Toshiaki Okuno

Selective FWM-based Wavelength Conversion Realized by Highly Nonlinear Fiber

Selective four-wave-mixing-based wavelength conversions from L-band to S-band using newly developed highly nonlinear fiber with high 4th-order dispersion are demonstrated by adjusting pump wavelengths, in which conversion bandwidths can be narrowed to about 10nm.

Water-peak-suppressed non-zero dispersion shifted fiber for full spectrum coarse WDM transmission in metro networks

We have successfully developed the water-peak-suppressed NZ-DSF best suited for full spectrum CWDM transmission in the metro networks. Its chromatic dispersion is well under control so as to match directly modulated DFB-LDs and future high-bit-rate transmission in the entire wavelength band. Transmission experiments including the 1.4 /spl mu/m signal wavelength have verified its transmission performance in a wide spectral range from 1.3 /spl mu/m to 1.6 /spl mu/m.

Compact Er:Yb:glass-laser-based supercontinuum source for high-resolution optical coherence tomography

We present a low coherence light source by direct super-continuum generation from a diode-pumped, passively modelocked Er:Yb:glass-laser, which generates 198 fs transform-limited pulses with an average power of 100 mW at a repetition rate of 75 MHz. The pulse train is launched into a dispersion optimized highly nonlinear fiber for spectral broadening. The optical bandwidth spans from 1150 nm to 2400 nm, which is more than one octave. The potential for ultrahigh-resolution optical coherence tomography (OCT) is demonstrated by coherence measurements supporting an axial resolution of 3.5 microm in air.

High-Speed Scanning for the Quantitative Evaluation of Glycogen Concentration in Bioethanol Feedstock Synechocystis sp. PCC6803 Using a Near-Infrared Hyperspectral Imaging System with a New Near-Infrared Spectral Camera

In the present study, the high-speed quantitative evaluation of glycogen concentration accumulated in bioethanol feedstock Synechocystis sp. PCC6803 was performed using a near-infrared (NIR) imaging system with a hyperspectral NIR spectral camera named Compovision. The NIR imaging system has a feature for high-speed and wide area monitoring and the two-dimensional scanning speed is almost 100 times faster than the general NIR imaging systems for the same pixel size. For the quantitative analysis of glycogen concentration, partial least squares regression (PLSR) and moving window PLSR (MWPLSR) were performed with the information of glycogen concentration measured by high performance liquid chromatography (HPLC) and the calibration curves for the concentration within the Synechocystis sp. PCC6803 cell were constructed. The results had high accuracy for the quantitative estimation of glycogen concentration as the best squared correlation coefficient R2 was bigger than 0.99 and a root mean square error (RMSE) was less than 2.9%. The present results proved not only the potential for the applicability of NIR spectroscopy to the high-speed quantitative evaluation of glycogen concentration in the bioethanol feedstock but also the expansivity of the NIR imaging instrument to in-line or on-line product evaluation on a factory production line of bioethanol in the future.

Fiber-Broadened Passively Modelocked Er: Yb: Glass Laser for High-Resolution Optical Coherence Tomography

We demonstrate a low coherence light source by directly launching the output of a femtosecond diode-pumped modelocked Er:Yb:glass laser into a highly-nonlinear fiber. The measured interferogram supports a depth resolution of 4 mum in air.

Imaging of Hydrophilicity and its Inhomogeneity on a Titanium Dioxide Film Exposed to Ultraviolet Irradiation Using a Newly Developed Near-Infrared Camera

This study has investigated hydrophilicity changes and their inhomogeneity of TiO2 films on Pyrex glasses by near-infrared (NIR) spectral imaging. Near-infrared spectra of TiO2 films in the 9000–4000 cm−1 region were measured using a newly developed NIR camera named Compovision. A band in the 5400–4800 cm−1 region, which is assigned to a combination (v2 + v3) mode of bending (v2) and antisymmetric stretching (v3) modes of the H2O molecule, was clearly identified and its intensity increased with time in the air. It is interesting that the increased rate rose with ultraviolet (UV) light irradiation (300–400 nm, 1 mW cm−2) compared to without UV light irradiation. This result suggested that the hydrophilicity of TiO2 was enhanced about twice upon the UV light irradiation. Moreover, the NIR images clarified spatial distributions of the hydrophilicity on the TiO2 surface with a significantly wide area (20 × 40 mm) and a high speed (within 5 s for one image). This rapid imaging system enabled us to detect the hydrophilicity change during only 1 min. The potential of this camera is quite superior, not only for basic research, but also for diverse industrial applications.

Octave spanning supercontinuum from compact passively mode-locked Er:Yb:glass laser

By using a recently developed nonlinear fiber, we achieve octave-spanning spectrum directly from a diode-pumped passively mode-locked 250-fs Er:Yb:glass laser without any amplification stage. Applications for CEO phase stabilization and optical clocking are discussed.

Performance improvement by a broadband super-luminescent diode light source in 1.7-μm spectroscopic spectral-domain optical coherence tomography for lipid distribution imaging in a coronary artery

We develop a 1.7-μm optical coherence tomography (OCT) system using a broadband light source based on superluminescent diodes (SLDs) and investigated the possibility of plaque detection by a spectroscopic OCT (S-OCT) method. The SLD-based light source realizes an output power about 20mW and a 3-dB bandwidth over 120nm for optimization of driving current in each SLD. Regarding performance of the 1.7-μm spectral-domain OCT system with the light source, the system sensitivity is 104dB in maximum at the A-scan rate of 47kHz, which is fifty times as high as that in the previous study with a super-continuum light source. Moreover, we perform visualization of lipid distribution at the A-scan frame of 47kHz by an in-vitro artery model which is made of a piece of porcine coronary artery and a lardfilled nylon tube as a plaque phantom. We confirm that the sensitivity and specificity between artery and plaque area in optimal condition for lipid detection at a specific frame image is over 90% and there are high lipid scores at the inside of plaque phantom in other frame images at the same condition. It indicates the possibility of plaque detection in intravascular OCT.

Compact white light continuum source ranging from 1.1 μm to 2.5 μm for optical sensing and monitoring

We have successfully demonstrated white-light continuum (WLC) generation in the near-infrared (NIR) region from 1.1 μm to 2.5 μm using specially designed highly nonlinear optical fibers. A passively mode-locked diode-pumped Er:Yb:glass laser with a semiconductor saturable-absorber mirror (SESAM) successfully generates femtosecond pulses with about 90 mW average output power, which is sufficient to produce the WLC with over 40 mW power without any additional optical amplification. This WLC source is expected to be suitable for many applications, such as laser radar systems and optical gas sensing.

Recent progress on highly nonlinear fibers

Recent evolution of silica-based nonlinear fibers and their applications are reviewed. Important design issues of the fiber in order to enhance the nonlinearity and tailor the dispersion performance are discussed. In addition, recent demonstration results such as ultra-broadband wavelength conversion and supercontinuum generation experiments are also introduced in this paper.