Light-current Characteristics Research Articles

Laser diode driver on a programmable system on a chip.

A comprehensive solution of a laser diode (LD) driver with temperature control using a programmable system on a chip is proposed as an alternative to dedicated devices. A digital proportional integral differential controller is used for regulating the LD temperature. The light-current characteristics and frequency response of the LD are measured using an external photodiode and interrogated by an integrated transimpedance amplifier. The 0.084% stability, 2kHz bandwidth, and 0.11% full scale current error are demonstrated. The LD overshoot protection is digitally implemented, providing a soft start. While the circuit is initially optimized for a 3W infrared LD, instructions are provided for fine-tuning the design according to specific LD requirements.

Particle swarm optimization-assisted approach for the extraction of VCSEL model parameters.

We propose a direct particle swarm optimization (PSO) method for extracting the parameters of a physical model describing the behavior of vertical-cavity surface-emitting lasers (VCSELs), starting from the light-current (L-I) characteristics and the small signal modulation (S21) responses, at different currents and temperatures. With an optimal choice of hyperparameters of the algorithm, the method is able to predict parameters that accurately reproduce the behavior of the device. Its prediction capabilities are compared to those of two commonly used nonlinear optimizers (Interior Point and Levenberg-Marquardt), to benchmark its performances.

Internal optical loss and light-current characteristic in injection lasers

Possibility of tailoring the light-current characteristic (LCC) shape in quantum dot (QD) lasers by varying uniformity of QDs is discussed. Making the QD ensemble less uniform results in roll-over in the LCC. The second branch in the LCC appears with making the QD ensemble even less uniform.

Time-resolved measurements of light–current characteristic and mode competition in pulsed THz quantum cascade laser

Quantum cascade lasers (QCL) are widely adopted as prominent and easy-to-use solid-state sources of terahertz radiation. Yet some applications require generation and detection of very sharp and narrow terahertz-range pulses with a specific spectral composition. We have studied time-resolved light-current (L–I) characteristics of multimode THz QCL operated with a fast ramp of the injection current. Detection of THz pulses was carried out using an NbN superconducting hot-electron bolometer with the time constant of the order of 1 ns while the laser bias current was swept during a single driving pulse. A nonmonotonic behavior of the L–I characteristic with several visually separated subpeaks was found. This behavior is associated with the mode competition in THz QCL cavity, which we confirm by L–I measurements with use of an external Fabry–Perot interferometer for a discrete mode selection. We also have demonstrated the possibility to control the L–I shape with suppression of one of the subpeaks by simply adjusting the off-axis parabolic mirror for optimal optical alignment for one of the laser modes. The developed technique paves the way for rapid characterization of pulsed THz QCLs for further studies of the possibilities of using this approach in remote sensing.

Studying the light current characteristics of VCSEL by changing oxide confinement aperture

GaAs-based VCSELs with oxide-confined (OC) are performed by using fine selective radial “oxidation of AlAs-rich (AlGaAs) layers” from outside to the device axis leaving the central part unaffected. Such oxide apertures produced inside the cavities enhance the radial confinements related to current spreading and to a field that is optical altogether. A Modern design with a single fundamental mode is proposed to reduce threshold current operation to the extent of higher output by using the two OC VCSELs. Both of the oxide apertures were added to the node position of the resonator standing wave. Then, the diameters of together apertures can be adjusted independently giving VCSEL design an extra degree of freedom that allows optimization. It found that when both apertures had a radius of 4.2 µm, the low threshold current operation at a higher extent output is achieved with a single fundamental mode.

The Effect of the Carrier Drift Velocity Saturation in High-Power Semiconductor Lasers at Ultrahigh Drive Currents

Experimental light-current characteristics of high-power semiconductor lasers operating at ultrahigh drive currents have been studied in terms of numerical models taking into account the effect of the carrier drift velocity saturation. It was shown that the simplest diffusion-drift (DD) model underestimates the optical loss at high drive currents, which leads to overestimation of the peak optical power when compared with the experimental results. The inclusion of the carrier drift velocity saturation effect into the DD model results in that a strong-electric-field domain is formed at the interface with the active region on the side of the p-emitter already at low drive currents. The amplitude of this field substantially grows as the current increases further, which restricts application of this model to description of high-power semiconductor lasers at high drive currents. With the nonlocal energy-balance model used to describe the carrier transport in the laser heterostructure, it becomes possible to take into account the effect of carrier heating by the electric field. As a result of the carrier heating, the drift velocity decreases and the concentration of excess carriers in the waveguide layer grows, compared with the simplest DD model. The inclusion of the additional internal optical loss mechanism obtained in the energy-balance model provided a satisfactory coincidence of the calculated light-current characteristics with the experimental dependences.

Evanescently Coupled DBR Laser Arrays in the 760–770 nm Wavelength Range

In this letter, we present evanescently coupled semiconductor laser arrays designed with a distributed Bragg reflector section for spectrally narrow emission and a combined waveguide section for high optical output powers. These devices were designed and fabricated in the AlGaAs material system with an InGaAsP quantum well providing emission in the 760–770 nm wavelength range. Measurements of the light-current characteristics reveal high optical output powers of 600 mW at 20 °C and 700 mW at 5 °C limited by thermal rollover without any signs of a catastrophic optical mirror damage or rapid power degradation. Spectrally narrow emission of 0.2 nm at −3 dB and a high wavelength stability with a small current tuning coefficient of 0.7 pm/mA were found. Far-field investigations reveal pre-dominant coupling of lowest order in-phase supermode emission without any sections for adjusting the phase of the electrical field vector for adjacent elements.

Electrical and optical properties of photodiode structures formed by surface polymerization of P(Egdma-Vpca)-Swcnt films on n-si

Abstracts Poly (ethylene glycol dimethacrylate-1-vinyl-1H-pyrrole-2-carboxylic acid)/carbon nanotube, single-walled)/n-Si ([P(EGDMA-VPCA)-SWCNT]/n-Si) photodiode structures was fabricated by using surface polymerization method. While electrical properties were measured at different temperatures, optical properties were measured at room temperatures. Dark and light current characteristics were investigated. Spectral photoresponse measurements of the structure were realized at room temperature. They showed that the fabricated structure exhibited rectification behavior, which makes it a good nominee for optoelectronic implementation area.

Digitally Chirped Multilayer Quantum Dot Lasers with Dual-Wavelength Lasing Emissions

The dual-wavelength lasing emissions of digitally chirped multilayer quantum dot (QD) lasers are investigated both experimentally and theoretically. The two lasing wavelengths are both identified as ground-state (GS) emissions but originated from different stacks of QD multilayers. The lasing spectra exhibited broadening and splitting properties by injecting more current. Moreover, the wavelength-resolved light-current characteristics reveal that first GS lasing intensity upon the threshold of second GS transitions neither saturates nor droops with increasing injection current, but increases with slightly reduced slope efficiency. A theoretical model is developed for digitally chirped multilayer QD lasers. The simulation results qualitatively reproduce the experimental observations.

Evolution of light‐current characteristic shape in high‐power semiconductor quantum well lasers

The light-current characteristic (LCC) of semiconductor quantum well lasers is theoretically studied. It is discussed here that, due to internal optical absorption loss, which depends on the electron and hole densities in the optical confinement layer, (i) roll-over of the LCC occurs with increasing injection current, and, (ii) depending on the parameters of laser structures, the LCC can have two branches, i.e. the optical emission at two different output powers will be possible within a certain range of injection currents.

Electrical and optical properties of photodiode structures formed by surface polymerization of [P (EGDMA-VPCA)-SWCNT] films on n-GaAs

Poly (ethylene glycol dimethacrylate-1-vinyl-1H-pyrrole-2-carboxylic acid)/carbon nanotube, single-walled)/n-GaAs ([P (EGDMA-VPCA)-SWCNT]/n-GaAs) photodiode structures were fabricated by using surface polymerization method. Electrical and optical properties were measured at several temperatures. Dark and light current characteristics were investigated. Spectral photoresponse measurements of the structure were made at room temperature. The maximum open circuit voltage (Voc) and short-circuit current (Isc) values for the diode under 20 mW/cm2 were obtained to be 0.52 V and 54.63 μA respectively. That showed that the fabricated structure exhibited rectification behavior that makes it a good candidate for optoelectronic device applications.

Enhanced Device Performance of GaInN-Based Green Light-Emitting Diode with Sputtered AlN Buffer Layer

In this study, we compared the device performance of GaInN-based green LEDs grown on c-plane sapphire substrates with a conventional low temperature GaN buffer layer to those with a sputtered-AlN buffer layer. The light output power and leakage current characteristics were significantly improved by just replacing the buffer layer with a sputtered-AlN layer. To understand the origin of the improvement in performance, the electrical and optical properties were compared by means of electro-reflectance spectroscopy, I–V curves, electroluminescence spectra, L–I curves, and internal quantum efficiencies. From the analysis of the results, we concluded that the improvement is mainly due to the mitigation of strain and reduction of the piezoelectric field in the multiple quantum wells active region.

Wide-Temperature-Range (25–80 °C) 53-Gbaud PAM4 (106-Gb/s) Operation of 1.3-μm Directly Modulated DFB Lasers for 10-km Transmission

A 1.3- μ m directly modulated distributed feedback laser was newly developed by adopting an asymmetric corrugation pitch modulated grating structure and an InGaAlAs multiquantum well active layer with both a high optical confinement factor and a high differential gain. A low threshold current and a large saturation current in light-current characteristics at high temperature were obtained and a high 3-dB bandwidth and a high relaxation oscillation frequency in electro-optical characteristics were also achieved over a wide temperature range. As a result, clear back-to-back eye openings were achieved for 26-Gbaud PAM4 (53-Gb/s) operation from 25 to 95 °C with large outer extinction ratio and sufficiently small transmission dispersion eye closure quaternary. Furthermore, 53-Gbaud PAM4 (106-Gb/s) operation from 25 to 80 °C was successfully demonstrated for both back-to-back and after 10-km single mode fiber transmission. These excellent characteristics make our DFB laser a promising cost-effective and compact transceiver with low power consumption for next-generation 400GbE applications.

Chirped multilayer quantum-dot mode-locked lasers with dual-wavelength and ground-state lasing emissions

Monolithic passively mode-locked lasers are investigated based on chirped multilayer InAs/InGaAs quantum-dot (QD) structure. The forward and backward tracings of light–current characteristics show two kinks and two hysteresis loops. The optical spectra reveal two lasing wavelengths around 1273 and 1230 nm, which are identified as two ground-state emissions of two differently chirped QD layers. The corresponding radio-frequency (RF) spectra of high-speed detector reveal two RF peaks at 16.21 and 16.03 GHz, which are attributed to fundamental mode-locking of two respective wavelengths. The laser pulses are confirmed by optical autocorrelator to exhibit dual-wavelength mode-locking. The pulsed characteristics of two lasing wavelengths are also discussed in terms of operating conditions.

Power Characteristics and Temperature Dependence of the Angular Beam Divergence of Lasers with a Near-Surface Active Region

Results are presented of a study of light–current characteristics and far-field patterns of emission of stripe lasers with coupled planar waveguides. This configuration makes it possible to suppress the generation of excited modes and to have a small (about 0.9 μm) depth of the active region from the surface of the laser crystal. A high-temperature stability of the angular emission divergence (34.0° ± 1.5°) in the temperature range 20–80°C is demonstrated. The largest value of the output power is limited to 12.2 W in the continuous-wave mode by the catastrophic mirror damage.

Мощностные характеристики и температурная зависимость угловой расходимости излучения лазеров с приповерхностной активной областью

AbstractResults are presented of a study of light–current characteristics and far-field patterns of emission of stripe lasers with coupled planar waveguides. This configuration makes it possible to suppress the generation of excited modes and to have a small (about 0.9 μm) depth of the active region from the surface of the laser crystal. A high-temperature stability of the angular emission divergence (34.0° ± 1.5°) in the temperature range 20–80°C is demonstrated. The largest value of the output power is limited to 12.2 W in the continuous-wave mode by the catastrophic mirror damage.

Research on Photoelectric Characteristics of VCSEL

In order to simulate the light-current (LI) characteristics of the Vertical Cavity Surface Emitting Laser (VCSEL), we adopted the simplex method to determine the optimal solution of the model parameters on the basis of experimental data. Besides, improvement was made to fit the current-voltage (IV) data using the relationship which accounted for a resistance in series with a diode, and it was more appropriate to fit LI curves according to the model evaluation index. Furthermore, the improved model can be applied to fit the LI curves at different ambient temperatures, and it illustrates that maximum value of the output power decreases as the ambient temperature increases.

Quantum Efficiency of Quantum Dot Lasers

The quantum efficiency relates the calculated to the measured external threshold current of a laser. This quantity is often estimated from the length dependence of the external differential efficiency above threshold, assuming the carrier density is pinned. Often it is also assumed that the internal current varies linearly with the external current; it is shown here this is not the case due to the effect of stimulated emission on the current-voltage relation of the active region. Furthermore, it has been observed that spontaneous emission from inhomogeneous quantum dots does not pin above threshold which questions the determination of their optical loss. This nonpinning is reproduced by a model in which the laser photon rate equation is coupled to rate equations for the occupation of dot states mediated by a thermal phonon distribution. The threshold current from this model agrees with a Fermi–Dirac calculation but the external efficiency above threshold is lower and its length dependence gives a smaller value of mode loss than the input value. The reasons for this behavior are analyzed and it is concluded that a Fermi–Dirac calculation does not represent the light–current characteristics in quantum dot lasers at room temperature.

Room-Temperature Spin Polariton Diode Laser.

A spin-polarized laser offers inherent control of the output circular polarization. We have investigated the output polarization characteristics of a bulk GaN-based microcavity polariton diode laser at room temperature with electrical injection of spin-polarized electrons via a FeCo/MgO spin injector. Polariton laser operation with a spin-polarized current is characterized by a threshold of ∼69 A/cm^{2} in the light-current characteristics, a significant reduction of the electroluminescence linewidth and blueshift of the emission peak. A degree of output circular polarization of ∼25% is recorded under remanent magnetization. A second threshold, due to conventional photon lasing, is observed at an injection of ∼7.2 kA/cm^{2}. The variation of output circular and linear polarization with spin-polarized injection current has been analyzed with the carrier and exciton rate equations and the Gross-Pitaevskii equations for the condensate and there is good agreement between measured and calculated data.

Increase in the internal optical loss with increasing pump current and the output power of quantum well lasers

The operating characteristics of semiconductor quantum-well lasers, calculated with consideration for an increase in the internal optical loss in the waveguide region with increasing pump current, are presented. The condition of global electroneutrality in the structure is used. This condition consists in that the total charge of electrons in the 2D active region (quantum well) and bulk waveguide region (optical confinement layer) is equal to the total charge of holes in these two regions. Good agreement between the calculated and experimentally determined light–current characteristics is obtained.