CN116388975A - Continuous variable quantum key distribution method based on internal modulation pulse light source - Google Patents
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Abstract
The invention discloses a continuous variable quantum key distribution method based on an internal modulation pulse light source, which comprises the following steps: the transmitting end provides signal light and local oscillation light for the receiving end, or the transmitting end provides signal light for the receiving end, and the receiving end provides local oscillation light; the receiving end interferes the signal light and the local oscillation light, and extracts the component with channel noise and the initial data thereof from the interference result; the receiving end processes the component with the channel noise and the initial data thereof to obtain the amplitude modulation information related to the channel noise, namely the initial key. The invention fully utilizes the characteristic of random phase difference between front and rear pulses generated by the internal modulation pulse light source, and ensures that the detection result does not depend on the phase difference, does not need any phase feedback and compensation, and has simpler modulation mode; the higher extinction ratio and the higher intensity of the light pulse can be obtained, so that the transmission distance is longer and the detection efficiency is higher; the double-light source frequency locking technology with higher complexity can be avoided, and the complexity of the system is reduced.
Description
Technical Field
The invention relates to the technical field of quantum key distribution, in particular to a continuous variable quantum key distribution method based on an internal modulation pulse light source.
Background
With the rapid development of quantum information technology, key distribution (Quantum Key Distribution, QKD) has achieved very significant and important outcomes in the last three decades as one of the important branches. QKD can be categorized into discrete variable class (Discrete Variable, DV) protocols and continuous variable class (Continuous Variable, CV) protocols, depending on the dimensions of the source coding space. Unlike DV-QKD, the Hilbert space in which the quantum states used for encoding in CV-QKD systems are located is infinite-dimensional and continuous, and the carrier of information is no longer the polarization or phase of a single photon, but the canonical components of the optical field (the "position" and "momentum" in phase space). Since the carrier of the information is a continuous variable, this increases the number of key bits that can be carried per pulse, which can still provide great potential for the improvement of the final security code rate, although not every bit will become the final security key. Experimental research shows that the continuous variable quantum key distribution system has the advantages of high safety code rate in middle and short distance, compatibility with a classical optical communication system and the like, and has been rapidly developed in recent ten years.
The CV-QKD system can be divided into a Gaussian modulation scheme and a discrete modulation scheme according to the different numbers of the information source end modulation coherent states; the different positions of the receiving and transmitting ends of the system reference local oscillator light source are divided into two main types, namely a random local oscillator CV-QKD system and a local oscillator CV-QKD system.
The channel-associated local oscillation CV-QKD system based on Gaussian modulation coherent state protocol has the earliest development and highest maturity. In the scheme, time division and polarization multiplexing are adopted, so that the influence of leaked light noise on quantum signal light when local oscillation light reaches a receiving end is avoided, and local oscillation light pulses with extremely high extinction ratio are required to be prepared at a transmitting end. The high extinction ratio light pulse is obtained by externally modulating continuous light by adopting a cascade amplitude modulator. The external modulation scheme has two problems, namely, complex feedback control software and hardware are required to be designed aiming at the bias point drift of the amplitude modulator, and the system is complex and has high cost; and the insertion loss of the two cascade modulators is about 6-10 dB, so that the finally generated pulse light intensity is weaker, the intensity (transmission distance) of local oscillation light reaching a receiving end is influenced, and the detection capability of a system detector is further influenced.
The current mainstream system schemes all need to modulate the amplitude and the phase of the signal light at the transmitting end so as to construct two-dimensional Gaussian random variables in the phase space, namely an x component and a p component. And because coherent detection is mostly adopted in the system, when modulated signal light reaches a receiving end to interfere with local oscillation light after being transmitted by an optical fiber channel, phase drift is inevitably generated. Phase drift compensation is required to obtain random data with a certain correlation at the transceiver. Particularly, in the local oscillation system, because the receiving end and the transmitting end respectively adopt two different lasers, in order to obtain a stable interference result, phase compensation is needed, frequencies of the two lasers are needed to be locked, and the complexity and the implementation difficulty of the system are high.
Disclosure of Invention
In view of the above, the present invention provides a continuous variable quantum key distribution method based on an internally modulated pulse light source to solve the above technical problems.
The invention discloses a continuous variable quantum key distribution method based on an internal modulation pulse light source, which comprises the following steps:
the transmitting end provides signal light and local oscillation light for the receiving end, or the transmitting end provides signal light for the receiving end, and the receiving end provides local oscillation light;
the receiving end interferes the signal light and the local oscillation light, and extracts the component with channel noise and the initial data thereof from the interference result;
the receiving end processes the component with the channel noise and the initial data thereof to obtain the amplitude modulation information related to the channel noise, namely the initial key.
Further, the sending end provides signal light and local oscillator light to the receiving end, including:
the transmitting end internally modulates a pulse light source to output pulse light, the pulse light is split into signal light and local oscillation light through a first coupler, and the signal light enters a second coupler together with the local oscillation light passing through a first delay line after passing through an amplitude modulator and an attenuator to finish beam combination.
Further, the receiving end interferes the signal light and the local oscillator light, including:
after the combined signals enter a receiving end, beam splitting is completed through a third coupler, local oscillation light obtained after beam splitting is split into two beams through a second delay line and a fourth coupler, one beam directly enters a sixth coupler, and the other beam enters a seventh coupler after passing through a 90-degree phase shifter;
the split signal light is split into two beams after passing through a fifth coupler, wherein one beam directly enters the sixth coupler, and the other beam enters a seventh coupler after passing through a 90-degree phase shifter;
the local oscillation light and the signal light interfere in pairs in a sixth coupler and a seventh coupler respectively, wherein the signals interfered in the sixth coupler enter a first differential amplifier through a first detector and a second detector respectively; the signals after interference in the seventh coupler enter the second differential amplifier through the third detector and the fourth detector respectively.
Further, the second delay line is a polarization maintaining fiber, so that delay difference exists when the local oscillation light and the signal light split by the third coupler reach the sixth coupler and the seventh coupler, and the delay difference of the local oscillation light and the signal light realized by combining the first delay line of the transmitting end is ensured to be a multiple of the inverse of the system repetition frequency, namely, the delay difference of the local oscillation light and the signal light is equal to the integral multiple of the period.
Further, the transmitting end does not perform phase modulation, and the local oscillation light does not interfere with the signal light from the same light source at the same time, but interferes with the signal light of the next period.
Further, the sending terminal provides signal light to the receiving terminal and local oscillation light to the receiving terminal, including:
the first internal modulation pulse laser of the transmitting end outputs pulse light, and outputs an optical signal after passing through an amplitude modulator and an attenuator;
when the optical signal reaches the receiving end, the optical signal passes through a second delay line and is divided into two beams with equal intensity through a fourth coupler, one beam directly enters the sixth coupler, and the other beam reaches a seventh coupler after passing through a 90-degree phase shifter; at this time, the second internal modulation pulse laser in the receiving end outputs pulse light, becomes local oscillation light, has the same repetition frequency as the first internal modulation pulse laser, and is divided into two beams with equal intensity after passing through the fifth coupler, and then enters the sixth coupler and the seventh coupler respectively.
Further, the second delay line is a polarization maintaining fiber, so that the signal light and the local oscillation light can reach the fourth coupler and the fifth coupler at the same time.
Further, the receiving end interferes the signal light and the local oscillator light, including:
and after the signal light and the local oscillation light interfere with each other at the sixth coupler and the seventh coupler, the signal output by the sixth coupler enters the first differential amplifier through the first detector and the second detector respectively, and the signal output by the seventh coupler enters the second differential amplifier through the third detector and the fourth detector respectively.
Further, the extracting the component with channel noise and the initial data thereof from the interference result includes:
the signal output by the first differential amplifier is processed by an analog-to-digital converter to extract an x component, the expression is
Wherein E is L Is the amplitude of local oscillation light E s Is the amplitude of signal light, wherein->
Is the local oscillation optical phase at the ith moment, which is the same as the signal optical phase at the ith moment, namely +.>
The phase of the signal light at the (i+1) th moment,
obeying random uniform distribution;
the signal from the second differential amplifier is processed by an analog-to-digital converter to extract a p component therefrom, expressed as
Further, the receiving end processes the component with channel noise and initial data thereof to obtain amplitude modulation information related to the channel noise, namely an initial key, which comprises:
the data of the x-component and the p-component are named D1 and D2, respectively, where D is numerically calculated 1 And D 2 Sum of squares, i.e
And the result is signed to obtain E related to the modulation information of the transmitting end s I.e. the transceiver shares the initial key containing channel noise without phase compensation.
Further, the signal light provided by the transmitting end to the receiving end and the local oscillation light provided by the receiving end are pulse light generated by internal modulation, or one is pulse light generated by internal modulation, and the other is continuous light.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. compared with the narrow linewidth laser commonly used in the existing continuous variable quantum key distribution system, the internal modulation pulse laser is easier to be integrated in a chip mode, and the system integration level is higher;
2. the sending end of the continuous variable quantum key distribution system can realize random phase modulation without adding extra phase modulators and can realize high extinction ratio light pulse output without cascading two amplitude modulators, so the system has low performance requirement on a quantum random number generator, simpler structure and lower cost;
3. the scheme has wide application range, can be popularized to quasi-continuous modulation in continuous variable protocols, and can also be applied to discrete modulation protocols; the method can be applied to a random local oscillation system and a local oscillation system;
4. the scheme is applied to a local oscillator system, frequency locking of local oscillator light and signal light is not needed, and the system implementation difficulty and complexity are effectively reduced;
5. and the phase drift immunity is realized without complex active phase compensation.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments described in the embodiments of the present invention, and other drawings may be obtained according to these drawings for those skilled in the art.
FIG. 1 is a schematic diagram of a random local oscillator CV-QKD system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a local oscillator CV-QKD system according to an embodiment of the invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and examples, wherein it is apparent that the examples described are only some, but not all, of the examples of the present invention. All other embodiments obtained by those skilled in the art are intended to fall within the scope of the embodiments of the present invention.
The working principle of the internal modulation light source is that the driving current of the laser diode is controlled by external modulation voltage to realize the control of the light intensity of the laser, namely, when the driving current is switched below and above a threshold value, the output of the non-light and light alternate state is obtained so as to generate pulse light. The internally modulated pulsed light source has a naturally high extinction ratio due to the threshold operating characteristics of the laser diode. Meanwhile, as an external modulator is not needed, the total intensity of the output light pulse is higher. Most importantly, the phase difference between two adjacent pulsed lights output by the internally modulated pulsed light source obeys a uniform distribution of [0,2 pi ]. The invention designs a novel efficient continuous variable quantum key distribution scheme by utilizing the random characteristic of the phase difference.
Example 1
As shown in fig. 1, a pulse light source modulated in a transmitting end outputs pulse light, and the pulse light is split into an upper branch and a lower branch by a first coupler, which are respectively named as signal light and local oscillation light. The upper branch passes through an amplitude modulator and an attenuator and then enters a fiber channel after being combined with the lower branch passing through a first delay line and enters a second coupler; after the combined optical signals reach the receiving end, beam splitting is completed through a third coupler, local oscillation light is split into two beams through a second delay line and a fourth coupler, and signal light is split into two beams through a fifth coupler. The split local oscillation light and signal light are interfered in pairs at the sixth coupler and the seventh coupler, wherein interference signals which do not pass through the 90-degree phase shifter enter the first differential amplifier through the first detector and the second detector, interference signals which pass through the 90-degree phase shifter enter the second differential amplifier through the third detector and the fourth detector, and the acquisition of signals is completed through the analog-to-digital converter ADC.
Wherein the repetition frequency of the output pulse light of the internal modulation pulse laser is 100MHz, and the pulse width is 5ns;
the first coupler has a beam splitting ratio of 90:10, 10% intensity is transmitted through an upper branch, 90% intensity is transmitted through a lower branch, and the two branches are respectively named as signal light and local oscillator light;
wherein the amplitude modulator is an electro-optic intensity modulator, and the bandwidth is not lower than 100MHz; the frequency of a modulation signal loaded for the device is 100MHz, the width is not less than 5ns, the modulation amplitude value is random, and the realized amplitude modulation result obeys Rayleigh distribution;
the attenuator is a knob type adjustable mechanical attenuator, and the attenuation range is more than 30dB;
the first delay line is a polarization maintaining optical fiber, so that the delay time difference between the signal light and the local oscillation light reaching the second coupler is 5ns, wherein the signal light is behind and the local oscillation light is in front;
the second coupler is a polarization coupler, so that the signal light and the local oscillation light can complete polarization multiplexing;
the third coupler is a polarization coupler, so that the polarization demultiplexing of the signal light and the local oscillation light can be realized;
the second delay line is a polarization maintaining fiber, so that the delay difference when the local oscillation light and the signal light which are split by the third coupler reach the sixth coupler and the seventh coupler is 5ns, and the delay difference of the local oscillation light and the signal light which are realized by combining the first delay line of the transmitting end is ensured to be the inverse of the system repetition frequency, namely, the delay difference of the local oscillation light and the signal light is equal to the period.
The beam splitting ratio of the fourth coupler to the fifth coupler is 50:50;
the 90-degree phase shifter can realize loading 90-degree phase modulation on the input;
the sixth coupler and the seventh coupler are 2x2 couplers, and the beam splitting ratio is 50:50;
the first differential detector and the second differential detector can realize differential amplification of input signals;
in a conventional Gaussian modulation coherent state protocol random local oscillator CV-QKD system, a transmitting end needs to carry out Rayleigh distribution modulation on an amplitude modulator, uniformly distribute modulation on a phase modulator, and a homodyne detection result expression in a receiving end is as follows:
when the phase difference of the local oscillation light and the signal light is theta=pi/2, the detection result is p component, and when the phase difference is theta=0, the detection result is x component. In the phase space, the x component corresponds to the amplitude E of the local oscillation light L Amplitude E of quantum signal light s Phase difference of relative local oscillation light
Cosine product, i.e.)>
Wherein E is s Obeys [0,1 ]]Rayleigh distribution of->
Obeys [0,2 pi ]]Is a uniform distribution of (c).
In the scheme provided by the invention, the transmitting end does not carry out phase modulation, and the local oscillation light does not interfere with the signal light at the same moment, but interferes with the signal light of the next period.
In the interference structure that the local oscillation light does not pass through the 90-degree phase shifter, the x component expression extracted by the analog-to-digital converter after the differential amplifier is still
However, since the local oscillation light and the signal light interfere with each other at intervals, the phase difference between the local oscillation light and the signal light has a time expression of +.>
Because the local oscillation light and the signal light come from the same light source, the optical splitter is a beam splitter>
Thus, in this embodiment, the x component extracted by the detector is
Order the
Then->
Obeys [0,2 pi ]]Is a uniform distribution of (c). In combination with heterodyne detection, in the interference result of local oscillation light passing through a 90-degree phase shifter, the expression of the p component extracted by an analog-to-digital converter after a differential amplifier is +.>
The data of the x-component and the p-component are named D1 and D2, respectively, where D is numerically calculated 1 And D 2 Sum of squares, i.e.)>
And the result is signed to obtain E related to the modulation information of the transmitting end s At this time, due to the data result and +.>
Irrespective, i.e. the transceiver end now shares the initial key containing channel noise without phase compensation. Finally, the steps of parameter estimation, data error correction, private key amplification and the like are completed through data post-processing, and the receiving and transmitting ends realize the sharing of completely consistent random bits.
Example 2
As shown in fig. 2, the first internal modulation pulse laser at the transmitting end outputs pulse light, and the pulse light enters the optical fiber channel after passing through the amplitude modulator and the attenuator, and the signal is called a quantum optical signal at the moment; when the quantum optical signal reaches the receiving end, the quantum optical signal is firstly divided into two beams with equal intensity through a fourth coupler by a delay optical fiber, and one beam reaches a seventh coupler after passing through a 90-degree phase shifter; at this time, the second internal modulation pulse laser in the receiving end outputs pulse light to become local oscillation light, the repetition frequency of the local oscillation light is the same as that of the first internal modulation pulse laser, and the local oscillation light passes through the fifth coupler and then is divided into two beams with equal intensity. At the sixth coupler and the seventh coupler, the quantum signal light and the local oscillation light interfere in pairs, wherein interference signals which do not pass through the 90-degree phase shifter enter the first differential amplifier through the first detector and the second detector, interference signals which pass through the 90-degree phase shifter enter the second differential amplifier through the third detector and the fourth detector, and the acquisition of signals is completed through the ADC.
The first internal modulation pulse laser and the second internal modulation pulse laser output pulse light with the repetition frequency of 100MHz and the pulse width of 5ns;
wherein the amplitude modulator is an electro-optic intensity modulator, and the bandwidth is not lower than 100MHz; the frequency of a modulation signal loaded for the device is 100MHz, the width is not less than 5ns, the modulation amplitude value is random, and the realized amplitude modulation result obeys Rayleigh distribution;
the attenuator is a knob type adjustable mechanical attenuator, and the attenuation range is more than 30dB;
the second delay line is a polarization maintaining optical fiber, so that the signal light and the local oscillation light can reach the fourth coupler and the fifth coupler at the same time;
the beam splitting ratio of the fourth coupler to the fifth coupler is 50:50;
the 90-degree phase shifter can realize loading 90-degree phase modulation on the input;
the sixth coupler and the seventh coupler are 2x2 couplers, and the beam splitting ratio is 50:50;
the first differential detector and the second differential detector can realize differential amplification of input signals;
in a local oscillator CV-QKD system of a conventional Gaussian modulation coherent state protocol, a transmitting end needs to carry out Rayleigh distribution modulation on an amplitude modulator, carries out uniform distribution modulation on a phase modulator, and has the following expression under a homodyne detection result:
when the local oscillation optical phase θ=pi/2, the detection result is p component, and when θ=0, the detection result is x component. In the phase space, the x component corresponds to the amplitude E of the local oscillation light L Amplitude E of quantum signal light s Phase difference of relative local oscillation light
Cosine product, i.e.)>
Wherein E is s Obeys [0,1 ]]Rayleigh distribution of->
Obeys [0,2 pi ]]Is a uniform distribution of (c).
In the interference structure that the local oscillation light does not pass through the 90-degree phase shifter, the x component expression extracted by the analog-to-digital converter after the differential amplifier is still
However, as the local oscillation light and the signal light come from two different lasers, the phase difference of the two lasers is completely random, so that +.>
Then->
Obeys [0,2 pi ]]Is a uniform distribution of (c).
In combination with heterodyne detection, in the interference result of local oscillation light passing through a 90-degree phase shifter, the p component expression extracted by the analog-to-digital converter after the differential amplifier is as follows
The data of the x-component and the p-component are named D respectively 1 And D 2 Calculate D 1 And D 2 The square sum of the transmission end modulation information is obtained by opening the root number of the result s I.e. the transceiver end now shares the initial key with the channel noise. Finally, the steps of parameter estimation, data error correction, private key amplification and the like are completed through data post-processing, and the receiving and transmitting ends realize the sharing of completely consistent random bits.
In example 1 and example 2: the amplitude modulation can be realized by an internal modulation mode at the same time, and can also be realized by various photoelectric components and combination elements with different modulation rates, such as an electro-optical intensity modulator, an acousto-optic intensity modulator, a magneto-optic modulator and the like, and different modulation principles, and the amplitude modulation can be completed; the amplitude modulation data distribution can be a Rayleigh distribution and a Gaussian distribution which are modulated continuously, or can be four states, eight states, 256 states and the like which are modulated discretely; when the quantum signal light interferes with the local oscillator light, the interference delay delta t control follows the following principle:
when the equivalent sub-signal light and the local oscillator light are homologous and are internally modulated pulse light, the interference delay difference of the equivalent sub-signal light and the local oscillator light is an integral multiple of the pulse light period (delta t=nt, n is more than or equal to 1 and is a positive integer, wherein T is the period of the pulse light);
when the equivalent sub-signal light and the local oscillator light pulse are different in source: a. when the quantum signal light is pulse light with the same pulse width and repetition frequency as the local oscillation light, the local oscillation light pulse and the quantum signal light pulse time sequence are aligned, namely the light is aligned with the light part, and the no light part is aligned with the no light part; b. when the quantum signal light is continuous light (although the quantum signal light is continuous light, the modulation frequency is the same as that of the local oscillation light), the light position of the local oscillation light pulse is aligned with the time sequence position of the modulated signal light;
the internal modulation pulse light comprises quantum signal light and local oscillation light, and the generation principle is to control the internal driving current of the laser diode by utilizing an electric signal so as to realize the switching of the current intensity when the current intensity is higher/lower than a threshold value, thereby realizing the alternate output of light and no light. The driving signal provided for the laser diode can be an integrated chip, and is realized by software control; or may be generated by an external function generator, an arbitrary waveform generator, or the like.
Heterodyne detection means that in a receiving end, local oscillation light is split into first local oscillation light and second local oscillation light, quantum signal light is split into first signal light and second signal light, the first local oscillation light and the first signal light are interfered by a 2x2 coupler, interference results are respectively connected into two photodiodes, optical signals are converted into current, one regular component is obtained through output of a differential amplifier, and the regular component is called an x component; the second local oscillation light is interfered with the second signal light through a 2x2 coupler after passing through a 90-degree phase shifter or a phase modulator, the interference results are respectively connected into two photodiodes, and after the optical signals are converted into currents, one regular component, namely a p component, is obtained through the output of a differential amplifier.
The method adopts an internal modulation pulse light source, utilizes the characteristic that the phase difference between the front pulse and the rear pulse is subjected to random uniform distribution, and controls the delay difference between the reference light and the signal light to cause the periodic interference. The characteristic of random phase difference distribution between the front pulse and the rear pulse is fully utilized, the detection result does not depend on the phase difference, any phase feedback and compensation are not needed, and the modulation mode is simpler. The scheme can obtain higher optical pulse extinction ratio and optical pulse intensity in the random local oscillation system, so that the transmission distance is longer and the detection efficiency is higher; the scheme can avoid the double-light source frequency locking technology with higher complexity in the local oscillation system, and reduce the complexity of the system.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (11)
1. The continuous variable quantum key distribution method based on the internal modulation pulse light source is characterized by comprising the following steps of:
the transmitting end provides signal light and local oscillation light for the receiving end, or the transmitting end provides signal light for the receiving end, and the receiving end provides local oscillation light;
the receiving end interferes the signal light and the local oscillation light, and extracts the component with channel noise and the initial data thereof from the interference result;
the receiving end processes the component with the channel noise and the initial data thereof to obtain the amplitude modulation information related to the channel noise, namely the initial key.
2. The method of claim 1, wherein the transmitting end provides signal light and local oscillator light to the receiving end, comprising:
the transmitting end internally modulates a pulse light source to output pulse light, the pulse light is split into signal light and local oscillation light through a first coupler, and the signal light enters a second coupler together with the local oscillation light passing through a first delay line after passing through an amplitude modulator and an attenuator to finish beam combination.
3. The method of claim 2, wherein the receiving end interferes the signal light and the local oscillator light, and the method comprises:
after the combined signals enter a receiving end, beam splitting is completed through a third coupler, local oscillation light obtained after beam splitting is split into two beams through a second delay line and a fourth coupler, one beam directly enters a sixth coupler, and the other beam enters a seventh coupler after passing through a 90-degree phase shifter;
the split signal light is split into two beams after passing through a fifth coupler, wherein one beam directly enters the sixth coupler, and the other beam enters a seventh coupler after passing through a 90-degree phase shifter;
the local oscillation light and the signal light interfere in pairs in a sixth coupler and a seventh coupler respectively, wherein the signals interfered in the sixth coupler enter a first differential amplifier through a first detector and a second detector respectively; the signals after interference in the seventh coupler enter the second differential amplifier through the third detector and the fourth detector respectively.
4. A method according to claim 3, wherein the second delay line is a polarization maintaining fiber, so that delay differences exist when the local oscillator light and the signal light split by the third coupler reach the sixth coupler and the seventh coupler, so as to ensure that the delay differences of the local oscillator light and the signal light realized by combining the first delay line of the transmitting end are multiples of the inverse of the system repetition frequency, that is, the delay differences of the local oscillator light and the signal light are equal to integral multiples of the period.
5. The method according to claim 2, wherein the transmitting end does not perform phase modulation, and the local oscillation light does not interfere with the signal light from the same light source at the same time but interferes with the signal light of the next cycle thereof.
6. The method of claim 1, wherein the transmitting end provides signal light to the receiving end and the receiving end provides local oscillator light, comprising:
the first internal modulation pulse laser of the transmitting end outputs pulse light, and outputs an optical signal after passing through an amplitude modulator and an attenuator;
when the optical signal reaches the receiving end, the optical signal passes through a second delay line and is divided into two beams with equal intensity through a fourth coupler, one beam directly enters the sixth coupler, and the other beam reaches a seventh coupler after passing through a 90-degree phase shifter; at this time, the second internal modulation pulse laser in the receiving end outputs pulse light, becomes local oscillation light, has the same repetition frequency as the first internal modulation pulse laser, and is divided into two beams with equal intensity after passing through the fifth coupler, and then enters the sixth coupler and the seventh coupler respectively.
7. The method of claim 6, wherein the second delay line is a polarization maintaining fiber, so that the signal light and the local oscillation light reach the fourth coupler and the fifth coupler simultaneously.
8. The method of claim 6, wherein the receiving end interferes with signal light and local oscillator light, comprising:
and after the signal light and the local oscillation light interfere with each other at the sixth coupler and the seventh coupler, the signal output by the sixth coupler enters the first differential amplifier through the first detector and the second detector respectively, and the signal output by the seventh coupler enters the second differential amplifier through the third detector and the fourth detector respectively.
9. A method according to claim 3 or 8, wherein said extracting the component with channel noise and its initial data from the interference result comprises:
the signal output by the first differential amplifier is processed by an analog-to-digital converter to extract an x component, the expression is
Wherein E is L Is the amplitude of local oscillation light E s Is the amplitude of signal light, wherein->
Is the local oscillation optical phase at the ith moment, which is the same as the signal optical phase at the ith moment, namely +.>
The phase of the signal light at the (i+1) th moment,
obeying random uniform distribution;
the signal from the second differential amplifier is processed by an analog-to-digital converter to extract a p component therefrom, expressed as
10. The method of claim 9, wherein the receiving end processes the component with channel noise and initial data thereof to obtain amplitude modulation information related to channel noise, i.e., an initial key, comprising:
the data of the x-component and the p-component are named D1 and D2, respectively, where D is numerically calculated 1 And D 2 Sum of squares, i.e. D 1 2 +D 2 2 ＝E L 2 E s 2 E related to the modulation information of the transmitting end can be obtained by opening the root number of the result s I.e. the transceiver shares the initial key containing channel noise without phase compensation.
11. The method according to claim 1, wherein the signal light provided from the transmitting end to the receiving end and the local oscillation light provided from the receiving end are both pulse light generated by internal modulation, or one is pulse light generated by internal modulation, and the other is continuous light.
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