Needle optimization is a unique feature of OptiLayer, it is especially useful for solving complicated design problems.  Needle optimization is a process in which new layers are inserted into the design being optimized.  In automatic mode, the best place to insert a new layer is found automatically. An optimal thickness for the new layer is computed by a special OptiLayer procedure.

When the number of coating materials exceeds two, an optimal material is chosen among all materials automatically in the most optimal way.

After the insertion of each new layer, the number of layers in the stack is generally increased by two, i.e., a single layer has been divided into two pieces separated by a "new" thin layer which was inserted in it.  The resulting stack is then refined by one of the available optimization algorithms.

OptiLayer exploits the needle optimization technique in its genuine form. This technique is based on complicated mathematical ideas and computational algorithms. You can refer to the book "Basics of Optics of Multilayer Systems" by Sh.Furman and A.Tikhonravov for its detailed description.

Manual Needle Optimization mode assumes experience in optical coating design and used typically for solving complicated design problems.