CN111447013B - Four-order ultra-wideband signal generation device based on microwave photonics - Google Patents
Four-order ultra-wideband signal generation device based on microwave photonics Download PDFInfo
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- 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
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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
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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
- H04B10/508—Pulse generation, e.g. generation of solitons
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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
- H04B10/524—Pulse modulation
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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
- H04B10/54—Intensity modulation
- H04B10/541—Digital intensity or amplitude modulation
Abstract
A four-order ultra-wideband signal generation method and device based on microwave photonics belong to the technical field of microwave photonics. The device consists of a continuous wave laser, a polarization controller, an arbitrary waveform generator, an electric amplifier 1, an electric amplifier 2, an electric amplifier 3, an electric amplifier 4, a power divider 1, a power divider 2, a power divider 3, an electric delay line, a dual-polarization orthogonal phase shift keying modulator, a coupler, a direct current voltage stabilizing source 1, a direct current voltage stabilizing source 2, a direct current voltage stabilizing source 3, a direct current voltage stabilizing source 4, a direct current voltage stabilizing source 5, a direct current voltage stabilizing source 6, an optical delay line and a balanced photoelectric detector. By reasonably setting the operating point and the modulation index of the modulator, the generated ultra-wideband signal conforms to the power spectral density mask specified by the Federal communication Commission in the United states and has higher power efficiency. The device can realize two typical modulation modes used in communication, and therefore can be used as a signal source of an optical carrier ultra-wideband communication system.
Description
Technical Field
The invention belongs to the technical field of microwave photonics, and particularly relates to a microwave photonics fourth-order ultra-wideband signal generation method and device based on a dual-polarization quadrature phase shift keying modulator and a delay line filter.
Background
With the continuous improvement of the requirements of close-range broadband wireless communication on high transmission rate and available radio frequency resources, the ultra-wideband technology attracts attention by the characteristics of large bandwidth, high time domain resolution, multipath fading resistance, low power consumption and the like. Therefore, ultra-wideband technology has potential applications in many application areas, such as local area networks, wide area networks, sensing systems and navigation systems. The U.S. federal communications commission has specified ultra-wideband signals: its relative bandwidth cannot be below 20%, or its 10dB bandwidth is greater than 500 MHz. In addition, the frequency range of 3.1 to 10.6GHz is allocated to wireless indoor communication, so-called baseband ultra-wideband, and the power spectral density is limited to be below-41.3 dbm/MHz, which is also called ultra-wideband mask. Due to the limitation of the ultra-wideband power spectral density, the transmission distance of ultra-wideband signals in the air is limited to within a few meters. In order to solve this problem, an optical ultra-wideband technology based on microwave photonics has been proposed. In this case, it is desirable to produce an ultra-wideband signal in the optical domain, which can overcome the bandwidth limitations of electrical technology, and which omits redundant electrical-to-optical conversion. In an optical ultra-wideband network, an ultra-wideband signal is generated and modulated at a central station, then transmitted to a base station through a long-distance optical fiber, subjected to photoelectric conversion by a photoelectric detector in the base station, and finally emitted to the air by an antenna for wireless communication.
In order to fit the ultra-wideband mask to the maximum, i.e. to generate ultra-wideband signals with high power efficiency, two methods are generally used. The first is to design a waveform that can fit an ultra-wideband mask, but the designed complex signal is usually generated by an electrical device, which has certain difficulty, and the generated pulse is difficult to modulate. The second method is to perform a high order differentiation on the gaussian pulse to generate a high order ultra wideband signal. The method can be realized by using an optical device, and flexible modulation can be performed only by using an electric pulse sequence generator to output a coding signal.
Disclosure of Invention
The invention aims to provide a method and a device for generating a microwave photonics fourth-order ultra-wideband signal based on a dual-polarization quadrature phase shift keying modulator and a delay line filter. By reasonably setting the operating point and the modulation index of the modulator, the generated ultra-wideband signal conforms to the power spectral density mask specified by the Federal communication Commission in the United states and has higher power efficiency. The device can realize two typical modulation modes used in communication, and therefore can be used as a signal source of an optical carrier ultra-wideband communication system.
The structure of the four-order ultra-wideband signal generating device based on microwave photons is shown in figure 1 and comprises a continuous wave laser, a polarization controller, an arbitrary waveform generator, an electric amplifier 1, an electric amplifier 2, an electric amplifier 3, an electric amplifier 4, a power divider 1, a power divider 2, a power divider 3, an electric delay line, a dual-polarization quadrature phase shift keying modulator, a coupler, a direct-current voltage stabilizing source 1, a direct-current voltage stabilizing source 2, a direct-current voltage stabilizing source 3, a direct-current voltage stabilizing source 4, a direct-current voltage stabilizing source 5, a direct-current voltage stabilizing source 6, an optical delay line and a balanced photoelectric detector; the dual-polarization quadrature phase shift keying modulator is a commercial device integrated on a single chip and consists of a Y-shaped optical splitter, a quadrature phase shift keying modulator 1, a quadrature phase shift keying modulator 2, a 90-degree polarization rotator and a polarization beam combiner; the quadrature phase shift keying modulator 1 is composed of a Mach-Zehnder modulator 1a and a Mach-Zehnder modulator 1b which are embedded in two arms of a Megash-Zehnder modulator 1, an electric amplifier 1 and a direct current voltage stabilizing source 1 are connected with the Mach-Zehnder modulator 1a, an electric amplifier 2 and a direct current voltage stabilizing source 2 are connected with the Mach-Zehnder modulator 1b, and a direct current voltage stabilizing source 3 is connected with the Megash-Zehnder modulator 1; the quadrature phase shift keying modulator 2 is composed of a mach-zehnder modulator 2a and a mach-zehnder modulator 2b embedded in two arms of the mamch-zehnder modulator 2, an electric amplifier 3 and a direct current voltage stabilizing source 4 are connected with the mach-zehnder modulator 2a, the electric amplifier 4 and the direct current voltage stabilizing source 5 are connected with the mach-zehnder modulator 2b, and a direct current voltage stabilizing source 6 is connected with the mamch-zehnder modulator 2.
Continuous light output by the continuous wave laser (the laser output by the continuous wave laser is continuous, the interruption is avoided, the output power is unchanged, the light signal has only a single frequency, and the waveform in the time domain is a sine wave in an ideal state) is input into the dual-polarization quadrature phase shift keying modulator through the polarization controller, and the polarization controller is used for aligning the polarization state of the incident light with the main axis of the dual-polarization quadrature phase shift keying modulator. Meanwhile, a column of Gaussian pulse electrical signals are output from an arbitrary waveform generator and are divided into two paths of first branch electrical signals and second branch electrical signals with equal amplitude, power and frequency by a power divider 1, wherein the first branch electrical signals and the second branch electrical signals are respectively equal in amplitude, power and frequencyThe frequency of the second branch electric signal is the same as the frequency of the Gaussian pulse electric signal output by the arbitrary waveform generator, and the power of the first branch electric signal and the power of the second branch electric signal are about half of the power of the Gaussian pulse electric signal; the electrical signal of the second branch is input into an incoming delay line to introduce a delay tau 1 The amplitude, power, frequency of which remain constant, τ 1 Is approximately equal to half the full width at half maximum of the input gaussian pulse. Then, the first branch electric signal is divided into two paths of third branch electric signals and fourth branch electric signals with equal amplitude, power and frequency through the power divider 2, the power of the third branch electric signals and the power of the fourth branch electric signals are approximately equal to half of the power of the first branch electric signals, and the frequency of the third branch electric signals and the frequency of the fourth branch electric signals are the same as the frequency of the Gaussian pulse electric signals output by the arbitrary waveform generator. And then the second branch electric signal is divided into two paths of fifth branch electric signals and sixth branch electric signals with equal amplitude, power and frequency through the power divider 3, the power of the fifth branch electric signals and the power of the sixth branch electric signals are approximately equal to half of the power of the second branch electric signals, and the frequency of the fifth branch electric signals and the frequency of the sixth branch electric signals are the same as the frequency of the Gaussian pulse electric signals output by the arbitrary waveform generator. The electric amplifier 1, the electric amplifier 2, the electric amplifier 3 and the electric amplifier 4 are respectively introduced into the third branch electric signal, the fourth branch electric signal, the fifth branch electric signal and the sixth branch electric signal to respectively adjust the amplitude (V) of each branch electric signal 1a 、V 1b 、V 2a 、V 2b ) That is, the modulation indexes of the Mach-Zehnder modulators 1a, 1b, 2a, and 2b are adjusted (i.e., the modulation indexes of the Mach-Zehnder modulators 1a, 1b, and 2b are adjusted
V π Half-wave voltage of the modulator). When a continuous optical signal is input into the dual-polarization quadrature phase shift keying modulator, the Y-type optical splitter splits an incident optical signal into a seventh branch optical signal and an eighth branch optical signal which have equal power and frequency, the optical power of the seventh branch optical signal and the optical power of the eighth branch optical signal are approximately equal to half of the incident optical signal, and the frequency of the seventh branch optical signal and the frequency of the eighth branch optical signal are equal to the frequency of the incident optical signal. The seventh branch optical signal is inputted into the quadrature phase shift keying modulator 1, and the third branch electrical signal and the fourth branch electrical signal are dividedRespectively input to a Mach-Zehnder modulator 1a and a Mach-Zehnder modulator 1b through an electrical amplifier 1 and an electrical amplifier 2; controlling the output voltages of the direct current voltage stabilizing source 1, the direct current voltage stabilizing source 2 and the direct current voltage stabilizing source 3 to enable the Mach-Zehnder modulator 1a to work at the minimum transmission point and enable the Mach-Zehnder modulator 1b and the Mach-Zehnder modulator 1 to work at the maximum transmission point; then, the modulation index β of the Mach-Zehnder modulator 1a is adjusted by controlling the electric amplifiers 1, 2 1a And modulation index beta of Mach-Zehnder modulator 1b 1b Finally, the mach-zehnder modulator 1a outputs a gaussian pulse waveform with positive polarity, and the mach-zehnder modulator 1b outputs a double-gaussian pulse waveform with negative polarity (as shown on the left side of fig. 2 (a)), so that a positive second-order ultra-wideband optical signal (as shown on the right side of fig. 2 (a)) is obtained by combining the outputs of the quadrature phase shift keying modulator 1 and then enters the polarization beam combiner;
the optical signal of the eighth branch is input into the quadrature phase shift keying modulator 2, and the electrical signal of the fifth branch and the electrical signal of the sixth branch are respectively input into the Mach-Zehnder modulator 2a and the Mach-Zehnder modulator 2b through the electrical amplifier 3 and the electrical amplifier 4; controlling the output voltages of the direct current voltage stabilizing source 4, the direct current voltage stabilizing source 5 and the direct current voltage stabilizing source 6 to enable the Mach-Zehnder modulator 2b to work at the minimum transmission point, and enable the Mach-Zehnder modulator 2a and the March-Zehnder modulator 2 to work at the maximum transmission point; the modulation index beta of the Mach-Zehnder modulator 2a is adjusted by controlling the electric amplifiers 3, 4 2a And modulation index beta of Mach-Zehnder modulator 2b 2b Finally, the mach-zehnder modulator 2a outputs a negative-polarity gaussian pulse waveform, the mach-zehnder modulator 2b outputs a positive-polarity double-gaussian pulse waveform (as shown on the left side of fig. 2 (b)), and since the operating transmission points of the mach-zehnder modulator 2a and the mach-zehnder modulator 2b are opposite to the operating transmission points of the mach-zehnder modulator 1a and the mach-zehnder modulator 1b, the mach-zehnder modulator 2a and the mach-zehnder modulator 2b output waveforms opposite to the mach-zehnder modulator 1a and the mach-zehnder modulator 1b, and a delay τ is obtained by combining at the output of the quadrature phase shift keying modulator 2 1 A negative second-order ultra-wideband optical signal (as shown on the right side of fig. 2 (b)); then the polarization state of the negative second-order ultra-wideband optical signal is rotated by 90 degrees by a 90-degree polarization rotator, so that the polarization state of the negative second-order ultra-wideband optical signal and the polarization state of the positive second-order ultra-wideband optical signal form an orthogonal relation (as shown in the left side of fig. 2 (c)), and then the negative second-order ultra-wideband optical signal enters a polarization beam combiner; the positive second-order ultra-wideband optical signal and the negative second-order ultra-wideband optical signal output by the quadrature phase shift keying modulator 1 and the quadrature phase shift keying modulator 2 are combined through a polarization beam combiner, and then are divided into a ninth branch optical signal and a tenth branch optical signal through a coupler, the power of the ninth branch optical signal and the tenth branch optical signal is about half of that of the original optical signal, and the frequency of the ninth branch optical signal and the tenth branch optical signal is equal to that of the original optical signal; the ninth branch optical signal is input to a photoelectric detector 1 in the balanced photoelectric detector, and after photoelectric conversion, the positive second-order ultra-wideband optical signal and the negative second-order ultra-wideband optical signal with opposite polarities are combined to generate a positive third-order ultra-wideband signal (as shown in fig. 2 (c)); the optical signal of the tenth branch is delayed by tau through an optical delay line 2 ，τ 2 The magnitude of the input electric Gaussian pulse is approximately equal to half of the full width at half maximum of the input electric Gaussian pulse, then the input electric Gaussian pulse is input into a photoelectric detector 2 in a balanced photoelectric detector, and a negative third-order ultra-wideband signal is generated after photoelectric conversion (as shown in figure 2 (d)); finally, at the output end of the balanced photodetector, the two positive third-order ultra-wideband signals and the negative third-order ultra-wideband signal with opposite polarities are combined to generate a positive fourth-order ultra-wideband signal (as shown in fig. 2 (e)); a delay line filter consisting of a balanced photoelectric detector and a light delay line is used as a first-order differentiator, which is equivalent to performing first-order differentiation on a third-order ultra-wide signal, so that a positive fourth-order ultra-wide signal is generated; when the electrical delay line is switched from the first branch electrical signal to the second branch electrical signal, a negative fourth-order ultra-wideband signal can be generated, the principle of which is consistent with the principle of generating a positive fourth-order ultra-wideband signal, and a schematic diagram of the process of generating the negative fourth-order ultra-wideband signal is shown in fig. 2 (f).
The frequencies of the first, second, third and fourth order ultra-wideband signals are the same, but the amplitudes and powers are attenuated with the increase of the connecting devices.
To obtain the best power efficiency, power efficiency and four modulation indexes (beta) are established 1a 、β 1b 、β 2a 、β 2b ) The time delay of the electric time delay line, the time delay of the optical time delay line and the full width at half maximum of the Gaussian pulse output by the arbitrary waveform generator. Since the waveforms output by the quadrature phase shift keying modulator 1 and the quadrature phase shift keying modulator 2 are symmetrical, we let β be 1a ＝β 2a ＝β a ，β 1b ＝β 2b ＝β b . Since the delay of the electrical and optical delay lines is adjusted with the variation of the full width at half maximum of the electrical Gaussian pulse, we establish β a And beta b Power efficiency at different full widths at half maximum. The power efficiency is calculated by the formula
P out Representing the power density, P, of the generated fourth order ultra-wideband signal spectrum FCC Representing the power density of the ultra-wideband mask between 3.1 and 10.6 GHz. Firstly, a mathematic model of the system is established by Matlab, and then beta is calculated under the condition that input electric Gaussian pulse full widths at half maximum are different a ＝1～3、β b Power efficiency of different ultra-wideband signal frequency spectrums output when the frequency spectrum is 3-6 (the value interval is 0.02), and then drawing beta a 、β b And power efficiency, and assigning a value of 0 to the power efficiency calculated over the spectrum of the ultra-wideband mask. First, let the full width at half maximum of the electrical Gaussian pulse be 140ps, let the electrical delay be 60ps, let the optical delay be 60ps, obtain the relation curve as shown in FIG. 3(a), the result shows that when the modulation index is β a 1.74 and β b The optimum power efficiency is 44.09% at 4.76; let the full width at half maximum of the electrical Gaussian pulse be 128ps, the electrical delay be 55ps and the optical delay be 60ps, resulting in the relationship shown in FIG. 3(b), which indicates that when the modulation index is β a 1.82 and β b The optimal power efficiency is 51.12% when the power efficiency is 4.72; the full width at half maximum of the electrical Gaussian pulse was set at 112ps, the electrical delay was set at 50ps, and the optical delay was set at 60ps, and the results showed that when the modulation index was changed as shown in FIG. 3(c), the relationship was obtainedIs beta a 1.88 and beta b The optimal power efficiency is 54.16% when the power is 4.48; let the full width at half maximum of the electrical Gaussian pulse be 100ps, the electrical delay be 50ps, and the optical delay be 50ps, to obtain the relationship curve shown in FIG. 3(d), and the result shows that when the modulation index is β a 2.56 and beta b The optimum power efficiency is 31.73% at 5.78. By comparison, when the full width at half maximum of the electric Gaussian pulse output by the arbitrary waveform generator is 112ps, the electric delay is 50ps, the optical delay is 60ps, and the two modulation indexes are 1.88 and 4.88, the theoretical optimal power efficiency of 54.16% can be obtained. In the experiment, the modulation index β was controlled by controlling the electric amplifiers 1, 2, 3, and 4 1a ＝1.88、β 1b ＝4.48、β 2a ＝1.88、β 2b The power efficiency of the generated fourth order ultra wideband signal is 53.46%, close to the theoretical analysis value, 4.48.
Finally, two typical communication modulation modes can be realized by changing the bit code sequence output by the arbitrary waveform generator: on-off keying modulation and pulse position modulation. The data encoding sequence was designated "110101". To implement on-off keying modulation, the bit code sequence "0001000" output by the arbitrary waveform generator is made to represent the data code "1", and the bit code sequence "0000000" is made to represent the data code "0". To implement pulse position modulation, the bit sequence "0010000" is made to represent data "1", and the bit sequence "0000100" is made to represent data "0". Successful implementation of the two modulation modes proves that the device has the capability of being used as a signal source in a data communication system.
The invention selects the tunable laser with the wavelength of 1530 nm-1565 nm as the continuous wave light source; the coupler is a 5:5 coupler; the bandwidth of the dual-polarized quadrature phase shift keying modulator is 23 GHz; the bandwidth of the balanced photoelectric detector is 22 GHz; the output bit rate of the arbitrary waveform generator can reach 65Gb/s at most; the amplitude of the output voltage of the direct current voltage stabilizing source 1, the direct current voltage stabilizing source 2, the direct current voltage stabilizing source 3, the direct current voltage stabilizing source 4, the direct current voltage stabilizing source 5 and the direct current voltage stabilizing source 6 is adjustable within 1V-20V; the working bandwidth of the electric delay line is 0-6GHz, the delay range is 0-635ps, and the adjustment precision is 5 ps; the delay range of the optical delay line is 0-330ps, and the adjustment precision is 0.001 ps; the working bandwidths of the electric amplifier 1, the electric amplifier 2, the electric amplifier 3 and the electric amplifier 4 are 0-20 GHz, and the gain adjustable range is 19 dB-24 dB; the work bandwidths of the power divider 1, the power divider 2 and the power divider 3 are 0-18 GHz. The device of the invention is characterized in that:
(1) the dual-polarization quadrature phase shift keying modulator easy to integrate and the balanced photoelectric detector easy to integrate are adopted, the device is simple and compact in structure, and the integrated signal source in the light-carrying ultra-wideband communication system is facilitated to be realized.
(2) The high-order ultra-wideband signal is generated, and the frequency spectrum of the generated ultra-wideband signal is enabled to better fit a power spectral density mask specified by the Federal communication Commission in the United states by controlling the modulation index of the modulator, so that the power efficiency is higher.
(3) Two typical communication modulation modes can be realized, and the device can be used as a signal source of an optical carrier ultra-wideband communication system.
Drawings
FIG. 1: a schematic diagram of a microwave photon four-order ultra-wideband signal generating device;
FIG. 2: a schematic diagram of a pulse shape generation process;
FIG. 3: modulation index and power efficiency, at different full widths at half maximum: (a)140 ps; (b)128 ps; (c)112 ps; (d)100 ps;
FIG. 4: generating a third order ultra wideband signal;
FIG. 5: generating a fourth-order ultra wideband signal;
FIG. 6: two modulation formats implemented for the code "110101": (a) on-off keying modulation; (b) and (4) pulse position modulation.
Detailed Description
Example 1:
the laser source is a TSL-510 tunable laser of Santec company, and the wavelength range of the laser is 1510nm to 1630 nm; the polarization controller is a three-ring polarization controller of Sichuan catalp crown company; the dual-polarized quadrature phase shift keying modulator is FTM7977HQA of Fujitsu company, the bandwidth is 23GHz, the working light wavelength is 1530 nm-1610 nm, and the half-wave voltage is 3.5V; the arbitrary waveform generator is M8195A by agilent; the direct current voltage stabilizing source 1, the direct current voltage stabilizing source 2, the direct current voltage stabilizing source 3, the direct current voltage stabilizing source 4, the direct current voltage stabilizing source 5 and the direct current voltage stabilizing source 6 are all GPS-4303C of weft fixing company, and the output voltage amplitude is adjustable within 1V-20V; the balanced photodetector is DSC730 of Discoverysemi company, and the bandwidth is 22 GHz; the spectrum analyzer is N9010A of Agilent, and the bandwidth of a measuring signal range is 10 Hz-26.5 GHz; the oscilloscope is MSOV254A from Agilent, and the bandwidth of the measurement signal is 25 GHz; the electric delay line is PADL6 of GigaBaudics company, the working bandwidth is 0-6GHz, the delay range is 0-635ps, and the adjusting precision is 5 ps; the optical delay line is an adjustable optical delay line of Sichuan Laitessos photoelectric technology limited company, the delay range is 0-330ps, and the adjustment precision is 0.001 ps; the electric amplifier 1, the electric amplifier 2, the electric amplifier 3 and the electric amplifier 4 are all MD-20-M of Optilab corporation, the working bandwidth is 0-20 GHz, and the gain adjustable range is 19 dB-24 dB; the power divider 1, the power divider 2 and the power divider 3 are PE2084 of PASTERNACK company, and the working bandwidth is 0-18 GHz.
After the system is connected, all instrument and equipment switches are turned on to enable all equipment to be in a working state, firstly, the laser outputs an optical signal with the frequency of 193.414THz (the corresponding wavelength is 1550nm), the power of the optical signal is 11dBm, the optical signal is input into the dual-polarization quadrature phase shift keying modulator through the polarization controller, the optical signal is divided into a seventh branch optical signal and an eighth branch optical signal which are equal in power by the Y-shaped optical splitter in a halving mode, and the seventh branch optical signal and the eighth branch optical signal enter the quadrature phase shift keying modulator 1 and the quadrature phase shift keying modulator 2 respectively. The bit rate of the electric Gaussian pulse sequence output by the arbitrary waveform generator is 10Gb/s, the electric Gaussian pulse sequence is output in a bit coding mode of one 1 per 32 bits, the repetition rate of the electric Gaussian pulse is 312.5Mb/s, and the full width at half maximum of the output electric Gaussian pulse is set to be 112 ps. An electric Gaussian pulse signal output by the arbitrary waveform generator is input into the power divider 1 and is divided into a first branch electric signal and a second branch electric signal which are equal in amplitude, power and frequency, the second branch electric signal is connected with an electric delay line, and the delay of the electric delay line is set to be 50 ps. The first branch electrical signal is divided into a third branch electrical signal and a fourth branch electrical signal with equal amplitude, power and frequency by the power divider 2, the third branch electrical signal enters the mach-zehnder modulator 1a of the quadrature phase shift keying modulator 1 through the electrical amplifier 1, and the fourth branch electrical signal enters the mach-zehnder modulator 1b of the quadrature phase shift keying modulator 1 through the electrical amplifier 2. And controlling the output voltage of the direct current voltage stabilizing source 1 to be 3.5V, and controlling the output voltages of the direct current voltage stabilizing source 2 and the direct current voltage stabilizing source 3 to be 0V. The electrical amplifier 1 and the electrical amplifier 2 were adjusted so that the modulation indexes of the mach-zehnder modulators 1a and 1b were close to theoretical analysis values of 1.88 and 4.48. The second branch electrical signal is delayed by 50ps after being output from the electrical delay line, and is divided into a fifth branch electrical signal and a sixth branch electrical signal with equal amplitude, power and frequency by the power divider 3, the fifth branch electrical signal enters the mach-zehnder modulator 2a of the quadrature phase shift keying modulator 2 through the electrical amplifier 3, and the sixth branch electrical signal enters the mach-zehnder modulator 2b of the quadrature phase shift keying modulator 2 through the electrical amplifier 4. And then controlling the output voltage of the direct current voltage stabilizing source 5 to be 3.5V, and controlling the output voltage of the direct current voltage stabilizing source 4 and the direct current voltage stabilizing source 6 to be 0V. The electrical amplifiers 3 and 4 are adjusted so that the modulation indexes of the mach-zehnder modulators 2a and 2b are close to theoretical analytical values of 1.88 and 4.48. The output optical signal of the dual-polarization quadrature phase shift keying modulator is input into the optical coupler, and the optical signal is divided into a ninth branch optical signal and a tenth branch optical signal which have equal power. Wherein, the ninth branch optical signal enters the photodetector 1 of the balanced photodetector, and outputs a positive third-order ultra-wideband waveform after photoelectric conversion (as shown in fig. 4(a, b)). Fig. 4(a) is a time domain waveform of a generated positive third order ultra wideband signal, and fig. 4(b) is a frequency spectrum of the positive third order ultra wideband signal. The optical signal of the tenth branch is input into the light-incoming delay line, the delay time of the light delay line is set to be 60ps, then the optical signal output by the light delay line enters the photoelectric detector 2 of the balanced photoelectric detector, and the negative third-order ultra-wideband signal is output after photoelectric conversion (as shown in fig. 4(c, d)). Fig. 4(c) is a time domain waveform of the generated negative third order ultra wideband signal, and fig. 4(d) is a frequency spectrum of the negative third order ultra wideband signal. After coupling the outputs of photodetector 1 and photodetector 2 in the balanced photodetector, the balanced photodetector outputs a positive fourth order ultra wideband signal (as shown in fig. 5(a, b)). Fig. 5(a) is a time domain waveform of the generated positive fourth-order ultra-wideband signal, the full width at half maximum of which is 40ps, and the waveform has better symmetry. Fig. 5(b) is a frequency spectrum of the generated positive fourth-order ultra-wideband signal, the 10dB bandwidth of the signal is about 6.88GHz, the power efficiency of the signal is calculated to be 53.46%, the frequency spectrum is close to a theoretical value, no unnecessary component exists in a low frequency band, and the ultra-wideband mask is well attached. When the electrical delay line is switched from the second branch electrical signal to the first branch electrical signal, a negative fourth order ultra-wideband signal can be obtained at the output of the balanced photodetector (as shown in fig. 5(c, d)). Fig. 5(c) is a generated negative fourth order ultra-wideband signal time-domain waveform. Fig. 5(d) shows the frequency spectrum of the generated negative fourth-order ultra-wideband signal, which is almost identical to the frequency spectrum of the positive fourth-order ultra-wideband signal, and is better fit with the ultra-wideband mask.
Finally, in order to verify the application capability of the device in a data communication system, two typical modulation modes are realized: on-off keying modulation and pulse position modulation. The output data code sequence is designated as "110101". Firstly, in order to realize on-off keying modulation, an electric Gaussian pulse bit code sequence '0001000' output by an arbitrary waveform generator is made to represent a data code '1', and a bit code sequence '0000000' is made to represent a data code '0'. The bit code sequence output by the arbitrary waveform generator is set to "000100000010000000000000100000000000001000" and the bit rate is 10 Gb/s. Figure 6(a) shows the generated ook modulated quad ultra wideband pulse sequence. Then, in order to realize pulse position modulation, the bit sequence "0010000" is made to represent data "1", and the bit sequence "0000100" is made to represent data "0". The bit code sequence output by the arbitrary waveform generator is set to "001000000100000000100001000000001000010000" and the bit rate is 10 Gb/s. Fig. 6(b) shows the generated pulse position modulated four-order ultra-wideband pulse sequence, and it can be seen that there is a significant difference between the pulse positions of "1" and "0". Therefore, the device can be used as a signal source in an optical ultra-wideband communication system.
Claims (6)
1. A four-order ultra-wideband signal generating device based on microwave photons is characterized in that: the device consists of a continuous wave laser, a polarization controller, an arbitrary waveform generator, an electric amplifier 1, an electric amplifier 2, an electric amplifier 3, an electric amplifier 4, a power divider 1, a power divider 2, a power divider 3, an electric delay line, a dual-polarization orthogonal phase shift keying modulator, a coupler, a direct current voltage stabilizing source 1, a direct current voltage stabilizing source 2, a direct current voltage stabilizing source 3, a direct current voltage stabilizing source 4, a direct current voltage stabilizing source 5, a direct current voltage stabilizing source 6, an optical delay line and a balanced photoelectric detector; the dual-polarization quadrature phase shift keying modulator is a commercial device integrated on a single chip and consists of a Y-shaped optical splitter, a quadrature phase shift keying modulator 1, a quadrature phase shift keying modulator 2, a 90-degree polarization rotator and a polarization beam combiner; the quadrature phase shift keying modulator 1 is composed of a Mach-Zehnder modulator 1a and a Mach-Zehnder modulator 1b which are embedded in two arms of a Megash-Zehnder modulator 1, an electric amplifier 1 and a direct current voltage stabilizing source 1 are connected with the Mach-Zehnder modulator 1a, an electric amplifier 2 and a direct current voltage stabilizing source 2 are connected with the Mach-Zehnder modulator 1b, and a direct current voltage stabilizing source 3 is connected with the Megash-Zehnder modulator 1; the quadrature phase shift keying modulator 2 is composed of a Mach-Zehnder modulator 2a and a Mach-Zehnder modulator 2b which are embedded in two arms of the Mach-Zehnder modulator 2, an electric amplifier 3 and a direct current voltage stabilizing source 4 are connected with the Mach-Zehnder modulator 2a, the electric amplifier 4 and the direct current voltage stabilizing source 5 are connected with the Mach-Zehnder modulator 2b, and a direct current voltage stabilizing source 6 is connected with the Mach-Zehnder modulator 2;
inputting continuous light output by the continuous wave laser into a dual-polarization quadrature phase shift keying modulator through a polarization controller, wherein the polarization controller is used for aligning the polarization state of incident light with the main axis of the dual-polarization quadrature phase shift keying modulator; meanwhile, a column of Gaussian pulse electrical signals are output from an arbitrary waveform generator, and are firstly divided into two paths of first branch electrical signals and second branch electrical signals with equal amplitude, power and frequency by a power divider 1, the frequency of the first branch electrical signals and the frequency of the second branch electrical signals are the same as the frequency of the Gaussian pulse electrical signals output by the arbitrary waveform generator, and the power of the first branch electrical signals and the power of the second branch electrical signals are half of the power of the Gaussian pulse electrical signals; the electrical signal of the second branch is input into an incoming delay line to introduce a delay tau 1 The amplitude, power, frequency of which remain constant, τ 1 Is equal to half the full width at half maximum of the input gaussian pulse; then the first branch is connectedThe electric signal is divided into two paths of third branch electric signals and fourth branch electric signals with equal amplitude, power and frequency through the power divider 2, the power of the third branch electric signals and the power of the fourth branch electric signals are equal to half of the power of the first branch electric signals, and the frequency of the third branch electric signals and the frequency of the fourth branch electric signals are the same as the frequency of Gaussian pulse electric signals output by the arbitrary waveform generator; the second branch electric signal is divided into two paths of fifth branch electric signals and sixth branch electric signals with equal amplitude, power and frequency through a power divider 3, the power of the fifth branch electric signals and the power of the sixth branch electric signals are equal to half of the power of the second branch electric signals, and the frequency of the fifth branch electric signals and the frequency of the sixth branch electric signals are the same as the frequency of Gaussian pulse electric signals output by an arbitrary waveform generator; when a continuous optical signal is input into the dual-polarization quadrature phase shift keying modulator, the Y-type optical splitter divides an incident optical signal into a seventh branch optical signal and an eighth branch optical signal which have equal power and frequency, the optical power of the seventh branch optical signal and the optical power of the eighth branch optical signal are equal to half of the incident optical signal, and the frequency of the seventh branch optical signal and the frequency of the eighth branch optical signal are equal to the frequency of the incident optical signal; inputting a seventh branch optical signal into the quadrature phase shift keying modulator 1, and inputting a third branch electrical signal and a fourth branch electrical signal into the mach-zehnder modulator 1a and the mach-zehnder modulator 1b through the electrical amplifier 1 and the electrical amplifier 2, respectively; controlling the output voltages of the direct current voltage stabilizing source 1, the direct current voltage stabilizing source 2 and the direct current voltage stabilizing source 3 to enable the Mach-Zehnder modulator 1a to work at the minimum transmission point, and enable the Mach-Zehnder modulator 1b and the March-Zehnder modulator 1 to work at the maximum transmission point; then, the modulation index β of the Mach-Zehnder modulator 1a is adjusted by controlling the electric amplifiers 1, 2 1a And modulation index beta of Mach-Zehnder modulator 1b 1b Finally, enabling the Mach-Zehnder modulator 1a to output a Gaussian pulse waveform with positive polarity, enabling the Mach-Zehnder modulator 1b to output a double-Gaussian pulse waveform with negative polarity, and combining the waveforms at the output of the quadrature phase shift keying modulator 1 to obtain a positive and second-order ultra-wideband optical signal, and then enabling the signal to enter the polarization beam combiner; the optical signal of the eighth branch is input into the quadrature phase shift keying modulator 2, and the electrical signal of the fifth branch and the electrical signal of the sixth branch are respectively input into the Mach-Zehnder modulator 2a and the Mach-Zehnder modulator 2b through the electrical amplifier 3 and the electrical amplifier 4; controlling a direct current voltage stabilizing source 4,The output voltages of the direct current voltage stabilizing source 5 and the direct current voltage stabilizing source 6 enable the Mach-Zehnder modulator 2b to work at the minimum transmission point, and enable the Mach-Zehnder modulator 2a and the March-Zehnder modulator 2 to work at the maximum transmission point; the modulation index beta of the Mach-Zehnder modulator 2a is adjusted by controlling the electric amplifiers 3, 4 2a And modulation index beta of Mach-Zehnder modulator 2b 2b Finally, the Mach-Zehnder modulator 2a outputs a Gaussian pulse waveform with a negative polarity, the Mach-Zehnder modulator 2b outputs a double-Gaussian pulse waveform with a positive polarity, and the operating transmission points of the Mach-Zehnder modulator 2a and the Mach-Zehnder modulator 2b are opposite to the operating transmission points of the Mach-Zehnder modulator 1a and the Mach-Zehnder modulator 1b, so that the Mach-Zehnder modulator 2a and the Mach-Zehnder modulator 2b output waveforms opposite to the Mach-Zehnder modulator 1a and the Mach-Zehnder modulator 1b, and a delay tau is obtained by combining the waveforms at the output of the quadrature phase shift keying modulator 2 1 The negative second-order ultra-wideband optical signal; then the polarization state of the negative second-order ultra-wideband optical signal is rotated by 90 degrees by a 90-degree polarization rotator, so that the polarization state of the negative second-order ultra-wideband optical signal and the polarization state of the positive second-order ultra-wideband optical signal form an orthogonal relation, and then the negative second-order ultra-wideband optical signal enters a polarization beam combiner; the positive second-order ultra-wideband optical signal and the negative second-order ultra-wideband optical signal output by the quadrature phase shift keying modulator 1 and the quadrature phase shift keying modulator 2 are combined through a polarization beam combiner, and then are divided into a ninth branch optical signal and a tenth branch optical signal through a coupler, the power of the ninth branch optical signal and the tenth branch optical signal is half of that of the original optical signal, and the frequency of the ninth branch optical signal and the tenth branch optical signal is equal to that of the original optical signal; inputting the ninth branch optical signal into a photoelectric detector 1 in the balanced photoelectric detector, and combining a positive second-order ultra-wideband optical signal and a negative second-order ultra-wideband optical signal with opposite polarities to generate a positive third-order ultra-wideband signal after photoelectric conversion; the optical signal of the tenth branch is delayed by tau through an optical delay line 2 ，τ 2 The magnitude of the input electric Gaussian pulse is equal to half of the full width at half maximum of the input electric Gaussian pulse, then the input electric Gaussian pulse is input into a photoelectric detector 2 in a balanced photoelectric detector, and a negative third-order ultra wide band signal is generated after photoelectric conversion; finally, at the output end of the balanced photoelectric detector, two positive third-order ultra-wideband signals and two negative third-order ultra-wideband signals with opposite polarities are connectedCombining to generate a positive fourth-order ultra wideband signal; the delay line filter composed of the balanced photoelectric detector and the optical delay line is used as a first-order differentiator, which is equivalent to performing first-order differentiation on a third-order ultra-wide signal, thereby generating a positive fourth-order ultra-wide signal.
2. A microwave-photon-based fourth-order ultra-wideband signal generating device, as defined in claim 1, wherein: selecting a tunable laser with the wavelength of 1530 nm-1565 nm as a continuous wave light source; the coupler is a 5:5 coupler; the bandwidth of the dual-polarized quadrature phase shift keying modulator is 23GHz, and the bandwidth of the balanced photoelectric detector is 22 GHz; the output bit rate of the arbitrary waveform generator can reach 65Gb/s at most; the amplitude of the output voltage of the direct current voltage stabilizing source 1, the direct current voltage stabilizing source 2, the direct current voltage stabilizing source 3, the direct current voltage stabilizing source 4, the direct current voltage stabilizing source 5 and the direct current voltage stabilizing source 6 is adjustable within 1V-20V; the working bandwidth of the electric delay line is 0-6GHz, the delay range is 0-635ps, and the adjustment precision is 5 ps; the delay range of the optical delay line is 0-330ps, and the adjustment precision is 0.001 ps; the working bandwidths of the electric amplifier 1, the electric amplifier 2, the electric amplifier 3 and the electric amplifier 4 are 0-20 GHz, and the gain adjustable range is 19 dB-24 dB; the work bandwidths of the power divider 1, the power divider 2 and the power divider 3 are 0-18 GHz.
3. A fourth order ultra-wideband signal generating device based on microwave photons, as claimed in claim 1, wherein: the modulation index beta is controlled by controlling the electric amplifiers 1, 2, 3, 4 1a ＝1.88、β 1b ＝4.48、β 2a ＝1.88、β 2b The power efficiency of the generated fourth order ultra wideband signal is 53.46%, 4.48%.
4. A fourth order ultra-wideband signal generating device based on microwave photons, as claimed in claim 1, wherein: when the electric delay line is converted from the first branch electric signal to the second branch electric signal, a negative fourth-order ultra-wideband signal is generated.
5. A microwave-photon-based fourth-order ultra-wideband signal generating device, as claimed in claim 1, 2, 3 or 4, wherein: the two typical communication modulation modes of on-off keying modulation and pulse position modulation are realized by changing the bit code sequence output by an arbitrary waveform generator.
6. A fourth order ultra-wideband signal generating device based on microwave photons, as claimed in claim 5, characterized in that: the bit coding sequence '0001000' output by the arbitrary waveform generator represents the data code '1', the bit coding sequence '0000000' represents the data code '0', and the on-off keying modulation is realized; let the bit sequence "0010000" represent data "1" and let the bit sequence "0000100" represent data "0", implementing pulse position modulation.
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