arXiv subjects

Ichiro Jikuya

Publications and source records attributed to Ichiro Jikuya.

3 recordsLinked to original sources

arXiv2026

Millimeter-wave adaptive optics: Demonstrating closed-loop correction for lowest Zernike modes

We report on a five-element prototype wavefront sensor for millimeter-wave adaptive optics (MAO), enabling closed-loop correction of tip-tilt and defocus via secondary mirror (M2) displacement. MAO is essential for large ground-based millimeter/submillimeter telescopes to maintain surface accuracy under wind and thermal distortions. Our sensor, based on radio interferometry, measures excess path lengths from the primary mirror to a focal-plane receiver. A previous two-element prototype achieved < 10 um accuracy at the Nobeyama 45 m telescope. The new five-element system, operating at 20 GHz, was installed on the same telescope. A ``Moon-edge'' experiment confirmed detection of wavefront gradients through strong correlation with continuum flux. Implementing a PI controller closed the sensor-M2 loop, stably suppressing the lowest Zernike modes. This approach establishes a foundation for metrology in future large-aperture submillimeter facilities such as AtLAST/LST.

astro-ph.IM↗

arXiv2026

Anti-windup PI controller for millimeter-wave adaptive optics: a Nobeyama 45 m radio telescope simulation

This work addresses the control problem for Millimeter-wave Adaptive Optics (MAO), which we define as compensating for the distance variation between the primary reflector (M1) and the receiver. We utilize a measurement system developed by Tamura et al. to track these variations. The challenge is formalized as an asymptotic constant disturbance suppression problem. We demonstrate that an anti-windup proportional-integral (AWPI) controller effectively solves this problem while respecting the physical movement constraints of the optical driving system. Simulation results, based on the Nobeyama 45-m Telescope with a two-axis translating sub-reflector (M2), validate the performance of the proposed AWPI approach.

astro-ph.IM↗

arXiv2026

Control problem in millimeter-wave adaptive optics

Millimeter-wave Adaptive Optics (MAO) is essential for high-precision large-aperture submillimeter telescopes, requiring real-time compensation of wavefront errors by capturing them as spatially-discrete excess path length (EPL) fluctuations. This paper presents a unified control-theoretic framework for the EPL compensation problem. We first model the optical drive system as a plant where input commands relate to measured EPL through a first-order system representing mechanical response delay and a measurement matrix characterizing the actuator-to-sensor coupling. We mathematically formulate the control task as an asymptotic disturbance suppression problem, specifically targeting low-frequency disturbances such as thermal and wind-induced deformations. Second, we propose an Anti-Windup Proportional-Integral (AWPI) control law. By employing a decoupling strategy, the design is reduced to a loop-shaping problem for decoupled scalar sensitivity functions, ensuring both stability margins and asymptotic disturbance suppression of constant-valued disturbances. The anti-windup mechanism is integrated to maintain control continuity during the recovery from saturation, preventing undesirable discontinuities in the drive command. Third, we introduce practical operational tools: a manual focus adjustment scheme that allows observer intervention without interfering with the feedback loop, and the cosine similarity index to quantify the suppressibility of specific Zernike modes. Numerical simulations, incorporating a three-axis secondary reflector drive and five-point EPL measurements, demonstrate direction-dependent disturbance rejection and the suppression of von Karman-modeled wind turbulence, validating the effectiveness of the proposed framework for real-world telescope applications.

astro-ph.IM↗