__Answer:__

The spatiotemporal VCSEL model uses multimode laser rate equations in both frequency modes and transverse optical modes. There are a few of ways you could reduce the number of modes for examination:

- The most physical is to reduce the aperture size and thus the number of possible transverse modes will naturally decrease. You could adjust oxide aperture in the
**Geometry** tab. - You can use the
**Mode Selector** component located in **Receivers Library/Multimode**. All the modes would still be used in the actual VCSEL calculation, but you now extracted the particular one of interest. - Under the numerical tab of the
**Spatiotemporal VCSEL**, you can select the number of modes to use in the calculation. This will introduce inaccuracies; as it then removes a number of modes from the multimode rate equations.

I have attached an example OptiSystem file which demonstrates each of the choices above. If you just want to examine particular modes arising from the system, I would recommend option 2.

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