Classification of optical delay lines

Classification of optical delay lines
Optical Delay Lines are core devices in the fields of optical communication, laser technology, and precision optical measurement. Their core function is to control the propagation time of optical signals by accurately adjusting the length of the optical path, achieving delay adjustment from picosecond to microsecond levels. This technology plays an irreplaceable role in ultrafast laser systems, optical coherence tomography (OCT), optical communication synchronization, and precision optical measurements.
From a functional perspective, optical delay lines can be divided into two categories: fixed optical delay lines and adjustable optical delay lines. Fixed delay lines provide a constant optical path difference, with a simple structure and high stability, suitable for applications that require a fixed delay amount. Adjustable delay lines can dynamically adjust the delay amount, usually achieved through mechanical scanning methods such as moving mirrors or stretching optical fibers, to meet the needs of real-time control and precise calibration, which is particularly critical in experiments and systems that require dynamic response.
From a structural perspective, optical delay lines are mainly divided into two typical architectures: free space type and fiber optic type. The free space delay line forms an optical path by constructing a mirror group in free space, and changes the optical path length by precisely moving the mirrors. The advantage of this structure lies in its minimal dispersion, ability to support a wide range of delay adjustments, and stable optical performance; But its disadvantages are also obvious, including large size, extremely high alignment accuracy requirements, sensitivity to environmental vibrations, and the need for strict isolation and temperature control measures. Fiber optic delay lines use fiber winding or stretching to achieve delay function, which has the advantages of compact size, low insertion loss, and easy system integration and deployment; However, fiber optic types may introduce significant dispersion and nonlinear optical effects, leading to pulse broadening or distortion and affecting signal quality.
In practical engineering applications, free space delay lines are commonly used for high-precision and large-scale delay adjustment scenarios, such as ultrafast laser pulse shaping, femtosecond laser system calibration, etc; Fiber optic delay lines are more suitable for compact systems, optical communication equipment, and on-site deployment scenarios that require high volume and integration. In recent years, the number of hybrid structured optical delay lines has gradually increased, which combines free space structures with fiber optic technology. This not only retains a large adjustment range and low dispersion characteristics, but also improves the system’s integration and environmental adaptability.