We describe a method to estimate the capacity limit of fiber-optic communication systems (or ?fiber channels?) based on information theory. This paper is divided into two parts. Part 1 reviews fundamental concepts of digital communications and information theory. We treat digitization and modulation followed by information theory for channels both without and with memory. We provide explicit relationships between the commonly used signal-to-noise ratio and the optical signal-to-noise ratio. We further evaluate the performance of modulation constellations such as quadrature-amplitude modulation, combinations of amplitude-shift keying and phase-shift keying, exotic constellations, and concentric rings for an additive white Gaussian noise channel using coherent detection. Part 2 is devoted specifically to the "fiber channel.'' We review the physical phenomena present in transmission over optical fiber networks, including sources of noise, the need for optical filtering in optically-routed networks, and, most critically, the presence of fiber Kerr nonlinearity. We describe various transmission scenarios and impairment mitigation techniques, and define a fiber channel deemed to be the most relevant for communication over optically-routed networks. We proceed to evaluate a capacity limit estimate for this fiber channel using ring constellations. Several scenarios are considered, including uniform and optimized ring constellations, different fiber dispersion maps, and varying transmission distances. We further present evidences that point to the physical origin of the fiber capacity limitations and provide a comparison of recent record experiments with our capacity limit estimation.

Capacity Limits of Optical Fiber Networks

The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed

Photonic-Crystal Fibers

An applications-oriented review of optical parametric amplifiers in fiber communications is presented. The emphasis is on parametric amplifiers in general and single pumped parametric amplifiers in particular. While a theoretical framework based on highly efficient four-photon mixing is provided, the focus is on the intriguing applications enabled by the parametric gain, such as all-optical signal sampling, time-demultiplexing, pulse generation, and wavelength conversion. As these amplifiers offer high gain and low noise at arbitrary wavelengths with proper fiber design and pump wavelength allocation, they are also candidate enablers to increase overall wavelength-division-multiplexing system capacities similar to the more well-known Raman amplifiers. Similarities and distinctions between Raman and parametric amplifiers are also addressed. Since the first fiber-based parametric amplifier experiments providing net continuous-wave gain in the for the optical fiber communication applications interesting 1.5-/spl mu/m region were only conducted about two years ago, there is reason to believe that substantial progress may be made in the future, perhaps involving "holey fibers" to further enhance the nonlinearity and thus the gain. This together with the emergence of practical and inexpensive high-power pump lasers may in many cases prove fiber-based parametric amplifiers to be a desired implementation in optical communication systems.

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Fiber-based optical parametric amplifiers and their applications

Ultrafast fibre lasers are an important optical system with industrial, medical and purely scientific applications. Essential components and the operation regimes of ultrafast fibre laser systems are reviewed, as are their use in various applications.

Ultrafast fibre lasers

https://engineering.purdue.edu/~fsoptics/articles/Ultrafast_optical_pulse_shaping_tutorial-Weiner.pdf

Ultrafast optical pulse shaping: A tutorial review

The present invention relates to a dispersion-shifted fiber having a structure for effectively lowering polarization-mode dispersion. This dispersion-shifted fiber is a single-mode optical fiber mainly composed of silica glass and has a zero-dispersion wavelength set within the range of at least 1.4 µm but not longer than 1.7 µm. In particular, at least the whole core region of the dispersion-shifted fiber contains fluorine.

Dispersion-shifted fiber

Depolarized pump light is used in measurements of the nonlinear refractive index, n2, in optical fiber by the cross-phase-modulation method. High measurement repeatability within ±1% is obtained by this method. The nonlinear refractive index is determined for dispersion-shifted fiber, standard single-mode fiber, pure silica-core single-mode fiber, and dispersion-compensating fiber as 3.35 × 10−20, 2.96 × 10−20, 2.79 × 10−20, and 4.44 × 10−20 m2/W, respectively, at 1.55 μm. This shows that the nonlinear refractive indices of the optical fibers differ greatly according to glass composition.

Measurement of the nonlinear refractive index in optical fiber by the cross-phase-modulation method with depolarized pump light.

The temperature dependence of chromatic dispersion is examined for various types of fiber. Its coefficient is found to depend strongly on the dispersion slope. Dispersion-flattened fiber has a significantly low coefficient of -0.0005ps/nm/km/°C, compared with -0.0038ps/nm/km/°C for large-core nonzero dispersion-shifted fiber. Transmission lines with low dispersion slopes consisting of pure silica core fiber and dispersion-compensating fiber also exhibit low coefficients of less than -0.001ps/nm/km/°C because of their compensating effects.

Temperature dependence of chromatic dispersion in various types of optical fiber

The present invention relates to a dispersion-compensating fiber for improving a transmission system with it in total chromatic dispersion and dispersion slope in the 1.55 µm wavelength band. The dispersion compensating fiber according to the present invention is characterized by having the following characteristics for light in the 1.55 µm wavelength band: chromatic dispersion preferably not less than -40 ps/km/nm and not more than 0 ps/km/nm; dispersion slope not less than -0.5 ps/km/nm2 and not more than -0.1 ps/km/nm2; transmission loss not more than 0.5 dB/km; polarization mode dispersion not more than 0.7 ps.cndot.km-1/2; cut-off wavelength not lees than 0.7 µm and not more than 1.7 µm in the length of 2 m; and bending loss at a diameter of 20 mm, not more than 100 dB/m. The dispersion-compensating fiber is optically connected at a ratio of appropriate lengths with a dispersion-shifted fiber as a compensated object; which can improve a system including the dispersion-compensating fiber in a total chromatic dispersion and dispersion slope of the system in the 1.55 µm band.

Dispersion compensating fiber and optical transmission system including the same

An optical fiber suitable for use in a single fiber or multifiber optical connector or array is structured with a core region and a cladding region surrounding the core region, and exhibits a bending loss of a fundamental mode of the fiber at a wavelength λ is lower than 0.1 dB/m at a diameter of 15 mm, a mode-field diameter of the fundamental mode at an end of the fiber at the wavelength λ is between 8.0 μm and 50 λ, and a bending loss of a first higher-order mode at the wavelength λ is higher than 1 dB/m at a diameter of 30 mm. The fiber may be multistructured, wherein the cladding region comprises a main medium and a plurality of sub medium regions therein to form a spatially uniform average refractive index.

Masayuki Nishimura

Papers

Dispersion-shifted fiber

Measurement of the nonlinear refractive index in optical fiber by the cross-phase-modulation method with depolarized pump light.

Temperature dependence of chromatic dispersion in various types of optical fiber

Dispersion compensating fiber and optical transmission system including the same

Microstructured optical fiber