We present a slot optical waveguide ring resonator that can be used as a refractive index sensor. The proposed ring resonator works on the principle of coupling of the mode from the bus waveguide to the ring waveguide. The ring resonator was analyzed using the finite-difference time-domain method. Our proposed waveguide structure showed a sensitivity of 42 nm/RIU. Our aim is to design a chalcogenide ring resonator for refractive index sensing in midinfrared wavelengths.
We numerically designed the cladding pump light stripper with optimized parameters, the design slowly scattered the power in 2.3cm length and the structure shows a constant temperature in the cladding pump stripper region. We next fabricated the light stripper using a CO2 laser system. In the experiment, we demonstrated the stripping of 60W power from the cladding region, and the structure shows 30°C of constant temperature.
KEYWORDS: Optical coherence tomography, Image processing, Data processing, Parallel computing, Data acquisition, Signal processing, Doppler tomography, Digital signal processing, Graphics processing units, Neodymium
We demonstrate a real-time display of processed OCT images using multi-thread parallel computing with
a quad-core CPU of a personal computer. The data of each A-line are treated as one vector to maximize
the data translation rate between the cores of the CPU and RAM stored image data. A display rate of 29.9
frames/sec for processed OCT data (4096 FFT-size x 500 A-scans) is achieved in our system using a
wavelength swept source with 52-kHz swept frequency. The data processing times of the OCT image and
a Doppler OCT image with a 4-time average are 23.8 msec and 91.4 msec.
Experimental proof-of-concept is presented for a quasi-holographic solution to polarization-sensitive optical coherence tomography (PS OCT). Due to decoupling between the reference and sample beams by polarization, the solution seems acceptable to acquisition and communication of optical data in the nonlaboratory environment. The nonlab environment implies uncontrollable disturbances, e.g., temperature changes and mechanical effects happening under shop testing in industry or routine examinations in common clinics and hospitals. For mapping the collagen-related depolarization ratio of light backscattered from the human dermis, a phenomenological model is evolved from the theory of light depolarization in crystalline polymers. The model yielded a simplified intensity-based estimation algorithm. The design concept and the model rely on a submillimeter tumor thickness as a proofed prognostic factor and an important criterion for complementary functional diagnostics of skin cancers in their early phase. Choice of the model is inspired by similarity of structural and optical properties between liquid-crystal collagen fibers in the dermis and birefringent crystalline lamellae in some polymer materials. The model gives a plausible interpretation of a peculiarity of cumulative birefringence in the abnormal skin dermis. Following a top-down approach to design, the authors attempt to contribute to bridging the gap between practitioners' concerns and academic studies.
We demonstrate a novel implementation of spectral domain OCT by using a proposed sweeping detector at 1320 nm
wavelength range. A fiber pigtailed Fabry-Perot tunable filter is newly adapted to receive spectral interferometer
information using a photo-receiver instead of using charged couple detector arrays. In order to show a possibility of the
scheme in other view point, we have changed the position of the Fabry-Perot tunable filter of the interferometer. The
combination of a super luminescent LED and a semiconductor optical amplifier was used as an optical source. Its output
power is about 10 mW and the spectral bandwidth is about 60 nm. The filtered light after passing thorough the Fabry-
Perot tunable filter has 0.15 nm instantaneous spectral linewidth with 1.3 mW average output power. The system with an
axial resolution of 12 μm performed OCT imaging of a cornea of a rat eye proving potential about the application of the
proposed sweeping detector OCT.
A further insight into the prior concept of polarization sensitive optical coherence tomography system intended for non-laboratory
conditions is brought forward and an experimental proof-of-concept is presented. A phenomenological model
is adopted from the theory of light depolarization in crystalline polymers and modified to yield a simplified algorithm for
mapping depolarization ratio in dermis. The algorithm could distinguish between dermal layers with depleted collagen
content and normal dermis of normal perilesional skin. Dermis is simulated by bireringent lamellae of collagen arranged
chaotically in multiple layers parallel to the skin surface. Both the design concept and the model imply the sub-millimeter
tumor thickness as a proofed prognostic factor and an important criterion for complementary functional
diagnostics of skin cancers at their early phase of vertical growth. Choice of the model is inspired by similarity of
structural and optical properties between liquid-crystal collagen fibers in dermis and birefringent crystalline lamellae in
polymer materials. The numerical computation based on the model allowing for real characteristics of dermis gives
plausible interpreting of depolarization peculiarities caused by collagen depletion. Feasibility is discussed of exploiting
fiber optic analogs of achromatic retarders. Fabrication of the fiber retarders is shown to be realistic by making use of the
photonics technology possessed by the authors.
Ultrafast lasers have many applications mainly due to its two properties, the ultrashort pulse width and the ultrahigh intensity. Because the former is the main cause of the latter, it is very important to exactly measure the pulse width of the ultrafast laser. Currently, there are several different kinds of experimental methods to measure the ultrashort pulse width. Among those systems for this measurement, the autocorrelator using the second harmonic generation (SHG) is by far the most simple and basic method. This type of autocorrelators usually uses inorganic crystals, such as BBO, as the SHG medium. The thinner medium is necessary for analyzing the shorter laser pulses. However, the polishing process which is necessary for obtaining the optically good surfaces makes it difficult to reduce the thickness of medium as desired. We present an autocorrelator system which overcomes these shortcomings. Our system is based on the SHG using organic polymer. Polymers can be easily prepared in the form of thin film on the strong substrate through the process of spin casting. Thickness less than 1 m can be obtained without difficulties. Furthermore, due to its high nonlinearity, thin film of polymer can produce the bright second harmonic light. Polyurea was used as the second harmonic generation material of the autocorrelator because it has the pretty good transparency. An autocorrelator system based on the 397nm-thick poled polyurea thin film has been developed and used to measure the pulse width of a home-made Ti:sapphire laser oscillator. Then, the system was compared with that based on a 100 μm-thick BBO crystal, which is widely used. The pulse width of laser beam was measured to be 9.8 fs with the former. The value is believed to be more accurate than that of 7.2 fs measured with the latter.
We have demonstrated bandwidth control and reshaping of second harmonic (SH) curve in a periodically poled Ti:LiNbO3
(Ti:PPLN) waveguide ( period=16.6 um) by using a temperature-gradient-control technique and a local-temperature-control technique.
We have achieved more than 13 nm second harmonic phase-matching bandwidth and several useful shapes of SH curve such as almost ideal sinc function, and double peaks in a 74 mm long Ti:PPLN waveguide that has pre-chirped SH curve in room temperature.
We have demonstrated all-optical wavelength-selective single- and dual-channel dropping and wavelength conversion in a periodically poled Ti:LiNbO3 waveguide which has two second-harmonic phase-matching peaks by cascaded sum and difference frequency generation (cSFG/DFG). Less than -17 dB of channel dropping extinction ratio was observed with coupled pump power of 325 mW and the wavelength conversion efficiency was measured to be -7 dB with coupled pump power of 233 mW.
The development of a whole family of near and mid-IR quasi- phase matched parametric frequency converters with periodically poled in Ti:(Er:)LiNbO3 waveguides is reviewed. Due to high quality waveguides with very low losses and excellent homogeneity unprecedented conversion efficiencies have been achieved for second-harmonic generation, difference-frequency generation, optical parametric fluorescence and doubly as well as singly resonant optical parametric oscillation.
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