# An optical all-pass filter realized by using self-compensation of loss

## TL;DR

This paper presents a novel method to realize optical all-pass filters with inherent transmission loss by using self-compensation, demonstrated through a silicon-on-insulator structure, expanding practical applications of APFs.

## Contribution

It introduces a self-compensation technique for lossy all-pass filters, enabling their practical realization in optical systems where loss is unavoidable.

## Key findings

- Successfully fabricated a lossy APF using SOI technology.
- Demonstrated self-compensation of loss in optical APFs.
- The method can be extended to electrical APFs.

## Abstract

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 lossless, which is impossible in practice. Here we demonstrate a method of realizing an APF even when transmission loss exists, and a possible structure for realizing the lossy APF is proposed. The method indicates that a lossy APF can be realized by introducing self-compensation of loss to the structure of an ideal single-stage APF, and an APF based on silicon-on-insulator (SOI) 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.

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Source: https://tomesphere.com/paper/1905.10020