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 narrow band 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 received seed source may enable upstream communications at varying wavelengths. The fiber node may provide each seed source by filtering (e.g., by a grating filter) a broadband light source.

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, an apparatus includes a receiver comprising: a local oscillator laser providing a local oscillator signal, a detector circuit operable to receive a first optical signal and detect first data carried by the first optical signal based on the local oscillator signal, a reference clock circuit supplying a clock signal, a digital signal processor (DSP) operable to receive the first data and supply a control signal to the reference clock circuit based on the first data, the reference clock circuit being operable to adjust the clock signal based on the control signal; and a transmitter operable to output a second optical signal carrying second data, the second data having an associated rate that is based on the clock signal.

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.

An apparatus includes a first modulator configured to modulate a radio frequency (RF) input signal onto a first optical signal and a second modulator configured to modulate a local oscillator (LO) signal onto a second optical signal. The apparatus also includes a photonic integrated circuit having an optical demodulator configured to generate, using the modulated optical signals, I and Q signals representing a demodulated version of the RF input signal. The optical demodulator may include an optical filter bank having multiple optical filters, where different optical filters are configured to pass different frequencies or frequency ranges. The optical filters may include at least one narrowband optical filter and/or one or more tunable optical filters.

The narrowband optical filter(s) may be configured to isolate global navigation satellite system-related signals. The tunable optical filter(s) may be configured to isolate signals over a frequency range of about 900 MHz to about 12 GHz.

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.

Managing clock-data recovery for a modulated signal from a communication channel comprises: receiving the modulated signal and providing one or more analog signals, providing one or more digital input streams from samples of the analog signals, and processing the digital input streams to provide decoded digital data. The processing comprises: determining the decoded digital data based on information modulated over a plurality of frequency elements associated with the modulated signal, based at least in part on transforms of the digital input streams; a clock signal based on clock recovery from the digital input streams; and determining a clock phase error estimate associated with the determined clock signal based at least in part on a sum that includes different weights multiplied by different respective summands corresponding to different sets of frequency elements.

A LiDAR system includes an optical source for generating a continuous wave (CW) optical signal. A control processor generates a pulse-position modulation (PPM) signal, and an amplitude modulation (AM) modulator generates a pulse-position amplitude-modulated optical signal, which is transmitted through a transmit optical element into a region. A receive optical element receives reflected versions of the pulse-position amplitude-modulated optical signal reflected from at least one target object in the region. An optical detector generates a first baseband signal. A signal processor receives the first baseband signal and processes the first baseband signal to generate an indication related to a target object in the region.

A LiDAR system includes an optical source for generating a continuous wave (CW) optical signal. A control processor generates a pulse-position modulation (PPM) signal, and an amplitude modulation (AM) modulator generates a pulse-position amplitude-modulated optical signal, which is transmitted through a transmit optical element into a region. A receive optical element receives reflected versions of the pulse-position amplitude-modulated optical signal reflected from at least one target object in the region. An optical detector generates a first baseband signal. A signal processor receives the first baseband signal and processes the first baseband signal to generate an indication related to a target object in the region.

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.