New designs of optical devices, particularly for adding or dropping a selected wavelength or a group of wavelengths as well as multiplexing a plurality of signals into a multiplexed signal or demultiplexing a multiplexed signal into several signals are disclosed. According to one aspect of the present invention, an isolator core is built into the optical devices to stop a reflected signal from an optical file in the optical devices. As a result, the optical devices are amenable to small footprint, broad operating wavelength range, enhanced impact performance, lower cost, and easier manufacturing process.