Experimental studies of completely closed optical cavities enclosed with total-internal-reflection walls

In our previous work we proposed the completely closed optical cavity in which light rays with arbitrary directions are completely confined using total internal reflections by a single wall made of a transparent medium. Recently we have succeeded in the experimental confirmation of our proposal. Here, we will demonstrate the experimental results using a prototype cavity composed of GaP. In the cave 640 nm LED lights are confined and leakage is less than 10(-3). Also, external LED lights are rejected almost 99.9% by the single wall and cannot enter in the cave. Due to the high absorption loss of GaP the Q factor of the cavity is suppressed down and is estimated to be 1.4x10(6). The higher Q (~10(9)) is expected if the lower loss (>1%/cm) materials are usable. This device will be useful for many applications such as laser cavities, optical filters, tanks storing natural solar light, micro darkrooms, etc.