Arthur Nitkowski

From astronomy and telecommunications to biomedicine

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.

On-chip spectrometer for low-cost optical coherence tomography

Tornado Spectral Systems has developed a new spectrometer called OCTANE, the Optical Coherence Tomography Advanced Nanophotonic Engine, consisting of chip-based spectrometers for spectral domain optical coherence tomography (SD-OCT) systems. These devices include planar lightwave circuits with integrated waveguides fabricated on a planar silicon substrate. Our commercial prototypes include a NIR system centered at a wavelength of 860 nm, a spectral bandwidth of 70 nm, and 2048 output channels to record TE and TM polarizations independently at an 80 kHz line scan rate. Intended to support low-cost, high-volume applications, these spectrometers are well-suited to SD-OCT for both biological and industrial non-destructive testing applications.

Sensing systems using chip-based spectrometers

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.

OCTANE: An Integrated Spectrometer for Optical Coherence Tomography

We introduce the Optical Coherence Tomography Advanced Nanophotonic Engine. OCTANE is the first product line of silicon-chip-based spectrometers for spectral-domain OCT, tailored for low-cost, high-volume medical and industrial applications.

Nanophotonic Spectrometer for Optical Coherence Tomography

We introduce OCTANE, the first product line of chip-based spectrometers using silicon photonics for spectral domain optical coherence tomography (SD-OCT). It is well suited for low-cost, high-volume applications in both the medical and industrial fields.

Thermal-blooming compensation using target-in-the-loop techniques

We report experimental results that demonstrate compensation of extended turbulence and thermal-blooming of high-energy lasers using target-in-the-loop techniques in a scaled laboratory environment. For these experiments the deformable mirror figure was controlled by an algorithm designed to maximize the target-plane intensity as measured by a camera at the transmitter. Results using this TIL configuration were compared under identical conditions to results obtained under control of a Hartmann wavefront sensor and least-squares reconstructor. Experiments were performed for a variety of propagation scenarios anticipated for tactical HEL applications and in all cases the TIL system was seen to outperform the conventional Hartmann-driven adaptive-optics system. We will discuss the details of the the target-in-the-loop algorithm, the laboratory configuration, and the experimental results.

Comparison of cooperative and non-cooperative adaptive optics reference performance for propagation with thermal blooming effects

Atmospheric turbulence and laser-induced thermal blooming effects can degrade the beam quality of a high-energy laser (HEL) weapon, and ultimately limit the amount of energy deliverable to a target. Lincoln Laboratory has built a thermal blooming laboratory capable of emulating atmospheric thermal blooming and turbulence effects for tactical HEL systems. The HEL weapon emulation hardware includes an adaptive optics beam delivery system, which utilizes a Shack-Hartman wavefront sensor and a 349 actuator deformable mirror. For this experiment, the laboratory was configured to emulate an engagement scenario consisting of sea skimming target approaching directly toward the HEL weapon at a range of 10km. The weapon utilizes a 1.5m aperture and radiates at a 1.62 micron wavelength. An adaptive optics reference beam was provided as either a point source located at the target (cooperative) or a projected point source reflected from the target (uncooperative). Performance of the adaptive optics system was then compared between reference sources. Results show that, for operating conditions with a thermal blooming distortion number of 75 and weak turbulence (Rytov of 0.02 and D/ro of 3), cooperative beacon AO correction experiences Phase Compensation Instability, resulting in lower performance than a simple, open-loop condition. The uncooperative beacon resulted in slightly better performance than the open-loop condition.