CN107547138B - Frequency multiplication factor tunable phase coding signal optical generation device and method - Google Patents
Frequency multiplication factor tunable phase coding signal optical generation device and method Download PDFInfo
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Abstract
The invention relates to an optical generation device and method for a frequency multiplication factor tunable phase coding signal. The device comprises a laser, a DP-QPSK modulator, a microwave signal generator, an electric amplifier, a coding signal generator, a direct current power supply, a polarization controller, a polarizer, an optical amplifier and a photoelectric detector; the method comprises the following steps: the method comprises the steps of utilizing the nonlinear modulation characteristic of a DP-QPSK modulator, generating binary phase coding signals with different frequency multiplication factors according to requirements, wherein the frequency multiplication factors can be selected from one to four, and the frequency of the generated signals is tuned by adjusting the frequency of input microwave signals. The invention is based on an integrated modulator structure, has simple system composition and stable performance, overcomes the defects that the traditional electric domain generation pulse compression signal mode is limited by the speed and bandwidth of an electronic device, is difficult to generate or can not generate high-frequency signals, has poor frequency tunability and the like, greatly improves the frequency of generating phase coding signals, and has a great frequency tunable range.
Description
Technical Field
The invention belongs to the technical field of microwave signal generation, and particularly relates to an optical generation device and method for a frequency multiplication factor tunable phase coding signal.
Background
In a radar system, in order to make a radar signal have a long action distance, high ranging and speed measurement accuracy and good distance and speed resolution, a signal is firstly transmitted in a form of a large bandwidth and a long pulse, namely, the radar signal has a large time-bandwidth product. Traditional constant load frequency pulse radar, because the carrier frequency is invariable, its time bandwidth product is invariable, does not exceed 1, this has just caused constant load frequency pulse radar to be difficult to compromise working distance, range finding accuracy of testing the speed and range speed resolution simultaneously.
To solve this problem, the concept of pulse compression radar has been proposed. The pulse compression radar transmits wide pulses at a transmitting end to realize large action distance, speed measurement precision and speed resolution, and obtains narrow pulses at a receiving end through pulse compression to realize high distance measurement precision and distance resolution. The pulse compression radar well solves the contradiction between the radar action distance and the resolution capability. Common pulse compression signals include chirp signals, non-chirp signals, and phase-encoded signals, with binary phase-encoded signals being one of the most common radar pulse compression signals. Phase encoded signals can be generated in the electrical domain by means of frequency mixing, but the electronic device-based method is limited by electronic bottlenecks, the bandwidth is often limited, and the frequency of the generated signal is difficult to tune in a large frequency range, and particularly for phase encoded signals with extremely high frequencies, the electronic device-based generation cost is extremely high and even difficult to generate. With the continuous development of radar technology, the working frequency of radar is also continuously developed to a higher frequency band, and the traditional electronic technology is more and more difficult to meet new requirements in the continuous development process of radar technology.
In order to overcome the above disadvantages of the conventional electronic technology for generating radar pulse compression signals and meet the new requirements of the continuous development of radar technology, the generation of radar pulse compression signals by an optical method becomes a research hotspot in recent years, and a radar pulse compression signal generation method based on a microwave photon technology is widely researched.
The earliest method for optically generating phase-coded signals is realized by a spatial light modulator and free space transmission of optical signals, the method has high flexibility and good reconfigurability, and can generate radar pulse compression signals in various forms. In order to overcome the disadvantages of this type of method, an all-fiber method can be used to generate the phase-encoded signal. The generation of a pulse-compressed signal can be achieved, for example, by methods of optical spectral shaping and frequency-domain to time-domain mapping, but the time length of the signal generated by this method is limited, often less than 1 microsecond, which limits the range of use of this method. The method based on external modulation can generate phase coded signals with long time length, for example, related documents report a method for generating binary phase coded signals based on fundamental frequency and double frequency of a single polarization modulator, the method has a simple structure, but only can generate phase coded signals with the frequency multiplication factor of two at most; the binary phase coding signal generation method based on the single Mach-Zehnder modulator is also based on the single modulator, but only can generate the binary phase coding signal of the fundamental frequency; the method based on the polarization multiplexing double parallel Mach-Zehnder modulator and the balance detector can generate quadruple frequency binary phase coding signals, but the method has higher complexity and implementation cost due to the adoption of the balance detector; related documents also report a binary phase coding signal generation method based on the polarization multiplexing double-parallel Mach-Zehnder modulator and polarization modulator, frequency multiplication factors of the polarization multiplexing double-parallel Mach-Zehnder modulator and the polarization modulator can be adjusted in two, four and eight phases, although the method can realize tunable frequency multiplication factors, two optical modulators are needed, the system is complex and the cost is high, in addition, when the frequency multiplication factors are eight, an optical filter is needed for filtering, the system stability and the frequency tunable range of the method are limited, and meanwhile, the structure of the method is more complex.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a frequency multiplication factor tunable phase coding signal optical generation device and method, which use a single optical modulator structure to realize the phase coding signal generation with tunable frequency in a large range and variable frequency multiplication factor.
The invention adopts the following technical scheme for solving the technical problems:
an optical generation device of phase coding signals with tunable frequency multiplication factors is characterized in that: the device comprises a laser, a polarization multiplexing double parallel Mach-Zehnder modulator (DP-QPSK modulator), a microwave signal generator, an electric amplifier, a coding signal generator, a direct current power supply, a polarization controller, a polarizer, an optical amplifier and a photoelectric detector; two sub-double parallel Mach-Zehnder modulators (sub DP-MZMs) are integrated in the DP-QPSK modulator, optical signals output by the two sub DP-MZMs are coupled together through orthogonal polarization multiplexing and output at the output end of the DP-QPSK modulator, and each sub DP-MZM consists of a main Mach-Zehnder modulator (main MZM) and two sub MZMs; the DP-QPSK modulator is arranged on an emergent light path of the laser; the output end of the microwave signal generator is connected with the input end of an electric amplifier, and the output end of the electric amplifier is respectively connected with one radio frequency input port of two sub DP-MZMs of the DP-QPSK modulator; the output end of the coding signal generator is respectively connected with the other radio frequency input port of the two sub DP-MZMs of the DP-QPSK modulator; the output end of the direct current power supply is connected with a direct current bias input port of the DP-QPSK modulator; the output end of the DP-QPSK modulator is connected with the input end of the polarization controller, the output end of the polarization controller is connected with the input end of the polarizer, the output end of the polarizer is connected with the input end of the optical amplifier, and the output end of the optical amplifier is connected with the input end of the photoelectric detector; and the output end of the photoelectric detector generates a microwave phase coding signal.
The sub-DP-MZMs have the same structure and performance.
The sub DP-MZM has independent radio frequency signal input ports and DC bias input ports.
The microwave signals input to the DP-QPSK modulator have the same amplitude and phase.
The encoded signals input to the DP-QPSK modulator have the same amplitude and arrival time.
An included angle of 45 degrees is formed between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft.
A frequency multiplication factor tunable phase coding signal optical generation method comprises the following steps:
1) the optical signal output by the laser is input into an optical input port of the DP-QPSK modulator, and the optical signals output by the two sub DP-MZMs of the DP-QPSK modulator are respectively in two orthogonal polarization directions of the optical signal output by the DP-QPSK modulator;
2) according to the center frequency and the bandwidth of the phase coding signal to be generated, adjusting the frequency of the microwave signal generated by the microwave signal generator, and adjusting the rate of the coding signal generated by the coding signal generator;
3) adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees;
4) adjusting the direct current bias voltage to enable the sub MZM of the sub DP-MZM1, which inputs the encoding signal, to be biased at a minimum transmission point, and the sub MZM of the input microwave signal to be biased at the minimum transmission point; the sub MZM of the sub DP-MZM2 with the input encoding signal is biased at the minimum transmission point and the sub MZM of the input microwave signal is biased at the maximum transmission point;
5) when a phase encoding signal of an input microwave signal frequency needs to be generated, adjusting a direct current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at a maximum transmission point and a main MZM of the sub DP-MZM2 to be biased at an orthogonal transmission point;
6) when a phase encoding signal of input microwave signal frequency double frequency needs to be generated, adjusting direct current bias voltage to enable the main MZM of the sub DP-MZM1 to be biased at a quadrature transmission point and the main MZM of the sub DP-MZM2 to be biased at a maximum transmission point;
7) when a phase coding signal of input microwave signal frequency tripling is required to be generated, adjusting direct current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at a maximum transmission point and a main MZM of the sub DP-MZM2 to be biased at an orthogonal transmission point, and realizing the suppression of a fundamental frequency signal by adjusting the amplitude of the input microwave signal;
8) when a phase coding signal of input microwave signal frequency quadruple is required to be generated, adjusting direct-current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at an orthogonal transmission point and a main MZM of the sub DP-MZM2 to be biased at a maximum transmission point, and realizing the suppression of a double frequency signal by adjusting the amplitude of the input microwave signal;
9) according to the above arrangement, binary microwave phase-encoded signals of different multiplication factors are generated at the photodetector.
The invention utilizes the nonlinear modulation characteristic of the DP-QPSK modulator, can generate the microwave phase coding signal of fundamental frequency, double frequency, triple frequency or quadruple frequency of the input microwave signal without optical and electrical filtering, can generate the phase coding signal of high frequency by utilizing a low-frequency photoelectric device, and has a large frequency tunable range.
The invention has the following beneficial effects:
1. the invention can realize high frequency multiplication factor, utilizes low-frequency microwave signals to generate high-frequency phase coding signals, and reduces the requirements of the system on microwave local oscillation signals and the bandwidth of a photoelectric device;
2. the frequency of the phase coding signal generated by the invention is tunable in a large range;
3. the system of the invention has simple structure, is mainly based on a DP-QPSK modulator, has high system integration level and low realization cost.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
fig. 2 is a frequency spectrum diagram of a 15.8GHz baseband phase-encoded signal generated in embodiment 1 of the present invention;
fig. 3 is a time domain waveform diagram (solid line) of a 15.8GHz baseband phase-coded signal generated in embodiment 1 of the present invention and a phase information waveform diagram (dotted line) recovered from the waveform;
fig. 4 is a schematic diagram of the pulse compression performance (autocorrelation) of a 64-bit 15.8GHz baseband phase-coded signal in embodiment 1 of the present invention, in which the diagram is an enlarged diagram of an autocorrelation peak;
FIG. 5 is a spectrum diagram of a 15.8GHz double-frequency phase-encoded signal generated in embodiment 2 of the present invention;
fig. 6 is a time domain waveform diagram (solid line) of a 15.8GHz double frequency phase-encoded signal generated in embodiment 2 of the present invention and a phase information waveform diagram (dotted line) recovered from the waveform;
fig. 7 is a schematic diagram of the pulse compression performance (autocorrelation) of a 64-bit 15.8GHz doubled phase-encoded signal according to embodiment 2 of the present invention, in which the diagram is an enlarged diagram of the autocorrelation peak;
fig. 8 is a frequency spectrum diagram of a frequency tripling phase-encoded signal of 15.9GHz generated in embodiment 3 of the present invention;
fig. 9 is a time domain waveform diagram (solid line) of a frequency tripling phase-coded signal of 15.9GHz generated in embodiment 3 of the present invention and a phase information waveform diagram (dotted line) recovered from the waveform;
fig. 10 is a schematic diagram of the pulse compression performance (autocorrelation) of a 64-bit triple-phase encoded signal at 15.9GHz in embodiment 3 of the present invention, and the diagram is an enlarged diagram of the autocorrelation peak;
FIG. 11 is a frequency spectrum diagram of a quadruple frequency phase-encoded signal of 15.8GHz generated in embodiment 4 of the present invention;
fig. 12 is a time domain waveform diagram (solid line) of a quadruple frequency phase-coded signal of 15.8GHz generated in embodiment 4 of the present invention and a phase information waveform diagram (dotted line) recovered from the waveform;
fig. 13 is a schematic diagram of the pulse compression performance (autocorrelation) of a 64-bit quadruple phase-coded signal at 15.8GHz in embodiment 4 of the present invention, and the inset graph is an enlarged view of the autocorrelation peak.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
Referring to fig. 1, the present invention includes: the device comprises a laser 1, a DP-QPSK modulator 2, a microwave signal generator 3, an electric amplifier 4, a coding signal generator 5, a direct current power supply 6, a polarization controller 7, a polarizer 8, an optical amplifier 9 and a photoelectric detector 10. An output port of the laser 1 is connected with an optical input end of the DP-QPSK modulator 2, an output port of the microwave signal generator 3 is connected with an input port of the electric amplifier 4, an output port of the electric amplifier 4 is respectively connected with one radio frequency input port of two sub DP-MZMs of the DP-QPSK modulator 2, an output port of the coding signal generator 5 is respectively connected with the other radio frequency input port of the two sub DP-MZMs of the DP-QPSK modulator 2, and an output port of the direct current power supply 6 is connected with a direct current bias input port of the DP-QPSK modulator 2; an optical output port of the DP-QPSK modulator 2 is connected to an input port of the polarization controller 7, an output port of the polarization controller 7 is connected to an input port of the polarizer 8, an output port of the polarizer 8 is connected to an input port of the optical amplifier 9, and an output port of the optical amplifier 9 is connected to an input port of the photodetector 10. The output port of the photodetector 10 produces binary microwave phase-encoded signals of different multiplication factors.
The invention generates microwave phase coding signals, which comprises the following steps:
step one, inputting an optical signal output by a laser into an optical input port of a DP-QPSK modulator, wherein the optical signals output by two sub DP-MZMs of the DP-QPSK modulator are respectively in two orthogonal polarization directions of the optical signal output by the DP-QPSK modulator;
adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees;
step three, adjusting the frequency of the microwave signal generated by the microwave signal generator and adjusting the rate of the code signal generated by the code signal generator according to the central frequency and the bandwidth of the phase code signal required to be generated;
adjusting the direct-current bias voltage to bias the sub MZM of the input encoding signal in the sub DP-MZM1 at the minimum transmission point and bias the sub MZM of the input microwave signal at the minimum transmission point; biasing the sub MZM of the sub DP-MZM2 for the input encoded signal at the minimum transmission point and the sub MZM of the input microwave signal at the maximum transmission point;
step five, when a phase encoding signal of the input microwave signal frequency needs to be generated, adjusting the direct-current bias voltage to enable the main MZM of the sub DP-MZM1 to be biased at the maximum transmission point and the main MZM of the sub DP-MZM2 to be biased at the orthogonal transmission point; when a phase encoding signal of input microwave signal frequency double frequency needs to be generated, adjusting direct current bias voltage to enable the main MZM of the sub DP-MZM1 to be biased at a quadrature transmission point and the main MZM of the sub DP-MZM2 to be biased at a maximum transmission point; when a phase coding signal of input microwave signal frequency tripling is required to be generated, adjusting direct current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at a maximum transmission point and a main MZM of the sub DP-MZM2 to be biased at an orthogonal transmission point, and realizing the suppression of a fundamental frequency signal by adjusting the amplitude of the input microwave signal; when a phase coding signal of input microwave signal frequency quadruple is required to be generated, adjusting direct-current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at an orthogonal transmission point and a main MZM of the sub DP-MZM2 to be biased at a maximum transmission point, and realizing the suppression of a double frequency signal by adjusting the amplitude of the input microwave signal;
and step six, generating binary microwave phase coding signals with different frequency multiplication factors at the photoelectric detector according to the setting.
The concrete description is as follows:
let the laser output optical signal be E0exp(jωct) input microwave signal ofV0cos(ωst) inputting the coded signal as Vcs (t) in which E0Is the amplitude of the optical signal, omegacIs the angular frequency, V, of the optical signal0Is the amplitude, omega, of the microwave signalsIs the angular frequency, V, of the microwave signalcIs the encoded signal amplitude, and s (t) is the bipolar sequence (-1, +1), then the optical signal output by the DP-QPSK modulator is:
where α is the insertion loss of the modulator, VπIs the half-wave voltage of the DP-QPSK modulator,
andthe phase shift, θ, introduced by the main MZM of the two DP-MZMs, respectivelyi＝πVDCi/2Vπ，VDCi(i ═ 1,2,3,4) is the dc bias voltage for DP-QPSK, γ ═ pi Vc/2VπAnd k ═ pi V0/2VπIs the modulation index.
The signal is input to the polarizer through the polarization controller, and the main axis of the polarizer forms an angle of 45 degrees with one main axis of the DP-QPSK modulator through adjusting the polarization controller, wherein the output of the polarizer can be expressed as
Wherein A ═ θ1-θ3)/2，B＝(θ1+θ3)/2. The output of the polarizer is amplified and detected at the photodetector, and the output of the photodetector can be expressed as
When theta is2Pi/2 and theta4When 0, the above formula can be simplifiedIs composed of
It can be seen that the first term in the above equation is the dc term, the second term is the modulation term of the baseband, the third term is the high frequency term that modulates the baseband signal, and the fourth term is a clean carrier term without modulation.
When in useAnd is
When, the formula (4) can be simplified to
As can be seen from the above equation, at the output of the photodetector, a dc term, a baseband modulation term, and a high frequency modulation term are generated. Here, a is set to 0, B is set to pi/2 (θ)1＝θ2Pi/2), γ pi/2 to generate a binary phase encoded signal and maximize its amplitude, in which case the alternating term in the above equation can be expressed as
Wherein JnIs an n-th order bessel function of the first kind. Under small signal modulation conditions (κ)<<1) The third harmonic will be well suppressed, and a binary phase-encoded signal of the fundamental frequency is generated, which can be expressed as
To generate a frequency-tripled binary phase-coded signal, J can be made by increasing the modulation index1(k) ═ 0 implementation, where the fundamental signal is suppressed, the third harmonic, the frequency tripled signal, will dominate, and can be expressed as
When in use
And is
When, the formula (4) can be simplified to
As can be seen from the above equation, at the output of the photodetector, the dc term, the baseband modulation term, and the high frequency modulation term are included. Similarly, a is 0, B is pi/2 (θ)1＝θ2Pi/2), γ pi/2 to generate a binary phase-encoded signal and maximize its amplitude, the high-frequency modulation term of the above equation can be reduced to
The above equation contains a dc term and frequency doubling and frequency quadrupling terms. To generate a frequency doubled phase encoded signal, a small modulation index (k < <1) is used, where the quadruple is well suppressed, and the resulting frequency doubled phase encoded signal can be expressed as
To generate a quadruple frequency phase encoded signal, the frequency doubling term can be suppressed by increasing the modulation index. Let J2When (k) ═ 0, the frequency doubler is suppressed and the resulting quadrupled phase-encoded signal can be expressed as
Example 1
In the embodiment, the wavelength of the laser is 1550.55nm, the microwave signal generator generates a 15.8GHz microwave signal, and adjusts the DC bias voltage, so that the sub MZM of the sub DP-MZM1, which inputs the encoding signal, is biased at the minimum transmission point, and the sub MZM of the input microwave signal is biased at the minimum transmission point; biasing the sub MZM of the sub DP-MZM2 for the input encoded signal at the minimum transmission point and the sub MZM of the input microwave signal at the maximum transmission point; biasing the main MZM of sub DP-MZM1 at the maximum transmission point and the main MZM of sub DP-MZM2 at the quadrature transmission point; and adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees. When the encoded signal is a binary pseudorandom sequence of 1.58Gbps, the spectrum of the fundamental frequency binary phase encoded signal output at the photodetector is as shown in fig. 2. In order to study the coding performance, the input coded signal is made to be "0101" sequence of 1.58Gbps, and the time domain waveform diagram (solid line) of the generated binary phase coded signal and the phase information waveform diagram (dotted line) recovered from the waveform are shown in fig. 3, and it can be seen that there is a significant phase jump between adjacent symbols, and the phase jump value is about 180 ° as seen from the recovered phase information waveform diagram. In order to verify the pulse compression performance of the generated binary phase-coded signal, the input coded signal is a binary pseudo-random sequence of 64 bits and 1.58Gbps, and the pulse compression performance (autocorrelation) of the generated binary phase-coded signal is schematically shown in fig. 4, wherein the peak-to-side lobe ratio is 8.39dB, and fig. 4 is an enlarged diagram of the autocorrelation peak, the full width at half maximum of which is about 0.63ns, and the corresponding pulse compression ratio is 64.3.
Example 2
In the embodiment, the wavelength of the laser is 1550.55nm, the microwave signal generator generates a 7.9GHz microwave signal, and adjusts the DC bias voltage, so that the sub MZM of the sub DP-MZM1, which inputs the encoding signal, is biased at the minimum transmission point, and the sub MZM of the input microwave signal is biased at the minimum transmission point; biasing the sub MZM of the sub DP-MZM2 for the input encoded signal at the minimum transmission point and the sub MZM of the input microwave signal at the maximum transmission point; biasing the main MZM of sub DP-MZM1 at the quadrature transmission point and the main MZM of sub DP-MZM2 at the maximum transmission point; and adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees. When the coded signal is a binary pseudorandom sequence of 1Gbps, the spectrum of the binary phase coded signal output at the photodetector is as shown in fig. 5, and it can be seen that a modulation signal is generated at twice the frequency of the microwave signal, i.e. at 15.8GHz, and the fundamental frequency signal is well suppressed. In order to study the coding performance, the input coded signal is made to be "0101" sequence of 1.58Gbps, and the time domain waveform diagram (solid line) of the generated binary phase coded signal and the phase information waveform diagram (dotted line) recovered from the waveform are shown in fig. 6, and it can be seen that there is a significant phase jump between adjacent symbols, and the phase jump value is about 180 ° as seen from the recovered phase information waveform diagram. In order to verify the pulse compression performance of the generated binary phase-coded signal, the input coded signal is a binary pseudo-random sequence of 64 bits and 1.58Gbps, and the pulse compression performance (autocorrelation) of the generated binary phase-coded signal is schematically shown in fig. 7, wherein the peak-to-side lobe ratio is 8.01dB, and the diagram in fig. 7 is an enlarged diagram of the autocorrelation peak, the full width at half maximum of which is about 0.65ns, and the corresponding pulse compression ratio is 62.3.
Example 3
In the embodiment, the wavelength of the laser is 1550.55nm, the microwave signal generator generates a 5.3GHz microwave signal, and adjusts the DC bias voltage, so that the sub MZM of the sub DP-MZM1, which inputs the encoding signal, is biased at the minimum transmission point, and the sub MZM of the input microwave signal is biased at the minimum transmission point; biasing the sub MZM of the sub DP-MZM2 for the input encoded signal at the minimum transmission point and the sub MZM of the input microwave signal at the maximum transmission point; biasing the main MZM of sub DP-MZM1 at the maximum transmission point and the main MZM of sub DP-MZM2 at the quadrature transmission point; adjusting the polarization controller to make an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft 45 degrees, amplifying by an electric amplifier to make J1(κ) ═ 0 holds. When the code signal is a binary pseudo-random sequence of 1.59Gbps, the spectrum of the binary phase code signal output from the photodetector is as shown in FIG. 8, and it can be seen that a modulation signal is generated at a frequency which is three times the frequency of the microwave signal, i.e., at 15.9GHz, and fundamental, double and quadruple frequencies are generatedThe signal is well suppressed. In order to study the coding performance, the input coded signal is made to be "0101" sequence of 1.59Gbps, and the time domain waveform diagram (solid line) of the generated binary phase coded signal and the phase information waveform diagram (dotted line) recovered from the waveform are shown in fig. 9, and it can be seen that there is a significant phase jump between adjacent symbols, and the phase jump value is about 180 ° as seen from the recovered phase information waveform diagram. In order to verify the pulse compression performance of the generated binary phase-coded signal, the input coded signal is a binary pseudo-random sequence of 64 bits and 1.59Gbps, and the pulse compression performance (autocorrelation) of the generated binary phase-coded signal is schematically shown in fig. 10, wherein the peak-to-side lobe ratio is 7.46dB, and the enlarged diagram of fig. 10 is an autocorrelation peak, the full width at half maximum of which is about 0.68ns, and the corresponding pulse compression ratio is 59.2.
Example 4
In the embodiment, the wavelength of the laser is 1550.55nm, the microwave signal generator generates a 3.95GHz microwave signal, and adjusts the DC bias voltage, so that the sub MZM of the sub DP-MZM1, which inputs the encoding signal, is biased at the minimum transmission point, and the sub MZM of the input microwave signal is biased at the minimum transmission point; biasing the sub MZM of the sub DP-MZM2 for the input encoded signal at the minimum transmission point and the sub MZM of the input microwave signal at the maximum transmission point; biasing the main MZM of sub DP-MZM1 at the quadrature transmission point and the main MZM of sub DP-MZM2 at the maximum transmission point; and adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees. Theoretically should be amplified by an electrical amplifier to make J2The (k) ═ 0 holds to suppress the signal at the frequency doubling, but it is not possible to obtain a signal satisfying J because of the limitation of the output power of the amplifier in the experiment2The microwave signal amplitude (κ) ═ 0, and as large a signal amplitude as possible was used in the experiments. When the coded signal is a binary pseudo-random sequence of 1.58Gbps, the spectrum of the binary phase coded signal output from the photodetector is as shown in fig. 11, and it can be seen that a modulated signal is generated at four times the frequency of the microwave signal, i.e. at 15.8GHz, and the fundamental frequency and the triple frequency signals are well suppressed, but because of the power limitation of the microwave signal in the experiment, the double frequency signal cannot be suppressedHowever, it is known from theoretical analysis that by using a higher power microwave signal, the double frequency signal is well suppressed. In order to study the coding performance, the input coded signal is made to be "0101" sequence of 1.58Gbps, and the time domain waveform diagram (solid line) of the generated binary phase coded signal and the phase information waveform diagram (dotted line) recovered from the waveform are shown in fig. 12, and it can be seen that there is a significant phase jump between adjacent symbols, and the phase jump value is about 180 ° as seen from the recovered phase information waveform diagram. In order to verify the pulse compression performance of the generated binary phase-coded signal, the input coded signal is a binary pseudo-random sequence of 64 bits and 1.58Gbps, and the pulse compression performance (autocorrelation) of the generated binary phase-coded signal is schematically shown in fig. 13, wherein the peak-to-side lobe ratio is 7.69dB, and fig. 13 is an enlarged diagram of the autocorrelation peak, the full width at half maximum of which is about 0.68ns, and the corresponding pulse compression ratio is 59.6.
In summary, the optical generation apparatus and method for phase-encoded signals with tunable frequency multiplication factors provided by the present invention can generate binary phase-encoded signals of fundamental frequency, frequency doubling, frequency tripling or frequency quadrupling of input microwave signals by using the nonlinear modulation characteristic of the DP-QPSK modulator, and can generate phase-encoded signals with extremely high frequency by using high frequency multiplication factors. The invention has simple structure, is mainly based on a DP-QPSK modulator, has high system integration level and low realization cost.
Claims (3)
1. An optical generation device for frequency multiplication factor tunable phase-coded signals, characterized in that: the device comprises a laser, a polarization multiplexing double parallel Mach-Zehnder modulator (DP-QPSK modulator), a microwave signal generator, an electric amplifier, a coding signal generator, a direct current power supply, a polarization controller, a polarizer, an optical amplifier and a photoelectric detector; two sub-double parallel Mach-Zehnder modulators (sub DP-MZMs) are integrated in the DP-QPSK modulator, optical signals output by the two sub DP-MZMs are coupled together through orthogonal polarization multiplexing and output at the output end of the DP-QPSK modulator, and each sub DP-MZM consists of a main Mach-Zehnder modulator (main MZM) and two sub MZMs; the DP-QPSK modulator is arranged on an emergent light path of the laser; the output end of the microwave signal generator is connected with the input end of an electric amplifier, and the output end of the electric amplifier is respectively connected with one radio frequency input port of two sub DP-MZMs of the DP-QPSK modulator; the output end of the coding signal generator is respectively connected with the other radio frequency input port of the two sub DP-MZMs of the DP-QPSK modulator; the output end of the direct current power supply is connected with a direct current bias input port of the DP-QPSK modulator; the output end of the DP-QPSK modulator is connected with the input end of the polarization controller, the output end of the polarization controller is connected with the input end of the polarizer, the output end of the polarizer is connected with the input end of the optical amplifier, and the output end of the optical amplifier is connected with the input end of the photoelectric detector; the output end of the photoelectric detector generates a microwave phase coding signal; wherein:
the microwave signals input into the DP-QPSK modulator have the same amplitude and phase;
the coded signals input into the DP-QPSK modulator have the same amplitude and arrival time;
and adjusting the frequency of the microwave signal generated by the microwave signal generator and adjusting the rate of the code signal generated by the code signal generator according to the central frequency and the bandwidth of the phase code signal to be generated.
2. The frequency doubling factor tunable phase-encoded signal optical generation device of claim 1, wherein: the included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft is 45 degrees under the control of the polarization controller.
3. A method for optically producing a frequency doubling factor tunable phase encoded signal using the apparatus of claim 1, the method comprising the steps of:
1) the optical signal output by the laser is input into an optical input port of the DP-QPSK modulator, and the optical signals output by the two sub DP-MZMs of the DP-QPSK modulator are respectively in two orthogonal polarization directions of the optical signal output by the DP-QPSK modulator;
2) according to the center frequency and the bandwidth of the phase coding signal to be generated, adjusting the frequency of the microwave signal generated by the microwave signal generator, and adjusting the rate of the coding signal generated by the coding signal generator;
3) adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees;
4) adjusting the direct current bias voltage to enable the sub MZM of the sub DP-MZM1, which inputs the encoding signal, to be biased at a minimum transmission point, and the sub MZM of the input microwave signal to be biased at the minimum transmission point; the sub MZM of the sub DP-MZM2 with the input encoding signal is biased at the minimum transmission point and the sub MZM of the input microwave signal is biased at the maximum transmission point;
5) when a phase encoding signal of an input microwave signal frequency needs to be generated, adjusting a direct current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at a maximum transmission point and a main MZM of the sub DP-MZM2 to be biased at an orthogonal transmission point;
6) when a phase encoding signal of input microwave signal frequency double frequency needs to be generated, adjusting direct current bias voltage to enable the main MZM of the sub DP-MZM1 to be biased at a quadrature transmission point and the main MZM of the sub DP-MZM2 to be biased at a maximum transmission point;
7) when a phase coding signal of input microwave signal frequency tripling is required to be generated, adjusting direct current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at a maximum transmission point and a main MZM of the sub DP-MZM2 to be biased at an orthogonal transmission point, and realizing the suppression of a fundamental frequency signal by adjusting the amplitude of the input microwave signal;
8) when a phase coding signal of input microwave signal frequency quadruple is required to be generated, adjusting direct-current bias voltage to enable a main MZM of the sub DP-MZM1 to be biased at an orthogonal transmission point and a main MZM of the sub DP-MZM2 to be biased at a maximum transmission point, and realizing the suppression of a double frequency signal by adjusting the amplitude of the input microwave signal;
9) according to the above arrangement, binary microwave phase-encoded signals of different multiplication factors are generated at the photodetector.
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