Hi Rami,

You can use FDTD Lumerical: https://www.lumerical.com/products/fdtd-solutions/

It is not free, but you can start with a free 30-day trial. Lumerical has lot of application examples and you can refer to this particular example from Lumerical database: https://apps.lumerical.com/diffractive_optics_cavity_simple_high_q_example.html

Best Regards,

Vivek

Rami Zegadi

You can use OptiFDTD from Optiwave company. Its 32-bit version is free.

But you need to calculate the Q-factor manually by the common formula of (delta lambda/ lambda_0).

You can use meep.