6,129 research outputs found
Dispersive Fourier Transformation for Versatile Microwave Photonics Applications
Abstract: Dispersive Fourier transformation (DFT) maps the broadband spectrum of an ultrashort optical pulse into a time stretched waveform with its intensity profile mirroring the spectrum using chromatic dispersion. Owing to its capability of continuous pulse-by-pulse spectroscopic measurement and manipulation, DFT has become an emerging technique for ultrafast signal generation and processing, and high-throughput real-time measurements, where the speed of traditional optical instruments falls short. In this paper, the principle and implementation methods of DFT are first introduced and the recent development in employing DFT technique for widespread microwave photonics applications are presented, with emphasis on real-time spectroscopy, microwave arbitrary waveform generation, and microwave spectrum sensing. Finally, possible future research directions for DFT-based microwave photonics techniques are discussed as well
Photonics-enabled sub-Nyquist radio frequency sensing based on temporal channelization and compressive sensing
A novel approach to sensing broadband radio frequency (RF) spectrum beyond the Nyquist limit based on photonic temporal channelization and compressive sensing is proposed. A spectrally-sparse RF signal with unknown frequencies is modulated onto a highly chirped optical pulse. An optical channelizer slices the modulated pulse spectrum, which is equivalent to temporally sampling the RF waveform thanks to the dispersion-induced wavelength-to-time mapping. This serial-to-parallel conversion avoids the use of a high-speed detector and digitizer. Furthermore, compressive sensing with optical random demodulation is achieved using a spatial light modulator, enabling the system to capture the wideband multi-tone RF signal with a sampling rate far lower than the Nyquist rate. It is demonstrated that the temporal channelization system with a channel spacing of 20 GHz achieves RF spectrum sensing with a high resolution of 196 MHz. With an equivalent sampling rate of only 25 GHz, a 50-GHz broadband two-tone RF signal can be captured and reconstructed by the system thanks to compressive sensing with a compression ratio of 4
Multiheterodyne Detection and Sampling of Periodically Filtered White Light for Correlations at 20 km of Delay
A frequency comb is used as a set of coherent local oscillators to downconvert and spectrally compress white light that has been periodically filtered by a Fabry-Perot etalon. Multiheterodyne detection allows white light spread across 100 GHz of optical spectrum to be compressed to 5 GHz of radio frequency (RF) bandwidth for electronic sampling on an oscilloscope. Correlations are observed at delays of up to 20 km with a minimum resolution of less than 1 mm. Calculations show that resolution may be easily increased by increasing etalon finesse and frequency comb bandwidth
Photonic Filtering for Applications in Microwave Generation and Metrology
This work uses the photonic filtering properties of Fabry-Perot etalons to show improvements in the electrical signals created upon photodetection of the optical signal. First, a method of delay measurement is described which uses multi-heterodyne detection to find correlations in white light signals at 20 km of delay to sub millimeter resolution. By filtering incoming white light with a Fabry-Perot etalon, the pseudo periodic signal is suitable for measurement by combining and photodetecting it with an optical frequency comb. In this way, optical data from a large bandwidth can be downconverted and sampled on low frequency electronics. Second, a high finesse etalon is used as a photonic filter inside an optoelectronic oscillator (OEO). The etalon\u27s narrow filter function allows the OEO loop length to be extremely long for a high oscillator quality factor while still suppressing unwanted modes below the noise floor. The periodic nature of the etalon allows it to be used to generate a wide range of microwave and millimeter wave tones without degradation of the RF signal
Recent advances on time-stretch dispersive Fourier transform and its applications
The need to measure high repetition rate ultrafast processes cuts across multiple areas of science. The last decade has seen tremendous advances in the development and application of new techniques in this field, as well as many breakthrough achievements analyzing non-repetitive optical phenomena. Several approaches now provide convenient access to single-shot optical waveform characterization, including the dispersive Fourier transform (DFT) and time-lens techniques, which yield real-time ultrafast characterization in the spectral and temporal domains, respectively. These complementary approaches have already proven to be highly successful to gain insight into numerous optical phenomena including the emergence of extreme events and characterizing the complexity of laser evolution dynamics. However, beyond the study of these fundamental processes, real-time measurements have also been driven by particular applications ranging from spectroscopy to velocimetry, while shedding new light in areas spanning ultrafast imaging, metrology or even quantum science. Here, we review a number of landmark results obtained using DFT-based technologies, including several recent advances and key selected applications. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
Radio Astronomy in LSST Era
A community meeting on the topic of "Radio Astronomy in the LSST Era" was
hosted by the National Radio Astronomy Observatory in Charlottesville, VA (2013
May 6--8). The focus of the workshop was on time domain radio astronomy and sky
surveys. For the time domain, the extent to which radio and visible wavelength
observations are required to understand several classes of transients was
stressed, but there are also classes of radio transients for which no visible
wavelength counterpart is yet known, providing an opportunity for discovery.
From the LSST perspective, the LSST is expected to generate as many as 1
million alerts nightly, which will require even more selective specification
and identification of the classes and characteristics of transients that can
warrant follow up, at radio or any wavelength. The LSST will also conduct a
deep survey of the sky, producing a catalog expected to contain over 38 billion
objects in it. Deep radio wavelength sky surveys will also be conducted on a
comparable time scale, and radio and visible wavelength observations are part
of the multi-wavelength approach needed to classify and understand these
objects. Radio wavelengths are valuable because they are unaffected by dust
obscuration and, for galaxies, contain contributions both from star formation
and from active galactic nuclei. The workshop touched on several other topics,
on which there was consensus including the placement of other LSST "Deep
Drilling Fields," inter-operability of software tools, and the challenge of
filtering and exploiting the LSST data stream. There were also topics for which
there was insufficient time for full discussion or for which no consensus was
reached, which included the procedures for following up on LSST observations
and the nature for future support of researchers desiring to use LSST data
products.Comment: Conference summary, 29 pages, 1 figure; to be published in the Publ.
Astron. Soc. Pacific; full science program and presentations available at
http://science.nrao.edu/science/event/RALSST201
External Cavity Mode-locked Semiconductor Lasers For The Generation Of Ultra-low Noise Multi-gigahertz Frequency Combs And Applications In Multi-heterodyne Detection Of Arbitrary Optical Waveforms
The construction and characterization of ultra-low noise semiconductor-based mode-locked lasers as frequency comb sources with multi-gigahertz combline-to-combline spacing is studied in this dissertation. Several different systems were built and characterized. The first of these systems includes a novel mode-locking mechanism based on phase modulation and periodic spectral filtering. This mode-locked laser design uses the same intra-cavity elements for both mode-locking and frequency stabilization to an intra-cavity, 1,000 Finesse, Fabry-Pérot Etalon (FPE). On a separate effort, a mode-locked laser based on a Slab-Coupled Optical Waveguide Amplifier (SCOWA) was built. This system generates a pulse-train with residual timing jitter o
Development Toward a Ground-Based Interferometric Phased Array for Radio Detection of High Energy Neutrinos
The in-ice radio interferometric phased array technique for detection of high
energy neutrinos looks for Askaryan emission from neutrinos interacting in
large volumes of glacial ice, and is being developed as a way to achieve a low
energy threshold and a large effective volume at high energies. The technique
is based on coherently summing the impulsive Askaryan signal from multiple
antennas, which increases the signal-to-noise ratio for weak signals. We report
here on measurements and a simulation of thermal noise correlations between
nearby antennas, beamforming of impulsive signals, and a measurement of the
expected improvement in trigger efficiency through the phased array technique.
We also discuss the noise environment observed with an analog phased array at
Summit Station, Greenland, a possible site for an interferometric phased array
for radio detection of high energy neutrinos.Comment: 13 Pages, 14 Figure
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