Thursday, July 18, 2013

RET II: Revenge of the Photons!

I'm back at Boston University this summer for another six weeks of scientific bliss!  Loving the university, the co-workers, and, of course, the delicious food choices!

It's not all Jamba Juice and Starbucks though, let me tell you!

This summer Mrs. Chase and I are using a deformable mirror (more on that below) to help us control how light travels through fiber optic cables.  Here's the rundown:

  • In empty space (or in a uniform medium like air) light travels in straight lines.  However, it can be very useful to change the path that the light is taking.  Some common ways of controlling the path of light is to use mirrors or lenses to bounce or bend the light however you need.  Here you can see that we are using lots of lenses to control our laser light------------>  
  • Sometimes, lenses and mirrors are just not enough.  A fiber optic cable is what's known in the biz as a waveguide.  They are basically glass wires that use a phenomenon called total internal reflection to trap the light inside the fiber.  Once light has launched into the fiber, it will follow the path of the fiber, no matter how twisty or turny.  Here's a cool demonstration of total internal reflection using water as a waveguide.
  • So what we are interested in is controlling how the light will look when it comes out the other end of the fiber optic cable.  In a multimode fiber, the output light makes a speckle pattern.  Imagine that black and white static you get when your cable box is unplugged.  That's what we see.  So what if we could use a deformable mirror to change that static into one bright spot of light?
  • Hang on, what is a deformable mirror?!  If you didn't follow me last summer, a deformable mirror is just a mirror that can change shape to look however you want.  When you shine light on this deformed mirror, you change how the light looks when it bounces off.  This lets you fix any aberrations caused by anything messing up the light from giving you a good image.  
I'll let you know how all this is working out in my next post!  Stay tuned.