Filters are key devices in optical systems and are usually applied to signal suppression or selection based on their amplitude frequency responses. Different from amplitude filtering, an all-pass filter (APF) is a unique type of filter that exhibits a uniform amplitude and variable phase in the frequency response. Traditionally, an APF is designed to be ideal and waveguide loss as well as coupling loss are omitted, which is impossible in practice. Here we demonstrate a method of realizing an APF even when waveguide loss and coupling loss exist, and a feasible structure for realizing the APF with waveguide loss and coupling loss is proposed. The method indicates that an APF can be realized by introducing self-compensation of loss to the structure of an ideal single-stage APF, and further, an APF based on silicon-on-insulator foundry is fabricated and demonstrated. The method of self-compensation of loss can also be used to realize APFs in the electrical domain. We anticipate that our work will inspire realizations of more APF-related devices that once seemed impossible in practice, as well as loss related devices or structures.

中文翻译：

---

损耗自补偿实现光学全通滤波器

滤波器是光学系统中的关键器件，通常用于根据其幅频响应进行信号抑制或选择。与幅度滤波不同，全通滤波器 (APF) 是一种独特类型的滤波器，它在频率响应中表现出均匀的幅度和可变的相位。传统上，APF被设计为理想的，并且忽略了波导损耗和耦合损耗，这在实践中是不可能的。在这里，我们展示了一种即使存在波导损耗和耦合损耗也能实现 APF 的方法，并提出了一种实现具有波导损耗和耦合损耗的 APF 的可行结构。该方法表明，通过在理想的单级 APF 结构中引入损耗自补偿，可以实现 APF，进一步，制造并演示了基于绝缘体上硅代工厂的 APF。损耗自补偿的方法也可用于实现电气领域的APF。我们预计，我们的工作将激发更多的 APF 相关设备的实现，这些设备曾经在实践中似乎不可能，以及与损耗相关的设备或结构。