In order to achieve small size, light weight, and immunity to electromagnetic interference, it is desirable to replace bulky coaxial cables with optical fiber in advanced radar front-ends. Such applications require a large dynamic range that is beyond the reach of conventional intensity modulation–direct detection fiber-optic links. A coherent fiber-optic link employing an optical phase-locked loop (OPLL) phase demodulator has been proposed as a solution to this problem. The challenge is the practical realization of the OPLL demodulator that satisfies the stringent loop delay requirement. A novel attenuation counterpropagating (ACP) OPLL concept has been proposed and demonstrated as a solution. In this paper we review the recent progress in realizing chip-scale ACP-OPLL devices. In particular, we focus on the latest measurement results achieved using a hybrid integrated ACP-OPLL, as well as the design and performance potential of a monolithically integrated ACP-OPLL photonic integrated circuit.