Shigekazu Okumura

Temperature-Insensitive Eye-Opening under 10-Gb/s Modulation of 1.3-µm P-Doped Quantum-Dot Lasers without Current Adjustments

We demonstrate temperature-insensitive eye-opening under 10-Gb/s direct modulation of 1.3-µm p-doped quantum-dot lasers without using any current adjustments. The lasers show a 6.5-dB extinction ratio between 20°C and 70°C. An active region consisting of ten quantum-dot layers with p-type doping enabled this highly temperature-stable dynamic performance, which was much superior to conventional 1.3-µm quantum-well lasers. These results make it possible to use uncooled 1.3-µm quantum-dot lasers without any current adjustments.

1.3-

This paper describes 1.3-mum AlGaInAs multiple-quantum-well semi-insulating buried-heterostructure distributed-feedback lasers for high-speed direct modulation. Combination of large differential gain AlGaInAs quantum wells and semi-insulating buried-heterostructure for reduction of active region achieved 25 and 40 Gb/s direct modulation with the device having the cavity length of 150 mum. The device whose Bragg wavelength is longer than gain peak wavelength showed 25 Gb/s direct modulation characteristics with superior temperature characteristics. The relaxation oscillation frequency of this device was 15 GHz and higher up to 70degC. Clear eye-opening was observed and single-mode fiber transmission experiments showed low power penalty up to 70degC. With the device of negative detuning with larger differential gain, we achieved 40 Gb/s direct modulation. This device showed high relaxation oscillation frequency and slope of 20.5 GHz and 3.2 GHz/mA1/2, respectively. The 40 Gb/s eye opened clearly at 25degC and eye-opening was observed up to 50degC.

\mu

We succeeded in demonstrating single-photon generation from a single InAs quantum dot (QD) at a 1.55 µm band by current injection. A p–i–n light-emitting diode (LED), which includes a quantum dot layer, was grown on an n-InP substrate and fabricated into a nano scaled mesa structure with electrodes. Electrical pulses of 80 ps width were injected in order to generate excitons in quantum dots. We directly determined the electroluminescence (EL) and radiative lifetime of a single exciton to be 1.59 ns. Hanbury-Brown and Twiss (HBT)-type photon correlation measurements proved the antibunching behavior of exciton recombination in a current-injected quantum dot at a wavelength of 1551.2 nm. These measurements demonstrate that our QD LEDs are sources of triggered single photons in the C-band by current injection.

m AlGaInAs Multiple-Quantum-Well Semi-insulating Buried-Heterostructure Distributed-Feedback Lasers for High-Speed Direct Modulation

We investigate the exciton dynamics in a current-injected single InAs quantum dot (QD) which emits 1.55μm photons. Photon antibunching behavior is observed using a single electroluminescence line of a single QD. The radiative lifetime of this line determined by time-resolved measurement is 1.59ns. The single exciton recombination time agrees with the lifetime calculated with an eight-band kp model. We examine a high drive rate operation of the device by changing the delay time between two electrical pulses. These results demonstrate that our device has the potential to achieve telecommunication band subgigahertz single-photon emission with electrical pulses.

First Demonstration of Electrically Driven 1.55 µm Single-Photon Generator

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.

Exciton dynamics in current-injected single quantum dot at 1.55μm

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.

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

High relaxation oscillation frequency of 20.5 GHz and its slope of 3.2 GHz/mA1/2 were obtained by SI-BH 1.3-mum AlGaInAs MQW DFB lasers. Eye-opening up to 50degC was demonstrated as a result of 40-Gb/s direct modulation.

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

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.

40-Gb/s direct modulation of 1.3-μm semi-insulating buried-heterostructure AlGaInAs MQW DFB lasers

Low-drive-current 10-Gb/s operation at high temperatures was obtained for AlGaInAs buried-heterostructure λ/4-shifted DFB lasers. At 100 °C, f<inf>r</inf> at I<inf>th</inf> + 50 mA was 10.8 GHz and 10-Gb/s modulation was achieved at I<inf>mod</inf> = 22 mA<inf>p-p</inf>.

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 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.