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Normally, a warning that you are switching to out of core mode means that you don't have enough RAM (or enough accessible to use) for the solver, so it is swapping out to disk. I encourage you to take a look at your memory usage, how much RAM you have, notice if/when the program is swapping out to disk, look at your preferences settings in regard to memory usage, consider the discretization (linear, quadratic, etc), the mesh, and the solver. E.g., you could try a more memory efficient solver, such as one of the iterative solvers. I hope some of that helps. If not, consider posting your .mph file to the forum. Also, a warning message doesn't mean the program necessarily failed. It's just a warning. Did you try to plot the results?

Dear Robert

Thank you for your reply. I have ploted my result (see attachment). I didn't find the coupling and any waveform in waveguide. I don't know what issue did I have. Was my setting in COMSOL wrong? or. did the parameters which I have input (see attachment) have something issues in the wave coupling theory. Could you check it? and give me your advice. I want to upload my .mph file, but it is larger than 5MB even without both mesh and results data. Could you tell me how can I share my .mph to you. Maybe you can repeat my simulation using my parameters. The "Rectangular waveguides straight to ring coupler" is the model in the part library. Because the core height is smaller the core width, the max. size element of core is h_core/2.

Thank you! I am looking forward your kind reply! Have a nice day!

As the Comsol folks explain: "If your MPH-files are large, you can greatly reduce their size by selecting Clear All Built Meshes from the Mesh menu and Clear All Solutions from the Study menu, and then saving your MPH-files."

Please do that and upload your file and I will take a look at it.

Dear Robert

Thank you! I have done that. "If your MPH-files are large, you can greatly reduce their size by selecting Clear All Built Meshes from the Mesh menu and Clear All Solutions from the Study menu, and then saving your MPH-files."

But the size is still 6.7MB.

You called this the "Rectangular waveguides straight to ring coupler" sample file, but I couldn't find that. One of your pictures looks a lot like that in the "Optical Ring Resonator Notch Filter 3D" sample file. Ah hah, the pdf documentation for this optical ring model has something called a "Rectangular Waveguide Straight-to-Ring Coupler" in it, so I am concluding that this is indeed the model you are talking about. And... sorry, but I don't have the Wave Optics model. But others reading here may be able to help you. Now, in regard to shrinking your file size, in addition to clearing the solutions and the mesh (which is usually sufficient), here's even more suggestions. Choose File --> Compact History. Also, go to File --> Preferences --> Save, and then change "Optimize MPH-files for:" from "Speed" to "File size." Then save the file again. It really should be less than 5 MB.

Dear Robert

Thank you for your help. I can post the mph file in here. and I am so sorry to let you confusion. I hope you or other colleague can help me. I want to know what is my issue, the input data or the model or the setting of COMSOL.

Best Regards