Showing papers on "Optical fiber published in 1984"

Compression of optical pulses chirped by self-phase modulation in fibers

Abstract: The use of self-phase modulation in a single-mode fiber to chirp an optical pulse, which is then compressed with a grating-pair compressor, has been shown to be a practical technique for the production of optical pulses at least as short as 30 fsec. We report the results of a theoretical analysis of this process. Numerical results are presented for the achievable compression and compressed pulse quality as functions of fiber length and input pulse intensity. These results are given in normalized units such that they can be scaled to describe a wide variety of experimental situations and can be used to determine the optimum fiber length and compressor parameters for any given input pulse. Specific numerical examples are presented that suggest that the technique will generally be useful for input pulses shorter than about 100 psec. For energies of a few nanojoules per pulse, the compressed pulse widths will typically be in the femtosecond regime.

The soliton laser.

Abstract: The soliton laser, a novel concept in ultrashort-pulse lasers, is a mode-locked laser using pulse compression and solitons in a single-mode fiber to force the laser itself to produce pulses of a well-defined shape and width. Thus the fiber is in one way or another involved in the laser’s feedback loop. Although the basic concept is a general one, we report here primarily on the first successful version[1], based on a sync-pumped, mode-locked color-center laser operating in the 1.5 pm region. To date this color-center soliton laser has directly produced pulses as short as 130 fsec, and has allowed for the production of pulses of as little as 50 fsec FWHM, by compression in a second, external fiber. Other advantages include wide tunability (limited only by power requirements for soliton production in the fiber), output pulses that are always transform limited, easy adjustment for production of ~sech2 pulse shape. and a relative simplicity of construction.

Dispersion in GeO2-SiO2 glasses.

Abstract: Germania glass was prepared from high purity GeO2 powder. Refractive-index dispersion was used to calculate material dispersion and to provide a model for representing the dispersion of GeO2–SiO2 glasses. The wavelength of zero material dispersion is found to be in agreement with theoretical calculations. Modal propagation is modeled for a GeO2 core–silica clad fiber. Results support compositional dependence of profile dispersion in GeO2–SiO2 fibers.

Generation of a train of soliton pulses by induced modulational instability in optical fibers.

Abstract: The modulational instability of a cw optical signal in a glass fiber combined with an externally applied amplitude modulation can be utilized to produce a train of optical solitons with a wide range of pulse width (50–1 psec) and repetition period (≲250 psec).

Optical-fiber delay line signal processing

Abstract: Optical-fiber delay line devices offer great potential1 for the processing of broadband signals due to the large modulation bandwidth and low loss of the optical fiber itself, which for the case of single-mode fiber can have values of the order of 100 GHz-km and fractional dB/km, respectively. Signals to be processed are intensity modulated onto optical carriers, and the processed output signals are obtained by detection after the optical signals traverse the optical fiber circuitry. This paper is intended to provide a general overview of the elementary forms of fiber circuitry that are useful for signal processing as well as the complex filters and systems that they Gan be used to construct.

Fiber-optic lattice signal processing

Abstract: We discuss the implementation of fiber-optic lattice structures incorporating single-mode fibers and directional couplers. These fiber structures can be used to perform various high-speed time-domain and frequency-domain functions such as matrix operations and frequency filtering. In this paper we mainly consider systems in which the signals (optical intensities) and coupling coefficients are nonnegative quantities; these systems fit well in the theory of positive systems. We use this theory to conclude, for example, that for such systems the pole of the system transfer function with the largest magnitude is simple and positive-valued (in the Z-plane), and that the magnitude of the frequency response can nowhere exceed its value at the origin. We also discuss the effects of various noise phenomena on the performance of fiber-optic signal processors, particularly considering the effects of laser source phase fluctuations. Experimental results are presented showing that the dynamic range of the fiber systems, discussed in this paper, is limited, not by the laser source intensity noise or shot noise, but by the laser phase-induced intensity noise. Mathematical analyses of lattice structures as well as additional applications are also presented.

Nature of wavelength chirping in directly modulated semiconductor lasers

Abstract: Relations are derived concerning the inherent connection between frequency deviations and the optical power wave-form of a directly modulated semiconductor laser, providing for the first time a quantitative assessment of inherent optical fibre dispersion penalties of directly modulated lasers. The relations also indicate that control of chirp involves only the control of the intensity modulation characteristics and proper current drive of semiconductor lasers. Experimental measurement of FM and IM characteristics of a 1.55 μm DFB laser support the results.

Fiber Optic Communications

Abstract: Preface. 1. Fiber Optic Communications Systems. 2. Optics Review. 3. Lightwave Fundamentals. 4. Integrated Optic Waveguides. 5. Optic Fiber Waveguides. 6. Optical Sources and Amplifiers. 7. Light Detectors. 8. Couplers and Connectors. 9. Distribution Networks and Fiber Components. 10. Modulation. 11. Noise and Detection. 12. System Design. Bibliography. Answers. Index.

Optical Communication Systems

Abstract: Part 1 Elementary discussion of propagation in dielectric waveguides material dispersion total dispersion in multimode and monomode fibres attenuation mechanisms in optical fibres inelastic scattering and non-linear propagation effects system considerations electromagnetic wave propagation in step-index fibre wave and ray propagation in graded-index fibres single-mode fibres the fabrication of fibres, cables and passive components fibre parameters specification and measurement. Part 2 Sources and detectors basic semiconductor properties injection luminescence the design of LEDS for optical communication the basic principles of laser action semiconductor lasers semiconductor lasers for optical fibre communication systems semiconductor photodiode detectors avalanche photodiode detectors and photomultiplier tubes. Part 3 The receiver amplifier the regeneration of digital signals coherent systems unguided optical communication systems optical fibre communication systems.

Heavy metal fluoride glasses and fibers: A review

Abstract: A comprehensive summary is provided on the subject of heavy metal fluoride glasses. This includes discussions on glass compositions, preparation, structure, fiber drawing characteristics, and intrinsic and extrinsic optical properties. Other relevant glass and fiber characteristics such as strength, durability, and thermal Shock resistance are also outlined. Particular emphasis is given to the measurements of optical attenuation in fluoride glasses and their potential for use in ultralow-loss fiber optic waveguides. An excellent bibliography of recent work in the area of heavy metal fluoride glasses has been generated for those seeking more detailed information on this topic.

The rotation of the polarization in low birefringence monomode optical fibres due to geometric effects

Abstract: Monomode optical fibres of very low intrinsic linear and circular birefringence have been developed for use in polarimetric optical fibre sensors, most notably the fibre optic current sensor. The polarization of light travelling along such fibres is known to be modified by external stress applied to the fibre. In this paper it is shown that the polarization state may also be rotated if the path of the fibre is bent in a nonplanar curve. A theory is developed which enables the effect to be quantified and the results are shown to agree with some measurements on a fibre bent into a helix.

Laser-heated miniature pedestal growth apparatus for single-crystal optical fibers

Abstract: We have designed and built a single‐crystal fiber growth apparatus. The apparatus employs novel optical, mechanical, and electronic control systems that enable the growth of high optical quality single‐crystal fibers. We have grown oriented single‐crystal fibers of four refractory oxide materials, Al2O3, Cr:Al2O3, Nd:YAG, and LiNbO3. These materials exhibit similar growth characteristics and yield fibers of comparable quality. Fibers as small as 20 μm in diameter and as long as 20 cm have been grown. Measured optical losses at 1.06 μm for a 10‐cm‐long, 170‐μm‐diam Cr:Al2O3 fiber were 0.074 dB/cm.

Optical fiber hydrogen sensor

Abstract: A new type of hydrogen sensor is reported in which an optical fiber is used as the sensing element. The fiber is coated with palladium which expands on exposure to hydrogen. This changes the effective optical path length of the fiber, which is detected by interferometric techniques. Preliminary experiments have demonstrated the effect and suggest a high sensitivity and a wide dynamic range for this kind of sensor. The experimental results are compared to calculated optical path length changes. Application of this kind of sensor to the detection of other chemicals appears feasible.

Versatile, efficient Raman sampling with fiber optics

Abstract: Description d'un systeme dans lequel la lumiere laser et la diffusion Raman ont pour support des fibres optiques. Cette technique permet des analyses dans des environnements hostiles

Alignment of Gaussian beams.

Abstract: The design of a coupling between a semiconductor laser and a single-mode fiber, or between any two optical or acoustical elements that support Gaussian modes, is presented as a trade-off among coupling efficiency T(a), offset misalignment tolerance d(e), and angular misalignment tolerance theta(e). We show that these three parameters are subject to a trade-off limitation which takes the form 0 < T(a)(1/2)theta(e)d(e) < or = lambda/pi, and we show how to design a coupling so that the upper bound on the alignment product T(a)(1/2)theta(e)d(e) is achieved.

Optical power limits in multi-channel wavelength-division-multiplexed systems due to stimulated Raman scattering

Abstract: General expressions are derived to estimate transmitter power limitations due to stimulated Raman scattering in wavelength-division-multiplexed optical communication systems. These results are applicable to systems containing an arbitrary number of channels with arbitrary (but equal) channel separation.

Measurement of light gradients and spectral regime in plant-tissue with a fiber optic probe

Abstract: A method is described in which light gradients and spectral regime can be measured within plant tissue using fiber optics. A fiber optic probe was made by modifying a single optical fiber (200 μm diameter) so that it had a light harvesting end that was a truncated tip 20–70 μm in diameter. The probe was a directional sensor with a half-band acceptance angle of 17–20°. Light measurements were made as the fiber optic probe was driven through plant tissue by a motorized micromanipulator, and the light that entered the fiber tip was piped to a spectroradiometer. By irradiating green leaf tissue of the succulent Crassula falcata L. with collimated light and inserting the probe from different directions, it was possible to measure light quality and quantity at different depths. Collimated light was scattered completely by the initial 1.0 mm of leaf tissue, which also greatly attenuated all light except the green and far-red. Light scatter contributed significantly to light quantity and had a pronounced spectral structure. Immediately beneath the irradiated surface the amount of light at 550 nm was 1.2 times that of the incident light. The light gradient declined rapidly to 0.5 times incident light at 1.4 mm depth. In contrast, the amount of light at 750 nm increased during the initial 0.5 mm to 2.9 times incident light and then declined linearly to 0.5 times incident light at the dark side of the leaf (4.5 mm). The implications of the magnitude of the contribution of light scatter to the light gradient is also discussed.

On the theory of backscattering in single-mode optical fibers

Abstract: A new theory of backscattering in single-mode fibers is presented. It allows backscatter waveforms to be predicted for fibers of any refractive-index profile or scattering-loss distribution. The results agree with experimental data and provide confirmation of an earlier, more restricted theory.

Optical fiber waveguides in radiation environments, II

Abstract: This paper will review recent progress in understanding the behavior of optical fiber waveguides when they are exposed to ionizing radiation. Not only have the growth and recovery of the radiation-induced attenuations been thoroughly characterized, in some cases the defect centers which cause these absorptions have been identified, and means for reducing the radiation sensitivity of the fibers have become apparent. The behavior of the radiation-induced loss is described in terms of parameters such as fiber composition and dopants, fiber structure, wavelength and intensity of the light source, temperature, total dose, time after irradiation, dose rate, and radiation history.

Chalcogenide glass fibers for mid-infrared transmission

Abstract: Chalcogenide glass fibers for mid-infrared transmission have been fabricated in As-S, As-Ge-Se, and Ge-S glass systems using high purity materials. The preparation of unclad, Teflon FEP clad, and chalcogenide glass clad fibers and their transmission loss characteristics are reported. It is found that appropriate glass compositions for drawing low-loss fibers are limited to the narrow ranges in the glass-forming regions. The minimum losses obtained are 35 dB/km at 2.44μm for As 40 S 60 unclad fiber, 182 dB/km at 2.12 μm for As 38 Ge 5 Se 57 unclad fiber, and 148 dB/km at 1.68 μm for Ge 20 S 80 unclad fiber. It is shown that hydrogen impurity absorptions and short-wavelength weak absorption tails seriously enhance loss in the fibers. It is also suggested that ultralow loss cannot be achieved due to the existence of the weak absorption tail. However, it is expected that the chalcogenide glass fibers can be used in short fiber-length applications such as in the remote monitoring and delivery of CO laser radiation. This is due to their wide operating wavelength ranges of 0.9-6\mu m for As-S, 1.3-9\mu m for As-Ge-Se, and 0.8-5\mu m for Ge-S, in which losses can be reduced to below 1 dB/m.

Numerical study of optical soliton transmission amplified periodically by the stimulated Raman process.

Abstract: Stability of optical solitons amplified periodically by the stimulated Raman process in a fiber is numerically studied for various ranges of parameters. A stable transmission of ≳10-G bit soliton train can be achieved by a careful choice of parameters with reasonably large amplifier spacings (≃30 km) and small soliton and pump powers (≃30 mW).

Generation and measurement of optical pulses as short as 16 fs

Abstract: We describe measurements of pulses consisting of only eight optical periods. The pulses were produced by compression with a short optical fiber and a grating pair. Measurement was by autocorrelation using noncollinear second harmonic generation in a thin crystal of potassium dihydrogen phosphate.

Apparatus and method for in-vivo measurements of chemical concentrations

Abstract: A method and apparatus in which a blunt interior needle is positioned within a larger external needle and a sample cavity is formed at the blunt end of the interior needle. An optical fiber extends from the sample cavity up the interior needle and to a light source and light detector. A reflective surface is placed at the end of the sample cavity reflects light back to the optical fiber. A beam splitter separates the incident and reflected light. To make an in-vivo measurement of chemical concentrations in a body, the needle is inserted into the body and fluids are aspirated into the sample cavity. Light is then transmitted to the cavity by the optical fiber and is transmitted from the cavity to a detector by the same fiber. By measuring the amount of light reflected, one can determine the amount of light absorbed in the cavity and may thus determine concentrations of selected chemicals.

Excimer laser delivery system, angioscope and angioplasty system incorporating the delivery system and angioscope

Abstract: A system for the delivery of high power excimer laser energy includes an optical fiber of pure silica having an energy coupler at one end and a lens at the distal end. The energy coupler can be a funnel-shaped input to the fiber or it can be a water-filled cavity which acts as a buffer to decrease the apparent density of energy entering the fiber. The lens at the distal end of the fiber functions to concentrate the output beam so as to increase its density. The delivery system has particular utility in the field of angioplasty. In such an application, the delivery system can be used to transmit both laser and illuminating light so as to reduce the number of optical fibers that are required and thereby provide a system that is sufficiently small to be fed into a coronary artery. An ultra-thin image scope facilitates a determination of the distance of the distal end from the viewed object and hence the size of the object.

80× single‐stage compression of frequency doubled Nd:yttrium aluminum garnet laser pulses

Abstract: Single‐stage compression factors as high as 80× have been demonstrated for the 0.532‐μm optical pulses of a frequency doubled Nd:yttrium aluminum garnet laser using a single‐mode fiber and a modified grating‐pair delay line. Input optical pulses of 33‐ps duration have been compressed to 0.41‐ps duration. This represents the largest single‐stage compression factor reported to date. Subpicosecond optical pulses can be obtained directly from relatively long optical pulses without the use of a mode‐locked dye laser.

Fiber optic POs probe

Abstract: A fiber optic probe to be implanted in human body tissue for physiologic studies involving measurement and monitoring of the partial pressure of gaseous oxygen in the blood stream, which is coursing through a particular blood vessel in the body. The use of the probe is based on the principle of dye fluorescence oxygen quenching. Structurally the probe comprises two 150-micrometer strands of plastic optical fiber ending in a section of porous polymer tubing serving as a jacket or envelope for the fibers. The tubing is packed with a suitable fluorescent light-excitable dye placed on a porous adsorptive particulate polymeric support. The tubing or jacket is usually made of a hydrophobic, gas-permeable commercial material, known as Celgard, but other suitable hydrophobic gas-permeable material could be used for such structure. The fiber optic probe of the invention is of very small size and flexible so that it can easily be threaded through small blood vessels which are located in a variety of tissues of the body.

Damage‐resistant LiNbO3 waveguides

Abstract: The photorefractive effect (‘‘optical damage’’) severely limits the application of LiNbO3 in visible wavelengths We have found that proton exchanged LiNbO3, in which up to 70% of the Li ions are replaced by protons, exhibit no measurable index change with average intensities of visible light up to 5 kW/cm2 or peak pulse intensities of ∼5×108 W/cm2 in the guide These experiments demonstrate that the photorefractive sensitivity of proton exchanged waveguides is at least four orders of magnitude lower than that of conventional titanium diffused guides Similar results are obtained with titanium diffused waveguides which are subsequently proton exchanged

Physical interpretation of Petermann's strange spot size for single-mode fibres

Abstract: Petermann's mathematical definition of spot size using the modal near field and its derivative is proved to be √2 times the inverse of the RMS width of the observable modal far field. The theory of fibre optics is given in terms of the transformed field, which determines the far field. Dispersion, splice loss and excitation efficiency are discussed.

Optical fibre sensors

Abstract: An array of optical fibre sensors comprises an optical fibre structure having a series of reflective discontinuities formed by spaced fusion splices between fibre elements of different refractive indices. The structure may comprise a number of equal long lengths of fibre 4 of one refractive index joined by short lengths of fibre 5 of a different refractive index. One end of each short length is fully fusion spliced to one long fibre length (no reflective interface) whilst either the other end is partially fusion spliced or an index matching medium is disposed between the other end and the other long length in order to obtain a single reflective interface. Alternatively, alternate long lengths of fibre (6,7) with different refractive index may be partially fused together at their ends to form reflective interfaces (8). Pairs of laser pulses of slightly different frequency passing along a fibre having equally spaced reflective interfaces are partly reflected to a detector where they are heterodyned to detect phase shifts due to deformation forces (eg acoustic waves) acting on the fibre.