Northern Telecom Limited

Nortel Networks Corporation

Jun Yu

Claude Rolland

George H Thompson

Mark Acton Gibbon

David Owen Yevick

A Mach-Zehnder optical modulator is provided having first and second modulation electrodes on respective first and second interferometric arms for receiving modulating electric fields, and the two modulation electrodes are of different lengths, the ratio of the lengths being designed to control the relative bias of the two arms, thereby provide for adjustment and optimization of frequency chirp, in a positive or negative chirp MZ modulator or in a configurable chirp MZ modulator. The modulator may have an asymmetric input y-junction coupler and an asymmetric output y-junction coupler to provide unequal power splitting, and interferometric arms defining two optical paths, which may be of equal or unequal length so as to generate a fixed phase difference of 0, .pi. or .pi./2. Preferably, the device is operated with equal push-pull drive, although non-equal push pull drive may alternatively be used. The asymmetric modulation electrodes may be used in combination with an additional control electrode or pair of control electrodes, and with equal or non-equal power splitting. This structure is applicable to either semiconductor MZ modulators or lithium niobate MZ modulators, and provides additional flexibility to optmize frequency chirp.

Configurable chirp mach-zehnder optical modulator

A Mach Zehnder (MZ) modulator with improved coupling of input and output fibers is provided. The MZ modulator combines the advantages of weakly guided input sections with strongly guided sections to optimize the coupling efficiency and selectivity of the device. Improved coupling between weakly and strongly guided sections of waveguide is provided by an intermediate tapered waveguide section which provides gradually changing mode confinement, which reduces the mode mismatch loss and therefore suppresses the reflection at the junction between the weakly and strongly guided sections of the waveguide.

Coupling of strongly and weakly guiding waveguides for compact

A multi-quantum-well Mach-Zehnder optical phase modulator selectively generates positive and negative frequency chirp. The modulator has an asymmetric input y-junction coupler and an asymmetric output y-junction coupler joined by interferometric arms defining two optical paths of unequal length so as to generate a fixed phase difference of .pi. or an integral odd multiple thereof. The modulator has electrodes on each arm for receiving modulating electric fields in a push-pull relationship. A control electrode is provided on one of the arms for receiving a control electric field. The modulator, when driven without any control electric field generates negative frequency chirp, and selectively generates positive frequency chirp in response to adjustment of the control electric field. As an alternative, the length differential between respective arms can be selected to generate a phase difference of .pi./2, in which case control electrodes are required on each of the interferometric arms. A method of selectively generating a modulated optical signal having selectively configurable frequency chirp is also described.

Configurable chirp Mach-Zehnder optical modulator

A MQW semiconductor Mach Zehnder phase modulator is formed by two Y-junctions (12, 32), each having a single waveguide (14) optically coupled with two branch waveguides (18, 20). The branch waveguides of the two Y-juntions are optically coupled in Mach-Zehnder configuration that, under zero bias conditions, has one interferometric arm longer than the other to provide a .pi. phase shift. The additional length is preferably accommodated in the branches of the Y-junctions. The phase shift, in combination with voltage dependent absorption properties and non-linear phase variations of the MQW guided regions in the Mach-Zehnder modulator results in a negative chirp and high extinction ratio for an equal, push-pull device configuration.

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Stittsville, Canada

Jun Yu