The principal functionality of an optical fiber isolator is to block the reflection from the next segment of the optical link from entering the previous stages. It ensures the one-way transmission of light in the optical fiber. Single stage or dual-stage isolators provide different degrees of optical isolation. Two identical isolators or one WDM coupler and one isolator can also be fabricated inside a "single" package, which provides small component size and more reliable performance. Multimode isolators are useful with multimode fiber networks. Wide band isolator, covering S, C and L bands, can be used in DWDM optical amplifier design. We can also provide isolators at special wavelengths or polarization maintaining isolators.