Showing papers on "Optical fiber published in 1998"

Photonic Band Gap Guidance in Optical Fibers

Abstract: A fundamentally different type of optical waveguide structure is demonstrated, in which light is confined to the vicinity of a low-index region by a two-dimensional photonic band gap crystal. The waveguide consists of an extra air hole in an otherwise regular honeycomb pattern of holes running down the length of a fine silica glass fiber. Optical fibers based on this waveguide mechanism support guided modes with extraordinary properties.

Fiber optic test and measurement

Abstract: This is the most authoritative, complete source of test and measurement information for engineers who design and maintain fiber optic networks.This book presents measurement principles for characterizing all three basic components of a fiber optic communication system: the optical transmitter, fiber medium and optical receiver. It also covers system level measurements, and discusses the principles and limitations of current fiber optic testing equipment. It discusses testing to SONET/SDH international standards, and helps engineers choose the best approach to testing today's new erbium doped fiber amplifiers. The book provides detailed recommendations for understanding polarization states, and presents new methods for accurately characterizing the behavior of Wavelength Division Multiplexing (WDM) fiber systems. It includes detailed coverage of testing fiber in the local loop, using optical power meters and optical time domain reflectometers. It also reviews the latest state-of-the-art 10 Gb/s systems, and even faster systems on the horizon. The coverage is practical, helping professionals accurately measure and test fiber optic systems without becoming experts in theory.

Analysis of the response of long period fiber gratings to external index of refraction

Abstract: This paper demonstrates that the change in wavelength of a long period fiber grating attenuation band with changes in external index of refraction can be enhanced by proper selection of the grating period. We calculate and experimentally verify that the wavelength shift caused by changing the external index from n=1 to n=1.44 of the attenuation band which appears in the 1400-1600 nm region in a 200-/spl mu/m period grating is four times that in a 350-/spl mu/m period grating. Changes in the spectrum over a wavelength range from 1100 to 1600 nm and 1

Monitoring of downhole parameters and tools utilizing fiber optics

Abstract: The present invention provides systems utilizing fiber optics for monitoring downhole parameters and the operation and conditions of downhole tools. In one system fiber optics sensors are placed in the wellbore to make distributed measurements for determining the fluid parameters including temperature, pressure, fluid flow, fluid constituents and chemical properties. Optical spectrometric sensors are employed for monitoring chemical properties in the wellbore and at the surface for chemical injection systems. Fiber optic sensors are utilized to determine formation properties including resistivity and acoustic properties compensated for temperature effects. Fiber optic sensors are used to monitor the operation and condition of downhole devices including electrical submersible pumps and flow control devices. In one embodiment, a common fluid line is used to monitor downhole parameters and to operate hydraulically-operated devices. Fiber optic sensors are also deployed to monitor the physical condition of power lines supplying high electric power to downhole equipment. A light cell disposed downhole is used to generate electric power in the wellbore, which is used to charge batteries.

Apparatus and method for measuring optical characteristics of an object

Abstract: Color measuring systems and methods are disclosed. Perimeter receiver fiber optics are spaced apart from a central source fiber optic and receive light reflected from the surface of the object being measured. Light from the perimeter fiber optics pass to a variety of filters. The system utilizes the perimeter receiver fiber optics to determine information regarding the height and angle of the probe with respect to the object being measured. Under processor control, the color measurement may be made at a predetermined height and angle. Various color spectral photometer arrangements are disclosed. Translucency, fluorescence and/or surface texture data also may be obtained. Audio feedback may be provided to guide operator use of the system. The probe may have a removable or shielded tip for contamination prevention.

High-spatial-resolution distributed strain measurement in optical fiber with rayleigh scatter.

Abstract: A method of measuring strain over 30-cm intervals to an accuracy of10 microstrain in unaltered low-loss communications-grade single-modeoptical fiber is presented. The method uses a tunable external cavity diode laser to measure the reflected intensity of a reflector-fiber system as a function of wavelength. This measurement is performed with no strain applied to the fiber to produce a reference and then again after a strain has been induced. Cross correlation of the Rayleigh scatter spectra from a selected section of fiber in the strained and unstrained states determines the spectral shift resulting from the applied strain.

Properties of photonic crystal fiber and the effective index model

Abstract: We report on the waveguiding properties of a new type of low-loss optical waveguide. The photonic crystal fiber can be engineered to support only the fundamental guided mode at every wavelength within the transparency window of silica. Experimentally, a robust single mode has been observed over a wavelength range from 337nm to beyond 1550nm (restricted only by available wavelength sources). By studying the number of guided modes for fibers with different parameters and the use of an effective index model we are able to quantify the requirements for monomode operation. The requirements are independent of the scale of the fiber for sufficiently short wavelengths. Further support for the predictions of the effective index model is given by the variation of the spot size with wavelength,

Single-mode excitation of multimode fibers with ultrashort pulses.

Abstract: Single-mode excitation of step-index multimode fibers with light sources with short temporal coherence lengths is demonstrated. Multimode fiber designs with reduced microbending-induced mode coupling are described that allow the propagation of the fundamental mode over long lengths with negligible mode coupling even in the presence of tight fiber bends. At a wavelength of 1.56microm a fiber with a core diameter of 45microm can preserve the fundamental mode for a propagation length of ~20m . Such fibers allow coiling with a coil diameter as small as 7cm.

Detection of single infrared, optical, and ultraviolet photons using superconducting transition edge sensors

Abstract: We have demonstrated the use of superconducting transition edge sensors for the wide-band detection of individual photons from the mid infrared (IR), through the optical, and into the far ultraviolet (UV). These tungsten transition edge sensors are squares about 18 μm on a side and detect single photon events above a threshold of 0.3 eV (4 μm wavelength), with an energy resolution of 0.15 eV full width at half maximum, and with a risetime (falltime) of .5 μs (60 μs). The calibration data extend up to the UV cutoff of the fiber optic feed at 3.5 eV (350 nm).

Interrogation of fiber grating sensor arrays with a wavelength-swept fiber laser

Abstract: We demonstrate a novel application of a wavelength-swept fiber laser to fiber Bragg grating sensor-array interrogation. The laser provides high signal powers of >3 mW with <0.1-nm spectral resolution over a 28-nm wavelength span. Using time-interval counting, we demonstrate static-dynamic strain measurements with a resolution of 0.47mu? rms at a sampling rate of 250 Hz.

Spectrally encoded confocal microscopy.

Abstract: An endoscope-compatible, submicrometer-resolution scanning confocal microscopy imaging system is presented. This approach, spectrally encoded confocal microscopy (SECM), uses a quasi-monochromatic light source and a transmission diffraction grating to detect the reflectivity simultaneously at multiple points along a transverse line within the sample. Since this method does not require fast spatial scanning within the probe, the equipment can be miniaturized and incorporated into a catheter or endoscope. Confocal images of an electron microscope grid were acquired with SECM to demonstrate the feasibility of this technique.

An experimental and theoretical study of the offset launch technique for the enhancement of the bandwidth of multimode fiber links

Abstract: This paper reports an experimental and theoretical study of bandwidth enhancement in multimode fiber links achieved by using offset launch techniques. It is found, both from theory and experiment, that an up to four-fold bandwidth enhancement can be obtained compared to standard overfilled launch techniques despite exciting over 50% of the fiber modes, thus allowing good stability. The enhancement technique is found to be achieved for a range of fibers with different core diameters and core refractive index profiles. The level of bandwidth enhancement depends upon the inherent bandwidth of the fiber, being particularly effective in improving the performance of low bandwidth "worst case" fibers. The launch is found to be stable with respect to environmental variations, showing bandwidth enhancement for injection positions or connector offsets of up to 5 /spl mu/m from optimum. In addition, unlike many restricted launch techniques, it is found to be tolerant to angular fiber misalignment for angles up to 6/spl deg/ from normal.

Fiber optic connector assembly

Abstract: A fiber optic connector assembly is adapted for terminating at least one optical fiber of a fiber optic cable. The assembly includes a two-part elongated housing for receiving the fiber optic cable and defining a forward mating end and a rear end. The two parts of the housing extend along a substantial length of the housing through the rear end thereof. A ferrule is disposed within the forward end of the two-part housing for terminating the optical fiber. The two parts of the housing are juxtaposed and are adapted for receiving a crimp ring thereabout at the rear end of the housing. A pair of transversely spaced, complementarily engageable latches are operatively associated between the two housing parts. The pair of latches are disposed inside the outer profile of the housing and straddling opposite sides of the cable.

Gain characteristics of tellurite-based erbium-doped fiber amplifiers for 1.5-µm broadband amplification

Abstract: The signal-gain characteristics of tellurite-based erbium-doped fiber amplifiers are clarified based on spectroscopic properties and signal-gain measurements. The potential of tellurite-based erbium-doped fiber for use as a broadband light source is also described.

Multicore optical fibre

Abstract: An optical fiber for transmitting radiation comprising two or more core regions, two or more core regions, each core region comprising a substantially transparent core material and having a core refractive index, a core length, and a core diameter, wherein said core regions are arranged within a cladding region, said cladding region comprising a length of first substantially transparent cladding material, having a first refractive index, wherein said first substantially transparent cladding material has an array of lengths of a second cladding material embedded along its length, wherein the second cladding material has a second refractive index which is less than said first refractive index, such that radiation input to said fiber propagates along at least one of said core regions. The cladding region and the core regions may be arranged such that radiation input to said optical fiber propagates along one or more said lengths of said core regions in a single mode of propagation. The optical fiber may be used as a bend sensor, a spectral filter or a directional coupler. The invention also relates to a method of manufacturing a multicore optical fiber.

Mechanics of bond and interface shear transfer in optical fiber sensors

Abstract: Optical fiber sensors are emerging as a superior nondestructive means for condition evaluation of civil structures. The ability of an optical fiber sensor to monitor strain distribution in a structural material depends on the bonding characteristics between the material and the optical fiber. The strain field transferred from the structure to the optical fiber sensor generates changes in the characteristics of the light signal transmitted by the glass core of the optical fiber. Transduction of this signal will provide a means for measurement of strain. However, the mechanical properties of the protective coatings employed in conjunction with optical fibers alter the strain transduction capabilities of the sensor. A portion of the strain is absorbed by the protective coating of the optical fiber, and hence, only a segment of structural strain is sensed. In the study reported here, a model is introduced and tested through which it is possible to interpret the actual level of structural strains from the values measured by an optical fiber sensor. A number of realistic assumptions were introduced to simplify the development of the mathematical rigor. It was determined that the strain transfer characteristics of optical fibers depend on the mechanical properties of the glass core, the protective coating, and the gauge length of the optical fiber. Mathematical expressions are developed through which it is possible to describe the level of strain loss within the protective coating, and the amount transferred to the optical fiber core. The theoretical findings were verified through a series of experiments involving white light interferometry. The investigation encompassed repeated experiments with a range of fiber sensor gauge lengths. The experimental program included evaluation of strain transfer capabilities of coated as well as bare fibers.

Tapered fiber bundles for coupling light into and out of cladding-pumped fiber devices

Abstract: In accordance with the invention, light is coupled from a plurality of semiconductor emitters to a cladding-pumped fiber via tapered fiber bundles fusion spliced to the cladding-pumped fiber. Individual semiconductor broad stripe emitters can be coupled to individual multimode fibers. The individual fibers can be bundled together in a close-packed formation, heated to melting temperature, drawn into a taper and then fusion spliced to the cladding-pumped fiber. Advantageously, the taper is then overcoated with cladding material such as low index polymer. In addition, a fiber containing a single-mode core can be included in the fiber bundle. This single-mode core can be used to couple light into or out of the single-mode core of the cladding-pumped fiber.

Handbook of thermo-optic coefficients of optical materials with applications

Abstract: Preface. Introduction. Refractive Index: Introduction. Measurement. Dispersion Relations for Refractive Index. Derivation of the Sellmeier Coefficients. Sellmeier Coefficients. Comparison of Refractive Indexes. References. Thermo-Optic Coefficients: Definition. Measurement. Dispersion Relations. Derivation of the Sellmeier Coefficients: Nonlinear Crystals. Other Oxide and Laser Crystals. Halide Crystals/Glasses. Semiconductors. Optical Fiber/Optical Glasses. References. Applications: Nonlinear Optical Laser Devices: Noncritically Phase-Matched Second Harmonic Generations. Noncritical Optical Parametric Oscillators. Sum Frequency Generation. Optical Fiber Communication Systems: Chromatic Dispersion and Zero-Dispersion Wavelength. Thermo-Optic Switch. Optical Fiber Temperature Sensor. Thermo-Optic Modulators. References. Future Technology. Subject Index.

1.3-μm continuous-wave lasing operation in GaInNAs quantum-well lasers

Abstract: A 1.3-/spl mu/m continuous wave lasing operation is demonstrated, for the first time, in a GaInNAs quantum-well laser at room temperature. This lasing performance is achieved by increasing the nitrogen content (up to 1%) in GaInNAs quantum layer. It is thus confirmed that this type of laser is suitable for use as a light source for optical fiber communications.

Development of a fiber optic probe to measure NIR Raman spectra of cervical tissue in vivo.

Abstract: The goal of this study was to develop a compact fiber optic probe to measure near infrared Raman spectra of human cervical tissue in vivo for the clinical diagnosis of cervical precancers. A Raman spectrometer and fiber optic probe were designed, constructed and tested. The probe was first tested using standards with known Raman spectra, and then the probe was used to acquire Raman spectra from normal and precancerous cervical tissue in vivo. Raman spectra of cervical tissue could be acquired in vivo in 90 s using incident powers comparable to the threshold limit values for laser exposure of the skin. Although some silica signal obscured tissue Raman bands below 900 cm-1, Raman features from cervical tissue could clearly be discerned with an acceptable signal-to-noise ratio above 900 cm-1. The success of the Raman probe described here indicates that near infrared Raman spectra can be measured in vivo from cervical tissues. Increasing the power of the excitation source could reduce the integration time to below 20 s.

Strongly pumped fiber lasers

Abstract: Strongly pumped fiber lasers are analyzed, based on a rate equation model. Examples include Nd/sup 3+/-doped and Yb/sup 3+/-doped fiber lasers, with distributed Bragg reflector mirrors at either end. Approximate analytical and quasi-analytical expressions are shown to be in excellent agreement with the exact numerical solution of the rate equations, and both agree well with recently published experimental data.

In-situ real-time monitoring technique and apparatus for endpoint detection of thin films during chemical/mechanical polishing planarization

Abstract: A technique and apparatus is disclosed for the optical monitoring and measurement of a thin film (or small region on a surface) undergoing thickness and other changes while it is rotating. An optical signal is routed from the monitored area through the axis of rotation and decoupled from the monitored rotating area. The signal can then be analyzed to determine an endpoint to the planarization process. The invention utilizes interferometric and spectrophotometric optical measurement techniques for the in situ, real-time endpoint control of chemical-mechanical polishing planarization in the fabrication of semiconductor or various optical devices. The apparatus utilizes a bifurcated fiber optic cable to monitor changes on the surface of the thin film.

A femtosecond code-division multiple-access communication system test bed

Abstract: This paper reports comprehensive experimental results on a femtosecond code-division multiple-access (CDMA) communication system test bed operating over optical fiber in the 1.5 /spl mu/m communication band. Our test bed integrates together several novel subsystems, including low-loss fiber-pigtailed pulse shapers for encoding-decoding, use of dispersion equalizing fibers in dispersion compensated links for femtosecond pulse transmission and also in femtosecond chirped pulse amplification (CPA) erbium doped fiber amplifiers (EDFAs), and high-contrast nonlinear fiber-optic thresholders. The individual subsystems are described, and single-user system level experimental results demonstrating the ability to transmit spectrally encoded femtosecond pulses over a 2.5-km dispersion compensated fiber link followed by decoding and high contrast nonlinear thresholding are presented.

Gain-flattened tellurite-based EDFA with a flat amplification bandwidth of 76 nm

Abstract: We describe a tellurite-based Er/sup 3+/-doped fiber amplifier (EDFA) with a flat amplification bandwidth of 76 nm and a noise figure of less than 7 dB. Furthermore, a parallel-type amplifier composed of this EDFA and a 1.45-/spl mu/m-band Tm/sup 3+/-doped fluoride fiber amplifier achieved a flat amplification bandwidth of 113 nm.

Optical Coherence Tomographic Imaging of Human Tissue at 1.55 μm and 1.81 μm Using Er- and Tm-Doped Fiber Sources.

Abstract: We demonstrate two short-coherence-length, rare-earth-doped fiber optical sources for performing optical coherence tomography (OCT) in human tissue. The first source is a stretched-pulse, mode-locked Er-doped fiber laser with a center wavelength of 1.55 μm, a power of 100 mW, and a bandwidth of 80 nm. The second is a Tm-doped silica fiber fluorescent source emitting up to 7 mW of power at 1.81 μm with a bandwidth of 80 nm. The OCT imaging depth of penetration in in vitro human aorta is compared using these sources and conventional 1.3-μm sources. © 1998 Society of Photo-Optical Instrumentation Engineers.

Thermal effects in doped fibers

Abstract: A theoretical analysis of the pump-induced temperature change and associated thermal phase shift occurring in a pumped doped fiber is presented. Although the primary devices targeted are all-optical switches based on doped fibers, where such effects can be detrimental, this analysis is also applicable to lasers, amplifiers, and other doped fiber devices. The effects of a single pump pulse, multiple pulses and continuous wave (CW) pumping are investigated, both in the dynamic and steady-state regimes. Simple expressions are derived for the thermal relaxation time constant of a fiber, and for its steady-state temperature rise and thermal phase shift under CW pumping. This study predicts that in all-optical fiber switches utilizing a reasonably good dopant the thermal effect due to a single short pulse is negligible in all interferometers, while the steady-state effect can be sizable in a standard fiber Mach-Zehnder but is negligible in a twin-core fiber, a two-mode fiber, and a specially designed Mach-Zehnder interferometer.

Catheter guided by optical coherence domain reflectometry

Abstract: A guidance and viewing system based on multiplexed optical coherence domain reflectometry is incorporated into a catheter, endoscope, or other medical device to measure the location, thickness, and structure of the arterial walls or other intra-cavity regions at discrete points on the medical device during minimally invasive medical procedures. The information will be used both to guide the device through the body and to evaluate the tissue through which the device is being passed. Multiple optical fibers are situated along the circumference of the device. Light from the distal end of each fiber is directed onto the interior cavity walls via small diameter optics (such as gradient index lenses and mirrored corner cubes). Both forward viewing and side viewing fibers can be included. The light reflected or scattered from the cavity walls is then collected by the fibers and multiplexed at the proximal end to the sample arm of an optical low coherence reflectometer. The system may also be implemented in a nonmedical inspection device.

Sol-gel glass waveguide and grating on silicon

Abstract: This paper reports on the fabrication and characterization of hybrid organic-inorganic glass sol-gel slab and channel waveguides by ultraviolet light imprinting in thin films deposited by a one-step dip-coating process. The adjustment of chemical composition of the materials provides precise selection of refractive index from 1.48 to 1.52 at the wavelength of 632.8 mn. The refractive index of the waveguides at 1.55 /spl mu/m is similar to that of optical fiber, thus reducing the reflection loss between the two to less than 0.01 dB. The effect of ultraviolet light exposure and heat treatment on waveguide refractive index is studied. Fabrication parameters to produce ridge waveguides are optimized to achieve very smooth side walls. Propagation losses in these waveguides are /spl sim/0.1 dB/cm. Single mode buried waveguides, at 1.55 /spl mu/m wavelength, with circular mode profile are demonstrated.

Ionothermal delivery system and technique for medical procedures

Abstract: An Rf energy applicator with a working end that carries a bi-polar Rf electrode system for creating a Rf-tissue interaction or ionothermal effect in subsurface tissue (a first ionothermal system) which effect is focused by concurrent actuation of a photonic tissue-sensitizing system or photoconductance system (a second ionothermal system). The photonic energy system is adapted to create a "lens electrode" in subsurface tissue that enhances the targeted tissue's conductance of Rf current which serves as a means of focusing Rf ionothermal effects at a subsurface level. A dosimetry control system is provided that controls the dose and timing of Rf energy delivery as well as the dosimetry of photonic energy delivery. The ionothermal applicator has a handle portion coupled a tubular extending member. The distal termination of the probe has at least one pair of opposing conductive electrodes in a spaced relationship around a perimeter of the distal termination of the extending member. A remote Rf source (or generator) is connected to the device for delivering bi-polar Rf energy to the paired electrodes. An optical fiber (or fiber optic bundle) is provided in a central channel of the extending member which is capable of delivering a photonic (light) beam from a light source, such as a pulsed laser (or continuous wave (CW) diode laser).

Local birefringence measurements in single-mode fibers with coherent optical frequency-domain reflectometry

Abstract: Measurements of intrinsic and induced birefringence of optical fibers are performed at 1550 nm using the optical frequency-domain reflectometry technique. The experiment confirms the theoretical analysis, which predicts the appearance of oscillations on the detected Rayleigh backscattering intensity, with periods equal to the polarization beat length L/sub b/ and to L/sub b//2. Polarization mode-coupling length values are obtained from local birefringence and polarization mode dispersion measurements.