Swept coherent spectrum analysis of the complex optical field

Abstract

Swept coherent optical spectrum analysis is becoming a viable method for high-resolution spectral measurements. This technique is typically used to measure the power spectral density, however, the measurement of the spectral phase of periodically modulated optical signals is also possible. The adjacent spectral peaks are simultaneously observed by a modulated optical local oscillator. Optical mixing translates the phase difference between the adjacent optical spectral peaks to an easily measured low-frequency electrical signal. This process preserves phase relationships. Since the spectral phase is reconstructed from the phase difference between the adjacent spectral peaks, the common mode optical phase noise is cancelled. Simultaneous measurement of the spectral amplitude and phase results in complete characterization of the complex optical field of the modulated optical carrier. Knowledge of the complex optical field allows transformation from the frequency domain to the time domain by means of the inverse Fourier transform. Theoretical background and experimental results are included.