Jun Sakaguchi

305 Tb/s Space Division Multiplexed Transmission Using Homogeneous 19-Core Fiber

We report record capacity data transmission at 305 Tb/s over 10.1 km, using space division multiplexing (SDM) with 19 channels. To realize such a large SDM channel number, we fabricated a trench-assisted homogeneous 19-core fiber with average intercore crosstalk of about -32 dB at 1550 nm. We also fabricated a 19-channel SDM multiplexer/demultiplexer using free-space optics with low insertion losses and low additional crosstalk. The data signal transmitted through each SDM channel was 100 wavelength division multiplexing (100 GHz spacing) 2 × 86 Gb/s polarization-division-multiplexed quadrature phase shift keying signals and the spectral efficiency was 30.5 b/s/Hz.

Space Division Multiplexed Transmission of 109-Tb/s Data Signals Using Homogeneous Seven-Core Fiber

We achieved record 109-Tb/s transmission over 16.8 km, using space division multiplexing (SDM) together with conventional multiplexing technology. 7-core SDM, 97 WDM (100-GHz spacing), 2 × 86 Gb/s PDM-QPSK signals were used. The spectral efficiency was 11.2 b/s/Hz. SDM transmission was realized using a multi-core fiber with ultra-low-crosstalk (less than -90.0 dB/km at 1550 nm) and high performance SDM MUX/DEMUX. The overall SDM crosstalk of -53 dB caused almost no penalty for the PDM-QPSK transmission.

Experimental and theoretical investigation of the impact of ultra-fast carrier dynamics on high-speed SOA-based all-optical switches.

The impact of ultra-fast carrier dynamics in semiconductor optical amplifiers (SOAs) on switches based on cross-gain and cross-phase modulation is analyzed theoretically and experimentally. We find that ultra-fast effects lead to additional spectral broadening, which improves the optical signal-to-noise ratio for switches based on an SOA and an optical filter. For such switches, the influence of ultra-fast effects on the so-called nonlinear patterning effect is analyzed for three filter configurations: the asymmetric Mach-Zehnder interferometer (AMZI), a band-pass filter (BPF), and a cascade of an AMZI and a BPF. We conclude that fast carrier dynamics dramatically reduces nonlinear patterning and that the successful high-speed (>100 Gb/s) demonstrations in the literature rely on these effects.

Free-Space Coupling Optics for Multicore Fibers

In this letter, we report on coupling optics for connecting single-core single-mode fibers with multicore single-mode fibers. After a brief discussion of the options for such coupling systems, we describe our approach of using bulk optics to fabricate low-loss and low-crosstalk devices for both 7- and 19-core multicore fibers with the free-space design approach. This enables the use of the same coupling device with a variety of multicore fibers whose structural parameters differ from one sample to another. We present the results of experimental evaluations of these devices, discuss various causes of insertion loss, and analyze the coupling loss in detail.

High-capacity self-homodyne PDM-WDM-SDM transmission in a 19-core fiber

We investigate a high-capacity, space-division-multiplexed (SDM) transmission system using self-homodyne detection (SHD) in multi-core fiber (MCF). We first investigate SHD phase noise cancellation with both kHz and MHz range linewidths for both quadrature-phase shift-keyed (QPSK) and 16 quadrature-amplitude modulation (16QAM) signals, finding that phase noise cancellation in SHD enabled transmission with MHz linewidth lasers that resulted in error floors when using intradyne detection. We then demonstrate a high throughput SHD transmission system using low-cost, MHz linewidth distributed feedback lasers. We transmit a CW pilot-tone on a single core of a 10.1 km MCF span with the remaining 18 cores used to transmit 125 wavelength-division multiplexed (WDM) QPSK and polarization-division-multiplexed (PDM)-QPSK signals with 50 GHz channel spacing at 25 GBd. For PDM transmission and assuming a 7% forward-error correction overhead this is equivalent 210 Tb/s transmission with a SE of 33.4 b/s/Hz. High-capacity transmission is achieved despite high inter-core crosstalk, broad transmitter linewidth and narrow channel spacing, showing that combining SHD with MCF enables high throughput, low-cost transmission in next-generation optical networks.

Investigating self-homodyne coherent detection in a 19 channel space-division-multiplexed transmission link.

We investigate the performance of a self-homodyne coherent detection (SHCD) system using a 19 core multi-core fiber (MCF) and 16 wavelength-division-multiplexed channels. We show that SHCD, with the pilot-tone transmitted on a single MCF core and information carrying signals on the remaining cores, is compatible with space-division-multiplexed transmission, potentially relaxing laser linewidth and digital signal processing requirements due to phase noise cancellation. However, inter-core crosstalk can have an impact on performance and core selection.

OSNR Penalty of Self-Homodyne Coherent Detection in Spatial-Division-Multiplexing Systems

This letter presents a general model for the performance of spatial-division-multiplexing systems using self-homodyne detection. The model is applicable to single and dual polarization square M-quadrature amplitude modulation (QAM) signals, assuming arbitrary signal and pilot tone optical signal-to-noise ratios. Its validity is demonstrated using a seven-core multicore fiber link with quadrature phase shift keying and 16-QAM signals, comparing the performance of self-homodyne detection with intradyne detection.

Frequency-dependent electric dc power consumption model including quantum-conversion efficiencies in ultrafast all-optical semiconductor gates around 160 Gb/s

Based on nine up-to-date types of semiconductor-optical-amplifier (SOA) samples, we devised a power-consumption model of SOA-based all-optical gates as a tool to develop faster and more efficient OTDM systems for bitrates from 10 to 160 Gb/s and those over 160 Gb/s. The conventional effect of a continuous wave (cw) holding beam was included in the model. Furthermore, in this work we defined three step-wise quantum conversion efficiencies eta(1), eta(2), and eta(3) from current-injected carriers through photons. The dependence of each of the three efficiencies on the SOA-structure was studied. The total efficiency eta(T) observed for the nine SOAs ranged widely from 0.07 to 0.46. The validity of the power-consumption model was verified by systematically measuring the effective carrier recovery rate. According to our model, the power consumption of the best existing SOA-based gate for 160-Gb/s signals is 750 mW, and this increases at a rate approximately proportional to (bitrate)(2), and decreases proportionally to (1/etaT)(2).

Theoretical and experimental study of fundamental differences in the noise suppression of high-speed SOA-based all-optical switches.

We identify a fundamental difference between the ASE noise filtering properties of different all-optical SOA-based switch configurations, and divide the switches into two classes. An in-band ASE suppression ratio quantifying the difference is derived theoretically and the impact of the ASE filtering on the optical spectrum is verified experimentally using a hybrid DISC setup. ASE power suppression of around 3 dB over the total signal bandwidth is demonstrated.

Reduction of nonlinear patterning effects in SOA-based all-optical switches using optical filtering

We explain theoretically, and demonstrate and quantify experimentally, how appropriate filtering can reduce the dominant nonlinear patterning effect, which limits the performance of differential-mode SOA-based switches.