An amplitude modulation circuit includes: first, second, and third input terminals; first and second output terminals; a current source; first and second transistors including a base electrically connected to the first and second input terminals, a collector electrically connected to the first and second output terminals, and an emitter electrically connected to a grounding terminal via the current source; first and second resistive elements electrically connected between the first and second output terminals and a power line; and a first MOS transistor including a drain connected to the first output terminal, a source connected to the second output terminal, and a gate connected to the third input terminal. The MOS transistor is configured to operate in a non-saturated region, and a resistance between the source and the drain of the MOS transistor is larger than resistances of the first and second resistive elements.

An optical transmission and reception system includes an optical transmitter including an optical modulator that optically modulates a transmission signal containing a known signal inserted at predetermined intervals and transmits it to an optical transmission line, and an optical receiver including an optical RC circuit that converts an optical modulation signal received from the optical transmission line into a complex time series signal, a photoelectric conversion element that converts the complex time series signal into an electrical intensity signal, and a digital signal processing unit that performs learning using the known signal as a teaching signal and performs demodulation, based on learning results, using the electrical intensity signal received from the photoelectric conversion element.

An objective is to provide a communication system, a terminal, a communication method, and a program capable of improving the probability of successful authentication regardless of mobility of the terminal.

The communication system according to the present invention includes a terminal 30 including: a sensor unit 36 that senses a state of the terminal and includes at least one of an acceleration sensor, a gyro sensor, a position sensor, and a proximity sensor; an optical receiver 31 that receives an optical modulation signal and outputs an electrical signal; a correction circuit 34 that corrects the electrical signal on a basis of the state of the terminal sensed by the sensor unit 36 when one of the following is true: illuminance of light received from an optical transmitter 21 by the optical receiver 31 is equal to or lower than an illuminance threshold value; and a signal intensity of the electrical signal output by the optical receiver 31 is equal to or lower than an intensity threshold value; an authentication information checking circuit 32 that checks the authentication information contained in the electrical signal; and a terminal-side RF transmitter/receiver 33 that transmits the authentication information to a base station 20 via RF wireless communication.

An objective is to provide a communication system, a terminal, a communication method, and a program capable of improving the probability of successful authentication regardless of mobility of the terminal.

The communication system according to the present invention includes a terminal 30 including: a sensor unit 36 that senses a state of the terminal and includes at least one of an acceleration sensor, a gyro sensor, a position sensor, and a proximity sensor; an optical receiver 31 that receives an optical modulation signal and outputs an electrical signal; a correction circuit 34 that corrects the electrical signal on a basis of the state of the terminal sensed by the sensor unit 36 when one of the following is true: illuminance of light received from an optical transmitter 21 by the optical receiver 31 is equal to or lower than an illuminance threshold value; and a signal intensity of the electrical signal output by the optical receiver 31 is equal to or lower than an intensity threshold value; an authentication information checking circuit 32 that checks the authentication information contained in the electrical signal; and a terminal-side RF transmitter/receiver 33 that transmits the authentication information to a base station 20 via RF wireless communication.

A method for transmitting data carrying optical information over an optical channel, comprising the steps of providing an optical transmitter consisting of a light source being a Mode-Locked Optical Frequency Comb (MLFC) for generating a frequency comb of multiple carriers, each of which being modulated by a baseband signal; an optical modulator for modulating each and all of the multiple carriers in a modulation bandwidth extending up to the modes' frequency spacing between the multiple carriers; performing all-optical encoding of the modulated carriers by manipulating the optical amplitude and/or phase and/or polarization of all optically modulated carriers; and transmitting, by the optical transmitter, the encoded modulated carriers to an optical receiver, over an optical channel

A method for transmitting data carrying optical information over an optical channel, comprising the steps of providing an optical transmitter consisting of a light source being a Mode-Locked Optical Frequency Comb (MLFC) for generating a frequency comb of multiple carriers, each of which being modulated by a baseband signal; an optical modulator for modulating each and all of the multiple carriers in a modulation bandwidth extending up to the modes' frequency spacing between the multiple carriers; performing all-optical encoding of the modulated carriers by manipulating the optical amplitude and/or phase and/or polarization of all optically modulated carriers; and transmitting, by the optical transmitter, the encoded modulated carriers to an optical receiver, over an optical channel

An optical transmitter based on optical time division multiplexing is disclosed, which may solve the issues of complex structure and operation of a multilevel-OTDM-based optical transmitter while using a multilevel signal modulation format and OTDM technology that may increase the transmission rate of an optical transmitter with limited bandwidth.

A receiver system is provided for receiving a coherent Pulse Amplitude Modulation (PAM) encoded signal. The receiver system may include an optical polarization component configured to modulate a polarization of the received coherent PAM encoded signal. The receiver system may further include a digital signal processor (DSP) configured to perform polarization recovery between the received coherent PAM encoded signal and the LO signal using a first control loop, and to perform phase recovery between the received coherent PAM encoded signal and the LO signal using a second control loop.

Disclosed are an optical signal communication method, and an optical signal transmission device and an optical signal reception device which perform the method. The optical signal communication method may comprise the steps of: receiving input data to be modulated into an optical signal, modulating the input data into the optical signal, and transmitting the optical signal to an optical signal reception device, wherein the optical signal includes a start pulse and an end pulse, and a time interval between the start pulse and the end pulse is determined on the basis of a data value of the input data.

An apparatus for generating a time-delayed product of two independent signals includes a fixed-wavelength laser. A first optical modulator is optically coupled to the fixed-wavelength laser and configured to modulate a fixed wavelength optical carrier with a first input signal of a set of input signals. The apparatus also includes a tunable laser. A second optical modulator is optically coupled to the tunable laser and configured to modulate a tunable optical carrier with a second input signal of the set of input signals. The apparatus also includes a dispersive element coupled to the second optical modulator, a first optical detector coupled to the dispersive element, a third optical modulator optically coupled to the first optical detector and the first optical modulator, an optical 90-degree hybrid element optically coupled to the third optical modulator, and a plurality of optical detectors optically coupled to the optical 90-degree hybrid element.