PHTN 4661 Lab Report
In this lab, we use C++ to simulate a square core waveguide. We explore the properties and the fundamental mode of it. We are provided some header files and a main function under C++ language. And also two PDF files to indicate the things we should do and the principles of the lab. Now I am going to answer the questions one by one and explain the steps of the lab.
Preamble
Firstly we are provided a library of functions called the …Light Numerical Recipes‟(LNR) and a file called …square.dat‟ which contains the parameters of a waveguide. We do not need to change the file. In preamble, we just run the file and type in …square.dat‟ to read the parameters of the waveguide. And then the program shows the Effective index of it.Just like the following figure. To keep the display of the result, we add “cin >> filename;” at the bottom.
Problem1
With the given formula, we can calculate the V value easily by calculator. Here n co=1.450,
n c1=1.447, ρ=5. When λ=1.55,V=1.89 and the waveguide is single-moded.When λ=1.3,V=2.25 and the waveguide is not single-moded.
This result means a waveguide can be both single or multi-moded when the wavelength are different.
Problem2
In this step, we only change the middle part of the main_ file as follows
We use a loop to calculate the some thing as we did in preamble. The only difference is that we calculate a series of wavelength and write the results in a file called …results.txt‟. And we get results as follow
From the results, we can know the effective index at every wave length in the range of 1.6 to 1.2. And we find that when wavelength increases, the effective index decreases.
Problem3
We change the main part of main_ as flow. In the following steps, we do not change the wavelength of 1.55. And only calculate the situation when λ=1.55.
And we get a file called …results3.txt‟ to hold the intensity of the filed. The result is showed below.
And then we plot it using the FDM Plot.m. Then we get the plot like this:
Problem4
Now we we want to calculate the power in the core. So the main part is modified as follow:
Running this program, we get the following result:
When the wavelength is 1.55, around76% power are in the core. So the power is not in the core for all. There is some power outside the core. So the light travels alone both core and domain, but not strictly travel alone the core.。