The present disclosure relates to optical communications, and in particular, to a DWDM remote pumping system for improving an OSNR. The system includes remote pumping gain unit, preamplifier, and gain flattening filter sequentially connected. Remote pumping gain unit and preamplifier are cascaded one behind the other as a whole amplifier. Gain flattening filter is disposed at the preamplifier's output end. In the system, remote gain unit and preamplifier which have large impact on the OSNR of the entire system are optimally designed as a whole amplifier. In remote gain unit, gain flattening filter originally disposed between two erbium-doped fiber segments is moved back to preamplifier's output end for significant improvement of gain and noise figures of the remote gain unit while ensuring gain flatness of the entire transmission system, thus effectively improving the entire system's OSNR, improving operation stability and reliability, effectively reducing bit error rate, and facilitating system maintenance.

[PROBLEM TO BE SOLVED] To uninterruptedly change a band of an optical transmission path in a line IF section, which relays a signal transmitted to an optical transmission path in a client IF section to which a communication terminal is connected, to the same band as a changed band in the client IF section without suspending the communication in the line IF section. [SOLUTION] An optical transmission system 10A performs processing for changing a band of an optical fiber 15 in a line IF section (L section) that relays a signal from an optical fiber 12 in a client IF section (C section) to the same band as that in the C section. Line IF units 24A and 24B provided on both sides of the L section set a temporary evacuation lane p as an optical lane having a band different from those of a plurality of optical lanes 0 to n in the optical fiber 15 in the L section, selects either a change-target optical lane (for example, the optical lane 0) or the temporary evacuation lane p, the change-target optical lane being provided in the optical fiber 15 in the L section and having a band to be changed to a same band as a band in the C section, while causing a buffer unit 46 to absorb a delay difference between a signal received by the change-target optical lane and a signal received by the temporary evacuation lane p, and sets the optical lane not selected to have the same band as the band in the C section.

An optical transmission device includes a reception unit that receives a first signal light and a second signal light, the first and second lights having power levels that respectively correspond to transmission distances and being transmitted; an amplification unit that amplifies the first signal light and the second signal light in accordance with a signal light having a high power level from among the received first signal light and second signal light; and a transmission unit that performs transmission of the amplified first signal light and second signal light.

An object of the present invention is to provide an optical 90-degree hybrid circuit which is capable of easily adjusting the optical power ratio between signal and local oscillator and suppresses an optical system of an optical receiver becoming complex and optical receivers using the same. The optical 90-degree hybrid circuit for demodulating multilevel phase-modulated signals corresponding to individual polarized waves by multiplexing an optical wave having a predetermined plane of polarization contained in signal and local oscillator that has the same wavelength as the signal and has been adjusted to circularly-polarized signal, and polarization-splitting the multiplexed signal includes polarization splitting means (polarization splitting) for extracting an optical wave having a predetermined plane of polarization from the signal, a polarization conversion element for rotating a plane of polarization of the optical wave extracted from the polarization splitting means, and a polarizer that determines a plane of polarization of the signal before multiplexing the signal with the local oscillator, and the polarization splitting means, the polarization conversion element, and the polarizer adjust intensity of the optical signal (VOA function) in cooperation with each other.

Methods and apparatuses for restoring lost signal in a network transmission line are disclosed. A first optical signal transmitted from a first optical module is received at an optical switch, the first optical signal having a first optical spectrum with data encoded into the first optical signal. A second optical signal having a second optical spectrum corresponding to the first optical spectrum without data encoded into the second optical signal, is received at the optical switch, the second optical signal the second optical signal transmitted from an amplified spontaneous emission source. Detecting, at a first photo detector, a loss of optical spectrum in the first optical signal, and, in response to detecting the loss of optical spectrum in the first optical signal, switching the optical switch from passing the first optical signal to passing the second optical signal thereby supplying at least one idler carrier without data imposed.

An optical transmission device in an optical network in which a first optical path and a second optical path are set, the optical transmission device locating on the second optical path, the optical transmission device includes; a storage unit configured to store control data for a control of an optical transmission power to the second optical path, the control being performed based on a training signal received through the second optical path; and a controller configured to control the optical transmission power to the second optical path, based on the control data stored in the storage unit, according to a detection of an optical path change by which an optical path transmitting a main signal is changed from the first optical path to the second optical path.

An optical transmission apparatus includes: a wavelength selecting switch, including an input port and an output port having more ports than the input port, configured to perform an adjustment of a level of an optical signal from the input port to the output port; a first monitor configured to monitor the level of the optical signal at the input port unit; a second monitor configured to monitor the level of the optical signal at the output port unit; and a controller configured to control the wavelength selecting switch wherein the controller: calculates a virtual output value for the output port unit based on a first monitor result from the first monitoring unit, a second monitor result from the second monitoring unit, and a current adjustment value for the adjustment function; calculates a new adjustment value based on the virtual output value; and sets the new adjustment value to the adjustment.

Example embodiments of the present invention relate to optical wavelength directing devices used to construct compact optical nodes.

There is provided an optical transmission control device includes a memory, and a processor coupled to the memory and the processor configured to aggregate information of candidacy sections having a possibility that communication is discontinued among wavelength-multiplexed transmission sections, classify, based on the aggregated information, optical paths set between optical transmission devices into a first optical path on which, when communication in the candidacy sections is discontinued, an optical signal is not transmitted, and a second optical path on which, when the communication in the candidacy sections is discontinued, an optical signal is transmitted, and determine a wavelength allocation in a first wavelength group of the first optical path and a second wavelength group of the second optical path so that a difference in gain wavelength characteristics of the first optical path and the second optical path is equal to or less than a predetermined level.

An optical module includes an optical modulator that performs optical modulation of transmission data, an optical modulator controller that controls the optical modulator, a memory that stores corresponding relationships between temperatures and set data with which modulation of the optical modulator is to be performed at an operating point voltage, a temperature sensor that measures a temperature in the optical module; and a setting circuit that refers the memory and searches for set data corresponding to measured temperature, and set the set data to the optical modulator controller.