Laser resonators comprising mode-selective phase structures
AssigneeFraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.
InventorsUwe Detlef Zeitner, Reiner Guether
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Abstract
The invention relates to a laser resonator for semiconductor lasers having a waveguiding layer which is disposed between a substrate and a superstrate, the waveguiding layer, the substrate and/or the superstrate of the laser resonator having at least one phase structure which varies locally in such a manner that at least one predetermined laser mode is influenced in its propagation characteristic.
Claims32
Laser resonator for semiconductor lasers having a waveguide layer for a laser mode to be amplified which extends between a substrate layer and a superstrate layer and which is limited at two oppositely situated sides in extension direction of the waveguide layer by a first and a second end facet as resonator end faces, the two end faces establishing the propagation direction of the laser mode to be amplified,
- characterised in that
- the laser resonator between the two end facets has a first phase structure adjacent to the first end facet and a second phase structure adjacent to the second end facet, which vary locally in the plane of the waveguide layer in such a manner that at least one predetermined lateral laser mode in the plane of the waveguide layer and perpendicular to its propagation direction is phase-conjugated during passage through respectively one of the two phase structures, reflection at the adjacent end facet and repeated passage through the same phase structure, and the phase structures being configured in such a manner that a predetermined lateral laser mode is phase-conjugated during passage through the phase structure, reflection at the adjacent end facet and repeated passage through the same phase structure, which mode has, in the intermediate region between the first and the second phase structure, a strongly non-periodic varying phase front in the plane of the waveguide layer and laterally relative to the wave propagation direction.
Laser resonator according to one of the preceding claims, characterised in that at least one phase structure has a two-dimensionally varying refractive index in the plane of the waveguide layer.
Laser resonator according to the preceding claim, characterised in that the substrate, the waveguide layer and/or the superstrate have as phase structure a two-dimensionally varying refractive index in the plane of the waveguide layer.
Laser resonator according to one of the preceding claims, characterised in that at least one phase structure has a two-dimensionally locally varying thickness of the waveguide layer in the plane of the waveguide layer.
Laser resonator according to the preceding claim, characterised in that the waveguide layer adopts two different thicknesses in the region of the phase structures.
Laser resonator according to one of the preceding claims, characterised in that the waveguide layer has furthermore at least one radiation-deflecting structure which deflects the beam circulating in the waveguide layer.
Laser resonator according to the preceding claim, characterised in that the beam-deflecting structure is a mirror, a prism and/or a diffractive element.
Laser resonator according to one of the two preceding claims, characterised in that the beam-deflecting structure has a deeply etched channel, a Bragg grating with straight or curved grating channels, a prismatically configured region of the effective refractive index and/or a totally reflecting or totally mirror-coated region.
Laser resonator according to one of the three preceding claims, characterised in that the beam-deflecting structure is part of one of the end facets or is disposed between the two phase structures.
Laser resonator according to the preceding claim, characterised in that at least one reflecting structure has a channel with a width of the multiple of the wavelength of the circulating beam and a high effective refractive index difference in total reflection to adjacent regions.
Laser resonator according to the preceding claim, characterised in that the channel width varies locally.
Laser resonator according to one of the three preceding claims, characterised in that at least one reflecting structure has a Bragg grating which is disposed in such a manner that the circulating beam impinges on the grating channels at a non-perpendicular angle of incidence.
Laser resonator according to one of the preceding claims, characterised in that the end facets are planar or curved.
Laser resonator according to one of the preceding claims, characterised in that the predetermined laser mode has a constant phase in the waveguide plane along the end facets.
Laser resonator according to one of the preceding claims, characterised in that the wavefront of the predetermined laser mode has the same curve as the end facet in the waveguide plane along the end facet.
Laser resonator according to one of the preceding claims, characterised in that the thickness of the waveguide layer is dimensioned such that perpendicularly to the plane of the waveguide layer only one lateral mode is amplified and occurs or is guided.
Laser resonator according to one of the preceding claims, characterised in that strip electrodes adjacent to the waveguide layer for pumping the laser resonator are disposed at a spacing from the end facet in such a manner that they do not overlap the phase structures.
Method for producing a laser resonator according to one of the preceding claims,
- characterised in that,
- for the predetermined mode of the laser beam to be amplified, at one position in the region between two phase structures, a predetermined one-dimensionally lateral amplitude or phase distribution (Ao(x) or po(x)) of the wavefront, which extends in the plane of the waveguide layer, is prescribed, and
- the propagation of this mode between the two end facets is determined,
- the phase structures being determined in front of the two end facets such that the predetermined lateral phase distribution of the mode is constant after passing through each of the phase structures in the waveguide plane along the end facets.
Method according to the preceding claim, characterised in that a non-periodic phase distribution is prescribed as predetermined local phase distribution of the predetermined mode.
Method according to one of the two preceding claims, characterised in that a random phase distribution is prescribed as predetermined lateral phase distribution of the predetermined mode.
Method according to one of the three preceding claims, characterised in that a laterally statistically varying phase distribution in the waveguide plane is prescribed as predetermined lateral phase distribution.
Method according to the preceding claim, characterised in that those regions are determined in step a) in which the phase is smaller than the average phase and the corresponding regions are provided with a lower effective refractive index in step b).
Method according to one of the two preceding claims, characterised in that the corresponding regions are configured as thinned regions in step b).
Method according to one of the three preceding claims, characterised in that a common or two different threshold values are provided for the determination of the deviation of the phase in step a) and also for the cut-off criterion in step d).
Dependencies are inferred from the claim text.