Simple and robust symbol rate estimation method for digital coherent optical receivers

A novel symbol rate estimation (SRE) technique utilizing the clock tone (CT) obtained by Godard timing recovery algorithm is proposed. By this technique, the known sampling rate of the analog-to-digital converter (ADC) in digital coherent optical receivers can used as a reference to directly determine the unknown signal symbol rate. The impact of polarization mode dispersion (PMD) on the CT magnitude can be mitigated by using the hybrid correlation function (HCF) consisting of both auto-correlation function (ACF) and cross-correlation function (XCF) of the received signal spectrum, while the chromatic dispersion (CD) impact can be mitigated by adaptive CD compensation techniques. This technique is simple, accurate, applicable to advanced modulation formats commonly used, and robust to various link impairments. Numerical simulations and experimental results are presented to validate this technique.