Method and device for detecting motion

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.

2. The motion detector of claim 1 , wherein the controller is configured to analyze the measuring signal in conjunction with the phase of the laser current.

3. The motion detector of claim 1 , wherein the controller is configured to analyze the frequency spectrum of the detected light by separate spectrum analysis on up- and down-modulation segments of the laser wavelength.

4. The motion detector of claim 1 , further comprising a quadrature demodulator receiving the detector output signal and providing a quadrature demodulated signal to the controller, and wherein the controller is configured to analyze the frequency spectrum of the detected light by analysis of the frequency content of the quadrature demodulated signal such that a frequency corresponding to a speed of the relative movement of the object is discriminated from other frequencies in the spectrum.

5. A method for detecting a direction of relative movement of an object with respect to a semiconductor laser, the method comprising the steps of;

generating laser light using the semiconductor laser, the semiconductor laser having a thermal response frequency;

driving the laser with a rectangularly modulated Dc laser current having an amplitude and a modulaiton frequency which is greater than said thermal response frequency such as to triangularly modulate the wavelength of the laser light;

outputting a portion of the laser light as output light, the output light being directed toward the object;

allowing a portion of reflected light form the object interfere with the laser light;

using a portion of the laser light as a measuring beam

analyzing the frequency spectrum the measuring beam in conjunction with the modulated laser current in order to determine the direction of the relative movement of the object;

adjusting the 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; and

adjusting 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.

6. The method of claim 5 , wherein the step of analyzing the frequency spectrum of the measuring beam is done by separate spectrum analysis on up- and down-modulation segments of the laser wavelength.

7. The method of claim 5 , wherein the step of analyzing the frequency spectrum of the measuring beam is done by analysis of the frequency content of a quadrature demodulated signal such that a frequency corresponding to a speed of the relative movement of the object is discriminated from other frequencies in the spectrum.