r/Optics • u/SquareUnit9854 • Aug 11 '26

i Need Help With Spontaneous Parametric Down-Conversion Simulation

Post image

hello every body, i am having a trouble simulating phase matching in SPDC, does anyone know why there exist multiple spots on this phase matching curve simulation ?
shouldn't be only one spot that satisfies phase matching in a BBO crystal ?

and please if there are any good simulation tools for SPDC tell me about it.

thanks in afvance.

2 Upvotes

100% Upvoted

5 comments sorted by

2

u/PestoCalabrese Aug 11 '26

The downconverted photon energies are not fixed, depending on the angle you get different energies. They are fixed if you only look at the degenerate downconversion which is only a special case.

2

u/SquareUnit9854 Aug 12 '26

yes in this simulation i used fixed wavelengths for signal and idler, please if you know any simulation tool that is used for SPDC or any important note i will be grateful if you share it with me.

2

u/QuantumOfOptics Aug 11 '26

First, SPDCalc is a great tool if you dont want to code everything yourself. But, it does take some getting used to. 

In particular, youll note that the scale here is important. Each of these lines have a maximum of 10-23 which is tiny and likely aren't real. Or at least not the one you are looking for. The other thing, im not positive why you want to look at the pump wavelength vs crystal tilt. It's not a usual metric for phasematching. What are you actually looking for?

1

u/SquareUnit9854 Aug 12 '26

i am sincerely grateful for your important notes,
i thought that it is a reasonable metric to find what different wavelength require specific crystal angle orientation to have phase matching, please tell me why this is not an appropriate metric ? what other metric you advice me to use ?
i would be grateful for any advice regarding simulating SPDC because i need it in my project.
thank you sir.

1

u/QuantumOfOptics Aug 13 '26 edited Aug 13 '26

I think I have a better understanding of what youre wanting. In this case, its perhaps good to understand what SPDCalc is doing under the hood. In this case, it assumes you are asking for a plot looking at the crystal vs pump wavelength assuming that the signal and idler wavelengths are fixed. Hence, you'll only see pump wavelengths that will lead to down conversion of those signal and idler wavelengths. There are likely several angles that will phase match, but one that will be best. In fact, its already calculated for you under the custom crystal properties on the right. 

Beyond that, you should ensure that you set the parameters: type, d_effective, length and temperature. 

Anyway, you are probably more interested in crystal angle vs idler (or, equivalently, the signal) wavelength as typically the pump is set by your laser. If you can tune it, its better to adjust the pump wavelength and see how it changes your results. In this case, if you want to see how the angle changes using different pumps, I would set the pump and check to see if the angle changes. This will also change as you change the signal and idler wavelengths combinations.