How to Build an Optical Isolator with Stock Components

If components of your optical application creates specular reflections back into a laser's cavity, dangerous damage to the laser can occur. Hi! I'm Ehren, product line engineer at Edmund optics, and I'm going to demonstrate how an optical isolator constructed from stock components, an absorptive linear polarizer, and a quarter wave plate can be used to negate harmful effect using the different polarization states of light. For this demonstration, we purposely reflected the laser back in itself to simulate a back reflection. First, the beam is linearly polarized via the absorptive linear polarizer. Then the beam is circularly polarized via the quarter wave plate. This is achieved by rotating the slow axis of the quarter wave plate to 45 degrees to the incoming beams polarization state. When the circularly polarized beam undergoes a specular reflection at the mirror, it's handedness or direction of its polarization state changes. Simply put, the direction of the circularly polarized light spins the opposite direction of the incident beam. As the beam then travels back through the quarter wave plate, the circularly polarized light is converted to linearly polarized light again. However, due to the changing of the handedness at the mirror, this new linearly polarized light is oriented orthogonally with respect to the original polarization state meaning that the light cannot pass through the linear polarizer. The beam is present past the isolator as you can see by this beam splitter and screen arrangement. However, this beam splitter and screen arrangement show that the beam is present before the isolator meaning that there is a back reflection from the mirror and that the isolator is incorrectly aligned. When properly aligned, the beam remains present past the isolator but there is no back reflection before the isolator. This beam splitter and screen arrangement indicates that the isolator is properly aligned, that there is no back reflection, and the beam has been successfully isolated. For more information on how to integrate stock components into your application please visit us at www.edmundoptics.com Thanks for watching.