Abstract: Provided are an apparatus and method of generating a terahertz (THz) signal using a directly-modulated laser. An apparatus of generating a THz signal includes a first directly-modulated laser configured to output a local oscillator (LO) signal, a second directly-modulated laser configured to receive a baseband signal used as data and optically modulate the baseband signal, a band-pass filter configured to filter a spectral component of the baseband signal optically modulated and outputted through the second directly-modulated laser by using a specific frequency bandwidth, a coupler configured to couple the baseband signal filtered through the band-pass filter and the LO signal to each other, and a uni-travelling-carrier photodiode (UTC-PD) configured to generate a THz signal by beating the baseband signal and the LO signal coupled to each other.

Abstract: A method and apparatus for compensating an in- and quadrature-(IQ) imbalance are disclosed. The method and apparatus for compensating an in- and quadrature-(IQ) imbalance provide a technique for compensating a signal distortion caused by imperfect element features and various noises on a transmission link in terahertz wireless communication and improving transmission performance.

Abstract: A method of equalization for high-speed processing and an equalizer thereof are proposed. The method of equalization includes determining a filter coefficient applied to a transmitter equalizer provided with a 2-tap precoder according to an approximate channel response characteristic, generating a pre-equalization signal by removing precursor ISI of a transmission feedback signal by the precoder to which the filter coefficient is applied, so as to output the pre-equalization signal as a transmitting signal, and receiving a transmission signal and generating an equalization signal by removing postcursor ISI of the received transmission signal by a receiver equalizer provided with a feedback filter having auxiliary coefficients for compensating for a difference between an overall channel response of the transmission signal and a channel response based on the precoder.

Abstract: Provided are a method and apparatus for registering a new terminal using chromatic dispersion distance estimation. The method of registering a new terminal, performed by a transport unit (TU), includes performing frame synchronization through a downstream packet received from a transport node (TN), identifying a position of a frequency of a spectral null and a number of frequencies of spectral nulls through analysis on a frequency spectrum of the received downstream packet, estimating a transmission distance of an optical fiber to the TN, based on the identified position of the frequency of the spectral null and the identified number of frequencies of spectral nulls, and determining a timing of transmitting a registration request message, based on the estimated transmission distance, where the discovery information message is received from the TN.

Abstract: An apparatus and method for maintaining a wavelength interval of light sources are disclosed. The apparatus for maintaining a wavelength interval of light sources includes: a plurality of light sources configured to output light having different wavelengths and having a certain wavelength interval; a light reception unit configured to receive an optical signal in which at least some of the output light of each of the plurality of light sources is combined and output an electrical signal including a frequency component corresponding to the certain wavelength interval; and a controller configured to detect the frequency component corresponding to the certain wavelength interval from the electrical signal and control a wavelength of each of the plurality of light sources to maintain the certain wavelength interval based on the detected frequency component.

Abstract: Disclosed herein is an optical transmitter for generating a vestigial sideband (VSB) optical signal. The optical transmitter includes: a modulator configured based on a photonic integrated chip (PIC); an optical fiber block; and a lensed thin film filter implemented between the modulator configured based on the PIC and the optical fiber block. The PIC includes at least one grating coupler, and the lensed thin film filter is disposed so that an angle of an optical signal emitted from a first grating coupler of the PIC coincides with an angle of incident (AOI) of the lensed thin film filter to design the first grating coupler and the lensed thin film filter.

Abstract: Disclosed is a method and apparatus for phase error compensation having tolerance to a cyclic slip. The method includes determining first phase error candidates based on symbol phases of a first block of a received signal, determining an initial estimation error according to the first phase error candidates, determining second phase error candidates based on symbol phases of a second block of the received signal, determining a final estimation error according to the initial estimation error and the second phase error candidates, and compensating for a phase of the received signal according to the final estimation error.

Abstract: Provided are a Kramers—Kronig (KK) reception-based terahertz (THz) signal reception apparatus and a method for compensating a frequency offset using the same. A method of compensating for a frequency offset performed by a THz signal reception apparatus includes receiving, from a THz signal transmission apparatus, a THz signal including carrier signals corresponding to three different frequency bands, extracting, from the received THz signal, a reference carrier included in the THz signal or a sampling clock generated in a process of generating a data signal, and compensating for a frequency offset generated in a process of transmitting the THz signal by using the extracted reference carrier or sampling clock.

Abstract: Provided are an apparatus and method of generating a terahertz (THz) signal using a directly-modulated laser. An apparatus of generating a THz signal includes a first directly-modulated laser configured to output a local oscillator (LO) signal, a second directly-modulated laser configured to receive a baseband signal used as data and optically modulate the baseband signal, a band-pass filter configured to filter a spectral component of the baseband signal optically modulated and outputted through the second directly-modulated laser by using a specific frequency bandwidth, a coupler configured to couple the baseband signal filtered through the band-pass filter and the LO signal to each other, and a uni-travelling-carrier photodiode (UTC-PD) configured to generate a THz signal by beating the baseband signal and the LO signal coupled to each other.

Abstract: A method of generating a terahertz wave and apparatuses performing the method are disclosed. According to an example embodiment, a method of generating a terahertz wave includes outputting a laser comb by modulating a laser output from a laser source based on a linearly modulated frequency of an output that is output from a frequency source, and generating a terahertz wave based on a first comb line and a second comb line selected from the laser comb.

Abstract: Disclosed is a method and apparatus for phase error compensation having tolerance to a cyclic slip. The method includes determining first phase error candidates based on symbol phases of a first block of a received signal, determining an initial estimation error according to the first phase error candidates, determining second phase error candidates based on symbol phases of a second block of the received signal, determining a final estimation error according to the initial estimation error and the second phase error candidates, and compensating for a phase of the received signal according to the final estimation error.

Abstract: A method of generating a terahertz wave and apparatuses performing the method are disclosed. According to an example embodiment, a method of generating a terahertz wave includes outputting a laser comb by modulating a laser output from a laser source based on a linearly modulated frequency of an output that is output from a frequency source, and generating a terahertz wave based on a first comb line and a second comb line selected from the laser comb.

Abstract: A secure communication method and an apparatus performing the same are disclosed. The communication method includes receiving a signal encrypted based on at least one attractor and decrypting a security signal received using a neural network trained based on a training signal.

Abstract: A wireless signal transmitter and a wireless signal receiver are provided. The wireless signal transmitter includes an optical signal generation region that generates excitation light by beating two optical signals that have different wavelengths and that are output through different laser diodes, and a wireless signal generation region that modulates the excitation light output from the optical signal generation region into a wireless signal with a carrier frequency of a terahertz band, using a photomixer. The optical signal generation region and the wireless signal generation region may be connected by a multimode optical fiber to reduce a nonlinear effect occurring in an optical fiber. Also, the wireless signal receiver includes a signal processor, for example, an equalizer, for compensating for a modal dispersion, and may compensate for a modal dispersion caused by the multimode optical fiber used in the wireless signal transmitter.

Abstract: An optical transmission method for processing a signal based on direct detection includes setting, by an equalizer, an adaptive equalization coefficient by performing an equalization process during a training symbol field section in a frame of a received signal, performing, by a channel estimator, channel estimation to perform an equalization process of a soft output maximum likelihood sequence equalizer (MLSE) during the training symbol field section, driving the soft output MLSE, and compensating for, by the soft output MLSE, distortion of the received signal during a data symbol field section in the frame on the basis of the adaptive equalization coefficient and an estimated result value of a channel, and recovering, by an error corrector which allows soft-decision processing to be performed, the received signal by performing error correction on the received signal in which the distortion is compensated for.

Abstract: An optical transmission method for processing a signal based on direct detection includes setting, by an equalizer, an adaptive equalization coefficient by performing an equalization process during a training symbol field section in a frame of a received signal, performing, by a channel estimator, channel estimation to perform an equalization process of a soft output maximum likelihood sequence equalizer (MLSE) during the training symbol field section, driving the soft output MLSE, and compensating for, by the soft output MLSE, distortion of the received signal during a data symbol field section in the frame on the basis of the adaptive equalization coefficient and an estimated result value of a channel, and recovering, by an error corrector which allows soft-decision processing to be performed, the received signal by performing error correction on the received signal in which the distortion is compensated for.

Abstract: A method and apparatus for estimating a burst error. A burst error estimation method includes measuring a frequency of a spectrum null for an optical signal received through an optical receiver; determining whether the measured frequency of the spectrum null corresponds to an intermediate frequency of a baud rate; and estimating that a burst error occurrence condition is met when the frequency of the spectrum null is determined to correspond to the intermediate frequency of the baud rate.

Abstract: A method and apparatus for compensation of a chromatic dispersion through an optical compensation and an electronical compensation in optical communication. An optical communication method receives an optical signal, estimates a first transmission length based on a null component included in a frequency spectrum of the optical signal, optically compensates for a chromatic dispersion of the optical signal based on the first transmission length, estimates a second transmission length based on a null component included in a frequency spectrum of the compensated optical signal, and electronically compensates for a residual chromatic dispersion of the compensated optical signal based on the second transmission length.

Abstract: A method and apparatus for compensation of a chromatic dispersion through an optical compensation and an electronical compensation in optical communication. An optical communication method receives an optical signal, estimates a first transmission length based on a null component included in a frequency spectrum of the optical signal, optically compensates for a chromatic dispersion of the optical signal based on the first transmission length, estimates a second transmission length based on a null component included in a frequency spectrum of the compensated optical signal, and electronically compensates for a residual chromatic dispersion of the compensated optical signal based on the second transmission length.

Abstract: Disclosed is an optical receiver and an error correction method performed by the optical receiver, receiving, using a receiving antenna or a photodetector, a training signal in which an error occurs due to noise and distortion while being output from an optical transmitter and transmitted through a communication channel and identifying a hyperplane for classifying a probability that the received training signal is a training signal corresponding to a training signal output from the optical signal using a support vector machine (SVM) and learning a parameter of the identified hyperplane such that a classification error probability is minimized when the probability is extracted using the identified hyperplane, wherein the parameter of the identified hyperplane is used to correct an error occurring while a transmission signal output from the optical signal is received using the receiving antenna or the photodetector.