Method and device for detecting motion

摘要

A method for detecting motion direction of an object (4) comprises the steps of:
laser output light (L1) is generated, using a semiconductor laser (2) having a thermal response frequency (fr);the laser is driven with rectangularly modulated DC current (I) having a modulation frequency higher than said thermal response frequency (fr) and preferably higher than twice said thermal response frequency (fr), such as to triangularly modulate the wavelength of the laser output light;the laser output light is directed to the object;a portion of reflected light (L3) is allowed to interfere with light (L0) within the laser;a portion of the laser light is used as measuring beam (5);the frequency spectrum of the measuring beam (5) is analyzed in conjunction with the modulated laser current in order to determine the direction of movement of the object (4).

主权项

1. A motion detector, comprising:
a laser comprising a semi-transparent front mirror, a semi-transparent rear mirror, and a semiconductor laser body having a thermal response frequency between said two mirrors, the laser being configured to generate laser light within the laser body and to output a portion of the laser light at its front mirror as output light directed toward an object, and to output measuring light at its rear mirror, the laser further being designed to allow at least a portion of reflected light from the object to interfere with the laser light; a controllable laser current source configured to supply the laser with laser current such as to generate the laser light within the laser body; a controller configured to control the laser current source; a light detector for detecting at least a portion of the measuring light; wherein the controller is configured to control the laser current source such that it generates the laser current as a rectangularly modulated DC current having an amplitude and having a modulation frequency which is greater than said thermal response frequency so as to triangularly modulate the wavelength of the laser output light, wherein the controller is also configured to analyze the frequency spectrum of the detected measuring light in conjunction with the modulated laser current in order to determine a direction of relative movement of the object with respect to the motion detector, and wherein the controller is further configured to adjust modulation frequency of the rectangularly modulated DC current as a function of a speed of the relative movement of the object with respect to the motion detector, wherein the controller is further configured to adjust the amplitude of the rectangularly modulated DC current as the modulation frequency is adjusted so as to maintain a phase modulation depth of the laser light to be constant.