Abstract: An optical transmitter is disclosed in which the wavelength deviation occurred at the turning on from the disabled state to the enabled state by the negating of the Tx_Disable command is suppressed. The optical transmitter includes a semiconductor laser diode (LD) and an automatic temperature controller (ATC) circuit to drive the thermo-electric cooler (TEC). When the transmitter receives the Tx_Disable to start up the operation of the LD, a pulsed signal is generated in synchronizing with the transition of the Tx_Disable signal to momentarily enhance the cooling capacity of the TEC in order to compensate the increase of the temperature of the LD by the self heating, which prevents the output wavelength of the transmitter from deviating.

Abstract: The frequency chirp modulation response of a directly modulated laser is described using a small signal model that depends on slow chirp amplitude s and slow chirp time constant ?s. The small signal model can be used to derive an inverse response for designing slow chirp compensation means. Slow chirp compensation means include electrical compensation, optical compensation, or both. Slow chirp electrical compensation can be implemented with an LR filter or other RF circuit coupled to a direct modulation source (e.g., a laser driver) and the directly modulated laser. Slow chirp optical compensation can be implemented with an optical spectrum reshaper having a rounded top and relatively large slope (e.g., 1.5-3 dB/GHz). The inverse response can be designed to under-compensate, to produce a flat response, or to over-compensate.

Abstract: Demodulation apparatus for demodulating phase-modulated signals comprises a quadrature signal generator (QSG) for generating in-phase (I) and quadrature-phase (Q) signals in response to an unmodulated input signal. The QSG provides fast frequency tracking of the input signal and excludes any high-frequency content the input signal.

Abstract: A method of phase modulating optical radiation by the steps of phase modulating the optical radiation by using a modulator having an extinction ratio in order to provide a multilevel phase shift key signal, and applying to each optical pulse a phase-shift having an absolute value depending on the extinction ratio and a sign depending, for each of the optical pulses, on the respective optical phase value. An apparatus implementing the method is also disclosed.

Abstract: Provided herein are at least one embodiment of a system and method for reducing or eliminating crosstalk and associated distortion in a wavelength-division multiplexed optical signal transmitted over a fiber optic network by inversion of the RF signals that are inputs to the system.

Abstract: A method for generating D-N-PSK optical signals is disclosed wherein a laser is modulated to generate optical signal pairs including phase modulated and fixed phase portions, the phase modulated portions having a frequency encoding one or more data symbols and the fixed phase portion having a carrier frequency and a phase corresponding to the immediately preceding phase modulated portion. The output of the laser is passed through an optical spectrum reshaper having a transmission function chosen to attenuate a plurality of the phase modulated portions relative to the fixed phase portions. The phase modulated portions may have N frequency levels located on either side of the carrier frequency. One of the N frequency levels may be equal to the carrier frequency.

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: Systems and methods are provided for providing a hybrid signal having a reduced crest factor. A digital signal is generated that assumes one of a plurality of vector states at discrete sampling times, with each of the plurality of vector states having an associated phase. An analog signal is monitored to determine when a phase of the analog signal is aligned with the phase of a vector state assumed by the digital signal. A crest factor reduction is applied to the digital signal if the digital signal assumes a vector state having an associated phase aligned with the phase of the analog signal to provide a compressed digital signal. The compressed digital signal and the analog signal are combined to provide the hybrid signal. The analog signal is not altered prior to being combined with the compressed digital signal.

Abstract: The apparatus includes a pulse emitter and at least one line fiber for conveying at least one pulse in the line fiber. A spreader module for linearly spreading pulses is provided including a propagation medium that is dispersive and linear. The propagation medium presents accumulated chromatic dispersion that is high enough to lower the peak power of the pulse to below a predetermined threshold, where a signal above the threshold is subjected to non-linear distortion in the line fiber. The spreader module is disposed between the emitter and the line fiber.

Abstract: A driver circuit is coupled to an optical waveguide transmitter. The driver circuit has a current generator that is in series with the transmitter, and a current robbing circuit is coupled to the transmitter. The current robbing circuit is to divert first and second amounts of current from the transmitter, in accordance with predetermined values of first and second bit streams, respectively, in which data is received to be transmitted. Other embodiments are also described and claimed.

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: An optical transmitter is disclosed including a widely tunable laser coupled to a periodic optical spectrum reshaper (OSR) to convert frequency modulated pulses from the laser into amplitude modulated pulses. The laser is tuned to generate pulses corresponding to passbands of the OSR spanning a wide range of frequencies. The laser includes a gain section having an optical path length substantially shorter than the total optical path length of the laser. The laser may be a Y-branch laser having reverse-biased sampled gratings or ring resonator filters tuned by stripe heaters. The laser may also include a reflective external cavity section tunable by modulating the temperature of ring resonators or etalons. The OSR may be integrally formed with the external cavity of the ECL laser.

Abstract: The present application is directed to an apparatus and method for the automated compensation of dispersion over a broad wavelength range for coherent optical pulses. In one embodiment, the present application discloses an automatic dispersion compensating optical apparatus configured to change chirp introduced into an optical signal by an optical system in optical communication with the dispersion compensating optical apparatus and includes at least one wavelength-tunable source of coherent optical pulses configured to output at least one optical signal, at least one dispersion compensation device configured to receive the optical signal from the coherent source, and at least one controller in communication with the dispersion compensation device and configured to adjust chirp introduced into the optical signal by the dispersion compensation device as the wavelength of the optical signal is varied.

Abstract: A phase control arrangement has a structure in which a Superstructured fiber Bragg Grating (SSFBG) 40 has fifteen unit Fiber Bragg Gratings (FBGs) arranged in series in a waveguide direction. The SSFBG 40 is fixed to the core of an optical fiber 36 that includes a core 34 and cladding 32. The difference ?n between the maximum and minimum of the effective refractive index of the optical fiber is 6.2×10?5. The phase difference of Bragg reflected light from two unit diffraction gratings that adjoin one another from front to back and provide equal code values is given by 2?M+(?/2), where M is an integer. Further, the phase difference of the Bragg reflected light from two unit diffraction gratings that adjoin one another from front to back and provide different code values is given by 2?M+(2N+1)?+(?/2) where M and N are integers.

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: An optical transmitter is disclosed for transmitting a signal along a dispersive medium to a receiver. The optical transmitter generates adiabatically chirped profile having an initial pulse width and frequency excursion chosen such that high frequency data sequences include one bits that interfere destructively at a middle point of an intervening zero bit upon arrival at the receiver.

Abstract: A directly modulated optical transmitter for use with a fiber optical communications system operating in the 1550 nm wavelength band exhibits very low chirp. The chirp inherently present in a directly modulated laser is cancelled by a phase modulator which optically modulates the directly modulated laser light beam by applying a 180° phase delay to a split-off portion of the input radio frequency signal. This provides a low cost transmitter capable of operating in the 1550 nm band and with laser chirp effectively cancelled or substantially reduced, thereby avoiding distortions due to laser chirp interactions with the downstream optical fiber.

Abstract: A predistortion circuit provides a predistorted input signal that compensates for distortion generated by a non-linear amplifier such as a laser device. The predistortion circuit may be used in an optical transmitter designed for broadband applications, such as a laser transmitter used for forward path CATV applications. The predistortion circuit may include a primary signal path and a secondary signal path that receive an input signal. A second order distortion generator on the secondary signal path generates predistortion of a magnitude corresponding to the magnitude of, but at an opposite phase to, the distortion generated by the non-linear amplifier. The second order distortion generator includes diodes with an adjustable diode bias to control phase, magnitude and/or magnitude/phase versus frequency of the predistortion.

Abstract: The present invention utilizes field programmable gate arrays (FPGAs) to implement a parallel differential quadrature phase shift keying (DQPSK) precoder and a DQPSK optical transmitter with an automatic realignment process. The present invention can perform DQPSK preceding, modulation, and data stream realignment at any lower rate, and its upper rate is determined by capability in speed and logic resources and external connections of available integrated circuit technology.

Abstract: A peaking current generating section generates a spire-shaped peaking current that is in synchronism with the transitions of the digital signal, at the rising edge and the falling edge. A light emitting element driving section produces a driving current obtained by combining together a signal amplitude current according to the amplitude of the digital signal and the peaking current. Then, the light emitting element driving section drives a light emitting element by using the driving current. A signal analysis section analyzes the digital signal so as to set a control signal based on the pulse width of the digital signal. A clipping section clips the peaking current of the driving current according to the control signal set by the signal analysis section.

Abstract: A first peaking current generating section generates a first peaking current in synchronism with the transitions of a digital signal, being positive at the rising edge and negative at the falling edge. A second peaking current generating section generates a second peaking current in synchronism with the transitions of the digital signal, being negative at the rising edge and positive at the falling edge. A first light emitting element driving section produces a first driving current obtained by combining together a signal amplitude current according to the amplitude of the digital signal and a first peaking current. A second light emitting element driving section produces a second driving current obtained by combining together the signal amplitude current according to the amplitude of the digital signal and a second peaking current.

Abstract: Provided herein are embodiments of a device, method of use and system for a low-cost analog multi-wavelength video distribution transamplifier for CATV and FTTH networks having a broadband overlay. The transamplifier embodiments described herein allow the use of multiple wavelengths to segment logical service groups in a CATV distribution system and a FTTH system having a broadband overlay. Improved optical signal power performance can be achieved by using direct modulating transmitters and modulating the optical signal for with an external waveguide, thereby decreasing SBS and reducing non-linearities.

Abstract: According to the invention, a very narrow-band transfer signal (LS) is generated by serially connecting a frequency modulator (2) and an amplitude modulator (4). The frequency modulator (2) is operated at a modulation index which at least largely suppresses the carrier signal (TS) while the amplitude modulator (4) suppresses the broadband portion of the spectrum by fading out the transfer signal (LS) during frequency-shift keying.

Abstract: An optical signal transmitter of direct modulation, a method for transmitting optical signals, and an optical network are provided. The optical signal transmitter includes a laser diode operating at a bias current above a lasing threshold of the laser diode; a modulating device applies a modulation signal to the diode to produce a first output optical signal having first and second signal power levels; and a power level discriminator. The power level discriminator, from the received first output optical signal, generates a second output signal of significantly improved extinction ratio by reducing power of one of the first and second signal power levels of the first output optical signal.

Abstract: The invention relates to a compensator of attenuation drift in an optical multi-wavelength switch (MWS) which uses input signal amplitude dither and external VOA dither cancellation to determine relative position of MEMS micro mirror hence indirectly determining attenuation level.

Abstract: A system and method for increasing transmission distance and/or transmission data rates using tedons and an encoding scheme to reduce the number of ones in a data signal is described. For example, the method for increasing transmission distance and transmission data rate of a fiber optical communications link using tedons includes the steps of encoding a data signal to be transmitted using an encoding scheme that reduces a number of ones in the data signal, transmitting the encoded data signal over the fiber optical communications link, receiving the encoded data signal and decoding the encoded data signal.

Abstract: A transmitter-side transmission signal for compensating disturbances caused by e transmission properties of an optical transmission system is provided. A high-bit-rate-binary signal is serially introduced into an N-level-shift register. A bit pattern whose bit number depends on the transmission system disturbance influence is removed from the shift register and introduced into comparators connected to comparative-value registers. The comparative-value registers include values received from a transmission function and from various binary-bit patterns. In the comparators, the binary-bit pattern introduced is converted into a binary combination which is introduced into a digital-analog transducer, which transmits a compensation signal, corresponding to a discrete value for the amplitude or phase of the transmission signal corresponding a desired signal form, to a modulator.

Abstract: The present invention generally concerns the use of Bragg optical fibers in chirped pulse amplification systems for the production of high-pulse-energy ultrashort optical pulses. A gas-core Bragg optical fiber waveguide can be advantageously used in such systems to stretch the duration of pulses so that they can be amplified, and/or Bragg fibers can be used to compress optical signals into much shorter duration pulses after they have been amplified. Bragg fibers can also function as near-zero-dispersion delay lines in amplifier sections.

Abstract: A chirped pulse amplification (CPA) system and method is described wherein the dispersion of the system is tuned by actively tuning one or more system components, for example, using a temperature or strain gradient, or using actinic radiation. In other embodiments, an additional element, such as a modulator, is added to the CPA system to actively to tune the pulse. A pulse monitor is added to the system to measure an output pulse and provide feedback to one or more active tuning elements.

Abstract: A method and apparatus is provided for reducing clipping arising in an optical transmitter. The method begins by generating a frequency multiplexed sub-carrier signal onto which information is modulated at a plurality of different sub-carrier frequencies. The method continues by decorrelating in phase at least some pulses that are formed when two or more of the different sub-carrier frequencies are in phase with one another. An optical output produced by a laser is modulated in accordance with the frequency multiplexed sub-carrier signal after at least some of the pulses have been decorrelated in phase.

Abstract: Improved dispersion compensating circuits for optical transmission systems are disclosed. According to the improved method, there is provided a compensation circuit comprising a varactor diode network. The network is preferably inserted between a source of laser modulating signal and the laser. A low pass filter constructs the network. The network preferably includes an inductance and a combined circuit, which includes varactors. The network preferably provides an amplitude dependent delay of the modulating signal applied to the laser. In a first embodiment, a fixed capacitor is in series with a varactor and connected to a DC bias through inductor. In a second embodiment, second varactor is in series with varactor instead with an opposite polarity of a fixed capacitor as used in the first embodiment. In a third embodiment, two varactors 301 and 302 are used in place of the fixed capacitor in parallel.

Abstract: An optical transmitter comprising: an optical source modulated with an input digital data signal so as to generate a first, frequency-modulated digital signal; and an amplitude modulator, modulated with the logical inverse of the input digital data signal, for receiving the first, frequency-modulated signal and generating a second, amplitude-modulated and frequency-modulated digital signal; wherein the optical source and the amplitude modulator are each configured so as to produce positive transient chirp.

Abstract: An optical transmitter includes an optical modulator, an optical coupler, a crosspoint monitoring unit, a reference-value setting unit, and a bias circuit. The optical coupler splits an optical signal output from the optical modulator into a plurality of optical signals. The crosspoint monitoring unit receives part of the optical signals, and monitors a crosspoint of the optical signal output from the optical modulator. The reference-value setting unit sets a bias reference value to be assigned to the optical modulator based on an output of the crosspoint monitoring unit so that the crosspoint is constant. The bias circuit applies a bias to the optical modulator based on the bias reference value.

Abstract: Methods and apparatus (100) for composing, generating and transmitting information-bearing optical signals are provided. An information-bearing electrical signal is composed (108) having desirable spectral properties, preferably configured to ensure that undesired interference between electrical spectral components generated in a square-law direct detection process (120) at a corresponding optical receiver (104) is substantially avoided. Predistortion (110) is advantageously applied to transmitted signals, in order to account for a nonlinear relationship arising in a modulation process (114) between electrical signal amplitude and corresponding optical field amplitude. Orthogonal frequency division multiplexing (OFDM) techniques may be applied to composed signals having the desired characteristics, and additionally may facilitate the application of frequency domain equalisation (128) in order to mitigate transmission impairments, including dispersion.

Abstract: A system and method for generating an optical return-to-zero signal. The system includes an electro-optical conversion system. The electro-optical conversion system is configured to receive an input electrical non-return-to-zero signal, process information associated with the input electrical non-return-to-zero signal, and generate an output optical return-to-zero signal based on at least information associated with the input electrical non-return-to-zero signal. The output optical return-to-zero signal is an optical differential return-to-zero signal, and the optical differential return-to-zero signal is associated with a frequency chirp.

Abstract: Systems and methods for frequency-domain compensation in optical communication systems. In pre-equalization embodiments, the transmitter transforms the data stream into a frequency domain signal and applies a compensation filter before transforming it back into a pre-distorted time domain signal. As the pre-distorted time domain signal propagates through the optical channel, optical dispersion effects counter the pre-distortion, producing an equalized signal at the channel output. In post-equalization embodiments, the receiver transforms the received signal into a frequency domain signal and applies a compensation filter before transforming it back into an equalized time domain signal. Pre-equalization may prove less expensive due to the square-law characteristic of photodetectors employed by most receivers.

Abstract: In an optical transmitter of the invention, continuous light from a light source is a (CS)RZ-D(Q)PSK modulated by two optical modulators connected in series, and a part of the optical signal output from a post-stage optical modulator is branched by an output monitor section, and the power of a preset frequency component, excluding a frequency component corresponding to a baud rate, included in an electrical spectrum acquired by photoelectrically converting the branched beams is measured. The relative phase of drive signals applied to the optical modulators is then feed-back controlled so that the power becomes a minimum. As a result, a delay shift due to a temperature change or the like between drive signals applied to respective optical modulators, can be reliably compensated.

Abstract: An optical communication system combines strong electrical pre-filtering of data at the transmitter and digital feedback equalization (DFE) at the receiver to enhance spectral efficiency. The system can be applied to optical networking and digital communication systems, including binary modulated systems optical network systems.

Abstract: For transmitting information on an optical fiber, a plurality of information carrier channels at different carrier frequencies and a plurality of filling channels are used. The filling channels are transmitted together with the information carrier channels along the fiber. The total optical power of the information carrier channels and the filling channels transmitted on the fiber is maintained constant by compensating every change of the optical power of the information carrier channels by an inverse change of the optical power of the filling channels. The change of the optical power of the filling channels is distributed to the individual filling channels such that a minimum displacement of the center of gravity of the common spectrum of information carrier channels and filling channels results.

Abstract: A system and method for generating an optical return-to-zero signal. The system includes a bit separator configured to receive an electrical non-return-to-zero signal and generate a first signal and a second signal, and a driver configured to receive the first signal and the second signal and generate a driving signal. The driving signal is associated with a difference between the first signal and the second signal. Additionally, the system includes a light source configured to generate a light, and an electro-optical modulator configured to receive the light and the driving signal, modulate the light with the driving signal, and generate an optical signal. The electrical non-return-to-zero signal includes a first plurality of bits and a second plurality of bits. The first signal includes the first plurality of bits, and the second signal includes the second plurality of bits. The optical signal is an optical return-to-zero signal.

Abstract: A Peak-to-Average Power Ratio (PAPR) reduction apparatus and method in an OFDM communication system are provided. In the PAPR reduction method, magnitude and phase components are extracted from transmission sample data. Peaks having magnitude components exceeding a threshold are detected by comparing the extracted magnitude components with the threshold. The highest of the peaks is detected and compared with the threshold. If the highest peak is greater than the threshold, the highest peak is updated.

Abstract: An active cable that is configured to communicate over much of its length using one or more optical fibers, and that includes an integrated electrical connector at least one end. The active cable includes an integrated retiming mechanism. Thus, multiple links of cable may be used while reducing the chance that the jitter will exceed allowable limits. The cable may be an electrical to optical cable, and electrical to electrical cable, or one of many other potential configurations.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

Abstract: A transmission device having optical fiber high definition digital audio-video data interface (HDMI/DVI/UDI), in which optical fiber is utilized as the physical connection for the logical channels of the transmission device, and is used to carry images, voices and auxiliary data of the logic channels. For the half-duplex transmission mode utilized by the display data channel, the reverse unit, the serial unit, and the multi-serial unit are properly arranged, thus fulfilling the DC balance requirement of optical fiber transmission, and resolving the lower tolerance rate shortcomings of the I2C bus specification of display data channel (DDC) and the customer electronics control (CEC) channel.

Abstract: A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: An optical transmission system for transmitting an optical pulse in a dielectric waveguide, the system including a filter for altering a shape of the optical pulse in both amplitude and phase with respect to time so as to substantially suppress the generation of third-order nonlinearities and increase a power level of the optical pulse, the filter further providing a secure encrypted optical waveform that may be decrypted by a matching optical filter, the system allowing for energy sharing of the pulses to substantially increase system bandwidth.

Abstract: A multimode optical fibre communications system, and in particular to a system in which non-linearities in the propagation of the signal through a multimode optical communications channel degrade the signal presented to the receiver. The system includes an optical transmitter unit for connection to a multimode optical fibre transmission link. The transmitter unit has a data input for receiving an input data signal, a data signal processing circuit and a source of optical radiation. The data signal processing circuit is arranged to receive the input data signal from the data input and to provide a processed data signal to the source of optical radiation and the source of optical radiation is arranged to generate from this an optical signal for transmission by a multimode optical fibre.

Abstract: Certain aspects of a method and system for optimum channel equalization between a host Serializer-Deserializer (SerDes) and an optical module may compensate and reduce dispersion loss along an electrical transmit path of a transmitter and an optical transmit path coupled to the transmitter via pre-emphasis. The data degradation as a result of the dispersion loss along the electrical transmit path of the transmitter and the optical transmit path coupled to the transmitter may be recovered by equalizing signals received via an electrical receive path of a receiver communicatively coupled to the transmitter.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

Abstract: The present invention includes a fast algorithm to compute the pre-equalized waveform for simultaneous compensation of the self-phase modulation and chromatic dispersion experienced by a high-speed optical signal, e.g., at 10 Gb/s, and shows that it is used for an automatic self-adapting pre-equalization when the knowledge on transmission link details is inaccurate or incomplete.