bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Photosensitive Germanosilicate Fibre Codoped with Nitrogen
Authors: Dianov E.M. , Golant K.M. , Mashinsky V.M. , Medvedkov O.I. , Nikolin I.V. , Sazhin O.D. , Vasiliev S.A.
Published: December 2022

In-fiber grating writing based on the photorefractive effect is now attracting considerable interest [1]. However, photosensitivity of standard germanosilicate fibres with a moderate concentration of germanium in the core (5 ÷ 7 mol.% GeO2) is not large and does not allow efficient writing of refractive index gratings. To increase the writing efficiency, one has to increase the germanium concentration and/or load the fibre with hydrogen [2]. Increasing the germanium concentration results in a reduction of the mode spot size and in additional losses when the fibre is spliced with a standard telecommunication fibre. Hydrogen loading complicates the grating technology and raises losses in the IR region owing to the OH-group absorption. Therefore, optimization of the grating writing technology and development of novel types of photosensitive fibres are now high on the agenda.
Strong LP11-Mode Splitting in UV Side-Written Tilted Fiber Gratings
Authors: Johlen Dietmar , Klose Peter , Renner Hagen , Brinkmeyer Ernst
Published: December 2022

Dual-mode fiber gratings are promising components for mode converters and reflectionless band filters. In order to be able to use standard telecommunication fibers, which are single-moded at the wavelengths of interest, one can increase the refractive index by UV laser-beam side-writing such that higher modes propagate through the grating region. We show here that UV side-writing is an efficient method to increase the refractive index to allow higher modes to propagate. In addition, the problems of multiple resonant peaks due to weakly broken higher-mode degeneracy [1] is circumvented by breaking the degeneracy such strongly that the resonant peaks are spectrally widely separated.
Thermal stabilities of strong UV written gratings in sol-gel germanosilicate planar waveguides.
Authors: RAZAFIMAHATRATRA A. D. , BENATSOU M. , BOUAZAOUI M. , XIE W. X. , MATHIEU C. , DACOSTA A. , DOUAY M.
Published: December 2022

Bragg gratings inscriptions or UV direct patterning of single mode channel waveguides are key issues for the achievement of new integrated components. Photosensitivity was reported in planar waveguides elaborated by different processes: FHD [1], PECVD [2], sol-gel [3], ion implantation [4], sputtering [5]. The sol-gel approach allows to prepare planar waveguides at low cost and low temperature. Hence, this process can be easily applied to industrial procedure. Photoinduced refractive index of 3 10-5 was already reported in H2 loaded sol-gel germanosilicate waveguides using the 488nm of an argon ion laser [3]. Recently, UV light imprinted Bragg grating with 97% reflectivity was imprinted in an hybrid sol-gel silica glass waveguide on silicon [6].
Fabrication of In-Fibre Moiré Filters Using a 5cm non-dedicated chirped phase mask
Authors: Evcrall L A , Sugden K , Williams JAR , Bennion I , Liu X , Aitchison J S , De La Rue R M
Published: December 2022

Since the initial observation of photoinduced refractive index changes in optical fibres1, the area of application of fibre Bragg gratings has broadened from simple wavelength dependent reflectors to noise filtering, wavelength selection and as sensors.
Long Period Gratings Formed in Depressed Cladding Fibres
Authors: Dong Liang , Reekie Laurence , Cruz Jose L.
Published: December 2022

There has been a significant interest in long period gratings, primarily due to their applications in gain-flattened erbium doped fibre amplifiers [1]. Up till now, cladding modes supported by the glass-air interface of an optical fibre have been used in a forward mode coupling scheme involving also the guided fundamental mode of the optical fibre. Here we propose an alternative technique. In a single mode depressed cladding fibre of an appropriate design (an example is given in fig. 1), the higher order LP11 mode can be made to be a leaky mode in such a structure, i.e. it can propagate for a short length before being stripped off the high index region beyond the depressed cladding. This enables coupling between the guided fundamental LP01 and leaky LP11 modes, despite the fact that the optical fibre is single-moded. This coupling was first observed in [2], where a Bragg grating caused strong coupling into the backward-propagating leaky LP11 mode and much weaker coupling into a series of cladding modes. In a forward coupling scheme with a long period gratings (several hundred micrometres pitch), the LP01 mode can be coupled into the forward propagating leaky LP11 mode, therefore creating a loss peak in the transmission in the same way as when the LP01 mode is coupled into a cladding mode supported by the glass-air interface of the optical fibre which is subsequently stripped off over the coated section of the optical fibre. Two advantages are anticipated, I) potentially much stronger coupling due to the much large modal overlap possible and II), insensitivity to the glass-air interface as the LP11 mode is supported mainly by the core. It must be stressed that as the LP11 mode is an asymmetrical mode, the coupling from LP01 to LP11 will not occur if a circularly symmetrical grating is written over the core of the fibre, but this is not usually a problem when H2 or D2 loading is used, because of the asymmetry of the index change in such gratings due to strong absorption induced at the writing wavelength.
Narrow Transmission Bandpass Filters Using Bragg Grating-Assisted Mode Conversion
Authors: Canning J. , Moss D.
Published: December 2022

Fibre Bragg gratings are proving to be instrumental in enabling the introduction of WDM systems. They offer highly selective bandpass filtering needed for the transmission of multiple closely-spaced wavelengths. These gratings, however, tend to work in reflection since the large k-vector allows coupling from forward travelling modes to backward travelling modes. This has proved to be a major disadvantage since to operate in transmission requires the use of optical recirculators. However, gratings which operate using phase-matching in the forward direction tend to have long periods, determined by the beat length between two modes. Fundamental mode conversion [1,2] requires stripping of the higher order mode to achieve a loss bandpass. This is more readily achieved when conversion is to cladding modes [3]. Whilst these filters have very low reflections, they operate as loss filters and not transmission bandpass devices. Further, the loss bandwidth tends to be broad, on the order of 20nm, because of the small differences in modal dispersion [1-3]. On the other hand, grating dispersion has been used to achieve mode conversion in reflection over a small wavelength range [4]. In all these cases transmission notch filters are generally produced, whereas in most cases the opposite - a transmission bandpass filter - is desired.
Z-Scan Study of Thin Chalcogenide As2S3 Glass Films and Holographic Fabrication of Microlens Networks
Authors: Saliminia A. , Galstyan T. V. , Villeneuve A. , Richardson Kathleen
Published: December 2022

Chalcogenide glasses (ChG) have been shown to be very promising candidates for optical information storage and infrared communication systems [1]. The high photosensitivity of these materials in the visible (near bandgap for ChG) spectral band allows the fabrication of various photoinduced structures for integrated optical circuits [2]. The characterization of the light-induced complex refractive index changes (Δn) in ChG and the realization of new applications represent the goal of the present work. Namely, we report, we believe for the first time, the dynamic separation of different photoexcitation modes in ChG, and the holographic fabrication of one (1D) and two (2D) dimensional microlens networks. We study the ChG film refractive index (n), absorption (α) and thickness (d) photomodulation processes, both in steady state and in transient excitation regimes. We use dynamic holography [3] and Z-scan techniques [4] for this study. These techniques provide important information concerning both the dynamical and the steady-state excitation behavior of our ChG films. Different physical and photochemical mechanisms are responsible for the complex behavior of ChG [3] and their understanding and control is an important challenge for the possible applications.
A Thermally Poled Electrooptic Fiber
Authors: Long X.-C. , Brueck S. R. J.
Published: December 2022

We have reported1 previously on a planarized fiber-poling structure which allows us to apply a high field across a polished fiber and results in a linear electrooptic coefficient as high as 0.3 pm/V using a commercially available D-fiber. This fabrication technique has several advantages including: low cost volume manufacturing capability; planar structure to allow lithographic definition of high-speed circuits; and fiber ends unaffected by the processing to provide low-cost packaging and integration with fiber systems.
Novel Liquid and Liquid Crystal Cored Fibre Bragg Gratings
Authors: Kashyap Raman , Williams Doug L , Smith Ray P
Published: December 2022

Tunable filters are useful for a number of applications. Recently, fibre Bragg gratings were written in poled silica fibres[1]. The reflectivity of the grating and partial tuning was subsequently achieved by the application of an electric field. An alternative scheme for a tunable filter is proposed in this paper using liquid-crystal or liquid cores.
Bragg Gratings in Telecommunications Networks
Authors: Delevaque E. , Loisel B. , Bayon J.F. , Devoldere N. , Poignant H. , Bose D.
Published: December 2022

Photoinscription of Bragg gratings within optical waveguides has been shown as a promising technology in the optical telecommunications field. Many applications have already been demonstrated in transport, local or access networks. The robustness, stability and flexibility that photoimprinted components offer insure a fast widespread of their use in near close future telecommunications networks.
Impact of Hydrogen in-fiber and out-fiber Diffusion on central wavelength of UV-written Long Period Grating
Authors: Bakhti F. , Larrey J. , Sansonetti P. , Poumellec B.
Published: December 2022

Hydrogen loaded standard fibers are routinely used for writing fiber gratings as the diffusion of molecular hydrogen strongly enhances the fiber photosensitivity [1]. Out-fiber diffusion of molecular hydrogen occurs when fiber is removed from hydrogen pressure. If the out-fiber diffusion after few hours at room temperature has negligible effect on the value of the initial Bragg wavelength for classical Bragg gratings (FBG), for long-period gratings (LPG) we show that this out-diffusion considerably changes the value of the initial central wavelength. Furthermore, in a reciprocal way, the in-fiber diffusion of hydrogen in LPG can induce strong shift of the central wavelength. In this paper, we present for the first time to our knowledge, both theoretical and experimental studies on the impact of hydrogen in-fiber or out-fiber diffusion on Long-Period Gratings.
Efficient Active Bragg Grating Tunable Filters
Authors: Limberger H.G. , Ky N.H. , Costantini D.M. , Salathé R. P. , Müller C.A.P. , Fox G.R.
Published: December 2022

Reflection, transmission and loss filters based on fiber Bragg gratings are key components in future wavelength division multiplexing telecommunication networks. A shift of the Bragg wavelength, λ
B
, can be achieved by applying a strain or heating the fiber section containing the grating [1]. Here we report on Bragg grating devices that use a thin metallic coating to directly heat the fiber or a piezoelectric coating to strain it. Such integrated tunable filter devices show DC tuning [2-5] and modulation capabilities with promise for enhanced efficiency, reduced size, and low electrical power consumption.
Direct writing of planar waveguide devices using ultraviolet light
Authors: Svalgaard Mikael , Kristensen Martin
Published: December 2022

Ultraviolet (UV) induced Bragg gratings in optical waveguides have been under intense investigation in the past few years, currently leading to commercial applications in fiber based sensor and telecommunication networks. However, the one-dimensional geometry of optical fibers limits the range of possible UV induced index structures and hence also the functionality of devices based hereon. This situation is currently changing, partly due to the large UV induced index changes available when using hydrogen loaded glass1. Large index changes permit direct writing of buried waveguide cores directly in planar silica based thin films, hence expanding the regime of UV induced index structures from one to two dimensions. The potential functionality of UV written optical devices is correspondingly increased.
Writing Waveguides and Gratings in Silica and Related Materials by Femto-Second Laser
Authors: Hirao K.
Published: December 2022

With the goal of being able to create various optical glass devices for the telecommunications industry, the effects of 810 nm, femto-second laser radiation on various glasses were investigated. By focusing the laser beam via a microscope objective, transparent but visible, round-elliptical damage lines were successfully written inside high silica, borate, soda-lime-silicate, fluoride and chalcogenide bulk glasses. Micro-ellipsometer measurements of the damaged region in pure and Ge-doped silica glasses showed a 0.01-0.035 refractive index increase, depending on the radiation dose. The formation of several types of defects including Si’E or Ge’E centers, non-bridging oxygen hole centers, and peroxy radicals was also detected. These results suggest that multi-photon interactions are occurring in the glasses and that it is possible to write three dimensional optical circuits in bulk glasses via such a focused laser beam technique. The following is the technique to create waveguides.
Large SHG in UV-Poled Silica Glass
Authors: FUJIWARA Takumi , TAKAHASHI Masahide , IKUSHIMA Akira J.
Published: December 2022

A number of work have been reported on enhancement of the second-order nonlinearity in silica-related glasses, e.g. poling at elevated temperatures (200~500 °C) in bulk fused-silica [1], in sol-gel films [2], and in those of waveguide- and fiber forms, in addition [3,4]. Recently, a significant increase of the effective electro-optic (EO) coefficient in a germanosilicate fiber was reported [5], where UV irradiation was applied along with an intense electric poling field. The EO coefficient measured in the fiber poled in that way was comparable to r22 in LiNbO3. This “UV-poling" method has a further advantage of spatial resolution, which is useful to create periodically poled structures for the quasi phase-matching SHG and the EO-tunable Bragg gratings [6].
Effect of Minority Species on Thermal Poling of Fused Silica Glasses
Authors: Wada Noriyuki , Morinaga Kenji , Takebe Hiromichi , Pruneri Valerio , Kazansky Peter G.
Published: December 2022

High second-order nonlinearity (SON) in poled silica glasses [1] is of great interest for the development of linear electro-optic modulators and frequency converters monolithically integrated into optical fibres or planar glass waveguides. However, its origin [1, 2] is not fully understood. The extrinsic effects of poling time and voltage on second-harmonic (SH) generation in thermally-poled silica glass have been studied [1,3]. In particular the quadratic dependence of the maximum SH signal on the applied voltage indicated linear dependence of the SON on internal electric field [3]. There are several studies on intrinsic effects associated with defects [1, 4] and minority species such as OH [1,5] and Na [1, 6] in thermal poling of silica glasses. In this work we carried out a systematic analysis of oxygen related defects and impurities (OH and Na) in commercial fused silica glasses (without relying on their catalogue data) and discuss their effects on SON.
Improving the Nonlinearity of Silica by Poling at Higher Temperature and Voltage
Authors: Liu A. C. , Pureur D. , Digonnet M. J. F. , Kino G. S. , Knystautas E. J.
Published: December 2022

Thermal poling of silica offers the exciting prospect of achieving, for the first time, low-loss electro-optic switches and modulators in a fiber form, devices that can be fusion spliced to a single mode fiber with negligible loss, unlike any other existing modulator. For this to become possible, both the depth (a few microns) and the nonlinear coefficient (0.5-1 pm/V) of the nonlinear region induced in silica by standard thermal poling must be increased. These objectives may be met by optimizing the glass composition and/or the poling process.
Radiation-induced density and absorption changes in fused silica
Authors: Seward T.P. , Smith C. , Borrelli N.F. , Allan D.C , Araujo R.J.
Published: December 2022

A major growing application for fused silica is as microlithography lenses for integrated circuit manufacture using deep ultraviolet excimer laser radiation at 248 nm (KrF) and 193 nm (ArF) wavelengths. Such short wavelength radiation, while allowing higher image resolution, can cause structural changes in the glass which can adversely affect lens performance. These changes are manifest as color centers and glass densification.
Hydrogen, defects, and compaction of pure and doped vitreous silica
Authors: Shelby J.E. , Bergomi M.S.
Published: December 2022

Irradiation of vitreous silica results in the formation of optical defects and the compaction of the glass. Irradiation of silica doped with germanium or titanium results in the formation of many more defects, accompanied by compaction. Irradiation of undoped vitreous silica containing large quantities of dissolved molecular hydrogen eliminates the optical defects and reverses the compaction process so that the glass actually expands. Irradiation of hydrogen soaked silica doped with 4% germania results in increased optical absorption, but still leads to expansion of the glass. On the other hand, irradiation of hydrogen soaked silica which contains 3 to 8% titania leads to dramatic increases in optical absorption and to increased compaction of the glass.
Mechanisms of Index Change Induced by Near-UV Light In Hydrogen-Loaded Fibers
Authors: Grubsky V. , Starodubov D. S. , Feinberg J.
Published: December 2022

Bragg Gratings in optical fibers have been formed using a wide variety of writing wavelengths ranging from the visible at 488 nm (using 2 photon excitation) to the vacuum-UV at 157 nm. [1-4]. Recently fiber gratings were fabricated by a one-photon process with near-UV light [5-8]. However results with near UV fabrication are contradictory: no Bragg grating was observed in the fibers in the absence of hydrogen loading [5,6], gratings in hydrogen-loaded fibers were transient [6], stable Bragg gratings were demonstrated with and without hydrogen loading [7,8]. Here we present the data that can help to explain these apparently contradictory results.
Kinetics of defect centers formation and photosensitivity in Ge-SiO2 fibers of various compositions
Authors: Tsai Tsung-Ein , Friebele E. Joseph
Published: December 2022

It was reported that the Ge E' center is related to second harmonic generation (SHG) in Ge-SiO21. Since the Ge E' center is known as hole-trapping center, this suggests that the positive charge trapping sites for SHG in Ge-SiO2 are Ge E' centers. However, in a later, detailed thermal stability study, we reported2 that only a variant of the Ge E' center, i.e., Ge E’d1, has thermal stability similar to SHG. This suggests that not all of the observed Ge E' centers are charged.
Photosensitivity of oxygen deficient type bulk silica and fibers
Authors: Lee J.W. , Sigel G.H. , Li Jie
Published: December 2022

With the development of fiber gratings, the investigations of optical phenomena induced by UV-laser irradiation such as the photosensitivity of silica-based glasses and optical fibers have been areas of active research. The severe conditions implicit in the fiber fabrication process including high melting temperatures, shear stress, neck down and rapid quenching were found to generate structural defects that are different from those present in bulk rods. Subsequent exposure of the fibers to UV-laser radiation therefore results in the modified photosensitivity of the drawn fibers. In this study, the effects of UV excimer laser (KrF) irradiation on the optical properties of silica fibers are compared to bulk rods from which they have been drawn.
Dielectric Characteristics of Silica and Inference of Related Defects
Authors: Tomozawa Minoru , Shin Dong-Wook
Published: December 2022

There are various types of silica glasses made by different methods. They contain, in general, different levels of impurities such as sodium oxide, alumina and hydroxyls and have different fictive temperatures. Some investigators [1-3] reported anomalous electric and dielectric properties of silica glasses and attributed these anomalies to impurities. In order to resolve the cause of these anomalies, electric and dielectric properties of various silica glasses were measured as a function of temperatures [4-6].
Determination of the Visible-Range Optical Absorption Spectrum of Peroxy Radicals in Gamma-Irradiated Fused Silica
Authors: Griscom David L. , Mizuguchi Masafumi
Published: December 2022

The most fundamental defect centers induced by high-energy radiations (x rays, γ rays, electrons, protons, neutrons, or intense UV light) in amorphous silicon dioxide are E′ centers (≡Si·), nonbridging-oxygen hole centers (NBOHCs: ≡Si-O·), peroxy radicals (PORs: ≡Si-O-O·), and self-trapped holes (STHs), where the notation "≡"1). The E′ center has a strong optical absorption in the UV at 215 nm and no known absorptions in the visible range. Both the NBOHC and the POR are believed to have absorption bands near 260 nm, and the former exhibits a low-oscillator-strength band (f ≈ 4 – 8×10-4) near 600 nm.1-5 On fundamental grounds, the POR would be expected to have a corresponding transition near the same wavelength. Based on data for drawing-induced defects in optical fibers,4 the likely existence of such a band was previously inferred,1 but proof has been lacking. We report here unambigous spectral resolution of a POR absorption band near 630 nm, based on ESR and differential-optical isochronal-anneal studies of γ-irradiated high-purity silicas in bulk and optical-fiber forms, respectively.
The Point Defects with Low-Coordinated Si or Ge Atoms on Vitreous Silica Surface. Surface and Bulk Centers Comparison
Authors: Radzig Victor A.
Published: December 2022

Until recently, investigations of the surface and bulk defects in silica glass have developed virtually independent. Only in [1,2] some properties of the surface and bulk defects in vitreous silica were compared. Identification of the structure of defects in the bulk of silica glass is a considerably more complicated problem. This is explained by a wide variety of methods, which can be used to identify the structure of surface defects and reveal the mechanisms of their transformations under the action of different external factors (temperature, UV and γ-irradiation, reactions with different impurity molecules, the so-called technological impurities, etc.).
Local Kramers-Kronig analysis of UV induced absorption changes: Dynamics of excess loss induced by exposure to light at 248 nm or 193 nm in Ge:SiO2 preforms.
Authors: Leconte B. , Xie W. X. , Douay M. , Bernage P. , Niay P. , Bayon J.F. , Delevaque E. , Poignant H.
Published: December 2022

It is well known that exposure of a germanosilicate glass to light at 248 nm or 193 nm leads to a permanent change in the refractive index and in the absorption spectra at wavelength shorter than 350 nm. The changes in absorption spectra are assumed to result either from the creation of point defects (color center model)1,2 and/or from light induced structure changes in the glass (densification model)3,4. A Kramers-Kronig (KK) transformation of the changes in absorption enables one to determine the related changes in refractive index which in turn can be compared with those measured at the time of a grating inscription. However using this process is rather tricky since ideally the comparison requires that when writing a grating within a fiber, one measures the UV induced excess loss spectrum at each exposure time and at each place along the grating wavevector on the spectral range within which the absorption changes are observed. As the above mentioned procedure cannot be strictly followed, we suggested a simplified method5 for performing the KK analysis. We use this method to compare the index changes which can be ascribed to absorption changes occurring in the spectral range (220 - 350 nm) at the time of a grating inscription through exposure of a germanosilicate fiber either to a fringe pattern at 193 nm or 248 nm.
Links between writing and erasing (or stability) of Bragg gratings in disordered media.
Authors: Poumellec B.
Published: December 2022

A lot of experiments have been performed to measure the stability of Bragg gratings in silica based optical fibers for various temperatures. The most famous one is from Erdogan et al. [6, 7] who show a law like

1

1
+
a

t
α

with α increasing on the temperature. Applying this mathematical function systematically, various authors have found other variations. Furthermore, some stability measurements have been made according the writing conditions and in some glasses this has been found mutually dependent [1, 2].
Growth Kinetics Of Photoinduced Gratings And Paramagnetic Centers In High NA, Heavily Ge-Doped Silica Optical Fibers
Authors: Taunay T. , Tsai T.E. , Friebele E.J. , Niay P. , Bayon J.F.
Published: December 2022

The achievement of UV photoinduced refractive index changes in germanosilicate fibers paved the way for the development of fiber Bragg grating (FBG) based optical devices (e.g., filters, fiber lasers, sensors). Although the mechanisms underlying the UV photosensitivity are not fully understood, it is now well established that the refractive index changes are associated with a partial bleaching of an absorption band around 5 eV, arising from the Germanium Oxygen Defect Center (GODC). Several mechanisms have been proposed to explain the photosensitivity in germanosilicate fibers: color centers [1], stress relief [2] and compaction [3]. Depending on the Ge concentration and the experimental conditions used to write the gratings, three types of photosensitivity, type 1, type IIa and type 2 have been identified in unloaded Ge-doped silica fibers. The most commonly observed, type 1, arises in standard fibers ([GeO2] < 20 mol%) under either pulsed or cw UV exposure in the low fluence regime. Type 1 photosensitivity is characterized by a monotonie increase of both the mean refractive index <Δneff> and the induced refractive index modulation Δnmod under UV exposure. Unlike type 1, the most relevant feature of type IIa photosensitivity ([GeO2] > 25 mol%, ϕc ≈ 2µm) is the complex behavior of <Δneff> and Δnmod as a function of exposure time [4]. Indeed, with increasing UV exposure time, a partial or total bleaching of the saturated type I grating is followed by the formation of a new grating spectrum. At the time of the second grating growth, the shift experienced by the Bragg grating wavelength is nulled or slightly negative, indicating a negative refractive index change. Moreover, a noticeable difference between type 1 and type IIa photosensitivities is their markedly different thermal behavior. Type 1 gratings begin to anneal at temperatures as low as 300 C and are no longer observed at 550 C while type IIa gratings experience no annealing at temperatures below 450-500 C; a rapid decay is then observed at annealing temperatures ~600-700 C. Recent experiments have shown that the formation dynamics of type 1/IIa grating spectra are strongly affected when the gratings are written in strained fibers [5]. Using the “Photoelastic densification” model and stress dependence kinetics, it has been demonstrated that, under the assumption of a decrease in densification rate, stretching the fiber will in turn decrease the type 1 index modulation [3], [6]. Nevertheless the origin of type IIa photosensitivity in high NA Ge-doped silica fibers still remains unresolved.
Material and fiber device aspects of poled fused silica
Authors: Brueck S.R.J. , Alley T.G. , Myers R.A. , Long X.-C.
Published: December 2022

Since the discovery1 of a large, stable second-order χ(2) nonlinearity in temperature/electric field poled fused silica, there have been intensive efforts both to understand the microscopic mechanisms leading to the nonlinearity and to exploit the nonlinearity for planar waveguide and fiber devices. This paper will review the present status of both the fundamental studies and the device applications.
Photochromic/photoconductive effects in cadmium-alumino fluorosilicates
Authors: Cornelius L.K. , Tick P.A. , Borelli N.F.
Published: December 2022

A novel interaction was observed in cadmium-alumino fluorosilicate glasses when exposed to near UV radiation. Glasses high in cadmium were observed to be photochromic. Accompanying the darkening process was a change of up to five orders of magnitude in the DC conductivity. The process involved the formation of the cadmous ion (Cd+1) as an electron trap. A thin, transparent conductive skin could also be formed by appropriate heat treatments.
Optical absorption and magnetic circular dichroism of ER(3+)-doped aluminosilicate glasses
Authors: Johnson D.E. , Poulios D.P. , Bigelow N.P. , Spoonhower J.P.
Published: December 2022

The magnetic circular dichroism (MCD) and optical absorption spectra are reported for varying erbium(3+) concentrations in aluminosilicate glasses. Visible MCD data are obtained at a field strength of 1.8 Tesla and at a base temperature of 1.7 K. The temperature dependence in the range up to 300 K is also studied. A striking result of this work is the drastic change in both shape and position of many of the MCD absorption bands with erbium(3+) concentration. These changes give insight into the nature of the erbium ion’s crystal field and thus its local environment. The MCD (or Faraday) parameters are determined via the method of moments.
Effects of molecular hydrogen on low-intensity UV photochemistry of germanosilicate glasses.
Authors: Bagratashvili V. N. , Tsypina S. I. , Chernov P. V. , Rybaltovskii A. O. , Zavorotny Yu. V. , Dong L.
Published: December 2022

Germanosilicate glasses are known to posesses photorefractive (photosensitive) properties [1], that allows to fabricate refractive index gratings in germanosilicate optical fibers [2]. Hydrogen loading silica and germanosilicate glasses enhances its photosensitivity significantly [3-6]. Since the germanium-oxygen deficient center (GODC) is the main photosensitive defect in germanosilicate glasses, it is of particulary importance to reveal the role of molecular H2 in the processes of GODC phototransformation. In this work, we study the influece of molecular hydrogen impregnated into the glass network on the triplet decay time τT, luminescence intensity (T1 - S0, λmax=397 nm) and efficiency of GODC photodecay when excited with low-intensity UV light.
Preparation and nonlinear optical properties of Au/glass composite thin films
Authors: Tanahashi I. , Tohda T. , Inouye H. , Mito A.
Published: December 2022

Small metal particles embedded in glasses have been widely studied as resonant type third- order nonlinear optical materials for photonic devices. We have prepared Au/SiO2, Au/Al2O3, Au/TiO2 composite thin films by a multitarget sputtering method. The χ(3) and τ of the composite thin films were investigated by means of femtosecond Z-scan and pump-probe experiment, respectively. In the optical-absorption spectra of the three types of the films, the clear absorption peak due to the surface plasmon resonance of Au particles is observed. The imaginary part of χ(3) and τ for the Au/TiO2 film were -3.6 × 10−7 esu and ~2 ps, respectively. The χ(3) of Au/SiO2, Au/Al2O3, AU/tiO2 films increased in that order.
Nonlinear response of gold nanoparticles embedded in glass matrix
Authors: Inouye H. , Tanaka K. , Tanahashi I. , Hirao K.
Published: December 2022

Small metal particles embedded in glass matrix has been investigated energetically both in the application research field and in the basic research field, since the strong enhancement of the third-order nonlinear optical susceptibility is observed around the peak of the surface-plasmon resonance. The mechanism of the nonlinear response, however, has not been clarified yet. We measured transient absorption spectra to investigate the nonlinear response of the gold nanoparticle system by the femtosecond pump-probe method. It is concluded that the nonlinear response originates mainly from the hot electron which is raised by the incidence of the pump pulse in sub-picosecond region. In the long time-scale region, where the time resolution is longer than 5~ps, transient change of the lattice temperature plays an important roll of the nonlinear response.
The potentialities of the plasmachemical technology for fabrication of silica-based photosensitive optical fibers
Authors: Golant K.M. , Dianov E.M.
Published: December 2022

Irreversible refractive index changes in silica-based optical fibers under the action of UV radiation (photorefractive effect) are associated with the presence of oxygen vacancies in the core glass (Si-ODC & Ge-ODC). Although the microscopic mechanism of the photorefractive effect has not been established in detail, it is Ge-ODC that ensure UV light delivery into the fiber core owing to their strong absorption band centered at 242 nm. Naturally, one of the ways of increasing photosensitivity of silica-based fibers is optimization of the preform fabrication regimes with a view to maximize the Ge-ODC concentration.
Ion-exchange processes in silicate glasses: the role of oxygen
Authors: Belostotsky V.I.
Published: December 2022

Potassium and oxygen concentration profiles in soda-lime- silica glass subjected to an ion exchange in molten potassium nitrate at a temperature below the strain point of the glass were obtained by Auger electron spectroscopy. Measurement showed the excess of oxygen in the modified layer of glass and the similarity of the shapes of potassium and oxygen concentration profiles in the most part of the modified layer. Consequently, the replacement of smaller sodium ions by larger potassium ions is accompanied by oxygen diffusion from molten salt into glass. On the basis of these results, a microscopic model of ion-exchange processes in silicate glasses, including mixed alkali effect, was proposed.
Permanent refractive-index changes in pure GeO2 glass slabs induced by irradiation with below-gap light.
Authors: Watanabe Yuichi , Nishii Junji , Moriwaki Hiroyuki , Furuhashi Genjiro , Hosono Hideo , Kawazoe Hiroshi
Published: December 2022

Here we report on the permanent positive refractive-index changes in pure GeO2 glass slabs induced by illumination of light having the photon energy far below than the fundamental absorption edge. The mechanism for the formation of permanent refractive-index change is explained tentatively as a consequence of Kramers-Kronig principle for an additional absorption band induced in the glass via two-competitive photochemical reactions.
Defect population in Ge doped silica studied by fluorescence spectroscopy.
Authors: Poumellec B. , Cens H. , Trukhin A. , Krupa J. C. , Leconte B. , Bubnov M.
Published: December 2022

The interest for Ge doped SiO2 properties is revived by the search of optimisation of photorefractivity. The first step of the mechanism is an absorption at around 240-250 nm or 193 nm. Next step of the transformation leads to index change . Whatever it is connected to a special defect or not, the study of the defect population increases our understanding on that subject and for other applications (fiber line attenuation, nonlinear effect). In this paper, we show that UV spectrum of MCVD doped silica is composed of several gaussian components which appear at the same position and with the same width but varie in intensity depending on the samples. We try to systematize this population.
The role of extrinsic species on the nonlinear absorption of bulk and thin film sulfide glasses
Authors: Cardinal T. , Richardson K.A. , Shin H. , Stegeman G.I. , Glebov L. , Viens J.F. , Villeneuve A.
Published: December 2022

Commercial arsenic sulfide glasses have been prepared with different levels of purification. Linear and nonlinear absorption of both bulk and thin film materials have been measured. Analysis of the components of absorption edge and dependence on purification is discussed. Nonlinear photoinduced absorption measurements were made using femtosecond pulses in the spectral region of 1.5 μm from an optical parametric amplifier. The behavior of glasses prepared by melting or thermal evaporation techniques are compared.
Recoated temperature-insensitive long-period gratings
Authors: Abramov Anatoli A. , Hale Arturo , Vengsarkar Ashish M.
Published: December 2022

Long-period gratings are now being used as gain equalizers in broadband amplifiers1 and as band-rejection filters in a variety of applications.2 While these devices provide elegant in-fiber solutions to many problems in fiber communications, they can exhibit high temperature sensitivities if sufficient care is not taken in their design. When written in conventional communication-grade fibers, their spectra can shift by 4 - 10 nm per 100°C change in temperature. Two solutions to this problem have been successfully demonstrated using specially designed fibers, one based on tailoring the fiber refractive index profile3 and the other based on the use of appropriate dopant materials in the core.4 In this paper, we present long-period gratings written in conventional communication-grade fibers that use the properties of a specially-designed polymer recoat to provide the temperature-independent performance.
Recent advances in optical elastography and emerging opportunities in the basic sciences and translational medicine [Invited]
Authors: Leartprapun Nichaluk , Adie Steven G.
Published: December 2022

Optical elastography offers a rich body of imaging capabilities that can serve as a bridge between organ-level medical elastography and single-molecule biophysics. We review the methodologies and recent developments in optical coherence elastography, Brillouin microscopy, optical microrheology, and photoacoustic elastography. With an outlook toward maximizing the basic science and translational clinical impact of optical elastography technologies, we discuss potential ways that these techniques can integrate not only with each other, but also with supporting technologies and capabilities in other biomedical fields. By embracing cross-modality and cross-disciplinary interactions with these parallel fields, optical elastography can greatly increase its potential to drive new discoveries in the biomedical sciences as well as the development of novel biomechanics-based clinical diagnostics and therapeutics.
Switchable preamplifier for dual modal photoacoustic and ultrasound imaging
Authors: Yoo Jinhee , Oh Donghyeon , Kim Chulhong , Kim Hyung Ham , Um Ji-Yong
Published: December 2022

Photoacoustic (PA) imaging is a high-fidelity biomedical imaging
technique based on the principle of molecular-specific optical
absorption of biological tissue constitute. Because PA imaging shares
the same basic principle as that of ultrasound (US) imaging, the use
of PA/US dual-modal imaging can be achieved using a single system.
However, because PA imaging is limited to a shallower depth than US
imaging due to the optical extinction in biological tissue, the PA
signal yields a lower signal-to-noise ratio (SNR) than US images. To
selectively amplify the PA signal, we propose a switchable
preamplifier for acoustic-resolution PA microscopy implemented on an
application-specific integrated circuit. Using the preamplifier, we
measured the increments in the SNR with both carbon lead and wire
phantoms. Furthermore, in vivo whole-body PA/US
imaging of a mouse with a preamplifier showed enhancement of SNR in
deep tissues, unveiling deeply located organs and vascular networks.
By selectively amplifying the PA signal range to a level similar to
that of the US signal without contrast agent administration, our
switchable amplifier strengthens the mutual complement between PA/US
imaging. PA/US imaging is impending toward clinical translation, and
we anticipate that this study will help mitigate the imbalance of
image depth between the two imaging modalities.
Corneal endothelium assessment in specular microscopy images with Fuchs’ dystrophy via deep regression of signed distance maps
Authors: Sierra Juan S. , Pineda Jesus , Rueda Daniela , Tello Alejandro , Prada Angélica M. , Galvis Virgilio , Volpe Giovanni , Millan Maria S. , Romero Lenny A. , Marrugo Andres G.
Published: December 2022

Specular microscopy assessment of the human corneal endothelium (CE) in Fuchs’ dystrophy is challenging due to the presence of dark image regions called guttae. This paper proposes a UNet-based segmentation approach that requires minimal post-processing and achieves reliable CE morphometric assessment and guttae identification across all degrees of Fuchs’ dystrophy. We cast the segmentation problem as a regression task of the cell and gutta signed distance maps instead of a pixel-level classification task as typically done with UNets. Compared to the conventional UNet classification approach, the distance-map regression approach converges faster in clinically relevant parameters. It also produces morphometric parameters that agree with the manually-segmented ground-truth data, namely the average cell density difference of -41.9 cells/mm2 (95% confidence interval (CI) [-306.2, 222.5]) and the average difference of mean cell area of 14.8 µm2 (95% CI [-41.9, 71.5]). These results suggest a promising alternative for CE assessment.
Two-Photon Thermal Lensing Spectroscopy Using A Synchronously Pumped Dye Laser
Authors: Fang H. L. , Gustafson T. L. , Swofford R. L.
Published: December 2022

Recently the thermal lens effect has been developed as a sensitive technique for measuring two-photon absorption spectra of molecules with low fluorescence yields, where the normal two-photon excitation technique is difficult to apply. For centrosymmetric molecules, the two-photon technique permits a direct examination of even-parity transitions in weakly fluorescent molecules adding a new dimension to the electronic spectroscopy. It has been shown by Twarowski and Kliger1that the two-photon thermal lens can be observed if the laser frequency is coincident with a two-photon allowed band but with little one-photon absorption in molecules. Since the two-photon process depends quadratically upon the laser intensity, the temperature profile induced by two-photon absorption possesses a narrower spatial distribution than is expected for the corresponding temperature profile induced by one-photon absorption. Then the two-photon process might play a significant role because only the center of the heat distribution leads to the formation of the lens signal.
Room Temperature Excitonic Optical Bistability in GaAs Etalons
Authors: Gibbs H. M. , Tamg S. S. , Jewell J. L. , Weinberger D. A. , Tai K. , Gossard A. C. , McCall S. L. , Passner A. , Wiegmann W.
Published: December 2022

Optical bistable devices may someday be the key elements of all-optical logic and computing systems.1 Semiconductor devices appear particularly promising because of very large optical nonlinearities permitting the construction of very small devices. The goal is to develop small (≃ 1 μm), fast (≃ 1 ps), low-power (≃ 1 μW), high-temperature (≃ 300 K) devices. Herein is reported room-temperature operation of GaAs devices that are similar in size, speed, and power to the low-temperature pure-GaAs device.2
Implosion Experiments with Cryogenically Cooled Targets
Authors: Glass A. J. , Slater D. C. , Storm E. K.
Published: December 2022

In an idealized laser fusion target, there is an advantage to having the thermonuclear fuel in the form of a solid spherical shell with a void in the center of the sphere. Compared to a uniform gaseous fill, the solid layer configuration puts the fuel at much higher initial density, and allows the early stages of the implosion to proceed along a lower adiabat. At the peak of the implosion, this target would therefore have higher density and temperature than the initially gas-filled one. Ultimately this translates into more thermonuclear output at fixed laser input for the target with the fuel in a solid shell.
1% Stability 10Hz Mode-Locked Nd:YAG Laser
Authors: Kortz H. P.
Published: December 2022

A complete characterization of an actively/passively mode-locked Nd:YAG laser operated at 10pps is given. An optimization of the output stability down to ±1% for the pulse-train and ±3% for a single method were a stabilization of the pulse-train down to ±5% for Nd:Glass lasers. A lpps actively/passively mode-locked Nd:YAG laser is also described in the literature3, but no characteristics of the laser are given.
Efficient X-ray Preionization of a XeCl Laser
Authors: Shields H. , Alcock A.J.
Published: December 2022

The use of X-rays for gas discharge laser preionization offers the following potential advantages:

(i) a cleaner, higher penetration source of preionization electrons than that provided hy corona or uv spark sources, (ii) a more rugged, higher repetition rate source than electron beam preionization.
Hybrid Technique of Polygon-Based and Ray-Sampling Plane-Based methods in Full-Parallax High-Definition Computer Holography
Authors: Katsura Ryosuke , Matsushima Kyoji
Published: December 2022

Reconstructing photorealistic 3D images of deep objects is still challenging for full-parallax large-scale computer-generated holograms. To address this problem, we propose a hybrid technique based on physical simulation and multi-viewpoint images.
Fourier Holography at 600 GHz
Authors: Yuan Hui , Lisauskas Alvydas , Roskos Hartmut G.
Published: December 2022

Fourier imaging allows to record full scenes with a variable spatial resolu-tion down to the diffraction limit. Here, a 600-GHz Fourier holography system, based on subharmonic detection with CMOS transistors, is demonstrated.
Coherence optics to steer new trends in the digital holography
Authors: Singh Rakesh Kumar
Published: December 2022

Digital holography is an emerging method with a coherence light. Here, we discuss holography with a stochastic light and highlight the role of coherence optics in steering new trends in the DH.
Holographic optical element for digital lensless holographic microscopy's illumination
Authors: Lopera Maria J. , Trujillo Carlos
Published: December 2022

We present the development of a holographic optical element that creates a micrometrical point source producing the divergent spherical illumination needed for Digital Lensless Holographic Microscopy. Our proposal has been validated with biological samples.
(3+1)D Printing of Volume Holograms
Authors: Dinc Niyazi Ulas , Moser Christophe , Psaltis Demetri
Published: December 2022

We demonstrate fabrication of 3-Dimensional structures with arbitrary refractive index distribution by 2-Photon polymerization, which we call (3+1)D printing. We show experimental results of object beam reconstructions with micro-scale volume holograms that are pre-calculated digitally.
Quantum Holography With Undetected Photons
Authors: Töpfer Sebastian , Basset Marta Gilaberte , Fuenzalida Jorge , Steinlechner Fabian , Torres Juan P. , Gräfe Markus
Published: December 2022

We developed and experimentally characterized a imaging setup for holography with separated wavelengths in the detection and sampling, by combining the quantum imaging with undetected photons and digital phase shifting.
3D Imaging of Electrical-Thermal-Mechanical Deformation on Bonding Wire Loops using Phase-Sensitive Line-field Optical Coherence Tomography
Authors: Zhao Zhiyi , Zhang Zijian , Yang Xingyu , Hu Yihua , Xu Ju , Shen Yaochun
Published: December 2022

The repetitive electrical-thermal-mechanical deformation causes bonding wires failures that can damage whole power electronic modules. The LF-OCT can measure electrical-thermal-mechanical deformation on a bonding wire's loop, which can help the reliability analysis of bonding wires.