## 3 EDFA's Space Qualification and Test
### Thermal Vacuum Tests  
A prototype module of the CubeSat's EDFA was used several months before the final TVT for a preliminary functional long-duration test under high-temperature vacuum (hot cycling). The result of this test can be seen in Figure 8, which shows the dependence of the output optical power on the EDFA's temperature during one hour of continuous operation starting at a temperature of +55 \({}^{\circ}\)C. The EDFA's typical behavior can be confirmed, with the output power dropping as the temperature rises. Figure 9 shows a picture of the EDFA's module in the final stage of this test when its case temperature reached about +90 \({}^{\circ}\)C.  
The final thermal vacuum tests were performed within a vacuum range of \(10^{-6}\) to \(10^{-7}\) mbar and a temperature range of \(-30\)\({}^{\circ}\)C to +55 \({}^{\circ}\)C with a temperature variation rate of 1 \({}^{\circ}\)C/min. As shown in Figure 10, multiple functional tests were carried out, with the main emphasis on maintaining a dwell time of 1 h at extreme levels (\(-30\)\({}^{\circ}\)C and +55 \({}^{\circ}\)C) during three cycles each. The denomination of the functional tests depends on the cycle temperature and the sequential order. For example, FT1C is the first functional test of the cold cycles and FT3H is the third functional test of the hot cycles. All the functional tests during these extreme levels had a typical duration of 20 min. Figure 8: EDFA’s long-duration high-temperature vacuum test. Figure 7: EDFA module during vibration tests on the X-Y horizontal vibration bench (**left**) and \(Z\) vertical vibration bench (**right**). To monitor the EDFA's case temperature, type-K thermocouples (TC) were attached in the middle point of each case surface except for the top and bottom surfaces which had two TCs in each surface. As shown in Figure 11, the EDFA module was placed inside a jig with heaters in the cube sides. During the hot cycles (+55 \({}^{\circ}\)C), the case temperature reached a temperature of around +90 \({}^{\circ}\)C and during the cold cycles (\(-\)30 \({}^{\circ}\)C), the temperature reached around +10 \({}^{\circ}\)C at the end of the cycles (see Figure 10). Figure 11: EDFA module inside a jig with the heaters and thermocouples for the thermal vacuum tests. Figure 9: EDFA under high-temperature vacuum test. Figure 12 shows the result of the EDFA's module functional verification during a continuous 24 h thermal vacuum test including three cold cycles and three hot cycles. The EDFA's operation under extreme-temperature conditions can be understood from the results taken in this measurement campaign. The case temperature rises after the amplifier is enabled, which has a different impact on the optical output power depending on the temperature. The output power tends to fall when the temperature rises during the hot cycles and to rise with temperature during the cold cycles. This experiment was designed to achieve the required output optical power of 2 W (33 dBm) during the 20 min functional tests, in the beginning of the hot cycles and in the end of the cold cycles. An initial experiment (FT0) was performed under vacuum but in ambient temperature before the thermal cycling to confirm the negligible optical power loss (in the order of 0.1 dB) during the 20 min test. It can be observed that the optical power loss is around 1 dB after the 20 min test during the hot cycles after the EDFA has increased its temperature from about 30 \({}^{\circ}\)C to reach close to 90 \({}^{\circ}\)C, which was considered the maximum tolerable case temperature to avoid fatal failure. To reach 2-W after the 20 min test during the cold cycles, the initial temperature was set about 3 dB below. Two additional cold cycles (FT1C1 and FT1C2) were run to confirm the smaller power variation with less extreme cold temperatures. Table 1 shows the detailed numerical results of the full TVT campaign.