Abstract: An electrical-optical interface network for use in a carrier-sense, multiple-access system with collision-detection provides two-way transmission between an electrical circuit (5,7,9) and a pair of lightguides (21,22), but prevents signal transmission between the lightguides.

Abstract: The dispersive effects of frequency selective fading in a digital, FM, or AM radio system are reduced by means of an adaptive equalizer (11) comprising a cascade of feed-forward stages (1,2, . . . N), each of which includes: a first parallel wavepath (1-1, 1-2, . . . 1-N) including a first adjustable attenuator (20-1, 20-2, . . . 20-N); a second parallel wavepath (2-1, 2-2, . . . 2-N) including a second adjustable attenuator (21-1, 21-2, . . . 21-N) and delay means (22-1, 22-2, . . . 22-N); and means (23-1, 23-2, . . . 23-N) for combining the signals in said wavepaths and for coupling said combined signal to the next stage. By a suitable selection of parameters, according to two unique relationships, a transfer function can be realized which can compensate for amplitude and delay distortions caused by minimum and nonminimum phase fades.

Abstract: Small, highly sensitive uv detectors are fabricated utilizing the fluorescence induced in the core of an optical fiber when illuminated by uv radiation. The fluorescence light is then guided by the fiber itself, by a similar fiber or by a different optical fiber to a remote location and detected by a standard v1 detector. To determine the intensity of the uv, the sensor is calibrated at the wavelength of interest.

Abstract: The ridge-structure in a ridge waveguide laser is notched at periodic intervals to produce a longitudinally crenelated ridge, and the electrode on the ridge side of the laser is alloyed only to the topmost surfaces of the ridge. As a result, the active region of the laser is pumped only in the regions that are underneath the topmost surfaces of the ridge, and the laser is caused to prefer the longitudinal modes whose maxima coincide with the spatial Fourier components of the pumped regions.

Abstract: Tunable, polarization independent wavelength filtering is obtained in a circuit configuration comprising an input polarization selective coupler which separates the TM and TE mode waves. A first, wavelength selective mode converter, in the TE mode wavepath, converts the TE mode wave energy at the selected wavelength to the TM mode. Similarly, a second wavelength selective mode converter, located in the TM mode wavepath, converts the TM mode wave energy at the selected wavelength to the TE mode. An output polarization selective coupler combines the TE and TM mode wave energy at the selected wavelength in one output wavepath and combines the balance of the input signal in a second wavepath. By cascading a plurality of such circuits, each tuned to a different wavelength, a wavelength multiplexed signal can be demultiplexed.

Abstract: A signal recognition circuit (10) is disclosed which is capable of distinguishing between the digit tones used for dialing in multifrequency tone telephone sets, and spurious signals at the same frequencies, such as noise and voice. The discriminator comprises, in cascade, an AGC amplifier (11), an adjustable threshold comparator (12), and a signal validation circuit (13). The operation of the discriminator is based upon the fact that the true dialing tones have envelopes of constant magntiude whereas the spurious signals tend to have pronounced envelope variations. By the appropriate adjustment of the comparator threshold, these variations show up as gaps in the comparator output signal, which are readily detected by the validation circuit.

Abstract: A generalized polarization transformer (10) is disclosed that is capable, under electrical control, of transforming the polarization of a signal between two arbitrary states. In its most general form, the transformer comprises a variable input phase shifter (11) for varying the relative phase between an incident pair of orthogonally polarized wave components; a variable mode converter (12) for varying the relative amplitudes of said orthogonally polarized wave components; and a variable output phase shifter (13) for varying the relative phase between the wave components derived from said mode converters. For some applications, the output phase shifter is not required. In an alternative configuration, the input phase shifter and the mode converter are combined in a common constructure.

Abstract: The response, as a function of frequency, of electrooptic mode converters using comb electrodes has been found to include several peaks at frequencies above and below the desired frequency. These spurious peaks appear to be caused by fringing of the electric field which effectively changes the spatial period of the electrode fingers. To prevent this unwanted coupling, channels have been etched between the comb fingers. The result is to confine the electric field to the narrow region between opposing electrode fingers, thereby minimizing the spurious responses. It also serves to reduce the magnitude of the applied voltage required to produce the same field strength.

Abstract: The coupling efficiency between a pair of identical optical waveguides (11, 12) is modulated by a traveling electrical wave (14, 15). Because the propagating constants of the optical and modulating systems are not equal, the interaction between them is limited to periodic intervals along the optical wavepaths. By the appropriate selection of this spatial period, a velocity match between the modulating and optical systems is simulated.

Abstract: Optical fibers having enhanced mode coupling produced by an asymmetric refractive index profile that varies periodically along the length of the fiber are described. The prescribed variations are obtained by means of a fabrication process that includes periodically varying the source of at least one of the fiber materials in a direction transverse to the fiber-drawing direction. This transverse periodicity is translated into the desired longitudinal periodicity along the fiber by the fiber-drawing process.

Abstract: In a diversity signal combiner, the weaker of the two signals is attenuated an amount that varies as a function of the phase angle between the two signals. When the phase angle is small, the attenuation is small and the two signals add together. As the phase angle increases, the attenuation of the smaller of the two signals increases. For phase angles between 90 and 270 degrees, the contribution of the smaller signal is negligible. In digital systems, improvements in the bit error rate can be realized by introducing a 180 degree relative phase shift in the wavepath of the weaker signal whenever the phase angle exceeds a specified threshold.

Abstract: Transmission configurations are described for providing usable service despite the complete interruption of one or more of several transmission links. This is accomplished by encoding (11) the information content of each of a plurality of input signals (S.sub.1, S.sub.2 . . . S.sub.n) into a multiplicity of encoded signals (s.sub.1, s.sub.2 . . . s.sub.m) for simultaneous transmission along a multiplicity of transmission links (13.1, 13.2 . . . 13.m). At the receiver, a decoder (12) recovers the individual input signals. By accepting temporarily either a bandwidth or a signal-to-noise reduction, service is continued even though one or more of the transmission links fails.

Abstract: VAD torches include a plurality of coaxially aligned tubes. A typical outside diameter is about 1 inch. To fabricate smaller torch nozzles, spacers (20, 21, 22) are symmetrically placed between adjacent tubes (11, 12, 13, 14), and the entire tube assembly heated and drawn as a unit to reduce its diameter. The drawn tubes are then cut at a point along the reduced diameter region to produce a torch whose nozzle has the desired (i.e., reduced) diameter.

Abstract: Shaping of the refractive index profile of an optical fiber is typically achieved by changing the concentration of an index-modifying dopant within the glassy matrix preform. To measure the profile and the core diameter of the preform, in accordance with the present disclosure, the preform (10) is illuminated with a focused beam of ultraviolet radiation (15) whose beam width (w) is small compared to the preform core diameter (d). This induces a fluorescence along a thin pencil-like region (16) of the preform core whose intensity varies in proportion to the concentration of the dopant. Inasmuch as the latter is proportional to the refractive index, the intensity profile gives the index profile directly. A similar measure can also be made on fibers using microscopes for focusing the uv and observing the induced fluorescence. Use of this technique for controlling the rate at which a fiber is drawn is also described.

Abstract: An adaptive equalizer is disclosed comprising an amplitude equalizer circuit (12) having an adjustable Q, and a plurality of all-pass circuits (14,15) having adjustable delay bumps. A controller (18) adjusts the tuning, magnitude of the bumps, and the number of all-pass networks in the equalizer in response to variations in the power within a plurality of spectrum samples and the bit error rate of the equalizer output signal.

Abstract: In a space diversity receiver, the relative phase of the two received signals is varied in manner to minimize amplitude dispersion in the combined signal. A phase control signal is derived from the combined signal by phase modulating one of the received signals, and then detecting the fundamental amplitude component induced by said modulation within two selected portions of the combined signal spectrum. The fundamental component of the envelope modulation of the weaker of the two signal portions is used to control the relative phase of the two received signals so as to minimize the amplitude dispersion in the combined signal across the band. In the absence of inband phase dispersion needed in order for the compensating phase shift to effect the two signal portions differently, a relative delay is introduced in one of the two received signal paths.

Abstract: An adaptive multipath fade equalizer is disclosed comprising differencing means (24) for forming a difference between an input equal to said equalizer and a component of the equalizer output signal and a feedback loop (21) for coupling said component of output signal to the differencing means. The feedback loop includes a fixed delay T (22), a variable attenuator (23) and a variable phase shifter (25). A phase control network (30) and an attenuation control network (31) compare selected portions of the frequency spectrum of the signal and adjust the variable controls to minimize the effects of multipath fades upon the signal. It is an advantage of the equalizer that it automatically adjusts for changes in the frequency and depth of the fade notch.

Abstract: The proper utilization of that portion of the millimeter wave spectrum that is particularly highly absorbed by the atmosphere is shown in conserve frequency spectrum while permitting a high density of users operating in relatively close proximity.

Abstract: The reference signal applied to the differencing network of a differential feedback amplifier is shaped to conform to the natural gain-vs-frequency characteristic of the principal amplifier. This serves to minimize the amplitude of the error signal that the error amplifier must handle. As a result, the error amplifier is much smaller and can be optimized with respect to its noise and dispersion performance.

Abstract: A class of signal dividers and signal filters is disclosed comprising first and second wavepaths coupled at one end to a common input port and at their other ends to a summing network to form a sum signal, and to a differencing network to form a differencing signal. Phase shift means are included along at least one wavepath for producing a differential phase shift between signals in said two wavepaths. In order that such devices be capable of operation at very low frequencies (i.e., a few Hertz), be physically small, and be capable of being made by means of integrated circuit techniques, the phase shifters are made solely of R-C passive elements, or of other devices that can be readily integrated.