In week 6 we started to produce material for our poster. The aim is to collect information about fiber optics collaboratively. The topics for different teams are presented in Wiki-page: Optical fibers.
Using the collaborative inquiry technique, produce a first draft of your wiki page. Next week we study the pages more carefully and continue processing them.
Transparency (Thai)
Decibel (Binh)
Amplifiers / optical (Minh)
frequency (Phat)
depending variables (Phat)
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Background
What questions did the video/demo/simulation, etc. arise?
What questions did you pick up for further investigation?
Initial questions
How does it work …., what happens here, why ...?
Selected problem
What questions did you select to work in more details?
My explanation (original hypothesis)
What is your own explanation for your questions?
Critical evaluation
What strengths and weaknesses does your explanation have?
What I need to find out more?
How could I improve my explanation?
What do you not understand or know yet about this topic?
Finding more information
First you can list all the references to the additional material you find out in order to use them later.
Then try to understand what does it say about the problem.
Use your own language to explain the things. Don’t copy and paste text.
Use graphs and equations to illustrate
Additional questions
What new questions arised based on the new information?
How, what, why?
My new theories
Now I believe that …
You can continue the loop critical evaluation, finding more information, new questions, etc… in the given time limit.
Summary
In your own words, explain what have you done and what have you found. Evaluate critically how good your theory is. Compare to the information you find from the internet.
Background
The requirement is understand amplifier definition in optical fiber domain.
Initial questions
What is amplifier?
What is the roll of amplifier in optical fiber study?
Selected problem
All questions were selected to answer in detail.
My explanation
Amplification is required to solve the problem of degradation of signal transmitting in optical fibers.
Critical evaluation
More details and reading as well as reasoning that need to be provided.
Finding more information
Reading more in Fiber optics engineering of Mohammad Azadeh.
Final theory
Optical link has limit in range as there is always attenuation of propagating light in a normal fiber. One method to solve the problem is detect the optical signal before the critical low value and covert it back to electrical domain and create new copy of optical signal. Another method is using optical amplifier. Without need of converting back optical signal to electrical domain, an amplifier can be used in different applications. It can be use as an inline amplifiers to compensate the attenuation of optical signals as well as pre-amplifiers in optical detectors to improve sensitivity of the receiver or as power boosters to raise output power of an optical transmitter.[1,149]
There are two categories of amplifiers: semiconductor optical amplifiers (SOAs) and fiber amplifiers. Optical gain in semiconductors is based on forward-biased junction. Fiber amplifier contains optical fiber which is doped with a rare earth element such as neodymium (Nd) and praseodymium (pr) etc… The existence of dopants creates new energy bands within the fiber.
Figure1: Band diagram of a doped fiber amplifier. Copied from Azadeh, M. (2009). Fiber optics engineering.[1,150]
Figure 1 illustrates the dopants ions interact with the pump signal with frequency fp and goes to higher energy state Ep . The ions have short lifetime ( Tp ) and quickly move to lower energy band, Et , in which they have longer lifetime ( Tl ). Because Tl >> Tp , population inversion is created. Inverted system interacts with main signal of frequency f , results in amplification of signal as stimulated emission happens.
The erbium doped fiber amplifier (EDFA) is the most popular type as El – Eo exists in the wavelength of 1550 nm. In consequence, EDFA can amplify signal in lowest range of attenuation of silica fibers, results in the popularity of using in long distance communication. Typical EDFA amplifiers can supply gain in 30nm band (1530-1560 nm) with gain of 20-30 dB.
Figure 2: Sample EDFA configuration. Copied from Azadeh, M. (2009). Fiber optics engineering.[1,151]
Figure 2 shows one example of co-directional pumping as the main and pump signals travel in same direction. EDFAs have very important role in long-range optical fiber communication, and subjected to high interest of researching for increase of bandwidth and performance.