Refractive Index Fiber Laser Sensor by Using a Fiber Ball Lens Interferometer with Adjustable Free Spectral Range.

In this work, a fiber laser refractometer based on a fiber ball lens (FBL) interferometer is proposed. The linear cavity erbium-doped fiber laser uses an FBL structure acting as a spectral filter and sensing element for determining the RI of a liquid medium surrounding the fiber. The optical interrogation of the sensor is the wavelength displacement of the generated laser line as a function of the RI variations. For the proposed FBL interferometric filter, the free spectral range of its wavelength-modulated reflection spectrum is adjusted to maximum in order to obtain RI measurements in a range of 1.3939 to 1.4237 RIU, from laser wavelength displacements in a range from 1532.72 to 1565.76 nm. The obtained results show that the wavelength of the generated laser line is a linear function of the RI variations on the medium surrounding the FBL with a sensitivity of 1130.28 nm/RIU. The reliability of the proposed fiber laser RI sensor is analytically and experimentally investigated.

[Spectral correction of vision and electrophysiological measurements of the eye]. / Spektral'naia korrektsiia zreniia i élektrofiziologicheskie pokazateli glaza.

Spectral light filters - glasses and intraocular lenses - are widely used in ophthalmology and optometry. Light filters help increase vision clarity, contrast and quality in patients with ocular media opacities and other eye diseases. The article describes the types of light filters and the methods of their clinical application, and presents data on the influence of intra- and extraocular spectral correction on electrophysiological parameters of the retina.

Photoreceptor spectral tuning by colorful, multilayered facet lenses in long-legged fly eyes (Dolichopodidae).

The facet lenses of the compound eyes of long-legged flies (Dolichopodidae) feature a striking, interlaced coloration pattern, existing of alternating rows of green-yellow and orange-red reflecting facets, due to dielectric multilayers located distally in the facet lenses (Bernard and Miller. Invest Ophthalmol 7:416-434 (1968). We investigated this phenomenon in the dolichopodid Dolichopus nitidus by applying microspectrophotometry, electron microscopy and optical modeling. The measured narrow-band reflectance spectra, peaking at ~540 and ~590 nm with bandwidth ~105 nm, are well explained by a refractive index oscillating sinusoidally in six periods around a mean value of about 1.44 with amplitude 0.6. The facet lens reflectance spectra are associated with a spectrally restricted, reduced transmittance, which causes modified spectral sensitivities of the underlying photoreceptors. Based on the modeling and electroretinography of the dolichopodid Condylostylus japonicus we conjecture that the green and orange facets narrow the spectral bandwidths of blue and green central photoreceptors, respectively, thus possibly improving color and/or polarization vision.

A periodic spatio-spectral filter for event-related potentials.

With respect to single trial detection of event-related potentials (ERPs), spatial and spectral filters are two of the most commonly used pre-processing techniques for signal enhancement. Spatial filters reduce the dimensionality of the data while suppressing the noise contribution and spectral filters attenuate frequency components that most likely belong to noise subspace. However, the frequency spectrum of ERPs overlap with that of the ongoing electroencephalogram (EEG) and different types of artifacts. Therefore, proper selection of the spectral filter cutoffs is not a trivial task. In this research work, we developed a supervised method to estimate the spatial and finite impulse response (FIR) spectral filters, simultaneously. We evaluated the performance of the method on offline single trial classification of ERPs in datasets recorded during an oddball paradigm. The proposed spatio-spectral filter improved the overall single-trial classification performance by almost 9% on average compared with the case that no spatial filters were used. We also analyzed the effects of different spectral filter lengths and the number of retained channels after spatial filtering.

Effect of chromatic filters on visual performance in individuals with mild traumatic brain injury (mTBI): A pilot study.

PURPOSE: Spectral filters have been used clinically in patients with mild traumatic brain injury (mTBI). However, they have not been formally assessed using objective techniques in this population. Thus, the aim of the present pilot study was to determine the effect of spectral filters on reading performance and visuo-cortical responsivity in adults with mTBI. METHODS: 12 adults with mTBI/concussion were tested. All reported photosensitivity and reading problems. They were compared to 12 visually-normal, asymptomatic adults. There were several test conditions: three luminance-matched control filters (gray neutral density, blue, and red), the patient-selected 'precision tint lens' that provided the most comfort and clarity of text using the Intuitive Colorimeter System, and baseline without any filters. The Visagraph was used to assess reading eye movements and reading speed objectively with each filter. In addition, both the amplitude and latency of the visual-evoked potential (VEP) were assessed with the same filters. RESULTS: There were few significant group differences in either the reading-related parameters or VEP latency for any of the test filter conditions. Subjective improvements were noted in most with mTBI (11/12). CONCLUSIONS: The majority of patients with mTBI chose a tinted filter that resulted in increased visual comfort. While significant findings based on the objective testing were found for some conditions, the subjective results suggest that precision tints should be considered as an adjunctive treatment in patients with mTBI and photosensitivity.

Determination of linear x-ray attenuation coefficients of pathological brain tissues and use of filters in tissue contrast enhancement in computed tomography.

OBJECTIVE: X-ray attenuation coefficients are used in common radiological, pathological and spectroscopic examinations and in the determination of the radiation dose distribution in biological tissues. In radiology, these coefficients enable diagnosis by differentiating the abnormal tissues from the normal ones using their morphological structure and contrast differences. In this study, our aim is to precisely determine the linear x-ray attenuation coefficients of pathological brain tissues and to use x-ray beam filters to enhance the tissue contrast in computed tomography. MATERIALS AND METHODS: To directly measure the relative linear attenuation coefficients, an energy dispersive x-ray spectroscopy system (EDXRS-Canberra, Si(Li) with DSA-1000 spectrum analyzer 1998; CT, USA) was used with collimators and a medical-purpose x-ray tube (Siemens, Siremobil, 1985; Erlangen, Germany) in a linear geometry. RESULTS: Using a Mo filter with Computed Tomography CT and photon energies from 15 to 25 keV, EDXRS acquisitions were found to significantly distinguish grades of brain tumors (p<0.05). For the data acquired from CT systems with the decreasing filtered photon mean energy, the x-ray attenuation coefficients (i.e., the Hounsfield units) show that the ratio of EDXRS to CT for water's attenuation coefficient are increased. With our suggested x-ray filters, the tissue contrast has been found to be increased in ex vivo brain tumor slices compared with slices scanned in conventional CT scanners. CONCLUSION: X-ray attenuations measured with the EDXRS are found to be statistically more reliable because of the length of acquisition times in this study.