## Materials and Methods
### Optical Amplifier Characterization  
The goal of the optical amplifier characterization was to measure the performance of the FLAT as a function of input pump power, for a few lengths of fiber. The results from this experiment could be used to develop a computer model. Finally, the model could be used to make an amplifier design suitable for a SWaP constrained platform. The regime investigated for the optical amplifier characterization was a fixed pulse string at a repetition rate of 20 MHz. This regime had guard times on the order of what is anticipated for SWaP constrained platforms (\(\sim\)50 ns) that balance data rate and peak power produced. To capture the limiting case peak power generation for the link, data was recorded after the amplifier output decays to its steady state output (less than a few seconds). The experimental parameters used and ranges can be found in Table 2.  
Throughout the measurements, all of the fiber ends were cleaned at every connection and inspected with a fiber microscope. This was done to reduce the risk of fiber damage and to keep coupling losses as low as possible. All of the fiber optics from the pump and seed lasers up to the connector that interfaces with the erbium doped fiber entrance were left connected throughout all experimental runs. Additionally, all of the fiber optics between the output detectors and the connector that interfaces with the exit of the erbium doped fiber also remained connected throughout all experimental runs. The only optical components changed between measurements were the neutral-density (ND) filters on the U-bench, which have low insertion uncertainty, and the erbium doped fiber used for the experimental run. Connecting each erbium doped fiber may have introduced \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Repetition Rate & 20 MHz \\ Seed Peak Power at Entrance & 4.7 mW \\ Seed Pulse Width & 2.5 ns \\ Fiber Lengths & 26, 55, 86, 106 cm \\ Pump Power at Entrance & 0–300 mW \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The experimental parameters used for characterizing the FLAT. Figure 10: The TDC-GPX2 evaluation board used for laboratory testing of MOCT. The added SMA cables and resistors enable LVDS inputs for this development board. some coupling uncertainties when connected with the entrance and exit connectors. However, they were thoroughly inspected and cleaned before connecting to keep uncertainties low. Even with clean connectors, each fiber may have unique coupling losses at each end from manufacturing differences and different polishing batches. To measure the pump and seed laser signals, a detector was coupled to the connector that would join to the entrance of the erbium doped fiber. Each laser was separately turned on and the powers at the respective pickoffs to the entrance of the erbium doped fiber were measured. These measurements were used to determine the power at the erbium doped fiber entrance without needing to disconnect. The loss for the fiber optics after the exit of the erbium doped fiber was also measured. This loss was measured by directly connecting the fiber optics that were before and after the erbium doped fiber (with no ND filters). Each laser independently emitted light and measurements of the pickoff and the output detectors were recorded. Using the pickoff detector measurements and the calibration relating the pickoff measurements to the power at the erbium doped fiber entrance, the optical loss for each laser on the fiber optics after the erbium doped fiber was calculated. In this calculation, one uncertainty added is the coupling between the two sets of fiber optics, but this is assumed to be small compared to the losses from the exit fiber optics. A diagram of the FLAT characterization setup can be seen in Figure 11.  
A dynamic (pulsed), steady-state simulation was developed using the RP Fiber Power software (Version 7, RP Photonics Consulting GmbH, Bad Durrheim, Germany) [14] to model the performance of the FLAT.