Topic
Chirp
About: Chirp is a research topic. Over the lifetime, 14403 publications have been published within this topic receiving 178726 citations.
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TL;DR: In this paper, the amplification and subsequent recompression of optical chirped pulses were demonstrated using a system which produces 1.06 μm laser pulses with pulse widths of 2 ps and energies at the millijoule level.
3,961 citations
TL;DR: In this paper, the effect of the shape and the initial frequency chirp of input pulses on shape and spectrum of amplified pulses is discussed in detail and the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives.
Abstract: Amplification of ultrashort optical pulses in semiconductor laser amplifiers is shown to result in considerable spectral broadening and distortion as a result of the nonlinear phenomenon of self-phase modulation (SPM). The physical mechanism behind SPM is gain saturation, which leads to intensity-dependent changes in the refractive index in response to variations in the carrier density. The effect of the shape and the initial frequency chirp of input pulses on the shape and the spectrum of amplified pulses is discussed in detail. Particular attention is paid to the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives. The experimental results, performed by using picosecond input pulses from a 1.52- mu m mode-locked semiconductor laser, are in agreement with the theory. When the amplified pulse is passed through a fiber, it is initially compressed because of the frequency chirp imposed on it by the amplifier. This feature can be used to compensate for fiber dispersion in optical communication systems. >
1,175 citations
TL;DR: By incorporating a section of large positive-dispersion fiber in an all-fiber erbium ring laser, a fully self-starting source of 77-fs pulse with 90 pJ of energy and greater than 1 kW of peak power at a 45-MHz repetition rate is obtained.
Abstract: By incorporating a section of large positive-dispersion fiber in an all-fiber erbium ring laser, we obtain high-energy pulses with spectral widths of 56 nm. The chirp on these pulses is highly linear and can be compensated for with dispersion in the output coupling fiber lead. The result is a fully self-starting source of 77-fs pulse with 90 pJ of energy and greater than 1 kW of peak power at a 45-MHz repetition rate.
912 citations
TL;DR: Based on quantitative comparison, the chirp scaling algorithm provides image quality equal to or better than the precision range/Doppler processor, as defined by the system bandwidth.
Abstract: A space-variant interpolation is required to compensate for the migration of signal energy through range resolution cells when processing synthetic aperture radar (SAR) data, using either the classical range/Doppler (R/D) algorithm or related frequency domain techniques. In general, interpolation requires significant computation time, and leads to loss of image quality, especially in the complex image. The new chirp scaling algorithm avoids interpolation, yet performs range cell migration correction accurately. The algorithm requires only complex multiplies and Fourier transforms to implement, is inherently phase preserving, and is suitable for wide-swath, large-beamwidth, and large-squint applications. This paper describes the chirp scaling algorithm, summarizes simulation results, presents imagery processed with the algorithm, and reviews quantitative measures of its performance. Based on quantitative comparison, the chirp scaling algorithm provides image quality equal to or better than the precision range/Doppler processor. Over the range of parameters tested, image quality results approach the theoretical limit, as defined by the system bandwidth. >
897 citations
TL;DR: This paper contains many of the important analytical methods required for the design of a Chirp radar system, and a method to reduce the time side lobes by weighting the pulse energy spectrum is explained in terms of paired echoes.
Abstract: A new radar technique has been developed that provides a solution for the conflicting requirements of simultaneous long-range and high-resolution performance in radar systems. This technique, called Chirp at Bell Telephone Laboratories, recognizes that resolution depends on the transmitted pulse bandwidth. A long high-duty-factor transmitted pulse, with suitable modulation (linear frequency modulation in the case of Chirp), which covers a frequency interval many times the inherent bandwidth of the envelope, is employed. The receiver is designed to make optimum use of the additional signal bandwidth. This paper contains many of the important analytical methods required for the design of a Chirp radar system. The details of two signal generation methods are considered and the resulting signal waveforms and power spectra are calculated. The required receiver characteristics are derived and the receiver output waveforms are presented. The time-bandwidth product is introduced and related to the effective increase in the performance of Chirp systems. The concept of a matched filler is presented and used as a reference standard in receiver design. The effect of amplitude and phase distortion is analyzed by the method of paired echoes. One consequence of the signal design is the presence of time side lobes on the receiver output pulse analogous to the spatial side lobes in antenna theory. A method to reduce the time side lobes by weighting the pulse energy spectrum is explained in terms of paired echoes. The weighting process is described, and calculated pulse envelopes, weighting network characteristics and dele-???
889 citations