Wideband balanced photodetectors for classical and quantum light detection from optical and EUV sources to X-rays

The rapid development of coherent short-wavelength light sources in the extreme ultraviolet (EUV) and soft X-ray (SXR) regimes has created a growing need for advanced optoelectronic detection capabilities in this spectral range, particularly for quantum-noise-limited measurements, microelectronics and semiconductor metrology, and emerging quantum information applications. However, extending balanced photodetection to these wavelength regimes is severely hindered by a fundamental bandwidth-noise trade-off imposed by the exceptionally large junction capacitance of EUV-SXR silicon photodiodes. Here, we report the first application of a junction field-effect transistor (JFET) interface-based bootstrapped transimpedance amplifier architecture to large-area EUV-SXR photodiodes, overcoming the fundamental capacitance bottleneck that has previously prevented wideband balanced photodetection in this spectral range. By leveraging a low-noise JFET interface, we effectively isolate the photodiode capacitance and suppress the apparent input capacitance seen by the core amplifier. Combined with active compensation of parasitic feedback reactance, this architecture mitigates the conventional trade-off between detector active area and signal bandwidth. Experimentally, we achieved a system-level input-referred noise floor of 13 fA/Hz, closely approaching theoretical thermal limits. Furthermore, we achieved a six-fold extension in signal-to-noise-limited bandwidth. Through what we believe to be a novel grounded field plate, we also demonstrated a common-mode rejection ratio (CMRR) exceeding 30 dB up to 100 kHz, with the CMRR reaching 40 dB in the 2-20 kHz bandwidth, thereby reducing common-mode noise power by a factor of 10,000. Unlike single-photon detectors, this shot-noise-limited balanced photodetector is designed for homodyne-based classical and quantum optical measurements. This highly scalable, silicon-based architecture effectively bridges the short-wavelength detection gap, establishing a robust experimental platform for next-generation quantum-noise-limited and quantum-enhanced X-ray measurements, as well as ultra-sensitive inspection and metrology applications in high-numerical-aperture EUV lithography.