Consistent with the present disclosure, a photonic integrated circuit (PIC) is provided that has 2 N channels (N being an integer). The PIC is optically coupled to N optical fibers, such that each of N polarization multiplexed optical signals are transmitted over a respective one of the N optical fibers. In another example, each of the N optical fibers supply a respective one of N polarization multiplexed optical signals to the PIC for coherent detection and processing. A multiplexer and demultiplexer may be omitted from the PIC, such that the optical signals are not combined on the PIC. As a result, the transmitted and received optical signals incur less loss and amplified spontaneous emission (ASE) noise. In addition, optical taps may be more readily employed on the PIC to measure outputs of the lasers, such as widely tunable lasers (WTLs), without crossing waveguides. In addition, wavelength locker (WLL) circuitry may be provided on the PIC.

Adjustment of one or more control parameters of a section of an optical fiber network involves taking measurements of optical signals in the section, deriving estimated data from the measurements and from knowledge of the section, where the estimated data is a function of optical nonlinearity and of amplified spontaneous emission, and applying one or more control algorithms using the estimated data to adjust the one or more control parameters.

A processor of an apparatus is configured to apply one or more control algorithms using estimated data to adjust the one or more control parameters of a section of an optical fiber network. The estimated data are derived from measurements of optical signals in the section and from knowledge of the section. The estimated data is a function of optical nonlinearity and of amplified spontaneous emission.

Multiple receivers are comprised in a flexible coherent transceiver of a multi-span optical fiber network. Each of the multiple receivers is operative to handle communications on a respective channel. The multiple receivers measure optical characteristics. For each of the multiple receivers, the optical characteristics include optical nonlinear interactions on the respective channel, the optical nonlinear interactions being at least partially dependent from one span to another span. An optical power of a signal on each of the multiple channels is adjusted as a function of the optical characteristics.

An optical transmission apparatus includes a receiver configured to receive a wavelength division multiplexing optical signal including a first optical signal modulated based on a first modulation system and a second optical signal modulated based on a second modulation system with a higher multi-level degree than the first modulation system; a wavelength selective switch configured to attenuate power of the first optical signal to a first level and attenuate power of the second optical signal to a second level lower than the first level; an optical amplifier configured to amplify the wavelength division multiplexing optical signal including the first optical signal and the second optical signal output from the wavelength selective switch; and a transmitter configured to transmit the wavelength division multiplexing optical signal amplified by the optical amplifier.

Adjustment of one or more control parameters of a section of an optical fiber network involves taking measurements of optical signals in the section, deriving estimated data from the measurements and from knowledge of the section, where the estimated data is a function of optical nonlinearity and of amplified spontaneous emission, and applying one or more control algorithms using the estimated data to adjust the one or more control parameters.

Example embodiments of the present invention relate to optical wavelength directing devices used to construct compact optical nodes.

A dummy-light generating device includes a continuous wave (CW) light source that outputs CW light, a modulated-light generating unit that generates, using the CW light, first intensity-modulated light subjected to intensity modulation and second intensity-modulated light delayed by a half time of a modulation cycle of the first intensity-modulated light with respect to the first intensity-modulated light and having a polarization state e different from a polarization state e of the first intensity-modulated light, and a polarization combiner that performs polarization combination of the first intensity-modulated light and second intensity-modulated light and outputs light after the polarization combination as dummy light.

The differences in the power received from multiple optical network units connected to an optical hub may exceed an allowable dynamic range. The dynamic range may be reduced by determining the power received at the optical hub from each optical network unit and adjusting the power transmitted from one or more optical network units to reduce the overall dynamic range. For each optical network unit, the hub may determine the received optical power in an upstream signal from the optical network unit and receive a digital representation of the transmitted power. The hub may determine to adjust the optical power sent from one or more of the optical network units to reduce the dynamic range. The adjustments to the optical powers at the optical network units may be performed by sending commands from the optical hub to each adjusted optical network unit via a downstream signal.

An optical transmission apparatus includes a wavelength selection switch configured to: receive signal light, and attenuate power of the received signal light; an optical amplifier coupled to the wavelength selection switch and configured to optically amplify the attenuated signal light; and a processor configured to control the wavelength selection switch to attenuate power of signal light which passes a channel which is newly set by an attenuation amount based on information on light levels of spontaneous emission light generated by the optical amplifier.