CN113949459B - System and method for generating photoelectric mixed FSK (frequency Shift keying) signal based on intensity modulator and MZI (Mach Zehnder interferometer) cascade - Google Patents
System and method for generating photoelectric mixed FSK (frequency Shift keying) signal based on intensity modulator and MZI (Mach Zehnder interferometer) cascade Download PDFInfo
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Abstract
The invention relates to a photoelectric mixed FSK signal generating system and method, and belongs to the technical field of microwave photons. The invention provides a photoelectric mixed FSK signal generation method based on intensity modulator and MZI cascade connection, which enables the intensity modulator to work at the maximum point or the minimum point by combining single radio frequency drive and bias point control, and outputs a modulation optical signal required by electric FSK signal generation or optical FSK signal generation according to requirements; by combining an MZI structure consisting of a phase modulator controlled by binary coding through an adjustable optical fiber delay line, tunable optical filtering according to binary coding information is realized as required, and an optical signal or an optical FSK signal required by an electric FSK signal is generated; the frequency of the generated electric FSK signal is twice or 4 times that of the radio frequency driving signal.
Description
Technical Field
The invention relates to a photoelectric mixed FSK signal generating system and method based on an intensity modulator and MZI cascade connection, and belongs to the technical field of microwave photons.
Background
In a communication system, most communication channels are band-pass channels, digital baseband signals cannot be directly transmitted, certain parameters of carrier waveforms must be controlled by the baseband signals, and the parameters of carriers change along with the change of the baseband signals, wherein Frequency Shift Keying (FSK) converts different carrier signals into digital signals for information transmission, namely, the state of transmitted information is represented by the change of carrier frequency, and the frequency of the modulated carrier changes along with the change of the baseband signals.
In a common FSK modulation system, two different radio frequencies carry binary 1 and 0 signals, i.e. a constant amplitude signal passes binary 1 and 0 through different radio frequency signals. The method can be divided into two modes of a frequency keying method and a direct frequency modulation method, wherein the frequency keying method switches between different sine oscillators according to whether the bit of an input data stream is 0 or 1, has the advantages of good frequency stability and no excessive frequency, and is widely applied to a digital communication system. However, with the demands of high-speed, wide-band and large capacity of wireless communication, wide-band radar and electronic systems, it is undoubtedly required to have a high-frequency sine oscillator for implementing, which greatly increases the difficulty and complexity of system implementation. In addition, with the development of the optical communication technology, the optical FSK signal is used as an optical domain digital modulation code pattern, and can generate an optical carrier controlled by a binary coding sequence, the optical carrier can be used as an optical carrier signal in optical communication and a modulation optical carrier of a radio frequency signal, and the high-frequency tunable FSK signal generation is further realized by combining a multi-wavelength light source, so that the expansibility is strong.
The FSK signal generation based on the microwave photon technology is mainly realized by combining a microwave photon switch or a microwave photon filter with an electro-optical modulator, wherein the microwave photon switch controlled by a binary coding sequence is used for completing selection of light polarization state or light path selection, the electro-optical modulator is connected in parallel to complete loading of radio frequency signals and generation of sideband signals, and a photoelectric detector is used for optical sideband signal beat frequency and electro-optical conversion to obtain the required electric FSK signal. This method generally requires an additional polarization modulator or a phase modulator in combination with an optical coupler to construct an optical switch, and the frequency of the generated FSK signal is at most twice the frequency of the signal, with limited frequency increase. The latter firstly loads radio frequency signals and generates sideband signals through an electro-optical modulator, then further filters out needed optical sideband signals by using a microwave photon filter controlled by a binary coding sequence, and carries out optical sideband signal beat frequency and electro-optical conversion through a photoelectric detector to obtain needed electric FSK signals. The method generally adopts a phase modulator combined with an sgnac loop or a micro-loop filter to carry out microwave photon filtering, the phase modulator combined with the sgnac loop has a complex structure, and the microwave filter needs a thermal tuning mode to complete a filtering function, is easily influenced by the environment and is not stable enough. In addition, no matter the microwave photonic switch is combined with the electro-optical modulator to generate the FSK signal or the microwave photonic filter is combined with the electro-optical modulator to generate the FSK signal, only optical sideband acquisition and beat frequency are considered, and further the electric FSK signal generation is realized, and an optical FSK signal generation method is not considered.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems of limited signal frequency range and frequency hopping speed of the traditional electric FSK signal generation technology and the requirement of generating an optical FSK signal, a photoelectric mixed FSK signal generation method based on the cascade connection of an intensity modulator and an MZI is provided, the intensity modulator works at the maximum point or the minimum point by combining single radio frequency drive and bias point control, and a modulated optical signal required by electric FSK signal generation or optical FSK signal generation is output according to the requirement; by combining an MZI structure consisting of a phase modulator controlled by binary coding through an adjustable optical fiber delay line, tunable optical filtering according to binary coding information is realized as required, and an optical signal or an optical FSK signal required by an electric FSK signal is generated; the frequency of the generated electric FSK signal is twice or 4 times that of the radio frequency driving signal, namely, a high-frequency FSK signal can be obtained only by low-frequency driving, and the difficulty in generating the traditional electric FSK signal is overcome; the generated optical FSK signal can be directly used in all-optical digital communication, and the compatibility of the system is greatly improved.
The technical solution of the invention is as follows:
a photoelectric mixed FSK signal generating system based on intensity modulator and MZI cascade connection comprises a laser LD, a signal source MSG, a pulse waveform generator PPG, a direct current source DC, an intensity modulator IM, MZI units and a photodetector PD;
the MZI unit is used for realizing a tunable optical filtering function controlled by binary coded information, and comprises two 50 optical couplers OC1 and OC2, a phase modulator PM and an optical fiber delay line DL;
continuous optical signals output by a laser LD are sent to an optical input end of an intensity modulator IM, radio-frequency driving signals output by a signal source MSG are sent to a radio-frequency input end of the intensity modulator IM, direct-current bias voltage output by a direct-current source DC is loaded to a direct-current end of the intensity modulator IM, and the intensity modulator IM works at the maximum point or the minimum point as required by adjusting the output voltage of the direct-current source DC;
an optical signal output by the intensity modulator IM is sent to the MZI unit, filtering of an optical sideband signal output by the intensity modulator IM according to needs is achieved in the MZI unit according to binary coding information input by the pulse waveform generator PPG, and an optical signal or an optical FSK signal required by an electric FSK signal is obtained; the signal output by the MZI unit is further sent to a photoelectric detector PD for photoelectric conversion, and a frequency doubling electric FSK signal is output in a beat frequency mode;
the method for generating the electric FSK signal comprises the following steps: when the intensity modulator IM works at the maximum point, the intensity modulator IM outputs an optical sideband signal inhibiting odd orders, under a small signal model, an optical sideband above 2 orders can be ignored due to too small power, the intensity modulator IM output optical signal comprises an optical carrier and a +/-2 order sideband optical signal, the intensity modulator IM output optical signal then enters an MZI unit, the amplitudes of the optical carrier and the +/-2 order sideband optical signal are modulated by the MZI unit, when a binary coding information bit loaded to the MZI unit is '1', the MZI output optical signal only comprises the +/-2 order sideband optical signal, and when the binary coding information bit loaded to the MZI unit is '0', the MZI output optical signal outputs the optical carrier and the-2 order sideband optical signal; outputting an electric FSK signal by a photoelectric detector in a beat frequency mode, wherein when the binary coding information bit loaded to the MZI unit is '1', the output signal frequency of the photoelectric detector is 4 times of the radio frequency driving frequency, and when the binary coding information bit loaded to the MZI unit is '0', the output signal frequency of the photoelectric detector is 2 times of the radio frequency driving frequency; the frequency conversion speed of the generated electrical FSK signal is determined by the binary coded information bit speed;
the method for generating the optical FSK signal comprises the following steps: when the intensity modulator IM operates at the minimum point, the intensity modulator IM output suppresses the even-order optical sideband signal, and the intensity modulator IM output includes only the ± 1-order sideband optical signal under the small-signal model. The intensity modulator IM output optical signal enters the MZI unit subsequently, so that the amplitude of the +/-1 order sideband optical signal is modulated by the MZI unit, when the binary coding information bit loaded to the MZI unit is '1', the MZI unit output optical signal only comprises a +1 order sideband optical signal, and when the binary coding information bit loaded to the MZI unit is '0', the MZI unit output optical signal only comprises a-1 order sideband optical signal; thus, the MZI unit outputs an optical FSK signal controlled by binary coded information, and the frequency conversion speed of the generated optical FSK signal is determined by the bit speed of the binary coded information.
A method for generating an opto-electronic hybrid FSK signal based on a cascade of an intensity modulator and an MZI, the method comprising the steps of:
in a first step, the continuous optical signal output by the laser LD is applied to the optical input of the intensity modulator IM.
Secondly, a radio frequency driving signal output by a signal source MSG is sent to a radio frequency input end of an intensity modulator IM, a direct current bias voltage output by a direct current source DC is loaded to a direct current end of the intensity modulator IM, the intensity modulator IM works at the maximum point or the minimum point as required by adjusting the output voltage of the direct current source DC, and when an electric FSK signal needs to be generated, the IM works at the maximum point; when an optical FSK signal needs to be generated, IM works at a minimum point; the IM output optical signal is then sent to OC1 in MZI unit;
thirdly, dividing the received IM output optical signal into an upper branch and a lower branch by OC1 in the MZI unit, wherein the upper branch is sent to the optical input end of the optical fiber delay line DL, and the lower branch is sent to the optical input end of the phase modulator PM;
fourthly, an optical signal output by an optical output end of the optical fiber delay line DL is sent to an optical input port of OC2 in the MZI unit;
fifthly, loading binary coded information output by a pulse waveform generator PPG into a radio frequency input end of a phase modulator PM in the MZI unit, and then sending an optical signal output by the phase modulator PM to the other optical input port of OC2 in the MZI unit;
and sixthly, transmitting the optical signal output by the optical output end of the optical fiber delay line DL and the optical signal output by the phase modulator PM to OC2 in the MZI unit together, and combining the optical signals into one optical signal by the OC 2. When an optical FSK signal needs to be generated, OC2 directly outputs a +1 order or-1 order optical signal controlled by binary code information output by PPG, namely the optical FSK signal; when it is desired to generate an electrical FSK signal, the OC2 outputs an optical signal of order +2 & -2 or optical carrier & -2 controlled by the PPG output binary code information, which is then sent to a subsequent PD.
And seventhly, the PD outputs an electric FSK signal after photoelectric conversion, and the generation of the photoelectric mixed FSK signal based on the cascade connection of the intensity modulator and the MZI is completed.
Compared with the prior art, the invention has the following substantive differences and progresses:
(1) Compared with the existing signal generation method based on an optical switch mode, the method has the advantages that certain control is performed on the MZI unit constructed by combining the PM with the tunable optical delay line, specifically, binary coding information is used for controlling the working state of the PM, and meanwhile, through appropriate parameter control of the optical fiber delay line, the MZI unit outputs an optical signal or an optical FSK signal required by an electrical FSK signal according to the coding information, the photoelectric mixed FSK signal generation is realized on the same structure, meanwhile, the MZI unit is easy to realize chip integration, and the method has the advantages of simplicity in realization, stable performance, good universality and the like.
(2) Compared with the existing signal generation method based on the microwave photon technology, the invention enables the intensity modulator to work at the maximum point or the minimum point by combining single radio frequency drive and bias point control, and outputs the modulation optical signal required by electric FSK signal generation or optical FSK signal generation according to the requirement; by combining an MZI structure consisting of a Phase Modulator (PM) controlled by binary coding through an adjustable optical fiber delay line, tunable optical filtering controlled by binary coding information is realized as required, and an optical signal or an optical FSK signal required by an electric FSK signal is generated; the frequency of the generated electric FSK signal is twice or 4 times that of the radio frequency driving signal, namely, the high-frequency FSK signal can be obtained only by low-frequency driving, thereby overcoming the difficulty in generating the traditional electric FSK signal; the generated optical FSK signal can be directly used in all-optical digital communication, thereby realizing full-band covered FSK signal optical domain output and greatly improving the compatibility of the system. And the switching speed of the output frequency of the photoelectric mixed FSK signal is the speed of binary coded information and can reach ns level.
(3) The invention relates to a photoelectric mixed FSK signal generating system and method, and belongs to the technical field of microwave photons. The invention provides a photoelectric mixed FSK signal generation method based on intensity modulator and MZI cascade connection, which enables the intensity modulator to work at the maximum point or the minimum point by combining single radio frequency drive and bias point control, and outputs a modulation optical signal required by electric FSK signal generation or optical FSK signal generation according to requirements; the MZI structure formed by the adjustable optical fiber delay line and the phase modulator controlled by the binary coding is used for realizing tunable optical filtering according to binary coding information as required and generating an optical signal or an optical FSK signal required by an electric FSK signal; the frequency of the generated electric FSK signal is twice or 4 times that of the radio frequency driving signal.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention;
FIG. 2 is a simulation result of frequency-doubled electrical FSK signal generation according to the present invention;
FIG. 3 shows simulation results of 10GHz coherent demodulation for frequency-doubled electrical FSK signals according to the present invention;
FIG. 4 shows the simulation results of 20GHz coherent demodulation for frequency-doubled electrical FSK signals according to the present invention;
FIG. 5 is a simulation result of optical FSK signal generation according to the present invention;
FIG. 6 is a simulation result of 5GHz coherent demodulation for an optical FSK signal according to the invention;
fig. 7 shows simulation results of the present invention for 15GHz coherent demodulation of optical FSK signals.
Detailed Description
The invention mainly provides a photoelectric mixed FSK signal generation method based on intensity modulator and MZI cascade connection. The invention enables the intensity modulator to work at the maximum point or the minimum point by combining single radio frequency drive and bias point control, and outputs a frequency doubling electrical FSK signal to generate or an optical FSK signal to generate a required modulated optical signal according to requirements; by combining an MZI unit consisting of a phase modulator controlled by binary coding through an adjustable optical fiber delay line, tunable optical filtering controlled by binary coding information is realized as required, and an optical signal or an optical FSK signal required by a frequency doubling electrical FSK signal is generated; an electrical FSK signal with a frequency twice or 4 times the frequency of the radio frequency drive signal is obtained by means of a photodetector. The simulation result of frequency-doubled electrical FSK signal generation is shown in FIG. 2;
the specific implementation mode is an opto-electronic hybrid FSK signal generation method based on cascade connection of an intensity modulator and an MZI, as shown in FIG. 1. The laser pulse waveform generator mainly comprises a laser LD, a signal source MSG, a pulse waveform generator PPG, a direct current source DC, an intensity modulator IM, an MZI unit and a photodetector PD. The MZI implements a tunable optical filtering function controlled by binary coded information, and mainly includes two 50. The laser is connected with the optical input end of the intensity modulator, the optical output end of the intensity modulator is connected with the input end of a 50 optical coupler OC1 in the MZI unit, one output end of the 50 optical coupler OC1 in the MZI is connected with an optical delay line DL of the MZI unit, the other output end of the 50 optical coupler OC1 in the MZI is connected with the PM of the MZI unit, the output ends of the PM and the DL are connected with the input ends of the optical couplers OC2 respectively, the output end of the OC2 of the optical coupler is the optical output end of the MZI unit, and the optical output end of the MZI unit is connected with the optical input end of the photoelectric detector PD.
Continuous optical signals output by the laser are sent to an optical input end of the intensity modulator IM, radio-frequency driving signals output by the MSG are sent to a radio-frequency input end of the IM, direct-current bias voltage output by the DC is loaded to a direct-current end of the IM, and the IM can work at the maximum point or the minimum point as required by adjusting the output voltage of the DC. Optical signals output by the IM are sent to the MZI unit, and filtering of sideband signals output by the IM according to needs is achieved in the MZI unit according to binary coding information input by the PPG, so that optical signals or optical FSK signals required by the electrical FSK signals are obtained; and the signal output by the MZI unit is further sent to a photoelectric detector for photoelectric conversion, and an electric FSK signal is output in a beat frequency mode.
The second embodiment is the generation of frequency-doubled electrical FSK signals. The method comprises the following specific steps:
the method comprises the following steps: according to fig. 1, the optical signal output by the optical source is sent to the optical input terminal of the intensity modulator IM, the rf signal output by the MSG is sent to the rf input terminal of the IM, and the DC bias voltage output by the DC is applied to the DC terminal of the IM.
Step two: according to fig. 1, the optical signal output by the intensity modulator is sent to the input of a 50.
Continuous optical signal output by laserAnd sending the signals to an optical input port of the MZI unit, wherein the MZI can output a tunable high-frequency-multiplication FSK signal as required by properly adjusting the IM direct-current working point and the optical delay line delay, and assuming that the microwave signal output by the MSG has the expression:
V RF (t)=V sinωt (1)
where V is the amplitude of the microwave signal and ω is the angular frequency of the microwave signal. Assuming an IM two-arm phase difference introduced by the DC bias voltage ofWhen IM is operated at the maximum transmission point, the methodThe IM output light field is expressed as
In the formula J n (. Cndot.) is a class of n-th order Bessel functions,modulation factor of IM, V π The half-wave voltage of the IM is shown in the above formula, the IM output suppresses the optical signal of odd order, and in the small signal model, the optical sideband of 2 order or more can be ignored because of too small power, and then the IM output optical signal includes the optical carrier and the optical signal of ± 2 order sideband.
The optical signal output by the IM is then sent to the MZI unit, and the transmission function of the MZI unit is expressed as:
wherein φ = π s (t)/V PM Representing the phase offset introduced by the Phase Modulator (PM), s (t) being the sequence of binary coded information generated by the PPG, V PM For the half-wave voltage of the phase modulator in the MZI unit, τ represents the delay amount of the fiber delay line, and ω' is the central angular frequency of the input optical signal of the MZI unit.
The optical signal output by the MZI unit is
From the above equation, it can be seen that the amplitudes of the optical carrier and the ± 2 th order sideband optical signals are modulated by the MZI unit.
In one aspect, when the parameter setting satisfies the following condition:
as can be seen from the above equation, the optical carrier amplitude is 0, i.e., the optical carrier is suppressed. At this time, the output optical signal of the MZI unit only contains a ± 2-order sideband optical signal, and the ± 2-order sideband optical signal then enters the PD for beat frequency obtaining:
it can be seen that a microwave signal with a frequency of 4 omega is obtained at the PD output.
On the other hand, when the parameter setting satisfies the following condition:
as can be seen from the above equation, the amplitude of the +2 order optical sideband is 0, i.e., the +2 order optical sideband signal is suppressed. At this time, the output optical signal of the MZI unit only includes the optical carrier and the-2 order sideband optical signal, and the optical carrier and the-2 order sideband optical signal then enter the PD for beat frequency, so as to obtain:
it can be seen that a microwave signal with a frequency of 2 omega is obtained at the PD output.
According to the above analysis, microwave FSK signals with frequencies of 2 ω and 4 ω can be obtained by appropriately adjusting the parameters. For example, when the optical carrier frequency is ω c =193.1THz, microwave signal frequency ω =5GHz, and delay τ =25ps of the fiber delay line, by modulating the amplitude of the binary-coded information sequence s (t) such that
The output terminal of the PD is available
The modulation factor m of the modulator is adjusted by modulating the amplitude of the microwave signal, i.e. the amplitude of the two frequency components is equal, where m = π V/V π Is the modulation factor, V, of the modulator π Half-wave voltage of IM.
As can be seen from the above formula, the electrical signal output after the photoelectric detection is an FSK signal, and when the binary coded information bit loaded to the MZI unit is "1", the frequency of the output signal of the photoelectric detector is 4 times of the radio frequency driving frequency, and when the binary coded information bit loaded to the MZI unit is "0", the frequency of the output signal of the photoelectric detector is 2 times of the radio frequency driving frequency; the rate of frequency conversion of the generated electrical FSK signal is determined by the binary coded information bit rate.
Suppose the optical working frequency is 193.1THz, the output power is 20dBm, the bit rate of the digital sequence signal is 1Gbit/s, the extinction ratio of IM is 30dB, the half-wave voltage of IM is 5V, the extinction ratio of PM is 30dB, and the half-wave voltage of PM is 4V. The working frequency of the input radio frequency signal is 5GHz, and the delay amount of the optical fiber delay line is 25ps. The binary coded information s (t) = '01010011' output by the PPG is set, and the output result of the frequency-doubled electrical FSK signal obtained according to the present invention is shown in fig. 3, where the output signal includes two frequency components, 10GHz and 20GHz, and the two frequency components are determined by the binary coded information output by the PPG. Coherent demodulation with a 10GHz sine wave, the demodulated output signal is shown in fig. 4. Coherent demodulation with a 20GHz sine wave, the demodulated output signal is shown in fig. 5. As can be seen from the figure, the code sequence after demodulation and output is "01010011", and the demodulation signal conforms to the input binary coded information, so the method for generating the photoelectric mixed FSK signal based on the cascade of the intensity modulator and the MZI can generate a frequency-doubled electric FSK signal.
The third embodiment is the generation of an optical FSK signal, as shown in fig. 1. The method comprises the following specific steps:
the method comprises the following steps: according to fig. 1, the optical signal output by the optical source is sent to the optical input terminal of the intensity modulator IM, the rf signal output by the MSG is sent to the rf input terminal of the IM, and the DC bias voltage output by the DC is applied to the DC terminal of the IM.
Step two: according to fig. 1, the optical signal output by the intensity modulator is sent to the input of a 50 optical coupler OC1 of the MZI, OC1 is divided into two paths, one path is sent to the fiber delay line DL, the other path is sent to the phase modulator PM, the phase modulator is controlled by 01 encoded binary coded information, the binary coded information is given by PPG, which is equivalent to introducing an additional phase, whose value is determined by "0" or "1" coded information, through the phase modulator.
Similarly, assume that the IM two-arm phase difference introduced by the DC offset isWhen IM is operated at minimum transmission point, that isThe IM output light field is expressed as
From the above equation, the IM outputs the optical signal with suppressed even-order, and in the small-signal model, the optical sideband with the 2 nd order or higher can be ignored because the power is too small, and then the IM outputs the optical signal with the ± 1 st order sideband.
Then the optical signal output by the MZI unit is
In the formula, J n (. Cndot.) is a class of n-th order Bessel functions,modulation factor of IM, V π Half-wave voltage of IM; phi = pi s (t)/V PM Representing the phase offset introduced by the Phase Modulator (PM), s (t) being the sequence of binary coded information generated by the PPG, V PM τ represents the delay amount of the fiber delay line for the half-wave voltage of the phase modulator in the MZI cell.
As can be seen from the above equation, the amplitude of the + -1 order sideband optical signals is modulated by the MZI unit.
In one aspect, when the parameter setting satisfies the following condition:
as can be seen from the above equation, the +1 order sideband optical signal is suppressed. At this time, the output optical signal of the MZI unit only comprises a-1 order sideband optical signal.
On the other hand, when the parameter setting satisfies the following condition:
it can be seen from the above equation that the amplitude of the-1 order optical sideband is 0, i.e., the-1 order optical sideband signal is suppressed. At this time, the MZI unit output optical signal only includes the +1 order sideband optical signal. From the above analysis, an optical FSK signal can be obtained by appropriately adjusting the parameters. For example, when the optical carrier frequency is ω c =193.1THz, microwave signal frequency ω =5GHz, and delay τ =25ps of the fiber delay line, the amplitude of the binary-coded information sequence s (t) is modulated such that
The modulation index m is adjusted by adjusting the amplitude of the microwave signal, so that the amplitudes of the two frequency components are equal. As can be seen from the above equation, an optical FSK signal is efficiently generated.
When the optical working frequency is 193.1THz, the optical output power is 20dBm, the bit rate of binary coded information is 1Gbit/s, the extinction ratio of IM is 30dB, the half-wave voltage of IM is 5V, the extinction ratio of PM is 30dB, and the half-wave voltage of PM is 4V, the working frequency of the input rf signal is set to 5GHz, the delay amount of the optical fiber delay line is 25ps, the binary coded information s (t) = '01010011' output by PPG, the output result of the optical FSK signal obtained according to the present invention is shown in fig. 5, and it can be seen from the figure that the output signal includes two components of +1 order and-1 order optical sidebands, and the selection of the two sidebands is determined by the binary coded information s (t) output by PPG. After the output optical signals of the MZI unit are subjected to beat frequency with a laser with the frequency of 193.11THz, FSK electrical signals with the frequencies of 5GHz and 15GHz can be obtained. Coherent demodulation with a 5GHz sine wave, the demodulated output signal is shown in fig. 6. Coherent demodulation with a 15GHz sine wave, the demodulated output signal is shown in fig. 7. As can be seen from the figure, the code sequence after demodulation and output is "01010011", and the demodulated signal matches with the input binary coded information, so that FSK signals with frequencies of 5GHz and 15GHz, respectively, can be generated, that is, the optical-electrical hybrid FSK signal generation method based on the cascade of the intensity modulator and the MZI can effectively generate optical FSK signals.
Claims (10)
1. An opto-electronic hybrid FSK signal generation system based on intensity modulator and MZI cascade, characterized in that: the signal generation system comprises a laser LD, a signal source MSG, a pulse waveform generator PPG, a direct current source DC, an intensity modulator IM, an MZI unit and a photoelectric detector PD;
the MZI unit is used for realizing a tunable optical filtering function controlled by binary coded information and comprises an optical coupler OC1, an optical coupler OC2, a phase modulator PM and an optical fiber delay line DL;
continuous optical signals output by a laser LD are sent to an optical input end of an intensity modulator IM, radio-frequency driving signals output by a signal source MSG are sent to a radio-frequency input end of the intensity modulator IM, direct-current bias voltage output by a direct-current source DC is loaded to a direct-current end of the intensity modulator IM, and the intensity modulator IM works at the maximum point or the minimum point as required by adjusting the output voltage of the direct-current source DC;
an optical signal output by the intensity modulator IM is sent to the MZI unit, filtering of an optical sideband signal output by the intensity modulator IM as required is achieved in the MZI unit according to binary coding information input by the pulse waveform generator PPG, and an optical signal or an optical FSK signal required by an electrical FSK signal is obtained; the signal output by the MZI unit is further sent to a photoelectric detector PD for photoelectric conversion, and a frequency doubling electric FSK signal is output in a beat frequency mode.
2. The system according to claim 1, wherein the system comprises:
the method for generating the electric FSK signal comprises the following steps: when the intensity modulator IM is operated at the maximum point, the output of the intensity modulator IM suppresses the optical sideband signals of the odd order, the output optical signal of the intensity modulator IM comprises the optical carrier and the sideband optical signals of the +/-2 order, and the output optical signal of the intensity modulator IM subsequently enters the MZI unit, so that the amplitudes of the optical carrier and the sideband optical signals of the +/-2 order are modulated by the MZI unit.
3. The system of claim 2, wherein the system comprises an intensity modulator and an MZI cascade-based opto-electronic hybrid FSK signal generating system, and further comprises:
when the binary-coded information bit loaded into the MZI cell is "1", the MZI output optical signal contains only ± 2-order sideband optical signals.
4. An opto-electronic hybrid FSK signal generation system based on a cascade of an intensity modulator and an MZI according to claim 2 or 3, characterized in that:
when the binary-coded information bit loaded into the MZI cell is "0", the MZI outputs an optical carrier and a-2 order sideband optical signal.
5. The system according to claim 4, wherein the system comprises:
an electrical FSK signal is beat-frequency output by the photoelectric detector, and when the binary coded information bit loaded to the MZI unit is '1', the frequency of the output signal of the photoelectric detector is 4 times of the radio frequency driving frequency.
6. An opto-electronic hybrid FSK signal generation system based on a cascade of an intensity modulator and an MZI according to claim 4 or 5, characterized in that:
an electrical FSK signal is beat-frequency output by the photodetector, and when the binary coded information bit loaded to the MZI unit is "0", the frequency of the photodetector output signal is 2 times the radio frequency driving frequency.
7. The system of claim 2, wherein the system comprises an intensity modulator and an MZI cascade-based opto-electronic hybrid FSK signal generating system, and further comprises:
the rate of frequency conversion of the generated electrical FSK signal is determined by the binary coded information bit rate.
8. The system according to claim 1, wherein the system comprises:
the method for generating the optical FSK signal comprises the following steps: when the intensity modulator IM is operated at the minimum point, the intensity modulator IM output, which suppresses the optical sideband signals of the even order and comprises only the sideband optical signals of the ± 1 order, subsequently enters the MZI cell such that the amplitudes of the sideband optical signals of the ± 1 order are all modulated by the MZI cell.
9. The system of claim 8, wherein the system comprises an intensity modulator and an MZI cascaded opto-electronic hybrid FSK signal generator:
when the binary coded information bit loaded to the MZI unit is '1', the output optical signal of the MZI unit only comprises a +1 order sideband optical signal, and when the binary coded information bit loaded to the MZI unit is '0', the output optical signal of the MZI unit only comprises a-1 order sideband optical signal; thus, the MZI unit outputs an optical FSK signal controlled by binary coded information, and the frequency conversion speed of the generated optical FSK signal is determined by the bit speed of the binary coded information.
10. A photoelectric mixed FSK signal generation method based on intensity modulator and MZI cascade connection is characterized in that the method comprises the following steps:
firstly, loading a continuous optical signal output by a laser LD to an optical input end of an intensity modulator IM;
secondly, a radio frequency driving signal output by a signal source MSG is sent to a radio frequency input end of an intensity modulator IM, a direct current bias voltage output by a direct current source DC is loaded to a direct current end of the intensity modulator IM, the intensity modulator IM works at the maximum point or the minimum point as required by adjusting the output voltage of the direct current source DC, and when an electric FSK signal needs to be generated, the IM works at the maximum point; when an optical FSK signal needs to be generated, IM works at a minimum point; the IM output optical signal is then sent to OC1 in MZI unit;
thirdly, dividing the received IM output optical signal into an upper branch and a lower branch by an OC1 in the MZI unit, wherein the upper branch is sent to an optical input end of an optical fiber delay line DL, and the lower branch is sent to an optical input end of a phase modulator PM;
fourthly, an optical signal output by an optical output end of the optical fiber delay line DL is sent to an optical input port of OC2 in the MZI unit;
fifthly, loading binary coded information output by a pulse waveform generator PPG into a radio frequency input end of a phase modulator PM in the MZI unit, and then sending an optical signal output by the phase modulator PM to the other optical input port of OC2 in the MZI unit;
sixthly, transmitting the optical signal output by the optical output end of the optical fiber delay line DL and the optical signal output by the phase modulator PM to OC2 in the MZI unit, combining the optical signals into one optical signal by the OC2, and when the optical FSK signal needs to be generated, directly outputting a +1 order or-1 order optical signal controlled by the binary code information output by the PPG, namely the optical FSK signal, by the OC 2; when an electric FSK signal needs to be generated, the OC2 outputs an optical signal of +2 order & -2 order or optical carrier & -2 order controlled by the binary coding information output by the PPG, and the signal is then transmitted to a subsequent PD;
and seventhly, the PD outputs an electric FSK signal after photoelectric conversion, and the generation of the photoelectric mixed FSK signal based on the cascade connection of the intensity modulator and the MZI is completed.
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