62 results about "Polarization scrambling" patented technology

A polarization multiplexing transmitter which generates polarization-multiplexed signals which are arbitrarily polarization-scrambled at high speed, without adding a polarization modulator and a polarization scrambler. In the transmitter, an orthogonally polarized signal generator includes two optical modulators which modulate the electric fields of optical signals and generate two optical signals with mutually orthogonal polarized waves. The transmitter includes electric field mappers which convert two data strings into electric field signals, polarization mappers which give different polarized waves to the two signals, polarization rotators which rotate the polarized waves of the signals uniformly, a polarization multiplexer which multiplexes the two polarization-rotated signals, a polarization demultiplexer which demultiplexes the multiplexed signal into polarized wave components of optical signals generated by the orthogonally polarized signal generator, and a driver. The optical modulators are driven to make the two demultiplexed electric field signals consistent with the electric fields of optical signals modulated by the modulators.

The present invention discloses a fiber Bragg grating sensor system. The system according to the present invention comprises a wavelength tunable laser; a coupler for splitting output light from the wavelength tunable laser into two directions; a reference wavelength generating unit for receiving one directional output light from the coupler and for generating reference wave-lengths and an absolute reference wavelength in order to measure real-time wavelengths of the wavelength tunable laser; a fiber Bragg grating array for receiving the other directional output light from the coupler and for reflecting lights at each of the wave-lengths of the grating therein; a fiber grating wavelength sensing unit for measuring the time when each of the reflected lights from the fiber Bragg grating array is detected; a signal processing unit for figuring wavelength variation information with the use of the measured signals from the reference wavelength generating unit and for obtaining each of wavelengths of the detected lights from the fiber grating wavelength sensing unit; and a laser wavelength control feedback unit for applying AC voltage and DC voltage to the wavelength tunable filter in the wavelength tunable laser. Also, polarization dependency in the sensor system can be removed further installing a depolarizer or a polarization scrambler at the output end of the wavelength tunable laser. By applying the present invention, measurement accuracy of the grating sensor system 20 can be improved due to enhanced wavelength stability and suppression of polarization dependency. Therefore, the fiber Bragg grating sensor system based on the present invention would replace conventional structure / construction diagnosis systems.

The invention provides a system and method for secure communication that involve encoding and transmitting an optical orthogonal frequency division multiplexed (OFDM) signal. Each subcarrier of an optical carrier in OFDM transmission is modulated with data individually, and a variety of data format are used, such as QPSK, OOK, QAM, etc. The data format of each subcarrier may change in time according to a predetermined pattern. An optical receiver uncovers the data transmitted via an optical link. It is based on a coherent optical receiver and a digital signal processing (DSP) unit. A key to the data mapping and change is transmitted via the same optical link or by a separate channel. In one embodiment, the key is transmitted using quantum encryption technique. Besides subcarrier modulation encoding, the system may provide additional layers of security: optical carrier frequency hopping and polarization scrambling.

The present invention provides for the detection and display of polarization scrambling tissue without resolving the polarization state of the backscattered imaging beam. In one embodiment, we illuminate the tissue using two different polarizations. A first polarization determines a first image of high intensity while the second polarization determines a second image of low intensity. Comparison and combination of the first and second images determines tissue which scrambles the polarization in neighbouring detection cells.

A wavelength division multiplexing transmission system in which a first channel using an intensity modulation scheme and a second channel using a phase modulation scheme are present includes a polarization scrambler inserted into a signal path of either one of the first channel and the second channel to perform polarization scrambling, and a drive unit configured to drive the polarization scrambler at frequency greater than or equal to a value defined as: (bit rate of phase modulated signal) / (error correction frame length)×2.

The invention discloses a continuous variable quantum key distribution system based on Faraday-Michelson interference. A transmitting end is used for generating a pulse light source which is in accordance with the parameters such as repetition frequency, pulse width and so on, and modulating regular components X and P of a signal light; a communication channel is a light propagation channel, and used for transmitting the signal light modulated by the transmitting end and an unmodulated local oscillation light to a receiving end; a receiving end demodulation module realizes measurement and component selection: X or P; and a receiving end zero-difference detection module is used for performing detection processing, and acquiring modulation information data of a signal. The continuous variable quantum key distribution system based on the Faraday-Michelson interference provided by the invention introduces two unequal-arm Faraday-Michelson interference rings, and with the help of a Faraday polarization rotating mirror, the polarization scrambling in a pulse round trip process can be self-compensated, which is beneficial to improving the stability of the system and not easily interfered by polarization; and besides, long distance stable quantum key distribution can be realized in combination with an existing detection technology and a post-processing algorithm.

An apparatus for monitoring polarization-mode dispersion and chromatic dispersion in optical networks in accordance with the present invention comprises; an optical distributor for distributing input optical signals, a first light receiver for photoelectrically converting the optical signals distributed by the distributor, a second light receiver for photoelectrically converting the optical signals to measure the average power of the optical signals distributed by the distributor, a filter for filtering output signals from the first light receiver, a power meter for measuring the frequency band of the optical signals filtered by the filter, an analog-to-digital (A / D) converter for converting the analog signals from the first and the second receivers into digital signals, a microprocessor for monitoring the polarization-mode dispersion and the chromatic dispersion of the optical signals by means of the digital signals from the A / D converter, and further a polarization scrambler in the optical signal sending-end.

To generate light with the degree of polarization zeroed and the spread of an optical spectrum suppressed even with temporal overlapping between optical pulses each of which is polarized orthogonally to the succeeding pulse, a polarization scrambler includes an optical pulse generator that generates optical pulses with an intensity waveform repetition period T / 2 and an electrical field repetition period T in which the same intensity waveform is repeated every repetition period T / 2 and in which phase is inverted every repetition period T / 2, and an orthogonal polarization delay unit which receives each of the optical pulses, separates the optical pulse into two optical pulses with orthogonal states of polarization, and relatively shifts the temporal position of one of the two optical pulses from that of the other optical pulse by (2n−1)T / 4 (n is a natural number) to generate light in which each pulse is polarized orthogonally to a succeeding pulse.

The invention provides a measurement device independent quantum key distribution system and method. Polarization scrambling is carried out on polarization states of light pulse signals or light quantum signals at quantum state preparation sending ends, so the polarization states of the light pulse signals or the light quantum signals are uniformly distributed on the surface of a Poincare sphere, and the two ways of polarization scrambled light pulse signals or light quantum signals are transmitted to a measuring end for Bell state projection measurement through independent optical channels. At the measuring end, each way of light quantum signal is separated into two orthogonal polarization components, the polarization directions of the two ways of orthogonal polarization components are the same, and the Bell state projection measurement is carried out on the polarization components with the same polarization direction.

An optical signal of an optical transmission part is brought into a high-speed polarization scrambling state by a polarization scrambling part, and transmitted to en optical fiber transmission line as the optical signal from the optical transmitter. The optical signal passing through the optical fiber transmission line is inputted to an optical receiver. The optical signal inputted to the optical receiver is converted into an electric signal by a polarization dependent photoelectric detection part. The converted electric signal is inputted to a digital signal processing part having a polarization scrambling cancel part of canceling the polarization scrambling state by a digital signal processing operation. At the digital signal processing part, the polarization scrambling state of the electric signal is canceled, and a data signal is outputted.

In a repeaterless optical fiber transmission system, the invention proposes providing polarization scrambling means. This makes it possible to limit the amount of energy that is transferred by the Raman effect, while increasing the amount of power that can be injected into the link. The invention is equally applicable to the lightwaves used for carrying information and to the lightwaves used for pumping.

A polarization scrambler has a polarization state rotating unit rotating the polarization state of a signal light, and a rotation speed controlling unit controlling the rotation speed of the polarization state in the polarization state rotating unit on the basis of the speed and scheme of modulation of the signal light, and the value of polarization mode dispersion of a transmission path on which the signal light is to be transmitted. Degradation of the transmission quality due to PMD is more mitigated than the known techniques.

A small-spot imaging, spectrometry instrument for measuring properties of a sample has a polarization-scrambling element, such as a birefringent plate depolarizer, incorporated between the polarization-introducing components of the system, such as the beamsplitter, and the microscope objective of the system. The plate depolarizer varies polarization with wavelength, and may be a Lyot depolarizer with two plates, or a depolarizer with more than two plates (such as a three-plate depolarizer). Sinusoidal perturbation in the resulting measured spectrum can be removed by data processing techniques or, if the depolarizer is thick or highly birefringent, the perturbation may be narrower than the wavelength resolution of the instrument.

A system and method for multi-channel PMD / PDL / PDG mitigation, the system including polarization scramblers adapted to vary the state of polarization of an optical signal propagated through the system to effectively vary the polarization mode dispersion experienced by the signal during each burst-error-correcting-period of the forward error correction used in the system.

An apparatus for measuring a set of frequency-resolved states of polarization (SOP) of an optical signal includes a local oscillator (LO), a polarization scrambler, a coupler for mixing the polarization-scrambled signal with the optical signal to produce a heterodyned signal with a radio frequency (RF) component, and an analyzer for passing a fixed polarization component and resolving the polarization and frequency from the RF component. The apparatus is used for measuring, monitoring or compensating the polarization mode dispersion (PMD) in a working channel of an optical telecommunication system. A method for measuring frequency-resolved SOP of an optical signal includes tuning and polarization-scrambling a local oscillator (LO), mixing the scrambled LO with the optical signal, and resolving the RF signal in frequency and polarization. The method is applied to measure and monitor PMD in a working optical channel, and to dynamically compensate for the PMD.

The invention provides a system and method for secure communication that involve encoding and transmitting an optical orthogonal frequency division multiplexed (OFDM) signal. Each subcarrier of an optical carrier in OFDM transmission is modulated with data individually, and a variety of data format are used, such as QPSK, OOK, QAM, etc. The data format of each subcarrier may change in time according to a predetermined pattern. An optical receiver uncovers the data transmitted via an optical link. It is based on a coherent optical receiver and a digital signal processing (DSP) unit. A key to the data mapping and change is transmitted via the same optical link or by a separate channel. In one embodiment, the key is transmitted using quantum encryption technique. Besides subcarrier modulation encoding, the system may provide additional layers of security: optical carrier frequency hopping and polarization scrambling.

A polarization scrambler unit includes a plurality of polarization scramblers, a switching unit for coupling one of the polarization scramblers to a transmission line fiber, a detection unit for detecting an output signal from the polarization scrambler coupled to the transmission line fiber, and a controlling unit for switching, via the switching unit, between the polarization scramblers and another polarization scrambler whenever a false output signal is detected by the detection unit. Thus, the polarization scrambler unit has a redundant structure.

Provided is an erbium-doped fiber amplifier reducing transient phenomena of a signal-to-noise ratio and a bit error rate in a dynamic wavelength division multiplexing system and an amplifying method using the erbium-doped fiber amplifier. The erbium-doped fiber amplifier includes: a polarization scrambler modulating a polarization state of an input signal to remove a polarization of the input signal; an amplifier amplifying the input signal from which the polarization has been removed; a detector reading powers of input and output signals of the amplifier; and an automatic gain controller controlling currents of the pump LDs according to the powers of the input and output signals read by the detector 1630 to maintain the gain even if the power of input signal changes.

An apparatus for measuring a set of frequency-resolved states of polarization (SOP) of an optical signal includes a local oscillator (LO), a polarization scrambler, a coupler for mixing the polarization-scrambled signal with the optical signal to produce a heterodyned signal with a radio frequency (RF) component, and an analyzer for passing a fixed polarization component and resolving the polarization and frequency from the RF component. The apparatus is used for measuring, monitoring or compensating the polarization mode dispersion (PMD) in a working channel of an optical telecommunication system. A method for measuring frequency-resolved SOP of an optical signal includes tuning and polarization-scrambling a local oscillator (LO), mixing the scrambled LO with the optical signal, and resolving the RF signal in frequency and polarization. The method is applied to measure and monitor PMD in a working optical channel, and to dynamically compensate for the PMD.

A polarization scrambler has a polarization state rotating unit rotating the polarization state of a signal light, and a rotation speed controlling unit controlling the rotation speed of the polarization state in the polarization state rotating unit on the basis of the speed and scheme of modulation of the signal light, and the value of polarization mode dispersion of a transmission path on which the signal light is to be transmitted. Degradation of the transmission quality due to PMD is more mitigated than the known techniques.

The present invention provides for the detection and display of polarization scrambling tissue without resolving the polarization state of the backscattered imaging beam. In one embodiment, we illuminate the tissue using two different polarizations. A first polarization determines a first image of high intensity while the second polarization determines a second image of low intensity. Comparison and combination of the first and second images determines tissue which scrambles the polarization in neighboring detection cells.

A polarization scrambler and associated method for polarization scrambling are provided, wherein light is passed through a retarder whose eigen modes and delay vary with time and which is driven with alternating signals at two harmonic frequencies. One exemplary embodiment with an electrooptical wave plate operates with a horizontal or vertical input polarization and supplies output polarizations which vary with time and have uncorrelated normalized Stokes parameters. The polarization scrambler which is produced can be used in devices for detection of polarization mode dispersion.

An apparatus for monitoring polarization-mode dispersion and chromatic dispersion in optical networks in accordance with the present invention comprises; an optical distributor for distributing input optical signals, a first light receiver for photoelectrically converting the optical signals distributed by the distributor, a second light receiver for photoelectrically converting the optical signals to measure the average power of the optical signals distributed by the distributor, a filter for filtering output signals from the first light receiver, a power meter for measuring the frequency band of the optical signals filtered by the filter, an analog-to-digital (A / D) converter for converting the analog signals from the first and the second receivers into digital signals, a microprocessor for monitoring the polarization-mode dispersion and the chromatic dispersion of the optical signals by means of the digital signals from the A / D converter, and further a polarization scrambler in the optical signal sending-end.

A polarization scrambler, and associated method for polarization scrambling, is provided wherein light is passed through a time-variant retarder. At least after upstream connection or downstream connection of a time-invariant retarder, this time-variant retarder may be represented as a retarder with eigen modes which are uniformly distributed on the Poincaré sphere and with a delay of 5π / 6. An exemplary embodiment contains only two electro-optical wave plates, which are actuated by alternating signals containing harmonics. The polarization scrambler which is produced is independent of the input polarization of the light and can be used in devices for detection of polarization mode dispersion.

System and method for multi-channel PMD / PDL / PDG mitigation, the system includes a polarization scrambler adapted to change the polarity of an optical signal propagating through the system during each burst error correction period of the forward error correction used by the system Polarization state in order to effectively change the polarization mode dispersion experienced by the signal.

The invention discloses a method for detecting the phase type defect of an extreme ultraviolet mask based on polarization changes of scattered light. According to the method, an apparatus for detecting the phase type defect of the extreme ultraviolet mask based on the polarization changes of scattered light is arranged; a surface type information database is built by using a finite difference time-domain method; an elliptic polarization scattering measurement method is employed for acquiring information about polarization scrambling changes; a weighed least square regression method is used for processing polarization scrambling information introduced into the database; so the contour information of the defect is eventually obtained. The method has the characteristics of high detection precision, good defect identification capability, convenience and rapidness.

An optical signal of an optical transmission part is brought into a high-speed polarization scrambling state by a polarization scrambling part, and transmitted to en optical fiber transmission line as the optical signal from the optical transmitter. The optical signal passing through the optical fiber transmission line is inputted to an optical receiver. The optical signal inputted to the optical receiver is converted into an electric signal by a polarization dependent photoelectric detection part. The converted electric signal is inputted to a digital signal processing part having a polarization scrambling cancel part of canceling the polarization scrambling state by a digital signal processing operation. At the digital signal processing part, the polarization scrambling state of the electric signal is canceled, and a data signal is outputted.

A receiver (10) for an optical signal containing a time jitter and a time-varying distortion caused by a periodic polarization scrambled signal comprises at least one decision gate (11) and a clock recovery module (13) providing a clock signal (C) recovered from the optical signal to the at least one decision gate (11). The receiver (10) further comprises a scrambling frequency generator (16) synchronized to the scrambling frequency and phase of the polarization scrambled signal, a jitter function generator (17) generating a clock phase control signal (Δφb) reproducing the time jitter, and at least one clock phase modulator (14) modulating the phase of the clock signal (C) according to the clock phase control signal (Δφb).

A multi-wavelength optical signal copropagates through a fiber-optic communication link with a continuous-wave ancillary wavelength having an unknown state of polarization (SOP), which is scrambled periodically in time. The instantaneous value of polarization dependent loss (PDL) in the ancillary wavelength is monitored in real time, and is used as an error signal to adjust at least one polarization controller. Polarization scrambling is performed by periodically changing the SOP with time, such that the polarization-scrambled optical signal covers approximately an entire Poincaré sphere surface, preferably uniformly, during each time period. At an optical node between fibers, an adjustable PDL compensator contains two ordered pairs each consisting of one polarization controller and one optical element introducing fixed PDL.