One main issue in optics is how do we take our lab experiments that we put together on a 8' x 4' optical table and turn them into a packaged device that can be used in industry, or medicine, or at home. Optical circuits are not as easy to integrate as electrical circuits because they require such a wide range of materials and components and because each optical "wire" or fiber cable needs to be aligned to very tight tolerances. While there are a number of approaches to this problem, none of them have overcome all of these problems as of yet.
Robert McLeod's research group at CU Boulder is working on a new approach that will be able to incorporate all of the different components needed in today's optical systems, while also overcoming the difficulty of aligning these systems inside the circuit and for connecting to the outside world.
The images above show the process steps for this new method.
Step (a) is to start with a smooth substrate, possibly a piece of glass, but a number of materials would work for this.
Then Step (b) is to position the components necessary for the circuit above the substrate. These can be positioned relatively loosely and can include fibers for connecting to and from the circuit as well as beamsplitters, lasers, photorefractive crystals and other optical components.
After the components are in place, Step (c) is to pour the photopolymer material over the components. This works like an epoxy. When first mixed, it is liquid and can be poured over the substrate and completely encapsulate the components. The polymer then cures, holding the components in place.
Step (d) uses a confocal microscope in the red, where the material is not sensitive, to detect where each of the optical components really is. The advantage of this is that the position tolerances can be loose because this detection step allows us to find the components exactly and discover if they are off by a few microns or positioned at an angle.
Step (e) is the writing step. The photopolymers we use are sensitive to green light. This means that when we shine a focused green laser beam into the material, it creates an index change that resembles the shape of the writing beam. By dragging the focus from one optical component to another, we draw waveguides to connect each of the components. Since the waveguides can be drawn in 3D, we can correct for positioning errors in the fibers or optical components.
Step (f) is the final cure. We shine incoherent light onto the sample and fully cure it. The index structures we wrote in Step (e) are still there, but the sample is no longer sensitive to light.