Manabu Arikawa

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 phenome

We propose a multi-layer cascaded filter architecture consisting of differently sized strictly linear (SL) and widely linear (WL) filters to compensate for the relevant linear impairments in optical fiber communications including in-phase/quadrature (IQ) skew in both transmitter and receiver by using deep unfolding. To control the filter coefficients adaptively, we adopt a gradient calculation with back propagation from machine learning with neural networks to minimize the magnitude of deviation

We have developed a quantum memory that is completely compatible with current quantum information processing for continuous variables of light, where arbitrary frequency sidebands of a squeezed vacuum can be stored and retrieved using bichromatic electromagnetic induced transparency. The 2 MHz sidebands of squeezed vacuum pulses with temporal widths of 470 ns and a squeezing level of $\ensuremath{-}1.78\ifmmode\pm\else\textpm\fi{}0.02$ dB were stored for 3 $\ensuremath{\mu}$s in laser-cooled $^{

We experimentally demonstrated a long-haul wavelength-division multiplexed (WDM) and space-division multiplexed (SDM) transmission of 32-Gbaud polarization-division multiplexed quadrature phase-shift keying signals over 52-km coupled-4-core fiber spans with amplification by coupled-4-core erbium-doped fiber amplifiers (EDFAs). Error-free performance after forward error correction was achieved up to 2700 km. From converged multi-input multi-output filter coefficients, we estimated the mode depend

A probe light in a squeezed vacuum state was injected into cold 87Rb atoms with an intense control light in a coherent state. A sub-MHz window was created due to electromagnetically induced transparency, and the incident squeezed vacuum could pass through the cold atoms without optical loss, as was successfully monitored using a time-domain homodyne method.

We propose a monitoring method for individual impairments in a transmitter (Tx) and receiver (Rx) by using filter coefficients of multi-layer strictly linear (SL) and widely linear (WL) filters to compensate for relevant impairments where the filter coefficients are adaptively controlled by stochastic gradient descent with back propagation from the last layer outputs. Considering the order of impairments occurring in a Tx or Rx of coherent optical transmission systems and their non-commutativity

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

We investigate the rate adaptability of quadrature amplitude modulation (QAM)-based probabilistic constellation shaping (PCS) using a fixed forward error correction (FEC) scheme over a wide range of information rates (IRs). Blind adaptive equalization that does not sacrifice any of the IRs was adopted. We show that the conventional decision directed least mean square (DDLMS) algorithm can cause a problem of mis-convergence when it is applied to the PCS of a low IR. To avoid the mis-convergence o

We propose an adaptive multi-layer (ML) filter architecture to compensate for linear impairments that occur in transmitter (Tx) and receiver (Rx) components in ultra-long-haul optical fiber transmission systems, in which large chromatic dispersion (CD) accumulates in the received signal. The architecture consists of strictly linear (SL) and widely linear (WL) filter layers, and the coefficients of the ML filters are adaptively controlled by gradient calculation with back propagation and stochast

We propose a fractionally spaced frequency-domain adaptive multi-input multi-output (MIMO) filter architecture in which the sampling rate of input signals is below 2× oversampling with a non-integer oversampling factor for mode demultiplexing in long-haul transmission over coupled multi-core fibers. The frequency-domain sampling rate conversion to the symbol rate, i.e., 1× sampling, is placed after the fractionally spaced frequency-domain MIMO filter. The filter coefficients are adaptively contr

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 si

We applied several optimizers from the machine learning field to an adaptive MIMO equalizer for SDM transmission. We experimentally compared their convergence properties in a SDM transmission over a 52-km coupled-core 4-core fiber and 4-core EDFA and showed over 22% faster convergence with Adam.

We demonstrated long-haul transmissions over coupled four-core fibers (C4CFs) installed in a 15-km-long submarine cable. A small propagation-loss coefficient of 0.16 dB/km and spatial-mode dispersion coefficient of 5.1 ps/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\sqrt{\mathbf{km}}}$</tex-math></inline-formula> were confirmed after cabling. A recirculating loop consisting of two spans of a 60-km C4CF we

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.

We demonstrated a transoceanic-class long-haul transmission over 12-coupled-core fiber (12-CCF) with a standard cladding diameter of 125 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m. Nine-channel wavelength-division multiplexed (WDM) and 12-core spatial-division multiplexed 32-Gbaud polarization-division multiplexed quadrature phase shift keying signals were transmitted over