CN110535533B - Microwave photon orthogonal demodulation method and system based on time division multiplexing - Google Patents
Microwave photon orthogonal demodulation method and system based on time division multiplexing Download PDFInfo
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Abstract
The invention discloses a microwave photon orthogonal demodulation method and a system based on time division multiplexing, belonging to the technical field of microwave signal processing and comprising the following steps: s1: performing orthogonal down-conversion on the radio frequency signal and the local oscillator signal; s2: combining two paths of orthogonal medium frequency optical signals into one path; s3: converting the optical signal into a digital signal; s4: a digital baseband signal is obtained. The invention combines the demodulated I, Q optical signals into a path of optical signal through optical delay combination to carry out photoelectric conversion, filtering amplification and analog-to-digital conversion, and carries out shunting and delay alignment on the I, Q signal combined into a path in a digital domain; by windowing the input signals, the phenomenon that I, Q two paths of signals generate time domain overlapping mutual interference when combined into one path is avoided; for the requirement of continuous signal processing, the method is realized by dividing a plurality of time windows, respectively receiving the signals on a plurality of receiving channels and then performing digital time domain splicing, and I, Q imbalance of broadband signal quadrature demodulation is suppressed.
Description
Technical Field
The invention relates to the technical field of microwave signal processing, in particular to a microwave photon orthogonal demodulation method and a microwave photon orthogonal demodulation system based on time division multiplexing.
Background
With the development of electronic information technology, signal frequency bands are wider and wider. Meanwhile, in order to simplify the system design, it is desirable to perform uniform intermediate frequency digital signal processing on signals of each frequency band. The broadband receiver is used as a front-end device for acquiring information, the demand is more and more strong, the requirements on technical indexes and environmental adaptability are higher and higher, and the performance of the receiver plays an important role in information acquisition.
The traditional radio frequency signal receiver for realizing the ultra-wideband based on a pure microwave mode is limited by the performance limitations of devices such as a frequency converter, an ADC (analog-to-digital converter), a DAC (digital-to-analog converter) and the like, and needs to be realized by adopting a mode of segmented repeated frequency conversion or segmented analog quadrature modulation and demodulation, and the defects are that an analog receiving and transmitting channel is relatively complex, and indexes in a frequency band are not easy to guarantee. The method combines the microwave photon technology, adopts the optical orthogonal demodulation, realizes the analog demodulation of the broadband microwave signal by the photon technology, can realize the orthogonal demodulation of the ultra-wideband by utilizing the advantage of larger optical information processing bandwidth, and has important significance for the systems relating to the broadband microwave signal processing, such as radars, and the like.
The current microwave photon orthogonal demodulation technology research mainly focuses on realizing orthogonal down-conversion of a broadband radio frequency input signal and a local oscillator signal on an optical carrier frequency and outputting two paths of orthogonal intermediate frequency signals. However, the two orthogonal intermediate frequency signals obtained by the microwave photonic quadrature demodulation technology still need to be collected and converted into digital signals by two ADCs, and usually, a filter and a low-noise amplifier need to be introduced in front of the ADC in order to match the input signal strength of the ADC and filter out the out-of-band spurious signals. Therefore, although the microwave photonic quadrature demodulation technology is adopted to obtain the intermediate frequency signal with high orthogonality, for the whole digital receiving system, the orthogonality of the finally obtained digital I, Q signal will be reduced due to the difference of the amplitude-phase consistency of the ADC chip in the I, Q two-path receiving channel, the amplifier before the ADC chip and the filter. Even with microwave photonic quadrature demodulation techniques, the I, Q amplitude-phase balance of the receiver is still limited by the wide-band amplitude-phase consistency of the electronic components such as filters, amplifiers, ADCs, etc.
At present, in the microwave photonics direction, regarding the research on orthogonal demodulation of microwave signal light, the mainstream solution is to load a radio frequency signal onto an optical carrier, obtain an orthogonal local oscillator optical signal by performing 90 ° phase shift on the local oscillator optical signal, and then mix the orthogonal local oscillator optical signal with the radio frequency optical signal to obtain an orthogonal intermediate frequency signal.
The specific microwave photon orthogonal demodulation scheme mainly comprises two schemes: the microwave photonic quadrature demodulation method is based on an optical delay line, and the microwave photonic quadrature demodulation method is based on a 90-degree optical mixer.
The microwave photon orthogonal demodulation method based on the optical delay line comprises the following specific steps: after two paths of lasers with different wavelengths are combined into one path through a wavelength division multiplexer, local oscillation signals and radio frequency signals are loaded respectively through two stages of MZ modulators (Mach-Zehnder modulators) to realize optical frequency mixing; the two-stage modulators are combined by a wavelength division multiplexer in a shunting way, and a local oscillator phase shift of 90 degrees is introduced on one wavelength through an adjustable optical delay line, so that orthogonal down conversion on two optical carriers is realized; after the second-stage MZ modulator, two paths of optical carriers are separated through a wavelength division multiplexer, converted into electric signals through a PD (photoelectric detector), and then high-frequency components are filtered to form orthogonal outputs of an I path and a Q path. And when the frequency of the local oscillator LO is the same as the carrier frequency of the radio frequency signal, realizing zero intermediate frequency orthogonal demodulation.
In the microwave photon orthogonal demodulation method based on the optical delay line, I, Q two paths of optical signals are converted into electric signals through PD, and then enter ADC through a filter and an amplifier to be converted into digital signals. For quadrature demodulation processing of broadband radio frequency signals, although good quadrature characteristics can be maintained when a photoelectric detector is converted into an electric signal, I, Q imbalance of two signals is seriously deteriorated due to consistency differences of a microwave filter, an amplifier and an ADC, and performance of the whole optical quadrature demodulation system is affected.
The microwave photon orthogonal demodulation method based on the 90-degree optical mixer specifically comprises the following steps: a signal optical field loaded with a radio frequency signal and a local oscillator optical field loaded with a local oscillator signal enter a 90-degree optical mixer from two input ports; the signal light and the local oscillator light are respectively divided into two paths through two couplers, and the signal light and the local oscillator light are additionally introduced into one path of local oscillator light field
Phase shift of (2); the obtained two paths of orthogonal local oscillator light and two paths of signal light are respectively subjected to frequency mixing through two couplers, and optical signals output by the couplers are converted into two paths of orthogonal radio frequency signals through a double-balanced detector to suppress direct current components and common mode noise and output.
In the microwave photon quadrature demodulation method based on the 90-degree optical mixer, I, Q two paths of optical signals are converted into electric signals through the PD, and then the electric signals still need to enter the ADC through two paths of filters and amplifiers to be converted into digital signals. The performance of wideband quadrature demodulation of the entire optical quadrature demodulation system is still limited by the wideband uniformity of the electronic devices such as filters, amplifiers and ADCs.
In summary, in the microwave photonic quadrature demodulation method based on the optical delay line and the optical quadrature demodulation method based on the 90 ° optical mixer. Both implementations present the same difficulty in the face of wideband radio frequency signal processing, i.e., wideband signal quadrature demodulation performance of the entire optical quadrature demodulation system is limited by the wideband uniformity of the electronics, such as filters, amplifiers, and ADCs.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: how to solve the problem of consistency of a broadband microwave signal photon orthogonal demodulation system, and provides a microwave photon orthogonal demodulation method based on time division multiplexing.
The invention solves the technical problems through the following technical scheme, and the invention comprises the following steps:
s1: performing quadrature down conversion on radio frequency signal and local oscillator signal
Demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals, simultaneously performing windowing processing at the corresponding position of a link formed by the two paths of orthogonal intermediate frequency optical signals, and performing windowing processing on an input signal to avoid time domain overlapping and mutual interference generated when the I, Q two paths of signals are combined into one path;
s2: two orthogonal intermediate frequency optical signals are combined into one path
Performing delay beam combination processing on the two orthogonal intermediate frequency optical signals in the step S1, and combining the two orthogonal intermediate frequency optical signals into one optical signal;
s3: converting optical signals into digital signals
And performing photoelectric conversion, filtering amplification and analog-to-digital conversion on the I, Q optical signals combined into one path after the orthogonal demodulation in the step S2.
S4: obtaining a digital baseband signal
And recovering two paths of time-aligned I, Q digital baseband signals from the digital signal in the step S3 through digital signal processing.
Preferably, in step S1, the process of demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals includes:
s1011: combining two paths of optical signals with different wavelengths into one path, and loading a local oscillator signal onto the path of optical signal to form a primary local oscillator optical signal;
s1012: dividing the first-stage local oscillation optical signal in the step S1011 into two paths to obtain two paths of second-stage local oscillation optical signals, and introducing 90-degree phase shift on one path of second-stage local oscillation optical signals through an adjustable optical delay line;
s1013: combining the two-stage local oscillator optical signal introduced with 90-degree phase shift and the two-stage local oscillator optical signal not introduced with 90-degree phase shift into one path, loading the radio frequency signal to the local oscillator optical signal, and finally dividing the path of optical signal into two paths to form two orthogonal intermediate frequency optical signals.
Preferably, in the steps S1011 to S1013, the splitting and combining process is implemented by using a wavelength division multiplexer, the optical mixing process is implemented by using an MZ modulator, and the introducing the 90 ° phase shift is implemented by using an optical tunable delay line.
Preferably, in step S1, the windowing process is implemented by loading the window signal through the MZ modulator on the optical signal link or by introducing a high-speed rf switch on the rf signal input link.
Preferably, in step S2, the two orthogonal intermediate frequency optical signals are combined into one path by the delay fiber and the wavelength division multiplexer, so as to complete the delay beam combination process.
Preferably, in step S1, the process of demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals includes:
s1021: dividing a light source into two paths, loading a radio frequency signal to one path of optical signal, and loading a local oscillator signal to the other path of optical signal;
s1022: the optical signal loaded with the radio frequency signal and the optical signal loaded with the local oscillator signal enter a 90-degree optical mixer from two input ports, the radio frequency signal light and the local oscillator light in the 90-degree optical mixer are respectively divided into two paths, and a 90-degree phase shift is additionally introduced to one path of local oscillator optical signal;
s1023: and respectively mixing the two paths of orthogonal local oscillator light and the two paths of radio frequency signal light to obtain two paths of orthogonal intermediate frequency optical signals, wherein the first path of intermediate frequency optical signal is obtained by mixing one path of local oscillator light and one path of radio frequency signal light, and the second path of intermediate frequency optical signal is obtained by mixing the local oscillator light with the phase shifted by 90 degrees and the other path of radio frequency signal light.
Preferably, in the steps S1021 to S1023, the splitting and combining process and the introducing of the 90 ° phase shift are both implemented by using a 90 ° optical mixer, and the loading process of the local oscillator signal and the radio frequency signal is implemented by using an MZ modulator.
Preferably, in the step S1, the windowing process is implemented by loading the window signal on the optical signal link through the electro-optical modulator, or by introducing the high-speed rf switch on the rf signal input link.
Preferably, in step S2, after the delay introduced by the delay fiber in the two paths of optical signals in the first path of intermediate frequency optical signals is delayed, the two paths of orthogonal intermediate frequency optical signals are combined into one path, so as to complete the delay and beam combination processing.
Preferably, in step S1, the specific time window during the windowing process is to select a time slice in the continuous input signal or a periodic time slice in the continuous input signal, so as to implement time division multiplexing reception on a single receiving channel.
Preferably, for a scene needing to acquire continuous signals, a plurality of time windows are divided in the windowing processing process so as to be respectively received on a plurality of receiving channels, and for the requirement of continuous signal processing, the requirement can be met by dividing the plurality of time windows to be respectively received on the plurality of receiving channels and then performing digitized time domain splicing, and the time division multiplexing optical orthogonal demodulation scheme avoids the problem of consistency of electrical processing of I, Q two paths of signals and can inhibit I, Q imbalance of broadband signal orthogonal demodulation.
The invention also provides a microwave photon orthogonal demodulation system based on time division multiplexing, which comprises:
the down-conversion module is used for demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals;
the windowing module is used for windowing the corresponding positions of the links formed by the two paths of orthogonal intermediate frequency optical signals;
the time delay beam combination module is used for carrying out time delay beam combination processing on two paths of orthogonal intermediate frequency optical signals and combining the two paths of optical signals into one path of optical signal;
the analog-to-digital conversion module is used for converting the combined optical signal into an electric signal through a photoelectric detector, and converting the electric signal into a digital signal after filtering, amplifying and ADC (analog-to-digital converter) acquisition;
the signal processing and recovering module is used for recovering the digital signals into two paths of I, Q digital baseband signals aligned in time through digital signal processing;
the central processing module is used for sending instructions to other modules to complete related actions;
the down-conversion module, the windowing module, the delay beam combining module, the analog-to-digital conversion module and the signal processing and recovering module are all electrically connected with the central processing module.
Compared with the prior art, the invention has the following advantages: the microwave photon orthogonal demodulation method based on time division multiplexing combines the demodulated I, Q optical signals into one path of optical signals through optical delay combination to perform photoelectric conversion, filtering amplification and analog-to-digital conversion, and performs shunting and delay alignment on the I, Q signals combined into one path in a digital domain; by windowing the input signals, the phenomenon that I, Q two paths of signals generate time domain overlapping mutual interference when combined into one path is avoided; for the requirement of continuous signal processing, the time domain splicing can be realized by dividing a plurality of time windows to respectively receive signals on a plurality of receiving channels and then digitalizing the signals, the problem of consistency of electrical processing of I, Q two paths of signals is solved by the time division multiplexing optical orthogonal demodulation scheme, I, Q imbalance of broadband signal orthogonal demodulation can be inhibited, and the method is worthy of popularization and application.
Drawings
FIG. 1 is a schematic general flow chart of a microwave photon orthogonal demodulation method based on time division multiplexing according to the invention;
fig. 2 is a schematic flow chart of the working principle of the microwave photon orthogonal demodulation method based on time division multiplexing in the third embodiment of the present invention;
FIG. 3 is a schematic view of a windowing principle in a third embodiment of the present invention;
fig. 4 is a schematic diagram of an operating principle of a time division multiplexing microwave photonic quadrature demodulation method based on an optical delay line in a third embodiment of the present invention;
fig. 5 is a schematic diagram of an operating principle of a time division multiplexing microwave photonic quadrature demodulation method based on a 90 ° optical mixer in the third embodiment of the present invention.
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
Example one
As shown in fig. 1, the present embodiment provides a technical solution: a microwave photon orthogonal demodulation method based on time division multiplexing comprises the following steps:
s1: performing quadrature down conversion on radio frequency signal and local oscillator signal
Demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals, simultaneously performing windowing processing at the corresponding position of a link formed by the two paths of orthogonal intermediate frequency optical signals, and performing windowing processing on an input signal to avoid time domain overlapping and mutual interference generated when the I, Q two paths of signals are combined into one path;
s2: two orthogonal intermediate frequency optical signals are combined into one path
Performing delay beam combination processing on the two orthogonal intermediate frequency optical signals in the step S1, and combining the two orthogonal intermediate frequency optical signals into one optical signal;
s3: converting optical signals into digital signals
And performing photoelectric conversion, filtering amplification and analog-to-digital conversion on the I, Q optical signals combined into one path after the orthogonal demodulation in the step S2.
S4: obtaining a digital baseband signal
And recovering two paths of time-aligned I, Q digital baseband signals from the digital signal in the step S3 through digital signal processing.
In step S1, the process of demodulating the radio frequency signal and the local oscillator signal into two orthogonal intermediate frequency optical signals is as follows:
s1011: combining two paths of optical signals with different wavelengths into one path, and loading a local oscillator signal onto the path of optical signal to form a primary local oscillator optical signal;
s1012: dividing the first-stage local oscillator optical signal in the step S1011 into two paths to obtain two paths of second-stage local oscillator optical signals, and introducing 90-degree phase shift to one path of second-stage local oscillator optical signals;
s1013: combining the two-stage local oscillator optical signal introduced with 90-degree phase shift and the two-stage local oscillator optical signal not introduced with 90-degree phase shift into one path, loading the radio frequency signal to the local oscillator optical signal, and finally dividing the path of optical signal into two paths to form two orthogonal intermediate frequency optical signals.
In the steps S1011 to S1013, the splitting and combining process is implemented by using a wavelength division multiplexer, the optical mixing process is implemented by using an MZ modulator, and the introducing of the 90 ° phase shift is implemented by using an optical tunable delay line.
In step S1, the windowing process is implemented by loading the window signal on the optical signal link through the MZ modulator, or by introducing the high-speed rf switch on the rf signal input link.
In step S2, the two orthogonal intermediate frequency optical signals are combined into one path by the delay fiber and the wavelength division multiplexer, so as to complete the delay beam combination process.
The embodiment also provides a microwave photon orthogonal demodulation system based on time division multiplexing, which includes:
the down-conversion module is used for demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals;
the windowing module is used for windowing the corresponding positions of the links formed by the two paths of orthogonal intermediate frequency optical signals;
the time delay beam combination module is used for carrying out time delay beam combination processing on two paths of orthogonal intermediate frequency optical signals and combining the two paths of optical signals into one path of optical signal;
the analog-to-digital conversion module is used for converting the combined optical signal into an electric signal through a photoelectric detector, and converting the electric signal into a digital signal after filtering, amplifying and ADC (analog-to-digital converter) acquisition;
the signal processing and recovering module is used for recovering the digital signals into two paths of I, Q digital baseband signals aligned in time through digital signal processing;
the central processing module is used for sending instructions to other modules to complete related actions;
the down-conversion module, the windowing module, the delay beam combining module, the analog-to-digital conversion module and the signal processing and recovering module are all electrically connected with the central processing module.
Example two
As shown in fig. 1, the present embodiment provides a technical solution: a microwave photon orthogonal demodulation method based on time division multiplexing comprises the following steps:
s1: performing quadrature down conversion on radio frequency signal and local oscillator signal
Demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals, simultaneously performing windowing processing at the corresponding position of a link formed by the two paths of orthogonal intermediate frequency optical signals, and performing windowing processing on an input signal to avoid time domain overlapping and mutual interference generated when the I, Q two paths of signals are combined into one path;
s2: two orthogonal intermediate frequency optical signals are combined into one path
Performing delay beam combination processing on the two orthogonal intermediate frequency optical signals in the step S1, and combining the two orthogonal intermediate frequency optical signals into one optical signal;
s3: converting optical signals into digital signals
And performing photoelectric conversion, filtering amplification and analog-to-digital conversion on the I, Q optical signals combined into one path after the orthogonal demodulation in the step S2.
S4: obtaining a digital baseband signal
And recovering two paths of time-aligned I, Q digital baseband signals from the digital signal in the step S3 through digital signal processing.
In step S1, the process of demodulating the radio frequency signal and the local oscillator signal into two orthogonal intermediate frequency optical signals is as follows:
s1021: dividing a light source into two paths, loading a radio frequency signal to one path of optical signal, and loading a local oscillator signal to the other path of optical signal;
s1022: the optical signal loaded with the radio frequency signal and the optical signal loaded with the local oscillator signal enter a 90-degree optical mixer from two input ports, the radio frequency signal light and the local oscillator light in the 90-degree optical mixer are respectively divided into two paths, and a 90-degree phase shift is additionally introduced to one path of local oscillator optical signal;
s1023: and respectively mixing the two paths of orthogonal local oscillator light and the two paths of radio frequency signal light to obtain two paths of orthogonal intermediate frequency optical signals, wherein the first path of intermediate frequency optical signal is obtained by mixing one path of local oscillator light and one path of radio frequency signal light, and the second path of intermediate frequency optical signal is obtained by mixing the local oscillator light with the phase shifted by 90 degrees and the other path of radio frequency signal light.
In steps S1021 to S1023, the splitting and combining process and the introducing of the 90 ° phase shift are both implemented by using a 90 ° optical mixer, and the loading process of the local oscillator signal and the radio frequency signal is implemented by using an MZ modulator.
In step S1, the windowing process is implemented by loading a window signal on the optical signal link through the electro-optical modulator, or by introducing a high-speed rf switch on the rf signal input link.
In the step S2, after two paths of optical signals in the first path of intermediate frequency optical signal are delayed by the delay optical fiber, the two paths of orthogonal intermediate frequency optical signals are combined into one path, so as to complete the delay beam combination processing, and the 90 ° optical mixer can output four paths of intermediate frequency signals, which are divided into two groups and connected with two balanced detectors to form balanced reception; or only two paths of intermediate frequency signals can be output and are respectively connected with two common photoelectric detectors.
In step S1, the specific time window in the windowing process is to select a time slice in the continuous input signal or a periodic time slice in the continuous input signal, so as to implement time division multiplexing reception on a single channel.
For a scene needing to acquire continuous signals, a plurality of time windows are divided in the windowing processing process so as to be respectively received on a plurality of receiving channels, and for the requirement of continuous signal processing, the requirement can be met by dividing the plurality of time windows to be respectively received on the plurality of receiving channels and then carrying out digitalized time domain splicing, and the time division multiplexing optical orthogonal demodulation scheme avoids the problem of consistency of electrical processing of I, Q two paths of signals and can inhibit I, Q imbalance of broadband signal orthogonal demodulation.
The embodiment also provides a microwave photon orthogonal demodulation system based on time division multiplexing, which includes:
the down-conversion module is used for demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals;
the windowing module is used for windowing the corresponding positions of the links formed by the two paths of orthogonal intermediate frequency optical signals;
the time delay beam combination module is used for carrying out time delay beam combination processing on two paths of orthogonal intermediate frequency optical signals and combining the two paths of optical signals into one path of optical signal;
the analog-to-digital conversion module is used for converting the combined optical signal into an electric signal through a photoelectric detector, and converting the electric signal into a digital signal after filtering, amplifying and ADC (analog-to-digital converter) acquisition;
the signal processing and recovering module is used for recovering the digital signals into two paths of I, Q digital baseband signals aligned in time through digital signal processing;
the central processing module is used for sending instructions to other modules to complete related actions;
the down-conversion module, the windowing module, the delay beam combining module, the analog-to-digital conversion module and the signal processing and recovering module are all electrically connected with the central processing module.
EXAMPLE III
The present embodiment provides a time division multiplexing microwave photon orthogonal demodulation method, and a schematic flow chart of the working principle thereof is shown in fig. 2:
the radio frequency signal and the local oscillator signal are demodulated into I, Q two paths of intermediate frequency optical signals by a microwave photon orthogonal demodulation technology, and the used microwave photon orthogonal demodulation technology can adopt an optical delay line method, a 90-degree optical mixer and other methods. The two paths of orthogonal intermediate frequency optical signals after demodulation are delayed and combined to form one path of optical signal, the two paths of optical signals are converted into an electric signal through a Photoelectric Detector (PD), the electric signal is converted into a digital signal after filtering, amplification and ADC (analog to digital converter) acquisition, and finally the two paths of I, Q digital signals aligned in time are recovered through digital signal processing.
By adopting the time division multiplexing microwave photon orthogonal demodulation method, I, Q two paths of signals are digitally received through a receiving channel consisting of a photoelectric detector, a filter, an amplifier and an ADC, and the problem of amplitude-phase consistency of electronic devices during multipath receiving is solved.
Because I, Q two paths of signals are merged into one path for receiving, the time division multiplexing optical orthogonal demodulation system needs to perform windowing processing on continuously input signals, and the influence on the receiving effect caused by the overlapping of time existing when I, Q two paths of signals are delayed and combined is avoided. The specific time window can only adopt one time segment in the continuous input signal or adopt periodic time segments in the continuous input signal to carry out time division multiplexing single-channel receiving.
For a scene needing to acquire continuous signals, further time division multiplexing processing can be performed through a microwave photon orthogonal demodulation system with a plurality of paths of single receiving channels, a specific windowing principle schematic diagram is shown in fig. 3, the input continuous signals are divided into three paths through three periodic time windows, each path is a periodic signal with a duty ratio of 33%, I, Q two paths of optical signals are output through optical orthogonal demodulation processing, and digital acquisition and digital domain delay recovery are performed through the time division multiplexing microwave photon orthogonal demodulation system to obtain I, Q two paths of digital signals. After being digitalized, the three signals are subjected to time domain splicing in a digital domain to recover I, Q continuous two-path orthogonal digital signals.
As shown in fig. 4, the time division multiplexing microwave photon orthogonal demodulation method based on the optical delay line: the optical orthogonal demodulation processing part of the front end is the same as the optical orthogonal demodulation method based on the optical delay line. The input radio frequency signal and two paths of orthogonal local oscillator optical signals are mixed through optical processing to form two paths of orthogonal intermediate frequency optical signals. The difference between the optical orthogonal demodulation part and the optical orthogonal demodulation part of the optical orthogonal demodulation method based on the optical delay line is that a first-stage MZ modulator loading window signal is additionally introduced after a radio frequency signal is loaded, and windowing processing is carried out on an input signal, so that the duty ratio of the signal accords with the processing capacity of a time division multiplexing receiving system. Then two paths of orthogonal intermediate frequency optical signals are combined into one path through a delay optical fiber and a wavelength division multiplexer, and the combined optical signals are converted into electric signals by a photoelectric detector. And a path of digital signal is obtained after passing through a low-pass filter, an amplifier and an ADC, and the I, Q signal combined into a path is subjected to shunting and delay alignment in a digital domain.
The windowing can also be done by introducing a high-speed rf switch before the rf input signal is modulated onto the optical carrier by the MZ modulator.
For continuous signal processing requirements, the relative delay of the window signal of each link is controlled through joint processing of the multi-path time division multiplexing microwave photon orthogonal demodulation systems, so that different time segments of continuous signals are respectively processed by each path of time division multiplexing microwave photon orthogonal demodulation system, and finally splicing of each time segment is completed in a digital domain, and the orthogonal demodulation of the continuous signals is realized.
The digital splicing processing specifically includes demultiplexing the acquired time division multiplexing I, Q signals (respectively taking out time slices corresponding to the I, Q signals), obtaining I, Q data which are baseband I, Q signals, and finding the starting time of I, Q data when the I, Q data are demultiplexed.
For joint processing of continuous signals in a multi-path time division multiplexing system, I, Q data demodulated from each path need to be spliced in time sequence, and a time window starting node of I, Q data needs to be found.
As shown in fig. 5, the time division multiplexing microwave photonic quadrature demodulation method based on the 90 ° optical mixer: in the method, the window signal can be realized by loading the window signal on an optical signal link through an electro-optical modulator, and the windowing processing can also be realized by introducing a high-speed electric switch on a radio-frequency input signal, so that the duty ratio of the signal accords with the processing capacity of a time division multiplexing receiving system.
The optical carrier after windowing is divided into two paths through an optical coupler, radio frequency signals and local oscillation signals are loaded through an MZ modulator respectively, and then the two paths of optical signals are sent to 90-degree optical mixing to achieve optical orthogonal demodulation. Two paths of I optical signals obtained by demodulation are introduced into the same time delay through a time delay optical fiber, then are combined with two paths of Q optical signals into one path through two optical couplers, and are sent into a double balanced detector (BPD) to be converted into electric signals. Then the I, Q combined digital signal is obtained through a low-pass filter, an amplifier and an ADC. The I, Q signals that are combined into a single path are split and delay aligned in the digital domain.
The 90-degree optical mixer can output four paths of intermediate frequency signals, and the four paths of intermediate frequency signals are divided into two groups to be connected with two balance detectors to form balanced receiving; or only two paths of intermediate frequency signals can be output and are respectively connected with two common photoelectric detectors, the 90-degree optical mixer in the embodiment outputs four paths of intermediate frequency signals, and the four paths of intermediate frequency signals are divided into two groups and are connected with two balance detectors to form balanced receiving.
The windowing can also be done by introducing a high-speed rf switch before the rf input signal is modulated onto the optical carrier by the MZ modulator.
For continuous signal processing requirements, the relative delay of the window signal of each link is controlled through the joint processing of the multi-path time division multiplexing microwave photon orthogonal demodulation systems, so that each path of time division multiplexing microwave photon orthogonal demodulation system respectively processes different time segments of continuous signals, and finally the splicing of each time segment is completed in a digital domain, thereby realizing the orthogonal demodulation of the continuous signals.
To sum up, in the microwave photonic orthogonal demodulation method based on time division multiplexing in each group of embodiments, the demodulated I, Q optical signals are combined into one optical signal through optical delay and combination, and are subjected to photoelectric conversion, filtering amplification and analog-to-digital conversion, and the I, Q signal combined into one optical signal is subjected to splitting and delay alignment in a digital domain; by windowing the input signals, the phenomenon that I, Q two paths of signals generate time domain overlapping mutual interference when combined into one path is avoided; for the requirement of continuous signal processing, the time domain splicing can be realized by dividing a plurality of time windows to respectively receive signals on a plurality of receiving channels and then digitalizing the signals, the problem of consistency of electrical processing of I, Q two paths of signals is solved by the time division multiplexing optical orthogonal demodulation scheme, I, Q imbalance of broadband signal orthogonal demodulation can be inhibited, and the method is worthy of popularization and application.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A microwave photon orthogonal demodulation method based on time division multiplexing is characterized by comprising the following steps:
s1: performing quadrature down conversion on radio frequency signal and local oscillator signal
Demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals, and performing windowing processing at the corresponding position of a link formed by the two paths of orthogonal intermediate frequency optical signals;
s2: two orthogonal intermediate frequency optical signals are combined into one path
Performing delay beam combination processing on the two orthogonal intermediate frequency optical signals in the step S1, and combining the two orthogonal intermediate frequency optical signals into one optical signal;
s3: converting optical signals into digital signals
Converting the optical signal in the step S2 into an electrical signal, and converting the electrical signal into a digital signal after filtering, amplifying and collecting the electrical signal;
s4: obtaining a digital baseband signal
And recovering two paths of time-aligned I, Q digital baseband signals from the digital signal in the step S3 through digital signal processing.
2. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 1, characterized in that: in step S1, the process of demodulating the radio frequency signal and the local oscillator signal into two orthogonal intermediate frequency optical signals is as follows:
s1011: combining two paths of optical signals with different wavelengths into one path, and loading a local oscillator signal onto the path of optical signal to form a primary local oscillator optical signal;
s1012: dividing the first-stage local oscillation optical signal in the step S1011 into two paths to obtain two paths of second-stage local oscillation optical signals, and introducing 90-degree phase shift on one path of second-stage local oscillation optical signals through an adjustable optical delay line;
s1013: combining the two-stage local oscillator optical signal introduced with 90-degree phase shift and the two-stage local oscillator optical signal not introduced with 90-degree phase shift into one path, loading the radio frequency signal to the local oscillator optical signal, and finally dividing the path of optical signal into two paths to form two orthogonal intermediate frequency optical signals.
3. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 2, characterized in that: in step S1, the windowing process is implemented by loading a window signal on the optical signal link, or by introducing a high-speed rf switch on the rf signal input link.
4. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 3, characterized in that: in step S2, the two orthogonal intermediate frequency optical signals are combined into one path by the delay fiber and the wavelength division multiplexer, so as to complete the delay beam combination process.
5. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 1, characterized in that: in step S1, the process of demodulating the radio frequency signal and the local oscillator signal into two orthogonal intermediate frequency optical signals is as follows:
s1021: dividing a light source into two paths, loading a radio frequency signal to one path of optical signal, and loading a local oscillator signal to the other path of optical signal;
s1022: the optical signal loaded with the radio frequency signal and the optical signal loaded with the local oscillator signal enter a 90-degree optical mixer from two input ports, in the 90-degree optical mixer, the radio frequency signal light and the local oscillator light are respectively divided into two paths, and a 90-degree phase shift is additionally introduced to one path of local oscillator optical signal;
s1023: and respectively mixing the two paths of orthogonal local oscillator light and the two paths of radio frequency signal light to obtain two paths of orthogonal intermediate frequency optical signals, wherein the first path of intermediate frequency optical signal is obtained by mixing one path of local oscillator light and one path of radio frequency signal light, and the second path of intermediate frequency optical signal is obtained by mixing the local oscillator light with the phase shifted by 90 degrees and the other path of radio frequency signal light.
6. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 5, characterized in that: in step S1, the windowing process is implemented by loading the window signal on the optical signal link through the electro-optical modulator, or by introducing the high-speed rf switch on the rf signal input link.
7. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 6, characterized in that: in step S2, after the delay introduced by the delay fiber in the first path of intermediate frequency optical signal is delayed, the two orthogonal intermediate frequency optical signals are combined into one path, thereby completing the delay beam combination process.
8. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 1, characterized in that: in step S2, the specific time window during the windowing process is to select a time slice in the continuous input signal or a periodic time slice in the continuous input signal, so as to receive on the time division multiplexing single channel.
9. The microwave photonic quadrature demodulation method based on time division multiplexing of claim 8, characterized in that: for a scene needing to acquire continuous signals, a plurality of time windows are divided in the windowing processing process, so that the time windows are respectively received on a plurality of receiving channels.
10. A microwave photonic quadrature demodulation system based on time division multiplexing, which is characterized in that the microwave photonic quadrature demodulation method according to any one of claims 1 to 9 is used for quadrature demodulation of microwave signals, and comprises:
the down-conversion module is used for demodulating the radio frequency signal and the local oscillator signal into two paths of orthogonal intermediate frequency optical signals;
the windowing module is used for windowing the corresponding positions of the links formed by the two paths of orthogonal intermediate frequency optical signals;
the time delay beam combination module is used for carrying out time delay beam combination processing on two paths of orthogonal intermediate frequency optical signals and combining the two paths of optical signals into one path of optical signal;
the analog-to-digital conversion module is used for converting the combined optical signal into an electric signal through a photoelectric detector, and converting the electric signal into a digital signal after filtering, amplifying and ADC (analog-to-digital converter) acquisition;
the signal processing and recovering module is used for recovering the digital signals into two paths of I, Q digital baseband signals aligned in time through digital signal processing;
the central processing module is used for sending instructions to the down-conversion module, the windowing module, the delay beam combination module, the analog-to-digital conversion module and the signal processing recovery module to complete related actions;
the down-conversion module, the windowing module, the delay beam combining module, the analog-to-digital conversion module and the signal processing and recovering module are all electrically connected with the central processing module.
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