The best fit we obtained (see equation (2)) are: From theory we can deduce that F ($_{M}$ L , $_{R}$th. ) = 1 (i.e., after normalization by M th. 00 ). We have thus F ($_{M}$ L , $_{R}$fit ) = 1 Let | Ψ in 〉 = E$_{x}$ | x 〉 + E$_{y}$ | y 〉 and | Ψ out 〉 = E ′ x | x 〉 + E ′ y | y 〉 be respectively the incident and transmitted electric fields when we consider the left handed planar chiral structure. We have where ˆ J L is the operator associated with the Jones matrix J $_{L}$. The mathematical definition of planar chirality is that whatever the mirror symmetry operation ˆ Π in the plane X-Y we have ˆ J ˆ Π − ˆ Π ˆ J = 0. It equivalently states that ˆ Π ˆ J ˆ Π − 1 = ˆ J . If we consider for example the mirror reflection through the Y axis (see Fig. 1) we have the matrix representation (in the cartesian basis) Π = Π − 1 =    − 1 0 0 1    and consequently which agrees with equation (1) and constitutes an other optical definition of chirality. The previous equations are used in order to interpret the results of Fig. 3 of the main article. Indeed from equations (8) and (9) we obtain 12 ˆ Π ˆ J $_{L}$ˆ Π − 1 = ˆ J R = ˆ J L (9) ˆ Π | Ψ out 〉 = ˆ J $_{R}$ˆ Π | Ψ in 〉 . (10) | Ψ out 〉 = ˆ J L | Ψ in 〉 (8) M $_{L}$fit =     1 . 000 0 . 033 − 0 . 116 − 0 . 023 0 . 033 0 . 951 0 . 043 − 0 . 282 − 0 . 116 0 . 043 0 . 951 0 . 304 0 . 023 0 . 282 − 0 . 304 0 . 902    $^{,}$ M $_{R}$fit =     1 . 000 0 . 0359 0 . 125 0 . 026 0 . 039 0 . 949 − 0 . 044 0 . 283 0 . 125 − 0 . 044 0 . 948 0 . 311 − 0 . 026 − 0 . 283 − 0 . 311 0 . 897    $^{.}$ (7) VII. APPENDIX D: SYMMETRIES DUE TO CHIRALITY [INTERPRETING FIGURE 2].