32 research outputs found
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Numerical model of optical coherence tomographic vibrography imaging to estimate corneal biomechanical properties
Most techniques measuring corneal biomechanics in vivo are biased by side factors. We demonstrate the ability of optical coherence tomographic (OCT) vibrography to determine corneal material parameters, while reducing current prevalent restrictions of other techniques (such as intraocular pressure (IOP) and thickness dependency). Modal analysis was performed in a finite-element (FE) model to study the oscillation response in isolated thin corneal flaps/eye globes and to analyse the dependency of the frequency response function on: corneal elasticity, viscoelasticity, geometry (thickness and curvature), IOP and density. The model was verified experimentally in flaps from three bovine corneas and in two enucleated porcine eyes using sound excitation (100–110 dB) together with a phase-sensitive OCT to measure the frequency response function (range 50–510 Hz). Simulations showed that corneal vibration in flaps is sensitive to both, geometrical and biomechanical parameters, whereas in whole globes it is primarily sensitive to corneal biomechanical parameters only. Calculations based on the natural frequency shift revealed that flaps of the posterior cornea were 0.8 times less stiff than flaps from the anterior cornea and cross-linked corneas were 1.6 times stiffer than virgin corneas. Sensitivity analysis showed that natural vibration frequencies of whole globes were nearly independent from corneal thickness and IOP within the physiological range. OCT vibrography is a promising non-invasive technique to measure corneal elasticity without biases from corneal thickness and IOP
On-chip Mach-Zehnder interferometer for OCT systems
By using integrated optics, it is possible to reduce the size and cost of a bulky optical coherence tomography (OCT) system. One of the OCT components that can be implemented on-chip is the interferometer. In this work, we present the design and characterization of a Mach-Zehnder interferometer consisting of the wavelength-independent splitters and an on-chip reference arm. The Si3N4 was chosen as the material platform as it can provide low losses while keeping the device size small. The device was characterized by using a home-built swept source OCT system. A sensitivity value of 83 dB, an axial resolution of 15.2 μm (in air) and a depth range of 2.5 mm (in air) were all obtained
Real-Time Measurements of Photonic Microchips with Femtometer-Scale Spectral Precision and Ultra-High Sensitivity
Photonic integrated circuits (PICs) are enabling major breakthroughs in a
number of areas, including quantum computing, neuromorphic processors, wearable
devices, and more. Nevertheless, existing PIC measurement methods lack the
spectral precision, speed, and sensitivity required for refining current
applications and exploring new frontiers such as point-of-care or wearable
biosensors. Here, we present the Sweeping Optical Frequency Mixing Method
(SOHO), surpassing traditional PIC measurement methods with real-time
operation, 30 dB higher sensitivity, and over 100 times better spectral
resolution. Leveraging the frequency mixing process with a sweeping laser and
custom control software, SOHO excels in simplicity, eliminating the need for
advanced optical components and additional calibration procedures. We showcase
its superior performance on ultrahigh-quality factor (Q) fiber-loop resonators
(Q = 46M) as well as microresonators realized on a new optical waveguide
platform. An experimental spectral resolution of 19.1 femtometers is
demonstrated using an 85-meter-long unbalanced fiber Mach Zehnder
Interferometer, constrained by noise resulting from the extended fiber length,
while the theoretical resolution is calculated to be 6.2 femtometers, limited
by the linewidth of the reference laser. With its excellent performance
metrics, SOHO has the potential to become a vital measurement tool in
photonics, excelling in high-speed and high-resolution measurements of weak
optical signals
Modulation in InAs quantum dot waveguides
Modulation in molecular beam epitaxy grown self-assembled InAs quantum dot waveguides have been studied at 1500 nm as a function of wavelength and voltage. Enhanced electro-optic coefficients compared to bulk GaAs were observed. © 2007 Optical Society of America
Spectral domain optical coherence tomography imaging with an integrated optics spectrometer
We designed and fabricated an arrayed-waveguide grating (AWG) in silicon oxynitride as a spectrometer for spectral domain optical coherence tomography (SD-OCT). The AWG has a footprint of only 3.0 cm x 2.5 cm, operates at a center wavelength of 1300 nm, and has 78 nm free spectral range. OCT measurements are performed that demonstrate imaging up to a maximum depth of 1 mm with an axial resolution of 19 mu m, both in agreement with the AWG design parameters. Using the AWG spectrometer combined with a fiber-based SD-OCT system, we demonstrate cross-sectional OCT imaging of a multilayered scattering phantom. (C) 2011 Optical Society of Americ
Interleaved Silicon Nitride AWG Spectrometers
Interleaved arrayed waveguide gratings (AWGs) have a great potential in providing large channel counts and narrower channel spacings for many applications, including optical communication, spectroscopy, and imaging. Here, a 75-channel silicon nitride based interleaved AWG was experimentally demonstrated. The design is comprised of a 3-channel primary AWG with 1 nm of resolution and three 25-channel secondary AWGs each with 3 nm of resolution. The final device has a spectral resolution of 1 nm over 75 nm bandwidth centered at 1550 nm. Its performance is compared with a conventional AWG spectrometer with 75 nm of bandwidth and 1 nm of resolution. The interleaved AWG demultiplexer showed lower crosstalk and better uniformity in addition to being two times smaller than the conventional design
Investigating the Potential of Thin Silicon Nitride Membranes in Fiber-Based Photoacoustic Sensing
The detection of methane, a strong greenhouse gas, has increased in importance due to rising emissions, which partly originate from unreported and undetected leaks in oil and gas fields. The gas emitted by these leaks could be detected using an optical fiber-based photoacoustic sensor called PAS-WRAP. Here, we investigate the potential of silicon-based membranes as more sensitive microphones in the PAS-WRAP concept. Toward this goal, we built a setup with which the frequency response of the membranes was interrogated by an optical fiber. Multiple mounting mechanisms were tested by adapting commercial interferometry systems (OP1550, ZonaSens, Optics11 B.V.) to our case. Finally, methane detection was attempted using a silicon nitride membrane as a sensor. Our findings show a quality factor of 2.4 at 46 kHz and 33.6 at 168 kHz for a thin silicon nitride membrane. This membrane had a frequency response with a signal-to-background ratio of 1 ± 0.7 at 44 kHz when tested in a vacuum chamber with 4% methane at 0.94 bar. The signal-to-background ratio was not significant for methane detection; however, we believe that the methods and experimental procedures that we used in this work can provide a useful reference for future research into gas trace detection with optical fiber-based photoacoustic spectroscopy
Ultrawide-bandwidth on-chip spectrometer design using band-pass filters
Here, we present the design and simulation of an ultrawide-bandwidth on-chip spectrometer that can be used in various applications, e.g. spectral tissue sensing. It covers 1200 nm wavelength range (400 nm-1600 nm) with 2 nm spectral resolution. The overall design size is only 3 × 3 cm2. The ultra-wide spectral range is made possible by using novel on-chip band-pass filters for the coarse wavelength division. The fine resolution is provided by the arrayed waveguide gratings. The band-pass filter is formed by using bend waveguides and adiabatic full-couplers. The additional loss caused by the band-pass filter is relatively small. The proposed spectrometer covers entire 400 nm-1600 nm range continuously with low crosstalk values. We envision that this design can be used in several different applications including food safety, agriculture, industrial inspection, optical imaging, and biomedical research
Raman Signal Amplification in Photonic Crystal Microring Resonators
We report on microring resonator with integrated photonic crystal that is capable of supporting discrete Raman signals with 7 orders of magnitude enhancement in the spectral range of 2-5 pm. The proposed platform can be used for advanced spectroscopic sensing applications