The technical process of spin coating polymer thin film used in thermo-optical switches fabrication was thoroughly described. High performance polymer films were prepared, whose refractive index, thickness and loss were tested. The effects of each technical parameter, as spin coating rate, solution concentration, spin coating time etc., on the optical and mechanical properties of the polymer thin film wave-guide were analyzed. An experiential equation was also given by least square fit method. The prepared films had comparatively low loss, desired thickness, and were of perfect quality. Some other thin film qualities as absorption spectrum and surface profile were also given to show the characteristics of the films.
Maleic anhydride-terminated polyimides(PMI) and copolyimides(PI) ,which are appropriate to fabricate PLC waveguides because of their very high thermal stability, excellent manufacturing performance, regulative refractive index, were prepared from 2,2’-bis-(3,4-dicarboxyphenyl)-hexafluoroproane dianhydride(6FDA), pyromellitic
dianhydride(PMDA), maleic anhydride(MA), and 4,4’-oxydianiline(ODA) through two steps. The behaviors of crosslinked ractions occurred at the terminating maleic anhydride unites, thermal stability and optical properties (refractive index and optical losses) influenced by cured temperature were demonstrated through thermal analyses(thermogravimetric analyses(TGA) and differential scanning calorimetry(DSC)), IR Spectra and measurements of refractive index and optical losses. The results indicate that the exothermal crosslink reactions begin above 260°C and almost terminate after curing at 310°C for PMI, and its 5wt%-loss temperature is up to 447°C, which is closed to the PI’s(499°C). The refractive index decreases relatively significantly(4.1%) and optical losses increase from 1.86 to 2.62 dB/cm while the cured temperature increasing from 250°C up to 350°C.