Abstract: A semiconductor diode laser (1) with a monitor diode (2) includes a semiconductor body with a substrate (4) and a superimposed layer structure (5) having an active layer (6) and a pn junction (7) with which radiation (24) can be generated. The monitor diode (2) is separated from the diode laser by a groove (10) which extends into the substrate (4) and of which one of the walls forms an end face of the laser. The groove (10) and the monitor diode (2) are present at the side where the main radiation beam (24) emerges, while the active layer (6) extends over at most only a small portion, preferably at most 20%, of the length of the monitor diode (2). The length in the monitor diode over which absorption takes place is preferably smaller than the absorption length for the emitted laser radiation.

Abstract: A tunable semiconductor diode laser with distributed reflection (DBR semiconductor laser) having a wide wavelength range is a suitable transmitter or local oscillator in a receiver in heterodyne and coherent optical glass fiber communication systems. Such a diode includes, in addition to the Bragg section in which the Bragg reflection takes place, an active section in which the radiation-emitting active region is present. When such a semiconductor diode laser is further provided with a so-called phase section, tuning is possible over a large wavelength range within one oscillation mode. A laser which is continuously tunable over the whole wavelength range is obtained by provided a mechanism by which the intensity of radiation which is reflected at the junction between the active section and the phase section is made low with respect to the intensity of the radiation which returns from the phase section to the active section.

Abstract: In DFB/DBR semiconductor diode lasers, competition may arise between the DFB (Distributed Feed-Back) mode corresponding to the period of the grid present and the FP (=Fabry-Perot) mode determined by the relative distance of the mirror surfaces, as a result of which the laser does not operate in one single mode. By providing an antireflex layer, this problem is suppressed, but other disadvantages are obtained, such as a large line width. However, by providing a phase layer on the antireflection coating, the operation of the laser in a single mode is combined with a comparatively narrow line width. Furthermore, a reflective coating can be applied to the phase layer. In this case, both the module and the phase of the effective reflection can be adjusted substantially independently of each other, as a result of which a narrow line width and SLM can be more readily combined.

Abstract: A semiconductor laser of the distributed feedback (DFB or DBR) type is bounded in the longitudinal direction by end surfaces at right angles to the active region and at least one of these end faces is provided with an anti-reflection layer in order to suppress Fabry-Perot modes. In order to obtain an optimum effect, an anti-reflection layer of hafnium oxide is used. The invention is used with great advantage in lasers of the DCPBH (Double Channel Planar Buried Hetero-structure) type.

Abstract: An electret transducer comprising a diaphragm (3) arranged between first (1 or 1') and second electrodes with at least one electrode (2) arranged at some distance from the diaphragm as a stationary electrode formed with holes (5). An air gap (4) is formed between the diaphragm (3) and said electrode (2). In the case of one air gap the air gap width d and the area A (7) enclosed by four holes which are situated nearest each other in said electrode (2) are selected so that the following equation is satisfied ##EQU1## where .eta. is the dynamic viscosity of the air in the air gap. In the case of an air gap on each side of the diaphragm, the air gap widths d.sub.1 and d.sub.2 and the said areas A.sub.1 and A.sub.