Methods for estimating the Effective Modal Bandwidth (EMB) of laser optimized Multimode Fiber (MMF) at a specified wavelength, λ.sub.S, based on the measured EMB at a first reference measurement wavelength, λ.sub.M. In these methods the Differential Mode Delay (DMD) of a MMF is measured and the Effective Modal Bandwidth (EMB) is computed at a first measurement wavelength. By extracting signal features such as centroids, peak power, pulse widths, and skews, as described in this disclosure, the EMB can be estimated at a second specified wavelength with different degrees of accuracy. The first method estimates the EMB at the second specified wavelength based on measurements at the reference wavelength. The second method predicts if the EMB at the second specified wavelength is equal or greater than a specified bandwidth limit.

Chromatic dispersion compensation is performed in one or more pluggable optical transceiver (POT) devices operating within an intensity-modulated direct-detection (IMDD) optical network. Compensation is performed within each POT using an electrical and/or optical chromatic dispersion module which are controlled by a set of parameters. A network computing device includes a computer processor and a host management interface for communicating with the POT. In the event of a link failure, the computer processor determines a second set of parameters to control the one or more dispersion compensation module(s) of the POT. The second set of parameters are different from a first set of parameters used to control the one or more compensation module(s) in the case of a first optical path. The computer processor causes the POT to use the second set of parameters in place of the first set of parameters.

Chromatic dispersion compensation is performed in one or more pluggable optical transceiver (POT) devices operating within an intensity-modulated direct-detection (IMDD) optical network. Compensation is performed within each POT using an electrical and/or optical chromatic dispersion module which are controlled by a set of parameters. A network computing device includes a computer processor and a host management interface for communicating with the POT. In the event of a link failure, the computer processor determines a second set of parameters to control the one or more dispersion compensation module(s) of the POT. The second set of parameters are different from a first set of parameters used to control the one or more compensation module(s) in the case of a first optical path. The computer processor causes the POT to use the second set of parameters in place of the first set of parameters.

A skew compensation system for a coherent optical communication network includes a transmitter modulator having a first driver input for receiving a first signal from a first channel, a second driver input for receiving a second signal from a second channel, a source input for receiving a continuous wave source signal, and a modulation output in communication with an optical transport medium of the network. The system further includes a tunable delay line disposed between the second channel and the second driver input for inserting a pre-determined training sequence onto the second signal prior to the second driver input, and a processor for determining a skew amount between the second signal at the second driver input and the first signal at the first driver input, calculating a pre-compensation value corresponding to the skew amount, and reducing the skew amount at the modulation output according to the pre-compensation value.

A computation unit uses an assumed chromatic dispersion amount to compensate for dispersion of a coherently received optical signal and performs arithmetic of a signal power of the optical signal that is dispersion compensated. The computation unit performs computation of an evaluation function when a signal power and a delayed signal power obtained by applying a predetermined delay to the signal power satisfy a threshold condition. The evaluation function is a function for evaluating whether the assumed chromatic dispersion amount is a chromatic dispersion amount of the optical signal using the difference between the signal power and the delayed signal power. The chromatic dispersion amount calculation unit calculates a chromatic dispersion amount of the optical signal based on the computation result of the evaluation function by the computation unit when each of a plurality of different assumed chromatic dispersion amounts is used.

A coherent optical data receiver having a digital signal processor (DSP) capable of mitigating equalization-enhanced phase noise (EEPN). In an example embodiment, the DSP mitigates EEPN by applying individual phase adjustments to different spectral slices of a digital stream carrying CD-compensated digital samples of the received optical data signal. In different embodiments, the individual phase adjustments can be dynamically selected based on symbol decisions taken prior to EEPN mitigation, based on transmitted pilot symbols, and/or using moving averages computed for different spectral slices. Some embodiments are suitable for handling polarization-division-multiplexed optical data signals. Some embodiments are advantageously capable of producing an effective SNR gain of approximately 1 dB.

A method including transmitting an intensity-modulated light through a mode conditioner to generate a mode-conditioned intensity-modulated light in one or a plurality of launch conditions and transmitting the mode-conditioned intensity-modulated light through a multimode optical fiber under test (FUT) to excite a plurality of modes of the FUT. The method further includes converting the mode-conditioned intensity-modulated light transmitted through the FUT into an electrical signal, measuring, based on the electrical signal, a complex transfer function CTF(f) of the FUT, and obtaining an output pulse based on the measured complex transfer function CTF(f) from one or a plurality of launch conditions and an assumed input pulse using the equation: P.sub.out (t)=.sup.−1(CTF(f)*(P.sub.in(t))). Wherein, P.sub.out (t) is the output pulse, .sup.−1(CTF(f)*(P.sub.in(t))) is the inverse Fourier transform of the function CTF(f)*(P.sub.in (t)), and (P.sub.in(t)) is the Fourier transform of the assumed input pulse. Additionally, the method includes calculating modal bandwidth of the FUT based on P.sub.out(t).

This application provides a signal processing method and apparatus, and a coherent receiver. The signal processing method includes: obtaining P real-number signals; performing at least number theoretic transform NTT processing on the P real-number signals to obtain P transform-domain first real-number signals; performing at least clock recovery on the P transform-domain first real-number signals to obtain P transform-domain second real-number signals; performing at least polarization compensation and inverse number theoretic transform INTT processing on the P transform-domain second real-number signals to obtain m time-domain complex-number signals X and m time-domain complex-number signals Y; and performing phase recovery and decoding on the m time-domain complex-number signals X and the m time-domain complex-number signals Y to obtain bit signals.

Joint estimation of the framer index and the frequency offset in an optical communication system are described among various other features. A transmitter can transmit data frames using pilot and framer symbols. A receiver can estimate the framer index and frequency offset using the pilot and framer symbols, and identify the beginning of a header portion of a data frame. By identifying the beginning of the header portion of a data frame, the receiver can synchronize, with less error, the data transmitted by the transmitter and the data it received. To further improve the framer index estimation, a lock indicator signal can be generated to signal to other receiver components that the estimated framer indices are reliable. The receiver can determine frequency offset and additional framer index estimations with increased reliability when performed after the lock indicator signal is generated.

An optical communication fiber link including a monitoring system connected to an optical fiber transmitting electromagnetic radiation including a communication. The monitoring system includes a detection system detecting a scattering of the electromagnetic radiation from the optical fiber. The monitoring system monitors the scattering for an abnormal change and determines, from the abnormal change, an absence or a presence of a fault in the optical fiber.