Let say I have a Mode-locked linear cavity fibre laser with 3m meter PM980 used for connect components within the cavity. Also, I am using a chirped fibre bragg grating (CFBG) for dispersion compensation.

PM980 has GVD of 0.014 ps^2/m

CFBG has D parameter = 0.42 ps/nm and reflection bandwidth of 9nm

laser pulse has FWHM width of 6nm

My first question is:

how to convert ps/nm of CFBG into ps^2/m?

is it simple as using β2​=−2πc \ λ^2.D​ (since D is given in ps/nm, do I need to multiply it with pulse's bandwidth or CFBG bandwidth?)

Second question:

PM980 used within the cavity is 3m. Since in a linear cavity round-trip length is calculated as 2L, therefore, to calculate total group delay dispersion, one should multiply 2 x 3m ?

Thanks in advance!