CN1034146C - Program control/manual continuously adjustable narrow line wide cavity semiconductor laser - Google Patents

Abstract

The present invention belongs to the field of the structural design of a continuous tunable laser device. The present invention puts forward a structure for biasing a grating rotating shaft and a semiconductor optical axis of an external cavity for a distance h so as to achieve that the movement synchronisation of a grating feedback wavelength and resonance frequency can be realized by only rotating the grating. Meanwhile, the device has a plurality of advantages of simple structure, high tuning precision, large tuning range, small linewidth, etc., and can be conveniently accessed with a universal computer by taking the measures of an aspheric lens with a large numerical value, the parallel placement of a grating nick and a semiconductor plane surface, etc. Various functions of tuning frequency, wavelength calibration, power output, automatically monitoring temperatures, etc. are realized, and the present invention has a wide application prospect.

Description

The program control/manual continuously adjustable narrow line wide cavity semiconductor laser

The invention belongs to laser technology field, particularly continuously adjustable external-cavity semiconductor laser structural design.

Continuously adjustable narrow line wide cavity semiconductor laser is the essential important light source in field such as optical communication, light exchange, light wave element test, spectrum analysis, Fibre Optical Sensor and metering detection.Be the focus of studying in the world for many years always, begin to occur product in recent years.External-cavity semiconductor laser by: the external reflectance device that places the semiconductor laser (LD) on the cooler and be placed on LD one side is formed, scioptics coupling between LD and the external reflectance device.The usual method that realizes continuous tuning is to adopt grating to make the external feedback element, and the moving with long variation the in chamber of feedback centre wavelength that requires grating to rotate to cause causes the mobile of resonance frequency to equate.According to grating equation:

2dSin θ=K λ (1) and condition of resonance: $L=q\·\frac{\mathrm{\λ}}{2}---\left(2\right)$ Can obtain the continuous tuning condition is: $\frac{\mathrm{\δL}}{\mathrm{\δ\θ}}=L\·\mathrm{Ctg\θ}---\left(3\right)$

In the above-mentioned formula: λ is a laser oscillation wavelength, and L is that exocoel is long, and θ is the grating incidence angle, d is a grating constant, and K is that the optical grating diffraction level is inferior, adopts first-order diffraction light K=1 usually, q is a positive integer, and δ L and δ θ are respectively the long and synchronous variable quantities of grating corner in continuous tuning requirement chamber.In order to satisfy (3) formula, need grating to rotate and carry out synchronously with long adjusting the in chamber.For this reason, existing technical scheme majority is to adopt the complicated mechanical drive mechanism to make grating do the two dimensional motion of rotation and translation, the scheme that also has is to go into optics F-P thin plate in the laserresonator interpolation, this method needs the motion of Synchronization Control grating and thin plate, and its system is also very complicated, and the common issue with of above-mentioned two kinds of schemes is because complicated in mechanical structure, control system is loaded down with trivial details, be difficult for accomplishing mode hopping often taking place, single mode stability difference and cost height synchronously.

Common outside cavity gas laser produces the mode hopping phenomenon and is operated in the reason that mode hopping takes place at the fixed frequency place in tuning process be that the spectral region broad of grating feedback wavelength can allow a plurality of longitudinal modes vibrations simultaneously in the feedback spectral line scope of broad.The loss difference that exocoel causes is not enough to allow main mould that the limit mould is curbed, between the different longitudinal modes in the feedback light spectral limit because of the disturbance saltus step of tuning asynchronous or temperature, electric current, acoustic vibration.Now also last enough attention and the effective solution of obtaining of this mode hopping factor.

In addition, for realizing the automatic control of laser tuning and frequency-selecting, more existing Tunable External Cavity Semiconductor Laser have been equipped with dedicated microcomputer, tuning precision is lower mostly, function singleness can not realize human-computer dialogue, and the difference that can not adapt to the different application occasion flexibly requires and costs an arm and a leg.

The objective of the invention is to for overcoming the weak point of above-mentioned prior art, a kind of new continuously adjustable external-cavity semiconductor laser is proposed, promptly take off-axis that grating is set, a rotating shutter can make moving of grating feedback centre wavelength and resonance frequency carry out synchronously.

The present invention has simple in structure, and it is convenient to exchange, stable performance, the tuning precision height, wavelength scaling shows convenient, accurately, and can with the universal microcomputer interface, the automatic selection that realizes function is plurality of advantages such as control automatically.

The present invention proposes a kind of continuously adjustable external-cavity semiconductor laser by grating and transmission mechanism thereof, lens and semiconductor laser are formed, it is characterized in that being provided with the optical axis spacing that rotation axis and the said lens and the semiconductor laser of the transmission mechanism of said grating form is h, and satisfies h=bSin θ+LCos ³θ/Sin θ, wherein: b is the distance of grating and rotating shaft, and θ is the angle of grating normal and optical axis, and L is the exocoel effective cavity length.

Operation principle of the present invention is described as follows in conjunction with Fig. 1:

The optical axis X that semiconductor laser 1 and lens 2 are formed, with the rotating shaft center O of grating g at a distance of h, exocoel is long to be L, the normal of grating g and optical axis X angle are θ, when grating rotates a low-angle δ θ (to g ') the chamber personal attendant be changed to δ L, because of δ θ is very little,

δ R=R δ θ (5) again

h＝bSinθ＋RCOSθ $=\mathrm{bSin}+\frac{\mathrm{\&delta;R}}{\mathrm{\&delta;\&theta;}}\&CenterDot;\mathrm{COS\&theta;}$ $=\mathrm{bSin\&theta;}+\frac{\mathrm{\&delta;l}}{\mathrm{\&delta;\&theta;}}\&CenterDot;\mathrm{<figure-callout\; id="2"\; label="CO\; S"\; filenames="C9410635500101.png"\; state="\{\{state\}\}">CO</figure-callout>}{S}^{}{}^2\mathrm{\&theta;}---\left(6\right)$

With the continuous tuning condition $\frac{\mathrm{\&delta;L}}{\mathrm{\&delta;\&theta;}}=\mathrm{Ctg\&theta;}\&CenterDot;L\left(3\right)$ Formula substitution (6) formula obtains $h=\mathrm{bSin\&theta;}+\frac{\mathrm{<figure-callout\; id="3"\; label="CO\; S"\; filenames="C9410635500101.png"\; state="\{\{state\}\}">CO</figure-callout>}{S}^{}{}^3\mathrm{\&theta;}}{\mathrm{Sin\&theta;}}\&CenterDot;L---\left(7\right)$

Therefore as long as satisfy the condition of (7) formula, moving of grating feedback centre wavelength and resonance frequency carried out synchronously.

The present invention overcomes common outside cavity gas laser to produce the mode hopping phenomenon in tuning process, has taked to press the measure of narrow grating feedback live width to comprise: GRIN Lens or the microcobjective of 1) selecting the non-spherical lens replacement prior art of big numerical aperture for use.Improve grating resolution with this, the grating distinguishing ability: $\mathrm{\&delta;\&lambda;}=\frac{\mathrm{\&lambda;}}{\mathrm{KN}},$ Wherein λ is a wavelength, and N is the order of spectrum for the grating fringe number in the irradiation hot spot, K.Therefore, the hot spot that incides on the grating is big more, and grating fringe is close more, and then resolution is high more, adopts the non-spherical lens of big numerical aperture (NA) high coupling efficiency, and facula area is increased, thereby has pressed the feedback live width of light canopy narrow;

2) the semiconductor junction plane is become parallel placement with the grating indentation, semiconductor laser (LD) active area is reduced grating feedback beam subtended angle, because the luminous waveguide of LD cross section is asymmetric, be flat rectangle (being generally 0.2 * 10 μ m), therefore LD junction plane and parallel placement of grating rag and vertical placement mutually, the feedback subtended angle of permission reception differ greatly (0.2: 10).Existing structure is considered coupling efficiency and oscillation threshold, usually the LD junction plane is placed with the grating indentation is vertical, the active area opening is 10 μ m, and the present invention takes parallel placement, and the active area opening is 0.2 μ m, make that the grating feedback line is roomy to be reduced greatly, thereby guarantee not mode hopping.

The present invention not only has characteristics simple in structure, with low cost, and only adjusts that the grating angle can reach grating feedback wavelength and resonance frequency moves synchronous purpose.Have stable performance, the tuning precision height, tuning range is big, and that feedback line width, wavelength scaling show is convenient, accurately, can be easily and the universal microcomputer interface, realize multiple function selecting and control, can extensively adapt to the different application needs of different field.

Brief Description Of Drawings

Fig. 1 is a principle of the invention schematic diagram,

Fig. 2 is a kind of example structure schematic diagram of the present invention, and wherein 2 (1) is front view, and 2 (2) is vertical view.

Fig. 3 is the wavelength scaling cell schematics of present embodiment, and wherein 3 (1) is structural representation, and 3 (2) is circuit theory diagrams.

Fig. 4 is the computer control unit schematic diagram of present embodiment.

Fig. 5 is a present embodiment computer control flow chart.

The present invention design a kind of manually/program control continuously adjustable narrow line wide cavity semiconductor laser embodiment, its structure is described in detail as follows respectively in conjunction with each accompanying drawing shown in Fig. 2～5:

One, manual external-cavity semiconductor laser: mainly comprise laser diode (LD) and front and back collimating lens 210 thereof, grating and transmission mechanism 220 thereof, wavelength scaling unit 250 3 parts.The present embodiment each several part is installed in and constitutes an integral body in the box body, and box body is divided into the inner box 204 with excellent heat insulation property, and has the outer box 202 of metal of better heat radiating effect.Each several part has convenient modular construction of exchanging, and is very easy to the replacing of different wave length device, has also improved the stability of integral device greatly.Below each several part is described in detail respectively.

Laser and lens component comprise that the LD that the surface is coated with anti-reflection film is fixed on heat sink 211, the LD two ends are respectively and are installed in two lens drums 213,214 on the lens carrier 212, wherein in the lens drum 213 non-spherical lens is housed, the laser beam that it will be dispersed becomes directional light directive light canopy, be placed in the lens drum 214 of the LD other end GRIN Lens is installed, it is transformed into laser beam outside the directional light output laser, heat sink 211 and lens carrier 212 all be welded on the semiconductor cooler 215 refrigerator 215 and laser base 201 Joints.In addition, below device pedestal, placed another group refrigerator, to realize temperature control to whole device.Grating 221 and its transmission mechanism are installed on laser base 201 Joints tuning 222.

The quiet transmission mechanism of light comprises, grating seat 223, bar 224, eccentric wheel 225, fixed pulley and fixed pulley axis 226, and wire-drawing wheel 227, pitman shaft 228 and spring leaf 229 are formed.Adopt the grating of 1200/mm in the present embodiment, grating is fixed on the grating seat 223, adjusts grating and makes its indentation with respect to the parallel placement of the junction plane of laser LD, and the rotating shaft of grating seat and grating be at a distance of b=2mm, with laser optical axis h=4.56mm apart.Knob 203 inch outside rotation is fixed on laser outside the box 202, pitman shaft 228 rotates thereupon, backguy is rotated pitman shaft 228 through fixed pulley 226 and is passed to wire-drawing wheel 227, and the external diameter of the wire-drawing wheel of present embodiment is 5 times of pitman shaft, so rotational angle has been segmented 5 times.The rotation of wire-drawing wheel 227 drives the eccentric wheel of fixing on it 225 through wheel shaft and rotates, connecting rod 224 is clamped on the eccentric wheel 225 with spring leaf 229, connecting rod 224 swings up and down thereupon when eccentric wheel 225 rotates, grating seat 223 is fixed on one with connecting rod 224 and also swings around axle thereupon, when the suitable eccentric size eccentric wheel of present embodiment design alternative rotates 360 °, the light canopy swings back and forth 10 °, thereby angle has been segmented 18 times again, improve tuning precision greatly, again because through backguy, the connecting rod secondary transmits, the shake of tuning knob 203, and distortion can not passed on the grating seat 223, thereby the assurance grating is only done stably and is rotated, and makes laser tuning stable.

The wavelength positioning unit comprises speculum 31, detector 32, aperture 33 and switching circuit as shown in Figure 3, wherein speculum 31 is fixed among Fig. 2 tuning 222, grating 221 zero order light reflected can be changed direction directive detector 32.Utilize grating zero level output light direction and wavelength that only one-to-one correspondence is arranged, output light is directed on the detector array with aperture through speculum, adjustment by reflector position and distance, realization have only when exocoel be tuned to during a certain special wavelength, some detectors just can receive grating zero level output light.The present embodiment laser output wavelength is 1.5 μ m, and tuning range is 100nm; Adopt the array of 11 detectors.Demarcating a wavelength every 10nm, is 1.48 μ m from 1.48～1.58 μ m, 1.49 μ m ... 1.57 μ m, 1.58 μ m are totally 11 special wavelength, use detector PD respectively ₁～PD ₁₁Receive.When a certain detector receives 0 grade of output light time, show this moment grating be tuned to a certain special wavelength, adopt switching circuit that this detector is linked to each other with a light-emitting diode, light-emitting diode is lighted.Switching circuit is mainly by operational amplifier (0P07), voltage comparator (LM393), switch triode 3DK, formations such as LED, shown in Fig. 3 (2), its principle is: when illumination is mapped on the detector PD, on PD, produce electric current and be injected into operational amplifier (0P07) through voltage comparator (LM393), thereby making on the switch triode 3DK conducting luminous tube LED has electric current to flow through, make LED luminous as indicating illumination is arranged to detector this moment, when unglazed the photograph, 3DK ends, no current flows through among the LED, and indication is extinguished.The components and parts of above-mentioned detector array and diaphragm and switching circuit all are fixed on (see figure 2) on the interior base plate of device box, light-emitting diode is installed on the front panel of device, one red pointer also is housed simultaneously to link to each other with pulley, backguy, during the rotary tuning button, drive pointer movement, can indicate two wavelength between the special wavelength and approximately be worth.

Two, program control external-cavity semiconductor laser: above-mentioned manual semiconductor laser links to each other with a universal microcomputer and promptly constitutes program control external-cavity semiconductor laser, can realize the selection and the control of the various functions such as control of automatic tuning, wavelength scaling, power detection and device temperature, with the difference of hand gear is to link to each other with eccentric wheel with stepper motor in the grating transmission mechanism to drive grating seat and grating swing, replaces fixed pulley, backguy and tuning knob.Because the light canopy is not directly installed on the motor revolving shaft, but take to have the cam friction drive mechanism of amplification, lowered requirement and difficulty, can be easy to accomplish the tuning precision of per step less than 1GHz to the segmentation of motor corner.Present embodiment is to 1.5 μ m lasers, 10 ° of corners of the corresponding grating of tuning range 100nm utilize the cam drive structure, make a step of standard change 1.8 ° (or 3.6 °, 7.2 °) motor can one the step only change somewhat or several seconds, promptly be sub-divided into every ten thousand steps of the number of turns by every 2000 steps of circle.This enforcement all-purpose computer is by mould/number and D/A interface, with stepper motor, refrigerator, Laser Power Devices etc. partly link to each other respectively, realization is described the control principle of each several part respectively to tuning, the temperature of laser, the monitoring of power and the functions such as demarcation demonstration of wavelength in conjunction with Fig. 4.

1, automatic tuning and Wavelength calibration:

The position of calculating grating by the wavelength X of input, i.e. the rotational angle of stepping motor, the drive current of D/A switch interface control step motor four phases after power amplification by four tunnel 12 rotate in place grating then.

2, monitoring temperature:

Measure the temperature of the heat sink and outside cavity gas laser inner bottom plating of LD tube core respectively with two thermistors, after voltage amplification by mould/number conversion interface input computer of 12 of two-way, as the temperature value of reality.The temperature of setting is imported by keyboard, and the error signal between actual temperature and the set point is controlled the refrigeration electric current of two refrigerators respectively as the output of 16 D/A translation interfaces of two-way, thereby control LD tube core is heat sink and the temperature of laser base board.

3, constant biasing and power monitoring:

The direct current biasing of laser is provided by one tunnel 16 D/A translation interface.The voltage of the corresponding D/A interface of value of the bias current of keyboard input, the constant-current source that is converted to 0～200mA scope through V/I (voltage/current) is added on the laser.

Luminous power is surveyed by PIN, through one tunnel 12 mould/number conversion interface input computer.

The control system workflow as shown in Figure 5.

Initial reset behind the starting up comprises zero setting such as step motor drive electric current, laser bias current, temperature control electric currents.Accept keyboard input then, treat input temp and bias current after, postpone to wait for, stablize rear motor to initial position, accept the wavelength that keyboard is imported again, by the rotation of software control motor grating is put in place.

Temperature control and power monitoring carry out (employing timer interrupt mode) in real time, in case that temperature control or luminous power, bias current occur is unusual, start protection immediately, make bias current, the warm electric current zero setting of control, in order to avoid damage laser.

The main performance index of present embodiment is as follows:

Wavelength: 850nm, 1300nm, 1550nm

Tuning range: the 850nm wave band is 20nm

The 1300nm wave band is 50nm

The 1550nm wave band is 100nm

Live width: 100KHg

Power output＞2mw

Light velocity angle of divergence 2mrad

Frequency stability 50MHg/ hour (no Automatic Frequency Control measure)

2MHg/ hour (adding the frequency feedback automatic control system)

Claims (5)

1, a kind of continuously adjustable external-cavity semiconductor laser is by grating and transmission mechanism thereof, lens and semiconductor laser are formed, it is characterized in that being provided with the optical axis spacing that rotation axis and the said lens and the semiconductor laser of the transmission mechanism of said grating form is h, and satisfies h=bSin θ+LCos ³θ/Sin θ, wherein: b is the distance of grating and rotating shaft, and θ is the angle of grating normal and optical axis, and L is the exocoel effective cavity length; Said lens are the non-spherical lens of big numerical aperture; Said semi-conductive junction plane becomes parallel placement with the grating indentation.

2, laser as claimed in claim 1, it is characterized in that said lens are formed by the non-spherical lens and the GRIN Lens that split at the big numerical aperture at semiconductor laser two ends, said semiconductor laser and front and back lens are placed on the semiconductor cooler as integral body, the junction plane of semiconductor laser becomes parallel placement with the grating indentation, said grating transmission mechanism is a cam friction transmission mechanism, above-mentioned each building block all is installed on the interior base of a box body, and base is installed one group of refrigerator down in the box body.

3, laser as claimed in claim 4, it is characterized in that said grating cam friction transmission mechanism comprises the grating seat with the mutually solid fixed grating of a connecting rod one end, eccentric wheel, one end and said connecting rod are fixed, the other end grips said eccentric spring leaf with connecting rod, by the assembly pulley that wheel shaft links to each other with said eccentric wheel, the tuning knob that links to each other with said pulley.

4, as claim 4 or 5 described lasers, it is characterized in that comprising by receiving the catoptrical speculum of said grating zero level and receive aperture before the detector array that mirror reflects has the light of special wavelength is arranged on each detector and the wavelength scaling of being formed by operational amplifier, switch triode light-emitting diode that switching circuit constituted, display unit respectively.

5, laser as claimed in claim 4, it is characterized in that said cam friction transmission mechanism comprises the grating seat with the fixed grating of a connecting rod one end Joint, eccentric wheel, one end with said connecting rod fixedly the other end grip said eccentric spring leaf with connecting rod, the stepper motor by wheel shaft links to each other with said eccentric wheel also comprises a universal microcomputer, by mould/number, the D/A interface respectively with said stepper motor, the temperature control temperature-measuring thermistor, the refrigerator laser power supply joins.

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