Quantum Dot Lasers Research Articles

Monolithic integration of embedded III-V lasers on SOI

Silicon photonic integration has gained great success in many application fields owing to the excellent optical device properties and complementary metal-oxide semiconductor (CMOS) compatibility. Realizing monolithic integration of III-V lasers and silicon photonic components on single silicon wafer is recognized as a long-standing obstacle for ultra-dense photonic integration, which can provide considerable economical, energy-efficient and foundry-scalable on-chip light sources, that has not been reported yet. Here, we demonstrate embedded InAs/GaAs quantum dot (QD) lasers directly grown on trenched silicon-on-insulator (SOI) substrate, enabling monolithic integration with butt-coupled silicon waveguides. By utilizing the patterned grating structures inside pre-defined SOI trenches and unique epitaxial method via hybrid molecular beam epitaxy (MBE), high-performance embedded InAs QD lasers with monolithically out-coupled silicon waveguide are achieved on such template. By resolving the epitaxy and fabrication challenges in such monolithic integrated architecture, embedded III-V lasers on SOI with continuous-wave lasing up to 85 °C are obtained. The maximum output power of 6.8 mW can be measured from the end tip of the butt-coupled silicon waveguides, with estimated coupling efficiency of approximately -6.7 dB. The results presented here provide a scalable and low-cost epitaxial method for the realization of on-chip light sources directly coupling to the silicon photonic components for future high-density photonic integration.

Refractory times for excitable dual-state quantum dot laser neurons.

Excitable photonic systems show promise for ultrafast analog computation, several orders of magnitude faster than biological neurons. Optically injected quantum dot lasers display several excitable mechanisms with dual-state quantum lasers recently emerging as true all-or-none excitable artificial neurons. For use in applications, deterministic triggering is necessary and this has previously been demonstrated in the literature. In this work we analyze the crucially important refractory time for this dual-state system, which defines the minimum time between distinct pulses in any train.

Enhancement in electro-optic performance of InAlGaAs/GaAs quantum dot lasers by ex situ thermal annealing.

This Letter reports the growth, fabrication, and characterization of molecular beam epitaxy (MBE)-grown quaternary InAlGaAs/GaAs quantum dot (QD) lasers emitting at sub-900 nm. The presence of Al in QD-based active regions acts as the origin of defects and non-radiative recombination centers. Applying optimized thermal annealing annihilates the defects in p-i-n diodes, thus lowering the reverse leakage current by six orders of magnitude compared to as-grown devices. A systematic improvement in the optical properties of the devices is also observed in the laser devices with increasing annealing time. At an annealing temperature of 700°C for 180 s, Fabry-Pérot lasers exhibit a lower pulsed threshold current density at infinite length of 570 A/cm2.

Nanotechnology and Quantum Dot Lasers

In this paper, we reviewed the recent literature on quantum dot lasers. First, we started with the physics of quantum dots. These nanostructures provide limitless opportunities to create new technologies. To understand the applications of quantum dots, we talked about the quantum confinement effect versus dimensionality and different fabrication techniques of quantum dots. Secondly, we examined the physical properties of quantum dot lasers along with the history and development of quantum dot laser technology and different kinds of quantum dot lasers compared with other types of lasers. Thirdly, we made a market search on the practical usage of quantum dot lasers. Lastly, we predicted a future for quantum dot lasers.

Analysis and Demonstration of the Quantum Dot Lasers

Contemporarily, with the rapid development of laser techniques, various types of lasers have been invented covering almost all the visible wavelength and even near infrared or ultraviolet wavelength. However, the properties of laser can be boosted and enhanced with the state-of-art techniques to fulfill the needs for advanced applications. With the invention and realization of quantum dots, it is feasible to enhance the performance of the laser feature (e.g., spread, efficiency, luminosity) based on the dose of the quantum dots. This study will discuss the realization of the quantum dot lasers and demonstrate the different types of ways as well as performances. Specifically, lasers based on self-assembled quantum dots, colloidal quantum dots, and carbon quantum dots will be discussed. According to the analysis, the features and construction methods as well as drawbacks of different types of quantum dots laser are clarified.s Overall, these results shed light on guiding further exploration of quantum dot lasers as well as implementations of quantum dots.

Recent Progress of Non-Cadmium and Organic Quantum Dots for Optoelectronic Applications with a Focus on Photodetector Devices

Quantum dots (QDs) are zero-dimensional (0D) nanomaterials with charge confinement in all directions that significantly impact various applications. Metal-free organic quantum dots have fascinating properties such as size-dependent bandgap tunability, good optical absorption coefficient, tunability of absorption and emission wavelength, and low-cost synthesis. Due to the extremely small scale of the materials, these characteristics originated from the quantum confinement of electrons. This review will briefly discuss the use of QDs in solar cells and quantum dots lasers, followed by a more in-depth discussion of QD application in photodetectors. Various types of metallic materials, such as lead sulfide and indium arsenide, as well as nonmetallic materials, such as graphene and carbon nanotubes, will be discussed, along with the detection mechanism.

Low-threshold visible InP quantum dot and InGaP quantum well lasers grown by molecular beam epitaxy

III-V lasers based on self-assembled quantum dots (QDs) have attracted widespread interest due to their unique characteristics, including low threshold current density (Jth), low sensitivity to backreflections, and resistance to threading dislocations. While most work to date has focused on 1.3 μm InAs/GaAs QDs, InP QDs have also aroused interest in lasers emitting at visible wavelengths. Molecular beam epitaxy (MBE) enables the growth of high-density InP/AlGaInP QDs on exact (001)-oriented GaAs substrates but requires a relatively low substrate temperature of <500 °C. The low substrate temperature used for phosphide growth in MBE leads to degraded optical properties and makes post-growth annealing a crucial step to improve the optical quality. Here, we report the exceptional thermal stability of InP/AlGaInP QDs grown using MBE, with up to 50× improvement in room temperature photoluminescence intensity with the optimization of annealing temperature and time. We also demonstrate the room temperature pulsed operation of InP multiple quantum dot (MQD) lasers on GaAs (001) emitting close to 735 nm with Jth values of 499 A/cm2 after annealing, a factor of 6 lower than their as-grown counterparts and comparable to such devices grown by MOCVD. In0.6Ga0.4P single quantum well (SQW) lasers on GaAs (001) also exhibit a substantial reduction in Jth from 340 A/cm2 as-grown to 200 A/cm2 after annealing, emitting at 680 nm under pulsed operation conditions. This work shows that post-growth annealing is essential for realizing record-performance phosphide lasers on GaAs grown by MBE for applications in visible photonics.

Experimental Investigation on the Mode Characteristics of an Excited-State Quantum Dot Laser under Concave Mirror Optical Feedback

In this paper, we experimentally investigated the mode configuration of an excited-state quantum dot laser (ESQDL) under concave mirror optical feedback, and the influences of the feedback strength on the mode characteristics were analyzed. The results showed that after introducing concave mirror optical feedback, some longitudinal modes of the excited-state (ES) existing in a free-running ESQDL could be suppressed. When the feedback strength increased to a certain extent, the ground-state (GS) emission occurred and co-existed with the ES emission. By further increasing the feedback strength, all the longitudinal modes of the ES emission were suppressed, and only the longitudinal modes of the GS emission could be observed. As a result, the emission-state switching from the ES to GS emission was realized. When the ESQDL was biased at a larger current, the feedback strength required to achieve emission-state switching was stronger.

Improvement of Absorption and Emission Phenomena of 1.55µm Quantum Dot Laser using Indium Nitride

This paper presents the improvement of emission and absorption phenomena of 1.55µm quantum dot laser by enhancing the stability of oscillation frequency and minimizing absorption loss. Among the key parameters related to these absorption and emission phenomena, the effective density of state, rate of change of carrier mobility, and optical feedback level were extensively investigated to reduce the fluctuation of the oscillation frequency of the emitted light as well as the absorption loss. These phenomena were investigated through mathematical analysis and numerical simulation using AlN, GaN, and InN quantum dots as the active material of the laser structure. The numerical results were compared, confirming that the InN quantum dot in the active layer significantly improved the absorption and emission phenomena of the quantum dot laser. At the same time, InN is capable of emitting light at a wavelength of 1.55µm due to its band gap of 0.7eV. Consequently, InN has a superior potentiality to other existing materials to fabricate the quantum dot laser operating at the 1.55µm wavelength, which is the window of an optical fiber communication system that offers the lowest attenuation. Therefore, the InN quantum dot laser is expected to be a promising candidate not only in the field of semiconductor technology but also in the field of optical communication in the imminent future.

Systematic Study of External Optical Feedback Tolerance in 1300 nm Quantum Dot Lasers

Resilience of 1300nm In(Ga)As/GaAs quantum dot lasers to external optical feedback is systematically investigated from − 10°C to 85 °C. The high-resolution spectral and current-dependent linewidth enhancement factor is measured for all modes in the positive net modal gain region. Complimentary to that, analysis of the free-running and under deployment specific feedback relative intensity noise is discussed in the context of compliance against the IEEE 802.3ah specifications at the full range of temperatures.

Tailored Frequency Conversion Makes Infrared Light Visible for Streak Cameras

Streak cameras are one of the most common and convenient devices to measure pulsed emission, e.g., from semiconductor lightsources with picosecond time resolution. However, they are most sensitive in the visible range and possess low or negligible efficiency in the infrared and telecom regime. In this work, we present a frequency conversion based on sum-frequency generation that converts infrared to visible signals while preserving their temporal properties, making them detectable with a streak camera. We demonstrate and verify the functionality of our device by converting the emission from a quantum dot laser.

On the relation between electrical and electro-optical properties of tunnelling injection quantum dot lasers

Abstract We present a comprehensive study of the temperature dependent electronic and optoelectronic properties of a tunnelling injection quantum dot laser. The optical power-voltage (P opt–V) characteristics are shown to be correlated with the current-voltage (I–V) and capacitance-voltage (C–V) dependencies at low and elevated temperatures. Cryogenic temperature measurements reveal a clear signature of resonant tunnelling manifested in periodic responses of the I–V and P opt–V characteristics, which diminish above 60 K. The C–V characteristics reveal a hysteresis stemming from charging and de-charging of the quantum dots, as well as negative capacitance. The latter is accompanied by a clear peak that appears at the voltage corresponding to carrier clamping, since the clamping induces a transient-like effect on the carrier density. C–V measurements lead also to a determination of the dot density which is found to be similar to that obtained from atomic force microscopy. C–V measurements enable also to extract the average number of trapped electrons in each quantum dot which is 0.95. As the important parameters of the laser have signatures in the electrical and electro-optical characteristics, the combination serves as a powerful tool to study intricate details of the laser operation.

InAs/GaAs quantum-dot lasers grown on on-axis Si (001) without dislocation filter layers.

InAs/GaAs quantum dot (QD) laser monolithically grown on silicon is one of the potential approaches to realizing silicon-based light sources. However, the mismatch between GaAs and Si generates a high density of threading dislocations (TDs) and antiphase boundaries (APBs), which trap carriers and adversely affect device performance. In this paper, we present a simple method to reduce the threading dislocation density (TDD) merely through GaAs buffer, eliminating the intricate dislocation filter layers (DFLs) as well as any intermediate buffer layers whose compositions are different from the target GaAs. An APB-free epitaxial 2.5 µm GaAs film was grown on exact Si (001) by metalorganic chemical vapor deposition (MOCVD) with a TDD of 9.4 × 106 cm-2. InAs/GaAs QDs with a density of 5.2 × 1010 cm-2 were grown on this GaAs/Si (001) virtual substrate by molecular beam epitaxy (MBE) system. The fabricated QD laser has achieved a single facet room temperature continuous-wave output power of 138 mW with a threshold current density of 397 A/cm2 and a lasing wavelength of 1306 nm. In this work, we propose a simplified method to fabricate high-power QD lasers, which is expected to promote the application of photonic integrated circuits.

High-temperature continuous-wave operation of 1310 nm InAs/GaAs quantum dot lasers

Here we report 1.3 μm electrical injection lasers based on InAs/GaAs quantum dots (QDs) grown on a GaAs substrate, which can steadily work at 110 °C without visible degradation. The QD structure is designed by applying the Stranski–Krastanow growth mode in solid source molecular beam epitaxy. The density of InAs QDs in the active region is increased from 3.8 × 1010 cm−2 to 5.9 × 1010 cm−2. As regards laser performance, the maximum output power of devices with low-density QDs as the active region is 65 mW at room temperature, and that of devices with the high-density QDs is 103 mW. Meanwhile the output power of high-density devices is 131 mW under an injection current of 4 A at 110 °C.

Extreme temperature operation for broad bandwidth quantum-dot based superluminescent diodes

The high-temperature resilience of quantum-dot (QD) laser materials is exploited to realize a broad spectral bandwidth emitter in the near infrared. For an InAs/GaAs-based QD-superluminescent light emitting diode (SLEDs), we introduced a 2000 μm long, 5 μm width ridge waveguide that is tilted by 7° and composed of eight multi-sections. With increased temperature operation over 160 °C, the spectral bandwidth is dramatically increased by thermally excited carrier transition in ES1 and ES2. Additionally, the positive net-modal gain is demonstrated at the high operating temperatures, and this is exploited in the QD-SLEDs operating at 180 °C, which exhibit a −3 dB linewidth of 270 nm and a power of 0.34 mW. The simplicity of this approach, utilizing heat alone, is contrasted with other approaches for the extremely broad spectral bandwidth emitter.

Self-Assembled and Wavelength-Tunable Quantum Dot Whispering-Gallery-Mode Lasers for Backlight Displays.

Thanks to the narrow line width and high brightness, colloidal quantum dot (CQD) lasers show promising applications in next-generation displays. However, CQD laser-based displays have yet to be demonstrated because of two challenges in integrating red, green, and blue (RGB) lasers: absorption from red CQDs deteriorates the optical gain of blue and green CQDs, and imbalanced white spectra lack blue lasing due to the high lasing threshold of blue CQDs. Herein, we introduce a facile surfactant-free self-assembly method to assemble RGB CQDs into high-quality whispering-gallery-mode (WGM) RGB lasers with close lasing thresholds among them. Moreover, these RGB lasers can lase nearly independently even when they are closely integrated, and they can construct an ultrawide color space whose color gamut is 105% of that of the BT.2020 standard. These combined strategies allow us to demonstrate the first full-color liquid crystal displays using CQD lasers as the backlight source.

Optical gain and threshold current density of strained wurtzite GaN/AlGaN quantum dot lasers

In this work, the influences of biaxial compressive and tensile strains on optical gain and threshold current density are investigated theoretically as a function of the side lengths of the quantum box in the GaN/Al0.2Ga0.8N structure by using a model based on the density matrix theory of semiconductor lasers with relaxation broadening. For various side lengths of the quantum box, we compare the spectra gain curves of compressive, tensile-strained, and unstrained structures of the GaN/Al0.2Ga0.8N cubic quantum-dot (QD) laser. The dependence of peak optical gain on carrier density and the modal gain on current density is plotted too for all cases. The results reveal that many enhancements can be made to the laser structure by introducing -0.5% compressive strain: a higher value of optical gain of 18421 cm-1 at L=60A, a lower value of transparency of carrier density of Ntr=0.13*10¨¨19 cm-3and transparency current density of Jtr=26.9 A/cm and a lower threshold current density of Jth= 78.87 A/cm2 at L=100 A.

Improving structure design of active region of InAs quantum dots by using InAs/GaAs digital alloy superlattice

A 1.3-μm InAs quantum dot laser has been successfully fabricated on a GaAs(100) substrate by molecular beam epitaxy (MBE) technique through using InAs/GaAs digital alloy superlattices instead of the conventional InGaAs layer. The samples grown by conventional growth method and the digital alloy superlattice growth method are characterized by atomic force microscope (AFM) and photoluminescence (PL) spectroscopy. It is found that 8-period sample possesses a low quantum dot density and poor luminescence performance. With the increase of the number of growth periods, the quantum dot density of the sample increases and the luminous performance improves. This indicates that the quality of the grown sample improves with the increase of InAs/GaAs period of the InGaAs layer. When the total InAs/GaAs period is 32, the quantum dot density of the sample is high and the luminescence performance is good. After the experimental measurement, the sample DAL-0 fabricated by conventional growth method and the sample DAL-32 (32-periods InAs/GaAs digital alloy superlattices) are utilized to fabricate quantum dot laser by standard process. The performances of two types of quantum dot lasers obtained with different growth methods are characterized. It is found that the InAs quantum dot lasers fabricated by the sample grown by digital alloy superlattice method have good performances. Under continuous wave operation mode, the threshold current is 24 mA corresponding to a threshold current density of 75 A/cm<sup>2</sup>. The highest operation-temperature reaches 120 ℃. In addition, InAs quantum dot laser using digital alloy superlattice has good temperature stability. Its characteristic temperature is 55.4 K. Compared with the traditional laser, the InAs quantum dot laser grown by InAs/GaAs digital alloy superlattice has good performance in terms of threshold current density, output power and temperature stability, which indicates that high-quality laser can be obtained by this growth method. Using the InAs/GaAs digital alloy superlattice growth method, the InGaAs composition can be changed without changing the temperature of the source oven. Thus InAs quantum dot lasers with different luminescence wavelengths can be obtained through this growth method. The InAs/GaAs digital alloy superlattice structure can be used to realize different averaging of In content in the growth structure. The method provides a new idea for designing and growing the active region of quantum dot laser.

Near-infrared self-assembled laser based on Ag<sub>2</sub>Se quantum dots

The development of colloidal near-infrared quantum dot (QD) lasers has been hindered by the high state degeneracy of lead salt QDs and the difficulty in coupling colloidal QDs to the resonant cavity. In this study, we show that the above challenges can be addressed by the self-assembly laser based on Ag<sub>2</sub>Se QDs. The Ag<sub>2</sub>Se QDs with the lowest quantized states 2-fold degeneracy are used to replace lead salt quantum dots to achieve low threshold near-infrared optical gain. We employ the finite element method to in depth analyze the mode field distribution and oscillation mechanism of the coffee-ring microcavity. Our results reveal that the light field oscillates in a zig-zag path along the cross-sectional area, indicating strong coupling between the QDs and the cavity mode. Furthermore, we investigate the relationship of cavity length with free spectrum range and laser emission wavelength. Using this relationship and the gain spectrum characteristics of Ag<sub>2</sub>Se QDs, we design a single-mode near-infrared laser and conduct a comprehensive analysis. The simulation results are used to fabricate a single-mode near-infrared Ag<sub>2</sub>Se QD coffee-ring microlaser, which exhibits a linewidth of 0.3 nm and a threshold of 158 μJ/cm<sup>2</sup>. Currently, it holds the record for the lowest laser threshold among near-infrared colloidal QD lasers. The increasing of the laser cavity length leads the emission wavelength to increase from 1300 nm to 1323 nm. In addition, the toxicity of Ag<sub>2</sub>Se QD is remarkably negligible. Our work promotes the development of environment-friendly near-infrared lasers toward practical lasers.

Information encoding using two-level generation in a quantum dot laser

We propose an approach for encoding and transmitting information based on the use of a quantum dot laser, which, depending on the injection current, emits either one of two or simultaneously two spectral components, with different wavelengths. When the laser is modulated by current, each lasing line is detected by an independent photodiode, and thus the information is encoded by both the intensity of each line and its wavelength. Keywords: quantum dot lasers, two-state lasing, multilevel signaling, wavelength- division multiplexing.