Duanhua Kong

The Fabrication of Eight-Channel DFB Laser Array Using Sampled Gratings

An eight-channel monolithically integrated complex-coupled distributed-feedback laser array based on sampled gratings has been designed and fabricated. Selective lasing at different wavelengths is obtained. The frequency separation between each adjacent channel is about 200 GHz. The typical threshold current is between 30 and 40 mA. The optical output power of each channel is about 10 mW at an injection current of 100 mA. The continuous tuning of emission wavelength with injected currents is also demonstrated.

InP-based deep-ridge NPN transistor laser

We report an InP-based deep-ridge NPN transistor laser (TL, λ∼1.5 μm). By placing the quantum well (QW) active material above the heavily Zn-doped base layer, both the optical absorption of the heavily p-doped base material and the damage of the quality of the QWs resulted from the Zn diffusion into the QWs are decreased greatly. CW operation of the TL is achieved at -40 °C, which is much better than the shallow-ridge InP-based NPN TL. With future optimization of the growth procedure, significant improvement of the performance of the deep-ridge InP-based NPN TLs is expected.

A ridge width varied two-section index-coupled DFB self-pulsation laser with a wide continuously tunable frequency range

A 1.55 mu m InGaAsP-InP index-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. A record wide self-pulsation tuning range above 450 GHz has been achieved for this index-coupled DFB SPL. Furthermore, frequency locking to an optically injected modulated signal is successfully demonstrated.

Temperature performance of the edge emitting transistor laser

The characteristic temperature (T0) of the edge emitting transistor laser (TL) is studied numerically. For the deep-ridge TL, the common base (CB) mode characteristic temperature (T0,CB) is a lot lower than the common emitter (CE) mode characteristic temperature (T0,CE), which is comparable to a conventional laser. This is resulted from the increase of the emitter to base current gain with the base current, which amplifies the increase of the CB threshold current with temperature. For the shallow-ridge TL, the T0,CE is found to be also rather low and is only slightly higher than the T0,CB. This can be attributed to the large fraction of electron current in the total base current, which is related to the large thickness of base layer and the insertion of quantum wells in the TL.

Formation trends of ordered self-assembled nanoislands on stepped substrates

The growth of ordered self-assembled nanoislands on stepped substrates is studied systematically by kinetic Monte Carlo simulations. As the terrace width is small, the formation of nanoislands is confined in the steps and nanoislands ordered in lines or nanowires can be obtained. The Schwoebel barrier at the step edges has a great influence on the evolution of both the size and space distributions of the islands. When the terrace width is relatively large, self-ordering of nanoislands in the center regions of the terraces happens. An unexpected trend of the nanoisland self-ordering is found as the deposition thickness is larger than 0.2 ML, which can be related to the attractive migrations between nearby islands.

Self-pulsation in a two-section DFB laser with a varied ridge width

A 1.55 mu m InGaAsP-InP two-section DFB laser with a variable ridge width has been fabricated. Self-pulsations with frequencies around 3 GHz and 40 GHz are observed. The pulsation mechanisms related to the two frequencies are discussed and the tunability of generated self-pulsations is studied.

A widely tunable ridge width varied two-section partly gain-coupled DFB self-pulsation laser for optical microwave generation

A partly gain-coupled ridge varied two-section DFB self-pulsation laser for optical microwave generating has been fabricated. It produces microwave with a wide tuning range of more than 135GHz. A successful locked to the microwave frequencies of 30GHz, 40GHz, 50GHz, 60GHz are demonstrated and a timing jitter below 300fs is detected.

Control of the lasing wavelength by a sampled grating in a complex-coupled DFB laser

The lasing wavelength of a complex-coupled DFB laser is controlled by a sampled grating. The key concepts of the approach are to utilize the -1st order (negative first order) reflection of a sampled grating for laser single mode operation, and use conventional holographic exposure combined with the usual photolithography to fabricate the sampled grating. The typical threshold current of the sampled grating based DFB laser is 32 mA, and the optical output is about 10 mW at an injected current of 100 mA. The lasing wavelength of the device is 1.5356 mu m, which is the -1st order wavelength of the sampled grating.

Growth Simulations of Self-Assembled Nanowires on Stepped Substrates

The growth of self-assembled nanowires on stepped substrates is modeled by means of kinetic Monte Carlo simulations. It is found that the energy barrier at the step edges has a great effect on the formation of nanoislands on stepped substrates. As the barrier is smaller than 0.1 eV, nanowires with high aspect ratios can be obtained. The width, aspect ratio, and separation of the nanowires can be controlled flexibly by the width of the steps or terraces of the substrates. The effects of growth temperature and postgrowth annealing time on the morphology of the nanowires are studied. The nanowires are found to be more robust than the self-assembled nanoislands formed on plane substrates. Strain is shown to increase the width and decrease the aspect ratio of the nanowires. The scaled nanowire length distribution is also studied. As the coverage is larger than 0.2 ML, the distribution is apparently different from that at lower coverage, which reflects the different growth mechanisms of the nanowires at different layer thickness.

Research status of electro-absorption modulated lasers

This talk will introduce the fabrication methods of electro-absorption modulated lasers (EMLs) and the latest results of EMLs fabricated by a novel technology named selective area growth double-stack active layer (SAG-DSAL) developed by the authors.