Ciena Corporation

Mohammad Sotoodeh

Gary Mak

Yves Beaulieu

James St Harley

Mark Andrew Hawryluck

Douglas McGhan

Anant Grewal

A method of controlling a multiple sub-carrier optical channel of an optical communications system. The multiple sub-carrier optical channel includes at least two sub-carriers modulated with respective sub-channel data streams within a spectral range allocated to a single optical channel of the optical communications system. A transmitter modem of the optical communications system applies a respective dither signal to each sub-carrier. A receiver modem of the optical communications system detects a respective quality metric of each sub-carrier. A respective optimum power level of each sub-carrier is estimated based on the applied dither signals and the detected quality metrics. A respective power level of each sub-carrier is then adjusted in accordance with the estimated respective optimum power level of each sub-carrier.

Subcarrier power balance control

A modulator bias selection method, a coherent optical transmitter, and optical modulator solve the problem of generating a correct constellation using the bias points with the minimum phase adjustment range. The optimum modulator bias systems and methods include a coherent optical transmitter with control of four (XI, XQ, YI, YQ) quadrature data signals via a transmitter (Tx) application specific integrated circuit (ASIC), with a modulator bias controller which implements an algorithm to find the optimum bias points. The optimum bias points yield a correct constellation with minimum phase/bias adjustment. An algorithm is used to find the optimum bias solution using fast, simple method, adjusting only one quadrature at a time and exploiting a control feature of the Tx ASIC. This algorithm is significantly simpler than a generalized search, is a local algorithm, and uses only DC power measurement at the transmitter.

Optimum modulator bias systems and methods in coherent optical transmitters

A method of controlling an optical transmitter having a Dual Parallel Mach-Zehnder (DPMZ) modulator. An I-Q power balance between respective branches of the DPMZ modulator is detected, and at least one parameter of the DPMZ modulator is adjusted to drive the I-Q power balance to a predetermined target value. An optical transmitter may have Quad Parallel Mach-Zehnder (QPMZ) modulator having a pair of parallel DPMZ modulators for modulating respective X- and Y-polarization lights. In such cases, an X-Y power imbalance between the two polarization lights is detected, and at least one parameter of the QPMZ modulator is adjusted to drive the X-Y power imbalance to a predetermined value.

Quadrature power balance control in optical transmitters

A method of controlling a polar optical transmitter comprising a dual-branch Mach-Zehnder (MZ) modulator driven by a pair of independent electrical drive signals. A cost function is provided which defines a relationship between a control parameter of the optical transmitter and a power level of an output optical signal generated by the MZ modulator. A selected component of the electrical drive signals is dithered using a predetermined dither signal. A modulation depth of the output optical signal power level corresponding to the dither signal is detected, and the control parameter adjusted based on the cost function and the detection result.

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Ottawa, Canada

Mohammad Sotoodeh