Uncrewed Systems Technology 044 l Xer Technolgies X12 and X8 l Lidar sensors l Stan UGV l USVs insight l AUVSI Xponential 2022 l Cobra Aero A99H l Accession Class USV l Connectors I Oceanology International 2022

43 Lidar sensors | Focus If the silicon wafer includes structured recesses, the glass can be moulded into these embossed recessed structures when the silicon-glass bond is raised to temperatures above the transformation temperature of the glass. The glass then becomes a highly viscous fluid that can be pressed into moulds, for example, when the external pressure exceeds the gas pressure in the recessed moulds. The resulting glass structures are exposed by dissolving the original silicon wafer in a caustic bath. This process of high-viscosity moulding has been further developed by using a low gas pressure in suitable furnaces to form shapes in a glass wafer by blowing. This allows glass shapes to be formed with the shapes determined only by the viscosity, surface tension and pressure conditions inside and outside the previously created volumes in the silicon wafer.  The surfaces of glass shapes generated in this way are created without material contact, and are therefore flat, with a roughness of less than 1 nm, which is essential for optical applications. As these shapes are produced on silicon wafers, a large number of optically identical components are always produced simultaneously, leading to low production costs. Alongside the glass manufacturing processes, simulation programs are also used to optimise the shaping. Optical measurement techniques have been set up to characterise the finished components. The technology also makes it possible to feed electrical contacts through a glass wafer, or to precisely mount individual components such as laser diodes or lens elements on a carrier wafer using high- precision laser soldering, and then to encapsulate them together with a suitable glass wafer. Virtually any desired optical or opto-mechanical assembly can be implemented, operated under vacuum or even filled with different gases. MEMS switches The same technique for building the mirrors is also being used to improve the performance of a modulator. Rather than use a mirror, MEMS structures are built on a standard CMOS chip-making process to use an electric field to switch the different beams from a laser array. This allows an array of 16,384 pixels on a 1 cm 2 chip. When the switch turns on a pixel, it emits a laser beam and captures the reflected light. Each pixel is equivalent to 0.6 º of the array’s 70 º field of view. A 3D image is built up by cycling rapidly through the array. A prototype system built using this design currently has a range of 10 m, although 100 m is definitely possible and researchers believe they can achieve a range of 300 m. Metamaterial beam scanning Another approach blends the worlds of ToF with digital cameras. The missing link for this is the beam steering. This uses a combination of a metamaterial built using semiconductor technology with a liquid crystal. The metamaterial is created from 3D structures on the surface of a semiconductor chip that allows the phase of the incident light to be tuned. Each pixel on the surface is a phase delay element, and by programming many thousands of these elements with the right voltages the beam can be directed by combining constructive and destructive interference. The infrared laser used in a Lidar has a small wavelength, typically 905, 940 or 1550 nm, so the structures need to be less than 100 nm. This is suitable for semiconductor manufacturing processes that can currently manufacture structures with a minimum feature size of 5 nm. Adding the 3D optical structures allows the liquid crystal to switch in a smaller area and, critically, allows it to switch at speeds of microseconds rather Uncrewed Systems Technology | June/July 2022 A silicon wafer with a metamaterial for steering a laser beam (Courtesy of Lumotive) A metamaterial array helps reduce the size of a Lidar sensor (Courtesy of Lumotive)