Optical system for synthesizing plural light beams

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide an optical system which can synthesize a plurality of light beams of substantially the same wavelength with a small angle difference between the light beams, without making a substantial loss.
According to one aspect of the invention, there is provided an optical system which comprises a light refracting member having at least one face, first light emitting means for emitting a first parallel light beam and permitting it to pass through the light refracting member so that the light beam is applied to the face of the light refracting member at an angle of incidence equal to at least the critical angle, is then totally reflected from the surface of the light refracting member and is transmitted or travels in a specified direction; second light beam emitting means for emitting a second parallel light beam to the face of the light refracting member at an angle of incidence substantially equal to the Brewster's angle so that the second parallel light beam is refracted at an angle of refraction substantially equal to the Brewster's angle as viewed from the refractive side of the refractive member and then travels in a direction which defines a predetermined angle with said specified direction; and reflection preventing means provided on the face of the light refractive member for making the angle of refraction of the second parallel light beam approach to the critical angle so as to reduce the angle defined by the predetermined angle and the specified angle.
In this optical system, the first parallel light beam is totally reflected by the face of the light refractive member, while the second parallel light beam is refracted by the face at the angle of refraction substantially equal to the Brewster's angle as viewed from the refractive side of the refractive member, and is allowed to run at the specified angular difference taken with respect to the first parallel light beam.
And the second parallel light beam has its angle of refraction made to approach to the critical angle by means of the reflection preventing means