A multi-port fiber optic device (100) includes a pair of opposite collimators (50, 51), of which each includes a V-groove dual fiber ferrule (20, 21) with a GRIN rod lens (2, 1). At least one band-pass DWDM thin film filter (4) is securely sandwiched between the two opposite GRIN rod lens (2, 1) of the pair of collimators (20, 21). The V-groove dual fiber ferrule (20, 21) is used to couple light in and out thereof and tune the thin film filter center wavelength to the ITU grid. The light coupled in from the input fiber (13) of the V-groove dual fiber ferrule (20) will be collimated and transmitted to the DWDM thin film filter (4). The part of the in-pass-band light will pass through the filter (4) as performing a demultiplexed channel and is successively coupled into the other collimator (21) aside.