Method and device for regulating the average wavelength of a laser, especially a semiconductor laser
View Patent ↗The invention relates to a method for regulating the average wavelength of a laser, especially a semiconductor laser, comprising a wavelength-selective, at least partially reflecting optical element ( 27 ) and being operated in a unimodal manner. The inventive method involves the following steps: a control variable influencing the optical resonator length (L opt ) of the laser ( 29 ) over a pre-determined range is modified continuously or step-by-step; the characteristic of the optical monitoring power (P mon ) which is influenced in this way and emerges on the side opposite the optical output of the laser ( 29 ), or the characteristic of a detection variable dependent on the optical monitoring power, is detected continuously or step-by-step; and the control variable influencing the optical resonator length (L opt ) is regulated in such a way that a pre-defined value of the increase of the characteristic of the optical monitoring power (P mon ) or the characteristic of the detection variable dependent on the optical monitoring power, is reached in a point inside the control variable range, or a pre-defined value of a functional dependence (F(dP mon /dL opt )) is reached, containing the increase of the characteristic of the optical monitoring power (P mon ) or of the characteristic of the detection variable dependent on the optical monitoring power. Furthermore, the invention relates to a device for carrying out the inventive method.
1. A method for controlling the center wavelength of a laser that has a wavelength-selective, partially reflective optical element and is operated in a single-mode manner, comprising the acts of:
modifying a control quantity influencing the optical resonator length of the laser over a predetermined range;
detecting a curve of at least one of:
an optical monitor power that is influenced by modification of the control quantity and is emitted through the side facing away from the optical output of the laser; and
a detection quantity dependent on the optical monitor power; and
adjusting the control quantity in response to the act of detecting, the adjusting being based on an averaging function of the curve.
2. The method of claim 1 , wherein the control quantity is adjusted such that, at a point within the range for the control quantity, a predetermined value for the slope of the curve of the optical monitor power is reached.
3. The method of claim 1 , wherein the control quantity is adjusted such that, at a point within the range for the control quantity, a predetermined value for the slope of the curve of the detection quantity is obtained.
4. The method of claim 1 , wherein the control quantity is adjusted such that a predetermined value of a functional dependency (F(dP mon /dL opt )) is reached, wherein:
P mon represents the optical monitor power;
L opt represents the optical resonator length; and
the predetermined value of the functional dependency contains the slope of the curve of the optical monitor power or of the curve of the detection quantity.
5. The method of claim 4 , wherein the functional dependency (F(dP mon /dL opt ))=(dP mon /dL opt )/|P mon |.
6. The method of claim 1 , wherein the detection quantity comprises an output signal of a monitor diode.
7. The method of claim 1 , wherein the control quantity comprises a triggering signal of a heating or cooling device for changing the temperature of a subrange of the optical path of a resonator of the laser.
8. The method of claim 1 , wherein the control quantity comprises a triggering signal for modifying an axial position of a partially reflective, wavelength-selective, optical element.
9. The method of claim 1 , wherein the control quantity comprises a triggering signal for changing mechanical tension conditions within at least a subrange of the laser.
10. The method of claim 1 , wherein the control quantity is modified periodically, a width of the predetermined range being selected so that a change of the center wavelength of the optical output power of the laser for each value of the control quantity lies in the predetermined range within specified boundaries.
11. The method of claim 10 , wherein, after each pass through the predetermined range for the control quantity, the slope of the curve is determined at a point substantially in a center of the predetermined range for the control quantity.
12. The method of claim 10 , wherein, after each pass through the predetermined range for the control quantity, an average slope of the curve is determined in either a subrange of the predetermined range or in the entire predetermined range for the control quantity.
13. The method of claim 1 , wherein modifying the control quantity is performed such that a spectral component thereby generated in the entire spectrum of the optical monitor power lies outside a frequency range of an optical data signal with which the laser is driven.
14. The method of claim 1 , wherein the width of the predetermined range for the control quantity is selected so that, for a pass through the predetermined range, a change in the optical data output power lies within predetermined boundaries.
15. A device for controlling the center wavelength of a laser that has a wavelength-selective, partially reflective optical element and is operated in a single-mode manner, comprising:
a controllable device for changing an optical resonator length of the laser;
a device for detecting a curve of at least one of:
an optical monitor power emitted through a side facing away from an optical output of the laser; and
a detection quantity dependent on the optical monitor power; and
an evaluation and control unit that:
receives a detection signal corresponding to the curve;
generates a control signal based on an averaging function of the curve to change the optical resonator length; and
feeds the control signal to the controllable device.
16. The device of claim 15 , further comprising a monitor diode that sends the detection signal to the evaluation and control unit.
17. The device of claim 15 , wherein the controllable device comprises one of a controllable heating device and a controllable cooling device.
18. The device of claim 15 , further comprising one of a lowpass filter and a bandpass filter that is adapted to allow a frequency band of the control signal to pass.
19. The device of claim 15 , further comprising one of a heating device and a cooling device for maintaining a substantially constant temperature of the optical element.
20. The device of claim 15 , further comprising a device for controlling an operating point of the laser that receives the detection signal that has been passed through a lowpass filter adapted to pass substantially only a constant component of the detection signal.