Ayahito Uetake

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.

Demonstration of transverse-magnetic dominant gain in quantum dot semiconductor optical amplifiers

We demonstrated transverse-magnetic (TM)-mode dominated gain at the 1.5μm wavelength in semiconductor optical amplifiers (SOAs) with columnar quantum dots (QDs). We show that we can control the polarization dependence of optical gain in QD-SOAs by changing the height and tensile-strained barrier of columnar QDs. The TM mode gain is 17.3dB and a gain of over 10dB was attained over a wide wavelength range of 200nm. The saturation output power is 19.5dBm at 1.55μm.

Internal Strain of Self-Assembled InxGa1-xAs Quantum Dots Calculated to Realize Transverse-Magnetic-Mode-Sensitive Interband Optical Transition at Wavelengths of 1.5 µm bands

We calculated the interband optical transition energies in self-assembled InxGa1-xAs quantum dots on InP as functions of the strain, composition, and height of dots on the basis of the kp perturbation theory. We found that a transverse-magnetic (TM)-mode-sensitive optical transition at wavelengths in the range from 1.5 to 1.6 µm is achieved due to the light-hole valence band when the crystal lattice is expanded in the same direction of growth as the in-plane lattice matched to the substrate at x≤0.4, or when the lattice is compressed in the growth direction with the in-plane lattice relaxed at x≥0.6. We propose barrier structures covering the dots in order to realize these conditions, leading to TM-mode-sensitive quantum dots for polarization-independent optical amplifiers.

4-Wavelength 25.8-Gbps directly modulated laser array of 1.3-μm AlGaInAs distributed-reflector lasers

AlGaInAs distributed-reflector-laser arrays with four different wavelengths on LAN-WDM grid are demonstrated. Each laser provided output power of over 10 mW at 50°C under simultaneous operation and operated at 25.8 Gbps under push-pull driving configuration.

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.

50-Gbps direct modulation using 1.3-µm AlGaInAs MQW distribute-reflector lasers

50-Gbps direct modulation is demonstrated for the first time using a short cavity 1.3-μm wavelength distributed-reflector laser. Clear eye openings with dynamic extinction ratios of 5 dB were obtained up to 50°C and 10-km fiber transmissions were confirmed.

Polarization-Insensitive GaInNAs–GaInAs MQW-SOA With Low Noise Figure and Small Gain Tilt Over 90-nm Bandwidth (1510–1600 nm)

rdquoWe developed a broadband polarization-insensitive multiquantum-well (MQW) semiconductor optical amplifier (SOA) for application as an optical switch in broadcast-and-select-type optical packet switching systems. We adopted a GalnNAs-GalnAs MQW structure active layer to decrease the noise figure (NF) around the gain peak wavelength together with a small gain tilt in the C-band. The device exhibited a smaller NF on the shorter wavelength side of the gain peak compared with a GalnNAs strained-bulk SOA. The reduced NF resulted in a large effective gain bandwidth of up to 90 nm (1510-1600 nm). The device also exhibited the small gain tilt (<1.2 dB) and small polarization-dependent gain (<0.8 dB) in the C-band.

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

1.3-μm-Wavelength AlGaInAs Multiple-Quantum-Well Semi-Insulating Buried-Heterostructure Distributed-Reflector Laser Arrays on Semi-Insulating InP Substrate

1.3-μm-wavelength AlGaInAs distributed-reflector laser arrays on semi-insulating InP substrate for high-speed direct modulation are investigated to realize compact and low-power-consumptive optical modules. Combination of AlGaInAs quantum wells with large differential gain and semi-insulating buried-heterostructure for reduction of the volume in active region achieved high-speed direct modulation. The fabricated lasers in the array lase with different wavelengths with stable single-longitudinal mode. Clear eye-opening and large mask margin were obtained in push-pull driving at 25.8 Gb/s direct modulation with coplanar electrode and semi-insulating InP substrate. Comparison of modulation waveform under simultaneous operation of neighbor lasers shows that crosstalk between lasers in the array is small. Clear eye-openings, large mask margins, and 10-km fiber transmission of four different wavelength lasers on LAN-WDM grid are demonstrated under 28-Gb/s operation at 50 °C. For further high-speed operation, 43-Gb/s direct modulation were performed. These results indicate that the 1.3-μm AlGaInAs DR laser arrays are promising as light sources for 100-Gb/s Ethernet and higher speed transmission.