Abstract: An RF-lightwave transmitter performs successive conversions of an information-bearing input signal in order to generate an output signal suitable for transmission in a wireless communications system. The transmitter includes a high-efficiency FM laser connected to a FM discriminator. In operation, the laser converts an RF signal into a frequency-modulated optical signal, and the discriminator converts this signal into an amplitude-modulated optical signal. The discriminator performs its conversion using a high slope-efficiency linear transfer function which ensures that the AM optical signal varies in accordance with a desired operational performance. The transmitter also includes a photodiode which converts the AM signal output from the optical discriminator back into an RF signal for transmission. Experimental results demonstrated that a transmitter of this type is able to realize greater than 10 dB RF insertion gain at less than 0 dBm optical power, with a high spurious-free dynamic range and low noise.

Abstract: A communication apparatus for use with a light source providing a light beam having a wavelength ?. The apparatus comprises at least one optical modulator adapted to modulate the light beam to a modulated light signal which comprises at least two additional spectral components, one of which at a wavelength of ?+?? and the other at a wavelength of ????. The apparatus further comprises an optical splitting device adapted for coupling to the at least one optical modulator, for splitting the modulated light signal into at least two similar modulated light signals and at least two optical filters, each adapted to receive one of said at least two similar modulated light signals and to allow one of said at least two additional spectral components to egress therefrom.

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

Abstract: Systems, apparatuses, and methods for driving an optical source with a current source. The optical source driver has a primary control loop having a DC—DC converter and an operational amplifier, wherein the DC—DC converter has a power input, a power output connected to the input of the optical source, and a control input, and wherein the operational amplifier has a first input connected between the optical source and the current source, a second input, and an output connected to the control input of the DC—DC converter, for controlling the output of the DC—DC converter in response to a control signal at the second input.

Abstract: A detector outputs a detection signal indicating amplitude variation of an input frequency-multiplexed signal. An amplitude controller adjusts the amplitude of the frequency-multiplexed signal by referring to the detection signal. A modulator modulates the amplitude-adjusted frequency-multiplexed signal to produce a predetermined modulated signal. A second multiplexer multiplexes the modulated signal and the detection signal to produce a multiplexed signal. An optical transmitter converts the multiplexed signal into an optical signal, and then sends it out to an optical transmission path. An optical receiver converts the received optical signal into an electrical signal. A separator separates the modulated and detection signals from the electrical signal. A demodulator demodulates the modulated signal to output the frequency-multiplexed signal. An amplitude adjuster adjusts the amplitude of the frequency-multiplexed signal by referring to the detection signal to reproduce the original amplitude variation.

Abstract: In the multi-value modulation apparatus, one optical intensity detecting unit detects optical intensity of a modulation optical signal generated by one optical modulation signal generating unit and output from the variable optical attenuator. The detected optical intensity is provided to the comparator. Another optical intensity detecting unit detects optical intensity of a modulation optical signal output from another optical modulation signal generating unit. The attenuator attenuates the optical intensity detected by the another optical intensity detecting unit, and provides it to the comparator. The output of the comparator is provided to the optical variable attenuator as a control signal. The variable optical attenuator controls optical intensity of the modulation optical signal based on the control signal.

Abstract: A method and system for demultiplexing non-intensity modulated wavelength division multiplexed (WDM) signals includes receiving a WDM signal having a plurality of non-intensity modulated optical information signals. A plurality of the non-intensity modulated optical information signals are converted to intensity modulated signals while the plurality of non-intensity modulated optical information signals are multiplexed in at least a portion of the WDM signal.

Abstract: A method and system for dispersion control of electromagnetic signals in communication networks by narrowing the widths of electromagnetic pulses such as modulated laser signals. Generally, in the preferred embodiment, the present invention utilizes a feedback loop based on dither frequency modulation which dynamically adjusts the alignment of the laser center frequency with the filter passband. In this way, there is an acceptable tradeoff between optical power and pulse width, so a higher power laser can be used to generate a narrower optical pulse. The narrower pulses then travel farther in the fiber link before reaching their dispersion limit. It is believed that, by using this invention, existing link distance could be doubled, while re-using existing installed singlemode fiber. The systems employing the feedback loop may be information carrying or control systems.

Abstract: An optical transmission system includes a current source for outputting a drive current, a semiconductor laser for converting the drive current into a stimulated emission light and producing the same, a drive circuit for converting a transmission data signal into a modulation control signal and outputting the same, an optical modulator for receiving the stimulated emission light and a shading control signal for interrupting light emission and producing and outputting transmission signal light by changing an amount of transmission of the stimulated emission light according to the shading control signal, and a shading element for receiving the transmission signal light and a shading control signal for interrupting light emission and interrupting the transmission of the transmission signal light according to the shading control signal whereby an optical signal having wrong optical wavelength is rapidly prevented.

Abstract: An optical single-sideband modulated signal generator, comprising optical modulation means for amplitude-modulating an optical carrier by an electric modulation signal to obtain an optical double-sideband modulated signal, and optical signal sideband suppressor means for suppressing either one of the sidebands of the optical double-sideband modulated signal to derive therefrom an optical single-sideband modulated signal. The optical modulation means provides, respectively, first optical double-sideband modulated signal and second optical double-sideband modulated signal on branched optical waveguide paths, which have at least one optical carrier phase-shifter for establishing a relative phase difference of 90° between baseband signal components at the branched optical waveguide paths and at least one delay means for compensation for a relative delay difference between the baseband signal components at the branched optical waveguide paths.

Abstract: The device includes an oscillator (1) to generate an electrical signal of a predetermined frequency and a signal divider (2) to split the electrical signal into first and second signals. The frequency of the second signal is tripled by tripler (3) and the tripled second signal is recombined with the first signal at signal adder (9) to produce a combined electrical signal. This combined electrical signal drives a Mach-Zehnder modulator (10).

Abstract: An optical carrier notch filter includes an optical coupler with at least first, second and third ports. The first port is configured to receive an output that includes an optical carrier and interleaved optical single sideband signals. An optical bandpass filter is coupled to a port of the optical coupler. The optical bandpass filter separates the output into a transmitted signal that contains the optical carrier, and a reflected signal that includes the interleaved optical single sideband signals. The reflected signal is reflected from the optical bandpass filter to the third port of the optical coupler.

Abstract: Changing the phrases when mixing of optical modes gives rise to intensity effects. This occurs in multi-mode interferometer (MMI) or arrayed waveguide gratings (AWG). Here we use an electro-arefractive modulator, with a quadratic electro-optic effect that has an optical transfer function (Or power vs voltage (L-V) curve) given by is Pout=Pin (1+? cos ?)/2 where asymmetry factor ? measures the extinction ratio and the phase difference ? between arms is ? ? ? V 2 V ? 2 ? ? ? V 2 V ? 2 . In turn, the voltage V is expressed as a sum of the DC bias and RF drive V=VDC+VRF.

Abstract: A method and system for generating both return-to-zero (RZ) and carrier suppressed return-to-zero (CSRZ) shaped signals using only a single optical modulator. The system includes: a switch for receiving a data signal and a clock signal as inputs, and outputting a voltage signal; a unit for controllably adjusting the phase of said clock signal before input to the switch; an optical modulator for receiving a continuous wave light (CW) signal and the voltage signal as inputs, and outputting one of an RZ and a CSRZ signal. To generate a CSRZ signal, the optical modulator is biased at a transmission minimum level signal. To generate an RZ signal, the optical modulator is biased at a transmission maximum level and the clock signal is phase shifted. Also disclosed is an optical communication transceiver including a plurality of optical modulator circuits generating both RZ and CSRZ signals.

Abstract: Timing alignment between a pulse carver (i.e., intensity modulator) and a phase modulator, e.g., in a return-to-zero (RZ) differential phase-shift keying (DPSK) optical transmitter, is monitored by filtering a signal from the transmitter and measuring the power of the filtered signal. In certain embodiments, the filter has a birefringent device (such as a polarization-maintaining fiber) and a polarizer. The polarizer may be a rotating polarizer with a rotating quarter-wave plate in front of it. In other embodiments, the filter is a periodic filter such as a Mach-Zehnder interferometer or an etalon filter. Regardless, the measured power may be used to generate control signals used to variably delay the signals that drive the phase modulator and/or the pulse carver to compensate for detected misalignment. The measured power may also be used to monitor the bit-error-rate degradation caused by timing misalignment between the pulse carver and the phase modulator.

Abstract: The present invention relates to a method for generating a single-sideband optical signal. According to the method, as data signals having a 90-degree phase difference with respect to input data signals, which are NRZ signals at 10 Gb/s, 0.5-bit delay data signals are generated by a 0.5-bit delay circuit for obtaining a delay corresponding to ?/2 of the bit period of the input data signal. An SSB optical signal produced from the data signals and the 0.5-bit delay data signals is generated through an optical filter. Further, to eliminate a residual intensity-modulated component, the generated SSB optical signal is fed back to appropriately adjust the center frequency of the optical filter. The carrier output frequency of a semiconductor laser can be adjusted instead of the center frequency of the optical filter. When an RZ signal is used as an input data signal, a 0.25-bit delay circuit is used.

Abstract: A received binary signal (BS) is sampled with different thresholds, the sampling results are integrated and stored. The measured probability distributions or probability density distributions can be used to draw conclusions concerning the signal quality (for example, the bit error rate) and to optimize the system.

Abstract: In analyzing radiation from a communication link, single-photon counting can be used to advantage especially at low levels of radiation energy, e.g. in the detection of optical radiation. Preferred detection techniques include methods in which (i) received optical radiation is intensity-modulated in accordance with a preselected code, (ii) wherein it is the optical radiation which is intensity-modulated with the preselected code, and (iii) wherein the radiation modulated with a preselected code is received. For registration of the signals received by a sensing element of a single-photon detector, time of arrival is recorded, optionally in conjunction with registration of time intervals. Advantageously, in the interest of minimizing the number of pulses missed due to close temporal spacing of pulses, D-triggers can be included in counting circuitry.

Abstract: An optical transmitter includes a laser driver capable of receiving data and applying the data to drive a laser diode over a transmission line having first and second ends. The first end of the transmission line is coupled to an output of the laser driver. A first terminal of an amplifier is coupled to the second end of the transmission line. A second terminal of the amplifier is coupled to the laser diode. The signal amplitude applied at the first terminal controls optical output amplitude of the laser diode.

Abstract: An on-chip parallel data generator, including a Built In Self Test (BIST) generator, is integrated into a laser driver array of a parallel optical communication transmitter so that all optical outputs switch simultaneously. The BIST generator requires only one clock input which clocks the BIST generator for all channels. The optical outputs respond to either the on-chip BIST generator or the electrical inputs if a valid signal is present on the inputs.

Abstract: This invention extends the range of optical data of mobile device by trading speed for distance as well as integrating a plurality of pulses over time to define a single bit of information. The present invention uses a number of integrated pulses to represent a single bit instead of utilizing a one to one correspondence between pulses and bits. The present invention executes a range extender application which executes on the mobile device without any hardware modification to the mobile device. The range extender application causes the optical transmitter to “stutter” or repetitively emanate the identical pulse representing a bit of information. Sufficient photons are thereby gathered at a receiver to reach a predetermined threshold. A tradeoff of the data transmission frequency in this invention is that a signal intensity drops by a factor of 100 when distance increases by a factor of 10 yielding a distance/intensity ratio of {fraction (1/10)}.

Abstract: The present invention relating to a device and method for multiplication of repetition frequency in optical pulse trains. The device and the method multiply repetition frequency of optical pulse train generated with ML-FRL with high stability. The device comprises an optical fiber ring composed of optical fibers, an optical amplifier and a modulator for optically modulating, and an electric signal generator generating high frequency signals. The device generates an optical pulse train of repeating frequency of fm, when applying electric signals of frequency of fm to the modulator. In addition to the construction, the stabilized optical pulse generator comprises a filter passing through frequencies of integer multiple of the applied modulation frequency fm, and a composite cavity composed of a plurality of optical fibers of which lengths are different each other.

Abstract: An optical transmitter and a method for generating a digital optical signal sequence are provided. The optical transmitter has light transmitters which are independently drivable and generate an optical signal for each of the bits of a digital electrical signal sequence that is to be converted into a digital optical signal sequence. The optical signals are combined and superposed into an optical signal path. A control device is provided for distributing the bits between the light transmitters.

Abstract: In an optical transmitter which modulates a continuous-wave optical carrier with an electrical data pulse, the carrier is modulated with a clock signal having ½n (where n is an integer equal to or greater than unity) of the frequency of a fundamental sinusoidal component of the data pulse so that the modulated carrier contains at least a center frequency spectral component. On the modulated optical carrier a filtering operation is performed so that the filtered carrier contains a carrier frequency component and first sideband components. Before or after the clock modulation is performed, the data pulse is used to perform data modulation on the optical carrier.

Abstract: A system and method for transmission of data modulated spectrally enriched optical pulses via an error free propagation region of an optical fiber, in which the optical pulses generated by an optical transmitter have a spectrum that is substantially wider than the spectrum of Fourier-transform limit at an input of the error-free propagation region. The spectral width of the optical pulses gradually narrows while transmitting along this region and becomes comparable to the Fourier-transform limit at an output of this region. Linear and non-linear distortions are compensated within the error free propagation region respectively by deployment of dispersion compensating units and phase modulation of transmitted optical pulses for providing them with an appropriate frequency chirp having shape comparable with a frequency chirp induced by a self-phase modulation of the optical fiber but having opposite sign.

Abstract: A frequency translating device (FTD) includes at least one light-activated resistor (LAR) connected to down-convert a radio frequency (RF) to an intermediate frequency (IF) and to up-convert an IF to an RF and a source of modulated light that is optically connected to the LAR. The source of modulated light is modulated in response to a local oscillator (LO) and the LAR is activated in response to the modulated light. Modulated light can be generated from a light source and an LO by, for example, directly modulating the light source, modulating a transmission switch that blocks the transmission of light to the LAR, or modulating a light path switch. The LAR-based FTD can be used as a reciprocal FTD to characterize another FTD in a three-pair measurement system. An FTD may include more than one LAR to form, for example, single-balanced and double-balanced LAR-based FTDs.

Abstract: A system which improves wavelength tolerance, compensates dispersion in a simple way, reduces limitation of the fiber input power is disclosed. The operation includes receiving a clock signal from a system clock source; modulating a single mode optical signal based on the clock signal and generating an optical pulse signal having two longitudinal modes, the frequency interval thereof being n×B, n being a natural number and B being a transmission speed; generating a partial response signal by converting a binary NRZ signal from a digital signal source in synchronism with the system clock source; and modulating the optical pulse signal based on the partial response signal, and outputting a binary RZ modulated signal. The binary RZ modulated signal is input into a receiver, where two partial response components in the optical spectra of the input signal are divided, and one or both of the components are received.

Abstract: A system and method for transmitting data modulated spectrally enriched optical pulses with a frequency chirp via an error free propagation region of an optical fiber, in which spectrum of optical pulses gradually depletes from the spectrum that is substantially wider than the spectrum of Fourier-transform limit at an input of the error-free propagation region and becomes comparable to the Fourier-transform limit at an output of this region. The gradual depletion of the spectrum is achieved by utilizing a frequency chirp converter having a dispersion sign opposite to a dispersion sign of the optical fiber.

Abstract: A method and apparatus are provided for transmitting and receiving multiple RF/microwave subcarriers on a single optical wavelength over an optical link. The method includes the steps of modulating a plurality of RF/microwave subcarrier frequencies with a respective communication signal and modulating an optical carrier wave with the plurality of modulated RF/microwave subcarrier frequencies.

Abstract: The present invention discloses an electro-optical element and a method for generating an amplitude-modulated optical signal (24). The element comprises a semiconductor substrate (12), an electro-optical modulation structure arranged on the substrate (12), a first terminal (22) for supplying an optical signal (20) to be modulated, a second terminal (28) for supplying an electrical modulation signal, and a modulation area adapted for modulating the optical signal (20) with the electrical modulation signal (50). According to one aspect of the invention, a limiter (30) is provided for limiting the electrical modulation signal. The limiter (30) is arranged on the substrate (12) and is operatively connected between a second terminal (28) and the modulation area.

Abstract: An optical link is operative for transmitting a microwave signal in modulated optical form over an optical fiber. The optical link has a transmitter and a receiver. The transmitter splits and converts the microwave signal into two separate optical signals, each of which represents either the positive varying part of the microwave signal or the negative varying part of the microwave signal. The receiver combines the two separate optical signals and converts them back into the microwave signal.

Abstract: A duobinary optical transmission apparatus has a characteristic of phase intersection without using an existing feedback-type precoder and an electrical low-pass filter, thereby eliminating the influence by pseudo random bit sequence. The invention realizes a transmission system having increased immunity against dispersion of an optical fiber, and thus can increase transmission distance and transmission speed of an optical signal. The duobinary optical transmission apparatus includes: a light source outputting an optical carrier; an NRZ optical signal generating section receiving an NRZ electrical signal, modulating the optical carrier into an NRZ optical signal according to the NRZ electrical signal, and outputting the NRZ optical signal; and a duobinary optical signal generating section receiving the NRZ electrical signal and modulating the NRZ optical signal into a duobinary optical signal.

Abstract: A transmitter that performs stimulated Brillouin scattering suppression is provided. The transmitter includes a non-linear device having an optical input adapted to receive an optical signal, an amplitude modulation input adapted to receive an amplitude modulation signal, a phase modulation input and an output. The transmitter also includes a stimulated Brillouin scattering (SBS) oscillator/driver having first and second oscillators coupled to the phase modulation input of the non-linear device and an amplifier coupled to the output of the non-linear device. The transmitter further includes a laser coupled to the optical input of the non-linear device.

Abstract: In a coherent optical receiver, an incoming optical signal is combined with a local oscillator (LO) optical signal and the combined optical signals are detected by an optical detector and receiver arrangement. The receiver produces first and second loop control signals having respectively relatively slow and fast response speeds dependent upon frequency and phase variations between the incoming signal and the LO signal. An electrical source produces an electrical signal having a GHz frequency controlled by the second control signal. An optical source produces an optical signal with a first component having a first frequency controlled by the first control signal, and a second component having a frequency offset from the first frequency by a second frequency dependent upon the frequency of the electrical signal. The LO signal is derived from the second optical component via an optical filter and amplifier.

Abstract: A system that transmits amplitude modulated data in a wavelength-encoded format and then uses a wavelength-sensitive receiver to convert the received optical signal back to the original amplitude modulated data. This system enables transmission of optical signals that are less sensitive to attenuation and attenuation changes. This system is applicable to data in digital, multilevel, or analog formats.

Abstract: An optical transmitter, consisting of a radiation source which is adapted to generate a base optical beam with a base wavelength. The transmitter further consists of at least one modulator which is coupled to modulate the base optical beam so as to generate multiple carrier beams at respective side-bands of the base wavelength and to introduce information into the carrier beams for transmission thereby to a receiver.

Abstract: An 90 degree AP on-off keying (OOK) transmission format is used to suppress intra-channel FWM and significantly extend reach in high bit rate, long-haul fiber optic transmission systems. The pulse stream with the aforementioned format can be either chirped or chirp-free, and can for example, be generated with a pulse generator (e.g., a Mach-Zehnder (MZ) modulator) by mixing two electrical signals, one used to create an intensity modulation and the other a phase modulation in the pulse generator. The electrical signals can be two properly skewed sinusoidal electrical signals at half of the desired data rate, and can thereby create a pulse stream in which the maximum optical phase modulation occurs at the intensity peak of each pulse and is 90 degrees out of phase with its nearest neighbors. Alternatively, a 90 degree AP pulse train can be generated by a single phase modulator followed by a delay interferometer with a time delay of approximately ⅔ of the bit period of the data in the data stream.

Abstract: An optically modulated signal is generated for use in transporting data by generating a so-called sub-carrier modulated optical signal and, then, vector modulating the sub-carrier modulated optical signal to yield the desired modulated optical signal for transmission. The vector modulation includes a phase component and an amplitude component. In one specific embodiment of the invention, the vector modulation is effected by splitting the sub-carrier modulated optical signal comprising a carrier and an at least one unmodulated sub-carrier into a plurality of similar optical signals, phase modulating the carrier of each of the similar optical signals with the data and delaying the resulting optical signals in a prescribed manner relative to one another. Then, the “delayed” signals are combined to yield the signal comprising the vector modulated sub-carrier modulated optical signal to be transmitted. Wherein a signal can be “delayed” by a zero (0) delay interval.

Abstract: A system and method for identifying one or more characteristics of an optical signal, in which a transmitter is operable to transmit an optical signal and a receiving unit is operable to receive the optical signal. The transmitter has a laser for generating the optical signal and an encoding unit adapted to control the laser to activate and deactivate the optical signal during a laser shutdown state based on a predetermined code. The receiving unit has an optical receiver optically coupled to the transmitter by a light transmission medium and is operable to receive the optical signal from the transmitter. The receiving unit also has a decoder measuring at least one of an active time of the optical signal and the inactive time between active times of the optical signal. The decoder determines at least one of the one or more characteristics of the optical system based on at least one of the active time or the inactive time.

Abstract: A regenerator for an RZ optical signal transmission system applies a relative time shift to the signals as a function of their intensity and includes an intensity modulator for modulating the shifted signals. The shift between signals corresponding to a “zero” value and signals corresponding to a “one” value is such that the modulation intensity for signals corresponding to a “zero” value is less than the modulation intensity for signals corresponding to a “one” value. A shift equal to half the bit time between signals corresponding to a “one” value and signals corresponding to a “zero” value can therefore be chosen. The modulation intensity is then maximum for signals corresponding to a “one” value and minimum for signals corresponding to a “zero” value. The regenerator limits noise in the “zeros” of an RZ signal and regenerates the “ones”.

Abstract: An object of the invention is to provide a control system in which the phase shift between drive signals of an optical modulator can be reliably detected and compensated by a simple configuration. To this end, a control apparatus of the invention, for an optical modulator generating a signal light of a CS-RZ modulation system or the like by two LN modulators connected in series, detects the phase shift between drive signals given to the former and latter stage LN modulators, or judges the phase shift between the drive signals based on intensity information of the electric spectrum of the signal light output from the optical modulator, to control the phases of the drive signals so as to minimize the phase shift. As a result, the phase shift between the drive signals can be reliably detected and compensated by an electric circuit with a simple configuration.

Abstract: A multi-wavelength light source apparatus includes a tunable light source, optical intensity modulator, optical coupler, annular optical delay circuit, and optical gate device. The tunable light source successively changes and outputs a plurality of output lights different in wavelength from one another. The optical intensity modulator outputs a modulated signal light obtained by modulating an amplitude of the output light outputted from the tunable light source over a predetermined time. The optical coupler is optically connected to the optical intensity modulator, and receives the light outputted from the optical intensity modulator. The annular optical delay circuit is optically connected to the optical coupler, and delays a part of the output light outputted from the optical intensity modulator over a time longer than the predetermined time.

Abstract: A method and apparatus for information modulation for impulse radios are presented in both single-tone and pulse stream configurations. The modulation techniques include combinations of amplitude and phase modulation. The modulation techniques include both digital and analog schemes, including baseband on/off keying modulation, wavelet on/off keying modulation, pulse-position modulation, and FM modulation. Techniques for varying the modulation rate are also provided. Additionally, harmonics impulse ratio configurations are presented to take advantage of the modulation techniques.

Abstract: Optical sources and transmitters for transmitting data in a spectro-temporally encoded light signal are provided. The optical source includes a pumped gain medium for generating ASE radiation. A wavelength dependent reflector is provided backward of the gain medium for reflecting wavebands adapted for spectro-temporal encoding. In one embodiment, a modulator and an encoder are provided outside of the source for embedding data into the generated signal spectro-temporally encoding this signal. In another embodiment, the wavelength dependent reflector acts as the encoder, and the modulator is provided inside the source.

Abstract: A method and apparatus for placing synchronous amplitude modulation onto an optical data signal. An amplitude modulator imparts periodic intensity modulation to an optical signal on which data has been, or will be, modulated. A phase modulator may also be provided to impart synchronous phase modulation to the optical signal, and a polarization modulator may be provided to impart polarization modulation.

Abstract: An optical transmission system is provided, which permits high-precision optical transmission of a signal even if the signal has a high accurate timing, an indefinite period, and a DC component. The transmitting side is provided with a rise edge detecting circuit 1 for detecting the rise edge of a transmitting signal waveform, a transmitting pulse generating circuit 2 for generating a transmitting pulse signal (b) constituted by a pair of opposite-polarity pulses inverting their polarities at the detected timing, and a light intensity modulation circuit 3 for generating a light intensity modulated signal (c) based on the pulse signal (b). The receiving side is provided with an AC-coupled receiving circuit 4 for receiving the light intensity modulated signal (c) and extracting therefrom only an AC component, and a discrimination circuit 5 for discriminating the rise timing from the received signal.

Abstract: A wavelength-division multiplex optical transmission system is provided with: preliminary optical modulators 111 to 11n for outputting optical signals having different wavelengths from each other after being modulated by communications signals 11 to 1n that are signals to be supplied to specific optical receiving parts; an optical fiber 510 for transmitting the multiplexed optical signal; a subsequent optical modulator 210 for collectively modulating the transmitted optical signal so as to collectively modulate the optical signals being multiplexed by a broadcast signal 20 that is to be supplied equally to all optical receiving parts; and an optical fiber 520 for transmitting the modulated optical signal. A frequency band for the broadcast signal 20 is set not to overlap with any of those of the communications signals 11 to 1n.

Abstract: Amplitude modulation is performed for a signal light with a modulation signal having the same cycle as that of an optical pulse to be extracted by using an optical modulator. At this time, timing is adjusted so that the peak of the optical pulse of the channel to be extracted of the signal light becomes the largest. A spectrum of the amplitude-modulated signal light is expanded according to the size of the peak of the optical pulse by a spectrum expander. Then, part of the expanded spectrum is extracted with a band pass filter, whereby the optical pulse of the desired channel is extracted.

Abstract: A high efficiency light emitting diode (LED) driver circuit utilizes a capacitor to regulate the LED driving current. The voltage across the capacitor is monitored to maintain a preselected low threshold voltage on the capacitor, which determines the LED optical emission intensity. The capacitor provides the LED driver current by discharging through the LED during transmission intervals, and the power supply for the device is used only to maintain the capacitor charge level. The LED driver circuit accordingly operates at high efficiency with low power consumption. The LED driver current can be regulated by changing the low and high threshold voltages of the capacitor pump controller, thereby to control the optical intensity of the LED.

Abstract: A multilevel light-intensity modulating circuit for suppressing the amplitude distortion regarding intermediate levels, caused by the conversion from a multilevel electric signal to a multilevel modulated optical signal. The circuit comprises a section for distributing an input optical carrier into n-channel optical carriers; n light-intensity modulators for modulating intensities of the optical carriers by using input two-level electric signals; a control section for producing a phase difference between the n-channel two-level modulated optical signals; a control section for assigning a different light intensity to each of the n-channel two-level modulated optical signals; and a section for combining the n-channel two-level modulated optical signals obtained via the control sections, and outputting a 2n-level modulated optical signal. The phase difference and the different light intensity are defined in advance so as to produce the 2n-level modulated optical signal.