Isivinini lapho igagasi legagasi lendiza ye-monochromatic lisakazeka khona ngendlela evamile libizwa ngokuthi isivinini sesigaba segagasi. Isivinini esihamba ngaso amandla egagasi lokukhanya sibizwa ngokuthi i-ray velocity. Indlela ukukhanya okuhamba ngayo njengoba kubonwa yiso lomuntu isiqondiso lapho ukukhanya kuhamba khona.

Ngekristalu eyodwa engeyona enozibuthe, isivinini sesigaba se-planar light wave sincike lapho usuka khona ugesi. D kanye namandla kazibuthe H, kuyilapho isiqondiso sokusakazeka kwamandla kwegagasi lokukhanya sincikene nalo H kanye nokuqina kwenkundla kagesi E. I-dielectric constant ye-anisotropic optical media iyi-tensor ye-second-order.D futhi E ngokuvamile azihambisani, ngakho-ke isiqondiso sesivinini sesigaba v kanye nesivinini somugqa v_r ngokuvamile azihambisani. I-Engeli efakiwe α phakathi kwabo kubizwa ngokuthi i-discrete angle, okuwumsebenzi wokuqondiswa kwesivinini sesigaba (noma isivinini se-ray) kanye nesiqondiso D (noma E) (njengoba kukhonjisiwe emfanekisweni ongezansi). Isivinini sesigaba kanye nesivinini somugqa ngokuvamile azilingani, futhi ubudlelwano phakathi kwakho bunjalov=v_rcosα.

Isilinganiso sesivinini ukukhanya okuhamba ngaso ku-vacuum (c) kusivinini sesigaba sayo v endaweni enikeziwe ku-anisotropic optical medium ibizwa ngokuthi inkomba ye-refractive yaleyo ndlela. Ngokufanayo, isilinganiso sec ngesivinini somsebe endaweni ethile n_r=c/v_r ibizwa ngokuthi inkomba ye-refractive ye-ray kuleyo ndawo.

I-WISOPTIC wave-plates