207 results about "Fiber chromatic dispersion" patented technology

A modelocked linear fiber laser cavity with enhanced pulse-width control includes concatenated sections of both polarization-maintaining and non-polarization-maintaining fibers. Apodized fiber Bragg gratings and integrated fiber polarizers are included in the cavity to assist in linearly polarizing the output of the cavity. Very short pulses with a large optical bandwidth are obtained by matching the dispersion value of the fiber Bragg grating to the inverse of the dispersion of the intra-cavity fiber.

A suite of optical performance monitoring (OPM) methods, based on optical subcarrier multiplexing, are described by the invention. The strength of this approach lies in the simplicity of double sideband subcarrier signals and the fact that these signals travel the complete optical path with the baseband signal of interest. The subcarrier signals can be recovered using techniques described in the application and are immune to fiber dispersion induced fading.

A method and apparatus for estimating fiber dispersion in an optical communication system including transmitting an optical signal carrying a unique word along an optical communication path, receiving the optical signal carrying the unique word from the optical communication path, producing an electrical signal corresponding to the received unique word, and processing the electrical signal corresponding to the received unique word to produce an estimate of the fiber dispersion in the optical communication system.

Systems and method of compensating for transmission impairment are disclosed. One such method comprises receiving a wavelength-division multiplexed optical signal. The received optical signal has been distorted in the physical domain by an optical transmission channel. The method further comprises propagating the distorted optical signal backward in the electronic domain in a corresponding virtual optical transmission channel. The backward propagation fully compensates for fiber dispersion, self-phase modulation, and cross-phase modulation (XPM) and partially compensates for four-wave mixing (FWM).

The invention provides a new method for precisely measuring optical fiber length by adoption of a vector network analyzer. The vector network analyzer is introduced, the phase zero making technology is combined, and therefore the defects that a back scattering method is poor in measuring precision, many in interference factor of a pulse method, short in measuring distance and the like are overcome, and the shortcomings that a traditional phase shifting method is narrow in frequency measuring range of a phase meter and poor in phase measuring stability are overcome; in the long-distance transmission of optical fibers, due to widening of optical pulses caused by optical fiber dispersion, time amount of optical pulse delay is replaced with the phase variable quantity generated by measuring optical signals in transmission in the optical fibers, the accuracy value of the optical fiber length is calculated, and therefore the influence of the optical fiber dispersion on a measuring result of the optical fiber length is reduced.

Link robustness, chromatic dispersion and polarization mode dispersion (PMD) immunity can be improved in fiber optical system by using a method for receiving an optical double sideband signal over an optical fiber system, comprising the steps of splitting the received optical double sideband signal into an upper sideband signal and a lower sideband signal, photodetecting the upper sideband and the lower sideband, equalizing the photodetected upper sideband signal and the lower sideband signal, and combining the equalized upper sideband signal with the equalized lower sideband signal. While PMD compensation is envisioned as a major application, one may also use the method and system for chromatic dispersion compesation or dispersion slope compensation in high bit rate systems, i.e. using dispersion compensation fiber (DCF) for coarse compensation and diversity receiver with electrical equalizer for fine tuning.

The invention relates to a fiber bragg grating demodulating device and method based on chromatic dispersion Mach-Zehnder interferometry. The fiber bragg grating demodulating device comprises a broadband light source, a narrow-linewidth sweep frequency laser device, a first photoswitch, an optoisolator, a semiconductor optical amplifier, a pulse digital signal source, an optical circulator, a second photoswitch, a reference grating, a sensing grating array, a Faraday rotating mirror, a first optical coupler, dispersion compesation fiber, monomode optical fiber, a second optical coupler, a photoelectric detector set, a data collecting card and an upper computer. The optical fiber dispersion effect and the traditional Mach-Zehnder interferometry are combined to construct chromatic dispersion Mach-Zehnder interferometry, optical path difference caused by the chromatic dispersion effect is used for achieving phase sensibilization, interference information of all gratings in a quasi-distributed fiber bragg grating array is recorded through high-speed time-domain optical pulses, a multi-phase demodulating technology is used for processing time domain interference signals, high-sensitivity and high-speed demodulation of the fiber bragg grating array is achieved, and the demodulating device has the advantages of being high in interference resistance and capable of achieving distributed measurement.

The invention discloses an SVM (support vector machine)-based nonlinear damage removing device of a coherent optical communication system. The device disclosed by the invention comprises a chromatic dispersion compensating unit, an SVM array unit, an SVM training unit, a logical processing unit and a sign deciding unit, wherein the chromatic dispersion compensating unit is used for compensating optical fiber dispersion applied to receiving signals; the SVM array unit is used for carrying out binary classification on the receiving signs according to different classification rules via a plurality of SVMs; the SVM training unit is used for defining a classification hyper plane of each SVM in the device according to a certain training sequence; the logical processing unit is used for performing logical operation on classification results of each SVM to acquire type signs corresponding to the signals; and the sign deciding unit is used for decoding the signal type signs to binary sequences corresponding to the signals. The SVM-based nonlinear damage removing device of the coherent optical communication system can be used for removing optical nonlinear damage to the signals by virtue of the nonlinear classification characteristic of the SVM. Without requirements of knowing the nonlinear characteristic of optical fibers, the nonlinear damage removing effect is ensured and the processing complexity is only decided by the number of a small quantity of support vectors.

A dispersion and loss spectrum auto-correction distributed optical fiber Raman temperature sensor has a dual fiber pulsed laser module with dual Raman wavelength shifts. The laser module is composed of a power supply (11), an electronic switch (12), a primary laser (13) and a secondary laser (14), a first combiner (15), a bidirectional coupler (16), a multimode fiber (17), an integrated optical fiber wavelength division multiplexer (18), a second combiner (19), a direct detection system (20), a signal collection and processing system (21) and a display (22). The sensor uses two light sources that have two Raman wavelength shifts, wherein the central wavelength of backward anti-Stokes Raman scattering peak of the primary light source coincides with that of the backward Stokes scattering peak centre wavelength of the secondary light source, and the time domain reflection signal of the one-way optical fiber Rayleigh scattering is deducted. Based on the optical fiber Raman scattering temperature measurement principle, the dispersion and loss spectrum auto-correction method and the optical time domain reflection principle, the optical fiber dispersion and the loss spectrum can be self-corrected, and the random power loss caused by bending and stretching in installation can also be auto-corrected.

The invention relates to a receiving end equilibrium method and system based on frequency domain communication channel estimation. The method comprises the following steps: training sequences with flat spectrum characteristics are inserted into signals at the transmitting terminal, the received training sequences are transformed into the frequency domain at the receiving end through fast Fourier transformation, the transfer function of a communication channel is obtained through dividing the ideal spectrum corresponding to the frequency domain, and then the reciprocal of the transfer function is taken and is transformed into the time domain through the fast Fourier transformation so as to obtain time domain filter tapping coefficient; thereafter, filtering is performed to data signals in the time domain through utilizing the time domain filter tapping coefficient, so that signaling equilibrium is realized. The system includes various modules realizing the corresponding functions. The method and the system combine characteristic of avoidance in cost caused by inserting cyclic prefix/suffix of time domain equilibrium and the characteristic of simple communication channel estimation of the frequency domain equilibrium; on the condition that the optical fiber dispersion is smaller or the dispersion is compensated by other arithmetic, the phase noise compensation is efficiently performed; the arithmetic complexity is small; the calculation time can be saved.

Embodiments of the present invention generally relate to high energy, ultrashort pulses from a net normal dispersion ytterbium fiber laser with an anomalous dispersion higher-order mode fiber. More specifically, embodiments of the present invention relate to a fiber oscillator with all-fiber dispersion compensation delivering pulse parameters comparable to solid-state oscillators having good compensation of higher order dispersion and intracavity nonlinearities. In one embodiment of the present invention, an oscillator comprises a length of single mode fiber and a length of higher-order mode fiber, where the group delay dispersion (GDD) of the higher-order mode fiber is chosen to match 50% or more of the GDD of the single mode fiber; wherein a third-order dispersion of the oscillator matches a nonlinear phase buildup in a cavity of the oscillator, and the nonlinear phase buildup is dependent upon the pulse energy of the oscillator.

The invention discloses a device and method for realizing microwave frequency conversion by utilizing a double-drive DPMZM, relates to the technical field of microwaves and the technical field of optical communication, and is mainly used for frequency conversion of a microwave signal. The method comprises a light source, a radio-frequency signal source, an intrinsic signal source, an electric shunt device, a phase shifter, the double-drive DPMZM and a photoelectric detector (as drawing show). Double-sideband modulation of a radio-frequency signal and a single-sideband modulation of an intrinsic signal are respectively realized by utilizing the double-drive DPMZM; an optical carrier of an output signal of the double-drive DPMZM can be inhibited by reasonably setting a parameter; and, a frequency conversion signal can be obtained after the frequency of the output signal of the double-drive DPMZM is beaten through the photoelectric detector. The scheme has relatively high conversion efficiency; and furthermore, the power periodic fading due to optical fibre dispersion in a signal transmission process can be avoided.

An optical communications system comprises a transmitter, a receiver and an optical communications link between the transmitter and receiver. The transmitter comprises a current-driven directly modulated laser for providing a modulated optical signal and a current controller for controlling the current waveform applied to the laser. The current waveform applied to the laser is determined to compensate for the effects of the laser non-linearities and the fiber chromatic dispersion. This system applies pre-compensation to the directly modulated laser input current waveform to provide both pre-compensation for chromatic dispersion and compensation for the non-linearities of the directly modulated laser. These are two of the main limiting factors in providing a low cost high data rate and long reach optical communications system.

The present invention allows an operator to individually control the power level of each communication channel in a network without affecting other parameters of the channels. Each optical transmitter contains a voltage controlled variable optical attenuator which is controlled by a microcontroller to attenuate the optical communication signal to a desired level. The operator can adjust each transmitter separately to overcome the variability in the output optical power of each transmitter, the flatness of the WDM component, EDFA flatness, dispersion of the fiber, etc.

The invention discloses an apparatus and method for realizing instantaneous microwave frequency measurement by dual polarization modulators. The invention relates to the technical fields of microwave and optical communication, and is mainly used for the measurement of microwave signal frequency. The method, as shown in the drawing, includes a light source, a signal source, the dual polarization modulators, a single-mode fiber, a coupler, a polarization controller, a polarizer, and a photoelectric detector, and the microwave signals of the unknown frequency generated by the signal source are modulated by the dual polarization modulators to obtain polarization multiplexing signals. Through the fiber dispersion, the polarization multiplexing signals are divided into two paths, one is maintained at the same polarization state, the other one is converted into a linear polarization signal through the polarization controller and the polarizer. The photoelectric detector detects the two signals, measures the power values and establishes the power comparison functions. According to the correspondence relation, the measured frequency can be estimated. By changing the polarization state of one signal, the measurement scope can be adjusted, the realization is simple, the resolution is high, and the measurement error is less.

The invention relates to a terahertz time domain spectral radiation and detecting device. In the terahertz time domain spectral radiation and detecting device, femto second laser which is emitted from a femto second laser device is divided into pump light and probe light. Furthermore the pump light and the probe light are transmitted in a hollow photonic crystal fiber. In the terahertz time domain spectral radiation and detecting device, through reasonably selecting central wavelength of a pulse which is output from the femto second laser device, a two-order fiber dispersion which is generated in transmission of a laser pulse in the hollow photonic crystal fiber is a negative value, and the two-order fiber dispersion is neutralized with a positive dispersion which is generated by an optical isolator, a beam splitter, etc. The terahertz time domain spectral radiation and detecting device prevents inconvenience and cost of grating or a pair of prisms for compensating the dispersion. Secondly, because the pulse is basically transmitted in the hollow photonic crystal fiber, the energy of the pulse with pulse width of dozens of femto seconds can reach several hundreds of nanojoules. Furthermore pulse width increase because of self phase modulation is prevented. A high-energy laser pulse is supplied for a terahertz radiation device and a detecting device.

The invention relates to a microwave same-frequency signal interference suppression and down-conversion receiving device and method, and belongs to the technical field of microwave signal processing.The microwave same-frequency signal interference suppression and down-conversion receiving device comprises a laser, polarization multiplexing DP-MZMs (dual-parallel Mach-Zehnder modulators) , a received signal simulator, an interference signal simulator, a local oscillator signal generator, a DC power supply, a polarization controller, a polarizer, an optical amplifier and a photoelectric detector, wherein the DP-MZMs are DP-QPSK (dual-polarization quadrature phase shift keying) modulators, one DP-MZM of the DP-QPSK modulators is used for suppressing an interference signal in received signalsin an optical domain and coupled with a local oscillator light signal generated by the other DP-MZM of the DP-QPSK modulators, and photovoltaic conversion is conducted at the photoelectric detector so that optical down conversion of the received signals is achieved. Same-frequency interference suppression and optical down-conversion of the received signals can be achieved simultaneously, and influence of optical fiber dispersion on same-frequency interference suppression level and power of the received signals in the signal optical fiber transmission process is reduced.

The invention pertains to optical fiber transmission systems, and is particularly relevant to transmission of large volumes of data over long distances at high rates. An improved apparatus and method for measuring dispersion in a fiber span is disclosed. In particular, the invention teaches a highly accurate technique for measuring the fiber dispersion at a single wavelength. Transmitter and receiver structure and data processing algorithms are disclosed. An improved apparatus and method for measuring dispersion in a fiber span. In particular, the invention teaches a highly accurate technique for measuring the fiber dispersion at a single wavelength. Transmitter and receiver structure and data processing algorithms are disclosed.

The invention discloses a laser frequency scanning interferometer dispersion phase compensation method based on a focusing definition evaluation function, which relates to a high-resolution laser frequency scanning interferometer dispersion compensation method and aims at solving the problems that the in the existing method, the measurement resolution is low, and influences on measurement signals need to be compensated. A measurement signal beat frequency model in a high-resolution laser frequency scanning interferometer fiber dispersion condition is built; and a phase method is adopted to compensate fiber dispersion of the measurement signal beat frequency model: (1) the measurement signal is multiplied by a complex phase compensation item, and through adjusting a dispersion compensation coefficient, dispersion phase distortion in the measurement signal is compensated; (2) a focusing definition evaluation function is put forward to serve as a standard to judge whether phase distortion in the measurement signal beat frequency model obtains compensation; and (3) trichotomy is adopted to find the best dispersion compensation coefficient to compensate the fiber dispersion of the high-resolution laser frequency scanning interferometer. The method of the invention is applied to the field of high-resolution laser frequency scanning interferometers.

When a high data rate optical signal travels through a fiber link, its high frequency components tend to experience higher losses due to fiber dispersion (modal and/or chromatic). The loss of high frequency components causes the optical eye to close and the sensitivity to degrade. Disclosed is an apparatus and method for an optical transmitter that relies on anti-causal pre-emphasis to counteract the effect of relaxation oscillation, and therefore brings improvements to optical eye symmetry and mask margin (MM).

The invention relates to a device and method for estimating optical fiber chromatic dispersion through a low-speed coherent detection and neural network, and belongs to the technical field of the communication. The method comprises the following steps: step one, performing low-speed detection on an optical signal after being transmitted through an optical fiber link by using a low-speed detectionunit, producing a data set through a data preprocessing unit, and dividing the data set into a training set and a test set by using a data set classification unit; step two, constructing a neural network unit, setting a neural network parameter, and training the constructed neural network by using the training set produced in the step one; step three, estimating the chromatic dispersion of the test set divided in the step one by using the neural network unit trained in the step two, wherein the estimation method comprises the step of performing weighted average by using the output of the neural network unit and the reference chromatic dispersion. The chromatic dispersion estimation on the signal sampled in low rate is realized, the receiving end cost is greatly reduced, the defect that thecyclic training sequence signal is required for performing chromatic dispersion estimation is solved, and an operation of changing a transmitting end is unnecessary.