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Photonics
Volume 1
Issue 4
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Photonics, Volume 1, Issue 4 (December 2014) – 21 articles , Pages 283-612

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967 KiB  
Review
Dispersive Fourier Transformation for Versatile Microwave Photonics Applications
by Chao Wang
Photonics 2014, 1(4), 586-612; https://doi.org/10.3390/photonics1040586 - 18 Dec 2014
Cited by 27 | Viewed by 11388
Abstract
Dispersive Fourier transformation (DFT) maps the broadband spectrum of an ultrashort optical pulse into a time stretched waveform with its intensity profile mirroring the spectrum using chromatic dispersion. Owing to its capability of continuous pulse-by-pulse spectroscopic measurement and manipulation, DFT has become an [...] Read more.
Dispersive Fourier transformation (DFT) maps the broadband spectrum of an ultrashort optical pulse into a time stretched waveform with its intensity profile mirroring the spectrum using chromatic dispersion. Owing to its capability of continuous pulse-by-pulse spectroscopic measurement and manipulation, DFT has become an emerging technique for ultrafast signal generation and processing, and high-throughput real-time measurements, where the speed of traditional optical instruments falls short. In this paper, the principle and implementation methods of DFT are first introduced and the recent development in employing DFT technique for widespread microwave photonics applications are presented, with emphasis on real-time spectroscopy, microwave arbitrary waveform generation, and microwave spectrum sensing. Finally, possible future research directions for DFT-based microwave photonics techniques are discussed as well. Full article
(This article belongs to the Special Issue Microwave Photonics)
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883 KiB  
Article
Single-Fiber Reflectance Spectroscopy of Isotropic-Scattering Medium: An Analytic Perspective to the Ratio-of-Remission in Steady-State Measurements
by Daqing Piao and Joel W. Slaton
Photonics 2014, 1(4), 565-585; https://doi.org/10.3390/photonics1040565 - 16 Dec 2014
Cited by 1 | Viewed by 6562
Abstract
Recent focused Monte Carlo and experimental studies on steady-state single-fiber reflectance spectroscopy (SfRS) from a biologically relevant scattering medium have revealed that, as the dimensionless reduced scattering of the medium increases, the SfRS intensity increases monotonically until reaching a plateau. The SfRS signal [...] Read more.
Recent focused Monte Carlo and experimental studies on steady-state single-fiber reflectance spectroscopy (SfRS) from a biologically relevant scattering medium have revealed that, as the dimensionless reduced scattering of the medium increases, the SfRS intensity increases monotonically until reaching a plateau. The SfRS signal is semi-empirically decomposed to the product of three contributing factors, including a ratio-of-remission (RoR) term that refers to the ratio of photons remitting from the medium and crossing the fiber-medium interface over the total number of photons launched into the medium. The RoR is expressed with respect to the dimensionless reduced scattering parameter , where is the reduced scattering coefficient of the medium and is the diameter of the probing fiber. We develop in this work, under the assumption of an isotropic-scattering medium, a method of analytical treatment that will indicate the pattern of RoR as a function of the dimensionless reduced scattering of the medium. The RoR is derived in four cases, corresponding to in-medium (applied to interstitial probing of biological tissue) or surface-based (applied to contact-probing of biological tissue) SfRS measurements using straight-polished or angle-polished fiber. The analytically arrived surface-probing RoR corresponding to single-fiber probing using a 15° angle-polished fiber over the range of agrees with previously reported similarly configured experimental measurement from a scattering medium that has a Henyey–Greenstein scattering phase function with an anisotropy factor of 0.8. In cases of a medium scattering light anisotropically, we propose how the treatment may be furthered to account for the scattering anisotropy using the result of a study of light scattering close to the point-of-entry by Vitkin et al. (Nat. Commun. 2011, doi:10.1038/ncomms1599). Full article
(This article belongs to the Special Issue Biomedical Optics and Optical Imaging)
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Review
Time-Resolved Fluorescence in Photodynamic Therapy
by Shu-Chi Allison Yeh, Michael S. Patterson, Joseph E. Hayward and Qiyin Fang
Photonics 2014, 1(4), 530-564; https://doi.org/10.3390/photonics1040530 - 9 Dec 2014
Cited by 30 | Viewed by 10309
Abstract
Photodynamic therapy (PDT) has been used clinically for treating various diseases including malignant tumors. The main advantages of PDT over traditional cancer treatments are attributed to the localized effects of the photochemical reactions by selective illumination, which then generate reactive oxygen species and [...] Read more.
Photodynamic therapy (PDT) has been used clinically for treating various diseases including malignant tumors. The main advantages of PDT over traditional cancer treatments are attributed to the localized effects of the photochemical reactions by selective illumination, which then generate reactive oxygen species and singlet oxygen molecules that lead to cell death. To date, over- or under-treatment still remains one of the major challenges in PDT due to the lack of robust real-time dose monitoring techniques. Time-resolved fluorescence (TRF) provides fluorescence lifetime profiles of the targeted fluorophores. It has been demonstrated that TRF offers supplementary information in drug-molecular interactions and cell responses compared to steady-state intensity acquisition. Moreover, fluorescence lifetime itself is independent of the light path; thus it overcomes the artifacts given by diffused light propagation and detection geometries. TRF in PDT is an emerging approach, and relevant studies to date are scattered. Therefore, this review mainly focuses on summarizing up-to-date TRF studies in PDT, and the effects of PDT dosimetric factors on the measured TRF parameters. From there, potential gaps for clinical translation are also discussed. Full article
(This article belongs to the Special Issue Biomedical Optics and Optical Imaging)
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401 KiB  
Review
Refractive Index Measurement of Liquids Based on Microstructured Optical Fibers
by Susana Silva, Paulo Roriz and Orlando Frazão
Photonics 2014, 1(4), 516-529; https://doi.org/10.3390/photonics1040516 - 8 Dec 2014
Cited by 31 | Viewed by 7075
Abstract
This review is focused on microstructured optical fiber sensors developed in recent years for liquid RI sensing. The review is divided into three parts: the first section introduces a general view of the most relevant refractometric sensors that have been reported over the [...] Read more.
This review is focused on microstructured optical fiber sensors developed in recent years for liquid RI sensing. The review is divided into three parts: the first section introduces a general view of the most relevant refractometric sensors that have been reported over the last thirty years. Section 2 discusses several microstructured optical fiber designs, namely, suspended-core fiber, photonic crystal fiber, large-core air-clad photonic crystal fiber, and others. This part is also divided into two main groups: the interferometric-based and resonance-based configurations. The sensing methods rely either on full/selective filling of the microstructured fiber air holes with a liquid analyte or by simply immersing the sensing fiber into the liquid analyte. The sensitivities and resolutions are tabled at the end of this section followed by a brief discussion of the obtained results. The last section concludes with some remarks about the microstructured fiber-based configurations developed for RI sensing and their potential for future applications. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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Article
WDM Optical Access Network for Full-Duplex and Reconfigurable Capacity Assignment Based on PolMUX Technique
by Jose Mora, Beatriz Ortega, Fulvio Grassi and Jose Capmany
Photonics 2014, 1(4), 503-515; https://doi.org/10.3390/photonics1040503 - 3 Dec 2014
Cited by 3 | Viewed by 5192
Abstract
We present a novel bidirectional WDM-based optical access network featuring reconfigurable capacity assignment. The architecture relies on the PolMUX technique allowing a compact, flexible, and bandwidth-efficient router in addition to source-free ONUs and color-less ONUs for cost/complexity minimization. Moreover, the centralized architecture contemplates [...] Read more.
We present a novel bidirectional WDM-based optical access network featuring reconfigurable capacity assignment. The architecture relies on the PolMUX technique allowing a compact, flexible, and bandwidth-efficient router in addition to source-free ONUs and color-less ONUs for cost/complexity minimization. Moreover, the centralized architecture contemplates remote management and control of polarization. High-quality transmission of digital signals is demonstrated through different routing scenarios where all channels are dynamically assigned in both downlink and uplink directions. Full article
(This article belongs to the Special Issue Microwave Photonics)
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441 KiB  
Article
Dental Imaging Using Mesoscopic Fluorescence Molecular Tomography: An ex Vivo Feasibility Study
by Feixiao Long, Mehmet S. Ozturk, Mark S. Wolff, Xavier Intes and Shiva P. Kotha
Photonics 2014, 1(4), 488-502; https://doi.org/10.3390/photonics1040488 - 3 Dec 2014
Cited by 9 | Viewed by 7155
Abstract
Some dental lesions are difficult to detect with traditional anatomical imaging methods, such as, with visual observation, dental radiography and X-ray computed tomography (CT). Therefore, we investigated the viability of using an optical imaging technique, Mesoscopic Fluorescence Molecular Tomography (MFMT) to retrieve molecular [...] Read more.
Some dental lesions are difficult to detect with traditional anatomical imaging methods, such as, with visual observation, dental radiography and X-ray computed tomography (CT). Therefore, we investigated the viability of using an optical imaging technique, Mesoscopic Fluorescence Molecular Tomography (MFMT) to retrieve molecular contrast in dental samples. To establish feasibility of obtaining 3-D images in teeth using MFMT, molecular contrast was simulated using a dye-filled capillary that was placed in the lower half of human tooth ex vivo. The dye and excitation wavelength were chosen to be excited at 650–660 nm in order to simulate a carious lesion. The location of the capillary was varied by changing the depth from the surface at which the dye, at various concentrations, was introduced. MFMT reconstructions were benchmarked against micro-CT. Overall; MFMT exhibited a location accuracy of ~15% and a volume accuracy of ~15%, up to 2 mm depth with moderate dye concentrations. These results demonstrate the potential of MFMT to retrieve molecular contrast in 3-D in highly scattering tissues, such as teeth. Full article
(This article belongs to the Special Issue Microwave Photonics)
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552 KiB  
Article
Performance Analysis of a Hybrid Raman Optical Parametric Amplifier in the O- and E-Bands for CWDM PONs
by Sasanthi Peiris, Nicholas Madamopoulos, Neophytos A. Antoniades, Dwight Richards and Roger Dorsinville
Photonics 2014, 1(4), 473-487; https://doi.org/10.3390/photonics1040473 - 1 Dec 2014
Cited by 2 | Viewed by 5632
Abstract
We describe a hybrid Raman-optical parametric amplifier (HROPA) operating at the O- and E-bands and designed for coarse wavelength division multiplexed (CWDM) passive optical networks (PONs). We present the mathematical model and simulation results for the optimization of this HROPA design. Our analysis [...] Read more.
We describe a hybrid Raman-optical parametric amplifier (HROPA) operating at the O- and E-bands and designed for coarse wavelength division multiplexed (CWDM) passive optical networks (PONs). We present the mathematical model and simulation results for the optimization of this HROPA design. Our analysis shows that separating the two amplification processes allows for optimization of each one separately, e.g., proper selection of pump optical powers and wavelengths to achieve maximum gain bandwidth and low gain ripple. Furthermore, we show that the proper design of optical filters incorporated in the HROPA architecture can suppress idlers generated during the OPA process, as well as other crosstalk that leaks through the passive optical components. The design approach enables error free performance for all nine wavelengths within the low half of the CWDM band, assigned to upstream traffic in a CWDM PON architecture, for all possible transmitter wavelength misalignments (±6 nm) from the center wavelength of the channel band. We show that the HROPA can achieve error-free performance with a 170-nm gain bandwidth (e.g., 1264 nm–1436 nm), a gain of >20 dB and a gain ripple of <4 dB. Full article
(This article belongs to the Special Issue Nonlinear Fiber Optics)
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1107 KiB  
Article
Linearization Technologies for Broadband Radio-Over-Fiber Transmission Systems
by Xiupu Zhang, Ran Zhu, Dongyan Shen and Taijun Liu
Photonics 2014, 1(4), 455-472; https://doi.org/10.3390/photonics1040455 - 26 Nov 2014
Cited by 54 | Viewed by 9523
Abstract
Linearization technologies that can be used for linearizing RoF transmission are reviewed. Three main linearization methods, i.e. electrical analog linearization, optical linearization, and electrical digital linearization are presented and compared. Analog linearization can be achieved using analog predistortion circuits, and can be used [...] Read more.
Linearization technologies that can be used for linearizing RoF transmission are reviewed. Three main linearization methods, i.e. electrical analog linearization, optical linearization, and electrical digital linearization are presented and compared. Analog linearization can be achieved using analog predistortion circuits, and can be used for suppression of odd order nonlinear distortion components, such as third and fifth order. Optical linearization includes mixed-polarization, dual-wavelength, optical channelization and the others, implemented in optical domain, to suppress both even and odd order nonlinear distortion components, such as second and third order. Digital predistortion has been a widely used linearization method for RF power amplifiers. However, digital linearization that requires analog to digital converter is severely limited to hundreds of MHz bandwidth. Instead, analog and optical linearization provide broadband linearization with up to tens of GHz. Therefore, for broadband radio over fiber transmission that can be used for future broadband cloud radio access networks, analog and optical linearization are more appropriate than digital linearization. Generally speaking, both analog and optical linearization are able to improve spur-free dynamic range greater than 10 dB over tens of GHz. In order for current digital linearization to be used for broadband radio over fiber transmission, the reduced linearization complexity and increased linearization bandwidth are required. Moreover, some digital linearization methods in which the complexity can be reduced, such as Hammerstein type, may be more promising and require further investigation. Full article
(This article belongs to the Special Issue Microwave Photonics)
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359 KiB  
Article
Grating Configurations for the Spectral Selection of Coherent Ultrashort Pulses in the Extreme-Ultraviolet
by Fabio Frassetto, Paolo Miotti and Luca Poletto
Photonics 2014, 1(4), 442-454; https://doi.org/10.3390/photonics1040442 - 26 Nov 2014
Cited by 7 | Viewed by 5793
Abstract
The design and realization of grating instruments to handle and condition coherent ultrafast pulses in the extreme ultraviolet spectral region are discussed. The main application of such instruments is the spectral selection of high-order laser harmonics and free-electron-laser pulses in the femtosecond time [...] Read more.
The design and realization of grating instruments to handle and condition coherent ultrafast pulses in the extreme ultraviolet spectral region are discussed. The main application of such instruments is the spectral selection of high-order laser harmonics and free-electron-laser pulses in the femtosecond time scale. Broad-band monochromators require the use of diffraction gratings at grazing incidence. Here, we discuss two configurations useful for the realization of grating monochromator with ultrafast response: the single-grating design, applied to high-order laser harmonics, and the time-delay-compensated configuration with two gratings, applied to free-electron lasers. Full article
(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)
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2544 KiB  
Article
Characteristics of Resonantly-Guided Modes in Microstructured Optical Fibers
by Yasuo Ohtera, Haruka Hirose and Hirohito Yamada
Photonics 2014, 1(4), 432-441; https://doi.org/10.3390/photonics1040432 - 21 Nov 2014
Cited by 2 | Viewed by 5199
Abstract
Modal characteristics of resonantly-guided modes (RGMs) in microstructured fibers were investigated through numerical simulation. The modes of interest are supported in a class of fibers consisting of a circularly arranged periodic array of high index rods embedded in a low index cladding. Light [...] Read more.
Modal characteristics of resonantly-guided modes (RGMs) in microstructured fibers were investigated through numerical simulation. The modes of interest are supported in a class of fibers consisting of a circularly arranged periodic array of high index rods embedded in a low index cladding. Light is confined and guided by the guided-mode resonance (GMR) that the rod array exhibit. According to the numerical analysis we clarified that duplicated transverse modes having the same radial mode number for TM and TE modes were supported. Also the existence and detailed mode profiles of hybrid modes were confirmed. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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421 KiB  
Article
Design and Performance of a Multi-Point Scan Confocal Microendoscope
by Matthew D. Risi, Houssine Makhlouf, Andrew R. Rouse, Anthony A. Tanbakuchi and Arthur F. Gmitro
Photonics 2014, 1(4), 421-431; https://doi.org/10.3390/photonics1040421 - 20 Nov 2014
Cited by 6 | Viewed by 6949
Abstract
Confocal fluorescence microendoscopy provides high-resolution cellular-level imaging via a minimally invasive procedure, but requires fast scanning to achieve real-time imaging in vivo. Ideal confocal imaging performance is obtained with a point scanning system, but the scan rates required for in vivo biomedical [...] Read more.
Confocal fluorescence microendoscopy provides high-resolution cellular-level imaging via a minimally invasive procedure, but requires fast scanning to achieve real-time imaging in vivo. Ideal confocal imaging performance is obtained with a point scanning system, but the scan rates required for in vivo biomedical imaging can be difficult to achieve. By scanning a line of illumination in one direction in conjunction with a stationary confocal slit aperture, very high image acquisition speeds can be achieved, but at the cost of a reduction in image quality. Here, the design, implementation, and experimental verification of a custom multi-point aperture modification to a line-scanning multi-spectral confocal microendoscope is presented. This new design improves the axial resolution of a line-scan system while maintaining high imaging rates. In addition, compared to the line-scanning configuration, previously reported simulations predicted that the multi-point aperture geometry greatly reduces the effects of tissue scatter on image quality. Experimental results confirming this prediction are presented. Full article
(This article belongs to the Special Issue Biomedical Optics and Optical Imaging)
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554 KiB  
Article
Fibre Coupled Photonic Crystal Cavity Arrays on Transparent Substrates for Spatially Resolved Sensing
by Mark G. Scullion, Matthias Fischer and Thomas F. Krauss
Photonics 2014, 1(4), 412-420; https://doi.org/10.3390/photonics1040412 - 3 Nov 2014
Cited by 8 | Viewed by 6990
Abstract
We introduce a photonic crystal cavity array realised in a silicon thin film and placed on polydimethlysiloxane (PDMS) as a new platform for the in-situ sensing of biomedical processes. Using tapered optical fibres, we show that multiple independent cavities within the same waveguide [...] Read more.
We introduce a photonic crystal cavity array realised in a silicon thin film and placed on polydimethlysiloxane (PDMS) as a new platform for the in-situ sensing of biomedical processes. Using tapered optical fibres, we show that multiple independent cavities within the same waveguide can be excited and their resonance wavelength determined from camera images without the need for a spectrometer. The cavity array platform combines sensing as a function of location with sensing as a function of time. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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561 KiB  
Article
Effects of Temperature and Axial Strain on Four-Wave Mixing Parametric Frequencies in Microstructured Optical Fibers Pumped in the Normal Dispersion Regime
by Javier Abreu-Afonso, Antonio Díez, Jose Luis Cruz and Miguel V. Andrés
Photonics 2014, 1(4), 404-411; https://doi.org/10.3390/photonics1040404 - 29 Oct 2014
Cited by 7 | Viewed by 5104
Abstract
A study of the effect of temperature and axial strain on the parametric wavelengths produced by four-wave mixing in microstructured optical fibers is presented. Degenerate four-wave mixing was generated in the fibers by pumping at normal dispersion, near the zero-dispersion wavelength, causing the [...] Read more.
A study of the effect of temperature and axial strain on the parametric wavelengths produced by four-wave mixing in microstructured optical fibers is presented. Degenerate four-wave mixing was generated in the fibers by pumping at normal dispersion, near the zero-dispersion wavelength, causing the appearance of two widely-spaced four-wave mixing spectral bands. Temperature changes, and/or axial strain applied to the fiber, affects the dispersion characteristics of the fiber, which can result in the shift of the parametric wavelengths. We show that the increase of temperature causes the signal and idler wavelengths to shift linearly towards shorter and longer wavelengths, respectively. For the specific fiber of the experiment, the band shift at rates ­–0.04 nm/ºC and 0.3 nm/ºC, respectively. Strain causes the parametric bands to shift in the opposite way. The signal band shifted 2.8 nm/me and the idler -5.4 nm/me. Experimental observations are backed by numerical simulations. Full article
(This article belongs to the Special Issue Nonlinear Fiber Optics)
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1972 KiB  
Article
Asymmetric Wave Propagation Through Saturable Nonlinear Oligomers
by Daniel Law, Jennie D'Ambroise, Panayotis G. Kevrekidis and Detlef Kip
Photonics 2014, 1(4), 390-403; https://doi.org/10.3390/photonics1040390 - 27 Oct 2014
Cited by 6 | Viewed by 4696
Abstract
In the present paper we consider nonlinear dimers and trimers (more generally, oligomers) embedded within a linear Schrödinger lattice where the nonlinear sites are of saturable type. We examine the stationary states of such chains in the form of plane waves, and analytically [...] Read more.
In the present paper we consider nonlinear dimers and trimers (more generally, oligomers) embedded within a linear Schrödinger lattice where the nonlinear sites are of saturable type. We examine the stationary states of such chains in the form of plane waves, and analytically compute their reflection and transmission coefficients through the nonlinear oligomer, as well as the corresponding rectification factors which clearly illustrate the asymmetry between left and right propagation in such systems. We examine not only the existence but also the dynamical stability of the plane wave states. Lastly, we generalize our numerical considerations to the more physically relevant case of Gaussian initial wavepackets and confirm that the asymmetry in the transmission properties also persists in the case of such wavepackets. Full article
(This article belongs to the Special Issue Nonlinear Fiber Optics)
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1262 KiB  
Article
Guided-Mode Resonance Grating with Self-Assembled Silver Nanoparticles for Surface-Enhanced Raman Scattering Spectroscopy
by Jing Yang, Fanghui Ren, Xinyuan Chong, Donglei Fan, Swapnajit Chakravarty, Zheng Wang, Ray T. Chen and Alan X. Wang
Photonics 2014, 1(4), 380-389; https://doi.org/10.3390/photonics1040380 - 23 Oct 2014
Cited by 18 | Viewed by 10566
Abstract
We designed and fabricated guided-mode resonance (GMR) gratings on indium-tin-oxide (ITO) thin film to generate a significantly enhanced local electric field for surface-enhanced Raman scattering (SERS) spectroscopy. Ag nanoparticles (NPs) were self-assembled onto the surface of the grating, which can provide a large [...] Read more.
We designed and fabricated guided-mode resonance (GMR) gratings on indium-tin-oxide (ITO) thin film to generate a significantly enhanced local electric field for surface-enhanced Raman scattering (SERS) spectroscopy. Ag nanoparticles (NPs) were self-assembled onto the surface of the grating, which can provide a large amount of “hot-spots” for SERS sensing. The ITO gratings also exhibit excellent tolerance to fabrication deviations due to the large refractive index contrast of the ITO grating. Quantitative experimental results of 5,5’-dithiobis(2-nitrobenzoic acid) (DTNB) demonstrate the best enhancement factor of ~14× on ITO gratings when compared with Ag NPs on a flat ITO film, and the limit of detection (LOD) of DTNB is as low as 10 pM. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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1153 KiB  
Article
Wide-Field OCT Angiography at 400 KHz Utilizing Spectral Splitting
by Laurin Ginner, Cedric Blatter, Daniel Fechtig, Tilman Schmoll, Martin Gröschl and Rainer A. Leitgeb
Photonics 2014, 1(4), 369-379; https://doi.org/10.3390/photonics1040369 - 23 Oct 2014
Cited by 19 | Viewed by 8897
Abstract
Optical angiography systems based on optical coherence tomography (OCT) require dense sampling in order to maintain good vascular contrast. We demonstrate a way to gain acquisition speed and spatial sampling by using spectral splitting with a swept source OCT system. This method splits [...] Read more.
Optical angiography systems based on optical coherence tomography (OCT) require dense sampling in order to maintain good vascular contrast. We demonstrate a way to gain acquisition speed and spatial sampling by using spectral splitting with a swept source OCT system. This method splits the recorded spectra into two to several subspectra. Using continuous lateral scanning, the lateral sampling is then increased by the same factor. This allows increasing the field of view of OCT angiography, while keeping the same transverse resolution and measurement time. The performance of our method is demonstrated in vivo at different locations of the human retina and verified quantitatively. Spectral splitting can be applied without any changes in the optical setup, thus offering an easy way to increase the field of view of OCT in general and in particular for OCT angiography. Full article
(This article belongs to the Special Issue Optics and Technologies for Ophthalmology and Visual Science)
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541 KiB  
Review
The Role of Ultraviolet Radiation in the Ocular System of Mammals
by Mercede Majdi, Behrad Y. Milani, Asadolah Movahedan, Lisa Wasielewski and Ali R. Djalilian
Photonics 2014, 1(4), 347-368; https://doi.org/10.3390/photonics1040347 - 22 Oct 2014
Cited by 12 | Viewed by 15553
Abstract
With decreasing levels of ozone in the atmosphere, we are being exposed to higher levels of ultraviolet radiation (UVR) than ever before. UVR carries higher energy than visible light, and its effects on tissues include DNA damage, gene mutations, immunosuppression, oxidative stress and [...] Read more.
With decreasing levels of ozone in the atmosphere, we are being exposed to higher levels of ultraviolet radiation (UVR) than ever before. UVR carries higher energy than visible light, and its effects on tissues include DNA damage, gene mutations, immunosuppression, oxidative stress and inflammatory responses. In the eye, UVR is strongly associated with the development of basal and squamous cell carcinoma of the eyelid, pterygium, photokeratitis, climatic droplet keratopathy, ocular surface squamous neoplasia, cataracts, and uveal melanoma, and is weakly associated with age-related macular degeneration. Despite overwhelming evidence regarding the deleterious effects on UVR, public health measures to encourage UV protection of the eyes is generally lacking. Options for photoprotection include sunglasses, wide brim hats, windshields, plastic films for side windows in cars, UV blocking contact lenses, and following the UV Index report daily. The American National Standards Institute currently has regulations regarding properties of UV blocking sunglasses; however, compliance in the US is not mandatory. On the other hand, UVR does have therapeutic applications in the eye, particularly, riboflavin activated by ultraviolet A light (UVA) radiation is used clinically to slow the progression of keratoconus, post-LASIK keratectasia, and bullous keratopathy by crosslinking corneal collagen fibers. Additionally, riboflavin activated by UVA has been shown to have antibacterial, antiviral, and antiparasitic effects. This is clinically relevant in the treatment of infectious keratitis. Finally, exposure to low levels of light in the UV spectrum has been found to regulate the growth of the eye and lack of adequate exposure may increase the risk of development and progression of myopia. Full article
(This article belongs to the Special Issue Optics and Technologies for Ophthalmology and Visual Science)
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649 KiB  
Review
Passive Optical Access Networks: State of the Art and Future Evolution
by Tommaso Muciaccia, Fabio Gargano and Vittorio M. N. Passaro
Photonics 2014, 1(4), 323-346; https://doi.org/10.3390/photonics1040323 - 13 Oct 2014
Cited by 52 | Viewed by 11718
Abstract
In the very last years, optical access networks are growing very rapidly, from both the network operators and the research interests points of view. Fiber To The Home (FTTH) is already a reality in plenty of real contexts and there has been a [...] Read more.
In the very last years, optical access networks are growing very rapidly, from both the network operators and the research interests points of view. Fiber To The Home (FTTH) is already a reality in plenty of real contexts and there has been a further stimulus to the proposal of new solutions and the investigation of new possibilities, in order to optimize network performance and reduce capital and operational expenditure. A complete and systematic overview of passive optical access networks is presented in this paper, concerning both the hot research topics and the main operative issues about the design guidelines and the deployment of Passive Optical Networks (PON) architectures, nowadays the most commonly implemented approach to realize optical fiber links in the access networks. A comparison of advantages and disadvantages of different multiplexing techniques is discussed, with specific reference to WDM-based networks, almost universally considered as the enabling technology for future proof bandwidth requirements. An exhaustive summary is also given about the-state-of-the-art of modulation and encoding techniques recently proposed by the scientific community, as well as the open challenges (such as colorless and coolerless ONUs) for telecom companies and international standardization compliance. Full article
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2467 KiB  
Article
Infrared Retinoscopy
by Ying-Ling Chen, Lei Shi, James W. L. Lewis and Ming Wang
Photonics 2014, 1(4), 303-322; https://doi.org/10.3390/photonics1040303 - 3 Oct 2014
Cited by 4 | Viewed by 16026
Abstract
Infrared RetinoscopyRetinoscopy could be a more effective and versatile clinical tool in observing a wide range of ocular conditions if modifications were made to overcome the inherent difficulties. In this paper, a laboratory infrared retinoscope prototype was constructed to capture the digital images [...] Read more.
Infrared RetinoscopyRetinoscopy could be a more effective and versatile clinical tool in observing a wide range of ocular conditions if modifications were made to overcome the inherent difficulties. In this paper, a laboratory infrared retinoscope prototype was constructed to capture the digital images of the pupil reflex of various types of eye conditions. The captured low-contrast reflex images due to intraocular scattering were significantly improved with a simple image processing procedure for visualization. Detections of ocular aberrations were demonstrated, and computational models using patients’ wavefront data were built to simulate the measurement for comparison. The simulation results suggest that the retinal stray light that is strongly linked to intraocular scattering extend the detection range of illuminating eccentricity in retinoscopy and make it more likely to observe ocular aberrations. Full article
(This article belongs to the Special Issue Optics and Technologies for Ophthalmology and Visual Science)
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Communication
Clinical Trials of Exterior Non Implanted Interference-Based Extended Depth of Focus Intra Ocular Lens Design
by Zeev Zalevsky, Ido Raveh, Ofer Limon, Shai Ben Yaish, Karen Lahav Yacouel, Ravid Doron and Alex Zlotnik
Photonics 2014, 1(4), 296-302; https://doi.org/10.3390/photonics1040296 - 2 Oct 2014
Cited by 2 | Viewed by 5177
Abstract
In this paper, we present the clinical trials performed with intra ocular lens (IOL) design, realizing an interference-based extended depth of focus concept, with an external glass plate. The purpose of such extended depth of focus-based IOL design is to prevent cataract patients [...] Read more.
In this paper, we present the clinical trials performed with intra ocular lens (IOL) design, realizing an interference-based extended depth of focus concept, with an external glass plate. The purpose of such extended depth of focus-based IOL design is to prevent cataract patients from needing to use different types of glasses (for reading and for distance vision) after undergoing surgery. Full article
(This article belongs to the Special Issue Optics and Technologies for Ophthalmology and Visual Science)
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Article
Fiber-Based Polarization Diversity Detection for Polarization-Sensitive Optical Coherence Tomography
by Hamid Pahlevaninezhad, Anthony M. D. Lee, Lucas Cahill, Stephen Lam, Calum MacAulay and Pierre Lane
Photonics 2014, 1(4), 283-295; https://doi.org/10.3390/photonics1040283 - 30 Sep 2014
Cited by 8 | Viewed by 9186
Abstract
We present a new fiber-based polarization diversity detection (PDD) scheme for polarization sensitive optical coherence tomography (PSOCT). This implementation uses a new custom miniaturized polarization-maintaining fiber coupler with single mode (SM) fiber inputs and polarization maintaining (PM) fiber outputs. The SM fiber inputs [...] Read more.
We present a new fiber-based polarization diversity detection (PDD) scheme for polarization sensitive optical coherence tomography (PSOCT). This implementation uses a new custom miniaturized polarization-maintaining fiber coupler with single mode (SM) fiber inputs and polarization maintaining (PM) fiber outputs. The SM fiber inputs obviate matching the optical lengths of the two orthogonal OCT polarization channels prior to interference while the PM fiber outputs ensure defined orthogonal axes after interference. Advantages of this detection scheme over those with bulk optics PDD include lower cost, easier miniaturization, and more relaxed alignment and handling issues. We incorporate this PDD scheme into a galvanometer-scanned OCT system to demonstrate system calibration and PSOCT imaging of an achromatic quarter-wave plate, fingernail in vivo, and chicken breast, salmon, cow leg, and basa fish muscle samples ex vivo. Full article
(This article belongs to the Special Issue Biomedical Optics and Optical Imaging)
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