Methods and apparatus are provided for receiving an optical signal. In one aspect, a method includes receiving a first optical signal comprising time division multiplexed transmissions from a plurality of optical transmitters, and determining that a transmission is not received during a time period from a first optical transmitter of the optical transmitters that is scheduled to transmit during the time period. A second optical signal is inserted into the first optical signal during the time period, the second optical signal having at least a non-zero power portion.

A method and apparatus for wavelength allocation for bidirectional optical access. The wavelength allocation method sets a first central wavelength for the optical path terminal to perform downstream transmission to the optical network unit, and a second central wavelength for the optical network unit to perform upstream transmission to the optical network terminal. At this time, the first center wavelength and the second center wavelength are separated by a predetermined wavelength interval, and the first center wavelength is set larger than the second center wavelength.

Methods, systems, and devices for network communications to reduce optical beat interference (OBI) in upstream communications are described. For example, a fiber node may provide a narrow band seed source to injection lock upstream laser diodes. Therefore, upstream communications from each injection locked laser diode may primarily include the wavelength associated with each seed source. The seed sources may be unique to each end device and configured to minimize OBI. That is, the upstream laser diodes may be generic, but the received seed source may enable upstream communications at varying wavelengths. The fiber node may provide each seed source by filtering (e.g., by a grating filter) a broadband light source.

The present invention discloses a passive optical network communications method: reporting, by an optical network unit, ONU, a calibration record of the ONU, where the calibration record includes an ID of a calibrated wavelength channel; sending a first message to the ONU when the OLT determines, according to the calibration record, that a target wavelength channel ID corresponding to a target wavelength channel to which the ONU needs to switch is not in the calibration record, where the first message includes a forced wavelength switching flag; and instructing the ONU to switch to the calibrated target wavelength channel. In this way, the ONU can implement wavelength switching quickly after calibrating a new wavelength channel so as to perform data communication over the calibrated new wavelength channel.

The present invention discloses a device and a method for monitoring two-stage faults of a TDM-PON with high precision. A two-stage TDM-PON system includes an OLT I, a feeder fiber II, a stage-1 1:n optical splitter III, a stage-1 branch fiber IV, a stage-2 1:n optical splitter V, a stage-2 branch fiber VI, and an optical network unit (ONU) VII. A two-stage optical network monitoring system includes a monitoring part on the OLT I side and a monitoring part on the ONU VII side, where the monitoring part on the OLT I side includes a control-end isolator-free semiconductor laser, a control-end coupler, a control-end optical coupling device, a control-end photodetector, an integrated signal acquisition and processing device, and an optical coupling device; and the monitoring part on the ONU VII side is similar to the monitoring part of the OLT I side.

Methods and apparatus are provided for receiving an optical signal. In one aspect, a method includes receiving a first optical signal comprising time division multiplexed transmissions from a plurality of optical transmitters, and determining that a transmission is not received during a time period from a first optical transmitter of the optical transmitters that is scheduled to transmit during the time period. A second optical signal is inserted into the first optical signal during the time period, the second optical signal having at least a non-zero power portion.

A node configured to operate in an optical network includes P switching planes interconnected by an SS cross-plane switch, P>1; and N.sub.i degrees per switching plane P.sub.i where i=1 to P, each degree formed by corresponding degree components having R ports, wherein a first set of ports of the R ports is for intra-plane switching, a second set of ports of the R ports is for inter-plane switching, and a third set of ports of the R ports is for in-plane add/drop. S is greater than or equal to a sum of a number of degrees across all of the P switching planes. R is greater than or equal to a sum of the first set of ports, the second set of ports, and the third set of ports.

Systems and methods for optical modulation index calibration in a CATV network.

Methods, systems, and devices for network communications to reduce optical beat interference (OBI) in upstream communications are described. For example, a fiber node may provide a narrow band seed source to injection lock upstream laser diodes. Therefore, upstream communications from each injection locked laser diode may primarily include the wavelength associated with each seed source. The seed sources may be unique to each end device and configured to minimize OBI. That is, the upstream laser diodes may be generic, but the received seed source may enable upstream communications at varying wavelengths. The fiber node may provide each seed source by filtering (e.g., by a grating filter) a broadband light source.

The present invention discloses a device and a method for monitoring two-stage faults of a TDM-PON with high precision. A two-stage TDM-PON system includes an OLT I, a feeder fiber II, a stage-1 1:n optical splitter III, a stage-1 branch fiber IV, a stage-2 1:n optical splitter V, a stage-2 branch fiber VI, and an optical network unit (ONU) VII. A two-stage optical network monitoring system includes a monitoring part on the OLT I side and a monitoring part on the ONU VII side, where the monitoring part on the OLT I side includes a control-end isolator-free semiconductor laser, a control-end coupler, a control-end optical coupling device, a control-end photodetector, an integrated signal acquisition and processing device, and an optical coupling device; and the monitoring part on the ONU VII side is similar to the monitoring part of the OLT I side.