Abstract: Indiscriminately exciting the modes of a multi-mode optical fiber amplifier is avoided by an optical fiber amplifier design in which the excitation of pump modes in the core of a multi-mode fiber is controlled by controlling the pump light launching. The pump light is directed substantially along the center axis of a multi-mode fiber within a predetermined launch angle. Rather than exciting all modes, only lower order modes are affected.

Abstract: This invention is a new optical packaging and interconnection technology which is particularly effective in not only addressing the problem of attaching fiber pigtails to glass waveguide silicon devices, but also in isolating these waveguide devices from the deleterious effects of their external environment. An important aspect of the invention lies in the novel realization that the foregoing objectives may be achieved by covering the device with a thin silica coverplate affixed with a low index epoxy, which act as an extended cladding layer for optically confining the optical radiation below the coverplate.

Abstract: This invention is concerned with coupling optical energy efficiently by means of a microlens at an end of an optical fiber, the microlens being capable of improved coupling efficiency exceeding 55 percent (-2.5 dB), with coupling efficiencies of about 90 percent or more (less than 0.45 dB and as low as 0.22 dB loss) for uncoated lenses and of 95 percent or more for antireflection coated lenses being obtainable. An optimal microlens shape is substantially a hyperboloid of revolution having a relatively short focal length, f, e.g., for a mode radius of the optical device .omega..sub.0 =1 .mu.m and a mode radius of the optical fiber .omega..sub.1 =5 .mu.m, f.perspectiveto.12 .mu.m. The microlens having the substantially hyperboloid of revolution shape may be produced by laser micromachinning technique. The optical fiber with the novel microlens at its end may be used in optical communication packages comprising the fiber and an optical device.

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 .theta. 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.

Abstract: An apparatus and method are disclosed for fabricating an expanded beam cylindrical terminated optical fiber taper from a reduced diameter preform rod. The present invention comprises uniformly heating the circumference of a predetermined portion at an intermediate point of the preform rod to a predetermined temperature and then uniformly pulling the preform rod while continuing to heat additional material of the preform rod to produce a pair of expanded beam cylindrically terminated optical fiber tapers connected by a predetermined length cylindrical central section of standard optical fiber having a uniform diameter less than that of the original preform rod.

Abstract: An optical fiber is disclosed which comprises (a) a central core section of constant thickness which terminates in an outwardly gradually expanded end section, and (b) a cladding layer enveloping the core. Both the core and the cladding layer are of constant compositions throughout the fiber's length and width. Additionally, the difference between the refractive indices of the core and the cladding layer remains constant throughout the length of the fiber. Where the core gradually increases in width in the outwardly expanded end section of the fiber, the V number increases in like manner. In such optical fiber, propagation of a predetermined mode or modes is maintained throughout the entire length of the fiber, so long as the expansion of the end section occurs gradually over the order of many wavelengths.

Abstract: An access port assembly (10) for a main lightwave transmission fiber (16) is made by machining a notch (26) into it by carbon dioxide laser nibbling to form notch faces (28, 30) which extend into the core region (18). The end face (32) of a second, receiving fiber (12) is placed in contact with the notch faces (28) to optically couple it to the core (18) of the main fiber (16). An optical epoxy cement (34) holds the two members in position and matches and index of refraction. A third, transmitting fiber (14) is similarly connected to the main fiber (16) in a second notch and is perpendicular to the receiving fiber (12).

Abstract: A fused silica glass optical fiber 10 is machined by a pulsed infrared laser beam 20 from a carbon dioxide laser 22 focussed by a germanium lens 24. The beam has a power density of about 70,000 watts per square centimeter at the focussed machining region b and is pulsed at about one pulse per second with a one-half second pulse duration. The fiber workpiece edge is gradually brought into the beam from the side to result in progressive flash evaporation.

Abstract: The present invention relates to a mode scrambling arrangement for a multimode or graded-index optical fiber and, more particularly, to an optical fiber mode scrambler achieved by forming a deformation as, for example, a groove or notch on one side of the multimode or graded-index optical fiber orthogonal to the longitudinal axis thereof. The groove or notch can be produced by any suitable etching or machining process to extend through the cladding layer and at least very slightly into the outer surface of the core of the multimode or graded-index optical fiber. The depth of the groove or notch into the core can be controlled by monitoring the mode pattern in the multimode fiber during the etching or machining process to provide maximum mode scrambling with minimal loss.

Abstract: The invention relates to a hand-held device for detecting whether or not an optical fiber is carrying a light signal. The device includes a spring loaded hook for grabbing an exposed optical fiber anywhere along its length, thereby introducing microbending, a photodetector for responding to the presence of light emitted in the proximity of the microbend, and a light emitting diode connected by way of an amplifier to the photodetector for indicating when a light signal has been detected. Upon release of the spring loaded hook, the fiber returns to its normal state. The device can be easily modified to indicate not only the presence of a light signal, but also the strength of the signal and the direction in which the signal is being transmitted.

Abstract: Various techniques for examining the core region of optical fibers and fiber preforms involve placing a portion of the fiber/preform in an index-matching fluid and transversely illuminating the immersed portion. As described herein, the use of an index-matching fluid can be eliminated by illuminating the fiber/preform with a diverging beam. By the suitable selection of parameters, refraction at the air-fiber/preform interface can produce a well colliminated beam within the core region.

Abstract: Small, highly sensitive uv detectors are fabricated utilizing the fluorescence induced in the core of an optical fiber when illuminated by uv radiation. The fluorescence light is then guided by the fiber itself, by a similar fiber or by a different optical fiber to a remote location and detected by a standard v1 detector. To determine the intensity of the uv, the sensor is calibrated at the wavelength of interest.

Abstract: VAD torches include a plurality of coaxially aligned tubes. A typical outside diameter is about 1 inch. To fabricate smaller torch nozzles, spacers (20, 21, 22) are symmetrically placed between adjacent tubes (11, 12, 13, 14), and the entire tube assembly heated and drawn as a unit to reduce its diameter. The drawn tubes are then cut at a point along the reduced diameter region to produce a torch whose nozzle has the desired (i.e., reduced) diameter.

Abstract: Shaping of the refractive index profile of an optical fiber is typically achieved by changing the concentration of an index-modifying dopant within the glassy matrix preform. To measure the profile and the core diameter of the preform, in accordance with the present disclosure, the preform (10) is illuminated with a focused beam of ultraviolet radiation (15) whose beam width (w) is small compared to the preform core diameter (d). This induces a fluorescence along a thin pencil-like region (16) of the preform core whose intensity varies in proportion to the concentration of the dopant. Inasmuch as the latter is proportional to the refractive index, the intensity profile gives the index profile directly. A similar measure can also be made on fibers using microscopes for focusing the uv and observing the induced fluorescence. Use of this technique for controlling the rate at which a fiber is drawn is also described.

Abstract: A method of observing the core region of optical fibers and fiber preforms is disclosed comprising the step of inducing fluorescence in at least one of the index-modifying dopants present in the core being observed by illuminating said fiber/preform with radiation at the peak absorption wavelength for said dopant, and observing the region between the fluorescing edges of said fiber/preform. The core diameter can be determined by measuring the distance between said edges. This technique can be utilized to control the fiber pulling rate during fabrication.

Abstract: The refractive index profile of an optical fiber preform is controlled during manufacture by illuminating the gaseous precursor being fed to the preform substrate tube with ultraviolet radiation, measuring the intensity of either the uv that traverses the gas or the induced fluorescence, comparing this measurement with a reference signal, generating an error signal, in response to this comparison, and controlling composition of the gaseous precursor in response to said error signal. A similar technique can be used to control the thickness and refractive index of each layer deposited upon the substrate tube by forming an x-ray shadowgraph of the layers as they are deposited and comparing the shadowgraph characteristics with appropriate reference signals to form a second set of error signals. The latter are then used to fine tune the fabrication process. The invention can also be employed in conjunction with the vapor axial deposition method of fabricating preforms.

Abstract: A sensitive, nondestructive method of viewing the internal structure of multilayered optical fiber preforms is described. The method comprises the steps of transversely illuminating the preform, and intercepting the light that traverses the preform on a viewing screen. To obtain a complete picture, the preform is rotated 360 degrees about its axis. The technique provides a detailed view of the core size and eccentricity, and of the structure of the multilayered core.

Abstract: Techniques are disclosed for determining the distribution of dopants in optical fibers and fiber preforms by observing the reaction of a fiber/preform to uv illumination. One technique measures the fluorescence induced by the uv. A second method measures the absorption of uv by the dopants. Thus, by determining the intensity distribution of radiant energy from the fiber/preform, the dopant distribution can be determined as a function of distance from the center of the fiber/preform.

Abstract: An optical fiber is drawn from an appropriate preform using a laser whose output power is varied periodically at a rate greater than ten times a second. A fiber drawn in this manner has periodic variations in diameter which enhance the mode conversion properties of the fiber and thereby reduce the pulse dispersion of a signal transmitted through the waveguide.

Abstract: The concentricity or eccentricity of a plastic coating on an optical fiber is determined by monitoring the absence or presence, respectively, of a particular intensity peak in the backscattered light pattern generated by a light beam incident upon the fiber as the fiber is drawn, coated and pulled through the light beam. The particular intensity peak monitored results from the rays of minimum deviation which traverse the optical fiber only once as the incident rays are refracted and reflected through the coated fiber to form the backscattered light pattern. The position of the coating applicator is automatically adjusted if this intensity peak is electronically detected.