Marvin Chodorow

All-single-mode fiber resonator

An all-fiber-ring resonator has been constructed using a single strand of single-mode optical fiber and a directional coupler. Derivation of the resonator finesse in terms of fiber and directional coupler parameters is given. A finesse of 80 has been achieved experimentally. Applications of such a fiber-ring resonator are discussed.

All-fiber stimulated Brillouin ring laser with submilliwatt pump threshold

An all-fiber ring resonator, constructed from a single strand of single-mode optical fiber and a directional coupler, is shown to have a low threshold for stimulated Brillouin laser action. The 10-m-perimeter fiber ring resonator has a low round-trip loss of under 3.5% and an inherent pump-power enhancement of approximately 30. Lasing threshold for the 4.0-microm-core fiber occurred with a pump power of 0.56 mW at lambda = 6328 A and 1.74 mW at lambda = 5145 A.

CROSS-WOUND TWIN HELICES FOR TRAVELING-WAVE TUBES

This paper describes a structure, namely, a cross‐wound twin helix which overcomes the disadvantages of a conventional helix for high‐voltage traveling‐wave tubes. The disadvantages of a single helix suitable for high voltages are: (1) the impedance for electron interaction is reduced because of the energy content of the noninteracting space harmonics, and (2) the high impedance of some of the space harmonics can result in backward‐wave oscillation. In a structure consisting of two helices wound in opposite directions, the symmetry of the fields results in most of the electric energy being stored in the fundamental component and most of the magnetic energy in the space harmonics. This results in a higher impedance for the fundamental component and a reduced impedance for the space harmonics. Typical numbers for dimensions suitable for 10‐kv operation are an increase of a factor of 2 in the fundamental impedance and a reduction of a factor of about 20 in the −1 space harmonic for the twin helix as compared to the single helix.

Re-Entrant Fiberoptic Approach To Rotation Sensing

We are investigating a new approach to inertial rotation sensing which we refer to as an active re-entrant Sagnac system (ARS). It is aimed at rotation rates extending to very low values, as required in such amplications as navigation, guidance and geophysical measurements. It employs a multiturn fiber optic loop containing an internal optical amplifier, and uses pulsed optical signals introduced by an external laser oscillator which make multiple recirculations around the loop. Its output signal is a time-sampled sinusoidal waveform having the same frequency as the beat frequency in a standard oscillating ring laser gyro (RLG) having the same loop diameter. Like the RLG, it is basically an integrating rate gyro, in which digital cycle counting is used to determine the angle turned through. It is basically free of the mode locking effect encountered with RLGs, and has prospect for higher sensitivity to rotation. Experiments using cw light are described, which include new re-sults on removing instabilities and environmental sensitivities from fiber gyros. Initial experiments on pulsed recirculation without an amplifier are described, which affirm the basic recirculation principle. Work is beginning on development of a fiber amplifier for use in a full ARS experiment.

Oblique, off‐specular, linear, and nonlinear observations with a scanning micron wavelength acoustic microscope

We have constructed a micron wavelength acoustic microscope having a novel geometry which accentuates detail in acoustic imaging while providing ease in focusing, enhanced resolution, and the observation of third‐order nonlinear products (2F1‐F2). Convergent, acoustic beams generated by curved transducers provide very high power densities at the acoustic lens and focus. Oblique acoustic illumination of surfaces gives directionality to the image and the use of a second transducer position, removed from the specularly reflected beams, reduces undesired nonlinear interaction in the intervening liquid (water) medium. Increased resolution and sharper images are obtained by observing the second harmonic via the difference frequency (third‐order product 2F1‐F2) which falls back into the initial frequency range, ∼600 MHz. However, significant effects due to nonlinear interaction identified with the object have not yet been observed.

Oblique incidence reflection acoustic imaging

The authors report here recent advances in reflection acoustic microscopy using an obliquely incident focused acoustic beam. Results show that, in addition to exaggerated surface contouring on objects such as integrated circuits and blood cells, a contrast enhancement is observed which facilitates the study of thin‐film polymers such as MylarX (Dupont). A theoretical explanation is presented which describes these results and provides a means of predicting which objects are best studied in the normal incidence and oblique incidence reflection acoustic microscopes.

Nonlinear acoustic off‐axis imaging

Nonlinear imaging, in which object acoustic illumination is at a frequency ω and the output is detected at 2ω, has been complicated by competing nonlinear generation from the propagation medium between the object and the output lens. However, recent results with a nonspecular oblique incidence acoustic reflection microscope show interesting object nonlinear generation from polyvinylidine fluoride (PVF)2 and mica in granite. These micrographs will be presented and discussed.

Current Distribution in Modulated Magnetically Focused Electron Beams

Detailed measurements have been made of the dc and rf current distribution in a modulated, magnetically focused electron beam having normalized parameters in the range of values appropriate for practical medium‐power and high‐power klystrons. The ratio of the total rf current to the total dc current in the beam as a function of drift distance was determined experimentally under Brillouin‐flow conditions for selected values of α (the ratio of the rf voltage at the input gap to the dc beam voltage). These experimental values are compared with the results predicted theoretically. Similar experimental results are presented for higher focusing fields. Detailed radial distributions of the dc and rf current were experimentally determined by using an iris (a plate with a small hole) to allow only a small portion of the beam to be selected at any radial position. These measurements were made at various values of α and drift distance. The results for small values of α show, as predicted by theoretical consideration...

Propagation and Variable Delay on a Periodic Circuit of YIG Spheres

A microwave‐propagating structure has been investigated which is composed of a periodic, linear array of coupled YIG spheres operating in the uniform precession mode. Theoretical and experimental data on the propagation characteristics are presented. Both forward and backward types of waves exist. The system has characteristics of an electronically controllable filter and delay line whose properties are controlled by varying the applied dc magnetic field. Delay times in the nanosecond to microsecond range, with control of group velocities over a range of 5 to 1 or more, at signal attenuations on the order of 0.03 dB/nsec of total delay, appear possible.

Microwave tubes and semiconductor devices, G. D. Sims and I. M. Stephenson

The object of the book, as stated by the authors, is to present an up-to-date and readable survey of the principles of operation and uses of microwave valves. On this score, it is the reviewers feeling that the authors have succeeded. The scope of the book covers practically all microwave tube types, including traveling-wave tubes, klystrons, backward-wave amplifiers, parametric amplifiers, magnetrons, etc. There is a chapter on masers and on semiconductor devices.