September 2018
Spotlight Summary by Orges Furxhi
Ka-band microwave photonic ultra-wideband imaging radar for capturing quantitative target information
Wang and co-authors demonstrate a Ka-band frequency modulated continuous wave (FMCW) ultra-wideband microwave photonic imaging radar. In conventional FMCW radar, a continuous wave signal with frequency that varies linearly with time (a chirp) is used to resolve the range of reflecting targets in the scene. Since the frequency is changing linearly over time, the reflected and local signal differ in frequency by an amount proportional to the reflected signal travel time; the range is then directly proportional to the beat frequency resulting from mixing the reflected signal with the local signal.
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.
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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.
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Article Information
Ka-band microwave photonic ultra-wideband imaging radar for capturing quantitative target information
Anle Wang, Jianghai Wo, Xiong Luo, Yalan Wang, Wenshan Cong, Pengfei Du, Junkai Zhang, Biao Zhao, Jin Zhang, Yong Zhu, Jiangqiao Lan, and Lan Yu
Opt. Express 26(16) 20708-20717 (2018) View: Abstract | HTML | PDF