An All-Solid Athermal Multimode-Interference Cascaded Device for Wavelength-Locking

We demonstrate a passive, material-based athermalization of all-fiber architectures consisting of cascaded multimode-interference (MMI) devices. Specifically, the athermal MMI filter used for in-line thermo-optic compensation consists of a no-core multimode fiber, which is spliced between two single-mode fibers, and is partly covered with a polymer coating. The design of the temperature-compensation unit is straightforward and its fabrication is simple. The applicability of our approach is experimentally verified by fabricating wavelength-locked MMI lasers with a temperature sensitivity lower than 1.0 pm/°C, which is several times smaller than that achieved with other fiber-optic devices and is comparable to that targeted in silicon photonics.