Dispersive Delay Line Research Articles

Real-time spectral analysis of far-infrared laser pulses using an SAW dispersive delay line

Spectral analysis of high-power pulsed D2O lasers has been accomplished using SAW dispersive delay lines. Both the contributions of longitudinal modes and the tuning of the stimulated Raman line at 385 μm have been observed.

A wide-band high-Q dispersive delay line for square-wave signals

A long delay line, having controllable dispersive characteristics, suitable for delaying wide–band square–wave signals using only a single adaptive delay element, is proposed and experimentally demonstrated.

Analysis of compression of frequency-chirped optical pulses using dispersive bulk and surface phonon-polariton propagation modes at CO2 laser frequencies

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.

Optical pulse generation from FM laser using gain dispersion

The possibility of new type of optical pulse compression utilizing dispersion effect of laser gain is discussed. An experiment using a 1.06 μm Nd:YAG laser for a dispersive delay line was performed to demonstrate the possibility, where cw FM laser, instead of frequency-swept pulses, was e,ployed. The FM laser of 100 GHz bandwidth at 144 MHz repetition frequency, which was generated from another Nd:YAG laser, was observed to pulsate with 1.2 ns pulsewidth after passing through the dispersive delay line consisting of laser medium. Several times power amplification due to the laser gain was also obtained in the dispersive delay line.

Optical pulse squaring effects in a dispersive delay line

Abstract : Temporal squaring effects are produced using a pair of diffraction gratings on 30 psecduration 1.06 micrometer pulses that were negatively self phase modulated in cesium vapor. The results are in good agreement with the theory, which is discussed in detail. Further enhancement of the squaring by a saturable absorber is also discussed.

Optical pulse squaring effects in a dispersive delay line

Using a pair of diffraction gratings, we have produced temporal squaring effects on 30 ps duration 1.06 μm pulses that were negatively self phase modulated in cesium vapor. The results are in good agreement with the theory, which is discussed in detail. Further enhancement of the squaring by a saturable absorber is also discussed.

Realization of a dispersive delay line for an ultrasonic non-destructive testing system using pulse compression

The key element in the implementation of an ultrasonic pulse compression system for non-destructive testing is the dispersive delay device. From system considerations it is concluded that an ultrasonic strip delay line is the most appropriate device to be used in the system. The design as well as the characteristics of a 1–8 MHz aluminium strip delay line having a linear dispersive delay of 420 µs and a bandwidth of 200 kHz is described in detail. Performance of the line in an operating ultrasonic pulse compression system is presented and demonstrates the practicability of the approach. The particular method of implementing the delay device offers advantages in simplicity, inexpensive-ness and ease of construction.

Dispersive propagation in surface-acoustic-wave pulse-compression filters

The phase response of a dispersive interdigital delay line is shown to be affected by dispersion of the surface wave. A device with a time–bandwidth product of 850 and a nonlinear group-delay characteristic gave results consistent with dispersion due to mass loading and topographic effects.

Pulse compression techniques in ultrasonic non-destructive testing

The development of a pulse compression system applicable to ultrasonic flaw detection is described. The use of pulse compression technique permits a pulse-echo detection system to operate with long transmitted pulses for increased sensitivity, but without sacrificing resolution. The described system is economically implemented using an aluminium strip dispersive delay line. The operating system achieves a time-bandwidth product of 84 and sidelobe levels of —25 dB. Experimental evidence of the system's capabilities is presented.

Examples of manufactured dispersive delay lines using acoustic surface waves

Two kinds of dispersive delay lines operating in radars at the present time are described as examples of manufactured acoustic surface-wave components. These lines were designed some yearsago for a non-linear chirp impulse response and they are used as pulse expander and weighting matched pulse compressor. These dispersive delay lines consist of metallic interdigital transducers deposited on piezoelectric quartz substrates.The first kind of line, which was produced in quantity, (about 180 units) has a compression ratio equal to 23.5. The relative sidelobe level of the compressed pulse is −26 dB. The delay varies by 4 μs in a 7 MHz frequency range, the centre frequency being 30 MHz.A sampled transducer with variable finger pair spacing is used for the second kind of line in order to limit the number of fingers. The delay change is 25 μs for a 1 MHz frequency range centred at 30 MHz. The compression ratio and the relative sidelobe level of the compressed pulse are 19.2 and −24 dB respectively.

Properties and applications of reflective-array devices

The use of reflective arrays in surface-wave devices has yielded new devices such as resonators in addition to an enlarged parameter range for devices such as radar pulse expanders and compressors. A number of different grating geometries, substrates, and types of reflectors have been employed in resonators, band-pass filters, filter banks, oscillators, and dispersive delay lines. Simple, yet accurate, models have been developed for design and analysis of reflection gratings in these applications. The major application of reflective arrays has been in radar pulse compressors wherein low spurious levels and precise phase and amplitude response have been achieved in devices with time-bandwidth products as large as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . Other signal-processing applications such as chirp-z transforms can exploit the large time-bandwidth products available in reflective-array devices.

Microwave magnetostatic delay devices based on epitaxial yttrium iron garnet

Low-loss magnetostatic wave (MSW) propagation in epitaxial yttrium iron garnet (YIG) films allows the development of a technology which is complementary to that of surface acoustic waves (SAW's), but capable of operation in the microwave range from 1 to greater than 12 GHz. Experimental low-loss dispersive and nondispersive tapped delay lines are described. Future developments of MSW's involving signal routing by etched waveguides and periodic resonator structures are discussed, and the properties of MSW's at microwave frequencies are compared with those of SAW's at VHF/UHF.

Microwave device applications of epitaxial magnetic garnets

The microwave device applications of epitaxial garnet films grown by liquid phase epitaxy and vapour phase epitaxy on gadolinium gallium garnet substrates are reviewed. Materials preparation techniques and quality in terms of ferrimagnetic resonance linewidth are discussed. Emphasis is directed towards the present status of tunable bandstop and bandpass filters and magnetostatic wave delay lines. Dispersive and non-dispersive tapped delay lines operating at frequencies up to X-band are described.

Surface Acoustic Wave Time-Base Correction Systems

Surface-wave acoustic delay lines are adapted to time-base correctors. The basic theory of operation is described. Particular emphasis is placed on the system design which employs the dispersive surface-wave delay lines. Of interest for the future are devices made by the same techniques and processes as used for the semiconductor industry. Surface-wave delay lines satisfy these criteria and therefore, future time-base correctors will no doubt be constructed of large blocks of integrated packages. Soon, time-base correctors with wider correction ranges and other desirable characteristics will be fit into a reasonably sized space at a reasonable cost.

Waveguide Sandwich Filters

A new class of waveguide filters is introduced, constructed from several thin plates sandwiched together. The combination of alternate plates having large and small rectangular apertures leads to a propagating structure which possesses a bandstop response and prescribed characteristic impedance. This basic element may be used as a simple compact bandstop filter, particularly where the main passband and stopband are well separated, such as in harmonic rejection. For filters with many stopbands, combinations of several waveguide sandwich filter elements are used to provide the main passband and the required attenuation characteristics in the prescribed stopbands. Although the filter is ideally suited for bandstop filtering due to its small size, low cost, low loss, and high power handling capability, additional applications to bandpass filtering and dispersive delay line operation are also cited.

Practical surface acoustic wave devices

A tutorial discussion is presented on selected surface acoustic wave (SAW) devices for the use of engineers and electronic systems designers. Currently practical components for use in radar systems, communications systems, and as frequency domain filters are described. Emphasis is placed on nondispersive and dispersive delay lines, devices for generating and detecting various radar waveforms, devices for generating and detecting fixed and programmable biphase and multiphase codes, and broad-band and narrow-band filters. The device possibilities of several new approaches are described, including multistrip couplers, nonlinear convolvers, reflective structures, and overlay films. It is concluded that, while SAW devices have found many applications in large radar systems because of their size, cost effectiveness, and reliability, wide-scale applications, for example as frequency domain filters, will be needed to justify continued research in this field. Wide-scale applications will come as systems engineers realize the potential of these devices and confidently design them into their systems.

Convolution and Correlation Using Nonlinear Interactions of Lamb Waves

Excitation of Lamb waves in several of the lower order modes has been demonstrated on polarized plates of PZT using interdigital transducers. It is shown that these waves cannot only be used in dispersive delay lines, but also that convolution and correlation can be efficiently performed using the nonlinear interaction between acoustic plate waves propagating in the same or different modes. The fact that plate modes exist with a broad range of velocities while they maintain the accessibility and high energy density of surface waves enables these devices to combine the advantages of pre- vious bulk and surface wave methods.

The IMCON Pulse Compression Filter and Its Applications

The IMCON is a reflection-mode dispersive delay line capable of high performance in large time-bandwidth product pulse compression systems. As developed in this paper, the unique characteristics of the IMCON are obtained by reflection from a double grating array that is applied to the surface of a strip. Current models of the device have center frequencies in the 4-30-MHz range with bandwidth up to 15 MHz, dispersion to 320 /spl mu/s time sidelobes on the order of --40 dB (with equalization), and other spurious signals at least 70 dB below the compressed output. The characteristics of IMCON operation are developed from a consideration of the device's transfer function. In particular, the IMCON'S high linearity and low sensitivity to fabrication and propagation problems are shown to be due to a unique error rejection effect. By comparison, the error rejection characteristics of single grating and dispersive transducer devices are found to be inferior to the IMCON. Data derived from operating pulse compression systems are utilized to demonstrate the low time sidelobe and high time-bandwidth capability of the IMCON.

Investigation of the surface acoustic wave properties of heteroepitaxial ZnO layers on Al2O3

Experimental data are given showing the relationship of phase velocity, group velocity, and electromechanical coupling coefficient as a function of the normalized thickness h/λ for epitaxial (112̄0) ZnO on (011̄2) Al2O3. Delay time vs frequency for dispersive delay lines fabricated from epitaxial ZnO on Al2O3 is also given. Using these data, design criteria and assessments are made for the use of this composite material in fabrication of a dispersive delay-line device.

Creatinine distribution dynamics in the dog.

The dynamics of the distribution of creatinine infused into 5 anesthetized, heparinized dogs in moderate diuresis were analyzed in terms of the simplest serial compartmental model (4 chambers with passive exchanges) which would describe the data accurately. During 3-hr experiments, the intravenous infusion rate was continuously varied over a wide range, resulting in large variations in arterial plasma concentration (measured continuously by AutoAnalyzer), thus providing an exacting test of the model. Input into first chamber of the model was the experimental rate of creatinine infusion. Output, also from this chamber, was determined by matching the integral of the product of clearance times the concentration of the first chamber (delayed 2 min) to the observed creatinine output measured over 10-min periods. The concentration in this chamber, after passing through a dispersive delay line analogous to the AutoAnalyzer, was matched to the observed AutoAnalyzer record by varying the volumes of the chambers and the passive exchange rates. This simple model provides an accurate description of the observed creatinine concentration and output and therefore can be used either as a building block in more extensive descriptive systems or as a basis for summarizing and comparing data obtained under varied physiological or pathological conditions.