CN111193548B - Microwave photon waveform generation device and method based on cyclic frequency shift - Google Patents
Microwave photon waveform generation device and method based on cyclic frequency shift Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
- H04B10/505—Laser transmitters using external modulation
- H04B10/5053—Laser transmitters using external modulation using a parallel, i.e. shunt, combination of modulators
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/5165—Carrier suppressed; Single sideband; Double sideband or vestigial
Abstract
The invention relates to a microwave photon waveform generating device based on cyclic frequency shift, which comprises a laser, a cyclic frequency shift module, a photoelectric detector and a 90-degree electric phase shifter, wherein the laser is optically connected with an optical input port b of the cyclic frequency shift module, an optical input port of the photoelectric detector is optically connected with an optical output port c of the cyclic frequency shift module, and the 90-degree electric phase shifter is electrically connected with an output port of the photoelectric detector. The invention provides a microwave photon waveform generation device and method based on cyclic frequency shift, which can realize the waveform generation of a broadband tunable microwave signal with second-order harmonic components completely suppressed.
Description
Technical Field
The invention relates to the technical field of microwave photons, in particular to a microwave photon waveform generating device and a microwave photon waveform generating method based on cyclic frequency shift.
Background
In recent years, an arbitrary waveform generation technique based on microwave photonics, in which rectangular waves and triangular waves play an important role in optical frequency conversion, pulse compression, signal reproduction, and the like, has been a hot point of research due to its wide application in radar, measurement, wireless communication, and microwave signal processing. The traditional arbitrary waveform generation technology based on electronics is limited by the sampling rate, so that high-frequency arbitrary waveform signals are difficult to generate; the method based on microwave photonics can effectively break through 'electronic bottleneck', has the advantages of large bandwidth, low transmission loss, high isolation and the like, and realizes the generation of any microwave waveform signals with high frequency and large bandwidth in the optical domain.
Generally, an arbitrary waveform (OWAG) generated by light is generally classified into a fourier synthesis method, a frequency-time mapping method, and an external modulation method, in which the external modulation method directly externally modulates continuous light, and controls the amplitude and phase of a modulation sideband by using various modulation effects in a modulation process, so that the method has simplicity and high efficiency, thereby gaining wide attention. Common external modulation methods include single frequency rf signal driven dual parallel Mach Zehnder modulator DPMZM (f.z.zhang, x.z.ge, s.l.pan. triangular pulse generation using a dual-parallel Mach-Zehnder modulator by a single-frequency radio frequency signal [ J ]. Optics Letters,38(21): 4491-: 145-. For generating the triangular wave, the above methods all obtain first-order and third-order harmonic components with a frequency ratio of 1:3 and an amplitude ratio of 1:9 by controlling a modulation coefficient and a bias voltage, the two harmonics are just equal to the first two fourier series components of the triangular wave, but the second-order harmonic component cannot be completely suppressed, so that certain influence is generated on the accuracy of the waveform.
Therefore, in order to solve the problems in the prior art, a microwave photonic waveform generating apparatus and method based on cyclic frequency shift are needed to be developed, which can realize the waveform generation of a broadband tunable microwave signal with a second-order harmonic component being completely suppressed.
Disclosure of Invention
The invention overcomes the defects of the prior art, provides the microwave photon waveform generation device and method based on the cyclic frequency shift, and can realize the waveform generation of the broadband tunable microwave signal with the second-order harmonic component completely suppressed.
In order to achieve the purpose, the invention adopts the technical scheme that: a microwave photon waveform generation device and method based on cyclic frequency shift comprise a laser, a cyclic frequency shift module, a photoelectric detector and a 90-degree electric phase shifter, wherein the laser is optically connected with an optical input port b of the cyclic frequency shift module, an optical input port of the photoelectric detector is optically connected with an optical output port c of the cyclic frequency shift module, and the 90-degree electric phase shifter is electrically connected with an output port of the photoelectric detector.
In a preferred embodiment of the present invention, the optical coupler, the polarization controller, the modulator, the optical amplifier, the optical bandpass filter and the 45-degree polarization rotator are optically connected in sequence; and the modulator is electrically connected to the microwave source.
In a preferred embodiment of the present invention, the modulator is a dual parallel mach-zehnder modulator.
In a preferred embodiment of the invention, the modulator operates in a carrier-suppressed single sideband modulated CS-SSB state.
In a preferred embodiment of the present invention, the filter curve of the optical bandpass filter is flat-top or trapezoidal.
In a preferred embodiment of the invention, the laser generates light at a carrier frequency f0(ii) a Frequency shift signal f generated by microwave sourcesThe filter curve of the optical band-pass filter is adjusted to be flat-top or trapezoidal by being loaded on an electric input port of the modulator, and the output frequency of the filter is f after the photoelectric detector or the 90-degree electric phase shiftersA rectangular wave or a triangular wave.
In a preferred embodiment of the present invention, the method of the microwave photon waveform generating device based on cyclic frequency shift comprises:
step one, generating a frequency shift, wherein the frequency generated by a laser is f0The optical carrier wave enters the circulating frequency shift module through one optical input port b of the optical coupler in the circulating frequency shift module, a frequency shift signal generated by the microwave source is loaded on the optical carrier wave by using the double parallel Mach-Zehnder modulator, the frequency of the optical carrier wave is shifted to the short wavelength direction, and the frequency shift amount is the frequency f of the microwave sources；
Secondly, enabling the frequency shift polarization to be carried out, and rotating the polarization direction by 45 degrees after the frequency-shifted light wave passes through a 45-degree polarization rotator;
step three, circularly shifting frequency, and outputting frequency difference f between 4 adjacent spectral lines by a circularly shifting frequency module after 3 times of circulationsThe spectral lines with the polarization direction difference of 45 degrees are subjected to photoelectric conversion by a photoelectric detector, and the output frequency is f after the photoelectric detector or a 90-degree electric phase shiftersIs rectangularA wave or a triangular wave;
and step four, outputting microwave photon waveforms, wherein the frequency interval in a series of spectral lines with equal frequency intervals output by utilizing a cyclic frequency shift module is 2fsThe characteristic that the polarization directions of spectral lines are vertical can effectively inhibit second-order harmonic waves in rectangular waves or triangular waves, and the generation of broadband tunable microwave waveforms with the second-order harmonic waves completely inhibited can be realized.
In a preferred embodiment of the present invention, when the filter curve of the optical bandpass filter is a flat-top rectangle, the photodetector outputs a rectangular wave.
In a preferred embodiment of the present invention, when the filter curve of the optical bandpass filter is trapezoidal, the 90-degree electric phase shifter outputs a triangular wave.
The invention solves the defects existing in the background technology, and has the beneficial effects that:
the invention provides a microwave photon waveform generation device and method based on cyclic frequency shift, which can realize the waveform generation of a broadband tunable microwave signal with second-order harmonic components completely suppressed.
The invention utilizes the frequency shift and polarization rotation characteristics of the cyclic frequency shift module to ensure that the frequency interval is 2fsThe polarization directions of the spectral lines are vertical, so that second-order harmonic components are effectively inhibited, and the generation of microwave waveforms with pure spectral components is realized; due to the adoption of electro-optic modulation, the generation of the microwave waveform with tunable frequency is realized by changing the frequency of the microwave source.
Drawings
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is a diagram of a microwave photonic waveform generation apparatus based on cyclic frequency shift according to the present invention;
FIG. 2 represents a filter curve of an optical bandpass filter corresponding to the generation of a square wave;
fig. 3 represents a schematic diagram of the polarization directions of the spectral lines output by the circular frequency shift cavity.
FIG. 4 is a graph of a filter curve of a filter for generating a triangular wave representing a flat region + a linear region (a dotted line portion is a filter curve);
fig. 5 is a graph representing a linear region + a flat region (a dotted line portion is a filter curve) in a filter curve of a filter for generating a triangular wave.
FIG. 6 is a diagram illustrating different microwave waveforms generated by different filtering curves of an optical bandpass filter under the same frequency shift amount in an embodiment of the present invention, wherein the waveforms correspond to a rectangular wave of 20 GHz;
fig. 7 shows different microwave waveforms generated when the filtering curves of the optical bandpass filters are different under the condition of the same frequency shift amount in the embodiment of the invention, wherein the waveforms correspond to triangular waves of 20 GHz.
FIG. 8 is a time-domain waveform diagram of triangular waves with different frequencies generated by different frequency shift amounts under the condition of the same waveform in the embodiment of the present invention, wherein the triangular waves have 5 GHz;
FIG. 9 is a spectrum diagram of triangular waves with different frequencies generated according to different frequency shifts when the waveforms are the same in the embodiment of the present invention.
Wherein FIG. 1 is numbered: 1. the device comprises a laser, a 2, 2 x 2 optical coupler, a 3, a polarization controller, a 4, a double parallel Mach-Zehnder modulator, a 5, an optical amplifier, a 6, an optical bandpass filter, a 7, 45-degree polarization rotator, a 8, a microwave source, a 9, a cyclic frequency shift module, a 10, a photoelectric detector and an 11, 90-degree electric phase shifter.
Detailed Description
For a better understanding of the invention by those skilled in the art, the invention is described in further detail below with reference to the accompanying drawings and examples.
The embodiments described below are only a part of the embodiments of the present invention, and not all of them; based on the embodiments of the present invention, other embodiments used by those skilled in the art without any creative effort belong to the protection scope of the present invention.
As shown in fig. 1, the present embodiment discloses a microwave photon waveform generating device and method based on cyclic frequency shift, including a laser 1, a cyclic frequency shift module 9, a photodetector 10, and a 90-degree electrical phase shifter 11, where the laser 1 is optically connected to an optical input port b of the cyclic frequency shift module 9, the optical input port of the photodetector 10 is optically connected to an optical output port c of the cyclic frequency shift module 9, and the 90-degree electrical phase shifter 11 is electrically connected to an output port of the photodetector 10. The optical coupler 2, the polarization controller 3, the modulator 4, the optical amplifier 5, the optical bandpass filter 6 and the 45-degree polarization rotator 7 are connected in turn in an optical manner; and the modulator 4 and the microwave source 8 are electrically connected. The modulator 4 employs a double parallel mach-zehnder modulator.
In a preferred embodiment of the invention, the modulator 4 operates in a carrier-suppressed single sideband modulation, CS-SSB, state. The filter curve of the optical bandpass filter 6 is flat-topped or trapezoidal. The optical carrier frequency f generated by the laser 10(ii) a Frequency shift signal f generated by microwave source 8SThe filter curve of the optical band-pass filter 6 is adjusted to be flat-top or trapezoidal by being loaded on an electric input port of the modulator 4, and the output frequency of the filter is f after the photoelectric detector 10 or the 90-degree electric phase shifter 11sA rectangular wave or a triangular wave.
In a preferred embodiment of the present invention, the method of the microwave photon waveform generating device based on cyclic frequency shift comprises: step one, generating a frequency shift, wherein the frequency generated by the laser 1 is f0The optical carrier wave enters the cyclic frequency shift module 9 through one optical input port b of the optical coupler 2 in the cyclic frequency shift module 9, a frequency shift signal generated by the microwave source 8 is loaded on the optical carrier wave by using a double parallel Mach-Zehnder modulator, the frequency of the optical carrier wave is shifted to the short wavelength direction, and the frequency shift amount is the frequency f of the microwave source 8s(ii) a Secondly, enabling the frequency shift polarization to be carried out, and rotating the polarization direction by 45 degrees after the frequency-shifted light wave passes through a 45-degree polarization rotator 7; step three, circularly shifting frequency, after 3 times of circulation, the circularly shifting frequency module 9 outputs frequency difference f between 4 adjacent spectral linessThe spectral lines with 45-degree difference in polarization direction are subjected to photo-electric conversion by the photoelectric detector 10, and the output frequency is f after the photoelectric detector 10 or the 90-degree electric phase shifter 11sA rectangular wave or a triangular wave of (1); step four, outputting microwave photon waveform, and utilizing a series of spectral lines with equal frequency intervals output by the cyclic frequency shift module 9, wherein the frequency interval is 2fsThe characteristic that the polarization directions of spectral lines are vertical can effectively inhibit second-order harmonic waves in rectangular waves or triangular waves and realize that the second-order harmonic waves are finishedFully suppressed broadband tunable microwave waveform generation.
In a preferred embodiment of the present invention, when the filter curve of the optical bandpass filter 6 is a flat-topped rectangle, the photodetector 10 outputs a rectangular wave. Or, when the filter curve of the optical bandpass filter 6 is trapezoidal, the triangular wave is output after the 90-degree electric phase shifter 11.
In a preferred embodiment of the present invention, a waveform-tunable, frequency-tunable microwave waveform is generated in the time domain, and a power or amplitude-time curve is obtained.
The working principle of the invention is as follows: a microwave photon waveform generator based on cyclic frequency shift is shown in figure 1, wherein the frequency generated by a laser 1 is f0After the optical carrier wave enters the cyclic frequency shift module 9, the frequency shift signal f generated by the microwave source 8 is processed by using a double parallel Mach-Zehnder modulatorsThe carrier is loaded on an optical carrier to generate +1 order optical sidebands and-3 order sidebands of the optical carrier, and electro-optic modulation and electro-optic frequency shift of microwave signals are realized simultaneously. After the frequency-shifted light wave passes through the 45-degree polarization rotator 7, the polarization direction is rotated by 45 degrees. The passband range of the optical tunable bandpass filter is controlled to be f0～f0+3fs. Adjusting the modulation factor such that J1Far greater than J-3So that the-3 rd order optical sidebands are negligible and therefore the frequency increases f for each pass of the lightwave through the dual parallel mach-zehnder modulatorsThe polarization direction of the optical wave is rotated by 45 degrees every time the optical wave passes through the cyclic frequency shift module 9. After three times of cyclic frequency shift, the cyclic frequency shift module 9 outputs four adjacent frequencies with the interval fsThe spectral line with the polarization direction difference of 45 degrees controls the filtering curve of the optical band-pass filter 6 to output the frequency f after the photoelectric detector 10 or the 90-degree electric phase shifter 11sBy changing the frequency of the microwave source 8, the generation of a microwave waveform with tunable frequency can be realized.
The principle of the microwave photon waveform generation based on the cyclic frequency shift is as follows: let the optical carrier frequency be f0Strength of E0The polarization direction is the y-axis, so the jones vector of the optical carrier is:
t represents time, j represents an imaginary unit;
the double parallel Mach-Zehnder modulator (DPMZM) works in a carrier suppression single side band CS-SSB modulation state and is equivalent to a frequency shifter, and the frequency shift amount is equal to the frequency f of a microwave source loaded on the DPMZMs. The delay of the ring cavity is tau, and the frequency of the cyclic frequency shift cavity to the ring cavity is f0+ifsThe response of the optical signal of (i ═ 1, 2, 3) is hiDetermined by the gain of the optical amplifier 5 and the filter curve of the optical bandpass filter; the jones matrix for the 45-degree polarization rotator 7 is:
wherein G is the jones matrix of the 45-degree polarization rotator 7;
thus after 1 cycle, the output light field intensity is:
after 2 cycles, the output light field intensity is:
after 3 cycles of circulation, the output light field intensity is:
the gain of the optical amplifier is adjusted,and the response curve of the optical band-pass filter is flat-top, h i1, so equation 5 can be written as:
n represents the number of cycles;
adjusting the ring cavity delay so that fsτ is integer, so equation 6 can be further simplified to:
the gain of the optical amplifier and the pass band and the filter curve of the optical bandpass filter are controlled, so that the cyclic frequency shift cavity finally outputs 4 frequency intervals as the same frequency shift amount f through an output port csThe flat optical frequency comb having the polarization directions different by 45 degrees between the adjacent spectral lines, as shown in fig. 2, enters the photodetector to realize the optical-electrical conversion. Because the polarization directions of adjacent spectral lines are different by 45 degrees, and the polarization directions of the alternate spectral lines are different by 90 degrees as shown in FIG. 3, the suppression frequency of 2f can be effectively controlledsSo that only the frequency f is the final photocurrent frequency componentsAnd 3fsPhotocurrent of (2): 1 st root of f0Line sum 2 nd f0+f s2 nd and 3 rd f0+2fsSpectral line, 3 rd spectral line and 4 th f0+3fsBeat frequency between spectral lines to obtain frequency f s1 st and 4 th lines are beat-frequency to obtain a frequency of 3fsOf the electrical signal of (a).
Therefore, the expression of the light intensity finally output by the circular frequency shift cavity is as follows:
the fourier expansion of a rectangular wave can be approximated as:
wherein, S (t) is a time domain expression symbol of the rectangular wave, A is the direct current amplitude of the rectangular wave, and theta represents the initial phase of the fundamental wave in the rectangular wave.
Comparing equation 8 and equation 9, it can be seen that the device can achieve generation of rectangular waves.
For a triangular wave, its fourier expansion is:
wherein, T (t) is a time domain expression symbol of the triangular wave, B is a direct current amplitude of the triangular wave, and theta represents an initial phase of a fundamental wave in the triangular wave.
Since the power of the higher harmonic component decays very rapidly, only the third harmonic component is generally considered. As can be seen from equation 10, similar to the rectangular wave, the fourier expansion of the triangular wave also contains only the odd-order harmonic component, so the second-order harmonic component can still be suppressed by the apparatus shown in fig. 1.
For rectangular waves, the ratio of first-order harmonic components to third-order harmonic components is 3, when the spectrum output by the circular frequency shift cavity is flat, the ratio of the first-order harmonic components to the third-order harmonic components after beat frequency is just 3, the phase ratio is 1:3, and a pi phase delay is opposite in phase, so that the Fourier expansion form of the rectangular waves is just met. However, for a triangular wave, the ratio of the first and third harmonic components is 9, which are in phase and satisfy a 1:3 ratio. Therefore, when the filter curve of the circular frequency shift cavity is flat-topped, the output spectrum cannot satisfy the amplitude relation of 9: 1 after beat frequency and cannot satisfy the phase relation of 1: 3.
In order to solve the size relationship between the first-order harmonic component and the third-order harmonic component, the filter curve of the circular frequency shift cavity needs to be changed, and here, the rectangular filter is not changed into the trapezoidal filter, namely, the filter curve has both a flat area and a linear area.
For equation 5, if the optical filter is consideredThe filter curve is not flat, then hiIs a variable, still let fsSince τ is integer, equation 5 can be rewritten as:
wherein HnRepresenting the frequency f in the output spectrum of the cyclic frequency shift cavity0+nfsThe magnitude of the field strength of the spectral line of (a). Therefore, the expression of the light intensity finally output by the circular frequency shift cavity is as follows:
for a triangular wave, the ratio of the first and third harmonic weightings is 9: 1, so:
H0H1+H1H2+H2H3＝9H0H3(ii) a Equation 13;
suppose f0、f0+fs、f0+2fsIn the flat region of the filter curve, i.e. H0＝H1＝H2Then H is0＝4H3，f0+3fsIn a linear region, so that the light intensity ratio of the four spectral lines is I0∶I1∶I2∶I3After conversion to logarithmic coordinates, the power of the first three spectral lines is equal, and the ratio of the power of the fourth spectral line is 12dB10lg16 ≈ 12. Therefore, when selecting the filter of the cyclic frequency shift cavity, it is only necessary to satisfy the above relationship, and the filter curve is as shown in fig. 4.
In the same way, when f0In the linear region of the filter curve, f0+fs、f0+2fs、f0+3fsIn the flat region of the filter curve,i.e. H1＝H2＝H3Then H is1＝4H0So that the ratio of the light intensities of the four spectral lines output by the circular frequency shift cavity is I0∶I1∶I2∶I3After conversion to logarithmic coordinates, the power of the last three spectral lines is equal to the power of the first spectral line by 12dB, so that when selecting the filter of the circular frequency shift cavity, the above relationship is only required to be satisfied, and the filter curve is as shown in fig. 5.
From the above discussion, it can be known that by reasonably setting the filter curve of the filter, the first and third harmonic components after the beat frequency can satisfy the 9: 1 relationship, and equation 12 can be rewritten as:
I∝9E0 2cos(2πfst+2πf0τ)-E0 2cos(2π·3fst+2π·3f0τ)
＝9E0 2cos(2πfst+2πf0τ)+E0 2cos(2π·3fst+2π·3f0τ + π); equation 14;
from the Fourier expansion 10 of the triangular wave, it can be seen that the magnitudes of the first and third harmonics need to satisfy not only the 9: 1 relationship, but also their phases need to satisfy the 1:3 relationship. As can be seen from equation 14, the phase of the current harmonic component passing through the photodetector after the beat frequency does not satisfy the phase relationship of the triangular wave harmonic component, and therefore, a 90-degree electrical phase shifter is introduced after the photodetector, and the experimental block diagram is shown in fig. 1, then equation 14 can be rewritten as:
in summary, by reasonably setting the filter curve of the filter and introducing the 90-degree phase shifter after the photodetector, the generation of the triangular wave can be realized in the electrical domain by using the polarization characteristic of the cyclic frequency shift cavity.
Example 1
Under the condition of the same frequency shift quantity, different microwave waveforms are correspondingly generated by different filtering curves of the band-pass filter.
Wavelength lambda of optical carrier 1550nm and frequency shift fs20GHz, loop delay τ 10-8s, the optical carrier power is 0dBm, when the filter curve of the filter is flat-top, the generated rectangular wave is as shown in fig. 6, and the period of the obtained rectangular wave is 50 ps.
When the filter curve of the adjusting filter is trapezoidal, other parameters are kept unchanged, a 90-degree electric phase shifter is added behind the photoelectric detector, and the generated triangular wave is shown in fig. 7.
In summary, under the condition of the same frequency shift amount, the device and the method can realize the generation of the microwave waveform with tunable waveform.
Example 2
Under the condition of the same waveform, the different frequency shift amounts correspondingly generate triangular waves with different frequencies.
In example 1, the frequency shift amount was 20GHz, the frequency shift amount was adjusted to 5GHz, the obtained triangular wave frequency was 5GHz, and the time domain waveform was as shown in fig. 8. Fig. 9 is a spectrum diagram corresponding to a 5GHz triangular wave, and it can be seen from the spectrum diagram that only the first-order 5GHz harmonic and the third-order 15GHz harmonic are included, and the power ratio of the first-order 5GHz harmonic and the third-order 15GHz harmonic is about 20dB, and is close to the ideal power ratio of 19.085 dB.
In summary, under the condition that the waveform is kept unchanged, the device and the method can realize the generation of the microwave waveform with adjustable frequency.
In light of the foregoing description of the preferred embodiment of the present invention, it is to be understood that various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (8)
1. A microwave photon waveform generation device based on cyclic frequency shift comprises a laser (1), a cyclic frequency shift module (9), a photoelectric detector (10) and a 90-degree electric phase shifter (11), and is characterized in that: the laser (1) is optically connected with an optical input port b of the cyclic frequency shift module (9), an optical input port of the photoelectric detector (10) is optically connected with an optical output port c of the cyclic frequency shift module (9), and the 90-degree electric phase shifter (11) is electrically connected with an output port of the photoelectric detector (10); the cyclic frequency shift module (9) comprises an optical coupler (2), a polarization controller (3), a modulator (4), an optical amplifier (5), an optical bandpass filter (6) and a 45-degree polarization rotator (7); the optical coupler (2), the polarization controller (3), the modulator (4), the optical amplifier (5), the optical bandpass filter (6) and the 45-degree polarization rotator (7) are connected in turn in an optical manner; and the modulator (4) is electrically connected with the microwave source (8); the end b of the optical coupler (2) is an optical input port b of the cyclic frequency shift module (9), and the end c of the optical coupler (2) is an optical output port c of the cyclic frequency shift module (9); the a end of the optical coupler (2) is optically connected with the 45-degree polarization rotator (7), and the d end of the optical coupler (2) is optically connected with the polarization controller (3).
2. A cyclic shift frequency based microwave photonic waveform generation apparatus as claimed in claim 1, wherein: the modulator (4) adopts a double parallel Mach-Zehnder modulator.
3. A cyclic shift frequency based microwave photonic waveform generation apparatus as claimed in claim 1, wherein: the modulator (4) operates in a carrier-suppressed single sideband modulated CS-SSB state.
4. A cyclic shift frequency based microwave photonic waveform generation apparatus as claimed in claim 1, wherein: the filtering curve of the optical band-pass filter (6) is flat-top or trapezoidal.
5. A cyclic shift frequency based microwave photonic waveform generation apparatus as claimed in claim 1, wherein: the optical carrier frequency generated by the laser (1) is f0(ii) a Frequency shift signal f generated by microwave source (8)sAn electrical input port of the modulator (4) is loaded to adjust the filter curve of the optical band-pass filter (6)Is flat-top or trapezoidal, and can output frequency f after the photoelectric detector (10) or the 90-degree electric phase shifter (11)sA rectangular wave or a triangular wave.
6. The method of any one of claims 2-5 for a microwave photonic waveform generation apparatus based on cyclic frequency shift, comprising:
step one, generating a frequency shift, wherein the frequency generated by the laser (1) is f0The optical carrier wave enters the cyclic frequency shift module (9) through one optical input port b of the optical coupler (2) in the cyclic frequency shift module (9), a frequency shift signal generated by the microwave source (8) is loaded on the optical carrier wave by using the double parallel Mach-Zehnder modulator, the frequency of the optical carrier wave is shifted to the short wavelength direction, and the frequency shift amount is the frequency f of the microwave source (8)s；
Secondly, enabling the frequency shift polarization to be carried out, and rotating the polarization direction by 45 degrees after the frequency-shifted light wave passes through a 45-degree polarization rotator (7);
step three, circularly shifting frequency, and after 3 times of circulation, the circularly shifting frequency module (9) outputs frequency difference f between 4 adjacent spectral linessThe spectral lines with the polarization direction difference of 45 degrees are subjected to photoelectric conversion through a photoelectric detector (10), and the output frequency is f after the photoelectric detector (10) or a 90-degree electric phase shifter (11)sA rectangular wave or a triangular wave of (1);
and step four, outputting microwave photon waveforms, wherein the frequency interval in a series of spectral lines with equal frequency intervals output by utilizing the cyclic frequency shift module (9) is 2fsThe characteristic that the polarization directions of spectral lines are vertical can effectively inhibit second-order harmonic waves in rectangular waves or triangular waves, and the generation of broadband tunable microwave waveforms with the second-order harmonic waves completely inhibited can be realized.
7. A method of generating a microwave photonic waveform based on cyclic frequency shift according to claim 6, wherein: when the filtering curve of the optical band-pass filter (6) is a flat-top rectangle, the photoelectric detector (10) outputs a rectangular wave.
8. A method of generating a microwave photonic waveform based on cyclic frequency shift according to claim 6, wherein: when the filter curve of the optical band-pass filter (6) is trapezoidal, a triangular wave is output after the 90-degree electric phase shifter (11).
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| CN103220045A (en) * | 2013-04-25 | 2013-07-24 | 上海大学 | Circulating frequency shifting comb spectrum generating system based on intensity modulation and application method of circulating frequency shifting comb spectrum generating system |
| CN107919914A (en) * | 2017-12-20 | 2018-04-17 | 西安电子科技大学 | Quadruple signal is generated based on double-parallel modulator and realizes the device and method of microwave photon phase shift |
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