Harish R. D. Sunak

Launching light from semiconductor lasers into multimode optical fibers having hemispherical ends and taper-with-hemisphere ends

The plane ends (PE) of various multimode optical fibers have been transformed into (a) hemispherical ends (HE) and (b) taper-with-hemisphere ends (TE) by using a microtorch and also a CO2 laser for HE only. We confirmed that the launching efficiency eta from semiconductor lasers into multimode fibers is much greater than TE and HE compared with PE, with TE being the most efficient. A rigorous comparison between these three launching arrangements is reported here for the first time together with detailed analysis of similar published work. The effect of various misalignments is also investigated and compared for the three fiber terminations.

Launching light from semiconductor lasers into plane-ended multimode optical fibers

A systematic and detailed study of launching light from semiconductor lasers into plane-ended multimode optical fibers has been carried out--we believe for the first time. Three different semiconductor lasers and four multimode fibers having numerical apertures in the 0.16-0.40 range were used. Simple theoretical models developed for the launching efficiency eta give good agreement with experimental results. We show how erroneous results can be obtained when considering only the stimulated emission of the lasers in calculating eta. The dependence of eta on axial, lateral, and angular misalignments is also investigated and explained qualitatively with ray optics.

Launching Light from Semiconductor Lasers into Single-Mode Fiber Optical Waveguides

In this report, problems relating to couplings of semiconductor lasers with monomode optical fibers are considered. Particular emphasis will be placed on the techniques for increasing the launching efficiency η in presence of various misalignments of the sources and fibers.

Measurements of Mode Conversion Co-Efficients in Multimode Optical Fibres

In order to assess quantitatively the quality of optical fibres we are now producing routinely in our laboratories, we have carried out preliminary measurements, with a very simple system, and calculated the normalized mode conversion co-efficient (D). The values of D obtained are of the order of 2 × 10-5 rad-2 m-1 for our fibres and these compare very favourably with the results obtained in other laboratories.

Pulse dispersion measurements in conventional Selfoc fibers.

Measurements of pulse dispersion in conventional Selfoc fibers have been carried out. The principal light source was a pulsed mode-locked ruby laser. Qualitative agreement has been found with theory, which predicts multimode operation and, hence, large pulse dispersion in such fibers under greatly mismatched launching conditions. Under such conditions, we have observed dispersion equivalent to ~20 nsec/km.