A high-resolution coherent optical spectrum analyzer eliminating the mirror effect via Hilbert transform

Compared with traditional grating-based spectrometers, a coherent optical spectrum analyzer (COSA) can provide much higher resolution by converting optical spectral signals into electrical beat signals via heterodyne detection. However, the heterodyning process produces two symmetric sideband peaks for each spectral component, i.e., the mirror effect, which fundamentally limits the resolution. To overcome this constraint, we introduce an instantaneous frequency masking algorithm to eliminate the mirror effect in this study. Experimental results demonstrate a spectral resolution of 2 MHz using the same hardware previously limited to 6 MHz. Furthermore, a compact silicon-photonic wavelength reference for sweep linearization is utilized in the system, achieving long-term wavelength accuracy of ±0.1 pm. The proposed method establishes a cost-effective new paradigm for surpassing the inherent resolution limits of COSA.