OPTICAL ISOLATOR

PURPOSE:To inhibit light from returning a laser oscillation device as a light source if the light shifts in potical path and, therefore, to prevent deterioration in frequency characteristics, oscillation mode change, noise generation, etc., from from occurring by boring a transmission hole in a Faraday rotator holder in the shape of a frustum of cone having a conic surface at a specific angle to the axis. CONSTITUTION:The light emitted by the semiconductor laser oscillation device 14 is collimated by a condenser lens 16 into parallel light, which is transmitted through an optical isolator as shown by solid lines l. If the emitted laser light shifts forth or back, or right or left, the optical path shifts and the light is passed through the condenser lens 16 and incident on the optical isolator as shown by broken lines l', but reflected by the conic surface 26 which forms the conic hole 24 in the Faraday rotator holder 20, and is open in the direction of the incident light and at the specific angle to the axis of the rotator holder 20 to change in optical path, so that the light never returns to the semiconductor laser oscillation device 14.