Abstract: In a synchronous circuit, a synchronizing signal generator combines either an optical BPSK signal or local oscillation light with a phase-shifted signal to produce different optical signals, one of which for use in producing a signal demodulated from the BPSK signal is square-law detected, and calculates the optical signal detected to convert the signal into an electric signal. The generator produces an electric phase-locking signal which will be a demodulated signal from the BPSK signal on the basis of the electric signal. The phase-locking signal is used as a modulating signal by an intensity-modulating circuit to modulate an incident continuous light into an optical intensity-modulated signal, which is optoelectrically converted and square-law detected by an optoelectric converter. The converted signal is used by an optical VCO circuit as a phase error signal to adjust the phase or frequency of the local oscillation light, which is supplied to the signal generator.

Abstract: A self-polarization diversity technique to combat PMD in a direct-detection optical OFDM system. This technique does not require any dynamic polarization control, and can simultaneous compensate PMD in a WDM system with one device. Simulation results show that this technique virtually completely eliminates the PMD impairments in direct-detection optical OFDM systems.

Abstract: In various exemplary embodiments, the present invention provides coherent non-differential detection systems and methods for the detection of optical communication signals by the Brillouin fiber amplification of an optical communication signal carrier, the coherent non-differential detection systems including: a Sagnac loop including a single-mode fiber span; a fiber span with negligible birefringence (i.e. a spun fiber span or the like); or a fiber loop with negligible birefringence (i.e. a spun fiber loop or the like).

Abstract: The present invention relates generally to the transport and processing of optical communication signals. More specifically, the present invention relates to systems and methods for the polarization insensitive coherent detection of optical communication signals with Brillouin amplification of the associated signal carrier and the polarization division multiplexed transmission of optical communication signals without polarization tracking at the associated receiver(s).

Abstract: A receiving apparatus and method for processing a differential phase shift keying signal carrying a plurality of symbols are disclosed to provide for improved compensation of linear and non-linear noise in phase modulated optical transmission. The receiving apparatus comprises an input unit for receiving electrical signals derived from an optical signal and a calculation unit for calculating a current value of a decision variable. The current value is indicative of a differential phase shift in the optical signal between a currently received symbol and a previously received symbol as a function of the optical signal power of the optical signal for the currently received symbol and at least one previous value of the decision variable. The receiving apparatus also comprises a decision unit for determining the differential phase shift from the current value of the decision variable obtained from the calculation unit to obtain the currently received symbol.

Abstract: Demodulating an optical Differential Phase-Shift Keying (DPSK) signal is accomplished using a self-homodyne receiver for receiving the optical signal. A converter converts the optical signal received by the self-homodyne receiver into a representative electrical signal. A processor that processes the representative electrical signal using decision feedback multi-symbol detection in order to obtain a decision variable that indicates a differential phase-shift in the optical signal.

Abstract: A linear phase demodulator/down-converter comprises an optical amplitude modulator for modulating the amplitude of an optical input signal, a photo-detector, a loop filter and an optical phase modulator provided with a light source. The optical phase modulator/down-converter provides optical down conversion, optical up conversion, or a combination thereof. The photo-detector can be a balanced photo-detector. Linear phase demodulation and/or down conversion is performed completely in the optical domain.

Abstract: An apparatus, a polarization diversity receiver and a method of receiving a received optical signal. In one embodiment, the apparatus includes: (1) an optical device configured to separate in-phase and quadrature components of a received optical signal, to transmit the in-phase components to a first optical output thereof and to transmit the quadrature components to a second optical output thereof, (2) a first polarization splitter coupled to receive light at the first optical output and (3) a second polarization splitter coupled to receive light at the second optical output.

Abstract: The receiver comprises a first optical fibre input element (2) through which an information carrying element (S1) circulates, a local laser unit (3), an optical detection unit (4) and a differential demodulation unit (5). Characterised in that the information carrying signal (S1) of the input optical fibre (2) and the light beam (h1) generated by the local laser unit (3) are connected and detect in an optical detection block (4), which converts the information carrying signal (S1) into an electrical information carrying signal (S2) to be processed electrically in a demodulation unit (5) which performs a differential demodulation of the phase and quadrature components thereof, and subsequently combines same. The result in an optical receiver (1) with homodyne optical detection, the wavelengths of the input signal S1 and the synthonised light beam h1 coinciding, with high tolerance to the phase noise generated by optical communications lasers and not requiring use of an optical phase monitor (OPLL).

Abstract: A calculation processing unit controls temperature of a Peltier device based on a slope of a waveform obtained by subtracting a waveform of a B-arm monitoring signal from a waveform of an A-arm monitoring signal and a value obtained by subtracting a value B of the B-arm monitoring signal from a value A of the A-arm monitoring signal. Similarly, the calculation processing unit controls a phase of the A-arm and a phase of the B-arm. An A-arm side micro-controller controls temperature of an A-arm side heater 22 based on the value of the A-arm monitoring signal, and controls the phase of the A-arm. A B-arm side micro-controller controls temperature of a B-arm side heater based on the value B of the B-arm monitoring signal, and controls the phase of the B-arm.

Abstract: Tunable receivers and techniques for receiving an electrical oscillator signal in the RF, microwave or millimeter spectral range based on photonics technology to use both (1) photonic or optical components and (2) electronic circuit components.

Abstract: A received RZ-DPSK signal is guided to an interferometer. The interferometer comprises a 1-bit delaying element in an upper arm. A balanced photodiode converts a pair of optical signals output from the interferometer into electrical signal. A high-pass filter, which has a cut-off frequency equal or approximately equal to the symbol rate of transmission data, filters the signal output from the balanced photodiode. A BPSK demodulator circuit demodulates the output signal of the high-pass filter.

Abstract: An apparatus and method for extracting an optical clock signal are provided. The apparatus includes a first reflection filter selecting and reflecting only a first frequency component in an input optical signal; a first Fabry-Perot laser diode matching the first frequency component reflected by the first reflection filter with a predetermined output mode and outputting the first frequency component in the predetermined output mode; a second Fabry-Perot laser diode selecting a second frequency component in an input optical signal that has not been reflected but has been transmitted by the first reflection filter, matching the second frequency component with a predetermined output mode, and outputting the second frequency component in the predetermined output mode; and a photodetector receiving the first frequency component from the first Fabry-Perot laser diode and the second frequency component from the second Fabry-Perot laser diode and beating them to extract a clock signal.

Abstract: A WDM communication system having two optical-frequency comb sources (OFCSs) that are substantially phase-locked to one another, with one of these OFCSs used at a transmitter to produce a WDM communication signal and the other OFCS used at a receiver to produce multiple local-oscillator signals suitable for homodyne detection of the WDM communication signal received from the transmitter. In one embodiment, the transmitter has (i) a first OFCS adapted to generate a first frequency comb and (ii) an optical modulator adapted to use the first frequency comb to generate a WDM communication signal having at least two beacon lines for transmission to the receiver. The receiver has a second OFCS adapted to produce a second frequency comb having the beacon frequencies, with the phases of the corresponding comb lines being locked to the phases of the beacon lines of the received WDM signal.

Abstract: A method of receiving optical channels including providing an optical band filter configured to filter at least one optical channel from a multiple channel optical signal and provide a band filtered optical signal. A periodic filter is configured to filter and/or shape one channel from the band filtered optical signal and provide the periodic filtered, shaped signal to a receiver and other optical system. The invention also relates to corresponding systems and apparatuses.

Abstract: An optical data signal can be sampled by linearly combining the optical data signal with optical sampling pulses, and delivering the combination to first and second balanced detectors. The optical data signal and the optical sampling pulse are configured to have a first phase difference at the first balanced detector and a second phase difference at the second balanced detector. Typically, a difference between the first phase difference and the second phase difference is configured to be about 90 degrees. In-phase and quadrature balanced detector outputs can be combined as a sum of squares to produce a linear sampling signal representative of data signal intensity, and the sample pulses can be configured to temporally step through the optical data signal so that a sampled representation of the optical data signal is obtained.

Abstract: A frequency-agile optical transceiver includes a shared local oscillator (LO), a coherent optical receiver and an optical transmitter. The LO operates to generate a respective LO optical signal having a predetermined LO wavelength. The coherent optical receiver is operatively coupled to the LO, and uses the LO signal to selectively receive traffic of an arbitrary target channel of an inbound broadband optical signal. The optical transmitter is also operatively coupled to the LO, and uses the LO to generate an outbound optical channel signal having a respective outbound channel wavelength corresponding to the LO wavelength.

Abstract: A waveform shaping apparatus has a first integrating circuit 152, a second integrating circuit 153, and a first comparison circuit 154. The first and second integrated circuits 152 and 153 are connected in series with each other, and so operate that, when a voltage signal loner than a predetermined period and larger than a predetermined amplitude is fed to the first integrating circuit 152, the voltage signal is made higher than a first reference voltage and is then output to he second integrating circuit 153 and, when the voltage signal fed to the first integrating circuit 152 is shorter than the predetermined period, the voltage signal is made lower than the first reference voltage and is then outputted from the second integrating circuit 153. The first comparison circuit 154 compares a voltage contained in the voltage signal outputted from the second integrating circuit 153 with the first reference voltage, and outputs the comparison result.

Abstract: In a first broad aspect the invention provides an optical hybrid. The optical hybrid has an input for receiving an incoming optical signal containing data and a local oscillator optical signal and an output for releasing first and second output optical signals having a known phase relationship between them. In a specific and non-limiting example of implementation the phase relationship is 90 degrees. In this specific case the output signals are described as an in-phase and quadrature signals. The optical hybrid has an optical processing entity for deriving the first and second output optical signals from the incoming optical signal and the local oscillator signal. The optical processing entity including a loss element and a phase delay element for subjecting at least a component of an optical signal that exists in the processing entity to a known degree of attenuation and phase delay.

Abstract: The receiver features a first splitter which divides a differential phase modulated signal into three signal components from which at least two signal components are routed via timers. The first timer has a delay of a half period of the carrier signal and thereby serves in a conventional way for phase comparison and thus for demodulation. The second timer is adjustable and is used to compensate for the dispersion.

Abstract: A method and apparatus for receiving narrowband filtered optical PSK signals, including converting PSK optical signals into intensity-modulated signals at a receiver, and introducing a desired amplitude imbalance between the first and the second intensity-modulated signals to improve receiver performance.

Abstract: A system and method for superheterodyne detection in accordance with the invention. The system comprises a first conversion unit for performing a first heterodyne operation on an optical input signal to generate an electrical IF signal. A second conversion unit is electrically or optically coupled to the first conversion unit. The second conversion unit performs a second heterodyne operation to generate an electrical output signal suitable for signal processing.

Abstract: A WDM receiver that includes a single, delay interferometer coupled to an N-channel wavelength-demultiplexing filter provides for the simultaneous conversion of a multiplex of N differential-phase-shift-keyed modulated optical signals of different wavelengths into N intensity-modulated optical signal channels. The Nintensity-modulated optical signals may be individually detected by a bank of N photodiode circuits to recover the modulated data stream or used for optical amplification, regeneration, processing, control, or modulation.

Abstract: Demodulating an optical Differential Phase-Shift Keying (DPSK) signal is accomplished using a self-homodyne receiver for receiving the optical signal. A converter converts the optical signal received by the self-homodyne receiver into a representative electrical signal. A processor that processes the representative electrical signal using decision feedback multi-symbol detection in order to obtain a decision variable that indicates a differential phase-shift in the optical signal.

Abstract: A DQPSK optical signal is split by the splitter 1 into Data 1 and Data 2 systems. For each system, a phase-modulated optical signal is converted into an intensity modulated electric signal, and clock reproduction and data reproduction are independently carried out for each system. While a phase difference occurs between the data of each system, a clock signal having an intermediate phase of the reproduced clock of each system is generated to latch data of both systems by using the clock signal. This results in the data of both systems having the same phase.

Abstract: An optical coherent receiver in one embodiment has a heterodyne configuration, and in another embodiment has a homodyne configuration, in each configuration employs multiple feedback signaling and analog/digital processing to optimize response to a modulated optical input signal, the provision of both individual RF I and RF Q channel outputs.

Abstract: An optical device extracts an information bearing sideband such as an FSK or SCM signal (label) from a composite signal that includes the sideband and an orthogonally modulated signal such as an intensity modulated signal (payload) by employing polarization beam splitting and polarization transformation. Polarization transformation is accomplished by splicing the optical signal into a polarization maintaining fiber at a desired angle so that it is separated into two orthogonal polarizations that experience differential group delay in the fiber. The fiber is characterized by a beat length Lbeat and the fiber is designed to have a length substantially equal to (Lbeat×fc)/2?f, wherein the sidebands of the composite signal are separated by a wavelength difference ?f and fc is the nominal center frequency of the composite signal. This device has been shown to be useful for extracting GMPLS LSC level wavelength labels from either an FSK/IM composite signal or an SCM/IM composite signal.

Abstract: An apparatus and method for demultiplexing multiple wavelengths of light. In one embodiment, an optical signal having a plurality of wavelengths is provided to an optical-to-electrical (OE) circuit configured to convert optical signals into electrical signals. The optical signal may include a plurality of wavelengths. The OE circuit converts the optical signal into a first electrical signal. The first electrical signal is received by a demodulating circuit, which also receives a demodulating signal. The demodulating circuit combines both the first electrical signal and the demodulating signal in order to produce a second electrical signal. Both the second electrical signal and the demodulating signal correspond to one of the wavelengths in the optical signal.

Abstract: A frequency-agile optical transceiver includes a shared local oscillator (LO), a coherent optical receiver and an optical transmitter. The LO operates to generate a respective LO optical signal having a predetermined LO wavelength. The coherent optical receiver is operatively coupled to the LO, and uses the LO signal to selectively receive traffic of an arbitrary target channel of an inbound broadband optical signal. The optical transmitter is also operatively coupled to the LO, and uses the LO to generate an outbound optical channel signal having a respective outbound channel wavelength corresponding to the LO wavelength.

Abstract: The present invention comprises an optical communication system, including apparatuses and methods, which use coherence multiplexing to optically multiplex different signals that may have varying protocols or operate at different speeds, onto a single wavelength channel which is dense wavelength division multiplexed with other channels for optical communication. The apparatuses and methods of the optical communication system also enable the dropping and inserting of selected single protocol signals at intermediate sites of a DWDM communication link which is less costly and makes less wasteful use of optical wavelength channels for the communication of lower data rate information.

Abstract: The present invention provides several embodiments of a video carrier signal detection circuit included in an optical transmitter for either disabling an oscillator that provides dithering tones or attenuating the power level of the dither tones. A first detection circuit detects the presence of a video carrier signal by analyzing a known video channel. The power level of a video sync pulse included in the known video channel is then compared to a reference power level. A second detection circuit compares the composite power level of the RF signals in a predetenmined frequency spectrum with a reference power level to determine either the presence of a video carrier signal or an increase in the channel loading. Upon detection of a video carrier signal or an increase in composite power, an enable signal is provided to either the oscillator or an attenuating device depending upon the detection circuit.

Abstract: Optical transmitter/receivers for use in a DWDM systems are provided. Transmission of data signals in a quadrature-return-to-zero (QRZ) format achieves a data transmission rate equal to eight times a base data rate, i.e., 80 Gbps over a 100 GHz channel if the base data rate is 10 Gbps, with high non-linear performance by setting the polarization state of the data bands such that non-linear effects induced by PMD are reduced. Additionally, a transmitter achieves a transmission data rate equal to 16 times the base data rate by sharpening the QRZ pulses and interleaving pulse-sharpened QRZ data signals in the time domain, further doubling the data rate. Using counterpropagation in the transmitter, carrier signals and data signals traverse the same length of fiber, reducing fringing effects in the transmitter. Related techniques enhance reception and detection of data at high data rates. A local pulse-sharpened carrier is mixed with a QRZ data signal at a detector reducing amplification noise by a factor of two.

Abstract: A light demultiplexer in which a signal and a noise in each channel may be distinctly separated is provided. The light demultiplexer comprises a light-receiving element array for receiving light beams demultiplexed every wavelength from a wavelength multiplexed light beam and arranged in a straight line. The light-receiving element array includes a plurality of light-receiving elements for monitoring signals, and a plurality of light-receiving elements for monitoring noises. The light-receiving elements for monitoring signals and the light-receiving elements for monitoring noise are alternately arrayed in a straight line the direction thereof is the same as that of the arrangement of the demultiplexed light beams.

Abstract: An apparatus and method is disclosed for receiving packets having a wide dynamic range of power levels over a shared medium in a communications system. The receiver responds to a packet with a different power level within an inter-packet time and maintains a constant logic level for a long string of ‘ones’ or ‘zeros’ within a packet. An AC-coupled pre-amplifier provides a voltage signal having a slowly decaying power level for a long string of ‘ones’ or ‘zeros’ within the packet. A differential amplifier with hysteresis, ignores the slowly decaying power level of a long string of ‘ones’ or ‘zeros’ within the packet and does not overwrite the power level of the long string until it detects the end of the string.

Abstract: Method and apparatus for reducing intra-channel distortions of received data resulting from non-linear signal propagation includes parallel detection subcircuits for determining output values of sequentially provided optical data bits such that each of the sequentially provided optical data bits is processed by only one of the parallel detection subcircuits. Two parallel detection subcircuits process the input optical data bits according to even valued and odd valued clock signals. Each subcircuit has first and second signal analyzers to detect the value of the input optical data bit and a first memory unit and a second memory unit connected to the first and second signal analyzers. The input value of clock information provided to the first and second memory units of the first parallel subcircuit are 180° out of phase with input values indicative of a clock speed provided to the second parallel subcircuit.

Abstract: A large time constant is caused due to parasitic capacitance at an anode terminal of a photodetector of an optical receiver. Therefore, an optical receiver wherein a variable negative capacitor mainly including an NPN-type transistor operable at high speed is configured and is connected to the input terminal of a preamplifier to which the output of the photodetector is input so that parasitic capacitance caused in the photodetector and due to packaging is equivalently reduced and the fluctuation of parasitic capacitance caused due to manufacturing dispersion is also compensated is provided.

Abstract: The present invention is a decoder for decoding a signal. The decoder includes a discriminator and a threshold generator. The discriminator receives the signal and generates an output voltage equal to a first voltage if the signal is less than a threshold level that is input to the discriminator and equal to a second voltage if the signal is greater than the threshold level. The threshold level depends on the output from the discriminator in a preceding time interval that depends on the impulse response of a transmission link through which the input signal has passed. The threshold generator implements a low-pass analog filter that receives the output voltage during each of the clock periods and generates therefrom a filtered output signal.

Abstract: An optical signal receiver apparatus is comprised of a photodiode for converting an input photo-signal into a photoelectric current and an integrated circuit having a transimpedance amplifier for converting the photoelectric current into a voltage signal and amplifying it. The power source line of the photodiode can be shortened by supplying a power source current to the photodiode through a current detector in the integrated circuit. In addition, a current drain circuit is used to drain a DC current from the input side of the transimpedance amplifier on the basis of the detection result obtained by the current detector. The current drain circuit is operated when a photoelectric current is output from the photodiode.