1. EDFA Amplifier
Raman Amplifier
Semiconductor Amplifier
A COMPARISON BASED STUDY

2. Prepared and Presented By:
Saimunur Rahman
Metric No: C093003
Dept. of Computer Science & Engineering
International Islamic University Chittagong

3. Introduction to Optical Amplifiers
 In order to transmit signals over long distances (>100 km) it is necessary to
compensate for attenuation losses within the fiber.
 Initially this was accomplished with an optoelectronic module consisting of
an optical receiver, a regeneration and equalization system, and an optical
transmitter to send the data.
 Although functional this arrangement is limited by the optical to electrical
and electrical to optical conversions.
 Several types of optical amplifiers have since been demonstrated to
replace the OE –electronic regeneration systems.

4. Introduction to Optical Amplifiers
(Cont.)
 These systems eliminate the need for E-O and O-E conversions.
 This is one of the main reasons for the success of today’s optical
communications systems.

5. Optical Amplifiers
 The general form of an optical amplifier:

6. Optical Amplifier Types
 Some types of Optical Amplifiers are:
 Semiconductor optical amplifiers(SOAs)
 Fiber Raman and Brillouin amplifiers
 Rare earth doped fiber amplifiers
 The most practical optical amplifiers to date include the SOA and EDFA
types.
 New pumping methods and materials are also improving the performance
of Raman amplifiers.

7. Today we shall talk about these
Optical Amplifiers
and
some comparisons among them.

8. EDFA Amplifier
An Overview

9. A figure of EDFA Device

10. Inside an EDFA

11. History of EDFA Amplifier
 Before the invention of EDFAs regenerators we're used to amplify signal
which was very costly and inefficient to use.
 Idea for EDFA invented in 1960s
 First commercial viable EDFA invented in 1987 by researchers from
Southampton University and AT&T Bell Laboratories.

12. What is EDFA Amplifier?
 EDFA stands for Erbium Doped Fiber Amplifier.
 Where, Erbium is a chemical element of lanthanide series in periodic table.
 Erbium symbol is Er and atomic number is 68.
 Erbium looks like a silvery-white solid metal when artificially isolated.
 Erbium's principal uses involve its pink-colored Er3+ ions, which have
optical fluorescent properties particularly useful in certain laser
applications.
 Erbium-doped glasses or crystals can be used as optical amplification
media, where erbium (III) ions are optically pumped at around 980 nm or
1480 nm and then radiate light at 1530 nm in stimulated emission.

13. What is EDFA Amplifier? (Cont.)
Fig: Erbium-colored glass
 This process results in an unusually mechanically simple laser optical
amplifier for signals transmitted by fiber optics.
 This is known as Erbium Doped Fiber Amplifier or simply EDFA.

14. Erbium doped fiber: Profile

15. Basic EDFA overview
 EDFA convert optical signal to another amplified optical signal without
using any electrical domain.
Fig: Basic Block diagram of EDFA

16. Working Principle of EDFA
Fig: Energy level transferring block

17. Working Principle of EDFA (Cont.)
 The 980 nm pump laser excites erbium ions from lower energy level 1 into a
higher energy level 3.
 From level 3 the erbium ions goes to level 2.
 From level 2 the erbium ion into x which 1550nm signal which jumps back to
lower level 1.
 In this there is emission of 1550nm photon.
 This process is known a stimulated emission.
 EDFA has an amplification window for optical wave analysis for which the
optical fiber has useable gain.
 This wavelength range is gain able by a properties of dopained ion, the glass
structure of optical fiber and the wavelength and power of pump laser.

18. Schematic diagram of EDFA

19. Gain Spectrum for EDFA
 Since the gain spectrum of erbium resembles a 3-
level atom it is possible to model the gain
properties using this approach.
 Several different wavelength bands have been
designated for wavelength division multiplexing
and EDFAs have been designed to operate in
these bands.
 The divisions have been designated as:
 S-Band1480-1520nm
 C-Band1521-1560 nm
 L-Band 1561-1620nm

20. Optical Gain of EDFA
 Rare earth doped optical amplifiers work much like a laser.
 The primary difference is that they do not have a resonator.
 Amplification occurs primarily through the stimulated mission process.
 The medium is pumped until a population inversion state is achieved.
Pump powers are typically several 20-250 mW. An isolator is used to
reduce reflections at the input to the amplifier. A narrow band optical filter
is used to reduce transmission of amplified spontaneous emission
frequency components.
 The resultant optical gain depends both on the optical frequency and the
local beam intensity within the amplifier section.

21. Optical Gain of EDFA (Cont.)
 For basic discussion consider a two-level homogeneously broadened
medium.
 The gain coefficient can be expressed as:
 Here, 𝑔0 is the peak gain,ω is the optical frequency of the incident signal,
𝜔0 is the transition frequency, P is the optical power of the incident signal,
T2 is the dipole relaxation time, and Ps is the saturation power.
 Typically T2 is small < 1ps, and the saturation power Ps depends on gain
medium parameters such as the fluorescence time and the transition cross
section.

22. Gain and noise figure of EDFA (Sample)
Fig: A Characteristic plot of gain and noise figure for an erbium doped fiber
amplifier pumped ~30 mW at 980 nm.

23. EDFA Gain Equalization
 Gain equalization can be accomplished in
several ways:
 Thin film filters
 Long period fiber gratings
 Chirped fiber Bragg gratings

24. Gain Flattering

25. Characteristics of EDFAs:
(Advantages)
 High power transfer efficiency from pump to signal power (> 50%).
 Wide spectral band amplification with relative flat gain (>20dB) – useful for
WDM applications.
 Saturation output> 1mW (10 to 25 dBm).
 Gain-time constant long (>100 msec) to overcome patterning effects and
inter-modulation distortions( low noise).
 Large dynamic range.
 Low noise figure.
 Polarization independent.
 Suitable for long-haul applications.

26. Disadvantages of EDFAs:
 Relatively large devices (km lengths of fiber) – not easily integrated with
other devices.
 ASE – amplified spontaneous emission. There is always some output even
with no signal input due to some excitation of ions in the fiber –
spontaneous noise.
 Cross-talk effects.
 Gain saturation effects.

27. Applications of EDFA
 EDFA can be used as:
 Power amplifiers
 In‐line amplifiers,
 As well as pre‐amplifiers.

28. Raman Amplifier
An Overview

29. A figure of Raman Amplifier Device

30. History of Raman Amplifier
 The Raman scattering of light was discovered more than 70 years ago and
was named after one of the authors of the discovery.
 In 1971 Stolen et al experimentally observed the stimulated Raman
emission in a single-mode optical fiber.
 This experiment was the beginning of more than 25yearsdevelopment of
practical Raman fiber amplifiers and lasers.
 In 1980 the Raman amplifier was started.
 From 1990 we are practically using these devices for communication.

31. What is Raman Amplifier?
 A Raman amplifier is a device which takes input 𝜔𝑠 and amplified in the
same direction or opposite direction with pump laser 𝜔𝑃.
 Here is a very important rule/formula we must consider for this
amplification.
Wavelength 𝝎𝒔 < Wavelength 𝝎𝑷
Usually a few tens of nm
𝜔𝑠
𝜔𝑃
𝜔𝑠

32. The mechanism behind Raman
Amplifier
 The mechanism behind the Raman amplification is Stimulated Raman
Scattering (SRS).
 SRS is a non linear effect of optical fiber.
 For the SRS the optical power must b greater than the threshold to happen
at least minimum 500mW. This is a codition.
 Now we will look at how it actually happens.

33. The mechanism behind Raman
Amplifier (Cont.)
 The photon of pump beam ωp is scattered by
molecules in the fiber medium and become the
lower energy photon ωs .
 The valance of the energy becomes vibration and
dissipated in the fiber medium.
 For instance optical power this non linear effect can
transfer most of the pump power ωp into signal
power ωs.

34. Raman Gain Coefficient
 The frequency difference between ωp and
ωs has to match a relationship in order to
fully use of this non linear effect.
 This is sown here by using Raman gain
coefficient graph.

35. Raman Gain Coefficient (Cont.)
 First picture is showing the pump laser at
1535nm which has more higher signal to
data signal.
 In second picture, the pump laser power
transferred to the signal power as shown
here.

36. Raman Amplifier Types
 There are basically two types of Raman amplifiers
as given here:
 Distributed Raman Amplifier (DRA) uses the
transmission fiber itself as the medium, into which
a backward pump is injected.
 Discrete (Lumped) Raman Amplifier (RA) The
amplifier consists of a coil of dedicated fiber
together with pumps.

37. Real World Raman Amplifier
Application
 For getting the full benefits of
amplification EDFA and Raman
amplifiers as used together.
 Distributed amplifier amplifies the
signal in a backward direction.
 EDFA amplifier amplifies the signal in a
forward direction.
 Here we have shown the figure of
signal levels and how it changed.

38. Properties of Raman Amplifiers:
 The peak resonance in silica fibers occurs about
13THz from the pump wavelength. At 1550nm this
corresponds to a shift of about 100 nm.
 As indicated power is transferred from shorter
wavelengths to longer wavelengths.
 Coupling with the pump wavelength can be
accomplished either in the forward or counter
propagating direction.
 Power is coupled from the pump only if the signal
channel is sending a 1 bit.

39. Pump Arrangement to Extend the
Range for St. Raman Amplification:
 An array of laser diodes can be used to
provide the Raman pump.
 The beams are combined and then coupled
to the transmission fiber.
 The pump beams can counter propagate to
the direction of the signal beams.

40. Difficulties with Raman Amplifiers
 The Pump and amplified signals are at different wavelengths. Therefore the
signal and the pump pulses will separate due to dispersion (waveguide
dispersion) after a certain propagation distance.
 A 1 psec pump pulse at 600nm separates from a 1 psec Stokes pulse in~30 cm.
 A second problem is that the pump power decreases along the fiber length
due to linear absorption and scattering – Raman gain is greater at the input
end.
 A final problem results from amplifying spontaneous Raman photons. This
occurs when the pump power is increased to offset attenuation losses and
spontaneous Raman photons are coupled into the guided mode all along the
length of the fiber. This increases noise.

41. A discrimination between EDFA and RA
after a long brief

42. Combined EDFA and RA
 With only an EDFA at transmit end the
optical power level decreases over the fiber
length.
 With an EDFA and Raman the minimum
optical power level occurs toward the
middle, not the end of the end of the fiber.

43. Application of Raman Amplifier
 Raman Amplifiers can be used as:
 Pre‐amplifiers
 Power amplifiers
 Distributed amplifiers in a number of digital and analogical transmission experi
ments.

44. Semiconductor
Amplifier
An Overview

45. A figure of Semiconductor Amplifier
Device

46. Semiconductor Amplifier
 An electrical current passed through the device
that excites the electrons in the active region.
 When photon(light) travel through the active
region it can cause these electron to lose some of
their extra energy in the form of more photons
that match the wavelength of the initial ones.
 Therefore, an optical signal passing through the
active region is amplified and is said to have
experienced “gain”.

47. Semiconductor Amplifier (Cont.)
 Both edges of the SOA are designed to have very low reflectivity so that
there are no unwanted reflections of the signal within the semiconductor
itself.
 This is the main difference from regular laser that have reflective facets in
order to build up the intensity of light within the semiconductor material.

48. SOA: Amplification Process
 Semiconductor have valance and conduction
band.
 At thermal equilibrium valance band has higher
population.
 Under population inversion condition
conduction band will have higher population.
 Population inversion is achieved by forward
biasing the p-n junction.

49. SOA Design

50. Characteristics of SOA:
 Polarization dependent – require polarization maintaining fiber.
 Relatively high gain ~20 dB.
 Output saturation power 5-10 dBm.
 Large BW.
 Can operate at 800,1300,and 1500nm wavelength regions.
 Compact and easily integrated with other devices

51. Characteristics of SOA (Cont.)
 Can be integrated into arrays
 High noise figure and cross-talk levels due to nonlinear phenomenon such
as 4-wave mixing. This feature restricts the use of SOAs.
 Limited in operation below 10Gb/s. (Higher rates are possible with lower
gain.)

52. SOA Vs. Semiconductor Laser
 Both are similar and in principle and construction.
 Essentially Fabry-Perot cavities, with amplification achieved by external
pumping.
 The key of SOA is to preventing self-oscillations gathering laser output.
 SOAs is electrically pumped by injected current.

53. SOA Applications
 Power booster.
 In-line amplifier.
 Detector preamplifier.
 Optical switching element.
 Wavelength converter.

54. Optical Amplifiers (in short)
Advantages
And
Disadvantages

55. Er‐Doped Fiber Amplifier EDFA
Advantages:
 High gain (40–50 dB),
 Low noise (3–5 dB),
 Low polarization sensitivity,
 EDFAs are fully compatible with the rest of the fiber optic transmission link.
Limitations:
 Large size,
 High pump power consumption (efficiency ‐ 10dB/1mW).

56. Raman Amplifier (RA)
Advantages:
 Low noise (3–5 dB).
 Wide gain bandwidth (up to 10 nm).
 Distributed amplification within the transmission fiber.
Limitations:
 Low gain (10 dB).
 Requirement of high pump power.

57. Semiconductor Optical Amplifier
Advantages:
 Small size.
 Transmission bidirectional.
 Smaller output power then EDFA.
 Less expensive then EDFA.
Limitations:
 Lower gain (20–30 dB) then EDFA.
 Higher noise (7–12 dB) then EDFA.
 Polarization dependence.
 High nonlinearity.

58. A short comparison
Between
discussed amplifiers

59. Optical Amplifier: Comparison

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61. Question/ Answer
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