We designed and fabricated a 1310 nm/1550 nm demultiplexer with a directional coupler for optical fiber communication systems with much increased transmission capacity. We also propose novel design methods to reduce its length and improve its performance. First, the device length was reduced by using the generalized extinction ratio curve, which was normalized by the normalized frequency (v). Second, the lateral shift and the curved waveguide for the optimization of input region were adopted to improve the extinction ratio, and the shift is to outward of a directional coupler. Lateral shift reduces discrepancy between the two transfer coefficients, Cve and Cvo, and curved input waveguide controls mode profile asymmetrically to minimize the effect of these without serious decrease in transfer efficiency. For a given interaction length of 1.948 mm, the 1310 nm and 1550 nm wavelength light transfer to the cross state and the bar state, respectively. Above results are used to fabricate of a demultiplexer operating at 1310 nm and 1550 nm with the extinction ratios of -29.64 dB at 1310 nm and -20.32 dB at 1550 nm, respectively. The demultiplexer device was fabricated with polymer materials on a fused glass substrate. The core of the device was formed by micro-transfer molding technique with the polydimethylsiloxane (PDMS) mold. We found that these novel devices can be formed in optical fiber communication systems.