Abstract: A data modulator unit generates a DQPSK optical signal in accordance with a data signal. A phase shift unit provides a phase difference of ?/2 between a pair of arms. A photodetector converts an output signal of the data modulator unit into an electrical signal. A filter is a low-pass filter with a cut-off frequency lower than a symbol frequency, and filters an output signal of the photodetector. A monitor unit detects power of an output signal of the filter. A phase difference control unit adjusts the amount of phase shift in the phase shift unit so as to minimize power of an output signal of the filter.

Abstract: In a fixed delay optical communication system, rate adjustable differential phase shift key (DPSK) techniques eliminate the need for multiple comparing modules, each corresponding to a different data rate. Setting alternative data rates at integer multiples of the fundamental data rate of the optical communication system allows the system to process the respective integer number of symbols per period of the system, wherein the period of the system is the inverse of the fundamental data rate. Pulse carving techniques may be used to set the duty cycle of clock levels associated with a clock signal. The clock levels may be combined with respective symbols to provide optical symbols having a duty cycle less than 100%.

Abstract: A method of converting a modulated optical signal to an encoded electrical signal is provided. The method utilizes a device comprising an electrooptic sideband generator, an optical filter, and an optical/electrical converter. Initially, the modulated optical signal, which carries encoded optical data, is directed to an optical input of the electrooptic sideband generator. The electrooptic sideband generator is driven to generate frequency sidebands about a carrier frequency of the input optical signal. The optical filter is utilized to discriminate between the frequency sidebands and the carrier frequency and combine sidebands-of-interest to yield at least one frequency-converted optical signal comprising a millimeter wave modulation frequency. The frequency converted optical signal carries the encoded optical data and the modulation frequency is a function of the spacing of the sidebands-of-interest.

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: RF and microwave devices and techniques are disclosed for processing RF and microwave signals by using (1) photonic or optical components and (2) RF and microwave components. In some implementations, a part of the processing is performed in the RF and microwave domain such as applying a microwave or RF input signal to control an optical modulator, and another part of the processing is performed in the optical domain such as optical filtering of the modulated optical beam to select desired microwave or RF spectral components. The frequency of a selected spectral component can be tuned by either tuning the frequency of the optical beam that is modulated by the optical modulator or a filter that is used to filter modulated optical beam.

Abstract: A WDM optical transmission system of the invention: detects an optical waveform of an intensity-modulated optical signal adjacent to a phase-modulated optical signal in a wavelength range; calculates a phase modulation drive waveform for canceling XPM of the phase-modulated optical signal affected by the adjacent intensity-modulated optical signal in the optical transmission path, based on the detected result; and additionally phase-modulates the phase-modulated optical signal synchronously with the adjacent intensity-modulated optical signal, according to the drive waveform, to thereby compensate the XPM. As a result, excellent transmission characteristics can be realized.

Abstract: The present invention discloses an optical transmitter that provides a function to vary the rate of the increase of the bias and modulation currents and their practical values during the APC feedback loop is left unstable without prolonging this unstable period. The optical transmitter of the invention includes a controller configured to read initial parameters from the memory, to increase the bias and modulation currents in stepwise based on thus read initial parameters, and to begin the automatic feedback control to keep the optical output from the laser diode constant after the bias and modulation currents reach their temporarily target values.

Abstract: There is provided an optical modulation signal generating device in which an operation speed is not limited by a relaxation oscillation frequency of a laser, and high-speed modulation and long-distance transmission can be performed. The optical modulation signal generating device converts a signal from a signal source into an optical signal and outputs the optical signal to a transmission medium having frequency dispersion. The optical modulation signal generating device includes an optical source (102) for performing frequency modulation by the signal from the signal source to generate an optical signal having only a frequency modulation component, and a frequency filter (103) for converting the frequency modulation component of the optical signal into an intensity modulation component and a frequency modulation component.

Abstract: In a quantum cryptographic transmitter (11), a phase modulator (1103, 1104) and an LN intensity modulator (1105) apply optical phase modulation and light intensity modulation to an optical signal based on desired data to generate a desired optical signal to be transmitted to a quantum cryptographic receiver (13). Based on the number of photons detected from the desired optical signal, a bias control circuit (1108) controls an operating point in light intensity modulation of the LN intensity modulator (1105).

Abstract: A non-feedback pre-encoder for optical DQPSK modulation includes four differential encoders, two power splitters, two delay lines, one exclusive OR gate and a cross switch. Each of two data streams input to the pre-encoder is divided into two identical streams by one of the power splitter, called an upper stream and a lower stream, respectively. Every upper stream is differentially encoded by one of the differential encoders, and outputs of the differential encoders are fed into the XOR gate. An output of the XOR gate drives the cross switch as a control signal. Two lower input data stream are delayed in the delay lines, and fed into the cross switch. The outputs of the cross switch are differentially encoded, separately, where outputs of the pre-encoder are provided. The invention eliminates the speed limitation due to the electrical propagation by constructing an all-forward control signal.

Abstract: An optical modulator is provided which includes: an optical splitting part that splits an input light wave into two light waves; two optical waveguides that propagate the two light waves into which the input light wave is split, respectively; a first SSB modulating part that is provided in one of the two optical waveguides and modulates a light wave, which propagates into the first SSB modulating part, with a carrier frequency so that the light wave is converted into a different light wave having a single side band; a second SSB modulating part that is provided in the other of the two optical waveguides and modulates a light wave, which propagates into the second SSB modulating part, with a data signal in order to generate a signal light wave having a different single side band; and an optical combining part that combines the light wave modulated by the first SSB modulating part with the signal light wave generated by the second SSB modulating part.

Abstract: An optical transmitter is provided which optimizes DC bias voltage input to an optical modulator employing a duo-binary modulation scheme. The optical transmitter including a signal combiner which converts an electrical signal for optical transmission into a high-speed electrical signal, and an optical modulator which receives and modulates the high-speed electrical signal from the signal combiner further includes a frequency divider to divide frequency of a sinusoidal watchdog clock signal from the signal combiner and to output the divided signal to be added to direct current (DC) bias voltage input to the optical modulator; and a bias voltage modifier to adjust the DC bias voltage by analyzing the modulated electrical signal from the optical modulator. Accordingly, it is possible to conveniently optimize the DC bias voltage with a simple design.

Abstract: A system and method for encoding an analog input signal for optical transmission, including driving a voltage controlled oscillator with an analog input signal to produce a frequency modulated electrical signal having a frequency proportional to the amplitude of the input signal, and applying the frequency modulated electrical signal to a multiple quantum well modulating retroreflector. The retroreflector receives optical energy from a laser source and modulates the optical energy with the frequency modulated signal to produce an output optical signal.

Abstract: Described are an FSK modulator and a method for large-alphabet FSK modulation. The FSK modulator and the method are based on filtering of a multi-tone optical source such as a mode-locked laser which provides a comb distribution of tones. A frequency-selective component selects for transmission a subset of the tones. In various embodiments the frequency-selective component is a Mach-Zehnder interferometer filter or a microring resonator filter. A second frequency-selective component selects a subset of the tones from the comb distribution provided by the first frequency-selective component. Still more frequency-selective components can be used according to the number of tones supplied by the multi-tone optical source to the FSK modulator. The optical signal exiting the last frequency-selective component includes only a single tone which corresponds to the symbol to be transmitted.

Abstract: An object of this invention is to provide a modulator, an optical transmitter and an optical transfer device which can modulate a channel signal while suppressing residual AM signals regardless of the frequency of a channel signal and suppressing deterioration of the channel signal due to impossibility of giving a sufficient FM demodulation amplitude.

Abstract: The present invention discloses a transmitter and receiver for optical communications system, which provide compensation of the optical link nonlinearity. M-PSK modulating is used for data embedding in an optical signal in each WDM channel using orthogonal frequency division multiplexing (OFDM) technique. At the receiver side electrical output signals from a coherent optical receiver are processed digitally with the link nonlinearity compensation. It is followed by the signal conversion into frequency domain and information recovery from each subcarrier of the OFDM signal. At the transmitter side an OFDM encoder provides a correction of I and Q components of a M-PSK modulator driving signal to compensate the link nonlinearity prior to sending the optical signal to the receiver.

Abstract: An interference-rejection coding method for an optical wireless communication system and such an optical wireless communication system are provided. The coding method uses delay modulation, block code techniques and filtering to reduce the low frequency interference from light sources. A plurality of codewords from the block codes are reserved for performing digital data recovery. The invention removes the need of analog clock data recovery circuit, and does not require complex hardware for realization. Therefore, it can be applied to a wide range of applications, such as optical WLAN, data transmission of medical facilities, wireless communication in the aircraft, encrypted data transmission network, and low-priced transmission interfaces.

Abstract: An optical communication system and method of use are described.

Abstract: A system having a first optical modulator operates in a non-linear region thereof and fed by: an input radio frequency signal; and, a first optical frequency signal having a wavelength ?2. A second optical modulator operates in a linear region thereof and fed by: a fractional portion of the input radio frequency signal phase shifted relative to the input radio frequency signal by n? radians where n is an odd integer; and a second different optical frequency signal wavelength ?1. A first photodiode is fed by an output of the first optical modulator. A second photodiode is fed by an output of the second optical modulator and a fractional portion of an output of the first optical modulator. An amplifier is fed by the second photodiode. A subtractor is fed by the amplifier and the first photodiode.

Abstract: There is provided an optical modulator capable of controlling the phase of a USB signal and the phase of an LSB signal of an optical FSK modulated signal. A modulation signal is applied to a main Mach-Zehnder electrode (or an electrode C) (11) of a main Mach-Zehnder waveguide (MZC) (8) to switch the USB signal and the LSB signal, and so FSK modulation can be made. In order to control the phase of the optical signal to be outputted from the main Mach-Zehnder waveguide (MZC) (8), bias voltage is applied to the main Mach-Zehnder electrode (11), and the phases of the USB signal and the LSB signal are controlled. By doing so, FSK modulation with adjusted phases can be performed.

Abstract: The present invention provides a method and an FSK/IM receiver to solve the problem of burst-mode detection of frequency modulated labels on an ASK (or IM) payload. In accordance with one embodiment of the present invention, two FSK tones of an input FSK/IM optical signal are separated and communicated to a balanced detector. At the balanced detector, the two FSK tones are subtracted from each other and result in an AC-coupled data stream. The AC-coupled data stream is communicated to a Schmitt-trigger where the hysteresis of the Schmitt-trigger finally eliminates any residual ASK (or IM) payload in the recovered output data. The present invention provides both single channel and WDM solutions.

Abstract: It is an object to provide an optical frequency control device or the like which can quickly carry out control over a wide frequency range. The object is achieved by an optical frequency control device or the like comprised of an optical SSB modulator (2), a bias voltage source (3) for applying a bias voltage to the optical SSB modulator (2), and a modulating signal source (4) for applying a modulating signal to the optical SSB modulator (2), wherein the modulating signal source (4) is provided with an arbitrary waveform generator (5) for generating an electrical signal with an arbitrary waveform, and an electrical signal multiplier (6) for multiplying a frequency of the electrical signal generated by the arbitrary waveform generator (5).

Abstract: A portable communication system provides a universal transmitter that couples to a communication device having an audio port, e.g., a cellular phone audio port, and which transforms the sound output into signals, e.g., infrared pulses, for transmission to a wireless receiver, e.g., a behind the ear or in the ear receiver.

Abstract: Provided is an optical transmission circuit capable of realizing a high-quality optical signal waveform with low power consumption. An optical transmission circuit (10) includes: a laser diode (800); a modulator (900) for supplying a differential modulation current to an anode terminal and a cathode terminal of the laser diode (800) through transmission lines (301 to 304); a current source (101) for supplying a forward bias current to the laser diode (800); and a magnetic sheet (wave absorber) (400) disposed so as to cover at least a part of the transmission lines (303 and 304). An impedance of the laser diode (800) is lower than characteristic impedances of the transmission lines (301 to 304) which are formed so that the characteristic impedances thereof are matched to an output impedance of the modulator (900).

Abstract: RF and microwave devices and techniques are disclosed for processing RF and microwave signals by using (1) photonic or optical components and (2) RF and microwave components. In some implementations, a part of the processing is performed in the RF and microwave domain such as applying a microwave or RF input signal to control an optical modulator ,and another part of the processing is performed in the optical domain such as optical filtering of the modulated optical beam to select desired microwave or RF spectral components. The frequency of a selected spectral component can be tuned by either tuning the frequency of the optical beam that is modulated by the optical modulator or a filter that is used to filter modulated optical beam.

Abstract: A method and system is disclosed for making timing alignment for a data transmission system, the method comprising providing a reference clock signal with a first frequency to a multiplexer through a phase shifter, generating a multiplexed signal with a second frequency by the multiplexer, wherein the second frequency follows the first frequency and is higher than the first frequency by a predetermined proportion, sending the multiplexed signal to a modulator, and phase shifting the reference clock signal by the phase shifter before the reference clock signal is provided to the multiplexer, wherein a timing of the multiplexed signal at the second frequency level can be adjusted by adjusting a timing of the reference clock signal at the lower first frequency level.

Abstract: A method and apparatus for providing a supervisory channel in a wavelength division multiplexing (WDM) fiber-optic communication system uses a controlled optical attenuator disposed in an optical path between a demultiplexer (DMUX) and a multiplexer (MUX) of an Optical Add-Drop Multiplexer (OADM.

Abstract: An optical device includes: a substrate side waveguide formed on a substrate; and a plurality of optical elements fixed on the substrate. The substrate side waveguide and an optical element side waveguide formed in each of the plurality of optical elements forms a continuous optical waveguide path.

Abstract: A fiber optic communication system, comprising: an optical signal source adapted to produce a frequency modulated signal; and an optical spectrum reshaper adapted to receive the frequency modulated signal and output a substantially amplitude modulated signal; wherein the optical spectrum reshaper limits the bandwidth of the frequency modulated signal.

Abstract: An optical transmission system which provides bandwidth restricted optical signal comprises an input terminal (10) for accepting an electrical binary signal, an amplifier (12) for amplifying said electrical binary signal to the level requested for operating an electrical-optical converter (16) such as a Mach Zehnder light modulator, a bandwidth restriction means (14) which is for instance a low pass filter for restricting bandwidth of said electrical binary signal, and an electrical-optical conversion means (16) such as a Mach Zehnder light modulator for converting electrical signal to optical signal. Because of the location of the low pass filter (14) between an output of the amplifier (12) and the Mach Zehnder light modulator (16), the amplifier (12) may operate in saturation region to provide high level output signal enough for operating the Mach Zehnder light modulator, and a signal shaped by the low pass filter (14) is applied to the Mach Zehnder light modulator (16) with excellent waveform.

Abstract: An optical FSK modulator which can be used for an optical information communication is provided.

Abstract: An all optical network for optical signal traffic has at least a first ring with at least one transmitter and one receiver. The first ring includes a plurality of network nodes. At least a first add/drop broadband coupler is coupled to the first ring. The broadband coupler includes an add port and a drop port to add and drop wavelengths to and or from the first ring, a pass-through direction and an add/drop direction. The first add/drop broadband coupler is configured to minimize a pass-through loss in the first ring and is positioned on the first ring.

Abstract: An optical transmitter is disclosed wherein a directly modulated laser outputs a frequency modulated signal through a semiconductor optical amplifier. Both the optical transmitter and semiconductor amplifier are modulated according to an output of a digital data source. An optical filter is positioned to receive an output of the semiconductor optical amplifier and has a frequency dependent transmission function effective to convert the amplified signal into a filtered signal having enhanced amplitude modulation. In some embodiments, the semiconductor optical amplifier is coupled to the digital data source by means of a compensation circuit configured to high-pass filter the output of the digital signal source. In other embodiments, the semiconductor optical amplifier is coupled to the digital data source by means of a compensation circuit configured to produce an output including a first-order time derivative of the output of the digital signal source.

Abstract: There is provided a fiber optic transmission system, comprising: an optical signal source adapted to produce a frequency modulated signal; and a multi-ring resonator optical spectrum reshaper (OSR) adapted to convert the frequency modulated signal into a substantially amplitude modulated signal. And there is provided a method for transmitting an optical signal through a fiber comprising: producing a frequency modulated signal; passing the frequency modulated signal through a multi-ring resonator optical spectrum reshaper (OSR) so as to convert the frequency modulated signal into a substantially amplitude modulated signal; and passing the substantially amplitude modulated signal into the fiber.

Abstract: An optical modulator achieving high extinction ratio and an optical modulator system. By a control system performing an adjustment method comprising predetermined steps by applying a bias voltage daringly to a modulation electrode for switching the USB signal and LSB signal of an established optical SSB modulator or optical FSK modulator, a means for adjusting bias voltage applied to each bias electrode preferably automatically is provided and a bias point where the extinction ratio of an optical modulator is maximized can be obtained.

Abstract: A polarization duobinary optical transmitter is disclosed. The transmitter includes a precoder for coding an electric signal and a light source for generating continuous light. The transmitter also includes a chirped-free modulator for generating an NRZ signal including first and second polarization light beams orthogonal to each other by modulating the light with the electric signal and a band-pass filter for limiting neighbor frequency bands between the first and second polarization light beams.

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 provides a new architecture for a communication system between head-ends and end-users which expands bandwidth and reliability of the communication system. A mux-node receives communication signals from a head-end and forwards the received communication signals to one or more mini-fiber nodes. The connection to the head-end is via a small number of optical fibers and the connections to each of the mini-fiber nodes may be via one or more optical fibers that may provide full duplex communication. The head-end may communicate with the mux-node using digital or digital and analog signals. The mini-fiber nodes may combine the signals received from the head-end with loop-back signals used for local media access control prior to forwarding the signals to the end-users. Upstream data are received by the mini-fiber nodes and transmitted to the mux-node.

Abstract: An optical transmission apparatus employing an FSK scheme is disclosed. The optical transmission apparatus includes a light generator arranged to generate a first tone signal having a first frequency and a second tone signal having a second frequency. The optical transmission apparatus also includes a light modulator including a second modulator for selectively outputting one of the first tone signal and the second tone signal input from the light generator according to input data.

Abstract: A method and system is disclosed for making time alignment for a data transmission system. A first reference clock signal is provided to a first multiplexer coupled to a data modulator through a data driver, and a second reference clock signal is provided to a second multiplexer coupled to a clock modulator through a clock driver. Phase adjustment of the reference clock signal are conducted before the first reference clock signal is provided to the first multiplexer, wherein the phase adjustment aligns a timing of data modulated by the data modulator with a periodically modulated light source generated by the clock modulator.

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 communication system includes an optical transmitter which is differentially driven and an optical receiver that outputs a differential signal. The optical transmitter creates the differential drive signal from an input signal and delivers the differential drive signal to a laser. The differential drive signal is generated with a transformer and RF chokes for floating the laser above ground. The signal detected by the receiver is input as a differential signal to a transformer which then passes the signal through amplifiers and a filter. The optical communication system provides an increased spurious-free dynamic range which is well suited for RF signals and other analog signals.

Abstract: An optical wavelength multiplexing frequency shift keying modulation system. The system includes an optical wavelength multiplexing signal acquisition unit for outputting an optical wavelength multiplexing signal. A n optical frequency shift keying modulation unit acquires an optical frequency shift keying signal, including an upper side band signal and a lower side band signal, by performing frequency modulation to the optical wavelength multiplexing signal output from the optical wavelength multiplexing signal acquisition unit. An optical frequency shift keying signal separation unit separates the optical frequency shift keying signal output from the optical frequency shift keying modulation unit into an upper side band signal and a lower side band signal.

Abstract: A transmitter formed of two or more light-emitting sections such as LEDs, which are physically arranged in a predetermined manner, is disposed in the real world object, and each light-emitting section transmits data by flashing at a flashing pattern representing the transmission data of a predetermined bit length. A receiver, on the other hand, includes a photoreceiving section formed from a two-dimensional photoreceiving surface, decodes the transmission data on the basis of the photoreceived flashing pattern, and recognizes the spatial information of an object on the basis of the flashing position on the two-dimensional photoreceiving surface. Therefore, information, such as an ID, can be obtained from the object in the real world, and also, the spatial position of the object can be recognized at the same time.

Abstract: An apparatus for generating a Carrier-Suppressed Return-to-Zero (CS-RZ) signal is disclosed. The apparatus includes a mixer, a Low Pass Filter (LPF), a driver amplifier and a single external modulator. The mixer generates a modulator input by mixing data with a half clock signal. The LPF band-limits the modulator input data into low frequency band data. The driver amplifier amplifies the modulator input data generated by the mixing of the mixer and the band-limiting of the LPF. The external modulator generates CS-RZ signal, in which the phases of adjacent pulses have been inverted, by applying bias voltage to the modulator input data to be placed at the null point of the transfer function of the external modulator.

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: 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 apparatus and a method for transmitting at least a digital optical signal with return-to-zero phase-shift keying, employing a single optical modulator with dual-drive design, the encoded optical signal having improved spectral efficiency and performances and being generated by transmitters with simplified scheme; an optical communication system comprising the transmitting apparatus, a transmission line and an apparatus to receive the optical signal.

Abstract: A method and apparatus for controlling bias and alignment in an optical signal transmitter for providing intensity modulation and DPSK modulation to an optical signal, e.g. in an RZ-DPSK modulation format. Output power in dither signals applied to the bias signals may be detected by a low speed photodetector. One or more of the bias signals may be adjusted in a low speed control loop in response to an error signal obtained by mixing the detected signal with the low frequency dither signals.

Abstract: A wavelength access server (WAS) architecture provides aggregation of traffic streams of diverse data communication protocols as well as provision of wavelength resources in an optical transport network. The WAS provides functions such as service traffic adaptation, traffic aggregation and segmentation, traffic classification, optical inter-working and system management. In particular, system management includes aspects such as signaling, connection management, resource co-ordination, protection prioritization and access policy management.