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Showing papers on "Chirp published in 1978"


Journal ArticleDOI
TL;DR: In this paper, it was shown that phase modulation on a pulse may be reversed in time (e.g., positive chirp to negative) by degenerate four-wave mixing in an optically thin nonlinear medium.
Abstract: A simple theory shows that phase modulation on a pulse may be reversed in time (e.g., positive chirp to negative) by degenerate four‐wave mixing in an optically thin nonlinear medium. In thick media, the reflected pulse field is not truly time reversed, but is proportional to the time integral of the conjugate incident field.

51 citations


Journal ArticleDOI
TL;DR: In this paper, the envelope and frequency characteristics of the output pulse of a high repetition rate hybrid TEA-CO 2 laser are presented, and both the intrapulse and interpulse laser frequency stabilities are experimentally determined at repetition rates up to 300 Hz.
Abstract: The envelope and frequency characteristics of the output pulse of a high repetition rate hybrid TEA-CO 2 laser are presented. Both the intrapulse and interpulse laser frequency stabilities are experimentally determined at repetition rates up to 300 Hz. The recovery of the CW laser signal following the generation of the TEA laser pulse is analyzed theoretically and experimentally. Short term reproducibilities of ±2 MHz are observed at a pulse repetition rate of 300 Hz with initial chirp rates of about 1.5 MHz/μs. Improvements and limits on power and repetition rate are discussed.

31 citations


Proceedings ArticleDOI
21 Dec 1978
TL;DR: The application of fiber optics to modern radar system design is examined in this paper, where the more conventional uses of fiber optic devices to transmit wideband signals as well as the less common use of their stable transmission delay characteristics to form active circuit elements within a radar are presented.
Abstract: The application of fiber optics (FO) to modern radar system design is examined This paper presents the more conventional uses of fiber optics to transmit wideband signals as well as the less common use of their stable transmission delay characteristics to form active circuit elements within a radar The stable delay characteristics of fiber optic devices are exploited in the design of such radar circuits as a high frequency oscillator, phased array antenna, precision pulse generator, AID converter, MTI system and chirp generator The capability of fiber optics to transmit wideband information over long distances is being exploited to develop a radar remoting system for control, power, status, voice and video signals Three hundred signals are time division multiplexed over seven optical fibers for a distance of 1200 feet Future development of new materials for fiber optics will permit operation at IR frequencies and lower line loss for new applications

28 citations


Patent
31 Jan 1978
TL;DR: In this paper, a light beam deflection system and frequency shift arrangement disposed up-stream of a focussing lens is presented, where the modulated beam is deflected and is then directed along with the unmodulated beam through the lens so that the beams combine with each other to form a read-out interference pattern on the hologram.
Abstract: A hologram-containing storage medium is rapidly scanned or swept by a sinusoidal spatial fringe pattern, the spatial frequency of which varies with time. This may be achieved by the use of a suitable light beam deflection system and frequency shift arrangement disposed up-stream of a focussing lens. The deflection system and frequency shift arrangement may incorporate a pair of light beams, such as those obtained from a laser, a source of coherent monochromatic light. A single deflector-frequency shifter, such as an acousto-optic element and an electro-mechanical deflector may be disposed in the path of one of the beams, with a prescribed carrier modulation frequency applied to shift the frequency of that one beam relative to that of the other beams. The modulated beam is deflected and is then directed along with the unmodulated beam through the focussing lens so that the beams combine with each other to form a read-out interference pattern on the hologram. Alternatively, a respective frequency shifter, such as an acousto-optic modulator may be disposed in the path of each of the pair of beams and a separate modulation frequency signal applied to each modulator. The frequency difference between the two signal sources represents the temporal frequency carrier component of the interference pattern. The beams are also deflected relative to one another and the light which is then diffracted by the hologram impinges upon a single photo-detector, whereby a signal representative of the original data, together with the imparted modulation components, is derived. The temporal and spatial modulation components introduced in the signal beam by the frequency-shift, deflection system are then removed, to obtain only the original data. In accordance with the invention, a constant scan frequency may be used or the frequency shift of a light beam may be caused to vary with time (e.g. ω(t)=kt) so as to effectively create a travelling optical chirp. In each case, the interference pattern created on the hologram for reading out the data will contain a translating sinusoidal fringe system with a time varying spatial frequency, and the output of the photo-detector represents the integral of the product of hologram transmissivity and the illumination intensity pattern, which may then be demodulated to obtain the original data.

22 citations


Journal ArticleDOI
TL;DR: In this paper, a TEA-CO 2 laser utilizing a double-discharge technique has been constructed and operated under single-mode conditions, achieving a lifetime of 10 6 pulses.

18 citations


Patent
12 Jun 1978
TL;DR: In this paper, a device for suppressing the interference echo signals in an optical pulse compression radar was proposed. But the interference was not suppressed by the interference component of the output signal from the first mixer, and a second mixer receiving, on the one hand, the signal thus filtered and then said relay signal, and delivering to the processing circuit a signal of a frequency equal to the difference of the frequencies of the input signals.
Abstract: A device for suppressing the interference echo signals in an optical pulse compression radar comprising, at the transmitting side, a circuit for generating electrical signals of determined duration and with a frequency variable as a function of time, called chirps, an optical transmitter comprising a continuous transmission source modulated by the chirps and, at the receiving side, a receiver for deriving chirps from the light signals received and a processing circuit for the chirps supplied by the receiver, comprising a first mixer receiving from said receiver the reception chirp and from said circuit the transmission chirp and then, when the latter is ended, a relay signal of a determined frequency, said first mixer delivering a signal of a frequency equal to the difference of the frequencies of the input signals, a filter for filtering out the interference component of the output signal from the first mixer, and a second mixer receiving, on the one hand, the signal thus filtered and, on the other hand, the transmission chirp and then said relay signal, and delivering to said processing circuit a signal of a frequency equal to the difference of the frequencies of the input signals.

13 citations


Proceedings ArticleDOI
01 Jan 1978

11 citations


Patent
23 Oct 1978
TL;DR: In this article, an acousto-optic cell is used to modulate coherent light from a lasing element, which is then used to generate an output pulse, while using a multi-tapped delay line to allow a shorter period between pulses.
Abstract: A multiple pulse laser from a single resonant cavity. An acousto-optic cells used to modulate coherent light from a lasing element. Either multiple chirp signals or a masked mirror are used to provide distinct pulses of light. Through proper choice of materials for the acousto-optic cell and use of divergent optics, a higher power level is obtained. Use of a multi-tapped delay line permits a shorter period between pulses due to the linear superposition principle. When the mask embodiment is used, the acousto-optic cell focuses light which scans across the mask. Whenever the focused light passes through the mask, lasing occurs which generates an output pulse.

9 citations


Proceedings ArticleDOI
01 Jan 1978

7 citations


Proceedings ArticleDOI
01 Jan 1978
TL;DR: In this paper, a 1.0 GHz LiNbO3 RAC filter with flat amplitude chirp-type transducers and apodized reflective gratings with constant groove depth was proposed.
Abstract: This paper reports the development of a 1.0 GHz LiNbO3 RAC filter having 500 MHz bandwidth and 1.0 psec. dispersive delay. The filter configuration contains flat amplitude chirp-type (rather than periodic) transducers and apodized reflective gratings with constant groove depth, instead of uniform gratings with depth weighing. Using the conventional configuration a RAC filter with these parameters would be quite difficult and expensive for two reasons. First, producing an accurate depth-weighted groove profile involves special ion-etching equipment and procedures. The technique is further complicated by the comparatively short gratings required to produce as little as 1.0 psec. dispersive delay. Second, fabrication of 500 MHz bandwidth transducers has always been relegated to the domain of expensive scanning electron microscope (SEM) microfabrication. The use of this novel RAC filter configuration enabled the device to be fabricated using optically produced masks, optical photolighography and uniform ion etching. Initial results indicate that low cost, high-yield production will be a corollary to this process. The filter was designed using an existing transducer model and a RAC grating model which includes apodization and non-synchronous scattering loss. The total measured loss of 45 dB is within 1 dB of the theoretical prediction. Measured RMS phase error, without phase correction, is typically less than loo. The input transducer maintains linear operation for CW input levels up to about +22 am, indicating that the RAC filter can be employed to generate a 500 MHz bandwidth chirp waveform having a 37 dB signal to noise ratio.

7 citations


Patent
08 Nov 1978
TL;DR: In this paper, a frequency sweep or "chirp" is provided in the excitation laser radiation at a controlled rate and over a range of frequencies which is limited to prevent loss of selectivity.
Abstract: Method and apparatus for achieving isotopically selective adiabatic inversion, particularly for improved isotope separation efficiency. In a preferred embodiment for practicing the invention, chirped laser radiation induces photoionization of a vapor state material in isotopically selective excitation and ionization energy steps. A frequency sweep or "chirp" is provided in the excitation laser radiation at a controlled rate and over a range of frequencies which is limited to prevent loss of selectivity in the excitation. The frequency swept radiation has a theoretical capability of producing 100% inversion of ground state particles in the vapor. The features of the invention additionally permit excitation of a material to very high energy states useful in producing high frequency, ultraviolet lasing.

Patent
08 Dec 1978
TL;DR: In this paper, a hand held short range FM radar device is provided employing a unique tracking circuit and a predistortion circuit to linearize the sweep function to a Gunn oscillator which produces the rf signal.
Abstract: A hand held, short range FM radar device is provided employing a unique tracking circuit and a predistortion circuit to linearize the sweep function to a Gunn oscillator which produces the rf signal. A parabolic generator comprising a linear operational amplifier and passive elements connected thereto is used to shape the saw tooth sweep signal to the Gunn oscillator. The output is directly read out on an LED display; an audio signal is also produced whose frequency is a function of target distance.

Journal ArticleDOI
TL;DR: It is shown that the convolver can easily generate ambiguity functions for virtually any waveform, and specific results for signals such as Barker codes and linear FM (chirp) waveforms are presented.
Abstract: A technique for receiving radar pulse trains is presented [which can be of a variable format in the sense that they vary from pulse to pulse]. The heart of the receiver is a sufrace ascoustic wave (SAW) convolver. In addition to prsenting experimental results for variable format waveform reception, it is shown that the convolver can easily generate ambiguity functions for virtually any waveform, and specific results for signals such as Barker codes and linear FM (chirp) waveforms are presented.

Journal ArticleDOI
TL;DR: Weighting functions for maximizing the signal-to-noise ratio (SNR) or for producing desired close-in sidelobe performance are derived, as is an exact expression for the transmitted spectrum.
Abstract: Generating chirp waveforms by means of phase coding yields a simple, cost-effective mechanization. The coding process, however, introduces phase errors whose effect must be included in the design. An approximate analysis is presented, valid for moderate to high compression ratios, which allows error effects on compressed pulse amplitude and sidelobes to be calculated in a simple manner. The anaylsis provides criteria for selecting the coding bit width (sample rate), weighting network bandwidth, and phase-coder quantization interval and transition times. Weighting functions for maximizing the signal-to-noise ratio (SNR) or for producing desired close-in sidelobe performance are derived, as is an exact expression for the transmitted spectrum. Numerical results are presented for Gaussian and the maximum-SNR weighting. The results indicate that performance will be satisfactory for many applications.

Proceedings ArticleDOI
01 Jan 1978
TL;DR: In this article, the adaptive line enhancer (ALE) was applied to the case of sinusoids whose frequencies slowly vary in time, and a time-varying eigenvalue-eigenvector description of the expected filter impulse response vector was developed for any slowly nonstationary input.
Abstract: The Adaptive Line Enhancer (ALE) was first described by Widrow et al, as a practical on-line technique for separating the coherent components from the incoherent components of an input signal. Subsequent work has shown this same adaptive filtering structure to be applicable to maximum entropy spectral estimation, predictive deconvolution, and narrowband interference rejection, as well as other applications which have historically used matrix inversion and Levinson's algorithm techniques. While an often cited advantage of adaptive filtering is its tolerance of slowly time-varying input statistics, the existing analyses of the ALE have concentrated on the stationary case. This paper extends these results, applying the theory to the case of inputs containing sinusoids whose frequencies slowly vary in time. This is approached by developing a time-varying eigenvalue-eigenvector description of the expected filter impulse response vector which holds for any slowly nonstationary input. These results are then used to predict the expected impulse response vector for the ALE input of stationary white noise plus a sinusoid with linearly swept frequency. The response of the ALE for this particular input signal provides useful benchmarks for dealing with more complex forms of frequency modulation.

Journal ArticleDOI
TL;DR: Experimental results showing operation with sine and cosine inputs demonstrate processor performance in computing real and imaginary Fourier-transform components to an accuracy equivalent to 6 bits.
Abstract: A fast-Fourier-transform (f.f.t.) processor based on the chirp transform algorithm implemented with surface-acoustic-wave (s.a.w.) chirp filters is reported. Using commercially available s.a.w. devices the processor computes a 128-point (nominal) f.f.t. in 25 ?s, permitting real-time operation over 4 MHz bandwidth. Experimental results showing operation with sine and cosine inputs demonstrate processor performance in computing real and imaginary Fourier-transform components to an accuracy equivalent to 6 bits.

Proceedings ArticleDOI
15 Sep 1978
TL;DR: The selective remval of jamming noise (by transform gating) for a continuous PSK Barker encoded binary input signal along with som probability of error data for this system is demonstrated.
Abstract: htched filtering can be implemented in a variety of ways using an assortment of devices. One straightfornard technique employs the Si-onLiNbO structure as a progranrmable correlator. A mre versatile configuration, however, can be realized by the utilization of chirp devices. With these devices, signal Fourier (chirp) transforms are readily obtainable and correlation follows with an inverse transformstion of the product of transforms. '&is paper demonstrates the selective remval of jamming noise (by transform gating) for a continuous PSK Barker encoded binary input signal along with som probability of error data for this system. me output of this system, in the absence of noise, consists of a continuous stream of plus and minus correlation peaks. The technique for transforming continuous signals, based upon the knowledge of the region of transform validity, will be discussed. 3



Patent
15 Dec 1978
TL;DR: In this article, a sweep signal generator based on the sweep voltage correlation value was used to acquire the input signal of the highest level by setting up a Sweep signal generator and closing the phase synchronous loop via the signal generator.
Abstract: PURPOSE:To acquire the input signal of the highest level by setting up a sweep signal generator based on the sweep voltage correlation value and closing the phase synchronous loop via the signal generator.

Proceedings ArticleDOI
01 Jan 1978
TL;DR: In this article, an IC to perform a complete 32-point DFT with the chirp Z-transform algorithm has been developed, using a two-level polysilicon coplanar electrode process.
Abstract: An IC to perform a complete 32-point DFT with the chirp Z-transform algorithm has been developed, using a two-level polysilicon coplanar electrode process. Chip contains CCD filters, MDACs, ROM and clock logic.

Patent
16 Dec 1978
TL;DR: In this article, the authors proposed to realize processing capacity (n+1) times as much as that of a conventional device and to realize a wide-range device which has excellent signal process capacity, by using a plural number, e.g.n + 1 of chirp filters with simple constitution which are fabricated easily.
Abstract: PURPOSE:To realize processing capacity (n+1) times as much as that of a conventional device and to realize a wide-range device which has excellent signal process capacity, by using a plural number, e.g.n + 1 of chirp filters with simple constitution which are fabricated easily.

Journal ArticleDOI
TL;DR: In this article, an analysis is given for the compression of linearly chirped optical pulses propagating in dispersive absorbing media, including the influence of thin dielectric films on the surface propagation mode.
Abstract: An analysis is given for the compression of linearly chirped optical pulses propagating in dispersive absorbing media. Numerical calculations are reported for frequency‐chirped CO2 laser pulses which propagate as phonon polaritons in α‐quartz or as surface phonon polaritons on BeO, including the influence of thin dielectric films on the surface propagation mode. Quantitative evaluation is made of the use of these modes to form dispersive optical pulse delay lines. It is shown that absorption limits both the usable propagation length and the curvature of the dispersion curves. For the materials considered, this approach is restricted to 10‐psec pulses having THz chirp bandwidths, with large accompanying absorption losses.

Proceedings ArticleDOI
01 Sep 1978
TL;DR: In this article, a cavity stabilised two diode array has given output powers of low at 10% efficiency with less than 0.5 MHz chirp for 1?sec pulses.
Abstract: High efficiency indium phosphide oscillators have been developed for pulsed applications in the 12 to 18 GHz frequency range. The development of low thermal resistance structures has enabled long pulse or high duty factor operation to be readily achieved. Individual devices have given peak powers of low at efficiencies of up to 17% and peak powers of 40W at efficiencies of greater than 10% have been obtained from multiple diode arrays. A cavity stabilised two diode array has given output powers of low at 10% efficiency with less than 0.5 MHz chirp for 1?sec pulses. CW priming has been used to obtain minimal delay and jitter of the leading edge of the rf pulse and intraspectral line noise of ?80 dbc/Hz.

Journal ArticleDOI
TL;DR: A new method offering relaxation of the traditional holographic restriction on the allowable velocity of a moving object, that is, that the change of path difference between the object and reference beams has to be negligible during exposure of a hologram is described.
Abstract: This paper describes a new method offering relaxation of the traditional holographic restriction on the allowable velocity of a moving object, that is, that the change of path difference between the object and reference beams has to be negligible during exposure of a hologram. The proposed method depends on the frequency chirp of the laser pulse used for the hologram recording canceling the Doppler frequency shift due to the motion of the object. Experimental verification is also shown.

Journal ArticleDOI
TL;DR: In this article, the Fourier transform technique is used to scan optical images by storing a chirp surface wave signal and an optical pattern simultaneously, which can improve a dynamic range and a signal-to-noise ratio in comparison with a single scan pulse method.
Abstract: A novel optical imaging method by using a memory-correlator in which a laser pulse acts to store wideband surface wave signals in surface states of a semiconductor is described. The Fourier transform technique is used to scan optical images by storing a chirp surface wave signal and an optical pattern simultaneously, which can improve a dynamic range and a signal-to-noise ratio in comparison with a single scan pulse method.

Journal ArticleDOI
TL;DR: An equalization technique is described suitable for operation in a chirp radar system in which the signal is transmitted over a channel dominated by phase nonlinearities.
Abstract: An equalization technique is described suitable for operation in a chirp radar system in which the signal is transmitted over a channel dominated by phase nonlinearities. It is shown that the system is easily implementable, and an analysis of system performance will be presented.

Proceedings ArticleDOI
10 Apr 1978
TL;DR: 2-D processing can offer significant advantages over the standard spectral estimation procedures used to obtain spectrograms because the frequency data is correlated in time, a fact ignored in conventional spectrogram procedures.
Abstract: In this paper we demonstrate a new application of two-dimensional (2-D) signal processing. The 2-D data consists of frequency-time plots or spectrograms derived from non-stationary one-dimensional data. We show that 2-D processing can offer significant advantages over the standard spectral estimation procedures used to obtain spectrograms. These advantages mainly occur because the frequency data is correlated in time, a fact ignored in conventional spectrogram procedures. Recursive fan type filters are designed by the homomorphic method and applied to the spectrogram data. Significant improvement is obtained for a simulation consisting of chirp type signals in white noise.

Proceedings ArticleDOI
08 Dec 1978
TL;DR: Real-time Fourier transformation techniques for performing broadband spectral analysis and correlation using SAW chirp transformation using the Chirp Transform are concentrated on.
Abstract: Recent improvements in broadband, large time-bandwidth product surface acoustic wave (SAW) chirp filters have led to significant advances in the implementation of the Chirp Transform algorithm for analog signal processing. This paper concentrates on real-time Fourier transformation techniques for performing broadband spectral analysis and correlation using SAW chirp transformation. First, the fundamentals of the SAW chirp filter and the Chirp Transform algorithm are reviewed. Next, chirp transform system architectures are discussed, including the relationship between SAW filter de-sign and signal processor bandwidth, resolution and signal to noise ratio. Performance data is then presented for a new radar pulse-compression processor* which utilizes the Chirp Transform and incorporates state-of-the-art SAW chirp filters to perform cross-correlation between large time-bandwidth product waveforms. This "programmable" correlator is compatible with arbitrarily coded signals up to 60 psec long, with up to 60 MHz bandwidth. Finally, the SAW chirp transform is compared with other techniques for performing Fourier transformation, and specific applications of this technology for spectral analysis and correlation are discussed.

25 Apr 1978
TL;DR: In this paper, the disperson is such as to prodce a 'chirp' frequency modulation on a transmitted pulse, and the channel itself may be used as the matched receiving filter by transmitting a time reversed (chirped) waveform and letting the dispersion effect compress the waveform.
Abstract: : The Arctic Basin provides a unique channel for acoustic propagation. The two features peculiar to the polar environment that most strongly influence the transmission of underwater sound are the permanent ice cover and the uniform sound speed structure. As a result, only a few low order modes will propagate through it to great distances and the non-linear frequency dependent time delay of the channel may be accurately computed. In the Arctic channel, the disperson is such as to prodce a 'chirp' frequency modulation on a transmitted pulse. Consequently the channel itself may be used as the matched receiving filter by transmitting a time reversed (chirped) waveform and letting the dispersion effect compress the waveform. This process will be strictly range dependent. (Author)