CN101604818A - Continuous mode-hop-free tunable grating external-cavity diode laser - Google Patents

Abstract

Disclose a kind of continuous mode-hop-free tunable grating external-cavity diode laser in the embodiments of the invention, having comprised: at least one optical module of forming by gain media and collimating lens, tuner and at least one diffraction grating; The coherent beam that described gain media sent becomes directional light through behind the described collimating lens, described directional light by described diffraction grating diffraction after, the part diffraction light directly becomes the first output laser that is output, another part diffraction light returns in the described gain media along former input path, in described gain media, vibrate, when being amplified to, become the second output laser above the laser oscillation threshold; Described diffraction grating is arranged on the described tuner; Described tuner drives described diffraction grating and rotates around a rotating shaft that is positioned at the back side of described diffraction grating; Described rotating shaft is parallel with the Difraction surface of described diffraction grating and vertical with the optical axis of laser.By using above-mentioned laser, can realize mode jump free continuous tuning, and reduce the production cost of described laser laser frequency.

Description

Continuous mode-hop-free tunable grating external-cavity diode laser

Technical field

The present invention relates to semiconductor laser field, refer in particular to a kind of continuous mode-hop-free tunable grating external-cavity diode laser.

Background technology

The wavelength tuning technology of light source is the important component part in the laser technology, and tunable grating external-cavity semiconductor laser (GTECL, Grating-tuned external cavity lasers) the outstanding advantages such as spectral purity height, wavelength wide coverage, compact conformation, conversion efficiency height, single mode output, cost are low, good reliability because it has, therefore be widely used in numerous areas such as optical communication, light exchange, optical storage, optic fiber gyroscope, measurement, high resolution spectral measuring and biomedicine, great application prospect has been arranged.

In the prior art, the tunable grating external-cavity semiconductor laser generally has two types.A kind of is Li Teluo (Littrow) type tunable grating external-cavity semiconductor laser, and another kind is Li Teman-Mai Te koff Littman-Metcalf type tunable grating external-cavity semiconductor laser.Below will be introduced this laser of two types respectively.

The tunable grating external-cavity semiconductor laser of Littrow type can produce the laser beam of the frequency adjustable that live width is very narrow, optical coherence is very high, and in the production of actual product, the GTECL laser of Littrow type has very compactness and the simple cavity resonator structure of form, this resonant cavity generally only comprises three optics: as the semiconductor laser of gain medium, as the diffraction grating of frequency-selecting element with the collimating lens of laser beam collimation, thereby can realize simplifying very much and manufacture process cheaply.For example, a kind of tunable grating external-cavity semiconductor laser that Wieman and Hollberg proposed (referring to document " ' UsingDiode Lasers for Atomic Physics ' by Carl E.Wieman and Leo Hollberg; Review ofScientific Instruments; Vol.62; Pages 1-19; January, 1991 ") is exactly a kind of more typical Littrow type tunable grating external-cavity semiconductor laser.

Fig. 1 is the schematic diagram of Littrow type tunable grating external-cavity semiconductor laser in the prior art one.As shown in Figure 1, this tunable grating external-cavity semiconductor laser comprises: semiconductor laser (Laser diode) 101, collimating lens 102 and diffraction grating (diffraction grating) 103.Wherein, semiconductor laser 101 has a rear surface 106 and a front surface 107; The light beam that is produced in this semiconductor laser 101 can obtain directional light after passing through collimating lens 102, and this directional light incides on the diffraction grating 103 back by these diffraction grating 103 diffraction; Wherein, zero order diffracted light can be directly as output laser 104, first-order diffraction light then returns in the semiconductor laser 101 along former input path, after process is vibrated, is amplified in semiconductor laser 101, become output laser 105, thereby realize single longitudinal mode (SLM, single longitudinalmode) the laser output of narrow linewidth.

In above-mentioned tunable grating external-cavity semiconductor laser, diffraction grating 103 can around order by G and perpendicular to the rotation of the fixedly rotating shaft of paper direction, wherein, described G point is the intersection point on optical axis 100 and diffraction grating 103 surfaces.When with diffraction grating 103 during, can realize tuning to the frequency of output laser or wavelength around the rotation of above-mentioned fixedly rotating shaft.But when carrying out continuous tuning according to the design of above-mentioned resonant cavity, the single longitudinal mode pattern of above-mentioned laser might jump to another longitudinal mode suddenly by a longitudinal mode, thereby produces the phenomenon of mode hopping (mod hopping).The phenomenon of this mode hopping is on laser output frequency, generation is equivalent to the frequency agility of laser longitudinal mode spacing, then the characteristics of laser frequency continuous tuning have been destroyed, accuracy for frequency tuning, the application that linearity of tuning degree and other depend on frequency Tuning Characteristics all can produce adverse influence, therefore should avoid as far as possible, thereby require to realize no mode hopping (MHF, mod-hop-free) the tuning or wavelength tuning of cline frequency.

For the phenomenon of above-mentioned mode hopping, can illustrate accordingly by formula as described below.

According to grating equation: λ (θ)=2d _gSin θ (1.1)

And condition of resonance: $N\·\frac{\mathrm{\λ}}{2}=L_{\mathrm{MG}}---\left(1.2\right)$

As can be known: $N=\frac{L_{\mathrm{MG}}}{d_g\·\sin \mathrm{\θ}}---\left(1.3\right)$

Wherein, N represents the modulus of N longitudinal mode in the resonant cavity, and N is an integer; λ (θ) represents laser oscillation wavelength, and promptly by the selected Wavelength of Laser of grating dispersion (grating dispersion), this optical maser wavelength is relevant with θ, and promptly the value of λ (θ) will change with the variation of θ; L _MGThe optical distance that expression is ordered to G from M point (being the intersection point of the rear surface 106 of optical axis 100 and semiconductor laser 101), the i.e. optical length of exocoel (can abbreviate external cavity length as, down together); d _gThe delineation density (groovingdensity) of expression diffraction grating 103; θ represents the incidence angle of laser beam incident to diffraction grating 103, is the angle of diffraction also.

As shown in Figure 1, L _MGAnd d _gIt generally all is constant; When diffraction grating 103 during around the rotation of above-mentioned fixedly rotating shaft, the big young pathbreaker of diffraction angle changes, and by formula (1.2) as can be known, the laser frequency or the optical maser wavelength of this laser output also will change this moment; And by formula (1.3) as can be known, when the size of diffraction angle changes, modulus N also will change thereupon, and promptly modulus N is not a constant with respect to the change of diffraction angle, thereby when the change of diffraction angle is big, mode hopping (+1 or-1 quantity change takes place the value that is modulus N) will take place; That is to say that laser shown in Figure 1 when coming that by the rotation diffraction grating laser frequency or optical maser wavelength carried out tuning (promptly changing the frequency of output laser) phenomenon of mode hopping will take place.Therefore, above-mentioned Littrow type GTECL only can realize that very little or limited MHF is tuning, and can not carry out the MHF continuous tuning to laser frequency or wavelength.

In the prior art, also has another kind of Littrow type tunable grating external-cavity semiconductor laser.For example, Trutna Jr. is in U.S. Patent No. 6,731, disclosed a kind of tunable grating external-cavity semiconductor laser in 661.Fig. 2 is the schematic diagram of Littrow type tunable grating external-cavity semiconductor laser in the prior art two.As shown in Figure 2, this tunable grating external-cavity semiconductor laser also comprises: semiconductor laser 101, collimating lens 102 and diffraction grating 103.Different with the tunable grating external-cavity semiconductor laser among Fig. 1 is, the rotating shaft of diffraction grating 103 is L among Fig. 2, this rotating shaft L is positioned on the intersection point of rear surface 106 extended lines of the Difraction surface extended line of diffraction grating 103 and semiconductor laser 101, and this rotating shaft L is perpendicular to the paper direction.When diffraction grating 103 during, also can realize tuning to output laser frequency or wavelength around fixing rotating shaft L rotation.

In like manner, according to grating equation: λ (θ)=2d _gSin θ (2.1)

And condition of resonance: $N\·\frac{\mathrm{\λ}}{2}=L_{\mathrm{MG}}\left(\mathrm{\θ}\right)---\left(2.2\right)$

And the optics of intra resonant cavity all is under the situation of perfect condition, can have:

L _MG(θ)＝OM·tanθ(2.3)

Hence one can see that: $N=\frac{\stackrel{\‾}{\mathrm{OM}}}{d_g\·\cos \mathrm{\θ}}---\left(2.4\right)$

Wherein, L _MG(θ) distance of expression from the M point on the rear surface 106 of semiconductor laser 101 to the center on diffraction grating 103 surfaces, i.e. external cavity length; This external cavity length is relevant with θ, i.e. L _MGValue (θ) will change with the variation of θ; OM represents from rotating shaft L to semiconductor laser the distance that the M on 101 the rear surface 106 is ordered.

By formula (2.4) as can be known, as OM and d _gWhen constant, if rotation diffraction grating 103 makes diffraction angle change, then modulus N also will change, and promptly modulus N neither constant with respect to the change of diffraction angle.When the change of diffraction angle is big, mode hopping (+1 or-1 quantity change takes place the value that is modulus N) will take place.Therefore, compare with the tunable grating external-cavity semiconductor laser among Fig. 1, though the tunable grating external-cavity semiconductor laser among Fig. 2 can produce relatively large MHF tuning range, but its modulus N still depends on diffraction angle, therefore, when the excursion of diffraction angle was big, still can't keep N was constant.So, in tunable grating external-cavity semiconductor laser shown in Figure 2, also can't realize MHF continuous tuning to laser frequency.

In order to solve the above problems, in the prior art, by using the Littman-Metcalf cavity resonator structure, made the adjustable GTECL laser of a kind of broadband MHF, i.e. Littman-Metcalf type tunable grating external-cavity semiconductor laser.The structure of the resonant cavity of the laser of the type is disclosed in many pieces of documents or patent.For example, the United States Patent (USP) (No.5 of the United States Patent (USP) of Luecke (No.5,319,668), Sacher, 867,512), the United States Patent (USP) (No.5 of the United States Patent (USP) of Lang (No.5,771,252), Zhang, 802,085) and United States Patent (USP) (No.6,606,340), the United States Patent (USP) (No.6 of the United States Patent (USP) of Zhang (No.6,608,847), Zhang, 788,726), United States Patent (USP) (No.6,940 of Zhang, 879) and the United States Patent (USP) of Le (No.7,388,890) etc.

Fig. 3 is the schematic diagram of Littman-Metcalf type tunable grating external-cavity semiconductor laser in the prior art three.As shown in Figure 3, this Littman-Metcalf type tunable grating external-cavity semiconductor laser also comprises a plane mirror 108 except comprising semiconductor laser 101, collimating lens 102 and diffraction grating 103.Wherein, rotating shaft L is positioned on the intersection point of reflecting surface extended line of the Difraction surface extended line of rear surface 106 extended lines, diffraction grating 103 of semiconductor laser 101 and plane mirror 108, and this rotating shaft L is perpendicular to the paper direction; The Q point is the reflection ray of ordering by G and the intersection point of plane mirror 108.At this tunable grating external-cavity semiconductor laser, diffraction grating 103 maintains static, and plane mirror 108 then can be around fixing rotating shaft L rotation.When plane mirror 108 when rotating shaft L rotates, diffraction angle changes, outer cavity long (being the summation of the light path between two of distance between 2 of M, the G and G, the Q points) also changes; When rotating shaft L is in suitable position, can make the modulus N of this moment remain a constant, thereby it is constant to keep modulus N when laser frequency changes, thereby realizes mode jump free continuous tuning laser frequency.

Analyze as can be known from principle, when if laser design shown in Figure 3 is in the ideal operation state, for example, optical dispersion does not take place in employed optical device in the resonant cavity of this laser, when perhaps the optics in the chamber can be registered to corresponding position exactly, then the semiconductor laser of this Littman-Metcalf type can produce the MHF tuning range that covers whole maximum by the spectral region that diffraction grating produced.But, because the restriction of industrial manufacturing technology and assembling and setting means, in the actual product of tunable grating external-cavity semiconductor laser shown in Figure 3, generally all there is the problem of equipment chromatic dispersion and optics positions misalignment, thereby also limited the MHF tuning range of this laser greatly.

In order to overcome above-mentioned problem, Zhang and Hakuta have proposed a kind of cavity resonator structure with the automatic adjustment of optics positions and passive compensation, so that realize that above-mentioned broadband MHF is tuning.But even so, in the manufacture process of above-mentioned laser, still exist complicated optics and mechanical registeration, the extra material cost of optics, the cavity size and the very slow problems such as tuned speed of super large.

In summary, all exist above-mentioned problems in the prior art in the employed laser, thereby limited the tunable grating external-cavity semiconductor laser greatly in various Application for Field.Therefore, people be starved of a kind of continuous no mode hopping and low cost of manufacture, can batch process, the tunable grating external-cavity semiconductor laser of high stability and compact conformation, to realize mode jump free continuous tuning to laser frequency.

Summary of the invention

In view of this, the main purpose of the embodiment of the invention is to provide a kind of continuous mode-hop-free tunable grating external-cavity diode laser, thereby can realize the mode jump free continuous tuning to laser frequency, and reduces the production cost of described laser.

For achieving the above object, the technical scheme in the embodiment of the invention is achieved in that

A kind of continuous mode-hop-free tunable grating external-cavity diode laser, this laser comprises: at least one optical module of being made up of gain media and collimating lens, tuner and at least one diffraction grating;

The coherent beam that described gain media sent becomes directional light through behind the described collimating lens, described directional light by described diffraction grating diffraction after, the part diffraction light directly becomes the first output laser that is output, another part diffraction light returns in the described gain media along former input path, in described gain media, vibrate, when being amplified to, become the second output laser above the laser oscillation threshold;

Described diffraction grating is arranged on the described tuner; Described tuner drives described diffraction grating and rotates around a rotating shaft that is positioned at the back side of described diffraction grating; Described rotating shaft is parallel with the Difraction surface of described diffraction grating and vertical with the optical axis of laser.

The position of the described rotating shaft that sets in advance satisfies condition: in the tuning process of the output laser frequency of described laser, be a constant by the modulus of the selected longitudinal mode of resonant cavity of described laser.

Radius of turn when described diffraction grating carries out described the rotation is the vertical range of described rotating shaft to the Difraction surface of described diffraction grating.

Described tuner also is used for the position of the described rotating shaft of real time altering, perhaps is used for the relative position of described rotating shaft of real time altering and described diffraction grating.

Described tuner comprises: drive unit and rotating basis; Described rotating basis is connected with described drive unit;

Described rotating basis is used for supporting or installing described diffraction grating;

Described drive unit is used to drive described rotating basis and rotates around described rotating shaft to drive described diffraction grating; And be used for the position of the described rotating shaft of real time altering, perhaps be used for the relative position of described rotating shaft of real time altering and described diffraction grating.

Described drive unit is rotation motor, stepping motor or microelectromechanical systems.

Described tuner also comprises: control device and encoder;

Described encoder is used to follow the tracks of moving of described rotating basis, and tracking results is sent to described control device;

Described control device, be used for according to selected output optical maser wavelength and described tracking results, the mobile of described rotating basis optionally controlled, thereby in the laser of the required frequency of output, the laser frequency of being exported is carried out mode jump free continuous tuning.

Described laser comprises a plurality of diffraction grating;

Described a plurality of diffraction grating is arranged on the described tuner; Described tuner drives described a plurality of diffraction grating all around same rotating shaft rotation; Described rotating shaft is parallel with the Difraction surface of described diffraction grating and vertical with the optical axis of laser;

Described optical module utilizes the mode jump free continuous tuning of any one set on described tuner diffraction grating realization to the laser frequency of required output.

Described laser also comprises: be arranged at the partially reflecting mirror on the light path between described collimating lens and the described diffraction grating;

Described partially reflecting mirror has been used to produce the 3rd output laser and filtering the 4th of spectral noise and has exported laser.

Described partially reflecting mirror is spectroscope, spatial filter or coupled fiber.

Described laser also comprises: coupling device;

Described coupling device is used for a branch of at least output laser coupled with described laser to required single mode or multimode fiber.

Described laser also comprises: be arranged at described tuner one or more groups optical module all around;

Every group of optical module all utilizes the mode jump free continuous tuning of any one set on described tuner diffraction grating realization to the laser frequency of required output.

In summary, provide a kind of continuous mode-hop-free tunable grating external-cavity diode laser in the embodiments of the invention.Because comprise a tuner and at least one diffraction grating in this continuous mode-hop-free tunable grating external-cavity diode laser, diffraction grating is arranged on the tuner; Tuner then is used to drive the rotating shaft rotation of described diffraction grating around a back side that is positioned at this diffraction grating that sets in advance, and this rotating shaft is parallel with the Difraction surface of this diffraction grating and vertical with the optical axis of laser, therefore can realize mode jump free continuous tuning, and reduce the production cost of described laser laser frequency.

Description of drawings

Fig. 1 is the schematic diagram of Littrow type tunable grating external-cavity semiconductor laser in the prior art one.

Fig. 2 is the schematic diagram of Littrow type tunable grating external-cavity semiconductor laser in the prior art two.

Fig. 3 is the schematic diagram of Littman-Metcalf type tunable grating external-cavity semiconductor laser in the prior art three.

Fig. 4 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention one.

Fig. 5 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention one.

Fig. 6 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention two.

Fig. 7 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention three.

Fig. 8 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention four.

Embodiment

For making the purpose, technical solutions and advantages of the present invention express clearlyer, the present invention is further described in more detail below in conjunction with drawings and the specific embodiments.

Fig. 4 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention one.As shown in Figure 4, the tunable grating external-cavity semiconductor laser among the present invention comprises: gain media (gainmedium) 401, collimating lens 402 and diffraction grating 403.Wherein, described gain media 401 and collimating lens 402 can be formed an optical module; Described gain media 401 is used to produce the stable gain of light, and sends coherent beam; For example, this gain media 401 can comprise that the rear surface 406, one of a total reflection or partial reflection are coated with antireflection (AR, anti-reflection) the preceding output surface 407 of coating and a semiconductor laser chip (this chip can be the Fabry-Pero N-type semiconductor N chip of laser of using always, also can be other the device with similar functions); M point among the figure is the intersection point of the rear surface 406 of optical axis 400 and gain media 401; The G point is the intersection point of optical axis 400 and diffraction grating 403; Therefore, the external resonant cavity of this laser (being called for short exocoel, down together) is limited by the rear surface 406 and the diffraction grating 403 of gain media 401.Gain media 401 output surface 407 in the past sends coherent beam, and this coherent beam becomes directional light through behind the described collimating lens 402, and this directional light incides generation diffraction in back on the diffraction grating 403; The light of 403 diffraction of diffracted grating, part diffraction light (for example, zero order diffracted light) can directly become be output first output laser (for example, output laser 404), and another part diffraction light (for example, first-order diffraction light, or the order of diffraction of high-order more) then is back to the rear surface 406 of gain media 401 along former input path, this rear surface 406 is again with the light reflected back diffraction grating 403 that is returned, the rest may be inferred, vibrated in described gain media 401 up to this diffraction light, be amplified to when surpassing the laser oscillation threshold, this diffraction light can be used as the second output laser (for example, output laser 405).Hence one can see that, and the external cavity length in the resonant cavity of this laser is the summation of the light path between M point and the G point.

In order to realize mode jump free continuous tuning to laser frequency, in technical scheme of the present invention, also comprise a tuner 409 in the laser shown in Figure 4, this tuner 409 can be formed a tuning block with above-mentioned diffraction grating 403; Described diffraction grating is arranged on the described tuner; And this tuner 409 is used to drive above-mentioned diffraction grating 403, makes that this diffraction grating 403 can be around the rotating shaft rotation at the back side that is positioned at described diffraction grating that sets in advance; Described rotating shaft parallel with the Difraction surface of described diffraction grating and 400 vertical (be described rotating shaft for by O point and the rotating shaft vertical) with the paper direction with the optical axis of laser, be described rotating shaft not on the extended line of the Difraction surface of described diffraction grating 403, and be positioned at the back side of described diffraction grating 403.In addition, this tuner 409 also can be used for the position (promptly changing the position of described rotating shaft) that real time altering O is ordered, or is used for the relative position (promptly changing the relative position of described rotating shaft and diffraction grating 403) of real time altering O point and diffraction grating 403.Radius of turn when described diffraction grating 403 carries out above-mentioned rotation is: described O point (described rotating shaft) is to the vertical range of the Difraction surface of diffraction grating 403, and the available OP of this distance represents; Wherein, the P point is the intersection point of O point to the Difraction surface of the vertical line of the Difraction surface of diffraction grating 403 and this diffraction grating 403.

In an embodiment of the present invention, when above-mentioned diffraction grating 403 during,, and be positioned at the back side of described diffraction grating 403 because this rotating shaft is on the extended line of the Difraction surface of described diffraction grating 403 around the rotation of above-mentioned rotating shaft; But also can in advance or be provided with the position of this rotating shaft and/or the relative position of this rotating shaft and diffraction grating 403 in real time, therefore the requirement that above-mentioned tunable grating external-cavity semiconductor laser can be tuning according to laser frequency, carry out design flexible, the MHF that satisfies modulus N by the selected longitudinal mode of resonant cavity of described laser and be a constant is tuning, so can realize mode jump free continuous tuning to laser frequency without any need for other control mode that adds or means, and can produce the MHF tuning range that covers whole maximum by the spectral region that diffraction grating produced, thereby simplify the resonator structure of laser, reduce the production cost of described laser.Below will the concrete principle of above-mentioned realization mode jump free continuous tuning be introduced.

Fig. 5 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention one.As shown in Figure 5, when above-mentioned diffraction grating 403 around above-mentioned when crossing rotating shaft that O order and rotating an angle μ, the position of diffraction grating 403 has taken place to move, therefore, the angle of diffraction becomes θ ' by θ, the G point has moved to G ' point, and promptly variation has all taken place for the angle of diffraction of this laser and external cavity length, thereby can utilize above-mentioned variation to realize tuning to laser frequency.

When diffraction grating 403 is in initial condition, when also not beginning to rotate, the angle of diffraction is θ, and the delineation density of establishing diffraction grating 403 is d _g, then according to condition of resonance as can be known, this moment, the centre wavelength by these diffraction grating 403 selected laser was:

λ(θ)＝2d _g·sinθ(4.1)

As shown in Figure 5, when the angle of diffraction was θ, the external cavity length of this laser was that the M point is to the light path summation L between the G point _Light(θ), then as can be known according to grating equation:

Wherein, N (θ) represents when the angle of diffraction is θ, the modulus of N longitudinal mode in the resonant cavity of above-mentioned tunable grating external-cavity semiconductor laser, and N (θ) is an integer.

When tuner 409 drives above-mentioned diffraction grating 403 after the rotating shaft that the above-mentioned O of mistake is ordered rotates to an angle, for example, diffraction grating 403 rotates to the angle of diffraction when being the position of θ ', G point on the Difraction surface of diffraction grating 403 has moved to G ' position, at this moment, the external cavity length of this laser light path summation L that is the M point between G ' _Light(θ '), promptly variation has taken place in the external cavity length of this laser:

L _Light(θ ')=L _Light(θ)-and GG ' (θ ', θ) (4.3)

Wherein, and GG ' (θ ', θ) be the variable quantity of the external cavity length of this laser.

According to the light path among Fig. 5 as can be known:

$\stackrel{\‾}{G{G}^{\′}}({\mathrm{\θ}}^{\′},\mathrm{\θ})=r_0\·\frac{1-\cos (\mathrm{\θ}-{\mathrm{\θ}}^{\′})}{\cos \left({\mathrm{\θ}}^{\′}\right)}+t_0\·\frac{\sin (\mathrm{\θ}-{\mathrm{\θ}}^{\′})}{\cos \left({\mathrm{\θ}}^{\′}\right)}---\left(4.4\right)$

Wherein, r ₀=OP=OP ', t ₀=GP, OP, OP ' and GP represent an O respectively to the distance between some P, P ' and the some G, and GP represents that the G point is to the distance between the P point.According to as can be known shown in Figure 5, r ₀And t ₀Be that the position of ordering with O has the parameter of determining relation; After position that O is ordered is determined, perhaps after the relative position of O point and diffraction grating 403 is definite, r ₀And t ₀Value also just be determined thereupon; Conversely speaking, also can be according to r ₀And t ₀Value determine the position of some O or the relative position of definite O point and diffraction grating 403.

When the angle of diffraction is θ ' time, if N (θ ') is illustrated in the modulus of N longitudinal mode in the resonant cavity of above-mentioned tunable grating external-cavity semiconductor laser, and N (θ ') is an integer, and λ (θ ') is for having the centre wavelength by these diffraction grating 403 selected laser, this moment:

λ(θ′)＝2d _g·sinθ′，

According to above-mentioned formula (4.1)～(4.5) as can be known:

$\frac{N\left({\mathrm{\θ}}^{\′}\right)}{N\left(\mathrm{\θ}\right)}=\frac{\sin \left(\mathrm{\θ}\right)}{\sin \left({\mathrm{\θ}}^{\′}\right)}[1-{\mathrm{\α}}_1\·\frac{1-\cos (\mathrm{\θ}-{\mathrm{\θ}}^{\′})}{\cos \left({\mathrm{\θ}}^{\′}\right)}-{\mathrm{\α}}_2\·\frac{\sin (\mathrm{\θ}-{\mathrm{\θ}}^{\′})}{\cos \left({\mathrm{\θ}}^{\′}\right)}]---\left(4.6\right)$

Wherein, α ₁=r ₀/ L _Light(θ) and α ₂=t ₀/ L _Light(θ).Described α ₁And α ₂Expression can be by changing the position r of rotating shaft ₀And t ₀, or the relative position that changes rotating shaft and diffraction grating is adjusted the size of value of modulus N of the resonant cavity longitudinal mode of laser.

By above-mentioned formula (4.6) as can be known, in order to realize that all laser frequencies are all realized the MHF continuous tuning, then in the tuning process of whole laser frequency, all need to make by the modulus N (θ) of the selected longitudinal mode of resonant cavity ' be a constant, promptly satisfy the mode jump free continuous tuning condition:

N (θ ')/N (θ)=1, or | N (θ ')-N (θ) |≤1 (4.7)

In the laser in actual application environment, because the gain bandwidth of gain media 11 is limited, therefore only need satisfy above-mentioned mode jump free continuous tuning condition, can guarantee to carry out mode jump free continuous tuning in the given frequency range in above-mentioned finite gain bandwidth.By above-mentioned formula (4.6) as can be known, only need the suitable r that adjusts in the formula (4.6) ₀And t ₀, then can satisfy above-mentioned mode jump free continuous tuning condition at an easy rate, thereby can easily realize all laser frequencies are all realized the MHF continuous tuning.

Because the change of the position (being the position that O is ordered) of diffraction grating 403 and/or rotating shaft will cause above-mentioned r ₀And t ₀The change of value, therefore, in technical scheme of the present invention, also can adjust in real time with the mode that adds FEEDBACK CONTROL by the position (being the position of described rotating shaft) that O is ordered, perhaps, change two above-mentioned coordinate r by the absolute position that diffraction grating 403 and O are ordered or the real-time adjustment of relative position ₀And t ₀Value, make above-mentioned mode jump free continuous tuning condition on bigger frequency tuning range, to be met.

As shown in Figure 5, after position that O is ordered is determined, perhaps after the relative position of O point and diffraction grating 403 is definite, r ₀And t ₀Value also be determined thereupon.Therefore, in technical scheme of the present invention, can be according to practical situations, select the position that O is ordered in advance or in real time, the relative position of perhaps in advance or in real time selected O point and diffraction grating 403, make described diffraction grating 403 around order by O perpendicular to the rotation of the rotating shaft of paper direction the time, the cavity length of the laser at these diffraction grating 403 places has suitable length exporting the laser of required frequency, and realizes the mode jump free continuous tuning to the laser frequency of being exported.

In technical scheme of the present invention, the rotation selected and diffraction grating 403 of the relative position of the above-mentioned position that O is ordered or O point and diffraction grating 403 all can be realized by tuner 409.Described tuner 409 can be a various fixing or dynamic apparatus for adjusting position commonly used in the art.For example, in specific embodiments of the invention, can comprise a drive unit and rotating basis (base) (all not shown among Fig. 4 and Fig. 5) in the described tuner 409.Described diffraction grating 403 is arranged on the described rotating basis, and described rotating basis is connected with drive unit, and this rotating basis can be used for supporting or described diffraction grating 403 being installed, and can change the position of diffraction grating 403 according to the driving of drive unit; Described drive unit, can be used for driving described rotating basis rotates around described rotating shaft to drive described diffraction grating 403, also can be used to change the position that O orders or the relative position of O point and diffraction grating 403, thereby make that this diffraction grating 403 can be around rotating to the desired position by O point and the rotating shaft vertical with the paper direction.Wherein, described drive unit can be rotation motor, stepping motor, microelectromechanical systems (MEMS), or other can realize the equipment of above-mentioned driving; The connected mode of described drive unit and rotating basis can be used direct fixed form, and (for example, the swivel bearing of rotation motor or stepping motor is directly fixedlyed connected with rotating basis, or fixedlys connected by the universal joint transition and with rotating basis; The connection of swivel bearing guarantees that rotating basis can rotate or mobile shaft by O point and the rotating shaft vertical with paper), or the connected mode of using always in other this area, do not repeat them here.

In addition, in described tuner 409, also can comprise control device and encoder (for example, linear encoder or motor rotary encoder; All not shown among Fig. 4 and Fig. 5).Wherein, described encoder is used to follow the tracks of moving of rotating basis, and tracking results is sent to described control device.Moving of described rotating basis can be that translation, rotation or translation add rotation.Wherein, the translation by rotating basis can change the position of described rotating shaft or change the relative position of described rotating shaft and described diffraction grating; The rotation of described rotating basis then can make the diffraction grating on the described rotating basis rotate around described rotating shaft.Described control device then is used for according to selected output Wavelength of Laser and described tracking results, the mobile of rotating basis optionally controlled, thereby in the laser of the required frequency of output, the laser frequency of being exported is carried out mode jump free continuous tuning.Hence one can see that, by aforesaid tuner 409, can realize the mode jump free continuous tuning to the laser frequency of being exported in the laser of the required frequency of output.

In tunable grating external-cavity semiconductor laser shown in Figure 5, can be used as having of output laser: 1) the formed output laser of directly exporting by the Difraction surface reflection back of diffraction grating 403 404 of laser; 2) by the Difraction surface reflected back gain media 401 of diffraction grating 403, and after in gain media 401, amplifying, from the output laser 405 of rear surface 406 outputs of gain media 401 through vibration.

But, in above-mentioned output laser 404 and output laser 405, all there is higher relatively spectrum " noise ", this spectrum " noise " is for deriving from the light source spontaneous radiation (SSE in the gain media 401, source spontaneous emission) and amplified spontaneous emission (ASE, amplified spontaneousemission).The existence of above-mentioned spectrum " noise " has caused adverse influence for the coherence and the intensity of the laser of being exported.Therefore, in technical scheme of the present invention, also can in tunable grating external-cavity semiconductor laser shown in Figure 5, add a partially reflecting mirror, be used for the spectrum " noise " (promptly exporting ASE and SSE composition in the laser) of " removing " above-mentioned output laser.

Fig. 6 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention two.As shown in Figure 6, tunable grating external-cavity semiconductor laser among the present invention is except comprising gain media 401, collimating lens 402, diffraction grating 403 and tuner 409, also comprise a partially reflecting mirror 601 on the light path that is arranged between collimating lens 402 and the diffraction grating 403, this partially reflecting mirror 601 can be set up or rotate to required arbitrarily angled according to the actual requirements, is used for the spectral noise of filtering output laser.Preferable, this partially reflecting mirror 601 can be the spatial filter of spectroscope or other form.Because the wavelength of described spectrum " noise " is different from the optical maser wavelength of being exported, on spatial distribution, above-mentioned spectrum " noise " can be expelled or be departed from the light path of described output laser by the diffraction of diffraction grating 403.Therefore, can be by inserting the above-mentioned spectrum " noise " in next thoroughly " removing " the described output laser of above-mentioned partially reflecting mirror (for example, spectroscope, spatial filter or coupled fiber).

In an embodiment of the present invention, above-mentioned partially reflecting mirror 601 is exported respectively after the laser by this partially reflecting mirror 601 can being divided into two bundle laser, beam of laser wherein is output laser 602, because " removings " of above-mentioned partially reflecting mirror 601 acts on, thereby make and no longer comprise above-mentioned spectrum " noise " (promptly not comprising ASE and SSE composition in this output laser 602) in this output laser 602; Another Shu Jiguang is output laser 603, and this output laser 603 is traditional tunable laser bundle, wherein still comprises above-mentioned spectrum " noise " (promptly still comprising ASE and SSE composition in this output laser 603), and opposite with the direction of above-mentioned output laser 602.

By tunable grating external-cavity semiconductor laser as shown in Figure 6, we (are for example obtaining traditional tunable laser bundle, output laser 404,405,603 etc.) time, (for example can also obtain to remove spectrum " noise " laser beam (promptly not comprising ASE and SSE composition), that have high coherence, high spectral purity, output laser 602), thereby improved the performance of above-mentioned tunable grating external-cavity semiconductor laser, expanded the range of application of above-mentioned tunable grating external-cavity semiconductor laser effectively.

In addition; in an embodiment of the present invention; for the mode jump free continuous tuning laser that above-mentioned tunable grating external-cavity semiconductor laser is produced is realized coupling with corresponding single mode or multimode fiber 620; can also comprise a coupling device 610 as shown in Figure 6 in the above-mentioned tunable grating external-cavity semiconductor laser, this coupling device 610 can be used for output laser coupled with above-mentioned laser in required single mode or multimode fiber 620.Below, we will be example with output laser 405, and technical scheme of the present invention is introduced.

This coupling device 610 comprises: light beam harvester 611, optical isolator 612 and calibration lens 613.Wherein, light beam harvester 611 is used to gather the output laser 405 from rear surface 406 outputs of above-mentioned gain media 401, and the output laser that will collect is transported to optical isolator 612; Described optical isolator 612 is used to prevent the interference of external feedback light, and realizes the unidirectional output of above-mentioned output laser; Described calibration lens 613 are used for the laser of described optical isolator 612 outputs is collimated, and make the laser of this output become parallel laser beam; Perhaps be used for the laser of described optical isolator 612 outputs is focused on, make the laser of this output be coupled in the corresponding optical fiber 620.

In addition, on the direction of the output laser 404,603 of above-mentioned tunable grating external-cavity semiconductor laser or 602, also can use above-mentioned coupling device 610 respectively, thus with above-mentioned output laser coupled in required optical fiber.

In technical scheme of the present invention, also can the tuning block in the above-mentioned tunable grating external-cavity semiconductor laser be further improved, with multiple scanning speed (sweeping rate) and the tuned speed that improves above-mentioned tunable grating external-cavity semiconductor laser.

Fig. 7 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention three.As shown in Figure 7, the tunable grating external-cavity semiconductor laser among the present invention comprises: gain media 401, collimating lens 402, tuner 409, partially reflecting mirror 601, coupling device 610 and at least one diffraction grating 403.In specific embodiments of the invention, above-mentioned tunable grating external-cavity semiconductor laser can comprise one or more diffraction grating 403, but, will be that example describes below to comprise three diffraction grating 403 in this tunable grating external-cavity semiconductor laser in order better technical scheme of the present invention to be introduced.

As shown in Figure 7, above-mentioned three diffraction grating 403 are arranged on the tuner 409, thereby form a tuning block with this tuner 409.Described tuner 409 comprises: the rotating basis (base) and the drive unit that are used to install and support described diffraction grating 403; Described rotating basis is connected with described drive unit; Described ways of connecting can be a connected mode commonly used in this area, and for example, described rotating basis can be connected by swivel bearing (rotation bearing) with described stepping motor.Wherein, described three diffraction grating 403 are arranged on the rotating basis of tuner 409; This rotating basis can be around by the O point and perpendicular to the rotation of the rotating shaft of paper direction; Described stepping motor, can be used for driving described rotating basis by described swivel bearing, make this rotating basis to be rotated according to the rotary speed that is provided with, be arranged on the position of each diffraction grating 403 on the rotating basis with change, make the position of the some diffraction grating 403 in above-mentioned a plurality of (Figure 7 shows that three) diffraction grating 403 can satisfy the mode jump free continuous tuning condition, thereby realize mode jump free continuous tuning the laser frequency of the required output of laser.

In above-mentioned tunable grating external-cavity semiconductor laser, described tuner can drive above-mentioned a plurality of grating all around same rotating shaft (being above-mentioned by the O point and perpendicular to the rotating shaft of paper direction) rotation, the radius of turn of each diffraction grating can be identical, also can be different, can adjust according to actual needs, be that the position of described three diffraction grating on described tuner 409 (comprises the angle between each diffraction grating, the distance that the relative position that each diffraction grating and O are ordered and each diffraction grating are ordered to O), all can determine according to formula (4.6) and actual applied environment; In addition, above-mentioned drive unit can be that stepping motor or other can be realized the equipment of above-mentioned driving.

As shown in Figure 7 as can be known, owing to have a plurality of diffraction grating in the above-mentioned tunable grating external-cavity semiconductor laser, therefore at described tuner 409 in by O point and the process that rotates a circle perpendicular to the rotating shaft of paper direction, each optical module of being made up of gain media and collimating lens all can utilize the mode jump free continuous tuning of any one set on described tuner diffraction grating realization to the laser frequency of required output, therefore this tunable grating external-cavity semiconductor laser can carry out repeatedly mode jump free continuous tuning by above-mentioned a plurality of diffraction grating to the laser of being exported respectively, thereby reduced the cycle between each mode jump free continuous tuning, improved the sweep speed and the tuned speed of above-mentioned tunable grating external-cavity semiconductor laser.

In addition, in tunable grating external-cavity semiconductor laser shown in Figure 7, a diffraction grating can be comprised, also a plurality of diffraction grating can be comprised.The number of above-mentioned diffraction grating can set in advance according to concrete actual demand.

In addition, in tunable grating external-cavity semiconductor laser shown in Figure 7, also can select whether to be provided with above-mentioned partially reflecting mirror 601 and/or coupling device 610 according to actual needs, promptly above-mentioned partially reflecting mirror 601 and coupling device 610 are not the necessary component in the above-mentioned tunable grating external-cavity semiconductor laser.

Fig. 8 is the schematic diagram of the tunable grating external-cavity semiconductor laser in the embodiment of the invention four.As shown in Figure 8, in order better to improve the utilance of above-mentioned diffraction grating, can also around the tuner in the tunable grating external-cavity semiconductor laser 409, one or more groups optical module be set.Wherein, every group of optical module all comprises a gain media 401 and a collimating lens 402, also can comprise partially reflecting mirror 601 and coupling device 610.Therefore, when tuner 409 when rotating by the O point and perpendicular to the rotating shaft of paper direction, every group of optical module all can utilize the mode jump free continuous tuning of any one set on the tuner 409 diffraction grating realization to the laser frequency of required output separately, thereby can further improve utilance to above-mentioned diffraction grating, reduce the cycle between each mode jump free continuous tuning, improve the sweep speed and the tuned speed of above-mentioned tunable grating external-cavity semiconductor laser, realize the output of multi-pass laser.

In addition, among Fig. 8 in set many groups optical module, optical module on the same group can not selected different gain medias, different collimating lens, different diffraction grating or different partially reflecting mirrors, produce the output laser of different wave length, to realize unique multi-wavelength, the output of multi-pass laser.

In summary, in technical scheme of the present invention, provide the continuous mode-hop-free tunable grating external-cavity diode laser of various ways.The said structure compactness that is provided among the application of the invention embodiment, can realize multi-functional output continuous mode-hop-free tunable grating external-cavity diode laser, can realize mode jump free continuous tuning to laser frequency, and can reduce production costs, improve the sweep speed and the tuned speed of laser, therefore thereby make above-mentioned continuous mode-hop-free tunable grating external-cavity diode laser have bigger MHF tuning capability, can be widely used in that laser absorption spectrum is measured (high-resolution laser metrology) and such as atomic clock, laser cooling/laser trap, in the spectrum sensors (spectroscopic sensor) such as battlefield (on-field) biochemical analysis device.

In addition, because the continuous mode-hop-free tunable grating external-cavity diode laser that is provided in the technical scheme of the present invention is the tunable grating external-cavity semiconductor laser of Littrow type, therefore very compactness and form are simple for the cavity resonator structure of laser, and can realize multi-functional output, thereby can realize simplifying very much and manufacture process cheaply, and have cost low, can batch process, advantage such as high stability and compact conformation.

The above is preferred embodiment of the present invention only, is not to be used to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (12)

1, a kind of continuous mode-hop-free tunable grating external-cavity diode laser is characterized in that, this laser comprises: at least one optical module of being made up of gain media and collimating lens, tuner and at least one diffraction grating;

The coherent beam that described gain media sent becomes directional light through behind the described collimating lens, described directional light by described diffraction grating diffraction after, the part diffraction light directly becomes the first output laser that is output, another part diffraction light returns in the described gain media along former input path, in described gain media, vibrate, when being amplified to, become the second output laser above the laser oscillation threshold;

Described diffraction grating is arranged on the described tuner; Described tuner drives described diffraction grating and rotates around a rotating shaft that is positioned at the back side of described diffraction grating; Described rotating shaft is parallel with the Difraction surface of described diffraction grating and vertical with the optical axis of laser.

2, laser according to claim 1 is characterized in that,

The position of the described rotating shaft that sets in advance satisfies condition: in the tuning process of the output laser frequency of described laser, be a constant by the modulus of the selected longitudinal mode of resonant cavity of described laser.

3, laser according to claim 1 is characterized in that:

Radius of turn when described diffraction grating carries out described the rotation is the vertical range of described rotating shaft to the Difraction surface of described diffraction grating.

4, laser according to claim 1 is characterized in that:

Described tuner also is used for the position of the described rotating shaft of real time altering, perhaps is used for the relative position of described rotating shaft of real time altering and described diffraction grating.

5, laser according to claim 4 is characterized in that, described tuner comprises: drive unit and rotating basis; Described rotating basis is connected with described drive unit;

Described rotating basis is used for supporting or installing described diffraction grating;

Described drive unit is used to drive described rotating basis and rotates around described rotating shaft to drive described diffraction grating; And be used for the position of the described rotating shaft of real time altering, perhaps be used for the relative position of described rotating shaft of real time altering and described diffraction grating.

6, laser according to claim 5 is characterized in that:

Described drive unit is rotation motor, stepping motor or microelectromechanical systems.

7, laser according to claim 5 is characterized in that, described tuner also comprises: control device and encoder;

Described encoder is used to follow the tracks of moving of described rotating basis, and tracking results is sent to described control device;

Described control device, be used for according to selected output optical maser wavelength and described tracking results, the mobile of described rotating basis optionally controlled, thereby in the laser of the required frequency of output, the laser frequency of being exported is carried out mode jump free continuous tuning.

8, laser according to claim 1 is characterized in that,

Described laser comprises a plurality of diffraction grating;

Described a plurality of diffraction grating is arranged on the described tuner; Described tuner drives described a plurality of diffraction grating all around same rotating shaft rotation; Described rotating shaft is parallel with the Difraction surface of described diffraction grating and vertical with the optical axis of laser;

Described optical module utilizes the mode jump free continuous tuning of any one set on described tuner diffraction grating realization to the laser frequency of required output.

9, laser according to claim 1 is characterized in that, described laser also comprises: be arranged at the partially reflecting mirror on the light path between described collimating lens and the described diffraction grating;

Described partially reflecting mirror has been used to produce the 3rd output laser and filtering the 4th of spectral noise and has exported laser.

10, laser according to claim 9 is characterized in that:

Described partially reflecting mirror is spectroscope, spatial filter or coupled fiber.

11, according to claim 1 or 9 described lasers, it is characterized in that described laser also comprises: coupling device;

Described coupling device is used for a branch of at least output laser coupled with described laser to required single mode or multimode fiber.

12, laser according to claim 1 is characterized in that, described laser also comprises: be arranged at described tuner one or more groups optical module all around;

Every group of optical module all utilizes the mode jump free continuous tuning of any one set on described tuner diffraction grating realization to the laser frequency of required output.

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