Provided are methods for optical communication, comprising: generating a phase difference signal with heterodyne or homodyne phase-locked-loop (PLL) from between an optical input signal and a local laser source; controlling the local laser source with the phase difference signal; demodulating the optical input signal using the local laser source as a carrier signal to generate a baseband output signal; and controlling the heterodyne or homodyne PLL and the demodulation with an electrical oscillator signal. Also provided are related methods.

Embodiments of the present invention disclose an optical signal transmission system and an optical signal transmission method. A specific solution is as follows: a first coherent transceiver is configured to: convert N channels of downlink data into N modulating signals, convert the N modulating signals into a first wavelength division multiplexing signal, and send the first wavelength division multiplexing signal to an optical transport unit; the optical transport unit is configured to: receive the first wavelength division multiplexing signal, convert the first wavelength division multiplexing signal into N second optical signals, and correspondingly send the N second optical signals to N second coherent transceivers; and one of the N second coherent transceivers is configured to: receive the N second optical signals, and process the N second optical signals to obtain information in downlink data carried in the N second optical signals.

Embodiments of the present invention disclose an optical signal transmission system and an optical signal transmission method. A specific solution is as follows: a first coherent transceiver is configured to: convert N channels of downlink data into N modulating signals, convert the N modulating signals into a first wavelength division multiplexing signal, and send the first wavelength division multiplexing signal to an optical transport unit; the optical transport unit is configured to: receive the first wavelength division multiplexing signal, convert the first wavelength division multiplexing signal into N second optical signals, and correspondingly send the N second optical signals to N second coherent transceivers; and one of the N second coherent transceivers is configured to: receive the N second optical signals, and process the N second optical signals to obtain information in downlink data carried in the N second optical signals.

An analog front-end module of an ultra-wideband optical receiver including a transimpedance amplifying unit and a distributed amplifier unit is provided. The transimpedance amplifying unit is configured to convert an externally-inputted current signal into a voltage signal, amplify the voltage signal, and then output a voltage-amplified signal. The distributed amplifier unit includes an input transmission network, an input matching load, an output transmission network, an output matching load, and a plurality of gain units. The input transmission network is configured to receive the voltage-amplified signal and distribute the voltage-amplified signal to each gain unit for further amplification. The input matching load is configured to absorb the voltage-amplified signal reflected to the transimpedance amplifying unit. The output transmission network is configured to superimpose amplified signals outputted from the gain units and output in combination. The output matching load is configured to absorb the amplified signals transmitted in an opposite direction.

An analog front-end module of an ultra-wideband optical receiver including a transimpedance amplifying unit and a distributed amplifier unit is provided. The transimpedance amplifying unit is configured to convert an externally-inputted current signal into a voltage signal, amplify the voltage signal, and then output a voltage-amplified signal. The distributed amplifier unit includes an input transmission network, an input matching load, an output transmission network, an output matching load, and a plurality of gain units. The input transmission network is configured to receive the voltage-amplified signal and distribute the voltage-amplified signal to each gain unit for further amplification. The input matching load is configured to absorb the voltage-amplified signal reflected to the transimpedance amplifying unit. The output transmission network is configured to superimpose amplified signals outputted from the gain units and output in combination. The output matching load is configured to absorb the amplified signals transmitted in an opposite direction.

Provided is an optical receiver including: a heterodyne detection unit that converts, by heterodyne detection, a subcarrier multiplexed signal in which a plurality of optical signals transmitted from a plurality of optical transmitters are multiplexed, into an electrical signal in an intermediate frequency band; a filter unit that removes a carrier component from the electrical signal in the intermediate frequency band, generated by the conversion, to extract a subcarrier component; an analog-digital conversion unit that performs analog-digital conversion on a signal having the subcarrier component, extracted by the filter unit; and a digital signal processing unit that performs digital signal processing for each subcarrier on a digital signal generated by the analog-digital conversion performed by the analog-digital conversion unit.

Provided is an optical receiver including: a heterodyne detection unit that converts, by heterodyne detection, a subcarrier multiplexed signal in which a plurality of optical signals transmitted from a plurality of optical transmitters are multiplexed, into an electrical signal in an intermediate frequency band; a filter unit that removes a carrier component from the electrical signal in the intermediate frequency band, generated by the conversion, to extract a subcarrier component; an analog-digital conversion unit that performs analog-digital conversion on a signal having the subcarrier component, extracted by the filter unit; and a digital signal processing unit that performs digital signal processing for each subcarrier on a digital signal generated by the analog-digital conversion performed by the analog-digital conversion unit.

An injection locked transmitter for an optical communication network includes a primary seed laser source input substantially confined to a single longitudinal mode, an input data stream, and a laser injected modulator including at least one secondary laser having a resonator frequency that is injection locked to a frequency of the single longitudinal mode of the primary seed laser source. The laser injected modulator is configured to receive the primary seed laser source input and the input data stream, and output a laser modulated data stream.

An injection locked transmitter for an optical communication network includes a primary seed laser source input substantially confined to a single longitudinal mode, an input data stream, and a laser injected modulator including at least one secondary laser having a resonator frequency that is injection locked to a frequency of the single longitudinal mode of the primary seed laser source. The laser injected modulator is configured to receive the primary seed laser source input and the input data stream, and output a laser modulated data stream.

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 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 collected seed source may enable upstream communications at varying wavelengths. The end device may provide upstream communications by externally modulating a signal generated by the injection locked laser diode.