Polarization encoding chip and encoding method for quantum key distribution

Abstract

The application discloses a polarization encoding chip and an encoding method for quantum key distribution. Three phase modulators are arranged in the polarization encoding unit, so that polarization encoding can be realized with low driving voltage and less level, without monitoring and compensation devices, so that the chip is easier to realize and has better high and low temperature stability. In addition, a pre-compensation unit realized by the phase modulator is arranged outside the polarization encoding unit, so that the attenuation change introduced by the phase modulator in the polarization encoding process can be compensated, the total attenuation of the polarization encoding module on the optical signal is a fixed value, the power balance of different polarization states is effectively ensured, the requirement of quantum key distribution is better met, correction of power imbalance is not needed, and the security code rate is improved.

Description

Technical Field

[0001] This invention relates to the field of quantum secure communication, and specifically to a polarization-coded chip and encoding method for quantum key distribution. Background Technology

[0002] Quantum key distribution (QKD) is based on the principles of quantum mechanics. Due to the quantum no-cloning and uncertainty principles, it is a theoretically provable unconditionally secure key distribution system.

[0003] Quantum key distribution often involves complex optical signal encoding and decoding processes. Currently, the required encoders and decoders are often based on a combination of traditional fiber optic devices, which are large in size and expensive.

[0004] Polarization coding schemes are one of the mainstream quantum key distribution schemes. They are mainly implemented through a phase modulation-based polarization coding process, that is, for two light components with polarization states of |H> and |V>, a phase difference is formed between the two light components through phase modulation. The two components, after being vector-composed, will form a polarization state as follows: The polarized light signal. Therefore, it can be seen that the phase difference between the two components of the input light signal can be adjusted using a phase modulator. The required polarization coding is implemented on the optical signal.

[0005] Currently, mainstream polarization encoders are implemented using a combination of fiber optic devices and polarization-maintaining phase modulators, which generally result in large size and high cost. To address this, existing technologies have proposed solutions for implementing optical signal encoding and decoding on optical chips, thus providing an important approach to achieving small-size, low-cost, and highly stable quantum key distribution devices.

[0006] Figure 1 This paper illustrates a prior art polarization coding QKD system based on a silicon-based integrated chip, which constructs a polarization encoder using a beam splitter, a polarization rotating beam combiner, and a silicon-based phase shifter.

[0007] In QKD systems, silicon-based phase modulators based on the plasmon dispersion effect generally suffer from modulation-dependent losses, meaning that the attenuation varies depending on the phase being modulated. Therefore, the attenuation of the input optical signal varies when modulating different polarization states, ultimately leading to unbalanced power in the output polarized optical signal. However, in quantum key distribution, theoretically, all dimensions except polarization must be indistinguishable. Therefore, existing technologies have proposed solutions that sacrifice a certain security key generation rate to address this problem, but this reduction in key generation rate is also detrimental to quantum key distribution.

[0008] Furthermore, polarization modulation in the QKD system is based on phase adjustment, and the polarization state of the output light can be written as... It is related to the modulated phase difference. Currently, the half-wave voltage (the driving voltage required to achieve a π phase shift) of silicon-based phase modulators is generally large. For quantum key distribution, at least four polarization states are generally required for encoding, for example... At that time, the encoder outputs |+>; At that time, the encoder outputs |R>; At that time, the encoder outputs |->; At this time, the encoder outputs |L>. Therefore, the maximum drive voltage often needs to reach 1.5 times the half-wave voltage, and it also needs to be able to switch rapidly between four different levels (0, 0.5 times the half-wave voltage, half-wave voltage, and 1.5 times the half-wave voltage). This places high demands on the drive circuit, requiring complex solutions and expensive components, or even making it impossible to implement. Furthermore, as the drive voltage increases, devices such as power amplifiers are often required. When four levels are required in quantum key distribution, the power amplifier operates at different operating points, and the final output drive voltage is affected by environmental factors such as temperature, introducing significant encoding errors. This often requires the design of monitoring and compensation units for compensation, but the technical complexity and cost of such monitoring and compensation units are very high. Summary of the Invention

[0009] To address the aforementioned problems in existing technologies, this invention proposes a polarization-encoded chip and encoding method for quantum key distribution. By incorporating three phase modulators within the polarization encoding unit, polarization state encoding can be achieved with lower driving voltages and fewer different voltage levels. This eliminates the need for complex monitoring and compensation devices on the chip, making the polarization encoding chip easier to implement and providing better high and low temperature stability. Furthermore, by setting a pre-compensation unit implemented by phase modulators outside the polarization encoding unit, when attenuation changes occur during different polarization encoding of the optical signal, an additional modulation phase is applied to the optical signal corresponding to the modulation phase of the phase modulator in the polarization encoding unit, introducing additional attenuation. This ensures that the total attenuation generated by the polarization encoding module on the optical signal is a preset fixed value, effectively guaranteeing power balance across different polarization states, better meeting the requirements of quantum key distribution, eliminating the need for power imbalance correction, and improving the secure key generation rate.

[0010] The first aspect of the present invention relates to an on-chip polarization coding method for quantum key distribution, comprising a decoy state coding step, an intensity modulation step, and a polarization coding step;

[0011] The decoy state coding step is used to decoy state code the optical signal;

[0012] The intensity modulation step is used to modulate the intensity of the optical signal;

[0013] The polarization encoding step is used to polarize the optical signal, and includes encoding sub-steps;

[0014] In the encoding sub-step, the optical signal is split into first and second components; the first component undergoes two phase modulations, with the modulation phases being the first phase, respectively. Second phase A phase modulation is performed on the second component, and the modulation phase is the third phase. Furthermore, the phase-modulated first and second components are polarized and combined, j = 1, ..., N, where N is a natural number.

[0015] Further, in the encoding sub-step, the first phase Second phase and the third phase Configured to form a phase difference between the first and second components The phase difference Selected from the preset first phase set.

[0016] Furthermore, the polarization encoding step further includes a pre-compensation sub-step for phase modulation of the optical signal, wherein the modulation phase is the fourth phase.

[0017] The fourth phase The total attenuation value IL of the optical signal in the polarization encoding step is set to a fixed value.

[0018] Furthermore, the polarization encoding step further includes a fixed value setting sub-step, wherein the fourth phase is set... The phase difference is zero. The total attenuation value IL(j) when taking values ​​in the first phase set is set as the fixed value, and the maximum value among the total attenuation values ​​IL(j) is set as the fixed value.

[0019] Optionally, the first phase set includes 0, π / 2, π, and 3π / 2. The phase combination formed by the first phase, the second phase, and the third phase... Selected from the phase group set [(0, 0, 0), (0, π / 2, 0), (π / 2, π / 2, 0), (0, 0, π / 2)].

[0020] A second aspect of the present invention relates to a polarization coding chip for quantum key distribution, comprising a decoy state coding module, an intensity modulation module, and a polarization coding module;

[0021] The decoy state encoding module is configured to perform decoy state encoding on the optical signal;

[0022] The intensity modulation module is configured to perform intensity modulation on the optical signal;

[0023] The polarization encoding module is configured to perform polarization encoding on the optical signal and includes a polarization encoding unit;

[0024] The polarization encoding unit includes a first optical beam splitter, a first phase modulator, a second phase modulator, a third phase modulator, and a polarization beam combiner; wherein,

[0025] The first optical beam splitter is configured to split the optical signal into first and second components;

[0026] The first, second, and third phase modulators are disposed between the first optical beamsplitter and the polarization beam combiner, wherein the first phase modulator is used to modulate the first phase on the first component. The second phase modulator is used to modulate the second phase on the first component. The third phase modulator is used to modulate a third phase on the second component.

[0027] The polarization combiner is configured to combine the first and second components.

[0028] Furthermore, the first phase Second phase and the third phase Configured to form a phase difference between the first and second components The phase difference Selected from the preset first phase set.

[0029] Furthermore, the polarization encoding module also includes a pre-compensation unit;

[0030] The pre-compensation unit includes a fourth phase modulator, which is used to phase modulate the optical signal, and the modulation phase is the fourth phase.

[0031] The fourth phase It is configured such that the total attenuation value IL of the optical signal in the polarization encoding module is a fixed value.

[0032] Furthermore, the fixed value is in the fourth phase When it is zero, the phase difference The maximum value of the total attenuation value IL(j) when taking values ​​in the first phase set.

[0033] Optionally, the first phase set includes 0, π / 2, π, and 3π / 2. The phase combination formed by the first phase, the second phase, and the third phase... Selected from the phase group set [(0, 0, 0), (0, π / 2, 0), (π / 2, π / 2, 0), (0, 0, π / 2)].

[0034] Furthermore, the decoy state coding module includes a Mach-Zehnder interferometer, which has a second optical beam splitter, a fifth phase modulator, a sixth phase modulator, and a third optical beam splitter;

[0035] The second optical beam splitter is configured to split the optical signal into two components;

[0036] The fifth phase modulator is configured to perform phase modulation on one of the two components;

[0037] The sixth phase modulator is configured to perform phase modulation on the other of the two components;

[0038] The third optical beam splitter is configured to cause interference between the two components.

[0039] Preferably, the first output terminal of the third optical beam splitter is connected to an adjustable optical attenuator; and / or, the second output terminal of the third optical beam splitter is connected to a photodiode.

[0040] Optionally, the tunable optical attenuator is implemented based on the carrier injection principle or based on a Mach-Zehnder interferometer; and / or, the photodiode is a germanium photodiode epitaxially grown on silicon material.

[0041] Furthermore, the intensity modulation module includes a fourth optical beam splitter, a seventh phase modulator, and the first optical beam splitter.

[0042] Preferably, the optical beam splitter is a multimode interferometer or a directional coupler; and / or, the polarization beam combiner is a two-dimensional grating; and / or, the phase modulator is a high-speed phase modulator based on the principle of plasma dispersion; and / or, the sixth and seventh phase modulators are low-speed phase modulators based on the thermo-optic effect; and / or, the polarization encoding chip is made of silicon. Attached Figure Description

[0043] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This illustrates a prior art polarization-encoded QKD system based on a silicon-based integrated chip;

[0046] Figure 2 An example of a polarization-coded chip for quantum key distribution according to the present invention is shown. Detailed Implementation

[0047] In the following description, 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 in order to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited to the embodiments disclosed herein.

[0048] Figure 2 An example of a polarization-coded chip for quantum key distribution according to the present invention is shown.

[0049] like Figure 2 As shown, the polarization encoding chip according to the present invention may include a decoy state encoding module, an intensity modulation module, and a polarization encoding module, which are used to perform decoy state encoding, intensity modulation, and polarization encoding on the optical signal, respectively. The polarization encoding chip receives the input optical signal via the input waveguide 100 and outputs the polarization-encoded optical signal via the output waveguide 800.

[0050] In this invention, the polarization coding module includes a polarization coding unit for implementing polarization coding on an optical signal. For example... Figure 2 As shown, the polarization coding unit may include a first optical beam splitter 204, a polarization beam combiner 700, and a first phase modulator 303, a second phase modulator 304, and a third phase modulator 305 disposed between the first optical beam splitter 204 and the polarization beam combiner 700.

[0051] In the polarization coding unit, the first optical beam splitter 204 splits the optical signal into first and second components, and outputs the first and second components through its first and second split ends, respectively.

[0052] The first beam splitter 204 is connected to the first input of the polarization combiner 700 via a first waveguide, and the second beam splitter is connected to the second input of the polarization combiner 700 via a second waveguide, thereby allowing the first and second components to be transmitted to the polarization combiner 700.

[0053] At polarization combiner 700, the first and second components are polarized and combined to form a polarization-coded optical signal, which is then output through output waveguide 800.

[0054] First and second phase modulators 303 and 304 are formed on the first waveguide, thereby allowing the first component to be phase modulated twice before it reaches the polarization combiner 700, wherein the first phase modulator 303 modulates the first phase on the first component. The second phase modulator 304 modulates the second phase on the first component. Simultaneously, a third phase modulator 305 is formed on the second waveguide to modulate the third phase on the second component before it reaches the polarization combiner 700. Where j = 1, ..., N, and N is a natural number.

[0055] Therefore, in the polarization encoding process, it is permissible to reasonably set the first phase. Second phase and the third phase The combination of the first and second components forms a phase difference corresponding to the polarization encoding between them. in, It can be selected from the first phase set, which corresponds to the polarization state that needs to be encoded in the adopted polarization encoding scheme.

[0056] For example, in a conventional four-polarization-state encoding scheme, encoding is required between four polarization states: |+>, |R>, |->, and |L>. Correspondingly, phase differences of magnitude 0, π / 2, π, and 3π / 2 need to be formed between the first and second components. At this point, the first phase set is [0, π / 2, π, 3π / 2], where N = 4.

[0057] As mentioned above, by means of the polarization coding unit of the present invention, the first phase can be utilized. Second phase and the third phase The combination of these factors achieves this phase difference.

[0058] Table 1 shows the first phase. Second phase and the third phase Several phase combinations can be used to achieve the phase difference in the first phase set required for polarization encoding.

[0059]

[0060] (Table 1)

[0061] Therefore, by utilizing the polarization encoding unit of this invention, the phase modulator can achieve the four polarization states required by the polarization encoding scheme by providing a maximum modulation phase of π / 2. That is, the maximum driving voltage required by the polarization encoding unit of this invention is only 0.5 times the half-wave voltage, which is reduced to 1 / 3 of the maximum driving voltage required by existing technologies. This significantly reduces the driving voltage of the polarization encoding unit and decreases the requirements on the driving circuit. Furthermore, it is noted that in the polarization encoding unit of this invention, the modulation phase of each phase modulator only needs to switch between 0 and π / 2. In other words, the driving signal used for the phase modulator only needs to switch between two different levels, which is only half the number of four level signals required by existing schemes. This significantly reduces the complexity of the driving circuit control process and improves its usability and stability. Therefore, the polarization encoding chip using this polarization encoding unit can use a lower driving voltage, is easier to implement, has good high and low temperature stability, requires no complex monitoring and compensation, and its cost and size do not increase significantly.

[0062] Furthermore, considering that the uneven attenuation in existing polarization coding processes is due to the introduction of different attenuations into the optical signal when performing different polarization coding, therefore, as Figure 2 As shown, the present invention also introduces a pre-compensation unit in the polarization encoding module, which adds a pre-compensation step for attenuation of the optical signal on the basis of the original polarization encoding process, compensates for the attenuation difference in the polarization encoding process, and ensures that the total attenuation value generated by the polarization encoding module on the optical signal is a fixed value when encoding different polarization states, that is, the different polarization optical signals output by its polarization encoding have the same power (light intensity).

[0063] Furthermore, such as Figure 2 As shown, the pre-compensation unit of this invention does not employ conventional intensity modulation devices or functional structures such as intensity modulators. Instead, it proposes to implement this pre-compensation unit using a fourth phase modulator 302, specifically for the application scenario of polarization coding chips. While conventional devices such as intensity modulators have power regulation functions, they are not entirely suitable for solving the attenuation imbalance problem of polarization coding chips. In existing coding chips, the attenuation difference of phase modulators corresponding to different modulation phases is relatively small, thus requiring high power regulation accuracy to compensate for this difference. In contrast, conventional power regulation devices such as intensity modulators have excessively large regulation ranges, requiring complex control processes to achieve this attenuation compensation; at the same time, the structure of such power regulation devices is relatively complex, unnecessarily increasing the complexity of chip fabrication processes and hindering miniaturization.

[0064] In the pre-compensation unit of this invention, the passive variation in the phase modulator is compensated by the active attenuation change of one phase modulator, thereby overcoming the attenuation imbalance problem caused by such undesired attenuation value changes. Furthermore, the pre-compensation unit of this invention can have the same characteristics as the phase modulator in the polarization coding unit, thus allowing the required attenuation compensation to be provided in a very simple manner, and its compensation accuracy is consistent with the attenuation change accuracy in the polarization coding unit, enabling very precise attenuation compensation; moreover, both have consistent environmental stability, thus allowing for stable compensation effects. Simultaneously, the pre-compensation unit implemented using a phase modulator requires a relatively simple manufacturing process and a relatively small size, which is highly advantageous for the chip.

[0065] Specifically, in the pre-compensation unit of the present invention, the fourth phase modulator 302 can perform phase modulation on the optical signal, and its modulation phase is the fourth phase. This achieves synchronization with the fourth phase in the optical signal. The corresponding attenuation serves as attenuation pre-compensation.

[0066] In this invention, a fourth phase is reasonably set in the pre-compensation unit. It can always keep the total attenuation value IL of the optical signal in the polarization encoding module at a fixed value.

[0067] Therefore, this fixed value can be set in advance using a fixed value setting step. As an example, in the fixed value setting step, the fourth phase can be... The value is zero, and each phase value in the first phase set is set as the phase difference. The total attenuation value IL(j) generated by the polarization encoding module on the optical signal is recorded. Therefore, the maximum value of the total attenuation value IL(j) can be set to a fixed value.

[0068] Subsequently, multiple fourth phases can be obtained in advance to ensure that the total attenuation value IL of the encoding module is fixed. and phase difference The phase combination. Therefore, when performing polarization encoding, the phase difference required for polarization encoding can be conveniently determined. Determine the fourth phase Therefore, a phase difference can be formed between the first and second components in the polarization coding unit. The optical signal is modulated by the fourth phase modulator 302 in the pre-compensation unit with a fourth phase value. Phase modulation ensures that the total attenuation value IL generated on the optical signal by the polarization encoding module during polarization encoding is a preset fixed value. Therefore, the polarization encoding module can stably output optical signals with different polarization states but the same power.

[0069] like Figure 2 As shown, as an example, the decoy state coding module can be implemented using a Mach-Zehnder interferometer, which has a second optical beam splitter 201, a fifth phase modulator 301, a sixth phase modulator 401, and a third optical beam splitter 202.

[0070] In the decoy state encoding module, the second optical beam splitter 201 splits the optical signal into two components. The fifth phase modulator 301 and the sixth phase modulator 401 modulate the phase of one of the two components, respectively. The two modulated components eventually interfere at the third optical beam splitter 202. Therefore, by adjusting the modulation phase provided by the fifth phase modulator 301, decoy state encoding (e.g., generating the signal state and the decoy state) of the optical signal can be achieved. Specifically, the sixth phase modulator 401 can be adjusted before decoy state encoding to ensure the Mach-Zehnder interferometer is at the correct operating point.

[0071] Preferably, an adjustable optical attenuator 500 and a photodiode 600 can be connected to the two outputs of the third optical beam splitter 202, respectively, thereby allowing the power of the input optical signal to be monitored by means of the photodiode 600 and the optical signal to be attenuated to the single-photon level by means of the adjustable optical attenuator 500.

[0072] As an example, the tunable optical attenuator 500 can be implemented based on the carrier injection principle or based on a Mach-Zehnder interferometer.

[0073] As an example, photodiode 600 can be a germanium photodiode epitaxially grown on silicon material.

[0074] See also Figure 2 As an example, the intensity modulation module can be implemented using a fourth optical beam splitter 203, a seventh phase modulator 402, and a first optical beam splitter 204. Those skilled in the art will understand that in the intensity modulation module, the optical signal can be intensity modulated by adjusting the modulation phase of the seventh phase modulator 402.

[0075] In a preferred embodiment, the polarization-encoded chip can be formed of silicon. For example, the first to seventh phase modulators, the first to fourth optical beamsplitters, the polarization combiner 700, and the corresponding waveguides can be implemented using silicon.

[0076] Preferably, the first to fourth optical beam splitters can be multimode interferometers or directional couplers.

[0077] Preferably, the polarization combiner 700 can be a polarization rotation combiner, such as a two-dimensional grating.

[0078] Preferably, the first to seventh phase modulators can be high-speed phase modulators based on the principle of plasma dispersion effect, such as carrier deposition type, carrier injection type or carrier depletion type.

[0079] In addition, the sixth and seventh phase modulators can also be low-speed phase modulators based on the thermo-optical effect.

[0080] In summary, the polarization coding chip of this invention can effectively ensure power balance across different polarization states, better meeting the requirements of quantum key distribution, eliminating the need for power imbalance correction, and thus improving the secure key generation rate. Furthermore, it allows for polarization state encoding with lower driving voltages and fewer different voltage levels, eliminating the need for complex monitoring and compensation processes on the chip. The polarization coding chip is easier to implement and exhibits better high and low temperature stability.

[0081] Meanwhile, this invention also discloses an on-chip polarization coding method for quantum key distribution, which includes a decoy state coding step, an intensity modulation step, and a polarization coding step. The decoy state coding step is used to perform decoy state coding on the optical signal, the intensity modulation step is used to modulate the intensity of the optical signal, and the polarization coding step is used to perform polarization coding on the optical signal.

[0082] The polarization encoding step of the present invention may include an encoding sub-step, wherein: the optical signal is split into first and second components; and phase modulation is performed twice on the first component, the modulation phases of which are respectively the first phase. Second phase A phase modulation is performed on the second component, and its modulation phase is the third phase. Then, the phase-modulated first and second components are polarized and combined to generate a polarization-coded optical signal.

[0083] In the encoding sub-step, the first phase Second phase and the third phase It is configured to form a phase difference between the first and second components. Wherein, the phase difference δ Selected from the preset first phase set.

[0084] For a first set of phases including 0, π / 2, π, and 3π / 2, a phase combination consisting of the first, second, and third phases can be selected from the phase group set [(0, 0, 0), (0, π / 2, 0), (π / 2, π / 2, 0), (0, 0, π / 2)]. This allows for polarization coding schemes to be implemented with lower driving voltages.

[0085] Furthermore, the polarization encoding step of the present invention may further include a pre-compensation sub-step for performing a fourth phase adjustment on the optical signal. Phase modulation. Therefore, the fourth phase can be rationally configured according to the polarization coding. This ensures that the total attenuation value IL of the optical signal in the polarization encoding step is a fixed value.

[0086] To determine this fixed value, the polarization encoding step may further include a fixed value setting sub-step, wherein the fourth phase is set to a fixed value. The value is zero, and the phase difference is recorded. The total attenuation value IL(j) is taken from the first phase set, and the maximum value among the total attenuation values ​​IL(j) is set to this fixed value. This allows compensation for the attenuation changes introduced into the optical signal when different polarization states are encoded during the polarization coding process, ensuring that the optical signal has a fixed total attenuation value in the polarization coding step, thus obtaining polarization coding that is more consistent with quantum key distribution.

[0087] Although the present invention has been described above with reference to the accompanying drawings and specific embodiments, those skilled in the art will readily recognize that the above embodiments are merely exemplary and 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 on-chip polarization coding method for quantum key distribution, comprising a decoy state coding step, an intensity modulation step, and a polarization coding step; The decoy state coding step is used to decoy state code the optical signal; The intensity modulation step is used to modulate the intensity of the optical signal; The polarization encoding step is used to polarize the optical signal, and includes encoding sub-steps; In the encoding sub-step, the optical signal is split into first and second components; the first component undergoes two phase modulations, with the modulation phases being the first phase, respectively. Second phase A phase modulation is performed on the second component, and the modulation phase is the third phase. Furthermore, the phase-modulated first and second components are polarized and combined, j = 1, ..., N, where N is a natural number.

2. The on-chip polarization coding method as described in claim 1, wherein, In the encoding sub-step, the first phase Second phase and the third phase Configured to form a phase difference between the first and second components The phase difference Selected from the preset first phase set.

3. The on-chip polarization coding method as described in claim 2, wherein, The polarization encoding step further includes a pre-compensation sub-step for phase modulation of the optical signal, wherein the modulation phase is the fourth phase. The fourth phase The total attenuation value IL of the optical signal in the polarization encoding step is set to a fixed value.

4. The on-chip polarization coding method as described in claim 3, wherein, The polarization encoding step further includes a fixed value setting sub-step, wherein the fourth phase is set... The phase difference is zero. The total attenuation value IL(j) when taking values ​​in the first phase set is set as the fixed value, and the maximum value among the total attenuation values ​​IL(j) is set as the fixed value.

5. The on-chip polarization coding method according to any one of claims 2-4, wherein, The first phase set includes 0, π / 2, π, and 3π / 2.

6. The on-chip polarization coding method as described in claim 5, wherein, Phase combination formed by the first phase, the second phase and the third phase Selected from the phase group set [(0, 0, 0), (0, π / 2, 0), (π / 2, π / 2, 0), (0, 0, π / 2)].

7. A polarization coding chip for quantum key distribution, comprising a decoy state coding module, an intensity modulation module, and a polarization coding module; The decoy state encoding module is configured to perform decoy state encoding on the optical signal; The intensity modulation module is configured to perform intensity modulation on the optical signal; The polarization encoding module is configured to perform polarization encoding on the optical signal and includes a polarization encoding unit; The polarization encoding unit includes a first optical beam splitter, a first phase modulator, a second phase modulator, a third phase modulator, and a polarization beam combiner; wherein, The first optical beam splitter is configured to split the optical signal into first and second components; The first, second, and third phase modulators are disposed between the first optical beamsplitter and the polarization beam combiner, wherein the first phase modulator is used to modulate the first phase on the first component. The second phase modulator is used to modulate the second phase on the first component. The third phase modulator is used to modulate a third phase on the second component. The polarization combiner is configured to combine the first and second components.

8. The polarization encoding chip as described in claim 7, wherein, First phase Second phase and the third phase Configured to form a phase difference between the first and second components The phase difference Selected from the preset first phase set.

9. The polarization encoding chip as described in claim 8, wherein, The polarization encoding module also includes a pre-compensation unit; The pre-compensation unit includes a fourth phase modulator, which is used to phase modulate the optical signal, and the modulation phase is the fourth phase. The fourth phase It is configured such that the total attenuation value IL of the optical signal in the polarization encoding module is a fixed value.

10. The polarization encoding chip as described in claim 9, wherein, The fixed value is in the fourth phase When it is zero, the phase difference The maximum value of the total attenuation value IL(j) when taking values ​​in the first phase set.

11. The polarization encoding chip as described in claim 8, wherein, The first phase set includes 0, π / 2, π, and 3π / 2.

12. The polarization encoding chip as described in claim 11, wherein, Phase combination formed by the first phase, the second phase and the third phase Selected from the phase group set [(0, 0, 0), (0, π / 2, 0), (π / 2, π / 2, 0), (0, 0, π / 2)].

13. The polarization encoding chip according to any one of claims 7-12, wherein, The decoy state coding module includes a Mach-Zehnder interferometer, which has a second optical beam splitter, a fifth phase modulator, a sixth phase modulator, and a third optical beam splitter; The second optical beam splitter is configured to split the optical signal into two components; The fifth phase modulator is configured to perform phase modulation on one of the two components; The sixth phase modulator is configured to perform phase modulation on the other of the two components; The third optical beam splitter is configured to cause interference between the two components.

14. The polarization encoding chip as described in claim 13, wherein, The first output terminal of the third optical beam splitter is connected to an adjustable optical attenuator; and / or, the second output terminal of the third optical beam splitter is connected to a photodiode.

15. The polarization encoding chip as described in claim 14, wherein, The tunable optical attenuator is implemented based on the carrier injection principle or based on a Mach-Zehnder interferometer; and / or, the photodiode is a germanium photodiode epitaxially grown on silicon material.

16. The polarization encoding chip as described in claim 13, wherein, The intensity modulation module includes a fourth optical beam splitter, a seventh phase modulator, and the first optical beam splitter.

17. The polarization encoding chip as described in claim 16, wherein: The optical beam splitter is a multimode interferometer or a directional coupler; and / or... The polarization beam combiner is a two-dimensional grating; and / or The phase modulator is a high-speed phase modulator based on the principle of plasmonic dispersion; and / or The sixth and seventh phase modulators are low-speed phase modulators based on the thermo-optic effect; and / or, The polarization encoding chip is made of silicon.

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