CN200987037Y - Q-modulated semiconductor laser device with electroabsorption line structure - Google Patents

Abstract

The utility model discloses a Q-modulating semiconductor laser with an electroabsorption grating structure, which comprises a distributed feedback grating with a lambada/4 phase shift. Two upper electrodes, separating from each other reciprocally, deposit on the top of the grating. One electrode deposits on the base of the laser as a public place. The first upper electrode, covering a part of the grating, comprises a phase shift area and provides light gain for the laser through the inserted constant current. The second electrode, covering the rest of the grating away from the phase shift area, is the Q-modulator of the laser. The electric signal adds to the second electrode to change the wave guide absorption coefficient of the modulator area with the electroabsorption grating structure and the Q value of the laser, thus changing the laser threshold and the output power. The Q-modulating semiconductor laser of the utility model has the advantage of integration, high speed, high extinction ratio, low wavelength chirp and low cost and so on.

Description

A kind of Q-semiconductor laser modulation that has electric absorption grating structure

Technical field

The utility model relates to semiconductor laser and modulator, relate in particular to a kind of with utilize electric current to inject or the electric absorption effect changes the Q-modulator single chip integrated quarter-wave phase shift distributed feedback laser or the distributed Bragg reflection laser of laser quality factor.

Background technology

High speed semiconductor laser and modulator are the key elements of current optical fibre communication system.Increasing sharply of internet transmission amount requires these optical elements can handle the bit rate that more strengthens.Directly carrying out the light signal strength modulation by the bias current that changes laser is the simplest method, and it does not need an external modulator.But directly the laser of modulation has basic speed limit, and shows building up, and its frequency equals its relaxation oscillation frequency.Wavelength chirp is another problem of direct modulated laser.When the input drive current of laser changed, carrying object density and refractive index be all along with variation, thereby make wavelength also along with change.Optical maser wavelength changes respectively round about when pulse is risen and descend.Bit rate is high more, and it is obvious to warble, and its effect is widened laser linewidth.Phenomenon is serious under wideer laser linewidth situation because CHROMATIC DISPERSION IN FIBER OPTICS effect, pulse broaden, thus the restriction transmission range.

People can allow laser works at continuous wave (CW) state, and modulate it with an external modulator.Can eliminate the problem of above-mentioned building up like this, and reduce and warble.Electroabsorption modulator (EAM) is a fine selection as external modulator, and it is by applying the absorption coefficient that a signal of telecommunication changes it.When modulator is that the output beam of laser during at the state of opening can pass to low-loss modulator, and when modulator be that light energy will be by portion's absorption greatly during at the state that closes.The advantage of this electroabsorption modulator and other modulator comparison is: low driving voltage, and small size, and can be integrated with distributed feed-back (DFB) or distributed Bragg reflector (DBR) laser monolithic.The structure and the laser of electroabsorption modulator are closely similar, and just its active layer forbidden band band gap is slightly different.Another difference is that it is to be operated in reverse bias condition.When the reverse biased of input data signal change modulator, the absorption coefficient of modulator waveguide changes, thus the variation that causes exporting optical power.

Though relatively directly the modulated laser electroabsorption modulator has significantly improved the performance of warbling, the problem of warbling still exists, because variations in refractive index is accompanied by the modulation of absorption coefficient inevitably.And modulator to warble be dynamic, change along with the variation of actual driving voltage.Can now electroabsorption modulator can provide the modulation rate of about 10Gb/s, reach higher speed (more than 40Gb/s) and do not cause that sizable parasitic phase modulation can't affirm simultaneously.And its extinction ratio performance is undesirable, and inserts to exist between the performances such as loss and speed and meet each other half way.In addition, single chip integrated Electroabsorption Modulated Laser (EML) needs repeatedly epitaxial growth, so complex process, the manufacturing cost costliness.

The method of another kind of light modulated is to use Mach-Ceng Te (Mach-Zehnder is called for short MZ) interferometer, makes of the material (as lithium niobate LiNbO3 crystal) with strong electro optic effect.Change refractive index and optical path length by applying voltage, the phase contraposition that makes optical signalling propagate in every road of MZ interferometer is mutually modulated.The light beam of two out of phase modulation is just combined and can convert phase modulated to intensity modulated.If the phase modulated in two light paths is equal and opposite in direction but opposite in sign just in time, this modulator will not have any warbling, and this means that output signal has only intensity modulated and do not have parasitic phase place or frequency modulation(FM).But this external modulator is very expensive, and be difficult to and the laser monolithic integrated, only be used at present in long distance and the extra long distance transmission system.

Summary of the invention

The purpose of this utility model is at the deficiencies in the prior art, propose a kind of Q-semiconductor laser modulation that has an electric absorption grating structure with at a high speed, the monolithic of the low modulator of warbling is integrated, solve conventional semiconductor laser and modulator cost height, not easy of integration, wavelength chirp is made problems such as complexity.

The purpose of this utility model is achieved through the following technical solutions:

A kind of Q-semiconductor laser modulation that has electric absorption grating structure, comprise a phase shift distributed feedback grating that is embedded in the active waveguide structure, two first top electrodes that are separated from each other and second top electrode are covered in top and bottom electrode as the common ground face of gain regions and modulator region respectively; Described phase shift distributed feedback grating is divided into first, second portion and third part successively, and wherein first and second portion are separated by phase-shifted region; Described first top electrode that is deposited on gain regions covers first, second portion and the phase region therebetween of described grating, and a constant current injected active optical waveguide under this electrode, described second top electrode that is covered in modulator region covers the third part of described grating.

Phase shift in the described phase shift distributed feedback grating equals quarter-wave.

The relative opposite side of grating pattern of phase-shifted region one side is counter-rotating mutually in the described phase shift distributed feedback grating.

Phase-shifted region in the described phase shift distributed feedback grating comprises one section waveguide with different effective refractive indexs.

The operation wavelength of the corresponding laser in center, forbidden band of described third part grating cycle decision.

The loss of described modulator region fiber waveguide changes along with forward biased current signal.

The loss of described modulator region fiber waveguide changes along with back-biased voltage signal.

The beneficial effect that the utlity model has is:

The utility model utilize a new principle mechanisms with semiconductor laser with at a high speed, the low Q-modulator monolithic of warbling is integrated, realize high-performance, undersized generating laser, have low cost and the making simple advantage similar simultaneously with direct modulated laser.

2. the utility model has multiple different specific constructive form, comprises based on different structures such as quarter-wave phase shift distributed feedback laser and distributed Bragg grating lasers.

3. the utility model is separated the zone of modulation function and gain function, the latter is by the constant current pumping, this has not only reduced wavelength chirp, also improved modulating speed, therefore with respect to direct modulation or external electroabsorption modulator, modulator length of the present utility model is wanted much shorter, thereby littler electric capacity is arranged, higher speed.

4. the utlity model has integrated, at a high speed, advantages such as High Extinction Ratio, low wavelength chirp and low cost.

Description of drawings

Fig. 1 is based on the schematic diagram of the Q-semiconductor laser modulation of first kind of implementation method of the present utility model, and its structure has distributed feed-back (DFB) grating of quarter-wave phase shift.

Fig. 2 is that modulator region is in transparent (unlatching) and during (closing) state of absorption, light is from the reflectance spectrum of gain region one side incident laser device structure.

Fig. 3 is that the modulator region absorption coefficient is respectively i) α=0; Ii) α=500cm ^-1Iii) α=500cm ^-1And refractive index has increased by 0.005 o'clock DBR grating reflection spectrum (a) and phase change on reflection (b) in modulator one side of phase-shifted region.

Fig. 4 is that the absorption coefficient of modulator region is respectively α=0, and α=500cm ^-1The time laser structure transmission small signal gain spectrum.

Fig. 5 is the functional relation of the gain for threshold value coefficient and the modulator absorption coefficient of laser.

Fig. 6 is modulator light distribution in the laser structure when being in unlatching (a) respectively and closing (b) state.Wherein phase shift is produced by the quarter-wave displacement.

Fig. 7 is the light distribution in the laser structure when modulator is in unlatching (a) and cuts out (b) state.Wherein phase shift is to be realized by one the 50 long grating fragment with different effective refractive indexs of μ m.

Fig. 8 is based on the schematic diagram of the Q-semiconductor laser modulation of second kind of implementation method of the present utility model, and its structure has the distributed Bragg reflection optical grid.

Embodiment

Below with reference to the accompanying drawings and embodiment, describe the utility model in detail.

Q-semiconductor laser modulation of the present utility model has multiple different concrete structure, and wherein laser resonator can be respectively based on the distributed feed-back that has phase shift (DFB) grating or distributed Bragg reflection (DBR) grating.

The Q factor of laser resonator or claim that quality factor is what to be used for weighing be fed by optical resonantor from the light of laser gain medium, the high Q factor mean that light propagates each and be subjected to less loss back and forth in resonator.The principle of Q-modulation is to utilize a device that can change the resonator Q factor to change the laser Output optical power, and this has been applied in the accent Q dyestuff or solid state laser that produces periodic short pulse.Usually realize transferring the art methods of Q to comprise: in optical resonator, use revolving mirror, or use electric light or acousto-optic modulator.But these methods are all infeasible for small semiconductor laser.

For the modulation of semiconductor laser, reducing wavelength chirp is the aspect that very important needs are considered.The United States Patent (USP) 4 of authorizing on May 19th, 1,667, R.C.Alferness etc. has described the method for placing electric modulator in laserresonator in 331, but this method is insuperior feasible, because make the complexity, also can introduce and the similarly significant wavelength chirp of direct modulated laser except increasing.

2003 on February 11, authorize United States Patent (USP) 6,519,270 in, H.B.Kim and J.J.Hong has described a composite chamber laser that is shaped as by distribution as unimodal feedback laser and passive optical waveguide set of regions.Refractive index by the modulation passive wave guide, thereby the phase place of cleavage surface effective reflectivity after the modulation passive wave guide, and then the modulated laser frequency, resemble the narrow-band optical filter that constitutes by the Mach-Zehnder interferometer by placing one then in the laser front, frequency modulation(FM) is converted into intensity modulated.Though this modulator also is the rear end that is placed on laser, what it changed is not the Q value of laser, and is phase place, causes the modulation rather than the intensity modulated of frequency.Frequency modulation(FM) is converted into the needed narrow band filter of intensity modulated makes it be difficult to be applied to common communication system, needed active-the integrated making that also makes device of the passive wave guide difficulty and expensive that becomes.

One piece is entitled as " Q-modulation of a surface emitting laser and an integrated detunedcavity ", S.R.A.Dods, and M.Ogura, IEEE Journal of Quantum Electronics, vol.30, pp.1204-1211,1994 paper describe and have analyzed and the vertical integrated surface emitting vertical cavity laser of an off resonance cavity, can realize the modulation of laser intensity by the refractive index in the change off resonance cavity.Same principle is used in the United States Patent (USP) 6,215,805 of the B.Sartorius and M.Moehrle that authorizes 2004 on April 10.In above two prior aries, a resonant cavity that reflector is a micro-off resonance of laser chamber, its reflectivity highly dispersed on the laser works wavelength that is to say that reflectance spectrum shows a sharp-pointed undershoot near optical maser wavelength.High reflectivity chromatic dispersion is essential, and small variations in refractive index just can cause the very big change of reflector reflectivity in the resonant cavity of off resonance like this, thus modulated laser output.Yet, this art methods has very big defective: 1) under nearly condition of resonance, the reflectivity height depends on wavelength, therefore need require accurately to proofread and correct their resonance wavelength according to the off resonance between pre-determined two resonant cavitys, this is difficulty very, and is also very sensitive to making.2) reflectivity change that refraction index changing causes in the off resonance cavity is accompanied by very big phase change, and this will cause the very high-chip of optical maser wavelength.

For having overcome the defective of prior art approach, the utility model people has proposed a kind of new structure in a relevant Chinese invention patent application (application number is 200610050484.6), by using the back reflector of an antiresonance chamber as semiconductor laser, the reflectivity of this reflector can change by the optical absorption that changes antiresonance chamber inner waveguide material.Compare with resonant cavity, the reflectivity in antiresonance chamber and the reflectance varies that caused by optical loss modulation weaken greatly to the dependence of wavelength, and caused phase change is also quite little during reflectivity change, so wavelength chirp is very low.Usually need the air groove of vertical deep erosion to realize that the monolithic in laserresonator and modulator antiresonance chamber is integrated in the said structure.

The utility model discloses another kind of Q-semiconductor laser modulation structure, realizes the modulation of reflectivity and laser quality factor by the absorption coefficient that changes rear reflector part grating, does not need the air groove of vertical deep erosion.The structural design of laser and its rear reflector makes that its reflected phase will is almost constant when reflectivity change, and therefore this implementation method only can be introduced very little wavelength chirp.Its modulation scheme do not need to use to wavelength sensitive cavity resonator structure.The variation of optical loss can be injected by electric current and be realized, can use and the gain medium identical materials, has therefore simplified making greatly.To describe the details of the monolithic Q-semiconductor laser modulation structure that realizes above mechanism below in detail.

Fig. 1 is first kind of concrete structure of implementing of the present utility model, it be one with the single chip integrated distribution as unimodal feedback semiconductor laser that has the quarter-wave phase shift of electric absorption Q-modulator, comprise the DFB grating 130 of a λ/4 phase shifts, be divided into gain regions and modulator region.Gain regions comprises phase-shifted region 100, and the waveguide that has grating 101 and 102 districts that are positioned at the phase-shifted region both sides.Gain regions is covered by first top electrode 108, and is sandwiched between first top electrode 108 and the grounding electrode 120.When direct current injected by first top electrode 108, gain regions provided the gain of light for laser.Modulator region 105 is residue grating parts of leaving phase-shifted region, laser is played the effect of Q-modulation.The signal of telecommunication is added in modulator region by second top electrode 110, changes the Q value of laser by the absorption coefficient that changes this zone waveguide, thereby changes threshold current and power output.Light beam 140 is from the front end face of gain regions, the end face outgoing of just opposite with a modulator side.

Waveguiding structure generally comprises resilient coating 116, and the waveguide core layer 114 and the surface coating 112 of the gain of light is provided during the electric pump Pu, and they all are deposited in the substrate 118.Waveguide core layer 114 preferably comprises multi-quantum pit structure, and resembles suitable doping the conventional laser structure sheaf in each layer.On cross section, waveguide is processed to the ridge waveguide of standard, also to obtain the restriction of optical mode in the horizontal direction.The upper surface that isolated mutually top electrode 108 and electrode 110 are deposited on gain regions and modulator region respectively, the back side of substrate also deposits layer of metal electrode 120 as public grounding electrode.Electrode pair 108/120 is used for injecting so that the gain of light to be provided for active gain regions carries out electric current.Thereby electrode pair 110/120 is used for changing the absorption coefficient (utilize electric current inject or reverse biased) of modulator region waveguide changes the Q value of laser.

Can use different waveguide material structures to make these two zones be optimized respectively at gain regions and modulator region.In the actual fabrication process, this can realize by band gap engineering after etching-regrowth techniques or the growth such as the quantum well hybrid technology.Simpler way then is to adopt same laser layer structure, but applies different voltage or electric current, to obtain two performances that the zone is different.Gain regions adopts strong electric current pumping to produce the gain of light, and modulator region then changes between transparent (little electric current injection) and (zero current injection) two states of absorption.

In order to illustrate the operation principle of the utility model Q-modulated laser, we consider a concrete example.In this example, the rectangular distribution of grating index, and n ₁=3.215, n ₂=3.21 (Δ n=0.005), the grating cycle is Λ=0.2412 μ m, operation wavelength is λ=1550nm.The modulator zone length L _m=150 μ m.The gain region total length is 400 μ m, and (length that is to say zone 101 and 102 is respectively L to λ/4 phase-shifted region distance modulated devices, 100 μ m ₁=300 μ m, and L ₂=100 μ m).Laser cavity Q value can be obtained by Q=λ/Δ λ, and wherein Δ λ is the live width of the resonance peak of transmissivity or reflectance spectrum when gain regions is pellucidity.

Fig. 2 is that modulator region is in transparent (unlatching) and during (closing) state of absorption, light incides the reflectance spectrum of this laser structure from gain regions one side.Wherein, establish the modulation areas absorption coefficient and be respectively α=0 (opening), and α=500cm ^-1(pass).The half range overall with (FWHM) of reflection peak is respectively 0.1nm and 0.37nm during two states, and corresponding Q value is 15500 and 4189.

Phase shift DFB grating also can be regarded as a Fabry Perot chamber that has two speculums that are made of distributed Bragg reflection optical grid (DBR).First DBR is 101 district's parts on the phase-shifted region right side, and second DBR is by forming in 102 districts in phase-shifted region left side part and modulator region 105.Optical maser wavelength is determined by following condition of resonance:

$\frac{4\mathrm{\πn}}{\mathrm{\λ}}(L_p+\frac{\mathrm{\Λ}}{2})+{\mathrm{\Φ}}_1+{\mathrm{\Φ}}_2=2\mathrm{m\π}---\left(1\right)$

N is the average effective refractive index of phase-shifted region in the following formula, and Λ=λ/2n is the grating cycle, L _pBe the amount (i.e. the length in zone 100) of phase shift, Φ ₁And Φ ₂Be first and the phase change on reflection of second DBR with respect to phase-shifted region, m is an integer.There is a wavelength window that is referred to as the forbidden band in the DBR grating, and the wide part that wavelength is within this window can be reflected.For the wavelength at center, DBR forbidden band, Φ ₁=Φ ₂=0.When m=1, L _p=λ/4n, this corresponding quarter-wave phase shift.The DFB structure of above-mentioned quarter-wave phase shift can be reversed with respect to opposite side by the raster pattern with phase shift position one side and realize that this can utilize opposite polarity photoresist to realize in the preparing grating process.

Fig. 3 is second DBR grating reflection rate spectrum (a) and the corresponding phase change (b) thereof that is made of above-mentioned 102 and 105 districts.Light is from phase-shifted region 100 incidents, and the absorption coefficient of modulator region 105 is respectively α=0 and α=500cm ^-1The absorption that we can see modulator from figure can cause the very big variation of reflection peak, and it but is minimum that the phase change of following is simultaneously located at peak wavelength (center in forbidden band).The variation of reflectivity causes the variation of the Q value of laser cavity, thereby changes laser threshold.By (1) formula as can be known, minimum phase change is corresponding to the wavelength chirp of minimum, and this is very important.

In semi-conducting material, according to Wayne Kramer-Krona peaceful (Kramer-Kronig) relation, the invariably accompany change of refractive index of the change of absorption, under some working condition, the change of this refractive index may be very large.It can be used for strengthening the modulation to laser threshold.Yet change of refractive can cause the variation of moving of peak value and reflected phase will, increases wavelength chirp.Add DBR grating region 102 (L in above-mentioned example at modulator region and phase shift zone ₂=100 μ m) peak value is moved and the phase change minimum.Fig. 3 has also provided when modulator region and has been in absorbing state (α=500cm ^-1), the refractive index of following simultaneously increases DBR grating reflection rate spectrum and phase change at 0.005 o'clock.The reflection peak that variations in refractive index causes moves has only 0.35nm.Under the situation that does not have DBR district 102, moving of modulator region reflection peak calculated by (2) formula:

$\mathrm{\Δ\λ}=\frac{\mathrm{\Δn}}{n}\mathrm{\λ}---\left(2\right)$

With the calculation of parameter in the above-mentioned example, the wavelength that causes thus moves and is Δ λ=1550 * 0.005/3.215=2.4nm.Therefore, adding DBR district 102 at modulator and phase-shifted region can reduce wavelength greatly and move.In addition, from Fig. 5 (b), can find out, very not remarkable in the phase change of the central area in forbidden band yet.Along with L ₂Reduce, peak value moves corresponding increase with phase change.On the other hand, the efficient of modulation is along with L ₂Increase and reduce.Therefore, selecting L ₂Value the time we need take all factors into consideration, this depends on that also grating index is poor.

Compare with 1/4th phase shift Distributed Feedback Lasers of direct modulation, from (1) and (2) formula as can be known, the Q-modulated laser in the utility model reducing aspect the wavelength chirp tangible advantage is arranged.For those direct modulated lasers,,, be 2.4nm in the fluctuation of above-mentioned example medium wavelength by (2) Shi Kede owing to the refractive index of whole laser structure all can be along with modulated current changes.And in structure of the present utility model, owing to only modulate the loss of that a part of grating that leaves phase-shifted region, a phase-shifted region refractive index n in (1) formula and a DBR district phase place Φ ₁To remain unchanged, and have only the phase place Φ in the 2nd DBR district ₂Can be along with the slight variation of modulated current.But according to Fig. 5 (b), this phase change can be minimized by 102 section length that design is between modulator region and the phase-shifted region.Therefore, wavelength chirp can reduce widely.

Fig. 4 is in the above-mentioned example, and gain coefficient is g=9.25cm ^-1, absorption coefficient is respectively α=0, and α=500cm ^-1Two kinds of modulator state the time laser structure transmission small signal gain spectrum.Owing to there is quarter-wave phase shifts in the DFB grating, optical maser wavelength is in the center, forbidden band.When modulator is in pellucidity (α=0), the gain for threshold value coefficient of zlasing mode is 9.25cm ^-1When modulator is in absorbing state, and absorption coefficient is α=500cm ^-1The time, it is 38cm that the gain for threshold value coefficient increases ^-1, and wavelength still remains unchanged for λ=1549.711nm.As consider variations in refractive index in calculating, then the gain for threshold value coefficient becomes 41.5cm ^-1, and optical maser wavelength is the 1549.745nm place, drift only has 0.034nm.Compare with the wavelength chirp of several nanometers of traditional direct modulation Distributed Feedback Laser, this numeral has reduced by 2 orders of magnitude.

The greatest differences of zlasing mode threshold value has shown that utilizing Q-modulator loss of the present utility model to change realizes that the Q-modulation is effective way under the two states of modulator region.The gain of light that produces when the constant current of pumping gain region is lower than that modulator is in the laser threshold of absorbing state but when being in the laser threshold of pellucidity far above it, the output of laser will be subjected to being added in the modulation of the modulator two ends signal of telecommunication.The phase change that is accompanied by the modulation of Q value only can cause very low wavelength chirp, and this phase change is little as almost can to ignore, and this is a significant advantage of the present utility model.

Fig. 5 has provided the functional relation of the gain for threshold value coefficient and the modulator absorption coefficient of laser.Can see that the absorption coefficient when modulator only is 200cm ^-1The time, this threshold value just have up to 300% difference.In the above-described embodiment, the effective refractive index in opening modulated device zone preferably can be identical with gain regions.When device was worked, gain regions was by a relative stronger electric current pumping, so that provide gain for laser.If the waveguide material of modulator region and gain regions, shape of cross section and grating cycle are all the same, modulation areas can be with same current density injection current in opening.Yet even under opening, modulator region generally there is no need also to inject so big electric current, causes big total driving power because big electric current injects.In general, in opening, as long as just add and to allow the enough transparent electric current of waveguide enough.Because the current density of gain regions and modulator region is different, the effective refractive index in these two zones also has small difference.This effect can be by changing the modulator region waveguide the shape (as the ridge width) of cross section compensate, just adopt different ridges wide at gain regions and modulator region, can reduce transition loss with a width gradual change structure in addition.

Light distribution in laser structure when Fig. 6 has provided modulator and is in unlatching (a) respectively and closes (b) state, this is to be g=8.8cm at gain coefficient ^-1, absorption coefficient is respectively=and 0 and α=500cm ^-1In time, calculate.Can see that under opening, light intensity is exponential increase from two ends to central authorities, up to reach maximum in the phase shift position.When modulator forwarded closed condition to, light intensity weakened significantly, and distribution also can change.The uneven field distribution of this extreme, the particularly summit that phase-shifted region is sharp-pointed under opening cause very strong effects of spatial and gain saturation.

In order to alleviate effects of spatial, phase shift can be slightly different by an effective refractive index, and the wave guide zone with length-specific realizes.Let us is considered another example, in this example, and the modulator zone length L _m=150 μ m, gain region is L by two length ₁=250 μ m and L ₂=100 μ mDBR districts form, and they are L by a length _p=50 μ m phase-shifted regions separate.Phase-shifted region has same grating periods lambda=0.2412 μ m, but its effective refractive index has been reduced to 3.204, and other regional effective refractive index then is 3.2125.

Fig. 7 (a) and (b) provided modulator respectively at opening (α=0) and closed condition (α=500cm ^-1) time light distribution, used gain coefficient g=8.2cm during calculating ^-1Compare with Fig. 8, it is not too remarkable that the light intensity of phase-shifted region becomes.During wavelength X=1549.75nm, the laser threshold gain coefficient is 8.6cm under the modulator opening ^-1, closed condition (α=500cm ^-1) be down 29cm ^-1In this example, the phase-shifted region of DFB grating can be by the wide waveguide of different ridges, and perhaps the different current density of electrode injection by a separation realizes.

In the utility model, transfer the mechanism of Q also can be applied to traditional Distributed Feedback Laser that has uniform grating (promptly not having phase-shifted region).Yet in this case, the DBR grating of modulator zone just needs a forbidden band with the off resonance of DFB district.In order to access single mode, can use the DFB grating of fractionated gain coupling, be similar to G.P.Li, T.Makino and H.Lu are at its paper " Simulation and interpretation oflongitudinal-mode behavior in partly gain-coupled InGaAsP/InP multiquantum-wellDFB lasers ", IEEE Photonics Technology Letters, vol.4, no.4 is as described in pp.386～388,1993.In this case, optical maser wavelength is in long wave direction one side in DFB forbidden band.According to thought of the present utility model, the grating of modulator region need be operated in the high reflectance state, is near its center, forbidden band.This a bit is very important, because shown in Fig. 3 (b), wavelength is when the center in forbidden band, and the phase difference of opening and closed condition is minimum.Therefore, the off resonance of the wavelength of DBR modulator region and DFB gain regions is necessary, can reduce wavelength chirp like this.The off resonance of wavelength can be by adjusting the structure of cross section waveguide, and for example wave guide ridge is wide or the grating cycle realizes.Thereby also can between DFB district and modulator zone, add the center, forbidden band that optical maser wavelength is adjusted on modulator region DBR grating in a fixing or adjustable phase place zone.For phase change and the wave length shift that the variations in refractive index that reduces to be accompanied by the loss modulation causes, can between modulator and phase place/DFB district, add the DBR district of another fixed current injection.DBR district that this fixed current injects and phase region and DFB district can use gain region of the common formation of a public electrode, are similar to the embodiment among Fig. 1.

Q-semiconductor laser modulation of the present utility model also can adopt the form of distributed Bragg laser.Fig. 8 has provided another embodiment of the present utility model.Laser by two DBR gratings 231 and 232 and the gain waveguide district 200 that is between these two gratings form.The wave guide zone 201 that comprises DBR grating 231 is passive and is substantially transparent with the wave guide zone 202 that comprises a part of DBR grating 232.Gain region does not comprise grating, and it is sandwiched between the pair of electrodes 208/120 and is used to provide the gain of light.The modulator region of being made up of another part DBR grating 232 205 also is between the pair of electrodes 110/120, and this electrode is used for changing the optical loss of fiber waveguide therebetween, thereby changes Q value and laser threshold and power output.

Obviously, the DBR grating 201 in the scheme shown in Figure 10 can be replaced by the cleavage surface of a partial reflection, and this face can plate dielectric film, also can not plate.

Q-modulated laser of the present utility model has many good qualities.Because modulation function and gain regions are separated, the latter is by the constant current pumping, this has not only reduced wavelength chirp, also improved modulating speed, because with respect to direct modulation or external electroabsorption modulator, modulator length of the present utility model is wanted much shorter, thereby the speed of littler electric capacity and Geng Gao is arranged.With respect to the electroabsorption modulator that is placed on the outgoing laser beam path, owing to use the extinction ratio of Q switching mechanism the utility model modulator also to want high many, and do not need very long modulator length.And it also inevitably can the produce power loss unlike external electroabsorption modulator.

Embodiment of the present utility model just is used for the utility model of explaining; rather than the utility model limited; in the protection range of spirit of the present utility model and claim, any modification and change to the utility model is made all fall into protection range of the present utility model.For example, the structural principle of the Q semiconductor laser modulation in the utility model also can be applied to vertical cavity surface emissivity laser.

Claims (7)

1. Q-semiconductor laser modulation that has electric absorption grating structure, it is characterized in that: comprise a phase shift distributed feedback grating that is embedded in the active waveguide structure, two first top electrodes that are separated from each other and second top electrode are covered in top and bottom electrode as the common ground face of gain regions and modulator region respectively; Described phase shift distributed feedback grating is divided into first, second portion and third part successively, and wherein first and second portion are separated by phase-shifted region; Described first top electrode that is deposited on gain regions covers first, second portion and the phase region therebetween of described grating, and a constant current injected active optical waveguide under this electrode, described second top electrode that is covered in modulator region covers the third part of described grating.

2. a kind of Q-semiconductor laser modulation according to claim 1 is characterized in that: the phase shift in the described phase shift distributed feedback grating equals quarter-wave.

3. a kind of Q-semiconductor laser modulation according to claim 2 is characterized in that: the relative opposite side of grating pattern of phase-shifted region one side is counter-rotating mutually in the described phase shift distributed feedback grating.

4. a kind of Q-semiconductor laser modulation according to claim 2 is characterized in that: the phase-shifted region in the described phase shift distributed feedback grating comprises one section waveguide with different effective refractive indexs.

5. a kind of Q-semiconductor laser modulation according to claim 1 is characterized in that: the operation wavelength of the corresponding laser in center, forbidden band of described third part grating cycle decision.

6. a kind of Q-semiconductor laser modulation according to claim 1, it is characterized in that: the loss of described modulator region fiber waveguide changes along with forward biased current signal.

7. a kind of Q-semiconductor laser modulation according to claim 1, it is characterized in that: the loss of described modulator region fiber waveguide changes along with back-biased voltage signal.

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