Atomic magnetometers (AMs) are widely acknowledged as one of the most sensitive kind of instruments for bio-magnetic field measurement. Recently, there has been growing interest in developing chip-scale AMs through nanophotonics and current CMOS-compatible nanofabrication technology, in pursuit of substantial reduction in volume and cost. In this study, an integrated polarization-splitting grating coupler is demonstrated to achieve both efficient coupling and polarization splitting at the D1 transition wavelength of rubidium (795 nm). With this device, linearly polarized probe light that experienced optical rotation due to magnetically induced circular birefringence (of alkali medium) can be coupled and split into individual output ports. This is especially advantageous for emerging chip-scale AMs in that differential detection of ultra-weak magnetic field can be achieved through compact planar optical components. In addition, the device is designed with silicon nitride material on silicon dioxide that is deposited on a silicon substrate, being compatible with the current CMOS nanofabrication industry. Our study paves the way for the development of on-chip AMs that are the foundation for future multi-channel high-spatial resolution bio-magnetic imaging instruments.
Recent years have seen rapid development of chip-scale atomic devices due to their great potential in the field of biomedical imaging, namely chip-scale atomic magnetometers that enable high resolution magnetocardiography (MCG) and magnetoencephalography (MEG). For atomic devices of this kind, vertical cavity surface emitting lasers (VCSELs) have become the most crucial components as integrated pumping sources, which are attracting growing interest. In this paper, the application of VCSELs in chip-scale atomic devices are reviewed, where VCSELs are integrated in various atomic bio-sensing devices with different operating environments. Secondly, the mode and polarization control of VCSELs in the specific applications are reviewed with their pros and cons discussed. In addition, various packaging of VCSEL based on different atomic devices in pursuit of miniaturization and precision measurement are reviewed and discussed. Finally, the VCSEL-based chip-scale atomic magnetometers utilized for cardiac and brain magnetometry are reviewed in detail. Nowadays, biosensors with chip integration, low power consumption, and high sensitivity are undergoing rapid industrialization, due to the growing market of medical instrumentation and portable health monitoring. It is promising that VCSEL-integrated chip-scale atomic biosensors as featured applications of this kind may experience extensive development in the near future.
Wavelength-selective thermal emitters have been frequently adopted as a typical platform for emissivity engineering to achieve desired target emissivity spectra for broad applications such as thermal camouflage, radiative cooling, and gas sensing, etc. However, previous design methods fail to tackle the simultaneous design of both materials and structures, either fixing materials to design structures or fixing structures to select proper materials, hindering the establishment of a general design framework for emissivity engineering applicable across different applications. Herein, we employ the deep Q-learning network algorithm, a reinforcement learning method based on deep learning framework, to design multilayer wavelength-selective thermal emitters for a diverse range of applications, including thermal camouflage, radiative cooling and gas sensing. With magnetron sputtering, these emitters are fabricated and measured, validating the desired emissivity spectra with the designed ones. The main merits of the deep Q-learning algorithm include that it can 1) autonomously select suitable materials from a self-built material library and 2) autonomously optimize structures, thus realizing simultaneous optimization of materials and structures for various emissivity engineering applications. The present method is demonstrated to be feasible and efficient in designing multilayer wavelength-selective thermal emitters, offering a general framework for emissivity engineering and paving the way for efficient design of nonlinear optimization problems across various physical fields.
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