CN112364998B

CN112364998B - Phase randomness test device and method

Info

Publication number: CN112364998B
Application number: CN202011101225.8A
Authority: CN
Inventors: 陈柳平; 王其兵; 万相奎
Original assignee: Guokaike Quantum Technology Beijing Co Ltd
Current assignee: Guokaike Quantum Technology Beijing Co Ltd
Priority date: 2020-10-15
Filing date: 2020-10-15
Publication date: 2021-11-16
Anticipated expiration: 2040-10-15
Also published as: CN112364998A

Abstract

The invention relates to a phase randomness test device and a method, wherein the device comprises an interference module, a phase adjustment module, a detection acquisition module and an analysis module, wherein the interference module is connected with a light source to be tested, and is used for splitting an original pulse light signal with random phase sent by the light source to be tested into a plurality of light signals so as to enable the plurality of light signals to interfere to obtain an interference light signal; the phase adjusting module is arranged in a first arm optical path of the interference module and adjusts the phase of an optical signal transmitted by the first arm according to a phase adjusting strategy; the detection acquisition module detects and acquires the interference light signal to obtain the maximum value of the peak amplitude of the interference light signal in different phases; and the analysis module obtains a test curve for determining the randomness of the phase according to a preset analysis strategy based on the maximum value of the peak amplitude of the collected different phases. The device and the method can test the phase randomness of the pulse light emitted by the light source to be tested.

Description

Phase randomness test device and method

Technical Field

The present invention relates to the field of secure communications technologies, and in particular, to a phase randomness testing apparatus and method.

Background

In the field of Quantum secret communication, unlike a traditional secret communication system that encrypts and transmits information itself, a QKD (Quantum Key Distribution) system is a system that encrypts an information physical layer to realize secret communication, that is, encrypts a carrier carrying information in a communication process.

Taking quantum key distribution in an optical fiber as an example, the QKD system uses single-photon pulses as carriers, and transmits classical binary bit information of 0 and 1 by encrypting the single-photon pulses. Thus, QKD systems utilize single-photon pulse transmitting and receiving devices to achieve secure communication of information physical layer encryption. In the process of quantum key distribution, any eavesdropping aiming at the key needs to measure the quantum state formed by single photon pulses, but according to the unclonable principle of quantum mechanics, any measurement can change the quantum state per se to cause high bit error rate, so that an eavesdropper can be found.

In the development process of the QKD system, people make a step-by-step exploration, and a BB84 protocol, an Ekert91 protocol, a BBM92 protocol, a decoy state protocol, a measuring Device-Independent Quantum Key Distribution protocol (MDI-QKD), and the like appear in sequence. In practical engineering applications, the mainstream way of the QKD system is to implement quantum secure communication based on the decoy BB84 protocol, where the light source is an important component in the quantum secure communication QKD system. Because the preparation condition of the ideal single photon light source is immature at present, the attenuated weak coherent pulse light source is generally adopted as the light source in quantum communication. Based on the trick-state BB84 protocol, it is required that the phase of the pulsed light source is random. At present, the preparation methods of the pulse light source are divided into an internal modulation method and an external modulation method. In theory, the phase of the pulsed light source obtained in the former is random, the phase of the pulsed light source obtained in the latter is fixed, and the phase of the pulsed light source obtained in the latter can be random by adding a phase randomization module. No instrument or method for testing the prepared result exists at present no matter which preparation method is adopted, so that the design of a method and a device for testing the phase randomness of the pulse light source is crucial in quantum secret communication.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides a phase randomness testing device and a phase randomness testing method, which are used for testing the phase randomness of a laser light source.

In order to solve the above technical problem, according to an aspect of the present invention, the present invention provides a phase randomness test apparatus, including an interference module, a phase adjustment module, a detection and collection module, and an analysis module, where the interference module is configured to be connected to a light source to be tested, and splits an original pulse light signal with a random phase emitted by the light source to be tested into multiple light signals, so that the multiple light signals interfere to obtain an interference light signal, where a light path difference Δ L = nT between any two light signals in the split multiple light signals, T is a period of the pulse light signal, and n is a natural number greater than 0; the phase adjustment module is configured to be disposed in a first arm optical path of the interference module, and adjust a phase of an optical signal transmitted through the first arm according to a phase adjustment strategy; the detection acquisition module is configured to detect and acquire the interference light signal to obtain a peak amplitude maximum of the interference light signal at different phases; and the analysis module obtains a test curve for determining the randomness of the phase according to a preset analysis strategy based on the maximum value of the peak amplitude of the collected different phases.

Preferably, the testing device further comprises one or more attenuation modules configured to be disposed in one or more second arm optical paths of the interference module to adjust the optical intensity of the optical signal transmitted through the second arm, so that the insertion loss of the plurality of interfered optical signals is consistent.

Preferably, the interference module includes a beam splitting unit and a beam combining unit, wherein the beam splitting unit is configured to split an original pulsed light signal with a random phase emitted by a light source to be tested into a first light signal and one or more second light signals; the first optical signal is transmitted to the phase adjusting module through a first arm; the phase adjusting module adjusts the first optical signal according to a phase adjusting strategy and then outputs a third optical signal; the one or more second optical signals are conveyed to the respective attenuation modules via the corresponding one or more second arms; the attenuation module adjusts the light intensity of the second optical signal and outputs a fourth optical signal with insertion loss consistent with that of the third optical signal; the beam combining unit is configured to receive the third optical signal and one or more of the fourth optical signals and output an interference optical signal of the third optical signal and the fourth optical signal.

Preferably, the interference module further includes a michelson interferometer or an AMZ interferometer, and the phase adjustment module and the attenuation module are respectively disposed in the optical paths of the first arm and the second arm of the michelson interferometer or the AMZ interferometer.

Preferably, the interference module further comprises a circulator or an isolator configured to have a first interface connected to the light source to be measured and a second interface connected to the michelson interferometer.

Preferably, the first arm in the interference module is a long arm or a short arm, and correspondingly, the second arm is a short arm or a long arm.

Preferably, the phase adjustment module includes: a phase modulator or phase shifter configured to adjust a phase of an input optical signal thereof in accordance with a phase control signal, and a phase adjustment control unit; the phase adjustment control unit is configured to output a phase control signal to the phase modulator or fiber phase shifter according to a phase adjustment strategy.

Preferably, the attenuation module further comprises an attenuator configured to adjust the light intensity of its input optical signal by a preset attenuation amount.

Preferably, the attenuation module further comprises a light intensity detection unit and a light intensity adjustment control unit configured to detect the light intensities of a plurality of optical signals output by the interference module and not interfered at the time of initialization, wherein the plurality of optical signals comprise an optical signal passing through the phase adjustment module and an optical signal passing through the attenuator; the light intensity adjusting control unit is configured to generate an attenuation amount according to the light intensity of the optical signal passing through the phase adjusting module and the optical signal input by the attenuator, and output the attenuation amount to the attenuator.

Preferably, the detection acquisition module comprises a photoelectric detector, a data acquisition unit and a data processing unit; wherein the photodetector is configured to detect the interfering light signal to generate a corresponding electrical pulse signal; the data acquisition unit is configured to acquire an electric pulse signal of the interference light signal to obtain the electric pulse peak amplitude; the data processing unit is configured to compare a plurality of pulse peak amplitudes of the same phase to obtain a peak amplitude maximum of the phase.

Preferably, the analysis module comprises: a contrast calculation unit and a curve generation unit; wherein the contrast calculation unit is configured to calculate the contrast between the maximum pulse peak amplitude values of different phases of the interference light signal and the pulse peak amplitude value of the light source to be measured; the curve generation unit is configured to generate a peak contrast-phase curve based on test data of the phase and its peak amplitude contrast, wherein the phase variation range is 0-2 pi.

Preferably, the analysis module is further configured to generate a peak-to-phase curve based on the test data for the phase and its peak amplitude maximum.

Preferably, the test device further comprises an output module configured to be connected to the analysis module and configured to output or/and display the obtained test curve and/or test data.

Preferably, the testing apparatus further includes a parameter configuration module, which is configured to be connected to the phase adjustment module, the detection and acquisition module, and the analysis module, so as to configure parameters required by each module.

Preferably, the testing device further comprises a main control module, which is configured to be connected with the phase adjusting module, the detection and acquisition module, the analysis module and the attenuation module respectively, and coordinate the work of each module.

According to another aspect of the present invention, the present invention also provides a phase randomness testing method, comprising the steps of:

splitting an original pulse light signal with a random phase emitted by a light source to be detected into at least a first light signal and a second light signal, wherein the optical path difference Delta L = nT of the first light signal and the second light signal, T is the period of the pulse light signal, and n is a natural number;

adding a phase adjusting device in an optical path of a first optical signal, wherein the phase adjusting device adjusts the phase of the first optical signal according to a phase adjusting strategy to obtain a third optical signal;

the third optical signal and the second optical signal are interfered to obtain an interference optical signal;

detecting and collecting the interference light signal, and obtaining the maximum value of the peak amplitude of the interference light signal after phase adjustment; and

and obtaining a corresponding test curve according to a preset analysis strategy based on the collected peak amplitudes of different phases.

Preferably, the test method further comprises the steps of:

arranging an attenuator on an optical path of the second optical signal, and controlling the attenuator to attenuate the light intensity of the second optical signal to obtain a fourth optical signal with insertion loss consistent with that of the third optical signal; and

and the third optical signal and the fourth optical signal interfere to obtain the interference optical signal.

Preferably, the phase adjustment strategy comprises: sequentially changing the phase of the first optical signal according to the formula (1-1);

（1-1）；

wherein i

；k=64~2048；

。

Preferably, the preset analysis policy is:

calculating the contrast ratio of the maximum value of the pulse peak amplitude of the interference optical signal in different phases and the corresponding pulse peak amplitude of the light source to be detected; and

a peak contrast-phase curve is generated based on the phase and its peak amplitude contrast test data.

Preferably, the contrast is a ratio of a maximum value of a peak amplitude of the interference light to a peak amplitude of a pulse of the light source to be measured, or an absolute value of a difference.

Preferably, the preset analysis policy is: a peak-to-phase curve is generated based on the test data for the phase and its peak amplitude maximum.

Based on that attenuated weak coherent light sources can be adopted as single photon sources in a decoy BB84 protocol, pulse phase randomization of the weak coherent light sources is required, the device and the method provided by the invention can realize detection and analysis of the phase randomness of the laser light sources of any product, can be applied to random detection in any product design module in the quantum information technology, have wide application range and high accuracy, and provide a quantitative analysis method for phase randomness of the random number information entropy sources based on phase noise quantum.

Drawings

Preferred embodiments of the present invention will now be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of a phase randomness test apparatus provided according to an embodiment of the present invention;

FIG. 2 is a functional block diagram of the structure of an interference module according to one embodiment of the present invention;

FIG. 3 is a schematic diagram of an optical signal according to one embodiment of the present invention;

FIG. 4 is a functional block diagram of a phase adjustment module according to an embodiment of the present invention;

FIG. 5 is a functional block diagram of a detection acquisition module according to one embodiment of the present invention;

FIG. 6 is an electrical signal schematic of an interfering optical signal according to one embodiment of the present invention;

FIG. 7 is a functional block diagram of the structure of an analysis module according to one embodiment of the present invention;

FIG. 8 is a phase-peak contrast curve according to one embodiment of the present invention;

FIG. 9 is a phase-peak plot according to one embodiment of the present invention;

FIG. 10 is a graph of a probability distribution of peak amplitudes according to one embodiment of the invention;

FIG. 11 is a functional block diagram of a phase randomness test apparatus according to another embodiment of the present invention;

FIG. 12 is a functional block diagram of the structure of an intervention module in accordance with one embodiment of the present invention;

FIG. 13 is a functional block diagram of the structure of an attenuation module according to one embodiment of the present invention;

FIG. 14 is a functional block diagram of the structure of an interferometric module according to another embodiment of the invention;

FIG. 15 is a functional block diagram of a phase randomness test apparatus according to another embodiment of the present invention;

FIG. 16 is a flow diagram of a phase randomness test method according to an embodiment of the present invention;

FIG. 17 is a schematic block diagram of a phase randomness test apparatus according to yet another embodiment of the present invention;

FIG. 18 is a phase randomness test procedure flow diagram according to one embodiment of the present invention; and

fig. 19 is a flowchart of a test procedure in the flowchart shown in fig. 18.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof and in which is shown by way of illustration specific embodiments of the application. In the drawings, like numerals describe substantially similar components throughout the different views. Various specific embodiments of the present application are described in sufficient detail below to enable those skilled in the art to practice the teachings of the present application. It is to be understood that other embodiments may be utilized and structural, logical or electrical changes may be made to the embodiments of the present application.

Fig. 1 is a schematic block diagram of a phase randomness testing apparatus for testing the phase randomness of pulsed light with random phases according to an embodiment of the present invention. In this embodiment, the phase randomness testing device 2 at least includes an interference module 20, a phase adjusting module 21, a detection and collection module 22, and an analysis module 23, and the phase randomness testing device 2 in this embodiment is described with reference to a structure diagram of the interference module 20 shown in fig. 2 and an optical signal diagram shown in fig. 3.

The pulse laser 1 is used as a light source to be measured, and generates pulsed light 50 with random phases, and the pulsed light is input into the interference module 20 through the optical fiber interface. The interference module 20 in this embodiment is an unequal arm MZ (Mach-Zehnder) interferometer, abbreviated as an AMZ interferometer. The interference module 20 includes a beam splitting unit 201 and a beam combining unit 202, such as a half-silvered beam splitter. An incident light path of the beam splitting unit 201 is connected to the pulse laser 1 through an interface, and splits an original pulse light 50 signal with a random phase emitted by the pulse laser 1 into a first light signal 51 and a second light signal 52. The first optical signal 51 is transmitted to the phase adjustment module through a first arm, in this embodiment, the first arm is a short arm, and the phase adjustment module 21 is disposed in the short arm. The phase adjustment module 21 shifts the phase of the input first optical signal 51 according to the phase adjustment strategy, so as to obtain a third optical signal 53, and transmits the third optical signal to the beam combining unit 202. The beam combining unit 202 receives the third optical signal 53 and the fourth optical signal 54 output by the phase adjusting module 21, wherein the second optical signal 52 is the fourth optical signal 54 after reaching the beam combining unit 202 through the transmission of the long arm, and since the optical lengths of the two arms are different, for example, the optical path difference Δ L = nT, T is the period of the pulse optical signal, and n is a natural number, the pulse corresponding relationship between the third optical signal 53 and the fourth optical signal 54 is as shown in fig. 3. The third optical signal 53 and the fourth optical signal 54 interfere at the beam combining unit 202, and an interference optical signal 55 is output.

The interference module 20 in this embodiment splits the pulsed light 50 generated by the pulse laser 1 with random phases into two beams, or may split the pulsed light into multiple beams, and the multiple beams interfere with each other to obtain an interference signal. When the optical signal is divided into a plurality of beams, a phase adjusting module is arranged on one arm to adjust the phase of the optical signal transmitted by the arm.

Fig. 4 is a schematic block diagram of the structure of the phase adjustment module 21 in one embodiment. The Phase adjustment module 21 includes a Phase Modulator (PM) 211 and a Phase adjustment control unit 212. The phase modulator 211 adjusts the phase of its input optical signal according to the phase control signal, and the element having the same function may also be a phase shifter, such as a fiber phase shifter FPS. The phase adjustment control unit 212 outputs a phase control signal to the phase modulator 211 or the fiber phase shifter according to a phase adjustment strategy. Wherein the phase adjustment strategy comprises a specific phase value adjusted each time. For example, change the second order in accordance with the formula (1-1)A phase of an optical signal

A test cycle is completed.

（1-1）

Wherein the content of the first and second substances,

and k ranges from 64 to 2048.

The phase adjustment strategy also includes a phase shift period T1 or a phase shift frequency, i.e. a time interval for which the phase shift is performed, e.g. T1=1s, 10s, etc., i.e. the phase shift is performed every 1s or 10 s.

Taking T1=1s as an example, the phase adjustment control unit 212 sends a phase control signal to the phase modulator 211 or the fiber phase shifter FPS every 1s, where the phase control signal includes a phase angle that needs to be adjusted each time. For example, when k =200, i =1, phase at the first adjustment

(ii) a At adjustment 2, i =2, phase

(ii) a Third adjustment, i =3, phase

… … up to phase

A test cycle is completed, i.e. a test cycle is ended.

FIG. 5 is a functional block diagram of a detection acquisition module according to one embodiment of the present invention. In the present embodiment, the detection acquisition module 22 includes a photodetector 221, a data acquisition unit 222, and a data processing unit 223. The photodetector 221 may be a PN junction photodetector, a PIN photodetector, an Avalanche Photodiode (APD) detector, or a pull-through avalanche photodiode (RAPD) detector, etc., for converting the interference optical signal 55 into an electrical signal, such as the electrical signal shown in fig. 6. The electric pulse signal corresponding to the optical pulse is obtained at this time, and may be a voltage signal or a current signal as shown in the figure.

When the adjustment control unit 212 sends a phase control signal to the phase modulator 211 or the fiber phase shifter FPS once, the data acquisition unit 222 acquires the electrical signal of the interference light signal in a set acquisition period T2 to obtain the peak value of the electrical pulse. When the phase randomness test device 2 is started up, an initialization process is performed, in which the data acquisition unit 222 searches for a peak position of the electrical signal, and samples are taken at the point each time after the peak position is confirmed. Finding the location of the peak can be accomplished once during system initialization.

The acquisition period T2 when the data acquisition unit 222 acquires data may adopt a system period, i.e., the pulse period T of the pulse laser 1, i.e., T2= T. It may also be a small multiple of the system period, such as T2=0.1T, 0.5T, or an integer multiple, such as T2=2T, 3T, etc. Within a phase shift period T1 (e.g., 0.01 s) with a fixed phase (e.g., 0.01 pi), the data acquisition unit 222 can acquire a plurality of peak positions of the electrical signal, i.e., a plurality of peak amplitudes. For example, when the pulse frequency is 100MHz, the period T =10^-8And s. When the acquisition period is the same as the pulse period, i.e., T1= T2= T =10^-8s, 10 can be collected⁸Data, i.e. 10⁸The peak amplitude of each pulse.

The data processing unit 223 compares the peak amplitudes of the pulses in the same phase to obtain the maximum peak amplitude. As with the previous embodiment, the data processing unit 223 is at 10⁸The maximum value was found in the data.

Therefore, after the processing of the detection and acquisition module 22, a plurality of groups of phases and peak amplitude maximum values of interference light signals thereof can be obtained, and the phases and the corresponding peak amplitude maximum values can be stored in a memory (not shown in the figure) as test data or directly sent to the analysis module 23.

The analysis module 23 obtains a corresponding test curve according to a preset analysis strategy based on the test data, i.e. the peak amplitude maximum values corresponding to different phases (in the following description, the peak amplitude maximum value processed by the analysis module 23 is simply referred to as a peak amplitude for convenience of description). FIG. 7 is a functional block diagram of an analysis module according to one embodiment of the present invention. In the present embodiment, the analysis module 23 includes a contrast calculation unit 231 and a curve generation unit 232. The contrast calculation unit 231 reads a peak amplitude P1 corresponding to one phase from the memory, and calculates the contrast C1 of the two according to the peak amplitude P0 of the pulse corresponding to the light source to be measured. The pulse amplitude P0 of the light source to be tested can be preset in the system manually, or can be obtained by connecting the pulse laser 1 to the photodetection module 22 for numerical measurement before testing. The contrast C is the ratio or difference of the two peak amplitudes. I.e. C1= P1/P0, or C1= | P0-P1 |. In the present embodiment, the ratio of two peak amplitudes is taken as the contrast. Based on the method, the pulse peak amplitude contrast of each different phase is calculated. The curve generating unit 232 generates a phase-peak contrast curve based on the phase and the corresponding peak amplitude contrast, as shown in fig. 8, wherein the phase variation range is 0-2 pi. Alternatively, in another embodiment, analysis module 23 generates a peak-to-phase curve based on the phase and corresponding pulse peak amplitude. As shown in fig. 9.

As can be seen from the above description, when the phase modulator is set to a fixed phase, for example, to 0, the interference peak amplitude is monitored for a period of time to be P1 (so that the peak amplitudes of a plurality of pulses are obtained, and the maximum value of the peak amplitudes obtained through comparison is referred to as P1). Similarly, the peak amplitude of the phase modulator is monitored as P2 when it is set to 0.1 π, and so on to Pn. When the pulsed light 50 emitted by the laser generator 1 is pulsed light with random phases, the original pulsed light is split and then interfered by two front and rear pulses to obtain interference light, and because the phases of the original pulsed light are random, the phases of a plurality of split pulsed light are different, and the amplitudes after interference are also different. When a large number of different phase interferences occur over time, the resulting amplitude distribution is theoretically all from 0 to VPP and exhibits the amplitude-probability distribution curve shown in fig. 10. The peak amplitude of each phase at this time coincides with P1= P2= P3= … … = Pn.

If the pulse phases are not random, for example, the phases φ 1 and φ 2 of the two preceding and following pulses have a fixed relationship, and the amplitude after interference is a fixed value P, then the phases 0, 0.1 π and 0.2 π … … π are sequentially added to φ 1, so that the relationship of the amplitudes P21, P22 and P23 … … P2n they interfere with is unequal, theoretically, a sine curve, and at this time, the phases are not random, and the phase randomization requirement cannot be satisfied. Thus, in the phase randomization analysis process, the randomness of the phase randomization can be measured by the amplitude fluctuation range in the amplitude-phase curve or the contrast fluctuation range in the contrast-phase curve.

To more conveniently verify randomness, in some embodiments, randomness may be more intuitively represented in a graphical manner using brightness. For the amplitude-phase curve or the contrast-phase curve, the amplitude 0.5 is used as the luminance 0 value, the luminance higher than 0.5 is positive luminance, and the luminance lower than 0.5 is negative luminance. The continuous time period is elapsed and the luminance value is accumulated and converted into positive luminance. Poor randomness is indicated if discernable brightness variations occur. Randomness is good if no discernable brightness variation can occur. Thus, the display of the display and the brightness sensitivity of the human eye can be used to meet the usual randomness requirements. For amplitude-probability curves, which are more sensitive, poor randomness will change the shape of the curve. By performing independence analysis on the amplitude-probability curve and the standard curve, the correlation degree of the amplitude-probability curve and the standard curve can be obtained. If the degree of association satisfies the independence condition, the randomness may be considered to be unsatisfactory.

In this embodiment, in order to obtain or change various parameter values in the phase randomness test device 2, such as a parameter k in formula 1-1, or a phase shift period or an acquisition period, or output test data, or calculate a test curve, please refer to fig. 1, the phase randomness test device 2 further includes a data interface 24, which is connected to the upper computer 3, and is configured to receive data from the upper computer 3 and send the data to a corresponding module, or send data in the analysis module 23 and a test result to the upper computer 3.

In another embodiment, as shown in fig. 11, a schematic block diagram of a phase randomness testing apparatus according to another embodiment of the present invention is shown. In the present embodiment, the difference from the embodiment shown in fig. 1 is that a parameter configuration module 25 and an output module 26 are included in the present embodiment. Wherein, the parameter configuration module 25 and the output module 26 may form a user interface, and the parameter configuration module 25 includes an input device, such as a touch screen and an adjusting knob. The output module 26 may include a liquid crystal display, a digital tube, and the like for displaying curves, numbers, and the like. The output module 26 may also include the aforementioned data interface 24 for outputting data to the upper computer.

Figure 12 is a schematic diagram of an interference module according to another embodiment of the present invention. Compared to the interference module shown in fig. 2, in the present embodiment, the phase adjustment module 21 is disposed in the long-arm optical path, and the attenuation module 28 is disposed in the short arm of the interference module 20 a. For attenuating the light intensity of the first optical signal 51 so as to make the insertion loss of the third optical signal 53 and the fourth optical signal 54 inputted to the beam combining unit 202 consistent to improve the interference effect.

As shown in fig. 13, the attenuation module 28 includes an attenuator 281 disposed in the short arm optical path of the interference module 20a, and adjusting the light intensity of the input optical signal according to a preset attenuation amount. The attenuation can be preset in the attenuator 281 after measurement before testing. For example, the light source to be measured emits low-frequency (the pulse period T is greater than two times the arm length difference delay value) pulsed light, the oscilloscope is connected to the output end of the interferometer, the pulsed light wave curve transmitted through the two arms can be measured through the oscilloscope, and the attenuation amount is calibrated according to the pulsed light wave curve.

In another embodiment, a light intensity detecting unit 282 and a light intensity adjusting control unit 283 are further included. The attenuator 281 is disposed in the short arm optical path of the interference module 20a, and adjusts the optical intensity of the input optical signal according to the attenuation control signal. The light intensity detecting unit 282 is connected to the output end of the beam combining unit 202, and during the system initialization process, the pulse laser sends a low-frequency pulse, and forms two pulses without interference after passing through the AMZ or michelson interferometer module, and the two pulses pass through the photoelectric detecting unit and the analog-to-digital converting unit in the light intensity detecting unit 282 and are output to the light intensity adjusting and controlling unit 283 in the form of light intensity electric signals. The light intensity adjustment control unit 283 analyzes and compares the two light intensity electric signals sent from the light intensity detection unit 282 to obtain an attenuation amount, and sends the attenuation amount to the attenuator 281 through an attenuation control signal, so that the attenuator 281 adjusts the light intensity of the received pulsed light according to the attenuation amount. In one embodiment, the light intensity detecting unit 282 may be the detection and collection module 22. When the system is initialized, the detection and acquisition module 22 performs photoelectric detection and analog-to-digital conversion, outputs the light intensity signal to the light intensity adjustment control unit 283, and obtains the attenuation amount by the light intensity adjustment control unit 283.

Figure 14 is a schematic diagram of an interference module according to another embodiment of the present invention. In this embodiment, the interference module is a michelson interferometer, and the phase adjusting module and the attenuation module are respectively disposed in the long-arm optical path and the short-arm optical path of the michelson interferometer, or, of course, the phase adjusting module and the attenuation module may be respectively disposed in the short-arm optical path and the long-arm optical path. The phase adjusting module can adopt a phase modulator or a fiber phase shifter. In order to prevent the second beam of interference light signal generated by the beam splitting unit in the michelson interferometer from entering the pulse laser 1, a circulator 27 or an isolator is added before the input interface of the michelson interferometer.

Fig. 15 is a schematic block diagram of a phase randomness test apparatus according to another embodiment of the present invention. In this embodiment, the phase randomness test device 2b includes an interference module 20b, a phase modulator 21b or a fiber phase shifter, a detection and acquisition unit 22b and an analysis unit 23b, a communication module 24b, an attenuator 28b, a main control module 291b, a user interface 292b, and a memory 293 b. The difference from the apparatus in fig. 1 is that the present embodiment combines the control units of the respective modules together, i.e., the main control module 291 b. Thus, the control of the phase modulator 21b, the detection and acquisition unit 22b, the attenuator 28b and the analysis unit 23b, and the acquisition of parameters required to be obtained before the test, such as the pulse peak value of the light source to be tested, the attenuation of the attenuator 28b, etc., are all performed by the main control module 291 b. The user may enter parameter values, such as the phase shift period, the amount of attenuation of the attenuator 28b, settings for the analysis method, etc., through the user interface 292 b. The test curve may also be viewed through the user interface 292 b. The communication module 24b can be connected and communicated with other devices, such as an upper computer, a workstation and the like. The upper computer or the workstation can read data in the memory 293b in the testing device, or send the data and the set parameters to the testing device. The communication module 24b may employ any wired or wireless communication method.

The pulse laser 1b generates pulse light with random phases, the pulse light is input into the interference module 20b through an optical fiber interface, the pulse light is divided into two beams through the beam splitting unit 201b, and one beam is output to the beam combining unit 202b after being subjected to phase shifting through the phase modulator 21 b; the other beam is attenuated by the attenuator 28b and output to the beam combining unit 202 b. The two beams interfere with each other in the beam combining unit 202 b. The phase modulator 21b adjusts the phase of its input optical signal according to the phase control signal sent by the main control module 291 b. The attenuator 28b adjusts the light intensity of the input optical signal according to the attenuation amount in the attenuation control signal sent by the main control module 291b, so that the insertion loss of the two beams of light interfering in the beam combining unit 202b is consistent, and a good interference effect is obtained.

The detection and acquisition unit 22b performs photoelectric conversion, analog-to-digital conversion, and data processing on the interference light output by the interference module 20b, and then obtains a maximum peak amplitude value for a fixed phase.

The analysis unit 23b analyzes the collected data according to the analysis strategy specified by the main control module 291b, so as to obtain a peak contrast-phase curve as shown in fig. 8 or a peak amplitude-phase curve as shown in fig. 9.

FIG. 16 is a flow chart of a phase randomness test method according to one embodiment of the present invention. The method comprises the following steps:

step S1, splitting an original pulsed light signal with a random phase emitted by a light source to be measured into at least a first light signal and a second light signal, where a difference Δ L = nT between optical paths of the first light signal and the second light signal, T is a period of the pulsed light signal, and n is a natural number greater than 0.

In step S2, two beams of light with different optical paths interfere with each other, so as to obtain an interference light signal.

Step S3 is to adjust the phase of the first optical signal according to the set phase. For example, the phase of the first optical signal is sequentially changed according to the formula (1-1); when in use

Completing a test cycle;

（1-1）；

wherein the content of the first and second substances,

，k=64~2048。

and step S4, performing photoelectric detection on the interference light signal to obtain an electric signal of the interference light signal.

Step S5, collecting the electrical signal of the interference optical signal after each phase adjustment to obtain a plurality of peak amplitudes of the interference optical signal at the fixed phase. When the test device is initialized, the method further comprises a process of searching a pulse peak value, and sampling is carried out at the point every time after the peak value position is confirmed.

In step S6, a plurality of peak amplitudes obtained at a fixed phase are compared to obtain a peak amplitude maximum.

In step S7, it is determined whether a test cycle is completed, i.e., whether the phase is equal to 2 pi. If a test cycle is completed, in step S8, based on the maximum value of the peak amplitudes of the collected different phases, a corresponding test curve is obtained according to a preset analysis strategy; if not, the process returns to step S3 for phase shifting.

In one embodiment, in step S8, the preset analysis strategy is to obtain a peak contrast-phase curve. Therefore, the peak amplitude of the interference light at different phases and the peak amplitude of the original pulse light signal need to be compared to obtain the peak contrast; and then drawing a peak contrast-phase curve as a test curve based on the phase and the corresponding peak contrast.

In another embodiment, in step S8, the preset analysis policy is: a peak-to-phase curve is generated based on the phase and the peak amplitude of the corresponding pulse.

Fig. 17 is a schematic structural diagram of a phase randomness test device 2c according to another embodiment of the present invention. In the present embodiment, the phase randomness test device 2c is provided with a pulse fiber input interface for connecting the pulse laser 1 c. A communication interface connected with the communication module 27c is also provided for connecting with an upper computer. The user interface 26c is a touch screen with input and display functions. The user interface 26c is connected to a main control module 25c, the main control module 25c is connected to the phase modulators 21c and attenuators 28c connected to the two arms of the AMZ interferometer 20c, and the main control module 25c is further connected to the optical signal detection and acquisition unit 22c and the randomness analysis unit 23 c. The optical fiber input interface further comprises a selection switch 4c, which comprises two terminals, one is a test terminal for connecting the input optical signal to the AMZ interferometer 20c, and the other is a pulse amplitude measurement terminal for connecting the input optical signal to the optical signal detection and acquisition unit 22c to obtain the pulse amplitude of the light source to be tested. The main control module 25c is a central control module formed by various industrial personal computers, such as a single chip microcomputer, and is configured to complete acquisition of various parameters and data in a test process, and send related control instructions to the phase modulator 21c, the attenuator 28c, the optical signal detection and acquisition unit 22c, and the randomness analysis unit 23c according to a test flow, so that each device and unit coordinate to complete the test process. In this embodiment, the interference module is an AMZ interferometer, where Δ L = nT, T is a period of a pulse optical signal, and n is a natural number greater than 0. The main control module 25c in this embodiment may include a plurality of operating modes, such as a debug mode, an initialization mode, a test mode, and the like. The debugging mode can be used for debugging various parameters, such as the peak amplitude of pulsed light emitted by the light source to be tested, the attenuation of the attenuator, and the like. And searching and determining the peak position of the pulse amplitude in the initialization mode, and using the peak position as a data acquisition position in the test process. In the test mode, the main control module 25c sets the phase of the phase adjuster according to the phase shift period and the phase value of each phase shift, controls the optical signal detection and acquisition unit 22c to perform photoelectric conversion and analog-to-digital conversion on the optical signal, and obtains the maximum value of the peak amplitude in the period. The main control module 25c sets an analysis strategy used by the randomness analysis unit 23c, for example, peak amplitude-phase analysis, peak amplitude contrast-phase analysis, or peak-probability analysis. The randomness analyzing unit 23c receives the data collected by the detection collecting unit 22c, analyzes the data according to the analysis method set by the main control module 25c, sends the result to the main control module 25c or stores the result in a memory, and notifies the main control module 25 c. And when receiving the analysis result, the main control module 25c displays the analysis result to a user interaction interface and outputs the analysis result to the upper computer through a communication interface.

The following description briefly describes the test procedure with reference to the test apparatus shown in fig. 17 and the flowchart shown in fig. 18:

step S1c, the device connects. The laser output interface of the pulse laser 1c is connected to the fiber input interface of the phase randomness test device 2 c. If necessary, the device is connected with an upper computer through a communication interface.

And step S2c, acquiring parameter values required in the test process. Some parameters may be entered through the user interface 26c, such as the phase shift period T1, the data acquisition period T2, and the value of k in equation 1-1. The parameters such as the pulse amplitude of the pulse laser 1c used in the peak contrast-phase analysis method and the attenuation of the attenuator for attenuating the input optical signal need to be adjusted in the field. In debugging parameters, the main control module 25c may be set in a debugging mode through the user interactive interface 26 c. The optical selection switch 4c is set to the pulse amplitude measurement terminal through the user interface 26c to connect the optical signal input from the pulse laser 1c to the optical signal detection acquisition unit 22 c. The optical signal detection and acquisition unit 22c obtains the pulse peak amplitude of the pulse laser 1c through photoelectric conversion, analog-to-digital conversion and data processing, and sends the pulse peak amplitude to the main control module 25 c. The main control module 25c stores the pulse peak amplitude of the pulse laser 1c or sends it to the randomness analyzing unit 23 c. In order to obtain the attenuation amount of the attenuator for attenuating the input optical signal, the pulse laser 1c sends a low-frequency pulse, two pulses which are not interfered are formed after passing through the AMZ or michelson interferometer module, light intensity values of the two pulses are obtained respectively through photoelectric detection and analog-to-digital conversion of the optical signal detection and acquisition unit 22c and are sent to the main control module 25c, and the main control module 25c analyzes and compares the two light intensity values to obtain the attenuation amount and sends the attenuation amount to the attenuator 28 c.

In step S3c, the test apparatus is initialized. During initialization, the pulse laser 1c outputs a pulse light signal, and an interference light signal is obtained through the interferometer, and the optical signal detection and acquisition unit 22c detects the interference light signal to obtain an electric pulse signal, and performs data acquisition at different positions to determine the position of the amplitude peak. After the peak position of the amplitude value is determined, the data acquisition position is fixed.

And step S4c, testing. The test procedure is shown in fig. 19.

In step S41c, the main control module 25c sets a phase adjustment serial number i = 1.

In step S42c, the main control module 25c determines the currently adjusted phase according to equation (1-1), and when i =1,

and sets the phase-shift phase of the phase modulator 21c to 0.

（1-1）

In step S43c, interference occurs. The pulse light signal emitted by the pulse laser 1c is split into a first light signal and a second light signal, wherein the first light signal passes through the phase modulator 21c arranged on the long arm, the second light signal passes through the attenuator 28c arranged on the short arm, and the two light signals with different optical paths interfere with each other in the beam combining unit, so that an interference light signal is obtained.

In step S44c, the peak amplitude maximum value is acquired. The optical signal detection and acquisition unit 22c performs photoelectric conversion on the interference optical signal, acquires data at a position determined during initialization, to obtain a peak amplitude of each pulse, and compares the peak amplitudes to obtain a maximum value of the current peak amplitude.

In step S45c, it is determined whether the phase shift period T1 has been reached. If so, returning to step S46c, and if not, returning to step S44c, continuing data collection and processing.

And step S46c, judging whether the current phase-shifting phase is 2 pi or not, if so, ending the test, and if the current phase-shifting phase is less than 2 pi, adding 1 to the adjustment sequence number in step S47c, and returning to step S42 c.

Step S5c, randomness analysis. The optical signal detection and acquisition unit 22c sends the maximum peak amplitude value corresponding to the phase-shifted phase to the randomness analysis unit 23c, and the randomness analysis unit 23c performs analysis according to the analysis method set by the main control module 25c to obtain a corresponding test curve, such as a peak contrast-phase curve shown in fig. 8, or a peak-phase curve shown in fig. 9, or a peak-probability distribution curve shown in fig. 10.

And step S6c, outputting the test result. In this embodiment, the randomness analyzing unit 23c sends the obtained test curve to the main control module 25c, and the main control module 25c displays the test curve in the user interaction interface 26 c. Or the upper computer output through the communication interface displays or prints.

The phase randomness testing device and method provided by the invention have the advantages that:

(1) based on that the attenuated weak coherent light source can be adopted as a single photon source in a decoy BB84 protocol, the pulse phase randomization of the weak coherent light source is required, but the phase randomness of the weak coherent light source is not detected in the current commercial products, and the device provided by the invention can realize the detection and analysis of the phase randomness;

(2) the invention provides a quantitative analysis method for phase randomness based on the phase noise quantum random number information entropy source;

(3) the method can be applied to any product design module in the quantum information technology for randomness detection;

(4) the test provided by the invention can be used as an instrument and equipment for detecting and analyzing the phase randomness of the pulse light source of any product.

The above embodiments are provided only for illustrating the present invention and not for limiting the present invention, and those skilled in the art can make various changes and modifications without departing from the scope of the present invention, and therefore, all equivalent technical solutions should fall within the scope of the present invention.

Claims

1. A phase randomness test apparatus comprising:

the interference module is configured to be connected with a light source to be detected, split an original pulse light signal with random phase emitted by the light source to be detected into a plurality of light signals, and enable the plurality of light signals to interfere to obtain an interference light signal, wherein the optical path difference Delta L between any two light signals in the split plurality of light signals is nT, T is the period of the pulse light signal, and n is a natural number greater than 0;

a phase adjustment module configured to be disposed in a first arm optical path of the interference module, to adjust a phase of an optical signal transmitted through the first arm according to a phase adjustment strategy;

a detection acquisition module configured to detect and acquire the interference light signal to obtain a peak amplitude maximum of the interference light signal at different phases; and

the analysis module is configured to obtain a test curve for determining phase randomness according to a preset analysis strategy based on the collected peak amplitude maximum values of different phases;

wherein the preset analysis policy is:

calculating the contrast between the maximum value of the pulse peak amplitude of the interference optical signal in different phases and the corresponding pulse peak amplitude of the light source to be detected, and generating a peak contrast-phase curve based on the phase and the test data of the peak amplitude contrast; and/or

A peak-to-phase curve is generated based on the test data for the phase and its peak amplitude maximum.

2. The test device of claim 1, further comprising:

one or more attenuation modules configured to be disposed in one or more second arm optical paths of the interference module to adjust the optical intensity of the optical signals transmitted through the second arm to make the insertion loss of the plurality of interfered optical signals consistent.

3. The testing device of claim 2, wherein the interference module comprises:

the device comprises a beam splitting unit, a light source detection unit and a control unit, wherein the beam splitting unit is configured to split an original pulse light signal with random phase emitted by the light source to be detected into a first light signal and one or more second light signals; the first optical signal is transmitted to the phase adjusting module through a first arm; the phase adjusting module adjusts the first optical signal according to a phase adjusting strategy and then outputs a third optical signal; the one or more second optical signals are conveyed to the respective attenuation modules via the corresponding one or more second arms; the attenuation module adjusts the light intensity of the second optical signal and outputs a fourth optical signal with insertion loss consistent with that of the third optical signal; and

a beam combining unit configured to receive the third optical signal and one or more of the fourth optical signals and output an interference optical signal of the third optical signal and the fourth optical signal.

4. The test device of claim 2, wherein the interference module comprises a michelson interferometer or an AMZ interferometer, and the phase adjustment module and the attenuation module are respectively disposed in first and second arm optical paths of the michelson interferometer or the AMZ interferometer.

5. The test device of claim 4, wherein the interference module further comprises a circulator or isolator configured with a first interface connected to a light source under test and a second interface connected to a Michelson interferometer.

6. A test device according to any one of claims 2-5, wherein the first arm is a long arm or a short arm, and the second arm is a short arm or a long arm, respectively.

7. The testing device of claim 1, wherein the phase adjustment module comprises:

a phase modulator or fiber phase shifter configured to adjust the phase of its input optical signal in accordance with a phase control signal; and

a phase adjustment control unit configured to output a phase control signal to the phase modulator or fiber phase shifter according to a phase adjustment strategy.

8. The testing device of claim 2, wherein the attenuation module further comprises:

the attenuator is configured to adjust the light intensity of the input optical signal according to a preset attenuation amount.

9. The testing device of claim 8, wherein the attenuation module further comprises:

a light intensity detection unit configured to detect light intensities of a plurality of optical signals output by the interference module without interference at initialization, wherein the plurality of optical signals include an optical signal passing through the phase adjustment module and an optical signal passing through the attenuator; and

and the light intensity adjusting control unit is configured to generate an attenuation amount according to the light signal passing through the phase adjusting module and the light intensity of the input light signal of the attenuator and output the attenuation amount to the attenuator.

10. The testing device of claim 1, wherein the probe acquisition module comprises:

a photodetector configured to detect the interfering light signal to generate a corresponding electrical pulse signal;

a data acquisition unit configured to acquire an electrical pulse signal of the interference light signal to obtain the electrical pulse peak amplitude; and

a data processing unit configured to compare a plurality of pulse peak amplitudes of the same phase to obtain a peak amplitude maximum of the phase.

11. The testing device of claim 1, wherein the analysis module comprises:

a contrast calculation unit configured to calculate contrasts of pulse peak amplitude maximum values of different phases of the interference light signal and a pulse peak amplitude of the light source to be measured; and

a curve generation unit configured to generate a peak contrast-phase curve based on test data of the phase and its peak amplitude contrast, wherein the phase variation range is 0-2 pi.

12. The testing device of claim 11, wherein the analysis module is further configured to generate a peak-to-phase curve based on test data for phase and its peak amplitude maximum.

13. The test device of claim 1, further comprising an output module configured to be connected to the analysis module and configured to output or/and display the obtained test curve and/or test data.

14. The testing device of claim 13, further comprising a parameter configuration module configured to couple with the phase adjustment module, the detection and collection module, and the analysis module to configure parameters required by each module.

15. The testing device of claim 2, further comprising a master control module configured to be connected to the phase adjustment module, the detection and collection module, the analysis module, and the attenuation module, respectively, to coordinate operations of the modules.

16. A phase randomness test method, comprising:

splitting an original pulse light signal with a random phase emitted by a light source to be detected into at least a first light signal and a second light signal, wherein the optical path difference Delta L of the first light signal and the second light signal is nT, T is the period of the pulse light signal, and n is a natural number;

acquiring a corresponding test curve according to a preset analysis strategy based on the maximum value of the peak amplitude of the collected different phases;

wherein the preset analysis policy is:

17. The testing method of claim 16, wherein configured further comprises:

18. The testing method of claim 16, wherein the phase adjustment strategy comprises: sequentially changing the phase of the first optical signal according to the formula (1-1);

wherein i is 1 to (k + 1); k is 64-2048;

19. the test method according to claim 16, wherein the contrast is a ratio of a maximum value of a peak amplitude of the interference light to a peak amplitude of a pulse of the light source to be tested, or an absolute value of a difference.