Masaki Kohtoku - IEEE Xplore Author Profile

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We propose an SOA with U-turn shape deep-ridge passive waveguide for integration on a silicon photonics platform. We fabricated the U-turn waveguide with the bending radius of 75 μm, and good gain characteristics were obtained in the entire C-band.Show More
We report novel high-bandwidth InP-based Mach-Zehnder modulator and in-phase/quadrature (IQ) modulators that we realized by combining an n-i-p-n heterostructure and a capacitively loaded traveling wave electrode. The extremely low electrical and optical loss structure enhances the 3-dB electro-optic bandwidth of over 67 GHz without degrading other properties such as driving voltage and optical los...Show More
We developed an eight-channel (8ch) reflection-type transversal filter (RTF) with a 9 × 9 multimode interference coupler on an InP wafer to prove channel scalability of RTFs. Fabricated two types of 8ch RTF with different sizes (1-mm and 1.5-mm long) exhibited comparable filter performance and peak wavelength fluctuation less than 1 nm, and each excess loss from a designed transmittance was about ...Show More
InP-based MZ modulators are suitable for realizing coherent pluggable transceivers. They offer compact size, low driving voltage and high performance. Targeting lower power consumption, we employed a reduced driving voltage and an athermal twin-IQ modulator.Show More
We have developed a novel electroabsorption modulator (EAM)-integrated distributed feedback laser (EA-DFB laser), in which an EAM functioning as an external modulator is integrated in a Mach-Zehnder interferometer (MZI). The MZI-type EAM (MZEA) modulates light intensity by both optical absorption and interferometric extinction. As a result, it improves the extinction ratio (ER) of a conventional E...Show More
We have achieved the first 25-Gb/s operation for a metamorphic laser with a high characteristic temperature (T0=187 K) at 1.3 μm on a GaAs substrate using a thin metamorphic buffer to suppress wafer curvature.Show More
This paper describes tunable diode laser spectroscopy and its laser light source technologies especially for InP-based distributed feedback lasers operating in the 2-2.3 μm region. Application examples including isotope ratio analysis are also introduced.Show More
A 4 × 25-Gb/s electroabsorption modulator integrated with a distributed feedback (DFB) laser (EADFB laser) array monolithically integrated with a low-loss optical multiplexer (MUX) is developed for 100 GbE transmitters for the first time. A cascaded Mach-Zehnder (MZ) filter, which has no intrinsic loss, is used as the MUX. The design and fabrication of the MZ-MUX for 100 GbE are thoroughly describ...Show More
We developed a reflection-type 4x1 transversal filter (TF) on an InP substrate as a compact and low-loss wavelength multiplexer (MUX) for monolithically integrated light source arrays. The filter has a satisfactory MUX function and is very compact of about 900 Pm x 50 Pm which is one twentieth of a size of a conventional 4x1 TF. It is suitable for a MUX of a monolithically integrated light source ...Show More
A MZ optical modulator (MZM) with a novel planar structure was proposed. A single-RF drive push-pull MZM with a simple coplanar waveguide (CPW) was fabricated by utilizing a (110)-oriented InP substrate in terms of the crystallographic orientation dependence of the electro-optic Pockels effect. The device exhibits a 3 dB-EO bandwidth of 30 GHz and 40 Gb/s NRZ high speed modulation.Show More
We demonstrated a 1.3-μm-range laser with a high characteristic temperature (T0 = 220 K) and the highest operating temperature (200 °C) ever reported for a metamorphic laser. The temperature characteristics were greatly improved by inserting a p-InGaAlAs electron stopper layer. In addition, we realized a high fr value with a low injection current using a short cavity (L = 200 μm) laser operating a...Show More
We demonstrate 50-Gb/s direct modulation by using 1.3-μm distributed-feedback lasers with a ridge waveguide structure. We employed InGaAlAs material for a multiple-quantum well to obtain a low damping factor K, and fabricated a ridge waveguide structure buried in benzocyclobutene to realize a structure with a low parasitic capacitance. In addition, to obtain high maximum frequency relaxation oscil...Show More
We demonstrated a 1.3-μm-range metamorphic short cavity laser with a high characteristic temperature (T0=200K). The bias current for 10-Gbps modulation at high temperature was reduced and we revealed the potential for low-power consumption operation.Show More
A 1.3-μm-range metamorphic InGaAs laser with high characteristic temperature (T0 = 220 K) and the highest operating temperature (200 °C) ever reported for a metamorphic laser has been achieved by inserting an electron stopper layer in the p-cladding layer.Show More
In this paper, we describe polarization-insensitive phase trimming of silica-based waveguides with both 193- and 244-nm ultraviolet (UV) light and the trimming of both phase error and polarization dependence. A wide beam of 193-nm UV light from an ArF excimer laser is useful for phase trimming multiple waveguides. We utilize stress-release grooves to control birefringence generation while phase tr...Show More
We describe a technique designed to compensate for the residual temperature sensitivity of an athermal silica-based arrayed-waveguide grating (AWG) and its application to a 50-GHz-spacing multi/demultiplexer with a low loss and a wide passband. The device has a Mach-Zehnder interferometer (MZI)-synchronized configuration, in which the AWG and the MZI are athermalized with resin-filled grooves. The...Show More
The interconnection of waveguides inside a silica-based planar lightwave circuit (PLC) is demonstrated both two- and three-dimensionally by using a femtosecond laser. The waveguides written with a femtosecond laser can be successfully connected to waveguides inside a PLC with low loss. Unlike previous work on the direct writing of 2-D and 3-D waveguides in bulk glass, the waveguide must be written...Show More
We have achieved a silica-based PLC thermooptic switch with a power consumption of only 30 mW without any deterioration in the optical properties by using a tapered narrow ridge structure. To reduce the power consumption further, we propose a novel structure, the suspended narrow ridge structure, which has the advantages of both the tapered narrow ridge structure and the already reported suspended...Show More