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Thank you for posting this question. I am sorry to reply you late as my colleage is out of office longer than expected.

The equations are from references listed at the bottom of the page.

I do not have access to the papers.

Beta2 is the 2nd derivative of beta, whereas delta_beta is the difference of inversed group velocity (with coefficients). The group velocity is the inverse of 1st derivative of beta. So the delta_beta2 is simular to beta2 in the sense of unit, as it is a difference. however it may omitted delta_w or assuming it is unit or other assumption, or simply it missed some quantity.

I would strongly suggest that you refer to the reference papers to make sure the theory is correct. I believe the solver its self uses correct formula (and it is discrete), as customers use it to design optical circuits with agreement to the experiments.

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