What Are EDFA And EYDFA?

EDFA is an active optical device that amplifies weak 1550nm optical signals by doping the core of an optical fiber with rare earth element "Erbium (Er)", utilizing the stimulated emission effect of erbium ions.

Key features: low noise, high gain, wide bandwidth

Ports:

1. Signal input port (IN): Connect the weak 1550nm signal that needs to be amplified (such as the signal after optical fiber transmission loss, or the weak signal before the receiver). The input power is typically -30 to -10 dBm and must match the type of optical fiber (e.g., SMF-28).

2. Signal output port (OUT): Outputs the amplified 1550nm signal (for subsequent transmission or reception). The output power is typically between 0 to 20dBm (milliwatts level), with a low reflection design (to avoid signal return interference).

3. Pump Port: Connects to the pump laser to provide excitation energy for the erbium ions (core energy input port). Main pump wavelengths: 980nm (low noise) or 1480nm (high gain); pump power 100~500mW.

4. Monitoring Port (MON): Extracts 1%~5% of the output signal for real-time monitoring of the amplified signal's power and wavelength stability (for operational use). The output power is much lower than the main signal (usually -20~-10dBm), which does not affect the transmission of the main signal.

Operating Principle:

1. Pump Excitation (Energy Injection)The pump laser injects 980nm/1480nm pump light through the "pump port," and the Er³⁺ ions in the core absorb the pumping energy, transitioning from the ground state (4I₁₅/₂) to a high-energy excited state (980nm pump → 4I₁₁/₂; 1480nm pump → 4I₉/₂).

2. Population Inversion (Condition for Amplification)The high-energy Er³⁺ ions are highly unstable and rapidly drop to a metastable state (4I₁₃/₂) via "non-radiative transitions" (with a lifetime of about 10ms, allowing for long-term retention); when the number of Er³⁺ ions in the metastable state significantly exceeds that of the ground state ions, a "population inversion" occurs (a core condition for optical amplification).

3. Signal Amplification (Stimulated Emission)The 1550nm signal light that needs to be amplified enters the erbium-doped fiber through the "input port." The photon energy of the signal light perfectly matches the transition energy from the metastable state to the ground state of the Er³⁺ ions, exciting the metastable Er³⁺ ions to rapidly transition back to the ground state and release new photons that are identical in frequency, phase, and polarization to the signal light; these new photons superconductively combine with the original signal light, achieving "exponential amplification" of the signal power, which is ultimately output through the "output port."

Applications:

1. Long-distance optical fiber communication backbone network, serving as a "line amplifier", deployed in intercity and transoceanic optical cables to compensate for signal attenuation.

2. Optical fiber communication terminal, where the receiver end acts as a pre-amplifier to amplify weak signals, enhancing the receiving sensitivity of mobile base stations and optical modems.At the transmitter end, it acts as a power amplifier to slightly increase transmission power, such as the optical signal output of 5G base stations.

3. In CATV (Cable Television) systems, amplifying television signals in the 1550nm wavelength range to achieve coverage for hundreds of kilometers, avoiding picture quality degradation due to attenuation.

4. Optical fiber sensing systems, amplifying weak optical signals from strain and temperature sensors, such as real-time monitoring of bridges and oil and gas pipelines, extending sensing distance (up to over 100 kilometers).

Doping both erbium ions and ytterbium ions in the optical fiber core, utilizing the mechanism of ytterbium ions "efficiently absorbing pump light and transferring energy to erbium ions," achieves high power optical signal amplification devices in the 1550nm wavelength band, breaking through the power limits of EDFA.

Key features: Compared to EDFA, it has higher pump absorption efficiency, stronger high power tolerance, and higher output power.

Ports:

1. Signal Input Port (IN): Connects to 1550nm signal (weak or medium power signal), with a wider input power range (-20 to 0dBm) and high power tolerance (to avoid burning out).

2. Signal Output Port (OUT): Outputs high power 1550nm signal (for laser applications or high power transmission), with output power ranging from 1W to 1kW (from watt to kilowatt level), requiring high power connectors (such as FC/APC high power version), with burn protection and light leakage prevention.

3. Pump Port: Multiple pumps can be injected in combination to increase total pump power (the core of high power output). Mainstream pump wavelengths: 808nm (low cost) or 915nm (high efficiency); single pump power of 5 to 20W, total power of multiple pumps can reach over 50W.

4. Monitoring/Control Port: ① Monitors output power and temperature (to avoid overheating); ② External control module for adjusting pump power/gain. The monitoring port extracts 0.1% to 1% of the signal (to avoid affecting high power output); the control port supports RS485/Ethernet protocol.

Operating Principle:

1. Pump Excitation (Ytterbium Ion Preference) Multi-pump lasers inject pump light at 808nm/915nm through the "pump port". The ytterbium ions (Yb³⁺) in the fiber core preferentially absorb energy, transitioning from the ground state (²F₇/₂) to the excited state (²F₅/₂).

2. Energy Transfer (Ytterbium to Erbium) The excited ytterbium ions do not directly emit photons; instead, they efficiently transfer energy to adjacent erbium ions (Er³⁺) through "non-radiative energy transfer," allowing the erbium ions to transition from the ground state (4I₁₅/₂) to a metastable state (4I₁₃/₂). This step addresses the low efficiency of erbium ion direct absorption of pump light in EDFA and avoids energy waste caused by high concentrations of erbium ions.

3. Signal Amplification (Erbium Ion Stimulated Emission) Consistent with EDFA: The 1550nm signal light excites metastable erbium ions to transition, releasing frequency-matched photons to achieve signal amplification. Due to the stronger energy transferred by ytterbium ions, it can support higher power signal output (watt-level / kilowatt-level).

Applications:

1. High-power fiber communication, used as a "power amplifier" for metropolitan area networks and access networks, enhances the total output power of multi-channel signals, such as in suburban optical networks covering more than 50 kilometers.

2. Industrial-grade fiber lasers, serving as core amplification devices, output kilowatt-level 1550nm lasers used for metal cutting (stainless steel, aluminum alloy), welding, and surface treatment (such as automobile manufacturing, aerospace).

3. Medical laser equipment, outputting watt-level lasers used for ophthalmic surgery (such as cataract treatment), dermatological treatments (such as pigmentation removal, hair removal) - the 1550nm wavelength has moderate tissue penetration in the human body with minimal damage.

4. Space optical communication, where EYDFA acts as the ground station power amplifier in satellite-to-ground laser communications, outputting high-power signals to overcome atmospheric loss, such as laser data transmission from Beidou satellites.

5. In the field of scientific research, used for laser spectral analysis, lidar (such as atmospheric pollutant monitoring), and as a laser driving source for inertial confinement fusion (ICF).