Optical calibration systems of the Pacific Ocean Neutrino Experiment

Abstract

This work presents the design and performance characterization of the optical calibration systems produced for the Pacific Ocean Neutrino Experiment (P-ONE). These include novel light-pulse driver circuitry based on gallium nitride field-effect transistor technology and its application to directional and isotropic, self-monitoring optical calibration instruments. A total of 330 directional light pulsers and two isotropic, 17-inch calibration modules (P-CALs) were produced for the first P-ONE line. We present the designs and performance of both the directional and isotropic calibration devices and perform detailed optical characterizations of both full-production batches. In a wavelength range of $365-520\,$nm, our developed driver circuits achieve emission intensities up to $10^{11}\,$photons and pulse widths as small as $1.4\,$ns, respectively. Light-pulse drivers and self-monitoring electronics in the P-CAL were characterized using the same experimental setup, and the instrument's optical-isotropy design was optimized in combination with a dedicated GEANT4-based simulation framework. The optimized P-CAL achieves a simulated isotropy grade of $1.00 \pm 0.01$ across the entire $4 π$ solid angle range. These simulation investigations were explicitly confirmed by dedicated measurements in both air and water using two independent experimental setups, and we report the results. With this, a detailed performance estimate for deployed P-CAL modules in P-ONE was possible.

Figures (24)

• Figure 1: Conceptual view of the optical calibration systems planned for P-ONE. The image shows a schematic view of a cluster of P-ONE detection lines together with illustrations of the optical emission profiles of directional, isotropic, and axicon flashers.
• Figure 2: Concept of directional flashers in P-ONE-1. The images show (a) details of the directional flasher concept and (b) their integrated layout in P-OM and P-CAL (*); adapted from ghuman_situ_2025.
• Figure 3: (a) Baseline schematic of the GaN FET pulser circuit design showing core switching components, bias voltage, and AC-coupled trigger monitor for time-stamping (reproduced with permission from henningsen_picosecond_2023henningsen_self-monitoring_2020 and modified) and (b) a photograph of an assembled flasher PCB.
• Figure 4: Photon yield (top), time profile (center) and spectrum (bottom) results for all directional flasher units that passed QC. Lines and shaded bands show the median and [$25-75$]% quantiles, respectively. For the photon yield, the fit combines a linear component with a reverse-sigmoid activation function, intended to model the lasing onset. For the time profile and spectrum, the continuous lines are obtained by linear interpolation of raw timing and spectral data, binned in [20]ps and [2]nm intervals, respectively. Top- and center-row figures are partly reproduced from ghuman_situ_2025.
• Figure 5: Aging test results for one of each flasher board type. Shown are the relative light yield and rise time of the observing SiPM for flasher pulses as a function of total operating time. Yield medians across different channels have been artificially offset to improve visual separation. Flashers were operated at a bias voltage of [24]V and a frequency of [100]kHz. The corresponding P-ONE equivalent lifetime is shown as a second axis.