CN113949459A

CN113949459A - System and method for generating photoelectric mixed FSK signal based on intensity modulator and MZI cascade connection

Info

Publication number: CN113949459A
Application number: CN202110992290.2A
Authority: CN
Inventors: 蒋炜; 秦伟泽; 谭庆贵; 李小军; 梁栋; 赵莹; 惠金鑫
Original assignee: Xian Institute of Space Radio Technology
Current assignee: Xian Institute of Space Radio Technology
Priority date: 2021-08-27
Filing date: 2021-08-27
Publication date: 2022-01-18
Anticipated expiration: 2041-08-27
Also published as: CN113949459B

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; 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.

Description

System and method for generating photoelectric mixed FSK signal based on intensity modulator and MZI cascade connection

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 the radio frequency signal and generates the sideband signal through the electro-optical modulator, then further filters the needed optical sideband signal by the microwave photon filter controlled by the binary coding sequence, and carries out the optical sideband signal beat frequency and the electro-optical conversion through the photoelectric detector to obtain the needed electric FSK signal. 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; 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, 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, 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 50:50 optical couplers OC1 and OC2, a phase modulator PM and a fiber delay line DL;

a continuous optical signal output by the laser LD is sent to an optical input end of the intensity modulator IM, a radio frequency driving signal output by the signal source MSG is sent to a radio frequency input end of the intensity modulator IM, a direct current bias voltage output by the direct current source DC is loaded to a direct current end of the intensity modulator IM, and the intensity modulator IM is enabled to work at a maximum point or a 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 is enabled to work at a maximum point or a minimum point as required by adjusting the output voltage of the direct current source DC, and when an electric FSK signal is required 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 the 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 the optical input end of the fiber delay line DL, and the lower branch is sent to the optical input end of the phase modulator PM;

fourthly, the optical signal output by the optical output end of the fiber delay line DL is sent to an optical input port of OC2 in the MZI unit;

fifthly, loading binary coding information output by the pulse waveform generator PPG to 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 end of the OC2 in the MZI unit;

sixthly, the optical signal output by the optical output end of the fiber delay line DL and the optical signal output by the phase modulator PM are sent to the OC2 in the MZI unit together, and combined 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 the binary code information output by the 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 formed by 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 present 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 modulation optical signal required by frequency doubling electric FSK signal generation or optical FSK signal generation according to requirements; the MZI unit which is formed by combining an adjustable optical fiber delay line with a phase modulator controlled by binary coding realizes tunable optical filtering controlled by binary coding information as required to generate an optical signal or an optical FSK signal required by a frequency doubling electrical FSK signal; 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 electric 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 mainly 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 photoelectric detector PD. The MZI realizes a tunable optical filtering function controlled by binary coded information, and mainly comprises two 50:50 optical couplers OC1 and OC2, a phase modulator PM and a fiber delay line DL. The laser is connected with an optical input end of the intensity modulator, an optical output end of the intensity modulator is connected with an input end of a 50:50 optical coupler OC1 in the MZI unit, one output end of a 50:50 optical coupler OC1 in the MZI unit is connected with an optical delay line DL of the MZI unit, the other output end of a 50:50 optical coupler OC1 in the MZI unit is connected with a PM of the MZI unit, output ends of the PM and the DL are connected with input ends of the optical coupler OC2 respectively, an output end of OC2 of the optical coupler is an optical output end of the MZI unit, and an optical output end of the MZI unit is connected with an optical input end of the photodetector PD.

The continuous optical signal output by the laser is sent to the optical input end of the intensity modulator IM, the radio frequency driving signal output by the MSG is sent to the radio frequency input end of the IM, the DC bias voltage output by the DC is loaded to the DC 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 50:50 optical coupler OC1 of the MZI unit, OC1 is split into two paths, one path is sent to the fiber delay line, the other path is sent to the phase modulator PM, the phase modulator is controlled by 01-coded binary coded information, which is given by PPG, which is equivalent to introducing an additional phase θ through the phase modulator, whose value is determined by "0" and "1" coded information.

Continuous optical signal output by laser

Sending the signals to an optical input port of an MZI unit, wherein the MZI can output a tunable high-frequency-multiplication FSK signal as required by properly adjusting an IM direct-current working point and optical delay line delay, and assuming that the microwave signal output by the MSG has the following expression:

V_RF(t)＝V sinωt (1)

wherein V is the amplitude of the microwave signal and ω is the microwave signalAngular frequency of the sign. Assuming an IM two-arm phase difference introduced by the DC bias voltage of

When IM is operated at the maximum transmission point, the method

The 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_πThe 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 phi ═ pi s (t)/V_PMRepresenting the phase offset introduced by the Phase Modulator (PM), s (t) is the binary coded information sequence generated by the PPG, V_PMFor 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-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_c193.1THz, microwave signal frequency ω 5GHz, delay τ 25ps, by modulating the amplitude of the binary coded information sequence s (t) to makeTo obtain

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 ═ pi V/V_πIs the modulation factor, V, of the modulator_πIs the 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 output signal frequency of the photoelectric detector is 4 times the radio frequency driving frequency, and when the binary coded information bit loaded to the MZI unit is "0", the output signal frequency of the photoelectric detector is 2 times 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.

It is assumed that the optical operating 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 25 ps. 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 is consistent with the input binary coded information, so the method for generating the photoelectric mixed FSK signal based on the cascade connection 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:

Step two: according to fig. 1, the optical signal output by the intensity modulator is fed to the input of a 50:50 optical coupler OC1 of the MZI, OC1 is split into two paths, one path is fed to the fiber delay line DL and the other path is fed to the phase modulator PM, the phase modulator is controlled by 01-coded binary coded information, which is given by PPG, which is equivalent to introducing an additional phase through the phase modulator whose value is determined by "0" or "1" coded information.

Similarly, assume that the IM two-arm phase difference introduced by the DC offset is

When IM is operated at the minimum transmission point, the method

The 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 cell is

In the formula, J_n(. cndot.) is a class of n-th order Bessel functions,

modulation factor of IM, V_πHalf-wave voltage of IM; phi ═ pi s (t)/V_PMRepresenting the phase offset introduced by the Phase Modulator (PM), s (t) is the binary coded information sequence generated by the PPG, V_PMτ represents the delay amount of the fiber delay line for the half-wave voltage of the phase modulator in the MZI cell.

From the above equation, the amplitude of the ± 1 st 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 sideband optical signal of-1 order.

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 output optical signal of the MZI unit includes only the +1 order sideband optical signal. According to the above analysis, an optical FSK signal can be obtained by appropriately adjusting the parameters. For example, when the optical carrier frequency is ω_c193.1THz, microwave signal frequency ω 5GHz, delay τ 25ps of the fiber delay line, by modulating the amplitude of the binary coded information sequence s (t) 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 operating frequency is 193.1THz, the optical output power is 20dBm, the bit rate of the binary coded information is 1Gbit/s, the extinction ratio of IM is 30dB, the half-wave voltage of IM is 5V, PM, and the half-wave voltage of PM is 4V, the operating 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) output by the PPG is '01010011', 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 optical sideband components of +1 order and-1 order, and the selection of the two sidebands is determined by the binary coded information s (t) output by the 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 is consistent with the input binary coded information, so that FSK signals with frequencies of 5GHz and 15GHz respectively can be generated, i.e. the optical-electrical mixed FSK signal generation method based on the cascade connection of the intensity modulator and the MZI can effectively generate optical FSK signals.

Claims

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;

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.

2. The system of claim 1, wherein the system comprises an intensity modulator and an MZI cascade-based opto-electronic hybrid FSK signal generating system, and further 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. The system according to claim 2 or 3, wherein the system comprises:

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 of claim 4, wherein the system comprises an intensity modulator and MZI cascaded opto-electronic hybrid FSK signal generator system, and further 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. The system according to claim 4 or 5, 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 '0', the frequency of the output signal of the photoelectric detector is 2 times of 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 of claim 1, wherein the system comprises an intensity modulator and an MZI cascade-based opto-electronic hybrid FSK signal generating system, and further 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 suppresses the optical sideband signals of the even order, the intensity modulator IM output comprises only the ± 1 order sideband optical signals, the intensity modulator IM output optical signal then enters the MZI unit such that the amplitudes of the ± 1 order sideband optical signals are all modulated by the MZI unit.

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;

sixthly, 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 are sent to an OC2 in the MZI unit, and the optical signals are combined into one optical signal by an OC2, and when the optical FSK signal needs to be generated, the OC2 directly outputs a +1 order or-1 order optical signal controlled by the PPG output binary code information, namely, the optical FSK signal; when an electrical 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 information of the binary code output by the PPG, and the signal is then transmitted to a subsequent PD;