Showing papers on "Fiber Bragg grating published in 1989"

Formation of Bragg gratings in optical fibers by a transverse holographic method

Abstract: Bragg gratings have been produced in germanosilicate optical fibers by exposing the core, through the side of the cladding, to a coherent UV two-beam interference pattern with a wavelength selected to lie in the oxygen-vacancy defect band of germania, near 244 nm. Fractional index perturbations of approximately 3 x 10(-5) have been written in a 4.4-mm length of the core with a 5-min exposure. The Bragg filters formed by this new technique had reflectivities of 50-55% and spectral widths, at half-maximum, of 42 GHz.

Efficient Er3+‐doped optical fiber amplifier pumped by a 1.48 μm InGaAsP laser diode

Abstract: Optical gain characteristics of an Er3+ ‐doped silica fiber have been studied by end pumping with a 1.48 μm InGaAsP high‐power laser diode. A gain as high as 12.5 dB was obtained for an absorbed pump power of 16 mW with a 3‐m‐long fiber. By constructing an Er3+ fiber ring cavity with a 3 dB single‐mode fiber coupler, we have obtained continuous wave laser oscillation at a wavelength of 1.553 μm.

Method and apparatus for fabricating microlenses on optical fibers

Abstract: This invention concerns with a process and apparatus for fabricating microlenses on optical fibers. A pulsed laser beam and an end portion of a fiber are arranged relative to each to another so that the laser beam is incident on the end portion of the fiber at an acute angle θ to the longitudinal axis of the fiber. The angle is selected to attain a desired curvature of a lens formed by ablation and heating of the end portion of the fiber by the laser beam. A movement of the fiber and the laser relative each to another results in progressive engagement of the end portion of the fiber with the laser for a preselected distance so as to produce a short taper with a lens at the end thereof. In the preferred embodiment, the fiber rotated about its axis within a passage of the holder which moves the end-portion of the fiber into and through the laser beam resulting in the said lens. The precise repeatability of the lens formation may be controlled by a computer.

Fiber optic sensors

Abstract: Serveral improvements in fiber optic sensing systems are disclosed. One improvement incorporates a dielectric filter applied directly to the sensing end of an optical fiber detector which has the characteristic that it reflects back a reference light beam of one wavelength while passing a sensing signal of a different wavelength which is modulated in some predetermined fashion beyond the filter. Both light signals are reflected back through the fiber and are, accordingly, attenuated in the identical or nearly identical fashion in response to various noise sources. The ratio of the intensity of the two signals is proportional to the sensed parameter and renders the system essentially self-compensating. The dielectric filter is preferably directly coated onto the exit end of the fiber through vapor deposition techniques. Time division multiplexing is used to sequentially fire plural light sources and a single photodetector is used for measuring the intensity of the reflected back signals of the various wavelengths. Another improvement encompasses the detection unit in which the input and reflected signals are separated using an off-axis parabolic mirror which provides excellent separation efficiency. According to another principal feature of this invention, a concave surface is formed at the fiber end which increases the numerical aperture of the fiber which provides greater sensitivity to the deflection of a pressure sensitive diaphragm spaced from the confronting the fiber end.

Temperature compensated fiber-optic pressure sensor

Abstract: A pressure sensor comprises a chamber formed from two members micromachined in silicon or a similar substance. The members define a chamber with at least one pressure sensitive membrane and an optic fiber extending through the chamber parallel to the membrane. The membrane may have an optical grating formed thereon which may be coated with a surface plasmon supporting substance. Light is injected into the fiber with a wavelength that couples with the grating on the membrane, either in a Bragg relationship or in coupling to a surface plasmon. The coupling, and thus the light lost from the fiber, varies with separation between the membrane and fiber and thus with the pressure outside the chamber. The members also include a thicker wall which is not pressure sensitive but which couples with an identifiably distinct portion of the light in the optic fiber to provide a temperature compensated reference. The pressure sensor can be made very small and rugged for combustion chamber pressure sensing in an engine and for other uses where very small pressure sensors are required.

Optical integrated circuit and optical apparatus

Abstract: An optical integrated circuit and an optical apparatus used in optical communication or an opto-electronics apparatus such as an optical disk recording apparatus, in which various kinds of aberration caused by wavelength variation of a light source when a semiconductor laser is used as the light source. An aberration correcting grating having such grating pitches as to nearly satisfy the Bragg condition preferably with respect to a certain wavelength of the semiconductor laser beam is used. As a result, lowering of incidence (entrance) and radiation (exit) coupling efficiencies of the grating coupler and aberration such as chromatic aberration can be prevented. Even if a multi-mode semiconductor laser is used as a light source, the characteristics of the optical integrated circuit and optical apparatus do not vary largely.

High channel density, broad bandwidth wavelength division multiplexer with highly non-uniform Bragg-Littrow holographic grating

Abstract: A wavelength division multiplexer/demultiplexer having optical path lengths between a fiber array and a Fourier transform lens, and between a dispersion grating and the lens equal to the focal length of the lens. The equal optical path lengths reduce losses due to angular acceptance mismatch in the multiplexer. Close orientation of the fiber array about the optical axis and the use of a holographic dispersion grating reduces other losses in the system. Multi-exposure holographic dispersion gratings enable the multiplexer/demultiplexer for extremely broad-band simultaneous transmission and reflection operation. Individual Bragg plane sets recorded in the grating are dedicated to and operate efficiently on discrete wavelength ranges. A volume Bragg vertically non-uniform holographic grating enables operation of the multiplexer or other devices that act on light waves according to wavelength over nearly the full usable 0.8-1.3 μm wavelength range.

Laser catheter system

Abstract: A fiber optic device for remote delivery of intense ultraviolet optical signals comprising an excimer laser source and an optical fiber. The output of the pulsed, transverse discharge, high pressure laser source is coupled to an articulating reflection mechanism which directs the pulsed laser output to an input end of the optical fiber. The optical fiber serves to transmit the light from the laser source to a remote location or target. The excimer laser further comprises a segmented first elongated laser electrode and a coextensive second laser electrode which is substantially solid. The discharge is stabilized by inductors connected to each segment of the first electrode and further by preionization electrodes located adjacent and coextensive with the second electrode. The preionization electrodes comprise a central conductor surrounded by a dielectric sleeve. The laser further comprises a closed gas system for the lasing medium gas. The gas system comprises a circulating blower, a heat exchanger and a cryogenic trap. The optical fiber comprises a central core having a substantially constant index of refraction and a cladding having an index of refraction which varies as the radius of the cladding. Thus, the invention advantageously permits high intensity ultraviolet light to be generated over extended periods of time utilizing a sealed laser and furthermore delivers the high intensity ultraviolet light to a remote location through an optical fiber with minimal damage to the fiber. The system is particularly well suited for application as a percutaneously introduced laser angioplasty system for removal of vascular obstructions.

Miniature fiber optic pressure sensor

Abstract: A pressure sensor comprises a chamber formed from two members micromachined in silicon or a similar substance. The members define a chamber with at least one pressure sensitive membrane and an optic fiber extending through the chamber parallel to the membrane. The membrane has an optical grating formed thereon which may be coated with a surface plasmon supporting substance. Light is injected into the fiber with a wavelength that couples with the grating on the membrane, either in a Bragg relationship or in coupling to a surface plasmon. The coupling, and thus the light lost from the fiber, varies with separation between the membrane and fiber and thus with the pressure outside the chamber. The members may also include a thicker wall which is not pressure sensitive but which couples with an identifiably distinct portion of the light in the optic fiber to provide a temperature compensated reference. The pressure sensor can be made very small and rugged for combustion chamber pressure sensing in an engine and for other uses where very small pressure sensors are required.

Fiber embedded grating frequency standard optical communication devices

Abstract: A narrowband laser source includes an optical fiber section including a core centered on a longitudinal axis and a cladding surounding the core, and having a grating region embedded in the core. The grating region includes a multitude of Bragg grating elements extending with a substantially equal longitudinal spacing substantially normal to the longitudinal axis for the grating region to significantly reduce the amount of light passing therethrough when the frequency of such light is in a predetermined narrow range around and including a predetermined center frequency, to an extent proportionate to the deviation of such frequency from the center frequency. A portion of the light emitted by a laser at a frequency dependent on the amount of electric energy applied to the laser is supplied into the core of the fiber section for propagation toward the grating region. The amount of light passing through the grating region is detected, and the amount of energy applied to the laser is varied in dependence on the extent of deviation of the frequency of such light from the center frequency in such a sense as to reduce the extent of such deviation.

Device for compensating for thermal instabilities of laser diodes

Abstract: The present invention proposes a dielectric waveguide formed on a substrate of ultra-low thermal expansion glass which is assembled with a commercially available diode laser to create a temperature stabilized laser. The waveguide comprises multiple dielectric films which have equal and opposite temperature induced changes in refractive index with respect to each other into which is formed a Bragg grating, the grooves of which are sufficiently shallow to allow penetration of light into the waveguide of 1 mm to 1 cm. This provides a signal which is both narrowband and frequency stable so that the optical signal can be guaranteed to remain in a given narrow frequency band. The dielectric layers are deposited using ion assisted deposition (IAD) to provide uniform, high density films with reduced index-temperature coefficients and increased density, resulting in a waveguide with near-zero temperature variations in refractive index. After fabrication, the waveguide is assembled to the diode laser, creating a temperature stabilized laser which operates within 1 Å of the target wavelength over the temperature range from 20° C. to 70° C. In one embodiment a temperature stabilized laser is used to pump a Nd:YAG laser providing a stable, high power optical signal.

Observation of ultrafast nonlinear polarization switching induced by polarization instability in a birefringent fiber rocking filter

Abstract: Ultrafast all-optical switching between two orthogonal linear polarizations in a periodically twisted fiber filter is discussed. The dependence of the switching characteristics on the input power and operating wavelength is considered. >

Erbium-doped fiber amplifier coupling device

Abstract: This invention is directed toward reducing substantially the loss incurred when two optical fibers of different mode diameters are coupled together. In this invention, the coupling of one fiber to that of another where the fibers are of different mode diameters is not with a tapered fusion, core-to-core splice, but with an evanescent field fiber coupler. Briefly, to achieve amplification of a weak optical signal, an amplifying fiber is inserted into the system at one or a plurality of locations. More specifically, at a desired location, the transmission fiber is severed to provide two sections and the severed sections are transversely coupled to the amplifying fiber. The weak signal from the first section of the transmission fiber is coupled into the amplifying fiber via a first evanescent field type of fiber coupler; and the amplified signal is coupled from the amplifying fiber to the second section of the transmission fiber via a second evanescent field type of fiber coupler. The first evanescent field type of fiber coupler is designed to couple substantially all of the signal energy from the first section of the transmission fiber to the amplifying fiber and to couple substantially none of the laser diode pump signal or energy from the amplifying fiber to the transmission fiber. The second evanescent field type of fiber coupler is designed to couple substantially all of the signal energy in the amplifying fiber to the transmitting fiber and substantially no laser diode pump energy is transferred from the amplifying fiber to the transmission fiber. Either or both cut ends of the transmission fiber can be coupled to monitor devices to detect and determine the value of the signal being coupled into and/or out of the amplifying fiber to control, for example, the gain of the amplifying fiber.

Optical device with mode selecting grating

Abstract: An optical fiber has a beveled end surface and a Bragg reflector grating formed on the end surface to form a single mode reflector for a semiconductor laser. A transmission fiber with a beveled end is fused to the beveled grating to form a continuous transmission line having an internal reflective grating.

Broadband optical fiber laser

Abstract: An optical fiber laser includes a single-mode optical fiber doped with a lasing material such as Neodymium. The optical fiber is pumped with a pump optical signal having a pump wavelength selected to cause spontaneous emission of an optical signal at a second wavelength different from the pump wavelength. The optical fiber is formed into a laser cavity such as by including a suitable reflector at each of the two ends of a suitable length of the optical fiber so that the emitted optical signal oscillates therein. One of the reflectors has a reflectivity at the wavelength of the emitted light so that most (e.g., approximately 95%) of the emitted light is reflected back into the laser cavity and a smaller portion (e.g, approximately 5%) is transmitted through the mirror as a laser output signal. Alternatively, the optical fiber can be formed into a ring laser structure using an optical coupler that couples a substantial portion (e.g., approximately 95%) of the emitted light back into the ring for recirculation therein and provides a smaller portion of the emitted light (e.g., approximately 5%) as a laser output signal. The wavelength of the pump optical signal is selected to be outside the pump variable tuning range of the Neodymium-doped optical fiber (i.e., the range of pump wavelengths which stimulate emitted wavelengths having a average wavelengths with a generally one-to-one correspondence to the pump wavelength). Pumping with a pump signal outside the pump variable tuning ranges causes the emitted light to have a broad spectral envelope of longitudinal modes having emission wavelengths corresponding to substantially all the pump variable tuning range. Thus, by pumping the optical fiber with a single pump wavelength, a broadband laser output signal is generated.

Coupling of multiple laser beams to a single optical fiber

Abstract: An apparatus and method for coupling a parallel array of laser beams into a single optical fiber. The increased optical laser power, if that of helium-neon lasers, can be used for photodynamic therapy of cancer with hematoporphyrin derivatives.

Doped optical fiber laser amplifier

Abstract: An erbium-doped fiber laser amplifier (1), characterized by the fact that said fiber (3) is doped to a concentration lying in the range 5 ppm to 50 ppm, that the length of said fiber lies in the range 250 m to 30 m depending on the selected concentration of doping, and that the radial position of the doped zone substantially coincides with the energy maximum of the set of propagation modes in said fiber at the pumping wavelength.

Er-doped optical fiber laser device

Abstract: An Er-doped optical fiber laser device adapted for pumping by light from a pumping light source in an erbium (Er)-doped optical fiber which enters a single mode at the wavelength of amplified light. In accordance with the present invention, the Er-doped optical fiber is further doped with at least one of holmium (Ho), thulium (Tm) and dysprosium (Dy). The pumping light source emits light in a 1.1 to 1.4 μm band. The output light from the pumping light source and signal light incident to the Er-doped optical fiber are combined by a combining optical fiber coupler.

Multi-core optical waveguide bragg grating light redirecting arrangement

Abstract: An optical waveguide light redirecting arrangement includes an optical waveguide having at least two solid portions each of which guides light in a path along a longitudinal axis, with at least one grating region being embedded in each solid portion. Each grating region includes a multitude of grating elements extending at such identical longitudinal spacings and at such an identical angle relative to the longitudinal axis as to redirect light reaching the grating elements between the path of one and the path of the other of the waveguiding portions.

Mode-locked fiber laser with a fiber phase modulator.

Abstract: FM mode-locked operation of a single-mode Nd3+-doped fiber laser has been achieved with an integrated fiber phase modulator. The technique permits a low-loss cavity configuration, resulting in low threshold and high slope efficiency. Pulses of ~200psec duration are observed at a repetition rate of 417 MHz with an average output power of 15 mW.

Fiber optic laser beam delivery system

Abstract: The invention relates to a laser light beam delivery system for delivering a laser light beam from a source remote from the laser originating the light. The delivery system consists of an optical fiber having a double taper, i.e., a taper portion at each end with the fiber tapering at the input end and at the output end to a diameter substantially greater than the actual diameter of the fiber. This permits high power transmission capabilities in as much as the greater diameter portions distribute the average energy such that no damage to the fiber is presented.

Compound Bragg reflection filters made by spatial frequency doubling lithography

Abstract: A report is presented on the fabrication of complex Bragg filters with resonant wavelengths near 1.55 mu m, patterned by photolithography using a high-resolution deep ultraviolet stepper. The projection of gratings with quarter-micrometer features was made possible by the use of spatial frequency-doubling lithography. A single chip, processed entirely in the silicon facility, was used to demonstrate five Bragg reflectors of different wavelengths, a quarter-wave shifted resonator, broadband stacked filters with as many as 15 uniform Bragg reflector sections of different Bragg wavelengths, and broadband stacked filters containing a passband within the reflection band. The filters exhibited nearly ideal spectral behavior. >

Bragg gratings on InGaAsP/InP waveguides as polarization independent optical filters

Abstract: The fabrication and operation of Bragg gratings for future wavelength-division multiplexing (WDM) devices in integrated optical circuits are discussed. Crosstalk attenuation of more than 20 dB with respect to the optical power and spectral bandwidths of up to 2.2 nm were achieved. Polarization-independent operation of the gratings, an important qualification for their operation in fiber optical transmission systems, was demonstrated with a filter bandwidth of 0.2 nm at -10 dB and channel spacings as small as 1 nm. >

Fiber optic probe for measuring reflectance spectrum

Abstract: In an fiber optic probe for measuring reflectance spectrum, a light illuminating optical fiber 1 and a light receiving optical fiber 2 are coupled in parallel to form a fiber bundle (3). A lens (4) is provided over end surfaces of the light illuminating optical fiber and the light receiving optical fiber at the end portion of the fiber bundle. The fiber bundle is inserted in a heat shrinkable polyethylene tube and the tube is shrunken by heat to form a coating layer (6). The coating layer extends toward the end of the fiber bundle to cover the periphery of the lens, so that the lens is fixed to the fiber bundle.

Photorefractive effect in bulk glass and devices made therefrom

Abstract: The photorefractive effect results in a change in the refractive index of bulk chalcogenide glass when it is exposed to certain wavelengths of light, in particular, sub-band-gap light. The effect results in a variety of device structures including a fiber optic faceplate; an optical waveguide; a fiber tap; a lens and a Bragg grating. Methods for fabricating the various devices are described.

Distributed bragg reflector laser for frequency modulated communication systems

Abstract: To overcome the deleterious effects of the nonuniform frequency modulation response in semiconductor lasers due to current injection in direct frequency modulation applications, it has been determined that the linewidth enhancement factor α be made as large as possible. In one embodiment, distributed Bragg reflector lasers well suited for frequency modulation lightwave communication systems are designed to have an integrated feedback element such as a corrugation grating whose effective pitch is selected to cause the Bragg wavelength and, therefore, the laser operating wavelength to be longer than the wavelength at substantially the maximum gain or gain peak in the semiconductor structure. That is, the wavelength of the grating is effectively detuned toward the longer wavelength and lower energy side of the peak of the gain profile. Such detuning increases the linewidth enhancement factor in such a way that the nonuniform frequency modulation response and its effects are minimized and, in some cases, substantially eliminated.

Gain compression and asymmetric gain due to the Bragg grating induced by the standing waves in Fabry-Perot lasers

Abstract: The Bragg grating induced by the pattern of standing waves in a Fabry-Perot laser diode is shown to give a significant contribution to nonlinear gain. An analytic expression is derived for the contribution leading to a simple universal relation between the damping rate of relaxation oscillations, the square of the relaxation resonance frequency, and the carrier diffusion time. The effect of the standing wave grating cannot explain present data from various experiments, which indicated that there must be additional important contributions to nonlinear gain. >

Fiber optic safety system

Abstract: A system for detecting energy leakage from an optical fiber transmitting high power laser beams. A second optical fiber is placed together with the laser power transmitting fiber into a jacketing tube or conduit. The second fiber is connected at one end to a light source and at the other end to a photosensitive diode. Leakage of laser energy from the power transmitting fiber will cause a failure of the second optical fiber, reducing or terminating the transmission of light to the photosensitive diode. Energy leakage from the laser power transmitting fiber can therefore be detected by monitoring the output of the photosensitive diode.