How To Achieve Lower Voltage in Electro-Optic Modulator?

Hi to all,

I have simulated an electro-optic Mach-Zehnder modulator in DEVICE. I run the simulation in different voltages (0~25), in order to achieve an acceptable phase shift. But the required voltage is about 27 volts which is a high voltage.
How can I have a lower voltage to get a better result? And is it possible to make the voltage lower by doping? Or are there any other ways to do this?

Please guide me through this,

Thanks in advance.

Hi @ifariborz, I am assuming that you are using a depletion type modulator. In such a modulator the way to have a lower Vpi would be to modulate the charge quickly which depends on the capacitance of the pn junction. So you will have to increase the junction capacitance to lower the Vpi. To increase the junction capacitance you will have to increase the doping at the junction. However please note that this will also increase the loss at zero bias.

Thank you for the help.
I did the required stuff, it is helping, but I have a problem with doping, and I don’t know the exact amount of it.
Is it something limited, or I just can dope the region in higher values.
Another question is that, can we dope an insulator? because the EO polymer is an insulator and I want to dope it.

This is the modulator simulation in DEVICE.

Thank you a lot.

Hi @ifariborz, the geometry of your device is different than what I had in mind. Can you please explain the operating mechanism of your modulator?

Here, we have a contact in top of the silicon and two at the sides. The contacts at the sides are grounded.
When I apply a voltage to modulator, the difference in the refractive indices of EO polymer in two gaps between Si and Ag appears.
But it’s not the required value to make a phase shift and could make the wave destructive at the output.
So I need a higher amount of voltage to make this phase shift, and it is about 27 volts.

And I’m really thankful for your attention @aalam.

Hi @ifariborz, since your modulation mechanism is different from a depletion type modulator, I do not think increasing the doping can help. While I am not exactly sure on how to increase the modulation efficiency of your device, there are probably two things you can try,

  1. Increase the overlap of the optical mode with the EO polymer somehow.

  2. Increase the electric field in the EO polymer to get a bigger change in index. You can probably make the EO polymer layer slightly thinner to achieve this. However this may affect the overlapping in point 1 in an adverse way.

Hopefully other users can chime in with their opinions!

Hi @aalam
Thanks for your time and help.
I appreciate it.
I will try these ways, and I hope to get the good result.

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Would you have a reference paper that may allow us to understand a bit more of this type of device? If you can upload the electrical and optical simulation project files, we are happy to take a closer look at it.

In the meanwhile, I think it is worth looking at this MZI modulator example to learn the suggested simulation approach of a typical EO modulator.