Following the widespread implementation of silicon photonics technology, the emergence of applications in optogenetics, biosensing, augmented reality, and atomic-molecular-optical physics has highlighted a need for integrated photonic platforms operating at visible and ultraviolet wavelengths. Conventional materials for integrated photonics are not well-suited to the task; silicon's 1.1 eV bandgap thwarts its usefulness for wavelengths shorter than the near infrared, and as wavelengths decrease toward the ultraviolet, silicon nitride likewise begins to falter and strong material absorption takes hold. Meanwhile, aluminum oxide grown by atomic layer deposition (ALD) is a largely unexplored material which exhibits low material loss deep into the ultraviolet. ALD alumina keeps several desirable characteristics of silicon nitride; namely easy deposition on a variety of substrates and processing with commonly-available tooling. Here I discuss recent work developing ALD aluminum oxide for building integrated photonic systems, with an emphasis on fabrication and recent measured results. I review results for waveguides and resonators in the visible-to-ultraviolet regime, using both vertical grating couplers and inverse-taper edge couplers for input/output. Measured ring resonators at λ = 405 nm exhibit intrinsic quality factors exceeding 470,000, and propagation loss is measured from 0.5 dB/cm at λ = 461 nm to < 3 dB/cm at λ = 370 nm.
We demonstrate an integrated photonic platform for control of complex atomic systems. The platform includes multiple waveguide layers and a suite of passive photonic circuit components supporting a wavelength range from 370-1100 nm. In particular, we demonstrate a novel dual-layer vertical grating coupler used for efficiently directing visible light to precise positions above the chip surface. These circuits are compatible with traditional CMOS fabrication techniques and are well suited for improving the scalability of quantum information processing systems based on trapped-ion technology. A chip-scale waveguide platform at visible wavelengths could also prove useful in a variety of bio-photonic and sensing applications requiring precise light delivery or readout in a compact footprint.
We report on an optically pumped vertical-external-cavity surface-emitting laser diode coupled by a high reflectance volume holographic grating (VHG). The major feature of such a system is very narrow linewidth and high degree of power scalability, required for pumping upper energy levels of a gain medium. The cavity design lends itself to scaling to 2D VECSEL arrays suitable for low cost, high brightness pump sources.
Electrically-injected vertical external cavity surface emitting laser (VECSEL) arrays are an attractive source for lowcost, high-brightness applications. Optical pumping can be used to investigate the emission properties of such devices without undergoing complex device fabrication. The design of such arrays is based on a single VECSEL chip, a 2D lens array, and a flat output coupling dichroic mirror. In this work, we report on the demonstration of an optically pumped, coherently-coupled VECSEL array. The array achieves a maximum total output power of >60 mW and lasing spectrum indicates single-mode operation. Near-field characterization reveals 37 individual lasing elements in a hexagonal array. Far-field measurements show an interference pattern which is consistent with inphase coherent coupling, with >60% of the total output power present in the on-axis central lobe. The physical origin of coherent coupling is attributed to diffractive coupling. The simplicity of the optical cavity design suggests scalability to much larger arrays, making the result of particular interest to the development of low-cost, highbrightness diode sources.
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