Single-mode fiber-optic directional coupler.
A low-loss compact single-mode fiber optical directional coupler (SMF-ODC) is developed for use in SMF reflectometers or gyroscopes. The SMF-ODC is made of two sapphire ball lenses, a half-mirror, and two ferrules. Two fibers (endfaces are concave) are aligned parallel to each other in the ferrule. The optical and mechanical axes are tilted. Cross-talk light from fibers or lenses is avoided. The SMF-ODC excess loss is 1.5-2.5 dB at the 1.2-1.5-microm wavelength range. The directivity is 53 (51) dB at the 1.3 (1.53)-microm wavelength. The light polarization dependency is < or =0.1 dB. The return loss is > or =43 dB.
Masuda
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Fujitsu Laboratories, Ltd., 1015 Kamikodanaka Nakahara-ku, Kawasaki 211, Japan.
Iwama
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