Scientific-Atlanta, Inc.

Verifiber Technologies, Inc.

Other

Leo J Thompson

Rezin E Pidgeon, Jr

Frank R Little

Emmanuel Anemogiannis

John Alexander Ritchie, Jr

Herman A Kruse

Gregory T Dubberly

Catherine W Jelinek

Munther A Al-Khalil

James O Farmer

Leo Montreuil

Lamar E West, Jr

Joseph Graham Mobley

William P Lafay

Steven Veneman

Anatoly Kozushin

Frederick T Zendt

Scott R Siclari

David M Fellows

Martin A Cowen

Christopher P Lewis

Lamar E West

Rezin E Pidgeon

A plurality of optical communications systems including a SPW modulator are described. The communications systems include an optical transmitter coupled to an optical fiber communications link which carries a optically modulated information signal to an optical receiver. The laser transmitter includes a laser light source which is optically coupled to a SPW modulator which has been particularly adapted for broadband communications by selecting its transfer characteristic and modulation structure. A broadband signal containing a plurality of information channels, for example CATV channels, is applied to it modulator electrodes. The modulation signal varies the power coupling between the guided laser light source signal and a SPW in the modulator. The result is an intensity modulated optical signal that is output to the optical fiber for transmission to the optical receiver of the system. Alternatively, the communications system includes a high power laser coupled to an optical splitter to divide its output power in two or more optical source outputs. Each optical source output is then used to drive an associated SPW modulator. Each of the modulators receives a broadband signal with which to modulate its optical source. After modulation, the modulated lightwave from a modulator is coupled to a corresponding optical fiber for carriage to an optical receiver. In this manner, several broadband information signals can be communicated over the system using only one laser source. A net benefit from using one higher power laser, rather than several lower power ones, is one of cost, purity and similarity of the several signals. This configuration is enhanced by the lower loss and higher linearity of the SPW modulators. Further, several WDM embodiments including those having serially cascaded SPW modulators are provided. The transfer characteristic of the SPW modulators are tailored to either be more efficient for an analog or a digital modulation signal by adding or subtracting grating effects.

Optical surface plasmon-wave communications systems

A method and apparatus for detecting a fault, such as a break or crack in a fiber optic cable. A test device transmits into a first end of fiber bundle under test a first pulse of optical energy. The time duration and/or intensity of the pulse propagating through the fiber after being reflected back through the fiber are determined and stored in memory. At a later point in time this step is repeated with a second pulse. If the propagation time and/or intensity of the second pulse varies by greater than a predetermined amount from that of the first pulse an alarm condition is indicated. From the propagation time of the second pulse a length is calculated and provided to the user. This length corresponds to the location of the fault.

Apparatus and method for detecting optical fiber fault location

A method and apparatus for distinguishing between fiber types having different dispersion characteristics and arbitrary lengths is disclosed. An optical pulse having a predetermined wavelength and predetermined time width is propagated through the fiber and then detected. The optical pulse after being fed through the fiber is measured at different wavelengths along with the length of the fiber. If the measured pulse is within a predetermined amount at the determined length, then fiber under test corresponds to a type having a first dispersion characteristic. If it is determined that the measured pulse is within a second amount, then the fiber under test corresponds to a type having a second dispersion characteristic. Alternately one or more optical pulses of arbitrary width each having different wavelengths after being propagated through the fiber under test is fed through a plurality of filters and detected. The wavelength of the pulse of the smallest time duration is detected and a corresponding dispersion characteristic is then indicated.

Apparatus for detecting fibers with different dispersion characteristics

A cable television system employs two-way communication between a headend and at least one subscriber terminal. The two-way communication is provided by having separate frequency bands for each communication path. The frequency bands do not overlap and the higher frequency band is used for subscriber terminal to headend transmissions. A line amplifier is provided that employs two diplex filters each connected to both a forward and reverse amplifier. The high pass portions of the diplex filters are formed from both lumped and distributed components.

Bi-directional cable television system including a UHF filter

An amplifier circuit for a cable access television line amplifier has a circuit input and a circuit output and includes a first cascode amplifier having a first input and a first output, and a second cascode amplifier having a second input and a second output where the second cascode amplifier is coupled in a push-pull arrangement with the first cascode amplifier. The amplifier circuit further includes input circuitry for coupling the circuit input to the first and second inputs and output circuitry for coupling the first and second outputs to the circuit output. The first cascode amplifier includes a first field effect transistor coupled to the first input; the second cascode amplifier includes a second field effect transistor coupled to the second input; the first cascode amplifier further includes a third field effect transistor coupled to the first output; and the second cascode amplifier further includes a fourth field effect transistor coupled to the second output. An alternative amplifier circuit for a cable access television line amplifier has a circuit input and a circuit output and includes a first transimpedance amplifier having a first input and a first output, and a second transimpedance amplifier having a second input and a second output where the second transimpedance amplifier being coupled in a push-pull arrangement with the first transimpedance amplifier.

Field effect transistor cable television line amplifier

A broadband communications system for coupling telephony or other digital networks to a CATV network. The system transmits a multiplex of telephony signals in the forward band of the CATV network. Each forward channel is QPR modulated on a carrier and contains multiple subscriber telephony signals. The forward telephony channels are demodulated and demultiplexed by a plurality of subscriber terminals into the individual telephony signals directed to an addressed subscriber. Audio and control signals returning from the subscriber are digitized into standard telephony signals and QPSK modulated on a carrier onto the reverse band of the CATV network. The multiplicity of reverse band telephony channels are demodulated and multiplexed into a standard telephony signal which is directly interfaced to the telephony network. The reverse band modulators are frequency agile and modulate telephony signals from a subscriber in a selected one or more frequency subbands in the reverse band of the subscription network, so as to provide selectably changeable frequencies and selectably variable bandwidth in the reverse band commensurate with a selected subscriber communication feature. e.g. a single voice line, multiple voice lines, ISDN service, data communications services, security monitoring services, etc.

Frequency agile broadband communications system

An optical communications system including a plurality of modulated radio frequency carriers which span more than an octave in bandwidth. In one implementation, the carriers are grouped into ranges which span less than an octave in bandwidth and the individual groups are transmitted over unique optical links. In another implementation, the groups are multiplexed on one optical link by using different wavelengths. In still another implementation, several of the bands are up-converted to the highest band of interest and then transmitted, either over single or multiple links. The resulting optical signals are demodulated and then down-converted before they are recombined into the broadband signal in excess of an octave in bandwidth.

Method and apparatus for transmitting broadband amplitude modulated

A broadband communications system for coupling telephony or other digital networks to a CTV network. The system includes transmitting a multiplex of telephony signals in 3 MHz channels in the forward band of the CTV network. Each 3 MHz channel is QPR modulated on a carrier and contains multiple subscriber telephony signals. The forward telephony channels are demodulated and demultiplexed by a plurality of subscriber terminals into the individual telephony signals directed to an addressed subscriber. The individually addressed telephony signal is then applied to a line card which connects the subscriber telephone equipment to the system. Audio and control signals returning from the subscriber are digitized into standard telephony signals and modulated on a carrier in 50 kHz reserved telephony channels onto the reverse band of the CTV network. The multiplicity of reverse band telephony channels are demodulated and multiplexed into a standard telephony signal which can be directly interfaced to the telephony network. In the illustrated embodiment, the CTV network has a fiber to the serving area architecture that can be used to increase the number of reverse band channels which are available to the broadband communications system. Several configurations for the system are described where the input and output interface can both be coupled at the headend or both coupled at a fiber node, or either one coupled at the headend while the other is coupled at a fiber node.

Broadband communications system

A combination surge and diplex filter is provided for a CATV distribution amplifier. In a first preferred implementation, an integrated surge and high pass filter section is provided when the CATV amplifier is used only in the forward direction. Provision is made for a plug-in low pass filter section which is matched to the high pass filter section. The plug-in low pass section is used to form a diplex filter if the reverse direction capability of the CATV system is required from the distribution amplifier. In a second preferred implementation, the integrated surge and high pass filter section is segmented into a surge filter segment which is designed as a divisible part of the high pass filter section. A plug-in module is then provided with a high pass filter segment having those components of the high pass filter section which were not necessary for surge protection and a low pass filter section matched to the high pass filter section. The plug-in module is utilized to form a diplex filter, if the reverse direction capability of the CATV system is required from the distribution amplifier.

Combination surge and diplex filter for CATV distribution systems

An optical communications system including a plurality of modulated radio frequency carriers which span more than an octave in bandwidth. In one implementation, the carriers are grouped into ranges which span less than octave in bandwidth and separately transmitted over uique optical links. In another implementation, the groups are multiplexed on one optical link by using different wavelengths. In still another implementation, several of the bands are up-converted to the highest band of interest and then transmitted, either over single or multiple links. The resulting signals are demodulated and then down-converted before they are recombined into the broadband signal in excess of an octave in bandwidth.

Apparatus for transmitting data spread across at least a portion of the bandwidth of a cable television channel comprises a carrier signal oscillator, a frequency divider, a pseudorandom sequence generator and two exclusive OR gates. A first exclusive OR gate serves to spread a data signal across the pseudorandom noise sequence generator having a much higher chip rate than the bit rate of the data signal. The second exclusive OR gate modulates the spread spectrum data signal to a carrier frequency for transmission over the cable television channel. The apparatus may be applied for return path transmission in the 0-30 megahertz band which is high susceptible to interference noise and provides approximately a 20 dB signal to interference ratio advantage over known data coding and transmission schemes. A microprocessor normally present in a cable television terminal may format data for transmission, control the spread spectrum modulation process and control gain control circuitry for introducing an appropriate power level into the cable plant.

Cable television spread spectrum data transmission apparatus

Scrambling and descrambling systems utilizing jamming signals provide improved pictures with minimal distortion due to ghosts and artifacts. The television signal is combined with a jamming signal or signals located preferably in the vestigial sideband (VSB) of the modulated picture carrier and at about a null in the spectrum of the modulation of the picture carrier by the horizontal sync. The jamming signal or signals also preferably are placed between the harmonic components of the horizontal sync which define the horizontal sync spectrum and at frequencies which comply with governmental regulations respecting frequency locations of strong signals of CATV purposes. The jamming signals are generated by phase locking to the horizontal sync signals of the television signals or to a submultiple of the horizontal sync frequency. Artifacts are further reduced by preemphasis of the transmitted television signal in the sideband opposite to that in which the jamming signal or signals are located and spaced by an equal frequency increment from the location of the jamming signal energy. In order to extract the jamming signal, so as to descramble the television signal for reproduction in the subscriber's television receiver, a network including at least one surface acoustic wave (SAW) resonator device is embedded in an all-pass network which allows essentially lossless transmission of the television signal spectrum, except for the jamming signal energy and enables that energy to be located close to (e.g., approximately 228 KHz) from the picture carrier in the VSB for enhanced security.

Growing community of inventors

Lilburn, GA, United States of America

Leo J Thompson