Photonics is an inherently interdisciplinary endeavor, as technologies and techniques invented or developed in one
scientific field are often found to be applicable to other fields or disciplines. We present two case studies in which
optical spectroscopy technologies originating from stellar astrophysics and optical telecommunications multiplexing
have been successfully adapted for biomedical applications. The first case involves a design concept called the High
Throughput Virtual Slit, or HTVS, which provides high spectral resolution without the throughput inefficiency typically
associated with a narrow spectrometer slit. HTVS-enhanced spectrometers have been found to significantly improve the
sensitivity and speed of fiber-fed Raman analysis systems, and the method is now being adapted for hyperspectral
imaging for medical and biological sensing. The second example of technology transfer into biomedicine centers on
integrated optics, in which optical waveguides are fabricated on to silicon substrates in a substantially similar fashion as
integrated circuits in computer chips. We describe an architecture referred to as OCTANE which implements a small and
robust "spectrometer-on-a-chip” which is optimized for optical coherence tomography (OCT). OCTANE-based OCT
systems deliver three-dimensional imaging resolution at the micron scale with greater stability and lower cost than
equivalent conventional OCT approaches. Both HTVS and OCTANE enable higher precision and improved reliability
under environmental conditions that are typically found in a clinical or laboratory setting.
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.
In this paper, we report on a compact prototype capable both of lensfree imaging, Raman spectrometry and scattering
microscopy from bacteria samples. This instrument allows high-throughput real-time characterization without the need
of markers, making it potentially suitable to field label-free biomedical and environmental applications.
Samples are illuminated from above with a focused-collimated 532nm laser beam and can be x-y-z scanned. The bacteria
detection is based on emerging lensfree imaging technology able to localize cells of interest over a large field-of-view of
Raman signal and scattered light are then collected by separate measurement arms simultaneously. In the first arm the
emission light is fed by a fiber into a prototype spectrometer, developed by Tornado Spectral System based on Tornado’s
High Throughput Virtual Slit (HTVS) novel technology. The enhanced light throughput in the spectral region of interest
(500-1800 cm-1) reduces Raman acquisition time down to few seconds, thus facilitating experimental protocols and
avoiding the bacteria deterioration induced by laser thermal heating. Scattered light impinging in the second arm is
collected onto a charge-coupled-device. The reconstructed image allows studying the single bacteria diffraction pattern
and their specific structural features.
The characterization and identification of different bacteria have been performed to validate and optimize the acquisition
system and the component setup.
The results obtained demonstrate the benefits of these three techniques combination by providing the precise bacteria
localization, their chemical composition and a morphology description. The procedure for a rapid identification of
particular pathogen bacteria in a sample is illustrated.