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 coupled to a photonics die. The thin film filters are arranged above corresponding grating couplers in the 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.

Embodiments of this disclosure provide an apparatus and method for monitoring a polarization dependent loss, a receiver and a communication system. The apparatus for monitoring a polarization dependent loss includes: a first processing unit configured to process received optical signals, to obtain a first correlation matrix of noise signals in the received optical signals and a second correlation matrix of second signals or other signals in the received optical signals other than first signals or spectral feature signals having predetermined spectral features; a matrix subtraction unit configured to subtract the second correlation matrix by the first correlation matrix, to obtain a third matrix; and a calculating unit configured to perform singular value decomposition on the third matrix, and calculate a polarization dependent loss according to a result of the singular value decomposition. According to the embodiments of this disclosure, the polarization dependent loss may be calculated more accurately.

A transmitter transmitting a polarization multiplexed optical signal, includes: a light source; a generating unit configured to split a light of the light source into first and second polarized lights, optically modulate the first and second polarized lights based on an electric data signal, and multiplex the first polarized light optically-modulated and the second polarized light optically-modulated to generate the polarization multiplexed optical signal; and a coupling unit configured to couple a first reference light having a frequency different from a frequency of the light of the light source with the first polarized light and couple a second reference light having a frequency different from the frequency of the light of the light source with the second polarized light, wherein the first reference light and the second reference light have different frequencies.

Embodiments of this disclosure provide a method and apparatus for estimating polarization dependent loss (PDL) and a receiving device. The method includes: performing equalization processing on pre-processed dual-polarization state signals; performing correlation operations on the equalized dual-polarization state signals and unequalized dual-polarization state signals; constructing an estimation matrix based on a result of the correlation operations; and calculating a polarization dependent loss of the dual-polarization state signals by using one or more feature values of the estimation matrix. Hence, not only PDL in an optical fiber link may be accurately estimated, but also off-line digital signal processing may be performed at a receiver, without needing to incur extra hardware overhead.

An optical transmission device includes a plurality of transmitting/receiving units provided on a substrate, each transmitting/receiving unit includes: an optical transmitter; an optical receiver; a polarization combiner/splitter; and a connection portion. In the connection portions which are arranged at the positions symmetrical to each other, a direction opposite, with respect to a virtual symmetry axis, to a direction of a main electric field on a plane perpendicular to an emission direction of an optical wave of the connection portion which is emitted from one of the connection portions to an outside is substantially orthogonal to a direction of a main electric field on a plane perpendicular to an emission direction of an optical wave of the connection portion which is emitted from the other of the connection portions to an outside.

An apparatus includes a polarization beam splitter (PBS) and an optical detector. The PBS is configured to receive a polarized optical signal transported via an optical communication path of an optical network. The detector is configured to receive from the PBS a first polarization component of the optical signal, and to produce a first electrical measure of the first polarization component. A processor is configured to determine a dynamic metric of the optical communication path based at least on the first electrical measure. Some embodiments also include a second detector configured to receive from the PBS a second polarization component of the optical signal. The second detector produces a second electrical measure of the second polarization component, and the processor is configured to determine the dynamic metric based on both the first and second electrical measures.

An optical transmission method wavelength-multiplexing and transmitting multiple channels including data. The data are composed of data areas independent between the channels and data areas non-independent between the channels. Data patterns of the data areas non-independent between the channels are variable. The data patterns of the data areas non-independent between the channels are set so that in time periods of the non-independent data areas on an optical transmission section, a time period during which polarization states of the multiple channels are correlated in the optical transmission section has a length such that an error rate is less than or equal to a threshold value, the error rate being determined from a temporal distribution of bit errors obtained from a result of error decision after demodulation in an optical receiver.

An optical transmitter transmits optical signal including a first signal and a second signal. The second signal is subjected to change in a polarization state relative to a polarization state of the first signal. An optical receiver analyzes a reception characteristic of the second signal and detects, based on the analyzed result, a polarization state of the first signal indicative of a higher signal quality than that of the second signal.

A method of controlling a transmission signal, includes transmitting a training signal including four polarization states having a given relation; and performing rotation control and transmission power level control of a polarization component of a data signal, based on a rotation control matrix for a polarization state and an inverse-operation control matrix for a power level imbalance, which are estimated from Stokes parameters related to input power level present on a Poincare sphere acquired from the training signal and Stokes parameters related to output power level present on the Poincare sphere.

In accordance with an example embodiment of the present invention, there is provided an apparatus comprising a dual-rail encoder (120) configured to receive light from a light source and to output dual-rail encoded light, a combiner (130) configured to convert the dual-rail encoded light into polarization encoded light, and at least one processing core configured to obtain compensation adjustment information concerning a fiber (145) and to control the dual-rail encoder (120) based at least in part on the compensation adjustment information.