Abstract: A coherent optical receiving device capable of digital equalization of an optical input, and a method thereof. The coherent optical receiving device includes a chromatic dispersion compensating unit configured to comprise a filter for chromatic dispersion compensation and compensate for chromatic dispersion with respect to a digital signal that corresponds to an optical input using the filter; a decoder configured to generate a bit sequence of the signal which has been compensated for chromatic dispersion; a bit error calculating unit configured to calculate a bit error amount in the bit sequence; and a controller configured to monitor the bit error amount, determine a filter coefficient that makes the bit error amount a minimum, and set the determined filter coefficient in the chromatic dispersion compensating unit.

Abstract: An optical transmitting apparatus optically modulates a transmitting signal to transmit the signal to an optical receiving apparatus using a phase of two optical carriers having each wavelength, and an optical receiving apparatus demodulates an optical signal having a modulated phase with intensity modulation to detect a transmitting signal.

Abstract: Provided are a network node which has a wavelength switching cross-connection function and can thus interconnect paths of a wavelength-division-multiplexed optical signal and convert wavelengths, and an operating method of the network node. Accordingly, it is possible to provide a multi-degree cross-connection system having a simple structure at lower cost by allowing transmission of optical signals supposed not to be added/dropped at a network node without converting them into electrical signals and performing O/E conversion or E/O conversion only on optical signals supposed to be added/dropped at a network node. In addition, it is possible to increase the expandability of networks by regenerating degraded signals and which can effectively utilize bandwidths by grooming low-speed electrical digital hierarchy signals and transmitting them as high-speed optical signals.

Abstract: Provided is a coherent optical receiving apparatus and an optical signal processing method. The coherent optical receiving apparatus may include an optical hybrid unit to generate an optical signal by combining a first optical signal inputted from an optical transmitting apparatus and a second optical signal inputted from a local oscillator, a polarization demuxer to demultiplex the optical signal outputted from the optical hybridizing unit, a frequency offset compensator to estimate a frequency offset of at least one of even-numbered samples and odd-numbered samples, and to compensate for a frequency offset of the even-numbered samples and a frequency offset of the odd-numbered samples using the at least one estimated frequency offset, and a carver distortion compensator to compensate for phase distortions of the samples for which the compensation for the frequency offset is performed, the phase distortions being generated by the optical transmitting apparatus.

Abstract: Provided is a multi-ring network operating method of cross-connecting at least two ring networks, the method including connecting an input working ring and an input protection ring of a ring network to an output working ring and an output protection ring of another ring network and then performing cross-connection between the same or different ring networks by using a multi-dimensional cross-connect apparatus. In the multi-ring operating method, a plurality of ring networks can be connected regardless of the protection method used by the ring networks, and the original protection method of each ring network can remain after they are connected.

Abstract: An apparatus for receiving optical signals in DQPSK and method of controlling a phase offset in receiving optical signals for DQPSK is provided. An original optical signal modulated in DQPSK is received. The original optical signal is delayed by one bit to make a delay optical signal such that an interference on the original optical signal and the delay optical signal is performed. A control signal is generated by use of an interference result between the original optical signal and the delay optical signal. A phase offset for the interference between the original optical signal and the delay optical signal is controlled by use of the generated control signal. In receiving optical signals, the phase offset between the delay optical signal and the original optical signal is precisely controlled, thereby optimizing the transfer characteristics of an optical delay interferometer.

Abstract: An apparatus and method for protection switching of an optical channel at each node in an optical network based on wavelength division multiplexing optical transmission technology are provided. The method can be applied to any node having at least two optical fiber inputs and outputs. The apparatus includes: a splitter receiving an electrical signal and splitting the received electrical signal into a plurality of electrical signals which are substantially identical to the received electrical signal; an output switching unit selecting output paths of the electrical signals split by the splitter according to an optical channel path control command of the optical network; and a plurality of optical transponders being assigned to the respective output paths of the electrical signals, converting the electrical signal input by the selection of the output switching unit to an optical signal, and transmitting the converted optical signal to another node of the optical network.

Abstract: An optical node capable of supporting a mesh-type optical network is provided.

Abstract: An OFDM receiver for compensating for I/Q imbalance is provided. The OFDM receiver includes an I/Q demodulator demodulating a received signal into a baseband in-phase (I) channel signal and a baseband quadrature (Q) channel signal, and an I/Q imbalance compensator compensating for imbalance between the I-channel signal and the Q-channel signal in a time domain. Accordingly, it is possible to solve the I/Q imbalance and suppress degradation in the performance of the OFDM communication device.

Abstract: An OFDM optical transmitter and optical transmission method is provided. The OFDM optical transmitter includes a signal converter controlling amplitude of each of data signals according to a position of each of the data signals and converting the controlled data signal into a time-domain signal. Accordingly, it is possible to generate optical OFDM carriers which are uniform in size.

Abstract: Disclosed are a digital equalization apparatus for a coherent optical receiver and a digital equalization method for a coherent optical receiver, capable of compensating for chromatic dispersion and polarization impairment through a digital signal processing, and capable of performing a clock recovery and a data recovery through a digital symbol synchronization. The digital equalization apparatus and the method compensate for various impairments occurring on an optical path in a digital manner and achieve synchronization through a simple structure.

Abstract: Provided are a channel express/add optical module and a method of channel express/add in an optical add/drop multiplexer node using the channel express/add optical module. The channel express/add optical module comprises: a multiplexer/demultiplexer which demultiplexes a multiplexed optical signal having a plurality of wavelengths into individual wavelength optical signals or multiplexes a plurality of different wavelength optical signals; a plurality of 1×2 switches each of which includes a first output end that guides the demultiplexed different wavelength optical signals to output them thereto and a second output end through which new wavelength optical signals; and a plurality of reflectors each of which reflects the optical signal output to the first output end so that the optical signal is feedback to the multiplexer/demultiplexer via the 1×2 switches.

Abstract: Provided are a photonic cross-connector system, a wavelength division multiplexing (WDM) system using the photonic cross-connector system, and an optical communication network based on the WDM system. The photonic cross-connector system includes: an optical coupler branching an input optical signal into a plurality of paths; a wavelength selective switch (WSS) extracting at least one wavelength signal from the input optical signal and outputting the extracted wavelength signal to at least one port; a WDM multi-casting apparatus simultaneously copying and reproducing the input optical signal into different wavelengths and changing modulation methods of the input optical signal into different types of modulation methods; an optical transmitter and/or receiver branching and coupling the input optical signal; and a control system controlling the optical coupler, the WSS, the WDM multicasting apparatus, and the optical transmitter and/or receiver.

Abstract: Provided is a channel assignment method in a wavelength-division-multiplexed transmission system. The channel assignment method includes obtaining information about signal modulation schemes from a plurality of optical transmitters, and assigning channels to the respective optical transmitters in consideration of the obtained information about the signal modulation schemes. Accordingly, in transmission of channels of different modulation formats, cross phase modulation is minimized, thereby reducing inter-channel interference.

Abstract: An optical transmitting apparatus is disclosed. The optical transmitting apparatus outputs a signal having the same phase characteristics as a Return-to-Zero Differential Phase-Shift-Keying (RZ-DPSK) signal by using a single phase modulator. Accordingly, it is possible to generate RZ-DPSK signals without using a separate RZ modulator.

Abstract: An optical transmission apparatus for high-speed optical signal transmission is provided. The optical transmission apparatus includes an optical modulator which includes first and second modulators of a Mach-Zehnder (MZ) interferometer type which are connected in parallel, and an output stabilizer which controls biases for the first modulator, the second modulator and the optical modulator and stabilizes a final output optical signal of the optical modulator. The optical transmission apparatus can perform a stable optical signal output.

Abstract: Provided is a digital signal synchronization device of a coherent optical receiver. The digital signal synchronization device includes a digital signal processing unit to perform synchronization on a digital signal of an output optical signal generated by interfering an optical signal received through an optical fiber with an optical signal of laser output from a local oscillator and to perform decoding using the synchronized digital signal, and a digital signal managing unit to monitor the digital signal processing unit to output data of the optical signal normally, which has been received through the optical fiber, according to the synchronized digital signal.

Abstract: Provided is an optical network in which a wavelength division multiplexing-based optical transmission scheme is implemented. An apparatus for cross-connecting an optical path includes a path switch including a plurality of input terminals receiving optical signals from other nodes, and a plurality of output terminals sending the optical signals to the other nodes, the path switch switching the path of the optical signal so that the optical signal input via one of the input terminals is output to one of the output terminals; and a wavelength converter converting a wavelength of the optical signal input via the input terminal and outputting the wavelength-converted optical signal to the output terminal according to a switching result of the path switch.

Abstract: Provided are a network node which has a wavelength switching cross-connection function and can thus interconnect paths of a wavelength-division-multiplexed optical signal and convert wavelengths, and an operating method of the network node. Accordingly, it is possible to provide a multi-degree cross-connection system having a simple structure at lower cost by allowing transmission of optical signals supposed not to be added/dropped at a network node without converting them into electrical signals and performing O/E conversion or E/O conversion only on optical signals supposed to be added/dropped at a network node. In addition, it is possible to increase the expandability of networks by regenerating degraded signals and which can effectively utilize bandwidths by grooming low-speed electrical digital hierarchy signals and transmitting them as high-speed optical signals.

Abstract: A network node and method for guaranteeing the role of an optical supervisory channel (OSC) in an optical transport network (OTN) are provided. In the network node, at least two OSC units are multiplexed, one of the OSC units is set as a main unit, the other OSC unit is set as an auxiliary unit; and the auxiliary unit is activated when the main unit cannot be operated. Thereby, the network node can guarantee the stable role of the OSC.