| 摘要 |
PURPOSE:To eliminate an evil effect of the returned light to be exerted on a semiconductor laser by deciding the length of an optical path provided between an optical information board and a semiconductor laser which is turned on and off via a high frequency oscillating circuit so that the prescribed conditions are satisfied. CONSTITUTION:A semiconductor laser 1 is turned on and off by a high frequency oscillating circuit 17 in a cycle ratio (a) which is turned on and off with a frequency (f), where 0<a<=0.5 is satisfied. The laser beam given from the laser 1 irradiates an optical information board 6 set at a position separated from the laser 1 by an optical path length l via a beam splitter 16 and a mirror 4. Then the return light corresponding to the information given from the board 6 is detected by a detector 11. The length l is decided to satisfy the conditions of an equation I , therefore, a part 9'd of the return light passed through the splitter 16 reaches the laser 1 while the laser 1 is kept off. Thus it is possible to eliminate an evil effect of said return light to be excerted the laser 1. In this case, (c) and (n) in the equation show the laser light speed in the air and an integer >=1, respectively. |
