Publisher’s Note: This paper, originally published on 18 September 2018, was replaced with a corrected/revised version on 28 May 2020. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
During the past decade, significant advancement has been made on InGaAsP/InP Geiger-mode APDs (GmAPDs) through improvements of material growth, device design and operating circuitry. With the increase in device performance and the growing maturity of device fabrication technology, high performance, large format InGaAsP/InP GmAPD arrays have been successfully designed and manufactured. These arrays have single photon sensitivity in the short wavelength infrared (SWIR) spectral band and can provide 3-D imagery. InGaAsP/InP GmAPD arrays provide an enabling technology for many active optical applications, such as 3-D light detection and ranging (LiDAR) and other photon-starved applications where single photon sensitivity in the SWIR band is critical. InGaAsP/InP-based Geigermode LiDAR has been extensively used on airborne platforms. By using optical wavelengths along with sub-ns laser pulse widths, 3-D Geiger-mode LiDAR techniques provide centimeter-scale range resolution over extremely long distances on the order of tens of kilometers. Through the use of high-performance single photon detectors, Geiger-mode LiDAR systems achieve an order of magnitude improvement in mapping rate over other competing LiDAR technologies. A more recent exciting application of InGaAsP/InP GmAPD-based LiDAR is to enable advanced driver assistance systems (ADAS) and vehicle autonomy on automotive platforms. The single-photon sensitivity of GmAPDs and greater eye-safety of diode lasers at wavelengths beyond 1400 nm provide disruptive automotive LiDAR performance that will be essential to future autonomous vehicle navigation. Single photon sensitivity and simple pixel circuit operation enable the reduction in overall system SWaP, while the scalability of these semiconductor devices enables dramatic reduction in LiDAR cost.
The operation of avalanche photodiodes in Geiger mode by arming these detectors above their breakdown voltage provides high-performance single photon detection in a robust solid-state device platform. Moreover, these devices are ideally suited for integration into large format focal plane arrays enabling single photon imaging. We describe the design and performance of short-wave infrared 3D imaging cameras with focal plane arrays (FPAs) based on Geigermode avalanche photodiodes (GmAPDs) with single photon sensitivity for laser radar imaging applications. The FPA pixels incorporate InP/InGaAs(P) GmAPDs for the detection of single photons with high efficiency and low dark count rates. We present results and attributes of fully integrated camera sub-systems with 32 × 32 and 128 × 32 formats, which have 100 μm pitch and 50 μm pitch, respectively. We also address the sensitivity of the fundamental GmAPD detectors to radiation exposure, including recent results that correlate detector active region volume to sustainable radiation tolerance levels.
The unparalleled sensitivity of 3D LADAR imaging sensors based on single photon detection provides substantial benefits for imaging at long stand-off distances and minimizing laser pulse energy requirements. To obtain 3D LADAR images with single photon sensitivity, we have demonstrated focal plane arrays (FPAs) based on InGaAsP Geiger-mode avalanche photodiodes (GmAPDs) optimized for use at either 1.06 μm or 1.55 μm. These state-of-the-art FPAs exhibit excellent pixel-level performance and the capability for 100% pixel yield on a 32 x 32 format. To realize the full potential of these FPAs, we have recently developed an integrated camera system providing turnkey operation based on FPGA control. This system implementation enables the extremely high frame-rate capability of the GmAPD FPA, and frame rates in excess of 250 kHz (for 0.4 μs range gates) can be accommodated using an industry-standard CameraLink interface in full configuration. Real-time data streaming for continuous acquisition of 2 μs range gate point cloud data with 13-bit time-stamp resolution at 186 kHz frame rates has been established using multiple solid-state storage drives. Range gate durations spanning 4 ns to 10 μs provide broad operational flexibility. The camera also provides real-time signal processing in the form of multi-frame gray-scale contrast images and single-frame time-stamp histograms, and automated bias control has been implemented to maintain a constant photon detection efficiency in the presence of ambient temperature changes. A comprehensive graphical user interface has been developed to provide complete camera control using a simple serial command set, and this command set supports highly flexible end-user customization.
We present results obtained from 3D imaging focal plane arrays (FPAs) employing planar-geometry InGaAsP/InP
Geiger-mode avalanche photodiodes (GmAPDs) with high-efficiency single photon sensitivity at 1.06 μm. We report
results obtained for new 32 x 128 format FPAs with 50 μm pitch and compare these results to those obtained for 32 x 32
format FPAs with 100 μm pitch. We show excellent pixel-level yield-including 100% pixel operability-for both
formats. The dark count rate (DCR) and photon detection efficiency (PDE) performance is found to be similar for both
types of arrays, including the fundamental DCR vs. PDE tradeoff. The optical crosstalk due to photon emission induced
by pixel-level avalanche detection events is found to be qualitatively similar for both formats, with some crosstalk
metrics for the 32 x 128 format found to be moderately elevated relative to the 32 x 32 FPA results. Timing jitter
measurements are also reported for the 32 x 128 FPAs.
We report on the development of focal plane arrays (FPAs) employing two-dimensional arrays of InGaAsP-based
Geiger-mode avalanche photodiodes (GmAPDs). These FPAs incorporate InP/InGaAs(P) Geiger-mode avalanche
photodiodes (GmAPDs) to create pixels that detect single photons at shortwave infrared wavelengths with high
efficiency and low dark count rates. GmAPD arrays are hybridized to CMOS read-out integrated circuits (ROICs) that
enable independent laser radar (LADAR) time-of-flight measurements for each pixel, providing three-dimensional
image data at frame rates approaching 200 kHz. Microlens arrays are used to maintain high fill factor of greater than
70%. We present full-array performance maps for two different types of sensors optimized for operation at 1.06 μm
and 1.55 μm, respectively. For the 1.06 μm FPAs, overall photon detection efficiency of >40% is achieved at <20 kHz
dark count rates with modest cooling to ~250 K using integrated thermoelectric coolers. We also describe the first
evalution of these FPAs when multi-photon pulses are incident on single pixels. The effective detection efficiency for
multi-photon pulses shows excellent agreement with predictions based on Poisson statistics. We also characterize the
crosstalk as a function of pulse mean photon number. Relative to the intrinsic crosstalk contribution from hot carrier
luminescence that occurs during avalanche current flows resulting from single incident photons, we find a modest rise
in crosstalk for multi-photon incident pulses that can be accurately explained by direct optical scattering.
We report on the development of 32 x 32 focal plane arrays (FPAs) based on InGaAsP/InP Geiger-mode avalanche
photodiodes (GmAPDs) designed for use in three-dimensional (3-D) laser radar imaging systems at 1064 nm. To our
knowledge, this is the first realization of FPAs for 3-D imaging that employ a planar-passivated buried-junction InP-based
GmAPD device platform. This development also included the design and fabrication of custom readout integrate
circuits (ROICs) to perform avalanche detection and time-of-flight measurements on a per-pixel basis. We demonstrate
photodiode arrays (PDAs) with a very narrow breakdown voltage distribution width of 0.34 V, corresponding to a
breakdown voltage total variation of less than +/- 0.2%. At an excess bias voltage of 3.3 V, which provides 40% pixel-level
single photon detection efficiency, we achieve average dark count rates of 2 kHz at an operating temperature of
248 K. We present the characterization of optical crosstalk induced by hot carrier luminescence during avalanche
events, where we show that the worst-case crosstalk probability per pixel, which occurs for nearest neighbors, has a
value of less than 1.6% and exhibits anisotropy due to isolation trench etch geometry. To demonstrate the FPA
response to optical density variations, we show a simple image of a broadened optical beam.
Pharmaceutical initiatives use analytical tools to monitor powders flowing through granulating, blending, and tablet
formation steps. Two critical parameters that drive the quality and efficiency of drugs are the concentration of actives in
the tablet, and the dissolution properties of the tablet. In order to ensure that these are within the target design space, it is
important that component concentrations, particle size distributions, and cluster size are monitored throughout the
manufacturing process. Standard optical techniques detect scattered light from spots that encompass many components
in the blend. Efforts to extract composition and blend uniformity based on chemometric analyses are complex and often
intractable. A highly spatially resolved spectral imager could simplify the chemometrics if the effective spatial
resolution can separate most particles from neighboring particles. The effective spatial resolution is a function of the
incident spot size, multiple scattering events, and the collection optics. This paper assesses the degree of spectral mixing
due to particle-particle scattering as a function of incident spot size. Our real-time optical design is enabled by a high
spectral brightness supercontinuum source, a MEMs-based spectral scan mechanism, confocal spatial scanning optics,
and high gain * bandwidth detection.