Showing papers on "Photonic-crystal fiber published in 1977"

Pulse delay measurements in the zero material dispersion wavelength region for optical fibers.

Abstract: Subnanosecond pulses in the 1120-1550-nm region are generated by multiple-order stimulated Raman scattering in a small core single-mode silica fiber pumped by a Q-switched and mode-locked Nd:YAG laser at 1064 nm. These near ir pulses are injected into various km long test fibers, and relative time delay changes between different wavelengths are used to determine dispersion in a region where fiber material dispersion is small. Zero material dispersion has been observed in germanium and boron-doped single-mode and multimode est fibers.

Wavelength multiplexing in multimode optical fibers.

Abstract: The capacity of optical fiber transmission systems could be increased by multiplexing several signals at different wavelengths on each fiber. This paper considers various multiplex system designs that might be used with multimode fiber transmission systems. In each case, the required multiplexer size and material properties are calculated as functions of the basic parameters of the fiber system. For fiber systems of the type currently being tested, a compact (~2 mm in diameter × 1 cm long), rugged, three-channel multiplexer could be constructed using a blazed plane reflection grating and graded-refractive-index (GRIN) optics; and it appears that such devices could be produced using available materials and technology. Multiplexers using thick gratings or multilayer dielectric filters are larger, more complicated, and require materials at the very edge of available technology. Multiplexers using a multiple thick grating or hologram could be even smaller than the blazed-grating devices, but materials having the required characteristics have not been demonstrated.

Evolution of polarization along a single‐mode fiber

Abstract: The local parameters of linear and circular birefringence are nondestructively measured along a single‐mode optical fiber by electro‐optic and magneto‐optic modulation of the polarization in the fiber. A complete mapping of the evolution of the state of polarization is obtained and is compared with a theoretical model.

Optical fiber acoustic sensor

Abstract: A new class of hydrophones is currently being developed, which utilize optical beams and interface directly to fiber optic transmission and processing links. Some of these sensors employ an optical fiber itself as the transduction element and possess significant advantages and versatility. The details of these fiber sensors and their advantages are discussed.

Coupling arrangements between a light-emitting diode and an optical fiber waveguide and between an optical fiber waveguide and a semiconductor optical detector

Abstract: A terminating portion of an optical fiber waveguide having a polished beveled end is laterally disposed directly on the light-emitting surface of a light-emitting diode (LED). The light power coupled into the fiber consists of two components: the light power directly coupled into the fiber all along the region of contact between the fiber and the light-emitting surface; and the light power reflected by the beveled end and directed along the fiber axis.

Profile synthesis in multicomponent glass optical fibers

Abstract: It is proposed that the concentration profiles of the components of a multicomponent glass be specified independently in order to synthesize an optical fiber having several optimized transmission characteristics. Assuming a linear relationship between concentration and refractive index, we show how the synthesis procedure operates for ternary glasses and illustrate the method by computing the concentration profiles required to realize a SiO2–GeO2–P2O5 fiber with minimum modal dispersion over a wide range of wavelengths (∂α/∂λ =0).

Polarization optics of liquid-core optical fibers.

Abstract: Whereas straight liquid-core optical fibers have the capability of transporting linearly polarized light with any incident polarization angle, bent fibers exhibit form birefringence with the principal axes fixed to the plane of curvature. The effect of this curvature-dependent birefringence can be compensated by either periodically altering the plane of curvature by 90° or winding the fiber into a helix.

Acoustic Clad Fiber Delay Lines

Abstract: V. CONCLUSIONS Although the various intensities of a diffracted light wave are described in a totally different way in the Raman-Nath and in the Bragg region, the final results for the molecular parameters G and T are identical. Furthermore, we found in both the cases the same correction term containing p . This term is not negligible for the first diffraction order in the Bragg region and for higher diffraction orders in the Raman-Nath region.

A new LED structure with a self-aligned sphere lens for efficient coupling to optical fibers

Abstract: A practical new structure of the high radiance GaAs-GaAlAs LED with a self-aligned sphere lens has been developed for efficient coupling to low-less optical fibers as a light source for fiber optic communications. In this new configuration, the sphere lens is automatically settled into the center of the light-emitting surface by an etched hole containing clear epoxy resin. When applied to a low-loss optical fiber ( NA = 0.14 , core diameter: 80 µm), a coupling efficiency in excess of 9 percent has been reproducibly achieved for an LED structure with an emitting-area diameter of 35 µm and with a lens having a diameter of 100 µm and a refractive index of 2.0. Using an LED with a light-emitting-layer carrier concentration of 3 × 1018/cm3, an optical power of 150 to 200 µW coupled into the fiber and a cut-off frequency (optical power down to ½) of about 90 MHz have been reproducibly obtained.

Polarization-insensitive integrated-optical switches: a new electrode design

Abstract: The combination of two different types of electrodes in integrated optical switches is shown to permit polarization-insensitive operation. The ability to process arbitrarily polarized light is critical to the use of integrated optical devices with glass fiber transmission lines, due to the rapid changes in polarization state of light propagating in the fibers. We examine the performance of a Δβ reversal switch which uses two different types of electrodes and show that polarization-insensitive operation is readily achievable.

Plastic focusing fiber for imaging applications

Abstract: This paper presents a fabrication method and image transmission characteristics of a plastic focusing fiber which is flexible and has a nearly parabolic refractive index distribution. A new fabrication method is given, and the optimum control of index profile has been attained in order to reduce the aberration for imaging. A prototype fiber scope with TV monitor using the plastic fiber was made. Resolving power of 5–6 l/mm was shown to be attainable for fibers 3 mm in diameter and 150 mm in length.

Efficient power combiner for multiplexing multiple sources to single‐fiber optical systems

Abstract: Efficient combining of optical power from three input optical fibers to a single trunk fiber is demonstrated using fibers of different core/cladding diameters in a biconical taper configuration. The combiners have insertion loss less than 1 dB and optical isolation greater than −50 dB.

Optical fiber splicing with a low-power CO(2) laser.

Abstract: Low loss splicing of silica fibers by means of a 5-W CO2 laser has been demonstrated. Step-index fibers with a core diameter of 56 μm and an outer diameter of 154 μm were fused together. The chopped laser beam, effectively 2.3 W and about 1.0 mm in beam-spot diameter, was moved across the fiber ends at a speed of 10 μm/sec. Ninety percent of twenty-one splices had losses less than 0.12 dB with a minimum loss of 0.02 dB. Good reproducibility of the low loss splice was achieved by contacting the fibers tightly before fusing them together.

Refractive-index profile determination of optical fibers from the diffraction pattern

Abstract: Universitat Wuppertal, Fachbereich 13, D-5600 Wuppertal 1, Federal Republic of Germany. Received 12 May 1977. Recently, Okoshi and Hotate presented a method for de­ termining the refractive-index profile in an optical fiber, ap­ plicable to an arbitrary profile provided φ = 2kΔnro « 1 (k = 2π/λ is the wavenumber, An the index-difference between core and cladding, and ro the core radius). This was done by measuring the scattering pattern for a normally incident laser beam. The advantage over alternative techniques is that it is nondestructive. An elaborate setup, however, has been used to collect and process the data. In this Letter we propose a modified scheme for the same class of fibers resulting in a considerable simplification in the theoretical model as well as in the experimental setup. Okoshi and Hotate considered their experimental results to be caused by a scattering process and used the induced dipole method. It is much easier, however, to discuss the data on the basis of a diffraction phenomenon. From this point of view the fiber, which is immersed into index-matching oil, introduces a phase shift. In other words, the distribution of the complex light amplitudes, which can be considered to be constant in front of the fiber, is changed to Uo(x) = exp[jφ(x)] in a plane directly behind it. φ(x) denotes the phase shift and is given by φ{x) = ∫ kΔn(x,z)dz, where the z axis is in the direction of the laser beam and the x axis is perpendicular to the z and the fiber axis. Keeping in mind the assumption φ « 1 (which only applies to rather thin fibers), the object dis­ tribution Uo can be approximated by U0(x) ≈ 1 + jφ(x). Thus, neglecting the undiffracted light and assuming that An has azimuthal symmetry, the Fourier transform properties of Fraunhofer diffraction yield

Polycrystalline fiber optical waveguides for infrared transmission

Abstract: A new type of fiber optical waveguide utilizing TlBr and KRS‐5 has been prepared; its infrared transparency extends to wavelengths well beyond those transmitted by known glassy materials.

Fiber optical communications devices

Abstract: Both low attenuation silica optical fibers with peak transmission in the wavelength regions of 0.85 μm, and 1.05 μm, and improved lasers at both wavelengths are now available. In this review paper, the principal components for emission, modulation and detection are described. The characteristics of both semiconductor lasers, made of GaAs and related compounds, emitting at 0.85 μm or 1.05 μm and high neodymium-content lasers are discussed. For modulation, current modulation of GaAs lasers and external electro-optic modulation are considered. Concerning detection, the realisation of Si photodetectors suitable at 0.85 μm and the new photodetectors at 1.05 μm from Ga1−x In x As are reviewed.

Planar fiber optic star and access coupler

Abstract: A planar, optical star and access coupler for multiterminal communication systems which use multimode fibers as the transmission line either as a plurality of single fiber lines, in multichannel fiber cable or in minibundles. The fibers are placed in a row so that the core ends abut the end of a high-aspect angle rectangular cross section clad ribbon fiber which is preferably not as thick as the diameter of the core of the individual fibers for optimum packing fraction loss. Optical radiation, such as from a laser or light-emitting diode, entering the ribbon-fiber mixer element from all of the fibers on one end will be mixed by the ribbon fiber and be transmitted equally on each of the output fibers. Also, radiation from any one fiber will be divided equally between all of the transmission fibers on the opposite end of the ribbon fiber.

Pulse circulation measurement of transmission characteristics in long optical fibers.

Abstract: A pulse circulation method to measure the length dependence of transmission characteristics in optical fibers is described. In principle, the method has the advantage that no unnecessary power is branched off in the loop. Using this method, the length dependence of transmission characteristics of step and graded index fibers has been measured and found to be different in both cases. It is concluded that the difference is due to the material dispersion effect, which significantly influences pulse spreading in long length graded index fibers.

Group velocity matching in optical fibers.

Abstract: Group velocity matching has been observed in an optical fiber. The matching occurred in a fiber Raman oscillator pumped by mode-locked laser pulses. The group velocity difference between pump and Stokes pulses due to material dispersion was compensated for by the group delay between two different waveguide modes.

Coupler for optical fiber waveguides and method of constructing same

Abstract: A method for constructing and an apparatus for accessing individual or multiple guided optical fiber modes. Coupling can be accomplished at any point along an optical fiber through the fiber cladding. The coupler is based upon a technique for converting a guided optical mode into a leaky mode by varying the index of refraction of the optical fiber cladding. Transforming between the leaky mode radiation and a desired spatial power distribution is accomplished by a holographic coupler. Other propagating modes are unaffected by the coupling region. This coupling method and apparatus has application when it is required to make multiple taps along a common optical fiber as well as when it is necessary to access individual fiber modes.

Single-fiber duplex coupler

Abstract: A bidirectional optical communication system which includes a transmissionine which directs radiation onto a reflective surface through which a smaller-diameter fiber is inserted. The smaller-diameter fiber directs radiation into the larger-diameter fiber for transmission away from the reflective surface simultaneous with radiation transmitted through the larger-diameter fiber toward the reflective surface. A reflective surface and small fiber may be at each end of the larger-diameter fiber for bidirectional operation.

Frequency domain measurements of dispersion in multimode optical fibers

Abstract: A newly developed technique for directly measuring fiber dispersion in the frequency domain as a function of wavelength is described. A number of germanium‐ and boron‐doped fibers have been examined. The least dispersive borosilicate graded‐index fiber has a 1‐dB bandwidth of 1 GHz, after 1.07 km of propagation at λ=908 nm. Frequency domain measurements were inverted into the time domain after assuming that the phase of a power transfer function could be calculated from its amplitude spectrum.

Optical fiber coating concentricity: measurement and analysis

Abstract: Backscattering of laser light that is incident at right angles to the axis of an optical fiber is utilized to evaluate the degree of eccentricity of a plastic jacket on the fiber. An analytical treatment of the problem based on ray optics is shown to be in excellent agreement with experiments, which are capable of detecting core-to-jacket offsets on the order of 1 μm.

Characteristics of a fiber-optic Raman laser

Abstract: The frequency spectrum of a continuous wave fiber-optic Raman laser is measured and observed to consist of several discrete lines covering a 3-nm spectral range. The output of the laser also contains damped transients which are attributed to strong pump-depletion effects in the fiber. Previously observed degradation of the fiber has been reduced in the later devices.

Fiber‐optical relay

Abstract: Metallic pads on optical fibers are heated by the absorption of light at the 1‐μW–10‐mW power level. Due to differential thermal expansion, the fibers bend, and, by misaligned coupling, modulate guided light signals. An optically operated relay, a narrow‐band audio‐frequency resonator, and a self‐commutating optically powered oscillator are demonstrated.