Stable opto-electronic oscillators (OEOs) are realized using long fiber delay lines and changes in the index of refraction of high quality factor delay line results in temperature sensitivity of OEOs. Temperature sensitivity of various OEOs is measured to compare index of refraction variation of standard (SMF-28) and photonic crystal fiber (PCF). Both hollow-core (HC) and solid-core (SC) versions of PCF are quantified. SC-PCF exhibited a factor of three reductions in the rate of index of refraction change (about +4.7 ppm/°C) with temperature over SMF-28 (about 12 ppm/°C) based OEO. Although HC-PCF have a greater attenuation per unit length,but those fibers have demonstrated a negative rate of change (about ? 0.6 ppm/°C) in the effective index of refraction with temperature and prospect of thermal stability in the OEO using passive techniques is great when a combination of HC-PCF and SMF-28 are employed as fiber delay lines. Stable opto-electronic oscillators (OEOs) are realized using long fiber delay lines and changes in the index of refraction of high quality factor delay line results in temperature sensitivity of OEOs. Temperature sensitivity of various OEOs is measured to compare index of refraction variation of standard Both hollow-core (HC) and solid-core (SC) versions of PCF are quantified. SC-PCF exhibited a factor of three reductions in the rate of index of refraction change (SMF-28) and photonic crystal fiber (about +4.7 ppm / ° C) with temperature over SMF-28 (about 12 ppm / ° C) based OEO. Although HC-PCF has a greater attenuation per unit length, but those fibers have demonstrated a negative rate of change ? 0.6 ppm / ° C) in the effective index of refraction with temperature and prospect of thermal stability in the OEO using passive techniques is great when a combination of HC-PCF and SMF-28 are employed as fiber delay lines.