This paper describes a method for measuring modal birefringence in optical fibers. It combines an interferometric technique with wavelength scanning and allows a high precision, nondestructive measurement of the birefringence along different sections of a long optical fiber. The experimental results for hi-bi fibers, 10-meters and 100-meters long, are presented. An accuracy of about 0.1% is achieved in the spectral range of 600 - 850 nm.
The use and applications of optical fibers have been increased dramatically over the years. A need to improve the quality and increase the yield of optical fibers and optical multifiber systems leads to studies related to the manufacturing process of optical fibers. This paper presents a combination of analytical and numerical work on the thermal analysis of the heating region. During the process various phenomena occur in the heating region: As the glass rod is pulled downward, it stretches and a neckdown shape is formed at its lower end. This stretching affects the air flow patterns in the furnace as well as the heat transfer in the glass and its surroundings. The preform is heated radially by a radiative heater. The radiation effects were taken into consideration. Axial and radial heat conduction, and convective heat transfer from the surface of the preform were also accounted for. A coupled form of the boundary layer equations combined with the conduction equation in the glass was solved considering the above phenomena. The temperature distribution in the glass for various drawing conditions was calculated. The flow patterns in the glass were observed and a sample study of the air flow in the furnace is presented. Also, the shape of the glass preform was evaluated for various drawing parameters.
This paper presents results of a numerical simulation of the air flow in an optical fiber drawing furnace for a variety of processing conditions of industrial interest. The numerical model was based on PHOENICS, a fluid-flow simulation computer program, and was verified experimentally by flow visualization and thermal anemometry. Flow patterns in the area between the preform and the furnace walls were obtained for various furnace configurations. Results show that the air flow changes significantly by changing the geometry of the entrance and exit of the furnace.
Photoinduced optical phenomena in silica fibers have received attention because of the demonstration of photoinduced second harmonic generation and photorefractive index gratings. For Ge doped fibers the mechanism responsible for both effects has been correlated with bleaching by UV irradiation of defects associated with the Ge ion. The effects of processing on UV bleaching of defects in high purity GeO2 have been examined. Bleaching kinetic studies indicate that processing variables such as melting temperature have a strong influence upon the bleaching of defects in GeO2 glasses.
Cold wall melting with high frequency induction heating has the advantage that no impurities are introduced in the glass during the melting process. Different types of optical glasses were tested. With one exception all optical glasses took power in the high frequency electric field in the range from 0.5 to 3 MHz at a sufficiently high temperature. A good correlation between the electrical conductivity of the glass melt measured with 10 kHz and the penetration depth of the electrical field can be found.
The methods commonly employed to prepare optical fibers from halide glasses are described. Since these approaches can limit the choices of compositions which can be used, two new processing methods are being developed which could, in principal, improve the capability of forming technology.
High-precision optical systems demanded by much of today's advanced technology requires a renewed interest in optical glasses. Improvements in the manufacturing process of established optical glass, and the development of new specialty glasses (e.g., low index, high index, UV, or IR glasses) makes glass a viable option for many applications that heretofore required the use of other less desirable materials, such as hygroscopic crystals, or materials with a high thermal coefficient of refractive index. A review of current applications for optical glass and a look at future needs are discussed.
In large laser systems such as NOVA at Lawrence Livermore National Laboratory the active laser glass is surrounded by a cladding glass. The purpose of this glass is to absorb 1.06 micrometers laser light and prevent parasitic laser action from occurring due to amplified spontaneous emission (ASE). Currently, the cladding glass utilizes the base composition equivalent to the active laser glass with copper doping. The copper produces the required absorption coefficient, approximately 2.8/cm. The cladding glass has a high coefficient of thermal expansion which results in the degradation of the optical properties of the laser disc due to thermally induced strain. To eliminate this problem the concept of a near zero expansion glass-ceramic cladding material was developed.
Waveguide lasers formed by ion exchange in rare-earth-doped glasses have emerged as an attractive new technology on the threshold of commercial insertion. These devices can be used as both laser oscillators and optical amplifiers. In this article, we review ion exchange and glass composition. We then discuss the performance of ion-exchanged waveguide lasers made in silicate and phosphate glasses.
The Nd-doped phosphate laser glass described herein can withstand 2.3 times greater thermal loading without fracture, compared to APG-1 (commercially available average-power glass from Schott Glass Technologies). The enhanced thermal loading capability is established on the basis of the intrinsic thermomechanical properties (expansion, conduction, fracture toughness, and Young's modulus), and by direct thermally induced fracture experiments using Ar-ion laser heating of the samples. This Nd-doped phosphate glass (referred to as APG-t) is found to be characterized by a 29% gain cross section and a 25% longer low-concentration emission lifetime.
We report recent results from our work on the fabrication of neodymium waveguide lasers. Several neodymium doped glasses. APG-1, LG-680, BK 7 and S 3 made by Schott Glass Technologies, Inc. were studied as candidates for use as waveguide lasers. It was found that S 3, a standard ophthalmic glass, had the best ion-exchange properties of any of the glasses studied. A waveguide laser was successfully made using the neodymium doped S 3 glass.
Electron radiation presents a peril to the qualification and use of glass on space-based optical systems. Radiation testing of glass for use in harsh radiation environments commonly centers around x-ray, gamma-ray, neutron, and proton radiation. Because of their relatively low energy and density, the effect of electron radiation is often considered negligible. However, during qualification of the TOPEX laser retroreflector array glass, 250 krad (Si) doses of 1.25 MeV electrons were shown to cause significant damage in several glass samples. Electron radiation will generate centers of high potential within the glass and when large enough cause a dielectric breakdown, whereby forming Lichtenberg patterns. These patterns significantly reduce transmission and are good scattering centers. The effect of electron radiation on six types of glass at incremental dosages between 0.25 Mrad and 55 Mrad is presented. The results of electron radiation on a magnesium fluoride anti-reflection coating also are discussed.
Solid optics is a design strategy which has no air spaces throughout the entire optical path and therefore produces extremely rugged optical systems. In an ideal solid system, lens elements, refractive or diffractive, beam splitters, sources, detectors, and any other optical elements are cemented together to form a single rigid assembly. The resulting system, essentially a solid block of glass, is impervious to misalignment. Certain systems such as analogue optical computers, for example, are ideally suited to the advantages of solid optical design schemes. A solid correlator system is presented and a designer's wish list is discussed.
A new glass system based on a range of lead-indium phosphate compositions has been developed. These glasses have a relatively high index of refraction (1.8 - 1.9) in the visible region and exhibit moderate dispersion (typical Abbe number of 32). The ultraviolet absorption edge occurs near 300 nm and the glasses strongly absorb in the infrared at wavelengths greater than 2800 nm. The glasses can be prepared at relatively low temperatures (900 - 1000 degree(s)C) and are easily poured at temperatures near 800 degree(s)C due to their low melt viscosities. Lead-indium phosphate glasses exhibit good chemical durability and resistance to both weathering and intense gamma-irradiation. These materials have a glass transition temperature of 430 degree(s)C, and thermal expansion coefficients in the range of 11 to 12 X 10-6/ degree(s)C. The structure of these glasses consists of a distribution of chains of PO4 tetrahedra held together by bonding between the non- bridging oxygen of the tetrahedra and the metal cations. The polyphosphate chain distribution was determined using the technique of high-performance liquid chromatography. The high index of refraction of lead-indium phosphate glasses makes them attractive for several applications such as high-numerical-aperture optical fibers and specialty lenses. Optical fibers up to 60 m in length have been drawn, and several simple lenses have been designed, ground, and polished. Preliminary results on the ability to directly cast optical components of lead- indium phosphate glass are also discussed as well as the suitability of these glasses as a host medium for rare-earth ion lasers and amplifiers.
Glasses containing a post-thermally developed CuClBr microcrystalline phase were stretched under an applied stress at a temperature above the strain-point. The resulting glass was optically transparent and birefringent. The stretched glass was heated under reducing conditions to effect the reduction of the Cu-halide particles to Cu metal thereby rendering the glass polarizing. The polarizing behavior is compared to that of Ag/Ag-halide containing glasses which are made in the same manner. The polarizing behavior of the two glasses is very similar except for the wavelength region below 500 nm. The absence of a crossover of the parallel and perpendicular polarization transmittances in the Cu/Cu-halide glass suggests a visible polarizer application.
Exciton absorption bands near 400 nm indicate the precipitation of cuprous halides in certain alkali borosilicate glasses. The precise shape of the absorption can be altered by varying the ratio of bromide to chloride or by varying the heat treatment. The influence of the matrix glass composition on the strength of the exciton bands is discussed.
Barium gallogermanate glasses are a relatively new family of glasses with tremendous potential for both fiber and bulk optical applications. This ternary system has a broad region of glass forming ability, excellent stability with respect to crystallization, and transmission beyond 5 micrometers . This paper reports the effects of composition and processing on properties critical to both fiber and bulk optical applications of these glasses.
The optical properties of the CaO-Al2O3-B2O3 glasses are reported in this paper. The variation of refractive index, dispersion, ultra-violet absorption and density with composition is in agreement with the dielectric properties results previously published. Inflections in the physical property curves are discussed in terms of formation of the non- bridging oxygens. Infrared spectroscopy suggests the presence of the boroxol groups up to 40 mol% CaO. The tetraborate groups gradually diminish on increasing the CaO concentration higher than 25 mol%.
Sol-gel processes provide techniques to prepare materials which contain silicate and organic groups in a single amorphous phase. Such materials can possibly possess a resultant combination of beneficial physical and chemical properties from silicate glass and organic polymeric materials. Also, silica glasses containing organic components in their network can more readily dissolve organic dyes, and therefore be used in optical fibers to promote optical amplifier capabilities. The properties of such solid materials intimately relate to the structural arrangements in the materials. Infrared and Raman spectroscopy have been applied in this study to obtain valuable information for sol-gel condensates from the tetramethoxysilane (TMOS)/diethoxydimethylsilane (DEDMS)/methyltrimethoxysilane (MTMS) system. Compositions in this system can possess methyl-bonded silicon atoms in their structural networks in contrast to silica gels and glasses. The resulting differences that are noted in the distributions of the three-fold (Si-O)3 ring and the four-fold (Si-O)4 ring structures of these materials with respect to silica gels and glasses are discussed on the basis of observed infrared and Raman spectra. Also, structural changes occurring during the heat treatment of gels that were prepared from binary TMOS/DEDMS mixtures were also investigated using infrared spectroscopy.
Investigation results of the nonlinear interaction of short laser pulses with chalcogenide glasses are briefly described. The most characteristic peculiarities of the investigated nonlinear light transmission are discussed. A physical model, taking into account the light interaction with nonequilibrium phonons, is considered for the explanation of the experimental results. The results of the numerical calculations of the phenomenological equations are compared with the experimental data.
With several different glasses for nonlinear optical materials we first observed the far field multiple-ring fringes in them using a cw Ar+ laser as a light source at 514.5 nm and 488.0 nm, respectively. The central brightness of multiple-ring fringes could be controlled through changing incident power or the sample position near the focus. This phenomenon is considered as a result of spatial self-phase modulation caused from self-focusing. The thresholds of fringes and the thresholds of laser damage in three kinds of glasses are different from one another. Moreover, the far-field fringes of reflecting light were watched carefully. The light power limiter of optical density D equals log 1/T(lambda ) equals (infinity) can be constructed with the phenomenon.
The affects of iron on the structure, physical, and optical properties of several iron phosphate and sodium-iron phosphate glasses were investigated using x-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy, and infrared spectroscopy (IR). Archimedes method, differential scanning colorimeter and Able refractometer measurements were used to determine the glass density (d), transition temperature (Tg), and refractive index (n), respectively. XPS and Mossbauer spectra showed the presence of iron in both the Fe2+ and Fe3+(4- and 6-coordinated) states. With the increase of Fe2O3 content in the iron phosphate glasses and the increase of Na2O content in the sodium-iron phosphate glasses, the Fe2+/Fe ratio decreases and the Fe3+(4-coordinated)/Fe ratio increases. The infrared measurements showed that the increase in the Fe2O3 content or the Na2O content caused a change in coordination from FeO6 to FeO4. Finally, the relationship between the properties and the Fe2+Fe3+(4-coordination) ratio is discussed briefly.
Results on the development and characterization of new oxide and non-oxide glasses for integrated optics are reported. We have developed many special oxide glass compositions with low (1.49) and high (1.78) refractive indices including phosphate, silicate, and germanate glasses. Optical and physical-chemical properties of these glasses have been studied. The influence of two-, three-, and four-valence metal oxides on performance of ion-exchanged planar waveguides was investigated. Lastly, recent preliminary results on the optimization of non-oxide glasses for nonlinear applications are presented. Processing issues related to the production of low loss waveguides are described.