A Look At The Optics That Drive UAVs

By John Oncea, Editor

The UAV market is poised to hit $38.3B by 2027, driven by demand from both military and commercial sectors. Optics and fiber optics play a crucial role in keeping UAVs in the air.

The unmanned aerial vehicle (UAV) market is projected to reach $38.3 billion by 2027 according to MarketsandMarkets, growth attributed to the increased adoption of unmanned aircraft systems in commercial applications and increased procurement of UAVs by military forces worldwide.

The acceptance of UAVs, more commonly known as drones, has been steadily increasing for use by law enforcement and commercial applications due to their cost-effectiveness and technological advancements over the past several years. The military’s demand for C4ISR capabilities (Command, Control, Communications, Computers (C4) Intelligence, Surveillance, and Reconnaissance (ISR)) is also driving the demand for UAVs.

“Drones are used to gather data about ongoing and life-threatening military missions with the help of their C4ISR capabilities which are used to reinforce, boost, or implement command and control strategies and directives within military and intelligence frameworks,” writes MarketsandMarkets. “C4ISR powered by AI uses machine learning to identify and classify tanks and other vehicles, improves image feeds, and also provides driving assistance by giving early warning on obstacles and changing ground conditions. Governments are also quickly adopting these technologies to improve their defense arsenal.”

Between the civil and commercial and defense and government markets, it is the latter that is expected to record the highest growth rate during the forecast period. “Rising demand from the defense sector for surveillance, reconnaissance, and border security is boosting the demand for drones,” MarketsandMarkets writes. “The increasing demand for tactical drones that can be hand-launched and have an endurance of about 2 hours with suitable payload capacities to provide the required surveillance information has led to the growth of the tactical drones segment of the UAV.”

Tactical drones include decoy drones, swarm drones, and combat UAVs – all specifically designed to perform a particular set of duties – including aerial combat duties and lethal or swarm tasks. Exo-stratospheric drones such as the MQ-9 Reaper, a well-known battlefield drone used extensively worldwide, also fall in this category.

The Optics That Power UAVs

UAVs utilize various optical components for communication, guidance, data transmission, and image capture and these components are technologically well beyond the types of elements found in drones for recreational use.

“Visible camera systems are used for applications such as aerial photography, detect-and-avoid, and target detection and tracking,” writes Unmanned Systems Technology. “Thermal imaging systems, which may be Short Wavelength Infrared (SWIR), Medium Wavelength Infrared (MWIR), or Long Wavelength Infrared (LWIR), are commonly used for surveillance, search and rescue (SAR) and industrial inspection.”

UAVs require lenses that come in various shapes and can be made from different materials. When capturing imagery from a distance, UAVs need lenses with long focal lengths. Rather than using multiple lenses for each field of view, drone camera lenses with continuous zoom can help reduce size and weight.

Optical windows are manufactured from materials with different refractive indices to maximize transmission for specific wavelengths, such as ultraviolet, visible, or infrared. Optical domes serve as protective structures for imaging assemblies that need to balance transmission and durability. They are typically made using materials such as sapphire, UV-fused silica, and plastics. The domes can be coated to increase their robustness and transmission or to reduce reflection.

“Optical filters are designed to transmit only selected wavelengths whilst blocking everything that is not required,” Unmanned Systems Technology adds. “They may be used to reduce reflection, or for applications such as precision agriculture where specific reflected wavelengths can be used to provide information about plant health and hydration.”

When choosing optics for UAVs, Knight Optical writes the following considerations need to be made:

• Small form factor lenses for miniature gimbals
• Ultra-lightweight zoom and fixed focus lenses for size and weight savings
• High optical performance for accurate bore sight
• Low power consumption for UAVs
• High durability for hard carbon (LRHC) AR coatings
• Fast FOV change for UAVs that capture imagery at great distances
• Continuous zoom for UAVs that capture imagery at great distances 

“Environmental factors like lighting, temperature, humidity, and vibration also can affect the optics,” adds Knight Optical. “For example, lens designers can use software to model the air inside and outside of the lens at different pressure values, and then design a lens that can tolerate these shifts. 

“Drones often use a combination of guidance systems, including optical guidance systems that use cameras or other optical sensors to capture visual information and infrared guidance systems that use infrared sensors to detect and track heat signatures emitted by objects.”

Don’t Forget Fiber Optics

Fiber optics play a relatively new but rapidly growing role relative to UAVs, enabling efficient communication, data transmission, and improved guidance systems. “Utilized as the primary communications conduit between ground control and the antenna controlling the UAV, fiber optics provide a very fast and efficient means for transmitting a very large amount of data over long distances,” Timbercon writes.

UAVs rely on communication links to control the vehicle, transmit data, and receive information. As the information being sent and received is critical, high bandwidth and rapid transmission over long distances are essential for the success of UAV operations. Fiber optics technology provides the required bandwidth and transmission capabilities, making it an ideal solution for these applications. Additionally, fiber optics offer immunity to electromagnetic interference (EMI) and radio frequency interference (RFI), further enhancing the reliability of this technology for UAV use.

In some cases, UAVs deploy a fiber optic cable during flight to maintain communication with the operator. For instance, a Russian kamikaze FPV drone was found to carry a spool of fiber optic cable linked to a high-speed optical transceiver, allowing communication without radio interference, according to Military View.

Earlier anti-tank missile systems used copper cables for guidance. For example, the TOW-2 anti-tank missile system employed copper cables deployed during flight. However, these cables had limitations in terms of maximum impact distance (up to 3.9 km). The advent of fiber optics led to an improved version called the Enhanced Fiber Optic Guided Missile (EFOG-M) which allowed real-time video signals to be transmitted from the missile to the operator, enhancing guidance capabilities beyond the line of sight.

While fiber optic cables are lighter and smaller than copper cables, they are more expensive and require more protection due to the fragility of the individual fibers, notes Unmanned Systems Technology, adding that fiber optic cabling is manufactured in two primary types – single-mode and multi-mode.

• Single-mode fibers have smaller diameters and force the light into a smaller beam, resulting in less attenuation, and can be used for longer distances.
• Multi-mode fibers have a larger core and allow multiple pulses to be sent through the cable at once, allowing more data transmission but increasing the potential for attenuation.

“As modern UAVs … handle more and more data from HD cameras and other sensors, and share information through increasingly large networks, (fiber optics) technology has seen increased usage,” Unmanned Systems Technology writes. “Higher bandwidth, faster transfer speeds, and lower size and weight of fiber optic technology make it highly suited to many UAV platforms.”