CN115412170A - Multisource nonlinear distortion suppression method based on double-drive Mach-Zehnder modulator - Google Patents

Multisource nonlinear distortion suppression method based on double-drive Mach-Zehnder modulator Download PDF

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CN115412170A
CN115412170A CN202210631042.XA CN202210631042A CN115412170A CN 115412170 A CN115412170 A CN 115412170A CN 202210631042 A CN202210631042 A CN 202210631042A CN 115412170 A CN115412170 A CN 115412170A
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张进
张德培
王亚兰
王安乐
王党卫
刘晓彤
彭小牛
李东宇
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Air Force Early Warning Academy
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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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • H04B10/2543—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to fibre non-linearities, e.g. Kerr effect
    • 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
    • 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
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Abstract

The invention relates to the field of optical communication and microwave photon, in particular to a multisource nonlinear distortion suppression method based on a double-drive Mach-Zehnder modulator, which outputs optical carriers through a laser, modulates radio-frequency signals onto the optical carriers through the double-drive Mach-Zehnder modulator, respectively inputs radio-frequency signals with the phase difference of 90 degrees at two sides of an upper branch and a lower branch through a power divider and a phase shifter, adjusts bias voltage to output single-side band signals with-1-order side bands suppressed, respectively introduces amplitude-phase relation to 0,1 and 2-order side bands through a programmable optical filter, suppresses the amplitude of the carrier to be one third of the original amplitude, reverses the phase by 180 degrees, and finally transmits the signals to a photoelectric detector for demodulation, so that the suppression of IMD3 can be realized, and simultaneously, since the adjusted carrier waves are the XMD can also be suppressed, the problem of nonlinear distortion can be overcome by simultaneously suppressing IMD3 and XMD in a microwave photon link, thereby improving the linearity of the microwave photon link under broadband signals.

Description

Multisource nonlinear distortion suppression method based on double-drive Mach-Zehnder modulator
Technical Field
The invention relates to the field of optical communication and microwave photon, in particular to a multisource nonlinear distortion suppression method based on a dual-drive Mach-Zehnder modulator.
Background
Microwave Photonic links (MPL, microwave Photonic links) have the advantages of large bandwidth, light weight, low loss, electromagnetic interference resistance and the like, so that the Microwave Photonic technology is widely applied to the fields of satellite communication, radars, radio Over Fiber (ROF), and the like. ROF is one of the important applications of microwave photonics, and is generally composed of a central office, a fiber link, and a remote antenna unit. The microwave signal is modulated to the optical signal at the central station, then the modulated optical signal is transmitted through the optical fiber link, and after reaching the base station, the microwave signal is demodulated through photoelectric conversion and then transmitted through the antenna for the user to use. In recent years, the development of wireless over fiber technologies has been rapid, and services have been diversified, because optical fibers with the advantages of large bandwidth and low loss are used as media for transmission, and high-frequency wireless signals are transmitted.
The spurious-free dynamic range (SFDR) is an important performance indicator of the ROF system, and is defined as the range of the input power of the rf signal or the corresponding range of the output power of the rf signal when the output power of the signal is greater than the noise power and the intermodulation distortion power is less than the noise power. However, due to the nonlinear response of the electro-optical modulation, the generated intermodulation distortion will cause the spurious-free dynamic range to be limited, and it is difficult to satisfy the requirement of a large dynamic transmission system, wherein the Third order intermodulation distortion (IMD 3) is very close to the fundamental wave signal in the frequency domain, and is difficult to filter, which is a main obstacle to achieving the spurious-free dynamic range improvement. In addition to the harmonic and intermodulation distortions that are typically present in narrowband and single carrier microwave photonic link systems, several nonlinear distortions may be present in both wideband and multi-carrier microwave photonic link systems, further limiting the dynamic range of the link. The theory shows that in a broadband and multi-carrier frequency system, carrier intermodulation distortion and third-order intermodulation distortion are third-order distortion, and the stronger the carrier is, the more serious the carrier intermodulation distortion is, the same serious the dynamic range of a microwave photonic link is affected. Therefore, how to suppress IMD3 and XMD becomes an urgent problem to be solved to realize the microwave photonic link dynamic range improvement.
Disclosure of Invention
Therefore, the invention provides a multi-source nonlinear distortion suppression method based on a dual-drive Mach-Zehnder modulator, which is used for overcoming the problem of how to simultaneously suppress IMD3 and XMD in the prior art.
In order to achieve the purpose, the multi-source nonlinear distortion suppression method based on the double-drive Mach-Zehnder modulator comprises a laser, the double-drive Mach-Zehnder modulator, a long optical fiber, a programmable optical filter, a photoelectric detector, a power divider and a phase shifter. The output end of the laser is connected with the optical input end of the double-drive Mach-Zehnder modulator, the output end of the double-drive Mach-Zehnder modulator is connected with the long optical fiber and then connected with the input end of the programmable optical filter, and the output end of the programmable optical filter is connected with the photoelectric detector.
The multisource nonlinear distortion suppression method based on the double-drive Mach-Zehnder modulator comprises the following steps:
step s1, outputting an optical carrier by a laser, and modulating a radio frequency signal to the optical carrier by a double-drive Mach-Zehnder modulator;
step s2, respectively inputting radio frequency signals with the phase difference of 90 degrees at two sides of the upper and lower branches through a power divider and a phase shifter;
step s3, the system realizes single-sideband transmission, simultaneously considers the suppression of IMD3 and XMD of the system, and adjusts bias voltage to enable the output to be a single-sideband signal with suppressed-1-order sideband;
step s4, respectively introducing amplitude-phase relations to 0,1 and 2-order sidebands through a programmable optical filter, inhibiting the carrier amplitude to be one third of the original amplitude, and turning the phase by 180 degrees;
and s5, transmitting the carrier wave to a photoelectric detector for demodulation, and realizing the suppression of IMD3 and XMD.
Further, in the step s1, the expression of the output optical carrier is as follows:
Figure RE-GDA0003911340900000021
wherein E 0 For outputting light intensity, omega, to the laser c Is the angular frequency of the optical carrier signal.
Further, in the step s2, after passing through the first Y-shaped waveguide, the upper branch optical signal is represented by formula (1):
Figure RE-GDA0003911340900000022
the lower branch optical signal is shown in formula (2):
Figure RE-GDA0003911340900000023
further, on the premise that the upper branch optical signal is calculated by using the formula (2) and the lower branch optical signal is calculated by using the formula (3), the upper branch input radio frequency signal is calculated according to the formula (2) and the lower branch input radio frequency signal is calculated according to the formula (3), and the upper branch bias voltage is recorded as V bias1 Initial phase is δ 1 The amplitude of the radio frequency signal is marked as A 1 And the angular frequency of the input radio frequency signal of the upper branch is recorded as omega RF And the lower branch bias voltage is denoted as V bia The initial phase is δ 2 The amplitude of the radio frequency signal is marked as A 2 And the angular frequencies of the lower branch input radio frequency signals are respectively marked as omega RF
The upper branch input radio frequency signal is as shown in formula (4):
V 1 ＝V bias +A 1 sin(ω RF t+δ 1 ) (4)
the lower branch input radio frequency signal is as shown in formula (5):
V 2 ＝V bias2 +A 2 sin(ω RF t+δ 2 ) (5)。
further, on the premise that the upper branch output optical field is calculated by using equation (6) and the lower branch output optical field is calculated by using equation (7), an output DDMZM is calculated according to equations (6) and (7), and the output DDMZM is represented by equation (8):
Figure RE-GDA0003911340900000031
since the output can be rewritten as shown in equation (9) in relation to the difference between the output and the bias voltages of the upper and lower arms and the phase difference of the input signal,
Figure RE-GDA0003911340900000032
wherein exp (j [ theta + msin (omega)) RF t)]) As a first part, exp (jmsin (ω) RF t+δ 2 ) Is) is a second portion of the first portion,
Figure RE-GDA0003911340900000033
to change the bias current only shifts the sideband angles as a whole,
Figure RE-GDA0003911340900000034
in order to change the initial angle of the input radio frequency, the influence on each sideband is inconsistent;
where m is the modulation index of the RF signal, θ is the phase, J k (m) a k-th order class 1 shell with a parameter mThe Sehr coefficients, k are integers.
Further, on the premise that the output DDMZM is calculated using equation (9), the side band amplitude angle is adjusted by equation (10) to achieve suppression of IMD3,
Figure RE-GDA0003911340900000041
further, let ω be during the calculation 1 And ω 2 Setting omega for the angular frequency of a diphone signal 1 <ω 2 If the upper branch input rf signal and the lower branch input rf signal input diphone signal are the following signals:
V 1 ＝V bias +A 1 [sin(ω 1 t)+sin(ω 2 t)] (11)
Figure RE-GDA0003911340900000042
the output signal of the DDMZM is obtained according to equations (11) and (12):
Figure RE-GDA0003911340900000043
further, since a signal capable of generating IMD3 distortion exists within ± 2-order sidebands and-1-order sidebands are suppressed, the-2-order sidebands can be also ignored, and the combination of the output signals of the DDMZM can be simplified into equations (14) and (15):
Figure RE-GDA0003911340900000051
Figure RE-GDA0003911340900000052
wherein, the first and the second end of the pipe are connected with each other,
Figure RE-GDA0003911340900000053
for the-2 order sideband, since the-1 order is suppressed, the IMD3 signal cannot be generated and can be omitted.
Further, amplitude-phase relation is respectively introduced to 0,1,2 order sidebands through programmable optical filters
Figure RE-GDA0003911340900000054
Figure RE-GDA0003911340900000055
And with
Figure RE-GDA0003911340900000056
The output electrical signal is:
Figure RE-GDA0003911340900000061
in the formula (16) of the above formula,
Figure RE-GDA0003911340900000062
the amplitude of the suppressed carrier wave is 1/3 of the original amplitude, and the phase is turned over by 180 degrees; IMD3 suppression can be achieved while XMD is also suppressed because it is the carrier that is suppressed.
Compared with the prior art, the invention has the advantages that the laser outputs optical carriers, radio frequency signals are modulated onto the optical carriers through the double-drive Mach-Zehnder modulator, the radio frequency signals with the phase difference of 90 degrees are respectively input to the two sides of the upper and lower branches through the power divider and the phase shifter, the bias voltage is adjusted to output single-side-band signals with suppressed-1-order side bands, the amplitude-phase relation is respectively introduced into 0,1 and 2-order side bands through the programmable optical filter, the amplitude of the suppressed carriers is one third of the original amplitude, the phase is inverted by 180 degrees, and finally the signals are transmitted to the photoelectric detector for demodulation, so that the suppression of IMD3 can be realized, and simultaneously, since the adjusted carriers are adopted, XMD can also be suppressed, and the problem of nonlinear distortion is solved by simultaneously suppressing the IMD3 and XMD in the microwave photon link, so that the linearity of the microwave photon link under broadband signals is improved.
Drawings
FIG. 1 is a flow chart of a multi-source nonlinear distortion suppression method based on a dual-drive Mach-Zehnder modulator according to the present invention;
fig. 2 is a schematic block diagram of dynamic range enhancement based on single-sideband transmission of a DDMZM modulator according to the present invention;
fig. 3 is a block diagram of a modulation module.
Detailed Description
In order that the objects and advantages of the invention will be more clearly understood, the invention is further described below with reference to examples; it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and do not limit the scope of the present invention.
Fig. 1 is a schematic diagram illustrating a dynamic range enhancement based on single-sideband transmission of a DDMZM modulator according to the present invention; the device comprises a laser, a modulation module, a long optical fiber, an optical filter and a photoelectric detector. The radio frequency input signal S2 is modulated to an optical signal S1 output by a laser through a modulation module to obtain a single sideband modulation signal S3. The modulation signal S3 passes through an optical filter and then outputs a modulation signal S4 with a specific carrier sideband ratio, and finally, the modulation signal S5 is demodulated by a photoelectric detector to realize the output of a radio frequency signal S5.
The invention discloses a multisource nonlinear distortion suppression method based on a double-drive Mach-Zehnder modulator, which comprises the following steps:
step s1, outputting an optical carrier by a laser, and modulating a radio frequency signal to the optical carrier by a double-drive Mach-Zehnder modulator;
step s2, respectively inputting radio frequency signals with the phase difference of 90 degrees at two sides of the upper and lower branches through a power divider and a phase shifter;
step s3, the system realizes single sideband transmission, simultaneously considers the suppression of IMD3 and XMD of the system, and adjusts the bias voltage to output as a single sideband signal with suppressed-1 order sideband;
step s4, introducing amplitude-phase relations to 0-order sidebands, 1-order sidebands and 2-order sidebands through the programmable optical filter respectively, restraining the carrier amplitude to be one third of the original amplitude, and turning the phase by 180 degrees;
and step s5, transmitting the carrier to a photoelectric detector for demodulation, and realizing the suppression of IMD3 and XMD.
Specifically, the laser is a distributed feedback laser; the microwave signal source is a direct digital frequency synthesizer; the long optical fiber is a 1km single-mode optical fiber; the input end node of the photoelectric detector can add an optical amplifier for optical signal amplification.
Specifically, please refer to fig. 2, which is a structural diagram of the modulation module; the modulation module consists of a double-drive Mach-Zehnder modulator, a power divider and a phase shifter. The power divider divides the radio frequency input into two paths, one path is transmitted to an upper branch of the modulator, the other path generates 90-degree phase shift through the phase shifter and is transmitted to a lower branch of the modulator, and the single-side band signal transmission is realized by adjusting the bias voltage.
Further, in the step s1, the expression of the output optical carrier is as follows, and the output light intensity of the laser is recorded as E 0 The angular frequency of the optical carrier signal is denoted as ω c ：
Figure RE-GDA0003911340900000071
Further, in step s2, after passing through the first Y-shaped waveguide, the upper branch optical signal is as shown in formula (1):
Figure RE-GDA0003911340900000081
the lower branch optical signal is as shown in formula (2):
Figure RE-GDA0003911340900000082
further, an upper branch optical signal is calculated using the formula (2) and the formula (c) is used3) On the premise of calculating the lower branch optical signal, calculating the upper branch input radio frequency signal according to the formula (2), calculating the lower branch input radio frequency signal according to the formula (3), and recording the upper branch bias voltage as V bia The initial phase is δ 1 The amplitude of the radio frequency signal is marked as A 1 And the angular frequency of the input radio frequency signal of the upper branch is recorded as omega RF And the lower branch bias voltage is denoted as V bias2 The initial phase is δ 2 The amplitude of the radio frequency signal is marked as A 2 And the angular frequency of the lower branch input radio frequency signal is respectively marked as omega RF
The upper branch input radio frequency signal is as shown in formula (4):
V 1 ＝V bias1 +A 1 sin(ω RF t+δ 1 ) (4)
the lower branch input radio frequency signal is as shown in formula (5):
V 2 ＝V bias +A 2 sin(ω RF t+δ 2 ) (5)。
further, on the premise that the upper branch input radio frequency signal is calculated by using the formula (4) and the lower branch input radio frequency signal is calculated by using the formula (5), the upper branch output optical field is calculated according to the formula (4) and the lower branch output optical field is calculated according to the formula (5), and the half-wave voltage is recorded as V π ，
The upper branch output light field is as shown in formula (6):
Figure RE-GDA0003911340900000083
the lower branch output light field is as shown in formula (7):
Figure RE-GDA0003911340900000084
further, on the premise that the upper branch output optical field is calculated by using equation (6) and the lower branch output optical field is calculated by using equation (7), an output DDMZM is calculated according to equations (6) and (7), and the output DDMZM is represented by equation (8):
Figure RE-GDA0003911340900000085
since the output can be rewritten as shown in equation (9) in relation to the difference between the output and the bias voltages of the upper and lower arms and the phase difference of the input signal,
Figure RE-GDA0003911340900000091
wherein, exp (j [ theta + msin (omega)) RF t)]) As a first part, exp (jmsin (ω) RF t+δ 2 ) Is) is a second portion of the first portion,
Figure RE-GDA0003911340900000092
to change the bias current only shifts the sideband angles as a whole,
Figure RE-GDA0003911340900000093
in order to change the initial angle of the input radio frequency, the influence on each sideband is inconsistent;
where m is the modulation index of the RF signal, θ is the phase, J k (m) is a k-th order Bessel coefficient of class 1 for parameter m, k being an integer.
Further, on the premise that the output DDMZM is calculated by using equation (9), the system wants to realize single-sideband transmission, and simultaneously considers the suppression of IMD3 and XMD of the system, the sideband needs to be considered as ± 2 order, one of ± 1 order sidebands needs to be suppressed, the scheme enables the-1 order sideband to be suppressed, the 0 and +2 order sidebands need not be 0, the suppression of IMD3 can be realized by adjusting the sideband amplitude angle, the suppression of IMD3 is realized by adjusting the sideband amplitude angle by equation (10),
Figure RE-GDA0003911340900000094
further, in the calculation process, ω is set 1 And ω 2 Setting omega for the angular frequency of a diphone signal 1 <ω 2 If the upper branch input rf signal and the lower branch input rf signal input diphone signal are the following signals:
V 1 ＝V bias1 +A 1 [sin(ω 1 t)+sin(ω 2 t)] (11)
Figure RE-GDA0003911340900000095
the output signal of the DDMZM is obtained according to equations (10) and (11):
Figure RE-GDA0003911340900000101
further, since a signal capable of generating IMD3 distortion exists within ± 2-order sidebands and-1-order sidebands are suppressed, the-2-order sidebands can be also ignored, and the combination of the output signals of the DDMZM can be simplified into equations (14) and (15):
Figure RE-GDA0003911340900000102
Figure RE-GDA0003911340900000111
wherein the content of the first and second substances,
Figure RE-GDA0003911340900000112
for the-2 order sideband, since the-1 order is suppressed, the IMD3 signal cannot be generated and can be omitted.
At IMD3 frequency 2 omega 2 -ω 1 For example, a light field analysis of IMD3 inhibition theory was performed: as shown in equation (17):
Figure RE-GDA0003911340900000113
further, by a programmable optical filterRespectively introducing amplitude-phase relation to 0,1,2 order sidebands
Figure RE-GDA0003911340900000114
Figure RE-GDA0003911340900000115
And
Figure RE-GDA0003911340900000116
the output electrical signal is:
Figure RE-GDA0003911340900000117
Figure RE-GDA0003911340900000121
in the formula (16) of the method,
Figure RE-GDA0003911340900000122
the amplitude of the suppressed carrier wave is 1/3 of the original amplitude, and the phase is turned over by 180 degrees; IMD3 suppression can be achieved, while XMD is also suppressed because it is the carrier that is suppressed.
Furthermore, the invention outputs optical carriers through a laser, radio frequency signals are modulated onto the optical carriers through a double-drive Mach-Zehnder modulator, radio frequency signals with the phase difference of 90 degrees are respectively input to the two sides of an upper branch and a lower branch through a power divider and a phase shifter, bias voltage is adjusted to enable the output to be single-side-band signals with-1 order sidebands suppressed, amplitude-phase relations are respectively introduced to 0,1 and 2 order sidebands through a programmable optical filter, the amplitude of the suppressed carrier is one third of the original amplitude, the phase is inverted by 180 degrees, and finally the phase is transmitted to a photoelectric detector for demodulation, so that the suppression of IMD3 can be realized, XMD can also be suppressed because the adjusted carrier is the carrier, and the problem of multi-source nonlinear distortion is solved by simultaneously suppressing IMD3 and XMD in a microwave photonic link, thereby improving the linearity of the microwave photonic link under broadband signals.
Furthermore, the multi-source nonlinear distortion suppression method based on the double-drive Mach-Zehnder modulator does not relate to a complex structure, the multi-source nonlinear distortion suppression method fully utilizes the electro-optic modulation principle, simultaneously suppresses IMD3 and XMD in the microwave photon link to overcome the problem of multi-source nonlinear distortion, and improves the linearity of the microwave photon link under a broadband signal.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is apparent to those skilled in the art that the scope of the present invention is not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can be within the protection scope of the invention.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention; various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A multi-source nonlinear distortion suppression method based on a dual-drive Mach-Zehnder modulator is characterized by comprising the following steps:
step s1, outputting an optical carrier by a laser, and modulating a radio frequency signal to the optical carrier by a double-drive Mach-Zehnder modulator;
step s2, respectively inputting radio frequency signals with the phase difference of 90 degrees at two sides of the upper and lower branches through a power divider and a phase shifter;
step s3, the system realizes single sideband transmission, simultaneously considers the suppression of IMD3 and XMD of the system, and adjusts the bias voltage to output as a single sideband signal with suppressed-1 order sideband;
step s4, respectively introducing amplitude-phase relations to 0,1 and 2-order sidebands through a programmable optical filter, inhibiting the carrier amplitude to be one third of the original amplitude, and turning the phase by 180 degrees;
and step s5, transmitting the carrier to a photoelectric detector for demodulation, and realizing the suppression of IMD3 and XMD.
2. The method for suppressing the multi-source nonlinear distortion based on the double-drive Mach-Zehnder modulator according to claim 1, characterized in that in the step s1, the expression of the output optical carrier is as follows, and the output light intensity of the laser is recorded as E 0 The angular frequency of the optical carrier signal is denoted as ω c ：
Figure RE-FDA0003911340890000011
3. The method for suppressing multi-source nonlinear distortion based on the dual-drive mach-zehnder modulator according to claim 2, wherein in the step s2, after passing through the first Y-shaped waveguide, the upper branch optical signal is represented by formula (1):
Figure RE-FDA0003911340890000012
the lower branch optical signal is as shown in formula (2):
Figure RE-FDA0003911340890000013
4. the method for suppressing multi-source nonlinear distortion based on the dual-drive mach-zehnder modulator according to claim 3, wherein on the premise that the upper branch optical signal is calculated by using the formula (2) and the lower branch optical signal is calculated by using the formula (3), the upper branch input radio frequency signal is calculated according to the formula (2) and the lower branch input radio frequency signal is calculated according to the formula (3), and the upper branch bias voltage is represented as V bias The initial phase is δ 1 The amplitude of the radio frequency signal is marked as A 1 And will be atThe input radio frequency signal angular frequency of the branch is marked as omega RF And the lower branch bias voltage is denoted as V bias2 The initial phase is δ 2 The amplitude of the radio frequency signal is marked as A 2 And the angular frequency of the lower branch input radio frequency signal is respectively marked as omega RF ，
The upper branch input radio frequency signal is as shown in formula (4):
V 1 ＝V bias1 +A 1 sin(ω RF t+δ 1 ) (4)
the lower branch input radio frequency signal is as shown in formula (5):
V 2 ＝V bias +A 2 sin(ω RF t+δ 2 ) (5)。
5. the multi-source nonlinear distortion suppression method based on the dual-drive mach-zehnder modulator according to claim 4, characterized in that on the premise that the upper branch input radio frequency signal is calculated by using formula (4) and the lower branch input radio frequency signal is calculated by using formula (5), the upper branch output optical field is calculated according to formula (4) and the lower branch output optical field is calculated according to formula (5), wherein the half-wave voltage is denoted as V π ，
The upper branch output light field is as shown in formula (6):
Figure RE-FDA0003911340890000021
the lower branch output light field is as shown in formula (7):
Figure RE-FDA0003911340890000022
6. the dual-drive mach-zehnder modulator-based multi-source nonlinear distortion suppression method according to claim 5, wherein on the premise that the upper-branch output optical field is calculated by using equation (6) and the lower-branch output optical field is calculated by using equation (7), an output DDMZM is calculated according to equations (6) and (7), and the output DDMZM is represented by equation (8):
Figure RE-FDA0003911340890000023
the output is rewritten according to the difference between the output and the bias voltages of the upper and lower arms and the phase difference of the input signal, and the rewritten output is expressed by the following formula (9):
Figure RE-FDA0003911340890000024
wherein exp (j [ theta + msin (omega)) RF t)]) As a first part, exp (jm sin (ω) RF t+δ 2 ) Is) is a second portion of the first portion,
Figure RE-FDA0003911340890000031
to change the bias current only shifts the sideband angles as a whole,
Figure RE-FDA0003911340890000032
in order to change the initial angle of the input radio frequency, the influence on each sideband is inconsistent;
where m is the modulation index of the RF signal, θ is the phase, J k (m) is a k-th order Bessel coefficient of class 1 for parameter m, k being an integer.
7. The dual-drive Mach-Zehnder modulator-based multi-source nonlinear distortion suppression method according to claim 6, characterized in that, on the premise that the output DDMZM is calculated by using the formula (9), the sideband amplitude angle is adjusted by the formula (10) to realize suppression of IMD3,
Figure RE-FDA0003911340890000033
8. double drive based mach in accordance with claim 7A method for suppressing multi-source non-linear distortion of a Gade modulator is characterized in that the angular frequency omega of a two-tone signal is set in the calculation process 1 And ω 2 Setting ω 1 <ω 2 The upper branch input radio frequency signal and the lower branch input radio frequency signal input two-tone signal can be obtained as follows:
V 1 ＝V bias1 +A 1 [sin(ω 1 t)+sin(ω 2 t)] (11)
Figure RE-FDA0003911340890000034
the output signal of the DDMZM is obtained according to equations (11) and (12):
Figure RE-FDA0003911340890000035
9. the dual-drive mach-zehnder modulator-based multi-source nonlinear distortion suppression method according to claim 8, wherein the signal capable of generating IMD3 distortion exists within ± 2-order sidebands and-1-order sidebands are suppressed, ignoring-2-order sidebands to reduce the combination of the output signals of the DDMZM into equations (14) and (15):
Figure RE-FDA0003911340890000041
Figure RE-FDA0003911340890000042
wherein the content of the first and second substances,
Figure RE-FDA0003911340890000043
for the-2 order sideband, since the-1 order is suppressed, the IMD3 signal cannot be generated and can be omitted.
10. The multi-source nonlinear distortion suppression method based on the dual-drive Mach-Zehnder modulator of claim 9, characterized in that an amplitude-phase relation is respectively introduced to 0,1,2 order sidebands through programmable optical filters
Figure RE-FDA0003911340890000051
Figure RE-FDA0003911340890000052
And
Figure RE-FDA0003911340890000053
to achieve IMD3 and XMD suppression, the output electrical signal is as shown in equation (16):
Figure RE-FDA0003911340890000054
in the formula (16) of the above formula,
Figure RE-FDA0003911340890000055
the amplitude of the suppressed carrier wave is 1/3 of the original amplitude, and the phase is reversed by 180 degrees.
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