A method by which a transmission terminal transmits a signal in an optical wireless communication system can comprise: transmitting a first optical signal including a reference signal to a reception terminal having established a communication link with the transmission terminal; receiving feedback information about the first optical signal from the reception terminal; and transmitting a second optical signal to the reception terminal on the basis of the feedback information, wherein an orbital angular momentum (OAM) mode of the second optical signal can be selected on the basis of the feedback information.

An apparatus for mitigating polarization dependent loss (PDL) in an optical signal-to-noise ratio (OSNR) of a modulated optical signal is disclosed. The apparatus may comprise a spectrum analyzer to measure an optical power spectrum of a modulated optical signal. The apparatus may also comprise a measuring unit to select a first portion of the modulated optical signal and a second portion of the modulated optical signal, where each of the first and second portions of the modulated optical signals may include an independent noise distribution indicative of PDL, and measure a time-varying parameter of the first and second portions. The apparatus may also include a signal processor to PDL in an OSNR by transforming any elliptical polarization associated with the independent noise distribution into a ball polarization, determining a correlation between time-varying parameters of the first and second portions, and calculating a PDL mitigated OSNR.

This application provides an optical emission apparatus, an optical communication system, and an optical communication method. Light beams of N optical emission units in the optical emission apparatus are adjusted, so that an optical power of entering an optical receiving apparatus is maximized, and impact of a speckle caused by turbulence is minimized, thereby improving receiving efficiency of an optical antenna. The optical emission apparatus includes a first optical splitter and N optical emission units, where N is an integer greater than 1; the first optical splitter is configured to transmit received same signal light to the N optical emission units; and the N optical emission units are configured to output the signal light from the first optical splitter, to obtain light beams distributed based on a preset proportion.

Systems and methods include receiving (S11) data for a plurality of elements associated with an optical network; determining (S12) an incremental noise penalty for each element of the plurality of elements based on the received data; and storing (S13) the incremental noise penalty for each element of the plurality of elements. The steps can further include determining (S14) Signal-to-Noise Ratio (SNR) across an optical path in the optical network by concatenating associated incremental noise penalties for each element in the optical path along with corrections. The present disclosure includes a fast, nonlinear estimation process with improved accuracy for low loss spans compared to traditional closed-form GN models, as well as a method to determine the coherent nonlinear penalty in an arbitrary concatenation of mixed heterogeneous fibers which is not considered by existing fast nonlinear interference calculation methods.

Provided is a monitoring apparatus capable of efficiently optimizing the transmission efficiency of an entire network. The monitoring apparatus (1) includes a variable parameter changing unit (2), a monitoring information acquisition unit (4), and an estimation unit (6). The variable parameter changing unit (2) changes a variable parameter for at least one of multiple network apparatuses that constitute an optical communication network transmitting an optical signal by wavelength division multiplexing. The monitoring information acquisition unit (4) acquires monitoring information related to a state of optical communication from at least one of the multiple network apparatuses. The estimation unit (6) estimates at least one penalty for a receiving side, using the monitoring information.

Provided is a monitoring apparatus capable of efficiently optimizing the transmission efficiency of an entire network. The monitoring apparatus (1) includes a variable parameter changing unit (2), a monitoring information acquisition unit (4), and an estimation unit (6). The variable parameter changing unit (2) changes a variable parameter for at least one of multiple network apparatuses that constitute an optical communication network transmitting an optical signal by wavelength division multiplexing. The monitoring information acquisition unit (4) acquires monitoring information related to a state of optical communication from at least one of the multiple network apparatuses. The estimation unit (6) estimates at least one penalty for a receiving side, using the monitoring information.

A decoder for determining an estimate of a vector of information symbols carried by optical signals propagating along a multi-core fiber in an optical fiber transmission channel according to two or more cores is provided. The decoder is implemented in an optical receiver. The optical signals are encoded using a space-time coding scheme and/or scrambled by at least one scrambling device arranged in the optical fiber transmission channel according to a predefined scrambling function. The decoder comprises a processing unit configured to adaptively: determine, in response to a temporal condition, one or more channel quality indicators from the optical signals; determine a decoding algorithm according to a target quality of service metric and on the one or more channel quality indicators; update the predefined scrambling function and/or the space-time coding scheme depending on the target quality of service metric and on the one or more channel quality indicators. The decoder further comprises a symbol estimation unit configured to determine an estimate of a vector of information symbols by applying the decoding algorithm to the optical signals.

There is provided a method, apparatus and system for determining multipath interference (MPI) in optical communications. It is object of embodiments of the present disclosure to provide an effective, low-cost way of detecting or measuring MPI. To effectively detect and measure the MPI, multiple zero-power gaps are inserted into the transmission signal (optical signal) in time domain. In some embodiments, at least some of the zero-power gaps inserted in the main signal do not overlap the zero-power gaps of the reflection of the main signal. Using the zero-power gaps contained the main signal and the reflection (where applicable), power inside and outside the zero-power gaps are determined. Then, the strength of the MPI is determined based on the determined power inside and outside the zero-power gaps.

Systems and methods for avoiding fiber damage of an optical fiber link are provided. A method, according to one implementation, includes monitoring optical signals transmitted along an optical fiber link from an output port of a first card to an input port of a second card. In response to detecting a fiber disconnection state when an amplifier of the first card is operating in a normal condition, the amplifier of the first card enters a forced Automatic Power Reduction (APR) condition. In addition to potentially reducing the risk of eye damage from laser light emitted from the optical fiber link, the forced APR condition is configured to allow for an uninterrupted debugging procedure. Also, the method includes returning the amplifier of the first card from the forced APR condition back to the normal operating condition after receiving an indication that the fiber disconnection state has cleared.

A method may include obtaining a topology of an optical network. The topology may indicate multiple optical links within the optical network. The method may also include determining a signal noise tolerance for each of multiple optical signal types supported by the optical network and obtaining an optical noise for each of the multiple optical links. The method may also include determining a number of the multiple optical signal types that each of the multiple optical links is able to support based on the optical noise for each of the optical links and the signal noise tolerance for each of the multiple optical signal types and ranking the multiple optical links based on the number of the multiple optical signal types that each of the optical links is able to support.