Semiconductor optical amplifier-based nonlinear optical-loop mirror with feedback

The behavior of a semiconductor optical amplifier (SOA)-based nonlinear loop mirror with feedback has been investigated as a potential device for all-optical signal processing. In the feedback device, input signal pulses (ones) are injected into the loop, and amplified reflected pulses are fed back into the loop as switching pulses. The feedback device has two stable modes of operation - block mode, where alternating blocks of ones and zeros are observed, and spontaneous clock division mode, where halving of the input repetition rate is achieved. Improved models of the feedback device have been developed to study its performance in different operating conditions. The feedback device could be optimized to give a choice of either of the two stable modes by shifting the arrival time of the switching pulses at the SOA. Theoretically, it was found possible to operate the device at only tens of fJ switching pulse energies if the SOA is biased to produce very high gain in the presence of internal loss. The clock division regime arises from the combination of incomplete SOA gain recovery and memory of the startup sequence that is provided by the feedback. Clock division requires a sufficiently high differential phase shift per unit differential gain, which is related to the SOA linewidth enhancement factor.

Travelling-wave model of semiconductor optical amplifier based non-linear loop mirror

A travelling-wave model of a semiconductor optical amplifier based non-linear loop mirror is developed to investigate the importance of travelling-wave effects and gain/phase dynamics in predicting device behaviour. A constant effective carrier recovery lifetime approximation is found to be reasonably accurate (±10%) within a wide range of control pulse energies. Based on this approximation, a heuristic model is developed for maximum computational efficiency. The models are applied to a particular configuration involving feedback.

Impedance analysis of Al2O3/H-terminated diamond metal-oxide-semiconductor structures

Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al2O3 is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed.

Temperature-dependent internal quantum efficiency of blue high-brightness light-emitting diodes

Internal quantum efficiency (IQE) of a blue high-brightness InGaN/GaN light-emitting diode (LED) was evaluated from the external quantum efficiency measured as a function of current at various temperatures ranged between 13 and 440 K. Processing the data with a novel evaluation procedure based on the ABC-model, we have determined the temperature-dependent IQE of the LED structure and light extraction efficiency of the LED chip. Separate evaluation of these parameters is helpful for further optimization of the heterostructure and chip designs. The data obtained enable making a guess on the temperature dependence of the radiative and Auger recombination coefficients, which may be important for identification of dominant mechanisms responsible for the efficiency droop in III-nitride LEDs. Thermal degradation of the LED performance in terms of the emission efficiency is also considered.

Simultaneous demultiplexing, data regeneration, and clock recovery with a single semiconductor optical amplifier-based nonlinear-optical loop mirror

We demonstrate simultaneous demultiplexing, data regeneration and clock recovery at 10Gbits/s, using a single semiconductor optical amplifier–based nonlinear-optical loop mirror in a phase-locked loop configuration.

Bistability and hysteresis in an optically injected two-section semiconductor laser

The effect of coherent single frequency injection on two-section semiconductor lasers is studied numerically using a model based on a set of delay differential equations. The existence of bistability between different continuous-wave and nonstationary regimes of operation is demonstrated in the case of sufficiently large linewidth enhancement factors. © 2014 American Physical Society.

Optical trapping with superfocused high-M2 laser diode beam

Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of 'interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140º and rounded tip area as small as 10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of 11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160º axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.

Optical trapping with Bessel beams generated from semiconductor lasers

In this paper, we study generation of Bessel beams from semiconductor lasers with high beam propagation parameter M2 and their utilization for optical trapping and manipulation of microscopic particles including living cells. The demonstrated optical tweezing with diodegenerated Bessel beams paves the way to replace their vibronic-generated counterparts for a range of applications towards novel lab-on-a-chip configurations.

Manipulation of microparticles using Bessel beams from semiconductor lasers

Optical manipulation of microscopic objects (including living cells) using Bessel beams from semiconductor lasers has been demonstrated for the first time. In addition, it has been found in the experiments that a Bessel beam of sufficient power from a semiconductor laser makes it possible to manipulate simultaneously several microscopic objects captured into its central lobe and the first ring. © 2014 Pleiades Publishing, Ltd.

High-power operation of quantum-dot semiconductor disk laser at 1180 nm

In this letter, we report on a high-power operation of an optically pumped quantum-dot semiconductor disk laser designed for emission at 1180 nm. As a consequence of the optimization of the operation conditions, a record-high continuous-wave output power exceeding 7 W is obtained for this wavelength at a heat-sink temperature of 2 °C. A wavelength tuning over a range of 37 nm is achieved using a birefringent filter inside the cavity.

Semiconductor saturable absorber mirror passively Q-switched 2.97 μm fluoride fiber laser

A diode-cladding-pumped mid-infrared passively Q-switched Ho 3+-doped fluoride fiber laser using a reverse designed broad band semiconductor saturable mirror (SESAM) was demonstrated. Nonlinear reflectivity of the SESAM was measured using an in-house Yb3+-doped mode-locked fiber laser at 1062 nm. Stable pulse train was produced at a slope efficient of 12.1% with respect to the launched pump power. Maximum pulse energy of 6.65 μJ with a pulse width of 1.68 μs and signal to noise ratio (SNR) of ~50 dB was achieved at a repetition rate of 47.6 kHz and center wavelength of 2.971 μm. To the best of our knowledge, this is the first 3 μm region SESAM based Q-switched fiber laser with the highest average power and pulse energy, as well as the longest wavelength from mid-infrared passively Q-switched fluoride fiber lasers. © 2014 SPIE.

Optical trapping with Bessel beams generated from semiconductor lasers

In this paper, we demonstrate, for the first time to the best of our knowledge, utilization of Bessel beams generated from a semiconductor laser for optical trapping and manipulation of microscopic particles including living cells. © 2014 OSA.

Assembly of a high-dielectric constant thin TiOX layer directly on H-terminated semiconductor diamond

A high-dielectric constant (high-k) TiOx thin layer was fabricated on hydrogen-terminated diamond (H-diamond) surface by low temperature oxidation of a thin titanium layer in ambient air. The metallic titanium layer was deposited by sputter deposition. The dielectric constant of the resultant TiOx was calculated to be around 12. The capacitance density of the metal-oxide-semiconductor (MOS) based on the TiOx/H-diamond was as high as 0.75 µF/cm2 contributed from the high-k value and the very thin thickness of the TiOx layer. The leakage current was lower than 10-13 A at reverse biases and 10-7A at the forward bias of -2 V. The MOS field-effect transistor based on the high-k TiOx/H-diamond was demonstrated. The utilization of the high-k TiOx with a very thin thickness brought forward the features of an ideally low subthreshold swing slope of 65 mV per decade and improved drain current at low gate voltages. The advantages of the utilization high-k dielectric for diamond MOSFETs are anticipated.

Mode-locked semiconductor disk lasers

This paper will review the recent advances in the field of ultrashort pulse generation from optically pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs). In this review, we will summarize the most significant results presented over the last 15 years, before highlighting recent breakthroughs related to mode-locked VECSELs by different research groups. Different mode-locking techniques for OP-VECSELs are described in detail. Previously, saturable absorbers, such as semiconductor saturable absorber mirrors—external, or internal as in mode-locked integrated external-cavity surface emitting lasers (MIXSEL)—, and recently, novel-material-based carbon-nanotube and graphene saturable absorbers have been employed. A new mode-locking method was presented and discussed in recent years. This method is referred to as self-mode-locking or saturable-absorber-free operation of mode-locked VECSELs. In this context, we particularly focus on achievements regarding self-mode-locking, which is considered a promising technique for the realization of high-power, compact, robust and cost-efficient ultrashort pulse lasers. To date, the presented mode-locking techniques have led to great enhancement in average powers, peak powers, and repetition rates that can be achieved with passively mode-locked VECSELs.