Yasumasa Kawakita

A novel straight arrayed waveguide grating with linearly varying refractive-index distribution

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.

Wavelength demultiplexer using GaInAs-InP MQW-based variable refractive-index arrayed waveguides fabricated by selective MOVPE

A GaInAs-InP multiple quantum well (MQW)-based wavelength demultiplexer composed of an arrayed waveguide in which the refractive index varies across the array was fabricated. Since optical path length differences between waveguides in the array are achieved through refractive-index differences that are controlled by SiO/sub 2/ mask design in selective metal-organic vapor phase epitaxy (MOVPE), straight waveguide gratings having reduced optical propagation losses can be achieved. Furthermore, by employing MQW waveguides, variations in the refractive index may be induced through an applied electric field, allowing the device to manipulate wavelengths dynamically. A straight arrayed waveguide device having a 1.4% difference in refractive index was fabricated using an asymmetric side mask via a single selective MOVPE growth. The achievement of a diffraction angle difference of 4.40/spl deg/ between wavelengths of 1520 and 1580 nm was confirmed experimentally. In addition, a preliminary wavelength demultiplexer with a wavelength separation of approximately 25 nm and a free spectral range (FSR) of approximately 100 nm was also fabricated.

Wavelength demultiplexing and optical deflection in variable refractive-index waveguide array based on selectively grown GaInAs/InP MQW structure

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 SiO 2 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.

Arrayed waveguides with linearly varying refractive index distribution and its application for wavelength demultiplexer

Arrayed waveguides using GalnAs/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.

A novel wavelength dividing and switching device using arrayed waveguides

Summary form only given. Optical space switching - the rearrangement of the optical paths in a network - can provide the greater flexibility and reliability required for managing high-bandwidth networks. As a new optical space switching device, we have proposed an optical wavelength switching device using arrayed waveguides that have different refractive index by MOVPE selective area growth based on InGaAs/InP MQW structures.

Improvements of crosstalk in variable-refractive index waveguide array demultiplexer

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.

Proposal of arrayed waveguides optical deflector and wavelength divide optical switch

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 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 1x16 MMI waveguide. In the experiment, we fabricated the 1x16 MMI waveguide using GaInAs/InP MQW structure, and 0.88dB fluctuation of the output light was obtained for the 1.56μm 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.

size and density control of InAs quantum dots by selective MOVPE growth employing stripe mask array and composition-varied GaInAs layer

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

Size and density control of InAs quantum dots by selective MOVPE growth using narrow stripe mask array

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. Semiconductor self-assembled quantum dots (QDs) grown via Stranski-Krastanov (S-K) growth mode that have zero-dimensional carrier confinement structure are predicted to have unique physical properties 1) and are expected to be applicable in such semiconductor optical devices as laser, semiconductor optical amplifier (SOA), wavelength converters and optical switches . In particular, it is significant to apply QDs for telecommunication devices due to their several advantages compared with conventional quantum well (QW)-based devices. Most of work has concentrated on InAs and GaInAs QDs grown on GaAs substrates, which allow lasing wavelengths as long as 1.3 μm. However, in order to fabricate devices operating in the telecommunication wavelength range, the growth of InAs QDs on InP substrates advantageous. In recent years, QDs on InP substrates have been shown to emit in the wide wavelength range of 1.2–2.0 μm with high efficiency, which is suitable for the telecommunication wavelength range. To realize wide wavelength range QDs in a single integrated optical device, a technique to control self-assembled QDs size in the same plane is important. As a simple fabrication method for this requirement, a selective area growth by metal-organic vapor phase epitaxy (MOVPE) has been reported . In this study, 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 (referred to simply as “wide mask”), which shown schematically in Fig.1, was demonstrated for controlling size and density of QDs. It is advantageous that QWs of varying thickness are formed in the growth region by altering the growth rate, which depends on the number of array and width of wide mask . This technique was applied to control the size of quantum dot, in other words bandgap energy. A 300-nm thick SiO2 film was deposited by plasma enhanced chemical vapor deposition (PECVD) on a (100)-oriented InP substrate, and stripe array or windows orientated parallel to the [011] direction were then formed. The array region consists of 16 stripes with window width of 4 μm and stripe width of 3 μm. In the following experiment, the wide mask width of 100 and 300 μm are used. First, the dependence of dot density and size of InAs QDs on the array number was investigated. Selective MOVPE growth was performed in a vertical reactor at a growth conditions optimized identified in the previous work. After the growth of Ga0.47In0.53As buffer layer, InAs QDs were grown on the mask-patterned InP substrate. The lattice mismatch between InAs and Ga0.47In0.53As is 3.2%. The growth temperature and growth pressure of Ga0.47In0.53As buffer layer were 640oC and 100 Torr and those of InAs QDs were 540oC and 15 Torr, respectively. The supplied source was TE-Ga, TM-In, and tB-As with a V/III ratio of 7 for GaInAs and 237 for InAs. The density and size of QDs are measured by atomic force microscopy (AFM). The size and density in No. 1 were slightly differ from No. 16 as shown in Fig. 2. The growth rate is 0.27 ML/sec and the source supply time is 7 sec. The differences of height and density were obtained between both sides of the array due to the lateral vapor diffusion (LVD) and surface migration from mask region. However, QDs are coalesced each other due to the large amount of materials from the wide mask. Using the wide mask Ww=300 μm, the average diameter of 46, 44 nm, the height of 8.18, 7.59 nm, and the density of 3.80×10, 3.52×10 cm were obtained in the No. 1 and No. 16, respectively. To avoid the coalescence of QDs, improvement of the growth conditions are required. In this study, we applied the reduction of growth rate down to 0.016 ML/sec and the source supply time is 40 sec. The difference of size and density were successfully obtained at both sides of the array as shown in Fig. 3. the coalescent of QDs were remarkably reduced and, JWAB3-P3