Abstract: A signal transmission device drives a light-emitting element and outputs an optical signal depending on a data signal from an electronic device. The device includes an element driving portion which supplies a driving current to the light-emitting element, wherein the driving current is obtained by superimposing a modulation current on a bias current, the modulation current being dependent on the data signal indicating emitting information of the light-emitting element. A temperature compensation portion of the device controls the bias current and the modulation current depending on the temperature so that a temperature-current characteristic of the light-emitting element is reproduced based on the voltage which is dependent on the temperature and the voltage which is independent from the temperature, thereby performing current control depending on the temperature.

Abstract: The invention relates to a method for coupling a first and second laser (1, 2) having an adjustable difference of their pulse frequencies, which is not equal to zero, wherein the method comprises the following steps: derivation of a first harmonic signal and a signal of the Mth harmonic from the time progression of the light intensity of the pulses emitted by the first laser, mixing of the first harmonic signal and the signal of the Mth harmonic, in order to obtain a first mixed signal, derivation of a second harmonic signal and a signal of the Nth harmonic from the time progression of the light intensity of the pulses emitted by the second laser, mixing of the second harmonic signal and the signal of the Nth harmonic, in order to obtain a second mixed signal, wherein the first and second harmonic signal and the Mth and Nth harmonic are selected in such a manner that the frequencies of the first and second mixed signal are identical, wherein the method furthermore comprises regulation of the pulse frequen

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: The present disclosure provides a multi-carrier optical transmitter, receiver, transceiver, and associated methods utilizing offset quadrature amplitude modulation thereby achieving significant increases in spectral efficiency, with negligible sensitivity penalties. In an exemplary embodiment, an optical transmitter includes circuitry configured to generate a plurality of optical subcarriers, a plurality of data signals for each of the plurality of subcarriers, and a plurality of modulator circuits for each of the plurality of subcarriers, wherein each of the plurality of modulator circuits includes circuitry configured to offset an in-phase component from a quadrature component of one of the plurality data signals by one-half baud period.

Abstract: An optical transceiver includes an optical IC coupled to a processor IC. For transmit, the optical IC can be understood as a transmitter IC including a laser device or array. For receive, the optical IC can be understood as a receiver IC including a photodetector/photodiode device or array. For a transmitter IC, the processor IC includes a driver for a laser of the transmitter IC. The driver includes an equalizer that applies high frequency gain to a signal transmitted with the laser device. For a receiver IC, the processor IC includes a front end circuit to interface with a photodetector of the receiver IC. The front end circuit includes an equalizer that applies high frequency gain to a signal received by the receiver IC. The driver can be configurable to receive a laser having either orientation: ground termination or supply termination.

Abstract: A method and system for transparent timing of an Ethernet signal over an optical transport network are disclosed. In one embodiment, a transceiver includes a first clock recovery circuit, a first synchronizer and an asynchronous mapper. The first clock recovery circuit recovers a first clock from a first signal received from an Ethernet network. The first synchronizer multiplies the first clock by a ratio M/N to produce a second clock to time a second signal transmitted over the optical transport network. M and N are integers.

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: An optical transmitter utilizing a multi-level data modulator to produce a PDM-QPSK signal, a one-bit delay interferometer configured to correlate the multi-level data modulated signal and an optical filter configured to combine the correlated multi-level data modulated signal with one or more neighboring signals prior to transmitting over one of a plurality of optical channels. The PDM-QPSK correlated signal is configured to reduce the signal spectrum thereby increasing spectral efficiency of the transmitted signal.

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 multi-wavelength optical transmission system includes a plurality of primary optical transmitters, each being configured to provide directly modulated analog optical signals at non-uniformly spaced apart wavelengths. An optical multiplexer having a plurality of optical input ports receives the analog optical signals from each of the plurality of primary optical transmitters and provides a wavelength division multiplexed signal over an optical fiber coupled at an output thereof. A spare optical transmitter is coupled to an input port of the optical multiplexer and, in response to detecting failure of a failed one of the plurality of primary optical transmitters, is tuned to provide a directly modulated analog optical signal at a spare wavelength that is selected as to be non-uniformly spaced relative to at least some of the non-uniformly spaced apart wavelengths according to tuning data.

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: Distortion and aliasing reduction for digital to analog conversion. Synthesis of one or more distortion terms made based on a digital signal (e.g., one or more digital codewords) is performed in accordance with digital to analog conversion. The one or more distortion terms may correspond to aliased higher-order harmonics, distortion, nonlinearities, clipping, etc. Such distortion terms may be known a priori, such as based upon particular characteristics of a given device, operational history, etc. Alternatively, such distortion terms may be determined based upon operation of a device and/or based upon an analog signal generated from the analog to conversion process. For example, frequency selective measurements made based on an analog signal generated from the digital to analog conversion may be used for determination of and/or adaptation of the one or more distortion terms. One or more DACs may be employed within various architectures operative to perform digital to analog conversion.

Abstract: The present invention provides a nonlinear compensating apparatus and method and a transmitter. The nonlinear compensating apparatus includes: an information sequence acquiring unit, configured to acquire a symbol information sequence of the pulse signal; a perturbation quantity acquiring unit, configured to calculate the weighted sum of interaction items of pulses on one or more moments relative to the current moment, to obtain the perturbation quantity produced on a transmission link with a certain length, and rotate the obtained perturbation quantity by a predetermined phase; and an information compensating unit, configured to calculate the difference between the symbol information sequence and the perturbation quantity to obtain a compensated symbol information sequence. With the embodiments of the present invention, the performance of the system, especially the performance of NRZ (Not Return to Zero) code, may be further improved.

Abstract: A system and method are provided for controlling the pre-emphasis applied to an optical signal, in which the output level of individual transmitters is controlled in order to reach a pre-defined desired value of a quality metric. Transmitters are able to adjust their output power without external control in such a way as to optimise the power distribution across the system.

Abstract: A method and system for transient and switching stabilization of a fiber optic transport system. One or more data-bearing channels are coupled to an optical fiber. The data-bearing channels are distributed among a plurality of frequency sub-bands. A set of control channels is also coupled to the optical fiber. Each control channel includes a pair of signals at separate frequencies. There is at least one control channel in each of the plurality of frequency sub-bands. The pair of signals of a control channel are cross-polarized. Optical power in at least one of the plurality of sub-bands is measured. Responsive to the measured optical power, the optical power of a control channel is adjusted to maintain a substantially constant power of a sub-band that contains the adjusted control channel.

Abstract: A transmission device has a light emitting element for converting an electric signal to an optical signal and transmitting the same, and a drive section for outputting the optical signal from the light emitting element and driving the light emitting element by providing the electric signal to the light emitting element. The electric signal provided by the drive section to the light emitting element is a waveform deformed signal having a waveform in which a time required for a fall is longer than a time required for a rise in a binary signal having a signal of high level and a signal of low level.

Abstract: An optical transceiver includes an optical transmitter. The optical transmitter varies the wavelength of its output beam in accordance with the setting of a digital to analog converter. Two split beams emerging respectively from beam splitters are introduced into a photodetector and a wavelength filter, respectively. A quotient is calculated by dividing the digital value output from an analog to digital converter (ADC) by the digital value output from another ADC. A memory address m is then determined based on this quotient without making any calculation for compensating for the imperfect characteristics of the wavelength filter. A wavelength notification value is then selected from a wavelength notification table based on the determined memory address m, and sent to the system host.

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: An optical transmission system having an optical source, an optical dispersion compensation filter optically connected to the optical source, and a control system. The optical source generates a modulated optical signal having an optical spectrum and a value of dispersion robustness. The optical dispersion compensation filter has at least two cascaded optical resonators and a periodic transfer function rigidly translatable in the frequency spectrum to obtain translation in frequency of the transfer function without a substantial change in shape, and characterized by a free spectral range. The control system acts on the optical dispersion compensation filter in order to rigidly translate the transfer function along the frequency spectrum in first and second positions in the frequency spectrum. The translation of the transfer function between the first and the second positions is smaller than the free spectral range.

Abstract: A chromatic dispersion compensation system for an optical transmission system incorporates circuitry which determines the length of an optical fiber extending between an output amplifier and an input amplifier. Based on fiber type, the total chromatic dispersion on the fiber is determined. Compensation can then be automatically implemented.

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: An optical transmission system, where in an optical transmitter a detection bit having a specific pattern set according to the number of bits to be transmitted within one symbol time, is imparted with respect to a transmission signal in which transmission information has been encoded according to a preset format, and an optical signal generated by modulating light according to the transmission signal is transmitted to a transmission line. In an optical receiver, logic inversion or bit swap of received data is detected and compensated by using the detection bit included in the received signal, a decoding process of the compensated received signal is executed. As a result, when an optical signal capable of transmitting multi-bit information within one symbol time is transferred, it is possible to realize excellent transmission characteristics, by reliably compensating an error in received data caused by the modulation format or the multiplex system of the optical signal.

Abstract: A method for stabilizing multi-channel optical signal wavelengths includes the following steps. A first detecting signal is stacked on a plurality of driving signals in sequence. A plurality of optical signals generated after being driven by the plurality of driving signals is combined into one optical total signal. A wavelength detection is performed on the optical total signal. A second detecting signal with a frequency band the same as that of the first detecting signal is extracted from the signals obtained after the wavelength detection. The wavelength of the optical signal in the corresponding channel among the multiple channels is controlled according to the second detecting signal. A device for stabilizing multi-channel optical signal wavelengths is also provided. Using the above method or device, the multi-channel optical signal wavelengths can be stabilized, which requires less elements, and has a simple circuit structure, a high integration level, and a low cost.

Abstract: Methods and devices for compensating for chromatic dispersion are shown that include receiving an input data signal, applying a filter to the data signal, and outputting a CD compensated signal. Applying the filter includes convolving known filter coefficients with a plurality of delayed versions of the data signal using addition and at least one inverse sign operation or using lookup tables and combining outputs to produce a CD compensated 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.

Abstract: Exemplary methods and systems for applying a correction to an initiated signal are disclosed. In some examples the correction may be a compensation for dispersion present, e.g., in an optical signal. An exemplary method may include receiving an initiated signal, and forming a curved surface with a first array of discrete elements. The exemplary method may further include impinging the initiated signal upon the curved surface, thereby applying a correction to the initiated signal determined at least in part by the curved surface.

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: A plurality of inductors are connected in series between a load resistor and a first transistor, and a plurality of second transistors provided in parallel are connected to the plurality of inductors.

Abstract: An integrated circuit die has a transistor circuitry section for implementing information handling operations. Optical circuitry is within the single semiconductor die. The optical circuitry includes a laser transmitter and is operably coupled to the transistor circuitry section. The transistor circuitry section originates information. The optical circuitry transmits the information in a laser beam through a wave guide to the edge of the integrated circuit die.

Abstract: A transmitter reduces or minimizes pulse narrowing. In one approach, an optical transmitter is designed to transmit data over an optical fiber at a specified data rate using on-off keying. The transmitter includes a pre-converter electrical channel and a limiting E/O converter. The pre-converter electrical channel produces a pre-converter signal that drives the limiting E/O converter. The pre-converter electrical channel is designed to reduce pulse narrowing in the pre-converter signal. In one implementation, the pre-converter electrical channel includes a pre-emphasis filter that is designed to minimize pulse width shrinkage.

Abstract: Provided is a channel assignment method in a wavelength-division-multiplexed transmission system. The channel assignment method includes obtaining information about signal modulation schemes from a plurality of optical transmitters, and assigning channels to the respective optical transmitters in consideration of the obtained information about the signal modulation schemes. Accordingly, in transmission of channels of different modulation formats, cross phase modulation is minimized, thereby reducing inter-channel interference.

Abstract: An optical transmission apparatus for suppressing deterioration of transmission quality due to XPM in a wavelength division multiplexing optical communication system in which an intensity modulation optical signal and a phase modulation optical signal exist in a mixed form. The apparatus has an intensity inversion signal light output section which outputs light having an intensity pattern obtained by inverting intensity changes of the intensity modulation optical signal near a wavelength of the intensity modulation optical signal in arrangement on wavelength axis of optical wavelengths that can be multiplexed as a wavelength division multiplexed signal as intensity inversion signal light, and a wavelength division multiplexed optical signal output unit which wavelength-division-multiplexes the intensity modulation optical signal, the phase modulation optical signal and light from the intensity inversion signal light output section and outputs a wavelength division multiplexed optical signal.

Abstract: A tunable photonic channelizer includes an optical signal generator and an optical modulator. The optical modulator receives a first optical signal as an input from the optical signal generator and modulates the first optical signal to create a second optical signal. The tunable photonic channelizer includes an optical filter that is selectively tunable. The optical filter receives the second optical signal, filters the second optical signal, provides a third optical signal as a filtered version of the second optical signal. The tunable photonic channelizer includes a feedback loop between the optical filter and the optical signal generator to provide temperature and/or environmental feedback from the optical filter to the optical signal generator to enable the first optical signal to float in relation to the temperature and/or environmental feedback.

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: An aspect of the embodiments utilizes an optical transmission apparatus which includes a rough adjustment execution portion that monitors a bit error rate of an optical signal for set values of a dispersion compensator where the set values have been set less closely to each other within a dispersion compensation control range than when a wavelength dispersion value set in the dispersion compensator is determined, and carries out a rough adjustment to determine a comparison threshold value used to set the wavelength dispersion value based on the monitored bit error rate, and a fine adjustment execution portion that monitors the bit error rate for the dispersion compensator the set values have been set more closely to each other, and carries out an adjustment to determine a wavelength dispersion value corresponding to the midpoint between the two acquired bit error rates as the wavelength dispersion value of the dispersion compensator.

Abstract: A method of controlling the operating parameters of an optical modulator, without using a dither signal, is provided. Past operating parameters are compared to present operating parameters using a quality of modulation signal obtained by cross-correlating the data modulation signal used to drive the optical modulator with the modulated optical signal output from the optical modulator. The quality of modulation signal is used to optimize the operating parameters (e.g., bias point) of the optical modulator, or other operating parameters of the arrangement, such as the modulator drive level, timing alignment, etc.

Abstract: A communication system and a timing control method are proposed that optimize timing in a sender and thereby enable information to be stably transmitted at the right timing. Under instructions from a timing controller in a receiver, the timing of driving a phase modulator in a sender is shifted by one step after another, and the then amount of clock shift and result of interference are monitored at the receiver and stored in a memory. The optimum timing is determined based on the stored data. Thus, a clock for driving the phase modulator in the sender can be set at the right timing. This is equivalent to compensating for group velocity dispersion due to wavelength dispersion that occurs when an optical signal channel and a clock signal channel are transmitted by wavelength division multiplexing transmission.

Abstract: Equipped between a transmitter 20 and an optical multiplexer module 25 of a division/multiplexer unit 24 are band-pass filters 23-1 through 23-m letting only a light of right wavelength pass while reflecting other wavelengths light. The transmitter 20 is equipped with a reflection light monitor 26 for monitoring a reflection light from the band-pass filters 23-1 through 23-m for examining an intensity of a reflection light. A wavelength of a light oscillated by a tunable laser diode (LD) unit 21 is controlled so as to make the intensity of the light smaller than a threshold value.

Abstract: Examples of apparatus and methods are provided for controlling a bias in an optical modulator. An exemplary apparatus may comprise an optical modulator operable to modulate an optical signal. The optical modulation apparatus may comprise a photodetector disposed to receive at least a portion of the modulated optical signal. The optical modulation apparatus may comprise a bias controller coupled to both the optical modulator and the photodetector. The bias controller may be configured to receive a dither signal and to produce a bias feedback signal for the optical modulator. The bias feedback signal may be based on a ratio between an odd order harmonic signal of the modulated optical signal and an even order harmonic signal of the modulated optical signal.

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: An optical transmitter utilizing a multi-level data modulator to produce a PDM-QPSK signal, a one-bit delay interferometer configured to correlate the multi-level data modulated signal and an optical filter configured to combine the correlated multi-level data modulated signal with one or more neighboring signals prior to transmitting over one of a plurality of optical channels. The PDM-QPSK correlated signal is configured to reduce the signal spectrum thereby increasing spectral efficiency of the transmitted signal.

Abstract: An optical transmitter is disclosed wherein a signal processor receives a data stream and outputs a drive signal for a laser, where the drive signal encodes each bit of the data stream according to the values of adjacent bits effective to compensate for spreading of bits within the fiber. The output of the laser is input to an optical spectrum reshaper that outputs a signal having an enhanced extinction ratio.

Abstract: Photonic integrated circuits (PICs) may include transmit and receive PICs that include individually tunable optical elements. In one implementation, a device may include a number of optical elements that form a number of optical channels. Tuners may be used to modify a property associated with the at least one of the optical elements where the modified properties of the optical elements adjust a frequency grid of the optical channels.

Abstract: A channel alignment system in an optical communication network includes logic to sample power of a quadrature amplitude modulation (QAM) channel at a component downstream from a QAM modulator. The system determines if the sampled channel power has a sufficient level. The system signals power control logic of the QAM modulator to adjust a gain of the sampled channel.

Abstract: A topology for optical transceiver components comprises an electrical signal interface stage, a data timing and signal reformatting stage, and an optical fiber interface stage. Unlike transceiver components known in the art, functions having signals with the most jitter are partitioned into the electrical signal interface stage. Data timing functions, for example retiming or clock and data recovery, are included in the data timing and reformatting stage. Output jitter from the data timing and signal reformatting stage is approximately equal to jitter in a clock signal, enabling use of semiconductor components having jitter greater than SONET limits and thereby increasing a value of production yield. Embodiments of the invention are well suited for 40 G transmitters and receivers in nonconnectorized surface mount packages. 40 G transceivers built in accord with the invention are expected to have lower cost, smaller size, and higher production yield than 40 G transceivers known in the art.

Abstract: A signal Data1 and Data2 are output from a DQPSK signal source. The output signal is input to the modulator drivers 1 and 2 of the differential output. A drive signal is applied from the drivers 1 and 2 to a modulator, and modulated light is output. An optical coupler 20 branches modulator output, and a power monitor 21 detects the power of the branched light. A detection result is transmitted to an amplitude control unit 22. The amplitude control unit 22 adjusts the amplitude of the drivers 1 and 2 such that the detection result of the power monitor 21 can be the maximum.

Abstract: Predistortion logic for an optical communications laser or optical modulator, includes predistortion logic embodied in a field programmable gate array (FPGA). A first analog to digital converter (ADC) provides a representation of an RF signal at an input of the FPGA. A digital to analog converter provides a representation of an output of the FPGA to a laser or modulator.

Abstract: There is provided a signal transmission device which transmits, in the form of an optical signal, multivalued data which shifts through three or more plurality of logical values, and includes: a light emitting element which outputs light having an intensity corresponding to a power supply current supplied thereto; a current source which is capable of supplying the light emitting element with the power supply current which has a plurality of current values corresponding to the plurality of values through which the multivalued data shifts; and a modulating section which modulates the current value of the power supply current supplied from the current source, in response to a shift of the multivalued data.

Abstract: A digital filter is provided for processing an electrical input signal to be conveyed through an optical communications system. The processing generates a predistorted electrical signal using a compensation function that substantially mitigates for intra-channel non-linearity imparted to the communications signal by the optical communications system. The digital filter has a memory having a limited size storing a reduced data set used for approximating an original, unreduced data set used to implement the compensation function. The reduced data set is used for the digital filter to apply the compensation function to mitigate the intra-channel non-linearity over longer transmission distances of the optical communications system than would be possible without the use of the reduced data set.