CN102340100B - 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 the optical maser wavelength of grating external-cavity laser or the tuning of frequency, wherein achieving when selecting the tuning center of rotation of grating or speculum quasi synchronous tuning.

Background technology

Often need to carry out tuning to produced optical maser wavelength or frequency in grating external-cavity laser, be thisly tuningly by rotating shutter thus change the incidence angle of light on grating and the angle of diffraction or realize by rotating speculum thus changing the angle of diffraction of light on grating.

The grating external cavity semiconductor laser of three types is respectively illustrated in Fig. 1, Fig. 2 and Fig. 3.Wherein shown in Fig. 1 is the external-cavity semiconductor laser of conventional glancing incidence (namely incidence angle is greater than the angle of diffraction) structure, and this structure is also referred to as Littman structure; Shown in Fig. 2 is a kind of novel external-cavity semiconductor laser of plunderring diffraction (namely the angle of diffraction is greater than incidence angle) structure proposed in Chinese patent application 200810097085.4 by same applicant; And be the external-cavity semiconductor laser of conventional Littrow structure shown in Fig. 3, there is no speculum in the structure shown here, thus carry out tuning by means of only rotating shutter.

Below for the basic structure of Mingguang City's grid outside cavity gas laser grating-feedback extended-cavity diode laser (ECDL) and principle.As shown in Figures 1 to 3, LD represents semiconductor laser tube, AL represents aspheric collimation lens, and G represents grating, and M represents feedback reflector mirror, N represents grating normal, θ i represents the incidence angle of light on grating, and θ d represents the angle of diffraction of light on grating, and Δ θ is the difference of incidence angle and the angle of diffraction, the i.e. light path increment that produces for tracavity optical element (gain media of such as aspheric collimation lens and LD) of Δ θ=θ i-θ d, Δ x.

Plunder in diffraction structure shown in the glancing incidence structure shown in Fig. 1 and Fig. 2, the laser that semiconductor laser tube LD sends, after aspherical mirror AL collimates, incides on diffraction grating G.The first-order diffraction light normal incidence of grating G, on feedback reflector mirror M, after this light beam is reflected in mirror M, along with incident light conllinear and reverse path, by former road by after grating again diffraction, turns back in semiconductor laser tube through aspherical mirror AL.

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

In order to the Tuning Principle of external-cavity semiconductor laser is described, introduce rectangular coordinate system xOy in the accompanying drawings, wherein O point represents the laser beam that sends of semiconductor laser tube LD and the grating G intersection point at the Difraction surface of initial position, x-axis is through O point and the light conllinear that sends of direction and LD is reverse, y-axis through O point and and direction vertical with x-axis upwards.

The Difraction surface of equivalence LD back end reflective face, grating G is all vertical with xOy coordinate plane with these three planes of reflecting surface of mirror M.Represent the plane at light canopy Difraction surface place and the intersection of xOy coordinate plane with SG, O point is positioned on this intersection; SL represents the plane at place, equivalent LD back end reflective face and the intersection of xOy coordinate plane, and it is l1 apart from the distance of O point; SM represents the plane at reflecting surface place and the intersection of xOy coordinate plane of feedback reflector mirror M, and it is l2 apart from the distance of O point.

At the glancing incidence shown in Fig. 1 and Fig. 2 and plunder in diffraction structure, l1 and l2 represents the optical distance of O point to equivalent LD back end reflective face and feedback reflector mirror M respectively, i.e. two sub-cavity lengths of grating external-cavity, the optical cavity length of whole semiconductor laser represents with their sum l=l1+l2.In the Littrow structure shown in Fig. 3, the actual optical cavity length of semiconductor laser is the distance l1 of O point to equivalent LD back end reflective face.

When rotating shutter G or mirror M are carried out tuning, rotation axis is vertical with xOy coordinate plane, and the intersection point (i.e. center of rotation) of this rotation axis and xOy coordinate plane represents with coordinate P (x, y) in Fig. 1 to 3.In order to contribute to analyzing, introduce distance parameter u, v and w, wherein u represents the distance of center of rotation P to intersection SM; V represents the distance of center of rotation P to intersection SG; W represents the distance of center of rotation P to intersection SL.Here the sign convention of each parameter u, v and w value is as follows: when light and center of rotation when the homonymy of respective planes intersection with on the occasion of representing, and to represent by negative value when light and center of rotation are respectively in the both sides of respective planes intersection.When grating G or feedback reflector mirror M rotates around P point, distance v or u remains unchanged.

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

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

2. the frequency-selecting effect that the value of the chamber length of the equivalent F-P cavity formed by SL, SM, SG and change determine.

In the process being axle rotating shutter or speculum with center of rotation P, the frequency-selecting effect of grating and the frequency-selecting effect of F-P cavity all change.Generally speaking, above-mentioned change is not synchronous, and this changes causing the mode hopping of zlasing mode, has interrupted the continuous tuning of laser frequency, the laser frequency that thus can obtain not mode hopping time continuous tuning coverage very little, be such as 1 to 2GHz.

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

Suppose that grating or speculum are α relative to the angle that its initial position rotates after rotation tuning, then laser beam round phase place change ψ after a week in F-P cavity can be expressed as:

ψ＝ψ ₀+A(α)·[B·sinα+C·(l-cosα)] (1)

Wherein ψ 0 represents that light beam is in the change of the intracavity round trip initial phase of a week before rotation tuning, and A (α) is the function relevant with tuning rotational angle α, and ψ 0, B and C are the functions irrelevant with angle [alpha].ψ 0, A (α), B with C are relevant with the initial parameter of external-cavity semiconductor laser, and these initial parameters comprise initial angle (as initial incidence angle θ i, initial diffraction angle d etc.), initial position (l1 and l2 as long in initial cavity, initial distance u, v and w etc.) and grating constant etc.When meeting the tuning condition of Complete Synchronization, phase place change ψ should have nothing to do with tuning rotational angle α, B and C namely in formula 1 all should be zero.

Now, the distance parameter realizing the tuning center of rotation P0 of Complete Synchronization should meet:

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

That is, the center of rotation P0 meeting simultaneous tuning restrictive condition should be positioned on the optical grating diffraction surface plane at place and the intersection SG of xOy coordinate plane; Meanwhile, center of rotation P0 to the distance u0 of speculum reflecting surface place plane is identical with the absolute value of P0 to the distance w0 of place, equivalent LD back end reflective face plane and symbol is contrary.

When represent with coordinate P0 (x0, y0) this meet the center of rotation of simultaneous tuning restrictive condition time, 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, the equivalent cavity that l is F-P cavity when initial position (namely rotational angle α is zero) is long, d is grating constant, and θ i is the incidence angle of light beam on grating, and λ is optical maser wavelength.

Illustrate in figures 4 and 5 respectively about glancing incidence and the simultaneous tuning of plunderring diffraction structure.

Fig. 6 shows the simultaneous tuning of Littrow structure, owing to not having speculum in Littrow structure, is namely equivalent to u0=w0, and the distance parameter constraints thus described by formula (2) becomes:

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

Namely simultaneous tuning center P0 should be positioned at the point of intersection of straight line SG and SL.

When representing with coordinate P0 (x0, y0), due to θ i=θ d=θ in Littrow structure, actual optical cavity length is l1, and the distance parameter constraints thus described by formula (3) becomes:

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

As can be seen from explanation above, no matter be adopt coordinate parameter or distance parameter, the position of simultaneous tuning center of rotation P0 always will be described by the equation group of two equations, above-mentioned two constraintss must being met simultaneously, this means to need two adjusting mechanisms possessing independent degree when designing laser.And, be no matter when glancing incidence, plunder diffraction or Littrow structure, 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 the structural design of laser, adjustment and application very unfavorable and difficult, causes the complexity of mechanical system simultaneously, and adds destabilizing factor.

In reality, large continuous not mode hopping tuning range also can be subject to the impact of many other factorses, and such as whether LD surface is coated with anti-reflection film and coating quality etc.But general more or less a hundred the GHz even continuous tuning coverage of the laser frequency of tens GHz can meet the demand of quite a lot of application.

Summary of the invention

The technical problem to be solved in the present invention finds a kind of method of grating external-cavity laser being carried out to near-synchronous tuning (i.e. quasi-synchronous tuning), it need not be subject to the tuning constraints restriction of stringent synchronization, make adjusting mechanism more stable, reliable and simple, make again simultaneously obtained continuously not mode hopping tuning range to be similar to stringent synchronization tuning, can not the quality of appreciable impact laser.

According to the present invention, this technical problem is solved for carrying out tuning method to grating external-cavity laser by a kind of, be wherein that center of rotation rotates the grating of laser or speculum with a quasi-synchronous tuning point, during turning the optical grating diffraction surface plane at place or the distance between the plane at speculum reflecting surface place and this quasi-synchronous tuning point are remained unchanged, thus realize the quasi-synchronous tuning of the frequency-selecting effect of grating resonant cavity, wherein determine described quasi-synchronous tuning point in the following manner:

Determine a simultaneous tuning point P0 (x0, y0), make when with this simultaneous tuning point P0 for center of rotation rotating shutter or speculum time, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, quasi-synchronous tuning scope provides in the following method:

If given frequency tuning range is

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

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

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

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

Grating is rotated:

$l\left(\mathrm{\α}\right)=\frac{\mathrm{SS}\left(\mathrm{\α}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\θl}-\mathrm{\θd}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\α}\right)}[Y\sin \mathrm{\α}+X(l-\cos \mathrm{\α})\left]\right]---\left(17\right)$

$\frac{2\cos \frac{\mathrm{\θl}-\mathrm{\θd}}{2}|Y\sin \mathrm{\α}+X(l-\cos \mathrm{\α})|}{\mathrm{SS}\left(\mathrm{\α}\right)}\≤\frac{\mathrm{\λ}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}---\left(18\right)$

Grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

Speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

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

Optionally, quasi-synchronous tuning scope described in the method is following scope further:

Determine simultaneous tuning point (x0, y0), during with this simultaneous tuning point for center of rotation rotating shutter or speculum, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of laser.Do coordinate transform, grating rotated and regulates:

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

Speculum is regulated:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \mathrm{\Δ\θ}+(y-y0)\cos \mathrm{\Δ\θ}]\\ X=[(x-x0)\cos \mathrm{\Δ\θ}-(y-y0)\sin \mathrm{\Δ\θ}]\end{array}\right.---\left(9\right)$

Quasi-synchronous tuning scope is positioned at region that two parabolas being described by (10) comprise and two parabolical symmetry axis described by (11) and the region that comprises between parabola top outer is formed.

$\left\{\begin{array}{c}X\≤-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\≥\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

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

Wherein a, b, c are defined as, and rotate for grating:

$\begin{array}{c}a=\frac{\mathrm{\λ}\left(0\right)}{8\cos \frac{\mathrm{\Δ\θ}}{2}}\\ b=\frac{\mathrm{\λ}\left(0\right)}{8\cos \frac{\mathrm{\Δ\θ}}{2}}\frac{\cos \left(\mathrm{\θi}\right)+\cos \left(\mathrm{\θd}\right)}{\mathrm{SS}\left(0\right)}\\ c=0\end{array}---\left(12\right)$

Speculum is rotated:

$\begin{array}{c}a=\frac{\mathrm{\λ}\left(0\right)}{4}\frac{\sin \mathrm{\θd}}{\mathrm{SS}\left(0\right)}\\ b=\frac{\mathrm{\λ}\left(0\right)}{4}\frac{\cos \mathrm{\θd}}{\mathrm{SS}\left(0\right)}\\ c=\frac{\mathrm{\λ}\left(0\right)}{4}\frac{\sin \mathrm{\θi}}{\mathrm{SS}\left(0\right)}.\end{array}---\left(13\right)$

According to the present invention, additionally provide corresponding outside cavity gas laser, comprising the quasi-synchronous tuning mechanism for performing above-mentioned quasi-synchronous tuning method, this quasi-synchronous tuning mechanism around the quasi-synchronous tuning center of rotation rotating shutter determined as mentioned above or speculum, thus realizes the quasi-synchronous tuning of grating resonant cavity frequency-selecting effect.Wherein said outside cavity gas laser both can be Littman structure or plunder diffraction structure, also can be Littrow structure.When Littrow structure outside cavity gas laser, due to difference Δ θ=0 of incidence angle and the angle of diffraction, two the parabolical symmetry axis thus limited by formula (10) are parallel to the radiation direction incided on grating.

By technical scheme of the present invention, decrease the constraints number of simultaneous tuning, make adjusting mechanism only need one to adjust the degree of freedom.And the position of center of rotation need not be subject to the restriction can not leaving grating surface place plane intersection line SG again, this makes simultaneous tuning have selection more flexibly and larger performance leeway, is easy to design the near-synchronous rotational frequency or wavelength tuning that realize laser.

Accompanying drawing explanation

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 plunders 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 the determination of prior art for the tuning center of rotation of conventional synchronous of Littman structure;

Fig. 5 shows the determination of prior art for the tuning center of rotation of the conventional synchronous of plunderring diffraction structure;

Fig. 6 shows the determination of prior art for the tuning center of rotation of conventional synchronous of Littrow structure;

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

Fig. 8 show according to the embodiment of the present invention when grating rotation tuning for the determination of quasi-synchronous tuning center of rotation of plunderring diffraction structure;

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

Figure 10 show according to the embodiment of the present invention when speculum rotation tuning for the determination of quasi-synchronous tuning center of rotation of plunderring diffraction structure;

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

Figure 12 shows the quasi-synchronous tuning mechanism according to embodiment of the present invention Littman structure fringe external-cavity semiconductor laser when grating rotation tuning;

Figure 13 shows the quasi-synchronous tuning mechanism of plunderring diffraction structure grating external-cavity semiconductor laser according to the embodiment of the present invention when grating rotation tuning;

Figure 14 shows the quasi-synchronous tuning mechanism according to embodiment of the present invention Littman structure fringe external-cavity semiconductor laser when speculum rotation tuning;

Figure 15 shows the quasi-synchronous tuning mechanism of plunderring diffraction structure grating external-cavity semiconductor laser according to the embodiment of the present invention when speculum rotation tuning; And

Figure 16 shows the quasi-synchronous tuning mechanism according to embodiment of the present invention Littrow structure fringe external-cavity semiconductor laser.

Embodiment

The present invention is based on following discovery: at above-mentioned formula ψ=ψ ₀in tuning phase place change described by+A (α) [Bsin α+C (l-cos α)], tuning rotational angle α when representing with radian be one much smaller than 1 and close to zero small quantity.According to Taylor series expansion theorem, Section 1 sin α in the bracket of known formula 1 is the odd higher order term from the single order item of tuning rotational angle α, and Section 2 (1-cos α) is the even higher order term from the second order term of tuning rotational angle α, it is a small quantity than sin α more high-order, to the contribution of round phase place change ψ much smaller than sin α.Therefore, if the phase place change that Section 2 causes is less than the phase changing capacity that not mode hopping allows, first approximation can be made to round phase place change ψ, namely omit second order term in formula 1 and more higher order term thereof.If ignore the Section 2 in the bracket of formula 1, then coming and going phase place change ψ can approximate representation be:

ψ＝ψ ₀+A(α)·B·sinα (6)

In the case, change ψ and tuning rotational angle α to make round phase place and have nothing to do, coefficient B can be made to be zero.That is:

B＝0 (7)

This approximate quasi-synchronous tuning that is called as is similar to, under this is approximate, external laser cavity frequency is tuned as quasi-synchronous tuning, the center of rotation of corresponding grating or speculum is called as quasi-synchronous tuning center of rotation Pq, and 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, i.e. ψ ≈ ψ 0, is similar to a constant had nothing to do with tuning rotational angle.In actual applications, the tuning range of outside cavity gas laser parameter and tuning rotational angle α almost meets this approximate condition completely.

According to the present invention, this technical problem is solved for carrying out tuning method to grating external-cavity laser by a kind of, be wherein that center of rotation rotates the grating of laser or speculum with a quasi-synchronous tuning point, during turning the optical grating diffraction surface plane at place or the distance between the plane at speculum reflecting surface place and this quasi-synchronous tuning point are remained unchanged, thus realizes the quasi-synchronous tuning of the frequency-selecting effect of grating resonant cavity.Wherein, described quasi-synchronous tuning point is determined in the following manner:

Do coordinate transform, grating rotated and regulates:

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

Wherein, Δ θ=θ i-θ d;

Speculum is regulated:

$\left\{\begin{array}{c}Y=[(x-x0)\sin \mathrm{\Δ\θ}+(y-y0)\cos \mathrm{\Δ\θ}]\\ X=[(x-x0)\cos \mathrm{\Δ\θ}-(y-y0)\sin \mathrm{\Δ\θ}]\end{array}\right.---\left(9\right)$

Quasi-synchronous tuning scope is positioned at region that two parabolas being described by (10) comprise and two parabolical symmetry axis described by (11) and the region that comprises between parabola top outer is formed.

$\left\{\begin{array}{c}X\≤-\frac{{(Y+b)}^2}{2(a+c)}-\frac{a-c}{2}\\ X\≥\frac{{(Y-b)}^2}{2(a+c)}+\frac{a-c}{2}\end{array}\right.---\left(10\right)$

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

Wherein a, b, c are defined as, and rotate for grating:

$\begin{array}{c}a=\frac{\mathrm{\λ}\left(0\right)}{8\cos \frac{\mathrm{\Δ\θ}}{2}}\\ b=\frac{\mathrm{\λ}\left(0\right)}{8\cos \frac{\mathrm{\Δ\θ}}{2}}\frac{\cos \left(\mathrm{\θi}\right)+\cos \left(\mathrm{\θd}\right)}{\mathrm{SS}\left(0\right)}\\ c=0\end{array}---\left(12\right)$

Speculum is rotated:

$\begin{array}{c}a=\frac{\mathrm{\λ}\left(0\right)}{4}\frac{\sin \mathrm{\θd}}{\mathrm{SS}\left(0\right)}\\ b=\frac{\mathrm{\λ}\left(0\right)}{4}\frac{\cos \mathrm{\θd}}{\mathrm{SS}\left(0\right)}\\ c=\frac{\mathrm{\λ}\left(0\right)}{4}\frac{\sin \mathrm{\θi}}{\mathrm{SS}\left(0\right)}.\end{array}---\left(13\right)$

In reality, general more or less a hundred the GHz even continuous tuning coverage of the laser frequency of tens GHz can meet the demand of quite a lot of application.Therefore quasi-synchronous tuning scope can also provide in the following method.

If given frequency tuning range is

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

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

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

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

Grating is rotated:

$\begin{array}{c}l\left(\mathrm{\α}\right)=\frac{\mathrm{SS}\left(\mathrm{\α}\right)}{\mathrm{SS}\left(0\right)}[l_0-\frac{2\cos \frac{\mathrm{\θl}-\mathrm{\θd}}{2}\mathrm{SS}\left(0\right)}{\mathrm{SS}\left(\mathrm{\α}\right)}[Y\sin \mathrm{\α}+X(l-\cos \mathrm{\α})\left]\right]\\ \left(17\right)\frac{2\cos \frac{\mathrm{\θl}-\mathrm{\θd}}{2}|Y\sin \mathrm{\α}+X(l-\cos \mathrm{\α})|}{\mathrm{SS}\left(\mathrm{\α}\right)}\≤\frac{\mathrm{\λ}\left(0\right)}{4}\frac{1}{\mathrm{SS}\left(0\right)}\end{array}---\left(18\right)$

Grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

Speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

Described frequency tuning range is made to be not less than the some institute compositing area of Δ v so quasi-synchronous tuning scope also may be defined as those.Usually this region is greater than the region defined by (10) and (11), has more Practical significance and value.

According to the present invention, additionally provide corresponding grating external-cavity laser, comprising the quasi-synchronous tuning mechanism for performing above-mentioned quasi-synchronous tuning method, this quasi-synchronous tuning mechanism around the quasi-synchronous tuning center of rotation rotating shutter determined as mentioned above or speculum, thus realizes the quasi-synchronous tuning of grating resonant cavity frequency-selecting effect.Wherein said grating external-cavity laser both can be Littman structure or plunder diffraction structure, also can be Littrow structure.When Littrow structure external-cavity semiconductor laser, due to difference Δ θ=0 of incidence angle and the angle of diffraction, two the parabolical symmetry axis thus limited by formula (10) are parallel to the radiation direction incided on grating.When described grating external-cavity laser be Littman structure or plunder diffraction structure structure laser time, and by with described quasi-synchronous tuning point (Pq) for center of rotation rotating shutter carries out tuning, two the parabolical symmetry axis wherein limited by formula (10) are when grating rotation tuning, be parallel to the angular bisector of angle between light that the normal of mirror M and semiconductor laser tube LD send, when speculum rotation tuning, be parallel to initial position (namely rotational angle x the is zero) normal direction of mirror M.

Below for the comparatively normal grating external cavity semiconductor laser used, the specific embodiment of the present invention is described.

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

Fig. 7 and Fig. 8 shows rotating shutter and carries out tuning situation, and now the incidence angle θ i of light on grating G and diffraction angle d all changes.Thus, from the actual physics of laser spatially, in xOy coordinate plane, meet the center of rotation Pq (xq of quasi-synchronous tuning condition, yq) can be regarded as, be extended to two parabolas limited by formula (10) near P0 point from the center of rotation P0 (x0, y0) the simultaneous tuning condition of routine, and formula (11) limit between this two parabolical symmetry axis and parabola top outer in institute's inclusion region.

For glancing incidence and the external-cavity semiconductor laser of plunderring diffraction structure, when grating rotation tuning (Fig. 7 and Fig. 8), the distance of two that are limited by formula (10) parabolical symmetry axis distance stringent synchronization tuning point is respectively+-b, and is parallel to the angular bisector of angle between light that the normal of mirror M and semiconductor laser tube LD send.

Fig. 9 and Figure 10 shows rotation speculum and carries out tuning situation, when speculum rotation tuning (Fig. 9 and Figure 10), the distance of two that are limited by formula (10) parabolical symmetry axis distance stringent synchronization tuning point is respectively+-b, and be parallel to the external-cavity semiconductor laser (Figure 11) of initial position normal direction for Littrow structure of mirror M, be equivalent to mirror M overlap with equivalent LD back end reflective face, rotating shutter G carries out tuning, the distance of two the parabolical symmetry axis distance stringent synchronization tuning point now limited by formula (10) is respectively+-b, and be parallel to the light that semiconductor laser tube LD sends.In this region determined according to the present invention, the large simultaneous tuning scope being obviously better than other position can be obtained, and more close to simultaneous tuning point P0 (x0, y0), the simultaneous tuning scope obtained is larger.

Figure 12 and Figure 13 respectively illustrates glancing incidence structure and the quasi-synchronous tuning mechanism of plunderring diffraction structure external-cavity semiconductor laser when rotating shutter carries out tuning.

As shown in figure 12, semiconductor laser tube LD sends that such as power is 30mW, wavelength is the laser beam of 689nm, through focal length be 4mm, numerical aperture be 0.6 aspheric collimation lens AL collimate after, incide incisure density be 1800g/mm, there is suitable diffraction efficiency, on groove size is 12.5mm × 12.5mm, thickness is 6mm holographic diffraction grating G, the zeroth order diffraction light of grating G or directly mirror reverberation are as the output beam of laser.The first-order diffraction light normal incidence of grating is on plane mirror M, and on M, after reflection, light is reversed, and along the path reverse with former incident beam conllinear, along former road after grating again diffraction, turns back in semiconductor laser tube LD.

Laser tube LD such as adopts temperature sensor and semiconductor cooler to realize temperature by heat sink 2 and controls.The specific implementation of quasi-synchronous tuning mechanism is described below: collimating lens AL is adjusted by mirror holder 4 and fixes, diffraction grating G is fixed on adjusting bracket and moves on plate 6, the adjustment screw 8 and 9 that its direction is determined on plate 7 by adjusting bracket adjusts, can also carry out fine tuning by the piezoelectric ceramic 10 on dynamic plate, mirror M is fixing on base 13 by fixed mount 11.The frequency-selecting effect of exocoel and grating realizes by rotating diffraction grating G around accurate synchronous axial system center Pq.Such as, the angle being changed diffraction grating G by micrometer adjusting screw 8 carries out coarse adjustment, and/or finely tunes through applying control voltage at piezoelectric ceramic 10.

In the Littman structure external-cavity semiconductor laser shown in Figure 12, the quasi-synchronous tuning center of rotation Pq (xq, yq) that grating rotates is positioned at by (10) and the quasi-synchronous tuning region described by (11).The distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and be Δ θ/2 with the angle of x-axis negative direction, now due to θ i > θ d, thus Δ θ > 0.

The glancing incidence similar of plunderring shown in diffraction structure external-cavity semiconductor laser and Figure 12 of the grating rotation tuning shown in Figure 13, difference is only that the position of mirror M is different, makes θ i < θ d, thus Δ θ < 0.Grating rotates quasi-synchronous tuning center of rotation Pq (xq, yq) and is positioned at equally by (10) and the quasi-synchronous tuning region described by (11).The distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and is Δ θ/2 with the angle of x-axis negative direction, but the incline direction of this straight line is contrary with Figure 12 Suo Shi.

Similarly, Figure 14 and Figure 15 respectively illustrates and rotates glancing incidence structure and the quasi-synchronous tuning mechanism of plunderring diffraction structure external-cavity semiconductor laser when speculum carries out tuning.

In the quasi-synchronous tuning mechanism shown in Figure 14 and Figure 15, grating G is fixing on base 13 by fixed mount 11, mirror M is fixed on adjusting bracket and moves on plate 6, the adjustment screw 8 and 9 that its direction is determined on plate 7 by adjusting bracket adjusts, and also finely tunes by the piezoelectric ceramic 10 on dynamic plate.By rotating around accurate synchronous axial system center Pq the frequency-selecting effect that mirror M realizes exocoel and grating.Such as, the angle being changed mirror M by micrometer adjusting screw 8 carries out coarse adjustment, and/or finely tunes through applying control voltage at piezoelectric ceramic 10.

In the Littman structure external-cavity semiconductor laser of the speculum rotation tuning shown in Figure 14, speculum rotates quasi-synchronous tuning center of rotation Pq (xq, yq) and is positioned at by (10) and the quasi-synchronous tuning region described by (11).The distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and be Δ θ with the angle of x-axis negative direction, now due to θ i > θ d, thus Δ θ > 0.

Speculum shown in Figure 15 rotate quasi-synchronous tuning plunder shown in diffraction structure external-cavity semiconductor laser and Figure 14 to plunder diffraction structure similar, difference is only that the position of mirror M is different, make θ i < θ d, thus Δ θ < 0.Speculum rotates quasi-synchronous tuning center of rotation Pq (xq, yq) and is positioned at equally by (10) and the quasi-synchronous tuning region described by (11).The distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and is Δ θ with the angle of x-axis negative direction, but the incline direction of this straight line is contrary with Figure 14 Suo Shi.

Figure 16 shows the schematic diagram of the Littrow structure external-cavity semiconductor laser of quasi-synchronous tuning, wherein θ i=θ d=θ.As shown in figure 16, the first-order diffraction light of grating G is along the path reverse with former incident beam conllinear, and Yan Yuanlu turns back in semiconductor laser tube LD.In its quasi-synchronous tuning mechanism, grating G is fixed on adjusting bracket and moves on plate 6, and this dynamic plate 6 adjusts by the adjustment screw 8 and 9 of determining at adjusting bracket on plate 7.The tuning of optical maser wavelength is realized by rotating diffraction grating G around accurate synchronous axial system center Pq.Such as, change light beam by micrometer adjusting screw 8 and/or piezoelectric ceramic 10 and incide angle on diffraction grating G, and the adjustment of the aligning of accurate synchronous axial system center Pq and grating G realizes by adjustment screw 9.

As can see from Figure 16, in Littrow structure external-cavity semiconductor laser, quasi-synchronous tuning center of rotation Pq (xq, yq) is positioned at by (10) and the quasi-synchronous tuning region described by (11).The distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and parallel with x-axis.

Those skilled in the art are known, and the LASER Light Source of the grating external-cavity laser in above-mentioned example also can select the LASER Light Source of other type except semiconductor laser tube; Wavelength and power output also can select other numerical value; 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, 1/2 wave plate can be put between LASER Light Source and grating in order to adjust feedback power.

Claims (12)

1. one kind for carrying out the method for quasi-synchronous tuning to grating external-cavity laser, wherein with a quasi-synchronous tuning point Pq be center of rotation rotating shutter outside cavity gas laser grating or speculum, during turning the optical grating diffraction surface plane at place or the distance between the plane at speculum reflecting surface place and this quasi-synchronous tuning point Pq are remained unchanged, thus realize the quasi-synchronous tuning of the frequency-selecting effect of grating resonant cavity, wherein determine described quasi-synchronous tuning point Pq in the following manner:

Determine a simultaneous tuning point P0 (x0, y0), make when with this simultaneous tuning point P0 for center of rotation rotating shutter or speculum time, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, quasi-synchronous tuning scope provides in the following method:

Do coordinate transform, grating rotated and regulates:

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

Speculum is regulated:

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

If given frequency tuning range is

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{1\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

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

Light path l (α) is rotate for speculum with the boundary condition of generation mode hopping:

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

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

Grating is rotated:

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

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

Grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

Speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

The scope of quasi-synchronous tuning point Pq makes described 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, described quasi-synchronous tuning scope is following scope further:

Determine simultaneous tuning point (x0, y0), during with this simultaneous tuning point for center of rotation rotating shutter or speculum, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of laser, do coordinate transform, grating is rotated and regulates:

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

Speculum is regulated:

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

The scope of described quasi-synchronous tuning point Pq is positioned at region that two parabolas being described by (10) comprise and two parabolical symmetry axis described by (11) and the region that comprises between parabola top outer is formed,

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

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

Wherein a, b, c are defined as, and rotate 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

Speculum is rotated:

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

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

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

3. method according to claim 2, it is characterized in that, described grating external-cavity laser is Littman structure or plunders diffraction structure laser, and by with described quasi-synchronous tuning point (Pq) for center of rotation rotating shutter or speculum carry out tuning, the distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and when grating rotation tuning, be approximately parallel to the angular bisector of angle between light that the normal of mirror M and semiconductor laser tube LD send, when speculum rotation tuning, be parallel to the initial position normal direction of mirror M.

4. method according to claim 2, is characterized in that, described grating external-cavity laser is Littrow structure laser, and by with described quasi-synchronous tuning point (Pq) for center of rotation rotating shutter carries out tuning; The distance of two the parabolical symmetry axis distance stringent synchronization tuning point wherein limited by formula (10) is respectively+-b, and is parallel to the radiation direction incided on grating.

5. a Littman structure or plunder the grating external-cavity laser of diffraction structure, comprise: LASER Light Source (1), aspheric collimation lens (3), grating (12) and speculum (5), wherein said laser also comprises quasi-synchronous tuning mechanism, described quasi-synchronous tuning mechanism rotates described grating (12) or speculum (5) around a quasi-synchronous tuning center of rotation Pq, during turning the optical grating diffraction surface plane at place or the distance between the plane at speculum reflecting surface place and this quasi-synchronous tuning point Pq are remained unchanged, thus realize the quasi-synchronous tuning of grating resonant cavity frequency-selecting effect, wherein determine described quasi-synchronous tuning point Pq in the following manner:

Determine a simultaneous tuning point P0 (x0, y0), make when with this simultaneous tuning point P0 for center of rotation rotating shutter or speculum time, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, quasi-synchronous tuning scope provides in the following method:

Do coordinate transform, grating rotated and regulates:

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

Speculum is regulated:

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

If given frequency tuning range is

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{1\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

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

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

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

Grating is rotated:

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

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

Grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

Speculum rotation situation:

SS(α)＝sinθi+sin(θd-α) (20)

The scope of described quasi-synchronous tuning point Pq makes described 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, described quasi-synchronous tuning scope is following scope further: determine a simultaneous tuning point (x0, y0), during with this simultaneous tuning point for center of rotation rotating shutter or speculum, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of laser, do coordinate transform, grating is rotated and regulates:

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

Speculum is regulated:

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

The scope of described quasi-synchronous tuning point Pq is positioned at region that two parabolas being described by (10) comprise and two parabolical symmetry axis described by (11) and the region that comprises between parabola top outer is formed,

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

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

Wherein a, b, c are defined as, and rotate 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

Speculum is rotated:

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

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

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

7. grating external-cavity laser according to claim 5, it is characterized in that, described quasi-synchronous tuning mechanism adjusts the rotational angle of described grating (12) or speculum (5) by adjustment screw (8), and/or by finely tuning this rotational angle in the upper control voltage that applies of piezoelectric ceramic (10).

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

9. the grating external-cavity laser of a Littrow structure, comprise: LASER Light Source (1), aspheric collimation lens (3) and grating (12), wherein said grating external-cavity laser also comprises quasi-synchronous tuning mechanism, described quasi-synchronous tuning mechanism rotates described grating (12) around a quasi-synchronous tuning center of rotation (Pq), distance between the plane at during turning place, optical grating diffraction surface and this quasi-synchronous tuning point (Pq) is remained unchanged, thus realizes the quasi-synchronous tuning of grating resonant cavity frequency-selecting effect; Wherein determine described quasi-synchronous tuning point Pq in the following manner:

Determine a simultaneous tuning point P0 (x0, y0), make when with this simultaneous tuning point P0 for center of rotation rotating shutter time, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of grating external-cavity laser, quasi-synchronous tuning scope provides in the following method:

Do coordinate transform, grating rotated and regulates:

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

If given frequency tuning range is

$\mathrm{\&Delta;v}=\frac{c}{\mathrm{\&lambda;}\left(0\right)}(\frac{l_0}{l\left({\mathrm{\&alpha;}}_{+}\right)}-\frac{l_0}{1\left({\mathrm{\&alpha;}}_{-}\right)})---\left(14\right)$

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

Light path l (α) with the boundary condition that mode hopping occurs is:

Grating is rotated:

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

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

Grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

The scope of described quasi-synchronous tuning point Pq makes described 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, described quasi-synchronous tuning scope is following scope further: determine a simultaneous tuning point (x0, y0), during with this simultaneous tuning point for center of rotation rotating shutter, remain unchanged at the round phase difference of the resonant cavity inner laser light beam of laser, do coordinate transform, grating is rotated and regulates:

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

The scope of described quasi-synchronous tuning point Pq is positioned at region that two parabolas being described by (10) comprise and two parabolical symmetry axis described by (11) and the region that comprises between parabola top outer is formed,

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

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

Wherein a, b, c are defined as, and rotate 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。

11. grating external-cavity lasers according to claim 9, it is characterized in that, described quasi-synchronous tuning mechanism adjusts the rotational angle of described grating (12) by adjustment screw (8), and/or by finely tuning this rotational angle in the upper control voltage that applies of piezoelectric ceramic (10).

12. grating external-cavity lasers according to claim 9, is characterized in that, put into 1/2 wave plate further in order to adjust feedback power between described LASER Light Source and grating.