Time-of-flight range imaging cameras measure distance and intensity simultaneously for every pixel in an image. With
the continued advancement of the technology, a wide variety of new depth sensing applications are emerging; however
a number of these potential applications have stringent electrical power constraints that are difficult to meet with the
current state-of-the-art systems. Sensor gain modulation contributes a significant proportion of the total image sensor
power consumption, and as higher spatial resolution range image sensors operating at higher modulation frequencies (to
achieve better measurement precision) are developed, this proportion is likely to increase. The authors have developed
a new sensor modulation technique using resonant circuit concepts that is more power efficient than the standard mode
of operation. With a proof of principle system, a 93-96% reduction in modulation drive power was demonstrated across
a range of modulation frequencies from 1-11 MHz. Finally, an evaluation of the range imaging performance revealed
an improvement in measurement linearity in the resonant configuration due primarily to the more sinusoidal shape of the
resonant electrical waveforms, while the average precision values were comparable between the standard and resonant
We present the temperature dependence of absorption and reduced scattering coefficients of 1.8% Intralipid measured by frequency-domain photon-migration spectroscopy between 710 and 850 nm. These measurements were made in the physiologically relevant 30 to 40°C temperature range. The temperature coefficients for absorption were consistent during heating and cooling and follow closely other reported results. The change in absorption coefficient at 740 nm suggests that a minimum temperature change of 4°C is observable within the error limits. We found that the reduced scattering coefficient shows a hysteresis with temperature at 740 nm. The temperature coefficient for reduced scattering determined from heating cycle measurements agrees with theory and other measurements within the error limits.
We present a wavelength-tunable frequency-domain instrument for the characterization of liquid turbid media. The instrument employs a tunable titanium-sapphire laser modulated by an acousto-optic modulator. The absorption and reduced scattering coefficient of Intralipid® 20%, diluted to concentrations of 0.94 to 4.00%, are measured over the wavelength range 710 to 850 nm at 10-nm intervals. The standard measurement errors for the absorption and reduced scattering coefficients are 1 and 2.5%, respectively. Extrapolation to 0% Intralipid® concentration gives an absorption coefficient that closely follows that of water, overestimating the absorption of pure water by less than 10%. The reduced scattering coefficient is compared at 750 nm with published results and is found consistent within the experimental error. We compare the reduced scattering coefficient to an estimate based on Mie theory and find the reduced scattering coefficient underestimated the Mie theory result by about 9%.
Range imaging cameras measure depth simultaneously for every pixel in a given field of view. In most implementations
the basic operating principles are the same. A scene is illuminated with an intensity modulated light source and the
reflected signal is sampled using a gain-modulated imager. Previously we presented a unique heterodyne range imaging
system that employed a bulky and power hungry image intensifier as the high speed gain-modulation mechanism. In this
paper we present a new range imager using an internally modulated image sensor that is designed to operate in
heterodyne mode, but can also operate in homodyne mode. We discuss homodyne and heterodyne range imaging, and
the merits of the various types of hardware used to implement these systems. Following this we describe in detail the
hardware and firmware components of our new ranger. We experimentally compare the two operating modes and
demonstrate that heterodyne operation is less sensitive to some of the limitations suffered in homodyne mode, resulting
in better linearity and ranging precision characteristics. We conclude by showing various qualitative examples that
demonstrate the system's three-dimensional measurement performance.
Excitation and localization of surface plasmon polariton modes in metal-dielectric structures can be utilized to construct
unique nanophotonic materials and devices with tuneable optical transmission. We present selective polariton generator
(SPG) designs that demonstrate selective light transmission based on surface plasmon antennae principles. These
polarisation-sensitive structures can selectively generate and transport polaritons of a desired wavelength through
subwavelength apertures. By specifying geometry and orientation we can control the operational characteristics of these
elements. By varying SPG designs around a central nanohole we are able to achieve operation of nanophotonic devices
where optical transmission peak wavelengths are controlled via the polarisation state of the incident photons. The design
considerations of grating periods, corrugation fan angles, transmission due to inner ring variations, and spectral
separation of paired SPGs were investigated along with the potential of flanking the structures with Bragg reflector
corrugations. The simulations were compared with the experimental results for agreement of the models, which could
lead to experimental investigations of more complex structure.
The temperature dependence (30 to 40°C) of near-infrared spectra (500 to 1100 nm) of whole human blood, including red blood cells with intact physiological function, is investigated. Previous studies have focused on hemoglobin solutions, but the operation of red blood cells is critically dependent on intact cell membranes to perform normal oxygen transport and other physiological functions. Thus measurements of whole blood are more directly related to changes that occur in vivo. In addition to the response of hemoglobin to temperature in the spectra, a temperature response from water in the plasma is also detected. The temperature response of the water absorption at 960 nm is approximately ten times smaller than the temperature response of the oxyhemoglobin component in the blood at 610 nm. However, it is the most significant temperature effect between 800 and 1000 nm. This work will aid the precision and understanding of full spectrum near-infrared measurements on blood.
A hyperspectral imaging system is in development. The system uses spatially modulated Hadamard patterns to encode image information with implicit stray and ambient light correction and a reference beam to correct for source light changes over the spectral image capture period. In this study we test the efficacy of the corrections and the multiplex advantage for our system. The signal to noise ratio (SNR) was used to demonstrate the advantage of spatial multiplexing in the system and observe the effect of the reference beam correction. The statistical implications of the data acquisition technique, illumination source drift and correction of such drift, were derived. The reference beam correction was applied per spectrum before Hadamard decoding and alternately after decoding to all spectra in the image. The reference beam method made no fundamental change to SNR, therefore we conclude that light source drift is minimal and other possibly rectifiable error sources are dominant. The multiplex advantage was demonstrated ranging from a minimum SNR boost of 1.5 (600-975 nm) to a maximum of 11 (below 500 nm). Intermediate SNR boost was observed in 975-1700 nm. The large variation in SNR boost is also due to some other error source.
Lab on chip (LOC) systems often require the controlled movement of individual biological cells. Automated operation
of these systems usually requires detectors to track individual cells. Electrical methods involving measurement of the
conductivity or permittivity of regions between two electrodes are capable of providing this information. However, these
detection systems can interfere with other dielectrophoretic LOC cell handling systems. Conversely optical systems are
immune to electrical interference. Many LOC devices are fabricated with only the top surface of the device being
transparent to light, precluding the use of transmitted optical detection. This is often due to the use of silicon, a favoured
substrate. Here we present a low cost optical system suitable for detecting biological cells in microfluidic channels.
A flow cell with a fluid microlayer approximately 105±10μm deep was fabricated having a 100±10μm thick glass
window, and a reflective base layer. The reflective base was formed by thermal evaporation of gold onto a substrate.
Particles within a microfluidic layer were epi-illuminated by a standard (red) laser DVD pickup unit. The flow cell
permitted the laser beam to be focussed onto the gold reflector, and back through a beamsplitter onto a photodiode. This
system was tested using polystyrene beads that were representative of biological cells. The position of the focal point significantly affected the base line reflected signal, but this micron scale position sensitivity could be overcome using the magnetic focussing coil of the DVD pickup. In this system, polystyrene beads down to 3μm in diameter were successfully detected.
Surface plasmon resonance (SPR) has been used for some time in chemical and biological sensors. Some of the schemes
for exciting surface plasmons include prisms and gratings. Grating-based optical SPR sensors have been demonstrated,
which use light intensity variations at resonance or wavelength interrogation. Recently, a gold grating made from a
commercial recordable compact disk was used for excitation of surface plasmons and SPR imaging. In this paper, we
present a new grating configuration that combines the benefits of multi-angle interrogation with interferometric
measurement techniques. This gives array sensing capability over a wide refractive index range. The set-up is based on
the gold grating of commercially available recordable compact disks, which are mass produced by injection-moulding,
resulting in low cost and disposable grating substrates. The potential of using this system for large sample number
analysis is demonstrated.
We present partial least squares (PLS) regressions to predict the composition of raw, unhomogenised milk using visible to near infrared spectroscopy. A total of 370 milk samples from individual quarters were collected and analysed on-line by two low cost spectrometers in the wavelength ranges 380-1100 nm and 900-1700 nm. Samples were collected from 22 Friesian, 17 Jersey, 2 Ayrshire and 3 Friesian-Jersey crossbred cows over a period of 7 consecutive days. Transmission spectra were recorded in an inline flowcell through a 0.5 mm thick milk sample. PLS models, where wavelength selection was performed using iterative PLS, were developed for fat, protein, lactose, and somatic cell content. The root mean square error of prediction (and correlation coefficient) for the nir and visible spectrometers respectively were 0.70%(0.93) and 0.91%(0.91) for fat, 0.65%(0.5) and 0.47%(0.79) for protein, 0.36%(0.49) and 0.45%(0.43) for lactose, and 0.50(0.54) and 0.48(0.51) for log10 somatic cells.
Currently, the state of the art of mastitis detection in dairy cows is the laboratory-based measurement of somatic cell count (SCC), which is time consuming and expensive. Alternative, rapid, and reliable on-farm measurement methods are required for effective farm management. We have investigated whether fluorescence lifetime measurements can determine SCC in fresh, unprocessed milk. The method is based on the change in fluorescence lifetime of ethidium bromide when it binds to DNA from the somatic cells. Milk samples were obtained from a Fullwood Merlin Automated Milking System and analysed within a twenty-four hour period, over which the SCC does not change appreciably. For reference, the milk samples were also sent to a testing laboratory where the SCC was determined by traditional methods. The results show that we can quantify SCC using the fluorescence photon migration method from a lower bound of 4x105 cells mL-1 to an upper bound of 1 x 107 cells mL-1. The upper bound is due to the reference method used while the cause of the lower boundary is unknown, yet.
The orthogonal axes of illumination, flow, and detection in conventional sorting flow cytometers can limit accuracy or throughput when making fluorescence measurements on a spherical cells. A new radially symmetric optical configuration has been designed to overcome these problems. Both illumination and fluorescence collection are performed by a single optical element which encircles the sample stream flow axis. Unlike existing epi-illumination flow cytometer designs, these optics are compatible with electrostatic sorting. The resolution of this system is currently being evaluated for DNA chromosome content measurement with an ultimate goal of separation of X- and Y- chromosome-bearing mammalian spermatozoa. We describe the new optical configuration and present preliminary results of instrument performance. Comparison with a conventional orthogonal optical geometry is made using fluorescent microspheres, chicken red blood cells and chinchilla sperm.