Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

WDM networks make a very effective utilization of the fiber bandwidth and offer flexible interconnections based on wavelength routing. In high capacity, dynamic WDM networks, blocking due to wavelength contention can he reduced by wavelength conversion. Wavelength conversion addresses a number of key issues in WDM networks including transparency, interoperability, and network capacity. Strictly transparent networks offer seamless interconnections with full reconfigurability and interoperability. Wavelength conversion may be the first obstacle in realizing a transparent WDM network. Among numerous wavelength conversion techniques reported to date, only a few techniques offer strict transparency. Optoelectronic conversion (O/E-E/O) techniques achieve limited transparency, yet their mature technologies allow deployment in the near future. The majority of all-optical wavelength conversion techniques also offer limited transparency but they have a potential advantage over the optoelectronic counterpart in realizing lower packaging costs and crosstalk when multiple wavelength array configurations are considered. Wavelength conversion by difference-frequency generation offers a full range of transparency while adding no excess noise to the signal. Recent experiments showed promising results including a spectral inversion and a 90 nm conversion bandwidth. This paper reviews various wavelength conversion techniques, discusses the advantages and shortcomings of each technique, and addresses their implications for transparent networks.

Wavelength conversion technologies for WDM network applications

Quantitative Optical Coherence Tomography Angiography of Choroidal Neovascularization in Age-Related Macular Degeneration

Optical Coherence Tomography Angiography of Optic Disc Perfusion in Glaucoma

Purpose To compare optic disc perfusion between normal subjects and subjects with glaucoma using optical coherence tomography (OCT) angiography and to detect optic disc perfusion changes in glaucoma. Design Observational, cross-sectional study. Participants Twenty-four normal subjects and 11 patients with glaucoma were included. Methods One eye of each subject was scanned by a high-speed 1050-nm–wavelength swept-source OCT instrument. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to compute 3-dimensional optic disc angiography. A disc flow index was computed from 4 registered scans. Confocal scanning laser ophthalmoscopy (cSLO) was used to measure disc rim area, and stereo photography was used to evaluate cup/disc (C/D) ratios. Wide-field OCT scans over the discs were used to measure retinal nerve fiber layer (NFL) thickness. Main Outcome Measures Variability was assessed by coefficient of variation (CV). Diagnostic accuracy was assessed by sensitivity and specificity. Comparisons between glaucoma and normal groups were analyzed by Wilcoxon rank-sum test. Correlations among disc flow index, structural assessments, and visual field (VF) parameters were assessed by linear regression. Results In normal discs, a dense microvascular network was visible on OCT angiography. This network was visibly attenuated in subjects with glaucoma. The intra-visit repeatability, inter-visit reproducibility, and normal population variability of the optic disc flow index were 1.2%, 4.2%, and 5.0% CV, respectively. The disc flow index was reduced by 25% in the glaucoma group ( P = 0.003). Sensitivity and specificity were both 100% using an optimized cutoff. The flow index was highly correlated with VF pattern standard deviation ( R 2  = 0.752, P = 0.001). These correlations were significant even after accounting for age, C/D area ratio, NFL, and rim area. Conclusions Optical coherence tomography angiography, generated by the new SSADA, repeatably measures optic disc perfusion and may be useful in the evaluation of glaucoma and glaucoma progression.

This paper demonstrates new wavelength swept light source technology, MEMS tunable VCSELs, for OCT imaging.
The VCSEL achieves a combination of ultrahigh sweep speeds, wide spectral tuning range, flexibility in sweep
trajectory, and extremely long coherence length, which cannot be simultaneously achieved with other technologies. A
second generation prototype VCSEL is optically pumped at 980nm and a low mass electrostatically tunable mirror
enables high speed wavelength tuning centered at ~1310nm with ~110nm of tunable bandwidth. Record coherence
length >100mm enables extremely long imaging range. By changing the drive waveform, a single 1310nm VCSEL was
driven to sweep at speeds from 100kHz to 1.2MHz axial scan rate with unidirectional and bidirectional high duty cycle
sweeps. We demonstrate long range and high resolution 1310nm OCT imaging of the human anterior eye at 100kHz
axial scan rate and imaging of biological samples at speeds of 60kHz - 1MHz. A first generation 1050nm device is
shown to sweep over 100nm. The results of this study suggest that MEMS based VCSEL swept light source technology
has unique performance characteristics and will be a critical technology for future ultrahigh speed and long depth range
OCT imaging.

/pdf/mems-tunable-vcsel-light-source-for-ultrahigh-speed-60khz-1r3vp5scr0.pdf

MEMS tunable VCSEL light source for ultrahigh speed 60kHz - 1MHz axial scan rate and long range centimeter class OCT imaging

We developed a micromotor based miniature catheter with an outer diameter of 3.2 mm for ultrahigh speed endoscopic swept source optical coherence tomography (OCT) using a vertical cavity surface-emitting laser (VCSEL) at a 1 MHz axial scan rate. The micromotor can rotate a micro-prism at several hundred frames per second with less than 5 V drive voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back to acquire a three-dimensional (3D) data set covering a large area on the specimen. The VCSEL provides a high axial scan rate to support dense sampling under high frame rate operation. Using a high speed data acquisition system, in vivo 3D-OCT imaging in the rabbit GI tract and ex vivo imaging of a human colon specimen with 8 μm axial resolution, 8 μm lateral resolution and 1.2 mm depth range in tissue at a frame rate of 400 fps was demonstrated.

/pdf/ultrahigh-speed-endoscopic-optical-coherence-tomography-264sxiqzyz.pdf

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology

A resonant coupler has a coupling region having first and second ends, a coupling length, and a tapered variable width, such that a phase matching condition for the waveguide is met within the coupling length. In an exemplary embodiment the first and second ends each have a corresponding variable width which varies at a rate greater than the variable width of the coupling length. In yet another embodiment the coupling region has an electrically sensitive phase matching characteristic and an electrode in operative relation with the coupling region for varying the phase matching characteristic.

Resonantly coupled waveguides using a taper

An agile optical imaging system for optical coherence tomography imaging using a tunable source comprising a wavelength tunable VCL laser is disclosed. The tunable source has long coherence length and is capable of high sweep repetition rate, as well as changing the sweep trajectory, sweep speed, sweep repetition rate, sweep linearity, and emission wavelength range on the fly to support multiple modes of OCT imaging. The imaging system also offers new enhanced dynamic range imaging capability for accommodating bright reflections. Multiscale imaging capability allows measurement over orders of magnitude dimensional scales. The imaging system and methods for generating the waveforms to drive the tunable laser in flexible and agile modes of operation are also described.

Agile imaging system

The output optical beam from an angled-facet semiconductor laser diode is made to propagate parallel to the optical axis of the laser package with low optical back-reflection. In this way, the angled-facet devices are made compatible with conventional semiconductor laser packages enabling them to be economically incorporated in a wide-range of external semiconductor lasers and amplified spontaneous emission sources. The parallel beam is achieved by tilting the laser diode with respect to the front and back surfaces of the package.

Peter J. S. Heim

Papers

MEMS tunable VCSEL light source for ultrahigh speed 60kHz - 1MHz axial scan rate and long range centimeter class OCT imaging

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology

Resonantly coupled waveguides using a taper

Agile imaging system

Laser diode package