Abstract: The turn-on delay of a gas laser is significantly reduced by inducing a transient electric field of sufficient intensity to induce ionization in a localized region of the laser adjacent to the anode. This is accomplished by means of a coupler which couples the voltage applied to the cathode to a region of the laser immediately adjacent to the anode electrode.

Abstract: The turn-on delay of a cold cathode gas tube, such as a gas laser, is significantly reduced by the inclusion of an electric field concentrator in a region of the tube between the tube anode and cathode. The concentrator can take the form of a projecting conductive member having a sharp corner, linear or curved knife edge, needle like points, or combinations of such geometries.

Abstract: Stabilized, single-mode operation of semiconductor lasers is obtained by introducing longitudinally spaced variations in the effective refractive index along the active waveguiding medium, where said index changes have a spatial period corresponding to many half-wavelengths of the guided optic wave. Because the spatial period of the variations is relatively long, as opposed to half an optical wavelength used in the prior art distributed feedback lasers, a laser in accordance with the invention is much easier to fabricate.

Abstract: Prior art techniques for velocity matching the optical wave and the modulating electrical wave in traveling wave, electrooptic devices includes the use of phase reversals and intermittent interaction. This results in a device whose frequency response includes a single peak. It has been discovered that by reducing the length of the interaction intervals between the electrical and optical systems, a multiplicity of harmonically related frequency peaks can be obtained. Furthermore, by combining the phase reversal and intermittent interaction techniques in a common device, the available bandwidth can be doubled.

Abstract: An active tap for use in an optical multiple access network is disclosed. The tap comprises a semiconductor substrate on which the electronics associated with an active parallel path are fully integrated. These include optical detectors, amplifiers and light emitters formed using standard semiconductor fabrication techniques. A section of fiber, incorporated as an integral part of the tap structure, is provided with a pair of longitudinally spaced discontinuities for deflecting a portion of the incident signal onto the detector and for redirecting the output from the light emitter along the through-path. Alternatively, the tap substrate can be provided with a groove for receiving a fiber segment located anywhere along the distribution network.

Abstract: A new Raman gain medium, comprising an optical fiber into which molecular gas has been diffused, is disclosed. This new medium combines the advantages of a fiber, i.e., long interaction path, low loss, controllable dispersion, and convenience in handling, with the large Raman wave number shift of the gas, i.e., 4136 cm.sup.-1 for H.sub.2 in silica. A laser made with such a medium can provide a relatively high power, tunable, coherent signal source in the near and far infrared regions.

Abstract: The efficiency of packet switching networks is improved by using a collision avoidance technique rather than collision detection. The subscriber links are connected to a common node. A collision avoidance circuit in each link monitors the node to determine whether it is in a busy or idle status. The first message to arrive places the node in a busy status at which time all other, nontransmitting links are disconnected, thereby avoiding a collision. Later arriving messages are stored in buffers at each subscriber location and are transmitted when the node is again idle. In this manner messages are transmitted on a first-come basis, and can be of arbitrary duration regardless of bit rate.

Abstract: In a disconnectable low-loss optical connection for optical fibers, each fiber in a pair of optical fibers is surrounded by a connector body to the conical frustum mating end of which is applied a tiny, transparent, flexible index matching dome of silicone rubber or equivalent material. The connector bodies are held together by mating to each other or to a common alignment receptacle having conically hollow receiving surfaces, so that the fiber ends are aligned and the domes touch and flex completing the optical connection.

Abstract: In a radio communication system, an adaptive transmitter power control system is described wherein the signal level at each receiver is monitored and a control signal, which is a function of the signal level, is transmitted back to the transmitting station to adjust the transmitter output power, as required. By transmitting the lowest power level consistent with system objectives, the repeater circuits operate in a highly linear mode, and cochannel interference is significantly reduced.

Abstract: Various techniques for examining the core region of optical fibers and fiber preforms involve placing a portion of the fiber/preform in an index-matching fluid and transversely illuminating the immersed portion. As described herein, the use of an index-matching fluid can be eliminated by illuminating the fiber/preform with a diverging beam. By the suitable selection of parameters, refraction at the air-fiber/preform interface can produce a well colliminated beam within the core region.

Abstract: In a digital, time division multiplex communication system, a first-in, first-out buffer (10) at each subscriber station is employed to establish a conference call. The digital words of the conferees being listened to are entered into the buffer as they are received. They are then read out at a different bit rate such that they all occupy an equal fraction of the word period. The words are decoded in a standard D/A converter (11) and combined in a filter (12).

Abstract: A velocity match between a traveling optical wave and an interacting traveling electrical wave having a different velocity of propagation is simulated by shaping the electrical signal path so that interaction between the two waves occurs along selected regions of the electrical signal wavepath. In particular, the electrical wavepath bends away from the optical wavepath at uniformly spaced intervals to produce regions of no interaction along the electrical wavepath. This technique is employed to modulate optical waves via the electrooptic effect.

Abstract: A new transmission system configuration is disclosed which takes advantage of the special properties of lightwave devices and the extensive availability of frequency space on optical fibers. The system employs a combination of time and frequency multiplexing at the transmitter, and frequency demultiplexing at the receiver. An advantageous result of combining time and frequency multiplexing is to relax the tolerance requirements on filters at the transmitter. A further advantage is to minimize the effects of mode dispersion introduced by the fiber.

Abstract: By introducing an asymmetry in the effective refractive index profile of a waveguide, wave energy can be extracted from the waveguide by radiation at wavelengths greater than a critical wavelength, where the latter is a function of the effective index distribution. This technique is employed to develop a variety of optical wavelength filters.

Abstract: Single mode lasers are advantageously stabilized in order to prevent a side mode from growing to a level where partition noise effects degrade high speed performance. To obtain such spectral stability, the powers in the two adjacent side modes are measured, and the operating temperature of the laser varied in response to changes in their relative powers. Optimally, the gain curve peak is made to coincide with the preferred cavity mode.

Abstract: A simulated velocity match between a traveling optical wave and a traveling electrical modulating wave is obtained in traveling wave, velocity mismatched electrooptic devices by introducing, at longitudinally spaced intervals along the electrical signal wavepath, means for producing the equivalent of a 180 degree phase shift in the effect of the modulating signal upon the operative electrooptic parameter of said device. This technique is employed to minimize the effect of walk-off due to velocity mismatch in modulators, phase shifter and mode converters.

Abstract: In a double-clad, single mode fiber with depressed inner cladding, reduced losses at the longer wavelengths are realized when the ratio of the radius of the inner cladding to the radius of the core is at least 6.5 to 1.

Abstract: Because of the very large variety of useful filter configurations, it is highly desirable to have a generalized circuit topology from which all specific filters can be derived. A generalized switched-capacitor biquadratic active filter comprises a pair of operational amplifiers (10, 11), each of which has an unswitched feedback capacitor (D, B) connected between its output port (3, 3') and its inverting input port (1, 1'). A third through-switched capacitor (C) provides feedback between the output port (3') of the second amplifier (11) and the inverting input port (1) of the first amplifier (10). A diagonally-switched capacitor (A) couples the output port (3) of the first amplifier (10) to the inverting input port (1') of the second amplifier (11). The noninverting input ports (2, 2') of the two amplifiers are connected to signal ground.

Abstract: Switched capacitor topologies currently in use are susceptible to the deleterious effects of the parasitic capacitances associated with the switches. Topologies that are immune to these effects are disclosed. A first such embodiment comprises a first switch (22, 32), a capacitor (23, 33), and a second switch (24, 34) connected in series between one input terminal (1) and one output terminal (3) of the network. Third and fourth switches (26, 35 and 27, 36) are connected between the junctions (98, 42 and 99, 43) of the capacitor and the first and second switches, respectively, and the common junction (97, 41) of the second input and second output terminals (2, 4). A second embodiment is also disclosed.

Abstract: A method of fabricating an optical fiber having an asymmetric refractive index profile that varies periodically along the length of the fiber is 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.