In-Fiber Mach-Zehnder Interferometer Based on Er Doped Up-Taper and Peanut-Shaped Fiber Structure in Fiber Ring Laser

It is demonstrated that in this paper a peanut shaped structure cascaded with up-taper fiber structure can realize the inter mode interference between the Erbium doped fiber (EDF) core mode and cladding modes in fiber ring laser (FRL). A simple and inexpensive Mach-Zehnder interferometer (MZI) based on this structure is proposed. Shown from experimental results, the optical intensity of the core mode can be coupled into the cladding modes in the first peanut-shaped structure. Then, the light in the cladding modes can be recoupled into the core mode in the up-taper structure. A high-quality interference spectrum with a signal to noise ratio about 50 dB was observed. Besides, the structure exhibits good mechanical stability when compared to MZIs based on taper or offset structure. The temperature sensitivity of the FRL sensor is 301 pm/°C and the RI sensitivity is 156 nm/RIU. This kind of MZI will have potential applications in remote sensing technique and the development of life and health.