CN118282506B - Time delay calibration method and communication device for photoelectric detection array - Google Patents
Time delay calibration method and communication device for photoelectric detection array Download PDFInfo
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Abstract
The invention provides a time delay calibration method and a communication device for a photoelectric detection array, and relates to the technical field of optical signal communication. The invention receives the pulse signals output by each pixel point included in the photoelectric detection array and the time stamp corresponding to each pulse signal, wherein the time stamp is used for representing the arrival time of the pulse signals; determining the photoelectric link delay corresponding to the pulse signal output by each pixel point according to the time stamp corresponding to the pulse signal output by each pixel point; and performing time delay compensation on the pulse signals output by each pixel point according to the photoelectric link time delay corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration. The method provided by the invention can rapidly and accurately determine the link delay time corresponding to each pixel included in the photoelectric detection array, and further complete the time delay calibration of signals, thereby improving the accuracy of codeword judgment and detection precision.
Description
Technical Field
The present invention relates to the field of optical signal communication technologies, and in particular, to a time delay calibration method and a communication device for a photoelectric detection array.
Background
In recent years, with the continuous enhancement of scientific detection capability and the popularization of advanced detection equipment, the deep space communication bandwidth requirement is rapidly increased. Compared with microwave communication, the space optical communication using laser as a carrier has the advantages of high energy efficiency, long transmission distance, large bandwidth and the like, and is gradually dominant in the field of deep space exploration. Deep space laser communication links are typically photon starved channels. Pulse Position Modulation (PPM) is energy efficient when the average power is limited, and at the same time, the photo-detection array becomes the preferred detector for deep space optical communication due to the high detection sensitivity. Therefore, the single photon communication mode of the pulse position modulation combined photoelectric detection array becomes a preferred mode of high-speed high-sensitivity deep space communication.
However, in the photodetection array, time delay in the photodetection link may affect system performance, and the photodetection array includes a plurality of pixels, each of which is connected to a photodetection link, and the link delay time of each pixel is inconsistent due to the difference of the inherent characteristics of the devices, resulting in a deviation in the time of receiving a signal for each pixel. Such time offset may affect the decision of the reception slot in the pulse position modulation based communication system, thereby affecting codeword decision and detection accuracy.
Therefore, a time delay calibration method is needed to determine the link delay time corresponding to each pixel included in the photoelectric detection array, so as to complete the time delay calibration of the pulse signal, thereby improving the accuracy of codeword decision and detection precision.
Disclosure of Invention
The embodiment of the invention provides a time delay calibration method and a communication device for a photoelectric detection array, which can quickly and accurately determine the link delay time corresponding to each pixel included in the photoelectric detection array, so as to finish time delay calibration of signals, thereby improving the accuracy of codeword judgment and detection precision.
In order to achieve the above purpose, the embodiment of the present invention adopts the following technical scheme:
In a first aspect, a time delay calibration method for a photo-detection array is provided, and the time delay calibration method is applied to a data processing module of a communication device, where the communication device further includes the photo-detection array, and the photo-detection array includes a plurality of pixels, each pixel being configured to convert a received optical signal into a pulse signal, and the method includes: receiving a pulse signal output by each pixel point included in the photoelectric detection array and a time stamp corresponding to each pulse signal, wherein the time stamp is used for representing the arrival time of the pulse signal; determining the photoelectric link delay corresponding to the pulse signal output by each pixel point according to the time stamp corresponding to the pulse signal output by each pixel point; and performing time delay compensation on the pulse signals output by each pixel point according to the photoelectric link time delay corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration.
In a possible implementation manner of the first aspect, determining, according to a timestamp corresponding to the pulse signal output by each pixel point, a photoelectric link delay corresponding to the pulse signal output by each pixel point includes: normalizing the time stamp corresponding to the pulse signal output by each pixel point so that the time stamp corresponding to the pulse signal output by each pixel point is positioned in the same pulse period; generating a log-likelihood function corresponding to each pixel point according to the timestamp corresponding to the pulse signal output by each pixel point, wherein the log-likelihood function is used for representing a photon arrival probability density function of the pulse signal under the conditions based on the influence of the dead time and time jitter of the detector; solving the log-likelihood function based on a maximum-likelihood estimation algorithm, and determining a corresponding input value under the condition that the function value of the log-likelihood function corresponding to each pixel point is the maximum value; and determining the input value corresponding to each pixel point as the photoelectric link delay corresponding to the pulse signal output by each pixel point.
In a possible implementation manner of the first aspect, generating a log likelihood function corresponding to each pixel according to a timestamp corresponding to a pulse signal output by each pixel includes:
In a possible implementation manner of the first aspect, the generating a log likelihood function corresponding to each pixel according to a timestamp corresponding to a pulse signal output by each pixel includes:
Determining a probability P Poi(n1,μTs) of the number n 1 of photons reaching the photo-detection array for a preset duration T s, wherein the probability P Poi(n1,μTs) is determined by the following formula:
Where μ is the average photon number in photons per second (pps);
determining probability density function of photon arrival time t r of each pixel point The determined formula of (2) is:
Determining detection time jitter delta of a photoelectric detection array, wherein a function model f δ (delta) of the detection time jitter delta is a Gaussian variable with a mean value of 0 and a variance of sigma 2, and a determination formula of the detection time jitter delta is as follows:
where σ is the response time jitter of the photodetector array.
Probability density function based on photon arrival time of each pixel pointAnd a function model f δ (δ) that detects the time jitter δ determines a distribution function f (t) of photons detected by each pixel at time t, wherein the distribution function f (t) is a distribution function taking into account the dead time and the influence of the time jitter on each pixel; the determination formula of the distribution function f (t) of photons detected by each pixel point at the time t is as follows:
When the light pulse is fixed in the first time slot and the photoelectric link delay τ i exists in the ith pixel point, determining a probability density function f (t|τ i),f(t|τi) of the time t of arrival of the photon according to a distribution function f (t) of the photon detected by each pixel point at the time t is as follows:
Wherein τ i is the photoelectric link delay of the ith pixel point;
Determining the log likelihood function of the ith pixel point according to the time stamps { t i1,ti2,...,tiN } corresponding to the N pulse signals of the ith pixel point Log likelihood functionThe method comprises the following steps:
Wherein C is a constant.
In a possible implementation manner of the first aspect, the communication device further includes a bias amplifier, an input end of the bias amplifier is connected to an output end of each pixel included in the photo detection array, an input end of the digital time converter is connected to an output end of the bias amplifier, and an output end of the digital time converter is connected to an input end of the data processing module; the bias amplifier is used for carrying out signal amplification processing on the pulse signals output by each pixel point and sending the amplified pulse signals to the digital time converter; the digital time converter is used for generating a corresponding time stamp according to the arrival of each pulse signal of each pixel point at the digital time converter.
In a possible implementation manner of the first aspect, performing delay compensation on the pulse signal output by each pixel according to the photoelectric link delay corresponding to the pulse signal output by each pixel, to obtain a pulse signal corresponding to each pixel after calibration is completed, where the method includes: adding the photoelectric link delay corresponding to the pulse signal output by each pixel point and the time stamp to determine a calibration time stamp corresponding to the pulse signal output by each pixel point; and calibrating the pulse signals corresponding to each pixel point based on the calibration time stamp corresponding to the pulse signals output by each pixel point, so as to obtain the pulse signals corresponding to each pixel point after calibration.
In a possible implementation manner of the first aspect, after determining the sum of the optical-electrical link delay and the timestamp corresponding to the pulse signal output by each pixel point as the calibration timestamp corresponding to the pulse signal output by each pixel point, the method further includes: under the condition that the iteration times are smaller than or equal to a preset threshold value, determining the sum of the photoelectric link time delay and the time stamp corresponding to the pulse signal output by each pixel point as a calibration time stamp corresponding to the pulse signal output by each pixel point, determining the photoelectric link time delay corresponding to the pulse signal output by each pixel point according to the calibration time stamp corresponding to the pulse signal output by each pixel point, updating the calibration time stamp corresponding to the pulse signal output by each pixel point according to the sum of the photoelectric link time delay and the calibration time stamp corresponding to the pulse signal output by each pixel point, and adding 1 to the iteration times; and under the condition that the iteration times are larger than a preset threshold value, calibrating the pulse signals corresponding to each pixel point based on the calibration time stamp corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration.
In one possible implementation manner of the first aspect, the photodetection array includes a superconducting nanowire single photon detector SNSPD array or a single photon avalanche diode SPAD array.
The beneficial effects of the invention are as follows: the method provided by the invention is based on the time sequence characteristics of the output signals of the photoelectric detection array, the photoelectric link time delay of each pulse signal is determined through a maximum likelihood estimation algorithm according to the time stamp of the pulse signal output by each pixel point, and then the time compensation basis can be provided for subsequent signal judgment by calibrating the pulse signal output by the photoelectric detection array, so that the error code performance of the system is effectively improved through a software algorithm under the condition of not increasing hardware cost. Compared with the existing time delay calibration method, the method can improve the accuracy and detection precision of codeword judgment.
In other words, the method provided by the invention carries out normalization processing on the time stamp of the pulse signal output by each pixel point, then obtains the photoelectric link delay corresponding to each pixel point based on the photoelectric link delay estimation algorithm of the maximum likelihood estimation algorithm, and then realizes time calibration of the pulse signal output by each pixel point, and in the calibration process, the hardware circuit corresponding to each pixel point is not required to be changed, so that the system complexity improvement and the cost increase caused by adding hardware devices such as a variable delay line, a high-speed switch and the like can be avoided. Moreover, the method provided by the invention has the advantages of high applicability and robustness. Aiming at the time sequence characteristics of pulse signals output by the photoelectric detection array, under the condition of being limited based on nonideal factors such as detection dead time, time jitter and the like existing in an actual system, an estimation algorithm can adapt to the actual engineering application environment by adopting a maximum likelihood estimation method, and the use requirements of users under different use scenes are met. Finally, the method provided by the invention can quickly calibrate the pulse signal output by each pixel point, effectively shorten the debugging and optimizing time of the communication device, eliminate the need of manually adjusting hardware circuit parameters, and effectively improve the communication efficiency.
In a second aspect, a communication device is provided, including a photoelectric detection array, a bias amplifier, a digital time converter and a data processing module, where an output end of the photoelectric detection array is connected with the bias amplifier, an output end of the bias amplifier is connected with the digital time converter, and an output end of the digital time converter is connected with the data processing module; the photoelectric detection array comprises a plurality of pixel points; each pixel point included in the photoelectric detection array is used for receiving the optical signal sent by the sending end and converting the optical signal into a pulse signal; the bias amplifier is used for carrying out signal amplification processing on the pulse signals output by each pixel point and sending the amplified pulse signals to the digital time converter; the digital time converter is used for generating a corresponding time stamp according to the moment when each pulse signal of each pixel point reaches the digital time converter; the data processing module is used for receiving pulse signals output by each pixel point included in the photoelectric detection array and time stamps corresponding to each pulse signal, and the time stamps are used for representing the arrival time of the pulse signals; the photoelectric link delay corresponding to the pulse signals output by each pixel point is determined according to the time stamp corresponding to the pulse signals output by each pixel point; and the photoelectric link delay compensation module is also used for carrying out delay compensation on the pulse signals output by each pixel point according to the photoelectric link delay corresponding to the pulse signals output by each pixel point, so as to obtain the pulse signals corresponding to each pixel point after calibration.
In a possible implementation manner of the second aspect, the data processing module is specifically configured to: normalizing the time stamp corresponding to the pulse signal output by each pixel point so that the time stamp corresponding to the pulse signal output by each pixel point is positioned in the same pulse period; generating a log-likelihood function corresponding to each pixel point according to the timestamp corresponding to the pulse signal output by each pixel point, wherein the log-likelihood function is used for representing a photon arrival probability density function of the pulse signal under the conditions based on the influence of the dead time and time jitter of the detector; solving the log-likelihood function based on a maximum-likelihood estimation algorithm, and determining a corresponding input value under the condition that the function value of the log-likelihood function corresponding to each pixel point is the maximum value; and determining an input value corresponding to each pixel point as a photoelectric link delay corresponding to the pulse signal output by each pixel point, wherein the photoelectric link delay corresponding to the pulse signal output by each pixel point is smaller than or equal to the pulse period of the pulse signal.
In a third aspect, an electronic device is provided, the electronic device comprising a memory, one or more processors; the memory is coupled with the processor; wherein the memory has stored therein computer program code comprising computer instructions which, when executed by the processor, cause the electronic device to perform the time delay calibration method for a photo detection array as in any of the implementations of the first aspect.
In a fourth aspect, there is provided a computer readable storage medium comprising computer instructions which, when run on an electronic device, cause the electronic device to perform a time delay calibration method for a photo detection array as in any of the implementations of the first aspect.
In a fifth aspect, a computer program product is provided which, when run on a computer, causes the computer to perform the time delay calibration method for a photo detection array as in any of the implementations of the first aspect.
It will be appreciated that the advantages achieved by the communication device according to the second aspect, the electronic apparatus according to the third aspect, the computer readable storage medium according to the fourth aspect, and the computer program product according to the fifth aspect may refer to the advantages in any one of the possible designs of the first aspect and the advantages will not be repeated here.
Drawings
Fig. 1 is a schematic diagram of a hardware structure of a communication device according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method for calibrating time delay of a photo-detection array according to an embodiment of the present invention;
FIG. 3 is a flow chart of another method for calibrating time delay of a photo-detection array according to an embodiment of the present invention;
FIG. 4 shows a plurality of optical link delays τi and τi of optical signals received by an SNSPD array according to an embodiment of the present invention A relationship graph between the two;
FIG. 5 is a method flow diagram illustrating yet another method for time delay calibration of a photo-detection array according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a pulse signal according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of experimental results of a time delay calibration method for a photo-detection array according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a hardware configuration of another data processing module according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention. Wherein, in the description of the present invention, "/" means that the related objects are in a "or" relationship, unless otherwise specified, for example, a/B may mean a or B; the "and/or" in the present invention is merely an association relationship describing the association object, and indicates that three relationships may exist, for example, a and/or B may indicate: there are three cases, a alone, a and B together, and B alone, wherein a, B may be singular or plural. Also, in the description of the present invention, unless otherwise indicated, "a plurality" means two or more than two. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, at least one (one) of a, b, or c may represent: a, b, c, a-b, a-c, b-c, or a-b-c, wherein a, b, c may be single or plural.
In addition, in order to facilitate the clear description of the technical solution of the embodiments of the present invention, in the embodiments of the present invention, the words "first", "second", etc. are used to distinguish the same item or similar items having substantially the same function and effect. It will be appreciated by those of skill in the art that the words "first," "second," and the like do not limit the amount and order of execution, and that the words "first," "second," and the like do not necessarily differ.
Meanwhile, in the embodiments of the present invention, words such as "exemplary" or "such as" are used to mean serving as examples, illustrations or explanations. Any embodiment or design described herein as "exemplary" or "e.g." in an embodiment of the present invention is not to be taken as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "such as" is intended to present related concepts in a concrete fashion that may be readily understood.
In recent years, with the continuous enhancement of scientific detection capability and the popularization of advanced detection equipment, the deep space communication bandwidth requirement is rapidly increased. Compared with microwave communication, the space optical communication using laser as a carrier has the advantages of high energy efficiency, long transmission distance, large bandwidth and the like, and is gradually dominant in the field of deep space exploration. Deep space laser communication links are typically photon starved channels. Pulse Position Modulation (PPM) is energy efficient when the average power is limited, and at the same time, the photo-detection array becomes the preferred detector for deep space optical communication due to the high detection sensitivity. Therefore, the single photon communication mode of the pulse position modulation combined photoelectric detection array becomes a preferred mode of high-speed high-sensitivity deep space communication.
However, in the photodetection array, time delay in the photodetection link may affect system performance, and the photodetection array includes a plurality of pixels, each of which is connected to a photodetection link, and the link delay time of each pixel is inconsistent due to the difference of the inherent characteristics of the devices, resulting in a deviation in the time of receiving a signal for each pixel. Such time offset may affect the decision of the reception slot in the pulse position modulation based communication system, thereby affecting codeword decision and detection accuracy.
Therefore, a time delay calibration method is needed to determine the link delay time corresponding to each pixel included in the photoelectric detection array, so as to complete the time delay calibration of the pulse signal, thereby improving the accuracy of codeword decision and detection precision.
In view of this, an embodiment of the present invention provides a time delay calibration method for a photodetection array, which is applied to a data processing module of a communication device, where the communication device further includes a photodetection array, and the photodetection array includes a plurality of pixels, each pixel being configured to convert a received optical signal into a pulse signal, and the method includes: receiving a pulse signal output by each pixel point included in the photoelectric detection array and a time stamp corresponding to each pulse signal, wherein the time stamp is used for representing the arrival time of the pulse signal; determining the photoelectric link delay corresponding to the pulse signal output by each pixel point according to the time stamp corresponding to the pulse signal output by each pixel point; and performing time delay compensation on the pulse signals output by each pixel point according to the photoelectric link time delay corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration.
The method provided by the embodiment of the invention is based on the time sequence characteristics of the output signals of the photoelectric detection array, the photoelectric link time delay of each pulse signal is determined through a maximum likelihood estimation algorithm according to the time stamp of the pulse signal output by each pixel point, and then the pulse signal output by the photoelectric detection array is calibrated. Compared with the existing time delay calibration method, the method can improve the accuracy and detection precision of codeword judgment.
In other words, the method provided by the embodiment of the invention carries out normalization processing on the time stamp of the pulse signal output by each pixel point, then obtains the photoelectric link time delay corresponding to each pixel point based on the photoelectric link time delay estimation algorithm of the maximum likelihood estimation algorithm, and then realizes time calibration of the pulse signal output by each pixel point, and in the calibration process, the hardware circuit corresponding to each pixel point is not required to be changed, so that the system complexity promotion and the cost increase caused by adding hardware devices such as a variable delay line, a high-speed switch and the like can be avoided. Moreover, the method provided by the embodiment of the invention has the advantages of high applicability and robustness. Aiming at the time sequence characteristics of pulse signals output by the photoelectric detection array, under the condition of being limited based on nonideal factors such as detection dead time, time jitter and the like existing in an actual system, an estimation algorithm can adapt to the actual engineering application environment by adopting a maximum likelihood estimation method, and the use requirements of users under different use scenes are met. Finally, the method provided by the embodiment of the invention can quickly calibrate the pulse signal output by each pixel point, effectively shorten the debugging and optimizing time of the communication device, eliminate the need of manually adjusting hardware circuit parameters, and effectively improve the communication efficiency.
In some embodiments, the time delay calibration method for a photo detection array provided by the embodiments of the present invention may be performed by the communication device 100. Fig. 1 shows a schematic hardware structure of a communication device according to an embodiment of the present invention. The communication device 100 comprises a photoelectric detection array 110, a bias amplifier 120, a digital time converter 130 and a data processing module 140, wherein the output end of the photoelectric detection array 110 is connected with the bias amplifier 120, the output end of the bias amplifier 120 is connected with the digital time converter 130, and the output end of the digital time converter 130 is connected with the data processing module 140; the photo-detection array 110 includes a plurality of pixel points; each pixel point included in the photoelectric detection array 110 is configured to receive an optical signal sent by the sending end 200, and to convert the optical signal into a pulse signal; the bias amplifier 120 is configured to perform signal amplification processing on the pulse signal output by each pixel, and is further configured to send the amplified pulse signal to the digital time converter 130;
the digital time converter 130 is configured to generate a corresponding timestamp according to a time when each pulse signal of each pixel arrives at the digital time converter 130;
The data processing module 140 is configured to receive a pulse signal output by each pixel point included in the photoelectric detection array and a timestamp corresponding to each pulse signal, where the timestamp is used to characterize an arrival time of the pulse signal; the photoelectric link delay corresponding to the pulse signals output by each pixel point is determined according to the time stamp corresponding to the pulse signals output by each pixel point; and the photoelectric link delay compensation module is also used for carrying out delay compensation on the pulse signals output by each pixel point according to the photoelectric link delay corresponding to the pulse signals output by each pixel point, so as to obtain the pulse signals corresponding to each pixel point after calibration.
In some embodiments, the data processing module 140 is specifically configured to: normalizing the time stamp corresponding to the pulse signal output by each pixel point so that the time stamp corresponding to the pulse signal output by each pixel point is positioned in the same pulse period; generating a log-likelihood function corresponding to each pixel point according to the timestamp corresponding to the pulse signal output by each pixel point, wherein the log-likelihood function is used for representing a photon arrival probability density function of the pulse signal under the conditions based on the influence of the dead time and time jitter of the detector; solving the log-likelihood function based on a maximum-likelihood estimation algorithm, and determining a corresponding input value under the condition that the function value of the log-likelihood function corresponding to each pixel point is the maximum value; and determining an input value corresponding to each pixel point as a photoelectric link delay corresponding to the pulse signal output by each pixel point, wherein the photoelectric link delay corresponding to the pulse signal output by each pixel point is smaller than or equal to the pulse period of the pulse signal.
In a physical implementation, the above-described devices (e.g., the photodetector array 110, the bias amplifier 120, the digital-to-time converter 130, and the data processing module 140) may be devices in the same device, respectively. Or at least two of the devices may be provided in the same apparatus, i.e. as different devices in one apparatus, e.g. in a manner similar to the arrangement of the apparatuses or devices in a distributed system.
In one possible implementation, the photodetection array 110 comprises a superconducting nanowire single photon detector (superconducting nanowire single photon detector, SNSPD) array or a single photon avalanche diode (single photon avalanche diode, SPAD) array. It should be noted that, the photo-detection array 110 may be any other type of photo-detection array having a plurality of pixels, and the implementation of the photo-detection array 110 according to the embodiments of the present invention is not particularly limited.
For ease of explanation, the following embodiments will be explained with the photodetection array 110 as an SNSPD array.
By way of example, the data processing module 140 may be any electronic device having data processing capabilities, such as a general purpose computer, a personal computer, a notebook computer, a switch or tablet computer, etc., and the specific implementation of the communication apparatus 100 is not limited herein.
It is to be understood that the configuration illustrated in this embodiment does not constitute a specific limitation on the communication apparatus 100. In other embodiments of the present invention, communication device 100 may include more or less components than illustrated, or certain components may be combined, or certain components may be split, or different arrangements of components. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.
The time delay calibration method for the photoelectric detection array provided by the embodiment of the invention is described below with reference to the accompanying drawings.
Fig. 2 is a flowchart of a time delay calibration method for a photoelectric detection array according to an embodiment of the present invention. Alternatively, the method may be performed by the data processing module 140 included in the communication device 100 having the hardware configuration shown in fig. 1. The method may comprise the steps of:
S1, receiving pulse signals output by each pixel point included in the photoelectric detection array and time stamps corresponding to the pulse signals, wherein the time stamps are used for representing arrival time of the pulse signals.
S2, determining the photoelectric link delay corresponding to the pulse signals output by each pixel point according to the time stamp corresponding to the pulse signals output by each pixel point.
Specifically, each pixel point in the plurality of pixel points included in the photoelectric detection array is configured with a photoelectric link, wherein the photoelectric link comprises a bias circuit, a readout circuit and the like, and the delay difference is the photoelectric link delay due to the fact that the bias circuit, the readout circuit and the like connected with each pixel point in the photoelectric detection array have device parameter deviation and the length of a connecting line is different, so that the transmission delay of output signals of each pixel point is different.
In one possible implementation manner, referring to fig. 3, S2 specifically includes the following steps:
S21, normalizing the time stamp corresponding to the pulse signal output by each pixel point so that the time stamp corresponding to the pulse signal output by each pixel point is positioned in the same pulse period;
s22, generating a log likelihood function corresponding to each pixel point according to the timestamp corresponding to the pulse signal output by each pixel point.
Wherein the log likelihood function is used to characterize the photon arrival probability density function of the pulse signal based on the influence of detector dead time, time jitter.
Specifically, since the timestamp determined by the digital time converter is formed by the sum of the response time of photons generated by the photoelectric detection array, the photoelectric link delay and the detector jitter, determining the photoelectric link delay requires determining a probability density function of the photon response time and the detector jitter.
In one possible implementation manner, S22 specifically includes the following steps:
Determining a probability P Poi(n1,μTs) of the number n 1 of photons reaching the photo-detection array for a preset duration T s, wherein the probability P Poi(n1,μTs) is determined by the following formula:
Where μ is the average photon number in photons per second (pps);
it should be noted that, in the measurement of the photoelectric link phase of the receiving system of the photoelectric detection array-digital time converter, a pulse with a fixed position is generated from the transmitting end, and reaches each pixel point included in the photoelectric detection array through a channel with a specific attenuation, and a photon reaching the target surface of the pixel point can be regarded as a poisson process.
Determining probability density function of photon arrival time t r of each pixel pointThe determined formula of (2) is:
Determining detection time jitter delta of a photoelectric detection array, wherein a function model f δ (delta) of the detection time jitter delta is a Gaussian variable with a mean value of 0 and a variance of sigma 2, and a determination formula of the detection time jitter delta is as follows:
where σ is the response time jitter of the photodetector array.
Specifically, the detected time jitter δ is typically modeled as a gaussian variable with a mean of 0 and a variance of σ 2, that is to say the variance of the gaussian variable is σ 2.
It should be understood that the specific implementation form of the function model of detecting the time jitter δ of the photoelectric detection array according to the embodiment of the present invention is not particularly limited, and the user may build the function model of detecting the time jitter δ according to the actual use scenario.
Probability density function based on photon arrival time of each pixel pointAnd a function model f δ (δ) that detects the time jitter δ determines a distribution function f (t) of photons detected by each pixel at time t, wherein the distribution function f (t) is a distribution function taking into account the dead time and the influence of the time jitter on each pixel; the determination formula of the distribution function f (t) of photons detected by each pixel point at the time t is as follows:
When the light pulse is fixed in the first time slot and the photoelectric link delay τ i exists in the ith pixel point, determining a probability density function f (t|τ i),f(t|τi) of the time t of arrival of the photon according to a distribution function f (t) of the photon detected by each pixel point at the time t is as follows:
Wherein τ i is the photoelectric link delay of the ith pixel point;
Determining the log likelihood function of the ith pixel point according to the time stamps { t i1,ti2,...,tiN } corresponding to the N pulse signals of the ith pixel point Log likelihood functionThe method comprises the following steps:
Wherein C is a constant.
It should be understood that the ith pixel point is one of a plurality of pixel points included in the photo detection array 110.
S23, solving the log-likelihood function based on a maximum-likelihood estimation algorithm, and determining the corresponding input value under the condition that the function value of the log-likelihood function corresponding to each pixel point is the maximum value;
s24, determining the input value corresponding to each pixel point as the photoelectric link delay corresponding to the pulse signal output by each pixel point.
Exemplary, where the photo-detection array is an SNSPD array, see FIG. 4, FIG. 4 is a plurality of photo-link delays τi and τ of optical signals received by the SNSPD arrayA graph of the relationship between the two. When the response time jitter of the SNSPD is σ=0.2. When the total photon number received by the TDC is n=4×107, the actual link distance is divided by the transmission speed of electrons in the cable (2×10×8m/s), so as to obtain the actual time delay of the photoelectric link, which is determined to be 7.48ns. The black squares in the figure represent the locations of the transmitted signal pulses. The resulting opto-electronic link time delay was 7.5ns. As can be seen from fig. 4, the method provided by the embodiment of the invention can quickly and accurately determine the time delay τi of the photoelectric link.
It should be noted that, in the above example, the optical signal transmitted by the receiving transmitting end of the SNSPD array is a processed optical signal, where the processing procedure of the optical signal is to divide the transmitted optical signal into two signals with different power levels through a 10/90 beam splitter. The strong signal is monitored using an optical power meter, while the weak signal is the optical signal sent to the SNSPD array. It should be appreciated that, to ensure that the output optical power falls within the applicable range of the SNSPD, embodiments of the present invention attenuate the optical signal with a variable optical attenuator to meet the detection threshold requirement. Wherein, the variable optical attenuator is used for maintaining the stability of SNSPD detection efficiency. On the other hand, since the SNSPD is sensitive to polarization, the embodiment of the invention uses the polarization controller to control the polarization state of the optical signal so as to ensure the quantum detection efficiency.
In this way, the method provided by the embodiment of the invention further determines the photoelectric link delay corresponding to each pixel point according to the photon response time and the probability density function of the detector jitter by determining the photon response time and the probability density function of the detector jitter, thereby completing the calibration of the pulse signal output by each pixel point and improving the accuracy and detection precision of codeword judgment.
And S3, performing time delay compensation on the pulse signals output by each pixel point according to the photoelectric link time delay corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration.
As can be seen from the above S1-S3, the method provided by the embodiment of the present invention is based on the time sequence characteristics of the output signals of the photodetection array, determines the delay of the optical link of each pulse signal according to the time stamp of the pulse signal output by each pixel point through the maximum likelihood estimation algorithm, and then calibrates the pulse signal output by the photodetection array. Compared with the existing time delay calibration method, the method can improve the accuracy and detection precision of codeword judgment.
In other words, the method provided by the embodiment of the invention carries out normalization processing on the time stamp of the pulse signal output by each pixel point, then obtains the photoelectric link time delay corresponding to each pixel point based on the photoelectric link time delay estimation algorithm of the maximum likelihood estimation algorithm, and then realizes time calibration of the pulse signal output by each pixel point, and in the calibration process, the hardware circuit corresponding to each pixel point is not required to be changed, so that the system complexity promotion and the cost increase caused by adding hardware devices such as a variable delay line, a high-speed switch and the like can be avoided. Moreover, the method provided by the embodiment of the invention has the advantages of high applicability and robustness. Aiming at the time sequence characteristics of pulse signals output by the photoelectric detection array, under the condition of being limited based on nonideal factors such as detection dead time, time jitter and the like existing in an actual system, an estimation algorithm can adapt to the actual engineering application environment by adopting a maximum likelihood estimation method, and the use requirements of users under different use scenes are met. Finally, the method provided by the embodiment of the invention can quickly calibrate the pulse signal output by each pixel point, effectively shorten the debugging and optimizing time of the communication device, eliminate the need of manually adjusting hardware circuit parameters, and effectively improve the communication efficiency.
In some embodiments, referring to fig. 5, S3 specifically includes the following steps:
s41, determining the sum of the photoelectric link time delay and the time stamp corresponding to the pulse signal output by each pixel point as a calibration time stamp corresponding to the pulse signal output by each pixel point;
For example, when the photoelectric link delay corresponding to the pulse signal output by the pixel point a is 1ms and the time stamp is 5ms, the calibration time stamp corresponding to the pulse signal output by the pixel point a is 6ms.
S42, calibrating the pulse signals corresponding to the pixel points based on the calibration time stamp corresponding to the pulse signals output by the pixel points, and obtaining the pulse signals corresponding to the calibrated pixel points.
In other embodiments, the step S3 specifically includes the following steps:
under the condition that the iteration times are smaller than or equal to a preset threshold value, determining the sum of the photoelectric link time delay and the time stamp corresponding to the pulse signal output by each pixel point as a calibration time stamp corresponding to the pulse signal output by each pixel point, determining the photoelectric link time delay corresponding to the pulse signal output by each pixel point according to the calibration time stamp corresponding to the pulse signal output by each pixel point, updating the calibration time stamp corresponding to the pulse signal output by each pixel point according to the sum of the photoelectric link time delay and the calibration time stamp corresponding to the pulse signal output by each pixel point, and adding 1 to the iteration times; and under the condition that the iteration times are larger than a preset threshold value, calibrating the pulse signals corresponding to each pixel point based on the calibration time stamp corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration.
By setting the iteration times, the method provided by the embodiment of the invention can calibrate the pulse signals output by each pixel point for multiple times under the condition that the iteration times are not reached, and can effectively improve the accuracy of calibration, thereby meeting the use requirements of users in different use scenes.
In order to facilitate understanding of the present solution, a time delay calibration method for a photo-detection array according to an embodiment of the present invention is described below based on a specific example.
As shown in fig. 6, the pulse signal corresponding to the dashed line is a pulse signal that is not time-calibrated by the method provided by the embodiment of the present invention, and the pulse signal corresponding to the solid line is a pulse signal that is not time-calibrated by the method provided by the embodiment of the present invention, and as can be seen from fig. 6, the result shows that, in the case that the time delay of each link in the SNSPD is not time-calibrated by the method provided by the embodiment of the present invention, the pulse signal corresponding to the dashed line may be detected at the non-pulse position by the pulse signal corresponding to the dashed line. However, in the case of time alignment by the method provided by the embodiment of the present invention, the signal pulses can be detected by the digital-to-time converter at the same time. Therefore, the method provided by the invention can effectively calibrate the pulse signal and can improve the accuracy and detection precision of codeword judgment.
In another example, referring to fig. 7, fig. 7 is a schematic diagram of experimental results of a time delay calibration method for a photoelectric detection array according to an embodiment of the present invention, and fig. 7 includes experimental results of measuring different photoelectric link delays of a photoelectric link using SNSPD at different input powers μ. In the sub-graph a, sub-graph b, sub-graph c, and sub-graph d included in fig. 7, each dot represents probability statistics obtained by collecting data using a digital time converter, and the solid line represents photon arrival probabilities determined by the method provided by the embodiment of the present invention, respectively. As can be seen from fig. 7, along with the increase of the photon counting rate, the curve of the photon arrival probability determined by the method provided by the embodiment of the present invention is aligned with the experimental data on each photon counting rate, which can also be understood that the method provided by the present invention can accurately determine the photon arrival probability under the condition of different input power μ, and further accurately obtain the photoelectric link delay corresponding to each pixel point, so as to complete the time delay calibration of the pulse signal.
The foregoing description of the embodiments of the present invention has been presented primarily in terms of methods. It will be appreciated that the data processing module 140, in order to implement the above-described functions, includes at least one of a corresponding hardware structure and software module for performing the respective functions. Those of skill in the art will readily appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as hardware or combinations of hardware and computer software. Whether a function is implemented as hardware or computer software driven hardware depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the embodiments of the present invention.
The embodiment of the present invention may divide the data processing module 140 into functional units according to the above method example, for example, each functional unit may be divided into each function by the data processing module 140, or two or more functions may be integrated into one processing unit. The integrated units may be implemented in hardware or in software functional units. It should be noted that, in the embodiment of the present invention, the division of the units is schematic, which is merely a logic function division, and other division manners may be implemented in actual practice.
Fig. 8 is a schematic diagram of a hardware structure of a data processing module according to an embodiment of the present invention. The data processing module 140 includes: the device comprises a receiving unit 810 and a determining unit 820, wherein the receiving unit 810 is used for receiving a pulse signal output by each pixel point included in the photoelectric detection array and a time stamp corresponding to each pulse signal, and the time stamp is used for representing the arrival time of the pulse signal; the determining unit 820 is configured to determine a photoelectric link delay corresponding to the pulse signal output by each pixel according to the timestamp corresponding to the pulse signal output by each pixel; the determining unit 820 is further configured to perform delay compensation on the pulse signal output by each pixel according to the photoelectric link delay corresponding to the pulse signal output by each pixel, so as to obtain a pulse signal corresponding to each pixel after calibration is completed.
It should be understood that, for the specific description of the above alternative modes, reference may be made to the foregoing method embodiments, and no further description is given here. In addition, any explanation and description of the beneficial effects of the data processing module 140 provided above may refer to the corresponding method embodiments described above, and will not be repeated.
Embodiments of the present invention also provide a computer readable storage medium having stored therein at least one computer instruction that is loaded and executed by a processor to implement the methods of the various embodiments above. For the explanation of the relevant content and the description of the beneficial effects in any of the above-mentioned computer-readable storage media, reference may be made to the above-mentioned corresponding embodiments, and the description thereof will not be repeated here.
The embodiment of the invention also provides a chip. The chip has integrated therein control circuitry and one or more ports for implementing the functions of the data processing module 140 described above. Optionally, the functions supported by the chip may be referred to above, and will not be described herein.
Those of ordinary skill in the art will appreciate that a program implementing all or part of the steps of the above embodiments may be stored in a computer readable storage medium by a program to instruct related hardware. The above-mentioned storage medium may be a read-only memory, a random access memory, or the like. The processing unit or processor may be a central processing unit, a general purpose processor, an application SPECIFIC INTEGRATED circuit, an ASIC, a microprocessor (DIGITAL SIGNAL processor, DSP), a field programmable gate array (field programmable GATE ARRAY, FPGA) or other programmable logic device, transistor logic device, hardware component, or any combination thereof.
Embodiments of the present invention also provide a computer program product comprising instructions which, when run on a computer, cause the computer to perform any of the methods of the above embodiments. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions in accordance with embodiments of the present invention are produced in whole or in part. The computer may be a general purpose computer, a special purpose computer, a computer network, or other programmable apparatus. The computer instructions may be stored in or transmitted from one computer-readable storage medium to another, for example, a website, computer, server, or data center via a wired (e.g., coaxial cable, fiber optic, digital subscriber line (digital subscriber line, DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. Computer readable storage media can be any available media that can be accessed by a computer or data storage devices, such as servers, data centers, etc., that contain an integration of one or more available media. The usable medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., SSD), etc.
It should be noted that the above-mentioned devices for storing computer instructions or computer programs, such as, but not limited to, the above-mentioned memories, computer-readable storage media, communication chips, etc., provided by the embodiments of the present invention have non-volatility (non-trans itory). Those skilled in the art will appreciate that in one or more of the examples described above, the functions described in the embodiments of the present invention may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, these functions may be stored on or transmitted over as one or more instructions or code on a computer-readable storage medium. Computer-readable storage media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (8)
1. A time delay calibration method for a photo-detection array, characterized by a data processing module applied to a communication device, the communication device further comprising a photo-detection array comprising a plurality of pixels, each of the pixels for converting a received optical signal into a pulse signal, the method comprising:
Receiving a pulse signal output by each pixel point and a time stamp corresponding to each pulse signal, wherein the pulse signal is included in the photoelectric detection array, and the time stamp is used for representing the arrival time of the pulse signal;
determining the photoelectric link delay corresponding to the pulse signals output by each pixel point according to the time stamp corresponding to the pulse signals output by each pixel point;
performing time delay compensation on the pulse signals output by each pixel point according to the photoelectric link time delay corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration;
Determining the photoelectric link delay corresponding to the pulse signal output by each pixel according to the timestamp corresponding to the pulse signal output by each pixel, including:
normalizing the time stamp corresponding to the pulse signal output by each pixel point so that the time stamp corresponding to the pulse signal output by each pixel point is positioned in the same pulse period;
Generating a log-likelihood function corresponding to each pixel point according to a time stamp corresponding to the pulse signal output by each pixel point, wherein the log-likelihood function is used for representing a photon arrival probability density function of the pulse signal under the condition of being based on the influence of dead time and time jitter of a detector;
Solving the log-likelihood function based on a maximum-likelihood estimation algorithm, and determining a corresponding input value under the condition that the function value of the log-likelihood function corresponding to each pixel point is the maximum value;
And determining the input value corresponding to each pixel point as the photoelectric link delay corresponding to the pulse signal output by each pixel point.
2. The method of claim 1, wherein the generating a log likelihood function corresponding to each pixel according to the timestamp corresponding to the pulse signal output by each pixel comprises:
determining a probability P Poi(n1,μTs) of the number of photons n 1 reaching the photo-detection array for a preset duration T s, wherein the probability P Poi(n1,μTs) is determined by the following formula:
Where μ is the average photon number in photons per second (pps);
determining probability density function of photon arrival time t r of each pixel point The determined formula of (2) is:
Determining a detection time jitter delta of the photoelectric detection array, wherein a function model f δ (delta) of the detection time jitter delta is a Gaussian variable with a mean value of 0 and a variance of sigma 2, and a determination formula of the detection time jitter delta is as follows:
Wherein sigma is the response time jitter of the photo-detection array;
probability density function based on photon arrival time of each pixel point And determining a distribution function f (t) of photons detected by each pixel point at a time t by a function model f δ (delta) for detecting the time jitter delta, wherein the distribution function f (t) is a distribution function under the condition that the dead time and the influence of the time jitter on each pixel point are considered; the determination formula of the distribution function f (t) of photons detected by each pixel point at the time t is as follows:
when the light pulse is fixed in the first time slot and the photoelectric link delay τ i exists in the ith pixel point, determining a probability density function f (t|τ i),f(t|τi) of the time t when the photon arrives according to the distribution function f (t) of the photon detected by each pixel point at the time t is as follows:
Wherein τ i is the photoelectric link delay of the ith pixel point;
Determining a log likelihood function l (τi) of the ith pixel according to the time stamps { t i1,ti2,...,tiN } corresponding to the N pulse signals of the ith pixel, wherein the log likelihood function l (τi) is as follows:
Wherein C is a constant.
3. The method of claim 2, wherein the communication device further comprises a bias amplifier having an input coupled to an output of each pixel included in the photodetector array and a digital-to-time converter having an input coupled to an output of the bias amplifier and an output coupled to an input of the data processing module;
the bias amplifier is used for carrying out signal amplification processing on the pulse signals output by each pixel point and sending the amplified pulse signals to the digital time converter;
The digital time converter is used for generating a corresponding time stamp according to the arrival of each pulse signal of each pixel point at the digital time converter.
4. The method of claim 3, wherein performing delay compensation on the pulse signal output by each pixel according to the photoelectric link delay corresponding to the pulse signal output by each pixel to obtain the pulse signal corresponding to each pixel after calibration, includes:
Determining the sum of the photoelectric link time delay and the time stamp corresponding to the pulse signal output by each pixel point as a calibration time stamp corresponding to the pulse signal output by each pixel point;
and calibrating the pulse signals corresponding to the pixel points based on the calibration time stamp corresponding to the pulse signals output by the pixel points, so as to obtain the pulse signals corresponding to the pixel points after calibration.
5. The method of claim 4, wherein after determining the sum of the optical-electrical link delay and the time stamp corresponding to the pulse signal output by each pixel point as the calibration time stamp corresponding to the pulse signal output by each pixel point, the method further comprises:
Under the condition that the iteration times are smaller than or equal to a preset threshold value, determining the sum of the photoelectric link time delay and the time stamp corresponding to the pulse signals output by each pixel point as the calibration time stamp corresponding to the pulse signals output by each pixel point, determining the photoelectric link time delay corresponding to the pulse signals output by each pixel point according to the calibration time stamp corresponding to the pulse signals output by each pixel point, updating the calibration time stamp corresponding to the pulse signals output by each pixel point according to the sum of the photoelectric link time delay and the calibration time stamp corresponding to the pulse signals output by each pixel point, and adding 1 to the iteration times;
And under the condition that the iteration times are larger than a preset threshold value, calibrating the pulse signals corresponding to each pixel point based on the calibration time stamp corresponding to the pulse signals output by each pixel point, and obtaining the pulse signals corresponding to each pixel point after calibration.
6. The method of claim 5, wherein the photodetection array comprises a superconducting nanowire single photon detector, SNSPD, array or a single photon avalanche diode, SPAD, array.
7. The communication device is characterized by comprising a photoelectric detection array, a bias amplifier, a digital time converter and a data processing module, wherein the output end of the photoelectric detection array is connected with the bias amplifier, the output end of the bias amplifier is connected with the digital time converter, and the output end of the digital time converter is connected with the data processing module;
The photoelectric detection array comprises a plurality of pixel points; each pixel point included in the photoelectric detection array is used for receiving an optical signal sent by a sending end and converting the optical signal into a pulse signal;
the bias amplifier is used for carrying out signal amplification processing on the pulse signals output by each pixel point and sending the amplified pulse signals to the digital time converter;
The digital time converter is used for generating a corresponding time stamp according to the moment when each pulse signal of each pixel point reaches the digital time converter;
The data processing module is used for receiving pulse signals output by each pixel point included in the photoelectric detection array and time stamps corresponding to the pulse signals, and the time stamps are used for representing the arrival time of the pulse signals; the photoelectric link delay corresponding to the pulse signals output by each pixel point is determined according to the time stamp corresponding to the pulse signals output by each pixel point; the photoelectric link delay compensation circuit is also used for carrying out delay compensation on the pulse signals output by each pixel point according to the photoelectric link delay corresponding to the pulse signals output by each pixel point, so as to obtain the pulse signals corresponding to each pixel point after calibration is completed;
the data processing module is specifically configured to:
normalizing the time stamp corresponding to the pulse signal output by each pixel point so that the time stamp corresponding to the pulse signal output by each pixel point is positioned in the same pulse period;
Generating a log-likelihood function corresponding to each pixel point according to a time stamp corresponding to the pulse signal output by each pixel point, wherein the log-likelihood function is used for representing a photon arrival probability density function of the pulse signal under the condition of being based on the influence of dead time and time jitter of a detector;
Solving the log-likelihood function based on a maximum-likelihood estimation algorithm, and determining a corresponding input value under the condition that the function value of the log-likelihood function corresponding to each pixel point is the maximum value;
And determining the input value corresponding to each pixel point as the photoelectric link time delay corresponding to the pulse signal output by each pixel point, wherein the photoelectric link time delay corresponding to the pulse signal output by each pixel point is smaller than or equal to the pulse period of the pulse signal.
8. An electronic device, comprising:
A processor; a memory for storing the processor-executable instructions;
Wherein the processor is configured to execute the instructions to implement the time delay calibration method for a photodetection array according to any of claims 1-6.
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