Telecommunications Research Laboratories

Robert James Davies

Michal Mieczyslaw Okoniewski

David E Dodds

John Godfrey McRory

James William Haslett

Jan Conradi

Christopher D Holdenried

Sean V Hum

An electro-optic modulator structure for particular use in narrowband optical subcarrier systems. A traveling wave is established across the active region of the device, instead of a standing wave. This is accomplished through the use of a directional resonator structure that prevents reverse-traveling waves from being established within the resonator. Hence, the electric field is applied to the traveling optical wave in a similar fashion to a traveling-wave modulator, except that the traveling wave has a much greater amplitude due to the build-up of energy inside the resonator. Since the modulator is operated in a traveling-wave fashion, it can be tuned to operate at any frequency using tuning elements, regardless of the length of the active region. Furthermore, the microwave and optical signals can be velocity-matched to mitigate optical transit time effects that are normally associated with a resonant modulator utilizing a standing-wave electrode structure.

Electro-optic modulator with resonator

An apparatus for modulating information bearing symbols onto an optical carrier includes a polybinary coder that operates on a binary information signal to produce an envelope compatible polybinary signal; and an optical single sideband modulator that modulates an optical carrier with the envelope compatible polybinary signal to produce a single sideband optical signal. This provides an improvement over both polybinary signaling and optical single sideband. This action combines the chromatic dispersion advantages of SSB modulation with the DC level and bandwidth reduction of duo-binary coding.

Optical duobinary single sideband modulator

A parallel-summation logarithmic amplifier is described that uses a novel topology of cascaded and parallel amplifiers to achieve extremely high bandwidth. Included in the topology is a unique delay matching scheme for logarithmic amplifiers that is amenable to fabrication in integrated circuit form. The result is flat group delay over broad frequency ranges and different power levels. The resulting log amplifier is suitable for radar applications and for use in high data rate fiber-optic networks. Also described is a unique design process that yields a set of amplifier gains that closely approximate a logarithm. Also described is the novel idea of using a parallel feedback amplifier (PFA) in piecewise-approximate logarithmic amplifiers. This innovation allows for the design of broadband amplifiers with significantly different gains and similar phase characteristics, which is extremely useful when designing high-frequency logarithmic amplifiers.

Logarithmic amplifier

A method and apparatus for harmonically upconverting a phase and/or amplitude modulated subcarrier signal to a higher frequency through a non-linear optical link is disclosed. The method requires that a bandpass signal, with a carrier frequency at a submultiple of the desired radio transmission frequency, be frequency translated in a non-linear two-port device. To avoid the inherent distortion inflicted on the information signal in harmonic upconversion, a predistortion technique is outlined. This consists of phase compression in the case of a phase modulated signal, amplitude scaling in the case of amplitude only and combined phase-amplitude predistortion for QAM type signals. With predistortion on the subcarrier signal input to the non-linear two-port, the resulting upconverted signal may be transmitted in a standard form suitable for demodulation at the signal destination without special equipment.

Non-linear subcarrier predistortion and upconversion system

Bandwidth reduction methods and apparatus that offset the effects of dispersion on a signal transmitted through an optical fiber. The apparatus and methods employ a generator of modulated optical signals in cascade with a modulator. One of the generator and the modulator may be an optical intensity or amplitude modulator and the other a phase (or frequency) modulator. With the application of specific signals, the cascaded generator and modulator produce an optical signal with reduced energy in one half of the transmission bandwidth. One important benefit in the method is the fact that by exploiting the less obvious spectral characteristics of single sideband signals, a simple modulator design is achieved. All of the designs exploit a method of generating analytic signals via hybrid modulation.

Hybrid single sideband optical modulator

An apparatus for implementing post-detection dispersion compensation on a minimum-phase optical single sideband signal propagating along an optical fiber, in which the optical fiber induces phase distortion on the minimum-phase optical single sideband signal. The apparatus comprises a first envelope detector adapted to be coupled with the optical fiber and having as output an envelope signal representing the envelope of the minimum-phase optical single sideband signal, a phase synthesizer connected to the output of the first envelope detector for generating a phase signal representing the phase of the minimum-phase optical single sideband signal, a combiner having as input the envelope signal and the phase signal and having as output a complex signal whose phase is obtained from the phase signal and whose amplitude is obtained from the envelope signal, a complex antidispersive filter connected to receive the complex signal and configured to remove optical fiber induced phase distortion from the complex signal to produce a filtered output; and a second envelope detector connected to the complex antidispersive filter to recover an information signal from the filtered output. A corresponding method of post-detection dispersion compensations is also disclosed.

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Calgary, Canada

Robert James Davies