SEMICONDUCTOR LASER WITH INTEGRATED PHOTOTRANSISTOR
The present invention relates to a semiconductor laser for use in an optical module for measuring distances and/or movements, using the self-mixing effect. The semiconductor laser comprises a layer structure including an active region ( 3 ) embedded between two layer sequences ( 1, 2 ) and further comprises a photodetector arranged to measure an intensity of an optical field resonating in said laser. The photodetector is a phototransistor composed of an emitter layer (e), a collector layer (c) and a base layer (b), each of which being a bulk layer and forming part of one of said layer sequences ( 1, 2 ). With the proposed semiconductor laser an optical module based on this laser can be manufactured more easily, at lower costs and in a smaller size than known modules.
1 . A vertical cavity surface emitting laser, comprising
a layer structure including an active region embedded between two layer sequences and
a photodetector arranged to measure an intensity of an optical field resonating in said laser, wherein the photodetector is a phototransistor comprising an emitter layer (e), a collector layer (c) and a base layer (b), each of which being a bulk layer and forming part of one of said layer sequences ( 1 , 2 ), the phototransistor being arranged in a portion of the layer sequence in which the intensity of the optical field still exceeds 10% of a peak intensity which is achieved in the vicinity of the active region.
2 . (canceled)
3 . The vertical cavity surface emitting laser according to claim 1 , wherein the phototransistor is arranged in one of two halves of the layer sequence which half is located closer to the active region 1 .
4 . The vertical cavity surface emitting laser device according to claim 1 , wherein the two layer sequences are designed to form end mirrors of the laser, and the emitter layer (e), the collector layer (c) and the base layer (b) are formed by appropriately adapting bandgaps of layers of the layer sequences.
5 . The vertical cavity surface emitting laser according to claim 4 , wherein the collector layer (c) is formed of a high bandgap material and the base layer (b) and the emitter layer (e) are formed of a low bandgap material having a bandgap which is lower than the photon energy of the optical field resonating in the laser.
6 . The vertical cavity surface emitting laser according to claim 1 , wherein the emitter layer is set to ground potential.
7 . The vertical cavity surface emitting laser according to claim 1 , wherein the thickness of a region formed by the base (b) and emitter layers (e) is equal to one quarter of an optical wavelength of the optical field and said region is arranged such that the base layer (b) is in an optical field intensity peak and the emitter layer (e) is at a null of the optical field.
8 . Optical sensor module for measuring distances and/or movements including at least one vertical cavity surface emitting laser according to claim 1 emitting a measuring beam which, when reflected by an object, re-enters the laser cavity and generates a self-mixing effect which is measured by said phototransistor.
9 - 10 . (canceled)