Naoki Futakuchi

Demonstration of an optical isolator with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift

We present the experimental study of an optical isolator with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift. The isolator is equipped with an optical interferometer composed of tapered couplers, nonreciprocal phase shifters, and a reciprocal phase shifter. The nonreciprocal phase shifter was constructed by wafer direct bonding between the semiconductor guiding layer and the magneto-optic cladding layer. The isolator, designed for the 1.55-mum wavelength, was fabricated to investigate the characteristics of each component. By applying an external magnetic field to the nonreciprocal phase shifter, we achieved an isolation ratio of approximately 4.9 dB in the interferometric isolator.

X-ray ctr scattering measurement of inp/ingaas/inp interface structures fabricated by different growth processes

Hetero-interfaces of InP/InGaAs (three monolayers (ML))/InP samples grown by organometallic vapor phase epitaxy (OMVPE) were investigated using X-ray crystal truncation rod (CTR) measurement. The samples were prepared with three different source-gas flow-sequences: (a) conventional sequence, (b) growth interruption, and (c) Ga and In source-gas pulse injection. The results of the X-ray CTR measurement showed that the interfaces between InP cap and InGaAs layers of (b) and (c) were sharper than that of (a) as intended. However, the amount of As in (b) was less than that designed since As atoms desorbed even from the InGaAs layer during the growth interruption. Surprisingly, the Ga atoms distributed wider and peak compositions of Ga were smaller than those designed for all the samples. It means that the quantum well structures are far from those designed and expected. It suggests that more efforts are necessary to control the distribution of group-III atoms after we solved the problem of group-V atom distributions.

Analysis of GaInAsP Surfaces by Contact-Angle Measurement for Wafer Direct Bonding with Garnet Crystals

GaInAsP surfaces with various treatments were analyzed by contact-angle measurement for wafer direct bonding between GaInAsP and garnet crystals. The contact angle of a water droplet was measured to estimate the hydrophilicity of the wafer surfaces. The most hydrophilic surface was obtained after an O2 plasma activation process. Direct bonding was successfully achieved between GaInAsP activated by O2 plasma and garnet crystals.

Laterally coupled strained MQW ridge waveguide distributed-feedback laser diode fabricated by wet-dry hybrid etching process

The fabrication and the characteristics of the laterally coupled GaInAsP-InP quantum-well ridge waveguide distributed-feedback (DFB) lasers are presented. The electron beam (EB) lithography and the wet and dry hybrid etching technique have been used to fabricate the deep grating structures for the DFB lasers on and beside the sidewalls of the narrow ridge waveguide. The threshold current was 18.5 mA at 20/spl deg/C, and the sidemode suppression ratios (SMSRs) were ensured to be more than 40 dB for as-cleaved devices with various cavity lengths. The continuous-wave output powers of over 15 mW/facet have been observed, while transverse and longitudinal modes have remained in single mode at this output level.

28-ps switching window with a selective area MOVPE all-optical MZI switch

The first dynamic all-optical switching of a bandgap-engineered Mach-Zehnder interferometer semiconductor optical amplifier all-optical switch was achieved. A 28-ps switching window was successfully confirmed. This is the first demonstration of a bandgap-engineered large-scale all-optical photonic integrated circuit with either selective-area-growth or quantum-well-intermixing techniques.

Performance analysis of waveguide-type InGaAsP/InP fully-depleted optical thyristors for optical communication system

1.55 um PnpN optical thyristor as a smart optical switch has potential applications in advanced optical communication systems. It can be used as a header processor in optical asynchronous transfer mode (ATM) and as a hard limiter in optical code division multiple access (CDMA) system. For those applications, however, relatively slow switching speed of the optical thyristor is the major limiting factor. To enhance the switching characteristics, depleted optical thyristor (DOT) has been proposed, in which majority carriers in the center n- and p-layers can be fully depleted by applying a reverse-bias pulse. Recently, we proposed a novel waveguide type 1.55 micrometer InGaAsP/InP DOTs. In this presentation, using the finite difference method (FDM), we calculate the effects of such parameters as doping concentration, thickness of the outer and inner layers of the thyristor to find out the optimized structure in the view of fast and low power consuming operation, low reverse full-depletion voltage, high optical confinement factor. With these results, a waveguide type 1.55 micrometer DOT is fabricated with metal organic chemical vapor deposition (MOCVD) and measured on the switching voltage with the size. The results of the simulation are compared with those of the experiment.

Direct Bonding between Quaternary Compound Semiconductor and Garnet Crystals for Integrated Optical Isolator

An integrated optical isolator employing a nonreciprocal phase shift is very attractive because it does not need phase matching. We have investigated a novel configuration of the integrated optical isolator, employing the nonreciprocal phase shift, in which the magnetooptic waveguide has a magnetic garnet/GaInAsP/InP structure. The wafer direct bonding technique is necessary to realize this structure. The direct bonding between quaternary III–V compound semiconductors and garnet crystals was experimentally studied. The bonding was achieved by chemical treatment and subsequent heat treatment at temperatures ranging from 110 to 330°C. Cross-sectional scanning electron microscope (SEM) images indicated that there were no gaps between the two wafers in contact.

Waveguide-type PnpN optical thyristor operating at 1.55 μm

Waveguide-type PnpN depleted optical thyristors operating at 1.55 /spl mu/m are proposed and fabricated for the first time. In the optical thyristors, we employ InGaAs-InP multiple quantum-well (MQW) and InGaAsP bulk layers for the active n- and p-layers. The thyristors show sufficient nonlinear s-shape I-V characteristics and spontaneous emission along the waveguide. Very low switching voltages of 2.1 and 2.0 (V) for bulk and MQW thyristors with L=300 /spl mu/m and 350 /spl mu/m respectively are measured.

Optical characteristics of PnpN optical thyristor operating at 1.55 μm

InGaAs/InP multiple quantum well (MQW) PnpN depleted op- tical thyristors (DOTs) operating at 1.55 mm are proposed and fabricated. To analyze their switching characteristics, we simulate nonlinear s-shape current-voltage curves using the finite difference method (FDM) associ- ated with the current-oriented method. Using the FDM, we calculate the effects of such parameters as doping concentration and the thicknesses of the outer and inner layers of the thyristor to determine an optimized structure in the view of fast and low-power-consuming operation. With these results, we fabricate waveguide- and vertical-type InGaAs/InP MQW PnpN DOTs. The waveguide-type DOT shows sufficient nonlinear s-shape I-V characteristics with a switching voltage of 4.03 V and a holding voltage of 1.77 V, and spontaneous emission along the wave- guide. The current-voltage characteristics of the vertical-type DOT are shown very well under 150 mW of input power, while the s-shape disap- pears at 200 mW.

Design and Measurement of Waveguide-Type PnpN Optical Thyristors for Optical Communications

Waveguide-type InGaAs/InP multiple quantum well PnpN depleted optical thyristors operating at 1.55 µm are proposed and fabricated for the first time. In this paper, using the finite difference method (FDM), we calculate the effects of parameters such as doping concentration and the thicknesses of the outer and inner layers of the thyristor to determine the optimized structure in the view of fast and low-power-consuming operation. With these results, the fabricated optical thyristor shows sufficient nonlinear s-shape I–V characteristics with a switching voltage of 4.03 V, a holding voltage of 1.77 V, and spontaneous emission along the waveguide.