Compressive sensing has been used to demonstrate scene reconstruction and source localization in a wide variety of devices. To date, optical compressive sensors have not been able to achieve significant volume reduction relative to conventional optics of equivalent angular resolution. Here, we adapt silicon-photonic optical phased array technology to demonstrate, to our knowledge, the first application of compressive imaging in a photonicintegrated device. Our novel sensor consists of an 8 × 8 grid of grating couplers with a spacing of 100 μm. Path-matched waveguides route to a single multimode interferometer (MMI), which mixes and randomizes the signals into 64 outputs to be used for compressed sensing. Our device is fully passive, having no need for phase shifters, as measurement matrix calibration makes the measurements robust to phase errors. For testing, we use an Amplified Spontaneous Emission (ASE) source with a bandwidth of 40 nm, centered at 1545 nm. We demonstrate simultaneous multi-point (2 sources demonstrated in this work) brightness recovery and localization with better than 10 arcsecond precision in a sub-millimeter thick form-factor. We achieve a single source recovery rate higher than 99.9% using 10 of the 64 outputs, and a 90% recovery rate with only 6 outputs, 10 times fewer than the 64 needed for conventional imaging. This planar optical phased array compressive sensor is well-suited for imaging sparse scenes in applications constrained by form factor, volume, or high-cost detectors, with the potential to revolutionize endoscopy, beam locators, and LIDAR.
Recent advances in silicon photonics have enabled large-scale optical phased arrays for applications such as beam steering and directional light detection. However, to date, these results have only been applied to coherent light. Many applications, including passive imaging with natural illumination, require operation using incoherent and/or broadband light. Here we implement an optical phased array designed for these applications using a planar, fractal, pathlength-matching architecture known as an “H-tree”. We demonstrate electronic beamsteering and natural light imaging using this flat, broadband, photonic-integrated device.
KEYWORDS: Charge-coupled devices, Imaging systems, Optical filtering, Cameras, CCD cameras, Oscilloscopes, Inspection, Back illuminated sensors, Sensors, Signal to noise ratio
Many applications, such as industrial inspection and overhead reconnaissance benefit from line scanning architectures where time delay integration (TDI) significantly improves sensitivity. CCDs are particularly well suited to the TDI architecture since charge is transferred virtually noiselessly down the column. Sarnoff's TDI CCDs have demonstrated extremely high speeds where a 7200 x 64, 8 um pixel device with 120 output ports demonstrated a vertical line transfer rate greater than 800 kHz.
The most recent addition to Sarnoff's TDI technology is the implementation of extended dynamic range (XDR) in high speed, back illuminated TDI CCDs. The optical, intrascene dynamic range can be adjusted in the design of the imager with measured dynamic ranges exceeding 2,000,000:1 with no degradation in low light performance. The device provides a piecewise linear response to light where multiple slopes and break points can be set during the CCD design. A description of the device architecture and measured results from fabricated XDR TDI CCDs are presented.
Robin Dawson, Robert Andreas, James Andrews, Mahalingham Bhaskaran, Robert Farkas, David Furst, Sergey Gershstein, Mark Grygon, Peter Levine, Grazyna Meray, Michael O'Neal, Steve Perna, Donald Proefrock, Michael Reale, Ramazan Soydan, Thomas Sudol, Pradyumna Swain, John Tower, Pete Zanzucchi
New applications for ultra-violet imaging are emerging in the fields of drug discovery and industrial inspection. High throughput is critical for these applications where millions of drug combinations are analyzed in secondary screenings or high rate inspection of small feature sizes over large areas is required. Sarnoff demonstrated in1990 a back illuminated, 1024 X 1024, 18 um pixel, split-frame-transfer device running at > 150 frames per second with high sensitivity in the visible spectrum. Sarnoff designed, fabricated and delivered cameras based on these CCDs and is now extending this technology to devices with higher pixel counts and higher frame rates through CCD architectural enhancements. The high sensitivities obtained in the visible spectrum are being pushed into the deep UV to support these new medical and industrial inspection applications. Sarnoff has achieved measured quantum efficiencies > 55% at 193 nm, rising to 65% at 300 nm, and remaining almost constant out to 750 nm. Optimization of the sensitivity is being pursued to tailor the quantum efficiency for particular wavelengths. Characteristics of these high frame rate CCDs and cameras will be described and results will be presented demonstrating high UV sensitivity down to 150 nm.
A family of backside illuminated CCD imagers with 6.6 micrometers pixels has been developed. The imagers feature full 12 bit (> 4,000:1) dynamic range with measured noise floor of < 10 e RMS at 5 MHz clock rates, and measured full well capacity of > 50,000 e. The modulation transfer function performance is excellent, with measured MTF at Nyquist of 46% for 500 nm illumination. Three device types have been developed. The first device is a 1 K X 1 K full frame device with a single output port, which can be run as a 1 K X 512 frame transfer device. The second device is a 512 X 512 frame transfer device with a single output port. The third device is a 512 X 512 split frame transfer device with four output ports. All feature the high quantum efficiency afforded by backside illumination.
A backside illuminated time delay integration (TDI) charge coupled device (CCD) technology has been developed. Imagers have been demonstrated at 13 pm pixel size and 8 pm pixel size. Photocomposition (stitching) has been employed to realize TDI iinagers of length < 60 mm. Performance has been enhanced in the areas of quantum efficiency, dynamic range, modulation transfer function (MTF), and line scan rates. The focus of this work has been to develop this new generation of line scan imagers for advanced reconnaissance applications. The enhancements permit the deployment of new camera systems with higher sensitivity, and higher resolution. To support the deployment of this technology into rugged environments, a custom packaging technology has been 'developed. The packages provide a hermetic enclosure for the CCD and establish precise alignment of the CCD pixels to the package mounting fixture. This paper will summarize the design features of the 13 pm pixel and 8 jim pixel TDI arrays. Measured performance will be presented. Future plans for this backside illuminated TDI technology will be discussed.
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