Light intensity modulation method based on Sagnac interference structure

Abstract

The present invention provides a light intensity modulation method based on a Sagnac interference structure, which relates to the technical field of quantum information and optical fiber communication. The method comprises: determining a predetermined distance between a phase modulator and a center position of a Sagnac modulation ring according to a target modulation condition, so that a reverse pulse of the th period and a positive pulse of the th period enter the phase modulator at the same time, and a reverse pulse of the th period and a positive pulse of the th period enter the phase modulator at the same time; determining waveform parameters of an electrical signal according to a predetermined modulation rate and a predetermined modulation period; determining parameters of a phase modulator according to a predetermined modulation rate threshold; determining a first duration according to a target modulation form; and realizing light intensity modulation of a light pulse by a Sagnac interference structure according to the waveform parameters of the electrical signal, the parameters of the phase modulator and the first duration.

Description

Technical Field

[0001] The present invention relates to the field of quantum information and optical fiber communication technology, and more specifically, to a light intensity modulation method based on a Sagnac interference structure. Background Art

[0002] Actual electronic systems cannot generate ideal rectangular wave modulation signals, and the rising and falling edges always last for a period of time and cannot approach 0. Since the modulated pulses in the traditional intensity modulator based on the Sagnac interference structure need to avoid the non-ideal modulation signal area, in addition, under the condition of limited light speed, the round-trip structure requires the light pulse that enters the intensity modulator later to wait for the previous light pulse to leave the intensity modulator before entering, and each cycle needs to be modulated twice. Therefore, the modulation rate is greatly limited and cannot meet the needs of today's high-speed communication systems. Summary of the invention

[0003] In view of this, the present invention provides a method for light intensity modulation based on a Sagnac interference structure. The method comprises: determining a predetermined distance between a phase modulator and a center position of a Sagnac modulation ring according to a target modulation condition so that The reverse pulse of the first cycle The positive pulses of the first cycle enter the above phase modulator at the same time, and the The reverse pulse of the first cycle The positive pulses of cycles enter the above phase modulator at the same time; among them, is a natural number greater than or equal to 2, is less than and is an integer not equal to 0; wherein the phase modulator is configured to modulate the optical pulse using an electrical signal; wherein the optical pulse entering the Sagnac modulation ring is decomposed into the positive pulse and the reverse pulse, and the positive pulse and the reverse pulse respectively travel in opposite directions for one cycle and then meet; according to a predetermined modulation rate and a predetermined modulation period, the waveform parameters of the electrical signal are determined; according to a predetermined modulation rate threshold, the parameters of the phase modulator are determined; according to the target modulation form, the first duration is determined ; wherein the target modulation form is that the positive pulse of each cycle is located at the center of the flat area of ​​the electrical signal; according to the waveform parameters of the electrical signal, the parameters of the phase modulator and the first duration , to achieve the light intensity modulation of the above-mentioned light pulses in the Sagnac interference structure.

[0004] According to an embodiment of the present invention, the waveform parameters of the electrical signal are determined according to the predetermined modulation rate and the predetermined modulation period, including: the waveform parameters of the electrical signal include a first time length and the second time length ; Among them, the first time length is the time length of the flat area of ​​the above-mentioned electrical signal; the above-mentioned second time length is the rising edge time length of the above electrical signal and the falling edge time length The maximum value between

[0005] in, ; ; ;

[0006] in, is the above-mentioned predetermined modulation rate, is the above-mentioned predetermined modulation period; In order to consider the time margin of the above flat area in actual situations, is the speed of light; is the length of the above phase modulator, is the refractive index of the crystal inside the above phase modulator.

[0007] According to an embodiment of the present invention, determining the parameters of the phase modulator according to the predetermined modulation rate threshold comprises: determining the parameters of the phase modulator according to the predetermined modulation rate threshold , determine the parameters of the above phase modulator and ;

[0008] in, .

[0009] According to an embodiment of the present invention, the first duration is determined according to the target modulation form. The method comprises: adjusting the time difference between the moment when the electrical signal is loaded on the phase modulator and the moment when the optical pulse is generated according to the target modulation form, and obtaining a relationship curve of the output light intensity of the phase modulator corresponding to different time differences; determining the first duration according to the relationship curve ;in, .

[0010] According to an embodiment of the present invention, the method further includes: determining the time difference corresponding to the center position of the stable area of ​​the relationship curve as the first duration .

[0011] According to an embodiment of the present invention, the above method also includes: before the above optical pulse enters the above phase modulator, it also includes: determining the pulse sequence of the above electrical signal according to the target modulation result; wherein the above target modulation result is the target optical pulse sequence after the above phase modulator modulates the above optical pulse.

[0012] According to an embodiment of the present invention, the method further comprises: determining a second duration according to a comparison result between the target optical pulse sequence and the actual optical pulse sequence output by the phase modulator ; Among them, the second duration To make the The positive pulse of the first cycle The electrical signals correspond to: is an integer.

[0013] According to an embodiment of the present invention, the method further includes: obtaining an experimental modulation result; when the experimental modulation result indicates that the phase change obtained by high-level modulation is more than the phase change obtained by low-level modulation by π, determining the half-wave voltage of the pulse sequence of the electrical signal by the difference between the voltage corresponding to the high level and the voltage corresponding to the low level. .

[0014] According to an embodiment of the present invention, the above experimental modulation result is obtained by scanning the above electrical signal.

[0015] According to an embodiment of the present invention, the method further comprises: using a signal generator to generate a pulse sequence of the electrical signal.

[0016] The present invention can determine the parameters of the phase modulator by presetting the modulation rate and the modulation rate threshold to select the phase modulator; by setting the position of the phase modulator in the Sagnac modulation ring, the reverse pulse of each cycle can enter the phase modulator simultaneously with the positive pulses of other subsequent cycles. This avoids the reverse pulse of each cycle from being interfered by the electrical signal of the positive pulse of the same cycle, and can realize the modulation of the positive pulses and reverse pulses of different cycles in the same modulation cycle, so that the phase modulator with the selected parameters can perform one modulation in each modulation cycle, thereby improving the modulation rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0018] Figure 1 A flow chart of a light intensity modulation method based on a Sagnac interference structure according to an embodiment of the present invention is shown.

[0019] Figure 2 Schematic diagram showing the modulation rate threshold of the Sagnac interferometer structure under ideal conditions.

[0020] Figure 3 Schematic diagram showing the modulation rate threshold of the Sagnac interference structure under non-ideal conditions.

[0021] Figure 4 A schematic diagram showing a predetermined modulation rate threshold of a light intensity modulation method based on a Sagnac interference structure according to an embodiment of the present invention is shown.

[0022] Figure 5 A schematic diagram showing a predetermined modulation rate threshold of a light intensity modulation method based on a Sagnac interference structure according to another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0024] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0025] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0026] By utilizing the properties of quantum mechanics such as the non-cloning of single photons and the principle of state superposition, quantum key distribution (QKD) can enable the two parties in remote communication: the sender Alice and the receiver Bob, to generate and share a random key of the same length as the plaintext, thereby achieving unconditionally secure and confidential communication in the sense of information theory.

[0027] However, the single photon source required by QKD in actual systems is difficult to prepare. Usually, a weak coherent light source is used, which is obtained by attenuating the laser light source. The number of photons in a weak coherent light source follows a Poisson distribution, in which there is a non-negligible multi-photon component. For the multi-photon component, the eavesdropper Eve can use a photon-number splitting (PNS) attack to eavesdrop. The presence of multi-photon components greatly reduces the secure coding rate and secure communication distance of the QKD system based on a weak coherent light source.

[0028] In response to this, researchers proposed a solution called the decoy state. In this solution, the transmitter Alice randomly prepares a variety of phase-randomized weak coherent pulses of different light intensities, one of which is a signal state for generating keys, and the rest are decoy states. By mixing the decoy state into the signal state, the receiver Bob can determine whether there is an eavesdropper Eve eavesdropping based on the abnormality of the statistical results of the detected coherent states of various intensities. In summary, the decoy state method can make the experiment equivalent to using only single-photon pulses. For the security of quantum cryptography, this is equivalent to turning an actual imperfect light source into a perfect single-photon source.

[0029] The decoy state method requires the assumption that users can accurately, randomly, and independently modulate coherent states with different average photon numbers. However, as QKD systems gradually move toward higher speeds, researchers have found that in high-speed systems, limited modulation bandwidth can lead to correlations between adjacent pulses, namely, pattern effects, which eavesdroppers can use to attack the system, thereby reducing the security key rate and threatening the security of decoy state QKD systems.

[0030] In response to this, researchers developed the Sagnac modulator, which has the advantages of accurate modulation, insensitivity to noise, immunity to environmental interference, and reduced pattern effects. Its basic principle is to decompose a beam of light into two beams through a beam splitter, which travel in opposite directions in the same loop and then meet. The two beams of light are subjected to different phase modulations when passing through the intensity modulator in the loop, resulting in a phase difference. According to the light intensity formula after the interference of two beams in optics, different interference modulated light intensities can be obtained by controlling the phase difference of the two beams of light.

[0031] However, the round-trip structure of the Sagnac modulator will limit the maximum repetition frequency of the system. Actual electronic systems cannot generate ideal rectangular wave modulation signals, and the rising and falling edges will always last for a period of time and cannot approach 0. Since the modulated pulses in the traditional intensity modulator based on the Sagnac interference structure need to avoid the non-ideal modulation signal area, in addition, under the condition of limited light speed, the round-trip structure makes the light pulse that enters the intensity modulator later must wait until the previous light pulse leaves the intensity modulator before entering, and each cycle needs to be modulated twice. Therefore, the modulation rate is greatly limited, which is difficult to meet the needs of today's high-speed communication systems.

[0032] An embodiment of the present invention provides a light intensity modulation method based on a Sagnac interference structure.

[0033] Figure 1 A flow chart of a light intensity modulation method based on a Sagnac interference structure according to an embodiment of the present invention is shown.

[0034] like Figure 1As shown, the method includes operations S110 to S150.

[0035] In operation S110, according to the target modulation condition, a predetermined distance between the phase modulator and the center position of the Sagnac modulation ring is determined so that the first The reverse pulse of the first cycle The positive pulse of the first cycle enters the phase modulator at the same time, and the The reverse pulse of the first cycle The positive pulses of each cycle enter the phase modulator simultaneously.

[0036] in, is a natural number greater than or equal to 2, is less than An integer not equal to 0.

[0037] For example, , , that is, the reverse pulse of the first cycle and the positive pulse of the second cycle enter the phase modulator at the same time, and the reverse pulse of the second cycle and the positive pulse of the third cycle enter the phase modulator at the same time.

[0038] For example, , , that is, the reverse pulse of the 12th cycle and the positive pulse of the 7th cycle enter the phase modulator at the same time, and the reverse pulse of the 13th cycle and the positive pulse of the 8th cycle enter the phase modulator at the same time.

[0039] According to an embodiment of the present invention, the phase modulator is configured to modulate the optical pulse using an electrical signal; wherein the optical pulse entering the Sagnac modulation ring is decomposed into a positive pulse and a reverse pulse, and the positive pulse and the reverse pulse meet after traveling in opposite directions for one circle.

[0040] In operation S120, waveform parameters of the electrical signal are determined according to a predetermined modulation rate and a predetermined modulation period.

[0041] In operation S130, parameters of a phase modulator are determined according to a predetermined modulation rate threshold.

[0042] In operation S140, a first duration is determined according to the target modulation format. .

[0043] According to an embodiment of the present invention, the target modulation form is that the positive pulse of each cycle is located at the center of the flat area of ​​the electrical signal.

[0044] In operation S150, according to the waveform parameters of the electrical signal, the parameters of the phase modulator and the first duration , realizing the light intensity modulation of light pulses by Sagnac interference structure.

[0045] The present invention can determine the parameters of the phase modulator by presetting the modulation rate and the modulation rate threshold to select the phase modulator; by setting the position of the phase modulator in the Sagnac modulation ring, the reverse pulse of each cycle can enter the phase modulator simultaneously with the positive pulses of other cycles. This avoids the reverse pulse of each cycle from being interfered by the electrical signal of the positive pulse of the same cycle, and can realize the modulation of the positive pulses and reverse pulses of different cycles in the same modulation cycle, so that the phase modulator with the selected parameters can perform a modulation once in each modulation cycle, thereby improving the modulation rate.

[0046] According to an embodiment of the present invention, the waveform parameters of the electrical signal include a first time length and the second time length ; Among them, the first time length is the duration of the flat area of ​​the electrical signal; the second duration is the duration of the rising edge of the electrical signal and the falling edge time length The maximum value between

[0047] (1)

[0048] (2)

[0049] (3)

[0050] in, is the predetermined modulation rate, is a predetermined modulation period; In order to consider the time margin of the flat area in actual situations, is the speed of light; is the length of the phase modulator, is the refractive index of the crystal inside the phase modulator.

[0051] According to an embodiment of the present invention, the electrical signal is a rectangular wave modulation signal, and the non-ideal rectangular wave modulation signal has a rising edge, a flat region and a falling edge.

[0052] According to an embodiment of the present invention, according to a predetermined modulation rate threshold , determine the parameters of the phase modulator and ;

[0053] (4).

[0054] According to an embodiment of the present invention, the predetermined modulation rate is the modulation rate of the phase modulator of the light intensity modulation method based on the Sagnac interference structure, and the predetermined modulation rate threshold is a parameter that needs to be considered when selecting the phase modulator device parameters, and the predetermined modulation rate threshold needs to be greater than the predetermined modulation rate.

[0055] According to an embodiment of the present invention, in an ideal case, formula (2) indicates that the first time length of the electrical signal is twice the time length of the optical pulse propagating in the phase modulator. The waveform parameters of the electrical signal can be set according to the predetermined modulation rate and the predetermined modulation period. According to formula (4), the predetermined modulation rate threshold can be selected to select the length of the phase modulator and the refractive index of the crystal inside the phase modulator, so as to realize that the phase modulator modulates the positive pulse and the reverse pulse of different periods once within one modulation period.

[0056] According to an embodiment of the present invention, the time difference between the moment when the electrical signal is loaded on the phase modulator and the moment when the optical pulse is generated is adjusted according to the target modulation form, and a relationship curve of the output light intensity of the phase modulator corresponding to different time differences is obtained. According to the relationship curve, the first duration is determined ;in, .

[0057] According to an embodiment of the present invention, the target modulation form is that the positive pulse of each cycle is located at the center of the flat area of ​​the electrical signal. Through the first modulation experiment, the target modulation form is constructed, and the time difference between the moment when the electrical signal is loaded on the phase modulator and the moment when the optical pulse is generated is adjusted. When the relationship curve is in a stable area, the corresponding time difference is kept unchanged.

[0058] According to an embodiment of the present invention, the time difference corresponding to the center position of the stable area of ​​the relationship curve is determined as the first duration , and obtain the target modulation form.

[0059] According to an embodiment of the present invention, in a Sagnac interference structure, the positive pulse and the reverse pulse modulated by the phase modulator will interfere with each other, and the output light intensity is obtained according to the interference effect.

[0060] According to an embodiment of the present invention, the corresponding relationship between the output light intensity of the phase modulator modulating the positive pulse and the different time differences, that is, the positive pulse is located at different positions in the waveform of the electrical signal, and the output light intensity of the Sagnac interference structure corresponding to the phase modulator modulating the optical pulse is different. The first modulation experiment is carried out by scanning method in 0~ In the range of 0.01 Scan the time difference for the step length. When the measured electrical signal is delayed for the first time length When , the output light intensity of the corresponding Sagnac interference structure tends to be stable.

[0061] According to an embodiment of the present invention, before the optical pulse enters the phase modulator, it also includes: determining the pulse sequence of the electrical signal according to the target modulation result; wherein the target modulation result is the target optical pulse sequence after the phase modulator modulates the optical pulse.

[0062] For example, the modulated target optical pulse sequence is 01101001. When the electrical signal loaded by the positive pulse and the electrical signal loaded by the reverse pulse in the same cycle are both high or low levels, the modulated optical pulse sequence is 1; when the electrical signal loaded by the positive pulse and the electrical signal loaded by the reverse pulse in the same cycle are different high and low levels, the modulated optical pulse sequence is 0, and the pulse sequence of the electrical signal can be determined to be 100011011.

[0063] According to an embodiment of the present invention, the second duration is determined based on a comparison result between the target optical pulse sequence and the actual optical pulse sequence output by the phase modulator. Among them, the second duration To make the The positive pulse of the first cycle The electrical signals correspond to: is an integer.

[0064] For example, , modify the pulse sequence of the electrical signal and move the pulse sequence of the electrical signal as a whole. For example, if the original pulse sequence of the electrical signal is 101100XXXX, change the pulse sequence of the original electrical signal to 100XXXX so that the first The flat area The modulation is performed with a positive pulse of one cycle.

[0065] For example, , the pulse sequence of the original electrical signal is 101100XXXX, the pulse sequence of the original electrical signal is changed to XXX101100XXXX, so that the first The flat area The modulation is performed with a positive pulse of one cycle.

[0066] According to the embodiment of the present invention, by adjusting the second time length, the modulation effect of the optical pulse output in any period can be determined.

[0067] According to an embodiment of the present invention, a signal generator is used to generate a pulse sequence of electrical signals.

[0068] According to an embodiment of the present invention, the signal generator and the phase modulator may be connected via a cable.

[0069] According to an embodiment of the present invention, an experimental modulation result is obtained. When the experimental modulation result indicates that the phase change obtained by high-level modulation is more than the phase change obtained by low-level modulation by π, the difference between the voltage corresponding to the high level and the voltage corresponding to the low level is used to determine the half-wave voltage of the pulse sequence of the electrical signal. .

[0070] According to an embodiment of the present invention, the experimental modulation result is obtained by scanning the electrical signal. The half-wave voltage of the pulse sequence of the electrical signal can be determined based on the experimental modulation result. .

[0071] According to the embodiment of the present invention, the high level and the low level of the electrical signal are adjusted simultaneously, and the difference between the high level and the low level changes following the scanning electrical signal.

[0072] According to an embodiment of the present invention, the amplitude range of the electrical signal output by the signal generator is , corresponding to the highest voltage that the signal generator can output, and corresponding to the lowest voltage that the signal generator can output. The high and low levels generated by the signal generator are output alternately. The electrical signal is scanned with a step size of 0.01V, and the output light intensity of the Sagnac interference structure during the scanning of the electrical signal is observed. The half-wave voltage is determined by the experimental modulation results. .

[0073] According to an embodiment of the present invention, both the operation of determining the half-wave voltage and the operation of determining the first duration need to observe the output light intensity of the Sagnac interference structure, and the operation of determining the half-wave voltage needs to be performed after the operation of determining the first duration. If the operation of determining the half-wave voltage is performed first, then after the operation of determining the first duration, the half-wave voltage of the electrical signal will change.

[0074] According to the embodiment of the present invention, the half-wave voltage can be determined so that the electrical signal can have the effect of modulating the optical pulse.

[0075] According to an embodiment of the present invention, the light intensity modulation of the optical pulse by the phase modulator is completed by setting the pulse sequence of the electrical signal and the half-wave voltage of the electrical signal.

[0076] According to an embodiment of the present invention, when the light intensity is modulated using the Sagnac interference structure, a traveling wave modulation method is adopted, that is, the electrical signal travels along with the light pulse in a certain direction.

[0077] According to an embodiment of the present invention, a positive pulse is a light pulse in the same direction as the electrical signal, and a reverse pulse is a light pulse in the opposite direction to the electrical signal. The time interval between two adjacent light beams emitted by the light source is the light pulse period.

[0078] Figure 2 Schematic diagram showing the modulation rate threshold of the Sagnac interferometer structure under ideal conditions.

[0079] like Figure 2 As shown in the figure, the horizontal axis represents the spatial position of the light pulse relative to the phase modulator in the Sagnac interference structure, and the vertical axis represents the time. The arrow heading to the right represents a positive pulse, and "1 positive" represents the positive pulse of the first cycle; the arrow heading to the left represents a reverse pulse, and "1 reverse" represents the reverse pulse of the first cycle.

[0080] like Figure 2 As shown, in At this moment, the positive pulse of the first cycle enters the phase modulator, and the reverse pulse of the first cycle must wait for the positive pulse to leave the phase modulator before entering the phase modulator, otherwise the reverse pulse of the first cycle will be modulated by the electrical signal following the positive pulse.

[0081] According to an embodiment of the present invention, the time when the first cycle of the reverse pulse enters the phase modulator is , then the duration of the positive pulse of the first cycle traveling in the phase modulator is It can be expressed as:

[0082] (5).

[0083] According to an embodiment of the present invention, the positive pulse of the second cycle must wait for the reverse pulse of the first cycle to leave the phase modulator before entering the phase modulator. The time when the reverse pulse of the first cycle leaves the phase modulator is , then the duration of the first cycle of the reverse pulse in the phase modulator is It can be expressed as:

[0084] (6).

[0085] According to an embodiment of the present invention, the ideal modulation period It can be expressed as:

[0086] (7).

[0087] According to an embodiment of the present invention, the ideal modulation rate threshold It can be expressed as:

[0088] (8).

[0089] According to an embodiment of the present invention, since in actual situations, the electronic system cannot generate an ideal rectangular wave modulation signal, and the rising edge and the falling edge always last for a period of time and cannot approach 0, the modulation rate threshold is limited.

[0090] Figure 3Schematic diagram showing the modulation rate threshold of the Sagnac interference structure under non-ideal conditions.

[0091] like Figure 3 As shown, the direction is upward and from Time to An arrow pointing right at the moment indicates a positive pulse, and "1 positive" indicates a positive pulse of the first cycle; an arrow pointing downward and pointing left indicates a negative pulse, and "1 negative" indicates a negative pulse of the first cycle. A rectangular wave modulation signal indicates an electrical signal.

[0092] It should be noted that only the electrical signal in the phase modulator will modulate the optical pulse. Figure 3 The rectangular wave modulation signal shown is only to better illustrate the traveling wave modulation process.

[0093] According to an embodiment of the present invention, the first time length Indicates the duration of the flat area of ​​the electrical signal; the duration of the rising edge of the electrical signal is expressed as The length of the falling edge of the electrical signal is expressed as express.

[0094] like Figure 3 As shown, in At this moment, the positive pulse of the first cycle enters the phase modulator, then the reverse pulse of the first cycle must wait after the positive pulse leaves. The time when the first cycle of the reverse pulse enters the phase modulator is , then the time it takes for the positive pulse of the first cycle to travel through the phase modulator and completely leave It can be expressed as:

[0095] (9).

[0096] According to an embodiment of the present invention, after the reverse pulse of the first cycle leaves the phase modulator, the positive pulse of the second cycle must wait for time before entering the phase modulator.

[0097] According to an embodiment of the present invention, the time when the first cycle of the reverse pulse leaves the phase modulator is , then the time it takes for the first cycle of the anti-pulse to travel in the phase modulator and for the electrical signal it carries to completely leave the phase modulator is It can be expressed as:

[0098] (10).

[0099] According to an embodiment of the present invention, the non-ideal modulation period It can be expressed as:

[0100] (11).

[0101] According to an embodiment of the present invention, the non-ideal modulation rate threshold can be expressed as:

[0102] (12).

[0103] According to an embodiment of the present invention, in the modulation method of the Sagnac interference structure, each cycle needs to modulate the positive pulse and the negative pulse separately, that is, modulate twice per cycle, which limits the modulation rate of the Sagnac interference structure.

[0104] Figure 4 The schematic diagram of the predetermined modulation rate threshold of the optical intensity modulation method based on the Sagnac interference structure according to an embodiment of the present invention is shown.

[0105] As Figure 4 shown, the arrow with an upward direction and a rightward traveling direction from time to time represents the positive pulse, and " positive" represents the positive pulse of the th cycle; the arrow with a downward direction and a leftward traveling direction represents the negative pulse, and " negative" represents the negative pulse of the th cycle. The rectangular wave modulation signal represents the electrical signal.

[0106] It should be noted that only the electrical signal located inside the phase modulator can modulate the optical pulse, Figure 4 and the shown rectangular wave modulation signal is only for better demonstrating the process of traveling wave modulation.

[0107] As Figure 4 shown, at time, the positive pulse of the th cycle and the negative pulse of the th cycle enter the phase modulator simultaneously. At time, the positive pulse of the th cycle and the negative pulse of the th cycle enter the phase modulator simultaneously, then the traveling duration of the negative pulse of the th cycle inside the phase modulator

[0108] can be expressed as:

[0109] As Figure 4 shown, the negative pulse of the th cycle must wait for the The falling edge of the electrical signal corresponding to the positive pulse of the first cycle completely leaves the phase modulator and then enters the phase modulator. Similarly, The reverse pulse of the first cycle must wait for the The falling edge of the electrical signal corresponding to the positive pulse of a cycle completely leaves the phase modulator and then enters the phase modulator.

[0110] According to an embodiment of the present invention, the electrical signal loaded on the phase modulator can be a high level or a low level according to the actual modulation situation. Select the rising edge time length of the electrical signal Or the falling edge time length The maximum time length.

[0111] According to an embodiment of the present invention, The time when the anti-pulse of a cycle enters the phase modulator is , then The time it takes for the electrical signal loaded by the positive pulse of a cycle to completely leave is It can be expressed as:

[0112] (14).

[0113] According to an embodiment of the present invention, ideally, the first time length of the electrical signal is set is twice the time the light pulse travels in the phase modulator:

[0114] (15).

[0115] According to an embodiment of the present invention, the predetermined modulation period in an ideal situation is It can be expressed as:

[0116] (16).

[0117] According to an embodiment of the present invention, the predetermined modulation rate threshold It can be expressed as:

[0118] (17).

[0119] Figure 5 A schematic diagram showing a predetermined modulation rate threshold of a light intensity modulation method based on a Sagnac interference structure according to another embodiment of the present invention is shown.

[0120] like Figure 5 As shown, the direction is upward and from Time to An arrow pointing right at the moment indicates a positive pulse, and "4 positive" indicates a positive pulse in the 4th cycle; an arrow pointing downward and pointing left indicates a reverse pulse, and "3 reverse" indicates a reverse pulse in the 3rd cycle.

[0121] It should be noted that only the electrical signal in the phase modulator will modulate the optical pulse. Figure 5 The rectangular wave modulation signal shown is only to better illustrate the traveling wave modulation process.

[0122] According to an embodiment of the present invention, the required predetermined modulation rate is determined based on the actual quantum information security system, specific experimental content, experimental equipment data parameters, etc.

[0123] For example, a predetermined modulation rate .

[0124] According to an embodiment of the present invention, the waveform parameters of an ideal electrical signal are determined according to an actual quantum information security system and a predetermined modulation rate, and the parameters of a phase modulator that meet the requirements are selected according to a predetermined modulation rate threshold.

[0125] For example, determining the minimum first time length of the electrical signal , the second time length in non-ideal conditions , for example, the length of the phase modulator is selected , the refractive index of the crystal inside the phase modulator to meet:

[0126] (18).

[0127] According to an embodiment of the present invention, the phase modulator is placed at a predetermined distance from the center position of the Sagnac modulation ring so that the first The positive pulse of the first cycle and the The anti-pulse of one cycle enters both ends of the phase modulator at the same time.

[0128] For example, the predetermined distance is , so that the positive pulse of the third cycle and the reverse pulse of the fourth cycle enter the two ends of the phase modulator at the same time. The predetermined distance formula can be expressed as:

[0129] (19).

[0130] in, represents the refractive index of the single-mode fiber of the transmission fiber that transmits the optical pulse in the Sagnac modulation ring, .

[0131] According to an embodiment of the present invention, the first duration is set so that the optical pulse of each cycle can be located at the center of the flat region of the electrical signal.

[0132] According to an embodiment of the invention, a pulse train and a half-wave voltage of an electrical signal are determined.

[0133] According to an embodiment of the present invention, the light source generates light pulses at a predetermined modulation rate, the voltage peak value of the traveling wave electrical signal of the phase modulator is a half-wave voltage, the modulation frequency is a predetermined modulation rate, and the light pulses can be modulated after the electrical signal is delayed for a first time length and a second time length, and the maximum repetition frequency is a predetermined modulation rate threshold.

[0134] The present invention, through the design of the modulation mode, replaces the modulation mode that can only modulate the positive pulse and the reverse pulse separately in one cycle with the modulation mode that modulates the positive pulse and the reverse pulse of different cycles in one cycle, thereby improving the modulation rate of the Sagnac interference structure. The modulation mode that modulates twice in each cycle is adjusted to the electrical signal modulating a pair of positive pulses and reverse pulses of different cycles in one modulation cycle, that is, modulating once in each cycle, thereby reducing the frequency requirement of the light intensity modulation system based on the Sagnac interference structure on the electrical signal, and reducing the bandwidth burden of the system.

[0135] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination advantageously. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A light intensity modulation method based on Sagnac interference structure, characterized in that: include: According to the target modulation condition, the predetermined distance between the phase modulator and the center position of the Sagnac modulation ring is determined so that The reverse pulse of the first cycle The positive pulses of the first cycle enter the phase modulator at the same time, and the The reverse pulse of the first cycle The positive pulses of cycles enter the phase modulator simultaneously; wherein, is a natural number greater than or equal to 2, is less than and is an integer not equal to 0; wherein the phase modulator is configured to modulate the optical pulse using an electrical signal; wherein the optical pulse entering the Sagnac modulation ring is decomposed into the positive pulse and the reverse pulse, and the positive pulse and the reverse pulse respectively travel in opposite directions for one cycle and then meet; Determining waveform parameters of the electrical signal according to a predetermined modulation rate and a predetermined modulation period; Determining parameters of the phase modulator according to a predetermined modulation rate threshold; Determine the first duration according to the target modulation form ; Wherein, the target modulation form is that the positive pulse of each cycle is located at the center of the flat area of ​​the electrical signal; According to the waveform parameters of the electrical signal, the parameters of the phase modulator and the first duration , realizing the light intensity modulation of the light pulse by the Sagnac interference structure.

2. The light intensity modulation method based on Sagnac interference structure according to claim 1, characterized in that: Determining the waveform parameters of the electrical signal according to a predetermined modulation rate and a predetermined modulation period includes: The waveform parameters of the electrical signal include a first time length and the second time length ; Wherein, the first time length is the time length of the flat area of ​​the electrical signal; the second time length is the rising edge time length of the electrical signal and the falling edge time length The maximum value between in, ; ; ; in, is the predetermined modulation rate, is the predetermined modulation period; In order to consider the time margin of the flat area in actual situations, is the speed of light; is the length of the phase modulator, is the refractive index of the crystal inside the phase modulator.

3. The light intensity modulation method based on Sagnac interference structure according to claim 2, characterized in that: Determining the parameters of the phase modulator according to a predetermined modulation rate threshold comprises: According to the predetermined modulation rate threshold , determine the parameters of the phase modulator and ; in, .

4. The light intensity modulation method based on Sagnac interference structure according to claim 2, characterized in that: The first duration is determined according to the target modulation form. include: According to the target modulation form, adjusting the time difference between the moment when the electrical signal is loaded on the phase modulator and the moment when the optical pulse is generated, to obtain a relationship curve of the output light intensity of the phase modulator corresponding to different time differences; According to the relationship curve, the first duration is determined ;in, .

5. The light intensity modulation method based on Sagnac interference structure according to claim 4, characterized in that: The first duration is determined according to the relationship curve. include: The time difference corresponding to the center position of the stable area of ​​the relationship curve is determined as the first duration .

6. The light intensity modulation method based on Sagnac interference structure according to claim 1, characterized in that: Before the optical pulse enters the phase modulator, the method further comprises: Determining a pulse sequence of the electrical signal according to a target modulation result; The target modulation result is a target optical pulse sequence after the optical pulse is modulated by the phase modulator.

7. The light intensity modulation method based on Sagnac interference structure according to claim 6, characterized in that: Also includes: Determine the second duration according to the comparison result between the target optical pulse sequence and the actual optical pulse sequence output by the phase modulator ; wherein the second duration Used to make the positive pulse of the kth period correspond to the m+kth electrical signal; in, is an integer.

8. The light intensity modulation method based on Sagnac interference structure according to claim 6, characterized in that: Also includes: Get experimental modulation results; When the experimental modulation result indicates that the phase change modulated by the high level is more than the phase change modulated by the low level by π, the difference between the voltage corresponding to the high level and the voltage corresponding to the low level is used to determine the half-wave voltage of the pulse sequence of the electrical signal. .

9. The light intensity modulation method based on Sagnac interference structure according to claim 8, characterized in that: The experimental modulation result is obtained by scanning the electrical signal.

10. The light intensity modulation method based on Sagnac interference structure according to claim 6, characterized in that: Also includes: A signal generator is used to generate a pulse sequence of the electrical signal.

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