Showing papers on "Optical fiber published in 1985"

Distributed optical fibre Raman temperature sensor using a semiconductor light source and detector

Abstract: The letter reports on the first experimental measurements of the temperature distribution along silica-based optical fibres using a semiconductor laser source and an avalanche photodiode detector. Previous results by the same authors demonstrated the first use of the Raman scattering technique, but used a less practical ion laser source and a photomultiplier detector.

Guided acoustic-wave Brillouin scattering.

Abstract: Forward light scattering by the thermally excited guided acoustic modes of an optical fiber produce numerous narrow lines not predicted by the usual theory of Brillouin scattering. Optical heterodyne detection has been used to resolve the scattering spectrum which begins at about 20 MHz and extends to the detection limit. A simple theory quantitatively accounts for the frequencies, polarizations, and intensities of the components. The light scattering from these modes constitutes a thermal-noise source in optical fibers that may prove significant in other experiments.

Precision time domain reflectometry in optical fiber systems using a frequency modulated continuous wave ranging technique

Abstract: This paper describes a novel optical time domain reflectometer which uses a frequency-modulated single-mode semiconductor laser as the optical source. The new system offers a potential distance resolution of the order of 1 mm over ranges limited by the source linewidth. In this paper, a theoretical assessment of the features which determine the available performance of the system is followed by some experimental results which confirm these general trends. Applications of this system include short range fault location in situations where resolution of the order of centimeters is required, and as a novel discrimination technique for optical sensor multiplexing systems.

Method for producing glass preform for optical fiber

Abstract: A rod-in-tube method for producing a glass preform for use in the fabrication of an optical fiber, which comprises steps of inserting a glass rod (13) as a core material in a glass tube (12) as a cladding material, fusing and closing one end of the cladding material, filling a gap between the core and cladding materials with an atmosphere containing at least one gaseous halogen-containing compound and then heating the core and cladding materials at a temperature not lower than 1,900°C to collapse the gap between them and to fuse them together, from which glass preform, an optical fiber with low attenuation of light transmission is fabricated.

Method for impressing grating within fiber optics.

Abstract: A method of establishing a dielectric periodic index of refraction phase grating (16) upon the core (19) of an optical waveguide (15) by intense angled application of several tranverse beams (99) of ultraviolet light, enabling the establishment of a distributed, spatially resolving optical fiber strain gauge (13).

Visible fluorescence spectral diagnostic for laser angiosurgery

Abstract: A method of diagnosis of the type of tissue in an artery, including distinguishing artery wall from atheromateous plaque is described, in which a catheter with one or more optical fibers is enclosed at a distal end by an optical shield transparent to light radiation and wherein the proximal end of the catheter and optical fibers are coupled to a source of optical radiation. The catheter is inserted into an artery until the optical shield is brought into contact with a suspected arterial lesion or other tissue to be diagnosed. An optical fiber is selected and light coupled from the source at a wavelength of about 480 nm enters the proximal end of the optical fiber and is transmitted by the selected optical fiber to the distal end out the optical shield and impineges on the suspected lesion. The scattered and fluorescence light is returned to the proximal end of the selected optical fiber, and is coupled to a spectral analyzer wherein the fluorescence or scattered light excited by said light is analyzed to determine if the material contacted by the optical shield and, in particular, the portion irradiated by the incident light from the selected optical fiber is healthy arterial tissue or plaque or other material. This determination is made by observing at the proximal end of the selected fiber the fluorescence excited by the light to analyze the spectral profile in the range of 520-610 nm, where peaks occur. A determination is made from the ratios of fluorescence peak heights at 550 nm and 600 nm and the valley at 580 nm, or by analyzing other fluorescence wavelengths, whether the tissue being analyzed is artery wall, plaque, blood, or other tissue.

Coherence multiplexing of fiber-optic interferometric sensors

Abstract: This paper describes a method of multiplexing several optical signals onto a single spatial channel (eg, a single-mode fiber) using a short coherence length continuous wave light source Several system configurations which utilize this technique are proposed, and some design considerations are discussed Experimental results for a single sensor and receiver are presented and compared with theoretical predictions

Optical wave breaking of pulses in nonlinear optical fibers

Abstract: A new effect appears in femtosecond optical pulse compression, using single-mode fibers, that we describe as optical wave breaking. In the fiber, frequency-shifted light in the leading and trailing edges of a pulse overtakes unshifted light in the pulse tails. Mixing of these overlapping frequency components generates sidelobes on the pulse spectrum. The effect often leads to computational instabilities, but careful numerical simulations, including fiber loss, give results in excellent agreement with experiment.

Fiber optic ocular endoscope

Abstract: An ocular endoscope having a minimum cross-section and designed primarily for use in treating, diagnosing and investigating problems associated with the eye. The probe associated with the endoscope comprises a first bundle of fiber optics carrying light for illumination, a second coaxial bundle of fiber optics terminating in a lens and adapted to view areas being illuminated completely surrounded by a plastic sheath that is semi-rigid and malleable and capable of assuming and holding a preferred shape. In the preferred embodiment a cross-sectional area is elliptical and the sheath contains a port in the area of maximum curvature, which port is adapted to receive a probe. The probe is preferably malleable and may be hollow for accepting instruments or fiber optics connected to an external source of coherent light in the form of a laser for treating purposes.

Polarization-state control schemes for heterodyne or homodyne optical fiber communications

Abstract: In heterodyne or homodyne optical fiber communications, the fluctuation of the polarization state in the fiber may deteriorate the receiver sensitivity. This paper reviews the principles and features of six polarization-state control schemes so far proposed, including two new attempts, one using Faraday rotators and the other using rotatable fiber cranks (RFC's), both of which have been proposed very recently. Experiments simulating actual optical heterodyne receivers are also described.

Optical pulse compression to 8 fs at a 5‐kHz repetition rate

Abstract: Single amplified 40‐fs optical pulses are compressed to 8‐fs duration at a 5‐kHz repetition rate using self‐phase modulation in a single‐mode optical fiber.

Theoretical analysis of optical fiber laser amplifiers and oscillators

Abstract: Using the formalism of mode overlap, a theoretical analysis of optically pumped fiber laser amplifiers and oscillators is developed. The concept of normalized overlap coefficients is introduced to account for the effects of the transverse structure of the interacting signal and pump modes on the device characteristics. Simple and accurate closed-form expressions are derived for the gain of fiber amplifiers and the threshold and energy conversion efficiency of fiber laser oscillators in terms of the fiber and laser material parameters and the pump and signal modes. When applied to step-index Nd:YAG fiber lasers, this study predicts optimum fundamental mode oscillation in fibers with a V number of 5-25 with submilliwatt thresholds and nearly quantum-limited conversion efficiencies.

Monomode optical fibre interferometers for precision measurement

Abstract: The evolution of optical interferometers into extreme resolution large dynamic range sensors implemented in a guided wave form is discussed. The design and performance of fibre optic interferometric sensors optimised for specific periodic and quasi-steady-state measurands such as rotation, magnetic field, temperature, etc., are described.

Comparison of single-mode fiber dispersion measurement techniques

Abstract: This paper describes state-of-the-art techniques for characterizing dispersion in single-mode fibers. Special emphasis is placed on achieving high measurement accuracy within the 1.1-1.7 \mu m wavelength region.

Apparatus for producing a cylindrical pattern of light and method of manufacture

Abstract: The present invention discloses an optical radiating apparatus constructed on one end of a light-conducting optical fiber such that, upon encountering this radiator, light is caused to leave the fiber and radiate in a cylindrical pattern with respect to the central axis of the fiber. This optical radiator is constructed such that the pattern of radiated light is nearly uniform in intensity in a cylindrical pattern, without areas of light intensity significantly different from the average distribution around the circumference of the cylinder. The present invention also discloses a method to manufacture the above-described light radiating apparatus, ensuring uniformity of light intensity and the ability to transmit relatively intense light without developing regions of optical, thermal or mechanical damage, and without the need to reshape the core of the optical fiber.

Distributed, spatially resolving optical fiber strain gauge.

Abstract: A distributed, spatially resolving optical fiber strain gauge in which the core of the optical fiber is written with periodic grating patterns effective for transmitting and reflecting light injected into the core. Spectral shifts in the transmitted and reflected light indicate the intensity of strain or temperature variations at positions of the grating corresponding to the associated wavelengths of injected light.

Mode mixer for a laser catheter

Abstract: A mode mixer is described for mixing themodes of optical fibers in a laser catheter adapted to be inserted in arteries for treatment of arterial tissue or obstructions. The mode mixer creates microbends in the fibers by physically deforming the fibers, such as by mechanically pressing the fibers against a rigid member to adjust the spot size of light exiting the fibers.

Self‐induced polarization changes in birefringent optical fibers

Abstract: Exact solutions are presented for the intensity‐dependent polarization state of a light wave in a birefringent optical fiber. The theory takes into account both the linear polarization evolution and the nonlinear ellipse rotation. It is shown that, contrary to current belief, self‐induced polarization changes are possible even with equal excitation of the fiber’s principal axes. The theory is applicable to the operation of recently demonstrated fiber‐optic logic gates, pulse shapers, and intensity discriminators.

Experimental demonstration of soliton propagation in long fibers: loss compensated by Raman gain.

Abstract: With sufficient Raman gain to compensate exactly for net fiber energy loss, we have demonstrated distortionless propagation of 10-psec FWHM fundamental (N = 1) soliton pulses (λ = 1.56 μm) over a 10-km length of singlemode fiber. The implications of this experiment for development of an all-optical, high-bit-rate, long-distance telecommunications system are discussed briefly.

Fluid flow sensing apparatus for in vivo and industrial applications employing novel differential optical fiber pressure sensors

Abstract: An optical fiber fluid flow device is provided for in vivo determination of blood flow in arteries. The device includes a fiber optical fluid pressure measuring device having at least first and second optical fiber sensors which optical fiber sensors are positioned in the blood passage and in a restricted flow area in the blood passage and the two fiber optical pressure fluid sensors are connected to an interferometer associated with an opto-electronic demodulator which has an output signal representing the differential pressure between the two sensed area. The device also has utility in industrial applications.

Synchronous, asynchronous, and data rate transparent fiber optic communications link

Abstract: An optical fiber communications link which by means of pulse-width-modulation (PWM) encoding supports either synchronous or asynchronous data transmission and operation over a wide range of data rates. The link utilizes a PWM encoder which accepts either synchronous (clock plus data) or asynchronous (data only) binary inputs and generates a PWM encoded waveform. This waveform is transmitted via an optical transmitter, optical channel (e.g., fiber optics) and optical receiver to the PWM decoder which reconstructs the binary inputs. The optical receiver contains a receiver circuit for assuring automatic gain control regardless of the duty cycle. In the synchronous mode of operation the unsymmetrical clock output is restored to symmetry by using a clock symmetry restoration technique.

Spectral windowing of frequency‐modulated optical pulses in a grating compressor

Abstract: Spectral windowing or apodization of the spatially dispersed frequency components within a grating compressor has been used to control the temporal shape of compressed optical pulses. Windowing of undesirable high and low‐frequency components, which are not linearly chirped, results in nearly complete elimination of the energy in the wings of the compressed pulse. We have applied this technique to improve the quality of pulses from a mode‐locked neodymium: yttrium aluminum garnet laser compressed to less than 2 ps using a fiber and double‐pass grating pair with an internal aperture.

Generation and detection of squeezed states of light by nondegenerate four-wave mixing in an optical fiber.

Abstract: Nondegenerate four-wave mixing in a single-mode optical fiber is proposed as a method of squeezed state generation. An analysis of the near-degenerate mixing process for forward propagation in realistic fibers is presented along with the theory of an experimentally feasible detection strategy. The effects of the quantum nature of the optical nonlinearity and absorption are modeled by treating the fiber medium as a collection of anharmonic oscillators. Methods of suppressing undesired effects such as stimulated Brillouin scattering are presented as is a technique for providing the phase-shifted local oscillator wave necessary for the detection of squeezing. Preliminary experiments on fiber characterization and the detection of four-wave parametric fluorescence are described.

Hybrid optical integrated circuit

Abstract: A hybrid optical integrated circuit having a high-silica glass optical waveguide formed on a silicon substrate, an optical fiber and an optical device coupled optically to the optical waveguide, and an optical fiber guide and an optical device guide on the substrate for aligning the optical fiber and the optical device at predetermining positions, respectively, relative to the optical waveguide. Islands carrying electrical conductors are disposed on the substrate. A first electrical conductor film is formed on the substrate. Second electrical conductor films are formed on the top surfaces of the optical waveguide, the optical fiber guide, the optical device guide and the islands and are electrically isolated from the first electrical conductor film. An electrical conductor member is provided to feed electric power from the first and second electric conductor films to the optical device which needs the power supply. The optical waveguide, the optical fiber guide, the optical device guide and the islands are formed from the same high-silica glass optical waveguide film. Alignment of various portions is facilitated when assembling the circuit. A high coupling efficiency is realized with a low cost.

Optical guiding in a free-electron laser.

Abstract: By use of two-dimensional approximations for the equations that describe a high-gain free-electron laser (FEL) amplifier, and the properties of optical fibers, it is shown that the coherent interaction between the light and the electron beam in a FEL can optically guide the light. In the exponential-gain regime, the FEL performance in the presence of strong diffraction can be simply described by a cubic equation for the complex gain and the dispersion relation for an optical fiber. The phenomenon of optical guiding is illustrated with two-dimensional numerical simulations. The phenomenon has applications to short-wavelength FEL's, to directing of intense light, and to bending of x-rays.

Electrical and fiber optic connector assembly

Abstract: An electrical and fiber optic connector assembly terminates the electrical conductors and fiber optic transmission members of a cable so that the electrical conductors are electrically connected to electrical terminals latchably mounted in a housing member and for electrical connection to electrical paths of a circuit board and the fiber optic transmission members are optically connected to transmitting and sensing photoelectric devices which are mounted in the housing member and also electrically connected to electrical terminals latchably mounted in the housing member for electrical connection to electrical paths of the circuit board.

Fiber optic switch

Abstract: A fiber optic switch producing optical connections with very low light losses. The switch has constant mechanical and optical properties over long periods of operation. Adjusting elements act on the end of at least one light conductor to move the end face of the light conductor in the axial and transverse directions. The end face can then be moved opposite to and into contact with the end face of another light conductor.

Optical fiber coupler with tunable coupling ratio and method of making

Abstract: An optical coupler for single mode optical signals having a tunable (variable) coupling ratio, and a method of fabricating the coupler. A pair of virtually identical optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, each being tapered toward the waist in such a manner as to ensure adiabatic propagation of light in the structure. An optical signal carried by one fiber first passes through a decreasing taper region and then passes through an increasing taper region of one or the other fiber (or both). The decreasing taper rate of the input portion of one fiber is such that the optical signal radiates out of the core (where V=1 locally) and into the cladding, as it approaches the waist. The increasing taper rates of the output portions of the two fibers are such that a predetermined coupling ratio is obtained. The coupler is bent in the region of the waist whereby a coupling ratio can be selected between the incoming fiber portions having the decreasing taper and the outgoing fibers having increasing tapers.