Optical Shutter for Dynamic Active Electro-Optical Range Gating Systems

RT&L FOCUS AREA(S): Sensors, Electronics, and Electronic Warfare TECHNOLOGY AREA(S): Microelectronics, Space, GWR OBJECTIVE: Develop a compact, free-space electro-optical (EO) shutter to regulate photons arriving at a laser-based remote sensing receiver and to detect weak returns from targets largely obscured by strong returns from overhead tree canopies or camouflage. DESCRIPTION: The government seeks to develop a compact, low-cost, dynamic optical shutter/isolation capability for integration with existing and/or future active remote sensing platforms. The system shall be capable of operating with a high repetition rate (Objective: 100 kHz) pulsed, polarized output, free-space pulsed lasers (1064 nm), and deployable in-line with narrow field of view imaging lidar systems. The device shall have an acceptance angle of 1 degree or more, maintain and select polarization, and be bi-directional. It shall facilitate on-demand pico- and nanosecond gating between 200 pm to 100 ns, ideally, of both a pulsed laser source and the time-delayed return of reflected pulses off a far-field target. The capability can build on Pockels Cell/Q-Switch technology and represents a new functional implementation and developmental evolution of this technology because it leverages recent advances in crystal growth, electrode design, and voltage control electronics. It promises to dramatically improve the three-dimensional (3D) imaging performance of long-standoff active EO systems. The proposed range gating technology will be demonstrated as a breadboard prototype. By providing exquisite temporal power control over in-situ scene illumination (transmitter) and received backscatter, it should improve the performance of traditional Geiger-mode lidar systems by improving the probably of detection of targets under canopy, while conferring improved system-level optical damage tolerance to both inadvertent and adversarial sources of high-intensity illumination. Such a capability will allow for improvements in the ability of single-photon and conventional linear-mode lidar systems to image past highly reflective objects (such as canopy) by selectively and effectively attenuating these returns, while simultaneously improving sensor sensitivity with respect to far-field target objects in the human activity layer. Because of the notional design of such a system, this capability, as developed, also lends itself for use in dynamic in-sensor attenuation of highly reflective objects in scene and undesired sources of active illumination within the field of regard. It affords the entire system an additional degree of protection against optical damage and provides additional capabilities in the areas of pulse picking and/or pulse slicing. In addition, it confers the potential to pick pulses out of a multi-pulse train (e.g., MHz pulse repetition frequency), reduce the pulse width of nanosecond pulses into the picosecond range, and selectively gate far-field returns based on the mission profile. PHASE I: Develop one or more proof-of-concept component designs and modeling analysis that meet the technical performance requirements outlined above. PHASE II: Build a monolithic optical assembly that is fixture mountable to a standard imperial optical breadboard, and associated electrical equipment, suitable for bench testing. Identify paths to a production-ready device that can be integrated into a long-standoff 3D imaging system. PHASE III DUAL USE APPLICATIONS: The desired Pockels cell will improve both passive and active imaging systems that require nonmechanical high-speed optical shutters and signal attenuators, specifically those already using optical components based on the Pockels effect.