Structure analysis of optical fiber coupler with infrared spectrometry

Abstract

To obtain excellent performance optical fiber couplers, the structural difference of SiO₂ in couplers with different manufacturing techniques was investigated. With 740-FT-IR infrared spectrometric analyzer, the infrared absorption spectrum of SiO₂ in couplers at different drawing velocities was measured, and two characteristic peaks in the wavenumber range of 650–2000 cm⁻¹ were observed. One characteristic peak is at about 943 cm⁻¹, which is attributed to Si-O-Si bond asymmetric stretching vibration, the other is at about 773 cm⁻¹, which is attributed to Si-O-Si bond symmetric stretching vibration. From the infrared spectrum, it is found that the intensity and wave-number of the characteristic peaks are related to the manufacturing technique of couplers. The characteristic peak at about 943 cm⁻¹ becomes steeper when increasing the drawing velocity. At the drawing velocity of 150 µm/s, the distance between the two characteristic peaks is maximum, and then the optical fiber coupler has excellent performance, indicating that the performance of the optical fiber coupler has a close relationship with the wavenumber of the two characteristic peaks.

Keywords

optical fiber coupler / fused biconical taper / infrared spectrometry / SiO₂ / structure