Frequency Selective Element Research Articles

A Low-Loss Diffraction Grating Frequency Multiplexer

A quasi-optical frequency multiplexer based on a blazed diffraction grating is studied. Experimental data, supported by semi-quantitative theoretical considerations, show that the multiplexer is an efficient channel-dropping filter well suited to use in the millimeter wave region. A feature of the grating multiplexer which sets it apart from conventional designs is its ability to drop several channels using a single frequency-selective element, namely, a diffraction grating. This economy of hardware results in a simple, compact structure. The channels of the experimental multiplexer have typical bandwidths of ~540 MHz with loss of ~1 dB. The width of the impulse response at half amplitude is ~1.5 ns. Return loss within a channel is typically 15-20 dB. Comparisons with other millimeter wave multiplexer designs are discussed.

Frequency-locking of a CW dye laser to some absorption lines of a neon discharge by a Faraday filter

Single-mode oscillations of a CW dye laser at the center of five absorption lines from the 1s states to the 2p states of neon were obtained by means of a neon discharge Faraday filter, without any other frequency-selective elements. The most striking thing observed is that saturated absorption takes place at the center of several absorption lines in a Faraday filter, in addition to optical rotation.

Silicon, monolithic optical integrated circuits for laser system applications

Monolithic optical integrated circuits comprised of input coupler, waveguide, frequency selective element, and integrated detector for 1.06 μm laser applications are discussed. In particular, the analyses, fabrication, and design‐optimization of these circuits as well as experimental results for them are presented.

A directional coupler with large waveguide separation

We discuss experimental results of a directional coupler, fabricated by ion implantation through a conventionally produced photoresist mask into fused quartz. The waveguides are 5 μm wide and separated by 5 μm. Though the separation is very large the coupling length is about 4 mm at λ = 676 nm. This can be explained by a special waveguide type similar to slab-coupled waveguides which causes a high field penetration of the guided wave into the surrounding. The dependence of the coupler on various technological parameters is given and the use as a frequency selective element is experimentally demonstrated.

Single-line operation of a 2-W longitudinal cw CO chemical laser with no frequency-selective element in the optical cavity

An experimental condition has been found for the CO chemical laser where it would appear that vibration-vibration relaxation processes (V-V) compete with stimulated emission to force the laser to operate in essentially a single line ν = 10–9, P(17). No frequency-selective element has been used in the laser cavity. Experimental data and results of computations on a laser model are presented to support this suggestion. A cw power of 7 W has also been achieved in this longitudinal flow system with the addition of cold CO (300 °K) for the chemical efficiency of ∼ 3.2%, one of the highest values for any system reported at the present time.

A computational theory of short pulse generation

The semi-classical equations for the electric field and population inversion in a two-level medium are simplified for the case of a saturable absorber cell which is shorter than the length of fluctuations in the optical-pulse envelope. The spatial coordinates in the cell are effectively lumped, and the integration is reduced to the one dimension of time. The pulse is passed through an amplifying medium and frequency selective elements by a fast Fourier transform into its spectral components. The case of pulse formation in a ruby laser, starting from a noise fluctuation is computed for the parameters of a recently reported accurate measurement of pulse duration. Good agreement is obtained with experiment. Finally, a pulse length is predicted for a cavity containing an etalon which cancels gain narrowing.

Digital single-sideband mixer

A single-sideband (SSB) frequency converter using only exclusive-or logic gates and no reactive or frequency-selective analog circuit elements takes square-wave inputs at two arbitrary frequencies f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and generates an output waveform whose principal spectral component is at either f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> +f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> or f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> -f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , selectably. A pair of outputs is generated in phase quadrature.

A Thick-Film Television Video IF Amplifier Using Compatible Components

This paper describes development of a Thick-Film Television Video IF Amplifier Module. Discrete high-Q components compatible with thick-film techniques have been developed at Texas Instruments Incorporated. Their effectiveness as adjustable reactive elements has been successfully demonstrated by incorporating them in hybrid modules and using them as frequency selective elements in a commercial television receiver. Adequate tuning control has been achieved using airbrasive techniques to remove core material from toroidal transformers and to decrease the conductive surface area of flip-chip capacitors. Considerable attention is devoted to selection of magnetic and dielectric materials and to the shape and size of components consistent with adequate volumetric effi-efficiency. Suggestions in connection with automatic alignment procedures which circumvent the need for conventional slug adjustment and observation are also included.

Phonon-Terminated Optical Masers

The characteristics of phonon-terminated coherent oscillation associated with ${\mathrm{Ni}}^{2+}$, ${\mathrm{Co}}^{2+}$, and ${\mathrm{V}}^{2+}$ ions in rutile and perovskite fluorides are described. Continuous tunability over portions of the vibronic continuum of ${\mathrm{Ni}}^{2+}$ in Mg${\mathrm{F}}_{2}$ has been demonstrated. The system has been thermally tuned in discontinuous segments over a total wavelength span from 1.62 to 1.80 \ensuremath{\mu}, the longest continuous segment being 250 \AA{} (82 ${\mathrm{cm}}^{\ensuremath{-}1}$). Alternatively, a frequency-selective element (prism) has been used to vary the oscillation frequency (at a fixed temperature of 85\ifmmode^\circ\else\textdegree\fi{}K) in discontinuous segments between 1.62 and 1.84 \ensuremath{\mu}. The discontinuities are a consequence of structure present in the vibronic continuum of ${\mathrm{Ni}}^{2+}$ in Mg${\mathrm{F}}_{2}$. Continuous-wave oscillation has been obtained from ${\mathrm{Ni}}^{2+}$ ions in Mg${\mathrm{F}}_{2}$ and Mn${\mathrm{F}}_{2}$, requiring, respectively, less than 65 and 240 W of power into a tungsten lamp. Both systems display continuous spiking, and the spectral distributions of maser emission may be very complex.

Piezoelectric Materials, A Review of Progress

This paper is a review of the properties of the more important piezoelectric materials. Section I discusses the basic principles of the phenomena of piezoelectricity and elasticity from the standpoint of crystal physics. Section II is a brief account of the electrical measurements of piezoelectric vibrators which are required to determine the basic parameters defining the piezoelectric, elastic and dielectric properties of the material. Sections III and IV, respectively, give the properties of a range of piezoelectric crystals and ceramics including, in the most important cases, some of the derived properties which affect the use of the materials in practical devices. It is concluded that it is unlikely that new piezoelectric crystals will be found to replace those in use at present for frequency control and selection but that there is greater scope for new piezoelectric ceramics for use as electromechanical transducers or as frequency selective elements where the highest stability is not required.

Impulse noise in narrow-band fm receivers

THE RELATIVELY NARROW BAND FM communication receivers designed for use in mobile equipment are subject to disturbances caused by ignition systems in automobiles as well as to other disturbances of a similar transient nature. R-f signals are radiated from such ignition systems and these noise signals combine with the desired carrier to produce impulse-noise interference. When the disturbances are of a magnitude considerably greater than the desired information signal, and assuming that the receiver operates in accordance with the theoretical principles of frequency modulation, the receiver will respond only to the transient noise signal for the duration of the noise impulses. This results in receiver “blanking.” If the disturbing signal is of approximately the same amplitude as the desired signal, the two signals combine in the receiver to produce sudden changes in phase. These sudden phase variations result in large frequency excursions at the discriminator and cause shock excitation of the audio section of the receiver. Thus, when the interfering signal is either greater than or approximately equal to the amplitude of the desired signal, information will be lost. It is, therefore, desirable to design the frequency-selective elements in such a manner as to minimize this type of interference.

Impulse noise in narrow-band FM receivers

THE RELATIVELY NARROW BAND FM communication receivers designed for use in mobile equipment are subject to disturbances caused by ignition systems in automobiles as well as to other disturbances of a similar transient nature. R-f signals are radiated from such ignition systems and these noise signals combine with the desired carrier to produce impulse-noise interference. When the disturbances are of a magnitude considerably greater than the desired information signal, and assuming that the receiver operates in accordance with the theoretical principles of frequency modulation, the receiver will respond only to the transient noise signal for the duration of the noise impulses. This results in receiver “blanking.” If the disturbing signal is of approximately the same amplitude as the desired signal, the two signals combine in the receiver to produce sudden changes in phase. These sudden phase variations result in large frequency excursions at the discriminator and cause shock excitation of the audio section of the receiver. Thus, when the interfering signal is either greater than or approximately equal to the amplitude of the desired signal, information will be lost. It is, therefore, desirable to design the frequency-selective elements in such a manner as to minimize this type of interference.