We report on lasing wavelength switching effects in InAs/InGaAs/GaAs quantum dot (QD) edge-emitting lasers activated by electrical and additional optical pumping provided by another edge-coupled QD laser. The lasers under study operate either on the ground state (GS) or on the excited state (ES). Optical pumping is provided by either GS (1260 nm) or ES (1180 nm) emission. Thus, we have evaluated four combinations of lasing modes and pumping wavelengths. Pumping of QD laser operating on ES transition with light from the GS transition results in suppression of ES lasing, with only GS emission detected. In the other three cases, optical pumping does not change the lasing mode. The switching effects resemble the behavior of biological neurons and can be useful for designing neuromorphic photonic integrated circuits.

The increasing demand for wearable health trackers has sparked the development of innovative sensor technologies based on nanomaterials. Zinc oxide (ZnO) has emerged as a promising platform due to its low toxicity, piezoelectric and semiconductor properties, making it ideal for advanced sensor applications. In this study, we fabricate flexible pressure sensors employing ZnO nanowires encapsulated in a polymer matrix. The hydro- thermal growth method allows for the simple fabrication of the devices. The sensors demonstrate both resistive and capacitive responses to an external load, enabling accurate pressure measurements. The sensors exhibit a wide measurement range of up to 2 MPa with a detection limit as low as 10 Pa and a sensitivity of up to 4 %center dot kPa-1 . Additionally, we demonstrate the response to changes in temperature that can be distinguished from the response to a change in a mechanical load allowing for simultaneous pressure and temperature readings. Overall, our results suggest the prospects for these feasible, multifunctional flexible sensors to be utilized in portable health diagnostic systems and electronic skin.

We demonstrate that microlasers with an anisotropic cavity (lima & ccedil;on- or quadrupole-shaped) containing quantum well-dots in the active region are able to operate under continuous wave current injection at 90 degrees C. Deviation of the cavity shape from circular leads to the directionality of the emission in the lateral direction, while the quality factor of the structures and threshold current remain almost unchanged. The quality factor is estimated to be at least 105. A single lobe dominates in the far field of lima & ccedil;on-shaped microlasers, while quadrupole-shaped microlasers are characterized by two lobes emitted in opposite directions. The lobe of the directional diagram of the lima & ccedil;ons has an angular size of about 50 degrees in the lateral direction and about 8 degrees in the vertical direction. The measured far-field profiles of these microlasers are in excellent agreement with simulations results.

Light emitting diodes (LEDs) based on III-V semiconductors are in great demand for many applications and tend to be miniaturized. However, with downscaling of planar LEDs, the surface states on the structure sidewalls, acting as nonradiative recombination centers, begin to play a significant role and deteriorate the device performance. The transition from planar to nanowire-based geometry helps to overcome this limitation. Here, we introduce a bottom-up microLED structure based on epitaxial GaP/GaAsPN/GaP nanowire arrays grown on low-cost Si(111) wafers. The active region demonstrates bright photoluminescence in the red spectral region while the radial p-i-n structure allows for electrical pumping. The opto-electrical characteristics and performance of the suggested microLEDs remain with the miniaturization of the devices down to microscale equivalent lateral size. Moreover, we didn't observe an efficiency cliff even for current density exceeding 300 A cm-2. The proposed architecture paves the way to a new generation of nanowire-based microLEDs.

We study the current-controlled lasing switching from the ground state (GS) to the excited state (ES) transition in broad-area (stripe width 100 mu m) InGaAs/GaAs quantum well-dot (QWD) and quantum well (QW) lasers. In the lasers with one QWD layer and a 0.45 mu m-thick GaAs waveguide, pure GS lasing takes place up to an injection current as high as 8 A (40 kA/cm2). In contrast, in QW lasers with a similar design, ES lasing emerges already at 3 A (15 kA/cm2). The ES lasing in the QWD lasers is observed only in the devices with a waveguide thickness of 0.78 mu m that supports a 2nd order transverse mode at the wavelength of the ES transition. Increasing the modal gain in the lasers with 0.78 mu m-thick waveguide by using two QWD layers in the active region suppresses the ES lasing. (c) 2024 Optica Publishing Group. All (AI) training, and similar technologies, are reserved.

The static and dynamic characteristics of waveguide photodetectors with an absorbing region based on InGaAs/GaAs quantum well-dots were studied at room temperature. The absorption band of InGaAs/GaAs quantum well-dots is in the spectral range from 900 to 1100 nm. The waveguide photodetectors have a width of 50 μm and a length of the absorbing region from 92 μm to 400 μm. A low dark current density (1.1 and 22 μA/cm 2 at -1 and -20 V) and cut off frequency of 5.6 GHz, limited by the time constant of a parasitic equivalent electric RC-circuit, were obtained. Keywords:waveguide photodetector, modulation frequency, quantum well-dots, integrated photonics.

In this work, we have grown vertically oriented ZnO microstructures via low-temperature hydrothermal method using microsphere photolithography and followed by etching to prepare the growth substrate and establish ZnO nucleation areas. The synthesized structures were rod-shaped ZnO microcrystals with a height of 5 mu m and a diameter of about 400 nm. Such structures were encapsulated in polydimethylsiloxane (PDMS) for ZnO-PDMS membrane formation. Based on this membrane, flexible and solid pressure sensors were fabricated. All sensors have been studied using electrical impedance spectroscopy in terms of the change in resistance and electrical capacitance when pressure is applied. A correlation between the electrical characteristics of such sensors and an applied mechanical pressure was demonstrated. One of such sensors shows the possibility of synchronous measurement of pressure and temperatures in the range of 25 degrees C - 100 degrees C was demonstrated. Fabricated sensors can find their application in the field of personalized healthcare and for the advancement of electronic skin (E-skin).

In this work, we investigate microlasers with InGaAs/GaAs quantum well-dots in the active region with broken rotational symmetry of the cavity. For the first time, lasing at elevated temperatures has been demonstrated for limaçon-and quadrupole-shaped injection microlasers. Deviation of the cavity shape from the circular leads to the directionality of the emission in the lateral direction. The quality factor of structures is estimated to be at least $10^{5}$. The minimum linewidth was found to be $\sim 200 \mathrm{MHz}$. The emitted power in the selected direction increases with increasing deformation parameter and achieves 3 times more than that of the symmetric microcavity in the range of 40 degrees.

We report on the implementation of a terahertz two-photon quantum cascade laser operating in a continuous wave mode. Lasers that can emit two photons as a result of the relaxation of a single electron between two states of the same parity have been discussed since the early days of the laser era, but implementation has been hampered by the lack of a suitable gain medium. The semiconductor structure of a quantum cascade laser seems to be an ideal medium for realizing such two-photon emission. Our work demonstrates dual-band laser radiation in the range of 3.1-3.9 THz (104-130 cm(-1)) at temperatures up to 90 K.

A technique is proposed for determining the temperature of a laser diode operating in a continuous mode, as well as thermal resistance of the device by comparing its current-voltage characteristic with pulsed current-voltage characteristics measured at different temperatures. The technique was applied to a ∅200 μm half-disk microlaser with an active region based on InGaAs/GaAs quantum dots. It was found that at currents corresponding to the peak laser power and lasing quenching due to overheating of the active region, the device temperature reaches 101 and 149°C, respectively. The thermal resistance of the laser is 110 K/W.

The temperature characteristics of ring lasers with a diameter of 480 μm of an original design with an active region based on 10 layers of InAs/InGaAs/GaAs quantum dots are studied. The lasers demonstrated a low threshold current density (200 A/cm2 at 20oC), the characteristic temperature of the threshold current in the range of 20-100oC was 68 K, the maximum lasing temperature was as high as 130oC. These values are only slightly inferior to the parameters of the edge-emitting lasers fabricated from the same epitaxial wafer. Keywords: semiconductor ring lasers, InAs/GaAs quantum dots, optical waveguide, temperature characteristics.

The power and temperature characteristics of Ø200 µm half-disk microlasers with a half-ring metal contact and high-density InGaAs/GaAs quantum dots are studied. In a continuous wave (CW) mode, the maximal optical power at 20°C was 134 mW, and the maximal CW lasing temperature reached 113°C. In a pulsed regime the maximal optical power of 1.6 W, limited by catastrophic degradation, was achieved. By comparing the CW and pulsed current–voltage characteristics, the dependence of a microlaser temperature on CW pumping current was determined. At CW currents corresponding to the maximal wall-plug efficiency, the maximal optical power, and complete lasing quenching, the laser temperatures were 60, 99, and 149°C, respectively.

A model is proposed that makes it possible to analytically analyze the speed performance of a waveguide p-i-n photodiode with a light-absorbing region representing a multilayered array of quantum dots separated by undoped spacers. It is shown that there is an optimal number of layers of quantum dots, as well as an optimal thickness of the spacers, which provide the widest bandwidth. The possibility of achieving a frequency range (at the level of -3 dB) above 20 GHz for waveguide photodiodes based on InGaAs/GaAs quantum well-dots is shown Keywords: photodiode, quantum dots, speed.

We report on half-ring lasers that are 100–200 µm in diameter and are fabricated by cleaving the initial full rings into halves. Characteristics of the half-ring and half-disk lasers fabricated from the same wafer are compared. The active area of the microlasers is based on the quantum heterostructures of mixed (0D/2D) dimensionality, referred to as quantum well-dots with very high material gain. Half-ring lasers show directional light emission and single-mode lasing near the threshold. A maximal continuous-wave output power of 76 mW is achieved for a half-ring that is 200 µm in diameter. Half-rings demonstrate better wall-plug efficiency as compared to half-disks. Lasing in pulse mode is observed up to 140 °C, the characteristic temperature is 100–125 K, depending on the half-ring size. P-side down bonding onto Si-board significantly improves power and temperature characteristics. In CW mode, lasing is maintained up to 97 °C, limited by active-area overheating.

In this work, we study the characteristics of semiconductor microlasers based on the heterostructure with two coupled waveguides intended to improve heat dissipation in cw regime. We analysed total output optical loss of the microlasers, their spectral characteristics, output power, emission pattern and thermal resistance. We observed that the use of the principle of two coupled resonant planar waveguides, active and passive, as well as p-side down bonding, significantly reduces the thermal resistance of microlasers and improves their performance.

In the present work, we study the possibility of the emission output of a semiconductor microring laser through a radially coupled optical waveguide. Room temperature lasing has been achieved in continuous wave regime with the wavelength of similar to 1090 nm. The characteristics of microlasers with and without waveguide have been compared. We have performed a spatial scanning with simultaneous detection of the laser radiation at an injection current above the threshold. We have observed an increase in the output power up to two times due to the use of a coupled waveguide.

A model is proposed that makes it possible to analytically analyze the speed performance of a waveguide p-i-n photodiode with a light-absorbing region representing a multilayered array of quantum dots separated by undoped spacers. It is shown that there is an optimal number of layers of quantum dots, as well as an optimal thickness of the spacers, which provide the widest bandwidth. The possibility of achieving a frequency range (at the level of -3 dB) above 20 GHz for waveguide photodiodes based on InGaAs/GaAs quantum well-dots is shown.

The static and dynamic characteristics of waveguide photodetectors with an absorbing region based on InGaAs/GaAs quantum well-dots were studied at room temperature. The absorption band of InGaAs/GaAs quantum well-dots is in the spectral range from 900 to 1100 nm. The waveguide photodetectors have a width of 50 µm and a length of the absorbing region from 92 µm to 400 µm. A low dark current density (1.1 и 22 μA/cm^2 at -1 и -20 V) and cut off frequency of 5.6 GHz, limited by the time constant of a parasitic equivalent electric RC circuit, were obtained.

We discuss the origin of optical losses in microdisk lasers with a dense array of InGaAs quantum dots in the active region. In particular, we study the effect of microlaser diameter $\mathbf {D}$ variation from 15 to $200~\mu \text{m}$ on optical losses of different nature. A strong dependence of the lasing wavelength on the diameter is observed: the blue-shift with decreasing disk size implies an increase in optical losses, although in the case of an ideal cylinder, a noticeable optical loss should appear only at diameters comparable to the wavelength of light. A comparison of the spectral characteristics of microlasers with those of broad-area stripe lasers, for which optical loss can be easily found, gives a tool to evaluate optical loss in microdisk lasers, which was found to be unexpectedly high. It changes $\boldsymbol {\propto }\mathbf {D}^{\mathbf {-1}}$ from $\sim 100$ cm−1 in the smallest microlasers to ~ 5 cm−1 in the largest ones. Several possible physical mechanisms of the appearance of optical losses in microlasers are considered, such as radiative loss due to the curvature of the cylindrical cavity, free carrier absorption, light scattering due to roughness of the side walls, and absorption of light in the near-surface region. The latter type of optical loss was found to be the dominant one and can explain the experimental results once the absorbing layer with a thickness of $2~\mu \text{m}$ was suggested. Using the Gaussian approximation for Using the Gaussian approximation for the gain spectrum, the wavelength-loss relationship was simulated and a good agreement with the experimental dependence was found. The variation of the experimental results on optical loss for nominally identical microlasers was attributed to the variation of the scattering loss. The same reason can explain the scatter of the slope efficiency, which varies from $\sim ~0.03$ to 0.25 W/A being governed by the ratio of the scattering loss to the surface absorption loss.

We discuss the static characteristics and high-frequency performance of microdisk lasers with an active region based on dense array of InGaAs/GaAs quantum well-dots having the improved thermal resistance. The decrease in thermal resistance of the microlasers is achieved by epi-side down bonding on a heat-conducting Si substrate. Compared to the characteristics of initial microlasers, the bonding results in a in thermal resistance decreasing by a factor of 2.3 (1.8) in microdisks with a diameter of 19 (31)µm, Further improvement of heat removal is achieved by a thinner epitaxial structure between the active region and the heatsink, realized by concept of two coupled resonant planar waveguides. Using this method, we managed to place the active region at a distance of only 870 nm from the surface of the heterostructure and achieve the record low thermal resistance of 0.17 K/mW in bonded lasers.