A probe generator includes: a first demultiplexer configured to branch a first optical signal having a first wavelength into at least two first polarized optical signals; a first adjustor configured to adjust the first polarized optical signals such that the first polarized optical signals have the same polarization direction and to combine the adjusted first polarized optical signals into a second optical signal; a first modulator configured to branch the second optical signal into at least two first split optical signals and to intensity-modulate each of the first split optical signals with first pilot signals; a second adjustor configured to adjust the first split optical signals intensity-modulated by the first modulator such that the intensity-modulated first split optical signals have different polarization directions; and an output unit configured to combine the first split optical signals adjusted by the second adjustor to generate a probe optical signal to be output.

A polarization multiplex optical transmitter circuit can provide compensation for the transmission PDL while reducing decrease in transmission power. The polarization multiplex optical transmitter circuit includes a beam divider circuit configured to divide light outputted from a light source, optical phase shifters provided in at least one of two waveguides connected to output terminals of the beam divider circuit, a light wave synthesizer circuit connected to the two waveguides, first and second optical transmitters coupled to two output terminals of the light wave synthesizer circuit, a polarization multiplexer configured to synthesize two output polarized waves from the first and second optical transmitters, and a polarization rotator provided between the first and second optical transmitters and the polarization multiplexer and coupled to at least one of the first and second optical transmitters.

A polarization multiplex optical transmitter circuit can provide compensation for the transmission PDL while reducing decrease in transmission power. The polarization multiplex optical transmitter circuit includes a beam divider circuit configured to divide light outputted from a light source, optical phase shifters provided in at least one of two waveguides connected to output terminals of the beam divider circuit, a light wave synthesizer circuit connected to the two waveguides, first and second optical transmitters coupled to two output terminals of the light wave synthesizer circuit, a polarization multiplexer configured to synthesize two output polarized waves from the first and second optical transmitters, and a polarization rotator provided between the first and second optical transmitters and the polarization multiplexer and coupled to at least one of the first and second optical transmitters.

Methods, systems, and devices for network communications to reduce optical beat interference (OBI) in upstream communications are described. For example, a fiber node may provide a narrow band seed source to injection lock upstream laser diodes. Therefore, upstream communications from each injection locked laser diode may primarily include the wavelength associated with each seed source. The seed sources may be unique to each end device and configured to minimize OBI. That is, the upstream laser diodes may be generic, but the received seed source may enable upstream communications at varying wavelengths. The fiber node may provide each seed source by filtering (e.g., by a grating filter) a broadband light source.

Methods, systems, and devices for network communications to reduce optical beat interference (OBI) in upstream communications are described. For example, a fiber node may provide a narrow band seed source to injection lock upstream laser diodes. Therefore, upstream communications from each injection locked laser diode may primarily include the wavelength associated with each seed source. The seed sources may be unique to each end device and configured to minimize OBI. That is, the upstream laser diodes may be generic, but the received seed source may enable upstream communications at varying wavelengths. The fiber node may provide each seed source by filtering (e.g., by a grating filter) a broadband light source.

An optical transmission device includes a first wavelength multiplexer, a second wavelength multiplexer, a wavelength converter and a third wavelength multiplexer. The first wavelength multiplexer multiplexes optical signals in a first wavelength band to generate first wavelength multiplexed light. The second wavelength multiplexer multiplexes optical signals in the first wavelength band to generate second wavelength multiplexed light in a first polarization. The wavelength converter converts a wavelength of the second wavelength multiplexed light from the first wavelength band into a second wavelength band by a cross phase modulation among the second wavelength multiplexed light, first pump light in a second polarization and second pump light in the second polarization. The second polarization is orthogonal to the first polarization. The third wavelength multiplexer multiplexes the second wavelength multiplexed light whose wavelength has been converted by the wavelength converter and the first wavelength multiplexed light.

An optical transmission device includes a first wavelength multiplexer, a second wavelength multiplexer, a wavelength converter and a third wavelength multiplexer. The first wavelength multiplexer multiplexes optical signals in a first wavelength band to generate first wavelength multiplexed light. The second wavelength multiplexer multiplexes optical signals in the first wavelength band to generate second wavelength multiplexed light in a first polarization. The wavelength converter converts a wavelength of the second wavelength multiplexed light from the first wavelength band into a second wavelength band by a cross phase modulation among the second wavelength multiplexed light, first pump light in a second polarization and second pump light in the second polarization. The second polarization is orthogonal to the first polarization. The third wavelength multiplexer multiplexes the second wavelength multiplexed light whose wavelength has been converted by the wavelength converter and the first wavelength multiplexed 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.

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.

A novel digital signal processing scheme (DSP) for quadrature duobinary (QDB) spectrum shaped polarization multiplexed quadrature phase shift keying (PM-QPSK) based on multi-modulus blind equalizations (MMBE) is proposed and demonstrated with both simulation and experimental results. The key algorithms for this novel digital signal processing scheme include the cascaded multi-modulus algorithm (CMMA) for blind polarization de-multiplexing, multi-modulus QPSK partitioning frequency offset estimation (FOE) and two stage carrier phase recovery (CPR) with maximum likelihood phase estimation. The final signal is detected by maximum-likelihood sequence detection (MLSD) for data BER measurement. The feasibility of the proposed digital signal processing scheme is demonstrated by the experiment of 112 Gb/s QDB spectrum shaped PM-QPSK signal with a 25 GHz bandwidth waveshaper for Nyquist WDM channels.