Abstract: A system is described for randomly addressing any one of a plurality of remotely located stations connected by means of an electromagnetic wavepath. At the addressing point an addressing signal, comprising a series of m signal bursts, is generated and coupled onto the wavepath (11), where m is an integer and corresponds to the number of stations the addressed station is away from the addressing point. Each remote station includes means (33, 34, 41, 43) for deleting one signal burst and retransmitting the remaining signal bursts. Each station also includes means (34, 38, 42, 43, 44, 50, 51) for recognizing when only a single signal burst is received and for responding in a prescribed manner. By means of such a "count-down" technique, the m.sup.th station from the addressing station is accessed. it is an advantage of such a system that the addressing circuit is the same at all the remote stations.

Abstract: Techniques are disclosed for determining the distribution of dopants in optical fibers and fiber preforms by observing the reaction of a fiber/preform to uv illumination. One technique measures the fluorescence induced by the uv. A second method measures the absorption of uv by the dopants. Thus, by determining the intensity distribution of radiant energy from the fiber/preform, the dopant distribution can be determined as a function of distance from the center of the fiber/preform.

Abstract: Prior art circuits used in space diversity systems for combining the two received signals employ either continuously variable phase shifters, which have return-to-zero problems, or 90 degree phase steppers which combine the signals to within .+-.45 degrees. Both of these limitations are avoided by the use of the combination of a continuously variable phase shifter (14) and a 90 degree phase stepper (13). Control means (19, 20) are provided for actuating the stepper when the phase shift introduced by the variable phase shifter reaches a prescribed limit.

Abstract: Integrated optics directional coupler modulator/switches are improved by the disclosed configurations for switching optical modes of both polarizations at once. In one configuration a pair of parallel optical waveguides are provided having material presenting first and second wavenumbers .beta. for the TE and TM modes. Two independently tunable control signals are applied to an electrode assembly arranged so that each wavenumber is substantially tunable relative to the other thereby permitting substantially complete switching of both of the modes. In an exemplary embodiment, the material is lithium niobate or lithium tantalate with its c-axis perpendicular to the waveguides and oriented between 15 and 75 degrees, suitably at 45 degrees, to the substrate plane. Pairs and triplets of electrodes are used as appropriate to provide vertical and horizontal electric field components so as to independently tune the waveguide wavenumbers and coupling.

Abstract: The problems associated with large bandwidth requirements and of precisely controlling the relative magnitudes of the distortion components generated in predistorters are resolved in a bridge-type cuber circuit (10). The cuber comprises a resistive bridge (R.sub.1, R.sub.2, R.sub.3, R.sub.4) which includes a pair of oppositely-poled diodes (D1, D2 and D3, D4) connected in parallel with the resistor (R.sub.1, R.sub.3) in each branch (25, 26) of one pair of opposite branches of said bridge. The parameters of the cuber, which is balanced with respect to fundamental frequency signals, are adjusted so that predominantly third order intermodulation components are generated, and an impedance match with the signal source is obtained.The cuber circuit is used in a predistorter for cancelling third order distortion components produced in nominally linear amplifiers.

Abstract: A repeatered submarine cable has a composite inner conductor for accommodating a system of optical fibers therein. The cable strength members include a central elongated filament and plural layers of stranded steel wires separated from the central filament by an annular insulating core member, in which the optical fibers are embedded. A metallic tubular jacket surrounds the stranded steel layers to provide both a DC path for powering the optical repeaters and a hermetic moisture barrier for the fibers.

Abstract: A 90 degree phase stepper is described comprising a tandem array of three, 3 db hybrid couplers where the first and third couplers are of one variety (either 90 degree or 180 degree couplers) and the second is of the other variety. A pair of variable phase shifters are located in the two wavepaths connecting the first and second couplers, and a single variable phase shifter is included in one of the two wavepaths connecting the second and third couplers. Each phase shifter introduces either a zero or a 180 degree phase shift. By the appropriate selection of phase shifts, the phase of the output signal can be stepped in 90 degree increments. The stepper is designed for use in the signal combining circuit of a space diversity system. It is an advantage of the circuit that all of the received signal is preserved.

Abstract: A 90 degree phase stepper is described comprising a tandem array of one 90 degree hybrid coupler and one 180 degree hybrid coupler. A phase shifter, capable of introducing either zero or 180 degrees of phase shift, is included in each of the two wavepaths connecting the two couplers. By the appropriate selection of phase shifts, the phase of the output signal can be continuously increased or decreased in 90 degree or 180 degree increments.

Abstract: A multiplex radio transmission system is provided with facilities for initiating protective switching from a working channel to an idle channel of the system when the signal to interference ratio on the working channel falls below a predetermined threshold value. A precise square-law detector derives, from the separate information and interference components of a signal on the working channel, a DC component and a difference-beat AC component which are processed to yield a quantity indicative of the desired signal to interference ratio. When such ratio falls below the predetermined threshold value, switching to an idle channel occurs in a manner similar to conventional signal-to-noise dependent protective switching arrangements.

Abstract: The problems of high cost, high loss and incomplete distortion compensation are resolved in a distortion generating circuit which employs a nonlinear phase modulator (70, FIG. 7) and a linear phase shifter (71) as a means of generating selected distortion signal components. The circuit includes an output coupler (30) and an output coupler (31) interconnected by means of a pair of wavepaths (32, 33). The nonlinear phase modulator (70), which includes a nonlinear reactive element (37), is disposed in one of the wavepaths (32). The linear phase shifter (71) is included in the other wavepath (33). By the appropriate adjustment of the linear phase shift in wavepath (33) the entire gamut of distortion characteristics can be compensated. Distortion generating circuits of the type disclosed can be employed as either predistorters or as postdistorters to compensate for the nonlinearities in electromagnetic signal devices, such as amplifiers.

Abstract: A complementary distortion circuit for reducing the level of IM products in the output of a TWT amplifier. One embodiment of the invention includes a 3 db, 90.degree. coupler to divide the input signal into two components of equal amplitude but differing phase with an IM generator positioned in the path of each component. The IM generator may comprise non-linear phase modulators or non-linear amplitude modulators. The two components are then re-combined in a second, 3 db, 90.degree. coupler. The non-linear phase-modulators may comprise varactors and the non-linear amplitude modulators may comprise varistors. The unit is intended to operate in the microwave region.

Abstract: A method of fabricating an optical fiber connector is disclosed using a transfer molding process employing a precision die whose interior surface defines a frustum for forming the mating surface of the connector. The fiber is inserted through the mold cavity and extends through an aperture in the end surface of the frustum and through an annulus disposed outside of the mold cavity immediately adjacent to the aperture. At the transfer molding temperature, the annulus expands inward radially, simultaneously sealing the aperture and centering the fiber. After curing, the excess fiber is removed, and a flexible, dome-shaped contacting member is formed over the fiber end.

Abstract: An optical waveguide in which intermodal coupling is deliberately induced. Perturbations are introduced along the waveguide. The perturbations have a spatial frequency that varies along the guide from f.sub.1 to f.sub.2, where f.sub.2 is .ltoreq. the critical frequency above which coupling to unguided modes occurs and f.sub.1 corresponds to the beat between the n.sup.th and the (n + 1).sup.th modes, the lowest modes of interest propagating in the guide.

Abstract: Third order IM distortion in a microwave repeater is measured in situ by applying a small amount of low frequency amplitude-modulation to the payload signal while at the same time adding a test-tone of fixed frequency and amplitude. At the repeator's output, a pair of synchronous detectors, driven in phase quadrature by the test-tone generator, measure the modulation depth of the test-tone. This modulation depth is now a measure of the degree of distortion in the repeater.

Abstract: A method of breaking a rod of brittle material, such as a glass optical fiber, so as to yield a mirrorlike surface across the entire rod end is described. This is achieved by establishing a decreasing tensile stress across the cross section of the rod which, at all points, is greater than zero but less than the threshold stress at which a mist zone forms. This is conveniently achieved by simultaneously applying longitudinal tension to the rod and bending it. A convenient hand tool for breaking optical fibers is also described.