N221-044 TITLE: Compact, High Performance Mid-Wave Infrared Sensor for Intermittent Deployment

OUSD (R&E) MODERNIZATION PRIORITY: Microelectronics

TECHNOLOGY AREA(S): Sensors

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a compact and high performance mid-wave infrared (MWIR) imaging sensor for intermittent deployment on Unmanned Arial Vehicles (UAV) in environments where attrition is expected.

DESCRIPTION: Infrared (IR) imaging sensors (IR cameras) are especially useful for intelligence, surveillance, reconnaissance, and tracking (ISRT) missions as well as target acquisition for weapons and fire control systems. The mid wave infrared (MWIR) band is particularly attractive for conditions of high humidity, poor visibility, and nighttime use. Highly sophisticated MWIR cameras are expensive but fully justified when deployed to high-value platforms such as surface warships and combat aircraft and where exists the near certainty that the platform will be recovered, such as with large UAVs. In these cases, not only must the MWIR imaging sensor meet extensive performance requirements (i.e., field of view, resolution, sensitivity, frame rate, slew rate, stabilization) but expectations for continuous use over long periods as well.

Not every application demands both the full range of performance and the requirement for repeated long-term operation. There are many instances when an imaging sensor of modest performance, compact size, and low cost can perform much needed, but short duration tasks. For example, a small UAV with a suitably chosen imaging sensor can be launched from virtually anywhere to "pop up" and view targets that are still over the horizon for mast-mounted sensors. Small UAVs can be sent out to closely monitor and interrogate suspect vessels, floating debris, and indented shorelines, inlets, coves, and other littoral waters hidden by barrier islands. These missions are, by nature, intermittent and of typically short duration. These missions also have a high probability of loss of the UAV due to weather conditions, enemy action, or errors made during recovery. Consequently, the imaging sensor, like the UAV, must be very affordable.

The affordability of any imaging sensor is improved by trading off performance. Native resolution � that is, pixel count of the Focal Plane Array (FPA), can be reduced if the sensor is intended to approach the target of interest. For the same reason, large aperture, long focal length, and zooming lenses are not required. Acceptable image stabilization can be achieved electronically and the sensor can be aimed by maneuvering the UAV, simplifying the sensor mount. Taken collectively, these trade-offs can greatly reduce the sensor cost. Decreasing the specifications for environmental ruggedization and operational durability normally required of military systems results in a system (sensor plus small UAV) that is highly compact, affordable, energy efficient, easily manufactured, and therefore widely deployable.

This is already the case for small UAVs fitted with cameras for amateur and commercial photography in the visible spectrum. However, comparable systems for imaging in the IR suffer from additional factors that drive up cost substantially. IR FPAs (and especially MWIR FPAs) are comparatively expensive. In addition, to achieve acceptable imaging, MWIR FPAs must also be cooled to elevated cryogenic temperatures, most typically between 120 K and 150 K (depending on FPA material and wavelength cutoff). Consequently, the basic MWIR sensor package (not including the image processor and mounting and positioning hardware) incorporates the FPA, the read-out integrated circuit (ROIC), the optics, and the cooling hardware in a tightly integrated package. The cost is typically an order of magnitude more than for a comparable imaging sensor (comparable in format and resolution) in the visible spectrum.

Recent improvements in MWIR FPA technology have resulted in small pixel (8 micron or less) FPAs that have lower manufacturing cost. However, the use of smaller pixels requires faster (larger) optics to maintain sensitivity comparable to the larger pixel technology. So the cryo-cooler becomes the dominant cost component and the optics become the dominant weight component. However, being typically used in large, expensive, and high performance IR cameras, neither component has benefitted much from targeted research designed to reduce cost and weight.

The Navy needs a low cost, highly compact, and energy efficient MWIR imaging sensor package for intermittent, short duration missions where attrition is expected. In this context, "sensor package" is understood to include the FPA, ROIC, cryo-cooler, optics, and the enclosure that isolates the cooled components from the outside ambient temperature. The FPA must have a format of at least 1000 x 1000 pixels with small pitch (8 microns or less) and be integrated with a ROIC having the capability for high dynamic range (using variable integration time). The sensor is required to be able to focus to a blur spot of no larger than 1-2 sensor pixels in each direction. The full framerate must be at least 60 frames per second with the capability to increase the framerate to 240-1000Hz in small Regions of Interest (ROI) with addressable windowing.

Innovation is desired that fundamentally reduces the size and weight of the optical components. For the defined FPA format and pixel pitch, a 6� field of view (FOV) with conventional optics (lenses) is considered typical and is taken as the benchmark for comparison of sensor performance and Size, Weight, and Power and Cost (SWaP-C) where the power is understood to be the power required by the cryo-cooler and the FPA/ROIC pair. Solutions may incorporate gradient index optics, flat optics, microlensing, or other techniques that meet benchmark performance while reducing SWaP-C.

The integration of the FPA and ROIC with an affordable, compact, and efficient cryo-cooler is considered the key challenge in this effort. Because it has mainly been used for sophisticated, persistent systems, available cryo-cooler technology is typically specified for 10,000 to 20,000 hours of Mean Time Between Failure (MTBF). This results in greatly overpriced coolers for platforms whose total operational time will likely be less than ten hours accumulated during a handful of mission deployments. Specifically, the operational MTBF of the desired sensor package is relaxed to a value of 500 hours. The 500-hour MTBF is specified as "operational" to distinguish from the period of time that the sensor package is expected to sit unused between missions. In addition, when between missions, the sensor package must sit "cold". That is, no power shall be required to maintain the functionality and reliability of the sensor package when not in use. The sensor package must also be cable of imaging at full performance within a minimum 120 seconds of deployment in ambient temperatures ranging from -5 �C to 45 �C. The time from deployment to operation is assumed to be determined by sensor cool-down and solutions that minimize this time are highly desirable (below 60 seconds is a goal). The attritable nature of the mission set anticipates no more than ten operational deployments before loss. However, to accommodate periodic system checks, training, and aborted missions, the sensor package should be designed to withstand 100 on-off cycles before failure with 99% confidence. Mission duration is not anticipated to exceed 60 minutes.

The benchmark for cooling is 120-150 K, consistent with HgCdTe, nbn, or Strained layer Superlattice (SLS) background-limited High Operating Temperature (HOT) FPA technology. FPAs that operate at warmer temperatures are acceptable but the solution must convincingly demonstrate that the warmer sensor package meets or exceeds the performance, size, weight, and (especially) cost of a same size, format, and pitch HOT FPA, properly cooled and operated. The sensor package must be a closed system, only requiring external electrical power and data lines for operation. The most compact and efficient solution is desired and design for depot-level repair is not needed. Solutions that require pre-mission preparation, recharging of cooling fluids, periodic field maintenance, or specialized storage conditions are unacceptable. The 1.0 megapixel FPA is defined as the minimum size of interest for the anticipated mission set. It is also chosen as a reasonable size for demonstration. The solution however should be scalable (upward) in size with proportional increases in size, weight, and power consumption. No fundamental limit should restrict the technology to the 1.0 megapixel format and the optics should allow for individual designs with different (fixed) fields of view in the range 3� to 10� (minimum). Within these limits, any cooling technology is acceptable. A final projected sensor package cost (for the 1.0 megapixel-size sensor package, including the cryo-cooler) of $2000, when produced in quantities of 1000 or more, is the goal.

The sensor package will be demonstrated by fabrication, testing, and delivery of at least two successful prototypes. The sensor package does not include power supplies, the image processing board, static mounting hardware, or the display. However, these items must be delivered for successful demonstration of the prototype. The electrical inputs and outputs of the sensor package shall be commercially available connectors and the connectors are considered an integral part of the sensor package.

PHASE I: Propose a concept for a MWIR imaging sensor package that meets the parameters stated in the Description. Demonstrate the feasibility of the concept in meeting the Navy need through a combination of analysis, modeling, and simulation. The Phase I Option, if exercised, will include the sensor package specification, preliminary optics design, interface requirements, performance test specification, reliability test plan, and capabilities description necessary to build and evaluate a prototype solution in Phase II.

PHASE II: Develop and demonstrate a prototype MWIR imaging sensor package based on the concept and specifications resulting from Phase I. Demonstrate the prototype meets the parameters described in the Description through testing in a laboratory environment. The laboratory environment will be provided by the company. Multiple prototypes (or partial prototypes) may be produced during execution of this effort as the design process is assumed to be necessarily iterative in nature. However, at the conclusion of Phase II, two final (best performing) prototypes will be delivered, one with a 3� FOV and one with a 6� FOV, to the Naval Research Laboratory (NRL) along with complete test data and final manufacturing cost estimates. The image processing board, display, and any specialized fixturing or equipment necessary to replicate testing of the prototype sensor packages shall also be delivered to NRL.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Government use by scaling the technology to meet specific sensor program requirements and identifying specific manufacturing steps that require maturation, maturing those steps and processes, establishing a hardware configuration baseline, producing production level documentation, and transitioning the sensor package into production. Assist the Government in integration of the sensor package into next higher assemblies and deployable systems.

The technology resulting from this effort is anticipated to have applications in law enforcement, security monitoring, search and rescue, and remote imaging applications for commercial and scientific programs.

REFERENCES:

1. Gibson, Daniel, et al. "GRIN Optics for Multispectral Infrared Imaging" Proceedings of the SPIE, Infrared Technology and Applications XLI 9451 June 2015: 7 pages. https://spie.org/Publications/Proceedings/Paper/10.1117/12.2177136?origin_id=x4323&start_year=2015.
2. Banerji, Sourangsu, et al. "Imaging with Flat Optics: Metalenses or Diffractive Lenses?" Optica 6 6 2019: 805-810. https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-6-6-805&id=413582.
3. Curlier, Patrick. "Low-Cost Cryocooler Review for Intermediate Cooling Temperature" Proceedings of the SPIE, Infrared Detectors and Focal Plane Arrays IV 2746 June 1996: 7 pages. https://spie.org/Publications/Proceedings/Paper/10.1117/12.243043?origin_id=x4323&start_year=1996.
4. Arts, R., et al. "Miniature cryocooler developments for high operating temperatures at Thales Cryogenics" Proceedings of the SPIE, Infrared Technology and Applications XLI, 9451 May 2015: 12 pages. https://spie.org/Publications/Proceedings/Paper/10.1117/12.2176323?origin_id=x4323&start_year=2015.

KEYWORDS: Imaging Sensors; MWIR Imaging; Cryo-Cooler; Focal Plane Array; Gradient Index Optics; Microlensing