CN114265261B - High-speed photon analog-to-digital conversion method and system based on pulse processing - Google Patents

Abstract

The invention discloses a high-speed photon analog-to-digital conversion method and system based on pulse processing. The method includes the following steps: S1. A mode-locked laser generates an ultrashort optical pulse, and the ultrashort optical pulse enters a Mach-Zehnder modulation working in a linear region After the generator, linear optical sampling is completed on the radio frequency signal generated by the signal generator; S2. The signal sampled in step S1 is subjected to spectrum shaping in the programmable spectrum shaper, and the output spectrum is consistent, power-weighted, and multi-wavelength overlapped in the time domain Pulse; S3. The multi-wavelength pulse train output by step S2 passes through the single-mode dispersion fiber and then the pulse walks away, and the pulses of different bands generate different delays in the time domain and spread evenly; S4. The sampling pulses separated in the time domain pass through The photodetector converts this into an electrical signal, which is compared to a threshold level set by a comparator to produce a digitally quantized signal. The invention reduces the time jitter and improves the sampling rate of the photon analog-to-digital conversion system.

Description

A high-speed photon analog-to-digital conversion method and system based on pulse processing

Technical Field

The present invention belongs to the technical field of optical communication signal processing, and in particular relates to a high-speed photon analog-to-digital conversion method and system based on pulse processing.

Background Art

Analog-to-digital converter (ADC) is an irreplaceable bridge between the analog world and the digital world. With the continuous increase in data transmission capacity, the demand for fast conversion between analog signals and digital signals in transmitters, receivers and various gateway nodes of communication system links has increased rapidly. At present, electronic ADC technology has become quite mature, especially the widespread application of microelectronics technology has greatly improved the processing speed, reliability and integration of electronic solutions. However, in the high-frequency range, due to the influence of aperture time jitter, decision accuracy and system noise, it is difficult to increase the sampling rate to more than 10GS/s. For electronic ADCs with an effective number of bits of 4, the sampling rate of 8GS/s has almost reached the limit.

Conversion rate and accuracy are the main performance indicators of ADC. At present, among electronic ADCs, Flash ADC is the ADC with the simplest structure and the fastest conversion rate. It can achieve 8 to 10-bit resolution at a sampling rate of hundreds of MHz. The sampling rate of Flash ADC using bipolar technology can reach the GHz level, but with the improvement of conversion accuracy, its power consumption and size will also increase exponentially. Electronic Flash ADC is a fully parallel ADC. For an N-bit electronic Flash ADC, the entire circuit includes ^2N resistors and ^2N -1 comparators. It can be seen that the size and area required for the entire analog-to-digital conversion system are relatively large. The input signal of the electronic Flash ADC is input into the comparator array in parallel, so the entire quantization process is parallel. Each analog-to-digital conversion is carried out simultaneously, and the conversion speed is extremely fast, while the conversion speed will not increase with the increase of conversion accuracy. However, with the increase of conversion accuracy, the number of required resistors and comparators will increase exponentially with the conversion accuracy N, resulting in a sharp increase in the size and power consumption of the entire analog-to-digital conversion system, which is not conducive to chip integration. In addition, the jitter of the electronic clock is large, which will reduce the signal-to-noise ratio of the electronic Flash ADC. Therefore, how to use a simple and effective method to simplify the system structure and improve the system performance is still a problem that deserves attention of current technicians. Compared with electronic ADC, photon ADC has many advantages. Photon ADC can achieve higher sampling rate and conversion rate. The time jitter of the pulse sequence generated by the mode-locked laser is more than two orders of magnitude smaller than the jitter of the electronic clock. The electronic Flash ADC compares the amplitude of the sampling point with the different threshold levels of multiple comparators at the same time. In order to reduce the number of comparators and simplify the structure, this can be regarded as weighting the amplitude of the same sampling point by a certain proportion and then comparing it with the same threshold level. However, the existing electronic Flash ADC has the technical defects of complex structure, numerous comparators, difficulty in integration and large time jitter. The present invention is an optical implementation of the electronic Flash ADC.

Summary of the invention

The purpose of the present invention is to provide a high-speed photon analog-to-digital conversion method and system based on pulse processing to address the defects of existing electronic Flash ADCs, such as complex structure, numerous comparators, difficulty in integration and large time jitter.

The present invention uses a mode-locked laser to provide ultrashort optical pulses, and uses a Mach-Zehnder modulator to implement high-speed sampling of radio frequency signals generated by a signal generator; a programmable spectrum shaper is used to perform spectrum shaping on the sampled ultrashort optical pulses to implement weighted multi-wavelength sampling pulses, and the shaped signal passes through a section of single-mode dispersion optical fiber to perform pulse walk-off in the time domain. The walk-off signal is photoelectrically converted by a photodetector and enters a comparator for quantization, thereby realizing the conversion of analog signals to digital signals. The present invention solves the technical problems of the existing electronic Flash ADC, which has a complex structure, numerous comparators, is not easy to integrate, and has large time jitter, and greatly improves the sampling rate of the photon analog-to-digital conversion system. At the same time, the system is simple and easy to implement.

In order to achieve the above objectives, the present invention adopts the following technical solutions:

A high-speed photon analog-to-digital conversion method based on pulse processing comprises the following steps:

S1. The mode-locked laser generates an ultrashort optical pulse, which enters the Mach-Zehnder modulator working in the linear region and completes linear optical sampling of the RF signal generated by the signal generator;

S2. The signal sampled in step S1 is spectrally shaped in a programmable spectrum shaper to output multi-wavelength pulses with consistent spectrum intervals, power weighting and overlap in the time domain;

S3. The multi-wavelength pulse train output in step S2 passes through a section of single-mode dispersion fiber and then pulses walk off, and pulses of different wavelengths are evenly spread out with different delays in the time domain;

S4. The sampling pulses separated in the time domain are converted into electrical signals by the photodetector, and compared with the threshold level set by the comparator to generate digital quantization signals.

Furthermore, in step S1, the repetition time of the ultrashort optical pulse generated by the mode-locked laser is Δt, and the radio frequency signal generated by the signal generator is V _s (t).

Further, in step S1, the ultrashort optical pulse generated by the mode-locked laser and the radio frequency signal generated by the signal generator are optically sampled in a Mach-Zehnder modulator, and the expression of the light intensity I _o ⁱ (i＝1,2,...,N) output by the Mach-Zehnder modulator is:

Wherein, N represents the number of wavelengths of the multi-wavelength pulse, _Ii represents the light intensity corresponding to the i-th wavelength, _Vπ represents the half-wave voltage of the Mach-Zehnder modulator, and _Vbias represents the DC bias voltage.

Furthermore, in step S1, the Mach-Zehnder modulator operates in the linear region, i.e., the orthogonal bias point. The modulator output light intensity can be regarded as:

where _kp is a constant related to the intensity modulation coefficient.

Furthermore, in step S2, the spectrum intervals of the weighted multi-wavelength pulses overlapping in the time domain are consistent, and the corresponding power weighting ratio is:

P ₁ :P ₂ :...:P _N =2 ^N-1 :2 ^N-2 :...:1.

Further, in step S3, the sampled weighted multi-wavelength pulses pass through a section of single-mode dispersion optical fiber, and pulses of different wavelength bands are separated in the time domain by different delays, wherein the delay is:

Δτ＝DLΔλ

Among them, Δτ represents the delay difference between adjacent wavelength pulses, D represents the dispersion coefficient of single-mode dispersion fiber, L represents the fiber length, and Δλ represents the interval between adjacent wavelengths.

Further, in step S4, the threshold of the comparator is set to:

代表第一个量化步长边界值，I_o ¹代表最大光功率对应的光脉冲的光强。in,

represents the first quantization step boundary value, and I _o ¹ represents the light intensity of the optical pulse corresponding to the maximum optical power.

The present invention also discloses a high-speed photon analog-to-digital conversion system based on pulse processing, which includes a mode-locked laser, a Mach-Zehnder modulator, a signal generator, a programmable spectrum shaper, a single-mode dispersion optical fiber, a photodetector and a comparator; the mode-locked laser is used to generate an ultrashort optical pulse sequence, and its output port is connected to the input port of the Mach-Zehnder modulator, the signal generator is connected to the radio frequency port of the Mach-Zehnder modulator, the signal generator is used to generate a radio frequency signal to be converted, and the Mach-Zehnder modulator is used to realize optical sampling of the radio frequency signal by the optical pulse; the output port of the Mach-Zehnder modulator The optical port is connected to the input port of a programmable spectrum shaper, which is used to perform spectrum shaping on optical pulses to generate weighted multi-wavelength pulses overlapping in the time domain; the output port of the programmable spectrum shaper is connected to the input port of a single-mode dispersion optical fiber, which is used to delay pulses of different wavelength bands in the multi-wavelength pulses and separate them in the time domain; the output port of the single-mode dispersion optical fiber is connected to the input port of a photodetector, which is used to convert the multiplexed optical signal into an electrical signal; the output port of the photodetector is connected to a comparator, which is used to quantize the sampling signal.

Compared with the prior art, the present invention has the advantages of:

The present invention solves the technical problems of the existing electronic Flash ADC, such as complex structure, numerous comparators, difficulty in integration and large time jitter. The present invention uses a mode-locked laser to generate an ultrashort optical pulse sequence, reduces time jitter, greatly improves the sampling rate of the photon analog-to-digital conversion system, adopts a non-uniform quantization coding scheme to effectively improve the quantization signal-to-noise ratio of small signals, and realizes the serial output of all-optical digital quantization signals by utilizing the broadening characteristics of pulses during transmission in a dispersive medium; at the same time, the present invention only uses one Mach-Zehnder modulator, avoids the problem of signal synchronization but inconsistent response caused by the parallel structure of the modulator, eliminates the influence of polarization light walk-off introduced by the non-equal arm length interferometer, reduces the system complexity, and greatly improves the scalability and ease of integration of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a flow chart of a high-speed photon analog-to-digital conversion method based on pulse processing;

FIG2 is a schematic diagram of the structure of a high-speed photon analog-to-digital conversion system based on pulse processing;

FIG. 3 is a diagram showing the quantization result of the quantizer.

The codes in the figure are: 1. mode-locked laser; 2. Mach-Zehnder modulator; 3. signal generator; 4. programmable spectrum shaper; 5. single-mode dispersion fiber; 6. photodetector; 7. comparator.

DETAILED DESCRIPTION

The following describes the embodiments of the present invention through specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

The present invention aims at the defects and limitations of the prior art and provides a high-speed photon analog-to-digital conversion method and system based on pulse processing. The following embodiments all take 4-bit photon analog-to-digital conversion as an example.

Embodiment 1:

1 to 3 , this embodiment provides a high-speed photon analog-to-digital conversion method based on pulse processing, comprising the following steps:

S1, a mode-locked laser 1 generates an ultrashort optical pulse, and after the ultrashort optical pulse enters a Mach-Zehnder modulator 2 operating in a linear region, linear optical sampling is performed on a radio frequency signal generated by a signal generator 3;

S2, the signal sampled in step S1 is spectrally shaped in a programmable spectrum shaper 4, and multi-wavelength pulses with consistent spectrum intervals, power weighting and overlap in the time domain are output;

S3, the multi-wavelength pulse train output in step S2 undergoes pulse walk-off after passing through a section of single-mode dispersion optical fiber 5, and pulses in different wavelength bands generate different delays in the time domain and spread out evenly;

S4. The sampling pulses separated in the time domain are converted into electrical signals by the photodetector 6, and then compared with the threshold level set by the comparator 7 to generate a digital quantization signal.

More specifically, in step S1 of this embodiment, the repetition time of the ultrashort optical pulse generated by the mode-locked laser 1 is Δt, and the radio frequency signal generated by the signal generator 3 is V _s (t).

其中i＝1,2,3,4。The ultrashort optical pulse generated by the mode-locked laser 1 and the radio frequency signal generated by the signal generator 3 are optically sampled in the Mach-Zehnder modulator 2, wherein the Mach-Zehnder modulator 2 operates in the linear region, and the output light intensity can be expressed as:

Where i=1,2,3,4.

In step S2 of this embodiment, the programmable spectrum shaper 4 performs spectrum shaping on the sampled signal, and outputs weighted multi-wavelength pulses with uniform spectrum intervals and a power ratio of 8:4:2:1.

In step S3 of this embodiment, the sampled weighted multi-wavelength pulse passes through a section of single-mode dispersion optical fiber 5, and pulses in different wavelength bands are separated in the time domain by different delays, wherein the delay is: Δτ=DLΔλ.

Among them, Δτ represents the delay difference between adjacent wavelength pulses, D represents the dispersion coefficient of single-mode dispersion fiber, L represents the fiber length, and Δλ represents the interval between adjacent wavelengths.

In step S4 of this embodiment, the comparator 7 threshold is set to:

代表第一个量化步长边界值，I_o ¹代表最大光功率对应的光脉冲的光强。当光电探测器6输出电流强度小于比较器7阈值时，比较器7输出数字信号“0”，否则输出“1”，最终，4个波长可以实现5个量化级，分别是0000,0001,0011,0111,1111，实现数字量化信号的串行输出。in,

represents the first quantization step boundary value, and I _o ¹ represents the light intensity of the optical pulse corresponding to the maximum optical power. When the output current intensity of the photodetector 6 is less than the threshold of the comparator 7, the comparator 7 outputs a digital signal "0", otherwise it outputs "1". Finally, the four wavelengths can achieve five quantization levels, namely 0000, 0001, 0011, 0111, and 1111, realizing the serial output of digital quantization signals.

Embodiment 2:

2 , this embodiment provides a high-speed photon analog-to-digital conversion system based on pulse processing, including: a mode-locked laser 1, a Mach-Zehnder modulator 2, a signal generator 3, a programmable spectrum shaper 4, a single-mode dispersion fiber 5, a photodetector 6 and a comparator 7; the specific connection relationship is as follows:

The output port of the mode-locked laser 1 is connected to the input port of the Mach-Zehnder modulator 2; the signal generator 3 is connected to the radio frequency port of the Mach-Zehnder modulator 2; the output port of the Mach-Zehnder modulator 2 is connected to the input port of the programmable spectrum shaper 4; the output port of the programmable spectrum shaper 4 is connected to the input port of the single-mode dispersion fiber 5; the output port of the single-mode dispersion fiber 5 is connected to the input port of the photodetector 6; the output port of the photodetector 6 is connected to the comparator 7. In this embodiment, the mode-locked laser is used to generate an ultrashort optical pulse sequence; the Mach-Zehnder modulator is used to realize optical sampling of radio frequency signals by optical pulses; the signal generator is used to generate radio frequency signals to be converted; the programmable spectrum shaper is used to perform spectrum shaping on optical pulses to generate weighted multi-wavelength pulses overlapping in the time domain; the single-mode dispersion fiber is used to delay pulses of different wavelength bands in the multi-wavelength pulses, and separate them in the time domain; the photodetector is used to convert the multiplexed optical signal into an electrical signal; and the comparator is used to quantize the sampled signal. The specific implementation steps of this embodiment are as follows:

S1, the mode-locked laser 1 generates an ultrashort optical pulse, and after the ultrashort optical pulse enters the Mach-Zehnder modulator 2 working in the linear region, the linear optical sampling of the radio frequency signal generated by the signal generator 3 is completed.

其中i＝1,2,3,4。Specifically, the repetition time of the ultrashort optical pulse generated by the mode-locked laser 1 is Δt, and the radio frequency signal generated by the signal generator 3 is V _s (t). The ultrashort optical pulse generated by the mode-locked laser 1 and the radio frequency signal generated by the signal generator 3 are optically sampled in the Mach-Zehnder modulator 2, wherein the Mach-Zehnder modulator 2 operates in the linear region, and the output light intensity can be expressed as:

Where i=1,2,3,4.

S2. The signal sampled in step S1 is spectrum shaped in the programmable spectrum shaper 4 to output multi-wavelength pulses with consistent spectrum intervals, power weighting and overlap in the time domain.

Specifically, the programmable spectrum shaper 4 performs spectrum shaping on the sampled signal, and outputs weighted multi-wavelength pulses with uniform spectrum intervals and a power ratio of 8:4:2:1.

S3. After the multi-wavelength pulse train outputted in step S2 passes through a section of single-mode dispersion optical fiber 5, pulse walk-off occurs, and pulses in different wavelength bands generate different delays in the time domain and spread out evenly.

Specifically, the sampled weighted multi-wavelength pulse passes through a section of single-mode dispersion optical fiber 5, and pulses in different wavelength bands are separated in the time domain by different delays, wherein the delay is: Δτ=DLΔλ.

Among them, Δτ represents the delay difference between adjacent wavelength pulses, D represents the dispersion coefficient of single-mode dispersion fiber, L represents the fiber length, and Δλ represents the interval between adjacent wavelengths.

S4. The sampling pulses separated in the time domain are converted into electrical signals by the photodetector 6, and then compared with the threshold level set by the comparator 7 to generate a digital quantization signal.

Among them, the comparator 7 threshold is set to:

代表第一个量化步长边界值，I_o ¹代表最大光功率对应的光脉冲的光强。当光电探测器6输出电流强度小于比较器7阈值时，比较器7输出数字信号“0”，否则输出“1”，最终，4个波长可以实现5个量化级，分别是0000,0001,0011,0111,1111，实现数字量化信号的串行输出。in,

represents the first quantization step boundary value, and I _o ¹ represents the light intensity of the optical pulse corresponding to the maximum optical power. When the output current intensity of the photodetector 6 is less than the threshold of the comparator 7, the comparator 7 outputs a digital signal "0", otherwise it outputs "1". Finally, the four wavelengths can achieve five quantization levels, namely 0000, 0001, 0011, 0111, and 1111, realizing the serial output of digital quantization signals.

In summary, the present invention discloses a high-speed photon analog-to-digital conversion method and system based on pulse processing. The present invention uses a mode-locked laser to provide ultrashort optical pulses, and uses the ultrashort optical pulses through a Mach-Zehnder modulator to achieve high-speed sampling of radio frequency signals generated by a signal generator; the sampled ultrashort optical pulses are spectrally shaped by a programmable spectrum shaper to generate weighted multi-wavelength sampling pulses, and the shaped signals are pulsed out in the time domain through a section of single-mode dispersion optical fiber, and the signals after the walk-off are photoelectrically converted by a photodetector and enter a comparator for quantization, thereby realizing the conversion of analog signals to digital signals. The present invention is an optical realization of an electronic Flash ADC, which solves the technical problems of the existing electronic Flash ADC, such as complex structure, numerous comparators, difficulty in integration and large time jitter. The present invention uses a mode-locked laser to generate an ultrashort optical pulse sequence, reduces time jitter, greatly improves the sampling rate of a photon analog-to-digital conversion system, adopts a non-uniform quantization coding scheme to effectively improve the quantization signal-to-noise ratio of small signals, and realizes the serial output of all-optical digital quantization signals by utilizing the broadening characteristics of pulses during transmission in a dispersive medium. At the same time, the present invention uses only one Mach-Zehnder modulator, avoids the signal synchronization and response inconsistency problems caused by the parallel structure of the modulator, and eliminates the influence of polarization light walk-off introduced by a non-equal arm length interferometer.

Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (10)

1. The high-speed photon analog-to-digital conversion method based on pulse processing is characterized by comprising the following steps of:

s1, an ultra-short light pulse is generated by a mode-locked laser, and after the ultra-short light pulse enters a Mach-Zehnder modulator working in a linear region, linear light sampling is completed on a radio frequency signal generated by a signal generator;

s2, performing spectrum shaping on the signal sampled in the step S1 in a programmable spectrum shaper, and outputting multi-wavelength pulses which are consistent in spectrum interval, weighted in power and overlapped in time domain;

s3, pulse walk-off occurs after the multi-wavelength pulse output in the step S2 passes through the single-mode dispersion optical fiber, and the pulses in different wave bands are uniformly unfolded by generating different time delays in the time domain;

s4, the sampling pulse separated in the time domain is converted into an electric signal through a photoelectric detector, and the electric signal is compared with a threshold level set by a comparator to generate a digital quantized signal.

2. The method of claim 1, wherein in step S1, the repetition time of the ultrashort optical pulse generated by the mode-locked laser is Δt, and the rf signal generated by the signal generator is V _s (t)。

3. The high-speed photon analog-to-digital conversion method based on pulse processing as claimed in claim 2, wherein in step S1, ultra-short light pulse generated by mode-locked laser and radio frequency signal generated by signal generator are optically sampled in mach-zehnder modulator, and light intensity I outputted by mach-zehnder modulator _o ⁱ The expression of (2) is:

wherein N represents the number of wavelengths of the multi-wavelength pulse, I _i Representing the intensity of light corresponding to the i-th wavelength, i=1, 2,.. _π Representing half-wave voltage of Mach-Zehnder modulator, V _bias Representing a dc bias voltage.

4. A high-speed photon analog-to-digital conversion method based on pulse processing according to claim 3, wherein in step S1, the mach-zehnder modulator operates in a linear region, i.e., an orthogonal bias point; the modulator output light intensity is expressed as:

wherein ,k_p Is a constant related to the intensity modulation factor.

5. The method for high-speed photon analog-to-digital conversion based on pulse processing according to claim 4, wherein in step S2, the weighted multi-wavelength pulses overlapped in time domain have identical spectrum intervals, and the corresponding power weighting ratio is:

P ₁ :P ₂ :...:P _N ＝2 ^N-1 :2 ^N-2 :...:1。

6. the method of high-speed photon analog-to-digital conversion based on pulse processing according to claim 5, wherein in step S3, the multi-wavelength pulse passes through a section of single-mode dispersion fiber, and pulses in different wavebands generate different delays which are separated from time domain, wherein the delays are:

Δτ＝DLΔλ

where Δτ represents the delay difference of adjacent wavelength pulses, D represents the dispersion coefficient of the single-mode dispersive fiber, L represents the fiber length, and Δλ represents the adjacent wavelength spacing.

7. The method of high-speed photon analog-to-digital conversion based on pulse processing according to claim 6, wherein in step S4, the threshold of the comparator is set as follows:

wherein ,

represents the first quantization step boundary value, I _o ¹ Representing the intensity of the light pulse corresponding to the maximum light power.

8. The high-speed photon analog-to-digital conversion system based on pulse processing is characterized by comprising a mode-locked laser, a Mach-Zehnder modulator, a signal generator, a programmable spectrum shaper, a single-mode dispersion optical fiber, a photoelectric detector and a comparator; the output port of the mode-locked laser is connected with the input port of the Mach-Zehnder modulator, the signal generator is connected with the radio frequency port of the Mach-Zehnder modulator, the output port of the Mach-Zehnder modulator is connected with the input port of the programmable spectrum shaper, the output port of the programmable spectrum shaper is connected with the input port of the single-mode dispersion optical fiber, the output port of the single-mode dispersion optical fiber is connected with the input port of the photoelectric detector, and the output port of the photoelectric detector is connected with the comparator.

9. The pulse processing-based high-speed photon analog-to-digital conversion system according to claim 8, wherein the repetition time of the ultra-short light pulse generated by the mode-locked laser is Δt, and the radio frequency signal generated by the signal generator is V _s (t)。

10. The high-speed photon analog-to-digital conversion system based on pulse processing as claimed in claim 9, wherein said ultra-short light pulse generated by said mode-locked laser and the radio frequency signal generated by the signal generator are optically sampled in a mach-zehnder modulator, the intensity of light I output by the mach-zehnder modulator _o ⁱ The expression of (2) is:

wherein N represents the number of wavelengths of the multi-wavelength pulse, I _i Representing the intensity of light corresponding to the i-th wavelength, i=1, 2,.. _π Representing half-wave voltage of Mach-Zehnder modulator, V _bias Representing a dc bias voltage.

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