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FPGA-based real time control of ELTs adaptive optics system

Abstract 165

Submitted by Luis Fernando RODRIGUEZ-RAMOS


L. F. Rodríguez-Ramos (1), Y. M. Hernando (1), J. J. Piqueras Meseguer (1), J. J. Díaz García (1), M. R. García-Talavera (1), J. M. Rodríguez Ramos (2)


(1) IAC; (2) ULL (University of La Laguna)


Real Time Control has been clearly identified as a separate highly challenging field within Adaptive Optics, where a big number of computations have to be performed at the kilohertz rate to properly actuate the deformable mirror(s) before the input wavefront(s) information has become obsolete.

When considering extremely large telescopes, the number of guide stars, wavefront sensors mirrors and actuators rises to a level where the amount of processing needed exceeds the capability of today’s conventional processors and even from the expectations given by Moore’s law for the next years.

FPGA (Field Programmable Gate Arrays) technology has been proposed to overcome this problem by using its massively parallel nature and its superb speed, effectively used when their design is done using high level programming tools and flexibility and ease of adaptation can be routinely obtained. Two main drawbacks have been identified: Lower flexibility in comparison with conventionally programmed processors (microprocessor, DSP, GPU) and need of using fixed point arithmetic in order to maintain the amount of silicon employed in a practical size.

From 2005 on, the Technology Division of the Institute of Astrophysics of the Canary Islands has undertaken a number of technology developments for testing the viability of applying this technology to an adaptive optics system. Laboratory and telescope systems have been developed and specific test oriented to quantitatively measure the effect of using fixed point arithmetic have been carried out with success. Moreover, a conceptual design for laser guide star wavefront sensor has been developed and found to be perfectly viable with an extremely small size and power consumption, obviously complying with the bandwidth requirements.

After a short introduction summarizing the achievements within the field of FPGA-based real time controllers for AO, we present a correlation based Shack-hartmann wavefront sensor, specialy adequate for ELT laser guide star wavefront sensing.