High spectral efficiency offered by the coherent optical communication links makes them attractive for the nextgeneration optical communication links. Using advanced modulation schemes such as dual-polarization quadrature-amplitude modulation (DP-QAM) data rates beyond 200 Gb/s can be achieved. A key component of such links is the wide-bandwidth and high-linearity coherent optical receiver. In this paper, we present a fully differential (FD) optical receiver architecture consisting of a variable-gain transimpedance amplifier (VG-TIA) followed by a VG amplifier (VGA). The proposed optical receiver employs a dual-feedback automatic gain control (AGC) loop that controls both the front-end VG-TIA and the following VGA to achieve both low-noise and high-linearity operation. A new photodiode (PD) dc current cancellation scheme is developed and implemented for the full differential front-end TIA. A prototype dual-TIA chip is fabricated in a 0.13-μm SiGe BiCMOS √ process. The presented TIA achieves 20-pA√Hz input-referred noise (IRN) density, 27-GHz, 3-dB bandwidth, and 1.5% total harmonic distortion (THD) at 1-mApp input PD current and 500-mV_pp output voltage swing. This enables the 34-GBd operation with the bit error rate (BER) of 10-10 and 5.4 × 10^-4 using DP-QPSK and DP-16-QAM formats at optical signal-tonoise ratios (OSNRs) of 25 and 30 dB, respectively, demonstrating the 100and 200-Gb/s single wavelength optical coherent receiver operation. The dual-TIA chip occupies an area of 1.4 mm × 1.6 mm and consumes 313 mW per channel at 34 GBd from a 3.3-V supply.