Delay control can be achieved by changing the transmission distance of light (one-way or two-way) or adjusting the refractive index of optical fibers. For example, a manually adjustable delay line can change the optical path by moving the reflector through a screw guide, with a delay range of up to 50 millimeters. Adjustable fiber delay lines achieve nanosecond to picosecond time delay control by adjusting the transmission path length or refractive index of optical signals in the fiber.
Mainly based on the transmission characteristics of optical fibers and the combination of electronic or mechanical control technology. The optical signal is first converted into a form suitable for optical fiber transmission, and then transmitted through optical fibers. By using built-in electronic control systems or mechanical adjustment mechanisms, the length of optical fibers can be accurately controlled or the propagation speed of optical signals in optical fibers can be changed. For example, special structures such as fiber Bragg gratings and fiber circulators can be used to adjust the delay time of optical signals. For example, an electrically adjustable fiber optic delay line integrates a precision electric motor and control system internally. When receiving a control signal, the electric motor drives the fiber optic cable to undergo small length changes, or affects the refractive index of the fiber optic cable by changing environmental parameters such as electric and magnetic fields around the fiber optic cable, thereby changing the propagation time of the optical signal in the fiber optic cable and achieving delay control.
Main types
Free space type: The optical signal is emitted from the input fiber collimator, reflected by a movable mirror, and returned to the output end. By adjusting the displacement of the mirror and changing the optical path length, delay adjustment is achieved. It is commonly used in laser rangefinder calibration, optical coherence tomography medical imaging, etc.
Fiber winding type: Utilizing the fixed delay characteristics of long-distance optical fibers, multiple gear adjustments are achieved by switching between different lengths of fibers. It has a compact structure, strong anti-interference ability, and is suitable for the optical signal synchronization needs of data centers.
RF fiber type: modulates RF signals into optical signals, transmits them through optical fibers, and then demodulates them into electrical signals. By controlling the length of the fiber or integrating adjustable optical devices, nanosecond level dynamic delay can be achieved, which can be used for phased array radar beamforming, antenna calibration, etc.