A receiver for an optical communications system which corrects distortion of a received signal. A clock recovery system utilising a feedback and feedforward system are provided. The feedback loop comprises a phase detector and a clock source, while the feedforward loop comprises the phase detector and a delay element for delaying the output of distortion correction system. The feedback loop has a significantly lower bandwidth than the feedforward path. There are also provided methods of optimising tap weights and of acquiring initial tap weights.

In one embodiment, an apparatus comprises: a coherent optical receiver front-end circuit to receive an optical signal comprising information and further to receive a local oscillator optical signal, and output an orthogonal electrical signal based on the optical signal; a processing circuit coupled to the coherent optical receiver front-end circuit to receive the orthogonal electrical signal and process the orthogonal electrical signal to generate therefrom sum of squares information; and a non-coherent receiver coupled to the processing circuit to recover the information from the sum of squares information. Other embodiments are described and claimed.

Aspects of the present disclosure describe distributed fiber optic sensing (DFOS) systems, methods, and structures that advantageously sense/monitor intra-data center operations using self-coherent detection. Advantageously, sensing signal(s) and data signal(s) are optically multiplexed such that the sensing signal(s) are generated and detected using the same optoelectronic components as data generation and detection while requiring only minimal changes to transponder arrangements and no additional bandwidth to digital-to-analog converters (DAC) or analog-to-digital converters (ADC).

Aspects of the subject disclosure may include, for example, a substrate, comprising a first layer, a second layer, and an intermediary layer between the first layer and the second layer, a first pair of traces positioned in the first layer, a second pair of traces positioned in the second layer, and a jumper configuration at least partially defined in the intermediary layer, wherein the jumper configuration comprises a pair of vias that are configured for coupling the first pair of traces and the second pair of traces and for providing common mode rejection (CMR) filtering between first signals on the first pair of traces and second signals on the second pair of traces. Other embodiments are disclosed.

A reception unit, in which a range of an electric band is in a range from Be to +Be and Be >B/2 is satisfied, receives signal light of a symbol rate B generated by optically modulating transmission data, performs digital coherent reception by interfering the received signal light with the local oscillation light generated by the local oscillation light source, converts the signal light into an electric digital signal, and output the digital signal, and a frequency offset compensation unit provided in a digital signal processing unit estimates a frequency offset amount generated in the digital signal in a range of B/2 or more and +B/2 or less in accordance with a frequency difference between the signal light and the local oscillation light, and perform frequency offset compensation for the digital signal on the basis of the estimated frequency offset amount to compensate the frequency offset amount in a range of B/2 or more and +B/2 or less and compensate so as to remain the frequency offset amount of an integral multiple of the symbol rate B when the frequency offset amount is in a range of less than B/2 and a range of more than +B/2.

An optical transmission apparatus includes an optical transmitter that generates an optical signal in an uplink direction by modulating output light of a laser that outputs light of a first frequency with a subcarrier on which transmission data is superimposed, a heterodyne detection unit that receives an optical signal in a downlink direction by heterodyne detection, a control unit that calculates a first intermediate frequency based on the frequency of the downlink signal received by the heterodyne detection and the first frequency of the laser, and controls the first frequency of the laser when there is a difference between the calculated first intermediate frequency and a reference second intermediate frequency by a threshold or more.

The present disclosure provides a coherent optical receiving method and receiver capable of detecting an optical signal transmitted at a high transmission rate while having low complexity and bit error rate, the coherent optical receiving method comprising the steps of: receiving a transmission optical signal that is transmitted by being offset QAM modulated so that an I signal and a Q signal from a transmitter have a delay time difference equal to an offset time as a reception optical signal; generating a local optical signal having a frequency difference within a bandwidth range from the transmission optical signal by a local oscillator; obtaining a beating optical signal by beating the reception optical signal and the local optical signal; receiving the beating optical signal by a balanced photo detector to obtain a reception signal; and restoring data transmitted by the transmitter from the reception signal.