A method for receiving a modulated receive signal, with a transmission unit having a laser and an electro-absorption modulator. The received optical receive signal is directed towards the laser; due to the irradiance of the optical receive signal onto the laser, the optical frequency of the light radiated from the laser is adapted to and/or aligned with the optical frequency of the received optical receive signal; the light radiated from the laser and the optical receive signal received via the optical waveguide are overlapped in the electro-absorption modulator; the thus-created overlapping signal from the electro-absorption modulator is converted into an electrical receive signal, in particular into an electrical current signal; and a receive signal is provided which corresponds to the electrical receive signal or is derived from same.

A method for receiving a modulated receive signal, with a transmission unit having a laser and an electro-absorption modulator. The received optical receive signal is directed towards the laser; due to the irradiance of the optical receive signal onto the laser, the optical frequency of the light radiated from the laser is adapted to and/or aligned with the optical frequency of the received optical receive signal; the light radiated from the laser and the optical receive signal received via the optical waveguide are overlapped in the electro-absorption modulator; the thus-created overlapping signal from the electro-absorption modulator is converted into an electrical receive signal, in particular into an electrical current signal; and a receive signal is provided which corresponds to the electrical receive signal or is derived from same.

A self-coherent optical data receiver configured to use direct detection of optical signals that is compatible with full (amplitude/phase) electric-field reconstruction. To enable the latter, the direct-detected optical signal includes CW light whose carrier frequency is spectrally aligned with a roll-off edge of the data-modulated portion of the signal. In an example embodiment, the receiver may employ two digital filters placed upstream and downstream, respectively, of the field-reconstruction circuit. The upstream filter is configurable to at least partially cancel the effects of SSBI caused by the direct detection. The downstream filter can be configured to perform electronic dispersion compensation and/or electronic polarization demultiplexing. In different embodiments, a filter controller may operate to adaptively change the filter coefficients of the upstream filter based on different signals generated within the digital receive chain. For example, the filter controller can use either input or output of the downstream filter for this purpose.

A self-coherent optical data receiver configured to use direct detection of optical signals that is compatible with full (amplitude/phase) electric-field reconstruction. To enable the latter, the direct-detected optical signal includes CW light whose carrier frequency is spectrally aligned with a roll-off edge of the data-modulated portion of the signal. In an example embodiment, the receiver may employ two digital filters placed upstream and downstream, respectively, of the field-reconstruction circuit. The upstream filter is configurable to at least partially cancel the effects of SSBI caused by the direct detection. The downstream filter can be configured to perform electronic dispersion compensation and/or electronic polarization demultiplexing. In different embodiments, a filter controller may operate to adaptively change the filter coefficients of the upstream filter based on different signals generated within the digital receive chain. For example, the filter controller can use either input or output of the downstream filter for this purpose.

An optical receiver is provided with: an optical reception circuit which receives wavelength multiplexed light including signal light, converts the signal light into an electrical signal by coherent detection of the signal light using local oscillation light, and outputs the power of the local oscillation light, the bit error rate of the signal light and the electrical signal; and a controller which monitors the power of the local oscillation light and the bit error rate, calculates the signal-to-noise ratio of the signal light on the basis of the power of the local oscillation light and the bit error rate, and finds the number of wavelengths of the wavelength multiplexed light and the power per wavelength of the signal light on the basis of the signal-to-noise ratio and the power of the local oscillation light.

Methods, systems, transceivers, and apparatus are included for clock synchronizing an optical system and multiple leaf systems. In some implementations, a transceiver includes a receiver and a transmitter. The receiver includes an optical hybrid circuit operable to receive a first modulated optical signal and local oscillator light and to supply optical mixing products based on the first modulated optical signal and the local oscillator light. A photodiode circuit operable to supply an electrical signal based on the optical mixing products. An analog-to-digital conversion circuitry operable to supply digital signals based on the electrical signal. A digital signal processor operable to generate a supply signal based on the digital signals and provide the supply signal to a reference clock circuit for generating a clock signal. The transmitter is operable to output a second modulated optical signal that includes a timing of data based on the clock signal.

Methods, systems, transceivers, and apparatus are included for clock synchronizing an optical system and multiple leaf systems. In some implementations, a transceiver includes a receiver and a transmitter. The receiver includes an optical hybrid circuit operable to receive a first modulated optical signal and local oscillator light and to supply optical mixing products based on the first modulated optical signal and the local oscillator light. A photodiode circuit operable to supply an electrical signal based on the optical mixing products. An analog-to-digital conversion circuitry operable to supply digital signals based on the electrical signal. A digital signal processor operable to generate a supply signal based on the digital signals and provide the supply signal to a reference clock circuit for generating a clock signal. The transmitter is operable to output a second modulated optical signal that includes a timing of data based on the clock signal.

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

The present invention, which is used for continuous variable quantum key distribution (CVQKD) with asynchronous local oscillators, relates to a system for performing a phase compensation of a scheme of using LO phase estimation and feedback at a receiver (Bob) using a pilot signal from a transmitter (Alice) and a scheme of measuring quantum state data using an LO having a predetermined phase at the receiver (Bob) and estimating and feeding back an LO phase through multi-dimensional reconciliation (MDR).

The present invention, which is used for continuous variable quantum key distribution (CVQKD) with asynchronous local oscillators, relates to a system for performing a phase compensation of a scheme of using LO phase estimation and feedback at a receiver (Bob) using a pilot signal from a transmitter (Alice) and a scheme of measuring quantum state data using an LO having a predetermined phase at the receiver (Bob) and estimating and feeding back an LO phase through multi-dimensional reconciliation (MDR).