Showing papers on "Photonic-crystal fiber published in 1989"

Electric current sensors employing spun highly birefringent optical fibers

Abstract: The theory of highly elliptically birefringent fibers fabricated by spinning a linearly birefringent fiber during the draw is described. These fibers are particularly interesting for application as Faraday-effect fiber current monitors, since, in contrast to conventional fibers, they can be wound in small multiturn coils while retaining their sensitivity. The fiber and its application in three optical schemes are modeled using Jone calculus and are also experimentally investigated. A simple optical configuration is proposed, combining the elliptically birefringent fiber and a broad-spectrum light source. An accurate, compact, and robust current monitor is obtained. The sensor is characterized by a measurement repeatability of +or-0.5%, a temperature drift of 0.05%/ degrees C and a sensitivity of 1 mA RMS/Hz/sup 1/2/. Further, the performance of this sensor with optimized fiber length for a given measurement bandwidth is predicted. >

Efficient coupling of a semiconductor laser to an optical fiber by means of a tapered waveguide on silicon

Abstract: A Si3N4 core waveguide, matched to a laser mode, is adiabatically tapered into a SiO2:P core waveguide, matched to a fiber mode. When used to couple the light from a semiconductor laser into an optical fiber, a loss of 3.1 dB is obtained, compared to a loss of 4.5 dB obtained with a lensed fiber.

Polarization-Maintaining optical fiber for coupler fabrication

Abstract: Polarization-maintaining coupler is made by a biconically-tapered-fused process from two short lengths of an optical fiber, each having a small, oval stress-applying region that substantially contacts the core. The area of the stress-applying region of the optical fiber is less than 10 percent, preferably less than 2 percent, that of the optical fiber and preferably is contiguous with the core. Couplers of highest quality are made from quartz glass fibers having a birefringence between 1 and 3 x 10⁻⁴. It is believed that the principal axes of the oval stress-applying regions of those couplers of highest quality have been collinear or parallel. To permit a coupler to be handled, it can be mounted on a quartz glass substrate with the coupler suspended in air and then potted in a cured elastomer.

An apparatus for optically connecting a single-mode optical fiber to a multi-mode optical fiber

Abstract: An apparatus connects a single-mode optical fiber (2) in a transmitting side to a multi-mode optical fiber (4) in a receiving side without a deterioration of baseband transmission characteristics. The apparatus optically connects the single-mode fiber (2) to the multi-mode fiber (4) with an optical axes displacement therebetween, so that an optical signal to a multi-mode optical fiber (4) from a single mode optical fiber (2) is incident in a steady state mode including not only lower mode, but higher mode. In one embodiment, the optical axes displacement is achieved by axial displacement (d) between the single-mode fiber (2) and multimode fiber (4). In another embodiment, the optical axes displacement is achieved by an angle displacement between the single-mode fiber and multi-mode fiber.

Interferometric Measurements Of Strain Concentrations Induced By An Optical Fiber Embedded In A Fiber Reinforced Composite

Abstract: An optical fiber embedded between layers of structural fibers in a composite deforms together with a composite structure and modulates light passing through the optical fiber. This effect has been implemented in the form of so-called "smart skins". By analyzing the changes of light transmitted by an embedded fiber dangerous strain levels in the structure as well as failure of the material can be detected. A system of such optical sensors embedded in a structure could act as the nervous system of this structure. Several important questions must be answered before the concept of embedding optical fibers in a composite structure can be commercialized. How does the presence of optical fibers in a composite affect its mechanical performance? How does an embedded fiber affect the strain distribution in its vicinity? What is the relationship between the strain distribution and the layup of the surrounding composite? What can be done to prevent the negative effects of the introduction of an extra fiber into a structure? This work addresses some of these questions. Preliminary results of experimental tests performed on representative composite specimens are presented. A discussion of the results and plans for the future are provided.

Optoelectronic technology and lightwave communications systems

Abstract: 1 Optical Fiber Waveguides.- 1. Transmission Properties of Optical Fibers.- 2. Measurement and Characterization of Optical Fibers.- 3. Advanced Single-Mode Fiber Designs for Lightwave Systems Applications.- 4. Polarization-Maintaining Optical Fibers.- 5. Transmission Limitations in Fibers due to Nonlinear Optical Effects.- 2 Fiber-Joining Technology and Passive Optical Components.- 6. Optical Fiber Connectors, Splices, and Jointing Technology.- 7. Passive Components for Optical Coupling and WDM Applications.- 3 Semiconductor Laser Sources and Photodetectors.- 8. Basic Physics of Semiconductor Lasers.- 9. Fabrication and Characterization of Semiconductor Lasers.- 10. Transverse Mode Control in Semiconductor Lasers.- 11. Longitudinal Mode Control in Laser Diodes.- 12. Modulation Properties of Semiconductor Lasers.- 13. High-Power Semiconductor Lasers.- 14. Photodetectors for Long-Wavelength Lightwave Systems.- 4 Optical Transmitters and Receivers.- 15. Semiconductor Laser Transmitters.- 16. Optical Receivers.- 5 Applications of Optoelectronics in Lightwave Systems.- 17. Optical Communications: Single-Mode Optical Fiber Transmission Systems.- 18. Optical Fiber Communication Systems: Local Area Networks.- 19. Future Applications of Optical Fiber Networks.- 20. Free-Space Optical Communication Systems.- 21. Optical Fiber Sensor Technology.- 22. Optoelectronic Information Processing: Laser Bar Code and Laser Printer Systems.- 6 Future Optoelectronic Technology and Transmission Systems.- 23. Optoelectronic Integrated Circuits.- 24. Coherent Optical Fiber Communication Systems-The Promise for the Future.- 7 Impacts on the Information Society.- 25. The Impact of Optoelectronics Technology on the Information Society.

Stress-induced birefringence fibers designed for single-polarization single-mode operation

Abstract: By a simple numerical method, it is shown that a stress-induced birefringence fiber can be operated as a single-polarized single-mode fiber if absorption loss is introduced in the stress-applying regions and the refractive index of the regions is raised to a level between the effective indices of the two fundamental polarization modes. Numerical results also show that the characteristics of this fiber are sensitive to the refractive index and the location of the stress-applying regions, but rather insensitive to the size of these regions. >

Optical fiber transmission path with dispersion compensation

Abstract: An optical fiber transmission path wherein total dispersion of the system is compensated by use of fibers composed of glasses with total dispersion of opposite signs at the operating wavelength for the system. With silica-based fibers, CdF 2 --LiF--AlF 3 --PbF 2 --KF--YF 3 fluoride glass-based fibers may be used for a system with 1.55 μm operating wavelength.

Observation of ultrafast nonlinear polarization switching induced by polarization instability in a birefringent fiber rocking filter

Abstract: Ultrafast all-optical switching between two orthogonal linear polarizations in a periodically twisted fiber filter is discussed. The dependence of the switching characteristics on the input power and operating wavelength is considered. >

Optical fiber chemical sensors utilizing dye‐doped silicone polymer claddings

Abstract: Transparent dimethyl siloxane network polymers with refractive indices near 1.40 may be applied to fused silica fibers (n = 1.458) as they are drawn to produce plastic-clad silica (PCS) optical fibers. The evanescent tail of the light energy propagating in the core of such fibers extends into the silicone cladding, where it interacts with chemical species present in the polymer. If the silicone is doped with a dye, the absorption spectrum or fluorescence spectrum of the dye is reflected in the transmission spectrum of the fiber. Further, if the dye changes its absorption spectrum or fluorescence spectrum as a result of diffusion of a chemical species into the silicone, the change is detectable in the fiber output. The polymer material properties which determine the performance of these sensors are described, along with examples of sensors for ammonia and oxygen which utilize either color changing or fluorescent dyes.

Method for manufacturing a fiber type coupler

Abstract: A method for manufacturing a fiber type coupler of the present invention by fusing and elongating a plurality of optical fibers is characterized in that a multi-wire optical fiber wire is used as the plurality of optical fibers.

Fiber optic array

Abstract: A fiber optic array is disclosed for use in an optical scanning device. The array (10) includes a substrate (16) and a plurality of optical fibers (12) arranged on the substrate (16) to form a linear array of the fibers. Each of the fibers (12) is received in grooves (28a-28g) in the substrate (16) to precisely space the fibers (12) relative to each other. Each fiber (12) is adapted to receive light from a source (22) such as a laser diode. In order to increase the packing density of the fibers (12) in the array (10), the fibers (12) are closely spaced relative to each other on the substrate (16). The fibers (12) are arranged in aligned sets of grooves (28a-28g) which are spaced apart by planar areas (29a-29f) on the substrate (16), and the pitch of the grooves (28a-28g) in successive sets decreases as the fibers (12) approach an output end (17) of the array to draw the fibers (12) closer together at this end.

Metallic bond for mounting of optical fibers to integrated optical chips

Abstract: A method for pigtailing an optical fiber (18) to a lithium niobate integrated optical device (I/O chip) (12) is shown and described wherein the bonding between the I/O chip and the optical fiber is a metallic bond. The lithium niobate may be attached to a metallic substrate (14) which is welded to a metallic fiber optic carrier (16) which is in turn welded to a metallized optical fiber. The fiber optic carrier may also be made of non-metallic materials which are given a metallic coating prior to attachment to the I/O chip by means of a metallic bond such as welding.

A new single-polarization optical fiber

Abstract: In the single-polarization optical fiber, two isolated stress-applying parts contribute to radiate one of the two orthogonal polarization modes due to the asymmetrical geometric-index effect in addition to a stress-induced birefringence effect without bending the fiber. The loss spectra for x- and y-polarizations and the length dependence of the crosstalk show that the present fiber exhibits single-polarization characteristics. >

Optical Fiber Coupling Approaches For Multi-Channel Laser And Detector Arrays

Abstract: Two fiber-optic coupling approaches are described for providing accurate and simultaneous alignment between four multimode fibers and a four-channel GaAs laser and detector array. The fiber-detector array coupling approach provides less than 0.2 dB loss with better than -20 dB optical crosstalk between adjacent channels. The fiber-laser array coupling approach provides -3 dB coupling loss for each of four fiber-laser channels.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laser-to-fiber coupling via optical fiber up-tapers

Abstract: A method for coupling single-mode fiber to laser diodes with high efficiency and greatly reduced alignment sensitivities is discussed. It consists of a spherical ruby lens and a single-mode optical fiber up-taper. Using a double-channel planar buried heterostructure (DCPBH) laser, more than 60% of the light from the lens is coupled into a single-mode fiber via the taper. The lateral and axial tolerances of the lens-taper arrangement are reduced by factors of 20 and 1000 times, respectively, compared with laser coupling to a lensed single-mode fiber. These relaxed alignment tolerances have the potential to allow the taper to interface with a hermetically-sealed laser-lens package via a window and a connector on the package exterior. >

Optical Characteristics Of Fiber Optic Evanescent Wave Sensors

Abstract: Experimental results are reported for an unclad multimode optical fiber whose lateral surface is immersed in dilute fluorescein solution. This system provides a physical basis for fiber optic fluoroimmunoassay independent of immunochemical binding and kinetics. The excitation of fluorescein by evanescent wave interaction and subsequent detection of fluorescence from the optical fiber endface by the reciprocal process was studied. A systematic variation of optical launch conditions and cladding refractive index was completed. These results are compared with a semi-classical optical model which has been developed for this purpose. This predictive model yields results which for the first time are fully quantitative. Good agreement has been obtained between the experiments and the model. Additionally, sensitivity to 10 -9 molar solution has been obtained.

Optical fiber-to-channel waveguide coupler

Abstract: A micromanipulator and UV curing adhesive allows a precise end-on coupling of an optical fiber to a film optical waveguide on a substrate. Such a coupling facilitates the optical processing of data on active or passive optoelectronic chips with the inherent advantages of parallel, high speed capability. After coarse STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. BACKGROUND OF THE INVENTION Technological advances in optical communications and in optical data processing have seen the emergence of thin-film optical and electro-optical logic elements in conjunction with optical fibers and have led to high speed signal processing concepts wherein fibers would be used as interconnecting optical channels, delay lines or shift registers. Thin film guided wave devices are strong candidates to perform terminal functions in optical fiber communication systems. These applications require practical fiber-to-thin film coupling methods and in some cases precise specification and control over the optical delay from one integrated optical element through an optical fiber to another integrated optical element via some coupling regions. Consequently, a decisive need has been recognized for a reliable permanent coupling of single mode optical fibers to channel thin-film optical waveguides and efforts are underway to develop the technique for fiber-film channel waveguide coupling with an emphasis on suitability to different waveguide materials, stability and producibility. These desirable characteristics must further be carefully chosen to assure compatibility with existing methods to produce maximum coupling efficiency and with waveguide device requirements such as electrical access. Some single mode optical fibers and thin-film channel waveguides can be used to perform in the 800-1600 nm wavelength region although other regions can be selected as a particular application dictates. Typically channel waveguides have been fabricated in LiNbO 3 by Ti indiffusion (Ti:LiNbO 3 ) or in other transparent substrates with rib or with strip-loaded waveguides since such structures are widely used for active and passive thin film devices. Designers have two options for coupling the energy from the fiber to the thin-film waveguides, namely via evanescent wave coupling between the two waveguides or by end-on launching. End-on coupling has an appeal due to its applicability to different waveguide materials such as GaAs and Si 3 N 4 and for simplicity. In fact, in recent years more research has been devoted to the end-on configuration which is practical and not material specific. Coupling efficiency is vital and clearly a challenge since the optical waveguides are microns in size, mode patterns from two different types of waveguides must be matched, and film and fiber edge conditions must be controlled. Several publications which show the use of fibers and thin-film optical logic elements and the coupling efficiencies of such structures are available, for example the article by G. M. Dillard et al entitled "Fiber and Integrated Optics Techniques for Radar and Communications Signal Processing," National Telecommunications Conference Record VIII, pages 37.5-1 to 37.5-5 (December 1976) and 0. G. Ramer's article "Single Mode Fiber-To-Channel Waveguide Coupling," appearing in J. Opt. Comm. 2, 122, (1981) and R. C. Alferness's article "Efficient Single-Mode Fiber to Titanium Diffused Lithium Niobate Waveguide Coupling for Lambda Equals 1.32 Micron," IEEE J. Ouantum Electron. QE-18, 1807, (1982). The best figures known to be reported for Ti:LiNbO 3 waveguides are ninety-five percent (-0.2dB) coupling efficiency when Lambda equals 633 nm and a fiber waveguide fiber insertion loss of 1dB for a 1 cm long waveguide when Lambda equals 1.32 microns. These figures were arrived at by R. C. Alferness et al in the article cited above and by M. Papuchon et al in their article entitled "High Coupling Efficiencies Between Single Mode Optical Fibers and Ti Diffused LiNbO 3 Waveguides" Paper FB3-1 at the Topical Meeting on Integrated Guided Wave Optics, Pacific Grove, Calif., Jan. 6-8, 1982. Micromanipulators were used to position the fibers in the experiments of these last two articles. The figures of Alferness and Papuchon exceeded theoretical estimates for this type of coupling, see the article by W. K. Burns et al entitled "End Fire Coupling Between Optical Fibers and Diffused Channel Waveguides" Applied Optics 16, 2048, (1977). The couplings of the Burns article involved calculation of the overlap integral of the fiber and channel waveguide modes. The transverse fields of these optical modes are modeled as circular and rectangular Gaussian functions respectively. Optimum conditions for coupling were calculated as well as the adverse effects of waveguide tilt, off-set and end separation. For example, to keep each of these loss contributions below ten percent (-0.5 dB) for typical Ti:LiNbO 3 waveguides and fibers that tilt should be less than about one degree, the off-set less than about 0.8 microns and the end separation less than about twenty microns, note 0. G. Ramer's "Controlled Fiber Optic Switching" Hughes Research Laboratory Air Force Technical Report, AFWAL-TR-81-1002 December 1980. Although low loss, adjustable connectors have been reported for fiber-film coupling, techniques for permanently joining many fibers to a thin film waveguide chip are needed ultimately. The first adjustable connector applied double eccentric cylindrical supports permitting the alignment of two single-mode waveguide components, see J. Guttmann et al's article "Optical Fiber-Stripline-Coupler" Applied Optics 14, 1225 (1975). A second approach uses etched Si V-grooves for fiber positioning, see L. P. Boivin "Thin Film Laser to Fiber Coupler" Applied Optics 13, 391 (1974). A flip-chip orientation for the thin film channel waveguides and tapered fibers transverse to the coupling fibers for fine height adjustment is discussed in the article by C. H. Bulmer entitled "High Efficiency Flip-Chip Coupling Between Single-Mode Fibers and LiNbO 3 Channel Waveguides" Applied Physics Letters 37, 351 (1980). These techniques appear limited to one or two fibers per chip facet. Other approaches for attaching fibers permanently to LiNBO 3 channel waveguides have been implemented in varying degrees. A coupler disclosed by J. Noda et al in the article "Single-Mode Optical Waveguide Fiber Coupler" Applied Optics 17, 2092 (1978) holds the fiber in place with a jig attached to the chip carrier. Fine adjustment is accomplished by set screws and a final step of plastic molding fixes the fiber in place. Apparently this approach is not suitable for more than one or two fibers per chip edge owing to the size of the positioning fixture. Another technique used Si V-grooves to support fibers in positions determined by photolithographic masking and preferential chemical etching. The grooves can be defined to the same accuracy as the channel waveguide lithography and the etching has excellent control and reproducibility. In this scheme the accuracy of a fiber core position naturally depends upon the uniformity of the fiber outer diameter and its concentricity with the core. Various methods are used for aligning the Si carrier chip with the waveguide chip and subsequently cementing them. Another coupler disclosed by H. P. Hsu et al in "Multiple Fiber End Fire Coupling With Single-Mode Channel Waveguides" Applied Physics Letters 33, 603 (1978) uses etched V-grooves in Si for both fiber holding and as alignment markers to bring the flip-chip LiNbO 3 waveguides into proper registration before cementing. Fibers are then placed in the grooves, however, permanent attachment was not reported. Another V-groove approach disclosed by O. G. Ramer et al in "Experimental Integrated Optic Circuit Losses and Fiber Pigtailing of Chips" IEEE J. Ouantum Electron. QE-17,970 (1981) epoxies the fibers in the V-grooves and polishes the Si and fiber end surfaces flat together. Then the Si chip is epoxied to a holder which offers micrometer adjustment in the transverse directions after the epoxy has cured. An initial version had an external micropositioner which adjusted the Si chip into place and was removed after the epoxy step. However, this arrangement apparently tended to suffer misalignment from stress which was placed on the Si chip by the curing epoxy. A waveguide switch network is coupled to four output fibers in the arrangement disclosed by M. Kondo et al in "Integrated Optical Switch Matrix for Single-Mode Fiber Networks" IEEE J. Quantum Electronics QE-18, 1759 (1982). The fibers are sandwiched between two Si chips etched with V-grooves and the chips are positioned and epoxied to a mount carrying the switch chip. Mention is made of the difficulty in epoxying the fibers and Si chips for fine positioning, but the details were not presented. In summary the methods of the prior art for permanently attaching multiple fibers depend upon aligning them relative to each other by their outer diameters using the very accurate V-grooves. Thus, the core locations depend upon the fiber qualities of circularity and concentricity. The Si chip is then positioned to align the V-grooves or the fibers in them with the channel waveguides and an adhesive is applied to fix positions. Apparently, the chip positioning can be done well within the required accuracy but stress from the curing epoxy causes misalignment. Thus, a continuing need exists in the state of the art for an optical fiber to channel waveguide coupler that accurately positions end-on couplings for being cemented in place without the creation of misaligning strains.

Fiber lasers with loop reflectors.

Abstract: The theory of homogeneously broadened four level fiber lasers, which use fiber loops as distributed reflective elements, is examined. Such cavities can be made entirely from rare earth doped fiber. The amplifying characteristics of doped fiber loops are examined. The threshold pump power and the loop reflectivity necessary to optimize the lasing output power from an oscillator formed from two loops in series are predicted.

Embedded optical fiber sensors for materials evaluation

Abstract: Optical fiber waveguides embedded within materials have been applied to the measurement of chemical changes, strain, and temperature inside materials. This paper reviews some of the research that has been performed in this area over the past 10 years and cites the theoretical and demonstrated performance of such sensors for material evaluation during its manufacturing, in service lifetime and degradation periods.

Fiber Optic Cure Sensor for Thermoset Composites

Abstract: We present recent experimental verification of a new in-situ fiber optic sensor [1] for detecting the curing of thermoset composites. This device is sensitive to the difference between the refractive index of the curing polymer matrix within the composite and that of a fully-cured reference fiber made of the same thermoset material. The method is indifferent to temperature variations imposed during the cure process.

Photorefractive effect in bulk glass and devices made therefrom

Abstract: The photorefractive effect results in a change in the refractive index of bulk chalcogenide glass when it is exposed to certain wavelengths of light, in particular, sub-band-gap light. The effect results in a variety of device structures including a fiber optic faceplate; an optical waveguide; a fiber tap; a lens and a Bragg grating. Methods for fabricating the various devices are described.

Spectral behavior of a low-cost all-fiber component based on untapered multifiber unions

Abstract: Untapered multifiber unions are reported to show a spectral behavior similar to the tapered ones. Their oscillatory behavior does not depend on the biconical regions. This suggests a novel way to make low-cost all-fiber devices with applications as passive components such as optical filters and wavelength multiplexers/demultiplexers. Two types of multimode fibers have been studied and information about the index profile influence has been obtained. Polarization insensitivity and temperature stability have been observed. >

Synthesis Of Interference Patterns In Few-Mode Optical Fibers

Abstract: When a single-mode fiber is operated at a wavelength shorter than its nominal wave-lenght, few lower-order modes are excited and an interference pattern develops which is sensitive to differential phase variations of the modes. Intensity patterns resulting from the interference of the pairs of modes LPoi, LP11 and LP11, LP21 are examined. By proper choices of phase and amplitude of the interfering modes, one,two and three-lobe patterns can be synthesized which exhibit oscillatory or rotational behavior in response to an external disturbance. Launching conditions for achieving such patterns are discussed. Sensor applications of few-mode fibers, particularlyfor strain and temperature sensing, are addressed.

Methods of making optical fiber and products produced thereby

Abstract: An improved multimode optical fiber having substantially higher bandwidth and lower loss is made by controlling process parameters such as the volume of the silica which is deposited in each pass of a torch assembly (41) along a substrate tube (31) to form a preform tube which is collapsed to provide a preform (80) from which the optical fiber is drawn. As a result, the amplitude variation of the refractive index across each layer is controlled to be within desired limits. Should the volume of the silica deposited in each pass be controlled to control the amplitude variation, the thicknesses of the outermost deposited glassy layers in the preform tube are greater and those of the innermost layers are less than those of layers in a preform tube made by prior art MCVD processes. Because the difference in the index of refraction across each glassy layer is reduced, the bandwidth is enhanced and the loss of the drawn optical fiber is reduced over those properties of optical fiber drawn from preforms made by prior art MCVD processes. Inasmuch as the inventive process also allows a higher deposition rate than before, it may be used to produce single-mode optical fiber at lower costs than before achieved.

Compact optical fiber coupler

Abstract: An optical coupler for coupling light between a light emitter and an optical fiber includes a substrate for maintaining a bend in an optical fiber through which light can be coupled between an optical fiber core and the light emitter. The substrate includes a cavity which extends in a direction substantially perpendicular to a plane defined by the fiber bend so as to enable the light emitter to be secured to the substrate to minimize a propagation distance of light to be coupled through the substrate. The light emitter includes first and second substantially spherical lenses, one of which being disposed in the cavity so as to increase optical coupling efficiencies and result in a compact coupler design.

Method for the manufacture of an optical fiber coupler

Abstract: In a method of making an optical fiber coupler through heat elongation of optical fibers, the performance of the coupled optical fibers is measured after the optical fibers are heat elongated at least once, and based on the measured elongation length and the performance of the coupled optical fibers, a functional equation representing their relationship is determined by approximate calculation. The functional equation is used to calculate an elongation length which provides the intended performance of the coupled optical fibers, and then the optical fibers are heat elongated to the calculated length.