Control information is embedded in the signal passing through an optical amplifier by varying the power level of that amplifier’s pumped laser source. Choosing the best adjustment may include choosing an adjustment that causes a lower amount of vibration than adjustments not chosen. Such shock absorbing device for a rack and pinion type steering device has a high shock absorbing capability. The memory gate comprises a doped polycrystal silicon film with a sheet resistance lower than that of the control gate comprising a polycrystal silicon film formed by ion implantation of impurities to the undoped silicon film.