Laser systems with ultra-stable and narrow linewidth operation are a crucial part for many quantum computing and quantum sensing technologies, such as trapped ion and neutral ion approaches. The particular interest in this work is the fabrication of a 935 nm Distributed Bragg reflector (DBR) laser which can be used to repump Yb ions permitting Doppler cooling. DBR’s can provide output powers in the range of hundreds of milliwatts with stable narrow linewidth operation, with small system size and without the complexity of the external cavity configuration, thus providing an excellent solution for quantum technologies. Furthermore, the development in laser technologies is enabling the scalability and commercial use of quantum technologies where single frequency DBR lasers can be used as a part of a multiwavelength laser platform. In this work we have demonstrated high-power and narrow linewidth operation at 935 nm. The in-house epitaxial design is based on AlGaAs structure including an AlGaInAs active area. The position of the active region is optimized with asymmetric waveguides to enhance the device performance. The lasers are fabricated using metalorganic vapor phase deposition (MOCVD) after which the surface gratings are defined by electron beam lithography (EBL). The high-aspect ratio gratings are etched by inductively coupled plasma reactive ion etching (ICP-RIE). For device optimization purposes the gain medium section lengths, grating periods and cavity lengths were varied to find the optimal performance.
Lasers are a key enabling technology in the field of quantum computing, quantum sensing and quantum metrology. These applications require technically challenging properties from the lasers in use, such as stable and precisely controlled wavelength, up to watt level output power, and a narrow linewidth. Semiconductor diode lasers offer a very compact size, low power consumption, as well as scalability of cost and manufacturing volume due to their wafer scale manufacturing process. The monolithic integration of frequency selection on-chip in Distributed Bragg reflector (DBR) lasers offers advantages such as higher robustness, reduced system complexity and smaller size compared to external cavity frequency selection configurations. Thus, DBR lasers provide an optimal solution for a compact narrow linewidth laser source for selected quantum applications. Bandgap engineering of semiconductor gain media enables emission across the spectrum from UV to mid-IR. Wavelengths matching atomic transitions in the 7xx nm wavelength region include 760 nm and 770 nm for Yb, and 780 nm and 795 nm for Rb. In this work we describe the design, manufacturing, and performance of DBR lasers in the 7xx nm wavelength regime. The effects of key device design parameters are investigated to optimize the device performance. These include emitter width, gain and grating length, grating duty cycle, and residual layer thickness. To further scale the laser output power, tapered amplifiers are manufactured and characterized. The lasers are integrated into a laser system platform containing optical isolation, fiber coupling, low-noise laser drivers and temperature controllers. The system includes features such as compact footprint, controlled environment, cloud-connectivity and predictive maintenance.
Laser systems are utilized in quantum for various applications. Multiple wavelengths and tailored solutions are required depending on the technology that the laser will be applied to. For instance, lasers can be used for controlling particles and molecules, including excitations of the quantum systems. Key performance requirements for lasers used in these applications include narrow linewidth, frequency stability, and single-frequency operation. This performance can be achieved with laser diodes with integrated gratings, such as distributed Bragg reflector (DBR) and distributed feedback (DFB) structures. Laser diodes offer benefits such as low power consumption, compact size, and easy integrability to photonic integrated circuits. In addition, on-chip integrated gratings have advantages over external cavity diode lasers: reduced complexity in systems, smaller size, and better robustness. In this work, we present narrow linewidth DBR laser diode operating in the 650 nm wavelength regime which is required for quantum applications such as repumping in trapped Ba+ ion computing. In-house epitaxial design is based on a GaAs/AlInP/AlGaInP structure, including GaInP quantum well. Grating region is implemented as surface grating, requiring electron beam lithography (EBL) and high-aspect ratio etching by inductively coupled plasma reactive ion etching (ICP-RIE). Results for multiple variants are presented to achieve optimal device performance and grating coupling efficiency, targeting narrow linewidth operation required for quantum applications such as trapped ion computing.
Quantum information processing based on trapped ion technology is one of the leading platforms, heavily relying on a set of single-frequency lasers in its core operations. Narrow linewidth lasers perform atom photoionization, cooling, state-preparation and read-out. In this work we demonstrate in-house designed and fabricated optically pumped semiconductor laser gain mirror comprised of InGaAs quantum wells and GaAs/AlAs distributed Bragg reflector. We demonstrate in-house designed and fabricated single-frequency laser operating at 493 nm for Ba+ cooling. Inherent power scaling potential, efficient intracavity frequency conversion, coupled with sub-MHz linewidth and wide gain tuneability make VECSELs advantageous semiconductor laser platform for various quantum technology applications.
We report on tailoring capabilities in the 7xx nm wavelength range utilizing GaAsP or InGaAsP quantum wells (QW) embedded in AlGaAs. Laser structures are grown using metal-organic chemical vapor deposition. Wafers and manufactured lasers are thoroughly characterized, and lifetime tests are performed to validate laser reliabilities. Changing QW parameters enables us to tune the wavelength or polarization of the laser emission.
Vertical-cavity surface-emitting lasers (VCSELs) have recently paved their way into the 3D sensing market, specifically in mobile device applications. Vertical emission of VCSELs enables arranging single emitters into high-power 2D arrays. Thus, VCSEL arrays require efficient heat management which can be implemented by the means of packaging, both to improve thermal conductivity and to keep VCSEL chips intact. This becomes particularly important when considering also very high-density laser arrays and 2D matrices for quantum computing targeting a larger number of parallel outputs. Despite VCSELs decreased temperature sensitivity, their internal efficiency strongly depends on the internal temperature rise, which is defined by the dissipated power and thermal impedance of the laser assembly. Thermal impedance effect is more notable in the proximity to the gain medium, resulting into a drastic temperature gradient due to relatively thick substrate and its poor thermal conductivity. This prevents efficient heat dissipation in the gain media and creates a need for additional heat sinking. In this work, the improved heat sinking is implemented by packaging VCSEL arrays onto AIN sub mounts and subsequently encapsulating them into a thermally conductive and optically transparent epoxy. Thus, the closest proximity of the gain media to the heat sink is established, leading to an enhanced heat flow. Quantitative evaluation of the heat flow is performed by determining thermal resistance, defined as a ratio of the shift rates in the emission spectrum produced by varying pumping current and the heat sink temperature. The evaluation of thermal resistance of the devices with and without epoxy, not reported earlier, is performed to quantitively demonstrate the obtained improvements in the heat flow, efficiency, and output power.
The demand for fiber lasers has increased due to widening of application areas and higher power levels. As fiber lasers have become the main workhorse for high power material processing applications and competition among fiber laser manufacturers have become more evident, the laser manufacturers are in the process to find ways to lower overall cost of ownership to become more competitive. Key areas to look at are the efficiency of the fiber laser, especially the efficiency of the diode pump modules, and the higher reliability of its’ components. There is increasing demand for high power, high brightness, and higher efficiency laser diodes for kW-level fiber laser pumping. We present high-efficiency and high brightness laser diode optimized for lowered operating voltage while maintaining high power conversion efficiency of 60%. The laser diode design is a single quantum-well InGaAs/AlGaAs structure with graded index profile and large optical cavity design. The laser is fabricated into 4 mm long chips with a 94 μm emitter stripe indented for standard 105/125 μm core fiber laser pumping. The chips are mounted on AlN carrier and characterized as chip-on-submount. The laser produces 12.6 W optical power at 13 A and 1.62 V, reaching 60% conversion efficiency at operating point. The beam divergence angles are 8.5° horizontal and 34° vertical enabling high brightness and efficient fiber coupling. Furthermore, the lasers are reliability tested where they show outstanding reliability without sudden failures and ware-out rate less than 1% per 1000 hour over several thousand hours of testing.
Individually addressable laser diode arrays (IABs) are commercially demonstrated in the printing industry. These laser arrays are typically working at 8xx nm and 9xx nm wavelengths. Individually addressable laser diode arrays operating in visible region has been less reported and especially with limited commercial success. Yet, there is increasing interest in different variants of visible laser arrays not only in printing industry, but also in various display applications including head-up-displays and AR/VR products for different fields like automotive, consumer and medical markets. In this work we report the state-of-the-art high brightness individually addressable diode laser arrays operating at visible red wavelengths. The single-mode red IAB design is scalable from a few individually addressable emitters to tens of emitters per array with a highly uniform operation and repeatability and can be applied over the whole visible red spectrum from 630nm to 690nm. The individually addressable arrays at 640-660nm with a dense <100μm device pitch produce a record 3W total output power per array, with 0.85 W/A slope efficiency. The red IABs show excellent uniformity and stable long-term operation and are perfectly suited e.g. for various display applications or wherever there is a need for commercially viable high brightness individually addressable visible laser arrays.
Vertical-cavity surface-emitting lasers (VCSELs) have just recently started generating a lot of interest as the illumination source in the multitude of commercial applications. VCSELs capability to provide narrow spectrum emission with low temperature sensitivity and high beam quality, coupled with the possibility of nanosecond pulses generation, makes VCSELs an excellent laser platform for the outdoors, high-precision time-of-flight (ToF) and structured light applications. These advantageous features of VCSELs emission arise from their vertical cavity geometry, which also enables possible VCSELs direct integration onto circuitry and allows power scaling by arranging single-emitting VCSELs into compact high-power 2D arrays. These benefits have made VCSEL the current most popular illumination source for the 3D sensing applications both in the consumer market (e.g. proximity sensors for face and gesture recognition) as well as in the industrial sector (e.g. automotive short- to middle-range LiDAR and in-cabin monitoring). We present development results of both high-efficiency VCSEL single-emitters and multi-Watt VCSEL arrays emitting at the 940 nm purposed for 3D sensing applications. The VCSEL development involved optimization of epitaxial design in terms of DBR doping concentrations and the material content of the bottom DBR and oxide layer. While, on the other hand, optimization of the device parameters and processes targeted oxide aperture and mesa diameters, as well as etching depth. Wet thermal oxidation process has been specifically developed to facilitate precise oxidation depth control, run-torun reproducibility, and uniformity on the wafer scale. Successful VCSEL development is attributed to the Modulight’s full-cycle in-house semiconductor fabrication capabilities.
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