Our proposed approach for increasing the transmission capacity is to reduce the channel spacing of a DWDM-direct system for broadband access to the minimum while keeping the employed optical band-pass filter technologies. We have measured the complex transfer functions of FBG with 55 GHz full width half maximum (FWHM) bandwidth, and evaluated the minimal channel spacing of 2.5 Gbit/s DWDM-direct systems for broadband access with optical filter of the kind. For the DWDM-direct system for broadband access with 55 GHz FBG a satisfactory performance is achieved with a 50 GHz channel interval at the 2.5 Gbit/s data transmission speed. These results provide limitations which are required to take into consideration for realization of DWDM-direct system for broadband access with FBG technology.