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Erbium Doped Fiber Amplifiers (EDFA) - Coggle Diagram
Erbium Doped Fiber Amplifiers (EDFA)
Principle
Active Medium
Ions serve as the active medium for optical gain
Excitation Process
1) Optical pumping excites ions to higher energy states
2) Stimulated emission occurs when incoming photons trigger ion photon emission
3) Results in optical gain
Core Material
Ytterbium (Yb)
Holmium (Ho)
Neodymium (Nd)
Thulium (Tm)
Erbium (Er)
Spectral Range
Depends on the type of ion used
Covers a broad spectrum: visible to infrared region
807 nm
Pumping
Three-Level System at 807 nm
Ions pumped from 4I15/2 to 4I9/2.
Fast relaxation (~1 µs) to 4I13/2
Enables population inversion for amplification.
Slow radiative decay (~14 ms)
First Semiconductor Pump
Leads to emission at 1520-1560 nm.
Operated at 807 nm using AlGaAs lasers.
Amplification
It occurs at 4I13/2 to 4I15/2 with emission of another photon
Excited-state absorption (ESA)
will increase
additional absorption of pump photons (807 nm) include transitions from 4I13/2 to 2H11/2
Pumping Efficiencies
0.8 dB/mW at 820 nm
Lower than efficiencies at 980 nm and 1480 nm (11 dB/mW at 980 nm)
Gain Achievements
Requires pumping power of 40–50 mW
Achieved with AlGaAs semiconductor lasers
30 dB gain achievable
Reducing Pump Power
Use fluorophosphate fibers
Use silica fibers doped with aluminum and phosphorus
1480 nm
Advantages
Higher Tolerance to Wavelength Variations
Easier Monomode Operation
Cheaper Multimode Pump Lasers
Better Field Overlap in Fiber Core
Wide Pump Wavelength Range
Disadvantages
Higher Pump Power Requirement
Higher ASE Noise
Difficult Population Inversion
Introduction
Definition & Importance
Used in optical communication
Most deployed fiber amplifier
Amplification Window
Works in the third transmission window
Wavelength range: 1530 nm – 1570 nm
Suitable for silica-based optical fiber
Implementation Components
Pump Laser: 980 nm, 1480 nm
Isolators: Used for stabilization
Amplifiers and Components
Types of EDFA Amplifiers
Boost Amp: Strengthens signals before transmission
Boost/Line Amp: Used in long-distance transmission
Pre-Amp: Used for weak signal amplification
Components Inside an EDFA
WDM Coupler: Merges input signal with pump lasers inside the Er-doped fiber
Monitoring Output Ports: Helps control power levels
Isolator: Prevents backward ASE (Amplified Spontaneous Emission)
Key Optical Components
Wavelength Coupler (WC): Merges optical signals
Termination: Manages excess energy
Pump Laser Diode (980 nm, 1480 nm): Provides energy for signal amplification
Remote Pumping
used in order not to have to electrically feed the amplifiers and remove electronic parts
Pumping
Energy Level Broadening
Occurs when erbium ions (Er³⁺) are doped into silica fiber
Energy Level Transitions
Pump Absorption Wavelengths:
514 nm, 530 nm, 665 nm, 800 nm, 980 nm, 1480 nm
Fast (1 µs) non-radiative decay
Excitation Levels:
4I9/2, 4I11/2, 4I13/2, 4I15/2
Emission Range: 1520-1560 nm (14 ms lifetime)
Pumping Wavelengths
Possible at 532 nm, 670 nm, 807 nm, 980 nm, 1480 nm
Semiconductor pump lasers are commonly used at 820 nm, 980 nm, and 1480 nm
Historical Developments
Early Pumps
Used high-power visible pumps (argon ion, Nd:YAG, dye lasers)
Led to inefficient and bulky amplifiers
Modern Approach
Uses semiconductor pump lasers for efficiency
980 nm
Mechanism
Pumping at 980 nm excites ⁴I₁₅/₂ → ⁴I₁₃/₂.
Fast non-radiative decay to ⁴I₁₃/₂.
Uses Er³⁺ energy levels.
Optical amplification in the 1520-1560 nm range.
Applications
Semiconductor lasers with emission spectra in the 980-1480 nm range.
Optical amplifiers in fiber-optic communication.
Advantages
High ground-state absorption cross-section.
Most efficient among 807 nm, 980 nm, and 1480 nm.
Requires less power.
High slope efficiency: 11 dB/mW.
Absence of ESA (Excited State Absorption).
Produces less Amplified Spontaneous Emission (ASE) noise.
Gain
Dependence on Pump Power
Initial Phase: Gain increases exponentially as pump power increases, exciting more erbium ions.
Saturation Phase: At high pump power, most erbium ions are excited, and further increase in power has minimal effect.
Dependence on Fiber Length
Initial Increase: Gain increases with fiber length.
Optimum Fiber Length: A peak gain value is reached at an optimum fiber length.
Excess Fiber Length Issue: Beyond the optimum length, gain decreases because the pump power is insufficient, leading to photon absorption instead of amplification.