Polarimetry imaging technology has progressed rapidly in recent years. It promises advances in various fields of application, including remote sensing, medical imaging, molecular sensing, and many areas of defense and homeland security application. Conventional polarimetry is not flexible and has remained difficult to implement due to the complexity of optics and moving parts, and generally, it is bulky and costly. Recent advances in the design, micro/nanofabrication, and testing of metasurfaces have opened tremendous opportunities by simplifying the optics pathway. These sub-wavelength and flat structures can be engineered to transform the propagation, phase, and polarization of light. It is now conceivable to replace the carefully aligned optical components with a single well-designed metasurface. In this work, we present the design, fabrication, and integration of a multiplexed dielectric metasurface operating at 532 nm, which is of great interest for underwater imaging. The metasurface developed in this work spatially diffracts polarizations, resulting in demultiplexing the polarization, and the intensity of each polarization was recorded to determine the Stokes parameters. We will discuss the optimization process of designing the dielectric metasurface to recover the Stokes parameters for imaging and the degree of polarization. With the FDTD simulation, we explored the metasurface design parameter space to achieve better transmission and phase control. The incorporation of Pancharatnam–Berry phase and cross-talk among the orthogonal components of linearly and circularly polarized light were evaluated. The designed metasurface was fabricated using electron beam lithography and ICP-RIE etching. Finally, the fabricated metasurface was integrated with a time-of-flight multi-pixel imager.
Active illumination with underwater laser imaging has unique advantages for the identification of underwater objects, especially in shallow waters, complex marine environments and inaccessible locations. Laser intensity images embody valuable information that can be utilized for object recognition; however, backscattered light from the water column and other particulates blur the resulting laser images, rendering the objects in the images unintelligible. Although over the years a variety of deblurring and other image restoration and enhancement algorithms have been proposed, these works primarily consider optical images of scenery, not monotone underwater images of objects, for which contours are more critical. This work proposes the utilization of edge metrics to evaluate the efficacy of image restoration and enhancement algorithms for underwater laser images. Our results provide insight into the best methods for improving underwater laser image quality for object recognition.
Quantum devices have the potential to revolutionize applications in computing, communications, and sensing; however, current state-of-art resources must operate at extremely low temperatures, making the routing of microwave control and readout signals challenging to scale. Interest in microwave photonic solutions to this problem has grown in recent years, in which control signals are delivered to the cold stage via optical fiber, where they are converted to electrical signals through photodetection. Overall link performance depends strongly on the characteristics of the photodiode, yet detailed measurements of many detector properties remain lacking at cold temperatures. In this work, we examine and compare the performance of a modified uni-traveling carrier photodiode (MUTC-PD) at both room (300 K) and liquid nitrogen (80 K) temperatures, focusing in particular on responsivity, bandwidth, and linearity. In line with previous work, we find a sharp reduction in responsivity at 1550 nm as temperature decreases, while RF bandwidth remains steady. Interestingly, our linearity tests reveal that the RF output saturates more quickly at 80 K, suggesting reduced linearity with lower temperature, the cause of which is still under investigation. Our results should help contribute to the understanding and future design of highly linear cryogenic quantum links.
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