Improved performance of InGaAs/GaAs microdisk lasers epi-side down bonded onto a silicon board
We study the impact of improved heat removal on the performance
of InGaAs/GaAs microdisk lasers epi-side down
bonded onto a silicon substrate. Unlike the initial characteristics
of microlasers on a GaAs substrate, the former’s
bonding results in a decrease in thermal resistance by a factor
of 2.3 (1.8) in microdisks with a diameter of 19 (31) m,
attributed to a thinner layered structure between the active
region and the substrate and the better thermal conductivity
of Si than GaAs. Bonded microdisk lasers show a
2.4–3.4-fold higher maximum output power, up to
21.7 mW, and an approximately 20% reduction in the
threshold current. A record high 3 dB small-signal modulation
bandwidth of 7.9 GHz for InGaAs/GaAs microdisk
lasers is achieved.
High-performance injection microdisk (MD) lasers grown on Si substrate are demonstrated for the first time, to the best of our knowledge. Continuous-wave (CW) lasing in microlasers with diameters from 14 to 30 μm is achieved at room temperature. The minimal threshold current density of 600 A/cm2600 A/cm2 (room temperature, CW regime, heatsink-free uncooled operation) is comparable to that of high-quality MD lasers on GaAs substrates. Microlasers on silicon emit in the wavelength range of 1320–1350 nm via the ground state transition of InAs/InGaAs/GaAs quantum dots. The high stability of the lasing wavelength (𝑑𝜆/𝑑𝐼=0.1 nm/mAdλ/dI=0.1 nm/mA) and the low specific thermal resistance of 4×10−3°C×cm2/W4×10−3°C×cm2/W are demonstrated.
An InAs/InGaAs quantum dot laser with a heterostructure epitaxially grown on a silicon substrate was used to fabricate injection microdisk lasers of different diameters (15–31 µm). A post-growth process includes photolithography and deep dry etching. No surface protection/passivation is applied. The microlasers are capable of operating heatsink-free in a continuous-wave regime at room and elevated temperatures. A record-low threshold current density of 0.36 kA/cm2 was achieved in 31 µm diameter microdisks operating uncooled. In microlasers with a diameter of 15 µm, the minimum threshold current density was found to be 0.68 kA/cm2. Thermal resistance of microdisk lasers monolithically grown on silicon agrees well with that of microdisks on GaAs substrates. The ageing test performed for microdisk lasers on silicon during 1000 h at a constant current revealed that the output power dropped by only ~9%. A preliminary estimate of the lifetime for quantum-dot (QD) microlasers on silicon (defined by a double drop of the power) is 83,000 h. Quantum dot microdisk lasers made of a heterostructure grown on GaAs were transferred onto a silicon wafer using indium bonding. Microlasers have a joint electrical contact over a residual n+ GaAs substrate, whereas their individual addressing is achieved by placing them down on a p-contact to separate contact pads. These microdisks hybridly integrated to silicon laser at room temperature in a continuous-wave mode. No effect of non-native substrate on device characteristics was found.
Lasers based on semiconductor whispering gallery mode (WGM) resonators represent a perfect platform for active small footprint high-sensitive devices for biodetection. Biochemical samples typically require aqueous solution, and the resonator should be placed into a cuvette with water or in a microfluidic chip. The characteristics of modern semiconductor WGM lasers with an active region based on InAs/InGaAs quantum dots (QDs) make them promising for creating compact highly sensitive devices for biodetection. Deep localization of carriers in InAs/InGaAs QDs and suppressed lateral migration helps us to obtain room-temperature lasing in microdisk lasers immersed in an aqueous medium. In this work, we studied the sensitivity of the microdisk laser resonance spectral position to the refractive index of the surrounding material by changing the salinity of the water solution. We also successfully detected model proteins (secondary antibodies attached to the microdisk surface) via measurement of the lasing threshold power. The proteinprotein interaction on the microdisk surface manifests itself by an increase in the laser threshold power. Thus, in this work we demonstrated, for the first time, the possibility of using QD semiconductor microdisk lasers for detection of proteins in a microfluidic device.
Microdisk lasers having III-V core coated with TiO2 shell are studied under optical pumping. Initial core microdisk lasers with 5-10 µm diameter comprising five layers of InAs/In0.15Ga0.85As quantum dots demonstrate room temperature lasing with excellent characteristics at the ground state optical transition in the 1.28-1.30 µm spectral range. Deposition of the TiO2 dielectric shell results in a decimation of the whispering-gallery-modes of the microdisk resonator and, for thicker (> 100 nm) shells, in a blue shift of the lasing wavelength. Using numerical analysis we demonstrate that coating III-V core microdisk with high-index shell causes strong penetration of the 2nd and 3rd radial modes into the shell, whereas the 1 st radial mode remains nearly undisturbed. Though optical loss added by TiO2 dielectric shell are low (it does not exceed 2 cm-1 even for 250 nm-thick TiO2 layer), mode leakage to TiO2 results in decrease of the optical confinement factor and increase in the threshold pump power. This effect is more pronounced in microlasers of the smallest diameter studied (5 µm). Thus, beside other applications, TiO2 shell can be used for mode selection in microdisk lasers or for selective outcoupling of the emission to waveguide structure, which requires proper adjustment of the TiO2 shell thickness and microdisk diameter.
A method of hybrid integration of quantum dot microdisk lasers with silicon wafer is proposed and realized. In addition to the possibility of combining microlasers with various silicon-based electronic and photonic devices, this makes it possible to significantly improve heat removal from the active region of the microlaser. The thermal resistance normalized to the mesa area reaches the level of about 0.002 (K/W)*cm2, which is significantly lower than the corresponding values of QD microlasers on GaAs substrate and monolithically grown on Si. As a result, the threshold current as well as current-induced shift of emission wavelength are reduced in continuous-wave regime.
We show that using dense arrays of InGaAs quantum well-dots enables uncooled high-frequency applications with a GHz-range bandwidth. A maximum 3-dB modulation frequency of about 6 GHz was found. The K-limited maximal frequency of 13 GHz was estimated from the modulation response analysis. The experimental values of the energy-todata reaches 1.5 pJ/bit for the smallest diameter under study (10 μm). A 23 μm in diameter microlaser exhibits open eye diagram up to 12.5 Gbit/s and is capable of error-free 10 Gbit/s data transmission at 30ºC without temperature stabilization. Our results demonstrate the potential to achieve miniature high-speed on-chip light sources for optical communication applications using lasers with a diameter of only a few micrometers.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.