Laser ranging measurements using incoherent pulse compression of complementary code pairs is reported. The two bipolar codes are converted to unipolar representations using a pulse position modulation algorithm, and used in succession in intensity modulation of a laser ranging source. Reflected echoes from a wall target are directly and incoherently detected. The cross-correlation between each of the two collected echoes and its respective, reference bipolar sequence, that is digitally stored at the receiver, is calculated. The two correlation functions are then added together. The off-peak aperiodic correlation functions of two codes sum up to zero, hence they are particularly suitable for low-sidelobe radar and laser ranging and detection systems. The scheme does not require the preservation of phase information in transmission or reception and provides superior sidelobe suppression compared with that of longer single codes. The code pairs are scalable to arbitrary lengths through simple procedures. Simulated and experimental ranging measurements in the presence of additive noise are discussed. The distance to the target could be recovered based on weak collected echoes, with an average optical power as low as 2 nW, without averaging over repeating measurements.
A microwave-photonic, ultra-wideband (UWB) noise radar system is proposed and demonstrated.
The system brings together photonic generation of UWB waveforms and fiber-optic distribution.
The use of UWB noise provides high ranging resolution and better immunity to interception and
jamming. Distribution over fibers allows for the separation the radar-operating personnel and
equipment from the location of the front-end. The noise waveforms are generated using the
amplified spontaneous emission that is associated with stimulated Brillouin scattering in a standard
optical fiber, or with an erbium-doped fiber amplifier. Our experiments demonstrate a proof of
concept for an integrated radar system, driven by optically generated UWB noise waveforms of
more than 1 GHz bandwidth that are distributed over 10 km distance. The detection of concealed
metallic object and the resolving of two targets with the anticipated ranging resolution are reported.