Abstract: The present invention relates to an apparatus and method for automatically correcting a bias voltage for a carrier suppressed pulse generating modulator using the phase distribution of the output pulses, which automatically detects an optimal bias voltage for the carrier suppressed pulse generating modulator and stabilizes the bias voltage. In the bias voltage automatic correction method and apparatus of the present invention, an optimal bias voltage for the modulator is set to a bias voltage that is obtained when mean power of an optical signal output from the modulator is highest. The varying direction of the bias voltage is detected on the basis of the phase variations in the output optical signal of the modulator according to the bias voltage variations is detected, and the bias voltage is corrected oppositely to the varying direction of the bias voltage.

Abstract: Provided are an optical fiber amplification method and apparatus for controlling a gain. Initial values including target gains of first and second amplifications for an optical amplifier amplifying the input light signal are set. Power of the input light signal is measured and the power of first and second backward pump lights proceeding in the opposite direction to the input light signal is controlled based on the measured power. The input light signal is firstly amplified and a first amplification gain of the amplified light signal is calculated. Power of a first forward pump light proceeding in the same direction as the input light signal is controlled so that the first amplification gain can be substantially equal to the target gain of the first amplification. The firstly amplified light signal is secondly amplified and a second amplification gain with respect to the input light signal is calculated.

Abstract: A tunable high-order Bessel low pass filter which is applied to a multi-rate duobinary generation system of an optical communication system.

Abstract: Provided are an apparatus for optimizing bias voltage of an electro-optic modulator, a method therefor, and an optical transmission system using the method. The present research provides a bias voltage optimizing apparatus of an electro-optic modulator that can stabilize bias voltage supplied to the electro-optic modulator through automatic bias voltage initialization control by considering the point that the form of an optical output signal and the intensity of a clock component are changed according to the bias voltage of the electro-optic modulator, a method therefor and an optical transmission system using the method.

Abstract: The present invention relates to a method for revising a wavelength of the EML by controlling a working temperature based on arithmetic functional relations between the DC-Offset voltage and the wavelength and between the working temperature and the wavelength, and a computer-readable recording medium thereof. The method includes the steps of: re-setting initial values of a working temperature, a amplifying voltage and the DC-Offset voltage; determining a wavelength with respect to the re-set DC-Offset voltage based on a functional relation between the DC-Offset voltage and the wavelength of the EML; and determining the revising working temperature for the determined wavelength based on the functional relation between the working temperature and the wavelength of the EML, and re-setting the working temperature with the revising working temperature.

Abstract: A low-noise optical fiber amplifier for performing a long-distance optical transmission in a wavelength division multiplexing optical transmission apparatus is provided. This amplifier includes a first optical fiber amplifier having a pre-stage optical fiber, and a first coupler for supplying pump light to the pre-stage optical fiber; a dispersion compensating Raman amplifier (DCRA) connected to the first optical fiber amplifier and having a dispersion compensating optical fiber (DCF) that compensates for the dispersion accumulated in an optical line and generates a Raman gain, and a second coupler for supplying Raman pump light onto the DCF; and a second optical fiber amplifier connected to the DCRA, and including a post-stage optical fiber and a third coupler for supplying pump light onto the post-stage optical fiber. Accordingly, this optical fiber amplifier is used for terrestrial WDM optical transmission, and thus has remarkably low noise figure compared to the existing optical amplifiers.

Abstract: The method for operating an optical transponder, which performs maintenance of a signal in the optical transponder having a digital wrapper in an optical transmission system including multiple layers, includes (a) calling a processor for processing an interrupt when the interrupt is generated from the digital wrapper according to monitoring of a received signal; (b) the called processor detecting what defect is generated in the received signal and detecting whether or not the received signal requires maintenance; (c) performing defect processing in the case that a defect is detected at (b) or is cancelled; and (d) controlling the digital wrapper according to the defect and maintenance processing result.

Abstract: Disclosed herein is a method of optimizing an output signal of an optical receiver using FEC and an optical receiving system using the method. In the method of the present invention, optical signals transmitted through an optical cable are converted into digital data of bits “1” and “0” on the basis of a reference voltage, and errors generated during transmission of the optical signals are corrected using the FEC. The method includes extracting numbers of occurrence of errors for bits “1” and “0” recovered through the FEC. Thereafter, the extracted numbers of occurrence of errors for bits “1” and “0” are compared with each other. A reference voltage used to judge levels of the signals to be level “1” or “0” is controlled if the numbers of occurrence of errors for bits “1” and “0” are not equal to each other.

Abstract: An optical receiver in an optical communication system, and more particularly, to a method and an apparatus for optimizing a decision level of a signal output from an optical receiver to obtain a minimum bit error rate (BER) by measuring output characteristics of the optical receiver and adjusting a reference voltage of the optical receiver based on a measurement result. The provided method includes measuring the strength of an electric signal at a modulated frequency out of the frequency elements of the output electric signal in the optical receiver, generating a reference voltage based on the strength data of the electric signal, inputting the reference voltage to the optical receiver and re-measuring the strength of the electric signal output from the optical receiver to determine whether the strength of the signal is minimum, and maintaining the reference voltage when the strength of the signal is minimum and adjusting the reference voltage in other cases.

Abstract: Provided are an optical fiber amplification method and apparatus for controlling a gain. Initial values including target gains of first and second amplifications for an optical amplifier amplifying the input light signal are set. Power of the input light signal is measured and the power of first and second backward pump lights proceeding in the opposite direction to the input light signal is controlled based on the measured power. The input light signal is firstly amplified and a first amplification gain of the amplified light signal is calculated. Power of a first forward pump light proceeding in the same direction as the input light signal is controlled so that the first amplification gain can be substantially equal to the target gain of the first amplification. The firstly amplified light signal is secondly amplified and a second amplification gain with respect to the input light signal is calculated.

Abstract: A low-noise optical fiber amplifier for performing a long-distance optical transmission in a wavelength division multiplexing optical transmission apparatus is provided. This amplifier includes a first optical fiber amplifier having a pre-stage optical fiber, and a first coupler for supplying pump light to the pre-stage optical fiber; a dispersion compensating Raman amplifier (DCRA) connected to the first optical fiber amplifier and having a dispersion compensating optical fiber (DCF) that compensates for the dispersion accumulated in an optical line and generates a Raman gain, and a second coupler for supplying Raman pump light onto the DCF; and a second optical fiber amplifier connected to the DCRA, and including a post-stage optical fiber and a third coupler for supplying pump light onto the post-stage optical fiber. Accordingly, this optical fiber amplifier is used for terrestrial WDM optical transmission, and thus has remarkably low noise figure compared to the existing optical amplifiers.

Abstract: An apparatus and a method for modulating the optical intensity, with the noises suppressed by using a linear optical modulator, are disclosed, so that the characteristics of signals transmitted from an optical communication system can be improved, and that the resolution of the measured physical quantities can be improved in an optical measuring instrument. The method is carried out in the following manner. That is, the magnitude of frequency is measured by utilizing pilot signals and electrical signals to transfer negatively fed-back signals to an optical intensity modulator. The phase is delayed by generating pilot signals so as to suppress an amplitude noise from the pilot signal caused by nonlinear modulation at the optical intensity modulator. A linear modulation is carried out on the phase-delayed signals and on optical signals from an external source to provide a linear component.

Abstract: An apparatus and a method for modulating the optical intensity, with the noises suppressed by using a linear optical modulator, are disclosed, so that the characteristics of signals transmitted from an optical communication system can be improved, and that the resolution of the measured physical quantities can be improved in an optical measuring instrument. The method is carried out in the following manner. That is, the magnitude of frequency is measured by utilizing pilot signals and electrical signals to transfer negatively fed-back signals to an optical intensity modulator. The phase is delayed by generating pilot signals so as to suppress an amplitude noise from the pilot signal caused by nonlinear modulation at the optical intensity modulator. A linear modulation is carried out on the phase-delayed signals and on optical signals from an external source to provide a linear component.