The CHARGE solver in DEVICE is now capable of performing self-consistent electro-thermal simulations. The PIN Mach Zehnder modulator example have been updated to include effects of self heating using this new feature.
The p-i-n Mach-Zehnder modulator is operated in forward bias mode. At an operating voltage of more than 1 V, a significant amount of current will flow through the device which will contribute to Joule heating. The heating will increase the temperature of the waveguide which will increase the effective index of the optical mode. This will work against the index modulation due to charge injection and the performance of the modulator will be degraded. To properly model the performance of the modulator, a self-consistent electro-thermal simulation is necessary. This can be easily done in DEVICE by using the "coupled" mode in the CHARGE solver. In the "coupled" mode, the CHARGE solver couples internally with the HEAT solver and performs a self-consistent eletro-thermal simulation.
Check out this example at: https://kb.lumerical.com/en/index.html?pic_modulators_pin_mzi.html