Abstract: An analogue to digital converter (100) is arranged to receive and process an analogue optical input signal (110) to produce an N bit digital optical output signal (140) quantised to 2N levels, where N is greater than or equal to 2. The converter (100) has an input (115) for receiving the optical input signal (110) and N processing channels (131, 132, 133) which arc each coupled to the input, at least one of said processing channels comprising an optical processing circuit (201, 202, 203, 204, 205, 206, 207) arranged to generate a plurality of digital optical output signals. The optical processing circuit is arranged to change the state of each digital optical output signal corresponding to a respective different value of the analogue optical input signal, and an optical combining circuit (301, 302, 303, 304) for combining the optical output signals in signal order to generate one bit of the N-bit digital optical signal.

Abstract: Systems and methods for converting wideband signals in the optical domain are provided. A device for obtaining a digital representation of a received signal may include a spatially dispersive element that may be configured to spatially disperse frequencies in an optical-domain representation of the received signal; a spatial light modulator that may be configured to mix the dispersed optical frequencies by imposing a mixing matrix on an optical intensity of the dispersed optical frequencies; an optical sensor that may be configured to obtain an electrical representation of the mixed dispersed optical frequencies; and a signal recovery processor that may be configured to obtain a digital representation of the received signal based on the electrical representation and the mixing matrix. The signal recovery processor may be further configured to determine a modulation format of the digital representation and may demodulate the digital representation based on the modulation format.

Abstract: A method and apparatus for receiving a digital signal having a plurality of significant bits of resolution. The apparatus includes a mode locked laser comprising a single output. The apparatus also includes a beam divider operable to receive the single output. The apparatus also includes a plurality of optical modulators operable to communicate with said beam divider and operable to receive a respective plurality of signals corresponding to a plurality of significant bits of resolution. Optionally, the apparatus also includes a source operable to output a digital waveform with the plurality of signals corresponding to the plurality of significant bits of resolution of the digital waveform, the plurality of signals operable to drive the plurality of optical modulators.

Abstract: A method and apparatus for encoding data. A first pair of optical signals having a first phase difference is generated in response to receiving an input signal having a voltage. A second pair of optical signals having a second phase difference is generated in response to receiving an input signal having a voltage. The first pair of optical signals is combined to form a first optical signal having a first intensity. The second pair of optical signals is combined to form a second optical signal having a second intensity. The first intensity of the first optical signal reaches a peak at a different time from the second intensity of the second optical signal.

Abstract: A device for generating an electrical signal with a wide band arbitrary waveform includes at least two continuous wave lasers each being adapted to produce light at a different wavelength. The device also includes at least one pulse generator adapted to convert the light from the lasers into optical pulse trains and a plurality of optical modulators. Each modulator is adapted to receive an optical pulse train at at least one wavelength and modulate the optical pulse train in response to an electromagnetic signal. An optically dispersive element is adapted to receive the optical pulse trains from the modulators and to introduce a wavelength dependent delay between the optical pulse trains. The device further includes a photodetector for receiving the modulated dispersed optical pulse trains and producing an analogue electrical signal in response thereto.

Abstract: An analog to digital converter (ADC) structure and method includes a photonic filter bank having at least two filters. The at least two filters are configured to create a corresponding spectral tributary from an input signal at a target rate, and the at least two filters are configured to exhibit orthogonality properties between respective tributaries. An optical/electrical (O/E) converter is coupled to each of the at least two filters in a respective spectral tributary to convert an optical input to an electrical output. An analog to digital converter (ADC) is coupled to each of the O/E converters in a respective spectral tributary to sample the electrical output at a fraction of a target rate and to convert a sampled analog electrical output into a digital signal. A synthesis filter is coupled to each of the ADCs in a respective spectral tributary to reconstruct the input signal digitally at the target rate.

Abstract: A power amplifier architecture includes a plurality of non-linear optically driven power amplifier modules. The plurality of non-linear optically driven power amplifier modules are selectively connectable utilizing a programmable algorithm for combining at least two modules of the plurality of non-linear optically driven power amplifier modules in a time sequence yielding a piecewise approximation of a continuous waveform. The power amplifier architecture further includes at least one RF drive selectively connected to at least one of the plurality of non-linear optically driven power amplifier modules via an optical signal link generating a separate drive signal for each of the plurality of non-linear optically driven power amplifier modules.

Abstract: In an inventive photonic analog-to-digital signal converter (ADC), multiple opto-electric sampling devices are employed to successively sample an analog signal input. Optical clock signals having the same frequency but different clock phases are used, which are associated with the opto-electric sampling devices, respectively. Each sampling device takes samples of the analog signal input in response to the optical clock signal associated therewith. The resulting samples are processed to produce quantized samples. The inventive ADC outputs a digital signal representing the quantized samples.

Abstract: In general, a method includes comparing a first input signal with a second input signal to produce an output signal. The first input signal corresponds to an amount of light detected by a sensor, and the second input signal corresponds to an aggregated value of the output signal. The method may also include aggregating the output signal in a digital accumulator and converting a digital signal from an output of the digital accumulator to an analog signal.

Abstract: A method and apparatus for encoding data. A first pair of optical signals having a first phase difference is generated in response to receiving an input signal having a voltage. A second pair of optical signals having a second phase difference is generated in response to receiving an input signal having a voltage. The first pair of optical signals is combined to form a first optical signal having a first intensity. The second pair of optical signals is combined to form a second optical signal having a second intensity. The first intensity of the first optical signal reaches a peak at a different time from the second intensity of the second optical signal.

Abstract: According to one embodiment of the invention, a digital to analog converter for converting a digital signal to an analog optical signal includes a light source and a plurality optical switches. Each optical switch is responsive to a respective one of a plurality of bits of a digital signal to selectively allow transmission of light from the light source through the switch. The digital to analog converter also includes a light combination system operable to combine the light passed through each of the switches and produce an analog optical signal indicative of the digital signal.

Abstract: A digital-to-analog converter (DAC) includes multiple electro-optical converters to generate multiple first optical signals in response to multiple input signals, multiple optical attenuators to attenuate intensities of the first optical signals and to generate multiple second optical signals, an optical coupler to combine the second optical signals and to generate a third optical signal, and a photodetector to convert the third optical signal into an electrical analog signal.

Abstract: In general, a method includes comparing a first input signal with a second input signal to produce an output signal. The first input signal corresponds to an amount of light detected by a sensor, and the second input signal corresponds to an aggregated value of the output signal. The method may also include aggregating the output signal in a digital accumulator and converting a digital signal from an output of the digital accumulator to an analog signal.

Abstract: A monitoring device in an analog-to-digital converter, the monitoring device including a monitoring module configured to receive a first radio frequency signal provided by a first radio frequency modulator and a second radio frequency signal provided by a second radio frequency modulator. The first radio frequency signal being associated with a laser data and a radio frequency input signal. The laser data being associated with a radio frequency oscillator signal. The second radio frequency signal being associated with the laser signal and the radio frequency oscillator signal. The monitoring module is configured to determine a modification factor based on the first radio frequency signal and the second radio frequency signal.

Abstract: Provided herein are segmented digital to analog converters (DACs), methods for use therewith, and systems that include one or more such DACs. According to an embodiment, a DAC includes a plurality of sub-DACs, a DAC input adapted to receive a multi-bit digital input and a DAC output adapted to output an analog output current in response to and indicative of the digital input. Each sub-DAC is adapted to receive a separate reference current that specifies a transfer function of the sub-DAC. A magnitude of the reference current provided to each sub-DAC is separately programmable to thereby separately control a gain of each sub-DAC.

Abstract: The present invention is a remote input analog-to-digital conversion (ADC) system. The system may generate low jitter, short duration optical pulses to allow for high performance sampling of an antenna signal at a remote end of the system. The system may utilize phase modulation and IQ demodulation (with a reference optical pulse stream) using separate analog-to-digital converters for I and Q to overcome linearity limitations. Low sampling rate analog-to-digital converters may be utilized by the system by using parallel, low optical pulse repetition rate paths and/or optical demultiplexer switching trees. The system is an optical fiber system.

Abstract: An optical clock for generating a series of optical clock pulses, comprises a laser source for generating output having a plurality of spectral components ?1, ?2, . . . ?N, an amplitude-modulator arranged to cooperate with the laser source to produce a series of intermediate optical pulses each having the plurality of spectral components, and optical fibre arranged to provide dispersion of each intermediate optical pulse to form a plurality of component pulses each corresponding to a spectral component and to compress each component pulse, the spectral width of each spectral component being sufficient to inhibit stimulated Brillouin scattering (SBS) of the component pulses within the optical fibre. The optical clock may be used for analogue-to-digital conversion of an electrical signal, in which application pulses of respective spectral components are demultiplexed and subsequently detected and digitised in parallel, providing for faster conversion.

Abstract: A digital-to-analog converter (DAC) includes multiple electro-optical converters to generate multiple first optical signals in response to multiple input signals, multiple optical attenuators to attenuate intensities of the first optical signals and to generate multiple second optical signals, an optical coupler to combine the second optical signals and to generate a third optical signal, and a photodetector to convert the third optical signal into an electrical analog signal.

Abstract: An analog-to-digital converter includes a first switch circuit, a first integrator, a second switch circuit, a second integrator, a quantizer and a digital-to-analog converter. The first switch circuit receives an external analog signal, outputs the analog signal in reverse phase, and outputs the analog signal in positive phase. The first integrator receives and integrates the analog signal with cross-coupling. The second switch circuit outputs an output of the first integrator and a common mode output potential of the first integrator. The second integrator samples and integrates an output of the second switch circuit. The quantizer single-bit-quantizes an output of the second integrator to provide the output as a digital signal output. The digital-to-analog converter receives an output of the quantizer and provides the output as an analog signal output. Each of the first and second integrators receives and integrates an output of the digital-to-analog converter with cross-coupling.

Abstract: An all-optical combined serial-to-parallel and digital-to-analog convertor using standard WDM technology is realized. The system is based on bit interleaving and cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA). The optical system can operate on multiple-bit digital words at a very high bit rate. The analog output forms series of pulses with the amplitude of each pulse taking one of the eight discrete values. A low pass filter may be used to turn this bit stream into a continuous waveform, and thus arbitrary waveforms are generated. Unlike many current digital-to-analog converter designs, which double in size with each additional bit, the design presented here allows a linear growth in components, thus making higher bit systems practical.

Abstract: In an inventive photonic analog-to-digital signal converter (ADC), multiple opto-electric sampling devices are employed to successively sample an analog signal input. Optical clock signals having the same frequency but different clock phases are used, which are associated with the opto-electric sampling devices, respectively. Each sampling device takes samples of the analog signal input in response to the optical clock signal associated therewith. The resulting samples are processed to produce quantized samples. The inventive ADC outputs a digital signal representing the quantized samples.

Abstract: A data encoding method is provided. In this method, a plurality of n-bit input codes is converted into a plurality of ML block codes, wherein every bit in each of the block codes has at least one identical bit adjacent horizontally or vertically to the bit.

Abstract: A time-stretched enhanced recording scope (TiSER) is described using time stretch analog-to-digital conversion in a real-time burst mode. A chirped optical signal is modulated in response to receiving segments of an input signal. The optical signal with its modulated input signal, is stretched through an optical medium and digitized to represent the waveform segment. TiSER provides ultra-fast real-time sampling within short segment bursts of the original input signal while providing an ability to detect non-repetitive events. Methods and apparatus are also described for providing real-time information about inter-symbol information (ISI), rapidly determining bit-error rates (BER), performing time-domain reflectometry (TDR), generating eye diagrams for serial data, facilitating digital correction of data, clock recovery, optical carrier phase recovery, and otherwise increasing the speed and/or accuracy of a diverse range of high-speed signal measurement and processing activities.

Abstract: A device for generating an electrical signal with a wide band arbitrary waveform comprising (i) at least two continuous wave lasers each being adapted to produce light at a different wavelength; (ii) at least one pulse generator adapted to convert the light from the lasers into optical pulse trains; (iii) a plurality of optical modulators, each modulator being adapted to receive an optical pulse train at least one wavelength and modulate the optical pulse train in response to an electromagnetic signal; (iv) an optically dispersive element adapted to receive the optical pulse trains from the modulators and to introduce a wavelength dependent delay between the optical pulse trains; and, (v) a photodetector for receiving the modulated dispersed optical pulse trains and producing an analogue electrical signal in response thereto.

Abstract: A delay device that provides a delay amount to at least one of the in-phase signal and the quadrature signal, and a delay control section that controls the delay amount provided by the delay device based on a quality of the signals when the in-phase signal and the quadrature signal, to the at least one of which the delay amount is provided, at the delay device are converted into digital signals by the analog-digital converter, and the digital signal processing is carried out at the processor are provided. Thereby, the signal quality of recovered data at a receiving end of a multi-level phase modulation communication system is improved.

Abstract: An optical quantizing unit includes an optical divider dividing 1st optical pulses to be quantized and sending the divided 1st optical pulses into a plurality of paths; a plurality of optical filters passing with different transmittances the divided 1st optical pulses; and an optical threshold filter sequentially receiving the 1st optical pulses, and sending 2nd optical pulses when light intensities of the 1st optical pulses are above a preset threshold value.

Abstract: An Analog to Digital (AD) converter and an AD converting method are provided. The AD converter includes one or more stators, and one or more actuators that move according to an input voltage. The digital output of the AD converter is determined based on an arrangement of the stators and the positions of the actuators relative to the stators. The AD converter can achieve high resolution and/or high speed with lower power consumption.

Abstract: An analog-to-digital (“A/D”) converter includes; a photocurrent integrator which integrates photocurrent and stores the integrated photocurrent in a feedback capacitor in the form of voltage, and a discharger which attenuates the voltage out from the photocurrent integrator in the form of an exponential function.

Abstract: According to one embodiment of the invention, a digital to analog converter for converting a digital signal to an analog optical signal includes a light source and a plurality optical switches. Each optical switch is responsive to a respective one of a plurality of bits of a digital signal to selectively allow transmission of light from the light source through the switch. The digital to analog converter also includes a light combination system operable to combine the light passed through each of the switches and produce an analog optical signal indicative of the digital signal.

Abstract: An analog to digital converter (ADC) structure and method includes a photonic filter bank having at least two filters. The at least two filters are configured to create a corresponding spectral tributary from an input signal at a target rate, and the at least two filters are configured to exhibit orthogonality properties between respective tributaries. An optical/electrical (O/E) converter is coupled to each of the at least two filters in a respective spectral tributary to convert an optical input to an electrical output. An analog to digital converter (ADC) is coupled to each of the O/E converters in a respective spectral tributary to sample the electrical output at a fraction of a target rate and to convert a sampled analog electrical output into a digital signal. A synthesis filter is coupled to each of the ADCs in a respective spectral tributary to reconstruct the input signal digitally at the target rate.

Abstract: A display device that is capable of displaying predetermined display information in each of a plurality of display areas includes a setting unit for setting display control information that represents the position and size of the display area and the switching of the display information for when a predetermined event is detected, based on user inputs; and a display control unit for controlling one display including the multiple display areas such that the display information is displayed in each of the multiple display areas, based on the display control information set by the setting unit. Upon detection of the event, the display control unit switches the position or size of the display area where the display information for the detected event is displayed based on the display control information.

Abstract: A high speed optical analog/digital conversion process with a simple configuration, in which an optical-pulse branching delay multiplexer generates as many duplicates of each optical pulse as the predetermined number of bits by branching each optical pulse string obtained by sampling an input optical analog signal, and generates a temporally consecutive optical pulse string by multiplexing the duplicated optical pulses with a predetermined intensity difference and time difference. An optical encoder and an optical-threshold processing unit perform an encoding and a quantization of an optical pulse string, and output an optical digital signal corresponding to the optical analog signal.

Abstract: In one embodiment, an opto-electronic analog-to-digital converter is provided that includes: an optical comb generator for generating a plurality of optical comb lines; a tunable optical filter adapted to select a portion of the optical comb lines responsive to an analog signal being digitized; a diffractive media for spatially mapping the selected optical comb lines and an array of photodetectors for detecting the spatially mapped optical comb lines.

Abstract: An optical analog-to-digital converter (ADC) is disclosed which converts an input optical analog signal to an output optical digital signal at a sampling rate defined by a sampling optical signal. Each bit of the digital representation is separately determined using an optical waveguide interferometer and an optical thresholding element. The interferometer uses the optical analog signal and the sampling optical signal to generate a sinusoidally-varying output signal using cross-phase-modulation (XPM) or a photocurrent generated from the optical analog signal. The sinusoidally-varying output signal is then digitized by the thresholding element, which includes a saturable absorber or at least one semiconductor optical amplifier, to form the optical digital signal which can be output either in parallel or serially.

Abstract: According to one embodiment of the invention, a digital to analog converter for converting a digital signal to an analog optical signal includes a light source and a plurality optical switches. Each optical switch is responsive to a respective one of a plurality of bits of a digital signal to selectively allow transmission of light from the light source through the switch. The digital to analog converter also includes a light combination system operable to combine the light passed through each of the switches and produce an analog optical signal indicative of the digital signal.

Abstract: Embodiments of the present disclosure include apparatuses, systems, and methods of providing optical digital to analog conversion. A method embodiment includes receiving an optical signal that includes a plurality of wavelengths, splitting the received optical signal into a plurality of optical beams each including the plurality of wavelengths, modifying the particular wavelengths present in at least one of the plurality of optical beams based on a digital input, and recombining the plurality of optical beams to produce an optically converted multi-wavelength analog optical signal.

Abstract: An imaging system including column-parallel ADCs that operate in response to a single slope global ramp signal and a matched global ramp line signal that has a voltage representative of a dark pixel value. The signal paths of the global ramp signal and the matched global ramp line signal are matched to minimize noise effects. Prior to performing a pixel read operation, the global ramp signal is increased through a first voltage range (below the dark pixel value) to ensure that the column-parallel ADCs are operating in a linear range. The first voltage range can be adjusted to cancel offset error associated with the column parallel ADCs. The column-parallel ADCs provide output signals having a full voltage swing between VDD and ground.

Abstract: The invention provides a solid-state image sensor comprising a pixel array, a reading circuit, an analog-to-digital (A/D) circuit, a decoding circuit, a driving circuit, a power array, a spare circuit, a fuse array, and a repair unit. When one described element fails, a repair procedure is applied to select a corresponding element from the spare circuit to replace the failed element via the fuse array.

Abstract: An optically isolated circuit device includes a first opto-isolator circuit that is driven by a first clock signal, and the output of the first opto-isolator circuit is used to drive a phase-locked loop (PLL) that is configured to synthesize a second clock signal having a frequency that is a multiple of the first clock signal frequency. The second clock signal is used as an input to a suitable clocked circuit of a type that benefits from optical isolation, such as an analog-to-digital converter (ADC).

Abstract: An optical quantizing unit includes an optical divider dividing 1st optical pulses to be quantized and sending the divided 1st optical pulses into a plurality of paths; a plurality of optical filters passing with different transmittances the divided 1st optical pulses; and an optical threshold filter sequentially receiving the 1st optical pulses, and sending 2nd optical pulses when light intensities of the 1st optical pulses are above a preset threshold value.

Abstract: The present invention provides an optical DVI cable and optical signal transmission equipment which can prevent the leakage of laser light to the outside. The optical DVI cable includes (1) a transmission side unit having a laser light emitting element unit, and configured and arranged to convert input electrical signals into optical signals and to transmits the optical signals, (2) a reception side interface unit configured and arranged to receive the optical signals transmitted from the transmission side interface unit, and (3) a connecting cable having metal wires to supply power to the laser light emitting element unit, and optical fibers to transmit optical signals. The transmission side unit may include a power supply terminal. In this case, the metal wires supply power to the laser light emitting element unit from the transmission side unit via the reception side unit.

Abstract: An optical signal is copressively sampled using an imaging system. The imaging system is created from a plurality of subimaging systems. Each subimaging system comprises a subaperture and a plurality of sensors. The optical signal is collected at each subaperture of the plurality of subimaging systems at a single time step. The optical signal is transformed into a subimage at each subimaging system of plurality of subimaging systems. The subimage includes at least one measurement from a plurality of sensors of each subimaging systems. An image of the optical signal is calculated from the sampling function and each subimage, spatial location, pixel sampling function, and point spread function of each subimaging system of the plurality of subimaging systems. The sampling function is selected so that the number of measurements from a plurality of subimages is less than a number of estimated optical signal values in the image.

Abstract: An optically sampling device optically samples an optical analog signal using a sampled signal having a predetermined sampling frequency, and outputs control light having a pulse train of an optically sampled optical analog signal. A signal generating device generates a pulse train of signal light which is synchronized with the sampled signal. An optical encoding device optically encodes the pulse train of the signal light according to the control light, by using optical encoders each including nonlinear optical loop mirrors, and outputs pulse trains of optically encoded signal light from said optical encoders, respectively. An optically quantizing device performs optical threshold processing on the pulse trains of optically-encoded signal light to optically quantize them, by using at least one of optical threshold processors each of which is connected to each of said optical encoders and includes a nonlinear optical device, and outputs optically quantized pulse trains as optical digital signals.

Abstract: An optical receiving device of the present invention receives optical signals from an optical transmitting device which uses a modulation format wherein an optical intensity waveform of each symbol is return-to-zero (RZ) pulse, and converts the received optical signals into digital signals by a conversion process of an analog to digital (AD) converter. A control-value calculating unit subsequent to the AD converter digitally processes the digital signals, retrieves an absolute value of the digital signals or a value corresponding one-to-one with the absolute value of the digital signals, estimates errors from an appropriate timing of a sampling timing in the AD converter based on the absolute value of the digital signals or the value corresponding one-to-one with the absolute value of the digital signals, and calculates a control value controlling the sampling timing based on the estimated errors.

Abstract: The invention relates to an optical device, apt to generate and process optical codes at least one wavelength, comprising P inputs s, with 1?s?P, and P?1, and N outputs k, with 1?k?N and N?1, characterized in that it is apt to simultaneously generate and process Nc?2, made of C chips with time interval ?, with C?2, characterized in that the transfer function Tsk(f) from the input s to the output k satisfies the following formula: where: Fv is a transfer function of an optical filter, for v=0, 1 . . . , V?1, av is a constant value, for v=0, 1, . . . , V?1 Ssk is an integer number (Ssk?Z), Nk is a constant value, for k=2, . . . N, and V is a positive integer number with 1?V?log2N. The invention further relates to a set of optical codes, apt to be generated, in particular, by such optical device, and to networks and apparatus comprising such optical device.

Abstract: An optical digital-to-analog (D/A) converter and a method of optically converting digital data into analog form. In one embodiment, the optical D/A converter includes: (1) a splitter configured to receive and split an input coherent optical carrier into a plurality of mutually coherent optical carriers, (2) a switching stage coupled to the splitter and including a corresponding plurality of selector switches configured to pass or interrupt selected ones of the plurality of coherent optical carriers responsive to pattern bits, (3) an amplitude and phase offset stage coupled to the switching stage and including a corresponding plurality of amplitude and phase offset units configured to offset amplitudes or phases of passed ones of the plurality of mutually coherent optical carriers responsive to offset signals and (4) a combiner coupled to the amplitude and phase offset stage and configured to recombine the mutually coherent optical carriers to yield an optical output signal.

Abstract: An optical quantizing unit includes an optical divider dividing 1st optical pulses to be quantized and sending the divided 1st optical pulses into a plurality of paths; a plurality of optical filters passing with different transmittances the divided 1st optical pulses; and an optical threshold filter sequentially receiving the 1st optical pulses, and sending 2nd optical pulses when light intensities of the 1st optical pulses are above a preset threshold value.

Abstract: An optical quantizing unit includes an optical divider dividing 1st optical pulses to be quantized and sending the divided 1st optical pulses into a plurality of paths; a plurality of optical filters passing with different transmittances the divided 1st optical pulses; and an optical threshold filter sequentially receiving the 1st optical pulses, and sending 2nd optical pulses when light intensities of the 1st optical pulses are above a preset threshold value.

Abstract: A sampled-data-integrating front end is employed to convert an optical signal to a digital electrical signal. The front end includes a photodetector and an array of parallel conversion circuits, each including an activation switch, a charge amplifier and an Analog to Digital Converter (“ADC”). The charge amplifier includes a reset switch, a capacitor, and an amplifier. The resent switch is operable to discharge the capacitor. The capacitor is operable to charge to the voltage of a signal charge when the activation switch is closed, and to hold that voltage after the activation switch is opened. The amplifier is operable to provide current at the voltage across the capacitor for a period sufficient to enable the ADC to obtain an accurate sample. The parallel conversion circuits are time-interleaved to provide a selected resolution in the digital electrical representation of the optical signal.

Abstract: An optically sampling device optically samples an optical analog signal using a sampled signal having a predetermined sampling frequency, and outputs control light having a pulse train of an optically sampled optical analog signal. A signal generating device generates a pulse train of signal light which is synchronized with the sampled signal. An optical encoding device optically encodes the pulse train of the signal light according to the control light, by using optical encoders each including nonlinear optical loop mirrors, and outputs pulse trains of optically encoded signal light from said optical encoders, respectively. An optically quantizing device performs optical threshold processing on the pulse trains of optically-encoded signal light to optically quantize them, by using at least one of optical threshold processors each of which is connected to each of said optical encoders and includes a nonlinear optical device, and outputs optically quantized pulse trains as optical digital signals.