http://ocw.mit.edu/courses/mechanical-engineering/2-71-optics-spring-2009/

are these courses required fee???

No. MIT's open courseware usually consists of recorded courses held at MIT, recitation video clips, and supplementary material like problem sets. All the material is available all the time, because unlike with coursera you don't actually sign up for any course. You just get all the materials for the course, and you can watch every single lecture in the course as many times as you wish. Generally, I've reviewed and/or recommended such courses for students who want supplementary material or a refresher, rather than as a course, but the times I have recommended them as courses I've generally found that students (and colleagues!) find them helpful. In particular, they find that the complete access to all the material, the fact that every lecture is recorded such that it is almost like being in the class, and in general the ability to structure the learning process makes up for online courses like those from coursera in which you have to sign up at particular times, the "pro" of being able to ask the instructor questions is offset by the "con" of the non-traditional ways in which the material is presented (through short clips, Q & A sessions, no full lectures, etc.), and finally often enough people just don't have the time to integrate a course schedule into their schedule. MIT OCW (among other similar sources from Stanford, Harvard, Cambridge, etc.) provides all the material that students taking the class would get (minus the textbook(s) they'd have to purchase) all at once.

Thanx for your reply i did not find nano-photonics course in MIT O.C

Why some courses vedios in OCW is not available??? and how can we get that course ??????