This paper describes a dense, high-speed, and low-power CMOS optical receiver implemented in a 65-nm CMOS technology. High data rate is achieved using an RC double-sampling front-end and a novel dynamic offset-modulation technique. The low-voltage double-sampling technique provides high power efficiency by avoiding linear high-gain elements conventionally employed in transimpedance-amplifier (TIA) receivers. In addition, the demultiplexed output of the receiver helps save power in the following digital blocks. The receiver functionality was validated by electrical and optical measurements. The receiver achieves up to 24 Gb/s data rate with better than 160-μA current sensitivity in an experiment performed by a photodiode current emulator embedded on-chip. Optical measurements performed by a 1550-nm wire-bonded photodiode show better than - 4.7-dBm optical sensitivity at 24 Gb/s. The receiver offers peak power efficiency of 0.36 pJ/b at 20 Gb/s from a 1.2-V supply and occupies less than 0.0028 mm² silicon area.