CN101789826A - Method and device for generating frequency doubling millimeter wave - Google Patents
Method and device for generating frequency doubling millimeter wave Download PDFInfo
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Abstract
The embodiment of the invention discloses a method and a device for generating frequency doubling millimeter wave. The method comprises the following steps that: an intensity modulator modulates a radio frequency signal onto an optical wave, outputs an optical carrier and two n-order optical sidebands and separates the optical carrier and the two n-order optical sidebands; a baseband signal is loaded onto the optical carrier via the intensity modulator; the two n-order optical sidebands are locked by a laser; the optical carrier loaded with baseband data and the two locked n-order optical sidebands are subject to four-wave mixing to generate an optical millimeter wave signal with 4n-time frequency of the radio frequency signal; and the optical millimeter wave signal is subject to beat frequency to generate an electric millimeter wave signal. The device comprises: a modulation module, a mode locking module, a four-wave mixing module and a beat frequency module. The invention provides a method and a device for generating frequency doubling millimeter wave, which can generate millimeter wave signals with high frequency and quality by utilizing low radio frequency source.
Description
Technical Field
The present invention relates to the field of Radio-over-Fiber (ROF) communication systems, and more particularly, to a method and an apparatus for generating frequency-doubled millimeter waves.
Background
With the increasing demand of users for data services such as multimedia, the Fiber-optic wireless communication is developing towards high capacity and high rate, and Millimeter-wave Radio-over-Fiber (mif) technology is receiving more and more attention due to its characteristics of high capacity, low cost, and being suitable for forming a micro-cellular or Pico-cellular system (Pico-cell), and becomes one of the candidates for next-generation high-speed mobile communication.
The ROF system is composed of three parts, namely a Central Station (CS), an optical fiber link and a Base Station (BS). And generating optical millimeter waves at the central station, loading the baseband data signals onto the optical millimeter waves, and sending the optical millimeter waves to the base station through the optical fiber. And the base station completes photoelectric conversion and sends out the signal through an antenna, and simultaneously, the wireless signal received by the base station is converted into an optical signal through electric-to-optical conversion and sent back to the central station. In the ROF system, the base stations share the signal processing unit of the central station, which reduces the number of expensive signal processing units, thereby simplifying the complexity of the system.
Since the generation technology of optical millimeter waves is directly related to the cost performance of the ROF system, it has been widely studied. The optical millimeter wave generation techniques that have been proposed so far can be summarized into three types: direct modulation, external intensity modulation, and optical heterodyne techniques. For direct modulation, the technique is only applicable to low frequency systems because semiconductor lasers and light emitting diodes have relaxation oscillation and frequency chirp characteristics; for the external intensity modulation technology, the cost is high because a high-speed modulator with high price is adopted; since the optical heterodyne technology can generate high-quality high-frequency millimeter waves at a low cost, it is naturally a hot spot of current research.
The optical heterodyne method is to generate a pair of optical coherent longitudinal mode signals with a distance of required millimeter wave frequency by using a low-frequency radio frequency source, and then to access the signals into a photodiode for beat frequency, so that millimeter wave generation can be realized.
In the prior art, there is a device for generating frequency-doubled millimeter waves by using a light heterodyne method based on a four-wave mixing effect. However, since the four-wave mixing (FWM) effect is a nonlinear effect, when it is applied in a highly nonlinear optical fiber or Semiconductor Optical Amplifier (SOA) to achieve frequency doubling, the signal-to-noise ratio of the resulting millimeter wave is low, and the phase noise is high, i.e. the quality of the millimeter wave is poor.
Disclosure of Invention
In view of the above, the present invention provides a method and apparatus for generating frequency-doubled millimeter waves, so as to generate high-quality frequency-doubled millimeter waves.
The invention provides a method for generating frequency doubling millimeter waves, which comprises the following steps:
step A: modulating a radio frequency signal onto a light wave through an intensity modulator, and outputting a light carrier and two n-order light sidebands;
and B: loading a baseband signal onto an optical carrier through an intensity modulator, and locking the two n-order optical sidebands from the laser;
and C: carrying out four-wave mixing on the optical carrier loaded with the baseband signal and the two locked n-order optical sidebands to generate an optical carrier millimeter wave signal with 4n times of radio frequency signal frequency;
step D: and carrying out beat frequency on the optical millimeter wave signal to generate an electric millimeter wave signal.
Preferably, the step a specifically includes: a distributed feedback laser (DFB) generates a light wave, a millimeter wave signal source generates a radio frequency signal, and the light wave and the radio frequency signal are sent to an intensity modulator; adjusting the reference voltage and the modulation index of the intensity modulator to enable the modulated output to keep an optical carrier and two n-order optical sidebands; separating the optical carrier from the two n-order optical sidebands.
Preferably, the step B specifically includes: the separated optical carrier and the baseband signal are modulated together by an intensity modulator, and the intensity modulator outputs the optical carrier loaded with the baseband signal; the slave laser locks two n-order optical sidebands and filters the optical sidebands of other orders; the two n-order optical sidebands enter the optical circulator with the optical carrier carrying the baseband signal, and the two n-order optical sidebands are enhanced by the signal generated from the laser.
Preferably, the step C specifically includes: coupling the optical carrier of the loaded baseband signal and the two locked n-order optical sidebands; sending the coupled optical carrier and the two n-order optical sidebands into a four-wave mixing medium for four-wave mixing; and filtering the four-wave mixed signal into two n-order optical sidebands through a tunable optical filter, and filtering out an optical carrier through a fiber Bragg grating to obtain an optical carrier millimeter wave signal with the radio frequency signal frequency of 4n times.
Preferably, the step D specifically includes: the optical millimeter wave signal is amplified by the erbium-doped fiber amplifier and then transmitted to a base station through a standard single mode fiber; the amplified optical millimeter wave signal is filtered by a tunable optical filter to remove the spontaneous radiation noise of the erbium-doped fiber amplifier; and the optical millimeter wave signal subjected to noise filtering is subjected to beat frequency by a photodiode to generate an electric millimeter wave signal.
Preferably, the two n-order optical sidebands are two second-order optical sidebands or two fourth-order optical sidebands.
Preferably, the slave laser is a fabry-perot laser (FP-LD), a distributed feedback laser (DFB) or a Tunable Laser (TLD).
Preferably, the four-wave mixing medium is a Semiconductor Optical Amplifier (SOA) or a highly nonlinear optical fiber (HNLF).
The invention provides a device for generating frequency doubling millimeter waves, which comprises a modulation module, a mode locking module, a four-wave mixing module and a beat frequency module; the modulation module is used for modulating a radio frequency signal onto an optical wave, outputting an optical carrier and two n-order optical sidebands, and loading a baseband signal onto the optical carrier; the mode locking module is used for locking the two n-order optical sidebands; the four-wave mixing module is used for carrying out four-wave mixing on the optical carrier loaded with the baseband signal and the two locked n-order optical sidebands to generate an optical millimeter wave signal with 4n times of radio frequency signal frequency; the beat frequency module is used for carrying out beat frequency on the optical millimeter wave signal to generate an electric millimeter wave signal.
Preferably, the modulation module specifically includes: signal generation unit, modulation unit and separation unit.
Preferably, the mode locking module specifically comprises a mode locking unit and a reinforcing unit.
Preferably, the four-wave mixing module specifically includes: coupling unit, four-wave mixing unit and filtering unit.
Preferably, the beat module specifically includes: the device comprises an amplifying unit, a noise filtering unit and a beat frequency unit.
According to the technical scheme, the method and the device for generating the frequency doubling millimeter waves have the advantages that the technology of combining injection mode locking and four-wave mixing is adopted, and through injection mode locking of the laser, the optical signal-to-noise ratio of the locked coherent light double longitudinal mode signals and the signal-to-noise ratio of millimeter wave electric signals generated after beat frequency are high, and the phase noise is low, so that the frequency doubling millimeter waves with good quality can be generated.
Drawings
Fig. 1 is a method for generating frequency-doubled millimeter waves according to an embodiment of the present invention;
fig. 2 is another method for generating frequency-doubled millimeter waves according to an embodiment of the present invention;
fig. 3 is a device for generating frequency-doubled millimeter waves according to an embodiment of the present invention;
fig. 4 is another apparatus for generating frequency-doubled millimeter waves according to an embodiment of the present invention.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.
Referring to fig. 1, in an embodiment 1 of the method for generating frequency-doubled millimeter waves provided by the present invention, the present embodiment may specifically include the following steps:
step 101: the intensity modulator modulates the radio frequency signal onto the light wave, outputting a light carrier and two second-order optical sidebands.
In a specific implementation, the radio frequency signal and the light wave are first fed into an intensity modulator. By adjusting the reference voltage and the modulation index of the intensity modulator, only an optical carrier and two second-order optical sidebands are reserved in an output signal, and the even-order optical sidebands except the two second-order optical sidebands and all odd-order optical sidebands are suppressed. And separating the output optical carrier and the two second-order optical sidebands.
According to the present invention, the reference voltage and the modulation index of the intensity modulator may be adjusted such that the output signal only retains the optical carrier and the two fourth-order optical sidebands, so as to generate a millimeter wave signal with a higher frequency, which is not particularly limited.
Step 102: the baseband signal is loaded onto an optical carrier by an intensity modulator.
The separated optical carrier and the baseband signal are sent to an intensity modulator, and the baseband signal is loaded on the optical carrier by adjusting the intensity modulator.
Step 103: the slave laser locks the two second order optical sidebands.
The slave laser in this embodiment is a fabry-perot laser (FP-LD). Adjusting a bias current of a Fabry-Perot laser (FP-LD) to lock the two second-order optical sidebands, specifically comprising: by adjusting the bias current of a Fabry-Perot laser (FP-LD), the unnecessary optical sidebands except the two second-order optical sidebands are filtered out, the optical signal-to-noise ratio of the two locked second-order optical sidebands is improved, and the phase noise is reduced; and amplifying and reinforcing the two second-order optical sidebands to enable the two second-order optical sidebands to become pump light.
Of course, the slave laser may be a distributed feedback laser (DFB) or a Tunable Laser (TLD), and the present invention is not particularly limited thereto.
Here, the order of step 102 and step 103 may be interchanged, and is not particularly limited herein.
Step 104: and carrying out four-wave mixing on the optical carrier loaded with the baseband signal and the two locked second-order optical sidebands to generate an optical carrier millimeter wave signal with the frequency of eight times of the radio frequency signal.
And sending the two second-order optical sidebands, namely the pump light and the optical carrier of the loaded baseband signal into a semiconductor optical amplifier together, completing four-wave mixing of the pump light and the optical carrier of the loaded baseband signal in the Semiconductor Optical Amplifier (SOA), and generating an optical carrier millimeter wave signal with the frequency of eight times of a radio frequency signal.
Of course, the Semiconductor Optical Amplifier (SOA) may be replaced by a highly nonlinear optical fiber (HNLF), and the present invention is not particularly limited thereto.
Step 105: and carrying out beat frequency on the optical millimeter wave signal to generate an electric millimeter wave signal.
And the optical millimeter wave signal is transmitted to a base station through an optical fiber link, and is subjected to beat frequency through a photodiode to generate an electric millimeter wave signal. The signal-to-noise ratio of the generated electric millimeter wave signal is also improved, and the phase noise is correspondingly reduced.
If the baseband signal needs to be recovered, the generated electric millimeter wave signal and the millimeter wave local oscillator are only required to be subjected to frequency mixing, and then the signal after frequency mixing is subjected to low-pass filter to filter out the high-frequency signal, so that the baseband signal can be obtained.
It can be seen from the above embodiments that the present invention adopts a technology combining injection mode locking and four-wave mixing to generate frequency-doubled millimeter waves, and injects mode locking through a fabry-perot laser (FP-LD), locks two second-order optical sidebands, and filters out other unnecessary optical sidebands, where the optical signal-to-noise ratio of the two locked second-order optical sidebands and the signal-to-noise ratio of the electrical millimeter wave signal generated after beat frequency are both improved, and accordingly, the phase noise is both reduced, and therefore, the signal quality of the generated electrical millimeter waves is better.
Referring to fig. 2, in another embodiment 2 of the method for generating frequency-doubled millimeter waves provided by the present invention, the present embodiment may specifically include the following steps:
step 201: a distributed feedback laser (DFB) generates a light wave, a millimeter wave signal source generates a radio frequency signal, and the light wave and the radio frequency signal are fed into an intensity modulator.
Generating an optical wave from a distributed feedback laser (DFB), said optical wave being sent to an intensity modulator; meanwhile, a radio frequency signal with the frequency of 5GHz is generated by the millimeter wave signal source, and the radio frequency signal with the frequency of 5GHz is also sent to the intensity modulator.
Step 202: and adjusting the reference voltage and the modulation index of the intensity modulator to output an optical carrier and two second-order optical sidebands.
The light waves generated in step 201 and the radio frequency signal with the frequency of 5GHz are sent to an intensity modulator, and the odd-order optical sideband and most of the even-order optical sideband in the mixed signal are suppressed by adjusting the reference voltage and the modulation index of the intensity modulator, so that the output signal only has an optical carrier and two second-order optical sidebands.
Of course, the reference voltage and the modulation index of the intensity modulator may also be adjusted so that only the optical carrier and two fourth-order optical sidebands remain in the output signal, which may generate a millimeter wave signal with a higher frequency, and the present invention is not limited thereto.
Step 203: separating the optical carrier and the two second order optical sidebands.
The optical carrier and the two second order optical sidebands output by the intensity modulator are filtered via an optically interleaved comb filter such that the optical carrier and the two second order optical sidebands are separated.
Step 204: and the separated optical carrier and the baseband signal are modulated together by an intensity modulator, and the intensity modulator outputs the optical carrier loaded with the baseband signal.
The optical carrier separated by the optical interleaver is fed to an intensity modulator, and at the same time, a baseband signal is fed to the intensity modulator, which is loaded on the optical carrier by adjusting a reference voltage and a modulation index of the intensity modulator.
Step 205: and the slave laser locks two second-order optical sidebands and filters the optical sidebands of other orders.
The slave laser in this embodiment is a fabry-perot laser (FP-LD). And locking the two second-order optical sidebands by adjusting the bias current of a Fabry-Perot laser (FP-LD), so that the frequency intervals of the two second-order optical sidebands and the optical carrier are respectively 10GHz, and meanwhile, filtering out other unnecessary optical sidebands except the two second-order optical sidebands to reduce the phase noise of the two second-order optical sidebands and improve the optical signal-to-noise ratio of the two second-order optical sidebands.
Of course, the slave laser can also be replaced by a distributed feedback laser (DFB) or a Tunable Laser (TLD).
Here, the order of step 204 and step 205 may also be interchanged.
Step 206: the two second order optical sidebands enter the optical circulator with the signal generated from the laser, which is enhanced by the signal generated from the laser.
Two second order optical sidebands separated by the optical interleaver are fed into the optical circulator, and at the same time, the signal generated by the fabry-perot laser (FP-LD) is also fed into the optical circulator, and the two second order optical sidebands are amplified and enhanced under the action of the signal generated by the laser, so that the two second order optical sidebands become pump light.
In addition, the direct modulation bandwidth of the laser can be increased by locking the two second-order optical sidebands, and the direct modulation bandwidth of-3 dB is increased in the embodiment.
Step 207: coupling the optical carrier of the loaded baseband signal and the two locked second-order optical sidebands.
And the optical carrier for loading the baseband signal and the two locked second-order optical sidebands, namely the pump light, are both sent into the optical coupler for coupling.
Step 208: and sending the coupled optical carrier and the two second-order optical sidebands into a four-wave mixing medium for four-wave mixing.
The coupled optical carrier and pump light output by the optical coupler are sent to a four-wave mixing medium, which is a Semiconductor Optical Amplifier (SOA) in this embodiment, and four-wave mixing is implemented in the Semiconductor Optical Amplifier (SOA). Of course, the Semiconductor Optical Amplifier (SOA) can also be replaced by a highly nonlinear fiber (HNLF).
Step 209: and filtering the four-wave mixed signal into two second-order optical sidebands through a tunable optical filter, and filtering out an optical carrier through an optical fiber Bragg grating to obtain an optical carrier millimeter wave signal with the frequency eight times of the radio frequency signal.
A four-wave mixed signal output by a Semiconductor Optical Amplifier (SOA) is filtered out pump light, namely the two second-order optical sidebands, through a tunable optical filter; then, the optical carrier is filtered out through an optical circulator and an optical Bragg grating in sequence, and further the optical millimeter wave signal which is eight times of the frequency of the radio frequency signal, namely the optical millimeter wave signal of 40GHz, is obtained.
Step 210: and the optical millimeter wave signal is amplified by the erbium-doped fiber amplifier and then transmitted to the base station through the standard single-mode fiber.
The optical millimeter wave signal with the frequency of 40GHz generated in step 209 is amplified by the erbium-doped fiber amplifier, and the amplified optical millimeter wave signal is transmitted to the base station through the optical fiber link. In this embodiment, the optical fiber link is a standard single mode optical fiber.
Step 211: and filtering the amplified optical millimeter wave signal by a tunable optical filter to remove the spontaneous radiation noise of the erbium-doped fiber amplifier.
Because the erbium-doped fiber amplifier can generate spontaneous radiation noise, the optical millimeter wave-carrying signal output from the erbium-doped fiber amplifier needs to be filtered by the tunable optical filter to remove the radiation noise carried by the optical millimeter wave-carrying signal, so that the phase noise of the optical millimeter wave-carrying signal is reduced, and the quality of the optical millimeter wave-carrying signal is improved.
Step 212: and the optical millimeter wave signal subjected to noise filtering is subjected to beat frequency by a photodiode to generate an electric millimeter wave signal.
The optical millimeter wave signal output by the tunable optical filter is sent to the photodiode, and the beat frequency is completed in the photodiode to generate a 40GHz electric millimeter wave signal. The generated electric millimeter wave signal has higher signal-to-noise ratio, low phase noise and better quality.
The invention adopts the combination of injection mode locking and four-wave mixing to generate frequency doubling millimeter waves so as to transmit baseband signals. By adjusting the bias point of the intensity modulator and the bias current of the Fabry-Perot laser (FP-LD), the optical sideband of the Fabry-Perot laser (FP-LD) is selected to carry out injection mode locking, two second-order optical sidebands are locked, and other unnecessary optical sidebands are filtered, so that the signal-to-noise ratio of the generated millimeter wave signal is improved, the phase noise is reduced, and the quality of the generated millimeter wave signal is better.
In addition, the injection mode locking can also improve the direct modulation bandwidth of the laser, and the injection mode locking has high application value in the aspects of baseband signal optical up-conversion, uplink signal optical down-conversion and the like. In addition, the invention utilizes the millimeter wave signal source with lower frequency to generate the millimeter wave with high frequency, thereby effectively reducing the frequency requirement of the system on the local vibration source of the millimeter wave and reducing the bandwidth requirement of the optical modulator, thereby reducing the manufacturing cost of the system and saving the cost.
Referring to fig. 3, in an embodiment 1 of the apparatus for generating frequency-doubled millimeter waves according to the present invention, the apparatus in this embodiment specifically includes: a modulation module 301, a mode locking module 302, a four-wave mixing module 303 and a beat frequency module 304.
The modulation module 301 is configured to modulate a radio frequency signal onto an optical wave, and output an optical carrier and two second-order optical sidebands, and is further configured to load a baseband signal onto the optical carrier.
In a specific implementation, the modulation module 301 first receives the optical wave and the radio frequency signal entering therein. The modulation module 301 modulates the radio frequency signal onto the optical wave by adjusting the reference voltage and the modulation index, and only the optical carrier and two second-order optical sidebands are retained in the output signal, and the even-order optical sidebands except the two second-order optical sidebands and all odd-order optical sidebands are suppressed. The modulation module 301 is further configured to receive an optical carrier and a baseband signal, load the baseband signal on the optical carrier, and output the optical carrier loaded with the baseband signal.
According to the present invention, the modulation module 301 may further adjust the reference voltage and the modulation index such that the output signal only retains the optical carrier and the two fourth-order optical sidebands, so as to generate the millimeter wave signal with a higher frequency, which is not particularly limited by the present invention.
The mode locking module 302 is used to lock the two second order optical sidebands.
The mode locking module 302 first locks the two second-order optical sidebands so that the two second-order optical sidebands are respectively spaced at equal frequencies from the optical carrier. The two second order optical sidebands are then acted upon by the signal that it emits and the two second order optical sidebands so as to be intensified, making them pump light. The mode locking module 302 can also filter out the other unnecessary optical sidebands except the two second-order optical sidebands, so that the optical signal-to-noise ratio of the two locked second-order optical sidebands is improved, and meanwhile, the phase noise is reduced.
The four-wave mixing module 303 is configured to perform four-wave mixing on the optical carrier of the loaded baseband signal and the two locked second-order optical sidebands to generate an optical millimeter wave signal with a radio frequency signal frequency eight times higher;
the four-wave mixing module 303 first receives two second-order optical sidebands, i.e., pump light and optical carriers of the loaded baseband signal, which enter the four-wave mixing module 303, performs four-wave mixing on the pump light and the optical carriers of the loaded baseband signal, and then filters out the pump light and the optical carriers to generate an optical millimeter wave signal with the frequency eight times of the radio frequency signal.
The beat frequency module 304 is configured to perform beat frequency on the optical millimeter wave signal to generate an electrical millimeter wave signal.
The beat frequency module 304 first receives the optical millimeter wave signal transmitted by the optical fiber link, and then performs beat frequency on the optical millimeter wave signal to generate an electrical millimeter wave signal. The signal-to-noise ratio of the generated electric millimeter wave signal is high, the phase noise is low, and the signal quality of the electric millimeter wave is good.
It can be seen from the above embodiments that the present invention employs a technology combining injection mode locking and four-wave mixing to generate frequency-doubled millimeter waves, locks two second-order optical sidebands through the mode locking module 302, and filters out other unnecessary optical sidebands, where the optical signal-to-noise ratio of the two locked second-order optical sidebands and the signal-to-noise ratio of the electric millimeter wave signal generated after beat frequency are both improved, and accordingly, the phase noise is both reduced, and therefore, the signal quality of the generated electric millimeter wave is better.
Referring to fig. 4, in another embodiment 2 of the apparatus for generating frequency-doubled millimeter waves provided by the present invention, the apparatus in this embodiment specifically includes: signal generating section 401, modulating section 402, separating section 403, mode locking section 404, enhancing section 405, coupling section 406, four-wave mixing section 407, filtering section 408, amplifying section 409, noise filtering section 410, and beat frequency section 411.
In the present embodiment, the function of the modulation module 301 is realized by three units, i.e., a signal generation unit 401, a modulation unit 402, and a separation unit 403.
The signal generation unit 401 is used to generate optical wave and radio frequency signals.
In this embodiment, the signal generating unit 401 includes a distributed feedback laser (DFB) and a millimeter wave signal source, the distributed feedback laser (DFB) generates an optical wave and sends the optical wave to the modulating unit 402, and the millimeter wave signal source generates a radio frequency signal with a frequency of 5GHz and sends the radio frequency signal with the frequency of 5GHz to the modulating unit 402.
The modulation unit 402 is used to adjust the reference voltage and the modulation index, and output an optical carrier and two second-order optical sidebands.
The modulation unit 402 is an intensity modulator. The intensity modulator receives the optical waves and the radio frequency signals with the frequency of 5GHz transmitted by the signal generating unit 401, and suppresses odd-order optical sidebands and most of even-order optical sidebands in the mixed signals by adjusting the reference voltage and the modulation index, so that only optical carriers and two second-order optical sidebands exist in the output signals.
Of course, the intensity modulator may also be configured to keep only the optical carrier and the two fourth-order optical sidebands in the output signal by adjusting the reference voltage and the modulation index, so as to generate a millimeter wave signal with a higher frequency, which is not particularly limited in the present invention.
The separation unit 403 is used to separate the optical carrier and the two second-order optical sidebands.
The separation unit 403 is an optical interleaver comb filter. The optical interleaved comb filter receives the optical carrier and the two second-order optical sidebands output by the intensity modulator, separates and outputs the optical carrier and the two second-order optical sidebands.
The modulation unit 402 is further used to load a baseband signal onto an optical carrier
The optical carrier separated and output by the optical interleaver is sent to the modulation unit 402, and at the same time, a baseband signal is also sent to the modulation unit 402, and the modulation unit 402 loads the baseband signal on the optical carrier and outputs the baseband signal by adjusting the reference voltage and the modulation index of the intensity modulator.
In this embodiment, the function of the mode locking module 302 is realized by two units, i.e., the mode locking unit 404 and the strengthening unit 405.
The mode locking unit 404 is used to lock two second-order optical sidebands and filter out other-order optical sidebands.
The mode locking unit 404 in this embodiment is a fabry-perot laser (FP-LD). And locking the two second-order optical sidebands by adjusting the bias current of a Fabry-Perot laser (FP-LD), so that the frequency intervals of the two second-order optical sidebands and the optical carrier are respectively 10GHz, and meanwhile, filtering out other unnecessary optical sidebands except the two second-order optical sidebands to reduce the phase noise of the two second-order optical sidebands and improve the optical signal-to-noise ratio of the two second-order optical sidebands.
Of course, the mode locking unit 404 may also be replaced by a distributed feedback laser (DFB) or a Tunable Laser (TLD).
The enhancement unit 405 is used to enhance the two second order optical sidebands.
The stiffening unit 405 is an optical circulator. Two second order optical sidebands separated and output by the optical interleaver are fed into the optical circulator, and at the same time, a signal generated by a Fabry-Perot laser (FP-LD) is also fed into the optical circulator, and the two second order optical sidebands are amplified and intensified by the signal generated from the laser, so that the two second order optical sidebands become pump light.
In this embodiment, the function of the four-wave mixing module 303 is realized by three units, i.e., a coupling unit 406, a four-wave mixing unit 407, and a filtering unit 408.
The coupling unit 406 is used to couple the optical carrier carrying the baseband signal and the two second-order optical sidebands being locked.
The coupling unit 406 is an optical coupler. And the optical carrier for loading the baseband signal and the two locked second-order optical sidebands, namely the pump light, are both sent into the optical coupler for coupling.
The four-wave mixing unit 407 is configured to perform four-wave mixing on the coupled optical carrier and the two second-order optical sidebands.
In this embodiment, the four-wave mixing unit 407 is a Semiconductor Optical Amplifier (SOA). The coupled optical carrier and pump light output by the optical coupler are sent to a Semiconductor Optical Amplifier (SOA) where four-wave mixing is achieved. Of course, the Semiconductor Optical Amplifier (SOA) can also be replaced by a highly nonlinear fiber (HNLF).
The filtering unit 408 is used to filter out the optical carrier and the two second-order optical sidebands.
The filtering unit 408 includes a tunable optical filter, an optical circulator, and a fiber bragg grating. A four-wave mixed signal output by a Semiconductor Optical Amplifier (SOA) is filtered out pump light, namely the two second-order optical sidebands, through a tunable optical filter; then, the optical carrier is filtered out through an optical circulator and an optical Bragg grating in sequence, and further an optical millimeter wave signal which is eight times of the frequency of the radio frequency signal, namely an optical millimeter wave signal of 40GHz, is obtained.
In this embodiment, the function of the beat frequency module 304 is realized by three units, namely, an amplifying unit 409, a noise filtering unit 410, and a beat frequency unit 411.
The amplification unit 409 is used for amplifying the optical millimeter wave signal.
The amplifying unit 409 is an erbium-doped fiber amplifier. The optical millimeter wave signal with the frequency of 40GHz output by the filtering unit 408 is transmitted to the erbium-doped fiber amplifier, and the erbium-doped fiber amplifier amplifies and outputs the optical millimeter wave signal. The amplified optical millimeter wave signal output by the erbium-doped fiber amplifier is transmitted to the base station through the optical fiber link. In this embodiment, the optical fiber link is a standard single mode optical fiber.
The noise filtering unit 410 is used for filtering the spontaneous emission noise generated by the amplifying unit 409.
The noise filtering unit 410 is a tunable optical filter. Since the erbium-doped fiber amplifier can generate spontaneous radiation noise, the optical millimeter wave signal output from the erbium-doped fiber amplifier is sent to the noise filtering unit 410, and the tunable optical filter filters the radiation noise carried in the optical millimeter wave signal, so that the phase noise of the optical millimeter wave signal is reduced, and the quality of the optical millimeter wave signal is improved.
The beat unit 411 is used to convert the optical millimeter wave signal into an electrical millimeter wave signal.
The beat unit 411 is a photodiode. The millimeter-wave optical carrier signal output by the tunable optical filter is sent to the beat unit 411, and the beat frequency is completed in the photodiode, so as to generate a 40GHz millimeter-wave electrical signal. The generated electric millimeter wave signal has high signal-to-noise ratio, low phase noise and good quality.
The invention adopts the combination of injection mode locking and four-wave mixing to generate frequency doubling millimeter waves so as to transmit baseband signals. By adjusting the bias point of the intensity modulator and the bias current of the Fabry-Perot laser (FP-LD), the optical sideband of the Fabry-Perot laser (FP-LD) is selected to carry out injection mode locking, two second-order optical sidebands are locked, and other unnecessary optical sidebands are filtered, so that the signal-to-noise ratio of the generated millimeter wave signal is improved, the phase noise is reduced, and the quality of the generated millimeter wave signal is better.
In addition, the injection mode locking can also improve the direct modulation bandwidth of the laser, and the injection mode locking has high application value in the aspects of baseband signal optical up-conversion, uplink signal optical down-conversion and the like. In addition, the invention utilizes the millimeter wave signal source with lower frequency to generate the millimeter wave signal with high frequency, thereby effectively reducing the frequency requirement of the system on the millimeter wave local vibration source and reducing the bandwidth requirement of the optical modulator, thereby reducing the system cost and saving the cost.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The term "comprising", without further limitation, means that the element so defined is not excluded from the group consisting of additional identical elements in the process, method, article, or apparatus that comprises the element.
For the device embodiments, since they substantially correspond to the method embodiments, reference may be made to the partial description of the method embodiments for relevant points. The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
The foregoing is directed to embodiments of the present invention, and it is understood that various modifications and improvements can be made by those skilled in the art without departing from the spirit of the invention.
Claims (10)
1. A method of generating frequency-doubled millimeter waves, comprising the steps of:
step A: modulating a radio frequency signal onto a light wave through an intensity modulator, and outputting a light carrier and two n-order light sidebands;
and B: loading a baseband signal onto an optical carrier through an intensity modulator, and locking the two n-order optical sidebands from the laser;
and C: carrying out four-wave mixing on the optical carrier loaded with the baseband signal and the two locked n-order optical sidebands to generate an optical carrier millimeter wave signal with 4n times of radio frequency signal frequency;
step D: and carrying out beat frequency on the optical millimeter wave signal to generate an electric millimeter wave signal.
2. The method of claim 1, wherein step a comprises the steps of:
the DFB generates a light wave, the millimeter wave signal source generates a radio frequency signal, and the light wave and the radio frequency signal are sent to the intensity modulator;
adjusting the reference voltage and the modulation index of the intensity modulator to enable the modulated output to keep an optical carrier and two n-order optical sidebands;
separating the optical carrier from the two n-order optical sidebands.
3. The method of claim 1, wherein step B comprises the steps of:
the separated optical carrier and the baseband signal are modulated together by an intensity modulator, and the intensity modulator outputs the optical carrier loaded with the baseband signal;
the slave laser locks two n-order optical sidebands and filters the optical sidebands of other orders;
the two n-order optical sidebands enter the optical circulator with the signal generated from the laser, which reinforces the two n-order optical sidebands.
4. The method of claim 1, wherein step C comprises the steps of:
coupling the optical carrier of the loaded baseband signal and the two locked n-order optical sidebands;
sending the coupled optical carrier and the two n-order optical sidebands into a four-wave mixing medium for four-wave mixing;
and filtering the four-wave mixed signal into two n-order optical sidebands through a tunable optical filter, and filtering out an optical carrier through an optical fiber Bragg grating to obtain an optical carrier millimeter wave signal with the radio frequency signal frequency of 4n times.
5. The method of claim 1, wherein said step D comprises the steps of:
the optical millimeter wave signal is amplified by the erbium-doped fiber amplifier and then transmitted to a base station through a standard single mode fiber;
the amplified optical millimeter wave signal is filtered by a tunable optical filter to remove the spontaneous radiation noise of the erbium-doped fiber amplifier;
and the optical millimeter wave signal subjected to noise filtering is subjected to beat frequency by a photodiode to generate an electric millimeter wave signal.
6. The method of any one of claims 1 to 5, wherein the two n-order optical sidebands are two second-order optical sidebands or two fourth-order optical sidebands.
7. A method according to any one of claims 1 to 5, wherein the slave laser in step B is a Fabry-Perot laser FP-LD, DFB or a tunable laser TLD.
8. The method according to any one of claims 1 to 5, wherein the four-wave mixing medium in step C is a semiconductor optical amplifier SOA or a highly nonlinear optical fiber HNLF.
9. A device for generating frequency doubling millimeter waves is characterized by comprising a modulation module, a mode locking module, a four-wave mixing module and a beat frequency module;
wherein,
the modulation module is used for modulating a radio frequency signal onto an optical wave, outputting an optical carrier and two n-order optical sidebands, and loading a baseband signal onto the optical carrier;
the mode locking module is used for locking the two n-order optical sidebands;
the four-wave mixing module is used for carrying out four-wave mixing on the optical carrier loaded with the baseband signal and the two locked n-order optical sidebands to generate an optical millimeter wave signal with 4n times of radio frequency signal frequency;
the beat frequency module is used for carrying out beat frequency on the optical millimeter wave signal to generate an electric millimeter wave signal.
10. The apparatus according to claim 9, wherein the modulation module comprises a signal generation unit, a modulation unit and a separation unit; the mode locking module specifically comprises a mode locking unit and a reinforcing unit; the four-wave mixing module specifically comprises a coupling unit, a four-wave mixing unit and a filtering unit; the beat frequency module specifically comprises an amplifying unit, a noise filtering unit and a beat frequency unit.
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| CN104601240B (en) * | 2014-12-24 | 2017-02-22 | 宁波大学 | System and method for generating millimeter waves based on chalcogenide glass optical fiber four-wave mixing effect |
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| CN113900315A (en) * | 2021-08-20 | 2022-01-07 | 清华大学 | Low stray high order frequency multiplication system and method based on optical sideband injection locking |
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