Abstract: According to an embodiment, a semiconductor device includes an analog/digital conversion unit, a pulse width modulation unit outputting a transmission signal, the transmission signal being a pulse pattern corresponding to a digital signal output from the analog/digital conversion unit, a reference signal generation unit generating a reference signal, the reference signal being a fixed pulse pattern. The device includes a first control unit selecting one of the transmission signal and the reference signal, a light emitting element drive unit outputting a drive current based on the transmission signal or the reference signal, a light emitting element driven by the light emitting element drive unit. The device includes an optical receiving unit converting the optical signal into a voltage signal, and a demodulation unit demodulating the voltage signal into a digital signal based on the transmission signal or the reference signal.

Abstract: A driver for shaping a drive signal includes a pre-emphasis circuit, an offset adjustment circuit, and an amplifier. The pre-emphasis circuit symmetrically emphasizes a rising edge portion and a falling edge portion of the drive signal. The offset adjustment circuit applies a direct-current offset to the drive signal. The amplifier amplifies the drive signal with the direct-current offset adjusted by the adjustment circuit. The amplifier has an input-output characteristic with a nonlinear portion. The offset adjustment circuit adjusts the direct-current offset so that the drive signal is amplified in the nonlinear portion.

Abstract: A distortion compensation circuit compensates for distortion generated by one or more non-linear elements such as a laser device and may include a primary signal path for carrying an input signal and one or more secondary signal paths for generating distortion. The distortion compensation circuit may also include one or more controllable phase inverters on at least one of the paths. For example, the secondary signal path may include a distortion generator to produce distortion products from the input signal and a signal controlled phase inverter that inverts the phase of the distortion products. The distortion generator and phase inverter may be combined as an invertible distortion generator. The phase inversion may be controlled in response to a phase inversion control signal generated based on one or more parameters such as temperature.

Abstract: To efficiently apply jitter to an optical signal using a simple configuration, provided is an optical signal output apparatus that outputs an optical pulse pattern signal including jitter, the optical signal generating apparatus comprising a light source section that outputs an optical signal having an optical frequency corresponding to a frequency control signal; an optical modulation section that modulates the optical signal output by the light source section, according to a designated pulse pattern; and an optical jitter generating section that delays an optical signal passed by the optical modulation section according to the optical frequency, to apply jitter to the optical signal.

Abstract: 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.

Abstract: An optical receiver comprising a frontend configured to receive an optical signal and convert the optical signal into a plurality of digital electrical signals comprising a plurality of spectrally shaped subcarrier signals carrying symbol mapped data information, and a digital signal processor (DSP) unit coupled to the frontend and configured to receive the digital signals from the frontend, demulitplex the digital signals into the subcarrier signals, and compensate chromatic dispersion (CD) for each of the subcarrier signals by applying an equalizer, wherein each of the subcarrier signals is associated with a unique tone frequency and a unique spectral shape. Also disclosed is an optical transmitter comprising a digital signal processor (DSP) unit configured to map data symbols onto a plurality of electrical subcarrier signals that are non-overlapping and spectrally shaped in a frequency domain.

Abstract: A system and method for optimizing an optical RF photonic link system is presented. The system comprises a modulator subsystem in which nonlinear response is compensated by an envelope precompensation method and employs an optical filter to suppress optical carriers and extract modulated sidebands, an optical amplifier, and an array of photodetectors, each having a plurality of pairs of diodes. The modulator subsystem performs optical filtering on the signal, the signal is amplified by the optical amplifier and sent to the array of photodetectors. The optical amplifier can be an erbium doped fiber amplifier, or a phase sensitive amplifier. The optical power can be delivered to each diode of the array of photodetectors via a photonic integrated circuit.

Abstract: A voltage generator (400) includes a resistor ladder including resistors (4000-4008) which divide a supplied voltage to generate a plurality of reference voltages, a resistor (4009) provided between a power supply voltage (VCC) and one terminal of the resistor ladder, and a resistor (4010) provided between a power supply voltage (VEE) and the other terminal of the resistor ladder.

Abstract: A vector sum phase shifter includes a 90° phase shifter (1) which generates an in-phase signal (VINI) and a quadrature signal (VINQ) from an input signal (VIN), a four-quadrant multiplier (2I) which changes the amplitude of the in-phase signal (VINI) based on a control signal (CI), a four-quadrant multiplier (2Q) which changes the amplitude of the quadrature signal (VINQ) based on a control signal (CQ), a combiner (3) which combines the in-phase signal (VINI) and the quadrature signal (VINQ), and a control circuit (4). The control circuit (4) includes a voltage generator which generates a reference voltage, and a differential amplifier which outputs the difference signal between a control voltage (VC) and the reference voltage as the control signal (CI, CQ). The differential amplifier performs an analog operation of converting the control voltage (VC) into the control signal (CI, CQ) similar to a sine wave or a cosine wave.

Abstract: Compensation for in-phase (I) and quadrature (Q) timing skew and offset in an optical signal may be achieved based on the correlation between derivatives of I and Q samples in the optical signal. The magnitude of the correlation between derivatives is measured to determine the presence of skew. Correlation between derivatives may be coupled with frequency offset information and/or with trials having additional positive and negative skew to determine presence of skew. Correlations are determined according to pre-defined time periods to provide for continued tracking and compensation for timing skew that may result from, for example, thermal drift.

Abstract: A method of protection switching between first and second transceivers where dispersion compensation is effected electrically in the transmitters. The method includes detecting, at the second transceiver, a signal failure of a signal transmitted from the first transceiver and, upon detecting the signal failure, signalling the first transceiver to change its compensation function. The signalling can be done by encoding overhead bits in a signal transmitted from the second to the first transceiver. Another method of protection switching includes both transceivers toggling alternate reception paths upon detecting a signal failure and changing their dispersion compensation function to that of their respective alternate path.

Abstract: In an optical transmission apparatus, a light-emitting laser varies its output wavelength when applied with a wavelength control signal for switching wavelengths. A wavelength controller outputs the wavelength control signal, and a filter unit subjects the wavelength control signal to a filtering process to remove high-frequency noise superimposed on the wavelength control signal. The filter unit stops the filtering process during the wavelength control and executes the filtering process during the operation.

Abstract: A distortion compensation circuit including a configurable delay may be used with one or more non-linear elements, such as a laser, to compensate for distortion generated by the non-linear element(s), for example, in broadband RF applications. Embodiments of the distortion compensation circuit may include a primary signal path with a configurable delay segment and a secondary signal path including at least one distortion generator. The configurable delay segment may be selectively configured to provide different delay settings to accommodate different RF loading conditions such that the delayed RF signal on the primary signal path is aligned with the distortion products generated on the secondary signal path when combined to form an RF signal with distortion compensation.

Abstract: A printed circuit board includes a substrate, a signal output circuit formed on the substrate for outputting a clock signal, a shield for covering the signal output circuit, a power supply wiring for connecting the signal output circuit and a power source, and a trap filter provided to the power supply wiring and provided inside the shield, for attenuating a frequency component corresponding to a frequency of clock signal. The trap filter includes a resonance circuit having one portion of the power supply wiring, an inner-layer wiring of the substrate located below the one portion of the power supply wiring, an inner-layer ground wiring of the substrate located below the inner-layer wiring, and a via hole for connecting the one portion of the power supply wiring and the inner-layer wiring.

Abstract: A fiber optic network reduces distortion present in modulated optical signals received at an optical receiver from an optical transmitter via a fiber optic link. The optical receiver analyzes a received modulated optical signal, where the wavelength of the received signal is periodically varied at the transmitter around a center wavelength over a wavelength range. Based on the analysis, the receiver generates a link transmission curve indicative of the optical power of the received signal over the wavelength range. The network disclosed herein subsequently uses the link transmission curve to reduce the distortion caused by misalignment between the operating wavelength of a transmitter laser and a peak power wavelength at the peak power of the link transmission curve. For example, the transmitter may adjust the laser operating wavelength based on a control signal received from the receiver and generated at the receiver based on the link transmission curve.

Abstract: A system and methods are provided for converting a first temporally short and spectrally broad optical pulse into a train of spectrally narrow and distinct optical pulses. This involves receiving, on a first I/O channel, the first optical pulse associated with a plurality of wavelengths and performing wavelength division demultiplexing on the first optical pulse at an optical unit housed on an optical chip to output a plurality of second optical pulses on different ones of a plurality of second I/O channels, each of the second optical pulses associated with a unique wavelength range from the first optical pulse. This also involves receiving the second optical pulses at loop mirrors in the second I/O channels, wherein the second I/O channels are patterned as waveguides in the optical chip and reflecting, at the loop mirrors, the second optical pulses back to the optical unit.

Abstract: Disclosed is an optical system including a polychromatic optical source emitting multiple transverse modes, an optical link having at least one portion of multimode optical fiber, and an optical device positioned between the optical source and the input of the multimode optical fiber. The optical device can modify the distribution of the energy coupling of the transverse modes emitted by the source in the propagation modes of the multimode optical fiber. The optical system makes it possible to use low-cost transverse multimode optical sources for producing high-bandwidth Ethernet transmission networks having excellent performance.

Abstract: An optical transmitter is provided for transmitting a wavelength multiplexed signal comprising an intensity modulation optical signal and a phase modulation optical signal through a transmission line. The optical transmitter includes a bit time difference given signal generator for generating at least two optical signals having a bit time difference therebetween, from the wavelength multiplexed signal. The optical transmitter further includes a wavelength multiplexed signal output unit to which at least two optical signals are input from the bit time difference given signal generator, and which generates and outputs a wavelength multiplexed signal in which the bit time difference was given between the phase modulation optical signal and the phase modulation optical signal.

Abstract: A method (10) of compensating phase noise in a coherent optical communications network. The method comprises: receiving a traffic sample (12); receiving an optical carrier and determining a phase noise estimate for the optical carrier (14); and removing the phase noise estimate from the traffic sample to form a phase noise compensated traffic sample (16).

Abstract: An optical transmission apparatus is provided with an optical filter on a transmission line between a reception end of a transmission line and an OSC receiver. The optical filter has transmission characteristics such as to pass main signal light and optical supervisory channel light (OSC light), and to cut off noise light contained in at least one end portion band on a short wavelength side and a long wavelength side of an OSC transmission band used for reception of OSC light. By such a configuration, even in a case where the OSC light is Raman amplified and transmitted, the influence of noise light due to Raman amplification can be reduced, and OSC light can be received reliably, enabling high dependability to be realized.

Abstract: A distortion compensation circuit with frequency detection may be used with one or more non-linear elements, such as a laser, to compensate for frequency-dependent distortion generated by the non-linear element(s), for example, in broadband multichannel RF applications. Embodiments of the distortion compensation circuit may include a frequency detector circuit that detects changes in frequency loading conditions in the distortion compensation circuit such that distortion compensation may be adjusted to compensate for distortion under different frequency loading conditions. In a multichannel RF system with multiple channel operation modes, for example, the frequency detector circuit may detect changes in the frequency loading condition as a result of changing operation modes.

Abstract: An apparatus and method for correcting for the polarization mode distortion of an optical signal is described. The optical data signal to be transmitted is processed by a switch configured to place the signal into a plurality of polarization states on a periodic basis. At the receiving end of the system, a portion to the signal is coupled to a polarimeter and the wavelength-dependent state of polarization (SOP) of the received signal determined for the plurality of polarization states imposed on the transmitted signal. The data for two of the transmitted polarization states is selected to be used as the basis for correcting the SOP so as to compensate for the wavelength dependence thereof. The corrections may be applied in an optical pulse shaper.

Abstract: An optical phase conjugator that can be deployed within a long-haul fiber-optic link of an optical WDM system to improve the system's tolerance to intra- and inter-channel nonlinear effects. In one embodiment, the optical phase conjugator has a digital signal processor configured to perform, in the digital electrical domain, a phase-conjugation transformation for various components of a WDM signal so that certain signal distortions imposed on that signal in the front portion of the fiber-optic link are reduced in the back portion of the link. Advantageously, the optical phase conjugator is flexibly configurable to employ an input-to-output carrier-frequency-mapping configuration that is most beneficial under particular operating conditions. mapping configuration that is most beneficial under particular operating conditions.

Abstract: Proposed is a light module (110) comprising at least two primary light sources (111,112,113) capable of emitting a primary color light. This allows the light module to emit light having intensity (Y) and color coordinates (x,y) through additive color mixing of the constituent primary colors. The light module further comprises an modulator (115) capable of modulating the primary light sources enabling embedment of data in the light emitted. The modulator (115) is arranged to modulate the color coordinates of the light emitted for embedding the data. This is especially advantageous as the sensitivity of the human eye to changes in color is lower than to changes in intensity. The invention thus advantageously allows embedding the data into the light emitted from the light modules (110) of an illumination system (100) without reducing the performance of its primary function as an aid to human vision.

Abstract: A method and system for generating multi-subcarriers is disclosed. Re-circulating frequency shifters—based on the frequency shifting in two cascading phase modulators—are used to generate 112 subcarriers with stable architecture since there is no direct current bias in phase modulators.

Abstract: The present invention provides a system, apparatus, and method for efficient optical amplification and transmission of a data-encoded optical signal within a networking device, such as a transmitter or receiver. In various embodiments of the invention, an optical duobinary signal or hybrid duobinary signal is generated and shaped in preparation for amplification of the optical signal by an SOA. The deleterious impact of SOA fast gain dynamics may be reduced by taking advantage of characteristics of a duobinary or hybrid duobinary signal (e.g., a relatively lower pulse amplitude and no phase encoded data) and shaping the optical duobinary pulse (e.g., smoothing amplitude swings within the signal and spectral compression).

Abstract: An apparatus for preventing collision of upstream signals is provided. The apparatus is suitable for a time division multiplexing (TDM) passive optical network (PON). The apparatus includes an optical coupler device, an optic-electron converter (O/E), a control system, and an optical signal switch module. The O/E is coupled to the optical coupler device, the control system is coupled to the O/E, and the optical signal switch module is coupled to the optical coupler device and the control system. The optical coupler device receives a first optical signal and splits the first optical signal into a second optical signal and a third optical signal. The O/E converts the second optical signal into a first electrical signal. The control system generates a control signal according to the first electrical signal. The optical signal switch module determines whether to stop the third optical signal from passing the apparatus according to the control signal.

Abstract: A distortion compensation circuit compensates for distortion generated by one or more non-linear elements such as a laser device and/or an optical fiber and may include a primary signal path for carrying an input signal and a secondary signal paths for generating distortion. The distortion compensation circuit may also include a controllable phase inverters and a tunable filter. For example, the secondary signal path may include a distortion generator to produce distortion products from the input signal and a signal controlled phase inverter that inverts the phase of the distortion products and a tunable filter that adjusts the phase of the frequency dependent distortion. The phase inversion and tunable filter may be controlled in response to control signals generated based on one or more parameters such as, for example, laser power, input RF channel loading, temperature, and fiber length.

Abstract: A device is provided for use with a dither tone signal and an information signal. The device includes a laser diode, an electro-optic modulator, a first filter and a second filter. The laser diode can output a first light signal, whereas the electro-optic modulator can transmit a second light signal. The first filter can generate a first filtered signal based on the information signal. The second filter can generate a second filtered signal based on the dither tone signal. The first light signal is based on the dither tone signal, the information signal and the first filtered signal. The second light signal is based on the first light signal, the information signal, the dither tone signal and the second filtered signal. The filtered signals reduce or cancel the undesired leaked/interfering signals.

Abstract: A communication device includes a signal correcting unit that performs signal correction on an electric signal indicating information to be transmitted to reduce signal deterioration occurring in transmission of the electric signal; a conversion unit that converts the electric signal subjected to the signal correction into a digital signal on which information indicating the signal correction performed by the signal correcting unit is superimposed; and a light-emitting element that emits light in accordance with the digital signal converted by the conversion unit.

Abstract: An optical transmitter includes: a pre-compensator calculating an electrical field of an optical signal subjected to an electronic pre-compensation with respect to an input digital signal; a parallelizer parallelizing the electrical field of the optical signal calculated by the pre-compensator; a plurality of optical modulators modulating an optical signal based on each of parallelized electrical fields of optical signals; and a time-division multiplexer time-division-multiplexing an optical signal output from the plurality of the optical modulators.

Abstract: A data transport card comprising an interface to receive high speed data streams from at least one client, and a pluggable conversion module which converts said data streams into optical data signals and couples these optical data signals into at least one wavelength division multiplexing channel for transport of said optical data signals via an optical fiber.

Abstract: A method includes delivering an electrical signal over an electrical conductor to a transmitter module, which includes a memory holding compensation values corresponding respectively to different conductor lengths. One or more of the compensation values is retrieved from the memory of the transmitter module, and a waveform of the electrical signal is modified responsively to the retrieved compensation values. The electrical signal having the modified waveform is transmitted using the transmitter module over a communication link.

Abstract: An arrangement for providing pulse compression at the output of an optical continuum source (advantageously used in spectral slicing applications) includes a section of higher-order mode (HOM) fiber configured to exhibit a predetermined dispersion in at least a portion of the predetermined wavelength range and an effective area greater than 40 ?m2, the dispersion of the HOM fiber selected to compensate for the dispersion introduced by the optical continuum source. The HOM fiber generates a compressed pulse output therefrom. An input mode converter is used to convert the created continuum from the fundamental mode associated with the conventional continuum sources to the higher-order mode(s) supported by the HOM fiber used to perform pulse compression. A bandpass filter is used to limit the bandwidth of the continuum signal to that associated with both the efficient conversion range of the mode converter and desired dispersion characteristic of the HOM fiber.

Abstract: A printed circuit board includes a substrate, a signal output circuit formed on the substrate for outputting a clock signal, a shield for covering the signal output circuit, a power supply wiring for connecting the signal output circuit and a power source, and a trap filter provided to the power supply wiring and provided inside the shield, for attenuating a frequency component corresponding to a frequency of clock signal. The trap filter includes a resonance circuit having one portion of the power supply wiring, an inner-layer wiring of the substrate located below the one portion of the power supply wiring, an inner-layer ground wiring of the substrate located below the inner-layer wiring, and a via hole for connecting the one portion of the power supply wiring and the inner-layer wiring.

Abstract: Methods and systems are provided for cancellation of chromatic dispersion combined laser phase noise. A method may include measuring a differential of laser phase noise using two optical pilot signals, the pilot signals each having a different optical frequency, or using an optical carrier and a pilot signal. The method may also include determining an approximate laser phase noise present in an optical system based on the measured differential of laser phase noise. The method may further include compensating for laser phase noise based on the determined approximate laser phase noise.

Abstract: Provided is a multi-value optical transmitter in which a DC bias may be controlled to be stabilized so as to obtain stable optical transmission signal quality in multi-value modulation using a dual-electrode MZ modulator. The multi-value optical transmitter includes: D/A converters for performing D/A conversion on first and second modulation data which are set based on an input data series, so as to generate a first and a second multi-value signal, respectively; a dual-electrode MZ modulator including phase modulators for modulating light from a light source based on the first multi-value signal and the second multi-value signal, so as to combine optical signals from the phase modulators to output the optical multi-value signal; an optical output power monitor for detecting average power of the optical multi-value signal; and a DC bias control unit for controlling a DC bias for the dual-electrode MZ modulator, so as to maximize the average power.

Abstract: A method reduces time-varying polarization crosstalk due to XPolM by transmitting multi-dimensional orthogonal constellations. Three variants of crosstalk-free constellations are provided: Grassmann constellations, unitary constellations, and rotation codes. The method uses the Grassmann constellations and the unitary constellations to deal with fiber nonlinearity by applying as a polarization-time coding. The rotation codes exploit a fiber channel characteristic to improve performance and to reduce computational complexity. The underlying orthogonality behind those constellations enables the receiver to decode it as if there is no polarization crosstalk. Moreover, the required computational complexity at the receiver is significantly reduced because neither crosstalk cancellers nor channel estimators are needed.

Abstract: In a method for transmission of digital data in an optical free-space transmission system in which a binary code sequence produced from the digital data is used to transmit amplitude-modulated light waves across an optical free space between a transmitter and a receiver, according to a first aspect, the binary code sequence is produced such that a modulation frequency of the light waves determined by the binary code sequence has a value of 70 Hertz. According to a second aspect, ‘t’ light waves are modulated with the binary code sequence and binary data are transmitted in blocks during a first time period, and non-modulated light waves are emitted during second time periods, wherein the light intensities of the time periods are selected so that the quantities of light transmitted in two periods correspond to predetermined quantities of light.

Abstract: Included are a first modulator, a second modulator, a first optical amplifier that amplifies an output of the first modulator at an amplification factor based on a first bias signal, a second optical amplifier that amplifies an output of the second modulator at an amplification factor based on a second bias signal, an optical phase adjuster that phase-rotates an output of the second optical amplifier, an optical multiplexer that multiplexes an output of the first optical amplifier with an output of the optical phase adjuster, and a second bias corrector that generates a first pulse signal and a second pulse signal, which are complementary to each other, and obtains a first bias value and a second bias value based on a change of strength of an output signal of the optical multiplexer. The first and second pulse signals are superimposed on the first and second bias signals, respectively.

Abstract: To reduce emission of an unintentional electromagnetic wave even if a frequency of a clock signal being output is high, a printed circuit board (10) includes: a substrate (101); signal output circuits (102 and 103) formed on the substrate (101), for outputting a clock signal; power supply wirings (109 and 110) for connecting the signal output circuits (102 and 103) and a power source; and trap filters (107 and 108) provided to the power supply wirings (109 and 110), for attenuating a frequency component corresponding to a frequency of the clock signal.

Abstract: A method of processing data is provided that includes receiving a plurality of binary electronic signals and generating an optical signal by a number of lasers that is equal to or greater than the number of binary electronic signals. The optical signal is generated at one of a plurality of intensity levels, and each intensity level represents a particular combination of bit values for the plurality of binary electronic signals. The optical signal is converted into an electronic signal having the plurality of intensity levels. An apparatus for processing data is provided that includes a plurality of lasers configured to emit light at a plurality of frequencies, and a plurality of modulators configured to receive a plurality of binary electronic signals and to modulate the light emitted by the lasers. An apparatus for transmitting data is provided that includes a photo receiver and an electronic signal generator.

Abstract: According to an embodiment, a semiconductor device includes an analog/digital conversion unit, a pulse width modulation unit outputting a transmission signal, the transmission signal being a pulse pattern corresponding to a digital signal output from the analog/digital conversion unit, a reference signal generation unit generating a reference signal, the reference signal being a fixed pulse pattern. The device includes a first control unit selecting one of the transmission signal and the reference signal, a light emitting element drive unit outputting a drive current based on the transmission signal or the reference signal, a light emitting element driven by the light emitting element drive unit. The device includes an optical receiving unit converting the optical signal into a voltage signal, and a demodulation unit demodulating the voltage signal into a digital signal based on the transmission signal or the reference signal.

Abstract: An improved precompensation circuit includes a greatly improved differentiator in the dispersion precompensation path, a preprocessor in the dispersion precompensation path for reducing f2?f1 type Composite Second Order (CSO) distortion, and a broadband phase shifter for compensating undesired vector interaction between the laser predistortion and dispersion compensation.

Abstract: A system for reducing clipping may be used between a multichannel RF source and a laser to reduce or correct clipping that might occur in the laser as a result of negative spikes or peaks in a multichannel RF signal. The system generally includes a clipping correction circuit that receives the multichannel RF signal and responsive to the RF signal, prevents one or more of the negative peaks in the RF signal from causing clipping. The clipping correction circuit may either detect an envelope of the RF signal and/or may detect one or more peaks in the RF signal. One or more negative peaks may be prevented from causing clipping by adjusting a bias current provided by a bias control circuit and/or by modifying the RF signal with one or more clipping correction pulses coinciding with one or more negative peaks.

Abstract: A method for multiscale sampling for wide dynamic range electro-optic receivers is presented. The method comprises obtaining a signal, reproducing the signal into first and second signals, scaling one signal with respect to the other, modulating both signals with the same modulation function, and utilizing the resulting vector response function to invert the response of the link over a greater dynamic range than would otherwise be possible with a single instance of the modulated signal. The sealed modulation response may be obtained by splitting the signal into two polarizations and utilizing a modulator having different response for the two polarizations, or by utilizing two modulators.

Abstract: Methods of transmitting an optical signal through optical fiber in a manner suppressing stimulated Brillouin scattering (SBS) are provided. A light beam emitted from a light source is modulated by driving either the light source or a separate phase modulator or both simultaneously with a separate high frequency signal dithered by one or more low frequency dithering signals of a frequency or frequencies lower than that of the high frequency signal. Thereafter, the light beam is further modulated externally with an RF information-carrying signal. The high frequency signal is at least twice a highest frequency of the RF information-carrying signal. The light beam modulated with the RF information-carrying signal is coupled into optical fiber.

Abstract: A WDM transmission apparatus to receive or relay WDM light in a WDM transmission system, includes a measuring unit configured to measure an optical level of each channel transmitted by the WDM light; an adjusting unit configured to adjust a resolution of the measuring unit; and a processing unit configured to obtain, for each channel, optical level information which represents an optical level respectively measured with a resolution corresponding to a bit rate of a transmission signal of each channel.

Abstract: A modulated optical system with cross-modulation compensation reduces or corrects cross-modulation that might occur at a target frequency range in a multichannel RF signal that modulates a laser. The system detects the cross-modulation, for example, by detecting an envelope of the RF signal or by detecting RF power fluctuations, generates a cross-modulation detection signal, filters the cross-modulation detection signal at the target frequency range, and imparts a compensating cross-modulation to the RF signal in response to the filtered cross-modulation detection signal.

Abstract: An optical transmission apparatus according to the present invention comprises: a plurality of optical modulating sections serially connected to each other via optical fibers; driving sections corresponding to the optical modulating sections; delay amount varying sections that provide variable delay amounts for modulating signals to be input to the driving sections, to adjust timing between drive signals to be provided for the optical modulating sections; temperature monitoring sections that monitor the temperature of each of the optical fibers and the like; and a delay amount control section that controls the delay amount in each of the delay amount varying sections based on the monitored temperatures.