Yohei Sakamaki

69.1-Tb/s (432 × 171-Gb/s) C- and extended L-band transmission over 240 km Using PDM-16-QAM modulation and digital coherent detection

We demonstrate the record total capacity of 69.1 Tb/s with a spectral efficiency of 6.4 b/s/Hz by employing 21.4-Gbaud 16-QAM modulation, blind digital coherent detection, and 10.8-THz ultra-wideband amplification in the C- and extended L-bands.

Ultra-High Capacity WDM Transmission Using Spectrally-Efficient PDM 16-QAM Modulation and C- and Extended L-Band Wideband Optical Amplification

This paper describes ultrahigh capacity transmission based on spectrally-efficient multi-level modulation and wideband optical amplification techniques. 21.4-Gbaud polarization-division multiplexed (PDM) 16-ary quadrature amplitude modulation (QAM) signals are generated by utilizing an optical synthesis technique, wavelength-multiplexed with 25-GHz spacing by optical pre-filtering, and received by an intradyne coherent receiver based on digital signal processing (DSP) with pilotless algorithms. These techniques realize a spectral efficiency (SE) of 6.4 b/s/Hz. Furthermore, a hybrid amplification technique that combines distributed Raman and dual-band erbium-doped amplifiers (EDFAs) realizes 10.8-THz signal bandwidth in C- and extended L-bands. By using these techniques, we successfully demonstrate 69.1 Tb/s transmission over 240 km of low loss pure silica core fibers.

New Optical Waveguide Design Based on Wavefront Matching Method

We have studied the wavefront matching (WFM) method, which synthesizes optimum waveguide patterns from the desired characteristics, and demonstrated its feasibility. In this paper, we expand this method to create optimum waveguide shapes with low-loss and low-wavelength dependence in waveguide lenses, Y-branches, and waveguide crossings. We describe the design procedures for each waveguide element and report the experimental results as proof of concept. The measured results agree well with our design requirements, and the waveguide patterns designed by the WFM method exhibit better characteristics than the reference patterns.

Experimental demonstration of multi-degree colorless, directionless, contentionless ROADM for 127-Gbit/s PDM-QPSK transmission system

We experimentally demonstrate the feasibility of a multi-degree colorless, directionless, and contentionless (C/D/C-less) ROADM node composed of high port count wavelength-selective switches and transponder aggregators using silica-based planar lightwave circuit technology. The experimental results show that the introduction of a C/D/C-less function to a multi-degree ROADM node induces no significant penalty in a 127-Gbit/s PDM-QPSK signal transmission.

Compact 111-Gbit/s integrated RZ-DQPSK modulator using hybrid assembly technique with silica-based PLCs and LiNbO 3 devices

We developed a compact RZ-DQPSK modulator using six arrayed optical phase modulators with an LN waveguide, two PLCs with 1×2 couplers and a U-turned waveguide. This modulator exhibited good 111-Gbit/s CSRZ-DQPSK modulation performance.

64QAM Modulator With a Hybrid Configuration of Silica PLCs and LiNbO

Quadrature amplitude modulation (QAM) is a promising approach for increasing the spectral efficiency of wavelength-division-multiplexing transmission, but its optical implementation is challenging. We demonstrate a 64-level QAM (64QAM) modulator, which uses a signal synthesis in the optical domain. We achieved an integration of low-loss asymmetric couplers and three quadrature-phase-shift-keying modulation circuits using a hybrid configuration of silica-based planar lightwave circuits and an array of LiNbO3 phase modulators. The modulator successfully operated at 60 Gb/s (10 Gbaud).

_{3}

In this paper, we describe the procedure for designing low-loss Y-branch waveguides by the wavefront matching (WFM) method, and report experimental results as proof of concept. The designed Y-branches were fabricated using silica-based planar lightwave circuit (PLC) technology. A Y-branch fabricated with a 0.45%-Delta waveguide exhibited a low excess loss of less than 0.2 dB over a wide wavelength range of 1250 to 1650 nm. In addition, we demonstrate that the WFM-designed Y-branches enable us to provide compact 1 times 32 splitters with an average insertion loss of 16.0 dB at a wavelength of 1550 nm. In addition, we present some experimental results obtained using samples with different Delta values, and show that our design method is more efficient for a higher Delta waveguide suitable for functional PLC devices.

Phase Modulators

We developed an 86-Gbit/s DQPSK modulator by using four arrayed optical phase modulators with an LN waveguide and two 1times4 coupler PLCs by adopting the WFM technique. This modulator exhibited excellent DQPSK modulation performance

Low-Loss Y-Branch Waveguides Designed by Wavefront Matching Method

We designed waveguide crossings with small angles by the wavefront matching method to reduce excess loss and crosstalk. The designed waveguide crossings were fabricated using silica-based planar lightwave circuit (PLC) technology. We experimentally obtained excess loss and crosstalk values of less than 0.3 and -30 dB, respectively, for a crossing angle of 5deg, and of less than 0.1 and -38 dB, respectively, for an angle of 20deg, in the 1530-1565-nm wavelength range. The designed waveguide crossings are promising as basic circuit elements for realizing more compact PLC devices

86-Gbit/s differential quadrature phase-shift-keying modulator using hybrid assembly technique with planar lightwave circuit and LiNbO3 devices

This paper describes a waveguide crossing design that uses the wavefront matching (WFM) method. The WFM method enables us to design waveguide crossings with lower loss than simple crossings composed of two straight waveguides, without any crosstalk degradation. We report the procedure for designing waveguide crossings based on the WFM method and some experimental results. For experimental confirmation, we made a waveguide crossing test circuit using silica-based planar lightwave circuit (PLC) technology. By comparing the results obtained with samples constructed with different Delta waveguides, we show that our design method is very efficient for higher Delta waveguides suitable for high-density integration. In addition, we describe an example application of our designed crossings to an integrated PLC device, namely a wavelength multiplexer with a variable optical attenuator. We show that waveguide crossings designed by the WFM method are useful for improving the loss characteristic of highly integrated PLC devices.