Tomoji Terakado

An experiment on high-speed optical time-division switching

An experimental high-speed optical time-division switching system has been realized. The system is able to exchange digitally encoded color video signals at 256-Mbit/s highway speed. Bistable laser diodes and directional coupler switch matrices are adopted as optical memories and optical read/write gates, respectively, in an optical time switch. The bistable laser diode operates as an optical flip-flop circuit which can be set and reset by optical and electrical signals, respectively. 256-Mbit/s highway speed has been realized with sufficient input highway operating margin using the same wavelength as that of bistable laser diodes for an electrooptical converter. Results of this experiment will be helpful data for use in constructing future optical telecommunications networks, where a variety of broad-band services need to be realized.

Low threshold λ = 1.3 μm multi-quantum well laser diodes grown by metalorganic vapor phase epitaxy using tertiarybutylarsine and tertiarybutylphosphine precursors

Abstract Low threshold λ = 1.3 μm InGaAsP multi-quantum well (MQW) lasers have been realized by metalorganic vapor phase epitaxy (MOVPE) using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP). Quaternary InGaAsP growth with TBA and TBP have demonstrated an improved group-V compositional controllability, compared to that with the conventional hydrides AsH 3 and PH 3 . As a result, the base InGaAsP MQW wafers have exhibited an excellent photoluminescence (PL) wavelength uniformity with the standard deviation of 2.6 nm over a 2-inch wafer, and the PL full width at half maximum (FWHM) of 8.3 meV at 4.2 K. Laser characteristics, such as threshold and efficiency, were comparable to those grown by hydrides. The threshold currents for 70%/95% coated 170 μm long devices were as low as 9 and 22 mA at 20 and 85°C, respectively. Thus, TBA and TBP are applicable for long wavelength lasers as substitutes for AsH 3 and PH 3 .

Selective MOVPE growth of InGaAsP and InGaAs using TBA and TBP

Selective metalorganic vapor phase epitaxial (MOVPE) growth of InGaAs(P) using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) was systematically investigated for the first time. Selective growth was successfully achieved and the growth structure was as excellent as the structure using AsH3/PH3. Vapor phase lateral diffusion of group-III species, which is the major mechanism of selective MOVPE, can be easily controlled over the wide range of V/III ratio with using TBA/TBP. From this feature, we propose the selectively grown multiple quantum well waveguide structures which have excellent bandgap controllability by using TBA/TBP.

Turn‐off characteristics of bistable laser diode

Turn‐off characteristics for tandem‐electrode bistable laser diodes (bistable LD’s) were analyzed both experimentally and theoretically. A long tail in the light output waveform was observed when the turn‐off injection current was near the switch‐down current. Rate equations were solved with adiabatic approximation and gave a good explanation indicating that the tail was due to the relatively slow recovery of the saturable absorber. The analysis also showed that the turn‐off time for bistable LD’s can be reduced to that for ordinary laser diodes, with sufficiently small injection current. Subnanosecond operation for bistable LD’s was found possible under optimal turn‐off injection current.

5:1 on‐off contrast InGaAs/InP multiple quantum well Fabry–Perot étalon modulator

We report the first demonstration of an InGaAs/InP multiple quantum well Fabry–Perot etalon modulator. The obtained on‐off contrast is 5:1 at −16 V applied voltage for 1540 nm wavelength light. The absorption coefficient of the multiple quantum well around 1540 nm increases from 1000 to 6300 cm−1 as the applied voltage increases from 0 to −16 V, and the relative refractive index change is up to −0.9%.

Monolithically integrated high-speed light source using 1.3-µm wavelength DFB-DC-PBH laser

The first monolithic high-speech light source, consisting of an InGaAsP/InP DFB laser, metal-insulator-semiconductor field-effect transistors, and a monitoring photodiode, has been fabricated. Small-signal modulation bandwidth up to 4 GHz was successfully achieved. The device design, fabrication procedures, and operating characteristics for the integrated light source are described.

Band‐gap discontinuity control for InGaAs/InGaAsP multiquantum‐well structures by tensile‐strained barriers

The changes in InGaAsP conduction‐ and valence‐band edge energies due to tensile strain, have been measured by optical methods at 77 K. The measured increases in the conduction‐ and valence‐band edge energies for the 0.5% tensile‐strained InGaAsP, compared to the unstrained InGaAsP (1.2 μm band‐gap wavelength), are 70 and 38 meV, respectively. The experimentally obtained values are in accordance with calculated values. The results show that the ratio of the conduction‐ and valence‐band discontinuities in InGaAs/InGaAsP multiquantum‐well structures can be controlled by the tensile‐strained barrier.

A new technique for fabrication of OEICs-the etched back planar process-and its application to the fabrication of planar embedded InP-InGaAs p-i-n photodiodes

The etched back planar process utilizes a nonselective reactive ion beam etching (RIBE) technique both for semiconductor layers and for photoresist. Application of the technique to the fabrication of a planar InP-InGaAs embedded p-i-n photodiode is discussed. The groove depth on the wafer was reduced from 5.3 mu to 0.6 mu m, and the wafer was nearly planarized. Estimates based on photoluminescence intensity variation and the characteristics of the fabricated p-i-n photodiode indicate that little damage was incurred during the process. These results indicate that fabrication of planar OEICs by means of this process is feasible.<<ETX>>

High-quality 1.3 /spl mu/m AlGaInAs MQW by narrow-stripe selective metalorganic vapor-phased epitaxy and its application in buried heterostructure laser diodes

High-quality 1.3 /spl mu/m AlGaInAs MQW by narrow-stripe selective MOVPE has been investigated and then applied to an AlGaInAs BH laser diode by using an Al-oxidation-free process. A low threshold current of 9.0 mA and a relaxation frequency of more than 10 GHz were obtained at 85/spl deg/C.