FMCW lidar laser system and operating method for such a laser system
A laser system may include a semiconductor laser configured to emit laser radiation in continuous wave operation at M modes having differing angular frequencies, where 2≤M and where n=[1; M] . A tuning apparatus may periodically modify the angular frequencies where a variation of each angular frequency is smaller by at least a factor of 2 than a mode distance between the relevant adjacent angular frequencies. A detector has an upper cutoff frequency which is smaller by at least a factor of 10 than the smallest of the mode distances. A beam splitter may guide the M modes each to the detector and to an object, such that the detector may detect, for each of the M modes, portions of the laser radiation reflected by the object and portions of the laser radiation which come optically directly from the semiconductor laser.
1 . A laser system comprising:
a semiconductor laser configured to emit laser radiation in continuous wave operation in M modes with mutually different angular frequencies, M being a natural number and 2≤M≤30;
a tuning apparatus configured to periodically change the angular frequencies so that a variation of each of the angular frequencies is smaller by at least a factor of 2 than a mode distance between respective adjacent angular frequencies,
wherein the mode distance is a spacing difference between one angular frequency of one mode to a next nearest angular frequency of another nearest mode of the M modes;
a detector whose upper cutoff frequency is smaller by at least a factor of 10 than a smallest one of the mode distances; and
a beam splitter configured to guide the M modes of the laser radiation in each case to the detector and to an object, so that the detector is also configured to detect, for the M modes, in each case portions of the laser radiation reflected by the object as well as portions of the laser radiation which come optically directly from the semiconductor laser.
2 . The laser system according to claim 1 ,
wherein the laser system is a frequency modulated continuous wave lidar system, such that the detector is configured to detect, on the basis of the M modes, an angular frequency shift which occurs upon reflection of the laser radiation at the object, in order to determine a distance and/or radial velocity of the object relative to the laser system.
3 . The laser system according to claim 1 ,
wherein a resonator of the semiconductor laser comprises a geometric resonator length ranging from 5 mm to 10 mm, inclusive,
wherein the geometric resonator length is defined by facets of the semiconductor laser.
4 . The laser system according to claim 1 ,
further comprising a mode limiting apparatus configured to limit M to at most 5 such that: 2≤M≤5.
5 . The laser system according to claim 4 ,
wherein the mode limiting apparatus comprises a higher order diffraction grating,
wherein the mode limiting apparatus is integrated in the semiconductor laser.
6 . The laser system according to claim 1 ,
wherein the semiconductor laser is free of a mode limiting apparatus such that: 6≤M≤20.
7 . The laser system according to claim 1 ,
wherein the tuning apparatus is at least partially integrated in or on the semiconductor laser.
8 . The laser system according to claim 7 ,
wherein the tuning apparatus is configured to vary an operating current intensity of the semiconductor laser.
9 . The laser system according to claim 1 ,
wherein the tuning apparatus is located completely outside the semiconductor laser and/or at a distance from the semiconductor laser.
10 . The laser system according to claim 1 , wherein:
the mode distances are each greater than 5 GHz and less than 0.9 THz;
the variations of each of the angular frequencies due to the tuning apparatus each range from 0.2 GHz to 4 GHz inclusive;
mode widths of the M modes are each less than 1 MHz;
an average wavelength of the laser radiation ranges from 850 nm to 1600 nm, inclusive; and
a temporal change of the average wavelength is smaller by at least a factor 10 3 than a temporal change of the angular frequencies due to the variation by the tuning apparatus.
11 . The laser system according to claim 1 ,
wherein relative intensities of the M modes to each other vary by at most 1% during a tuning cycle of the tuning apparatus.
12 . The laser system according to claim 1 ,
wherein a semiconductor layer sequence of the semiconductor laser comprises exactly one active zone.
13 . The laser system according to claim 1 ,
wherein the laser system is free of an additional optical amplification component configured to post-amplify the laser radiation emitted by the semiconductor laser, and free of an active thermal stabilization.
14 . The laser system according to claim 1 ,
further comprising light collecting optics for the portions of the laser radiation of the M modes reflected back to the laser system at the object,
wherein the light collecting optics are configured to treat all M modes equally.
15 . A method for operating a laser system according to claim 1 , wherein the method comprises:
providing the laser system; and
current feeding the semiconductor laser, so that from the beam splitter in continuous wave operation the M modes of the laser radiation are guided respectively to the detector and to the object, so that the detector for the M modes receives in each case the portions of the laser radiation reflected by the object and also the portions of the laser radiation which come optically directly from the semiconductor laser.
16 . A laser system comprising:
a semiconductor laser configured to emit laser radiation in continuous wave operation in M modes with mutually different angular frequencies, M being a natural number;
a tuning apparatus configured to periodically change the angular frequencies so that a variation of each of the angular frequencies is smaller by at least a factor of 2 than a mode distance between respective adjacent angular frequencies,
wherein the mode distance is a spacing difference between one angular frequency of one mode to a next nearest angular frequency of another nearest mode of the M modes;
a detector whose upper cutoff frequency is smaller by at least a factor of 10 than a smallest one of the mode distances; and
a beam splitter configured to guide the M modes of the laser radiation in each case to the detector and to an object, so that the detector is also configured to detect, for the M modes, in each case portions of the laser radiation reflected by the object as well as portions of the laser radiation which come optically directly from the semiconductor laser, wherein the laser system further comprises a mode limiting apparatus configured to limit M to at most 5 such that 2≤M≤5, or the laser system is free of a mode limiting apparatus and either 6≤M≤20 or 11≤M≤30.