下村 和彦

We have successfully demonstrated a GalnAs/InP multiple quantum well (MQW)-based wavelength switch composed of the straight arrayed waveguide with linearly varying refractive index distribution by changing the refractive index using thermo-optic effect. Since optical path length differences between waveguides in the array were achieved through refractive index differences that were controlled by SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), wavelength demultiplexing, and the output port switching in each wavelength of light by the refractive index change in the array waveguides through the thermooptic effect were achieved. We have obtained the wavelength switching and the change of transmission spectra in each output ports. Copyright © 2008 The Institute of Electronics, Information and Communication Engineers.

Fabrication and application for wavelength demultiplexer, wavelength selective switch and light emitting diode of a novel GaInAs/InP MQW and InAs/InP QDs waveguide array with gradually varying bandgap wavelength by using selective MOVPE growth are presented. ©2008 IEEE.

We have successfully demonstrated the GaxIn1-xAs cap layer dependence on the self assembled Stranski - Krastanov (S-K) InAs quantum dots (QDs) using double-cap procedure and MOVPE selective area growth. ©2008 IEEE.

我々はGaInAs/InP MQW構造を用いたアレイ導波路型波長分割光スイッチの研究を行っている.このアレイ導波路は,MOVPE選択成長法において非対称SiO_2マスクパターンを用いることにより,MQW層厚を徐々に変化させ,それぞれの導波路において階段型屈折率分布を有する構造となっている.この構造により,アレイ導波路を伝搬する光はそれぞれ異なる位相で出射するため,互いに干渉し波面の揃う方向に回折する.また,回折角は波長に依存することから,波長の異なる光の集光する位置はそれぞれ異なり,異なる波長を別々に取り出すことが可能となる.したがって,曲げ導波路を用いない直線型波長分波器の実現が期待できる。今回、この階段型屈折率分布アレイ導波路おける熱光学効果を用いた光スイッチの測定及び金属薄膜ヒータの構造を変更することで消費電力の低減を確認したので報告する.

We have demonstrated the influence of growth conditions on the size of InAs quantum dots grown on InP (001) substrates by means of low-pressure MOVPE under the Stranski-Krastanov growth mode. We have shown the relation between standard deviation of the lateral and vertical size of quantum dots and growth rate, growth temperature, and supply of InAs. (c) 2006 Elsevier B.V. All rights reserved.

The selective area growth by low-pressure MOVPE using a SiO2 narrow stripe mask array with a wide SiO2 mask at one side of the array was performed for controlling size and density of quantum dots (QDs). To obtain the QD size difference much further, we have tried the 'double-cap' procedure in the selective area growth, and we have successfully controlled the emission from InAs QDs in 75 nm wavelength range on the single chip. (c) 2006 Elsevier B.V. All rights reserved.

Low-pressure selective MOVPE has been performed to fabricate a GaInAs/InP MQW-based arrayed waveguide wavelength demultiplexer having, a linearly varying refractive-index distribution. By means of an asymmetric SiO2 mask with a wide mask section on one side of the array, waveguides of different thickness are fabricated on (100)-oriented n-InP substrates. In this report, desired characteristics of the waveguide array are obtained by a simple method for estimating strain in the GaInAs wells layer in an MQW waveguide from only the result of simple measurements: conventional X-ray diffraction (XRD), photoluminescence (PL) peak wavelength, and well layer thickness. (c) 2006 Elsevier B.V. All rights reserved.

We have obtained the 140 nm wavelength emission range from the self-assembled InAs QDs array waveguides on the InP substrate by employing the selective MOVPE growth using asymmetrical mask and the double-cap procedure of QDs.

Crosstalk reduction by designing the mask pattern in the tilted waveguide respect to [011] direction on InP substrate is investigated and great reduction of crosstalk was achieved. © 2006 Optical Society of America.

A GaInAs/InP multiple quantum well (MQW)-based wavelength demultiplexer composed of a waveguide array in which the refractive index varies across the array yielded successful results of wavelength demultiplexing and optical deflection. Since optical path length differences between waveguides in the array are achieved through refractive-index differences controlled by the SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), a straight waveguide grating can be formed with reduced optical propagation losses. A straight waveguide array device with a 1.4% refractive-index difference was fabricated. The fabrication of a preliminary wavelength demultiplexer was also achieved, for which a wavelength separation with an approximately 25 nm spacing and free spectral range (FSR) of approximately 100 nm were obtained. Moreover, an optical deflector was investigated and primitive deflection was achieved at 1460 and 1490 nm incident wavelengths.

Form and density control of self-assembled InAs quantum dots (QDs) was demonstrated by the selective MOVPE growth using SiO2 narrow stripe mask array. Variation of size and density were successfully obtained at across the array.

Selective MOVPE growth of self-assembled InAs quantum dots (QDs) using a SiO2 narrow stripe mask array and composition-varied GaInAs layers successfully yielded a variation of size across the array while keeping density.

GaInAs/TnP MQW-based arrayed-waveguide wavelength demultiplexer with linearly varying refractive-index distribution has been achieved by low-pressure selective MOVPE. Using an asymmetric SiO2 mask with wide mask on one side of the array, waveguides with different array thickness are fabricated parallel to the [0 1 1] direction on (1 0 0)oriented n-InP substrates under growth conditions of 640 degreesC and 100 Torr. To connect the arrayed waveguides to the input and output star couplers based on Rowland circle geometry for focus of light, arrayed waveguides tilted with respect to the [0 1 1] direction were required for interfacing with a star coupler. In this paper, the cross-sectional profiles of the tilted waveguides are investigated, revealing the transformation of the waveguide profiles from trapezoidal profiles with sidewall (l l 1)B planes to inverted trapezoidal profiles without exposed (I I 1)B planes with increasing tilt angle with respect to the [0 1 1] direction. (C) 2004 Elsevier B.V. All rights reserved.

Wavelength demultiplexing in GaInAs/InP MQW-based straight arrayed waveguide with linearly varying refractive-index distribution yielded successful results. The fabrication of the device was achieved with single selective MOVPE growth, obtaining a wavelength separation with around 25 nm spacing and a free spectral range of approximately 100 nm.

A novel arrayed waveguide grating in which refractive index varies across the array fabricated by metal-organic vapor phase epitaxy (MOVPE) selective area growth is proposed. The waveguide thickness increases from one end and refractive index increases accordingly and the phase of propagating light in each arrayed waveguide is different. Therefore, straight waveguides are possible, reducing device dimensions and optical propagation losses. As the experimental results, fabrication of sample devices is achieved in a single pass using a MOVPE selective area growth technique and simple wavelength separation of the fabricated devices yielded successful results.

Arrayed waveguldes using GaInAs/InP MQW with linearly varying refractive index distribution were fabricated by selective MOVPE. We investigated the waveguide structure dependence on growth condition and mask geometry, and demonstrated the successful wavelength demultiplexing.

我々はGalnAs/InPMQW構造を用いたアレイ導波路型波長分割光スイッチの研究を行っている.このアレイ導波路は,MOVPE選択成長法において非対称SiO_2マスクパターンを用いることにより, MOW層厚を徐々に変化させ,それぞれの導波路において階段型屈折率分布を有する構造となっている.この構造により,アレイ導波路を伝搬する光はそれぞれ異なる位相で出射するため,互いに干渉し波面の揃う方向に回折する.また,回折角は波長に依存することから,波長の異なる光の集光する位置はそれぞれ異なり,異なる波長を別々に取り出すことが可能となる.したがって,曲げ導波路を用いない直線型波長分波器の実現か期待できる.今回, MOVPE選択成長法により階段型屈折率分布を有するアレイ導波路を作製した.また,波長分割デバイスへ応用するにあたり,初期実験としてフレネル領域における回折像-入射波長依存性の測定を行ったので報告する.

We report the thickness control of an arrayed waveguide using MOVPE selective area growth. The asymmetric mask pattern in which a wide mask is placed next to one side of an arrayed waveguide, results in a gradient change of the thickness in array waveguides. The growth enhancement factor in the arrayed waveguide depends on the growth condition, such as growth temperature and pressure. We also estimated the material compositions distribution in the arrayed waveguide from the difference between the photoluminescence and the bandgap calculated from the thickness. Moreover, we compared the growth enhancement factor when the mask pattern had no arrayed waveguide. (C) 2002 Elsevier Science B.V. All rights reserved.

This paper proposes an optical deflector using an arrayed waveguide with a staircase-like refractive index profile. This device is an optical deflector using an array waveguide with the refractive index different in each of the component waveguides. Optical deflection is accomplished by application of a voltage. In order to study the deflection properties, a theoretical analysis of the structure, device parameters, deflection angle, and number of resolution points is carried out. As a method of realizing an arrayed waveguide with built-in refractive index steps, selective organometallic vapor phase epitaxial growth is used for fabrication of an array waveguide with multiple quantum well structures. Initial experimental results are reported here. (C) 2003 Wiley Periodicals, Inc.

我々はGaInAs/InP MQW構造を用いたアレイ導波路型波長分割光スイッチの研究を行っている.このアレイ導波路は,MOVPE選択成長法において非対称SiO_2マスクパターンを用いることにより,MQW層厚を徐々に変化させ,それぞれの導波路において階段型屈折率分布を有する構造となっている.この構造により,アレイ導波路を伝搬する光はそれぞれ異なる位相で出射するため,互いに干渉し波面の揃う方向に回折する.また,回折角は法長に依存することから,波長の異なる光の集光する位置はそれぞれ異なり,異なる波長を別々に取り出すことが可能となる.したがって,曲げ導波路を用いない直線型波長分波器の実現が期待できる.今回,MOVPE選択成長法により階段型屈折率分布を有するアレイ導波路を作製した.また,波長分割デバイスへ応用するにあたり,初期実験としてフレネル領域における回折像-入射波長依存性の測定を行ったので報告する.

GaInAs/InP多重量子井戸構造をもつアレイ導波路に電界を印加し必要な位相変化を得る波長可変型CWDM用一波分波器を提案する.この分波器を実現するため多重井戸量子構造における波長毎の屈折率変化特性および吸収特性の電界依存性を求め,低損失でかつ高い屈折率変化が得られる電界強度を求めた.また,多重井戸量子構造における絶縁耐力を求め電界強度の限界から分波器の波長可変特性を求めた.これらの特性を基に一波分波器の分波特性をTEおよびTMモードについて数値解析により確認した.

We report the fabrication and characterization of ZnCdSe/BeZnTe superlattices (SLs) visible LEDs which were grown on InP substrates by molecular beam epitaxy (MBE). Applying the MgSe/BeZnTe SL for a p-cladding layer of the LED structure, the carrier confining effect was enhanced. The evaluation of the LEDs under pulsed current injections at room temperature (RT) resulted in observation of single peak emissions in the visible range, i.e. at 640 and 554 nm, corresponding to the different layer thickness combinations of the ZnCdSe/BeZnTe SLs active layers. A simple aging test of the LED was performed under the injection current density of 28 A/cm(2). In spite of the higher dislocation density of the LED, in mid 10(5) cm(-2), a relatively longer lifetime over 130 h was confirmed.

Refractive indices of BeZnTe, ZnCdSe/BeZnTe superlattices (SLs) and MgSe/BeZnTe SLs grown on InP substrates were measured for the first time. The refractive index of BeZnTe with a wide bandgap (E-g) of 3.12 eV was higher than that of ZnCdSe with a narrower E-g of 2.1 eV. This tendency in BeZnTe is unexpected, because for other materials, wider bandgaps may generally give lower indices. The refractive indices of the ZnCdSe/BeZnTe and MgSe/BeZnTe SLs were controlled in the wide range by changing the layer thickness combination. Waveguide analysis is performed for laser structures consisting of ZnCdSe/BeZnTe SL active layer and MgSe/BeZnTe SL p-cladding layer. As a result, optical confinement factors around 5.9% are estimated at a wavelength of 564 nm.

We have proposed the optical deflector using arrayed waveguides that have different refractive index fabricated by MOVPE selective area growth. By placing the asymmetric width of SiO2 mask pattern on both sides of the arrayed waveguide, the thickness of the each waveguide in the array has changed gradually. And the phase change in each arrayed waveguide results the deflection of the light. In this device, we have numerically calculated and fabricated the 1xN multi-mode interference (MMI) star coupler using GaInAs/InP MQW structure to input the light equally for each arrayed waveguide. From the numerical calculation, we obtain 0.42dB fluctuation of the output light power in each waveguide in the 1 x 16 MMI waveguide. In the experiment, we fabricated the 1 x 16 MMI waveguide using GaInAs/InP MQW structure, and 0.88dB fluctuation of the output light was obtained for the 1.56mum wavelength input light. And further, we have numerically calculated the wavelength demultiplexing and switching performance in this device. We have obtained the wavelength dependence of output power in 8 arrayed waveguides that have 1.0% refractive index difference in both sides of the arrayed waveguide. From this analysis, we can exchange the output ports of each wavelength by controlling the refractive index in the arrayed waveguide.

Novel ZnCdSe/BeZnTe type-II superlattices (SLs) are very attractive For active layers of new visible light emitting devices using II-VI compounds on InP substrates. It is expected that the transition energy of the SL can be controlled in a wide visible range from 761 to 397 nut by only changing layer-thickness combinations. In this study, the ZnCdSe/BeZnTe SLs grown on InP substrates by molecular beam epitaxy with the shutter Control method for the first time. In the X-ray diffraction measurements, sharp satellite peaks from the SL structures could be observed, which indicates that high crystal qualities and steep interfaces between ZnCdSe and BeZnTe layers were obtained by using the shutter control method. For the SL samples with several layer-thickness combinations, wide-range visible emissions from 740 to 507 nut could be observed in the Pl measurements at 15 K. The PL peaks are comparable to theoretical transition energies calculated for ZnCdSe/BeZnTe SL structures. A double hetero (DH) structure consisting of ZnCdSe/BeZnTe SLs and BeZnTe cladding layers was fabricated. In the PL spectrum of the DH sample at 15 K. sharp peak emissions at 517 and 614 nm could be observed.

ZnCdSe/BeZnTe II-VI compound superlattices (SLs) were grown on InP substrates by molecular beam epitaxy for the first time. In the X-ray diffraction studies, definite satellite Peaks were observed for each sample, which indicates that fine periodic SL structures were obtained. For SL samples with several layer thickness combinations, wide-range visible emissions from 740 to 507 nm were observed during photoluminescence (PL) studies at 15 K. Comparison of PL emission properties at 15 K for a ZnCdSe/BeZnTe SL and ZnCdSe bulk samples showed the superior emission intensity of the SL sample, A double hetero-structure (DH) consisting of ZnCdSe/BeZnTe SLs and BeZnTe cladding layers was fabricated. In the PL spectrum of the DH sample at 15 K, sharp emission peaks at 517 and 604 nm were observed. Visible light emitting diodes were fabricated by applying ZnCdSe/BeZnTe SLs as the active layer, and were evaluated under pulsed current injections at room temperature. A single-peak yellow-green emission around 562 nm was obtained.

BeZnCdSe quaternaries, MgSe/BeZnCdSe superlattice (SL) and BeZnCdSe quantum well (QW) structures were grown on InP substrates by molecular beam epitaxy for the first time. As for a lattice-matched Be-0.08(Zn0.30Cd0.70)(0.92)Se sample, a single-peak photoluminescence (PL) spectrum was observed at the temperature range from 15K to room temperature. The PL peak wavelength and the full-width at half-maximum (FWHM) value at 15 K were 572 nm and 8.8 meV, respectively. PL measurements of MgSe/BeZnCdSe SL samples were observed single-peak emissions in the green-to-blue color range from 525 to 470 nm at 15 K with changing MgSe layer-thickness ratio from 0.20 to 0.60. As for the QW sample consisting of four BeZnCdSe QWs with a different well width, PL peaks corresponding to each QW were observed in the wavelength range from 459 to 561 nm at 15 E(. By fitting calculated transition energies in the QWs to the PL peak energies. the band offset ratio between the BeZnCdSe well and the MgSe/BeZnCdSe SL barrier was estimated to be DeltaE(c) : DeltaE(v) = 9 : 1. (C) 2001 Elsevier Science B.V. All rights reserved.