광섬유 간섭계를 이용한 다중모드 광섬유 대역폭 측정에 관한 연구

Abstract

Local area networks (LANs) employing optical fibers are set up in apartments, offices, vehicles, and aircraft that require web browsing, document transmission, multimedia transmission, etc. Most optical fibers used in these applications are multimode fibers (MMFs) because they have a higher tolerance to bend loss than single mode fibers (SMFs). Further, they are easier to handle and cheaper than SMFs. The increasing demand in data transmission bandwidth requires us to check MMFs that are already installed for bandwidth. However, former measurement methods such as the RF spectrum analysis method and the time-of-flight method requires heavy equipment, hence are not portable. However, the optical frequency domain reflectometry (OFDR) method has equipment that is portable. In this thesis, we demonstrate the measurement of bandwidth of multimode fibers by using OFDR. Broadband light passing through the multimode fiber causes phase differences, which are linear to the frequency; hence, an oscillating optical spectrum that has some periods relating to modal dispersion is obtained. We can thus obtain the modal dispersion by applying Fourier transform to the optical spectrum. Furthermore, for the first time, we also calculated the phase information of the Fourier transform to make modal dispersion reliable. This can help in accurately determining where dispersion occurred. Finally, we calculated the 3-dB Bandwidth, which is often specified for optical fibers, using relations between modal dispersion and bitrate capacity, which is related to the 3-dB bandwidth directly.