Polarization-maintaining fibers and their applications are reviewed. The classification of high-birefringent fibers and low-birefringent fibers and their fabrication methods and characteristics are discussed in Section II. Analytical methods and numerical methods for fiber design on the birefringence are presented in Section III. Degradation factors of polarization maintenance expressed as crosstalk or mode-coupling parameters caused by internal origins such as structural imperfections, wavelength, and nonlinear effects, and by external origins such as temperature fluctuations, mechanical perturbations, and electromagnetic effects, are discussed in Section IV. Characterization methods on beat length, mode coupling, stress distribution, and mechanical strength are presented in Section V. Applications to the fiber devices and nonlinear effects, and splicing methods for the polarization-maintaining fibers are described in Sections VI and VII.

Polarization-maintaining fibers and their applications

A light-emitting gallium nitride-based compound semiconductor device of a double-heterostructure. The double-heterostructure includes a light-emitting layer formed of a low-resistivity In x Ga 1-x N (0<x<1) compound semiconductor doped with p-type and/or n-type impurity. A first clad layer is joined to one surface of the light-emitting layer and formed of an n-type gallium nitride-based compound semiconductor having a composition different from the light-emitting layer. A second clad layer is joined to another surface of the light-emitting layer and formed of a low-resistivity, p-type gallium nitride-based compound semiconductor having a composition different from the light-emitting layer.

Light-emitting gallium nitride-based compound semiconductor device

A gallium nitride-based III-V Group compound semiconductor device has a gallium nitride-based III-V Group compound semiconductor layer provided over a substrate, and an ohmic electrode provided in contact with the semiconductor layer. The ohmic electrode is formed of a metallic material, and has been annealed.

Gallium nitride-based III-V group compound semiconductor device and method of producing the same

Gallium nitride-based III-V group compound semiconductor

By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

In a single mode optical fiber comprising a core made of glass and a cladding surrounding the core and made of glass, when a difference A between refractive indices n. and n2 of the core and cladding is expressed by the refractive indices n, and n2 are determined to satisfy a relation 1.0 < A < 3.6 and a diameter of the core is determined according to this value of A. When the refractive index difference A and the diameter of the core are determined in this manner, the optical fiber would have a wider band transmission characteristics than the prior art optical fiber, thus enabling higher degree of wavelength multiplexing.

Single mode optical fibers

A rigorous theoretical analysis has been presented of the stress birefringence Bs and the polarization dispersion Ds in single-polarization fibers. Both Bs and Ds vary considerably in dependence on normalized frequency v, and the v-value dependence of Bs and Ds is strongly affected by the anisotropic stress distribution in the fiber. It is shown that the experimental results agree well with the calculated ones.

Polarization properties of single-polarization fibers

A method of fabricating a single-mode optical fiber preform wherein a core torch produces fine glass particles eccentrically with respect to the center area of a flame stream, the core torch being so arranged as to blow the flame stream at an angle inclined to a seed rod. The porous glass body forming the core is grown on one end of the rod and in the direction of the axis of the rod. A cladding layer is formed on the periphery of the porous glass core body by at least one torch for forming the cladding. The obtained porous glass body is heated and vitrified into a transparent glass body, which is sealed in a silica tube for jacketting to form a single-mode optical fiber preform. At least one exhaust port is disposed within a distance of 1 mm to 50 mm from the periphery of the porous glass body and in the vicinity of the growing surface of the glass body to exhaust residual glass fine particles and undesired gases. A porous glass body having a diameter of 20 mm or less is easily formed. Single-mode optical fiber having a cladding-to-core-diameter ratio of 3 or more is fabricated by the VAD method. Accordingly, a long-length and low-loss single-mode optical fiber is mass-produced.

Fabrication method of single-mode optical fiber preforms

PURPOSE:To obtain high efficiency light emitting element in a visible range near blue range by forming a single hetero-junction from N type AlxGal-xN film and P type AlyGal-yN film. CONSTITUTION:An N type AlxGal-xN(0<x<=1) film 4 is formed on an insulating substrate 3. Then, an ohmic electrode 5 is formed on the film 4. A P type Aly Gal-yN(0<y<=1) film 6 is accumulated on the film 4 to form a single hetero junction. Then, an ohmic electrode 5 is formed on the film 6. When thus formed, a DC voltage of positive polarity is applied to the P type electrode, and a DC voltage of negative polarity is applied to the N type electrode, and a light is emitted at P-N junction. In this manner, a high efficiency light emitting element in visible range near blue range can be obtained.

Semiconductor hetero-junction element

A simple and novel fabrication technique for a fiber-type polarizer has been developed, and the polarization characteristics of the polarizer have been investigated. The polarizer is formed from a single-mode fiber composed of a concentric core and a silica cladding having a B(2)O(3)-doped silica portion. The cladding is etched off asymmetrically by utilizing the etching-speed difference between pure silica and B(2)O(3)-doped silica in 49% HF. The Al film is subsequently evaporated onto the etched portion. The extinction ratios of polarizers with various buffer-layer thicknesses were measured at two wavelengths, lambda = 1.15 pm and lambda = 1.29 microm. The maximum measured extinction ratio was 37 dB at lambda = 1.29 microm for a 4-cm-long polarizer.

Edahiro Takao

Papers

Single mode optical fibers

Polarization properties of single-polarization fibers

Fabrication method of single-mode optical fiber preforms

Semiconductor hetero-junction element

Fabrication of single-mode fiber-type polarizer.