We investigate a semiconductor optical amplifier (SOA) preamplifier model by suitably choosing the material and device parameters for the SOA to reduce the amplified spontaneous emission (ASE) noise at low range of 22.3 µW with 0.1-mW input power for a PIN receiver. Our proposed SOA optical preamplifier is found to be more relaxed from the optical alignment and antireflection coating, eliminates the need for optical filter, and gives large tolerance for an input light wavelength of more than 100 nm. We also investigate the receiver sensitivity for different bit rates. We show that receiver sensitivity is –69.9 dBm at a bit error rate (BER) of 4.6×10–10 for 10 Gbit/s and for the 40 Gbit/s bit rate the improved receiver sensitivity is –19.2 dBm with a PIN receiver. We also observe a sensitivity of –40.5 dBm at 40 Gbit/s with a differential phase shift keying (DPSK) receiver. Further, the impact of amplified spontaneous emission power, gain variation with input light wavelength, and optical gain for the TE & TM modes with input power for the PIN & DPSK receivers is illustrated. We show that the optical gain of the SOA is polarization independent and remains constant at 30.06 dB up to gain saturation. We also show that the DPSK receiver suffers less from ASE noise. The variation of material loss, length, and bias current for our SOA preamplifier to optimize the receiver sensitivity is further illustrated.