Biography
Biography: Takashi Matsui
Abstract
Space division multiplexing (SDM) technology has been received increasing attention to increase transmission capacity extremely, which can overcome the capacity limit of the existing single-mode fi bers (SMFs). The SDM transmission can be realized by using a multi-core fi ber (MCF) or few-mode fi ber (FMF). In particular, the FMF can increase the number of spatial channels greatly by utilizing the mode division multiplexing (MDM) technology with the MIMO processing. Here, the MDM transmission raises some new issues which have not been considered in the SMF based transmission system. In particular, the diff erential modal delay (DMD) and the mode dependent loss (MDL) are unique of the FMF based transmission line. Th e larger DMD increases the complexity of the MIMO receiver. Th e MDL severely restricts the transmission speed and/or distance. Th erefore, it is important to specify these parameters of the FMF to construct the MDM transmission line. The DMD measurement method is well-established based on the time-of-fl ight method since it is also necessary to specify the bandwidth of existing multi-mode fi bers. Th e MDL is induced by some factors in the transmission line such as diff erential modal attenuation of fi bers, splices and devices and the mode conversion in the fi ber and at splices. Th erefore, it is important to specify the modal dependence of the loss factors for the FMF. Th e loss measurement of the FMF can be conducted with the conventional test procedure by utilizing the mode multiplexer which has suffi ciently high mode extinction ratio. However, the increase in the number of modes degrades the mode extinction ratio, which degrades the measurement accuracy. Recently, measurement methods of each mode in the FMF have been proposed by considering the mode power ratio, which is the variable mode power ratio method and the mode fi lter based OTDR method. Th ey can off er suffi ciently high accuracy of less than 0.005dB/km for two-mode fi bers. Th e splice loss is estimated by using the mode-fi eld diameter (MFD) for SMFs in general. We have investigated the applicability of the conventional near-fi eld pattern (NFP), far-fi eld pattern (FFP) and variable aperture (VA) methods to the higher-order modes in the FMFs. We found that the MFD values from the FFP and VA methods provided the splice loss value which well-agreed with the experimental results. Th erefore, it can be considered that the effective MFD value by utilizing these two methods is appropriate to consider the splice loss properties of the FMF. Th e loss and spice characteristics of the FMF directly eff ects on the transmission performance and it is essential to establish the specifi cations and their test procedures of the FMF for the interconnectivity and mass productivity. It can be considered that new approaches to control the characteristics of each mode are required to reduce the DMD and MDL for the FMF based transmission line.