High-Resolution Low-Sidelobe Laser Ranging Based on Incoherent Pulse Compression

A technique for high-resolution laser detection and ranging with strong sidelobe suppression is experimentally demonstrated. This method relies on the transmission of a long unipolar sequence of intensity-modulated pulses, the incoherent direct detection of reflected echoes, and subsequent processing by proper digital filters at the receiver end. The obtained sidelobe suppression nearly replicates that of the bipolar sequences, even though the transmitted sequence is unipolar. Both the transmitted sequence and the receiver-end filter are derived from a bipolar code through a pulse position modulation algorithm. Mismatched filters are used for further sidelobe suppression. Due to the processing gain, ranging measurements are successfully performed at signal-to-noise ratios as low as -20 dB. A range change of 2.5 cm is accurately resolved. The proposed method provides the sidelobe suppression of a complex coherent receiver while using simple incoherent detection.