Showing papers on "Optical fiber published in 1980"

Experimental Observation of Picosecond Pulse Narrowing and Solitons in Optical Fibers

Abstract: This paper reports narrowing and splitting of 7-ps-duration pulses from a mode-locked color-center laser by a 700-m-long, single-mode silica-glass fiber, at a wavelength (1.55 \ensuremath{\mu}m) of loss and large but negative group-velocity dispersion. At certain critical power levels, the observed behavior is characteristic of solitons.

Bending-induced birefringence in single-mode fibers

Abstract: In a bent optical fiber, lateral internal stress induces a birefringence, betab. At lambda = 0.633 microm in a silica fiber, betab = 7.7 X 10(7) r2 /R2 deg/m, where r is the fiber radius and R is the bending radius.

Elimination of drift in a single-mode optical fiber interferometer using a piezoelectrically stretched coiled fiber

Abstract: The feasibility of maintaining a single-mode optical fiber interferometer in quadrature is demonstrated using a servo driven piezoelectrically stretched coiled fiber. The controller has a range of ~10(-5)-1000 rad with a stress voltage coefficient of ~27pi rad/V.

Computation of mode properties in optical fiber waveguides by a propagating beam method

Abstract: Propagating beam solutions for optical waveguides can be made to generate such mode-related properties as propagation constants, relative mode powers, and group delays with high precision and considerable flexibility. These quantities are needed in the analysis of optical fiber dispersion. The technique requires the generation of correlation functions from the numerical solutions of a wave equation. These correlation functions are in turn Fourier-transformed with respect to axial distance z. The resulting spectra display sharp resonances corresponding to mode groups, and the positions and heights of these resonances determine the previously mentioned mode properties. The spectral analysis is made highly accurate by the use of line-shape fitting techniques. With this method, mode group delays can be determined to a precision of +/-0.12 psec/km using a computation covering a 5-cm propagation path.

Thermally induced nonreciprocity in the fiber-optic interferometer.

Abstract: A fiber-optic coil for use as the sensor loop of a fiber optic gyroscope includes a first optical fiber segment wound as radially successive coiled layers around a coil bobbin in a first region thereof, and a second optical fiber segment wound as radially successive coiled layers around the coil bobbin in an axially adjacent second region thereof. The first and second optical fiber seg ments are joined to each other through a longitudinal middle portion, which is positioned in the radially in nermost coiled layers of the first and second optical fiber segments adjacent to a longitudinal center of said coil bobbin. Each of the first and second optical fiber segments is wound in alternate axial directions in the radially successive coiled layers. The first and second optical fiber segments may be integrally joined to each other by the longitudinal middle portion, or may be separate from, but joined to, each other by a depolarizer across the longitudinal middle portion.

Fiber-optic rotation sensing with low drift.

Abstract: Fiber-optic rotation sensing with an extrapolated drift of 1 deg/h1/2 is accomplished by operating the Sagnac interferometer from a truly single-mode common input–output port in connection with a phase-modulation scheme and active polarization stabilization.

Nonlinearity in fiber transmission

Abstract: Procedures are presented for estimating critical powers for nonlinear optical processes in single-mode fiber transmission systems. Crosstalk due to Raman gain in multiplexed systems can appear at powers of a few mW. The effects of self-phase modulation and stimulated Brillouin scattering can appear around 100 mW while typical stimulated Raman threshold powers are a few watts.

Birefringence induced by bends and twists in single-mode optical fiber

Abstract: Bend-induced retardation and twist-induced rotation in single-mode optical fibers are important variables in the design of optical fiber current measurement systems. Bend-induced retardation varies with the square of the curvature and is believed caused by a waveguide geometry effect. Twist-induced rotation varies with the angle through which the fiber is twisted and is produced by torsional strain in the fiber. Both effects were found highly reproducible and to have small temperature dependence. Neither effect should significantly limit the performance of optical measurement systems using single-mode fibers.

Optical-pulse equalization of low-dispersion transmission in single-mode fibers in the 1.3 - 1.7-microm spectral region.

Abstract: We describe a simple optical-pulse-equalization technique for minimizing pulse dispersion in a single-mode fiber transmission system utilizing the positive- and the negative-dispersion characteristics of single-mode fibers on both sides of a zero-chromatic-dispersion wavelength.

Applications of GRIN-rod lenses in optical fiber communication systems.

Abstract: Graded-refractive-index-rod lenses (GRIN-rod lenses) have a number of features that make them particularly suitable for use in optical devices for manipulating and processing the optical signals in fiber communication systems. Such lenses can be cemented directly to the other elements of a device, thus giving a structure that is compact, solid, stable, and rugged. They also have significantly smaller aberrations than equivalent simple homogeneous lenses, and this results in lower insertion losses. Designs for various GRIN-rod lens devices, including connectors, attenuators, directional couplers, switches, isolators and wavelength-division multiplexers are reviewed. A consistent set of loss estimates is provided for all the device designs considered.

Analysis of the backscattering method for single-mode optical fibers

Abstract: The theory of the backscattering method, which so far has been known only for multimode fibers, is extended to single-mode fibers. Under certain conditions the result of the present investigation is nearly the same as for multimode fibers although the theory in the latter case is based on a ray optical approach.

Fiber optic temperature sensing

Abstract: Fiber optic waveguides exhibiting a blackout phenomenon can be used for temperature sensing. A temperature sensing waveguide can be used in such applications as maintaining a material within a selected temperature range, freeze protection viscosity control of liquids in pipelines, leak detection of cryogenic fluids, fire detection, application of heat-recoverable materials, battery charging, and fluid level detection. Novel waveguides exhibiting blackout at selected temperatures for use in these applications are described.

Single-mode fiber-optic polarizer.

Abstract: A technique is presented for the fabrication of high-quality single-mode fiber-optic polarizers. Properties of polarizers made using this technique include extinction ratios in excess of 60 dB as well as low loss for the desired polarization.

Fiber optic strain sensor.

Abstract: An optical fiber (10) having at least two cores (12 & 14) positioned in a common cladding (16) can be fabricated to be responsive to strain or hydrostatic pressure (20) but not to temperature through the selection of materials, spacing and shape of the cores and cladding in the fiber. Accordingly, the cross-talk between adjacent cores (12 & 14) in the optical wave-guide (10) can be optimized to respond to a change in hydrostatic pressure (20) or in unidirectional strain along the length of the fiber. The strain or pressure change, can be determined by measuring (22 & 24) the relative intensity of light emerging from the different cores of the fiber. A larger unambiguous range for strain or hydrostatic pressure (20) changes can be provided by a multi-core optical fiber embodiment.

Proposal for detection of magnetic fields through magnetostrictive perturbation of optical fibers.

Abstract: The possibility of detecting magnetic fields by a magnetostrictive straining of optical fibers is investigated. The effect of shot noise and the limiting sensitivity are considered.

Control for laser hemangioma treatment system

Abstract: A laser for directing a nominally 5 micron wavelength beam at a hemangioma or other variegated lesion. A fiber optic bundle for intercepting radiation reflected from the lesion at an intensity corresponding with the color intensity of the region at which the beam is directed. The output beam from the fiber optic bundle modulates a photodetector stage whose amplified output drives a galvanometer. The galvanometer shaft is coupled to the shaft of a potentiometer which is adjustable to regulate the laser power supply and, hence, the laser output energy level so laser beam energy is reduced when high absorption regions in the lesion are being scanned by the beam and increased as low absorption regions are being scanned.

Efficient coupling from semiconductor lasers into single-mode fibers with tapered hemispherical ends.

Abstract: An efficient coupling from semiconductor lasers in the 1.3-μm range into single-mode fibers with tapered hemispherical ends (TH fiber) is described. Coupling efficiency of more than 35% is attainable with TH fiber coupling. Optimum radius of the end hemisphere is ∼20 μm and is obtained with good reproducibility by drawing the fiber in an arc discharge. It was found that changes in laser characteristics due to reflected light are far less for TH fiber coupling than for flat-end coupling. Stable coupling modules using TH fiber coupling were fabricated for system use.

Static pressure sensitivity amplification in interferometric fiber-optic hydrophones

Abstract: The induced optical phase change produced when a static pressure is applied to the test arm of an interferometric single-mode fiber optic hydrophone is examined in terms of hydrostatic and radial mechanical models. The expressions for the models are given in terms of a 3-D solution to the equations of elastostatics for multilayered cylinders. The induced phase change is calculated using both models for various values of the diameter and elastic properties of fiber jacket materials. It is shown that the phase change predicted from the 3-D approach for each model can be adequately described in terms of much simpler 2-D plane strain models. Calculations show that the hydrophone sensitivity of a jacketed fiber is amplified compared with a bare fiber. The largest increase in sensitivity is predicted with the radial model. Calculated sensitivities for the hydrostatic model are shown to correspond closely in value with static pressure sensitivity measurements for the experimental arrangement used here.

Microoptic grating multiplexers and optical isolators for fiber-optic communications

Abstract: As new optical devices for increasing further the utility of and to expand the application of fiber-optic communications, grating multiplexers and isolators have been developed for 0.8 μm band employing microoptic approach. The development of these devices is the subject of this paper. The devices have desirable features of small size, compactness, high optical performances, and high reliability. The grating multiplexer consists of a graded-index rod, a blazed reflection grating replicated onto the graded-index rod slanting facet or a wedge facet, and an input-output fiber array. Simple calculations have been done to determine necessary element parameters for a given channel spacing. Experimental results are presented for five-channel multiplexers devised using a SELFOC®lens. Around 3 dB insertion loss and less than -30 dB crosstalk have been obtained for about 35 nm channel spacing in overall device size of 18 \times 13 \times 50 mm. Faraday rotation optical isolators for 0.8 μm band have been miniaturized by employing an efficient paramagnetic glass Faraday rotator, a magnet with a through hole and a folded optics in the Faraday rotator. The path number in the folded optics has been optimized in terms of trading-off between the magnet size and the insertion loss. A 0.9 dB insertion loss including fiber coupling loss and 36 dB isolation have been obtained in overall device size of 24 \times 24.5 \times 42 mm. Results on the temperature and wavelength dependence of the isolation are also presented. In addition, fundamental properties of optical circulators for 0.8 μm band and optical isolators and circulators both for 1.3 μm band, developed as extended modifications of the optical isolators for 0.8 μm band, are briefly described.

Optical fibre magnetic field sensors

Abstract: A class of high sensitivity fibre-optic magnetic sensors has been developed and successfully tested in the laboratory for the first time. The magnetic sensors employ magnetostrictive jacketing materials in conjunction with conventional single-mode optical fibres. An all-fibre Mach-Zender interferometer was used to detect the magnetically induced changes in optical path length which arise because of strains transferred to the fibre from the magnetostrictive jacket.

Self-confinement of multimode optical pulse in a glass fiber

Abstract: The nonlinear change of the dielectric constant (Kerr effect) in a glass fiber can be utilized to self-confine optical pulses in a multimode fiber at wavelengths longer than 1.3 μm. The range of the deviation in the group velocity Δνg of the different modes to be confined is given by Δνg2/νg2 ≤ 2(∂νg/∂f × f/νg)n2/n0|E|2, where f and νg are the frequency and the group velocity, respectively, of the mode; n0 and n2 (= 3 × 10−22 m2/V2) are the linear and nonlinear indices of refraction; and E is the peak electric field averaged over the cross sections of the fiber.

Frequency dependence of modal noise in multimode optical fibers

Abstract: Under certain conditions a changing speckle pattern exists at the output plane of a multimode fiber, resulting in modal noise which can degrade the error performance of a fiber data link. Fiber motion is the usual cause of such speckle change, and Daino et al. have studied the first-order statistics of such modal noise, assuming a single frequency source. But source frequency variation can also cause modal noise; and source frequency diversity has been shown effective in its reduction. In this paper we use a speckle theory approach to study the frequency dependence of modal noise. We have measured and analyzed the correlation of two speckle patterns as a function of source frequency difference, and the speckle spatial frequency distribution as a function of fiber parameters. We have also measured the speckle contrast as a function of fiber length for several sources and fiber types. Such information permits the prediction of the modal noise statistics, from which corresponding changes in error rates can be derived.

Sum-frequency light generation in optical fibers.

Abstract: The generation in an optical-fiber waveguide of a spectral continuum spanning 29000 cm−1 from the near infrared to the ultraviolet is reported. A Q-switched and mode-locked Nd:YAG laser is used to excite the fiber. An unexpected phenomenon is the generation of sum-frequency light derived from the pump frequency and the characteristic Raman Stokes frequencies of fused silica. This light is observed as visible light in cladding modes of the fiber.

Fiber optic pressure sensor

Abstract: We propose a new transduction mechanism for fiber optic pressure sensing: pressure‐induced microbending, which produces excess optical attenuation in the fiber. A simple bending transducer has been used to determine the response of a step‐index multimode fiber to changes in applied pressure. The potential (low frequency) acoustic sensitivity of such a transducer, calculated from this measured response, is approximately 100 μPa into a 1‐Hz detection bandwidth.

Stress-induced index profile distortion in optical waveguides

Abstract: The residual thermal stresses in optical waveguide fibers can be large enough to cause substantial changes in the refractive-index profile and to create optical anisotropy. This paper presents a method of calculating these effects and illustrates the influence of various dopants on the magnitudes of the stresses.

High birefringence in tension-coiled single-mode fibers.

Abstract: Coiling a single-mode fiber of radius r under tension onto a cylinder of radius R produces a linear birefringence of βtc ≃ 28 × 107∊2r/R deg/m in the fiber at λ = 0.63 μm, where ∊z is the relative fiber elongation. Polarization beat lengths down to 2.5 cm have been realized this way, providing excellent polarization holding.

Characteristics of a hemispherical microlens for coupling between a semiconductor laser and single-mode fiber

Abstract: A hemispherical microlens is fabricated on the end of a single-mode fiber by an electric arc discharge technique. It improves coupling efficiency between InGaAsP lasers with buried heterostructure geometry and single-mode fiber. The lowest coupling loss of 2.9 dB is achieved with the optimum lens radius of 8.5 μm. This loss is 4.4 dB lower than that with a butt joint. Experimental results of coupling efficiency and alignment tolerances in coupling with different lens radii in the range of 3.5-17 \mu m are discussed in detail. The results are in good agreement with theoretical values derived by Gaussian beam and paraxial ray approximations.

Visible light apparatus for curing photo-curable compositions

Abstract: There is provided a device for efficient production of light in the low visible range for photo-curing materials, the device being particularly adapted for dental applications. The efficient light source comprises a tungsten halogen lamp with a concentrating reflector which reflects visible light and passes middle and far infrared wavelengths. A filter system is provided comprising a dichroic heat reflecting filter which efficiently passes light from 400 to 700 nm and reflects energy in the visible red and near infrared wavelengths back to the lamp envelope, thus enhancing lamp halogen cycle efficiency. The dichroic heat reflecting filter is followed by a dielectric filter which provides a high efficiency bandpass at the desired visible range. A highly efficient fiber optic light guide is positioned to receive the focused and filtered light and to transmit it to a reduced surface light applying tip at the end of a handpiece. The fiber light guide is encased in a specially designed sheathing which provides protection to the optical fibers and carries two electrical conductors which are connected between a control switch on the handpiece and the power supply for the lamp.