Amplicadores opticos

Optical Amplification

Source: Master 7_5

Optical Amplifiers
An optical amplifier is a device which amplifies the optical signal directly without ever changing it to electricity. The light itself is amplified. Reasons to use the optical amplifiers: Reliability Flexibility Wavelength Division Multiplexing (WDM) Low Cost Variety of optical amplifier types exists, including: SemiconductorOptical Amplifiers (SOAs) Erbium Doped Fibre Amplifiers (EDFAs) (most common)

Traditional Optical Communication al System
Loss compensation: Repeaters at every 20 20-50 km

Optically Amplified Systems
EDFA = Erbium Doped Fibre Amplifier e

Optical Amplification

Variety of optical amplifier types exist, including:
Semiconductor optical amplifiers Optical fibre amplifiers (Erbium DopedFibre Amplifiers) Distributed fibre amplifiers (Raman Amplifiers)

Optical fibre amplifiers are now the most common type One of the most successful optical processing functions Also used as a building block in DWDM systems
Source: Master 7_5

Overview

Erbium doped fibre amplifiers Amplifier applications Issues: Gain flattening and Noise Raman amplification

Basic EDF Amplifier Design• Erbium-doped fiber amplifier (EDFA) most common doped
– Commercially available since the early 1990’s – Works best in the range 1530 to 1565 nm – Gain up to 30 dB (1000 photons out per photon in!)

• Optically transparent
– “Unlimited” RF bandwidth – Wavelength transparent

Input 1480 or 980 nm Pump Laser

Coupler

Isolator Output Erbium Doped Fiber

Erbium Doped Fibre AmplifierA pump optical signal is added to an input signal by a WDM coupler Within a length of doped fibre part of the pump energy is transferred to the input signal by stimulated emission For operation circa 1550 nm the fibre dopant is Erbium Pump wavelength is 980 nm or 1480 nm, pump power circa 50 mW Gains of 30-40 dB possible
Isolator Input Isolator

WDM

Output Erbium Doped Fibre

Pump Source= Fusion Splice
Source: Master 7_5

Interior of an Erbium Doped Fibre Amplfier (EDFA)

WDM Fibre coupler

Pump laser

Erbium doped fibre loop

Fibre input/output
Source: Master 7_5

Operation of an EDFA

Power level

980 nm signal

1550 nm data signal

Power interchange between pump and data signals

Power level 980 nm signal

1550 nm data signal

Input

IsolatorIsolator

Output

WDM

Erbium Doped Fibre

= Fusion Splice

Pump Source

Physics of an EDFA

Erbium Properties

•

Erbium: rare element with phosphorescent properties
– Photons at 1480 or 980 nm activate electrons into a metastable state – Electrons falling back emit light in the 1550 nm range

540 670 820 980 Metastable state Ground state 1480

• •

Spontaneousemission
– Occurs randomly (time constant ~1 ms)

Stimulated emission
– By electromagnetic wave – Emitted wavelength & phase are identical to incident one

Erbium Doped Fibre Amplifiers

Consists of a short (typically ten metres or so) section of fibre which has a small controlled amount of the rare earth eleme erbium added to the glass in the form of ment an ion (Er3+). The principle involvedis the principle of a laser. When an erbium ion is in a high-energy state, a photon of light will stimulate it to energy give up some of its energy (also in the form of light) and return to a lower-energy (more stable) state (“stimulated emission”) emission”). The laser diode in the diagram generates a high high-powered (between 10 and 200mW) beam of light at a wavelength such that the erbium ionswill absorb it and jump to their excited state. (Light at either 980 or 1,480 nm wavelengths.)

Er+3 Energy Levels
• Pump: 980 or 1480 nm Pump power >5 mW • Emission: 1.52-1.57 µm Long living upper state (10 ms) Gain ≅ 30 dB

EDFA Operation
1. 2. 3. 4. A (relatively) high-powered beam of light is mixed with the input signal using a wavelength selective coupler. The mixed light is guided...