As optical radar apparatuses capable of setting a detection area in a widthwise direction of a road surface, there are apparatuses such as those disclosed in Japanese Utility Model Laid-Open Nos. 59-117980 and 59-117981.
In the apparatus disclosed in Japanese Utility Model Laid-Open No. 59-117980, shown in FIGS. 7A and 7B, light from a light source is condensed to some extent by a lens to obtain a first detection range .theta.T1, and the light source is suitably moved to obtain a second detection range .theta.T2 wider than the first detection range .theta.T1 in a widthwise direction of a road surface by changing the degree of condensing of the lens.
In the apparatus disclosed in Japanese Utility Model Laid-Open No. 59-117981, shown in FIG. 8, light from a light source traveling through a lens is diffused by a prism to increase an expansion angle in a road surface direction, thereby setting a detection range wide in a widthwise direction of a road surface.
In the apparatus disclosed in Japanese Utility Model Laid-Open No. 59-117980 among the above-described conventional apparatuses, shown in FIGS. 7A and 7B, however, light cannot be emitted simultaneously for the first detection range .theta.T1 and the second detection range .theta.T2, and the detection range is set one-sidedly, since the detection range is changed by moving the light source.
The apparatus disclosed in Japanese Utility Model Laid-Open No. 59-117981, shown in FIG. 8, entails the problem of a reduction in the maximum detection distance because light is uniformly diffused by the prism. Because of this problem, it is not possible to meet a demand heretofore made for widening the detection range in a widthwise direction of a road surface in a short-distance area without reducing the maximum detection distance when an optical radar apparatus is used for an inter-vehicle control or an obstacle detecting apparatus.
The present invention has been achieved in consideration of the above-described problems, and an object of the present invention is to provide an optical radar apparatus capable of increasing the expansion angle in a road surface direction in a short-distance range without setting the detection range one-sidedly and without sacrificing the maximum detection distance.