In this work, Wang and coauthors generate and demodulate a wide-bandwidth chirp using microwave photonic devices. In their microwave photonic radar, a low-frequency chirp signal is mixed with a continuous wave laser using a Mach-Zehnder Mixer (MZM). This operation generates radio frequency (RF) harmonics riding on an optical carrier; the third harmonic is enhanced using a combination of MZM biasing and optical filters. This signal is split and part of it is used as the detection local oscillator (LO) signal while the rest is down-converted back to RF band using the photoelectric conversion property of a high bandwidth photodiode. This RF signal is then amplified and transmitted with the antenna. The signal reflected by the scene is captured by the receiver antenna, amplified, and supplied to a second MZM. In the MZM, the received signal is mixed with the LO signal. The output of the mixer is detected with a photodiode and the frequency of the supported signal encodes range information about the scene like in conventional FMCW.
The authors demonstrate how the ultra-wide-band radar can be used to extract centimeter-scale range measurements at kilometer distances. They use inverse synthetic aperture radar methods to measure and reconstruct images of fast-moving airborne targets at long ranges; they also demonstrate synthetic aperture radar measurements and images collected from a moving vehicle. Using the mature photonics platform, microwave photonic radar approaches have the potential to overcome some of the challenges of the electronic technologies. The system and applications demonstrated in this paper show the great potential of microwave photonics radar for remote sensing applications.
You must log in to add comments.