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Showing papers on "Chirp published in 2000"


Journal ArticleDOI
TL;DR: An upper bound for the number of the detectable chirp components using the DCFT is provided in terms of signal length and signal and noise powers, and it is shown that the N-point DCFT performs optimally when N is a prime.
Abstract: The discrete Fourier transform (DFT) has found tremendous applications in almost all fields, mainly because it can be used to match the multiple frequencies of a stationary signal with multiple harmonics. In many applications, wideband and nonstationary signals, however, often occur. One of the typical examples of such signals is chirp-type signals that are usually encountered in radar signal processing, such as synthetic aperture radar (SAR) and inverse SAR imaging. Due to the motion of a target, the radar return signals are usually chirps, and their chirp rates include the information about the target, such as the location and the velocity. In this paper, we study discrete chirp-Fourier transform (DCFT), which is analogous to the DFT. Besides the multiple frequency matching similar to the DFT, the DCFT can be used to match the multiple chirp rates in a chirp-type signal with multiple chirp components. We show that when the signal length N is prime, the magnitudes of all the sidelobes of the DCFT of a quadratic chirp signal are 1, whereas the magnitude of the mainlobe of the DCFT is /spl radic/N. With this result, an upper bound for the number of the detectable chirp components using the DCFT is provided in terms of signal length and signal and noise powers. We also show that the N-point DCFT performs optimally when N is a prime.

329 citations


Journal ArticleDOI
TL;DR: The rising chirp may be of clinical use in assessing the integrity of the entire peripheral organ and not just its basal end, and is compatible with earlier experimental results from recordings of compound action potentials (CAP).
Abstract: This study examines auditory brainstem responses (ABR) elicited by rising frequency chirps. The time course of frequency change for the chirp theoretically produces simultaneous displacement maxima by compensating for travel-time differences along the cochlear partition. This broadband chirp was derived on the basis of a linear cochlea model [de Boer, “Auditory physics. Physical principles in hearing theory I,” Phys. Rep. 62, 87–174 (1980)]. Responses elicited by the broadband chirp show a larger wave-V amplitude than do click-evoked responses for most stimulation levels tested. This result is in contrast to the general hypothesis that the ABR is an electrophysiological event most effectively evoked by the onset or offset of an acoustic stimulus, and unaffected by further stimulation. The use of this rising frequency chirp enables the inclusion of activity from lower frequency regions, whereas with a click, synchrony is decreased in accordance with decreasing traveling velocity in the apical region. The use of a temporally reversed (falling) chirp leads to a further decrease in synchrony as reflected in ABR responses that are smaller than those from a click. These results are compatible with earlier experimental results from recordings of compound action potentials (CAP) [Shore and Nuttall, “High synchrony compound action potentials evoked by rising frequency-swept tonebursts,” J. Acoust. Soc. Am. 78, 1286–1295 (1985)] reflecting activity at the level of the auditory nerve. Since the ABR components considered here presumably reflect neural response from the brainstem, the effect of an optimized synchronization at the peripheral level can also be observed at the brainstem level. The rising chirp may therefore be of clinical use in assessing the integrity of the entire peripheral organ and not just its basal end.

303 citations


Journal ArticleDOI
TL;DR: The spectral behavior of a white-light continuum generated in air by 2-TW femtosecond laser pulses at 800 nm shows that the continuum's intensity increases strongly with the laser energy and depends on the initial chirp.
Abstract: We investigated the spectral behavior of a white-light continuum generated in air by 2-TW femtosecond laser pulses at 800 nm. The spectrum extends at least from 300 nm to 4.5 mum. From 1 to 1.6 mum the continuum's intensity increases strongly with the laser energy and depends on the initial chirp.

228 citations


Journal ArticleDOI
TL;DR: In this paper, a saddle point integration method for solving the resulting line integral of a particular moment generating function is adopted, and a closed-form approximation for the bit error probability is also provided, which is within 0.01 dB from the exact numerical results.
Abstract: A novel approach to analytically evaluate the bit error probability in optically preamplified direct-detection systems is presented, which can take into account the effects of pulse shaping, chirping, filtering at the transmitter and the receiver, both pre- and postdetection, chromatic dispersion, and ASE noise. The method is computationally very fast in that the saddle point integration method for solving the resulting line integral of a particular moment generating function is adopted. A closed-form approximation for the bit error probability is also provided, which is within 0.01 dB from the exact numerical results.

198 citations


Journal ArticleDOI
TL;DR: In this article, a tunable dispersion compensating device, based on thermally actuated fiber gratings, is proposed for high-speed wavelength-division-multiplexed lightwave systems.
Abstract: Dispersion management is becoming paramount in high-speed wavelength-division-multiplexed lightwave systems, that operate at per-channel rates of 40 Gb/s and higher. The dispersion tolerances, in these systems, are small enough that sources of dispersion variation, that are negligible in slower systems, become critically important to network performance. At these high-bit rates, active dispersion compensation modules may be required to respond dynamically to changes occurring in the network, such as variations in the per-channel power, reconfigurations of the channel's path that are caused by add-drop operations, and environmental changes, such as changes in ambient temperature. We present a comprehensive discussion of an emerging tunable dispersion compensating device, based on thermally actuated fiber gratings. These per-channel devices rely on a distributed on-fiber thin film heater, deposited onto the outer surface of a fiber Bragg grating. Current flowing through the thin film generates resistive heating at rates that are governed by the thickness profile of the metal film. A chirp in the grating is obtained by using a thin-film, whose thickness varies with position along the length of the grating in a prescribed manner; the chirp rate is adjusted by varying the applied current. The paper reviews some of the basic characteristics of these devices and their implementation, in a range of different applications, including the mitigation of power penalties associated with optical power variations. We present detailed analysis of the impact of group-delay ripple and polarization-mode dispersion on systems performance, and present results from systems experiments, that demonstrate the performance of these devices at bit rates of 10, 20, 40 and 160 Gb/s. We also discuss advantages and disadvantages of this technology, and compare to other devices.

196 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) laser at room temperature and found that low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers.
Abstract: We have examined the dynamic properties of high-aspect-ratio InAs-quantum-dot (QD) lasers at room temperature. A novel characteristic of low chirp in the lasing wavelength under 1-GHz current modulation was found in the quantum dot lasers. This is more than one order of magnitude less than the typical chirp (0.2-nm) found in a conventional quantum well laser that we used as a reference. Low chirp was obtained not only in the ground state lasing but in the second level lasing of quantum dots as well.

190 citations


Journal ArticleDOI
TL;DR: In this article, the angular chirp of ultrashort laser pulses is investigated analytically and experimentally, based on interferometric field autocorrelation (FIAR).
Abstract: We investigate analytically and experimentally various aspects of the angular chirp of ultrashort laser pulses. This type of chirp is easily produced by slight misalignment of standard pulse stretcher and/or compressor setups. Angular chirp leads to tilted pulse fronts in the near field and to a strong reduction of intensity in the focus. The effect is rather difficult to observe with standard diagnostic techniques. We present a method that is based on interferometric field autocorrelation and allows us to measure the angular chirp reliably. Suggestions on how to avoid this effect are outlined as well.

178 citations


Journal ArticleDOI
TL;DR: Control over the vibrational dynamics through parameterizations of linear chirp, impulsive-stimulated-Raman-scattering, and phase-locked double pulses is demonstrated.

176 citations


Proceedings ArticleDOI
19 May 2000
TL;DR: This work reports on the use of broadband chirp signals for spread spectrum systems in indoor applications and presents simulations and measurement results from demonstrator systems which use surface acoustic wave (SAW) devices for the generation and matched altering of the chirP signals.
Abstract: We report on the use of broadband chirp signals for spread spectrum systems in indoor applications. The presented system concepts make use of chirp transmission and pulse compression. Different modulation schemes for the chirp signals resulting in different system performance and complexity are compared in terms of bit error rate for the AWGN channel and for frequency selective indoor radio channels. We present simulations and measurement results from demonstrator systems which use surface acoustic wave (SAW) devices for the generation and matched altering of the chirp signals. The RF and IF frequency and transmission bandwidth of the presented systems are 2.4 GHz, 348.8 MHz, and 80 MHz, respectively. Due to the processing gain of 16 dB-made possible by the use of SAW devices-and the large transmission bandwidth the system is insensitive against frequency selective fading, CW interference and noise.

144 citations


Journal ArticleDOI
TL;DR: In this paper, the experimental results for the cross phase modulation induced transient absorption signal in a 1 mm thick fused silica plate using a white light continuum as a probe were compared with those obtained theoretically by numerically solving the set of nonlinear coupled wave equations describing the propagation of the pump and the probe.
Abstract: We present experimental results for the cross phase modulation (xpm) induced transient absorption signal in a 1 mm thick fused silica plate using a white light continuum as a probe. The fused silica plate mimics the entrance window of a commercial flow cell commonly used in liquid-phase transient absorption measurements. The experimental results are compared with those obtained theoretically by numerically solving the set of nonlinear coupled wave equations describing the propagation of the pump and the probe. The simulations allow for the different group velocities of the pump and probe pulses, and include the influence of the first and second order dispersion on the continuum probe. From the calculations the physical origin of the complex oscillatory feature observed around the zero time delay of each wavelength of the (chirped) continuum has been accurately identified. The influence of propagation effects arising from the finite thickness of the sample is discussed in great detail, and the necessity to work with thin samples, preferably free-flowing jets, is emphasized. The good agreement between theory and experiment indicates that the xpm artifact may be useful for characterizing the continuum probe, in particular its chirp.

136 citations


Journal ArticleDOI
TL;DR: An analytical expression relating the group delay at the output of the AOPDF to the input acoustic signal is obtained with coupled-wave theory in the case of collinear and quasi-collinear bulk acousto-optic interactions.
Abstract: Acousto-optic programmable dispersive filters (AOPDF) can compensate in real time for large amounts of group-delay dispersion. This feature can be used in chirped-pulse amplification femtosecond laser chains to compensate adaptively for dispersion. An analytical expression relating the group delay at the output of the AOPDF to the input acoustic signal is obtained with coupled-wave theory in the case of collinear and quasi-collinear bulk acousto-optic interactions and also in the case of planar waveguides and optical fibers. With this relation, the acoustic signal that will induce an arbitrary group-delay variation with frequency can be easily obtained. Numerical simulations are shown to support the principle of arbitrary group-delay control with an AOPDF.

Journal ArticleDOI
TL;DR: Good agreement was found between the experimental results and numerical pulse-propagation studies, and the phase of the spectrally compressed pulse was found to be constant over the spectral and temporal envelopes, which is indicative of a transform-limited pulse.
Abstract: We demonstrate near-transform-limited pulse generation through spectral compression arising from nonlinear propagation of negatively chirped pulses in optical fiber. The output pulse intensity and phase were quantified by use of second-harmonic generation frequency-resolved optical gating. Spectral compression from 8.4 to 2.4 nm was obtained. Furthermore, the phase of the spectrally compressed pulse was found to be constant over the spectral and temporal envelopes, which is indicative of a transform-limited pulse. Good agreement was found between the experimental results and numerical pulse-propagation studies.

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a new technique for the direct, real-time, femtosecond scale temporal measurement based on the conversion of temporal information to the spectral domain.
Abstract: We demonstrate a new technique for the direct, real-time, femtosecond scale temporal measurement based on the conversion of temporal information to the spectral domain. The potential of the method has been experimentally investigated with an optical fiber spectral compressor device, first stretching and up-chirping the pulses in a prism dispersive delay line, and afterwards compensating the induced chirp by means of cross-phase modulation in a single-mode fiber. Spectro-temporal imaging (STI) reduces the problem of high-resolution temporal measurements to standard spectrometry.

Journal ArticleDOI
TL;DR: In this article, the authors describe the theoretical and experimental study of a new technique for optical frequency domain ranging (OFDR) by a frequency-shifted feedback (FSF) laser.
Abstract: This paper describes the theoretical and experimental study of a new technique for optical frequency domain ranging (OFDR) by a frequency-shifted feedback (FSF) laser. In conventional OFDR, a frequency chirped single-mode laser is used as a light source to convert a distance into a beat frequency, and a tradeoff exists between measurement range and resolution. The FSF laser output consists of periodically generated chirped frequency components whose chirp rate is faster than 100 PHz/s (P=10/sup 15/), By use of the FSF laser, the tradeoff is removed and long-distance high-resolution OFDR is realized In the experiment, a distance of 18.5 km was measured with a resolution of 20 mm.

Journal ArticleDOI
TL;DR: It is demonstrated that each component is a narrow-band signal with decreasing instantaneous frequency defined by its instantaneous amplitude and its instantaneous phase, which can be accurately represented by a polynomial having an order of thirty.
Abstract: Describes a new approach based on the time-frequency representation of transient nonlinear chirp signals for modeling the aortic (A2) and the pulmonary (P2) components of the second heart sound (S2). It is demonstrated that each component is a narrow-band signal with decreasing instantaneous frequency defined by its instantaneous amplitude and its instantaneous phase. Each component Is also a polynomial phase signal, the instantaneous phase of which can be accurately represented by a polynomial having an order of thirty. A dechirping approach is used to obtain the instantaneous amplitude of each component while reducing the effect of the background noise. The analysis-synthesis procedure is applied to 32 isolated A2 and 32 isolated P2 components recorded in four pigs with pulmonary hypertension. The mean /spl plusmn/ standard deviation of the normalized root-mean-squared error (NRMSE) and the correlation coefficient (/spl rho/) between the original and the synthesized signal components were: NRMSE=2.1/spl plusmn/0.3% and /spl rho/=0.97/spl plusmn/0.02 for A2 and NRMSE=2.52/spl plusmn/0.5% and /spl rho/=0.96/spl plusmn/0.02 for P2. These results confirm that each component can be modeled as mono-component nonlinear chirp signals of short duration with energy distributions concentrated along its decreasing instantaneous frequency.

Journal ArticleDOI
TL;DR: In many applications, shot-to-shot frequency correction can be disregarded, which will result in increased speed and simplicity of the data-acquisition system, so Doppler wind measurements with high efficiency and duty cycles to be made, even on airborne and spaceborne platforms.
Abstract: A coherent Doppler lidar system was frequency stabilized in a master-slave configuration by a phase-modulation technique. The short-term frequency stability, ~0.2 MHz rms, was maintained in a vibrational environment on a ship during a field campaign in the tropical Pacific Ocean. The long-term frequency stability was <2.6 kHz/h. Thus, in many applications, shot-to-shot frequency correction can be disregarded, which will result in increased speed and simplicity of the data-acquisition system. A frequency chirp could not be detected. These properties permit Doppler wind measurements with high efficiency and duty cycles to be made, even on airborne and spaceborne platforms.

Journal ArticleDOI
TL;DR: A new STFD-based wideband root-MUSIC estimator is proposed that employs an extended coherent signal-subspace principle involving coherent averaging over a pre-selected set of time-frequency points rather than the conventional frequency-only averaging procedure.
Abstract: The recently developed concept of narrowband spatial time-frequency distributions (STFDs) is extended to the wide-band case. A new STFD-based wideband root-MUSIC estimator is proposed. This technique employs an extended coherent signal-subspace (CSS) principle involving coherent averaging over a pre-selected set of time-frequency points rather than the conventional frequency-only averaging procedure.

Journal ArticleDOI
TL;DR: In this paper, a noncollinear optical parametric amplifier (NOPA) was used to generate coherent down-converted pulses compressible to the TL pulse with more than a 150-THz bandwidth.
Abstract: Transform-limited (TL) visible pulses with as short a duration as 4.7 fs with a 5 μJ pulse energy have been generated for the first time from a novel noncollinear optical parametric amplifier (NOPA). Both signal–idler group-velocity matching and pulse-front matching are essential to generate coherent down-converted pulses compressible to the TL pulse with more than a 150-THz bandwidth. Tunable operation with bandwidth-limited sub-10-fs pulses in the visible (550–700 nm) and near-infrared (900–1300 nm) ranges, achieved by increasing the seed chirp, is also a remarkable property. The NOPA is believed to be on useful light source for ultrafast spectroscopy on an extremely short time-scale.

Patent
13 Jun 2000
TL;DR: In this article, an optical waveguide provided with a linearly chirped Bragg reflective grating is employed as a device that provides linear dispersion compensation, which can be rendered adjustable by adjustment of the magnitude of axial strain imposed upon the grating.
Abstract: An optical waveguide (11, 71) provided with a linearly chirped Bragg reflective grating (13, 73) can be employed as a device that provides linear dispersion compensation. The amount of the linear dispersion thereby provided can be rendered adjustable by adjustment of the magnitude of axial strain imposed upon the grating. If the chirp is purely linear, and if also, the strain is at all times uniform along the length of the grating, adjustment of the strain magnitude will have no such effect. This requires the presence of a quadratic chirp term, but such a term introduces its own transmission penalty. This penalty is compensated at least in part by causing the light to make a reflection in a further Bragg reflection grating (14, 74) whose quadratic component of chirp has the opposite sign to that of the other Bragg reflection grating, but a substantially matched modulus. The effect of the strain is to scale the effective pitch of the Bragg reflection grating by scaling its physical pitch. An alternative way of achieving a similar effect is to change the effective refractive index of the waveguide in which the grating is formed, for instance by changing its temperature.

Journal ArticleDOI
TL;DR: With certain reasonable restrictions, chirped long-period gratings are found to be a viable and desirable alternative to existing dispersion compensation techniques.
Abstract: Chirped long-period fiber gratings are analyzed for management of dispersion in optical fiber communications systems. A ray model is used to derive simple analytic expressions that describe the transmission, chromatic delay, and dispersion properties of chirped long-period fiber gratings. A numerical model based on coupled-mode theory is used to verify the accuracy of the analytic expressions and explore design issues of the chirped long-period grating. With certain reasonable restrictions, chirped long-period gratings are found to be a viable and desirable alternative to existing dispersion compensation techniques.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the performance of the optical signal whose chirp is controlled by utilizing phase modulation in semiconductor optical amplifier (SOA) with both simulations and experiments.
Abstract: We examine the fiber transmission performance of the optical signal whose chirp is controlled by utilizing phase modulation in semiconductor optical amplifier (SOA) with both simulations and experiments. This chirp control technique converts a positive chirp created by electroabsorption (EA) modulator into negative chirp, which reduces the waveform degradation due to the chromatic dispersion in transmission over standard single-mode fiber (SMF). It also provides an optical gain that is sufficient to compensate the insertion loss of the EA modulator. We investigate how the chirp control is affected by the input power to the SOA and the carrier lifetime of the SOA. As the SOA input power increases, the negative chirp becomes large, while the waveform is largely distorted due to gain saturation. However, the waveform distortion at high SOA input powers can be shaped by using a frequency discriminator. The acceleration of the carrier lifetime also reduces the waveform distortion due to gain saturation. We demonstrate that the chirp control technique is effective even for a high bit rate optical signal up to 10 Gb/s, when the carrier lifetime is expedited by optical pumping.

Proceedings ArticleDOI
07 May 2000
TL;DR: In this paper rigorous theoretical performance bounds are constructively established for the joint transmitter-target-channel-receiver optimization problem in the presence of additive colored noise (ACN), (e.g., interference multipath).
Abstract: Recent advances in linear amplifier and arbitrary waveform generation technology have spawned interest in adaptive transmitter systems as a means for both optimizing target signal gain and enhancing ID. In this paper rigorous theoretical performance bounds are constructively established for the joint transmitter-target-channel-receiver optimization problem in the presence of additive colored noise (ACN), (e.g., interference multipath). For the ACN case, an analytical solution is obtained as an eigenvector (with associated maximum eigenvalue) of a homogeneous Fredholm integral equation of the second type. The kernel function is Hermitian and is obtained from the cascade of the target impulse response with the ACN whitening filter. The theoretical performance gains achievable over conventional transmitter strategies (e.g., chirp) are presented for various simulation scenarios including interference multipath mitigation. Also discussed is the potential effectiveness of an optimal discriminating pulse solution for the N-target ID problem that arises naturally from the theory.

Journal ArticleDOI
TL;DR: In this paper, a two-level model is used to examine the condition for the so-called positive chirp pulses and a four level model is designed to demonstrate for molecular systems the correlation between the sign of the chirps and the excited state population.
Abstract: Detailed theoretical analysis and numerical simulation indicate that nearly complete electronic population inversion of molecular systems can be achieved with intense positively chirped broadband laser pulses. To provide a simple physical picture, a two-level model is used to examine the condition for the so-called π pulses and a four-level model is designed to demonstrate for molecular systems the correlation between the sign of the chirp and the excited state population. The proposed molecular π pulse is the combined result of vibrational coherence in the femtosecond regime and adiabatic inversion in the picosecond regime. Numerical results for a displaced oscillator, for LiH and for I2, show that the proposed molecular π pulse scheme is robust with respect to changes in field parameters such as the linear positive chirp rate, field intensity, bandwidth, and carrier frequency, and is stable with respect to thermal and condensed phase conditions including molecular rotation, rovibronic coupling, and elec...

Proceedings ArticleDOI
TL;DR: A scaleable configuration is presented for an aperture synthesis array operating in the frequency range from the ionospheric cut off at about 10 MHz to about 160 MHz where existing telescopes are confusion limited.
Abstract: The LOw Frequency ARray (LOFAR) is the Digital Software Radio Telescope that has been under study by the NFRA and the NRL for the last two years. A scaleable configuration is presented for an aperture synthesis array operating in the frequency range from the ionospheric cut off at about 10 MHz to about 160 MHz where existing telescopes are confusion limited. Both the array and the antenna station have a fractal structure following an exponential scaling law, which by appropriate weighting can provide a field of view and a synthesized resolution pattern of almost constant angular size independent of frequency. The processing architecture is scaleable as well and allows optimum distribution of the total processing power over signal and data processing tasks, by trading processed bandwidth in beam-formers and correlators for advanced processing like interference rejection, multi-beaming, pulsar processing, decade-wide chirp processing. The phased array antenna station provides a set of beams, which extends about a steradian on the sky and can be configured such that all relevant science objects are covered simultaneously. The pipelined self-calibration processing provides a clean image every third of a day, improving the sensitivity by a factor eight after two month of repeated observing. Based on the fast expansion of high performance processing technology, it is only after 2003 that signal and data processing will no longer dominate the cost of LOFAR in producing a confusion limited sky survey at sub mJy level.

Patent
05 Mar 2000
TL;DR: In this paper, a matched filter employing a template of the chirp waveform pattern is used to detect the amount of rotation of the CHIRP within the received signal for each symbol.
Abstract: A spread spectrum data communication system utilizing a modulation technique referred to as differential code shift keying (DCSK) transmits data in the form of time shifts between consecutive circularly rotated waveforms of length T known as spreading waveforms. A plurality of bits are transmitted during each symbol period which is divided into a plurality of shift indexes with each shift index representing a particular bit pattern. The spreading waveform is rotated by an amount in accordance with the data to be transmitted or is conveyed in the difference between two consecutive rotations. A correlator (42) employing a matched filter having a template of the chirp waveform pattern is used to detect the amount of rotation of the chirp within the received signal for each symbol. The received data is fed into a shift register (38) and circularly rotated. For each rotation shift, the matched filter generates a correlation sum. The shift index chosen for each symbol corresponds to the shift index that yields the maximum correlation sum (44). Differential shift indexes are generated by subtracting the currently received shift index from the previously received shift index. The differential shift index is then decoded to yield the originally transmitted data.

Patent
25 May 2000
TL;DR: In this paper, an apparatus and method of measuring the gap between one substantially planar object, such as a mask, and a substrate was proposed, which achieved a high degree of sensitivity, accuracy, capture range, and reliability, through a novel design of a mark located only on the mask-plate.
Abstract: An apparatus and method of measuring the gap between one substantially planar object, such as a mask, and a second planar object, such as a substrate. The invention achieves a high degree of sensitivity, accuracy, capture range, and reliability, through a novel design of a mark located only on the mask-plate. The light is inclined to the surfaces so associated optical components do not interrupt the exposing beam used in lithography. The same optics are used as for aligning overlay. Each gapping mark on the mask-plate includes one or more two-dimensional gratings (1441, 1442), each with period constant in the incident plane, but varying in the transverse plane as shown in the enlargements (1443, 1444). When illuminated, two images are formed of each of the two-dimensional gratings, with fringes resulting from interference between paths having traveled different distances through the gap and the mask-plate as a result of successive diffractions and reflections. Phase and geometric measurements from these images yield accurate measurement of the gap between the plates. Direct calibration, referenced to the light-wavelength, is obtained from a diffractive Michelson technique that uses a linear grating also included within the gapping mark.

Journal ArticleDOI
TL;DR: The derivation and performance analysis of two joint estimators of doppler shift and Doppler rate-the chirp embedded in correlated compound-Gaussian clutter based on the maximum likelihood principle and target signal second-order cyclostationarity are derived.
Abstract: Signal detection of known (within a complex scaling) rank one waveforms in non-Gaussian distributed clutter has received considerable attention. We expand on published solutions to consider the case of rank one waveforms that have some unknown parameters, i.e., signal amplitude, initial phase, Doppler shift, and Doppler rate of change. The contribution of this paper is the derivation and performance analysis of two joint estimators of Doppler shift and Doppler rate-the chirp embedded in correlated compound-Gaussian clutter. One solution is based on the maximum likelihood (ML) principle and the other one on target signal second-order cyclostationarity. The hybrid Cramer-Rao lower bounds (HCRLBs) and a large sample closed-form expression for the mean square estimation error (only for the Doppler shift) are also derived. Numerical examples are provided to show the behavior of the proposed estimator under different non-Gaussian clutter scenarios.

Journal ArticleDOI
TL;DR: In this paper, a femtosecond vibrational wave-packet dynamics in a cyanine molecule is observed to be strongly dependent on the chirp direction of the excitation pulse.
Abstract: Femtosecond vibrational wave-packet dynamics in a cyanine molecule is observed to be strongly dependent on the chirp direction of the excitation pulse. The slow-decay component associated with an oscillatory structure, which corresponds to the excited-state lifetime and a vibrational mode of 160±10 cm−1, respectively, is measured by the femtosecond time-resolved transmission spectroscopy. The excited-state population is substantially decreased and enhanced in the cases of negatively chirped (NC) and positively chirped (PC) excitations, respectively. A quantum mechanical calculation by means of the split operator scheme is performed to reproduce the wave-packet propagation after the chirped pulse excitation. The calculation shows that the spatial distribution of the wave packet for the NC case is narrower than that for the PC case during the excitation, and that the overlap integral between the excited- and ground-state wave packets determines the efficiency of the population dumping.

Patent
09 Feb 2000
TL;DR: In this paper, a nonlinearly chirped fiber grating (1020a) was proposed for achieving tunable dispersion compensation, dispersion slope compensation, polarization mode dispersion, chirp reduction in directly modulated diode lasers, and optical pulse manipulation.
Abstract: A nonlinearly chirped fiber grating (1020a) for achieving tunable dispersion compensation, dispersion slope compensation, polarization mode dispersion, chirp reduction in directly modulated diode lasers, and optical pulse manipulation. A dynamical dispersion compensation mechanism can be implemented in a fiber communication system (1001) based on a such a nonlinearly chirped fiber grating (1020a).

Journal ArticleDOI
TL;DR: In this article, the application of a different type of signal, the FM slide or chirp, for fisheries and oceanographic acoustic assessment is described and the basic theory of FM slides as well as some of the factors that must be considered when implementing this signal type in actual systems are described.