Software-synchronized all-optical sampling for fiber communication systems

TLDR

The study introduces a software‑synchronized all‑optical sampling system that generates synchronous eye diagrams, measures accurate Q values without clock recovery, supports up to 160 Gb/s at 100 MHz sampling, and provides a theory for Q estimation versus gate width. The system employs a software‑synchronization algorithm that determines the offset between data and sampling rates, automatically identifies pattern lengths, applies noise averaging, and uses a 100‑MHz sampling rate to enable accurate Q measurement and synchronous eye diagram generation, with a theoretical model linking Q to sampling gate width. The algorithm proved robust to poor signal quality, adding under 100‑fs timing drift, enabling pulse‑level investigation of detrimental effects, while the system’s high bandwidth sampled more noise, yielding lower Q values than conventional electrical sampling.

Abstract

This paper describes a software-synchronized all-optical sampling system that presents synchronous eye diagrams and data patterns as well as calculates accurate Q values without requiring clock recovery. A synchronization algorithm is presented that calculates the offset frequency between the data bit rate and the sampling rate, and as a result, synchronous eye diagrams can be presented. The algorithm is shown to be robust toward poor signal quality and adds less than 100-fs timing drift to the eye diagrams. An extension of the software synchronization algorithm makes it possible to automatically find the pattern length of a periodic data pattern in a data signal. As a result, individual pulses can be investigated and detrimental effects present on the data signal can be identified. Noise averaging can also be applied. To measure accurate Q values without clock recovery, a high sampling rate is required in order to establish the noise statistics of the measured signal before any timing drift occurs. This paper presents a system with a 100-MHz sampling rate that measures accurate Q values at bit rates as high as 160 Gb/s. The high bandwidth of the optical sampling system also contributes to sampling more noise, which in turn results in lower Q values compared with conventional electrical sampling with a lower bandwidth. A theory that estimates the optically sampled Q values as a function of the sampling gate width is proposed and experimentally verified.