Abstract: An optical transmitter is discloses having a gain section and a phase section. The phase section is modulated to generate a frequency modulated signal encoding data. The frequency modulated signal is transmitted through an optical spectrum reshaper operable to convert it into a frequency and amplitude modulated signal. In some embodiments, a driving circuit is coupled to the phase and gain sections is configured to simultaneously modulate both the phase and gain sections such that the first signal is both frequency and amplitude modulated.

Abstract: This invention provides a flat dispersion frequency discriminator (FDFD) capable of having a substantially flat dispersion with either a positive or negative dispersion along the spectrum region of the discriminator. This way, a FDFD may not cause substantial distortion of the intensity patter of its output to minimize the occurrence distortion due to overshooting or undershooting of the intensity pattern depending on the relative spectral alignment of the laser output relative to the filter transmission.

Abstract: An optical transmitter comprising: (i) an electrical switch; (ii) a laser array comprising a plurality of tunable laser elements; and (iii) an Optical Spectrum Reshaper (OSR) used to reshape the output pulses from the laser elements in the laser array; wherein the electrical switch takes an input electrical digital signal and selectively directs it to a specific laser element in the DFB laser array.

Abstract: A transmitter includes a frequency modulated laser. An optical spectrum reshaper (OSR) is positioned to receive the frequency modulated signal and has a transmission function effective to convert the frequency modulation to amplitude modulation. An optical fiber channel has a first end positioned to receive the filtered signal and a second end proximate a receiver. A filter is positioned between the second end and the receiver and has a peak transmission frequency thereof located on a transmission edge of the OSR, such as at a peak logarithmic derivative value of the transmission function of the optical spectrum reshaper. In some embodiments a first OSR is positioned to receive the frequency modulated signal and configure to output a filtered signal wherein high frequency portions are more attenuated than low frequency portions. A second OSR at the receiver attenuates the low frequency portions substantially more than the high frequency portions.

Abstract: This invention generally relates to an optical filter for a fiber optic communication system. An optical filter may be used, following a directly modulated laser source, and converts a partially frequency modulated signal into a substantially amplitude modulated signal. The optical filter may compensate for the dispersion in the fiber optic transmission medium and may also lock the wavelength of the laser source.

Abstract: A system for generating a return-to-zero differentially-phase-shift-keyed (RZ-DPSK) optical signal comprising: a driver comprising an N-level digital multilevel transformer (DMT) configured to receive a two level digital electrical signal representing 1s and 0s and output a N-level electrical signal, wherein N>2; an FM source configured to receive the N-level electrical signal output by the driver and generate an optical frequency modulated signal; and an optical spectrum reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate the desired RZ-DPSK optical signal.

Abstract: Apparatus and methods for driving a transmitter to generate DNPSK signals is disclosed including generating N data streams comprising data symbols and for each of a plurality of sets of N simultaneous data symbols of the N data streams, imposing signals are on L of a plurality of signal lines, with the value of L corresponding to values of the N simultaneous data symbols. Signals on the plurality of signal lines are ANDed with a clock signal synchronized with the N data streams to produce RZ signals. The RZ signals are summed and the summed signal is input to a laser that produces an output having frequency modulation corresponding to the magnitude of the summed signal. The output of the laser is passed through an optical discriminator.

Abstract: This invention generally relates to an optical filter for a fiber optic communication system. An optical filter may be used, following a directly modulated laser source, and converts a partially frequency modulated signal into a substantially amplitude modulated signal. The optical filter may compensate for the dispersion in the fiber optic transmission medium and may also lock the wavelength of the laser source.

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 invention, in one form, is a fiber optic system having an optical signal source adapted to produce a frequency and amplitude modulated optical digital signal and a semiconductor optical amplifier adapted to receive the frequency and amplitude modulated optical digital signal and generate negative transient chirp at the transitions between bits. In another form, the invention is a fiber optic system having an optical source adapted to generate a frequency modulated signal, a semiconductor optical amplifier adapted to receive and amplify the frequency modulated signal, and an optical spectrum reshaper adapted to receive the amplified frequency modulated signal and to utilize the amplified frequency modulated signal to increase the amplitude modulation of the signal.

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: 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: An optical transmitter is disclosed wherein a modulating signal, such as an NRZ signal, encoding data is combined with a time derivative of the modulating signal and coupled to a directly modulated laser in order to generate artificial transient chirp in the output of the laser effective to substantially compensate for dispersion experienced by the output of the laser traveling through a dispersive medium such as an optical fiber. In some embodiments, the time derivative is added to the modulating signal only at the falling edges of the modulating signal.

Abstract: A fiber optic transmitter comprising a digital driver adapted to adjust the crossing point of a digital base signal, an optical source adapted to receive the digital base signal and produce a frequency modulated optical signal, and an optical spectrum reshaper adapted to convert the frequency modulated optical signal to an amplitude modulated optical signal. A method for transmitting a signal, comprising: adjusting the crossing point of a digital base signal; providing the adjusted signal to an optical source to produce a frequency modulated optical signal; and providing the frequency modulated optical signal to an optical spectrum reshaper to convert the frequency modulated optical signal to an amplitude modulated optical signal.

Abstract: A fiber optic communication system comprising: an optical signal source adapted to produce a binary amplitude modulated signal; and an optical spectrum reshaper adapted to receive the amplitude modulated signal and to change the instantaneous frequency of the signal at its 0-to-1 and 1-to-0 transitions so as to change the instantaneous frequency of the signal so that it is substantially constant across the 1 pulse. A method for transmitting a signal through a fiber, comprising: generating a second signal from the signal, wherein the second signal comprises a intensity profile and an adiabatic frequency profile; generating a third signal from the second signal, wherein the third signal comprises a intensity profile and a flat-topped frequency profile.

Abstract: This invention provides a system that combines a wavelength multiplexer with an FM discriminator for chirp reduction and wavelength locker in a filter to produce a wavelength division multiplexed signal with reduced chirp. A partially frequency modulation laser signal is converted into a substantially amplitude modulation laser signal. This conversion increases the extinction ratio of the input signal and further reduces the chirp. A wavelength division multiplexing (WDM) method is used for transmitting high capacity information through fiber optics systems where digital information is carried on separate wavelengths through the same fiber. Separate transmitters normally generate their respective signals that are transmitted at different wavelengths. These signals are then combined using a wavelength multiplexer to transmit the high capacity information through the fiber optic system.

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: 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 fiber optic communication system comprising: an optical signal source adapted to receive a binary first signal and generate a binary second signal, wherein the binary first signal has an amplitude modulated component, wherein the binary second signal has an amplitude modulated component and a frequency modulated component, and further wherein the binary second signal is characterized in that the higher intensity 1 bits are red shifted relative to the lower intensity 0 bits; a semiconductor optical amplifier (SOA) adapted to receive the binary second signal and generate a binary third signal, wherein the binary third signal has an amplitude modulated component and a frequency modulated component, and further wherein the semiconductor optical amplifier operates in saturation; and an optical spectrum reshaper (OSR) adapted to reshape the binary third signal into a binary fourth signal, wherein the binary fourth signal has an amplitude modulated component and a frequency modulated component.

Abstract: An optical system comprising a frequency modulated laser source adapted to produce a frequency modulated optical beam, an optical spectrum reshaper (OSR) adapted to receive the frequency modulated optical beam from the laser source and convert it into an amplitude modulated optical beam, a focusing lens adapted to receive the amplitude modulated optical beam from the OSR and focus the same, and an optical fiber adapted to receive the amplitude modulated optical beam from the focusing lens and transmit an optical signal; characterized in that the OSR has a central axis, the focusing lens has a central axis, and the optical fiber has a central axis, with the central axis of the optical fiber being laterally offset from at least one of the central axis of the OSR and the central axis of the focusing lens so as to effect spatial filtering and thereby generate the desired optical transmission characteristics for the resulting optical signal in the optical fiber.