bluuebunny/crossref_metadata_2025 huggingface dataset:
Advances in Fiber Grating Sensors
Authors: Morey W. W. , Ball G. A. , Meltz G. , Dunphy J.R. , Kersey A.D.
Published: February 2023

Properly annealed fiber gratings can be used as sensor transducer elements at temperatures of 400° C over long periods of time without measurable changes. At 650° C, however, a problem was observed with creep or hysteresis of the grating response. At even higher temperatures diffusion of the core material will become a problem for long term operation. A couple new decoding schemes for fiber grating sensors use matched gratings and acousto-optic tunable filter in the decoding unit These systems can measure many grating transducer elements simultaneously with high sensitivity. Short cavity fiber lasers that utilized fiber gratings can also act as sensor transducer elements giving one ultra high sensitivities that are limited by the fundamental noise in the fiber. One fiber laser sensor uses hetrodyning to generate a signal that can be measured on an RF spectrum analyzer. New techniques for simultaneous measurement of temperature and strain will also be discussed.
Super coupled mode equations for periodic superstructure Bragg gratings
Authors: de Sterke C. Martijn , Broderick Neil G.R.
Published: February 2023

Periodic superstructure Bragg gratings are gratings in which in which at least one of the grating parameters vary periodically. They have been studied theoretically [1,2], as well as experimentally in both semiconductor [3-6], and in optical fibers geometries [7-9]. In particular, the recent work in fiber Bragg gratings has focused on sampled gratings in which the grating is made to vanish periodicially, as illustrated in Fig. 1. This figure shows schematically the refractive index n as a function of position. Note that the superstructure period Γ is much larger than the period of the underlying grating, d.
Asymetrical UV-Written Fibre Fabry-Perot for WDM Soliton Frequency-Guiding and Equalization
Authors: Riant I. , Borne S. , Sansonetti P.
Published: February 2023

Single made fibre soliton transmission is of great interest for high bit rate-long haul optically amplified links [1], but requires in-line frequency-guiding filters to decrease temporal fitter of the soliton pulses [2], We here report the realization of asymetrical UV-written fibre Fabry-Pérot filter suitable for both frequency-guiding of WDM soliton transmission and equalization, to compensate, for instance, the asymetries brought between the different channels by the erbium-doped fibre amplifier gain. Such solution offers filter fabrication simplicity, straightforward splicing to other fibres, and extremely low insertion loss.
Imaging the Frequency Doubling Grating in Optical Fibers
Authors: Carvalho I. C. S. , Reigada D. C. , Garcia F. C. , Hering E. N. , Margulis W. , Laurell F. , Lesche B.
Published: February 2023

It is now generally believed that second harmonic generation in an optical fiber can be attributed to the creation of a permanent dc electric field grating along the fiber. The grating allows for quasi phase matching and gives rise to high conversion efficiencies. Imaging the grating with micrometer spatial resolution has so far been a difficult task because the cladding of the fiber shields efficiently the core from the environment. Indirect techniques have been employed, such as probing the small changes in the spontaneous Raman spectrum scattered as side-light1. Besides being of difficult interpretation, such technique gives low signal-to-noise ratio measurements.
Optical Preparation of Polymers for Frequency Doubling
Authors: Nunzi J.M. , Fiorini C. , Charra F.
Published: February 2023

The discovery that combinations of optical fields could exhibit polarity opens up new possibilities for optical handling of molecules [1], A standard situation in which an optical field exhibits polarity is the coherent superposition of a field Eω at a fundamental frequency ω with its harmonic E2ω at frequency 2ω. It is pictured in Figure 1. Polarity of the cubic interferences appears in the non-zero average cube
t
where the subscript t holds for time average.
Photosensitivity in planar waveguides
Authors: Kitagawa T. , Hibino Y. , Abe M.
Published: February 2023

Silica-based planar lightwave circuits (PLCs) are promising as practical optical circuits with excellent levels of performance [1]. Four generations of PLCs, including the Mach-Zehnder interferometer and arrayed-waveguide grating configurations, have been developed using GeO2-SiO2 waveguides with low propagation and fiber-connection losses fabricated on silicon substrates [2]. The PLCs have been used in feasibility experiments on advanced optical communication systems, such as wavelength division multiplexing (WDM) systems, optical switching systems, and optical access networks. In addition to the family of PLCs, Er3+-doped P2O5-SiC2 waveguides have been fabricated in order to achieve optical amplification in PLC devices [3].
Microscopic investigations of Bragg gratings photowritten in germanosilicate fibers
Authors: Douay M. , Ramecourt D. , Taunay T. , Bernage P. , Niay P. , Dacosta A. , Mathieu C. , Bayon J.F. , Poumellec B.
Published: February 2023

In 1978, K. O. Hill et al. [1] reported the first observation of photosensitivity in a germanosilicate fiber. Interest in understanding and optimizing this phenomenon was further heightened when Meltz et al. demonstrated that an external exposure method could form a grating for use in telecommunication windows [2]. Three mechanisms have been suggested in order to explain the refractive index changes induced in the fiber core. The first is based on a colour - center model [3]. The bleaching of the UV absorption band at 242nm leads through Kramers - Kronig relationship to a refractive index changes in the visible and infrared part of the spectrum. The second is based on UV induced stress relief of the fiber core [4]. The last model is based on structural modifications which induced compaction in the glass matrix [5]. Such UV induced densification has been already reported in preform plates as a change of volume leading to corrugations at the sample surface [6]. These experiments were performed on bulk sample. Therefore, it is of interest to confirm if compaction is photoinduced or not in photosensitive fibers. The aim of this work is to make microscopic investigations of the fiber core at the Bragg grating place in order to look if the UV exposure changes the structural or chemical properties of the material. The characterization of the grating structure photowritten in the optical fiber was realized by Atomic Force Microscopy on etched fibers.
UV-induced photochemical reactions and point defects in photorefractive SiO2:GeO2 and implanted SiO2 glasses
Authors: Hosono Hideo , Nishii Junji , Kawazoe Hiroshi
Published: February 2023

SiO2:Ge(10 %) glasses prepared by the vapor phase deposition were exposed tp ultraviolet radiation from a filtered Hg discharge lamp ( 4.9 eV )and excimer lasers ( ArF : 6.4 eV, KrF : 5.0 eV, and XeCl 4.0 eV). Two photochemical reaction channels were ascertained : (1) The exposure to the lamp irradiation ( ~ 16 mW/cm2) induced Ge E' centers accompanied by bleaching of the absorption component (peaking at 5.06 eV) due to the neutral oxygen monovacancies ( NOMV ) and emergence of an intense band near 6.4 eV and a shoulder at around 5.7 eV. (2) Irradiation with the excimer lasers ( pulse duration; 20 ns ) generated two types of paramagnetic defects, electron trapped centers ( GEC)1 associated with four-fold coordinated two Ge ions or a Ge ion and a Si ion and a self-trapped hole center ( STH: bridging oxygen trapping a hole )2. The striking difference in induced ESR centers are evident in fig. 1. The former and the latter were concluded to be caused via one-photon and two-photon absorption processes ( an example indicating 2-photon process is shown for ArF laser in fig.2), respectively.
Bragg Grating Photoinscription within Various Types of Fibers and Glasses
Authors: Niay P. , Bernage P. , Douay M. , Taunay T. , Xie W.X. , Martinelli G. , Bayon J.F. , Poignant H. , Delevaque E.
Published: February 2023

Optical fiber photosensitivity can be triggered by photochemical processes associated with a large variety of dopants. Thus, photosensitivity in germanosilicate fibers has been related to absorption of light at a germanium defect absorption band located near 5 eV [1] [2]. Photosensitivity in rare-earth doped glasses or optical fibers has been demonstrated by pumping of ion transitions. For example, we have recently reported permanent index changes in Ce3+ doped ZBLAN, HBLAN and ZBLALi fluorozirconate glasses or fibers through the pumping of 4f → 5d Ce3+ transitions using a pulsed laser [3] [4]. In most of the experiments dealing with rare-earth or germanium doped glasses or fibers, it was reported that grating inscriptions led to broad absorption changes which were attributed to photoinduced charge transfer from donors to trap sites. This suggests that charge transfer is a common effect involved in grating photoinscription within all the up to now studied insulating glass fibers. Experiments have been carried out with a view to finding other analogies or differences between photosensitive behaviors of gratings written in various glasses. The aim of the talk is to report results of these experiments with a specific emphasis on the dynamics of grating formation.
Large Photo-Induced Index Changes in Sn-codoped Germanosilicate Fibres
Authors: Dong L. , Cruz J.L. , Reekie L. , Xu M.G. , Payne D.N.
Published: February 2023

There has been a surge of interests in photosensitive fibre gratings in recent years chiefly due to their ease of fabrication and numerous application. Although very large photo-induced index changes have been achieved in pure germanosilicate fibres, an enhanced photosensitivity is desirable to enable gratings to be written with ease and with much cheaper laser source. Stronger photosensitivity also opens up many new applications. Boron-codoping in germanosilicate fibres has been reported to give a much enhanced photosensitivity comparing to that in pure germanosilicate fibres [1], but gratings in those fibres have a much poorer high temperature stability and the B-codoping can also give rise to excessive loss at the important telecommunication window of 1.55 μm. Some post-fabrication techniques have also been devised, i.e. H2/O2 flame-brushing of a germanium doped fibre [2] and Low-temperature hydrogen loading [3], but they are very time-consuming and there are also large induced losses [3]. In this paper, we report on enhanced photosensitivity in Sn-codoped germanosilicate fibres. The gratings in the Sn-doped fibres also have a much improved high temperature stability than those in B-codoped fibres. Unlike B-codoping, Sn- codoping does not introduce significant loss at the important telecommunication window of 1.55 μm.
Hydrogen-enhanced UV photosensitivity of optical fibers: Mechanisms and reliability
Authors: Lemaire Paul J. , Erdogan Turan
Published: February 2023

The use of optical fiber gratings1 has rapidly increased in recent years, due to the invention of the side-writing technique,2 and to the availability of fibers with enhanced photosensitivity. Enhanced photosensitivity has been achieved in various ways, most of which serve to increase the concentration of “native” defects in the fibers.3,4,5,6 More recently the UV photosensitivity of optical fibers has been greatly enhanced by “loading” the fibers with molecular H2 or D2 at high pressure.7 Subsequent exposure of the sensitized fiber to intense UV light at wavelengths less than about 248nm causes the physically dissolved H2 to react with cation dopants resulting in the formation of defects which cause large increases in the refractive index of the glass. This high pressure H2 sensitization technique has been used to great advantage in the UV writing of gratings in optical fibers, and has also been used to sensitize planar waveguides for the UV patterning of waveguide devices,8 and in bulk glasses for demonstration of holographic data storage.9 The UV induced index changes can readily exceed the initial core-to- cladding index difference in GeO2 doped fibers, permitting the UV writing of strong gratings in virtually any GeO2 doped optical fiber. The enhanced photosensitivity is sufficient to allow strong gratings to be written in several minutes using pulsed laser systems (~10-30Hz) at typical irradiances of several 100's mJ/cm2. For instance, in standard single mode fiber (3.5% GeO2) index changes of Δn=5x10-3 can be easily achieved and Δn's of 0.011 have been attained with longer exposures. Recent results have shown that H2 sensitization can also be used to advantage in P2O5 doped waveguides and fibers, either by using 193nm excimer irradiation10 or by using simultaneous heating and UV exposure at 248nm.11 One advantage of using H2 sensitization is that any existing fiber (that is either Ge or P doped) can be sensitized after it has been drawn and coated. Hydrogen molecules readily diffuse through polymer coatings and silica claddings at low temperatures, allowing the loading to be done at temperatures as low as 22-75°C, without degradation of polymer coatings. Figure 1 shows the transmission spectrum for a strong grating written in a standard (3.5% GeO2) single mode fiber that was H2 sensitized with 3.3% H2.
Growth Dynamics of Fiber Bragg Gratings Written with a KrF Excimer Laser
Authors: Williams Glen M. , Putnam Martin A. , Tsai Tsung E. , Askins Charles G. , Friebele E. Joseph
Published: February 2023

For the production of single shot fiber Bragg gratings1-3 in-line during the fiber drawing process, a knowledge of the effects of exposure conditions and material composition of fiber can be of crucial importance. During in-line production, one is not afforded the possibility of exposing the fiber incrementally to repeated laser shots until the correct grating reflectivity is achieved. Single shot writing of gratings in many different types of fibers indicates that the maximum index change in the Type I regime (<1 J/cm2, yielding a spectrally narrow and smooth reflectivity) from a single shot is on the order 10-5. For many applications (ie sensor arrays) this index change produces reflectivites that are more than adequate for good system performance. However, for certain applications greater reflectivies are required. In an effort to better control and possibly improve the photosensitivity of optical fibers at 248 nm we studied the growth dynamics of fiber Bragg gratings in various fibers under various exposure conditions.
Photosensitisation of Phosphosilicate Fibre Bragg Gratings
Authors: Canning J. , Pasman R. , Sceats M.G.
Published: February 2023

Photolytic grating writing in phosphorous doped waveguides has recently been possible only with substantial hydrogen loading [1-3]. In [1] this has been demonstrated for phosphosilicate planar waveguides using 193nm whilst for aluminophosphosilicate fibres the writing wavelength was the 248nm KrF line [2]. We have recently demonstrated photosensitivity at 193nm in phosphosilicate fibres [3] fabricated by the flash condensation technique [4]. This technique appears unique in that it has pre-existing phase separation within the fibre [5] which assists in the incorporation of up to 14wt% of rare-earth ions. In addition to showing significantly better performance than at 240nm under similar irradiation conditions the induced photosensitivity was found to be dependent on slow chemical sensitisation with hydrogen prior to irradiation. Fig. 1 is a comparison between the expected diffusion profile for hydrogen loading at 373K and 40atm and the saturated reflectivities obtained for various loading times. The importance of hydrogen loading is accentuated with the observation of only transient gratings (Fig 2) without loading. The decay profile of these gratings cannot be accounted for by a single relaxation process. Instead, we propose that (1) there are several contributions to the index change in which one mechanism promotes the next, and (2) the role of hydrogen is to quench the back reactions. A two step process suggests that memory effects, such as presensitisation, may be observed. In this paper, we use a novel side diffraction technique [6] for measuring the index contrast to demonstrate that these phosphosilicate glass fibres exhibit large photolytic presensitisation.
Ion Implantation Induced Photosensitivity in Silica and Ge-Doped Silica
Authors: Essid M. , Verhaegen M. , Allard L.B. , Brebner J.L. , Albert J.
Published: February 2023

Photosensitivity can be induced in silica1 and Ge-doped silica2 by high energy ion implantation. The optical absorption induced in the ultraviolet region by the implantation can be substantially reduced by exposure to excimer laser light resulting in a polarisation dependent3 change in the refractive index at longer wavelengths. This refractive index change can be related to the variation in the absorption by Kramers-Kronig analysis4,5. We describe here, the result of a series of experiments undertaken to determine the effects of ion implantation on the photosensitivity of silica and Ge-doped silica planar waveguide structures.
Effective Indices of the Propagating Modes in Planar Waveguides Measured with UV-Induced Bragg Gratings
Authors: Hübner Jörg , Poulsen Christian V. , Rasmussen Thomas , Andersen Lars-Ulrik Aaen , Kristensen Martin
Published: February 2023

The design and development of integrated optical components require precise information about the propagating modes in the planar waveguides and their effective refractive indices (neff). Most of the standard telecommunication waveguides and fibers produced today contain germanium in the core and are therefore photosensitive. A long Bragg-Grating with very low refractive index change can be used to characterize the mode propagation in a waveguide because each mode will have a different effective refractive index and thus the corresponding transmission dip of the grating will be located at a characteristic centre wavelength.
Thermal stability of direct UV-written channel waveguides
Authors: Poulsen Christian V.
Published: February 2023

An important issue of the UV-induced effects in germanium doped silica glasses is the long term stability. Investigations concerning the thermal stability show a major difference between effects induced by low and high intensity [1] (type I and type II). In this paper, the thermal response of UV-induced waveguides in germanium doped silica glass is investigated, as a function of UV-intensity.
Characterisation of Long Phase Masks for Writing Fibre Bragg Gratings
Authors: Ouellette François , Krug Peter A. , Pasman Remco
Published: February 2023

The use of phase masks for writing fibre Bragg gratings was first demonstrated by Anderson et al [1]. These masks are etched in silica (for high transmission at the writing wavelength), and can be fabricated by either photolithographic techniques or electron beam lithography. It was demonstrated afterwards that long gratings can be written by scanning a narrow beam along a phase mask-fibre assembly [2]. The length of gratings is then limited by the length of the mask. Since very long gratings are useful for dispersion compensation, as well as very narrow reflection filters, there is a strong interest in the fabrication of very long phase masks. While in principle there is no limit to photolithographic techniques, the size of the optics required sets a practical limit, and masks greater than 5 cm diameter are prohibitively expensive. On the other hand, to date electron beam lithography can fabricate masks up to 14 cm in length. In this process, the pattern is divided into fields, and parallel lines are scanned with the electron beam in the photoresist across the width of the field. The process is then repeated at a new position until the whole mask is written. Sometimes, this process results in a phase jump between the fields of the grating, called a "stitching error". In this paper, we analyse the consequences of this stitching error, and present experimental characterization of gratings written with long phase masks fabricated by electron beam lithography.
UV Excited Poling of Germanosilicate Fibre
Authors: Fleming S.C. , Fujiwara T. , Wong D.
Published: February 2023

Lithium niobate is well known as a material with a high electro-optic coefficient which makes it well suited to applications as an electro-optic modulator or a non-linear optical element. However it has a number of drawbacks, particularly high coupling losses to standard fibre and low photorefractive damage threshold, which have prompted the investigation of electro-optic effects in glassy materials, most notably silica.
Second Harmonic Generation in Low-Water Fused Silica by Proton Implantation
Authors: Henry Leanne J. , Alley Thomas G. , Rand Dennis S. , Kester John J.
Published: February 2023

Second harmonic generation (SHG) in poled fused silica, which was first reported by Myers, Mukherjee and Brueck(1) in 1991, has increased in importance because of a multitude of potential device applications. Such applications include electro-optic switching, frequency doubling crystals, parametric amplification, parametric oscillation, and linear electro-optic modulation/frequency conversion which can be monolithically integrated into optical fibers and planar integrated circuit geometries. Because of these potential applications, much work has been done to understand the phenomenon of SHG in poled fused silica.
Grating Structure in Self-Pumping Barium Titanate by Local Erasure
Authors: Brody P. S.
Published: February 2023

The photorefractive grating structure in self-pumping crystals is often difficult to assess, since observations of dielectric grating structures are difficult. Observations of patterns of scattered light within the self-pumping crystal can be used, but the results are often ambiguous.
Self-Pumped Phase Conjugation in the Red in Photorefractive Ba2-xSrxK1-yNayNb5O15 and SrxBa1-xNb2O6 with Cerium in 9-Fold Coordinated Sites
Authors: Montgomery Steven R. , Yarrison-Rice Jan , Pederson Donald O. , Salamo Gregory J. , Miller Mary J. , Clark William W. , Wood Gary L. , Sharp Edward J. , Neurgaonkar Ratnakar R.
Published: February 2023

We report the first observation of self-pumping1 in Ba.5Sr1.5K.25Na.75Nb5O15 (BSKNN-III) and Sr.6Ba.4Nb2O6 (SBN) with Cerium in 9-fold coordinate sites. Phase-conjugate reflectivities on the order of 20% have been observed from both crystals along with relatively fast response times. The observations reported here were carried out at laser wavelengths of 647 nm and 676 nm.
Phase-Conjugate Multimode Fiber Gyro
Authors: McMichael Ian , Beckwith Paul , Yeh Pochi
Published: February 2023

Modal scrambling is a source of noise and signal fading in fiber-optic gyros1 and therefore the best fiber-optic gyros use single-mode polarization preserving fiber and couplers2. Phase-conjugation can be used to correct for modal scrambling3-5 and to make fiber-optic gyros6-9. In this paper we describe and demonstrate the combination of these two possiblities; a phase-conjugate fiber-optic gyro using multimode fiber.
Optical Parallel Communication with Photorefractive Material
Authors: He Qichi , Duthie J. Graeme , Shamir Joseph , Caulfield H. John
Published: February 2023

We demonstrate optical parallel-transmission by Double Phase-Conjugate Mirror (DPCM) of BaTiO3. Temporal information can be exchanged simultaneously and independently between two or more separate lasers.
Photorefractive Diffraction Gratings in KTN:Cr, Fe in the Paraelectric Phase Using the Quadratic Electrooptic Effect
Authors: Agranat Aharon , Sayano Koichi , Yariv Amnon
Published: February 2023

Potassium tantalate niobate (KTN) was one of the first photorefractive (PR) crystals to be discovered(1,2,3). However since its discovery, very little has been done in order to explore its PR properties.

The chemical composition of KTN is given by KTa1−xNbxO3 where x denotes the niobium concentration. KTN undergoes a ferroelectric phase transition at a temperature Tc which depends on x (roughly 8.5K/1% per mole of Nb). For low Nb concentrations the phase transition is second order and it becomes first order for x ≥ 0.3.(4)
Comparison of Picosecond Photorefractive Effects in BaTiO3 and GaAs
Authors: Smirl Arthur L. , Valley George C. , Bohnert K. , Boggess Thomas F.
Published: February 2023

Here, we compare the speed, magnitude, and origin of the photorefractive responses of 3aTiO3 and GaAs on picosecond time scales using two-beam mixing, three-beam transient grating and four-wave mixing techniques. We also measure the dark current decay time and the erasure fluence for picosecond pulses. These materials were chosen for their contrasting properties. BaTiO3 has a relatively large electro-optic coefficient (r13n3≃350, r33n3≃1200), but exhibits a small mobility1 (μ≃1 cm2/Vs) and is believed to have a subnanosecond recombination time.2 By comparison, GaAs has a much smaller electro-optic coefficient (r41n3≃60), a large mobility (μ≃6000 cm2/Vs), and a recombination time that can exceed a nanosecond. Our measurements differ from more conventional cw and nanosecond experiments, not only in providing enhanced time resolution, but in that the generation rate can significantly exceed the recombination rate, and large numbers of free photoionized carriers can be produced. The Drude-Lorentz (or band filling) change in the refractive index associated with these free carriers is the source of a second refractive grating. We monitor and separate the contributions of both grating sources in both two-beam mixing and three-pulse transient grating geometries.
Conical Diffraction in LiNbO3:Fe Crystal
Authors: Chen F.Z. , Liu W.H. , Qiu Y.S. , Lu T.S.
Published: February 2023

The studies of cones of diffracted light on the illumination of a previously laser-exposed LiNbO3:Fe crystal have been reported [1-3]. Here we report the observation of additional diffracted cones which strongly depend on the relative directions of both the writing and reconstructing beams with respect to the crystal axis. Furthermore, the intensity distribution of the diffracted cones are related to the combinations of various polarizations of the writing and reconstructing beams.
Materials Parameters of Photorefractive Crystals from Anisotropic Diffraction Measurements
Authors: Temple D. A. , Hathcock R. S. , Warde C.
Published: February 2023

Anisotropic gratings in BaTiO3 are used to determine electrooptic coefficient ratios, quantum efficiency, diffusion lengths, and the a to c axis ratios of the mobilities and dielectric constants.
Influence of Material Properties on Photorefractive Effects in Semi-Insulating GaAs*
Authors: Cheng Li-Jen
Published: February 2023

Semi-insulating gallium arsenide(GaAs) is a potential photorefractive material for real-time volume holography and optical processing applications. The advantages of these photorefractive compound semiconductors include fast response1,2, high sensitivity3,4, and operation in infrared wavelengths compatible with semiconductor lasers5 as well as VLSI technology. In addition, large-size crystals of high-quality for electronic applications are commercially available.
Beam coupling in KNbO3 at 442 nm
Authors: Rytz D. , Klein M.B. , Valley G.C. , Wechsler B.A.
Published: February 2023

The photorefractive properties and applications of KNbO3 and KNbO3:Fe have been investigated for quite some time by Günter and co-workers [1]. Relatively little, however, is known about KNbO3:Mn, a new photorefractive material used recently in a nonreciprocal optical transmission device [2].
Application of thermodynamic defect model to modification of the photorefractive properties of BaTiO3
Authors: Wechsler B.A. , Klein M.B.
Published: February 2023

Since the early development of photorefractive materials, a great deal of attention has been directed toward optimizing the properties of photorefractive oxide crystals. In general, the approach has been to alter the populations of participating species by intentional doping during crystal growth [1,2] and/or by post-growth heat treatment under various partial pressures of oxygen [1,3]. Recent experiments performed with BaTiO3 [4,5] have produced somewhat differing results. There has been little theoretical understanding of the effects of doping and oxidation/reduction treatments on the defect structure and hence the photorefractive properties of such crystals.
A Comparative study of the photorefractive effect in Bi12SiO20 Crystals
Authors: Strohkendl F.P. , Tayebati P. , Hellwarth R.W.
Published: February 2023

We perform beam-coupling and erasure experiments in four different nominally undoped Bi12SiO20 (BSO) crystals. We use the theory of electron-hole competition1,2 in photorefractive gratings to analyze our data. We determine the diffusion- lengths
Ke−1,  Kn−1 for electrons and holes, the ratio S of hole to electron absorption, the Debye screening wavevector ko, the total absorption coefficient and the quantum efficiency.
Characterization of Defects in Bi12GeO20 by Specific Thermal and Optical Spectroscopic Methods
Authors: Gies J.G. , Zielinger J.P. , Benjelloun N. , Tapiero M. , Launay J.C. , Marsaud F.
Published: February 2023

The photorefractive materials Bi12SiO20 (BSO) and Bi12GeO20 (BGO) are among the most sensitive for reversible volume holographic recording [1]. The band transport model in conjunction with a simple two energy level diagram is commonly used to describe grating formation [2]. The recording light excites electrons from an energy level A located at 2.6 eV below the conduction band to this latter [3]. The free photoelectrons drift under the action of an applied electric field from illuminated to unilluminated zones where they remain trapped at a level B 1.3 eV below the conduction band.
Photorefractive Properties of Iron-doped InP at 1.06 μm
Authors: McCahon S. , Klein M.B. , Valley G.C.
Published: February 2023

There is an ongoing need for efficient nonlinear materials at wavelengths in the near infrared for applications such as optical data processing and spatial light modulation. Compound semiconductors such as GaAs and InP are particularly promising for these applications. While the photorefractive properties of GaAs have been studied in some detail [1-3], there is less data on InP [1]. The purpose of the work described here was to determine the photorefractive properties of Fe-doped InP in both the steady state and transient regime, and relate them to properties measured by conventional electronic techniques.
Spatial harmonics of photorefractive grating induced by sinusoidal optical intensity variation in a BaTiO3 crystal.
Authors: Lee Yeon H. , Hellwarth R.W.
Published: February 2023

We report the first measurements on spatial harmonics of a photorefractive grating. Our method was to create a photorefractive grating with 2 crossed 515 nm plane waves such that the grating wavevector was parallel to the c-axis of a BaTiO3 crystal. We measured the amplitudes of the fundamental and first and second spatial harmonics of the resulting photorefractive grating by measuring the strength of the Bragg scattering of a 633 nm laser from them. We performed these measurements for various values of the grating period ℓg, and as a funciton of the intensity ratio of the two "writing" 515 nm beams. We performed numerical solutions of the model of Kukhtarev1 for these parameters and found excellent agreement with our data.
Influence of the polarization Direction on two-beam coupling in photorefractive Bi12SiO20: diffusion Regime
Authors: Mallick S. , Rouede D.
Published: February 2023

The presence of natural optical activity in Bi12SiO20, renders the two-beam coupling effects in this crystal highly sensitive to the polarization direction of the interacting beams. We derive analytic expressions for the steady state signal amplification when a strong pump beam and a weak signal beam write a grating G through the diffusion of photo-electrons. Two commonly used transverse configurations, G// <001>and G//<110>, are studied. We prove the experimentally found fact that only the <001> orientation is suitable for signal amplification. The results obtained for the diffusion regime can be applied, without significant error, to the more common and more intricate drift regime in which a bias electric field is applied to the crystal to enhance the coupling effect.
Dilated Acousto-Optic Switches for Low-Crosstalk Wavelength Routing in WDM Systems
Authors: Smith D. A. , d’Alessandro A. , Baran J. E.
Published: February 2023

The method of cascading acousto-optic switches is shown, both theoretically and experimentally, to reduce the many interchannel crosstalk mechanisms which degrade the system performance of wavelength-routed dense wavelength multiplexed optical communication systems. Two integrated acousto-optic switches were cascaded and examined for one and two-stage switch performance, including bandpass, sidelobe levels, bar and cross-state extinctions insertion loss and imposed frequency shifts. The expanded, or dilated, version of the switch showed dramatic improvement in most figures of merit, with an expected doubling of loss. In addition, it is shown that the operating window of the switch is significantly broadened by dilation. Sidelobe suppression, achieved through apodization of the acousto-optic interaction strength, combines with dilation, is shown to reduce channel spacing as well as improve tolerance of the system to wavelength registration errors.
“Broadcast and Switch” — A New Class of WDM Networks for High Switching-Speed, High Connectivity Applications
Authors: Sharony Jacob
Published: February 2023

An architecture using star-couplers and wavelength-selective switches is described. This architecture features faster switching, higher connectivity, reduced complexity and much fewer wavelengths compared to star-based networks.
Photonics in Switching: European Systems Demonstrators and the Long Term Perspective
Authors: Thylén Lars
Published: February 2023

Status in the area of photonics in switching in Europe, highlighted by systems demonstrators, is reviewed, and the long term perspective for photonics in switching is discussed.
High-Speed Photonic Switching in Corporate Networks
Authors: Martinson Thomas M.
Published: February 2023

The last decade has witnessed important advances in the area of optical communications. Unfortunately, technological progress has often outpaced system developments. Breakthroughs in wavelength conversion devices, high performance lasers, optical amplification, high-speed switching, and high-density optoelectronic integration have not always been matched by corresponding system applications [1-3]. As a result, optics remains mostly confined to the transport of information whereas switching and processing are still heavily dominated by electronics. Successful photonic switching applications will certainly for some time to come depend on both electronic and optical capabilities.
Efficient Implementation Methodology for 3-D Space-Invariant Hypercube-Based Free-Space Optical Interconnection Networks
Authors: Louri Ahmed , Sung Hongki
Published: February 2023

A new design methodology for constructing three-dimensional optical space-invariant hypercube interconnection networks is presented. The methodology allows the construction of larger hypercube networks from smaller networks in a systematic and incremental fashion. It is shown that the proposed methodology greatly improves area utilization as compared with previous methods. Due to its totally space-invariant nature, the resulting three-dimensional hypercube networks are highly amenable to optical implementations using simple optical hardware such as multiple imaging components and space-invariant holographic techniques.
2-D WDM Optical Interconnections Using Multiple-Wavelength VCSEL’s for Simultaneous and Reconfigurable Communication Among Many Planes
Authors: Willner A. E. , Leight J. E. , Chang-Hasnain C. J.
Published: February 2023

We propose and analyze a novel interconnection configuration in which one 2-dimensional plane can communicate simultaneously and reconfigurably with many planes by using WDM. This system incorporates arrays of multiple-wavelength VCSEL’s as well as wavelength-selective detecting planes. High signal contrast ratio with low power penalty can be achieved for a Δλ>30nm, limited only by the detector spectral response. In addition, system capacity is significantly enhanced over more traditional techniques by using WDM pixels.
Variable Optical Delay Line for Frame Synchronizer in Photonic ATM Switching System
Authors: Ozeki Takeshi , Shimizu Yukio , Sharma Manish , Ibe Hiroyuki
Published: February 2023

Photonic ATM switching system with hypercube topology is one of the promising photonic switching systems which utilize the high speed transmission ability of photonics technology [1] [2].
Polarization Independent Optical Modulation with Tensile-Strained GaAs-InAIAs Quantum Wells grown on GaAs Substrate
Authors: Chan Yuen-Chuen , Tada Kunio
Published: February 2023

Large field-induced optical absorption and refractive index variations through the quantum confined Stark effect in quantum well structures have prompted the development of many high performance compact optical modulating devices1). However, several shortcomings are present and one of them is a strong polarization dependent characteristic in lattice-matched systems2). This is due to the fact that the dipole moments of electron-heavy/light hole transitions show a strong polarization dependence, such that while TE mode light, with the electric vector parallel to the quantum well layers, interacts with both heavy and light hole transitions, only electron-light hole transitions are involved in the TM mode polarization, where the electric vector is perpendicular to the quantum well layers3). Moreover, in an unstrained quantum well, the valence bands for the heavy and light holes are degenerate and hence the electron-heavy hole transition always lead the electron-light hole transition at the absorption edge due to the heavy hole’s larger effective mass. As a result, there exists a large difference in the optical absorption and refractive index variation at the absorption edge between the TE and TM mode polarizations.
Monolithic Integration of Quantum Well Optical Waveguides with Heterojunction Bipolar Electronics for Wavelength Switching
Authors: Zucker J. E. , Chen Yi , Divino M. D. , Chandrashekar S. , Joyner C. H. , Dentai A. G. , Burrus C. A.
Published: February 2023

Most near-term photonic switching systems exploit optical devices for their large bandwidth but still require electronics for memory, logic, and control functions. Hence there is great interest in monolithically integrating electronics and photonics12. For example, packet header interpretation and routing can be acheived with an optoelectronic circuit consisting of integrated photodetector, transistor electronics, and space-division switches. If, as an overlay to the space-division fabric, wavelength division multiplexing (WDM) is used, then switching capacity can be tremendously increased. Even greater WDM network flexiblity is attained if there is some means for channel reuse such as wavelength conversion.
Functional Photonic Switching Device by Vertical and Direct Integration of Six Heterojunction Phototransistors and Two Laser Diodes
Authors: Noda Susumu , Shibata Kimitaka , Ahamady Vahid , Sasaki Akio
Published: February 2023

Much interest has been emerging in optical signal processing and optical computing. In these fields, various functional devices are greatly demanded. A vertical and direct integration of a light-receiving device and a light-emitting device is an attractive method to achieve these functional devices [1–5]. The integrated device exhibits not only the simple combined characteristics of constituent devices but also the more elevated characteristics due to their internal optical couplings. For example, the integrated device composed of four heterojunction phototransistors (HPTs) and one laser diode (LD) offers the functions of light-controlled optical bistability, light-controlled optical thresholding, and optical tristability [6].
Optical Crossbar Switch with Semiconductor Optical Amplifiers
Authors: McAdams L. R. , Gerrish A. M. , Kalman R. F. , Goodman J. W.
Published: February 2023

Semiconductor optical amplifiers (SOAs) have a number of attractive properties for use in photonic switches. SOAs offer nanosecond switching times, extinction ratios in excess of 40 dB, and small signal gains of approximately 15 dB. In addition they can be monolithically integrated, and thus can potentially be fabricated in volume and used in large switch matrices. Here we report on our recent demonstration of an 8×8 optical crossbar switch based upon discrete SOAs. Other authors [1-3] have reported on SOA-based optical switches at the device level. Our work focuses on the demonstration of the technology at the system level. This demonstration is a significant step towards the widespread use of SOA-based optical switches because it provides a testbed for exploring and identifying the relationships between device parameters and system performance requirements. A block diagram of the optical crossbar switch is shown in Figure 1. The switch is constructed in a modular fashion and consists of optical, digital, analog, and computer modules. Figure 2 shows two photographs of the completed optical crossbar switch.
Optical Fiber Interconnection Links for High-Speed Switching and Computer Systems
Authors: Nakagami Takakiyo
Published: February 2023

Among the various optical interconnection technologies being researched today, optical fiber interconnection is one of the most practical for near-term applications. [1] It is very effective for solving the recent problem of data transfer bottlenecks in advanced switching systems and computers. [2]-[4] The merits of optical transmission, including wide bandwidth, immunity to electromagnetic interference, ground-isolation capability, and small cable size, also favor in such short-distance applications. Since their circuit boards and units usually have parallel I/O interfaces, multi-fiber parallel transmission has the advantages of compatibility to the conventional system designs as well as the capacity for high overall transmission throughputs. This paper discusses the technical issues associated with the optical fiber interconnection links mainly focusing on parallel links and touching upon recent developments in Japan. [5]-[12]
An Intelligent Channel Selector for Wavelength-Division and Time-Division Hybrid Multiplexed Network
Authors: Siumosaka Naoki , Shiozawa Takahiro
Published: February 2023

Recently, requirement has been increasing for large capacity optical network, for example, for a video signal distribution system in broadcasting studio[1], which has been undergoing a process of complete digitalization. A wavelength-division and time-division hybrid multiplexed (WD/TD) network[2] is an attractive candidate for this purpose, because the attainable multiplexity is given by the product of WD and TD multiplexities. In order to realize WD/TD network, WD/TD channel discrimination and tracking control when receiving a channel are indispensable techniques. In this paper, a highly intelligent WD/TD channel selector is described for practical broadcasting studio application. Results for WD/TD channel selection and tracking control are shown to demonstrate the developed selector performance.
2-D WDM Optical Interconnects Using Multiple-Wavelength VCSEL's for Simultaneous and Reconfigurable Communication between Many Planes
Authors: Willner A. E. , Chang-Hasnain C. J. , Leight J. E.
Published: February 2023

The ability to connect efficiently many high-speed ports is of critical importance for large-capacity data processing. By taking advantage of the parallel nature of light, two-dimensional (2-D) optical planes can be employed to avoid the eventual electronic bottlenecks of reduced speed and increased power consumption.[1-3] However, a basic problem arises in the optical-plane solution when one plane wishes to communicate simultaneously or reconfigurably with many subsequent planes. Traditional optical systems solve this problem in two ways as shown in Fig. 1. The first method is for each plane to detect a data packet and then, if it was not intended for that plane, retransmit it to the next plane. The disadvantages include the possibility of an electronic high-speed bottleneck as well as the wasting of capacity, real estate, and optical hardware. The second method involves etching large via-holes in each plane's substrate as a window such that an unobstructed and permanent optical path is created between a transmitting pixel on plane i and a detecting pixel on plane j.[4] This second approach solves the electronic bottleneck but wastes real estate and allows only a given static configuration between any two planes.
Translation of laser tuning experiments into networks
Authors: Giglmayr Josef
Published: February 2023

Experiments on tunable lasers have been presented which show the high performance of devices as well as their capability to be integrated.1 The aim of the present paper is to discuss some of the problems which arise if they are composed to an optical frequency division multiplexing (OFDM) system based on a multistage interconnection network with regular space-frequency interconnects. There the space interconnects (links) are deflected in a regular manner and at each link a fixed number of frequency channels is assumed which also are permuted according to a certain rule which is repeated at each stage. In this way, the least number of stages is needed for the nonblocking interconnection. The general concept presented may be extended to highly regular structures (nearest-neighbour interconnects).
Practical demonstration of a freespace optical crossbar switch
Authors: White H. J. , Brownjohn N. A. , Stace C. , Proudley G. M. , Walker A. C. , Taghizadeh M. R. , Robertson B. , Barrett C. P. , Birch M. J.
Published: February 2023

The use of free-space optics to perform high bandwidth connections for computing applications has been widely discussed in the literature. In this paper we present the practical results of a free-space optical crossbar switch which uses a ferroelectric liquid crystal spatial light modulator as the active switching element. This work has formed part of a collaborative project entitled OCPM which is concerned with developing optical free-space crossbar switching technology for use as the communications fabric for parallel computing systems. The OCPM project (Optically Connected Parallel Machines) is a collaboration between British Aerospace (Sowerby Research Centre), Meiko, BNR Europe, Heriot-Watt University, the University of Bath and Thorn EMI CRL. The project is coordinated by British Aerospace and is funded in part by the DTI and SERC.
An Efficient Implementation Methodology for 2-D Space-invariant Hypercube-based Free-space Optical Interconnection Networks
Authors: Louri Ahmed , Sung Hongki
Published: February 2023

One of the most popular interconnection networks for parallel computers today is the binary n-cube, also called the hypercube, interconnection network. The attractiveness of the hypercube topology is its small diameter, simple and efficient message routing algorithms, strong connectivity, regularity, symmetry, and fault-tolerance. Unfortunately, conventional VLSI technology seems to be reaching its fundamental physical limits and is, therefore, unable to implement large-scale interconnection networks based on the hypercube topology (or any other topology for that matter) that provide high communication bandwidth, short latency, and reasonable power requirements[1].