Wang Hai-Long

Multicolor InAs/InP(100) Quantum Dot Laser

We report on a three-colour InAs/InP(100) quantum dot laser under continuous wave mode at an operation temperature of 20°C. Three lasing peaks are observed simultaneously, the high-energy peak undergoes continuous blueshift, while the splitting energy gap between the low-energy peaks is somewhat fixed as the injection current increases. The maximum output power from one facet without coating is more than 34 mW with a slope efficiency of 102 mW/A just above the threshold current. Three peaks of differential efficiency of output power are observed, just corresponding to each peak in lasing spectra, respectively. At the same time, the far-field distribution shows only a single transverse mode over the full range of injection current.

Electronic States of a Shallow Hydrogenic Donor Impurity in Different Shaped Semiconductor Quantum Wells

The shallow hydrogenic donor impurity states in square, V-shaped, and parabolic quantum wells are studied in the framework of effective-mass envelope-function theory using the plane wave basis. The first four impurity energy levels and binding energy of the ground state are more easily calculated than with the variation method. The calculation results indicate that impurity energy levels decrease with the increase of the well width and decrease quickly when the well width is small. The binding energy of the ground state increases until it reaches a maximum value, and then decreases as the well width increases. The results are meaningful and can be widely applied in the design of various optoelectronic devices.

External Electric Field Effect on Hydrogenic Donor Impurity in Zinc-Blende InGaN Quantum Dot

The binding energy of a hydrogenic donor impurity in zinc-blende (ZB) InGaN quantum dot (QD) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position, QD size and the external electric field. The symmetry of the electron probability distribution is broken and the maximum of the donor binding energy is shifted from the centre of QD in the presence of the external electric field. The degenerating energy levels for symmetrical positions with respect to the centre of QD are split. The splitting increases with the increase of QD height while the splitting increases up to a maximum value and then decreases with the increase of QD radius.

High Intensity Single-Mode Peak Observed in the Lasing Spectrum of InAs/GaAs Quantum Dot Laser

We report on abnormal lasing spectra of InAs/GaAs quantum dot lasers, where a single-mode peak exists with optical intensity several times larger than that of other modes. The maximum side mode suppression ratio of the single-mode peak is measured to be 10.11 dB at 29°C with injection current of 413 mA. It is found that the emergence of this abnormal lasing spectrum happens in a certain range of operation temperature and current. The sharp increase in optical intensity of the single-mode peak is closely related to the disappearance of optical lasing modes located at the higher energy side of the enhanced mode.

Simultaneous measurement of phase retardation and optic axis of wave plates

A simple method used for simultaneous measurement of phase retardation and optic axis of wave plate by employing 1/4 wave plate is demonstrated. The theoretical analysis of the measuring principle is presented in detail. In the measurement, after adjusting a standard 1/4 wave plate and the fast (slow) axis of the plate to be measured parallel to the pass axis of the polarizer, the plate to be measured is rotated by 450 counterclockwisly. A stepping motor is used to rotate the analyzer. The experimental data are collected by a photodetector and then sent to a computer. According to the output data curve, the phase retardation and optic axis of the plate to be measured can be obtained simultaneously. To test the feasibility of the method, a λ /2 and a λ /8 wave plates are used as examples to demonstrate the measurement procedures. The phase retardation measurement accuracy is better than 0.5 × 10−2. This method can be used to measure the arbitrary phase retardation conveniently.

Junction-Temperature Measurement in InAs/InP(100) Quantum-Dot Lasers

We report on the measurement of junction temperature of the InAs/InP(100) quantum dot lasers working in the 1.55 μm wavelength region. The measurement is based on analyzing the temperature induced mode shift of the Fabry—Perot cavity. Under pulsed operation mode, more than 20°C junction temperature rise is measured for the quantum-dot (QD) laser when the duty cycle is increased from 1% to 95%. For a reference quantum well laser, the junction temperature rise is obtained as only around 3°C. The large junction temperature rise might be a crucial factor to improve the performance of QD lasers.

Fabrication of Hinged Mirrors Using a Strain-Driven Self-Assembly Method on a GaAs Substrate

Hinged mirror arrays are widely utilized for display applications and optical communication. They can be fabricated by an self-assembly technique using the strain in lattice-mismatched epitaxial layers. A multilayer structure including a strain-compensated layer, a digital alloy sacrificial layer and a strain bilayer, is grown by molecular-beam epitaxy. Self-assembly hinged mirrors on a GaAs substrate have been successfully fabricated by photolithography and selective etching. The hinge fabrication method with a strain bilayer is simple and flexible. Structures formed by multiple hinged plates will enable the self-assembly of more complex three-dimensional microstructures.

Design of coating for broadband polarization — independent beam splitters and analysis of its optical performance

A design of coating on the entrance surface of the beam splitters with a transparent thin film of certain refractive index and thickness was presented. For this kind of beam splitters, it was possible to realize polarization-independent beam-splitting for chosen wavelength λ with incident angle ϕ. In addition, the simulation results using the coating designable software (Auto film) were consistent with the theoretical results, and the beam splitters are not sensitive to the small errors of film-thickness and film refractive-index over a broad spectra.