Harmonic Lightwaves, Inc.

Charles H Gall

Chien-Yu Kuo

Alan C Nilsson

Moshe Nazarathy

Joseph Kleefeld

Alfred Nicholson Riddle

Daniel Bianu

Harry Chou

An optical transmission system enables launching at least 17 dBm of optical power at 1550 nm wavelength into an e.g. 50 km long span of standard telecommunications single-mode optical fiber, without incurring unacceptable penalties from stimulated Brillouin scattering, damage to optical phase modulators from excessive drive power or thermal effects, or signal degradations caused by the SBS suppression. High frequency modulation of the laser drive current is combined with lower frequency modulation of the phase of the laser output light that is itself varied over a range of approximately 25 MHz. This two tone modulation raises the SBS threshold to greater than 17 dBm in the 1550 nm wavelength region when the laser has a line width less than 10 MHz, under cw operation. By thereby dividing the task of spectral partitioning between the laser and the phase modulator, the RF input power level to the phase modulator is manageable and the laser operates in a regime that does not cause clipping.

Multi-tone phase modulation for light wave communication system

A bridge T attenuator which includes PIN diodes in both the bridge arm and in the shunt arm, and in which the current through the shunt arm is controlled with respect to the current through the bridge arm, so that the product of these two currents equals a constant. This is accomplished by a feedback loop. Thus a relatively simple, inexpensive, and entirely analog solution is provided for a bridge T attenuator to be used with a radio frequency signal, so that a prescribed level of attenuation set by a user may be maintained while the impedance is maintained at a fixed value over the entire attenuation range.

Control circuit and method for direct current controlled attenuator

A generalized frequency dependent predistortion circuit for nonlinear optic devices such as semiconductor lasers and light emitting diodes includes a pre-filter and post-filter associated with a linearizer (distorter). A multi-channel sub-carrier electrical signal is input to a splitter which provides on a primary path a signal to a time delay and hence to a coupler to the secondary paths. In the first secondary path, a pre-filter provides a signal to a second order distorter. This signal is then subject to a post-filter and then to a variable attenuator. In the second secondary path, a third order distorter again has an associated pre-filter and post-filter with a variable attenuator downstream of the post-filter. The variable attenuators in each path provide frequency independent attenuation. In one version the distorters in both paths are nonlinear diode circuits. The second secondary path provides very low fundamental leak-through. The pre- and post-filters are of similar design with differing component values, each filter being an integral equalizing filter which arbitrarily manipulates phase and amplitude in a frequency dependent fashion. Each is a synthesized filter tuned or built to a specific complex frequency-dependent profile to linearize a particular individual laser unit.

Predistorter for high frequency optical communications devices

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Newark, CA, United States of America

Charles H Gall