Phase coding method and phase coding device for TF-QKD
By setting the bias voltage for pre-compensation based on the phase coding type of the current and previous pulses in TF-QKD, the problem of phase coding effect is solved, the coding rate and security are improved, and the use of high-speed DAC is avoided.
Patent Information
- Application Number
- CN202511159671.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-19
- Publication Date
- 2025-10-10
AI Technical Summary
The phase coding in the existing TF-QKD technology has a phase code effect, which leads to phase differences and security issues, and the use of high-speed DAC affects practicality.
Pre-compensation is performed by setting the bias voltage based on the phase encoding type of the current pulse and the previous pulse. The phase pattern effect is reduced through the test stage and the phase modulation stage. A limited electrical channel is used to ensure that the phases of pulses with the same phase encoding are close.
The impact of phase pattern effects is reduced, the coding rate is improved, the security of the QKD protocol is maintained, and dependence on high-speed DAC is avoided.
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Figure CN120768545A_ABST
Abstract
Description
Technical Field
[0001] The present invention proposes a phase encoding method and a phase encoding device for TF-QKD, which relate to the field of quantum communication technology. Background Art
[0002] TF-QKD is a new quantum key distribution protocol. Currently, the most commonly used TF-QKD uses phase encoding. The principle is that Alice and Bob, the transmitters, each encode a light pulse with a random phase. The detector then performs a joint measurement of the two light pulses, one from Alice and the other from Bob. The measurement result is related to the phase difference between the two light pulses. To improve the coding rate, the transmitter needs to accurately encode the phase information of the light pulses. Specifically, the phases of light pulses with the same phase encoding (such as the phase encoding of π) must be as consistent as possible, and the phase difference of light pulses with different phase encodings must be as close to the actual phase difference as possible.
[0003] Currently, phase encoding uses a phase modulator (PM) to modulate the phase of an optical pulse. The principle is that light changes its phase after passing through an optical waveguide loaded with a bias voltage, and the amount of phase change is related to the bias voltage. When N random phases need to be modulated in TF-QKD, the usual practice is to set N bias voltages (called N phase plates), corresponding to the phase n=0,1,...N-1, such as Figure 1 Typically, N = 16. Within the time window of a pulse, one of N bias voltages is applied to modulate the phase of the pulse.
[0004] However, the bias voltage's control of phase may be affected by the bias voltage of the previous pulse. If the previous pulse's encoding phase is different, the actual controlled phase of the same encoded time window will be different. This phenomenon is called the phase patterning effect. The phase patterning effect can cause pulses with the same phase encoding to differ in phase, which can cause additional phase differences at the detection end, resulting in inconsistent measurement results and encoding, causing additional errors and reducing the code rate. It can also cause the phase information of the pulse to be associated with the phase information of the previous pulse, affecting the security of the QKD protocol.
[0005] To reduce the impact of pattern effects on phase modulation, one solution is to use a DAC to pre-compensate the phase modulation voltage of each pulse based on the difference in the phase modulation voltage of the previous pulse. However, QKD pulses are high-frequency signals, requiring expensive high-speed DACs, which limits the practicality of TF-QKD. Summary of the Invention
[0006] To address the aforementioned technical issues, the present invention proposes a phase encoding method and device for TF-QKD. This method pre-compensates the voltage by setting bias voltages based on the phase encoding types of the current and previous pulses. It also provides a solution for reducing the phase pattern effect using a limited electrical channel. This approach minimizes the phases of pulses with the same phase encoding without increasing the number of voltage signals, thereby reducing the impact of the pattern effect and improving the coding rate.
[0007] A phase encoding method for TF-QKD, comprising: a testing phase and a phase modulation phase;
[0008] During the testing phase, a coding voltage signal is set for each combination of the current pulse phase and the previous pulse phase;
[0009] In the modulation stage, the phase signal is translated into the coded voltage signal set in the test stage, the coded voltage signal is converted into a bias voltage, and the bias voltage is applied through a phase modulator to modulate the phase of the optical pulse.
[0010] Preferably, during the test phase, the phase is set The corresponding voltage is V k ,k=0,1,...,N-1; N is the total number of phase plates, k is the serial number of the phase plate,
[0011] Increase the voltage of the phase modulator from 0 until the intensity of the light pulse measured by the detection module reaches the maximum. Let the maximum intensity of the light pulse measured by the detection module be I1, and record the voltage of the phase modulator at this time as V′0;
[0012] Increase the voltage of the phase modulator until the intensity of the light pulse measured by the detection module is minimum. Let the minimum intensity of the light pulse measured by the detection module be I2, and record the voltage of the phase modulator at this time as V' N / 2 ;
[0013] when When V′0 and V′ N / 2 The voltage of the phase modulator is adjusted between , so that the intensity of the light pulse detected by the detection module is The voltage of the phase modulator at this time is recorded as V' k ;
[0014] when When V′ N / 2 and 2V′ N / 2 -V′0, the voltage of the phase modulator is adjusted so that the intensity of the light pulse detected by the detection module is The voltage of the phase modulator at this time is recorded as V' k .
[0015] Preferably, the voltage of the phase modulator is adjusted to 0, and after stabilization, the light pulse intensity I0 measured by the detection module is recorded. The voltage of the phase modulator is increased, and the detected light pulse intensity is observed:
[0016] If the light pulse intensity is reduced, the initial phase difference is recorded as
[0017] If the light pulse intensity increases, the initial phase difference is recorded as
[0018] Preferably, the specific modulation steps in the modulation stage are as follows:
[0019] S21, preset voltage signals V0, V1, ... V in the translation module k ,...V N-1 , set the binary operation f(m,n), where m, n=0,1,...,N-1, if the coded voltage signal V in the test phase mn is the voltage V k , set f(m,n)=k;
[0020] S22, the random number generator generates a random signal and organizes it into a phase-coded signal; the transmitting end records the phase-coded sequence and outputs the phase-coded sequence to the translation module;
[0021] S23, the translation module translates the phase signal into a coded voltage signal based on the phase coding signal of the current pulse and the previous pulse: if the phase coding of the previous pulse is The current pulse phase is encoded as The output current pulse coding voltage signal is V f(m,n) ;
[0022] S24 , the digital-to-voltage conversion module converts the input coded voltage signal into a bias voltage, and outputs the bias voltage to the phase modulator to perform phase modulation of the optical pulse.
[0023] The present invention also proposes a phase encoding device for TF-QKD, characterized in that it is used to implement the above-mentioned phase encoding method for TF-QKD, and the phase encoding device includes: a test phase device and a phase modulation phase device;
[0024] During the test phase, the device is used to set a coding voltage signal for each combination of a current pulse phase and a previous pulse phase;
[0025] The phase modulation stage device is used to translate the phase signal into the coded voltage signal set in the test stage, convert the coded voltage signal into a bias voltage, and load the bias voltage through the phase modulator to modulate the phase of the optical pulse.
[0026] Preferably, the test phase device includes: a light source, a beam splitter, a phase modulator, an interferometer and a detection module;
[0027] The phase modulation stage device includes a random number generator, a translation module, a digital-to-voltage conversion module and a phase modulator.
[0028] Preferably, the random number generator generates a random number for encoding the phase of the optical pulse to generate a phase signal;
[0029] The translation module translates the phase signal into a coded voltage signal set in the test phase;
[0030] The digital-to-voltage conversion module converts the coded voltage signal into a bias voltage;
[0031] The phase modulator is used to modulate the phase of the optical pulse according to the applied bias voltage.
[0032] Preferably, during the test phase, the light pulse emitted by the light source in the device is split by a beam splitter into two light signals with an intensity ratio of 1:1 and enters two arms respectively; one arm performs phase modulation using a phase modulator; the modulated light signals are combined by interference from an interferometer; and a detection module is located at one port of the interferometer to measure the intensity of the light pulse.
[0033] Compared with the prior art, the present invention has the following beneficial technical effects:
[0034] 1. TF-QKD's phase encoding method pre-compensates the voltage of the current phase based on the previous pulse phase, reducing the phase pattern effect.
[0035] 2. The phase encoding method and phase encoding device of TF-QKD pre-set the encoding voltage signal, and pre-compensate the phase modulation voltage while maintaining the existing number of modulation voltages and without increasing the number of electrical signal channels in the digital-to-voltage conversion module. BRIEF DESCRIPTION OF THE DRAWINGS
[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.
[0037] Figure 1 is a schematic diagram of the phase plate;
[0038] Figure 2 Setting up an existing QKD phase modulation device;
[0039] Figure 3Device setup for the testing phase;
[0040] Figure 4 Set up for phase modulation stage device;
[0041] Figure 5 This is an actual phase curve diagram in the prior art when the phase of the previous pulse is different. DETAILED DESCRIPTION
[0042] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.
[0043] In the drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the various components in the system, the connection relationship of the various parts in the device is shown, which only clearly distinguishes the relative position relationship between the various components, and does not constitute a limitation on the signal transmission direction, connection sequence and structural size, size and shape of each part within the component or structure.
[0044] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.
[0045] The existing phase modulation device is set as Figure 2 As shown, the random number generator generates a digital signal for encoding phase, and the digital-to-voltage conversion module converts the encoding phase The digital signal is directly converted into the bias voltage V of the current time window k ,k=0,1,...,N-1, loaded onto the phase modulator PM to perform phase modulation.
[0046] In order to reduce the code effect, the present invention adopts a pre-compensation method. Based on the phase coding of the current pulse and the previous pulse, the phase coding signal generated by the random number generator is translated into an appropriate voltage signal, so that the phases of the pulses with the same phase coding are finally modulated by the phase modulator PM as close as possible.
[0047] To achieve the above effects, the technical solution of the present invention includes two phases: a testing phase and a phase modulation phase. In the testing phase, a coded voltage signal is set; in the modulation phase, the phase signal is translated into the coded voltage signal determined in the testing phase, thereby performing phase modulation.
[0048] (1) Testing phase
[0049] During the test phase, the device settings are as follows: Figure 3 As shown, it includes: a light source, a beam splitter, a phase modulator, an interferometer and a detection module.
[0050] A light pulse emitted by a light source is split by a 50:50 beam splitter (BS) into two beams with a 1:1 intensity ratio. Each beam then enters one arm. A phase modulator (PM) performs phase modulation on one arm. The modulated optical signals are then combined by an interferometer (PBS). A detection module, located at one port of the interferometer (PBS), measures the intensity.
[0051] Setting the encoding voltage signal includes the following steps:
[0052] (1) Set the phase of the kth phase plate The corresponding voltage is V k ,k=0,1,...,N-1;
[0053] Where N is the total number of phase plates, and k is the phase plate number.
[0054] The light source periodically sends light pulses, and the voltage of the phase modulator is increased from 0 until the intensity of the light pulse measured by the detection module is the maximum. The voltage of the phase modulator at this time is recorded as V'0. The voltage of the phase modulator is increased until the intensity of the light pulse measured by the detection module is the minimum. The voltage of the phase modulator at this time is recorded as V' N / 2 .
[0055] Assuming that the maximum intensity of the light pulse measured by the detection module is I1 and the minimum intensity of the light pulse is I2, the light intensity after interference beam combining is in is the phase difference between the two optical pulses of the upper and lower arms.
[0056] Except V′0 and V′ N / 2 The remaining voltage V' k Determined using the following method:
[0057] when When V′0 and V′ N / 2 The voltage of the phase modulator is adjusted between , so that the intensity of the light pulse detected by the detection module is The voltage of the phase modulator at this time is recorded as V' k .
[0058] when When V′ N / 2 and 2V′ N / 2 -V′0, the voltage of the phase modulator is adjusted so that the intensity of the light pulse detected by the detection module is The voltage of the phase modulator at this time is recorded as V' k .
[0059] Setting Phase The corresponding voltage V k =V′ k -V′0, where k=0,1,...,N-1.
[0060] It should be noted that V k is the voltage corresponding to the phase of the kth phase piece, V′ k is the voltage before zero point correction, V′ k It is necessary to subtract the zero point voltage V′0 to obtain V k .
[0061] In a preferred embodiment, for the previous optical pulse phase The current pulse phase is In the case of , the following steps are used to verify the coded voltage signal, where m and n represent the serial numbers of the phase piece:
[0062] (2) Determine the initial phase of the interferometer;
[0063] Since the test intensity needs to be compared with the reference intensity in the subsequent step (3), the determination of the reference intensity requires the determination of the initial phase difference θ corresponding to 0 voltage. Therefore, the voltage of the phase modulator is adjusted to 0. After stabilization, the light pulse intensity I0 measured by the detection module is recorded. The voltage of the phase modulator is slightly increased (optionally, not exceeding (V′)). N / 2 -V′0) / 10), observe the intensity of the detected light pulse;
[0064] If the light pulse intensity is reduced, the initial phase difference is recorded as
[0065] If the pulse intensity is increased, the initial phase difference is recorded as
[0066] (3) Based on the test results, for each combination of "current pulse phase + previous pulse phase" at V k Select the corresponding coded voltage signal,
[0067] S11, set the voltage of the phase modulator, set the voltage of the previous time window of the phase modulator to V m , the test time window voltage is V k, let k be selected from nt,n-t+1,...,n+t, where t is a pre-set scanning range, optionally, set t=2;
[0068] S12, the detection module records the pulse intensity of the test time window and compares it with the reference intensity Make comparisons;
[0069] S13, let k traverse nt,n-t+1,...,n+t, select the pulse intensity of the test time window and the reference intensity I n The closest k, V k Set to the encoding voltage signal V mn .
[0070] (2) Phase modulation stage
[0071] The phase modulation stage device settings are as follows Figure 4 As shown, it includes a random number generator, a translation module, a digital-to-voltage conversion module and a phase modulator:
[0072] The random number generator generates random numbers for encoding the phase of the optical pulse and generating a phase signal;
[0073] The translation module translates the phase signal into a coded voltage signal set in the test phase;
[0074] The digital-to-voltage conversion module converts the coded voltage signal into a bias voltage;
[0075] The phase modulator PM is the same as the phase modulator PM used in the test phase, and is used to modulate the phase of the optical pulse according to the applied bias voltage.
[0076] In the prior art, the phase of the previous pulse will affect the actual phase of the next pulse, resulting in a certain deviation between the actual phases when the set phases are the same. Figure 5 The graph shows the actual phase of the 15th phase plate when the previous pulse phase is different, according to the prior art. Different colored lines represent the actual phase of the 15th phase plate corresponding to the different phases of the previous pulse. The abscissa in the graph is the modulation voltage signal time, in 10 ps. The abscissa values from 5 to 35 represent the modulation voltage signal time of the previous pulse, and the abscissa values from 45 to 75 represent the modulation voltage signal time required to adjust to the 15th phase plate. The ordinate represents the actual phase of the 15th phase plate, in degrees.
[0077] Therefore, based on the above Figure 5 The defects of the prior art shown above require that the influence of the pattern effect be reduced. The present invention uses the following process to perform phase modulation:
[0078] S21, preset voltage signals V0, V1, ... V in the translation module k ,...V N-1 , set the binary operation f(m,n), where (where m, n=0,1,...,N-1), if the coded voltage signal V in the test phase mn is the voltage signal V k , set f(m,n)=k.
[0079] S22. The random number generator generates a random signal, records and organizes it into a phase-coded signal, and then outputs the phase-coded sequence to the translation module.
[0080] S23. The translation module translates the phase signal into a coded voltage signal based on the phase coding signals of the current pulse and the previous pulse.
[0081] The translation method is: if the previous pulse phase code is The current pulse phase is encoded as The voltage signal of the current pulse output is V f(m,n) .
[0082] S24 , the digital-to-voltage conversion module converts the input coded voltage signal into a bias voltage, and outputs the bias voltage to the phase modulator to perform phase modulation of the optical pulse.
[0083] The above process can achieve the following effects: the previous pulse phase encoding is The current pulse phase is encoded as When (where m, n = 0, 1, ..., N-1), the voltage signal of the current time window is set to the coded voltage signal V in the test phase by translation. mn , thus achieving phase encoding without adding additional voltage signals When the same phase-coded pulse is modulated, the phases of the optical pulses actually modulated by the phase modulator are as close as possible.
[0084] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, and 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-mentioned methods. Among them, any reference to memory, database or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may 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). The database involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processor involved in the various embodiments provided herein may be, but are not limited to, a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, and the like.
[0085] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0086] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.
Claims
1. A phase encoding method for TF-QKD, characterized in that: include: Testing phase and phase modulation phase; During the testing phase, a coding voltage signal is set for each combination of the current pulse phase and the previous pulse phase; In the modulation stage, the phase signal is translated into the coded voltage signal set in the test stage, the coded voltage signal is converted into a bias voltage, and the bias voltage is applied through a phase modulator to modulate the phase of the optical pulse.
2. The phase encoding method for TF-QKD according to claim 1, wherein: During the test phase, set the phase The corresponding voltage is V k ,k=0,1,...,N-1; N is the total number of phase plates, k is the serial number of the phase plate, Increase the voltage of the phase modulator from 0 until the intensity of the light pulse measured by the detection module reaches the maximum. Let the maximum intensity of the light pulse measured by the detection module be I1, and record the voltage of the phase modulator at this time as V′0; Increase the voltage of the phase modulator until the intensity of the light pulse measured by the detection module is minimum. Let the minimum intensity of the light pulse measured by the detection module be I2, and record the voltage of the phase modulator at this time as V' N / 2 ; when When V′0 and V′ N / 2 The voltage of the phase modulator is adjusted between , so that the intensity of the light pulse detected by the detection module is The voltage of the phase modulator at this time is recorded as V' k ; when When V′ N / 2 and 2V′ N / 2 -V′0, the voltage of the phase modulator is adjusted so that the intensity of the light pulse detected by the detection module is The voltage of the phase modulator at this time is recorded as V' k .
3. The phase encoding method for TF-QKD according to claim 2, characterized in that: Adjust the voltage of the phase modulator to 0. After stabilization, record the light pulse intensity I0 measured by the detection module. Increase the voltage of the phase modulator and observe the detected light pulse intensity: If the light pulse intensity is reduced, the initial phase difference is recorded as If the light pulse intensity increases, the initial phase difference is recorded as 4. The phase encoding method for TF-QKD according to claim 2, characterized in that: The specific modulation steps in the modulation stage are as follows: S21, preset voltages V0, V1, ... V in the translation module k ,...V N-1 , if the coding voltage signal V mn is the voltage V k , set the binary operation f(m,n)=k, m, n=0,1,...,N-1; S22, the random number generator generates a random signal and organizes it into a phase-coded signal; the transmitting end records the phase-coded sequence and outputs the phase-coded sequence to the translation module; S23, the translation module translates the phase signal into a coded voltage signal based on the phase coding signal of the current pulse and the previous pulse: if the phase coding of the previous pulse is The current pulse phase is encoded as The output current pulse coding voltage signal is V f(m,n) ; S24 , the digital-to-voltage conversion module converts the input coded voltage signal into a bias voltage, and outputs the bias voltage to the phase modulator to perform phase modulation of the optical pulse.
5. A phase encoding device for TF-QKD, characterized in that: For implementing the phase encoding method for TF-QKD according to any one of claims 1 to 4, the phase encoding device comprises: a test phase device and a phase modulation phase device; During the test phase, the device is used to set a coding voltage signal for each combination of a current pulse phase and a previous pulse phase; The phase modulation stage device is used to translate the phase signal into the coded voltage signal set in the test stage, convert the coded voltage signal into a bias voltage, and load the bias voltage through the phase modulator to modulate the phase of the optical pulse.
6. The phase encoding device for TF-QKD according to claim 5, characterized in that: The test phase devices include a light source, a beam splitter, a phase modulator, an interferometer and a detection module; The phase modulation stage device includes a random number generator, a translation module, a digital-to-voltage conversion module and a phase modulator.
7. The phase encoding device for TF-QKD according to claim 6, characterized in that: The random number generator generates a random number for encoding the phase of the optical pulse to generate a phase signal; The translation module translates the phase signal into a coded voltage signal set in the test phase; The digital-to-voltage conversion module converts the coded voltage signal into a bias voltage; The phase modulator is used to modulate the phase of the optical pulse according to the applied bias voltage.
8. The phase encoding device for TF-QKD according to claim 6, characterized in that: During the testing phase, the light pulse emitted by the light source in the device is split by a beam splitter into two light signals with an intensity ratio of 1:1, which enter the two arms respectively; one arm uses a phase modulator to perform phase modulation; the modulated light signals are combined by an interferometer; and a detection module is located at one port of the interferometer to measure the intensity of the light pulse.