New designs of optical devices, particularly for multiplexing or demultiplexing as well as adding or dropping are disclosed. According to one aspect of the designs, one or more beam redirecting parts (e.g., prisms or mirrors) are used in an optical device to redirect a beam for at least two purposes: to increase a distance between two optical parts that are not positioned along an optical path, by using one or two of such beam redirecting parts, and to minimize an angle of incidence (AOI) to an optical filter or to adjust the AOI to an optimum value. As a result, devices employing the techniques provide small AOL and flexibility in adjustment and are amenable to small footprint, broad operating wavelength range, enhanced impact performance, lower cost, and easier manufacturing process.