Intensity modulation device for QKD

Abstract

The invention provides an intensity modulation device for a QKD, and relates to the technical field of quantum communication, the intensity modulation device comprises a beam splitter, a beam combiner and an intensity modulation basic unit, when signal light and vacuum state pulse signals are modulated, the influence of a code pattern effect on output light intensity and relevance is greatly reduced, and the intensity of the output light intensity is modulated based on the construction of the basic intensity modulation unit. The intensity modulation device can limit the influence of the small change of the voltage on the output intensity within a small range when the intensity output is maximum, realizes modulation of a signal state, a decoy state and a vacuum state based on the intensity modulation device, limits the ratio of the light intensity change caused by the code pattern effect to the output light intensity within a small range, and improves the light intensity modulation efficiency. Side channels on a time domain are reduced, and modulation of a signal state, a decoy state and a vacuum state is realized.

Description

Technical Field

[0001] The present invention provides an intensity modulation device for QKD, which relates to the technical field of quantum communication. Background Art

[0002] The decoy state method is an important means to enhance the security of existing QKD protocols. The QKD protocol based on decoy states requires the preparation of at least three kinds of optical pulses with different intensities: signal states, decoy states, and vacuum states, which has higher requirements for the intensity modulation of QKD optical pulses.

[0003] The principle of existing commercial intensity modulators (IMs) is as Figure 1 shown: The light input to the IM is split with a splitting ratio of 1:1 and enters the MZ interferometer. There are lithium niobate waveguides in the upper and lower paths of the interferometer, and external electrodes apply bias voltages to the upper and lower waveguide paths to modulate the light entering the two lithium niobate waveguides into opposite phases, forming a phase difference. The two beams of light interfere and combine after passing through the lithium niobate waveguides. Let the intensity of the input light be I in , and the intensity of the output light after interference and combination is We change α by adjusting the bias voltage, thereby changing the output light intensity to achieve intensity modulation.

[0004] When the existing intensity modulators are applied to the QKD protocol with decoy states, the following problems exist:

[0005] The voltage-frequency response curve of the modulator is usually not flat. Therefore, when modulating signal pulses, especially when modulating high-frequency signals, the historical signal sequence may affect the amplitude of future modulation signals. For example, when the previous pulse is a signal state, a vacuum state, or a decoy state, and the next pulse is modulated to a signal state, the amplitude of this signal state may be different. That is, the pulse intensity is correlated with the amplitude of the previous pulse, and this phenomenon is called the patterning effect. The patterning effect may generate a time-domain related side channel, affecting the communication security of QKD.

[0006] The change rate of the output intensity I out with respect to the phase difference α is When α = 0 or π, the intensity of the modulation output is the maximum / minimum. At this time, since the intensity-phase change rate is the smallest, that is, the intensity changes less when the bias voltage changes, the patterning effect is smaller; while when modulating decoy states, since the decoy state intensity is between the signal state and the vacuum state, sinα is relatively large at this time, so the intensity changes more when the bias voltage changes, resulting in a greater patterning effect for decoy state pulses and a greater impact on communication security.

[0007] Previously, post - processing was mostly used in QKD to reduce the influence of the pulse pattern effect, and specific pulses were discarded according to the correlation between the front and back pulses. However, post - processing means discarding some pulses, thus reducing the key generation rate of QKD.

[0008] In existing patents (such as CN114338004B, CN115333724A, CN113079007A), by adjusting the splitting ratio and changing the connection structure between IMs, when modulating the signal state, decoy state, and vacuum state, each IM can be at the maximum intensity or extinction, thereby reducing the influence of the pulse pattern effect. However, in the above - mentioned solutions, even when each IM is at the maximum intensity or extinction, the pulse pattern effect still exists. In particular, the pulse pattern effect in the signal state and decoy state is difficult to be restricted within a small range, affecting communication security. Summary of the Invention

[0009] To solve the above - mentioned technical problems, the present invention proposes a basic intensity - modulation unit based on a Mach - Zehnder interferometer for QKD, which includes: a beam splitter (BS), a Mach - Zehnder interferometer, multiple serially - connected intensity modulators, a phase - modulation element, a polarization - maintaining beam splitter (PBS), and a variable optical attenuator.

[0010] The input light is split by the BS with an intensity ratio of 1:1 and enters the two arms of the Mach - Zehnder interferometer respectively. Among them, there are multiple serially - connected intensity modulators in the upper arm; the lower arm is provided with a phase - modulation element and a variable optical attenuator, and the light passing through the two arms is combined by polarization - maintaining interference of the PBS and then output.

[0011] In a preferred embodiment, when in use, it is initialized according to the following steps:

[0012] Adjust the bias voltage of each intensity modulator so that the peak power of the optical signal in the upper arm is the maximum and the extinction ratio in the vacuum state is the highest. Adjust the attenuation of the variable optical attenuator so that the peak powers of the optical signals in the two arms of the Mach - Zehnder interferometer are the same.

[0013] Keep the intensity modulators and the variable optical attenuator unchanged, and adjust the phase - modulation element until the power of the interference output of the light passing through the two arms is the minimum.

[0014] In a preferred embodiment, after initialization, during use, keep the phase modulator and the variable optical attenuator unchanged. When all the intensity modulators are adjusted to the maximum intensity, the output of the basic intensity - modulation unit is the minimum at this time; when all the intensity modulators are adjusted to the minimum intensity, the output of the basic intensity - modulation unit is the maximum at this time.

[0015] The present invention also proposes a basic intensity - modulation unit based on a Sagnac interferometer for QKD, which includes: a Sagnac interferometer, a beam splitter (BS), multiple serially - connected intensity modulators, and a unidirectional isolator.

[0016] The input optical signal passes through an optical isolator, allowing the input light to enter the Sagnac interferometer unidirectionally. The optical signal entering the Sagnac interferometer is split by a beam splitter (BS) in a 1:1 intensity ratio and enters the clockwise and counterclockwise directions of the Sagnac interferometer respectively. A plurality of intensity modulators are connected in series at the entrance near the counterclockwise direction in the Sagnac interferometer, and the light in the clockwise and counterclockwise directions is combined by interference through the BS and then output.

[0017] In a preferred embodiment, the method to maximize the output optical intensity of the basic intensity modulation unit is as follows: during the time period t1 of the optical pulse cycle, each intensity modulator is adjusted to the minimum intensity to achieve extinction of the intensity modulator; in the remaining time periods, each intensity modulator is adjusted to the maximum intensity. Where the time t1 satisfies the condition that during the time period t1, the optical pulse in the counterclockwise optical path passes through each intensity modulator, while the optical pulse in the clockwise optical path does not pass through any intensity modulator. The method to minimize the output optical intensity of the basic intensity modulation unit is to adjust each intensity modulator to the maximum intensity during the optical pulse cycle.

[0018] In a preferred embodiment, the upper arm or the counterclockwise optical path is defined as the modulation optical path, and the lower arm or the clockwise optical path is defined as the constant optical path. The maximum output optical intensity of the basic intensity modulation unit is I, the maximum output optical intensity of the modulation optical path is I, and the output optical intensity of the constant optical path is I. Let the ratio of the output to the input optical intensity of the nth intensity modulator in the modulation optical path be a n +Δa n where a n is the ratio under ideal conditions, and Δa n is the change in the ratio caused by external interference.

[0019] The output optical intensity of the modulation optical path is:

[0020]

[0021] The optical intensity after beam combination is:

[0022]

[0023] When the output optical intensity of the basic intensity modulation unit is maximized, each a n = 0. Considering the influence of Δa n , the output optical intensity is:

[0024]

[0025] When the output optical intensity of the basic intensity modulation unit is minimized, each a n = 1. Considering the influence of Δa n , the output optical intensity is:

[0026]

[0027] In a preferred embodiment, when k = 4, during the modulation of the luminous state, the ratio of the output of each intensity modulator to the input optical intensity is set as: 1 - Δa - Δa'. When the input optical intensity is I, the output optical intensity of the intensity modulation basic unit is: I(1 - 2(Δa + Δa′)) 2 ). When the extinction ratio of each intensity modulator is 20 dB, each |Δa n | ≤ 10e-2; during the modulation of the extinction state, the output optical intensity of the intensity modulation basic unit is During the modulation of the luminous state, the output optical intensity of the intensity modulation basic unit is I; the extinction ratio is The fluctuation of the luminous state intensity is not greater than

[0028] The present invention also proposes an intensity modulation device for QKD, including a beam splitter, a combiner, and the above-mentioned intensity modulation basic unit;

[0029] The input optical signal is split by a beam splitter into several paths of light with different intensities. Each path is modulated by one or more series-connected intensity modulation basic units, and the modulated light is combined by a combiner and then output; the intensity modulation device for QKD uses one path to emit light and the other paths to be in extinction, modulating three or more signal states, decoy states, and vacuum state optical pulses with different intensities.

[0030] Compared with the prior art, the input light is split into two paths by a beam splitter, and the splitting ratio is η, where 0 < η < 0.5; a plurality of the above-mentioned intensity modulation basic units are respectively connected in series on each arm to perform intensity modulation, and the light of the two arms is combined after modulation to output signal state, decoy state, and vacuum state optical pulses;

[0031] When all the intensity modulation basic units on the upper path are in extinction and all the intensity modulation basic units on the lower path output the maximum, a signal state optical pulse is output;

[0032] When all the intensity modulation basic units on the upper path output the maximum and all the intensity modulation basic units on the lower path are in extinction, a decoy state optical pulse is output;

[0033] When the intensity modulation basic units on both the upper and lower paths output the minimum, a vacuum state optical pulse is output;

[0034] In a preferred embodiment, the intensity ratio of the signal state and decoy state optical pulses is (1 - η):η.

[0035] Compared with the prior art, the present invention has the following beneficial technical effects:

[0036] (1) A basic unit for intensity modulation in QKD, which can limit the influence of a small change in voltage on the output intensity within a small range when the intensity output is maximum.

[0037] (2) An intensity modulation device for QKD, constructed based on the basic unit of intensity modulation, which can limit the ratio of the light intensity change caused by the pattern effect to the output light intensity within a small range when preparing the signal state and the decoy state, and reduce the side channel in the time domain. Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 Schematic diagram of the principle of the existing intensity modulator;

[0040] Figure 2 Schematic diagram of the structure of the basic unit of intensity modulation based on the MZ interferometer;

[0041] Figure 3 Schematic diagram of the structure of the basic unit of intensity modulation based on the Sagnac interferometer;

[0042] Figure 4 Time domain schematic diagram of the intensity modulator in the counterclockwise optical path when the output of the basic unit of intensity modulation based on the Sagnac interferometer is maximum;

[0043] Figure 5 Time domain schematic diagram of the intensity modulator in the clockwise optical path when the output of the basic unit of intensity modulation based on the Sagnac interferometer is maximum;

[0044] Figure 6 Schematic diagram of the structure of the intensity modulation device in Embodiment 3. Detailed Embodiments

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0046] In the attached drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the components in the system and show the connection relationships of the various parts of the device, only the relative positional relationships between the components are clearly distinguished, and this does not constitute a limitation on the signal transmission direction, connection sequence, and the sizes, shapes of the various parts of the components or structures.

[0047] Secondly, the so-called "one embodiment" or "embodiment" herein refers to specific features, structures, or characteristics that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or selectively exclusive embodiments from other embodiments.

[0048] There are two alternative structures for the structure of the intensity modulation basic unit for QKD based on an interferometer of the present invention, which will be described in Embodiment 1 and Embodiment 2 respectively.

[0049] Embodiment 1

[0050] The intensity modulation basic unit based on an MZ interferometer in this embodiment is as Figure 2 shown. It includes: a BS, an MZ interferometer, a plurality of serially connected intensity modulators, a phase modulation element, a PBS, and a variable optical attenuator.

[0051] The input light is split into two beams by the BS and enters the two arms of the MZ interferometer respectively. Among them, the upper arm is provided with k serially connected intensity modulators IM (in the figure, k = 2 is taken as an example, namely IM1 and IM2). The higher the value of k, the higher the extinction ratio that can be adjusted for this path; the lower arm is provided with a phase modulator PM (or a phase shifter PS) and a variable optical attenuator ATT. The PBS performs polarization-maintaining interference beam combination on the light from the two arms and then outputs it.

[0052] When in use, it is initialized according to the following steps:

[0053] Step 1: Adjust the bias voltage of each intensity modulator IM in the upper arm containing the intensity modulator IM so that the peak power of the upper arm is the largest and the extinction ratio in the vacuum state is the highest. Adjust the attenuation of the ATT so that the peak powers of the two arms of the MZ interferometer are the same.

[0054] Step 2: Keep the intensity modulator IM and the variable optical attenuator ATT unchanged, and adjust the phase modulator PM until the power of the interference output of the path of the IM at the position of the transmitted signal and the path of the phase modulator PM is the smallest.

[0055] Usage method: After the initialization is completed, keep the phase modulator PM and the variable optical attenuator ATT unchanged during the use process. Adjust all the intensity modulators IM in the optical path of the upper arm to the maximum, and at this time the output of the intensity modulation device is the smallest; adjust all the intensity modulators IM to the minimum, and at this time the output of the intensity modulation device is the largest.

[0056] Example 2

[0057] The basic intensity modulation unit based on the Sagnac interferometer in this embodiment is as Figure 3 shown. It includes: a Sagnac interferometer, a beam splitting prism, a plurality of serially connected intensity modulators, and a unidirectional isolator;

[0058] The input optical signal is split by the beam splitting prism BS in a 1:1 ratio and enters the clockwise and counterclockwise directions of the Sagnac interferometer respectively. k IMs are serially connected at the entrance near the counterclockwise direction in the Sagnac interferometer (taking k = 2, IM1 and IM2 as examples in the figure). The light in the clockwise and counterclockwise directions is combined by interference through BS and used as the output. The unidirectional isolator can make the input light enter the Sagnac interferometer unidirectionally and prevent the returned light from affecting the light source end device.

[0059] For the basic intensity modulation unit based on the Sagnac interferometer, the way to make the output of the basic intensity modulation unit maximum is: in the time period t1 of the optical pulse period, each intensity modulator is adjusted to the minimum intensity to make the intensity modulator extinct; in the remaining time periods, each intensity modulator is adjusted to the maximum intensity. Where the time t1 satisfies: within the time period t1, the optical pulse in the counterclockwise optical path passes through each IM, while the optical pulse in the clockwise optical path does not pass through any IM. Figure 4 And Figure 5 is the time domain schematic diagram of the counterclockwise and clockwise intensity modulators when the output of the basic intensity modulation unit is maximum. As shown in the figure, the arrival times of the counterclockwise and clockwise optical pulses at the intensity modulator are inconsistent. Therefore, in the time period t1, each IM is adjusted to the minimum intensity to make the intensity modulator IM extinct; in the remaining time periods, each IM is adjusted to the maximum intensity. The optical pulse in the counterclockwise direction is intensity modulated and extinct within the time period t1, while the optical pulse in the clockwise direction does not fall within t1 and is not extinct.

[0060] The way to make the output of the intensity modulation unit minimum is: in the optical pulse cycle, each intensity modulator is adjusted to the maximum intensity. At this time, the counterclockwise and clockwise optical pulses interfere and extinguish, and the output optical intensity of the basic intensity modulation unit is the lowest, which is the extinction state.

[0061] The following analyzes the principles of the basic intensity modulation units in Example 1 and Example 2.

[0062] In Example 1, assuming that the optical intensities of the upper and lower arms are I 1 and I 2 respectively, when the phase difference between the upper and lower arms is α, the optical intensity after interference and beam combination is When the phase difference is π, the upper and lower paths interfere and extinguish, and at this time the combined optical intensity is the minimum.

[0063] Initialize adjustment step 2 to use PM to adjust the phase difference between the upper and lower arms to interference extinction, so the phase difference between the upper and lower arms is π at this time.

[0064] In Embodiment 2, due to the half-wave loss, there is a phase difference of π between the counterclockwise optical path and the clockwise optical path.

[0065] Therefore, both Embodiment 1 and Embodiment 2 are the interference output of the modulation optical path with a phase difference of π (referring to the optical path with intensity change during modulation, which is the upper arm in Embodiment 1 and the counterclockwise optical path in Embodiment 2) and the constant optical path (referring to the optical path with stable intensity during modulation, which is the lower arm in Embodiment 1 and the clockwise optical path in Embodiment 2). The maximum output light intensity of the intensity modulation basic unit is I, and the maximum output light intensity of the modulation optical path is I. Let the ratio of the output to the input light intensity of the nth (n = 1, 2,..., k) IM be a n +Δa n where a n is the ratio in the ideal case, and Δa n is the change in the ratio caused by external interferences such as the pattern effect.

[0066] The output light intensity of the modulation optical path is:

[0067]

[0068] Also, since the output light intensity of the constant optical path of the intensity modulation basic unit in this embodiment is I, the combined light intensity is:

[0069]

[0070] For the intensity modulation basic unit in this embodiment, when the output is maximum, each a n = 0. Considering the influence of Δa n , the output is:

[0071]

[0072] When the output is minimum, each a n = 1. Considering the influence of Δa n ,

[0073]

[0074] When k ≥ 3, the intensity modulation basic unit in this embodiment can make the influence caused by the pattern effect at the maximum output smaller than that of the existing IM in terms of magnitude. Taking k = 4 as an example, analyze the influence of the pattern effect.

[0075] When modulating the luminescence state, assume that the ratio of the output to the input optical intensity of each IM is 1 - Δa - Δa', where Δa is the influence independent of timing, and Δa' is the influence caused by the pattern effect. Then, if modulated by IM, the ratio of the intensity change caused by the pattern effect to the optical pulse intensity is (neglecting higher-order small quantities) Δa'. When modulating using the basic intensity modulation unit in Embodiment 1 or 2, when the input optical intensity is I, the output is: I(1 - 2(Δa + Δa′) 2 ), and the ratio of the intensity change caused by the pattern effect to the optical pulse intensity is (neglecting higher-order small quantities): 2Δa′ / (2Δa + Δa′).

[0076] Since both Δa and Δa′ are numbers much smaller than 1, the ratio of the intensity change caused by the pattern effect of the basic intensity modulation unit in this embodiment to the optical pulse intensity is much smaller than that of IM. Using the basic intensity modulation unit in this embodiment can reduce the influence of the pattern effect during the luminescence state.

[0077] At the same time, the basic intensity modulation unit in this embodiment can ensure a high extinction ratio.

[0078] Taking k = 4 as an example, the extinction ratio of the IM used in the embodiment is 20 dB. Since the extinction ratio of each IM is less than or equal to Therefore, each |Δa n | ≤ 10e - 2. The output of the basic intensity modulation unit in the extinction state is And the output in the luminescence state is I (neglecting higher-order small quantities). Therefore, when k = 4, the extinction ratio of the basic intensity modulation unit in this embodiment is That is, the intensity modulation device in this embodiment has a higher extinction ratio than IM when k = 4.

[0079] In addition, the extinction ratio of the IM used in the embodiment is 20 dB. According to the above analysis, each |Δa n | ≤ 10e - 2, then the fluctuation of the intensity of the basic intensity modulation unit in the luminescence state is not greater than At the 10e - 4 level.

[0080] Embodiment 3

[0081] Embodiments 1 and 2 describe a basic intensity modulation unit (hereinafter referred to as IM*). The effect is to reduce the pattern effect when the output intensity is maximum without affecting the extinction ratio. Embodiment 3 is to implement QKD intensity modulation based on IM*, and uses the intensity modulation unit components in Embodiments 1 and 2 to modulate the structures of three states with different intensities, which can reduce the pattern effect of each state.

[0082] In practical applications, N IM*s can be connected in series to further improve the extinction ratio. The light can be split by a beam splitter into several paths of light with different intensities, and each path is modulated by one or more series-connected IM*s. After modulation, the light is combined by interference and then output. By using one path to emit light and the other paths to achieve extinction, states with three or more different intensities can be modulated.

[0083] The following calculates the fluctuation and extinction ratio after series connection with N = 2, k = 4, and an IM extinction ratio of 20 dB.

[0084] The maximum fluctuation of the output after series connection is not greater than the sum of the fluctuations of the two IM*s. Based on the calculations in Example 1 and Example 2, the fluctuation of a single IM* is not greater than 2×10e-4, so the total fluctuation is not greater than 4×10e-4.

[0085] Based on the calculations in Example 1 and Example 2, the extinction ratio of each IM* can reach 34 dB. Therefore, the extinction ratio in the extinction state after series connection can reach 68 dB.

[0086] The following examples provide an intensity modulation device based on IM*, which can prepare signal states, decoy states, and vacuum states with different intensities.

[0087] The structure of the intensity modulation device in the example is as Figure 3 shown. The input light is split into two paths by a beam splitter with a splitting ratio of η, where 0 < η < 0.5. N IM*s are respectively connected in series on each arm to perform intensity modulation. The light from the two arms is combined after modulation as the output optical pulse.

[0088] The intensity modulation device prepares signal states, decoy states, and vacuum states according to the following rules:

[0089] When all IM*s on the upper path are in the extinction state and all IM*s on the lower path output the maximum value, a signal state is output;

[0090] When all IM*s on the upper path output the maximum value and all IM*s on the lower path are in the extinction state, a decoy state is output;

[0091] When all IM*s on both the upper and lower paths output the minimum value, a vacuum state is output.

[0092] In the example, the intensity ratio of the signal state and the decoy state modulated by the intensity modulation device is (1 - η):η.

[0093] Furthermore, by increasing the number of N and the number of IMs connected in series in the basic intensity modulation unit IM*, the ratio of the light intensity change caused by the pattern effect to the pulse light intensity in the signal state and the decoy state can be further reduced, thereby reducing the side channel in the time domain and enhancing the security of QKD.

[0094] Compared with existing IMs, the intensity modulation basic unit IM* in Embodiment 1 or 2 can achieve reducing the influence caused by small voltage variations when the output is maximum, so as to avoid the pattern effect when modulating optical pulse patterns with random intensities. Since the present invention pays more attention to whether the prepared signal state and decoy state contain time-domain information, using the intensity modulation based on IM* can effectively reduce the time-domain side channels caused by the pattern effects of the signal state and decoy state, thereby enhancing security.

[0095] Those skilled in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above various methods. Among them, any reference to a memory, database, or other medium used in the various embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memories can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memories can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The databases involved in the various embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the various embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logic devices, data processing logics based on quantum computing, etc., without limitation.

[0096] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0097] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. An intensity modulation basic unit based on MZ interferometer for QKD, characterized in that: include: BS, MZ interferometer, multiple serially connected intensity modulators, phase modulation elements, PBS and variable optical attenuator; The input light is split into two arms of the MZ interferometer at a 1:1 intensity ratio by the BS, where the upper arm has multiple intensity modulators connected in series, and the lower arm is equipped with a phase modulation element and a variable optical attenuator. The light passing through the two arms is combined by the PBS polarization-maintaining interference and then output.

2. The intensity modulation basic unit based on MZ interferometer for QKD according to claim 1, characterized in that: When using, follow the steps below to initialize: Adjust the bias voltage of each intensity modulator so that the peak power of the optical signal in the upper arm is the largest and the vacuum extinction ratio is the highest, and adjust the attenuation of the variable optical attenuator so that the peak power of the optical signal in the two arms of the MZ interferometer is the same; Keep the intensity modulator and variable optical attenuator unchanged, and adjust the phase modulation element until the power of the light interference output passing through the two arms is minimum.

3. The intensity modulation basic unit based on MZ interferometer for QKD according to claim 2, characterized in that: After initialization is completed, the phase modulator and variable optical attenuator are maintained unchanged during use, and the intensity of all intensity modulators is adjusted to the maximum, at which time the output of the intensity modulation basic unit is the minimum; the intensity of all intensity modulators is adjusted to the minimum, at which time the output of the intensity modulation basic unit is the maximum.

4. A basic unit for intensity modulation based on Sagnac interferometer for QKD, characterized in that: include: Sagnac interferometer, BS, multiple intensity modulators in series, and unidirectional isolators; The input optical signal passes through a unidirectional isolator, so that the input light enters the Sagnac interferometer in one direction. The optical signal entering the Sagnac interferometer is split by the BS at a 1:1 intensity ratio and enters the clockwise and counterclockwise directions of the Sagnac interferometer respectively. In the Sagnac interferometer, multiple intensity modulators are connected in series near the counterclockwise entrance, and the clockwise and counterclockwise lights are output after being combined by the BS interference.

5. The intensity modulation basic unit based on Sagnac interferometer for QKD according to claim 4, characterized in that: The way to maximize the output light intensity of the intensity modulation basic unit is: adjust each intensity modulator to the minimum intensity within the t1 time period of the light pulse cycle to make the intensity modulator extinguish; During the remaining time periods, each intensity modulator is adjusted to the maximum intensity; The t1 time satisfies: within the t1 time period, the light pulse of the counterclockwise optical path passes through each intensity modulator, while the light pulse of the clockwise optical path does not pass through any intensity modulator; the way to minimize the output light intensity of the intensity modulation basic unit is: adjust each intensity modulator to the maximum intensity within the optical pulse period.

6. The intensity modulation basic unit according to claim 1 or 5, wherein the upper arm or the counterclockwise optical path is defined as a modulated optical path, and the lower arm or the clockwise optical path is defined as a constant optical path, characterized in that: The maximum output light intensity of the intensity modulation basic unit is I, the maximum output light intensity of the modulated light path is I, and the output light intensity of the constant light path is I; let the ratio of the output to input light intensity of the nth intensity modulator of the modulated light path be a n +Δa n , where a n is the ratio under ideal conditions, Δa n is the ratio change caused by external interference; The output light intensity of the modulated optical path is: The light intensity after beam combination is: When the intensity modulation basic unit outputs the maximum light intensity, each a n =0, considering Δa n The output light intensity is: When the intensity modulation basic unit outputs the minimum light intensity, each a n =1, considering Δa n The output light intensity is:

7. The intensity modulation basic unit according to claim 6, characterized in that: When k=4, when modulating the luminous state, the ratio of the output of each intensity modulator to the input light intensity is: 1-Δa-Δa', when the input light intensity is I, the output light intensity of the intensity modulation basic unit is: I(1-2(Δa+Δa') 2 ); When the extinction ratio of each intensity modulator is 20dB, each |Δa n |≤10e-2; when modulating the extinction state, the output light intensity of the intensity modulation basic unit is When modulating the luminous state, the output light intensity of the intensity modulation basic unit is I; the extinction ratio is The fluctuation of the luminescent state intensity is no greater than 8. An intensity modulation device for QKD, characterized in that: It comprises a beam splitter, a beam combiner and an intensity modulation basic unit as described in any one of claims 1 to 7; A beam splitter is used to split the input optical signal into several paths of light with different intensities, each path is modulated by one or more intensity modulation basic units connected in series, and the modulated light is combined by a beam combiner and then output; the intensity modulation device for QKD adopts a method in which one path is illuminated and the other paths are extinguished to modulate three or more signal state, decoy state and vacuum state light pulses with different intensities.

9. The intensity modulation device for QKD according to claim 8, characterized in that The input light is split into two paths by a beam splitter, and the splitting ratio is η, where 0<η<0.5; a plurality of intensity modulation basic units are connected in series on each arm to perform intensity modulation, and the light of the two arms is combined after modulation to output signal state, decoy state and vacuum state light pulses; When all the intensity modulation basic units of the uplink are extinguished and the output of all the intensity modulation basic units of the downlink is maximum, a signal state optical pulse is output; When the output of all the intensity modulation basic units in the upper path is maximum and all the intensity modulation basic units in the lower path are extinguished, the decoy state light pulse is output; When the output of both the upper and lower intensity modulation basic units is minimum, a vacuum state light pulse is output.

10. The intensity modulation device for QKD according to claim 9, characterized in that: The intensity ratio of the signal state and decoy state light pulses is (1-η):η.

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