Mr. Ich V. Pham Profile

Ich V. Pham

Control Engineer at Lockheed Martin Corp

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Proceedings Article | 27 June 2006 Paper

Amplitude and phase controlled adaptive optics system

Ich Pham, Sam Ma

Proceedings Volume 6272, 62721Q (2006) https://doi.org/10.1117/12.673611

KEYWORDS: Phase shift keying, Adaptive optics, Spatial light modulators, Actuators, Modulation, Transmitters, Receivers, Sensors, Laser sources, Wavefronts

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An adaptive optics (AO) system is used to control the deformable mirror (DM) actuators for compensating the optical effects introduced by the turbulence in the Earth's atmosphere and distortions produced by the optical elements between the distant object and its local sensor. The typical AO system commands the DM actuators while minimizing the measured wave front (WF) phase error. This is known as the phase conjugator system, which does not work well in the strong scintillation condition because both amplitude and phase are corrupted along the propagation path. In order to compensate for the wave front amplitude, a dual DM field conjugator system may be used. The first and second DM compensate for the amplitude and the phase respectively. The amplitude controller requires the mapping from DM1 actuator command to DM2 intensity. This can be obtained from either a calibration routine or an intensity transport equation, which relates the phase to the intensity. Instead of a dual-DM, a single Spatial Light Modulator (SLM) may control the amplitude and phase independently. The technique uses the spatial carrier frequency and the resulting intensity is related to the carrier modulation, while the phase is the average carrier phase. The dynamical AO performance using the carrier modulation is limited by the actuator frequency response and not by the computational load of the controller algorithm. Simulation of the proposed field conjugator systems show significant improvement for the on-axis performance compared to the phase conjugator system.

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