Shuichi Tomabechi

Monolithically Integrated 8:1 SOA Gate Switch With Large Extinction Ratio and Wide Input Power Dynamic Range

A monolithic 8:1 SOA gate switch that integrates an 8-ch SOA gate array, an 8:1 optical coupler, and a 1-ch SOA gate was developed for use in a large scale optical packet switching system. A 250-mum-long compact field-flattened coupler (FFC) produces a very small channel-imbalance together with a compact total chip size of 3.0 times 1.0 mm. The device exhibited a large ON-state gain of >14.3 dB and a small total gain deviation of 3.0 dB. The optimized passive waveguide structure successfully suppressed the stray light, which resulted in a record-high ON-OFF extinction ratio of >70 dB. We used a thin tensile-strained multi-quantum well (MQW) active layer which can attain high-saturation output power, low noise, and polarization insensitivity for SOA gates. Due to the coexistence of a high saturation output power and a low noise figure, the device exhibited a very wide input power dynamic range of 20.5 dB for a 10-Gb/s NRZ signal.

Suppression of threshold voltage shift for normally-Off GaN MIS-HEMT without post deposition annealing

In this paper, we present a method of reducing threshold voltage shift for normally-off GaN MIS-HEMT by the optimization of dielectric deposition conditions. High-temperature deposition of Al2O3 insulator decreases the impurities in a dielectric film, leading to small C-V and I-V hysteresis under large positive gate voltage operation. Moreover, Al2O3 deposited at high temperature achieve high quality interface and bulk without post deposition annealing (PDA), preventing the degradation of electrodes and crystallization of insulator film. The fabricated device shows small C-V and I-V hysteresis, with a breakdown voltage of greater than 600 V.

Polarization-insensitive Monolithically-integrated 8:1 SOA Gate Switch with Large Gain and High Extinction Ratio

We developed a monolithic 8:1 SOA gate switch for use in a broadband optical packet-switching system. The device exhibited a large gain of > 12.3 dB and a high extinction ratio of > 65 dB.

10 Gb/s Wavelength-Tunable EML with Continuous Wavelength Tuning Covering 50 GHz × 8 Channels on ITU Grid

A wavelength-tunable EA-modulated laser (wavelength-tunable EML) using tunable distributed amplification (TDA) structure was demonstrated. An 80 km transmission of 10 Gb/s signals was confirmed on 8 channels on ITU grid using the devices simple, continuous tuning mechanism.

Mode-Hop-Free and Electrically Wavelength-Tunable Laser Array with 39.5 nm Tuning Range using Tunable Distributed Amplification DFB Structure

An electrically wavelength-tunable laser array with tunable distributed amplification (TDA) DFB structure has been developed for the first time. A tuning range of 39.5 nm has been achieved by monolithic array of 8-channel mode-hop-free lasers

Low dislocation density InAlN/AlN/GaN heterostructures grown on GaN substrates and the effects on gate leakage characteristics

This paper reports on the electrical characterization of Ni/Au Schottky diodes fabricated on InAlN high-electron-mobility transistor (HEMT) structures grown on low dislocation density free-standing GaN substrates. InAlN HEMT structures were grown on sapphire and GaN substrates by metal-organic vapor phase epitaxy, and the effects of threading dislocation density on the leakage characteristics of Ni/Au Schottky diodes were investigated. Threading dislocation densities were determined to be 1.8 × 104 cm−2 and 1.2 × 109 cm−2 by the cathodoluminescence measurement for the HEMT structures grown on GaN and sapphire substrates, respectively. Leakage characteristics of Ni/Au Schottky diodes were compared between the two samples, and a reduction of the leakage current of about three to four orders of magnitude was observed in the forward bias region. For the high reverse bias region, however, no significant improvement was confirmed. We believe that the leakage current in the low bias region is governed by a dislo...

Uncooled 40-Gbps direct modulation of 1.3-µm-wavelength AlGaInAs distributed reflector lasers with semi-insulating buried-heterostructure

1.3-µm-wavelength AlGaInAs distributed reflector lasers were investigated for uncooled high-speed direct modulation. 40-Gbps modulation under low driving current of 50 mA up to 50°C and 40-Gbps eye opening at 85°C are demonstrated.

High efficiency, wide range and completely transparent wavelength conversion method using replicas generated by dual pump nearly-degenerated four-wave mixing in a Mach-Zehnder interferometer SOA

The novel technique for completely transparent wavelength conversion using replicas by dual pump nearly-degenerated FWM in a Mach-Zehnder interferometer SOA has enabled 16-nm conversion of a 10-Gb/s signal with high efficiency of -6.0 dB.

Highly Uniform Eight-Channel SOA-Gate Array With High Saturation Output Power and Low Noise Figure

A high-power eight-channel semiconductor optical amplifier gate array was developed for application as an optical switch in broadcast-and-select-type optical packet switching systems. The device exhibited a low polarization-dependent gain (<0.8 dB), a high extinction ratio (>60 dB), a low noise figure (<6.2 dB), and a high saturation output power (> +18.2 dBm) for all eight channels. It also exhibited very high interchannel uniformity of less than 0.3 dB for all characteristics.

Advantages of the AlGaN spacer in InAlN high-electron-mobility transistors grown using metalorganic vapor phase epitaxy

We demonstrate the advantages of an AlGaN spacer layer in an InAlN high-electron-mobility transistor (HEMT). We investigated the effects of the growth parameters of the spacer layer on electron mobility in InAlN HEMTs grown by metalorganic vapor phase epitaxy, focusing on the surface roughness of the spacer layer and sharpness of the interface with the GaN channel layer. The electron mobility degraded, as evidenced by the formation of a graded AlGaN layer at the top of the GaN channel layer and the surface roughness of the AlN spacer layer. We believe that the short migration length of aluminum atoms is responsible for the observed degradation. An AlGaN spacer layer was employed to suppress the formation of the graded AlGaN layer and improve surface morphology. A high electron mobility of 1550 cm2 V−1 s−1 and a low sheet resistance of 211 Ω/sq were achieved for an InAlN HEMT with an AlGaN spacer layer.