Typical 2X2 Fused Dual Clad Fiber (FDCF) couplers have Dual-Clad (DC) fiber in 2 opposite leads and multimode (MM) fiber in other 2 arms. DC input fiber can be optionally replaced with matching single-mode (SM) fiber, and MM output fiber can be terminated to form 2x1 FDCF coupler. Manufacturing process offers broad wavelength range and 100% transmission for SM fiber input. Applications include OCT and super resolution imaging, fiber sensors, spectroscopy, and confocal/fluorescence microscopy.