Showing papers on "Optical fiber published in 1982"

Optical fiber sensor technology

Abstract: The current state of the art of optical fiber sensors is reviewed. The principles of operation are detailed and the various types of fiber sensors are outlined. Achievable performance and limitations are discussed and a description of technology used to fabricate the sensor is presented. The characteristics of acoustic, magnetic, gyro, laser diode, and other sensors are described. Trends in the development of this sensor technology and expected application areas are briefly outlined.

Parametric amplification and frequency conversion in optical fibers

Abstract: We find that the parametric four-photon gain for light pulses decreases for fibers longer than a characteristic length. This length is related to the common experimental observation that stimulated parametric emission is usually prominent only in short fibers while in long fibers stimulated Raman scattering dominates. Despite the fact that the actual process involves an intensity dependent bandwidth and broadening of the pump linewidth from self-phase modulation, it is possible to develop a simple expression for the characteristic length which requires only the initial pump linewidth and the low-power parametric bandwidth. This bandwidth can often be estimated from the pump wavelength and the measured frequency shift between the pump and the generated waves. Expressions for gain and amplification are derived from coupled wave equations and in the Appendixes it is shown that these are of the same form as the planewave equations, but modified by coupling coefficients called overlap integrals.

Compression of femtosecond optical pulses

Abstract: We describe the generation and measurement of optical pulses as short as 30 fs. The pulses are produced using self‐phase modulation in a short 15‐cm optical fiber followed by a grating compressor.

Intensity discrimination of optical pulses with birefringent fibers.

Abstract: An intensity discriminator for optical pulses can be made with a birefringent fiber. Such a discriminator would be useful for separating the intense subpicosecond pulses formed by solitonlike compression from the weaker uncompressed background. The discriminator utilizes an intensity-dependent state of polarization out of the fiber.

Optical pulse compression based on enhanced frequency chirping

Abstract: Through numerical simulations, we show that, under relatively general conditions, passage of an intense picosecond pulse through a single‐mode optical fiber can cause the pulse to become strongly frequency broadened with a positive chirp (linear frequency sweep) describing essentially all of the energy of the output pulse. Also, because the optical fiber supports only a single transverse mode, the entire output beam profile has the same frequency modulation. These two features allow for unprecedented optical pulse compression.

Influence of curvature on the losses of doubly clad fibers

Abstract: The loss increase of the HE(11) mode of a doubly clad (depressed-index) fiber due to constant curvature is considered. The calculations presented in this paper are based on a simplified theory. We find that for typical fibers the leakage loss of the HE(11) mode begins to increase significantly when the radius of curvature of the fiber axis reaches the 1-10-cm range.

Analysis of a tunable single mode optical fiber coupler

Abstract: We report the operation and the theoretical modeling of an efficient, tunable, and low-loss single mode fiber coupler. The coupler design follows a scheme previously reported, in which two optical fibers mounted in curved grooves in separate quartz substrates are polished until sufficient cladding material has been removed to permit optical coupling between the mated polished faces of the fibers. The results of a computer analysis of the distributed coupling taking place between the fibers are discussed, emphasizing the intuitive dependences of the coupling coefficient and effective interaction length of the device on its geometrical parameters. A detailed experimental analysis of fiber couplers follows in which we characterize two types of couplers made with different brands of single-mode fibers. Operation up to 100 percent coupling ratio and 50 dB extinction ratio between coupled and direct branch as well as operation in overcoupling regimes are demonstrated, both at visible and infrared signal wavelengths. Tuning curves are shown that emphasize the excellent tunability properties of such couplers in which the coupling ratio can be smoothly and continuously tuned between 0 and 100 percent. Experimental evidence of the relatively low loss level and very low polarization dependence of the fiber couplers are also presented. All experimental results, including an analysis of the influence of the refractive index of the intermediate layer of index-matching liquid between the polished faces of the fibers, are found to be very well predicted by our theoretical model.

All-fiber stimulated Brillouin ring laser with submilliwatt pump threshold.

Abstract: An all-fiber ring resonator, constructed from a single strand of single-mode optical fiber and a directional coupler, is shown to have a low threshold for stimulated Brillouin laser action. The 10-m-perimeter fiber ring resonator has a low round-trip loss of under 3.5% and an inherent pump-power enhancement of approximately 30. Lasing threshold for the 4.0-microm-core fiber occurred with a pump power of 0.56 mW at lambda = 6328 A and 1.74 mW at lambda = 5145 A.

Passive stabilization scheme for fiber interferometers using (3×3) fiber directional couplers

Abstract: A passive stabilization scheme using a (3×3) fiber directional coupler in an all fiber Mach–Zehnder interferometer and suitable signal processing has been successfully demonstrated. A stable output with large signal dynamic range and a minimum detectable phase shift in the microradian range has been achieved.

Fluorescent immunoassay employing optical fiber in capillary tube

Abstract: Fluorescent immunoassay apparatus and method employing a disposable consisting, in a preferred embodiment, of a short length of precise diameter capillary tubing having an axially disposed optical fiber to which is immobilized a monolayer of a component of the antibody-antigen complex (e.g., an antibody), an inert diluent, and a preload of a known amount of tagged complement to the immobilized component (e.g., a fluorescent-tagged antigen). The dimensions of the fiber and the capillary tubing are chosen so as to allow the tube to fill itself by capillary action once an end of the tube is immersed into the sample. Precise timing and ballistic measurements may, if desired, be avoided by insuring the incubation time is larger than the diffusion time necessary to scavenge the volume between the fiber and the capillary tubing. Fluorimetric measurement is made by total reflection fluorescence techniques.

Optical Fiber Sensor Technology

Abstract: The current state of the art of optical fiber sensors is reviewed. The principles of operation are detailed and the various types of fiber sensors are outlined. Achievable performance and limitations are discussed and a description of technology used to fabricate the sensor is presented. The characteristics of acoustic, magnetic, gyro, laser diode, and other sensors are described. Trends in the development of this sensor technology and expected application areas are briefly outlined.

An introduction to optical fibers

Abstract: An introduction to optical fibers , An introduction to optical fibers , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Fiber-Optic Fabry-Perot Interferometer and its Sensor Applications

Abstract: Fiber-optic Fabry-Perot interferometers using monomode fibers are fabricated and their basic properties of finesse, polarization, and thermal response are studied. Fiber-optic Fabry-Perot interferometers are applied to the sensors of temperature, mechanical vibration, acoustic wave including human voice, ac voltage, and ac and dc magnetic fields. It has been demonstrated that a fiber-optic Fabry-Perot interferometer can simplify the interferometric fiber sensor sys-tem and that high measurement sensitivity can be obtained by using a high-finesse and/or long-distance fiber Fabry-Perot interferometer.

Fiber-optic Fabry-Perot interferometer and its sensor applications

Abstract: Fiber-optic Fabry-Perot interferometers using monomode fibers are fabricated and their basic properties of finesse, polarization, and thermal response are studied. Fiber-optic Fabry-Perot interferometers are applied to the sensors of temperature, mechanical vibration, acoustic wave including human voice, ac voltage, and ac and dc magnetic fields. It has been demonstrated that a fiber-optic Fabry-Perot interferometer can simplify the interferometric fiber sensor system and that high measurement sensitivity can be obtained by using a high-finesse and/or long-distance fiber Fabry-Perot interferometer.

Development of low- and high-birefringence optical fibers

Abstract: The polarization properties of single-mode optical fibers are easily modified by environmental factors. While this can be exploited in a number of fiber sensor devices, it can be troublesome in applications where a stable output polarization-state is required. Fibers with both low and high birefringence have been developed to enhance or diminish their environmental sensitivity, and recent progress in each area is reviewed. Low-birefringence fibers are described which are made by spinning the preform during the draw. In addition, developments in high-birefringence fibers which maintain a polarization state over long lengths are summarized. The effect on performance of external factors such as bends, transverse pressure, and twists is analyzed. Consideration is also given to polarization mode-dispersion as a potential limiting factor in ultrahigh bandwidth systems.

Infrared optical fibers

Abstract: A state of the art review of nonsilica based infrared fibers is presented. Two types of fiber materials have been investigated- crystals and glasses. Crystal fiber work appears to be focused on development of short haul CO 2 laser power delivering lines at 10.6 μm. The maximum delivering power of the CW CO 2 laser has reached up to about 100 W by the polycrystalline KRS-5 fiber. A number of glass fibers are being developed in fluorides, sulfides, and heavy metal oxides. The best optical attenuation of each glass fiber has been respectively reduced to 21 dB/km at 2.55 μm for ZrF 4 -based glass fiber with a core-clad structure, 78 dB/km at 2.4 μm for As-S unclad glass fiber, and 13 dB/km at 2.05 μm (70 dB/km at 2.40 μm) for GeO 2 -Sb 2 O 3 glass fiber with a core-clad structure. Recent progress of these infrared fibers offers great potential for new wavelength fiber links operating in the 2-10\mu m region which have not been realized by silica-based fiber.

Observation of stimulated Brillouin scattering in low-loss silica fibre at 1.3 μm

Abstract: Stimulated Brillouin scattering (SBS) in low-loss single-mode silica fibre is observed at 1.32 μm using a continuous-wave single-frequency Nd:YAG laser. The threshold for SBS is 5 mW and the transmitted power reaches a saturated maximum for launch powers exceeding about 10 mW. A conversion efficiency of 65% is observed. The Stokes frequency shift is 12.7±0.2 GHz.

Coated optical fiber

Abstract: An optical fiber coating comprising a thermoplastic rubber block copolymer reduces microbending losses over a wide service temperature range, typically down to at least -40 degrees Celsius, while obtaining an upper temperature limit of typically at least 90 degrees Celsius. The processing properties, including shelf life, cure rate, and toughness, are superior to typical prior art materials, such as silicones. The inventive coating can be used as the inner coating of a dual-layer coated fiber or as an outer or single coating layer.

Microbending of optical fibers for remote force measurement

Abstract: A system for remote measurement of structural forces includes a plurality of microbend transducers mounted along the length of the structure for microbending an optical fiber in response to structural forces, such as stress acting upon an oil or gas pipeline or the like. An optical time domain reflectometer (OTDR) has a light source for launching a pulsed optical signal for passage through the fiber and a photodetector for sensing as a function of time the intensity of backscattered light reflected back through the fiber, wherein this sensed time function is correlated directly with discrete longitudinal positions along the length of the fiber and the structure. When one or more of the microbend transducers is activated to induce a microbend in the fiber in response to localized forces acting upon the structure, a portion of the backscattered light is lost at the microbend. This attenuation in backscattered light intensity is sensed quantitatively and positionally identified by the photodetector. Specific preferred constructions for microbend transducers and system arrangements particularly adapted for detecting structural strain in an oil or gas pipeline are disclosed.

Fiber optic directional coupler

Abstract: Apparatus and method of manufacture for coupling optical power between two strands of fiber optic material in a given direction of propagation. The coupler employs generally parallel, intersecting strands of fiber optic material having the cladding removed on one side thereof to within a few microns of the fiber cores in the region of intersection to permit light transfer between the strands.

Fiber optic pressure sensor with temperature compensation and reference

Abstract: An intravascular catheter tip fiber optic pressure sensor wherein a lens element at the end of the fiber optic collimates the light emanating from the fiber and directs the light in a column towards a closely spaced reflecting diaphragm. The diaphragm is pressure responsive and modulates the focal length of the lens-diaphragm-mirror combination. Three optic fibers traverse the length of the hollow catheter tube, one carrying transmitted light to the tip, one carrying the reflected light from the diaphragm (i.e. the signal), and the third fiber carrying a reflected reference light. The reference detector provides a signal level to control the level of intensity of the light source.

Optical Fiber Sensor for Measuring Refractive Index

Abstract: An optical fiber sensor for measuring a liquid refractive index is proposed. When an optical fiber is bent and part of its cladding is stripped off, the light energy (E) emerging from the fiber depends on the refractive index of the surrounding medium (nm). The change in nm can be found from E. The light output energy and the measuring sensitivity are calculated numerically as a function of nm for several values of the bending radius R. The fundamental characteristics of the sensor, made of a plastic fiber, are investigated using lamp oil and light oil as specimens, and a measurement accuracy of nm to the third decimal place is easily obtained. As applications of this sensor, measurement of liquid density and detection of oil are described.

Chemically etched conical microlenses for coupling single-mode lasers into single-mode fibers

Abstract: Coupling efficiency between a laser diode and a single-mode fiber can be greatly increased by using a lensing scheme to match their respective modes. We propose a simple method to selectively etch a fiber end to produce a conical lens whose base coincides with the fiber core. If needed, this lens may be fire polished or arc melted into a hemispherical lens of the same diameter. We present a general theoretical design of both these lenses. We find that high coupling efficiency is expected in cases of practical interest. Initial experimental results are reported in which coupling losses as low as 3 dB were obtained.

Optical near-field scanning microscope

Abstract: This optical near-field scanning microscope comprises an "objective" (aperture) attached to the conventional vertical adjustment appliance and consisting of an optically transparent crystal having a metal coating with an aperture at its tip with a diameter of less than one wavelength of the light used for illuminating the object. Connected to the aperture-far end of the "objective" is a photodetector via an optical filter and an optical fiber glass cable. Scanning the object is done by appropriately moving the support along x/y-coordinates. The resolution obtainable with this microscope is about 10 times that of state-of-the-art microscopes.

Propagation in Doubly Clad Single-Mode Fibers

Abstract: General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters inner cladding/core radii ratio and inner cladding/core index differences ratio. LP01, LP11, and LP02 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 µm.

Measurement of stresses in optical fiber and preform

Abstract: A method of measuring the stresses, residual or applied, in an optical fiber or preform is presented. It is shown that the stress profiles can be obtained from the Abel transform of the derivative of the retardation. The axial stress profile is shown to bear the same shape as the refractive-index profile. Measurement results indicate that the applied tension during the fiber drawing process is frozen into the fiber, consequently affecting the intrinsic strength of the fiber. The method of estimating the fiber drawing tension from the fiber stress profile is also given.

Compact optical isolator for fibers using birefringent wedges

Abstract: A new type of optical isolator for fibers is proposed in this paper. A birefringent wedge used to separate and combine the polarized light is developed, giving the isolator low forward loss and high isolation. The antireflection process at the fiber endface reduces the forward loss and reflected return. A forward loss of 0.8 dB, a backward loss of 35 dB, and a reflected return of −32 dB were obtained. These characteristics were measured from fiber to fiber using multimode fibers with 50-μm core diam at a wavelength of 1.3 μm. Details of the design, fabrication, and characteristics of this isolator are presented.

Coupled-mode theory of nonlinear propagation in multimode and single-mode fibers: envelope solitons and self-confinement

Abstract: A set of equations describing pulse propagation in multimode optical fibers in the presence of an intensity-dependent refractive index is derived by taking advantage of the coupled-mode theory usually employed for describing the influence of fiber imperfections on linear propagation. This approach takes into account in a natural way the role of the waveguide structure in terms of the propagation constants and the spatial configurations of the propagating modes and can be applied to the most general refractive-index distribution. The conditions under which soliton propagation and longitudinal self-confinement can be achieved are examined.