According to the InAs/GaAs submonolayer quantum dot active region,we demonstrate a bent-waveguide superluminescent diode emitting at a wavelength of around 970 nm.At a pulsed injection current of 0.5 A,the device exhibits an output power of 24 mW and an emission spectrum centred at 971 nm with a full width at half maximum of 16 nm.
We report the effect of the GaAs spacer layer thickness on the photoluminescence(PL) spectral bandwidth of InAs/GaAs self-assembled quantum dots(QDs).A PL spectral bandwidth of 158 nm is achieved with a five-layer stack of InAs QDs which has a 11-nm thick GaAs spacer layer.We investigate the optical and the structural properties of the multilayer-stacked InAs/GaAs QDs with different GaAs spacer layer thicknesses.The results show that the spacer thickness is a key parameter affecting the multi-stacked InAs/GaAs QDs for wide-spectrum emission.
Quantum-dot laser diodes (QD-LDs) with a Fabry-Perot cavity and quantum-dot semiconductor optical amplifiers (QD-SOAs) with 7°tilted cavity were fabricated.The influence of a tilted cavity on optoelectronic active devices was also investigated.For the QD-LD,high performance was observed at room temperature.The threshold current was below 30 mA and the slope efficiency was 0.36 W/A.In contrast,the threshold current of the QDSOA approached 1000 mA,which indicated that low facet reflectivity was obtained due to the tilted cavity design.A much more inverted carrier population was found in the QD-SOA active region at high operating current,thus offering a large optical gain and preserving the advantages of quantum dots in optical amplification and processing applications.Due to the inhomogeneity and excited state transition of quantum dots,the full width at half maximum of the electroluminescence spectrum of the QD-SOA was 81.6 nm at the injection current of 120 mA,which was ideal for broad bandwidth application in a wavelength division multiplexing system.In addition,there was more than one lasing peak in the lasing spectra of both devices and the separation of these peak positions was 6-8 nm,which is approximately equal to the homogeneous broadening of quantum dots.
A broadband tunable grating-coupled external cavity laser is realized by employing a self-assembled InAs/GaAs quantum-dot (QD) superluminescent diode (SLD) as the gain device. The SLD device is processed with a bent-waveguide structure and facet antireflection (AR) coating. Tuning bandwidths of 106 nm and 117 nm are achieved under 3-A and 3.5-A injection currents, respectively. The large tuning range originates essentially from the broad gain spectrum of self-assembled QDs. The bent waveguide structure combined with the facet AR coating plays a role in suppressing the inner-cavity lasing under a large injection current.
This paper reports the fabrication of J-shaped bent-waveguide superluminescent diodes utilizing an InAl- GaAs/AlGaAs quantum dot active region. The emission spectrum of the device is centred at 884 nm with a full width at half maximum of 37 nm and an output power of 18 mW. By incorporating an Al composition into the quantum dot active region, short-wavelength superluminescent diode devices can be obtained. An intersection was found for the light power-injection current curves measured from the straight-waveguide facet and the bent-waveguide facet, respectively. The result is attributed to the conjunct effects of the gain and the additional loss of the bent waveguide. A numerical simulation is performed to verify the qualitative explanation. It is shown that bent waveguide loss is an important factor that affects the output power of J-shaped superluminescent diode devices.
A broadband external cavity tunable laser is realized by using a broad-emitting spectral InAs/GaAs quantum dot (QD) gain device. A tuning range of 69 nm with a central wavelength of 1056 nm, is achieved at a bias of 1.25 kA/cm2 only by utilizing the light emission from the ground state of QDs. This large tunable range only covers the QD ground-state emission and is related to the inhomogeneous size distribution of QDs. No excited state contributes to the tuning bandwidth. The application of the QD gain device to the external cavity tunable laser shows its immense potential in broadening the tuning bandwidth. By the external cavity feedback, the threshold current density can be reduced remarkably compared with the free-running QD gain device.
