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A fiber connector polished at 8° angle to minimize back-reflections. Essential for high-power Raman links.
The gradual reduction of optical signal power with distance, measured in dB/km. For SMF, typical loss is 0.2 dB/km at 1550 nm.
The long-haul portion of a telecom network connecting major data centers and regions. Raman amplifiers are heavily deployed here.
The 1530–1565 nm window in silica fibers, historically the main transmission band because of its low attenuation and compatibility with EDFAs. Most backbone systems are optimized for C-band.
The spreading of optical pulses due to wavelength-dependent speed in the fiber, measured in ps/nm·km. Must be managed in high-speed networks.
Laser safety classifications for high-power pumps (>500 mW). Require strict handling, interlocks, and alarms.
A CW laser emits a continuous, unmodulated optical beam with constant amplitude and power over time, unlike pulsed lasers that emit short bursts.
Pump light launched in the opposite direction to the signal (from receiver back toward the transmitter), reducing noise accumulation.
A form of WDM with very closely spaced channels (often 50 GHz or 100 GHz apart), enabling dozens to hundreds of channels in a single fiber.
Dispersion-Compensating Fiber (DCF) is a specially engineered fiber with high negative chromatic dispersion used to counterbalance the positive dispersion accumulated in standard transmission fibers (like SMF or DSF).
Dispersion-Shifted Fiber (DSF) is a single-mode optical fiber designed so that its zero-dispersion wavelength is shifted from ~1310 nm to the 1550 nm region, where fiber loss is minimal.
Configuration where the existing transmission fiber provides continuous gain along tens of kilometers, improving OSNR and reducing nonlinearities.
Uses the existing transmission fiber as the gain medium. Pump light is injected along long spans (50–100 km), giving continuous distributed gain.
A noise mechanism where light undergoes two successive Rayleigh backscattering events in the fiber, becoming amplified and degrading OSNR.
The 1360–1460 nm region of optical fiber. Historically limited by the “water peak” (high OH absorption around 1383 nm), but low-water-peak fibers have made E-band transmission more practical.
A nonlinear effect where three optical waves interact in a fiber to generate a fourth wave, potentially causing crosstalk between WDM channels.
The uniformity of amplifier gain across a wavelength band. Multi-pump schemes are designed to flatten the Raman gain profile.
The 1570–1610 nm region, adjacent to C-band, offering extra spectrum for DWDM systems. Frequently used to expand fiber capacity without laying new cables.
Uses a short segment (1–2 km) of specially engineered fiber for localized amplification, operating like a discrete amplifier module.
Medium-distance optical networks (tens to hundreds of km) typically connecting cities or regional hubs. Usually dominated by EDFAs due to shorter spans.
Interference caused by multiple reflections inside the fiber link. It can create ghost channels and degrade coherent detection.
The measure of amplifier-added noise relative to an ideal noiseless amplifier. For EDFAs typically ~4–5 dB, for Raman ~6–8 dB.
Undesired interactions in optical fibers at high power, such as four-wave mixing, self-phase modulation, and cross-phase modulation. Raman amplifiers can mitigate some of them.
A device that selectively transmits light at certain wavelengths while blocking others. Used in WDM systems for channel separation, noise suppression, or band selection.
A passive device that blocks reflected pump or signal light from propagating backward, protecting lasers and reducing noise.
A key quality metric comparing signal power to noise power in a given bandwidth. High OSNR is essential for advanced modulation formats (100G, 400G, 800G).
The orientation of the electric field of light as it propagates. In optical fibers, polarization effects can influence signal quality, leading to impairments like PMD.
A fiber impairment caused by birefringence, where different polarization states travel at slightly different speeds.
High-power lasers (commonly 1420–1490 nm) that inject energy into the transmission fiber to generate Raman amplification. Their stability and wavelength choice determine system gain.
A parameter describing the efficiency of Raman scattering in a given fiber. Higher Raman gain coefficient means more pump energy is transferred to the signal per unit length.
The broadband response curve of Raman amplification, with a width of ~6 THz (~50–100 nm). Allows simultaneous amplification of many WDM channels.
The frequency difference between pump and signal photons, ~13.2 THz in silica. Defines the wavelength separation between pump and amplified signal.
The measure of how much light is reflected back at connectors or splices. Higher ORL means lower reflections, which is critical for Raman systems.
The 1460–1530 nm region, providing additional spectrum below C-band. It is less common in commercial systems but increasingly studied for future high-capacity networks.
A fiber segment between two active nodes (amplifiers or ROADMs). Raman amplifiers extend the span length by adding distributed gain.
Uneven amplification across wavelengths, often requiring multiple pump wavelengths or gain-flattening filters.
A nonlinear optical process where high-power pump photons transfer energy to lower-frequency signal photons via molecular vibrations in silica fiber. Basis of Raman amplification.
Transoceanic optical cables where amplifiers must be extremely reliable. Raman amplification is used to maximize reach without regenerators.
The >1625 nm region, beyond L-band. Fiber attenuation rises sharply here, so it is less widely used, but still valuable for testing, monitoring, and some niche transmission applications.
A method of combining multiple optical signals at different wavelengths into the same fiber to increase capacity. Channels remain independent and can be added or dropped at network nodes.
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