Questions Directed to Dr. N. S. Kapany - SPIE Session 1-2 Q. (R. Carroll Beaty) - In attempting to achieve high transmission for long fibers, how strong an effect does the cladding material transmission factor have? That is to say, should the cladding material have a very high transmission for the wavelengths one is interested in transmitting via the fiber?
A comparison is made between clad fibers and lens-like guides with parabolic index profiles, from several points of view: delay distortion, beam capacity per unit cross section, ability to negotiate bends, and deterioration of transmission due to imperfections. Parabolic index profile guides and single mode fibers with any profile (approximately rectangular, parabolic, etc.) are equally promising and attractive for long-distance optical trans-mission from several points of view, namely, capacity per unit cross section, delay distortion, and ability to negotiate bends. Nevertheless, their tolerance of imperfections is markedly different. Though insensitive to diameter changes, the multimode parabolic index profile guide is quite sensitive to systematic or random departure of refractive index profile from ideal. On the other hand, single mode guides are sensitive to random changes of both the index profile and the guide width. Both of them produce scattering loss.
A statistical analysis of degradation in a scanned image has been carried out by Beall. (Ref. 1) In the above analysis, the mean-squared value of the error function between the object and image was used as a measure of the degree of fidelity in the image, and numerical data have been published for several particular cases. A similar approach to image transfer in optical fiber bundles is presented. In this paper, the one-dimensional line-scan analysis proposed by Beall is extended to encompass a two-dimensional sampling process for evaluating the image transfer in a fiber bundle. Interesting results occur when the evaluation technique is extended to the comparison of the imaging properties of a static bundle and a bundle which is scanned dynamically. (Ref. 2) This analysis indicated that there is a significant difference in resolution between the static case and the dynamically-scanned case. The difference is found to be largely determined by the fiber configuration within the bundle. Experimental results in the case of the static bundle will be presented.
In the last decade low light level image intensifier systems have come into widespread use not only in the military but also in such fields as astronomy, medicine, and spectrometry. Many companies are now producing these high gain tubes, and each tube has slightly different design parameters. Figure 1 shows a basic schematic of the image intensifier tube used in this study.
Applications of fiber optics are increasing in scope and importance in medical, commercial, and military fields. One example of this is the application of fiber optics to low light level image intensifier systems in the form of faceplates and flexible fiber optic ropes. Some uses of fiber optic components in image intensifier systems are illustrated in Figure 1. Faceplates are employed in three-stage image intensifier tubes as field flatteners for the electron optics, as windows of the tubes, as optical coupling devices, and as heat sinks to protect the delicate photocathodes and phosphors. A flexible fiber optic tope which is directly coupled to an image intensifier tube can be used in a remote viewing station. A fiber optic rope of up to twelve feet can be used in this application.
Because of increased interest in new fiber optic illumination applications within the past few years, product requirements have dictated numerous environmental and mechanical testing techniques to be developed. The purpose of this paper is to describe these parameters and the methods used to define the product capabilities of the incoherent fiber optic bundle. Since the sole purpose of a flexible bundle is to transmit effective light, this basic criteria is utilized to measure the capability of the combined fiber bundle and jacketing in hostile environments including extreme temperature and humidity, mechanical stress, as well as various chemical fluids. The importance of these measurements for customer and manufacturer's product specifications has led to the development of several testing techniques and equipment believed to be unique in this field. Environmental life requirements must be realistically defined according to particular application needs, therefore these tests and variations are presented to be used as a general format for specifications and standards in the industry. In discussing this subject, we shall first consider different applications that required this area of development, the system of transmission measurement utilized, and finally the various environmental tests themselves.
In recent years technological forecasting has been a subject of great interest in many companies. One need only count the number of books and articles published and the number of seminars sponsored by various groups to realize that many people have become extremely interested in the techniques used to project technological trends. Some of the methods of technological forecasting we are using at Texas Instruments and our experience with the effectiveness of these methods are discussed in this paper.
Fiber Optics has been successfully employed to perform. the functions of image dissection and scanning in Facsimile Transmission. Two opera tional models have been developed and constructed on this program to incor porate the concept (Figure 1). One was designed to scan copy. 8-1/2 inches wide, the other, 18-5/8 inches wide. Both instruments possess the unique capability of continuously scanning copy of any length and generating a single which is suitable for a conventional GXC-5 Facsimile Recorder. Both instruments are open-throated so that copy wider than the scan area can be fed, though them.
One of the major technical contributions to the military operations in Southeast Asia has been the development of night vision instrumentation for use by our armed forces in night warfare. The basic electro-optical device which has made these extraordinary instruments possible is the three-stage image intensifier utilizing fiber optic face-plates for coupling the component stages together. The plates also serve to correct the field curvature of the electron optics in the separate tube modules. The performance of the image intensifier is in large measure governed by the properties of these fiber optic faceplates. This paper will include a description of the optical and physical properties of the fiber optic plates and the methods for testing and evaluation. Some of the performance characteristics of the intensifier tubes and the night vision instruments will be presented and the possibility of combining these instruments with flexible fiber optic relays will also be discussed.
The fiber optics bundle to be discussed in this paper is used on the INFANT System. The INFANT, which stands for Iroquois Night Fighter And Night Tracker, is a system built under the direction of the U.S. Army Electronics Command's Night Vision Labora-tories in Fort Belvoir, Virginia. It is a system on a helicopter (see Figure 1) enabling pilots and co-pilots to "see" under low-light conditions.
The TRASER system is now capable of delivering the design-goal specifications of revenue-accuracy current measurements under any ambient temperature condi-tions from -70 F to + 170 F and from line-charging through full-fault current levels, with other interest-ing advantages. Twin channels of identical measurement, with milli-second throwover between channels, insure service availability at all times. In addition to a power supply activated by potential of the energized line, separate power sources operated by line current are provided for each channel. Full operation is accomplished within two milliseconds after closing into a short circuit, as suringprotective relay operating during the first current loop if desired. Solid-state relay logic is highly compatible with output of solid-state 'Decoders' of the TRASER system, thus promising simplified static relay designs without input-current transformers and with more freedom from high-energy stray transients which interfere with present relay designs. EHV provides a chance for electronics to reduce costs and weights, eliminate oil, and greatly improve the protective signal accuracy.
This paper will discuss the use of fiber optic faceplates to solve the problem which arises when visual displays such as cathode ray tubes and rear projection screens are viewed under high ambient light conditions.
Conventional gaging methods have been used for all sorts of measurements for many years and have been completely satisfactory in most applications. However, there is a growing number of cases where special gaging methods must be used for one reason or another. These special methods include optics, magnetics, pneumatics, hydraulics and several others. In some cases these methods have a direct mechanical readout while in others they convert the measurement to a electrical signal and condition it to provide additional information about the measurement. The gaging method presented in this paper uses fiber optic light lines to provide information about the measurement.
A piece of glass fiber or rod with a radially parabolic vaiation of refractive index, named SELFOC(.4), has been prepared by exchanging thallium ions for potassium ions. As a light guide for optical communication use, SELFOC(.4)fiber has many advantages over reported ones from the view-point of flexibility, distortion of optical pulse, economical production, etc. The mode pattern of a laser beam was scarcely deformed after passing through a SELFOC()fiber, curved in a radius of curvature 10 cm, of one meter in length and 0.25 mm in diameter. SELFOC(g)fiber was used as connectors in an experimental optical com-munication system. 11-0 Attenuation in SELFOC '-- fiber has been decreased to a value 80 - 250 dB/km at 0.63A and will be still improved. Then, long SELFOCQV cables may be utilized for a long distance transmission line. A cylindrical rod of SELFOC() has the same optical performance as that of a single or sequence of optical lens. Although its resolving power under white light illumination is still poor, a short SELFOC () lens and a SELFOCTO fiber of 10 cm in length can be applied to medical endoscopes. Further, a conical 814.1,110C(,) was used to guide a 1aser beam on the small surface of an avalanche photo-diode. SELFOC( will be widely utilized in optical communication, optic, ,1 data processing, optical instruments and opto-electronic devices.
Compatible core and clad glasses transmitting peak uv radiation at 320nm have been developed for fiber optic applications. Research was conducted to formulate compositions having high transmission in the near- and medium-ultraviolet region and capable of being fabricated into fiber optic faceplates for ultra-high resolution cathode ray tubes. The glass forming the radiation transmitting core is a lanthanum-zinc-borate composition having an index of refraction (nd) of 1.71 and peak internal transmission of over 80% at 320nm for 1/4-in. thick-ness. A matching potassium-alumino-boro-silicate cladding glass having a low index of refraction (nd = 1.47) was also developed. Both glasses possessed compatible coefficients of thermal expansion and softening points to produce faceplates having fiber centers approaching five microns in spacing. A theoretical numerical aperture in excess of 0.8 is achieved with these glasses.
Testing for optical transmission of a multiple channel fiber optic block at a number of different geographic locations presents serious problems in correlating the results. In one of these situations, there was a requirement to test the light transmission of a single-input, 13-channel-output fiber optic block. Each output channel was to be tested twice: once within . 010 inches from the output surface and again at .375 inches from the exit surface. In addition, the test cycle was to be held to six minutes (10/hour). The testing was to take place at two vendor locations and at International Business Machines Corporation's Systems Manufacturing Division plant at Poughkeepsie, New York. The test results had to be accurate to 10% from tester to tester and repeatable within 5%. Specifications were met by using a single photovoltaic cell to measure the input light to the block and to take both of the channel output measurements. The photocell responses were recorded on a strip chart recorder. By adjusting the recorder to read the photocell response to the input light as full scale, and by using recorder paper graduated from 0 to 100, the optic block outputs were displayed directly in percent transmission on a hard copy output. In order to shorten the test cycle and to reduce the influence of the operator on the results, the equipment was automated. Thus the photocell was automatically indexed across the output face of the fiber optic block. To insure uniformity between the pieces of test equipment, the mechanical components of the test fixture and indexing mechanism were held to precise tolerances. The results were a maximum tester to tester correlation error of 9.4%, a repeatability error of less than 5% on each tester, and a two-minute test cycle per unit.
The theory of MTF measurements on fiber optics is analyzed and demon strated in a practical application. A production unit of a new MTF meter, made for measurements of fiber optics only, is exhibited for the first time, showing how an unskilled operator can make reliable and repeatable MTF graphs of fiber optics on a production scale. This is done by scanning the entire surface of a flexible bundle, and by measuring small surface elements in various directions, thus obtaining information as to the transmission efficiency of the entire bundle under test.