Our Semiconductor Optical Amplifier (SOA) is evaluated as a pre-amplifier, having 30-dB gain at 1310 nm and 0.3-A, in the 100GBASE-LR4 over 10, 20, 30 and 40-km Single Mode Fibers (SMF). Its Optical Signal Noise Ratio (OSNR) is linear to input power, and thus degrades over lower inputs causing thicker data waveforms at longer SMFs. Across higher inputs, the dominant effect is data pattern shown as multiple overshoots of bit 1. The longer Pseudo-Random Binary Sequence (PRBS) and slow SOA’s response worsen pattern effect. Our SOA’s response is approximate 60 ps. Comparing at 10 ^-11 Bit Error Rate (BER), the SOA’s Input Power Dynamic Range (IPDR) is reduced from 9.75 dB using shorter PRBS7 to 3.4 dB using PRBS31. The BER results of 1-channel amplification at 6 SOA’s inputs confirm both OSNR degradation and pattern effect. The optimal input with minimum BER is -13 dBm, corresponding to 40-km SMF’s attenuation. All BER curves of 4-channel amplification after 10, 20, 30 and 40-km SMFs are plotted. As SMF expands, the additional penalties due to Chromatic Dispersion (CD) at 10 ^-9 BER rise from 0.25 dB to 1 dB. Comparing 1 and 4-channel amplifications, the additional penalties due to Cross Gain Modulation (XGM) are 2-2.25 dB. Ultimately, our pre-amplifier SOA can extend the 10-km limit of 100GBASE-LR4 link to 40 km with a total penalty of 5.75 dB. Furthermore, it can be applied as the inline-amplifier to achieve 80-km distance, based on 10 ^-12 BER result at -5 dBm received power by QSFP28 transceiver.