Incoherent compression of complementary code pairs for laser ranging and detection

A scheme for the incoherent compression of complementary code pairs is proposed and demonstrated in a laser range-finding experiment. The off-peak aperiodic auto-correlations of complementary bipolar codes sum up to zero, hence they are attractive for radar and laser ranging systems. In incoherent compression, the two codes are converted to unipolar representations using a pulse position modulation algorithm prior to transmission. Following incoherent detection, the two received echoes are compressed through digital filtering, and added together to obtain strong sidelobe suppression. The scheme does not require the preservation of phase information in transmission or reception, and the length of the code pairs is scalable through simple procedures. Incoherent compression is particularly attractive for photonic implementations, in which direct detection is phase insensitive. A peak-to-sidelobe ratio of 42 dB is obtained in a laser range-finding experiment using 832 bits-long codes.