• Korean Journal of Optics and Photonics
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• v.18 no.4
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• pp.280-285
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• 2007

Based on the multimode fiber taper, a mode size converter for effective optical beam coupling between laser and optical fiber or between the two different optical fibers has been proposed and demonstrated. The device has a multimode input end and a single mode output end. The influence of various parameters, including device structure and launching conditions, on the coupling efficiency has been theoretically analyzed. The theoretical results revealed that the gaussian beam can be coupled into a single mode fiber without considerable insertion loss. The proposed multimode fiber taper has been fabricated using heating and pulling equipment incorporating two micro-torches. Experimental results showed that an optical beam with $50\;{\mu}m$ of large beam size was effectively coupled into single mode fiber through the multimode fiber taper. The insertion loss of the device was 1.3 dB.

• Journal of the Optical Society of Korea
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• v.13 no.2
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• pp.234-239
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• 2009

This paper presents a theoretical and experimental investigation of the transmission and sensing characteristics of the biconically tapered cladded multimode fibers. The beam propagation method was used to examine the transmission characteristics with various structural parameters. The results show that the transmission of the biconically tapered cladded multimode fibers is sensitive to the mode of the input optical beam and the refractive index of the external medium. A refractive index sensor for the external medium was proposed based on the theoretical analysis, and its feasibility was demonstrated experimentally.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.420-427
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• 1993

Dielectric thin film mirrors are embedded in multimode and single-mode fibers by a fusion splicing technique. The fibers with $45{\circ}$ angled embedded mirrors serve as ultra-compact directional couplers with low excess optical loss of 0.2 dB for multimode and 0.5 dB for single mode at 1.3 ${\mu}m$ and excellent mechanical properties. The reflectance is wavelength dependent and strongly polarization depencient. Far-field scans of the reflected output power measured with a white-light source show a pattern which is almost circularly symmetric with aspect ratio of 1.09 at 5% of the peak power. The splitting ratio in a multimode coupler measured with a diode laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers, indicating that these couplers are less susceptible to modal noise occuring in optical fiber communication systems. Spectral properties of multilayer internal mirrors normal to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.