We have developed an automated, wide-field optical coherence tomography (OCT)-based imaging device (OTIS<sup>TM</sup> Perimeter Medical Imaging) for peri-operative, ex-vivo tissue imaging. This device features automated image acquisition, enabling rapid capture of high-resolution (15 μm) OCT images from samples up to 10 cm in diameter. We report on the iterative progression of device development from phantom and pre-clinical (tumor xenograft) models through to initial clinical results. We discuss the challenges associated with proving a novel imaging technology against the clinical “gold standard” of conventional post-operative pathology.
Tornado Spectral Systems has developed a new chip-based spectrometer called OCTANE, the Optical Coherence Tomography Advanced Nanophotonic Engine, built using a planar lightwave circuit with integrated waveguides fabricated on a silicon wafer. While designed for spectral domain optical coherence tomography (SD-OCT) systems, the same miniaturized technology can be applied to many other spectroscopic applications. The field of integrated optics enables the design of complex optical systems which are monolithically integrated on silicon chips. The form factors of these systems can be significantly smaller, more robust and less expensive than their equivalent free-space counterparts. Fabrication techniques and material systems developed for microelectronics have previously been adapted for integrated optics in the telecom industry, where millions of chip-based components are used to power the optical backbone of the internet. We have further adapted the photonic technology platform for spectroscopy applications, allowing unheard-of economies of scale for these types of optical devices. Instead of changing lenses and aligning systems, these devices are accurately designed programmatically and are easily customized for specific applications. Spectrometers using integrated optics have large advantages in systems where size, robustness and cost matter: field-deployable devices, UAVs, UUVs, satellites, handheld scanning and more. We will discuss the performance characteristics of our chip-based spectrometers and the type of spectral sensing applications enabled by this technology.
Tornado Spectral Systems (TSS) has developed High Throughput Virtual Slit (HTVS) technology that improves the
performance of spectrometers by factors of several while maintaining system size. In the simplest configuration, the
HTVS allows optical designers to remove the lossy slit from a spectrometer, greatly increasing throughput without a
loss of resolution. This is especially useful in many standoff applications, where every photon matters.
TSS has tested multiple configurations of HTVS spectral sensing and spectral imaging technology, including
standoff sensing, point scan imaging, long-slit pushbroom imaging and similar configurations. The HTVS
throughput-resolution advantage allows us to increase scanning speed, decrease system size, decrease aperture,
decrease source intensity requirements or some combination of all four. HTVS technology expands the realm of
viable spectral imaging applications. We discuss the applicability of this technology to spectral imaging and
standoff sensing and present experimental results from several prototype and production spectrometers.
Traditional spectrometer design requires trading off between resolution and throughput (two key parameters which define performance) and physical size. Increasing the internal beam diameter is the simplest method of improving the performance of an otherwise optimized spectrometer. Sadly, this increased beam size also directly translates into increased system volume, weight, and cost. Functional limitations on size (and thus performance) can also prevent spectroscopy from being used in applications where it would otherwise be a perfect fit. Tornado Spectral Systems’ (TSS) High Throughput Virtual Slit (HTVS) redefines the performance-size limit by replacing the traditional slit in a spectrometer, allowing for designs that exceed traditional limitations on size and performance. Spectrometers can be made smaller while maintaining performance or system performance can be increased without increasing spectrometer size. Dispersive spectrometer theory is presented and used to construct a simulation that evaluated spectrometer performance based on volume for a slit-only and HTVS enabled instrument. Results show that as long as detector height is a non-limiting factor, HTVS enabled spectrometers have the potential to outperform slit-only spectrometers by factors up to several at equivalent volumes.
Integrated optical semiconductor sensors are a promising technology for both lab-on-a-chip and molecular imaging
applications due to their low cost, small size, high sensitivity, and flexible designs. We present the design and fabrication
of a GaAs-based monolithically integrated fluorescence sensor incorporating 670nm VCSELs and PIN photodetectors.
This is the first integrated, VCSEL-based fluorescence sensor with excitation at a far-red wavelength and is specifically
designed for in vivo sensing applications. In addition, we discuss considerations to simultaneously achieve high power
VCSELs and low dark current PIN photodetectors required for sensitive fluorescence detection. These fabricated sensors
incorporate 670nm VCSELs emitting 2.0mW at room temperature (RT) with adjacent detectors exhibiting RT dark less
than 2pA/mm<sup>2</sup> (100mV reverse bias). Fluorescence emission filters suitable for transmitting Cy5.5 fluorescent dye
emission were integrated with the photodetectors. The sensor detects Cy5.5 molecules in vitro at 5nM concentration with
linear response for concentrations up to 25μM. These miniature sensors are suitable for portable diagnostic assays and in
vivo rodent studies.
We present the design and fabrication of an implantable fluorescence biosensor suitable for continuously monitored,
freely-moving in vivo rodent studies. The GaAs-based semiconductor sensor incorporates an un-cooled photodetector
with a 670nm vertical-cavity surface-emitting laser (VCSEL) optimized for sensing fluorescent Cy5.5 dye. For filtering
unwanted spectra, a combination of physical and spectral blocking layers yields OD5 excitation rejection at the detector.
The sensor detects near-IR fluorescent Cy5.5 molecules in vitro at 100nM concentration (in a 100μL volume) with linear
response for concentrations up to 25μM. In a preliminary study in a living mouse, subcutaneously injected dye (1μM
Cy5.5 in 50μL) was detected. This technology has the potential to enable new studies of living systems in applications
that require long-term, continuous fluorescence sensing.