ee 230 optical fiber communication lecture 7 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
EE 230: Optical Fiber Communication Lecture 7 PowerPoint Presentation
Download Presentation
EE 230: Optical Fiber Communication Lecture 7

Loading in 2 Seconds...

play fullscreen
1 / 28

EE 230: Optical Fiber Communication Lecture 7 - PowerPoint PPT Presentation


  • 148 Views
  • Uploaded on

EE 230: Optical Fiber Communication Lecture 7. Optical Amplifiers-the Basics. From the movie Warriors of the Net. Amplifier Types and Applications. Amplifiers are used to overcome fiber loss They are used in 4 basic applications: In-line amplifiers for periodic power boosting

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'EE 230: Optical Fiber Communication Lecture 7' - damita


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
ee 230 optical fiber communication lecture 7
EE 230: Optical Fiber Communication Lecture 7

Optical Amplifiers-the Basics

From the movie

Warriors of the Net

amplifier types and applications
Amplifier Types and Applications

Amplifiers are used to overcome fiber loss

They are used in 4 basic applications:

In-line amplifiers for periodic power boosting

Power Amplifier to increase the power to greater

levels than possible from the source

Pre-amplifier to increase the received power sensitivity

Distribution loss compensation in local area or cable networks

Fiber Optics Communication Technology-Mynbaev & Scheiner

characteristics of all amplifiers
Characteristics of all amplifiers
  • They operate by creating a population inversion, where there are more individuals in a high energy state than in a lower one
  • The incoming pulses of signal on the fiber induce stimulated emission
  • They saturate above a certain signal power
  • They add noise to the signal
inhomogeneous gain broadening
Inhomogeneous Gain Broadening

Inhomogeneous broadening

The individual atomic responses within and inhomogeneously broadened transition all add up to yield the measured lineshape

A Gaussian inhomogeneously broadened atomic lineshape such as produced by doppler broadening in atoms

Lasers-Siegman

unstimulated population densities in 2 level atom
Unstimulated Population densities in 2 ‘ level atom

Energy levels 1 and 2 and their decay times. By means of pumping, the population density of level 2 is increased at the rate R2 while that of level 1 is decreased at the rate R1

Idealy t21~tsp<<t20 so t2~tsp

For large DN or No (also called inversion density)

We want t2 long, but t21 not too small, t1 and R1 large

ideal amplifier system
Ideal Amplifier System

Third excited state with very short lifetime,

no fluorescence

Second excited state with very long

lifetime and high cross section for

stimulated emission

Pump process

with large cross

section

Energy gap between first and

second excited states matches

telecommunication frequencies

First excited state with very short

lifetime

noise figure measurement
Noise Figure Measurement

Fiber Optics Communication Technology-Mynbaev & Scheiner

3 main types and 3 big ideas
3 main types and 3 Big Ideas
  • The main types of optical amplifiers are:
    • Semiconductor amplifiers (lasers that aren’t lasing)
    • Doped fiber amplifiers
    • Raman and Brillouin Amplifiers
  • The three big ideas
    • Gain and gain bandwidth
    • Gain saturation
    • Noise and noise figure
semiconductor optical amplifiers
Semiconductor Optical Amplifiers

Fiber Optics Communication Technology-Mynbaev & Scheiner

types of soa
Types of SOA
  • Fabry-Perot Amplifier
    • High gain but non-uniform gain spectrum
  • Traveling wave amplifier
    • Broadband but very low facet reflectivities are needed
  • Gain as a function of frequency
    • Ripples are caused by the cavity modes
    • The overall gain curve is due to the width of the atomic transition in the semi-conductor

Fundamentals fo Multiaccess Optical Fiber Networks

Dennis J. G. Mestgagh

amplifier bandwidths
Amplifier Bandwidths

Comparison of the bandwidths of Fabry Perot and Traveling wave amplifiers

Fiber Optics Communication Technology-Mynbaev & Scheiner

traveling wave soa
Traveling Wave SOA

To make a traveling wave Semiconductor Optical Amplifier the Fabry-Perot cavity resonances must be supressed. To accomplish this the reflectivity must be reduced.

Three approaches are commonly used:

Anti-reflection coating

Tilted Active Region

Use of transparent window regions

Fiber Optics Communication Technology-Mynbaev & Scheiner

saturation power
Saturation Power

Semiconductor Optical amplifiers saturate silmilarly to a 2 level atom

The typical saturation output power for

SOAs is around 5-10 mW

Gain saturation and saturation power

Fiber Optics Communication Technology-Mynbaev & Scheiner

crosstalk in semiconductor amplifiers
Crosstalk in Semiconductor Amplifiers

Rate equation for pump current

If Φ suddenly goes to zero, as in 1-0 sequence,

Time constant is (ns)

If Φ suddenly turns on,

which is smaller

parameters on previous slide
Parameters on previous slide
  • N=carrier density (cm-3)
  • I=pump current (amp=coul/s)
  • q=charge on electron (coul)
  • L,w,d=cavity dimensions (cm3)
  • =recombination lifetime (s)
  • =confinement factor (unitless)
  • =photon density (cm-3)
  • a=gain coefficient (cm-1)
crosstalk in semiconductor amplifiers23
Crosstalk in semiconductor amplifiers

If time constant for spontaneous decay of excited state is shorter than the bit duration, the population of the excited state will vary sharply with the optical power in the fiber, and gain will depend on the fraction of 1s and 0s in the data stream.

If time constant is long, then the population in the excited state will be constant, dependent upon the pump power but not the signal power.

reduction of polarization dependence
Reduction of Polarization Dependence
  • Three main approaches
  • Connect the amplifiers in series
    • Residual facet reflectivity
    • can cause undesired coupling between amplifiers resulting in poor noise and dynamic performance
  • Connect them in parallel
    • Good solution but complex
  • Double pass with polarizaion
  • rotation
    • Automatic 6 db loss due to coupler

Fiber Optics Communication Technology-Mynbaev & Scheiner

undesired effects in an soa
Undesired effects in an SOA
  • Cross saturation can cause undesired coupling between channels
    • This can be used for wave length conversion and “controlling light with light”
  • If used for multiple channels in a switched network gain must be adjusted as channels are added and dropped
  • Four wave mixing is also quite pronounced in SOAs
    • Causes undesired coupling of light between channels
    • Can however also be used to advantage in wavelength converters.
  • High coupling loss
  • Polarization sensitive gain

Fiber Optics Communication Technology-Mynbaev & Scheiner

semiconductor amplifier advantages
Semiconductor amplifier advantages
  • Are the right size to be integrated with waveguide photonic devices (short path length requirement)
  • Can easily be integrated as preamplifiers at the receiver end
  • Use same technology as diode lasers
  • Gain relatively independent of wavelength
  • Are pumped with current, not another laser
semiconductor amplifier disadvantages
Semiconductor amplifier disadvantages
  • Polarization dependence
  • Self-phase modulation leading to chirp
  • Cross-phase modulation
  • Four-wave mixing and crosstalk
  • Extremely short (ns) excited state lifetimes