CN107733529B - Triangular wave and square wave signal optical generation and transmission device and method - Google Patents
Triangular wave and square wave signal optical generation and transmission device and method Download PDFInfo
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Abstract
The invention relates to a device and a method for optically generating and transmitting triangular wave and square wave signals, belonging to the technical field of microwave signal generation and transmission. A first-order optical sideband and a third-order optical sideband are generated by utilizing the modulation characteristic of a carrier-restraining single sideband of a double-parallel Mach-Zehnder modulator (DP-MZM) in the DP-QPSK modulator and are coupled with an optical carrier signal output by the other DP-MZM in the DP-QPSK modulator, triangular wave or square wave signals can be generated and optical fiber transmission of the signals can be realized by adjusting the amplitude of input microwave signals and the phase of the optical carrier signal, and through optical fiber transmission, optical amplifier amplification and photoelectric detector detection, and the waveform distortion caused by optical fiber dispersion can be overcome by adjusting the phase of the optical carrier. The invention generates triangular wave and square wave signals, overcomes the defects of limited repetition rate and poor tunability of the signals generated by the traditional electric domain generating method, can be used for long-distance transmission, and expands the application range of the signals.
Description
Technical Field
The invention relates to a device and a method for optically generating and transmitting triangular wave and square wave signals, belonging to the technical field of microwave signal generation and transmission.
Background
In the fields of modern radar, signal processing, wired wireless communication and the like, microwave arbitrary waveform signals have very wide application. Of the various microwave waveform signals, triangular wave signals and square wave signals are the two most commonly used signals. With the continuous development of electronic technology, various electronic systems are also developing towards high frequency band and large bandwidth, and therefore, the requirement for the speed of microwave waveform signals is higher and higher. However, the conventional microwave signal generation technology based on electronic devices is limited by electronic bottlenecks, the timing jitter of the generated microwave waveform signals is large, the electromagnetic interference is serious, and the generation cost of the microwave waveform signals with high repetition rate is extremely high or even difficult to generate, which greatly limits the development and application of high-frequency electronic systems.
The microwave signal generation technology based on microwave photonics can generate various microwave signals including microwave carrier signals, microwave phase coding signals, triangular wave signals, square wave signals and sawtooth wave signals, and the advantages of large bandwidth, high frequency, no electromagnetic interference and the like of the optical technology are utilized, so that the quality, the frequency and the bandwidth of the generated microwave signals can be greatly improved, and the microwave signal generation technology has wide application prospect. At present, triangular and square wave signals can be generated by a method of spectrum shaping and frequency domain to time domain mapping (j.ye, l.yan, w.pan, b.luo, x.zou, a.yi, and s.yao, Photonic generation flexible-shared pulses based on frequency to time conversion, op.lett.2011, 36(8):1458), but different spectrum shaping filters are required to be used for generating different waveforms by adopting the method, so that the reconfigurability of the system is poor. The triangular wave and square wave signals can also be generated by controlling the frequency domain electrical harmonics, and the basic principle of the method is to approximate the Fourier series of the triangular wave or square wave signals by controlling the electrical harmonics. For example, a triangular wave signal may be generated by cascading a mach-zehnder modulator (MZM) with a length of dispersive optical fiber (j.li, x.zhang, b.hraimel, t.nin, l.pei, and k.wu, Performance analysis of a photonic-associated periodic-shaped pulse generator, IEEE/osaj.light.technol.2012, 30(11):1617), but this method has the disadvantage of requiring the use of a different length of dispersive optical fiber when generating a triangular wave signal repetition frequency variation. In order to achieve more convenient repetition frequency tuning, a Triangular wave signal generating method based on a single dual parallel Mach-Zehnder modulator (DP-MZM) is proposed (f.zhang, x.ge, and s.pan, Triangular pulse generation using a dual-parallel Mach-Zehnder modulator drive by a single-frequency radio frequency signal, Opt let.2013, 38(21):4491), which is simple in structure, but has a disadvantage in that if the generated signal needs to be transmitted through an optical fiber, the system is difficult to compensate for the relative phase change between harmonics introduced by the optical fiber dispersion, which may cause serious distortion of the generated signal. In addition, triangular wave and square wave signals can be realized by combining a polarization modulator with Sagnac interference (w.liu and j.yao, Photonic generation of microwave wave for ms base on a polarization modulator in a Sagnac loop, IEEE/osaj.lightw.technol.2014,32(20):3637), but the method adopts an optical band-pass filter and an interferometer structure, so that the system is complex and the stability is reduced.
Disclosure of Invention
The invention provides a device and a method for optically generating and transmitting triangular wave and square wave signals aiming at the defects of the prior art, and the device and the method are used for generating and transmitting the triangular wave and square wave signals with tunable repetition frequency in a large range by using a single optical modulator structure.
The invention adopts the following technical scheme for solving the technical problems:
a triangular wave and square wave signal optical generating and transmitting device is characterized in that: the device comprises a laser, a polarization multiplexing double parallel Mach-Zehnder modulator (DP-QPSK modulator), a microwave signal generator, a 90-degree mixer, a direct current power supply, a polarization controller, a polarizer, a single-mode optical fiber, an optical amplifier and a photoelectric detector; two sub Mach-Zehnder modulators (DP-MZM) are integrated in the DP-QPSK modulator, optical signals output by the two sub DP-MZMs are coupled together through orthogonal polarization multiplexing and output at the output end of the DP-QPSK modulator, and the sub DP-MZM consists of a main Mach-Zehnder modulator (main MZM) and two sub MZMs; the DP-QPSK modulator is arranged on an emergent light path of the laser; the output end of the microwave signal generator is connected with the input end of the 90-degree mixer, and two output ends of the 90-degree mixer are respectively connected with two radio frequency input ports of one sub DP-MZM of the DP-QPSK modulator; the direct current power supply is connected with two radio frequency input ports of the other sub DP-MZM of the DP-QPSK modulator; the direct current bias input port of the DP-QPSK modulator is connected with a direct current power supply; the output end of the DP-QPSK modulator is connected with the input end of the polarization controller, the output end of the polarization controller is connected with the input end of the polarizer, the output end of the polarizer is connected with the input end of the single-mode optical fiber, the output end of the single-mode optical fiber is connected with the input end of the optical amplifier, and the output end of the optical amplifier is connected with the input end of the photoelectric detector; the output end of the photoelectric detector outputs a triangular wave signal or a square wave signal.
The sub-DP-MZMs have the same structure and performance.
The sub DP-MZM has independent radio frequency signal input ports and DC bias input ports.
The microwave signals input into the DP-QPSK modulator have the same amplitude and 90-degree phase difference, the microwave signals with different amplitudes are input according to the difference of generated waveform signals, and the microwave signals with different frequencies are input according to the difference of the frequencies of the generated waveform signals.
The DC signals input into the two RF input ports of the DP-QPSK modulator have the same amplitude, and the amplitude is determined by the type of generated signal, the repetition frequency of the signal and the length of the single-mode optical fiber in the device.
An included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft is 45 degrees.
The single-mode optical fiber realizes the transmission function of the generated triangular wave and square wave signals.
A method for optically generating and transmitting triangular wave and square wave signals comprises the following steps:
1) inputting an optical signal with the wavelength of lambda output by a laser into an optical input port of a DP-QPSK modulator, wherein optical signals output by two sub DP-MZMs of the DP-QPSK modulator are respectively in two orthogonal polarization directions of the optical signal output by the DP-QPSK modulator;
2) adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees;
3) adjusting direct-current bias voltage to enable two sub MZMs of the sub DP-MZM, to which microwave signals are input from the radio-frequency input port, to be biased at a minimum transmission point and a main MZM to be biased at an orthogonal transmission point;
4) the two paths of microwave signals input into the modulator have a phase difference of 90 degrees, and the amplitude and the frequency of the microwave signals input into the modulator are adjusted according to the type of the generated signals and the repetition frequency of the signals;
5) adjusting direct-current bias voltage to enable two sub MZMs of the sub DP-MZM with the direct-current signal input by the radio frequency input port to be respectively biased at a maximum transmission point and a minimum transmission point, and enable a main MZM to be biased at an orthogonal transmission point;
6) two paths of direct current signals input into the radio frequency input port of the modulator have the same amplitude, and the amplitude of direct current voltage input into the radio frequency input port of the modulator is adjusted according to the type of the generated signals, the signal repetition frequency and the optical fiber transmission distance, so that the compensation of the dispersion induced waveform distortion is realized;
7) the optical signal output by the polarizer is transmitted by a single-mode optical fiber and amplified by an optical amplifier, and then is detected at a photoelectric detector to generate a triangular wave or square wave signal.
The invention utilizes the inhibiting carrier single sideband modulation characteristic of one DP-MZM of the DP-QPSK modulator to generate a first-order optical sideband and a third-order optical sideband, and is coupled with an optical carrier signal output by the other DP-MZM of the DP-QPSK modulator, triangular wave or square wave signals can be generated and optical fiber transmission of the signals can be realized by adjusting the amplitude of input microwave signals and the phase of the optical carrier signal, and through optical fiber transmission, optical amplifier amplification and photoelectric detector detection, and the waveform distortion caused by optical fiber dispersion can be overcome by adjusting the phase of the optical carrier. The invention generates triangular wave and square wave signals, overcomes the defects of limited repetition rate and poor tunability of the signals generated by the traditional electric domain generating method, can be used for long-distance transmission, and expands the application range of the signals.
The invention has the following beneficial effects:
1. the invention can selectively generate triangular wave signals or square wave signals according to the requirements, and has stronger flexibility;
2. the triangular wave signal and the square wave signal generated by the invention have large tunable range of repetition frequency and are mainly limited only by the working bandwidth of the modulator and the working bandwidth of the photoelectric detector;
3. the triangular wave signal and the square wave signal generated by the invention can be transmitted in a long distance through the optical fiber, and the distortion introduced by the optical fiber dispersion can be compensated by adjusting the initial phase of the optical carrier signal.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a spectrum diagram of an input microwave signal with a frequency of 10GHz according to example 1 of the present invention, (a) a spectrum diagram of a suppressed-carrier single sideband signal of the DP-MZM output of the input microwave signal, and (b) a spectrum diagram of an output optical signal of a polarizer;
fig. 3 is a waveform and a frequency spectrum diagram of a 3GHz triangular wave signal generated in embodiment 1 of the present invention, (a) a time domain waveform diagram, and (b) an electrical frequency spectrum diagram corresponding to the time domain waveform;
fig. 4 is a waveform and a frequency spectrum diagram of a 7GHz triangular wave signal generated in embodiment 1 of the present invention, (a) a time-domain waveform diagram, and (b) an electrical frequency spectrum diagram corresponding to the time-domain waveform;
fig. 5 is a waveform and a frequency spectrum diagram of a 13GHz triangular wave signal generated in embodiment 1 of the present invention, (a) a time-domain waveform diagram, and (b) an electrical frequency spectrum diagram corresponding to the time-domain waveform;
fig. 6 is a time domain waveform diagram of a 7GHz triangular wave signal after transmission through a 10km optical fiber and dispersion compensation in embodiment 1 of the present invention, (a) a waveform diagram of a triangular wave signal after transmission through a 10km optical fiber, and (b) a waveform diagram after dispersion compensation through dc offset control.
Fig. 7 is a waveform and a spectrum diagram of a 3GHz square wave signal generated in embodiment 2 of the present invention, (a) a time domain waveform diagram, and (b) an electrical spectrum diagram corresponding to the time domain waveform;
fig. 8 is a waveform and a spectrum diagram of a 5GHz square wave signal generated in embodiment 2 of the present invention, (a) a time domain waveform diagram, and (b) an electrical spectrum diagram corresponding to the time domain waveform;
fig. 9 is a waveform and a spectrum diagram of a 7GHz square wave signal generated in embodiment 2 of the present invention, (a) a time domain waveform diagram, and (b) an electrical spectrum diagram corresponding to the time domain waveform;
fig. 10 is a time domain waveform diagram of a 5GHz square wave signal after transmission through a 10km optical fiber and dispersion compensation in embodiment 2 of the present invention, (a) a waveform diagram of a square wave signal after transmission through a 10km optical fiber, and (b) a waveform diagram after dispersion compensation by dc bias control.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
Referring to fig. 1, the apparatus of the present invention comprises: the device comprises a laser 1, a DP-QPSK modulator 2, a microwave signal generator 3, a 90-degree mixer 4, a direct current power supply 5, a polarization controller 6, a polarizer 7, a single-mode optical fiber 8, an optical amplifier 9 and a photoelectric detector 10. An output port of the laser 1 is connected with an optical input end of the DP-QPSK modulator 2, an output port of the microwave signal generator 3 is connected with an input port of the 90-degree mixer 4, two output ports of the 90-degree mixer 4 are respectively connected with two radio frequency input ports of one sub DP-MZM of the DP-QPSK modulator 2, two output ports of the direct current power supply 5 are respectively connected with two radio frequency input ports of the other sub DP-MZM of the DP-QPSK modulator 2, and other output ports of the direct current power supply 5 are connected with a direct current bias input port of the DP-QPSK modulator 2; an optical output port of the DP-QPSK modulator 2 is connected with an input port of a polarization controller 6, an output port of the polarization controller 6 is connected with an input port of a polarizer 7, an output port of the polarizer 7 is connected with an input port of a single-mode optical fiber 8, an output port of the single-mode optical fiber 8 is connected with an input port of an optical amplifier 9, and an output port of the optical amplifier 9 is connected with an input port of a photoelectric detector 10. The output port of the photodetector 10 produces a triangular or square wave signal.
The invention generates and transmits triangular wave and square wave signals, which comprises the following steps:
step one, inputting an optical signal with a wavelength of lambda output by a laser into an optical input port of a DP-QPSK modulator, wherein optical signals output by two sub DP-MZMs of the DP-QPSK modulator are respectively in two orthogonal polarization directions of the optical signal output by the DP-QPSK modulator;
adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees;
adjusting direct-current bias voltage to enable two sub MZMs of the sub DP-MZM inputting microwave signals by the radio frequency input port to be biased at a minimum transmission point and enable a main MZM to be biased at an orthogonal transmission point;
step four, the two paths of microwave signals input into the modulator have a phase difference of 90 degrees, and the amplitude and the frequency of the microwave signals input into the modulator are adjusted according to the type of the generated signals and the repetition frequency of the signals;
adjusting the direct current bias voltage to enable two sub MZMs of the sub DP-MZM with the direct current signal input by the radio frequency input port to be respectively biased at a maximum transmission point and a minimum transmission point, and enable the main MZM to be biased at an orthogonal transmission point;
step six, two paths of direct current signals input into the radio frequency input port of the modulator have the same amplitude, and the amplitude of direct current voltage input into the radio frequency input port of the modulator is adjusted according to the type of the generated signals, the signal repetition frequency and the optical fiber transmission distance, so that the compensation of the dispersion induced waveform distortion is realized;
and seventhly, detecting and generating triangular wave or square wave signals at the photoelectric detector after the optical signals output by the polarizer are transmitted by the single-mode optical fiber and amplified by the optical amplifier.
The specific principle is illustrated as follows:
according to the above-mentioned bias point setting, the output optical signal of the sub-DP-MZM, in which the microwave signal is input to the RF input port, can be expressed as
Wherein E is1Is the amplitude of the optical signal, omegacIs the angular frequency of the optical signal, m ═ pi V0/VπIs the modulation index, V0Is the amplitude, omega, of the input microwave signalsIs the angular frequency, V, of the input microwave signalπIs the half-wave voltage of the DP-QPSK modulator, JnIs an n-th order bessel function of the first kind. It can be observed from the above equation that at the output of the DP-MZM, all of the even-order optical sidebands and the (4k-1) order optical sidebands are suppressed, with only the (4k +1) order optical sidebands present, k being an integer.
The output optical signal of the sub DP-MZM with the DC signal input at the RF input port can be expressed as
Wherein E is2Is the amplitude of the optical signal, V△Is the value of the dc voltage input to the rf port of the modulator,
is the initial phase of the optical signal.
Controlled by a polarization controller, the included angle between the main shaft of the polarizer and one main shaft of the DP-QPSK modulator is 45 degrees, so that the optical signal output by the polarizer is
Under small signal modulation conditions (m < <1), sidebands other than the optical carrier and one of the first-order optical sidebands in the optical signal are well suppressed. Since triangular and square signals are required to be generated and third harmonic is required, the modulation index is increased here to make the third-order optical sidebands have larger power, so that the above formula can be expressed in consideration of only the third-order optical sidebands
The light signal is detected by a photoelectric detector to obtain the light current of
Wherein R is the responsivity of the photodetector
In order to generate a triangular wave signal, the following condition needs to be satisfied
Namely, it is
Wherein p is an integer. The above condition can be achieved by controlling the amplitude of the microwave signal and the dc signal input to the rf port of the DP-QPSK modulator.
In order to generate a square wave signal, the following conditions need to be satisfied
Namely, it is
Wherein p is an integer. The above condition can be achieved by controlling the amplitude of the microwave signal and the dc signal input to the rf port of the DP-QPSK modulator.
When triangular wave and square wave signals are transmitted in the optical fiber, the phase relation between the optical carrier and the sideband waves is changed by the dispersion of the optical fiber, the generated signals are distorted and even unusable, and when the length of the optical fiber is L, the optical signals transmitted by the optical fiber can be expressed as
The signal is detected by a photoelectric detector to generate photocurrent
Wherein, theta0,θ+1And theta-3It is the phase shift introduced by the fiber dispersion, and it can be observed that the amplitude term of the generated photocurrent is the same as the photocurrent generated without the fiber transmission, but the phase term of the generated photocurrent is different from the photocurrent generated without the fiber transmission, so that the phase of the generated photocurrent should satisfy the following condition in order to generate the triangular signal
Namely, it is
In order to generate a square wave signal, the phase thereof needs to satisfy the following conditions
Namely, it is
From the fiber dispersion theory, it can be obtained
Thus, it is possible to provide
Wherein λcIs the center wavelength of the optical signal, af is the frequency separation of the carrier and the first-order optical sidebands, which is the same as the repetition frequency of the generated signal, and D is the dispersion coefficient of the fiber. The initial phase of the optical carrier required after the optical fiber transmission can be calculated according to the equations (17) and (18), and then the direct current voltage value required to be loaded can be obtained according to the equation (2).
Example 1
In the embodiment, the wavelength of an optical signal output by a laser is 1550.55nm, and a direct current bias voltage is adjusted, so that two sub MZMs of a sub DP-MZM inputting a microwave signal by a radio frequency input port are biased at a minimum transmission point, and a main MZM is biased at an orthogonal transmission point; two sub MZMs of a sub DP-MZM which inputs a direct current signal at a radio frequency input port are respectively biased at a maximum transmission point and a minimum transmission point, and a main MZM is biased at an orthogonal transmission point. And adjusting the amplitude of the microwave signal and the amplitude of the direct current signal input into the radio frequency input port of the DP-QPSK modulator to enable the equation (7) to be satisfied. At this time, when the frequency of the input microwave signal is 10GHz, the spectrogram of the suppressed carrier single sideband signal generated by the DP-MZM of the input microwave signal and the spectrogram of the output light signal of the polarizer are shown in FIG. 2. Fig. 2(a) is a spectrum diagram of a suppressed carrier single sideband signal generated by a sub DP-MZM of an input microwave signal, and it can be seen that the power difference between a first-order optical sideband and a third-order optical sideband is 18.91dB, and fig. 2(b) is a spectrum diagram of an optical signal output by the suppressed carrier single sideband signal and an optical carrier signal output by another sub DP-MZM coupled at a polarizer. Because the power difference of the two optical sidebands is 18.91dB, the power difference of the first harmonic and the third harmonic generated by the beat frequency of the optical carrier signal and the two optical sidebands respectively is 18.91dB theoretically, which is close to the theoretical value of 19.08dB obtained by the Fourier series expansion of the triangular wave signal, and the triangular wave signal can be well approximated. The frequency of the input microwave signal is adjusted to obtain a corresponding optical signal, and the optical signal output by the polarizer is input into a photoelectric detector for detection to generate a triangular wave signal with a corresponding repetition frequency. Fig. 3(a) is a waveform diagram of a 3GHz triangular wave signal generated by the present invention, and fig. 3(b) is a corresponding electrical spectrum diagram. It can be seen that a triangular wave signal with a repetition frequency of 3GHz is generated, and in addition, the power difference between the first harmonic and the third harmonic is 18.38dB, which is close to the theoretical value of 19.08 dB. In order to study the repetition frequency tunability of the system and increase the frequency of the input microwave signal, fig. 4(a) is a waveform diagram of a 7GHz triangular wave signal generated by the present invention, and fig. 4(b) is a corresponding electrical spectrum diagram. It can be seen that a triangular wave signal with a repetition frequency of 7GHz is generated, and further, the power difference between the first harmonic and the third harmonic is 19.19dB, which is close to the theoretical value of 19.08 dB. Fig. 5(a) is a waveform diagram of a 13GHz triangular wave signal generated by the present invention, and fig. 5(b) is a corresponding electrical spectrum diagram. It can be seen that a triangular wave signal with a repetition frequency of 13GHz is generated, and in addition, the power difference between the first harmonic and the third harmonic is 19.67dB, which is close to the theoretical value of 19.08 dB. Fig. 6 is a time domain waveform diagram of a 7GHz triangular wave signal after transmission through a 10km optical fiber and dispersion compensation, wherein fig. 6(a) is a waveform diagram of the triangular wave signal after transmission through the 10km optical fiber, and fig. 6(b) is a waveform diagram of the triangular wave signal after dispersion compensation through dc offset control. It can be observed that the waveform without dispersion compensation generates serious distortion, and the distortion is well overcome after the dispersion compensation controlled by the direct current bias, and the waveform of the triangular wave signal is recovered.
Example 2
In the embodiment, the wavelength of an optical signal output by a laser is 1550.55nm, and a direct current bias voltage is adjusted, so that two sub MZMs of a sub DP-MZM inputting a microwave signal by a radio frequency input port are biased at a minimum transmission point, and a main MZM is biased at an orthogonal transmission point; two sub MZMs of a sub DP-MZM which inputs a direct current signal at a radio frequency input port are respectively biased at a maximum transmission point and a minimum transmission point, and a main MZM is biased at an orthogonal transmission point. And adjusting the amplitude of the microwave signal and the amplitude of the direct current signal input into the radio frequency input port of the DP-QPSK modulator to enable the equation (9) to be satisfied. The difference from embodiment 1 is that the present embodiment requires a larger modulation index to be used for generating the square wave signal. Fig. 7(a) is a waveform diagram of a 3GHz square wave signal generated by the present invention, and fig. 7(b) is a corresponding electrical spectrum diagram. It can be seen that a square wave signal with a repetition frequency of 3GHz is generated, and in addition, the power difference between the first harmonic and the third harmonic is 9.95dB, which is close to the theoretical value of 9.54 dB. In order to study the repetition frequency tunability of the system and increase the frequency of the input microwave signal, fig. 8(a) is a waveform diagram of a 5GHz square wave signal generated by the present invention, and fig. 8(b) is a corresponding electrical spectrum diagram. It can be seen that a square wave signal with a repetition frequency of 5GHz is generated, and in addition, the power difference between the first harmonic and the third harmonic is 10.18dB, which is close to the theoretical value of 9.54 dB. Fig. 9(a) is a waveform diagram of a 7GHz square wave signal generated by the present invention, and fig. 9(b) is a corresponding electrical spectrum diagram. It can be seen that a square wave signal with a repetition frequency of 7GHz is generated, and in addition, the power difference between the first harmonic and the third harmonic is 9.76dB, which is close to the theoretical value of 9.54 dB. Fig. 10 is a time domain waveform diagram of a 5GHz square wave signal after transmission through a 10km optical fiber and dispersion compensation, wherein fig. 10(a) is a waveform diagram of a square wave signal after transmission through a 10km optical fiber, and fig. 10(b) is a waveform diagram after dispersion compensation through dc bias control. It can be observed that the waveform without dispersion compensation generates serious distortion, and the distortion is well overcome after the dispersion compensation controlled by the direct current bias, and the waveform of the square wave signal is recovered.
In summary, the apparatus and method for generating and transmitting triangular and square wave signals optically provided by the present invention can generate triangular or square wave signals by using the nonlinear modulation characteristic of the DP-QPSK modulator, and the triangular and square wave signals generated by the present invention can be widely tunable in repetition frequency and can be transmitted through optical fibers. In the embodiment of the present invention, limited by the limits of the bandwidth of the employed optoelectronic device, the power of the input microwave signal, etc., only the triangular wave signal with the repetition frequency of 3GHz to 13GHz and the square wave signal with the repetition frequency of 3GHz to 7GHz are generated, theoretically, the repetition frequency of the triangular wave signal and the square wave signal generated by the present invention can be greater than the result in the embodiment, for example, a DP-QPSK modulator with the bandwidth of 23GHz is used, and when the bandwidth of the photodetector is greater than 69GHz (the bandwidth of the actual commercial photodetector is greater than 100GHz), the triangular wave signal and the square wave signal with the repetition frequency of 23GHz can be generated.
Claims (3)
1. An optical generation and transmission device for triangular wave and square wave signals, which is characterized in that: the device comprises a laser, a polarization multiplexing double parallel Mach-Zehnder modulator (DP-QPSK modulator), a microwave signal generator, a 90-degree mixer, a direct current power supply, a polarization controller, a polarizer, a single-mode optical fiber, an optical amplifier and a photoelectric detector; two sub-double parallel Mach-Zehnder modulators (DP-MZM) are integrated in the DP-QPSK modulator, optical signals output by the two sub-DP-MZMs are coupled together through orthogonal polarization multiplexing and output at the output end of the DP-QPSK modulator, and each sub-DP-MZM consists of a main Mach-Zehnder modulator (main MZM) and two sub-MZMs; the DP-QPSK modulator is arranged on an emergent light path of the laser; the output end of the microwave signal generator is connected with the input end of the 90-degree mixer, and two output ends of the 90-degree mixer are respectively connected with two radio frequency input ports of one sub DP-MZM of the DP-QPSK modulator; the direct current power supply is connected with two radio frequency input ports of the other sub DP-MZM of the DP-QPSK modulator; the direct current bias input port of the DP-QPSK modulator is connected with a direct current power supply; the output end of the DP-QPSK modulator is connected with the input end of the polarization controller, the output end of the polarization controller is connected with the input end of the polarizer, the output end of the polarizer is connected with the input end of the single-mode optical fiber, the output end of the single-mode optical fiber is connected with the input end of the optical amplifier, and the output end of the optical amplifier is connected with the input end of the photoelectric detector; the output end of the photoelectric detector outputs a triangular wave signal or a square wave signal; wherein:
microwave signals input into two radio frequency input ports of the DP-QPSK modulator have the same amplitude and 90-degree phase difference; the direct current signals input into the two radio frequency input ports of the DP-QPSK modulator have the same amplitude; adjusting direct-current bias voltage to enable two sub MZMs of the sub DP-MZM with the direct-current signal input by the radio frequency input port to be respectively biased at a maximum transmission point and a minimum transmission point, and enable a main MZM to be biased at an orthogonal transmission point; the transmission of the generated triangular wave and square wave signals is realized through a single mode fiber.
2. The apparatus for optical generation and transmission of triangular and square wave signals according to claim 1, wherein: the included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft is 45 degrees under the control of the polarization controller.
3. A method for optically generating and transmitting triangular wave and square wave signals, the method comprising the steps of:
1) inputting an optical signal with the wavelength of lambda output by a laser into an optical input port of a DP-QPSK modulator, wherein optical signals output by two sub DP-MZMs of the DP-QPSK modulator are respectively in two orthogonal polarization directions of the optical signal output by the DP-QPSK modulator;
2) adjusting the polarization controller to enable an included angle between one polarization main shaft of the DP-QPSK modulator and the polarizer main shaft to be 45 degrees;
3) adjusting direct-current bias voltage to enable two sub MZMs of the sub DP-MZM, to which microwave signals are input from the radio-frequency input port, to be biased at a minimum transmission point and a main MZM to be biased at an orthogonal transmission point;
4) the two paths of microwave signals input into the modulator have a phase difference of 90 degrees, and the amplitude and the frequency of the microwave signals input into the modulator are adjusted according to the type of the generated signals and the repetition frequency of the signals;
5) adjusting direct-current bias voltage to enable two sub MZMs of the sub DP-MZM with the direct-current signal input by the radio frequency input port to be respectively biased at a maximum transmission point and a minimum transmission point, and enable a main MZM to be biased at an orthogonal transmission point;
6) two paths of direct current signals input into the radio frequency input port of the modulator have the same amplitude, and the amplitude of direct current voltage input into the radio frequency input port of the modulator is adjusted according to the type of the generated signals, the signal repetition frequency and the optical fiber transmission distance, so that the compensation of the dispersion induced waveform distortion is realized;
7) the optical signal output by the polarizer is transmitted by a single-mode optical fiber and amplified by an optical amplifier, and then is detected at a photoelectric detector to generate a triangular wave or square wave signal.
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| CN109714107A (en) * | 2019-03-07 | 2019-05-03 | 西安电子科技大学 | Microwave light dispersion compensation method based on PDM-DPMZM chain-circuit system |
| CN110233675B (en) * | 2019-06-12 | 2020-12-18 | 南京航空航天大学 | Multifunctional microwave photonic module and signal processing method and device based on same |
| CN111585660B (en) * | 2020-04-20 | 2022-12-16 | 复旦大学 | Terahertz wave signal generator based on dual-polarization MZM modulator and communication system |
| CN111982167B (en) * | 2020-07-22 | 2021-06-22 | 北京邮电大学 | Device and method for inhibiting nonlinear damage in RoF system |
| CN112152720B (en) * | 2020-09-25 | 2022-02-22 | 中国科学院半导体研究所 | Multi-frequency-band double-chirp microwave signal generation and optical fiber dispersion resistant transmission system and method |
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