Power transmitting capabilities of polycrystalline (PC) KRS-5 fibers have remarkably increased since the first report by researchers at Hughes Research Laboratories. Maximally transmitted power of CW CO2 laser beam through PC KRS-5 fiber has reached up to about 100W. The power density at the fiber input end is 36 KW/cm2 and remarkable damage is not observed. Mechanical properties of PC KRS-5 fiber is superior to any other PC fiber, therefore PC KRS-5 fiber is a hopeful waveguide for the practical use of CO2 laser power transmission. And also it is applicable for IR sensor systems in a short range. When the power transmission capabilities of PC KRS-5 fiber will be attained up to several hundreds watt, it will be widely used in the field of the CO2 laser machining.
μPlastic clad, easy to handle fibers have been made starting from high softening point As15Ge30Se55 glass compositions. The 10.6 μm typical losses are within the 10-16 dB/m range. Such fibers are useful for applications which require little power transmission.
A variety of new multicomponent glasses based on the fluorides of heavy metals has been developed. The ZrF4 based glasses are suitable for fiber fabrication operating in the mid IR region with optical window in the 0.25 to 6-7μ range. A new family of glasses based on thorium and rare earth fluoride with a large optical window 0.3 - 9μ is presented. A critical comparison of the advantages as well as the problems associated with these new materials and fiber fabrication techniques is given.
Heavy-metal fluoride glasses offer substantial promise for mid-infrared and multispectral optical components such as laser windows, IR-domes, laser hosts and infrared fiber optics. Potential uses for IR-transmitting fibers, for example, include nuclear radiation-resistant links, ultra-long repeaterless communications links, remoting of IR sensor focal planes, and medical applications such as surgery and cauterization. The fluoride glasses developed to date possess continuous high transparency from the near-UV to the mid-IR, as well as low refractive index (≈1.5) and low material dispersion. In this paper, we update some of our previous comparative studies of fluorozirconate and fluorohafnate glasses. Recent results concerning the visible to infrared refractive index and material dispersion of fluoride glasses are also presented, along with preliminary optical data on new fluoride compositions which do not contain zirconium or hafnium fluoride.
This paper reviews some recent developments in the field of infra-red transmitting glasses. A variety of heavy metal fluoride glasses are currently being investigated with a view to fabricating high performance optical fibre systems. In order to assess the bandwidth potential of these fibres, a computer model of fibre dispersion has been developed, in which accurate calculations of the materials, waveguide, profile and total dispersions are made over a broad wavelength range. Predictions are also made of the range of choice in Δn and core diameter available to give zero total dispersion at particular wavelengths in practical fibres made with these materials.
Pure and doped ZnCl2 glass has been fabricated for possible use as a 10.6 µm fiber material. The glass shows good optical transparency at 10 μm, but the hygroscopic nature of ZnC12 makes a practical fiber from this material a difficult challenge.
The previously published calculations for λo, the wavelength where the material dispersion parameter is zero, have been extended in two directions. First, the calculation of mixed glass compositions shows that the intermediate values are not linear with composition but show significant and non-symmetrical deviations. Second, it has now been possible to calculate the material dispersion slope, that is (λ/c)(d3n/dλ3), at λo. Large and important variations are found, both between the oxide and halide systems, as well as within them.
Laser pulse compression by the process of stimulated Brillouin scattering in a tapered glass fiber is discussed. A 20 mJ pulse from a Nd:YAG laser is compressed from 20 nsec to 3 nec in a fiber 7 feet long.
Multiple-order stimulated Raman scattering in CBrC13 filled hollow-core silica fibers has been used to generate radiation between 1.3 and 2.3µm using peak powers of 11 kW from a 1.06 µm Nd:YAG laser. This radiation could be useful for experiments with infrared fibers. Extension of this technique to 6 μm wavelength and beyond is predicted.
There is an interest in the study of nonlinear propagation along distributed electrical transmission lines. This is because these lines serve as useful models for nonlinear wave motion with dispersion in many interesting physical systems. Recently nonlinear wave motion with dispersion has been shown to produce solitons in optical fibers. To design infrared fibers with exotic properties, one often needs exotic materials. It is costly in time and money to try to produce these by strictly trial and error methods. Thus the usefulness of models becomes clear. Of course the electrical distributed lines themselves have an obvious direct application to integrated circuit parametric amplifiers, harmonic generators and shock wave generators for pulse shaping. They also have applications to secret or secure coding systems using two soliton interactions and to data transmission using solitons.
The status of hollow waveguides with metallic walls for guidance of infrared radiation is reviewed. Emphasis is placed on rectangular and circular cross-sections. It is shown that flexibility can be obtained with the rectangular cross-section, but not with the circular cross-section.
The coupled-modes formalism is used to study the losses of bent hollow IR waveguides. The circular metallic waveguide is studied for large bending radii. The slab waveguide is studied in detail in the mild-bending, whispering-gallery and transition regions; and the results are compared with those obtained by other methods.
Germanate glass optical fiber has been drawn from the preform glass rod synthesized by vapor phase reaction. The attenuation loss as low as 13 dB/km at 1.1 an wavelength has been obtained for the silicone clad fiber, and 134 dB/km at 2.38 μm has been obtained for the fiber with thin germanate glass cladding. If the germanate glass fiber which is designed ideally and which has the reduced water content as low as 1 ppb that has been already achieved for the high silica fiber fabricated by the vaporphase axial deposition (VAD) method is prepared, the attenuation loss less than 0.1 dB/km is supposed to be achievable in a practical sense around 2.2-2.4 µm wavelength.
Using the technique of rolling, KCl single crystals were reduced to round polycrystalline fibers with surfaces which duplicate the surface of the rolls. Crystals were rolled at 300°C to 1.5 mm diameter for a reduction in area of 90%. Due to the imperfections in the cast iron rolls, the fiber surface that was duplicated was of only fair quality. This led to the design of improved rolls with polished surfaces.
Chalcogenide glasses containing the elements: As, Si, Ge, Sb, and Se or Te have been prepared. A new technique of preparing the raw material and subsequently drawing fibers has been developed in order to avoid the forming of oxygen compounds. The fibers have been drawn from oxygen free raw material inside an Ar atmosphere glove box. The fibers drawn to date have a diameter of 50-500 μm and length of several meters. Preliminary attenuation measurements indicate that the attenuation is better than 0.1 dB/cm. By improving the preparation of materials and the drawing technique, we expect to reach a better transmission.
Transmittance measurements were made on short lengths of arsenic trisulfide, arsenic tri-selenide, and KRS-5 fibers at the 10.6- μm wavelength. Significant absorption was noted in all of the fibers; however, improvements in transmittance can be postulated.
A state-of-the-art review of Pb-salt diode lasers is presented. Operational data on typical devices are shown, and the opto-electronic properties of the ternary Pb-salt crystal systems Pb1-xCdxS, PbS1-xSex, Pb1-xSnxSe, Pb1-xSnxTe, PbTe1-xSex, Pb1-xGexTe and Pb1-xGexS are discussed. Recent data on device reliability as well as current areas of R & D are reviewed. Areas of application include infrared spectroscopy, industrial process monitoring, isotope retio studies and infrared fiber studies. System configurations designed specifically for the assessment of infrared fiber losses and dispersion characteristics are discussed.
The expansion of electro optic systems and sensors in military helicopter avionics systems has resulted in severe competition for existing space. In particular the forward looking hemispherical quadrant is the essential location of choice for all such optical systems. Outboard mounting is severly limited by shadowing effects and the aircraft undercarriage is similarly limited by the nose low aspect in normal helicopter flight. Development of a fiber optic capable of transmitting 10.6u in a coherent single mode with an acceptable transmission loss promises to minimize the physical space required in the nose of aircraft and thereby provide extended functional use of the clear field of view. The requirements for such a fiber optic system are presented and a projected application is described.
An infrared (IR) fiber receiver has been developed for use in detecting CO2 laser pulses. In the first phase of the development we measured the optical and mechanical properties of our KRS-5 IR fibers between -40 and 40°C. In the second phase we built a simple demonstration device consisting of a 10-m-length of fiber and a HgCdTe detector.
Infrared transmitting silver halide fibers 0.3 - 1 mm diameter were fabricated by extrusion, and were found to have losses of about 6 dB/m, at λ = 10.6 µm. Infrared heterodyne experiments have been carried out using these fibers. Two stabilized CO2 lasers, of frequencies ωl and ω2, were used. The two laser beams were coupled into a single infrared fiber, using a Y coupler, with no other optics. Both beams were transmitted through this fiber to a fast IR detector. A heterodyne signal at a beat frequency ω1 - ω2 was obtained from the detector.
Recent advances in infrared (IR) optical fibers have made possible such applications as remote temperature sensing and reformatting of an IR source or focal plane. In this article it is shown that extruded T1BrI (KRS-5) fibers have high transmittance over a large portion of the IR wavelength region which allows the source irradiance to be measured in several spectral bands as required for accurate temperature determination. Some limitations of their use in reformatting an IR source are discussed.
DeShazer: During this meeting, IR fibers have been viewed from two aspects - materials and applications. We have had an interesting mix of chemists and physicists, engineers and opticians attending the meeting because of the varied expertise needed to address these questions. While silica glasses are exclusively used for current fiber systems operating at wavelengths less than 2 μm, the material choice has not yet been made for IR fibers at the longer wavelengths. Papers were presented at this meeting on the possible choices, which can be grouped into four general headings, as we have done in the table: hollow waveguides, glasses, polycrystals, and crystals. For the 2 to 5 μm spectrum, the choice appears to be fluoride glass, although the exact glass composition needs to be determined for good fiber drawing properties. For wavelengths longer than 5 μm, however, there is no unanimous choice. Polycrystalline KRS-5 fiber has been the current selection for CO2 laser fiber systems at 10.6 μm, but it exhibits many drawbacks such as large scattering loss, short shelf-life and possible photosensitivity. Chalcogenide glasses, such as arsenic triselenide, have high absorption losses at 10.6 μm, in spite of much past effort to improve the material. Is there hope in producing a highly transparent glass at 10.6 μm? If not chalcogenide glasses, maybe chloride glasses will succeed for fibers at 10 μm. Single-crystal fibers promise low loss, but is it realistic to talk about making a single crystal fiber 10 km long?