We demonstrate an electro-optic imaging system for measuring millimeter-wave propagation along a coplanar waveguide (CPW). A polarization-resolved microscope images small electro-optic effects due to millimeter-wave voltages between the signal and ground of the CPW. Dual electro-optic frequency combs demonstrate time-domain waveform imaging on-wafer with >100 GHz of bandwidth. A second configuration demonstrates continuous wave optically-derived vector network analysis with measurement planes on-wafer, filling the role of multiple electronic network analyzers but with instantaneous bandwidth and time-domain capability that cannot be achieved otherwise.
We demonstrate ultrawideband mmWave waveform generation based on optical frequency combs and additive frequency synthesis. We generate an electro-optic frequency comb, apply fine amplitude and phase control to pairs of comb lines (beat notes), and demultiplex the beat notes to multiple uni-traveling carrier photodiodes, which are connected on-wafer to a mmWave frequency combiner.
Using multi-tier microwave S-parameter and power calibrations, we demonstrate on-wafer mmWave power levels up to +12.7 dBm and fine amplitude and phase control with 0.1 dB and 25 mrad resolutions respectively. We apply this fine resolution to arbitrary waveform generation with 100 GHz of instantaneous bandwidth on a single photodiode. We also summarize new results with five photodiodes connected to an on-wafer frequency combiner and our efforts to integrate NIST’s high-power amplifiers up to 500 GHz and beyond.
This paper reports progress on a type of ultrafast photoconductive source that can be driven at 1550 nm but exhibits the robustness of GaAs (e.g., low-temperature-grown GaAs) driven at 780 nm. The approach is GaAs doped heavily with Er (≈4x1020 cm-3 or 2% atomic-Er-to-Ga fraction) such that ErAs nanoparticles form spontaneously during epitaxial growth by MBE. The nanoparticles are mostly spherical with a diameter of a few nm while the packing density is estimated as high as ~2.2x1019/cm3. Yet, the Er-doped GaAs epilayer maintains excellent structural quality and smooth surface morphology. A photoconductive switch coupled to a 4-turn square spiral antenna is fabricated and characterized. At least ~40 μW average THz power is generated when the device is biased at 75 V and pumped with a 1550-nm 90-fs-short pulsed laser having average power ~85 mW. This research is significant for 1550-nm-technologycompatible, cost-effective THz sources.
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