CN102340100A - Grating outer-cavity laser and quasi-synchronization tuning method thereof - Google Patents

Abstract

The invention provides a quasi-synchronization tuning method for the laser wavelength or frequency of a grating outer-cavity laser, and also provides a corresponding laser. One quasi-synchronization tuning point (Pq) serves as a rotating center to rotate a grating or a reflecting mirror so as to realize the quasi-synchronization tuning of the frequency-selecting action of the grating and a resonant cavity. From the practical physical space of the laser, on an xOy coordinate plane, a rotation center Pq(xq, yq) satisfying the quasi-synchronization tuning condition can be seen as that a rotation center P0 (x0,y0) is expanded to an area contained by two parabolas near the P0 point under the common quasi-synchronization tuning condition. According to the method, lasers can be approximately and synchronously tuned by a simple and flexible design.

Description

Grating external-cavity laser and quasi-synchronous tuning method thereof

Technical field

The present invention relates to tuning to the optical maser wavelength of grating external-cavity laser or frequency, wherein when selecting the tuning center of rotation of grating or speculum, realized quasi synchronous tuning.

Background technology

In the grating external-cavity laser, often need carry out the optical maser wavelength that produced or frequency tuning, thereby thereby this tuning be through rotating shutter change light in the incidence angle on the grating and the angle of diffraction, or realize through rotating the angle of diffraction of speculum change light on grating.

In Fig. 1, Fig. 2 and Fig. 3, show three types grating external cavity semiconductor laser respectively.Wherein shown in Figure 1 is the ECLD of glancing incidence (being that incidence angle is greater than the angle of diffraction) structure of routine, and this structure also is called as the Littman structure; Shown in Fig. 2 is a kind of novel ECLD of plunderring diffraction (being that the angle of diffraction is greater than incidence angle) structure that in one Chinese patent application 200810097085.4, is proposed by same applicant; And be the ECLD of conventional Littrow structure shown in Fig. 3, in this structure, do not have speculum, thereby only carry out tuning through rotating shutter.

The basic structure and the principle of Mingguang City's grid outside cavity gas laser so that grating feedback external cavity semiconductor laser (ECDL) is example below.Shown in Fig. 1 to 3, LD representes semiconductor laser tube, and AL representes the aspheric surface collimating lens; G representes grating, and M representes the feedback reflector mirror, and N representes the grating normal; θ i representes the incidence angle of light on grating, and θ d representes the angle of diffraction of light on grating, and Δ θ is the poor of the incidence angle and the angle of diffraction; Be Δ θ=θ i-θ d, Δ x is the light path increment that optical element in the chamber (the for example gain media of aspheric surface collimating lens and LD) is produced.

In glancing incidence structure shown in Figure 1 and shown in Figure 2 plunderring in the diffraction structure, the laser that semiconductor laser tube LD sends incides on the diffraction grating G behind aspherical mirror AL collimation.The first-order diffraction light positive of grating G is incident on the feedback reflector mirror M, this light beam after being reflected on the mirror M, along with incident light conllinear and reverse path, by grating once more behind the diffraction, AL turns back in the semiconductor laser tube through aspherical mirror by former road.

In Littrow structure shown in Figure 3, the laser that semiconductor laser tube LD sends incides on the diffraction grating G behind aspherical mirror AL collimation.The first-order diffraction light of grating G along with incident light conllinear and reverse path, directly turn back in the semiconductor laser tube by former road through aspherical mirror AL.Can see that incidence angle and the angle of diffraction of light beam on grating equates i.e. θ i=θ d=θ, thereby Δ θ=0 in the Littrow structure.

For the tuning principle of ECLD is described; Introduced rectangular coordinate system xOy in the accompanying drawings; Wherein the laser beam that sent of O point expression semiconductor laser tube LD and grating G are at the intersection point of the Difraction surface of initial position; It is reverse that the x beam warp is crossed the light conllinear that O point and direction and LD send, and the y beam warp is crossed O point and and direction vertical with the x axle upwards.

The Difraction surface of equivalence LD rear end reflecting surface, grating G and these three planes of reflecting surface of mirror M are all vertical with the xOy coordinate plane.Represent the plane at place, optical grating diffraction surface and the intersection of xOy coordinate plane with SG, the O point is positioned on this intersection; SL representes the plane at reflecting surface place, equivalent LD rear end and the intersection of xOy coordinate plane, and the distance that it is ordered apart from O is l1; SM representes plane and the intersection of xOy coordinate plane at the reflecting surface place of feedback reflector mirror M, and the distance that it is ordered apart from O is l2.

Glancing incidence illustrated in figures 1 and 2 with plunder in the diffraction structure; L1 and l2 represent the optical distance of O point to equivalent LD rear end reflecting surface and feedback reflector mirror M respectively; Be two subcavities length of grating external-cavity, the optical cavity length of entire semiconductor device is represented with their sum l=l1+l2.In Littrow structure shown in Figure 3, the actual optical cavity length of semiconductor laser be O point reflecting surface to equivalent LD rear end apart from l1.

Carry out when tuning when rotating shutter G or mirror M, rotation axis is vertical with the xOy coordinate plane, and (x y) representes the intersection point of this rotation axis and xOy coordinate plane (being center of rotation) with coordinate P in Fig. 1 to 3.In order to help to analyze, introduced apart from parameter u, v and w, wherein u representes the distance of center of rotation P to intersection SM; V representes the distance of center of rotation P to intersection SG; W representes the distance of center of rotation P to intersection SL.Here the sign convention of each parameter u, v and w value is following: when homonymy at the respective planes intersection of light and center of rotation, use on the occasion of representing, and represent with negative value during the both sides at the respective planes intersection respectively when light and center of rotation.As grating G or feedback reflector mirror M during, remain unchanged apart from v or u around the rotation of P point.

In grating external cavity semiconductor laser, two principal elements of decision optical maser wavelength or frequency are:

1. by incidence angle and the value of the angle of diffraction and the frequency-selecting effect that variation determined of light on grating;

2. the frequency-selecting effect that is determined by long value in the chamber in SL, SM, the formed equivalent F-P of SG chamber and variation.

Be in the process of a rotating shutter or speculum with center of rotation P, the frequency-selecting effect of grating and the frequency-selecting effect in F-P chamber all change.Generally speaking, above-mentioned change is not synchronous, and this mode hopping that will cause zlasing mode changes, and has interrupted the continuous tuning of laser frequency, thus the laser frequency that can access the continuous tuning coverage during mode hopping is very not little, for example be 1 to 2GHz.

In order to realize the simultaneous tuning of optical maser wavelength or frequency, promptly realize on a large scale the not frequency continuous tuning of mode hopping, need the center of rotation P that grating G or feedback reflector mirror M are selected in the destination.

Suppose that after the rotation tuning grating or speculum are α with respect to the angle that its initial position rotates, then the phase change ψ that in the F-P chamber, comes and goes after a week of laser beam can be expressed as:

ψ＝ψ ₀+A(α)·[B·sinα+C·(1-cosα)] (1)

Light beam round one all initial phases in the chamber changed before wherein ψ 0 was illustrated in rotation tuning, and A (α) is and the relevant function of tuning rotational angle α, and the function that ψ 0, B and C are and angle [alpha] is irrelevant.ψ 0, A (α), B are relevant with the initial parameter of ECLD with C, and these initial parameters comprise initial angle (like initial incidence angle θ i, initial diffraction angle d etc.), initial position (like the long u of initial cavity and l2, initial distance u, v and w etc.) and grating constant d or the like.When satisfying the condition of complete simultaneous tuning, phase change ψ should be irrelevant with tuning rotational angle α, and promptly B in the formula 1 and C all should be zero.

At this moment, realize should the satisfying of center of rotation P0 of complete simultaneous tuning apart from parameter:

$\left\{\begin{array}{c}u0+w0=0\\ v0=0\end{array}\right.---\left(2\right)$

That is to say that the center of rotation P0 that satisfies the simultaneous tuning restrictive condition should be positioned on the intersection SG of surperficial plane that belongs to of optical grating diffraction and xOy coordinate plane; Simultaneously, center of rotation P0 to plane, mirror reflects surface place reflecting surface belongs to the identical and opposite in sign of the absolute value apart from w0 on plane to equivalent LD rear end apart from u0 and P0.

When with coordinate P0 (x0, y0) during this center of rotation that satisfies the simultaneous tuning restrictive condition of expression, for glancing incidence with plunder diffraction structure and can obtain:

$\left\{\begin{array}{c}x0=\mathrm{ld}\sin \mathrm{\θi}/\mathrm{\λ}\\ y0=\mathrm{ld}\cos \mathrm{\θi}/\mathrm{\λ}\end{array}\right.---\left(3\right)$

Wherein x0, y0 represent abscissa and the ordinate of simultaneous tuning center of rotation P0 respectively, and l is that the equivalent cavity in the F-P chamber when initial position (being that rotational angle α is zero) is long, and d is a grating constant, and θ i is the incidence angle of light beam on grating, and λ is an optical maser wavelength.

About glancing incidence and the simultaneous tuning of plunderring diffraction structure respectively shown in Fig. 4 and Fig. 5.

Fig. 6 shows the simultaneous tuning of Littrow structure, owing in the Littrow structure, do not have speculum, promptly is equivalent to u0=w0, thereby formula (2) is described becomes apart from parameter constraints:

$\left\{\begin{array}{c}w0=0\\ v0=0\end{array}\right.---\left(4\right)$

It is the intersection point place that simultaneous tuning center P 0 should be positioned at straight line SG and SL.

When with coordinate P0 (x0, y0) when expression since in the Littrow structure θ i=θ d=θ, actual optical cavity length is l1, thereby formula (3) is described becomes apart from parameter constraints:

$\left\{\begin{array}{c}x0=l1\\ y0=\frac{l1}{\tan \mathrm{\θ}}\end{array}\right.---\left(5\right)$

Can find out from top explanation; No matter be to adopt the coordinate parameter or apart from parameter; The position of simultaneous tuning center of rotation P0 always will be described by the equation group of two equations; Must satisfy above-mentioned two constraintss simultaneously, this means needs two adjusting mechanisms that possess the independence and freedom degree when the design laser.And, no matter being, plunderring under the diffraction or the situation of Littrow structure at glancing incidence, the planar S G at place, optical grating diffraction surface all can not be left in the position of simultaneous tuning center of rotation P0.This restriction makes that structural design, adjustment and the application of laser are very unfavorable and difficult, has caused the complexity of mechanical system simultaneously, and has increased destabilizing factor.

In the reality, big continuously not the mode hopping tuning range also can receive many other factorses influences, for example whether the LD surface is coated with anti-reflection film and coating quality etc.Yet the continuous tuning coverage of the laser frequency of general more or less a hundred GHz even tens GHz can satisfy quite a lot of demands of applications.

Summary of the invention

The technical problem that the present invention will solve is to find a kind of method of the grating external-cavity laser being carried out near-synchronous tuning (being quasi-synchronous tuning); It needn't receive the tuning constraints limit of strict synchronism; Make adjusting mechanism stable more, reliable and simple; Make again simultaneously resulting continuously not the mode hopping tuning range to be similar to strict synchronism tuning, quality that can the appreciable impact laser.

According to the present invention; This technical problem is used for that the grating external-cavity laser is carried out tuning method and solves through a kind of; Be grating or the speculum that center of rotation is rotated laser wherein with a quasi-synchronous tuning point; The plane at the plane at place, feasible optical grating diffraction during turning surface or place, mirror reflects surface and the distance between this quasi-synchronous tuning point remain unchanged; Thereby realize the quasi-synchronous tuning of the frequency-selecting effect of grating resonant cavity, wherein confirm said quasi-synchronous tuning point in the following manner:

Confirm a simultaneous tuning point P0 (x0; Y0); Make that when being center of rotation rotating shutter or speculum remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, the quasi-synchronous tuning scope provides with following method with this simultaneous tuning point P0:

If given frequency tuning range does

$\mathrm{\Δv}=\frac{c}{\mathrm{\λ}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\α}}_{+}\right)}-\frac{l_0}{l\left({\mathrm{\α}}_{-}\right)})---\left(14\right)$

Wherein c is a vacuum light speed, and λ (0) is a laser center wavelength, l ₀Be laser initial cavity long (being that the chamber of rotational angle α when being zero is long) that mode hopping did not allow for α ± be respectively to the tuning maximum angle of positive and negative both direction.Light path l (α) is to rotate for speculum with the boundary condition that mode hopping takes place:

$l\left(\mathrm{\α}\right)=\frac{\mathrm{SS}\left(\mathrm{\α}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\α}\right)}[Y\sin \mathrm{\α}+X(1-\cos \mathrm{\α})\left]\right]---\left(15\right)$

$\frac{|Y\sin \mathrm{\α}+X(1-\cos \mathrm{\α})|}{\mathrm{SS}\left(\mathrm{\α}\right)}\≤\frac{\mathrm{\λ}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(16\right)$

Rotate for grating:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;<figure-callout\; id="2"\; label="d"\; filenames="HSA00000205418500071.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(17\right)$

$\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;<figure-callout\; id="2"\; label="d"\; filenames="HSA00000205418500071.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(18\right)$

The grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

The speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

So the quasi-synchronous tuning scope definition makes tuning range be not less than the some institute compositing area of Δ v for those.

Optional, the said quasi-synchronous tuning scope of this method further is following scope:

(x0 y0), when being center of rotation rotating shutter or speculum with this simultaneous tuning point, remains unchanged at the round phase difference of the resonant cavity inner laser light beam of laser to confirm a simultaneous tuning point.Do coordinate transform, rotate for grating and regulate:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}+(y-y0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}]\\ X=[(x-x0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}-(y-y0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}]\end{array}\right.---\left(8\right)$

Regulate for speculum:

$\left\{\begin{array}{c}Y=(x-x0)\sin \mathrm{\&Delta;\&theta;}+(y-y0)\cos \mathrm{\&Delta;\&theta;}\\ X=(x-x0)\cos \mathrm{\&Delta;\&theta;}-(y-y0)\sin \mathrm{\&Delta;\&theta;}\end{array}\right.---\left(9\right)$

The quasi-synchronous tuning scope is positioned at the zone that is comprised between two regional and (11) described two parabolical symmetry axis and parabola top outer that parabola comprised being described by (10) and constitutes.

$\left\{\begin{array}{c}X\&le;-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\&GreaterEqual;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

-b≤Y≤b and $-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HSA00000205418500071.png"\; state="\{\{state\}\}">c</figure-callout>}}{2}\&le;X\&le;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}---\left(11\right)$

A wherein, b, c is defined as, and rotates for grating:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}\frac{\cos \left(\mathrm{\&theta;i}\right)+\cos \left(\mathrm{\&theta;d}\right)}{\mathrm{SS}\left(0\right)}---\left(12\right)$

c＝0

Rotate for speculum:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\cos \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}---\left(13\right)$

$c=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;i}}{\mathrm{SS}\left(0\right)}.$

According to the present invention; Corresponding outside cavity gas laser also is provided; Comprising the quasi-synchronous tuning mechanism that is used to carry out above-mentioned quasi-synchronous tuning method; This quasi-synchronous tuning mechanism is around quasi-synchronous tuning center of rotation rotating shutter or the speculum confirmed as stated, thus the quasi-synchronous tuning of realization grating resonant cavity frequency-selecting effect.Wherein said outside cavity gas laser both can be the Littman structure or plunder diffraction structure, also can be the Littrow structure.Under the situation of Littrow structure outside cavity gas laser, because difference Δ θ=0 of incidence angle and the angle of diffraction, thereby be parallel to the radiation direction that incides on the grating two parabolical symmetry axis that formula (10) limits.

Through technical scheme according to the invention, reduced the constraints number of simultaneous tuning, make adjusting mechanism only need an adjustment degree of freedom.And the position of center of rotation needn't receive the restriction that can not leave grating surface place plane intersection line SG again, and this makes simultaneous tuning have more flexibly and selects and bigger performance leeway, is easy to design near-synchronous rotational frequency or the wavelength tuning of realizing laser.

Description of drawings

Fig. 1 shows the simplification view of the grating external cavity semiconductor laser of prior art Littman (glancing incidence) structure;

Fig. 2 shows the simplification view that prior art is plunderred the grating external cavity semiconductor laser of diffraction structure;

Fig. 3 shows the simplification view of the grating external cavity semiconductor laser of prior art Littrow structure;

Fig. 4 shows prior art confirming to the conventional simultaneous tuning center of rotation of Littman structure;

Fig. 5 shows prior art confirming to the conventional simultaneous tuning center of rotation of plunderring diffraction structure;

Fig. 6 shows prior art confirming to the conventional simultaneous tuning center of rotation of Littrow structure;

Fig. 7 shows according to the embodiment of the invention confirming to the quasi-synchronous tuning center of rotation of Littman structure when the grating rotation tuning;

Fig. 8 shows according to the embodiment of the invention confirming to the quasi-synchronous tuning center of rotation of plunderring diffraction structure when the grating rotation tuning;

Fig. 9 shows according to the embodiment of the invention confirming to the quasi-synchronous tuning center of rotation of Littman structure when the speculum rotation tuning;

Figure 10 shows according to the embodiment of the invention confirming to the quasi-synchronous tuning center of rotation of plunderring diffraction structure when the speculum rotation tuning;

Figure 11 shows according to the embodiment of the invention confirming to the quasi-synchronous tuning center of rotation of Littrow structure;

Figure 12 shows the quasi-synchronous tuning mechanism according to embodiment of the invention Littman structure fringe ECLD when the grating rotation tuning;

Figure 13 shows the quasi-synchronous tuning mechanism of plunderring diffraction structure grating ECLD according to the embodiment of the invention when the grating rotation tuning;

Figure 14 shows the quasi-synchronous tuning mechanism according to embodiment of the invention Littman structure fringe ECLD when the speculum rotation tuning;

Figure 15 shows the quasi-synchronous tuning mechanism of plunderring diffraction structure grating ECLD according to the embodiment of the invention when the speculum rotation tuning; And

Figure 16 shows the quasi-synchronous tuning mechanism according to embodiment of the invention Littrow structure fringe ECLD.

Embodiment

The present invention is based on following discovery: at above-mentioned formula ψ=ψ ₀In the described tuning phase change of+A (α) [Bsin α+C (1-cos α)], tuning rotational angle α when representing be with radian one much smaller than 1 and approach zero small quantity.According to the Taylor series expansion theorem; Can know that first sin α in the bracket of formula 1 is the strange time higher order term that the single order item from tuning rotational angle α begins; And second (1-cos α) idol time higher order term that to be the second order term from tuning rotational angle α begin; It is one than the sin α small quantity of high-order more, to the contribution that comes and goes phase change ψ much smaller than sin α.Therefore, if second phase change that causes less than the phase changing capacity that mode hopping did not allow, can be made first approximation to coming and going phase change ψ, promptly omit second order term and higher order term more thereof in the formula 1.If ignore second in the bracket of formula 1, be but then come and go phase change ψ approximate representation:

ψ＝ψ ₀+A(α)·B·sinα (6)

In the case, to come and go phase change ψ irrelevant with tuning rotational angle α in order to make, and can make that coefficient B is zero.That is:

B＝0 (7)

This approximate to be called as quasi-synchronous tuning approximate, and at the quasi-synchronous tuning that is tuned as of this approximate external laser cavity frequency down, the center of rotation of corresponding grating or speculum is called as quasi-synchronous tuning center of rotation Pq, its coordinate can be expressed as Pq (xq, yq).In this approximate extents, the round phase change that tuning rotational angle α causes can be ignored, and promptly ψ ≈ ψ 0 is similar to a constant that has nothing to do with tuning rotational angle.In practical application, the tuning range of outside cavity gas laser parameter and tuning rotational angle α almost completely satisfies this approximate condition.

According to the present invention; This technical problem is used for that the grating external-cavity laser is carried out tuning method and solves through a kind of; Be grating or the speculum that center of rotation is rotated laser wherein with a quasi-synchronous tuning point; The plane at the plane at place, feasible optical grating diffraction during turning surface or place, mirror reflects surface and the distance between this quasi-synchronous tuning point remain unchanged, thus the quasi-synchronous tuning of the frequency-selecting effect of realization grating resonant cavity.Wherein, confirm said quasi-synchronous tuning point in the following manner:

Do coordinate transform, rotate for grating and regulate:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}+(y-y0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}]\\ X=[(x-x0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}-(y-y0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}]\end{array}\right.---\left(8\right)$

Wherein, Δ θ=θ i-θ d;

Regulate for speculum:

$\left\{\begin{array}{c}Y=(x-x0)\sin \mathrm{\&Delta;\&theta;}+(y-y0)\cos \mathrm{\&Delta;\&theta;}\\ X=(x-x0)\cos \mathrm{\&Delta;\&theta;}-(y-y0)\sin \mathrm{\&Delta;\&theta;}\end{array}\right.---\left(9\right)$

The quasi-synchronous tuning scope is positioned at the zone that is comprised between two regional and (11) described two parabolical symmetry axis and parabola top outer that parabola comprised being described by (10) and constitutes.

$\left\{\begin{array}{c}X\&le;-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\&GreaterEqual;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

-b≤Y≤b and $-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HSA00000205418500071.png"\; state="\{\{state\}\}">c</figure-callout>}}{2}\&le;X\&le;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}---\left(11\right)$

A wherein, b, c is defined as, and rotates for grating:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}\frac{\cos \left(\mathrm{\&theta;i}\right)+\cos \left(\mathrm{\&theta;d}\right)}{\mathrm{SS}\left(0\right)}---\left(12\right)$

c＝0

Rotate for speculum:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\cos \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}---\left(13\right)$

$c=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;i}}{\mathrm{SS}\left(0\right)}$

In the reality, the continuous tuning coverage of the laser frequency of general more or less a hundred GHz even tens GHz can satisfy quite a lot of demands of applications.Therefore the quasi-synchronous tuning scope can also be used

Following method provides.

If given frequency tuning range does

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{l\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

Wherein c is a vacuum light speed, and λ (0) is a laser center wavelength, l ₀For the laser initial cavity is long, the chamber when promptly rotational angle α is zero is long, and mode hopping did not allow for α ± be respectively to the tuning maximum angle of positive and negative both direction.Light path l (α) is to rotate for speculum with the boundary condition that mode hopping takes place:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(15\right)$

$\frac{|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(16\right)$

Rotate for grating:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;<figure-callout\; id="2"\; label="d"\; filenames="HSA00000205418500071.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(17\right)$

$\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;<figure-callout\; id="2"\; label="d"\; filenames="HSA00000205418500071.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(18\right)$

The grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

The speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

So also may be defined as those, the quasi-synchronous tuning scope make said frequency tuning range be not less than the some institute compositing area of Δ v.Usually should the zone greater than by (10) and (11) defined zone, have more Practical significance and value.

According to the present invention; Corresponding grating external-cavity laser also is provided; Comprising the quasi-synchronous tuning mechanism that is used to carry out above-mentioned quasi-synchronous tuning method; This quasi-synchronous tuning mechanism is around quasi-synchronous tuning center of rotation rotating shutter or the speculum confirmed as stated, thus the quasi-synchronous tuning of realization grating resonant cavity frequency-selecting effect.Wherein said grating external-cavity laser both can be the Littman structure or plunder diffraction structure, also can be the Littrow structure.Under the situation of Littrow structure ECLD, because difference Δ θ=0 of incidence angle and the angle of diffraction, thereby be parallel to the radiation direction that incides on the grating two parabolical symmetry axis that formula (10) limits.When said grating external-cavity laser is a Littman structure or when plunderring diffraction structure structure laser; And through being that the center of rotation rotating shutter carries out tuning with said quasi-synchronous tuning point (Pq); Two parabolical symmetry axis that wherein limited formula (10) are when the grating rotation tuning; The angular bisector that is parallel to angle between the normal of mirror M and the light that semiconductor laser tube LD sends; When the speculum rotation tuning, be parallel to initial position (being that rotational angle α the is zero) normal direction of mirror M.

Be example with the grating external cavity semiconductor laser that often uses below, embodiment of the present invention is described.

Fig. 7 to 11 has expressed the various execution modes of the quasi-synchronous tuning center of rotation of confirming the grating external-cavity laser according to the present invention respectively.

Fig. 7 and Fig. 8 show rotating shutter and carry out tuning situation, and incidence angle θ i and the diffraction angle d of light this moment on grating G all changes.Thereby; See from the actual physics space of laser, on the xOy coordinate plane, satisfy the center of rotation Pq (xq of quasi-synchronous tuning condition; Yq) can be regarded as; Center of rotation P0 under the simultaneous tuning condition of routine (x0 y0) is extended near the P0 point two parabolas that limited formula (10), and between these two the parabolical symmetry axis that limited of formula (11) and the parabola top outer in institute's inclusion region.

For glancing incidence and the ECLD of plunderring diffraction structure; When the grating rotation tuning (Fig. 7 and Fig. 8); Two parabolical symmetry axis that limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and be parallel to the angular bisector of angle between the normal of mirror M and the light that semiconductor laser tube LD sends.

Fig. 9 and Figure 10 show the rotation speculum and carry out tuning situation; When the speculum rotation tuning (Fig. 9 and Figure 10); Two parabolical symmetry axis that limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b; And be parallel to the ECLD (Figure 11) of the initial position normal direction of mirror M for the Littrow structure, be equivalent to mirror M and overlap with equivalent LD rear end reflecting surface, rotating shutter G carries out tuning; Two parabolical symmetry axis that limited formula (10) this moment apart from the distance of strict synchronism tuning point be respectively+-b, and be parallel to the light that semiconductor laser tube LD sends.In determined this zone, can obtain obviously to be superior to the big simultaneous tuning scope of other position, and (x0, y0), resulting simultaneous tuning scope is just big more near simultaneous tuning point P0 more according to the present invention.

Figure 12 and Figure 13 show rotating shutter respectively and carry out glancing incidence structure and the quasi-synchronous tuning mechanism of plunderring the diffraction structure ECLD when tuning.

Shown in figure 12; Semiconductor laser tube LD for example sends, and power is that 30mW, wavelength are the laser beam of 689nm; Through focal length is after 4mm, numerical aperture are 0.6 aspheric surface collimating lens AL collimation; To incide incisure density be 1800g/mm, have suitable diffraction efficiency, groove area size is on the holographic diffraction grating G of 6mm for 12.5mm * 12.5mm, thickness, the zeroth order diffraction light of grating G or directly mirroring light as the output beam of laser.The first-order diffraction light positive of grating incides on the plane mirror M, and reflection back light is reversed on M, along with the reverse path of former incident beam conllinear, once more behind the diffraction, turn back among the semiconductor laser tube LD through grating along former road.

Laser tube LD for example adopts temperature sensor and semiconductor cooler to realize temperature control through heat sink 2.The concrete realization of quasi-synchronous tuning mechanism is described below: collimating lens AL is adjusted through mirror holder 4 and is fixing; Diffraction grating G is fixed on the moving plate 6 of adjusting bracket; Its direction can be adjusted through the adjustment screw 8 and 9 that adjusting bracket is decided on the plate 7; Can also carry out fine tuning through the piezoelectric ceramic 10 on the moving plate, mirror M is fixed on the base plate 13 through fixed mount 11.The frequency-selecting effect of exocoel and grating realizes through rotating diffraction grating G around accurate center of rotation Pq synchronously.For example, carry out coarse adjustment, and/or finely tune through apply control voltage at piezoelectric ceramic 10 through the angle that micrometer adjusting screw 8 changes diffraction grating G.

In Littman structure ECLD shown in Figure 12, (xq yq) is positioned at by (10) and (11) described quasi-synchronous tuning zone the quasi-synchronous tuning center of rotation Pq that grating rotates.Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and with the angle of x axle negative direction be Δ θ/2, this moment is because θ i＞θ d, thereby Δ θ＞0.

Grating rotation tuning shown in Figure 13 plunder diffraction structure ECLD and glancing incidence similar shown in Figure 12, difference only is that the position of mirror M is different, makes θ i＜θ d thereby Δ θ＜0.Grating rotates quasi-synchronous tuning center of rotation Pq, and (xq yq) is positioned at by (10) and (11) described quasi-synchronous tuning zone equally.Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and with the angle of x axle negative direction be Δ θ/2, but the incline direction of this straight line and shown in Figure 12 opposite.

Similarly, Figure 14 and Figure 15 show respectively and rotate speculum and carry out glancing incidence structure and the quasi-synchronous tuning mechanism of plunderring the diffraction structure ECLD when tuning.

In Figure 14 and quasi-synchronous tuning mechanism shown in Figure 15; Grating G is fixed on the base plate 13 through fixed mount 11; Mirror M is fixed on the moving plate 6 of adjusting bracket; Its direction can be adjusted through the adjustment screw 8 and 9 that adjusting bracket is decided on the plate 7, also can finely tune through the piezoelectric ceramic 10 on the moving plate.Through rotating the frequency-selecting effect that mirror M realizes exocoel and grating around accurate center of rotation Pq synchronously.For example, carry out coarse adjustment, and/or finely tune through apply control voltage at piezoelectric ceramic 10 through the angle that micrometer adjusting screw 8 changes mirror M.

In the Littman structure ECLD of speculum rotation tuning shown in Figure 14, speculum rotates quasi-synchronous tuning center of rotation Pq, and (xq yq) is positioned at by (10) and (11) described quasi-synchronous tuning zone.Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and with the angle of x axle negative direction be Δ θ, this moment is because θ i＞θ d, thereby Δ θ＞0.

Speculum shown in Figure 15 rotate quasi-synchronous tuning to plunder the diffraction structure ECLD similar with the diffraction structure of plunderring shown in Figure 14, difference only is the position difference of mirror M, makes θ i＜θ d thereby Δ θ＜0.Speculum rotates quasi-synchronous tuning center of rotation Pq, and (xq yq) is positioned at by (10) and (11) described quasi-synchronous tuning zone equally.Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and with the angle of x axle negative direction be Δ θ, but the incline direction of this straight line and shown in Figure 14 opposite.

Figure 16 shows the sketch map of the Littrow structure ECLD of quasi-synchronous tuning, wherein θ i=θ d=θ.Shown in figure 16, the first-order diffraction light of grating G along with the reverse path of former incident beam conllinear, Yan Yuanlu turns back among the semiconductor laser tube LD.In its quasi-synchronous tuning mechanism, grating G is fixed on the moving plate 6 of adjusting bracket, and this moving plate 6 can be adjusted through the adjustment screw 8 and 9 of deciding at adjusting bracket on the plate 7.Realize the tuning of optical maser wavelength through rotating diffraction grating G around accurate center of rotation Pq synchronously.For example, change light beam through micrometer adjusting screw 8 and/or piezoelectric ceramic 10 and incide the angle on the diffraction grating G, and the aligning adjustment of accurate center of rotation Pq synchronously and grating G can realize through adjustment screw 9.

Can see that from Figure 16 in Littrow structure ECLD, (xq yq) is positioned at by (10) and (11) described quasi-synchronous tuning zone quasi-synchronous tuning center of rotation Pq.Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and parallel with the x axle.

Those skilled in the art can know that the LASER Light Source of the grating external-cavity laser in the above-mentioned example also can be selected the LASER Light Source of other type for use except semiconductor laser tube; Wavelength and power output also can be selected other numerical value for use; Grating also can adopt balzed grating, or transmission grating, and it can have other incisure density, size and thickness; Collimating lens also can adopt other focal length and numerical aperture.In addition, can put into 1/2 wave plate between LASER Light Source and the grating in order to the adjustment feedback power.

Claims (12)

1. method that is used for the grating external-cavity laser is carried out quasi-synchronous tuning; Wherein be the grating or the speculum of center of rotation rotating shutter outside cavity gas laser with a quasi-synchronous tuning point Pq; The plane at the plane at place, feasible optical grating diffraction during turning surface or place, mirror reflects surface and the distance between this quasi-synchronous tuning point Pq remain unchanged; Thereby realize the quasi-synchronous tuning of the frequency-selecting effect of grating resonant cavity, wherein confirm said quasi-synchronous tuning point Pq in the following manner:

Confirm a simultaneous tuning point P0 (x0; Y0); Make that when being center of rotation rotating shutter or speculum remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, the quasi-synchronous tuning scope provides with following method with this simultaneous tuning point P0:

Do coordinate transform, rotate for grating and regulate:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}+(y-y0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}]\\ X=[(x-x0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}-(y-y0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}]\end{array}\right.---\left(8\right)$

Regulate for speculum:

$\left\{\begin{array}{c}Y=(x-x0)\sin \mathrm{\&Delta;\&theta;}+(y-y0)\cos \mathrm{\&Delta;\&theta;}\\ X=(x-x0)\cos \mathrm{\&Delta;\&theta;}-(y-y0)\sin \mathrm{\&Delta;\&theta;}\end{array}\right.---\left(9\right)$

If given frequency tuning range does

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{l\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

Wherein c is a vacuum light speed, and λ (0) is a laser center wavelength, l ₀For the laser initial cavity is long, mode hopping did not allow for α ± be respectively to the tuning maximum angle of positive and negative both direction, Δ θ=θ i-θ d, and θ i representes the incidence angle of light on grating, θ d representes the angle of diffraction of light on grating;

Light path l (α) is to rotate for speculum with the boundary condition that mode hopping takes place:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(15\right)$

$\frac{|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(16\right)$

Rotate for grating:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;d}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(17\right)$

$\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;d}}{2}|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(18\right)$

The grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

The speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

The scope of quasi-synchronous tuning point Pq makes said frequency tuning range be not less than the some institute compositing area of Δ v for those.

2. method according to claim 1 is characterized in that, said quasi-synchronous tuning scope further is following scope:

(x0 y0), when being center of rotation rotating shutter or speculum with this step tuning point, remains unchanged at the round phase difference of the resonant cavity inner laser light beam of laser to confirm a simultaneous tuning point.Do coordinate transform, rotate for grating and regulate:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}+(y-y0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}]\\ X=[(x-x0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}-(y-y0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}]\end{array}\right.---\left(8\right)$

Regulate for speculum:

$\left\{\begin{array}{c}Y=(x-x0)\sin \mathrm{\&Delta;\&theta;}+(y-y0)\cos \mathrm{\&Delta;\&theta;}\\ X=(x-x0)\cos \mathrm{\&Delta;\&theta;}-(y-y0)\sin \mathrm{\&Delta;\&theta;}\end{array}\right.---\left(9\right)$

The scope of said quasi-synchronous tuning point Pq is positioned at the zone that is comprised between two regional and (11) described two parabolical symmetry axis and parabola top outer that parabola comprised being described by (10) and constitutes.

$\left\{\begin{array}{c}X\&le;-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\&GreaterEqual;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

-b≤Y≤b and $-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\&le;X\&le;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}---\left(11\right)$

A wherein, b, c is defined as, and rotates for grating:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}\frac{\cos \left(\mathrm{\&theta;i}\right)+\cos \left(\mathrm{\&theta;d}\right)}{\mathrm{SS}\left(0\right)}---\left(12\right)$

c＝0

Rotate for speculum:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\cos \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}---\left(13\right)$

$c=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;i}}{\mathrm{SS}\left(0\right)}.$

3. method according to claim 1 is characterized in that, said grating external-cavity laser is the Littman structure or plunders diffraction structure structure laser, and through being that the center of rotation rotating shutter carries out tuning with said quasi-synchronous tuning point (Pq).Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b; And when the grating rotation tuning; The approximate angular bisector that is parallel to angle between the normal of mirror M and the light that semiconductor laser tube LD sends; When the speculum rotation tuning, be parallel to the initial position normal direction of mirror M.

4. method according to claim 1 is characterized in that, said grating external-cavity laser is a Littrow structure laser, and through being that the center of rotation rotating shutter carries out tuning with said quasi-synchronous tuning point (Pq); Two parabolical symmetry axis that wherein limit formula (10) apart from the distance of strict synchronism tuning point be respectively+-b, and be parallel to the radiation direction that incides on the grating.

5. a Littman structure or plunder the grating external-cavity laser of diffraction structure; Comprise: LASER Light Source (1), aspheric surface collimating lens (3), grating (12) and speculum (5); Wherein said laser also comprises quasi-synchronous tuning mechanism; Said quasi-synchronous tuning mechanism rotates said grating (12) or speculum (5) around a quasi-synchronous tuning center of rotation Pq; The plane at the plane at place, feasible optical grating diffraction during turning surface or place, mirror reflects surface and the distance between this quasi-synchronous tuning point Pq remain unchanged, thus the quasi-synchronous tuning of realization grating resonant cavity frequency-selecting effect; Wherein confirm said quasi-synchronous tuning point Pq in the following manner:

Confirm a simultaneous tuning point P0 (x0; Y0); Make that when being center of rotation rotating shutter or speculum remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, the quasi-synchronous tuning scope provides with following method with this simultaneous tuning point P0:

If given frequency tuning range does

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{l\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

Wherein c is a vacuum light speed, and λ (0) is a laser center wavelength, l ₀For the laser initial cavity is long, mode hopping did not allow for α ± be respectively to the tuning maximum angle of positive and negative both direction, Δ θ=θ i-θ d, and θ i representes the incidence angle of light on grating, θ d representes the angle of diffraction of light on grating; Light path l (α) is to rotate for speculum with the boundary condition that mode hopping takes place:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(15\right)$

$\frac{|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(16\right)$

Rotate for grating:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;d}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(17\right)$

$\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;d}}{2}|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(18\right)$

The grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

The speculum rotation situation:

SS(α)＝sin?θi+sin(θd-α) (20)

The scope of said quasi-synchronous tuning point Pq makes said frequency tuning range be not less than the some institute compositing area of Δ v for those.

6. grating external-cavity laser according to claim 5; It is characterized in that; Said quasi-synchronous tuning scope further is following scope: confirm a simultaneous tuning point (x0; Y0), when being center of rotation rotating shutter or speculum, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of laser with this step tuning point.Do coordinate transform, rotate for grating and regulate:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}+(y-y0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}]\\ X=[(x-x0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}-(y-y0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}]\end{array}\right.---\left(8\right)$

Regulate for speculum:

$\left\{\begin{array}{c}Y=(x-x0)\sin \mathrm{\&Delta;\&theta;}+(y-y0)\cos \mathrm{\&Delta;\&theta;}\\ X=(x-x0)\cos \mathrm{\&Delta;\&theta;}-(y-y0)\sin \mathrm{\&Delta;\&theta;}\end{array}\right.---\left(9\right)$

The scope of said quasi-synchronous tuning point Pq is positioned at the zone that is comprised between two regional and (11) described two parabolical symmetry axis and parabola top outer that parabola comprised being described by (10) and constitutes.

$\left\{\begin{array}{c}X\&le;-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\&GreaterEqual;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

-b≤Y≤b and $-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\&le;X\&le;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}---\left(11\right)$

A wherein, b, c is defined as, and rotates for grating:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}\frac{\cos \left(\mathrm{\&theta;i}\right)+\cos \left(\mathrm{\&theta;d}\right)}{\mathrm{SS}\left(0\right)}---\left(12\right)$

c＝0

Rotate for speculum:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\cos \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}---\left(13\right)$

$c=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;i}}{\mathrm{SS}\left(0\right)}.$

7. grating external-cavity laser according to claim 5; It is characterized in that; Said quasi-synchronous tuning mechanism adjusts the rotational angle of said grating (12) or speculum (5) through adjustment screw (8), and/or comes this rotational angle is finely tuned through on piezoelectric ceramic (10), applying control voltage.

8. grating external-cavity laser according to claim 5 is characterized in that, further puts into 1/2 wave plate between said LASER Light Source and the grating in order to the adjustment feedback power.

9. the grating external-cavity laser of a Littrow structure; Comprise: LASER Light Source (1), aspheric surface collimating lens (3) and grating (12); Wherein said grating external-cavity laser also comprises quasi-synchronous tuning mechanism; Said quasi-synchronous tuning mechanism rotates said grating (12) around a quasi-synchronous tuning center of rotation (Pq); The plane at place, feasible optical grating diffraction during turning surface and the distance between this quasi-synchronous tuning point (Pq) remain unchanged, thereby realize the quasi-synchronous tuning of grating resonant cavity frequency-selecting effect; Wherein confirm said quasi-synchronous tuning point Pq in the following manner:

Confirm a simultaneous tuning point P0 (x0; Y0); Make that when being center of rotation rotating shutter or speculum remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, the quasi-synchronous tuning scope provides with following method with this simultaneous tuning point P0:

If given frequency tuning range does

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{l\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

Wherein c is a vacuum light speed, and λ (0) is a laser center wavelength, l ₀For the laser initial cavity is long, mode hopping did not allow for α ± be respectively to the tuning maximum angle of positive and negative both direction, Δ θ=θ i-θ d, and θ i representes the incidence angle of light on grating, θ d representes the angle of diffraction of light on grating; Light path l (α) is to rotate for speculum with the boundary condition that mode hopping takes place:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(15\right)$

$\frac{|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(16\right)$

Rotate for grating:

$l\left(\mathrm{\&alpha;}\right)=\frac{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;d}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}[Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})\left]\right]---\left(17\right)$

$\frac{2\cos \frac{\mathrm{\&theta;i}-\mathrm{\&theta;d}}{2}|Y\sin \mathrm{\&alpha;}+X(1-\cos \mathrm{\&alpha;})|}{\mathrm{SS}\left(\mathrm{\&alpha;}\right)}\&le;\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(18\right)$

The grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

The speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

The scope of said quasi-synchronous tuning point Pq makes said frequency tuning range be not less than the some institute compositing area of Δ v for those.

10. grating external-cavity laser according to claim 9; It is characterized in that; Said quasi-synchronous tuning scope further is following scope: confirm a simultaneous tuning point (x0; Y0), when being center of rotation rotating shutter or speculum, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of laser with this step tuning point.Do coordinate transform, rotate for grating and regulate:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}+(y-y0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}]\\ X=[(x-x0)\cos \frac{\mathrm{\&Delta;\&theta;}}{2}-(y-y0)\sin \frac{\mathrm{\&Delta;\&theta;}}{2}]\end{array}\right.---\left(8\right)$

Regulate for speculum:

$\left\{\begin{array}{c}Y=(x-x0)\sin \mathrm{\&Delta;\&theta;}+(y-y0)\cos \mathrm{\&Delta;\&theta;}\\ X=(x-x0)\cos \mathrm{\&Delta;\&theta;}-(y-y0)\sin \mathrm{\&Delta;\&theta;}\end{array}\right.---\left(9\right)$

The scope of said quasi-synchronous tuning point Pq is positioned at the zone that is comprised between two regional and (11) described two parabolical symmetry axis and parabola top outer that parabola comprised being described by (10) and constitutes.

$\left\{\begin{array}{c}X\&le;-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\&GreaterEqual;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

-b≤Y≤b and $-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\&le;X\&le;\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}---\left(11\right)$

A wherein, b, c is defined as, and rotates for grating:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{8\cos \frac{\mathrm{\&Delta;\&theta;}}{2}}\frac{\cos \left(\mathrm{\&theta;i}\right)+\cos \left(\mathrm{\&theta;d}\right)}{\mathrm{SS}\left(0\right)}---\left(12\right)$

c?＝0

Rotate for speculum:

$a=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}$

$b=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\cos \mathrm{\&theta;d}}{\mathrm{SS}\left(0\right)}---\left(13\right)$

$c=\frac{\mathrm{\&lambda;}\left(0\right)}{4}\frac{\sin \mathrm{\&theta;i}}{\mathrm{SS}\left(0\right)}.$

11. grating external-cavity laser according to claim 9; It is characterized in that; Said quasi-synchronous tuning mechanism adjusts the rotational angle of said grating (12) through adjustment screw (8), and/or comes this rotational angle is finely tuned through on piezoelectric ceramic (10), applying control voltage.

12. grating external-cavity laser according to claim 9 is characterized in that, further puts into 1/2 wave plate between said LASER Light Source and the grating in order to the adjustment feedback power.

Images