A method and apparatus for synchronizing nodes in a communication network. A such as an EPoC, PON, or EPoC/PON hybrid access network. The network node receives or originates a ToD value and calculates future ToD value for a second node, which the first node includes in a ToD message for sending to the second node. The ToD message preferably includes a correction based on an OFDM ranging delay value and an adjustment based on a total transmit/receive PHY path asymmetry value with respect to the two nodes. A similar future ToD message is preferably sent to each downstream node that the first node is serving.

A receiver for fiber optic communications.

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 then process data received from the transmitter in a manner synchronous to the manner in which the data was transmitted by the transmitter.

Embodiments of this disclosure provide a signal transmission apparatus, a carrier phase recovery apparatus and method. By inserting phase modulation signals with variable amplitudes into data modulation signals and performing carrier phase recovery on received signals at a receiving end according to the phase modulation signals, the apparatuses and methods are applicable to communications systems of various modulation formats and are compatible with existing communications systems, and calculation complexity is relatively low. Furthermore, as the amplitudes of the inserted phase modulation signals are variable, the phase modulation signals may be flexibly configured in data modulation signals, to lower redundancy and influence on the system capacity is relatively small.

A method includes receiving an optical signal through an optical link and determining a receiving power for the optical link. The method further includes comparing the receiving power for the optical link to a first receiving power threshold and transitioning a clock and data recovery circuit form a normal mode to a holdover mode when the receiving power is less than the first receiving power threshold. The clock and data recovery circuit, when operating in the holdover mode, configured to hold a recovered clock to a known-good clock frequency. When the receiving power for the optical link is greater than a second receiving power threshold, the method initiates a transition of the clock and data recovery circuit from the holdover mode to the normal mode and reacquires synchronization between the recovered clock and a current rate of the incoming data stream using the known-good clock frequency.

A digital instruction is generated regarding one or more electrical-to-optical conversion impairments induced at the transmitter of an optical communication system. The digital instruction may be used by the transmitter to reduce the impairments. Alternatively, or additionally, the digital instruction may be used by the receiver of the optical communication system to compensate for the impairments

An apparatus comprises: a first input tap; a first optical modulator coupled to the first input tap; a first output tap coupled to the first optical modulator so that the first optical modulator is positioned between the first input tap and the first output tap; and a controller indirectly coupled to the first input tap and the first output tap.

A signal processing method executed by a transmission device, the signal processing method includes receiving a plurality of frame signals; extracting a plurality of synchronization signals each for performing frame synchronization and separating data of each of the plurality of frame signals, from the received plurality of frame signals; storing the data of each of the plurality of frame signals in a memory intermittently, using respective pulse widths of the plurality of synchronization signals as intervals, based on timing at which the plurality of synchronization signals are extracted; detecting timing at which data at a predetermined location in the frame signal is written to the memory, from the timing at which the plurality of synchronization signals are extracted; and reading data of each of the plurality of frame signals from the memory according to the detected timing.

The disclosure provides methods, apparatus and computer-readable media for synchronization over an optical network. A method comprises: receiving, from a client, a request to initiate a synchronization service for a client node coupled to the optical communication network; and, in response to the request, establishing a synchronization service to the client node via a virtual synchronization network utilizing the optical communication network. The synchronization service utilizes a bidirectional optical channel established via the optical communication network for the transmission of synchronization data for the client.

A data storage system is disclosed that includes a recirculating loop storing data in motion. The data may be carried by a signal via the loop including one or more satellites or other vessels that return, for example by reflection or regeneration, the signals through the loop. The loop may also include a waveguide, for example an optical fiber, or an optical cavity. Signal multiplexing may be used to increase the contained data. The signal may be amplified at each roundtrip and sometimes a portion of the signal may be regenerated.