Manabu Arikawa

A shared carrier reception and processing scheme for compensating frequency offset and phase noise of space-division multiplexed signals over multicore fibers

We propose a noise resistant method to compensate frequency offset and phase noise based on shared carrier reception for SDM signals. We demonstrate improvement in the transmission of 112Gb/s PM-16QAM over 294km MCF.

Real-time evaluation of optical nonlinear effects on 112Gbps PM-QPSK signal in dispersion managed links

We demonstrate the impact of nonlinear effects on dispersion managed links with a FPGA-based 112Gbps real-time receiver. We clarify that PM-RZ-QPSK provides superior robustness, whereas PM-NRZ-QPSK offers better total performance resulting from higher OSNR sensitivity.

112Gb/s optical transponder with PM-QPSK and coherent detection employing parallel FPGA-based real-time digital signal processing, FEC and 100GbE Ethernet interface

We demonstrate 112Gb/s transmission using PM-QPSK format and FPGA-based real-time digital signal processing. By employing framed processing architecture for polarization demultiplexing and carrier phase estimation, stable operation of error free after FEC and wide frequency offset have been achieved.

Crosstalk reduction using bidirectional signal assignment over square lattice structure 16-core fiber for gradual upgrade of SSMF-based lines

We demonstrate crosstalk reduction using bidirectional signal assignment on WDM transmission of 256 Gb/s PM-16QAM over square lattice structure 16-core fiber. Mixed SSMF and MCF transmission with 6 spans of MCF is possible with Q crosstalk penalty below 0.5 dB.

Transmission of a 127 Gb/s PM-QPSK signal over a 3350 km SMF-only line with chromatic dispersion compensation using real-time DSP [Invited]

We experimentally confirmed the effectiveness of chromatic dispersion compensation by overlap frequency-domain equalization in real-time digital signal processing for a 127 Gb/s polarization-multiplexed quadrature phase shift keying (PM-QPSK) signal up to 56,200 ps/nm. We verified a penalty lower than 0.55 dB for accumulated dispersion over a 3350 km single-mode-fiber- (SMF-) only transmission line. We also demonstrated the transmission of a 127 Gb/s PM-QPSK signal in a 50-GHz-spacing 5-channel wavelength division multiplexing configuration over the same SMF-only line with a received Q factor of 10.1 dB.

Crosstalk Reduction With Bidirectional Signal Assignment on Square Lattice Structure 16-Core Fiber Over WDM Transmission for Gradual Upgrade of SMF-Based Lines

C-band and L-band wavelength division multiplexing (WDM) transmission performance was improved by using bidirectional signal assignment (BSA) to reduce crosstalk (XT) in square lattice structure 16-core fiber. Transmission of 16 WDM channels with 256-Gb/s polarization multiplexed-16 quadrature amplitude modulation signals on a 50-GHz grid with a net spectral efficiency of 4 b/s/Hz over 55-km of 16-core fiber spans was achieved. Use of BSA to reduce XT extended the transmission distance to 880 km in both types of transmission. Furthermore, transmission was achieved over eight mixed spans consisting of 16-core fiber and conventional single-mode fiber (SMF), demonstrating the possibility of gradually upgrading standard SMF-based lines to multicore fiber-based lines. With BSA, six 16-core fiber spans can be acceptable if the Q penalty from XT is below 0.5 dB.

Performance of mode diversity reception of a polarization-division-multiplexed signal for free-space optical communication under atmospheric turbulence

We investigated the performance of mode diversity reception of a polarization-division-multiplexed (PDM) signal with few-mode-fiber (FMF) coupling for high-speed free-space optical communications under atmospheric turbulence. Optical propagation through eigenmodes of a FMF yields coupling between different linearly polarized (LP) modes in orthogonal polarizations, which causes power imbalance and loss of the orthogonality of multiplexed signals within each individual LP mode. Due to this phenomenon, the architecture of mode diversity combining affects the receiver performance. We numerically simulated the power fluctuation coupled to each LP mode after atmospheric propagation and FMF propagation in the condition of an optical downlink from a low-Earth-orbital satellite to the ground. We found that full receiver-side multiple-input multiple-output (Rx-MIMO) architecture in three-mode diversity reception improved the performance by 5 dB compared with selection combining (SC) of signals decoded individually in LP modes, and that it mitigated the required transmitted power by 6 dB compared with reception with single mode fiber (SMF) coupling. We also experimentally confirmed in three-mode diversity reception of a 128 Gb/s PDM-quadrature phase-shift keying with a diffuser plate as a turbulence emulator, that full Rx-MIMO with adaptive filters could work under severe fading and that it outperformed SC.

Mode diversity coherent receiver with few-mode fiber-coupling for high-speed free-space optical communication under atmospheric turbulence

We report investigations on the mode diversity receiver applied in optical links from low-earth-orbital satellites to a ground terminal. We numerically simulated temporal power variations coupled to each mode of a FMF under atmospheric turbulence at several elevation angles. For weak influence of turbulence, the optical beam mainly coupled to the fundamental mode of the FMF; for strong influence of turbulence, it coupled significantly to higher order modes of the FMF and mode diversity reception was more effective. Emulating the fast-changing coupled power to each mode of the FMF with variable optical attenuators and arbitrary waveform generators, we experimentally evaluated the performance of three-mode diversity reception of 10 Gb/s QPSK. Digital signal processing was performed on 20-ms-long successively acquired data bursts, which were long enough to contain typical features of fading. We confirmed that digital combining could track the severe power variations regardless of elevation angles. We extended our investigation to the possibility of more severe conditions and we showed through simulation further improvement using multiple mode diversity receivers combined with aperture diversity.

Performance improvement in LEO-to-ground free space optical communication systems with adaptive distributed frame repetition

We proposed and evaluated the effectiveness of a simple rate control technique of Adaptive Distributed Frame Repetition (ADFR), which achieves both high speed link in the stable condition and suppresses the influence of turbulence-induced fading in the unstable condition. In order to estimate its performance in the LEO-to-Ground link with 10-Gb/s modulation speed, we developed a numerical simulator which enables us to calculate the frame error rate and the throughput under the specific turbulence condition emulated by random phase screens. We confirmed that ADFR can increase the link duration and the capacity by increasing the tolerance to the fading especially in the region of lower elevation angle. In addition, we evaluated its effectiveness through the comparison with the general adaptive rate control, in which the receiver sensitivity can be manipulated in accordance with the link conditions. The results show that ADFR provides similar performances with the sufficient received optical power.

Demonstration of turbulence-tolerant free-space optical communication receiver using few-mode-fiber coupling and digital combining

We improved the coupling efficiency to the free-space optical receiver by using a few-mode fiber with the optical signal distorted with a turbulence emulator. We demonstrated digital maximum ratio combining over 10-Gb/s BPSK transmission mitigated fading, relaxing the required transmitted power by 5 dB.