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Dielectric waveguides
Published in G. Someda Carlo, Electromagnetic Waves, 2017
The simplest and most widely used designs give fibers whose ≥0 is close to 1.3 μm, i.e., in the spectral range which is called, as we said before, “second window”. These fibers are usually referred to as standard single-mode fibers. However, the growing interest in exploiting the “third window,” where losses pass through their minimum value, and optical amplifiers are commercially available, has encouraged the design of fibers whose zero-dispersion wavelength λ0 is close to 1.5 μm. These are referred to as dispersion shifted (DS) fibers. Typically, their refractive index profile is more complicated than the single step considered here. The reader who is interested in more details should consult many of the books quoted at the end of this chapter. More complicated fibers have been envisaged, where total dispersion is kept below a given upper limit over the whole range from 1.3 μm to 1.55 μm. They are referred to as dispersion flattened fibers. However, interest in these appears to be low, in recent times.
Characteristics of Optical Fiber
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Video Transmission, 2013
David R. Goff, Kimberly Hansen, Michelle K. Stull
While very high, fiber's potential bandwidth falls short of infinite. In single wavelength systems, chromatic dispersion limits the bandwidth. Operating a fiber at the zero-dispersion wavelength, also called the zero-dispersion point, with a monochromatic light source, yields a large fiber bandwidth. Figure 5.2 (next page) shows the bandwidth-distance product for a hypothetical single-mode fiber. The center wavelength for the light source lies on the x-axis. The figure shows three curves with FWHM giving values of 2 nm, 5 nm, and 10 nm. Full width half maximum represents the width of the spectral emission at the 50% amplitude points. The most narrow source shown, FWHM = 2 nm, offers a bandwidth-distance product of over 30,000 GHz·km at a center wavelength of 1310 nm, the fiber's zero-dispersion wavelength. As the center wavelength moves even a few nanometers from 1310 nm, the fiber's bandwidth-distance product drops dramatically. At a center wavelength of 1320 nm, the fiber's bandwidth-distance product has dropped by a factor of 30, to 1,000 GHz·km. Wider optical sources offer even lower bandwidth. Using a very narrow light source tuned exactly for the fiber's zero-dispersion wavelength would yield a bandwidth peak much higher than those shown in the plot.
Optical Fiber
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Reference Guide, 2002
David R. Goff, Kimberly Hansen, Michelle K. Stull
NDSF: Commonly referred to as standard single-mode silica fiber, this optical fiber is also known as non dispersion-shifted fiber (NDSF). SMF-28, made by Corning, is among the most popular NDSF deployed today. NDSF has an operating wavelength for zero chromatic dispersion (called λ0) of 1310 nm. Chromatic dispersion causes a pulse to spread out as it travels along a fiber due to the fact that the different wavelength components that constitute the pulse travel at slightly different speeds in the fiber. The further away the wavelength is from λ0 the greater the degree of dispersion and hence distortion. The fiber zero dispersion wavelength, or λ0, is the wavelength at which chromatic dispersion is zero. Transmission wavelengths used with erbium-doped fiber amplifier systems (1550 nm window) undergo significant chromatic dispersion with NDSF and require dispersion compensation, particularly at 10 Gbit/s or higher data rates. Typical optical losses range from 0.21 to 0.25 dB/km.
Effect of four-wave mixing on the loss budget of four-channel multiplexing NG-PON systems
Published in Journal of Modern Optics, 2021
Yan Xu, Peihua Yu, Zhengxuan Li, Yingxiong Song, Min Wang
As illustrated in Section 4, the zero-dispersion wavelength of the fibre used was measured to be approximately 1317 nm. Therefore, the zero-dispersion wavelength was set to 1317 nm in the simulation, and the transmission performance was evaluated. In this situation, the zero-dispersion wavelength was far away from all four channels. Figure 5(a) and (b) show the BER curves of 25G NRZ and 50G PAM4 signals in the BtB and 25-km transmission cases under an 8-dBm/ch launch power, respectively. No sensitivity penalty was introduced after fibre transmission, meaning that the FWM had a negligible influence in this situation. The acquired eye diagrams of 25G NRZ and 50G PAM4 signals after 25-km transmission also verify this view, as shown in the inset of Figure 5(a) and (b), respectively. A loss budget as high as 36.2 dB was achieved for the NRZ transmission system, and 25.7 dB was obtained for the PAM4 system. It is concluded that the loss budget requirement is always satisfied when transmitting NRZ signals in this case. However, the loss budget of the PAM4 system cannot meet the basic demand (29 dB). Therefore, additional equipment or methods are required to satisfy the loss budget. In Section 4, the experimental results are presented to confirm the reliability of the simulation further.