CN118300696A

CN118300696A - QKD time-dependent light source side channel suppression method and transmitting end thereof

Info

Publication number: CN118300696A
Application number: CN202410382298.0A
Authority: CN
Inventors: 张万里; 姜聪; 周飞; 李方柯; 刘杨; 王向斌
Original assignee: Jinan Institute of Quantum Technology
Current assignee: Jinan Institute of Quantum Technology
Filing date: 2024-03-29
Publication date: 2024-07-05

Abstract

The invention provides a QKD time-dependent light source side channel inhibition method and a transmitting end thereof, wherein the extinction ratio of a laser light source is improved by simply adjusting the parameters of the laser light source or the parameters of a polarization coding module (such as the shape of a phase modulation signal and/or the arrival time difference of two pulse components relative to a phase modulator) are adjusted, the relevance of the weak light polarization state and polarization coding information among light pulses is weakened, the time-dependent light source side channel is inhibited, the manufacturing process of an intensity modulator is not needed, and the safety limitation caused by imperfect devices can be well overcome, so that the safety of a QKD process is greatly improved in a simple mode and at low cost.

Description

QKD time-dependent light source side channel suppression method and transmitting end thereof

Technical Field

The invention relates to the technical field of quantum secret communication, in particular to a method for inhibiting a QKD time correlation light source side channel and a transmitting end capable of defending the QKD time correlation light source side channel attack.

Background

Quantum Key Distribution (QKD) is fundamentally different from classical key systems in that it uses a single photon or entangled photon pair as the carrier of the key, which in principle can provide unconditionally secure secret communication for users, whose security is ensured by quantum mechanics rationales (hessian-parcels, measurement collapse theory, quantum unclonable theorem, etc.). Because no ideal single photon source is practically available at present, the pulse can be randomly modulated into weak coherent states (signal states and decoy states) with different intensities by adopting a decoy state method, so that the safety of a QKD system formed by a plurality of non-ideal single photon sources is equivalent to that of a QKD system formed by an ideal single photon source. Over the last decade of development, QKD systems based on decoy approaches have begun to move toward the stage of commercial development.

However, the security theory of existing commercial QKD systems does not fully incorporate various types of imperfect side channels, such as the polarization encoded BB84-QKD system that is more mature for commercial, in some cases, the intensity of the light between pulses is greater than zero and can be modulated by the encoder, resulting in a time-dependent light source side channel. Therefore, taking necessary measures in an actual system, suppressing the time-dependent light source side channel has an important meaning for enhancing the actual security of QKD.

Fig. 1 shows a transmitting end of a polarization encoded QKD system based on the BB84 protocol of the prior art, which includes a pulse laser PL, an intensity modulator IM1, a polarization encoder PE, a polarization controller PC, and an attenuator ATT1. In the transmitting end shown in fig. 1, the pulse laser PL emits coherent optical pulses of a certain repetition rate and identical intensity; these light pulses are then randomly modulated into signal states and decoy states by the intensity modulator IM 1; the light pulse modulated by the intensity is then passed through a polarization encoder PE, applied with polarization encoding information, and then polarization compensated by a polarization controller PC; the polarization-compensated pulse finally passes through an attenuator ATT1 to be attenuated to the single photon energy level, enters a quantum channel through an outlet IO of a transmitting end, reaches a receiving end and is detected.

In the prior art, the pulsed laser PL has two common implementations: firstly, the light pulse is directly formed by a gain switch semiconductor laser GSSL, as shown in figure 2, and at the moment, the light pulse can be obtained by modulating in the gain switch laser; the second is composed of a continuous laser CWL and an intensity modulator IM2, and the light pulse can be obtained by external modulation of the continuous laser (CWL) with the intensity modulator IM2, as shown in FIG. 3. There are two implementations of polarization encoder PE that are widely used at present: one is to use Faraday Interferometer (FI) principles, as shown in fig. 4, which comprises a beam splitter BS1, a phase modulator PM and two faraday mirrors FM; another is to use the Sagnac Interferometer (SI) principle, which, as shown in fig. 5, comprises a customized polarizing beam splitter CPBS, a phase modulator PM and a delay line DL.

For the transmitting end of the polarization encoding QKD system based on BB84 protocol using the above-mentioned common implementation, there is usually a time-dependent light source side channel, which threatens QKD security, for example, the following reasons:

One is that because the pulse laser PL is implemented by either the gain-switched semiconductor laser GSSL or the combination of the continuous laser CWL and the intensity modulator IM2, the extinction ratio of the pulses generated by the pulse laser PL is always limited due to practical device manufacturing process problems, the weak light intensity between the light pulses is always greater than zero, and the polarization state of the weak light entering the polarization encoder PE is linearly polarized due to the polarization effect of the intensity modulator IM 1.

Secondly, when the weak light enters the polarization encoder PE (faraday interferometer FI or sagnac interferometer SI) in two paths, the weak light on a certain path is inevitably modulated by the phase modulator PM. Ultimately resulting in a weak light polarization state of the output with a high correlation to the polarization states of its neighboring pulses. For example, as shown in fig. 6, in a QKD system employing a sagnac interferometer SI, a commonly used modulated electrical signal contains a high level, a low level, and an intermediate level (which is typically zero) for one cycle. To achieve polarization modulation, the conventional QKD system generally only considers ensuring that light pulses traveling clockwise and counterclockwise in the sagnac interferometer SI are modulated by high and low levels, respectively, so that by controlling the difference between the high and low levels, the phase difference across the two light pulses can be controlled, thereby controlling the polarization state of the light pulses output by the polarization encoder. However, the inventors have noted that in a typical period, the light at other (time) locations (i.e., the weak light portion outside the light pulse) will undergo corresponding phase modulation in response to the applied modulation voltage when passing through the phase modulator PM, resulting in that at regions 1,2, 3 and 4, the output phase difference of the two weak light pulses has a certain relationship with the output phase difference of the two light pulses, as shown in fig. 6, for example, and thus, when the transmitting end modulates the different polarization states of the pulses, the weak light between the pulses will also be modulated into corresponding different polarization states, i.e., the polarization states of the two are correlated, thereby creating a time-dependent light source side channel, which affects the practical safety of QKD.

In order to suppress the QKD time-dependent light source side channel to enhance the practical security of QKD, solutions are generally employed in the prior art that increase the extinction ratio of the intensity modulator IM in the transmitting end, thereby minimizing the intensity of light between light pulses (i.e., weak light intensity). However, due to the problem of the current IM fabrication process of the intensity modulator, the extinction ratio cannot be infinitely high, so that the existing solution is only to reduce the imperfections of the device as much as possible, and cannot fundamentally solve the problem, and often needs to resort to a more complex fabrication process level.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, the present invention proposes a method for suppressing a QKD time-dependent light source side channel, and a transmitting end capable of defending a QKD time-dependent light source side channel attack, in which the correlation between the polarization state of weak light and polarization encoding information between light pulses is reduced by simply adjusting parameters of a laser light source to increase its extinction ratio and/or adjusting parameters of a polarization encoding module (e.g., the shape of a phase modulating signal and/or the arrival time difference of two pulse components with respect to a phase modulator), and the QKD time-dependent light source side channel is suppressed, without depending on the manufacturing process of an intensity modulator, so that the security limitation caused by device imperfections can be well overcome, thereby greatly improving the security of the QKD process in a simple manner and at low cost.

In particular, a first aspect of the present invention relates to a QKD time-dependent light source side channel suppression method for generating laser pulses and polarization encoding the laser pulses to generate signal light pulses; wherein,

Setting a ratio of a pulse trigger current to an off current for a gain-switching semiconductor laser within a range defined by a maximum value and a minimum value when generating the laser pulse with the gain-switching semiconductor laser, the minimum value being a ratio that causes the laser pulse generated by the gain-switching semiconductor laser to have a extinction ratio of 20dB, the maximum value being a maximum ratio that causes the laser pulse generated by the gain-switching semiconductor laser to be unchanged in shape and random in phase; and/or

When polarization encoding is achieved by dividing the laser pulse into two laser pulse components to counter-propagate along a loop and phase modulating the two laser pulse components by means of a phase modulator in the loop, the modulated electrical signal for phase modulation is set to contain no intermediate level portion and the duration T _H of the high level portion is set to T _P≤T_H≤T–3T_E–T_P or the duration T _L of the low level portion is set to T _P≤T_L≤T–3T_E–T_P, T being the time period of the modulated electrical signal, T _P being the duration of the laser pulse component, T _E being the duration of the edge signal portion in the modulated electrical signal; and/or

When polarization encoding is achieved by dividing the laser pulse into two laser pulse components to counter-propagate along a loop and phase modulating the two laser pulse components by means of a phase modulator in the loop, the time difference T _D of arrival of the two laser pulse components at the phase modulator is such that T _P+T_E≤T_D≤T_H+T_L+T_E–T_P,T_P is the duration of the laser pulse component, T _E is the duration of the edge signal portion in the modulated electrical signal, T _H is the duration of the high level portion in the modulated electrical signal, and T _L is the duration of the low level portion in the modulated electrical signal.

Preferably, the ratio of the pulse triggering current to the closing current is set at or near the maximum value, i.e. the deviation from the maximum value does not exceed 50% of the maximum value.

Preferably, the time difference T _D is made equal to T _P+T_E or near T _P+T_E, i.e. no deviation from T _P+T_E more than 50% of T _P+T_E.

Preferably, the duration T _H or T _L is set to T _P or near T _P, i.e. no deviation from T _P by more than 50% of T _P.

A second aspect of the present invention relates to a transmitting end capable of suppressing a QKD time-dependent light source side channel, which includes a light source module and a polarization encoding module;

the light source module is used for generating laser pulses;

The polarization encoding module is used for polarization encoding the laser pulse to generate a signal light pulse, and is configured to: polarization encoding of the laser pulse is achieved by dividing the laser pulse into two laser pulse components to counter-propagate along a loop and phase modulating the two laser pulse components by means of a phase modulator in the loop;

Wherein the modulated electrical signal for phase modulation does not contain an intermediate level portion, and the duration T _H of the high level portion satisfies T _P≤T_H≤T–3T_E–T_P or the duration T _L of the low level portion satisfies T _P≤T_L≤T–3T_E–T_P, T is a time period of the modulated electrical signal, T _P is a duration of the laser pulse component, and T _E is a duration of the edge signal portion in the modulated electrical signal; and/or

The time difference T _D between the arrival of the two laser pulse components at the phase modulator satisfies T _P+T_E≤T_D≤T_H+T_L+T_E–T_P,T_P as the duration of the laser pulse component, T _E as the duration of the edge signal portion of the modulated electrical signal, T _H as the duration of the high level portion of the modulated electrical signal, and T _L as the duration of the low level portion of the modulated electrical signal.

Further, the light source module includes a gain-switching semiconductor laser, and a ratio of a pulse trigger current to an off current for the gain-switching semiconductor laser is within a range defined by a maximum value, which is a ratio that makes a laser pulse generated by the gain-switching semiconductor laser have a extinction ratio of 20dB, and a minimum value, which is a maximum ratio that makes a laser pulse generated by the gain-switching semiconductor laser unchanged in shape and random in phase.

Preferably, the ratio of the pulse triggering current to the closing current is at or near the maximum value, i.e. the deviation from the maximum value does not exceed 50% of the maximum value.

Preferably, said time difference T _D is equal to T _P+T_E or is around T _P+T_E, i.e. does not deviate from T _P+T_E by more than 50% of T _P+T_E.

Preferably, the duration T _H or T _L is T _P or near T _P, i.e. does not deviate more than 50% from T _P by T _P.

Further, the polarization encoding module comprises a sagnac interferometer formed by means of a polarizing beam splitter and a phase modulator; and/or the transmitting end further comprises an intensity modulation module, a polarization control module and an attenuation module, wherein the intensity modulation module is used for carrying out intensity modulation on the laser pulse to randomly generate a signal state or a decoy state, the polarization control module is used for carrying out polarization compensation on the signal light pulse, and the attenuation module is used for attenuating the signal light pulse to a single photon level.

Drawings

Fig. 1 schematically illustrates an example of a transmitting end of a prior art polarization encoded QKD system based on the BB84 protocol;

Fig. 2 schematically illustrates an example of a prior art light source module for use at the transmit end of a polarization encoded QKD system;

Fig. 3 schematically illustrates another example of a prior art light source module for use at the transmit end of a polarization encoded QKD system;

FIG. 4 schematically illustrates an example of a prior art polarization encoder for polarization encoding the transmit side of a QKD system;

FIG. 5 schematically illustrates another example of a prior art polarization encoder for polarization encoding the transmit side of a QKD system;

fig. 6 schematically illustrates an example of a polarization encoding process in a sender of a polarization encoded QKD system;

Fig. 7 schematically illustrates an example of a polarization encoding process in the transmit-side of the polarization encoded QKD system of the present invention.

Detailed Description

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are provided by way of illustration to fully convey the spirit of the invention to those skilled in the art to which the invention pertains. Thus, the present invention is not limited to the embodiments disclosed herein.

As described above, in the polarization encoded QKD system based on the BB84 protocol, the transmitting end may generally include the light source module PL, the intensity modulation module IM1, the polarization encoding module PE, the polarization control module PC, and the attenuation module ATT1.

The light source module is used for generating laser pulses to obtain coherent state light pulses with certain repetition frequency and same intensity.

As an example, the light source module may include a gain-switching semiconductor laser GSSL, as shown in fig. 2; or by a continuous laser CWL and an intensity modulator IM2, as shown in fig. 3.

The intensity modulation module IM1 is used to randomly intensity modulate the laser pulses to produce, for example, signal states and decoy states. As an example, the intensity modulation module may be implemented by means of an intensity modulator IM 1.

The polarization modulation module PE is used to apply polarization encoded information on the laser pulses to generate signal light pulses.

As previously mentioned, fig. 4 and 5 show different implementations of the polarization modulation module PE, respectively.

As shown in fig. 4, the polarization modulation module PE may be implemented using a faraday interferometer structure formed by means of a beam splitter BS1, a phase modulator PM and two faraday mirrors FM1/FM 2. In fig. 4, the laser pulse is equally divided into two laser pulse components, i.e., a first laser pulse component and a second laser pulse component, by a beam splitter BS 1; the first laser pulse component enters a first arm optical path comprising a phase modulator PM and a first faraday mirror FM1, and the second laser pulse component enters a second arm optical path comprising a second faraday mirror FM 2; the first and second laser pulse components are simultaneously returned to the beam splitter BS1 by the reflection of the faraday mirror, wherein different phase differences are modulated on the first and second laser pulse components by the phase modulator, and the returned first and second laser pulse components are combined at the beam splitter BS1 to form signal light pulses, and the polarization states of the signal light pulses are correlated with the modulated phase differences, thereby realizing polarization modulation of the laser pulses.

As shown in fig. 5, the polarization modulation module PE may also be implemented using a sagnac interferometer (S I) structure formed by means of a polarization beam splitter CPBS, a phase modulator PM and a delay line DL. In fig. 5, the laser pulse is equally divided into two laser pulse components, i.e., a first laser pulse component and a second laser pulse component, whose polarization directions are perpendicular to each other, via a polarization beam splitter CPBS; the two laser pulse components enter the sagnac loop formed by the delay line DL simultaneously in opposite directions and return to the polarizing beam splitter CPBS simultaneously, wherein by modulating the different phase differences between the first and second laser pulse components with a phase modulator, the returned first and second laser pulse components will form a signal light pulse at the polarizing beam splitter, and the polarization state of which is related to the modulated phase difference, whereby polarization modulation of the laser pulse is achieved.

The polarization control module PC is configured to perform polarization compensation on the polarization-encoded signal light pulse. As an example, the polarization control module PC may be implemented by means of a polarization controller.

The attenuation module ATT1 is used to attenuate the intensity of the signal light pulses to a single photon energy level before outputting them outwards. Therefore, the signal light pulse at the single photon energy level can finally enter the quantum channel through the outlet IO of the transmitting end.

Accordingly, in the polarization encoding method based on the BB84 protocol, a laser pulse generation step, a polarization encoding step, and optionally an intensity modulation step, a polarization compensation step, and an optical attenuation step may be generally included.

The laser pulse generation step is for generating coherent laser pulses having a certain repetition frequency and the same intensity by means of the light source module PL.

In the intensity modulation step, the laser pulses may be randomly intensity modulated by means of an intensity modulation module, thereby forming a signal state and a decoy state.

In the polarization modulation step, polarization encoded information may be applied to the intensity-modulated laser pulse by means of a polarization modulation module, thereby generating a signal light pulse.

In the polarization compensation step, the signal light pulse can be subjected to corresponding polarization compensation by the polarization control module.

The optical attenuation step is used for attenuating the signal light pulse subjected to polarization compensation to a single photon energy level so as to output the signal light pulse with the single photon level through an outlet IO vector subchannel of the transmitting end.

For a better understanding of the working principle of the QKD time-dependent light source side channel suppression scheme of the present invention, the QKD time-dependent light source side channel suppression method of the present invention will be specifically described below with reference to fig. 6 and 7, which are particularly applicable to the transmitting end of the polarization encoding QKD system based on the BB84 protocol and the corresponding polarization encoding method shown in fig. 1-5.

According to the present invention, to suppress QKD time-dependent light source side channels, the extinction ratio of the light source module (i.e., the difference in intensity between the laser pulses output by the light source module and the weak light between the pulses) can be increased by appropriately adjusting the parameters of the light source module PL to relatively or absolutely reduce the intensity of the weak light between the generated laser pulses. Therefore, for the single photon level signal light pulse finally output by the transmitting end, the absolute intensity of weak light among the signal light pulses is further reduced, the side channel is weakened, and greater difficulty is brought to the measurement of an eavesdropper, so that the time-dependent light source side channel is restrained to a certain extent.

In this solution, which is distinguished from the prior art, the inventors have further studied the light source module PL typically realized with the aid of a gain-switched semiconductor laser, and have found that this object can be conveniently achieved with the aid of two parameters "pulse trigger current" and "off current" in a gain-switched semiconductor laser.

According to the invention, when generating laser pulses with GSSL, a continuous bias current can be applied to GSSL first, on which a periodic square-wave current signal (for example, a standard square-wave with positive negative and equal absolute value) is superimposed, wherein: the high current (i.e. the maximum current) after superposition is larger than the threshold current of the GSSL itself, namely the pulse trigger current, which is used for triggering and generating pulses; the low current (i.e., the minimum current) after superposition is lower than the threshold current of the GSSL itself, i.e., the "off current", which is used to suppress the pulse, producing only weak light.

Therefore, the invention proposes that the extinction ratio control (improvement) of the GSSL output laser pulse can be achieved in an accurate and convenient manner by increasing the ratio of the pulse trigger current to the off current.

Specifically, a maximum value and a minimum value may be set for the ratio of the pulse trigger current to the off current for GSSL, wherein the minimum value is a ratio that causes the laser pulse generated by GSSL to have an extinction ratio of 20dB, and the maximum value is a maximum ratio that causes the laser pulse generated by GSSL to have no change in shape and phase randomness (determined, for example, during the increasing of the ratio). By adjusting the pulse trigger current and the off current of GSSL such that the ratio of the two is within the range defined by the maximum and minimum values described above, the QKD time-dependent light source side channel can be suppressed to some extent.

In a preferred example, the ratio of the pulse trigger current and the off current may be set as close as possible to the maximum value, e.g. at or near the maximum value. In the present invention, "near" means that the deviation from the reference value (here, the maximum value) is not more than 50% of the reference value.

According to the invention, the QKD time-dependent light source side channel can also be suppressed by eliminating/suppressing the correlation between the weak light polarization states between the signal light pulses and the polarization encoded information on the signal light pulses. For this reason, by properly adjusting the parameters of the polarization encoding module PE, the generation of a polarization state related to the polarization encoding information on weak light between the signal light pulses during the polarization encoding process can be avoided.

In a first aspect of this way of suppressing the correlation can be achieved by adjusting the time difference parameter of arrival of two laser pulse components in the loop that are transmitted in opposite directions at the phase modulator.

In the polarization encoding module shown in fig. 5, when the polarization encoding of the laser pulse is implemented by dividing the laser pulse into two laser pulse components and making the two laser pulse components enter the same loop to be transmitted along the loop in opposite directions, and phase modulating the two laser pulse components traveling along the loop in opposite directions by means of a phase modulator in the loop, the time difference between the time positions where the two laser pulse components are subjected to phase modulation can be shortened as much as possible, so that the level difference and the phase difference of weak light between the two laser pulse components are more zero, therefore, the output polarization state of the weak light is always a fixed polarization state no matter how the polarization state of the laser pulse is modulated, and the suppression of the time-dependent light source side channel is implemented.

In particular, with continued reference to fig. 6, in such a suppression scheme implemented based on time difference of arrival parameters, the modulated electrical signal (which has a time period T) may generally comprise a high level portion (which has a duration T _H), a low level portion (which has a duration T _L), a middle level portion (which has a duration T _M, and typically zero level), and (typically three identical) edge signal portions (which have a duration T _E), the time difference between the arrival of two laser pulse components (in the sagnac interferometer SI) at the position of the phase modulator PM being T _D, and the duration of the laser pulse component (laser pulse) being T _P. At this time, the position of the phase modulator PM in the loop may be adjusted, for example, such that this arrival time difference T _D satisfies the following relationship: t _P+T_E≤T_D≤T_H+T_L+T_E–T_P. By making the time difference T _D take the value in the above range, the level difference and the phase difference of weak light between the two laser pulse components can be more zero, so that the time-dependent light source side channel is reduced to a certain extent.

In a preferred example, the time difference T _D may be made as close to T _P+T_E as possible. For example, by adjusting the position of the phase modulator PM in the loop, the time difference T _D is equal to T _P+T_E or in the vicinity of T _P+T_E. Similarly, by "near" is meant that the deviation from the reference value (here T _P+T_E) is no more than 50% of the reference value.

In a second aspect of this way of suppressing the correlation can also be achieved by adjusting the parameters of the modulated electrical signal for phase modulation.

For example, in the polarization encoding module shown in fig. 5, when polarization encoding of a laser pulse is achieved by dividing the laser pulse into two laser pulse components and causing the two laser pulse components to enter the same loop and to be transmitted in opposite directions along the loop, the two laser pulse components transmitted in opposite directions are phase-modulated by means of a phase modulator in the loop, a modulated electric signal for the phase modulator may be specially configured to remove an intermediate level (e.g., zero level) portion of the modulated electric signal, while setting a duration difference between a high level portion and a low level portion of the modulated electric signal to be as large as possible, for example, as shown in fig. 7, such that a duration T _L of the low level portion is much longer than a duration T _H of the high level (or vice versa).

Specifically, in the suppression scheme implemented based on modulation electric signal adjustment of the present invention, the duration T _H of the high-level portion in the modulation electric signal may be set to T _P≤T_H≤T–3T_E–T_P, or the duration T _L of the low-level portion may be set to T _P≤T_L≤T–3T_E–T_P. Under the phase modulation effect provided by the modulated electric signal with specific configuration, the level difference and the phase difference of weak light between two paths of laser pulse components are more zero, so that the output polarization state of the weak light is always a fixed polarization state no matter how the polarization state of the laser pulse is modulated, and the output polarization state of the weak light is not related to the polarization state of the laser pulse, thereby realizing the suppression of a time-related light source side channel to a certain extent.

In a preferred example, the duration T _H of the high-level portion or the duration T _L of the low-level portion may be set as close to T _P as possible. For example, T _H or T _L is set to T _P or in the vicinity of T _P. Similarly, by "near" is meant that the deviation from the reference value (here T _P) is no more than 50% of the reference value.

As will be appreciated by those skilled in the art, the above-described time-dependent light source side channel suppression schemes (e.g., the light source parameter adjustment scheme, the modulated electrical signal parameter adjustment scheme, and the arrival time difference scheme) may be used in the transmitting end separately according to practical situations, or may be used in the transmitting end together in any combination, so as to effectively suppress the QKD time-dependent light source side channel in the transmitting end.

In summary, in the QKD time-dependent light source side channel suppression method and the transmitting end structure provided by the invention, the extinction ratio of the laser light source is allowed to be improved by simply adjusting the parameters of the laser light source, and/or the correlation between the weak light polarization state and the polarization coding information among light pulses is eliminated by adjusting the parameters of the polarization coding module, so that the QKD time-dependent light source side channel is effectively suppressed, the manufacturing process of an intensity modulator is not needed, the safety limitation caused by imperfect devices is overcome, and the safety of the QKD process is greatly improved in a simple manner and at low cost.

While the invention has been described in connection with the specific embodiments illustrated in the drawings, it will be readily appreciated by those skilled in the art that the above embodiments are merely illustrative of the principles of the invention, which are not intended to limit the scope of the invention, and various combinations, modifications and equivalents of the above embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1.A method of QKD time-dependent optical source side channel suppression for generating laser pulses and polarization encoding the laser pulses to generate signal light pulses; wherein,

2. The suppression method according to claim 1, wherein the ratio of the pulse trigger current and the off current is set to the maximum value or the deviation from the maximum value is not more than 50% of the maximum value.

3. The inhibition method according to claim 1, wherein the time difference T _D is made equal to T _P+T_E or the deviation from T _P+T_E does not exceed 50% of T _P+T_E.

4. The inhibition method of claim 1, wherein the duration T _H or T _L is set to T _P or does not deviate from T _P by more than 50% of T _P.

5. A transmitting end capable of suppressing QKD time correlation light source side channel includes a light source module and a polarization coding module;

the light source module is used for generating laser pulses;

6. The transmitting terminal of claim 5, wherein the light source module comprises a gain-switching semiconductor laser, and a ratio of a pulse trigger current to an off current for the gain-switching semiconductor laser is within a range defined by a maximum value and a minimum value, the minimum value being a ratio of laser pulses generated by the gain-switching semiconductor laser to have a extinction ratio of 20dB, the maximum value being a maximum ratio of laser pulse shapes generated by the gain-switching semiconductor laser to be unchanged and phase-random.

7. The transmitting end of claim 6, wherein the ratio of the pulse trigger current to the off current is the maximum value or does not deviate from the maximum value by more than 50% of the maximum value.

8. The transmitting end of claim 5, wherein the time difference T _D is equal to T _P+T_E or does not deviate from T _P+T_E by more than 50% of T _P+T_E.

9. The transmitting end of claim 5, wherein the duration T _H or T _L is T _P or does not deviate from T _P by more than 50% of T _P.

10. The transmitting end of any of claims 5-9, wherein the polarization encoding module comprises a sagnac interferometer formed by means of a polarizing beam splitter and a phase modulator; and/or

The transmitting end further comprises an intensity modulation module, a polarization control module and an attenuation module, wherein the intensity modulation module is used for modulating the intensity of the laser pulse to randomly generate a signal state or a decoy state, the polarization control module is used for carrying out polarization compensation on the signal light pulse, and the attenuation module is used for attenuating the signal light pulse to a single photon level.