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.
Lasers have multiple applications in the field of quantum. A few examples are cooling and repumping lasers for atoms and ions used in constructing qubits, frequency combs and atomic clocks. The performance required from a laser solution varies between the applications, however, single-mode operation, narrow spectral linewidth, and extreme frequency stability over operation lifetime are demanded for any of the applications. Use of semiconductor laser diode as a laser source offers multiple advantages, such as tunability by current and temperature, small size, and low energy consumption. Narrow spectral linewidths from semiconductor lasers can be achieved by the means of external cavities, or monolithic approaches such as distributed Bragg reflector (DBR) and distributed feedback (DFB) lasers. The selection of the most suitable solution depends on the required output power, linewidth, and mode-hop free tuning range requirements. The use of monolithic on-chip gratings for wavelength stabilization decreases system complexity and increases overall rigidity compared to external cavity solutions. In this work, we present device-level results for our 780 nm DBR laser design and compare them to the simulations. The 780 nm wavelength range is of particular interest for quantum computing due to the Rb atom D2 line. For optimization purposes, devices with varied grating designs, ridge geometries and gain area lengths were fabricated and measured. Future improvements related to device processing, design, and extending to other wavelengths are discussed.
In interferometry, spectroscopy, and holography, HeNe lasers or semiconductor lasers with external wavelength stabilization have been widely used to achieve the required narrow linewidth at 633 nm. Semiconductor lasers utilizing wavelength selective grating fabricated on semiconductor chip enable the miniaturization of laser systems while also providing numerous advantages such as low energy consumption, reliability and tunability by temperature and injection current. Moreover, DBR gratings reduce the complexity of the laser system compared to external cavity solutions where integration of multiple components is required. DBR gratings on semiconductor surface are fabricated without epitaxial regrowth step that could degrade the performance and lifetime of the device. In addition, low-order surface gratings are providing higher reflectivity than high-order gratings which could lead to a decreased emission linewidth and the output power. To this end, at red emission region low-order gratings require a small pitch, which in combination with the required etching depth for surface gratings leads to high aspect ratio gratings. In this work, Modulight demonstrates the fabrication of high aspect ratio low-order DBR surface gratings to optimize the device performance. DBR gratings are fabricated by electron beam lithography (EBL) method to achieve the required tight pitch patterns. EBL gratings are etched to AlGaAs or AlInP cladding layer using inductively coupled plasma reactive ion etching (ICP-RIE) to produce the desired high aspect ratio structures with smooth vertical side profiles. These two cladding materials are compared based on the etching profiles and device performance.
Laser diode solutions for quantum systems have highly variable requirements, depending on the technology and purpose of the laser used in the application – for instance, quantum control of particles or molecules and excitation of the quantum systems. Requirements of the laser systems used in the mentioned applications are highly demanding, such as single-mode operation, frequency stability over operation lifetime and narrow spectral linewidth. Narrow spectral linewidth can be achieved with distributed Bragg reflector (DBR), distributed feedback (DFB) lasers and external cavities. Wavelength of laser diode and light output power can vary depending on the intended application. For further efficiency, such emitters can be fabricated in arrays, eliminating the need for multiple single-emitter chips. Individually addressability of the emitters further enhances the efficiency. Examples of different applications using laser diodes described earlier are frequency comb generation, single-photon emitters, and timing sources for picosecond pulses. In this work, we present our results in 780 nm region DFB laser diodes. Gratings were implemented within the structure, including overgrowth step. Multiple variants in grating pitch were introduced for structure and design optimization purposes. Future improvements in the device processing, design, and reliability are discussed. 780 nm region laser diodes are used in multiple quantum systems, such as atomic clocks and manipulation of Rb atoms. In addition, it can be used for terahertz wave generation.
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