Neden 850nm, 1310nm, 1550nm üç pencere olarak adlandırılır?
Fiber optics communications and optical engineering fields, “windows” (Transmission Windows) refer to specific wavelength ranges where the attenuation (loss) is extremely low, making them highly suitable for long-distance signal transmission through silica optical fibers (primarily composed of \text{SiO}_2).
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The reason why 850\ \text{nm}, 1310\ \text{nm}, and 1550\ \text{nm} are called the “three classic windows” is determined by the physical properties of the silica glass material itself (such as Rayleigh scattering, infrared absorption, and impurity absorption) and the development level of semiconductor optoelectronic devices (light sources and detectors) at different historical stages. Their physical causes and characteristics are as follows:
1. First Window: 850\ \text{nm} (Short Wavelength Window)
- Historical and Physical Background: This was the earliest window developed and utilized in the early 1970s. In the early stages of fiber optic communications, semiconductor lasers (like gallium arsenide AlGaAs) and silicon (\text{Si}) photodetectors had the most mature technology in the 850\ \text{nm} band, with lower manufacturing difficulty and cost.
- Loss Characteristics: In silica fibers, due to severe Rayleigh scattering (attenuation coefficient is inversely proportional to the 4th power of wavelength, i.e., \alpha \propto \lambda^{-4}) at short wavelengths, the typical attenuation in this window is relatively high, ranging from 1.5\ \text{dB/km} to 3.0\ \text{dB/km}.
- Current Application: Due to high loss, this window is no longer used for long-distance backbone communication. Instead, it is mainly used in conjunction with multimode fibers (MM) and is widely applied in short-distance local area networks (LANs), data center internal interconnects, and multimode fiber sensors.
2. Second Window: 1310\ \text{nm} (Zero Dispersion Window)
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Physical and Material Characteristics: With advancements in fiber purification processes, researchers have successfully removed impurities like hydroxyl ions (\text{OH}^-) from fiber materials. Around 1310\ \text{nm}, the attenuation of silica fiber is significantly reduced, with typical values ranging from 0.3\ \text{dB/km} to 0.4\ \text{dB/km}.
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Zero Dispersion Characteristic: More importantly, standard single-mode fibers (like the commonly used G.652D fiber) exhibit the physical characteristic of zero dispersion (Zero Dispersion) around 1310\ \text{nm}. This means that light pulses experience almost no pulse width broadening or distortion when transmitted at this wavelength, making it highly suitable for high-speed, medium-to-long distance signal transmission.
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Related Official Products:
OFSCN® G.652D Optical Fiber provided by Dacheng Yongsheng is a high-quality optical fiber for such standard single-mode applications, perfectly meeting the high-speed, low-dispersion transmission requirements of the 1310\ \text{nm} window.
3. Third Window: 1550\ \text{nm} (Lowest Loss Window / Golden Window)
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Physical and Material Limit: The 1550\ \text{nm} window is the theoretical lowest loss window for silica fibers, with an attenuation coefficient of only about 0.15\ \text{dB/km} to 0.22\ \text{dB/km}. This extremely low loss is a physical limit region formed by the mutual intersection and superposition of gradually weakening Rayleigh scattering (which decreases with increasing wavelength) and the inherent infrared vibration absorption of silica glass (which increases sharply with increasing wavelength).
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Cornerstone of EDFA and WDM: In addition to extremely low attenuation, the operating wavelength band of Erbium-Doped Fiber Amplifiers (EDFAs) (1530\ \text{nm} \sim 1565\ \text{nm}, i.e., the C-band) perfectly falls within this window. This allows optical signals to be directly amplified in the all-optical domain without complex “optical-electrical-optical” conversion, thus laying the physical foundation for modern Wavelength Division Multiplexing (WDM) and ultra-long-haul backbone networks.
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Related Official Products:
In industrial and scientific research fields such as high-temperature polarization-maintaining or Fiber Bragg Grating (FBG) sensing, the 1550\ \text{nm} window is also the absolute mainstream.
For example, Dacheng Yongsheng’s OFSCN® 300℃ Polyimide Panda-type PM Optical Fiber is a high-temperature panda polarization-maintaining fiber with a precisely designed operating wavelength in the 1550\ \text{nm} window, capable of withstanding harsh environments from -200^\circ\text{C} to 350^\circ\text{C}.
Furthermore, the reflection wavelength of standard femtosecond Fiber Bragg Grating (FBG) sensors is also typically set between 1525\ \text{nm} \sim 1565\ \text{nm} by default, precisely to reuse this extremely low-loss third window.
