An optical frequency comb was generated from a single quantum dot laser diode (QD-LD) in the 1-µm waveband using an Sb-irradiated InGaAs/GaAs QD active medium. A single-mode-selection technique and interference injection-seeding technique are proposed for selecting the optical mode of a QD optical frequency comb laser (QD-CML). In the 1-µm waveband, a wavelength-tunable single-mode light source and a multiple-wavelength generator of a comb with 100-GHz spacing and ultrafine teeth are successfully demonstrated by applying the optical-mode-selection techniques to the QD-CML. Additionally, by applying the single-mode-selection technique to the QD-CML, a 10-Gbps clear eye opening for multiple-wavelengths in 1-µm waveband photonic transport over a 1.5-km-long holey fiber is obtained.
Modulation characteristics of a novel InGaAs/InAlAs multiple quantum well (MQW) microring-enhanced Mach-Zehnder modulator (MRE-MZM) is investigated in detail and its low-voltage operation with high extinction ratio is demonstrated. The MZM has a single microring resonator in one arm and is driven by the change in electrorefractive index induced by the quantum-confined Stark effect in the MQW core layer. As the MQW, a multiple five-layer asymmetric coupled quantum well (FACQW) is used to obtain a large electrorefractive index change. The driving voltage of the proposed MZM is significantly reduced owing to the enhanced phase shift in the microring resonator. High-mesa waveguide structures are grown by solid-source molecular beam epitaxy and fabricated by inductively coupled plasma etching. A directional coupler with an asymmetric branching ratio is used as an input coupler to prevent the degradation of the extinction ratio of the MZM. The extinction ratio of the fabricated MRE-MZM is approximately 27 dB. The product of the half-wave voltage and phase shifter length, V(π) · L, is 1.7 Vmm in static modulation. This value is one-quarter that of a conventional MZM with the same waveguide structure.
We demonstrated an all-optical flip-flop and inverter using two adjacent lasing wavelengths (FSR = 1.7 nm) from an InGaAs/InGaAsP multiple quantum well (MQW) microring laser. The main lasing wavelength (1567.54 nm) and both side adjacent lasing wavelengths (1565.84 and 1569.24 nm) were used as the injection light wavelength. These operations were realized in the same device with different injected currents. The injected light power and detuning dependence of the inverter operation were clarified.
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