Known semiconductor lasers of the type defined in the introduction, also referred to in the art as so-called DFB (distributed feedback) laser diodes, have a lattice structure which extends through the laser layer and which facilitates the construction of a monomode laser diode in which, in contrast to multi-mode laser diodes, laser radiation with one specified laser mode is emitted and other modes are suppressed by the lattice structure. The production of the DFB laser diodes constructed in the known manner proves extremely costly, in particular due to the production and test process employed and the high reject quota associated therewith. For the production of the known DFB laser diodes on the basis of a wafer on a semiconductor substrate base, epitaxy is used to form the structure of the semiconductor wafer on the semiconductor substrate. For the formation of the lattice structure in the laser layer, when approximately half the layer height of the epitaxial structure has been reached the epitaxial growth is interrupted and the lattice structure is introduced in a lithographic—and removal process. Then the epitaxial growth is continued. The interruption of the epitaxy in the formation of the laser layer and the following overgrowth of the lattice structure introduced into the half-layer induces defects in the laser layer which disadvantageously affect the properties of the laser layers and possibly manifest in a higher current consumption or a reduced life of the laser diodes.
As a result of the mutual influences between the laser layer and the lattice structure formed in the laser layer in terms of the amplification properties of the semiconductor laser wafer, the properties of a semiconductor laser wafer produced in the described way cannot be predetermined in an exact manner. As the properties of the semiconductor laser wafer cannot be determined until after the conclusion of the epitaxial growth and the complete formation of the laser layer in the test operation, the amplification spectrum of the semiconductor laser wafer also cannot be determined until after the formation of the lattice structure in the laser layer, with the result that the lattice structure cannot be accurately adapted to the amplification spectrum of the laser layers and consequently the known DFB laser diodes also cannot be produced in a precise manner in accordance with predefined specifications relating to the desired laser mode or the desired wavelength. Rather, the structure of the known DFB laser diodes described in the foregoing requires a production process in which different lattice structures must be formed in the laser layer of a semiconductor laser wafer in order that, by checking the laser diodes separated from the semiconductor laser wafer, precisely those laser diodes which emit the desired laser mode with the desired wavelength can be retrospectively determined. It is thus apparent that the structural design of the known DFB laser diodes necessitates the production of a plurality of laser diodes in order that the laser diodes suitable for the intended application, i.e. those laser diodes which emit a laser radiation with the desired wavelength, can be selected from this plurality of laser diodes by testing of their laser properties.
USPTO Backgrounds
USPTO Backgrounds