Showing papers on "Mode scrambler published in 1985"
TL;DR: In this paper, an experimental investigation of mode coupling in a multimode graded-index fiber as a function of the periodic microbend amplitude was carried out using computer-generated holograms as mode selecting spatial filters.
32 citations
TL;DR: In this article, the authors reported the conversion efficiency of a gyrotron TEOn-to-TEO1/TEO2 hybrid mode at 70 GHz with axisymmetric radius perturbations.
Abstract: This work reports calculations and measurements on mode converters for the transformation of TEOn gyrotron mode mixtures (primarily TEO2) into the linearly polarized HE11 hybrid mode at 70 GHz. This mode is ideal for quasi-optical launching systems for ECRH of plasmas. Mode transducers with axisymmetric radius perturbations convert the gyrotron TEOn mode composition into the TEO1 mode. Proper matching of the phase differences between the various modes and of the perturbation amplitudes of the several converter sections is required. The TEO1 wave is used for long-distance transmission through smooth-walled overmoded waveguides. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TEO1 mode into the polarized TE11 wave. The experimentally determined ΣTEOn-to-TEO1 conversion efficiency is (98.5±1)% (99% predicted) while the TEO1-to-TE11 transformer has a (94±2)% efficiency (93% theoretically); ohmic losses are included. The “Gaussian-like” HE11 mode with axisymmetric power distribution and almost no cross polarization is produced in a circumferentially corrugated TE11-to-HE11 mode transducer with a measured conversion efficiency of (98.3±1.5)% (98.5% predicted). The overall efficiency of the complete mode converter system in the desired mode was determined to be (91±2.5)%. High-power operation (200kW, 100ms) has been successfully demonstrated.
31 citations
TL;DR: In this article, the authors evaluated the coupling coefficient of a single-mode fiber having an elliptical core with 10 percent ellipticity at wavelengths of 0.85 and 1.3 μm.
Abstract: Polarization mode coupling coefficient is evaluated from the measurement of polarization mode dispersion as a function of fiber length in a single-mode fiber having an elliptical-core with 10-percent ellipticity. The modal dispersion measurement are carried out by the improved spatial technique based on an optical heterodyne detection at the wavelengths of 0.85 and 1.3 μm. The coupling coefficients are evaluated from the measurements to be 3.4 \times 10^{-3} and 4.6 \times 10^{-3} m-1for modal-birefringence magnitudes of 8 \times 10^{-6} and 3 \times 10^{-6} , respectively. The coupling coefficients obtained from the dispersion measurement are coincident with those evaluated from the extinction-ratio measurements. In addition, dependence of the coupling coefficient on propagation constant difference between the two orthogonally polarized HE 11 modes is investigated based on Lorentzian power spectrum model.
22 citations
TL;DR: This paper theoretically analyze the loss and branching ratio of multimode optical branching waveguides by using a ray tracing method to obtain less mode-dependent branching characteristics and finds that an optimum length to achieve a low loss and stable branching ratio exists.
Abstract: In this paper, we theoretically analyze the loss and branching ratio of multimode optical branching waveguides by using a ray tracing method to obtain less mode-dependent branching characteristics. First, a 2 × 2 optical mixing and branching waveguide with a step-index profile are considered. It is found that an optimum length to achieve a low loss and stable branching ratio exists. Second, a waveguide with mode scrambler is investigated. By sacrificing some amount of insertion loss, the mode dependence can be minimized.
7 citations
TL;DR: A theoretical analysis for the mode exciters based on geometrical ray optics approximation is presented and it is shown that optical loss measurements under steady-state distribution can be done by using either SGS or GSG modeexciters which consist of either small core or low NA fibers.
Abstract: Mode exciters which consist of alternate concatenation of step-index (S) and graded-index (G) fibers are used widely for the measurement of transmission characteristics (optical loss and baseband frequency response) of multimode fibers. This paper presents a theoretical analysis for the mode exciters based on geometrical ray optics approximation. The mode power distribution controlling effect of the exciters, excited mode power distribution in the test fiber, and accuracy and reproducibility of optical loss measurements are clarified theoretically. It is shown that optical loss measurements under steady-state distribution can be done by using either SGS or GSG mode exciters which consist of either small core or low NA fibers.
6 citations
Patent•
08 Nov 1985
TL;DR: In this article, a mode scrambling arrangement for a multimode or graded-index optical fiber was proposed, where a deformation on one side of the optical fiber orthogonal to the longitudinal axis was created by an etching or machining process to extend through the cladding layer and at least very slightly into the outer surface of the core.
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 (13) as, for example, a groove or notch on one side of the multimode or graded-index optical fiber (10, 11, 12) orthogonal to the longitudinal axis (14) thereof. The groove or notch can be produced by any suitable etching or machining process to extend through the cladding layer (11) and at least very slightly into the outer surface of the core (10) 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.
1 citations