A self-generated local oscillator signal broadband tunable microwave photonic frequency conversion system

Abstract

The present application relates to the field of optical communication technology, especially to a kind of local oscillator signal self-generation's broadband tunable microwave photon frequency conversion system, including a tunable laser, a phase shifter, an electric power divider, a double parallel Mach-Zehnder modulator, a phase modulator, two optical couplers, two photoelectric detectors, an optical circulator, an adjustable optical delay line, a low-noise amplifier, a phase-shifted Bragg grating;Phase modulator, optical circulator, low-noise amplifier, second photoelectric detector and optical fiber constitute an optoelectronic oscillation loop;Laser, first optical coupler, double parallel Mach-Zehnder modulator, second optical coupler, first photoelectric detector constitute a radio frequency optical signal generation optical branch;Optical local oscillator signal and radio frequency optical signal are mixed in first photoelectric detector Output, obtain the required frequency conversion signal, solve the problem that external local oscillator source is needed in conventional frequency conversion technology.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a broadband tunable microwave photonic frequency conversion system that generates its own local oscillator signal. Background Technology

[0002] Microwave photonics (MWP) is an emerging technology that organically integrates microwave and photonic technologies. It combines the precision of microwave technology with the broadband capabilities of photonics, and has been widely researched and applied in both military and civilian fields.

[0003] Microwave photonic frequency conversion, as one of the core applications of microwave photonics technology, is currently a hot research direction in the field. Traditional frequency conversion processing is mostly based on electronic technology, mainly through the nonlinearity of electronic devices such as diodes, transistors, or field-effect transistors. As the frequency increases, the frequency conversion efficiency of the electrical domain method is low, and the noise increases significantly, requiring increased system complexity and cost to effectively process high-frequency microwave signals. Microwave photonic frequency conversion technology transfers microwave signals to the optical domain for transmission and processing, greatly improving the ability to handle high-frequency and broadband microwave signals. Microwave photonic frequency conversion links are usually based on superheterodyne structures to modulate the externally input local oscillator (LO) signal and radio frequency (RF) signal onto an optical carrier to achieve optical mixing. Then, the difference frequency or sum frequency of the RF signal and the LO signal is obtained through photoelectric conversion, thereby realizing the frequency conversion output. However, the frequency of the externally input LO signal determines the frequency of the mixed output. In order to directly realize multi-band frequency conversion of RF signals, how to combine the generation of the LO signal and achieve tunability of the LO signal frequency is a challenge.

[0004] Frequency conversion based on microwave photonics technology generally adopts a superheterodyne structure, which modulates the radio frequency (RF) signal and the local oscillator (LO) signal onto an optical carrier, and then obtains the difference frequency or sum frequency of the RF signal and the LO signal through photoelectric conversion (Zhou Jianwei, Li Jianqiang, et al. Integrated RF front-end based on microwave photonics technology. Radio Engineering, 46(9):6-9(2016).). However, such schemes require an external input LO signal to achieve frequency conversion, and their frequency conversion tunability is limited. Recently, researchers have proposed microwave photonics frequency conversion technology based on photoelectric oscillators, which combines the advantage of photoelectric oscillators in generating low phase noise LO signals to achieve direct frequency conversion processing, providing a new technical approach for realizing microwave photonics frequency conversion without LO input. However, the tunability of such schemes is limited by the performance of OEO, and can usually only achieve frequency up-conversion or frequency down-conversion, and the frequency conversion output may contain other spurious components. Therefore, it is of great significance to realize a broadband tunable low spurious frequency conversion technology by combining OEO LO generation technology.

[0005] Chinese Patent Publication No. CN 108809437 B discloses a microwave photonic down-conversion device and method based on bidirectional cyclic frequency shifting. The device comprises a laser, a cyclic frequency shifting module, and a photodetector. The cyclic frequency shifting module includes a 2×2 optical coupler, a polarization controller, a dual-drive electro-optic intensity modulator, an electric local oscillator, an optical amplifier, an optical bandpass filter, and an optical tunable delay line. In the cyclic frequency shifting module, the first-order optical sidebands of the optically carried radio frequency signal to be converted and the electric local oscillator signal simultaneously move towards each other with the same frequency shift step. Finally, the photodetector detects the two nearest-neighboring, oppositely shifted optical sidebands, realizing the down-conversion of the radio frequency signal. Utilizing the opposite frequency shifting characteristics of the cyclic frequency shifting module, by changing the frequency of the electric local oscillator, a wide-range and tunable microwave signal can be down-converted at low-frequency electric local oscillators. Therefore, it is evident that the above technical solution also suffers from the problem of requiring an external local oscillator for frequency conversion. Summary of the Invention

[0006] To address this, the present invention provides a broadband tunable microwave photonic frequency conversion system that generates its own local oscillator signal. This system generates a local oscillator optical signal through an optoelectronic oscillation loop for mixing and output, overcoming the problem that conventional frequency conversion technologies in the prior art require an external local oscillator source. Furthermore, it combines tunable OEO mixing to achieve tunable frequency conversion of radio frequency signals and utilizes a special modulation mode to achieve low spurious output.

[0007] To achieve the above objectives, the present invention provides a broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal, comprising a tunable laser, a phase shifter, an electrical power divider, a dual parallel Mach-Zehnder modulator, a phase modulator, two optical couplers, two photodetectors, an optical circulator, a tunable optical delay line, a low-noise amplifier, and a phase-shifted Bragg grating.

[0008] The optical coupler includes a first optical coupler and a second optical coupler;

[0009] The photodetector includes a first photodetector and a second photodetector;

[0010] The phase modulator, the optical circulator, the low-noise amplifier, the second photodetector, and the optical fiber constitute a photoelectric oscillation loop to generate a local optical oscillator signal.

[0011] The laser, the first optical coupler, the dual parallel Mach-Zehnder modulator, the second optical coupler, and the first photodetector constitute a radio frequency optical signal generation optical branch for outputting radio frequency optical signals;

[0012] The optical local oscillator signal and the radio frequency optical signal are mixed and output in the first photodetector to obtain the desired frequency conversion signal.

[0013] Furthermore, the output of the tunable laser is connected to the first optical coupler to split the optical carrier equally into two optical branches for transmission;

[0014] The output of the first optocoupler includes a first output port and a second output port;

[0015] The first output port is connected to the optical input port of the dual parallel Mach-Zehnder modulator.

[0016] The radio frequency input port is connected to the input port of the power divider, and the first output port of the power divider is connected to the input port of the dual parallel Mach-Zehnder modulator, so as to realize single-sideband intensity modulation with carrier suppression based on electro-optic modulation.

[0017] The dual parallel Mach-Zehnder modulator outputs a +1 order optical sideband.

[0018] Furthermore, the second output port of the first optical coupler is connected to the optical input port of the phase modulator, and the optical output port of the phase modulator is connected to the first port of the optical circulator;

[0019] The second port of the optical circulator is connected to the incident port of the phase-shifted Bragg grating, and the transmission port of the phase-shifted Bragg grating is connected to the second input port of the second optical coupler, so as to convert the optical signal output by the phase modulator into intensity modulation after reflection by the phase-shifted Bragg grating;

[0020] The third port of the optical circulator is connected to the input of the tunable optical delay line, and the output of the tunable optical delay line is connected to the input of the second photodetector to generate the required optical true delay.

[0021] Furthermore, the output terminal of the second photodetector is connected to the low-noise amplifier, and the output terminal of the low-noise amplifier is connected to the radio frequency input terminal of the phase modulator to form a photoelectric oscillator loop, so as to achieve stable oscillation output and generate the required optical local oscillator signal at the input port of the phase-shifted Bragg grating.

[0022] Furthermore, the tunable laser tunes the final output frequency by adjusting its output frequency, and the phase-shifted Bragg grating is configured with the following strategy based on the output frequency of the tunable laser:

[0023] When the output frequency of the tunable laser is less than the notch frequency of the phase-shifted Bragg grating, the +1 sideband of the local oscillator spectrum output from the transmission port of the phase-shifted Bragg grating is coupled to the +1 order radio frequency sideband and transmitted to the first photodetector for demodulation, and the first photodetector outputs a down-conversion demodulated signal.

[0024] When the output frequency of the tunable laser is greater than the notch frequency of the phase-shifted Bragg grating, the -1 sideband of the local oscillator spectrum output from the transmission port of the phase-shifted Bragg grating is coupled to the +1 order radio frequency sideband and transmitted to the first photodetector for demodulation. The first photodetector outputs an up-conversion demodulated signal.

[0025] Furthermore, the tunable laser includes a distributed feedback laser with tunable output frequency.

[0026] Furthermore, the optical coupler includes a 1:1 optical power divider.

[0027] Furthermore, the power divider includes a 1:1 power divider.

[0028] Furthermore, the parameters of the first photodetector and the second photodetector are the same.

[0029] Compared with existing technologies, the advantages of this invention lie in its proposal of a broadband tunable microwave photonic frequency conversion technology that self-generates local oscillator signals. On one hand, it generates local oscillator optical signals through an optoelectronic oscillation loop for mixing and output, solving the problem of conventional frequency conversion technologies requiring an external local oscillator source. On the other hand, it combines tunable OEO mixing to achieve tunable frequency conversion of radio frequency signals and utilizes a special modulation mode to achieve low spurious output. This technical solution can be applied to radar systems, wireless communication, and other application fields.

[0030] Furthermore, this invention can achieve tunable frequency conversion output of broadband signals without the need for an external local oscillator signal source, possessing high-frequency broadband signal processing capabilities and flexible reconfigurability, and can play a certain technical value in the fields of radar and communication applications oriented towards high frequencies. Attached Figure Description

[0031] Figure 1 This is a block diagram illustrating the principle of the broadband tunable microwave photonic frequency conversion technology for self-generated local oscillator signal of the present invention.

[0032] Figure 2 This is a schematic diagram of the spectrum at point A in embodiment A of the present invention;

[0033] Figure 3 This is a schematic diagram of the spectrum at point B in embodiment B of the present invention;

[0034] Figure 4 This is a schematic diagram of the spectrum at point C in an embodiment of the present invention;

[0035] In the figure: 1, first optical coupler; 2, second optical coupler; 3, first photodetector; 4, second photodetector. Detailed Implementation

[0036] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0037] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0038] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0039] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0040] Please see Figure 1 The diagram shown is a block diagram illustrating the principle of the broadband tunable microwave photonic frequency conversion technology for self-generated local oscillator signal according to the present invention. The present invention provides a broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal, comprising a tunable laser, a phase shifter, an electrical power divider, a dual parallel Mach-Zehnder modulator, a phase modulator, two optical couplers, two photodetectors, an optical circulator, a tunable optical delay line, a low-noise amplifier, and a phase-shifted Bragg grating.

[0041] An optical coupler includes a first optical coupler and a second optical coupler; a photodetector includes a first photodetector and a second photodetector.

[0042] A phase modulator, an optical circulator, a low-noise amplifier, a second photodetector, and an optical fiber constitute an optoelectronic oscillation loop to generate an optical local oscillator signal.

[0043] A laser, a first optical coupler, a dual parallel Mach-Zehnder modulator, a second optical coupler, and a first photodetector constitute a radio frequency optical signal generation optical branch for outputting radio frequency optical signals.

[0044] The optical local oscillator signal and the radio frequency optical signal are mixed and output in the first photodetector to obtain the desired frequency conversion signal.

[0045] Specifically, the output of the tunable laser is connected to the first optical coupler to split the optical carrier equally into two optical branches for transmission;

[0046] The output of the first optocoupler includes a first output port and a second output port;

[0047] The first output port is connected to the optical input port of the dual parallel Mach-Zehnder modulator.

[0048] The radio frequency input port is connected to the input port of the power divider, and the first output port of the power divider is connected to the input port of the dual parallel Mach-Zehnder modulator, which is used to realize single-sideband intensity modulation with carrier suppression based on electro-optic modulation.

[0049] Among them, the dual parallel Mach-Zehnder modulator outputs a +1 order optical sideband.

[0050] Specifically, the second output port of the first optical coupler is connected to the optical input port of the phase modulator, and the optical output port of the phase modulator is connected to the first port of the optical circulator.

[0051] The second port of the optical circulator is connected to the incident port of the phase-shifted Bragg grating, and the transmission port of the phase-shifted Bragg grating is connected to the second input port of the second optical coupler, so as to convert the optical signal output by the phase modulator into intensity modulation after reflection by the phase-shifted Bragg grating;

[0052] The third port of the optical circulator is connected to the input of the tunable optical delay line, and the output of the tunable optical delay line is connected to the input of the second photodetector to generate the required optical true delay.

[0053] Specifically, the output of the second photodetector is connected to a low-noise amplifier, and the output of the low-noise amplifier is connected to the radio frequency input of the phase modulator to form a photoelectric oscillator loop, which is used to achieve stable oscillation output and generate the required optical local oscillator signal at the input port of the phase-shifted Bragg grating.

[0054] Specifically, the tunable laser tunes the final output frequency by adjusting the output frequency, and the phase-shifted Bragg grating is configured with the following strategy based on the output frequency of the tunable laser:

[0055] When the output frequency of the tunable laser is less than the notch frequency of the phase-shifted Bragg grating, the +1 sideband of the local oscillator spectrum output from the transmission port of the phase-shifted Bragg grating is coupled with the +1 order radio frequency sideband and transmitted to the first photodetector for demodulation. The first photodetector outputs the down-conversion demodulated signal.

[0056] When the output frequency of the tunable laser is greater than the notch frequency of the phase-shifted Bragg grating, the -1 sideband of the local oscillator spectrum output from the transmission port of the phase-shifted Bragg grating is coupled with the +1 order radio frequency sideband and transmitted to the first photodetector for demodulation. The first photodetector outputs the up-conversion demodulated signal.

[0057] Specifically, tunable lasers include distributed feedback lasers with tunable output frequencies.

[0058] Specifically, optical couplers include 1:1 optical power dividers.

[0059] Specifically, power dividers include 1:1 power dividers.

[0060] Specifically, the parameters of the first photodetector and the second photodetector are the same.

[0061] The specific implementation steps are as follows:

[0062] Step 1: The angular frequency of the output optical carrier of the tunable laser is expressed as ω. LD The center angular frequency of the input broadband signal is denoted as ω. RF Due to the effect of the 90° RF input bridge, the dual parallel Mach-Zehnder modulator operates in carrier-suppressed single-sideband modulation mode. At this time, the output of the dual parallel Mach-Zehnder modulator is as follows: Figure 2 The schematic diagram of the spectrum at point A shows that it only contains the +1 order optical sideband after the carrier wave is suppressed.

[0063] Step 2: When the output frequency of the tunable laser is set to the left of the notch position of the phase-shifted Bragg grating, the spectrum of the input to the second optocoupler of the opto-oscillation loop is as follows: Figure 3 The schematic diagram of the spectrum at point B shows that at this point, the phase-shifted Bragg grating transmits a +1 order local oscillator spectrum, and the angular frequency of this local oscillator signal is expressed as ω. LO .

[0064] Step 3: The generated local oscillator optical signal and the +1st order optical sideband of the radio frequency are input into the first photodetector after passing through the second optical coupler. The final output signal's angular frequency ω OUT =ω RF -ω LO At this point, downconversion of the input radio frequency signal can be achieved;

[0065] When the laser's output frequency is set to the right of the notch position of the phase-shifted Bragg grating, the phase-shifted Bragg grating transmits a +1 order local oscillator spectrum with an angular frequency ω. LO When the value is negative, it can realize the upconversion of the input radio frequency signal, that is, the switching of upconversion and downconversion functions, and the final output frequency can be tuned by changing the output frequency of the tunable laser.

[0066] This solution can achieve tunable frequency conversion output of broadband signals without the need for an external local oscillator signal source. It has high-frequency broadband signal processing capabilities and flexible reconfigurability, and can play a certain technical value in the fields of radar and communication applications oriented towards high frequency.

[0067] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A broadband tunable microwave photonic frequency conversion system with self-generated local oscillator signal, characterized in that, It includes a tunable laser, a phase shifter, an electrical power divider, a dual parallel Mach-Zehnder modulator, a phase modulator, two optical couplers, two photodetectors, an optical circulator, a tunable optical delay line, a low-noise amplifier, and a phase-shifted Bragg grating. The optical coupler includes a first optical coupler and a second optical coupler; The photodetector includes a first photodetector and a second photodetector; The phase modulator, the optical circulator, the low-noise amplifier, the second photodetector, and the optical fiber constitute a photoelectric oscillation loop to generate a local optical oscillator signal. The tunable laser, the first optical coupler, the dual parallel Mach-Zehnder modulator, the second optical coupler, and the first photodetector constitute a radio frequency optical signal generation optical branch for outputting radio frequency optical signals. The radio frequency input port is connected to the input port of the power divider, and the first output port of the power divider is connected to the input port of the dual parallel Mach-Zehnder modulator, so as to realize single-sideband intensity modulation with carrier suppression based on electro-optic modulation; wherein the dual parallel Mach-Zehnder modulator outputs a +1 order optical sideband. When the output frequency of the tunable laser is less than the notch frequency of the phase-shifted Bragg grating, the +1 sideband of the local oscillator spectrum output from the transmission port of the phase-shifted Bragg grating is coupled to the +1 order radio frequency sideband and transmitted to the first photodetector for demodulation, and the first photodetector outputs a down-conversion demodulated signal. When the output frequency of the tunable laser is greater than the notch frequency of the phase-shifted Bragg grating, the -1 sideband of the local oscillator spectrum output from the transmission port of the phase-shifted Bragg grating is coupled with the +1 order radio frequency sideband and transmitted to the first photodetector for demodulation. The first photodetector outputs an up-conversion demodulated signal. The optical local oscillator signal and the radio frequency optical signal are mixed and output in the first photodetector to obtain the desired frequency conversion signal.

2. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 1, characterized in that, The output of the tunable laser is connected to the first optical coupler to split the optical carrier equally into two optical branches for transmission. The output of the first optocoupler includes a first output port and a second output port; The first output port is connected to the optical input port of the dual parallel Mach-Zehnder modulator.

3. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 2, characterized in that, The second output port of the first optical coupler is connected to the optical input port of the phase modulator, and the optical output port of the phase modulator is connected to the first port of the optical circulator. The second port of the optical circulator is connected to the incident port of the phase-shifted Bragg grating, and the transmission port of the phase-shifted Bragg grating is connected to the second input port of the second optical coupler, so as to convert the optical signal output by the phase modulator into intensity modulation after reflection by the phase-shifted Bragg grating; The third port of the optical circulator is connected to the input of the tunable optical delay line, and the output of the tunable optical delay line is connected to the input of the second photodetector to generate the required optical true delay.

4. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 3, characterized in that, The output of the second photodetector is connected to the low-noise amplifier, and the output of the low-noise amplifier is connected to the radio frequency input of the phase modulator to form a photoelectric oscillator loop, which is used to achieve stable oscillation output and generate the required optical local oscillator signal at the input port of the phase-shifted Bragg grating.

5. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 1, characterized in that, The tunable laser includes a distributed feedback laser with tunable output frequency.

6. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 1, characterized in that, The optical coupler includes a 1:1 optical power divider.

7. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 1, characterized in that, The power divider includes a 1:1 power divider.

8. The broadband tunable microwave photonic frequency conversion system for self-generated local oscillator signal according to claim 1, characterized in that, The parameters of the first photodetector and the second photodetector are the same.

Images