Ciena Corporation

Nortel Networks Corporation

Gary Mak

Mohammad Sotoodeh

Yves Beaulieu

Eric Maniloff

Edgar Velez

David W Boertjes

Simon P Parry

Shiguang Guo

Andy Rowland

Franz Li Mok

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

The invention pertains to methods, apparatus, and systems for controlling the sub-carrier frequencies in an optical frequency division multiplex communication system by using a metric available from the sub-carrier modem's digital receive block as an indicator of cross-talk between sub-carriers and adjusting the sub-carrier frequency separation as a function of that metric.

Method and apparatus for sub-carrier frequency 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 for adaptive automatic gain control and an automatic gain control circuit are provided. A predetermined waveform is injected into the automatic gain control circuit. A signal is sampled at at least one point in the automatic gain control circuit in which the sampled signal includes the injected predetermined waveform. A small-signal control characteristic is calculated using the sampled at least one signal. A determination is made as to whether the calculated small-signal control characteristic is valid. In the case of a valid determination, the calculated small-signal control characteristic is used to adjust the gain of the automatic gain control circuit.

Method and circuit for adaptive automatic gain control

In a first broad aspect the invention provides an optical hybrid. The optical hybrid has an input for receiving an incoming optical signal containing data and a local oscillator optical signal and an output for releasing first and second output optical signals having a known phase relationship between them. In a specific and non-limiting example of implementation the phase relationship is 90 degrees. In this specific case the output signals are described as an in-phase and quadrature signals. The optical hybrid has an optical processing entity for deriving the first and second output optical signals from the incoming optical signal and the local oscillator signal. The optical processing entity including a loss element and a phase delay element for subjecting at least a component of an optical signal that exists in the processing entity to a known degree of attenuation and phase delay. The phase relationship between the output optical signals is dependant at least in part on at least one of the degree of attenuation and phase delay.

Optical hybrid

A method for determining optical power in a WDM optical signal that includes extracting a representative portion of the optical signal with wavelengths within some band &#x3b4; wherein &#x3b4; is a subset of &#x394;, the set of all channel wavelengths present in the optical signal and measuring the intensity of the extracted optical signal to determine the optical power per channel for any of the channels whose wavelengths are within the band &#x3b4;.

Optical performance monitoring scheme

Optical receiving methods and systems are disclosed. One such optical receiving system includes an optical amplifier operable to produce amplified optical signals satisfying a filterless detection specification limit, and an optical detector locatable in unfiltered communication with the optical amplifier to receive the amplified optical signals therefrom.

Optical amplification and receiving system and method

In a method and apparatus for tracking dynamic characteristics of an optical amplifier, optical signal probes are used to determine the gain and the corner frequency of the optical amplifier. A first optical probe having a predetermined modulation frequency above an expected corner frequency of the amplifier is used to estimate the gain of the optical amplifier. A second optical probe signal having a second predetermined modulation frequency at or below the expected corner frequency of the amplifier is used to estimate the corner frequency. These parameters can be used to optimize gain control of an optical amplifier.

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Ottawa, Canada

Gary Mak