Shinichi Aozasa

Single-mode hole-assisted fiber with low bending loss characteristics

We review the design and transmission characteristics of hole-assisted fiber (HAF) as a candidate for bending loss insensitive fiber (BIF). We also investigate the applicability of single-mode and hole-assisted type BIF to future access networks.

Silica-based PLC with heterogeneously-integrated PDs for one-chip DP-QPSK receiver.

We fabricated a DP-QPSK receiver PLC by the heterogeneous integration of eight high-speed PDs on a compact silica-based PLC platform with a PBS, 90-degree optical hybrids and a VOA. 32 Gbaud DP-QPSK signal demodulation was successfully demonstrated.

Demonstration of carrier envelope offset locking with low pulse energy

We demonstrate a carrier-envelope-offset (CEO)- locked frequency comb with 230-pJ fiber coupling pulse energy by using a passively mode-locked Er-fiber amplifier laser. For the generation of an octave-bandwidth spectrum in a highly nonlinear fiber and the second harmonic in a self-referenced interferometer with the lower pulse energy, we use a tellurite photonic crystal fiber and a direct-bonded quasi-phasematched LiNbO3 ridge waveguide, respectively. Our method is feasible for locking the CEO with a lower pulse energy to obtain a low-noise and highaccuracy optical frequency comb at telecommunications wavelengths.

Transmission over large-core few-mode photonic crystal fiber using distance-independent modal dispersion compensation technique

We propose a transmission distance-independent technique for modal dispersion compensation over few-mode fiber that uses a single-input multiple-output configuration and adaptive equalization. Our technique can compensate for the modal dispersion of a signal with 1-tap FIR filters regardless of the amount of modal delay difference, and enables us to utilize fiber with a large core and few modes as a long-haul transmission line. We also show numerically the advantage of few-mode photonic crystal fiber (PCF) for realizing a larger effective area (A(eff)), and finally we report a transmission over a large-core two-mode PCF with A(eff)>280 μm(2).

New approach to achieving a carrier-envelope phase-locked frequency comb with 25-GHz mode spacing

We propose an approach to achieving a carrier-envelope phase-locked frequency comb with 25-GHz mode spacing at 1.5 μm. We demonstrate octave-spanning supercontinuum generation with the widest mode spacing ever achieved using a CW laser diode.

Optimal design of 4LP-mode multicore fibers for high spatial multiplicity

High spatial multiplicity fiber designs are presented for homogeneous and heterogeneous 4LP-mode multicore fibers (MCFs) that support six spatial modes per core. The high-spatial-density 4LP-mode MCF design methodology is explained in detail. The influence of the number of cores on the cladding diameter (Dcl) and relative core multiplicity factor (RCMF) is investigated. The optimal core designs and MCF layouts with square and triangular lattices maintain glass fiber reliability (maximum Dcl = 250 μm). For homogeneous 4LP-mode MCFs, a 19-core triangular-lattice fiber gives the highest RCMF of 61.7. For heterogeneous 4LP-mode MCFs, an RCMF of 65.4 is obtained for a 21-core square-lattice fiber.

400-G coherent receiver using silica-based heterogeneously-integrated PLC with newly developed waveplate type PBS

We report a one-chip 400-G coherent receiver that employs a heterogeneously integrated silica-based PLC with low-loss three-branched spot size converters, an extinction ratio tunable PBS and 16 InP-PDs. 32-Gbaud DP-16QAM signal demodulation was successfully demonstrated.

Thermal via technology for silica-based planar lightwave circuit

We propose the first thermal via technology for a silica-based planar lightwave circuit (PLC) to enable us to stack electronic components such as transimpedance amplifiers (TIAs) on a PLC. This is possible because the effective heat dissipation of the via can prevent the performance degradation of the TIA. The temperature increase of the TIAs was suppressed to only 8.7°C by the thermal vias, while it was 15.7°C without them. Silica-based PLCs with thermal vias will be a key technology for compact high performance PLC devices.

Efficient Carrier-Envelope Offset Locking with a Simplified Configuration of an f-to-2f Interferometer

We demonstrate a carrier-envelope-offset (CEO) locking of a frequency comb in the 1.5-µm band with 500-pJ laser pulse energy. To achieve the CEO locking in the 1.5-µm band with low laser pulse energy, we improve the efficiency of the laser coupling into our tellurite photonic crystal fiber using angled V-groove splicing. In addition, we use a minimum number of optics in a collinear f-to-2f interferometer to avoid connection and propagation losses. Our method does not need any devices for group delay adjustment. Since we use a short, highly nonlinear fiber with low chromatic dispersion for octave-spanning supercontinuum (SC) generation, the group delay between the short- and long-wavelength on an octave-wide SC spectrum is about 3 ps, which does not cause serious degradation of the CEO beat signal.

Demonstration of locking carrier envelope offset by using low pulse energy

We demonstrate a carrier-envelope-offset (CEO)-locked frequency comb with 230-pJ fiber coupling pulse energy by using a passive-modelocked Er-fiber amplifier laser. We succeeded in CEO stabilization at telecommunications wavelengths using the lowest fiber coupling pulse energy.