JOURNAL
APRIL 25, 2008Today, I started off my day in the lab by making a circular ruler in order to measure the radius in a precise manner. Last week when we conducted the experiment, we realized that two circles were formed and therefore, to kill one of the reflections, Dr. Noe suggested that we color the center of the circular ruler with black ink to stop the reflection. I printed out the circular ruler that I made with xfig. Since this was supposed to be placed under water, we thought that it would be better if we laminated the ruler with a thin sheet of plastic. At first we wanted to use the fishtank as the container but realizing that it was too small, we used another container. We cut the laminated ruler so that it would fit into the container and also taped the edges to ensure that it was completely sealed. We also taped the ruler to the container so that it would not float up when the container was filled with water. When it was all set up, I directed the green laser beam normal to the surface of the water. Unfortunately, we did not see a circle at all until I directed the laser away from the black spot in the center. This is when we realized that coloring the center black was not a great idea because it killed all of the reflection. However, even after directing the laser somewhere else, we observed the opposite of what we were supposed to observe. Instead of a dark circle with light around it, we observed a bright circle with darkness around it. This is when we realized that this happened last time as well. If the paper was not placed directly under the water, we would observe the opposite of what we are supposed to observe. We took a tiny piece of paper and placed it over the black spot. Still, we observed the same thing. This was when we realized that not only did it matter if the laser directly hit the paper, even the reflected ray would have to directly hit the paper in order for the experiment to work. Finally, we placed a bigger piece of white paper directly under the water, directed the light, and saw a dark circle with light around it. I still have to figure out why placing a plastic sheet between the water and hte paper did not work. Another thing I need to improve is to make a better circular scale so that the radius can be measured accurately. When I return to the lab next week, I'm going to make sure I work on this experiment more carefully, avoiding small errors if possible. APRIL 24, 2008After weeks of trying to understand what Total Internal Reflection(TIR) meant, I think I have finally started to get a grip on this topic. TIR is a phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle, or the angle of incidence, with respect to the normal to the surface. If the index of refraction is lower on the other side of the boundary, no light can pass through and thus, all of the light is reflected. Dr. Noe found a paper by D.C. Look Jr titled "Novel demonstration of total internal reflection". The paper provides an alternative method of measuring the index of refraction of different liquids. I decided to duplicate this experiment in order to observe the results. The experiment summarized by this paper was conducted using a laser, a transparent medium with an unknown index of refraction, and a white diffusely reflecting undersurface. A laser beam was directed normal to the surface of the medium. When this is done, one should be able to observe the a dark circle of radius R with light surrounding it. By taking careful measurements, one can determine the index of refraction of the liquid by plugging the values into the formula: Sqrt(1+((4h^2)/(r^2)))where h is the depth of the water. My goal in this experiment is to figure out if this formula is in fact accurate. I would also like to find out why this formula works. I started off on Friday by using water as my liquid. I filled a little rectangular container with water and placed it on top of a piece of white paper. I directed a green laser normal to the surface of the liquid. However, I observed the complete opposite of what I should have seen. After thinking about it for a while, Dr. Noe suggested that I try it again by placing the white piece of paper inside the container and then filling it up with liquid. When I tried that, it worked. This week, my goal is to figure out why it mattered where the white paper was placed. I also need to figure out a better way of carrying out this experiment in order to be able to get accurate measurements. APRIL 15, 2008After several days of searching for a good project idea, I think I finally found something that I am interested in. This week Dr. Noe gave me an article titled, "Novel Demonstration of Total Internal Reflection" by D.C. Look, Jr. This article provides an alternate way of measuring the index of refraction of a liquid. Since it sounded interesting, I decided to try it out. I went back to the xfig program and played around with it. I tried to copy the image that was provided in the article just for practice.Diagram from the article by D.C. Look, Jr MARCH 28, 2008Yay, I made this drawing with xfig.
MARCH 24, 2008Now that Spring break is over, it is time to get back in the lab and start working on my project idea. I am still trying to get a grip of what I really want to do with my ideas but I feel like I definitely have a better understanding of what fiber optics really is. My next step is to narrow my interests down to something that can be achieved in this lab. MARCH 18, 2008The WSE 187 class started on February 1st. It has been a little more than a month and a half since I began this journey and I have learned a lot so far. From all the little discussions in class to all the experiments conducted to demonstrate different phenomenas, I have started to see what 'research' truly means. I have been thinking about the different project ideas. I am an electrical engineering major and have always been interested in fiber optics. Therefore, my first choice was to do something that involved this topic. I looked up information online to get a better sense of what optical fibers really were. I learned from various websites that optical fibers are thin strands of glass, thinner than human hair, that are used to transmit light through them. An optical fiber has three layers. The innermost layer is known as the Core. The Core is the thin glass center of the fiber where the light travels. The second layer is known as the Cladding. This layer is the outer optical meterial that surrounds the core that reflects the light back into the core. The last layer is called the Buffer Coating which is a plastic coating that protects the fiber from damage and moisture. Another thing I learned was that there are two types of fibers: Single-mode fibers and Multi-mode fibers. The single-mode fibers have small cores that transmit infrared laser light. Multi-mode fibers have larger cores that transmit infrared light from light-emitting diodes.Optical fibers can also be made of plastic which transmit visible red light through LEDs. |