CN104678595B - A kind of laser phase modulation method for effectively suppressing amplitude-frequency effect - Google Patents
A kind of laser phase modulation method for effectively suppressing amplitude-frequency effect Download PDFInfo
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- CN104678595B CN104678595B CN201510067742.0A CN201510067742A CN104678595B CN 104678595 B CN104678595 B CN 104678595B CN 201510067742 A CN201510067742 A CN 201510067742A CN 104678595 B CN104678595 B CN 104678595B
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
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Abstract
The invention discloses a kind of laser phase modulation method for effectively suppressing amplitude-frequency effect, include the following steps：a）The single-frequency continuous laser that single longitudinal mode laser produces first is input to amplitude modulator；b）Then microwave signal source and direct voltage source is loaded to the amplitude modulator to modulate into line amplitude；c）The pure-tone pulse light that the amplitude modulator exports is input to phase-modulator again and carries out spectrum widening；d）Finally phase-modulator loading non-sine shape radio-frequency signal source is modulated to obtain gaussian-shape spectrum light pulse；The non-sine shape radio-frequency signal source is by the way that to sinusoidal radio frequency signal, shaping produces in proportion.The laser phase modulation method provided by the invention for effectively suppressing amplitude-frequency effect, modulate to obtain gaussian-shape light pulse by loading non-sine shape radio-frequency signal source to phase-modulator, so as to which there is good inhibiting effect to transmitting amplified amplitude-frequency effect, the flatness of system output spectral line is greatly improved.
Description
Technical field
The present invention relates to a kind of laser phase modulation method, more particularly to a kind of laser phase for effectively suppressing amplitude-frequency effect
Modulator approach.
Background technology
In inertial confinement fusion (ICF) laser driver, generally use phase modulation technique carries out single longitudinal mode laser
Video stretching achievees the purpose that nonlinear effect in suppression system (SBS), and is introduced into the amplitude-frequency after phase modulation technique in system
Effect (FM-AM) substantially increases.In current high-power optical system, in order to effectively inhibit stimulated Brillouin scattering
(SBS), heavy caliber silica optical element is protected, the safe operation flux of system is improved, using broadband light as seed light source.
The common method for producing broadband light is to introduce phase modulation module to carry out video stretching to single longitudinal mode laser.The conventional method of broadening
It is by radio frequency amplifying unit (amplification factor is adjustable), by the high frequency sinusoidal signal with certain duty cycle and certain repetition rate
Amplitude be amplified, and by adjusting the amplification factor of amplifying unit, the modulation depth of adjustment phase place modulator, and then adjust
Save the spectral width of output optical pulse.But the broadband light that this method produces is inevitable in the transmission amplification process of system
Ground can bring amplitude-frequency effect (FM-AM), namely the frequency modulation(PFM) (FM) of light pulse to cause the amplitude of optical pulse time domain waveform to be modulated
(AM).This effect causes original smooth light pulse to occur spike vibration in time domain waveform, influences the shaping of laser pulse
Ability, reduces the safe operation flux of system.
The content of the invention
The technical problems to be solved by the invention are to provide a kind of laser phase modulation method for effectively suppressing amplitude-frequency effect,
There can be good inhibiting effect to transmitting amplified amplitude-frequency effect, greatly improve the flatness of system output spectral line.
The present invention is to provide a kind of effectively suppression amplitude-frequency effect to solve the technical solution that above-mentioned technical problem uses
Laser phase modulation method, includes the following steps：A) the single-frequency continuous laser that single longitudinal mode laser produces first is input to amplitude
Modulator；B) then microwave signal source and direct voltage source is loaded to the amplitude modulator to modulate into line amplitude；C) again by institute
The pure-tone pulse light for stating amplitude modulator output is input to phase-modulator progress spectrum widening；D) finally to the phase-modulation
Device loading non-sine shape radio-frequency signal source is modulated to obtain gaussian-shape light pulse.
Above-mentioned effective laser phase modulation method for suppressing amplitude-frequency effect, wherein, the phase-modulator is lithium niobate
Crystal, modulated light pulse are gaussian-shape chirped optical pulse.
Above-mentioned effective laser phase modulation method for suppressing amplitude-frequency effect, wherein, the non-sine shape radio-frequency signal source
By the way that to sinusoidal radio frequency signal, shaping produces in proportion.
Above-mentioned effective laser phase modulation method for suppressing amplitude-frequency effect, wherein, the non-sine shape radio-frequency signal source
Generation process it is as follows：The sine wave that frequency is w, 2w is taken respectively, by Amplitude Ration 4：1, phase difference is that the odd-multiple of π is overlapped
After obtain.
Above-mentioned effective laser phase modulation method for suppressing amplitude-frequency effect, wherein, further include and gaussian-shape light pulse is led to
Cross input amplifier and be amplified processing, the gaussian-shape light impulse length is 0.3nm, the gain line-type of the input amplifier
Bandwidth is 1nm, centre wavelength 1053nm.
The present invention contrast prior art has following beneficial effect：The laser provided by the invention for effectively suppressing amplitude-frequency effect
Phase modulating method, modulates to obtain gaussian-shape light pulse by loading non-sine shape radio-frequency signal source to phase-modulator, so that
There can be good inhibiting effect to transmitting amplified amplitude-frequency effect, greatly improve the flatness of system output spectral line.
Brief description of the drawings
Fig. 1 is the laser phase modulation apparatus structure schematic diagram that the present invention effectively suppresses amplitude-frequency effect；
Fig. 2 is gain narrowing and gain saturaition action effect figure；
Fig. 3 is the distorted waveform schematic diagram that existing shape of a saddle spectrum occurs under gain narrowing and gain saturaition；
Fig. 4 is the distorted waveform schematic diagram that gaussian-shape spectrum of the present invention occurs under gain narrowing and gain saturaition；
Fig. 5 is the Fourier expansion schematic diagram for the non-sine shape signal that the present invention uses；
Fig. 6 is two fittings and preferable nonsinusoidal signal comparison schematic diagram that the present invention uses.
In figure：
1 single longitudinal mode laser, 2 amplitude modulator, 3 microwave signal source
4 direct voltage source, 5 phase-modulator, 6 non-sine shape radio-frequency signal source
Embodiment
The invention will be further described with reference to the accompanying drawings and examples.
Fig. 1 is the laser phase modulation apparatus structure schematic diagram that the present invention effectively suppresses amplitude-frequency effect.
Fig. 1 is referred to, the laser phase modulation method provided by the invention for effectively suppressing amplitude-frequency effect includes the following steps：
Step S1：The single-frequency continuous laser that single longitudinal mode laser 1 produces first is input to amplitude modulator 2；
Step S2：Then microwave signal source 3 and direct voltage source 4 is loaded to the amplitude modulator 2 to modulate into line amplitude；
Step S3：The pure-tone pulse light that the amplitude modulator 2 exports is input to phase-modulator 5 again and carries out spectrum exhibition
It is wide；
Step S4：Gaussian-shape light arteries and veins finally is obtained to 6 modulation of the phase-modulator 5 loading non-sine shape radio-frequency signal source
Punching.
The laser phase modulation method provided by the invention for effectively suppressing amplitude-frequency effect, wherein, the phase-modulator 5 is
Lithium columbate crystal, modulated light pulse are gaussian-shape chirped optical pulse.The non-sine shape radio-frequency signal source 6 is by sine
Shaping produces radiofrequency signal in proportion.Specifically, it is that will carry out shaping in advance for the radiofrequency signal for modulating lithium columbate crystal,
Non-sine shape rf modulated signal is produced, lithium columbate crystal is acted on, so as to produce a kind of chirped laser of gaussian-shape.This
Kind chirped laser has good inhibiting effect to transmitting amplified amplitude-frequency effect.
The operation principle of the present invention is as follows：
High power output is carried at the same time, it is necessary to single-frequency narrow-pulse laser in order to ensure to export laser-quality in ICF systems
Phase-modulation is carried out, by spectrum widening.The stretched-out spectrum for the saddle-shape that sinusoidal radio frequency signal phase modulation modulation crystal obtains, this
The new phase modulating method provided is invented, by producing non-sine modulated signal to rf modulated signal shaping, for phase
Modulator can obtain the stretched-out spectrum of Gaussian.
Light pulse is when being subsequently transmitted amplification, since Gain-narrowing effect makes pulse narrow through spectrum, gain saturatiuon
Effect makes impulse waveform gradually move (red shift) to long wavelength to Front movement, i.e. pulse frequency spectrum.Both effects will all change
The spectrum distribution of pulse, causes the modulation of pulse temporal waveform.Fig. 2 is narrow for gain saturaition in transmission amplification process and gain
Change effect caused by effect collective effect.Fig. 3 and Fig. 4 sets forth in identical amplifier gain bandwidth and centre wavelength
Under (gain line-type bandwidth is 1nm, centre wavelength 1053nm), when input pulse bandwidth is 0.5nm, pulsewidth is 2ns, two classes
The spectral change of wideband pulse and corresponding time waveform.
Fig. 3 left sides are the distorted waveform schematic diagram that shape of a saddle spectrum occurs under gain narrowing, and the right is shape of a saddle spectrum
The distorted waveform schematic diagram occurred under gain saturaition；Fig. 4 left sides occur abnormal for gaussian-shape spectrum under gain narrowing
Become waveform diagram, the right is the distorted waveform schematic diagram that gaussian-shape spectrum occurs under gain saturaition；As seen from the figure, nothing
By be shape of a saddle light pulse or gaussian-shape light pulse after amplifier, spectral sideband is in the presence of losing and frequency spectrum is unbalance shows
As.But two distinct types of wideband pulse is amplified through transmission, there are different degrees of amplitude tune for its output pulse waveform
System.Wherein, the time waveform of shape of a saddle light pulse rises and falls maximum, and the time waveform of gaussian-shape light pulse rises and falls then relatively
It is small.It can thus be appreciated that when 5 output waveform of phase-modulator is the light pulse of gaussian-shape, the amplitude-frequency effect that introduces after transmission is amplified
It is minimum.
Regrettably current used phase modulation technique, modulated spectral shape is the shape of a saddle, it uses high
Frequency sinusoidal signal is loaded on phase-modulator, so that broadening obtains the stretched-out spectrum.And the light pulse of such a shape is follow-up
Larger amplitude-frequency effect can be brought in transmission amplification process.New phase modulating method provided by the invention, is penetrated by non-sine
Frequency signal modulation lithium columbate crystal, can obtain the broadening type spectrum of Gaussian, so as to solve asking for amplitude-frequency effect in ICF systems
Topic.
Non-sine shape radio frequency source can be obtained by the shaping by a certain percentage of multiple radiofrequency signals.For obtaining Gaussian exhibition
Non-sine shape modulated signal used in wide spectrum is described as follows：The mathematics general formula of non-sine shape modulated signal is represented by y=ax2
+bx+c.Wherein, x is time term, and y is modulated signal amplitude item, and c is constant term, can be saved.And what b was represented is modulated RF
The delay of flashlight, in the case of ideal synchronisation is considered, can also save.After normalization, a values can be omitted, therefore, the present invention is right
Expression formula is y=x2Modulated signal decomposed, wherein x is time term, and y is modulated signal amplitude item, utilize Fourier level
Number expansion obtains：
bn=0
Preceding ten of the series are taken to map, as shown in Figure 5, it can be seen that in addition to first and second, every amplitude is close
Null value, and the amplitude much smaller than first, second, therefore preceding two frequencies represented can be used non-just to this as the waveform of w, 2w
String signal is simulated, its amplitude divides ratio -4：1 (i.e. amplitude proportion 4：1, phase difference is the odd-multiple of π), wherein w is by non-sine
Shape signal is determined.Fig. 6 be only with two fit solutions compared with preferable non-sine shape result, it can be seen that both are poor
Not less, so as to preferably realize the simulation to non-sine shape modulated signal.
It can be seen from the above that non-sine shape modulated signal can be obtained, realizes Gaussian spectrum to modulating signal shaping in proportion
Broadening, so as to suppress the amplitude-frequency effect of ICF systems.For the technique effect of the quantitative analysis present invention, define pulse top and rise and fall
The scale factor of (modulation degree)：
In formula：Amax is certain maximum of pulse amplitude modulation；Amin is its adjacent minimum.In general, the change model of R
Enclose for 0~200%, R it is bigger represent pulse top modulation degree it is bigger, beam quality is poorer.
For identical amplifier gain situation (gain line-type bandwidth 1nm), the shape of a saddle and gaussian-shape two are quantitatively calculated
The top modulation degree of class pulse, it is as a result as shown in the table：
By table as it can be seen that in the case of identical amplifier gain, input shape of a saddle light pulse is caused than Gaussian light pulse
Time waveform modulation is much greater.So the Gaussian stretched-out spectrum that non-sine shape signal modulation lithium columbate crystal is obtained, than
The shape of a saddle stretched-out spectrum that conventional method obtains, can preferably ensure the flatness of system output spectral line, effectively suppress amplitude-frequency
Effect.
Although the present invention is disclosed as above with preferred embodiment, so it is not limited to the present invention, any this area skill
Art personnel, without departing from the spirit and scope of the present invention, when can make a little modification and it is perfect, therefore the present invention protection model
Enclose to work as and be subject to what claims were defined.
Claims (5)
- A kind of 1. laser phase modulation method for effectively suppressing amplitude-frequency effect, it is characterised in that include the following steps：A) the single-frequency continuous laser that single longitudinal mode laser produces first is input to amplitude modulator；B) then microwave signal source and direct voltage source is loaded to the amplitude modulator to modulate into line amplitude；C) the pure-tone pulse light that the amplitude modulator exports is input to phase-modulator again and carries out spectrum widening；D) non-sine shape radio-frequency signal source finally is loaded to the phase-modulator, i.e. the mathematics of modulated signal amplitude and time leads to Formula is y=ax2+ bx+c, wherein x are time term, and y is modulated signal amplitude item, and a, b, c is parameter item, and a is secondary term system Number, b is Monomial coefficient, and c is constant term, and modulation obtains gaussian-shape spectrographic pulse, i.e. gaussian-shape frequency domain.
- 2. the laser phase modulation method as claimed in claim 1 for effectively suppressing amplitude-frequency effect, it is characterised in that the phase Modulator is lithium columbate crystal, and modulated light pulse is gaussian-shape chirped optical pulse.
- 3. the as claimed in claim 1 laser phase modulation method for effectively suppressing amplitude-frequency effect, it is characterised in that it is described it is non-just String shape radio-frequency signal source is by the way that to sinusoidal radio frequency signal, shaping produces in proportion.
- 4. the as claimed in claim 3 laser phase modulation method for effectively suppressing amplitude-frequency effect, it is characterised in that it is described it is non-just The generation process of string shape radio-frequency signal source is as follows：The sine wave that frequency is w, 2w is taken respectively, by Amplitude Ration 4：1, phase difference is π's Odd-multiple obtains after being overlapped.
- 5. such as Claims 1 to 4 any one of them effectively suppresses the laser phase modulation method of amplitude-frequency effect, its feature exists In further including and be amplified processing by input amplifier to gaussian-shape light pulse, the gaussian-shape light impulse length is 0.3nm, the gain line-type bandwidth of the input amplifier is 1nm, centre wavelength 1053nm.
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| CN106546340B (en) * | 2016-10-08 | 2018-12-25 | 中国科学院上海光学精密机械研究所 | The recognition methods of amplitude-frequency modulation laser signal |
| CN113504644A (en) * | 2021-07-21 | 2021-10-15 | 中国工程物理研究院激光聚变研究中心 | Method for inhibiting amplitude frequency effect in high-power laser device |
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