Showing papers on "Optical fiber published in 1996"

Long-period fiber gratings as band-rejection filters

Abstract: We present a new class of long-period fiber gratings that can be used as in-fiber, low-loss, band-rejection filters. Photoinduced periodic structures written in the core of standard communication-grade fibers couple light from the fundamental guided mode to forward propagating cladding modes and act as spectrally selective loss elements with insertion losses act as backreflections <-80 dB, polarization-mode-dispersions <0.01 ps and polarization-dependent-losses <0.02 dB.

Optical fiber long-period grating sensors.

Abstract: We present a novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes. Temperature, strain, and refractive-index resolutions of 0.65 °C, 65.75 μ∈, and 7.69 × 10−5, respectively, are demonstrated for gratings fabricated in standard telecommunication fibers.

Hybrid fiber Bragg grating/long period fiber grating sensor for strain/temperature discrimination

Abstract: We demonstrate a novel sensor which uses the difference in strain and temperature response of fiber Bragg gratings and a long period fiber grating to discriminate between strain and temperature induced wavelength shifts. Sensor interrogation is performed entirely on the fiber Bragg grating reflection signals. Strain and temperature were simultaneously measured to /spl plusmn/9 /spl mu/strain and /spl plusmn/1.5/spl deg/C over a wide range of conditions.

Long-period fiber-grating-based gain equalizers.

Abstract: Long-period fiber gratings are used to flatten the gain spectrum of erbium-doped fiber amplifiers. A broadband amplifier with <0.2-dB gain variation over 30 nm is presented. We also show that a chain of amplifiers can be equalized, leading to a bandwidth enhancement by a factor of 3.

Fiber optic smart structures

Abstract: Fiber optic sensor technology has experienced tremendous growth since its early beginnings in the 1970's with early laboratory demonstrations of fiber optic gyros and acoustic sensors and the introduction of the first commercial intensity and spectrally based sensors. These early efforts were followed by a tremendous growth of interest in the 1980's when the number of workers in the field increased from perhaps a few hundred to thousands. The result was the introduction in the 1990's of the first mass produced fiber optic sensors that are being used to support navigation and medical applications. The number of fiber optic sensor products can be expected to grow tremendously in the years to come as rapid progress continues to be made in the related optoelectronic and communication fields. This paper provides an overview of some of the technologies being used to support fiber optic sensor development and how they are being applied.

Near-Field Optics: Theory, Instrumentation, and Applications

Abstract: THEORY AND INSTRUMENTATION. Imaging. The Tapered Optical Fiber and Other Sensing Elements. NSOM Theory. NSOM Instrumentation. Optical Tunneling Microscopes. PRACTICE. Contrast. Intensity. Polarization. Wavelength. Amplitude and Phase. Time. Plasmons. APPLICATIONS. Surface Chemistry. Biology. Materials Science. Information Storage. Non-Visible Wavelength Instruments. RELATED TECHNIQUES AND CONCLUSION. Related Techniques and Unusual Configurations. Conclusions and Future Directions. Index.

Noninvasive medical monitoring instrument using surface emitting laser devices

Abstract: A medical monitoring instrument such as a pulse oximeter uses vertical cavity surface emitting laser diodes (VCSELs) to produce at least two high intensity, essentially monochromatic light beams. The VCSELs are located either in: (1) the probe itself, (2) the connector to the probe, or (3) the monitor box connected with an optical fiber to the probe.

Broadband fiber optical parametric amplifiers

Abstract: The bandwidth of a single-pump fiber optical parametric amplifier is governed by the even orders of fiber dispersion at the pump wavelength. The amplifier can exhibit gain over a wide wavelength range when operated near the fiber's zero-dispersion wavelength. It can also be used for broadband wavelength conversion,with gain. We have experimentally obtained gain of 10-18 dB as the signal wavelength was tuned over a 35-nm bandwidth near 1560 nm.

Analysis of OH absorption bands in synthetic silica

Abstract: The presence of bound hydroxyl (SiOH) in silica is well known to produce an optical fundamental absorption band at about 2.7 μm. For optical fiber applications the influence of the corresponding overtones and combination modes on the absorption spectrum are of significant importance. A literature review is presented which reveals uncertainties regarding the correct absorption band intensities as well as their spectral positions. We present precise data on spectral position and relative intensities of OH absorption bands in state of the art synthetic silica. Our investigations cover the influence of different manufacturing techniques, OH content, and a comparison of bulk and fiber data. With the knowledge of the conversion factors between the intensities of different OH absorption bands it is possible to predict the entire OH related transmission performance of an optical component by measurement of a single absorption band, e.g., the fundamental mode at 2.7 μm or the 1.38 μm band in the low loss range of optical fibers.

Direct continuous-wave measurement of n(2) in various types of telecommunication fiber at 1.55 microm.

Abstract: A method for measuring the nonlinear refractive index of optical fibers with an error of less than 5% is demonstrated. The technique is based on measuring the nonlinear phase shift experienced by a dual-frequency beat signal, permitting a simple, highly sensitive, accurate, repeatable, and easily automated measurement procedure and sampling. Measurements of the nonlinear coefficient in standard telecommunication, dispersion-shifted, and a number of dispersion-compensated fibers are presented.

Fiber-optic evanescent wave biosensor for the detection of oligonucleotides

Abstract: An automated optical biosensor system based on fluorescence excitation and detection in the evanescent field of a quartz fiber was used to detect 16-mer oligonucleotides in DNA hybridization assays. A biotinylated capture probe was immobilized on the fiber surface via avidin or streptavidin. The hybridization with fluorescein-labeled complementary strands was monitored in real time by fluorescence detection. The double strands formed by hybridization could be dissociated by chemical or thermal regeneration, allowing one to perform hundreds of assay cycles with the same fiber. The signal loss during long-time measurements, i.e., consecutive hybridization assays, can be described by a single-exponential function. Over more than 200 cycles, the net signal decreased by 50% with a signal variation of 2.4% after correction for this signal loss. By binding the capture probe with the 5‘-end to the optical fiber surface, and by using a 50% (w/w) aqueous urea solution for chemical regeneration, the duration of an a...

Exact compensation for both chromatic dispersion and Kerr effect in a transmission fiber using optical phase conjugation

Abstract: We propose a new method to compensate exactly for both chromatic dispersion and self-phase modulation in a transmission fiber, where the light intensity changes due to fiber loss and amplifier gain. This method utilizes optical phase conjugation (OPC). The pulse shape is precompensated before OPC by transmission through a fiber with large dispersion. A computer simulation demonstrates effective compensation for waveform distortion in a 40 Gb/s NRZ intensity-modulated light transmission.

Optical Fiber Communication Systems

Abstract: The Communications Toolbox: Introduction. Probability and Random Variables. Some Important Probability Distributions. Signals and Systems. Random Processes. Spectral Analysis. Narrowband Signals and Systems. Elements of Detection Theory. From Light to Signals. Basic Optical Fiber Communications Components: Introduction. The Refractive Index and the Laws of Reflection and Refraction. Total Internal Refraction. Step Index Fibers and Slab Waveguides. Maxwell's Equations in the Slab Waveguide. Even Propagation Modes. Odd Propagation Modes. Number of Modes and Single-Mode Fibers. Phase Velocity. Group Velocity. Attenuation and Dispersion. Dispersion-Shifted and Dispersion-Flattened Fibers. Polarization-Maintaining and Single-Polarization Fibers. The P-N Junction. Single Heterostructure. Double Heterostructure. LED Physical Structure. The LED Rate Equation. LED Output Spectrum. LED Modulation Response. The Fabry-Perot Resonator. Semiconductor Laser Physical Structure. Laser Output Spectrum--Spectral Width and Linewidth. Bragg Reflections. Distributed Feedback (DFB) and Distributed Bragg Reflection (DBR) Lasers. Rate Equations. The Steady-State Solution to the Rate Equations. Laser Modulation--Step Response. Laser Modulation--Sinusoidal Frequency Response. Relative Intensity Noise (RIN), Phase and Frequency Noise, Chirp. Laser Package. The PIN Photodiode. The Avalanche Photodiode, ADP. Basic Binary Optical Communication System: Introduction. System Description. Performance Evaluation. Coherent Systems: Motivations and Basics. Fundamental Receiver Sensitivity--Homodyne Systems. Heterodyne Systems--Synchronous Detection. Heterodyne Systems--Asynchronous Detection. Heterodyne Systems--Weakly Synchronous Detection. Summary and Comparison of Fundamental Sensitivities. Optical Hybrids. Phase Noise and Linewidth. Synchronous Systems. Asynchronous Systems. Weakly Synchronous Systems. How to Deal with Phase Noise--Summary. Polarization Fluctuations. Appendix A--Statistics of Phase Noise to Amplitude Conversion. Appendix B--Evaluation of Averages by Quadrature Rules. Optical Amplifiers: Introduction. Semiconductor Amplifiers. Erbium-Doped Fiber Amplifier. Comparison of Major SOA and EDFA Characteristics. Other Fiber Amplifiers. Soliton Systems: Intuitive Explanation of Solitons. Advantages of Solitons for Long Distance Transmission. Derivation of Solitons. Amplitude, Duration, Energy, and Power. Higher-Order Solitons. Qualitative Physical Explanation of Solitons. Estimation of Peak Pulse Power Required for Solitons. Fiber Loss and its Compensation. Lumped Amplifiers in Soliton Systems. Polarization Dispersion. Amplified Spontaneous Emission Noise in Soliton Systems. Error Rates in Soliton Systems. Soliton Experiments. Using Recirculating Loops. Wavelength Division Multiplexing with Solitons. Bidirectional Soliton Systems. Sources of Soliton Pulses. Beyond the Gordon-Haus Limit. Multichannel Systems: Introduction. Time-Division Multiplexing (TDM). Wavelength-Division Multiplexing. Subcarrier Multiplexing. Code-Division Multiplexing. Space-Division Multiplexing. Network Issues.

Theory of fiber-optic, evanescent-wave spectroscopy and sensors.

Abstract: A general theory for fiber-optic, evanescent-wave spectroscopy and sensors is presented for straight, uncladded, step-index, multimode fibers. A three-dimensional model is formulated within the framework of geometric optics. The model includes various launching conditions, input and output end-face Fresnel transmission losses, multiple Fresnel reflections, bulk absorption, and evanescent-wave absorption. An evanescent-wave sensor response is analyzed as a function of externally controlled parameters such as coupling angle, f number, fiber length, and diameter. Conclusions are drawn for several experimental apparatuses.

Laser spectroscopy of atoms guided by evanescent waves in micron-sized hollow optical fibers.

Abstract: We report the first laser spectroscopic experiments on the Rb beam guided by blue-detuned evanescent waves in micron-sized hollow fibers. The two-step photoionization spectra show the long-range dispersive properties of dipole interaction between guided atoms and evanescent waves. A large enhancement factor of 20 in in the transmitted atomic flux is obtained at optimal conditions and the total guidance efficiency is estimated to be above 40%. The state- and species-selective guide with proper frequency detunings of the guide laser realizes in-line spatial separation of two stable Rb isotopes.

Virtual retinal display with fiber optic point source

Abstract: A virtual retinal display utilizes photon generation and manipulation to create a panoramic, high resolution, color virtual image that is projected directly onto the retina of the eye. The virtual retinal display includes a source of photons, the photons being modulated with video information and scanned by a scanning system in a raster type of pattern directly onto the retina of the user's eye. A single, monofilament optical fiber (300) of very small diameter couples light from the photon generator (308, 314) to the scanning system (16) so as to provide to the scanning system a point source of light at the fiber's exit aperture (306). The photon generator may utilize coherent or non-coherent light. Further, the photon generator may utilize color light emitters so as to scan a colored virtual image directly onto the retina of the user's eye.

The acousto-optic effect in single-mode fiber tapers and couplers

Abstract: All-fiber acousto-optic devices based on the null fused taper coupler have been successfully demonstrated as frequency shifters, variable splitters, switches and tunable filters. In this paper, the interaction upon which these devices are based has been extensively analyzed under a set of approximations that are valid in most cases. Simple analytical expressions for the important properties are derived, which provide a set of design rules for such devices.

Multiple wavelength generation with Brillouin/erbium fiber lasers

Abstract: Brillouin/erbium fiber lasers, which have recently been demonstrated, operate with a combination of Brillouin gain and gain in erbium-doped fiber. In this letter, we describe techniques for cascading the Brillouin/erbium fiber laser to generate optical combs, and experimentally demonstrate optical comb generation. Internal and external cascading techniques are demonstrated. The line spacing in the combs is approximately 10 GHz, with operation in the 1550-nm region.

Optical multiplexing device

Abstract: An optical multiplexing device spatially disburses collimated light from a fiber optic waveguide into individual wavelength bands, or multiplexes such individual wavelength bands to a common fiber optic waveguide or other destination. The optical multiplexing device has application for dense channel wavelength division multiplexing (WDM) systems for fiber optic telecommunications, as well as compact optical instrument design. Multiple wavelength light traveling in a fiber optic waveguide is separated into multiple narrow spectral bands directed to individual fiber optic carriers or detectors. An optical block has an optical port for passing the aforesaid multiple wavelength collimated light, and multiple ports arrayed in spaced relation to each other along a multiport surface of the optical block. A continuous, variable thickness, multi-cavity interference filter extends on the multiport surface of the optical block over the aforesaid multiple ports. At each of the multiple ports the continuous interference filter transmits a different wavelength sub-range of the multiple wavelength collimated light passed by the optical port, and reflects other wavelengths. Multicolor light passed to the optical block from the optical port is directed to a first one of the multiple ports on an opposite surface of the optical block. The wavelength sub-range which is "in-band" of such first one of the multiple ports is transmitted through that port by the local portion of the continuous, variable thickness interference filter there, and all other wavelengths are reflected. The light not transmitted through the first port is reflected to strike a second port, at which a second (different) wavelength band is transmitted and all other light again reflected. The reflected optical signals thus cascades in a "multiple-bounce" sequence down the optical block of the multiplexing device, sequentially removing each channel of the multiplexed signal. In reverse operation, individual channels are combined in the optical block and transmitted through the optical port.

Improved apparatus for picosecond pump‐and‐probe optical measurements

Abstract: We present an improved method for making pump‐and‐probe optical measurements in the picosecond to nanosecond time range. In this type of measurement, a pump light pulse is used to excite the sample and the resulting changes in the optical properties are investigated by means of a probe pulse that is time‐delayed relative to the pump pulse. In most measurements of this type, a mechanical stage is used to introduce the variable time delay of the probe pulse. As a result of imperfections in the stage motion, alignment problems, and divergence of the probe beam, it has been difficult to make accurate measurements when the time delay of the probe relative to the pump is in the range above a few hundred picoseconds. To overcome these difficulties, we have developed an apparatus that utilizes a single‐mode optical fiber. In order to demonstrate the performance of this system, we present results of experiments in which the flow of heat from a thin film into a substrate has been measured.

Fibre-optic evanescent field absorption sensor based on a U-shaped probe

Abstract: A fibre-optic evanescent field absorption sensor based on a U-shaped sensing probe is described. The influences of fibre core diameter, bending radius of the probe and the refractive index of the fluid on the sensitivity of the sensor are evaluated experimentally. The results are compared with the theoretical results obtained using geometrical optics and based on two-dimensional treatment. A good qualitative agreement is found between them.

Fiber optic linked flame sensor

Abstract: A fiber optic linked flame sensor for continuous optical monitoring of the combustion process within the combustion chamber of a gas turbine engine. The system includes a high temperature optical probe, a fiber optic cable, and electro-optics module. The high temperature probe is mounted on the engine skin and sighted in a manner so as to view the combustion process taking place at its origin just aft to the fuel nozzle. The appropriately constructed fiber optic cable connects the high temperature probe with the electro-optics module. The radiation transmitted via the fiber optic cable is then received by an ultraviolet photodiode located in the electro-optics module and coupled with appropriate electronics.

Optical fiber resistant to hydrogen-induced attenuation

Abstract: Improved single-mode optical waveguide fibers comprising a central core region, surrounded by an inner cladding region through which light at a chosen signal wavelength will propagate to an appreciable degree along with propagation of same in the central core region, the inner core region further surrounded by an outer cladding region, the improvement comprising germanium dioxide in the inner cladding region at a concentration within the range of about .005 percent by weight to about 1 percent by weight of said inner cladding region, effective to significantly reduce the concentration of oxygen atoms in the inner cladding region which are available to form defects that cause hydrogen-induced attenuation. Also provided are core preforms, overclad preforms, and processes for making the fibers, core preforms and overclad preforms.

SBS threshold of a fiber with a Brillouin frequency shift distribution

Abstract: The SBS threshold of a fiber with Brillouin frequency shift distribution along its length is investigated theoretically and experimentally. We obtain a simple equation for estimating the SBS threshold from the effective gain coefficient, which is calculated by using the Brillouin frequency distribution along its length. The dopant concentration dependence of the Brillouin frequency shift are measured for fibers with an F and GeO/sub 2/ codoped silica core. The evaluated frequency shift per unit of dopant concentration is 277 MHz/wt% and 45 MHz/wt% for F and GeO/sub 2/, respectively, at 1.55 /spl mu/m. The SBS threshold of a fiber with a nonuniform Brillouin frequency shift distribution prepared by the VAD method is investigated experimentally. The fiber exhibits 7 dB improvement in its SBS threshold. This value is in good agreement with one estimated by calculating the effective gain coefficient. This simple equation will be useful for estimating the SBS threshold of various fibers.

Laser-fabricated low-loss single-mode raised-rib waveguiding devices in polymers

Abstract: Organic polymeric materials offer a versatile medium for the creation of low-cost large-area optical guided-wave structures. In this work, we report on the use of a novel maskless laser-based microfabrication technique for the photochemical delineation of raised-rib single-mode waveguiding devices in polymers. This technology relies on accurate control of small refractive index differences (which is achieved by using intermiscible acrylate monomers), use of high-contrast photochemical response, as well as precise control of laser writing parameters. The devices reported here have cross-sectional dimensions and numerical apertures that match single-mode glass optical fibers. They exhibit very low losses of 0.03 dB/cm at 840 nm and exceptional thermal stability. We present the operational characteristics of bends, Y-branches, and directional couplers fabricated using this technology and compare these characteristics with those predicted from theory.

Fiber optic cable assembly for interconnecting optical fibers within a receptacle mounted within the wall of an enclosure

Abstract: The fiber optic interconnection apparatus includes a receptacle mounted at least partially within a wall of an enclosure, such as an optical network unit, a network interface device or a splice closure, and a fiber optic cable assembly for mating with the receptacle. By mating the fiber optic cable assembly with the receptacle in a predetermined aligned manner, one or more optical fibers of the fiber optic cable on which the fiber optic cable assembly is mounted can be optically interconnected with respective optical fibers held by the receptacle which extend through the receptacle and into the enclosure. Since the optical fibers which extend through the receptacle and into the enclosure may have been previously terminated, such as during the initial configuration of the enclosure in which the optical fibers are spliced or otherwise connected to other optical fibers or to active equipment within the enclosure, the fiber optic interconnection apparatus permits the optical fibers of the fiber optic cable to be appropriately terminated within the enclosure without requiring the enclosure to be opened. The components within the enclosure are therefore protected from damage which might otherwise result from opening the enclosure to terminate the optical fibers.

Principles of Lightwave Communications

Abstract: Light Propagation in Optical Fibres Optical Waveguides Dispersion and Attenuation in Optical Waveguides Optical Detection Theory Optical Receivers Heterodyne Systems Modes in Cylindrical Waveguides Delay and Dispersion in Linear Systems Shot Noise Bounds and Approximations Saddlepoint Approximation Optimal Linear Receivers DPSK Receiver Phase Noise.

Cross-phase modulation in fiber links with multiple optical amplifiers and dispersion compensators

Abstract: We have theoretically and experimentally investigated the cross-phase modulation (XPM) effect in optical fiber links with multiple optical amplifiers and dispersion compensators. Our theory suggests that the XPM effect can be modeled as a phase modulator with inputs from the intensity of copropagating waves. The frequency response of the phase modulator corresponding to each copropagating wave depends on fiber dispersion, wavelength separation, and fiber length. The total XPM-induced phase shift is the integral of the phase shift contributions from all frequency components of copropagating waves. In nondispersive fibers, XPM is frequency-independent; in dispersive fibers, XPM's frequency response is approximately inversely proportional to the product of frequency, fiber dispersion, and wavelength separation. In an N-segment amplified link, the frequency response of XPM is increased N-fold, but only in very narrow frequency bands. In most other frequency bands, the amount of increase is limited and almost independent of N. However, in an N-segment amplified link with dispersion compensators, the frequency response of XPM is increased N-fold at all frequencies if the dispersion is compensated for within each fiber segment. Thus, the XPM-induced phase shift is smaller in systems employing lumped dispersion compensation than in systems employing distributed dispersion compensation.

Extrinsic optical-fiber ultrasound sensor using a thin polymer film as a low-finesse Fabry-Perot interferometer.

Abstract: Theoretical and experimental aspects of an extrinsic optical-fiber ultrasound sensor are described. The sensor is based on a thin transparent polymer film acting as a low-finesse Fabry-Perot cavity that is mounted at the end of a multimode optical fiber. Performance was found to be comparable with that of a piezoelectric polyvinylidene dinuoride-membrane (PVDP) hydrophone with a sensitivity of 61 mV/MPa, an acoustic noise floor of 2.3 KPa over a 25-MHz bandwidth, and a frequency response to 25 MHz. The wideband-sensitive response and design flexibility of the concept suggests that it may find application as an alternative to piezoelectric devices for the detection and measurement of ultrasound.

Lasers and Electro-optics

Abstract: 1. Electromagnetic waves, light, and lasers 2. Optical frequency amplifiers 3. Introduction to two practical laser systems 4. Optical resonators containing amplifying media 5. Laser radiation 6. Control of laser oscillators 7. Optically pumped solid-state lasers 8. Gas lasers 9. Molecular gas lasers I 10. Molecular gas lasers II 11. Tunable lasers 12. Semiconductor lasers 13. Passive optical systems 14. Periodic optical systems, resonators and inhomogenous media 15. Optics of Gaussian beams 16. Optical fibers and waveguides 17. Optics of anisotropic media 18. The electro-optic and acousto-optic effects and modulation of light beams 19. Introduction to nonlinear processes 20. Wave propagation in nonlinear media 21. Detection of optical radiation 22. Coherence theory 23. Laser applications Index.