Hiroki Yaegashi

Generation of polarization entangled photon pairs at telecommunication wavelength using cascaded χ (2) processes in a periodically poled LiNbO 3 ridge waveguide

We report the generation of high-purity correlated photon-pairs and polarization entanglement in a 1.5 μm telecommunication wavelength-band using cascaded χ((2)):χ((2)) processes, second-harmonic generation (SHG) and the following spontaneous parametric down conversion (SPDC), in a periodically poled LiNbO(3) (PPLN) ridge-waveguide device. By using a PPLN module with 600%/W of the SHG efficiency, we have achieved a coincidence-to-accidental ratio (CAR) higher than 4000 at 7.45×10(-5) of the mean number of the photon-pair per pulse. We also demonstrated that the maximum reach of the CAR was truly dark-count-limited by the single-photon detectors used here. This indicates that the fake (noise) photons were negligibly small in this system, even though the photon-pairs, the Raman noise photons, and the pump photons were in the same wavelength band. Polarization entangled photon pairs were also generated by constructing a Sagnac-loop-type interferometer which included the PPLN module and an optical phase-difference compensator to observe maximum entanglement. We achieved two-photon interference visibilities of 99.6% in the H/V basis and 98.7% in the diagonal basis. The peak coincidence count rate was approximately 50 counts per second at 10(-3) of the mean number of the photon-pair per pulse.

Design of Polarization-Independent Si-Wire-Waveguide Wavelength Demultiplexer for Optical Network Unit

We report the design of a compact wavelength demultiplexer using a Si wire waveguide as an optical network unit. We use a Mach–Zehnder lattice interferometeric filter structure to attain a flat-top response. The large wavelength dispersion of the Si wire waveguide requires special design considerations for widely separated wavelength channels. Preliminary experimental results obtained by the device fabricated in a silicon-on-insulator wafer showed a flat-top filter response.

Polarization-, Wavelength-, and Filter-Free All-Optical Clock Recovery in a Passively Mode-Locked Laser Diode With Orthogonally Pumped Polarization-Diversity Configuration

We proposed and demonstrated all-optical clock recovery system using a monolithic mode-locked laser diode (MLLD) that operated with less sensitivity to the polarization and the wavelength of the input data signals also with no bandpass filter to eliminate the input signal-components. The keys to this new technique are the MLLD integrated with a tensile-strained quantum-well saturable absorber and a new polarization-diversity setup by signal input orthogonally polarized to the lasing polarization of the MLLD. This approach was experimentally validated in the 40 Gbps clock recovery experiments. The results exhibited excellent performance of the clock recovery with low timing jitters (<0.3 ps) remaining small dependence on the wavelength and the polarization of the input data signals and input-signal suppression less than -30 dB with no use of the bandpass filter. We also succeeded in the stable clock recovery for the input of polarization-scrambled data signals.

Mach-Zehnder filter using multiple Si waveguide structure sections for polarization independence and improved fabrication/temperature tolerance

We report the design of the Mach-Zehnder interferometer wavelength filter using multiple Si waveguide structure sections. Tolerance to width error, temperature shift and polarization independence can be attained.

Polarization rotation Bragg diffraction using Si wire waveguide grating and polarization rotator

We report polarization independent Bragg grating wavelength filter with high diffraction efficiency. A rib waveguide polarization rotator and antisymmetric grating structure for fundamental to first order diffraction are used to generate the polarization rotation Bragg diffraction. The diffraction efficiencies and peak wavelengths become the same for two orthogonal input polarizations. Strong diffraction is attained easily. The concept was verified by simulation and experiment. Polarization independent band-pass filter consisting of polarization beam splitter and polarization rotation Bragg diffraction was experimentally demonstrated.

Polarization-Insensitive Clock Recovery Operation in a Monolithic Passively Mode-Locked Distributed-Bragg-Reflector Laser Integrated With a Tensile-Strained Multiple-Quantum-Well Saturable Absorber

A 40-GHz monolithic mode-locked laser diode integrated with a tensile-strained multiple-quantum-well saturable absorber was developed for the purpose of polarization-insensitive all-optical clock recovery in a single chip of a semiconductor device. Clock recovery with small polarization sensitivity less than 0.2 dB was successfully achieved. We also demonstrated a stable clock recovery from polarization-scrambled data signals.

Silicon waveguide polarization rotation Bragg grating with phase shift section and sampled grating scheme

We describe a Bragg grating with a phase shift section and a sampled grating scheme that converts input polarization to orthogonal polarization. A very narrow polarization-independent wavelength peak can be generated by phase shift structures and polarization-independent multiple diffraction peaks by sampled gratings. The characteristics of the device were examined by transfer matrix and finite-difference time-domain methods.

Demonstration of 25-Gbps optical data links on silicon optical interposer using FPGA transceiver

We demonstrated a 25-Gbps error-free data link on a silicon optical interposer. The experimental results verified that our interposer is compatible with high-performance FPGAs, and transmitter pre-emphasis and receiver equalization reduced bit error rate of the optical data link.

Si wire optical waveguide wavelength demultiplexer for ONU

We report a compact wavelength demultiplexer design for widely separated wavelengths used in ONU. The Mach-Zehnder lattice interferometeric filter structure is chosen. The large wavelength dispersion of the Si wire waveguide requires special design considerations.

Optical Feedback-Tolerant 1.3 μm Gain-Coupled DFB lasers for isolator-free micro-BOSA modules

Gain-coupled (GC)-DFB-LD tolerant to optical feedback was developed for low-cost, isolator-free optical subassembly module. GC-DFB-LD into isolator-free micro-BOSA module has power penalty less than 0.3 dB after 25 km transmissions at 1.25 Gb/s with -15 dB optical feedback.