Fast calibration UV LED system for CALICE scintillator based tile hadron calorimeter

We report on latest version of the calibration and monitoring system for the scintillator tile hadron calorimeter (ARCAL) for the ILC. Distribution of the light uses notched fibers, developed at our laboratory. One slab layer of the engineering ARCAL prototype is just being built and tested in the laboratory, uses 864 SiPMs embedded in small scintillator tiles and represents a part of the biggest planned detector equipped with SiPMs. Since SiPMs are sensitive to changes in temperature and operation voltage they need to be monitored. The monitoring system has to have sufficient flexibility to perform several different tasks. The self-calibration property of the SiPMs can be used for the gain monitoring using a low intensity of the LED light. A routine monitoring of all SiPMs during test beam operations is achieved with a fixed-intensity light pulse. The full SiPM response function is cross-checked by varying the light intensity from zero to the saturation level. In calibration systems we developed, we concentrate especially on the last aspect a high dynamic range of precise, few nanosecond pulses.