We describe a re-configurable scanning lidar system which can accommodate either a single element detector operating
in a scanning mode or a 32 x 32 array detector operating in a non-scanning mode. The system uses a time-of-flight
approach in conjunction with the single-photon counting technique to produce 3D images of non-cooperative targets at
ranges of greater than one kilometre. Results of data acquired with a single-element detector in a scanning mode at 2.9
km and 4.6 km are reported. The field of view (FoV) was illuminated through a transmitter in a bi-static mode using 125
kHz repetition rate laser pulses at a wavelength of 1550 nm with an average optical power of 0.5W.
Recent developments in 3D imaging lidar are presented. Long range 3D imaging using photon counting is now a possibility, offering a low-cost approach to integrated remote sensing with step changing advantages in size, weight and power compared to conventional analogue active imaging technology. We report results using a Geiger-mode array for time-of-flight, single photon counting lidar for depth profiling and determination of the shape and size of tree canopies and distributed surface reflections at a range of 9km, with 4μJ pulses with a frame rate of 100kHz using a low-cost fibre laser operating at a wavelength of λ=1.5 μm. The range resolution is less than 4cm providing very high depth resolution for target identification. This specification opens up several additional functionalities for advanced lidar, for example: absolute rangefinding and depth profiling for long range identification, optical communications, turbulence sensing and time-of-flight spectroscopy. Future concepts for 3D time-of-flight polarimetric and multispectral imaging lidar, with optical communications in a single integrated system are also proposed.
This paper discusses the system engineering challenges involved with the transmission of optically encoded data through water. The scenarios of data transmission from an airborne platform to a submerged platform and data transmission from a submerged platform to another submerged platform will be discussed. A photon-counting experimental system was constructed to investigate the transmission of optical data through a 1m long tank of water. This test system incorporated a laser diode operating at a wavelength of 450nm and an optical receiver containing a shallow junction, silicon single photon avalanche diode. The optical data was transmitted through the tank containing ~100 litres of water at transmission rates equivalent to 40Mb/s. The attenuation of the optical path was increased by increasing the level of scattering of the photons using Maalox. The effects on the temporal distribution of photons in the optical pulse from adding Maalox are also discussed. The synchronisation of the transmitter and receiver clocks was investigated using reference headers appended to the encoded message signal which the receiver used to correct for timing drift. The performance of this experimental system and experimental results are discussed.
This paper reports the performance of a long range 3D imaging system operating at a wavelength of 1550nm incorporating a Geiger mode 32x32 array InGaAs/InP camera. A cross-correlation technique were used to mitigate range aliasing and therefore enable the measurement of the absolute range to single or multiple surfaces within the instantaneous field of view of each pixel in the 2D array. The system uses a fibre amplified laser source operating at an average pulse repetition rate of 125kHz with pulse energies of 2.4μJ per pulse. Measurements of the absolute range to remote manmade Lambertian surfaces and foliage at ranges up to 10km with range accuracy of better than 4cm are reported. The simultaneous imaging and measurement of the absolute range of two remote manmade Lambertian surfaces separated by >1km is also presented.
We report on the performance of a photon-counting optical communication system which was used to
transmit optical data at clock rates (not detection rates) of 40Mb/s at a wavelength of 450nm. The
transmitted test data patterns comprised of one page of ASCII text preceded by a pseudo-random sequence
used as a timing reference pattern by the receiver. The optical data patterns were transmitted through an
aquarium tank containing ~110 litres of water and were detected at the receiver by a shallow junction
silicon single photon avalanche diode detector. An antacid, brand name Maalox, was introduced into the
tank to increase the scattering of the optical pulses. The bit error rate and bit rate of the transmitted data
were investigated for a range of Maalox concentrations. The optical attenuation and pulse distortion caused
by the introduction of Maalox was also investigated.
Typical commercially available airborne lidar systems utilise analogue avalanche photodiodes to detect the return pulses
but can be restricted to operation at low altitudes because of the weak pulse energies associated with returns from
Lambertian surfaces. The ultra high sensitivity of single photon avalanche diodes have been demonstrated in many
applications such as time-resolved photoluminescence and quantum key distribution and with their ability to detect
single photons with high efficiency these devices are potential candidates for use in high altitude lidar systems. However,
the long hold-off times of these devices has been a cause for concern in an application where rapid data collection is
necessary. This paper discusses the use of single photon avalanche diodes in high altitude lidar systems. The general
requirements for a lidar system are described and the performance of single photon avalanche diode devices is predicted
for both static and scanned lidar systems.
This paper describes a rapid data acquisition photon-counting time-of-flight ranging technique that is
designed for the avoidance of range ambiguity, an issue commonly found in high repetition frequency timeof-
flight systems. The technique transmits a non-periodic pulse train based on the random bin filling of a
high frequency time clock. A received pattern is formed from the arrival times of the returning single photons
and the correlation between the transmitted and received patterns was used to identify the unique target timeof-
flight. The paper describes experiments in free space at over several hundred meters range at clock
frequencies of 1GHz. Unambiguous photon-counting range-finding is demonstrated with centimeter
Proc. SPIE. 6900, Quantum Sensing and Nanophotonic Devices V
KEYWORDS: Mirrors, Photon counting, 3D acquisition, Detection and tracking algorithms, Sensors, Semiconductor lasers, Data processing, Signal processing, Single photon detectors, Pulsed laser operation
Time-correlated single-photon counting techniques using individual optimized detectors have been applied to
time-of-flight ranging and depth imaging. This paper describes recent progress in photon-counting systems
performing surface mapping of non-cooperative targets. This includes systems designed for short ranges of the
order of 1-50 meters, and longer ranges of up to ten kilometers. The technique has also been applied to distributed
surfaces. We describe the measurement approach, techniques used for scanning, as well as the signal analysis
methodology and algorithm selection.
The technique is fundamentally flexible: the trade-off between the integrated number of counts (or acquisition
time) against range repeatability or depth resolution allows its application in a number of diverse fields. The
inherent time gating of the technique, allied to the spatial filtering provided by small active area single-photon
detectors, can lead to operation under high ambient light conditions even with low average optical power pulsed
We have demonstrated three-dimensional imaging of meter-dimensioned objects where reverse engineering
methods using cooperative targets cannot be routinely employed: e.g. delicate objects, or objects with more than
one reflective surface. Using more advanced signal processing algorithms, we have been able to improve the system
performance significantly, as measured by the depth resolution at short and long ranges. Furthermore, the
application of these methodologies has allowed us to characterize the positions and amplitudes of multiple returns.
Hence, the approach can be used for characterization of distributed non-cooperative targets at kilometer ranges,
even in environments where low-light level and and/or eye-safe operation is necessary.
The technique has also been applied in conjunction with a rapid scanning approach, to acquire three-dimensional
information of a target scene with frame times of approximately 1 second.
Quantum communications is an emerging field with many promising applications. Its usefulness and range of
applicability in optical fiber will depend strongly on the extent to which quantum channels can be reliably transported
over transparent reconfigurable optical networks, rather than being limited to dedicated point-to-point links. This
presents a number of challenges, particularly when single-photon quantum and much higher power classical optical
signals are combined onto a single physical infrastructure to take advantage of telecom networks built to carry
conventional traffic. In this paper, we report on experimental demonstrations of successful quantum key distribution
(QKD) in this complex environment, and on measurements of physical-layer impairments, including Raman scattering
from classical optical channels, which can limit QKD performance. We then extend the analysis using analytical models
incorporating impairments, to investigate QKD performance while multiplexed with conventional data channels at other
wavelengths. Finally, we discuss the implications of these results for evaluating the most promising domains of use for
QKD in real-world optical networks.
A novel system for ultra-long-distance quantum key distribution in optical fiber, incorporating ultra-low-noise transition-edge
sensor (TES) photodetectors, is described. Integration of the TES detectors into the system was facilitated with a
unique optically switched interferometer design. The performance of the system over 101 km of dark, single-mode fiber
at 1550 nm and a clock rate of 1 MHz is described. Secret-key bits were produced after error correction and privacy
amplification when using mean photon numbers of 0.01, 0.0148, 0.02, 0.0304, and 0.2 photons/pulse at the output of the
transmitter. At a mean photon number of 0.1 photons per pulse at the transmitter, a transmission line loss of 29.92 dB,
roughly equivalent to 150 km of optical fiber, could be tolerated and secret bits extracted from the transmitted key.
Quantum communications is fast becoming an important component of many applications in quantum information
science. Sharing quantum information over a distance among geographically separated nodes using photonic qubits
requires a reconfigurable transparent networking infrastructure that can support quantum information services. Using
quantum key distribution (QKD) as an example of a quantum communications service, we investigate the ability of fiber
networks to support both conventional optical traffic and single-photon quantum communications signals on a shared
infrastructure. The effect of Raman scattering from conventional channels on the quantum bit error rate (QBER) of a
QKD system is analyzed. Additionally, the potential impact and mitigation strategies of other transmission impairments
such as four-wave mixing, cross-phase modulation, and noise from mid-span optical amplifiers are discussed. We also
review recent trends toward the development of automated and integrated QKD systems which are important steps
toward reliable and manufacturable quantum communications systems.
A novel, user-friendly quantum key distribution (QKD) system operating at a wavelength of 1550nm and at a clock rate of 10MHz was constructed to explore the compatibility of this emerging technology with the optical fiber network environment. Custom circuit boards providing the low-level control and sensing functions for both the transmitter and receiver were developed, allowing software-based system reconfiguration via USB interface to personal computers. The computer control allowed the user to change operating parameters such as detector bias voltages and pulse delays and also allowed for self-tuning of the system. Epitaxx avalanche photodiodes, operated in Geiger mode, were used to detect the single photons. A complete QKD protocol stack incorporating the "sifting", reconciliation, privacy amplification, authentication and key confirmation functions was implemented in software. The system was tested over twenty five kilometers of dark underground fiber, producing 18.6 million sifted bits, with a sifted bit error rate of 4.9% at an average number of photons per pulse of 0.2, during a continuous 12-hour period of self-sustaining operation: a small portion of the secret bits distilled from each session's sifted bits were used to authenticate the next session. A total of 6.8 million shared secret bits were produced.
Quantum key distribution (QKD) is an emerging technology for secure distribution of keys between users linked by free-space or fiber optic transmission facilities. QKD has usually been designed for and operated over dedicated point-to-point links. However, the commercial world has been developing increasingly sophisticated fiber networks, with basic networking functions such as routing and multiplexing performed in the optical domain. One of the most important practical questions for the future of QKD is to what extent it can benefit from these trends, either to expand the capabilities of dedicated quantum networks, or to avoid the need for dedicated networks by combining quantum and conventional optical signals onto a single infrastructure.
In this paper, we report on systematic investigations of these issues using a 1310-nm weak-coherent, phase-encoded B92 prototype QKD system developed by Los Alamos that includes the implementation of error correction, privacy amplification, and authentication. We have demonstrated reconfigurability of QKD networks via optical switching and successful QKD operation in the presence of amplified DWDM signals over 10 km of fiber. We have identified anti-Stokes Raman scattering of the DWDM signals in the fiber as a dominant transmission impairment for QKD, and developed filtering architectures to extend transmission distances to at least 25 km. We have also measured noise backgrounds and polarization variations in network fibers to understand applicability to real-world networks. We will discuss the implications of our results for the choice of QKD wavelengths, wavelength-spacing between QKD and conventional channels, and QKD network architectures.