Tadashi Kasamatsu

1.50-mum-band gain-shifted thulium-doped fiber amplifier with 1.05- and 1.56-mum dual-wavelength pumping

We propose and demonstrate a 1.50-mum- band gain-shifted thulium-doped fiber amplifier (TDFA) by using a novel dual-wavelength (1.05and1.56 -mum) pumping scheme for what we believe is the first time. By providing a small amount of 1.56-mum power to a conventional upconversion-pumped TDFA, we successfully demonstrated a small-signal gain larger than 25 dB and a noise figure of 5 dB in a 1475-1510-nm band.

1.49-/spl mu/m-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems

This paper describes in detail the amplification characteristics of gain-shifted thulium-doped fiber amplifiers (GS-TDFAs) operating in the 1480to 1510-nm wavelength region (1.49-/spl mu/m S-band) for use in wavelength-division-multiplexing (WDM) systems. Gain shifting of a TDFA, which normally has a gain band at 1.47 /spl mu/m (S/sup +/-band), is achieved by two types of dual-wavelength pumping: (1) 1.05 and 1.56 /spl mu/m or (2) 1.4 and 1.56 /spl mu/m. The main pump source at 1.05 or 1.4 /spl mu/m creates population inversion between /sup 3/F/sub 4/ (upper laser level) and /sup 3/H/sub 4/ (lower laser level), while the auxiliary pump source at 1.56 /spl mu/m reduces the average fractional inversion down to approximately 0.4, which is a desired level for gain shifting. We show experimentally that the former provides a low internal noise figure (<4 dB) due to high fractional inversion at the input end of a thulium fiber, while the latter provides a very high optical efficiency but a higher internal noise figure (/spl sim/5 dB) due to the lower fractional inversion at the input end. These characteristics were verified by numerical simulation based on a comprehensive rate equation modeling. We demonstrated a 1.4- and 1.56-/spl mu/m laser-diode-pumped GS-TDFA with an optical efficiency of 29.3% and high output power of +21.5 dBm. Gain flatness and tilt control were also investigated. These results strongly confirm the feasibility of using GS-TDFAs in practical ultralarge-capacity WDM networks.

Temperature dependence and optimization of 970-nm diode-pumped Yb:YAG and Yb:LuAG lasers

We have investigated the temperature dependence of output performances for 970-nm diode-pumped Yb:YAG (Yb(3+):Y(3)Al(5)O(12)) and Yb:LuAG (Yb(3+):Lu(3)Al(5)O(12)) lasers over the wide temperature range from 80 to 310 K. Temperature-optimized operation was experimentally demonstrated at around 160 K and was theoretically confirmed by taking into account the absorption spectra change of Yb crystals at low temperatures. Cooling the crystal to below 160 K caused a narrowing of the absorption bandwidth and led to a decrease in output power and efficiency.

Gain-shifted dual-wavelength-pumped thulium-doped fiber amplifier for WDM signals in the 1.48-1.51-μm wavelength region

We constructed a gain-shifted dual-wavelength-pumped (1.05/1.56 /spl mu/m) thulium doped fiber amplifier (TDFA) for wavelength-division-multiplexing (WDM) signals in the 1.48-1.51-/spl mu/m, wavelength region. We obtained a gain of larger than 20 dB and a noise figure of less than 7 dB in the range from 1478 to 1505 nm. Amplifier saturated output power was +20.1 dBm with an optical-to-optical conversion efficiency of 9.1% for 12-channel WDM signals. We also obtained a successful bit error rate performance for signals modulated at 10 Gb/s when the gain-shifted TDFA was used in an optical preamplifier configuration. These results confirm the feasibility of using the gain-shifted TDFA as both a booster and an optical preamplifier in WDM networks.

Palm-top-size, 1.5 kW peak-power, and femtosecond (160 fs) diode-pumped mode-locked Yb+3:KY(WO4)2 solid-state laser with a semiconductor saturable absorber mirror.

We report a palm-top-size femtosecond diode-pumped mode-locked Yb(+3):KY(WO(4))(2) solid-state laser with a semiconductor saturable absorber mirror utilizing soliton mode locking for shortening the cavity to 50 mm. An average output power of 680 mW and a pulse width of 162 fs were obtained at 1045 nm with a repetition rate of 2.8 GHz, which led to a peak power of 1.5 kW. Average power fluctuations of a modularized laser source were found to be +/-10% for the free-running 3000 h operation and +/-1% for the power-controlled 2000 h operation.

Novel 1.50-μm Band Gain-Shifted Thulium-Doped Fiber Amplifier by using Dual Wavelength Pumping of 1.05 µm and 1.56 μm

We propose and demonstrate a 1.50-µm-band gain-shifted thulium-doped fiber amplifier (TDFA) by using a novel dual wavelength (1.05/1.56 µm) pumping scheme for the first time. By providing a small amount of 1.56-µm power to the conventional TDFA, we successfully demonstrated a small-signal gain of >25 dB and a noise figure of 5 dB in the 1475- to 1510-nm band.

A pilot study of photoacoustic imaging system for improved real-time visualization of neurovascular bundle during radical prostatectomy

Photoacoustic imaging, a noninvasive imaging based on optical excitation and ultrasonic detection, enables one to visualize the distribution of hemoglobin and acquire a map of microvessels without using contrast agents. We examined whether it helps visualize periprostatic microvessels and improves visualization of the neurovascular bundle.

Laser-diode-pumped Nd:YAG active-mirror laser.

We describe a simple design, laser-diode-pumped cw Nd:YAG active-mirror laser and present a thermal analysis of the crystal. A cw output power of 2.4 W and an M(2) beam quality value of less than 1.9 at an incident pumping power of 8.9 W were obtained. From the thermal analysis we predict that the output power can be increased by increasing the pump beam diameter and the pump power at a constant excitation density.

1 PM SPECTRALLY NARROWED ARF EXCIMER LASER INJECTION LOCKED BY FOURTH HARMONIC SEED SOURCE OF 773.6 NM TI:SAPPHIRE LASER

We have achieved spectrum narrowing to 1 pm in a high‐power ArF excimer laser injection locked by an all solid‐state fourth harmonic (193.4 nm) seed source of 773.6 nm Ti:sapphire laser radiation. Superior laser properties such as sufficient output energy (90 mJ/pulse, 50 pps), locking efficiency exceeding 90%, wavelength drift less than 0.4 pm, and spectrum bandwidth fluctuation less than 0.2 pm were obtained, which meet the requirements for 1 Gbit dynamic random access memory microlithography.

Laser tissue interaction of a continuous wave 2μm, 3μm cascade oscillation fiber laser: sharp incision with controlled coagulation layer thickness

We studied coagulation layer controlled incision with newly developed continuous wave 2 micrometer, 3 micrometer cascade oscillation fiber laser in vitro. Since this laser device simultaneously oscillates 2 micrometer and 3 micrometer radiation, we could change tissue interaction by arranging power ratio of 2 micrometer to 3 micrometer radiation. About one watt of total irradiation power with various power ratios was focused to extracted fresh porcine myocardium or anesthetized rabbit on an automatic moving stage to obtain line incision. Macro photograph and microscopic histology were used to observe tissue interaction phenomenon. The incised specimen showed that precise cutting groove with thin coagulation layer was attained by a 3 micrometer based radiation, meanwhile addition of 2 micrometer radiation to 3 micrometer radiation made coagulation layer thicker. A heat conduction simulator using finite-element method was used to qualitatively explain obtained coagulation layer thickness. This precise incision with controllable side coagulation layer may effective to control bleeding during incision, for instance, for skin, liver, and kidney incisions. Pure continuous wave radiation of 2 micrometer and 3 micrometer may eliminate stress wave induced tissue damage which is frequently found in Ho:YAG and/or Er:YAG tissue interactions. Moreover, sapphire fiber might offer flexible power delivery to this new laser to establish endoscopic application and/or to improved beam handling.