Significance: Current methods for analyzing pathological muscle tissue are time consuming and rarely quantitative, and they involve invasive biopsies. Faster and less invasive diagnosis of muscle disease may be achievable using marker-free in vivo optical sensing methods.
Aim: It was speculated that changes in the biochemical composition and structure of muscle associated with pathology could be measured quantitatively using visible wavelength optical spectroscopy techniques enabling automated classification.
Approach: A fiber-optic autofluorescence (AF) and diffuse reflectance (DR) spectroscopy device was manufactured. The device and data processing techniques based on principal component analysis were validated using in situ measurements on healthy skeletal and cardiac muscle. These methods were then applied to two mouse models of genetic muscle disease: a type 1 neurofibromatosis (NF1) limb-mesenchyme knockout (Nf1Prx1 − / − ) and a muscular dystrophy mouse (mdx).
Results: Healthy skeletal and cardiac muscle specimens were separable using AF and DR with receiver operator curve areas (ROC-AUC) of >0.79. AF and DR analyses showed optically separable changes in Nf1Prx1 − / − quadriceps muscle (ROC-AUC >0.97) with no differences detected in the heart (ROC-AUC <0.67), which does not undergo gene deletion in this model. Changes in AF spectra in mdx muscle were seen between the 3 week and 10 week time points (ROC-AUC = 0.96) and were not seen in the wild-type controls (ROC-AUC = 0.58).
Conclusion: These findings support the utility of in vivo fiber-optic AF and DR spectroscopy for the assessment of muscle tissue. This report highlights that there is considerable scope to develop this marker-free optical technology for preclinical muscle research and for diagnostic assessment of clinical myopathies and dystrophies.
There is growing demand for biodegradable polymer fibres in tissue engineering and nerve regeneration. We demonstrate a scalable and inexpensive fabrication technique to produce polycaproactone (PCL) fibres using fibredrawing technique. Here we report on the first successful drawing of hollow-core and solid-core PCL fibres of different cross sections. The demonstrated capacity to tailor the surface morphology of PCL fibres, together with their biodegradability and tissue compatibility, makes them a unique material base for tissue engineering and nerve regeneration applications.
KEYWORDS: Solar concentrators, Solar energy, Waveguides, New and emerging technologies, Buildings, Photovoltaics, Light, Absorption, Signal attenuation, Photons, Molecules
Luminescent solar concentrators (LSCs) offer the prospect of reducing the cost of solar energy, and are a promising candidate for building integrated photovoltaic (PV) structures. However, the realization of commercially viable efficiency of LSCs is currently hindered by reabsorption losses. In this work, a method is introduced for reducing reabsorption as well as improving directional emission in LSCs by using stimulated emission. Light from a seed laser (potentially an inexpensive laser diode) passes through the entire length of the LSC panel, modifying the emission spectrum of excited dye molecules such that it is spectrally narrower, at wavelengths that minimize reabsorption, and directed by the seed laser towards a small target PV cell. A mathematical model of such a system is presented which identifies different physical parameters responsible for the power conversion efficiency and gives the net effective output power.
Alexander Argyros, Sergio Leon-Saval, Richard Lwin, Richard Provo, Stuart Murdoch, John Harvey, Jessienta Anthony, Rainer Leonhardt, Alessandro Tuniz, Boris Kuhlmey, Simon Fleming
Polymer optical fibres (POF) have historically focused on applications in data transmission over short distances, using
highly multimode step-index or graded-index fibre designs. This paper will focus on a qualitatively different type of
polymer fibres - microstructured polymer optical fibres (mPOF) - which allow a wider variety of fibre designs and
optical properties to be achieved. Fibres with similar properties to conventional step- and graded-index POF can be made
for data transmission applications, as well as single-mode fibres which can be used for grating inscription and gratingbased
sensing. The use of microstructures can also be extended to longer wavelengths for the transmission of THz
radiation, and both solid-core and hollow-core mPOF-based THz waveguides have been demonstrated. Finally, the
development and extension of mPOF to form metal-dielectric structures for the manufacture of metamaterials using
fibre-drawing methods will be discussed. Such drawn-metamaterials with electric and magnetic responses at THz
frequencies have been demonstrated.
A comparison is made between unpackaged and packaged distributed feedback (DFB) fibre lasers
using the Michelson interferometer configuration for delayed self-heterodyne interferometery (MIDSHI)
to ascertain the improvements to the external environmental noise, quantified by reductions in
the Gaussian linewidth. Voigt fitting is used to extract and separate out the Lorentzian and Gaussian
linewidth contributions and therefore the associated sources of noise. Significant improvements in the
Gaussian linewidth were achieved as a result of significant reductions in the sensitivity of the DFB
laser to external perturbations using packaging. However, a broadening of the laser Lorentzian
linewidth was observed.
The use of Faraday rotator mirrors in a Michelson interferometer configuration is shown to
significantly improve resolution and coherence for delayed self-heterodyne interferometry.
In the paper, we report experimental results of the effect of UV-light exposure on the profile of thermal poling induced
second-order optical nonlinearity (SON) in twin-hole optical fibers. Before UV-exposure, uniform thermal poling at
320°C and 3.5 kV along a 5-7 cm long section of twin-hole fiber produced a uniform SON of 0.263 pm/V in the fiber
core. A focused light beam from a frequency-doubled Ar+ laser operating at 244 nm was used to locally erase the
induced nonlinearity in the fibers to create a periodic structure for quasi-phase matching applications. The UV-exposed
fibers were then observed under a second-harmonic microscope to characterize the distribution profile of any residual
nonlinearity after exposure. Effects of scanning speeds of the laser beam on the length of nonlinearity-erased section and
amplitude of the residual nonlinearity were investigated. It was found that the required UV-light fluence to fully erase
the induced nonlinearity is only ~0.5% of that typically required for fabricating fiber Bragg gratings.
Laser ultrasonic nondestructive evaluation (NDE) methods have been proposed to replace conventional in vivo dental clinical diagnosis tools that are either destructive or incapable of quantifying the elasticity of human dental enamel. In this work, a laser NDE system that can perform remote measurements on samples of small dimensions is presented. A focused laser line source is used to generate broadband surface acoustic wave impulses that are detected with a simplified optical fiber interferometer. The measured surface wave velocity dispersion spectrum is in turn used to characterize the elasticity of the specimen. The NDE system and the analysis technique are validated with measurements of different metal structures and then applied to evaluate human dental enamel. Artificial lesions are prepared on the samples to simulate different states of enamel elasticity. Measurement results for both sound and lesioned regions, as well as lesions of different severity, are clearly distinguishable from each other and fit well with physical expectations and theoretical value. This is the first time, to the best of our knowledge, that a laser-based surface wave velocity dispersion technique is successfully applied on human dental enamel, demonstrating the potential for noncontact, nondestructive in vivo detection of the development of carious lesions.
Stable second-order nonlinearity (SON) was created in Pyrex borosilicate glass by the temperature/electric field thermal
poling method. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic
microscopy. It was found that the SON was located in a narrow layer around 1.9 μm under the anode surface. An
effective d33 as high as 0.24 pm/V was obtained; a value comparable to that obtained in fused silica samples. The
migration of different mobile alkali ions during the poling process was characterized with energy dispersive x-ray
spectrometry in conjunction with scanning electron microscopy (SEM). It was found that Na was depleted from a region
about 3.3 μm beneath the anode surface, while K was first depleted from the immediate region under the anode, and then
accumulated in the Na-depleted region with its peak at ~1.8 μm beneath the anode. SEM observation of the cross-section
of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched
trench, ~1.8 μm under the anode edge and ~0.3 μm in width; while in post-annealed samples, no such etched trench
could be observed. A frozen-in space-charge field due to charge migration is believed to be responsible for the creation
of the SON and the altered etching rate in the poled region.
The utilization of scintillation light as a measure of radiation dose has many attractive features for medical applications. When high doses of ionizing radiation are being administered to cancer patients, precise and accurate dosimetry in terms of absolute dose and its location are essential. Fiber Optic Dosimeters [FOD] are unique in this pplication, since compared to other medical radiation dosimeters, they are smaller, more reliable and most significantly, they are human tissue equivalent. The principal limitation of the FOD is its signal to noise ratio, a feature that we discuss in terms of materials science and physical optics. The aim of this study is to outline a theoretical approach to dosimeter design based on geometrical optics that has the potential to increase the signal and decrease the noise.
Microstructured optical fibres (MOFs) have aroused great interest in recent years because of their unusual optical properties. These include their ability to be effectively single moded over a very large range of wavelengths, tailorisable dispersion, high or low non-linearity(depending on the hole design) and large core single mode fibres. We have recently fabricated the first Microstructured Polymer Optical Fibres (MPOFs), which further extend the range of possibilities in MOFs. The properties of polymers can be tailored to specific applications (eg:made highly non-linear or having gain) in a way that is not possible in glass. Further, the large range of fabrication methods available in polymers, including casting and extrusion, mean that the structures that can be obtained are very difficult to make by capillary stacking- the method used in glass MOFs. Here we present the latest results from our group using MPOFs, including single mode fibre and Bragg fibres.
It is demonstrated that strong Bragg and long-period gratings can be written using the frequency tripled output from a high repetition rate Q-switched Nd:YAG laser. The refractive index modulation induced by the pulsed near-UV light is estimated to be about 4.5x10-4, estimated both based on the periodic transmission property of long- period gratings and the reflectance of uniform Bragg gratings. Although a peak pulse intensity of the near-UV light as high as 2x107 W/cm2 has been used, no loss due to laser induced damage to the core was observed.
Silica glass can be poled either thermally or with UV exposure during application of a strong electric field. Such treatment allows electret formation. So normally isotropic glass can become anisotropic via formation of a frozen-in field. This produces non-zero second-order nonlinearity in glass. After such poling treatment a change in the third- order nonlinearity has been observed. In this paper we examine if modification of the third-order nonlinearity is real or some artifact. To do this the DC third-order nonlinearity was measured before poling, after poling and then after erasure of the second-order nonlinearity. It was found that modification of the third-order nonlinearity remains after erasure of the frozen-in field. The reason for modification of the third-order nonlinearity is still not understood. It may be due to some kind of structural modification of the glass. It is known that impurity ionic species are moved through the glass during poling. This movement of ions under the high field may be sufficient to modify the glass structure. From our results, it is clear that the second-order nonlinearity is predominantly caused by formation of a frozen-in field. The increase of the third-order nonlinearity is independent of existence of a frozen-in field after poling.
Silica glass plays a key role in photonic systems because of its excellent optical properties, such as low loss, low fabrication cost and high photo-refractive damage threshold. Unfortunately, silica, being centrosymmetric, has no intrinsic linear electro-optic (LEO) coefficient or second-order nonlinearity (SON). However, thermal poling has been demonstrated to produce a LEO coefficient and SON of approximately 1 pm/V in silica glass and fiber. It is necessary to understand the mechanism of thermal poling in order to achieve a larger, stable and reliable LEO effect. A series of thermal poling experiments on silicate fiber was carried out. The in situ measurements of the total LEO coefficients (the sum of the poling field induced LEO coefficient and the thermal poling induced residual LEO coefficient) suggest movement of charges. Thermal poling induced residual LEO coefficients are measured in situ during prolonged negative thermal poling. Both the shielding field and the ionization field are frozen-in at room temperature and lead to LEO effect. The time evolution of the residual LEO coefficients shows that the competition between the shielding and ionization fields is a linear process. Using this new understanding, a specialty optical fiber was developed for the production of thermally poled optical fiber devices.
Recent work on the thermal poling of silicate optical fiber is presented. This paper includes the background on thermal poling, optimization of poling conditions, lifetime of the electro-optic effect as well as discussions on the change in (chi) (3) after poling and the validity of the frozen-in field model for thermal poling.
Electro-optic modulators and switches are important components for photonic systems. Existing technologies (such as lithium niobate) have significant drawbacks in terms of coupling losses to fiber, photorefractive damage and cost. Silica, especially fiber, based devices would be ideal; unfortunately silica, being centrosymmetric, has no intrinsic bulk electro-optic characteristics. However an electro-optic coefficient can be induced by silica by poling. By thermal poling, an electro-optic coefficient of around 1 pm/V has been produced in bulk silica; whilst scientifically interesting, this is insufficient for practical devices, especially as the values for fiber are much smaller. Recent work on UV excited poling has produced values around 6 pm/V in fiber; sufficient to realize fiber devices a few centimeters long, requiring only a few volts for switching. To perform UV-poling, optical fiber with internal electrodes is produced by milling holes into the fiber preform, close and parallel to the core, and then pulling at sufficiently low temperature to avoid closure of the holes into which the fine wire electrodes are subsequently introduced. A voltage is applied to the electrodes to produce a strong electric field (approximately 100/V/micrometers ) in the fiber core which is also exposed to UV laser radiation. After removal of irradiation and field an electro-optic coefficient of around 6 pm/V is measured. By applying a modulating voltage to the internal electrodes this electro-optic coefficient may be used to effect phase or polarization modulation (and amplitude modulation in a suitable structure). Furthermore, by periodic UV-poling, electrically tunable in-fiber Bragg gratings may be produced. Details of the fiber and device geometry, the processing conditions, the measurement techniques, the device performance and potential applications of this exciting new technology will be presented.
The current status of the praseodymium doped fluoride fiber amplifier (PDFFA), the preferred fiber amplifier at 1.3 micrometers , is reviewed. Small-signal gains of 30dB are achievable, together with output powers of 200mW, and a noise figure of 4-7dB. 1.3- micrometers transmission offers the advantage of operating near the zero dispersion wavelength of standard telecommunications fiber, allowing high speed links with simple transmitters.
We report the noise and gain characteristics of a 1.3 micrometers PDFFA, in both the small and large signal regime. The small-signal noise performance shows a value of 5 dB at 1.3 micrometers , reducing to < 4 dB for wavelengths < 1.28 micrometers , and increasing to > 7 dB for wavelengths > 1.32 micrometers . No noise penalty has been observed in saturation for output powers as high as + 17 dBm, corresponding to 10 dB gain compression. Crosstalk measurements show a 3 dB rollover frequency of 6 kHz.
The erbium doped silica fibre amplifier has become almost universal in the 1.53-1.57?m band, due to its high gain and power handling, good linearity, and lack of crosstalk[1]. In this paper, we report results on amplification at wavelengths as long as 1.62?m in the erbium/silica system, greatly extending the existing gain window.
A novel image scanning technique, the pulse counting method, has been
developed for geometric parameter measurement of optical fibers. The theory
and implement of this technique are described. Experimental results show that the
resolution and the repeatability of the system with this technique are O.OO5pm
and O.lpm (3a) , respectively.
Indexing Words: Image Scanning; Geometric Measurement; Optical Fibers;
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