E. S. Semenova

1060-nm Tunable Monolithic High Index Contrast Subwavelength Grating VCSEL

We present the first tunable vertical-cavity surface-emitting laser (VCSEL) where the top distributed Bragg reflector has been completely substituted by an air-cladded high-index-contrast subwavelength grating (HCG) mirror. In this way, an extended cavity design can be realized by reducing the reflection at the semiconductor-air interface using an anti-reflective coating (ARC). We demonstrate how the ARC can be integrated in a monolithic structure by oxidizing AlGaAs with high Al-content. The HCG VCSEL has the potential to achieve polarization stable single-mode output with high tuning efficiency. The HCG VCSEL shows a total tuning range of 16 nm around an emission wavelength of 1060 nm with 1-mW output power.

Metamorphic 1.5 µm-range quantum dot lasers on a GaAs substrate

1.5 µm-range laser diodes based on InAs/InGaAs quantum dots (QDs) grown on metamorphic (In, Ga, Al)As layers, which were previously deposited on GaAs substrates using a defect reduction technique (DRT), are studied. More than 7 W total output power operation in the pulsed mode is shown in broad area lasers. It is shown that the narrow stripe lasers operate in the continuous wave (CW) and the single transverse mode at current densities up to 22 kA cm−2 without significant degradation. CW output power in excess of 220 mW at 10 °C heat sink temperature is demonstrated. 800 mW single-mode output power in the pulsed regime is obtained. It is also shown that the lasers demonstrate the absence of beam filamentation up to the highest current densities studied. First studies on the dynamics of the lasers show a modulation bandwidth of ~3 GHz, limited by device heating. Eye diagrams at 2.5 Gbit s−1 and room temperature (RT) have been performed. Aging tests demonstrate >800 h of CW operation at ~50 mW at 10 °C heat sink temperature and >200 h at 20 °C heat sink temperature without decrease in optical output power. The results indicate the high potential of metamorphic growth using the DRT for practical applications, such as 1500 nm GaAs vertical cavity surface emitting lasers (VCSELs).

Metamorphic growth for application in long-wavelength (1.3–1.55 µm) lasers and MODFET-type structures on GaAs substrates

In the present work we report on the optimization of MBE growth conditions and design of metamorphic In(Al)(Ga)As/GaAs heterostructures. This results in a strong decrease in the density of threading dislocations in the upper (active) layers and the improvement of surface morphology. Room-temperature mobility in metamorphic modulation-doped InGaAs/InAlAs heterostructures was 8100?cm2?V?1?s?1, which is comparable to that of InP-based structures and noticeably superior to pseudomorphic GaAs-based structures. InAs quantum dots formed in a metamorphic InGaAs matrix on a GaAs substrate were used for lasers with promising characteristics (emitting wavelengths of 1.46??m, with threshold current densities of 1.4?kA?cm?2).

Degradation-robust single mode continuous wave operation of 1.46μm metamorphic quantum dot lasers on GaAs substrate

Narrow ridge lasers of 1.5μm range based on InAs∕InGaAs quantum dots grown on metamorphic (In,Ga,Al)As layers deposited on GaAs substrates using defect reduction technique are studied. It is shown that the lasers operate continuous wave (cw) in a single transverse mode. Single-mode 800mW output power in the pulsed regime is obtained for a 6μm ridge width. The dynamic studies of the lasers show a modulation bandwidth of ∼3GHz. Aging tests demonstrate >800h of cw operation at ∼50mW at 10°C (60°C) and >200h at 20°C (70°C) heat sink (junction) temperature without noticeable degradation.

Resonant MEMS Tunable VCSEL

We demonstrate how resonant excitation of a microelectromechanical system can be used to increase the tuning range of a vertical-cavity surface-emitting laser twofold by enabling both blue- and red-shifting of the wavelength. In this way, a short-cavity design enabling wide tuning range can be realized. A high-index-contrast subwavelength grating vertical-cavity surface-emitting laser with a monolithically integrated antireflection coating is presented. By incorporating an antireflection coating into the air cavity, higher tuning efficiency can be achieved at low threshold current. The first result shows 24-nm continuous resonant tuning range around an emission wavelength of 1060 nm with 0.9 mW output power.

High external differential efficiency and high optical gain of long-wavelength quantum dot diode laser

Abstract Long-wavelength (1.29 μm ) lasers grown on GaAs and based on several planes of self-organized quantum dots in an external quantum well demonstrate significant improvement of the external differential efficiency (88%) and the characteristic temperature (150 K ) . This is due to suppression of carrier pile-up in the waveguide region in combination with extended range of optical loss in which the ground-state lasing survives.

Nano-engineered high-confinement AlGaAs waveguide devices for nonlinear photonics

The combination of nonlinear and integrated photonics enables applications in telecommunication, metrology, spectroscopy, and quantum information science. Pioneer works in silicon-on-insulator (SOI) has shown huge potentials of integrated nonlinear photonics. However, silicon suffers two-photon absorption (TPA) in the telecom wavelengths around 1550 nm, which hampers its practical applications. To get a superior nonlinear performance, an ideal integrated waveguide platform should combine a high material nonlinearity, low material absorption (linear and nonlinear), a strong light confinement, and a mature fabrication technology. Aluminum gallium arsenide (AlGaAs) was identified as a promising candidate for nonlinear applications since 1994. It offers a large transparency window, a high refractive index (n≈3.3), a nonlinear index (n2) on the order of 10-17 m2W−1, and the ability to engineer the material bandgap to mitigate TPA. In spite of the high intrinsic nonlinearity, conventional deep-etched AlGaAs waveguides exhibit low effective nonlinearity due to the vertical low-index contrast. To take full advantage of the high intrinsic linear and nonlinear index of AlGaAs material, we reconstructed the conventional AlGaAs waveguide into a high index contrast layout that has been realized in the AlGaAs-on-insulator (AlGaAsOI) platform. We have demonstrated low loss waveguides with an ultra-high nonlinear coefficient and high Q microresonators in such a platform. Owing to the high confinement waveguide layout and state-of-the-art nanolithography techniques, the dispersion properties of the AlGaAsOI waveguide can be tailored efficiently and accurately by altering the waveguide shape or dimension, which enables various applications in signal processing and generation, which will be reviewed in this paper.

Butt-joint integration of active optical components based on InP/AlInGaAsP alloys

We demonstrate all-active planar high quality butt-joint (BJ) integration of a QW Semiconductor Optical Amplifier (SOA) and MQW Electro-Absorption Modulator (EAM) based on an InP/AlInGaAsP platform. The degradation of the optical properties in the vicinity of ~1 μm to the BJ interface was determined by means of μPL measurements.

Improvement of light-current characteristic linearity in a quantum well laser with asymmetric barriers

The effect of asymmetric barriers on the light-current characteristic (LCC) of a quantum well laser was studied theoretically and experimentally. It is shown that the utilization of asymmetric barriers in a waveguide prevents the nonlinearity of LCC and, consequently, allows rising of the maximum output power.