Abstract: A passive optical attenuating device comprises an optical waveguide adapted to receive optical radiation and absorb, along its length, at least 0.2 dB/m of the optical radiation. The waveguide section may be coupled to a low-loss optical fiber so as to receive an optical signal to be attenuated therefrom. In accordance with one aspect of the invention, at least one region of the waveguide is doped with a transition metal to achieve a pre-selected absorptivity per unit length so that a controlled degree of attenuation can be achieved.

Abstract: In accordance with the invention, an optical four-wave mixer for producing a phase-conjugated signal comprises a source of optical input signals, a fiber laser for receiving the signals, and a detector for selectively detecting the frequency-shifted signals produced by four-wave mixing. The laser can be a rare-earth doped fiber laser with a fiber cavity phase matched to the input signals. The frequency-shifted output signals have an inverted spectral waveform as compared with the input signals. The mixer can be made in compact form with a cavity length as small as 100 m and can provide inverted signals at the same intensity as the input signals, making the mixer particularly useful for providing spectral inversion in an optical communications system.

Abstract: Signal energy in an installed optical fiber is extracted without using a physical connector, by an improved process in which the fiber is bent to within a prescribed range of angles, then controllably heated, and thereafter controllably cooled. The resulting structure exhibits relatively low permanent stress. A fiber end conventionally placed at the bend point receives unusually useful amounts of optical signal which can be routed to optical branch circuits in, for example, a building or a LAN.

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: Applicants have discovered photo-induced second harmonic generation in rare earth doped glass bodies free of germanium. Moreover, applicants have discovered that multivalent rate-earth doped glass bodies can be made with conversion efficiency of second harmonic generation in excess of 10.sup.-3 % per watt, exceeding the reproducible efficiency of germanium doped glass. In accordance with the invention, a light source of a desired frequency comprises a body of glass doped with a multivalent rare earth element, an optical input source of light at one-half the desired frequency, and utilization means for receiving light passing through said body and utilizing light at the desired frequency.

Abstract: Reproducible doped optical fiber preforms having a predetermined dopant concentration level are fabricated by inserting a doped filament into a completed preform prior to consolidation and final collapse so that the filament and dopant materials are centrally located in the core region upon formation of the preform. Doped fiber is drawn from the doped preform using standard fiber drawing techniques.

Abstract: This invention is a rare earth doped optical amplifier with increased gain and lowered pump thresholds. The amplifying scheme is based on a 3 level lasing system rather than the more prevalent 4 level lasing system. Additionally, the transmission mode of the optical fiber at the pump wavelength has a radius which is substantially equal to or greater than the radius of the distribution profile of the rare earth ions in the fiber amplifier core. With the inventive amplifier, a gain of 37 dB and a saturation power of 11.3 dBm has been obtained with only 54 mW of launch power at .lambda.=1.49 .mu.m.

Abstract: It has been discovered that fused silica doped with approximately equimolar amounts of Al and P, has advantageous properties that make such co-doped glass useful in a variety of applications, including optical fiber, especially polarization-maintaining optical fiber, and planar waveguides in optical and optoelectronic devices. In particular, such co-doped fused silica can have a refractive index that is lower than, or at least not significantly greater than, that of pure fused silica, even though both Al and P individually are known up-dopants for silica. The co-doped fused silica also can have a relatively low working temperature, while otherwise maintaining many of the desirable properties of fused silica, e.g., chemical inertness and relatively low coefficient of thermal expansion.

Abstract: An array connector for optical fibers is disclosed which utilizes a plurality of grooves formed in the array substrate to hold the fibers. The connector is to be used with fibers having at least one sectional view substantially flattened side, where polarization maintaining fibers may be formed to assume this shape. The grooves are formed to have a relatively flat bottom surface so that the flattened side of the fiber is positioned to coincide with this flat bottom surface. The grooves themselves may have any desired cross section. A coverplate with corresponding grooves may be utilized to form an interlocking structure to prevent any lateral movement by the fibers. When used in association with polarization maintaining fibers, the connector of the present invention will preserve the polarization through the connection by preventing any axial angular motion. The connector may be used to align a plurality of fibers with another plurality of fibers or, alternatively, with a plurality of optical waveguides.

Abstract: Silica-based optical fiber comprising at least a core and a cladding surrounding the core, both core and cladding material produced by a vapor phase deposition process. The core and/or the cladding comprise at least two substituents, one chosen from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, and the 4f-type rare earths (the "modifiers"), and the other chosen from B, Al, Ga, In, P, As, and Sb (the "homogenizers"). The maximum concentration of the substituents in the fiber is such that 3<(n.sub.1 M+n.sub.2 H)/H<20, preferably<10, where n.sub.1 and n.sub.2 are the valences of the modifier and the homogenizer, respectively, and M and H are the concentration, in mole %, of modifier and homogenizer, respectively. Fiber according to the invention comprises at least 50, frequently more than 80% by weight, SiO.sub.2, and further has a maximum modifier concentration of at least 0.2 mole %, preferably at least 1 mole %.

Abstract: Optical fibers doped with nonglass forming refractory oxides, such as alumina and zirconia, are disclosed. Devitrification is retarded by adding an additional glass forming component, such as P.sub.2 O.sub.5, and by rapidly quenching the heated glass. Aluminum and zirconium-containing precursor vapors are formed by passing halide gas over heated aluminum or zirconium wire.

Abstract: The present invention relates to a technique for producing polarization-preserving and single polarization optical fibers. As disclosed, high birefringence is introduced into the preform by deforming the fiber preform such that a cladding layer becomes flat and highly conformable, while the core remains hard and substantially round. In particular, a cladding layer with a relatively low melting point is utilized such that when the preform is heated the cladding becomes liquified while the core remains solid. The preform may then be deformed so that the cladding layer is substantially flattened. Standard drawing techniques may then be utilized to form polarization-preserving fibers and single polarization fibers from the preform.

Abstract: An inline single-mode fiber attenuator (10) is disclosed which may be formed by a tandem combination of a birefringent polarization-preserving fiber (12) and a single polarization fiber (14). The birefringent fiber functions as a variable wave plate and the single polarization fiber functions as a fiber polarizer. By continuously changing the local birefringence of the birefringent fiber with, for example, tension, pressure, or temperature, the phase difference between the two polarization components of light traveling through the birefringent fiber is continuously modified. The difference in phase causes suppression of one of the polarization components as it enters the fiber polarizer and, therefore, the output of the fiber polarizer, the sum of the two polarizations, is attenuated. The attenuator may be tuned by changing the local birefringence of the birefringent fiber.

Abstract: The present invention relates to a single-mode single-polarization optical fiber which is capable of functioning as an in-line fiber polarizer which allows only one polarization of the fundamental mode to propagate along the fiber. In structure, the fiber comprises a central core region (10) and a cladding region (12) which is substantially in contact with the central core region. The various regions are formed such that the refractive index of an outer cladding region is greater than the refractive index of an inner cladding region but less than that of the core region. The arrangement of the present invention produces stress-birefringence between the cladding regions and the central core region sufficient to split the two orthogonal polarizations (n.sub..parallel. and n.sub..perp.) of the fundamental mode such that the desired polarization propagates freely and the undesired polarization is attenuated by tunneling through the cladding layers.

Abstract: A lightguide fiber preform is made by depositing optically suitable layers of doped silicon dioxide on an inner wall of a rotating glass substrate tube (31) which is exposed to a moving zone of heat during a deposition mode and during a mode when the tube is collapsed. During each of a plurality of passes of a torch assembly (50) in the collapse mode following deposition, a contact device (101) is in continuous engagement with the tube and is caused to apply forces to each successive increment of its length following exposure to at least an initial portion of the zone of heat to collapse incrementally the tube. Between successive ones of the plurality of passes, the contact device is moved inwardly of the tube so that each increment of length is exposed to forces which as between the successive passes are applied at points incrementally closer to the longitudinal axis (36) of the tube.

Abstract: This invention is a technique for fabricating optical fibers using thermophoretically enhanced particle deposition. In this process a cooling liquid such as water is poured over the substrate upon which deposition occurs in order to thermophoretically enhance the deposition. It has been found that despite the significant thermal shock that such water imparts to the tube, and despite previous difficulty with cracking because of thermal stresses which may develop, especially upon cooling, applicants have found that structural integrity may be maintained and enhanced deposition rates result.