Methods and apparatus for registering a mobile device such as a mobile node or mobile router with a Home Agent in an asymmetric link environment. A primary mirror reflects light rays to form a first set of light rays to a secondary mirror that has a generally concave shape coupled to the housing. The scrambler is configured to output a control signal activated when an address for accessing a memory cell of a complementary bit line is inputted. Then, the nanocrystallites andor the seed layer are removed from the upper region of the trench by means of an etching process.