A fiber-optic communication system having two optical channels characterized by different respective group velocities. In an example embodiment, the system comprises an optical receiver capable of measuring a difference in the time of arrival thereto, by way of the two optical channels, of the corresponding signal disturbances caused by a remote ambient event, such as an earthquake or a lightning strike. A signal processor of the receiver can then use the measured time-of-arrival difference to estimate the distance, along the fiber, to the location of the remote ambient event. In some example embodiments, the two optical channels may be different wavelength channels or different spatial modes of a multimode fiber. In some example embodiments, at least one of the two channels may be a payload-data-bearing channel.

An echo cancellation method includes steps of (a) extracting phase-distortion estimates, (b) reconstructing an echo signal, (c) generating a clean signal, and (d) producing a primary signal. Step (a) includes extracting, from a first phase signal, a plurality of phase-distortion estimates, the first phase signal having been estimated from an echo-corrupted signal received at a first coherent transceiver of a coherent optical network. Step (b) includes reconstructing an echo signal from the plurality of phase-distortion estimates and a transmitted signal transmitted by the first coherent transceiver. Step (c) includes generating a clean signal as a difference between the reconstructed echo signal and the first phase signal. Step (d) includes producing a primary signal by mapping each of a plurality of clean-phase estimates of the clean signal to one of a plurality of constellation symbols associated with a modulation scheme of the primary signal.

A polarization dependent loss (PDL) compensation device for an optical system can be configured to output a compensating PDL to at least partially cancel a PDL of the optical system. In certain embodiments, the device can include a first polarization controller configured to modify a state of polarization of an optical signal, a PDL emulator disposed upstream of the first polarization controller and configured to output the compensating PDL upstream of the first polarization controller, and a second polarization controller disposed upstream of the PDL emulator and configured to modify a state of polarization of the optical signal upstream of the PDL emulator.

Free space optical systems and methods of controlling the same for reducing signal fading of encoded optical beams transmitted in a communication channel are provided. Adjacent pairs of a plurality of apertures are separated by a distance being at least greater than the coherence width of the propagation medium of the communication channel. Due to averaging of the beams, variation in power at an optical receiver is reduced. By using an optical resonator in the optical receiver, the beams are converted into an intensity modulation on a non-interfering basis, thereby permitting recovery and decoding of the signal.

Optical transmitters, receivers, and methods are described in an optical network. An optical transmitter comprises an encoder configured to receive an input data stream and to encode the input data stream into a signal. The signal is defined as a sequence of regular units, and a rotator is configured to receive each unit of the signal and to output, for each given input unit with an input state of polarization (SOP), a respective given output unit associated with an output SOP. The output SOP of the given output unit is different from a corresponding output SOP of each other output unit that is immediately adjacent to the given output unit. The output SOPs of the units in a transmitted signal may form an alternating pattern (or other repeating pattern), which may help to lower the average BER, in particular, due to forward error correction (FEC).

Systems, computer-implemented methods, and computer program products to facilitate rotated polarization detection and adjustment are provided. According to an embodiment, a system can comprise a memory that stores computer executable components and a processor that executes the computer executable components stored in the memory. The computer executable components can comprise an optical component that can comprise a polarization monitor component that can detect a rotated polarization state of an optical signal. The computer executable components can further comprise a second optical component that can comprise a polarization controller component that can control a rotation polarization state of the second optical component. The computer executable components can further comprise a feedback loop component that can couple the polarization monitor component to the polarization controller component.

The invention presents an equalizing device, a corresponding method and an optical signal with a frame structure for enabling the method. The equalizing device includes a first 2×2 MIMO equalizer configured to perform a first equalization on the digital signal, supported by a 2×2 MIMO channel estimation of the channel based on the digital signal. Further, the device includes a second 2×2 MIMO equalizer, arranged after the first equalizer and configured to perform a second equalization on the digital signal, supported by a State of Polarization (SOP) estimation of the optical signal based on the digital signal.

An optical transmission apparatus, includes, a light source configured to output a plurality of light beams having different wavelengths to an optical fiber, a receiver configured to receive, from the optical fiber, a reflected light beam corresponding to each of the wavelengths of the plurality of light beams, and a signal processing circuit configured to estimate a polarization fluctuation portion based on a polarization state of the received reflected light beam corresponding to each of the plurality of wavelengths.

An optical communication system is configured to transmit and receive at least four multiplexed, differently-polarized, optically-transmitted signals. Each signal is associated with a predefined state of polarization. An optical transmitter is configured to transmit multiplexed, differently polarized, optically transmitted signals. An optical receiver is configured to receive the optically transmitted signals. The system includes a multi-polarization analyzer circuit configured to obtain an analyzed signal for each of the polarized signals in Stokes space. The analyzer circuit is configured to determine if the multiplexed signal has been transformed by extreme polarization-dependent loss (PDL), the receiver correcting for the extreme polarization-dependent loss.

Methods and systems for eliminating polarization dependence for 45 degree incidence MUX/DEMUX designs may include an optical transceiver, where the optical transceiver comprises an input optical fiber, a beam splitter, and a plurality of thin film filters arranged above corresponding grating couplers in a photonics die. The transceiver may receive an input optical signal comprising different wavelength signals via the input optical fiber, split the input optical signal into signals of first and polarizations using the beam splitter by separating the signals of the second polarization laterally from the signals of the first polarization, communicate the signals of the first polarization and the second polarization to the plurality of thin film filters, and reflect signals of each of the plurality of different wavelength signals to corresponding grating couplers in the photonics die using the thin film filters.