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This program is funded by the National Science Foundation through grant number PHY-1157044.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Increasing Efficiency of Fiber Optics with a 178 Degree Axicon

We found the transmitted power through a 250 micron fiber with just a 500 mm lens to be 2.32 mW. The power before the fiber is 3.72 mW. This gives an efficiency of 57.6%. Transmitted powers and efficiencies of different diameter fibers with the axicon are shown below.

Figure 1: This graph shows the transmitted power through a fiber of a certain diameter.

Figure 2: This graph shows the efficiency through a fiber of a certain diameter.

Now there is two key points that are important to these results. First, the transmitted power of 2.08 mW we got for the 250 micron fiber was a continuous improvement. Each new try, we got a better transmitted power. Thus, with a bit more tweaking that power of 2.08 mW can be a much larger power. Second, the 300 – 500 micron fibers were 4 feet long instead of 3 feet. Thus, we would get much higher powers through the other fibers if we used 3 feet long fibers for them.

Difference Frequency Generation

We were able to confirm DFG by showing Phase Matching through the AgGaS2 (Silver Thiogallate) DFG crystal. We used a 1470 nm signal beam and a 1750 nm idler beam with 83% of the energy being the signal and 17% of the energy being the idler. Our resulting wavelength was 9200 nm and we plotted the phase matching of the crystal as shown below in figure 1. The maximums occurred at 0 degrees (or 360 degrees) and at 130 degrees. The minimums occurred at 60 degrees and at 250 degrees.

Figure 3: Phase Matching of DFG crystal

After this we went on to find the largest power we could create after the crystal with our setup. We found a largest power after our crystal when we adjusted the signal beam to 1450 nm and the idler beam to 1705 nm. The energy split between the signal and the idler was 66% signal and 34% idler. This gave us a resulting wavelength of 9700 nm. With this configuration, we got a power of 10.5 mW after the DFG. We also measured the power of light through the germanium window with and without a calcite crystal and found that we were getting better results without the calcite (the calcite is aligned so that signal and idler lose overlap in time). Powers observed from this are shown in figure 2 below.

Figure 4: Powers of variating setups when signal is1450 nm and idler is 1705 nm

Figure 5: Summary of Results in last paragraph.

For more on my DFG project click here