WO1992011672A1 - Dispositif pour la stabilisation d'une source de lumiere laser - Google Patents

Dispositif pour la stabilisation d'une source de lumiere laser Download PDF

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Publication number
WO1992011672A1
WO1992011672A1 PCT/AT1991/000135 AT9100135W WO9211672A1 WO 1992011672 A1 WO1992011672 A1 WO 1992011672A1 AT 9100135 W AT9100135 W AT 9100135W WO 9211672 A1 WO9211672 A1 WO 9211672A1
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WIPO (PCT)
Prior art keywords
frequency
modulation
resonator
light source
laser
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PCT/AT1991/000135
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German (de)
English (en)
Inventor
Harald Telle
Original Assignee
Tabarelli, Werner
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Publication of WO1992011672A1 publication Critical patent/WO1992011672A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters
    • H01S5/0683—Stabilisation of laser output parameters by monitoring the optical output parameters
    • H01S5/0687—Stabilising the frequency of the laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/139—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
    • H01S3/1398—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length by using a supplementary modulation of the output
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating

Definitions

  • the invention relates to a device for stabilizing a laser light source, in which the light intensity in the laser resonator changes its optical length, in particular for stabilizing a laser diode, the device comprising:
  • an external resonator arranged outside the laser resonator for frequency-selective feedback of light from the laser light source into the laser resonator, a control device for regulating at least one operating parameter that changes the emission frequency of the free-running laser light source, in particular the injection current of a laser ⁇ diode,
  • a regulating device for regulating the phase position (feedback phase) of the light fed back from the external resonator into the laser resonator relative to the phase position of the light in the laser resonator
  • a modulation device for modulating an operating parameter which changes the emission frequency of the free-running laser light source, in particular the injection current of a laser diode.
  • laser diodes are very suitable for this, since they have a large amplification range and can also run in a single longitudinal mode.
  • free-running laser diodes that is to say laser diodes which are only tuned via their operating parameters (injection current or laser temperature) without external optical feedback, cannot be tuned over a large frequency range (in the order of magnitude of 100 GHz and above).
  • tuning through the laser operating parameters leads to abrupt, non-phase-traceable changes in the emission frequency.
  • the coherence length is more typical, free running Single-mode laser diodes well below one meter, which means that these laser diodes are not suitable, for example, for distance measurements over long distances.
  • the frequency-selective optical feedback ensures that even with operating parameters in which the emission frequency of the free-running laser diode (ie without optical feedback from the outside) lies within a certain range (namely the snap-in range) next to the resonance center frequency, an actual emission ⁇ frequency, which is practically on the resonance center frequency.
  • the frequency-selective optical feedback alone is sufficient to stabilize the emission of the laser diode, ie to keep a narrow-band emission line on the resonance * - center frequency of the external resonator.
  • External interference and aging of the laser diode mean that long-term stability can only be achieved by additional electronic controls.
  • a regulating device for regulating an operating parameter, in particular the injection current, which changes the emission frequency of the free-running laser diode.
  • This regulation ensures that the emission frequency of the free-running laser diode is at least in the lies around the resonance center frequency of the external resonator, so that the frequency-selective optical feedback is able to guide the actual emission frequency to the resonance center frequency of the external resonator.
  • the emission frequency of the free-running laser diode corresponding to the current operating parameters does not exactly match the resonance center frequency of the external resonator, the actual emission frequency (although only slightly due to the frequency-selective optical feedback) deviates somewhat from the resonance center frequency. This deviation can be detected and a control signal can be obtained from it in order to regulate the operating parameters of the laser diode in such a way that the emission frequency of the free-running laser diode always corresponds exactly to the resonance center frequency of the external resonator.
  • a control device for controlling the phase position of the light fed back from the external resonator into the laser resonator relative to the phase position of the light in the laser resonator is also necessary.
  • This regulation of the feedback phase can take place in a manner known per se by regulating the distance from the laser diode to the external resonator, for example by guiding the light beam via a piezoelectrically adjustable mirror. At this distance, the absolute size is less important than the proportion deviating from an integer multiple of half the wavelength (feedback phase).
  • Two independent control loops are required for the control of the operating parameters and the control of the feedback phase described above.
  • the injection current of the laser diode suggests modulating the injection current of the laser diode.
  • This modulation induces frequency modulation in the light emitted by the laser diode.
  • This frequency modulation is detected in the transmission of the external resonator and a control signal is determined therefrom for regulating the feedback phase.
  • the light fed back into the laser resonator is amplitude-modulated with a second frequency via an acousto-optical modulator.
  • the resonance center frequency of the external resonator can be tuned. So that the optical feedback is able to keep the actual emission frequency of the laser diode always at this resonance center frequency, the emission frequency of the free-running laser diode (for example via the injection current) must also be controlled via the first regulation described above, so that the emission frequency of the free-running laser diode is always in the snap-in area around the resonance center frequency. It is also necessary to regulate the feedback phase in an independent, second control loop (cf. Dahmani's work mentioned at the beginning).
  • a detector device for detecting a modulation with twice the modulation frequency is provided in the light emitted by the laser light source, this detector device emitting a control signal dependent on the modulation stroke of the aforementioned modulation to the control device for regulating the feedback phase .
  • the measure according to the invention makes it possible, in addition to the regulation of the emission frequency of the free-running laser light source, to obtain an independent control signal for regulating the feedback phase by changing an operating parameter, and thus to implement a laser light source which is stable over the long term or can be quickly and broadly phase-traced.
  • the basic idea is the following: By modulating an operating parameter of the laser light source, which influences the emission frequency of the free-running laser light source, frequency modulation is generated in the light emitted by the laser light source.
  • the injection current can be superimposed on a small, high-frequency alternating current.
  • the stroke of this frequency modulation is strongly suppressed in comparison to a free-running laser diode by the frequency-selective optical feedback from the external resonator, for example by a factor of 50.
  • the alternating current amplitude superimposed on the injection current can be chosen, for example, so that the modulation index, i.e. the ratio of the modulation stroke to the modulation frequency is small compared to 1 when the feedback parameters are optimally set.
  • the optical frequency spectrum of the laser light source consists of a central carrier and side bands arranged symmetrically thereto at a distance from the modulation frequency and integer numbers Multiples of it.
  • the relative strength of the sidebands is determined by the square of the order corresponding to the Bessel function, the modulation index being the argument of the Bessel function.
  • the feedback phase drifts away from its optimal value (in which the field vector of the feedback light is perpendicular to the field vector of the light in the laser resonator) , an amplitude modulation with twice the modulation frequency appears in the light (reflected by the external resonator).
  • a detector device can now be provided for the detection of this amplitude modulation at twice the modulation frequency, a control signal for the control device for controlling the feedback phase being obtained from the size of this amplitude modulation (modulation stroke). The control device then automatically adjusts the feedback phase until the amplitude modulation at twice the modulation frequency assumes a predetermined value or a minimum at which the feedback phase is optimal.
  • the light emitted by the laser diode is frequency-modulated due to the modulation of the injection current, the intensity of the first and second order sidebands also depends on the feedback phase. With an optimal feedback phase, all side bands are strongly suppressed. If the feedback phase deviates from the optimal value, the intensity of the sidebands will increase, and with it the modulation deviation of the frequency modulation.
  • the detector device comprises a photodetector and a mixer connected downstream of it, which, in addition to a signal input for the possibly amplified photocurrent from the photodetector, has a reference input for receiving a signal coming from the modulation device and via a frequency - Has doubler-guided reference signal with twice the modulation frequency. It is thus possible to convert the alternating current signal emitted by the photodetector into the baseband and to use it as an error signal for the feedback phase control loop. In principle, regulation via edge stabilization is possible. However, it is more favorable to use a modulation method to determine a control signal for the feedback phase control.
  • a phase modulation device is provided for small-stroke modulation of the feedback phase
  • a phase-sensitive detector device is also provided which consists of a momentary modulation stroke of the (amplitude) modulation, which oscillates with the phase modulation frequency in the case of the signal representing the double modulation frequency, provides a control signal of odd symmetry for the control device for controlling the feedback phase.
  • the current modulation frequency is advantageously in the order of 10 to 100 MHz
  • the phase modulation frequency of the feedback phase caused by the phase modulation device is significantly lower and is preferably in the kHz range.
  • the feedback phase can be modulated in a simple manner by the laser beam being see laser diode and external resonator is guided over a piezoelectrically adjustable mirror, which is periodically adjusted with the phase modulation frequency by small fractions of a wavelength.
  • phase-sensitive detection for example with a lock-in amplifier
  • a control signal error signal with odd symmetry is obtained, which the control device for controlling the feedback phase is supplied.
  • Control signal occurs as a product of two modulations carried out from the outside and is therefore largely immune to technical faults, offsets, etc.
  • the control device for the feedback phase then follows the control signal, for example the piezoelectrically adjustable mirror, as a function of this control signal that the feedback phase is optimal.
  • the control of the feedback phase just described with evaluation of an (amplitude) modulation occurring at twice the modulation frequency, has a wide control bandwidth and is therefore particularly suitable for systems in which the emission frequency is in the order of 100 GHz over a tuning range and should be phased through (and as quickly as possible).
  • tuning can be carried out by tuning the resonance center frequency of the external resonator, a first control device ensuring that the operating parameters of the laser light source are carried along in such a way that the emission frequency of the free-running laser diode is always within the latching range now moving with the resonance center frequency lies.
  • a second control loop keeps the feedback phase at its optimum value while tuning the frequency.
  • (Amplitude) modulation sets a modulation of the operating parameters determining the emission frequency of the free-running laser diode or one of these operating parameters (for example the Injection current) ahead.
  • this modulation results in frequency modulation of the light emitted by the laser diode, the frequency spectrum naturally also having first-order sidebands lying symmetrically thereto in addition to the carrier frequency.
  • the beat signals between the carrier and the left first-order sideband and between the carrier and the right first-order sideband cancel each other out exactly. Due to this "balance", no amplitude modulation is initially visible.
  • phase-sensitive rectification can be used to emit a control signal which is dependent on the modulation stroke and the phase position of the aforementioned amplitude modulation with the simple modulation frequency, for regulating at least one operating parameter of the laser light source.
  • the first-order sidebands also automatically occur, which ultimately lead to an amplitude modulation together with the carrier in the light reflected by the resonator if the actual emission frequency of the laser diode deviates from the resonance center frequency of the external resonator, with the modulation stroke the. mentioned Amplitude modulation with the simple modulation frequency receives a dispersion curve-like course over the frequency.
  • a continuously phase-traceable frequency tuning range of over 100 GHz has already been achieved.
  • a mode selector is an external reflector which is arranged in the vicinity of the laser diode resonator. If the frequency is to be tuned, the distance of this reflector from the laser diode resonator must also be traveled. This requires a third control loop (the first control loop controls the injection current, for example, so that the frequency of the free-running laser diode lies in the snap-in range around the resonance center frequency of the external resonator; the second control controls the feedback phase).
  • the latter can be mounted on a piezo ceramic and the distance to the laser diode can be modulated, the modulation frequency being of the order of magnitude of approximately 100 Hz . It was observed that the power of the light transmitted by the partially transparent mode selector depends on the position of the mode selector and that the
  • Modulation receives a transmission curve similar to a resonance line.
  • the transmitted light is thus modulated, and a control signal for tracking the mode selector can be obtained via phase-sensitive rectification.
  • the modulation of the mode selector induces a low frequency modulation in the laser light source.
  • a device for modulating at least one operating parameter of the laser light source with the reflector modulation frequency to be provided in the laser by the reflector modulated at a distance from the laser light source to compensate for light source-induced frequency modulation.
  • 1 shows a schematic representation of an exemplary embodiment of the device according to the invention.
  • 2 shows a diagram to show the frequency response of a laser diode with and without frequency-selective optical feedback and to show the snap-in area.
  • 3 shows the essential components of a frequency spectrum of a frequency-modulated oscillation.
  • 4 shows a piezoelectrically adjustable external mode selector and its control loop.
  • the actual optical laser system is arranged in the area 1 surrounded by dashed lines and essentially comprises a laser diode LD and a V-shaped resonator with mirrors Ml, M2 and M3, with the light path between the laser diode LD and external resonator, a mirror 3 and a collision lens L is arranged.
  • the laser diode can be, for example
  • GaAlAs laser diode with an emission wavelength of approx. 830 nm and an output power of approx. 15 mW.
  • the external resonator M1, M2, M3 is a so-called Fox-Smith resonator, in which only the internal field passing through the folding mirror M2 is fed back into the laser light source LD, while the light reflected at the folding mirror is fed into the actual output light beam of the optical laser system goes.
  • other resonators could also be used, in which the light reflected at the coupling mirror does not get directly back into the laser diode.
  • a tilted convocal Fabry-Perot etalon would be suitable. In an experimental setup, the resonator length was approx.
  • the resonator mirror Ml is mounted on a miniature loudspeaker LS, with which a change in length and thus a change in the resonance center frequency of the external resonator M1, M2, M3 is possible without substantially misaligning the resonator.
  • other adjustment mechanisms for a resonator mirror for example piezoelectric adjustment elements.
  • f F denotes the frequency of the free-running laser diode, that is to say the frequency with which the laser diode would run without optical feedback from an external resonator given given operating parameters (injection current, temperature) .
  • f g denotes the system frequency, ie the frequency actually emitted from the external resonator and the set operating parameters when there is feedback.
  • f denotes the central carrier frequency of the light actually emitted by the laser diode.
  • F R denotes that due to the length of the resonator (and, if appropriate by the refractive index of the medium contained therein) defined resonance center frequency of the external resonator.
  • the frequency-selective optical feedback from the external resonator M1, M2, M3 is in principle able, without additional electronic control loops, to keep the system frequency f g at the resonator center frequency f R , provided the operating parameters (injection current and temperature of the laser diode) are such are set that the frequency of the free-running laser diode defined thereby lies in the snap-in area around the resonance center frequency f R of the external resonator, ie does not deviate too far from the resonance center frequency of the external resonator. This is explained in more detail below with reference to FIG. 2.
  • the system frequency f g (ie the actually emitted frequency) is plotted against the frequency of the free-running laser diode.
  • the origin of the axis cross shown in FIG. 2 lies at the resonance center frequency f R of the external resonator. Without frequency-selective optical feedback, the system frequency changes linearly with the frequency of the freewheeling the laser diode, as indicated by the dashed line 4.
  • the straight line 4 in FIG. 2 does not run exactly below 45 * to the two axes only because a different division is used on the X-axis and the Y-axis.
  • a unit of length on the X axis corresponds to five times the frequency of the same unit of length on the Y axis.
  • the frequency curve indicated by line 5 is obtained by frequency-selective optical feedback from an external resonator.
  • the system frequency f s corresponds to the frequency of the free-running laser diode f F and the resonance center frequency f R of the external resonator. 2.
  • the frequency of the free-running laser diode now deviates from the resonance center frequency of the external resonator, for example due to a slight change in the injection current or the temperature, the actual selective changes due to the frequency-selective optical feedback ⁇ Lich emitted system frequency within the 1 snap range hardly.
  • the frequency-selective optical feedback thus ensures that the actually emitted system frequency fg is kept essentially at the resonance center frequency of the external resonator even with small deviations in the frequency of the free-running laser diode.
  • this purely optical frequency-selective feedback is not sufficient to keep the laser diode at the resonance center frequency for a long time.
  • additional electronic control loops are necessary to ensure, on the one hand, that the frequency f F determined by the operating parameters is free ⁇ fenden laser diode is at least in the latching area 1 (preferably controlled to the resonance center frequency f R ).
  • an additional control of the feedback phase is also necessary, which supports the phase control which automatically proceeds as a result of the optical feedback from the external resonator and ensures that the feedback phase is just such that the feedback field is at 90 ° to the field in the resonator of the laser diode.
  • a first control device regulates the injection current of the laser diode LD via the current control SR in such a way that the system frequency f s is kept at the resonator center frequency f R of the external resonator M1, M2, M3. (The temperature of the laser diode only needs to be roughly pre-controlled.)
  • This control device comprises a modulation device for modulating the injection current of the laser diode.
  • the modulation device essentially consists of the HF synthesizer SY, which supplies a small AC component with a modulation frequency of 35 MHz.
  • the modulation frequency is denoted by f m ⁇ (j .
  • This injection current modulation generates a frequency modulation of the light emitted by the laser diode, so that the emission spectrum essentially looks as it is shown in FIG. 3: in addition to the system carrier frequency f s there are symmetrical first and second order sidebands at a distance of the single and double modulation frequency f m ⁇ (j . higher order sidebands can be neglected and are therefore not shown in detail.
  • a pure frequency modulation is - as is already mentioned at the beginning - not detectable by a photodetector.
  • This amplitude modulation can be detected by the photodetector (for example an Si-PIN photodiode PD1), the resulting photocurrent representing the amplitude modulations of the detected light.
  • the photodetector for example an Si-PIN photodiode PD1
  • Beam splitter can be branched off in front of the photodetector PD1.
  • the photocurrent from the photodetector PD1 is amplified in the amplifier AMP1 and synchronously demodulated in a double-balanced mixer DBM1.
  • the reference signal required for this with the modulation frequency f m ⁇ (j is also taken from the RF synthesizer SY.
  • An RF phase shifter PSl serves to establish the required quadrature relation between the two mixer inputs. PSl can also be selected.
  • the control signal (error signal) present at the mixer output which is proportional to the deviation of the system frequency f g from the resonator center frequency f R , is passed through an
  • the feedback phase of the light fed back from the external resonator into the laser resonator is regulated relative to the phase position of the light in the laser resonator, with the second control signal required for this being obtained in the light emitted by the laser diode after a Amplitude modulation at twice the modulation frequency (2f mod ) is observed.
  • the component oscillating at twice the modulation frequency contains information about the deviation of the feedback phase from its optimal value.
  • a phase shifter PS2 is provided to set the necessary quadrature phase relation between the two inputs of the mixer DBM2.
  • the output signal of the mixer DBM2 reflects the modulation stroke of the amplitude modulation with twice the modulation frequency 2f mo £ j and is used according to the invention to regulate the feedback phase.
  • an electronic filter FI1 is provided in front of the mixer DBM2, which essentially only amplifies the component of the amplifier AMP2 which oscillates at twice the modulation frequency 2f mo (j If a very selective filter is used, instead of the mixer DBM2, a squaring device could also be provided (not shown), in which the signal modulated at twice the modulation frequency is multiplied by itself in order to adjust the modulation stroke of this Am ⁇ to provide corresponding output modulation component.
  • the piezo actuator PZT2 on which the mirror 3 is attached, is modulated with a small stroke with a frequency of approximately 1 kHz coming from the phase modulation generator, so that the feedback phase is also modulated with a small stroke with this phase modulation frequency.
  • the phase modulation frequency is substantially lower than the current modulation frequency f mocjf, so that there is no disruptive mutual influence.
  • the modulation stroke is, for example, in the 10 nm range, which corresponds to a feedback phase stroke of approximately 100 mrad.
  • the phase-sensitive detector device is a lock-in amplifier which receives the signal coming from the mixer DBM2 at a signal input and which furthermore has a reference input via which a reference signal oscillating with the phase modulation frequency is output the phase modulation generator is received.
  • the signal generated via the lock-in amplifier is passed to the input of the high-voltage amplifier (not shown) of the piezo actuator PZT2 in order to adjust the mirror 3 and thus the feedback phase to the optimum value. This closes the feedback phase locked loop.
  • the detector device for detecting the component of the modulated light which oscillates at twice the modulation frequency is arranged in the beam path of the light reflected by the external resonator M1, M2, M3. It is thus possible to use one and the same photodetector PD1 for regulating the system frequency via the operating parameters and regulating the feedback phase.
  • the system remains locked onto the resonator center frequency of the external resonator practically indefinitely, even if the resonance center frequency of the resonator is fast (in the order of a few GHz per second) and wide (in the order of 100 GHz and above) is tuned. Since the control stroke of the first control circuit is limited (to the injection flow), the temperature of the laser diode must be roughly controlled if the resonator center frequency is tuned further. The first control circuit then ensures through precise control of the injection current that the frequency of the free-running laser diode remains exactly at the resonator center frequency.
  • the resonance center frequency of the external resonator M1, M2, M3 is adjusted via a movable mirror M1, which is mounted on a loudspeaker LS.
  • the operating parameters of the laser diode must be regulated or controlled so that the emission frequency of the free-running laser diode always remains in the pulling range of the now changing resonance center frequency.
  • the laser diode temperature which is determined, for example, by a Peltier element 6, is particularly suitable for coarse control for tuning over a large frequency range.
  • a periodic or linear temperature setpoint curve is specified via a generator G, for example.
  • the temperature controller then carries out a synchronous adjustment of the temperature of the laser diode and the position of the resonator mirror Ml.
  • a synchronous adjustment (with control) is of course not perfectly possible.
  • the remaining small deviations between the system frequency fg and the resonance center frequency f R of the external resonator can, however, be quickly and exactly corrected by regulating the injection current as described above.
  • an external reflector MS acting as a mode electrode is arranged outside the resonator of the laser light source LD which reflects back at least part of the light into the laser resonator.
  • the distance of this mode selector from the laser resonator must also be controlled.
  • a third control loop is provided, which is shown schematically in FIG. 4.
  • the position of the mode selector MS is in this case determined by the amplifier OP2 via the Operations ⁇ voltage supplied through a voltage applied to the input of this operational amplifier OP2 bias and bias ann e i ne mode m to be selected manually.
  • a reflector modulation frequency of the order of magnitude of approximately 100 Hz is superimposed on this bias voltage. The distance of the reflector (mode selector MS) is thus modulated.
  • the reflector MS is designed to be partially transparent and the transmitted power depends on the distance of the reflector from the laser diode.
  • the light transmitted by the reflector is thus also amplitude-modulated with the reflector modulation frequency in the order of 100 Hz.
  • the photodetector PD2 detects and this amplitude modulation leads to a corresponding of the current signal to the signal input S1 of a lock-in amplifier.
  • the reflector modulation frequency U mod is fed to the reference input RI.
  • the lock-in amplifier now demodulates the amplitude modulation component at the reflector modulation frequency (phase-sensitive rectification) and emits a control signal which, after integration in the correspondingly connected operational amplifier 0P2, is fed to the input of the operational amplifier OP2, which is then fed via the piezo Element PZT sets the mode selector to the correct distance from the laser light source.
  • the mode selector control loop is thus closed.
  • a device which modulates the current of the laser diode slightly with the reflector modulation frequency and thus the through to compensate for the modulated reflector MS-induced frequency modulation.
  • This device CC for current modulation supplies an output current which is superimposed on the injection current of the controls shown in FIG. 1.
  • a neutral filter NF prevents disruptive reflection from the photodetector into the laser diode LD.
  • FIG. 5 shows a typical course of the electrical signal on the photodiode PD1 at the double modulation frequency (S 2 f m ⁇ i) as a function of the feedback phase RKP, ie as a function of the position of the piezo element PZT2 on which the Mirror 3 is mounted.
  • regulation to the extremum A takes place by means of a modulation method (modulation of the feedback phase with 1 kHz by PMG).
  • the advantage of this modulation method is that fluctuations in the signal level do not disturb.
  • the control device for the feedback phase can therefore always set the position of the piezo element PZT2 exactly such that the signal assumes the extremum A at twice the modulation frequency S 2 f- mo ( _) and the feedback phase is thus correct.
  • FIG. 6 A simplified embodiment of the device according to the invention is shown in FIG. 6. This is simplified in two ways compared to the previously described device. First of all, it should be mentioned that in the device shown in FIG. 6, the first control circuit which regulates the operating parameters of the laser diode LP ( ⁇ MP1, DBM1, PSI, SY, INTI, SR) is the same as that in FIG 1 shown embodiment and here in Fig. 6 is generally designated by the reference number 10.
  • a simplification in the embodiment shown in FIG. 6 is firstly that by using a highly selective filter FI1 at twice the modulation frequency S fmod (70 MHz) the mixer DBM2 of FIG. 1 is omitted. Second, there is no modulation of the feedback phase. Rather, a "static control" takes place on the feedback phase B shown in FIG. 5, in which the signal is regulated at the double modulation frequency s 2fmod to the Pe ⁇ T el .
  • a rectifier 11 is connected downstream of the filter FI1, the output of which leads to a differential amplifier 12. An offset signal corresponding to the level C is fed to the second input of the differential amplifier 12. The output of the differential amplifier 12 then controls the piezo element PZT2 and thus defines the position of the feedback phase.
  • the feedback phase is also regulated by means of a modulation method by regulating the photoelectric signal present at the second modulation frequency to the extremum A of FIG. 5.
  • Laser diodes are certainly advantageous laser light sources. What is essential, however, is the property of the light source that its optical length changes when the light intensity changes in the laser resonator. This is the prerequisite for the frequency-selective optical feedback to allow the emission frequency to snap to the resonant center frequency of the external resonator.
  • other resonators for example tilted confocal Fabry-Perot etalons, can also be used instead of the V-shaped resonator shown.
  • the adjustment of the feedback phase could also be done, for example, via a regulated phase shifter element in the beam path between the external resonator and the laser light source.

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  • Semiconductor Lasers (AREA)

Abstract

Dispositif pour la stabilisation d'une source de lumière laser, dans lequel l'intensité lumineuse dans le résonateur laser modifie la longueur optique de ce dernier, en particulier pour la stabilisation d'une diode laser (LD). Le dispositif comprend un résonateur externe (M1, M2, M3) monté à l'extérieur du résonateur laser, pour la rétroaction, sélective en fréquence, de la lumière émanant de la source laser (LD). Par ailleurs, il est prévu un premier organe de réglage servant à régler au moins un paramètre de fonctionnement (courant d'injection d'une diode laser) modifiant la fréquence d'émission de la source de lumière laser (LD) librement émise. En outre, le dispositif comprend un organe de réglage servant à régler la position de phase (phase de rétroaction) de la lumière rétroactivée par le résonateur externe dans le résonateur laser, par rapport à la position de phase de la lumière dans ledit résonateur, ainsi qu'un dispositif modulateur destiné à moduler un paramètre de fonctionnement (courant d'injection d'une diode laser) modifiant la fréquence d'émission de la source de lumière laser librement émise. Pour obtenir un signal de réglage indépendant, destiné à régler la phase de rétroaction, il est prévu un dispositif détecteur (PD1, AMP2, FI1, DBM2, PS2, FD) pour la détection d'une modulation à fréquence de modulation double (2fmod) dans la lumière émise par la source laser, ce dispositif détecteur fournissant à l'organe de réglage (PMG, LIA, INT1, PZT2,3) un signal de réglage fonction de l'amplitude de la modulation précitée, en vue de régler la phase de rétroaction.
PCT/AT1991/000135 1990-12-20 1991-12-18 Dispositif pour la stabilisation d'une source de lumiere laser WO1992011672A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ATA2608/90 1990-12-20
AT260890A AT395497B (de) 1990-12-20 1990-12-20 Einrichtung zur stabilisierung einer laserlichtquelle

Publications (1)

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WO1992011672A1 true WO1992011672A1 (fr) 1992-07-09

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PCT/AT1991/000135 WO1992011672A1 (fr) 1990-12-20 1991-12-18 Dispositif pour la stabilisation d'une source de lumiere laser

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EP (1) EP0563193A1 (fr)
AT (1) AT395497B (fr)
WO (1) WO1992011672A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112968344A (zh) * 2021-02-03 2021-06-15 北京理工大学 基于复合光锁相光纤激光器扫频线性化和相干增强方法
CN114826426A (zh) * 2022-06-24 2022-07-29 国科大杭州高等研究院 一种参数自适应的高精度数字激光锁相系统及方法

Citations (1)

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Publication number Priority date Publication date Assignee Title
US4907237A (en) * 1988-10-18 1990-03-06 The United States Of America As Represented By The Secretary Of Commerce Optical feedback locking of semiconductor lasers

Patent Citations (1)

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US4907237A (en) * 1988-10-18 1990-03-06 The United States Of America As Represented By The Secretary Of Commerce Optical feedback locking of semiconductor lasers

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Title
E. DE CLERCQ ET AL. 'Design of an optically pumped Cs laboratory frequency standard', Frequency standards and metrology,1989,Springer -Verlag, Berlin, Heidelberg, Seiten 120-124 in der Anmeldung erw{hnt *
JOURNAL OF OPTICAL COMMUNICATIONS. Bd. 5, Nr. 2, Juni 1984, BERLIN DE Seiten 46 - 49; O. STROBEL: 'Simultaneous wavelength and power stabilization of a GaAlAs semiconductor laser applying a single detector scheme' *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112968344A (zh) * 2021-02-03 2021-06-15 北京理工大学 基于复合光锁相光纤激光器扫频线性化和相干增强方法
CN114826426A (zh) * 2022-06-24 2022-07-29 国科大杭州高等研究院 一种参数自适应的高精度数字激光锁相系统及方法

Also Published As

Publication number Publication date
ATA260890A (de) 1992-05-15
EP0563193A1 (fr) 1993-10-06
AT395497B (de) 1993-01-25

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