Real-time large deflection sensing of continuum dexterous manipulators (CDM) is essential and challenging for many minimally invasive surgery (MIS) applications. To this end, the feasibility of using Fiber Bragg Grating (FBG) sensors to detect large CDM deflections was demonstrated. Previous studies by our group proposed attaching an FBG array along with two nitinol (NiTi) wires as substrates to form a triangular cross section capable of large deflection detection for a 35 mm CDM. The strenuous fabrication procedure, however, relies on trial and error to ensure accurate attachment of components. In this paper, we propose a novel design for assembling large deflection FBG sensors utilizing a custom-design three-lumen polycarbonate tube with circular cross section. The proposed design eliminates fabrication challenges by embedding the FBG array and NiTi wires inside the tube in a more robust, repeatable, time-efficient and cost-effective (compared to multicore fibers) manner. Calibration experiments of the sensor assembly alone and inside the CDM indicate consistent linear (R2~0.99) wavelength-curvature relationship. Experimental results show 3.3% error in curvature detection.