Bandwidth Improvement in a Resonant Optical MST-Probe Applicable to Near-Field Imaging

In this letter, we address the design, implementation, and performance assessment of a broadband optical near-field (NF) probe based on the modulated scatterer technique (MST). The MST probe incorporates a photodiode, a short dipole, and a matching network, which improves the scattering level and operating bandwidth of the probe. The probe was fabricated on a perforated ceramic substrate to achieve a lower permittivity, resulting in more accurate measurements. As a con sequence of using a perforated substrate, the structural scattering of the probe decreases considerably. The impact of the proposed matching network on the frequency performance of the probe was investigated and experimentally verified. The probe was also validated by measuring the transversal E-field of a 50-Ω microstrip transmission line at different frequencies. Measurement and simulation results are in good agreement, which proves the accuracy of the measurement data by the proposed probe.