Tomoaki Uno

InP MESFET Grown by MOCVD

MESFET devices with 2 µm gate length have been fabricated on InP epitaxial layers grown by the MOCVD technique on Fe-doped semi-insulating InP substrates. The best electrical properties of InP epitaxial films have been measured and are n=2.7×1015 cm-3 and µ=3500 cm2/Vs at room temperature. The barrier height and the ideality factor of Au-n InP Schottky diode were estimated to be 0.66 eV and 1.18, respectively. Depletion mode n-channel MESFET has shown transconductance of ~90 mS/mm and the saturation drain current of ~20 mA at zero gate bias.

Thulium:ZBLAN blue fiber laser pumped by two wavelengths

We demonstrate and analyze an upconversion blue fiber laser pumped by two wavelengths. Lasing at 0.48 mum with very low pump threshold power is obtained from a Tm-doped fluorozirconate fiber that is counterpropagating pumped by 1.21- and 0.649-mum light. We employed a rate-equation analysis using parameters obtained by fitting to the experimental data to predict the 0.48-mum output characteristics as a function of fiber length and output reflectivity.

Hybridly integrated optical transceiver module for access networks

Hybridly integrated optical transceiver modules for 1.3 /spl mu/m wavelength TDM (Time-Division-Multiplexing) bi-directional transmission and 1.3/1.55 /spl mu/m WDM (Wavelength-Division-Multiplexing) bi-directional transmission are demonstrated. Surface mounted laser diode and PIN photodiode are passively aligned to a fiber-embedded optical circuit. The module consists of a transmitting 1.3 /spl mu/m laser diode mounted on a silicon substrate with a V-groove for fiber attachment and a receiving photodiode surface mounted onto a glass substrate which has embedded in it a single mode fiber for input/output. Either power splitting 3 dB filter or wavelength selective WDM filter (1.55 /spl mu/m reflective) is inserted into the embedded fiber which directs the incoming signal light to the photodiode. The optical transceiver characteristics are as follows. The output power was greater than 2 mW for TDM transceiver and 4 mW for WDM transceiver, considering a 20% coupling efficiency to the single mode fiber. The responsivity of the photodiode were 0.97 A/W for WDM transceiver at 1.55 /spl mu/m, and 0.46 A/W for TDM transceiver at 1.3 /spl mu/m. Stable operation characteristics are obtained in the wide temperature range of -40/spl sim/85/spl deg/C.

Second-order distortion of amplified intensity-modulated signals with chirping in erbium-doped fiber

Second-order distortion produced in an erbium-doped fiber amplifier (EDFA) is investigated theoretically and experimentally. Rate equations for intermodulation products are led by the perturbation method. From numerical calculation, it is shown that optimum combinations of input power to EDFA and signal wavelength exist that give a distortion-free condition, Improvement of the composite second-order (CSO) distortion, which results from the cancellation of the laser distortion and the gain tilt induced distortion, was confirmed for VHF multichannel transmission. Furthermore, CSO distortion-free transmission in cascaded EDFAs has been demonstrated for a 42-channel AM-SCM signal by experimentally determining the optimum operating condition of the EDFA such that each amplifier generates no additive distortion.

Extremely low tail current optical transceiver module for passive double star TDMA networks

Summary form only given. We believe we have demonstrated extremely low tail current 1.3-μm laser diode/photodiode (LD/PD) transceiver module for OSU application for the first time. Also high performance is obtained over a wide temperature range from -40 C to +850 C. These features will help make PDS-TDMA architecture more attractive for subscriber loop networks.

Novel 1.3/1.55 /spl mu/m dual-wavelength receiver having embedded fiber circuit for optical subscriber systems

Summary form only given. We propose and demonstrate a novel dual-wavelength receiver, which has an embedded fiber circuit that demultiplexes 1.3- and 1.55-/spl mu/m signals to separate photodiodes mounted on a single-substrate surface. The circuit contains wavelength separation filters placed in slits fabricated in the fiber path by a conventional cutting saw. Low-circuit loss and high-receiver performance is realized for both WDM signals.

780 nm GaAlAs distributed feedback lasers

Abstract The 780 nm GaAlAs distributed feedback lasers have been fabricated by hybrid liquid phase epitaxy and metalorganic chemical vapor deposition growth technology. These lasers utilize the buried twin-ridge substrate structure, which allows very effective current confinement and spatial mode stabilization. The continuous wave operation with a threshold current of 64 mA at room temperature is obtained by the best choice of the corrugation period. The maximum output power is as high as 10 mW and the single longitudinal mode operation is maintained from −20°C to 45°C.

Fluoride-based fiber lasers: prospects for the future

Rare earth ion doped fiber devices can achieve high efficiencies and high output powers due to their advantages of high optical pump power densities over long interaction lengths. With the advent of fluoride-based fibers, breakthroughs into both the short- and long-wavelength regions not possible with silica-based fibers have achieved. The low phonon energy and high rare earth ion doping concentrations of fluorides allow multi-level transition processes such as upconversion. This paper reviews some of the recent advances in fluoride-based fiber lasers and amplifiers, and takes a look at the major issues, mainly from an industrial viewpoint. The primary issue of cost has hampered commercialization and widespread acceptance of these devices. The future prospects of fluoride-based fiber devices will be discussed from the viewpoint of industrial applications.

Hybrid integration of 1.3-/spl mu/m transmitter and 1.55-/spl mu/m receiver with fiber-embedded circuit

The high cost of manufacturing multiwavelength optical transmitter and receiver components is one of the biggest hindrances to widespread acceptance of wavelength-division multiplexing (WDM) optical subscriber loop networks for broadband multimedia systems. One proposed solution is to passively align laser diodes and photodiodes to waveguides in a circuit-like structure. We have previously proposed the use of a fiber-embedded circuit for a WDM receiver module. Because the fiber-embedded circuit is an in-line device, as opposed to a line-terminating device, this approach can be extended to include a passively aligned LD for the transmitter function. We demonstrate a novel WDM transceiver module with a hybridly integrated 1.3-/spl mu/m laser diode and 1.55-/spl mu/m PIN photodiode, which were passively aligned to a fiber-embedded circuit. Transmission output power >1.5 mW and detector responsivity of 0.8 A/W were obtained.