Abstract: An embodiment includes an input node, a shunt impedance electrically connected to the input node, and at least one shunt diode connected in series with the shunt impedance. The input node receives an electrical signal from a signal generator. A bias current is applied to the shunt diode from a bias supply. In response, the shunt diode generates second-order distortion and substantially no third-order distortion. The level of bias current is adjusted to substantially eliminate any third-order distortion while the shunt impedance is adjusted so that the appropriate amount of second-order distortion is generated as predistortion. The predistortion is then provided to a nonlinear device, such as a laser, where it operates to substantially cancel inherent distortion generated by the nonlinear device.

Abstract: An optical transmitter (405) includes a distributed feedback semiconductor laser (100) operated in a linear regime below a threshold associated with stimulated Brillouin scattering to generate an optical signal. A resistor (125) or other heater is physically coupled to the semiconductor laser (100), and a modulated current source (120) drives the resistor (125) with a triangle waveform (300), thereby varying an optical wavelength of the optical signal such that the optical signal and a double Rayleigh backscattered signal are characterized, at the optical receiver (410), by different optical frequencies. As a result, interference generated by Rayleigh backscattering is minimized at the optical receiver (410).

Abstract: A distortion circuit for linearizing third-, fifth- and seventh-order distortion components in a non-linear optical communications system includes at least one group of series connected diodes coupled to a common input terminal for receiving a signal source at one end and to an inductor and a capacitor at the other end, a resistance coupled to the common input terminal and a bias source for providing a bias current to the group of series connected diodes. The distortion circuit may be implemented as a predistortion circuit in the headend of the optical communications system or as a postdistortion circuit at the receiving end.

Abstract: 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.

Abstract: A broadband matching network closely matches the output impedance of a broadband amplifier to the input impedance of a laser over a broad frequency band to facilitate efficient transfer of power therebetween. As a result, the broadband amplifier does not have to generate high output power levels that cause intermodulation distortion. The matching network includes a pair of matching transformers having toroidal cores and a filter circuit.

Abstract: A predistortion circuit for an optical communications system includes a main path for an RF modulating signal and a predistortion path for a predistortion signal, which signals are combined to modulate a laser diode. The distortion path includes a distortion generator which generates a distortion signal which is substantially the same as the distortion generated by the modulation of the transmission system with the RF modulating signals. In one implementation, the distortion generator comprises a square law device which preferably is a field effect type device. The square law device operational characteristic closely mimics the major component of distortion in optical communications systems, composite second order (CSO) distortion. In a second implementation, two square law devices are coupled in an anti-phase arrangement to substantially cancel odd order distortion components from the distortion signal and to enhance even order distortion components, particularly CSO.

Abstract: 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.

Abstract: 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.

Abstract: A laser diode protection circuit which monitors the r.f. modulation level of the input modulating signal to the laser diode and disconnects the laser diode from the r.f. modulating signal when it exceeds an acceptable level. The circuit further monitors the output of the d.c. power supply which provides the d.c. bias current to the laser diode. The circuit disconnects the laser diode from the r.f. modulating signal when the output of the power supply falls below an acceptable level.

Abstract: An apparatus and method is disclosed which phase locks a frequency-agile modulated output signal to any selected channel of a comb generated output. The phase error of an input signal is tracked, the input signal is modulated up to a carrier output frequency, and the modulated output frequency is locked to the comb generator output by subtracting the input signal and negating the phase error.

Abstract: 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.