CN102340100B

CN102340100B - Grating outer-cavity laser and quasi-synchronization tuning method thereof

Info

Publication number: CN102340100B
Application number: CN201010236535.0A
Authority: CN
Inventors: 王少凯; 臧二军; 李烨; 曹建平; 方占军
Original assignee: National Institute of Metrology
Current assignee: National Institute of Metrology
Priority date: 2010-07-22
Filing date: 2010-07-22
Publication date: 2015-06-03
Anticipated expiration: 2030-07-22
Also published as: CN102340100A

Abstract

The invention provides a method for quasi-synchronously tuning the laser wavelength or frequency of a grating external cavity laser, and also provides a corresponding laser. The grating or mirror is rotated with a quasi-synchronous tuning point (Pq) as the center of rotation, so as to realize the quasi-synchronous tuning of the frequency selection function of the grating and the resonant cavity. From the perspective of the actual physical space of the laser, on the xOy coordinate plane, the rotation center Pq(xq, yq) that satisfies the quasi-synchronous tuning condition can be regarded as the rotation center P0(x0, y0) under the conventional synchronous tuning condition Expand to the area included by the two parabolas near the P0 point. According to the present invention, near-synchronous tuning of laser light is achieved with a simple and flexible design.

Description

Grating External Cavity Laser and Its Quasi-synchronous Tuning Method

技术领域technical field

本发明涉及对光栅外腔激光器的激光波长或频率的调谐，其中在选择光栅或反射镜的调谐转动中心时实现了准同步的调谐。The present invention relates to the tuning of the laser wavelength or frequency of a grating external cavity laser, wherein quasi-synchronous tuning is achieved when selecting the tuning rotation center of the grating or mirror.

背景技术Background technique

在光栅外腔激光器中往往需要对所产生的激光波长或频率进行调谐，这种调谐是通过转动光栅从而改变光线在光栅上的入射角和衍射角、或者通过转动反射镜从而改变光线在光栅上的衍射角来实现的。In the grating external cavity laser, it is often necessary to tune the wavelength or frequency of the generated laser. This tuning is to change the incident angle and diffraction angle of the light on the grating by rotating the grating, or to change the angle of light on the grating by rotating the mirror. The diffraction angle is achieved.

在图1、图2和图3中分别示出了三种类型的光栅外腔半导体激光器。其中图1所示的是常规的掠入射(即入射角大于衍射角)结构的外腔半导体激光器，这种结构也被称为Littman结构；图2中所示的是由同一申请人在中国专利申请200810097085.4中提出的一种新型的掠衍射(即衍射角大于入射角)结构的外腔半导体激光器；而图3中所示的是常规的Littrow结构的外腔半导体激光器，在该结构中没有反射镜，因而仅通过转动光栅来进行调谐。Three types of grating external cavity semiconductor lasers are shown in Fig. 1, Fig. 2 and Fig. 3 respectively. Figure 1 shows a conventional external cavity semiconductor laser with grazing incidence (that is, the angle of incidence is greater than the diffraction angle), which is also called the Littman structure; what is shown in Figure 2 is patented by the same applicant in China Application 200810097085.4 proposes a new type of grazing diffraction (that is, the diffraction angle is greater than the incident angle) structure of the external cavity semiconductor laser; and shown in Figure 3 is a conventional Littrow structure of the external cavity semiconductor laser, there is no reflection in this structure mirror, thus tuning is performed only by turning the grating.

下面以光栅反馈外腔半导体激光器(ECDL)为例来说明光栅外腔激光器的基本结构与原理。如图1至3所示，LD表示半导体激光管，AL表示非球面准直透镜，G表示光栅，M表示反馈反射镜，N表示光栅法线，θi表示光线在光栅上的入射角，θd表示光线在光栅上的衍射角，Δθ为入射角与衍射角之差，即Δθ＝θi-θd，Δx为腔内光学元件(例如非球面准直透镜和LD的增益介质)所产生的光程增量。In the following, the grating-feedback external cavity semiconductor laser (ECDL) is taken as an example to illustrate the basic structure and principle of the grating external cavity laser. As shown in Figures 1 to 3, LD represents a semiconductor laser tube, AL represents an aspheric collimator lens, G represents a grating, M represents a feedback mirror, N represents the grating normal, θi represents the incident angle of light on the grating, θd represents The diffraction angle of light on the grating, Δθ is the difference between the incident angle and the diffraction angle, that is, Δθ=θi-θd, and Δx is the optical path increment produced by the optical elements in the cavity (such as aspheric collimating lens and LD gain medium).

在图1所示的掠入射结构和图2所示的掠衍射结构中，半导体激光管LD发出的激光经非球面镜AL准直后，入射到衍射光栅G上。光栅G的一级衍射光正入射在反馈反射镜M上，该光束在反射镜M上被反射后，沿着与入射光共线且反向的路径，按原路被光栅再次衍射后，经非球面镜AL返回到半导体激光管中。In the grazing incidence structure shown in Figure 1 and the grazing diffraction structure shown in Figure 2, the laser light emitted by the semiconductor laser tube LD is collimated by the aspheric mirror AL and then incident on the diffraction grating G. The first-order diffracted light of the grating G is incident on the feedback reflector M. After being reflected on the reflector M, the light beam follows the path collinear and opposite to the incident light, and is diffracted again by the grating according to the original path. The spherical mirror AL returns to the semiconductor laser tube.

在图3所示的Littrow结构中，半导体激光管LD发出的激光经非球面镜AL准直后，入射到衍射光栅G上。光栅G的一级衍射光沿着与入射光共线且反向的路径，按原路直接经非球面镜AL返回到半导体激光管中。可以看到，在Littrow结构中光束在光栅上的入射角和衍射角相等，即θi＝θd＝θ，因而Δθ＝0。In the Littrow structure shown in Figure 3, the laser light emitted by the semiconductor laser tube LD is collimated by the aspheric mirror AL and then incident on the diffraction grating G. The first-order diffracted light of the grating G returns to the semiconductor laser tube directly through the aspheric mirror AL along the path collinear and opposite to the incident light. It can be seen that in the Littrow structure, the incident angle and diffraction angle of the light beam on the grating are equal, that is, θi=θd=θ, thus Δθ=0.

为了说明外腔半导体激光器的调谐原理，在附图中引入了直角坐标系xOy，其中O点表示半导体激光管LD所发出的激光光束与光栅G在初始位置的衍射表面的交点，x轴经过O点且方向与LD发出的光线共线反向，y轴经过O点并与x轴垂直且方向向上。In order to illustrate the tuning principle of the external cavity semiconductor laser, a Cartesian coordinate system xOy is introduced in the accompanying drawings, where O point represents the intersection point of the laser beam emitted by the semiconductor laser tube LD and the diffraction surface of the grating G at the initial position, and the x axis passes through O point and the direction is collinear and opposite to the light emitted by LD, the y-axis passes through point O and is perpendicular to the x-axis and the direction is upward.

等效LD后端反射面、光栅G的衍射表面和反射镜M的反射表面这三个平面均与xOy坐标平面垂直。用SG表示光棚衍射表面所在的平面与xOy坐标平面的交线，O点位于该交线上；SL表示等效LD后端反射面所在的平面与xOy坐标平面的交线，它距O点的距离为l1；SM表示反馈反射镜M的反射表面所在的平面与xOy坐标平面的交线，它距O点的距离为l2。The three planes of the equivalent LD back end reflective surface, the diffractive surface of the grating G and the reflective surface of the mirror M are all perpendicular to the xOy coordinate plane. Use SG to indicate the intersection line between the plane where the diffractive surface of the light booth is located and the xOy coordinate plane, and point O is located on the intersection line; The distance is l1; SM represents the intersection of the plane where the reflection surface of the feedback mirror M is located and the xOy coordinate plane, and its distance from point O is l2.

在图1和图2所示的掠入射和掠衍射结构中，l1和l2分别表示O点到等效LD后端反射面和反馈反射镜M的光学距离，即光栅外腔的两个子腔长度，整个半导体激光器的光学腔长用它们之和l＝l1+l2来表示。在图3所示的Littrow结构中，半导体激光器的实际光学腔长即为O点到等效LD后端反射面的距离l1。In the grazing incidence and grazing diffraction structures shown in Fig. 1 and Fig. 2, l1 and l2 represent the optical distances from point O to the equivalent LD back-end reflection surface and feedback mirror M, respectively, that is, the lengths of the two subcavities of the grating external cavity , the optical cavity length of the entire semiconductor laser is represented by their sum l=l1+l2. In the Littrow structure shown in Figure 3, the actual optical cavity length of the semiconductor laser is the distance l1 from the point O to the reflective surface at the back end of the equivalent LD.

当转动光栅G或反射镜M进行调谐时，转动轴与xOy坐标平面垂直，该转动轴与xOy坐标平面的交点(即转动中心)在图1至3中用坐标P(x，y)来表示。为了有助于分析，引入了距离参量u、v和w，其中u表示转动中心P到交线SM的距离；v表示转动中心P到交线SG的距离；w表示转动中心P到交线SL的距离。这里各参量u、v和w取值的符号规定如下：当光线与转动中心在相应平面交线的同侧时用正值表示，而当光线与转动中心分别在相应平面交线的两侧时用负值表示。当光栅G或反馈反射镜M围绕P点转动时，距离v或u保持不变。When the grating G or mirror M is turned for tuning, the axis of rotation is perpendicular to the xOy coordinate plane, and the intersection of the axis of rotation and the xOy coordinate plane (that is, the center of rotation) is represented by coordinates P(x, y) in Figures 1 to 3 . In order to facilitate the analysis, the distance parameters u, v and w are introduced, where u represents the distance from the rotation center P to the intersection line SM; v represents the distance from the rotation center P to the intersection line SG; w represents the rotation center P to the intersection line SL distance. Here, the signs of the values of the parameters u, v and w are stipulated as follows: when the ray and the center of rotation are on the same side of the intersection line of the corresponding plane, it is represented by a positive value, and when the ray and the center of rotation are on the two sides of the intersection line of the corresponding plane respectively Represented by a negative value. When the grating G or feedback mirror M rotates around point P, the distance v or u remains constant.

在光栅外腔半导体激光器中，决定激光波长或频率的两个主要因素是：In a grating external cavity semiconductor laser, the two main factors that determine the laser wavelength or frequency are:

1.由光线在光栅上的入射角和衍射角的取值和变化所决定的选频作用；1. The frequency selection effect determined by the value and change of the incident angle and diffraction angle of light on the grating;

2.由SL、SM、SG所形成的等效F-P腔的腔长的取值和变化所决定的选频作用。2. The frequency selection effect determined by the value and change of the cavity length of the equivalent F-P cavity formed by SL, SM, and SG.

在以转动中心P为轴转动光栅或反射镜的过程中，光栅的选频作用和F-P腔的选频作用均发生改变。一般而言，上述改变不是同步的，这将引起激光模式的跳模变化，中断了激光频率的连续调谐，因而能够得到的激光频率不跳模时的连续调谐范围非常小，例如为1至2GHz。During the process of rotating the grating or the mirror with the rotation center P as the axis, the frequency selection function of the grating and the frequency selection function of the F-P cavity both change. Generally speaking, the above-mentioned changes are not synchronous, which will cause the mode-hopping change of the laser mode, interrupting the continuous tuning of the laser frequency, so the continuous tuning range of the laser frequency without mode-hopping is very small, for example, 1 to 2 GHz .

为了实现激光波长或频率的同步调谐，即实现大范围不跳模的频率连续调谐，需要有目的地选择光栅G或反馈反射镜M的转动中心P。In order to achieve synchronous tuning of the laser wavelength or frequency, that is, continuous frequency tuning without mode hopping in a wide range, it is necessary to select the rotation center P of the grating G or the feedback mirror M purposefully.

假设在转动调谐之后光栅或反射镜相对于其初始位置转动的角度为α，则激光光束在F-P腔内往返一周后的相位变化ψ可表示为：Assuming that the angle of rotation of the grating or mirror relative to its initial position after rotational tuning is α, the phase change ψ of the laser beam after a round trip in the F-P cavity can be expressed as:

ψ＝ψ₀+A(α)·[B·sinα+C·(l-cosα)] (1)ψ＝ψ ₀ +A(α)·[B·sinα+C·(l-cosα)] (1)

其中ψ0表示在转动调谐之前光束在腔内往返一周的初始相位变化，A(α)是与调谐转动角度α有关的函数，而ψ0、B和C是与角度α无关的函数。ψ0、A(α)、B和C与外腔半导体激光器的初始参数有关，这些初始参数包括初始角度(如初始入射角θi、初始衍射角θd等)、初始位置(如初始腔长l1和l2、初始距离u、v和w等)、以及光栅常数d等等。当满足完全同步调谐的条件时，相位变化ψ应当与调谐转动角度α无关，即公式1中的B和C均应为零。where ψ0 represents the initial phase change of the beam in the cavity for a round trip before rotation tuning, A(α) is a function related to the tuning rotation angle α, and ψ0, B and C are functions independent of the angle α. ψ0, A(α), B and C are related to the initial parameters of the external cavity semiconductor laser, these initial parameters include the initial angle (such as the initial incident angle θi, the initial diffraction angle θd, etc.), the initial position (such as the initial cavity length l1 and l2 , the initial distance u, v and w, etc.), and the grating constant d and so on. When the condition of fully synchronous tuning is met, the phase change ψ should have nothing to do with the tuning rotation angle α, that is, both B and C in formula 1 should be zero.

此时，实现完全同步调谐的转动中心P0的距离参量应满足：At this time, the distance parameter of the rotation center P0 to realize complete synchronous tuning should satisfy:

$\{\begin{matrix} u u 00 + + w w 00 = = 00 \\ v v 00 = = 00 \end{matrix} - - - - - - ((22))$

也就是说，满足同步调谐限制条件的转动中心P0应当位于光栅衍射表面所在的平面与xOy坐标平面的交线SG上；同时，转动中心P0到反射镜反射表面所在平面的距离u0和P0到等效LD后端反射面所在平面的距离w0的绝对值相同而符号相反。That is to say, the rotation center P0 that satisfies the synchronous tuning restriction should be located on the intersection line SG between the plane where the grating diffraction surface is located and the xOy coordinate plane; at the same time, the distances u0 and P0 from the rotation center P0 to the plane where the reflective surface of the mirror is located are equal to The absolute value of the distance w0 of the plane where the reflective surface at the rear end of the effective LD is located is the same but the sign is opposite.

当用坐标P0(x0，y0)表示这种满足同步调谐限制条件的转动中心时，对于掠入射和掠衍射结构可以得到：When the coordinate P0(x0, y0) is used to represent the center of rotation that satisfies the synchronous tuning constraints, for the grazing incidence and grazing diffraction structures, we can get:

$\{\begin{matrix} x x 00 = = ld ld sin sin θi θ i / / λ λ \\ y the y 00 = = ld ld cos cos θi θ i / / λ λ \end{matrix} - - - - - - ((33))$

其中x0、y0分别表示同步调谐转动中心P0的横坐标和纵坐标，l为在初始位置(即转动角度α为零)时的F-P腔的等效腔长，d为光栅常数，θi为光束在光栅上的入射角，λ为激光波长。Among them, x0 and y0 respectively represent the abscissa and ordinate of the synchronous tuning rotation center P0, l is the equivalent cavity length of the F-P cavity at the initial position (that is, the rotation angle α is zero), d is the grating constant, and θi is the beam at The angle of incidence on the grating, λ is the laser wavelength.

关于掠入射和掠衍射结构的同步调谐分别在图4和图5中示出。Synchronous tuning for grazing-incidence and grazing-diffraction structures is shown in Fig. 4 and Fig. 5, respectively.

图6示出了Littrow结构的同步调谐，由于在Littrow结构中没有反射镜，即相当于u0＝w0，因而公式(2)所描述的距离参量约束条件变为：Fig. 6 shows the synchronous tuning of the Littrow structure, since there is no reflector in the Littrow structure, that is, equivalent to u0=w0, thus the distance parameter constraints described in formula (2) become:

$\{\begin{matrix} w w 00 = = 00 \\ v v 00 = = 00 \end{matrix} - - - - - - ((44))$

即同步调谐中心P0应位于直线SG和SL的交点处。That is, the synchronous tuning center P0 should be located at the intersection of straight lines SG and SL.

当用坐标P0(x0，y0)表示时，由于在Littrow结构中θi＝θd＝θ，实际光学腔长为l1，因而公式(3)所描述的距离参量约束条件变为：When represented by the coordinates P0(x0, y0), since θi=θd=θ in the Littrow structure, the actual optical cavity length is l1, so the distance parameter constraints described by formula (3) become:

$\{\begin{matrix} x x 00 = = l l 11 \\ y the y 00 = = \frac{l l 11}{tan the tan θ θ} \end{matrix} - - - - - - ((55))$

从上面的说明可以看出，无论是采用坐标参量还是距离参量，同步调谐转动中心P0的位置总是要由两个方程的方程组来描述，必须同时满足上述两个约束条件，这意味着在设计激光器时需要两个具备独立自由度的调整机构。而且，无论是在掠入射、掠衍射还是Littrow结构的情况下，同步调谐转动中心P0的位置均不能离开光栅衍射表面所在的平面SG。这种限制使得激光器的结构设计、调整和应用十分不利和困难，同时造成了机械系统的复杂性，并增加了不稳定因素。From the above description, it can be seen that no matter whether the coordinate parameter or the distance parameter is used, the position of the synchronous tuning rotation center P0 is always described by a system of two equations, and the above two constraints must be satisfied at the same time, which means that in Two adjustment mechanisms with independent degrees of freedom are required when designing a laser. Moreover, no matter in the case of grazing incidence, grazing diffraction or Littrow structure, the position of the synchronous tuning rotation center P0 cannot leave the plane SG where the diffraction surface of the grating is located. This limitation makes the structural design, adjustment and application of the laser very unfavorable and difficult, and at the same time causes the complexity of the mechanical system and increases the instability.

实际中，大的连续不跳模调谐范围还会受到许多其它因素影响，例如LD表面是否镀有增透膜和镀膜质量等。然而，一般近百个GHz甚至几十个GHz的激光频率的连续调谐范围已经能够满足相当多应用的需求。In practice, the large continuous non-mode-hopping tuning range will also be affected by many other factors, such as whether the surface of the LD is coated with an anti-reflective coating and the quality of the coating. However, the continuous tuning range of the laser frequency of nearly a hundred GHz or even tens of GHz can meet the requirements of quite a few applications.

发明内容Contents of the invention

本发明要解决的技术问题是找到一种对光栅外腔激光器进行近似同步调谐(即准同步调谐)的方法，它不必受到严格同步调谐的约束条件限制，使得调整机构更加稳定、可靠和简单，同时又使得所得到的连续不跳模调谐范围近似于严格同步调谐，不会显著影响激光器的品质。The technical problem to be solved by the present invention is to find a method for approximately synchronous tuning (i.e., quasi-synchronous tuning) of grating external cavity lasers, which does not have to be restricted by strict synchronous tuning constraints, making the adjustment mechanism more stable, reliable and simple. At the same time, the obtained continuous non-mode-hopping tuning range is similar to strict synchronous tuning, which will not significantly affect the quality of the laser.

根据本发明，该技术问题通过一种用于对光栅外腔激光器进行调谐的方法来解决，其中以一个准同步调谐点为转动中心转动激光器的光栅或反射镜，使得在转动期间光栅衍射表面所在的平面或反射镜反射表面所在的平面与该准同步调谐点之间的距离保持不变，从而实现光栅和谐振腔的选频作用的准同步调谐，其中以下述方式确定所述准同步调谐点：According to the invention, this technical problem is solved by a method for tuning a grating external cavity laser, in which the grating or mirror of the laser is rotated around a quasi-synchronous tuning point, so that during the rotation the diffractive surface of the grating lies The distance between the plane of the plane or the reflective surface of the mirror and the quasi-synchronous tuning point remains constant, thereby realizing the quasi-synchronous tuning of the frequency selection effect of the grating and the resonant cavity, wherein the quasi-synchronous tuning point is determined in the following manner :

确定一个同步调谐点P0(x0，y0)，使得当以该同步调谐点P0为转动中心转动光栅或反射镜时，在光栅外腔激光器的谐振腔内激光光束的往返相位差保持不变，准同步调谐范围用下面的方法给出：Determine a synchronous tuning point P0 (x0, y0), so that when the grating or reflector is rotated with the synchronous tuning point P0 as the rotation center, the round-trip phase difference of the laser beam in the resonant cavity of the grating external cavity laser remains unchanged. The synchronous tuning range is given by:

设给定的频率调谐范围为Set the given frequency tuning range as

$Δv Δv = = \frac{c c}{λ λ ((00))} ((\frac{{l l}_{00}}{l l (({α α}_{+ +}))} - - \frac{{l l}_{00}}{l l (({α α}_{- -}))})) - - - - - - ((1414))$

其中c为真空光速，λ(0)为激光中心波长，l₀为激光器初始腔长(即转动角度α为零时的腔长)，α±分别为不跳模所允许的向正负两个方向调谐的最大角度。光程l(α)与发生跳模的边界条件为，对于反射镜转动：Where c is the speed of light in vacuum, λ(0) is the center wavelength of the laser, l ₀ is the initial cavity length of the laser (that is, the cavity length when the rotation angle α is zero), and α± are respectively the positive and negative directions allowed by non-mode hopping Maximum angle for direction tuning. The boundary condition between optical path l(α) and mode hopping is, for mirror rotation:

$l l ((α α)) = = \frac{SS SS ((α α))}{SS SS ((00))} [[{l l}_{00} - - \frac{SS SS ((α α))}{SS SS ((00))} [[Y Y sin sin α α + + X x ((l l - - cos cos α α))]]]] - - - - - - ((1515))$

$\frac{| | Y Y sin sin α α + + X x ((l l - - cos cos α α)) | |}{SS SS ((α α))} \leq \leq \frac{λ λ ((00))}{44} \frac{l l}{SS SS ((00))} - - - - - - ((1616))$

对于光栅转动：For raster rotation:

$l l ((α α)) = = \frac{SS SS ((α α))}{SS SS ((00))} [[{l l}_{00} - - \frac{22 cos cos \frac{θl θl - - θd θd}{22} SS SS ((00))}{SS SS ((α α))} [[Y Y sin sin α α + + X x ((l l - - cos cos α α))]]]] - - - - - - ((1717))$

$\frac{22 cos cos \frac{θl θl - - θd θd}{22} | | Y Y sin sin α α + + X x ((l l - - cos cos α α)) | |}{SS SS ((α α))} \leq \leq \frac{λ λ ((00))}{44} \frac{11}{SS SS ((00))} - - - - - - ((1818))$

光栅转动情况：Grating rotation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)SS(α)＝sin(θi-α)+sin(θd-α) (19)

反射镜转动情况：Mirror rotation:

SS(α)＝sinθi+sin(θd-α) (20)SS(α)＝sinθi+sin(θd-α) (20)

所以准同步调谐范围定义为那些使得调谐范围不小于Δv的点所组成区域。So the quasi-synchronous tuning range is defined as the area composed of points such that the tuning range is not smaller than Δv.

可选的，该方法所述准同步调谐范围进一步为以下范围：Optionally, the quasi-synchronous tuning range described in this method is further in the following range:

确定一个同步调谐点(x0，y0)，以该同步调谐点为转动中心转动光栅或反射镜时，在激光器的谐振腔内激光光束的往返相位差保持不变。做坐标变换，对于光栅转动调节：A synchronous tuning point (x0, y0) is determined, and when the grating or reflector is rotated with the synchronous tuning point as the center of rotation, the round-trip phase difference of the laser beam in the resonant cavity of the laser remains unchanged. Do coordinate transformations, for raster rotation adjustments:

$\{\begin{matrix} Y Y = = [[((x x - - x x 00)) sin sin \frac{Δθ Δθ}{22} + + ((y the y - - y the y 00)) cos cos \frac{Δθ Δθ}{22}]] \\ X x = = [[((x x - - x x 00)) cos cos \frac{Δθ Δθ}{22} - - ((y the y - - y the y 00)) sin sin \frac{Δθ Δθ}{22}]] \end{matrix} - - - - - - ((88))$

对于反射镜调节：For mirror adjustment:

$\{\begin{matrix} Y Y = = [[((x x - - x x 00)) sin sin Δθ Δθ + + ((y the y - - y the y 00)) cos cos Δθ Δθ]] \\ X x = = [[((x x - - x x 00)) cos cos Δθ Δθ - - ((y the y - - y the y 00)) sin sin Δθ Δθ]] \end{matrix} - - - - - - ((99))$

准同步调谐范围位于由(10)描述的两条抛物线所包含的区域以及(11)所描述的两条抛物线的对称轴和抛物线顶部外侧之间所包含的区域构成。The quasi-synchronous tuning range is formed by the region contained by the two parabolas described in (10) and the region contained between the symmetry axis of the two parabolas described in (11) and the top outside of the parabola.

$\{\begin{matrix} X x \leq \leq - - \frac{{((Y Y + + b b))}^{22}}{22 ((a a + + c c))} - - \frac{a a - - c c}{22} \\ X x &GreaterEqual; &Greater Equal; \frac{{((Y Y - - b b))}^{22}}{22 ((a a + + c c))} + + \frac{a a - - c c}{22} \end{matrix} - - - - - - ((1010))$

-b≤Y≤b且 $- \frac{{(Y + b)}^{2}}{2 (a + c)} - \frac{a - c}{2} \leq X \leq \frac{{(Y - b)}^{2}}{2 (a + c)} + \frac{a - c}{2} - - - (11)$ -b≤Y≤b and $- \frac{{(Y + b)}^{2}}{2 (a + c)} - \frac{a - c}{2} \leq x \leq \frac{{(Y - b)}^{2}}{2 (a + c)} + \frac{a - c}{2} - - - (11)$

其中a，b，c的定义为，对于光栅转动：Where a, b, c are defined as, for grating rotation:

$\begin{matrix} a a = = \frac{λ λ ((00))}{88 cos cos \frac{Δθ Δθ}{22}} \\ b b = = \frac{λ λ ((00))}{88 cos cos \frac{Δθ Δθ}{22}} \frac{cos cos ((θi θ i)) + + cos cos ((θd θd))}{SS SS ((00))} \\ c c = = 00 \end{matrix} - - - - - - ((1212))$

对于反射镜转动：For mirror rotation:

$\begin{matrix} a a = = \frac{λ λ ((00))}{44} \frac{sin sin θd θd}{SS SS ((00))} \\ b b = = \frac{λ λ ((00))}{44} \frac{cos cos θd θd}{SS SS ((00))} \\ c c = = \frac{λ λ ((00))}{44} \frac{sin sin θi θ i}{SS SS ((00))} . . \end{matrix} - - - - - - ((1313))$

根据本发明，还提供了相应的外腔激光器，其中包括用于执行上述准同步调谐方法的准同步调谐机构，该准同步调谐机构围绕如上所述确定的准同步调谐转动中心转动光栅或反射镜，从而实现光栅和谐振腔选频作用的准同步调谐。其中所述外腔激光器既可以是Littman结构或掠衍射结构，也可以是Littrow结构。在Littrow结构外腔激光器的情况下，由于入射角与衍射角之差Δθ＝0，因而由公式(10)限定的两条抛物线的对称轴平行于入射到光栅上的光线方向。According to the present invention, there is also provided a corresponding external cavity laser, which includes a quasi-synchronous tuning mechanism for performing the above-mentioned quasi-synchronous tuning method, and the quasi-synchronous tuning mechanism rotates the grating or mirror around the quasi-synchronous tuning rotation center determined as described above , so as to realize the quasi-synchronous tuning of the frequency selection effect of the grating and the resonant cavity. Wherein the external cavity laser can be a Littman structure, a grazing diffraction structure, or a Littrow structure. In the case of a Littrow external cavity laser, since the difference between the incident angle and the diffraction angle Δθ=0, the symmetry axes of the two parabolas defined by formula (10) are parallel to the direction of light incident on the grating.

通过本发明所述技术方案，减少了同步调谐的约束条件数目，使得调整机构只需要一个调整自由度。而且转动中心的位置不必再受到不能离开光栅表面所在平面交线SG的限制，这使得同步调谐具有更灵活的选择和更大的发挥余地，易于设计实现激光的近似同步转动频率或波长调谐。Through the technical proposal of the invention, the number of constraints for synchronous tuning is reduced, so that the adjustment mechanism only needs one adjustment degree of freedom. Moreover, the position of the rotation center does not have to be limited by the intersection line SG of the plane where the grating surface is located, which makes the synchronous tuning more flexible and more room to play, and is easy to design and realize the approximate synchronous rotational frequency or wavelength tuning of the laser.

附图说明Description of drawings

图1示出了现有技术Littman(掠入射)结构的光栅外腔半导体激光器的简化视图；Fig. 1 shows the simplified view of the grating external cavity semiconductor laser of prior art Littman (grazing incidence) structure;

图2示出了现有技术掠衍射结构的光栅外腔半导体激光器的简化视图；Fig. 2 shows the simplified view of the grating external cavity semiconductor laser of prior art grazing diffraction structure;

图3示出了现有技术Littrow结构的光栅外腔半导体激光器的简化视图；Fig. 3 shows the simplified view of the grating external cavity semiconductor laser of prior art Littrow structure;

图4示出了现有技术针对Littman结构的常规同步调谐转动中心的确定；Fig. 4 shows the determination of the conventional synchronously tuned center of rotation for the Littman structure in the prior art;

图5示出了现有技术针对掠衍射结构的常规同步调谐转动中心的确定；Figure 5 shows the prior art determination of the center of rotation for conventional synchronously tuned grazing diffractive structures;

图6示出了现有技术针对Littrow结构的常规同步调谐转动中心的确定；Fig. 6 shows the determination of the conventional synchronously tuned center of rotation for the Littrow structure in the prior art;

图7示出了根据本发明实施例在光栅转动调谐时针对Littman结构的准同步调谐转动中心的确定；7 shows the determination of the quasi-synchronous tuning center of rotation for the Littman structure during grating rotational tuning according to an embodiment of the present invention;

图8示出了根据本发明实施例在光栅转动调谐时针对掠衍射结构的准同步调谐转动中心的确定；Fig. 8 shows the determination of the quasi-synchronous tuning center of rotation for a grazing diffractive structure during grating rotational tuning according to an embodiment of the present invention;

图9示出了根据本发明实施例在反射镜转动调谐时针对Littman结构的准同步调谐转动中心的确定；FIG. 9 shows the determination of the quasi-synchronous tuning center of rotation for the Littman structure during mirror rotation tuning according to an embodiment of the present invention;

图10示出了根据本发明实施例在反射镜转动调谐时针对掠衍射结构的准同步调谐转动中心的确定；FIG. 10 illustrates the determination of the quasi-synchronous tuning center of rotation for a grazing diffractive structure during rotational tuning of a mirror according to an embodiment of the present invention;

图11示出了根据本发明实施例针对Littrow结构的准同步调谐转动中心的确定；Figure 11 shows the determination of the quasi-synchronous tuning center of rotation for the Littrow structure according to an embodiment of the present invention;

图12示出了根据本发明实施例在光栅转动调谐时Littman结构光栅外腔半导体激光器的准同步调谐机构；Fig. 12 shows a quasi-synchronous tuning mechanism of a Littman structure grating external cavity semiconductor laser during grating rotation tuning according to an embodiment of the present invention;

图13示出了根据本发明实施例在光栅转动调谐时掠衍射结构光栅外腔半导体激光器的准同步调谐机构；Fig. 13 shows a quasi-synchronous tuning mechanism of a grating external cavity semiconductor laser with a grazing diffraction structure when the grating is rotated and tuned according to an embodiment of the present invention;

图14示出了根据本发明实施例在反射镜转动调谐时Littman结构光栅外腔半导体激光器的准同步调谐机构；Fig. 14 shows a quasi-synchronous tuning mechanism of a Littman structured grating external cavity semiconductor laser when the mirror is rotated and tuned according to an embodiment of the present invention;

图15示出了根据本发明实施例在反射镜转动调谐时掠衍射结构光栅外腔半导体激光器的准同步调谐机构；以及15 shows a quasi-synchronous tuning mechanism of a grating external cavity semiconductor laser with a grazing diffraction structure when the mirror is rotated and tuned according to an embodiment of the present invention; and

图16示出了根据本发明实施例Littrow结构光栅外腔半导体激光器的准同步调谐机构。FIG. 16 shows a quasi-synchronous tuning mechanism of a Littrow grating external cavity semiconductor laser according to an embodiment of the present invention.

具体实施方式Detailed ways

本发明是基于以下发现：在上述公式ψ＝ψ₀+A(α)·[B·sinα+C·(l-cosα)]所描述的调谐相位变化中，调谐转动角度α在用弧度表示时是一个远小于1且接近于零的微小量。根据泰勒级数展开定理，可知公式1的中括号内的第一项sinα是从调谐转动角度α的一阶项开始的奇次高阶项，而第二项(1-cosα)是从调谐转动角度α的二阶项开始的偶次高阶项，它是一个比sinα更高阶的微小量，对往返相位变化ψ的贡献远小于sinα。因此，如果第二项引起的相位变化小于不跳模所允许的相位变化量，可以对往返相位变化ψ作一阶近似，即略去公式1中的二阶项及其更高阶项。如果忽略公式1的中括号内的第二项，则往返相位变化ψ可近似表示为：The present invention is based on the discovery that in the tuning phase change described by the above formula ψ=ψ ₀ +A(α)[B sinα+C(l-cosα)], the tuning rotation angle α when expressed in radians is a tiny amount that is much smaller than 1 and close to zero. According to the Taylor series expansion theorem, it can be seen that the first term sinα in the square brackets of Formula 1 is an odd-order higher-order term starting from the first-order term of the tuning rotation angle α, and the second term (1-cosα) is from the tuning rotation angle α The even-order higher-order term starting from the second-order term of angle α, which is a tiny quantity higher order than sin α, contributes much less to the round-trip phase change ψ than sin α. Therefore, if the phase change caused by the second term is smaller than the allowable phase change without mode hopping, a first-order approximation can be made to the round-trip phase change ψ, that is, the second-order term and its higher-order terms in Equation 1 are omitted. If the second term in the square brackets of Equation 1 is ignored, the round-trip phase change ψ can be approximated as:

ψ＝ψ₀+A(α)·B·sinα (6)ψ＝ψ ₀ +A(α)·B·sinα (6)

在此情况下，为了使往返相位变化ψ与调谐转动角度α无关，可令系数B为零。即：In this case, in order to make the round-trip phase change ψ independent of the tuning rotation angle α, the coefficient B can be set to zero. Right now:

B＝0 (7)B＝0 (7)

这种近似被称为准同步调谐近似，在这一近似下对外腔激光器频率的调谐为准同步调谐，相应的光栅或反射镜的转动中心被称为准同步调谐转动中心Pq，其坐标可表示为Pq(xq，yq)。在这种近似范围内，调谐转动角度α引起的往返位相变化可以忽略，即ψ≈ψ0，近似于一个与调谐转动角度无关的常数。在实际应用中，外腔激光器参数及调谐转动角度α的调谐范围几乎完全满足这一近似条件。This approximation is called the quasi-synchronous tuning approximation. Under this approximation, the frequency tuning of the external cavity laser is quasi-synchronous tuning. The corresponding rotation center of the grating or mirror is called the quasi-synchronous tuning rotation center Pq, and its coordinates can be expressed as is Pq(xq, yq). In this approximate range, the round-trip phase change caused by the tuning rotation angle α can be ignored, that is, ψ≈ψ0, which is approximately a constant independent of the tuning rotation angle. In practical applications, the parameters of the external cavity laser and the tuning range of the tuning rotation angle α almost completely satisfy this approximate condition.

根据本发明，该技术问题通过一种用于对光栅外腔激光器进行调谐的方法来解决，其中以一个准同步调谐点为转动中心转动激光器的光栅或反射镜，使得在转动期间光栅衍射表面所在的平面或反射镜反射表面所在的平面与该准同步调谐点之间的距离保持不变，从而实现光栅和谐振腔的选频作用的准同步调谐。其中，以下述方式确定所述准同步调谐点：According to the invention, this technical problem is solved by a method for tuning a grating external cavity laser, in which the grating or mirror of the laser is rotated around a quasi-synchronous tuning point, so that during the rotation the diffractive surface of the grating lies The distance between the plane of the plane or the plane where the reflective surface of the mirror is located and the quasi-synchronous tuning point remains constant, thereby realizing the quasi-synchronous tuning of the frequency selection effect of the grating and the resonant cavity. Wherein, the quasi-synchronous tuning point is determined in the following manner:

做坐标变换，对于光栅转动调节：Do coordinate transformations, for raster rotation adjustments:

其中，Δθ＝θi-θd；Among them, Δθ=θi-θd;

对于反射镜调节：For mirror adjustment:

对于反射镜转动：For mirror rotation:

实际中，一般近百个GHz甚至几十个GHz的激光频率的连续调谐范围已经能够满足相当多应用的需求。因此准同步调谐范围还可以用下面的方法给出。In practice, the continuous tuning range of laser frequencies of nearly a hundred GHz or even tens of GHz can meet the needs of quite a few applications. Therefore, the quasi-synchronous tuning range can also be given by the following method.

设给定的频率调谐范围为Set the given frequency tuning range as

其中c为真空光速，λ(0)为激光中心波长，l₀为激光器初始腔长，即转动角度α为零时的腔长，α±分别为不跳模所允许的向正负两个方向调谐的最大角度。光程l(α)与发生跳模的边界条件为，对于反射镜转动：Where c is the speed of light in vacuum, λ(0) is the center wavelength of the laser, l ₀ is the initial cavity length of the laser, that is, the cavity length when the rotation angle α is zero, and α± are the positive and negative directions allowed by non-mode hopping The maximum angle for tuning. The boundary condition between optical path l(α) and mode hopping is, for mirror rotation:

对于光栅转动：For raster rotation:

$\begin{matrix} l l ((α α)) = = \frac{SS SS ((α α))}{SS SS ((00))} [[{l l}_{00} - - \frac{22 cos cos \frac{θl θl - - θd θd}{22} SS SS ((00))}{SS SS ((α α))} [[Y Y sin sin α α + + X x ((l l - - cos cos α α))]]]] \\ ((1717)) \frac{22 cos cos \frac{θl θl - - θd θd}{22} | | Y Y sin sin α α + + X x ((l l - - cos cos α α)) | |}{SS SS ((α α))} \leq \leq \frac{λ λ ((00))}{44} \frac{11}{SS SS ((00))} \end{matrix} - - - - - - ((1818))$

光栅转动情况：Grating rotation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)SS(α)＝sin(θi-α)+sin(θd-α) (19)

反射镜转动情况：Mirror rotation:

SS(α)＝sinθi+sin(θd-α) (20)SS(α)＝sinθi+sin(θd-α) (20)

所以准同步调谐范围还可定义为那些使得所述频率调谐范围不小于Δv的点所组成区域。通常该区域大于由(10)和(11)所定义的区域，更具有实用意义与价值。Therefore, the quasi-synchronous tuning range can also be defined as the area composed of points such that the frequency tuning range is not smaller than Δv. Usually this area is larger than the area defined by (10) and (11), and has more practical significance and value.

根据本发明，还提供了相应的光栅外腔激光器，其中包括用于执行上述准同步调谐方法的准同步调谐机构，该准同步调谐机构围绕如上所述确定的准同步调谐转动中心转动光栅或反射镜，从而实现光栅和谐振腔选频作用的准同步调谐。其中所述光栅外腔激光器既可以是Littman结构或掠衍射结构，也可以是Littrow结构。在Littrow结构外腔半导体激光器的情况下，由于入射角与衍射角之差Δθ＝0，因而由公式(10)限定的两条抛物线的对称轴平行于入射到光栅上的光线方向。当所述光栅外腔激光器是Littman结构或掠衍射结构结构激光器时，并通过以所述准同步调谐点(Pq)为转动中心转动光栅来进行调谐，其中由公式(10)限定的两条抛物线的对称轴当光栅转动调谐时，平行于反射镜M的法线与半导体激光管LD发出的光线之间夹角的角平分线，当反射镜转动调谐时，平行于反射镜M的初始位置(即转动角度x为零)法线方向。According to the present invention, there is also provided a corresponding grating external cavity laser, which includes a quasi-synchronous tuning mechanism for performing the quasi-synchronous tuning method described above, the quasi-synchronous tuning mechanism rotates the grating or reflector around the quasi-synchronous tuning rotation center determined as described above mirror, so as to realize the quasi-synchronous tuning of the frequency selection effect of the grating and the resonant cavity. Wherein the grating external cavity laser can be a Littman structure, a grazing diffraction structure, or a Littrow structure. In the case of a Littrow external cavity semiconductor laser, since the difference between the incident angle and the diffraction angle Δθ=0, the symmetry axes of the two parabolas defined by formula (10) are parallel to the direction of light incident on the grating. When the grating external cavity laser is a Littman structure or a grazing diffraction structure laser, it is tuned by rotating the grating with the quasi-synchronous tuning point (Pq) as the center of rotation, wherein the two parabolas defined by formula (10) When the grating is rotated and tuned, it is parallel to the angle bisector of the angle between the normal of the mirror M and the light emitted by the semiconductor laser tube LD. When the mirror is rotated and tuned, it is parallel to the initial position of the mirror M ( That is, the rotation angle x is zero) in the normal direction.

下面以较常使用的光栅外腔半导体激光器为例，来说明本发明的具体实施方式。The specific implementation manner of the present invention will be described below by taking the commonly used grating external cavity semiconductor laser as an example.

图7至11分别表示出了根据本发明确定光栅外腔激光器的准同步调谐转动中心的各种实施方式。7 to 11 respectively show various implementations of determining the quasi-synchronous tuning rotation center of a grating external cavity laser according to the present invention.

图7和图8示出了转动光栅进行调谐的情况，此时光线在光栅G上的入射角θi和衍射角θd均发生改变。因而，从激光器的实际物理空间上看，在xOy坐标平面上，满足准同步调谐条件的转动中心Pq(xq，yq)可以看作是，从常规的同步调谐条件下的转动中心P0(x0，y0)拓展到P0点附近的由公式(10)限定的两条抛物线，和公式(11)所限定的该两条抛物线的对称轴和抛物线顶部外侧之间所包含区域内。Fig. 7 and Fig. 8 show the situation of rotating the grating for tuning, at this time, both the incident angle θi and the diffraction angle θd of the light on the grating G are changed. Therefore, from the perspective of the actual physical space of the laser, on the xOy coordinate plane, the rotation center Pq(xq, yq) satisfying the quasi-synchronous tuning condition can be regarded as the rotation center P0(x0, yq) under the conventional synchronous tuning condition y0) extends to the two parabolas defined by the formula (10) near the point P0, and the area contained between the axis of symmetry of the two parabolas and the outside of the top of the parabola defined by the formula (11).

对于掠入射和掠衍射结构的外腔半导体激光器来说，当光栅转动调谐时(图7和图8)，由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，且平行于反射镜M的法线与半导体激光管LD发出的光线之间夹角的角平分线。For external cavity semiconductor lasers with grazing incidence and grazing diffraction structures, when the grating is rotated and tuned (Fig. 7 and Fig. 8), the distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are respectively +-b, and parallel to the angle bisector of the angle between the normal of the mirror M and the light emitted by the semiconductor laser tube LD.

图9和图10示出了转动反射镜进行调谐的情况，当反射镜转动调谐时(图9和图10)，由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，且平行于反射镜M的初始位置法线方向对于Littrow结构的外腔半导体激光器来说(图11)，相当于反射镜M与等效LD后端反射面重合，转动光栅G来进行调谐，此时由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，且平行于半导体激光管LD发出的光线。在根据本发明所确定的这个区域内，可以获得明显优于其它位置的大的同步调谐范围，且越接近同步调谐点P0(x0，y0)，所得到的同步调谐范围就越大。Figure 9 and Figure 10 show the situation of rotating the mirror for tuning. When the mirror is rotated and tuned (Figure 9 and Figure 10), the distance between the axis of symmetry of the two parabolas defined by formula (10) and the strictly synchronous tuning point are +-b respectively, and are parallel to the normal direction of the initial position of the mirror M. For the external cavity semiconductor laser with Littrow structure (Fig. 11), it is equivalent to the coincidence of the mirror M and the equivalent LD back-end reflection surface, and the rotation of the grating G for tuning, the distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are +-b respectively, and they are parallel to the light emitted by the semiconductor laser tube LD. In this region determined according to the present invention, a larger synchronous tuning range can be obtained which is obviously better than other positions, and the closer to the synchronous tuning point P0 (x0, y0), the larger the synchronous tuning range obtained.

图12和图13分别示出了转动光栅进行调谐时掠入射结构和掠衍射结构外腔半导体激光器的准同步调谐机构。Fig. 12 and Fig. 13 respectively show the quasi-synchronous tuning mechanism of the external cavity semiconductor laser with the grazing incidence structure and the grazing diffraction structure when the grating is rotated for tuning.

如图12所示，半导体激光管LD发出例如功率为30mW、波长为689nm的激光光束，经过焦距为4mm、数值孔径为0.6的非球面准直透镜AL准直后，入射到刻线密度为1800g/mm、具有适当衍射效率、刻线面积大小为12.5mm×12.5mm、厚度为6mm的全息衍射光栅G上，光栅G的零阶衍射光或直接镜反射光作为激光器的输出光束。光栅的一级衍射光正入射到平面反射镜M上，在M上反射后光线被反向，沿着与原入射光束共线反向的路径，沿原路经光栅再次衍射后，返回到半导体激光管LD中。As shown in Figure 12, the semiconductor laser tube LD emits a laser beam with a power of 30mW and a wavelength of 689nm. After being collimated by an aspheric collimator lens AL with a focal length of 4mm and a numerical aperture of 0.6, it is incident on the reticle with a density of 1800g. On a holographic diffraction grating G with proper diffraction efficiency, 12.5mm×12.5mm in size, and 6mm in thickness, the zero-order diffracted light or direct specular reflection light of the grating G is used as the output beam of the laser. The first-order diffracted light of the grating is incident on the plane reflector M, and after being reflected on M, the light is reversed, along the path collinear and reversed with the original incident beam, and after being diffracted again by the grating along the original path, it returns to the semiconductor laser Tube LD.

激光管LD通过热沉2例如采用温度传感器和半导体制冷器实现温度控制。下面描述准同步调谐机构的具体实现：准直透镜AL通过镜架4被调整和固定，衍射光栅G被固定在调节架动板6上，其方向可通过调节架定板7上的调节螺钉8和9进行调整，还可以通过动板上的压电陶瓷10进行细调，反射镜M通过固定架11固定在底板13上。外腔和光栅的选频作用通过围绕准同步转动中心Pq转动衍射光栅G来实现。例如，通过微调螺钉8改变衍射光栅G的角度进行粗调，和/或经过在压电陶瓷10施加控制电压进行微调。The temperature of the laser tube LD is controlled by using a heat sink 2 such as a temperature sensor and a semiconductor refrigerator. The specific implementation of the quasi-synchronous tuning mechanism is described below: the collimator lens AL is adjusted and fixed through the mirror frame 4, the diffraction grating G is fixed on the moving plate 6 of the adjusting frame, and its direction can be adjusted through the adjusting screw 8 on the fixed plate 7 of the adjusting frame and 9 for adjustment, and can also be fine-tuned through the piezoelectric ceramics 10 on the moving plate, and the reflector M is fixed on the base plate 13 through the fixing frame 11. The frequency selection function of the external cavity and the grating is realized by rotating the diffraction grating G around the quasi-synchronous rotation center Pq. For example, coarse adjustment is performed by changing the angle of the diffraction grating G through the fine adjustment screw 8 , and/or fine adjustment is performed by applying a control voltage to the piezoelectric ceramic 10 .

在图12所示的Littman结构外腔半导体激光器中，光栅转动的准同步调谐转动中心Pq(xq，yq)位于由(10)与(11)所描述的准同步调谐区域内。其中由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，并且与x轴负方向的夹角为Δθ/2，此时由于θi＞θd，因而Δθ＞0。In the Littman structure external cavity semiconductor laser shown in Fig. 12, the quasi-synchronous tuning rotation center Pq(xq, yq) of the grating rotation is located in the quasi-synchronous tuning region described by (10) and (11). The distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are +-b respectively, and the included angle with the negative direction of the x-axis is Δθ/2. At this time, since θi>θd, Δθ >0.

图13所示的光栅转动调谐的掠衍射结构外腔半导体激光器与图12所示的掠入射结构类似，区别仅在于反射镜M的位置不同，使得θi＜θd，因而Δθ＜0。光栅转动准同步调谐转动中心Pq(xq，yq)同样位于由(10)与(11)所描述的准同步调谐区域内。其中由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，并且与x轴负方向的夹角为Δθ/2，但该直线的倾斜方向与图12所示相反。The grating rotation-tuned grazing diffraction external cavity semiconductor laser shown in Figure 13 is similar to the grazing incidence structure shown in Figure 12, the only difference is that the position of the mirror M is different, so that θi<θd, so Δθ<0. The quasi-synchronous tuning rotation center Pq(xq, yq) of the grating rotation is also located in the quasi-synchronous tuning area described by (10) and (11). The distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are +-b respectively, and the included angle with the negative direction of the x-axis is Δθ/2, but the inclination direction of the straight line is the same as that shown in Figure 12 Shown is the opposite.

类似地，图14和图15分别示出了转动反射镜进行调谐时掠入射结构和掠衍射结构外腔半导体激光器的准同步调谐机构。Similarly, FIG. 14 and FIG. 15 respectively show the quasi-synchronous tuning mechanisms of the external cavity semiconductor lasers with the grazing incidence structure and the grazing diffraction structure when the mirror is rotated for tuning.

在图14和图15所示的准同步调谐机构中，光栅G通过固定架11固定在底板13上，反射镜M被固定在调节架动板6上，其方向可通过调节架定板7上的调节螺钉8和9进行调整，也可通过动板上的压电陶瓷10进行微调。通过围绕准同步转动中心Pq转动反射镜M来实现外腔和光栅的选频作用。例如，通过微调螺钉8改变反射镜M的角度进行粗调，和/或经过在压电陶瓷10施加控制电压进行微调。In the quasi-synchronous tuning mechanism shown in Figure 14 and Figure 15, the grating G is fixed on the bottom plate 13 through the fixing frame 11, and the mirror M is fixed on the moving plate 6 of the adjusting frame, and its direction can be adjusted by adjusting the fixed plate 7 of the frame. The adjustment screws 8 and 9 can be adjusted, and the piezoelectric ceramics 10 on the moving plate can also be fine-tuned. The frequency selection function of the external cavity and the grating is realized by rotating the mirror M around the quasi-synchronous rotation center Pq. For example, coarse adjustment is performed by changing the angle of the mirror M through the fine adjustment screw 8 , and/or fine adjustment is performed by applying a control voltage to the piezoelectric ceramic 10 .

在图14所示的反射镜转动调谐的Littman结构外腔半导体激光器中，反射镜转动准同步调谐转动中心Pq(xq，yq)位于由(10)与(11)所描述的准同步调谐区域内。其中由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，并且与x轴负方向的夹角为Δθ，此时由于θi＞θd，因而Δθ＞0。In the mirror rotation-tuned Littman external-cavity semiconductor laser shown in Figure 14, the mirror rotation quasi-synchronous tuning rotation center Pq(xq, yq) is located in the quasi-synchronous tuning region described by (10) and (11) . The distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are +-b respectively, and the included angle with the negative direction of the x-axis is Δθ. At this time, since θi>θd, Δθ>0 .

图15所示的反射镜转动准同步调谐的掠衍射结构外腔半导体激光器与图14所示的掠衍射结构类似，区别仅在于反射镜M的位置不同，使得θi＜θd，因而Δθ＜0。反射镜转动准同步调谐转动中心Pq(xq，yq)同样位于由(10)与(11)所描述的准同步调谐区域内。其中由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，并且与x轴负方向的夹角为Δθ，但该直线的倾斜方向与图14所示相反。The mirror rotation quasi-synchronously tuned grazing diffraction external cavity semiconductor laser shown in Figure 15 is similar to the grazing diffraction structure shown in Figure 14, the only difference is that the position of the mirror M is different, so that θi<θd, so Δθ<0. The mirror rotation quasi-synchronous tuning rotation center Pq(xq, yq) is also located in the quasi-synchronous tuning region described by (10) and (11). The distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are +-b respectively, and the included angle with the negative direction of the x-axis is Δθ, but the inclination direction of the straight line is the same as that shown in Figure 14 on the contrary.

图16示出了准同步调谐的Littrow结构外腔半导体激光器的示意图，其中θi＝θd＝θ。如图16所示，光栅G的一级衍射光沿着与原入射光束共线反向的路径，沿原路返回到半导体激光管LD中。在其准同步调谐机构中，光栅G被固定在调节架动板6上，该动板6可通过在调节架定板7上的调节螺钉8和9进行调整。通过绕准同步转动中心Pq转动衍射光栅G来实现激光波长的调谐。例如，通过微调螺钉8和/或压电陶瓷10改变光束入射到衍射光栅G上的角度，而准同步转动中心Pq和光栅G的对准调整可通过调整螺钉9来实现。FIG. 16 shows a schematic diagram of a quasi-synchronously tuned Littrow external cavity semiconductor laser, where θi=θd=θ. As shown in Figure 16, the first-order diffracted light of the grating G returns to the semiconductor laser tube LD along the original path along the collinear and reverse path with the original incident light beam. In its quasi-synchronous tuning mechanism, the grating G is fixed on the moving plate 6 of the adjusting frame, and the moving plate 6 can be adjusted through the adjusting screws 8 and 9 on the fixed plate 7 of the adjusting frame. The laser wavelength is tuned by rotating the diffraction grating G around the quasi-synchronous rotation center Pq. For example, the angle at which the light beam is incident on the diffraction grating G is changed by the fine adjustment screw 8 and/or the piezoelectric ceramic 10 , and the alignment adjustment between the quasi-synchronous rotation center Pq and the grating G can be realized by the adjustment screw 9 .

从图16中可以看到，在Littrow结构外腔半导体激光器中，准同步调谐转动中心Pq(xq，yq)位于由(10)与(11)所描述的准同步调谐区域内。其中由公式(10)限定的两条抛物线的对称轴距离严格同步调谐点的距离分别为+-b，并且与x轴平行。It can be seen from Fig. 16 that in the Littrow external cavity semiconductor laser, the quasi-synchronous tuning rotation center Pq(xq, yq) is located in the quasi-synchronous tuning region described by (10) and (11). The distances between the symmetry axes of the two parabolas defined by formula (10) and the strictly synchronous tuning point are respectively +-b, and are parallel to the x-axis.

本领域技术人员可知，上述例子中的光栅外腔激光器的激光光源除了半导体激光管以外也可选用其它类型的激光光源；波长和输出功率也可以选用其他数值；光栅也可采用闪耀光栅或透射光栅，其可以具有其它刻线密度、大小和厚度；准直透镜也可以采用其它焦距和数值孔径。此外，激光光源和光栅之间可以放入1/2波片用以调整反馈功率。Those skilled in the art know that the laser source of the grating external cavity laser in the above example can also be selected from other types of laser sources besides the semiconductor laser tube; the wavelength and output power can also be selected from other values; the grating can also be a blazed grating or a transmission grating , which can have other reticle densities, sizes and thicknesses; collimator lenses can also use other focal lengths and numerical apertures. In addition, a 1/2 wave plate can be placed between the laser source and the grating to adjust the feedback power.

Claims

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:

\{\begin{matrix} Y = [(x - x 0) \sin \frac{Δθ}{2} + (y - y 0) \cos \frac{Δθ}{2}] \\ X = [(x - x 0) \cos \frac{Δθ}{2} - (y - y 0) \sin \frac{Δθ}{2}] \end{matrix} - - - (8)

Speculum is regulated:

\{\begin{matrix} Y = [(x - x 0) \sin Δθ + (y - y 0) \cos Δθ] \\ X = [(x - x 0) \cos Δθ - (y - y 0) \sin Δθ] \end{matrix} - - - (9)

If given frequency tuning range is

Δv = \frac{c}{λ (0)} (\frac{l_{0}}{l (α_{+})} - \frac{l_{0}}{1 (α_{-})}) - - - (14)

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 (α) = \frac{SS (α)}{SS (0)} [l_{0} - \frac{SS (α)}{SS (0)} [Y \sin α + X (1 - \cos α)]] - - - (15)

\frac{| Y \sin α + X (1 - \cos α) |}{SS (α)} \leq \frac{λ (0)}{4} \frac{1}{SS (0)} - - - (16)

Grating is rotated:

l (α) = \frac{SS (α)}{SS (0)} [l_{0} - \frac{2 \cos \frac{θ 1 - θd}{2} SS (0)}{SS (α)} [Y \sin α + X (1 - \cos α)]] - - - (17)

\frac{2 \cos \frac{θ 1 - θd}{2} | Y \sin α + X (1 - \cos α) |}{SS (α)} \leq \frac{λ (0)}{4} \frac{1}{SS (0)} - - - (18)

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:

\{\begin{matrix} Y = [(x - x 0) \sin \frac{Δθ}{2} + (y - y 0) \cos \frac{Δθ}{2}] \\ X = [(x - x 0) \cos \frac{Δθ}{2} - (y - y 0) \sin \frac{Δθ}{2}] \end{matrix} - - - (8)

Speculum is regulated:

\{\begin{matrix} Y = [(x - x 0) \sin Δθ + (y - y 0) \cos Δθ] \\ X = [(x - x 0) \cos Δθ - (y - y 0) \sin Δθ] \end{matrix} - - - (9)

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,

\{\begin{matrix} X \leq - \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{matrix} - - - (10)

-b≤Y≤b and

- \frac{{(Y + b)}^{2}}{2 (a + c)} - \frac{a - c}{2} \leq X \leq \frac{{(Y - b)}^{2}}{2 (a + c)} + \frac{a - c}{2} - - - (11)

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

a = \frac{λ (0)}{8 \cos \frac{Δθ}{2}}

b = \frac{λ (0)}{8 \cos \frac{Δθ}{2}} \frac{\cos (θi) + \cos (θd)}{SS (0)} - - - (12)

c＝0

Speculum is rotated:

a = \frac{λ (0)}{4} \frac{\sin θd}{SS (0)}

b = \frac{λ (0)}{4} \frac{\cos θd}{SS (0)} - - - (13)

c = \frac{λ (0)}{4} \frac{\sin θi}{SS (0)} .

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:

Do coordinate transform, grating rotated and regulates:

\{\begin{matrix} Y = [(x - x 0) \sin \frac{Δθ}{2} + (y - y 0) \cos \frac{Δθ}{2}] \\ X = [(x - x 0) \cos \frac{Δθ}{2} - (y - y 0) \sin \frac{Δθ}{2}] \end{matrix} - - - (8)

Speculum is regulated:

\{\begin{matrix} Y = [(x - x 0) \sin Δθ + (y - y 0) \cos Δθ] \\ X = [(x - x 0) \cos Δθ - (y - y 0) \sin Δθ] \end{matrix} - - - (9)

If given frequency tuning range is

Δv = \frac{c}{λ (0)} (\frac{l_{0}}{l (α_{+})} - \frac{l_{0}}{1 (α_{-})}) - - - (14)

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 (α) = \frac{SS (α)}{SS (0)} [l_{0} - \frac{SS (α)}{SS (0)} [Y \sin α + X (1 - \cos α)]] - - - (15)

\frac{| Y \sin α + X (1 - \cos α) |}{SS (α)} \leq \frac{λ (0)}{4} \frac{1}{SS (0)} - - - (16)

Grating is rotated:

l (α) = \frac{SS (α)}{SS (0)} [l_{0} - \frac{2 \cos \frac{θ 1 - θd}{2} SS (0)}{SS (α)} [Y \sin α + X (1 - \cos α)]] - - - (17)

\frac{2 \cos \frac{θ 1 - θd}{2} | Y \sin α + X (1 - \cos α) |}{SS (α)} \leq \frac{λ (0)}{4} \frac{1}{SS (0)} - - - (18)

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:

\{\begin{matrix} Y = [(x - x 0) \sin \frac{Δθ}{2} + (y - y 0) \cos \frac{Δθ}{2}] \\ X = [(x - x 0) \cos \frac{Δθ}{2} - (y - y 0) \sin \frac{Δθ}{2}] \end{matrix} - - - (8)

Speculum is regulated:

\{\begin{matrix} Y = [(x - x 0) \sin Δθ + (y - y 0) \cos Δθ] \\ X = [(x - x 0) \cos Δθ - (y - y 0) \sin Δθ] \end{matrix} - - - (9)

\{\begin{matrix} X \leq - \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{matrix} - - - (10)

-b≤Y≤b and

- \frac{{(Y + b)}^{2}}{2 (a + c)} - \frac{a - c}{2} \leq X \leq \frac{{(Y - b)}^{2}}{2 (a + c)} + \frac{a - c}{2} - - - (11)

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

a = \frac{λ (0)}{8 \cos \frac{Δθ}{2}}

b = \frac{λ (0)}{8 \cos \frac{Δθ}{2}} \frac{\cos (θi) + \cos (θd)}{SS (0)} - - - (12)

c＝0

Speculum is rotated:

a = \frac{λ (0)}{4} \frac{\sin θd}{SS (0)}

b = \frac{λ (0)}{4} \frac{\cos θd}{SS (0)} - - - (13)

c = \frac{λ (0)}{4} \frac{\sin θi}{SS (0)} .

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:

\{\begin{matrix} Y = [(x - x 0) \sin \frac{Δθ}{2} + (y - y 0) \cos \frac{Δθ}{2}] \\ X = [(x - x 0) \cos \frac{Δθ}{2} - (y - y 0) \sin \frac{Δθ}{2}] \end{matrix} - - - (8)

If given frequency tuning range is

Δv = \frac{c}{λ (0)} (\frac{l_{0}}{l (α_{+})} - \frac{l_{0}}{1 (α_{-})}) - - - (14)

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

Grating is rotated:

l (α) = \frac{SS (α)}{SS (0)} [l_{0} - \frac{2 \cos \frac{θ 1 - θd}{2} SS (0)}{SS (α)} [Y \sin α + X (1 - \cos α)]] - - - (17)

\frac{2 \cos \frac{θ 1 - θd}{2} | Y \sin α + X (1 - \cos α) |}{SS (α)} \leq \frac{λ (0)}{4} \frac{1}{SS (0)} - - - (18)

Grating rotation situation:

SS(α)＝sin(θi-α)+sin(θd-α) (19)

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:

\{\begin{matrix} Y = [(x - x 0) \sin \frac{Δθ}{2} + (y - y 0) \cos \frac{Δθ}{2}] \\ X = [(x - x 0) \cos \frac{Δθ}{2} - (y - y 0) \sin \frac{Δθ}{2}] \end{matrix} - - - (8)

\{\begin{matrix} X \leq - \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{matrix} - - - (10)

-b≤Y≤b and

- \frac{{(Y + b)}^{2}}{2 (a + c)} - \frac{a - c}{2} \leq X \leq \frac{{(Y - b)}^{2}}{2 (a + c)} + \frac{a - c}{2} - - - (11)

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

a = \frac{λ (0)}{8 \cos \frac{Δθ}{2}}

b = \frac{λ (0)}{8 \cos \frac{Δθ}{2}} \frac{\cos (θi) + \cos (θd)}{SS (0)} - - - (12)

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.