Satoshi Shinada

Tunable All-Optical Wavelength Conversion of 160-Gb/s RZ Optical Signals by Cascaded SFG-DFG Generation in PPLN Waveguide

We report, for the first time, tunable all-optical wavelength conversion of 160-Gb/s return-to-zero (RZ) optical signals based on cascaded sum- and difference-frequency generation in a periodically poled LiNbO3 waveguide. The distorted signals due to limited phase-matching bandwidth during conversion were compensated by spectral reshaping. We achieved error-free tunable wavelength conversion with a bit-error rate of less than 10-9 for 160-Gb/s RZ signals in a 23-nm tuning range over the C-band

Surface plasmon resonance on microaperture vertical-cavity surface-emitting laser with metal grating

We proposed a microaperture vertical-cavity surface-emitting laser (VCSEL) with metal grating for the enhancement of optical near-field induced by surface plasmon resonance. We carried out the two-dimensional modeling on the near-field intensity at a microaperture surrounded by a grating in a silver film. An increase in throughput through the microaperture was obtained by the control of a surface plasmon mode, which is strongly dependent on some structural parameters of the grating, such as the period and the depth of a grating, and so on. We also fabricated a microaperture VCSEL with concentric circular grating, exhibiting a large enhancement in peak intensity. The intensity is eight times larger than that of a single-aperture device without grating.

Development of optical packet and circuit integrated ring network testbed

We developed novel integrated optical packet and circuit switch-node equipment. Compared with our previous equipment, a polarization-independent 4 × 4 semiconductor optical amplifier switch subsystem, gain-controlled optical amplifiers, and one 100 Gbps optical packet transponder and seven 10 Gbps optical path transponders with 10 Gigabit Ethernet (10GbE) client-interfaces were newly installed in the present system. The switch and amplifiers can provide more stable operation without equipment adjustments for the frequent polarization-rotations and dynamic packet-rate changes of optical packets. We constructed an optical packet and circuit integrated ring network testbed consisting of two switch nodes for accelerating network development, and we demonstrated 66 km fiber transmission and switching operation of multiplexed 14-wavelength 10 Gbps optical paths and 100 Gbps optical packets encapsulating 10GbE frames. Error-free (frame error rate < 1×10(-4)) operation was achieved with optical packets of various packet lengths and packet rates, and stable operation of the network testbed was confirmed. In addition, 4K uncompressed video streaming over OPS links was successfully demonstrated.

Phase-squeezing properties of non-degenerate PSAs using PPLN waveguides

We investigate the phase squeezing characteristics of non-degenerate phase-sensitive-amplifiers (PSAs) based on periodically-poled-lithium-niobate (PPLN) waveguides. We implement two PSA configurations with phase insensitive idler generation performed in both highly-non-linear-fiber (HNLF) and PPLN waveguides. In both cases we demonstrate regeneration of a noisy BPSK signal, despite net signal attenuation in the phase sensitive PPLN, and show that the level of phase squeezing varies with the phase sensitive dynamic range (PSDR). We observe that weak idler generation in the PPLN limits the achievable PSDR and that use of HNLF for idler generation leads to the largest PSDR. However, in phase regeneration measurements we observe that the pump phase modulation, required to overcome stimulated Brillouin scattering, adds significant amplitude noise, which increases with the PSDR.

Multi-oxide layer structure for single-mode operation in vertical-cavity surface-emitting lasers

We propose a novel vertical-cavity surface emitting laser (VCSEL) with Al(Ga)As multi-oxide layer (MOX) structure for the purpose of enlarging window aperture maintaining single transverse mode operation. We have fabricated an InGaAs-GaAs VCSEL with the proposed MOX structure formed on GaAs (311)B substrate. We have performed a numerical simulation to investigate single-mode behavior of the proposed structure and showed a possibility of single-mode VCSELs with a large active area. We have fabricated an 11-/spl mu/m current aperture 960-nm wavelength VCSEL with this MOX structure. The threshold current and voltage were 1.0 mA and 2.0 V, respectively, which are comparable to those of conventional oxide VCSELs. In 8-/spl mu/m aperture, single-mode operation was maintained with a driving current up to four times the threshold.

High Extinction-Ratio Integrated Mach–Zehnder Modulator With Active Y-Branch for Optical SSB Signal Generation

We propose a high extinction-ratio (ER) Mach-Zehnder modulator (MZM) with an active Y-branch optical intensity trimmer. In addition, we investigate a high ER integrated MZM for optical single-sideband (SSB) signal generation, where the active Y-branch trimmers are embedded in a dual-parallel MZM. Optical SSB generation with high suppression ratio of main carrier (47 dB) and undesired sidebands (>42 dB) is achieved by optimizing the optical amplitude imbalances corresponding to the ER.

Highly strained GaInAs-GaAs quantum-well vertical-cavity surface-emitting laser on GaAs (311)B substrate for stable polarization operation

We have realized high-quality GaInAs-GaAs quantum wells (QWs) with high strain of over 2% on GaAs (311)B substrate for a polarization controlled vertical-cavity surface-emitting laser (VCSEL). By increasing the In composition in GaInAs, the optical anisotropy in photoluminescence (PL) intensity was increased. The anisotropy of 50% was obtained at 1.15 /spl mu/m emission wavelength. We have demonstrated edge-emitting lasers and VCSELs emitting at over 1.1 /spl mu/m on GaAs (311)B substrate for the first time. The 1.15-/spl mu/m edge-emitting laser showed a characteristic temperature of 210 K and the threshold current density of 410 A/cm/sup 2/. The threshold current and lasing wavelength of VCSELs are 0.9 mA and 1.12 /spl mu/m, respectively. The orthogonal polarization suppression ratio was 25 dB and CW operation up to 170/spl deg/C without a heat sink was achieved.

Analysis and fabrication of microaperture GaAs-GaAlAs surface-emitting laser for near-field optical data storage

We have proposed a microaperture vertical cavity surface-emitting laser (VCSEL) for use in near-field optical data storage. We carried out the near-field analysis of microaperture VCSEL using two-dimensional (2-D) finite element method. We calculated the distribution of optical near-field generated near a microaperture, and showed that the spot size is potentially smaller than 100 nm, which is less than wavelength by a factor of 8. We fabricated a VCSEL loaded by an Au film on the top surface for blocking the emitting light and formed a subwavelength-size aperture using focused ion beam (FIB) etch through this film. Single-mode operation was obtained for a microaperture VCSEL with 3-/spl mu/m square active region. The differential quantum efficiency was increased by a factor of 3 in comparison with that before forming a 400-nm square aperture. We estimated the power density of light radiated from a 400-nm square aperture to be 0.17 mW//spl mu/m/sup 2/. In addition, we measured the near-field distribution of a 200-nm square aperture VCSEL by using a scanning near-field microscope.

Single high-order transverse mode surface-emitting laser with controlled far-field pattern

Single transverse mode vertical-cavity surface-emitting lasers (VCSELs) with high output power are important for high-speed data links, optical recording, laser processing, and so on. We demonstrate a single high-order transverse mode VCSEL with narrow trenches formed on its top surface by using a focused ion beam. The formation of four straight cross trenches resulted in the selection of a stable LP/sub 41/ mode oscillation. A large far-field angle of the LP/sub 41/ mode, which causes a low coupling efficiency even with a multimode fiber, was drastically reduced by loading a phase shift layer. A single-lobe far-field pattern with low scattering loss was realized by loading a spatial phase shift of SiO/sub 2/. We evaluated a coupling efficiency with a single-mode fiber including its alignment tolerance. The controlled far-field pattern enables lens-free direct coupling with a single-mode fiber even for large active-area VCSELs.

160-Gb/s all-optical phase-transparent wavelength conversion through cascaded SFG-DFG in a broadband linear-chirped PPLN waveguide.

We experimentally demonstrated ultra-fast phase-transparent wavelength conversion using cascaded sum- and difference-frequency generation (cSFG-DFG) in linear-chirped periodically poled lithium niobate (PPLN). Error-free wavelength conversion of a 160-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) signal was successfully achieved. Thanks to the enhanced conversion bandwidth in the PPLN with linear-chirped periods, no optical equalizer was required to compensate the spectrum distortion after conversion, unlike a previous demonstration of 160-Gb/s RZ on-off keying (OOK) using fixed-period PPLN.