There was a download of OptSim 3.6 on the developer's website when we last checked. We cannot confirm if there is a free download of this software available. This program is a product of RSoft. We recommend checking the downloaded files with any free antivirus. Commonly, this program's installer has the following filename: optsim.exe. The software is included in Photo & Graphics Tools. The most popular version of the OptSim is 3.6.
From the developer:
OptSim is RSoft's award-winning software tool for the design and simulation of optical communication systems at the signal propagation level. With state-of-the-art simulation techniques, an easy-to-use graphical user interface and lab-like measurement instruments, OptSim provides unmatched accuracy and usability.
You may want to check out more software, such as AutoCAD OwnerGuard, Block CAD or BabyaCAD, which might be related to OptSim.