Takahito Tanimura

Implementation efficient nonlinear equalizer based on correlated digital backpropagation

One stage per span is commonly considered as the lower boundary for implementation complexity of nonlinear equalizer based on digital backpropagation. The proposed method overcomes this boundary and improves the efficiency by about four times.

Experimental demonstration of a format-flexible single-carrier coherent receiver using data-aided digital signal processing

We experimentally demonstrate the use of data-aided digital signal processing for format-flexible coherent reception of different 28-GBd PDM and 4D modulated signals in WDM transmission experiments over up to 7680 km SSMF by using the same resource-efficient digital signal processing algorithms for the equalization of all formats.

Improvements to Digital Carrier Phase Recovery Algorithm for High-Performance Optical Coherent Receivers

The Viterbi-and-Viterbi (V-V) algorithm is widely used to recover the carrier phase in optical digital coherent receivers. For simplicity, the basic V-V algorithm assumes constant carrier phase within the average duration. However, this basic assumption is probably violated by factors such as laser frequency offset and nonlinear XPM. In order to improve the basic V-V carrier phase recovery, five methods are introduced, verified, and analyzed. All these methods are compatible with parallel implementation that is mandatory for a realistic DSP circuit. The Q-improvement brought by each algorithm is analyzed together with the complexity of each. Among the five methods, the laser frequency offset compensation expands the tolerable frequency offset to 0.37 symbol rate, and the optimum weighted averaging in conjunction with normalization processing improves the Q-value by 2 dB under severe XPM condition.

Interplay between local oscillator phase noise and electrical chromatic dispersion compensation in digital coherent transmission system

We demonstrate that the interplay between local oscillator phase noise and electrical chromatic dispersion compensation induces timing jitter as well as intensity noise. The interplay is investigated in 3000 km-long transmission (accumulated dispersion of 47,000 ps/nm) without optical dispersion compensation.

Superimposition and detection of frequency modulated tone for light path tracing employing digital signal processing and optical filter

We propose a novel method for light path tracing and demonstrate it in 112Gb/s DP-16QAM transmission. The S/N of the detected label exceeds 24dB after 20span transmission. No crosstalk was observed in neighboring DWDM channels.

Digital clock recovery algorithm for optical coherent receivers operating independent of laser frequency offset

We propose a digital clock recovery algorithm and demonstrate its tolerance to at least 5 GHz laser frequency mismatch in a 43 Gb/s DP-RZ-QPSK receiver after 1200 km transmission.

Experimental Investigation of 126-Gb/s 6PolSK-QPSK signals

We experimentally generate 28-GBd 6PolSK-QPSK signals by utilizing a high-speed 4-channel DAC and an integrated dual-polarization I/Q modulator. In WDM transmission experiments over up to 4800 km standard single-mode fiber, we compare the performance of 126-Gb/s 6PolSK-QPSK and 112-Gb/s PDM-QPSK signals.

Network innovations brought by digital coherent receivers

Operational efficiency improvements of optical networks enabled by digital coherent receivers are discussed in view of reliability, agility, performance and reduced operational complexity. Several specific technologies are briefly introduced to deliver some more insight.

Novel wide-range frequency offset compensator demonstrated with real-time digital coherent receiver

A novel frequency offset estimator is proposed and implemented in a 1 Gbit/s real-time coherent receiver to demonstrate all-digital frequency offset compensation up to plusmn0.4 symbol rate.

Experimental characterization of nonlinearity mitigation by digital back propagation and nonlinear polarization crosstalk canceller under high PMD condition

Impact of PMD is evaluated on nonlinear mitigation algorithm. While the backpropagation showed consistent improvement regardless of PMD, the best performance was found under different PMD conditions depending on fiber input power and channel spacing.