Single-core fiber core diameter is 9 microns.

Single-core fiber core diameter is 9 microns.

• A. 9 microns
• B. 8 microns
• C. 10 microns
• D. 12 microns

Answer: (A)

Single-mode operation hinges on keeping the core diameter small enough so only the fundamental light path propagates at the operating wavelengths. For telecom-grade silica fiber, the conventional core diameter that achieves this single-mode behavior is about 9 microns, with a cladding around 125 microns. This size keeps the mode count at typical wavelengths (roughly 1300–1550 nm) such that higher-order modes don’t fit, minimizing modal dispersion and preserving a clean, single light path. If the core were noticeably larger, multiple modes could travel simultaneously, leading to pulse spreading and degraded performance. The 9-micron core is the standard specification used in practice, while the other diameters would either diverge from standard telecom fibers or risk supporting additional modes under operating conditions.

Single-mode operation hinges on keeping the core diameter small enough so only the fundamental light path propagates at the operating wavelengths. For telecom-grade silica fiber, the conventional core diameter that achieves this single-mode behavior is about 9 microns, with a cladding around 125 microns. This size keeps the mode count at typical wavelengths (roughly 1300–1550 nm) such that higher-order modes don’t fit, minimizing modal dispersion and preserving a clean, single light path. If the core were noticeably larger, multiple modes could travel simultaneously, leading to pulse spreading and degraded performance. The 9-micron core is the standard specification used in practice, while the other diameters would either diverge from standard telecom fibers or risk supporting additional modes under operating conditions.