CN103048714A - Reflection type volume Bragg grating and application of reflection type volume Bragg grating - Google Patents

Abstract

The invention discloses a reflection type volume Bragg grating and application of the reflection type volume Bragg grating. The spatial frequency, the refractive index modulation quantity, the two-beam incident wavelength and the grating thickness of the reflection type volume Bragg grating meet the following relationship models shown as the accompanying drawing, wherein F shows an implicit function between delta n and f, f is the spatial frequency of the grating, delta n is the refractive index modulation quantity, the parameter t is the thickness of the reflection type volume Bragg grating, the value is 2mm to 3mm, n<av> is the average refractive index of the volume Bragg grating, lambda 0 is the wavelength of light incident under the Bragg condition, and the wavelength alpha of the other incident light is equal to the sum of lambda 0 and delta lambda. Two beams of laser with different wavelengths are simultaneously incident on the grating surface, one beam of laser meets the Bragg condition, the efficient diffraction can be realized, the other beam of laser does not meet the Bragg condition, the complete diffraction is realized, and the two beams of laser with different wavelengths can realize the space stacking.

Description

A kind of reflection-type Volume Bragg grating and application thereof

Technical field

The present invention relates to high-power fiber laser technology field, refer more particularly to a kind of reflection-type Volume Bragg grating and application thereof for the synthesis of superlaser.

Background technology

High-power fiber laser has broad application prospects in industrial, military etc., and the continuation of simple optical fiber power improves restriction and expense and the costliness thereof that is subject to the factors such as nonlinear effect, optical damage and fire damage.Therefore how multi beam miniwatt fiber laser is combined efficiently, obtained high-power output, become important research direction of current research personnel.At present general optical fiber beam combination technology mainly comprises coherent beam combination and spectral beam combining, and coherent beam combination can obtain single output wavelength, for obtaining efficient synthetic fibre-optical laser power, need to carry out strict control to characteristics such as the phase place of each light beam of beam combination, polarization states; It is to adopt dispersion element to make each unit light beam near field and far field overlaid that frequency spectrum closes the bundle ultimate principle, and allow each unit wavelength that gap is arranged, thereby improve the output power of whole system, these characteristics of closing the bundle technology are to realize than being easier to, and reasonable beam quality can also be provided.

The clear a kind of photo-thermal of the human hairs such as the Leonid B. Glebov of University of Florida is sold off (PTR) unorganic glass (being again fotoceram), be produced on the irradiation that PTR Volume Bragg grating on glass (VBG) can bear superlaser, this glass has photosensitivity in ultraviolet, and this glass has good mechanical attributes and refractive index stability, makes Volume Bragg grating become the synthetic desirable device of superlaser.

Summary of the invention

Technical matters to be solved by this invention provides a kind of reflection-type Volume Bragg grating and application, reaches the efficient beam combination effect of superlaser.

For solving the problems of the technologies described above, the invention provides a kind of reflection-type Volume Bragg grating, the satisfied following relational model between the spatial frequency of described reflection-type Volume Bragg grating, refractive index modulated quantity, two bundle incident wavelengths and the grating thickness:

$F(f,\mathrm{\&delta;n})=\frac{\mathrm{\&kappa;}{{\mathrm{\&lambda;}}_0}^2\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">f</figure-callout>}}{2\mathrm{\&pi;}{\mathrm{tn}}_{\mathrm{av}}}-\mathrm{\&delta;n}=0---\left(i\right),$

$F(f,\mathrm{\&delta;n})=(\frac{1}{\mathrm{\&epsiv;}}-1)\sin h^{2}A+B-1=0---\left(\mathrm{ii}\right)$

Among formula (i), (ii), F represents the implicit function between δ n and the f, and described reflection-type Volume Bragg grating thickness t is 2mm～3mm, and δ n is refractive index modulated quantity, and f is the grating spatial frequency, constant κ=arctanh (γ), γ=9.9 * (10 ^-4~ 10 ^-6), n _AvMean refractive index for Volume Bragg grating; $A={({\left(\frac{2\mathrm{\&pi;}{n}_{\mathrm{av}}\mathrm{t\&delta;n}}{{\mathrm{\&lambda;}}_0^{2}f}\right)}^2-{\left(\frac{\mathrm{\&pi;ft\&Delta;\&lambda;}}{{\mathrm{\&lambda;}}_0}\right)}^2)}^{1/2},B={\left(\frac{{\mathrm{\&lambda;}}_0{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{\&Delta;\&lambda;}}{{2n}_{\mathrm{av}}\mathrm{\&delta;n}}\right)}^2,$ The scope of ε is 10 ^-4~ 10 ^-6, λ ₀Be the light beam wavelength with Bragg condition incident, and another Shu Bochang is λ=λ ₀The BEAM SQUINT Bragg condition incident of+Δ λ.

The present invention provides the application process of above-mentioned reflection-type Volume Bragg grating simultaneously, its application process is: the laser of two bundle different wave lengths is incided grating surface simultaneously, wherein a branch ofly satisfy Bragg condition, can high efficiency diffraction, another bundle does not satisfy Bragg condition, almost completely transmission, but the just stack of implementation space of laser of this two bundles different wave length.

Beneficial effect: according to the relational model of the above two formulas incident light for specific wavelength and wavelength interval, based on the reflection-type Volume Bragg grating of certain grating thickness, can determine spatial frequency and the refractive index modulated quantity of Volume Bragg grating.Reflection-type Volume Bragg grating with this grating thickness, spatial frequency and refractive index modulated quantity can be realized the spectral efficient beam combination of incident.

Description of drawings

Below in conjunction with the drawings and specific embodiments technical scheme of the present invention is further described in detail.

Fig. 1 is non-inclined reflection type body grating structural representation of the present invention.

Fig. 2 is that bragg wavelength is 1080nm, in the different diffraction efficiency situations, and the variation relation figure of grating thickness and refractive index modulated quantity.

Fig. 3 is spatial frequency and refractive index modulated quantity variation relation figure.

Embodiment

Be illustrated in figure 1 as the non-tilter optical grating construction of reflection-type synoptic diagram, dotted line represents the transmission path of light beam, I _iBe incident beam, I _dBe diffracted beam, θ _iBe incident angle,

Be the Bragg angle in the body grating, θ _dBe angle of diffraction,

Be the pitch angle of grating, N _fBe the normal orientation of light beam plane of incidence, Λ is the body grating cycle, K _GBe grating vector,

Be the incident light position vector, refractive index is

T is grating thickness, n _AvMean refractive index for Volume Bragg grating; δ n is refractive index modulated quantity; F is the grating spatial frequency, f=1/ Λ,

Actual refractive index after the expression index modulation.

Below concise and to the point theoretical derivation of the present invention described.By the coupled wave theory of Kogelinik as can be known, the non-tilter grating diffration of reflection-type efficient is

$\mathrm{\&eta;}={(1+\frac{1-{\mathrm{\&xi;}}^2/{\mathrm{\&phi;}}^2}{\mathrm{<figure-callout\; id="2"\; label="sin\; h"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">sin</figure-callout>}{h}^{}{}^2\sqrt{{\mathrm{\&phi;}}^2-{\mathrm{\&xi;}}^2}})}^{-1}---\left(1\right)$

In the formula (1), ζ is the phase shift factor, and φ is that phase place is invaded the factor,

When light beam wavelength departed from Δ λ with respect to the bragg wavelength existence, diffraction efficiency was

$\mathrm{\&eta;}\left(\mathrm{\&Delta;\&lambda;}\right)={(1+\frac{1-{\left(\frac{{\mathrm{\&lambda;}}_0{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{\&Delta;\&lambda;}}{{2n}_{\mathrm{av}}\mathrm{\&delta;n}}\right)}^2}{\sin h^2{({\left(\frac{2\mathrm{\&pi;}{n}_{\mathrm{av}}\mathrm{t\&delta;n}}{{\mathrm{\&lambda;}}_0^{2}f}\right)}^2-{\left(\frac{\mathrm{\&pi;ft\&Delta;\&lambda;}}{{\mathrm{\&lambda;}}_0}\right)}^2)}^{1/2}})}^{-1}---\left(2\right)$

One, for non-tilter Bragg grating, if incident light satisfies Bragg condition fully, namely the wavelength departure amount Δ λ of the relative Bragg condition of incident light is zero, and then the expression formula of diffraction efficiency (2) can be reduced to

${\mathrm{\&eta;}}_0=\mathrm{<figure-callout\; id="2"\; label="tan\; h"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">tan</figure-callout>}{h}^{}{}^2\frac{2\mathrm{\&pi;}{\mathrm{tn}}_{\mathrm{av}}\mathrm{\&Delta;n}}{{{\mathrm{\&lambda;}}_0}^{2}f}---\left(3\right)$

For making the incident light diffraction efficiency that satisfies Bragg condition fully maximum, according to hyperbolic tangent function character, obtained by formula (3)

$F(f,\mathrm{\&delta;n})=\frac{\mathrm{\&kappa;}{{\mathrm{\&lambda;}}_0}^2\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">f</figure-callout>}}{2\mathrm{\&pi;}{\mathrm{tn}}_{\mathrm{av}}}-\mathrm{\&delta;n}=0---\left(4\right)$

Wherein, κ=arctanh (γ), γ=9.9 * (10 ^-4~ 10 ^-6), F represents the implicit function relation between δ n and the f.

Two, for the incident light that departs from bragg wavelength, its wavelength X=λ ₀+ Δ λ.Reach efficient beam combination efficient for reaching the two-beam that satisfies the bragg wavelength condition and depart from the bragg wavelength condition, should make the diffraction efficiency that departs from the bragg wavelength incident light enough little.Got by formula (2):

$F(f,\mathrm{\&delta;n})=(\frac{1}{\mathrm{\&epsiv;}}-1)\sin h^{2}A+B-1=0---\left(5\right)$

Wherein, $A={({\left(\frac{2\mathrm{\&pi;}{n}_{\mathrm{av}}\mathrm{t\&delta;n}}{{\mathrm{\&lambda;}}_0^{2}f}\right)}^2-{\left(\frac{\mathrm{\&pi;ft\&Delta;\&lambda;}}{{\mathrm{\&lambda;}}_0}\right)}^2)}^{1/2},B={\left(\frac{{\mathrm{\&lambda;}}_0{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HDA00002671434900021.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{\&Delta;\&lambda;}}{{2n}_{\mathrm{av}}\mathrm{\&delta;n}}\right)}^2,$ The scope of ε is 10 ^-4~ 10 ^-6

Three, according to hyperbolic tangent function character, by formula (3) as can be known, can make diffraction efficiency infinitely approach 100% by increasing grating thickness or refractive index modulated quantity.Fig. 2 is that bragg wavelength is 1080nm, in the different diffraction efficiency situations, and the variation relation figure of grating thickness and refractive index modulated quantity.Diffraction efficiency is respectively 1--95% among Fig. 2,2--97%, 3--99%, 4--99.9%, 5--99.99% along with the increase refractive index modulated quantity of thickness reduces, makes diffraction efficiency reach more than 99% in order to guarantee refractive index modulated quantity at lower numerical value simultaneously, rule of thumb be worth, the thickness of grating should not be lower than 2mm.The larger refractive index modulated quantity of grating thickness is also lower simultaneously, for making body grating larger operability is arranged when making, and reduces the absorption of body grating, and the thickness of grating should not surpass 3mm.The selective body grating thickness is 2mm in the present embodiment.

Four, wavelength is λ ₀Light beam with Bragg condition incident, and another Shu Bochang is λ=λ ₀The BEAM SQUINT Bragg condition incident of+Δ λ.For guaranteeing the efficient beam combination of laser of this two bundles different wave length, application formula (4) and formula (5) two formulas then can be determined spatial frequency and the refractive index modulated quantity of body grating.Spatial frequency as shown in Figure 3 and refractive index modulated quantity change curve.Under the condition of specific two bundle incident lights, formula (4) and formula (5) be corresponding two curves take spatial frequency and refractive index modulated quantity as variable that generate among Fig. 3 respectively, and wherein one is the family curve that incident light satisfies Bragg condition, has the diffraction efficiency maximum; Another is the family curve that incident light departs from Bragg condition, has the diffraction efficiency minimum, the intersection point of these two curves then satisfies simultaneously incident light and satisfies Bragg condition, has the diffraction efficiency maximum and incident light departs from Bragg condition, has the characteristic of diffraction efficiency minimum, therefore be spatial frequency and the corresponding coordinate points of refractive index modulated quantity of optimum.

Experimental verification shows, the non-tilter Bragg grating of reflection-type that adopts the present invention to obtain reaches more than 95% for the beam combination efficient of specific wavelength.

It should be noted last that, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although with reference to preferred embodiment the present invention is had been described in detail, those of ordinary skill in the art is to be understood that, can make amendment or be equal to replacement technical scheme of the present invention, and not breaking away from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (2)

1. a reflection-type Volume Bragg grating is characterized in that, the satisfied following relational model between the spatial frequency of described reflection-type Volume Bragg grating, refractive index modulated quantity, two bundle incident wavelengths and the grating thickness:

$F(f,\mathrm{\&delta;n})=\frac{\mathrm{\&kappa;}{{\mathrm{\&lambda;}}_0}^{2}f}{2\mathrm{\&pi;}{\mathrm{tn}}_{\mathrm{av}}}-\mathrm{\&delta;n}=0---\left(i\right),$

$F(f,\mathrm{\&delta;n})=(\frac{1}{\mathrm{\&epsiv;}}-1)\sin h^{2}A+B-1=0---\left(\mathrm{ii}\right)$

Among formula (i), (ii), F represents the implicit function between δ n and the f, and f is the grating spatial frequency, δ n is refractive index modulated quantity, and parameter t is described reflection-type Volume Bragg grating thickness, and value is 2mm～3mm, constant κ=arctanh (γ), γ=9.9 * (10 ^-4~ 10 ^-6), n _AvMean refractive index for Volume Bragg grating; $A={({\left(\frac{2\mathrm{\&pi;}{n}_{\mathrm{av}}\mathrm{t\&delta;n}}{{\mathrm{\&lambda;}}_0^{2}f}\right)}^2-{\left(\frac{\mathrm{\&pi;ft\&Delta;\&lambda;}}{{\mathrm{\&lambda;}}_0}\right)}^2)}^{1/2},B={\left(\frac{{\mathrm{\&lambda;}}_0{f}^2\mathrm{\&Delta;\&lambda;}}{{2n}_{\mathrm{av}}\mathrm{\&delta;n}}\right)}^2,$ The scope of ε is 10 ^-4~ 10 ^-6, λ ₀Be a branch of light wavelength with Bragg condition incident, another bundle incident light wavelength is λ=λ ₀+ Δ λ Δ λ is the wavelength departure amount of the relative Bragg condition of this incident light.

2. the application of the described reflection-type Volume Bragg grating of claim 1 is characterized by: the laser of two bundle different wave lengths incided described reflection-type Volume Bragg grating surface simultaneously, wherein a branch ofly satisfies Bragg condition, and can high efficiency diffraction; Another bundle departs from Bragg condition, almost completely transmission, the stack that the laser of this two bundles different wave length can the implementation space.

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