Methods, systems, and apparatus, including computer programs encoded on computer storage media, for clock synchronizing an optical system and multiple leaf systems. In some implementations, a method includes: first data is received from an optical system. The first data is detected using a local oscillator signal provided by a local oscillator laser. The first data is processed using a first sampling rate. A frequency of a clock signal supplied by a reference clock is adjusted based on the processed first data. Second data is transmitted to the optical system at a rate based on the clock signal.

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for clock synchronizing an optical system and multiple leaf systems. In some implementations, a method includes: first data is received from an optical system. The first data is detected using a local oscillator signal provided by a local oscillator laser. The first data is processed using a first sampling rate. A frequency of a clock signal supplied by a reference clock is adjusted based on the processed first data. Second data is transmitted to the optical system at a rate based on the clock signal.

A receiver system is provided for receiving a coherent Pulse Amplitude Modulation (PAM) encoded signal. The receiver system may include an optical polarization component configured to modulate a polarization of the received coherent PAM encoded signal. The receiver system may further include a digital signal processor (DSP) configured to perform polarization recovery between the received coherent PAM encoded signal and the LO signal using a first control loop, and to perform phase recovery between the received coherent PAM encoded signal and the LO signal using a second control loop.

Dynamic error-quantizer tuning systems and methods prevent misconvergence to local minima by using a dynamic quantizer circuit that controls reference voltages of three or more comparators that are independently adjusted to modify the transfer function of the dynamic quantizer circuit. A weighted sum of the comparator outputs is subtracted from the input to form an error signal in a control loop. The ratio of the reference voltages is chosen to reduce or eliminate local minima during a convergence of the control loop and is set to values that minimize a mean squared error signal with respect to discrete modulation states of the input after the convergence of the control loop is complete.

Dynamic error-quantizer tuning systems and methods prevent misconvergence to local minima by using a dynamic quantizer circuit that controls reference voltages of three or more comparators that are independently adjusted to modify the transfer function of the dynamic quantizer circuit. A weighted sum of the comparator outputs is subtracted from the input to form an error signal in a control loop. The ratio of the reference voltages is chosen to reduce or eliminate local minima during a convergence of the control loop and is set to values that minimize a mean squared error signal with respect to discrete modulation states of the input after the convergence of the control loop is complete.

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.

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.

Provided is a coherent detection implementing apparatus, system and method. The apparatus includes: a first transceiver unit, configured to send an optical signal in a first direction to a second device, wherein the optical signal in the first direction includes a direct current optical signal with a first wavelength and a modulated optical signal with a second wavelength; and configured to receive an optical signal in a second direction from the second device; and a first coherent receiver, connected with the first transceiver unit, and configured to take a part of the direct current optical signal with the first wavelength in the optical signal in the first direction as a Local Oscillator (LO) light for coherent reception, perform coherent frequency mixing between the LO light and the optical signal in the second direction, and demodulate the optical signal in the second direction.

A receiving unit (2020) generates a received frame from a modulated optical signal. The modulated optical signal is generated such that a transmission symbol is generated by mapping an encoded bit string obtained by encoding a transmission bit string to an m-dimensional symbol space, a transmission frame is generated by mapping the transmission symbol to an n-dimensional frame space (n<m), and an optical carrier wave is modulated by using the transmission frame. A converting unit (2040) generates candidate vectors (m-dimensional vectors belonging to a partial symbol space within the symbol space) by using a received frame. A first computing unit (2070) computes a probability of that the transmission symbol belonging to the partial symbol space is transmitted for each partial symbol space. A second computing unit (2080) computes a log-likelihood ratio of each bit of the encoded bit string by using the probability.

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.