A microwave photon harmonic down-conversion method and device with high conversion efficiency

Abstract

A microwave photon harmonic down-conversion method and device with high conversion efficiency, relating to the field of optoelectronics. The bias current of the first slave semiconductor laser is adjusted, and the wavelength and power of the master semiconductor laser are adjusted through a photoelectric oscillation loop, so that it is injected and locked to a certain comb tooth of the first slave semiconductor laser. When the radio frequency signal is loaded onto the optical modulator, a double-sideband signal is generated, including a ‑1-order sideband and a +1-order sideband of equal power. The wavelength and power of the cavity mode of the second slave semiconductor laser are adjusted, and the ‑1-order sideband of the generated double-sideband signal is in the gain region, and the amplified ‑1-order sideband beats with the comb teeth of the optical frequency comb on the second photodetector to generate an intermediate frequency signal. The optical frequency comb generated by the present invention can generate high-quality microwave signals by itself. At the same time, the frequency of the microwave signal generated can be flexibly adjusted by changing the bias current of the first slave semiconductor laser, providing a tunable local oscillator for down-conversion, thereby achieving a flexible down-conversion effect.

Description

Technical Field

[0001] The invention relates to the field of optoelectronics, and in particular to a microwave photon harmonic down-conversion method and device. Background Art

[0002] With the development of 5G, millimeter wave communications, modern electronic warfare receivers, the Internet of Things and other emerging technologies, microwave down-converters provide an effective way to meet the urgent needs of processing and receiving ultra-high frequency signals. Traditional microwave systems use electrical mixers to achieve frequency down-conversion, which has disadvantages such as small bandwidth, poor isolation, weak anti-electromagnetic interference ability, and high nonlinear effects. To solve these problems, a microwave photonic down-converter (PMDC) is proposed, which has infinite isolation between the microwave input and the local oscillator. In the optical domain, PMDC control is achieved through three key steps: 1) Converting radio frequency (RF) to optical signal. 2) Generating local oscillator optical signal. 3) Generating intermediate frequency (IF) by beating the optical microwave signal of LO and RF on a low-speed photodetector. Usually, due to the narrow bandwidth of direct modulation, the local oscillator is modulated onto the optical carrier by a dual parallel Mach-Zehnder modulator, a cascaded or parallel electro-optical modulator. On the other hand, researchers are also committed to improving the conversion efficiency, for example, based on the stimulated Brillouin scattering loss spectrum, the conversion efficiency reached 11.3 dB to suppress the optical carrier.

[0003] In recent years, the optoelectronic properties of semiconductor lasers have received extensive attention. Optical injection (OI) technology is applied in PMDC to increase the direct modulation bandwidth, and sideband injection locking or harmonic injection locking based on single-cycle oscillation is used. In order to further increase the working bandwidth, a photonic microwave harmonic down-converter (PMHDC) based on an optical frequency comb (OFC) is proposed. 75-110 GHz RF signals can be down-converted. In addition to cascade modulators and semiconductor optical amplifiers, OFC can also be generated through the gain switching effect, which has the advantages of easy implementation, high robustness and stability. The local oscillator is crucial in the above system, and its quality will also affect the phase noise of the intermediate frequency signal. The optoelectronic oscillator can obtain ultra-low phase noise and high-frequency microwave signals, avoiding the use of local oscillators in PMDC systems. In order to obtain a wider bandwidth, self-oscillating OFCs are proposed, which are expected to be applied to PMHDC. However, an external modulator is still required to generate OFC, which increases the system cost. At the same time, low conversion efficiency is also a problem that PMHDC needs to solve. Summary of the invention

[0004] The present invention provides a microwave photon harmonic down-conversion method and device with high conversion efficiency, and the generated optical frequency comb itself can generate high-quality microwave signals. At the same time, the frequency of the generated microwave signal can be flexibly adjusted by changing the bias current of the first slave semiconductor laser, providing a tunable local oscillator for down-conversion, thereby achieving a flexible down-conversion effect.

[0005] A microwave photon harmonic down-conversion device with high conversion efficiency comprises a master semiconductor laser, wherein the output end of the master semiconductor laser is connected to the input end of a first optical splitter, the output end of the first optical splitter is respectively connected to the input ends of a first optical circulator and an optical modulator, the output end of the first optical circulator is connected to the input end of a second optical splitter, the output end of the second optical splitter is respectively connected to the input ends of a first photodetector and an optical coupler, the output end of the first photodetector is connected to the input end of an electric amplifier, the electric amplifier is connected to the input end of a first slave semiconductor laser via a bandpass filter, and the first slave semiconductor laser is connected to the first optical circulator;

[0006] The output end of the optical modulator is connected to the input end of the second optical circulator, the second optical circulator is connected to the input end of the erbium-doped fiber amplifier through the optical coupler, the output end of the erbium-doped fiber amplifier is connected to the input end of the second photodetector, and the output end of the second photodetector is connected to the input end of the output intermediate frequency signal;

[0007] The input radio frequency signal is connected to the optical modulator, and the second slave semiconductor laser is connected to the second optical circulator.

[0008] Preferably, the splitting ratio of the first beam splitter and the second beam splitter of the present invention is 5:5.

[0009] Preferably, the coupling ratio of the optical coupler of the present invention is 5:5.

[0010] The frequency conversion method of the microwave photon harmonic down-conversion device according to the present invention comprises the following steps:

[0011] Step 101: supplying power to the master semiconductor laser, the first slave semiconductor laser, the second slave semiconductor laser, the first photodetector, the electric amplifier, the erbium-doped fiber amplifier, and the second photodetector, so that the above components are in working state;

[0012] In step 102, the bias current of the first slave semiconductor laser is adjusted to generate an optical frequency comb with a relaxation oscillation frequency as the comb tooth interval through an optoelectronic oscillation loop;

[0013] Step 103: adjusting the wavelength and power of the master semiconductor laser so that the master semiconductor laser is injection-locked to a comb tooth of the first slave semiconductor laser, and all the comb teeth are coherent with the cavity mode of the master semiconductor laser;

[0014] Step 104, loading the radio frequency signal onto the optical modulator, which generates a double-sideband signal including a -1st order sideband and a +1st order sideband of equal power;

[0015] Step 105, adjusting the wavelength and power of the cavity mode of the second slave semiconductor laser so that it is injection locked by the cavity mode of the master semiconductor laser, and a gain region is formed near it, so that the -1 order sideband of the double-sideband signal generated in step 104 is in the gain region, and the -1 order sideband is amplified;

[0016] Step 106: The amplified -1st order sideband beats with the teeth of the optical frequency comb on the second photodetector to generate an intermediate frequency signal.

[0017] The general down-conversion system needs to provide a stable and high-quality microwave signal to generate the local oscillator, but the optical frequency comb generated by the present invention can generate high-quality microwave signals by itself. At the same time, the frequency of the generated microwave signal can be flexibly adjusted by changing the bias current of the first slave semiconductor laser, providing a tunable local oscillator for down-conversion, thereby achieving the effect of flexible down-conversion.

[0018] The microwave photon harmonic down-conversion device of the present invention provides gain by light injection, and the frequency conversion gain is as high as 14.9 dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural diagram of the microwave photon harmonic down-conversion device of the present invention.

[0020] Figure 2 The present invention is a flow chart of the microwave photon harmonic down-conversion method.

[0021] Figure 3 The diagrams are wavelength-power relationship and frequency offset-power relationship of the microwave photon harmonic down-conversion system of the present invention.

[0022] Figure 4 When the frequency of the RF signal is 12GHz-40GHz, the corresponding spectrum diagram and the corresponding frequency conversion efficiency diagram are shown.

[0023] Figure 5 This is the relationship between frequency and power when the RF signal power is -25dBm and the frequency is 40GHz. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0025] like Figure 1As shown, a microwave photon harmonic down-conversion device with high conversion efficiency includes a master semiconductor laser, the output end of the master semiconductor laser is connected to the input end of a first optical splitter, the output end of the first optical splitter is respectively connected to the input ends of a first optical circulator and an optical modulator, the output end of the first optical circulator is connected to the input end of a second optical splitter, the output end of the second optical splitter is respectively connected to the input ends of a first photodetector and an optical coupler, the output end of the first photodetector is connected to the input end of an electric amplifier, the electric amplifier is connected to the input end of a first slave semiconductor laser through a bandpass filter, and the first slave semiconductor laser is connected to the first optical circulator;

[0026] The output end of the optical modulator is connected to the input end of the second optical circulator, the second optical circulator is connected to the input end of the erbium-doped fiber amplifier through the optical coupler, the output end of the erbium-doped fiber amplifier is connected to the input end of the second photodetector, and the output end of the second photodetector is connected to the input end of the output intermediate frequency signal;

[0027] The input radio frequency signal is connected to the optical modulator, and the second slave semiconductor laser is connected to the second optical circulator.

[0028] The splitting ratio of the first optical splitter and the second optical splitter is 5:5. The coupling ratio of the optical coupler is 5:5.

[0029] like Figure 2 As shown, the frequency conversion method of the microwave photon harmonic down-conversion device according to the present invention comprises the following steps:

[0030] Step 101: supplying power to the master semiconductor laser, the first slave semiconductor laser, the second slave semiconductor laser, the first photodetector, the electric amplifier, the erbium-doped fiber amplifier, and the second photodetector, so that the above components are in working state;

[0031] In step 102, the bias current of the first slave semiconductor laser is adjusted to generate an optical frequency comb with a relaxation oscillation frequency as the comb tooth interval through an optoelectronic oscillation loop;

[0032] Step 103: adjusting the wavelength and power of the master semiconductor laser so that the master semiconductor laser is injection-locked to a comb tooth of the first slave semiconductor laser, and all the comb teeth are coherent with the cavity mode of the master semiconductor laser;

[0033] Step 104, loading the radio frequency signal onto the optical modulator, which generates a double-sideband signal including a -1st order sideband and a +1st order sideband of equal power;

[0034] Step 105, adjusting the wavelength and power of the cavity mode of the second slave semiconductor laser so that it is injection locked by the cavity mode of the master semiconductor laser, and a gain region is formed near it, so that the -1 order sideband of the double-sideband signal generated in step 104 is in the gain region, and the -1 order sideband is amplified;

[0035] Step 106: The amplified -1st order sideband beats with the teeth of the optical frequency comb on the second photodetector to generate an intermediate frequency signal.

[0036] There are two principles for realizing the microwave photon harmonic down converter with high conversion efficiency: the generation of self-starting optical frequency comb and the sideband selective amplification characteristics under optical injection locking. The light emitted by the master semiconductor laser (ML) is amplified by the first erbium-doped fiber amplifier and then divided into two paths by the first optical power divider with a splitting ratio of 5:5, one for the self-starting optical frequency comb generation part and the other for the sideband amplification selection part. In the optical frequency comb generation part, the light of the master semiconductor laser is injected into the first slave semiconductor laser after passing through the first optical circulator, and then input into the second optical splitter through the first optical circulator. The splitting ratio of the second optical splitter is 5:5, and one path is input into the first photodetector. The electrical signal after photoelectric conversion is input into the electrical amplifier. After the low-frequency component is filtered out by the bandpass filter, the signal directly modulates the light emitted by the first slave semiconductor laser through the modulation port of the first slave semiconductor laser, thereby forming an optoelectronic oscillation loop. Since the modulation efficiency of the first slave semiconductor laser is the highest at the relaxation oscillation frequency, after passing through the optoelectronic oscillation loop, the relaxation oscillation frequency and its frequency doubling become the microwave signals existing in the loop. Since the gain in the loop is high enough and the microwave signal power is large enough, the first slave semiconductor laser is in the gain switching state at this time, and the optical frequency comb with the slave semiconductor laser as the core is generated. Adjust the wavelength of the master semiconductor laser so that it is within the locking range of a comb tooth of the optical frequency comb, and the optical frequency comb will be locked by the cavity mode of the master semiconductor laser. At this time, any comb tooth of the optical frequency comb is coherent with the cavity mode of the master semiconductor laser. The other path of the first optical splitter passes through the input optical modulator. After the high-frequency RF signal modulates the cavity mode of the master semiconductor laser through the modulator, double-sidebands distributed on both sides of the cavity mode are generated. Then the double-sideband optical signal is injected into the second slave semiconductor laser through the second optical circulator. At this time, a Gaussian gain zone will be generated around the second slave semiconductor laser. Adjust the cavity mode interval and power of the master semiconductor laser and the second slave semiconductor laser so that the -1 order sideband of the double-sideband signal falls within the gain zone, and the -1 order sideband will be amplified. Then, the output light of the second slave semiconductor laser passes through the second optical circulator, and then the other light of the second beam splitter passes through an optical coupler with a coupling ratio of 5:5 and is input into the erbium-doped fiber amplifier. Since the -1-order sideband is coherent with the cavity mode of the main semiconductor laser, and the cavity mode of the main semiconductor laser is coherent with any comb tooth of the optical frequency comb, the -1-order sideband is coherent with any comb tooth of the optical frequency comb. The output optical power is adjusted to be lower than the maximum input power of the second photodetector. The -1-order sideband and the comb tooth closest to it beat in the second photodetector to generate an intermediate frequency signal, which is then output. As a result, the input high-frequency RF signal will be down-converted to an intermediate frequency signal.

[0037] like Figure 1 As shown, the microwave photon harmonic down-conversion device of the present invention is composed of a master semiconductor laser, a first optical splitter, a first optical circulator, a second optical splitter, a first photodetector, an electric amplifier, a bandpass filter, a first slave semiconductor laser, an optical modulator, a second optical circulator, an optical coupler, an erbium-doped fiber amplifier, a second slave semiconductor laser and a second photodetector. Among them, the master semiconductor laser and the first optical splitter, the first optical splitter and the first optical circulator, the first optical circulator and the second optical splitter, the first optical circulator and the first slave semiconductor laser, the second optical splitter and the first photodetector, the first optical splitter and the optical modulator, the optical modulator and the second optical circulator, the second optical circulator and the optical coupler, the optical coupler and the erbium-doped fiber amplifier, the erbium-doped fiber amplifier and the second photodetector, the second optical circulator and the second slave semiconductor laser, and the second optical splitter and the optical coupler are connected by single-mode optical fiber, which is indicated by black solid lines in the figure. The second is connected between the semiconductor laser and the bandpass filter, between the bandpass filter and the electrical amplifier, between the electrical amplifier and the first photodetector, and between the input radio frequency signal and the optical modulator with radio frequency cables. The second photodetector outputs the intermediate frequency signal with a radio frequency cable, and the radio frequency cable is represented by a black dotted line.

[0038] The light emitted by the master semiconductor laser (ML) is amplified by the first erbium-doped fiber amplifier and then divided into two paths by the first optical power splitter with a splitting ratio of 5:5, one of which is the self-starting optical frequency comb generation part and the other is the sideband amplification selection part. In the optical frequency comb generation part, the light of the master semiconductor laser is injected into the first slave semiconductor laser after passing through the first optical circulator, and then input into the second optical splitter through the first optical circulator. The splitting ratio of the second optical splitter is 5:5, and one path is input into the first photodetector. The electrical signal after photoelectric conversion is input into the electrical amplifier. The low-frequency component is filtered out by the bandpass filter, and the signal directly modulates the light emitted by the first slave semiconductor laser through the modulation port of the first slave semiconductor laser, thereby forming an optoelectronic oscillation loop. Since the modulation efficiency of the first slave semiconductor laser is the highest at the relaxation oscillation frequency, after passing through the optoelectronic oscillation loop, the relaxation oscillation frequency and its frequency doubling become the microwave signals existing in the loop. Since the gain in the loop is high enough and the microwave signal power is large enough, the first slave semiconductor laser is in a gain switching state, and an optical frequency comb with the slave semiconductor laser as the core is generated. Adjust the wavelength of the master semiconductor laser so that it is within the locking range of a comb tooth of the optical frequency comb, and the optical frequency comb will be locked by the cavity mode of the master semiconductor laser. At this time, any comb tooth of the optical frequency comb is coherent with the cavity mode of the master semiconductor laser. The other path of the first optical splitter passes through the input optical modulator. After the high-frequency RF signal modulates the cavity mode of the master semiconductor laser through the modulator, double-sidebands distributed on both sides of the cavity mode are generated. Then the double-sideband optical signal is injected into the second slave semiconductor laser through the second optical circulator. At this time, a Gaussian gain zone will be generated around the second slave semiconductor laser. Adjust the cavity mode interval and power of the master semiconductor laser and the second slave semiconductor laser so that the -1 order sideband of the double-sideband signal falls within the gain zone, and the -1 order sideband will be amplified. Then, the output light of the second slave semiconductor laser passes through the second optical circulator, and then the other light of the second beam splitter passes through an optical coupler with a coupling ratio of 5:5 and is input into the erbium-doped fiber amplifier. Since the -1-order sideband is coherent with the cavity mode of the main semiconductor laser, and the cavity mode of the main semiconductor laser is coherent with any comb tooth of the optical frequency comb, the -1-order sideband is coherent with any comb tooth of the optical frequency comb. The output optical power is adjusted to be lower than the maximum input power of the second photodetector. The -1-order sideband and the comb tooth closest to it beat in the second photodetector to generate an intermediate frequency signal, which is then output. As a result, the input high-frequency RF signal will be down-converted to an intermediate frequency signal.

[0039] When the down-conversion system is in operation, the bias current of the first slave semiconductor laser is set, the wavelength and power of the master semiconductor laser, and the wavelength and power of the second slave semiconductor laser are adjusted, and after the radio frequency signal is loaded onto the optical modulator, the intermediate frequency signal obtained has a frequency lower than 3 GHz, and the conversion efficiency is as high as 14.9 dB.

[0040] Specifically, since the relaxation oscillation frequency of the first slave semiconductor laser can be changed by adjusting its bias current, the comb tooth spacing of the generated optical frequency comb will change accordingly. Thus, a tunable, wide-spectrum optical frequency comb with a spectrum width of up to 110 GHz is obtained. The optical frequency comb provides a tunable, high-quality local oscillator for down-conversion. Therefore, the system does not require an additional local oscillator, and down-conversion is flexible.

[0041] Figure 3 It is a spectrum diagram in front of the second photoelectric detector and a spectrum diagram of the output intermediate frequency signal of the microwave photon harmonic down-conversion system of the present invention. Figure 3 The left side shows the spectrum in front of the second photodetector. The frequency of the RF signal is 38 GHz, the power is -25 dBm, and the comb tooth spacing of the generated optical frequency comb is 5.6895 GHz. It can be seen that compared with the +1-order sideband, the -1-order sideband is amplified by 23.04 dB, so the intermediate frequency signal power generated by the -1-order sideband and the comb tooth beat frequency of the optical frequency comb will also be gained. Figure 3 The right side shows the output IF signal spectrum, which has a frequency of 1.8259 GHz and an IF signal power of -10.81 dBm. Therefore, the conversion efficiency of down-converting the 38 GHz RF signal to the 1.8259 GHz IF signal is 14.19 dB.

[0042] like Figure 4 As shown, in a microwave photon harmonic down-conversion method provided in an embodiment of the present application, the frequency of the radio frequency signal (12 GHz-40 GHz) is changed, and the wavelength and power of the second slave semiconductor laser are adjusted so that the -1 order sideband is in the gain region. Figure 4 The corresponding spectra are shown above. Figure 4 The following is the calculated corresponding frequency conversion efficiency. It can be seen that the conversion efficiency is about 15dB. Since the spectrum width of the optical frequency comb is up to 110 GHz, RF signals up to 110 GHz can be converted with high conversion efficiency.

[0043] like Figure 5 As shown, in a microwave photon harmonic down-conversion method provided in an embodiment of the present application, the RF signal power is set to -25dBm and the frequency is 40GHz. By changing the bias current of the first slave semiconductor laser, the comb tooth spacing of the optical frequency comb changes, and the spacing between the -1 order sideband and the nearest comb tooth also changes, so the 40GHz RF signal can be flexibly down-converted to intermediate frequency signals of different frequencies. Figure 5 As shown, for a fixed frequency signal, the intermediate frequency signal frequency is tunable in the range of 0-2 GHz to meet different requirements.

[0044] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A frequency conversion method for a microwave photon harmonic down-conversion device, characterized in that The steps include: Step 101: supplying power to the master semiconductor laser, the first slave semiconductor laser, the second slave semiconductor laser, the first photodetector, the electric amplifier, the erbium-doped fiber amplifier, and the second photodetector, so that the above components are in working state; In step 102, the bias current of the first slave semiconductor laser is adjusted to generate an optical frequency comb with a relaxation oscillation frequency as the comb tooth interval through an optoelectronic oscillation loop; Step 103: adjusting the wavelength and power of the master semiconductor laser so that the master semiconductor laser is injection-locked to a comb tooth of the first slave semiconductor laser, and all the comb teeth are coherent with the cavity mode of the master semiconductor laser; Step 104, loading the radio frequency signal onto the optical modulator, which generates a double-sideband signal including a -1st order sideband and a +1st order sideband of equal power; Step 105, adjusting the wavelength and power of the cavity mode of the second slave semiconductor laser so that it is injection locked by the cavity mode of the master semiconductor laser, and a gain region is formed near it, so that the -1 order sideband of the double-sideband signal generated in step 104 is in the gain region, and the -1 order sideband is amplified; Step 106, the amplified -1 order sideband beats with the teeth of the optical frequency comb on the second photodetector to generate an intermediate frequency signal; The microwave photon harmonic down-conversion device comprises a master semiconductor laser, the output end of the master semiconductor laser is connected to the input end of a first optical splitter, the output end of the first optical splitter is respectively connected to the input ends of a first optical circulator and an optical modulator, the output end of the first optical circulator is connected to the input end of a second optical splitter, the output end of the second optical splitter is respectively connected to the input ends of a first photodetector and an optical coupler, the output end of the first photodetector is connected to the input end of an electric amplifier, the electric amplifier is connected to the input end of a first slave semiconductor laser through a bandpass filter, and the first slave semiconductor laser is connected to the first optical circulator; The output end of the optical modulator is connected to the input end of the second optical circulator, the second optical circulator is connected to the input end of the erbium-doped fiber amplifier through the optical coupler, the output end of the erbium-doped fiber amplifier is connected to the input end of the second photodetector, and the output end of the second photodetector is connected to the input end of the output intermediate frequency signal; The input radio frequency signal is connected to the optical modulator, and the second slave semiconductor laser is connected to the second optical circulator.

2. The frequency conversion method of the microwave photon harmonic down-conversion device according to claim 1, characterized in that The splitting ratio of the first beam splitter and the second beam splitter is 5:

5.

3. The frequency conversion method of the microwave photon harmonic down-conversion device according to claim 1, characterized in that The coupling ratio of the above optical coupler is 5:5.

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