Microwave photon frequency conversion system and method

Abstract

The invention discloses a microwave photon frequency conversion system and method, and belongs to the technical field of microwave photons. The system comprises a signal generation module, a channel switching module and a signal processing module which are connected in sequence, the signal generation module comprises a continuous light laser, a first coupler, a signal generation upper branch and a signal generation lower branch; the signal generation upper branch outputs a local oscillation optical frequency comb, and the signal generation lower branch outputs a carrier optical frequency comb; the channel switching module comprises a channel switching upper branch and a channel switching lower branch; the signal processing module comprises a first double-parallel Mach-Zehnder modulator, a second double-parallel Mach-Zehnder modulator, a second coupler, an erbium-doped optical fiber amplifier and an optical detector. According to the invention, the size and complexity of the system can be greatly reduced, large-span high-precision frequency conversion of ultra-wideband signals is realized, and the system has good reconfigurability.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave photons, and in particular relates to a microwave photon frequency conversion system and method. Background Art

[0002] Microwave frequency conversion technology is the basis of microwave signal transmission and processing, and is widely used in wireless communications, radar systems, phased array antennas, electronic warfare, and other fields. However, due to the "electronic bottleneck" limitation, the traditional electronic frequency conversion method is complex, the frequency is limited, the tuning is difficult, and it is susceptible to electromagnetic interference. It is difficult to achieve ultra-wideband, large-span high-precision frequency conversion and cannot meet current needs.

[0003] In recent years, the continuous development of microwave photonic technology has made ultra-wideband and large-span microwave frequency conversion possible. With the help of photon-assisted microwave technology, the advantages of optical domain broadband, high speed, low power consumption and anti-electromagnetic interference can be fully utilized to effectively break through the difficulties of frequency limitation and electromagnetic interference in traditional electronic solutions. However, the existing microwave photonic technology is difficult to achieve high-precision tuning. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a microwave photon frequency conversion system and method, which can significantly reduce the system volume and complexity, achieve large-span and high-precision frequency conversion of ultra-wideband signals, and have good reconstructability.

[0005] The present invention provides the following technical solutions:

[0006] In a first aspect, a microwave photon frequency conversion system is provided, comprising a signal generating module, a channel switching module and a signal processing module connected in sequence;

[0007] The signal generating module comprises a continuous light laser, a first coupler, a signal generating upper branch and a signal generating lower branch; the input end of the first coupler is connected to the continuous light laser, and the laser light generated by the continuous light laser is divided into two paths, which are respectively input into the signal generating upper branch and the signal generating lower branch; the signal generating upper branch outputs a local oscillator optical frequency comb, and the signal generating lower branch outputs a carrier optical frequency comb;

[0008] The channel switching module comprises a channel switching upper branch and a channel switching lower branch, both of which comprise a wavelength division multiplexer and an optical switch, wherein the input end of the wavelength division multiplexer is connected to the signal generation upper branch or the signal generation lower branch, and the output end is connected to the optical switch, so as to separate the local oscillator optical frequency comb or the carrier optical frequency comb into a plurality of comb teeth and input the comb teeth into the optical switch; the optical switch selects the comb teeth for output, and obtains the local oscillator comb teeth or the carrier comb teeth;

[0009] The signal processing module includes a first dual-parallel Mach-Zehnder modulator, a second dual-parallel Mach-Zehnder modulator, a second coupler, an erbium-doped fiber amplifier and a light detector; the input end of the first dual-parallel Mach-Zehnder modulator is connected to an optical switch to shift the frequency of the local oscillator comb teeth; the input end of the second dual-parallel Mach-Zehnder modulator is connected to the optical switch to load the carrier comb teeth with a signal; the output ends of the first dual-parallel Mach-Zehnder modulator and the second dual-parallel Mach-Zehnder modulator are both connected to the second coupler, the second coupler, the erbium-doped fiber amplifier and the light detector are connected in sequence, and the light detector outputs a frequency conversion signal.

[0010] As an optional technical solution of the present invention, the signal generation upper branch includes a first radio frequency source, a second radio frequency source, and a first dual-port Mach-Zehnder modulator and a second dual-port Mach-Zehnder modulator connected thereto;

[0011] The signal generation lower branch includes a third radio frequency source, a fourth radio frequency source, and a third dual-port Mach-Zehnder modulator and a fourth dual-port Mach-Zehnder modulator connected thereto;

[0012] The first radio frequency source is connected to the upper input terminals of the first dual-port Mach-Zehnder modulator and the second dual-port Mach-Zehnder modulator, respectively, and the second radio frequency source is connected to the lower input terminals of the first dual-port Mach-Zehnder modulator and the second dual-port Mach-Zehnder modulator, respectively;

[0013] The third RF source is connected to the upper input ends of the third dual-port Mach-Zehnder modulator and the fourth dual-port Mach-Zehnder modulator respectively, and the fourth RF source is connected to the lower input ends of the third dual-port Mach-Zehnder modulator and the fourth dual-port Mach-Zehnder modulator respectively.

[0014] As an optional technical solution of the present invention, the channel switching module also includes a signal generator; the signal generator is respectively connected to the optical switches in the channel switching upper branch and the channel switching lower branch, and inputs a comb selection control signal to the optical switch.

[0015] As an optional technical solution of the present invention, the signal processing module further includes a direct digital synthesizer; the direct digital synthesizer is connected to the first dual parallel Mach-Zehnder modulator and inputs a frequency shift control signal to the first dual parallel Mach-Zehnder modulator.

[0016] As an optional technical solution of the present invention, the input end of the first dual parallel Mach-Zehnder modulator is connected to the optical switch in the channel switching upper branch, and the input end of the second dual parallel Mach-Zehnder modulator is connected to the optical switch in the channel switching lower branch.

[0017] In a second aspect, a microwave photon frequency conversion method based on the microwave photon frequency conversion system of the first aspect is provided, comprising: the first coupler divides the laser light emitted by the continuous light laser into two paths, and inputs the two paths into a signal generation upper branch and a signal generation lower branch respectively, the signal generation upper branch outputs a local oscillator optical frequency comb, and the signal generation lower branch outputs a carrier optical frequency comb;

[0018] The wavelength division multiplexer in the channel switching upper branch separates the local oscillator optical frequency comb into a plurality of comb teeth and inputs the comb teeth into the optical switch, and the optical switch selects the comb teeth for output to obtain the local oscillator comb teeth; the wavelength division multiplexer in the channel switching lower branch separates the carrier optical frequency comb into a plurality of comb teeth and inputs the comb teeth into the optical switch, and the optical switch selects the comb teeth for output to obtain the carrier comb teeth;

[0019] The first dual parallel Mach-Zehnder modulator performs frequency shifting on the local oscillator comb teeth to obtain a frequency shifted local oscillator signal; the second dual parallel Mach-Zehnder modulator performs a load signal on the carrier comb teeth to obtain a modulated signal;

[0020] The second coupler combines the frequency-shifted local oscillator signal and the modulated signal to obtain a combined signal, and the erbium-doped fiber amplifier amplifies the combined signal and obtains a frequency-converted signal through the beat frequency of the optical detector.

[0021] As an optional technical solution of the present invention, the first coupler divides the laser light emitted by the continuous light laser into two paths, and inputs the signal generation upper branch and the signal generation lower branch respectively, including:

[0022] The laser emitted by the continuous light laser is expressed as:

[0023] ;

[0024] in, Represents the output light source, represents the amplitude of the input optical signal, represents the continuous light angular frequency, j represents an imaginary number, represents the natural exponential function, t represents the time variable;

[0025] The lasers of the upper branch for input signal generation and the lower branch for signal generation are expressed as:

[0026] ;

[0027] ;

[0028] in, Indicates that the input signal generates the laser of the upper branch, Indicates the input signal produces the laser in the lower branch.

[0029] As an optional technical solution of the present invention, the signal generation upper branch includes a first radio frequency source, a second radio frequency source, and a first dual-port Mach-Zehnder modulator and a second dual-port Mach-Zehnder modulator connected thereto;

[0030] The phase difference between the upper and lower arms of the first dual-port Mach-Zehnder modulator and the second dual-port Mach-Zehnder modulator is: , the frequency phase of the first RF source and the second RF source is the same, and the amplitude difference is , represents the modulator half-wave voltage, then the local oscillator optical frequency comb output by the upper branch of the signal generation is expressed as:

[0031] ;

[0032] in, represents the local oscillator frequency comb, and They represent the local oscillator frequency comb The amplitude and phase of the root comb teeth, Indicates The angular frequency of the root comb teeth, M represents the number of comb teeth on both sides of the center frequency selected by the local oscillator optical frequency comb, which is a positive integer;

[0033] The signal generation lower branch includes a third radio frequency source, a fourth radio frequency source, and a third dual-port Mach-Zehnder modulator and a fourth dual-port Mach-Zehnder modulator connected thereto;

[0034] The phase difference between the upper and lower arms of the third dual-port Mach-Zehnder modulator and the fourth dual-port Mach-Zehnder modulator is: , the frequency phase of the third RF source and the fourth RF source is the same, and the amplitude difference is , represents the modulator half-wave voltage, then the output carrier optical frequency comb of the signal generation branch is expressed as:

[0035] ;

[0036] in, represents the carrier optical frequency comb, and represent the amplitude and phase of the kth tooth of the carrier optical frequency comb, respectively. represents the angular frequency of the kth comb tooth, K represents the number of comb teeth on both sides of the center frequency selected by the carrier optical frequency comb, and is a positive integer.

[0037] As an optional technical solution of the present invention, the first dual parallel Mach-Zehnder modulator performs frequency shifting on the local oscillator comb teeth to obtain a frequency-shifted local oscillator signal, including:

[0038] The frequency-shifted local oscillator signal is expressed as:

[0039] ;

[0040] in, represents the frequency-shifted local oscillator signal, and They represent the amplitude and phase of the local oscillator comb teeth respectively, j represents an imaginary number, represents the angular frequency of the frequency shift control signal generated by the direct digital synthesizer, p represents the position of the local oscillator comb teeth, represents the output RF angular frequency of the first RF source and the second RF source, represents the continuous light angular frequency;

[0041] The second dual parallel Mach-Zehnder modulator loads a signal on the carrier comb teeth to obtain a modulated signal, including:

[0042] The modulation signal is expressed as:

[0043] ;

[0044] in, represents the modulation signal, and Respectively represent the amplitude and phase of the carrier comb, j represents an imaginary number, represents the input signal carrier angular frequency, q represents the carrier comb teeth, represents the output RF angular frequency of the third RF source and the fourth RF source, Represents the continuous light angular frequency.

[0045] As an optional technical solution of the present invention, the second coupler combines the frequency-shifted local oscillator signal and the modulated signal to obtain a combined signal, and the erbium-doped fiber amplifier amplifies the combined signal and obtains a frequency-converted signal by beating the optical detector, including:

[0046] The combined signal is expressed as:

[0047] ;

[0048] in, Indicates the combined signal;

[0049] The frequency of the frequency conversion signal obtained by the beat frequency of the photodetector is expressed as:

[0050] ;

[0051] in, represents the frequency of the frequency conversion signal, and n represents the number of the local oscillator optical frequency comb. Root comb teeth, represents the output RF frequencies of the third RF source and the fourth RF source, represents the input signal frequency, represents the frequency of the frequency shift control signal generated by the direct digital synthesizer, Indicates the output RF frequencies of the first RF source and the second RF source.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] A microwave photon frequency conversion system provided by the present invention realizes frequency conversion through a signal generating module, a channel switching module and a signal processing module, which can greatly reduce the volume and complexity of the system; large-span frequency conversion is realized through the channel switching module, and fine frequency conversion is realized through a first dual parallel Mach-Zehnder modulator, thereby realizing large-span and high-fine frequency conversion of ultra-wideband signals; output of different frequency schemes is realized by changing the optical switch control signal, without modifying the hardware parameters, and the frequency conversion range is tunable, which has good reconstructibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a structural diagram of a microwave photon frequency conversion system in an embodiment of the present invention;

[0055] Figure 2 is a schematic diagram of frequency selection in an embodiment of the present invention;

[0056] Figure 3 is an optical frequency comb spectrum diagram in an embodiment of the present invention;

[0057] Figure 4 is a spectrum diagram of a modulated signal and a combined signal in an embodiment of the present invention;

[0058] Figure 5 is a spectrum diagram of a frequency-converted signal in an embodiment of the present invention;

[0059] Figure 6 is a constellation diagram of a frequency conversion signal in an embodiment of the present invention;

[0060] Figure 7 is a test diagram of a frequency-shifted and frequency-converted signal in an embodiment of the present invention;

[0061] Figure 8 4 is a spectrum diagram of a signal after fine frequency shift in an embodiment of the present invention.

[0062] The markings in the figure are: 1. continuous light laser; 2. first coupler; 3. first radio frequency source; 4. second radio frequency source; 5. third radio frequency source; 6. fourth radio frequency source; 7. first dual-port Mach-Zehnder modulator; 8. second dual-port Mach-Zehnder modulator; 9. third dual-port Mach-Zehnder modulator; 10. fourth dual-port Mach-Zehnder modulator; 11. first wave demultiplexer; 12. second wave demultiplexer; 13. first optical switch; 14. second optical switch; 15. first dual parallel Mach-Zehnder modulator; 16. second dual parallel Mach-Zehnder modulator; 17. second coupler; 18. erbium-doped fiber amplifier; 19. optical detector; 20. signal generator; 21. direct digital synthesizer. DETAILED DESCRIPTION

[0063] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0064] Example 1

[0065] This embodiment provides a microwave photon frequency conversion system. Figure 1 As shown, it includes a signal generating module, a channel switching module and a signal processing module connected in sequence.

[0066] The signal generating module comprises a continuous light laser 1, a first coupler 2, a signal generating upper branch and a signal generating lower branch; the input end of the first coupler 2 is connected to the continuous light laser 1, and the laser light generated by the continuous light laser 1 is divided into two paths, which are respectively input into the signal generating upper branch and the signal generating lower branch; the signal generating upper branch outputs a local oscillator optical frequency comb, and the signal generating lower branch outputs a carrier optical frequency comb.

[0067] The signal generation upper branch includes a first radio frequency source 3, a second radio frequency source 4, and a first dual-port Mach-Zehnder modulator 7 and a second dual-port Mach-Zehnder modulator 8 connected thereto; the signal generation lower branch includes a third radio frequency source 5, a fourth radio frequency source 6, and a third dual-port Mach-Zehnder modulator 9 and a fourth dual-port Mach-Zehnder modulator 10 connected thereto. The first radio frequency source 3 is connected to the upper input ends of the first dual-port Mach-Zehnder modulator 7 and the second dual-port Mach-Zehnder modulator 8, respectively, and the second radio frequency source 4 is connected to the lower input ends of the first dual-port Mach-Zehnder modulator 7 and the second dual-port Mach-Zehnder modulator 8, respectively. The third radio frequency source 5 is connected to the upper input ends of the third dual-port Mach-Zehnder modulator 9 and the fourth dual-port Mach-Zehnder modulator 10, respectively, and the fourth radio frequency source 6 is connected to the lower input ends of the third dual-port Mach-Zehnder modulator 9 and the fourth dual-port Mach-Zehnder modulator 10, respectively.

[0068] The channel switching module includes a channel switching upper branch and a channel switching lower branch, and the channel switching upper branch and the channel switching lower branch both include a wavelength division multiplexer and an optical switch. The input end of the wavelength division multiplexer is connected to the signal generation upper branch or the signal generation lower branch, and the output end is connected to the optical switch, which is used to separate the local oscillator optical frequency comb or the carrier optical frequency comb into a plurality of comb teeth and input them into the optical switch; the optical switch selects the comb teeth for output to obtain the local oscillator comb teeth or the carrier comb teeth.

[0069] Furthermore, the channel switching module further includes a signal generator 20; the signal generator 20 is respectively connected to the optical switches in the channel switching upper branch and the channel switching lower branch, and inputs a comb selection control signal to the optical switch.

[0070] Furthermore, the channel switching upper branch includes a first wavelength division multiplexer 11 and a first optical switch 13 , and the channel switching lower branch includes a second wavelength division multiplexer 12 and a second optical switch 14 .

[0071] The signal processing module includes a first dual-parallel Mach-Zehnder modulator 15, a second dual-parallel Mach-Zehnder modulator 16, a second coupler 17, an erbium-doped fiber amplifier 18 and a photodetector 19; the input end of the first dual-parallel Mach-Zehnder modulator 15 is connected to an optical switch to shift the frequency of the local oscillator comb teeth; the input end of the second dual-parallel Mach-Zehnder modulator 16 is connected to an optical switch to load a signal on the carrier comb teeth; the output ends of the first dual-parallel Mach-Zehnder modulator 15 and the second dual-parallel Mach-Zehnder modulator 16 are both connected to the second coupler 17, the second coupler 17, the erbium-doped fiber amplifier 18 and the photodetector 19 are connected in sequence, and the photodetector 19 outputs a frequency conversion signal.

[0072] Furthermore, the signal processing module further comprises a direct digital synthesizer 21 ; the direct digital synthesizer 21 is connected to the first dual parallel Mach-Zehnder modulator 15 , and inputs a frequency shift control signal to the first dual parallel Mach-Zehnder modulator 15 .

[0073] Furthermore, the input end of the first dual parallel Mach-Zehnder modulator 15 is connected to the first optical switch 13 in the channel switching upper branch, and the input end of the second dual parallel Mach-Zehnder modulator 16 is connected to the second optical switch 14 in the channel switching lower branch.

[0074] Example 2

[0075] Based on Example 1, this embodiment provides a microwave photon frequency conversion method to achieve wide-span frequency conversion of broadband signals, with a frequency conversion frequency of more than 70 GHz, covering C, Ku, and K bands, and up to the EHF band, and supports high-precision tuning of the frequency conversion signal, with extremely strong flexibility, and has certain application potential in many fields such as wireless communications, radar systems, phased array antennas, and electronic warfare. It includes the following steps:

[0076] Step 1: The first coupler 2 divides the laser light emitted by the continuous light laser 1 into two paths, and inputs the signal generating upper branch and the signal generating lower branch respectively. The signal generating upper branch outputs a local oscillator optical frequency comb, and the signal generating lower branch outputs a carrier optical frequency comb.

[0077] Specifically, the laser emitted by the continuous light laser 1 is expressed as:

[0078] ;

[0079] in, Represents the output light source, represents the amplitude of the input optical signal, represents the continuous light angular frequency, j represents an imaginary number, represents the natural exponential function, and t represents the time variable.

[0080] The lasers of the upper branch for input signal generation and the lower branch for signal generation are expressed as:

[0081] ;

[0082] ;

[0083] in, Indicates that the input signal generates the laser of the upper branch, Indicates the input signal produces the laser in the lower branch.

[0084] The laser that generates the upper branch of the signal The signal is input into the first two-port Mach-Zehnder modulator 7, and the laser of the lower branch is generated. The output signal is input into the third two-port Mach-Zehnder modulator 9.

[0085] In this embodiment, the above branch is taken as an example to illustrate the first RF source 3, the second RF source 4 and the first dual-port Mach-Zehnder modulator 7 and the second dual-port Mach-Zehnder modulator 8 connected to the laser. The process of generating the local oscillator frequency comb by processing. The details are as follows:

[0086] The first RF source 3 and the second RF source 4 send RF signals to the first dual-port Mach-Zehnder modulator 7 and the second dual-port Mach-Zehnder modulator 8, which are respectively expressed as:

[0087] ;

[0088] ;

[0089] in, represents the radio frequency signal of the first radio frequency source 3, represents the amplitude of the radio frequency signal of the first radio frequency source 3, represents the output RF angular frequency of the first RF source 3 and the second RF source 4, represents the phase of the radio frequency signal of the first radio frequency source 3, represents the radio frequency signal of the second radio frequency source 4, represents the amplitude of the radio frequency signal of the second radio frequency source 4, Indicates the phase of the radio frequency signal of the second radio frequency source 4.

[0090] The output signal of the first dual-port Mach-Zehnder modulator 7 is expressed as:

[0091] ;

[0092] in, represents the output signal of the first two-port Mach-Zehnder modulator 7, represents the half-wave voltage of the first two-port Mach-Zehnder modulator.

[0093] The phase difference between the upper and lower arms of the first dual-port Mach-Zehnder modulator 7 and the second dual-port Mach-Zehnder modulator 8 is set to , the first RF source 3 and the second RF source 4 have the same frequency phase, and the amplitude difference is , at this time, the output signal of the first dual-port Mach-Zehnder modulator 7 is further simplified as:

[0094] ;

[0095] in, represents the simplified output signal, i represents the i-th comb tooth of the optical frequency comb output by the first dual-port Mach-Zehnder modulator 7, represents the Bessel function.

[0096] It can be seen from the expression that the signal output by the first dual-port Mach-Zehnder modulator 7 has multiple sidebands. When the amplitudes of the sidebands are not much different, an optical frequency comb is generated.

[0097] The function of the second dual-port Mach-Zehnder modulator 8 is the same as that of the first dual-port Mach-Zehnder modulator 7. The quality of the generated optical frequency comb is improved by cascading, and the local oscillator optical frequency comb is further simplified, which is expressed as:

[0098] ;

[0099] in, represents the local oscillator frequency comb, and They represent the local oscillator frequency comb The amplitude and phase of the root comb teeth, Indicates The angular frequency of the root comb teeth, M represents the number of comb teeth on both sides of the center frequency selected by the local oscillator optical frequency comb, which is a positive integer.

[0100] In the signal generation lower branch, the phase difference between the upper and lower arms of the third dual-port Mach-Zehnder modulator 9 and the fourth dual-port Mach-Zehnder modulator 10 is set to , the frequency phase of the third RF source 5 and the fourth RF source 6 is the same, and the amplitude difference is , represents the modulator half-wave voltage, then the carrier optical frequency comb output by the signal generation branch is expressed as:

[0101] ;

[0102] in, represents the carrier optical frequency comb, and represent the amplitude and phase of the kth tooth of the carrier optical frequency comb, respectively. represents the angular frequency of the kth comb tooth, K represents the number of comb teeth on both sides of the center frequency selected by the carrier optical frequency comb, and is a positive integer.

[0103] When the k value is positive, it means that the frequency in the local oscillator optical frequency comb and the carrier optical frequency comb is higher than the seed frequency. or root comb teeth; similarly, When the k value is negative, it means that the frequency of the local oscillator optical frequency comb and the carrier optical frequency comb is lower than the seed frequency. or Root comb teeth. and Further expressed as:

[0104] ;

[0105] .

[0106] The tooth spacings of the local oscillator optical frequency comb and the carrier optical frequency comb are controlled by the first RF source 3, the second RF source 4, the third RF source 5, and the fourth RF source 6, respectively. and .

[0107] Step 2: The wavelength division multiplexer in the upper branch of the channel switching separates the local oscillator optical frequency comb into a plurality of comb teeth and inputs the comb teeth into the optical switch, and the optical switch selects the comb teeth for output to obtain the local oscillator comb teeth; the wavelength division multiplexer in the lower branch of the channel switching separates the carrier optical frequency comb into a plurality of comb teeth and inputs the comb teeth into the optical switch, and the optical switch selects the comb teeth for output to obtain the carrier comb teeth.

[0108] In this embodiment, the local oscillator optical frequency comb is input to the first wavelet demultiplexer 11, and the carrier optical frequency comb is input to the second wavelet demultiplexer 12. The first wavelet demultiplexer 11 and the second wavelet demultiplexer 12 use 1×13 wavelet demultiplexers to separate the comb teeth into 13 frequency channels. The channel spacing and center frequency of the first wavelet demultiplexer 11 and the second wavelet demultiplexer 12 correspond to the comb tooth spacing and comb tooth frequency of the local oscillator optical frequency comb and the carrier optical frequency comb, respectively.

[0109] The 13 channels outputted by the first WDM 11 and the second WDM 12 are inputted into the first optical switch 13 and the second optical switch 14 in a one-to-one correspondence. The first optical switch 13 and the second optical switch 14 adopt 13×1 optical switches, and the positions of the local oscillator comb teeth and the carrier comb teeth outputted from the same output port differ by 1. Both optical switches are controlled by the comb teeth selection control signal outputted by the signal generator 20. In this embodiment, Figure 2 As shown, when the signal generator 20 outputs a signal of n, the first optical switch 13 selects to output the nth fundamental oscillation comb tooth, with a frequency of , then the second optical switch 14 outputs the n+1th carrier comb tooth, with a frequency of .

[0110] Step three: the first dual parallel Mach-Zehnder modulator 15 performs frequency shifting on the local oscillator comb teeth to obtain a frequency shifted local oscillator signal; the second dual parallel Mach-Zehnder modulator 16 performs a load signal on the carrier comb teeth to obtain a modulated signal.

[0111] The first dual parallel Mach-Zehnder modulator 15 performs frequency shifting on the local oscillator comb teeth, and the modulation format is carrier suppressed single sideband modulation to obtain a frequency shifted local oscillator signal. The local oscillator frequency after frequency shift is The frequency-shifted local oscillator signal is expressed as:

[0112] ;

[0113] in, represents the frequency-shifted local oscillator signal, and They represent the amplitude and phase of the local oscillator comb teeth respectively, j represents an imaginary number, represents the angular frequency of the frequency shift control signal generated by the direct digital synthesizer 21, p represents the position of the local oscillator comb teeth, represents the output RF angular frequency of the first RF source 3 and the second RF source 4, Represents the continuous light angular frequency.

[0114] The second dual parallel Mach-Zehnder modulator 16 loads the carrier comb teeth with a signal, and modulates the loaded signal by carrier suppressed single sideband modulation to obtain a modulated signal. The input signal frequency is , then the output frequency of the second dual parallel Mach-Zehnder modulator 16 is .

[0115] The modulation signal is expressed as:

[0116] ;

[0117] in, represents the modulation signal, and Respectively represent the amplitude and phase of the carrier comb, j represents an imaginary number, represents the input signal carrier angular frequency, q represents the carrier comb position, represents the output RF angular frequency of the third RF source 5 and the fourth RF source 6, Represents the continuous light angular frequency.

[0118] Step 4: The second coupler 17 combines the frequency-shifted local oscillator signal and the modulated signal to obtain a combined signal, the erbium-doped fiber amplifier 18 amplifies the combined signal, and the photodetector 19 beats the combined signal to obtain a frequency-converted signal.

[0119] The combined signal is expressed as:

[0120] ;

[0121] in, Indicates the combined signal.

[0122] After being amplified by the erbium-doped fiber amplifier 18, the frequency-converted microwave signal is obtained by heterodyning the photodetector 19 and is expressed as:

[0123] ;

[0124] in, represents the photocurrent signal output by the photodetector 19, represents the current response of the photodetector, and G represents the gain coefficient of the erbium-doped fiber amplifier.

[0125] The output microwave signal frequency is expressed as:

[0126]

[0127] in, Indicates the frequency of the variable frequency signal. is the carrier comb position, is the position of the local oscillator comb teeth. represents the output RF frequency of the third RF source 5 and the fourth RF source 6, represents the input signal frequency, represents the frequency of the frequency shift control signal generated by the direct digital synthesizer 21, Represents the output RF frequencies of the first RF source 3 and the second RF source 4.

[0128] In this embodiment, the signal generator outputs a signal of n, the first optical switch 13 selects to output the nth root oscillator comb tooth, and the second optical switch 14 outputs the n+1th carrier comb tooth, that is, , then the frequency of the frequency conversion signal obtained by the beat frequency of the light detector 19 is further expressed as:

[0129] ;

[0130] in, represents the frequency of the frequency conversion signal, and n represents the number of the local oscillator optical frequency comb. Root comb teeth, represents the output RF frequency of the third RF source 5 and the fourth RF source 6, represents the input signal frequency, represents the frequency of the frequency shift control signal generated by the direct digital synthesizer 21, Represents the output RF frequencies of the first RF source 3 and the second RF source 4.

[0131] Example 3

[0132] In this embodiment, the Optisystem 15.0 simulation software is used to set up a frequency conversion system simulation platform according to the parameter settings shown in Table 1.

[0133] Table 1 Frequency conversion system parameters

[0134] Parameter / Unit value Parameter / Unit value Laser frequency / THz 193.1 Laser line width / MHz 10 Laser power / dBm 0 Photodetector responsivity / (A·W-1) 1 Optical amplifier gain / dB 20 Input signal frequency / GHz 5 Optical amplifier noise figure / dB 4 Input optical signal amplitude / mA 200 First wave demultiplexer channel spacing / GHz 25 RF1 signal source frequency / GHz 25 Second wave demultiplexer channel spacing / GHz 30 RF2 signal source frequency / GHz 30

[0135] According to the frequency conversion method described in Example 2, the spectrum diagrams of the local oscillator optical frequency comb and the carrier optical frequency comb obtained by the simulation platform are as follows: Figure 3 shown. Figure 3 (a) is the local oscillator frequency comb, Figure 3(b) is the carrier optical frequency comb. As can be seen from the figure, the optical frequency comb generated by this scheme has clear teeth and a large coverage range. Within the 1.5 dB fluctuation range, 16 and 18 optical frequency combs can be reached respectively, and the power is greater than -20 dBm. According to the principle of the invention, only 13 comb teeth are needed to achieve a frequency conversion range from 10 GHz to a maximum of 70 GHz, so the optical frequency comb generated by this method can meet the requirements of this system.

[0136] The upper branch local oscillator frequency shift is set to 0 Hz, and the lower branch signal is input into the dual parallel Mach-Zehnder modulator. By adjusting the modulator bias point and the phase shift of the phase shifter, the signal carrier suppressed single sideband modulation is realized. The spectrum of the modulated signal and the combined signal is shown in the figure below. Figure 4 shown.

[0137] from Figure 4 It can be seen from (a) that after modulation, the right sideband is retained and the carrier suppression ratio reaches 36.7dB. Figure 4 (b) is the spectrum of the comb teeth selected by the upper branch and the comb teeth modulated by the lower branch after the combination, with a resolution of 1 KHz. Then, the combined signal is amplified by the erbium-doped fiber amplifier and input into the photodetector to obtain the frequency conversion signal.

[0138] To verify the frequency conversion range of the system, this embodiment implements the frequency conversion of 3 GHz and 5 GHz RF signals through simulation, as shown in FIG. Figure 5 As shown in (a)(d) in the figure. The simulation results show that when the input signal carrier is 3 GHz, the system can obtain 13 frequency signals with an interval of 5 GHz from 8 to 68 GHz by frequency conversion output; when the input signal carrier is 5 GHz, the system output is 13 frequency signals with an interval of 5 GHz from 10 to 70 GHz. At a resolution of 1 KHz, the signal-to-noise ratio after frequency conversion is greater than 50.6 dB and 49.7 dB, respectively, and the power fluctuations are 2.14 dB and 2 dB, respectively. Among them, the main reason for the fluctuation of the frequency conversion signal power at each frequency is the difference in the comb tooth power of the optical frequency comb as the carrier and the local oscillator source. This problem can be solved by further improving the quality of the optical frequency comb. In addition, although in Figure 5 In (d), it can be seen that some spurious frequencies overlap with the converted signal. However, the outputs of different frequencies of the system are separated from each other by demultiplexers and optical switches, so they do not actually cause interference.

[0139] In order to further verify the frequency conversion performance of the system, this embodiment realizes the frequency conversion of 3 GHz 512MSym / s QPSK and 5 GHz 512MSym / s QPSK signals through simulation. The original signal spectrum is shown in Figure 5(b)(e) shows that the signal spectrum obtained after frequency conversion is as follows Figure 5 As shown in (c) and (f), the signal-to-noise ratio of the QPSK signal after frequency conversion is greater than 31.2 dB and 30.6 dB, respectively. Due to the modulation of the broadband signal, the power fluctuation of each frequency output is degraded to a certain extent, and the fluctuation range is 3.19 dB and 4.59 dB, respectively.

[0140] In addition, in order to test the quality of the signal after frequency conversion in the system, this embodiment realizes the frequency conversion of 5 GHz 512MSym / s QPSK to 70 GHz through simulation, and its constellation diagram is as follows: Figure 6 As shown in (a), the error vector size is 6.970% (<17.50%); the 5GHz 300 MSym / s 8PSK signal is frequency-converted to 70 GHz, and the constellation diagram is as follows: Figure 6 As shown in (b), the error vector size is 7.509%; the 5 GHz 200 MSym / s 16QAM signal is frequency-converted to 70 GHz, and the constellation diagram is as follows: Figure 6 As shown in (c), the error vector size is 9.619% (<12.50%). The results show that the signal quality after frequency conversion meets the requirements of satellite communications, radar systems and other fields.

[0141] This embodiment tests the frequency shift effect of the system. The test results are as follows: Figure 7 As shown in the figure. Since the frequency shift method is carrier suppressed single sideband modulation, only the +1 order sideband of the signal is retained. Therefore, by changing the frequency of the input RF signal, the output signal can be controlled to shift to a low frequency. When the input signal is a 5 GHz RF signal, the frequency of the frequency shift signal is set to 100 MHz to 500 MHz, and the signal spectrum after frequency shift is shown in the figure below. Figure 7 (a) shows that the horizontal axis is the frequency offset, and the zero point of the coordinate corresponds to 70 GHz. Changing the input signal to a 512 MSym / s QPSK signal, the magnitude of the signal error vector after frequency shift is as follows: Figure 7 As shown in (b), it can be seen that the error vector magnitude of the signal after frequency shift is slightly degraded, but the overall change is not significant. In addition, this embodiment tests the error vector magnitudes of 13 frequencies of the QPSK signal after frequency conversion, as shown in FIG. Figure 7 As shown in (c), it can be seen that the signal error vector magnitude after frequency conversion fluctuates within 0.3%, which has good consistency.

[0142] This embodiment tests the fine frequency tuning capability of the system. The input signal is a 5 GHz RF signal, and the input frequency shift control signal frequency is set to 1MHz, 5MHz, 10MHz, 20MHz, and 50MHz respectively. The signal spectrum after frequency shift is as follows: Figure 8As shown. The 70GHz frequency conversion channel is still selected here. The horizontal axis in the figure is the frequency offset, and the zero point of the coordinate corresponds to 70 GHz. The final signal frequency shifts are 1.0070 MHz, 5.0048 MHz, 10.0097 MHz, 20.0195MHz and 50.0488 MHz, respectively. The frequency shift errors are all within 50 KHz, with high-precision frequency tuning capabilities. It is worth mentioning that due to the limitations of the simulation software, the highest accuracy tested in this article is 1MHz. According to the system principle, the minimum tuning accuracy can be less than 1MHz, and in practice it depends on the tuning accuracy of the RF source.

[0143] The frequency conversion range of the traditional microwave photonic frequency conversion system is mainly determined by the frequency of the RF signal input to the system. If the RF frequency is fixed, the frequency point obtained by the frequency conversion is also fixed. However, the tuning accuracy is poor when the RF signal frequency is directly changed. Especially at higher frequencies, the frequency shift of the RF signal after the frequency conversion will increase exponentially, often in the tens of megahertz. For example, if the RF source frequency in this system increases by 10MHz, the final frequency shift of the 70GHz signal after the frequency conversion is 130MHz. Here, the high-precision tuning proposed in this scheme refers to more fine tuning of the signal frequency after the frequency conversion. The frequency shift control signal of this system is a low-frequency electrical signal with low cost and mature technology. The frequency accuracy of current commercial devices can reach 0.1Hz, so high-precision frequency control can be achieved.

[0144] In the frequency conversion method proposed in Example 2, the spacing of the optical frequency comb teeth is controlled by the RF source, and the frequency shift of the local oscillator comb teeth is regulated by the RF signal output by the direct digital synthesizer. Therefore, the stability and tuning accuracy of the RF source will directly determine the tuning accuracy of this system. In addition, in order to achieve a better frequency shift effect and reduce the generation of spurious frequencies, the frequency shift control signal is input into a dual parallel Mach-Zehnder modulator for carrier suppressed single sideband modulation to achieve frequency shifting of the frequency conversion signal.

[0145] The simulation results show that the invented system has the ability to convert frequencies over a large span from 10 GHz to a maximum of 70 GHz, and can perform fine frequency tuning. The signal quality after frequency conversion meets the requirements of fields such as communications electronic warfare, satellite communications, and radar systems, and can meet the needs of large bandwidth, large span, and high-precision frequency conversion in many current fields.

[0146] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0147] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0148] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0149] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0150] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A microwave photon frequency conversion system, characterized in that: It includes a signal generating module, a channel switching module and a signal processing module connected in sequence; The signal generating module comprises a continuous light laser (1), a first coupler (2), a signal generating upper branch and a signal generating lower branch; the input end of the first coupler (2) is connected to the continuous light laser (1), and the laser light generated by the continuous light laser (1) is divided into two paths, which are respectively input into the signal generating upper branch and the signal generating lower branch; the signal generating upper branch outputs a local oscillator optical frequency comb, and the signal generating lower branch outputs a carrier optical frequency comb; The channel switching module comprises a channel switching upper branch and a channel switching lower branch, both of which comprise a wavelength division multiplexer and an optical switch, wherein the input end of the wavelength division multiplexer is connected to the signal generation upper branch or the signal generation lower branch, and the output end is connected to the optical switch, so as to separate the local oscillator optical frequency comb or the carrier optical frequency comb into a plurality of comb teeth and input the comb teeth into the optical switch; the optical switch selects the comb teeth for output, and obtains the local oscillator comb teeth or the carrier comb teeth; The signal processing module comprises a first dual-parallel Mach-Zehnder modulator (15), a second dual-parallel Mach-Zehnder modulator (16), a second coupler (17), an erbium-doped fiber amplifier (18) and a light detector (19); the input end of the first dual-parallel Mach-Zehnder modulator (15) is connected to an optical switch to perform frequency shifting on the local oscillator comb teeth; the input end of the second dual-parallel Mach-Zehnder modulator (16) is connected to an optical switch to load a signal on the carrier comb teeth; the output ends of the first dual-parallel Mach-Zehnder modulator (15) and the second dual-parallel Mach-Zehnder modulator (16) are both connected to the second coupler (17); the second coupler (17), the erbium-doped fiber amplifier (18) and the light detector (19) are connected in sequence; and the light detector (19) outputs a frequency-converted signal.

2. The microwave photon frequency conversion system according to claim 1, characterized in that: The signal generation upper branch comprises a first radio frequency source (3), a second radio frequency source (4), and a first dual-port Mach-Zehnder modulator (7) and a second dual-port Mach-Zehnder modulator (8) connected thereto; The signal generation lower branch comprises a third radio frequency source (5), a fourth radio frequency source (6), and a third dual-port Mach-Zehnder modulator (9) and a fourth dual-port Mach-Zehnder modulator (10) connected thereto; The first radio frequency source (3) is connected to the upper input ends of the first dual-port Mach-Zehnder modulator (7) and the second dual-port Mach-Zehnder modulator (8), respectively; and the second radio frequency source (4) is connected to the lower input ends of the first dual-port Mach-Zehnder modulator (7) and the second dual-port Mach-Zehnder modulator (8), respectively; The third radio frequency source (5) is connected to the upper input ends of the third dual-port Mach-Zehnder modulator (9) and the fourth dual-port Mach-Zehnder modulator (10), respectively, and the fourth radio frequency source (6) is connected to the lower input ends of the third dual-port Mach-Zehnder modulator (9) and the fourth dual-port Mach-Zehnder modulator (10), respectively.

3. The microwave photon frequency conversion system according to claim 1, characterized in that: The channel switching module also includes a signal generator (20); The signal generator (20) is respectively connected to the optical switches in the channel switching upper branch and the channel switching lower branch, and inputs a comb selection control signal to the optical switches.

4. The microwave photon frequency conversion system according to claim 1, characterized in that: The signal processing module also includes a direct digital synthesizer (21); The direct digital synthesizer (21) is connected to the first dual parallel Mach-Zehnder modulator (15) and inputs a frequency shift control signal to the first dual parallel Mach-Zehnder modulator (15).

5. The microwave photon frequency conversion system according to claim 1, characterized in that: The input end of the first dual parallel Mach-Zehnder modulator (15) is connected to the optical switch in the channel switching upper branch, and the input end of the second dual parallel Mach-Zehnder modulator (16) is connected to the optical switch in the channel switching lower branch.

6. A microwave photon frequency conversion method based on the microwave photon frequency conversion system according to any one of claims 1 to 5, characterized in that: include: The first coupler (2) divides the laser light emitted by the continuous light laser (1) into two paths, and respectively inputs the laser light into a signal generation upper branch and a signal generation lower branch, wherein the signal generation upper branch outputs a local oscillator optical frequency comb, and the signal generation lower branch outputs a carrier optical frequency comb; The wavelength division multiplexer in the channel switching upper branch separates the local oscillator optical frequency comb into a plurality of comb teeth and inputs the comb teeth into the optical switch, and the optical switch selects the comb teeth for output to obtain the local oscillator comb teeth; the wavelength division multiplexer in the channel switching lower branch separates the carrier optical frequency comb into a plurality of comb teeth and inputs the comb teeth into the optical switch, and the optical switch selects the comb teeth for output to obtain the carrier comb teeth; The first dual parallel Mach-Zehnder modulator (15) performs frequency shifting on the local oscillator comb teeth to obtain a frequency shifted local oscillator signal; the second dual parallel Mach-Zehnder modulator (16) performs a load signal on the carrier comb teeth to obtain a modulated signal; The second coupler (17) combines the frequency-shifted local oscillator signal and the modulated signal to obtain a combined signal, and the erbium-doped fiber amplifier (18) amplifies the combined signal, which is then beat by the optical detector (19) to obtain a frequency-converted signal.

7. The microwave photon frequency conversion method according to claim 6, characterized in that: The first coupler (2) divides the laser light emitted by the continuous light laser (1) into two paths, and inputs the two paths into a signal generation upper branch and a signal generation lower branch respectively, comprising: The laser light emitted by the continuous light laser (1) is expressed as: ； in, Represents the output light source, represents the amplitude of the input optical signal, represents the continuous light angular frequency, j represents an imaginary number, represents the natural exponential function, t represents the time variable; The lasers of the upper branch for input signal generation and the lower branch for signal generation are expressed as: ； ； in, Indicates that the input signal generates the laser of the upper branch, Indicates the input signal produces the laser in the lower branch.

8. The microwave photon frequency conversion method according to claim 7, characterized in that: The signal generation upper branch comprises a first radio frequency source (3), a second radio frequency source (4), and a first dual-port Mach-Zehnder modulator (7) and a second dual-port Mach-Zehnder modulator (8) connected thereto; The phase difference between the upper and lower arms of the first dual-port Mach-Zehnder modulator (7) and the second dual-port Mach-Zehnder modulator (8) is , the first RF source (3) and the second RF source (4) have the same frequency phase, and the amplitude difference is , represents the modulator half-wave voltage, then the local oscillator optical frequency comb output by the upper branch of the signal generation is expressed as: ； in, represents the local oscillator frequency comb, and They represent the local oscillator frequency comb The amplitude and phase of the root comb teeth, Indicates The angular frequency of the root comb teeth, M represents the number of comb teeth on both sides of the center frequency selected by the local oscillator optical frequency comb, which is a positive integer; The signal generation lower branch comprises a third radio frequency source (5), a fourth radio frequency source (6), and a third dual-port Mach-Zehnder modulator (9) and a fourth dual-port Mach-Zehnder modulator (10) connected thereto; The phase difference between the upper and lower arms of the third dual-port Mach-Zehnder modulator (9) and the fourth dual-port Mach-Zehnder modulator (10) is , the frequency phase of the third RF source (5) and the fourth RF source (6) is the same, and the amplitude difference is , represents the modulator half-wave voltage, then the output carrier optical frequency comb of the signal generation branch is expressed as: ； in, represents the carrier optical frequency comb, and represent the amplitude and phase of the kth tooth of the carrier optical frequency comb, respectively. represents the angular frequency of the kth comb tooth, K represents the number of comb teeth on both sides of the center frequency selected by the carrier optical frequency comb, and is a positive integer.

9. The microwave photon frequency conversion method according to claim 7, characterized in that: The first dual parallel Mach-Zehnder modulator (15) performs frequency shifting on the local oscillator comb teeth to obtain a frequency shifted local oscillator signal, including: The frequency-shifted local oscillator signal is expressed as: ； in, represents the frequency-shifted local oscillator signal, and They represent the amplitude and phase of the local oscillator comb teeth respectively, j represents an imaginary number, represents the angular frequency of the frequency shift control signal generated by the direct digital synthesizer (21), p represents the position of the local oscillator comb teeth, represents the output radio frequency angular frequency of the first radio frequency source (3) and the second radio frequency source (4), represents the continuous light angular frequency; The second dual parallel Mach-Zehnder modulator (16) loads a signal on the carrier comb teeth to obtain a modulated signal, including: The modulation signal is expressed as: ； in, represents the modulation signal, and Respectively represent the amplitude and phase of the carrier comb, j represents an imaginary number, represents the input signal carrier angular frequency, q represents the carrier comb teeth, represents the output radio frequency angular frequency of the third radio frequency source (5) and the fourth radio frequency source (6), Represents the continuous light angular frequency.

10. The microwave photon frequency conversion method according to claim 9, characterized in that: The second coupler (17) combines the frequency-shifted local oscillator signal and the modulated signal to obtain a combined signal, the erbium-doped fiber amplifier (18) amplifies the combined signal, and then beats the combined signal with the optical detector (19) to obtain a frequency conversion signal, including: The combined signal is expressed as: ； in, Indicates the combined signal; The frequency of the frequency conversion signal obtained by the beat frequency of the light detector (19) is expressed as: ； in, represents the frequency of the frequency conversion signal, and n represents the number of the local oscillator optical frequency comb. Root comb teeth, represents the output radio frequency frequencies of the third radio frequency source (5) and the fourth radio frequency source (6), represents the input signal frequency, represents the frequency of the frequency shift control signal generated by the direct digital synthesizer (21), Indicates the output radio frequency frequencies of the first radio frequency source (3) and the second radio frequency source (4).

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