SBIR-STTR Award

A major advance in submarine sensing technology was enabled in the early 2000s with the Navys Integrated Submarine Imaging Systems (ISIS) program, which has incorporated visual and digital imaging into photonic mast assemblies, providing all-weather, high-resolution imagery for data analysts. Next generation ISIS systems will see a size reduction and more advanced sensing capabilities, including multispectral imaging. The photonic mast will incorporate multiple transparencies including hyper-hemispheric domes to allow for 360 panoramic viewing, and will greatly increase battlefield situational awareness. The photonic mast windows must be durable and hydrophobic for the extreme maritime environment; and transmit over broad visible and infrared wavelength ranges to provide transparency for the range of sensors to be incorporated. The Navy has identified that current antireflection coatings do not adequately meet mission specifications for bandwidth, durability, and hydrophobicity; and cannot be reliably deposited on next generation ISIS hyper-hemispherical domes. An innovative and rugged solution to the AR problem is based on Random AntiReflective (RAR) textures imparted directly into the domed windows. Durable AR surface textures have been shown to exhibit ultra-hydrophobic properties, and possess optical performance that is far superior to thin film coatings with respect to transmission, bandwidth, and off-axis performance

Benefit:
Random AR technology applied to ISIS panoramic imaging masts head windows and hyper-spectral domes will provide unsurpassed broadband anti-reflection performance enabling low noise imaging and reducing visual vulnerability from sunlight glint. In addition, integrated AR nano-textures will provide structural hydrophobicity reducing corrosion and contamination of optical windows from shipboard salt spray, dirt, and grime; and eliminating the current need for routine hydrophobic treatments. The RAR fabrication process is adaptable to a variety of optical materials, can be generated in both windows and domes, and can be manufactured at costs equivalent to or less than existing thin-film coatings. RAR textures can be applied to existing imaging mast window designs as well as for future ISIS Block 5 hyper-hemispheres. The nanotexture AR solution will also be advantageous to other Naval transparencies including high-energy laser optics deployed in maritime environments, which are extremely vulnerable to contamination. Other commercial applications benefitting from a combination broadband anti-reflection solution with hydrophobic/self-cleaning functionality include solar cells, smartphones and television screens, car windshields, and building windows.

Keywords:
Hyper-hemisphere, Hyper-hemisphere, Motheye, antireflection, Multi-spectral, Random, hydrophobic, AR, nanotextures

A major advance in submarine sensing technology was enabled in the early 2000s with the advent of the Navys Integrated Submarine Imaging Systems (ISIS) program, which has incorporated visual and digital imaging into photonic mast assemblies, providing all-weather, high-resolution imagery. The Navy has identified that current antireflection (AR) coatings do not adequately meet photonic mast specifications for bandwidth, durability, and hydrophobicity. An innovative and rugged solution to the AR problem is based on Random AntiReflective (RAR) nanotextures imparted directly into the mast windows. The optical performance of nano-textures has been demonstrated to be far superior to thin film coatings with respect to transmission, bandwidth, off-axis performance, and laser power handling; as well as exhibiting ultra-hydrophobic properties in sea water. In Phase I, extreme optical performance and hydrophobicity was maintained in nanotextured fused silica after 8-days submerged in flowing sea water. The Phase II and Options effort will demonstrate extreme AR bandwidth in sapphire windows, extending from the visible out to the mid-wave infrared. Full-scale fused silica and sapphire photonic mast transparencies for various mast programs will be nanotextured and undergo extensive environmental durability testing in sea water, along with development of an automated cleaning system for shipboard use.

Benefit:
It is anticipated that the Phase II effort will provide a long life, high performance solution to current issues with photonic masts- specifically the absence of an antireflection or self cleaning treatment on the exterior face of the mast windows. The utilization on nanotextures will reduce reflections from the current heated head windows from 5% to less than 0.5%, and for broadband sapphire windows from 6% to less than 0.7%. This will provide unprecedented clarity for imaging sensors and laser rangefinders, the key components of the photonic mast. Secondly, cleaning and maintenance of the external surfaces of photonic mast and most naval transparencies in the harsh maritime environment is a major concern for the Navy. Currently, the photonic mast windows are cleaned with spraying and physical wiping, an inadequate approach for operability and system readiness. The introduction of super-hydrophobic nanotextures is expected to minimize or eliminate these concerns, enabling longer life and unprecedented high clarity in operation. The cleanliness and long-term durability of the window becomes more important as mast technology and requirements advance, as debris or water droplets on a window will detrimentally affect advanced multispectral sensor clarity, laser range finder capabilities, and potentially future design HEL systems. The salt water shedding nature of hydrophobic surfaces and cleaning techniques developed in Phase I and to be optimized in Phase II are expected to make a significant improvement to the clarity and functional lifetime of the mast windows. A milestone goal in the Phase II will be to formalize cleaning procedures for nanotextured windows such that minimal manual effort is required by Navy personnel, through the design and assembly of an automated pressure sprayer that can be placed in the proximity of the window. The automated cleaning system will provide on-demand clarity for constant-ready use, in the same manner that is envisioned for the Navys shipboard High Energy Laser and Integrated Optical-dazzler with Surveillance (HELIOS) system that is exposed to similar conditions of sea water. The demonstration that the hydrophobic nature of the surface-treated nanotextures are unaffected by extended salt water exposure was a major milestone of the Phase I effort. Beyond the submarine photonic mast program, shipboard Naval requirements for multi-spectral, MWIR, LWIR, SWIR, and visible camera windows requiring durability in a maritime environment will directly benefit from the results of this work. The Navy is also currently seeking improved laser induced damage thresholds for HEL optics (e.g. laser exit aperture windows) that require durability with partial and complete sea water immersion; and will have great interest in the results of laser damage testing of extended sea water exposed windows.

Keywords:
nanotexture, laser damage, antireflection, Motheye, hydrophobic, Sapphire, Photonic Mast, fused silica