A compact tunable optical true time delay consists of an optical subassembly to apply dispersion-free time delay to the input optical signal, and a mechanical subassembly to facilitate tuning the delay using a linear actuator. The deployment of a precision optical ferrule sliding in a precision split sleeve offers a self-contained and inexpensive method to minimize optical misalignment during the tuning process, which releases the burden of the mechanical subassembly and is also advantageous in keeping the device compact. The exterior dimension remains unchanged at any moment despite the interior motion. Both reflection-type and transmission-type optical time delays are introduced, driven either manually or electrically.