Study On Laser Linear Frequency Modulation In SAL

Synthetic Aperture Ladar (SAL) is a kind of imaging Ladar utilizing synthetic aperture technology to obtain high resolution images without large optics aperture. Compared with Synthetic Aperture Radar (SAR) using microwave as radiating SAL has many advantages due to its shorter radiative wavelength.Although the idea of synthetic aperture technology can be directly used to optical frequencies from microwave frequencies in principle, SAL still have a lot of difficulties in the launch, transmission, reception and processing of the laser signal, as laser wavelength is very short. SAL launches linear frequency modulation (LFM) laser signal and obtains received light phase information by detecting optical heterodyne. The linear frequency modulation of laser beam has been discussed in detail. In order to satisfy the large bandwidth requirements for SAL, it would be necessary to adopt a suitable LFM laser signal generation technology.In this paper, a method of changing the length of laser cavity based on the displacement property of piezoelectric (PZT) is adopted. The basic characteristics of LFM based on PZT are analyzed theoretically and experimentally. The experimental set-up that consists of a Michelson interferometer and measuring system is established. The results show that the modulation bandwidth could be as high as 9GHz.