Kamil Pierscinski, Piotr Gutowski, Dorota Pierscinska, Katarzyna Pieniak, Agata Krzastek, Dominika Niewczas, Grzegorz Sobczak, Iwona Sankowska, Aleksandr Kuzmicz, Jan Muszalski, Maciej Bugajski
In this work optimization of technology of QCLs operating at λ~13 µm wavelength is presented. The devices were grown by Molecular Beam Epitaxy and combined MBE and MOVPE overgrowth. Room temperature operation of QCLs was achieved. The influence of the waveguide design in terms of thickness, growth conditions as well as doping has been studied. We have performed electro-optical and spectral characterization of LWIR QCL extracting crucial device parameters. The analysis of laser parameters is presented. Additional results of single mode operation are presented for devices in coupled cavity configuration.
Acknowledgements: This work was supported by Polish National Science Centre (NCN) grant: SONATA BIS: UMO-2021/42/E/ST7/00263
Compact, multi-spectral laser sources emitting in the mid-infrared (mid-IR) are in high demand for applications. Integration of several multi-spectral, mid IR quantum cascade lasers on silicon-based waveguide platforms is a necessary step towards realization of functional and complex mid-infrared photonic integrated circuits. This paper focuses on the thermal aspects of integration of multi-spectral QCLs toward the integration of QCL chips on silicon-based platform. The experimental results registered by means of CCD-thermo-reflectance are supported by numerical simulations of heat dissipation. The effects of thermal cross-talk between individual emitters are presented and discussed, leading to design guidelines for placement of laser chips in mid-infrared integrated photonics systems.
Improving the heat dissipation in Quantum Cascade Lasers (QCLs) is important from the point of view of a growing number of their applications, which require better performance. In this paper, we propose and experimentally demonstrate the possibility of a significant reduction of Active Region (AR) temperature without sophisticated and fabrication-intensive means. We have examined the influence of electroplated gold thickness on thermal and electro-optical properties of InP-based QCLs. Numerical modeling, that we have performed, predicts a significant reduction of the laser core temperature of epi-side up mounted ridge waveguide QCLs with increased thickness of electroplated gold. Predictions of the numerical model have been confirmed experimentally by means of electro-optical, spectral, and thermal characterization.
Single mode emission is one of the crucial requirements for Quantum Cascade Lasers (QCLs), which are compact laser sources of infrared radiation in the mid-IR range (3–20 micrometers) and in the THz range (1–5 THz). This feature is particularly important in all spectroscopic applications such as industrial process monitoring, remote sensing, breath analysis for medical diagnostic or industrial process monitoring.
In this paper, we have proposed a modified approach to coupled cavity QCLs, based on multisection (three section) coupled cavity QCLs. The range of spectral tuning is very important from the point of view of applications in optical sensing techniques based on the intrapulse tuning of the laser emission.
We have designed and fabricated 3-section CC QCLs characterized by intrapulse wavelength tuning of 2.8 cm-1, obtained for 2 mirosecond pulse width. The device operates above room temperature. The improvement of the spectral tuning of 3-section device is compared to 2-section laser. The third section improved significantly the performance of the laser in terms of single mode intrapulse wavelength tuning.
The paper focuses on the design, fabrication and characterization of monolithic, coupled cavity two-section quantum cascade lasers. The devices were fabricated by reactive ion etching from InP-based heterostructure designed for emission in 9.x micrometer range. To make the device attractive for sensing applications, the idea of the coupled-cavity device was employed, giving the possibility of single longitudinal mode operation. We have previously presented devices fabricated by means of focused ion beam post-processing. However, FIB etching is challenging and time-consuming. In order to overcome the relatively low throughput of the FIB process, in this work, gaps separating sections were defined by dry etching during the fabrication process. Careful optimization of the dry etching process resulted in very good control of gap geometry. Quality of mirrors formed by RIE did not introduce high scattering loss into the cavity, as the threshold current density was not increased significantly. Devices routinely exhibited side mode suppression ratio of more than 20 dB. Approach to fabricate two-section devices by dry etching resulted in improved yield as well as high repeatability of the performance of individual devices.
Monolithic, electrically isolated, two-section devices were also fabricated and characterized. We will present a comparison of the performance of different designs and discuss their characteristics, fabrication challenges and stability against operating conditions.
In this paper the possibility of improvement of emitted beam quality of high-power laser diodes by stabilization of an optical field distribution in the junction plane, forced by lateral periodicity built into their wide-stripe waveguide is described. Current flow control by such periodic structure prevents the lateral current crowding, carrier accumulation at the stripe edges and optical far-field blooming typical for conventional wide-stripe laser diodes. As a result, stabilization of the lateral emitted beam divergence in wide drive current range of CW operation has been evidenced.
We report recent results of works on quantum cascade lasers at the Institute of Electron Technology. During that time we have developed technology of lasers emitting at wavelengths 9.0–9.5 μm and 4.7 μm, based on InGaAs/AlGaAs/GaAs and InAlAs/InGaAs/InP heterostructures; both lattice matched and strain compensated. The structures were grown by molecular beam epitaxy MBE and by metalorganic vapor phase epitaxy MOVPE. The InGaAs/AlGaAs/GaAs lasers were grown by MBE. For InP based lasers three types of structures were investigated; the one grown exclusively by MBE without MOVPE overgrowth, the second fabricated by hybrid approach combining MBE grown AlInAs/InGaAs active region with MOVPE grown InP top waveguide layer and the third one with both the top and the bottom InP waveguide grown by MOVPE. Regardless of the waveguide construction, the active region was grown by MBE in every case. The lasers were fabricated in double trench geometry using standard processing technology. The buried heterostructure lasers were also investigated.
An important issue in the technology of QCLs is the capability to extract heat out of the laser active area in order to reduce the increase of the temperature. High temperature not only reduces most performance metrics but also decreases device lifetime and impairs its reliability, leading to degradation of laser mirrors and destruction of the device.
In this paper, we report on the investigation of the temperature of QCLs based on different designs. QCLs are complex, multilayer structures, which require high current and voltage to polarize the structure in order to obtain level alignment. This results in high heat generation. Thermal limitations in case of QCL are the most critical factor decreasing the performance of a device. High electrical power combined with relatively low wall-plug efficiency results in high-temperature increase in the active core. Efficient heat dissipation is difficult due to hundreds of layers impeding thermal conductivity of the structure. Moreover, the materials composing the gain region are ternaries with a composition of roughly 50%, what results in thermal conductivity lower by a factor of 10 than in case of bulk InP. Knowledge of the temperature is gained through unique temperature measurement technique – CCD thermoreflectance (CCD TR). This method allows for rapid thermal characterization of QCLs, as the registration of high-resolution map of the whole facet of the device lasts only several seconds. CCD-TR allows accurate evaluation of the thermal characteristics of quantum cascade lasers.
Here, we report on the influence of design on thermal properties of QCLs. The design of waveguides and optical confinement in QCLs is essential. The increase of the optical confinement was frequently achieved by placing the active core between two InGaAs layers. However, low thermal conductivity of InGaAs layers results in inefficient dissipation of heat from the active core. By removing or significant reduction of the layers’ thickness, observed temperatures of the active core are significantly lower. The modifications include Experimental investigation proves that performance improvements can be gained by introducing modifications into the design of the structure. Based on experimental data, methods to further improve the performance of QCLs are discussed.
The quality of the die bonding is critical to the operation and reliability of the laser diodes since it can affect the
electrical, thermal, and optical properties of the device. We investigated the effect of mounting induced strain and
defects on the performance of high power laser. In this paper measurements of the temperature distribution, the
spontaneous emission spectrum and the electroluminescence along the cavity of quantum well lasers are presented. The
electro-optical parameters of the high output power laser diodes, such as emission wavelength, output power, threshold
current, slope efficiency, and operating lifetime are presented too. In the experiment, high power diode lasers emitting in
808 nm and 880 nm- range are investigated. We have observed that defect lines tend to create in areas where temperature
gradients were observed in thermovision measurements.
The quality of the beam emitted by high-power laser diodes is still the main disadvantage of these devices. One of the
ways to improve it is to design diode as a matrix of narrow active stripes – so called: phase-locked arrays. The optical
coupling which is occurs in such devices causes the emission in the form of a few almost diffraction limited beams
(lobes). Unfortunately, because of temperature dependence of refractive indices this coupling often disappears at high
drive currents. In this paper the CW operation (up to 4Ith) of the phase-locked semiconductor laser arrays is reported. The
devices are based on asymmetric heterostructure which is designed for improving thermal and electrical resistances. The
single supermode operation is obtained and the lasers are emitted up to 1 W of the optical power in CW.
The laser diodes (LD) have numerous applications and promise to become key elements for next generation laser
technologies. LD are usually operated under conditions of heavy thermal load. As a result, the devices are affected by
aging processes leading to changes of the operation parameters, degradation and, eventually, complete failure.
Degradation of high power semiconductor lasers remains a serious problem for practical application of these devices. We
investigated the effect of mounting induced strain and defects on the performance of high power laser. In this paper
measurements of the temperature distribution and the electroluminescence along the cavity of InGaAs quantum well
lasers before and after accelerated aging processes are presented. The electro-optical parameters of the high output power
laser diodes, such as emission wavelength, output power, threshold current, slope efficiency, and operating lifetime are
presented too.
Low quality of the optical beam emitted by high-power laser diodes is the main disadvantage of these devices. The two
most important reasons are highly non-Gaussian beam profile with relatively wide divergence in the junction plane and
the filamentation effect. Designing laser diode as an array of narrow, close to each other single-mode waveguides is one
of the solutions to this problem. In such devices called phase locked arrays (PLA) there is no room for filaments
formation. The consequence of optical coupling of many single-mode waveguides is the device emission in the form of
few almost diffraction limited beams. Because of losses in regions between active stripes the PLA devices have,
however, somewhat higher threshold current and lower slope efficiencies compared to wide-stripe devices of similar
geometry. In this work the concept of the high-power laser diode resonator consisted of joined PLA and wide stripe
segments is proposed. Resulting changes of electro-optical characteristics of PLA are discussed. The devices are based
on the asymmetric heterostructure designed for improvement of the catastrophic optical damage threshold as well as
thermal and electrical resistances. Due to reduced distance from the active layer to surface in this heterostructure, better
stability of current (and gain) distribution with changing drive level is expected. This could lead to better stability of
optical field distribution and supermodes control. The beam divergence reduction in the direction perpendicular of the
junction plane has been also achieved.
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