a ninth multimode interference coupler configured to split the optical signal output by the first phase modulation module so as to transmit the optical signal toward the third intensity modulation module and the attenuation monitoring module respectively;

[0034] A second optical signal output interface is also formed on the optical chip, which is configured to allow the optical signal output by the third intensity modulation module to be output externally.

[0035] Furthermore, the optical chip of the present invention further includes a second phase modulation module, and the second phase modulation module is arranged between the ninth multimode interference coupler and the third intensity modulation module.

[0036] Preferably, the first phase modulation module includes one phase modulator, and the second phase modulation module includes one or more phase modulators.

[0037] Furthermore, the optical chip of the present invention may further include a coherent detection module for allowing detection of a frequency difference between the optical signal and a frequency reference light.

[0038] Furthermore, the optical chip of the present invention is further formed with a third optical signal input interface for allowing input of the frequency reference light; and

[0039] The coherent detection module includes a tenth multimode interference coupler and an eleventh multimode interference coupler;

[0040] The tenth multimode interference coupler is configured to allow the optical signal input through the first optical signal input interface to be split so as to be transmitted toward the first intensity modulation module and the eleventh multimode interference coupler respectively;

[0041] The eleventh multimode interference coupler is configured to allow interference between the frequency reference light and the optical signal.

[0042] A second aspect of the present invention relates to a quantum key distribution system, comprising an injection-locked laser and the above-mentioned optical chip;

[0043] The injection-locked laser is configured to generate one of a first optical signal, a second optical signal, and a third optical signal within a time period;

[0044] The first optical signal comprises only a single optical pulse appearing at a first moment in a time period;

[0045] The second optical signal comprises only a single optical pulse occurring at a second instant in time within a time period;

[0046] The third optical signal includes two optical pulses, which appear at the first and second moments within a time period respectively and have a fixed phase difference;

[0047] The optical chip is configured to perform time phase encoding on the optical signal based on the BB84 protocol.

[0048] A third aspect of the present invention relates to a quantum key distribution system, comprising a frequency-locked laser and the above-mentioned optical chip;

[0049] The frequency-locked laser is configured to generate an optical signal in the form of continuous light;

[0050] The optical chip is configured to perform at least one of time phase encoding based on the BB84 protocol and encoding based on the TF-QKD protocol on the optical signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 An exemplary embodiment of an optical chip for quantum key distribution according to the present invention is schematically shown;

[0054] Figure 2 Schematically illustrates an exemplary embodiment of a quantum key distribution system according to the present invention;

[0055] Figure 3 Schematically shows a further embodiment of an optical chip for quantum key distribution according to the present invention;

[0056] Figure 4 Another exemplary embodiment of the quantum key distribution system according to the present invention is schematically shown. DETAILED DESCRIPTION

[0057] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example so as to fully convey the spirit of the present invention to those skilled in the art to which the present invention belongs. Therefore, the present invention is not limited to the embodiments disclosed herein.

[0058] According to the present invention, the optical chip for quantum key distribution can be used to receive an optical signal and encode it so that it carries coded information, thereby preparing an optical signal with a corresponding quantum state.

[0059] Figure 1 An exemplary embodiment of an optical chip for quantum key distribution according to the present invention is shown.

[0060] like Figure 1 As shown, the optical chip may include a first intensity modulation module, a second intensity modulation module and a first phase modulation module, and is formed with a first optical signal input interface 1 , a second optical signal input interface 2 and a first optical signal output interface 5 .

[0061] The first and second optical signal input interfaces serve as input ports of the optical chip, allowing optical signals generated by an external light source to be input into the optical chip.

[0062] The first optical signal output interface serves as an output port of the optical chip, and is used to allow, for example, an optical signal prepared in a quantum state to be output from the optical chip.

[0063] The first optical signal input interface 1 is designed to be connected to the first intensity modulation module, thereby allowing the input optical signal to be intensity modulated with the help of the first intensity modulation module, compensating for the different light intensity attenuation introduced when preparing different quantum states on the optical signal, and ensuring that the prepared optical signals in different quantum states meet the preset light intensity relationship, for example, optical signals with different quantum states have the same light intensity.

[0064] As a preferred example, the first intensity modulation module may include a first equal-arm interferometer having a first multimode interference coupler (MMI), a second multimode interference coupler, a first and a second arm formed between the first and the second multimode interference coupler, and a first phase modulator provided on the first and / or the second arm, such as Figure 1 shown.

[0065] The first multimode interference coupler is used to perform 1:1 splitting of the optical signal so that the optical signal enters the first and second arms respectively.

[0066] The first phase modulator is used to perform high-speed electro-optical phase modulation on the optical signal on the first and / or second arm to form a required phase difference between the optical signals on the two arms. Preferably, the first phase modulator can be a carrier dispersion phase modulator RF1.

[0067] The second multimode interference coupler is used to combine the phase-modulated optical signals on the two arms and cause interference.

[0068] Furthermore, a first phase shifter may be provided on the first and / or second arm of the first equal-arm interferometer to find the optimal working point of the first equal-arm interferometer. Preferably, the first phase shifter may be a thermally tuned phase shifter PS1.

[0069] The second optical signal input interface 2 is designed to connect to a second intensity modulation module, thereby allowing the second intensity modulation module to perform intensity modulation on the input optical signal and implement decoy state encoding on the optical signal, such as generating a signal state, a vacuum state or a decoy state.

[0070] At the same time, the second intensity modulation module can also be connected to the first intensity modulation module to allow the optical signal output by the first intensity modulation module to be intensity modulated by the second intensity modulation module, thereby realizing decoy state encoding on the optical signal.

[0071] As a preferred example, the second intensity modulation module may include a second equal-arm interferometer having a third multimode interference coupler, a fourth multimode interference coupler, a first and a second arm formed between the third and the fourth multimode interference couplers, and a second phase modulator provided on the first and / or the second arm, such as Figure 1 shown.

[0072] The third multimode interference coupler is used to perform 1:1 splitting of the optical signal so that the optical signal enters the first and second arms respectively.

[0073] The second phase modulator is used to perform high-speed electro-optical phase modulation on the optical signal on the first and / or second arm to form a required phase difference between the optical signals on the two arms. Preferably, the second phase modulator can be a carrier dispersion phase modulator RF2.

[0074] The fourth multimode interference coupler is used to combine the phase-modulated optical signals on the two arms and cause interference.

[0075] Furthermore, a second phase shifter may be provided on the first and / or second arm of the second equal-arm interferometer to find the optimal operating point of the second equal-arm interferometer. Preferably, the second phase shifter may be a thermally tuned phase shifter PS2.

[0076] The first phase modulation module is used to perform phase modulation on the optical signal to allow phase encoding to be achieved on the optical signal. As a preferred example, the first phase modulation module may include a phase modulator PM, such as Figure 1 shown.

[0077] As a preferred example, the first phase modulation module may be designed to be connected to the second intensity modulation module to perform phase modulation on the optical signal output by the second intensity modulation module to form an optical signal carrying coded information.

[0078] Furthermore, the optical chip may also include an attenuation monitoring module for allowing the intensity of the optical signal carrying the coded information to be attenuated to a preset level, such as a single photon level, before being output from the optical chip.

[0079] As a preferred example, the attenuation monitoring module may include a variable attenuator (VOA) for providing the required light intensity attenuation to the optical signal.

[0080] Furthermore, the attenuation monitoring module may also include a fifth multimode interference coupler for splitting the optical signal passing through the adjustable attenuator, wherein one component forms the optical chip output optical signal, and the other component forms the output light intensity monitoring optical signal. This allows the optical chip output optical signal to be detected by detecting the output light intensity monitoring optical signal, thereby determining the optical intensity of the optical chip output optical signal. This allows the attenuation value of the adjustable attenuator to be controlled based on this intensity information, ensuring that the optical chip output optical signal maintains a preset intensity level.

[0081] Therefore, if Figure 1 As shown, the two output ports of the fifth multimode interference coupler can be connected to the output light intensity monitoring interface 4 and the first optical signal output interface 5 of the optical chip respectively, so as to allow the output light intensity monitoring optical signal and the optical chip output optical signal to be output externally.

[0082] Preferably, in the attenuation monitoring module, the fifth multimode interference coupler is a 2*2 multimode interference coupler. At this time, a monitoring photodiode (for example Figure 1 MPD3 in the optical chip), and connect it to the fifth multimode interference coupler to provide a function of monitoring the attack light reversely injected into the optical chip through the first optical signal output interface 5.

[0083] The optical chip may also be provided with a synchronization optical path to allow power control of the synchronization optical signal. Figure 1 As shown, the synchronization optical path can connect the synchronization optical input interface 6 and the synchronization optical output interface 7 on the optical chip to allow the input / output of synchronization optical signals with respect to the optical chip.

[0084] As a preferred example, the synchronization optical path may include an adjustable attenuator, which is used to allow an attenuation function to be provided to the synchronization optical signal, thereby achieving power control thereof.

[0085] Furthermore, the synchronization optical path may further include a sixth multimode interference coupler, which is provided after the adjustable attenuator and is used to split the synchronization optical signal, wherein one component is used as the synchronization optical output signal and the other component is used as the synchronization optical monitoring signal. Therefore, a monitoring photodiode (e.g. Figure 1 MPD4 in is used to detect the synchronous optical monitoring signal to obtain the intensity information of the synchronous optical signal, thereby allowing the attenuation value of the adjustable attenuator to be controlled according to the intensity information, thereby ensuring that the intensity of the synchronous optical output signal is controlled at a preset level.

[0086] Figure 2 A specific embodiment of the quantum key distribution system according to the present invention is shown, which can at least be used to implement time phase encoding based on the BB84 protocol on an optical signal.

[0087] The quantum key distribution system may include an injection-locked laser and the above-mentioned optical chip.

[0088] An injection-locked laser is used as the light source to generate the optical signal to be encoded. This allows two consecutive pulsed optical signals to be generated within a time period, with a fixed phase difference between the two pulsed optical signals.

[0089] In the present invention, the injection-locked laser may be controlled to generate one of the first optical signal, the second optical signal, and the third optical signal.

[0090] The first optical signal consists of a single pulsed optical signal, which occurs at the first moment within a time period. The second optical signal consists of a single pulsed optical signal, which occurs at the second moment within a time period. The third optical signal comprises two optical pulses, which occur at the first and second moments within a time period, respectively, and have a fixed phase difference. The time interval between the first and second moments within a time period is t.

[0091] Therefore, when preparing the time state Z1 or Z0, the injection-locked laser can be controlled to generate the first or second optical signal; when preparing the phase state X0 or X1, the injection-locked laser can be controlled to generate the third optical signal.

[0092] As mentioned above, the optical signal generated by the injection-locked laser will be input into the optical chip via the first or second optical signal input port of the optical chip.

[0093] In the optical chip, the first intensity modulation module can provide intensity modulation for the optical signal to achieve dynamic power balancing of the optical signal and ensure that optical signals in different quantum states have the same power.

[0094] The second intensity modulation module can provide intensity modulation for the optical signal to perform decoy state encoding on the optical signal, thereby forming decoy state encoded information on the optical signal.

[0095] The first phase modulation module can provide phase modulation for the optical signal to form phase-encoded information on the optical signal. Those skilled in the art will appreciate that, when preparing the phase state, the first phase modulation module can be controlled to form a phase difference of zero or π between two signal light pulses in the third optical signal, thereby generating phase state information X0 or X1 on the optical signal. When preparing the time state, the first phase modulation module can either perform phase modulation on the optical signal or not.

[0096] Figure 3 A further embodiment of the optical chip according to the present invention is shown, which can be used to implement multiple phase coding schemes on optical signals, such as time phase coding based on the BB84 protocol, or multiple coding schemes based on the TF-QKD protocol.

[0097] like Figure 3 As shown, in Figure 1 Based on the optical chip shown, the optical chip may further include a third intensity modulation module for performing intensity modulation on the optical signal.

[0098] As an example, the third intensity modulation module may include a third equal-arm interferometer having a seventh multimode interference coupler, an eighth multimode interference coupler, a first and second arm formed between the seventh and eighth multimode interference couplers, and a third phase modulator arranged on the first and / or second arm.

[0099] The seventh multimode interference coupler is used to perform 1:1 splitting of the optical signal so that the optical signal enters the first and second arms respectively.

[0100] The third phase modulator is used to perform high-speed electro-optical phase modulation on the optical signal on the first and / or second arm to form a required phase difference between the optical signals on the two arms. Preferably, the third phase modulator can be a carrier dispersion phase modulator RF3.

[0101] The eighth multimode interference coupler is used to combine the phase-modulated optical signals on the two arms and cause interference.

[0102] Furthermore, a third phase shifter may be provided on the first and / or second arm of the third equal-arm interferometer to find the optimal operating point of the third equal-arm interferometer. Preferably, the third phase shifter may be a thermally tuned phase shifter PS3.

[0103] Those skilled in the art will understand that for an optical signal in the form of pulsed light, Figure 3 The optical chip shown can also use the first intensity modulation module, the second intensity modulation module and the first phase modulation module to implement the BB84 protocol-based decoy state and / or time phase encoding on the optical signal. The principle is similar to that described above, so it will not be repeated here.

[0104] exist Figure 3 In the optical chip shown, due to the presence of the third intensity modulation module, multiple TF-QKD codes can be implemented on optical signals (especially continuous optical signals). The specific working principle is as follows.

[0105] For a continuous optical signal input to the optical chip via the first optical signal input interface, one of the first, second, and third intensity modulation modules can be used to chop the continuous optical signal to form a pulsed optical signal; another of the first, second, and third intensity modulation modules can be used to implement decoy state encoding on the optical signal; and yet another of the first, second, and third intensity modulation modules can be used to switch the optical signal between a reference optical pulse and a quantum optical pulse. Those skilled in the art will appreciate that to achieve the so-called "switching of the optical signal between a reference optical pulse and a quantum optical pulse," intensity modulation can be used to provide a high intensity optical signal for a period of time, thereby serving as a reference optical pulse, or to provide a low intensity optical signal for a period of time, thereby serving as a quantum optical pulse.

[0106] As a preferred example, the first intensity modulation module can be used to chop the optical signal, the second intensity modulation module is used to encode the optical signal into a decoy state, and the third intensity modulation module is used to switch the optical signal between quantum light pulses and reference light pulses.

[0107] See further Figure 3 The optical chip may further include a ninth multimode interference coupler, which is configured to perform 1:1 splitting of the optical signal output by the first phase modulation module so that the optical signal is transmitted toward the third intensity modulation module and the attenuation monitoring module (i.e., the first optical signal output interface) respectively.

[0108] Specifically, the input end of the ninth multimode interference coupler can be connected to the output end of the first phase modulation module, and the two output ends are respectively connected to the input ends of the third intensity modulation module and the attenuation monitoring module, thereby allowing the optical signal output by the first phase modulation module to be divided into two components, and the first component is transmitted toward the third intensity modulation module, and the second component is transmitted toward the attenuation monitoring module.

[0109] At this time, the third intensity modulation module can be connected to the second optical signal output interface 8 on the optical chip to allow the optical signal output by the third intensity modulation module to be output externally. Preferably, a variable attenuator (VOA1) is provided between the third intensity modulation module and the second optical signal output interface 8 to control the power of the optical signal, for example, to a preset level.

[0110] To better understand Figure 3 The structure of the optical chip is shown in FIG. 1 . The working principle of implementing TF-QKD encoding on a continuous optical signal will be described in detail below.

[0111] In the optical chip of the present invention, when the continuous optical signal reaches the first intensity modulation module via the first optical signal input interface 1 , the first intensity modulation module can chop the continuous optical signal to generate a pulsed optical signal.

[0112] After being output from the first intensity modulation module, the pulsed light signal will travel along the optical path to the second intensity modulation module, which can implement decoy state encoding on the pulsed light signal.

[0113] The decoyed state-encoded pulsed optical signal continues to propagate along the optical path and reaches the first phase modulation module, which can perform phase modulation on the pulsed optical signal according to the corresponding TF-QKD protocol to form phase encoding on the optical signal.

[0114] For example, for the SNS-TFQKD protocol, the first phase modulation module can implement phase randomization between [0, 2π) on the optical signal, such as performing discrete random phase modulation between [0, 2π) in 16 equal parts.

[0115] For the TF-QKD protocol first proposed in 2018, four phase state encodings such as (0, π / 2, π, 3π / 2) can also be realized based on the phase randomization required by the SNS-TFQKD protocol.

[0116] For the non-phase post-selected NPP-TFQKD protocol, the phase state (0 and π) encoding corresponding to the random numbers 0 and 1 can be modulated in the coding mode, and the discrete random phase modulation of 16 equal parts between [0, 2π) can be achieved in the decoy mode.

[0117] The phase-modulated pulsed optical signal is split into a first component and a second component at the ninth multimode interference coupler. The first component travels along the optical path to the third intensity modulation module, where it switches between reference optical pulses and quantum optical pulses, and is ultimately output via the second optical signal output interface 8. The second component travels along the optical path to the attenuation monitoring module and is ultimately output via the first optical signal output interface 5. At this point, the optical signal output from the first optical signal output interface 5 can be used as test light for debugging the optical chip.

[0118] Those skilled in the art will understand that by providing a ninth multimode interference coupler in the optical chip, the optical signals and test optical signals based on the BB84 protocol generated by the optical chip will not pass through the third intensity modulation module, thereby avoiding unnecessary loss of these optical signals within the optical chip and reducing the power requirements and power consumption of the optical chip, which is very beneficial for chip design.

[0119] As previously mentioned, implementing a coding scheme based on the TF-QKD protocol typically requires 16 phase modulations between [0, 2π), which often poses a challenge to a single phase modulator. Therefore, the first phase modulation module can include multiple phase modulators, such as two or three, to coordinately implement various phase modulations on the optical signal.

[0120] In a preferred embodiment, only one phase modulator can be included in the first phase modulation module to reduce the loss experienced by the optical signal and test light under the BB84 protocol. In this case, a second phase modulation module can be provided between the ninth multimode interference coupler and the third intensity modulation module to cooperate with the first phase modulation module to achieve the desired multiple phase modulation amounts on the optical signal based on the TF-QKD protocol. As an example, the second phase modulation module can include one or more phase modulators.

[0121] Figure 3 The optical chip shown also allows for time phase encoding based on the BB84 protocol when the input optical signal is continuous light.

[0122] At this time, the optical chip receives the continuous optical signal via the first optical signal input interface 1 , and the continuous optical signal first reaches the first intensity modulation module along the optical path.

[0123] The first intensity modulation module chops the continuous optical signal to generate a pulsed optical signal, which will reach the second intensity modulation module along the optical path.

[0124] The second intensity modulation module performs intensity modulation on the pulse light signal to achieve decoy state coding.

[0125] The pulsed optical signal encoded by the decoy state reaches the first phase modulation module, which implements one of phase randomization and phase encoding on the optical signal.

[0126] The phase-encoded optical signal will reach the second phase modulation module after being acted upon by the ninth multimode interference coupler, and the second phase modulation module will implement the other of phase randomization and phase encoding on the optical signal.

[0127] After phase randomization and phase encoding, the optical signal reaches the third intensity modulation module, which can provide dynamic compensation for the quantum state of the optical signal to ensure that the optical signals in different quantum states meet the preset intensity relationship.

[0128] The dynamically compensated optical signal is finally outputted through the second optical signal output interface 8 at a preset light intensity level after being acted upon by the adjustable attenuator.

[0129] It can be seen that with the help of the optical chip of the present invention, not only can pulsed optical signals be time-phase encoded based on the BB84 protocol, but also continuous optical signals can be subjected to various TF-QKD encoding and time-phase encoding based on the BB84 protocol, while ensuring that the loss introduced on the optical signal is minimized when implementing various encoding schemes.

[0130] See further Figure 3 The optical chip may also include a coherent detection module for allowing detection of the frequency difference between the optical signal and a frequency reference light (e.g., generated by an external reference frequency light source), so that the frequency of the optical signal can be regulated according to the frequency difference and locked to the frequency of the reference frequency light source, thereby improving the quality of the coded optical signal output by the optical chip.

[0131] As a preferred example, the coherent detection module may include a tenth multimode interference coupler and an eleventh multimode interference coupler, and a third optical signal input interface 3 is formed on the optical chip for allowing input of frequency reference light.

[0132] The tenth multimode interference coupler is connected to the first optical signal input interface 1 and is used to split the optical signal input through the first optical signal input interface 1 so as to transmit the optical signal toward the first intensity modulation module and the eleventh multimode interference coupler respectively.

[0133] The eleventh multimode interference coupler is connected to the third optical signal input interface 3 and the tenth multimode interference coupler, respectively, and is used to allow the frequency reference light to interfere with the optical signal, so that the frequency difference between the optical signal and the frequency reference light can be determined by detecting the interference optical signal. For example, a photodetector (e.g., Figure 3 PD1 and PD2 in the figure are used to detect the interference light signal.

[0134] Figure 4 Another specific embodiment of the quantum key distribution system according to the present invention is shown, which allows the implementation of a time phase coding scheme based on the BB84 protocol and multiple coding schemes based on the TF-QKD protocol on a continuous optical signal.

[0135] The quantum key distribution system may include a frequency-locked laser and an optical chip.

[0136] A frequency-locked laser is used as a light source to generate the optical signal to be encoded, which is a continuous optical signal with frequency and phase locked.

[0137] The optical chip is used to implement a time phase coding scheme based on the BB84 protocol for continuous optical signals, as well as various coding schemes based on the TF-QKD protocol. The specific principles are detailed above and will not be repeated here.

[0138] It can be seen that the present invention proposes an optical chip design for quantum key distribution, which is suitable for implementation on silicon-based chips, can greatly reduce system costs, and is conducive to system cost reduction, miniaturization and integration. With the help of the optimized optical path structure in the optical chip, it is allowed to support the coding requirements of multiple protocols through multiple optical interfaces, such as time phase coding based on the BB84 protocol, and various coding schemes based on the TF-QKD protocol, etc., while avoiding the shortcomings that may be caused by the limitations of current chip etching technology, thereby providing an optical chip with a simple structure, easy to control and capable of realizing multiple coding functions. While supporting multiple coding functions, the optical chip according to the present invention also allows various coding and control functions to be realized under low power consumption conditions, thereby ensuring that the chip has high efficiency, which is extremely beneficial for chip design. Furthermore, the optical chip of the present invention also supports providing coding functions for pulsed light and continuous light, thereby greatly expanding its application scenarios.

[0139] Although the present invention has been described above through specific embodiments in conjunction with the accompanying drawings, it is easy for those skilled in the art to recognize that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention. They do not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. An optical chip for quantum key distribution, comprising a first intensity modulation module, a second intensity modulation module, and a first phase modulation module, and forming a first optical signal input interface, a second optical signal input interface, and a first optical signal output interface; The first and second optical signal input interfaces are configured to allow optical signals to be input into the optical chip; The first optical signal output interface is configured to allow an optical signal to be output from the optical chip; The first intensity modulation module is configured to perform intensity modulation on the optical signal input via the first optical signal input interface so that optical signals in different quantum states satisfy a preset light intensity relationship; The second intensity modulation module is configured to perform intensity modulation on an optical signal input via the second optical signal input interface or an optical signal output by the first intensity modulation module, so as to implement decoy state coding on the optical signal; The first phase modulation module is configured to perform phase modulation on the optical signal to implement phase encoding on the optical signal; The first and / or second intensity modulation module comprises an equal-arm interferometer; The equal-arm interferometer has two multimode interference couplers, a first arm and a second arm formed between the two multimode interference couplers, and a phase modulator arranged on the first arm and / or the second arm.

2. The optical chip according to claim 1, wherein: A phase shifter is provided on the first and / or second arm of the equal-arm interferometer, which is used to find the optimal working point of the equal-arm interferometer.

3. The optical chip according to claim 2, wherein: The phase modulator is a carrier dispersion phase modulator, and / or the phase shifter is a thermal tuning phase shifter.

4. The optical chip according to claim 1, further comprising: A synchronization optical path for performing power control on a synchronization optical signal; and / or, An attenuation monitoring module is configured to attenuate the optical signal outputted by the first optical signal output interface to a preset level.

5. The optical chip according to claim 4, wherein: The attenuation monitoring module includes an adjustable attenuator and a fifth multimode interference coupler; The adjustable attenuator is configured to allow attenuation of the optical signal; The fifth multimode interference coupler is configured to split the optical signal output by the adjustable attenuator to form an optical chip output optical signal and an output light intensity monitoring optical signal, wherein the output light intensity monitoring optical signal is used to allow monitoring of the light intensity of the optical chip output optical signal.

6. The optical chip according to claim 5, wherein: The fifth multimode interference coupler is a 2*2 multimode interference coupler; and The attenuation monitoring module further includes a monitoring photodiode, which is configured to be connected to the fifth multimode interference coupler to allow monitoring of attack light reversely injected into the optical chip through the first optical signal output interface.

7. The optical chip according to claim 4, wherein: The synchronization optical path includes an adjustable attenuator and a sixth multimode interference coupler; The adjustable attenuator is configured to allow control of the power of the synchronization optical signal; The sixth multimode interference coupler is configured to split the synchronization optical signal output by the adjustable attenuator to form a synchronization optical output signal and a synchronization optical monitoring signal, wherein the synchronization optical monitoring signal is used to allow monitoring of the light intensity of the synchronization optical output signal.

8. The optical chip according to claim 5, further comprising an output light intensity monitoring interface, a synchronization light input interface, and a synchronization light output interface; The output light intensity monitoring interface is configured to allow the output light intensity monitoring optical signal to be output from the optical chip; The synchronization optical input interface is configured to allow the synchronization optical signal to be input into the optical chip; The synchronization optical output interface is configured to allow a synchronization optical signal to be output from the optical chip.

9. The optical chip according to any one of claims 1 to 8, further comprising a third intensity modulation module, and when the optical signal input to the optical chip through any one of the first and second optical signal input interfaces is continuous light, One of the first, second and third intensity modulation modules is configured to allow the optical signal to be chopped to convert continuous light into pulsed light; Another one of the first, second and third intensity modulation modules is configured to allow decoy state encoding of the optical signal; Another one of the first, second and third intensity modulation modules is configured to enable switching of the optical signal between reference optical pulses and quantum optical pulses.

10. The optical chip according to claim 9, wherein: The third intensity modulation module includes an equal-arm interferometer having two multimode interference couplers, a first arm and a second arm formed between the two multimode interference couplers, and a phase modulator disposed on the first and / or second arm.

11. The optical chip according to claim 10, wherein: A phase shifter is provided on the first and / or second arm of the equal-arm interferometer in the third intensity modulation module, for finding the optimal working point of the equal-arm interferometer.

12. The optical chip according to claim 11, wherein: In the equal-arm interferometer of the third intensity modulation module, the phase modulator is a carrier dispersion phase modulator, and / or the phase shifter is a thermally tuned phase shifter.

13. The optical chip according to claim 9, wherein: The first intensity modulation module, the second intensity modulation module and the first phase modulation module are connected in series in sequence; and The optical chip further includes a ninth multimode interference coupler configured to split the optical signal output by the first phase modulation module so as to transmit the optical signal toward the third intensity modulation module and the attenuation monitoring module respectively; A second optical signal output interface is also formed on the optical chip, which is configured to allow the optical signal output by the third intensity modulation module to be output externally. 14 . The optical chip according to claim 13 , further comprising a second phase modulation module, wherein the second phase modulation module is disposed between the ninth multimode interference coupler and the third intensity modulation module.

15. The optical chip according to claim 14, wherein: The first phase modulation module includes one phase modulator, and the second phase modulation module includes one or more phase modulators.

16. The optical chip of claim 9, further comprising a coherent detection module configured to allow detection of a frequency difference between the optical signal and a frequency reference light.

17. The optical chip according to claim 16, further comprising a third optical signal input interface for allowing input of the frequency reference light; and The coherent detection module includes a tenth multimode interference coupler and an eleventh multimode interference coupler; The tenth multimode interference coupler is configured to allow the optical signal input through the first optical signal input interface to be split so as to be transmitted toward the first intensity modulation module and the eleventh multimode interference coupler respectively; The eleventh multimode interference coupler is configured to allow interference between the frequency reference light and the optical signal.

18. A quantum key distribution system comprising an injection-locked laser and the optical chip according to any one of claims 1 to 17; The injection-locked laser is configured to generate one of a first optical signal, a second optical signal, and a third optical signal within a time period; The first optical signal comprises only a single optical pulse occurring at a first instant in a time period; The second optical signal comprises only a single optical pulse occurring at a second instant in time within a time period; The third optical signal includes two optical pulses, which appear at the first and second moments within a time period respectively and have a fixed phase difference; The optical chip is configured to perform time phase encoding on the optical signal based on the BB84 protocol.

19. A quantum key distribution system comprising a frequency-locked laser and the optical chip according to any one of claims 9 to 17; The frequency-locked laser is configured to generate an optical signal in the form of continuous light; The optical chip is configured to perform at least one of time phase encoding based on the BB84 protocol and encoding based on the TF-QKD protocol on the optical signal.

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