Aspects of the disclosure provide for methods and systems for feedback control of mode MUX and DEMUX. An aspect of the disclosure provides for a method associated with a mode MUX. The method includes modulating each WDM signal of a first set of WDM signals with a pilot tone of different frequency. The method further includes spatially multiplexing the first set of WDM signals to generate a multi-mode signal. The method further includes detecting the pilot tones from the multi-mode signal. The method further includes tuning the mode MUX based on the detecting. Another aspect of the disclosure provides for a method associated with a mode DEMUX. The method includes spatially demultiplexing a multi-mode signal into a set of WDM signals. The method further incudes detecting pilot tones from the set of WDM signals and tuning the mode DEMUX based on the detecting.

A method of loading a fiber optic transport system includes detecting optical power in a frequency sub-band of optical spectrum, wherein the frequency sub-band includes data-bearing channels and at least one control channel; measuring optical power in the frequency sub-band; and adjusting optical power of the at least one control channel based on the measured optical power, wherein the optical power is adjusted through one of changing a current of control channel lasers and controlling a set of fast optical attenuators.

Provided is an optical transceiver including: an optical transmitter configured to sequentially generate a plurality of optical transmission signals each including transmission wavelength information and output the plurality of optical transmission signals to a connected multiplexer/demultiplexer; and a controller configured to generate the transmission wavelength information for each of the plurality of optical transmission signals.

The disclosed systems, structures, and methods are directed to monitoring performance of optical networks. Transmitted and received optical channel signal has both low-power gaps and an amplitude modulation pilot tone applied. The low-power gaps are applied at a gap frequency with gap power being lower than a signal power of the optical channel signal. The pilot tone is applied to the optical channel signal at a pilot tone modulation frequency, which is different from the gap frequency. Described methods include determining pilot tone modulation depth based on detected gap power in low-power gaps of the received optical channel signal. Amplifier spontaneous emission and nonlinear noise in optical link are detected separately. This permits determining and monitoring of optical signal-to-noise ratio.

An Optical Protection Switch (OPS) includes a splitter connected to a transmitted input and a path continuity monitor transmitter and configured to output the transmitted input with a path continuity monitor signal to two paths; a switch connected to a receiver output and configured to provide one of two receiver inputs each from one of the two paths based on a setting of the switch; and one or more path continuity monitor receivers connected to the two receiver inputs and configured to detect a corresponding path continuity monitor signal from a complementary OPS, wherein the setting of the switch is set based upon the received path continuity monitor signals. The one or more path continuity monitor receivers each have a narrow optical bandwidth relative to an overall optical bandwidth of the transmitted input.

An optical transmission apparatus includes a wavelength variable filter whose transmission light wavelength is variable; a receiver that receives light, the light being sent from another optical transmission apparatus and passing through the wavelength variable filter; a transmitter that sends to the another optical transmission apparatus, a utilization permission request for a second wavelength corresponding to a first wavelength of the light received by the receiver, the transmitter sending the utilization permission request as light of the second wavelength and in a form of a tone signal of a predetermined frequency; and a controller that, when receiving from the another optical transmission apparatus, a utilization permission notification of the second wavelength for a sender of the utilization permission request, configures a wavelength of a main signal to the second wavelength, the main signal being sent from the transmitter to the another optical transmission apparatus.

A system for loading a fiber optic transport system includes a wavelength selective switch (WSS) having inputs and an output connected to an optical fiber, wherein the inputs are connected to one or more lines having data-bearing channels thereon; and an amplified spontaneous emission (ASE) generator connected to one of the inputs of the WSS, wherein the WSS is configured to perform a channel addition through substitution of an ASE channel from the ASE generator for a data-bearing channel, and a channel deletion through substitution of a data-bearing channel for an ASE channel from the ASE generator, and wherein, to limit perturbations on the optical fiber due to channel additions and deletions, the WSS is configured to limit a number of channels that are switched at a same time for a set of channel additions or deletions.

A system for loading a fiber optic transport system includes a wavelength selective switch (WSS) having inputs and an output connected to an optical fiber, wherein the inputs are connected to one or more lines having data-bearing channels thereon; and an amplified spontaneous emission (ASE) generator connected to one of the inputs of the WSS, wherein the WSS is configured to perform a channel addition through substitution of an ASE channel from the ASE generator for a data-bearing channel, and a channel deletion through substitution of a data-bearing channel for an ASE channel from the ASE generator, and wherein, to limit perturbations on the optical fiber due to channel additions and deletions, the WSS is configured to limit a number of channels that are switched at a same time for a set of channel additions or deletions.

An Optical Protection Switch (OPS) includes a splitter connected to a transmitted input and a path continuity monitor transmitter and configured to output the transmitted input with a path continuity monitor signal to two paths; a switch connected to a receiver output and configured to provide one of two receiver inputs each from one of the two paths based on a setting of the switch; and one or more path continuity monitor receivers connected to the two receiver inputs and configured to detect a corresponding path continuity monitor signal from a complementary OPS, wherein the setting of the switch is set based upon the received path continuity monitor signals. The one or more path continuity monitor receivers each have a narrow optical bandwidth relative to an overall optical bandwidth of the transmitted input.

The disclosed systems, structures, and methods are directed to monitoring performance of optical networks. Transmitted and received optical channel signal has both low-power gaps and an amplitude modulation pilot tone applied. The low-power gaps are applied at a gap frequency with gap power being lower than a signal power of the optical channel signal. The pilot tone is applied to the optical channel signal at a pilot tone modulation frequency, which is different from the gap frequency. Described methods include determining pilot tone modulation depth based on detected gap power in low-power gaps of the received optical channel signal. Amplifier spontaneous emission and nonlinear noise in optical link are detected separately. This permits determining and monitoring of optical signal-to-noise ratio.