Collaborative Research: COMPACT SUB-1 Kelvin Resolution Video Rate 94 GHz Passive Imaging Camera using Optical UP-Conversion

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The potential benefits of passive millimeter-wave imaging have long been recognized. It is an enabling technology for imaging and detection in degraded visual environments. The large range of applications for this technology include astronomy, aerial reconnaissance, stand-off threat detection, portal screening, persistent surveillance, situational awareness, and video imaging navigation in the absence of GPS signals. Millimeter-wave imaging can provide for high resolution and has the added capability to "see through" smoke, fog, sandstorms, and clouds. Therefore, it can provide pilots with valuable situational awareness during hover, takeoff and landing operations. Further, millimeter-wave radiation penetrates through plastic and clothing. With these advantages in mind, a Passive Millimeter-Wave Imaging camera system can be used as a complementary sensing modality in the emerging field of multi-sensor data fusion, and in conjunction with visible spectrum and infra-red (IR) cameras, LADAR (Laser Radar, a.k.a. LIDAR), RFID, and other range sensors to achieve inferences not possible with a single sensing modality. To date, most fielded millimeter-wave imaging systems focus on body scanning, as encountered at airports and building entrances. These systems are considered effective, but not without drawbacks. Specifically, they are bulky, slow, expensive, conspicuous and not suitable for standoff imaging. Therefore, there is a need for low-cost, compact, sensitive, and versatile imaging systems to enable a broader field of imaging applications. Medical and other scientific fields can also benefit from a small and high-performance millimeter-wave imaging camera. The proposed research introduces a new millimeter-wave camera design with integrated antennas and a photonic chip front-end using optical up-conversion, all in a staring interferometric sparse array format for high contrast and high spatial resolution. In the proposed camera system, the incident millimeter-wave radiation modulates an optical signal within an optical electro-modulator. The modulated signal, which consists of the optical carrier and double sidebands, is then stripped of the carrier and one of the sidebands using an integrated on-chip optical bandpass filter before being projected onto a standard near-IR camera. A number of innovative approaches are proposed to achieve small camera footprint, sensitivity, low cost and better resolution: 1) front-end antenna array with integrated optical up-conversion for black-body radiation centered at 94 GHz without a need for amplification, 2) increased efficiency by directly integrating the millimeter-wave antenna onto the electro-optical modulator and the optical bandpass filter on a single chip, 3) electro-optical modulator architecture using the electro-optic effect in polymer material in the active area for low loss and high modulation efficiency, 4) engineered sol-gel properties that promote high polling efficiency, low optical propagation losses, and efficient single mode fiber coupling, 5) standard optical lens and near-IR commercial cameras for low cost and simple reconstruction of high resolution images, and 6) interferometric sparse staring array detector front-end architecture for video rate functionality that avoids RF refractive lens in the front-end. The impact of this research is profound at many levels. The proposed camera will have a transformational impact since it can be used in the same manner as an optical camera to identify and detect hidden objects below clothing or behind obscurants at high speed. The proposed millimeter-wave camera is of low cost, real time, high resolution and high contrast. Notably, the modulator developed for this camera will benefit a multitude of portable devices for other research fields and many applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.