Single-index fibers

Shirayev et al. have obtained minimum optical losses of 0.04 dB/m at 6.7 pm for a core-only Te2oAs3oSeso glass fiber [144]. Even though these losses are still too high for long-distance applications, they permit optical sensing on short and medium distances. 

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Figure 7.11 Thermal drawing of a core-only preform into a single-index fiber (pictures glass As2Se3].

B. MacChesney, D. W. Johnson, P.. Lemaire, L. G. Cohen, and E. M. Rabinovich, "FluorosUicate Substrate Tubes to Eliminate Leaky-Mode Losses in MCVD Single-Mode Fibers with Depressed Index Cladding," paper no. WH2 in Technica/ Digest of Optica/ Fiber Communications Conference, San Diego, Ca/if, Optical Society of America, Washington, D.C., 1985. 

Single Mode. The single-mode fiber has a step-index profile (Fig. 16.6c) and a small core diameter (typically 10 im) such that only one mode can travel through it. This is now the preferred system, particularly for long-distance transmission. The normal light source for multimode fibers is the light-emitting diode (LED). But... 

Tian, Z. Yam, S. S. Barnes, J. Bock, W. P. Greig J. M. Fraser H. P. Loock R. D. Oleschuk, Refractive index sensing with Mach Zehnder interferometer based on concatenating two single mode fiber tapers, IEEE Photon. Technol. Lett. 2008, 20, 626... 

Single-mode fibers have many advantages over multimode fibers. See Fig. 3. Compared to the 50 or 62.5 micron core diameter of typical graded-index multimode fibers, some single-mode fibers have a core diameter near... 

The spectral width of a pulse train emitted by a femtosecond laser can be significantly broadened in a single mode fiber [27]. This process that maintains the mode structure is described in the time domain by the optical Kerr effect or selfphase modulation. The first discussion is simplified by assuming an unchanging pulse-shape under propagation. After propagating the length l the intensity dependent refractive index n(t) = n0 + ri2/(f) leads to a self induced phase shift... 

We mentioned above three types of optical fibers step index single mode, step index multimode, and gradient index multimode. The last two types can carry more light that the step index single mode fiber. Lightness is a very important feature. Among the important features for such a system are the following (Oare, 1995) ... 

Figure 2.51. Cross-section image of an optical fiber. Shown is the propagation of Ught waves through an (a) step-index multimode fiber, (b) graded-index multimode fiber, and (c) single-mode fiber.

Single Mode Fiber (SMF) Graded Index Fiber (GIF) Careless Fiber(CF) Multimode Fiber(MMF)... 

Figure 12. Transmission losses of four optical fibers coated with different materials as a function of winding tension on a 25-cm diameter acrylic drum. The fibers are llO-um cladding diameter, 8-um core diameter single mode fibers. These fibers have a very small core-cladding refractive index difference and transmit only the fundamental, most axially directed light ray (mode). Coating thickness is 50 um. (Reproduced with permission from Ref. 28. Copyright 1981 Gordon and Breach Science Publishers.)...

FIGURE 32.15 Total internal reflection (TIR) along an optical fiber, (a) Step Index fiber (b) graded Index fiber (c) single mode fiber. The plot on the left is a variation of Rl (= n). 

Single-mode fibers are used to reduce the number of modes traveling down a fiber and therefore reduce modal dispersion. A single-mode fiber is basically a step index fiber with a very small core... 

Waveguide dispersion results from how waves traveling along a fiber interact with the profile in refractive index. Let us first discuss single mode fiber, since multimode fiber is treated somewhat differently. Various index profiies for singie mode fibers are shown in Figure 5. 

W. G. French, J. B. MacChesney, P. B. O Connor and G. W. Tasker, Fabrication of graded index and single mode fibers with silica cores, Bell System Technical Journal, 53,951 (1974). 

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