This paper outlines a proposal for a miniature form of laser beam circuitry. Index of refraction changes of the order of 10−2 or 10−3 in a substrate such as glass allow guided laser beams of width near 10 microns. Photolithographic techniques may permit simultaneous construction of complex circuit patterns. This paper also indicates possible miniature forms for a laser, modulator, and hybrids. If realized, this new art would facilitate isolating the laser circuit assembly from thermal, mechanical, and acoustic ambient changes through small overall size; economy should ultimately result.
Some theory describing the behavior of two coupled waves is presented, and it is shown that this theory applies to coupled transmission lines. A loose‐coupling theory, applicable when very little power is transferred between the coupled waves, shows how to taper the coupling distribution to minimize the length of the coupling region. A tight‐coupling theory, applicable when the coupling is uniform along the direction of wave propagation, shows that a periodic exchange of energy between coupled waves takes place provided that the attenuation and phase constants (α and β respectively) are both equal, or provided that the phase constants are equal and the difference between the attenuation constants (α1 − α2) is small compared to the coefficient of coupling c. Either (α1 − α2)/c or (β1 − β2)/c being large compared to unity is sufficient to prevent appreciable energy exchange between the coupled waves. Experimental work has confirmed the theory. Applications include highly efficient pure‐mode transducers in multi‐mode systems, and frequency‐selective filters.
The direction‐changing capability of electromagnetic waveguides may be limited not only by mode conversion but also by radiation if the transverse field extends indefinitely into a freely propagating region. This paper gives new, more accurate expressions for the permitted bending radius with respect to mode conversion, using coupled‐wave theory to categorize the wide variety of transmission media possible. This paper also makes a suggestion for estimating the permitted bending radius when radiation is a limitation. In single‐mode “open” waveguides that have transverse fields extending indefinitely into a freely propagating region (such as a dielectric waveguide), the permitted bending radius is limited by radiation effects, whereas in either the open or completely shielded multimode waveguides, the permitted bending radius is usually limited by mode conversion.
No abstract
The behavior and applications of ferrites in microwave circuits have been studied at the, Holmdel Radio Laboratory with particular emphasis on non‐reciprocal properties. There are numerous ways of building non‐reciprocal devices which accomplish the same function, and the authors propose at the outset that a terminology based on function be adopted. Definitions of the gyrator, circulator and isolator are given. A qualitative method of deducing the properties of new ferrite‐loaded circuits, termed “point‐field” analysis, has been particularly fruitful, in that it permitted the exploration of a wide variety of ferrite‐loaded circuits despite the absence of precise mathematical analyses. Faraday rotation in longitudinally‐magnetized ferrite‐loaded circuits has been studied; the effects of higher‐order modes, the reasons for variation in Faraday rotation as a function of frequency, and the optimum geometry for the ferrite loading are discussed. In transversely‐magnetized ferrite‐loaded rectangular waveguide it is shown that the single mode medium may be non‐reciprocal as to phase constant, attenuation constant, or distribution of field components in the cross‐section. The latter effect is called the “field‐displacement” effect. In transversely‐magnetized ferrite‐loaded round waveguide, either reciprocal or non‐reciprocal birefringence may be achieved and examples are given. Some non‐reciprocal ferrite‐loaded dielectric waveguides are discussed. In all of these forms of non‐reciprocal transmission media, gyrators, circulators and isolators may be built, and experimental data are reported on some of the possibilities. A brief review of prospective uses for these non‐reciprocal elements is given.
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