CN110707510A - Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering - Google Patents
Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering Download PDFInfo
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- CN110707510A CN110707510A CN201810747962.1A CN201810747962A CN110707510A CN 110707510 A CN110707510 A CN 110707510A CN 201810747962 A CN201810747962 A CN 201810747962A CN 110707510 A CN110707510 A CN 110707510A
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- brillouin scattering
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- domain mode
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- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S1/00—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range
Abstract
A Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering comprises a tunable laser, a phase modulator, an optical fiber, a circulator, a photoelectric detector, an electric amplifier, a power divider and a pump laser; the tunable laser, the phase modulator, the pump laser, the optical fiber and the photoelectric detector form a microwave photon filter, and the passband of the microwave photon filter is determined by the wavelength difference between the tunable laser and the gain spectrum. The mode locking in the Fourier domain can be realized by periodically adjusting the passband of the microwave photonic filter and synchronizing the change period of the filter with the one-cycle delay of the signal transmitted in the photoelectric oscillator loop, and the sweep frequency microwave signal with adjustable center frequency and bandwidth can be generated.
Description
Technical Field
The invention relates to the technical field of microwave photonics, in particular to a Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering.
Background
In systems such as wireless communication and radar, high requirements are imposed on the bandwidth, sensitivity, dynamic range and the like of a microwave signal source. From the source, microwave signal sources are required to have a wide tuning range, low phase noise and fast tuning capability.
The microwave signal source generally adopts a pure electronic means. For example, a frequency swept microwave signal with a frequency that varies with voltage can be easily generated using a voltage controlled oscillator. The sweep bandwidth and sweep speed can basically meet the requirements of the radar. However, its phase noise is poor at high frequencies, approximately-70 dBc/Hz @10 kHz. On the other hand, chirped microwave signals can also be generated by using a direct digital frequency synthesis technology, but the instantaneous bandwidth is narrow and is about GHz level. In order to overcome the technical problems encountered by microwave signal sources based on electronics, microwave signal generation technologies based on photonics have been developed at home and abroad in recent years. Compared with a pure electronic means, the microwave photon technology has the advantages of large bandwidth, low phase noise, flexible tuning and the like. The photoelectric oscillator technology is one of microwave photon technologies, and utilizes optical energy storage to obtain a high-performance resonant cavity to generate a microwave signal with ultra-low phase noise. The biggest bottleneck encountered by the conventional optoelectronic oscillator is the slow frequency tuning speed. This is mainly due to two factors, one is the slow tuning speed (in the order of tens of ms) of the electrical filters used for mode selection in the optoelectronic oscillator; secondly, when the electric filter tunes to a new frequency, the microwave signal needs to start oscillating again from noise, and the time needed for establishing stable oscillation is longer. In addition, in the frequency tuning process, since each frequency is oscillated from noise, the phases of signals of different frequencies are discontinuous, which deteriorates the phase noise of the frequency sweep signal.
In order to realize a low-phase-noise broadband fast frequency-sweeping microwave source, the invention provides a Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering.
Disclosure of Invention
In view of the above, it is a primary object of the present invention to provide a fourier domain mode-locked optoelectronic oscillator based on stimulated brillouin scattering, which is intended to at least partially solve at least one of the above technical problems.
In order to achieve the above object, the present invention provides a fourier domain mode-locked optoelectronic oscillator based on stimulated brillouin scattering, comprising: the device comprises a tunable laser, a phase modulator, a high nonlinear optical fiber, a circulator, a photoelectric detector, an electric amplifier, a power divider and a pumping laser;
the tunable laser, the phase modulator, the high nonlinear optical fiber, the circulator, the photoelectric detector and the pump laser are sequentially connected through the optical fiber; the photoelectric detector, the electric amplifier, the power divider and the phase modulator are sequentially connected through cables;
the tunable laser, the phase modulator, the pump laser, the high nonlinear fiber and the photoelectric detector form a microwave photon filter, and the passband of the microwave photon filter is determined by the wavelength difference between the tunable laser and the gain spectrum.
Based on the technical scheme, compared with the prior art, the Fourier domain mode-locked photoelectric oscillator based on the stimulated Brillouin scattering has the following beneficial effects:
(1) the frequency sweep microwave signal with adjustable center frequency and bandwidth broadband and low phase noise can be generated;
(2) through the selective amplification effect of the stimulated Brillouin scattering, when the wavelength corresponding to the gain spectrum of the stimulated Brillouin scattering excited in the high nonlinear optical fiber by the pump laser is equal to one sideband of the modulated wave, the sideband has larger gain relative to the other sideband, and the sideband and the optical carrier wave emitted by the light source beat in the photoelectric detector, so that a microwave signal corresponding to the frequency difference between the two can be obtained;
(3) the wavelength of an optical signal emitted by a laser is periodically changed through a periodic driving current, and the change of the wavelength of the optical signal is matched with the time of transmitting the signal in a photoelectric oscillator loop for one circle, so that different frequency components can pass through a microwave photon filter at different moments, and the frequency components are simultaneously stored in the photoelectric oscillator loop cavity, so that the new frequency components do not need to start oscillation starting through noise again, thus realizing a Fourier domain mode-locked photoelectric oscillator and generating a sweep frequency microwave signal;
(4) by controlling the dispersion of the photoelectric oscillator loop to zero, signals with different frequencies can have the same time delay in the loop;
(5) because an electric filter is not needed in the photoelectric oscillator loop, the frequency of the microwave signal generated by the loop only depends on the difference value between the light-emitting wavelength of the tunable laser and the wavelength corresponding to the stimulated Brillouin scattering, and therefore broadband tuning of the microwave signal can be achieved.
Drawings
FIG. 1 is a schematic structural diagram of a Fourier domain mode-locked optoelectronic oscillator based on stimulated Brillouin scattering according to the present invention;
in the above figures, the reference numerals have the following meanings:
1. a tunable laser; 2. a phase modulator; 3. a highly nonlinear optical fiber; 4. a circulator; 5. a photodetector; 6. an electrical amplifier; 7. a power divider; 8. a pump laser;
fig. 2 is a schematic diagram of a microwave photon filter based on stimulated brillouin scattering.
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
The invention discloses a Fourier domain mode-locked optoelectronic oscillator based on stimulated Brillouin scattering, which utilizes the modulation characteristic of a phase modulator, the nonlinear characteristic of a high nonlinear optical fiber, the quick wavelength adjustable characteristic of a tunable laser and the microwave generation performance of the optoelectronic oscillator to generate a sweep frequency microwave signal with adjustable center frequency and bandwidth and low phase noise.
Specifically, the invention discloses a Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering, which mainly comprises: tunable laser, phase modulator, optical fiber, circulator, photodetector, electrical amplifier, power divider and pump laser.
The tunable laser, the phase modulator, the optical fiber, the circulator, the photoelectric detector and the pump laser are sequentially connected through optical fiber jumpers; the photoelectric detector, the electric amplifier, the power divider and the phase modulator are connected in sequence through cables.
The tunable laser, the phase modulator, the pump laser, the optical fiber and the photoelectric detector form a microwave photon filter, and the passband of the microwave photon filter is determined by the wavelength difference between the tunable laser and the gain spectrum.
The tunable laser is a semiconductor laser with wavelength tuning speed up to GHz/mu s and can be continuously tuned.
Wherein the pump laser is a high power single wavelength laser, with a power range of e.g. 0-30dBm and a wavelength around e.g. 1550 nm.
Wherein, the optical fiber is a high nonlinear optical fiber, is a low-loss microwave energy storage element with optical nonlinearity, and the loss is lower than 0.2 dB/km; the length of the optical fiber is several meters to tens of kilometers, for example, 1 to 30000 meters, preferably 200 and 2000 meters.
Wherein the dispersion of the opto-electronic oscillator loop should be controlled to zero so that signals of different frequencies have the same delay in the loop.
The change period of the microwave photon filter is matched with the delay of a signal transmitted for a circle in a photoelectric oscillator loop, and the Fourier domain mode locking condition is met:
nT＝Tr；
wherein is a positive integer, T is the variation period of the microwave photon filter, TrIs the delay of one cycle of signal transmission in the optoelectronic oscillator loop.
The working process of the Fourier domain mode-locked photoelectric oscillator based on the stimulated Brillouin scattering is as follows: the optical carrier emitted by the tunable laser is modulated by a microwave signal on the phase modulator to generate two sidebands of a positive first order and a negative first order, and the other high-order sidebands can be ignored under small-signal modulation. The phase modulated signal is directly sent to the photoelectric detector to obtain only one direct current signal. Through the selective amplification effect of the stimulated Brillouin scattering, when the wavelength corresponding to the gain spectrum of the stimulated Brillouin scattering excited in the high-nonlinearity optical fiber by the pump laser is equal to one sideband of the modulated wave, the sideband has larger gain relative to the other sideband, and the frequency of the sideband and the optical carrier wave emitted by the light source are beaten in the photoelectric detector, so that a microwave signal corresponding to the frequency difference of the two can be obtained. The wavelength of an optical signal emitted by a laser is periodically changed through the periodic driving current, and the change of the wavelength of the optical signal is matched with the time of transmitting the signal in a ring of the photoelectric oscillator for one circle, so that different frequency components can pass through the microwave photon filter at different moments, and the frequency components are simultaneously stored in the ring cavity of the photoelectric oscillator, so that the new frequency components do not need to start oscillation again through noise, and therefore the Fourier domain mode-locked photoelectric oscillator is realized, and a sweep frequency microwave signal can be generated.
The technical solution of the present invention is further explained with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, a schematic structural diagram of a fourier domain mode-locked optoelectronic oscillator based on stimulated brillouin scattering according to the present invention mainly includes: 1 tunable laser 1, 1 phase modulator 2, 1 high nonlinear fiber 3, 1 circulator 4, 1 photodetector 5, 1 electrical amplifier 6, 1 power divider 7 and 1 pump laser 8. The tunable laser 1, the phase modulator 2, the high nonlinear optical fiber 3, the circulator 4, the photoelectric detector 5 and the pump laser 8 are connected in sequence through optical fibers. The photoelectric detector 5, the electric amplifier 6, the power divider 7 and the phase modulator 2 are connected in sequence through cables.
The optical carrier emitted from the tunable laser is modulated by the microwave signal on the phase modulator, producing two sidebands of positive and negative first order, the other higher order sidebands being negligible under small signal modulation. Because the positive first order sideband and the negative first order sideband are in opposite phases, the phase modulated signal is directly sent into the photoelectric detector to obtain only one direct current signal. Through the selective amplification effect of the stimulated Brillouin scattering, when the wavelength corresponding to the gain spectrum of the stimulated Brillouin scattering excited in the high-nonlinearity optical fiber by the pump laser is equal to one sideband of the modulated wave, the sideband has larger gain relative to the other sideband, and the original phase modulation is broken. The amplified sidebands and the optical carrier emitted by the light source are beaten in the photodetector and a microwave signal corresponding to the difference in frequency between the two is obtained, as shown in figure 2. The tunable laser 1, the phase modulator 2, the pump laser 8, the highly nonlinear optical fiber 3 and the photodetector 5 thus together form a microwave photonic filter whose passband is determined by the wavelength difference between the tunable laser and the gain spectrum.
The wavelength of an optical signal emitted by the laser is periodically changed through the periodic driving current, so that the change period of the microwave photon filter is matched with the delay of the signal transmitted for one circle in a photoelectric oscillator loop, and the Fourier domain mode locking condition is met:
nT＝Tr；
wherein n is a positive integer, T is a variation period of the microwave photonic filter, and TrIs the delay of one cycle of signal transmission in the optoelectronic oscillator loop. Different frequency components pass through the microwave photonic filter at different moments, and are stored in the ring cavity of the optoelectronic oscillator at the same time, so that new frequency components do not need to start oscillation again through noise, the Fourier domain mode-locked optoelectronic oscillator is realized, and a frequency-sweeping microwave signal can be generated.
Further, since no electric filter is needed in the proposed optoelectronic oscillator loop, the frequency of the microwave signal generated by the loop depends only on the difference between the light emitting wavelength of the tunable laser and the wavelength corresponding to the stimulated brillouin scattering, and therefore, broadband tuning of the microwave signal can be realized.
Furthermore, the above definitions of the various elements and methods are not limited to the specific structures, shapes or modes mentioned in the embodiments, and those skilled in the art may simply well-know substitutions for their structures, such as: an optical amplifier can be added in the system to amplify the signal; the positions of the power divider and the electric amplifier can be exchanged; the highly nonlinear optical fiber may be replaced with other types of optical fibers. Also, the attached drawings are simplified and are for illustration purposes. The number, shape, and size of the devices shown in the drawings may be modified depending on the actual situation, and the arrangement of the devices may be more complicated.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A Fourier domain mode-locked optoelectronic oscillator based on stimulated Brillouin scattering is characterized by comprising: the device comprises a tunable laser, a phase modulator, an optical fiber, a circulator, a photoelectric detector, an electric amplifier, a power divider and a pump laser;
the tunable laser, the phase modulator, the optical fiber, the circulator, the photoelectric detector and the pump laser are connected through optical fiber jumpers; the photoelectric detector, the electric amplifier, the power divider and the phase modulator are connected through cables;
the tunable laser, the phase modulator, the pump laser, the optical fiber and the photoelectric detector form a microwave photon filter, and the passband of the microwave photon filter is determined by the wavelength difference between the tunable laser and the gain spectrum.
2. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the tunable laser is a semiconductor laser with wavelength tuning speed up to GHz/μ s and capable of continuous tuning.
3. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the pump laser is a high-power single-wavelength laser with a power range of 0-30 dBm.
4. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the optical fiber is a high-nonlinearity optical fiber, and is a low-loss microwave energy storage element with optical nonlinearity, and the length of the optical fiber is 1-30000 m, preferably 200-2000 m.
5. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the dispersion of the optoelectronic oscillator loop is controlled to zero, so that signals of different frequencies have the same delay in the loop;
preferably, the variation period of the microwave photonic filter is matched with the delay of a signal transmitted in a photoelectric oscillator loop for one circle, and the fourier domain mode locking condition is met:
nT＝Tr；
wherein is a positive integer, T is the variation period of the microwave photon filter, TrIs the delay of one cycle of signal transmission in the optoelectronic oscillator loop.
6. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the tunable laser, the phase modulator, the high nonlinear optical fiber, and the circulator further include an optical amplifier in an optical path for amplifying an optical signal.
7. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the positions of the power divider and the electrical amplifier are interchanged.
8. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the passband of the microwave photonic filter is periodically tuned by periodically changing the emission wavelength of the pump laser.
9. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the optoelectronic oscillator loop is replaced by a single loop to a loop of 2 or more.
10. The stimulated brillouin scattering-based fourier-domain mode-locked optoelectronic oscillator according to claim 1, wherein the phase modulator is replaced with a polarization modulator.
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