Device for producing microwave signals

A device for generating microwave signals, e.g., for use in a distance and speed sensor in a motor vehicle, is provided. To this end, two laser sources are operated, whose emitted radiations are distinguished from each other by a set difference in wavelength. The two lasers are arranged in such a manner that the emitted laser beams overlap spatially. A photodiode is arranged in this region in which the two laser beams interfere. From the superimposition product of the two laser beams, this photodiode generates an electrical output signal that has the differential frequency of the two superimposed laser beams. In this context, the frequency difference of the two lasers is selected so that the frequency of the generated microwave radiation lies in the range of the radar beam to be generated.

FIELD OF THE INVENTION

The present invention relates to a device for generating microwave signals, e.g., for use in a distance and speed sensor in a motor vehicle.

BACKGROUND INFORMATION

From the publication “Optical Millimeter-Wave Systems for Broadband Mobile Communication, Devices and Techniques” by R.-P. Braun and G. Grokopf, published at the “International Zurich Seminar of Broadband Communications-Accessing, Transmission, Networking” at the ETH Zürich in February 1998, it is known that microwave frequencies may be generated by the superimposition of optical waves of semiconductor lasers of different wavelength in a transmitter, modulated, and transmitted.

SUMMARY

The present invention provides a device for generating microwave signals, e.g., for use in a motor vehicle.

To this end, two laser sources are operated, whose emitted radiations are distinguished from each other by a set difference in wavelength. The two lasers are arranged in such a manner that the emitted laser beams superimpose spatially. A photodiode is disposed in this region in which the two laser beams interfere. From the superimposition product of the two laser beams, this photodiode generates an electrical output signal which has the beat frequency of the two superimposed laser beams. The difference in frequency between the two lasers is selected so that the frequency of the resulting beat lies in the range of the microwave signals.

The device according to the present invention may have a compact configuration and, due to this, may be used in applications in which microwave signals are generated in the tightest space.

Moreover, the microwave signals may be generated with the aid of the emitted radiation of the two lasers that irradiate a photodiode in common.

The difference in the beat frequency generated by the two lasers may lie in the range between 50 GHz and 100 GHz.

The two lasers may be operated in an injection-locking operation, in that the radiation of a further or a plurality of further laser sources is injected into the two lasers.

The laser sources, the photodiode, a high-frequency filter, the high-frequency amplifier, as well as other possible components may be monolithically integrated on a single substrate.

The device may be operated in a motor vehicle, e.g., as a microwave generator for a distance and speed sensor.

DETAILED DESCRIPTION

FIG. 1shows an exemplary embodiment of the device according to the present invention. Master laser1generates a frequency-stable output radiation. It is divided in a power splitter2into two sub-beams and supplied to two laser sources3and4. The two laser sources3,4may be implemented in the form of two laser diodes. At this point, it should be pointed out that according to the present invention, master laser1and power splitter2do not necessarily have to be present. If both laser sources3,4emit a sufficiently frequency-stable output signal without master laser1, then it is possible to dispense with master laser1and power splitter2. In turn, these two laser sources3,4each generate an output radiation56.

The frequencies of the two output radiation beams5,6of laser sources3,4differ by the amount that is to be generated at the output of photodiode7as the frequency of the microwave signal to be generated. For example, if the microwave signal to be generated is to have a frequency of 76 gigahertz, then the frequencies of output radiations5,6of the two laser sources3,4differ by precisely this value, thus, by a frequency difference of 76 gigahertz, so that based on the mixing of the two beams5,6, which corresponds mathematically to a multiplication, due to the nonlinearity of photodiode7, the desired microwave output frequency of 76 gigahertz results.

These two radiation beams5,6of the two laser sources3,4are aligned spatially so that a region exists in which the two radiation beams5,6intersect. In this region of the superimposition, a photodiode7is placed which is irradiated by both radiation beams5,6simultaneously. To that end, the photodiode is selected so that its band width permits detection of the differential frequency, but frequencies which are very much higher than the differential frequency may not be resolved.

Due to the nonlinearity of photodiode7, resulting from the superimposed, optical input signal is an electrical output signal having the desired microwave frequency which has the frequency difference of the two radiation beams5,6. The output signal of this photodiode7is conducted via a high-frequency filter8, which may take the form of a band-pass filter. This filter8allows only the microwave signals to pass which lie in the output frequency band which is desired and is to be generated. Substantially higher or lower frequencies are filtered out of the input signal of filter8.

Finally, the microwave signal is amplified in a high-frequency amplifier9and fed to a further processing device10. Further processing device10may be a device for transmitting and receiving microwave radiation.

According to the present invention, the described device made of electrical and optical components may also be produced on a single substrate as a monolithic semiconductor chip. Moreover, it is within the scope of the device of the present invention that this device is mounted in a housing which is provided for a speed and distance control in a motor vehicle, the device of the present invention being used as a frequency generator.