We demonstrate the first 1050nm MEMS-eVCSEL co-packaged with a wideband amplifier to achieve over 70nm wavelength tuning at over 30mW of output power and SMSR greater than 40dB. Ophthalmic Optical Coherence Tomography Angiography (OCTA) images acquired at 800kHz A-scan rates showcase the telecom grade 14pin butterfly co-package as a path to low cost swept source OCT engines. Device design employs a strain-compensated InGaAs/GaAsP gain region disposed on a wideband fully oxidized GaAs/AlxOy back mirror capable of tuning ranges beyond 100nm. It has been suggested the wideband fully oxidized GaAs/AlxOy back mirror may pose risk to device lifetime reliability. However, over 9000hrs of lifetime testing validates reliability and projects device lifetimes exceed 20,000hrs under continuous use.
We report on a comparison between the piezoelectric and interferometric readouts of vibrations in quartz tuning forks (QTFs) when employed as sound wave transducers in quartz-enhanced photoacoustic trace gas sensors. We demonstrate the possibility to properly design the QTF geometry to enhance interferometric readout signal with respect to the piezoelectric one and vice versa. When resonator tubes are acoustically coupled with the QTFs, signal-to-noise ratio enhancements are observed for both readout approaches. These results open the way to the implementation of optical readout of QTF vibrations in applications where external electromagnetic field could distort the piezoelectric signal.
We report on the performance of new quartz tuning fork (QTF) designs optimized for quartz-enhanced photoacoustic spectroscopy (QEPAS). We investigated the impact on resonance properties of prong geometries differing from the standard rectangular one. We proposed a QTF with T-shaped prongs and a QTF with prongs having rectangular grooves carved on the surface. QTFs were implemented in a QEPAS sensor and performances were compared in terms of signalto-noise ratio (SNR). Then, QTFs were acoustically coupled with single- and dual-tube micro-resonator systems. A record x60 SNR enhancement factor with respect to the bare QTF was achieved with QTF having T-shaped prongs.
We report on a comparison between two quartz tuning forks (QTFs) employed for quartz-enhanced photoacoustic spectroscopy (QEPAS) having quadrupole and octupole electrode pattern configurations. With respect to the quadrupole, the implementation of the octupole pattern suppresses the fundamental mode and reduces by a factor of ~ 4.4 the electrical resistance for the first overtone mode with negligible variations of the related Q-factors. Both QTFs operating at the first overtone mode were implemented in a QEPAS sensor and the results showed that the octupole configuration provides a ~2.3 signal enhancement factor.
We report on the development of a gas sensor system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) for the detection of trace levels of ethylene using a quantum cascade laser operating at ~ 10.3 μm. To realize a compact sensor architecture, a dedicated acoustic detection module was designed and implemented. The module includes a QEPAS spectrophone, composed of a quartz tuning fork, a micro-resonator tube and a low-noise pre-amplifier chip for the signal readout. The volume of the ADM is ~30 cm3. A minimum detection limit of 30 part-per-billion in concentration was obtained with a data acquisition time of 10 s.
We present a portable multiphoton system designed for evaluating centimeter-scale surgical margins on surgical breast specimens in a clinical setting. The system is designed to produce large field of view images at a high frame rate, while using GPU processing to render low latency, video-rate virtual H&E images for real-time assessment. The imaging system and virtual H&E rendering algorithm are demonstrated by imaging unfixed human breast tissue in a clinical setting.
We report mid-infrared supercontinuum (SC) generation in a dispersion-engineered step-index indium fluoride fiber pumped by a femtosecond fiber laser near 2 μm. The SC spans 1.8 octaves from 1.25 μm to 4.6 μm with an average output power of 270 mW. The pump source is an all-fiber femtosecond laser that generates sub-100 fs pulses at 50 MHz repetition rate with 570 mW average power. The indium fluoride fiber used for SC generation is designed to have a zerodispersion wavelength close to 1.9 μm. Two fiber lengths of 30 cm and 55 cm are selected for the SC generation experiments based on the numerical modelling results. The measured spectra and the numerical modelling results are presented showing good agreement for both lengths. The femtosecond pumping regime is a key requirement for generating a coherent SC. We show by modelling that the SC is coherent for a pump with the same pulse width and energy as our fiber laser and added quantum-limited noise. The results are promising for the realization of coherent and high-repetition-rate SC sources, two conditions that are critical for spectroscopy applications using FTIR spectrometers. Additionally, the entire SC system is built using optical fibers with similar core diameters, which enables integration into a compact platform.
In this work, we report using an optical tweezers system to study the light-matter interaction and gradient optical forces of porous silicon nanoparticles. The particles are fabricated by first electrochemically etching a multi-layer porous film into a silicon wafer and then breaking up the film through ultrasonic fracturing. The particles have average pore diameters ranging from 20-30 nm. The fabricated batches of particles have diameters between approximately 100- 600nm. After fabrication, the particles are size-sorted by centrifugation. A commercially available optical tweezers system is used to systematically study the optical interaction with these nanoparticles. This work opens new strategic approaches to enhance optical forces and optical sensitivity to mechanical motion that can be the basis for future biophotonics applications.
Since the first demonstration of swept source optical coherence tomography (SS-OCT) imaging using widely tunable micro-electromechanical systems vertical cavity surface-emitting lasers (MEMS-VCSELs) in 2011, VCSEL-based SSOCT has advanced in both device and system performance. These advances include extension of MEMS-VCSEL center wavelength to both 1060nm and 1300nm, improved tuning range and tuning speed, new SS-OCT imaging modes, and demonstration of the first electrically pumped devices. Optically pumped devices have demonstrated continuous singlemode tuning range of 150nm at 1300nm and 122nm at 1060nm, representing a fractional tuning range of 11.5%, which is nearly a factor of 3 greater than the best reported MEMS-VCSEL tuning ranges prior to 2011. These tuning ranges have also been achieved with wavelength modulation rates of >500kHz, enabling >1 MHz axial scan rates. In addition, recent electrically pumped devices have exhibited 48.5nm continuous tuning range around 1060nm with 890kHz axial scan rate, representing a factor of two increase in tuning over previously reported electrically pumped MEMS-VCSELs in this wavelength range. New imaging modes enabled by optically pumped devices at 1060nm and 1300nm include full eye length imaging, pulsatile Doppler blood flow imaging, high-speed endoscopic imaging, and hand-held wide-field retinal imaging.
We developed an ultrahigh speed endoscopic swept source optical coherence tomography (OCT) system for clinical
gastroenterology using a vertical-cavity surface-emitting laser (VCSEL) and micromotor based imaging catheter, which
provided an imaging speed of 600 kHz axial scan rate and 8 μm axial resolution in tissue. The micromotor catheter was
3.2 mm in diameter and could be introduced through the 3.7 mm accessory port of an endoscope. Imaging was
performed at 400 frames per second with an 8 μm spot size using a pullback to generate volumetric data over 16 mm
with a pixel spacing of 5 μm in the longitudinal direction. Three-dimensional OCT (3D-OCT) imaging was performed in
patients with a cross section of pathologies undergoing standard upper and lower endoscopy at the Veterans Affairs
Boston Healthcare System (VABHS). Patients with Barrett’s esophagus, dysplasia, and inflammatory bowel disease
were imaged. The use of distally actuated imaging catheters allowed OCT imaging with more flexibility such as
volumetric imaging in the terminal ileum and the assessment of the hiatal hernia using retroflex imaging. The high
rotational stability of the micromotor enabled 3D volumetric imaging with micron scale volumetric accuracy for both en
face and cross-sectional imaging. The ability to perform 3D OCT imaging in the GI tract with microscopic accuracy
should enable a wide range of studies to investigate the ability of OCT to detect pathology as well as assess treatment
response.
In the last 2 years, the field of micro-electro-mechanical systems tunable vertical cavity surface-emitting lasers (MEMS-VCSELs)
has seen dramatic improvements in laser tuning range and tuning speed, along with expansion into unexplored
wavelength bands, enabling new applications. This paper describes the design and performance of high-speed ultra-broad
tuning range 1050nm and 1310nm MEMS-VCSELs for medical imaging and spectroscopy. Key results include
achievement of the first MEMS-VCSELs at 1050nm and 1310nm, with 100nm tuning demonstrated at 1050nm and
150nm tuning at shown at 1310nm. The latter result represents the widest tuning range of any MEMS-VCSEL at any
wavelength. Wide tuning range has been achieved in conjunction with high-speed wavelength scanning at rates beyond 1
MHz. These advances, coupled with recent demonstrations of very long MEMS-VCSEL dynamic coherence length,
have enabled advancements in both swept source optical coherence tomography (SS-OCT) and gas spectroscopy.
VCSEL-based SS-OCT at 1050nm has enabled human eye imaging from the anterior eye through retinal and choroid
layers using a single instrument for the first time. VCSEL-based SS-OCT at 1310nm has enabled real-time 3-D SS-OCT
imaging of large tissue volumes in endoscopic settings. The long coherence length of the VCSEL has also enabled, for
the first time, meter-scale SS-OCT applicable to industrial metrology. With respect to gas spectroscopy, narrow dynamic
line-width has allowed accurate high-speed measurement of multiple water vapor and HF absorption lines in the 1310nm
wavelength range, useful in gas thermometry of dynamic combustion engines.
Recent advances in swept-source / Fourier domain optical coherence tomography (SS-OCT) technology enable in vivo ultrahigh speed imaging, offering a promising technique for four-dimensional (4-D) imaging of the eye. Using an ultrahigh speed tunable vertical cavity surface emitting laser (VCSEL) light source based SS-OCT prototype system, we performed imaging of human eye dynamics in four different imaging modes: 1) Pupillary reaction to light at 200,000 axial scans per second and 9 μm resolution in tissue. 2) Anterior eye focusing dynamics at 100,000 axial scans per second and 9 μm resolution in tissue. 3) Tear film break up at 50,000 axial scans per second and 19 μm resolution in tissue. 4) Retinal blood flow at 800,000 axial scans per second and 12 μm resolution in tissue. The combination of tunable ultrahigh speeds and long coherence length of the VCSEL along with the outstanding roll-off performance of SS-OCT makes this technology an ideal tool for time-resolved volumetric imaging of the eye. Visualization and quantitative analysis of 4-D OCT data can potentially provide insight to functional and structural changes in the eye during disease progression. Ultrahigh speed imaging using SS-OCT promises to enable novel 4-D visualization of realtime dynamic processes of the human eye. Furthermore, this non-invasive imaging technology is a promising tool for research to characterize and understand a variety of visual functions.
KEYWORDS: Optical coherence tomography, Vertical cavity surface emitting lasers, Endoscopy, Imaging systems, Data acquisition, In vivo imaging, 3D acquisition, Colon, Image resolution, 3D image processing
We developed a micro-motor based miniature catheter with an outer diameter of 3mm for ultrahigh speed endoscopic optical coherence tomography (OCT) using vertical cavity surface-emitting laser (VCSEL) at a 1MHz axial scan rate. The micro-motor can rotate a micro-prism at 1,200-72,000rpm (corresponding to 20- 1,200fps) with less than 5V driving 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 for a long distance to acquire three-dimensional (3D) dataset covering a large area on the specimen. VCSEL provides high a-line rate to support dense sampling under high frame rate operation. With the use of a C++ based high speed data acquisition (DAQ) system, in vivo three-dimensional OCT imaging in rabbit GI tract with 1.6mm depth range, 11μm axial resolution, 8μm lateral resolution, and frame rate of 400fps is demonstrated.
We report on the investigation of crossed-Bessel-beam and hybrid Bessel-Gauss configurations for optical trapping of
microscopic particles. The non-diffractive nature of the Bessel beam removes the need for high-NA optics. Crossed
beam configurations allow creating trapping volumes with small aspect ratio, in comparison to single-beam Bessel traps
that create wave-guide like structures. We present numerical simulations of said geometries and present experimental
data of in-situ Bessel beam forces on polystyrene beads as precursor to the realization of a random access Bessel trap.
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.
MEMS tunable vertical cavity surface emitting laser (MEMS-VCSEL) development, over the past two decades, has
primarily focused on communications and spectroscopic applications. Because of the narrow line-width, single-mode
operation, monolithic fabrication, and high-speed capability of these devices, MEMS-VCSELs also present an attractive
optical source for emerging swept source optical coherence tomography (SSOCT) systems. In this paper, we describe the
design and performance of broadly tunable MEMS-VCSELs targeted for SSOCT, emphasizing 1310nm operation for
cancer and vascular imaging. We describe the VCSEL structure and fabrication, employing a fully oxidized
GaAs/AlxOy mirrors in conjunction with dielectric mirrors and InP-based multi-quantum well active regions. We also
describe the optimization of MEMs speed and frequency response for SSOCT. Key results include 1310 nm VCSELs
with >120nm dynamic tuning range and imaging rates near 1MHz, representing the widest VCSEL tuning range and
some of the fastest swept source imaging rates thus far obtained. We also describe how low-noise semiconductor optical
amplification boosts average optical power to the required levels, while maintaining superior OCT imaging quality and
state of the art system sensitivity. Finally, we present measured multi-centimeter dynamic coherence length, and discuss
the implications of VCSELs for OCT.
We demonstrate Optical Coherence Microscopy (OCM) for in vivo imaging of the rat cerebral cortex. Imaging does not
require addition of dyes or contrast agents, and is achieved through intrinsic scattering contrast and image processing
alone. Furthermore, we demonstrate in vivo, quantitative measurements of optical properties and angiography in the rat
cerebral cortex. Imaging depths greater than those achieved by conventional two-photon microscopy are demonstrated.
The performance and imaging characteristics of ultrahigh speed ophthalmic optical coherence tomography (OCT) are investigated. In vivo imaging results are obtained at 850nm and 1050nm using different configurations of spectral and swept source / Fourier domain OCT. A spectral / Fourier domain instrument using a high speed
CMOS linescan camera with SLD light source centered at 850nm achieves speeds of ~91,000 axial scans per second with ~3μm axial resolution in tissue. A spectral / Fourier domain instrument using an InGaAs linescan camera with SLD light source centered at 1050nm achieves ~47,000 axial scans per second with ~7μm resolution in tissue. A swept source instrument using a novel wavelength swept laser light source centered at 1050nm achieves 100,000
axial scans per second. Retinal diseases seen in the clinical setting are imaged using the 91kHz 850nm CMOS camera and 47kHz 1050nm InGaAs camera based instruments to investigate the combined effects of varying speed, axial resolution, center wavelength, and instrument sensitivity on image quality. The novel 1050nm swept
source / Fourier domain instrument using a recently developed commercially available short cavity laser source images at 100,000 axial scans per second and is demonstrated in the normal retina. The dense 3D volumetric data sets obtained with ultrahigh speed OCT promise to improve reproducibility of quantitative measurements,
enabling early diagnosis as well as more sensitive assessment of disease progression and response to therapy.
Colorectal cancer (CRC) is the second leading cause of cancer death in the United States. There is great interest in
studying the relationship among microstructures and molecular processes of colorectal cancer during its progression at
early stages. In this study, we use our multi-modality optical system that could obtain co-registered optical coherence
tomography (OCT) and fluorescence molecular imaging (FMI) images simultaneously to study CRC. The overexpressed
carbohydrate α-L-fucose on the surfaces of polyps facilitates the bond of adenomatous polyps with UEA-1
and is used as biomarker. Tissue scattering coefficient derived from OCT axial scan is used as quantitative value of
structural information. Both structural images from OCT and molecular images show spatial heterogeneity of tumors.
Correlations between those values are analyzed and demonstrate that scattering coefficients are positively correlated
with FMI signals in conjugated. In UEA-1 conjugated samples (8 polyps and 8 control regions), the correlation
coefficient is ranged from 0.45 to 0.99. These findings indicate that the microstructure of polyps is changed gradually
during cancer progression and the change is well correlated with certain molecular process. Our study demonstrated that
multi-parametric imaging is able to simultaneously detect morphology and molecular information and it can enable
spatially and temporally correlated studies of structure-function relationships during tumor progression.
Macroporous EH-PEG hydrogels fabricated by porogen-leaching method are characterized by optical coherence
tomography (OCT). High-resolution OCT visualizes the microstructures of the engineered tissue scaffolds in threedimensions.
It also enables subsequent image processing to investigate several key morphological design parameters for
macroporous scaffolds. Image processing algorithms are then presented to automatically quantify the pore size, porosity,
and pore interconnectivity. The results indicated that those parameters highly depend on the porogen size. Further,
fluorescence imaging was conducted to monitor the population of labeled human mesenchymal stem cells (hMSCs)
loaded on the surface of the scaffolds. The results revealed the hMSCs' viability as well as their infiltration into the
scaffold. The effect of infiltration is more profound in the scaffold of larger pore sizes, in accordance with the result
suggested by image analysis.
Ultrahigh speed Spectral/Fourier domain ophthalmic OCT imaging at 70,000-312,500 axial scans per second is
demonstrated using a high speed CMOS camera at 800 nm. Comparative imaging results of the fovea illustrate the
performance tradeoffs between different imaging speeds and spectrometer configurations. Dense 3D volumetric
acquisitions show minimal motion artifacts when acquired at 250,000 axial scans per second. The porous structure of the
lamina cribrosa is shown in en face images extracted from a dense volumetric acquisition of the optical nerve head
acquired at 106, 382 axial scans per second. Rapid repeated volume imaging (4D-OCT) shows blood flow in retinal
capillaries. Boundaries of the capillary network are enhanced by motion contrast. 3D volumetric data acquired at 49,000
axial scans per second using an InGaAs camera at 1050 nm is compared to volumetric data acquired at 101, 010 axial
scans per second using a CMOS camera at 800nm. Averaging of adjacent cross sectional scans in the volume is shown to
increase contrast in the images and reduce speckle. The enhanced penetration of the 1050 nm compared to the 800 nm
OCT imaging system is shown. Dense 2D/3D data sets and 4D-OCT repeated volume imaging promise alternative
methods for diagnosis and monitoring of disease.
Optical coherence tomography (OCT) provides high-resolution,
cross-sectional imaging of tissue microstructure in situ
and in real-time, while fluorescence molecular imaging (FMI) enables the visualization of basic molecular processes.
There are great interests in combining these two modalities so that the tissue's structural and molecular information can
be obtained simultaneously. This could greatly benefit biomedical applications such as detecting early diseases and
monitoring therapeutic interventions. In this research, a new optical system that combines OCT and FMI was developed.
The system demonstrated that it could co-register en face OCT and FMI images with a 2.4 x 2.4 mm field of view. The
transverse resolutions of OCT and FMI of the system are both 10 μm. Capillary tubes filled with Cy 5.5 fluorescent dye
in different concentrations (750nM to 24μM) under a scattering medium (1% - 2% intralipid) are used as the phantom.
En face OCT images of the phantoms were obtained and successfully co-registered with FMI images that were acquired
simultaneously. A linear relationship between FMI intensity and dye concentration was observed. The relationship between FMI intensity and target fluorescence tube depth measured by OCT images was also observed and compared with theoretical modeling. This relationship could help in correcting reconstructed dye concentration. Imaging of colon polyps of APCmin mouse model is presented as an example of biological applications of this co-registered OCT/FMI system. In conclusion, a co-registering OCT and FMI imaging system has been demonstrated. The system enables simultaneous visualization of tissue morphology and molecular information at high resolutions over a 2-3 mm field-of-view.
We have demonstrated that the 1.3 µm Swept-Source Optical Coherence Tomography (SS-OCT) may be used in vivo in a non invasive manner to analyze the characteristics of microablative injuries produced by fractional laser treatments. We have found that the depth of the ablative columns depended approximately linearly on the pulse energy ranging from 180±20 µm for 5 mJ laser pulses to 420±60 µm for 20 mJ pulses.
Ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) imaging using a CMOS line scan camera with acquisition rates of 70,000 - 312,500 axial scans per second is investigated. Several design configurations are presented to illustrate trade-offs between acquisition speed, sensitivity, resolution and sensitivity roll-off performance. We demonstrate: extended imaging range and improved sensitivity roll-off at 70,000 axial scans per second , high speed and ultrahigh resolution imaging at 106,382 axial scans per second, and ultrahigh speed imaging at 250,000-312,500 axial scans per second. Each configuration is characterized through optical testing and the trade-offs demonstrated with in vivo imaging of the fovea and optic disk in the human retina. OCT fundus images constructed from 3D-OCT data acquired at 250,000 axial scans per second have no noticeable discontinuity of retinal features and show that there are minimal motion artifacts. The fine structures of the lamina cribrosa can be seen. Long cross sectional scans are acquired at 70,000 axial scans per second for imaging large areas of the retina, including the fovea and optic disk. Rapid repeated imaging of a small volume (4D-OCT) enables time resolved visualization of the capillary network surrounding the INL and may show individual red blood cells. The results of this study suggest that high speed CMOS cameras can achieve a significant improvement in performance for ophthalmic imaging. This promises to have a powerful impact in clinical applications by improving early diagnosis, reproducibility of measurements and enabling more sensitive assessment of disease progression or response to therapy.
Studying hemodynamic changes during early mammalian embryonic development is critical for further advances in prevention, diagnostics, and treatment of congenital cardiovascular (CV) birth defects and diseases. Doppler optical coherence tomography (OCT) has been shown to provide sensitive measurements of blood flow in avian and amphibian embryos. We combined Doppler swept-source optical coherence tomography (DSS-OCT) and live mouse embryo culture to analyze blood flow dynamics in early embryos. SS-OCT structural imaging was used for the reconstruction of embryo morphology and the orientation of blood vessels, which is required for calculating flow velocity from the Doppler measurements. Spatially and temporally resolved blood flow profiles are presented for the dorsal aorta and a yolk sac vessel in a 9.5-day embryo. We demonstrate that DSS-OCT can be successfully used for structural analysis and spatially and temporally resolved hemodynamic measurements in developing early mammalian embryos.
A video-rate laser scanning microscope was developed as an imaging engine to integrate with other photonic building
blocks to fulfill various microscopic imaging applications. The system is quipped with diode laser source, resonant
scanner, galvo scanner, control electronic and computer loaded with data acquisition boards and imaging software.
Based on an open frame design, the system can be combined with varies optics to perform the functions of fluorescence
confocal microscopy, multi-photon microscopy and backscattering confocal microscopy. Mounted to the camera port, it
allows a traditional microscope to obtain confocal images at video rate. In this paper, we will describe the design
principle and demonstrate examples of applications.
Ophthalmic OCT was performed using a novel, compact external cavity semiconductor laser at ~850
nm. Retinal imaging was demonstrated with a resolution of <7 microns in tissue at a speed of
16,000 axial scans per second. The coherence length of the laser is >10 mm, enabling an axial
measurement range of ~2.5 mm. Real-time display and data streaming capabilities enable video-rate
imaging of the retina at >30 frames per second. High-definition and three-dimensional imaging
were demonstrated on normal retinas. The resolution of <7 microns in the retina is, to our
knowledge, the highest resolution achieved in the retina with swept source OCT to date. The long
coherence length of the laser enables high-sensitivity measurements over a large axial measurement
range. The speed of 16,000 axial scans per second is comparable to current spectrometer-based
spectral/Fourier domain OCT systems. The low cost and small footprint of our laser (~10 cm x 20
cm) may enable the development of OCT for novel applications. Further improvements in speed
will be possible by using alternative scanning methods.
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