A BiCMOS integrated optical receiver with high sensitivity and linearity is presented. An automatic gain control transimpedance amplifier and linear post amplifiers are used to maintain a high linearity with multilevel modulation. Using multilevel signaling and large-diameter integrated photodiodes make the presented optical receiver suitable for small-bandwidth high-attenuation large-core PMMA step index plastic optical fiber. A measured sensitivity of -31dBm (BER=10-9) at 250Mb/s is presented for a binary signal. A data rate of 500Mb/s and a sensitivity of -25dBm (BER=10-9) are achieved with four-level pulse amplitude modulation (4-PAM). An error-free transmission over 40m PMMA step index plastic optical fiber was achieved at 500Mb/s using 4-PAM signaling with the presented multilevel optical receiver.