CN111884727A - A high-speed photon digital-to-analog conversion method and system based on digital mapping - Google Patents

Abstract

The invention discloses a high-speed photon digital-to-analog conversion method and system based on digital mapping. Its system includes a broadband light source, a wavelength division multiplexer, N optical attenuators, N digital mappers, N Mach-Zehnder modulators, a wavelength division multiplexer, a photodetector, and a low-pass filter. The system uses a broad-spectrum light source to provide a continuous optical carrier, modulates the "down-converted" digital signal to an optical carrier of different frequencies through a Mach-Zehnder modulator, and the modulated signal is connected to a wavelength division multiplexer to realize digital signals with different weights After the weighted superposition of the photoelectric detector, the photoelectric conversion is performed by the photoelectric detector and the low-pass filter is connected for smoothing, so as to realize the conversion of digital signal to analog signal. The scheme uses digital mapping to perform down-frequency processing on the digital signal to be converted in advance, so as to use the existing conversion equipment to double the system conversion rate and system bandwidth. At the same time, the system has a simple structure and is easy to operate and integrate.

Description

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

technical field

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

Background technique

Digital-to-analog Converter (DAC) is an irreplaceable bridge between the digital world and the analog world. In recent years, in the fields of modern radar and wireless communication, the digital-to-analog converter is a key device to realize the conversion of digital signal to analog signal, and its performance directly affects the rate, bandwidth and accuracy of the entire signal processing system. With the development of radar and communication technology, ultra-wideband high-frequency signals generated and recovered by high-speed, high-precision digital-to-analog converters help to improve the performance of communication systems. However, due to inherent electronic limitations such as radio frequency delay, time jitter, and electromagnetic interference, traditional electronic DACs can only trade off between energy efficiency and bandwidth, and cannot improve conversion rate and conversion accuracy at the same time. high precision requirements. With the development of optical technology, the use of photonic technology to break through the bottleneck of clock jitter and electromagnetic interference in traditional solutions to achieve high-speed and high-precision digital-to-analog converters has attracted the attention of many researchers. The advantage of interference is to realize the conversion of digital signals to analog signals, and it is a very promising method to improve the performance of communication systems.

Existing optical digital-to-analog conversion schemes are classified into two categories: serial and parallel according to the input type of digital signals. In 2001, Japan's NTT company proposed an optical digital-to-analog conversion scheme based on weighted delay, which is the earliest optical serial input digital-to-analog scheme. Each channel is delayed by one bit period and then superimposed by an interferometer, and an optical decision gate is used to extract the analog signal formed by the corresponding digital signal conversion. However, the biggest disadvantage of this scheme is that the phase of each signal must be precisely controlled to achieve the same wavelength superposition, and a high-speed optical decision gate is required to extract the signal to realize the conversion of digital signal to analog signal. Tsinghua University proposed a photon digital-to-analog conversion scheme based on multi-wavelength weighted pulse sequences in 2008. The scheme uses dispersive fibers to disperse the weighted multi-wavelength pulse trains in the time domain and modulate the different weighted bits of the serial digital signal respectively. The signal of the dispersion compensation fiber realizes the weighted superposition of the modulated signal in the time domain, and the photoelectric detector is used to realize the photoelectric conversion and low-pass filtering to obtain the corresponding analog signal. This scheme has precise requirements on pulse period, fiber dispersion amount, etc., and the conversion accuracy is limited by the repetition period of multi-wavelength pulses. The photonic serial digital-to-analog conversion scheme can directly process and convert serial digital signals, and the system structure is simple, but the conversion rate is lower than that of the parallel scheme that can convert multiple bit digital signals at the same time. IPITEK proposed a parallel conversion scheme in 2003, which uses parallel electro-optic modulator arrays to realize parallel processing of digital signals, and then realizes incoherent superposition of modulated signals through photodetector arrays. This scheme has the advantages of high conversion rate and easy integration, but the response speed of the modulator, the extinction ratio, and the bandwidth of the photodetector will all become the limiting factors of the system performance. In 2007, Tsinghua University adopted a broad-spectrum light source based on the IPITEK parallel scheme to reduce interference noise in the process of incoherent superposition. In 2005, Osaka University proposed a photon digital-to-analog conversion scheme based on Nonlinear Optical Loop Mirror (NOLM), which uses NOLM reflection spectrum and transmission spectrum to control the pulse output direction and amplitude to achieve weighted superposition of signals with different bit weights. Get the corresponding analog signal output. The scheme utilizes the nonlinear principle of NOLM and the system has a fast response speed, but 2N-1 NOLMs are required to achieve N-bit conversion accuracy, and the system structure is complex. In 2014, the Chinese Academy of Sciences also proposed a photonic digital-to-analog conversion scheme based on a micro-ring resonator, which uses high and low voltages to control the shift of the resonant wavelength of the micro-ring resonator to achieve digital signal modulation. This scheme uses multiple micro-ring resonators to realize parallel digital-to-analog conversion. Micro-ring resonators have the advantages of ultra-small size and low power consumption, reducing system complexity and facilitating system integration, but the conversion rate of micro-ring resonators is not high. This results in a limited slew rate for the entire system. Therefore, how to use simple and effective methods to simplify the system structure and improve the system performance is still a problem worthy of attention.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a high-speed photon digital-to-analog conversion method and system based on digital mapping in view of the defects of the existing photon digital-to-analog conversion technology. Limited to the problems of existing equipment, the conversion rate of the photonic digital-to-analog conversion system is greatly improved, and the system is simple and easy to implement.

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

A high-speed photon digital-to-analog conversion method based on digital mapping, comprising the steps of:

S1. The broadband light source generates a continuous optical carrier, which is divided into N parallel optical carriers with different wavelengths after passing through the wavelength division multiplexer, and the N optical carriers pass through the optical carriers corresponding to each optical carrier in parallel respectively. After the attenuator, it continues to enter the Mach-Zehnder modulator corresponding to the optical attenuator;

S2. The N digital mappers all perform down-conversion processing on the digital signals input to themselves, and output two digital signals. The two digital signals output by each digital mapper enter the Mach- Zehnder modulator;

S3. Each of the N Mach-Zehnder modulators modulates the two channels of digital signals entering into its own onto the optical carrier entering its own, and outputs one optical modulation signal, and the N optical modulation signals enter the wavelength division multiplexer;

S4. The wavelength division multiplexer weights and superimposes N channels of optical modulation signals with different weights and outputs one channel of multiplexed optical signals. The multiplexed optical signals enter the photoelectric detector and are converted into electrical signals and then enter the low-pass filter for smoothing processing and get an analog signal.

Further, in step S1, the power ratio of N optical carriers after passing through the optical attenuators corresponding to each optical carrier is:

表示光载波经过第i个光衰减器后的功率，i＝1，2，3，......，N。in

Indicates the power of the optical carrier after passing through the i-th optical attenuator, i=1, 2, 3,...,N.

Further, the input digital signals D ₁ , D2 , . . . , D _N of the N digital mappers correspond to LSB, NLSB, . is the least significant bit, NLSB is the most significant bit closest to the LSB, and MSB is the most significant bit.

Further, the two digital signals S _i1 and S _i2 (i=1, 2, . . . , N) output by each digital mapper satisfy:

Wherein S _i1 represents the first digital signal output by the ith digital mapper, and S _i2 represents the second digital signal output by the ith digital mapper;

m=1, 2, . . . , n/2, n is the length of the input digital signal of the digital mapper, and V _s is the amplitude of the down-converted signal output by the digital mapper.

Further, the peak value of the digital signal output by each digital mapper is V _π .

Further, in the step S3, the initial phase of the modulation signal output by each Mach-Zehnder modulator is π.

Further, the initial phase of the modulation signal output by each Mach-Zehnder modulator is controlled by the bias voltage provided by the DC power supply, and the magnitude of the bias voltage is equal to V _π .

Further, in the step S3, the expression of the optical modulation signal intensity I _i (i=1, 2, . . . , N) output by each Mach-Zehnder modulator is:

Among them, α=πV _s /V _π represents the modulation depth, and T represents the bit period of the digital mapper output signal.

The invention also discloses a high-speed photon digital-to-analog conversion system based on digital mapping, which includes a wide-spectrum light source, a wave decomposition multiplexer, N optical attenuators, N digital mappers, N Mach-Zehnder modulators, wavelength division multiplexers, photodetectors, and low-pass filters;

Broad-spectrum light source for generating continuous optical carriers;

Wavelength division multiplexer, used to divide the continuous optical carrier into N parallel optical carriers of different wavelengths;

an optical attenuator, used to attenuate the optical power of its corresponding parallel optical carrier;

The digital mapper is used to down-convert the input digital signal and output two digital signals;

The Mach-Zehnder modulator is used to modulate the corresponding two digital signals to the corresponding optical carrier attenuated by the optical attenuator, and output one optical modulation signal;

The wavelength division multiplexer is used to weighted and superimpose N channels of optical modulation signals with different weights output by the N Mach-Zehnder modulators and output one channel of multiplexed optical signals;

a photodetector for converting the multiplexed optical signal into an electrical signal;

A low-pass filter, used to smooth the electrical signal and obtain an analog signal.

The advantages of the present invention are: compared with the traditional photon digital-to-analog conversion scheme, the scheme performs down-frequency processing on the digital signal, solves the problem that the speed of the photon digital-to-analog conversion system is limited by the existing equipment, and greatly improves the number of photons. The conversion rate of the analog conversion system, while the system is simple and easy to implement.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a flowchart of a high-speed photon digital-to-analog conversion method based on digital mapping;

2 is a schematic structural diagram of a high-speed photon digital-to-analog conversion system based on digital mapping;

Figure 3 is a schematic diagram of a digital mapper;

FIG. 4 is a comparison diagram of the input signal and the output signal of the digital mapper;

The codes in the figure are: 1. Broad-spectrum light source; 2. WDM; 3. First optical attenuator; 4. Second optical attenuator; 5. Third optical attenuator; 6. First Mach - Zehnder modulator; 7. Second Mach-Zehnder modulator; 8. Third Mach-Zehnder modulator; 9. First digital mapper; 10. Second digital mapper; 11. Third digital mapper 12. Wavelength division multiplexer; 13. Photodetector; 14. Low-pass filter.

Detailed ways

The embodiments of the present invention are described below through specific specific examples, 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 various details in this specification can also be modified or changed 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 may be combined with each other under the condition of no conflict.

The purpose of the present invention is to provide a high-speed photon digital-to-analog conversion method and system based on digital mapping in view of the limitations of the prior art. The following embodiments all take 3-bit photon digital-to-analog conversion as an example.

Example 1:

Referring to Figure 1, Figure 2, Figure 3, Figure 4, a high-speed photon digital-to-analog conversion method based on digital mapping is provided, comprising the steps:

S1. The broadband light source 1 generates a continuous optical carrier, which is divided into three parallel optical carriers with different wavelengths after passing through the wavelength division multiplexer 2, and the three optical carriers pass in parallel and correspond to each optical carrier. After the optical attenuator, it continues to enter the Mach-Zehnder modulator corresponding to the optical attenuator;

S2. Each of the three digital mappers down-converts the input digital signal and outputs two digital signals. The two digital signals output by each digital mapper enter the Mach- Zehnder modulator;

S3. Each of the three Mach-Zehnder modulators modulates the two channels of digital signals entering into their own onto the optical carrier entering their own, and outputs one channel of optical modulation signals, and the three channels of optical modulation signals enter the wavelength division multiplexer 12;

S4. The wavelength division multiplexer 12 weights and superimposes three optical modulation signals with different weights and outputs one multiplexed optical signal. The multiplexed optical signal enters the photodetector 13 and is converted into an electrical signal and then enters the low-pass filter 14. Smoothing and getting an analog signal.

In step S1, the broad-spectrum light source 1 generates a continuous optical carrier, which is divided into three parallel optical carriers with different wavelengths after passing through the wavelength division multiplexer 2, and the optical carrier passes through the first optical attenuator 3, the first optical attenuator 3, the second optical carrier in parallel The second optical attenuator 4 and the third optical attenuator 5 respectively enter the first Mach-Zehnder modulator 6 , the second Mach-Zehnder modulator 7 and the third Mach-Zehnder modulator 8 .

The continuous optical carrier generated by the broadband light source 1 is divided into three parallel optical carriers with different wavelengths after passing through the wavelength division multiplexer 2. After passing through the first optical attenuator 3, the second optical attenuator 4, and the third optical attenuator 5, the power ratio is Expressed as:

In step S2, the first digital mapper 9, the second digital mapper 10, and the third digital mapper 11 respectively generate two digital signals, and the generated digital signals enter the corresponding first Mach-Zehnder modulator 6 , the second Mach-Zehnder modulator 7, the third Mach-Zehnder modulator 8.

The input digital signals D ₁ , D ₂ , and D ₃ of the first digital mapper 9 , the second digital mapper 10 , and the third digital mapper 11 correspond to the LSB, NLSB, and MSB of the serial-to-parallel converted digital signal, respectively. Data string, where LSB is the least significant bit, NLSB is the effective bit closest to LSB, MSB is the most significant bit, and the output digital signal satisfies:

Among them, S _i1 represents the first digital signal output by the ith digital mapper, S _i2 represents the second digital signal output by the ith digital mapper, i=1, 2, 3; m=1, 2 , _. The peak value of the digital signal output by the digital mapper 11 is V _π ; the first Mach-Zehnder modulator 6, the second Mach-Zehnder modulator 7, and the third Mach-Zehnder modulator 8 are provided by the DC power supply with a magnitude of V _π . Bias voltage; the initial phase of the three-way modulation signal is π.

In step S3 , the first Mach-Zehnder modulator 6 , the second Mach-Zehnder modulator 7 and the third Mach-Zehnder modulator 8 output three optical modulation signals into the wavelength division multiplexer 12 .

The expression of the optical modulation signal intensity I _i (i=1, 2, 3) output by the first Mach-Zehnder modulator 6, the second Mach-Zehnder modulator 7, and the third Mach-Zehnder modulator 8 is: :

代表光载波经过第i个光衰减器之后的功率，α＝πV_s/V_π代表调制深度，T代表数字映射器输出信号的比特周期。in,

represents the power of the optical carrier after passing through the i-th optical attenuator, α=πV _s /V _π represents the modulation depth, and T represents the bit period of the output signal of the digital mapper.

In step S4, the wavelength division multiplexer 12 outputs a multiplexed optical signal, the multiplexed optical signal is converted into an electrical signal by the photodetector 13, and the electrical signal is input to the low-pass filter 14 for smoothing processing to realize a digital signal Conversion to analog signal.

Embodiment 2:

2, 3, and 4, a high-speed photon digital-to-analog conversion system based on digital mapping is provided, including: a broad-spectrum light source 1, a wavelength division multiplexer 2, a first optical attenuator 3, and a second optical attenuator 4. The third optical attenuator 5, the first Mach-Zehnder modulator 6, the second Mach-Zehnder modulator 7, the third Mach-Zehnder modulator 8, the first digital mapper 9, the second digital mapper 10, a third digital mapper 11, a wavelength division multiplexer 12, a photodetector 13, and a low-pass filter 14;

The broad-spectrum light source 1 is connected to the first optical attenuator 3, the second optical attenuator 4, and the third optical attenuator 5 through the WDM 2; the first optical attenuator 3, the second optical attenuator 4, the third optical attenuator The optical attenuators 5 are respectively connected to the first Mach-Zehnder modulator 6 , the second Mach-Zehnder modulator 7 and the third Mach-Zehnder modulator 8 .

The first digital mapper 9, the second digital mapper 10, and the third digital mapper 11 are respectively connected to the first Mach-Zehnder modulator 6, the second Mach-Zehnder modulator 7, and the third Mach-Zehnder modulator 8.

The first Mach-Zehnder modulator 6 , the second Mach-Zehnder modulator 7 , and the third Mach-Zehnder modulator 8 are connected to the wavelength division multiplexer 12 .

The wavelength division multiplexer 12 and the low-pass filter 14 are connected through the photodetector 13 .

Broad-spectrum light source 1, used to generate continuous optical carrier;

Wavelength demultiplexer 2, used to divide the continuous optical carrier into three parallel optical carriers of different wavelengths;

an optical attenuator, used to attenuate the optical power of its corresponding parallel optical carrier;

The digital mapper is used to down-convert the input digital signal and output two digital signals;

The Mach-Zehnder modulator is used to modulate the corresponding two digital signals to the corresponding optical carrier attenuated by the optical attenuator, and output one optical modulation signal;

The wavelength division multiplexer 12 is used for weighted superposition of three optical modulation signals with different weights output by the three Mach-Zehnder modulators and outputting a multiplexed optical signal;

a photodetector 13 for converting the multiplexed optical signal into an electrical signal;

The low-pass filter 14 is used for smoothing the electrical signal and obtaining an analog signal.

The input digital signal of the digital mapper (Digital-to-digital Converter, DDC) is the data with the same bit weight obtained after the serial-to-parallel conversion of the digital signal to be converted, which is represented by D. After the digital mapper, the output digital signal satisfies the following mapping relation:

Wherein, m=1,2,...,n/2, and n is the length of the input digital signal D of the digital mapper. The LSB, NLSB, MSB data strings are obtained after the serial-to-parallel conversion of the digital signal to be converted, which are respectively input to the three digital mappers. Taking one of the digital mappers as an example, assuming that the input signal D of the digital mapper is 1011011001, after passing through the digital mapper, two low-frequency signals S ₁ and S ₂ that satisfy the mapping relationship are output as 10111 and 11010, respectively. The frequency of the output signal of the digital mapper is half of the frequency of the input signal, which effectively realizes the frequency reduction of the digital signal and preserves the correlation between the output signal and the input signal. Double the bandwidth.

A high-speed photon digital-to-analog conversion method and system based on digital mapping proposed in the above embodiment, through the method of digital mapping, to solve the problem that the conversion rate of the photonic digital-to-analog conversion system is limited by the existing equipment, and the traditional photonic digital-to-analog conversion system. In contrast, this scheme uses digital mapping to perform down-frequency processing on the digital signal to be converted in advance, so that the existing conversion equipment can be used to double the system conversion rate and system bandwidth. At the same time, the system has a simple structure and is easy to operate and integrate.

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

Claims (9)

1. A high-speed photon digital-to-analog conversion method based on digital mapping is characterized by comprising the following steps:

s1, generating continuous light carriers by a wide-spectrum light source, dividing the continuous light carriers into N paths of parallel light carriers with different wavelengths after passing through a wavelength division demultiplexer, and continuously and respectively entering Mach-Zehnder modulators corresponding to optical attenuators after the N paths of light carriers respectively pass through the optical attenuators corresponding to each path of light carriers in parallel;

s2, N digital mappers carry out frequency reduction processing on the digital signals input into the N digital mappers and output two paths of digital signals, and the two paths of digital signals output by each digital mapper enter the Mach-Zehnder modulator corresponding to each digital mapper;

s3, the N Mach-Zehnder modulators modulate the two paths of digital signals entering the Mach-Zehnder modulators to optical carriers entering the Mach-Zehnder modulators, and output one path of optical modulation signals, and the N paths of optical modulation signals enter the wavelength division multiplexer;

s4, the wavelength division multiplexer performs weighted superposition on the N paths of optical modulation signals with different weights and outputs a path of multiplexing optical signal, and the multiplexing optical signal enters the photoelectric detector to be converted into an electric signal and then enters the low-pass filter to be smoothed to obtain an analog signal.

2. The method according to claim 1, wherein in step S1, the power ratio of N optical carriers passing through the optical attenuator corresponding to each optical carrier is:

wherein

The power of the optical carrier after passing through the ith optical attenuator is represented, i is 1,2,3, … …, N.

3. The method of claim 1, wherein in step S2, the input digital signals D of N mappers are inputted₁,D₂,...,D_NThe digital signal to be converted is respectively corresponding to LSB, NLSB and MSB data string after serial-parallel conversion, wherein the LSB is the least significant bit, the NLSB is the significant bit closest to the LSB, and the MSB is the most significant bit.

4. The high-speed photon digital-to-analog conversion method based on digital mapping as claimed in claim 3, wherein two paths of digital signals S outputted by each digital mapper_i1、S_i2(i ═ 1, 2.., N) satisfies:

wherein S_i1Representing the first digital signal, S, output from the ith digital mapper_i2Representing the second path of digital signals output by the ith digital mapper;

n/2, n is the length of the input digital signal of the digital mapper, V_sThe amplitude of the down-converted signal is output to the digital mapper.

5. The high-speed photon digital-to-analog conversion method based on digital mapping as claimed in claim 4, wherein the peak value of the digital signal output by each digital mapper is V_π。

6. The method according to claim 5, wherein in step S3, the initial phase of the modulation signal output by each Mach-Zehnder modulator is pi.

7. The digital mapping-based high-speed photon digital-to-analog conversion method according to claim 6, wherein the initial phase of the modulation signal output by each Mach-Zehnder modulator is controlled by a bias voltage provided by a DC power supply, and the magnitude of the bias voltage is equal to V_π。

8. The method according to claim 7, wherein in the step S3, each mach-zehnder modulator outputs an optical modulation signal intensity I_iThe expression of (i ═ 1, 2.., N) is:

wherein, alpha is pi V_s/V_πRepresenting the modulation depth and T representing the bit period of the output signal of the digital mapper.

9. A high-speed photon digital-to-analog conversion system based on digital mapping is characterized by comprising a wide spectrum light source, a wavelength division demultiplexer, N optical attenuators, N digital mappers, N Mach-Zehnder modulators, a wavelength division multiplexer, a photoelectric detector and a low-pass filter;

a broad spectrum light source for generating a continuous optical carrier;

the wavelength division demultiplexer is used for dividing the continuous optical carrier into N paths of parallel optical carriers with different wavelengths;

the optical attenuator is used for attenuating the optical power of the parallel optical carrier wave corresponding to the optical attenuator;

the digital mapper is used for carrying out frequency reduction processing on the digital signal input into the digital mapper and outputting two paths of digital signals;

the Mach-Zehnder modulator is used for modulating the two paths of digital signals corresponding to the Mach-Zehnder modulator onto the corresponding optical carrier attenuated by the optical attenuator and outputting one path of optical modulation signal;

the wavelength division multiplexer is used for performing weighted superposition on the N paths of optical modulation signals with different weights output by the N Mach-Zehnder modulators and outputting a path of multiplexing optical signal;

a photodetector for converting the multiplexed optical signal into an electrical signal;

and the low-pass filter is used for smoothing the electric signal and obtaining an analog signal.

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