CN105811235A - Multi-spectral modulation module for fiber laser - Google Patents

Abstract

The invention provides a multi-spectral modulation device for a fiber laser. The device can modulate monochromatic input signal light into multi-spectral signal light. The monochromatic signal light is superposed with a frequency modulation electric field in an electro-optical modulation crystal, thereby accomplishing modulation from the monochromatic signal light to the multi-spectral signal light. The optimal value of the amplitude of the frequency modulation electric field is selected via an optimization algorithm in a modulation circuit, so that the intensities of spectral lines of the multi-spectral signal light are equal, and then maximum output power is obtained.

Description

Optical fiber laser multiline modulation module

Technical field

The invention belongs to optical fiber laser modulation field, be specifically related to a kind of optical fiber laser multiline modulating equipment and method.

Background technology

Due to the stimulated Brillouin scattering (StimulatedBrillouinScattering of optical fiber in optical fiber laser and optical fiber passive transmission apparatus, the nonlinear effect such as SBS), make Output optical power be transferred to back scattering Brillouin light in a large number, cause output energy loss even optical fiber laser optical fiber passive transmission apparatus to damage.This nonlinear effect shows particularly evident in narrow linewidth (single-frequency) situation, is the principal element of restriction single frequency optical fiber laser power ascension.

Summary of the invention

The present invention adopts the method for multiline Electro-optical Modulation, and flashlight is modulated into a plurality of spectral line, reduces the impact of nonlinear effect.Adopt optimized algorithm simultaneously, when given spectrum number of lines, make each the intensity of spectral line modulated close, thus improving the output that laser instrument is overall.

The present invention proposes a kind of optical fiber laser multiline modulating device, including Electro-optical Modulation crystal, optical fiber output tail optical fiber, fiber optic splitter, modulation flashlight output tail optical fiber, photodetection oscillograph and modulation circuit, wherein, optical fiber output tail optical fiber is connected with whole modulating device, and modulation circuit controls the frequency modulation electric field amplitude A in modulation crystal_MO, laser is by entering fiber optic splitter after Electro-optical Modulation crystal modulation, in fiber optic splitter, the multiline flashlight after modulation is partly into modulation flashlight output tail optical fiber, is exported by multiline flashlight；Another part multiline flashlight enters photodetection oscillograph, and whether the multiline structure for observing output meets the requirements.

A kind of optical fiber laser multiline electrooptical modulation method, it is characterised in that the flashlight of optical fiber laser output is connected with Electro-optical Modulation crystal by optical fiber output tail optical fiber, with frequencies omega in flashlight₀Be f, amplitude with Electro-optical Modulation crystal medium frequency it is A_MOFrequency modulation electric field superposition, after superposition, electric field is frequency is ω₀The multiline flashlight of ± 2n π f, makes output flashlight be modulated to the multiline flashlight of different frequency by singlet.

For making each the intensity of spectral line of multiline flashlight after modulation close, obtain peak power output, the frequency modulation electric field amplitude A in described Electro-optical Modulation crystal_MOOptimal value is chosen by the optimized algorithm in modulation circuit.

Described optimized algorithm includes setting up object function and evaluation function F (A_MO), when N bar equifrequent interval multiline situation modulated by needs, wherein N is odd number, and total power normalization is 1, then modulating frequency is ω₀The multiline flashlight of ± 2n π f, described object function meets:

When n is when the upper value of integer [-(N-1)/2, (N-1)/2], corresponding spectral line desired value is sized to:

f_target(A_MO)=| J_n(A_MO)|²=1/N

When n is not when the upper value of integer [-(N-1)/2, (N-1)/2], corresponding spectral line desired value is sized to:

f_target(A_MO)=| J_n(A_MO)|²=0

Described evaluation function F (A_MO) can state with equation the following:

F(A_MO)=∑ | f² _real(A_MO)-f² _target|²

Wherein summation symbol represents all rank spectral line n summation, as actual each the intensity of spectral line f_realAnd corresponding spectral line desired value f (A)_target(A) close to time evaluation function minimum；

Described evaluation function F (A_MO) it is an one-dimensional functions, A_MOSpan [0 ,+∞) interval, evaluation function F (A_MO) there is following relation at F (0) point:

F(0)≥0

F′(0)≤0

This Functional Quality makes evaluation function F (A_MO) the one-dimensional optimal value choosing frequency modulation electric field amplitude without bounding algorithm being starting point with 0 can be adopted.

By the method for multiline modulating device provided by the invention and employing multiline Electro-optical Modulation, make monochromatic output flashlight be modulated into a plurality of spectral line, reduce the impact of nonlinear effect.Adopt optimized algorithm simultaneously, when given spectrum number of lines, make each the intensity of spectral line modulated close, thus improving the output that laser instrument is overall.

Accompanying drawing explanation

Fig. 1 multiline modulating device schematic diagram；

1 Electro-optical Modulation crystal；2 optical fiber output tail optical fibers；3 fiber optic splitters；4 modulation flashlight output tail optical fibers；5 photodetection oscillographs；6 modulation circuits

The first five rank Bessel function distribution schematic diagram of Fig. 2；The abscissa of figure is the independent variable of Bessel function, and vertical coordinate is the mould side of Bessel function；

Fig. 3 modulates constant power three spectral line evaluation function curve chart；The abscissa of figure is the frequency modulation electric field amplitude A of 2. Electro-optical Modulation crystal outputs_MO, vertical coordinate is the value F (A of evaluation function_MO)；

Fig. 4 is through the constant power three spectral line power distribution schematic diagram of ovennodulation, and in figure, abscissa is the sequence number n of each spectral line, and vertical coordinate is the intensity of corresponding sequence number spectral line.

Detailed description of the invention

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is illustrated.

Fig. 1 multiline modulating device schematic diagram.Including Electro-optical Modulation crystal 1, optical fiber output tail optical fiber 2, fiber optic splitter 3, modulation flashlight output tail optical fiber 4, photodetection oscillograph 5 and modulation circuit 6, it is characterised in that, optical fiber output tail optical fiber 2 is connected with whole modulating device, and modulation circuit 6 controls the frequency modulation electric field amplitude A in modulation crystal 1_MO, laser is by entering fiber optic splitter 3 after Electro-optical Modulation crystal modulation 1, in fiber optic splitter 3, the multiline flashlight after modulation is partly into modulation flashlight output tail optical fiber 4, is exported by multiline flashlight；Another part multiline flashlight enters photodetection oscillograph 5, and whether the multiline structure for observing output meets the requirements.

Assuming original signal just monochromatic light, the electric field amplitude of its light field can be expressed as:

$E=E_0{e}^{i{\mathrm{\ω}}_{0}t}$

Wherein ω₀Represent flashlight frequency, flashlight light intensity I₀It is proportional to | E₀|²。

The flashlight of optical fiber laser output is connected with Electro-optical Modulation crystal 1 by optical fiber output tail optical fiber 2, and flashlight is subject to frequency f and amplitude A in Electro-optical Modulation crystal 1_MOFrequency modulation electric field impact.The electric field amplitude of frequency modulation electric field has following form:

K_MO=A_MOsin(2πft)

Wherein A_MOBeing the amplitude of frequency modulation electric field in Electro-optical Modulation crystal, f represents the frequency of frequency modulation.

The impact of frequency modulation electric field shows as in flashlight with frequencies omega₀The electric field of vibration is overlapped mutually with the electric field in Electro-optical Modulation crystal 1, and the electric field amplitude after superposition can be write as:

E=E₀exp[iω₀t+iA_MOsin(2πft)]

The mode utilizing mathematics center pillar Bessel function series expansion analyzes the electric field after superposition, it is possible to electric field is written as form:

$\begin{array}{c}{E}_{\mathrm{PM}}=E_0{e}^{i{\mathrm{\ω}}_{0}t}\underset{-\∞}{\overset{\∞}{\mathrm{\Σ}}}{J}_n\left(A_{\mathrm{MO}}\right)e^{\mathrm{in}2\mathrm{\πft}}\\ =E_0{e}^{i{\mathrm{\ω}}_{0}t}{J}_0\left(A_{\mathrm{MO}}\right)+E_0{e}^{i({\mathrm{\ω}}_0\±2\mathrm{\πf})t}{J}_{\±1}\left(A_{\mathrm{MO}}\right)+E_0{e}^{i({\mathrm{\ω}}_0\±4\mathrm{\πf})t}{J}_{\±2}\left(A_{\mathrm{MO}}\right)+...\end{array}$

Wherein J_n(A_MO) represent n-th order post Bessel function.It can be seen that the electric field that flashlight is after ovennodulation is by original single-frequency ω₀It is ω that vibration becomes a series of frequency₀The superposition of ± 2n π f single-frequency vibration.The vibration of each single-frequency can be understood as frequencies omega₀The flashlight of ± 2n π f, signal light intensity is proportional to | E₀J_n(A_MO)|².Namely the vibration electric field that cycle is f produced in Electro-optical Modulation crystal 1, it is possible to making by its medium frequency is ω₀Monochromatic light produce the monochromatic superposition of a series of different frequencies, photodetection oscillograph 5 shows as flashlight and is become many spectral lines of different frequency from original singlet.

Gain principles according to optical fiber laser, when the light intensity of each spectral line is equal, can obtain maximum power output, namely need to select suitable frequency modulation electric field amplitude A_MOMake each the intensity of spectral line as far as possible equal.

In order to the monochromatic light exported from optical fiber laser being modulated to the multiline structure that intensity is equal or close, it is necessary to adopt optimized algorithm, choose suitable frequency modulation electric field amplitude A_MO.According to derivation above, frequency is ω₀The quasi-simple signal of multiline of ± 2n π f, the intensity proportional of each spectral line is in | E₀J_n(A_MO)|²。

Determine concrete modulation target for the ease of modulation circuit 6 and select modulation voltage, it is necessary to setting up object function and evaluation function respectively.The effect of object function is in that to set the target of multiline modulation, as the reference of modulated process Yu practical situation.

For example, it is desired to during modulation N bar equifrequent interval multiline situation (N is odd number), total power normalization is 1, then modulating frequency is ω₀Each bar spectrum object function of ± 2n π f meets:

1., when n is when the upper value of integer [-(N-1)/2, (N-1)/2], corresponding spectral line desired value is sized to:

f_target(A_MO)=| J_n(A_MO)|²=1/N

2., when n is not when the upper value of integer [-(N-1)/2, (N-1)/2], corresponding spectral line desired value is sized to:

f_target(A_MO)=| J_n(A_MO)|²=0

In order to find the frequency modulation electric field amplitude A of optimum_MO, make spectral line light intensity as close possible to f_target(A_MO), it is necessary to set up evaluation function F (A_MO).Evaluation function F (A_MO) be and frequency modulation electric field amplitude A_MORelevant one-variable function, its value is more little to be shown closer to object function.We use f_real(A_MO) expression modulation voltage is A_MOTime each modulation spectral line actual strength, according to practical situation, evaluation function F (A_MO) can describe by equation below:

F(A_MO)=∑ | f² _real(A_MO)-f² _target|²

Wherein summation symbol represents all rank spectral line n summation.As actual each the intensity of spectral line f_realAnd each the intensity of spectral line f of target (A)_target(A) close to time evaluation function minimum.

Evaluation function is an one-dimensional functions, span A_MO[0 ,+∞) interval.The different evaluation Function Extreme Value position of the spectrum number of lines N modulated as required also can change therewith.Mathematically assay function F (A_MO) Functional Quality, it is possible to obtain F (0) point have following relation:

F(0)≥0

F′(0)≤0

The one-dimensional frequency modulation electric field amplitude A finding optimum without bounding algorithm that it is starting point with 0 that this Functional Quality makes evaluation function to adopt_MO。

Such as, when target modulation spectral line is 3, its evaluation function F (A_MO) along with frequency modulation electric field amplitude A_MOVariation relation as shown in Figure 3.Evaluation function F (A can be found according to optimized algorithm_MO) extreme point.Work as A_MOWhen=1.4347, the intensity distributions of each rank spectral line is as shown in Figure 4, it is possible to obtain basic frequency and ω-ω₀π f tri-spectrum intensities in=± 2 are equal, i.e. J₀(A_MO)=J₁(A_MO), now it is modulated to equicohesive three line structures through the monochrome signal light of Electro-optical Modulation crystal 1.

In actual use, it is necessary to the optical fiber of optical fiber laser is exported tail optical fiber 2 and is connected with whole modulating device, laser is by entering fiber optic splitter 3 after Electro-optical Modulation crystal 1.In fiber optic splitter 3, after multiline flashlight after modulation is partly into modulation flashlight output tail optical fiber 4, being exported by multiline architecture signals light, another part enters photodetection oscillograph 5 after fiber optic splitter 3, and whether the multiline structure for observing output meets demand.

After determining the multispectral number of lines N needing output flashlight, the optimized algorithm in modulation circuit 6 can calculate the frequency modulation electric field amplitude A in Electro-optical Modulation crystal 1 according to spectral line number N_MO, and it is set as respective value.Such as in order to realize equal strength three line structure, according to calculating above, work as A_MOEvaluation function F (A when=1.4347_MO) there is minimum.Thus modulation circuit 6 can according to optimized algorithm by the frequency modulation electric field amplitude A in Electro-optical Modulation crystal 1_MOIt is set to 1.4347, now can observe contour three line structures accordingly in photodetection oscillograph 5, simultaneously corresponding output seed light is exported to next stage fiber amplifier amplification by modulating signal output tail optical fiber 4, it is achieved the high-power laser output of narrow linewidth multiline.

Claims (4)

1. an optical fiber laser multiline modulating device, including Electro-optical Modulation crystal (1), optical fiber output tail optical fiber (2), fiber optic splitter (3), modulation flashlight output tail optical fiber (4), photodetection oscillograph (5) and modulation circuit (6), it is characterized in that, optical fiber output tail optical fiber (2) is connected with whole modulating device, and modulation circuit (6) controls the frequency modulation electric field amplitude A in modulation crystal (1)_MOLaser is by entering fiber optic splitter (3) after Electro-optical Modulation crystal (1) modulation, in fiber optic splitter (3), the multiline flashlight after modulation is partly into modulation flashlight output tail optical fiber (4), is exported by multiline flashlight；Another part multiline flashlight enters photodetection oscillograph (5), and whether the multiline structure for observing output meets the requirements.

2. an optical fiber laser multiline electrooptical modulation method, it is characterised in that the flashlight of optical fiber laser output exports tail optical fiber (2) by optical fiber and is connected with Electro-optical Modulation crystal (1), with frequencies omega in flashlight₀Be f, amplitude with Electro-optical Modulation crystal (1) medium frequency it is A_MOFrequency modulation electric field superposition, after superposition, electric field is frequency is ω₀The multiline flashlight of ± 2n π f, makes output flashlight be modulated to the multiline flashlight of different frequency by singlet.

3. a kind of optical fiber laser multiline electrooptical modulation method according to claim 2, it is characterized in that, for making each the intensity of spectral line of multiline flashlight after modulation close, obtain peak power output, the frequency modulation electric field amplitude A in described Electro-optical Modulation crystal (1)_MOOptimal value is chosen by the optimized algorithm in modulation circuit (6).

4. a kind of optical fiber laser multiline electrooptical modulation method according to claim 3, it is characterised in that described optimized algorithm includes setting up object function and evaluation function F (A_MO), when N bar equifrequent interval multiline situation modulated by needs, wherein N is odd number, and total power normalization is 1, then modulating frequency is ω₀The multiline flashlight of ± 2n π f, described object function meets:

When n is when the upper value of integer [-(N-1)/2, (N-1)/2], corresponding spectral line desired value is sized to:

f_target(A_MO)=| J_n(A_MO)|²=1/N

When n is not when the upper value of integer [-(N-1)/2, (N-1)/2], corresponding spectral line desired value is sized to 0:

f_target(A_MO)=| J_n(A_MO)|²=0

Described evaluation function F (A_MO) can state with equation the following:

F(A_MO)₌∑|f² _real(A_MO)-f² _target|²

Wherein summation symbol represents all rank spectral line n summation, as actual each the intensity of spectral line f_realAnd corresponding spectral line desired value f (A)_target(A) close to time evaluation function minimum；

Described evaluation function F (A_MO) it is an one-dimensional functions, A_MOSpan [0 ,+∞) interval, evaluation function F (A_MO) there is following relation at F (0) point:

F(0)≥0

F′(0)≤0

This Functional Quality makes evaluation function F (A_MO) the one-dimensional optimal value choosing frequency modulation electric field amplitude without bounding algorithm being starting point with 0 can be adopted.