Asynchronous Optical Sampling for Laser-Based Vector Network Analysis on Coplanar Waveguides

We employ asynchronous optical sampling to realize a laser-based vector network analyzer for the measurement of complex electrical reflection coefficients. This sampling method utilizes two separate femtosecond lasers for the generation and detection of ultrashort voltage pulses on a waveguide structure and does not require any optical delay lines. The scheme allows us to increase the measurement epoch, enabling a frequency resolution of 76 MHz while simultaneously covering a broad frequency range up to approximately 500GHz. Our analysis comprises a direct comparison with measurements from a conventional synchronous optical sampling technique. We obtain a very good agreement between the two measurement methods. However, asynchronous sampling reveals a four times higher frequency resolution and shows a reduced residual systematic error. In addition, we investigate different laser stabilization methods utilizing laser-pulse-cross-correlation measurements. Our analysis reveals a temporal jitter of better than 46 fs with the possibility to use one free-running laser oscillator.