26 research outputs found
Quanta Burst Photography
Single-photon avalanche diodes (SPADs) are an emerging sensor technology
capable of detecting individual incident photons, and capturing their
time-of-arrival with high timing precision. While these sensors were limited to
single-pixel or low-resolution devices in the past, recently, large (up to 1
MPixel) SPAD arrays have been developed. These single-photon cameras (SPCs) are
capable of capturing high-speed sequences of binary single-photon images with
no read noise. We present quanta burst photography, a computational photography
technique that leverages SPCs as passive imaging devices for photography in
challenging conditions, including ultra low-light and fast motion. Inspired by
recent success of conventional burst photography, we design algorithms that
align and merge binary sequences captured by SPCs into intensity images with
minimal motion blur and artifacts, high signal-to-noise ratio (SNR), and high
dynamic range. We theoretically analyze the SNR and dynamic range of quanta
burst photography, and identify the imaging regimes where it provides
significant benefits. We demonstrate, via a recently developed SPAD array, that
the proposed method is able to generate high-quality images for scenes with
challenging lighting, complex geometries, high dynamic range and moving
objects. With the ongoing development of SPAD arrays, we envision quanta burst
photography finding applications in both consumer and scientific photography.Comment: A version with better-quality images can be found on the project
webpage: http://wisionlab.cs.wisc.edu/project/quanta-burst-photography
Challenges and prospects for multi-chip microlens imprints on front-side illuminated SPAD imagers
The overall sensitivity of frontside-illuminated, silicon single-photon avalanche diode (SPAD) arrays has often suffered from fill factor limitations. The fill factor loss can however be recovered by employing microlenses, whereby the challenges specific to SPAD arrays are represented by large pixel pitch (> 10 µm), low native fill factor (as low as ∼10%), and large size (up to 10 mm). In this work we report on the implementation of refractive microlenses by means of photoresist masters, used to fabricate molds for imprints of UV curable hybrid polymers deposited on SPAD arrays. Replications were successfully carried out for the first time, to the best of our knowledge, at wafer reticle level on different designs in the same technology and on single large SPAD arrays with very thin residual layers (∼10 µm), as needed for better efficiency at higher numerical aperture (NA > 0.25). In general, concentration factors within 15-20% of the simulation results were obtained for the smaller arrays (32×32 and 512×1), achieving for example an effective fill factor of 75.6-83.2% for a 28.5 µm pixel pitch with a native fill factor of 28%. A concentration factor up to 4.2 was measured on large 512×512 arrays with a pixel pitch of 16.38 µm and a native fill factor of 10.5%, whereas improved simulation tools could give a better estimate of the actual concentration factor. Spectral measurements were also carried out, resulting in good and uniform transmission in the visible and NIR
Correlated-photon imaging at 10 volumetric images per second
The correlation properties of light provide an outstanding tool to overcome
the limitations of traditional imaging techniques. A relevant case is
represented by correlation plenoptic imaging (CPI), a quantum-inspired
volumetric imaging protocol employing spatio-temporally correlated photons from
either entangled or chaotic sources to address the main limitations of
conventional light-field imaging, namely, the poor spatial resolution and the
reduced change of perspective for 3D imaging. However, the application
potential of high-resolution imaging modalities relying on photon correlations
is limited, in practice, by the need to collect a large number of frames. This
creates a gap, unacceptable for many relevant tasks, between the time
performance of correlated-light imaging and that of traditional imaging
methods. In this article, we address this issue by exploiting the photon number
correlations intrinsic in chaotic light, combined with a cutting-edge ultrafast
sensor made of a large array of single-photon avalanche diodes (SPADs). This
combination of source and sensor is embedded within a novel single-lens CPI
scheme enabling to acquire 10 volumetric images per second. Our results place
correlated-photon imaging at a competitive edge and prove its potential in
practical applications.Comment: 13 pages, 6 figure
Time-resolved laser speckle contrast imaging (TR-LSCI) of cerebral blood flow
To address many of the deficiencies in optical neuroimaging technologies such
as poor spatial resolution, time-consuming reconstruction, low penetration
depth, and contact-based measurement, a novel, noncontact, time-resolved laser
speckle contrast imaging (TR-LSCI) technique has been developed for continuous,
fast, and high-resolution 2D mapping of cerebral blood flow (CBF) at different
depths of the head. TR-LSCI illuminates the head with picosecond-pulsed,
coherent, widefield near-infrared light and synchronizes a newly developed,
high-resolution, gated single-photon avalanche diode camera (SwissSPAD2) to
capture CBF maps at different depths. By selectively collecting diffuse photons
with longer pathlengths through the head, TR-LSCI reduces partial volume
artifacts from the overlying tissues, thus improving the accuracy of CBF
measurement in the deep brain. CBF map reconstruction was dramatically
expedited by incorporating highly parallelized computation. The performance of
TR-LSCI was evaluated using head-simulating phantoms with known properties and
in-vivo rodents with varied hemodynamic challenges to the brain. Results from
these pilot studies demonstrated that TR-LSCI enabled mapping CBF variations at
different depths with a sampling rate of up to 1 Hz and spatial resolutions
ranging from tens of micrometers on the head surface to 1-2 millimeters in the
deep brain. With additional improvements and validation in larger populations
against established methods, we anticipate offering a noncontact, fast,
high-resolution, portable, and affordable brain imager for fundamental
neuroscience research in animals and for translational studies in humans.Comment: 22 pages, 7 figures, 4 table
A wideband high isolation CMOS T/R switch for x-band phased array radar systems
This paper presents an SPDT switch which is designed to operate at 8-12 GHz frequency range (X-Band), as a sub module of the front end circuit of a phased array radar. The switch distinguishes itself from its counterparts with its larger frequency range and higher isolation that is uniformly distributed over its bandwidth. It is fabricated using 0.25 mu m SiGe BiCMOS technology of IHP Microelectronics (Germany). As a new technique, shunt inductors are placed next to shunt transistors in order to improve trade-off between insertion loss and isolation. It has isolation higher than 30 dB in entire band, input referred 1dB compression point is 27.6 dBm, insertion loss is between 2.7-4.1 dB, input and output referred return losses are better than 11 dB in the frequency range of 8-12 Gliz