Downloaded from http://www.everyspec.com m MIL-STD-2 196(SH) 12 January 1989 MILITARY STANDARD GLOSSARY, FIBER OPTICS o:’.$.f$gziw, AMSC N/A FSC 60GP DISTRIBUTION STATEMENT A. Approved forpublic release; distribution is unlimited. Downloaded from http://www.everyspec.com MIL-STD-2 196(SH) 12 January 1989 FOREWORD 1. This military standard isapproved foruseby the~partmentof the Navy and is available fol use by all Departments and Agencies of the Department of Defense. 2. Every effort was made toensure this glossary inconsistent with published standards. Several glossaries in fiber optics have been prepared bystandards organimtions. In 1982 the National Institute of Standards and Technology, formerly the National Bureau of Standards, published PB82-166257, 0ptical Waveguide Commimications Glossary. Two years later, The’Instituteof Electrical and Electronics Engineers approved IEEE Standard 8I2-l984, Definitions of Terms Relating to Fiber Optics, forthemost part bmedonthe contents of PB82-166257. In 1986, FED- STD- 1037, Glossary of Telecommunication Terms, was issued by the General Services Ad- ministration. The U.S. Army Information Systems Engineering Support Activity was the preparing activity and the National Communications System wasthe assigned agency. Withan orientation toward telecommunications, about 10 percent of its content is devoted to fiberoptic. Shortly thereafter: the Electronic Industries Association published EIA-440A, Fiber Optic Terminology, agamconsisting primarily of PB82-166257. A glossary, IEC-Draft 731-OpticaI Communication, is being prepared by the International Electrotechnical Commission. Different areas of fiber optics were emphasized by each. None covered fiber optics science and technology in its entirety. Some emphasized theory while others covered technology or applications. Even if all of them were to be merged into one, fiber optics science and technology still would not be adequately covered, particularly in theareas of, electromagnetic theory, fiberoptic sensors, light sources, photodetectors, and other components used in fiberoptic system$ and several application areaa, such as telemetry, illumination, imaging,’ security systems, endoscopy, networking, and control systems. Format, deprecation, indexing, and cross referencing were handled differently by each. o 3. Many fiber optics terms occurring unmilitary standards, specifications, test methods, test procedures, handbooks, and manuals have not been covered by the published glossaries. This comprehensive standard attempts to bring together under one cover the advantages and benefits of all the published glossaries. The primary purpose of this standard is to standardize fiberoptic terminology for improved communication. Information inadequately cover the theory, prin- ciples, and technology of fiberoptic has been added tn accomplish the secondary purpose of this standard, namely to provide information in the, acience and technology of fiber optics. 4. Beneficial comments (recommendations, additions, deletions) andany pertinent data which may be of use in improving this document should be addressed to Commander, Naval Sea Systems Command, SEA 55 Z3, Department of ~he Navy, Washington, D. C.20362-5101, by using theself-addressed Standardization improvement Proposal (DD Form 1426) appearing at the end of this document or by letter. 1 ii Downloaded from http://www.everyspec.com MIL-STD-2 196(SH) 12 January 1989 CONTENTS PARAGRAPH ~ 1. SCOPE AND PURPOSE . 1 1.1 Scope . 1 1.2 Purpose . 1 2. APPLICABLE DOCUMENTS . 2 3. DEFINITIONS . 3 4. GENERAL REQUIREMENTS . ...235 5. DETAILED REQUIREMENTS . ...235 6. NOTES . ...235 6.1 Intended use . ...235 6.2 Organization . ...235 6.3 Subject term (key word) listing . ...235 . .. 0 111 Downloaded from http://www.everyspec.com MIL-STD-2 196(SH) 12 January 1989 1. SCOPE 1.1 -. This standard provides terms anddefinitions pertaining to fiber optics science and technology. 1.2 Pumose. Tbe purpose of this standard istoprovide andstandardize comprehensive and authoritative definitions of terms used in fiberoptic military standards, specifications, hand- books, test methods, test procedures, andother fiber optics documenty standardize the use of fiber optics terminology in the Department of Defensq and provide information on fundamental theory, principles, and concepts in fiberoptic science and technology. This standard covers fiber optics terminology used in describing, designing, fabricating, packaging, shipping, testing, evaluating, installing, operating, and maintaining fiberoptic systems and components. Downloaded from http://www.everyspec.com MIL-STD-2 196(SH) o 12 January 1989 3. DEFINITIONS A aberration. See chromatic aberration. absolute luminance threshold. The lowest limit of luminance necessary for visual perception to occur in a person with normal or average vision. absolute luminosity curve. The plot of spectral luminous efficiency versus optical wavelength, absorptance. See spectral absorptance, absorption. In the transmission of signals, such as electrical, electromagnetic, optical, and acoustic signals, the conversion of the transmitted energy into another form of energy, such as heat. Signal attenuation is notonly a consequence of absorption, but also of other phenomenon, such as reflection, refraction, scattering, diffusion, and spatial spreading. In the transmission of electromagnetic waves, such as Iightwaves, absorption includes the transference of some or all of theenergy contained in the wave tothesubstance or medium in which it ispropagating or upon which it is incident. Absorbed energy from a transmitted or incident lightwave is usually converted into heat witha resultant attenuation of thepower orenergy in the wave. In optical fibers, intrinsic absorption is caused by parts of the ultraviolet and infrared absorption bands. Extrinsic absorption is caused by impurities, such as bydroxyl, transition metal, and chlorine ion> silicon, sodium, boron, calcium, and germanium oxides; trapped water molecules, and defects caused by thermal and nuclear radiation exposure. Synonymous with material absorption. See band-edge absorption; hydroxyl ionabsorption; selective absorption. o absorption coefficient. The coefficient in the exponent of the absorption equation that expresses Bouger’s law, namely the bin the equation F= Foeax where F is the electromagnetic (light) field strength at the point x and FOis the initial value of field strength at x = O. absorption index. The ratio of the electromagnetic radiation absorption constant to the refractive index given by the relation K’ = KA/4mr where K is the absorption coefficient, A is the wavelength in vacuum, and n is the refractive index of the absorptive material. absorption loss. When an electromagnetic wave propagates in a propagation medium, the loss of wave energy caused. by intrinsic absorption, that is, by material absorption, and by impurities consisting primarily of metal and hydroxyl ions in the medium. Absorption losses may also be caused indirectly when light scattered by atomic defects is also absorbed. acceptance angle. In fiberoptic, half tbe vertex angle of that cone within which optical power may be coupled into bound modes of an optical waveguide. For an optical fiber, it is the maximum angle, measured from the longitudinal axis or centerline of the fiber to an incident ray, within which the ray will be accepted for transmission along the fiber, that is, total (internal) reflection of the incident ray will occur for long distances within tbe fiber core. If theaccep- tanceangle is exceeded, optical power in the incident ray will decoupled into leaky modes or o 3 Downloaded from http://www.everyspec.com MIL-STD-2 196(SH) 12 January 1989 rays, or lost by scattering, diffusion, or absorption in the cladding. For a cladded fiber in air, the o sine of the acceptance angle is given by the square root of tbe difference of the squares of the refractive indices of the fiber core and the cladding, that is, by the relation sinA = (n,z - nz2)L/2 where A is the acceptance angle and n,andnz are the refractive indices of the core and cladding respectively. If the refractive index is a function of distance from the center of the core, then the acceptance angle at a given distance from the center is given by the relation sinAr=(nr2- n22)’/2 where A,is the acceptance angle at a point on the entrance face of the fiber at a distance rfrom thecenter andnzis the minimum refractive index of the cladding. SinAandsinAr are the numerical apertures. Acceptance angles and numerical apertures for optical fibers are usually given forthe center of theendfaceof the fiber, that is, where the refractive index, and hence the NA, is the highest. Power maybe coupled into leaky modes atangles exceeding the acceptance angle; that is, at internal incidence angles less than the critical angle. See maximum acceptance angle. acceptance cone. In fiberoptic, that cone within which optical power may be coupled into the bound modes of an optical waveguide. The acceptance cone is derived by rotating the acceptance angle, that is, the maximum angle within which Iigbt will be coupled into abound mode, about the fiber axis. The acceptance cone foraround optical fiber is a solid angle whose included apex angle is twice the acceptance angle. Rays of light that are within the acceptance cone can be coupled into the end of an optical fiber and betotally internally reflected as it propagates along the core. Typically, anacceptance cone apex @gle is40 degrees. For noncircular waveguides,