Abstract: A method and apparatus for compressing data, particularly useful in a modem. The preferred method is implemented in a microprocessor within a modem, and dynamically adapts to changing data statistics. Parallel encoding and decoding tables are provided at the encoder and the decoder, and are updated for each character processed. Each table has a plurality of digital compression codes associated with characters of an alphabet. In response to an item of data presented for encoding, a compression code which corresponds to the character presented for encoding is selected using the encoding table. The selected compression code is provided as an output. Periodically, the association between the codes and the characters of the alphabet in the table is adjusted as a function of the frequency of occurrence of characters of the alphabet, over a plurality of characters.

Abstract: The preferred embodiment (11) of the modem comprises a control unit (13), a memory (27), a switch (14), and a modem engine (17). The modem engine (17) establishes communications with a modem (30) using conventional handshake methods. The control unit (13) then initiates a special handshake sequence composed of nonprintable, opposing characters to the modem (30) via the switch (14) and the modem engine (17). If the modem (30) completes the special handshake sequence then the control unit (13) and the modem (30) exchange the desired information. If the modem (30) does not complete the special handshake sequence then the preferred embodiment (11) functions as a conventional modem. The use of nonprinting, opposing characters for the special handshake sequence prevents the special handshake sequence from adversely affecting the external devices (10) (34).

Abstract: A dual wavelength optical source includes a monolithic integrated pair of series-opposition connected diodes, each fabricated for emitting light having a different wavelength than the other. Polarity of a common bias current conducted through the diodes is reversed for activating alternatively light emission from the diodes. Active emission regions of the diodes are stacked upon one another for efficiently coupling the resulting beams of the different wavelengths of emitted light through a surface into the core of a single mode optical fiber.

Abstract: Two-dimensional semiconductor chips are stacked to form a three-dimensional array in which coupling between chips is effected optically. This permits the use of smaller chips, with a corresponding higher yield, and serves to reduce the chip area required for interconnecting leads. It also reduces the internal interconnection path lengths which, at present, limit the speed of operation.

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: An electro-optic integrated circuit is disclosed wherein the long electrical connections normally present on a large scale integrated circuit are replaced by an optical waveguide layer. A plurality of epitaxial layers are grown on a single substrate and at least three of the plurality of epitaxial layers are grown with bandgaps that are suitable for optical sources, detectors and waveguiding. These primary layers are separated from each other by a barrier layer having a bandgap greater than either of the adjacent primary layers. Two of the layers adjacent to the substrate are grown to accommodate electrical devices that can be used to couple electrical signals to the optical source layers and to amplify electrical signals provided by the optical detection layer.

Abstract: Large current gains and high degrees of sensitivity to impinging primary photons are realized in photon feedback photodetectors embodying the invention. A photocurrent generated by an internal photodiode (10, 11) in response to the primary photons (6) causes secondary photons to be emitted by internal serially connected luminescence diodes (12, 13; 14, 15). Secondary photons traveling away from the photodiode are redirected by a reflector (16) to impinge on the photodiode and thereby sustain the photocurrent. Gains of the order of 100 are realized by these photodetectors.

Abstract: Longitudinal mode control is achieved in a heterojunction semiconductor laser (201-208) by doping the active region (203) of the laser with a deep level electron or hole trap. The trap is chosen to have a carrier capture cross section .sigma..sub.e and an optical cross section .sigma..sub.o such that the ratio of P, the average number of photons per cubic centimeter, to P.sub.s is between 0.1 and 100 where P.sub.s is equal to (N.sigma..sub.e V/.sigma..sub.o C.sub.o), N is the carrier density, V is the carrier thermal velocity, and C.sub.o is the speed of light in the material. In a specific embodiment the active region is bombarded by photons to achieve deep level electron traps in the active region.

Abstract: A semiconductor laser is disclosed wherein the active region has been doped with deep-level electron traps either by proton bombarding the active region or by doping with an impurity, such as oxygen, iron, or chromium. The density of traps is such that an optical absorption parameter of greater than 30 cm.sup.-1 is achieved. This laser, when combined with an ordinary photodiode, exhibits overall optical gain thereby permitting an array of optical logic circuits.

Abstract: An input voltage overload protection semiconductor structure useful with MOS circuitry consists of a p-region in an n-substrate with p+ type regions formed on both sides of the p-region and an n+ type region centrally located in the p-region. Input signals are applied to the first p+ region. The gate of an MOS structure to be protected from voltage overload is connected to the second p+ type region. A power supply used with the MOS structure is connected to the n+ region. This structure provides significantly greater load protection than the standard resistor-diode-resistor circuit.

Abstract: A foetal scalp electrode of simple construction, which is simple to operate, and which affords secure attachment to the foetal scalp, has a tubular torsional spring member encircling an electrically conductive wire between an electrical connector and an insulated head member, whereby relative rotation of the connector and head member respectively manually against the torsion and oppositely upon release of the connector causes an arcuate contact needle on one end of the wire to move respectively into and out of the head member, the head member being provided with a concave surface facing oppositely to a flat surface from which the needle is normally urged by the torsion, so that the head member can be held securely in one hand close to a foetal scalp with a finger resting in the concave surface, which is preferably formed with ribs extending transversely with respect to the axis of the tubular torsional spring member, so as to improve the grip afforded by a finger engaging the concave surface still further by

Abstract: A light-activated light-emitting device has at least one p-n junction provided with electrodes for confining light-emission to an area of the junction. It has been determined that light-emission can be activated by light impinging on the junction outside this confined area, so two optical fibers are provided, one being an input fiber for bringing activating light to the nonemitting sensitive part of the junction and the other fiber being an output fiber coupled to the light-emitting area. When the device is a p-n-p-n light-activated light-emitting switch provided with an RCL reset control circuit, a very inexpensive unidirectional optical pulse regenerator is obtained. The device in its various forms is advantageously suited for use in each of many stations along optical fiber data busses or in optical logic arrays because the unidirectional feature prevents light feedback between adjacent devices and consequently avoids spurious switching of a preceding device.