78 results about "Polarization-division multiplexing" patented technology

The invention relates to optical communication, in particular to compensation of non-linear distortions incurred in high bit-rate optical communication systems. A method and system for compensating self-phase modulation at an optical receiver of an optical transmission system using polarization division multiplexing and a modulation scheme with constant amplitude is proposed. The method comprises the step of performing a phase modulation on a received signal, wherein the received signal comprises two signal components associated with two orthogonal polarizations, each component comprising an in-phase sub-component and a quadrature-phase sub-component, thereby spanning a four-dimensional space. The phase modulation is determined by evaluating an error signal which depends on the distance in the four-dimensional space between the received signal after the phase modulation and a four-dimensional sphere defined by target constellation points of the optical transmission system.

A method, device, and system for polarization division multiplexing (PDM) and polarization division demultiplexing are provided in the field of communication and transmission. The device for polarization division demultiplexing includes a polarization controller (PC), a polarization beam splitter (PBS), a detection control module, an optoelectronic receiver 1, and an optoelectronic receiver 2. The PC is adapted to receive a PDM optical signal carrying an identification signal and perform polarization control on the PDM optical signal. The PBS is adapted to perform polarization division on the PDM optical signal carrying the identification signal after the polarization control. The detection control module is adapted to perform identification signal detection on the optical signal after the polarization division to obtain a power of the identification signal, and output a polarization control signal to control the PC according to a power change of the identification signal. The optoelectronic receiver 1 and the optoelectronic receiver 2 are adapted to perform demodulation reception on an X-polarization branch optical signal and a Y-polarization branch optical signal respectively to obtain a first original signal and a second original signal. Thereby, during polarization division demultiplexing, reversal of two demultiplexed polarization branches is effectively avoided.

An optical communication system having a transmitter in which a pair of optical signals having different frequencies are modulated using a duobinary encoding scheme, and then multiplexed using polarization division multiplexing. Advantageously, the frequency difference between the two signals can be less than the data rate conveyed by each signal, resulting in a narrow spectral bandwidth, while still allowing demultiplexing at a receiver using simple bandpass filters and without the need of any form of polarization tracking. A receiver has a beam splitter for splitting the received optical signal into two portions which are each directed, via respective bandpass filters centred at slightly different frequencies, to respective detectors. Advantageously, the frequency difference between the frequencies at which the bandpass filters are centred can be less than the data rate of a detected signal. The receiver does not require any polarization tracking or balancing, and accordingly is straightforward to implement

The invention discloses a microwave photonic down-conversion method based on a dual-drive polarization division multiplexing Mach-Zehnder modulator (PDM-MZM), and solves a problem of poor stability and noise performance in the prior art. The method comprises the following steps of inputting an optical carrier signal; generating a radio frequency signal and a local oscillator signal; setting a direct-current bias voltage of a sub-modulator; generating a modulation optical signal; carrying out beam splitting on the modulation optical signal; detecting the modulation optical signal; and restraining noise by an electric subtraction device. According to the method, the noise is restrained through dual-drive one-time modulation of the PDM-MZM and a difference obtained by the electric subtractiondevice, so that the stability and the noise performance are improved.

Disclosed is a passive optical network system using a time division multiplexing scheme. According to one exemplary embodiment, the passive optical network system includes a plurality of optical network units (ONUs); an optical line terminal (OLT) to be connected to the plurality of ONUs for communication and to transmit and receive an optical signal to and from the plurality of ONUs using a time division multiplexing (TDM) scheme, wherein each of the plurality of ONUs includes a light source that generates an optical signal with a predetermined intensity even in burst-off state; and an optical filter disposed on a receiving path of an optical receiver of the OLT to filter out an optical noise signal received from an ONU in burst-off state among the plurality of ONUs.

The invention discloses a time division multiplexing (TDM)-based low-reflectivity triangle spectrum-shaped fiber grating sensing system. The system mainly comprises a distribution feedback laser, an electro-optical modulator, a circulator, an optical amplifier, a triangle spectrum-shaped fiber grating sensor, a high-speed optical detector, a pulse signal generator and a signal acquisition device, wherein the distribution feedback laser is used for emitting narrow line-width laser; pulse signal light is formed by the narrow line-width laser through the electro-optical modulator or is generated by internal modulation through the distribution feedback laser; the pulse light passes through the circulator and then is reflected by a triangle spectrum-shaped fiber grating; the reflected light passes through the circulator to enter the optical amplifier and is amplified into the high-speed optical detector; and a light signal is converted into an electrical signal through the high-speed optical detector, and the electrical signal is converted into a digital signal and is processed through the signal acquisition device. In the system, the distribution feedback laser and the low-reflectivity triangle spectrum-shaped fiber grating sensor are combined, a large-scale fiber grating sensing network is constructed through TDM, and thousands of sensors are multiplexed on a single fiber, so that the costs of a light source and a wavelength detection device are reduced.

Blind polarization demultiplexing algorithms based on complex independent component analysis (ICA) by negentropy maximization for quadrature amplitude modulation (QAM) coherent optical systems are disclosed. The polarization demultiplexing is achieved by maximizing the signal's non-Gaussianity measured by the information theoretic quantity of negentropy. An adaptive gradient optimization algorithm and a Quasi-Newton algorithm with accelerated convergence are employed to maximize the negentropy. Certain approximate nonlinear functions can be substitutes for the negentropy which is strictly derived from the probability density function (PDF) of the received noisy QAM signal with phase noise, and this reduces the computational complexity. The numerical simulation and experimental results of polarization division multiplexing (PDM)-quadrature phase shift keying (QPSK) and PDM-16QAM reveal that the ICA demultiplexing algorithms are feasible and effective in coherent systems and the simplified ones can also achieve equivalent performance.

The invention provides an equilibrium method and equipment under an extreme scene in a coherent optical fiber polarization-division multiplexing system. The method comprises the following steps: performing segmented construction on an optical fiber channel with rotation of state of polarization RSOP and polarization division multiplexing PMD joint effect to acquire a signal damage model with two segments of equivalent structures of the PMD before the RSOP; performing window-split interception on a damage signal symbol sequence passing through the optical fiber channel to acquire a window-splitsignal; performing the PMD compensation on the PMD damage of the window-split signal at the frequency domain by using the Kalman filter equilibrium algorithm, and performing the RSOP compensation onthe RSOP damage of the window-split window at the time domain. Under the situations that the speed of the RSOP reaches up to million radians per second and the differential group delay of the PMD is multiple times of the symbol period, the equilibrium compensation work of the signal is finished; the error vector amplitude is much less than the forward error correction tolerance, and performs wellalong the optical signal-to-noise ratio change.

The invention relates to a three-dimensional real time super-resolution digital holography recording system, which belongs to the field of three-dimensional microscopic imaging technology and comprises an incident light generation system and a recording system. The incident light generation system comprises a femtosecond pulse laser, a frequency doubling crystal, a dichroscope, an optical path delay system and an unpolarized beam splitter. Said recording system comprises a microobjective and a series of polarized beam splitter and unpolarized beam splitter, a reflector, a digital camera and a computer holography image processing and reproducing system. With the technologies of wavelength division, angle division, time division and polarization division multiplexing and with the optical frequency doubling crystal, the lasers sent from the laser device can be divided into two lasers with different wavelengths to enter the recording system; then a digital holography record for the three-dimensional real time super-resolution imaging can be realized in one frame image of Charge Coupled Device (CCD) through a series of beam splitting, high resolution, large view field and large depth of field. The invention has the advantages of simple system and more information records, which can simultaneously improve the space resolution and time resolution and can be widely applied to the three-dimensional real time high-resolution imaging for the microscopic object.

Methods and apparatus for interrogating sets of optical elements having characteristic wavelengths spanning a sweep range while avoiding overlapping reflections from the different sets when performing a wavelength sweep are provided. One example method generally includes introducing a pulse of light, by an optical source, into an optical waveguide to interrogate at least first and second sets of optical elements, wherein the optical elements within each set have different characteristic wavelengths and wherein the first and second sets are separated in time such that a first time window over which light is reflected from the optical elements in the first set and reaches a receiver does not overlap with a second time window over which light is reflected from the optical elements in the second set and reaches the receiver; and processing the reflected light to determine one or more parameters corresponding to the optical elements.

Aspects of the invention provide transmitters and receivers for managing multiple optical signals. High order modulation, such as phase and/or amplitude modulation, is used to achieve multiple bits per symbol by transporting multiple asynchronous data streams in an optical transport system. One or more supplemental multiplexing techniques such as time division multiplexing, polarization multiplexing and sub-carrier multiplexing may be used in conjunction with the high order modulation processing. This may be done in various combinations to realize a highly spectrally efficient multi-data stream transport mechanism. The system receives a number of asynchronous signals which are unframed and synchronized, and then reframed and tagged prior to the high order modulation. Differential encoding may also be performed. Upon reception of the multiplexed optical signal, the receiver circuitry may employ either direct detection without a local oscillator or coherent detection with a local oscillator.

Methods and apparatus for fast sweeping a spectral bandwidth in order to distinguish among signals received from effectively wavelength division multiplexed (WDMed) and time division multiplexed (TDMed) optical components on a single fiber. For some embodiments, a method for interrogating optical elements having characteristic wavelengths spanning a sweep range is provided. The method generally includes introducing a pulse of light, by an optical source, into an optical waveguide to interrogate at least a first set of optical elements having different characteristic wavelengths by performing a sweep of wavelengths over a period of the pulse, wherein the period is less than a round-trip time for light reflected from an optical element closest to the optical source to reach a receiver and processing the reflected light to determine a parameter based on the times at which signals are received.

The invention provides a polarization multiplexing system for overcoming crosstalk between two polarization channels caused by an optical fiber PDL, and relates to the polarization multiplexing system which is characterized in that at the polarization multiplexing end, continuous light wave emitted by a distributed feedback laser DFB-LD is divided into two beams of light by a polarization-preserving coupler, wherein the first beam of light passes through an adjustable Faraday rotation piece, and the second beam of light passes through an optical fiber delay line formed by a polarization-preserving fiber PMF, so that coherence between the first and the second light beams can be eliminated; the first beam of light passes through a modulator and bears a first path of optical channel, and thesecond beam of light passes through the modulator and bears a second path of optical channel; and the two beams of light bearing the optical channels can complete multiplexing through the coupler andthen reaches the polarization demultiplexing end through a transmission link. The polarization multiplexing system for overcoming the crosstalk between the two polarization channels caused by the optical fiber PDL solves the problem that polarization signals at the demultiplexing end are influenced by PDL effect in a transmission optical fiber link and are no longer in orthogonality, leads the polarization signals received by the demultiplexing end to be orthogonal by a feedback control system, and eliminates the influence of the PDL in the transmission optical fiber link.

Disclosed herein is a modulator (50) for polarization-division multiplexing (PDM) transmission. The modulator (50) comprises first and second DP-MZMs (12, 28) associated with first and second polarizations, each DP-MZM (12, 28) having an input for an in-phase and a quadrature driving signal for modulating the in-phase and quadrature components of an optical signal according to respective transfer functions, and a detector (58) suitable for detecting light comprising at least a portion of the light outputted by the first DP-MZM (12) and a portion of the light outputted by the second DP-MZM (28). The modulator (50) is adapted to superimpose a first pilot signal on one of the in-phase and quadrature driving signals of the first DP-MZM (12) and on one of the in-phase and quadrature driving signals of the second DP-MZM (28), and a second pilot signal on the respective other of the in-phase and quadrature driving signals of the first and second DP-MZMs (12, 28). Further, the first and second pilot signals are chosen such that the signal detected by said detector (58) is indicative as to whether the slopes of the transfer functions are different for the in-phase and quadrature components of one of the first and second DP-MZMs (12, 28) and identical for the other of the first and second DP-MZMs (12, 28).

The invention discloses a demodulation system and method of a fiber grating sensor based on edge filtering and time division multiplexing. A plurality of fiber F-P lasers with different center wavelengths transmit laser signals of respective central wavelengths. The laser signals through a fiber into a circulator. The circulator injects a combined laser into a sensing unit. The sensing unit comprises a plurality of sets of sensing arrays connected in series. Each set of sensing arrays comprises a plurality of fiber gratings connected in series corresponding to different center wavelengths. Each of the sensing arrays is connected by a time division delay fiber. The circulator simultaneously receives the optical signal fed back by the sensing unit, and separates the different wavelengths ofthe incident light and transmits the same to a processing unit. The processing unit amplifies the optical signals of different wavelengths and performs edge filtering. The processing unit demodulatesthe fiber grating sensing arrays with the same wavelength type according to the signal return time. High frequency demodulation of a large-capacity fiber grating sensing array on a single fiber can beachieved by combining edge filtering and time division multiplexing.

The invention provides a bidirectional multi-service access ROF transmission system and method for realizing carrier wave reuse by applying polarization multiplexing. According to the invention, optical carrier wave inhibition signals whose energy is concentrated at positive and negative first-order sidebands is generated at a center station, then multi-service signals are modulated to the positive first-order optical sideband, the polarization state of the negative first-order sideband is controlled to form an included angle of 45 degrees with an original polarization state, and thus modulation of multi-service optical millimeter waves is completed. Optical signals are transmitted to a base station via a fiber link and are divided into two parts through polarization separation, one part is converted into multi-service electric millimeter waves through photoelectric detection and is sent by an antenna after amplification, and at a user unit, the antenna receives and respectively demodulates signals of each service; and the other part is taken as optical carrier waves of uplink signals for sending to the center station by carrying radiofrequency signals, and radio frequency baseband signals are obtained through photoelectric conversion at the center station.

The invention discloses an all-optical wavelength/code type conversion device, relates to the field of optical network communication, and realizes all-optical wavelength/code type conversion of various code type signals of polarization division multiplexing (PDM), orthogonal polarization and frequency division multiplexing (OPFDM), single polarization signals and the like. The device comprises a first pump light transmitting device, a second pump light transmitting device, a pump light controller and a polarization maintaining coupler, wherein the first pump light transmitting device transmits first pump light in an x polarization state; the second pump light transmitting device transmits second pump light in a y polarization state; the pump light controller adjusts the first pump light transmitting device and the second pump light transmitting device, so that the frequencies of the first and second pump light, the frequency of signal light to be converted and the frequency of conversion signal light of a target wavelength/code type meet a preset relationship; the first and second pump light are coupled by the polarization maintaining coupler and input into a nonlinear optical waveguide; and in the nonlinear optical waveguide, the signal light to be converted and dual pump light input by the polarization maintaining coupler are subjected to a four-wave mixing effect, and signal light with the target wavelength is generated. The device is mainly applied to an optical network.

The invention discloses a transmission system and method based on modular division multiplexing. The transmission system comprises a transmitting device and a receiving device, wherein the transmitting device comprises a signal source and a transmitter; the signal source provides at least one channel of electrical signals for the transmitter; and the transmitter modulates the electrical signals onto an optical carrier, converts the electrical signals into optical signals, divides the optical signals into multiple channels of optical signals in different modes, and multiplexes the optical signals together, so that modular division multiplexing signals are generated. According to the transmission system and method provided by the invention, the transmitter modulates the electrical signals into the optical signals, divides the optical signals into multiple channels of optical signals in different modes, and multiplexes the optical signals, so that the modular division multiplexing signalsare generated; the modular division multiplexing signals are transmitted to the receiving device through an optical fiber link; then, the receiving device de-multiplexes the signals into multiple channels of fundamental mode optical signals in the same mode; the optical power in each mode is reduced; therefore, the nonlinear effect excited by each mode is reduced; the total nonlinear effect is inhibited; the nonlinear tolerance of optical fiber transmission is improved in the optical fiber link transmission; and thus, the signal transmission quality and distance are improved.

The invention discloses a full-optical-wavelength conversion simplifying device and a full-optical-wavelength conversion simplifying method of a polarization multiplexing system without polarization crosstalk. A wavelength conversion structure of polarization diversity is adopted and two polarization beam splitters are used for respectively dividing signal light and pump light into two groups of mutually-orthorhombic polarization films; two baseband data signals are respectively modulated to two mutually-orthorhombic polarization modes of the signal light to form a modulating signal; the modulating signal and the pump light in the same polarization direction are coupled and then are respectively transmitted into two semiconductor optical amplifiers (SOA); and each SOA independently realizes the wavelength conversion in the same polarization direction. According to the full-optical-wavelength conversion simplifying device and the full-optical-wavelength conversion simplifying method, the crosstalk between polarization multiplexing channels, which is caused by the polarization dependence of a gain in polarization multiplexing wavelength conversion of one SOA, can be overcome; the performance of a wavelength conversion system is improved; the wavelength conversion device has a simple structure and the system is easily integrated; and the wavelength conversion device can be applied to a full-optical-wavelength conversion system of polarization multiplexing signals with the different modulating formats.

The invention provides a polarization multiplexing system based on direct detection of a Stokes space for realizing three-dimensional modulation on two paths of polarization states and improving the transmission rate and the dispersion tolerance of the system. The system comprises a polarization beam splitter, a single-side band modulator, an orthogonal modulator, a polarization beam combiner anda Stokes receiver, wherein the polarization beam splitter is used for dividing a light beam emitted by a laser into two orthogonal polarization states, wherein the first polarization state loads a single-side band signal, and a second polarization state loads a complex signal; the single-side band modulator is used for carrying out single-side band modulation on the single-side band signal loadedby the first polarization state; the orthogonal modulator is used for carrying out quadrature modulation on the complex signal loaded by the second polarization state; the polarization beam combiner is used for synthesizing the modulated signals on the first polarization state and the second polarization state into a polarization multiplexing signal to be transmitted out; and the Stokes receiver is used for receiving the polarization multiplexing signals, processing the received polarization multiplexing signal, and restoring the single-side band signal and the complex signal. The invention relates to the field of short-distance high-rate optical communication.

The invention relates to an integration optical waveguide three dimensional electric field measuring system and method based on time division multiplexing, and belongs to the electric field measuringtechnical field; the system comprises a polarization-maintaining laser source with a tunable wavelength, MZI type integration optical waveguide electric field sensors with two arms of asymmetrical lengths, a single-mode fiber, a polarization maintaining fiber, an optical switch, an optical combiner, a photoelectric detector and an electric signal processing unit. The integration optical waveguidethree dimensional electric field measuring system based on time division multiplexing employs the optical switch and the time division multiplexing technology to control the output wavelength of the polarization-maintaining laser source with the tunable wavelength, locks the static state working point of the three MZI type integration optical waveguide electric field sensors with two arms of asymmetrical lengths at [pi]/2, thus carrying out three dimensional measurements for the electric field in a random direction in a space.