Refraction is a basic beam bending effect at two media’s interface. While traditional studies focus on stationary boundaries, moving boundaries or potentials could enable new laws of refractions. Meanwhile, media’s discretization plays a pivotal role in refraction owing to Galilean invariance breaking principle in discrete-wave mechanics, making refraction highly moving-speed dependent. Here, by harnessing a synthetic temporal lattice in a fiber-loop circuit, we observe discrete time refraction by a moving gauge-potential barrier. We unveil the selection rules for the potential moving speed, which can only take an integer v = 1 or fractional v = 1/q (odd q) value to guarantee a well-defined refraction. We observe reflectionless/reflective refractions for v = 1 and v = 1/3 speeds, transparent potentials with vanishing refraction/reflection, refraction of dynamic moving potential and refraction for relativistic Zitterbewegung effect. Our findings may feature applications in versatile time control and measurement for optical communications and signal processing.

折射是两种介质界面处的基本光束弯曲效应。虽然传统研究关注的是静止边界，但移动边界或势能可以实现新的折射定律。同时，由于离散波力学中伽利略不变性破坏原理，介质的离散化在折射中起着关键作用，使得折射高度依赖于运动速度。在这里，通过利用光纤环路中的合成时间晶格，我们观察了移动规范势垒的离散时间折射。我们揭示了潜在移动速度的选择规则，它只能采用整数v = 1 或小数v = 1/ q (奇数q ) 值来保证明确定义的折射。我们观察v = 1 和v = 1/3 速度时的无反射/反射折射、折射/反射消失的透明势、动态移动势的折射以及相对论 Zitterbewegung 效应的折射。我们的研究结果可能会在光通信和信号处理的多功能时间控制和测量中得到应用。